Photocatalytic degradation kinetics of perfluorooctanoic acid (PFOA) in TiO2 dispersion and its mechanism

Decomposition of perfluorooctanoic acid( PFOA) is of prime importance since it is recognized as a persistent organic pollutant and is widespread in the environment. Heterogeneous photocatalytic decomposition of PFOA by TiO2( P25) was investigated under 254 nm UV light. Experimental conditions including initial pH,TiO2content and PFOA concentration,were varied to demonstrate their effects on the decomposition of PFOA. It was observed that the photocatalytic degradation kinetics of PFOA could be fitted to the quasi-first-order equation. The pH played a determinant role in the decomposition of PFOA and the presence of O2increased the degradation rate. Optimal conditions for a complete removal were obtained using 1. 5 g·L- 1TiO2at pH 3 in air atmosphere,with a rate constant of 0. 420 6 h- 1. The contribution experiments of various reactive species produced during the photocatalysis were also investigated with the addition of different scavengers and it was found that photogenerated holes( h+) was the major reactive species which was responsible for 66. 1% of the degradation rate,and the ·OH was involved in PFOA degradation as well. In addition,the photocatalytic experiment with the addition of NaF indicated that the adsorption of PFOA was of primary importance for the photocatalytic decomposition. Perfluorocarboxylic acids( PFCAs) with shorter carbon chain length as intermediates and products were identified with UPLC-QTOF /MS,and a possible mechanism for PFOA decomposition was proposed.