Concurrent reduction-adsorption of chromium using m-phenylenediamine-modified magnetic chitosan: kinetics, isotherm, and mechanism

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

A Comprehensive Review of the Current Progress of Chromium Removal Methods from Aqueous Solution

Chromium (Cr) exists in aqueous solution as trivalent (Cr³⁺) and hexavalent (Cr⁶⁺) forms. Cr³⁺ is an essential trace element while Cr⁶⁺ is a dangerous and carcinogenic element, which is of great concern globally due to its extensive applications in various industrial processes such as textiles, manufacturing of inks, dyes, paints, and pigments, electroplating, stainless steel, leather, tanning, and wood preservation, among others. Cr³⁺ in wastewater can be transformed into Cr⁶⁺ when it enters the environment. Therefore, research on Cr remediation from water has attracted much attention recently. A number of methods such as adsorption, electrochemical treatment, physico-chemical methods, biological removal, and membrane filtration have been devised for efficient Cr removal from water. This review comprehensively demonstrated the Cr removal technologies in the literature to date. The advantages and disadvantages of Cr removal methods were also described. Future research directions are suggested and provide the application of adsorbents for Cr removal from waters.

Eco-friendly adsorbents based on abietic acid, boswellic acid, and chitosan/magnetite for removing waste oil from the surface of the water

Petroleum oil leakage and industrial oily waste on the water surface are sustainable pollutions. The removal process by eco-friendly adsorbents is a critical challenge. It also requires sustainable treatment. The natural hydrophobic material such as abietic acid, boswellic acid, and chitosan was added to magnetite nanoparticles with different concentrations of 10, 15, and 20% on its surface. The magnetite acquires partially hydrophobic properties. The prepared natural adsorbents were analyzed by employing wide-angle X-ray diffraction (WAXD), vibrating sample magnetometer (VSM), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), particle size and zeta potential, and contact angle measurements. Chitosan adsorbs at the outer surface of magnetite nanoparticles while boswellic and abietic absorb in bulk. All prepared adsorbents are effective in adsorbing waste oil from the water surface. The contact angle of MB20 (magnetite/20 percent boswellic) is greater than that of MA20 and MC20 (magnetite/20% abietic or chitosan, respectively), indicating that it has more hydrophobic characteristics. The oil removal efficiency and adsorption capacity of MB20 are the highest values 57.6%, and 24 g/g, respectively. All eco-friendly adsorbents are nontoxic with low-cost production and are used many times.

Enhanced sequestration of Cr(VI) onto plant extract anchored on carbon-coated aluminium oxide composite

Aluminium oxide (ALU) and carbon-coated aluminium oxide modified with Kigelia africana leaf extract (KECA) were employed for the removal of toxic hexavalent chromium (Cr(VI)) from the aqueous phase. The adsorbents (ALU and KECA) were characterized by TGA, BET, FESEM, FTIR, Raman and XRD spectroscopic techniques. The potential of KECA and ALU to remove Cr(VI) from simulated wastewater was optimum at pH 2, sorbent dose of 0.025 g and a contact time of 200 min. Meanwhile, the uptake capacity of KECA and ALU was enhanced with an increase in sorbent dose, contact time and initial Cr(VI) concentration. The uptake of Cr(VI) onto the adsorbents ALU and KECA was kinetically best described by the pseudo-second-order and Elovich models, respectively. Besides, the equilibrium data acquired for ALU and KECA obeyed Freundlich and Langmuir isotherm models, respectively. ALU and KECA were observed to have optimum adsorption capacity of 56.45 mg g^-1 and 258.2 mg g^-1, respectively. The adsorption of Cr(VI) onto the adsorbents was thermodynamically feasible, endothermic in nature and entropy-driven. A decrease in efficiency was observed on regeneration of the absorbents, thus limiting their reusability. However, the presence of functional groups with reducing property in the extract of Kigelia africana leaves was noticed to enhance the capacity of the adsorbent to abstract Cr(VI) from the solution. Hence, this study demonstrates the potential of KECA to sequestrate Cr(VI) from an aqueous solution and provides a reference for its application to the treatment of Cr(VI)-laden industrial wastewater.

Polysaccharide-based (nano)materials for Cr(VI) removal

Chromium is a potentially poisonous and carcinogenic species, which originates from human activities and various industries such as leather, steel, iron, and electroplating industries. Chromium is present in various oxidation states, among which hexavalent chromium (Cr(VI)) is highly toxic as a natural contaminant. Therefore, chromium, particularly Cr(VI), must be eliminated from the environment, soil, and water to overcome significant problems due to its accumulation in the environment. There are different approaches such as adsorption, ion exchange, photocatalytic reduction, etc. for removing Cr(VI) from the environment. By converting Cr(VI) to Cr(III), its toxicity is reduced. Cr(III) is essential for the human diet, even in small amounts. Today, biopolymers such as alginate, cellulose, gum, pectin, starch, chitin, and chitosan have received much attention for the removal of environmental pollutants. Biopolymers, particularly polysaccharides, are very useful compounds due to their OH and NH₂ functional groups and some advantages such as biodegradability, biocompatibility, and accessibility. Therefore, they can be widely applied in catalytic applications and as efficient adsorbents for the removal of toxic compounds from the environment. This review briefly investigates the application of polysaccharide-based (nano)materials for efficient Cr(VI) removal from the environment using adsorption/reduction, photocatalytic, and chemical reduction mechanisms.

Biosorption of glycerol impurities from biodiesel production onto electrospun chitosan-based nanofibers: equilibrium and thermodynamic evaluations

The increase in biodiesel production has been leading to an excess amount of crude glycerol and, consequently, serious environmental issues. For this reason, electrospun chitosan-based nanofibers (CB-EN), composed by chitosan and poly(ethylene oxide) (PEO), were synthesized to apply in the biosorption of impurities from industrial glycerol. To evaluate the biosorption efficiency, the chitosan-based nanofiber was compared to other chitosan-based biosorbents (chitosan biopolymeric film and chitosan powder). The equilibrium and thermodynamic studies were successfully performed to comprehend the interaction mechanisms through the biosorption of glycerol pigments onto electrospun chitosan-based nanofibers. The temperature effect was evaluated by experimental equilibrium curves. Freundlich and BET models were used to estimate isotherm parameters. Gibbs free energy change, enthalpy change, entropy change, and isosteric heat of biosorption were quantified. The equilibrium curves showed that the highest equilibrium relative adsorption (340.7 g^-1) was reached at 60 °C. The BET model was the most suitable to represent the equilibrium behavior. The thermodynamic parameters indicated that the biosorption was spontaneous, exothermic, random, and energetic heterogeneous. Therefore, this work developed a green and efficient alternative to refine industrial glycerol. Graphical abstract Note: This data is mandatory. Please provide.

Adsorption and removal of chromium (VI) contained in aqueous solutions using a chitosan-based hydrogel

The aim of this work was to study the adsorption and removal of chromium (VI) ions contained in aqueous solutions using a chitosan-based hydrogel synthesized via chemical crosslinking of radical chitosan, polyacrylic acid, and N,N'-methylenebisacrylamide. Fourier-transform infrared spectroscopy confirmed the hydrogel synthesis and presence of reactive functional groups for the adsorption of chromium (VI) ions. The chromium (VI) adsorption mechanism was evaluated using non-linear Langmuir, Freundlich, Redlich-Peterson, and Sips isotherms, with the best fit found by the non-linear Redlich-Peterson isotherm. The maximum chromium (VI) adsorption capacities of the chitosan-based hydrogel were 73.14 and 93.03 mg metal per g dried hydrogel, according to the non-linear Langmuir and Sips isotherm models, respectively. The best kinetic fit was found with the pseudo-nth order kinetic model. The chromium (VI) removal percentage at pH 4.5 and 100 mg L^-1 initial metal concentration was 94.72%. The results obtained in this contribution can be useful for future works involving scale-up of a water and wastewater treatment method from a pilot plant to full-scale plant.

Concurrent adsorption and micro-electrolysis of Cr(VI) by nanoscale zerovalent iron/biochar/Ca-alginate composite

This study introduced a new approach for simultaneously enhancing Cr(VI) removal performance and mitigating release of dissolved Fe during nanoscale zero-valent iron (nZVI)-mediated reactions. After entrapping nZVI-impregnated biochar (BC) in the matrix of calcium-alginate (CA) bead, the physicochemical characterization of nZVI/BC/CA composites revealed that nZVI/BC particles were embedded inside CA having a spherical shape and several cracks on its outer layer. The multi-functionality of nZVI/BC/CA composites consisting of reductant (nZVI), porous adsorbent (BC), and external screening layer (CA) enhanced the removal of Cr(VI) with the maximum adsorption capacity of 86.4 mg/g (based on the Langmuir isotherm) and little release of dissolved Fe. With the XPS analysis and fitting results of kinetics (pseudo second order) and isotherms (Redlich-Peterson model), plausible removal mechanisms of Cr(VI) were simultaneous adsorption and micro-electrolysis reactions by nZVI/BC/CA composites. The practical applicability of nZVI/BC/CA composites was further demonstrated through the fixed-bed column experiments. These results provide new insights into the design of high-performance engineered biochar for wastewater treatment.