To obtain nanocrystalline TiO2/ZnO, the following procedure was used. Liquid TiCl3 was dissolved in water in the desired concentration. Two milliliters of TiCl3 (20-30 wt % in HCl,
Aldrich Chemicals, U.S.A.) was added to an ice-cooled mixture consisting of 20 mL of deionized water (18 M¿ cm). The pH was adjusted to 3.0-3.5 using a 7% ammonium hydroxide solution with constant stirring. After stirring for 30 min, a homogeneous violet-black colored solution was obtained, which was stable for a period of several hours at room temperature.Clean indium tin oxide (ITO) substrates were floated on the surface of the dilute solution at room temperature (27 °C) to deposit a thin film. The solution became turbid after soaking for a period of about 15 min. After soaking for 6 h, the substrate was carefully rinsed with deionized water, ultrasonically cleaned with deionized water, and then dried under flowing argon gas.