Koichi Takahama

Photocatalytic activity of titanium oxide prepared by liquid phase deposition (LPD)

Titanium oxide powder and thin films were prepared from an (NH4)2TiF6 aqueous solution upon addition of boric acid in a process denoted as liquid phase deposition (LPD). In this process, titanium oxide powder and films were formed by the chemical equilibrium reaction between titanium fluoro-complex ions and metal oxide in the aqueous solution. The prepared powder and deposited films showed some features which differed from titanium oxide prepared from titanium alkoxide. The prepared powder and the deposited films included anatase (TiO2) and showed photocatalytic activity without prior calcination. The decomposition rate of CH3CHO reached a maximum when the powder or films were calcined at 300 °C. The LPD process enabled a uniform layer of TiO2 film to form homogeneously on the entire surface of glass wool. The prepared TiO2 contained fluorine and nitrogen. The amount of these impurities was reduced upon calcination.

Micro- and Mesoporous Clays Pillared with SiO2-TiO2 Mixed Oxide Sols

The silicate layers of montmorillonite clay were pillared with SiO2—TiO2 mixed oxide sols. Though the SiO2 sols alone are negatively charged, the addition of a small amount of Ti4+ converts the sols to the positively charged ones, which can be ion exchanged with the interlayer cations of montmorillonite. The resulting pillared clays have a basal spacing expanded to a value larger than 40 A. The spacing and the high surface area are maintained on calcination up to 500°C. A structural model for the arrangement of the intercalated sol particles is proposed on the basis of the adsorption studies; the small SiO2—TiO2 sol particles are packed between the silicate layers and the micropores with a slit width of 10–12 A are formed in the interstices between the sol particles and the silicate layers. In an attempt to introduce mesopores between the silicate layers, the arrangements of the sol particles have been modified by the incorporation of organic cations and by using supercritical drying to the sol pillared clays swelled with water.