Pentafluoropropionic acid (CF3CF2COOH; PFPA) was decomposed to F- and CO2 with a water-soluble homogeneous photocatalyst, H3PW12O40. This is the first example of a photocatalytic system for C-F bond cleavage in a perfluorinated acid compound having both CF3- and -CF2- units. The catalytic reaction proceeds in water at room temperature under irradiation with UV-Vis light in the presence of oxygen. Gas chromatography-mass spectrometry (GC-MS) showed no trace of environmentally undesirable species such as CF4, which is often observed in the decomposition of perfluorinated compounds by extremely high energy techniques such as electron beam irradiation. In addition to F- ions, small amounts of trifluoroacetic acid (TFA) were detected in the reaction solution. The proposed reaction mechanism involves redox reactions of PFPA and TFA with the catalyst. (C) 2003 Elsevier B.V. All rights reserved.