Photo-reduction of bromate in drinking water by metallic Ag and reduced graphene oxide (RGO) jointly modified BiVO4 under visible light irradiation

Bromate (BrO3-), an oxyhalide disinfection by-product (DBP) in drinking water, has been demonstrated to be carcinogenic and genotoxic. In the current work, metallic Ag and reduced graphene oxide (RGO) co modified BiVO4 was successfully synthesized by a stepwise chemical method coupling with a photo deposition process and applied in the photo-reduction of BrO3- under visible light irradiation. In this composite, metallic Ag acted as an electron donor or mediator and RGO enhanced the BrO3- adsorption onto the surface of catalysts as well as an electron acceptor to restrict the recombination of photo generated electron-hole pairs. The Ag@BiVO4@RGO composite exhibited greater photo-reduction BrO3- performance than pure BiVO4, Ag@BiVO4 and RGO@BiVO4 under identical experimental conditions: initial BrO3- concentration 150 mu g/L, catalyst dosage 0.5 g/L, pH 7.0 and visible light (lambda > 420 nm). The photoluminescence spectra (PL), electron-spin resonance (ESR), photocurrent density (PC) and electrochemical impedance spectroscopy (EIS) measurements indicated that the modified BiVO4 enhanced the photo-generated electrons and separated the electron-hole pairs. The photocatalytic reduction efficiency for BrO3- removal decreased with the addition of electron quencher K2S2O8, suggesting that electrons were the primary factor in this photo-reduction process. The declining photo-reduction efficiency of BrO3- in tap water should attribute to the consumption of photo-generated electrons by coexisting anions and the adsorption of dissolved organic matter (DOM) on graphene surface. The overall results indicate a promising application potential for photo-reduction in the DBPs removal from drinking water. (C) 2016 Elsevier Ltd. All rights reserved.