TiO2 modified with both phosphate and platinum and its photocatalytic activities

A new hybrid modification method of TiO2 photocatalyst was developed and investigated. TiO2 modified with both phosphates and platinum nanoparticles on its surface (P-TiO2/Pt) was prepared by a simple two-step method using phosphoric acid (as phosphate source) and chloroplatinic acid (as platinum source). The coexistence of phosphate and platinum on the surface of TiO2 was confirmed by X-ray photoelectron spectroscopy and transmission electron micrography. P-TiO2/Pt showed a significantly higher photocatalytic activity than any of bare TiO2, P-TiO2, and Pt/TiO2 for the degradation of phenolic compounds (4-chlorophenol; bisphenol A; 2,4-dichlorophenoxyacetic acid (2,4-D)). In particular, P-TiO2/Pt minimized the production of toxic intermediate (2,4-dichlorophenol) during the photocatalytic degradation of 2,4-D. In accordance with the higher photocatalytic activities of P-TiO2/Pt, both the production of OH radicals and the photocurrent collection in the suspension were markedly enhanced upon the simultaneous platinization and phosphation of TiO2. The two surface species acted synergically to enhance the photocatalytic activity. The surface phosphation that should replace the surface hydroxyl groups on TiO2 favors the formation of unbound OH radicals instead of surface-bound OH radicals while the surface platinization accelerates the electron transfer with retarding the charge recombination. The phosphation of TiO2 was stable over a wide range of pH due to the strong chemical bonding of phosphate on TiO2 whereas the surface fluorination of TiO2, which can be similarly compared with the phosphation in its photocatalytic effect, is active only at acidic pH. P-TiO2/Pt showed a higher photocatalytic activity than Pt/TiO2 for the degradation of 2,4-D even at pH 11, under which condition the effect of surface fluorination of Pt/TiO2 completely disappeared. (C) 2011 Elsevier B.V. All rights reserved.