Preparation of meso-porous TiO₂ gels and their characterization

Mesoporous TiO₂ gels, which are attractive for their potential application to photocatalysts and electrodes for wet solar cells, have been prepared by a newly developed method and their microstructure was investigated. Monolithic gels were obtained by hydrolysis of Ti(n-C₄H₉O)₄ in an ethanol/ethylacetoacetate solution. The wet gels were aged and dried after immersion in an ethanol solution of surfactants, cetyltrimethylammonium chloride (CTAC) or benzyltrimethylammonium chloride (BTAC) (CTAC- or BTAC-modified xerogels). The organic substances in the gels can be removed by heating up to 500°C in air. After calcination at 600°C, emanation thermal analysis (ETA) and N₂-adsorption measurements were made. The BET surface area, the pore volume and the pore size increased as a result of surfactant modification. The most probable pore radius of the xerogel, BTAC-modified gels and CTAC-modified gel was 2.4, 2.8 and 5.0 nm, respectively. The pore size distribution of mesoporous TiO₂ gels depends on the size of surfactant micelles. The microstructure of mesoporous gels can be characterized by ETA. The ²²⁰Rn-release rate of the samples labelled with ²²⁸Th and ²²⁴Ra during heating was xerogel < BTAC-modified gel < CTAC-modified gel. The ²²⁰Rn release rate depends on the pore size of the gels as well as the surface areas.