Efficient degradation of refractory organics using sulfate radicals generated directly from WO3photoelectrode 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.