Photoelectrochemical properties of platinum(IV) chloride surface modified TiO2.

Anatase (TH), rutile (TiO2-R), and a mixture of anatase and rutile (P25) were surface modified by chemisorbed chloroplatinate(IV) complexes. All materials gave rise to anodic photocurrents when deposited on conducting glass and irradiated in the wavelength range of 330-650 nm. In the presence of formate "current-doubling" factors of 5-7 were measured. Flatband potentials were obtained by the suspension method through recording the photovoltage as function of the pH value. The value of -0.54 V as found for TH is shifted to -0.49, -0.45, and -0.28 V (vs. NHE, pH = 7) when the surface is covered by 1, 2, and 4 wt% of H2[PtCl6], respectively. The flatband potential shifts by 50 and 60 mV per pH unit for P25 and 4% H2[PtCl6]/TH, respectively, as found by a novel method based on the use of different pH-independent redox systems of the bipyridinium type. Whereas the rutile based material was inactive, the TH and P25 samples photocatalyzed the mineralization of 4-CP with visible light. Moreover, the capability of H2[PtCl6]/TH to mineralize also cyanuric acid, the end-product of atrazine decomposition in photocatalytic processes with unmodified TiO2, was observed upon UV and also visible light irradiation. From these experimental results an energy diagram is proposed to rationalize the reactions observed.