Hybrid lignin-silica as a green adsorbent towards methylene blue in batch and fixed-bed column

Hybrid lignin-silica as a green adsorbent towards methylene blue in batch and fixed-bed column | 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 Hybrid lignin-silica as a green adsorbent towards methylene blue in batch and fixed-bed column Co D. Pham, Khoi D. Tran, Phung K. Le This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4150815/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The number of research regarding the ‘lignin-silica complex first’ approach focusing on the synthesis of a long polymer with SiO 2 distributed on the surface has been increasing significantly in recent years. Despite being considered an abundant source for the recovery of this hybrid, black liquor has not been widely employed in the synthesis of lignin/silica-derived materials. In order to propose a solution to utilize the waste liquid from the cellulose production process instead of current synthesized silica-containing compounds in the synthesis of highly effective materials for environmental treatment, this study aims to produce a lignin-silica hybrid (LS) from black liquor generated from rice straw alkaline treatment via sol-gel process. The difference in the material characteristics determined by XRF, FT-IR, SEM, and isothermal nitrogen adsorption at 77K led to the different capacities in methylene blue (MB) adsorption. The SiO 2 content in the material increased with respect to pH value, which resulted in a higher specific surface area (S BET ). Specifically, the greater S BET belonged to LS recovered at pH = 9 (LS9) with a value of 166.5 m 2 /g. Additionally, the presence of numerous negatively charged groups (i.e., COO − , OH) and silanol in the LS structure resulted in a strong affinity towards MB, a cationic dye. LS9 exhibited a better performance in MB removal with a capacity of nearly 50 mg/g in comparison with the value of LS7, which was around 45 mg/g. Along with the proposed adsorption mechanism, kinetic adsorption, isothermal adsorption, and fixed-bed column adsorption were also investigated to interpret the adsorption processes. Environmental Engineering lignin-silica hybrids wastewater treatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction Organic-inorganic hybrids have been prospective candidates for the development of advanced and versatile materials in recent years. Through the sol-gel method, various organic polymers can be combined with silica, resulting in diverse silica-organic composites [ 1 ]. These hybrids can also incorporate lignin, one of the most abundant biopolymers on earth, offering substantial potential for various applications. However, due to its intricate chemical structure and heterogeneous nature, lignin extraction often requires harsh conditions, leading to depolymerization and alteration of its original chemical structure [ 2 ]. Consequently, lignin obtained under such circumstances is typically deemed a byproduct of primary processes like chemical pulp production. Despite not being a porous material, lignin contains numerous oxygen-containing groups, facilitating diverse interactions with other compounds, such as physical adsorption, hydrogen bonding, and electrostatic bonds [ 3 ]. Especially, the hydroxyl groups allow it to undergo condensation within the silica xerogel matrix, thereby influencing its pore structure. Therefore, silica, a widely used inorganic material, has been incorporated with lignin or lignin derivatives to prepare multifunctional lignin/silica composites which have been utilized in functional filler [ 4 ], polymers [ 5 ], energy storage systems [ 6 ], and wastewater treatment [ 7 ] especially. Wastewater from industry in general and textile in particular has been becoming more alarming than ever. Various organic dyes that are being used have harmful effects on humanity and the ecosystem [ 8 ]. Among them, methylene blue (MB), a synthetic dye, has been commonly employed in various industrial processes including dyeing and printing textiles, and in medical and laboratory settings. In some cases, MB could work as a biological stain and as an indicator in various chemical reactions. Despite not being regarded as a significant pollutant, like any substance, this organic compound can contribute to water pollution and has a strongly negative impact on human health in case it is not properly disposed of or released in large quantities into the environment [ 9 ]. Therefore, an enormous amount of research has been carried out to explore effective ways to capture MB. In distinct situations, methylene blue is treated by specific methods such as photodegradation [ 10 ], microbial degradation, membrane separation [ 11 ], and adsorption. Among these, adsorption is regarded to be an effective method for water treatment and an efficient separation process in general due to its low cost, ease of recovering compounds after the adsorption process, and biocompatibility [ 12 ]. For instance, the research conducted by Tetyana M. Budnyak et al. employed 3-Aminopropyltriethoxysilane (3-APTES) and tetraethoxysilane (TEOS) in the silica production process, which was then incorporated with lignin to fabricate lignin-silica hybrid. After a series of steps including sol-gel and vacuum drying process, the obtained material exhibited the MB adsorption capacity of 60 mg/g and was able to extract 80–99% of the dye in a pH range spanning from 3 to 10 [ 13 ]. In another circumstance, the surface of commercial silica Syloid 244 and lignin were activated using N-2-(aminoethyl)-3-aminopropyltrimethoxysilane and sodium iodate, respectively prior to the mixing stage. After vacuum evaporation, the sorbent was found to exhibit effective removal capability for nickel (II) and cadmium (II) ions. The maximum sorption capacities towards nickel (II) and cadmium (II) ions were determined to be 77.11 mg/g and 84.66 mg/g, respectively [ 14 ]. As highlighted previously, while lignin-silica hybrid materials with great potential in dyes and metal adsorption have been synthesized, most studies mainly emphasize the use of synthetic Si-containing compounds instead of natural silica. Additionally, the current production processes are relatively complicated, involving the activation of lignin and silica surfaces before synthesis, along with energy-intensive mixing steps. Consequently, the utilization of biomass sources abundant in silica and lignin, coupled with simplifying the process through simultaneous precipitation of these two substances, has become imperative and holds promise for addressing environmental concerns. Rice straw, which is originally known as agricultural waste, possesses a substantial amount of cellulose, lignin, and silica and is able to serve as a biomass source. Due to this characteristic, rice straw has been noticed not only for the paper industry but also for the production of value-added products based on cellulosic structure [ 15 – 16 ]. According to this basis, there are various published studies on cellulose production and nanocellulose synthesis. However, most of them have generated a significant amount of black liquor due to the low solid/liquid ratio during the alkaline treatment and bleaching process. There is a stage in this chain called pulping, which involves the separation of cellulose fibers from lignin and other components presenting in wood or other plant materials, generating a mixture of chemicals known as black liquor. This mixture contains lignin, cellulose, hemicellulose, and a variety of other organic and inorganic compounds [ 17 ]. From the very early days of the paper industry, black liquor has been considered a waste product and just simply burned to generate steam and electricity for the paper mill and this practice continues to this day [ 18 ]. Especially, as the world is facing the challenge of conserving non-renewable fossil fuels, global attention is turning to the production of renewable second-generation fuels. there has been growing interest in using black liquor as a feedstock for the production of advanced biofuels and biochemicals, particularly in countries with strong policies to support renewable energy and bioeconomy development. In the European Union, the Renewable Energy Directive requires members to increase the share of renewable energy in their transport sector to 10% by 2020, and up to 14% by 2030 [ 19 ]. Owing to the high percentage of silica and lignin components in black liquor, the preparation of lignin/inorganic composites from this waste is considered as potential and can provide a new approach towards a more valuable application of lignin-based products. The production of various types of materials from this spent liquor; therefore, has been evaluated as an appropriate solution not only to hinder the depletion of natural resources but also to solve environmental problems from waste. According to previous research, with distinct applied pH values in the precipitation stage of black liquor, the lignin-silica hybrid possesses a different silica/lignin ratio. More specifically, the impact of pH value on the structure of the precipitate was explored by Nghi et. al [ 20 ]. The pH value in the range of 8–10 was proven as the appropriate condition to obtain a SiO 2 -rich hybrid. Conversely, a low pH state could lead to a higher lignin recovery efficiency (66.75%) in comparison with others, which means a substantial amount of silica was eliminated. Based on these basics, in this research, black liquor from the cellulose alkaline pretreatment process was utilized to produce a lignin-silica hybrid (LS) with high silica content at pH value of 7 and 9. To determine the structural characteristics of the obtained material, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray fluorescence analysis (XRF), and isotherm nitrogen adsorption at 77K were employed. Besides, this study also aims to investigate the performance of LS samples as a bio-adsorbent in the removal of methylene blue at a static state. 2. Materials and methods 2.1 Materials Rice straw was harvested from An Giang province, Vietnam. The used chemicals were purchased from commercial agents and of analytical grade, including sodium hydroxide (NaOH, 99%) and sulfuric acid (H 2 SO 4 , 98%) without any further purification. The methylene blue (MB, C 16 H 18 N 3 SCl.3H 2 O) used in this experiment was of analytical grade. 2.2 Preparation of lignin-silica (LS ) A two-stage approach was applied to synthesize lignin-silica hybrid material. Rice straw was treated with sodium hydroxide 1% at 90°C for 2 hours at the solid-to-liquid ratio of 1:20 (g/mL). Then, the mixture was filtered to obtain black liquor (BL). Subsequently, the BL was precipitated by slowly adding sulfuric acid solution 20%, the simultaneous well-mixing was carried out to ensure the highest precipitation yield. The pH value of BL was adjusted to 7 and 9. Then, the system was left to age in 24 hours for stabilizing. The mixture was filtered in a vacuum filter to obtain precipitated lignin and silica, the final product described as lignin-silica hybrid samples (LS7, LS9) was washed with RO water several times to remove impurities and dried in an oven at 60°C for 24h (Scheme 1 ). 2.3 Characterization The present elements in LS samples were determined by the X-ray fluorescence spectrometer (XRF). The pore structure of LS samples was analyzed by the isotherm nitrogen adsorption at 77 K. The specific surface area and the pore size distribution were calculated using the (Brunauer-Emmett-Teller) BET model. Scanning electronic microscopy (SEM) (Hitachi Ltd., Japan, TM4000) was used to observe the sample morphology. Information about functional groups and covalent bonding in LS samples was acquired by Fourier Transform Infrared Spectroscopy (FTIR). 2.3.1 Batch adsorption experiments The MB adsorption experiments were conducted under ambient conditions in an aqueous phase. In a typical procedure, the lignin-silica hybrid (0.05 g) was added to 20 mL of the MB solution with a concentration of 25–500 ppm. The obtained mixture was then kept in a static stage for 5–150 min at room temperature. After the adsorption section, the solid material was separated by centrifugation. The absorbance of MB in the remainder liquid was determined using UV-VIS spectroscopy at the wavelength of 664 nm. The adsorption capacity at equilibrium is given by: $${q_e}=\frac{{({C_o} - {C_e})V}}{m}\,$$ 1 Where q e is the equilibrium adsorption capacity of adsorbent (mg/g), C o is the initial concentration of adsorbate solution (mg/L), C e is the equilibrium concentration of MB (mg/L), V is the volume of adsorbate solution (L), and m is the weight of adsorbent (g). 2.3.2 Adsorption kinetics The pseudo-first-order model is [ 21 ]: $${q_t}={q_e}(1 - {e^{ - {k_1}t}})$$ 2 Where q e is the equilibrium adsorption capacity of adsorbent (mg/g), q t is the adsorption capacity of adsorbent at time t (mg/g), k 1 is the pseudo-first-order constant (s − 1 ), and t is the adsorption time (s). The pseudo-second-order model based on equilibrium adsorption is [ 21 ] : $${q_t}={q_e}\frac{{{q_e}{k_2}t}}{{1+{q_e}{k_2}t}}$$ 3 Where q e is the equilibrium adsorption capacity of the adsorbent (mg/g). q t is the adsorption capacity of the adsorbent at time t (mg/g), k 2 is the pseudo-second-order constant (s − 1 ), and t is the adsorption time (s). 2.3.3 Adsorption isotherms The Langmuir equation is expressed as follows [ 22 ]: $${q_e}=\frac{{{Q_0}{K_1}{C_e}}}{{1+{K_1}{C_e}}}$$ 4 Where q e is the equilibrium adsorption capacity of adsorbent (mg/g), Q 0 is the maximum adsorption capacity (mg/g), K 1 presents the Langmuir adsorption constant, C e stands for the equilibrium concentration of dye (mg/L). The Freundlich equation is given by [ 22 ]: $${q_e}={K_F}C_{e}^{{1/n}}$$ 5 Where q e is the equilibrium adsorption capacity of adsorbent (mg/g), C e is the equilibrium concentration of dye (mg/L), and K F is the Langmuir adsorption constant. 2.4 Adsorption in fixed-bed column 2.4.1 Experimental set-up Continuous flow sorption experiments were conducted in a transparent cylindrical plastic column (2 cm internal diameter and 50 cm height). At the top of the column, an adjustable plunger was attached to maintain the uniform static head of the column. At the bottom of the column, a 0.5 mm stainless sieve was attached followed by glass wool. A 1 cm high layer of cotton was placed at the column base to provide support for the adsorbent. The uniform inlet flow of the solution into the column was maintained by an inlet valve (Scheme 2 ). A known quantity of LS7 was placed in the column to yield the desired bed height of the sorbent. Methylene blue solution of known concentration was pumped downward through the column at a desired flow rate. Samples were collected from the exit of the column at different time intervals and were analyzed for MB using UV-VIS spectrometry by monitoring the absorbance changes at a wavelength of maximum absorbance of 664 nm. Operation of the column was stopped when the effluent MB concentration exceeded a value of 99.5% of its initial concentration. 2.4.2 Analysis of column data The time for breakthrough appearance and shape of the breakthrough curve are very important characteristics for determining the operation and the dynamic response of an adsorption column. The breakthrough time (t b , the time at which dye concentration in the effluent reached 5 mg/L) and bed exhaustion time (t e , the time at which dye concentration in the effluent reached 99.5% of initial dry concentration) were used to evaluate the breakthrough curves. The total quantity of dye mass adsorbed in the column (mad) is calculated from the area above the breakthrough curve (outlet dye concentration (C) versus time (t)) multiplied by the flow rate. Dividing the dye mass adsorbed (mad) by the sorbent mass (M) leads to the uptake capacity (q e ) of the LS7. Effluent volume (V eff ) can be calculated as follows: \({V_{eff}}=F \times {t_e}\,\,\,\,\,\,\,(6)\) F is the volumetric flow rate (mL/min). The total amount of MB (m total ) sent through the column is calculated by the Eq. (6): \({m_{total}}=\frac{{{C_o}F{t_e}}}{{1000}}\,\,\,\,\,\,\,(7)\) where C o is the inlet dye concentration (mg/L). The total removal percent of MB (Column performance) with respect to flow volume can be also found in Eq. (7): \(Total\,removal\,(\% )=\frac{{{m_{ad}}}}{{{m_{total}}}} \times 100\,\,\,\,\,\,\,(8)\) 2.4.3 Modeling of column data Fixed-bed column adsorption is a commercial adsorption method that is used in many cases to eliminate toxicants, in which a solution of poisonous substances is fed continuously into the column. There are two types of fixed-bed column adsorption which are downstream flow which the solution is going from top to bottom of column and upstream flow which the solution is going from the opposite direction. In the column adsorption study, parameters such as bed height and adsorbate concentration are chosen to evaluate the performance of fixed-bed column adsorption and the maximum adsorption capacity. From that, a plot between C t /C o and time (min) is demonstrated which is known as the breakthrough curve and the derived parameters such as breakthrough time (t b ), exhaust time (t e ), breakthrough volume (v b ), exhaust volume (v e ), etc. Three models were employed to characterize the column breakthrough curves obtained at various bed heights, flow rates, and inflow MB concentrations. The Clark and modified dose-response models were among them. Clark model [ 23 ]: \(\frac{{{C_t}}}{{{C_o}}}={\left( {\frac{1}{{1+A{e^{ - rt}}}}} \right)^{1/(n - 1)}}\,\,\,\,\,\,\,(9)\) Where, A, r is the Clark parameter; n is the Freundlich constant. Thomas model [ 24 ]: \(\frac{{{C_t}}}{{{C_o}}}=\frac{1}{{1+{e^{\frac{{{K_{Th}}{q_o}m}}{v}{K_{Th}}{C_o}t}}}}\,\,\,\,\,\,\,(10)\) Where k Th is the Thomas rate constant (ml.min − 1 .mg − 1 ); q o is the equilibrium adsorbate uptake per g of the adsorbent (mg. g − 1 ); m is the amount of the adsorbent in the column (g); v is the flow rate of the solution passing through the column (ml. min − 1 ). Modified dose-response model [ 25 ]: \(\frac{{{C_t}}}{{{C_o}}}=1 - \frac{1}{{1+{{\left( {\frac{{vt}}{b}} \right)}^a}}}\,\,\,\,\,\,\,(11)\) Where, a, and b are parameters of the modified dose–response model; C t and t are gathered from the experiment process. The BDST model is generally accepted as the simplest approach and rapid prediction of adsorbent design and performance [ 26 ]. Among various parameters, the required bed depth for a specific adsorption time (service time) is an important design parameter [ 27 ]. The bed-depth service-time model can be used to estimate the required bed-depth for a given service-time. The BDST model is the transmutation of the Adams–Bohart model and can be expressed as follows: \({t_b}=\frac{{{N_o}}}{{{C_o}v}} - \frac{1}{{{k_{AB}}{C_o}}}\ln \left( {\frac{{{C_o}}}{{{C_b}}} - 1} \right)\,\,\,\,\,\,\,(12)\) Where t b (min) is the service time and C b (mg. L − 1 ) is the specific breakthrough concentration. A plot of service time t against Z should generate a straight line with a slope equal to N o /C o and an intercept of (1/k AB C o ). ln((C o /C b ) − 1). From the slope and intercept, both N o (g. L − 1) and k AB (mL.mg − 1 .min − 1 ) can be calculated. Once the constants of the model have been determined, the model can be used to estimate the service time for a given bed height and specific solute concentrations at the bed inlet and outlet. 3. Results & Discussion 3.1 Structural Characteristics of obtained lignin-silica hybrid samples (LS) at different pH values The FT-IR spectrum of lignin, silica, and the LSs are shown in Fig. 1 . Along with the presence of a broad peak in the range of 3600 − 3200 cm − 1 , which was due to the stretching vibration of O-H groups, a signal at 1705 cm − 1 was also found, and can be assigned to the stretching vibration of C = O groups that are present in the lignin molecule. The absorption band at around 1600 − 1500 cm − 1 which exhibits the aromatic skeletal vibration (C = C), confirms the presence of guaiacyl-syringyl lignin in both raw lignin and LS samples [ 28 ]. From another perspective, the effect of silica on the FT-IR spectrum could be found at 474 cm − 1 and between 1000–950 cm − 1 . This indicated the Si–O–Si bending region and Si–O–Si asymmetric stretching, respectively [ 29 ]. To date, the linkage between lignin and silica in plants in general and lignin-silica hybrid with natural silica in particular has not been conclusively demonstrated. However, it could be suggested that after the simultaneous precipitation, lignin and silica networks create a pristine structure due to the interweaving of these compounds. Owing to the increase of silica content in the structure of the LS hybrid, the intensity of the lignin signal changed inversely with the pH value. The difference in lignin and silica content is presented in Table 1 . While a high silica proportion was found in the LS9 at 63.80%, the silica percentage in LS7 was only 32.09%. Moreover, the degradation of carbohydrate component was demonstrated via loss on ignition value which means the LS7 possessed a higher amount of lignin with the loss on ignition of 57.82% when compared to this figure of LS9 of approximately 35%. Table 1 SiO 2 content in three different LS samples Sample SiO 2 (wt%) Loss on ignition (wt %) Others (wt%) LS9 63.80 35.08 1.12 LS7 32.09 57.82 10.09 In addition, these dissimilarities led to the difference in morphology of the lignin-silica hybrid, which was demonstrated in the SEM image (Fig. 2 ). It can be concluded that the hybrid samples witnessed the larger-sized blocks due to the increase of lignin component, which was consistent with the dropping of silica particles. The average dimension of LS7 and LS9 hybrid samples was generally in the range of 100–500 nm. And it was also found that these samples consisted of smooth clusters and rough clusters which indicates that small particles of silica are attached on the surface of lignin from the precipitation process. Table 2 BET surface area and pore volume of LS samples Samples BET surface area (m 2 /g) Total pore volume (cm 3 /g) LS7 46.9 0.29 LS9 166.5 0.38 The specific surface area of LS samples is displayed in Table 2 . Owing to the lower SiO 2 content, the LS7 possessed an S BET of less than 47 m 2 /g, whereas the higher recorded value was from LS9 (166.5 m 2 /g) and it was nearly 40% higher than the S BET of lignin-silica microparticles from the wheat husk (117.4 m 2 /g) [ 30 ]. The physisorption result of LS9 (Fig. 3 ) resembled the type IV curve, which is a common signal for mesoporous materials [ 31 ], while the curve of LS7 was typical for type III [ 32 ]. Moreover, LS9 also presented a noticeable rise in the N 2 uptake in comparison with LS7 (nearly 1.5 times differential). 3.2 Methylene blue adsorption capacity of different LS hybrid samples The effects of adsorption time and initial concentration on the MB removal effectiveness of LS samples were investigated. As shown in Fig. 4 a, the MB adsorption of LS7 and LS9 occurred rapidly in the first 20 min. The removal process then kept on at a quick pace until reached a plateau after about 60 min of interacting. At this point, the MB trapping capacity of LS samples could reach up to 45.8 mg/g for LS7, while the LS9 performed the best capturing ability with a better value of 48.9 mg/g. This might be deduced by the larger specific surface area of LS9 in comparison with others leading to a larger space for MB to attach. From Fig. 4 b, a similar trend was obtained from the investigation of initial MB concentration on the capture efficiency. The highest number of 49.2 mg/g belonged to LS9, and the uptake value of nearly 45 mg/g was from LS7. Generally, the adsorption quantity increased considerably when the initial concentration of MB increased from 0 to 160 ppm, leading to the high slope of the curve exhibiting the relationship between those two variables. Then, the change in the adsorbed quantity became less significant and stayed nearly stable when the initial concentration exceeded 200 ppm. This trend can be explained that as the initial concentration increases, the proportion of adsorbate molecules to available adsorption sites rises, leading to a stronger driving force for the capture process. Eventually, the active sites were mostly occupied and the number of available sites decreased, the trapping process would slow down and reach the equilibrium, even if the solution concentration increased further. In order to gain more understanding of the adsorption mechanism, the adsorption kinetics was studied. Generally, despite having a slight difference in the calculated adsorption capacity, the data fit revealed that the coefficients ( R 2 ) were approximately the same for the two models (Table 3 and Fig. 5 ). The correlation coefficient for first-order kinetic was in the range of 0.964–0.990, while this value for second-order kinetic was from 0.949 to 0.986. It means that the nature of the adsorption of MB on LS samples possibly followed both first-order and second-order kinetic models, which are supposed to be chemisorption and physisorption [ 33 ]. Table 3 Kinetic parameters of pseudo-first-order and -second-order models for the adsorption processes of LS samples Pseudo-first-order model Pseudo-second-order model No. Material Q e,cal (mg/g) k 1 x 10 − 2 (min -1 ) R 2 Q e,cal (mg/g) k 2 x 10 − 2 (g.mg -1 . min -1 ) R 2 1 LS7 43.9 6.4 0.964 50.6 0.2 0.949 2 LS9 48.9 4.3 0.990 58.2 0.1 0.986 Moreover, the distribution of adsorbates onto the surface of LS samples was investigated using Langmuir and Freundlich models. The Langmuir isotherm, one of the most common isotherm models, assumes monolayer adsorption, whereas the Freundlich equation refers to multilayer adsorption [ 34 ]. As shown in Table 4 and Fig. 6 , the experimental data fitted with the Langmuir isotherm (the correlation coefficients of over 0.9) for three LS samples. However, the estimated adsorption capacity based on the Langmuir equation was drastically higher than the experimental one, indicating that this model was not appropriate to describe the contact between methylene blue and active sites on the adsorbent surface. During the acidification process, SiO 2 was distributed unevenly on the surface of lignin-silica hybrids, which resulted in the non-uniformity of adsorptive sites. Table 4 Isotherms parameters for the adsorption of Methylene blue dye on the LS samples Langmuir Isotherm Freundlich Isotherm No. Material Q e,cal (mg/g) K L (L/mg) R 2 n K F R 2 1 LS7 57.4 0.009 0.976 2.5 4.2 0.889 2 LS9 64.5 0.009 0.955 2.5 4.8 0.853 The presence of functional groups in methylene blue and the formation of a linkage between adsorbent and adsorbate were confirmed, which can be seen in Fig. 7 . The FT-IR spectrum of LS samples after the adsorption process indicated the signal assigned to the stretching of -C-O-N (1600 − 1550 cm − 1 ) overlapping with aromatic skeletal vibration (C = C) of lignin, -NH 2 (1000 cm − 1 ), and N-H (900 − 800 cm − 1 ) [ 35 ]. The presence of the C-N-C group in the adsorbent led to the broader peak at around 500 cm − 1 when compared to the LS sample before the adsorption, which is also the region of Si-OH [ 20 ]. This result, therefore, could be considered as proof of the chemical interactions between lignin-silica hybrid and dye molecules, which showed a good agreement with the obtained data in adsorption kinetics analysis. The plausible adsorption mechanisms including the electrostatic interaction and hydrogen bonding between the adsorbent and dye molecules were illustrated in Fig. 8 . Numerous nitrogens with a free lone pair in MB can form a hydrogen bond with Si–OH, while Si–O − , which is created via the deprotonation of silanol groups, bonds to the N + centers [ 36 – 37 ]. Besides, the presence of carboxyl and hydroxyl groups in lignin contributed a lot to the formation of electrostatic bonds. Therefore, this possible mechanism could be considered as an explanation for the higher adsorption capacity of lignin-silica composite when compared to silica or lignin which is shown in the following section. In comparison with various types of materials generated from biomass (Table 5 ), the lignin-silica hybrid obtained in this study exhibited great potential. Despite being synthesized through a one-step process, all LS samples possessed higher capturing capacities than others whose activities were improved via more complex processes such as activation, modification, and pyrolysis. Due to the presence of both organic (lignin) and inorganic (SiO 2 ) moieties in the structure, the adsorption capacity of LS samples was significantly enhanced when compared to silica and some carbon-based materials alone. Table 5 Comparison of Methylene blue adsorption capacity of different materials synthesized from biomass No. Materials Adsorption capacity (mg/g) Ref. 1 LS7 45.5 This study 2 LS9 49.2 This study 3 Aminomethylated lignin-silica 42.19 [ 38 ] 4 Amorphous silica 22.7 [ 39 ] 5 Optimal Biochar from Argan Shells Powder 31.0 [ 40 ] 6 Activated carbon from tea waste using KOH 36.2 [ 41 ] 3.3 Fixed-bed column adsorption 3.3.1 Various models for MB adsorption in a fixed-bed column The breakthrough curves have been measured under various experimental conditions, including different bed heights and initial MB concentrations. But the initial solution pH and temperature are both kept constant at 7.0 and 298 K, respectively. The detailed experimental parameters were shown in Table 6 , Table 7 , and Table 8 . Then, the experimental data have been fitted by various models such as Thomas, Clark, and the modified dose-response model to explore the adsorption mechanism. As for the Clark model, based on Table 6 , the determination coefficients R 2 were not close to 1.0 and the calculated values of parameter n did not match the data fitted by the Freundlich model in bath studies. Meanwhile, the simulated results of Clark constant A were quite abnormal and differed from each other very much. Furthermore, based on this model, Clark constants, A and r, did not have any physical meanings. Accordingly, the Clark model was not advisable to be applied to study the breakthrough curves further. The Thomas model, which delineates the electrostatic and chemical forces governing the uptake of Methylene Blue (MB) molecules by materials, does not align well with the experimental data as can be seen in Fig. 10 . Therefore, the fitting results as shown in Table 7 were also quite good. From Table 7 , the determination coefficients R 2 were not close to 1.0. In accordance with the theoretical underpinnings of the Thomas model, materials exhibiting a monolayer electrochemical adsorption mechanism typically yield experimental data that conforms to the Thomas model. However, in this context, the experimental data deviates from the expected pattern, possibly attributable to the utilization of the Thomas model for medium breakthrough curves. This divergence highlights a disparity between the experimental data and the theoretical expectations inherent in the Thomas model[ 42 ]. Among them, the determination coefficients R2 by modified-dose response model were the highest which were all very close to 1.0. Furthermore, the theoretical MB uptakes qe,cal at varied conditions were not close to their corresponding experimental ones. The observed phenomenon can be elucidated by considering the residence time, which proves insufficient for the complete interaction between dye molecules and the adsorption surface, thereby preventing the saturation of all available adsorption sites. Although this circumstance may be considered an exception, it has been suggested that the modified dose-response model remains the most appropriate for characterizing the adsorption of Methylene Blue (MB) in the fixed-bed of LS7 composite. From a molecular-level perspective of the adsorption mechanism, LS7 composite exhibits a richness in carboxyl and hydroxyl groups derived from lignin. The adsorption of MB onto LS7 occurs through electrostatic interactions between anionic carboxyl groups and cationic MB molecules, aligning with a monolayer chemical adsorption process. Consequently, the modified dose-response model accurately delineates the column adsorption dynamics of MB onto the LS7 surface. Table 6 Clark parameters at different conditions No. C o (ppm) v (ml.min − 1 ) Z (cm) A r x 10 − 2 R 2 x 2 1 100 10 1 0.75 1.076 0.9802 0.00406 2 100 10 2 0.83 0.977 0.9791 0.00274 3 100 10 3 0.91 0.876 0.9777 0.00302 4 50 10 2 1.02 1.58 0.9706 0.00406 5 150 10 2 0.51 2.223 0.9093 0.0078 Table 7 Thomas parameters at different conditions No. C o (ppm) v (ml.min − 1 ) Z (cm) q o,cal (mg/g) k Th (ml.min − 1 .mg − 1 ) R 2 x 2 1 100 10 1 119.30 0.139 0.9698 0.0037 2 100 10 2 70.65 0.127 0.9667 0.00434 3 100 10 3 54.15 0.114 0.9633 0.00495 4 50 10 2 24.60 0.425 0.9579 0.00581 5 150 10 2 30.65 0.181 0.8924 0.00923 Table 8 Modified-dose response parameters at different conditions No. C0 (ppm) v (ml.min − 1 ) Z (cm) a b (ml) q 0,cal (mg/g) R 2 x 2 1 100 10 1 1.525 1037.42 20.74 0.9880 0.0015 2 100 10 2 1.614 1257.68 19.98 0.9914 0.0011 3 100 10 3 1.690 1505.56 17.65 0.9940 0.0008 4 50 10 2 1.823 941.81 21.60 0.9942 0.0008 5 150 10 2 1.025 301.79 20.76 0.9917 0.0007 3.3.2 Effect of bed height on breakthrough curve The effects of bed height on the adsorption performances of LS7 have been investigated over a range from 1.0 cm to 3.0 cm. The flow rate was fixed at 10 mL.min − 1 and the initial concentration of MB solution was 100 ppm. From Fig. 9 and Fig. 10 , it was found that the breakthrough time increased with increasing bed height as expected. It was due to the fact that as the bed height increased, MB had more time to contact with LS7 which resulted in a longer exhausting time and higher removal amount of MB [ 43 ]. In addition, the rate constant k Th decreased with increasing bed height, indicating the reduced reaction rate, which was ascribed to the longer contact time for higher bed depth. Table 9 BDST parameters at different C b /C o No. C o (ppm) v (ml.min − 1 ) C b /C o N o k AB R 2 1 100 10 0.05 9.615 27.518 0.9995 2 100 10 0.2 10.650 -0.456 0.9990 3 100 10 0.4 21.150 -0.0814 0.9959 4 100 10 0.6 27.845 -0.0331 0.9803 Figure 11 showed the plots of the service-time (t b ) at 5% (B), 20% (C), 40% (D), and 60% (E) breakthrough points, i.e., t b at C b /C o equal to 0.05, 0.2, 0.4 and 0.6, respectively, and all the calculated BDST constants listed in Table 9 . The determination coefficients R 2 all exceeded 0.99, indicating that the BDST model might be applicable to represent the MB adsorption in a fixed-bed column of LS7. The adsorption capacities calculated by this model, N 0 , were also roughly close to the experimental ones. The rate constant, k AB , characterized the rate of solute transfer from the fluid phase to the solid phase. As C b /C o increased, the concentration difference of MB between the fluid and the solid phase decreased, which would weaken the mass transfer and bring down the value of k AB . However, at C b /C o around 0.2, the simulated k AB was abnormal and showed negative values, which might be due to the limitation of the BDST model. Since the BDST model was derived from the Adams–Bohart model, it was only suitable for describing the initial part of the breakthrough curve as mentioned above. 3.3.3 Effect of initial concentration of MB solution on breakthrough curve The effects of initial MB concentration have been investigated at 50, 100, and 150 ppm, respectively. The bed height was 2 cm and the temperature was 298 K. The flow rate was fixed at 10 mL.min − 1 and the pH of MB solution was 7.0. It was illustrated in Fig. 12 that breakthrough time decreased with increasing MB concentration. Besides, as the influent concentration increased, sharper breakthrough curves were obtained. They both indicated that the adsorption sites were occupied much faster with the increase of MB concentration. In addition, from Table 8 , with the increase of initial MB concentration, the adsorption capacity q cal increased while the constant a decreased. It was due to the fact that the rate of mass transfer in the column turned slowly for higher concentrations of MB [ 44 ], which resulted in lengthening the contact time between solute and adsorbent and improved adsorption capacity. 4. Conclusions With the purpose of decreasing waste products in the cellulose extraction process and producing an efficient sorbent for the removal of dyes from aqueous solutions, black liquor was used in the synthesis of the lignin-silica composites via a one-step method lessening the necessity of synthesized silica-containing compound. The MB adsorption capacity of the obtained material was studied as a function of various parameters such as concentration of dye and contact time. Specifically, it was found that the hybrid synthesized at pH9 (LS9) showed a significant SiO 2 composition of 63.80 wt%, which was much higher than this number in the one synthesized at pH7 (about 2 times). When it comes to the specific surface area, LS samples witnessed an increase in S BET corresponding to pH value in the acidification stage. While the S BET of more than 166 m 2 /g belonged to LS9 and nearly 47 m 2 /g to LS7. Consequently, the results also showed that LS9 possessed a good adsorption capacity towards MB dye which was more than 10% higher in comparison with LS7. Moreover, the kinetic characteristics of MB uptake by LS composites followed more suitably the Langmuir isotherm model and pseudo-second-order models. It was found that bed height and initial MB concentration can affect the breakthrough curves obviously. Moreover, the modified dose-response model is found to be the most suitable one to describe the adsorption behaviors, according to the monolayer chemical adsorption mechanism. With achieved results, this study not only highlights a one-step method without any required modification to utilize black liquor in the synthesis of an effective material for organic dye treatment but also serves the dual advantages of protecting the environment and effectively enhancing the value of byproducts from agricultural production. Declarations CRediT authorship contribution statement Co D. Pham: Conceptualization, Data curation, Writing – original draft, Writing – review & editing. Khoi D. Tran: Conceptualization, Data curation, Writing – original draft, Writing – review & editing. Visualization, Writing – review & editing. Phung K. Le: Funding acquisition, Methodology, Project administration, Resources, Supervision, Writing – review & editing. Acknowledgments We acknowledge the support of time and facilities from Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for this study. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper. References S. Prabha, D. Durgalakshmi, S. Rajendran, and E. Lichtfouse, “Plant-derived silica nanoparticles and composites for biosensors, bioimaging, drug delivery and supercapacitors: a review,” Environ Chem Lett , vol. 19, no. 2, pp. 1667–1691, Apr. 2021, doi: 10.1007/s10311-020-01123-5. C. D. Pham et al. , “A review of the extraction methods and advanced applications of lignin-silica hybrids derived from natural sources,” Int J Biol Macromol , vol. 230, p. 123175, Mar. 2023, doi: 10.1016/j.ijbiomac.2023.123175. R. Salih et al. , “Lignin based microspheres for effective dyes removal: Design, synthesis and adsorption mechanism supported with theoretical study,” J Environ Manage , vol. 326, p. 116838, Jan. 2023, doi: 10.1016/j.jenvman.2022.116838. T. M. Budnyak et al. , “Membrane-Filtered Kraft Lignin–Silica Hybrids as Bio-Based Sorbents for Cobalt(II) Ion Recycling,” ACS Omega , vol. 5, no. 19, pp. 10847–10856, May 2020, doi: 10.1021/acsomega.0c00492. W. Liu et al. , “Sol-gel silica modified recovered lignin particles and its application as blend with HDPE,” Ind Crops Prod , vol. 189, p. 115842, Dec. 2022, doi: 10.1016/j.indcrop.2022.115842. C. D. Pham et al. , “The utilization of black liquor from rice straw pretreatment stage on the syntheses of carbon-based materials using in anodes ion-lithium batteries production,” Journal of Materials Science: Materials in Electronics , vol. 34, no. 4, p. 335, Feb. 2023, doi: 10.1007/s10854-023-09840-7. Ł. Klapiszewski, P. Bartczak, M. Wysokowski, M. Jankowska, K. Kabat, and T. Jesionowski, “Silica conjugated with kraft lignin and its use as a novel ‘green’ sorbent for hazardous metal ions removal,” Chemical Engineering Journal , vol. 260, pp. 684–693, Jan. 2015, doi: 10.1016/j.cej.2014.09.054. T. Hien Tran et al. , “A sustainable, low-cost carbonaceous hydrochar adsorbent for methylene blue adsorption derived from corncobs,” Environ Res , vol. 212, p. 113178, Sep. 2022, doi: 10.1016/j.envres.2022.113178. A. R. Disanto and J. G. Wagner, “Pharmacokinetics of Highly Ionized Drugs II: Methylene Blue—Absorption, Metabolism, and Excretion in Man and Dog after Oral Administration,” J Pharm Sci , vol. 61, no. 7, pp. 1086–1090, Jul. 1972, doi: 10.1002/jps.2600610710. V. Katheresan, J. Kansedo, and S. Y. Lau, “Efficiency of various recent wastewater dye removal methods: A review,” J Environ Chem Eng , vol. 6, no. 4, pp. 4676–4697, Aug. 2018, doi: 10.1016/j.jece.2018.06.060. T. A. Nguyen and R.-S. Juang, “Treatment of waters and wastewaters containing sulfur dyes: A review,” Chemical Engineering Journal , vol. 219, pp. 109–117, Mar. 2013, doi: 10.1016/j.cej.2012.12.102. M. Sari Yilmaz, “Graphene oxide/hollow mesoporous silica composite for selective adsorption of methylene blue,” Microporous and Mesoporous Materials , vol. 330, p. 111570, Jan. 2022, doi: 10.1016/j.micromeso.2021.111570. T. M. Budnyak et al. , “Methylene Blue dye sorption by hybrid materials from technical lignins,” J Environ Chem Eng , vol. 6, no. 4, pp. 4997–5007, Aug. 2018, doi: 10.1016/j.jece.2018.07.041. Ł. Klapiszewski, P. Bartczak, M. Wysokowski, M. Jankowska, K. Kabat, and T. Jesionowski, “Silica conjugated with kraft lignin and its use as a novel ‘green’ sorbent for hazardous metal ions removal,” Chemical Engineering Journal , vol. 260, pp. 684–693, Jan. 2015, doi: 10.1016/j.cej.2014.09.054. H. Beidaghy Dizaji et al. , “Generation of High Quality Biogenic Silica by Combustion of Rice Husk and Rice Straw Combined with Pre- and Post-Treatment Strategies—A Review,” Applied Sciences , vol. 9, no. 6, p. 1083, Mar. 2019, doi: 10.3390/app9061083. A. Sharma, G. Singh, and S. K. Arya, “Biofuel from rice straw,” J Clean Prod , vol. 277, p. 124101, Dec. 2020, doi: 10.1016/j.jclepro.2020.124101. N. T. Vo, C. D. Pham, T. B. Ly, M. D. T. Dang, N. H. N. Do, and P. K. Le, “Valorization of rice straw for valuable materials: towards a zero-waste recovery process,” Biomass Convers Biorefin , Aug. 2023, doi: 10.1007/s13399-023-04681-0. M. Naqvi, J. Yan, and E. Dahlquist, “Black liquor gasification integrated in pulp and paper mills: A critical review,” Bioresour Technol , vol. 101, no. 21, pp. 8001–8015, Nov. 2010, doi: 10.1016/j.biortech.2010.05.013. A. Jäger-Waldau, I. Kougias, N. Taylor, and C. Thiel, “How photovoltaics can contribute to GHG emission reductions of 55% in the EU by 2030,” Renewable and Sustainable Energy Reviews , vol. 126, p. 109836, Jul. 2020, doi: 10.1016/j.rser.2020.109836. N. H. Do et al. , “The novel method to reduce the silica content in lignin recovered from black liquor originating from rice straw,” Sci Rep , vol. 10, no. 1, p. 21263, Dec. 2020, doi: 10.1038/s41598-020-77867-5. E. D. Revellame, D. L. Fortela, W. Sharp, R. Hernandez, and M. E. Zappi, “Adsorption kinetic modeling using pseudo-first order and pseudo-second order rate laws: A review,” Clean Eng Technol , vol. 1, p. 100032, Dec. 2020, doi: 10.1016/j.clet.2020.100032. S. Kalam, S. A. Abu-Khamsin, M. S. Kamal, and S. Patil, “Surfactant Adsorption Isotherms: A Review,” ACS Omega , vol. 6, no. 48, pp. 32342–32348, Dec. 2021, doi: 10.1021/acsomega.1c04661. R. M. Clark, “Modeling TOC Removal by GAC: The General Logistic Function,” J Am Water Works Assoc , vol. 79, no. 1, pp. 33–37, Jan. 1987, doi: 10.1002/j.1551-8833.1987.tb02780.x. H. C. Thomas, “Heterogeneous Ion Exchange in a Flowing System,” J Am Chem Soc , vol. 66, no. 10, pp. 1664–1666, Oct. 1944, doi: 10.1021/ja01238a017. G. Yan, T. Viraraghavan, and M. Chen, “A new model for heavy metal removal in a biosorption column,” Adsorption Science and Technology , vol. 19, no. 1, pp. 25–43, 2001, doi: 10.1260/0263617011493953. Y. S. Al-Degs, M. A. M. Khraisheh, S. J. Allen, and M. N. Ahmad, “Adsorption characteristics of reactive dyes in columns of activated carbon,” J Hazard Mater , vol. 165, no. 1–3, pp. 944–949, Jun. 2009, doi: 10.1016/j.jhazmat.2008.10.081. H. Muhamad, H. Doan, and A. Lohi, “Batch and continuous fixed-bed column biosorption of Cd2+ and Cu2+,” Chemical Engineering Journal , vol. 158, no. 3, pp. 369–377, Apr. 2010, doi: 10.1016/j.cej.2009.12.042. B. Strzemiecka et al. , “Physicochemical Characterization of Functional Lignin–Silica Hybrid Fillers for Potential Application in Abrasive Tools,” Materials , vol. 9, no. 7, p. 517, Jun. 2016, doi: 10.3390/ma9070517. B. Strzemiecka, Ł. Klapiszewski, D. Matykiewicz, A. Voelkel, and T. Jesionowski, “Functional lignin-SiO 2 hybrids as potential fillers for phenolic binders,” J Adhes Sci Technol , vol. 30, no. 10, pp. 1031–1048, May 2016, doi: 10.1080/01694243.2015.1115602. J. Cui, H. Sun, X. Wang, J. Sun, M. Niu, and Z. Wen, “Preparation of siliceous lignin microparticles from wheat husks with a facile method,” Ind Crops Prod , vol. 74, pp. 689–696, Nov. 2015, doi: 10.1016/j.indcrop.2015.05.061. K. Sing, “The use of nitrogen adsorption for the characterisation of porous materials,” Colloids Surf A Physicochem Eng Asp , vol. 187–188, pp. 3–9, Aug. 2001, doi: 10.1016/S0927-7757(01)00612-4. Y. Zhang et al. , “The pore size distribution and its relationship with shale gas capacity in organic-rich mudstone of Wufeng-Longmaxi Formations, Sichuan Basin, China,” Journal of Natural Gas Geoscience , vol. 1, no. 3, pp. 213–220, Jun. 2016, doi: 10.1016/j.jnggs.2016.08.002. K.-D. Zhang et al. , “Adsorption Behavior of High Stable Zr-Based MOFs for the Removal of Acid Organic Dye from Water,” Materials , vol. 10, no. 2, p. 205, Feb. 2017, doi: 10.3390/ma10020205. K. Y. Foo and B. H. Hameed, “Insights into the modeling of adsorption isotherm systems,” Chemical Engineering Journal , vol. 156, no. 1, pp. 2–10, Jan. 2010, doi: 10.1016/j.cej.2009.09.013. A. H. Birniwa et al. , “Adsorption Behavior of Methylene Blue Cationic Dye in Aqueous Solution Using Polypyrrole-Polyethylenimine Nano-Adsorbent,” Polymers (Basel) , vol. 14, no. 16, p. 3362, Aug. 2022, doi: 10.3390/polym14163362. M. Afshari and M. Dinari, “Synthesis of new imine-linked covalent organic framework as high efficient absorbent and monitoring the removal of direct fast scarlet 4BS textile dye based on mobile phone colorimetric platform,” J Hazard Mater , vol. 385, p. 121514, Mar. 2020, doi: 10.1016/j.jhazmat.2019.121514. N. Mokhtari, M. Afshari, and M. Dinari, “Synthesis and characterization of a novel fluorene-based covalent triazine framework as a chemical adsorbent for highly efficient dye removal,” Polymer (Guildf) , vol. 195, p. 122430, May 2020, doi: 10.1016/j.polymer.2020.122430. T. M. Budnyak et al. , “Methylene Blue dye sorption by hybrid materials from technical lignins,” J Environ Chem Eng , vol. 6, no. 4, pp. 4997–5007, Aug. 2018, doi: 10.1016/j.jece.2018.07.041. C. D. Woolard, J. Strong, and C. R. Erasmus, “Evaluation of the use of modified coal ash as a potential sorbent for organic waste streams,” Applied Geochemistry , vol. 17, no. 8, pp. 1159–1164, Aug. 2002, doi: 10.1016/S0883-2927(02)00057-4. A. Ouedrhiri et al. , “Adsorption of the Methylene Blue Dye in Environmental Water Samples by Biochar Obtained from the Valorization of Argan Shells,” Physical Chemistry Research , vol. 10, no. 3, pp. 301–313, Sep. 2022, doi: 10.22036/PCR.2021.303554.1968. F. J. Tuli, A. Hossain, A. K. M. F. Kibria, A. R. M. Tareq, S. M. M. A. Mamun, and A. K. M. A. Ullah, “Removal of methylene blue from water by low-cost activated carbon prepared from tea waste: A study of adsorption isotherm and kinetics,” Environ Nanotechnol Monit Manag , vol. 14, p. 100354, Dec. 2020, doi: 10.1016/j.enmm.2020.100354. J. Song, W. Zou, Y. Bian, F. Su, and R. Han, “Adsorption characteristics of methylene blue by peanut husk in batch and column modes,” Desalination , vol. 265, no. 1–3, pp. 119–125, Jan. 2011, doi: 10.1016/j.desal.2010.07.041. R. M. Clark, “Modeling TOC Removal by GAC: The General Logistic Function,” Journal AWWA , vol. 79, no. 1, pp. 33–37, Jan. 1987, doi: 10.1002/j.1551-8833.1987.tb02780.x. G. Yan, T. Viraraghavan, and M. Chen, “A New Model for Heavy Metal Removal in a Biosorption Column,” Adsorption Science & Technology , vol. 19, no. 1, pp. 25–43, Feb. 2001, doi: 10.1260/0263617011493953. Schemes Schemes 1 and 2 are available in the Supplementary Files section. Additional Declarations The authors declare no competing interests. Supplementary Files Scheme1.png Scheme 1: Schematic diagram of lignin-silica hybrid production process Scheme2.png Scheme 2: Schematic diagram representing the fixed-bed column adsorption setup Cite Share Download PDF Status: Posted Version 1 posted 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-4150815","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":282775528,"identity":"9c351469-1ffd-40d2-96d4-97c419ad8712","order_by":0,"name":"Co D. Pham","email":"","orcid":"","institution":"Ho Chi Minh City University of Technology, Vietnam National University (VNU HCMUT)","correspondingAuthor":false,"prefix":"","firstName":"Co","middleName":"D.","lastName":"Pham","suffix":""},{"id":282775529,"identity":"ab073f2c-b47d-4708-b2ba-089a769db7ad","order_by":1,"name":"Khoi D. Tran","email":"","orcid":"","institution":"Ho Chi Minh City University of Technology, Vietnam National University (VNU HCMUT)","correspondingAuthor":false,"prefix":"","firstName":"Khoi","middleName":"D.","lastName":"Tran","suffix":""},{"id":282775530,"identity":"5121f731-2501-4a09-9b3b-26cc272df36c","order_by":2,"name":"Phung K. Le","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYDACCRBRwCBnAOUzNhCnxYDBGKzlAClaEjcQrcVcusfs4RcDm/Tt7KfTpD8w2MhuOMBj9gCfFss5Z8yNZQzScnf25G6TOMCQZgzUYm6AT4vBjRwzaQmDw7kbbvCCtBxO3HCALU2CCC3/0w0gWv4Tp0Xyg8GBBKiWA0AtzMfwarGckVYmzWCQbLjhTO5mizMGycYzDxPQYi6RvE3yR4WdvMHxsxtvVFTYyfYdb2zD7zAgZuZB5eJTD1XD+IOAolEwCkbBKBjhAADktEqDbG19JwAAAABJRU5ErkJggg==","orcid":"","institution":"Ho Chi Minh City University of Technology, Vietnam National University (VNU HCMUT)","correspondingAuthor":true,"prefix":"","firstName":"Phung","middleName":"K.","lastName":"Le","suffix":""}],"badges":[],"createdAt":"2024-03-22 15:36:10","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":true,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":true},"doi":"10.21203/rs.3.rs-4150815/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4150815/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":53370952,"identity":"66b66ce3-dd0f-4a39-890a-5b6cbdcea347","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":118717,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra lignin-silica hybrids precipitated at different pH values\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/64d17604a36c9afd60687a76.png"},{"id":53370954,"identity":"5bdd7179-59f3-4553-a063-fabb270fc0b2","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1051639,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSEM micrographs of LS7 (a,b) and LS9 (c,d) at different magnification\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/15ec31f3eab4436a13d85977.png"},{"id":53370961,"identity":"ae4298b1-cd63-4e35-a33e-65ff5b6ae8b9","added_by":"auto","created_at":"2024-03-25 07:55:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":68760,"visible":true,"origin":"","legend":"\u003cp\u003eNitrogen sorption isotherms at 77K of LS samples.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/3242b6e92154dd8456031c19.png"},{"id":53370963,"identity":"ce0b8006-49ce-4eb0-8286-f21165cde821","added_by":"auto","created_at":"2024-03-25 07:55:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":69627,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of the adsorption time (a) and initial concentration (b) of methylene blue on the adsorption capacity of LS samples\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/05ee9198626a7ce3f159ef14.png"},{"id":53371500,"identity":"d3d05f38-fb12-42ee-813c-863789de0455","added_by":"auto","created_at":"2024-03-25 08:03:28","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":124297,"visible":true,"origin":"","legend":"\u003cp\u003ePseudo-first-order (a) and pseudo-second-order models (b) of methylene blue adsorption processes employing LS samples\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/49c738efd3edac3a4271f7a6.png"},{"id":53370955,"identity":"a8f46e47-7b25-48bf-a4f0-9379a11b9844","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":106348,"visible":true,"origin":"","legend":"\u003cp\u003eMethylene blue adsorption isotherms of LS7 (a) and LS9 (b) fitting by the Langmuir model and Freundlich model\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/8f14f0e2e88dcdbd77733b53.png"},{"id":53371501,"identity":"2955cb20-81aa-43f0-a0e7-95d0119325b0","added_by":"auto","created_at":"2024-03-25 08:03:28","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":149695,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR of LS samples after methylene blue adsorption\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/1a4c604e2409cbcba584b461.png"},{"id":53370964,"identity":"1057c107-f9f9-41b8-b66c-55f911f4424d","added_by":"auto","created_at":"2024-03-25 07:55:29","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":158790,"visible":true,"origin":"","legend":"\u003cp\u003eProposed adsorption mechanism of MB on lignin-silica composite\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/dccca58f61fe6ad115dd3af1.png"},{"id":53370958,"identity":"e30f993b-57f1-4c41-8946-a9fe0f0bd47e","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":19656,"visible":true,"origin":"","legend":"\u003cp\u003eBreakthrough curve of MB adsorption at different bed heights\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/c597fc948c216c9c52ef8c3c.png"},{"id":53370957,"identity":"74a71b01-6f27-4121-bfbe-5ac0817f4757","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":99231,"visible":true,"origin":"","legend":"\u003cp\u003eFitting model for fixed-bed column adsorption: (a) 1 cm, (b) 2 cm, and (c) 3 cm\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/5596df6aac9059bf8c886e63.png"},{"id":53370960,"identity":"b2f60fa5-ffd3-4a17-acf4-ecba6dcbc7ff","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":16435,"visible":true,"origin":"","legend":"\u003cp\u003eBDST fitting curves\u003c/p\u003e","description":"","filename":"floatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/a4d9c76efc70cfe6182b4a53.png"},{"id":53370962,"identity":"3f655acb-7804-461d-863a-a4a6f5936a98","added_by":"auto","created_at":"2024-03-25 07:55:29","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":19652,"visible":true,"origin":"","legend":"\u003cp\u003eBreakthrough curve of MB adsorption at different initial concentrations of dye solution\u003c/p\u003e","description":"","filename":"floatimage14.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/c4aa3dd33b0e4d24fbb94a4c.png"},{"id":53371999,"identity":"ee86d142-7d9f-4138-8655-d8c536c12d0c","added_by":"auto","created_at":"2024-03-25 08:11:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2419927,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/7001fcb2-aab9-495c-bbb8-b4470a1f5c25.pdf"},{"id":53371499,"identity":"95d8b730-1be1-4a42-a85a-b015d2deb754","added_by":"auto","created_at":"2024-03-25 08:03:28","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":331193,"visible":true,"origin":"","legend":"\u003cp\u003eScheme 1: Schematic diagram of lignin-silica hybrid production process\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/937422a980e3e3ba9174f5e4.png"},{"id":53370951,"identity":"6c2e9fc3-c99b-467a-9c2f-fafd8a80f504","added_by":"auto","created_at":"2024-03-25 07:55:28","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":97064,"visible":true,"origin":"","legend":"\u003cp\u003eScheme 2: Schematic diagram representing the fixed-bed column adsorption setup\u003c/p\u003e","description":"","filename":"Scheme2.png","url":"https://assets-eu.researchsquare.com/files/rs-4150815/v1/e6c2157fe8f04f3e772c0609.png"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eHybrid lignin-silica as a green adsorbent towards methylene blue in batch and fixed-bed column\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOrganic-inorganic hybrids have been prospective candidates for the development of advanced and versatile materials in recent years. Through the sol-gel method, various organic polymers can be combined with silica, resulting in diverse silica-organic composites [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These hybrids can also incorporate lignin, one of the most abundant biopolymers on earth, offering substantial potential for various applications. However, due to its intricate chemical structure and heterogeneous nature, lignin extraction often requires harsh conditions, leading to depolymerization and alteration of its original chemical structure [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Consequently, lignin obtained under such circumstances is typically deemed a byproduct of primary processes like chemical pulp production. Despite not being a porous material, lignin contains numerous oxygen-containing groups, facilitating diverse interactions with other compounds, such as physical adsorption, hydrogen bonding, and electrostatic bonds [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Especially, the hydroxyl groups allow it to undergo condensation within the silica xerogel matrix, thereby influencing its pore structure. Therefore, silica, a widely used inorganic material, has been incorporated with lignin or lignin derivatives to prepare multifunctional lignin/silica composites which have been utilized in functional filler [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], polymers [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], energy storage systems [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and wastewater treatment [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] especially. Wastewater from industry in general and textile in particular has been becoming more alarming than ever. Various organic dyes that are being used have harmful effects on humanity and the ecosystem [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Among them, methylene blue (MB), a synthetic dye, has been commonly employed in various industrial processes including dyeing and printing textiles, and in medical and laboratory settings. In some cases, MB could work as a biological stain and as an indicator in various chemical reactions. Despite not being regarded as a significant pollutant, like any substance, this organic compound can contribute to water pollution and has a strongly negative impact on human health in case it is not properly disposed of or released in large quantities into the environment [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Therefore, an enormous amount of research has been carried out to explore effective ways to capture MB. In distinct situations, methylene blue is treated by specific methods such as photodegradation [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], microbial degradation, membrane separation [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], and adsorption. Among these, adsorption is regarded to be an effective method for water treatment and an efficient separation process in general due to its low cost, ease of recovering compounds after the adsorption process, and biocompatibility [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. For instance, the research conducted by Tetyana M. Budnyak et al. employed 3-Aminopropyltriethoxysilane (3-APTES) and tetraethoxysilane (TEOS) in the silica production process, which was then incorporated with lignin to fabricate lignin-silica hybrid. After a series of steps including sol-gel and vacuum drying process, the obtained material exhibited the MB adsorption capacity of 60 mg/g and was able to extract 80\u0026ndash;99% of the dye in a pH range spanning from 3 to 10 [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In another circumstance, the surface of commercial silica Syloid 244 and lignin were activated using N-2-(aminoethyl)-3-aminopropyltrimethoxysilane and sodium iodate, respectively prior to the mixing stage. After vacuum evaporation, the sorbent was found to exhibit effective removal capability for nickel (II) and cadmium (II) ions. The maximum sorption capacities towards nickel (II) and cadmium (II) ions were determined to be 77.11 mg/g and 84.66 mg/g, respectively [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs highlighted previously, while lignin-silica hybrid materials with great potential in dyes and metal adsorption have been synthesized, most studies mainly emphasize the use of synthetic Si-containing compounds instead of natural silica. Additionally, the current production processes are relatively complicated, involving the activation of lignin and silica surfaces before synthesis, along with energy-intensive mixing steps. Consequently, the utilization of biomass sources abundant in silica and lignin, coupled with simplifying the process through simultaneous precipitation of these two substances, has become imperative and holds promise for addressing environmental concerns. Rice straw, which is originally known as agricultural waste, possesses a substantial amount of cellulose, lignin, and silica and is able to serve as a biomass source. Due to this characteristic, rice straw has been noticed not only for the paper industry but also for the production of value-added products based on cellulosic structure [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. According to this basis, there are various published studies on cellulose production and nanocellulose synthesis. However, most of them have generated a significant amount of black liquor due to the low solid/liquid ratio during the alkaline treatment and bleaching process. There is a stage in this chain called pulping, which involves the separation of cellulose fibers from lignin and other components presenting in wood or other plant materials, generating a mixture of chemicals known as black liquor. This mixture contains lignin, cellulose, hemicellulose, and a variety of other organic and inorganic compounds [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. From the very early days of the paper industry, black liquor has been considered a waste product and just simply burned to generate steam and electricity for the paper mill and this practice continues to this day [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Especially, as the world is facing the challenge of conserving non-renewable fossil fuels, global attention is turning to the production of renewable second-generation fuels. there has been growing interest in using black liquor as a feedstock for the production of advanced biofuels and biochemicals, particularly in countries with strong policies to support renewable energy and bioeconomy development. In the European Union, the Renewable Energy Directive requires members to increase the share of renewable energy in their transport sector to 10% by 2020, and up to 14% by 2030 [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Owing to the high percentage of silica and lignin components in black liquor, the preparation of lignin/inorganic composites from this waste is considered as potential and can provide a new approach towards a more valuable application of lignin-based products. The production of various types of materials from this spent liquor; therefore, has been evaluated as an appropriate solution not only to hinder the depletion of natural resources but also to solve environmental problems from waste.\u003c/p\u003e \u003cp\u003eAccording to previous research, with distinct applied pH values in the precipitation stage of black liquor, the lignin-silica hybrid possesses a different silica/lignin ratio. More specifically, the impact of pH value on the structure of the precipitate was explored by Nghi et. al [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The pH value in the range of 8\u0026ndash;10 was proven as the appropriate condition to obtain a SiO\u003csub\u003e2\u003c/sub\u003e-rich hybrid. Conversely, a low pH state could lead to a higher lignin recovery efficiency (66.75%) in comparison with others, which means a substantial amount of silica was eliminated. Based on these basics, in this research, black liquor from the cellulose alkaline pretreatment process was utilized to produce a lignin-silica hybrid (LS) with high silica content at pH value of 7 and 9. To determine the structural characteristics of the obtained material, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray fluorescence analysis (XRF), and isotherm nitrogen adsorption at 77K were employed. Besides, this study also aims to investigate the performance of LS samples as a bio-adsorbent in the removal of methylene blue at a static state.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Materials\u003c/h2\u003e\n\u003cp\u003eRice straw was harvested from An Giang province, Vietnam. The used chemicals were purchased from commercial agents and of analytical grade, including sodium hydroxide (NaOH, 99%) and sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, 98%) without any further purification. The methylene blue (MB, C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e18\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eSCl.3H\u003csub\u003e2\u003c/sub\u003eO) used in this experiment was of analytical grade.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Preparation of lignin-silica (LS\u003cem\u003e)\u003c/em\u003e\u003c/h2\u003e\n\u003cp\u003eA two-stage approach was applied to synthesize lignin-silica hybrid material. Rice straw was treated with sodium hydroxide 1% at 90\u0026deg;C for 2 hours at the solid-to-liquid ratio of 1:20 (g/mL). Then, the mixture was filtered to obtain black liquor (BL). Subsequently, the BL was precipitated by slowly adding sulfuric acid solution 20%, the simultaneous well-mixing was carried out to ensure the highest precipitation yield. The pH value of BL was adjusted to 7 and 9. Then, the system was left to age in 24 hours for stabilizing. The mixture was filtered in a vacuum filter to obtain precipitated lignin and silica, the final product described as lignin-silica hybrid samples (LS7, LS9) was washed with RO water several times to remove impurities and dried in an oven at 60\u0026deg;C for 24h (Scheme \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3 Characterization\u003c/h2\u003e\n\u003cp\u003eThe present elements in LS samples were determined by the X-ray fluorescence spectrometer (XRF). The pore structure of LS samples was analyzed by the isotherm nitrogen adsorption at 77 K. The specific surface area and the pore size distribution were calculated using the (Brunauer-Emmett-Teller) BET model. Scanning electronic microscopy (SEM) (Hitachi Ltd., Japan, TM4000) was used to observe the sample morphology. Information about functional groups and covalent bonding in LS samples was acquired by Fourier Transform Infrared Spectroscopy (FTIR).\u003c/p\u003e\n\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n\u003ch2\u003e2.3.1 Batch adsorption experiments\u003c/h2\u003e\n\u003cp\u003eThe MB adsorption experiments were conducted under ambient conditions in an aqueous phase. In a typical procedure, the lignin-silica hybrid (0.05 g) was added to 20 mL of the MB solution with a concentration of 25\u0026ndash;500 ppm. The obtained mixture was then kept in a static stage for 5\u0026ndash;150 min at room temperature. After the adsorption section, the solid material was separated by centrifugation. The absorbance of MB in the remainder liquid was determined using UV-VIS spectroscopy at the wavelength of 664 nm. The adsorption capacity at equilibrium is given by:\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ1\" class=\"mathdisplay\"\u003e$${q_e}=\\frac{{({C_o} - {C_e})V}}{m}\\,$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere q\u003csub\u003ee\u003c/sub\u003e is the equilibrium adsorption capacity of adsorbent (mg/g), C\u003csub\u003eo\u003c/sub\u003e is the initial concentration of adsorbate solution (mg/L), C\u003csub\u003ee\u003c/sub\u003e is the equilibrium concentration of MB (mg/L), V is the volume of adsorbate solution (L), and m is the weight of adsorbent (g).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.3.2 Adsorption kinetics\u003c/h2\u003e\n\u003cp\u003eThe pseudo-first-order model is [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ2\" class=\"mathdisplay\"\u003e$${q_t}={q_e}(1 - {e^{ - {k_1}t}})$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere q\u003csub\u003ee\u003c/sub\u003e is the equilibrium adsorption capacity of adsorbent (mg/g), q\u003csub\u003et\u003c/sub\u003e is the adsorption capacity of adsorbent at time t (mg/g), k\u003csub\u003e1\u003c/sub\u003e is the pseudo-first-order constant (s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and t is the adsorption time (s).\u003c/p\u003e\n\u003cp\u003eThe pseudo-second-order model based on equilibrium adsorption is [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e] :\u003c/p\u003e\n\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ3\" class=\"mathdisplay\"\u003e$${q_t}={q_e}\\frac{{{q_e}{k_2}t}}{{1+{q_e}{k_2}t}}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere q\u003csub\u003ee\u003c/sub\u003e is the equilibrium adsorption capacity of the adsorbent (mg/g). q\u003csub\u003et\u003c/sub\u003e is the adsorption capacity of the adsorbent at time t (mg/g), k\u003csub\u003e2\u003c/sub\u003e is the pseudo-second-order constant (s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and t is the adsorption time (s).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.3.3 Adsorption isotherms\u003c/h2\u003e\n\u003cp\u003eThe Langmuir equation is expressed as follows [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ4\" class=\"mathdisplay\"\u003e$${q_e}=\\frac{{{Q_0}{K_1}{C_e}}}{{1+{K_1}{C_e}}}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere q\u003csub\u003ee\u003c/sub\u003e is the equilibrium adsorption capacity of adsorbent (mg/g), Q\u003csub\u003e0\u003c/sub\u003e is the maximum adsorption capacity (mg/g), K\u003csub\u003e1\u003c/sub\u003e presents the Langmuir adsorption constant, C\u003csub\u003ee\u003c/sub\u003e stands for the equilibrium concentration of dye (mg/L).\u003c/p\u003e\n\u003cp\u003eThe Freundlich equation is given by [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equ5\" class=\"mathdisplay\"\u003e$${q_e}={K_F}C_{e}^{{1/n}}$$\u003c/div\u003e\n\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere q\u003csub\u003ee\u003c/sub\u003e is the equilibrium adsorption capacity of adsorbent (mg/g), C\u003csub\u003ee\u003c/sub\u003e is the equilibrium concentration of dye (mg/L), and K\u003csub\u003eF\u003c/sub\u003e is the Langmuir adsorption constant.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4 Adsorption in fixed-bed column\u003c/h2\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.1 Experimental set-up\u003c/h2\u003e\n\u003cp\u003eContinuous flow sorption experiments were conducted in a transparent cylindrical plastic column (2 cm internal diameter and 50 cm height). At the top of the column, an adjustable plunger was attached to maintain the uniform static head of the column. At the bottom of the column, a 0.5 mm stainless sieve was attached followed by glass wool. A 1 cm high layer of cotton was placed at the column base to provide support for the adsorbent. The uniform inlet flow of the solution into the column was maintained by an inlet valve (Scheme \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eA known quantity of LS7 was placed in the column to yield the desired bed height of the sorbent. Methylene blue solution of known concentration was pumped downward through the column at a desired flow rate. Samples were collected from the exit of the column at different time intervals and were analyzed for MB using UV-VIS spectrometry by monitoring the absorbance changes at a wavelength of maximum absorbance of 664 nm. Operation of the column was stopped when the effluent MB concentration exceeded a value of 99.5% of its initial concentration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.2 Analysis of column data\u003c/h2\u003e\n\u003cp\u003eThe time for breakthrough appearance and shape of the breakthrough curve are very important characteristics for determining the operation and the dynamic response of an adsorption column. The breakthrough time (t\u003csub\u003eb\u003c/sub\u003e, the time at which dye concentration in the effluent reached 5 mg/L) and bed exhaustion time (t\u003csub\u003ee\u003c/sub\u003e, the time at which dye concentration in the effluent reached 99.5% of initial dry concentration) were used to evaluate the breakthrough curves. The total quantity of dye mass adsorbed in the column (mad) is calculated from the area above the breakthrough curve (outlet dye concentration (C) versus time (t)) multiplied by the flow rate. Dividing the dye mass adsorbed (mad) by the sorbent mass (M) leads to the uptake capacity (q\u003csub\u003ee\u003c/sub\u003e) of the LS7. Effluent volume (V\u003csub\u003eeff\u003c/sub\u003e) can be calculated as follows:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({V_{eff}}=F \\times {t_e}\\,\\,\\,\\,\\,\\,\\,(6)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eF is the volumetric flow rate (mL/min).\u003c/p\u003e\n\u003cp\u003eThe total amount of MB (m\u003csub\u003etotal\u003c/sub\u003e) sent through the column is calculated by the Eq.\u0026nbsp;(6):\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({m_{total}}=\\frac{{{C_o}F{t_e}}}{{1000}}\\,\\,\\,\\,\\,\\,\\,(7)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003cp\u003ewhere C\u003csub\u003eo\u003c/sub\u003e is the inlet dye concentration (mg/L).\u003c/p\u003e\n\u003cp\u003eThe total removal percent of MB (Column performance) with respect to flow volume can be also found in Eq.\u0026nbsp;(7):\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(Total\\,removal\\,(\\% )=\\frac{{{m_{ad}}}}{{{m_{total}}}} \\times 100\\,\\,\\,\\,\\,\\,\\,(8)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.3 Modeling of column data\u003c/h2\u003e\n\u003cp\u003eFixed-bed column adsorption is a commercial adsorption method that is used in many cases to eliminate toxicants, in which a solution of poisonous substances is fed continuously into the column. There are two types of fixed-bed column adsorption which are downstream flow which the solution is going from top to bottom of column and upstream flow which the solution is going from the opposite direction. In the column adsorption study, parameters such as bed height and adsorbate concentration are chosen to evaluate the performance of fixed-bed column adsorption and the maximum adsorption capacity. From that, a plot between C\u003csub\u003et\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e and time (min) is demonstrated which is known as the breakthrough curve and the derived parameters such as breakthrough time (t\u003csub\u003eb\u003c/sub\u003e), exhaust time (t\u003csub\u003ee\u003c/sub\u003e), breakthrough volume (v\u003csub\u003eb\u003c/sub\u003e), exhaust volume (v\u003csub\u003ee\u003c/sub\u003e), etc. Three models were employed to characterize the column breakthrough curves obtained at various bed heights, flow rates, and inflow MB concentrations. The Clark and modified dose-response models were among them.\u003c/p\u003e\n\u003cp\u003eClark model [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e]:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\frac{{{C_t}}}{{{C_o}}}={\\left( {\\frac{1}{{1+A{e^{ - rt}}}}} \\right)^{1/(n - 1)}}\\,\\,\\,\\,\\,\\,\\,(9)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eWhere, A, r is the Clark parameter; n is the Freundlich constant.\u003c/p\u003e\n\u003cp\u003eThomas model [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e]:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\frac{{{C_t}}}{{{C_o}}}=\\frac{1}{{1+{e^{\\frac{{{K_{Th}}{q_o}m}}{v}{K_{Th}}{C_o}t}}}}\\,\\,\\,\\,\\,\\,\\,(10)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eWhere k\u003csub\u003eTh\u003c/sub\u003e is the Thomas rate constant (ml.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e); q\u003csub\u003eo\u003c/sub\u003e is the equilibrium adsorbate uptake per g of the adsorbent (mg. g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e); m is the amount of the adsorbent in the column (g); v is the flow rate of the solution passing through the column (ml. min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e\n\u003cp\u003eModified dose-response model [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\frac{{{C_t}}}{{{C_o}}}=1 - \\frac{1}{{1+{{\\left( {\\frac{{vt}}{b}} \\right)}^a}}}\\,\\,\\,\\,\\,\\,\\,(11)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eWhere, a, and b are parameters of the modified dose\u0026ndash;response model; C\u003csub\u003et\u003c/sub\u003e and t are gathered from the experiment process.\u003c/p\u003e\n\u003cp\u003eThe BDST model is generally accepted as the simplest approach and rapid prediction of adsorbent design and performance [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. Among various parameters, the required bed depth for a specific adsorption time (service time) is an important design parameter [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. The bed-depth service-time model can be used to estimate the required bed-depth for a given service-time. The BDST model is the transmutation of the Adams\u0026ndash;Bohart model and can be expressed as follows:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({t_b}=\\frac{{{N_o}}}{{{C_o}v}} - \\frac{1}{{{k_{AB}}{C_o}}}\\ln \\left( {\\frac{{{C_o}}}{{{C_b}}} - 1} \\right)\\,\\,\\,\\,\\,\\,\\,(12)\\)\u003c/span\u003e \u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eWhere t\u003csub\u003eb\u003c/sub\u003e (min) is the service time and C\u003csub\u003eb\u003c/sub\u003e (mg. L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the specific breakthrough concentration. A plot of service time t against Z should generate a straight line with a slope equal to N\u003csub\u003eo\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e and an intercept of (1/k\u003csub\u003eAB\u003c/sub\u003eC\u003csub\u003eo\u003c/sub\u003e). ln((C\u003csub\u003eo\u003c/sub\u003e/C\u003csub\u003eb\u003c/sub\u003e)\u0026thinsp;\u0026minus;\u0026thinsp;1). From the slope and intercept, both N\u003csub\u003eo\u003c/sub\u003e (g. L\u0026thinsp;\u0026minus;\u0026thinsp;1) and k\u003csub\u003eAB\u003c/sub\u003e (mL.mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) can be calculated. Once the constants of the model have been determined, the model can be used to estimate the service time for a given bed height and specific solute concentrations at the bed inlet and outlet.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results \u0026 Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 Structural Characteristics of obtained lignin-silica hybrid samples (LS) at different pH values\u003c/h2\u003e\n\u003cp\u003eThe FT-IR spectrum of lignin, silica, and the LSs are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. Along with the presence of a broad peak in the range of 3600\u0026thinsp;\u0026minus;\u0026thinsp;3200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was due to the stretching vibration of O-H groups, a signal at 1705 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was also found, and can be assigned to the stretching vibration of C\u0026thinsp;=\u0026thinsp;O groups that are present in the lignin molecule. The absorption band at around 1600\u0026thinsp;\u0026minus;\u0026thinsp;1500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which exhibits the aromatic skeletal vibration (C\u0026thinsp;=\u0026thinsp;C), confirms the presence of guaiacyl-syringyl lignin in both raw lignin and LS samples [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. From another perspective, the effect of silica on the FT-IR spectrum could be found at 474 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and between 1000\u0026ndash;950 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This indicated the Si\u0026ndash;O\u0026ndash;Si bending region and Si\u0026ndash;O\u0026ndash;Si asymmetric stretching, respectively [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. To date, the linkage between lignin and silica in plants in general and lignin-silica hybrid with natural silica in particular has not been conclusively demonstrated. However, it could be suggested that after the simultaneous precipitation, lignin and silica networks create a pristine structure due to the interweaving of these compounds. Owing to the increase of silica content in the structure of the LS hybrid, the intensity of the lignin signal changed inversely with the pH value. The difference in lignin and silica content is presented in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. While a high silica proportion was found in the LS9 at 63.80%, the silica percentage in LS7 was only 32.09%. Moreover, the degradation of carbohydrate component was demonstrated \u003cem\u003evia\u003c/em\u003e loss on ignition value which means the LS7 possessed a higher amount of lignin with the loss on ignition of 57.82% when compared to this figure of LS9 of approximately 35%.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e content in three different LS samples\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSample\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e (wt%)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eLoss on ignition (wt %)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eOthers (wt%)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e63.80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e35.08\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.12\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e32.09\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e57.82\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10.09\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eIn addition, these dissimilarities led to the difference in morphology of the lignin-silica hybrid, which was demonstrated in the SEM image (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). It can be concluded that the hybrid samples witnessed the larger-sized blocks due to the increase of lignin component, which was consistent with the dropping of silica particles. The average dimension of LS7 and LS9 hybrid samples was generally in the range of 100\u0026ndash;500 nm. And it was also found that these samples consisted of smooth clusters and rough clusters which indicates that small particles of silica are attached on the surface of lignin from the precipitation process.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eBET surface area and pore volume of LS samples\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSamples\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eBET surface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTotal pore volume (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e46.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.29\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e166.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.38\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe specific surface area of LS samples is displayed in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Owing to the lower SiO\u003csub\u003e2\u003c/sub\u003e content, the LS7 possessed an S\u003csub\u003eBET\u003c/sub\u003e of less than 47 m\u003csup\u003e2\u003c/sup\u003e/g, whereas the higher recorded value was from LS9 (166.5 m\u003csup\u003e2\u003c/sup\u003e/g) and it was nearly 40% higher than the S\u003csub\u003eBET\u003c/sub\u003e of lignin-silica microparticles from the wheat husk (117.4 m\u003csup\u003e2\u003c/sup\u003e/g) [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. The physisorption result of LS9 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) resembled the type IV curve, which is a common signal for mesoporous materials [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e], while the curve of LS7 was typical for type III [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. Moreover, LS9 also presented a noticeable rise in the N\u003csub\u003e2\u003c/sub\u003e uptake in comparison with LS7 (nearly 1.5 times differential).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Methylene blue adsorption capacity of different LS hybrid samples\u003c/h2\u003e\n\u003cp\u003eThe effects of adsorption time and initial concentration on the MB removal effectiveness of LS samples were investigated. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea, the MB adsorption of LS7 and LS9 occurred rapidly in the first 20 min. The removal process then kept on at a quick pace until reached a plateau after about 60 min of interacting. At this point, the MB trapping capacity of LS samples could reach up to 45.8 mg/g for LS7, while the LS9 performed the best capturing ability with a better value of 48.9 mg/g. This might be deduced by the larger specific surface area of LS9 in comparison with others leading to a larger space for MB to attach.\u003c/p\u003e\n\u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb, a similar trend was obtained from the investigation of initial MB concentration on the capture efficiency. The highest number of 49.2 mg/g belonged to LS9, and the uptake value of nearly 45 mg/g was from LS7. Generally, the adsorption quantity increased considerably when the initial concentration of MB increased from 0 to 160 ppm, leading to the high slope of the curve exhibiting the relationship between those two variables. Then, the change in the adsorbed quantity became less significant and stayed nearly stable when the initial concentration exceeded 200 ppm. This trend can be explained that as the initial concentration increases, the proportion of adsorbate molecules to available adsorption sites rises, leading to a stronger driving force for the capture process. Eventually, the active sites were mostly occupied and the number of available sites decreased, the trapping process would slow down and reach the equilibrium, even if the solution concentration increased further.\u003c/p\u003e\n\u003cp\u003eIn order to gain more understanding of the adsorption mechanism, the adsorption kinetics was studied. Generally, despite having a slight difference in the calculated adsorption capacity, the data fit revealed that the coefficients (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) were approximately the same for the two models (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). The correlation coefficient for first-order kinetic was in the range of 0.964\u0026ndash;0.990, while this value for second-order kinetic was from 0.949 to 0.986. It means that the nature of the adsorption of MB on LS samples possibly followed both first-order and second-order kinetic models, which are supposed to be chemisorption and physisorption [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eKinetic parameters of pseudo-first-order and -second-order models for the adsorption processes of LS samples\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003ePseudo-first-order model\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003ePseudo-second-order model\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr style=\"height: 67.4375px;\"\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003eMaterial\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee,cal\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003e(mg/g)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003ek\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003ex 10\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e\u003c/sup\u003e \u003cstrong\u003e(min\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee,cal\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003e(mg/g)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003ek\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003ex 10\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e(g.mg\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e.\u003cstrong\u003emin\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 67.4375px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eLS7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e43.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e6.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.964\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e50.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.949\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eLS9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e48.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e4.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.990\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e58.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.986\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eMoreover, the distribution of adsorbates onto the surface of LS samples was investigated using Langmuir and Freundlich models. The Langmuir isotherm, one of the most common isotherm models, assumes monolayer adsorption, whereas the Freundlich equation refers to multilayer adsorption [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the experimental data fitted with the Langmuir isotherm (the correlation coefficients of over 0.9) for three LS samples. However, the estimated adsorption capacity based on the Langmuir equation was drastically higher than the experimental one, indicating that this model was not appropriate to describe the contact between methylene blue and active sites on the adsorbent surface. During the acidification process, SiO\u003csub\u003e2\u003c/sub\u003e was distributed unevenly on the surface of lignin-silica hybrids, which resulted in the non-uniformity of adsorptive sites.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eIsotherms parameters for the adsorption of Methylene blue dye on the LS samples\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eLangmuir Isotherm\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eFreundlich Isotherm\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMaterial\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee,cal\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003e(mg/g)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eL\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003e(L/mg)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eF\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e57.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.009\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.976\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.889\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e64.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.009\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.955\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.853\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe presence of functional groups in methylene blue and the formation of a linkage between adsorbent and adsorbate were confirmed, which can be seen in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. The FT-IR spectrum of LS samples after the adsorption process indicated the signal assigned to the stretching of -C-O-N (1600\u0026thinsp;\u0026minus;\u0026thinsp;1550 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) overlapping with aromatic skeletal vibration (C\u0026thinsp;=\u0026thinsp;C) of lignin, -NH\u003csub\u003e2\u003c/sub\u003e (1000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and N-H (900\u0026thinsp;\u0026minus;\u0026thinsp;800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. The presence of the C-N-C group in the adsorbent led to the broader peak at around 500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e when compared to the LS sample before the adsorption, which is also the region of Si-OH [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. This result, therefore, could be considered as proof of the chemical interactions between lignin-silica hybrid and dye molecules, which showed a good agreement with the obtained data in adsorption kinetics analysis.\u003c/p\u003e\n\u003cp\u003eThe plausible adsorption mechanisms including the electrostatic interaction and hydrogen bonding between the adsorbent and dye molecules were illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Numerous nitrogens with a free lone pair in MB can form a hydrogen bond with Si\u0026ndash;OH, while Si\u0026ndash;O\u003csup\u003e\u0026minus;\u003c/sup\u003e, which is created \u003cem\u003evia\u003c/em\u003e the deprotonation of silanol groups, bonds to the N\u003csup\u003e+\u003c/sup\u003e centers [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. Besides, the presence of carboxyl and hydroxyl groups in lignin contributed a lot to the formation of electrostatic bonds. Therefore, this possible mechanism could be considered as an explanation for the higher adsorption capacity of lignin-silica composite when compared to silica or lignin which is shown in the following section.\u003c/p\u003e\n\u003cp\u003eIn comparison with various types of materials generated from biomass (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e), the lignin-silica hybrid obtained in this study exhibited great potential. Despite being synthesized through a one-step process, all LS samples possessed higher capturing capacities than others whose activities were improved \u003cem\u003evia\u003c/em\u003e more complex processes such as activation, modification, and pyrolysis. Due to the presence of both organic (lignin) and inorganic (SiO\u003csub\u003e2\u003c/sub\u003e) moieties in the structure, the adsorption capacity of LS samples was significantly enhanced when compared to silica and some carbon-based materials alone.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab5\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eComparison of Methylene blue adsorption capacity of different materials synthesized from biomass\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMaterials\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAdsorption capacity (mg/g)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eRef.\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e45.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eThis study\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eLS9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e49.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eThis study\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAminomethylated lignin-silica\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e42.19\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e[\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAmorphous silica\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e22.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e[\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eOptimal Biochar from Argan Shells Powder\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e31.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e[\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eActivated carbon from tea waste using KOH\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e36.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e[\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Fixed-bed column adsorption\u003c/h2\u003e\n\u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n\u003ch2\u003e3.3.1 Various models for MB adsorption in a fixed-bed column\u003c/h2\u003e\n\u003cp\u003eThe breakthrough curves have been measured under various experimental conditions, including different bed heights and initial MB concentrations. But the initial solution pH and temperature are both kept constant at 7.0 and 298 K, respectively. The detailed experimental parameters were shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, and Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Then, the experimental data have been fitted by various models such as Thomas, Clark, and the modified dose-response model to explore the adsorption mechanism.\u003c/p\u003e\n\u003cp\u003eAs for the Clark model, based on Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the determination coefficients R\u003csup\u003e2\u003c/sup\u003e were not close to 1.0 and the calculated values of parameter n did not match the data fitted by the Freundlich model in bath studies. Meanwhile, the simulated results of Clark constant A were quite abnormal and differed from each other very much. Furthermore, based on this model, Clark constants, A and r, did not have any physical meanings. Accordingly, the Clark model was not advisable to be applied to study the breakthrough curves further.\u003c/p\u003e\n\u003cp\u003eThe Thomas model, which delineates the electrostatic and chemical forces governing the uptake of Methylene Blue (MB) molecules by materials, does not align well with the experimental data as can be seen in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e. Therefore, the fitting results as shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e were also quite good. From Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, the determination coefficients R\u003csup\u003e2\u003c/sup\u003e were not close to 1.0. In accordance with the theoretical underpinnings of the Thomas model, materials exhibiting a monolayer electrochemical adsorption mechanism typically yield experimental data that conforms to the Thomas model. However, in this context, the experimental data deviates from the expected pattern, possibly attributable to the utilization of the Thomas model for medium breakthrough curves. This divergence highlights a disparity between the experimental data and the theoretical expectations inherent in the Thomas model[\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eAmong them, the determination coefficients R2 by modified-dose response model were the highest which were all very close to 1.0. Furthermore, the theoretical MB uptakes qe,cal at varied conditions were not close to their corresponding experimental ones. The observed phenomenon can be elucidated by considering the residence time, which proves insufficient for the complete interaction between dye molecules and the adsorption surface, thereby preventing the saturation of all available adsorption sites. Although this circumstance may be considered an exception, it has been suggested that the modified dose-response model remains the most appropriate for characterizing the adsorption of Methylene Blue (MB) in the fixed-bed of LS7 composite. From a molecular-level perspective of the adsorption mechanism, LS7 composite exhibits a richness in carboxyl and hydroxyl groups derived from lignin. The adsorption of MB onto LS7 occurs through electrostatic interactions between anionic carboxyl groups and cationic MB molecules, aligning with a monolayer chemical adsorption process. Consequently, the modified dose-response model accurately delineates the column adsorption dynamics of MB onto the LS7 surface.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab6\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eClark parameters at different conditions\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eC\u003csub\u003eo\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(ppm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ev\u003c/p\u003e\n\u003cp\u003e(ml.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eZ\u003c/p\u003e\n\u003cp\u003e(cm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eA\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003er x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ex\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.75\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.076\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9802\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00406\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.83\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.977\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9791\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00274\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.91\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.876\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9777\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00302\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.02\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9706\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00406\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e150\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.51\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.223\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9093\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.0078\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab7\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eThomas parameters at different conditions\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eC\u003csub\u003eo\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(ppm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ev\u003c/p\u003e\n\u003cp\u003e(ml.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eZ\u003c/p\u003e\n\u003cp\u003e(cm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eq\u003csub\u003eo,cal\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mg/g)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ek\u003csub\u003eTh\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(ml.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ex\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e119.30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.139\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9698\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.0037\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e70.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.127\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9667\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00434\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e54.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.114\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9633\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00495\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e24.60\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.425\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.9579\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00581\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e150\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e30.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.181\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.8924\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.00923\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab8\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eModified-dose response parameters at different conditions\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eC0\u003c/p\u003e\n\u003cp\u003e(ppm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003ev\u003c/p\u003e\n\u003cp\u003e(ml.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eZ\u003c/p\u003e\n\u003cp\u003e(cm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003cp\u003e(ml)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eq\u003csub\u003e0,cal\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mg/g)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ex\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1.525\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1037.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e20.74\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.9880\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.0015\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1.614\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1257.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e19.98\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.9914\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.0011\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1.690\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1505.56\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e17.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.9940\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.0008\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1.823\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e941.81\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e21.60\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.9942\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.0008\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e150\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e1.025\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e301.79\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e20.76\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.9917\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.0007\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\n\u003ch2\u003e3.3.2 Effect of bed height on breakthrough curve\u003c/h2\u003e\n\u003cp\u003eThe effects of bed height on the adsorption performances of LS7 have been investigated over a range from 1.0 cm to 3.0 cm. The flow rate was fixed at 10 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the initial concentration of MB solution was 100 ppm. From Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e, it was found that the breakthrough time increased with increasing bed height as expected. It was due to the fact that as the bed height increased, MB had more time to contact with LS7 which resulted in a longer exhausting time and higher removal amount of MB [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e]. In addition, the rate constant k\u003csub\u003eTh\u003c/sub\u003e decreased with increasing bed height, indicating the reduced reaction rate, which was ascribed to the longer contact time for higher bed depth.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab9\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 9\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003e\u003cem\u003eBDST parameters at different C\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/C\u003c/em\u003e\u003csub\u003eo\u003c/sub\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNo.\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eC\u003csub\u003eo\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(ppm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ev\u003c/p\u003e\n\u003cp\u003e(ml.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eC\u003csub\u003eb\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eN\u003csub\u003eo\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ek\u003csub\u003eAB\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.05\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9.615\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e27.518\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.9995\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.650\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-0.456\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.9990\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21.150\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-0.0814\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.9959\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e27.845\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-0.0331\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.9803\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e showed the plots of the service-time (t\u003csub\u003eb\u003c/sub\u003e) at 5% (B), 20% (C), 40% (D), and 60% (E) breakthrough points, i.e., t\u003csub\u003eb\u003c/sub\u003e at C\u003csub\u003eb\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e equal to 0.05, 0.2, 0.4 and 0.6, respectively, and all the calculated BDST constants listed in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e. The determination coefficients R\u003csup\u003e2\u003c/sup\u003e all exceeded 0.99, indicating that the BDST model might be applicable to represent the MB adsorption in a fixed-bed column of LS7. The adsorption capacities calculated by this model, N\u003csub\u003e0\u003c/sub\u003e, were also roughly close to the experimental ones.\u003c/p\u003e\n\u003cp\u003eThe rate constant, k\u003csub\u003eAB\u003c/sub\u003e, characterized the rate of solute transfer from the fluid phase to the solid phase. As C\u003csub\u003eb\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e increased, the concentration difference of MB between the fluid and the solid phase decreased, which would weaken the mass transfer and bring down the value of k\u003csub\u003eAB\u003c/sub\u003e. However, at C\u003csub\u003eb\u003c/sub\u003e/C\u003csub\u003eo\u003c/sub\u003e around 0.2, the simulated k\u003csub\u003eAB\u003c/sub\u003e was abnormal and showed negative values, which might be due to the limitation of the BDST model. Since the BDST model was derived from the Adams\u0026ndash;Bohart model, it was only suitable for describing the initial part of the breakthrough curve as mentioned above.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n\u003ch2\u003e3.3.3 Effect of initial concentration of MB solution on breakthrough curve\u003c/h2\u003e\n\u003cp\u003eThe effects of initial MB concentration have been investigated at 50, 100, and 150 ppm, respectively. The bed height was 2 cm and the temperature was 298 K. The flow rate was fixed at 10 mL.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the pH of MB solution was 7.0. It was illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e that breakthrough time decreased with increasing MB concentration. Besides, as the influent concentration increased, sharper breakthrough curves were obtained. They both indicated that the adsorption sites were occupied much faster with the increase of MB concentration. In addition, from Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, with the increase of initial MB concentration, the adsorption capacity q\u003csub\u003ecal\u003c/sub\u003e increased while the constant a decreased. It was due to the fact that the rate of mass transfer in the column turned slowly for higher concentrations of MB [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e], which resulted in lengthening the contact time between solute and adsorbent and improved adsorption capacity.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eWith the purpose of decreasing waste products in the cellulose extraction process and producing an efficient sorbent for the removal of dyes from aqueous solutions, black liquor was used in the synthesis of the lignin-silica composites \u003cem\u003evia\u003c/em\u003e a one-step method lessening the necessity of synthesized silica-containing compound. The MB adsorption capacity of the obtained material was studied as a function of various parameters such as concentration of dye and contact time. Specifically, it was found that the hybrid synthesized at pH9 (LS9) showed a significant SiO\u003csub\u003e2\u003c/sub\u003e composition of 63.80 wt%, which was much higher than this number in the one synthesized at pH7 (about 2 times). When it comes to the specific surface area, LS samples witnessed an increase in S\u003csub\u003eBET\u003c/sub\u003e corresponding to pH value in the acidification stage. While the S\u003csub\u003eBET\u003c/sub\u003e of more than 166 m\u003csup\u003e2\u003c/sup\u003e/g belonged to LS9 and nearly 47 m\u003csup\u003e2\u003c/sup\u003e/g to LS7. Consequently, the results also showed that LS9 possessed a good adsorption capacity towards MB dye which was more than 10% higher in comparison with LS7. Moreover, the kinetic characteristics of MB uptake by LS composites followed more suitably the Langmuir isotherm model and pseudo-second-order models. It was found that bed height and initial MB concentration can affect the breakthrough curves obviously. Moreover, the modified dose-response model is found to be the most suitable one to describe the adsorption behaviors, according to the monolayer chemical adsorption mechanism. With achieved results, this study not only highlights a one-step method without any required modification to utilize black liquor in the synthesis of an effective material for organic dye treatment but also serves the dual advantages of protecting the environment and effectively enhancing the value of byproducts from agricultural production.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCo D. Pham: Conceptualization, Data curation, Writing \u0026ndash; original draft, Writing \u0026ndash; review \u0026amp; editing. Khoi D. Tran: Conceptualization, Data curation, Writing \u0026ndash; original draft, Writing \u0026ndash; review \u0026amp; editing. Visualization, Writing \u0026ndash; review \u0026amp; editing. Phung K. Le: Funding acquisition, Methodology, Project administration, Resources, Supervision, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe acknowledge the support of time and facilities from Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS. Prabha, D. Durgalakshmi, S. Rajendran, and E. Lichtfouse, \u0026ldquo;Plant-derived silica nanoparticles and composites for biosensors, bioimaging, drug delivery and supercapacitors: a review,\u0026rdquo; \u003cem\u003eEnviron Chem Lett\u003c/em\u003e, vol. 19, no. 2, pp. 1667\u0026ndash;1691, Apr. 2021, doi: 10.1007/s10311-020-01123-5.\u003c/li\u003e\n\u003cli\u003eC. D. Pham \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;A review of the extraction methods and advanced applications of lignin-silica hybrids derived from natural sources,\u0026rdquo; \u003cem\u003eInt J Biol Macromol\u003c/em\u003e, vol. 230, p. 123175, Mar. 2023, doi: 10.1016/j.ijbiomac.2023.123175.\u003c/li\u003e\n\u003cli\u003eR. Salih \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Lignin based microspheres for effective dyes removal: Design, synthesis and adsorption mechanism supported with theoretical study,\u0026rdquo; \u003cem\u003eJ Environ Manage\u003c/em\u003e, vol. 326, p. 116838, Jan. 2023, doi: 10.1016/j.jenvman.2022.116838.\u003c/li\u003e\n\u003cli\u003eT. M. Budnyak \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Membrane-Filtered Kraft Lignin\u0026ndash;Silica Hybrids as Bio-Based Sorbents for Cobalt(II) Ion Recycling,\u0026rdquo; \u003cem\u003eACS Omega\u003c/em\u003e, vol. 5, no. 19, pp. 10847\u0026ndash;10856, May 2020, doi: 10.1021/acsomega.0c00492.\u003c/li\u003e\n\u003cli\u003eW. Liu \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Sol-gel silica modified recovered lignin particles and its application as blend with HDPE,\u0026rdquo; \u003cem\u003eInd Crops Prod\u003c/em\u003e, vol. 189, p. 115842, Dec. 2022, doi: 10.1016/j.indcrop.2022.115842.\u003c/li\u003e\n\u003cli\u003eC. D. Pham \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;The utilization of black liquor from rice straw pretreatment stage on the syntheses of carbon-based materials using in anodes ion-lithium batteries production,\u0026rdquo; \u003cem\u003eJournal of Materials Science: Materials in Electronics\u003c/em\u003e, vol. 34, no. 4, p. 335, Feb. 2023, doi: 10.1007/s10854-023-09840-7.\u003c/li\u003e\n\u003cli\u003eŁ. Klapiszewski, P. Bartczak, M. Wysokowski, M. Jankowska, K. Kabat, and T. Jesionowski, \u0026ldquo;Silica conjugated with kraft lignin and its use as a novel \u0026lsquo;green\u0026rsquo; sorbent for hazardous metal ions removal,\u0026rdquo; \u003cem\u003eChemical Engineering Journal\u003c/em\u003e, vol. 260, pp. 684\u0026ndash;693, Jan. 2015, doi: 10.1016/j.cej.2014.09.054.\u003c/li\u003e\n\u003cli\u003eT. Hien Tran \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;A sustainable, low-cost carbonaceous hydrochar adsorbent for methylene blue adsorption derived from corncobs,\u0026rdquo; \u003cem\u003eEnviron Res\u003c/em\u003e, vol. 212, p. 113178, Sep. 2022, doi: 10.1016/j.envres.2022.113178.\u003c/li\u003e\n\u003cli\u003eA. R. Disanto and J. G. Wagner, \u0026ldquo;Pharmacokinetics of Highly Ionized Drugs II: Methylene Blue\u0026mdash;Absorption, Metabolism, and Excretion in Man and Dog after Oral Administration,\u0026rdquo; \u003cem\u003eJ Pharm Sci\u003c/em\u003e, vol. 61, no. 7, pp. 1086\u0026ndash;1090, Jul. 1972, doi: 10.1002/jps.2600610710.\u003c/li\u003e\n\u003cli\u003eV. Katheresan, J. Kansedo, and S. Y. Lau, \u0026ldquo;Efficiency of various recent wastewater dye removal methods: A review,\u0026rdquo; \u003cem\u003eJ Environ Chem Eng\u003c/em\u003e, vol. 6, no. 4, pp. 4676\u0026ndash;4697, Aug. 2018, doi: 10.1016/j.jece.2018.06.060.\u003c/li\u003e\n\u003cli\u003eT. A. Nguyen and R.-S. Juang, \u0026ldquo;Treatment of waters and wastewaters containing sulfur dyes: A review,\u0026rdquo; \u003cem\u003eChemical Engineering Journal\u003c/em\u003e, vol. 219, pp. 109\u0026ndash;117, Mar. 2013, doi: 10.1016/j.cej.2012.12.102.\u003c/li\u003e\n\u003cli\u003eM. Sari Yilmaz, \u0026ldquo;Graphene oxide/hollow mesoporous silica composite for selective adsorption of methylene blue,\u0026rdquo; \u003cem\u003eMicroporous and Mesoporous Materials\u003c/em\u003e, vol. 330, p. 111570, Jan. 2022, doi: 10.1016/j.micromeso.2021.111570.\u003c/li\u003e\n\u003cli\u003eT. M. Budnyak \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Methylene Blue dye sorption by hybrid materials from technical lignins,\u0026rdquo; \u003cem\u003eJ Environ Chem Eng\u003c/em\u003e, vol. 6, no. 4, pp. 4997\u0026ndash;5007, Aug. 2018, doi: 10.1016/j.jece.2018.07.041.\u003c/li\u003e\n\u003cli\u003eŁ. Klapiszewski, P. Bartczak, M. Wysokowski, M. Jankowska, K. Kabat, and T. Jesionowski, \u0026ldquo;Silica conjugated with kraft lignin and its use as a novel \u0026lsquo;green\u0026rsquo; sorbent for hazardous metal ions removal,\u0026rdquo; \u003cem\u003eChemical Engineering Journal\u003c/em\u003e, vol. 260, pp. 684\u0026ndash;693, Jan. 2015, doi: 10.1016/j.cej.2014.09.054.\u003c/li\u003e\n\u003cli\u003eH. Beidaghy Dizaji \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Generation of High Quality Biogenic Silica by Combustion of Rice Husk and Rice Straw Combined with Pre- and Post-Treatment Strategies\u0026mdash;A Review,\u0026rdquo; \u003cem\u003eApplied Sciences\u003c/em\u003e, vol. 9, no. 6, p. 1083, Mar. 2019, doi: 10.3390/app9061083.\u003c/li\u003e\n\u003cli\u003eA. Sharma, G. Singh, and S. K. Arya, \u0026ldquo;Biofuel from rice straw,\u0026rdquo; \u003cem\u003eJ Clean Prod\u003c/em\u003e, vol. 277, p. 124101, Dec. 2020, doi: 10.1016/j.jclepro.2020.124101.\u003c/li\u003e\n\u003cli\u003eN. T. Vo, C. D. Pham, T. B. Ly, M. D. T. Dang, N. H. N. Do, and P. K. Le, \u0026ldquo;Valorization of rice straw for valuable materials: towards a zero-waste recovery process,\u0026rdquo; \u003cem\u003eBiomass Convers Biorefin\u003c/em\u003e, Aug. 2023, doi: 10.1007/s13399-023-04681-0.\u003c/li\u003e\n\u003cli\u003eM. Naqvi, J. Yan, and E. Dahlquist, \u0026ldquo;Black liquor gasification integrated in pulp and paper mills: A critical review,\u0026rdquo; \u003cem\u003eBioresour Technol\u003c/em\u003e, vol. 101, no. 21, pp. 8001\u0026ndash;8015, Nov. 2010, doi: 10.1016/j.biortech.2010.05.013.\u003c/li\u003e\n\u003cli\u003eA. J\u0026auml;ger-Waldau, I. Kougias, N. Taylor, and C. Thiel, \u0026ldquo;How photovoltaics can contribute to GHG emission reductions of 55% in the EU by 2030,\u0026rdquo; \u003cem\u003eRenewable and Sustainable Energy Reviews\u003c/em\u003e, vol. 126, p. 109836, Jul. 2020, doi: 10.1016/j.rser.2020.109836.\u003c/li\u003e\n\u003cli\u003eN. H. Do \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;The novel method to reduce the silica content in lignin recovered from black liquor originating from rice straw,\u0026rdquo; \u003cem\u003eSci Rep\u003c/em\u003e, vol. 10, no. 1, p. 21263, Dec. 2020, doi: 10.1038/s41598-020-77867-5.\u003c/li\u003e\n\u003cli\u003eE. D. Revellame, D. L. Fortela, W. Sharp, R. Hernandez, and M. E. Zappi, \u0026ldquo;Adsorption kinetic modeling using pseudo-first order and pseudo-second order rate laws: A review,\u0026rdquo; \u003cem\u003eClean Eng Technol\u003c/em\u003e, vol. 1, p. 100032, Dec. 2020, doi: 10.1016/j.clet.2020.100032.\u003c/li\u003e\n\u003cli\u003eS. Kalam, S. A. Abu-Khamsin, M. S. Kamal, and S. Patil, \u0026ldquo;Surfactant Adsorption Isotherms: A Review,\u0026rdquo; \u003cem\u003eACS Omega\u003c/em\u003e, vol. 6, no. 48, pp. 32342\u0026ndash;32348, Dec. 2021, doi: 10.1021/acsomega.1c04661.\u003c/li\u003e\n\u003cli\u003eR. M. Clark, \u0026ldquo;Modeling TOC Removal by GAC: The General Logistic Function,\u0026rdquo; \u003cem\u003eJ Am Water Works Assoc\u003c/em\u003e, vol. 79, no. 1, pp. 33\u0026ndash;37, Jan. 1987, doi: 10.1002/j.1551-8833.1987.tb02780.x.\u003c/li\u003e\n\u003cli\u003eH. C. Thomas, \u0026ldquo;Heterogeneous Ion Exchange in a Flowing System,\u0026rdquo; \u003cem\u003eJ Am Chem Soc\u003c/em\u003e, vol. 66, no. 10, pp. 1664\u0026ndash;1666, Oct. 1944, doi: 10.1021/ja01238a017.\u003c/li\u003e\n\u003cli\u003eG. Yan, T. Viraraghavan, and M. Chen, \u0026ldquo;A new model for heavy metal removal in a biosorption column,\u0026rdquo; \u003cem\u003eAdsorption Science and Technology\u003c/em\u003e, vol. 19, no. 1, pp. 25\u0026ndash;43, 2001, doi: 10.1260/0263617011493953.\u003c/li\u003e\n\u003cli\u003eY. S. Al-Degs, M. A. M. Khraisheh, S. J. Allen, and M. N. Ahmad, \u0026ldquo;Adsorption characteristics of reactive dyes in columns of activated carbon,\u0026rdquo; \u003cem\u003eJ Hazard Mater\u003c/em\u003e, vol. 165, no. 1\u0026ndash;3, pp. 944\u0026ndash;949, Jun. 2009, doi: 10.1016/j.jhazmat.2008.10.081.\u003c/li\u003e\n\u003cli\u003eH. Muhamad, H. Doan, and A. Lohi, \u0026ldquo;Batch and continuous fixed-bed column biosorption of Cd2+ and Cu2+,\u0026rdquo; \u003cem\u003eChemical Engineering Journal\u003c/em\u003e, vol. 158, no. 3, pp. 369\u0026ndash;377, Apr. 2010, doi: 10.1016/j.cej.2009.12.042.\u003c/li\u003e\n\u003cli\u003eB. Strzemiecka \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Physicochemical Characterization of Functional Lignin\u0026ndash;Silica Hybrid Fillers for Potential Application in Abrasive Tools,\u0026rdquo; \u003cem\u003eMaterials\u003c/em\u003e, vol. 9, no. 7, p. 517, Jun. 2016, doi: 10.3390/ma9070517.\u003c/li\u003e\n\u003cli\u003eB. Strzemiecka, Ł. Klapiszewski, D. Matykiewicz, A. Voelkel, and T. Jesionowski, \u0026ldquo;Functional lignin-SiO \u003csub\u003e2\u003c/sub\u003e hybrids as potential fillers for phenolic binders,\u0026rdquo; \u003cem\u003eJ Adhes Sci Technol\u003c/em\u003e, vol. 30, no. 10, pp. 1031\u0026ndash;1048, May 2016, doi: 10.1080/01694243.2015.1115602.\u003c/li\u003e\n\u003cli\u003eJ. Cui, H. Sun, X. Wang, J. Sun, M. Niu, and Z. Wen, \u0026ldquo;Preparation of siliceous lignin microparticles from wheat husks with a facile method,\u0026rdquo; \u003cem\u003eInd Crops Prod\u003c/em\u003e, vol. 74, pp. 689\u0026ndash;696, Nov. 2015, doi: 10.1016/j.indcrop.2015.05.061.\u003c/li\u003e\n\u003cli\u003eK. Sing, \u0026ldquo;The use of nitrogen adsorption for the characterisation of porous materials,\u0026rdquo; \u003cem\u003eColloids Surf A Physicochem Eng Asp\u003c/em\u003e, vol. 187\u0026ndash;188, pp. 3\u0026ndash;9, Aug. 2001, doi: 10.1016/S0927-7757(01)00612-4.\u003c/li\u003e\n\u003cli\u003eY. Zhang \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;The pore size distribution and its relationship with shale gas capacity in organic-rich mudstone of Wufeng-Longmaxi Formations, Sichuan Basin, China,\u0026rdquo; \u003cem\u003eJournal of Natural Gas Geoscience\u003c/em\u003e, vol. 1, no. 3, pp. 213\u0026ndash;220, Jun. 2016, doi: 10.1016/j.jnggs.2016.08.002.\u003c/li\u003e\n\u003cli\u003eK.-D. Zhang \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Adsorption Behavior of High Stable Zr-Based MOFs for the Removal of Acid Organic Dye from Water,\u0026rdquo; \u003cem\u003eMaterials\u003c/em\u003e, vol. 10, no. 2, p. 205, Feb. 2017, doi: 10.3390/ma10020205.\u003c/li\u003e\n\u003cli\u003eK. Y. Foo and B. H. Hameed, \u0026ldquo;Insights into the modeling of adsorption isotherm systems,\u0026rdquo; \u003cem\u003eChemical Engineering Journal\u003c/em\u003e, vol. 156, no. 1, pp. 2\u0026ndash;10, Jan. 2010, doi: 10.1016/j.cej.2009.09.013.\u003c/li\u003e\n\u003cli\u003eA. H. Birniwa \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Adsorption Behavior of Methylene Blue Cationic Dye in Aqueous Solution Using Polypyrrole-Polyethylenimine Nano-Adsorbent,\u0026rdquo; \u003cem\u003ePolymers (Basel)\u003c/em\u003e, vol. 14, no. 16, p. 3362, Aug. 2022, doi: 10.3390/polym14163362.\u003c/li\u003e\n\u003cli\u003eM. Afshari and M. Dinari, \u0026ldquo;Synthesis of new imine-linked covalent organic framework as high efficient absorbent and monitoring the removal of direct fast scarlet 4BS textile dye based on mobile phone colorimetric platform,\u0026rdquo; \u003cem\u003eJ Hazard Mater\u003c/em\u003e, vol. 385, p. 121514, Mar. 2020, doi: 10.1016/j.jhazmat.2019.121514.\u003c/li\u003e\n\u003cli\u003eN. Mokhtari, M. Afshari, and M. Dinari, \u0026ldquo;Synthesis and characterization of a novel fluorene-based covalent triazine framework as a chemical adsorbent for highly efficient dye removal,\u0026rdquo; \u003cem\u003ePolymer (Guildf)\u003c/em\u003e, vol. 195, p. 122430, May 2020, doi: 10.1016/j.polymer.2020.122430.\u003c/li\u003e\n\u003cli\u003eT. M. Budnyak \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Methylene Blue dye sorption by hybrid materials from technical lignins,\u0026rdquo; \u003cem\u003eJ Environ Chem Eng\u003c/em\u003e, vol. 6, no. 4, pp. 4997\u0026ndash;5007, Aug. 2018, doi: 10.1016/j.jece.2018.07.041.\u003c/li\u003e\n\u003cli\u003eC. D. Woolard, J. Strong, and C. R. Erasmus, \u0026ldquo;Evaluation of the use of modified coal ash as a potential sorbent for organic waste streams,\u0026rdquo; \u003cem\u003eApplied Geochemistry\u003c/em\u003e, vol. 17, no. 8, pp. 1159\u0026ndash;1164, Aug. 2002, doi: 10.1016/S0883-2927(02)00057-4.\u003c/li\u003e\n\u003cli\u003eA. Ouedrhiri \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Adsorption of the Methylene Blue Dye in Environmental Water Samples by Biochar Obtained from the Valorization of Argan Shells,\u0026rdquo; \u003cem\u003ePhysical Chemistry Research\u003c/em\u003e, vol. 10, no. 3, pp. 301\u0026ndash;313, Sep. 2022, doi: 10.22036/PCR.2021.303554.1968.\u003c/li\u003e\n\u003cli\u003eF. J. Tuli, A. Hossain, A. K. M. F. Kibria, A. R. M. Tareq, S. M. M. A. Mamun, and A. K. M. A. Ullah, \u0026ldquo;Removal of methylene blue from water by low-cost activated carbon prepared from tea waste: A study of adsorption isotherm and kinetics,\u0026rdquo; \u003cem\u003eEnviron Nanotechnol Monit Manag\u003c/em\u003e, vol. 14, p. 100354, Dec. 2020, doi: 10.1016/j.enmm.2020.100354.\u003c/li\u003e\n\u003cli\u003eJ. Song, W. Zou, Y. Bian, F. Su, and R. Han, \u0026ldquo;Adsorption characteristics of methylene blue by peanut husk in batch and column modes,\u0026rdquo; \u003cem\u003eDesalination\u003c/em\u003e, vol. 265, no. 1\u0026ndash;3, pp. 119\u0026ndash;125, Jan. 2011, doi: 10.1016/j.desal.2010.07.041.\u003c/li\u003e\n\u003cli\u003eR. M. Clark, \u0026ldquo;Modeling TOC Removal by GAC: The General Logistic Function,\u0026rdquo; \u003cem\u003eJournal AWWA\u003c/em\u003e, vol. 79, no. 1, pp. 33\u0026ndash;37, Jan. 1987, doi: 10.1002/j.1551-8833.1987.tb02780.x.\u003c/li\u003e\n\u003cli\u003eG. Yan, T. Viraraghavan, and M. Chen, \u0026ldquo;A New Model for Heavy Metal Removal in a Biosorption Column,\u0026rdquo; \u003cem\u003eAdsorption Science \u0026amp; Technology\u003c/em\u003e, vol. 19, no. 1, pp. 25\u0026ndash;43, Feb. 2001, doi: 10.1260/0263617011493953.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Schemes ","content":"\u003cp\u003eSchemes 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Ho Chi Minh City University of Technology","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"lignin-silica hybrids, wastewater treatment","lastPublishedDoi":"10.21203/rs.3.rs-4150815/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4150815/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe number of research regarding the \u0026lsquo;lignin-silica complex first\u0026rsquo; approach focusing on the synthesis of a long polymer with SiO\u003csub\u003e2\u003c/sub\u003e distributed on the surface has been increasing significantly in recent years. Despite being considered an abundant source for the recovery of this hybrid, black liquor has not been widely employed in the synthesis of lignin/silica-derived materials. In order to propose a solution to utilize the waste liquid from the cellulose production process instead of current synthesized silica-containing compounds in the synthesis of highly effective materials for environmental treatment, this study aims to produce a lignin-silica hybrid (LS) from black liquor generated from rice straw alkaline treatment \u003cem\u003evia\u003c/em\u003e sol-gel process. The difference in the material characteristics determined by XRF, FT-IR, SEM, and isothermal nitrogen adsorption at 77K led to the different capacities in methylene blue (MB) adsorption. The SiO\u003csub\u003e2\u003c/sub\u003e content in the material increased with respect to pH value, which resulted in a higher specific surface area (S\u003csub\u003eBET\u003c/sub\u003e). Specifically, the greater S\u003csub\u003eBET\u003c/sub\u003e belonged to LS recovered at pH\u0026thinsp;=\u0026thinsp;9 (LS9) with a value of 166.5 m\u003csup\u003e2\u003c/sup\u003e/g. Additionally, the presence of numerous negatively charged groups (i.e., COO\u003csup\u003e\u0026minus;\u003c/sup\u003e, OH) and silanol in the LS structure resulted in a strong affinity towards MB, a cationic dye. LS9 exhibited a better performance in MB removal with a capacity of nearly 50 mg/g in comparison with the value of LS7, which was around 45 mg/g. Along with the proposed adsorption mechanism, kinetic adsorption, isothermal adsorption, and fixed-bed column adsorption were also investigated to interpret the adsorption processes.\u003c/p\u003e","manuscriptTitle":"Hybrid lignin-silica as a green adsorbent towards methylene blue in batch and fixed-bed column","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-25 07:55:23","doi":"10.21203/rs.3.rs-4150815/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"672fc6ad-3d9f-4a66-8727-8553dbab3597","owner":[],"postedDate":"March 25th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":29776217,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2024-03-25T07:55:24+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-25 07:55:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4150815","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4150815","identity":"rs-4150815","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}