A response surface modelling study for sorption of Cu, Ni, Zn and Cd using chemically modified poly(vinylpyrrolidone) and poly(vinylpyrrolidone--methylacrylate) hydrogels

Abstract

In this present study, response surface methodology was applied for the optimization and evaluation of different heavy-metal sorption processes. Poly(vinylpyrrolidone) and poly(vinylpyrrolidone- co -methylacrylate) hydrogels were used as pH-responsive adsorbents to investigate their efficiency in the uptake of Cu 2+ , Ni 2+ , Zn 2+ and Cd 2+ metal ions from aqueous solution in a batch reactor system. The effect of operational parameters such as initial pH and contact time were studied using central composite design. Analysis of variance depicted the central composite design model was significant for Cu 2+ , Ni 2+ , Zn 2+ and Cd 2+ metal ions removal by the investigated hydrogels. A comparison between the model results and experimental data showed that poly(vinylpyrrolidone- co -methylacrylate) possessed higher metal ions binding affinity than poly(vinylpyrrolidone) hydrogel. The heavy-metal ions sorption kinetic well fitted the pseudo second-order kinetic model. Evaluation of the intraparticle diffusion model suggested the sorption process occurred in two phases: surface sorption and intraparticle diffusion. Isothermic results revealed that Freundlich and Temkin isotherms best described the adsorbate–adsorbent interactions. Maximum sorption capacities were observed for Cu 2+ ion and were determined as 86.66 mg/g and 98.53 mg/g for poly(vinylpyrrolidone) and poly(vinylpyrrolidone- co -methylacrylate) hydrogels, respectively.