Titanium oxide photocatalyst, process for producing the same and application
View Patent ↗Titanium oxide-based photocatalysts which contain a metal halide in titanium oxide and which are prepared from titanium oxide and/or its precursor, which may optionally be heat treated, by contact with a reactive gas containing a metal halide of the formula MX n or MOX n (wherein M=a metal, X=a halogen, and n=an integer) with heating stably develop a high photocatalytic activity with visible light irradiation. The photocatalysts may subsequently be stabilized by contact with water or by heat treatment, and/or promoted by contact with a heteropoly acid and/or an isopoly acid so as to include a metal complex in the titanium oxide. Photocatalysts prepared in this manner exhibit novel ESR features. The present invention also provides methods for preparing these photocatalysts, a photocatalyst dispersion and a photocatalytic coating fluid containing such a photocatalyst, and photocatalytic functional products and methods for their manufacture using the photocatalyst.
1. A titanium oxide-based photocatalyst which is characterized by comprising a titanium oxide and an additional metal compound, and developing a photocatalytic activity by irradiation with visible light, the additional metal compound comprising at least one metal halide.
2. The titanium oxide-based photocatalyst as set forth in claim 1 wherein the content of the additional metal compound as a metal is at least 0.1 mass % and at most 300 mass % based on the titanium oxide.
3. The titanium oxide-based photocatalyst as set forth in claim 1 wherein the metal is at least one selected from Ti, Si, V, Sn, Sb, W, Nb, Bi, P, Mo, Cs, Ge, As, and Ce.
4. The titanium oxide-based photocatalyst as set forth in claim 1 wherein the halide is a chloride.
5. The titanium oxide-based photocatalyst as set forth in claim 1 wherein the titanium oxide has absorptivity for visible light.
6. The titanium oxide-based photocatalyst as set forth in claim 1 wherein the titanium oxide has oxygen defects.
7. The titanium oxide-based photocatalyst as set forth in claim 1 wherein the primary crystal structure of the titanium oxide is anatase.
8. A photocatalytic functional product characterized by comprising a substrate having a titanium oxide-based photocatalyst as set forth in claim 1 deposited on a surface of the substrate.
9. A photocatalytic functional product characterized by comprising a substrate having a film which comprises a titanium oxide-based photocatalyst as set forth in claim 1 and a binder component formed on a surface of the substrate, the content of the photocatalyst in the film being 5-95 mass %.
10. A photocatalyst dispersion characterized by comprising a titanium oxide-based photocatalyst as set forth in claim 1 dispersed in a solvent.
11. A photocatalyst dispersion as set forth in claim 10 wherein the photocatalyst has an average particle diameter of at most 500 nm.
12. A photocatalytic coating fluid characterized in that it is prepared using a photocatalyst dispersion as set forth in claim 11 .
13. A photocatalytic coating fluid characterized by comprising a titanium oxide-based photocatalyst as set forth in claim 1 in a solvent.
14. A photocatalytic coating fluid characterized by comprising a titanium oxide-based photocatalyst as set forth in claim 1 and a binder in a solvent, the content of the titanium oxide-based photocatalyst being in the range of 5-95 mass % based on the total nonvolatile content in the fluid.
15. A titanium oxide-based photocatalyst which is characterized by containing a metal halide in titanium oxide and having a thermal desorption spectrum in which a peak of a molecular ion or a fragment ion of a halogen-containing substance appears at a temperature of 623 K or higher.
16. A titanium oxide-based photocatalyst developing a photocatalytic activity by irradiation with visible light, which is characterized by having ESR spectrum measured at a temperature of at least 5 K in which a peak is observed in the range in which the g value is 1.950-2.030 when irradiated with visible light, that peak not being substantially observed in the dark.
17. The titanium oxide-based photocatalyst as set forth in claim 16 which has an ESR spectrum measured at a temperature lower than 77 K in which a peak appears in the range in which the g value is 1.986-1.994.
18. A titanium oxide-based photocatalyst developing a photocatalytic activity by irradiation with visible light, which is characterized by having an ESR spectrum measured at room temperature in a substantially oxygen-free atmosphere in which the highest peak observed in the range in which the g value is 1.950-2.030 when irradiated with visible light has a peak intensity with a half life of at least 3 minutes after the irradiation with visible light is stopped.
19. A titanium oxide-based photocatalyst prepared by a method for the preparation of a titanium oxide-based photocatalyst characterized in that titanium oxide and/or its precursor is brought into contact with a reactive medium containing a metal halide of the formula MX n or MOX n (wherein M=a metal, X=a halogen, and n=an integer).