New insights into colloidal GO, Cr(VI) and Fe(II) interaction by a combined batch, spectroscopic and DFT calculation investigation

In this paper, a variety of experimental techniques including batch equilibrium reactions, density functional theory (DFT) theoretical calculation, and X-ray spectroscopic techniques, were utilized to investigate the colloidal GO, Cr(VI) and Fe(II) interaction. The results indicated that a Cr(III)-Fe(III) precipitate could be formed when Fe(II) was added in Cr(VI) solution, and then Cr(VI) was adsorbed on the neoformed precipitate. The kinetics for all systems can be described by the pseudo-second-order model the best, suggesting chemical reaction mainly contributed to colloidal GO, Cr(VI) and Fe(II) interaction. There co-existed reductive and oxidative functional group on GO surfaces simultaneously, leading to the reduction Cr(VI) into Cr(III), and/or oxidation of Fe(II) into Fe(III), when Fe(II) and Cr(VI) were adsorbed on GO, individually. Furthermore, in comparison with individual GO and Fe(II) in solution, more Cr(VI) could be reduced into Cr(III) via Fe(II)-treated GO, due to the much higher reactivity of GO adsorbed Fe(II). So, GO demonstrated excellent adsorption and reduction capacity for Cr(VI) in the presence of Fe(II). These findings are vital to apply GO in the elimination of Cr(VI) from wastewater.