Efficient photodegradation of PFOA using spherical BiOBr modified TiO2 via hole-remained oxidation mechanism

Photo-induced holes (h+) oxidation is an efficient approach for perfluorooctanoic acid (PFOA; C7F15COOH) removal. To maintain a high amount of h+ on the surface of photocatalysts participating in the PFOA photodegradation could be a critical issue. Herein, a highly efficient spherical BiOBr-modified nano-TiO2 (P25) was synthesised and used for PFOA photodegradation through direct oxidation with h+. A high number of h+ could be generated and remain on the surface of P25/BiOBr due to the appropriate position of the conduction band (CB) and valence band (VB) levels between P25 and BiOBr. Meanwhile, PFOA molecules were coordinated to the P25/BiOBr's surface via unidentate binding, being directly activated and oxidised by h+, resulting in a decomposition yield of 99.5% (100 mg/L) under simulated solar light irradiation within 100 min, at the initial pH condition (3.5). A stepwise photodegradation pathway was proposed due to the significant intermediates detected as the short-chain perfluorinated carboxylic acids (C2-C7). Reactive oxygen species (ROS) generation, scavenging and trapping analysis indicated that the direct oxidation on h+ followed PFOA degradation. In a real aqueous environment of Tangxun lake (adjusted pH 3.5), stable common anions and natural organic matter (NOM) would restrain the PFOA photodegradation. However, adding 10 mg/L of NO3- or HA could reduce the inhibition effect of PFOA photodegradation. These findings gave an alternative strategy to drive an h+ directly oxidation to treat PFOA contaminated water bodies.