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

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 12 h 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 C₆ F₁₃COOH, 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 0.0031 min(-1), respectively, while rate constant values of PFOA defluorination for the UV/Fe-TiO₂, and UV/Cu-TiO₂ systems were 0.0048 and 0.0077 mg/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.