Adsorption of Lead and Nickel Ions by Semi-interpenetrating Network Hydrogel Based on Wheat Straw Cellulose: Kinetics, Equilibrium, and Thermodynamics

Abstract

A wheat straw cellulose-g-poly (potassium acrylate)/polyvinyl alcohol (WSC-g-PKA/PVA) semi-interpenetrating networks (semi-IPNs) hydrogel was synthesized by graft copolymerization and used for Pb(II) and Ni(II) adsorption from aqueous solution. The effects of solution pH value, contact time, initial concentration, and temperature on adsorption were investigated. The adsorption process was described by the adsorption models of Langmuir, Freundlich, and Dubinin–Radushkevic. The adsorption kinetics was analyzed using pseudo first- and second-order kinetic models, intraparticle diffusion model, and mass transfer model. Comparison analysis of linear least square method and nonlinear method for estimating the kinetics and isotherm parameters were also made. The results showed that nonlinear regression analysis could be a better way to obtain the model parameters. The pseudo second-order kinetic model was more suitable for describing the whole adsorption process, and both intraparticle diffusion with three steps and mass transfer were taking place in the adsorption. The equilibrium adsorption isotherm was closely fitted with both the Langmuir and Dubinin–Radushkevic model. The changes of free energy, enthalpy, and entropy of adsorption were evaluated for the adsorption of Pb(II) and Ni(II) by WSC-g-PKA/PVA, suggesting that the adsorption process was physical, spontaneous and endothermic.