Photocatalytic reduction of NO3- to produce NO2-, NH4+, and N-2 proceeded on BaLa4Ti4O15 powder under UV irradiation accompanied with photochemical decomposition of NO3- to NO2- and O-2 without any sacrificial reagents. Loading of Cu and Ni cocatalysts enhanced the photocatalytic reaction to form N-2. Ni was the most effective cocatalyst. The BaLa4Ti4O15 photocatalyst with the Ni cocatalyst loaded by an impregnation method and subsequent H-2 reduction showed high activity for the reduction of NO3- to form NO2-, NH4+, and N-2. O-2 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 N-2. The N-2 yield reached 85% in the presence of a boric acid after 10 h using a 400W high-pressure mercury lamp in 10 mmol/L of an aqueous NaNO3 solution, while it was 50% without the boric acid. The N-2 yield was almost 100% When 3 mmol/L of an aqueous NaNO3 solution was used with a boric acid. (C) 2015 Elsevier B.V. All rights reserved.