Effect of oxidants and metal ions on photodefluoridation of pentafluorobenzoic acid with ZnO

The photocatalytic CF bond cleavage in pentafluorobenzoic acid (PFBA) with ZnO using UV-C light has been investigated under different conditions. Strong CF 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 CF 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.