Niobium Oxide Photocatalytically Oxidizes Ammonia in Water at Ambient Conditions

Ammonia contamination in water is a signifcant environmental issue since it is toxic and leads to eutrophication. Photocatalysis has been investigated as a strategy for ammonia degradation but can potentially form toxic nitrite (NO₂^–) and nitrate (NO₃^–) byproducts. This work reports on the ability of niobium oxide (Nb₂O₅) to photocatalytically oxidize aqueous-phase ammonia (NH₃). Whereas as-synthesized Nb₂O₅ showed little catalytic activity (< 1% NH₃ conversion after 6 h of UV-C irradiation, at room temperature and atmospheric pressure, and under O₂ headspace), Nb₂O₅ treated in basic solution (OH-Nb₂O₅) was able to photocatalytically degrade NH₃ at ca. 9% conversion after six hours, with ca. 70% selectivity to the desired N₂, with a frst-order rate constant of ca. 12 times higher than the as synthesize catalyst (1.6 × 10^–3 min^–1 vs. 2.0 × 10^–2 min^–1). Raman spectroscopic analysis indicated the presence of terminal Nb=O species after base treatment of Nb₂O₅, implicating them as catalytically active sites. These results underscore how a simple structural modifcation can signifcantly affect photocatalytic activity for aqueous ammonia oxidation.

Keywords:
ammonia oxidation; photocatalysis; niobium oxide; aqueous ammonia