The photocatalytic C-F bond cleavage in pentafluorobenzoic acid (PFBA) with ZnO using UV-C light has been investigated under different conditions. Strong C-F bond is completely cleaved with ZnO under 150 min of UV-C light irradiation. The defluoridation is more with UV/ZnO process than with UV/TiO2 process at pH 5. The oxidants such as IO4-, BrO3-, S2O82- and ClO3- ions enhance the defluoridation rate of PFBA. On the contrary the addition of H2O2 decreases the rate. The order of their activities is IO4- > S2O82- > BrO3- > ClO3-. The C-F cleavage is also influenced by the addition of inorganic anions and metal ions. The GC-MS analysis of PFBA solution after irradiation with ZnO reveals the formation of pentafluorobenzene, pentafluorophenol and tetrafluoroquinone as intermediates. (c) 2007 Elsevier B.V. All rights reserved.