Investigation of photocatalytically-active hydrated forms of amorphous titania, TiO2•nH2O

Low temperature preparations of hydrated forms of amorphous titania, TiO2 center dot nH(2)O, have been obtained starting from Ti(n-butoxide)(4) in ethanol, acetone, hexane or tetrahydrofuran solutions by either slow evaporation (TiO2-Al) or from rapid precipitation in an aqueous HCl solution using ammonia (TiO2-A(2)). The washed products lost/reabsorbed water up to a maximum of 19 wt.% for samples of TiO2-Al (n similar to 1.0) and 9.9% for TiO2-A(2) (n similar to 0.5), determined from TGA, and exhibited an optical band gap of similar to 3.5 eV Under full spectrum irradiation in aqueous methanol solutions the photocatalytic rates for H, production reached a maximum of 314 and 1158 mu mol h(-1) g(-1) for bare and platinized (0.5 wt.%) samples of TiO2-Al, respectively, and 210 and 170 mu mol h(-1) g(-1) for TiO2-A2. The photocatalytic rates measured at a slightly elevated temperatureof 58 degrees C were up to 2 x greater than those measured nearer room temperature, while these rates were independent of the amount or type of solvent used in their preparation. The UV-vis diffuse reflectances, post irradiation, indicate a higher concentration of Ti3+ sites in TiO2-Al compared to TiO2-A2, and thus a higher density of active sites and reduced electron-hole recombination. (c) 2006 Elsevier B.V. All rights reserved.