Optimization of lead (II) and chromium (VI) adsorption using graphene oxide/ZnO/chitosan nanocomposite by response surface methodology

In this study graphene oxide (GO) synthesized by modified Hummer's method. Surface of GO was modified with biopolymer chitosan (CS) and then grafted with the ZnO nanoparticles. GO/ZnO/CS was investigated as adsorbent for the elimination of Pb (II) and Cr (VI) ions from aqueous solutions. The Box-Behnken Design (BBD) within the framework of response surface methodology (RSM) was employed to optimize different parameters, which including pH of the metal solution, initial metal ions concentration and contact time. The quadratic model was best fitted for characterizing the influence of adsorption parameters on adsorption capacity (qe) and percent removal (% R), exhibiting strong statistical support with R2 values and p-values. To explore the interactions between these parameters and determine the ideal conditions for removing Pb (II) and Cr (VI) ions, we employed second-order polynomial equations, performed analysis of variance (ANOVA), and generated three-dimensional surface plots. The optimum parameters for Pb (II) ions were pH 5, initial concentration 60 mg/L and 120 min contact time, with 110.88 mg/g adsorption capacity and 92.4 % removal efficiency. For Cr (VI) ions 84.5 mg/g adsorption capacity and 70.5 % removal was achieved at pH 2, 60 mg/L metal concentration at 112 min contact time.