Photocatalytic N 2 conversion to ammonia using efficient nanostructured solar-energy-materials in aqueous media: A novel hydrogenation strategy and basic understanding of the phenomenon

To reduce carbon dioxide emission and supply the nitrogen demand of living organisms, it is crucial to employ a green, solar-based strategy to produce ammonia in aqueous media under ambient conditions, via N2 reaction with transiently photogenerated H-atoms upon appropriate semiconductor materials. In this paper, by using a facile precipitation/calcination route, we synthesized some Fe2O3 and TiO2-based uniform nanoparticles and applied them in a water photosplitting setup to photosynthesize ammonia. The maximum yield was obtained for Fe2O3 and was interpreted in terms of its ability to temporarily store hydrogen atoms, adsorb nitrogen molecules, and harvest more photons in the visible region. Based on photocatalytic reduction of protons to H-atoms and stepwise hydrogenation of N≡N molecules on the photocatalyst surface, a reaction pathway was proposed. During this N2-photofixation process, the generation of hydrazine by-product was also predicted and confirmed by empirical evidence. Moreover, the role of hole-scavenger additive was discussed in detail from physicochemical standpoint.