Patent Application
20250025865
The present invention relates to a cocatalyst for hydrogen generation, a photocatalyst, a method for producing hydrogen, a hydrogen production apparatus, and a semiconductor material.
In recent years, development and utilization of an energy that does not depend on fossil resources such as petroleum have been demanded, and hydrogen (H2) has been attracting attention as a carrier of the energy. However, most of the hydrogen currently used is produced by reforming natural gas, and carbon dioxide emission accompanying the production is regarded as a problem. On the other hand, as a clean hydrogen production method without discharging carbon dioxide, there is known water decomposition using a semiconductor material that is excited by light as a photocatalyst. Patent Document 1 discloses a semiconductor material that can be used as the photocatalyst.
Patent Document 1 describes that the photocatalyst may include a cocatalyst and that a metal such as Pt or a metal oxide such as NiOx can be used as a cocatalyst for a hydrogen generation reaction (cocatalyst for hydrogen generation). With the cocatalyst, it is expected to improve hydrogen generation efficiency by photodecomposition due to suppression of recombination of excited carriers generated in a semiconductor material by light irradiation, promotion of a surface reaction, and the like. However, according to the studies by the present inventors, these cocatalysts in the related art are still insufficient for further improvement of the hydrogen generation efficiency.
The present invention is directed to providing a novel cocatalyst for hydrogen generation suitable for further improving the generation efficiency of hydrogen by a photocatalyst.
The present invention provides
In the formula (1), M is at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir,
When viewed from another aspect, the present invention provides
When viewed from another aspect, the present invention provides
When viewed from another aspect, the present invention provides
When viewed from another aspect, the present invention provides
In the formula (1), M is at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir,
According to the present invention, it is possible to provide a novel cocatalyst for hydrogen generation suitable for further improving the efficiency of hydrogen generation by a photocatalyst.
Hereinafter, an embodiment of the present invention will be described. The present invention is not limited to the embodiment described below.
A cocatalyst for hydrogen generation of the present embodiment includes a metal-organic framework (A) having a molecular structure represented by the following formula (1).
In the formula (1), M is at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir,
Typically, the molecular structure of the formula (1) is a kind of complex structure in which M is a metal nucleus and each of a structure including a first aromatic group, L1, and L2 and a structure including a second aromatic group, L3, L4 is a ligand (organic ligand). In a typical example, the molecular structure of the formula (1) has a planar four-coordinate structure.
M in the formula (1) may be any one of Ni, Co, Fe, Cu, Zn, Pd, Pt. Au, and Ir, or may be a combination of two or more of these metals. M may be, for example, at least one selected from Ni, Co, and Cu. M may be one that is Ni or one that is Co, or may be two that is a combination of Ni and Cu or two that is a combination of Co and Cu.
L1 to L4 are each independently at least one selected from S, Se, Te, NH, and O. L1 to L4 each independently may be at least one selected from S, Se, Te, and O, may be at least one selected from S, Se, and Te, may be at least one selected from S and Se, may be at least one selected from S and O, may be S, or may be O. All of L1 to L4 may be the same.
In the present specification, the term “aromatic group” means a group derived from an aromatic compound. The aromatic compound includes not only monocyclic compounds but also bicyclic, tricyclic, and polycyclic compounds. Two or more rings may form a condensed ring. The aromatic compound includes not only an aromatic hydrocarbon compound but also a heteroaromatic compound. Examples of the heteroatom of the heteroaromatic compound include N, O, and S. The aromatic compound may be a complex of a cyclic compound having aromaticity and a metal nucleus. Examples of the aromatic compound include benzene, triphenylene, hexaazatriphenylene, tricycloquinoazoline, porphyrin, benzoporphyrin, tetraazaporphyrin, phthalocyanine, subporphyrin, and subphthalocyanine. Examples of the cyclic compound that can form a complex with the metal nucleus include porphyrin, benzoporphyrin, tetraazaporphyrin, phthalocyanine, subporphyrin, and subphthalocyanine. Subporphyrin and subphthalocyanine include benzosubporphyrin and benzosubphthalocyanine, respectively.
At least one selected from the first aromatic group and the second aromatic group may be a group represented by the following formula (2a) or (2b). The group represented by the formula (2a) is a 6-valent group derived from benzene. The group represented by the formula (2b) is a 6-valent group derived from triphenylene.
The first aromatic group and the second aromatic group may be the same or different from each other.
At least one selected from a first ligand having a structure including the first aromatic group, L1, and L2 and a second ligand having a structure including the second aromatic group, L3, and L4 may be a C6L6 ligand represented by the following formula (3a). L11 to L16 in the formula (3a) are each independently an element that can be taken by L1 to L4 in the formula (1).
At least one selected from the first ligand having a structure including the first aromatic group, L1, and L2, and the second ligand having a structure including the second aromatic group, L3, and L4 may be a triphenylene-derived ligand represented by the following formula (3b). L21 to L26 in the formula (3b) are each independently an element that can be taken by L1 to L4 in the formula (1).
The first ligand and the second ligand may be the same or different from each other.
In a case where M and L in the formula (1) are Ni and S, respectively, and the first aromatic group and the second aromatic group are groups represented by the formula (2a), the molecular structure of the formula (1) is a bis(dithiolate) nickel structure. In a case where M and L in the formula (1) are Co and S, respectively, and the first aromatic group and the second aromatic group are groups represented by the formula (2a), the molecular structure of the formula (1) is bis(dithiolate) cobalt structure. In the present specification, a metal-organic framework (A) having one or two or more bis(dithiolate) nickel structures and a metal-organic framework (A) having one or two or more bis(dithiolate) cobalt structures are referred to as NiDT and CoDT, respectively.
The metal-organic framework (A) may include two or more molecular structures represented by the formula (1), or may be a polymer having the molecular structure described above. The metal-organic framework (A) that is a polymer body is particularly suitable for further improving the efficiency of hydrogen generation by a photocatalyst. The polymer body may have a structure in which two or more metal atoms (M in the formula (1)) are linked to each other by the first ligand and/or the second ligand.
The polymer body may have a one-dimensional structure in which the molecular structures of the formula (1) are linearly bonded, or may have a two-dimensional structure in which the molecular structures of the formula (1) are planarly bonded. The two-dimensional structure may be a planar structure. An example of the two-dimensional planar structure is shown in the following formula (4). In other words, the cocatalyst for hydrogen generation of the present embodiment may have a molecular structure represented by the following formula (4). The molecular structure of the formula (4) includes a metal atom M and a C6L6 ligand and has a six-fold symmetric structure. The molecular structure of the formula (4) has a graphene-like two-dimensional conjugated planar structure, and thus has particularly excellent conductivity and is chemically stable. These points can contribute to further improvement of the efficiency of hydrogen generation by a photocatalyst. In addition, the excellent conductivity is advantageous for construction of Z-Scheme (two-stage excitation energy acquisition mechanism) described below. As the conductivity, for example, an electrical conductivity of 1.0×102 S/cm or higher, and further 1.6×102 S/cm or higher can be achieved.
M in the formula (4) is the same as M in the formula (1), that is, at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir. In the formula (4), M may be, for example, one that is Ni or one that is Co, or may be two that is a combination of Ni and Cu or two that is a combination of Co and Cu. L11 to L16, L21 to L26, L31 to L36, L41 to L46, L51 to L56, and L61 to L66 are each independently an element that can be taken by L1 to L4 described above.
An example of the molecular structure of the formula (4) is shown in the following formula (4a). In the formula (4a), M is Ni, and all of L11 to L16, L21 to L26, L31 to L36, L41 to L46, L51 to L56, and L61 to L66 are S. The molecular structure of the formula (4a) includes Ni and a benzenehexathiol (C6S6) ligand. The metal-organic framework (A) having the molecular structure of the formula (4a) is a kind of NiDT. The C6S6 ligand can particularly contribute to further improvement of the efficiency of hydrogen generation by a photocatalyst.
Another example of the two-dimensional planar structure is shown in the following formula (4b). In other words, the cocatalyst for hydrogen generation of the present embodiment may have a molecular structure represented by the following formula (4b). The molecular structure of the formula (4b) includes a metal atom M and a C6L6 ligand and has a six-fold symmetric structure. The molecular structure of the formula (4b) has a graphene-like two-dimensional conjugated planar structure.
M in the formula (6) is the same as M in the formula (1), that is, at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir. L101 to L106, L111 to L116, L121 to L126, L 131 to L 136, L 141 to L146, L 151 to L156, and L161 to L166 are each independently an element that can be taken by L1 to L4 described above.
The cocatalyst for hydrogen generation of the present embodiment may have a molecular structure represented by the following formula (5). The molecular structure of the formula (5) includes a metal atom M and a ligand derived from triphenylene and has a six-fold symmetric structure. The molecular structure of the formula (5) has a graphene-like two-dimensional conjugated plane structure, and thus has particularly excellent conductivity and is chemically stable. These points can contribute to further improvement of the efficiency of hydrogen generation by a photocatalyst. In addition, the excellent conductivity is advantageous for construction of Z-Scheme (two-stage excitation energy acquisition mechanism) described below. As the conductivity, for example, an electrical conductivity of 1.0×102 S/cm or higher, and further 1.6×102 S/cm or higher can be achieved.
M in the formula (5) is the same as M in the formula (1), that is, at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir. In the formula (5), M may be, for example, one that is Ni or one that is Co, or may be two that is a combination of Ni and Cu or two that is a combination of Co and Cu. L211 to L214, L221 to L224, L231 to L234, L241 to L244, L251 to L254, and L261 to L264 are each independently an element that can be taken by L1 to L4 described above.
An example of the molecular structure of formula (5) is shown in the following formula (5a). In the formula (5a), M is two that is a combination of Co and Cu, and all of L211 to L214, L221 to L224, L231 to L234, L241 to L244, L251 to L254, and L261 to L264 are O. The molecular structure of the formula (5a) includes two that is a combination of Co and Cu and a ligand derived from oxytriphenylene. The ligand derived from oxytriphenylene can particularly contribute to further improvement of the efficiency of hydrogen generation by a photocatalyst.
In the present specification, the metal-organic framework (A) having a catecholate structure of the formula (5a) is referred to as CuCo-CAT.
Each of the molecular structures of the formulae (4), (4a), (4b), (5), and (5a) can be a minimum unit constituting the metal-organic framework (A). The molecular structure may further extend by bonding the above-described units to each other at wavy line portions of the formulae (4), (4a), (4b), (5), and (5a). The molecular structure may extend in a planar manner or may form a nanosheet. In other words, the cocatalyst for hydrogen generation of the present embodiment may be a nanosheet including the metal-organic framework (A) (which is not limited to the molecular structures represented by the formulae (4), (4a), (4b), (5), and (5a)), or a laminate including nanosheets laminated. The laminate may be sheet-shaped or particle-shaped. One nanosheet layer has a thickness of usually about 0.3 to 2.0 nm and may have a thickness of 0.5 to 1.0 nm. The laminate including nanosheets laminated has a size (a thickness in a case of the sheet shape, a primary particle size in a case of the particle shape) of, for example, 0.3 to 2000 nm, and may have a size of 50 to 200 nm. For the nanosheet and the sheet-shaped laminate, the size in an in-plane direction is not limited, but may be, for example, 1 nm or more and 10 μm or less, 50 nm or more and 5 μm or less, 100 nm or more and 2 μm or less, 200 nm or more and 1 μm or less, or 500 nm or more and 800 nm or less, in terms of the maximum length, in consideration of the efficiency as a cocatalyst. The sizes of the nanosheet and the laminate can be evaluated by, for example, image analysis of an observation image of the cocatalyst for hydrogen generation by SEM. The size is an average value of values measured for at least 50 cocatalyst for hydrogen generations. The primary particle size of a particle can be determined as a diameter of a circle having an area equal to the area of a particle to be measured on the observation image.
The cocatalyst for hydrogen generation of the present embodiment can be used for generation of hydrogen by being combined with a semiconductor catalyst that is excited by light. Generation of hydrogen is typically carried out by decomposition of water.
Light that excites the semiconductor catalyst is, for example, light including at least one selected from ultraviolet light, visible light, and near-infrared light. The light that excites the semiconductor catalyst may have a wavelength in a range of 300 nm or longer to 1200 nm or shorter.
In a typical example of the semiconductor catalyst with which the cocatalyst for hydrogen generation of the present embodiment is combined, an energy at the lower end of the conduction band in the semiconductor catalyst is negatively larger than a reduction potential of water (hydrogen generation potential).
In an example of the semiconductor catalyst with which the cocatalyst for hydrogen generation of the present embodiment is combined, the energy at the lower end of the conduction band in the semiconductor catalyst is negatively larger than the reduction potential of water, and an energy at the upper end of the valence band is positively larger than an oxidation potential (oxygen generation potential) of water. This example is suitable for generating not only hydrogen but also oxygen by decomposition of water by irradiation with light.
An example of the semiconductor catalyst is at least one selected from the group consisting of SrTiO3, K2Ti6O13, TiO2, Nb2O5, KTaO3/KNbO3 solid solution, ZnO, ZrO2, GaP, GaN, Si, CdS, CdSe, C3N4, and metal-doped forms thereof. The energy at the lower end of the conduction band in each of the above examples is negatively larger than the reduction potential of water. For SrTiO3, KTiO3, TiO2, Nb2O5, KTaNbO, ZnO, ZrO2, CdS, CdSe, and C3N4, the energy at the upper end of the valence band is positively larger than the oxidation potential of water. The semiconductor catalyst may be at least one selected from SrTiO3, KTiO3, KTaNbO, ZrO2, GaP, CdS, CdSe, and C3N4, metal-doped forms thereof, or may be at least one selected from SrTiO3 and a metal-doped form thereof. Examples of the metal to be used for doping include Al, Ga, In, Rh, Ir, Cr, Sb, La, Na, and Ta. The semiconductor catalyst may be SrTiO3:Al obtained by doping SrTiO3 with Al.
The semiconductor catalyst may be a catalyst (including a visible light responsive type) disclosed in each of JP 2017-154959 A. JP 2020-138188 A, and JP 2020-142213 A. However, the semiconductor catalyst is not limited to the above examples.
The semiconductor catalyst may be particle-shaped. The primary particle size of the particle-shaped semiconductor catalyst may be, for example, 1 nm or more and 500 μm or less, 5 nm or more and 20 μm or less, or 10 nm or more and 10 μm or less. The primary particle size of the semiconductor catalyst can be evaluated by, for example, image analysis of an observation image of the semiconductor catalyst by SEM. The primary particle size is an average value of values measured for at least 50 semiconductor catalysts.
The cocatalyst for hydrogen generation of the present embodiment and the semiconductor catalyst can be combined by, for example, mixing them. In addition, the cocatalyst for hydrogen generation and the semiconductor catalyst can be complexed by synthesizing the cocatalyst for hydrogen generation in the presence of the semiconductor catalyst and attaching the generated cocatalyst for hydrogen generation to the surface of the semiconductor catalyst. The cocatalyst for hydrogen generation of the present embodiment may be further combined with a cocatalyst for oxygen generation in addition to the semiconductor catalyst. Examples of the cocatalyst for oxygen generation include metals such as Mg, Ti, Mn, Fe, Co, Ni, Cu, Ga, Ru, Rh, Pd, Ag, Cd, In, Ce, Ta, W, Ir, Pt, and Pb, and oxides and composite oxides thereof. Preferred examples of the cocatalyst for oxygen generation include Mn, Co, Ni, Ru. Rh, and Ir, and oxides and composite oxides thereof, and more preferred examples thereof include Ir, MnOx, CoOx, NiCoOx, RuOx, RhOx, and IrOx.
A photocatalyst in which the cocatalyst for hydrogen generation and the semiconductor catalyst are combined can be used for, for example, hydrogen production or water decomposition. The photocatalyst (first photocatalyst) and another photocatalyst (second photocatalyst) in which the cocatalyst for oxygen generation and the semiconductor catalyst are combined may be used to construct a Z-Scheme in which hydrogen is generated by the first photocatalyst and oxygen is generated by the second photocatalyst. The Z-Scheme is particularly suitable for effective utilization of low-energy light such as visible light and improvement of a degree of freedom in selection of a semiconductor catalyst and design of a photocatalyst.
The photocatalyst in which the cocatalyst for hydrogen generation, the cocatalyst for oxygen generation, and the semiconductor catalyst are combined can be used, for example, for production of hydrogen and oxygen or decomposition of water.
The method and mode of use of the photocatalyst containing the cocatalyst for hydrogen generation of the present embodiment are not limited to the above examples.
The cocatalyst for hydrogen generation of the present embodiment can be formed, for example, by a liquid-liquid interface synthesis method in which a complex forming reaction is allowed to proceed at an interface between a first solution containing a metal atom M (typically containing it as an ion) and a second solution containing an organic ligand and being incompatible with the first solution. In addition, depending on the type of the cocatalyst for hydrogen generation, the cocatalyst for hydrogen generation may be formed by a gas-liquid interface synthesis method in which a second solution containing an organic ligand is dropped onto the surface of a first solution containing a metal atom M (typically containing it as an ion), and a complex formation reaction is allowed to proceed on the surface of the first solution while evaporating a solvent of the second solution. The first solution and the second solution in the liquid-liquid interface synthesis method and the gas-liquid interface synthesis method are, for example, an aqueous solution and an organic solution, respectively. In the liquid-liquid interface synthesis method, a sheet in which nanosheets of the metal-organic framework (A) are laminated is usually obtained. In the gas-liquid interface synthesis method, it is also possible to obtain a single-layer nanosheet of the metal-organic framework (A).
The photocatalyst of the present embodiment includes a semiconductor catalyst that is excited by light and the cocatalyst for hydrogen generation of the present embodiment. Examples of the cocatalyst for hydrogen generation and the semiconductor catalyst, and examples of the method and mode of use of the photocatalyst, including preferred examples, are as described above.
An amount of the cocatalyst for hydrogen generation contained in the photocatalyst may be, for example, 1 part by weight or less, 0.5 parts by weight or less, 0.1 parts by weight or less, 0.01 parts by weight or less, or even 0.001 parts by weight or less, with respect to 100 parts by weight of the semiconductor catalyst. The lower limit of the amount of the cocatalyst for hydrogen generation is, for example, 0.00001 parts by weight or more with respect to 100 parts by weight of the semiconductor catalyst.
In the photocatalyst, the cocatalyst for hydrogen generation is usually in contact with the semiconductor catalyst. The cocatalyst for hydrogen generation and the semiconductor catalyst may be joined to each other. The cocatalyst for hydrogen generation may be supported on the semiconductor catalyst. For example, the photocatalyst may have a configuration in which a fine cocatalyst for hydrogen generation is supported on a particle-shaped semiconductor catalyst. The cocatalyst for hydrogen generation may be sheet-shaped (flake) or may be in a form of irregular colloidal particles.
In a case where the cocatalyst for oxygen generation is further contained, the cocatalyst for oxygen generation is typically in contact with the semiconductor catalyst. The cocatalyst for oxygen generation and the semiconductor catalyst may be joined to each other. The cocatalyst for oxygen generation and the semiconductor catalyst can be joined by a known method such as an impregnation method or a photo-electrodeposition method.
An amount of the cocatalyst for oxygen generation that can be contained in the photocatalyst is, for example, 0.001 to 1 part by weight, and may be 0.005 to 0.5 parts by weight, with respect to 100 parts by weight of the semiconductor catalyst.
The photocatalyst is, for example, particle-shaped. However, the shape of the photocatalyst is not limited to the above example.
The photocatalyst of the present embodiment can be formed, for example, by mixing the cocatalyst for hydrogen generation of the present embodiment and the semiconductor catalyst. The mixing may be performed in a solution, such as an aqueous solution. In an example of mixing in a solution, a particle-shaped photocatalyst is mixed with a solution in which a sheet-shaped and/or particle-shaped cocatalyst for hydrogen generation is dispersed, and then the solvent of the solution is removed to obtain a photocatalyst. The dispersed solution may be a nanocolloidal solution.
The photocatalyst of the present embodiment can be used, for example, for generating hydrogen by decomposition of water. However, the use of the photocatalyst is not limited to the above example. When viewed from an aspect in which the use is not limited, the present invention provides a semiconductor material including:
a semiconductor that is excited by light; and
In the formula (1), M is at least one selected from Ni, Co, Fe, Cu, Zn, Pd, Pt, Au, and Ir,
Hereinafter, application examples of the cocatalyst for hydrogen generation and the photocatalyst of the present embodiment will be described. However, the mode of application of the cocatalyst for hydrogen generation and the photocatalyst is not limited to the following examples.
For example, hydrogen can be produced using the cocatalyst for hydrogen generation of the present embodiment or the photocatalyst of the present embodiment. From this aspect, the present invention provides a method for producing hydrogen, the method including obtaining hydrogen using the cocatalyst for hydrogen generation of the present embodiment or the photocatalyst of the present embodiment. In addition, from the above aspect, the present invention discloses a hydrogen production apparatus including a reaction unit including the cocatalyst for hydrogen generation of the present embodiment or the photocatalyst of the present embodiment. An example of the method for producing hydrogen includes irradiating the photocatalyst of the present embodiment with ultraviolet light and/or visible light to decompose water to produce hydrogen.
For example, water can be decomposed using the cocatalyst for hydrogen generation of the present embodiment or the photocatalyst of the present embodiment. From this aspect, the present invention provides a method for decomposing water, the method including decomposing water using the cocatalyst for hydrogen generation of the present embodiment or the photocatalyst of the present embodiment. In addition, from the above aspect, the present invention discloses a hydrogen production apparatus (water decomposition apparatus) including a reaction unit including the cocatalyst for hydrogen generation of the present embodiment or the photocatalyst of the present embodiment. In the method for decomposing water and the hydrogen production apparatus, hydrogen alone or hydrogen and oxygen may be obtained.
Examples of a mode in which a photocatalyst is used in each of the above-described methods and apparatuses include a mode in which particles of a photocatalyst are dispersed in a solution containing water (the solution may be water), a mode in which a molded body obtained by solidifying particles of a photocatalyst is placed in a solution, and a mode in which a composite including a photocatalyst layer containing a photocatalyst (for example, a laminate of a photocatalyst layer and a substrate) is placed in a solution. The solution including water may include a sacrificial reducing agent. As the sacrificial reducing agent, for example, methanol can be used. An amount of the sacrificial reducing agent added is not particularly limited and is, for example, in a range of more than 0) vol. % and less than 100 vol. %. However, the mode of using the photocatalyst is not limited to the above example. The hydrogen production apparatus (water decomposition apparatus) may include a reaction unit accommodating a solution in which particles of a photocatalyst are dispersed, a solution in which a molded body including a photocatalyst is placed, or a solution in which a composite including a photocatalyst layer is placed. The reaction unit may be a container that can accommodate each of the above solutions and has an opening or a window through which the accommodated solution can be irradiated with light.
The molded body obtained by solidifying the particles of the photocatalyst can be formed by, for example, sintering the particles or binding the particles using a binding agent such as a resin binder. As the resin binder, a resin having an excellent binding property such as a fluororesin may be used. The photocatalyst layer containing a photocatalyst may be the above molded body. Examples of the substrate to be combined with the photocatalyst layer include metal substrates such as a stainless steel substrate and an aluminum substrate, and a glass substrate.
The photocatalyst layer and a conductive layer may be laminated to form an electrode. According to the electrode including the photocatalyst layer, generation of hydrogen and decomposition of water can be further promoted by applying a bias voltage in addition to irradiation with light. Examples of the conductive layer include a layer containing conductive particles such as carbon particles and metal particles, and a conductive sheet such as a carbon sheet and a metal sheet. The electrode can be formed by, for example, forming a coating film containing particles of the photocatalyst on the surface of the conductive layer and then drying and/or sintering the coating film. However, the generation of hydrogen and the decomposition of water by the photocatalyst of the present embodiment may be performed without applying a bias voltage, in other words, without forming an electrode.
The production apparatus may include a member other than the reaction unit. Examples of the other member include a collection unit such as a tank for collecting generated hydrogen and/or oxygen, a light source for irradiating the solution, and a water supply unit for supplying water to the reaction unit. Examples of the light source include a lamp capable of emitting light similar to sunlight, such as a xenon lamp and a metal halide lamp, a mercury lamp, and an LED. In a case of irradiation with sunlight, the production apparatus may include an optical member such as a window or a mirror that transmits sunlight and guides the sunlight to the reaction unit.
Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the specific modes described below.
In Example 1, NiDT having a two-dimensional conjugated planar structure represented by the formula (4) or (4b) was prepared as the cocatalyst for hydrogen generation, and the hydrogen-generating capability and the water-decomposing capability when combined with the semiconductor catalyst were evaluated.
Six mg of benzenehexathiol (BHT) was weighed in a petri dish having a diameter of 12 cm and dispersed in 150 mL of degassed dichloromethane to form a saturated solution. Degassed water was then gently dropped onto the dichloromethane layer to completely cover the surface of the dichloromethane layer with an aqueous layer. Next, 20 mL of an aqueous solution in which 20 mg of nickel acetate (Ni(OAc)2) was dissolved was slowly added dropwise to the aqueous layer to be mixed. When allowed to stand for 24 hours, a glossy sheet-shaped NiDT was generated at a liquid-liquid interface between the dichloromethane layer and the aqueous layer. Next, the dichloromethane layer and the aqueous layer were removed by rinsing four times with pure dichloromethane and water, respectively, and then the remaining NiDT was dispersed in ethanol. Next, the NiDT dispersed in ethanol was subjected to pulverization treatment (rotation speed: 2000 rpm, treatment time: 45 minutes) using a bead mill (available from Aimex Co., Ltd., Easy Nano RMB II, bead diameter: 0.2 mm) to obtain NiDT as a fine sheet. All the above operations were carried out in a nitrogen atmosphere glovebox.
With reference to Chem. Rev. 2020, 120, 8536, SrTiO3 synthesized by a solid phase method was doped with Al by a molten salt method to prepare SrTiO3:Al. Specifically, the preparation method is as follows. Dried SrCO3 powder (1.48 g. 0.01 mol) and dried TiO2 powder (0.799 g, 0.01 mol) were mixed for 15 minutes using an agate mortar. The mixed powder was placed in a crucible made of alumina and fired at 1373 K for 10 hours using an electric furnace to obtain powder of SrTiO3 as a precursor. Generation of SrTiO3 was confirmed by X-ray diffraction. Next, the obtained SrTiO3 powder, SrCl2·6H2O powder, and Al2O3 powder were mixed at a mixing ratio (molar ratio) of 1:10:0.02, and further mixed for 15 minutes using a mortar. The mixed powder was placed in a crucible made of alumina and fired at 1373 K for 10 hours using an electric furnace to obtain powder of SrTiO3:Al. The obtained powder was washed three times with Milli-Q water (400 mL) and then dried overnight in a vacuum dryer.
Support of CoOx Particles on SrTiO3:Al Powder
In accordance with J. Phys. Chem. B 2003, 107, 7965, an aqueous cobalt nitrate (Co(NO3)2) solution as a precursor solution (Co content: 0.5 wt. %) and NaIO3 (0.01 mol) as an oxidation sacrificial agent were used to support CoOx particles as the cocatalyst for oxygen generation on SrTiO3:Al powder by a photo-deposition method. The amount of CoOx supported was 0.5 wt. % as Co. A xenon lamp (power: 300 W, wavelength λ>300 nm) was used as the light source and the irradiation time was 2 hours. The powder after light irradiation was washed three times with each of Milli-Q water (400 mL) and ethanol (50 mL), and then dried overnight in a vacuum drier. Hereinafter, SrTiO3:Al on which CoOx is supported is referred to as CoOx/SrTiO3:Al.
Support of NiDT on SrTiO3:Al and CoOx/SrTiO3:Al
NiDT was supported on SrTiO3:Al and CoOx/SrTiO3:Al by an impregnation method. Specifically, the supporting method is as follows. SrTiO3:Al (or CoOx/SrTiO3:Al) was placed in an evaporating dish, and an ethanol dispersion of NiDT (NiDT content: 1 wt. %) was added thereto. Next, the mixed solution was evaporated to dryness in a hot water bath while being stirred using a glass rod to obtain powder of SrTiO3:Al (or CoOx/SrTiO3: Al) on which NiDT was supported. The amount of NiDT supported was 1 wt. % in each case. Hereinafter, a sample in which only NiDT is supported on SrTiO3:Al is referred to as NiDT/SrTiO3:Al, and a sample in which NiDT and CoOx are co-supported on SrTiO3:Al is referred to as NiDT/CoOx/SrTiO3:Al.
Shapes of SrTiO3:Al, NiDT, and NiDT/SrTiO3:Al, and a state of NiDT supported on SrTiO3:Al were confirmed by observation using SEM (available from Carl Zeiss-SII Nano Technology, NVision 40) and elemental mapping using energy dispersive X-ray spectroscopy (EDX). Observation images of SrTiO3:Al, NiDT, and NiDT/SrTiO3:Al by SEM are shown in
For each of unmodified SrTiO3:Al and NiDT/SrTiO3:Al, a hydrogen (H2) generating capability by a photocatalytic reaction was evaluated. Evaluation was conducted by accommodating each powder (0.05 g) to be evaluated, Milli-Q water (80 mL), and methanol (20 mL) in a side-irradiation type cell (capacity: 192 mL) made of Pyrex (borosilicate glass) and performing irradiation with light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W). That is, the side-irradiation type cell accommodating each powder, Milli-Q water and methanol was connected to a closed circulation system, and then light including ultraviolet light was applied from a side surface of the side-irradiation type cell while stirring and mixing each powder, Milli-Q water, and methanol using a magnetic stirring bar and a magnetic stirrer. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system.
As shown in
For each of unmodified SrTiO3:Al and NiDT/SrTiO3:Al, a hydrogen generation overvoltage was evaluated by electrochemical measurement. The evaluation was performed as follows.
To a glassy carbon (GC) electrode available from BAS, 24 μL of an ethanol dispersion (5 mg/mL) of unmodified SrTiO3:Al or NiDT/SrTiO3:Al was added dropwise, followed by drying overnight to prepare a working electrode. Next, linear sweep voltammetry (LSV) measurement was performed using a Pt wire as a counter electrode, a silver/silver chloride electrode as a reference electrode, and a phosphate buffer solution (pH=7) as an electrolytic solution. Note that before the measurement, argon gas was bubbled for 30 minutes to remove dissolved oxygen in the electrolytic solution. The LSV measurement results for unmodified SrTiO3:Al and NiDT/SrTiO3:Al are shown in
For each of unmodified SrTiO3:Al and NiDT/SrTiO3:Al, a water-decomposing capability by the photocatalytic reaction was evaluated. Evaluation was conducted by accommodating each powder (0.05 g) to be evaluated and Milli-Q water (100 mL) in a side-irradiation type cell made of Pyrex and performing irradiation with light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W) in the same manner as described above. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system.
Next, with 40 hours as one cycle, the light irradiation was performed for three cycles. Between the cycles, the light irradiation was temporarily stopped and gas inside the closed circulation system was released.
Next, to further examine stability of NiDT, for a case where unmodified SrTiO3:Al was used, and an aqueous solution of nickel nitrate (Ni(NO3)2) as a Ni species (Ni content: 0.25 wt. %) was further added to the reaction solution, the generation rates of hydrogen and oxygen by decomposition of water were evaluated as described above. As shown in
The generation rates of hydrogen and oxygen by decomposition of water were evaluated in the same manner as described above except that NiDT/CoOx/SrTiO3:Al was used as the photocatalyst. The evaluated generation rates are shown in
Changes over time in the amounts of hydrogen and oxygen generated by decomposition of water were measured in the same manner as described above except that NiDT/CoOx/SrTiO3:Al and Pt/CoOx/SrTiO3:Al(SrTiO3:Al powder on which Pt particles and CoOx particles were co-supported) were used as the photocatalyst. The measurement results are indicated in
To verify this, evaluation of the activity for the reverse reaction was conducted. Evaluation was conducted in a gas phase by accommodating, as the photocatalyst, NiDT/SrTiO3:Al and Pt/SrTiO3:Al(SrTiO3:Al powder on which Pt particles were supported) (both 0.02 g) in a reaction vessel made of Pyrex. Specifically, the reaction vessel accommodating the photocatalyst was connected to a closed circulation system, then hydrogen gas (pressure: 180 Torr) and air (pressure: 450 Torr) were introduced into the closed circulation system connected to the reaction vessel in such a manner that the volumetric ratio of hydrogen to oxygen was 2:1, and the change in atmospheric pressure in the circulation system was measured with time in the dark without light irradiation. The measurement results are indicated in
From Example 1, it was confirmed that NiDT was a cocatalyst for hydrogen generation also having reaction selectivity as a molecular catalyst.
In Example 2, CoDT having a two-dimensional conjugated planar structure represented by the formula (4) was prepared as the cocatalyst for hydrogen generation, and the hydrogen-generating capability and the water-decomposing capability when combined with the semiconductor catalyst were evaluated.
In a petri dish having a diameter of 12 cm, 2 mg of BHT was weighed and dispersed in 70 mL of degassed dichloromethane to give a saturated solution. Then, degassed water (about 40 mL) was gently dropped on the dichloromethane layer to completely cover the dichloromethane layer with an aqueous layer. Next, 2 mL of an aqueous solution in which 40 mg of cobalt chloride (CoCl2·6H2O) was dissolved was slowly added dropwise to the aqueous layer to be mixed. When the aqueous solution was added dropwise four times in total and then allowed to stand for 48 hours, a glossy sheet-shaped CoDT was generated at the liquid-liquid interface between the dichloromethane layer and the aqueous layer. The dichloromethane layer and the aqueous layer were then removed by rinsing four times with pure dichloromethane and water, respectively, and the remaining CoDT was then dispersed in ethanol. The CoDT collected by filtration was subjected to ultrasonic treatment for 30 minutes to obtain a fine sheet of CoDT. An observation image of the obtained CoDT by SEM is shown in
Support of CoDT on SrTiO3:Al) The support of CoDT on SrTiO3:Al was carried out by an impregnation method in the same manner as the support of NiDT on SrTiO3:Al in Example 1. Hereinafter, a sample in which CoDT is supported on SrTiO3:Al is referred to as CoDT/SrTiO3:Al.
For CoDT/SrTiO3:Al, the water-decomposing capability by the photocatalytic reaction was evaluated. Evaluation was conducted by accommodating powder (0.05 g) of the sample to be evaluated and Milli-Q water (100 mL) in a side-irradiation type cell made of Pyrex, and applying light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W) in the same manner as described above. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system.
In Example 3, nanocolloids of NiDT having the two-dimensional conjugated planar structure represented by the formula (4) or (4b) were prepared as the catalyst for hydrogen generation, and the hydrogen-generating capability and the water-decomposing capability were evaluated when the nanocolloids were combined with the semiconductor catalyst.
In an eggplant flask having a capacity of 100 mL, 4.1 mg (0.015 mmol) of BHT and 6.5 mg (0.045 mmol) of benzene-1,2-dithiol (bdt) were weighed and dispersed in 50 mL of degassed dichloromethane to give a saturated solution. Separately from the above, 11.2 mg (0.045 mmol) of (CH3COO)2Ni·4H2O was weighed in another eggplant flask having a capacity of 50 mL, and dissolved in 50 mL of a degassed ammonia-ethanol mixed solvent (concentration: 0.2 mol/L). Next, a (CH3COO)2Ni solution was slowly added dropwise to the saturated solution and then allowed to stand for 12 hours to obtain a black NiDT nanocolloid (NiDT-NCs) solution. All the above operations were carried out in a nitrogen atmosphere glovebox.
Support of NiDT-NCs on SrTiO3:Al and CoOx/SrTiO3:Al
The support of NiDT-NCs on SrTiO3:Al and CoOx/SrTiO3:Al was carried out by the impregnation method in the same manner as the support of NiDT on SrTiO3:Al and CoOx/SrTiO3:Al in Example 1 except that the prepared NiDT-NCs solution (NiDT-NCs content: 1 wt. %) was used instead of the ethanol dispersion of NiDT. Hereinafter, a sample in which only NiDT-NCs is supported on SrTiO3:Al is referred to as NiDT-NCs/SrTiO3:Al, and a sample in which NiDT-NCs and CoOx are co-supported on SrTiO3:Al is referred to as NiDT-NCs/CoOx/SrTiO3:Al.
For each of NiDT-NCs/SrTiO3:Al and NiDT-NCs/CoOx/SrTiO3:Al, the water-decomposing capability by the photocatalytic reaction was evaluated. Evaluation was conducted by accommodating powder of the sample to be evaluated (0.05 g) and Milli-Q water (100 mL) in an upward-irradiation type cell made of Pyrex and applying light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W). That is, the upward-irradiation type cell accommodating each powder, Milli-Q water and methanol was connected to a closed circulation system, and then light including ultraviolet light was applied from an upper surface of the upward-irradiation type cell while stirring each powder, Milli-Q water, and methanol using a magnetic stirring bar and a magnetic stirrer. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system.
In Example 4, the hydrogen-generating capability and the water-decomposing capability when the amount of NiDT-NCs added to the semiconductor catalyst was changed were evaluated.
Support of NiDT-NCs on CoOx/SrTiO3:Al
The support was carried out in the same manner by an impregnation method as the support of NiDT-NCs on CoOx/SrTiO3:Al in Example 3 except that the amount of the NiDT-NCs solution (NiDT-NCs content: 1 wt. %) added to CoOx/SrTiO3:Al was adjusted to 0.05 wt. %, 0.10 wt. %, 0.25 wt. %, and 0.50 wt. % in terms of the amount of NiDT-NCs in the NiDT-NCs solution relative to SrTiO3:Al.
For each of NiDT-NCs/CoOx/SrTiO3:Al, the water-decomposing capability by the photocatalytic reaction was evaluated. Evaluation was conducted by accommodating powder (0.05 g) of the sample to be evaluated and Milli-Q water (100 mL) in a side-irradiation type cell made of Pyrex, and applying light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W) in the same manner as described above. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system. An analysis time and an amount of gas generated were plotted to create a time-gas generation amount graph, and the gas generation rates of the gases (hydrogen and oxygen) were calculated from the obtained graph. The gas generation rates are shown in
In Example 5, CuCo-CAT having the two-dimensional conjugated planar structure represented by the formula (5) or (5a) was prepared as the catalyst for hydrogen generation, and the hydrogen-generating capability and the water-decomposing capability when combined with the semiconductor catalyst were evaluated.
Synthesis of CuCo-CAT was carried out in accordance with a previous report (Adv. Mater. 2021, 33, 2106781). 0.15 mmol of Cu(OAc)2:H2O, 0.15 mmol of Co(OAc)2·4H2O, and 0.15 mmol of hexahydroxytriphenylene were suspended in 5 mL of a mixed solvent of water/dimethylformamide (1/1=v/v), sealed in a sealed vessel made of borosilicate glass, and subjected to ultrasonic treatment for 10 minutes. The obtained suspension was heated at 85° C. for 24 hours. Then, CuCo-CAT obtained as a black-blue precipitate was separated by filtration, washed with dimethylformamide, acetone, and methanol, and vacuum-dried for 24 hours. CuCo-CAT was refined as follows. 50 mg of CuCo-CAT was dispersed in 30 mL of methanol together with 170 g of zirconia beads of 100 μmφ, and pulverization treatment was performed at 2500 rpm for 2 hours using a bead mill (available from Aimex Co., Ltd., Easy Nano RMB II). The obtained suspension was filtered through a qualitative filter paper (available from ADVANTEC Co., Ltd., 2A (retained particle size: 5 μm)) to recover a filtrate containing refined CuCo-CAT.
Support of CuCo-CAT on SrTiO3:Al and CoOx/SrTiO3:Al
The support of CuCo-CAT on SrTiO3:Al and CoOx/SrTiO3:Al was carried out by an impregnation method. Specifically, the supporting method is as follows. SrTiO3:Al (or CoOx/SrTiO3:Al) was placed in an evaporating dish, and a methanol dispersion of CuCo-CAT (content of CuCo-CAT: 0.5 wt. %) was added thereto. Next, the mixed solution was evaporated to dryness in a hot water bath while being stirred using a glass rod to obtain powder of SrTiO3:Al (or CoOx/SrTiO3:Al) on which CuCo-CAT was supported. The amount of CuCo-CAT supported was 0.5 wt. % in each case. Hereinafter, a sample in which only CuCo-CAT is supported on SrTiO3:Al is referred to as CuCo-CAT/SrTiO3:Al, and a sample in which CuCo-CAT and CoOx are co-supported on SrTiO3:Al is referred to as CuCo-CAT/CoOx/SrTiO3:Al. The support of CoOx on SrTiO3:Al was carried out in the same manner as in Example 1 except that the content of Co in the aqueous cobalt nitrate solution was changed to 0.1 wt. % and the amount of CoOx supported was 0.1 wt. % as Co.
For CuCo-CAT/SrTiO3:Al and CuCo-CAT/CoOx/SrTiO3:Al, the water-decomposing capability by the photocatalytic reaction was evaluated. Evaluation was conducted by accommodating powder (0.05 g) of the sample to be evaluated and Milli-Q water (100 mL) in a side-irradiation type cell made of Pyrex, and applying light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W) in the same manner as described above. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system.
In Example 6, CuNi-CAT having a two-dimensional conjugated planar structure represented by the formula (5) (obtained by substituting Co of CuCo-CAT represented by the formula (5a) with Ni) was prepared as the catalyst for hydrogen generation, and the hydrogen-generating capability and the water-decomposing capability when combined with the semiconductor catalyst were evaluated.
Direct synthesis of CuNi-CAT on the surface of SrTiO3:Al was carried out with reference to a previous report (Adv. Mater. 2021, 33, 2106781). 0.05 mmol of Cu(OAc)2·H2O, 0.05 mmol of Ni(OAc)2·4H2O, 0.05 mmol of hexahydroxytriphenylene, 150) mg of SrTiO3:Al, and 8 mL of a mixed solvent of water/dimethylformamide (1/1=v/v) were suspended in a 30 mL glass vial and subjected to ultrasonic treatment for 10 minutes. The obtained suspension was transferred to a Teflon (trade name) vessel for hydrothermal synthesis (capacity: 100 mL) and heated at 85° C. for 10 hours. Then, the suspension was centrifuged, and SrTiO3:Al modified with CuNi-CAT was separated by filtration, washed five times with Milli-Q water, and vacuum-dried for 24 hours. Hereinafter, this sample will be referred to as CuNi-CAT/SrTiO3:Al.
For CuNi-CAT/SrTiO3:Al, the water-decomposing capability by the photocatalytic reaction was evaluated. Evaluation was conducted by accommodating powder of the sample to be evaluated (0.03 g) and 1 M (100 mL) of an aqueous KOH solution in a side-irradiation type cell made of Pyrex and applying light including ultraviolet light (wavelength λ>300 nm) from a xenon lamp (power: 300 W) in the same manner as described above. Gas generated by the light irradiation was analyzed with time by a gas chromatograph connected to the closed circulation system.
The cocatalyst for hydrogen generation of the present invention can be used in, for example, a photoreaction apparatus such as a hydrogen production apparatus that produces hydrogen by irradiation with light and a water decomposition apparatus that decomposes water by irradiation with light.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-103593 | Jun 2021 | JP | national |
This application is the U.S. National Stage entry of International Application No. PCT/JP2022/024714, filed on Jun. 21, 2022, which, in turn, claims priority to Japanese Patent Application No. 2021-103593, filed on Jun. 22, 2021, both of which are hereby incorporated herein by reference in their entireties for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/024714 | 6/21/2022 | WO |
