Adsorptive removal of multi-azo dye from aqueous phase using a semi-IPN superabsorbent chitosan-starch hydrogel

• Semi-IPN superabsorbent chitosan-starch hydrogel has been synthesized via chemical crosslinking.
• Swelling kinetic investigations were performed to examine the water retention capacity.
• Batch sorption studies were carried out to evaluate the performance of the hydrogel.
• Isotherm, kinetics and thermodynamic study was applied to best describe the sorption process.
• Sorption–desorption analyses were performed to demonstrate the reusability of the hydrogel.

This article reports the efficient removal of Direct Red 80 (DR80) dye from aqueous phase using a semi-interpenetrating network (IPN) superabsorbent chitosan-starch (ChS) hydrogel. In the present investigation, the influence of initial pH, ChS dose, initial dye concentration, temperature and effect of salts on the sorption of DR80 dye was evaluated. A maximum swelling capacity of 15 g/g was determined for ChS hydrogel. The sorption equilibrium data demonstrated good agreement with Freundlich isotherm. The sorption process best fitted the pseudo-second order kinetic model. Maximum uptake capacity of the hydrogel was determined as 312.77 mg/g. The mean sorption energy (E = 11.34–14.9 kJ/mol) demonstrated that DR80 sorption was mainly chemisorption. The temperature dependence data revealed the sorption process was spontaneous, endothermic and favourable at higher temperature based on the enthalpy (ΔH° = +83.68 kJ/mol) value obtained. Boyd model confirmed intraparticle diffusion was the limiting step for DR80 uptake. In addition, sorption/desorption studies were performed to investigate the reusability of ChS hydrogel which demonstrated significant sorption for four consecutive cycles.

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