PdSn/NiO/NaTaO3:La for photocatalytic ammonia synthesis by reduction of NO3− with formic acid in aqueous solution

Abstract

Photocatalytic ammonia synthesis is of great importance but remains very challenging in photocatalysis. Here, we fabricated a photocatalytic reaction system for the efficiently photocatalytic nitrate reduction to ammonia under UV irradiation using PdSn/NiO/NaTaO3:La as a photocatalyst in the presence of formic acid. Several important factors of the photocatalytic performance were investigated, including initial concentration of the nitrate solution, initial pH value and cocatalyst loadings. Nitrate conversion reaches 100% and ammonia selectivity is 72% over the optimum photocatalyst with 5% bimetallic PdSn alloy and 0.2% NiO loadings. The outstanding performance of photocatalyst can be ascribed to both the strong adsorption of nitrite on NiO and the efficient separation of electron-hole pairs by PdSn bimetallic alloy. Besides as the hole scavenger, formic acid also provides not only carboxyl anion radicals for nitrate reduction but also the in-situ buffer effect on ammonia formation. These results give inspiration for designing the reactive system with efficient photocatalytic ammonia synthesis.