Adsorption of malachite green from aqueous solution by using novel chitosan ionic liquid beads

Zinc oxide decorated plantain peel activated carbon for adsorption of cationic malachite green dye: Mechanistic, kinetics and thermodynamics modeling

Reports have shown that malachite green (MG) dye causes various hormonal disruptions and health hazards, hence, its removal from water has become a top priority. In this work, zinc oxide decorated plantain peels activated carbon (ZnO@PPAC) was developed via a hydrothermal approach. Physicochemical characterization of the ZnO@PPAC nanocomposite with a 205.2 m2/g surface area, porosity of 614.68 and dominance of acidic sites from Boehm study established the potency of ZnO@PPAC. Spectroscopic characterization of ZnO@PPAC vis-a-viz thermal gravimetric analyses (TGA), Fourier Transform Infrared Spectroscopy (FTIR), Powdered X-ray Diffraction (PXRD), Scanning Electron Microscopy and High Resolution - Transmission Electron Microscopy (HR-TEM) depict the thermal stability via phase transition, functional group, crystallinity with interspatial spacing, morphology and spherical and nano-rod-like shape of the ZnO@PPAC heterostructure with electron mapping respectively. Adsorption of malachite green dye onto ZnO@PPAC nanocomposite was influenced by different operational parameters. Equilibrium data across the three temperatures (303, 313, and 323 K) were most favorably described by Freundlich indicating the ZnO@PPAC heterogeneous nature. 77.517 mg/g monolayer capacity of ZnO@PPAC was superior to other adsorbents compared. Pore-diffusion predominated in the mechanism and kinetic data best fit the pseudo-second-order. Thermodynamics studies showed the feasible, endothermic, and spontaneous nature of the sequestration. The ZnO@PPAC was therefore shown to be a sustainable and efficient material for MG dye uptake and hereby endorsed for the treatment of industrial effluent.

Adsorption potential of ionic liquid-modified ZnO nanoparticles for highly efficient removal of azo dye: detailed isotherms and kinetics

In this study, bare and ionic liquid-modified ZnO nanoparticles have been fabricated using microwave irradiation method. The fabricated nanoparticles were characterized by different techniques, viz. XRD, FT-IR, FESEM, and UV-Visible spectroscopy, and were explored as adsorbent for effective sequestration of azo dye (Brilliant Blue R-250) from aqueous media. Various factors affecting the adsorption efficiency of synthesized nanoparticles (bare/ionic liquid-modified) such as concentration of dye, pH of reaction media, dose of nanoparticles, and reaction time were thoroughly investigated with varying experimental conditions; on a magnetic stirrer and in a sonicator. The results exhibited a high adsorption efficiency of ionic liquid-modified nanoparticles for removal of dye as compared to the bare one. Also, an enhanced adsorption was observed via sonication in comparison with magnetic stirring. Different isotherms such as Langmuir, Freundlich, and Tempkin were elaborated. Evaluation of adsorption kinetics showed a linear pseudo-second-order equation for adsorption process. The exothermic and spontaneous nature of adsorption was further confirmed by thermodynamic investigations. As per the results obtained, it is suggested that the fabricated ionic liquid-modified ZnO nanoparticles could successfully remediate the toxic anionic dye from aqueous media. Hence, this system can be utilized for large-scale industrial applications.

Glutaraldehyde and terephthaldehyde-crosslinked chitosan for cationic and anionic dyes removal from aqueous solutions: Experimental, DFT, kinetic and thermodynamic studies

Novel chitosan polymers were synthesized using two cross-linkers, Glutaraldehyde and Terephthaldehyde, to enhance stability and efficiency. Characterization techniques (XRD, FTIR, FE-SEM, TGA, DTG, BJH, and BET) confirmed successful synthesis. These polymers were employed as adsorbents for removing Malachite Green (MG) and Congo Red (CR) dyes from water. Batch experiments and DFT calculations investigated the adsorption process, thermodynamics, and kinetics. Results showed the CSGT-III polymer achieved the highest removal efficiency. For initial dye concentrations ([CR]o = 50 mg/L, [MG]o = 20 mg/L) and adsorbent doses (0.8 g/L for CR, 0.4 g/L for MG), removal efficiencies were 96.99 % for CR and 99.07 % for MG. Thermodynamic analysis confirmed the spontaneous nature of adsorption, and the process was endothermic for both dyes. The Langmuir model fitted adsorption isotherms well, indicating a homogeneous surface. Kinetic analysis revealed a pseudo-second-order model for both dyes.

Fabrication and characterisation of novel chitosan-based polymer inclusion membranes and their application in environmental remediation

Several water and wastewater technologies have been implored for the removal of dyes during wastewater treatments; however; different types have been reportedly found in surface and groundwater systems. Hence, there is a need to investigate other water treatment technologies for the complete remediation of dyes in aquatic environments. In this study, novel chitosan-based polymer inclusion membranes (PIMs) were synthesized for the removal of malachite green dye (MG) which is a recalcitrant of great concern in water. Two types of PIMs were synthesized in this study, the first PIM (PIMs-A) was composed of chitosan, bis-(2-ethylhexyl) phosphate (B2EHP), and dioctyl phthalate (DOP). While, the second PIMs (PIMs-B) were composed of chitosan, Aliquat 336, and DOP. The physico-thermal stability of the PIMs was investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), both PIMs demonstrated good stability with a weak intermolecular force of attraction amongst the various components of the membranes. The effects of the initial concentration of MG, pH of the MG solution, stripping solution, and time were investigated. At optimum conditions, both membranes (PIM-A and B) recorded the highest efficiencies of 96 % and 98 % at pH 4 and initial contaminants concentration of 50 mg/L, respectively. Finally, both PIMs were used for the removal of MG in different environmental samples (river water, seawater, and tap water) with an average removal efficiency of 90 %. Thus, the investigated PIMs can be considered a potential suitable technique for the removal of dyes and other contaminants from aquatic matrices.

Fabrication of chitosan@activated carbon composites in EmimAc for Cd(II) adsorption from aqueous solution: Experimental, optimization and DFT study

Adsorption efficiency of a duo-material blend featuring the fabrication of modified chitosan adsorbents (powder (C-emimAc), bead (CB-emimAc) and sponge (CS-emimAc)) for the removal of Cd(II) from aqueous solution was investigated. The chitosan@activated carbon (Ch/AC) blend was developed in a green ionic solvent, 1-ethyl-3-methyl imidazolium acetate (EmimAc) and its characteristics was examined using FTIR, SEM, EDX, BET and TGA. The possible mechanism of interaction between the composites and Cd(II) was also predicted using the density functional theory (DFT) analysis. The interactions of various blend forms (C-emimAc, CB-emimAc and CS-emimAc) with Cd(II) gave better adsorption at pH 6. The composites also present excellent chemical stability in both acidic and basic conditions. The monolayer adsorption capacities obtained (under the condition 20 mg/L [Cd], adsorbent dosage 5 mg, contact time 1 h) for the CB-emimAc (84.75 mg/g) > C-emimAc (72.99 mg/g) > CS-emimAc (55.25 mg/g), as this was supported by their order of increasing BET surface area (CB-emimAc (120.1 m²/g) > C-emimAc (67.4 m²/g) > CS-emimAc (35.3 m²/g)). The feasible adsorption interactions between Cd(II) and Ch/AC occurs through the O-H and N-H groups of the composites, as supported by DFT analysis in which an electrostatic interactions was predicted as the dominant force. The interaction energy (-1309.35 eV) calculated via DFT shows that the Ch/AC with amino (-NH) and hydroxyl (-OH) groups are more effective with four significant electrostatic interactions with the Cd(II) ion. The various form of Ch/AC composites developed in EmimAc possess good adsorption capacity and stability for the adsorption Cd(II).

Developing nano-micro size chitosan beads using imidazolium-based ionic liquid: A perspective

The aggressive search for unique materials in recent years has put forward chitosan and modified-chitosan as materials with unique structural and morphological characteristics for various important applications. Just as imidazolium-based ionic liquids are the commonly applied ionic liquids (ILs) type for chitosan modifications for various applications, their further modifications into beads for enhancing their properties is now gaining most attention. However, most of the currently prepared imidazolium ILs modified-chitosan beads are not in nano size due to preparation difficulties. In response to this and referencing the research works in the literature, the possible breakthrough directions including synthesis routes, and physical and mechanical transformation processes are proposed. These procedures are expected to provide certain theoretical and empirical basis, as well as technical guide for developing nano-micro size chitosan beads using imidazolium based ILs.

Synthesis and Characterization of Biodegradable Poly(vinyl alcohol)-Chitosan/Cellulose Hydrogel Beads for Efficient Removal of Pb(II), Cd(II), Zn(II), and Co(II) from Water

Globally, water contamination by heavy metals is a serious problem that affects the environment and human health. Adsorption is the most efficient way of water treatment for eliminating heavy metals. Various hydrogels have been prepared and used as adsorbents to remove heavy metals. By taking advantage of poly(vinyl alcohol) (PVA), chitosan (CS), cellulose (CE), and the process for physical crosslinking, we propose a simple method to prepare a PVA-CS/CE composite hydrogel adsorbent for the removal of Pb(II), Cd(II), Zn(II) and Co(II) from water. Structural analyses of the adsorbent were examined by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, and X-ray diffraction (XRD). PVA-CS/CE hydrogel beads had a good spherical shape together with a robust structure and suitable functional groups for the adsorption of heavy metals. The effects of adsorption parameters such as pH, contact time, adsorbent dose, initial concentration of metal ions, and temperature on the adsorption capacity of PVA-CS/CE adsorbent were studied. The adsorption characteristics of PVA-CS/CE for heavy metals may be completely explained by pseudo-second-order adsorption and the Langmuir adsorption model. The removal efficiency of PVA-CS/CE adsorbent for Pb(II), Cd(II), Zn(II), and Co(II) was 99, 95, 92, and 84%, respectively, within 60 min. The heavy metal's hydrated ionic radius may be crucial in determining the adsorption preference. After five consecutive adsorption-desorption cycles, the removal efficiency remained over 80%. As a result, the outstanding adsorption-desorption properties of PVA-CS/CE can potentially be extended to industrial wastewater for heavy metal ion removal.

Oxidized dextran-crosslinked ferrocene-chitosan-PEI composite porous material integrating adsorption and degradation to malachite green

Treating wastewater containing malachite green (MG) using porous materials with both adsorption and degradation functions have become a major challenge in achieving the carbon neutrality goal. Herein by incorporating the ferrocene (Fc) group as a Fenton active center, a novel composite porous material (DFc-CS-PEI) was prepared using chitosan (CS) and polyethyleneimine (PEI) as skeletons and oxidized dextran as a crosslinker. DFc-CS-PEI not only possesses satisfactory adsorption performance to MG but also excellent degradability in the presence of a minor amount of H₂O₂ (3.5 mmol/L) without any additional assistance, due to high specific surface area and active Fc group. The maximum adsorption capacity is ca. 177.73 ± 3.11 mg/g, outperforming most CS-based adsorbents. The removal efficiency of MG is significantly enhanced from 20 % to 90 % as DFc-CS-PEI and H₂O₂ coexist, due to ^·OH-dominated Fenton reaction, and remained in a wide pH range (2.0-7.0). Cl^- exhibits notable suppression on the degradation of MG because of quenching effects. Note that DFc-CS-PEI has a very small iron leaching (0.2 ± 0.015 mg/L), and can be rapidly recycled by simple water-washing, without any harmful chemicals and potential second pollution. Such versatility, high stability, and green recyclability make the as-prepared DFc-CS-PEI a promising porous material for the treatment of organic wastewater.

Effective Removal of Methylene Blue from Simulated Wastewater Using ZnO-Chitosan Nanocomposites: Optimization, Kinetics, and Isotherm Studies

Successful synthesis of ZnO-chitosan nanocomposites was conducted for the removal of methylene blue from an aqueous medium. Remarkable performance of the nanocomposites was demonstrated for the effective uptake of the dye, thereby achieving 83.77, 93.78 and 97.93 mg g^-1 for the chitosan, 5 wt.% ZnO-Chitosan and 10 wt.% ZnO-Chitosan, respectively. The corresponding adsorption efficiency was 88.77, 93.78 and 97.95 for the chitosan, 5 wt.% ZnO-Chitosan and 10 wt.% ZnO-Chitosan, respectively. Upon regeneration, good reusability of the nanocomposites was manifested for the continuous removal of the dye up to six consecutive cycles. The adsorption process was kinetically described by a pseudo-first order model, while the isotherms were best fitted by the Langmuir model.

Adsorptive removal of fluoride using ionic liquid-functionalized chitosan - Equilibrium and mechanism studies

In this study, novel biosorbents, based on chitosan and imidazolium ionic liquid, were prepared for the removal of fluoride from aqueous solutions. The adsorbents were characterized by FTIR, SEM-EDS and low-temperature nitrogen adsorption-desorption. To investigate the adsorption mechanism and behavior of chitosan adsorbents, batch experiments were conducted under different adsorbent dosages (2, 4, 10 g/L), pH (4, 7, 9) and initial concentration (0.5-25.0 mg/L). The influence of the method of synthesis of ionic liquid on the adsorption performance were also studied. Experimental data were evaluated by Freundlich, Langmuir and Sips models. The introduction of ionic liquid significantly improved the uptake of fluoride compared to pure chitosan. The adsorption was influenced by the experimental conditions, as well as the method of ionic liquid synthesis. The highest fluoride removal was observed at pH 4 and found to decrease with increasing pH. The removal efficiency and adsorption capacity values indicated that the dose of 4 g/L was the optimum adsorbent dosage. The equilibrium data fitted best with the Sips isotherm and the maximum adsorption capacity reached 8.068 mg/g for modified chitosan beads. The mechanism of fluoride adsorption onto ionic liquid-modified chitosan involves electrostatic attraction, ion exchange and ion pair interaction.

Modeling of malachite green adsorption onto novel polyurethane/SrFe12O19/clinoptilolite nanocomposite using response surface methodology and biogeography-based optimization-assisted multilayer neural network

This research studied the modeling of malachite green (MG) adsorption onto novel polyurethane/SrFe₁₂O₁₉/clinoptilolite (PU/SrM/CLP) nanocomposite from aqueous solutions by the application of biogeography-based optimization (BBO) algorithm-assisted multilayer neural networks (MNN-BBO) as a new evolutionary algorithm in environmental science. The PU/SrM/CLP nanocomposite was successfully fabricated and characterized by some spectroscopic analyses. Four variables influencing the removal efficiency were modeled by MNN-BBO and response surface methodology (RSM). The MNN-BBO model gave higher percentage removal (99.6%) about 7.6% compared to the RSM technique. Under optimal conditions obtained by MNN-BBO, the four independent variables including pH, shaking rate, initial concentration, and adsorbent dosage were 6.5, 255 rpm, 50 mg.L^-1, and 0.08 g, respectively. Under these conditions, the results were fitted well to the Langmuir isotherm with a monolayer maximum amount of sorbate uptake (q_max) of 68.49 mg.g^-1 and the pseudo-first-order kinetic pattern with the rate constant (K₁) of 0.01 min^-1 with the R² values of 0.9248 and 0.9980, respectively. The results of thermodynamics demonstrated that the MG uptake was not spontaneous due to the positive value of the adsorption ΔG. In addition, the positive values of ΔS (0.079 kJ/mol K) and ΔH (30.816 kJ/mol) indicated the feasible operation and endothermic approach, respectively. Besides, the wastewater investigations showed that the nanocomposite could be used as a new promising sorbent for efficient removal of MG (R% > 72) and magnetically separable from the real samples.

Tapping the potential of a glucosamine polysaccharide-diatomaceous earth hybrid adsorbent in the solid phase extraction of a persistent organic pollutant and toxic pesticide 4,4'-DDT from water

A chitosan (a glucosamine polysaccharide)-diatomaceous earth hybrid was studied for the adsorption of 4,4′-dichloro-diphenyl-trichloroethane (4,4′-DDT), a persistent organic pollutant and organochlorine pesticide compound from water. The diverse adsorption process parameters were studied and the modified adsorbent was characterized through XRD, SEM-EDX, FT-IR, XRF, BET and TGA analysis. The concentration of 4,4′-DDT was measured using gas chromatography-tandem mass spectrometry (GC-MS/MS) by adopting a validated analytical procedure. The Langmuir and Freundlich isotherms ascertained the adsorption capacity. The optimum pH and temperature for 4,4′-DDT adsorption were found to be between 5.0 and 7.0 and 20 and 30 °C respectively. Thermodynamic parameters confirmed that the adsorption of DDT on chitosan modified with diatomaceous earth was an exothermic process. The data obtained from kinetics and intra-particle diffusion showed that the composite material is able to sequester 4,4′-DDT and this is reflected in the Langmuir adsorption capacity of 0.968 mg g⁻¹. The adsorbed 4,4′-DDT was successfully eluted with ethyl acetate and recycling studies showed that the modified chitosan can be used for three cycles with significant adsorption performance and this adsorbent proved its efficacy in removing 4,4′-DDT from farm water.

A chitosan (a glucosamine polysaccharide)-diatomaceous earth hybrid was studied for the adsorption of 4,4′-dichloro-diphenyl-trichloroethane (4,4′-DDT), a persistent organic pollutant and organochlorine pesticide compound from water.

Synthesis of New Hybrid Structured Magnetite Crosslinked Poly Ionic Liquid for Efficient Removal of Coomassie Brilliant Blue R-250 Dye in Aqueous Medium

In this work, new crosslinked pyridinium poly ionic liquid and its magnetite hybrid structured composite were prepared and applied to remove the toxic dye Coomassie Brilliant Blue (CBB-R250) from aqueous solutions. In this respect, vinyl pyridine, maleic anhydride, and dibromo nonane were used to prepare crosslinked quaternized vinyl pyridinium/maleic anhydride ionic liquid (CQVP-MA). Furthermore, a linear copolymer was prepared by the reaction of vinyl pyridine with bromo nonane followed by its copolymerization with maleic anhydride in order to use it as a capping agent for magnetite nanoparticles. The monodisperse MNPs were incorporated into the crosslinked PIL (CQVP-MA) by ultrasonication to prepare CQVP-MA/Fe₃O₄ composite to facilitate its recovery using an external magnetic field and enhance its adsorption capacity. The chemical structures, thermal stabilities, zeta potential, particle size, EDS, and SEM of the prepared CQVP-MA and CQVP-MA/Fe₃O₄ were investigated. Adsorption kinetics, isotherms, and mechanisms of CB-R250 elimination from aqueous solutions using CQVP-MA and CQVP-MA/Fe₃O₄ were also studied, and the results revealed that the pseudo second-order kinetic model and the Langmuir isotherm model were the most suitable to describe the CBB adsorption from an aqueous solution. The adsorption capacities of CQVP-MA and CQVP-MA/Fe₃O₄ were found to be 1040 and 1198, respectively, which are more than those for previously reported material in the literature with reasonable stability for five cycles.

Construction of ionic liquid functionalized MXene with extremely high adsorption capacity towards iodine via the combination of mussel-inspired chemistry and Michael addition reaction

In this work, a highly efficient adsorbent based on ionic liquid functionalized MXene has been fabricated through the combination of mussel-inspired chemistry and Michael addition reaction. The surface of MXene was first coated with polydopamine (PDA) through self-polymerization of dopamine and the amino groups were introduced on the surface of MXene simultaneously. After that, the ene bond-containing ionic liquid was further immobilized on the surface of MXene-PDA to obtain MXene-PDA-IL. As a concept, the adsorptive removal of iodine using MXene-PDA-IL was conducted and the effects of various factors on the adsorption behavior were examined. The experimental data were analyzed by intermittent adsorption experiments, the adsorption kinetics, adsorption isotherm, adsorption thermodynamics, and cyclic adsorption experiments. We found that the adsorption procedure could reach equilibrium within 10 min after mixing adsorbent and iodine. The maximum adsorption capacity of MXene-PDA-IL towards iodine was as high as 695.4 mg g^-1, which is greater than most of reported adsorbents. Considered the advantages of mussel-inspired chemistry for surface functionalization and the adsorption capacity of ionic liquids, the method could be used for construct a number of composites with potential for adsorption applications.

Intriguing role of novel ionic liquids in stochastic degradation of chitosan

Green technique for hydrolysis of chitosan was developed using novel Brønsted Acidic Ionic Liquids (BAILs) as homogenous reusable catalysts. Efficiency of BAILs in controlling stochastic and irregular breakdown of chitosan was compared with that of mineral acids. Structural elucidation of the novel BAILs was performed using H¹-NMR evaluation and supplemented using mass spectroscopy. Additionally, thermal characterization was conducted using TGA-DTA analysis, while acidity was estimated by deriving the Hammet acidity function. BAILs investigated in this work enabled consistent production of LMWCS variants, with minimum formation of residual impurities. Around 80 % reduction in molecular weight was noted as compared to original under extreme conditions employed. Further, Box-Behnken Design (BBD) was implemented to optimize effect of processing parameters for conversion of chitosan to low molecular weight congeners.

Enhanced adsorption of acid Blue-25 dye onto chitosan/porous carbon composite modified in 1-allyl-3-methyl imidazolium bromide ionic liquid

In this study, chitosan/porous carbon composite (C-PC) modified in 1-Allyl-3-methyl imidazolium bromide [AMIM][Br] under airtight condition was prepared for the removal of Acid Blue-25 dye (AB-25) from aqueous medium. For comparison of adsorption efficiency of C-PC, chitosan-activated carbon composite (C-AC) was also prepared in 1% acetic acid. The adsorbents were characterised using SEM, EDX, XRD, BET, TGA and FTIR. The micrograph of C-PC revealed cavities and slightly rough surfaces dominated with similar sized and irregular shaped stone-like materials which differ from the precursors' micrograph. BET analysis revealed the domination of mesopores on the C-PC and C-AC surfaces, as the hydroxyl and amino group on C-PC are the main active sites for AB-25 dye uptake. The dye was better adsorbed onto C-PC at pH 2 and C-AC at pH 4. The adsorption capacity obtained for C-PC, C-AC, activated carbon (AC) and chitosan (CH) using Langmuir isotherm model are 3333.33 mg/g, 909.90 mg/g, 909.09 mg/g and 833.33 mg/g, respectively. The experimental data are well described by Langmuir and Fruendlich isotherms for adsorption of the dye onto C-PC, AC and CH. C-AC fitted into Langmuir isotherm only. The kinetics of the adsorption fitted into pseudo-second order indicating the possibility of chemical interactions in the adsorption process.

Chitosan modifications for adsorption of pollutants - A review

In recent times, research interest into the development of biodegradable, cost-effective and environmental friendly adsorbents with favourable properties for adsorption of pollutants is a challenge. Modification of chitosan via different physical and chemical methods have gained attention as a promising approach for removing organic (such as dyes and pharmaceuticals) and inorganic (such as metal/metal ions) pollutants from aqueous medium. In this regard, researchers have reported grafting and cross-linking approach among others as a potentially useful method for chitosan's modification for improved adsorption efficiency with respect to pollutant uptake. This article reviews the trend in chitosan modification, with regards to the summary of some recently published works on modification of chitosan and their adsorption application in pollutants (metal ion, dyes and pharmaceuticals) removal from aqueous medium. The review uniquely highlights some common cross-linkers and grafting procedures for chitosan modification, their influence on structure and adsorption capacity of modified-chitosan with respect to pollutants removal. Findings revealed that the performance of modified chitosan for adsorption of pollutants depends largely on the modification method adopted, materials used for the modification and adsorption experimental conditions. Cross-linking is commonly utilized for improving the chemical and mechanical stabilities of chitosan but usually decreases adsorption capacity of chitosan/modified-chitosan for adsorption of pollutants. However, literature survey revealed that adsorption capacity of cross-linked chitosan based materials have been enhanced in recently published works either by grafting, incorporation of solid adsorbents (e.g metals, clays and activated carbon) or combination of both prior to cross-linking.

Chitosan based antibacterial composite materials for leather industry: a review

Abstract

Chitosan is an amorphous translucent substance with a structural unit similar to the polysaccharide structure of the extracellular matrix, It has good antibacterial, biocompatible, and degradable properties. It has important application value in leather, water treatment, medicine, food and other fields, so chitosan and its modified products have received widespread attention. This article reviewed the preparation methods of chitosan-based antibacterial composites in recent years, including chitosan/collagen, chitosan/graphene, chitosan/tannic acid, and chitosan/polyethylene glycol composite materials, elaborates their modification methods and antibacterial mechanism were reviewed in detail, and its applications in the leather industry as antibacterial auxiliaries and water treatment antibacterial adsorption materials were discussed. Finally, the future development and challenges of chitosan-based composite materials in the leather industry were forecasted.

Graphical abstract

Novel 1-butyl-3-methylimidazolium bromide impregnated chitosan hydrogel beads nanostructure as an efficient nanobio-adsorbent for cationic dye removal: Kinetic study

In the present study, a novel 1-butyl-3-methylimidazolium bromide (BmImBr) impregnated chitosan beads were prepared and characterized using different methods, including XRD, FT-IR, EDX, SEM and BET. The FTIR analysis revealed that the BmImBr was successfully conjugated with the chitosan in the beads structure. The prepared beads were used as an efficient sorbent for the fast removal of methylene blue, as cationic dye model, from aqueous solution, whereas just 25 min was required to reach 86% removal efficiency. The increasing of BmImBr amount improved the adsorption performance of prepared beads. Also, it was found that the dye can be higher adsorbed on the beads surface by increasing the sorbent dosage and pH of solution, while the optimum dosage and pH were obtained 3 mg/L and 11, respectively. The kinetic study showed that the MB adsorption onto the CS-BmImBr beads follows the pseudo-fist order model and the intrinsic penetration controls the adsorption process. The properties of prepared chitosan- BmImBr IL conjugation confirmed that it can be exploited as an efficient adsorbent in the wastewater treatment.

Hexametaphosphate cross-linked chitosan beads for the eco-efficient removal of organic dyes: Tackling water quality

There is an increasing trend of developing various low-cost grafted natural amino polysaccharides for the biosorptive removal of noxious dye effluents like Malachite green (MG) and anionic Reactive Red-195 (RR-195) dyes from aqueous solution. Chemically cross-linked chitosan microsphere (CTS-HMP), a promising non-toxic biosorbent possessing high charge density and thermal stability was prepared by using hexametaphosphate as ionic cross-linker. Batch biosorption experiments were carried out under different temperatures (298, 308 and 318 K), pH (2.0-10.0), initial concentrations (25-250 mg L^-1), adsorbent dosage (0.01-0.1 g) and contact times (0-180 min) to understand the optimum experimental conditions and simultaneously evaluate the adsorption isotherms and kinetics of CTS-HMP. Biosorption equilibrium was established in 120 and 60 min for MG and RR-195 removal process. The pseudo-equilibrium process was best described by the pseudo-second-order kinetic (R² ≥ 0.98), Freundlich and Temkin isotherm model (R² ≥ 0.90). The removal rate of MG and RR-195 gradually increased (69.40 and 148 mg g^-1) at 250 mg L^-1 of initial concentration till 100 and 50 min of contact period in a single contaminant system, though the removal efficiency of acid dye was ~2 times higher compared to basic dye under optimum conditions (p < 0.05; t-test). Thermodynamic parameters indicated exothermic (MG) and endothermic (RR-195) nature of spontaneous dye removal. The activation energy of sorption (E_a) was <50 kJ mol^-1 which highlighted the importance of physical adsorption process. Therefore, the obtained results clearly validate the sustainable utilization of CTS-HMP as a promising functionalized chitosan microparticles/agent for removing dye effluents from the contaminated aqueous phase.

Microcrystalline Cellulose from Groundnut Shell as Potential Adsorbent of Crystal Violet and Methylene Blue. Kinetics, Isotherms and Thermodynamic Studies

The isolation of microcrystalline cellulose from a groundnut shell is reported. Adsorption experiments were carried out for the removal of cationic crystal violet and methylene blue and it follows Langmuir model. Positive enthalpy and negative free energy changes have shown endothermic and favorable processes. The results reflect good adsorption process.

Regeneration behavior of chitosan from ionic liquid using water and alcohols as anti-solvents

While ionic liquids (ILs) have been considered as effective and "green" solvents for biopolymer processing, regeneration of IL-dissolved biopolymers could largely impact biopolymer structure and properties. This study indicates that the reconstitution of chitosan structure during regeneration from 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) depends on anti-solvent (water, methanol or ethanol) largely. Irrespective of anti-solvent, the chitosan chemical structure was not varied by dissolution or regeneration. With water, the regenerated chitosan had the highest crystallinity index of 54.18%, followed by those with methanol (35.07%) and ethanol (25.65%). Water as an anti-solvent could promote chitosan chain rearrangement, leading to the formation of an ordered aggregated structure and crystallites. Density functional theory (DFT) simulation indicates that the number of hydrogen bonds formed between anti-solvents and [Emim][OAc] was in the order of water > methanol > ethanol. With water used for regeneration, the aggregation and rearrangement of chitosan chains occurred more easily.

Adsorption and desorption of malachite green by using chitosan-deep eutectic solvents beads

Chitosan-deep eutectic solvent (DES) beads were prepared from chitosan and DESs. The DESs used were choline chloride-urea (DES A) and choline chloride-glycerol (DES B). Both chitosan-DES beads were used to remove malachite green (MG) dye from an aqueous solution. The optimum pH for chitosan-DES A was recorded at pH 8.0 while optimum pH for chitosan-DES B was pH 9.0. The maximum adsorption capacity obtained for chitosan-DES A and chitosan-DES B were 6.54 mg/g and 8.64 mg/g, respectively. The optimum conditions for both chitosan-DES beads to remove MG were 0.08 g of adsorbent and 20 min of agitation time. Five kinetic models were applied to analyse the data and the results showed that the pseudo-second-order and intraparticle diffusion model fitted best with R² > 0.999. For the adsorption capacity, results show that the Freundlich and Langmuir adsorption isotherms fitted well with chitosan-DES A and chitosan-DES B, respectively. The maximum adsorption capacities (q_max) obtained from chitosan-DES A and chitosan-DES B were 1.43 mg/g and 17.86 mg/g, respectively. Desorption indicated good performance in practical applications.

The Application of Modified Natural Polymers in Toxicant Dye Compounds Wastewater: A Review

The utilization of various types of natural and modified polymers for removing toxicant dyes in wastewater generated by the dye industry is reviewed in this article. Dye wastewater contains large amounts of metals, surfactants, and organic matter, which have adverse effects on human health, potentially causing skin diseases and respiratory problems. The removal of dyes from wastewaters through chemical and physical processes has been addressed by many researchers. Currently, the use of natural and modified polymers for the removal of dyes from wastewater is becoming more common. Although modified polymers are preferred for the removal of dyes, due to their biodegradability and non-toxic nature, large amounts of polymers are required, resulting in higher costs. Surface-modified polymers are more effective for the removal of dyes from the wastewater. A survey of 80 recently published papers demonstrates that modified polymers have outstanding dye removal capabilities, and thus have a high applicability in industrial wastewater treatment.

Green synthesis of magnetic 3D bio-adsorbent by corn straw core and chitosan for methylene blue removal

In this work, a novel bio-adsorbent with a unique structure was prepared through one-step crosslinking in the emulsion using corn straw core (CSC), CoFe₂O₄ and chitosan (CS) as raw materials for adsorption of methylene blue (MB). The preparation method of the adsorbent was simple and environmentally friendly. In the adsorbent, the agricultural waste of CSC acted as scaffold and was wrapped with CS. CoFe₂O₄ was embedded in CS, giving magnetic property to the adsorbent, which was beneficial to the separation process. XRD, FTIR, SEM and TEM were utilized to characterize the adsorbent and the factors affecting adsorption removal efficiency were explored. The pseudo-second-order model and the Langmuir model described the adsorption behaviour well. The equilibrium adsorption capacity was 122 mg g^-1 for MB at 298 K. The thermodynamic studies suggested that the adsorption was a spontaneous, exothermic and randomness decrease process. MB loaded on the adsorbent could be desorbed by immersing in dilute acid solution, indicating that this kind of biomass adsorbent can be widely used in the field of adsorption.

Evaluation of Chemical Reactivity and Stability of Ionic Liquids Using Ab Initio and COSMO-RS model

In this study, the quantum chemical descriptors such as highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy, HOMO-LUMO energy gap, electrophilicity index, electronegativity, global hardness and global softness of five cations like 1-butyl-3-methylimidazolium [BMIM]⁺ , 1-pentyl-3-methylimidazolium [PMIM]⁺ , 1-hexyl-3-methylimidazolium [HMIM]⁺ , 1-heptyl-3-methylimidazolium [HEPMIM]⁺ and 1-octyl-3-methylimidazolium [OMIM]⁺ and five anions including butyl sulfate [BUSO₄ ]^- , pentyl sulfate [PENSO₄ ]^- , hexyl sulfate [HEXSO₄ ]^- , heptyl sulfate [HEPSO₄ ]^- , and octyl sulfate [OCTSO₄ ]^- and their combination of 25 ionic liquids (ILs) were predicted using ab initio method. To validate the findings, the sigma profiles and sigma potentials were generated for all the studied ILs. From this study, it was observed that imidazolium-based ILs with smaller anion size is the most favorable IL for the removal of pollutants from their resources and/or effluents. © 2020 Wiley Periodicals, Inc.

Ionic liquid-based water treatment technologies for organic pollutants: Current status and future prospects of ionic liquid mediated technologies

Water scarcity motivated the scientific researcher to develop efficient technologies for the wastewater treatment for its reuse. Ionic liquids have been applied to many industrial and analytical separation processes, but their applications in the wastewater treatment, especially in the removal of organic pollutants, are still not well explored. Potential applications of ionic liquids include solvent extraction, solvent membrane technologies and ionic liquid-modified materials that are mainly used as adsorbents. Aforementioned technologies have been examined for the abatement of phenol, chloro- and nitrophenols, toluene, bisphenol A, phthalates, pesticides, dyes, and pharmaceuticals etc. Present review enlightens the application of different ionic liquids in wastewater treatment and suggests the versatility of ionic liquids in the development of rapid, effective and selective removal processes for the variety of organic pollutants. Implementation of ionic liquid based technologies for wastewater treatment have lots of challenges including the selection of non-hazardous ionic liquids, technological applications, high testing requirements for individual uses and scaling-up of the entire pollutant removal, disposal, and ionic liquid regeneration process. Toxicity assessment of water soluble ionic liquids (ILs) is the major issue due to the widespread application of ILs and hence more exposure of environment by ILs. The development of effective technologies for the recovery/treatment of wastewater contaminated with ILs is necessary from the environmental point of view. Furthermore, the cost factor is the major challenge associated with ionic liquid-based technologies.

Impact of Counter Ions of Cationic Monomers on the Production and Characteristics of Chitosan-Based Hydrogel

Chitosan-based hydrogel has received considerable interests because of its appealing properties and applications in many areas. The primary objective of this work was to produce novel cationic chitosan-based hydrogels via polymerizing chitosan with two cationic monomers of the same structure but with different counter ions [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METMS) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC). Polymerization of chitosan with the cationic monomers performed under the conditions of 50 °C, 5 h, 7 pH, and 2/1 mol/mol monomer/chitosan led to chitosan-METMS and -METAC with the cationic charge densities of 3.22 and 2.88 mequiv/g, respectively. Elemental analysis, gel permeation chromatography, Fourier transform infrared, X-ray diffraction, and differential scanning calorimetry analyses were used to confirm the impact of counter ions of cationic monomers (i.e., polarizability of monomers) on their polymerization performance and the characteristics of induced chitosan-based hydrogels. Also, the results of this work postulated that the counter ions associated with the monomers could dramatically impact the water uptake and swelling properties of the generated chitosan-based hydrogels as well as their performance in adsorbing an anionic dye from a simulated solution.

Selectivity of deproteinization and demineralization using natural deep eutectic solvents for production of insect chitin (Hermetia illucens)

Selectivity of deproteinization and demineralization using natural deep eutectic solvents for preparation of insect chitin (Hermetia illucens) was investigated. The relationships between the pH and pKa values of NADESs and demineralization, deproteinization and crystallinity indexes of the obtained chitin were discussed, respectively. It was found that the acidic NADESs consist of basic hydrogen bond acceptor (HBA) and acidic hydrogen bond donor (HBD), or the alkali NADESs composed of acid HBA and alkali HBD were better for chitin products. After reused for three times, demineralization and deproteinization abilities of NADESs were not significantly decreased. Mechanistic analysis indicated that H⁺ released from HBA or HBD was the main reason for demineralization, whereas intermolecular and intramolecular hydrogen bond in NADESs facilitates the removal of protein. Overall, this report provides a preliminary reference for design of the sustainable NADESs for preparation of chitin from natural resources.