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

• Ni/BaLa4Ti4O15 photocatalyst showed high activity for reduction of NO3– to N2.
• The photocatalytic reaction proceeded by consumption of water as an electron donor.
• Control of solution pH played an important role for yielding N2 efficiently.

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 10 h using a 400 W high-pressure mercury lamp in 10 mmol/L of an aqueous NaNO3 solution, while it was 50% without the boric acid. The N2 yield was almost 100% when 3 mmol/L of an aqueous NaNO3 solution was used with a boric acid.

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