Adsorption of Cd²⁺ and Zn²⁺ on Carboxylated Polyvinyl Alcohol

Abstract

In this study, vinyl acetate (VAc) and acrylic acid (AA) was first copolymerized in methanol to prepare the copolymer of poly(VAc‐co‐AA). Then poly(VAc‐co‐AA) was modified through alcoholysis reaction to obtain a carboxyl modified polyvinyl alcohol (carboxyl modified PVA). The carboxyl modified polyvinyl alcohol was first used for the adsorption of heavy metal ions. The structure of the carboxyl modified polyvinyl alcohol was characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray Diffraction (XRD). The effect of pH, contact time and metal ion concentration on the adsorption were investigated. The optimum pH value was found out to be 6 for Zn2+ and 7 for Cd2+, respectively. The adsorption capacity of Cd2+ and Zn2+ increased rapidly in the first 36 h contact time and then leveled off. The adsorption capacity of Cd2+ and Zn2+ increased gradually with equilibrium concentration Ce up to 150 mg/L in the solution. The adsorption process obeyed the pseudo second‐order kinetics and Langmuir adsorption model. The highest metal uptake for Cd2+ and Zn2+ were 52.41 and 49.98 mg/g, respectively. In all adsorption processes, the enthalpy change (ΔH) and free energy change (ΔG) were negative, implying that the adsorption process was exothermic and spontaneous.