Heavy metals adsorption onto graphene oxide: effect of mixed systems anresponse surface methodology modeling

Competitive adsorption based removal of aqueous cadmium, chromium, and lead from tertiary mixed systems, was investigated using graphene oxide (GO). The surface characterization findings indicated that the produced GO is mesoporous with several oxygen based functional groups important for the adsorption of target heavy metal species. Under the respective tertiary competitive adsorption con-ditions, a near complete chromium removal was noted (~99%) at GO dosage of 0.5 g/L. Similarly the adsorption capacity of lead was also high at ~92% at a GO dosage of 0.5 g/L. Nevertheless, the cadmium showed a lower removal of ~51% under the competitive conditions. In general, the competitive removal of these heavy metals showed the following trend: chromium > lead > cadmium. These findings show that the synthesized graphene oxide preferentially adsorbs chromium and lead compared to cadmium. The oxygen surface functional groups, as indicated by the Fourier trans-form infrared spectroscopy analysis, are suggested to initiate the metal bonding and adsorption. Furthermore, the Brunauer–Emmett–Teller characterization results showed that the synthesized GO is mesoporous that is also supportive of an enhanced mass transfer to the surface bonding sites. The respective response surface methodology based process modeling and optimization also yielded good outcomes, for example, for lead removal, the respective analysis of variance findings showed that the GO dosage and concentration of lead and chromium are the significant model parameters with respective F-values of 267.48, 52.27, and 12.09, and respective p-values of <0.0001, <0.0001, and 0.0031. Furthermore, both the normal probability plot and the predicted vs. actual response plot also showed a good fit for the studied metal adsorption on to synthesized graphene oxide.