Oxidative polymerization of pyrrole photocatalyzed by TiO₂ nanoparticles and interactions in the composites

Oxidative polymerization of pyrrole is initiated by photoexcited TiO₂ nanoparticles. Pyrrole oligomers and polypyrrole (PPy) are continuously produced with reaction time. The conversion of pyrrole monomer changes as a function of the concentration of TiO₂ nanoparticles. It is found that PPy in the composite has the conjugated structure and is partially oxidized with a formation of positively charged N⁺. Results from X-ray photoelectron spectroscopy and Raman analysis consistently indicate that a strong interaction is established between the TiO₂ and PPy. According to the results of UV-vis spectroscopy, a mechanism of photocatalytic oxidation is proposed for this polymerization. The interaction between TiO₂ and PPy is found to arise from the photocatalytic reaction and discussed in terms of photoinduced Ti³⁺.