Effect of metal nanoparticles deposition on the photocatalytic oxidation of ammonia in aqueous suspensions

TiO2 powders modified through the deposition of surfactantstabilized preformed metal (Pt, Pd, Au and Ag) nanoparticles (NPs) were tested as photocatalysts in NH3 photo-oxidation in aqueous suspension. Mildly oxidized N2, together with nitrite and nitrate anions, were the main reaction products; their amount was monitored during the runs, together with the residual NH3 concentration in the aqueous phase. The effects induced by the type and amount of deposited metal NPs on both ammonia conversion (XNH3%) and on products selectivities (S%) were thus investigated systematically. Apart from Au-modified TiO2, the metal-modified powders exhibited increased photoactivity with respect to that of the naked semiconductor oxide, with Ag/TiO2 resulting the best performing photocatalyst in this reaction.