Sheet material with metal-organic framework and method for manufacturing said sheet material

Abstract

Provided is a sheet material configured so that a metal-organic framework is not likely to become separated. This sheet material comprises: a metal-organic framework including metal ions and an organic ligand; and a paper substrate including a fiber material. The fiber material includes a chelate fiber that has a chelate functional group capable of chelate bonding with the metal ions.

Description

Sheet material provided with metal organic framework and method for manufacturing same

[0001] The present invention relates to a sheet material having a metal-organic framework and a method for manufacturing the same. This application claims priority to Japanese Patent Application No. 2024-049928, filed on March 26, 2024, the entire contents of which are incorporated herein by reference.

[0002] In recent years, active research has been conducted on metal organic frameworks (MOFs) as materials used for gas storage and separation, deodorization, air and water purification, and the like. Metal organic frameworks have a lattice structure consisting of metal ions and organic ligands, and have extremely large specific surface areas and pore volumes. Furthermore, metal organic frameworks allow for a wide variety of structural designs by varying the types of metal ions and organic ligands, as well as their synthesis conditions. For this reason, they are expected to be used in a wide range of fields (see Patent Documents 1 and 2).

[0003] For example, Patent Document 1 discloses an adsorbent sheet material containing a metal-organic framework (porous metal complex) and organic fibers. Patent Document 1 describes the production of an adsorbent sheet material by a wet papermaking method including the following steps: a step of dispersing a metal-organic framework, organic fibers, and an organic binder in a solvent to prepare a dispersion slurry; a step of making paper from the dispersion slurry using a papermaking machine to form a sheet-like product; and a step of dehydrating and drying the sheet-like product.

[0004] Japanese Patent Application Publication No. 2013-154302 Japanese Patent Application Publication No. 2016-052620

[0005] Metal-organic frameworks are usually very small and difficult to handle. Furthermore, if the metal-organic framework is not firmly fixed to a substrate (paper substrate) containing a fibrous material, the metal-organic framework is likely to fall off the paper substrate. For example, if the metal-organic framework peels off in places on the paper substrate, this can lead to significant unevenness in the loading of the metal-organic framework.

[0006] The present invention has been made in view of the above points, and a main object of the present invention is to provide a sheet material in which the metal-organic framework is less likely to fall off from the paper base material.

[0007] The present inventors considered enhancing the interaction between a fiber material and a metal-organic framework to more firmly fix the metal-organic framework to the fiber material. As a result of extensive research, they created the present invention. The sheet material according to the present invention comprises a metal-organic framework containing metal ions and organic ligands, and a paper base material containing a fiber material, wherein the fiber material contains chelating fibers having chelating functional groups capable of chelating with the metal ions.

[0008] In the sheet material according to the present invention, the fiber material constituting the paper base material contains chelating fibers having chelating functional groups. This makes it easier for metal ions of the metal-organic framework to be firmly fixed to the fiber material via the chelating functional groups. Therefore, compared to a paper base material not containing chelating fibers, the metal-organic framework can be fixed relatively firmly to the fiber material. As a result, the integrity of the fiber material and the metal-organic framework is improved, and the metal-organic framework can be prevented from falling off the paper base material. This in turn makes it possible to uniformly arrange the metal-organic framework on the paper base material.

[0009] According to the present invention, it is possible to provide a sheet material in which the metal-organic framework is firmly fixed to the paper base material and is unlikely to fall off from the paper base material.

[0010] FIG. 1 is a flowchart showing a method for manufacturing a sheet material according to one embodiment. FIG. 2 is a flowchart showing a method for manufacturing a sheet material according to a modified example. FIG. 3A is a perspective view of an adsorption filter according to one embodiment. FIG. 3B is a front view of an adsorption filter according to one embodiment. FIG. 4 is a photograph of a paper substrate and a sheet material. FIG. 5A is an optical microscope image showing an enlargement of a portion of a sheet material according to a comparative example. FIG. 5B is an optical microscope image showing an enlargement of a portion of a sheet material according to an example.

[0011] Hereinafter, a sheet material according to one embodiment will be described with reference to the drawings. It should be noted that the embodiment described here is not intended to limit the present invention. Furthermore, the same reference numerals are used to designate components and parts that perform the same function, and redundant descriptions will be omitted or simplified as appropriate. Furthermore, in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) indicating a range includes not only the meaning of X or more and Y or less, but also the meanings of "greater than X" and "smaller than Y."

[0012] <Sheet Material> The sheet material disclosed herein essentially comprises (A) a metal-organic framework and (B) a paper substrate, and may further comprise (C) an organic binder and (D) various additives as necessary. The sheet material has the function of selectively capturing desired components from a fluid composition or the environment, and can be used for various purposes as an adsorbent, occluder, separator, etc. The sheet material can selectively capture desired components from a fluid composition or the environment, and can be used for various purposes as an adsorbent, occluder, separator, etc. For example, the sheet material can capture CO in the atmosphere. ２ The present invention can be suitably used for direct air capture (DAC), which directly captures and stores air, and for adsorbing and separating specific gas components from mixed gases.

[0013] (A) The metal-organic framework is composed of metal ions and organic ligands capable of bonding to the metal ions. The metal-organic framework typically has a highly regular lattice structure (a porous three-dimensional structure) composed of metal ions and organic ligands. The metal-organic framework is typically a porous metal complex having a plurality of pores capable of accommodating specific molecules. The metal-organic framework may be composed of metal ions and organic ligands, or may further contain other components. Note that the term "metal-organic framework" as used herein is synonymous with a porous coordination polymer (PCP) or a porous metal complex.

[0014] The metal ions form a lattice structure by bonding with the organic ligands. The metal ions are not particularly limited, and one or more types of ions known to be useful for this type of application can be appropriately used depending on, for example, the application of the sheet material, the type of organic ligand, and the molecules to be captured. The metal ions may be ions of heavy metals (metals with a specific gravity of 4 or more) or light metals (metals with a specific gravity of less than 4). The metal ions are preferably ions of metals belonging to Groups 2 to 14 of the periodic table, such as alkaline earth metals, noble metals, and rare earth metals. The metal ions may also be ions of metalloids belonging to Groups 13 to 16 of the periodic table, such as boron (B), germanium (Ge), arsenic (As), selenium (Se), tin (Sn), antimony (Sb), and tellurium (Te).

[0015] Examples of metals constituting the metal ions (and typical ion forms) include the metal ions listed on the website of Chelest Co., Ltd., which sells the "Chilest Fiber (registered trademark) series" that can be used as chelating fibers for the (B) paper substrate described below (URL: https: / / chelest.co.jp / products / fiber03 / ). Specific examples include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium ( Examples include Pd), silver (Ag), cadmium (Cd), indium (In), lanthanides, hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), thallium (Tl), lead (Pb), actinides, rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), meitnerium (Mt), ununnilium (Uun), and ununbium (Uub).

[0016] Among these, for use in DAC, ions of metals belonging to periods 3 to 5 of the periodic table are preferred, ions of metals belonging to periods 3 to 4 of the periodic table are more preferred, and ions of at least one of magnesium, chromium, cobalt, nickel, copper, and zinc are particularly preferred. ２ It is more preferable that the metal ions are divalent.

[0017] The organic ligand is an organic compound that has two or more sites in its molecule that can form coordinate bonds with the metal ions and that form a lattice structure by bonding with the metal ions. The organic ligand is not particularly limited, and one or more of those that have been known to be usable for this type of application can be appropriately used depending on, for example, the type of metal ion or the molecule to be captured. Specific examples of organic ligands include pyridines, pyrazines, pyrimidines, triazines, pyrazoles, imidazoles, triazoles, tetrazoles, dicarboxylic acids, tricarboxylic acids, and derivatives thereof.

[0018] In some preferred embodiments, the organic ligand is preferably an aromatic compound composed of the elements C, H, and N, and more preferably a heterocyclic aromatic compound containing one or two nitrogen atoms in the aromatic ring. For example, pyridines having a pyridine skeleton (pyridine and bipyridine) and pyrazines having a pyrazine skeleton (e.g., pyrazine) are preferred.

[0019] In some other preferred embodiments, the organic ligand is preferably a carboxylic acid compound, more preferably an aromatic carboxylic acid containing a benzene ring and at least one (preferably two or more) carboxyl group, such as 1,3-benzenedicarboxylic acid (isophthalic acid), 1,4-benzenedicarboxylic acid (terephthalic acid), 2,3-pyrazinedicarboxylic acid, or 3,5-pyridinedicarboxylic acid, or an aromatic tricarboxylic acid such as 1,3,5-benzenetricarboxylic acid (trimesic acid).

[0020] In some preferred embodiments, the metal-organic framework preferably has a lattice composed of the metal ions and the organic ligands that is a square lattice. The metal-organic framework is preferably a fluorinated metal-organic framework containing elemental fluorine. The metal-organic framework may further include an inorganic structural portion (inorganic chain) containing fluorine.

[0021] In some preferred embodiments, the metal-organic framework preferably contains nickel ions as metal ions and pyrazine as an organic ligand. For example, as described in International Publication No. 2016 / 162834, the metal-organic framework may be Ni(pyrazine) ions consisting of nickel ions and pyrazine. ２ The metal organic framework preferably includes nickel ions as metal ions, pyrazine as an organic ligand, and an inorganic structural portion, and has the following formula: NiMOF ５ (pyrazine) ２ However, the M element is preferably at least one selected from Al, Fe, V, and Nb. Among these, the M element is preferably Nb, and the metal organic framework is preferably a compound represented by the following formula: NiNbOF ５ (pyrazine) ２ According to the metal organic framework, for example, in the application of DAC, it is possible to reduce CO in the atmosphere. ２ can be efficiently collected and stored stably.

[0022] In some preferred embodiments, the metal organic framework is one that can be produced by, for example, the production method (so-called direct precipitation method) shown in FIG. 2 described later, and examples thereof include ELM-11, SIFSIX-3, HKUST-1, ZIF-8, MOF-5, MOF-74, and MOF-177. ELM-11, for example, is a metal organic framework that contains copper ions as metal ions, 4,4'-bipyridine as an organic ligand, and tetrafluoroborate ([BF ４ ] － ) and having the formula: Cu(bpy) ２ (BF ４ ) ２ ; where bpy is 4,4'-bipyridine. SIFSIX-3 is, for example, a compound having a copper ion as a metal ion, pyrazine as an organic ligand, and hexafluorosilicic acid ([SiF ６ ] ２－) and having the formula: Cu(pyrazine) ２ (SiF ６ ) ; SIFSIX-3 may be SIFSIX-3-Ni, which contains a nickel ion as the metal ion. HKUST-1, for example, contains a copper ion as the metal ion, 1,3,5-benzenetricarboxylic acid (trimesic acid) as the organic ligand, and a nitrate ion as the inorganic structural part, and is represented by the following formula: Cu ３ (btc) ２ where btc is 1,3,5-benzenetricarboxylic acid. HKUST-1 may be HKUST-1-Ni, which contains nickel ions as metal ions, or HKUST-1-Zn, which contains zinc ions.

[0023] (B) The paper substrate contains a fibrous material. The fibrous material is not particularly limited, and one or more types of fibrous materials known to be suitable for this type of application can be used as appropriate. Although not particularly limited, the average length of the fibrous material is typically preferably 0.01 μm to 30 mm. The average diameter of the fibrous material is typically preferably 1 nm to 0.1 mm. The aspect ratio of the fibrous material (ratio of average length to average diameter (average length / average diameter)) is preferably approximately 10 or more, for example, 100 or more, 1000 or more. The average length and average diameter can be number-average values ​​obtained by measurements based on electron microscope observation.

[0024] The fibrous material may be inorganic or organic. Examples of inorganic fibers include glass fibers, metal fibers, ceramic fibers, and carbon fibers. The fibrous material is preferably composed primarily of organic fibers (a component accounting for 50% or more by mass; the same applies below). In some embodiments, the fibrous material is preferably substantially free of inorganic fibers (particularly metal fibers) (unavoidable impurities may be tolerated). The fibrous material is preferably composed of organic fibers. The organic fibers may be natural fibers or chemically synthesized chemical fibers (artificial fibers). Examples of natural fibers include plant fibers such as pulp fibers, animal fibers, and mineral fibers. The chemical fibers may be recycled fibers, semi-synthetic fibers, or synthetic fibers. Examples of chemical fibers include cellulose fibers, aramid fibers, polyester fibers, polyethylene fibers, polypropylene fibers, acrylic fibers, rayon fibers, polyamide fibers, polyimide fibers, and polylactic acid fibers.

[0025] In the technology disclosed herein, at least a portion of the fiber material has a chelating functional group capable of chelating (coordinating) with the metal ion of the (A) metal-organic framework. In other words, the (B) paper substrate includes at least a first fiber material (hereinafter also referred to as "chelating fiber") having the chelating functional group. The chelating fiber is an ion-adsorbing fiber in which a chelating agent is chemically bonded to a base fiber. Although not particularly limited, the base fiber of the chelating fiber is preferably a cellulose fiber among the above-mentioned fiber materials. The chelating functional group may be unevenly distributed on the surface of the base fiber, for example, due to the manufacturing method. The chelating fiber is not particularly limited, and one or more conventionally known fibers can be used as appropriate, depending on, for example, the type of metal ion of the (A) metal-organic framework. The chelating fiber can be manufactured by a conventionally known manufacturing method, or a commercially available product can be purchased and used. Examples of commercially available chelating fibers include the "Chilest Fiber (registered trademark) series" manufactured by Chelest Co., Ltd. and the "Kanecaron (registered trademark) series" manufactured by Kaneka Corporation.

[0026] Specific examples of chelating fibers include carboxylic acid-type chelating fibers, phosphate-type chelating fibers, polyol-type chelating fibers, and amine-type chelating fibers, with carboxylic acid-type chelating fibers being preferred. Carboxylic acid-type chelating fibers have a chelating functional group containing, for example, an aminomonocarboxylic acid or an aminopolycarboxylic acid. Examples of aminomonocarboxylic acids and aminopolycarboxylic acids include iminoacetic acid, aminoacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, glutamic acid diacetic acid, ethylenediaminedisuccinic acid, and iminodiacetic acid. Commercially available aminocarboxylic acid-type chelating fibers include, for example, the "Chilest Fiber (registered trademark) IRY series" manufactured by Chelest Co., Ltd. Chelest Fiber (registered trademark) is a fiber in which a chelating agent is chemically bonded to cellulose fiber. The carboxylic acid type chelate fiber can be particularly suitably used when the metal ion of the (A) metal organic framework is an alkali metal ion, alkaline earth metal ion, heavy metal ion, noble metal ion, rare earth metal ion, or the like.

[0027] Phosphate-type chelating fibers have, as a chelating functional group, for example, a group containing aminophosphate or phosphoric acid. Polyol-type chelating fibers have, as a chelating functional group, for example, a group containing glucamine. Commercially available polyol-type chelating fibers include the "GRY series of Chelest Fiber (registered trademark)" manufactured by Chelest Co., Ltd. Polyol-type chelating fibers are particularly suitable for use when the metal ion of the (A) metal organic framework is a semimetal ion. Amine-type chelating fibers have, as a chelating functional group, for example, a group containing an amine or a hydroxylamine. Examples of amines include ethylenediamine, diethylenetriamine, triethylenetetramine, polyethylenepolyamine, polyethyleneimine, polyallylamine, pyrrole, and polyvinylamine.

[0028] In this embodiment, the (B) paper substrate further includes a fiber material (second fiber material) that does not have a chelate functional group in addition to a first fiber material (chelating fiber) that has a chelate functional group. This improves the mechanical strength and durability of the sheet material. When the total of the first fiber material and the second fiber material is 100% by mass, the proportion of the first fiber material (chelating fiber) is preferably 10% by mass or more, more preferably 20% by mass or more, or 30% by mass or more. This allows a larger amount of the (A) metal-organic framework to be supported, thereby achieving a high level of the effects of the technology disclosed herein. Furthermore, from the viewpoint of improving the mechanical strength (e.g., bending strength) and durability of the sheet material, the proportion of the first fiber material (chelating fiber) is preferably 95% by mass or less, more preferably 90% by mass or less, 80% by mass or less, or even 70% by mass or less, or even more preferably 50% by mass or less. When the total of the first and second fiber materials is 100% by mass, the proportion of the first fiber material is preferably 50% by mass ±20% by mass (30 to 70% by mass), and more preferably 30 to 50% by mass. This allows the effects of the technology disclosed herein to be achieved at a high level while also improving the mechanical strength and durability of the sheet material. However, in other embodiments, the paper substrate (B) may be composed solely of the first fiber material.

[0029] Although not particularly limited, the second fibrous material is preferably at least one of the above-mentioned fibrous materials: cellulose fiber, aramid fiber, pulp fiber, glass fiber, metal fiber, and ceramic fiber. The second fibrous material may be of the same type as the base fiber of the first fibrous material. For example, both the first fibrous material and the second fibrous material may contain organic fibers. For example, both the first fibrous material and the second fibrous material may contain cellulose fibers. By including the same type of fibers in the first fibrous material and the second fibrous material, the integrity of the paper substrate may be improved. The second fibrous material may be of a different type from the base fiber of the first fibrous material. For example, the first fibrous material may contain cellulose fibers, and the second fibrous material may be made of natural or inorganic fibers. For example, the first fibrous material may contain cellulose fibers, and the second fibrous material may be made of at least one of aramid fiber, pulp fiber, glass fiber, metal fiber, and ceramic fiber. By including different types of resin in the first fiber material and the second fiber material, various properties of the paper base material, such as durability, chemical resistance, corrosion resistance, heat resistance, etc., can be improved in a balanced manner.

[0030] The (C) organic binder is a component that enhances the bonding strength between the (A) metal-organic framework and the (B) paper base material. The sheet material of this embodiment does not contain an organic binder (although unavoidable impurities and the like are acceptable). This prevents the surface of the metal-organic framework from being covered with the organic binder, thereby increasing the contact area between the target of separation (e.g., gas) and the metal-organic framework, thereby further improving the performance of the sheet material (e.g., adsorption performance when used as an adsorbent). However, in other embodiments, the sheet material may contain an organic binder as needed.

[0031] Examples of organic binders include (meth)acrylic resins such as polyacrylic acid and polymethacrylic acid, polyester resins, polyvinyl alcohol resins, vinyl resins such as vinyl acetate, urethane resins such as polyurethane, celluloses such as methyl cellulose and ethyl cellulose, etc. The proportion of the organic binder is preferably kept to 5% by mass or less, and more preferably 3% by mass or less, 2% by mass or less, 1% by mass or less, or even 0.1% by mass or less (substantially no binder is included), when the entire sheet material is taken as 100% by mass.

[0032] (D) Various additives may be used, as appropriate, in one or more of those conventionally known to be usable for this type of application, for the purpose of improving various properties of the sheet material, such as mechanical strength and durability. Specific examples of additives include inorganic additives such as inorganic fillers and inorganic binders, and organic additives such as antioxidants, dispersants, flocculants, preservatives, stabilizers, and colorants (pigments, dyes, etc.). The proportion of these additives is preferably 10% by mass or less, more preferably 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less, when the entire sheet material is taken as 100% by mass.

[0033] As described above, in the sheet material of this embodiment, the fiber material constituting the paper base material contains chelating fibers having chelating functional groups. This makes it easier for metal ions of the metal-organic framework to be firmly fixed to the fiber material via the chelating functional groups. Therefore, compared to a paper base material not having chelating functional groups, the metal-organic framework can be fixed relatively more firmly to the fiber material. As a result, the integrity of the metal-organic framework and the fiber material is improved, and the metal-organic framework can be prevented from falling off the paper base material. Ultimately, the metal-organic framework can be uniformly arranged on the paper base material.

[0034] In the sheet material of this embodiment, at least a portion of the chelating functional groups are chelate-bonded (coordinate-bonded) to the metal ions. The metal ions of the fiber material are bonded to the metal ions of the metal-organic framework via chelate bonds, thereby more firmly fixing the metal-organic framework to the paper base material. Therefore, the metal-organic framework can be more effectively prevented from falling off the paper base material.

[0035] The sheet material of this embodiment can be suitably used for direct air capture (DAC). In DAC applications, the metal ions are preferably at least one of magnesium, chromium, cobalt, nickel, copper, and zinc. This allows CO 2 in the atmosphere to be removed. ２ can be efficiently collected and stored stably.

[0036] In the sheet material of this embodiment, the metal organic framework contains nickel ions as the metal ions, pyrazine as the organic ligand, and [NbOF ５ ] ２－ and having the following formula: NiNbOF ５ (pyrazine) ２ According to the metal organic framework, for example, in the application of DAC, it is possible to reduce CO in the atmosphere. ２ can be efficiently collected and stored stably.

[0037] In the sheet material of this embodiment, the paper base material includes a first fiber material having the chelating functional group and a second fiber material not having the chelating functional group, which improves the mechanical strength and durability of the sheet material.

[0038] In the sheet material of this embodiment, the first fiber material contains cellulose fibers, which are highly stable against heat and can exhibit excellent performance (e.g., adsorption performance when used as an adsorbent) even in high-temperature environments, for example, at around 80°C.

[0039] In the sheet material of this embodiment, the second fiber material includes at least one of cellulose fiber, aramid fiber, pulp fiber, glass fiber, metal fiber, and ceramic fiber, which can further improve the mechanical strength and durability of the sheet material.

[0040] In the sheet material of this embodiment, when the total of the first fiber material and the second fiber material is 100% by mass, the proportion of the first fiber material is 30 to 70% by mass, which allows for excellent performance (e.g., adsorption performance when used as an adsorbent) as well as high levels of mechanical strength and durability.

[0041] The sheet material of this embodiment does not contain an organic binder, and therefore the surface of the metal-organic framework is not covered with an organic binder, which increases the contact area between the target of separation (e.g., gas) and the metal-organic framework, thereby further improving the performance of the sheet material (e.g., adsorption performance when used as an adsorbent).

[0042] Some of the sheet materials of this embodiment do not contain an organic binder, and the fiber material is made of organic fibers, which can further improve the performance of the sheet material (for example, the adsorption performance when used as an adsorbent).

[0043] In some sheet materials of this embodiment, the fiber material includes a first fiber material composed of organic fibers and serving as a chelating fiber having a chelating functional group capable of chelating with a metal ion, and a second fiber material not having the chelating functional group. When the total of the first fiber material and the second fiber material is taken as 100% by mass, the proportion of the first fiber material is 30% by mass or more and 50% by mass or less. This allows the effects of including the first fiber material (chelating fiber) to be exerted at a high level over a long period of time. Specifically, by setting the proportion of the first fiber material to 30% by mass or more, a larger amount of the metal-organic framework can be supported, thereby achieving a high level of the effects of the technology disclosed herein. Furthermore, by setting the proportion of the first fiber material to 50% by mass or less, mechanical strength and durability can be increased. Therefore, both can be favorably balanced.

[0044] <Method 1 for manufacturing sheet material> Next, a preferred example of a method for manufacturing the above-mentioned sheet material will be described. According to the studies of the present inventors, there are metal-organic frameworks that can be generated by heating and those that can be generated at room temperature without heating. Therefore, it is preferable to change the manufacturing method depending on the type of metal-organic framework.

[0045] FIG. 1 is a flowchart showing a method for producing a sheet material according to this embodiment. As shown in FIG. 1, the production method according to this embodiment involves precipitating (synthesizing) a metal-organic framework by heating, and includes a mixing step S1a, a preparation step S1b, a heating and stirring step S2, a washing step S3, and a drying step S4. The order of the mixing step S1a and the preparation step S1b is not particularly limited; one of the steps may be performed first, or they may be performed approximately simultaneously. Furthermore, the washing step S3 is not necessarily required and may be omitted in other embodiments. The production method disclosed herein may further include other steps at any stage.

[0046] The mixing step S1a is a step of preparing a raw material solution of the metal-organic framework. Specifically, it is a step of mixing a metal ion source and an organic ligand source in a solvent to obtain a mixed solution. The solvent is typically water, but it may also be a mixed solvent mainly composed of water. As the solvent other than water that constitutes the mixed solvent, an organic solvent that can be uniformly mixed with water, such as a lower alcohol or a lower ketone, can be used. As the water, from the viewpoint of preventing the incorporation of impurities, ion-exchanged water, distilled water, ultrafiltered water, reverse osmosis water, etc. can be suitably used.

[0047] In this embodiment, water is first added as a solvent to a reaction vessel, and then a metal ion source and an organic ligand source are added to the reaction vessel as shown in Fig. 1. The order of addition is not particularly limited, but in this example, the metal ion source is added first and then the organic ligand source is added.

[0048] The metal ion source is a compound containing metal ions of the metal organic framework as described above. The metal ion source may be one type of compound, or two or more types of compounds may be used in combination. The metal ion source is herein a metal salt (specifically, NiNbOF ５ ・4H２ O), and Ni as the metal ion ２＋ and [NbOF as an anion of the inorganic structural portion] ５ ] ２－ When the metal ion source is in a powder form, it is preferable to add the powder to the reaction vessel after dissolving it in water as a solvent.

[0049] The organic ligand source is typically a compound containing an organic ligand of the metal-organic framework as described above. In this example, the organic ligand source is pyrazine. When the organic ligand source is in powder form, it is preferable to add the powder to the reaction vessel after dissolving it in water as a solvent.

[0050] Next, the metal ion source and the organic ligand source are mixed in a solvent to obtain a mixed solution. A conventional stirring and mixing device such as a magnetic stirrer, planetary mixer, or disperser can be used as appropriate for mixing. Mixing is preferably carried out until the mixed solution becomes homogeneous. The temperature environment of this step is preferably 10°C or higher, and more preferably 20°C or higher, from the viewpoint of increasing the solubility of the metal ion source and the organic ligand source. On the other hand, from the viewpoint of suppressing volatilization of the solvent and suppressing the reaction between the metal ion source and the organic ligand source, the temperature is preferably 100°C or lower, more preferably 50°C or lower, and more preferably 35°C or lower. In this manner, a mixed solution can be obtained.

[0051] The mixed solution is a raw material solution of the metal organic framework. ２＋ ) and an organic ligand (pyrazine) and an inorganic structural part ([NbOF ５ ] ２－ ) dissolved in water as a solvent. Although not particularly limited, the concentration of the metal ions in the mixed solution is preferably 0.1 to 2 mol / L, more preferably 0.3 to 1 mol / L, and even more preferably 0.5 to 0.7 mol / L. The concentration of the organic ligand in the mixed solution is not particularly limited, as it may vary depending on, for example, the concentration of the metal ions, but is preferably 1 to 10 mol / L, more preferably 2 to 7 mol / L, and even more preferably 5 to 6 mol / L.

[0052] The preparation step S1b is a step of preparing a paper substrate containing chelating fibers. The chelating fibers have chelating functional groups capable of chelating with at least the metal ions contained in the mixed solution (more specifically, the metal ion source). The paper substrate may be prepared by purchasing a commercially available product, or by preparing the paper substrate by a conventionally known method (e.g., wet papermaking) using a fiber material as a raw material. The paper substrate may be composed solely of chelating fibers (first fiber material), or may be composed of a fiber material (second fiber material) that does not have chelating functional groups in addition to the chelating fibers (first fiber material). In this embodiment, as shown in FIG. 1, a slurry is prepared by dispersing chelating fibers (first fiber material) and aramid fibers (second fiber material) in a solvent, and the slurry is then sheeted by a wet papermaking method to produce the paper substrate. In this manner, the paper substrate can be prepared.

[0053] The heating and stirring step S2 is a step in which synthesis of the metal-organic framework and supporting of the metal-organic framework on the paper substrate are carried out substantially simultaneously. Specifically, this is a step in which the paper substrate prepared in the preparation step S1b is immersed in the mixed solution obtained in the mixing step S1a, and heated and stirred to obtain a paper substrate on which the metal-organic framework is supported (MOF-supported paper substrate). For heating, a conventionally known heating device such as an autoclave, an oil bath, or a mantle heater can be appropriately used.

[0054] In this step, metal ions (e.g., Ni ２＋ When the paper substrate prepared in the preparation step S1b is immersed in a mixed solution in which metal ions (Ni) and an organic ligand (e.g., pyrazine) are dissolved, the metal ions are captured by the chelating functional groups of the chelating fibers, and typically, the metal ions are chelate-bonded to the chelating fibers. When the reaction vessel is heated in this state, a metal-organic framework containing metal ions and organic ligands is precipitated on the paper substrate (particularly on the surface of the paper substrate). Here, the metal ions (Ni) ２＋ ) and an organic ligand (pyrazine) and an inorganic structural part ([NbOF ５ ] ２－) is precipitated. At this time, in the chelate fiber, the metal ions bound to the chelating functional groups form a metal organic framework with the organic ligands. Therefore, the metal organic framework is fixed to the chelate fiber via the chelating functional groups.

[0055] The heating temperature is not particularly limited as it may vary depending on, for example, the types of metal ions and organic ligands, but is preferably higher than room temperature and equal to or higher than the boiling point of the solvent, and when the solvent contains water, it is preferably 100° C. or higher, for example, 100 to 200° C., or 100 to 150° C. In this specification, "room temperature" refers to a temperature at which no special heating or cooling is performed, and generally refers to a temperature range of 25° C.±10° C. (15 to 35° C.).

[0056] The retention time is not particularly limited, as it may vary depending on, for example, the concentrations of metal ions and organic ligands in the reaction solution, the heating temperature, etc., but is preferably approximately 1 to 72 hours, more preferably 2 to 48 hours, or 12 to 36 hours. In this step, it is preferable to stir the mixed solution from the viewpoint of promoting the precipitation of the metal-organic framework. For stirring, a conventional stirring and mixing device such as those described above can be used as appropriate. In this manner, an MOF-supported paper substrate can be obtained.

[0057] The washing step S3 is a step of washing the MOF-supported paper substrate obtained in the heating and stirring step S2 with a second solvent. In this embodiment, the solvent (water) contained in the mixed solution is replaced with the second solvent, and the supernatant is removed by centrifugation. The second solvent is preferably more volatile than the solvent contained in the mixed solution. The second solvent is typically an organic solvent, such as alcohol (ethanol) in this example. The solvent replacement and centrifugation are preferably performed multiple times (e.g., 2 to 3 times).

[0058] The drying step S4 is a step of drying the MOF-supported paper substrate after the washing step S3. The drying method is not particularly limited, and for example, conventionally known methods such as heat drying and vacuum drying can be appropriately employed. The drying temperature is preferably equal to or higher than the boiling point of the solvent contained in the mixed liquid, and if the solvent contains water, it is preferably 100°C or higher. The drying temperature is preferably equal to or lower than the heating temperature, and is more preferably, for example, 120°C or lower, or 110°C or lower. In this manner, the sheet material disclosed herein can be manufactured.

[0059] The manufacturing method of this embodiment includes a mixing step of mixing a metal ion source and an organic ligand source in a solvent to obtain a mixed solution, a preparation step of preparing a paper substrate containing chelating fibers having chelating functional groups capable of chelating with at least metal ions contained in the metal ion source, a heating and stirring step of immersing the paper substrate in the mixed solution and heating it to precipitate a metal-organic framework containing the metal ions and the organic ligands contained in the organic ligand source, thereby obtaining the paper substrate on which the metal-organic framework is supported, and a drying step of drying the paper substrate on which the metal-organic framework is supported. In the above aspect, the sheet material described above can be suitably manufactured by heating the chelating fibers and the metal ions in a state of contact (chelating bond) and precipitating the metal-organic framework.

[0060] In the manufacturing method of this embodiment, in the preparation step, a slurry containing the chelating fiber and a second fiber material having no chelating functional groups is formed into a sheet by a wet papermaking method to prepare a paper base material containing the chelating fiber and the second fiber material, thereby making it possible to suitably manufacture a sheet material having various properties, such as excellent mechanical strength and durability.

[0061] In some production methods of the present embodiment, in the heating and stirring step, the paper base material is immersed in the mixed solution and heated in a state in which the metal ions are captured by the chelating functional groups of the chelating fibers, thereby precipitating a metal-organic framework containing the metal ions captured by the chelating functional groups and the organic ligand contained in the organic ligand source, thereby obtaining the paper base material supported with the metal-organic framework. When the metal-organic framework is generated by heating, such a method can suitably produce the sheet material disclosed herein.

[0062] <Method for producing sheet material 2> Note that, while the production method shown in FIG. 1 involves precipitating the metal-organic framework by heating, for some types of metal-organic frameworks, a method for precipitating the metal-organic framework at room temperature without heating (so-called direct precipitation method) can be adopted. This makes it possible to produce the sheet material more simply. Such a method can be suitably applied, for example, when synthesizing the following types of metal-organic frameworks: ELM-11, SIFSIX-3, HKUST-1, ZIF-8, MOF-5, MOF-74, and MOF-177.

[0063] 2 is a flowchart showing a modified manufacturing method for a sheet material. As shown in FIG. 2, the modified manufacturing method includes a preparation step S11a, a preparation step S11b, a room-temperature stirring step S12, a cleaning step S13, and a drying step S14. The preparation step S11b, the cleaning step S13, and the drying step S14 are the same as the preparation step S1b, the cleaning step S3, and the drying step S4 of the manufacturing method shown in FIG. 1, respectively, and therefore will not be described in detail. The manufacturing method disclosed herein may further include other steps at any stage.

[0064] The preparation step S11a is a step of mixing a metal ion source into a solvent to obtain an initial solution. The solvent, metal ion source, and mixing method may be the same as those in the mixing step S1a described above. For example, the metal ion source is a copper ion source when synthesizing ELM-11-Cu, SIFSIX-3-Cu, HKUST-1-Cu, etc. The metal ion source may be a metal salt containing a metal ion and an inorganic structural portion. As an example, copper tetrafluoroborate can be used when synthesizing ELM-11-Cu, copper hexafluorosilicate hydrate can be used when synthesizing SIFSIX-3-Cu, and copper nitrate hexahydrate can be used when synthesizing HKUST-1-Cu. The initial solution here contains a metal ion (for example, Cu ２＋ The initial solution is an aqueous solution in which the anions of the inorganic structural moieties are dissolved in water as a solvent. Unlike the mixed solution shown in FIG. 1, the initial solution does not contain any organic ligands.

[0065] The room-temperature stirring step S12 is a step of obtaining an MOF-supported paper substrate by immersing the paper substrate prepared in the preparation step S11b in the initial solution obtained in the preparation step S11a, adding an organic ligand source, and stirring at room temperature. In this step, when the paper substrate prepared in the preparation step S11b is immersed in the initial solution in which metal ions have been dissolved, the metal ions are chelated to the chelating functional groups of the chelating fiber. In this state, an organic ligand source is further added, and the mixture is stirred and mixed at room temperature. The organic ligand source may be the same as that in the mixing step S1a described above. As an example, 4,4-bipyridine can be used to synthesize ELM-11-Cu, pyrazine can be used to synthesize SIFSIX-3-Cu, and trimesic acid can be used to synthesize HKUST-1-Cu. When the organic ligand source is added, a metal-organic framework containing metal ions and organic ligands is precipitated on the paper substrate. At this time, in the chelate fiber, the metal ions bound to the chelating functional groups form a metal-organic framework with the organic ligands. Therefore, the metal-organic framework is fixed to the chelate fiber via the chelating functional groups. The retention time in this step may be the same as that in the heating and stirring step S2 described above.

[0066] The manufacturing method of the modified example includes a preparation step of mixing a metal ion source in a solvent to obtain an initial solution, a preparation step of preparing a paper substrate containing chelating fibers having chelating functional groups capable of chelating with at least the metal ions, a room-temperature stirring step of immersing the paper substrate in the initial solution, adding an organic ligand source, and mixing at room temperature to precipitate a metal-organic framework containing the metal ions and the organic ligands, thereby obtaining the paper substrate supported with the metal-organic framework, and a drying step of drying the paper substrate supported with the metal-organic framework. Since the above embodiment does not require heating, the sheet material can be manufactured more easily, and manufacturing costs can be reduced.

[0067] In some production methods of the present embodiment, an initial solution not containing an organic ligand source is obtained in the preparation step. Furthermore, in the room temperature stirring step, the paper substrate is immersed in the initial solution, and an organic ligand source is added in a state in which the metal ions are captured by the chelating functional groups of the chelating fibers, and the mixture is mixed at room temperature to precipitate a metal-organic framework containing the metal ions captured by the chelating functional groups and the organic ligand, thereby obtaining the paper substrate supported with the metal-organic framework. When the metal-organic framework is generated at room temperature without heating, such a method can suitably produce the sheet material disclosed herein.

[0068] <Adsorption filter> The above-mentioned sheet material can be formed into various shapes, such as corrugated, honeycomb, slit, pleated, roll, etc., and used as an adsorption filter. By processing it into a formed body, the contact area per unit volume with the target of separation (e.g., gas) can be increased, and the performance of the sheet material can be better exhibited.

[0069] Fig. 3A is a perspective view of the adsorption filter 100, and Fig. 3B is a front view of the adsorption filter 100. The adsorption filter 100 is configured to include the above-mentioned sheet material. As shown in Fig. 3A, the adsorption filter 100 has a cylindrical outer shape. However, the outer shape of the adsorption filter 100 is not limited to a cylindrical shape, and various shapes can be used in other embodiments. The adsorption filter 100 in Fig. 3B comprises a molded body 10 in which the above-mentioned sheet material is molded into a corrugated (wave-shaped) or pleated shape. The adsorption filter 100 is configured to, for example, remove CO from the atmosphere. ２ It can be used for direct air capture (DAC), which directly captures and stores air, or for purifying exhaust gases emitted from engines of motorcycles, generators, etc.

[0070] The adsorption filter 100 can be manufactured, for example, by forming a sheet material into a corrugated shape (wave formation) or a pleated shape (pleat formation), overlapping and rolling the formed sheet material with a flat sheet material, and forming it into a cylindrical shape. Alternatively, for example, in the preparation step S1b of the manufacturing method shown in Figures 1 and 2, a fibrous material may be formed into a sheet by a wet papermaking method, and the sheet-like paper base material may be appropriately processed by folding or the like to form it into the desired shape, and then the heating and stirring step S2 or the room temperature stirring step S12 may be performed.

[0071] The adsorption filter 100 of this embodiment includes the above-mentioned sheet material. In this embodiment, the sheet material is formed into a corrugated, honeycomb, slit, pleated, or roll shape. This increases the contact area per unit volume with the target of separation (e.g., gas), allowing the sheet material to exhibit its performance better.

[0072] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples.

[0073] Test Example I: Examination of the Effectiveness of Chelate Fibers Comparative Example In the comparative example, a sheet material was produced using only a fiber material having no chelating functional groups (in other words, without using chelating fibers). First, 10.0 mL of pure water as a solvent was added to a reaction vessel, and NiNbOF as a metal ion source was added thereto. ５ ・4H ２ O (0.200 g, 0.60 mmol) dissolved in pure water was added, and further, pyrazine (0.389 g, 4.79 mmol) as an organic ligand source dissolved in pure water was added and mixed to obtain a mixed solution (mixing step). Also, aramid fibers having no chelating functional groups were dispersed in an aqueous solvent to prepare a slurry, which was then formed into a sheet by a wet papermaking method to prepare a paper base material (preparation step).

[0074] Next, the prepared paper substrate was impregnated with the mixed solution and heated in an autoclave at 130°C for 24 hours while stirring and mixing. As a result, a blue metal-organic framework (MOF) was precipitated from the mixed solution, and an MOF-supported paper substrate was obtained (heating and stirring step). Next, the obtained MOF-supported paper substrate was washed twice with 15 mL of ethanol to remove the solvent (washing step). Next, the washed MOF-supported paper substrate was vacuum-dried at 105°C for 24 hours (drying step). This resulted in a sheet material.

[0075] In the example, a sheet material was produced by mixing a chelating fiber (first fiber material) having a chelating functional group and an aramid fiber (second fiber material) not having a chelating functional group in a mass ratio of 1:1 (50 mass% each) in a preparation step. In this way, the sheet material was obtained in the same manner as in the comparative example, except that in the preparation step, the chelating fiber (first fiber material) and the second fiber material were dispersed in an aqueous solvent to prepare a slurry, and the slurry was formed into a sheet by a wet papermaking method to prepare a paper base material.

[0076] Figure 4 shows photographs of the paper substrate and sheet material according to the comparative example and the example. As shown in Figure 4, the amount of metal-organic framework (MOF) supported on the sheet material of the comparative example differed significantly between the two circled areas, resulting in significant unevenness in the support. Furthermore, as shown in Figure 5A, the sheet material of the comparative example was observed to be in an unstable state, with the MOF seemingly resting on the fibers.

[0077] In contrast, in the sheet material of the example using chelating fibers as the fiber material, a relatively large amount of metal-organic frameworks (MOFs) was observed to be uniformly fixed to the paper substrate compared to the sheet material of the comparative example. Furthermore, as shown in Figure 5B, in the sheet material of the example, the MOFs filled the spaces between the fibers compared to the sheet material of the comparative example, and it was observed that the integrity between the MOFs and the fiber material was enhanced. These results demonstrate the significance of the technology disclosed herein.

[0078] Test Example II: Study of the Blending Ratio of Fiber Materials In this test example, a first fiber material (chelate fiber) and a second fiber material (aramid fiber) were prepared and mixed in the ratios shown in Table 1 below. Similar to the "Example" of Test Example I described above, paper substrates (Examples 1 to 4) were produced by a wet papermaking method to obtain sheet materials. Then, similar to the above, the "supportability" was evaluated using photographs of the sheet materials. Furthermore, the mechanical strength (bending strength) of the sheet materials was evaluated by a bending test. The bending test was performed by placing a round rod (Φ10 mm) on the rectangular sheet material and bending the sheet material from the round rod as the starting point (axis) until the bending angle reached 90°. The evaluation results are shown in Table 1.

[0079]

[0080] In Table 1, the evaluation results are shown according to the following criteria. [Loading ability] - "△": Low loading amount. - "○": High loading amount, but relatively high loading unevenness. - "◎": High loading amount, and low loading unevenness. [Mechanical strength] - "△": Cracks occur in the sheet material during the bending test, and it breaks. - "○": Cracks occur in the sheet material during the bending test, but it does not break. - "◎": No cracks occur in the sheet material during the bending test, and it does not break.

[0081] As shown in Table 1, the "supportability" was good when the proportion of the first fiber material (chelating fiber) was high, such as 30%, 50%, and 70%, but the "mechanical strength" tended to drop sharply when the proportion of the first fiber material (chelating fiber) exceeded 50% by mass. Therefore, it was found that when the proportion of the first fiber material is 30 to 50% by mass, the effects of the technology disclosed herein can be stably exerted at a high level, and mechanical strength and durability can be increased, achieving a favorable balance between the two.

[0082] Although the preferred embodiments of the present invention have been described above, the above-described embodiments are merely examples, and the present invention can be embodied in various other forms.

[0083] 10 Molded object 100 Adsorption filter S1a Mixing process S1b, S11b Preparation process S2 Heating stirring process S3, S13 Washing process S4, S14 Drying process S11a Preparation process S12 Room temperature stirring process

Claims

1. A sheet material comprising: a metal-organic framework including a metal ion and an organic ligand; and a paper substrate including a fiber material, wherein the fiber material includes chelating fibers having chelating functional groups capable of chelating with the metal ion.

2. The sheet material according to claim 1, wherein at least a portion of said chelating functional groups are chelatingly bonded to said metal ions.

3. The sheet material according to claim 1 or 2, which is used for direct air capture (DAC).

4. The sheet material of claim 3, wherein the metal ions are at least one of magnesium, chromium, cobalt, nickel, copper, and zinc.

5. The metal organic framework comprises nickel ions as the metal ions, pyrazine as the organic ligand, and [NbOF ５ ] ２－ and having the following formula: NiNbOF ５ (pyrazine) ２ 3. The sheet material according to claim 1, wherein the sheet material is NbOFFIVE-1-Ni, which is represented by the formula:

6. The sheet material according to claim 1 or 2, wherein the paper substrate comprises a first fibrous material having the chelating functional group and a second fibrous material not having the chelating functional group.

7. The sheet material of claim 6, wherein the first fibrous material comprises cellulose fibers.

8. The sheet material of claim 7, wherein the second fibrous material comprises at least one of cellulose fibers, aramid fibers, pulp fibers, glass fibers, metal fibers, and ceramic fibers.

9. The sheet material according to claim 6, wherein the proportion of the first fiber material is 30% by mass or more and 70% by mass or less when the total of the first fiber material and the second fiber material is 100% by mass.

10. The sheet material according to claim 1 or 2, which does not contain an organic binder.

11. An adsorption filter comprising the sheet material according to claim 1 or 2.

12. The adsorption filter according to claim 11, wherein the sheet material is formed into a corrugated, honeycomb, slit, pleated, or roll shape.

13. A method for producing a sheet material comprising a metal-organic framework containing metal ions and organic ligands, and a paper base material containing a fiber material, wherein the metal-organic framework is produced by heating, the method comprising: a mixing step of mixing a metal ion source and an organic ligand source in a solvent to obtain a mixed solution; a preparation step of preparing a paper base material containing chelating fibers having chelating functional groups capable of chelating with at least metal ions contained in the metal ion source; a heating and stirring step of immersing the paper base material in the mixed solution and heating it to precipitate a metal-organic framework containing the metal ions and the organic ligands contained in the organic ligand source, thereby obtaining the paper base material on which the metal-organic framework is supported; and a drying step of drying the paper base material on which the metal-organic framework is supported.

14. A method for producing a sheet material comprising a metal-organic framework containing metal ions and organic ligands, and a paper base material containing a fiber material, wherein the metal-organic framework is generated at room temperature without heating, the method comprising: a preparation step of mixing a metal ion source in a solvent to obtain an initial solution; a preparation step of preparing a paper base material containing chelating fibers having chelating functional groups capable of chelating with at least the metal ions; a room-temperature stirring step of immersing the paper base material in the initial solution, adding an organic ligand source, and mixing at room temperature to precipitate a metal-organic framework containing the metal ions and the organic ligands, thereby obtaining the paper base material carrying the metal-organic framework; and a drying step of drying the paper base material carrying the metal-organic framework.

15. A method for manufacturing a sheet material according to claim 13 or 14, wherein in the preparation step, a slurry containing the chelating fiber and a second fiber material not having a chelating functional group is formed into a sheet by a wet papermaking method to prepare a paper base material containing the chelating fiber and the second fiber material.

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