Effects of the TiO2 phase in the photocatalytic oxidation of aqueous NH3

Pure brookite, anatase and rutile TiO2 nanopowders, synthesized through thermo-hydrolysis of TiCl4 and modified by the deposition of Pt nanoparticles, were tested in the photocatalytic oxidation of aqueous NH3. Ammonia conversion and the selectivity toward mildly oxidized N2 and highly oxidized nitrite and nitrate anions were monitored during the runs, employing both naked and Pt-modified semiconductor particles as photocatalysts. Pt addition largely increased the rate of ammonia conversion. Pure brookite powders modified with Pt nanoparticles, which already proved to be efficient photocatalysts in thermodynamically up-hill H2 production through photo-steam reforming of methanol, were found to be most efficient also in down-hill aqueous ammonia abatement, with the highest selectivity (ca. 30 %) toward innocuous N2, this parameter being pretty important in view of a large scale photo-abatement of NH3, where the amount of noxious nitrite and nitrate ions must be kept as low as possible. Furthermore, intriguing effects concerning the mechanism of NH3 degradation where observed upon Pt nanoparticles deposition on pure brookite powders.