Crystalline Mixed Phase (Anatase/Rutile) Mesoporous Titanium Dioxides for Visible Light Photocatalytic Activity

The high photocatalytic activity of mixed phase (80% anatase and 20% rutile) titanium dioxide (Degussa P25) has attracted a great deal of interest in recent years. However, its low efficiency in visible light and nonporous nature limits the potential use and capabilities. Here, we report a novel preparation method for crystalline, thermally stable (up to 800 degrees C) TiO2 materials with tunable anatase/rutile phase compositions (0-100%) and monomodal mesoporosity. The control of the phase compositions was achieved by framework vanadium doping and various applied heat treatments. Vanadium (0% to 10% doping) decreased the anatase-rutile transformation temperature (from 1000 to 600 degrees C) and shifted the absorption band to the visible light region (narrowed the band gap). The mesopore structure was preserved in mixed phase TiO2. These materials are members of the recently discovered University of Connecticut (UCT) mesoporous materials family. The UCT materials are randomly packed nanoparticle aggregates and mesopores that are formed by connected intraparticle voids. The synthesis of UCT materials relies on controlling the sol-gel chemistry of inorganic sols in inverse surfactant micelles and NOx (nitric oxides) chemistry. The visible light (>400 nm) photocatalytic activity of mixed phase mesoporous titania samples was studied. The highest photocatalytic activity was obtained by mesoporous titania with 61% anatase and 39% rutile composition. The catalyst can totally remove (100% conversion) methylene blue dye (MB) under visible light irradiation in 2 h, whereas commercial P25 was only able to remove 28% under the same reaction conditions. The mixed phase mesoporous material also shows high photocatalytic activity for degrading phenol and 4-chlorophenol under visible light irradiation. Moreover, the good crystallinity, high surface area (94 m(2)/g), and monomodal mesoporosity (around 5 nm) can be preserved even after three cycles of photocatalytic reactions.