Properties of photocatalysts with tunnel structures: formation of a surface lattice O− radical by the UV irradiation of BaTi4O9 with a pentagonal-prism tunnel structure

The UV irradiation of barium tetratitanate, BaTi 4 O 9 , with a unique pentagonal-prism tunnel structure, produced an EPR signal with g =2.018 and g =2.004 at 77 K: the signal had a short lifetime in vacuum, whereas it was stable in the presence of gaseous molecules (O 2 , H 2 , He, Ar) independently of the kinds of gases. The radical reacted with gaseous oxygen and formed O 3 − at room temperature. The species is assigned to an O − radical resulting from lattice oxygen at the surface, and its formation is closely related to the distorted TiO 6 octahedra forming the tunnel.