Efficient Decomposition of Perfluorocarboxylic Acids in Aqueous Suspensions of a TiO sub(2) Photocatalyst with Medium-Pressure Ultraviolet Lamp Irradiation under Atmospheric Pressure

Decomposition of environmentally persistent perfluorooctanoic acid (PFOA) in aqueous suspensions of a TiO sub(2) photocatalyst, with use of medium-pressure ultraviolet (MPUV) lamp irradiation alone, was examined under atmospheric pressure. Compared to direct photolysis, TiO sub(2) photocatalysis led to efficient PFOA decomposition and production of CO sub(2) and F super(-). PFOA decomposition followed pseudo-first-order kinetics, with observed rate constants of 1.3 10 super(-2) and 8.6 10 super(-2) dm super(3) h super(-1) in direct photolysis and TiO sub(2) photocatalysis, respectively. The latter (photocatalytic) rate constant is 5-100 times greater than those obtained in other published research on the photocatalytic decomposition of PFOA. In the proposed decomposition pathway, PFOA molecules adsorb onto the TiO sub(2) surface according to adsorption equilibrium in an aqueous suspension and could be easily decomposed by holes and radicals generated by MPUV lamp irradiation. Under the present reaction conditions, a narrow region of TiO sub(2) concentrations around 1.5 wt % showed the maximum extent of PFOA decomposition, CO sub(2) formation, and F super(-) formation. The optimum rate can be attributed to a trade-off between an increase of photon absorption by TiO sub(2) and a decrease in UV penetration below the surface of the TiO sub(2) suspension. In the 1.5 wt % TiO sub(2) photocatalyst concentration, 5 mM PFOA was almost totally decomposed during 4 h of MPUV lamp irradiation under atmospheric pressure.