Photocatalytic Abatement of Aqueous Ammonia on Ru/TiO2: Effects of the Route of Ru Nanoparticles Deposition on TiO2

The effects of TiO2 surface modification by Ru nanoparticles (NPs) deposition have been investigated in the photocatalytic decomposition of aqueous ammonia. Two main Ru NPs deposition routes were chosen, i.e. (i) the deposition of surfactant-stabilized preformed metal NPs and (ii) a modified version of the well-known deposition-precipitation technique, employing urea as precipitating agent. Other Ru/TiO2 photocatalysts were prepared (iii) by simply grafting Ru(III) metal ions on TiO2, which were tested either as prepared or (iv) after their thermal reduction under H2 atmosphere, in order to obtain Ru NPs in full metallic state. The role played also by the relative nominal metal amount on the so obtained photocatalyst powders was investigated in terms of both ammonia conversion and selectivity towards mildly oxidized N2 or highly oxidized nitrite and nitrate ions. The Ru NPs deposition technique was found to affect the reaction paths especially in terms of products selectivity, with fully reduced Ru NPs on TiO2 being able to promote the environmentally friendly, highly desirable photocatalytic conversion of ammonia into innocuous N2.