Efficient photoinduced conversion of an azo dye on hexachloroplatinate(IV)-modified TiO2 surfaces under visible light irradiation -: A photosensitization pathway

The titanium dioxide photocatalyst is employed to examine the influence of chemisorbed hexachloroplatinate(iv) anions (PtCl62-) on the surface of P-25 TiO2 particles on the photoinduced conversion of the azo dye Ethyl Orange (EO) in visible light-illuminated Pt-IV/TiO2 dispersions. Spin-trap electron spin resonance (ESR) spectral results, measurement of quantities of organoperoxides formed, total organic carbon (TOC) and chemical oxygen demand (CODC) assays, together with XPS evidence show that the self-sensitized transformation dynamics of the EO dye mediated by Pt-IV/TiO2 are much faster than those occurring on naked TiO2 under otherwise identical conditions of visible light irradiation. X-ray photoelectron spectral data also show that under the experimental conditions used, no Pt-0 formed on the titania particles during visible light irradiation. We propose a reaction mechanism in which the more rapid conversion of EO in the presence Of PtCl62- is caused principally by photoexcitation of the dye and not by localized excitation of the tetrachloroplatinate(iv)/TiO2 particles.