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Synergistic use of superabsorbent hydrogels has vital contribution to the daily life. This work gives an account of a facile approach to synthesize superabsorbent hydrogels based on Moringa oleifera gum and polyvinyl alcohol cross-linked with borax. Fourier transform infrared, X-ray diffraction, and scanning electron microscopy were employed to characterize the structure, crystallinity, and surface morphologies of the samples. The cross-link density, swelling ratio, reswelling, water retention properties, and salt sensitivity of hydrogels were investigated. Reaction parameters for the hydrogel synthesis were optimized on the basis of water absorbency, and the reaction condition of greater water absorbency after 12 h at room temperature was taken as an ideal condition. Optimum conditions were obtained as [poly(vinyl alcohol) PVA] = 10% (w/v) and [borax] = 1.05 × 10-3 mol/L. Under the optimized conditions, the maximum swelling ratio of MOG/PVA hydrogel reached 1163 g/g in deionized water and 290 g/g in 0.9 wt % NaCl solution. Furthermore, all hydrogels exhibited salt sensitivity and excellent water retention capacity under the high temperature state and displayed smart swelling behaviors in physiological saline solutions. The water absorbency, reusability, and salt sensitivity of the hydrogels give these smart polymer wide promising applications.

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[This corrects the article DOI: 10.1039/C9RA00356H.].

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A new adsorbent derived from the naturally occurring biopolymers, chitosan (CS) and carboxymethyl cellulose (CMC) was prepared by cross-linking them using EDTA. EDTA having high affinity for metal ions can be used to enhance the chelation properties of the adsorbent enormously. The product obtained (chitosan-EDTA-CMC, CSECM) was characterized by different techniques: FTIR, XRD, SEM/EDAX, TGA, and XPS. The parameters for evaluation of the adsorption properties for removal of Cu(II) ions from the aqueous solution were determined using the batch adsorption method by studying the effect of pH, contact time, initial ion concentration, and temperature on adsorption. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models were applied to study the kinetics of the adsorption process, whereas Langmuir, Freundlich, Temkin, and D-R models were applied to evaluate the thermodynamics of the adsorption process. The kinetic adsorption parameters were in best agreement with the pseudo-second-order model, while thermodynamic parameters best fitted to the Langmuir isotherm at different temperatures for adsorption of Cu(II) ions from aqueous solution with a maximum adsorption capacity of 142.95 mg/g at pH 5.5. CSECM showed excellent regeneration capability and recovery of the Cu(II) ion up to five cycles without the loss of the adsorption efficiency, which is the best characteristic to select the appropriate choice of the adsorbent. The adsorbent was also employed in batch experiments to evaluate the adsorption of hardness, producing common metal ions in single and real wastewater solutions.

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The prospective uses of natural gum polysaccharides in various aspects of food, water, energy, biotechnology, environment and medicine industries, have garnered a great deal of attention recently. Natural gums have gained widespread attention due to their availability, low cost, structural diversity and remarkable properties as 'green' bio-based renewable materials. Natural gums are obtainable as natural polysaccharides from various tree genera possessing exceptional properties, including their renewable, biocompatible, biodegradable, and non-toxic nature and their ability to undergo easy chemical modifications. Hydrogels based on natural gums offer several valuable properties when equated to synthetic origin. The fundamental objective of this review is to compile different strategies for the preparation of hydrogels based on several important commercially available gums (arabic, guar, gellan, ghatti, karaya, kondagogu, konjac, locust bean tamarind, tragacanth, tara and xanthan) for the greener synthesis and stabilization of metal/metal oxide NPs, production of electrospun fibers, water purification, drug delivery, tissue engineering, agriculture and for antimicrobial and biomedical applications.

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In this work, a simple method was developed for hydrogel preparation from 1,5-Diphenylcarbazide (DPC) and chitosan (CS) through Diazotization reaction of CS as a selective adsorbent (DPCCS) for Cu(II) ions. CS was treated with sodium nitrate and subsequent crosslinking reaction with DPC for the preparation of DPCCS. Different techniques were used for characterization of DPCCS. Various parameters such as, temperature, pH, and concentration of Cu(II) were used for adsorption studies. Kinetics of Cu(II) ion on DPCCS follows the Pseudo second order and equilibrium of adsorption occurs in short time. The equilibrium data was best fitted with the Langmuir isotherm and the maximum adsorption capacity of DPCCS was 185.505 mg g-1. Thermodynamic parameters ΔG°, ΔH° and ΔS° suggested that the adsorption of Cu(II) ion on the surfaces of DPCCS was spontaneous, endothermic and randomness of Cu(II) ion in the solution was enhanced respectively. Regeneration of DPCCS and Cu(II) ion recovery were studied up to five cycles without the lost of the adsorption capacity.

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A one pot approach has been explored to synthesize crosslinked beads from chitosan (CS) and carboxymethyl cellulose (CM) using arginine (ag) as a crosslinker. The synthesized beads were characterized by FTIR, SEM, EDX, XRD, TGA and XPS analysis. The results showed that CS and CM were crosslinked successfully and the obtained material (beads) was analyzed for adsorption of Cd(ii) and Pb(ii) by using batch adsorption experiments; parameters such as temperature, contact time, pH and initial ion concentration were studied. Different kinetic and thermodynamic models were used to check the best fit of the adsorption data. The results revealed that the kinetics data of the adsorption of Pb(ii) and Cd(ii) ions shows the best fit with the pseudo second order model whereas the thermodynamics data shows the best fit with the Langmuir isotherm with maximum adsorption capacities of 182.5 mg g-1 and 168.5 mg g-1 for Pb(ii) ions Cd(ii) ions, respectively. For the recovery and the regeneration after the one use of the beads, several adsorption-desorption cycles were carried out to check the reusability and recovery of both the metal ion and the adsorbent without the loss of maximum adsorption efficiency.

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The polyfunctional nature of chitosan enables its application not only in polymer technology but also shows their importance in the field of nanotechnology for the fabrication of the wide spectrum of functional nanomaterials in biomedical field. Chitosan is a poly aminosaccharide with appealing structure composed of ß-(1→4)-linked D-glucosamine (deacetylated unit) and N-acetyl-d-glucosamine (acetylated unit). It has various functional groups that enriches for various properties such as antibacterial, mucoadhasive, nontoxic, biodegradable, biocompatible. With the advancement of material technologies, chitosan is being chemically modified into self-assembled nanocomposites for advanced biomedical applications. This review article demonstrate the various schemes for the preparation of chitosan nanocomposites from different functional material, focusing on their application specifically in tissue engineering, drug and gene delivery, wound healing and bioimaging.

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The polyfunctional chitosan can act as the biological macromolecule ligand not only for the adsorption and the recovery of metal ions from an aqueous media, but also for the fabrication of novel adsorbents which shows selectivity and better adsorption properties. The unmodified chitosan itself, a single cationic polysaccharide, has hydroxyl and amine groups carrying complex properties with the metal ions. In addition, the selectivity of metal ions, the adsorption efficiency and adsorption capacity of the adsorbent can be modified chemically. This review covers the synthetic strategies of chitosan towards the synthesis of hetero-chitosan based adsorbents via chemical modifications in past two decades. It also includes how chemical modification influences the metal adsorption with N, O, S and P containing chitosan derivatives. Hope this review article provides an opportunity for researchers in the future to explore the potential of chitosan as an adsorbent for removal of metal ions from wastewater.

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A modified biomacromolecule, chitosan-thiosemicarbazide framework (TSCS) as an adsorbent for Cu(II) was prepared from dialdehyde chitosan through condensation reaction with thiosemicarbazide, stabilized by the reduction reaction with sodium borohydride. TSCS was characterized by means of FT-IR and XPS. Surface morphologies were studied by FESEM and BET, which revealed the highly macro porous structure. The thermal analyses was done through TGA showing much stable chemical configuration at about ≥400°C. The experimental equilibrium data was evaluated by Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. The Langmuir adsorption model was best fitted with experimental value, suggests the existence of monolayer coverage of adsorbed molecules with a maxima of 142.85mgg-1. The kinetic data was analyzed using pseudo-first-order, pseudo-second-order and intraparticle diffusion models and the pseudo-second-order kinetics were found for all the concentrations. The calculated thermodynamic parameters such as ΔGo, ΔH and ΔS were -2.33kJmol-1, 570.40Jmol-1 and 9.75Jmol-1K-1 respectively signifies the adsorption of Cu(II) onto TSCS is endothermic, spontaneous and a process of physisorption. The regeneration efficiency of the TSCS as an adsorbent was found to be ≥90-95% using 0.1M EDTA.

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