Junction Effect on the Photocatalytic Activity of Mixed-Phase TiCh Nanoparticles

摘要

TiO_2 is the most studied photocatalyst for environmental applications because of its high efficiency, nontoxicity, chemical and biological stability, and low cost (1). TiO_2 exists in three different crystalline habits: anatase, brookite and rutile. Anatase is generally accepted to be a photocatalyst more efficient than rutile and brookite but mixtures of the TiO_2 polimorphic phases often show photocatalytic activities superior than those of the pure phases (2). The coupling of different semiconductors possessing different energy levels for their corresponding conduction and valence bands is usually beneficial to enhance the photocatalytic activity (2, 3). The very active commercial Degussa P25, that is frequently used as a benchmark in heterogeneous photocatalysis, consists of a mixture of anatase and rutile. The present paper reports on the preparation and characterization of highly active TiO_2 photocatalysts prepared by thermohydrolysis of TiCl_4 in pure water at 100 °C. The reactivity of the various samples was tested for the photocatalytic degradation of 4-nitrophenol and compared to that of Degussa P25. The flat band potential and the band gap values of anatase, brookite and rutile were also determined. The results are discussed by taking account of the relative positions of the energy bands of the three TiO_2 phases.