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

Abstract

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 μg/L, catalyst dosage 0.5 g/L, pH 7.0 and visible light (λ > 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.