Patent Application
20240139723
This application claims priority to Japanese Patent Application No. 2022-175972 filed on Nov. 2, 2022, the entire contents of which are incorporated by reference herein.
The present invention relates to a photocatalyst decomposition system.
A technique for decomposing water with sunlight and generating hydrogen with high efficiency is a storable energy carrier production technique having a low cost without discharging CO2 and is expected to be applied to a renewable energy service and an environmental service such as hydrogen power generation and a hydrogen automobile that contributes to fossil fuel elimination.
Further, if a photocatalyst technique for decomposing a chemical substance having a large environmental influence is developed and becomes a technique that can use sunlight with high efficiency, the technique can be applied to production of a useful material by decomposing CO2 and methane discarded in not only water but also atmosphere, and NOx or a nitrate salt flowing into a water source from soil. Reduction of CO2 and methane contributes to inhibition of global warming, and NOx or a nitrate salt flowing into a water source from soil contributes to biodiversity through water or atmosphere. By not only decomposing but also converting such substances to a high-value substance such as alcohol or formic acid, such a technique is expected to be expanded as an industry with recycling-oriented PF through artificial photosynthesis as a substance generation system.
An example of such a technique is disclosed in PTL 1. PTL 1 discloses a water photolysis apparatus including a casing 1 that includes a light transmission window 12 configured to transmit sunlight L, and a photolysis layer 5 provided on the casing 1. There is disclosed a configuration in which the photolysis apparatus is provided in a state of floating on a water layer 9, water vapor is evaporated from the water layer 9 due to irradiation with sunlight L, the water vapor is introduced into the photolysis layer 5, photocatalyst particles 52 are excited by the sunlight L in the photolysis layer 5, and the introduced water vapor is decomposed into hydrogen and oxygen. According to the configuration in PTL 1, it is possible to provide a water photolysis apparatus that can more efficiently obtain hydrogen and oxygen by inhibiting a reverse reaction and that can further promote photolysis of water by effectively using solar energy.
In the related art, in a configuration of an apparatus for decomposing a liquid phase by using a photocatalyst, light is emitted to a photocatalyst in a state in which the photocatalyst is charged in water in a form of a powder or a thin film to decompose water. A gas obtained by decomposition is generated as air bubbles on a surface of the photocatalyst, a certain amount of the gas is desorbed into water and collected, and there is a portion covered with the generated air bubbles on the surface of the photocatalyst. Accordingly, a contact area between a catalyst and water is reduced, resulting in saturation or reduction of a reaction rate, and thus an object is to eliminate such a problem and maintain a high reaction rate.
As described above, since air bubbles or the like in a liquid phase may cause a reaction rate saturation or reduction, it is important to improve efficiency of the reaction by allowing the photocatalyst to react in a state of being charged in a gas phase to inhibit generation of air bubbles and to increase a contact surface area between the gas phase and the photocatalyst. In PTL 1 described above, the photocatalyst is supported in a state of being dispersed in a powder form on a porous material, it is difficult to form electrical continuity, and it is difficult to improve efficiency of the reaction by using an electrode or the like.
In view of the above circumstances, an object of the invention is to provide a photocatalyst decomposition system that can supply a gas phase containing a substance to be decomposed by a photocatalyst and that can perform decomposition of the substance more efficiently than in the related art.
According to an aspect of the invention for solving the above problem, a photocatalyst decomposition system includes: a gas phase generation apparatus configured to convert a liquid phase containing a decomposition object into a gas phase; and a photocatalyst member configured to come into contact with the gas phase to decompose the decomposition object by light from a light source and generate a gas phase. The photocatalyst member includes a base material formed of a porous material and a photocatalyst layer provided on a surface of the base material.
A more specific configuration of the invention is described in claims.
According to the invention, it is possible to provide a photocatalyst decomposition system that can supply a gas phase containing a substance to be decomposed by a photocatalyst and that can perform decomposition of the substance more efficiently than in the related art.
Objects, configurations, and effects other than those described above will be clarified by the following description of embodiments.
Hereinafter, a configuration of the invention will be described in detail with reference to the drawings.
As described above, a photocatalyst decomposition system according to the invention includes: a gas phase generation apparatus configured to convert a liquid phase containing a decomposition object into a gas phase; and a photocatalyst member configured to come into contact with the gas phase to decompose the decomposition object by light from a light source and generate a gas phase. The photocatalyst member includes a base material formed of a porous material and a photocatalyst layer provided on a surface of the base material. First, the photocatalyst member will be described.
The photocatalyst decomposition system according to the invention converts a liquid phase containing a decomposition object into a gas phase (vapor) and brings the gas phase into contact with the photocatalyst member to decompose the decomposition object. By providing the photocatalyst layer 201 on the base material 101 formed of the porous material as described above, a surface area of a photocatalytic reaction portion is increased, and further, a generated gas phase is released without remaining in the photocatalytic reaction portion. Accordingly, it is possible to prevent a phenomenon in which a surface of the photocatalyst layer 201 is covered with air bubbles generated when the liquid phase is brought into contact with the photocatalyst member, and to prevent a decrease in a contact area between the gas phase and the photocatalyst layer 201.
The photocatalyst member provided in the photocatalyst decomposition system according to the invention can decompose not only a gas phase but also a liquid phase.
The base material 101 is a material that transmits light having a wavelength of at least visible light or ultraviolet light, and is preferably a material having a three-dimensional block structure having a porous or reticular fiber material as a skeleton. The material of the base material 101 preferably contains SiO2, Al2O3, TiO2, MgO, ZnO, CaCO3, CaO, a transparent carbon nanotube (CNT), or SnO.
The photocatalyst layer 201 is not particularly limited, and for example, at least one of substances listed in the following (1) to (4) can be preferably used, or a combination of these substances may be used.
Particles of a co-catalyst material that promotes the photocatalytic reaction may be supported on, or a thin film of the co-catalyst material may be provided on at least a part of the photocatalyst layer 201. The co-catalyst material is not particularly limited, and WO3, Rh/Cr2O3, Ag, Rh/SrTiO3, Pt, CoO, Co3O4, IrO2, PtO2, phosphorus, NiO, RuO2, AgSbO3, or ZnRhOx can be preferably used.
A porosity (a volume ratio of the pore 102) of the photocatalyst member 200 is preferably 40% to 95% (40% or more and 95% or less). When the porosity is less than 40%, it is difficult to provide a sufficient surface area for the reaction of the photocatalyst layer 201. When the porosity exceeds 95%, it is difficult to secure strength of the photocatalyst member 200. The base material 101 preferably has a pore width of 10 μm to 500 μm.
A surface area in the pore of the nanoporous material is 10 m2/g to 1000 m2/g (general value). A pore size and material can have various variations (porous glass specific gravity: 1 g/cm2 to 2 g/cm2).
As a method for producing the photocatalyst member 200, the pore 102 in the porous material as the base material 101 can be subjected to immersion, vacuum impregnation, vacuum aeration, or spin coating with respect to a liquid obtained by mixing a liquid (MOD material) containing a metal organic compound that contains the material of the photocatalyst layer 201 and a metal complex solution or a metal-oxide colloid solution produced by a sol-gel method, followed by sintering to produce an object with photocatalyst coating and modification on an inner surface of the pore. Various photocatalyst materials can be synthesized by selectively using the above method. A coating film is continuous up to an internal structure, thereby enabling electrical conduction from the surface. In other words, an outer surface of the photocatalyst member 200 and a surface of the pore 102 in the photocatalyst member 200 have electrical continuity. A transparent conductive thin film layer may be provided on a surface of the photocatalyst layer 201 or between the base material 101 and the photocatalyst layer 201, and the photocatalyst layer 201 and the transparent conductive thin film layer may be electrically connected to each other.
Hereinafter, the photocatalyst decomposition system according to the invention including the above-described photocatalyst member will be described in detail.
In the vapor supply apparatus 301, a liquid phase (for example, water) 303 containing a decomposition object, which is supplied through a liquid phase (water) supply pipe 306, is heated using the sunlight 310 by a vapor generation member 304 provided in a vapor generation container 302 to generate vapor 305. The generated vapor is supplied to a photocatalyst decomposition apparatus 314 via a vapor transfer pipe 307.
In the photocatalyst decomposition apparatus 314, the supplied vapor 305 is supplied to the photocatalyst member 320 via a vapor introduction portion 315 and a vapor discharge portion 318.
The photocatalyst member 320 is divided into at least two photocatalyst members 401 and 402 by a separation film 319 formed by a proton conductive film, and electrodes 322 and 323 as voltage application apparatuses are connected to the at least two photocatalyst members 401 and 402, respectively, so that a potential can be adjusted. Furthermore, a gas or water vapor is supplied to the at least two photocatalyst members 401 and 402, respectively. A generated substance can be separated by adjusting the potential by the electrodes 322 and 323.
Generated gases 324 and 325 generated by decomposing the vapor 305 by the photocatalyst member 320 are discharged to the outside. For example, when the vapor 305 is water, oxygen (O2), hydrogen (H2), and water vapor (H2O) are discharged as the generated gas. The decomposition object is not limited to water and can also be carbon dioxide (CO2), nitrogen oxide (NOx), or methane (CH3). A gas phase generated by decomposition by the photocatalyst member 320 is collected by a collection apparatus.
According to the above-described photocatalyst decomposition system 300a in the invention, the decomposition object contained in the liquid phase can be decomposed efficiently by the photocatalyst after being converted into the gas phase by using natural energy such as sunlight. Since the photocatalyst member 320 used for decomposition by the photocatalyst has a reaction structure (which is porous) through which vapor can pass, a larger surface area can be used in a three-dimensional space.
Further, by providing the electrodes 322 and 323, the decomposition reaction by the photocatalyst can be controlled.
As described above, according to the invention, it is possible to provide a photocatalyst decomposition apparatus that can supply a gas phase containing a substance to be decomposed by a photocatalyst and that can perform decomposition of the substance more efficiently than in the related art.
The invention is not limited to the above-described embodiments, and includes various modifications. For example, the embodiments described above have been described in detail to facilitate understanding of the invention, and the invention is not necessarily limited to those including all the configurations described above. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, a part of the configuration of each embodiment may be added to, deleted from, or replaced with another configuration.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-175972 | Nov 2022 | JP | national |
