Photocatalytic disproportionation of nitrite to dinitrogen and nitrate in an aqueous suspension of metal-loaded titanium(iv) oxidenanoparticles

Abstract

Photocatalytic reaction of a nitrite ion in aqueous suspensions of bare and metal-loaded TiO₂ particles was examined without electron and hole scavengers under irradiation of UV light. In the bare TiO₂ system, disproportionation of NO₂⁻ to N₂ (or N₂O) and NO₃⁻ with nitrogen balance (NB) and redox balance (ROB) close to unity within experimental errors was observed, although the reaction was slow. Palladium (Pd)-loaded TiO₂ particles exhibited an extraordinarily large rate of disproportionation of NO₂⁻ in their aqueous suspension, i.e. NO₂⁻ was almost completely converted to N₂ (or N₂O) and NO₃⁻ even after only 3 h of photoirradiation, both the values of NB and ROB being close to unity. This result suggests that Pd loaded on TiO₂ particles acted as storage sites for photogenerated electrons and effectively transferred the electrons to NO₂⁻ and, therefore, that the reduction process in the photocatalytic disproportionation of NO₂⁻ was accelerated by Pd loaded on TiO₂. Effects of the amount of Pd and pH of the suspension on the reaction rate were also examined.