OPTIMIZATION PROCESS FOR THE REMOVAL OF HEAVY METALS FROM AQUEOUS SOLUTION USING GRAPHENE OXIDE NANOSHEETS AND RESPONSE SURFACE METHODOLOGY

Water pollution due to heavy metals has become a critical problem worldwide. In this study, the removal of chromium(III), cadmium and lead by graphene oxide adsorbent was examined. Graphene oxide nanosheets were synthesized through Hummer's method, and their characteristics were examined using FTIR, XRD, and SEM. The effect of independent variables, pH, contact time and initial concentration of solution on the removal efficiency of Cr(III), Cd2+ and Pb2+ was evaluated according to the experimental Box-Behnken Design using response surface methodology (RSM). Applying quadratic model, the adsorption rate of Cd2+ and Pb2+ was obtained as 99% and the adsorption rate of Cr(III) was obtained as 98%. ANOVA was applied as statistical analysis of responses. According to FESEM images, the average size of graphene oxide sheets was 1 to 3 mu m. After optimization by RSM, adsorption capacities of Cr(III), Pb2+ and Cd2+ were found to be 38 mg/g, 136 mg/g and 68 mg/g, respectively. Examination of isotherms suggested that Cd2+ and Cr(III) adsorptions follow Langmuir, and Pb2+ adsorption follows Freundlich isotherm. The results showed that graphene oxide has a good effect on removing Cr(III), Cd2+ and Pb2+ ions from aqueous solutions. pH of the solution and initial concentration of the contaminant had the highest effect on adsorption of the mentioned heavy metals. The results of RSM analysis showed that the obtained data were in agreement with the predicted model.