The effects of the TiO2 crystal structure and its surface modification with Pt nanoparticles on the photocatalytic oxidation of NH3 in the aqueous phase were studied with home-made TiO2 photocatalyst powders synthesized by a thermo-hydrolysis approach that allowed a fine control of the crystallographic phase composition. Ammonia conversion and the selectivity toward mildly oxidized N-2 and highly oxidized nitrite and nitrate anions were monitored during the runs. Pure brookite powders modified by Pt nanoparticles, deposited either from a colloidal suspension or by deposition-precipitation, were found to be the most efficient photocatalysts in NH3 degradation, with a desired good selectivity toward innocuous N-2. The photo-activity in NH3 oxidation was correlated to the crystallographic features of the investigated TiO2-based materials, also taking into account the effects induced on the reaction paths by the presence of Pt nanoparticles on TiO2. (C) 2014 Elsevier B.V. All rights reserved.