Improved photocatalysis of perfluorooctanoic acid in water and wastewater by Ga2O3/UV system assisted by peroxymonosulfate

Abstract

Perfluorooctanoic acid (PFOA) has attracted considerable attention worldwide due to its widespread occurrence and environmental impacts. This research focused on the photocatalytic process for the treatment of PFOA in water and wastewater. Gallium oxide (Ga₂O₃) and peroxymonosulfate (PMS) were mixed directly in PFOA solution, which was irradiated under different light sources. The treatment system showed excellent performance that 100% PFOA was degraded within 90 min and 60 min under 254 nm and 185 nm UV irradiation, respectively. Moreover, the degradation efficacy was unaffected by initial PFOA concentration from 50 ng L^-1 to 50 mg L^-1. Acidic solution (pH 3) improved the degradation process. The quantum yield in the PMS/Ga₂O₃ system under UV light (254 nm) was estimated to be 0.009 mol E^-1. Scavengers such as tert-butanol (t-BuOH), disodium ethylenediaminetetraacetate (EDTA-Na₂) and benzoquinone (BQ) were added into PFOA solution to prove that sulfate radicals (SO₄^•-), superoxide radical (O₂^•-) and photogenerated electrons (e^-) were the main active species with strong redox ability for PFOA degradation in PMS/Ga₂O₃/UV system. Combined with the intermediates analysis, PFOA was degraded stepwise from long chain compound to shorter chain intermediates. In addition, PFOA in real wastewater exhibited similar degradation efficiency, together with 75-85% TOC removal by Ga₂O₃/PMS under 254 nm UV irradiation. Therefore, Ga₂O₃/PMS system was highly effective for PFOA photodegradation under UV irradiation, which has potential to be applied for the perfluoroalkyl substances (PFAS) treatment in water and wastewater.

Keywords: PMS/Ga(2)O(3)/UV system; Perfluorooctanoic acid; Photocatalytic pathway; Quantum yield; Sulfate radicals.