Understanding the selectivity trend of water and sulfate (SO42−) oxidation on metal oxides: On-site synthesis of persulfate, H2O2 for wastewater treatment

Abstract

Herein, H2O2 production activity via two-electron water oxidation reaction is identified on metal oxides (WO3, TiO2, and BiVO4) in acidic SO42− involving electrolyte, in which persulfate (PS) acts as an intermediate. A deep understanding of mechanism of PS production reaction on metal oxides has been realized based on rigorous crystal plane analysis of WO3 and TiO2 by combining density functional theory calculations and zeta potential measurements. It is found that the binding-energy of adsorbed hydroxyl groups on dominant exposed crystal plane of WO3 is lower than that of TiO2, leading to more SO42− adsorption sites at the surface of WO3. Consequently, the formation of PS on WO3 surface is more favorable. Meanwhile, both SO4−· and OH· were detected in the electrolyte by electron paramagnetic resonance measurement, which play a crucial role in organic pollutants wastewater treatment, with a degradation efficiency of 96% in 90 min for a typical pollutant norfloxacin. This work can provide a novel insight for understanding the selectivity of water and SO42− species oxidation on metal oxides, and open a new way for both on-site H2O2 production and advanced oxidation processes application.