Sequestration of methylene blue dye using sodium alginate poly(acrylic acid)@ZnO hydrogel nanocomposite: Kinetic, Isotherm, and Thermodynamic Investigations

In this study, a sodium alginate poly(acrylic acid) (SA-poly(AA)) hydrogel and sodium alginate poly(acrylic acid)/zinc oxide (SA-poly(AA)/ZnO) hydrogel nanocomposite (HNC) was synthesized by in situ free-radical polymerization for the sequestration of toxic methylene blue (MB) dye from aqueous solution. The structural properties were analyzed using FTIR, XRD, SEM, TEM, TGA, and DMA The swelling analysis revealed that SA-poly(AA)/ZnO HNC exhibited high water uptake capacity. The kinetics, isotherms, and thermodynamics of adsorption were examined, and results showed that equilibrium data fitted the Langmuir isotherm model, and the adsorption kinetics of MB followed pseudo-second-order model. The maximum adsorption capacity was found to be 1129 mg/g for the SA-poly(AA) hydrogel and 1529.6 mg/g for the SA-poly(AA)/ZnO HNC in 0.25 g/L MB solution at pH 6.0 within 40 min. Thermodynamic parameters for SA-poly(AA) hydrogel and SA-poly(AA)/ZnO HNC substantiated the exothermic and endothermic nature of the adsorption processes, respectively. Moreover, SA-poly(AA)/ZnO HNC presented outstanding reusability with relatively better adsorption efficiencies as compared to SA-poly(AA) hydrogel.