Decomposition of perfluorooctanoic acid by ultraviolet light irradiation with Pb、Cu and Fe-modified titanium dioxide

Perfluorooctanoic acid (PFOA, C7F15COOH) is widely used in industrial and commercial applications. It has become a global concern due to its widespread occurrence in water bodies and adverse environmental impact. PFOA could not be effectively removed by the conventional UV/TiO2 system. This study synthesized metal-modified TiO2 catalyst and used it as a catalyst with light irradiation for PFOA decomposition. It was found that the metal-TiO2 catalyst could produce traps to capture photo-induced electrons or holes that lead to better photocatalytic efficiencies. Comparing TiO2 and three types of metal-modified TiO2 (Fe-TiO2, Cu-TiO2 and Pb-TiO2), Pb-TiO2 exhibited the highest catalytic activity during PFOA decomposition and defluorination. After 12 h of reaction, the PFOA decomposition and defluorination efficiencies by the UV/Cu-TiO2 system reached 99% and 22%, 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 kinetic was used to model the decomposition of PFOA. Rate constant values of PFOA decomposition for the UV/TiO2, UV/Fe-TiO2, UV/Cu-TiO2 and UV/Pb-TiO2 systems were 0.0158, 0.0891, 0.1837 and 0.5136 hr-1, respectively. The Fe-TiO2, Cu-TiO2 and Pb-TiO2 catalysts exhibited considerably higher activities than that of TiO2. 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 experimental results have demonstrated that the UV/Fe-TiO2, UV/Cu-TiO2 and UV/Pb-TiO2 systems could produce traps to capture photo-induced electrons, thereby reduce electron-hole recombination during photocatalytic reactions and consequently enhance the PFOA decomposition.