Preparation of a TiO2 nanoparticulate film using a two-dimensional sol-gel process

The preparation of a TiO2 thin film was investigated by a newly developed two-dimensional (2D) sol-gel process. When a chloroform solution of monomer or tetramer of tetrabutoxytitanium (TBT) was spread on the surface of an aqueous subphase, the TBT was hydrolyzed and polycondensed at the air/water interface to give floating gels. These gels were gathered by 2D compression to yield a uniform gel film on the water surface. The addition of chelating agents such as acetic acid and acetylacetone to the aqueous subphase or spreading solution was effective in suppressing the 2D hydrolysis/polycondensation reactions and in increasing the stability of the floating gel film. Up to 20 layers of the floating gel film prepared on aqueous acetic acid could be quantitatively transferred onto a suitable substrate using Langmuir-Blodgett techniques. The addition of n-octadecyl acetoacetate in the spreading solution of monomeric Ti butoxide and ethoxide resulted in quantitative transference of the gel films onto substrates without a limitation on the number of depositions. The deposited TiO2-based gel films could be converted into nanothick TiO2 films by calcination at 773 K for 30 min. It was suggested that the oxide films prepared from gel films of less than a few tens of layers were composed of quantum-size TiO2 particulates. The thickness and the density of the nanoparticulate TiO2 films could be controlled by the number of deposited gel film layers and the surface pressure of the gel film layer during deposition. The controllable thickness of the TiO2 film by one deposited gel film layer was estimated to be 2-3 Angstrom.