Photocatalytic reaction device and photocatalytic reaction method using the same

Abstract

To provide a photocatalytic reaction apparatus capable of conducting a photocatalytic reaction while enhancing conversion efficiency of solar energy, and a production method of a gas using the same.SOLUTION: A photocatalytic reaction apparatus has a light-transmittable reaction vessel 2 that accommodates water and a reaction solution containing a photocatalyst. The reaction vessel 2 is equipped with an inlet port 3 to introduce the reaction solution 5 into the reaction vessel 2 and an outlet port 8 to discharge the reaction solution 5 to the outside of the reaction vessel 2, and loaded with light-transmittable granular materials 4. A photocatalytic reaction accompanied by an oxidation reaction of water is conducted until the reaction solution 5 accommodated in the reaction vessel 2 is discharged from the outlet port 8. A production method of a gas uses the photocatalytic reaction apparatus.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photocatalytic reaction device for performing a photocatalytic reaction accompanied by a water oxidation reaction, and a photocatalytic reaction method using this photocatalytic reaction device, and more particularly, to a photocatalytic reaction device for efficiently introducing light energy such as sunlight into a photocatalyst to perform a photocatalytic reaction accompanied by a water oxidation reaction, and a photocatalytic reaction method using the same for performing a photocatalytic reaction accompanied by a water oxidation reaction. [Background technology]

[0002] Well-known technologies for utilizing solar energy include solar power generation and solar heat recovery, both of which are already in practical use. Meanwhile, artificial photosynthesis using solar energy is also known.

[0003] Artificial photosynthesis produces hydrogen and oxygen from water by irradiating a photocatalyst with light in the presence of water, and because it can recover chemical energy using sunlight, it allows for more efficient energy storage than electricity or heat. This also reduces the use of fossil fuels and captures (fixes) carbon dioxide (CO2), which leads to the suppression of CO2 emissions, a cause of global warming.

[0004] However, one of the technical challenges in artificial photosynthesis is the development of photocatalysts. That is, in the reaction for producing hydrogen and oxygen from water, the photocatalysts used are limited to specific oxide semiconductors such as titanium dioxide, and the problem is that the conversion efficiency of these is low. In addition, it would be ideal if water decomposition could be performed using a mechanism in which oxygen and hydrogen are produced simultaneously on a single photocatalyst (hereinafter referred to as the "single-step mechanism") (see Non-Patent Document 1), and although it is already known that this can be achieved by irradiation with ultraviolet light, the efficiency of solar energy utilization is still insufficient because light in the visible light region is not used.

[0005] So, Fe 3+ (iron(III) ion) / Fe 2+A method has been proposed for completely decomposing water through a two-step reaction (hereinafter referred to as the "two-step mechanism") by irradiating light in the presence of a redox medium that utilizes the change in iron (II) ions (see Patent Document 1). That is, the process involves generating oxygen from an aqueous solution containing iron (III) ions using light energy and a photocatalyst, and 3+ In the presence of photocatalyst, Fe 2+ The Fe produced in this process is then reduced to 2+ The aqueous solution containing Fe was electrolyzed. 3+ This process regenerates water and generates hydrogen by electrolysis, which makes it possible to produce hydrogen by decomposing water with only a small amount of electricity, which reduces costs by lowering the electrolysis voltage and also increases the conversion efficiency of solar energy.

[0006] The solar energy conversion efficiency is generally expressed as the ratio of the energy extracted to the solar energy incident on the substrate. In the case of the reaction using the iron ion redox medium described above, the efficiency is expressed as the ratio of the energy extracted to the solar energy incident on the substrate. 3+ Fe 2+ In the hydrogen production using the above-mentioned iron ion redox medium, the energy of sunlight is reduced to Fe 2+ It has been reported that the solar energy conversion efficiency reaches 0.35%, which is higher than the solar energy conversion efficiency of switchgrass, a weed known as a promising raw material crop for biofuels, which is 0.2% (see Non-Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3198298 [Non-patent literature]

[0008] [Non-Patent Document 1] Qian Wang and Kazunari Domen, Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies, Chemical Reviews vol. 120 No. 2 (2020) pp. 919-985 [Non-Patent Document 2] Kazuhiro Sayama, Yugo Mitsuishi, Research and development of solar hydrogen production, Synthesiology vol.7 No.2(2014)pp.81-92 Summary of the Invention [Problem to be solved by the invention]

[0009] The current challenge in recovering chemical energy through artificial photosynthesis is to reduce the cost. In the hydrogen production using the above-mentioned iron ion redox medium, in order to receive sunlight over a wider area and introduce light to the photocatalyst, Fe was added to the reaction solution containing the photocatalyst. 3+ The aqueous solution containing Fe was placed in an open pool. 3+ Fe 2+ The proposed solution would be reduced to toluene, the aqueous solution recovered from the pool, and electrolyzed in an electrolysis device to produce hydrogen.

[0010] However, if sunlight is incident on the surface of the pool at an angle, at least a portion of the sunlight will be reflected and lost. In addition, a horizontal installation like that of a pool would require a large installation area, so installation locations are limited.

[0011] One method for effectively utilizing reflected light is, for example, to load a photocatalyst onto a light-transmitting granular material and then store the granular material with the photocatalyst loaded in a pool or the like. However, if the loaded photocatalyst peels off and settles during the reaction, the irradiated light will no longer reach the photocatalyst, reducing the amount of reaction or causing the reaction to stop.

[0012] Therefore, an object of the present invention is to provide a photocatalytic reaction device capable of carrying out a photocatalytic reaction while increasing the solar energy conversion efficiency. Another object of the present invention is to provide a method for carrying out a photocatalytic reaction involving the oxidation of water while increasing the efficiency of solar energy conversion. [Means for solving the problem]

[0013] Therefore, the inventors have thoroughly investigated these problems and discovered that by using a photocatalytic reaction device in which a light-transmitting reaction vessel is filled with light-transmitting granular material, and by continuously or intermittently injecting a reaction solution containing water and a photocatalyst into this photocatalytic reaction device and irradiating it with sunlight, it is possible to carry out a photocatalytic reaction while increasing the solar energy conversion efficiency, thereby completing the present invention.

[0014] That is, the gist of the present invention is as follows. (1) Water, and Photocatalytic reactions are carried out using light with wavelengths of 400nm to 800nm. By photocatalysis or chemical reaction Photocatalytic reactions are carried out using light with wavelengths of 400nm to 800nm. A reaction solution containing a reaction precursor that will become a photocatalyst 、 Inject continuously or intermittently visible A light-transmitting reaction vessel; an inlet for receiving the reaction solution in the reaction vessel; an outlet for continuously or intermittently discharging the reaction solution to the outside of the reaction vessel; The reaction vessel is visible A granular material having optical transparency; A photocatalytic reaction device for a reaction solution comprising: (2) The photocatalytic reaction device according to (1), further comprising a gas exhaust port for exhausting gas generated in the reaction vessel. (3) The photocatalytic reaction device according to (1) or (2), further comprising a gas supply port for supplying a reaction gas used in the reaction in the reaction vessel from the outside. (4) The photocatalytic reaction device according to any one of (1) to (3), wherein the reaction solution further contains an oxidation-reduction product. (5) A photocatalytic reaction method for performing a photocatalytic reaction using the photocatalytic reaction device according to any one of (1) to (4), comprising the steps of: injecting the reaction solution from an inlet of the photocatalytic reaction device; and during the time period until the reaction solution injected into the reaction vessel is discharged from an outlet of the photocatalytic reaction device, Using light with wavelengths of 400nm to 800nm A photocatalytic reaction method for carrying out a photocatalytic reaction involving a water oxidation reaction. (6) The photocatalytic reaction method according to (5), wherein the photocatalytic reaction is carried out using sunlight. (7) The photocatalytic reaction method according to (5) or (6), in which the photocatalytic reaction device is set upright on an installation stand and the photocatalytic reaction is carried out. Effect of the Invention

[0015] According to the photocatalytic reaction device of the present invention, it is possible to carry out a photocatalytic reaction while increasing the solar energy conversion efficiency. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram for explaining the photocatalytic reaction device of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining the test photocatalytic reaction system used in the examples. [Diagram 3] FIG. 3 is a schematic diagram for explaining the state of the photocatalytic reaction device in Comparative Example 1. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram for explaining the state of the photocatalytic reaction device in Comparative Example 2. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described in detail below. In the present invention, a photocatalytic reaction device is used in which a light-transmitting reaction vessel is loaded with light-transmitting granules, and this photocatalytic reaction device is filled with a reaction solution containing water and a photocatalyst or a reaction precursor that chemically reacts with the photocatalyst in the reaction vessel (becomes a photocatalyst through a chemical reaction), and a photocatalytic reaction involving an oxidation reaction of water is carried out.

[0018] Here, as shown in FIG. 1, the photocatalytic reaction device 1 of the present invention has a light-transmitting reaction vessel 2 into which a reaction solution 5 containing water and a photocatalyst, or a reaction solution 5 containing water and a reaction precursor that chemically reacts with the photocatalyst in the reaction vessel, is continuously or intermittently injected, and this reaction vessel 2 is provided with an inlet 3 for allowing the reaction solution 5 as described above to be contained in the reaction vessel 2, and an outlet 8 for discharging the reaction solution 5 after the photocatalytic reaction to the outside of the reaction vessel 2, and this reaction vessel 2 is filled with light-transmitting granular material 4.

[0019] 1 shows an example in which a photocatalyst inlet 3a for supplying a reaction solution containing a photocatalyst or a reaction precursor and a redox inlet 3b for supplying a solution containing an oxidant / reducer (redox medium) (redox solution) are separately provided as the inlet 3 of the photocatalytic reaction device 1 in correspondence with a two-step mechanism type photocatalytic reaction as described later, but it is of course possible to use a single inlet 3. In the present invention, the reaction solution 5 refers to an aqueous solution containing at least both water and a photocatalyst (or a reaction precursor), and may further contain an oxidant / reducer (redox) in addition to these.

[0020] Among these, the reaction vessel 2 having optical transparency is preferably one having optical transparency not only for ultraviolet light but also for visible light, assuming sunlight as a suitable light source, and is preferably made of a material having a transmittance of 50% or more for light with a wavelength of at least 400 nm to 800 nm. For example, it may be made of inorganic materials such as quartz, borosilicate glass, soda-lime glass, and non-alkali glass, or resin materials having optical transparency such as acrylonitrile-styrene, polyethylene terephthalate, and polyethylene, but is not limited thereto. Here, the transmittance is the ratio of the intensity of light incident at a certain wavelength to the intensity of light after passing through a material having optical transparency. In the present invention, light other than sunlight may be used to carry out a photocatalytic reaction.

[0021] The form of the reaction vessel may be, for example, a single cylindrical type, but is not necessarily limited thereto, and may be a spherical or double-tube structured reaction vessel. In the case of a multiple tube structure such as a double tube, for example, it is possible to irradiate light from the inside by inserting a light source into the inner tube, and by mirror-finishing the wall surface of the inner tube between the inner and outer tubes, it is possible to efficiently irradiate light to the photocatalyst by reflecting the light arriving from the outer light source on the mirror-finished wall surface. Regarding the direction of light irradiation, when aiming to use sunlight, the sunlight may move relative to the reaction vessel, so that the reaction vessel may be irradiated from an oblique direction, or light reflected by a reflecting material such as a mirror may be irradiated, and the light irradiation direction is not necessarily limited to that shown in the following embodiment.

[0022] The granular material 4 to be loaded into the reaction vessel 2 should preferably have the same optical transparency as that of the reaction vessel 2, and preferably has a material with a transmittance of at least 50% for light with a wavelength of 400 nm to 800 nm. For example, the granular material 4 may be made of inorganic materials such as quartz, borosilicate glass, soda-lime glass, and non-alkali glass, or resin materials having optical transparency such as acrylonitrile-styrene, polyethylene terephthalate, and polyethylene, but is not limited thereto. By loading the granular material 4 into the reaction vessel 2, the photocatalyst 6 in the injected reaction solution 5 comes into contact with the granular material 4 or moves to the outlet 8 side of the reaction vessel 2 through the gaps between the particles of the granular material 4, so that the photocatalyst 6 can be prevented from settling in the reaction vessel 2, and the residence time while receiving light energy in the reaction vessel 2 can be secured, thereby performing a photocatalytic reaction accompanied by an oxidation reaction of water.

[0023] Alternatively, after loading the spheres into the reaction vessel 2, a reaction precursor that becomes a photocatalyst through a chemical reaction may be injected into the reaction vessel 2 to cause a chemical reaction, thereby precipitating the photocatalyst in the gaps between the granules 4, thereby causing the photocatalyst to be present in the gaps between the granules 4. As described above, according to the present invention, compared to the case where granules are used on which the photocatalyst is previously supported, the photocatalyst is also present in the gaps, making it possible to increase the amount of photocatalyst per unit volume in the reaction vessel.

[0024] Considering these functions, the size of the granular body 4 is preferably 0.01 mm to 30 mm, more preferably 0.05 mm to 15 mm, and even more preferably 0.1 mm to 5 mm. The shape of the granular body 4 is not particularly limited, and may be, for example, spherical, elliptical, cylindrical, angular, plate-like, or needle-like. Preferably, the granular body 4 is spherical or elliptical, because holes can be formed in the granular body 4 and light can penetrate deep inside.

[0025] On the other hand, the inlet 3 of the reaction vessel 2 may be any inlet capable of continuously or intermittently injecting the reaction solution 5 containing water and the photocatalyst or reaction precursor into the reaction vessel 2, and there are no particular limitations on its shape or installation location (position). The same is true for the outlet 8 of the reaction vessel 2, and there are no particular limitations on its shape or installation location (position) as long as it can discharge the reaction solution 5 to the outside of the reaction vessel 2. In addition, the photocatalytic reaction device 1 as shown in FIG. 1 can be installed vertically on an outdoor installation stand (not shown) or the like, for example, to carry out a photocatalytic reaction using sunlight. That is, in this photocatalytic reaction device 1, the inlet 3 is provided at the top of the reaction vessel 2, which is vertically upward, and the outlet 8 is provided at the bottom of the reaction vessel 2, which is vertically downward. In such a case, by providing a valve (not shown) capable of adjusting the flow rate in the inlet pipe (not shown) connected to the reaction vessel 2 and the outlet pipe (not shown) connected to the outlet 8, respectively, the reaction solution 5 contained in the inlet 3 can be discharged from the outlet 8 by gravity without using any power. Alternatively, as an example different from that of FIG. 1, both the inlet 3 and the outlet 8 may be provided at the top of the reaction vessel 2, and the reaction solution 5 contained in the reaction vessel 2 may overflow from the outlet 8. Moreover, since the photocatalytic reaction device of the present invention can be installed vertically, for example, by standing on an installation stand, the installation area can be reduced and the total cost can be reduced. Note that in the present invention, the reaction vessel 2 is installed vertically, but the installation form of the reaction vessel 2 may be, for example, horizontal or inclined, and is not necessarily limited thereto.

[0026] Here, a reaction solution containing a photocatalyst (or reaction precursor) and water may be directly injected from the injection port 3 of the reaction vessel 2, or a precursor solution of the photocatalyst (i.e., reaction precursor) may be injected through a plurality of raw material lines connected to the injection port 3, and these may be chemically reacted in the reaction vessel 2, so that a reaction solution containing a specified photocatalyst is stored in the reaction vessel 2.

[0027] On the other hand, in the present invention, as described specifically below, a plurality of inlets 3 may be provided in response to the case where a redox medium (oxidizing / reducing substance) used in the photocatalytic reaction is injected into the reaction vessel 2. Similarly, in the present invention, since the photocatalytic reaction is accompanied by the oxidation reaction of water, and the generation of O2 and H2 occurs, a gas exhaust port 7 may be provided in order to exhaust these gases from the reaction vessel 2 to the outside. Furthermore, a gas supply port (not shown) may be provided in the reaction vessel 2 in order to supply a reaction gas such as carbon dioxide used in the photocatalytic reaction from the outside. However, these may be shared with each other. For example, when the inlet 3 is used intermittently to accommodate the reaction solution in the reaction vessel 2, the gas generated in the reaction vessel 2, such as oxygen or hydrogen, may be exhausted to the outside through the inlet 3, or the reaction gas may be supplied through the inlet 3.

[0028] Furthermore, if the deposition of photocatalyst in the reaction vessel 2 becomes excessive, clogging problems will occur in the reaction vessel 2 or the exhaust port 8, hindering operation. Therefore, a system may be provided which constantly monitors the change in the level or filling mass of the reaction vessel 2, or, if a reaction solution recovery tank is provided downstream of the exhaust port 8 as described below, monitors the level or filling mass, and determines that a blockage has occurred when the level or filling mass of the reaction vessel 2 increases, or when the level or filling mass of the reaction solution recovery tank stops increasing or decreases, and injects water into the reaction vessel 2 through the injection port 3 or the like to re-dissolve the excess precipitated photocatalyst.

[0029] In the present invention, a circulation-type reaction system may be provided in which the reaction solution 5 discharged from the outlet 8 is reinjected from the inlet 3 by providing a circulation path section 9 as shown in Fig. 1. For example, the unreacted redox medium contained in the reaction solution 5 once circulated in the reaction vessel 2 is circulated again into the reaction vessel 2 via the circulation path section 9, thereby making it possible to increase the concentration of the redox medium after the reaction.

[0030] When circulating the reaction solution 5 through such a circulation path section 9, the photocatalyst contained in the reaction solution 5 may be separated and recovered from the reaction solution 5 by filtration or the like, or the photocatalyst may be returned directly to the reaction vessel 2 without being recovered. When the photocatalyst is separated and recovered, or when the photocatalyst is added to the reaction solution, it may be additionally injected through the injection port 3. In particular, when the concentration of the photocatalyst contained in the reaction solution is to be constant, it is preferable to separate and recover the photocatalyst when circulating the reaction solution 5, and to inject the photocatalyst when injecting the filtered reaction solution 5 from the injection port 3 into the reaction vessel, but this is not limiting.

[0031] When injecting at least water and a reaction solution containing a photocatalyst or a reaction precursor that becomes a photocatalyst by chemical reaction into the reaction vessel 2 or discharging from the outlet 8, the reaction solution may be injected or discharged continuously or intermittently. For example, when the reaction precursor chemically reacts to become a photocatalyst, the injection of the reaction solution containing the reaction precursor into the reaction vessel 2 may be stopped for the time required for the chemical reaction inside the reaction vessel 2, and then the reaction solution 5 may be injected. Also, as described above, in order to dissolve the excessively precipitated photocatalyst again or to clean the inside of the reaction vessel 2, the supply of the reaction solution 5 into the reaction vessel 2 may be stopped once, and water or the like may be injected intermittently from the inlet 3 of the reaction vessel 2.

[0032] The photocatalytic reaction in the present invention involves a water oxidation reaction using a photocatalyst. The photocatalytic reaction is not particularly limited, but preferred examples include the following photocatalytic reactions.

[0033] (One-step photocatalytic reaction) One of them is a one-step mechanism type photocatalytic reaction that can split water into hydrogen and oxygen in one step. In this case, for example, according to the above-mentioned Non-Patent Document 1, CdS, TaON, Ta3N5, LaTiO2N, MoS2, CaFeO4, CuNbO3, etc. are known as photocatalysts, which can split water with visible light. Specifically, by irradiating the photocatalyst with energy equal to or greater than the band gap, electrons in the valence band of the photocatalyst are excited to the conduction band, generating electrons in the conduction band and holes in the valence band. Water is oxidized by the holes to generate oxygen gas and protons [referred to as the "oxygen generation system" in reaction formula (1)], while the protons are reduced by the electrons to generate hydrogen gas [referred to as the "hydrogen generation system" in reaction formula (2)]. 2H2O → O2+ 4H + + 4e - (1) 4H + + 4e - → 2H2···(2)

[0034] (Two-step photocatalytic reaction) In addition, a two-step mechanism type photocatalytic reaction (also called a photocatalytic / electrolytic hybrid type) using a redox medium (oxidizing / reducing agent) can also be mentioned. In this case, for example, as shown in Patent Document 1 and Non-Patent Document 2, Fe 3+ / Fe 2+ Using a redox medium that utilizes the change in 3+ Fe 2+ At the same time, water is oxidized to produce oxygen (O2) gas. 2+By subjecting an aqueous solution containing the above to an electrolysis process, the water is reduced to generate hydrogen (H2) gas. Alternatively, there is another form of the two-step mechanism in which oxygen generation and hydrogen generation are separated into two types of photocatalysts and linked by a redox medium. In the oxygen generation system, holes oxidize water to generate oxygen, and at the same time reduce the oxidized form of the redox medium to generate a reductant. On the other hand, in the hydrogen generation system, excited electrons reduce water to generate hydrogen, and at the same time oxidize the reducted form of the redox medium to generate an oxidant (also called a Z-scheme reaction). By dividing the reaction into two steps like this, it becomes possible to decompose water and obtain hydrogen using only a small amount of electricity, making it possible to lower the electrolysis voltage.

[0035] In this case, the redox medium may be, for example, an iron ion-based medium as described above, or an iron ion-based medium such as I - / IO3 - Examples of the photocatalyst include iodine-based redox mediators such as iodine compounds that can take combinations such as those described above. The photocatalyst may be a material in which the upper end of the valence band in the band gap of the photocatalyst is located at an energy level that is more negative than the redox potential of oxygen and water, and the lower end of the conduction band in the band gap of the photocatalyst is located at an energy level that is more positive than the redox potential of the redox mediator. The photocatalyst is not limited to a single material, and may be a combination of two or more materials that can satisfy the above conditions. Specific examples of the photocatalyst include, but are not limited to, BiVO4-based and WO3-based materials, as well as iron oxide (Fe2O3), molybdenum sulfide (MoS2), and the like. In such a two-step mechanism type reaction, as shown in the following formula (3), Fe 3+ Fe 2+ The photocatalytic reaction according to the present invention involves the reduction of Fe to FeO and the oxidation of water to produce oxygen. 2+ The aqueous solution containing the above is removed from the container body, and hydrogen can be produced by separately carrying out the electrolytic reaction shown in the following formula (4). Photocatalytic reaction: 2H2O+4Fe 3+ →4Fe 2+ +O2+4H + (3) Electrolytic reaction: 4Fe 2+ +4H+ →4Fe 3+ +2H2···(4) When this reaction occurs, the solar energy conversion efficiency is 3+ Fe 2+ This can be expressed as the conversion rate that reduces to

[0036] (Photocatalytic reaction for carbon dioxide reduction) On the other hand, the reduction of carbon dioxide proceeds by irradiating the photocatalyst with light in the presence of carbon dioxide and water as reactive gases used in the photocatalytic reaction. That is, as in the above-mentioned photocatalytic reaction, when the photocatalyst is excited with light having an energy larger than its band gap, electrons are generated in its conduction band and holes are generated in its valence band, and thus, by using such a photocatalytic reaction, a reaction of producing sugar, oxygen, and the like from carbon dioxide and water is brought about. Among them, the photocatalyst used in such a case is ZrO2, etc., but it is sufficient that the upper end of the valence band in the band gap of the photocatalyst is located at an energy that is more negative than the redox potential of oxygen and water, and the lower end of the conduction band in the band gap of the photocatalyst is located at an energy that is more positive than the redox potential of carbon dioxide. As another photocatalyst, it is sufficient that the material is a combination of a metal complex catalyst that can cause the reduction of CO2 to occur preferentially over the reduction of water, and a semiconductor photocatalyst that can use water as a supply source of electrons. In addition, the photocatalyst is not limited to a single material, and it is sufficient that the above conditions are satisfied by combining two or more types of materials. In addition, in such a reaction related to carbon dioxide reduction, the reactions shown in the following formula (5) and formula (6) occur, and thus a reduced product of CO2 can be produced. In this case, oxygen is produced by oxidizing water. On the other hand, in the case of reduction of CO2, CO is shown as an example of a reduced product of CO2, but this is not necessarily limited to this. In addition to CO, examples include HCOOH, HCHO, CH3OH, and CH4. 2H2O →O2+4H + +4e - (5) CO2+2H + +2e -→CO+H2O (6) EXAMPLES

[0037] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0038] Example 1 Using the test photocatalytic reaction system shown in Figure 2, the following photocatalytic reaction was carried out. First, this test photocatalytic reaction system is configured to include a photocatalytic reaction device 1, a photocatalytic supply device 11, and a redox medium supply device 21. Of these, the photocatalytic reaction device 1 is the same as that shown in Fig. 1 above, and a borosilicate glass reaction vessel 2 with an internal volume of approximately 0.012 liters is filled with soda-lime glass granules 4 with a particle size of 0.6 mm. Here, ethanol is introduced into the reaction vessel to measure the liquid level, and then the filling height of the granules 4 is measured when the granules 4 are introduced and vibration is applied to fill the granules 4. The filling rate of the granules 4 is about 60%, which is calculated by dividing the liquid level of ethanol increased by the introduction of the granules 4 by the filling height of the granules 4.

[0039] The photocatalyst supplying device 11 is connected to the photocatalyst inlet 3a of the photocatalyst reaction device 1, and allows the reaction solution 5 containing water and the photocatalyst or a reaction precursor that chemically reacts with the photocatalyst in the reaction vessel 2 to be injected into the reaction vessel 2, and has two raw material supply lines so that BiVO4 used as the photocatalyst for the photocatalytic reaction according to this Example 1 is generated in the reaction tank 13. Of these, the raw material supplying line having the tank 11a and the valve 14a flows a liquid in which Bi(NO3)3·5H2O is dissolved in nitric acid at 0.4 mol / l, and the raw material supplying line having the tank 11b and the valve 14b flows a liquid in which NH4VO3 is dissolved in nitric acid at 0.4 mol / l, which is introduced into the reaction tank 13 to form a photocatalyst raw material mixture containing Bi(NO3)3·5H2O and NH4VO3 at 32 mmol / l each.

[0040] Then, in the reaction tank 13, the Bi(NO3)3·5H2O and NH4VO3 were chemically reacted to precipitate the BiVO4 photocatalyst. Here, a heating device (not shown) was attached to the reaction tank 13, and the photocatalyst raw material mixture was kept at 90°C for 6 hours to precipitate the BiVO4 photocatalyst. After that, the BiVO4 photocatalyst was washed with distilled water to remove nitric acid. Distilled water was added to prepare a photocatalyst dispersion solution, which was then injected into the reaction vessel 2 through the photocatalyst injection port 3a.

[0041] On the other hand, for the redox medium supply device 21, a redox solution in which Fe(ClO4)3 is dissolved is placed in the tank 11c and connected to the redox inlet 3b. Then, when the photocatalyst dispersion solution prepared in the reaction tank 13 and the redox solution placed in the tank 11c are mixed, the Fe in the photocatalyst dispersion redox solution is 3+ The concentrations and flow rates of the photocatalyst dispersion solution and the redox solution were adjusted so that the ion concentration was 2 mmol / l.

[0042] In addition, a solar simulator equipped with a xenon short arc lamp was used as the light used in the reaction. In this embodiment, the light was adjusted to 1 sun within the range of 400 to 800 nm. Specifically, a diffraction grating spectroradiometer was used to measure the spectrum of the light irradiated from the solar simulator, and the light intensity of the solar simulator was adjusted so that the light intensity was 1 sun. In this embodiment, the light used in the reaction was irradiated from a direction perpendicular to the direction from the inlets 3a and 3b of the reaction vessel toward the outlet 8.

[0043] The flow rate of the photocatalyst-dispersed redox solution (reaction solution) 5, which is obtained by mixing the photocatalyst-dispersed solution injected from the photocatalyst injection port 3a and the redox solution injected from the redox injection port 3b in the reaction vessel 2 filled with the granules 4, is 1.2×10 -3Injection was started so that the flow rate was 1.2 x 10 l / min. After the start of injection, the photocatalyst-dispersed solution and the redox solution were each continuously supplied to the reaction vessel 2. Meanwhile, the reaction solution recovery control valve 15 between the reaction solution recovery tank 16 and the reaction vessel 2 was closed, and the photocatalyst-dispersed redox solution was injected to fill the reaction vessel 2 with the solution, and then the reaction solution recovery control valve 15 was opened and the reaction vessel 2 was irradiated with light adjusted to 1 sun as described above. During the reaction, the photocatalyst-dispersed redox solution was continuously supplied to the reaction vessel 2, and at that time, the photocatalyst-dispersed redox solution 5 that had passed between the granules 4 filled in the reaction vessel 2 was discharged at a flow rate of 1.2 x 10 -3 The valve 15 is adjusted so that the flow rate is 1 l / min, and the solution is discharged from the reaction solution recovery port (discharge port) 8 and stored in the reaction solution recovery tank 16. At this time, the photocatalyst in the photocatalyst-dispersed redox solution flows through the gaps between the spheres in the reaction vessel 2 and is discharged from the discharge port 8 to the tank 16, but since the photocatalyst may be trapped in the gaps between the granules and the flow of only the photocatalyst may stop, or the photocatalyst may be repeatedly trapped in the gaps and then circulated, it is not necessary that all of the photocatalyst is discharged.

[0044] The Fe in the solution recovered in Tank 16 2+ The concentration of Fe in the photocatalyst-dispersed redox solution recovered from the reaction solution recovery tank 16 5 minutes after the reaction vessel 2 was irradiated with light was measured by a colorimetric method using phenanthroline. 2+ The concentration of Fe in the photocatalyst-dispersed redox solution recovered from the reaction solution recovery tank 16 10 minutes after the reaction vessel 2 was irradiated with light. 2+ The difference between the Fe concentration and the Fe concentration was calculated by dividing the difference by the elapsed time of 5 minutes. 2+ The production rate (mol / l / h) was determined. The results are shown in Table 1. In this embodiment, the photocatalyst dispersion solution and the redox solution were continuously supplied, respectively, to continuously supply the photocatalyst dispersion redox solution into the reaction vessel 2 to carry out the photocatalytic reaction, but the photocatalyst dispersion solution and the redox solution may be dispersed alternately, or the photocatalyst dispersion redox solution may be intermittently supplied to carry out the photocatalytic reaction in the reaction vessel 2.

[0045] Example 2 A photocatalytic reaction was carried out using the test photocatalytic reaction system shown in FIG. 2 in the same manner as in Example 1, except that the following photocatalytic precipitation reaction was carried out. A liquid obtained by dissolving Bi(NO3)3·5H2O in 0.4 mol / l of nitric acid was circulated from a raw material supply line having tank 11a and valve 14a, while a liquid obtained by dissolving NH4VO3 in 0.4 mol / l of nitric acid was circulated from another raw material supply line having tank 11b and valve 14b, and introduced into reaction tank 13 to form a photocatalyst raw material mixture containing 32 mmol / l each of Bi(NO3)3·5H2O and NH4VO3.

[0046] Next, the reaction solution recovery control valve 15 between the reaction solution recovery tank 16 and the reaction vessel 2 was closed, and the reaction vessel 2 filled with the granules 4 in the same manner as in Example 1 was filled with the photocatalyst raw material mixture obtained above. Then, a heating device (not shown) was attached to the reaction vessel 2, and the photocatalyst raw material mixture was maintained at 90°C for 6 hours in the reaction vessel 2 filled with the granules 4, thereby precipitating the BiVO4 photocatalyst in the gaps between the granules 4 in the reaction vessel 2.

[0047] On the other hand, for the redox medium supply device 21, a redox solution in which Fe(ClO4)3 is dissolved is placed in a tank 11c and connected to the redox injection port 3b. 3+ The redox solution was adjusted to have an ion concentration of 2 mmol / l. -3 Injection into the reaction vessel 2 filled with the granules 4 was started so as to obtain a flow rate of 1 / min. During the light irradiation, the redox solution was continuously injected into the reaction vessel 2.

[0048] Then, the reaction solution recovery control valve 15 was opened, and the discharge amount was 1.2×10 -3 The flow rate of the reaction vessel 2 was adjusted to 1 liter / min, and then the photocatalytic reaction was carried out in the same manner as in Example 1, except that light adjusted to 1 sun was irradiated onto the reaction vessel 2 in the same manner as in Example 1. 2+The production rate (mol / l / h) was obtained. The results are shown in Table 1. In this embodiment, the photocatalyst deposition process and the redox solution supply process are carried out separately, but these processes may be carried out simultaneously. In this embodiment, after the BiVO4 photocatalyst is deposited in the reaction vessel 2, only the redox solution is continuously circulated through the reaction vessel 2.

[0049] Comparative Example 1 The following photocatalytic reaction was carried out using a photocatalytic reaction device 18 shown in Fig. 3. In the photocatalytic reaction device 18 of Fig. 3, unlike the case of Fig. 2, the reaction vessel 2 is not filled with granular material 4. As in Example 1, a solution of Bi(NO3)3·5H2O dissolved in 0.4 mol / l nitric acid and a solution of NH4VO3 dissolved in 0.4 mol / l nitric acid were mixed in a reaction tank 13 and chemically reacted to synthesize a BiVO4 photocatalyst.

[0050] Next, Fe 3+ First, a redox solution adjusted by dissolving Fe(ClO4)3 so that the ion concentration was 2 mmol / l was introduced into a reaction vessel 2 made of borosilicate glass with an internal volume of approximately 0.012 liters. At that time, the reaction solution recovery control valve 15 between the reaction solution recovery tank 16 and the reaction vessel 2 was closed to inject the redox solution, and when the reaction vessel 2 was filled with the solution, the BiVO4 photocatalyst 6 synthesized in advance was introduced from the photocatalyst injection port 3a, and at the same time, the reaction solution recovery control valve 15 was opened, and the reaction vessel 2 was irradiated with light adjusted to 1 sun in the same manner as in Example 1. During the light irradiation, the BiVO4 photocatalyst 6 and the redox solution were continuously injected into the reaction vessel 2 from the injection port. During that time, the photocatalyst-dispersed redox aqueous solution (reaction solution) 5 containing the redox solution and the BiVO4 photocatalyst 6 was discharged from the reaction solution recovery port 8 and stored in the reaction solution recovery tank 16. Then, the Fe in the solution recovered in the reaction solution recovery tank 16 was removed from the reaction solution recovery port 8. 2+ The concentration of Fe in the photocatalyst-dispersed redox solution recovered from the reaction solution recovery tank 16 5 minutes after irradiation was measured by a colorimetric method using phenanthroline in the same manner as in Example 1. 2+The concentration of Fe in the photocatalyst-dispersed redox solution recovered from the reaction solution recovery tank 16 10 minutes after irradiation. 2+ The difference between the Fe concentration and the Fe concentration was calculated by dividing the difference by the elapsed time of 5 minutes. 2+ The production rate (mol / l / h) was calculated, and the results are shown in Table 1.

[0051] As can be seen from Table 1, in Comparative Example 1, Fe was more than that in Examples 1 and 2. 2+ The production rate decreased. This is because, as shown in FIG. 3, in Comparative Example 1, the BiVO4 photocatalyst reacted in the process of sinking under its own weight toward the bottom of the reaction vessel 2, and therefore the reaction amount was smaller than in these Examples.

[0052] Comparative Example 2 The following photocatalytic reaction was carried out using a photocatalytic reaction device 19 shown in Fig. 4. In the photocatalytic reaction device 19 of Fig. 4, unlike the case of Fig. 2, the reaction vessel 2 is not filled with granular material 4. As in Example 1, a solution of Bi(NO3)3·5H2O dissolved in 0.4 mol / l nitric acid and a solution of NH4VO3 dissolved in 0.4 mol / l nitric acid were mixed in a reaction tank 13 and chemically reacted to synthesize a BiVO4 photocatalyst.

[0053] Next, Fe 3+First, a redox solution adjusted by dissolving Fe(ClO4)3 so that the ion concentration is 2 mmol / l was introduced into a reaction vessel 2 made of borosilicate glass with an internal volume of approximately 0.012 liters. At that time, the reaction solution recovery control valve 15 between the reaction solution recovery tank 16 and the reaction vessel 2 was closed to inject the redox solution, and when the reaction vessel 2 was filled with the solution, the BiVO4 photocatalyst 6 synthesized in advance was introduced from the photocatalyst injection port 3a and left for about 1 hour until the BiVO4 photocatalyst 6 settled on the bottom of the reaction vessel 2. Thereafter, the reaction solution recovery control valve 15 was opened, and the reaction vessel 2 was irradiated with light adjusted to 1 sun in the same manner as in Example 1. During the light irradiation, the redox solution was continuously injected, and the photocatalyst was transported to the outlet 8 by the flow of the redox solution and discharged together with the redox solution. At this time, not all of the photocatalyst may be discharged, and a part may remain. The results are shown in Table 1.

[0054] As can be seen from Table 1, in this Comparative Example 2, Fe was lower than in Examples 1 and 2. 2+ The production rate was decreased, and was decreased compared to Comparative Example 1. This is probably because, as shown in Fig. 4, in Comparative Example 2, the BiVO4 photocatalyst was precipitated at the bottom of the reaction vessel 2 and the photocatalytic reaction occurred, so the reaction amount was extremely small.

[0055] [Table 1]

[0056] As described above, according to the present invention, for example, it is possible to perform a photocatalytic reaction while increasing the conversion efficiency of solar energy. Moreover, since the photocatalytic reaction device of the present invention can be installed vertically, for example, by standing on an installation stand, it is possible to reduce the installation area and reduce the total cost. [Explanation of symbols]

[0057] 1. Photocatalytic reaction device 2 Reaction vessel 3 Inlet 3a Photocatalyst injection port 3b Redox Inlet 4 Granules 5. Reaction solution 6 Photocatalyst 7 Gas exhaust port 8 Outlet 9 Circulation path section 11a, 11b Photocatalyst precursor tank 12a, 12b, 12c Pumps 13 Reaction tank 14a, 14b, 14c valves 15 Reaction solution recovery control valve 16 Reaction solution recovery tank 17a, 17b, 17c, 17d Exhaust valve 18 Photocatalytic reaction device 19 Photocatalytic reaction device 20 Injection valve 21 Redox medium supply device

Claims

1. a visible light transparent reaction vessel into which a reaction solution containing water and a photocatalyst that performs a photocatalytic reaction using light with a wavelength of 400 nm to 800 nm or a reaction precursor that becomes a photocatalyst that performs a photocatalytic reaction using light with a wavelength of 400 nm to 800 nm through a chemical reaction is continuously or intermittently injected; an inlet for receiving the reaction solution in the reaction vessel; an outlet for continuously or intermittently discharging the reaction solution to the outside of the reaction vessel; A granular material having visible light transparency contained in the reaction vessel; A photocatalytic reaction device for a reaction solution comprising:

2. 2. The photocatalytic reaction device according to claim 1, further comprising a gas exhaust port for exhausting gas generated in the reaction vessel.

3. 3. The photocatalytic reaction device according to claim 1, further comprising a gas supply port for supplying a reaction gas used in the reaction in the reaction vessel from the outside.

4. 4. The photocatalytic reaction device according to claim 1, wherein the reaction solution further contains an oxidation-reduction agent.

5. A photocatalytic reaction method for performing a photocatalytic reaction using the photocatalytic reaction device according to any one of claims 1 to 4, comprising the steps of injecting the reaction solution through an inlet of the photocatalytic reaction device, and performing a photocatalytic reaction involving a water oxidation reaction by utilizing light having a wavelength of 400 nm to 800 nm during the time period until the reaction solution injected into the reaction vessel is discharged through an outlet of the photocatalytic reaction device.

6. The photocatalytic reaction method according to claim 5 , wherein the photocatalytic reaction is carried out using sunlight.

7. 7. The photocatalytic reaction method according to claim 5, wherein the photocatalytic reaction device is set upright on an installation stand and the photocatalytic reaction is carried out.

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