Nitrate was photocatalytically reduced to nitrogen molecules with a high selectivity in a basic aqueous suspension of palladium and copper-loaded titanium(IV) oxide powders in the presence of oxalate anion as a hole scavenger.

Photocatalytic reduction of nitrate ion (NO 3 -) in an aqueous suspension of metal-loaded titanium(IV) oxide (TiO 2 ) was examined in the presence of oxalic acid (OA) as a hole scavenger. Conversion of NO 3 -into ammonia (NH 3 ) competed with hydrogen liberation, and the NH 3 production selectivity increased with the order of loaded metal, (Pt, Pd, Co) < (Ni, Au) < (Ag, Cu), which was attributable to the efficiency of reduction of protons by photogenerated electrons at the loaded metal, i.e., hydrogen overvoltage of the loaded metal.TiO 2 powder loaded with Cu showed higher NH 3 yield and selectivity as well as higher efficiency of OA consumption.TiO 2 with in situ-deposited Cu gave results comparable to those of a Cu pre-loaded photocatalyst.