Preparation of a novel graphene oxide/Fe-Mn composite and its application for aqueous Hg(II) removal

A novel graphene oxide/Fe-Mn (GO/Fe-Mn) composite was synthesized (molar ratio of Fe/Mn = 3/1 and mass ratio of Fe/GO = 1/7.5) and investigated for the sorption characteristics and mechanisms of aqueous mercury (Hg2+) as well as the biological effects to wheat and rice. Characterization tests showed that Fe-Mn oxides were impregnated onto GO sheets in an amorphous form through oxygen-containing functional groups (i.e., C=O, epoxy C-O-C, carboxyl O=C-O, and C-O) and pi-pi interactions. GO/Fe-Mn possessed large surface area, surface enhanced Raman scattering with more spa defects, and greater thermal stability than GO. XPS analysis revealed that Fe2O3, FeOOH, MnO2, MnOOH, and MnO were the dominant metal oxides in GO/Fe-Mn. Pseudo-second-order kinetic model and Sips isotherm model fitted well with the sorption kinetic and isotherm data. The maximum sorption capacity for mercury was 32.9 mg/g. Ligand exchange and surface complexation were the dominant mechanisms for mercury removal. GO/Fe-Mn greatly reduced the bioavailability of mercury to wheat and rice, even promoted the seedling growth. This work suggests that GO/Fe-Mn can be used as an effective and environmental friendly adsorbent in heavy metal remediation. (C) 2016 Elsevier B.V. All rights reserved.