Efficient Degradation of Refractory Organics Using Sulfate Radicals Generated Directly from WO3 Photoelectrode and the Catalytic Reaction of Sulfate

Abstract

An environment-friendly method of efficiently degrading refractory organics using SO4−• generated directly from a WO3 photoelectrode and a catalytic reaction of sulfate was proposed, in which the cycling process of SO42− → SO4−• → SO42− was achieved in the treatment of organic pollutants without any other activator and without the continuous addition of sulfate. The results show that the removal efficiency for a typical refractory organics of methyl orange (MO) with 5 mg/L was up to 95% within 80 min, and merely 3% by photolysis and 19% by photocatalysis, respectively, under similar conditions. The rate constant for the disposal of MO at pH 2, in which SO4−• instead of HO• is the main oxidizer confirmed by radical scavenger experiment, is up to 5.21 × 10−4 s−1, which was ~6.6 times that (7.89 × 10−5 s−1) under neutral condition, in which HO• is the main oxidizer. The concentration of active persulfate (S2O82−, SO52−, and SO4−•) species at pH 2 was up to 0.38 mM, which was ~16-fold as much as that (0.023 mM) in neutral conditions. The method provides a new approach for the treatment and resource utilization of sulfate wastewater.

Keywords

• sulfate radical
• photoelectrocatalysis
• WO3
• refractory organics
• sulfate wastewater