Preparation of a poly(acrylic acid) based hydrogel with fast adsorption rate and high adsorption capacity for the removal of cationic dyes

A biocompatible Dex-MA/PAA hydrogel was prepared through copolymerization of glycidyl methacrylate substituted dextran (Dex-MA) with acrylic acid (AA), which was applied as the adsorbent to remove cationic dyes from aqueous solutions. Dex-MA/PAA hydrogel presented a fast adsorption rate and the removal efficiency of Methylene Blue (MB) and Crystal Violet (CV) reached 93.9% and 86.4%, respectively within one minute at an initial concentration of 50 mg L⁻¹. The adsorption equilibrium data fitted the Sips isotherm model well with high adsorption capacities of 1994 mg g⁻¹ for MB and 2390 mg g⁻¹ for CV. Besides, dye adsorption occurred efficiently over the pH range 3–10 and the temperature range 20–60 °C. Moreover, the removal efficiencies for MB and CV were still >95% even after five adsorption/desorption cycles which indicates the robust nature of the Dex-MA/PAA hydrogel and its potential as an eco-friendly adsorbent for water treatment.

A biocompatible Dex-MA/PAA hydrogel was prepared through copolymerization of glycidyl methacrylate substituted dextran (Dex-MA) with acrylic acid (AA), which was applied as the adsorbent to remove cationic dyes from aqueous solutions.     

Synthesis and adsorption behavior of hydroxypropyl-β-cyclodextrin–polyurethane magnetic nanoconjugates for crystal and methyl violet dyes removal from aqueous solutions

In this study, hydroxypropyl-β-cyclodextrin (HPβCD), HPβCD-conjugated magnetic nanoparticles (HPMN) and HPβCD-conjugated magnetic nanoparticles with polyurethane networks (HPMNPU) were synthesized and used as adsorbents for the removal of crystal violet (CV) and methyl violet (MV) dyes from aqueous solutions. Magnetic nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results of characterization analyses indicated that HPβCD was successfully modified with magnetic nanoparticles and polyurethane networks. In this work, a novel definitive screening design (DSD) was initially used to investigate the adsorption and elimination of dye impurities. This method allows a drastic reduction in the number of experiments needed to investigate those systems characterized by a large number of variables. The effects of nine quantitative parameters were investigated: initial dye concentration, adsorbent dose, contact time, temperature, pH, ionic strength, HMDI/HP ratio, MN/HP ratio, and stirrer speed. Analysis of a DSD model revealed that only four variables, namely, adsorbent dose, contact time, initial dye concentration and HMDI/HP ratio were statistically significant. Compared with HPMN, HPMNPU nanocomposites showed better adsorption performance for the removal of CV and MV from aqueous solutions. The maximum adsorption capacity values of HPMNPU were approximately 1269 mg g⁻¹ and 1667 mg g⁻¹ for CV and MV, respectively. This study showed that HPMNPU adsorbents exhibited high adsorption performance for the removal of CV and MV from water and could be promising adsorbent materials for the efficient removal of cationic dyes from wastewaters.

Hydroxypropyl-β-cyclodextrin–polyurethane magnetic nanoconjugates possess adsorption properties favorablefor the purpose of removing crystal and methyl violet dyes.     

Fabrication of stable superabsorbent hydrogels for successful removal of crystal violet from waste water

Smart superabsorbent hydrogels consisting of acrylamide/sodium alginate (AS), acrylamide/sodium alginate/2-acrylamido-2-methylpropane sulphonic acid (ASA_x, x = amount of AMPS) were synthesized via free radical polymerization. The swelling behavior of the hydrogels was studied in distilled and tap water. It was found that by increasing the amount of 2-acrylamido-2-methylpropanesulphonic (AMPS) in the hydrogel composition, the hydrogel swelling capability was enhanced from 3685% for AS to 4797% for ASA₁ and 21 175% for ASA₂ in distilled water, while in tap water this property varied from 915% for AS to 988% and 1588% for ASA₁ and ASA₂, respectively. All the samples were found to be efficient for the removal of crystal violet from aqueous solution. The absorption efficiency and % removal increased from 1.78 mg g⁻¹ and 62.6% for AS to 3.31 mg g⁻¹ and 75% for ASA₁ and 3.34 mg g⁻¹ and 82.1% for ASA₂. The effects of pH, contact time, initial dye concentration and hydrogel dosage on the removal process were studied in detail. The mechanism of CV removal occurs according to the Freundlich isotherm following pseudo second order kinetics. The thermodynamic parameters showed that the sorption process is spontaneous and endothermic in nature. The superabsorbent hydrogels were regenerated and reused in six consecutive cycles with 5% decrease in efficiency.

Smart superabsorbent hydrogels consisting of acrylamide/sodium alginate (AS), acrylamide/sodium alginate/2-acrylamido-2-methylpropane sulphonic acid (ASA_x, x = amount of AMPS) were synthesized via free radical polymerization.     

Facile synthesis of MoO2/CaSO4 composites as highly efficient adsorbents for congo red and rhodamine B

A novel rod-shaped MoO₂/CaSO₄ composite was prepared by using hexa-ammonium molybdate and flue gas desulfurization gypsum via a simple mixed-solvothermal route. In this composite, CaSO₄ matrices are decorated with MoO₂ nanoparticles, and non-structural mesopores are formed via particle packing. Moreover, it displays an excellent adsorption capability towards anionic congo red (CR) and cationic rhodamine B (RhB). The adsorption quantities per unit mass and removal efficiencies of the two dyes are significantly influenced by adsorbent dose, solution pH, and temperature. The adsorption isotherm data can be best fitted by the Langmuir model, and the calculated maximum adsorption quantities at 303.5 K are 853.54 mg g⁻¹ for CR and 86.38 mg g⁻¹ for RhB, respectively, which are superior to other common adsorbents. The corresponding kinetic data can be well matched with the pseudo-second-order model. Additionally, the CR adsorption is an exothermic process, while the RhB adsorption is an endothermic process. Both of them are multi-step chemisorption processes influenced by surface adsorption and intra-particle diffusion. This MoO₂/CaSO₄ composite can be applied as an alternative adsorbent for removing organic dyestuffs from printing and dyeing wastewater.

A new kind of rod-shaped MoO₂/CaSO₄ composite, in which MoO₂ nanoparticles are supported on the surface of CaSO₄ matrices, was prepared via a mixed-solvothermal method for efficient removal towards congo red and rhodamine B.     

Biosorption of anionic and cationic dyes via raw and chitosan oligosaccharide-modified Huai Flos Chrysanthemum at different temperatures

Raw Huai Flos Chrysanthemum (HFC) and modified HFC (HFC@CO) were used for the first time as a biosorbent material to remove cationic dyes Malachite green (MG) and Crystal violet (CV), and anionic dyes Sunset yellow (SY), Lemon yellow (LY), and Carmine (CM), at different temperatures (5–50 °C). The highest removal rates (R) for dye adsorption were observed at low temperature (5 °C) and room temperature (20 °C). At high (500 mg L⁻¹) dye concentration, adsorption was completed within one minute, but the time required to reach adsorption equilibrium was longer than at the low (20 mg L⁻¹) concentration. The experimental data fitted very well to the Langmuir model and the values of the maximum adsorption capacity for SY, LY, CM, CV, and MG, were 481.41, 507.23, 141.78 mg g⁻¹, 526.32, and 769.23 mg L⁻¹, respectively. The adsorption data fit well to a pseudo-second-order kinetic model.

Raw Huai Flos Chrysanthemum and modified HFC were used for the first time as a biosorbent to remove cationic dyes Malachite green and Crystal violet, and anionic dyes Sunset yellow, Lemon yellow, and Carmine, at different temperatures (5–50 °C).     

Combined molecular dynamics simulations and experimental studies of the removal of cationic dyes on the eco-friendly adsorbent of activated carbon decorated montmorillonite Mt@AC

In recent years, the combination of experimental and theoretical study to explain adsorbate/adsorbent interactions has attracted the attention of researchers. In this context, this work aims to study the adsorption of two cationic dyes, namely methylene blue (MB) and crystal violet (CV), on a green adsorbent Montmorillonite@activated carbon (Mt@AC) composite and to explain the adsorption behavior of each dye by the molecular dynamics (MD) simulation method. The eco-friendly nanocomposite Mt@AC is synthesized and characterized by the analysis methods: XRD, FTIR, BET, TGA/DTA, SEM-EDS, EDS-mapping and zeta potential. The experimental results of adsorption equilibrium show that the adsorption of the two dyes is well suited to the Langmuir adsorption model. The maximum adsorption capacity of the two dyes reaches 801.7 mg g⁻¹ for methylene blue and 1110.8 mg g⁻¹ for crystal violet. The experimental kinetics data fit well with a pseudo-first order kinetic model for the two dyes with coefficient of determination R² close to unity, non-linear chi-square χ² close to zero and lower Root Mean Square Error RMSE (R² → 1 and χ² → 0, RMSE lower). Molecular dynamic simulations are run to gain insights on the adsorption process. According to the RDF analysis and interaction energy calculations, the obtained results reveal a better affinity of the CV molecule with both the AC sheet and montmorillonite framework as compared with MB. This finding suggests that CV is adsorbed to a larger extent onto the nanocomposite material which is in good agreement with the adsorption isothermal experiment observations.

Eco-friendly Mt@AC composite material was prepared and characterized for removal of cationic dyes from aqueous solutions. The Molecular dynamics simulation was applied for evaluating the adsorption mechanisms.     

Enhanced performance of hydroxyl and cyano group functionalized graphitic carbon nitride for efficient removal of crystal violet and methylene blue from wastewater

This work reports the synthesis of an innovative multifunctional carbon nitride based adsorbent and its successful application for the removal of crystal violet (CV) and methylene blue (MB) from wastewater. The functionalized graphitic carbon nitride (f/g-CN) adsorbent was produced by the pyrolysis of melamine followed by thermal alkali treatment to introduce OH, NH_x, and CN groups onto the graphitic carbon nitride (g-CN) surface. Experimental data obtained from batch tests revealed that the maximum adsorption capacities of g-CN and f/g-CN were found to be 28.9 and 239.0 mg g⁻¹ for MB, and 163.0 and 532.0 mg g⁻¹ for CV, respectively, at pH 8, 25 °C and after 90 min. This increase in adsorption capacity of f/g-CN can be explained by the presence of multiple functional groups in its structure. f/g-CN showed 100% removal for MB and CV with concentrations lower than 100 ppm and the equilibrium time required for the 100% removal of 500 ppb dye is 60 seconds. Additionally, the experimental data fitted well with the Langmuir isotherm model (R² = 0.992) and pseudo second order kinetic model (R² = 0.999) suggesting that the mechanism of adsorption is based on π–π stacking and electrostatic interactions between the NH_x and OH groups of f/g-CN and dye molecules with monolayer formation. Moreover, a reusability test showed that the adsorption capacity remained at around 90% after 7 cycles. This work highlights the merits of the prepared adsorbent f/g-CN which is an eco-friendly, stable, efficient, and reusable adsorbent for removing cationic dyes from wastewater.

This work reports the synthesis of an innovative multifunctional carbon nitride based adsorbent and its successful application for the removal of crystal violet (CV) and methylene blue (MB) from wastewater.     

Synthesis of ZSM-5 zeolites from biomass power plant ash for removal of ionic dyes from aqueous solution: equilibrium isotherm,kinetic and thermodynamic analysis

In this work, industrial biomass power plant ash was used to synthesize the ZSM-5 zeolites for the first time with the original intention to turn value-added material into wealth, and then committed to adsorption performance testing. Typical chemical structure and morphology of ZSM-5 zeolite were identified by comprehensive technologies. Uniquely, it was found that there was a low pressure hysteresis loop which was caused by crossed 10-membered rings in the N₂ adsorption–desorption isotherm. To investigate the adsorption performance for dyes, the zeolite samples were used to remove cationic (MB) and anionic (CR) dyes from aqueous. The results demonstrated that when it came to adsorbing MB, the isotherm was in line with the Redlich–Peterson model (R² > 0.99), whereas it was matched up with the Sips model (R² > 0.99) for adsorbing CR. Kinetic models were assigned to the pseudo-second order equation (R² ≥ 0.99) along with remarkable intraparticle diffusion. In the end, thermodynamic parameters were ΔG⁰ < 0, and E_a > 0. Especially, adsorbing MB was ΔS⁰ > 0, and ΔH⁰ > 0, whilst adsorbing CR was ΔS⁰ < 0, and ΔH⁰ < 0, which indicates that electrostatic interaction plays a significant role in the whole process. All in all, this work might encourage novel attempts to dispose of industrial biomass ash.

In this work, industrial biomass power plant ash was used to synthesize the ZSM-5 zeolites for the first time with the original intention to turn value-added material into wealth, and then committed to adsorption performance testing.     

Convenient pH-responsive removal of Acid Black 1 by green l-histidine/iron oxide magnetic nanoadsorbent from water: performance and mechanistic studies

This study was aimed at developing green histidine-modified Fe₃O₄ nanoparticles (His-MNPs) for the adsorptive removal of Acid Black 1 (AB1) from aqueous solution. The His-MNPs were characterized by atomic force microscopy, scanning electron microscopy-energy dispersive X-ray spectrometry, infra-red spectra and thermogravimetry. These MNPs were spherical (average diameter 11–28 nm) with polydispersity index of 1.40 and about 13% mass coating of histidine. To optimize AB1 adsorption on His-MNPs and understand its mechanism, the influences of different operational variables (pH, adsorbent amount, temperature, initial AB1 concentration, contact time, ionic strength, etc.) on adsorption were examined with adsorption isotherms, kinetics and thermodynamic studies. The AB1 adsorption from water was fast with equilibrium time ≤ 45 min. The adsorption equilibrium was best fitted to the Langmuir isotherm model (q_max = 166.7 mg g⁻¹ at the adsorbent dose of 0.2 g L⁻¹, temperature 30 °C and pH 4). The linearity order for other isotherms was as follows: Dubinin–Radushkevich (D–R) < Temkin < Freundlich. The kinetics of the AB1 adsorption demonstrated the best compliance with the pseudo-second-order model, predominantly controlled by film diffusion as compared to intraparticle diffusion. Thermodynamic parameters (ΔH° and ΔG°) reflected the exothermic and spontaneous adsorption process. The values of ΔG°, ΔH°, activation energy and D–R free adsorption energy were all consistent with the physisorptive removal of AB1. The spectral (electronic and IR) and pH studies further corroborated the mechanism of AB1 removal by His-MNPs. The His-MNPs showed efficient adsorption, easy regeneration and excellent reusability, assisted by their pH-responsive properties. The prepared adsorbent can provide a safe, effective and economical alternative strategy for removing azo dyes from wastewater.

Effective and eco-friendly separation of Acid Black 1 dye from water by electrostatic adsorption onto reusable Histidine-Fe₃O₄ nanoparticles, credited to their pH-responsiveness.     

Matrix-dispersed magnetic molecularly-imprinted polyaniline for the effective removal of chlorpyrifos pesticide from contaminated water

We report a new adsorbent nanocomposite material based on matrix-dispersed superparamagnetic iron oxide nanoparticles (SPIONs) in molecularly-imprinted polyaniline for the removal of chlorpyrifos (CPF), a hazardous organophosphate pesticide, from water. The synthesized magnetic molecularly-imprinted polymer (MMIP) was characterized by FTIR spectroscopy, XRD, magnetic susceptibility, DLS, zeta potential measurement, SEM and high-resolution TEM imaging. The average size of the naked SPIONs ranges from 15 to 30 nm according to the high-resolution TEM analysis. Moreover, the adsorption kinetics, thermodynamic parameters (ΔG, ΔH and ΔS), adsorption isotherms and rebinding conditions were investigated in detail. The proposed MMIP has an imprinting factor of 1.64. In addition, it showed a high experimental adsorption capacity of 1.77 mg g⁻¹ and a removal efficiency of nearly 80%. The fabricated MMIP material demonstrated excellent magnetic susceptibility allowing for easy separation using an external magnetic field. The adsorption mechanism of CPF onto the MMIP adsorbent followed the second-order kinetics model and fitted to the Temkin adsorption isotherm. By studying the adsorption thermodynamics, negative ΔG values (−1.955 kJ mol⁻¹ at room temperature) were obtained revealing that the adsorption process is spontaneous. Furthermore, the maximum adsorption capacity was obtained at room temperature (ca. 303 K), neutral pH and using a high CPF concentration.

An efficient magnetic molecularly-imprinted polymer adsorbent for removal of chlorpyrifos organophosphate pesticide from water is reported.     

Construction of a phosphate-rich polyacrylonitrile fiber surface microenvironment for efficient purification of crystal violet wastewater

Wastewater purification using fibrous adsorbents has received much attention due to their high efficiency, low cost, and recyclability. In this work, phosphate modified polyacrylonitrile fiber (B-PAN_EAPF) was prepared and used to remove cationic dyes. The B-PAN_EAPF showed the best adsorption capacity for crystal violet (CV) when compared with rhodamine B, methyl green, Victoria blue B, methylene blue, and neutral red. The adsorption tests revealed that the fiber possessed high adsorption efficiency and achieved semi-saturated adsorption within 15 min. The maximum adsorption capacity of 354.46 mg g⁻¹ as calculated by the Langmuir adsorption model was higher than many other adsorbents. Furthermore, the B-PAN_EAPF was used to remove 210 mL of CV in a continuous-flow process with a high removal efficiency over 90%. Besides, the phosphate functionalized fiber could easily decrease the concentration of CV to below 0.5 mg L⁻¹ which is below the maximum effluent discharge standard of 15 mg L⁻¹ prescribed in China. It could also be fully recovered and easily separated from the solution to achieve re-use 10 cycles. Moreover, the adsorption mechanism indicated that the adsorption process of the fiber for CV was mainly attributed to electrostatic interaction and hydrogen bonding. In conclusion, the results suggested that the B-PAN_EAPF characterized by its simplicity, efficiency, eco-friendliness, and reusability, could be a promising candidate for CV removal.

A novel recyclable phosphate functionalized polyacrylonitrile fiber shows excellent selectivity and adsorption capacity for crystal violet. It can be used to remove this dye in a flow process with high removal efficiency.     

Engineered Fe3 triangle for the rapid and selective removal of aromatic cationic pollutants: complexity is not a necessity

In this study, a low-cost oxo-bridged {Fe₃} triangular cluster was constructed based on a benzoate ligand via slow evaporation. The cluster was thoroughly characterized by FTIR and UV-visible spectroscopy, TGA, and PXRD, and the exact structure was elucidated by single-crystal XRD. The formation of C–H⋯π and π–π interactions is responsible for the extra stability of {Fe₃} clusters, which further enhances the dye adsorption property. The dye adsorption experiments performed on cationic [methylene blue (MB) and rhodamine-B (Rh-B)] as well as anionic [methyl orange (MO) and congo red (CR)] dyes revealed the ultimate selectivity of the present cluster towards the cationic ones. The {Fe₃} cluster exclusively adsorbs the cationic dyes, i.e., MB and Rh-B even in the presence of anionic dyes, i.e., CR and MO. The extra stability, reusability and high efficiency of the {Fe₃} molecular ensemble make it an attractive and fascinating material of importance. The kinetics analysis was evaluated employing different kinetics models. Furthermore, the plausible adsorption mechanism was also proposed, which suggests the interplay of cation–π and π–π interactions consolidating the efficient adsorption. Thus, the present work opens new doors for coordination chemists to further tune the structural features to modulate the adsorption/separation capacities of simple low-cost clusters for environmental protection for future efforts.

A Fe₃ triangle has been designed to serve as a filter for the elimination of cationic dye pollutants.     

Chitin/egg shell membrane@Fe3O4 nanocomposite hydrogel for efficient removal of Pb2+ from aqueous solution

The development of adsorbents by using the byproducts or waste from large-scale industrial and agricultural production is of great significance, and is considered to be an economic and efficient strategy to remove the heavy metals from polluted water. In this work, a novel chitin/EM@Fe₃O₄ nanocomposite hydrogel was obtained from a NaOH/urea aqueous system, where the proteins of egg shell membrane and Fe₃O₄ nanoparticles were chemically bonded to chitin polymer chains with the help of epichlorohydrin. Due to the existence of a large number of –NH₂, –OH, –CONH–, –COOH and hemiacetal groups, the adsorption efficiency for Pb²⁺ into the absorbent was dramatically enhanced. The experimental results revealed that the adsorption behavior strongly depends on various factors, such as initial pH, initial Pb²⁺ concentration, incubation temperature and contact time. The kinetic experiments indicated that the adsorption process for Pb²⁺ in water solution agreed with the pseudo-second-order kinetic equation. The film diffusion or chemical reaction is the rate limiting process in the initial adsorption stage, and the adsorption of Pb²⁺ into the nanocomposite hydrogel can well fit the Langmuir isotherm. Thermodynamic analysis demonstrated that such adsorption behaviors were dominated by an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

A novel kind of chitin/EM@Fe₃O₄ nanocomposite hydrogel derived from the biowastes of egg shell membrane and chitin was successfully prepared for efficient removal of Pb²⁺ from wastewater solution.     

Novel Al2O3/GO/halloysite nanotube composite for sequestration of anionic and cationic dyes

In this study, an Al₂O₃/graphene oxide/halloysite nanotube (Al₂O₃/GO/HNT) nanocomposite has been synthesized and used as an adsorbent for the sequestration of cationic methylene blue (MB) and anionic congo red (CR) dyes from wastewater. The properties of the synthesized Al₂O₃/GO/HNT were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Various factors such as pH, contact time, initial concentration and temperature have been investigated for evaluation of the optimum adsorption in the batch sorption experiment and experimental results showed the highest adsorption capacity was found to be 329.8 mg g⁻¹ for CR and 258.4 mg g⁻¹ for MB at an initial concentration of 500 mg l⁻¹ which was three times higher than the individual Al₂O₃ GO and HNT concentrations. Freundlich and Langmuir adsorption isotherm models were fitted to the experimental data and the results implied that the adsorption of MB well described with Langmuir and CR is related to the Freundlich isotherm model. The kinetics data of CR and MB adsorption was well fitted to pseudo-first-order. The calculated values for thermodynamic parameters indicated that the MB and CR adsorption process were spontaneous and exothermic in nature. The effectiveness of the Al₂O₃/GO/HNT composite was also tested for adsorption of Cu(ii), oxytetracycline (OTC) antibiotic, and 2-chlorophenol (2CP) and the results revealed that the Al₂O₃/GO/HNT composite is a promising adsorbent for the dyes as well as heavy metals and other organic pollutants.

In this study, an Al₂O₃/graphene oxide/halloysite nanotube (Al₂O₃/GO/HNT) nanocomposite has been synthesized and used as an adsorbent for the sequestration of cationic methylene blue (MB) and anionic congo red (CR) dyes from wastewater.     

Aqueous carbofuran removal using slow pyrolyzed sugarcane bagasse biochar: equilibrium and fixed-bed studies

Herein, biochar was produced by the slow pyrolysis of sugarcane bagasse at 500 °C in absence of oxygen. The resulting sugarcane bagasse biochar (SB500) was characterized and used for aqueous carbofuran sorptive removal. Batch carbofuran sorption studies were accomplished to ascertain the influence of solution pH, contact time, temperature (25, 35 and 45 °C) and adsorbate/adsorbent concentration. SB500 adsorbed more carbofuran at low pH values and less carbofuran at high pH values. The necessary sorption equilibrium, kinetic and thermodynamic parameters were determined. The equilibrium isotherm data were fitted to the Freundlich, Langmuir and Temkin models. The Langmuir equation best fitted the experimental sorption data. The maximum Langmuir adsorption capacity of 18.9 mg g⁻¹ was obtained at pH 6.0 and 45 °C. The enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) were evaluated. The fixed-bed carbofuran sorption studies were carried out using the optimum parameters determined via the batch studies. The necessary fixed-bed design parameters were obtained. Carbofuran desorption and SB500 regeneration were successfully achieved. About 96% of the total carbofuran was successfully desorbed from the exhausted biochar using 20 mL ethanol in 10 mL increments. Moreover, a possible carbofuran adsorption mechanism has been proposed. A number of interactions including (1) hydrogen bonding of the protonated and neutral carbofuran to biochar, (2) carbofuran sorption onto biochar via π–π electron donor–acceptor interactions and (3) carbofuran diffusion into the biochar pores were considered to explain the sorption mechanism. The batch and fixed-bed sorption results demonstrate that the sugarcane bagasse biochar (SB500) can be effectively used for the sustainable removal and recovery of carbofuran from water.

Sugarcane bagasse biochar was prepared, characterized and used for aqueous carbofuran removal. Sorption equilibrium and dynamics studies were carried out. An adsorption capacity of 19 mg g⁻¹ was obtained at 45 °C. Carbofuran adsorption mechanism has been proposed.     

Graphene oxide–chitosan hydrogel for adsorptive removal of diclofenac from aqueous solution: preparation,characterization, kinetic and thermodynamic modelling

This work aimed at developing a natural compound-based hydrogel adsorbent to remove diclofenac as a model pharmaceutical from water. First, graphene oxide–chitosan (GO–CTS) and amine graphene oxide–chitosan (AGO–CTS) hydrogel adsorbents were synthesized via a facile mechanical mixing method. The synthesized materials were characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, and thermogravimetric analysis (TGA) techniques. In the second stage, adsorption experiments were conducted to determine the best GO to CTS ratio and find the optimized adsorption parameters, including the initial drug concentration, adsorbent dosage, pH, and temperature. The results showed that the optimal GO to CTS mass ratio is 2 : 5 and thus the same ratio was selected as the AGO to CTS mass ratio to understand the effect of amine-functionalization on removal efficiency. The optimal adsorption parameters were determined to be pH of 5, C_i of 100 ppm and dosage of 1.5 g L⁻¹, where 90.42% and 97.06% removal was achieved for optimal GO–CTS and AGO–CTS hydrogel adsorbents, respectively. Langmuir and Freundlich isotherms models were employed to investigate the adsorption behavior of diclofenac onto the synthesized hydrogels. The results revealed that the adsorption tends to be of the monolayer type and homogeneous, as the results were in better accordance with the Langmuir model than the Freundlich model. The thermodynamics of adsorption demonstrated that the adsorption is exothermic, exhibiting higher removal efficiency at lower temperatures. Furthermore, Gibb''s free energy change of adsorption (ΔG) suggested that the adsorption is spontaneous, being more spontaneous for AGO–CTS than GO–CTS hydrogels. Finally, the regeneration ability of the hydrogel adsorbents was studied in five consecutive cycles. The adsorbent maintained its efficiency at a relatively high level for three cycles but a considerable decrease was observed between the third and the fourth cycle, indicating that the hydrogels were recoverable for three cycles.

This work aimed at developing a natural compound-based hydrogel adsorbent to remove diclofenac as a model pharmaceutical from water.     

Comparative study of Hg(ii) biosorption performance of xanthated and charred sugarcane bagasse from aqueous solutions

The main target of this study was to evaluate the efficiency of charred xanthated sugarcane bagasse (CXSB) and charred sugarcane bagasse (CSB) in the removal of Hg(ii) ions from aqueous media. Batch experiments were performed to study the experimental parameters such as effects of pH, concentration, contact time and temperature. The adsorption velocity of Hg(ii) onto CSB and CXSB was fast and reached equilibrium within 60 minutes. Isotherm and kinetic studies showed that Hg(ii) uptake using both the biosorbents followed Langmuir isotherm and pseudo second order kinetics. The maximum adsorption capacity of Hg(ii) at optimum pH 4.5 onto CSB and CXSB was found to be 125 mg g⁻¹ and 333.34 mg g⁻¹, respectively. A negative value of ΔG° and positive ΔS° value (0.24 kJ mol⁻¹ for CSB and 0.18 kJ mol⁻¹ for CXSB) for both the biosorbents confirm the spontaneous nature of Hg(ii) adsorption. A positive value of ΔH° (52.06 kJ mol⁻¹ for CSB and 30.82 kJ mol⁻¹ for CXSB) suggests the endothermic nature of biosorption. The investigated results shows that CXSB compared to CSB can be used as a low cost and environmentally benign bio-adsorbent for the removal of Hg(ii) ions from aqueous solutions.

Ion exchange adsorption mechanism of Hg(ii) onto the monomeric unit of charred xanthated sugarcane bagasse (CXSB).     

Decontamination of organic pollutants from aqueous media using cotton fiber–graphene oxide composite,utilizing batch and filter adsorption techniques: a comparative study

Cotton fiber–graphene oxide (C–GO) composite with high adsorptive properties towards the cationic dye, crystal violet (CV), was successfully fabricated by simple mixing of cotton fiber and GO in aqueous solution using a homogenizer. The as-prepared composite was characterized using TEM, SEM, LOM, XRD, FTIR, Raman and TGA. The characterization indicated that the formation of a homogeneous composite occurred via adequate mixing of the cotton fiber and GO. The fine structure of the obtained composite was successfully used in two adsorption techniques, namely batch adsorption and filter adsorption. Various parameters affecting batch adsorption, such as contact time, dye concentration, composite dose, NaCl dose, temperature and pH were investigated. In the filter adsorption mode, dye concentration, composite dose, NaCl dose, temperature, flow rate and pH were studied. A comparison study between the two techniques, i.e., batch adsorption and filter adsorption, are reported. The filter adsorption technique shows higher adsorption efficiency than the batch one, which was evident from the maximum adsorption capacity (Q°) values, obtained from the Langmuir isotherm. Further, the filter technique was developed and evaluated. This was achieved by regeneration, scaling-up and, finally, using another model of cationic dye (methylene blue).

Cotton fiber–graphene oxide (C–GO) composite with high adsorptive properties towards the cationic dye, crystal violet (CV), was successfully fabricated by simple mixing of cotton fiber and GO in aqueous solution using a homogenizer.     

Gallic acid-functionalized graphene hydrogel as adsorbent for removal of chromium (iii) and organic dye pollutants from tannery wastewater

The pollution caused by tannery wastewater containing high concentrations of trivalent chromium ions [Cr(iii)] and organic dyes has severely restricted the sustainable development of the leather industry. To address this problem, a three-dimensional (3D) porous graphene-based hydrogel with good mechanical strength and large surface area was fabricated by self-assembly of graphene oxide (GO) sheets reduced and modified by gallic acid (GA) through π–π interactions. As an adsorbent, this GA-functionalized graphene hydrogel (GA-GH) can effectively capture Cr(iii) by coordination complexation between Cr(iii) and deprotonated carboxylic groups of GA at pH ∼ 4.0. Moreover, GA-GH could be easily regenerated by desorption of adsorbed Cr(iii) at pH 2.0 and maintained its high adsorption capacity after multiple adsorption–desorption cycles, which was also helpful for reusing desorbed Cr(iii) as tanning agent. In addition, compared with a graphene hydrogel (GH) without modification by GA, adsorption capacity of GA-GH for organic dye was significantly improved due to the enhanced π–π interactions between the GA-GH and aromatic dyes.

The formation process of gallic acid functionalized graphene hydrogel (GA-GH).     

Solvothermal synthesis of poly(acrylic acid) decorated magnetic molybdenum disulfide nanosheets for highly-efficient adsorption of cationic dyes from aqueous solutions

Herein we report solvothermal synthesis of poly(acrylic acid) (PAA) decorated magnetic molybdenum disulfide nanosheets (MMoS₂/PAA) for highly efficient adsorption of three cationic dyes of basic fuchsin (BF), methylene blue (MB), and crystal violet (CV) from aqueous solutions. The synthesized MMoS₂/PAA was characterized by several techniques including transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), and dynamic light scattering (DLS). Due to the strong electrostatic interaction between cationic dyes and the anionic nanosheet surface, the obtained MMoS₂/PAA showed ultrafast adsorption of BF, MB and CV within 2 min with high adsorption capacities of 886.1, 709.0, and 633.6 mg g⁻¹, respectively, much higher than those materials reported recently. PAA molecules bound on the nanosheets played a crucial role in significantly enhancing the dye adsorption. The adsorption kinetics and isotherms of three dyes onto the MMoS₂/PAA were well described by the pseudo-second-order kinetic and the Langmuir models. Moreover, the MMoS₂/PAA also exhibited high removal efficiencies for various mixed-dye solutions. Besides, such a functional nanomaterial could be effectively recovered from dye solutions under an external magnetic field and reused for dye adsorption without compromising on its performance indicating it can serve as an excellent adsorbent for effective removal of a variety of cationic organic pollutants from industrial effluents.

Poly(acrylic acid) decorated magnetic MoS₂ nanosheets with high adsorption capacities for three cationic dyes have been successfully synthesized by a simple one-step solvothermal method.