Photocatalytic decomposition of perfluorooctanoic acid by transition-metal modified titanium dioxide

[Display omitted] •Cu–TiO2 catalysts show much better catalytic activity than TiO2.•The PFOA decomposition efficiencies reached 91% with UV/Cu–TiO2 system.•The intermediates of the PFOA decomposition reactions are detailed. Transition-metal modified TiO2 was used in a UV reactor to assist in decomposition of perfluorooctanoic acid (PFOA) in aqueous solutions. Comparing TiO2 and two types of metal-modified TiO2 (Fe–TiO2 and Cu–TiO2), Cu–TiO2 exhibited the highest catalytic activity during PFOA decomposition and defluorination. After 12h of reaction, the PFOA decomposition and defluorination efficiencies by the UV/Cu–TiO2 system reached 91% and 19%, respectively. PFOA was decomposed into fluoride ions (F−) and shorter perfluorinated carboxylic acids (PFCAs) such as C6F13COOH, C5F11COOH, C4F9COOH, C3F7COOH, C2F5COOH and CF3COOH. The pseudo-first-order and pseudo-zero-order kinetics were used to model the decomposition and defluorination of PFOA, respectively. Rate constant values of PFOA decomposition for the UV/TiO2, UV/Fe–TiO2, and UV/Cu–TiO2 systems were 0.0001, 0.0015, and 0.0031min−1, respectively, while rate constant values of PFOA defluorination for the UV/Fe–TiO2, and UV/Cu–TiO2 systems were 0.0048 and 0.0077mg/L·min−1, respectively. The photocatalysts were prepared by a photodeposition synthesis method and were characterized by scanning electron microscopy with energy-dispersive X-ray, X-ray diffraction and UV–vis spectrophotometry. The Fe–TiO2 and Cu–TiO2 catalysts exhibited considerably higher activities than that of TiO2. The experimental results have demonstrated that the UV/Fe–TiO2 and UV/Cu–TiO2 systems could produce traps to capture photo-induced electrons, thereby reduce electron–hole recombination during photocatalytic reactions and consequently enhance the PFOA decomposition.