An environment-friendly method of efficiently degrading refractory organics using SO 4 − • generated directly from a WO 3 photoelectrode and a catalytic reaction of sulfate was proposed, in which the cycling process of SO 4 2− → SO 4 − • → SO 4 2− 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 SO 4 − • 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 (S 2 O 8 2− , SO 5 2− , and SO 4 − •) 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.

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