Photocatalyst and method for producing a photocatalyst

Abstract

The photocatalyst comprises a support substrate having a flat surface, a metal oxide layer made of a metal oxide material and attached to the flat surface, and a carbon nitride layer made of polymeric carbon nitride that reacts to visible light and is fixed to the flat surface via the metal oxide layer. The carbon nitride layer is firmly fixed to the support substrate, and artificial photosynthesis can be performed by immersing it in a liquid.

Description

Technical Field

[0001] The technology disclosed herein relates to a photocatalyst and a method for manufacturing the photocatalyst. In particular, it relates to a photocatalyst that performs artificial photosynthesis using carbon nitride and the like.

Background Art

[0002] In recent years, as a means to address both climate change and the depletion of fossil fuels, research on carbon dioxide (CO2) reduction technology by artificial photosynthesis has been underway. Among them, the development of photocatalyst materials that function in response to visible light, which occupies most of the spectrum in sunlight, has attracted attention.

[0003] As a photocatalyst material, for example, there is carbon nitride (nitrogenated carbon: C3N4). Carbon nitride is a photocatalyst material that exhibits the function of decomposing water into hydrogen and oxygen upon irradiation with visible light. Here, in order for carbon nitride to efficiently absorb sunlight including visible light, it is advisable to immobilize carbon nitride on a flat surface such as a substrate so that the carbon nitride does not move and increase the light-receiving area.

[0004] Therefore, as a method for immobilizing carbon nitride on a substrate, for example, a method has been proposed in which a dispersion liquid in which carbon nitride generated by heating urea and melamine is dispersed in methanol is applied and dried for immobilization (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When industrializing and utilizing CO2 reduction technology using artificial photosynthesis, it is necessary to immerse the photocatalyst in water or an electron donor liquid filled in the reactor. However, the carbon nitride immobilization described in Patent Document 1 above assumes that hydrogen nitride is used as the light-emitting material. When hydrogen nitride is used as the light-emitting material, the hydrogen nitride is not exposed to liquid, nor is it subjected to forces such as liquid flow. Furthermore, the immobilized carbon nitride can be protected by sandwiching it between electrodes. Therefore, the immobilized state of carbon nitride can be maintained. On the other hand, when using carbon nitride as a photocatalyst in artificial photosynthesis, it is necessary to immobilize the carbon nitride so that it does not move even when exposed to liquid.

[0007] Therefore, in order to solve the above-mentioned problems, this disclosure aims to provide a photocatalyst with a configuration suitable for artificial photosynthesis and a method for producing the photocatalyst. [Means for solving the problem]

[0008] The photocatalyst disclosed herein comprises a support substrate having a flat surface, a metal oxide layer made of a metal oxide material attached to the flat surface, and a polymeric carbon nitride that reacts to visible light as a catalyst material, which is immobilized on the flat surface via the metal oxide layer that serves as a support. thicker than the metal oxide layer It comprises a carbon nitride layer.

[0009] Furthermore, the method for producing the photocatalyst described herein includes a metal oxide layer formation step of forming a metal oxide layer on a flat surface of a supported substrate, and a carbon nitride layer of polymerized carbon nitride on the metal oxide layer. , thicker than the metal oxide layer The method comprises a step of forming a carbon nitride layer and then immobilizing the carbon nitride layer using the metal oxide layer as a support. [Effects of the Invention]

[0010] According to the photocatalyst and method for producing the photocatalyst described herein, layered carbon nitride can be firmly immobilized on a support substrate, and a photocatalyst that can perform artificial photosynthesis by immersion in a liquid such as water can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] This diagram shows the configuration of the photocatalyst 10 according to Embodiment 1. [Figure 2] This diagram illustrates the procedure for the manufacturing process of the photocatalyst 10 according to Embodiment 2. [Modes for carrying out the invention]

[0012] The following description will explain the photocatalyst and its manufacturing method according to the embodiments, with reference to the attached drawings. In the following drawings, components with the same reference numerals are the same or equivalent and are common throughout the entire text of the embodiments described below. The forms of the components shown in the entire specification are merely examples and are not limited to the forms described in the specification. In particular, the combinations of components are not limited to the combinations in each embodiment, and components described in other embodiments can be applied to other embodiments. In the following description, the upper part of the figures will be referred to as the "upper side" and the lower part as the "lower side". The size relationships of the components in the drawings may differ from those in reality.

[0013] Embodiment 1. Figure 1 shows the configuration of the photocatalyst 10 according to Embodiment 1. The photocatalyst 10 in Embodiment 1 is constructed by laminating a support substrate 1, a metal oxide layer 2, and a carbon nitride layer 3 in that order.

[0014] The supporting substrate 1 is a flat plate-shaped substrate on which the metal oxide layer 2 and the carbon nitride layer 3 are supported and fixed. In Embodiment 1, the supporting substrate 1 is made of an inorganic material that is transparent in the visible light region (visible light). As a result, a reflector or the like can be attached to the back surface (bottom surface in Figure 1) of the supporting substrate 1, which is the visible light irradiation surface, on which the metal oxide layer 2 and the carbon nitride layer 3 are formed, so that the visible light that has passed through the metal oxide layer 2 and the carbon nitride layer 3 can be reflected. Therefore, visible light can be irradiated onto the carbon nitride layer 3 again from the back side. Here, for example, the transparent inorganic material is glass mainly composed of silicon dioxide (SiO2). An example of this type of glass is borosilicate-based heat-resistant hard glass containing boron. Borosilicate-based heat-resistant hard glass is a material that also has excellent chemical resistance.

[0015] The metal oxide layer 2 is a layer formed between the support substrate 1 and the carbon nitride layer 3. If the carbon nitride layer 3 is formed directly on the support substrate 1, the carbon nitride will easily peel off from the support substrate 1 in environments such as immersion in liquid. Therefore, in Embodiment 1, the photocatalyst 10 has a metal oxide layer 2 formed on the support substrate 1 that mainly functions as a carrier or base for fixing the carbon nitride layer 3 to the support substrate 1. In Embodiment 1, titanium oxide (TiO2) is used as the material for the metal oxide layer 2 as a metal oxide suitable for immobilizing carbon nitride. Although not particularly limited, the thickness of the metal oxide layer 2 is assumed to be approximately 20 μm.

[0016] Titanium dioxide is a white metal oxide that is also used as a photocatalytic material. The metal oxide used as the material for metal oxide layer 2 is not limited to titanium dioxide. However, titanium dioxide reacts to light with wavelengths shorter than ultraviolet light and functions as a catalyst, but does not react to visible light. Thus, it is preferable to use a material for metal oxide layer 2 that does not inhibit the reaction of carbon nitride in carbon nitride layer 3. Also, for example, the metal oxide used for metal oxide layer 2 may be a metal oxide with properties similar to titanium dioxide, in addition to titanium dioxide. Here, metal oxide layer 2 is composed of a single layer of titanium dioxide, but it may be composed of multiple layers made of multiple materials.

[0017] The carbon nitride layer 3 is a layer formed from polymerized carbon nitride. Carbon nitride acts as a catalyst when performing artificial photosynthesis, which converts visible light energy into chemical energy. Here, the carbon nitride layer 3 in Embodiment 1 is assumed to be a layer made of polymerized carbon nitride (for example, g-C3N4) with a triazine ring as its basic framework. However, it is not limited to this, and the carbon nitride layer 3 may be made of other polymerized hydrogen nitride. Here, the thickness of the carbon nitride layer 3 is assumed to be approximately 100 μm. However, the thickness of the layer is not limited to this, and the thickness of the layer may be changed according to the conditions under which it is used as a catalyst.

[0018] The photocatalyst 10, as configured in Embodiment 1, is immersed in a reactor into which water or the like is injected, and then irradiated with sunlight or the like. The carbon nitride absorbs light energy in the visible light region contained in sunlight and decomposes the water into hydrogen and oxygen. Subsequently, for example, the decomposed hydrogen is extracted and chemically bonded with carbon dioxide (CO2) to produce methanol, ethanol, etc., thereby reducing carbon dioxide to the product.

[0019] As described above, according to the photocatalyst 10 according to Embodiment 1, the metal oxide layer 2 is attached as a carrier, and the carbon nitride layer 3 serving as a catalyst is immobilized on the flat support substrate 1. For this reason, even when immersed in a liquid such as water, the carbon nitride layer 3 can maintain a strong fixation without peeling off from the substrate. Therefore, a highly reliable and long-life photocatalyst 10 can be obtained. And, the photocatalyst 10 according to Embodiment 1 can increase the light-receiving area by fixing carbon nitride in a layer on a flat plate, and can perform artificial photosynthesis efficiently.

[0020] Embodiment 2. In the above-described Embodiment 1, the photocatalyst 10 having a configuration in which the metal oxide layer 2 and the carbon nitride layer 3 are provided on the support substrate 1 has been described. In Embodiment 2, a method for manufacturing the photocatalyst 10 having the configuration as in Embodiment 1 will be described.

[0021] FIG. 2 is a diagram for explaining a procedure regarding a manufacturing process of the photocatalyst 10 according to Embodiment 2. In Embodiment 2, first, a metal oxide layer forming step of forming the metal oxide layer 2 on the plane of the support substrate 1 is performed. A dispersion liquid in which powdery metal oxide is dispersed by a liquid dispersant is applied on the plane of the support substrate 1 (step S1). Then, the support substrate 1 coated with the dispersion liquid is heated to evaporate the liquid and solidify the metal oxide (step S2). By heating, the metal oxide solidifies on the support substrate 1, and the metal oxide layer 2 is formed. Here, examples of the dispersant include pure water, acetylacetone solution, polyethylene glycol (PEG) solution, octylphenol ethoxylate solution, and the like. For example, pure water is considered to have no harm to organisms and no impact on the environment.

[0022] In addition, for the method of applying the dispersion liquid in which the metal oxide is dispersed, a technique for uniformly applying the liquid can be used. Examples of the coating technique include a squeegee method, a spin coating method, an electrostatic spraying method, and the like. Regarding heating, the support substrate 1 coated with the dispersion liquid is placed in a heating furnace (not shown), and for example, the temperature is raised to 450°C at a rate of 10°C / min. Then, at 450°C, the support substrate 1 coated with the dispersion liquid is heated for at least 1 hour. After heating, in order to apply carbon nitride and form the carbon nitride layer 3, the support substrate 1 on which the metal oxide layer 2 is formed is taken out of the heating furnace and cooled (step S3). Here, the cooling method is not particularly limited, but natural cooling is desirable.

[0023] Next, a carbon nitride layer forming step of forming a carbon nitride layer 3 on the metal oxide layer 2 is performed. Similar to the case of forming the metal oxide layer 2, a dispersion liquid in which powdery carbon nitride is dispersed by a dispersant is applied onto the metal oxide layer 2 (step S4). Then, the support substrate 1 coated with the dispersion liquid is heated to evaporate the dispersion liquid and solidify the metal oxide (step S5). By heating, the carbon nitride solidifies on the metal oxide layer 2, and the carbon nitride layer 3 is formed. The dispersant shall be a mixture such as pure water as in the case of forming the metal oxide layer 2. However, it is not particularly limited.

[0024] [[ID=e8]]In addition, for the method of applying the dispersion in which carbon nitride is dispersed, the same technique as in the case of forming the metal oxide layer 2 can be used. When heating the dispersion liquid containing carbon nitride, again, the support substrate 1 coated with the dispersion liquid is placed in the heating furnace, and for example, the temperature is raised to 350°C at a rate of 10°C / min. Then, at 350°C, the support substrate 1 coated with the dispersion liquid is heated for at least 1 hour. Here, although heating is performed at 350°C, it is not limited thereto. Here, as a result of trials and the like, if the heating temperature is low, such as about 300°C or lower, the removal of the liquid in the dispersion liquid containing carbon nitride becomes insufficient. Also, if the heating temperature is high, such as about 400°C or higher, the carbon nitride layer 3 is formed and the carbon nitride cannot be immobilized. Therefore, when heating the dispersion liquid containing carbon nitride, it is advisable to heat at a temperature higher than 300°C and lower than 400°C.

[0025] As described above, in Embodiment 2, the photocatalyst 10 is manufactured by forming a metal oxide layer 2 on the flat surface of the support substrate 1, and then forming a carbon nitride layer 3 on top of it. Therefore, even when immersed in a liquid such as water, the carbon nitride layer 3 does not peel off and maintains strong fixation, making it possible to obtain a long-life photocatalyst 10.

[0026] Furthermore, in the manufacturing method shown in Embodiment 2, a dispersion of metal oxide mixed with a liquid and a dispersion of carbon nitride mixed with a liquid are applied to a support substrate 1 and heated to form a metal oxide layer 2 and a carbon nitride layer 3. Therefore, each layer can be formed by an inexpensive and simple method. In addition, the heating temperature for the metal oxide and the heating temperature for the carbon nitride are set to different temperatures. At this time, the dispersion containing polymeric carbon nitride is heated at a rate of 10°C / min and heated at 350°C for 1 hour, and the dispersion containing metal oxide is heated at a rate of 10°C / min and heated at 450°C for 1 hour. Therefore, the liquid in the dispersion can be removed while controlling the temperature according to the material of each layer.

[0027] Embodiment 3. Although not specifically mentioned in the above-described embodiment 2, additional steps may be added before and after the coating and firing processes when forming the metal oxide layer 2 and the carbon nitride layer 3. For example, steps such as polishing the supported substrate 1 and polishing the metal oxide layer 2 and the carbon nitride layer 3 after they have been formed may be included.

[0028] Furthermore, in the above-described embodiment 2, the metal oxide layer 2 was formed on the supported substrate 1 by coating and heating the metal oxide, but the method is not limited to this. For example, the metal oxide layer 2 can also be formed by vapor deposition or sputtering of the metal oxide. [Explanation of Symbols]

[0029] 1. Supporting substrate, 2. Metal oxide layer, 3. Carbon nitride layer, 10. Photocatalyst.

Claims

1. A support substrate having a flat surface, A metal oxide is used as the material, and a metal oxide layer is applied to the aforementioned plane, A polymeric carbon nitride that reacts to visible light is used as a catalyst material, and is immobilized on the plane via the metal oxide layer that serves as a support, and a carbon nitride layer thicker than the metal oxide layer and A photocatalyst equipped with [the following features].

2. The photocatalyst according to claim 1, wherein the metal oxide is titanium oxide.

3. The photocatalyst according to claim 1 or claim 2, wherein the polymeric carbon nitride is polymeric carbon nitride having a triazine ring as its basic skeleton.

4. The photocatalyst according to claim 1 or claim 2, wherein the supported substrate is an inorganic material that is transparent in visible light.

5. The photocatalyst according to claim 4, wherein the inorganic material is a borosilicate-based heat-resistant hard glass.

6. A metal oxide layer formation step in which a metal oxide layer is formed on a flat surface of a supported substrate, A carbon nitride layer formation step is to form a carbon nitride layer on the metal oxide layer, the carbon nitride layer being thicker than the metal oxide layer, and the carbon nitride layer being immobilized using the metal oxide layer as a support. A method for producing a photocatalyst.

7. The method for producing a photocatalyst according to claim 6, wherein the metal oxide layer formation step involves applying a dispersion of the metal oxide mixed with a dispersant onto the supported substrate and heating to form the metal oxide layer.

8. The method for producing a photocatalyst according to claim 6 or 7, wherein the carbon nitride layer formation step involves applying a dispersion of polymeric carbon nitride mixed with a dispersant onto the metal oxide layer and heating to form the carbon nitride layer.

9. The method for producing a photocatalyst according to claim 7, wherein the temperature at which the metal oxide is heated and the temperature at which the polymeric carbon nitride is heated are different temperatures.

10. The method for producing a photocatalyst according to claim 9, wherein in the carbon nitride layer formation step, the applied polymeric carbon nitride is heated at 10°C / min and then heated at 350°C for 1 hour.

11. The method for producing a photocatalyst according to claim 9, wherein in the metal oxide layer formation step, the applied metal oxide is heated at 10°C / min and then heated at 450°C for 1 hour.

12. The method for producing a photocatalyst according to claim 7, any one of claims 9 to 11, wherein the dispersant is pure water, an acetylacetone solution, a polyethylene glycol solution, or an octylphenol ethoxylate solution.

13. A support substrate made of a borosilicate-based heat-resistant hard glass having a flat surface and being transparent in visible light, A metal oxide is used as the material, and a metal oxide layer is applied to the aforementioned plane, The polymeric carbon nitride that reacts to visible light is used as a catalyst material, and the carbon nitride layer is immobilized on the plane via the metal oxide layer that serves as a support. A photocatalyst equipped with [the following features].

14. A metal oxide layer formation step of forming a metal oxide layer on a plane of a supported substrate made of a borosilicate-based heat-resistant hard glass that is transparent in visible light, A carbon nitride layer formation step is performed in which a carbon nitride layer is formed on the metal oxide layer using polymerized carbon nitride, and the carbon nitride layer is immobilized using the metal oxide layer as a support. A method for producing a photocatalyst.

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