Enhanced photocatalytic activity of nafion-coated TiO₂

Photocatalytic degradation (PCD) of aqueous paraquat was accelerated by the addition of either phosphate or sulfate salt. Attachment of these anions to the TiO₂ surface possibly results in increased adsorption of the cationic paraquat species and in turn its photocatalysis rate. The same effect was obtained more consistently using the Nafion (an anionic polymer)-coated Ti0₂. Enhanced PCD of paraquat and some amine compounds was noted. However the anionic and neutral compounds were not affected significantly. Nafion proved to be stable against photocatalysis. It has been suggested that the degradation rate is larger for the cationic compounds with higher pK_a. For a phenol-paraquat-TiO₂ system, paraquat degradation did not begin till near-complete phenol removal. Using the Nafion-coated TiO₂, both phenol and paraquat degradations started simultaneously. Nevertheless, complete paraquat removal still took longer than phenol.