Heavy metal removal from wastewater using functionalized nano-structures and graphene oxide

Toxic heavy metals present in aqueous media threaten the survival of human beings and ecosystem, but mechanisms underlying their absorption by nanoparticles are limitedly studied. The Pb 2+ , Cu 2+ and Cd 2+ are taken as characteristic of heavy metals, while pristine and amine-functionalized graphene oxide (GO) nanosheets as absorbents. The combination of bench- and computer-based studies unraveled the effects of chemistry and thermodynamics of model heavy metals absorption by GO. Synthesis of 6-aminouracil functionalized GO (GO-A) and ethylenediamine functionalized GO (GO-E) reveled the higher potential of GO-E compared to GO and GO-A towards absorption of Pb 2+ , Cu 2+ and Cd 2+ , following the order GO-E > GO-A > GO. The topmost absorption capacity varied with pH of the solution, where the highest absorption capacity of GO-E towards Cd 2+ was evident, i.e. four to five times higher than those of Pb 2+ and Cu 2+ . Furthermore, the desorption behavior of the heavy metal ions from the GO surface was significant, indicating that GO could be reused after treated with hydrochloric acid solution. Gibbs free energy computations unraveled that Cd 2+ was spontaneously adsorbed to nanosheets compared to Pb 2+ and Cu 2+ . The role of surface chemistry was unraveled with GO-E compared to GO and GO-A in both gas and solvent phases.