Photocatalytic activity for water decomposition of RuO2-combined M2Ti6O13 (M = Na, K, Rb, Cs)

A series of hexatitanates, M2Ti6O13 (M = Na, K, and Rb), with rectangular tunnel structures and Cs2Ti6O13 with a layer structure were employed to reveal the role of metal oxide structures in photocatalysis. The photocatalytic activity for water decomposition of RuO2-supporting M2Ti6O13 was compared with the efficiency for the production of photoexcited charges (electrons and holes) which was evaluated by the intensity of ESR peaks. The hexatitanates with the tunnel structures showed high photocatalytic activities and photoexcited radical formation, thus indicating a close relationship between the photocatalytic activity and the efficiency of photoexcited charge formation. The role of distorted TiO6 octahedra in the tunnel structures is discussed.