[Si:1]([O-])([O-])([O-])[O-:2].[Na+].[Na+].[Na+].[Na+].S(=O)(=O)(O)[OH:11].[O:15](Cl)Cl.[Zr:18].[OH-:19].[Na+].[O:21]=[Al-:22]=O.[Na+]>[O-2].[Ti+4].[O-2].O>[OH-:2].[Si+4:1].[OH-:11].[OH-:15].[OH-:21].[OH-:19].[Zr+4:18].[OH-:2].[OH-:2].[OH-:2].[OH-:2].[Al+3:22].[OH-:2].[OH-:2]
Fine titanium oxide particle (Sakai Chemical Industry Co., Ltd., STR-100N) was added to water, to prepare 150 g/L aqueous slurry of TiO2. This slurry (5.0 L) was heated to 90° C. under stirring. While maintaining this temperature, a 150 g/L aqueous solution of sodium silicate, which corresponded to 6% by mass (in terms of SiO2) of TiO2, was added to the slurry. Then, 30% sulfuric acid was added thereto over 180 minutes such that the pH of the slurry should be 9. The resultant slurry was aged for 60 minutes. Next, under stirring, the temperature of the slurry was regulated so as to be 45° C. While the pH of the slurry was maintained to 8.5, a 100 g/L aqueous solution of zirconium oxychloride, which corresponded to 3.0% by mass (in terms of ZrO2) of TiO2, and 30% aqueous sodium hydroxide were added to the slurry as a single portion over 90 minutes. The resultant slurry was aged for 30 minutes. Then, under stirring, while the pH of the slurry was maintained to 8.5, a 250 g/L aqueous solution of sodium aluminate, which corresponded to 4.5% by mass (in terms of Al2O3) of TiO2, and 30% sulfuric acid were added to the slurry as a single portion over 120 minutes. The resultant slurry was aged for 30 minutes. Thus, on the surface of TiO2, coating layers of silicon hydroxide, zirconium hydroxide, and aluminum hydroxide were formed in the order as set forth.
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