Modification of Titanium Dioxide with Platinum Ions and Clusters:  Application in Photocatalysis

TiO 2 (commercial-P25 and synthesized by sol−gel method) was surface modified with platinum ions or Pt 3 (CO) 6 6 2- clusters to improve its photocatalytic activity. The physical properties of the synthesized photocatalysts were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer, Emmett and Teller adsorption (BET) methods. To characterize the absorption ability of visible light, the diffusion reflectance spectra (DRS) were recorded. The charge-carrier lifetimes in TiO 2 after UV illumination were determined by microwave absorption experiments using the time-resolved microwave conductivity (TRMC) method. The photocatalyst activity was examined by degradation of exemplary aqueous phase pollutants, such as Rhodamine B and phenol. The impact of the adsorbates on the photocatalytic activity depends strongly on the titania precursor (commercial or synthesized), the irradiation wavelength (UV or visible), and the model compound (dye or phenol). The results show that it is possible to enhance the P25 photocatalytic activity under UV−visible light by doping it with Pt clusters. Also, P25 doping with Pt(II) or Pt clusters results in enhancement of the activity under visible light. Pt(IV)/TiO 2 synthesized by sol−gel method exhibits better photoactivity under UV−visible and visible light compared to the unmodified titania. In all mentioned systems, a positive effect of modification with platinum clusters and, in particular, an important enhancement in photocatalytic activity under visible light were obtained. These results are explained by enhancement in visible light absorption and inhibition of charge-carrier recombination.