Synthesis of phosphotungstic acid-supported bimodal mesoporous silica-based catalyst for defluorination of aqueous perfluorooctanoic acid under vacuum UV irradiation

Phosphotungstic acid (H3PW12O40, HPW)/bimodal mesoporous silica (BMS) multifunctional catalysts were prepared and employed as photocatalyst for perfluorooctanoic acid (PFOA) degradation under vacuum ultraviolet light (VUV). Lower PFOA concentration, appropriate HPW/BMS dosage (0.2 g·L−1) and acidic condition (pH = 3-4) were more favorable for PFOA defluorination in VUV/HPW/BMS system. Furthermore, we analyzed the intermediates produced during PFOA decomposition by HPLC/MS/MS, which were shorter-chain perfluorinated carboxylic acids (PFCAs) with C7, C6, C5, C4, C3 and C2. The defluorination mechanism of PFOA was proposed, i.e., direct photolysis played an important role in PFOA defluorination under VUV radiation (λ = 185 nm), while the defluorination of PFOA was simultaneously photocatalytically decomposed and defluorinated in the presence of HPW/BMS (λ = 254 nm).