Photocatalyst and method for producing photocatalyst

Abstract

This photocatalyst is provided with: a support base material having a flat surface; a metal oxide layer that is made of a metal oxide and is applied to the flat surface; and a carbon nitride layer that is made of a polymeric carbon nitride that responds to visible light and is fixed to the flat surface via the metal oxide layer. The carbon nitride layer can be firmly fixed to the support base material, and by immersing the photocatalyst in a liquid, artificial photosynthesis can be performed.

Description

Photocatalyst and method for producing a photocatalyst

[0001] The technology disclosed herein relates to photocatalysts and methods for producing photocatalysts. In particular, it relates to photocatalysts that perform artificial photosynthesis using carbon nitride.

[0002] In recent years, artificial photosynthesis to produce carbon dioxide (CO2) has emerged as a means of addressing both climate change and the depletion of fossil fuels. ２ Research into reduction technologies is progressing. Among these, the development of photocatalytic materials that function in response to visible light, which accounts for the majority of the solar spectrum, is attracting attention.

[0003] Examples of photocatalytic materials include carbon nitride (C) ３ N ４ Carbon nitride is a photocatalytic material that exhibits the function of decomposing water into hydrogen and oxygen when irradiated with visible light. Here, in order for carbon nitride to efficiently absorb sunlight, which includes visible light, it is desirable to fix the carbon nitride to a flat surface such as a substrate so that the carbon nitride does not move and to 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 carbon nitride produced by heating urea and melamine is dispersed in methanol, and then the dispersion is applied and dried to immobilize the substrate (see, for example, Patent Document 1).

[0005] Japanese Patent Publication No. 2021-187709

[0006] Here, CO2 is used in artificial photosynthesis. ２When reduction technology is industrialized and utilized, it is necessary to immerse the photocatalyst in water or an electron donor liquid that is packed into 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 carbon nitride is used as a photocatalyst in artificial photosynthesis, it is necessary to immobilize it 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.

[0008] The photocatalyst described herein 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 immobilized on the flat surface via the metal oxide layer.

[0009] Furthermore, the method for producing a photocatalyst according to this disclosure comprises 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 formation step of forming a carbon nitride layer on the metal oxide layer using polymerized carbon nitride.

[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.

[0011] This figure shows the configuration of the photocatalyst 10 according to Embodiment 1. This figure illustrates the procedure for the manufacturing process of the photocatalyst 10 according to Embodiment 2.

[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 silicon dioxide (SiO₂ ２ The glass is primarily composed of ). Examples of this type of glass include borosilicate-based heat-resistant hard glass containing boron. Borosilicate-based heat-resistant hard glass is also a material with 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 the first embodiment, 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 the first embodiment, the metal oxide layer 2 is made of titanium oxide (TiO2) as a metal oxide suitable for immobilizing carbon nitride. ２ The material to be used is [material name]. Although not particularly limited, the thickness of the metal oxide layer 2 should be approximately 20 μm.

[0016] Titanium oxide 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 oxide. However, titanium oxide 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 oxide, other than titanium oxide. Here, metal oxide layer 2 is composed of a single layer of titanium oxide, but it may be composed of multiple layers made of multiple materials.

[0017] The carbon nitride layer 3 is a layer formed using polymerized carbon nitride as the material. 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 polymerized carbon nitride (for example, g-C) with a triazine ring as the basic framework. ３ N ４ The layer is assumed to be made of ). However, it is not limited to this, and the carbon nitride layer 3 may be made of other polymeric 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 configured in Embodiment 1 is immersed in a reactor filled with water or the like and irradiated with sunlight or the like. The carbon nitride absorbs the light energy in the visible light region contained in sunlight and decomposes water into hydrogen and oxygen. Thereafter, for example, the decomposed hydrogen is extracted and chemically bonded with carbon dioxide (CO ２ ), etc., to produce methanol, ethanol, etc., thereby reducing carbon dioxide to a 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 supporting base material 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 immobilizing the 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 supporting base material 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 the procedure regarding the 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 supporting base material 1 is performed. A dispersion liquid in which powdery metal oxide is dispersed by a liquid dispersant is applied on the plane of the supporting base material 1 (step S1). Thereafter, the supporting base material 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 supporting base material 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, etc. For example, pure water is considered to have no harm to organisms or influence on the environment.

[0022] Furthermore, for the coating method of the dispersion of metal oxides, techniques for uniformly coating the liquid can be used. Examples of coating techniques include the squeegee method, spin coating method, and electrostatic spraying method. For heating, the supported substrate 1 coated with the dispersion is placed in a heating furnace (not shown) and heated to 450°C at a rate of, for example, 10°C / min. The supported substrate 1 coated with the dispersion is then heated at 450°C for at least 1 hour. After heating, the supported substrate 1 with the metal oxide layer 2 formed on it is removed from the heating furnace and cooled in order to coat carbon nitride and form the carbon nitride layer 3 (step S3). There are no particular limitations on the cooling method, but natural cooling is preferable.

[0023] Next, a carbon nitride layer formation step is performed to form a carbon nitride layer 3 on the metal oxide layer 2. Similar to the process for forming the metal oxide layer 2, a dispersion of powdered carbon nitride using a dispersant is applied to the metal oxide layer 2 (step S4). Subsequently, the supported substrate 1 to which the dispersion has been applied is heated to evaporate the dispersion 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 is a mixture such as pure water, similar to the process for forming the metal oxide layer 2. However, it is not particularly limited.

[0024] Furthermore, the same technique as that used to form the metal oxide layer 2 can be used for coating the dispersion containing the dispersed carbon nitride. When heating the dispersion containing carbon nitride, the supported substrate 1 coated with the dispersion is placed again in the heating furnace and heated to 350°C at a rate of, for example, 10°C / min. The supported substrate 1 coated with the dispersion is then heated at 350°C for at least one hour. Although heating was done at 350°C here, it is not limited to this temperature. Based on the results of trials and other experiments, it has been found that if the heating temperature is low, such as below approximately 300°C, the removal of liquid from the dispersion containing carbon nitride becomes insufficient. Also, if the heating temperature is high, such as above approximately 400°C, it becomes impossible to form the carbon nitride layer 3 and immobilize the carbon nitride. Therefore, when heating the dispersion containing carbon nitride, it is best to heat it 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 Embodiment 2 described above, 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.

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

Claims

1. A photocatalyst comprising a support substrate having a flat surface, a metal oxide layer made of a metal oxide material and applied to the flat surface, and a carbon nitride layer made of a polymeric carbon nitride that reacts to visible light and immobilized on the flat surface via the metal oxide layer.

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 with a triazine ring as its basic skeleton.

4. The photocatalyst according to any one of claims 1 to 3, 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 method for producing a photocatalyst, comprising: 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 formation step of forming a carbon nitride layer on the metal oxide layer using polymerized carbon nitride.

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 or claim 8, wherein the temperature at which the metal oxide is heated and the temperature at which the polymeric carbon nitride is heated are different.

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 or claim 10, 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 any one of claims 7 to 11, wherein the dispersant is pure water, an acetylacetone solution, a polyethylene glycol solution, or an octylphenol ethoxylate solution.

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