TaON and MTaO2N (M: Ca, Sr, Ba), Ta5+-based (oxy)nitrides, were studied as visible-light-driven photocatalysts. Under visible light irradiation ( lambda greater than or equal to 420 nm), TaON oxidized water to O-2 and reduced H+ to H-2 in the presence of sacrificial reagents (Ag+ and methanol). TaON efficiently oxidized water into O-2, with a maximum quantum yield of 34%. H-2 evolution on TaON photocatalyst was found to be remarkably enhanced by adding Ru as a noble-metal cocatalyst. In contrast, MTaO2N did not oxidize water under photocatalytic reaction condition although the oxynitride evolved H-2 in the presence of methanol under visible light irradiation. (C) 2004 Elsevier B.V. All rights reserved.