Photocatalytic reduction of nitrate ions to dinitrogen over layered perovskite BaLa₄Ti₄O₁₅ using water as an electron donor

Photocatalytic reduction of NO₃^- to produce NO₂^-, NH₄⁺, and N₂ proceeded on BaLa₄Ti₄O₁₅ powder under UV irradiation accompanied with photochemical decomposition of NO₃^- to NO₂^- and O₂ without any sacrificial reagents. Loading of Cu and Ni cocatalysts enhanced the photocatalytic reaction to form N₂. Ni was the most effective cocatalyst. The BaLa₄Ti₄O₁₅ photocatalyst with the Ni cocatalyst loaded by an impregnation method and subsequent H₂ reduction showed high activity for the reduction of NO₃^- to form NO₂^-, NH₄⁺, and N₂. O₂ also formed as an oxidation product of water. The ratio of the number of reacted electron to that of hole was almost unity, indicating water was consumed as an electron donor for the reduction of NO₃^-. A boric acid of a buffer for pH control was effective to obtain a high yield of N₂. The N₂ yield reached 85% in the presence of a boric acid after 10h using a 400W high-pressure mercury lamp in 10mmol/L of an aqueous NaNO₃ solution, while it was 50% without the boric acid. The N₂ yield was almost 100% when 3mmol/L of an aqueous NaNO₃ solution was used with a boric acid.