Preparation of Gold Microcrystal-Doped TiO2, ZrO2 and Al2O3 Films Through Sol-Gel Process

Au-microcrystal-doped TiO₂, ZrO₂ and Al₂O₃ films were made by sol-gel dip-coating method using titanium, zirconium and aluminum alkoxides with HAuCl₄ · 4H₂O. The influence of the oxide matrix composition on the maximum amount of the Au microcrystals that can be incorporated in the oxide film was examined. Some amount of Au microcrystals were exhausted to the surface of Au microcrystal-doped oxide films when an excess amount of HAuCl₄ · 4H₂O was dissolved in the coating solution. The maximum amount of Au that can be incorporated in the oxide film was found to increase with the increase of the pH point at zero charge (PZC) of the matrix oxide. This should be due to the fact that AuCl ₄ ^- ions are charged negative and also Au microcrystals tend to charge negative, so that the oxide gel with high PZC, which has a tendency to charge positive, may fix the ions and/or microcrystals to its interior. A maximum amount of Au microcrystals as high as 12.6 vol% was attained in an Au:Al₂O₃ film.