Graphene oxide-mediated the reduction of U(VI), Re(VII), Se(VI) and Se(IV) by Fe(II) in aqueous solutions investigated via combined batch, DFT calculation and spectroscopic approaches

Abstract

Although thermodynamically feasible, reduction of U(VI), Re(VII), Se(VI) and Se(IV) in homogeneous Fe(II) solution could be hardly observed. Whereas, surface-mediated reduction by Fe(II) has been generally regarded as a major pathway for the immobilization of these radionuclides. In this paper, graphene oxide (GO) was firstly revealed to mediate the reduction of U(VI), Re(VII), Se(VI) and Se(IV) by aqueous Fe(II) via a combined batch, DFT calculation and spectroscopic investigation. The kinetics for all adsorption systems could be fitted by the pseudo-second-order model, which was indicative of a chemical interaction. The isotherms for all reaction systems could be described by the Freundlich model better than that by the Langmuir model. Spectroscopic studies indicated that the enhancement effects of GO were attributable to the facilitated electron transfer by the graphitic surfaces and particularly to the decreased Fe(III)-Fe(II) redox potential by surface adsorption of Fe(II) with O-bearing functional groups on GO. Additionally, the presence of coexisting dissolved fulvic acid (FA) could significantly promoted GO-mediated reduction, by enhancing the electron shuttle ability of GO. Therefore, owning to the combined strong mediation efficiency and excellent adsorption affinity, GO exhibited an important role in mediating the reductive immobilization of radionuclides in a wide range of redox-stratified environments.