Partially carboxymethylated and partially cross-linked surface of chitosan versus the adsorptive removal of dyes and divalent metal ions

Enhancing Wastewater Depollution: Sustainable Biosorption Using Chemically Modified Chitosan Derivatives for Efficient Removal of Heavy Metals and Dyes

Driven by concerns over polluted industrial wastewater, particularly heavy metals and dyes, this study explores biosorption using chemically cross-link chitosan derivatives as a sustainable and cost-effective depollution method. Chitosan cross-linking employs either water-soluble polymers and agents like glutaraldehyde or copolymerization of hydrophilic monomers with a cross-linker. Chemical cross-linking of polymers has emerged as a promising approach to enhance the wet-strength properties of materials. The chitosan thus extracted, as powder or gel, was used to adsorb heavy metals (lead (Pb2+) and copper (Cu2+)) and dyes (methylene blue (MB) and crystal violet (CV)). Extensive analysis of the physicochemical properties of both the powder and hydrogel adsorbents was conducted using a range of analytical techniques, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM), as well as 1H and 13C nuclear magnetic resonance (NMR). To gain a comprehensive understanding of the sorption process, the effect of contact time, pH, concentration, and temperature was investigated. The adsorption capacity of chitosan powder for Cu(II), Pb(II), methylene blue (MB), and crystal violet (CV) was subsequently determined as follows: 99, 75, 98, and 80%, respectively. In addition, the adsorption capacity of chitosan hydrogel for Cu(II), Pb(II), MB, and CV was as follows: 85, 95, 85, and 98%, respectively. The experimental data obtained were analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The isotherm study revealed that the adsorption equilibrium is well fitted to the Freundlich isotherm (R2 = 0.998), and the sorption capacity of both chitosan powder and hydrogel was found to be exceptionally high (approximately 98%) with the adsorbent favoring multilayer adsorption. Besides, Dubinin has given an indication that the sorption process was dominated by Van der Waals physical forces at all studied temperatures.

Colorimetric and Photothermal Dual-Modal Switching Lateral Flow Immunoassay Based on a Forced Dispersion Prussian Blue Nanocomposite for the Sensitive Detection of Prostate-Specific Antigen

Prostate-specific antigen (PSA) is a key marker for a prostate cancer diagnosis. The low sensitivity of traditional lateral flow immunoassay (LFIA) methods makes them unsuitable for point-of-care testing. Herein, we designed a nanozyme by in situ growth of Prussian blue (PB) within the pores of dendritic mesoporous silica (DMSN). The PB was forcibly dispersed into the pores of DMSN, leading to an increase in exposed active sites. Consequently, the atom utilization is enhanced, resulting in superior peroxidase (POD)-like activity compared to that of cubic PB. Antibody-modified DMSN@PB nanozymes serve as immunological probes in an enzymatic-enhanced colorimetric and photothermal dual-signal LFIA for PSA detection. After systematic optimization, the LFIA based on DMSN@PB successfully achieves a 4-fold amplification of the colorimetric signal within 7 min through catalytic oxidation of the chromogenic substrate by POD-like activity. Moreover, DMSN@PB exhibits an excellent photothermal conversion ability under 808 nm laser irradiation. Accordingly, photothermal signals are introduced to improve the anti-interference ability and sensitivity of LFIA, exhibiting a wide linear range (1-40 ng mL-1) and a low PSA detection limit (0.202 ng mL-1), which satisfies the early detection level of prostate cancer. This research provides a more accurate and reliable visualization analysis methodology for the early diagnosis of prostate cancer.

Comparative Analysis of Hydrogel Adsorption/Desorption with and without Surfactants

In this particular study, a hydrogel known as SAP-1 was synthesized through the grafting of acrylic acid-co-acrylamide onto pullulan, resulting in the creation of Pul-g-Poly (acrylic acid-co-acrylamide). Additionally, a sponge hydrogel named SAP-2 was prepared by incorporating the surfactant sodium dodecyl benzene sulfonate (SDBS) into the hydrogel through free radical solution polymerization. To gain further insight into the composition and properties of the hydrogels, various techniques, such as Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (1H NMR), atomic absorption spectroscopy, and field emission scanning electron microscopy (FE-SEM), were employed. Conversely, the absorption kinetics and the equilibrium capacities of the prepared hydrogels were investigated and analyzed. The outcomes of the investigation indicated that each of the synthesized hydrogels exhibited considerable efficacy as adsorbents for cadmium (II), copper (II), and nickel (II) ions. In particular, SAP-2 gel displayed a remarkable cadmium (II) ion absorption ability, with a rate of 190.72 mg/g. Following closely, SAP-1 gel demonstrated the ability to absorb cadmium (II) ions at a rate of 146.9 mg/g and copper (II) ions at a rate of 154 mg/g. Notably, SAP-2 hydrogel demonstrated the ability to repeat the adsorption-desorption cycles three times for cadmium (II) ions, resulting in absorption capacities of 190.72 mg/g, 100.43 mg/g, and 19.64 mg/g for the first, second, and third cycles, respectively. Thus, based on the abovementioned results, it can be concluded that all the synthesized hydrogels possess promising potential as suitable candidates for the adsorption and desorption of cadmium (II), copper (II), and nickel (II) ions.

Myrica esculenta Leaf Extract-Assisted Green Synthesis of Porous Magnetic Chitosan Composites for Fast Removal of Cd (II) from Water: Kinetics and Thermodynamics of Adsorption

Heavy metal contamination in water resources is a major issue worldwide. Metals released into the environment endanger human health, owing to their persistence and absorption into the food chain. Cadmium is a highly toxic heavy metal, which causes severe health hazards in human beings as well as in animals. To overcome the issue, current research focused on cadmium ion removal from the polluted water by using porous magnetic chitosan composite produced from Kaphal (Myrica esculenta) leaves. The synthesized composite was characterized by BET, XRD, FT-IR, FE-SEM with EDX, and VSM to understand the structural, textural, surface functional, morphological-compositional, and magnetic properties, respectively, that contributed to the adsorption of Cd. The maximum Cd adsorption capacities observed for the Fe3O4 nanoparticles (MNPs) and porous magnetic chitosan (MCS) composite were 290 mg/g and 426 mg/g, respectively. Both the adsorption processes followed second-order kinetics. Batch adsorption studies were carried out to understand the optimum conditions for the fast adsorption process. Both the adsorbents could be regenerated for up to seven cycles without appreciable loss in adsorption capacity. The porous magnetic chitosan composite showed improved adsorption compared to MNPs. The mechanism for cadmium ion adsorption by MNPs and MCS has been postulated. Magnetic-modified chitosan-based composites that exhibit high adsorption efficiency, regeneration, and easy separation from a solution have broad development prospects in various industrial sewage and wastewater treatment fields.

Development of high-capacity surface-engineered MXene composite for heavy metal Cr (VI) removal from industrial wastewater

The substantial quantity of Cr(VI) contaminants in the aqueous atmosphere is a major environmental fear that cannot be overlooked. For the first time, MXene and chitosan-coated polyurethane foam have been employed for wastewater treatment, including heavy metal ions (Cr (VI)) through a fixed-bed column study. It is also the most inexpensive, lightweight, and globally friendly material tested. The Mxene and chitosan-coated polyurethane foam hybrid materials were thoroughly investigated using FTIR (Fourier transform infrared), SEM (scanning electron microscope), XPS (X-ray photoelectron spectroscopy) and XRD (X-ray diffraction). The presence of the rough surface and the pore creation in the Mxene- MX₃@CS₃@PUF should rise its surface area, which is useful to interact the surface-active assembly of MX₃@CS₃@PUF and the Cr(VI) contaminations in the aqueous solution. With the help of the ion exchange mechanism and electrostatic contact, negatively charged MXene hexavalent ions were being adsorbed on the surface. MXene and chitosan have been coated on PUF foam in the form of three different layers, which shows the highest adsorption capacity, where up to ∼70% Cr (VI) was removed in the first 10 min and more than 60% elimination after 3 h when the metal ion concentration was 20 ppm. The electrostatic interaction between the negative charge MXene and the positive charge chitosan on the surface of PUF, which was absent in MX@PUF, is accountable for the high removal efficiency. This was done through a sequence of fixed-bed column studies, which took place in the continuous flowing of wastewater.

Insight into the adsorptive removal of ibuprofen using porous carbonaceous materials: A review

Over the last decade, the removal of pharmaceuticals from aquatic bodies has garnered substantial attention from the scientific community. Ibuprofen (IBP), a non-steroidal anti-inflammatory drug, is released into the environment in pharmaceutical waste as well as medical, hospital, and household effluents. Adsorption technology is a highly efficient approach to reduce the IBP in the aquatic environment, particularly at low IBP concentrations. Due to the exceptional surface properties of carbonaceous materials, they are considered ideal adsorbents for the IBP removal of, with high binding capacity. Given the importance of the topic, the adsorptive removal of IBP from effluent using various carbonaceous adsorbents, including activated carbon, biochar, graphene-based materials, and carbon nanostructures, has been compiled and critically reviewed. Furthermore, the adsorption behavior, binding mechanisms, the most effective parameters, thermodynamics, and regeneration methods as well as the cost analysis were comprehensively reviewed for modified and unmodified carbonaceous adsorbents. The compiled studies on the IBP adsorption shows that the IBP uptake of some carbon-based adsorbents is significantly than that of commercial activated carbons. In the future, much attention is needed for practical utilization and upscaling of the research findings to aid the management and sustainability of water resource.

Preparation of benzenesulfonyl hydrazone modified guar gum and its adsorption properties for dyes and phytotoxicity assays

Herein, a novel environmentally friendly benzenesulfonyl hydrazone modified guar gum (DGH) that carries excellent adsorption performance towards dyes was facilely prepared through oxidation and condensation. The structure, morphology, and physics-chemical of DGH were fully characterized by multiple analysis techniques. The as-prepared adsorbent yielded highly efficient separating performance towards multiple anionic and cation dyes, including CR, MG, and ST with the maximum adsorption capacity of 1065.3839 ± 10.5695, 1256.4467 ± 2.9425, and 1043.8140 ± 0.9789 mg/g at 298.15 K, respectively. The adsorption process well fitted the Langmuir isotherm models and the pseudo-second-order kinetic models. The adsorption thermodynamics revealed that the adsorption of dyes onto DGH was spontaneous and endothermic. The adsorption mechanism indicated that the hydrogen bonding and electrostatic interaction participated in the fast and efficient removal of dyes. Furthermore, the removal efficiency of DGH still remained above 90 % after six adsorption-desorption cycles, and the presence of Na⁺, Ca²⁺, and Mg²⁺ have weakly impacted the removal efficiency of DGH. The phytotoxicity assay was conducted via the germination of mung bean seeds, which confirmed the adsorbent can effectivity decreased the toxicity of dyes. Overall, the modified gum-based multifunctional material has good promising applications for wastewater treatment.

Preparation of manganese-oxides-coated magnetic microcrystalline cellulose via KMnO4 modification: Improving the counts of the acid groups and adsorption efficiency for Pb(II)

Herein, the manganese-oxides-coated magnetic microcrystalline cellulose (MnOx@Fe₃O₄@MCC) was prepared by coprecipitation and subsequently modified with KMnO₄ solution at room temperature, which was in turn applied for the removal of Pb(II) from wastewater. The adsorption properties of Pb(II) on MnOx@Fe₃O₄@MCC were investigated. The kinetics and isothermal data of Pb(II) were described well by the Pseudo-second-order model and the Langmuir isotherm model, respectively. At pH = 5, 318 K, the Langmuir maximum Pb(II) adsorption capacity of MnOx@Fe₃O₄@MCC was 446.43 mg/g, which is higher than many documented bio-based adsorbents. The results of Fourier transform infra-red and X-ray photoelectron spectroscopy indicated that the adsorption mechanisms for Pb(II) mainly involved surface complexation, ion exchange, electrostatic interaction and precipitation. Interestingly, the increased amount of carboxyl group on the surface of microcrystalline cellulose modified by KMnO₄ was one of the important reasons for the high Pb(II) adsorption performance of MnOx@Fe₃O₄@MCC. Furthermore, MnOx@Fe₃O₄@MCC exhibited excellent activity (70.6 %) after five consecutive regeneration cycles, indicating its high stability and reusability. Endorsing to the cost-effectiveness, environmentally friendliness, and reusable nature, MnOx@Fe₃O₄@MCC can be counted as a great alternative contender for the remediation of Pb(II) from industrial wastewater.

“Gamma Irradiation Synthesis of Carboxymethyl Chitosan-Nanoclay Hydrogel for the Removal of Cr(VI) and Pb(II) from Aqueous Media”

Hydrogel composites comprised of N,O carboxymethyl chitosan crosslinked with different weight ratios of acrylic acid and fabricated with nanoclay particle were prepared via gamma irradiation at 25 kGy irradiation dose. The prepared composites were coded as CsAA1Cl, CsAA2Cl and CsAA3Cl based on the weight ratio of acrylic acid to the chitosan derivative. The claimed hydrogels were characterized by FTIR, TGA and XRD. The TGA data implied that the incorporation of clay nanoparticles enhanced the thermal stability of the composites; the decomposition temperature increased up to 500 °C for CsAA3Cl. Three AFM outcomes were used to compare the surface features of the samples; topography, height and surface roughness. The topography data reveals that the nanoclay particles incorporated in CsAA3Cl are intercalated and exfoliated. Then, the optimized sorbent (CsAA3Cl) was investigated as green sorbents for chromium (VI) and lead (II). The data revealed that CsAA3Cl displayed maximum removal performance towards both lead and chromium with removal efficiencies 125 mg/g and 205 mg/g respectively at the optimum application conditions within 90 min only. Also, it was found that the optimum pH value was 9 for chromium and 8 for lead. The data proved that the adsorption of both cations followed pseudo-first order kinetic model. The prepared composites showed acceptable metal uptake capacity at three successive cycles.

Graphical Abstract

Mesoporous crosslinked chitosan-activated clinoptilolite biocomposite for the removal of anionic and cationic dyes

A mesoporous crosslinked chitosan-activated clinoptilolite biocomposite (CS-GA/ACP) was prepared with chitosan (CS) as the substrate and glutaraldehyde (GA) as the crosslinking agent. Structural analysis of the CS-GA/ACP composite beads was performed using FTIR, SEM, and BET techniques. The adsorption properties of the CS-GA/ACP for Congo red (CR) and methylene blue (MB) removal were examined using a batch method. The effects of CS loading, CS-GA/ACP dosages (0.005-0.25 g), pH values (3-11), initial concentrations (30-300 mg/L), contact time (5-120 min), ionic strength, and temperatures (25-65 ℃) on the adsorption of CR and MB on the CS-GA/ACP composite beads were investigated. The pseudo-second-order kinetics could better describe the adsorption process than the pseudo-first-order kinetics, and the Langmuir isotherms model agreed well with the experimental data. The maximum adsorption capacities of the CS-GA/ACP for CR and MB were 180.59 mg/g and 143.67 mg/g at 25 ℃, respectively. The proposed mechanism studies showed that the possible interaction between the adsorbent and dye molecules were Yoshida H-bonding, dipole-dipole H-bonding, electrostatic interaction and n-π interaction. The CS-GA/ACP can be recycled to remove dyes without significant loss of efficacy, and the adsorption of dyes on the CS-GA/ACP is spontaneous endothermic adsorption. Overall, the CS-GA/ACP showed an excellent performance for dyes removal in aqueous solution and could be a practical candidate for industrial applications.

Preparation and performance evaluation of chitosan/polyvinylpyrrolidone/polyvinyl alcohol electrospun nanofiber membrane for heavy metal ions and organic pollutants removal

In this work, a novel electrospun chitosan (CS)/polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) nanofibrous membrane was prepared to remove heavy metal ions and organic pollutants from water. The nanofiber morphologies were adjusted through the optimal electrospinning process parameters. Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations indicated that a well-crosslinked CS/PVP/PVA nanofiber film was formed. Under the optimize conditions, the obtained CS/PVP/PVA nanofiber membranes exhibited porous and uniform nanofibrous structures with an average diameter of 160 nm and a pure water permeability of 4518.91 L·m^-2·h^-1·bar^-1. In addition, the adsorption and separation performance of CS/PVP/PVA nanofiber membranes were evaluated with Cu(II), Ni(II), Cd(II), Pb(II) and Methylene Blue (MB), Malachite Green (MG) as target ions and dyes. The results showed that the retention rate of CS/PVP/PVA nanofiber membranes for Cu(II), Ni(II), Cd(II), Pb(II), MG and MB can reach 94.20%, 90.35%, 83.33%, 80.12%, 84.01% and 69.91%, respectively. The adsorption capacities of Cu(II), Ni(II), Cd(II), Pb(II), MG and MB were 34.79, 25.24, 18.07, 16.05, 17.86 and 13.27 mg g^-1. The adsorption kinetics of heavy metal ions and dyes by the nanofiber membranes can be explained by the Langmuir isotherm model and represented by the pseudo-second-order kinetic mechanism that determined the spontaneous chemisorption process. This study provides a synthetic approach to membranes for the removal of organic and heavy metal micropollutants from water.

Substantial improvement in the adsorption behavior of montmorillonite toward Tartrazine through hexadecylamine impregnation

In the present work, the surface of montmorillonite K10 was successfully modified by hexadecylamine surfactant (Mt-HDA) and its intercalation and characteristics were assessed by XRD, FTIR, SEM, EDX and BET methods. Also, its adsorption performance was systematically examined in the removal of Tartrazine (TZ), as a sulfonated azo dye model, from aqueous phase. Our results showed that the HDA modification remarkably improved the adsorption ability of montmorillonite toward TZ molecules. The highest adsorption efficiency was achieved >98% at the pH range of 4-6 within a fast process (less than 30 min). The maximum adsorption capacity Mt-HDA toward TZ molecules was found to be ~59 mg/g at 45 °C. The kinetic study indicated that the adsorption kinetic follows pseudo-second-order model, which shows the chemisorption process between Mt-HDA and TZ molecules. Besides, the adsorption isotherm showed the monolayer coverage of Mt-HDA surface adsorption sites, which was fitted with the Langmuir isotherm model in an exothermic process. The adsorption mechanism was studied.

The surfactant-ionic liquid bi-functionalization of chitosan beads for their adsorption performance improvement toward Tartrazine

In this study, the ionic liquid (Aliquat-336) and anionic surfactant (cetyltrimethylammonium bromide, CTAB) bi-functionalized chitosan beads were prepared and characterised using different techniques, including FTIR, XRD, SEM, EDS and BET surface area analysis. The characteristic analysis confirmed the successful conjugation of chitosan beads with both surfactant and ionic liquid. The novel fabricated beads (CS-CTAB-AL) were efficiently employed, as a high-performance adsorbent, for the removal of Tartrazine (TZ), an anionic food dye, from polluted water. The optimum adsorption of TZ onto the CS-CTAB-AL was found at 2 g L^-1 of adsorbent in the wide pH range of 4-11, whereas just 45 min was required to reach more than 90% adsorption efficiency in the studied conditions. Also, the adsorption and kinetic studies showed that the experimental data well fitted the pseudo-first-order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity of prepared beads was found to be 45.95 mg g^-1 at 45 °C. The adsorption properties of enabling CS-CTAB-AL conjugation introduced a new type of adsorbents, exploited the combination of ionic liquid and surfactant capabilities for wastewater treatment.

Removal of metal ions using a new magnetic chitosan nano-bio-adsorbent; A powerful approach in water treatment

In this study, a magnetic chitosan/Al₂O₃/Fe₃O₄ (M-Cs) nanocomposite was developed by ethylenediaminetetraacetic acid (EDTA) functionalization to enhance its adsorption behavior for the removal of Cd(II), Cu(II) and Zn(II) metal ions from aqueous solution. The results revealed that the EDTA functionalization of M-Cs increased its adsorption capacity ~9.1, ~5.6 and ~14.3 times toward Cu, Cd and Zn ions. The maximum adsorption capacity followed the order of Cd(II) > Cu(II) > Zn(II) and the maximum adsorption efficiency was achieved at pH of 5.3 with the removal percentage of 99.98, 93.69 and 83.81 %, respectively, for the removal of Cu, Cd and Zn ions. The metal ions adsorption kinetic obeyed pseudo-second-order equation and the Langmuir isothermal was found the most fitted model for their adsorption isothermal experimental data. In addition, the thermodynamic study illustrated that the adsorption process was exothermic and spontaneous in nature.

Hydrothermal synthesis of phosphorylated chitosan and its adsorption performance towards Acid Red 88 dye

Phosphorylated chitosan (P-CS) was successfully synthesized using a facile experimental setup of hydrothermal method that was applied to the adsorption of anionic Acid Red 88 (AR88) from aqueous media. The adsorption process obeyed the pseudo-second-order (PSO) kinetic model. In contrast, the adsorption isotherm conformed to the Langmuir model, with the maximum adsorption capacity (q_m = 230 mg g^-1) at 303 K. Both external and intraparticle diffusion strongly influenced the rate of adsorption. The insights from this study reveal that P-CS could be easily prepared and regenerated for reusability applications. The adsorption mechanism and intermolecular interaction between P-CS and AR 88 were investigated using Fourier transform infrared (FTIR) spectroscopy and calculations via Density Functional Theory (DFT). The key modes of adsorption for the P-CS/AR 88 system are driven by electrostatic attractions, H-bonding, and n-π interactions. The findings herein reveal that P-CS is a promising adsorbent for the removal of anionic dyes such as AR88 or similar pollutants from water.

Functional chitosan/glycidyl methacrylate-based cryogels for efficient removal of cationic and anionic dyes and antibacterial applications

In this study, we constructed a novel family of chitosan-based cryogels with antibacterial activity to treat different types of dye wastewater. Glycidyl methacrylate (GMA) cross-linked chitosan (CS) cryogels functionalized with negatively and positively molecules were prepared via thermo-crosslinking and freeze-drying methods. These chitosan-based cryogels present a well-defined three-dimensional microporous network structure with ultra-light and high porosity, and have high water absorption ability. For CS/GMA/SMA cryogels, 71.20% of Cationic Yellow X-8GL (CY) can be removed, and the process kinetics well corresponded to the Pseudo-second order model and Freundlich model. The quantity and percent of Reactive Yellow B-4RFN (RY) removal by CS/GMA/DMC cryogel reached at 224.6 mg/g and 96.11%, which closely fitted the Pseudo-second order model and Dubinin-Radushkevich isotherm. Furthermore, the chitosan-based cryogels showed antibacterial efficacies against E. coli and S. aureus. The prepared chitosan-based cryogels with adsorption and antibacterial properties have great potential for the remediation of dyeing wastewater.

Chitosan-based hybrid materials for adsorptive removal of dyes and underlying interaction mechanisms

Environmental pollution by dyes molecules has become a subject of intensive research in recent years due to their hazardous effects on human health, organisms, and animals. Effective treatment and removal of dye molecules from the environmental matrices and water sources are of supreme concern. The deployment of cheap, safe, green, sustainable, and eco-friendly materials to remove these pollutants from water is the main challenge during the last decades. Chitosan and its derivatives/composites, as a cheap, easily available, and environmentally friendly sorbent, have attracted increasing attention for the removal of dye molecules. This review article focuses on the application of chitosan and chitosan-based smart adsorbents for the removal of dyes. Recent methods for the preparation of chitosan-based composites and their application in the removal of dyes are discussed. Moreover, the possible mechanisms for the interaction of chitosan and chitosan-based adsorbents with dyes molecules were evaluated. Finally, future prospects of using chitosan as an adsorbent for the removal of dye molecules are directed.

Preparation of poly(sodium 4-styrene sulfonate) grafted magnetic chitosan microspheres for adsorption of cationic dyes

A novel adsorbent with high adsorption capacity to remove cationic dyes was synthesized. Sodium 4-styrene sulfonate (SSS) was grafted polymerization on the surface of magnetic chitosan microspheres via -NH₂/S₂O₈^2- surface initiating system, obtaining MCS-g-PSSS microspheres. The grafted microsphere was characterized by Fourier transforms infrared spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, vibration sample magnetometer and the Brunauer-Emmett-Teller. Cationic dyes were adsorbed by MCS-g-PSSS and methylene blue(MB) was acted as a typical example. The adsorption performance was explored by varying experimental conditions. The results showed the maximal adsorption capacity was 989 mg/g at pH 1 at 25 °C. The pseudo-second order model was found to be applicable for the adsorption kinetics. The adsorption capacity increased with rising temperature and it decreased owing to adding of ions. The adsorption isotherms were the best fitted by Langmuir. MCS-g-PSSS for MB showed high adsorption capacity due to the strong electrostatic interactions and π-π stacking, which was explained by FTIR and XPS and was verified by DFT calculations. The degree of adsorption spontaneity increased with rising the temperature. The grafted MCS-g-PSSS microspheres had high adsorption capacity for various kinds of cationic dyes and excellent for remove MB in the aqueous solution.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

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.

Robust cellulose-based composite adsorption membrane for heavy metal removal

Adsorptive membranes offer an effective mode to remove heavy metal ions from contaminated water, due to the synergies made possible by low-cost, high-affinity adsorbents and highly scalable filtration in one system. However, the development of adsorptive membranes is hampered by their instability in the aqueous phase and low binding affinity with a broad spectrum of heavy metals in a reasonable flux. Herein, a regenerated cellulose support membrane is strongly grafted with stable and covalent-bonded polyelectrolyte active layers synthesized by a reactive layer-by-layer (LBL) assembly method. The LBL assembled layers have been successfully tested by scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photo-electron spectroscopy. The covalent bonding provides the membrane with long-term stability and a tunable water flux compared to a membrane assembled by electrostatic bonding. The maximum adsorption capacity of the membrane active layers can reach up to 194 mg/g, showing more efficient adsorption at lower heavy metal concentration and higher pH value of feed solution. The membrane can remove multiple ions, such as Cu, Pb, and Cd, by adsorption and is easy to be regenerated and recovered. The strong covalent bonding can extend the membrane lifetime in water purification to remove multiple heavy metals at high efficiency.

Green Synthesis of A Novel MXene–CS Composite Applied in Treatment of Cr(VI) Contaminated Aqueous Solution

The considerable amount of Cr(VI) pollutants in the aqueous environment is a significant environmental concern that cannot be ignored. A series of novel Mxene–CS inorganic–organic composite nanomaterials synthesized by using the solution reaction method was applied to treat the Cr(VI) contaminated water. The Mxene–CS composites were characterized through SEM (scanning electron microscope), XRD (X–ray diffraction), XPS (X–ray photoelectron spectroscopy), and FTIR (Fourier transform infrared). The XRD patterns (observed at 2θ of 18.1°, 35.8°, 41.5°, and 60.1°) and the FT–IR spectra (-NH2 group for 1635 and 1517 cm−1, and -OH group for 3482 cm−1) illustrated that CS was successfully loaded on the Mxene. The effects of solution pH, the dosage of Mxene–CS, and duration time on the adsorption of Cr(VI) by synthesized Mxene–CS were investigated. The removal efficiency of Cr(VI) was increased from 12.9% to 40.5% with Mxene–CS dosage ranging from 0.02 to 0.12 g/L. The adsorption process could be well fitted by the pseudo–second–order kinetics model, indicating chemisorption occurred. The Langmuir isotherm model could be better to describe the process with a maximum adsorption capacity of 43.1 mg/g. The prepared novel Mxene–CS composite was considered as an alternative for adsorption of heavy metals from wastewater.

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.

Polydopamine-assisted grafting of chitosan on porous poly (L-lactic acid) electrospun membranes for adsorption of heavy metal ions

In this study, a versatile method for the manufacturing of chitosan-grafted porous poly (L-lactic acid) (P-PLLA) nanofibrous membrane by using polydopamine (PDA) as an intermediate layer has been developed. P-PLLA fibres were electrospun and collected as nano/micro fibrous membranes. Highly porous fibres could serve as a substrate for chitosan to adsorb heavy metal ions. Moreover, PDA was used to modify P-PLLA surface to increase the coating uniformity and stability of chitosan. Due to the very high surface area of P-PLLA membranes and abundant amine groups of both PDA and chitosan, the fabricated membranes were utilized as adsorbent for removal of copper (Cu²⁺) ions from the wastewater. The adsorption capability of Cu²⁺ ions was examined with respect to the PDA polymerization times, pH, initial metal ion concentration and time. Finally, the equilibrium adsorption data of chitosan-grafted membranes fitted well with the Langmuir isotherm with the maximum adsorption capacity of 270.27 mg/g.

Removal of Sr(II) from water with highly-elastic carboxymethyl chitosan gel

A carboxymethyl chitosan (O-CMC) gel was prepared by crosslinking and functionalizing with ethylenediaminetetraacetic acid (EDTA) using a one-pot reaction under mild conditions. Structural characterizations have revealed that the prepared O-CMC/EDTA gel has 3D porous structure with abundant carboxyl groups distributed in the pores. The prepared O-CMC/EDTA gel was used to adsorb Sr(II) ions in water while X-ray photoelectron spectroscopy (XPS) was used to explore the adsorption mechanism. In order to analyze the adsorption process, we performed the adsorption kinetics and isotherms. The results show that the maximum adsorption capacity of O-CMC/EDTA for Sr (II) ions is about 105.81 mg/g at pH = 7. Notably, it exhibited fairly high compression elasticity due to multiple hydrogen bonds in the network. The showed no deformation after 30 continuous compression cycles. The ratio of O-CMC:EDTA significantly influences the adsorption property by affecting the crosslinking degree as well as the number of active sites. The high adsorption capacity, elasticity, and reusability have demonstrated that the prepared material is an effective and promising adsorbent for Sr(II) removal.

Recyclable magnetic chitosan microspheres with good ability of removing cationic dyes from aqueous solutions

Sr_3.8Fe_25.7O_70.4-chitosan magnetic microparticles (Sr_3.8Fe_25.7O_70.4-CMNs) with a core-shell structure were synthesized, characterized and applied for the removal of two model cationic dyes. The results showed that these magnetic microparticles possess fast adsorption rate and high adsorption efficiency for both crystal violet (CV) and basic red 9 (BR9) at a temperature ranging 30 °C to 40 °C and suitable pH range (pH ≥ 7). The maximum removal efficiency for CV and BR9 attained to 94.5% and 97.5% in 30 min, which was significantly faster and higher than that of chitosan (<50% in 60 min) (P<0.01). And its maximum adsorption capacity for CV and BR9 reached 29.46 mg/g and 32.16 mg/g, respectively. The adsorption process of Sr_3.8Fe_25.7O_70.4-CMNs follows the Langmuir isotherm with a high correlation coefficient (R² > 0.97) and the pseudo-second-order model. Additionally, the synthesized Sr_3.8Fe_25.7O_70.4-CMNs were easy to regeneration and reuse, and the removal rate remained above 90% after 5 recycle times. This study would provide a new more environmental friendly material and method for the treatment of wastewater containing toxic dyes.

Uptake of Pb(II) Ions from Simulated Aqueous Solution via Nanochitosan

In this work, nanochitosan (NC) was prepared through ionic gelation using low molecular weight chitosan and maleic acid (MA). The synthesized NC was characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). During preparation, the particle size of the material depended on parameters such as concentration of chitosan and pH of the aqueous solution. After controlling the mentioned parameters, NC smaller than 100 nm was prepared. The chitosan and prepared NC were employed for the adsorption of Pb(II) from an aqueous solution in the form of a batch system. Among the sorption parameters, pH showed the strongest effect on the sorption process and removal of the maximum number of Pb(II) ions was obtained at pH value of 6. Pseudo-first-order and pseudo-second-order models were used to track the kinetics of the adsorption process. Langmuir and Freundlich’s isotherms were subjected to the absorption data to evaluate absorption capacity. NC proved to be an excellent adsorbent with a remarkable capacity to eliminate Pb(II) ions from aqueous solutions at multiple concentrations. The NC also showed better performance with a comparatively easier preparation process than in other reported work.