Photocatalysts with Tunnel Structures for Decomposition of Orgnic Compounds

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In sn attempt to develop a photocatalyst which has high dfficiency for the decomposition of toluene and water, alkaline metal bexa-titanates, M_2Ti_6O_<13> (M=Na, K,Rb) with a rectangular tunnel structute barium tetra-titanate, BaTi_4O_9, with a pentagonal-prism tunnel structure were combined with transition metals (Mn, Pt, Cu, Co, Fe, Ru, Ir, Ta) and their oxides. The decomposition of toluene on these photocatalysys wsa examined for gaseous mixtures of air-toluene and air-toluene-water. The highest photocatalytic activity wsa obtained for a RuO_2/BaTi_4O_9system in the presence of water, thus indicating that the decomposition of water is an important step in the reaction. A sol-gel method was employed to the preparation of fine BaTi_4O_9 particles. Upon heat treatment, the crystallization of the prepared gels occurred at around 873 K.Well-crystallized BaTi_4O_9 showed a single Raman peak at 860cm^<-1>, characteristic of a double bond-like short Ti-O bond and resulted in the enhancement of the photocatalytic activity for water decomposition. ESR spectra showed that active BaTi_4O_9 produced a signal with g=2.018 and g=2.004 at 77 K under UV irradiation in the presence of oxygen. This signal was assigned to a surface lattice O-radical which is proposed to be responsible for the photocatalysis as a hole trap center. The tunnel structure titanates are concluded to be useful for the development of photocatalysts with high efficiency for oxidation reactions.