Sheet-form photocatalyst and method for producing same

Abstract

According to one embodiment, the present invention addresses the problem of providing a novel photocatalyst for which there is used a sheet-form structure that contains titanic acid and / or a titanate such as an alkali metal titanate. The aforementioned problem is solved by a sheet-shaped photocatalyst that contains titanium oxide and / or a composite oxide of a titanium element and another metal element, wherein the titanium oxide and / or composite oxide of a titanium element and another metal element has a rod shape having an average diameter of 10.0 nm or greater and an average aspect ratio of 1.5-16.0, and titanium oxides and / or composite oxides of a titanium element and another metal element in the rod shape are connected to form a sheet shape.

Description

Sheet-shaped photocatalyst and its manufacturing method

[0001] The present invention relates to a sheet-shaped photocatalyst and a method for producing the same.

[0002] Titanate compounds are widely used in photocatalysts, phosphors, dye-sensitized solar cells, adsorbents, pigments, etc. Among them, some alkali metal titanates have been widely studied as purification materials for aqueous environments due to their ion exchange properties (see Patent Documents 1 to 4). The use of alkali metal titanates as photocatalysts has also been studied (see Non-Patent Document 1).

[0003] Japanese Patent Publication "Patent No. 4428541" Japanese Unexamined Patent Publication "JP 2015-64252 A" Japanese Patent Publication "Patent No. 7013067" Japanese Patent Publication "Patent No. 7462930"

[0004] Appl. Catal. B-Environ. 2006, 63, 20-30

[0005] An object of one aspect of the present invention is to provide a novel sheet-like photocatalyst using a sheet-like structure containing titanate containing a metal element such as an alkali metal or an alkaline earth metal. Another object of the present invention is to provide a novel sheet-like photocatalyst using a sheet-like structure containing titanate and / or titanic acid.

[0006] In order to solve the above-mentioned problems, a photocatalyst according to one embodiment of the present invention is a sheet-shaped photocatalyst containing a complex oxide of titanium and other metal elements and / or titanium oxide, wherein the complex oxide of titanium and other metal elements and / or titanium oxide has a rod shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped complex oxide of titanium and other metal elements and / or titanium oxide are linked to form the sheet shape.

[0007] In order to solve the above-mentioned problems, a method for producing a sheet-shaped photocatalyst according to one embodiment of the present invention comprises the steps of: forming a sheet-shaped structure M containing titanate and / or titanic acid, the sheet-shaped structure M being represented by the following formula (1): ｍ （２－Ｘ）／ｍ H Ｘ TiＹ O ２Ｙ＋１ ・nH ２ The method for producing a sheet-shaped photocatalyst includes a calcination step of calcining O (1) (wherein X is a real number of 0.50 to 2.00, Y is a real number of 2 to 8, n is a real number of 0 to 3, M is a metal atom, and m is the valence of the metal atom M) until rod-shaped objects having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced, and the rod-shaped objects are linked to form a sheet-shaped photocatalyst.

[0008] According to one aspect of the present invention, a photocatalyst having a specific shape can be easily produced using a sheet-like structure containing titanate and / or titanic acid containing a metal element such as an alkali metal or an alkaline earth metal.

[0009] 1 is a diffraction pattern showing the results of powder X-ray diffraction analysis of the calcined powders obtained in Examples 1 and 2, the sheet-like structure of Comparative Example 1, and the calcined powder obtained in Comparative Example 2. FIG. 2 is a scanning electron microscope photograph showing a portion of a rod-shaped composite oxide of titanium element and another metal element contained in the calcined powder of Example 1. FIG. 3 is a scanning electron microscope photograph showing a portion of the surface of the calcined powder of Example 1. FIG. 4 is a graph showing the results of evaluation of the photocatalytic properties of the photocatalyst obtained in Example 1 and the platinum nanoparticle-supported photocatalyst obtained in Example 3. FIG. 5 is a diffraction pattern showing the results of powder X-ray diffraction analysis of the calcined powder obtained in Example 4, the platinum nanoparticle-supported photocatalyst obtained in Example 5, and the sheet-like structure of Comparative Example 3. FIG. 6 is a scanning electron microscope photograph showing a portion of the rod-shaped titanium oxide contained in the calcined powder of Example 4. FIG. 7 is a scanning electron microscope photograph showing a portion of the surface of the calcined powder of Example 4. FIG. 8 is a graph showing the results of evaluation of the photocatalytic properties of the photocatalyst obtained in Example 4, the platinum nanoparticle-supported photocatalyst obtained in Example 5, and the sheet-like structure of Comparative Example 3. FIG. 1 is a schematic diagram showing the upcycling of a sheet-shaped ion exchanger after use in water treatment, water purification, etc. into a photocatalyst.

[0010] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[0011] The present inventors have discovered that when an ion exchanger using a sheet-like structure containing an alkali metal titanate, which they developed, is calcined after ion exchange, it is surprisingly possible to obtain a sheet-like calcined powder in which rod-shaped composite oxides of titanium and other metal elements are linked to form a sheet shape without causing aggregation during calcination. They have also discovered that the resulting sheet-like calcined powder has photocatalytic properties. Specifically, the present inventors have discovered that a novel sheet-like photocatalyst having a specific shape can be easily produced using a sheet-like structure containing a titanate containing a metal element such as an alkali metal or alkaline earth metal, and have thus completed the present invention.

[0012] Furthermore, the present inventors have found that even when a sheet-like structure containing titanate and / or titanic acid containing a titanate other than a titanate containing an alkali metal or alkaline earth metal element is fired, no aggregation occurs due to firing, and a sheet-like fired powder is obtained in which rod-shaped composite oxides of titanium and other metal elements and / or titanium oxides are linked to form a sheet, and that the resulting sheet-like fired powder has photocatalytic properties.

[0013] [1. Photocatalyst] A photocatalyst according to one embodiment of the present invention is a sheet-shaped photocatalyst containing a composite oxide of titanium element and another metal element, wherein the composite oxide of titanium element and another metal element has a rod shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped composite oxide of titanium element and another metal element is connected to form the sheet shape.

[0014] The photocatalyst according to one embodiment of the present invention contains a composite oxide of titanium and another metal element as a main component. In this specification, the term "main component" refers to the component that is contained in the largest amount in the material by mass.

[0015] The other metal element is not particularly limited, and examples thereof include alkali metals such as Li, Na, K, and Cs; alkaline earth metals such as Mg, Ca, Sr, and Ba; transition metals; and metals (including metalloids) belonging to Groups 12 to 16 of the periodic table. The transition metal is not particularly limited, and examples thereof include Co, Ni, and Cu. The metals belonging to Groups 12 to 16 of the periodic table are also not particularly limited, and examples thereof include Zn, Cd, and Pb. The other metal element may be a combination of two or more of the above-mentioned metals. In other words, the composite oxide of titanium and the other metal element may be a composite oxide of titanium and two or more metal elements selected from the above-mentioned metal elements. Furthermore, the composite oxide of titanium and the other metal element may contain multiple types of composite oxides.

[0016] The photocatalyst according to one embodiment of the present invention preferably contains 5% to 100% by weight of the composite oxide of titanium and other metal elements, but may contain 30% to 90% by weight, or 40% to 80% by weight of the composite oxide of titanium and other metal elements, relative to the photocatalyst. The photocatalyst may contain 50% by weight or more, 70% by weight or more, 90% by weight or more, or 100% by weight of the composite oxide of titanium and other metal elements, relative to the photocatalyst. By containing 40% by weight or more of the composite oxide of titanium and other metal elements, the photocatalyst can better maintain its sheet-like shape and exhibit catalytic activity, which is preferable.

[0017] A photocatalyst according to one embodiment of the present invention may further contain titanium oxide in addition to a complex oxide of titanium and another metal element. Hereinafter, this photocatalyst according to one embodiment of the present invention may be referred to as a "photocatalyst according to a second embodiment." That is, the photocatalyst according to the second embodiment of the present invention is a sheet-shaped photocatalyst containing a complex oxide of titanium and another metal element and titanium oxide, wherein the complex oxide of titanium and another metal element and titanium oxide have rod shapes with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped complex oxide of titanium and another metal element and titanium oxide are linked to form the sheet shape. Here, "the rod-shaped complex oxide of titanium and another metal element and titanium oxide are linked to form the sheet shape" means that the rod-shaped complex oxide and rod-shaped titanium oxide are linked to each other between the complex oxides, between the titanium oxides, and / or between the complex oxide and the titanium oxide to form the sheet shape. The photocatalyst according to the second embodiment of the present invention may contain titanium oxide in an amount of 0% to 95% by weight, 5% to 50% by weight, or 10% to 20% by weight relative to the photocatalyst.

[0018] A photocatalyst according to one embodiment of the present invention may contain titanium oxide instead of a composite oxide of titanium element and another metal element. Hereinafter, this photocatalyst according to one embodiment may be referred to as a "photocatalyst according to a third embodiment." That is, the photocatalyst according to the third embodiment of the present invention is a sheet-shaped photocatalyst containing titanium oxide, in which the titanium oxide has a rod shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped titanium oxide particles are connected to form the sheet shape.

[0019] In the composite oxide of titanium and other metal elements contained in the photocatalyst according to one embodiment of the present invention, the molar ratio of titanium to other metal elements (M / Ti) is not particularly limited, but is preferably 0.06 to 0.75, more preferably 0.18 to 0.75, and even more preferably 0.37 to 0.75. Note that, when the photocatalyst contains multiple types of composite oxides, the molar ratio of other metal elements to titanium refers to the ratio of the total number of moles of other metal elements to the total number of moles of titanium contained in the photocatalyst. The ratio of the total number of moles of titanium to the total number of moles of other metal elements contained in the photocatalyst can be determined by elemental analysis using, for example, an inductively coupled plasma optical emission spectrometer, an atomic absorption spectrometer, or an X-ray fluorescence spectrometer. Having the molar ratio within the above range is preferable because it more effectively maintains the sheet-like photocatalyst shape and exhibits photocatalytic activity. In this regard, in the composite oxide of titanium and other metal elements, the "molar ratio of other metal elements to titanium" means, when the composite oxide is a composite oxide of titanium and two or more metal elements, the ratio of the total number of moles of the other two or more metal elements to the number of moles of titanium. Furthermore, when the composite oxide of titanium and other metal elements contains multiple types of composite oxides and the abundance ratios of the composite oxides are known, the "molar ratio of other metal elements to titanium" may be a weighted average calculated from the abundance ratios of the composite oxides relative to the molar ratios of the other metal elements to titanium in each composite oxide.

[0020] The photocatalyst according to one embodiment of the present invention is in the form of a sheet of connected rod-shaped particles. A sheet-shaped photocatalyst is preferred because it prevents dispersion of the fine rod-shaped particles, increases the contact area with the interface because the particles do not aggregate, and allows promoter noble metal nanoparticles such as platinum nanoparticles to be supported evenly and highly dispersed on the surface of the rod-shaped particles, thereby maintaining the photocatalytic reaction sites.

[0021] The specific surface area of ​​the sheet-shaped photocatalyst according to one embodiment of the present invention is not particularly limited, and may be, for example, 5.0 m ２ / g to 250.0m ２ / g, and 10.0 m ２ / g to 230.0m ２ / g, and 15.0m ２ / g to 210.0m ２ / g, and 15.0m ２ / g to 180.0m ２ / g.

[0022] The average thickness of the sheet-shaped photocatalyst according to one embodiment of the present invention is not particularly limited, but is preferably 30.0 nm to 500.0 nm, for example, 50.0 nm to 500.0 nm, or 100.0 nm to 500.0 nm. An average thickness of 30.0 nm or more is preferable because it maintains the strength necessary to maintain the sheet shape. Furthermore, an average thickness of 500.0 nm or less is preferable because it maintains the reaction interface that contributes to the photocatalytic reaction.

[0023] The average area of ​​the sheet-shaped photocatalyst according to one embodiment of the present invention is not particularly limited, but is preferably 5.0 μm ２ ~500.0μm ２ and 10.0 μm ２ ~200.0 μm ２ 20.0 μm ２ ~100.0 μm ２ The average area of ​​the sheet may be 5.0 μm ２ If the average area of ​​the sheet is 500.0 μm or more, scattering into the environment during handling is prevented and dust is less likely to form, which is preferable. ２ If it is less than this, the difference in distribution of area values ​​can be reduced, and fine grain size can be expected, which is preferable.

[0024] The specific surface area, average thickness, and average area of ​​the sheet-shaped photocatalyst can be measured by the method described in the Examples.

[0025] In the photocatalyst according to one embodiment of the present invention, the composite oxide of titanium element and other metal element has a rod shape, and the rod-shaped composite oxide of titanium element and other metal element is connected to form a sheet shape.

[0026] The rod shape is not particularly limited as long as the average diameter of the rods is 10.0 nm or more and the average aspect ratio is 1.5 to 16.0, where the aspect ratio means the ratio of the rod length to the rod diameter (rod length / rod diameter).

[0027] The average diameter of the rods may be 10.0 nm or more, for example, 15.0 nm or more, or 30.0 nm or more. An average diameter of the rods of 10.0 nm or more is preferred because it is easy to maintain the sheet shape due to the connected structure. The upper limit of the average diameter of the rods is preferably 100.0 nm or less, for example, 70.0 nm or less, or 60.0 nm or less. An average diameter of the rods of 100.0 nm or less is preferred because particle coarsening due to the sintering reaction is suppressed.

[0028] The average aspect ratio of the rods may be 1.5 to 16.0, for example, 2.0 to 12.0, 3.0 to 10.0, or 5.0 to 9.0. An average aspect ratio of the rods of 1.5 or more is preferred because the sheet shape due to the connected structure is easily maintained. An average aspect ratio of the rods of 16.0 or less is preferred because particle coarsening due to the sintering reaction is suppressed. Here, the average aspect ratio of the rods can be determined by dividing the average length of the rods by the average diameter of the rods.

[0029] The average length of the rods is, for example, 15.0 nm to 1600.0 nm, preferably 15.0 nm to 300.0 nm, and may be, for example, 50.0 nm to 250.0 nm, or 90.0 nm to 210.0 nm. An average rod length of 15.0 nm or more is preferred because it ensures the strength required to maintain the sheet shape due to the linked structure. An average rod length of 300.0 nm or less is preferred because it reduces the rate of rod breakage.

[0030] The average diameter and average length of the rod-shaped composite oxide of titanium element and other metal element can be measured by the method described in the Examples.

[0031] When the photocatalyst according to one embodiment of the present invention further contains titanium oxide in addition to the composite oxide of titanium element and other metal element, the titanium oxide may also have a rod shape. The rod-shaped titanium oxide may be linked to each other and / or to the rod-shaped composite oxide of titanium element and other metal element to form a sheet shape.

[0032] When the photocatalyst according to one embodiment of the present invention contains titanium oxide instead of a composite oxide of titanium element and another metal element, the titanium oxide may also have a rod shape, and the rod-shaped titanium oxides may be connected to each other to form a sheet shape.

[0033] When the titanium oxide has a rod shape, the average diameter, average aspect ratio, and average length of the rods, as well as the methods for measuring the average diameter and average length of the rods, are the same as those for the rod-shaped composite oxide of titanium element and other metal element described above.

[0034] The photocatalyst according to one embodiment of the present invention may be a co-catalyst-supported photocatalyst in which a co-catalyst such as platinum nanoparticles is supported on the above-mentioned photocatalyst. By supporting a co-catalyst such as platinum nanoparticles, the photocatalytic properties can be improved.

[0035] [2. Method for producing photocatalyst] The method for producing a photocatalyst according to one embodiment of the present invention is not particularly limited as long as it is a method for producing the above-mentioned photocatalyst. The method for producing a photocatalyst according to one embodiment of the present invention comprises: ｍ （２－Ｘ）／ｍ H Ｘ Ti Ｙ O ２Ｙ＋１ ・nH ２ O (1) (wherein X is a real number of 0.50 to 2.00, Y is a real number of 2 to 8, n is a real number of 0 to 3, M is a metal atom, and m is the valence of the metal atom M) is fired until rod-shaped objects having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced.

[0036] Alternatively, a method for producing a photocatalyst according to one embodiment of the present invention includes the step of: ｍ （２－Ｘ）／ｍ H Ｘ Ti Ｙ O ２Ｙ＋１ ・nH ２ O (1) (wherein X is a real number of 0.50 to 1.50, Y is a real number of 2 to 8, n is a real number of 0 to 3, and M represents a metal atom) is fired until rod-shaped particles having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced.

[0037] (Sheet-like structure) The sheet-like structure contains, as a main component, a titanate and / or titanic acid represented by formula (1) (hereinafter, in this specification, the titanate and / or titanic acid represented by formula (1) may be referred to as a "raw titanate".) The sheet-like structure contains the raw titanate in an amount of more preferably 50 wt % or more, even more preferably 70 wt % or more, particularly preferably 90 wt % or more, and may contain 100 wt % of the raw titanate relative to the sheet-like structure.

[0038] X in formula (1), which represents the raw titanate, may be a real number between 0.50 and 2.00, or between 0.50 and 1.50, more preferably between 0.50 and 1.00, and even more preferably between 0.50 and 0.70. Y in formula (1) may be a real number between 2 and 8, more preferably between 2 and 6, and even more preferably between 2 and 4. n in formula (1) may be a real number between 0 and 3, more preferably between 0 and 2, and even more preferably between 0 and 1. Examples of M in formula (1), which represents a metal atom, include alkali metals such as Li, Na, K, and Cs; alkaline earth metals such as Mg, Ca, Sr, and Ba; transition metals; and metals (including metalloids) belonging to groups 12 to 16 of the periodic table. The transition metal is not particularly limited, but examples include Co, Ni, and Cu. The metal belonging to Groups 12 to 16 of the periodic table is not particularly limited, and examples thereof include Zn, Cd, and Pb. In formula (1), m represents the valence of the metal atom M. If the metal atom M is, for example, an alkali metal, m is 1, and if it is an alkaline earth metal, m is 2. The metal atom M in formula (1) may be a combination of two or more of the above-mentioned metals. In other words, the titanate may be a titanate containing titanium element and two or more metal elements selected from the above-mentioned metal elements. Furthermore, the sheet-like structure may contain multiple types of the titanate. Furthermore, the sheet-like structure may contain one or multiple types of the titanate and titanic acid.

[0039] In the sheet-like structure, the raw titanate is preferably fibrous, but may contain components having shapes other than fibrous. The content of components having shapes other than fibrous in the raw titanate is preferably 10% by mass or less, more preferably 1% by mass or less, relative to the total amount of the raw titanate. The sheet-like structure is preferably composed of fibrous components (an aggregate composed only of fibrous components). When the sheet-like structure is an aggregate composed only of fibrous components, the fibrous components adhere to each other through surface interactions, such as van der Waals forces. In this specification, "fibrous" means that the ratio of fiber length to fiber diameter (fiber length / fiber diameter) is greater than 16.

[0040] The fibrous component preferably has a layered structure, and more preferably has a structure in which two or more layers formed by adhesion of the fibrous components to each other are stacked.

[0041] The average thickness of the sheet-like structure is not particularly limited, but is preferably 30.0 nm to 500.0 nm, and may be, for example, 50.0 nm to 500.0 nm or 100.0 nm to 500.0 nm.

[0042] The average fiber diameter of the fibrous component is not particularly limited, but is preferably 5.0 nm to 70.0 nm, and may be, for example, 5.0 nm to 30.0 nm. The average fiber length of the fibrous component is also not particularly limited, but is preferably 50.0 nm to 700.0 nm, and may be, for example, 100.0 nm to 500.0 nm.

[0043] The average area of ​​the sheet-like structure is not particularly limited, but is preferably 5.0 μm ２ ~500.0μm ２ For example, 50.0 μm ２ ~300.0 μm ２ For example, 50.0 μm ２ ~100.0 μm ２ may be.

[0044] The average thickness and average area of ​​the sheet-like structure can be measured by the method described in the Examples. The average fiber diameter and average fiber length of the fibrous component can be measured by the method described in the Examples.

[0045] The sheet-like structure preferably contains, as a main component, a starting titanate containing a metal atom M, where X in formula (1) is a real number of 0.50 or more and less than 2.00, more preferably 0.50 to 1.50, Y is a real number of 2 to 8, and n is a real number of 0 to 3. Alternatively, the sheet-like structure further contains titanate H represented by the following formula (2) which does not contain a metal atom M, where X in formula (1) is 2.00, Y is a real number of 2 to 8, and n is a real number of 0 to 3: ２ Ti Ｙ O ２Ｙ＋１ ・nH ２ O (2) (wherein Y is a real number of 2 to 8, and n is a real number of 0 to 3). When the sheet-like structure contains titanic acid represented by formula (2), a photocatalyst containing titanium oxide in addition to a composite oxide of titanium and another metal is obtained.

[0046] Alternatively, the sheet-like structure may contain only a raw titanate not containing a metal atom M, i.e., titanic acid represented by the above formula (2), in which X is 2.00, Y is a real number of 2 to 8, and n is a real number of 0 to 3 in formula (1). When the sheet-like structure contains only titanic acid represented by formula (2), a photocatalyst containing titanium oxide is obtained instead of a composite oxide of titanium and another metal.

[0047] The sheet-like structure may be a sheet-like ion exchanger. Examples of the sheet-like ion exchanger include the sheet-like ion exchanger described in Patent Document 4 and the sheet-like ion exchanger described in Patent Document 4 in which an alkali metal such as K is used instead of Na. In the sheet-like ion exchanger, as the metal in formula (1), for example, Na ＋ , K. ＋In one embodiment of the present invention, the photocatalyst can be easily produced by calcining the sheet-like ion exchanger.

[0048] Alternatively, the sheet-like structure may be a sheet-like ion exchanger after ion exchange. The metal in formula (1) contained in the sheet-like ion exchanger after ion exchange is, for example, Na ＋ , K. ＋ As an example of a sheet-like ion exchanger in which alkali metal ions such as Na are electrostatically bonded, ＋ , K. ＋ The metal may be any metal that has been ion-exchanged with an alkali metal ion such as ammonium hydroxide, ... ＋ , K. ＋ etc. may be included.

[0049] The sheet-shaped ion exchanger has excellent metal ion exchange capacity and is therefore used in water treatment, water purification, and the like. As shown in FIG. 9 , conventionally, after use in water treatment, water purification, and the like, a titanate-containing sheet-shaped ion exchanger (which can also be said to adsorb metals through ion exchange, and is therefore labeled "adsorbent" in FIG. 9 ) may be reused by desorbing the metal ions captured by ion exchange. However, in most cases, the sheet-shaped ion exchanger is immobilized or solidified while still containing the captured metal ions, and then disposed of in a landfill. However, according to one embodiment of the present invention, a sheet-shaped ion exchanger used in water treatment, water purification, and the like can be reused by upcycling it into a photocatalyst. Such effects also contribute to the achievement of, for example, Goal 12 of the United Nations' Sustainable Development Goals (SDGs), "Responsible Consumption and Production."

[0050] (Firing step) A method for producing a photocatalyst according to one embodiment of the present invention includes a firing step of firing the sheet-like structure described above until rod-shaped objects having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced.

[0051] According to the photocatalyst production method of one embodiment of the present invention, by calcining the sheet-like structure in this step, it is possible to produce a photocatalyst according to one embodiment of the present invention, i.e., a sheet-like photocatalyst containing a composite oxide of titanium and other metal elements and / or titanium oxide, wherein the composite oxide of titanium and other metal elements and / or titanium oxide have a rod-like shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-like composite oxide of titanium and other metal elements and / or titanium oxide are connected to form the sheet shape. Therefore, in the calcination step, the sheet-like structure containing the starting titanate and / or titanic acid is calcined until the starting titanate and / or titanic acid is converted into a composite oxide of titanium and other metal elements and / or titanium oxide, which then assumes a rod-like shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0.

[0052] A specific method for firing the above-mentioned sheet-like structure until rod-shaped objects having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced includes, for example, a method in which an experiment is conducted by changing firing conditions such as the firing temperature, firing time, temperature rise rate, and firing atmosphere, thereby determining firing conditions for a specific sheet-like structure until rod-shaped objects are produced, and firing is then carried out according to those conditions.

[0053] In this step, the atmosphere in which the firing is carried out is not particularly limited, and the firing may be carried out in air or in an inert gas such as nitrogen, helium, argon, etc. The pressure in which the firing is carried out is also not particularly limited, and the firing may be carried out under normal pressure.

[0054] The firing temperature may be appropriately selected depending on the metal contained in the raw titanate or the raw titanic acid, and is, for example, 300° C. to 1000° C. When the metal element contained in the raw titanate is, for example, Ca, Co, or the like, or when the raw titanate is a titanic acid represented by the above formula (2), the firing temperature is more preferably 400° C. to 1000° C., and even more preferably 500° C. to 1000° C.

[0055] The firing time is not particularly limited, but is, for example, 0.5 to 3.0 hours. The method for raising the temperature to the firing temperature is not particularly limited, but may be, for example, at a rate of 5°C / min to 20°C / min.

[0056] (Ion Exchange Step) When the sheet-like structure is a sheet-like ion exchanger after ion exchange, the method for producing a photocatalyst according to one embodiment of the present invention may further include an ion exchange step.

[0057] The ion exchange step may be a step in which ion exchange is carried out by using a sheet-like ion exchanger for water treatment, water purification, etc., or a step in which ion exchange with a specific metal ion is actively carried out in order to produce a photocatalyst containing a composite oxide of titanium element and another specific metal element.

[0058] When ion exchange with a specific metal ion is performed, the sheet-shaped ion exchanger after ion exchange can be prepared, for example, by the following method: i) The sheet-shaped ion exchanger is added to an aqueous solution containing a salt of the specific metal (e.g., nitrate, sulfate, carbonate, acetate, etc.), and the solution is shaken, for example, at 5°C to 100°C for 2 to 72 hours to perform ion exchange. ii) The aqueous solution containing the sheet-shaped ion exchanger after ion exchange is subjected to solid-liquid separation. iii) The solid content is washed with distilled water and freeze-dried.

[0059] (Other Steps) The method for producing a photocatalyst according to one embodiment of the present invention may further include a step of producing a sheet-like structure containing the titanate and / or titanic acid.

[0060] The method for producing the sheet structure containing titanate is not particularly limited, but it can be produced by the method described in Patent Document 4, for example.

[0061] <Summary> One embodiment of the present invention includes the following configuration.

[0062] [1] A sheet-shaped photocatalyst containing a composite oxide of titanium and another metal element and / or titanium oxide, wherein the composite oxide of titanium and another metal element and / or titanium oxide has a rod shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped composite oxide of titanium and another metal element and / or titanium oxide are linked to form the sheet shape.

[0063] [2] The photocatalyst according to [1], wherein the average thickness of the sheet is 30.0 nm to 500.0 nm.

[0064] [3] The specific surface area of ​​the sheet is 5.0 m ２ / g to 250.0m ２ / g.

[0065] [4] The average area of ​​the sheet is 5.0 μm ２ ~500.0μm ２ The photocatalyst according to any one of [1] to [3],

[0066] [5] A sheet-like structure M containing titanate and / or titanic acid represented by the following formula (1): ｍ （２－Ｘ）／ｍ H Ｘ Ti Ｙ O ２Ｙ＋１ ・nH ２ O (1) (wherein X is a real number of 0.50 to 2.00, Y is a real number of 2 to 8, n is a real number of 0 to 3, M is a metal atom, and m is the valence of the metal atom M) until rod-shaped particles having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced, and the rod-shaped particles are linked to form a sheet-shaped photocatalyst.

[0067] Alternatively, one embodiment of the present invention includes the following configuration.

[0068] [1'] A sheet-shaped photocatalyst containing a complex oxide of titanium and another metal element, wherein the complex oxide of titanium and another metal element has a rod shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped complex oxide of titanium and another metal element is connected to form the sheet shape.

[0069] [2'] The photocatalyst according to [1'], wherein the average thickness of the sheet is 30.0 nm to 500.0 nm.

[0070] [3'] The specific surface area of ​​the sheet is 5.0 m ２ / g to 250.0m ２ The photocatalyst according to [1'] or [2'], wherein the photocatalyst has a surface area of ​​1000 nm or less.

[0071] [4'] The average area of ​​the sheet is 5.0 μm ２ ~500.0μm ２ The photocatalyst according to any one of [1'] to [3'],

[0072] [5'] A sheet-like structure M containing a titanate represented by the following formula (1'): ２－Ｘ H Ｘ Ti Ｙ O ２Ｙ＋１ ・nH ２ A method for producing a sheet-shaped photocatalyst, comprising a calcination step of calcining O (1') (wherein X is a real number of 0.50 to 1.50, Y is a real number of 2 to 8, n is a real number of 0 to 1, and M represents a metal atom) until rod-shaped objects having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced, and the rod-shaped objects are linked to form a sheet. Note that in formula (1'), when the valence of M is m, "M ２－Ｘ " is "M （２－Ｘ）／ｍ " can be rewritten as ".

[0073] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0074] [Measurement and Evaluation Methods] The measurement and evaluation methods for various items carried out in the examples and comparative examples will be explained below.

[0075] <Analysis by Powder X-ray Diffraction> Powder X-ray diffraction measurements were performed on the calcined powders obtained in Examples 1 and 2, the sheet-like structure of Comparative Example 1, the calcined powder obtained in Comparative Example 2, the calcined powder obtained in Example 4, the platinum nanoparticle-supported photocatalyst obtained in Example 5, and the sheet-like structure of Comparative Example 3 using a "D8 ADVANCE" manufactured by Bruker Japan K.K.

[0076] <Composition Analysis> The compositions of the sheet-like structures obtained in the Production Examples before and after ion exchange were determined by analysis using a high-frequency inductively coupled plasma optical emission spectrometer ("Optima 8300" manufactured by PerkinElmer Japan Co., Ltd. and "ICPS-8100" manufactured by Shimadzu Corporation) and the above-mentioned <Analysis by powder X-ray diffraction>. Specifically, first, Na or Ca was quantified for each sample using a high-frequency inductively coupled plasma optical emission spectrometer. Then, the composition of each sample was determined from the obtained measured values ​​of Na or Ca and the results of the crystalline phase confirmed by powder X-ray diffraction measurement.

[0077] The composition of each sample of the fired powder obtained in the examples and comparative examples was determined by the above-mentioned <Analysis by Powder X-ray Diffraction>.

[0078] <Analysis by Scanning Electron Microscope (SEM)> The sheet-like structures obtained in the Production Examples before and after ion exchange, and the fired powders obtained in the Examples and Comparative Examples, were observed using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation).

[0079] <Analysis by Transmission Electron Microscope (TEM)> The sheet-like structures obtained in the Production Examples before and after ion exchange, and the fired powders obtained in the Examples and Comparative Examples, were observed using a transmission electron microscope ("JEOL-2100" manufactured by JEOL Ltd. and "JEM-ARM200F (JEOL)" manufactured by JEOL Ltd.).

[0080] <Measurement of Average Thickness> The average thickness of the sheet-like structures before and after ion exchange obtained in Production Example 1, and the sintered powders obtained in Examples 1 and 2 and Comparative Example 1 was measured from images observed using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation). Specifically, the measurement object was observed using the scanning electron microscope, and 10 sheet-like structures or sintered powders were randomly selected. Then, the thickness of each of the SEM observation images of the selected 10 sheet-like structures or sintered powders was measured, and the average of the measured values ​​obtained at the 10 locations was taken as the average thickness of the measurement object.

[0081] <Measurement of Average Area> The average area of ​​the sheet-like structures before and after ion exchange obtained in Production Example 1, and the fired powders obtained in Examples 1 and 2 and Comparative Example 1 was measured using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation). Specifically, the measurement objects were observed using the scanning electron microscope, and 10 sheet-like structures or fired powders were randomly selected. Then, the area of ​​the selected 10 sheet-like structures or fired powders was measured from the SEM observation image. The average of the obtained 10 measured values ​​was taken as the average area of ​​the measurement objects.

[0082] <Measurement of Average Fiber Diameter> The average fiber diameter of the fibrous components contained in each of the sheet-like structures obtained in Production Example 1 before ion exchange was measured using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation). Specifically, the measurement object was observed using the scanning electron microscope, and one sheet-like structure was randomly selected. Next, 50 fibers were randomly selected from the fibers constituting the selected sheet-like structure. Then, for each of the selected 50 fibers, the fiber diameter (more specifically, the width at the center of the fiber in the longitudinal direction) was measured from an SEM image obtained at a magnification of 300,000 times. The arithmetic mean of the 50 measured values ​​obtained was taken as the average fiber diameter of the measurement object.

[0083] <Measurement of average fiber length> The average fiber length of the fibrous components contained in each of the sheet-like structures obtained in Production Example 1 before ion exchange was measured using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation). Specifically, the measurement object was observed using the scanning electron microscope, and one fibrous component was randomly selected. Next, 30 fibers of each selected fibrous component were randomly selected. The fiber length of each of the 30 selected fibers was measured from an SEM image obtained at a magnification of 100,000 times. The arithmetic mean value of the 30 measured values ​​obtained was taken as the average fiber length of the measurement object.

[0084] <Measurement of Average Rod Diameter> The average diameter of the rods contained in each of the sintered powders obtained in Examples 1 and 2 was measured using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation). Specifically, the measurement object was observed using the scanning electron microscope, and one piece of sintered powder was randomly selected. Next, 10 rods were randomly selected from the rods constituting the selected sintered powder. Then, for the selected 10 rods, the rod diameters (specifically, the width of the central part of the rod in the longitudinal direction) were measured from SEM images obtained under arbitrary magnification conditions. The average of the 10 measured values ​​obtained was taken as the average diameter of the measurement object.

[0085] <Measurement of Average Rod Length> The average length of the rods contained in each of the sintered powders obtained in Examples 1 and 2 was measured using a scanning electron microscope ("SU9000" manufactured by Hitachi High-Technologies Corporation). Specifically, the measurement object was observed using the scanning electron microscope, and one piece of sintered powder was randomly selected. Next, 10 rods were randomly selected from the rods constituting the selected sintered powder. Then, the rod lengths of the selected 10 rods were measured from SEM images obtained under arbitrary magnification conditions. The average value of the 10 measured values ​​obtained was taken as the average length of the measurement object.

[0086] <Measurement of specific surface area> Nitrogen adsorption / desorption measurements were carried out on the calcined powders obtained in Examples 1 and 2 using a gas adsorption measurement device ("NOVA4200e" manufactured by Anton Paar QuantaTec (formerly Quantachrome Instruments). As a pretreatment prior to the nitrogen adsorption / desorption measurements, the powders to be measured were heated in vacuum at 105°C for 3 hours. The nitrogen adsorption / desorption measurements were carried out at -196°C under liquid nitrogen. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method within the relative pressure range of 0.05 to 0.30 of the obtained nitrogen adsorption isotherm.

[0087] <Evaluation of Photocatalytic Properties> For the calcined powders obtained in Examples 1 and 2, the sheet-like structure of Comparative Example 1, the calcined powder obtained in Comparative Example 2, the platinum nanoparticle-supported photocatalyst obtained in Example 3, the photocatalyst obtained in Example 4, the platinum nanoparticle-supported photocatalyst obtained in Example 5, the sheet-like structure of Comparative Example 3, the photocatalyst obtained in Example 5, and the sheet-like structure of Comparative Example 4, 15 mg of the measurement target was dispersed in 15 mL of a 50 vol% aqueous methanol solution in a container, and the atmosphere in the container was replaced with an argon atmosphere. Thereafter, ultraviolet light was irradiated, and the generated hydrogen gas concentration was measured. The ultraviolet light irradiation was performed using a mercury lamp with an illuminance of 100 mW / cm. ２ The irradiation time was 3 hours. The generated gas was detected by gas chromatography.

[0088] [Production Example 1: Production of titanate-containing sheet structure (i)] 6.87 mL of a titanium(IV) sulfate aqueous solution (titanium(IV) sulfate content: 30% by mass) was added to 40.00 mL of a 10 mol / L sodium hydroxide aqueous solution and 9.17 mL of ultrapure water, and hydrothermal synthesis was carried out at 200°C for 1 day. The resulting product slurry was subjected to solid-liquid separation by suction filtration, and the solid was washed with ultrapure water. Next, the washed solid and 100 mL of ultrapure water were placed in a 500 mL bottomed cylindrical container made of fluororesin, and the solid was ultrasonically dispersed in water for 5 minutes. Next, the bottomed cylindrical container containing the solid dispersion was cooled in an ethanol bath cooled with liquid nitrogen, whereby the dispersion was frozen and then dried. Specifically, the bottomed cylindrical container containing the solid dispersion was first placed in an ethanol bath cooled with liquid nitrogen, and then cooled while being manually rotated at a rotation speed of 10 to 100 rpm (average of approximately 30 rpm) for 8 minutes around a central axis normal to the center of the bottom of the bottomed cylindrical container. The contents were then dried under reduced pressure for 48 hours. The dispersion was freeze-dried on the inner wall surface to obtain a dry powder. The obtained dry powder was analyzed by powder X-ray diffraction, SEM analysis, TEM analysis, and composition analysis. The results showed that the obtained dry powder contained Na. ０．９０ H １．１０ Ti ２ O ５ The titanate was fibrous, with an average fiber diameter of 8.7 nm and an average fiber length of 289.0 nm. The sheet-like structure had a layered crystal structure, with an average thickness of 129 nm and an average area of ​​59.4 μm. ２ It was.

[0089] Subsequently, 50 mg of the powder of the obtained sheet-like structure was added to 70 mL of a 4.0 mmol / L calcium nitrate aqueous solution and shaken at 25° C. for 1 day to obtain Na titanate. ＋ Ca ２＋The ion-exchanged aqueous solution containing the sheet-like structure was then subjected to solid-liquid separation, and the solid content was washed with distilled water and freeze-dried to obtain a dry powder. The powder of the sheet-like structure obtained after ion exchange was analyzed by powder X-ray diffraction, SEM analysis, TEM analysis, and composition analysis. Figure 1 shows the diffraction pattern by powder X-ray diffraction. In Figure 1, ○ indicates H ２ Ti ２ O ５ ・H ２ O peaks, and ◇ indicates CaTi ２ O ５ is a peak based on CaTiO ３ From FIG. 1, it can be seen that the obtained sheet-like structure (i) after ion exchange contains titanate, and CaTi ２ O ５ Titanium oxides represented by the formula: and CaTiO ３ The obtained sheet-like structure (i) after ion exchange did not contain any titanium oxide represented by the formula: （２－Ｘ）／２ H Ｘ Ti ２ O ５ (wherein X is a real number of 0 to 1.8), the titanate was fibrous, with an average fiber diameter of 7.5 nm and an average fiber length of 289.0 nm. The sheet-like structure had a layered structure, with an average thickness of 129.2 nm and an average area of ​​59.4 μm. ２ , specific surface area is 205.8 m ２ / g.

[0090] [Example 1: Production of photocatalyst] The ion-exchanged sheet-like structure (i) obtained in Production Example 1 was heated at a rate of 10°C / min, and once it reached 600°C, it was air-calcined for 2 hours to obtain a calcined powder, which was designated as calcined powder (1). The calcined powder (1) was analyzed by powder X-ray diffraction, SEM analysis, TEM analysis, and composition analysis. Figure 1 shows the diffraction pattern by powder X-ray diffraction. As can be seen from Figure 1, the calcined powder (1) obtained contained CaTi ２ O ５ Titanium oxides represented by the formula: and CaTiO ３It was shown that the composite oxide of titanium and other metal elements contained titanium oxide represented by the formula (I) and did not contain titanate contained before the heat treatment. The composite oxide of titanium and other metal elements had a rod shape with an average diameter of 19.7 nm and an average aspect ratio of 8.5, and as shown in Figures 2 and 3, the rod-shaped composite oxide of titanium and other metal elements was connected to form a sheet shape. Furthermore, although the titanate contained before the heat treatment had a layered structure, the obtained sheet did not have a layered structure (crystalline structure). The average thickness of the sheet was 111.4 nm and the average area was 55.9 μm. ２ , specific surface area is 44.5m ２ / g. When the photocatalytic properties of the calcined powder (1) were evaluated, approximately 0.4 mmol of hydrogen was generated per 1 g of catalyst after 3 hours of UV light irradiation. As shown in Figure 4, the photocatalytic powder in which platinum nanoparticles were supported on the calcined powder (1) generated approximately 11.9 mmol of hydrogen per 1 g of catalyst after 3 hours of UV light irradiation, demonstrating that the photocatalytic properties are significantly improved by supporting platinum nanoparticles.

[0091] [Example 2: Production of photocatalyst] The ion-exchanged sheet-like structure (i) obtained in Production Example 1 was heated at a rate of 10°C / min, and once it reached 800°C, it was air-calcined for 2 hours to obtain a calcined powder, which was designated as calcined powder (2). The calcined powder (2) was analyzed by powder X-ray diffraction, SEM analysis, TEM analysis, and composition analysis. As shown in Figure 1, the calcined powder (2) obtained contained CaTi ２ O ５ Titanium oxides represented by the formula: and CaTiO ３ It was shown that the composite oxide of titanium element and other metal elements contained titanium oxide represented by the formula (I) and did not contain titanate contained before the heat treatment. The composite oxide of titanium element and other metal elements had a rod shape with an average diameter of 54.8 nm and an average aspect ratio of 3.7, and although not shown, the rod-shaped composite oxide of titanium element and other metal elements was connected to form a sheet shape. Furthermore, although the titanate contained before the heat treatment had a layered structure, the obtained sheet did not have a layered structure (crystalline structure). The average thickness of the sheet was 228.7 nm and the average area was 66.9 μm. ２ , specific surface area is 19.3 m ２The calcined powder (2) was evaluated for photocatalytic properties, and was found to have photocatalytic properties.

[0092] Example 3 Production of Photocatalyst A 5 mg / mL aqueous solution of chloroplatinic acid was prepared, and 0.1 mL to 0.5 mL of this solution was diluted with water to make a total volume of 10 mL of aqueous solution. 50 mg of the calcined powder (1) obtained in Example 1 was added, and platinum nanoparticles were supported on the calcined powder (1) by a photoprecipitation method using ultraviolet light irradiation, thereby obtaining a platinum nanoparticle-supported photocatalyst.

[0093] The photocatalytic properties of the obtained platinum nanoparticle-supported photocatalyst were evaluated, and as shown in FIG. 4, the photocatalytic properties were significantly improved.

[0094] [Comparative Example 1] The sheet-like structure (i) after ion exchange obtained in Production Example 1 was used as the sheet-like structure of Comparative Example 1. When the photocatalytic properties of the sheet-like structure (i) of Comparative Example 1 were evaluated, the amount of hydrogen generated per 1 g of catalyst after 3 hours of ultraviolet light irradiation was approximately 0.17 mmol.

[0095] [Comparative Example 2] The sheet-like structure (i) obtained in Production Example 1 was heated at a rate of 10°C / min, and once it reached 400°C, it was air-calcined for 2 hours to obtain a powder of the calcined product, which was designated as calcined powder (3). The calcined powder (3) was analyzed by X-ray diffraction, SEM analysis, TEM analysis, and composition analysis. As shown in Figure 1, the obtained sheet-like structure after ion exchange contained titanate having a layered structure, and contained CaTi ２ O ５ Titanium oxides represented by the formula: and CaTiO ３ The obtained calcined powder (3) did not contain titanium oxide represented by the composition before calcination, Ca （２－Ｘ）／２ H Ｘ Ti ２ O ５ (wherein X is a real number between 0 and 1.8), the titanate was fibrous and had an average fiber diameter of 8.8 nm. The sheet-like structure had a layered structure and had an average thickness of 63.2 nm and an average area of ​​28.0 μm. ２ , specific surface area is 189.1 m ２When the photocatalytic properties of the calcined powder (3) of Comparative Example 2 were evaluated, the amount of hydrogen generated per 1 g of catalyst after 3 hours of ultraviolet light irradiation was about 0.08 mmol.

[0096] [Evaluation Results] The physical properties of the calcined powders (1) and (2) obtained in Examples 1 and 2, the sheet-like structure after ion exchange in Comparative Example 1, and the calcined powder (3) obtained in Comparative Example 2 were measured based on the measurement methods / evaluation methods described above. The results are shown in Table 1.

[0097] In Table 1, "-" indicates that no measurement was performed, but the fired powder (3) was clearly fibrous with an aspect ratio of more than 16.

[0098] [Production Example 2: Production of sheet structure (ii) containing titanic acid] The same procedure as in Production Example 1 was carried out to produce a sheet structure containing Na ０．９０ H １．１０ Ti ２ O ５ Thus, a powder of a titanate sheet structure represented by the formula:

[0099] Subsequently, 50 mg of the powder of the obtained sheet-like structure was added to 25 mL of 1.0 mol / L hydrochloric acid and shaken at 25° C. for 0.5 hours to obtain Na titanate. ＋ H ＋ The ion-exchanged aqueous solution containing the sheet-like structure was subjected to solid-liquid separation, and the solid was washed with distilled water and freeze-dried to obtain a dry powder. The powder of the sheet-like structure obtained after ion exchange was analyzed by powder X-ray diffraction and SEM analysis. Figure 5 shows the diffraction pattern by powder X-ray diffraction. In Figure 5, ○ indicates H ２ Ti ２ O ５ ・H ２ O is a peak due to low-crystalline titanic acid, and ▽ is TiO ２ This is a peak due to anatase. Fig. 5 shows that the obtained sheet-like structure (ii) after ion exchange contains titanic acid but does not contain titanium oxide.

[0100] [Example 4: Production of photocatalyst] The ion-exchanged sheet-like structure (ii) obtained in Production Example 2 was heated at a rate of 10°C / min, and once it reached 600°C, it was air-calcined for 2 hours to obtain a powder of the calcined product, which was designated as calcined powder (4). The calcined powder (4) was analyzed by powder X-ray diffraction and SEM analysis. Figure 5 shows the diffraction pattern by powder X-ray diffraction. As can be seen from Figure 5, the calcined powder (4) obtained contained TiO ２ The calcined powder (4) contained anatase, i.e., titanium oxide, but did not contain the titanic acid present before the heat treatment. As shown in Figure 6, the calcined powder (4) had rod-shaped particles with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0. As shown in Figure 7, the rod-shaped titanium oxide particles were connected to form a sheet. Furthermore, although the titanic acid present before the heat treatment had a layered structure, the resulting sheet did not have a layered (crystalline) structure. The photocatalytic properties of the calcined powder (4) were evaluated, and as shown in Figure 8, approximately 0.9 mmol of hydrogen was produced per gram of catalyst after 3 hours of UV light irradiation.

[0101] Example 5: Production of photocatalyst A 13 mg / mL aqueous solution of chloroplatinic acid was prepared, and 0.2 mL of this solution was diluted with water and methanol to a total volume of 10 mL. 50 mg of the calcined powder (4) obtained in Example 4 was added, and platinum nanoparticles were supported on the calcined powder (4) by photoprecipitation using ultraviolet light irradiation, thereby obtaining a platinum nanoparticle-supported photocatalyst. The obtained platinum nanoparticle-supported photocatalyst was analyzed by powder X-ray diffraction. Figure 5 shows the diffraction pattern by powder X-ray diffraction. As shown in Figure 5, the obtained platinum nanoparticle-supported photocatalyst contained TiO, as with the calcined powder (4). ２ It was shown to contain anatase, i.e., titanium oxide, and no titanate, which was present before the heat treatment.

[0102] The photocatalytic properties of the obtained platinum nanoparticle-supported photocatalyst were evaluated. As shown in Figure 8, the photocatalyst powder in which platinum nanoparticles were supported on the calcined powder (4) produced approximately 40.4 mmol of hydrogen per 1 g of catalyst after 3 hours of ultraviolet light irradiation, demonstrating that the photocatalytic properties were significantly improved by supporting platinum nanoparticles.

[0103] [Comparative Example 3] The sheet-like structure (ii) after ion exchange obtained in Production Example 2 was used as the sheet-like structure of Comparative Example 3. When the photocatalytic properties of the sheet-like structure (ii) of Comparative Example 3 were evaluated, as shown in Fig. 8, the amount of hydrogen generated per 1 g of catalyst after 3 hours of ultraviolet light irradiation was approximately 0.1 mmol, indicating that the photocatalytic properties were significantly lower than those of the calcined powder (4).

[0104] [Production Example 3: Production of titanate-containing sheet structure (iii)] The same procedure as in Production Example 1 was carried out to produce Na ０．９０ H １．１０ Ti ２ O ５ Thus, a powder of a titanate sheet structure represented by the formula:

[0105] Subsequently, 50 mg of the powder of the obtained sheet-like structure was added to 70 mL of a 4.0 mmol / L cobalt nitrate aqueous solution and shaken at 25° C. for 1 day to obtain Na titanate. ＋ Co ２＋ Thereafter, the aqueous solution containing the sheet-like structure after the ion exchange was subjected to solid-liquid separation, and the solid content was washed with distilled water and freeze-dried to obtain a dry powder (sheet-like structure (iii) containing titanate).

[0106] Example 6: Photocatalyst Production The ion-exchanged sheet-like structure (iii) obtained in Production Example 3 was heated at a rate of 10°C / min and air-calcined for 2 hours after reaching 800°C to obtain a calcined powder, designated calcined powder (5). The calcined powder (5) was analyzed by powder X-ray diffraction and SEM. The results of the powder X-ray diffraction analysis indicated that the calcined powder (5) contained titanium oxide and cobalt titanate. Furthermore, the results of SEM analysis indicated that the calcined powder (5) had rod-shaped particles with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped titanium oxide and cobalt titanate were connected to form a sheet shape. The photocatalytic properties of the calcined powder (5) were evaluated, and it was found to have photocatalytic properties.

[0107] According to one aspect of the present invention, a photocatalyst having a specific shape can be easily produced using a sheet-like structure containing a titanate such as an alkali metal titanate and / or titanic acid, which is therefore very useful in many technical fields including the chemical industry.

Claims

1. A sheet-shaped photocatalyst containing a composite oxide of titanium element and another metal element and / or titanium oxide, wherein the composite oxide of titanium element and another metal element and / or titanium oxide has a rod shape with an average diameter of 10.0 nm or more and an average aspect ratio of 1.5 to 16.0, and the rod-shaped composite oxide of titanium element and another metal element and / or titanium oxide are linked to form the sheet shape.

2. The photocatalyst according to claim 1, wherein the average thickness of the sheet is 30.0 nm to 500.0 nm.

3. The specific surface area of ​​the sheet is 5.0 m ２ / g to 250.0m ２ The photocatalyst according to claim 1 or 2, wherein the surface area of ​​the photocatalyst is 100 nm.

4. The average area of ​​the sheet is 5.0 μm ２ ~500.0 μm ２ The photocatalyst according to claim 1 or 2, 5. A sheet-like structure M containing titanate and / or titanic acid, represented by the following formula (1): ｍ （２－Ｘ）／ｍ H Ｘ Ti Ｙ O ２Ｙ＋１ ・nH ２ O (1) (wherein X is a real number of 0.50 to 2.00, Y is a real number of 2 to 8, n is a real number of 0 to 3, M is a metal atom, and m is the valence of the metal atom M) until rod-shaped particles having an average diameter of 10.0 nm or more and an aspect ratio of 1.5 to 16.0 are produced, and the rod-shaped particles are linked to form a sheet-shaped photocatalyst.

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