Highly efficient removal of cadmium from aqueous solution using polymer-stabilized zero-valent iron nanoparticles: equilibrium, kinetic and thermodynamic studies

Abstract

Bare zero-valent iron nanoparticles (bare-ZVIN) have a great tendency to aggregate, which drops their reactivity with pollutants. To address this issue, polyvinylpyrrolidone stabilized-ZVIN (PVP-ZVIN) was synthesized and used for the removal of Cd2+ from aqueous solution in a batch system. The effects of operation conditions such as the pH of aqueous solution (2-8), reaction time (0-120), adsorbent concentration (1-6 g L-1) and the initial Cd2+ concentration (10-60 mg L-1) on the removal efficiency of Cd2+ were studied. Furthermore, adsorption isotherm, kinetic and thermodynamic studies of Cd2+ removal were performed. Results of studies revealed that PVP could apparently enhance the colloidal stability of ZVIN and the removal efficiency of Cd2+. In addition, increasing ZVINs concentration from 1 to 6 g L-1 enhanced Cd2+ removal efficiency while a sharp decrease was observed in Cd2+ removal efficiency by increasing the initial concentration of Cd2+ from 10 to 60 mg L-1. The experimental results showed that maximum Cd2+ adsorption was obtained at pH 6 and 20 min contact time. Moreover, the experimental adsorption of isotherm and kinetic data were completely followed the Freundlich isotherm model and Pseudo first-order kinetic model with maximum coefficients of determination (R2) of >0.98 and >0.99, respectively. Also, the obtained results of thermodynamic studies implied the influence of endothermic and spontaneous nature of Cd2+ adsorption onto ZVINs surfaces, at temperature range of 293-303 K. The findings of this study demonstrated that ZVINs could be applied as applicable adsorbents to remove Cd2+ from aqueous solutions.