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, BaTi4O9, 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 (O2, H2, He, Ar) independently of the kinds of gases. The radical reacted with gaseous oxygen and formed O3− 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 TiO6 octahedra forming the tunnel.