Photocatalyst dispersion, photocatalyst coating film, photocatalyst powder, and method for using photocatalyst

Abstract

To provide a photocatalyst dispersion containing zirconium oxide, the dispersion enabling more effective expression of photocatalytic performance under excitation light with an excitation wavelength of 222 nm.SOLUTION: A photocatalyst dispersion comprising a photocatalyst containing zirconia, wherein the content of zirconia is 85 mass% or more and 100 mass% or less relative to the photocatalyst, the crystallite size of the photocatalyst is 8 nm or more and 15 nm or less, and the particle diameter D50 is 8 nm or more and 100 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photocatalyst dispersion, a photocatalyst coating, a photocatalyst powder, and a method for using the photocatalyst. [Background technology]

[0002] Photocatalysts are widely used by consumers for the purposes of sterilization, disinfection, deodorization, and decomposition of filth and harmful substances, etc. Titanium oxide, which is the most common photocatalyst, has a band gap of around 3 eV, so when used as a photocatalyst, it is excited by near-ultraviolet light with a wavelength of 300 to 400 nm, which has a corresponding amount of energy (see, for example, Patent Document 1).

[0003] Recently, there has been active development of titanium oxide for photocatalysis, aiming to expand the absorption band into the visible light region in order to utilize natural light and ambient light (see, for example, Patent Document 2). This trend is also seen in compounds other than titanium oxide (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-216530 [Patent Document 2] Patent Publication No. 2021-175697 [Patent Document 3] Japanese Patent Publication No. 2021-020222 [Non-patent literature]

[0005] [Non-Patent Document 1] Manuela Buonanno et al., “Far-UVCLight(222nm) efficiently and safely inactivates airborne human coronaviruses,” Sientifc Reports, 10, Article number: 10285 (2020) [Non-patent document 2] Takashi Kita, "Virus Inactivation by Ultraviolet Light and Demonstration Experiments," Chemistry and Industry, Chemical Society of Japan, January 1, 2022, pp. 26-28 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, it has been reported that UV lamps with a wavelength of 222 nm have a bactericidal effect and are harmless to humans (see, for example, Non-Patent Document 1). This means that 222 nm UV lamps have the potential to become as widespread in our living environments as fluorescent lamps. If they become such a common light source, they will be highly promising as excitation light for photocatalysts. Furthermore, since 222 nm UV light excites oxygen in the air but does not generate ozone (see, for example, Non-Patent Document 2), it has the advantage of being more illuminatingly efficient for photocatalysts than shorter wavelength UV light, such as the 185 nm wavelength of a mercury lamp. However, existing photocatalysts are not specifically designed to effectively utilize 222 nm excitation light.

[0007] The present invention has been made in consideration of the above problems, and its object is to provide a photocatalyst dispersion, photocatalyst coating, and photocatalyst powder containing zirconia that exhibit more effective photocatalytic performance than conventional methods when exposed to excitation light with an excitation wavelength of 222 nm. It is also an object of the present invention to provide a method for using a photocatalyst that uses the photocatalyst dispersion, photocatalyst coating, or photocatalyst powder. [Means for solving the problem]

[0008] The present invention provides the following: [1] A photocatalyst containing zirconia, The content of the zirconia is 85% by mass or more and 100% by mass or less relative to the photocatalyst, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D 50 A photocatalyst dispersion liquid characterized in that the particle size is 8 nm or more and 100 nm or less.

[0009] According to the above configuration, the crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, and the particle diameter D 50 Since the wavelength is 8 nm or more and 100 nm or less, the photocatalytic performance is more effectively expressed than before with respect to excitation light with an excitation wavelength of 222 nm. The inventors speculate that the reason for this is as follows. Regarding the crystallite diameter, if the crystallite size is too small, the band gap expands due to the quantum size effect, and the absorption efficiency of ultraviolet light with a wavelength of 222 nm decreases. Therefore, by setting the crystallite diameter to 8 nm or more, the photocatalytic performance is effectively expressed. Furthermore, the specific surface area, which is thought to be proportional to the amount of active sites of the photocatalyst, decreases as the crystallite diameter increases, and the photocatalytic performance also decreases. Therefore, by setting the crystallite diameter to 15 nm or less, the photocatalytic performance is effectively expressed. In addition, the particle diameter D 50 Regarding particle diameter D 50 If the particle diameter D is small, the crystallite diameter will also be small, and the photocatalytic performance will be reduced due to the quantum size effect. 50 By making the particle diameter D 8 nm or more, the photocatalytic performance is effectively expressed. 50 As the particle diameter D increases, the light with a wavelength of 222 nm is scattered, and the absorption efficiency decreases. 50 By making the particle size 100 nm or less, the photocatalytic performance is effectively exhibited. In the present invention, a KrCl excimer lamp is primarily assumed as the light source emitting excitation light with an excitation wavelength of 222 nm. However, light sources other than a KrCl excimer lamp that include this wavelength in their emission spectrum may also be used as long as they exhibit effects equivalent to those of the present invention.

[0010] Furthermore, the present invention provides the following: [2] The photocatalyst dispersion liquid according to [1], which has a light transmittance of 50% or more at a wavelength of 600 nm (optical path length of 10 mm) when dispersed in water at 1.0 mass % in terms of zirconium oxide.

[0011] If coarse particles are present in the photocatalyst, their light scattering effect may prevent efficient absorption of ultraviolet light with a wavelength of 222 nm. Therefore, if the light transmittance at a wavelength of 600 nm (optical path length: 10 mm) is 50% or more, it can be said that the content of coarse particles is low. In other words, if the light transmittance at a wavelength of 600 nm (optical path length: 10 mm) is 50% or more, ultraviolet light with a wavelength of 222 nm can be absorbed more efficiently.

[0012] Furthermore, the present invention provides the following: [3] Zirconium oxide equivalent: 1.0 x 10 -2 The methylene blue concentration was 1.0 × 10 -5 The methylene blue concentration after irradiating the water dispersion containing methylene blue (mol / L) with light of wavelength 222 nm using the following procedure is 1.0 × 10 -6 The photocatalyst dispersion liquid according to [1] or [2], wherein the photocatalyst dispersion liquid has a solubility of 100 mol / L or less. <Procedure> A Care222 (manufactured by Ushio Inc.) was used as a light source with an excitation wavelength of 222 nm. The distance between the light source irradiation window surface and the transmission surface of the quartz cell containing the methylene blue-added aqueous dispersion was set to 1.0 m, and the surfaces were kept horizontally facing each other. Light was irradiated for 85 hours using intermittent irradiation (setting mode 4 of this light source device), which alternated between 15 seconds of irradiation and 75 seconds of rest.

[0013] After irradiating the sample with 222 nm light, the concentration of methylene blue was 1.0 x 10 -6 When the concentration is 0.05 mol / L or less, it can be said that the photocatalytic performance is more effectively expressed.

[0014] Furthermore, the present invention provides the following: [4] A photocatalyst containing zirconia, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D 50 A photocatalytic coating film characterized in that the thickness is 8 nm or more and 100 nm or less.

[0015] According to the above configuration, the crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, and the particle diameter D 50 Since the wavelength is 8 nm or more and 100 nm or less, the photocatalytic performance is more effectively expressed than before with respect to excitation light with an excitation wavelength of 222 nm.

[0016] Furthermore, the present invention provides the following: [5] A photocatalyst containing zirconia is included. The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D 50 A photocatalytic powder characterized in that the particle size is 8 nm or more and 100 nm or less.

[0017] According to the above configuration, the crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, and the particle diameter D 50 Since the wavelength is 8 nm or more and 100 nm or less, the photocatalytic performance is more effectively expressed than before with respect to excitation light with an excitation wavelength of 222 nm.

[0018] Furthermore, the present invention provides the following: [6] A step A of preparing the photocatalyst dispersion liquid according to any one of the items [1] to [3], the photocatalyst coating film according to the item [4], or the photocatalyst powder according to the item [5]; A step B of irradiating the prepared photocatalyst dispersion liquid, the photocatalyst coating film, or the photocatalyst powder with light having a peak wavelength of 222 nm ± 2 nm; A method for using a photocatalyst, comprising:

[0019] According to the above configuration, the photocatalyst dispersion liquid, the photocatalyst coating film, or the photocatalyst powder is irradiated with light having a peak wavelength of 222 nm±2 nm, so that the photocatalytic performance is effectively expressed, and the effects of sterilization, disinfection, deodorization, and decomposition of harmful substances are excellent. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a photocatalyst dispersion, a photocatalyst coating film, and a photocatalyst powder containing zirconia that exhibit photocatalytic performance more effectively than conventional methods when exposed to excitation light with an excitation wavelength of 222 nm. It is also possible to provide a method for using a photocatalyst that uses the photocatalyst dispersion, the photocatalyst coating film, or the photocatalyst powder. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an X-ray diffraction spectrum of a powder obtained by drying the photocatalyst dispersion liquid of Example 1 at 100°C. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments. In this specification, zirconia (zirconium oxide) is a general term that includes 10 mass % or less of impurity metal compounds, including hafnia. In addition, in this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "substantially consist," and "consist only of."

[0023] [Photocatalyst dispersion] An example of the photocatalyst dispersion liquid according to this embodiment will be described below, however, the photocatalyst dispersion liquid of the present invention is not limited to the following example.

[0024] The photocatalyst dispersion liquid according to this embodiment is A photocatalyst containing zirconia is included, The content of the zirconia is 85% by mass or more and 100% by mass or less relative to the photocatalyst, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D 50 is 8 nm or more and 100 nm or less.

[0025] As described above, the photocatalyst contains zirconia. The photocatalyst may contain zirconia, and may contain a stabilizer in addition to zirconia as needed. That is, the photocatalyst may contain zirconia and a stabilizer. The stabilizer is usually dissolved in zirconia to form a solid solution, resulting in stabilized zirconia consisting of zirconia and the stabilizer.

[0026] The stabilizer is not particularly limited, but examples thereof include oxides of calcium, magnesium, yttrium, scandium, and lanthanoids.

[0027] The content of the zirconia is 85% by mass or more and 100% by mass or less relative to the photocatalyst. The photocatalyst dispersion liquid according to this embodiment focuses on the fact that zirconia exhibits higher photocatalytic performance than other metal oxides at an excitation wavelength of 222 nm, and since the content of the zirconia is 85% by mass or more relative to the photocatalyst, it functions suitably as a photocatalyst.

[0028] The content of the zirconia is preferably 90% by mass or more, and more preferably 95% by mass or more, based on the photocatalyst. The content of the zirconia is preferably 99.8 mass % or less, and more preferably 99.6 mass % or less, relative to the photocatalyst. The content of the zirconia is preferably 90% by mass or more and 99.8% by mass or less, and more preferably 95% by mass or more and 99.6% by mass or less, based on the photocatalyst.

[0029] When the photocatalyst contains a stabilizer, the content of the stabilizer can be more than 0 mass %, 1.0 mass % or more, and the like. When the photocatalyst contains a stabilizer, the content of the stabilizer can be 15% by mass or less, 12.0% by mass or less, or the like. When the photocatalyst contains a stabilizer, the content of the stabilizer can be more than 0 mass % and 15 mass % or less, or 1.0 mass % or more and 12.0 mass % or less, for example.

[0030] When the photocatalyst contains a stabilizer, the total amount of the zirconia and the stabilizer can be 95 mass % or more, 97 mass % or more, or the like. When the photocatalyst contains a stabilizer, the total amount of the zirconia and the stabilizer can be 100% by mass or less, 99.8% by mass or less, or the like. When the photocatalyst contains a stabilizer, the total amount of the zirconia and the stabilizer can be 95% by mass or more and 100% by mass or less, or 97% by mass or more and 99.8% by mass or less, for example.

[0031] The photocatalyst may contain an appropriate amount (for example, within a range of 5 mass % or less of all metal elements contained in the photocatalyst) of metals such as copper and platinum, in addition to zirconia and a stabilizer. A technique for improving photocatalytic performance by supporting metals such as copper and platinum for trapping excited electrons on titanium oxide is generally known, and this is because it is believed that the photocatalytic performance will not be reduced even if metals such as copper and platinum are similarly supported on the zirconia in the photocatalyst dispersion liquid of this embodiment.

[0032] The photocatalyst dispersion liquid preferably has a total content concentration of metal elements other than zirconium and hafnium of less than 15 mass% among all metal elements contained in the photocatalyst dispersion liquid. In the photocatalyst dispersion liquid according to this embodiment, it is not preferable from the viewpoint of efficiency as a photocatalyst that elements other than zirconium absorb excitation light with a wavelength of 222 nm. Therefore, when the total content concentration of metal elements other than zirconium and hafnium is less than 15 mass%, it can be said that the content of metal elements other than zirconium and hafnium is low, and it can be said that the photocatalyst dispersion liquid is efficient.

[0033] In particular, titanium oxide and tungsten oxide, which can be active species of photocatalysts, absorb ultraviolet light with a wavelength of 222 nm and are not expected to exhibit photocatalytic performance greater than that of zirconia, so it is more preferable that the photocatalyst dispersion liquid does not contain titanium or tungsten as metal elements.

[0034] The photocatalyst dispersion liquid preferably has a total content of metal elements excluding zirconium, calcium, magnesium, yttrium, scandium, and lanthanoids in all metal elements contained in the photocatalyst dispersion liquid, less than 5 mass % in terms of oxide.

[0035] The dispersion medium constituting the photocatalyst dispersion liquid is not particularly limited, but water (pure water, ion-exchanged water, etc.) is preferred because it has little absorption of light with a wavelength of 222 nm. When water is used as the dispersion medium, the particle diameter D 50 In addition, the visible light transmittance can be easily controlled.

[0036] The photocatalyst dispersion liquid has a particle diameter D 50 For example, the photocatalyst dispersion liquid may contain a minimum amount of organic and inorganic compounds for the purposes of dispersion and zeta potential adjustment, etc., in order to control the transmittance and visible light transmittance. For example, by adding an appropriate amount of hydrochloric acid to the photocatalyst dispersion liquid, the zeta potential of the zirconia particles can be adjusted to an appropriate positive potential, thereby suppressing the aggregation of the particles, thereby reducing the particle diameter D 50 , and the visible light transmittance can be suitably controlled.

[0037] The metal oxide concentration of the photocatalyst dispersion liquid is not particularly limited, but from the viewpoint of transport efficiency and dispersion stability, it may be within a range of, for example, 1% by mass or more and 40% by mass or less, or 10% by mass or more and 30% by mass or less.

[0038] The photocatalyst has a crystallite diameter of 8 nm or more and 15 nm or less. Because the photocatalyst has a crystallite diameter of 8 nm or more and 15 nm or less, the photocatalytic performance is more effectively expressed than in the past with respect to excitation light having an excitation wavelength of 222 nm. The inventors speculate that the reason for this is as follows. If the crystallite size is too small, the band gap expands due to the quantum size effect, and the absorption efficiency of ultraviolet light with a wavelength of 222 nm decreases. Therefore, by setting the crystallite diameter to 8 nm or more, the photocatalytic performance is effectively expressed. Furthermore, the specific surface area, which is thought to be proportional to the amount of active sites of the photocatalyst, decreases as the crystallite diameter increases, and the photocatalytic performance also decreases. Therefore, by setting the crystallite diameter to 15 nm or less, the photocatalytic performance is effectively expressed.

[0039] The crystallite size is preferably 8 nm or more, more preferably 10 nm or more. The crystallite size is preferably 14.9 nm or less, more preferably 13 nm or less. The crystallite size is preferably 8 nm or more and 14.9 nm or less, and more preferably 10 nm or more and 13 nm or less. The crystallite size is measured by the method described in the Examples.

[0040] The particle diameter D of the particles contained in the photocatalyst dispersion liquid 50 The particle diameter D of the particles contained in the photocatalyst dispersion liquid is 8 nm or more and 100 nm or less. 50 Since the wavelength is 8 nm or more and 100 nm or less, the photocatalytic performance is more effectively expressed than before with respect to excitation light with an excitation wavelength of 222 nm. The inventors speculate that the reason for this is as follows. Particle diameter D 50 If the particle diameter D is small, the crystallite diameter will also be small, and the photocatalytic performance will be reduced due to the quantum size effect. 50 By making the particle diameter D 8 nm or more, the photocatalytic performance is effectively expressed. 50 As the particle diameter D increases, the light with a wavelength of 222 nm is scattered, and the absorption efficiency decreases. 50 By making the particle size 100 nm or less, the photocatalytic performance is effectively exhibited.

[0041] The particle diameter D 50 is preferably 8 nm or more, more preferably 10 nm or more. The particle diameter D50 is preferably 96 nm or less, more preferably 30 nm or less. The particle diameter D 50 is preferably 8 nm or more and 96 nm or less, and more preferably 10 nm or more and 30 nm or less. The particle diameter D 50 The measurement method is the same as that described in the Examples.

[0042] The photocatalyst dispersion preferably has a light transmittance of 50% or more at a wavelength of 600 nm (optical path length of 10 mm) when the photocatalyst dispersion is made into an aqueous dispersion of 1.0 mass % in terms of zirconium oxide. If coarse particles exist in the photocatalyst, the particle diameter D 50 Even if the transmittance is within the above range, the light scattering effect may prevent efficient absorption of ultraviolet light with a wavelength of 222 nm. Therefore, if the light transmittance at a wavelength of 600 nm (optical path length: 10 mm) is 50% or more, it can be said that the content of coarse particles is low. In other words, if the light transmittance at a wavelength of 600 nm (optical path length: 10 mm) is 50% or more, ultraviolet light with a wavelength of 222 nm can be absorbed more efficiently.

[0043] The light transmittance at a wavelength of 600 nm is more preferably 51% or more, and even more preferably 65% ​​or more. The higher the light transmittance at a wavelength of 600 nm, the more preferable, and it is, for example, 90% or less, 80% or less, or the like. The light transmittance at a wavelength of 600 nm is more preferably 51% or more and 90% or less, and even more preferably 65% ​​or more and 80% or less.

[0044] The photocatalyst dispersion liquid has a zirconium oxide equivalent of 1.0 x 10 -2 The methylene blue concentration was 1.0 × 10 -5 The methylene blue concentration after irradiating the water dispersion containing methylene blue (mol / L) with light of wavelength 222 nm using the following procedure is 1.0 × 10 -6 It is preferably mol / L or less. <Procedure> A Care222 (manufactured by Ushio Inc.) was used as a light source with an excitation wavelength of 222 nm. The distance between the light source irradiation window surface and the transmission surface of the quartz cell containing the methylene blue-added aqueous dispersion was set to 1.0 m, and the surfaces were kept horizontally facing each other. Light was irradiated for 85 hours using intermittent irradiation (setting mode 4 of this light source device), which alternated between 15 seconds of irradiation and 75 seconds of rest.

[0045] After irradiating the sample with 222 nm light, the concentration of methylene blue was 1.0 x 10 -6 When the concentration is 0.05 mol / L or less, it can be said that the photocatalytic performance is more effectively expressed.

[0046] The methylene blue concentration after irradiation with light of 222 nm wavelength in the above procedure is more preferably 0.95×10 -6 mol / L or less, more preferably 0.8×10 -6 mol / L or less. The lower the methylene blue concentration after irradiation with light of 222 nm wavelength in the above procedure, the better. -6 mol / L or more, 0.2×10 -6 mol / L or more. The methylene blue concentration after irradiation with light of wavelength 222 nm in the above procedure is preferably 0.1 × 10 -6 mol / L or more 0.95×10 -6 mol / L or less, more preferably 0.2 × 10 -6 mol / L or more 0.8×10 -6 mol / L or less.

[0047] The photocatalyst dispersion liquid according to this embodiment can be obtained, for example, by the following method for producing a photocatalyst dispersion liquid.

[0048] [Method of manufacturing photocatalyst dispersion liquid] An example of a method for producing a photocatalyst dispersion liquid will be described below, however, the method for producing a photocatalyst dispersion liquid is not limited to the following example.

[0049] First, a zirconium oxide precursor is produced, then this zirconium oxide precursor is calcined to form zirconium oxide, and then this zirconium oxide is dispersed in a dispersion medium, thereby obtaining a zirconium oxide sol.

[0050] The zirconium oxide precursor may be any precursor that can be calcined to form zirconium oxide, and examples of such precursors include zirconium hydroxide. Many methods are known for obtaining zirconium hydroxide, including a method of neutralizing an aqueous zirconium salt solution with a base, and specifically, a method of neutralizing an aqueous zirconium oxychloride solution with aqueous ammonia.

[0051] The aqueous zirconium oxychloride solution may be prepared by dissolving zirconium oxychloride octahydrate crystals in water, or by dissolving basic zirconium carbonate in approximately two equivalents of hydrochloric acid relative to the zirconium to prepare an aqueous solution.

[0052] When the photocatalyst is stabilized zirconia, a method in which a predetermined amount of a salt of calcium, magnesium, yttrium, scandium, lanthanoid, or the like is added to an aqueous solution of zirconium oxychloride can be exemplified.

[0053] Next, zirconium hydroxide is calcined at a predetermined temperature to obtain zirconium oxide. The crystallite size of zirconium oxide is determined by the calcination temperature in this calcination step, so the calcination temperature is preferably 360°C or higher and 650°C or lower, and more preferably 400°C or higher and 600°C or lower. The crystallite diameter can be made 8 nm or more by setting the firing temperature to 360° C. or higher, and the crystallite diameter can be made 15 nm or less by setting the firing temperature to 650° C. or lower.

[0054] Next, the zirconium oxide obtained by the above-mentioned firing step is treated to have a particle diameter D 50 The particles are dispersed so that the particle size is 8 nm or more and 100 nm or less to obtain a zirconium oxide sol.

[0055] The dispersion method is not particularly limited, but wet grinding using grinding media and water as the solvent is preferred from the viewpoint of simplicity. In this dispersion step, in order to stabilize the dispersion, it is preferable to add an acid or a base to the dispersion solvent to control the zeta potential of the zirconium oxide sol.

[0056] Specific examples of the acid and base include nitric acid, hydrochloric acid, and ammonia. The particle diameter D of the zirconium oxide sol obtained in this dispersion step is 50 , and visible light transmittance depend on the combination of conditions such as the material of the grinding media during wet grinding, the shape of the grinding media, the diameter of the grinding media, the amount of grinding media used, the grinding strength (stirring speed if the grinding method is a stirring method), the amount of photocatalyst (zirconia, stabilized zirconia, etc.) to be ground, and the amount of acid or base added. Therefore, by adjusting the combination of these conditions, the particle diameter D 50 In general, by pulverizing the powder intensively, the particle diameter D 50 and visible light transmittance (light transmittance at a wavelength of 600 nm) become smaller, so the particle diameter D 50 If guidelines are given that the particle diameter D is 8 nm or more and 100 nm or less, and the light transmittance at a wavelength of 600 nm is 50% or more, a person skilled in the art can easily determine the desired particle diameter D without excessive trial and error. 50 and a zirconium oxide sol having a light transmittance of 600 nm. The crystallite size is hardly changed by the pulverization in this dispersion process. 50 , the visible light transmittance is controlled.

[0057] The zirconium oxide sol obtained in the dispersion step may be used as is as the photocatalyst dispersion liquid according to this embodiment, but may be further processed as needed. For example, the zirconium oxide sol contains the acid and base added during wet grinding, but these can be removed by purification such as ultrafiltration, or other components can be added. Furthermore, the zirconium oxide sol that has undergone the dispersion step may be further filtered or elutriated to remove coarse particles as needed.

[0058] Furthermore, the photocatalyst dispersion liquid according to this embodiment can also be used to produce zirconium oxide sol by utilizing a liquid phase reaction, such as hydrolysis of an aqueous zirconium salt solution or aging of zirconium hydroxide, without going through the production of zirconium oxide by firing as described above. Specifically, the crystallite size can be controlled by raising the temperature during aging of zirconium hydroxide. The temperature during the aging is preferably 30°C or higher and 100°C or lower, and more preferably 40°C or higher and 80°C or lower. The temperature rise rate during the aging is preferably 0.05° C. / hour or more and 1.0° C. / hour or less, and more preferably 0.1° C. / hour or more and 0.5° C. / hour or less. The retention time during the aging is preferably 10 minutes or more and 100 minutes or less, and more preferably 20 minutes or more and 60 minutes or less.

[0059] The method for producing a photocatalyst dispersion liquid according to this embodiment has been described above.

[0060] [Photocatalytic coating] The photocatalytic coating film according to this embodiment can be formed using the photocatalyst dispersion liquid. Specifically, for example, the photocatalyst dispersion liquid is applied or sprayed, and then dried.

[0061] Since the photocatalytic coating film is formed using the photocatalyst dispersion liquid, A photocatalyst containing zirconia is included, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D 50 is 8 nm or more and 100 nm or less.

[0062] The detailed structure of the photocatalyst in the photocatalytic coating film, the crystallite diameter of the photocatalyst, the particle diameter D 50 More preferable numerical ranges such as those described above in the section on photocatalyst dispersion liquid can be the same as those described above.

[0063] [Photocatalyst powder] The photocatalyst powder according to this embodiment can be produced using the photocatalyst dispersion liquid, specifically by drying and / or baking the photocatalyst dispersion liquid, for example.

[0064] Since the photocatalytic coating film is produced using the photocatalyst dispersion liquid, A photocatalyst containing zirconia is included, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D 50 is 8 nm or more and 100 nm or less.

[0065] The detailed structure of the photocatalyst in the photocatalyst powder, the crystallite diameter of the photocatalyst, the particle diameter D 50 More preferable numerical ranges such as those described above in the section on photocatalyst dispersion liquid can be the same as those described above.

[0066] [How to use photocatalyst] Hereinafter, a method for using the photocatalyst according to this embodiment will be described. The method of using the photocatalyst according to this embodiment is as follows: A step A of preparing the photocatalyst dispersion liquid, the photocatalyst coating film, or the photocatalyst powder; and step B of irradiating the prepared photocatalyst dispersion liquid, photocatalyst coating film, or photocatalyst powder with light having a peak at a wavelength of 222 nm±2 nm.

[0067] In the method for using the photocatalyst according to this embodiment, first, the photocatalyst dispersion liquid, the photocatalyst coating film, or the photocatalyst powder is prepared (Step A).

[0068] Next, the prepared photocatalyst dispersion liquid, photocatalyst coating film, or photocatalyst powder is irradiated with light having a peak at a wavelength of 222 nm±2 nm (step B).

[0069] The photocatalyst dispersion liquid, the photocatalyst coating film, or the photocatalyst powder contains zirconium oxide, which exhibits photocatalytic performance more effectively than conventional materials when exposed to excitation light with an excitation wavelength of 222 nm. According to the method of using the photocatalyst of this embodiment, the photocatalyst dispersion, the photocatalyst coating film, or the photocatalyst powder is irradiated with light having a peak wavelength of 222 nm±2 nm, so that the photocatalytic performance is effectively expressed, and excellent effects such as sterilization, disinfection, deodorization, and decomposition of harmful substances are achieved. [Example]

[0070] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Note that the photocatalyst dispersion liquids in the examples and comparative examples contain 1.3 to 2.5 mass % of hafnium oxide as an unavoidable impurity relative to zirconium oxide (calculated by the following formula (X)). <Expression(X)> ([Mass of hafnium oxide] / ([Mass of zirconium oxide]+[Mass of hafnium oxide]))×100(%)

[0071] The maximum and minimum contents of each component shown in the following examples should be considered as the preferred minimum and maximum contents of the present invention, regardless of the contents of other components. Furthermore, the maximum and minimum values ​​of the measured values ​​shown in the following examples should be considered to be the preferred minimum and maximum values ​​of the present invention, regardless of the content (composition) of each component.

[0072] The reagents used in the examples are listed below. Zirconium oxychloride aqueous solution (Daiichi Kigenso Kagaku Kogyo, ZC-20, 20.3% by mass in terms of ZrO2) Sodium hydroxide (Fujifilm Wako Pure Chemical Industries, over 97% by mass) 25% by mass sodium hydroxide aqueous solution (prepared by dissolving the above sodium hydroxide in ion-exchanged water) 25% by mass ammonia water (Sigma-Aldrich, special grade) 35% by weight hydrochloric acid (Sigma-Aldrich, special grade) Methylene blue (Tokyo Chemical Industry, over 98% by mass) Titanium(IV)oxide Aeroxide P25(ACROS ORGANICS)

[0073] [Preparation of photocatalyst dispersion liquid] Example 1 Pure water was added to 886.7 g of an aqueous zirconium oxychloride solution (containing 180.0 g of ZrO2) to make a total weight of 1000 g. Meanwhile, pure water was added to 747.9 g of a 25 mass % aqueous sodium hydroxide solution to make a total weight of 1400 g. The aqueous zirconium oxychloride solution prepared above was then added to the stirred aqueous sodium hydroxide solution prepared above, and the temperature was raised from room temperature (25°C) to 50°C over 2 hours. After reaching 50°C, the temperature was maintained for 30 minutes. The mixture was then allowed to cool naturally to room temperature. The pH of the solution at this time was 13.5. This solution was filtered and washed with 5000 g of pure water to remove impurities in the zirconium hydroxide, yielding 876 g of wet cake. 725 g of this wet cake was placed in a beaker, and pure water was added to make the total weight 1000 g. This was stirred for 10 minutes to uniformly disperse the zirconium hydroxide. Thereafter, 61 g of 35% by mass hydrochloric acid was added as a deflocculating agent, and the mixture was heated to 100° C. and stirred and maintained for 72 hours to obtain a zirconium oxide sol. The zirconium oxide sol was purified and concentrated by ultrafiltration to obtain a zirconium oxide sol having a pH of 3.3 and a ZrO2 concentration of 15 mass %. This zirconium oxide sol was used as the photocatalyst dispersion liquid according to Example 1.

[0074] Example 2 Pure water was added to 886.7 g of an aqueous zirconium oxychloride solution (containing 180.0 g of ZrO2) to make the total weight 1000 g. Meanwhile, pure water was added to 596 g of a 25 mass % aqueous ammonia solution to make the total weight 1200 g. The aqueous zirconium oxychloride solution prepared above was then added to the stirred aqueous ammonia solution. The pH of the solution at this time was 11.4. This solution was filtered and washed with 5000 g of pure water to remove impurities in the zirconium hydroxide, yielding 628 g of wet cake. 100 g of this wet cake was placed in an alumina crucible and calcined at 450°C for 3 hours. Zirconium oxide was obtained by this calcination. 26.0 g of the zirconium oxide, 73.3 g of ion-exchanged water, and 0.7 g of 60 mass % nitric acid were mixed and bead milled using 500 g of 0.1 mmφ milling media (material: stabilized zirconia, manufactured by Nikkato Corporation, product name: YTZ) and a benchtop bead mill RMB (manufactured by Imex Co., Ltd.) at 1600 rpm for 2 hours to obtain a zirconium oxide sol. The zirconium oxide sol was ultrafiltered using a membrane filter, washed once with 100 g of pure water containing 1.0 g of 35% by mass hydrochloric acid, and then washed four times with 100 g of pure water. This washing procedure was repeated four times to obtain a zirconium oxide sol with a pH of 3.3 and a ZrO2 concentration of 12% by mass. This zirconium oxide sol was used as the photocatalyst dispersion liquid of Example 2.

[0075] Example 3 The same procedure as in Example 2 was carried out except that 100 g of the wet cake was baked by holding it at 600° C. for 3 hours, and a photocatalyst dispersion liquid according to Example 3 was obtained.

[0076] Example 4 The same procedure as in Example 2 was carried out except that 100 g of the wet cake was calcined by holding it at 600°C for 3 hours and 500 g of 0.3 mmφ grinding media (material: stabilized zirconia, manufactured by Nikkato Corporation, product name: YTZ) was used, and a photocatalyst dispersion liquid of Example 4 was obtained.

[0077] Example 5 The same procedure as in Example 2 was carried out except that 100 g of the wet cake was calcined by holding it at 600°C for 3 hours and 500 g of 0.5 mmφ grinding media (material: stabilized zirconia, manufactured by Nikkato Corporation, product name: YTZ) was used, and a photocatalyst dispersion liquid of Example 5 was obtained.

[0078] Example 6 The same procedure as in Example 2 was carried out except that 100 g of the wet cake was calcined by holding it at 600°C for 3 hours and 500 g of 1.0 mmφ grinding media (material: stabilized zirconia, manufactured by Nikkato Corporation, product name: YTZ) was used, and a photocatalyst dispersion liquid of Example 6 was obtained.

[0079] (Comparative Example 1) A photocatalyst dispersion liquid according to Comparative Example 1 was obtained in the same manner as in Example 2, except that 100 g of the wet cake was baked by holding it at 350° C. for 3 hours.

[0080] (Comparative Example 2) A photocatalyst dispersion liquid according to Comparative Example 2 was obtained in the same manner as in Example 2, except that 100 g of the wet cake was baked by holding it at 700° C. for 3 hours.

[0081] (Comparative Example 3) Pure water was added to 886.7 g of an aqueous zirconium oxychloride solution (containing 180.0 g of ZrO2) to make the total weight 1000 g. Meanwhile, pure water was added to 747.9 g of a 25 mass % aqueous sodium hydroxide solution to make the total weight 1400 g, and the mixture was heated to 90°C. The aqueous zirconium oxychloride solution prepared above was then added to the stirred aqueous sodium hydroxide solution heated to 90°C and prepared above, and the mixture was then cooled to room temperature. The pH of the solution at this time was 13.7. This solution was filtered and washed with 5,000 g of pure water to remove impurities from the zirconium hydroxide, yielding 652 g of wet cake. 539 g of this wet cake was placed in a beaker, and pure water was added to make the total weight 1,000 g. This was stirred for 10 minutes to uniformly disperse the zirconium hydroxide. Thereafter, 61 g of 35% by mass hydrochloric acid was added as a deflocculating agent, and the mixture was heated to 100° C. and stirred and maintained for 72 hours to obtain a zirconium oxide sol. The zirconium oxide sol was purified and concentrated by ultrafiltration to obtain a zirconium oxide sol having a pH of 3.3 and a ZrO2 concentration of 15%. This zirconium oxide sol was used as a photocatalyst dispersion liquid according to Comparative Example 3.

[0082] Comparative Example 4 Titanium(IV) oxide Aeroxide R20 g of P25, 73.3 g of ion-exchanged water, and 0.7 g of 60% by mass nitric acid were mixed, and the mixture was milled using 500 g of 0.1 mmφ milling media (material: stabilized zirconia, manufactured by Nikkato Corporation, product name: YTZ) and a benchtop bead mill RMB (manufactured by Imex Co., Ltd.) at 1600 rpm for 2 hours to obtain a titanium oxide sol. The titanium oxide sol was ultrafiltered using a membrane filter, washed once with 100 g of pure water containing 1.0 g of 35% by mass hydrochloric acid, and then washed four times with 100 g of pure water. This washing procedure was repeated four times to obtain a titanium oxide sol with a pH of 3.5 and a TiO concentration of 12%. 15.0 g of this titanium oxide sol was mixed with 85.0 g of the zirconium oxide sol of Example 2 to prepare a photocatalyst dispersion liquid according to Comparative Example 4.

[0083] [Particle diameter D 50 Measurement of The photocatalyst dispersion liquids of the Examples and Comparative Examples were diluted with ion-exchanged water to 1.0 mass % in terms of ZrO2, and then placed in an apparatus (a dynamic light scattering particle size distribution measuring apparatus ("Zetasizer Nano ZS" manufactured by Malvern Panalytical)) to measure the particle diameter D of the photocatalyst dispersion liquid. 50 The results are shown in Table 1. <Measurement conditions> Measurement temperature: 25℃ Scattering angle: 173° Cell: Genuine disposable cell Repeat count: 3 (particle diameter D 50 is the average of three measurements)

[0084] [Crystallite size measurement] The photocatalyst dispersions obtained in the Examples and Comparative Examples were dried at 100°C and measured using an X-ray diffractometer (RINT2500, manufactured by Rigaku) ​​to obtain X-ray diffraction charts. The measurement conditions were as follows. Figure 1 shows the X-ray diffraction chart for Example 1. <Measurement conditions> Measurement equipment: X-ray diffraction equipment (Rigaku, RINT2500) Source: CuKα source Measurement method: θ-2θ continuous measurement Tube voltage: 50kV Tube current: 300mA Scanning angle: 2θ=10~50° Scanning speed: 1° / min

[0085] The crystallite size was calculated from the Bragg angles and half-widths of two peaks at approximately 2θ=28° and 31.5°, which were attributed to the monoclinic (−111) plane and (111) plane, respectively. Specifically, it was calculated using the following Scherrer formula. Crystallite diameter = K × λ / (β × cosθ) Here, K is the shape factor, λ is the wavelength of the X-ray (nm), β is the half-width of the peak (rad), and θ is the Bragg angle (°). In this example, K=0.94 and λ=0.1542 nm.

[0086] The Bragg angles of the peaks in Example 1 (see FIG. 1) were 28.09° and 31.39°, and the half-widths were 0.01331 rad and 0.01389 rad, respectively. The crystallite diameters corresponding to the peaks calculated by the Scherrer formula were 10.75 nm and 11.30 nm, respectively, and the average of these, 11.0 nm, was taken as the crystallite diameter value for Example 1. The crystallite diameters of the other examples and comparative examples were determined in the same manner. The results are shown in Table 1.

[0087] When the photocatalyst is stabilized zirconia, a peak of the tetragonal (101) plane or the cubic (111) plane appears near 2θ=30°. When a peak of the tetragonal (101) plane or the cubic (111) plane exists, the crystallite size is calculated by the following formula. [Crystallite diameter] = [Crystallite diameter calculated from tetragonal (101) face or cubic (111) face] × [Tetragonal phase ratio (%)] + [Average crystallite diameter calculated from monoclinic (-111) face and monoclinic (111) face] × {100 - [Tetragonal phase ratio (%)]} [Tetragonal phase ratio (%)]={It(101)+Ic(111)} / {It(101)+Ic(111)+Im(-111)+Im(111)}×100 Here, Im(-111) is the diffraction intensity of (-111) in the monoclinic phase, and Im(111) is the diffraction intensity of (111) in the monoclinic phase. The method for calculating the crystallite diameter calculated from the tetragonal (101) face or the cubic (111) face is the same as that for the monoclinic crystal. It(101) is the diffraction intensity of (101) in the tetragonal phase. Ic(111) is the diffraction intensity of (111) in the cubic phase.

[0088] [Measurement of light transmittance at 600 nm] First, the photocatalyst dispersions of the Examples and Comparative Examples were diluted with ion-exchanged water to 1.0% by mass in terms of zirconium oxide. Next, 3.0 g of the diluted solution (sample) was placed in a quartz cell with an optical path length of 10 mm and sealed with a plastic push-fit lid. Thereafter, the light transmittance at 600 nm was measured using a UV-Vis-NIR spectrophotometer. The results are shown in Table 1. <Measurement equipment and conditions> Measurement equipment: V-750 (JASCO) Method: Transmission method Measured concentration: 1.0% in terms of ZrO2 Optical path length: 10mm Cell material: Quartz

[0089] [Measurement of methylene blue concentration after irradiation with 222 nm light] First, ion-exchanged water and methylene blue were added to the photocatalyst dispersion liquids of the Examples and Comparative Examples, and the zirconium concentration was adjusted to 1.0 × 10 in terms of zirconium oxide. -2 Mass %, methylene blue concentration 1.0 × 10 -5 A methylene blue-added photocatalyst dispersion was prepared with a concentration of 1000 mol / L. Next, 3.0 g of the methylene blue-added photocatalyst dispersion liquid (sample) was placed in a quartz cell with an optical path length of 10 mm, and the cell was sealed with a plastic push-fit lid. Next, using a Care222 (manufactured by Ushio Inc.) as a light source with an excitation wavelength of 222 nm, the distance between the surface of the light source irradiation window and the surface of the transmission surface of the quartz cell containing the sample was set to 1.0 m, and the surfaces were kept horizontally facing each other.The light source was operated for 85 hours with intermittent irradiation (light source device setting mode 4), which alternated between 15 seconds of irradiation and 75 seconds of rest. The methylene blue concentration of the sample was then determined. The methylene blue concentration was determined by measuring the visible light transmittance of the sample in a quartz cell, and calculating the absorbance at 664 nm and the molar absorption coefficient ε = 9.5 × 10 using the Lambert-Beer law A = εcl (A: absorbance, ε: molar absorption coefficient (L / mol / cm), c: solute molar concentration (mol / L), l: optical path length (cm)). 4 The visible light transmittance was measured using an ultraviolet-visible-near-infrared spectrophotometer. The results are shown in Table 1. <Measurement equipment and conditions> Measurement equipment: V-750 (JASCO) Method: Transmission method Measured concentration: 1.0 x 10 in terms of ZrO2 -2 % Optical path length: 10mm Cell material: Quartz

[0090] [Metal concentration measurement] The photocatalyst dispersions of the examples and comparative examples were dissolved by heating in sulfuric acid, and then all metal elements were quantified by ICP-AES. The concentrations of metals other than Zr and Hf are shown in Table 1. <Measuring equipment> Measuring device: ULTIMA2 (manufactured by Horiba Ltd.)

[0091] [Table 1]

Claims

1. A photocatalyst containing zirconia is included, The content of the zirconia is 85% by mass or more and 100% by mass or less with respect to the photocatalyst, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D ５０ A photocatalyst dispersion liquid characterized in that the particle size is 8 nm or more and 100 nm or less.

2. 2. The photocatalyst dispersion liquid according to claim 1, wherein the photocatalyst dispersion liquid has a light transmittance of 50% or more at a wavelength of 600 nm (optical path length: 10 mm) when the photocatalyst dispersion liquid is 1.0 mass % in terms of zirconium oxide.

3. Zirconium oxide equivalent: 1.0 x 10 －２ The methylene blue concentration was 1.0 × 10 －５ The methylene blue concentration after irradiating the aqueous dispersion of methylene blue at a concentration of 1.0 × 10 mol / L with light of 222 nm wavelength according to the following procedure was 1.0 × 10 －６ 3. The photocatalyst dispersion liquid according to claim 1, wherein the photocatalyst dispersion liquid has a concentration of 1000 mol / L or less. <Procedure> A Care222 (manufactured by Ushio Inc.) was used as a light source with an excitation wavelength of 222 nm. The distance between the light source irradiation window surface and the transmission surface of the quartz cell containing the methylene blue-added aqueous dispersion was set to 1.0 m, and the surfaces were held horizontally facing each other. Light was irradiated for 85 hours using intermittent irradiation (light source device setting mode 4) that alternated between 15 seconds of irradiation and 75 seconds of rest.

4. A photocatalyst containing zirconia is included, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D ５０ A photocatalytic coating film characterized in that the particle size is 8 nm or more and 100 nm or less.

5. A photocatalyst containing zirconia is included, The crystallite diameter of the photocatalyst is 8 nm or more and 15 nm or less, Particle diameter D ５０ The photocatalytic powder is characterized in that the particle size is 8 nm or more and 100 nm or less.

6. A step A of preparing the photocatalyst dispersion liquid according to claim 1 or 2, the photocatalyst coating film according to claim 4, or the photocatalyst powder according to claim 5; A step B of irradiating the prepared photocatalyst dispersion liquid, the photocatalyst coating film, or the photocatalyst powder with light having a peak wavelength of 222 nm ± 2 nm; A method for using a photocatalyst, comprising:

Images