Method for regenerating a photocatalyst, method for manufacturing a photocatalyst supported by a co-catalyst, method for manufacturing a photocatalyst module, and method for operating a photocatalyst module.

Abstract

To provide a method for regenerating a photocatalyst and a method for operating a photocatalyst module which can restore a deteriorating photocatalytic activity.SOLUTION: A method for regenerating a photocatalyst includes irradiating the surface of a photocatalyst supporting a cocatalyst with light while a liquid containing a metallic compound, which is a precursor for the cocatalyst, is kept in contact therewith, so that the cocatalyst deposits on the photocatalyst surface. A method for operating a photocatalyst module includes using a cocatalyst-supporting water-splitting catalyst to split water by light, and supplying the water-splitting catalyst with water, to generate hydrogen and / or oxygen, wherein, when the activity of the photocatalyst deteriorates, a liquid of a metallic compound, which is a precursor for the cocatalyst, is made to exist within the module, and light irradiation causes a cocatalyst for photocatalysts to be deposited on the photocatalyst.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for regenerating a photocatalyst carrying a cocatalyst, a method for producing a cocatalyst-carrying photocatalyst, a method for producing a photocatalyst module, and a method for operating a photocatalyst module.

Background Art

[0002] In recent years, the development of high-performance photoenergy conversion systems using solar energy as a renewable energy has become increasingly important from the viewpoints of suppressing global warming and eliminating dependence on depleting fossil resources. Among them, the technology for producing hydrogen by decomposing water using solar energy can be used not only as a raw material supply technology for current oil refining, ammonia, and methanol but also as an energy carrier for fuel cells, and the social demand for its technology development is increasing more and more.

[0003] The water decomposition reaction by photocatalysts has been widely studied for a long time.

[0004] The decomposition reaction of water in an acidic aqueous solution on photocatalyst particles is estimated as follows.

[0005] H2O + 2h → 1 / 2O2 + 2H + (1) 2H + + 2e - → H2 (2) Similarly, in a basic solution, it is estimated as follows. 2H2O + 2e - → H2 + 2OH - [[ID=四十二]](3) 4OH - → O2 + 4e - + 2H2O (4)

[0006] Photocatalysts that cause such reactions are usually those in which a cocatalyst is supported on the surface of a photocatalyst semiconductor such as an oxide, oxynitride, or nitride. By supporting the cocatalyst, the activity of the photocatalyst can be improved (for example, paragraphs 0057 to 0066 of Patent Document 1).

[0007] As methods for supporting a cocatalyst on the surface of a photocatalyst, there are a method of dispersing and mixing the photocatalyst and the cocatalyst in an organic solvent, drying, and then heating (paragraphs 0068 to 0069 of Patent Document 1), a method of adding an aqueous solution of a salt for the cocatalyst to the photocatalyst, drying, and then heating (paragraph 0017 of Patent Document 2, paragraphs 0040 to 0042 of Patent Document 3), a photoelectrodeposition method in which a cocatalyst precursor is brought into contact with photocatalyst particles under light irradiation, and the cocatalyst precursor is deposited by oxidizing or reducing it with electrons and holes generated on the surface of the photocatalyst particles (Japanese Patent Application No. 2010-04104), and the like.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described above, photocatalysts for water decomposition reactions are usually supported with cocatalysts such as metals and metal oxides. On the other hand, as described above, the water decomposition reaction involves the generation of H + or OH - ions. If the movement of these ions between sites (hydrogen generation site and oxygen generation site) is slower than the ion generation rate, the ions may accumulate at each site, and the pH may vary significantly locally (for example, in a reaction in an acidic solution, if the oxygen generation reaction is very fast and the ion movement from the oxygen generation site to the hydrogen generation site is slow, the pH near the oxygen generation site will decrease). According to the pH-potential diagrams (Prouba diagrams) of various metals described in the literature Marcel Pourbaix, “Atlas of Electrochemical Equibria in Aqueous Solutions” (National Association of Corrosion Engineers, 1974), only Pt, Au, Ti, Ta, and Nb are stable (not corroded) in the pH range (pH=0~14) and potential range of the water splitting reaction; all others are corrosive. From this, it can be expected that not only RhCrOx, but most co-catalysts (co-catalysts made of metals other than Pt, Au, Ti, Ta, and Nb) are potentially subject to corrosion associated with the water splitting reaction and may leach out as water-soluble ions. Photocatalysts (photosemiconductors) have the ability to absorb light, but they usually do not have the activity to oxidize water or reduce protons without a co-catalyst (Chem. Rev. 2020, 120, 919-985). Therefore, if the co-catalyst is lost from the photocatalyst, the activity of the photocatalyst decreases.

[0010] One aspect of the present invention aims to provide a method for regenerating a photocatalyst and a method for operating a photocatalyst module that can enhance reduced photocatalytic activity. Another aspect of the present invention aims to provide a method for manufacturing a photocatalyst supported by a co-catalyst and a method for manufacturing a photocatalyst module that can easily support a co-catalyst. [Means for solving the problem]

[0011] The gist of this invention is as follows:

[0012] [1] A method for regenerating a photocatalyst, wherein the co-catalyst is deposited on the surface of a photocatalyst supported with a co-catalyst by irradiating it with light while a liquid containing a metal-containing compound, which is a precursor of the co-catalyst, is in contact with the surface of the photocatalyst.

[0013] [2] The method for regenerating a photocatalyst according to [1], wherein the light used is sunlight or an LED.

[0014] [3] The photocatalyst is installed in a photocatalyst module. [1] or [2] A method for regenerating the photocatalyst.

[0015] [4] A method for manufacturing a photocatalytic module in which a photocatalyst is installed inside, A method for manufacturing a photocatalytic module, comprising the step of placing a photocatalyst without a supporting co-catalyst inside the photocatalytic module, and then irradiating it with light while in contact with a liquid containing a metal-containing compound, which is a precursor of the co-catalyst, to precipitate the co-catalyst on the surface of the photocatalyst.

[0016] [5] A method for manufacturing a photocatalytic module according to [4], wherein the light irradiated is sunlight or LED light.

[0017] [6] The photocatalytic module is a water splitting module that decomposes water with a photocatalyst to generate hydrogen and / or oxygen. [4] or [5] A method for manufacturing the photocatalytic module.

[0018] [7] A method for operating a photocatalytic module having a co-catalyst-supported water splitting catalyst that splits water by light, wherein hydrogen and / or oxygen are generated by supplying water to the water splitting catalyst, A method for operating a photocatalytic module, wherein when the activity of the photocatalyst decreases, a liquid of a metal-containing compound, which is a precursor of a co-catalyst, is placed inside the module, and the photocatalytic co-catalyst is deposited on the photocatalyst by light irradiation.

[0019] [8] The method for operating the photocatalytic module described in [7], wherein the photocatalytic module performs the total decomposition of water. [Effects of the Invention]

[0020] According to one aspect of the present invention, the photocatalytic activity of a photocatalyst whose photocatalytic activity has decreased can be enhanced by re-supporting it with a co-catalyst. In one aspect of the present invention, the activity of the photocatalyst can be enhanced while the photocatalyst is present in the module (i.e., without dismantling the module). In one aspect of the present invention, the decrease in the activity of the photocatalyst can be suppressed. According to one aspect of the present invention, the efficiency of hydrogen production using a photocatalyst can be increased, or the cost of hydrogen production can be reduced. [Brief explanation of the drawing]

[0021] [Figure 1] This is a diagram showing the configuration of a photocatalytic panel. [Modes for carrying out the invention]

[0022] The present invention will be described in more detail below. [Photocatalyst] In this invention, the photocatalyst is a photocatalyst on which a co-catalyst is supported.

[0023] <Optical semiconductor> The optical semiconductor used in the present invention is a semiconductor that can generate holes and electrons by absorbing light, and is capable of catalyzing a photohydrolysis reaction. Preferably, it is a compound containing a metal element (including metalloid elements) that can become a d0 or d10 metal ion, and more preferably, it is a compound containing a d0 or d10 transition metal. Examples of metal elements that can become a d0 metal ion include Ti, Zr, Nb, Ta, V, W, and La. Examples of metal elements that can become a d10 metal ion include Zn, Ga, Ge, In, Sn, Sb, Pb, and Bi. Preferably, oxides, nitrides, oxynitrides, chalcogenides, or oxychalcogenides containing one or more elements selected from the group consisting of Ti, V, Ga, Zn, Bi, Nb, and Ta are used. Specifically, TiO2, CaTiO3, SrTiO3, aluminum-doped SrTiO3 (SrTiO3:Al), Sr3Ti2O7, Sr4Ti3O7, K2La2Ti3O 10 , Rb2La2Ti3O 10,Cs2La2Ti3O 10 ,CsLaTi2NbO 10 ,La2TiO5, La2Ti3O9, La2Ti2O7, La2Ti2O7:Ba, KaLaZr 0.3 Ti 0.7 O4, La4CaTi5O7, KTiNbO5, Na2Ti6O 13 , BaTi4O9, Gd2Ti2O7, Y2Ti2O7, (Na2Ti3O7, K2Ti2O5, K2Ti4O9, Cs2Ti2O5, H + -Cs2Ti2O5(H + -Cs is Cs is H + This indicates that ion exchange is taking place. (The same applies below) Cs2Ti5O 11 , Cs2Ti6O 13 H + -CsTiNbO5, H + -CsTi2NbO7, SiO2-pillared K2Ti4O9, SiO2-pillared K2Ti 2.7 Mn 0.3 O7, BaTiO3, BaTi4O9, AgLi 1 / 3 Ti 2 / 3 Titanium-containing oxides such as O2; titanium-containing oxynitrides such as LaTiO2N; titanium-containing (oxy) chalcogenides such as La5Ti2CuS5O7, La5Ti2AgS5O7, Y2Ti2O5S2, Gd2Ti2O5S2, Sm2Ti2O5S2; gallium-containing nitrides such as GaN:ZnO (ZnO solid solution of gallium-containing nitride); germanium-containing nitrides such as ZnGeN2:ZnO (ZnO solid solution of germanium-containing nitride); vanadium-containing oxides such as BiVO4, Ag3VO4; K4Nb6O 17 , Rb4Nb6O 17 , Ca2Nb2O7, Sr2Nb2O7, Ba5Nb4O 15 NaCa2Nb3O 10 ZnNb2O6, Cs2Nb4O 11 ,La3NbO7,H + -KLaNb2O7, H + -RbLaNb2O7, H + -CsLaNb2O7, H + -KCa2Nb3O 10SiO2-pillared KCa2Nb3O 10 (Chem.Mater.1996,8,2534.), H + -RbCa2Nb3O 10 H + -CsCa2Nb3O 10 H + -KSr2Nb3O 10 H + -KCa2NaNb4O 13 ), niobium-containing oxides such as PbBi2Nb2O9; niobium-containing oxynitrides such as CaNbO2N, BaNbO2N, SrNbO2N, LaNbON2; Ta2O5, K2PrTa5O 15 , K3Ta3Si2O 13 , K3Ta3B2O 12 , LiTaO3, NaTaO3, KTaO3, AgTaO3, KTaO3:Zr, NaTaO3:La, NaTaO3:Sr, Na2Ta2O6, K2Ta2O6(pyrochlore), CaTa2O6, SrTa2O6, BaTa2O6, NiTa2O6, Rb4Ta6O 17 H2La 2 / 3 Ta2O7, K2Sr 1.5 Ta3O 10 LiCa2Ta3O 10 ,KBa2Ta3O 10 Sr5Ta4O 15 Ba5Ta4O 15 H 1.8 Sr 0.81 Bi 0.19 Tantalum-containing oxides such as Ta2O7, Mg-Ta oxide (Chem.Mater.2004 16,4304-4310), LaTaO4, La3TaO7; tantalum-containing nitrides such as Ta3N5; and tantalum-containing oxynitrides such as CaTaO2N, SrTaO2N, BaTaO2N, LaTaO2N, Y2Ta2O5N2, and TaON can be used. Furthermore, the above compounds may contain different metals as dopants.

[0024] From the viewpoint of more efficiently generating photocatalytic water splitting reactions using sunlight, it is preferable to use SrTiO3:Al, known as a highly active total decomposition photocatalyst, and visible light-responsive photosemiconductors among the various photosemiconductors mentioned above. Specifically, BaNbO2N, TaON, Ta3N5, LaTiO2N, SnNb2O6, BaTaO2N, La5Ti2CuS5O7, La5Ti2Cu X Ag 1-X S5O7 (x is 0-1), BiVO4, Y2Ti2O5S2, Gd2Ti2O5S2, and Sm2Ti2O5S2 are preferred, and among these, BaNbO2N, TaON, Ta3N5, LaTiO2N, BaTaO2N, and La5Ti2Cu are particularly preferred. X Ag 1-X S5O7 (x is 0 to 1), BiVO4, GaN:ZnO, Y2Ti2O5S2, Gd2Ti2O5S2, and Sm2Ti2O5S2 are preferred. These compounds may be partially substituted with doping elements. The above various photosemiconductors can be easily synthesized by known synthesis methods such as solid-phase, solution, and flux methods.

[0025] The photocatalyst used does not need to be a single compound; a composite photocatalyst formed by combining multiple types of photosemiconductors with a carrier conductor can be used. When manufacturing a composite photocatalyst from multiple types of photosemiconductors, there are no particular restrictions on the method of selecting the types of photosemiconductors, but it is preferable to select two or more photosemiconductors with extremely different absorption ranges. This is because if the absorption ranges of the photosemiconductors are different, the absorption width of the resulting composite photocatalyst will be broadened, allowing for the utilization of more photons. Furthermore, different absorption ranges reduce the energy barrier with the co-catalyst and / or conductor, which is preferable because it allows for smoother charge transfer.

[0026] For example, when selecting two types of optical semiconductors, it is preferable that the absorption edge of one optical semiconductor is 350 nm to 550 nm and the absorption edge of the other optical semiconductor is 500 nm to 750 nm. When selecting three or more types of optical semiconductors, it is preferable that at least two of them have the above-mentioned absorption edges.

[0027] Furthermore, when comparing the absorption edges of two of the multiple types of optical semiconductors used, it is preferable to include optical semiconductors in which the difference in absorption edges is 25 nm or more. More preferably, the difference in absorption edges is 50 nm or more, and more preferably 250 nm or less. When selecting three or more types of optical semiconductors, it is preferable that at least two of the optical semiconductors have the above relationship, and it is even more preferable that all of the optical semiconductors have the above relationship with each other.

[0028] Examples of preferred combinations of optical semiconductors include GaN and LaTiO2N, GaN and BaTaO2N, TaON and LaTiO2N, BiVO4 and LaTiO2N, TaON and BaTaO2N, TaON and Ta3N5, and BiVO4 and BaTaO2N.

[0029] The form (shape) of the photosemiconductor is not particularly limited as long as it can function as a photocatalyst by supporting the co-catalyst described below. Particulate, lumpy, plate-like, etc., can be appropriately selected according to the installation method of the photocatalyst. A thin film (sheet) of the photosemiconductor can also be produced by growing crystals of the photosemiconductor on an electrode. However, the photosemiconductor must exist as a solid when in contact with a solution. When using the composite photocatalyst produced by the first aspect of the present invention as a photocatalyst for water splitting reactions, it is preferable to support the co-catalyst described below on the surface of the particulate photosemiconductor. In this case, the lower limit of the particle size of the photosemiconductor is preferably 50 nm or more, and the upper limit is preferably 500 μm or less.

[0030] In this application, "particle diameter" refers to the average value of the tangential diameter (Ferret diameter) in a constant direction (average particle diameter). This can be measured by known means such as XRD, TEM, and SEM, but measurement by SEM is preferred from the viewpoint of evaluating a wide range of particle diameters. When measuring with SEM, an observation image can be obtained in which at least several tens of particles can be observed at a magnification suitable for the target photocatalyst particle diameter. Then, the particle diameter can be measured by measuring the diameters of about 10 particles from the image and calculating the average value.

[0031] <Auxiliary catalyst or auxiliary catalyst source> In the present invention, the co-catalyst source refers to a substance (component, element, ion) that can become a co-catalyst when heated together with a photo-semiconductor in a liquid. For example, when a co-catalyst containing Co (such as CoOx, which is a co-catalyst for oxygen generation) is supported on a photo-semiconductor, a compound containing Co can be used as the co-catalyst source. Examples of compounds containing Co include salts containing Co, specifically Co(NO3)2, Co(NH3)6Cl3, Co(OAc)2, etc. Furthermore, sodium phosphate or sodium borate can be added and supported as CoPi or CoBi. It should be noted that the co-catalyst for oxygen generation is not limited to CoOx, and in the first aspect of the present invention, metals such as Cr, Sb, Nb, Th, Mn, Fe, Co, Ni, Ru, Rh, and Ir, their oxides, sulfides, or composite oxides (excluding CoOx) can also be supported as the co-catalyst for oxygen generation, and among these, these oxides are preferred because they are stable against oxidation. When supporting these, for example, salts containing these elements can be used as the co-catalyst source.

[0032] A hydrogen generation co-catalyst, different from the co-catalyst derived from the above-mentioned co-catalyst source, can also be supported on the optical semiconductor. For example, when Pt is supported on the optical semiconductor as a hydrogen generation co-catalyst, either pure Pt or a compound containing Pt can be used as the co-catalyst source. Examples of compounds containing Pt include salts containing Pt, such as H2PtCl6. It should be noted that the hydrogen generation co-catalyst is not limited to Pt, and in the first aspect of the present invention, Pd, Rh, Ru, Ni, Au, Fe, Ru-Ir, Pt-Ir, NiO, RuO2, IrO2, Rh2O3, Cr-Rh composite oxides, and sulfides obtained by adding sulfur or thiourea to these metals can also be supported as hydrogen generation co-catalysts, and among these, metals or oxidizable noble metal oxides are preferred because they have reducing ability. When supporting these, for example, salts containing these elements can be used as the co-catalyst source.

[0033] There are no particular restrictions on the method for manufacturing the photosemiconductor on which the co-catalyst is supported. There are also no particular restrictions on the method for manufacturing the co-catalyst-supported photocatalyst to be regenerated in the photocatalyst regeneration method of the present invention. For example, as described in Patent Documents 1 to 3, a method of mixing the photosemiconductor with the co-catalyst or co-catalyst source and heating it can be employed.

[0034] [Photocatalytic Module] The form of the photocatalytic module in which the above-mentioned co-catalyst-supported photocatalyst is arranged is not particularly limited, and it is sufficient if it has a module body having a water channel or storage section and a light-transmitting section provided in at least a part of the module body.

[0035] In one aspect of the present invention, water is flowed or stored in a channel or storage section to achieve an appropriate water depth. The water depth is preferably 0.01 to 100 mm, particularly 0.1 to 10 mm. A photocatalyst is placed in this channel or storage section, and light is irradiated through a light-transmitting section.

[0036] In another aspect of the present invention, water is present in the module such that the flow path or storage section is almost completely filled. In this case, the module may be a transparent tube. The photocatalyst may be placed on half of the inner surface of the tube, or on the axial portion.

[0037] The form in which the photocatalyst is present within the photocatalyst module is not particularly limited. For example, the photocatalyst can be attached to the inner surface of the module by methods such as spray coating, dip coating, screen printing, bar coating, or various pouring methods like those used for coating fluorescent lamps, where a coating slurry is applied while flowing onto the substrate surface. Alternatively, a substrate such as a sheet or plate with the photocatalyst attached can be placed inside the module, or a pre-molded substrate can be fitted with the photocatalyst and then installed.

[0038] [Method for regenerating photocatalysts] In one embodiment of a method for increasing the activity of a photocatalyst in a module whose photocatalytic activity has decreased, a co-catalyst precursor solution is supplied to a channel or storage section containing the photocatalyst, and the photocatalyst is irradiated with light to deposit the co-catalyst on the surface of the photocatalyst (hereinafter sometimes referred to as photoelectrodeposition).

[0039] As mentioned above, Pd, Rh, Ru, Ni, Au, Fe, Ru-Ir, Pt-Ir, NiO, RuO2, IrO2, Rh2O3, Cr-Rh composite oxides, core-shell type CrOx / Rh, etc. are used as co-catalysts for hydrogen production, and so co-catalyst precursors that produce these are used. Preferably, the co-catalyst precursor is a water-soluble salt of these metals, and among these, compounds that can reductively precipitate metals or oxides (e.g., Na3RhCl6, H2PtCl6, etc.) are preferred.

[0040] Since oxides or composite oxides of Cr, Sb, Nb, Th, Mn, Fe, Co, Ni, Ru, Rh, and Ir are used as co-catalysts for oxygen evolution, substances that produce these are used as co-catalyst precursors. Preferably, the co-catalyst precursor is a water-soluble salt of these metals, and a compound that can oxidatively precipitate oxides (for example, Co(NO3)2) is preferably used.

[0041] Water is preferably used as the solvent for the co-catalyst precursor solution, but a small amount (10 wt% or less) of a sacrificial reagent such as methanol may be added to enable efficient photoelectrodeposition.

[0042] The composition of the co-catalyst precursor aqueous solution is selected according to the composition of the desired co-catalyst. For example, when regenerating a photocatalyst supported with core-shell type CrOx / Rh as a co-catalyst for hydrogen production, a sequential process is performed in which an aqueous solution of Na3RhCl6, which is the Rh source, is supplied and photoelectrodeposition is carried out, followed by the supply of an aqueous solution of K2CrO4, which is the CrOx source, and photoelectrodeposition is carried out, or a mixed aqueous solution of Na3RhCl6 and K2CrO4 is supplied and photoelectrodeposition is carried out.

[0043] The supply amounts of the co-catalyst precursors Na3RhCl6 and K2CrO4 are adjusted according to the type of photocatalyst, the light source used, and the amount of Rh and CrOx present on the photocatalyst surface before treatment. This is because the photodeposition efficiency of the co-catalyst precursors differs depending on the type of photocatalyst and light source. If the amount of co-catalyst precursors is too high, the co-catalyst will excessively coat the photocatalyst surface, inhibiting the photocatalyst's light absorption and potentially reducing water splitting efficiency or wasting the co-catalyst precursors without photodeposition. Conversely, if the amount is too low, a sufficient amount of co-catalyst will not be supported, resulting in reduced water splitting efficiency.

[0044] The amount of Rh and CrOx present on the photocatalyst surface before regeneration can be quantified by ICP analysis, SEM-EDS analysis, etc.

[0045] The concentration of the co-catalyst precursor solution is preferably around 0.01 to 0.5 wt%, but is not limited to this.

[0046] There are no restrictions on the light source used in the photoelectrodeposition operation; for example, sunlight, simulated sunlight, LEDs, xenon lamps, and metal halide lamps can be used. However, sunlight is preferred from the viewpoint of applying it to a large number of modules (panels) already installed over a large area outdoors. Alternatively, LEDs are preferred from the viewpoint of selecting the energy efficiency of the irradiation lamp, the energy density of the irradiated light, and the wavelength of light.

[0047] In the photocatalyst regeneration method described above, the photocatalyst is regenerated while remaining within the module. In other words, the photocatalyst within the photocatalyst module is regenerated. To put it another way, the photocatalyst module containing the photocatalyst is regenerated.

[0048] However, in this invention, the photocatalyst may be removed from the photocatalyst module, regenerated in a reaction vessel using the above-mentioned co-catalyst precursor solution, and the regenerated photocatalyst may be incorporated into the module.

[0049] [Method for manufacturing a photocatalyst with a supporting co-catalyst] By supporting a co-catalyst on the surface of the optical semiconductor within the module in accordance with the regeneration method described above, a photocatalyst-supported co-catalyst can be manufactured. [Examples]

[0050] In the following test examples, examples, and comparative examples, a co-catalyst-supported photocatalyst (co-catalyst-supported RhCrOx / SrTiO3:Al) manufactured as described below was used.

[0051] [Method for manufacturing photocatalysts supported by auxiliary catalysts] <Preparation of photocatalyst SrTiO3:Al> 33g of strontium titanate SrTiO3 (High Purity Chemical Laboratory) and 0.28g of aluminum oxide Al2O3 (Sigma Aldrich) were mixed and thoroughly combined with 2.7g of separately pulverized strontium chloride SrCl214 (Kanto Chemical, 98.0%). This mixture was placed in an alumina crucible B5 (SSA-S, 280mL), covered, and calcined in an electric furnace at 1250°C for 48 hours. After cooling to room temperature, the sample was washed with water to obtain the photocatalyst aluminum-doped strontium titanate SrTiO3:Al.

[0052] <Preparation of the co-catalyst-supported photocatalyst RhCrCoOx / SrTiO3:Al> 327 mg of co-catalyst source (Na3RhCl6·nH2O (powder) Assay(Rh) 15.3%; manufactured by Mitsuwa Chemical Co., Ltd.), 5 mL of Cr(NO3)3 aqueous solution (0.192 mol / L; prepared using chromium(III) nitrate nonahydrate, purity: 98.0-103.0%, manufactured by Kanto Chemical Co., Ltd.), and 5 mL of Co(NO3)2 aqueous solution (0.170 mol / L; prepared using cobalt(II) nitrate hexahydrate, purity: 98.0%, manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) were added to a separable sample flask. Then 120 mL of ultrapure water was added, and the mixture was stirred until the co-catalyst source was homogenized in the flask. 50 g of SrTiO3:Al was added, and sonication was performed for 5 minutes while stirring with a Teflon rod.

[0053] The solvent was removed using a suspension evaporator and evaporated to dryness, after which the sample was dried at 60°C. The dried sample was lightly ground in an agate mortar, spread on a magnetic dish, and calcined at 275°C for 1 hour to obtain RhCrOx / SrTiO3:Al supported by a co-catalyst.

[0054] <Preparation of photocatalytic sheets> A transparent glass sheet (G-leaf, 250mm x 250mm x 0.1mm (t), manufactured by Nippon Electric Glass) was subjected to UV ozone treatment for 10 minutes. Then, a photocatalyst supported by a co-catalyst, RhCrCoOx / SrTiO3:Al, a chain-like silica colloid (Nissan Chemical Snowtex ST-OUP), and calcium chloride were mixed in pure water in a weight ratio of 4.0:1.0:0.046. This suspension was applied to a glass sheet, which was heated to 70°C, using a hand airbrush or an XY controlled coating device. The coated sample was then held at 90°C for 4 hours in an environment with 50% humidity.

[0055] [Photocatalytic panel for water splitting testing] The photocatalytic sheet manufactured as described above was incorporated into the test photocatalytic panel 1 shown in Figure 1.

[0056] The photocatalytic panel 1 comprises a rectangular base panel 2 installed at an inclination angle of 30° with respect to the horizontal plane, a rectangular photocatalytic sheet 3 provided on the base panel 2, a spacer 4 arranged to surround the entire circumference of the photocatalytic sheet 3, and a transparent glass plate 5. The transparent glass plate 5 is parallel to the base panel 2 and the photocatalytic sheet 3, and a water-permeable space S is formed between the transparent glass plate 5 and the photocatalytic sheet 3. The dimensions of the test apparatus are as follows.

[0057] Base panel 2: 295 x 295 mm square Photocatalytic sheet 3: 250 x 250 mm square Thickness of space S (distance between transparent glass plate 5 and photocatalytic sheet 3): 0.1 mm

[0058] Although not shown in the diagram, a water inlet is provided on the lower side of the base panel 2, and a gas outlet is provided on the upper side.

[0059] [Test Example 1] 1600 photocatalytic panels 1, as shown in Figure 1, were installed outdoors at a 30-degree angle, facing south, to receive sunlight. The amount of gas produced by supplying water (ion-exchanged water) was measured using a soap film flow meter, and this test was continued for approximately 7 months. As a result of this test, the hydrogen production rate, which indicates the water-splitting activity of the photocatalyst, was 5000 mL / min at the time of installation, but decreased to about 1000 mL / min after 7 months.

[0060] [Test Examples 2, 3] (Evaluation of water splitting activity of photocatalysts under LED irradiation) Water (ion-exchanged water) was injected into a new photocatalytic panel (Test Example 2) and a photocatalytic panel whose activity had decreased in the solar water splitting test in Test Example 1 (Test Example 3), and an LED (λ365nm, 20mW / cm²) was used to perform the test. 2 The hydrogen production rate, which indicates water splitting activity, was measured using a soap film flow meter after irradiating the film with light.

[0061] The hydrogen production rate, which indicates water splitting activity, was 12 mL / min for the photocatalyst (new photocatalyst) in the photocatalyst panel of Test Example 2, while the hydrogen production rate for the photocatalyst (photocatalyst with reduced activity) in the photocatalyst panel of Test Example 3 was 3.5–4.0 mL / min.

[0062] [Example 1 (Photocatalyst regeneration test)] In Test Example 1, after 7 months (after activity reduction), a regeneration solution consisting of an aqueous solution containing Na3RhCl6 at a concentration of 0.2 wt% of Rh relative to the amount of catalyst, and K2CrO4 (48.2 μmol / L) at a concentration of 0.1 wt% of Cr relative to the amount of catalyst, was injected into space S of photocatalytic panel 1. Subsequently, the activity was evaluated using the procedure for evaluating water splitting activity under LED irradiation as described above.

[0063] Approximately 3 hours after the start of light irradiation, the hydrogen production rate increased to 4.5–5.0 mL / min, and then increased to 6.0–6.5 mL / min after approximately 18 hours of irradiation. This result suggests that a CrOx / Rh core-shell type hydrogen production co-catalyst was photoelectrodeposited onto the photocatalyst surface, and the photocatalytic activity was restored.

[0064] [Comparative Example 1] In Example 1, the test was conducted under identical conditions except that only K2CrO4 at a concentration of 0.1 wt% Cr relative to the catalyst amount was injected. The hydrogen production rate after the start of light irradiation remained unchanged from 3.5 to 4.0 mL / min. This result suggests that both CrOx and Rh are necessary for the regeneration of the hydrogen production catalyst, and that the photocatalyst is not regenerated with CrOx alone (CrOx alone does not function as a co-catalyst).

[0065] [Comparative Example 2] In Example 1, the test was conducted under identical conditions except that only an aqueous Na3RhCl6 solution with a concentration of 0.2 wt% Rh relative to the amount of catalyst was injected. The hydrogen production rate after the start of light irradiation decreased from 3.5-4.0 mL / min to about 1 / 3 of that. This result suggests that both CrOx and Rh are necessary for the regeneration of the hydrogen production catalyst, and that with only Rh without CrOx, the reverse reaction proceeds, where the generated H2 reacts with O2 to form H2O.

[0066] The results of the above examples and comparative examples are summarized in Table 1.

[0067] [Table 1]

[0068] As shown in Table 1, even co-catalysts with a special shape, such as the core-shell type, which are not simply systems with only one type of co-catalyst, can be regenerated using the regeneration method of the present invention. Specifically, when a mixed aqueous solution of Na3RhCl6 + K2CrO4 capable of photoelectrodeposition of the core-shell type CrOx / Rh, a highly active co-catalyst for hydrogen production, was supplied, the hydrogen production rate after the decrease in activity recovered to about twice its original level. On the other hand, when an aqueous solution of K2CrO4 alone, in which only CrOx or only Rh is photoelectrodeposited, or an aqueous solution of Na3RhCl6 alone was supplied, no recovery of the hydrogen production rate was observed with CrOx alone. Furthermore, when an aqueous solution of Na3RhCl6 alone was supplied, the reverse reaction between the generated hydrogen and oxygen was promoted, and the hydrogen production rate actually decreased. From this, it is clear that the co-catalyst of a photocatalyst can be regenerated and its photocatalytic activity restored by irradiating light while in contact with an aqueous solution containing a metal-containing compound, which is a co-catalyst precursor corresponding to the composition of the target photocatalyst co-catalyst, and depositing the co-catalyst on the photocatalyst surface.

[0069] (Verification using sunlight) [Example 2 (Photocatalyst regeneration test)] In Test Example 1, after 7 months (after activity reduction), a regeneration solution consisting of an aqueous solution containing Na3RhCl6 at a concentration of 0.2 wt% Rh relative to the amount of catalyst, and K2CrO4 (48.2 μmol / L) at a concentration of 0.1 wt% Cr relative to the amount of catalyst, was injected into space S of photocatalytic panel 1. Subsequently, operation under sunlight was carried out for 5 days.

[0070] After 5 days of operation under sunlight, the hydrogen production rate increased to 1500 mL / min. This result suggests that the CrOx / Rh core-shell type hydrogen production co-catalyst was photoelectrodeposited onto the photocatalyst surface, restoring the photocatalytic activity.

[0071] The amount of cocatalysts in the photocatalyst was quantitatively analyzed by ICP-MS (Agilent 8900) before use in Test Example 1 (before activity decline), after 7 months in Test Example 1 (after activity decline), and after the photocatalytic activity was restored. The photocatalyst was sampled and analyzed from two locations after activity decline and regeneration. The results are shown in Table 2.

[0072] [Table 2]

[0073] As shown in Table 2, the regeneration method of the present invention makes it possible to regenerate photocatalytic activity even under sunlight, not just LED light. Furthermore, ICP-MS analysis of the amount of co-catalysts clearly shows that this recovery of photocatalytic activity is due to the recovery of the amount of co-catalysts. This clearly shows that it is not necessary to prepare an LED light source to regenerate the panel, and that the photocatalytic co-catalysts can be regenerated and photocatalytic activity restored simply by supplying a regeneration co-catalyst precursor solution while the panel remains installed outdoors.

[0074] Thus, this method allows for the restoration of water splitting activity without replacing the photocatalytic panel, using a simple technique of supplying a co-catalyst precursor aqueous solution to the panel and irradiating it with light. Furthermore, the water splitting module containing the photocatalyst can be regenerated without removing it from the main unit of the device. [Explanation of symbols]

[0075] 1. Photocatalytic panel 2 Base Panels 3. Photocatalytic sheet 4 Spacers 5. Transparent glass plate

Claims

1. A photocatalyst supported with a co-catalyst, a method for regenerating a photocatalyst whose activity has decreased, A method for regenerating a photocatalyst, comprising irradiating the surface of a photocatalyst whose activity has decreased with light while a liquid containing a metal-containing compound, which is a precursor of a co-catalyst, is in contact with the photocatalyst surface, thereby depositing a co-catalyst on the surface of the photocatalyst.

2. The method for regenerating a photocatalyst according to claim 1, wherein the light irradiated is sunlight or LED light.

3. The method for regenerating a photocatalyst according to claim 1 or 2, wherein the photocatalyst is installed within a photocatalyst module.

4. A method for manufacturing a photocatalytic module in which a photocatalyst is installed inside, The process involves placing a photocatalyst without a supporting co-catalyst within a photocatalyst module, and then irradiating the photocatalyst with light while a liquid containing a metal-containing compound, which is a precursor of the co-catalyst, is in contact with the photocatalyst, thereby depositing the co-catalyst on the surface of the photocatalyst. A method for manufacturing a photocatalytic module, wherein the photocatalytic module is a water splitting module that decomposes water with a photocatalyst to generate hydrogen and / or oxygen.

5. A method for manufacturing a photocatalytic module according to claim 4, wherein the light irradiated is sunlight or LED light.

6. A method for operating a photocatalytic module having a co-catalyst-supported water splitting catalyst that splits water by light, and generating hydrogen and / or oxygen by supplying water to the water splitting catalyst, A method for operating a photocatalytic module, wherein when the activity of the water splitting catalyst decreases, a liquid of a metal-containing compound, which is a precursor of a co-catalyst, is placed inside the module, and the co-catalyst is deposited on the water splitting catalyst by light irradiation.

7. The method for operating a photocatalytic module according to claim 6, wherein the photocatalytic module performs the total decomposition of water.

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