Removal of ammonium from water by a bentonite biochar composite

Removal of ammonium from water by a bentonite biochar composite | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Removal of ammonium from water by a bentonite biochar composite Nguyen Thi Hai, Thao Hoang-Minh, Do Trung Hieu, Ta Thi Hoai, Bui Van Dong, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4723030/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract A new adsorbent of bentonite biochar composite (BRK) from natural bentonite and rice husk was synthesized for removal of ammonium (NH 4 + ) from water. The preparation of the adsorbent consisted of a pyrolysis process at 400 °C and activation of biochar with KOH to obtain BRK. Various advanced techniques were applied to characterize the investigated adsorbent, including Fourier-transform infrared spectroscopy (FTIR), N 2 adsorption analysis, scanning electron microscopy (SEM) integrated with Energy-Dispersive X-ray (EDX) Spectroscopy. The point of zero charge of BRK was 9.1. The pH solution strongly affected BRK’s adsorption capacity to NH 4 + ions in the solution. The removal efficiencies of NH 4 + were considerably diminished in the presence of coexisting cations (Na + , K + , Ca 2+ , and Mg 2+ ). The Langmuir adsorption capacity of BRK for NH 4 + was in the following order: 22.51 mg/g (10 o C) > 20.57 mg/g (30 o C) > 16.22 mg/g (50 o C). The kinetic experiments demonstrated that the adsorption equilibrium was achieved after 30 mins of contact. The ion-exchange was found to be the main adsorption mechanism for removing NH 4 + by BRK. This study proved that BRK is a low-cost and sustainable adsorbent derived from natural bentonite and rice husk and it is advantageous for successfully removing NH 4 + from water. adsorption ammonium agricultural waste bentonite composite water treatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Ammonium (NH 4 + ) is an inorganic ion of nitrogen that is formed when organic molecules containing nitrogen are broken down and disposed of in urban wastewater and domestic wastewater. Ammonium contaminations are serious environmental issues in surface and groundwater which cause significant risks to ecosystems and human health [ 1 ]. This is due to the fact that NH 4 + has the potential to produce eutrophication and cause dissolved oxygen depletion. Thus, high NH 4 + concentrations may result in biodiversity loss, degradation of ecosystem functions, and toxicity to natural habitats and aquaculture [ 1 , 2 ]. According to the World Health Organization [ 3 ] in humans, NH 4 + concentrations above 200 mg/kg of body weight have the potential to be toxic or harmful to health. Many treatment approaches, such as biological treatment, adsorption, photoelectronic, chemical precipitation, air aeration, and ion exchange, were investigated to reduce the negative consequences of NH 4 + [ 1 , 4 ]. Among them, the biological process is the most cost-effective and successful approach for treating NH 4 + in a domestic wastewater treatment plant. The procedure and development rate of the microorganisms used, however, are impacted by variations in environmental and water variables, such as temperature, thus critically affecting the operation of the water treatment system. These above factors are known as disadvantages of this technology. While considering the removal efficiency, cost-effectiveness, and simple operation, adsorption has emerged as a promising method to tackle NH 4 + problems [ 1 ]. Still, there is always a challenge in developing suitable adsorbent materials that have high efficiency, low cost, and abundance [ 1 ]. Unlike metal-organic framework (MOF) materials, which are generally only used in laboratory settings due to their high cost, the adsorbents originating from agricultural waste and natural minerals are gaining much attention and are widely applied in both laboratory and field scales. This is because of their abundance of practicability, cost-effectiveness, stability, and renewability. Among these natural adsorbents such as bentonite, zeolite, and other natural clays (e.g. kaolinite, montmorillonite, vermiculite, and sepiolite), bentonite is widely used as clay adsorbent, owing to its cost-benefit, high content of montmorillonite (well-known clay mineral with high adsorption capacity), and worldwide distribution [ 1 , 5 ]. Bentonite possesses a 1:2 type layered structure, which consists of one silicon-oxygen tetrahedron sheet and two aluminum oxygen octahedron sheets. The layer might have a net negative charge, which could be readily balanced by several cations in aqueous solution (i.e., Na + , K + , Ca 2+ , and Mg 2+ ) and contribute to the ion exchange capability of bentonite [ 6 ]. Furthermore, bentonite has the ability to bind to strengthen composites with controlled particle size due to the high content of montmorillonite mineral in its structure [ 7 ]. Eventually, bentonite is eco-friendly and non-toxic to the subsequent treatment, thus also confirming its applicability and sustainability for water treatment purposes. Besides the above advantages, using adsorbent-based agricultural wastes for water treatment is also of great interest as a sustainable approach for added-values, zero-waste, and circular economy goals [ 8 ]. For carbonization of biomass and increase of adsorption capacity by improving cation exchange efficiency, specific surface area, and stable structure, various methods for preparation (e.g., pyrolysis, gasification, and hydrothermal carbonization) and modification (acids, alkali, oxidizing agents, and metal ions) of biochar were adopted [ 9 , 10 ]. Different oxidative reagents (e.g., HNO 3 , H 2 O 2 , and NaOH) were widely used to boost the quantity of oxygen-containing functional groups for NH 4 + adsorption [ 1 , 11 ]. Besides, to enhance contaminant removal capacity, the combination of biochar and additives (e.g., clay minerals, metal oxides, single metals or couple metals, and carbonaceous materials), known as biochar-based composites, were also studied [ 12 , 13 , 14 ]. In this concept, biochar provides a porous structure to support the distribution of additives within its lattice, and this incorporation enhances the overall sorption capacity of the composite material [ 12 ]. The composites between biochar and clay materials have been widely investigated and developed for removing both organic and inorganic pollutants such as Pb [ 15 ], Cd [ 16 ], antibiotic ciprofloxacin [ 17 ], methylene blue (MB) [ 14 ], phosphate and NH 4 + [ 18 , 19 ]. Biochar bentonite composite has recently been used for the simultaneous removal of phosphate and NH 4 + from water with maximum adsorption capacities of 132.2 and 39.5 mg/g [ 18 ]. This composite was prepared by introducing peanut shell powder and bentonite and modified by the pyrolysis process and reagents (MgCl 2 and NaOH) [ 18 ]. However, little attention was given to incorporate natural bentonite and rice husk–one of the most abundant agricultural wastes in Vietnam, for NH 4 + removal from aqueous solution. The National Environmental Assessment Report in the period 2016–2020 of Vietnam showed high concentrations of NH 4 + in the surface and groundwater which were as high as approximately 50 and 130 times higher than the allowable limits for surface (0.3 mg/L) and groundwater (1 mg/L) [ 20 ]. High NH 4 + concentrations (50–99 mg/L) were recorded in groundwater in the Red River Delta [ 21 ]. Of particular concern, local residents in some areas have been using groundwater contaminated with NH 4 + for drinking and domestic purposes [ 22 ]. Being the third largest rice exporter in the world in 2023 and with the availability of natural bentonite, a combination of bentonite and biochar derived from rice husk would contribute to not only tackling the NH 4 + pollution issue but also implementing waste-to-resource practice as a circular economy approach. In this study, a composite of bentonite and rice husk waste was prepared through a pyrolysis process and treated with KOH to enhance the cation exchange capacity (BRK). The successful fabrication of BRK adsorbent was confirmed throughout several characterization steps, including Fourier-transform infrared spectroscopy (FTIR), N 2 sorption analysis, and Scanning electron microscopy (SEM). In addition, the effects of several major factors for the removal of NH 4 + by BRK (i.e., pH solution, contact time, initial concentrations of NH 4 + , temperature, coexisting ions, and desorption) were evaluated by a series of batch experiments. 2. Materials and methods 2.1. Materials, chemicals, and reagents All analytical chemicals and reagents, including NH 4 Cl, NaOH, HCl, Ca(NO 3 ) 2 , Mg(NO 3 ) 2 , NaNO 3 , and KNO 3 in this study were purchased from Sigma-Aldrich and were used directly without any extra purification. A 1000 mg NH 4 + /L stock solution was prepared by diluting 4.394 g of salt NH 4 Cl into 1000 mL deionized water. The feed NH 4 + solutions used in the batch experiments were diluted from the stock solution using distilled water. In this study, natural bentonite was obtained from a bentonite mine in Di Linh district, Lam Dong province, Vietnam. Coarse fractions of non-clay size were removed by sieving and sedimentation and dried at 80 o C. The dried bentonite sample was then gently manual-milled in an agate mortar to obtain the material with a particle size of less than 40 µm. Chemical and mineral compositions of bentonite were prior characterized by Hoang-Minh et al. [ 23 ]. Raw rice husks (RH) were collected in Hanoi, Vietnam and then washed with deionized water. After drying at 80 o C in an oven, the rice husks were then grinned and sieved to obtain a particle size of 0.5 mm. These prepared bentonite and RH samples were stored in plastic bags for further synthesis steps. 2.2. Synthesis of bentonite-biochar composite materials The preparation of composite materials using bentonite and rice husk biochar, as well as their modification, via one and two stages, which is depicted in Fig. 1 . In particular, 50 g of bentonite was thoroughly mixed with 50 mL of deionized water in a beaker, and the mixture was agitated utilizing a magnetic stirrer for an hour. An amount of 25 g RH was then added to the bentonite mixture, and the beaker was continuously stirred for 24h. After that, the solid part was separated from the liquid phase using 0.45 µm filters and dried at 80 o C for the subsequent 48 h to obtain a raw mixture of RH and bentonite. In the first step, the pristine combination of bentonite and rice husk biochar underwent a pyrolysis process at 400 and 500 o C for 3 hours. The most typical pyrolysis temperatures (400 ℃ and 500 ℃) were selected for the modification of adsorbents [ 9 ]. The composite was then chemically modified via the second stage using KOH 2M. It should be noted that after each stage, the adsorbent was taken out of the mixture, bathed with distilled water until the solution was pH = 7, and then dried at 80 ℃ for the next stage and used for the preliminary experiment. Preliminary experiments for the determination of adsorbents were performed at identical conditions (i.e., pH = 7, material dosage = 2.0 g/L, initial NH 4 + concentration of 20 mg/L, and shaking speed = 160 rpm). The NH 4 + removal rate of natural bentonite, raw rice husk, biochars after pyrolysis, and biochars after activation with KOH is shown in Fig. 1 . Pyrolysis process (400–500°C) helped to improve removal efficiencies of bentonite (2.67%) and rice husk (1.13%) to 21.12–25.95% (biochar) (Fig. 1 ). KOH treatment increased 117–119% the removal efficiencies of NH 4 + from water. According to the preliminary results, bentonite biochar composite (BRK) (sample 5, pyrolysis temperature = 400 o C, KOH activated) was highlighted as the most effective material and was selected for further experiments. 2.3. Adsorption experiment The NH 4 + removal performance of BRK material was examined by batch-scale studies. The influence of the initial pH solution, contact time, and initial NH 4 + concentration at various temperatures on the NH 4 + removal was then investigated. All experiments were conducted at a constant material dosage of 2.0 g/L by adding 0.1 g of adsorbent into 50 mL of NH 4 + solution with predetermined concentrations in an Erlenmeyer flask. The mixture was shaken at 160 rpm in a DAIHAN Labtech (Model LSI-2) machine. The contact time was adjusted following each category of experiments. The mixtures were filtered through 0.45 µm filters to separate the liquid and solid phases after the interval period of time. The NH 4 + concentration in the liquid phase was then analyzed. To examine the effect of pH solution on NH 4 + removal using BRK adsorbent, the study was conducted under a wide pH range from 2 to 12. The initial NH 4 + concentration of 20 mg/L and contact time of 24 hours was set in this experiment. The pH solution was adjusted to the appropriate level using 0.1 M HNO 3 and NaOH. The kinetic adsorption was carried out in solution with pH = 7 and an initial NH 4 + concentration of 20 mg/L. The samples were taken at intervals of 1 min, 5 mins, 10 mins, 30 mins, 1 h, 2 h, 4 h, 8 h, 12 h, and 24 h. The isotherm adsorption was carried out at initial NH 4 + concentrations ranging from 5, 10, 20, 30, 50, 70, 100, 150, 200, and 300 mg/L. The experiments were performed at three levels of temperatures (10, 30, and 50°C). To investigate the effect of coexisting cation ions (Na + , K + , Ca 2+ , and Mg 2+ ) at three different initial concentrations (10, 50, and 100 mg/L) on BRK adsorbent, the test was conducted at an initial NH 4 + concentration of 20 mg/L and pH = 7. 2.4. Adsorbent properties and sample analysis The characterizations of adsorbents were determined using the Scanning Electron Microscopy (SEM), the Energy-Dispersive X-ray (EDX) Spectroscopy, the Fourier-Transform Infrared Spectroscopy (FTIR), N 2 adsorption analysis, and point of zero charge. In particular, Scanning Electron Microscopy (SEM- Nano SEM FEI-450) integrated with Energy-Dispersive X-ray (EDX) Spectroscopy (TEAM Apollo XL-EDAX) was used to determine the elemental compositions of adsorbents and to visualize in detail the topography and morphology of the sample. An EDX detector connected to a scanning electron microscope (SEM) produces an elemental spectrum. This spectrum displays the presence and strength of distinctive X-ray peaks for various elements, as well as the precise weight and atomic occupancy ratio of the constituent elements that make up the adsorbents. N 2 adsorption analysis was performed by Nova touch 4LX/Anton Paar, USA. The Jasco FT/IR-6300 spectrometer, which operated within a wavenumber ranging from 4000–500 cm − 1 , was used to detect the active functional groups available on the surface of the adsorbent. OriginPro peak-fitting method (OriginLab Corporation) was used to deconvolute the FTIR spectra. The drift method was used to calculate the BRK’s point of zero charge. The NH 4 + concentrations in water samples were measured by continuous flow analysis which named Skalar method at wavelength 630 nm (SKALAR model 21050900, Netherlands). For chlorine donation, sodium hypochlorite and nitroprusside catalysts were employed. Ammonium standard solution of 1000 mg/L and a blank solution were used to ensure the accuracy of the analysis. The analytical detection limit for NH 4 + is 5 µg/L. 2.5. Data analysis All tests were duplicated, and experiment results were expressed using the mean and standard deviation data. Isotherm and kinetic adsorption parameters were calculated using the Origin program. The calculation of NH 4 + adsorption capacity of adsorbents at the equilibrium time ( q e , mg/g) and at time interval t (qt, mg/g) was performed using equations given in our previous publication [ 24 ]. The best-fit model was determined by calculating the coefficient of determination ( R 2 ) and the chi-squared ( χ 2 ) value. Chi-squared ( χ 2 ) values and the coefficient of determination ( R 2 ) values were calculated to identify the best-fit model. A χ 2 value near 0 indicates that the data acquired by model application and the experimental data are similar, while a high χ 2 indicates a significant bias between the model and the experiment. 3. Results and discussion 3.1. Effects of pH solution The effect of pH solution on NH 4 + adsorption is presented in Fig. 2 . Generally, the NH 4 + adsorption capacity of BRK was strongly affected by pH solution (2.0–12.0). As a result, the adsorption process of NH 4 + on adsorbents was not favorably affected by acidic or alkaline conditions, with the pH range of 6 to 9 typically yielding the greatest equilibrium adsorption quantity. In this study, the ability of BRK to adsorb NH 4 + increases following the increase of initial pH and decreases sharply when pH > 9 (Fig. 2 ). Essentially, pH solution is also a significant factor as it determines NH 4 + speciation in water [ 25 ]. According to the NH 4 + species stability and a function of pH diagram, NH 4 + and its p K a value were determined to be approximately 9.3 (p K a) [ 25 ]. In other words, NH 4 + often exists as ionized NH 4 + when the pH solution is lower than 9.3. When the pH solution is greater than 9.3, the ammonia is found to be abundant and exists with its form of no charge (NH 3 ). Raising the pH of the solution will hasten the NH 3 ’s release from the solution since NH 3 in solution can readily cause volatility. As a result, solutions with pH values greater than 9.3 are anticipated to have a limited NH 4 + adsorption capability. At low pH values (2–4), proton H + from the acid environment had strong competition with ion NH 4 + in the active side of the material, as the repulsion between positive ions and NH 4 + in solution; therefore, BRK adsorbed a negligible amount of NH 4 + Fig. 2 . The removal efficiency of NH 4 + was remarkably reduced in an acid environment (pH < 3) [ 26 ]. This is because extremely acidic pH will enrich the solution with protons and limit the ionization process of the acidic functional groups on adsorbents, which will reduce the ion-exchange sites available for the adsorption of NH 4 + . Under weak acid and weak alkaline conditions (pH = 5–9), the ability to remove NH 4 + from the water of BRK was higher than in strong acid conditions and reached the highest value at pH = 6 (Fig. 2 ). As reported by Eturki et al. [ 27 ], their investigation also found that an ideal pH from 6 to 8 produced the greatest results. This change could be explained by: (1) the decrease of ion H + in solution led to the competition between H + and NH 4 + also reduced, (2) when the pH value reached 6–8, the deprotonation of some groups might occur on the surface of the material, so NH 4 + can be easily adsorbed onto BRK. Particularly, the prepared BRK adsorbent in this study had a point of zero charge (pH PZC ) at 9.1 (Fig. 2 ). These results demonstrate that the surface of BRK has a positive charge when pH solution pH PZC . At this time, positively charged NH 4 + ions were adsorbed on BRK via an ion exchange mechanism because the surface charge of BRK was positive when pH solution pH PZC , the negatively charged BRK can adsorb positively charged NH 4 + through an electrostatic attraction mechanism. On the other hand, with a pH value > 9, the solution was strongly alkaline and more negative due to the existence of the –OH group. Therefore, ion NH 4 + preferentially reacts with –OH to produce gas (NH 3 ). This result is in agreement with prior studies [ 11 , 28 ]. 3.2. Adsorption kinetics Figure 3 shows the effects of the contact time on the removal capacity of BRK toward NH 4 + . Adsorption kinetic data showed NH 4 + adsorption rate by BRK was rapid within the first 5 mins, then decreased with time, and reached the equilibrium state after 30 mins. Approximately 35, 43, and 50% NH 4 + from the solution was absorbed onto BRK at the early stage of 1, 5, and 10 mins, which indicated that BRK had a strong affinity toward NH 4 + ion. Obviously, within the first contact time of 15 mins, the adsorption performance of BRK increased significantly. This can be explained by the fact that at the initial stage, a large amount of vacant sites on the adsorbent’s surface that are available and not yet occupied readily interact with NH 4 + . Additionally, the active functional groups on BRK’s surface were available and readily for bonding with NH 4 + ions. After 30 mins, the adsorption capacity reached equilibrium, with their removal efficiency reaching 53%. In this period, the BRK’s active site had already started to connect to and bond with NH 4 + . As a result, there was a reduced space for NH 4 + to be adsorbed, which led to the amount of NH 4 + adsorbed by BRK reducing and BRK’s adsorption capacity decreasing. Therefore, the adsorption process approached saturation gradually. The adsorption capacity remained almost constant after 60 mins of adsorption when compared to the first 30 mins. The adsorption capacity and removal efficiency of BRK at 24 h was 5.34 mg/g and 54%, respectively. The adsorption capacity did not fluctuate significantly or was virtually unchanged. This is due to the fact that almost all BRK’s active site was occupied during this time. The experimental data were fitted using the Pseudo-First Order (PFO), Pseudo-Second Order (PSO), and Elovich models (Fig. 3 ). Kinetic adsorption data calculated from three models for NH 4 + is given in Table 1 . The value of Chi-squared ( χ 2 ) and the coefficient of determination ( R 2 ) for PFO, PSO, and Elovich model of BRK material were 0.13–0.95, 0.038–0.99, and 0.12–0.95, respectively. Adsorption by BRK was better described by the PSO model (with higher R 2 and lower χ 2 ) than that for the two other models. While the adsorption rate of the PFO model normally depends on the diffusion of adsorbates on the adsorbent’s surface, the adsorption rate by PSO is controlled by the interaction of adsorption sites with the adsorbate. On the other hand, in the PFO adsorption kinetic model, the number of uncopied adsorption active sites on the adsorbent’s surface does not control the adsorption rate. In contrast, the PSO model was related to the uncopied active site in the adsorbent. It is considered a chemical interaction between the adsorbent and the adsorbate. This result suggests that NH 4 + adsorption may be controlled by the chemisorption mechanism (ion exchange, electrostatic attraction, and complexation), which is primarily responsible for managing the contaminant's adsorption [ 29 ]. Alshameri et al. [ 30 ] investigated the adsorption test of natural clay materials toward NH 4 + ; they stated that the adsorption process of NH 4 + onto clay materials was presented by PSO kinetics. The NH 4 + adsorption process can be explained by the following steps: (1) moving NH 4 + from the liquid phase to the liquid-solid interface; (2) transferring the solid phase on the BRK’s surface; and (3) then diffusing into the BRK’s pores. Moreover, the experimentally derived adsorption capacities ( q t, e xp = 5.336 mg/g ) were nearly close to the computed data ( q t ,cal ) from the PSO model (Table 1 ) ( q e = 5.31 mg/g). The adsorption capacity obtained from the PFO kinetic model ( q e = 5.17 mg/g) was lower than that of experiment adsorption capacity. Table 1 Kinetic parameters for NH 4 + adsorption by BRK Models Unit BRK q exp mg/g 5.34 Pseudo-first order q e mg/g 5.17 k 1 1/min 1.06 R 2 0.95 ꭓ 2 0.13 Pseudo-second order qe mg/g 5.31 K 2 g/ mg × min 0.29 R 2 0.99 ꭓ 2 0.038 Elovich model α mg/(g×min) 4.97 x 10^6 β g/mg 4.21 R 2 0.95 ꭓ 2 0.12 3.3. Adsorption isotherms The effect of initial NH 4 + concentrations ( C o = 5–300 mg/L) on the adsorption capacity by BRK were evaluated at various temperatures through adsorption isotherms (Fig. 4 ). The results showed that temperature was a significant factor in the NH 4 + adsorption process. The NH 4 + absorption capability of BRK reduced as the temperature rose from 10°C to 50°C. In other words, the NH 4 + removal by BRK reached its highest at 10 ℃, and lowest at 50 ℃. These results also suggested that the NH 4 + adsorption process on BRK adsorbent was exothermic and the low-temperature environment is favorable. The observed trend of temperature influence was in agreement with previous findings on activated carbon made from coconut shells [ 31 ], corncobs [ 11 ], and modified bentonite [ 28 ]. The NH 4 + adsorption process onto modified bentonite and corncob waste-derived activated carbon constituted an exothermic reaction [ 11 , 28 ]. In addition, many others have documented comparable isotherm shape observations [ 28 ], when studying NH 4 + adsorption by materials derived from agriculture wastes or bentonite materials and their modified forms. The isothermal model fitting for NH 4 + adsorption onto BRK is provided in Fig. 4 . In this study, the adsorption process and adsorption behavior of NH 4 + on BRK were adequately described by the fit models, which comprised the Langmuir and Freundlich. The isotherm model fit data was calculated and presented in Table 2 . The results show that the Langmuir isotherm model was the best match for the experimental data of BRK at all three investigated temperatures (10, 30, and 50 ℃). This is due to R 2 and χ2 values at 10, 30, and 50 ℃ of the Langmuir model, which were larger and smaller, respectively, when compared to those of the Freundlich model. The NH 4 + maximum adsorption of BRK obtained from the Langmuir model were 22.51, 20.57, and 16.22 mg/g at 10, 30, and 50 ℃, respectively. Therefore, when the temperature increases to 50 ℃, the capability to absorb NH 4 + decreases approximately 28%, indicating that the interaction between BRK and NH 4 + becomes weaker following the increase in temperature. In addition, the results of the experiments demonstrated a good agreement with the Langmuir model, suggesting that the adsorption behavior of NH 4 + on the BRK was mainly determined by the formation of the adsorption monolayer. The adsorption process of NH 4 + on six natural clay materials (NCM) are also monolayer due to the isotherm adsorption data obtained which were coincident with the Langmuir model [ 30 ]. Table 2 Parameters of the adsorption isotherm onto BRK material Model Unit Temperatures 10 ℃ 30 ℃ 50 ℃ Langmuir model Q max mg/g 22.51 20.57 16.22 K L L/mg 0.037 0.04 0.054 R 2 0.99 0.98 0.99 X 2 0.47 0.83 0.32 Freundlich model K F (mg/g)/(mg/L) n 3.15 3.07 2.94 n F 0.36 0.35 0.32 R 2 0.93 0.91 0.90 X 2 3.11 3.63 2.63 Table 3 presents a comparison between the Langmuir maximum adsorption capacity of BRK and some other materials studied in the literature on removal of NH 4 + . As, expected, BRK adsorbents ( Q max = 20.57) demonstrated a higher adsorption capacity of NH 4 + than other materials such as the pristine biochar derived from maple wood (5.44 mg/g) [ 32 ], pine sawdust (5.38 mg/g) [ 33 ], the natural bentonite from Algeria (19.01 mg/g) [ 5 ], bentonite from Indonesia (12.37 mg/g) [ 34 ], the modified biochar of waste spruce sawdust (17.96 mg/g) [ 35 ], of corncob (17.03 mg/g) [ 11 ], the modified bentonite (5.66 mg/g) [ 28 ], and the composite of bentonite and hydrochar (23.67 mg/g) [ 34 ]. Table 3 The Langmuir maximum adsorption capacity of some investigated adsorbents toward NH 4 + Adsorbent Initial concentrations pH m/V Q max References BRK 5-300 7 2 20.57 This study Maple wood biochar 0–100 - 10 5.44 [ 32 ] Pine sawdust biochar 0–100 6 3 5.38 [ 33 ] Bentonite from Algeria 10–10000 7 5 19. [ 5 ] Bentonite from Indonesia 200 6 0.1–10 12.37 [ 34 ] Modified Biochar 10–110 7 2 17.96 [ 35 ] Corncob activated carbon 10–105 7 2 17.03 [ 11 ] Chemically Activated Biochar 50–600 8.4 4 14.34 [ 36 ] Modified bentonite 0–200 5–9 – 5.66 [ 28 ] Hydrochar from Koi fish 200 6 0.1–10 12.37 [ 34 ] Bentonite hydrochar composite 200 6 0.1–10 23.67 3.4. Effects of existing ions In this study, four commonly encountered cations (Na + , K + , Ca 2+ , and Mg 2+ ) have been selected to examine the (inhibitory) influence of these ions on the NH 4 + removal process by BRK (Fig. 5 ). These cations were tested at three initial concentrations of 10, 50, and 100 mg/L. The results showed that the removal efficiencies of NH 4 + had significantly decreased due to the strong competition between cations (Na + , K + , Ca 2+ , and Mg 2+ ) and NH 4 + ions in aqueous solution. Generally, when the concentration of co-existence cation was at 100 mg/L, the removal capacity of BRK toward NH 4 + decreased in the order of no competitor > K + > Na + > Mg 2+ > Ca 2+ . Similar trends were found in other studies [ 11 , 35 , 37 ]. Among investigated co-existing cations, divalent cations (Ca 2+ and Mg 2+ ) were found to possess more sway than monovalent cations (Na + and K + ) ( Fig. 5 ) . Because divalent cations have a divalent charge as opposed to monovalent cations, as a result, they have occupied more adsorption sites. In other words, they were stronger competitors for the adsorption site leading to reducing the removal efficiency of BRK [ 33 , 35 ]. Furthermore, it was shown that the two major components of water hardness, Ca and Mg, had concentration ranges between 80 and 200 mg/L. In fact, hard water inhibits the NH 4 + removal efficiency in wastewater treatment plants. Furthermore, the removal capacity of the adsorbent is observed to be influenced by the concentrations of cations. An increased amount of co-existing cations leads to a lower adsorption capacity (Fig. 5 ). 3.5. Adsorbent characteristics Figure 6 a displays the scanning electron microscopy (SEM) images of BRK before NH 4 + adsorption. The surface of BRK displays a multitude of holes and huge grooves of varying widths, indicating the composite of bentonite and biochar derived from rice husk materials had a porous and asymmetric surface structure. With its composition containing biochar materials, BRK had a rich porous structure. The SEM images of BRK showed that the activation mediated by KOH may promote BRK pore development, leading to the adsorption capacity of materials. This result is similar to those reported by others [ 38 , 39 ]. In addition, via the SEM image, it can be concluded that the BRK not only contains biochar adsorbent but also has bentonite in its composition. The presence of bentonite clay can be confirmed through the overlaid layer or plate-like appearance of bentonite (Fig. 6 a). Et-Tayea et al. [ 40 ] stated that the surface microscopic morphology of bentonite features aggregates of spherical, heterogeneous-sized bentonite grains with an impressive compact structure, as well as layered, overlapping layers. Or Ashiq et al. [ 17 ] prepared the composite of biochar based bentonite (MSW-BC) for removing antibiotic ciprofloxacin. The MSW-BC surface shares many similarities with the BRK surface. Its SEM image is characterized by a significant amount of pores, which constitute a property of biochar, and a plate-like layer, known to be a feature of bentonite. These results suggest that the BRK was successfully prepared. Figure 6 a also indicates the EDX results for composite of bentonite and biochar derived from rice husk (BRK) treated by KOH solution. Obviously, the BRK’s composition possesses C, O, Si, K, Ca, Fe. The presence of a large amount of K could be explained for the successful activation by KOH solution. Figure 6 b shows that there are no visible changes in the surface morphology of BRK after NH 4 + adsorption. The NH 4 + -laden BRK still exhibited a lot of pore and had a porous structure. There is one significant change in the weight percent of metal elements (K, Ca, Fe) in the NH 4 + -laden BRK. EDX data indicated that the weight percent of K, Ca, Fe decreased from 6,43–0.36%; 1,39% to 1,06%; 2,22 5 to 1.04%, respectively. Among them, the K element indicated a remarkably decreased rate than two other elements. This result is in line with the reports of Alshameri et al. [ 30 ] and Yu et al. [ 41 ]. This result suggests that it could be due to ion exchange of these elements with NH 4 + or called ion exchange mechanism. The FTIR spectra provide valuable information on the surface chemistry of BRK both before and after adsorption (Fig. 7 ). It can be seen that BRK possesses a lot of common functional groups that are found in other biochar adsorbents, such as OH, C = O, C = C, and CO [ 39 ]. They are pieces of evidence for confirming the presence of the biochar adsorbent in its component of BRK. The stretching vibration of –OH is specifically responsible for a noticeable broad peak located at 3425 cm − 1 on the surface of the BRK adsorbents before and after NH 4 + adsorption. The peak at about 1622 cm − 1 was identified as the stretching vibration of C = O in carboxyl groups or aliphatic ketone, whereas the bands at around 2372 cm − 1 were associated with the stretching vibrations of C = C and C-H [ 38 , 42 ]. In addition, a small peak at about 1031 cm − 1 observed in BRK pristine material was featured as the stretching vibration of Si-O, which is commonly found in bentonite clay materials [ 23 , 43 ]. All things considered, BRK was rich in functional surface groups which provided the basis for removing NH 4 + ions from aqueous solution. The infrared spectrum also revealed that the distinctive peaks at –OH had clearly shifted following adsorption, which was caused by the complexation of NH 4 + with oxygen-containing functional groups [ 44 ]. The surface properties information of BRK obtained by the nitrogen adsorption/desorption isotherm technique is provided in Table 4 . It can be seen from Table 4 , that the specific surface areas of BRK pristine and NH 4 + -laden BRK were 4.89 and 17.72 m2/g, respectively. Obviously, after NH 4 + adsorption, the specific surface area of BRK was gently increased. In addition, the pore volume of BRK was increased from 0.009 cm3/g to 0.024 cm3/g after the adsorption process. These particular results suggest that NH 4 + adsorbed on BRK via a pore-filling mechanism might be negligible. Table 4 The surface properties information of BRK Surface properties BRK pristine NH 4 + -laden BRK BET specific surface area ( S BET - m 2 /g) 4.89 17.72 Pore volume cm 3 /g 0.009 0.024 Pore radius (nm) 1.92 1.72 3.6. Possible adsorption mechanisms The previous mechanism studies found that the most predominant adsorption mechanisms in removal of NH 4 + by the clay materials and biochar adsorbents were ion exchange [ 11 , 30 ], electrostatic attraction [ 45 ], pore-filling mechanism, and surface complexation. Through a series of batch experiments conducted at a pH of 7.0 and characterization of pristine and NH 4 + laden BRK, the potential NH 4 + adsorption mechanism on BRK was identified. Firstly, the pristine BRK had a tiny specific surface area (4.89 m 2 /g). However, after the adsorption process, the BRK loaded with NH 4 + had a greater S BET (17.72 m 2 /g) than the pristine BRK. The findings suggested that the pore-filling mechanism may not be crucial to the adsorption process. Moreover, according to [ 41 ], there was no relationship between the NH 4 + adsorption capacity and the specific surface area. As mentioned in Section 3.1 , with its pH PZC at 9.1, BRK possessed a positive charge when pH solution of 7.0, thus positively charged NH 4 + ions were exchanged with positively charged BRK through an ion exchange mechanism. In other words, the ion exchange is of great significance in removing NH 4 + from the water environment. The ion exchange mechanism is also supported by the results of SEM/EDX that the percentage of K elements in pristine BRK decreased significantly (from 6.43–0.36%) after adsorption process, possibly due to ion exchange of K + with NH 4 + ions in solution [ 30 , 41 ]. Additionally, it was discovered by the FTIR analysis above that NH 4 + complexed with oxygen-containing functional groups on the surface of BRK, such as –OH, during the adsorption process. 4. Conclusions In this study, a bentonite biochar composite (BRK) from natural bentonite and rice husk was successfully synthesized at a pyrolysis temperature of 400°C and then treated with KOH. The batch experimental data showed that the adsorption capacity of BRK for NH 4 + significantly depended on the pH solution (2.0–12.0) and co-existing cations (Na + , K + , Ca 2+ , and Mg 2+ ). The PSO model provided a better description of the kinetic adsorption of NH 4 + on BRK than the PFO and Elovich models. BRK outperformed other adsorbents in the literature with a maximum Langmuir adsorption capacity of 20.57 mg NH 4 + /g at 30 ℃. The characterization of the adsorbent and batch investigations showed that the ion exchange was found to be the primary mechanism for the removal of NH 4 + by BRK. BRK is an effective and cost-effective material for the treatment of water contaminated with NH 4 + . Column and pilot field experiments using real water should be conducted for feasible assessment for the practical application of BRK. Declarations Acknowledgments: This study was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) (grant number 105.99-2019.311). Author contribution s Conceptualization: N.T.H., T.H.-M., N.T.H.H.; Methodology: N.T.H., T.H.-M., N.T.H.H., D.T.H., T.T.H., N.V.D., L.V.D.; Experiment: N.T.H., D.T.H., T.T.H., B.V.D.; Analysis: L.V.D., D.T.H., T.T.H.; Writing original draft: N.T.H.; Writing review and editing: T.H.-M., N.T.H.H., D.T.H., L.V.D., T.T.H., B.V.D. Funding This study was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) (grant number 105.99-2019.311). Ethical approval Not applicable. Consent to participate Not applicable. Consent to publish All the authors have agreed to publish this article. Competing interests The authors declare no competing interests. Availability All the data generated or analyzed during this study are available upon request. References Han B, Butterly C, Zhang W, He J-Z, Chen D (2021) Adsorbent materials for ammonium and ammonia removal: A review. J Clean Prod 283:124611. https://doi.org/10.1016/j.jclepro.2020.124611 Dias T, Clemente A, Martins-Loução MA, Sheppard L, Bobbink R, Cruz C (2014) Ammonium as a driving force of plant diversity and ecosystem functioning: observations based on 5 Years' manipulation of N dose and form in a mediterranean ecosystem. PLoS ONE 9(4):e92517. https://doi.org/10.1371/journal.pone.0092517 World Health Organization & International Programme on Chemical Safety (‎1996)‎ Guidelines for drinking-water quality. Vol. 2, Health criteria and other supporting information (2nd ed). World Health Organization. https://iris.who.int/handle/10665/38551 Zhou Y, Wang J (2023) Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective. Chemosphere 334:139027. https://doi.org/10.1016/j.chemosphere.2023.139027 Angar Y, Djelali NE, Kebbouche-Gana S (2017) Investigation of ammonium adsorption on Algerian natural bentonite. Environ Sci Pollut Res Int 24:11078–11089. https://doi.org/10.1007/s11356-016-6500-0 Bananezhad B, Islami MR, Ghonchepour E, Mostafavi H, Tikdari AM, Rafiei HR (2019) Bentonite clay as an efficient substrate for the synthesis of the super stable and recoverable magnetic nanocomposite of palladium (Fe 3 O 4 /Bentonite-Pd). Polyhedron 162:192–200. https://doi.org/10.1016/j.poly.2019.01.054 Seredych M, Ania C, Bandosz TJ (2016) Moisture insensitive adsorption of ammonia on resorcinol-formaldehyde resins. J Hazard Mater 305:96–104. https://doi.org/10.1016/j.jhazmat.2015.11.022 Stylianou M, Laifi T, Bennici S, Dutournie P, Limousy L, Agapiou, Papamichael I, Khiari B, Jeguirim M, Zorpas AA (2023) Tomato waste biochar in the framework of circular economy. Sci Total Environ 871:161959. https://doi.org/10.1016/j.scitotenv.2023.161959 Wang J, Wang S (2019) Preparation, modification and environmental application of biochar: A review. J Clean Prod 227:1002–1022. https://doi.org/10.1016/j.jclepro.2019.04.282 Xie L, van Zyl D (2020) Distinguishing reclamation, revegetation and phytoremediation, and the importance of geochemical processes in the reclamation of sulfidic mine tailings: A review. Chemosphere 252:126446. https://doi.org/10.1016/j.chemosphere.2020.126446 Vu MT, Chao H-P, Van Trinh T, Le TT, Lin C-C, Tran HN (2018) Removal of ammonium from groundwater using NaOH-treated activated carbon derived from corncob wastes: Batch and column experiments. J Clean Prod 180:560–570. https://doi.org/10.1016/j.jclepro.2018.01.104 Premarathna KSD, Rajapaksha AU, Sarkar B, Kwon EE, Bhatnagar A, Ok YS, Vithanage M (2019) Biochar-based engineered composites for sorptive decontamination of water: A review. J Chem Eng 372:536–550. https://doi.org/10.1016/j.cej.2019.04.097 Wang Y, Song X, Xu Z, Cao X, Song J, Huang W, Ge X, Wang H (2021) Adsorption of nitrate and ammonium from water simultaneously using composite adsorbents constructed with functionalized biochar and modified zeolite. Water Air Soil Pollut 232:198. https://doi.org/10.1007/s11270-021-05145-9 Yao Y, Gao B, Fang J, Zhang M, Chen H, Zhou Y, Creamer AE, Sun Y, Yang L (2014) Characterization and environmental applications of clay–biochar composites. J Chem Eng 242:136–143. https://doi.org/10.1016/j.cej.2013.12.062 Yao X, Zhongjie W, Mei C, Rongxin S, Lianke X, Renliang H (2021) Co-modification of biochar and bentonite for adsorption and stabilization of Pb 2+ ions. J Inorg Mater 36:1083–1090. https://doi.org/10.15541/jim20200745 Jing Y, Cao Y, Yang Q, Wang X (2020) Removal of cd (II) from aqueous solution by clay-biochar composite prepared from Alternanthera philoxeroides and bentonite. BioResources 15(1):598–615. https://doi.org/10.15376/biores.15.1.598-615 Ashiq A, Adassooriya NM, Sarkar B, Rajapaksha AU, Ok YS, Vithanage M (2019) Municipal solid waste biochar-bentonite composite for the removal of antibiotic ciprofloxacin from aqueous media. J Environ Manage 236:428–435. https://doi.org/10.1016/j.jenvman.2019.02.006 Xi H, Zhang X, Hua Zhang A, Guo F, Yang Y, Lu Z, Ying G, Zhang J (2022) Concurrent removal of phosphate and ammonium from wastewater for utilization using Mg-doped biochar/bentonite composite beads. Sep Purif Technol 285:120399. https://doi.org/10.1016/j.seppur.2021.120399 Medha I, Chandra S, Bhattacharya J, Samal B, Vanapalli KR (2023) Development of rice straw-derived biochar-bentonite composite and its application for in situ sequestration of ammonium and phosphate ions in the degraded mine soil. Environ Manage 71:1065–1086. https://doi.org/10.1007/s00267-022-01775-9 MONRE (2021) National Environmental Assessment Report in the period 2016–2020. Dan Tri Publishing House, p 168 Winkel LHE, Pham TKT, Vi ML, Stengel C, Amini M, Nguyen TH, Pham HV, Berg M (2011) Arsenic pollution of groundwater in Vietnam exacerbated by deep aquifer exploitation for more than a century. Proc Natl Acad Sci USA 108:1246–1251. https://doi.org/10.1073/pnas.1011915108 Hai NT, Hang HT, Hieu DT, Hien PT, Hoa BT, Hoang-Minh T, Ha NTH (2022) Groundwater quality in Tram Long commune, Ung Hoa district, Hanoi: current status and solutions. Proceedings of the International Conference on Sustainability in Environment and Agriculture (ICSEA2022), 115–121 Hoang-Minh T, Kasbohm J, Nguyen-Thanh L, Nga PT, Lai LT, Duong NT, Thanh ND, Thuyet NTM, Anh DD, Pusch R (2019) Use of TEM-EDX for structural formula identification of clay minerals: a case study of Di Linh bentonite, Vietnam. J Appl Crystallogr 52:133–147. https://doi.org/10.1107/S1600576718018162 Nguyen TH, Tran HN, Vu HA, Trinh MV, Nguyen TV, Loganathan P, Vigneswaran S, Nguyen TM, Trinh VT, Vu DL, Nguyen THH (2020) Laterite as a low-cost adsorbent in a sustainable decentralized filtration system to remove arsenic from groundwater in Vietnam. Sci Total Environ 699:134267. https://doi.org/10.1016/j.scitotenv.2019.134267 Langenfeld NJ, Kusuma P, Wallentine T, Criddle CS, Seefeldt LC, Bugbee B (2021) Optimizing nitrogen fixation and recycling for food production in regenerative life support systems. Front Astron Space Sci 8:699688. https://doi.org/10.3389/fspas.2021.699688 Karri RR, Sahu JN, Chimmiri V (2018) Critical review of abatement of ammonia from wastewater. J Mol Liq 261:21–31. https://doi.org/10.1016/j.molliq.2018.03.120 Eturki S, Ayari F, Jedidi N, Ben Dhia H (2012) Use of clay mineral to reduce ammonium from wastewater Effect of various parameters. Surf Engin Appl Electrochem 48:276–283. https://doi.org/10.3103/S1068375512030064 Cheng H, Zhu Q, Xing Z (2019) Adsorption of ammonia nitrogen in low temperature domestic wastewater by modification bentonite. J Clean Prod 233:720–730. https://doi.org/10.1016/j.jclepro.2019.06.079 Wang C, Liu X, Yang T, Sridhar D, Algadi H, Bin Xu B, El-Bahy ZM, Li H, Ma Y, Li T, Guo Z (2023) An overview of metal-organic frameworks and their magnetic composites for the removal of pollutants. Sep Purif Technol 320:124–144. https://doi.org/10.1016/j.seppur.2023.124144 Alshameri A, He H, Zhu J, Xi Y, Zhu R, Ma L, Tao Q (2018) Adsorption of ammonium by different natural clay minerals: Characterization, kinetics and adsorption isotherms. Appl Clay Sci 159:83–93. https://doi.org/10.1016/j.clay.2017.11.007 Boopathy R, Karthikeyan S, Mandal AB, Sekaran G (2013) Adsorption of ammonium ion by coconut shell-activated carbon from aqueous solution: kinetic, isotherm, and thermodynamic studies. Environ Sci Pollut Res 20:533–542. https://doi.org/10.1007/s11356-012-0911-3 Wang B, Lehmann J, Hanley K, Hestrin R, Enders A (2015) Adsorption and desorption of ammonium by maple wood biochar as a function of oxidation and pH. Chemosphere 138:120–126. https://doi.org/10.1016/j.chemosphere.2015.05.062 Yang HI, Lou K, Rajapaksha AU, Ok YS, Anyia AO, Chang SX (2018) Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars. Environ Sci Pollut Res 25:25638–25647. https://doi.org/10.1007/s11356-017-8551-2 Ismadji S, Tong DS, Soetaredjo FE, Ayucitra A, Yu WH, Zhou CH (2016) Bentonite hydrochar composite for removal of ammonium from Koi fish tank. Appl Clay Sci 119:146–154. https://doi.org/10.1016/j.clay.2015.08.022 Shang L, Xu H, Huang S, Zhang Y (2018) Adsorption of ammonium in aqueous solutions by the modified biochar and its application as an effective N-fertilizer. Water Air Soil Pollut 229:1–15. https://doi.org/10.1007/s11270-018-3956-1 Hsu D, Lu C, Pang T, Wang Y, Wang G (2019) Adsorption of Ammonium Nitrogen from Aqueous Solution on Chemically Activated Biochar Prepared from Sorghum Distillers Grain. Appl Sci 9:5249. https://doi.org/10.3390/app9235249 Hou J, Huang L, Yang Z, Zhao Y, Deng C, Chen Y, Li X (2016) Adsorption of ammonium on biochar prepared from giant reed. Environ Sci Pollut Res Int 23:19107–19115. https://doi.org/10.1007/s11356-016-7084-4 Liu H, Xu G, Li G (2021) Preparation of porous biochar based on pharmaceutical sludge activated by NaOH and its application in the adsorption of tetracycline. J Colloid Interface Sci 587:271–278. https://doi.org/10.1016/j.jcis.2020.12.014 Collivignarelli MC, Illankoon WAMAN, Milanese C, Calatroni S, Caccamo FM, Medina-Llamas M, Girella A, Sorlini S (2024) Preparation and modification of biochar derived from agricultural waste for metal adsorption from urban wastewater. Water 16(5):698. https://doi.org/10.3390/w16050698 Et-Tayea Y, Harrati A, Rachid A, Nasri H, Attou A, Arkame Y, Manni A, Mamouch Y, El Bouari A, El Khazanti F, Sadik C (2023) Mineralogical and physico-chemical characterization of bentonite materials from the Oued Zemmour area (Oriental Rif, Nador-Morocco): Valorization in ceramic field. Bol Soc Esp Ceram V 62:268–283. https://doi.org/10.1016/j.bsecv.2022.03.001 Yu Q, Xia D, Li H, Ke L, Wang Y, Wang H, Zheng Y, Li Q (2016) Effectiveness and mechanisms of ammonium adsorption on biochars derived from biogas residues. RSC Adv 6:88373–88381. https://doi.org/10.1039/C6RA16913A Liu X, Liao J, Song H, Yang Y, Guan C, Zhang Z (2019) A Biochar-Based Route for Environmentally Friendly Controlled Release of Nitrogen: Urea-Loaded Biochar and Bentonite Composite. Sci Rep 9:9548 Zhirong L, Azhar Uddin M, Zhanxue S (2011) FT-IR and XRD analysis of natural Na-bentonite and Cu(II)-loaded Na-bentonite. Spectrochim Acta Mol Biomol Spectrosc 79:1013–1016. https://doi.org/10.1016/j.saa.2011.04.013 An Q, Li Z, Zhou Y, Meng F, Zhao B, Miao Y, Deng S (2021) Ammonium removal from groundwater using peanut shell based modified biochar: Mechanism analysis and column experiments. J Water Process Eng 43:102219. https://doi.org/10.1016/j.jwpe.2021.102219 Sumaraj PLP (2017) Influence of surface chemistry of carbon materials on their interactions with inorganic nitrogen contaminants in soil and water. Chemosphere 184:532–547. https://doi.org/10.1016/j.chemosphere.2017.06.021 Additional Declarations No competing interests reported. Supplementary Files Graphicalabstract.png Graphical abstract Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 04 Sep, 2024 Reviews received at journal 03 Sep, 2024 Reviews received at journal 25 Aug, 2024 Reviewers agreed at journal 15 Aug, 2024 Reviewers agreed at journal 14 Aug, 2024 Reviewers invited by journal 26 Jul, 2024 Editor assigned by journal 16 Jul, 2024 Submission checks completed at journal 16 Jul, 2024 First submitted to journal 11 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4723030","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":336587245,"identity":"c1e2498c-4ace-4635-ae4f-5d34054de3ee","order_by":0,"name":"Nguyen Thi Hai","email":"","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":false,"prefix":"","firstName":"Nguyen","middleName":"Thi","lastName":"Hai","suffix":""},{"id":336587246,"identity":"f04dc62c-1286-4134-a50d-36c1f6f92bd0","order_by":1,"name":"Thao Hoang-Minh","email":"","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":false,"prefix":"","firstName":"Thao","middleName":"","lastName":"Hoang-Minh","suffix":""},{"id":336587247,"identity":"27e05d2a-4563-4109-bf53-4dc5af7ad9f1","order_by":2,"name":"Do Trung Hieu","email":"","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":false,"prefix":"","firstName":"Do","middleName":"Trung","lastName":"Hieu","suffix":""},{"id":336587248,"identity":"9cde8c1a-f9f0-45b6-af03-011d5f210e11","order_by":3,"name":"Ta Thi Hoai","email":"","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":false,"prefix":"","firstName":"Ta","middleName":"Thi","lastName":"Hoai","suffix":""},{"id":336587249,"identity":"30f9538d-9716-4400-8440-a731a5dab6e5","order_by":4,"name":"Bui Van Dong","email":"","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":false,"prefix":"","firstName":"Bui","middleName":"Van","lastName":"Dong","suffix":""},{"id":336587250,"identity":"f5c57dc9-2a3a-456b-92f1-b3d0643373b8","order_by":5,"name":"Luu Viet Dung","email":"","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":false,"prefix":"","firstName":"Luu","middleName":"Viet","lastName":"Dung","suffix":""},{"id":336587251,"identity":"8d5ce59b-f66a-478f-a13b-11a37e78acd7","order_by":6,"name":"Nguyen Thi Hoang Ha","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtklEQVRIiWNgGAWjYFACHgZmBgYbBsYGonWwgbWkka7lMAnOMpfvPcBcUHM+sXlGAuOHHwyH8whqsWzjS2Cecex2YuOMBGbJHobDxQS1GBzjMWDmYbttzDgjgUEa6KnEBuK0/DsH0sL8m3gtvG0H5IBa2IC22BCjJcfgMG9fshxjz8M2yx4DYrQcPmP4mOebHY9he/LhGz8qJAhrAYEDIMKwARSZBsSohwF5UhSPglEwCkbByAIA2HY1GkAQ4t4AAAAASUVORK5CYII=","orcid":"","institution":"Vietnam National University, Hanoi","correspondingAuthor":true,"prefix":"","firstName":"Nguyen","middleName":"Thi Hoang","lastName":"Ha","suffix":""}],"badges":[],"createdAt":"2024-07-11 09:08:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4723030/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4723030/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":62328231,"identity":"eb339217-06aa-4e3f-b4d8-df021458344d","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":141378,"visible":true,"origin":"","legend":"\u003cp\u003eProcedure of synthesis adsorbents and removal efficiency of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal by prepared materials\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/2b232f2b7846dc35c8fbac9b.png"},{"id":62328237,"identity":"7947f96a-04ac-4d3d-afdb-382fad59c6b3","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":364012,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of initial pH solution values on the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption capacity of BRK\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/ae8d1bb0701597752fb1eb57.png"},{"id":62328236,"identity":"ba349157-58a2-4c03-ac9d-02dd8111ef48","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1085719,"visible":true,"origin":"","legend":"\u003cp\u003eKinetics of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption by BRK\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/be8d29badea8a91ed167c5cd.png"},{"id":62328956,"identity":"22cb076c-f334-427d-a426-ba55832a1b45","added_by":"auto","created_at":"2024-08-13 03:21:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":479751,"visible":true,"origin":"","legend":"\u003cp\u003eAdsorption isotherms of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e onto BRK\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/7692062cf4996f0e844079e5.png"},{"id":62328239,"identity":"c209579c-faa3-4c71-b9e6-31f0fb47fcc4","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":344410,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of co-existing cations on the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption capacity of the BRK.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/d57e87c71d1cac4951917827.png"},{"id":62328234,"identity":"1f6731a9-78b0-439d-bb19-e26df832a6ac","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1735030,"visible":true,"origin":"","legend":"\u003cp\u003eSEM/EDX images of BRK before (a) and after (b) NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/ba24198e44a2af59a47f92a3.png"},{"id":62328238,"identity":"650f857f-2b11-4a10-b267-d3f34deaf4d3","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2183275,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of BRK before and after NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/bcc4a7bceeb1aeddb2f0a122.png"},{"id":62329619,"identity":"76b60c89-c6e5-46ec-a98c-52a46da1d1ae","added_by":"auto","created_at":"2024-08-13 03:29:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7257900,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/78b2123c-180f-418b-9b59-b0512e2d25cd.pdf"},{"id":62328233,"identity":"a2302856-6047-427f-b4ac-fe1667323a5e","added_by":"auto","created_at":"2024-08-13 03:13:12","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":326492,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"Graphicalabstract.png","url":"https://assets-eu.researchsquare.com/files/rs-4723030/v1/241d85fde6cb7de954f1e453.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Removal of ammonium from water by a bentonite biochar composite","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAmmonium (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) is an inorganic ion of nitrogen that is formed when organic molecules containing nitrogen are broken down and disposed of in urban wastewater and domestic wastewater. Ammonium contaminations are serious environmental issues in surface and groundwater which cause significant risks to ecosystems and human health [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. This is due to the fact that NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e has the potential to produce eutrophication and cause dissolved oxygen depletion. Thus, high NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentrations may result in biodiversity loss, degradation of ecosystem functions, and toxicity to natural habitats and aquaculture [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. According to the World Health Organization [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] in humans, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentrations above 200 mg/kg of body weight have the potential to be toxic or harmful to health.\u003c/p\u003e \u003cp\u003eMany treatment approaches, such as biological treatment, adsorption, photoelectronic, chemical precipitation, air aeration, and ion exchange, were investigated to reduce the negative consequences of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Among them, the biological process is the most cost-effective and successful approach for treating NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e in a domestic wastewater treatment plant. The procedure and development rate of the microorganisms used, however, are impacted by variations in environmental and water variables, such as temperature, thus critically affecting the operation of the water treatment system. These above factors are known as disadvantages of this technology. While considering the removal efficiency, cost-effectiveness, and simple operation, adsorption has emerged as a promising method to tackle NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e problems [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Still, there is always a challenge in developing suitable adsorbent materials that have high efficiency, low cost, and abundance [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUnlike metal-organic framework (MOF) materials, which are generally only used in laboratory settings due to their high cost, the adsorbents originating from agricultural waste and natural minerals are gaining much attention and are widely applied in both laboratory and field scales. This is because of their abundance of practicability, cost-effectiveness, stability, and renewability. Among these natural adsorbents such as bentonite, zeolite, and other natural clays (e.g. kaolinite, montmorillonite, vermiculite, and sepiolite), bentonite is widely used as clay adsorbent, owing to its cost-benefit, high content of montmorillonite (well-known clay mineral with high adsorption capacity), and worldwide distribution [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Bentonite possesses a 1:2 type layered structure, which consists of one silicon-oxygen tetrahedron sheet and two aluminum oxygen octahedron sheets. The layer might have a net negative charge, which could be readily balanced by several cations in aqueous solution (i.e., Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e) and contribute to the ion exchange capability of bentonite [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Furthermore, bentonite has the ability to bind to strengthen composites with controlled particle size due to the high content of montmorillonite mineral in its structure [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Eventually, bentonite is eco-friendly and non-toxic to the subsequent treatment, thus also confirming its applicability and sustainability for water treatment purposes.\u003c/p\u003e \u003cp\u003eBesides the above advantages, using adsorbent-based agricultural wastes for water treatment is also of great interest as a sustainable approach for added-values, zero-waste, and circular economy goals [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. For carbonization of biomass and increase of adsorption capacity by improving cation exchange efficiency, specific surface area, and stable structure, various methods for preparation (e.g., pyrolysis, gasification, and hydrothermal carbonization) and modification (acids, alkali, oxidizing agents, and metal ions) of biochar were adopted [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Different oxidative reagents (e.g., HNO\u003csub\u003e3\u003c/sub\u003e, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, and NaOH) were widely used to boost the quantity of oxygen-containing functional groups for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Besides, to enhance contaminant removal capacity, the combination of biochar and additives (e.g., clay minerals, metal oxides, single metals or couple metals, and carbonaceous materials), known as biochar-based composites, were also studied [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In this concept, biochar provides a porous structure to support the distribution of additives within its lattice, and this incorporation enhances the overall sorption capacity of the composite material [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe composites between biochar and clay materials have been widely investigated and developed for removing both organic and inorganic pollutants such as Pb [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], Cd [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], antibiotic ciprofloxacin [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], methylene blue (MB) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], phosphate and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Biochar bentonite composite has recently been used for the simultaneous removal of phosphate and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from water with maximum adsorption capacities of 132.2 and 39.5 mg/g [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. This composite was prepared by introducing peanut shell powder and bentonite and modified by the pyrolysis process and reagents (MgCl\u003csub\u003e2\u003c/sub\u003e and NaOH) [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, little attention was given to incorporate natural bentonite and rice husk\u0026ndash;one of the most abundant agricultural wastes in Vietnam, for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal from aqueous solution.\u003c/p\u003e \u003cp\u003eThe National Environmental Assessment Report in the period 2016\u0026ndash;2020 of Vietnam showed high concentrations of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e in the surface and groundwater which were as high as approximately 50 and 130 times higher than the allowable limits for surface (0.3 mg/L) and groundwater (1 mg/L) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. High NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentrations (50\u0026ndash;99 mg/L) were recorded in groundwater in the Red River Delta [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Of particular concern, local residents in some areas have been using groundwater contaminated with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e for drinking and domestic purposes [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Being the third largest rice exporter in the world in 2023 and with the availability of natural bentonite, a combination of bentonite and biochar derived from rice husk would contribute to not only tackling the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e pollution issue but also implementing waste-to-resource practice as a circular economy approach.\u003c/p\u003e \u003cp\u003eIn this study, a composite of bentonite and rice husk waste was prepared through a pyrolysis process and treated with KOH to enhance the cation exchange capacity (BRK). The successful fabrication of BRK adsorbent was confirmed throughout several characterization steps, including Fourier-transform infrared spectroscopy (FTIR), N\u003csub\u003e2\u003c/sub\u003e sorption analysis, and Scanning electron microscopy (SEM). In addition, the effects of several major factors for the removal of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e by BRK (i.e., pH solution, contact time, initial concentrations of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, temperature, coexisting ions, and desorption) were evaluated by a series of batch experiments.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials, chemicals, and reagents\u003c/h2\u003e \u003cp\u003eAll analytical chemicals and reagents, including NH\u003csub\u003e4\u003c/sub\u003eCl, NaOH, HCl, Ca(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, Mg(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, NaNO\u003csub\u003e3\u003c/sub\u003e, and KNO\u003csub\u003e3\u003c/sub\u003e in this study were purchased from Sigma-Aldrich and were used directly without any extra purification. A 1000 mg NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e/L stock solution was prepared by diluting 4.394 g of salt NH\u003csub\u003e4\u003c/sub\u003eCl into 1000 mL deionized water. The feed NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003esolutions used in the batch experiments were diluted from the stock solution using distilled water.\u003c/p\u003e \u003cp\u003eIn this study, natural bentonite was obtained from a bentonite mine in Di Linh district, Lam Dong province, Vietnam. Coarse fractions of non-clay size were removed by sieving and sedimentation and dried at 80 \u003csup\u003eo\u003c/sup\u003eC. The dried bentonite sample was then gently manual-milled in an agate mortar to obtain the material with a particle size of less than 40 \u0026micro;m. Chemical and mineral compositions of bentonite were prior characterized by Hoang-Minh et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Raw rice husks (RH) were collected in Hanoi, Vietnam and then washed with deionized water. After drying at 80 \u003csup\u003eo\u003c/sup\u003eC in an oven, the rice husks were then grinned and sieved to obtain a particle size of 0.5 mm. These prepared bentonite and RH samples were stored in plastic bags for further synthesis steps.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Synthesis of bentonite-biochar composite materials\u003c/h2\u003e \u003cp\u003eThe preparation of composite materials using bentonite and rice husk biochar, as well as their modification, via one and two stages, which is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In particular, 50 g of bentonite was thoroughly mixed with 50 mL of deionized water in a beaker, and the mixture was agitated utilizing a magnetic stirrer for an hour. An amount of 25 g RH was then added to the bentonite mixture, and the beaker was continuously stirred for 24h. After that, the solid part was separated from the liquid phase using 0.45 \u0026micro;m filters and dried at 80 \u003csup\u003eo\u003c/sup\u003eC for the subsequent 48 h to obtain a raw mixture of RH and bentonite.\u003c/p\u003e \u003cp\u003eIn the first step, the pristine combination of bentonite and rice husk biochar underwent a pyrolysis process at 400 and 500 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. The most typical pyrolysis temperatures (400 ℃ and 500 ℃) were selected for the modification of adsorbents [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The composite was then chemically modified via the second stage using KOH 2M. It should be noted that after each stage, the adsorbent was taken out of the mixture, bathed with distilled water until the solution was pH\u0026thinsp;=\u0026thinsp;7, and then dried at 80 ℃ for the next stage and used for the preliminary experiment.\u003c/p\u003e \u003cp\u003ePreliminary experiments for the determination of adsorbents were performed at identical conditions (i.e., pH\u0026thinsp;=\u0026thinsp;7, material dosage\u0026thinsp;=\u0026thinsp;2.0 g/L, initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration of 20 mg/L, and shaking speed\u0026thinsp;=\u0026thinsp;160 rpm). The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal rate of natural bentonite, raw rice husk, biochars after pyrolysis, and biochars after activation with KOH is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Pyrolysis process (400\u0026ndash;500\u0026deg;C) helped to improve removal efficiencies of bentonite (2.67%) and rice husk (1.13%) to 21.12\u0026ndash;25.95% (biochar) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). KOH treatment increased 117\u0026ndash;119% the removal efficiencies of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from water. According to the preliminary results, bentonite biochar composite (BRK) (sample 5, pyrolysis temperature\u0026thinsp;=\u0026thinsp;400 \u003csup\u003eo\u003c/sup\u003eC, KOH activated) was highlighted as the most effective material and was selected for further experiments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Adsorption experiment\u003c/h2\u003e \u003cp\u003eThe NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal performance of BRK material was examined by batch-scale studies. The influence of the initial pH solution, contact time, and initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration at various temperatures on the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal was then investigated. All experiments were conducted at a constant material dosage of 2.0 g/L by adding 0.1 g of adsorbent into 50 mL of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e solution with predetermined concentrations in an Erlenmeyer flask. The mixture was shaken at 160 rpm in a DAIHAN Labtech (Model LSI-2) machine. The contact time was adjusted following each category of experiments. The mixtures were filtered through 0.45 \u0026micro;m filters to separate the liquid and solid phases after the interval period of time. The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration in the liquid phase was then analyzed.\u003c/p\u003e \u003cp\u003eTo examine the effect of pH solution on NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal using BRK adsorbent, the study was conducted under a wide pH range from 2 to 12. The initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration of 20 mg/L and contact time of 24 hours was set in this experiment. The pH solution was adjusted to the appropriate level using 0.1 M HNO\u003csub\u003e3\u003c/sub\u003e and NaOH. The kinetic adsorption was carried out in solution with pH\u0026thinsp;=\u0026thinsp;7 and an initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration of 20 mg/L. The samples were taken at intervals of 1 min, 5 mins, 10 mins, 30 mins, 1 h, 2 h, 4 h, 8 h, 12 h, and 24 h. The isotherm adsorption was carried out at initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentrations ranging from 5, 10, 20, 30, 50, 70, 100, 150, 200, and 300 mg/L. The experiments were performed at three levels of temperatures (10, 30, and 50\u0026deg;C). To investigate the effect of coexisting cation ions (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e) at three different initial concentrations (10, 50, and 100 mg/L) on BRK adsorbent, the test was conducted at an initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration of 20 mg/L and pH\u0026thinsp;=\u0026thinsp;7.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Adsorbent properties and sample analysis\u003c/h2\u003e \u003cp\u003eThe characterizations of adsorbents were determined using the Scanning Electron Microscopy (SEM), the Energy-Dispersive X-ray (EDX) Spectroscopy, the Fourier-Transform Infrared Spectroscopy (FTIR), N\u003csub\u003e2\u003c/sub\u003e adsorption analysis, and point of zero charge. In particular, Scanning Electron Microscopy (SEM- Nano SEM FEI-450) integrated with Energy-Dispersive X-ray (EDX) Spectroscopy (TEAM Apollo XL-EDAX) was used to determine the elemental compositions of adsorbents and to visualize in detail the topography and morphology of the sample. An EDX detector connected to a scanning electron microscope (SEM) produces an elemental spectrum. This spectrum displays the presence and strength of distinctive X-ray peaks for various elements, as well as the precise weight and atomic occupancy ratio of the constituent elements that make up the adsorbents. N\u003csub\u003e2\u003c/sub\u003e adsorption analysis was performed by Nova touch 4LX/Anton Paar, USA. The Jasco FT/IR-6300 spectrometer, which operated within a wavenumber ranging from 4000\u0026ndash;500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, was used to detect the active functional groups available on the surface of the adsorbent. OriginPro peak-fitting method (OriginLab Corporation) was used to deconvolute the FTIR spectra. The drift method was used to calculate the BRK\u0026rsquo;s point of zero charge.\u003c/p\u003e \u003cp\u003eThe NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentrations in water samples were measured by continuous flow analysis which named Skalar method at wavelength 630 nm (SKALAR model 21050900, Netherlands). For chlorine donation, sodium hypochlorite and nitroprusside catalysts were employed. Ammonium standard solution of 1000 mg/L and a blank solution were used to ensure the accuracy of the analysis. The analytical detection limit for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is 5 \u0026micro;g/L.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Data analysis\u003c/h2\u003e \u003cp\u003eAll tests were duplicated, and experiment results were expressed using the mean and standard deviation data. Isotherm and kinetic adsorption parameters were calculated using the Origin program. The calculation of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption capacity of adsorbents at the equilibrium time (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e,\u003c/sub\u003e mg/g) and at time interval \u003cem\u003et (qt, mg/g)\u003c/em\u003e was performed using equations given in our previous publication [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The best-fit model was determined by calculating the coefficient of determination (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) and the chi-squared (\u003cem\u003eχ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) value. Chi-squared (\u003cem\u003eχ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) values and the coefficient of determination (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) values were calculated to identify the best-fit model. A \u003cem\u003eχ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e value near 0 indicates that the data acquired by model application and the experimental data are similar, while a high \u003cem\u003eχ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e indicates a significant bias between the model and the experiment.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Effects of pH solution\u003c/h2\u003e \u003cp\u003eThe effect of pH solution on NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Generally, the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption capacity of BRK was strongly affected by pH solution (2.0\u0026ndash;12.0). As a result, the adsorption process of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e on adsorbents was not favorably affected by acidic or alkaline conditions, with the pH range of 6 to 9 typically yielding the greatest equilibrium adsorption quantity.\u003c/p\u003e \u003cp\u003eIn this study, the ability of BRK to adsorb NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e increases following the increase of initial pH and decreases sharply when pH\u0026thinsp;\u0026gt;\u0026thinsp;9 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Essentially, pH solution is also a significant factor as it determines NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e speciation in water [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. According to the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e species stability and a function of pH diagram, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and its p\u003cem\u003eK\u003c/em\u003ea value were determined to be approximately 9.3 (p\u003cem\u003eK\u003c/em\u003ea) [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. In other words, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e often exists as ionized NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e when the pH solution is lower than 9.3. When the pH solution is greater than 9.3, the ammonia is found to be abundant and exists with its form of no charge (NH\u003csub\u003e3\u003c/sub\u003e). Raising the pH of the solution will hasten the NH\u003csub\u003e3\u003c/sub\u003e\u0026rsquo;s release from the solution since NH\u003csub\u003e3\u003c/sub\u003e in solution can readily cause volatility. As a result, solutions with pH values greater than 9.3 are anticipated to have a limited NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption capability.\u003c/p\u003e \u003cp\u003eAt low pH values (2\u0026ndash;4), proton H\u003csup\u003e+\u003c/sup\u003e from the acid environment had strong competition with ion NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e in the active side of the material, as the repulsion between positive ions and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e in solution; therefore, BRK adsorbed a negligible amount of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The removal efficiency of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e was remarkably reduced in an acid environment (pH\u0026thinsp;\u0026lt;\u0026thinsp;3) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. This is because extremely acidic pH will enrich the solution with protons and limit the ionization process of the acidic functional groups on adsorbents, which will reduce the ion-exchange sites available for the adsorption of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUnder weak acid and weak alkaline conditions (pH\u0026thinsp;=\u0026thinsp;5\u0026ndash;9), the ability to remove NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from the water of BRK was higher than in strong acid conditions and reached the highest value at pH\u0026thinsp;=\u0026thinsp;6 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). As reported by Eturki et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], their investigation also found that an ideal pH from 6 to 8 produced the greatest results. This change could be explained by: (1) the decrease of ion H\u003csup\u003e+\u003c/sup\u003e in solution led to the competition between H\u003csup\u003e+\u003c/sup\u003e and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e also reduced, (2) when the pH value reached 6\u0026ndash;8, the deprotonation of some groups might occur on the surface of the material, so NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e can be easily adsorbed onto BRK. Particularly, the prepared BRK adsorbent in this study had a point of zero charge (pH\u003csub\u003ePZC\u003c/sub\u003e) at 9.1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These results demonstrate that the surface of BRK has a positive charge when pH solution\u0026thinsp;\u0026lt;\u0026thinsp;pH\u003csub\u003ePZC\u003c/sub\u003e, and vice versa, the surface of BRK has a negative charge when pH solution\u0026thinsp;\u0026gt;\u0026thinsp;pH\u003csub\u003ePZC\u003c/sub\u003e. At this time, positively charged NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions were adsorbed on BRK via an ion exchange mechanism because the surface charge of BRK was positive when pH solution\u0026thinsp;\u0026lt;\u0026thinsp;pH\u003csub\u003ePZC\u003c/sub\u003e. When pH solution\u0026thinsp;\u0026gt;\u0026thinsp;pH\u003csub\u003ePZC\u003c/sub\u003e, the negatively charged BRK can adsorb positively charged NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e through an electrostatic attraction mechanism.\u003c/p\u003e \u003cp\u003eOn the other hand, with a pH value\u0026thinsp;\u0026gt;\u0026thinsp;9, the solution was strongly alkaline and more negative due to the existence of the \u0026ndash;OH group. Therefore, ion NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e preferentially reacts with \u0026ndash;OH to produce gas (NH\u003csub\u003e3\u003c/sub\u003e). This result is in agreement with prior studies [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Adsorption kinetics\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the effects of the contact time on the removal capacity of BRK toward NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e. Adsorption kinetic data showed NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption rate by BRK was rapid within the first 5 mins, then decreased with time, and reached the equilibrium state after 30 mins. Approximately 35, 43, and 50% NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from the solution was absorbed onto BRK at the early stage of 1, 5, and 10 mins, which indicated that BRK had a strong affinity toward NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ion. Obviously, within the first contact time of 15 mins, the adsorption performance of BRK increased significantly. This can be explained by the fact that at the initial stage, a large amount of vacant sites on the adsorbent\u0026rsquo;s surface that are available and not yet occupied readily interact with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e. Additionally, the active functional groups on BRK\u0026rsquo;s surface were available and readily for bonding with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions.\u003c/p\u003e \u003cp\u003eAfter 30 mins, the adsorption capacity reached equilibrium, with their removal efficiency reaching 53%. In this period, the BRK\u0026rsquo;s active site had already started to connect to and bond with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e. As a result, there was a reduced space for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e to be adsorbed, which led to the amount of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorbed by BRK reducing and BRK\u0026rsquo;s adsorption capacity decreasing. Therefore, the adsorption process approached saturation gradually. The adsorption capacity remained almost constant after 60 mins of adsorption when compared to the first 30 mins. The adsorption capacity and removal efficiency of BRK at 24 h was 5.34 mg/g and 54%, respectively. The adsorption capacity did not fluctuate significantly or was virtually unchanged. This is due to the fact that almost all BRK\u0026rsquo;s active site was occupied during this time.\u003c/p\u003e \u003cp\u003eThe experimental data were fitted using the Pseudo-First Order (PFO), Pseudo-Second Order (PSO), and Elovich models (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Kinetic adsorption data calculated from three models for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The value of Chi-squared (\u003cem\u003eχ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) and the coefficient of determination (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) for PFO, PSO, and Elovich model of BRK material were 0.13\u0026ndash;0.95, 0.038\u0026ndash;0.99, and 0.12\u0026ndash;0.95, respectively. Adsorption by BRK was better described by the PSO model (with higher \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e and lower \u003cem\u003eχ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) than that for the two other models. While the adsorption rate of the PFO model normally depends on the diffusion of adsorbates on the adsorbent\u0026rsquo;s surface, the adsorption rate by PSO is controlled by the interaction of adsorption sites with the adsorbate. On the other hand, in the PFO adsorption kinetic model, the number of uncopied adsorption active sites on the adsorbent\u0026rsquo;s surface does not control the adsorption rate. In contrast, the PSO model was related to the uncopied active site in the adsorbent. It is considered a chemical interaction between the adsorbent and the adsorbate. This result suggests that NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption may be controlled by the chemisorption mechanism (ion exchange, electrostatic attraction, and complexation), which is primarily responsible for managing the contaminant's adsorption [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Alshameri et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] investigated the adsorption test of natural clay materials toward NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e; they stated that the adsorption process of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e onto clay materials was presented by PSO kinetics. The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption process can be explained by the following steps: (1) moving NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from the liquid phase to the liquid-solid interface; (2) transferring the solid phase on the BRK\u0026rsquo;s surface; and (3) then diffusing into the BRK\u0026rsquo;s pores.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMoreover, the experimentally derived adsorption capacities (\u003cem\u003eq\u003c/em\u003e\u003csub\u003et,\u003cem\u003ee\u003c/em\u003exp =\u003c/sub\u003e 5.336 mg/g ) were nearly close to the computed data (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e,cal\u003c/sub\u003e) from the PSO model (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e = 5.31 mg/g). The adsorption capacity obtained from the PFO kinetic model (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e = 5.17 mg/g) was lower than that of experiment adsorption capacity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eKinetic parameters for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption by BRK\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModels\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBRK\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003eexp\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003ePseudo-first order\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1/min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eꭓ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003ePseudo-second order\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eqe\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.31\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eg/ mg \u0026times; min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eꭓ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.038\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003eElovich model\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eα\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg/(g\u0026times;min)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.97 x 10^6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eβ\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eg/mg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eꭓ\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Adsorption isotherms\u003c/h2\u003e \u003cp\u003eThe effect of initial NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentrations (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e = 5\u0026ndash;300 mg/L) on the adsorption capacity by BRK were evaluated at various temperatures through adsorption isotherms (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The results showed that temperature was a significant factor in the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption process. The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e absorption capability of BRK reduced as the temperature rose from 10\u0026deg;C to 50\u0026deg;C. In other words, the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal by BRK reached its highest at 10 ℃, and lowest at 50 ℃. These results also suggested that the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption process on BRK adsorbent was exothermic and the low-temperature environment is favorable. The observed trend of temperature influence was in agreement with previous findings on activated carbon made from coconut shells [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], corncobs [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], and modified bentonite [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption process onto modified bentonite and corncob waste-derived activated carbon constituted an exothermic reaction [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. In addition, many others have documented comparable isotherm shape observations [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], when studying NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption by materials derived from agriculture wastes or bentonite materials and their modified forms.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe isothermal model fitting for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption onto BRK is provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In this study, the adsorption process and adsorption behavior of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e on BRK were adequately described by the fit models, which comprised the Langmuir and Freundlich. The isotherm model fit data was calculated and presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The results show that the Langmuir isotherm model was the best match for the experimental data of BRK at all three investigated temperatures (10, 30, and 50 ℃). This is due to \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e and \u003cem\u003eχ2\u003c/em\u003e values at 10, 30, and 50 ℃ of the Langmuir model, which were larger and smaller, respectively, when compared to those of the Freundlich model. The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e maximum adsorption of BRK obtained from the Langmuir model were 22.51, 20.57, and 16.22 mg/g at 10, 30, and 50 ℃, respectively. Therefore, when the temperature increases to 50 ℃, the capability to absorb NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e decreases approximately 28%, indicating that the interaction between BRK and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e becomes weaker following the increase in temperature. In addition, the results of the experiments demonstrated a good agreement with the Langmuir model, suggesting that the adsorption behavior of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e on the BRK was mainly determined by the formation of the adsorption monolayer. The adsorption process of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e on six natural clay materials (NCM) are also monolayer due to the isotherm adsorption data obtained which were coincident with the Langmuir model [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameters of the adsorption isotherm onto BRK material\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eModel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eUnit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eTemperatures\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10 ℃\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30 ℃\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e50 \u003csup\u003e℃\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eLangmuir model\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003emg/g\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16.22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eL\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL/mg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.037\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.054\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eX\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eFreundlich model\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003e(mg/g)/(mg/L)\u003c/em\u003e\u003csup\u003e\u003cem\u003en\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eX\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents a comparison between the Langmuir maximum adsorption capacity of BRK and some other materials studied in the literature on removal of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e. As, expected, BRK adsorbents (\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e = 20.57) demonstrated a higher adsorption capacity of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e than other materials such as the pristine biochar derived from maple wood (5.44 mg/g) [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], pine sawdust (5.38 mg/g) [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], the natural bentonite from Algeria (19.01 mg/g) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], bentonite from Indonesia (12.37 mg/g) [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], the modified biochar of waste spruce sawdust (17.96 mg/g) [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], of corncob (17.03 mg/g) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], the modified bentonite (5.66 mg/g) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], and the composite of bentonite and hydrochar (23.67 mg/g) [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe Langmuir maximum adsorption capacity of some investigated adsorbents toward NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAdsorbent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInitial concentrations\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003em/V\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBRK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5-300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003eThis study\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaple wood biochar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026ndash;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePine sawdust biochar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026ndash;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBentonite from Algeria\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u0026ndash;10000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e19.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBentonite from Indonesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModified Biochar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u0026ndash;110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e17.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCorncob activated carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u0026ndash;105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e17.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemically Activated Biochar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50\u0026ndash;600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModified bentonite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026ndash;200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u0026ndash;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydrochar from Koi fish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBentonite hydrochar composite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Effects of existing ions\u003c/h2\u003e \u003cp\u003eIn this study, four commonly encountered cations (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e) have been selected to examine the (inhibitory) influence of these ions on the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal process by BRK (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). These cations were tested at three initial concentrations of 10, 50, and 100 mg/L. The results showed that the removal efficiencies of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e had significantly decreased due to the strong competition between cations (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e) and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions in aqueous solution. Generally, when the concentration of co-existence cation was at 100 mg/L, the removal capacity of BRK toward NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e decreased in the order of no competitor\u0026thinsp;\u0026gt;\u0026thinsp;K\u003csup\u003e+\u003c/sup\u003e \u0026gt; Na\u003csup\u003e+\u003c/sup\u003e \u0026gt; Mg\u003csup\u003e2+\u003c/sup\u003e \u0026gt; Ca\u003csup\u003e2+\u003c/sup\u003e. Similar trends were found in other studies [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong investigated co-existing cations, divalent cations (Ca\u003csup\u003e2+\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e) were found to possess more sway than monovalent cations (Na\u003csup\u003e+\u003c/sup\u003e and K\u003csup\u003e+\u003c/sup\u003e) \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e. Because divalent cations have a divalent charge as opposed to monovalent cations, as a result, they have occupied more adsorption sites. In other words, they were stronger competitors for the adsorption site leading to reducing the removal efficiency of BRK [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Furthermore, it was shown that the two major components of water hardness, Ca and Mg, had concentration ranges between 80 and 200 mg/L. In fact, hard water inhibits the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e removal efficiency in wastewater treatment plants. Furthermore, the removal capacity of the adsorbent is observed to be influenced by the concentrations of cations. An increased amount of co-existing cations leads to a lower adsorption capacity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Adsorbent characteristics\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea displays the scanning electron microscopy (SEM) images of BRK before NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption. The surface of BRK displays a multitude of holes and huge grooves of varying widths, indicating the composite of bentonite and biochar derived from rice husk materials had a porous and asymmetric surface structure. With its composition containing biochar materials, BRK had a rich porous structure. The SEM images of BRK showed that the activation mediated by KOH may promote BRK pore development, leading to the adsorption capacity of materials. This result is similar to those reported by others [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. In addition, via the SEM image, it can be concluded that the BRK not only contains biochar adsorbent but also has bentonite in its composition. The presence of bentonite clay can be confirmed through the overlaid layer or plate-like appearance of bentonite (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). Et-Tayea et al. [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] stated that the surface microscopic morphology of bentonite features aggregates of spherical, heterogeneous-sized bentonite grains with an impressive compact structure, as well as layered, overlapping layers. Or Ashiq et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] prepared the composite of biochar based bentonite (MSW-BC) for removing antibiotic ciprofloxacin. The MSW-BC surface shares many similarities with the BRK surface. Its SEM image is characterized by a significant amount of pores, which constitute a property of biochar, and a plate-like layer, known to be a feature of bentonite. These results suggest that the BRK was successfully prepared.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea also indicates the EDX results for composite of bentonite and biochar derived from rice husk (BRK) treated by KOH solution. Obviously, the BRK\u0026rsquo;s composition possesses C, O, Si, K, Ca, Fe. The presence of a large amount of K could be explained for the successful activation by KOH solution.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb shows that there are no visible changes in the surface morphology of BRK after NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption. The NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-laden BRK still exhibited a lot of pore and had a porous structure. There is one significant change in the weight percent of metal elements (K, Ca, Fe) in the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-laden BRK. EDX data indicated that the weight percent of K, Ca, Fe decreased from 6,43\u0026ndash;0.36%; 1,39% to 1,06%; 2,22 5 to 1.04%, respectively. Among them, the K element indicated a remarkably decreased rate than two other elements. This result is in line with the reports of Alshameri et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] and Yu et al. [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. This result suggests that it could be due to ion exchange of these elements with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e or called ion exchange mechanism.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe FTIR spectra provide valuable information on the surface chemistry of BRK both before and after adsorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). It can be seen that BRK possesses a lot of common functional groups that are found in other biochar adsorbents, such as OH, C\u0026thinsp;=\u0026thinsp;O, C\u0026thinsp;=\u0026thinsp;C, and CO [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. They are pieces of evidence for confirming the presence of the biochar adsorbent in its component of BRK. The stretching vibration of \u0026ndash;OH is specifically responsible for a noticeable broad peak located at 3425 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e on the surface of the BRK adsorbents before and after NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption. The peak at about 1622 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was identified as the stretching vibration of C\u0026thinsp;=\u0026thinsp;O in carboxyl groups or aliphatic ketone, whereas the bands at around 2372 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were associated with the stretching vibrations of C\u0026thinsp;=\u0026thinsp;C and C-H [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. In addition, a small peak at about 1031 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e observed in BRK pristine material was featured as the stretching vibration of Si-O, which is commonly found in bentonite clay materials [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. All things considered, BRK was rich in functional surface groups which provided the basis for removing NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions from aqueous solution. The infrared spectrum also revealed that the distinctive peaks at \u0026ndash;OH had clearly shifted following adsorption, which was caused by the complexation of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e with oxygen-containing functional groups [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe surface properties information of BRK obtained by the nitrogen adsorption/desorption isotherm technique is provided in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It can be seen from Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, that the specific surface areas of BRK pristine and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-laden BRK were 4.89 and 17.72 m2/g, respectively. Obviously, after NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption, the specific surface area of BRK was gently increased. In addition, the pore volume of BRK was increased from 0.009 cm3/g to 0.024 cm3/g after the adsorption process. These particular results suggest that NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorbed on BRK via a pore-filling mechanism might be negligible.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe surface properties information of BRK\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurface properties\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBRK pristine\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-laden BRK\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBET specific surface area (\u003cem\u003eS\u003c/em\u003e\u003csub\u003eBET\u003c/sub\u003e - m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePore volume cm\u003csup\u003e3\u003c/sup\u003e/g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.024\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePore radius (nm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Possible adsorption mechanisms\u003c/h2\u003e \u003cp\u003eThe previous mechanism studies found that the most predominant adsorption mechanisms in removal of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e by the clay materials and biochar adsorbents were ion exchange [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], electrostatic attraction [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], pore-filling mechanism, and surface complexation. Through a series of batch experiments conducted at a pH of 7.0 and characterization of pristine and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e laden BRK, the potential NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption mechanism on BRK was identified. Firstly, the pristine BRK had a tiny specific surface area (4.89 m\u003csup\u003e2\u003c/sup\u003e/g). However, after the adsorption process, the BRK loaded with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e had a greater S\u003csub\u003eBET\u003c/sub\u003e (17.72 m\u003csup\u003e2\u003c/sup\u003e/g) than the pristine BRK. The findings suggested that the pore-filling mechanism may not be crucial to the adsorption process. Moreover, according to [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e], there was no relationship between the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e adsorption capacity and the specific surface area.\u003c/p\u003e \u003cp\u003eAs mentioned in Section \u003cspan refid=\"Sec9\" class=\"InternalRef\"\u003e3.1\u003c/span\u003e, with its pH\u003csub\u003ePZC\u003c/sub\u003e at 9.1, BRK possessed a positive charge when pH solution of 7.0, thus positively charged NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions were exchanged with positively charged BRK through an ion exchange mechanism. In other words, the ion exchange is of great significance in removing NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from the water environment. The ion exchange mechanism is also supported by the results of SEM/EDX that the percentage of K elements in pristine BRK decreased significantly (from 6.43\u0026ndash;0.36%) after adsorption process, possibly due to ion exchange of K\u003csup\u003e+\u003c/sup\u003e with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions in solution [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Additionally, it was discovered by the FTIR analysis above that NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e complexed with oxygen-containing functional groups on the surface of BRK, such as \u0026ndash;OH, during the adsorption process.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this study, a bentonite biochar composite (BRK) from natural bentonite and rice husk was successfully synthesized at a pyrolysis temperature of 400\u0026deg;C and then treated with KOH. The batch experimental data showed that the adsorption capacity of BRK for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e significantly depended on the pH solution (2.0\u0026ndash;12.0) and co-existing cations (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e). The PSO model provided a better description of the kinetic adsorption of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e on BRK than the PFO and Elovich models. BRK outperformed other adsorbents in the literature with a maximum Langmuir adsorption capacity of 20.57 mg NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e/g at 30 ℃. The characterization of the adsorbent and batch investigations showed that the ion exchange was found to be the primary mechanism for the removal of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e by BRK. BRK is an effective and cost-effective material for the treatment of water contaminated with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e. Column and pilot field experiments using real water should be conducted for feasible assessment for the practical application of BRK.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u0026nbsp;\u003c/strong\u003eThis study was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) (grant number 105.99-2019.311).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u003c/strong\u003es\u003c/p\u003e\n\u003cp\u003eConceptualization: N.T.H., T.H.-M., N.T.H.H.; Methodology: N.T.H., T.H.-M., N.T.H.H., D.T.H., T.T.H., N.V.D., L.V.D.; Experiment: N.T.H., D.T.H., T.T.H., B.V.D.; Analysis: L.V.D., D.T.H., T.T.H.; Writing original draft: N.T.H.; Writing review and editing: T.H.-M., N.T.H.H., D.T.H., L.V.D., T.T.H., B.V.D.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This study was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) (grant number 105.99-2019.311).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publish\u003c/strong\u003e All the authors have agreed to publish this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability\u003c/strong\u003e All the data generated or analyzed during this study are available upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHan B, Butterly C, Zhang W, He J-Z, Chen D (2021) Adsorbent materials for ammonium and ammonia removal: A review. J Clean Prod 283:124611. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jclepro.2020.124611\u003c/span\u003e\u003cspan address=\"10.1016/j.jclepro.2020.124611\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDias T, Clemente A, Martins-Lou\u0026ccedil;\u0026atilde;o MA, Sheppard L, Bobbink R, Cruz C (2014) Ammonium as a driving force of plant diversity and ecosystem functioning: observations based on 5 Years' manipulation of N dose and form in a mediterranean ecosystem. PLoS ONE 9(4):e92517. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1371/journal.pone.0092517\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0092517\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWorld Health Organization \u0026amp; International Programme on Chemical Safety (\u0026lrm;1996)\u0026lrm; Guidelines for drinking-water quality. Vol. 2, Health criteria and other supporting information (2nd ed). World Health Organization. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://iris.who.int/handle/10665/38551\u003c/span\u003e\u003cspan address=\"https://iris.who.int/handle/10665/38551\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou Y, Wang J (2023) Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective. Chemosphere 334:139027. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2023.139027\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2023.139027\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAngar Y, Djelali NE, Kebbouche-Gana S (2017) Investigation of ammonium adsorption on Algerian natural bentonite. Environ Sci Pollut Res Int 24:11078\u0026ndash;11089. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-016-6500-0\u003c/span\u003e\u003cspan address=\"10.1007/s11356-016-6500-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBananezhad B, Islami MR, Ghonchepour E, Mostafavi H, Tikdari AM, Rafiei HR (2019) Bentonite clay as an efficient substrate for the synthesis of the super stable and recoverable magnetic nanocomposite of palladium (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/Bentonite-Pd). Polyhedron 162:192\u0026ndash;200. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.poly.2019.01.054\u003c/span\u003e\u003cspan address=\"10.1016/j.poly.2019.01.054\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSeredych M, Ania C, Bandosz TJ (2016) Moisture insensitive adsorption of ammonia on resorcinol-formaldehyde resins. J Hazard Mater 305:96\u0026ndash;104. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2015.11.022\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2015.11.022\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStylianou M, Laifi T, Bennici S, Dutournie P, Limousy L, Agapiou, Papamichael I, Khiari B, Jeguirim M, Zorpas AA (2023) Tomato waste biochar in the framework of circular economy. Sci Total Environ 871:161959. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2023.161959\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2023.161959\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang J, Wang S (2019) Preparation, modification and environmental application of biochar: A review. J Clean Prod 227:1002\u0026ndash;1022. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jclepro.2019.04.282\u003c/span\u003e\u003cspan address=\"10.1016/j.jclepro.2019.04.282\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXie L, van Zyl D (2020) Distinguishing reclamation, revegetation and phytoremediation, and the importance of geochemical processes in the reclamation of sulfidic mine tailings: A review. Chemosphere 252:126446. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2020.126446\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2020.126446\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVu MT, Chao H-P, Van Trinh T, Le TT, Lin C-C, Tran HN (2018) Removal of ammonium from groundwater using NaOH-treated activated carbon derived from corncob wastes: Batch and column experiments. J Clean Prod 180:560\u0026ndash;570. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jclepro.2018.01.104\u003c/span\u003e\u003cspan address=\"10.1016/j.jclepro.2018.01.104\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePremarathna KSD, Rajapaksha AU, Sarkar B, Kwon EE, Bhatnagar A, Ok YS, Vithanage M (2019) Biochar-based engineered composites for sorptive decontamination of water: A review. J Chem Eng 372:536\u0026ndash;550. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2019.04.097\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2019.04.097\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang Y, Song X, Xu Z, Cao X, Song J, Huang W, Ge X, Wang H (2021) Adsorption of nitrate and ammonium from water simultaneously using composite adsorbents constructed with functionalized biochar and modified zeolite. Water Air Soil Pollut 232:198. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11270-021-05145-9\u003c/span\u003e\u003cspan address=\"10.1007/s11270-021-05145-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao Y, Gao B, Fang J, Zhang M, Chen H, Zhou Y, Creamer AE, Sun Y, Yang L (2014) Characterization and environmental applications of clay\u0026ndash;biochar composites. J Chem Eng 242:136\u0026ndash;143. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2013.12.062\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2013.12.062\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao X, Zhongjie W, Mei C, Rongxin S, Lianke X, Renliang H (2021) Co-modification of biochar and bentonite for adsorption and stabilization of Pb\u003csup\u003e2+\u003c/sup\u003e ions. J Inorg Mater 36:1083\u0026ndash;1090. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.15541/jim20200745\u003c/span\u003e\u003cspan address=\"10.15541/jim20200745\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJing Y, Cao Y, Yang Q, Wang X (2020) Removal of cd (II) from aqueous solution by clay-biochar composite prepared from Alternanthera philoxeroides and bentonite. BioResources 15(1):598\u0026ndash;615. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.15376/biores.15.1.598-615\u003c/span\u003e\u003cspan address=\"10.15376/biores.15.1.598-615\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAshiq A, Adassooriya NM, Sarkar B, Rajapaksha AU, Ok YS, Vithanage M (2019) Municipal solid waste biochar-bentonite composite for the removal of antibiotic ciprofloxacin from aqueous media. J Environ Manage 236:428\u0026ndash;435. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2019.02.006\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2019.02.006\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXi H, Zhang X, Hua Zhang A, Guo F, Yang Y, Lu Z, Ying G, Zhang J (2022) Concurrent removal of phosphate and ammonium from wastewater for utilization using Mg-doped biochar/bentonite composite beads. Sep Purif Technol 285:120399. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.seppur.2021.120399\u003c/span\u003e\u003cspan address=\"10.1016/j.seppur.2021.120399\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMedha I, Chandra S, Bhattacharya J, Samal B, Vanapalli KR (2023) Development of rice straw-derived biochar-bentonite composite and its application for in situ sequestration of ammonium and phosphate ions in the degraded mine soil. Environ Manage 71:1065\u0026ndash;1086. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00267-022-01775-9\u003c/span\u003e\u003cspan address=\"10.1007/s00267-022-01775-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMONRE (2021) National Environmental Assessment Report in the period 2016\u0026ndash;2020. Dan Tri Publishing House, p 168\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWinkel LHE, Pham TKT, Vi ML, Stengel C, Amini M, Nguyen TH, Pham HV, Berg M (2011) Arsenic pollution of groundwater in Vietnam exacerbated by deep aquifer exploitation for more than a century. Proc Natl Acad Sci USA 108:1246\u0026ndash;1251. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1073/pnas.1011915108\u003c/span\u003e\u003cspan address=\"10.1073/pnas.1011915108\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHai NT, Hang HT, Hieu DT, Hien PT, Hoa BT, Hoang-Minh T, Ha NTH (2022) Groundwater quality in Tram Long commune, Ung Hoa district, Hanoi: current status and solutions. Proceedings of the International Conference on Sustainability in Environment and Agriculture (ICSEA2022), 115\u0026ndash;121\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHoang-Minh T, Kasbohm J, Nguyen-Thanh L, Nga PT, Lai LT, Duong NT, Thanh ND, Thuyet NTM, Anh DD, Pusch R (2019) Use of TEM-EDX for structural formula identification of clay minerals: a case study of Di Linh bentonite, Vietnam. J Appl Crystallogr 52:133\u0026ndash;147. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1107/S1600576718018162\u003c/span\u003e\u003cspan address=\"10.1107/S1600576718018162\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNguyen TH, Tran HN, Vu HA, Trinh MV, Nguyen TV, Loganathan P, Vigneswaran S, Nguyen TM, Trinh VT, Vu DL, Nguyen THH (2020) Laterite as a low-cost adsorbent in a sustainable decentralized filtration system to remove arsenic from groundwater in Vietnam. Sci Total Environ 699:134267. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2019.134267\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2019.134267\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLangenfeld NJ, Kusuma P, Wallentine T, Criddle CS, Seefeldt LC, Bugbee B (2021) Optimizing nitrogen fixation and recycling for food production in regenerative life support systems. Front Astron Space Sci 8:699688. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3389/fspas.2021.699688\u003c/span\u003e\u003cspan address=\"10.3389/fspas.2021.699688\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarri RR, Sahu JN, Chimmiri V (2018) Critical review of abatement of ammonia from wastewater. J Mol Liq 261:21\u0026ndash;31. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.molliq.2018.03.120\u003c/span\u003e\u003cspan address=\"10.1016/j.molliq.2018.03.120\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEturki S, Ayari F, Jedidi N, Ben Dhia H (2012) Use of clay mineral to reduce ammonium from wastewater Effect of various parameters. Surf Engin Appl Electrochem 48:276\u0026ndash;283. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3103/S1068375512030064\u003c/span\u003e\u003cspan address=\"10.3103/S1068375512030064\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheng H, Zhu Q, Xing Z (2019) Adsorption of ammonia nitrogen in low temperature domestic wastewater by modification bentonite. J Clean Prod 233:720\u0026ndash;730. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jclepro.2019.06.079\u003c/span\u003e\u003cspan address=\"10.1016/j.jclepro.2019.06.079\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang C, Liu X, Yang T, Sridhar D, Algadi H, Bin Xu B, El-Bahy ZM, Li H, Ma Y, Li T, Guo Z (2023) An overview of metal-organic frameworks and their magnetic composites for the removal of pollutants. Sep Purif Technol 320:124\u0026ndash;144. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.seppur.2023.124144\u003c/span\u003e\u003cspan address=\"10.1016/j.seppur.2023.124144\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlshameri A, He H, Zhu J, Xi Y, Zhu R, Ma L, Tao Q (2018) Adsorption of ammonium by different natural clay minerals: Characterization, kinetics and adsorption isotherms. Appl Clay Sci 159:83\u0026ndash;93. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.clay.2017.11.007\u003c/span\u003e\u003cspan address=\"10.1016/j.clay.2017.11.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoopathy R, Karthikeyan S, Mandal AB, Sekaran G (2013) Adsorption of ammonium ion by coconut shell-activated carbon from aqueous solution: kinetic, isotherm, and thermodynamic studies. Environ Sci Pollut Res 20:533\u0026ndash;542. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-012-0911-3\u003c/span\u003e\u003cspan address=\"10.1007/s11356-012-0911-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang B, Lehmann J, Hanley K, Hestrin R, Enders A (2015) Adsorption and desorption of ammonium by maple wood biochar as a function of oxidation and pH. Chemosphere 138:120\u0026ndash;126. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2015.05.062\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2015.05.062\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang HI, Lou K, Rajapaksha AU, Ok YS, Anyia AO, Chang SX (2018) Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars. Environ Sci Pollut Res 25:25638\u0026ndash;25647. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-017-8551-2\u003c/span\u003e\u003cspan address=\"10.1007/s11356-017-8551-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIsmadji S, Tong DS, Soetaredjo FE, Ayucitra A, Yu WH, Zhou CH (2016) Bentonite hydrochar composite for removal of ammonium from Koi fish tank. Appl Clay Sci 119:146\u0026ndash;154. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.clay.2015.08.022\u003c/span\u003e\u003cspan address=\"10.1016/j.clay.2015.08.022\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShang L, Xu H, Huang S, Zhang Y (2018) Adsorption of ammonium in aqueous solutions by the modified biochar and its application as an effective N-fertilizer. Water Air Soil Pollut 229:1\u0026ndash;15. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11270-018-3956-1\u003c/span\u003e\u003cspan address=\"10.1007/s11270-018-3956-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHsu D, Lu C, Pang T, Wang Y, Wang G (2019) Adsorption of Ammonium Nitrogen from Aqueous Solution on Chemically Activated Biochar Prepared from Sorghum Distillers Grain. Appl Sci 9:5249. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/app9235249\u003c/span\u003e\u003cspan address=\"10.3390/app9235249\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHou J, Huang L, Yang Z, Zhao Y, Deng C, Chen Y, Li X (2016) Adsorption of ammonium on biochar prepared from giant reed. Environ Sci Pollut Res Int 23:19107\u0026ndash;19115. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-016-7084-4\u003c/span\u003e\u003cspan address=\"10.1007/s11356-016-7084-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu H, Xu G, Li G (2021) Preparation of porous biochar based on pharmaceutical sludge activated by NaOH and its application in the adsorption of tetracycline. J Colloid Interface Sci 587:271\u0026ndash;278. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jcis.2020.12.014\u003c/span\u003e\u003cspan address=\"10.1016/j.jcis.2020.12.014\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCollivignarelli MC, Illankoon WAMAN, Milanese C, Calatroni S, Caccamo FM, Medina-Llamas M, Girella A, Sorlini S (2024) Preparation and modification of biochar derived from agricultural waste for metal adsorption from urban wastewater. Water 16(5):698. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/w16050698\u003c/span\u003e\u003cspan address=\"10.3390/w16050698\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEt-Tayea Y, Harrati A, Rachid A, Nasri H, Attou A, Arkame Y, Manni A, Mamouch Y, El Bouari A, El Khazanti F, Sadik C (2023) Mineralogical and physico-chemical characterization of bentonite materials from the Oued Zemmour area (Oriental Rif, Nador-Morocco): Valorization in ceramic field. Bol Soc Esp Ceram V 62:268\u0026ndash;283. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.bsecv.2022.03.001\u003c/span\u003e\u003cspan address=\"10.1016/j.bsecv.2022.03.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYu Q, Xia D, Li H, Ke L, Wang Y, Wang H, Zheng Y, Li Q (2016) Effectiveness and mechanisms of ammonium adsorption on biochars derived from biogas residues. RSC Adv 6:88373\u0026ndash;88381. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C6RA16913A\u003c/span\u003e\u003cspan address=\"10.1039/C6RA16913A\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu X, Liao J, Song H, Yang Y, Guan C, Zhang Z (2019) A Biochar-Based Route for Environmentally Friendly Controlled Release of Nitrogen: Urea-Loaded Biochar and Bentonite Composite. Sci Rep 9:9548\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhirong L, Azhar Uddin M, Zhanxue S (2011) FT-IR and XRD analysis of natural Na-bentonite and Cu(II)-loaded Na-bentonite. Spectrochim Acta Mol Biomol Spectrosc 79:1013\u0026ndash;1016. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.saa.2011.04.013\u003c/span\u003e\u003cspan address=\"10.1016/j.saa.2011.04.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAn Q, Li Z, Zhou Y, Meng F, Zhao B, Miao Y, Deng S (2021) Ammonium removal from groundwater using peanut shell based modified biochar: Mechanism analysis and column experiments. J Water Process Eng 43:102219. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jwpe.2021.102219\u003c/span\u003e\u003cspan address=\"10.1016/j.jwpe.2021.102219\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSumaraj PLP (2017) Influence of surface chemistry of carbon materials on their interactions with inorganic nitrogen contaminants in soil and water. Chemosphere 184:532\u0026ndash;547. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2017.06.021\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2017.06.021\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"colloid-and-polymer-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Colloid and Polymer Science](https://www.springer.com/journal/396) ","snPcode":"396","submissionUrl":"https://mc.manuscriptcentral.com/cps","title":"Colloid and Polymer Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"adsorption, ammonium, agricultural waste, bentonite, composite, water treatment","lastPublishedDoi":"10.21203/rs.3.rs-4723030/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4723030/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA new adsorbent of bentonite biochar composite (BRK) from natural bentonite and rice husk was synthesized for removal of ammonium (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) from water. The preparation of the adsorbent consisted of a pyrolysis process at 400 °C and activation of biochar with KOH to obtain BRK. Various advanced techniques were applied to characterize the investigated adsorbent, including Fourier-transform infrared spectroscopy (FTIR), N\u003csub\u003e2\u003c/sub\u003e adsorption analysis, scanning electron microscopy (SEM) integrated with Energy-Dispersive X-ray (EDX) Spectroscopy. The point of zero charge of BRK was 9.1. The pH solution strongly affected BRK’s adsorption capacity to NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions in the solution. The removal efficiencies of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e were considerably diminished in the presence of coexisting cations (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e). The Langmuir adsorption capacity of BRK for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e was in the following order: 22.51 mg/g (10 \u003csup\u003eo\u003c/sup\u003eC) \u0026gt; 20.57 mg/g (30\u003csup\u003e o\u003c/sup\u003eC) \u0026gt; 16.22 mg/g (50 \u003csup\u003eo\u003c/sup\u003eC). The kinetic experiments demonstrated that the adsorption equilibrium was achieved after 30 mins of contact. The ion-exchange was found to be the main adsorption mechanism for removing NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e by BRK. This study proved that BRK is a low-cost and sustainable adsorbent derived from natural bentonite and rice husk and it is advantageous for successfully removing NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e from water.\u003c/p\u003e","manuscriptTitle":"Removal of ammonium from water by a bentonite biochar composite","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-13 03:13:07","doi":"10.21203/rs.3.rs-4723030/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-04T06:57:31+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-03T08:52:30+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-26T01:23:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"216578946347318071134606932422105422501","date":"2024-08-15T08:24:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"83882122847309735947570977647330268178","date":"2024-08-14T23:13:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-26T08:40:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-16T06:05:37+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-16T06:05:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Colloid and Polymer Science","date":"2024-07-11T09:07:38+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"colloid-and-polymer-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Colloid and Polymer Science](https://www.springer.com/journal/396) ","snPcode":"396","submissionUrl":"https://mc.manuscriptcentral.com/cps","title":"Colloid and Polymer Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f1701d07-452f-409a-9995-53a52ebcee81","owner":[],"postedDate":"August 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-10-12T02:08:04+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-13 03:13:07","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4723030","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4723030","identity":"rs-4723030","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}