Photocatalysts with Tunnel Structures for Decomposition of Orgnic Compounds

为了开发高效降解甲苯和水的光催化剂，将具有矩形隧道结构的碱金属六钛酸盐M_2Ti_6O_<13>（M=Na，K，Rb）和具有五棱柱隧道结构的四钛酸钡BaTi_4O_9与过渡金属（Mn，Pt，Cu，Co，Fe，Ru，Ir，Ta）及其氧化物复合。以空气-甲苯和空气-甲苯-水混合气体为对象，考察了甲苯在这些光催化剂上的分解情况。RuO_2/BaTi_4O_9体系在有水存在时光催化活性最高，说明水的分解是反应的重要步骤。采用溶胶-凝胶法制备了BaTi_4O_9超细粒子。热处理后，所制备的凝胶在873 K左右开始结晶，结晶良好的BaTi_4O_9在860 cm ~ 2处出现一个拉曼峰<-1>，具有Ti-O短双键的特征，从而提高了光催化分解水的活性。ESR谱表明活性BaTi_4O_9在77 K时，在紫外光照射下，有氧存在时产生g=2.018和g=2.004的信号。这个信号被分配到一个表面晶格O-自由基，这是建议负责作为空穴陷阱中心的电子。隧道结构钛酸盐的结论是有用的开发与高效率的氧化反应的光催化剂。

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.