Plasma-engineered sugarcane bagasse: A novel strategy for efficient mercury removal from aqueous solutions

Plasma-engineered sugarcane bagasse: A novel strategy for efficient mercury removal from aqueous solutions | 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 Plasma-engineered sugarcane bagasse: A novel strategy for efficient mercury removal from aqueous solutions Angie Paola Santacruz Salas, Maria Lucia Pereira Antunes, Elidiane Cipriano Rangel, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4144021/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Nov, 2024 Read the published version in Environmental Science and Pollution Research → Version 1 posted 6 You are reading this latest preprint version Abstract Metal ion adsorption using agro-industrial residues has shown promising results in remediating contaminated waters. However, adsorbent effectiveness relies on their properties, often necessitating processing for modification. Considering this, plasma treatment is effective in modifying material surfaces physically and chemically. This study investigated the modification of sugarcane bagasse (SB) using plasma-treated and evaluated its efficacy as a novel adsorbent for mercury removal from aqueous solutions. SB underwent low-temperature plasma treatment with sulfur hexafluoride (SF6) as the working gas, varying treatment times (2, 30, and 60 minutes) and fixed powers (80, 190, and 300 W) at 16 Pa pressure. Characterization via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS/SEM), Fourier transform infrared spectroscopy (FTIR) and zero point of charge (pHpzc) revealed significant structural changes like increased in porosity and alteration in proportion atomic. Additionally, the successful incorporation of fluorine was confirmed in all treatment conditions, while sulfur was detected in only some samples. Amongst the tested conditions, the SB treated with 300 W for 60 minutes demonstrated the highest mercury removal efficiency, achieving an impressive 83.67% removal rate compared to untreated SB, which yielded only 57.95%. The adsorption mechanism exhibited both physical and chemical behavior, with chemisorption being the dominant process. The Freundlich model provided the best fit to the experimental data, with an R 2 value of 0.97. In conclusion, plasma treatment can be a promising alternative for improving the physical and chemical characteristics of SB adsorbents, thereby improving their efficiency in removing mercury from aqueous solutions. Sugarcane bagasse adsorption plasma treatment mercury water treatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Mercury (Hg) is a potentially harmful metal and one of the main chemical elements of concern to the World Health Organization (WHO). This persistent contaminant has the ability to bioaccumulate and biomagnify along the food chain. In addition, it has a high potential for neurotoxicity and teratogenicity, which may cause serious risks to human health and aquatic biota (Gyamfi et al. 2021 ; da Silva Montes et al. 2022 ; Marrugo-Madrid et al. 2022 ) Several physical, chemical and biological methods have been used for the removal of Hg ions from aqueous solutions, such as the membrane separation, reverse osmosis, chemical precipitation, electrochemical oxidation, ion exchange, adsorption, among others (Singh et al. 2021 ). However, many of these treatments require elevated investments and operational costs, as well as, most often present low efficiency to comply with international regulations (Licona-Aguilar et al. 2022 ). Adsorption has been recognized as a simpler, faster, effective, and economical technique compared to with other type of treatments (Shahabi Nejad and Sheibani 2022 ). Different types of materials can be used as adsorbents and agricultural residues, for example, are promising materials in this area due to their sustainable characteristics, low cost, high availability, adsorption capacity and possibility of easy regeneration (Sun et al. 2018 ). SB is a large-scale residue produced by the sugar industry. This material is mainly composed of cellulose (40–50%), hemicellulose (16–33%) and lignin (15–30%). It contains binding sites that are capable of capturing metal ions, making it a favorable low-cost adsorbent (Kulkarni et al. 2022 ; Bai et al. 2022 ; Nguyen et al. 2024 ). Diverse literature has evaluated the potential of SB for the removal of metal ions in aqueous solutions (Harripersadth et al. 2020 ; Ezeonuegbu et al. 2021 ; Kulkarni et al. 2022 ; Bai et al. 2022 ; Licona-Aguilar et al. 2022 ). Many of these studies evaluated the modification of the raw biomass to improve its physicochemical properties and enhance its removal efficiency (Khan et al. 2021 ). Several approaches are applied to adjust the surface physicochemical properties of this material. Even so, these methods generally have low modification efficiency, require longer treatment times, elevated temperatures, besides generating secondary residues (Zhang et al. 2022 ). In this scenario, plasma technology has been considered a potential tool for the modification of material properties. It is energy-efficient and environmentally friend once it does not generate appreciable waste or air emissions (Ribeiro 2017 ; Mohammed et al. 2021 ). This technology involves the use of an ionized gas containing energetic and reactive species that interact strongly with the surfaces of the materials, creating new active sites to bind functional groups and modify the structure of the treated material (Zhang et al. 2022 ). Plasma treatment is effective for surface functionalization, while maintaining the physical and chemical bulk properties of the material (Wang et al. 2018 ; Hu et al. 2020 ). For adsorbent materials, plasma treatments may improve the porous structure and increase the concentration of active functional groups on the surface, resulting in higher adsorption capacity for different types of contaminants (Zhang et al. 2019 ; Hu et al. 2020 ; Zhang et al. 2022 ). Based on that, the hypothesis tested in the present work is if the incorporation of another electronegative element on the structure of the SB, such as fluorine, together with the structural erosion provoked by F plasma, would influence the physicochemical properties of SB and especially its adsorbing efficiency. There are no reports in the literature on the low-pressure sulfur hexafluoride (SF 6 ) plasma treatments employed to incorporate active fluorine groups in agricultural residues like SB for adsorbing mercury from liquid effluents. Then, the objective of this study was to assess the modification of physicochemical structure of SB using plasma treatment and verify its influence in mercury adsorption capacity in aqueous solution. 2. Experimental 2.1 Preparation of biomass The adsorbent was produced using SB obtained from the São Paulo state region. The SB, Saccharum spp. species, underwent a series of preparation steps. Firstly, it was washed with running water to remove surface impurities. Afterward, the biomass was dried at 80°C in an oven with air circulation for 12 hours. Subsequently, the dried biomass was ground using a Willye-type knife mill (NL − 226–02 - New Lab) with a fixed rotation speed of 1730 rpm. Finally, the ground material was sieved through a 35 mesh (0.50 mm opening) to achieve a standardized particle size. 2.2 Treatment of SB in Sulfur hexafluoride Plasma The adsorbent was modified in reactive low-pressure plasma, established in a stainless-steel reactor with a volume of approximately 5 L. The reactor, schematically represented in Fig. 1 , is equipped with two horizontal, circular, and parallel plate electrodes. A vacuum pump, connected to the lowermost reactor’s fringe, reduces the system’s pressure down to 1.3 Pa (2.0 x 10 − 3 Torr). The system pressure is measured using a Pirani manometer (Edwards APGX). Gases are introduced into the system through stainless steel and polymeric pipes, and the flow control is achieved using needle valves. The plasma excitation signal is supplied by a Tokyo Hy-Power RF-300 W (13.56 MHz model) radio frequency power supply, connected to the lower electrode via a Tokyo Hy-Power MB-300 impedance coupler. Prior to the treatments, the samples were previously left in the oven at 120°C for 12 h to remove moisture from the environment. Subsequently, 3 g of the grounded SB was accommodated in a stainless-steel dish. The sample holder dish was positioned on the lowermost electrode of the reactor. The system was closed and pumped down to the base pressure of 3 Pa (2.25 x 10 − 2 Torr). After pressure stabilization, the ultra-pure Sulfur Hexafluoride SF 6 gas (99.99%) was introduced to achieve a working pressure of 16 Pa (1.2 x 10 − 1 Torr). Plasma was then ignited by the application of radiofrequency signal to the lower electrode whereas grounding the upper one. It was investigated the effect of the plasma power (80, 190 and 300 W) for three different exposure times (2, 30 and 60 min). The samples were labeled according to a standard format of "material, power and treatment time", ex. "SB 80 W 2 min" means that SB was modified in 80 W plasma and of 2 min duration. The plasma conditions used here were mainly based on the study of (Resende et al. 2018 ; Mohammed et al. 2021 ), with special attention on incorporating fluorine into an organic material and improving the physical characteristics of the adsorbent. 2.3 Adsorbent characterization The morphological structure and the porosity of the samples were assessed by Scanning Electron Microscopy (SEM) analysis, in the JEOL JSM-6010 Analytical SEM, equipped with a Dry SD Hyper X-ray detector (EX-94410T1L11) with resolution of 129 to 133 eV for the Mn Kα line at 3000 cp. The samples were initially affixed a stub utilizing double-sided carbon tape. In order to enhance the conductivity of the samples for SEM analysis, a thin conductive layer was applied via vacuum sputtering of the Au-Pd (gold-palladium) alloy. This process involved subjecting the samples to a current of 30 mA for 120 seconds using the Denton Vacuum Desk V apparatus. SEM micrographs were captured at magnifications of 500x, 1000x and 3500x, using an accelerating voltage of 10 kV, with a spot size of 30, which corresponds to a beam diameter of 10 mm. The semi-qualitative chemical composition of the samples was accessed using Energy Dispersive Spectroscopy (EDS). The detector attached to the microscope was utilized for EDS analysis, employing the same voltage and spot size as mentioned earlier. Selected areas at 1000x magnification were subjected to point and total chemical analysis. The elements studied in the research were: Carbon (C), Nitrogen (N), Oxygen (O), Silicon (Si), Potassium (K), Sulfur (S), Fluorine (F) and Mercury (Hg). Furthermore, Fourier Transform Infrared Spectroscopy (FTIR) was employed to identify the functional groups present on the surface of the adsorbents. The FTIR analysis was conducted using the FTIR-410 Spectrometer with diffuse reflectance module. The samples were mixed with KBr at a ratio of 99% KBr to 1% sample. Each sample underwent 128 scans within the range of 4000 to 500 cm − 1 . The zero point of charge (pHpzc) was determined according to the methodology described by (Gómez-Herrera 2021 ) and it was conducted on the adsorbent that presented the best characteristics in the step 2.3 and 2.4. To achieve this, 1 L of 0.01 mol/L NaCl solution was prepared with ultrapure water. Then it was divided into 50 mL Erlenmeyer flaks and in each one the pH was adjusted with values between 2 and 12 (increasing every 2 units). The pH adjustments were carried out using 0.1 mol/L hydrochloric acid (HCl) and 0.1 mol/L sodium hydroxide (NaOH). Next, 100 mg of the adsorbent was added to each solution, and the mixture was stirred at a speed of 175 rpm for 24 hours at a temperature of 25°C. The final pH was measured with a Tecnal digital pH meter (Tec-2). 2.4 Mercury Adsorption Study To compare the removal percent of mercury (Hg(II)) using the SB both with and without low-temperature plasma treatment obtained in this study, adsorption experiments were conducted under identical conditions. In each adsorption test, 25 mg of the respective adsorbent was suspended in 5 mL of a solution containing an initial concentration of 10 mg/L of Hg(II) at pH 7 and subjected to stirring at 175 rpm for 48 hours at a constant temperature of 25°C. The conditions mentioned earlier were carefully selected following a thorough initial literature review (Marins et al. 2002 ; Peng et al. 2017 ; Sun et al. 2018 ). Subsequently, 2 mL of each sample was collected, and the final concentration was quantified using an inductively coupled plasma optical emission spectrometer (ICP-OES) (Agilent Technologies, model 720 series). The ICP-OES parameters employed in these analyses include an axial torch, concentric nebulizer, a radio frequency (RF) generator set at 40 MHz, RF power at 1.1 kW, refrigerant gas flow rate (Argon) maintained at 15.0 L/min, auxiliary gas flow at 1.5 L/min, and a nebulizer flow of 200 kPa. The adsorption capacity and the removal efficiency of the adsorbents was calculated following the equations mentioned by (Tursi et al. 2022 ) (See supplementary material for more details). This step was undertaken to identify the adsorbent that had superior mercury removal percentage. The investigation of adsorption kinetics and isotherms was exclusively conducted on the adsorbent that exhibited the most favorable adsorption. 2.4.1 Adsorption Kinetics To generate the adsorption kinetics curve, 125 mg of adsorbent were placed in contact with 100 mL solution with an initial concentration of 10 mg/L Hg(II). Aliquots of 2 ml were taken at specific contact times of 0, 0.5, 1.5, 3, 6, 9, 24 and 48 hours. Pseudo-first-order (PFO) and pseudo-second-order (PSO) theoretical models were used to describe the mechanisms of Hg(II) adsorption on the adsorbent that showed the best results in the preliminary test (More details in the supplementary material). 2.4.2 Adsorption isotherms Adsorption isotherm experiments were conducted with initial Hg(II) concentrations ranging from 5 to 40 mg/L. The equilibrium period was set at 48 hours, and the dosages used were 1.25 g/L, 2.5 g/L, and 5 g/L. The resulting isotherms underwent analysis based on the Langmuir (Langmuir 1918 ) and Freundlich (Freundlich 1906 ) models (More details in the supplementary material). 3. Results and discussion 3.1 Characterization of the adsorbents The micrographs acquired from Scanning Electron Microscopy (SEM), presented in Fig. 2, show the surface morphology of the untreated (A) and of the plasma treated SB (B - J). Figure 2 - Scanning electron micrographs of the raw and of the plasma treated SB with different exposure times and excitation powers at ×500 and ×3000 magnifications. A) Untreated SB; B) SB 80 W 2 min; C) SB 190 W 2 min; D) SB 300 W 2 min; E) SB 80 W 30 min; F) SB 190 W 30 min; G) SB 190 W 60 min; G) SB 300 W 2 min; G) SB 300 W 30 min; G) SB 300 W 2 min. In Fig. 2.A, the micrograph reveals a fibrous and heterogeneous structure with few pores or with small pores that are not perceptible with the employed magnifications. Particulate material, rising from deteriorated regions of the fibers, is present in some surface regions, together with cracks. The structural complexity of the natural material is responsible for this heterogeneity and it was also reported by (Veiga et al. 2021 ; Liu et al. 2022a ). Upon the plasma treatment, morphological changes were detected with the modification degree being dependent on the plasma power and on the exposure time. The particulate and agglomerate content is reduced, indicating removal of the weakly connected material by the plasma. A clear improvement on the short-range surface smoothness is observed when comparing the higher magnification micrographs. Except for the fastest treatment (2 min), conducted at the lowest power (80 W), cracks are no longer evident after the treatment. However, a higher number of pores was identified, suggesting material removal is being favored from specific points of the biomass. Aside to this, there is rupture of the original continuous structure into large flakes of material, evidenced by the analysis of the inset (lower magnification of x500) micrographs. It is detected a general trend of increasing the flakes production with increasing the treatment intensity (time and/or power). According to Liu, Zhou, and Liu (Liu et al. 2022b ), the power elevation in helium plasmas could enhance the surface roughness due to the corrosive effect of plasma, resulting in a more irregular morphology. In the present work, two trends in opposition were detected as one considers the surface morphology of the treated samples: a reduction of the surface defects in the low-range scale and an elevation in a larger-range one. Thus, according to the above results plasma is removing material from the surface by chemical and physical reactions. In plasmas of SF 6 , it is observed the generation of SF 5 , SF 4 , SF 3 , SF 2 , SF, S, and F reactive groups (Resnik et al. 2018 ). The increment in the exposure time thus elevates the probability of material removal by some of the erosive species. Another phenomenon explaining the same effect, but with other consequences, is the removal of material by physical routes, that is, by ion bombardment. The collision of fast ions with the material surface transfer energy that can cause emission of groups together with structural and chemical modifications. For low energy ions, dissipation of energy occurs by means of nuclear collisions, that provide displacement of atoms from their position in the structure and thus its weakening and breakage. On the other hand, for more energetic ions energy dissipation by electronic events (excitations, ionizations, free radical generations) is favored, producing active dangling bonds that may recombine by C bonds unsaturation and chain crosslinking. Consequently, to understand the results obtained here it should be taken into account that fast ions will lose their energies primarily in electronic collision, producing crosslinkings and unsaturations, processes that improve the surface uniformity. When their energies are reduced, with increasing the penetration depth, nuclear events will be the main responsible for slowing down the ions, producing breakage of the SB polymeric backbones. With increasing treatment time and power this damage process is intensified flaking the overall SB structure. Thus, ion bombardment can contribute to the improvement of the surface uniformity due to dissipation of energy by electronic collision and to the structural rupture by deposition of energy from nuclear events. Moreover, ion bombardment favors the non-homogeneous removal of material. In the work of Man (Man et al. 2020 ), it was demonstrated that etching of SiO 2 coated with an CH x F layer, in SF 6 /CH 4 plasmas, is regulated, amongst others, by ion bombardment. The sputtering of groups from the CH x F top layer generates defect points where the reaction of neutral F can promptly erode the whole structure beneath, creating pores in the initially uniform layer. Thus, the observed pores in the treated SB investigated here (micrographs) are attributed to the simultaneous physical (sputtering) and chemical (etching) effect of the SF 6 plasmas as demonstrated in the work (Man et al. 2020 ). Therefore, all the modifications observed on the surface microstructure of the SB submitted to the plasma treatments, including pore formation, flaking and smoothening of the SB structure can be attributed to the physical and chemical effect of ion bombardment and to the etching caused by neutrals generated in SF 6 plasmas. The EDS results of the untreated and of the plasma treated SB samples are presented in Table 1 . The main elements observed on the surfaces of the untreated SB were carbon, oxygen and nitrogen, in good agreement with the results of (Rocha et al. 2015 ) in which was evaluated the composition of the bagasse from 60 varieties of sugarcane produced in Brazil. Aside to these elements, the treated samples also presented fluorine and, in some cases, sulfur. The untreated material is majorly composed of C with lower proportions of O and N. Hydrogen is also a component of the SB, but it is not detected by this methodology. According to Seah and collaborators (Seah et al. 2023 ) the structure of different woody and herbaceous biomasses is constituted by 6% of H. After the plasma treatment there is detection of small proportions of F in all the samples and of S (≤ 0.2%) only in the samples treated in the mild conditions (80 W, 2 and 30 min). Changes in the proportion of the other elements are also identified, but three major trends should be discussed here. Table 1 Semi-quantitative analysis results of atomic proportions of C, N, O, Si, K, F and S on the untreated and plasma treated SB. Sample C (%) N (%) O (%) Si (%) K (%) F (%) S (%) SB 86.3 1.1 11.2 0.4 0.6 - - SB 80 W 2 min 78.3 10.4 9.1 0.1 0.7 1.2 0.2 SB 80 W 30 min 79.3 11.3 8.5 0.1 0.3 0.4 0.1 SB 80 W 60 min 86.1 2.5 10.0 0.4 - 0.3 - SB 190 W 2 min 85.6 2.4 10.9 0.3 0.4 0.4 - SB 190 W 30 min 87.1 1.1 11.0 - 0.5 0.3 - SB 190 W 60 min 87.4 1.3 9.0 1.4 0.7 0.2 - SB 300 W 2 min 75.6 12.9 11.0 - 0.4 0.2 - SB 300 W 30 min 88.0 - 11.7 0.1 0.1 0.1 - SB 300 W 60 min 91.9 - 8.0 - 0.3 0.1 - The first one is related with the C content reduction for the treatments with the lowest power (80 W), for 2 and 30 min, and with the highest power (300 W) for 2 min. The concomitant falls in the C and in the O proportions for the samples treated in plasmas of 80 W (2 and 30 min) are followed by compensatory rise in the N proportion. On the other hand, for the highest power treatments (300 W, 2 min), despite the reduction in the C proportion is similar to that observed in the previous discussed samples, that of O is not. Only an oscillation in the O proportion is detected in this case, indicating now N is replacing only C. So, different changing mechanisms are taking place in the low and high-power regime. A reduction in the carbon proportion rice husk derived hybrid silica/carbon biochar was also reported by (Mohammed et al. 2021 ) and is very consistent with the erosive nature of electronegative SF 6 plasmas. The second trend observed in the Table 1 is the elevation of the C proportion beyond that observed for the untreated SB, for the highest power and exposure time treatments (300 W, 30 and 60 min). Proportion of O is only barely influenced in this case. However, N is no longer incorporated. The inclusion of N, as well as O, is proposed to happen, majorly, from reactions of active dangling bonds, left on the material structure after treatment, with atmospheric groups when the sample is removed of the vacuum chamber. The absence of N indicates that the trapped radical content decreases for treatments in plasmas of 300 W (30 and 60 min). Pendant bonds, generated from H and N abstraction, are being consumed by chain crosslinking and by unsaturation of chemical bonds. Just N realize it enough to explains the elevation in the C proportion, but O is also being abstracted in some of these treatments. The third aspect observed is related to the proportion of fluorine. Despite some oscillation, a general trend of decreasing F incorporation with increasing plasma excitation power and exposure time is detected. Fluorine inclusion occurs at low proportions (< 1.2%), showing that fluorination is not favored in the treatments conducted here. Possible neutral species produced in pure low pressure SF 6 plasmas are SF 6, SF 5, SF 4, SF 3, SF 2, SF, S, F and F 2 . Positive (SF 5 + , SF 4 + , SF 3 + , SF 2 + , SF + , S + and F + ) and negative (SF 6 − , SF 5 − , SF 4 − , SF 3 − , SF 2 − , F − and F 2 − ) ions may also be formed from the SF 6 precursor. Nevertheless, the dissociation behavior and thus the concentration of radicals and ions depend on the electronic density and temperature, which, in turn, rely on the pressure and applied power. It was demonstrated in the work developed by Levko and co-workers (Levko et al. 2013 ), on the evaluation of the neutral and ionized species distribution on SF 6 plasmas, using the one-dimensional fluid model, that an elevation in the plasma power provides an overall increment in density of electrons, positive and negative ions in the plasma. In all cases, the most abundant neutral fragment is SF 5 , followed by F and by SF 4 – SF 3 . The highest densities of SF 5 and F groups is explained by their formation route, due to direct electron impact, to be the most probable one by the reaction (Resnik et al. 2018 ) $${SF}_{z}+ {e}^{-}\to {SF}_{z-1}+F+{e}^{-}$$ 3 In the same work, it was shown that the most abundant charged species are SF 5 + followed by F − , SF 6 − , SF 3 + , SF 4 + . Negligible densities of SF 2 and SF 2 + were observe. Using a radiofrequency (13.56 MHz, 10 mTorr, 900–1700 W) capacitively coupled SF 6 plasma, Lallement and co-authors (Lallement et al. 2009 ) observed similar results concerning the most probable neutral and charged species as well as a trend of rise in the electron density with increasing plasma power, but a constancy in the electron temperature. Besides that, Amorim et al., (Amorim et al. 2020 ) stated that in low-pressure plasma, high electron temperatures generate an increase in fluoride concentration. This, combined with elevates electronegativity of SF 6, leads to the generation of negative ions, by reactions such as: $${SF}_{6}+ {e}^{-}\to {SF}_{6}^{-}$$ 4 Thus, plasma is composed of negative and positive ionized groups from SF 6 and also from O (reactor residual atmosphere), together with electrons. According to the previous discussion, an elevation in the concentration of ions and electrons is expected in SF 6 plasma with increasing the excitation power. But it is important to mention here that negative ions will be attracted to the grounded upper electrode of the reactor and repelled of the negatively biased sample holder (lowermost electrode). This can be pointed as one of the reasons why there was a low fluorine incorporation on the SB structure. Only neutral F species, orders of magnitude more abundant than ions, that can diffuse to the region where the SB was accommodated, are prone to react with the organic structure to be incorporated by means of CF x groups. In the first stage of this reaction, F has to recombine with C or H from the SB, generating volatile groups, with low sticking probabilities that are emitted, explaining material removal and dangling bonds formation on the material structure (Resende et al. 2018 ; Mohammed et al. 2021 ) This is another reason for the low F incorporation, that is, F is effectively acting as an eroding compound rather than a doping element. Fluorine inclusion would happen after the etching step. Ion bombardment of the bagasse with positive SF 6 fragments (SF 5 + SF 4 + , SF 3 + ) may also contribute to F incorporation, but still more with the atomic and molecular release and then with free-radical generation. The latter processes would enhance chain crosslinkings and bond unsaturation, explaining the low incorporation of atmospheric groups (N, O) observed in some samples as well as the reduction on the surface defects. The energy deposited in the material structure by ion bombardment tends to increase with the rise in the power and in the exposure time. The probability of neutral reactive radicals reaching the sample surface also increases with exposure time. Therefore, the low proportions of F detected in the samples studied here indicate that dangling bonds’ saturation by F is not an efficient process. The variation in the atomic proportions of O and N, together with that of F indicates the saturation of free radical is taking place during plasma treatment but also after it, when the sample is in contact with atmosphere. Furthermore, F should be concentrated on the topmost layers of the fibers, whereas EDS analysis is probing deeper untreated regions, promoting a mixed result of the treated and untreated regions. Finally, sulfur was detected only in the samples prepared in plasmas of low power (80 W) for low (2 min) and moderate (30 min) exposure times. Figure 3 highlights the points where sulfur was detected. Figure 3. A and Fig. 3. B correspond of the material treated in plasmas of 80 W for 2 and 30 minutes, respectively. Interestingly, higher power levels (190 and 300 W) and longer exposure times (60 min) did not contribute to S incorporation. The optimization of the structural healing (crosslinking and unsaturation) in these conditions are pointed as the responsible for the lack of S and the low proportion of F detected in these cases. With such results it is promptly observed that the highest F and S incorporation occurred for the lowest power plasma and for the lower exposure time (2 min). The proportion of C was the lowest in this sample while the N proportion was the highest indicating C and O are being replaced mainly by N. This inference is confirmed by the results of the sample prepared at the highest plasma power and exposure time where N was not detected and C proportion was the highest one. Based on that it is proposed that the plasma treatment is removing not only H, but also C and O (Si and K) from the biomass structure, generating active sites for atmospheric N and O incorporation, crosslinking, bonds unsaturation and F incorporation. The analysis of FTIR spectra of the of the as-received and the modified SB under various time intervals and pressures (Figure S1 , see material supplementary) shows the presence of aliphatic CH 2 groups of the lignin is evident by the bands at 2865 and 2918 cm − 1 (Manyatshe et al. 2022 ). Contributions due to OH stretching vibrations are detected at 3450–3650 cm − 1 (Abdulhameed et al. 2021 ; Bai et al. 2022 ). C oxidized groups are identified by the contributions at 1740 (C = O) (Ordonez-Loza et al. 2021 ) and 670 (C-OH in cellulose) cm − 1 . Peaks characteristics of lignin, normally found in 1616, 1586, 1508, (aromatic C = C) and 1234 (aromatic C-O) (Montero et al. 2018 ; Veiga et al. 2021 ; Dzoujo et al. 2022 ). The bands observed at 1740 and 1368, cm − 1 are attributed to the stretching of the COO- and CH = CH respectively. Those bands are related to hemicellulose and lignin compounds (Veiga et al. 2021 ; Sutthasupa et al. 2023 ). The bands around 1120 and 1149 cm − 1 are typical cellulose and hemicellulose peaks due to C-O and C-N stretching (Montero et al. 2018 ). It is a consensus in the literature (Luz et al. 2007 ), that SB is composed of different proportions of cellulose (C₆H₁₀O₅) n , hemicellulose (C 5 H 10 O 5 ) and lignin (C 81 H 92 O 28 ), together with mineral contaminants. The organic fraction of this material is composed of structures formed by aromatic carbon rings to which hydroxyls, methyl, methylene and others components are attached (Rocha et al. 2015 ; ALVES MACEDO 2020). Comparing the spectra of the as-received and of the plasma-treated SB reveals a general preservation of the material’s chemical structure. However, it should be considered that whereas the plasma treatment is changing the topmost layers of the material, the infrared inspection is reaching untreated deep layers. But even so, some modifications in the infrared spectra of the samples are indicatives of the plasma induced changes. New bands are detected at 2100 cm − 1 (C≡C) and 1114 cm − 1 (C-O), the latter spectral band mainly appears in the sample spectrum subjected to a longer duration and higher power treatment. Also, in the Fig. 4 .A and 4.B is observed a peak in 1900 cm − 1 which is related to stretching C = C = C (Merck 2021 ). Aside to this, the treatment results in alterations in the intensities of several bands, including OH at 3580 cm − 1 , CH 2 at 2918 cm − 1 , C = O at 1745 cm − 1 and C = C at 1586 cm − 1 . Specifically, unsaturation of C bonds, proposed in the interpretations of elemental composition of the samples, is then corroborated by the rise of C≡C (2100 cm − 1 ) band and by the growth of C = C one (1586 cm − 1 ). The peak ascribed to O-H stretching vibrations (3450–3650 cm − 1 ) exhibits heightened prominence in materials primarily treated with lower power. However, when the treatment power increases, its intensity decreases, probably because the plasma has a similar effect to heat treatment, that may lead to the release of part of the structural water contained in the plant material (Dzoujo et al. 2022 ). The intensity of the band at 1700 cm − 1 (aromatic C = O), is significantly increased after plasma treatment, particularly when using power levels of 80 and 190 W. This effect may be due to the conversion of C-OH groups into C = O due to H abstraction (F or ion bombardment). The transformation of C-OH groups into C = O also corroborates the idea of dangling bond consumption by unsaturation of bonds. After exposure to fluorine plasma, new peaks appeared in the range of 900 to 1300 cm − 1 , which may be related to CF x groups (CF, CF 2 , and CF 3 ) (Agopian et al. 2022 ; Zhou et al. 2023 ). The peaks observed at 700 − 600 cm − 1 correspond to the alkyl halides of CF (Mohammed et al. 2021 ). The rise of small bands around 1330 (CF 2 ) and 600–700 cm − 1 (CF) in the spectra of treated samples suggest F incorporation in low proportions, what is in good accordance with the compositional results obtained by EDS. In the spectra appears a peak in 1150 cm − 1 which can be attributed to the S = O symmetrical stretching of the sulfonate (Pavia et al. 2008 ).This result, combined with that of Table 1 , confirms the presence of sulfur incorporation, especially in the SB samples with a power of 80 W. Fluorine neutrals and charged species are majorly eroding and ion bombarding the material structure. It is also confirmed that dangling bonds generated by etching and sputtering are being consumed by unsaturation of C bonds and possibly by the counterpart process of crosslinking. The determination of the zero-charge pH (pH pzc ) plays a pivotal role in comprehending the electrostatic interaction dynamics between the adsorbate and the adsorbent. It is imperative for the charges on the adsorbent to be opposite those of the adsorbate, fostering a more robust interaction between the two entities, as emphasized by Alves Macedo (ALVES MACEDO 2020). In Fig. 4 , the pH pzc graph is presented for both untreated SB and SB treated at 300W for 60 minutes. The point of intersection on the curve with the x-axis signifies an equilibrium between negative and positive charges on the adsorbate's surface. Upon analysis, it is observed that the pHpzc of SB 300W 60 min is approximately 4.8. In contrast, the untreated SB exhibits a slightly higher difference pH pzc value, reaching 5.2. This suggests that the plasma treatment has not significantly altered the pH pzc . In conclusion, the surface of the adsorbent becomes positively charged at a pH 4.8. 3.2 Mechanism of modification Based on the above characterization results, the modification mechanisms can be inferred. Initially, during the treatment process, SF 6 is decomposed by the plasma, resulting in the formation of various ions, including SF 5 , SF 4 , SF 3 , SF 2 , SF, S, and F, however, since the radio frequency signal is connected to the lower electrode, the predominant interaction with the material will involve positive ions, specifically SF₃ + , SF₅ + , SF₂ + , SF + , F + and S₂F + . Figure 5 presents a conceptual model detailing the possible interactions between SF 6 ions and SB: (I) F, generated in the plasma, initiates an attack process on H, leading to the production of HF and the generation of free radicals within the structure. (II) Similarly, F generated in the plasma, attacks and binds to the structure, forming stable C-F bonds. (III) Various F species bind to carbon, leading to the generation of volatile CF4, accompanied by a reduction in the carbon content within the structure. This phenomenon is more evident in treatments performed with lower power and shorter time. (IV) S, generated in the plasma, binds to O within the structure, causing the incorporation of SO into the material. In addition, sulfur binds to N and O, forming volatile groups such as SN and SOF x , resulting in a decrease in the amount of O together with N. This phenomenon is clearly observed in Table 1 in the treatments performed with higher power and longer time. 3.3 Mercury adsorption studies Table 2 presents the results of the adsorption study of Hg(II) in aqueous solution conducted on both modified and unmodified adsorbents with plasma. Notably, all materials demonstrated an impressive removal percentage exceeding 50%. This remarkable performance can be attributed to the utilization of SB, a globally abundant bio-waste known for its high percentage of cellulose and lignin, surpassing that of other conventional agricultural wastes. Furthermore, SB boasts excellent chemical properties, including moisture content (4.4–8.7% by weight), ash content (0.90–9.6% by weight), volatile material (69.8–81.0% by weight), and carbon content (39.8–47.3% by weight) (Raj et al. 2022 ). These properties play a crucial role in facilitating an effective adsorption process. A significant effect was observed in the samples treated with plasma, where, as the power and treatment time increase, the adsorption capacity also rises. Particularly noteworthy is the SB treated for 60 minutes with a power of 300 W, which exhibited 25.72% more mercury removal compared to untreated SB. According to a study published by Kang et al. (Kang et al. 2020 ), there is a direct relationship between the adsorbent's surface area, the energy administered to the reactor (power), and the treatment time. Table 2 Results of the mercury adsorption study Adsorbent Final Hg(II) concentration (mg/L) % Removal Untreated SB 3.10 ± 0.48 57.95 ± 6.55 SB 80 W 2 min 3.19 ± 0.40 56.82 ± 5.38 SB 80 W 30 min 2.51 ± 0.45 65.90 ± 6.10 SB 80 W 60 min 2.71 ± 0.11 63.35 ± 1.55 SB 190 W 2 min 2.92 ± 0.36 60.40 ± 4.93 SB 190 W 30 min 2.59 ± 0.31 65.08 ± 4.17 SB 190 W 60 min 2.11 ± 0.19 71.47 ± 2.55 SB 300 W 2 min 2.99 ± 0.03 59.48 ± 0.42 SB 300 W 30 min 1.93 ± 0.06 73.90 ± 0.86 SB 300 W 60 min 1.21 ± 0.77 83.67 ± 1.04 For the adsorbents obtained through plasma treatment of 2 minutes (the shortest treatment time), the adsorption percentage results are either very close to the value obtained for untreated SB or lower. This effect can be explained by the initial interaction of the gas with the adsorbent during plasma production, possibly leading to the occlusion of pores with the fluorine and sulfur groups created in the plasma, preventing mercury from remaining on the adsorbent's surface (Kazak and Tor 2022 ). 3.3.1 Adsorption Kinetics Kinetic studies offer valuable insights into the adsorption rates of the adsorbent. The adsorption curves of the untreated and treated SB were fitted to Pseudo-first-order (PFO) and Pseudo-second-order (PSO) kinetic models. The fitting results are shown in Fig. 6 and Table 3 . In Fig. 6.A, the outcomes of mathematical modeling for untreated SB are showcased, revealing R 2 values of 0.98 for PFO and 0.99 for PSO. Similarly, Fig. 6.B depicts the graph for SB treated at 300 W for 60 minutes, displaying R 2 values of 0.97 for PFO and 0.98 for PSO. Table 3 Dynamic equation fitting parameters for adsorption kinetics Untreated SB PFO PSO Q e K 1 R 2 X 2 Q e K 2 R 2 X 2 4.27 ± 0.17 0.32 ± 0.045 0.98 0.080 4.72 ± 0.11 0.10 ± 0.010 0.99 0.020 SB 300 W 60 min PFO PSO Q e K 1 R 2 X 2 Q e K 2 R 2 X 2 6.13 ± 0.33 0.20 ± 0.032 0.97 0.21 6.97 ± 0.38 0.035 ± 0.0082 0.98 0.14 Table 3 - Dynamic equation fitting parameters for adsorption kinetics The reasonable fit of the mercury adsorption kinetics to the two models suggests that adsorption occurs through a combination of physical and chemical processes. Similar results were reported by Tang et al.(Tang et al. 2022 ) in a study of mercury adsorption with Sulphur biochar. The pseudo-first-order model describes physical adsorption based on a linear driving force of mass transfer at the liquid-solid interface (Bujdák 2020 ). Conversely, the pseudo-second-order model accounts for a limiting step associated with a chemical rate of valence forces interaction or electron transfer, rather than surface layer resistance forces (Gómez-Herrera 2021 ). It can be inferred that both the plasma's effect on the adsorbent's surface area and the incorporation of fluorine and sulfur functional groups played pivotal roles in the mercury ion adsorption process. Figure 6 - Kinetic Models of Hg(II) Adsorption in Aqueous Solutions by Plasma-Treated Adsorbent. A) Untreated SB; B) SB 300W 60min 3.3.2 Adsorption isotherms To analyze the adsorption behavior of the adsorbent SB 300 W 60 min and untreated SB for the removal of Hg(II) from aqueous solutions, the isothermal modeling was performed using the linearized forms of Langmuir and Freundlich models. Table 4 provides a detailed breakdown of the corresponding parameter values. Table 4 Dynamic equation fitting parameters for adsorption Isotherms. Sample Langmuir Freundlich qmax K L R 2 K f 1/n n R 2 Untreated 23.81 0.038 0.45 1.51 0,68 1.47 0.83 SB 300 W 60 min -163.93 0.0018 0.11 3.39 1,026 1.82 0.97 In the Langmuir model, a very low coefficient of regression for both adsorbents are observed, mainly for treated SB (R 2 = 0.11) indicating that this model does not adequately describe the adsorption phenomenon between the adsorbent and Hg. Therefore, the results for the adsorption capacity would not be valid. Freundlich model showed a better fit to the experimental data with an R 2 = 0.97 for modified SB and R 2 = 0.83 for unmodified SB, suggesting a non-uniform distribution of heterogeneous sites on the surface and a multi-layer adsorption process (Oumabady et al. 2022 ). K f values for the Freundlich isotherm are related to the capacity for Hg(II) adsorption on the adsorbent. In the results, K f demonstrated an increase from 1.51 mg/g to 3.39 mg/g when comparing untreated SB with treated SB. That value is higher than reported by (Bailon et al. 2022 ) for sulfur-impregnated biochar used to remove mercury from contaminated soils. The parameter n is 1.82, indicating a favorable adsorption since it falls within the range of 1 to 10. Moreover, values of n above 1 suggest a stronger adsorption force on the active sites of the adsorbent (Oumabady et al. 2022 ; Dermawan et al. 2022 ). Consequently, chemisorption predominates in this adsorption process, leading to the conclusion that the plasma treatment with fluoride enhances the adsorption capacity of mercury. 4. Conclusions The characterization results indicate that the low-temperature plasma effectively induces modifications in the adsorbents, preserving their main structure intact. SEM results indicated an augmentation in the porous structure as the treatment time increased. Additionally, EDS/MEV analysis demonstrated the incorporation of fluorine in all materials, whereas sulfur was only detected in certain samples. The carbon content increased with longer treatment times, whereas fluorine exhibited an inverse effect, potentially linked to the formation of HF. The highest removal efficiency for Hg was observed in SB treated with 300 W for 60 minutes, achieving a removal rate of 83.67%. The kinetic analysis provided valuable insights, revealing that the adsorption mechanism for SB treated at 300 W for 60 minutes exhibits both physical and chemical behaviors. Both first and second-order kinetic models demonstrated good fits to the data. However, the results of the adsorption isotherms displayed a superior fit with the Freundlich model, indicating that chemical adsorption predominated in this case and following plasma treatment. Consequently, the presence of active sites plays a crucial role in the effective removal of mercury. Based on the outcomes of this study, it can be concluded that the SF6 low-temperature plasma technique proves to be a successful method for enhancing the characteristics of SB. This, in turn, facilitates better adsorption of mercury ions from aqueous solutions, particularly when the pH is adjusted to 7. The results of this study show that low-temperature plasm technique can be used for modification of structure and physicochemical properties of the biomass opens a new perspective to produce new adsorbents useful in water treatment for inorganic contaminants removal. Declarations Ethical approval Ethical approval was not required due to this study did not involve human participants and/or animals. Consent to Participate Informed consent was obtained from all individuals who participated in the research. Consent to Publish All authors have given their consent for the publication of this article. Authors Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Angie Paola Santacruz Salas and Cláudia Hitomi Watanabe. The first draft of the manuscript was written by Angie Paola Santacruz Salas with support from Maria Lúcia Pereira Antunes. Maria Lúcia Pereira Antunes, Elidiane Cipriano Rangel and André Henrique Rosa helped supervise the project. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Funding This work was supported by A) Center for Basic and Interdisciplinary Applied Studies – CEIBA Foundation with the project Bécate Nariño (Colombia Agency), B) Program CAPES-PrInt process number 88887.310463/2018-00, C) International Cooperation Project number 88887.892017/2023-00 State of São Paulo Research Foundation - FAPESP (2022/00985-6), D) CNPq and Financier of Studies and Projects - FINEP 01.22.0290.00 (0080/21) (Brazilian Agencies). 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Journal of Alloys and Compounds 941:168998. https://doi.org/10.1016/j.jallcom.2023.168998 Supplementary Files SupplementarymaterialAppendix1.docx Cite Share Download PDF Status: Published Journal Publication published 26 Nov, 2024 Read the published version in Environmental Science and Pollution Research → Version 1 posted Editorial decision: Major Revision 02 Jul, 2024 Reviewers agreed at journal 20 May, 2024 Reviewers invited by journal 17 May, 2024 Editor invited by journal 22 Apr, 2024 Editor assigned by journal 28 Mar, 2024 First submitted to journal 26 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-4144021","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":303682790,"identity":"071dd675-b72c-4db4-b481-13a83124c258","order_by":0,"name":"Angie Paola Santacruz Salas","email":"","orcid":"","institution":"UNESP: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"Angie","middleName":"Paola Santacruz","lastName":"Salas","suffix":""},{"id":303682791,"identity":"f65bfa9a-82ef-4445-87f7-9afc57043bed","order_by":1,"name":"Maria Lucia Pereira Antunes","email":"","orcid":"","institution":"UNESP: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"Lucia Pereira","lastName":"Antunes","suffix":""},{"id":303682792,"identity":"c535491b-a3b8-45d9-98a5-d8c243290d33","order_by":2,"name":"Elidiane Cipriano Rangel","email":"","orcid":"","institution":"UNESP: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"Elidiane","middleName":"Cipriano","lastName":"Rangel","suffix":""},{"id":303682793,"identity":"bb485ee4-c491-4e5b-9002-679d582353e6","order_by":3,"name":"Cláudia Hitomi Watanabe","email":"","orcid":"","institution":"UNESP: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"Cláudia","middleName":"Hitomi","lastName":"Watanabe","suffix":""},{"id":303682794,"identity":"94ae5c93-599c-490c-a33f-3cb34977b2d7","order_by":4,"name":"André Henrique Rosa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYHACAyjNfABCSxCvhS2BZC08BsRp4Z/dvO3DB4Z7cvLtZ75JF1TU5TFI9z7Aq0XizrHimTMYio0NzuRuk55x5nAxg8xxA7xaGG7kGDPzMCQkbmAAauFtO5DYIJGGX4c8SMsfoJb5/W+eSfP+qyOsxQCkhQGopeFGDps0bwMzYS2GN9KKGXsMEowNbjwztuY5driYTeYYfi1yN5I3M/yoSJCT709+eJunpi6PX7oNvxao8xDMBDZiNKCABJJ1jIJRMApGwbAHAFjvP6WET3g4AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-2042-018X","institution":"Sao Paulo State University Julio de Mesquita Filho: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":true,"prefix":"","firstName":"André","middleName":"Henrique","lastName":"Rosa","suffix":""}],"badges":[],"createdAt":"2024-03-21 13:52:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4144021/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4144021/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11356-024-35585-9","type":"published","date":"2024-11-26T15:58:12+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57789956,"identity":"dfac6bf2-9f24-46dd-a40e-9bb1e78f6d7e","added_by":"auto","created_at":"2024-06-05 17:18:32","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1946255,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of the plasma treatment system\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/bb3106b88a11d23fc854c9cb.jpg"},{"id":57790801,"identity":"f1bc289c-eabf-458a-bd4b-0ad5ec47553e","added_by":"auto","created_at":"2024-06-05 17:26:32","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":100679,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron micrographs of the raw and of the plasma treated SB with different exposure times and excitation powers at ×500 and ×3000 magnifications. A) Untreated SB; B) SB 80 W 2 min; C) SB 190 W 2 min; D) SB 300 W 2 min; E) SB 80 W 30 min; F) SB 190 W 30 min; G) SB 190 W 60 min; G) SB 300 W 2 min; G) SB 300 W 30 min; G) SB 300 W 2 min.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/779c72ab0625ae3bde6ec023.jpg"},{"id":57791142,"identity":"6625762b-4ccf-4bf3-9c74-ca8188ad3878","added_by":"auto","created_at":"2024-06-05 17:34:32","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3444854,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the samples that showing the points where sulfur was detected. A) SB 80 W 2 min; B) SB 80 W 30 min\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/77ada73d65ab3159fac8521c.jpg"},{"id":57789957,"identity":"34c218e0-fae3-4807-96d1-662f0bc382d6","added_by":"auto","created_at":"2024-06-05 17:18:32","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":902402,"visible":true,"origin":"","legend":"\u003cp\u003epH\u003csub\u003epzc\u003c/sub\u003e of untreated SB and SB 300 W 2 min\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/acd0db421fe32bf7dca55e44.jpg"},{"id":57789960,"identity":"d350f96d-c3f8-4a6d-bbdb-072fe99911ce","added_by":"auto","created_at":"2024-06-05 17:18:32","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":106140,"visible":true,"origin":"","legend":"\u003cp\u003eConceptual model of the modification mechanism\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/6b0262256e08c2be2908e602.jpg"},{"id":57789961,"identity":"4b20dd24-c6cb-4961-b6de-75f08d39c183","added_by":"auto","created_at":"2024-06-05 17:18:32","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":147833,"visible":true,"origin":"","legend":"\u003cp\u003eKinetic Models of Hg(II) Adsorption in Aqueous Solutions by Plasma-Treated Adsorbent. A) Untreated SB; B) SB 300W 60min\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/6d1f4839af870070c70a8183.jpg"},{"id":70388854,"identity":"7f4a913e-a99a-47eb-9b4a-7856d4224303","added_by":"auto","created_at":"2024-12-02 17:27:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7404593,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/ef9af5a0-0eb8-4981-9eea-7552202893ff.pdf"},{"id":57789962,"identity":"9487ad88-6489-4631-96e2-b766220ec17d","added_by":"auto","created_at":"2024-06-05 17:18:32","extension":"docx","order_by":14,"title":"","display":"","copyAsset":false,"role":"supplement","size":415468,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementarymaterialAppendix1.docx","url":"https://assets-eu.researchsquare.com/files/rs-4144021/v1/a83166257d0f8ab1ecb5e971.docx"}],"financialInterests":"","formattedTitle":"Plasma-engineered sugarcane bagasse: A novel strategy for efficient mercury removal from aqueous solutions","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMercury (Hg) is a potentially harmful metal and one of the main chemical elements of concern to the World Health Organization (WHO). This persistent contaminant has the ability to bioaccumulate and biomagnify along the food chain. In addition, it has a high potential for neurotoxicity and teratogenicity, which may cause serious risks to human health and aquatic biota (Gyamfi et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; da Silva Montes et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Marrugo-Madrid et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eSeveral physical, chemical and biological methods have been used for the removal of Hg ions from aqueous solutions, such as the membrane separation, reverse osmosis, chemical precipitation, electrochemical oxidation, ion exchange, adsorption, among others (Singh et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, many of these treatments require elevated investments and operational costs, as well as, most often present low efficiency to comply with international regulations (Licona-Aguilar et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAdsorption has been recognized as a simpler, faster, effective, and economical technique compared to with other type of treatments (Shahabi Nejad and Sheibani \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Different types of materials can be used as adsorbents and agricultural residues, for example, are promising materials in this area due to their sustainable characteristics, low cost, high availability, adsorption capacity and possibility of easy regeneration (Sun et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSB is a large-scale residue produced by the sugar industry. This material is mainly composed of cellulose (40\u0026ndash;50%), hemicellulose (16\u0026ndash;33%) and lignin (15\u0026ndash;30%). It contains binding sites that are capable of capturing metal ions, making it a favorable low-cost adsorbent (Kulkarni et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Bai et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Nguyen et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Diverse literature has evaluated the potential of SB for the removal of metal ions in aqueous solutions (Harripersadth et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Ezeonuegbu et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kulkarni et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Bai et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Licona-Aguilar et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Many of these studies evaluated the modification of the raw biomass to improve its physicochemical properties and enhance its removal efficiency (Khan et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSeveral approaches are applied to adjust the surface physicochemical properties of this material. Even so, these methods generally have low modification efficiency, require longer treatment times, elevated temperatures, besides generating secondary residues (Zhang et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this scenario, plasma technology has been considered a potential tool for the modification of material properties. It is energy-efficient and environmentally friend once it does not generate appreciable waste or air emissions (Ribeiro \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Mohammed et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This technology involves the use of an ionized gas containing energetic and reactive species that interact strongly with the surfaces of the materials, creating new active sites to bind functional groups and modify the structure of the treated material (Zhang et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePlasma treatment is effective for surface functionalization, while maintaining the physical and chemical bulk properties of the material (Wang et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Hu et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For adsorbent materials, plasma treatments may improve the porous structure and increase the concentration of active functional groups on the surface, resulting in higher adsorption capacity for different types of contaminants (Zhang et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Hu et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBased on that, the hypothesis tested in the present work is if the incorporation of another electronegative element on the structure of the SB, such as fluorine, together with the structural erosion provoked by F plasma, would influence the physicochemical\u003c/p\u003e \u003cp\u003eproperties of SB and especially its adsorbing efficiency. There are no reports in the literature on the low-pressure sulfur hexafluoride (SF\u003csub\u003e6\u003c/sub\u003e) plasma treatments employed to incorporate active fluorine groups in agricultural residues like SB for adsorbing mercury from liquid effluents. Then, the objective of this study was to assess the modification of physicochemical structure of SB using plasma treatment and verify its influence in mercury adsorption capacity in aqueous solution.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation of biomass\u003c/h2\u003e \u003cp\u003eThe adsorbent was produced using SB obtained from the S\u0026atilde;o Paulo state region. The SB, Saccharum spp. species, underwent a series of preparation steps. Firstly, it was washed with running water to remove surface impurities. Afterward, the biomass was dried at 80\u0026deg;C in an oven with air circulation for 12 hours. Subsequently, the dried biomass was ground using a Willye-type knife mill (NL \u0026minus;\u0026thinsp;226\u0026ndash;02 - New Lab) with a fixed rotation speed of 1730 rpm. Finally, the ground material was sieved through a 35 mesh (0.50 mm opening) to achieve a standardized particle size.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Treatment of SB in Sulfur hexafluoride Plasma\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe adsorbent was modified in reactive low-pressure plasma, established in a stainless-steel reactor with a volume of approximately 5 L. The reactor, schematically represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, is equipped with two horizontal, circular, and parallel plate electrodes. A vacuum pump, connected to the lowermost reactor\u0026rsquo;s fringe, reduces the system\u0026rsquo;s pressure down to 1.3 Pa (2.0 x 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e Torr). The system pressure is measured using a Pirani manometer (Edwards APGX). Gases are introduced into the system through stainless steel and polymeric pipes, and the flow control is achieved using needle valves. The plasma excitation signal is supplied by a Tokyo Hy-Power RF-300 W (13.56 MHz model) radio frequency power supply, connected to the lower electrode via a Tokyo Hy-Power MB-300 impedance coupler.\u003c/p\u003e \u003cp\u003ePrior to the treatments, the samples were previously left in the oven at 120\u0026deg;C for 12 h to remove moisture from the environment. Subsequently, 3 g of the grounded SB was accommodated in a stainless-steel dish. The sample holder dish was positioned on the lowermost electrode of the reactor. The system was closed and pumped down to the base pressure of 3 Pa (2.25 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Torr). After pressure stabilization, the ultra-pure Sulfur Hexafluoride SF\u003csub\u003e6\u003c/sub\u003e gas (99.99%) was introduced to achieve a working pressure of 16 Pa (1.2 x 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e Torr). Plasma was then ignited by the application of radiofrequency signal to the lower electrode whereas grounding the upper one. It was investigated the effect of the plasma power (80, 190 and 300 W) for three different exposure times (2, 30 and 60 min). The samples were labeled according to a standard format of \"material, power and treatment time\", ex. \"SB 80 W 2 min\" means that SB was modified in 80 W plasma and of 2 min duration.\u003c/p\u003e \u003cp\u003eThe plasma conditions used here were mainly based on the study of (Resende et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Mohammed et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), with special attention on incorporating fluorine into an organic material and improving the physical characteristics of the adsorbent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Adsorbent characterization\u003c/h2\u003e \u003cp\u003eThe morphological structure and the porosity of the samples were assessed by Scanning Electron Microscopy (SEM) analysis, in the JEOL JSM-6010 Analytical SEM, equipped with a Dry SD Hyper X-ray detector (EX-94410T1L11) with resolution of 129 to 133 eV for the Mn Kα line at 3000 cp. The samples were initially affixed a stub utilizing double-sided carbon tape. In order to enhance the conductivity of the samples for SEM analysis, a thin conductive layer was applied via vacuum sputtering of the Au-Pd (gold-palladium) alloy. This process involved subjecting the samples to a current of 30 mA for 120 seconds using the Denton Vacuum Desk V apparatus. SEM micrographs were captured at magnifications of 500x, 1000x and 3500x, using an accelerating voltage of 10 kV, with a spot size of 30, which corresponds to a beam diameter of 10 mm.\u003c/p\u003e \u003cp\u003eThe semi-qualitative chemical composition of the samples was accessed using Energy Dispersive Spectroscopy (EDS). The detector attached to the microscope was utilized for EDS analysis, employing the same voltage and spot size as mentioned earlier. Selected areas at 1000x magnification were subjected to point and total chemical analysis. The elements studied in the research were: Carbon (C), Nitrogen (N), Oxygen (O), Silicon (Si), Potassium (K), Sulfur (S), Fluorine (F) and Mercury (Hg).\u003c/p\u003e \u003cp\u003eFurthermore, Fourier Transform Infrared Spectroscopy (FTIR) was employed to identify the functional groups present on the surface of the adsorbents. The FTIR analysis was conducted using the FTIR-410 Spectrometer with diffuse reflectance module. The samples were mixed with KBr at a ratio of 99% KBr to 1% sample. Each sample underwent 128 scans within the range of 4000 to 500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe zero point of charge (pHpzc) was determined according to the methodology described by (G\u0026oacute;mez-Herrera \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and it was conducted on the adsorbent that presented the best characteristics in the step 2.3 and 2.4. To achieve this, 1 L of 0.01 mol/L NaCl solution was prepared with ultrapure water. Then it was divided into 50 mL Erlenmeyer flaks and in each one the pH was adjusted with values between 2 and 12 (increasing every 2 units). The pH adjustments were carried out using 0.1 mol/L hydrochloric acid (HCl) and 0.1 mol/L sodium hydroxide (NaOH). Next, 100 mg of the adsorbent was added to each solution, and the mixture was stirred at a speed of 175 rpm for 24 hours at a temperature of 25\u0026deg;C. The final pH was measured with a Tecnal digital pH meter (Tec-2).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Mercury Adsorption Study\u003c/h2\u003e \u003cp\u003eTo compare the removal percent of mercury (Hg(II)) using the SB both with and without low-temperature plasma treatment obtained in this study, adsorption experiments were conducted under identical conditions. In each adsorption test, 25 mg of the respective adsorbent was suspended in 5 mL of a solution containing an initial concentration of 10 mg/L of Hg(II) at pH 7 and subjected to stirring at 175 rpm for 48 hours at a constant temperature of 25\u0026deg;C. The conditions mentioned earlier were carefully selected following a thorough initial literature review (Marins et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Peng et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Sun et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Subsequently, 2 mL of each sample was collected, and the final concentration was quantified using an inductively coupled plasma optical emission spectrometer (ICP-OES) (Agilent Technologies, model 720 series).\u003c/p\u003e \u003cp\u003eThe ICP-OES parameters employed in these analyses include an axial torch, concentric nebulizer, a radio frequency (RF) generator set at 40 MHz, RF power at 1.1 kW, refrigerant gas flow rate (Argon) maintained at 15.0 L/min, auxiliary gas flow at 1.5 L/min, and a nebulizer flow of 200 kPa.\u003c/p\u003e \u003cp\u003eThe adsorption capacity and the removal efficiency of the adsorbents was calculated following the equations mentioned by (Tursi et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) (See supplementary material for more details).\u003c/p\u003e \u003cp\u003eThis step was undertaken to identify the adsorbent that had superior mercury removal percentage. The investigation of adsorption kinetics and isotherms was exclusively conducted on the adsorbent that exhibited the most favorable adsorption.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1 Adsorption Kinetics\u003c/h2\u003e \u003cp\u003eTo generate the adsorption kinetics curve, 125 mg of adsorbent were placed in contact with 100 mL solution with an initial concentration of 10 mg/L Hg(II). Aliquots of 2 ml were taken at specific contact times of 0, 0.5, 1.5, 3, 6, 9, 24 and 48 hours.\u003c/p\u003e \u003cp\u003ePseudo-first-order (PFO) and pseudo-second-order (PSO) theoretical models were used to describe the mechanisms of Hg(II) adsorption on the adsorbent that showed the best results in the preliminary test (More details in the supplementary material).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 Adsorption isotherms\u003c/h2\u003e \u003cp\u003eAdsorption isotherm experiments were conducted with initial Hg(II) concentrations ranging from 5 to 40 mg/L. The equilibrium period was set at 48 hours, and the dosages used were 1.25 g/L, 2.5 g/L, and 5 g/L. The resulting isotherms underwent analysis based on the Langmuir (Langmuir \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1918\u003c/span\u003e) and Freundlich (Freundlich \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1906\u003c/span\u003e) models (More details in the supplementary material).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Characterization of the adsorbents\u003c/h2\u003e\n \u003cp\u003eThe micrographs acquired from Scanning Electron Microscopy (SEM), presented in Fig.\u0026nbsp;2, show the surface morphology of the untreated (A) and of the plasma treated SB (B - J).\u003c/p\u003e\n \u003cp\u003eFigure 2 - Scanning electron micrographs of the raw and of the plasma treated SB with different exposure times and excitation powers at \u0026times;500 and \u0026times;3000 magnifications. A) Untreated SB; B) SB 80 W 2 min; C) SB 190 W 2 min; D) SB 300 W 2 min; E) SB 80 W 30 min; F) SB 190 W 30 min; G) SB 190 W 60 min; G) SB 300 W 2 min; G) SB 300 W 30 min; G) SB 300 W 2 min.\u003c/p\u003e\n \u003cp\u003eIn Fig. 2.A, the micrograph reveals a fibrous and heterogeneous structure with few pores or with small pores that are not perceptible with the employed magnifications. Particulate material, rising from deteriorated regions of the fibers, is present in some surface regions, together with cracks. The structural complexity of the natural material is responsible for this heterogeneity and it was also reported by (Veiga et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Liu et al. \u003cspan class=\"CitationRef\"\u003e2022a\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eUpon the plasma treatment, morphological changes were detected with the modification degree being dependent on the plasma power and on the exposure time. The particulate and agglomerate content is reduced, indicating removal of the weakly connected material by the plasma. A clear improvement on the short-range surface smoothness is observed when comparing the higher magnification micrographs. Except for the fastest treatment (2 min), conducted at the lowest power (80 W), cracks are no longer evident after the treatment. However, a higher number of pores was identified, suggesting material removal is being favored from specific points of the biomass. Aside to this, there is rupture of the original continuous structure into large flakes of material, evidenced by the analysis of the inset (lower magnification of x500) micrographs. It is detected a general trend of increasing the flakes production with increasing the treatment intensity (time and/or power). According to Liu, Zhou, and Liu (Liu et al. \u003cspan class=\"CitationRef\"\u003e2022b\u003c/span\u003e), the power elevation in helium plasmas could enhance the surface roughness due to the corrosive effect of plasma, resulting in a more irregular morphology. In the present work, two trends in opposition were detected as one considers the surface morphology of the treated samples: a reduction of the surface defects in the low-range scale and an elevation in a larger-range one.\u003c/p\u003e\n \u003cp\u003eThus, according to the above results plasma is removing material from the surface by chemical and physical reactions. In plasmas of SF\u003csub\u003e6\u003c/sub\u003e, it is observed the generation of SF\u003csub\u003e5\u003c/sub\u003e, SF\u003csub\u003e4\u003c/sub\u003e, SF\u003csub\u003e3\u003c/sub\u003e, SF\u003csub\u003e2\u003c/sub\u003e, SF, S, and F reactive groups (Resnik et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e). The increment in the exposure time thus elevates the probability of material removal by some of the erosive species.\u003c/p\u003e\n \u003cp\u003eAnother phenomenon explaining the same effect, but with other consequences, is the removal of material by physical routes, that is, by ion bombardment. The collision of fast ions with the material surface transfer energy that can cause emission of groups together with structural and chemical modifications. For low energy ions, dissipation of energy occurs by means of nuclear collisions, that provide displacement of atoms from their position in the structure and thus its weakening and breakage. On the other hand, for more energetic ions energy dissipation by electronic events (excitations, ionizations, free radical generations) is favored, producing active dangling bonds that may recombine by C bonds unsaturation and chain crosslinking.\u003c/p\u003e\n \u003cp\u003eConsequently, to understand the results obtained here it should be taken into account that fast ions will lose their energies primarily in electronic collision, producing crosslinkings and unsaturations, processes that improve the surface uniformity. When their energies are reduced, with increasing the penetration depth, nuclear events will be the main responsible for slowing down the ions, producing breakage of the SB polymeric backbones. With increasing treatment time and power this damage process is intensified flaking the overall SB structure. Thus, ion bombardment can contribute to the improvement of the surface uniformity due to dissipation of energy by electronic collision and to the structural rupture by deposition of energy from nuclear events. Moreover, ion bombardment favors the non-homogeneous removal of material. In the work of Man (Man et al. \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e), it was demonstrated that etching of SiO\u003csub\u003e2\u003c/sub\u003e coated with an CH\u003csub\u003ex\u003c/sub\u003eF layer, in SF\u003csub\u003e6\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e plasmas, is regulated, amongst others, by ion bombardment. The sputtering of groups from the CH\u003csub\u003ex\u003c/sub\u003eF top layer generates defect points where the reaction of neutral F can promptly erode the whole structure beneath, creating pores in the initially uniform layer. Thus, the observed pores in the treated SB investigated here (micrographs) are attributed to the simultaneous physical (sputtering) and chemical (etching) effect of the SF\u003csub\u003e6\u003c/sub\u003e plasmas as demonstrated in the work (Man et al. \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eTherefore, all the modifications observed on the surface microstructure of the SB submitted to the plasma treatments, including pore formation, flaking and smoothening of the SB structure can be attributed to the physical and chemical effect of ion bombardment and to the etching caused by neutrals generated in SF\u003csub\u003e6\u003c/sub\u003e plasmas.\u003c/p\u003e\n \u003cp\u003eThe EDS results of the untreated and of the plasma treated SB samples are presented in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The main elements observed on the surfaces of the untreated SB were carbon, oxygen and nitrogen, in good agreement with the results of (Rocha et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e) in which was evaluated the composition of the bagasse from 60 varieties of sugarcane produced in Brazil. Aside to these elements, the treated samples also presented fluorine and, in some cases, sulfur.\u003c/p\u003e\n \u003cp\u003eThe untreated material is majorly composed of C with lower proportions of O and N. Hydrogen is also a component of the SB, but it is not detected by this methodology. According to Seah and collaborators (Seah et al.\u0026nbsp;\u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e) the structure of different woody and herbaceous biomasses is constituted by 6% of H. After the plasma treatment there is detection of small proportions of F in all the samples and of S (\u0026le; 0.2%) only in the samples treated in the mild conditions (80 W, 2 and 30 min). Changes in the proportion of the other elements are also identified, but three major trends should be discussed here.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSemi-quantitative analysis results of atomic proportions of C, N, O, Si, K, F and S on the untreated and plasma treated SB.\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\u003eC (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eN (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eO (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eK (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS (%)\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\u003eSB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.2\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\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 80 W 2 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 80 W 30 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\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\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 80 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86.1\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=\"char\"\u003e\n \u003cp\u003e10.0\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\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 190 W 2 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\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\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 190 W 30 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e87.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 190 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e87.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\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\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 2 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\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\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 30 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e91.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\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 \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eThe first one is related with the C content reduction for the treatments with the lowest power (80 W), for 2 and 30 min, and with the highest power (300 W) for 2 min. The concomitant falls in the C and in the O proportions for the samples treated in plasmas of 80 W (2 and 30 min) are followed by compensatory rise in the N proportion. On the other hand, for the highest power treatments (300 W, 2 min), despite the reduction in the C proportion is similar to that observed in the previous discussed samples, that of O is not. Only an oscillation in the O proportion is detected in this case, indicating now N is replacing only C. So, different changing mechanisms are taking place in the low and high-power regime. A reduction in the carbon proportion rice husk derived hybrid silica/carbon biochar was also reported by (Mohammed et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e) and is very consistent with the erosive nature of electronegative SF\u003csub\u003e6\u003c/sub\u003e plasmas.\u003c/p\u003e\n \u003cp\u003eThe second trend observed in the Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e is the elevation of the C proportion beyond that observed for the untreated SB, for the highest power and exposure time treatments (300 W, 30 and 60 min). Proportion of O is only barely influenced in this case. However, N is no longer incorporated. The inclusion of N, as well as O, is proposed to happen, majorly, from reactions of active dangling bonds, left on the material structure after treatment, with atmospheric groups when the sample is removed of the vacuum chamber. The absence of N indicates that the trapped radical content decreases for treatments in plasmas of 300 W (30 and 60 min). Pendant bonds, generated from H and N abstraction, are being consumed by chain crosslinking and by unsaturation of chemical bonds. Just N realize it enough to explains the elevation in the C proportion, but O is also being abstracted in some of these treatments.\u003c/p\u003e\n \u003cp\u003eThe third aspect observed is related to the proportion of fluorine. Despite some oscillation, a general trend of decreasing F incorporation with increasing plasma excitation power and exposure time is detected. Fluorine inclusion occurs at low proportions (\u0026lt;\u0026thinsp;1.2%), showing that fluorination is not favored in the treatments conducted here.\u003c/p\u003e\n \u003cp\u003ePossible neutral species produced in pure low pressure SF\u003csub\u003e6\u003c/sub\u003e plasmas are SF\u003csub\u003e6,\u003c/sub\u003e SF\u003csub\u003e5,\u003c/sub\u003e SF\u003csub\u003e4,\u003c/sub\u003e SF\u003csub\u003e3,\u003c/sub\u003e SF\u003csub\u003e2,\u003c/sub\u003e SF, S, F and F\u003csub\u003e2\u003c/sub\u003e. Positive (SF\u003csub\u003e5\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e S\u003csup\u003e+\u003c/sup\u003e and F\u003csup\u003e+\u003c/sup\u003e) and negative (SF\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, SF\u003csub\u003e5\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e F\u003csup\u003e\u0026minus;\u003c/sup\u003e and F\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) ions may also be formed from the SF\u003csub\u003e6\u003c/sub\u003e precursor. Nevertheless, the dissociation behavior and thus the concentration of radicals and ions depend on the electronic density and temperature, which, in turn, rely on the pressure and applied power. It was demonstrated in the work developed by Levko and co-workers (Levko et al. \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e), on the evaluation of the neutral and ionized species distribution on SF\u003csub\u003e6\u003c/sub\u003e plasmas, using the one-dimensional fluid model, that an elevation in the plasma power provides an overall increment in density of electrons, positive and negative ions in the plasma. In all cases, the most abundant neutral fragment is SF\u003csub\u003e5\u003c/sub\u003e, followed by F and by SF\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e\u0026ndash;\u003c/sup\u003e SF\u003csub\u003e3\u003c/sub\u003e. The highest densities of SF\u003csub\u003e5\u003c/sub\u003e and F groups is explained by their formation route, due to direct electron impact, to be the most probable one by the reaction (Resnik et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e)\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$${SF}_{z}+ {e}^{-}\\to {SF}_{z-1}+F+{e}^{-}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eIn the same work, it was shown that the most abundant charged species are SF\u003csub\u003e5\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e followed by F\u003csup\u003e\u0026minus;\u003c/sup\u003e, SF\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e. Negligible densities of SF\u003csub\u003e2\u003c/sub\u003e and SF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e were observe. Using a radiofrequency (13.56 MHz, 10 mTorr, 900\u0026ndash;1700 W) capacitively coupled SF\u003csub\u003e6\u003c/sub\u003e plasma, Lallement and co-authors (Lallement et al. \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e) observed similar results concerning the most probable neutral and charged species as well as a trend of rise in the electron density with increasing plasma power, but a constancy in the electron temperature. Besides that, Amorim et al., (Amorim et al. \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e) stated that in low-pressure plasma, high electron temperatures generate an increase in fluoride concentration. This, combined with elevates electronegativity of SF\u003csub\u003e6,\u003c/sub\u003e leads to the generation of negative ions, by reactions such as:\u003c/p\u003e\n \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$${SF}_{6}+ {e}^{-}\\to {SF}_{6}^{-}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThus, plasma is composed of negative and positive ionized groups from SF\u003csub\u003e6\u003c/sub\u003e and also from O (reactor residual atmosphere), together with electrons. According to the previous discussion, an elevation in the concentration of ions and electrons is expected in SF\u003csub\u003e6\u003c/sub\u003e plasma with increasing the excitation power. But it is important to mention here that negative ions will be attracted to the grounded upper electrode of the reactor and repelled of the negatively biased sample holder (lowermost electrode). This can be pointed as one of the reasons why there was a low fluorine incorporation on the SB structure. Only neutral F species, orders of magnitude more abundant than ions, that can diffuse to the region where the SB was accommodated, are prone to react with the organic structure to be incorporated by means of CF\u003csub\u003ex\u003c/sub\u003e groups. In the first stage of this reaction, F has to recombine with C or H from the SB, generating volatile groups, with low sticking probabilities that are emitted, explaining material removal and dangling bonds formation on the material structure (Resende et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Mohammed et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e\n \u003cp\u003eThis is another reason for the low F incorporation, that is, F is effectively acting as an eroding compound rather than a doping element. Fluorine inclusion would happen after the etching step. Ion bombardment of the bagasse with positive SF\u003csub\u003e6\u003c/sub\u003e fragments (SF\u003csub\u003e5\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003eSF\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e SF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) may also contribute to F incorporation, but still more with the atomic and molecular release and then with free-radical generation. The latter processes would enhance chain crosslinkings and bond unsaturation, explaining the low incorporation of atmospheric groups (N, O) observed in some samples as well as the reduction on the surface defects.\u003c/p\u003e\n \u003cp\u003eThe energy deposited in the material structure by ion bombardment tends to increase with the rise in the power and in the exposure time. The probability of neutral reactive radicals reaching the sample surface also increases with exposure time.\u003c/p\u003e\n \u003cp\u003eTherefore, the low proportions of F detected in the samples studied here indicate that dangling bonds\u0026rsquo; saturation by F is not an efficient process. The variation in the atomic proportions of O and N, together with that of F indicates the saturation of free radical is taking place during plasma treatment but also after it, when the sample is in contact with atmosphere. Furthermore, F should be concentrated on the topmost layers of the fibers, whereas EDS analysis is probing deeper untreated regions, promoting a mixed result of the treated and untreated regions.\u003c/p\u003e\n \u003cp\u003eFinally, sulfur was detected only in the samples prepared in plasmas of low power (80 W) for low (2 min) and moderate (30 min) exposure times. Figure\u0026nbsp;3 highlights the points where sulfur was detected. Figure\u0026nbsp;3. A and Fig.\u0026nbsp;3. B correspond of the material treated in plasmas of 80 W for 2 and 30 minutes, respectively. Interestingly, higher power levels (190 and 300 W) and longer exposure times (60 min) did not contribute to S incorporation. The optimization of the structural healing (crosslinking and unsaturation) in these conditions are pointed as the responsible for the lack of S and the low proportion of F detected in these cases.\u003c/p\u003e\n \u003cp\u003eWith such results it is promptly observed that the highest F and S incorporation occurred for the lowest power plasma and for the lower exposure time (2 min). The proportion of C was the lowest in this sample while the N proportion was the highest indicating C and O are being replaced mainly by N. This inference is confirmed by the results of the sample prepared at the highest plasma power and exposure time where N was not detected and C proportion was the highest one. Based on that it is proposed that the plasma treatment is removing not only H, but also C and O (Si and K) from the biomass structure, generating active sites for atmospheric N and O incorporation, crosslinking, bonds unsaturation and F incorporation.\u003c/p\u003e\n \u003cp\u003eThe analysis of FTIR spectra of the of the as-received and the modified SB under various time intervals and pressures (Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e, see material supplementary) shows the presence of aliphatic CH\u003csub\u003e2\u003c/sub\u003e groups of the lignin is evident by the bands at 2865 and 2918 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Manyatshe et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). Contributions due to OH stretching vibrations are detected at 3450\u0026ndash;3650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Abdulhameed et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Bai et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). C oxidized groups are identified by the contributions at 1740 (C\u0026thinsp;=\u0026thinsp;O) (Ordonez-Loza et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e) and 670 (C-OH in cellulose) cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Peaks characteristics of lignin, normally found in 1616, 1586, 1508, (aromatic C\u0026thinsp;=\u0026thinsp;C) and 1234 (aromatic C-O) (Montero et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e; Veiga et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Dzoujo et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). The bands observed at 1740 and 1368, cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to the stretching of the COO- and CH\u0026thinsp;=\u0026thinsp;CH respectively. Those bands are related to hemicellulose and lignin compounds (Veiga et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e; Sutthasupa et al. \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e). The bands around 1120 and 1149 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are typical cellulose and hemicellulose peaks due to C-O and C-N stretching (Montero et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIt is a consensus in the literature (Luz et al. \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e), that SB is composed of different proportions of cellulose (C₆H₁₀O₅)\u003csub\u003en\u003c/sub\u003e, hemicellulose (C\u003csub\u003e5\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e) and lignin (C\u003csub\u003e81\u003c/sub\u003eH\u003csub\u003e92\u003c/sub\u003eO\u003csub\u003e28\u003c/sub\u003e), together with mineral contaminants. The organic fraction of this material is composed of structures formed by aromatic carbon rings to which hydroxyls, methyl, methylene and others components are attached (Rocha et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e; ALVES MACEDO 2020). Comparing the spectra of the as-received and of the plasma-treated SB reveals a general preservation of the material\u0026rsquo;s chemical structure. However, it should be considered that whereas the plasma treatment is changing the topmost layers of the material, the infrared inspection is reaching untreated deep layers. But even so, some modifications in the infrared spectra of the samples are indicatives of the plasma induced changes. New bands are detected at 2100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026equiv;C) and 1114 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C-O), the latter spectral band mainly appears in the sample spectrum subjected to a longer duration and higher power treatment.\u003c/p\u003e\n \u003cp\u003eAlso, in the Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e.A and 4.B is observed a peak in 1900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which is related to stretching C\u0026thinsp;=\u0026thinsp;C\u0026thinsp;=\u0026thinsp;C (Merck \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). Aside to this, the treatment results in alterations in the intensities of several bands, including OH at 3580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, CH\u003csub\u003e2\u003c/sub\u003e at 2918 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, C\u0026thinsp;=\u0026thinsp;O at 1745 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and C\u0026thinsp;=\u0026thinsp;C at 1586 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Specifically, unsaturation of C bonds, proposed in the interpretations of elemental composition of the samples, is then corroborated by the rise of C\u0026equiv;C (2100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) band and by the growth of C\u0026thinsp;=\u0026thinsp;C one (1586 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e\n \u003cp\u003eThe peak ascribed to O-H stretching vibrations (3450\u0026ndash;3650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) exhibits heightened prominence in materials primarily treated with lower power. However, when the treatment power increases, its intensity decreases, probably because the plasma has a similar effect to heat treatment, that may lead to the release of part of the structural water contained in the plant material (Dzoujo et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe intensity of the band at 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (aromatic C\u0026thinsp;=\u0026thinsp;O), is significantly increased after plasma treatment, particularly when using power levels of 80 and 190 W. This effect may be due to the conversion of C-OH groups into C\u0026thinsp;=\u0026thinsp;O due to H abstraction (F or ion bombardment). The transformation of C-OH groups into C\u0026thinsp;=\u0026thinsp;O also corroborates the idea of dangling bond consumption by unsaturation of bonds.\u003c/p\u003e\n \u003cp\u003eAfter exposure to fluorine plasma, new peaks appeared in the range of 900 to 1300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which may be related to CF\u003csub\u003ex\u003c/sub\u003e groups (CF, CF\u003csub\u003e2\u003c/sub\u003e, and CF\u003csub\u003e3\u003c/sub\u003e) (Agopian et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e; Zhou et al. \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e). The peaks observed at 700\u0026thinsp;\u0026minus;\u0026thinsp;600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to the alkyl halides of CF (Mohammed et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). The rise of small bands around 1330 (CF\u003csub\u003e2\u003c/sub\u003e) and 600\u0026ndash;700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (CF) in the spectra of treated samples suggest F incorporation in low proportions, what is in good accordance with the compositional results obtained by EDS.\u003c/p\u003e\n \u003cp\u003eIn the spectra appears a peak in 1150 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which can be attributed to the S\u0026thinsp;=\u0026thinsp;O symmetrical stretching of the sulfonate (Pavia et al. \u003cspan class=\"CitationRef\"\u003e2008\u003c/span\u003e).This result, combined with that of Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, confirms the presence of sulfur incorporation, especially in the SB samples with a power of 80 W.\u003c/p\u003e\n \u003cp\u003eFluorine neutrals and charged species are majorly eroding and ion bombarding the material structure. It is also confirmed that dangling bonds generated by etching and sputtering are being consumed by unsaturation of C bonds and possibly by the counterpart process of crosslinking.\u003c/p\u003e\n \u003cp\u003eThe determination of the zero-charge pH (pH\u003csub\u003epzc\u003c/sub\u003e) plays a pivotal role in comprehending the electrostatic interaction dynamics between the adsorbate and the adsorbent. It is imperative for the charges on the adsorbent to be opposite those of the adsorbate, fostering a more robust interaction between the two entities, as emphasized by Alves Macedo (ALVES MACEDO 2020). In Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the pH\u003csub\u003epzc\u003c/sub\u003e graph is presented for both untreated SB and SB treated at 300W for 60 minutes. The point of intersection on the curve with the x-axis signifies an equilibrium between negative and positive charges on the adsorbate\u0026apos;s surface.\u003c/p\u003e\n \u003cp\u003eUpon analysis, it is observed that the pHpzc of SB 300W 60 min is approximately 4.8. In contrast, the untreated SB exhibits a slightly higher difference pH\u003csub\u003epzc\u003c/sub\u003e value, reaching 5.2. This suggests that the plasma treatment has not significantly altered the pH\u003csub\u003epzc\u003c/sub\u003e. In conclusion, the surface of the adsorbent becomes positively charged at a pH\u0026thinsp;\u0026lt;\u0026thinsp;4.8 and negatively charged at a pH\u0026thinsp;\u0026gt;\u0026thinsp;4.8.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Mechanism of modification\u003c/h2\u003e\n \u003cp\u003eBased on the above characterization results, the modification mechanisms can be inferred. Initially, during the treatment process, SF\u003csub\u003e6\u003c/sub\u003e is decomposed by the plasma, resulting in the formation of various ions, including SF\u003csub\u003e5\u003c/sub\u003e, SF\u003csub\u003e4\u003c/sub\u003e, SF\u003csub\u003e3\u003c/sub\u003e, SF\u003csub\u003e2\u003c/sub\u003e, SF, S, and F, however, since the radio frequency signal is connected to the lower electrode, the predominant interaction with the material will involve positive ions, specifically SF₃\u003csup\u003e+\u003c/sup\u003e, SF₅\u003csup\u003e+\u003c/sup\u003e, SF₂\u003csup\u003e+\u003c/sup\u003e, SF\u003csup\u003e+\u003c/sup\u003e, F\u003csup\u003e+\u003c/sup\u003e and S₂F\u003csup\u003e+\u003c/sup\u003e. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e presents a conceptual model detailing the possible interactions between SF\u003csub\u003e6\u003c/sub\u003e ions and SB: (I) F, generated in the plasma, initiates an attack process on H, leading to the production of HF and the generation of free radicals within the structure. (II) Similarly, F generated in the plasma, attacks and binds to the structure, forming stable C-F bonds. (III) Various F species bind to carbon, leading to the generation of volatile CF4, accompanied by a reduction in the carbon content within the structure. This phenomenon is more evident in treatments performed with lower power and shorter time. (IV) S, generated in the plasma, binds to O within the structure, causing the incorporation of SO into the material. In addition, sulfur binds to N and O, forming volatile groups such as SN and SOF\u003csub\u003ex\u003c/sub\u003e, resulting in a decrease in the amount of O together with N. This phenomenon is clearly observed in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e in the treatments performed with higher power and longer time.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Mercury adsorption studies\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e presents the results of the adsorption study of Hg(II) in aqueous solution conducted on both modified and unmodified adsorbents with plasma. Notably, all materials demonstrated an impressive removal percentage exceeding 50%. This remarkable performance can be attributed to the utilization of SB, a globally abundant bio-waste known for its high percentage of cellulose and lignin, surpassing that of other conventional agricultural wastes. Furthermore, SB boasts excellent chemical properties, including moisture content (4.4\u0026ndash;8.7% by weight), ash content (0.90\u0026ndash;9.6% by weight), volatile material (69.8\u0026ndash;81.0% by weight), and carbon content (39.8\u0026ndash;47.3% by weight) (Raj et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). These properties play a crucial role in facilitating an effective adsorption process.\u003c/p\u003e\n \u003cp\u003eA significant effect was observed in the samples treated with plasma, where, as the power and treatment time increase, the adsorption capacity also rises. Particularly noteworthy is the SB treated for 60 minutes with a power of 300 W, which exhibited 25.72% more mercury removal compared to untreated SB. According to a study published by Kang et al. (Kang et al. \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e), there is a direct relationship between the adsorbent\u0026apos;s surface area, the energy administered to the reactor (power), and the treatment time.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eResults of the mercury adsorption study\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAdsorbent\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFinal Hg(II) concentration (mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e% Removal\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\u003eUntreated SB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e57.95\u0026thinsp;\u0026plusmn;\u0026thinsp;6.55\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 80 W 2 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.82\u0026thinsp;\u0026plusmn;\u0026thinsp;5.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 80 W 30 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e65.90\u0026thinsp;\u0026plusmn;\u0026thinsp;6.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 80 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e63.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.55\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 190 W 2 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60.40\u0026thinsp;\u0026plusmn;\u0026thinsp;4.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 190 W 30 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e65.08\u0026thinsp;\u0026plusmn;\u0026thinsp;4.17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 190 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.47\u0026thinsp;\u0026plusmn;\u0026thinsp;2.55\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 2 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 30 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e73.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.04\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\u003eFor the adsorbents obtained through plasma treatment of 2 minutes (the shortest treatment time), the adsorption percentage results are either very close to the value obtained for untreated SB or lower. This effect can be explained by the initial interaction of the gas with the adsorbent during plasma production, possibly leading to the occlusion of pores with the fluorine and sulfur groups created in the plasma, preventing mercury from remaining on the adsorbent\u0026apos;s surface (Kazak and Tor \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.1 Adsorption Kinetics\u003c/h2\u003e\n \u003cp\u003eKinetic studies offer valuable insights into the adsorption rates of the adsorbent. The adsorption curves of the untreated and treated SB were fitted to Pseudo-first-order (PFO) and Pseudo-second-order (PSO) kinetic models. The fitting results are shown in Fig. 6 and Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. In Fig.\u0026nbsp;6.A, the outcomes of mathematical modeling for untreated SB are showcased, revealing R\u003csup\u003e2\u003c/sup\u003e values of 0.98 for PFO and 0.99 for PSO. Similarly, Fig. 6.B depicts the graph for SB treated at 300 W for 60 minutes, displaying R\u003csup\u003e2\u003c/sup\u003e values of 0.97 for PFO and 0.98 for PSO.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDynamic equation fitting parameters for adsorption kinetics\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eUntreated SB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003ePFO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003ePSO\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\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 \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eX\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\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\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 \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eX\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\u003e4.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.045\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.080\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.020\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eSB 300 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003e\u003cstrong\u003ePFO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003e\u003cstrong\u003ePSO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\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 \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eX\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\u003eQ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ee\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\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 \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eX\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\u003e6.13 \u0026plusmn;\u003c/p\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.035\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0082\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.14\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\u003eTable \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e - Dynamic equation fitting parameters for adsorption kinetics\u003c/p\u003e\n \u003cp\u003eThe reasonable fit of the mercury adsorption kinetics to the two models suggests that adsorption occurs through a combination of physical and chemical processes. Similar results were reported by Tang et al.(Tang et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) in a study of mercury adsorption with Sulphur biochar.\u003c/p\u003e\n \u003cp\u003eThe pseudo-first-order model describes physical adsorption based on a linear driving force of mass transfer at the liquid-solid interface (Bujd\u0026aacute;k \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e). Conversely, the pseudo-second-order model accounts for a limiting step associated with a chemical rate of valence forces interaction or electron transfer, rather than surface layer resistance forces (G\u0026oacute;mez-Herrera \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). It can be inferred that both the plasma\u0026apos;s effect on the adsorbent\u0026apos;s surface area and the incorporation of fluorine and sulfur functional groups played pivotal roles in the mercury ion adsorption process.\u003c/p\u003e\n \u003cp\u003eFigure 6 - Kinetic Models of Hg(II) Adsorption in Aqueous Solutions by Plasma-Treated Adsorbent. A) Untreated SB; B) SB 300W 60min\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.2 Adsorption isotherms\u003c/h2\u003e\n \u003cp\u003eTo analyze the adsorption behavior of the adsorbent SB 300 W 60 min and untreated SB for the removal of Hg(II) from aqueous solutions, the isothermal modeling was performed using the linearized forms of Langmuir and Freundlich models. Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e provides a detailed breakdown of the corresponding parameter values.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDynamic equation fitting parameters for adsorption Isotherms.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eLangmuir\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eFreundlich\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eqmax\u003c/strong\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eK\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eL\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth 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/th\u003e\n \u003cth 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/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e1/n\u003c/strong\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth 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/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUntreated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.038\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSB 300 W 60 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-163.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0018\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,026\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.97\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 the Langmuir model, a very low coefficient of regression for both adsorbents are observed, mainly for treated SB (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.11) indicating that this model does not adequately describe the adsorption phenomenon between the adsorbent and Hg. Therefore, the results for the adsorption capacity would not be valid.\u003c/p\u003e\n \u003cp\u003eFreundlich model showed a better fit to the experimental data with an R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.97 for modified SB and R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.83 for unmodified SB, suggesting a non-uniform distribution of heterogeneous sites on the surface and a multi-layer adsorption process (Oumabady et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). K\u003csub\u003ef\u003c/sub\u003e values for the Freundlich isotherm are related to the capacity for Hg(II) adsorption on the adsorbent. In the results, K\u003csub\u003ef\u003c/sub\u003e demonstrated an increase from 1.51 mg/g to 3.39 mg/g when comparing untreated SB with treated SB. That value is higher than reported by (Bailon et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) for sulfur-impregnated biochar used to remove mercury from contaminated soils. The parameter n is 1.82, indicating a favorable adsorption since it falls within the range of 1 to 10. Moreover, values of n above 1 suggest a stronger adsorption force on the active sites of the adsorbent (Oumabady et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e; Dermawan et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). Consequently, chemisorption predominates in this adsorption process, leading to the conclusion that the plasma treatment with fluoride enhances the adsorption capacity of mercury.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe characterization results indicate that the low-temperature plasma effectively induces modifications in the adsorbents, preserving their main structure intact. SEM results indicated an augmentation in the porous structure as the treatment time increased. Additionally, EDS/MEV analysis demonstrated the incorporation of fluorine in all materials, whereas sulfur was only detected in certain samples. The carbon content increased with longer treatment times, whereas fluorine exhibited an inverse effect, potentially linked to the formation of HF.\u003c/p\u003e \u003cp\u003eThe highest removal efficiency for Hg was observed in SB treated with 300 W for 60 minutes, achieving a removal rate of 83.67%. The kinetic analysis provided valuable insights, revealing that the adsorption mechanism for SB treated at 300 W for 60 minutes exhibits both physical and chemical behaviors. Both first and second-order kinetic models demonstrated good fits to the data. However, the results of the adsorption isotherms displayed a superior fit with the Freundlich model, indicating that chemical adsorption predominated in this case and following plasma treatment. Consequently, the presence of active sites plays a crucial role in the effective removal of mercury.\u003c/p\u003e \u003cp\u003eBased on the outcomes of this study, it can be concluded that the SF6 low-temperature plasma technique proves to be a successful method for enhancing the characteristics of SB. This, in turn, facilitates better adsorption of mercury ions from aqueous solutions, particularly when the pH is adjusted to 7.\u003c/p\u003e \u003cp\u003eThe results of this study show that low-temperature plasm technique can be used for modification of structure and physicochemical properties of the biomass opens a new perspective to produce new adsorbents useful in water treatment for inorganic contaminants removal.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eEthical approval\u0026nbsp;\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eEthical approval was not required due to this study did not involve human participants and/or animals.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eConsent to Participate \u0026nbsp;\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eInformed consent was obtained from all individuals who participated in the research.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eConsent to Publish\u0026nbsp;\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have given their consent for the publication of this article.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eAuthors Contributions\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Angie Paola Santacruz Salas and Cl\u0026aacute;udia Hitomi Watanabe. The first draft of the manuscript was written by Angie Paola Santacruz Salas with support from Maria L\u0026uacute;cia Pereira Antunes. Maria L\u0026uacute;cia Pereira Antunes, Elidiane Cipriano Rangel and Andr\u0026eacute; Henrique Rosa helped supervise the project. \u0026nbsp; All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by A) Center for Basic and Interdisciplinary Applied Studies \u0026ndash; CEIBA Foundation with the project B\u0026eacute;cate Nari\u0026ntilde;o (Colombia Agency), B) Program CAPES-PrInt process number 88887.310463/2018-00, C) International Cooperation Project number 88887.892017/2023-00 State of S\u0026atilde;o Paulo Research Foundation - FAPESP (2022/00985-6), D) CNPq and Financier of Studies and Projects - FINEP 01.22.0290.00 (0080/21) (Brazilian Agencies).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAuthor 1 has received research support from Company A, author 4 has received research support from Company B and author 5 has received research support from Company C and D.\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbdulhameed AS, Firdaus Hum NNM, Rangabhashiyam S, Jawad AH, Wilson LD, Yaseen ZM, Al-Kahtani AA, ALOthman ZA (2021) Statistical modeling and mechanistic pathway for methylene blue dye removal by high surface area and mesoporous grass-based activated carbon using K2CO3 activator. 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Journal of Alloys and Compounds 941:168998. https://doi.org/10.1016/j.jallcom.2023.168998\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Sugarcane bagasse, adsorption, plasma treatment, mercury, water treatment","lastPublishedDoi":"10.21203/rs.3.rs-4144021/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4144021/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMetal ion adsorption using agro-industrial residues has shown promising results in remediating contaminated waters. However, adsorbent effectiveness relies on their properties, often necessitating processing for modification. Considering this, plasma treatment is effective in modifying material surfaces physically and chemically. This study investigated the modification of sugarcane bagasse (SB) using plasma-treated and evaluated its efficacy as a novel adsorbent for mercury removal from aqueous solutions. SB underwent low-temperature plasma treatment with sulfur hexafluoride (SF6) as the working gas, varying treatment times (2, 30, and 60 minutes) and fixed powers (80, 190, and 300 W) at 16 Pa pressure. Characterization via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS/SEM), Fourier transform infrared spectroscopy (FTIR) and zero point of charge (pHpzc) revealed significant structural changes like increased in porosity and alteration in proportion atomic. Additionally, the successful incorporation of fluorine was confirmed in all treatment conditions, while sulfur was detected in only some samples. Amongst the tested conditions, the SB treated with 300 W for 60 minutes demonstrated the highest mercury removal efficiency, achieving an impressive 83.67% removal rate compared to untreated SB, which yielded only 57.95%. The adsorption mechanism exhibited both physical and chemical behavior, with chemisorption being the dominant process. The Freundlich model provided the best fit to the experimental data, with an R\u003csup\u003e2\u003c/sup\u003e value of 0.97. In conclusion, plasma treatment can be a promising alternative for improving the physical and chemical characteristics of SB adsorbents, thereby improving their efficiency in removing mercury from aqueous solutions.\u003c/p\u003e","manuscriptTitle":"Plasma-engineered sugarcane bagasse: A novel strategy for efficient mercury removal from aqueous solutions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-05 17:18:27","doi":"10.21203/rs.3.rs-4144021/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2024-07-03T03:44:44+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-05-20T12:33:18+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-17T12:31:05+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2024-04-22T17:12:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-28T05:56:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2024-03-26T14:56:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1af602ab-cbf7-47c8-a925-9235bd0555f1","owner":[],"postedDate":"June 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-02T17:22:06+00:00","versionOfRecord":{"articleIdentity":"rs-4144021","link":"https://doi.org/10.1007/s11356-024-35585-9","journal":{"identity":"environmental-science-and-pollution-research","isVorOnly":false,"title":"Environmental Science and Pollution Research"},"publishedOn":"2024-11-26 15:58:12","publishedOnDateReadable":"November 26th, 2024"},"versionCreatedAt":"2024-06-05 17:18:27","video":"","vorDoi":"10.1007/s11356-024-35585-9","vorDoiUrl":"https://doi.org/10.1007/s11356-024-35585-9","workflowStages":[]},"version":"v1","identity":"rs-4144021","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4144021","identity":"rs-4144021","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}