Langmuir Isotherm Model Research Articles

Efficient adsorption of fluorescein dye from aqueous solutions by Al/Th-MOF bimetal-organic frameworks: Adsorption isotherm, kinetics, DFT computation, and optimization via Box-Behnken design

Bimetal-organic frameworks, or MOFs, have sparked a lot of interest in the wastewater treatment industry. This study investigated the possibility of removing fluorescein dye (FS) employing bimetal-organic frameworks based on aluminum and thorium (Al/Th-MOF) from aqueous solutions. To investigate the properties of the material further, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, surface charge analysis, and X-ray diffraction (XRD) were used. Using these methods, we were able to identify the Al/Th-MOF's point of zero charge. Following adsorption, the adsorbent's large surface area of 2273.8 m2/g and pore volume of 1.4 cm3/g drop to 1678.9 m2/g and 0.96 cm3/g, individually. As this suggests, it is ideal that a portion of the FS was absorbed within the pores of the adsorbent. Through batch testing, it looked into the connection between adsorption equilibrium and pH levels, and found that changes in solution pH significantly affected adsorption behavior. Further studies with kinetic models led to the discovery of the pseudo-second-order model for FS adsorption on Al/Th-MOF. Furthermore, the Langmuir isotherm model accurately describes the adsorption process, suggesting that chemisorption played a major role in the process as a whole. To optimize factors such adsorbent dosage, time, solution pH, the response surface methodology (RSM) and Box-Behnken design (BBD) were used. As a consequence (ΔH°), (ΔS°), and (ΔG°) data the adsorption of FS employing Al/Th-MOF as an adsorbent is endothermic and spontaneous. Our study's studies have demonstrated that the Al/Th-MOF adsorbent combines a number of mechanisms, such as π-π interaction, H-bonding, pore filling, and electrostatic contact, to effectively remove FS dye from water-based solutions. The adsorption capacity of FS onto Al/Th-MOF reaches a maximum of 668.6 mg.g−1 at a pH value of 4, demonstrating that the adsorbent is particularly successful in removing FS from wastewater samples. Furthermore, the synthesized Al/Th-MOF adsorbent possesses outstanding render ability and cyclability for a maximum of eight adsorption-desorption cycles, suggesting that it could find application as an adsorbent in industrial environments. Overall, our research suggests that the adsorbent is a potential and novel approach for managing industrial effluent and water filtering.

KINETIC, ISOTHERM AND THERMODYNAMIC STUDIES OF THE ADSORPTION OF CRESOL RED DYE USING AGRICULTURAL WASTES

Agricultural wastes and plant biomass are alternative low-cost adsorbents because they can be used without or with a minimum processing. In the present study, batch experiments were carried out to study the adsorption of cresol red (CR) unto mango leaf (ML) and orange peel (OP). Several parameters that affect adsorption process such as pH, adsorbent dosage, contact time, initial dye concentration and temperature were investigated. FTIR and SEM were used to determine the functional group responsible for adsorption. The results revealed that the highest adsorption efficiency was at pH 5 for the two adsorbents. It was also discovered that CR removal efficiency increased with the increase in contact time and adsorbent dosage while adsorption capacity was higher with increase in initial dye concentration but removal efficiency was lowered. The kinetics conform with the pseudofirst-order kinetic model for mango leaf but conform with the pseudo-second-order kinetic for orange mesocarp due to the value of the correlation coefficient (R2). Based on the value of correlation coefficient, the experimental results for the removal by mango leaf best fitted the Langmuir isotherm model with monolayer adsorption capacity of 70.64 mg. g-1, while Freundlich isotherm model was best fitted to the experimental results for the adsorption of CR by Orange peel. The thermodynamic results revealed that the process is spontaneous and endothermic.

Dynamic intercalation of methylene blue in BC-MgFe-HT composite: Unveiling adsorption mechanisms for efficient wastewater treatment

Developing efficient and eco-friendly adsorbents for removing dye from wastewater presents a significant challenge. In this study, by combining MgFe-hydrotalcite (MgFe-HT) with bamboo charcoal (BC) we report the synthesis of a composite material named BC-MgFe-HT to achieve rapid and effective adsorption of methylene blue (MB) dye. The novelty of our work lies in the distinctive intercalation arrangement of the MB dye post-adsorption within the BC-MgFe-HT layers, which was quantitatively measured and found to be at an intercalation angle of approximately 44.26° rather than the conventional vertical positioning. This unique phenomenon indicates a dynamic rearrangement of the composite structure upon MB adsorption, significantly enhancing its adsorption capacity and efficiency. Comprehensive characterization of the BC-MgFe-HT composite was performed using the following techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area analysis, and thermogravimetric analysis (TGA). The adsorption studies demonstrated a maximum adsorption capacity of 194.09 mg/g within 20 min, attributed to the composite's high surface area, porous architecture, and dye intercalation capacity. Kinetic studies revealed that the pseudo-second-order (PSO) kinetics model best describes the adsorption process, while the Langmuir isotherm model provided the most accurate fit for the adsorption equilibrium data. These findings offer novel insights into the adsorption mechanisms of MB onto the BC-MgFe-HT composite, highlighting its potential for the design and optimization of composite materials for effective wastewater remediation.

The application of Rumex Abysinicus derived activated carbon/bentonite clay/graphene oxide/iron oxide nanocomposite for removal of chromium from aqueous solution

Rapid industrialization has significantly boosted economic growth but has also introduced severe environmental challenges, particularly in water pollution. This study evaluates the effectiveness of a nanocomposite composed of Rumex Abyssinicus Activated Carbon/Acid Activated Bentonite Clay/Graphene Oxide, and Iron Oxide (RAAC/AABC/GO/Fe3O4) for chromium removal from aqueous solutions. The preparation of the nanocomposite involved precise methods, and its characterization was performed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area analysis, and the point of zero charge (pHpzc). Batch adsorption experiments were designed using Design Expert software with a central composite design under response surface methodology. The factors investigated included pH (3, 6, and 9), initial Cr (VI) concentration (40, 70, and 100 mg/L), adsorbent dose (0.5, 0.75, 1 g/200 mL), and contact time (60, 90, and 120 min). Adsorption isotherms were analyzed using nonlinearized Langmuir, Freundlich, and Temkin models, while pseudo-first-order and pseudo-second-order models were applied to adsorption kinetics. Characterization revealed a pHpzc of 8.25, a porous and heterogeneous surface (SEM), diverse functional groups (FTIR), an amorphous structure (XRD), and a significant surface area of 1201.23 m2/g (BET). The highest removal efficiency of 99.91% was achieved at pH 6, with an initial Cr (VI) concentration of 70 mg/L, a 90 min contact time, and an adsorbent dose of 1 g/200 mL. Optimization of the adsorption process identified optimal parameters as pH 5.84, initial Cr (VI) concentration of 88.94 mg/L, contact time of 60 min, and adsorbent dose of 0.52 g/200 mL. The Langmuir isotherm model, with an R2 value of 0.92836, best described the adsorption process, indicating a monolayer adsorption mechanism. The pseudo-second-order kinetics model provided the best fit with an R2 value of 0.988. Overall, the nanocomposite demonstrates significant potential as a cost-effective and environmentally friendly solution for chromium removal from wastewater.

Removal of metaldehyde pesticide from aquatic media using modified cellulose obtained from Populus nigra plant, as potential adsorbent

Abstract In this study modified cellulose based adsorbent was prepared from Populus nigra plant, and used for elimination of metaldehyde (herbicide) from model waste water. The adsorbent was characterized through analytical technique such as FTIR, SEM, EDX and XRD for structural adsorption related parameters. The results of SEM showed the suitability of the material to be used as adsorbent and FTIR showed successful crosslinking of polyvinyl alcohol into cellulose structure. In order to get maximum reclamation benefits from adsorbent it was subjected to a number of tests evaluating the effect of metaldehyde concentration, sorbent dose, contact time, initial pH of solution and temperature. The maximum removal of 70 % was achieved under conditions of 80 mg/L metaldehyde concentration, 60 min contact time, pH of 8, 0.08 g sorbent dosage, and room temperature (25 °C). The Langmuir isotherm model with correlation coefficients of 0.9855 and maximum adsorption capacity recorded was 8.32 mg/g, while excellent agreement was shown by kinetic data with pseudo second order kinetic model with R 2 = 0.9876. Thermodynamic study indicated enthalpy change (ΔH° = −129 kJ/mol) to be negative, entropy change (ΔS° = 161.7 j/mol) positive, and the Gibbs free energy (ΔG) as negative showing that the process to be exothermic and feasible/spontaneous with an increase of randomness at solid liquid interface. The finding indicated that modified cellulose could be used as an efficient adsorbent for removal of metaldehyde from model waste water. However, further validation with other pollutants will be helpful in checking reproducibility of the present findings.

Properties of Biochar Prepared by Solar Pyrolysis and Its Adsorption of Cu<sup>2+</sup> in Water

This study investigates the potential of biochar produced via a solar pyrolysis system and its effectiveness in removing copper (Cu<sup>2+</sup>) ions from water, presenting a sustainable and energy-efficient method for biochar production and biomass recycling. Two common agricultural and livestock wastes, corn straw and cow dung, were used as raw materials to produce biochar. These materials underwent solar pyrolysis under limited oxygen conditions to produce biochar, which was then compared to biochar produced via traditional pyrolysis. The comparison involved elemental analyses, infrared spectroscopy, scanning electron microscopy, and specific surface area and pore size analysis to highlight differences in their physical and chemical properties. Adsorption experiments were conducted to evaluate the adsorptive capacity of biochar for copper ions (Cu<sup>2+</sup>) from water, determining the optimal pH conditions and underlying adsorption mechanisms. The findings reveal that biochar produced through solar pyrolysis exhibits similar properties and Cu<sup>2+</sup> adsorption capacities to those prepared by traditional methods. Specifically, cow dung biochar demonstrated a higher adsorption capacity for Cu<sup>2+</sup> compared to corn straw biochar. The Cu<sup>2+</sup> adsorption by corn straw biochar followed the Langmuir isothermal adsorption model and pseudo-second-order kinetic equation, whereas cow dung biochar conformed to the Freundlich isothermal adsorption model and pseudo-second-order kinetic equation. By demonstrating the comparable efficacy of solar pyrolysis biochar in heavy metal adsorption, this study highlights its potential for sustainable environmental remediation and biomass utilization.

Removal of copper and cobalt ions from aqueous solutions using starch‐xanthate based novel smart hydrogel via adsorption technique: Swelling, adsorption isotherm, and kinetic study

AbstractThe concentration of harmful metal ions is growing globally, which raises the risk to both human and ecological health. The use of “adsorption” technique has been found to be very effective, for the removal of toxic metal ions. Among other things, hydrogels as an adsorbent work effectively for the removal of toxic metal ions and other aquatic pollutants. The newly designed potato starch‐xanthate (SX) based hydrogel (SX‐modified hydrogel) has been synthesized using a mixture of acrylamide (AAm) and acrylic acid (AA) monomers, with the help of free‐radical graft copolymerization technique. The synthesized SX‐modified hydrogel has been characterized by several analytical techniques, namely, UV–visible (UV–vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric (TG) analysis, point of zero charge (ΔpHPZC) analysis, x‐ray diffraction (XRD) analysis, and scanning electron microscope (SEM) analysis. The main objective of the current work is to remove the Cu2+ and Co2+ ions from wastewater using SX‐modified hydrogel as well as to study the swelling and water retention properties of the SX‐modified hydrogel. The swelling ratio of SX‐modified hydrogel has been found to be 312.31, 374.01, and 410.20 g/g at optimum pH 10, temperature 35°C, time 675 min in gray wastewater, tap water, and distilled water, respectively. The maximum percentage removal of Cu2+ and Co2+ ions by SX‐modified hydrogel has been found as 97.7% and 94.2%, respectively, at optimum conditions. The Langmuir isotherm model fits best with the experimental data, with maximum adsorption capacity of 515.46 mg/g for Cu2+ and 483.09 mg/g for Co2+ ions, respectively. The kinetic studies suggest that the adsorption process is governed by the second order kinetic model with rate constant of 2.06 × 10−4 g/(mg min) for Cu2+ and 1.79 × 10−4 g/(mg min) for Co2+ ions, respectively. The negative ΔG values suggest the adsorption process is spontaneous in nature. In addition, the positive ΔH values support the adsorption process is endothermic in nature. The SX‐modified hydrogel showed a remarkable desorption efficiency with 96.7% for Cu2+ and 92.5% for Co2+ ions and reusability for four consecutive adsorption–desorption cycles. It can be concluded that the SX‐modified hydrogel has showed an effective, economical, easy, low energy consuming, and significant potential in the treatment of wastewater containing heavy metal ions.

PH Sensitive Dual Cross‐Linked Anionic and Amphoteric Interpenetrating Network Hydrogels for Adsorptive Removal of Anionic and Cationic Dyes

AbstractThe contamination of water by organic dye compounds are worldwide environmental problem due to their highly toxic nature. To address this environmental issue, a simple technique with highly efficient dye removal was developed to prepare pH‐ sensitive dual‐crosslinked anionic and amphoteric interpenetrating network (IPN) hydrogels based on Na‐carboxymethyl cellulose (Na‐CMC) using jute stick‐based cellulose. Crosslinked Na‐CMC and crosslinked κ‐carrageenan (KC) were interlaced by H‐bonding in anionic IPN hydrogel (An‐gel), but crosslinked Na‐CMC and crosslinked Chitosan (CS) were interlaced by electrostatic interaction in amphoteric IPN hydrogel (Am‐gel). In various operating conditions (pH, temperature, etc.) An‐gel displayed a higher number of swelling ratios of about 2560% at pH 7.2 and Am‐gel of about 1874% at pH 5.5. Based on the point of zero charge, An‐gel achieved the maximum removal efficiency of 81.62 % for methylene blue (MB) at pH 7.2, whereas Am‐gel achieved 85.38% removal efficiency for eosin yellow (EY) at pH 5.5. The adsorption kinetics of IPN hydrogels followed a pseudo‐second order model and best fitted by Langmuir isotherm model. The removal efficiency of MB and EY decreased slightly with increasing temperature. The values of ΔH°, ΔG°, and ΔS° indicated an exothermic, spontaneous, and disordered adsorption process.

Enhanced methylene blue adsorption using single-walled carbon nanotubes/chitosan-graft-gelatin nanocomposite hydrogels

In the present study, single-walled carbon nanotubes (SWCNTs) incorporating chitosan-graft-gelatin (CS-g-GEL/SWCNTs) hydrogels were fabricated with multiple advantages, including cost-effectiveness, high efficiency, biodegradability, and ease of separation for methylene blue (MB) dye from aqueous solution. To verify the successful formulation of the prepared hydrogels, various characterization methods such as NMR, FTIR, XRD, FE-SEM, TGA, BET, and EDX were employed. The removal efficiency of CS-g-GEL/SWCNTs nanocomposite hydrogel increased significantly to 98.87% when the SWCNTs percentage was increased to 20%. The highest adsorption was observed for pH = 9, an adsorbent dose = 1.5 g L−1, a temperature = 25 °C, a contact time = 60 min, and a contaminant concentration = 20 mg L−1. Based on the thermodynamic results, spontaneous adsorption occurred from a negative Gibbs free energy (ΔG°). In addition, the thermodynamic analysis of the adsorption process revealed an average enthalpy of − 21.869 kJ mol−1 for the adsorption process at a temperature range of 25–45 °C, which indicates its spontaneous and exothermic behavior. The Langmuir isotherm model was successfully used to describe the equilibrium behavior of adsorption. The pseudo-first-order model better described adsorption kinetics compared to the pseudo-second-order, intra-particle, and Elovich models. CS-g-GEL/SWCNTs hydrogels have improved reusability for five consecutive cycles, suggesting that they may be effective for removing anionic dyes from aquatic environments.

Adsorption of diclofenac by a novel H2SO4-CTAB co-modified granular spent bleaching earth carbon: Preparation, performance and mechanism

Diclofenac (DCF), a widely used pharmaceutical ingredient, exhibits long-lasting properties and significant ecotoxicity in aquatic ecosystems. In this study, a new granular adsorbent, GSBE@CH-CTAB, was synthesized to remove DCF by initially granulating powder spent bleaching earth carbon (SBE@C) with polytetrafluoroethylene (PTFE) emulsion as a binding agent, followed by a co-modification process involving H2SO4 and cetyltrimethyl ammonium bromide (CTAB). The adsorption capacity of the prepared adsorbent for DCF under the best conditions was 4.26 mg/g. In a wide pH range, GSBE@CH-CTAB could maintain a high adsorption capacity and show a good reusability. The presence of the three cations inhibited the adsorption of DCF (inhibition effect: Mg2+>Al3+>Na+). The adsorption process conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. From the theoretical evaluation results, it could be inferred that DCF molecules were adsorbed on GSBE@CH-CTAB surface in both horizontal and non-horizontal directions at all operating temperatures. The main mechanisms of adsorption included electrostatic interaction, pore filling interaction, π-π interaction and H bond interaction. The granular adsorbent GSBE@CH-CTAB prepared in this study could effectively remove DCF, treat waste with waste, and solve the problem that powder adsorbent was easy to lose and difficult to recover, which was of great significance for the remediation of polluted water.

Sorption behavior of strontium ions by graphene oxide decorated with chitosan nanoparticles from aqueous solutions

This study provides and investigates the fabrication of graphene oxide (GO) sheets decorated with chitosan nanoparticles (CSNP) through the hybridizing of GO and CS, by the addition of tetraethyl orthosilicate (TEOS) as a cross-linker agent. The fabricated GO-CSNP composite was characterized using several advanced techniques. Furthermore, various parameters affect the sorption of Sr(II), such as contact time, pH, initial concentration, dosage, temperature, and coexisting ions. The experimental results were in accordance with the pseudo-second-order reaction. The interaction mechanism between Sr(II) and GO-CSNP composite was accurately described by the Langmuir isotherm model with a maximum adsorption capacity of 473.93 mg/g. The GO-CSNP composite demonstrated exceptional selectivity for the sorption of Sr(II) over Y(III) at a high concentration ratio of 10:1 for Sr2+ to Y3+, respectively. Furthermore, the GO-CSNP adsorbent demonstrated considerable potential as a highly effective sorbent for the adsorption of Sr(II), Mo(VI), Cd(II), and Cs(I) ions. The results revealed that the prepared composite was effectively capable of removing various fission products.

Constructing molecular sieve-based MOFs nanofiber composites for separating Co(II) from wastewater

In addressing the crucial need for separating cobalt ions from leachate solutions of spent ternary lithium batteries (TLBs), this study focuses on the development of an innovative molecular sieve (MS)-based MOFs material, MS-MIL-53(Al), synthesized by combining MS with 2,5-dihydroxyterephthalic acid. Since the powdered MS-MIL-53(Al) material presents a granular powdery form, which is difficult to recover during the adsorption process, electrospun nanofibers denoted as MS-MIL-53(Al)/PAN, were fabricated and functionalized with hydroxylamine hydrochloride to create MS-MIL-53(Al)/AOPAN. Static adsorption experiments conducted with MS-MIL-53(AL)/AOPAN as the adsorbent in cobalt-containing wastewater revealed a maximum adsorption content of 65.3 mg/g for Co(II). Moreover, the material exhibited a tensile strength at the breaking point of 0.077 kPa, indicating its excellent mechanical properties. The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm model, showcasing a spontaneous, endothermic monolayer chemical adsorption behavior. XPS analysis highlighted the influence of hydroxy and amidoxime functional groups on Co(II) adsorption. Notably, MS-MIL-53(Al)/AOPAN displayed exceptional stability, retaining over 90 % of its adsorption capacity after five cycles, demonstrating its potential for efficient Co(II) separation in wastewater treatment. This study is the first to synthesize MOFs material using MS as the base material, showing potential cost reduction and enhanced adsorption capabilities, with implications for advancing the innovative use of MOFs.

Removal of nitrate ion from aqueous solution using palmyrah nut shell activated carbon: factorial optimization and equilibrium studies

Nitrate, a prevalent contaminant in drinking water due to its high solubility, poses health risks when consumed excessively. This study employed citric acid-activated carbon (CAC) derived from palmyrah to remove nitrate from drinking water. The physicochemical properties of non-activated carbon (NAC) and CAC were analyzed using SEM and FT-IR to identify microstructure and functional groups. Batch adsorption experiments with a full factorial design evaluated nitrate adsorption onto CAC, considering dosage, contact time, and solution pH. The activation treatment significantly enhanced adsorption efficacy compared to NAC. Optimal conditions were obtained statistically at pH 2, 60 min, and 1.5 g/L of adsorbent. These conditions were applied in groundwater from agricultural areas in Jaffna, Sri Lanka and significantly confirmed the removal efficiency of nitrate which was found to be 92% at pH 2 and adsorbent dosage of 6 g/L. The Freundlich isotherm model was best fit compared to Langmuir, Temkin and Dubinin-Radushkevich isothermal models. Accordingly, the most fitted kinetic model was pseudo-second-order and thermodynamic study revealed that the adsorption process was spontaneous and exothermic for nitrate removal. Overall, citric acid-modified palmyrah nutshell-derived activated carbon is an effective adsorbent for nitrate removal.

Synthesis of Fe3O4@SiO2–branched polyethylenimine nanospheres for removal of Cr(VI) and anionic dyes

There is a need to design and prepare new sorbents for the effective elimination of toxic metal ions and textile dyes from the environment. In the presented study, the preparation of magnetic functionalized silica composite nanospheres for the removal of inorganic and organic pollutants from aqueous solutions is reported. Firstly, the surface of silica coated magnetic nanospheres was functionalized with epoxy groups via a reaction of 3-glycidoxypropyltriethoxysilane. Then, the branched polyethylenimine (BPEI) was attached to generate positive functional charged groups on the on the Fe3O4@SiO2. The performance of the Fe3O4@SiO2-BPEI nanospheres for the removal of Cr(VI) and Congo Red (CR) and Trypan Blue (TB) dyes was studied under various experimental conditions. The optimum pHs values for adsorption of Cr(VI) ions, CR and TB dyes on the Fe3O4@SiO2-BPEI nanospheres were found to be at pH 2.0, and at pH 4.0, respectively. The maximum adsorption capacities of the Fe3O4-@SiO2-BPEI nanospheres for Cr(VI), CR, and TB were obtained as 356.7, 395.3, and 561.8 mg/g within 90 min equilibrium time, an initial concentration of 500 mg/L, and at 25 ºC, respectively. The adsorption of the tested pollutants were well described by the Langmuir isotherm model and second-order kinetic model. After ten reuse cycles, the adsorption capacity of Fe3O4-@SiO2-BPEI nanospheres was not significantly changed for the tested pollutants. The adsorption mechanism of Cr(VI), CR, and TB by the Fe3O4-@SiO2-BPEI nanospheres was evaluated to be related to ion exchange and ion exchange and/or hydrogen bonding interactions, respectively. The results also suggested that the presented adsorbent may serve as a multi-functional adsorbent for the remediation of industrial effluents. In addition, compared to the unmodified Fe3O4@SiO2, the Fe3O4@SiO2-BPEI nanospheres have antibacterial activities against Escherichia coli (American Type Culture Collection (ATCC) 12435), Pseudomonas aeruginosa (ATCC 10145), Listeria monocytogenes (ATCC 7644), and Staphylococcus aureus (ATCC 43300). Based on the obtained results from this work, the branched polyethylene functionalized magnetic silica nanospheres with antibacterial properties can be used as a potential adsorbent for the removal of metal ions and anionic dyes from wastewater.

Facile synthesis of poly(tannic acid-1,4-butanediamine) microsphere based on the “self-assembly to polymerization” mechanism and its fast removal feature toward Cr(VI) ions

To remediate toxic Cr(VI) ions in wastewater is a daunting environmental challenge nowadays, thus advanced adsorbents are developed and used to overcome the low removal rate of existing technologies. Herein, poly(tannic acid-1,4-butanediamine) (PTBA) microspheres were synthesized for the purpose of fast removal of Cr(VI) from the aqueous phase. The synthesis was based on the “self-assembly to polymerization” mechanism. The microstructures and chemical characteristics of the fresh and used adsorbents PTBA were characterized systematically by means of TEM, SEM, FT-IR, XPS, TGA and XRD. Effects of pH, contact time, Cr(VI) initial concentration, PTBA dosage, temperature, and the presence of foreign ions on the removal of Cr(VI) had been investigated sequentially. The results indicated that almost 100% of removal efficiency could be achieved in short time intervals, based on the initial concentration of Cr(VI). The spontaneous and endothermic adsorption behavior could be well described by the pseudo-2nd-order (P2O) and Langmuir isotherm models. Finally, the process of partial reduction of Cr(VI) to non-toxic Cr(III) during the adsorption process was explained. Overall, the refined PTBA adsorbent presents a satisfactory behavior to ameliorate the Cr(VI)-pollution elimination means.

Amphoteric chitosan derivatives for the removal of basic and reactive dyes from aqueous solutions

The present study describes the use of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide and 2-acrylamido-2-methyl-1-propanesulfonic acid as grafting agents to chitosan (CS) natural polymer were examined. Two chitosan derivatives were synthesized in this study, and then added in single-component aqueous solutions in order to study the removal of Methylene Blue (MB) and Remazol Brilliant Blue R (RBBR) dyes, by adsorption, in a more innovative way. The characterization of the chitosan derivatives was achieved via X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Adsorption efficiency of the chitosan derivatives was tested at several pH values (2–12) and for adsorbent’s dosage between 10 and 50 mg per 30 mL effluent. The rising of temperature from 25 to 65 °C led to increased adsorption capacity. Equilibrium data were fitted to both the more common Langmuir and Freundlich isotherm models, as well as the Sips isotherm model. Pseudo 1st and 2nd kinetic order equations and a relatively simple phenomenological kinetic model for adsorption kinetics, were studied as well as the thermodynamic parameters were calculated. The adsorption capacity for CS grafted with [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (CS-SBMA) was 238.1 and 244.5 mg/g for MB and RBBR removal, respectively, at 25 °C, while for CS grafted with 2-acrylamido-2-methyl-1-propanesulfonic acid (CS-AMPS) the adsorption capacity was 219.5 and 203.9 mg/g for MB and RBBR removal, respectively, at 25 °C.

Prospective application of eco-friendly banana peel reduced graphene oxide (BRGO) for aqueous Cr (VI) and acid dye adsorption: A waste utilization approach

Banana peels are an environmentally benign alternative to toxic reducing agents. Banana peel-reduced graphene oxide (BRGO) showed high performance in the adsorption of metal and dye ions. Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a Zeta potential analyzer were used to characterize the BRGO. Different influencing factors such as pH, dose, concentration, duration, and temperature, were studied to evaluate the efficiency of the adsorbent. The Langmuir and Freundlich isotherm models were fitted for Cr (VI) and acid dye adsorption. The maximum adsorption capacity (qm) of BRGO for Cr (VI) and AV54 dye were 135.87 and 110.74 mg/g, respectively. The pseudo-second-order kinetic model was better suited for Cr (VI) and AV54 dye adsorption, which indicated chemical adsorption. Thermodynamically, the adsorption exhibited spontaneity and was endothermic. Regeneration and reuse of adsorbents were also studied for potential use in treating tannery effluent.

Effectively removal of PPCPs by catalytic activated biochar derived from hazelnut shell: Modeled and predicted by machine learning

As a new type of environmentally friendly adsorbent, biochar has been increasingly applied in water pollution treatment. Herein, a catalyzed and activated biochar adsorbent (CABC) which was derived from hazelnut shell and modified by FeCl3 and ZnCl2 was synthesized successfully. The CABC was applied to remove two typical Pharmaceutical and Personal Products (PPCPs), sulfamethoxazole (SMX) and diclofenac (DCF). The CABC obtained high specific surface area of 1413.02 m2/g. The removal rates for SMX and DCF by CABC could reach 97.04 % and 98.65 %, respectively. The adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir isothermal model, which illustrated that the adsorption process conformed to chemical adsorption and monolayer adsorption. The thermodynamics indicated that the adsorption process was endothermic and could occur spontaneously. After 5 cycles, the CABC still remained a high removal efficiency of 77.7 % and 80.5 % for SMX and DCF, which showed a good reusability. The removal rates of CABC for multiple PPCPs had achieved over 77.7–98.0 %. In different actual wastewater, the removal rates of CABC for SMX and DCF ranged from 56.7 % to 97 %, demonstrating its excellent universality and practical value for utilization. Furthermore, three machine learning models based on Decision Tree, Random Forest and Gradient Boosting Decision Tree algorithm were applied to predict the removal efficiency and determine the relative importance of different influencing factors. The gradient boosting regressor model obtained the best predict performance with R2 at 0.9806 and 0.9840 for training set and testing set. And the importance analysis had shown that pH was the most important influencing factor with the importance value over 0.35. The adsorption mechanism between CABC and pollutants included pore adsorption, electrostatic interactions, intramolecular hydrogen bonding, the reaction with oxygen-containing functional groups and metal complexation. The prepared biochar adsorbent CABC possessed the potential for PPCPs removing. In addition, the machine learning method can play more and more undeniable role in subsequent water treatment. In future research, machine learning can be used to predict the adsorption performance of materials, enabling targeted design of materials. This will greatly save experimental time and cost losses, and can improve research efficiency.

Sustainable heavy metal (Cr(VI) ion) remediation: Ternary blend approach with chitosan, carboxymethyl cellulose, and bioactive glass

Heavy metal pollution poses a significant environmental challenge to worldwide, especially in developing countries. This study focuses on eliminating the heavy metal chromium (VI) ion from wastewater, employing an eco-friendly and economical ternary blend composed of Chitosan (CS), Carboxymethyl cellulose (CMC), and bioactive glass (BAG). The innovative bioactive glass is crafted from biosilica extracted from biowaste of cow dung ash, calcium oxide from eggshell ash, and phosphorus pentoxide. The CS/CMC/BAG blend is prepared via sol-gel method and characterized using XRD, FT-IR, TGA, BET, TEM and SEM revealing a porous structural morphology during blending. Batch adsorption studies explore various parameters such as pH, adsorbent dose, contact time and initial metal ion concentrations. The results are then evaluated through adsorption kinetics and adsorption isotherms (Langmuir, Freundlich, D-R, and Temkin isotherm modeling). The investigation concludes that the optimal conditions for Cr (VI) removal are pH 3, contact time of 300 min, adsorbent dosage of 0.5 g, and an initial metal ion concentration of 50 ppm. The adsorption isotherm model indicates an excellent fit with the Freundlich isotherm (R2 = 0.9576) and pseudo-second-order kinetics (R2 = 0.981). In summary, the CS/CMC/BAG ternary blend exhibits a remarkable ability to effectively remove heavy metal Cr(VI) ions from industrial wastewater.

Adsorption studies of methylene blue on cation-modified graphene oxide and graphene oxide/MXene membranes

Membranes prepared from graphene oxide (GO) have greater advantages over traditional materials for water treatment, while MXene is a good candidate for pollutant removal. However, the effect of different cations introduced into the prepared GO membranes on their adsorption performance must be further explored. In this study, a series of cation-modified GO and GO/MXene membranes were prepared based on the self-assembly of GO. Na+-modified membranes were found to be more effective at removing methylene blue (MB) than multivalent cation-modified GO membranes. However, the cation-modified GO/MXene membranes improved the MB adsorption efficiency, and the higher the ionic valence, the more pronounced the effect. In addition, the effects of the pH, temperature, contact time and initial concentration of MB on the adsorption performance of the membranes were investigated. The best removal of MB was achieved under neutral conditions, and the adsorption process was consistent with quasi-secondary kinetics and Langmuir isotherm models. The fitting results of the Langmuir isotherm model showed that the maximum adsorption capacities of the cation-modified GO membranes for MB were 654.9, 319.8, and 246.3 mg/g, respectively. The maximum adsorption capacities of the cation-modified GO/MXene membranes for MB were 687.3, 497.6, and 772.4 mg/g, respectively. Furthermore, the results of the intraparticle diffusion model revealed that the entire adsorption process was controlled by both external and internal diffusion. The thermodynamic analysis results indicated that the entire adsorption process was a heat-absorbing process and could proceed spontaneously. That the findings suggest that the Na+-modified GO and Al3+-modified GO/MXene membranes demonstrate the best adsorption effects and are promising adsorbents for MB removal.