Mechanism insight of PFOA degradation by ZnO assisted-photocatalytic ozonation: Efficiency and intermediates.

Zinc oxide (ZnO) nanorods were prepared by a directly pyrolysis method and employed as catalyst for perfluorooctanoic acid (PFOA) degradation. Comparative experiments were conducted to discuss the catalytic activity and flexibility of ZnO. After ZnO addition, the best PFOA degradation efficiency (70.5%) was achieved by ZnO/UV/O system, only 9.5% by sole ozonation and 18.2% by UV light irradiation. PFOA degradation was sensitive with pH value and temperature. The better PFOA removal efficiency was achieved at acidic condition. A novel relationship was found among PFOA degradation efficiency with hydroxyl radicals and photo-generated holes. Hydroxyl radicals generated on the surfaces of ZnO nanorods played dominant roles in PFOA degradation. PFOA degradation was found to follow the photo-Kolbe reaction mechanism. C-C shorter-chain perfluorocarboxylic acids and fluoride ion were detected as main intermediates during PFOA degradation process. Based on the results, a proposal degradation pathway was raised.