Photocatalysts with tunnel structures for decomposition of water. Part 1.—BaTi4O9, a pentagonal prism tunnel structure, and its combination with various promoters

Abstract

Photocatalysts have been prepared by impregnating barium tetratitanate, BaTi₄O₉, which has a pentagonalprism tunnel structure, with aqueous solutions of CoCl₂, Ni(NO₃)₂, In(NO₃)₃, RuCl₃, H₂IrCl₆ or H₂PtCl₆, and then activating with either reduction or oxidation. For decomposition of water under irradiation with light from a Xe lamp, reduction caused low photocatalytic activities. Oxidation of RuCl₃-impregnated BaTi₄O₉ at 848 K led to active photocatalysts which produce H₂ and O₂ in the correct stoichiometric ratio. The photocatalytic activity increased with an increase in the amount of loaded Ru until it reached 1 wt. %, and remained nearly constant up to 3 wt. %. The X-ray photoelectron spectra showed that the active Ru was in a tetravalent state, forming RuO₂ on the BaTi₄O₉ surface. UV diffuse reflectance spectra showed that BaTi₄O₉ had a threshold of absorption of light at around 410 nm which reached a maximum at 320 nm. From high-resolution transmission electron microscopy and microanalysis the spherical RuO₂ particles of 1.4–3.0 nm in diameter were found to be dispersed uniformly on the regular lattice of BaTi₄O₉. It is concluded that the pentagonal-prism tunnel structure of BaTi₄O₉ has a ‘nest’ effect and is responsible for the high dispersion of RuO₂ particles, which leads to the high photocatalytic activity.