Metal organic framework powder

Abstract

When a basic structure MOF that has only a ligand having two or more functional groups for coordination is specified as a ligand on the basis of the result of powder XRD analysis of this metal organic framework powder, the basic structure MOF has an octahedral particle shape. In an SEM image including 10 or more primary particles which have a particle diameter of 0.1 µm or more and in which at least one or more whole particle surfaces can be observed, if a ridge line having a length of 20 nm or less in a primary particle is assumed to be a point, the ratio of the number of primary particles in which all observed surfaces are triangular to the total number of primary particles observed is less than 40%. In the water vapor adsorption isotherm at 298 K, the ratio of the water vapor adsorption amount per unit volume of the metal organic framework powder to the water vapor adsorption amount per unit volume of the basic structure MOF when the relative pressure is 0.95 is 84% or more.

Description

metal organic structure powder

[0001] The present disclosure relates to metal-organic framework powders.

[0002] Metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs), are complex crystals formed by coordinate bonds between metal ions and organic ligands. They have a highly ordered porous coordination network structure formed by the metal ions and organic ligands, and contain numerous nanospaces within. By utilizing these nanospaces, MOFs can be used as materials for occluding and separating various substances, such as water vapor and other gases, or as catalytic materials. Various types of metal-organic frameworks have been known. For example, Patent Document 1 discloses a porous coordination polymer obtained by reacting metallic chromium or a chromium salt with trimesic acids and a specific acid having a pKa value smaller than that of the trimesic acids.

[0003] Japanese Patent Application Laid-Open No. 2007-51112

[0004] When a metal-organic framework is used as an adsorbent for water vapor and other gases, it is expected that the framework will be applied to an adsorption separation system for water vapor and other gases using processes such as pressure swing adsorption (PSA) and thermal swing adsorption (TSA). When the metal-organic framework is applied to the above-mentioned system, by packing a larger amount of the metal-organic framework into the device constituting the system, it becomes possible to increase the throughput and make the device more compact. In relation to making the device more compact, for example, Patent Document 1 describes that the amount of adsorbent used can be reduced by ensuring a large difference in the amount of adsorption and desorption of water vapor due to changes in relative vapor pressure in the adsorbent. However, improving the packing efficiency of a metal-organic framework as an adsorbent has not been sufficiently studied to date.

[0005] The present disclosure can be realized in the following aspects: (1) According to one aspect of the present disclosure, there is provided a metal organic framework powder that is an aggregate of metal organic framework particles. In this metal-organic framework powder, when a metal-organic framework having only ligands having two or more functional groups for coordination among the ligands constituting the metal-organic framework is identified as a basic structure MOF based on the results of powder XRD analysis of the metal-organic framework powder, the basic structure MOF has an octahedral particle shape, and in an SEM image of the metal-organic framework powder, the SEM image includes 10 or more primary particles having a particle diameter of 0.1 μm or more and at least one or more particle faces of which can be entirely observed, when ridges of 20 nm or less in length on the primary particles are assumed to be points, the ratio of the number of primary particles whose observed faces are all triangular to the total number of observed primary particles is less than 40%, and in a water vapor adsorption isotherm at 298 K, the ratio of the water vapor adsorption amount per unit volume when the relative pressure of the metal-organic framework powder is 0.95 to the water vapor adsorption amount per unit volume when the relative pressure of the metal-organic framework powder is 0.95 is 84% ​​or more. According to the metal-organic framework powder of this form, by substituting some of the ligands for the basic structure MOF having an octahedral particle shape, the shape of the crystal particles is deformed, thereby improving the packing efficiency of the metal-organic framework powder. Therefore, in an apparatus including the metal-organic framework powder, it is possible to realize a more compact apparatus by improving the packing efficiency of the metal-organic framework powder, and an increased throughput by being able to pack a larger amount of metal-organic framework powder. (2) In the metal-organic framework powder of the above form, the basic structure MOF may have an MIL-type crystal structure. With this configuration, since metal-organic frameworks having an MIL-type crystal structure are generally synthesized by hydrothermal synthesis, the metal-organic framework powder can be made to be relatively stable and resistant to decomposition in water. (3) In the metal-organic framework powder of the above form, the basic structure MOF may be MIL-101.With this configuration, MIL-101 is a metal-organic framework that adsorbs a relatively large amount of water, and the raw material costs for its production are relatively low, so that a metal-organic framework powder having these advantages can be obtained. (4) In the metal-organic framework powder of the above configuration, the primary particle diameter observed in an SEM image of the metal-organic framework powder may be 1 μm or less, and the particle size distribution of the metal-organic framework powder measured by a laser diffraction particle size distribution measurement method may have the strongest frequency peak in a region where the particle diameter is 1 μm or more. With this configuration, the aggregation of particles in the metal-organic framework powder progresses, thereby enhancing the effect of improving the packing efficiency and bulk density of the metal-organic framework powder. (5) In the metal-organic framework powder of the above configuration, a monocarboxylic acid may be contained as part of the ligand. With this configuration, it is possible to promote a change in the crystal particle shape resulting from substituting some of the ligands for the basic structure MOF, and therefore it becomes easier to obtain the effect of improving the packing efficiency of the metal-organic framework powder by substituting some of the ligands. (6) In the metal-organic framework powder of the above embodiment, the monocarboxylic acid may be formic acid. With this configuration, since formic acid has a relatively small acid dissociation constant pKa compared to other monocarboxylic acids such as acetic acid, the ion concentration of the monocarboxylic acid increases in the solution during synthesis of the metal-organic framework powder, making it easier for changes in the shape of the crystal particles to occur due to the addition of the monocarboxylic acid. This makes it possible to reduce the amount of monocarboxylic acid used as a raw material. The present disclosure can be realized in various forms other than those described above, and can be realized in the form of, for example, a method for producing a metal-organic framework powder, or a humidity control device such as a heat pump or a desiccant air-conditioning system that includes a metal-organic framework powder.

[0006] 1 is a flowchart outlining a method for producing a metal-organic framework powder; 2 is an explanatory diagram showing XRD charts of each sample side by side; 3 is an explanatory diagram showing an SEM image of the "0FA" sample; 4 is an explanatory diagram showing an SEM image of the "20FA" sample; 5 is an explanatory diagram showing an SEM image of the "30FA" sample; 6 is an explanatory diagram showing an SEM image of the "40FA" sample; 7 is an explanatory diagram showing a water vapor adsorption isotherm per unit mass measured at 298 K; 8 is an explanatory diagram showing a water vapor adsorption isotherm per unit volume at 298 K; 9 is an explanatory diagram showing a nitrogen adsorption isotherm per unit volume at 298 K; 10 is an explanatory diagram showing an oxygen adsorption isotherm per unit volume at 298 K; 11 is an explanatory diagram showing the results of an evaluation of the packing property of the metal-organic framework powder; and 12 is an explanatory diagram showing the results of measuring particle size distribution.

[0007] A. Structure of the metal-organic framework powder: The metal-organic framework powder of this embodiment is an aggregate of metal-organic framework particles, and has a first characteristic feature that, when a "metal-organic framework having, as ligands, only ligands having two or more functional groups for coordination among the ligands constituting the metal-organic framework" is identified as a "basic structure MOF" based on the results of powder XRD analysis of the metal-organic framework powder, such a basic structure MOF has an octahedral particle shape. Here, the metal-organic framework is a porous metal complex obtained by utilizing the self-organization of metal ions and organic ligands, and is a crystalline material that forms a highly regular array structure, and has countless nanospaces within the array structure, thereby exhibiting excellent properties as an adsorbent. In order to identify the above-mentioned basic structure MOF for a metal-organic framework powder, a powder XRD analysis is performed on the metal-organic framework powder of interest, and the obtained XRD chart is compared with the XRD pattern in the CIF file (the XRD pattern is data obtained by X-ray structural analysis and is included in the crystal structure data registered in accordance with the Common Information Format for Crystallography (CIF)), thereby identifying the basic structure MOF.

[0008] Here, the metal organic framework powder of this embodiment includes, as a ligand, a ligand having one functional group for coordination (hereinafter also referred to as a “second ligand”) in addition to a ligand having two or more functional groups for coordination (hereinafter also referred to as a “first ligand”). A metal organic framework generally includes a first ligand having two or more functional groups for coordination as a ligand that is arranged so as to surround a metal ion and forms a coordinate bond with the metal ion. This allows the crystal structure to grow three-dimensionally via the first ligand, forming a cubic crystal structure in which each constituent element is regularly arranged three-dimensionally. In other words, the “functional group for coordination” can be referred to as a functional group involved in crystal growth. The metal organic framework powder of this embodiment further includes a second ligand having only one functional group for coordination, which suppresses three-dimensional crystal growth and makes one-dimensional crystal growth more likely to proceed, thereby partially changing the regularity of the crystal structure. The above-mentioned basic structure MOF is specified as a metal organic framework having only the first ligand as a ligand, and has a highly regular crystalline structure. In the metal organic framework powder of this embodiment, the particle shape of such a basic structure MOF is an octahedron as described above.

[0009] As described above, in the metal-organic framework powder of this embodiment obtained by adding a second ligand in addition to a first ligand to the composition of a basic structure MOF, the peak pattern of the basic structure MOF is maintained in the XRD pattern up to a certain range of substitution ratio of the second ligand to the first ligand. For example, in the metal-organic framework powder, depending on the type of second ligand contained and the amount of the second ligand added, peaks not included in the XRD pattern of the basic structure MOF may occur. However, even in such cases, the peak pattern of the XRD pattern of the basic structure MOF is maintained. That is, the metal-organic framework powder of this embodiment improves the packing performance while suppressing a decrease in the water vapor adsorption amount of the metal-organic framework powder by adding a second ligand, as described below. However, when the crystal particle shape is modified while maintaining adsorption performance similar to that of the basic structure MOF, the XRD pattern maintains a pattern common to that of the basic structure MOF. Therefore, the metal-organic framework powder of this embodiment can be identified as a basic structure MOF by XRD analysis.

[0010] Note that the metal organic framework powder contains metal ions together with ligands, and generally, as long as the metal organic framework has the same ligands and the constituent elements are arranged with the same regularity, the crystal particle shape and crystal structure will be the same even if different types of metal ions with the same valence are contained. Therefore, when specifying the basic structure MOF for the target metal organic framework powder, it is not necessary to strictly specify the types of metal ions that constitute the metal organic framework powder. It is sufficient to compare the XRD chart obtained by powder XRD analysis with the XRD pattern in the CIF file, and identify the metal organic framework with a matching chart pattern as the basic structure MOF.

[0011] After identifying the basic structure MOF for the target metal-organic framework powder in this way, whether the identified basic structure MOF has an octahedral particle shape can be confirmed based on literature information, for example, if the basic structure MOF has been reported and is publicly known as general knowledge. For example, when the basic structure MOF is MIL-101, literature information indicates that the crystal particle shape is octahedral (Mahmoud Y. Zorainy et al., J. Mater. Chem. A, 2021, 9, 22159-22217; S. Yu et al., Chem. Eng. Sci., 2015, 135, 479-488). Alternatively, after identifying the basic structure MOF, the identified basic structure MOF can be synthesized or obtained by purchasing a commercially available product, and the particle shape of the basic structure MOF can be determined to be octahedral by observing its appearance, for example, using a scanning electron microscope (SEM). The particle shape of the basic structure MOF, "octahedron," refers to a regular octahedron-like shape in which the bases of two square pyramids are superimposed on each other.

[0012] The metal-organic framework constituting the metal-organic framework powder of this embodiment can be various metal-organic frameworks as long as the particle shape of the specified basic structure MOF is octahedral. However, it is desirable that the basic structure MOF has, for example, an MIL-type crystal structure. This is because metal-organic frameworks having an MIL-type crystal structure are generally synthesized by hydrothermal synthesis, and therefore are resistant to decomposition in water and have relatively high stability. Specifically, those having a cubic crystal structure are desirable, such as the MIL-100 system having trimesic acid as the first ligand and the MIL-101 system having terephthalic acid as the first ligand. Of these, MIL-101 is desirable. MIL-101 is represented by the composition formula (1) below.

[0013]

[0014] (wherein Me is a metal element, and X represents an element or atomic group that can be changed depending on the raw material used, and can be, for example, Cl or F.)

[0015] Terephthalic acid is a dicarboxylic acid having two carboxy groups as coordination functional groups (hydrophilic functional groups involved in crystal growth). MIL-101 is known as a metal-organic framework with a relatively high water adsorption capacity, and the raw material costs for production are relatively low. Therefore, metal-organic frameworks having a basic structure MOF of MIL-101 are particularly preferred as metal-organic frameworks used for adsorbing and separating water vapor. Furthermore, compared to basic structure MOFs, metal-organic frameworks having a basic structure MOF of MIL-101 exhibit a greater increase in nitrogen adsorption capacity per unit volume than the increase in oxygen adsorption capacity per unit volume, making them suitable for use, for example, as oxygen concentrators for separating oxygen from a nitrogen-oxygen mixture.

[0016] Furthermore, a metal-organic framework having a basic structure MOF of MIL-101 has the property that primary particles tend to aggregate relatively easily. For example, the primary particle diameter observed in an SEM image of the metal-organic framework powder can be 1 μm or less, and the particle size distribution of the metal-organic framework powder measured by a laser diffraction particle size distribution measurement method can have the strongest frequency peak in a region where the particle diameter is 1 μm or more. By progressing the aggregation of particles in the metal-organic framework powder in this way, it is possible to improve the packing efficiency and bulk density of the metal-organic framework powder. Note that "primary particle diameter is 1 μm or less" means that there are substantially no primary particles with a particle diameter exceeding 1 μm, and that even when the observation target in the SEM image is expanded to increase the number of primary particles observed, the proportion of particles with a primary particle diameter exceeding 1 μm is 1% or less.

[0017] Note that, as the second ligand contained in the metal-organic framework powder of this embodiment and having one functional group for coordination, various ligands can be selected, but it is preferable to use, for example, a monocarboxylic acid. Using a monocarboxylic acid as the second ligand can promote the change in crystal particle shape caused by the addition of the second ligand, making it easier to achieve the desired effect by adding the second ligand. Furthermore, it is preferable that the functional group for coordination possessed by the second ligand is the same as the functional group for coordination possessed by the first ligand. For example, when a dicarboxylic acid is used as the first ligand, it is preferable to use a monocarboxylic acid as the second ligand. This makes it possible to perform crystal growth via the first ligand and crystal growth via the second ligand in a common step, thereby simplifying the manufacturing process of the metal-organic framework powder. When a monocarboxylic acid is used as the second ligand, it is preferable to use, for example, formic acid as the second ligand. Since formic acid has a relatively small acid dissociation constant pKa compared to other monocarboxylic acids such as acetic acid, the ion concentration of the monocarboxylic acid increases in the solution during synthesis of the metal organic framework powder, making it easier for changes in the crystal particle shape due to the addition of the monocarboxylic acid to occur. This makes it possible to reduce the amount of monocarboxylic acid used as a raw material. Furthermore, it is desirable for the second ligand to have no cyclic hydrocarbon group, and to have a linear hydrocarbon group.

[0018] Furthermore, the metal organic framework powder of the present embodiment has a second feature that, when observed using a scanning electron microscope (SEM), in an SEM image including 10 or more primary particles each having a particle diameter of 0.1 μm or more and in which at least one or more particle surfaces can be observed in their entirety, when ridges of the primary particles each having a length of 20 nm or less are assumed to be points, the ratio of the number of primary particles whose observed surfaces are all triangular to the total number of observed primary particles is less than 40%.

[0019] Here, the reason why the SEM image to be observed must contain 10 or more particles of a specific shape with a particle diameter of 0.1 μm or more is because, when judging the state of the metal organic framework powder based on the particle shape, it is considered that the judgment should be based on a sufficient number of sufficiently grown crystal particles. Note that the above "particle diameter" refers to the maximum value of the distance between any two points on the periphery of a particle in the SEM image, i.e., the "absolute maximum length."

[0020] Furthermore, as described above, primary particles for which at least one or more particle surfaces can be observed in their entirety are used as the evaluation subject because, in this embodiment, the degree of deformation of the particle shape is evaluated for a metal-organic framework powder in which the crystal particles of the MOF basic structure are octahedral, and the degree of deformation of such particle shape is evaluated by the deformation of the shape of the particle surfaces. In a metal-organic framework in which the crystal particles of the MOF basic structure are octahedral, as in this embodiment, in addition to a first ligand having two or more functional groups for coordination, a second ligand having one functional group for coordination is included as a ligand, thereby deforming the crystal particles, and as described below, the vertices of the octahedral shape become rounded, resulting in a truncated octahedral shape. Furthermore, the higher the proportion of the second ligand, the greater the degree of deformation of the particle shape from the octahedral shape. Here, the degree of deformation of the particles constituting the metal-organic framework powder from the particle shape of the basic structure MOF is specified by the proportion of particles having faces that maintain a triangular shape as the shape of the observed particle faces. The metal-organic framework powder of this embodiment further adds a second ligand to the composition of the basic structure MOF, thereby deforming the octahedral particle shape as described above, and improving the packing efficiency of the metal-organic framework powder, as will be described later. The second characteristic point described above serves as an index for determining whether the particle shape of the metal-organic framework powder has been deformed to an extent that the effect of improving the packing efficiency is obtained.

[0021] Here, when making a judgment related to the second characteristic point, it is required that "all observed surfaces are triangular." Therefore, when the "primary particle for which at least one or more particle surfaces can be entirely observed" has two or more surfaces as surfaces for which the particle surface can be entirely observed, if any of the entirely observable particle surfaces has a non-triangular surface, the primary particle is judged to be a deformed particle that does not satisfy the above-mentioned requirement. In other words, the second characteristic point specifies the upper limit of the proportion of primary particles for which no deformation of particle shape is observed in a metal organic framework powder in which the particle shape of the basic structure MOF is octahedral.

[0022] Furthermore, as a third feature, the metal organic framework powder of this embodiment has a water vapor adsorption isotherm measured at 298 K, and the relative pressure (P / P ０ : P is pressure (Pa), P ０ is a saturated vapor pressure (Pa)) of 0.95, to the water vapor adsorption amount per unit volume when the metal organic framework powder of this embodiment has a characteristic that the ratio (hereinafter also referred to as "ratio of water vapor adsorption amount per unit volume to the basic structure MOF at 298 K") is 84% ​​or more. The above "ratio of water vapor adsorption amount per unit volume to the basic structure MOF at 298 K" is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more.

[0023] The metal-organic framework powder of this embodiment further contains a second ligand added to the basic structure MOF composition, and the addition of such a second ligand changes the water vapor adsorption amount per unit volume when the metal-organic framework powder is used as an adsorbent. As explained as the second feature, the addition of the second ligand can improve the packing efficiency of the metal-organic framework powder, but as the amount of the second ligand added becomes excessive, the water vapor adsorption amount per unit volume of the metal-organic framework powder tends to decrease. The third feature described above serves as an indicator for eliminating a state in which the addition of the second ligand reduces the water vapor adsorption amount per unit volume, thereby hindering the effect of improving the performance as an adsorbent (improving the water vapor adsorption amount per unit volume) due to the improved packing efficiency resulting from the addition of the second ligand.

[0024] The metal organic framework powder of this embodiment has a water vapor adsorption amount per unit volume of 150 cm in the range of relative pressure of 0.6 or more in the water vapor adsorption isotherm at 298 K. ３ (STP) cm －３ It is desirable that this is the case.

[0025] B. Method for producing metal-organic framework powder: Figure 1 is a flowchart showing an outline of the method for producing a metal-organic framework powder of this embodiment. When producing the metal-organic framework powder of this embodiment, first, raw materials for synthesizing the metal-organic framework powder are prepared and weighed (step T100). Specifically, raw materials including a compound serving as a metal ion source constituting the metal-organic framework, a first ligand, a second ligand, and a solvent are weighed. The types and combinations of these raw materials may be appropriately selected depending on the composition of the metal-organic framework powder to be produced.

[0026] As the metal ion source, metal salts such as nitrates, chlorides, oxides, etc. that generate the target metal ions can be used. For example, when producing a metal organic framework powder having a basic structure MOF of MIL-101(Cr), it is sufficient to prepare metal salts, chlorides, oxides, etc. that generate trivalent metal ions such as chromium. As the first ligand, for example, dicarboxylic acids such as the aromatic dicarboxylic acids including terephthalic acid, or tricarboxylic acids such as aromatic tricarboxylic acids including trimesic acid, as described above, can be suitably used. Furthermore, as the second ligand, for example, monocarboxylic acids such as formic acid, acetic acid, benzoic acid, etc. can be used.

[0027] The compounding ratio of the first ligand to the second ligand may be appropriately set according to the type (composition) of the metal-organic framework powder to be synthesized, so that the addition of the second ligand causes an appropriate deformation of the octahedral particle shape of the basic structure MOF that brings about the effect of improving packing efficiency. For example, assume a case in which a metal-organic framework powder is produced in which the basic structure MOF is MIL-101(Cr), terephthalic acid, which is a dicarboxylic acid, is used as the first ligand, and formic acid, which is a monocarboxylic acid, is used as the second ligand. Here, when the blending amount of the first ligand in the production of a basic structure MOF (MIL-101(Cr)) containing only the first ligand (terephthalic acid) as a ligand is taken as 100%, the ratio (molar ratio) of the blending amount of the first ligand reduced according to the blending amount of the second ligand in order to partially replace the first ligand with the second ligand (formic acid) in the metal organic framework powder of this embodiment is referred to as the "substitution ratio of the blending amount of the first ligand." Such a "substitution ratio (molar ratio) of the blending amount of the first ligand" is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. It is also preferably less than 40%, more preferably 38% or less, and even more preferably 35% or less.

[0028] The above-mentioned "amount (charge amount) of the first ligand when producing the basic structure MOF (MIL-101(Cr))" is a value set based on the ratio (molar ratio) of the first ligand to the metal ion source compound in the composition formula of the desired metal-organic framework to be produced. In step T100, the amounts of the raw material reagents can be appropriately adjusted, taking into consideration, for example, the purity of the raw material reagents used, so that a metal-organic framework of the desired composition can be obtained with sufficient purity.

[0029] As the solvent, for example, water, methanol, ethanol, N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), or a mixture thereof can be used, and may be appropriately selected depending on the types of other raw materials including the first and second ligands, etc.

[0030] After step T100, solvothermal synthesis is carried out using these raw materials (step T110). For example, the metal organic framework having the above-mentioned MIL-type crystal structure is generally suitable for hydrothermal synthesis using water as a solvent. For example, when a carboxylic acid is used as the first ligand, the carboxyl group, which is a functional group for coordination, is deprotonated to form "-CO ２ － " coordinates with the metal ion, and a crystal structure grows, synthesizing a metal-organic framework.

[0031] After the synthesis reaction is completed, the liquid containing the synthesized metal-organic framework is filtered (step T120) to recover a solid component containing the metal-organic framework. Then, components other than the metal-organic framework, specifically, remaining insoluble raw materials, in the solid component recovered in step T120 are dissolved (step T130). For example, when terephthalic acid is used as the first ligand and the metal-organic framework is synthesized by hydrothermal synthesis using water as the solvent, the solubility of terephthalic acid in water is relatively low. Therefore, the remaining terephthalic acid that is not used in the synthesis reaction can be recovered in the solid component as an unnecessary component. In such a case, by using an appropriate solvent such as dimethylformamide (DMF), the remaining insoluble raw materials can be dissolved without dissolving the metal-organic framework.

[0032] After dissolving the remaining insoluble raw materials, the liquid in which the remaining insoluble raw materials have been dissolved is filtered (step T140), thereby recovering a solid component containing the metal-organic framework with increased purity. The solid component recovered in step T140 is dried to remove the solvent (step T150), thereby obtaining a metal-organic framework powder.

[0033] C. Example of Use of Metal-Organic Framework Powder as Adsorbent: The metal-organic framework powder of this embodiment can be used, for example, as a water vapor adsorbent in a humidity control device. An example of a device including the metal-organic framework powder of this embodiment as a water vapor adsorbent will be described below.

[0034] (C-1) Heat Pump: The metal-organic structure powder of this embodiment can be used, for example, as a moisture absorbent included in an adsorption heat pump. The adsorption heat pump has a configuration that combines an adsorber configured as a heat exchanger filled with an adsorbent and an evaporator that evaporates water by the adsorption force of the adsorbent, or a configuration that combines an adsorber configured as a heat exchanger filled with an adsorbent and a condenser that condenses water vapor desorbed from the adsorbent using exhaust heat to turn it into water. In such an adsorption heat pump, the metal-organic structure powder of this embodiment can be used as the adsorbent included in the adsorbent.

[0035] (C-2) Desiccant Air Conditioning System: The metal-organic framework powder of this embodiment can be used as an adsorbent that is provided in a desiccant air conditioning system and adsorbs water vapor. A desiccant air conditioning system is an apparatus that includes a dehumidifying rotor made of an adsorbent, removes moisture from air such as outside air, and supplies air with an appropriately adjusted humidity to a room or the like. A rotor-shaped adsorbent is provided, and a portion of the rotor adsorbs moisture from air such as outside air. The portion of the rotor that adsorbs moisture moves as the rotor rotates, and is heated at its destination, thereby releasing moisture and humidifying the air in the room or the like. In such a desiccant air conditioning system, the metal-organic framework powder of this embodiment can be used as the adsorbent that constitutes the dehumidifying rotor.

[0036] According to the metal-organic framework powder of the present embodiment configured as described above, the packing efficiency of the metal-organic framework powder can be improved by the deformation of the crystal particles caused by adding a second ligand having one coordination functional group to the basic structure MOF. Therefore, in an apparatus including the metal-organic framework powder, the packing efficiency can be improved, thereby making the apparatus more compact, and it is possible to pack a larger amount of metal-organic framework powder, thereby increasing the throughput. Here, the improvement in the packing efficiency of the metal-organic framework powder as described above increases the bulk density of the metal-organic framework powder, thereby increasing the adsorption amount (e.g., water vapor adsorption amount) per unit volume of the metal-organic framework powder. The reason why the packing efficiency of the metal-organic framework powder is improved by the deformation of the crystal particles is thought to be that the shape of the crystal particles, which was octahedral in the basic structure MOF, becomes more spherical due to the deformation of the crystal particles, thereby increasing the fluidity and the degree of compactness during packing.

[0037] The effect of improving the packing efficiency in the metal organic framework powder of this embodiment is an effect that can be obtained not only when the metal organic framework powder is packed in a powder state, but also when it is molded into a pellet shape, etc. That is, even when the metal organic framework powder of this embodiment is molded, the bulk density of the obtained molded body can be increased by deforming the shape of the crystal particles through the addition of a second ligand, thereby obtaining the same effect.

[0038] <Preparation of Metal-Organic Framework Powder> As the metal-organic framework powder, MIL-101(Cr) containing only terephthalic acid as a ligand, and metal-organic framework powders in which formic acid, a second ligand, was added to MIL-101(Cr) at various ratios, were prepared based on the production method shown in Fig. 1. The produced metal-organic framework powders are represented by the composition formula (2) below.

[0039]

[0040] In the above formula (2), x represents the "proportion (molar ratio) of the amount of the first ligand reduced in accordance with the amount of the second ligand" when the second ligand (formic acid) is added, assuming that the "amount of the first ligand added when producing the basic structure MOF (MIL-101(Cr))" is 100%, and corresponds to the "substitution ratio of the amount of the first ligand added." The "amount of the first ligand added when producing the basic structure MOF" is a value set based on the ratio (molar ratio) of the first ligand to the metal ion source compound in the composition formula (2) (where x = 0). Six types of samples were prepared, with the "substitution ratio (molar ratio) x of the amount of the first ligand added" being 0%, 20%, 30%, 40%, 50%, and 60%. The samples with the "substitution ratio (molar ratio) x of the amount of the first ligand" of 0%, 20%, 30%, 40%, 50%, and 60% are also referred to as "0FA," "20FA," "30FA," "40FA," "50FA," and "60FA," respectively. The "0FA" sample is a sample with the same composition as the basic structure MOF. Note that, when the amount of the dicarboxylic acid first ligand is reduced by an amount equivalent to the above-mentioned molar ratio x% relative to the basic structure MOF, the amount of the monocarboxylic acid second ligand is set to an amount equivalent to a molar ratio twice the above-mentioned molar ratio x%.

[0041] When preparing each of the above samples, chromium nitrate (Cr(NO ３ ) ３ ), terephthalic acid, formic acid, and hydrochloric acid (HCl) were used. When preparing a sample having the "substitution ratio (molar ratio) of the blending amount of the first ligand" of x%, the blending amount [mmol] of each raw material was (Cr(NO ３ ) ３ : terephthalic acid : formic acid : HCl) = (8.0 : 8.0 × (1 − x / 100 ): 8.0 × ( x / 100 ) × 2 : 3.95). In step T100, 42 mL of pure water was further added to the above-mentioned raw materials.

[0042] In step T110, the raw material prepared in step T100 was placed in a 100 mL container made of PTFE (polytetrafluoroethylene), which was then sealed in a stainless steel container and subjected to hydrothermal synthesis at 220°C for 8 hours. Thereafter, in the filtration step of step T120, washing with methanol was performed three times. In step T130, the solid component recovered in step T120 was stirred in N,N-dimethylformamide (DMF) at room temperature for 12 hours or more to dissolve the remaining insoluble raw material, terephthalic acid. Thereafter, in the filtration step of step T140, washing with methanol was performed three times. In step T150, the solid component recovered in step T140 was dried at 80°C for 12 hours or more to obtain each sample, which was a metal-organic framework powder.

[0043] For "0FA" and "30FA," samples were further prepared with different washing conditions, with only steps T130 and T140 being changed. Specifically, the following washing step was performed instead of step T130. First, the solid component recovered in step T120 was washed by stirring in 300 mL of methanol for 2 hours or more, and then centrifuged at 3,500 to 20,000 rpm, and this operation was repeated twice. Thereafter, the obtained solid component was dried at 80°C for 12 hours or more. Then, 250 mg of the dried powder was dissolved in 20 mL of 1 M ammonium fluoride (NH ４ F) in an aqueous solution, and stirred overnight at room temperature. Then, in the filtration step of step T140, washing with pure water was performed three times. The samples for "0FA" and "30FA" under these different washing conditions were used in the measurement of nitrogen adsorption isotherms and oxygen adsorption isotherms, which will be described later.

[0044] <Powder X-ray Diffraction> Powder X-ray diffraction patterns were obtained for each of the samples "0FA," "20FA," "30FA," and "40FA" prepared as described above by the following method. First, each sample was pretreated by evacuating it at 125°C for at least 6 hours. Then, powder XRD analysis was performed using an X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation). XRD was measured using a CuKα radiation source, with a tube voltage of 40 kV and a tube current of 15 mA.

[0045] Figure 2 is an explanatory diagram showing the XRD charts of the samples "0FA," "20FA," "30FA," and "40FA" side by side. As shown in Figure 2, the XRD patterns of each sample match the peak patterns of the XRD chart of the CIF file of MIL-101(Cr). Based on the XRD patterns, it was confirmed that the basic structure MOF can be identified as MIL-101(Cr).

[0046] <Evaluation Based on Particle Shape> Each of the prepared samples "0FA", "20FA", "30FA", and "40FA" was evaluated based on the particle shape observed in SEM images. Prior to observation using a scanning electron microscope (SEM), each of the above samples was pretreated by evacuating at 125°C for 6 hours or more.

[0047] FIGS. 3 to 6 are explanatory diagrams showing SEM images of samples "0FA," "20FA," "30FA," and "40FA," respectively. The SEM images shown in FIGS. 3 to 6 all include 10 or more "primary particles having a particle diameter of 0.1 μm or greater and in which at least one or more particle surfaces can be observed in their entirety (hereinafter also referred to as "target particles")." In FIGS. 3 to 6, when ridges of 20 nm or less in length are assumed to be points in the "target particles," "primary particles in which all observed surfaces are triangular (hereinafter also referred to as "octahedral particles")" are indicated with a black star. Furthermore, when ridges of 20 nm or less in length are assumed to be points in the "target particles," "particles including surfaces that are not triangular (hereinafter also referred to as "deformed particles")" are indicated with a white star.

[0048] In the SEM image of the "0FA" sample in Figure 3, there are five "octahedral particles" marked with black stars and seven "deformed particles" marked with white stars, for a total of 12 "target particles." Therefore, the ratio of the number of "octahedral particles" marked with black stars to the total number of "target particles" observed was 42%.

[0049] In the SEM image of the "20FA" sample in Figure 4, there are four "octahedral particles" marked with black stars and 14 "deformed particles" marked with white stars, totaling 18 "target particles." Therefore, the ratio of the number of "octahedral particles" marked with black stars to the total number of "target particles" observed was 22%.

[0050] In the SEM image of the "30FA" sample in Fig. 5, there are 0 "octahedral particles" marked with black stars and 19 "deformed particles" marked with white stars, totaling 19 "target particles." Therefore, the ratio of the number of "octahedral particles" marked with black stars to the total number of "target particles" observed was 0%.

[0051] In the SEM image of the "40FA" sample in Fig. 6, there are 0 "octahedral particles" marked with black stars and 11 "deformed particles" marked with white stars, totaling 11 "target particles." Therefore, the ratio of the number of "octahedral particles" marked with black stars to the total number of "target particles" observed was 0%.

[0052] As described above, in the "20FA," "30FA," and "40FA" samples, which contained formic acid as a ligand, the ratio of the number of "octahedral particles" to the total number of "target particles" was less than 40%, unlike the "0FA" sample, when the edges of the "target particles" described above, each with a length of 20 nm or less, were assumed to be points. In the "0FA" and "20FA" samples, most of the particles that showed deformation from the "octahedral particles" were so-called truncated octahedral shapes. However, as the amount of formic acid substitution in the ligand increased, the proportion of particles with a large degree of deformation from the octahedral shape increased. Furthermore, in the "40FA" sample, as shown in Figure 6, "particles ND," which are aggregates of elongated rod-like particles (nanorod-like particles), were observed, which are particles with a particle shape completely different from the octahedral shape. Such nanorod-shaped particles are thought to be by-products whose crystal structure and particle shape are significantly different from those of MIL-101, resulting from the addition of a second ligand, which makes it easier for the growth of a one-dimensional crystal structure to proceed.

[0053] <Measurement of Water Vapor Adsorption Isotherm> For each of the prepared samples "0FA", "20FA", "30FA", "40FA", "50FA", and "60FA", a water vapor adsorption isotherm per unit mass was measured using Belsorp MAX (manufactured by Microtrac-Bell Co., Ltd.). First, each of the above samples was placed in a dedicated sample cell, and pre-treated by evacuating at 125°C for 6 hours or more. At this time, the amount of metal organic framework powder placed in the sample cell was set to an amount that would be about 100 mg after the above pre-treatment. The sample mass after the above pre-treatment was used to derive an adsorption isotherm per unit mass. Then, under a temperature condition of 298 K (25°C), a relative pressure (P / P ０ : P is pressure (Pa), P ０ The adsorption isotherms per unit mass on the adsorption and desorption sides were measured in the saturated vapor pressure (Pa) range of 0 to 0.95. The adsorption isotherms per unit mass were measured when the relative pressure change was 0.05 or the adsorption amount change per unit mass was 200 cm. ３ g －１ Data was recorded every 30 seconds. When measuring the water vapor adsorption isotherm, equilibrium was determined when the pressure change was less than 0.3% at 25°C for 300 seconds. The water vapor adsorption isotherm per unit volume was determined and evaluated using the water vapor adsorption isotherm per unit mass measured as described above and the bulk density calculated by the method described below.

[0054] Fig. 7 is an explanatory diagram showing the water vapor adsorption isotherm per unit mass measured at 298 K. As shown in Fig. 7, the water vapor adsorption isotherms per unit mass of "0FA" and "20FA" were almost the same. Furthermore, when comparing "20FA," "30FA," "40FA," "50FA," and "60FA," which contain a second ligand, the water vapor adsorption amount per unit mass decreased as the proportion of the second ligand increased in the relative pressure range of 0.6 or higher.

[0055] 8 is an explanatory diagram showing the water vapor adsorption isotherm per unit volume obtained using the water vapor adsorption isotherm per unit mass shown in FIG. 7 and the bulk density calculated by the method described below. As shown in FIG. 8, in the range of relative pressures of 0.6 or more, "20FA" and "30FA" had a larger water vapor adsorption amount per unit volume than "0FA", while "40FA", "50FA", and "60FA" had a smaller water vapor adsorption amount per unit volume than "0FA". In the range of relative pressures of 0.6 or more, "40FA", "50FA", and "60FA" had smaller water vapor adsorption amounts per unit volume in this order. In this case, "20FA" and "30FA" had a water vapor adsorption amount per unit volume of 150 cm in the range of relative pressures of 0.6 or more. ３ (STP) cm －３ That was all.

[0056] Furthermore, based on the water vapor adsorption isotherm per unit volume in Figure 8, the ratios of the water vapor adsorption amounts per unit volume for the other metal organic framework powders at a relative pressure of 0.95 to the water vapor adsorption amount per unit volume for "0FA" corresponding to the basic structure MOF at a relative pressure of 0.95 were determined. As a result, "20FA" and "30FA" had higher water vapor adsorption amounts per unit volume than "0FA", the ratio for "20FA" being 108% and the ratio for "30FA" being 112%. In contrast, the ratio for "40FA" was 83%, the ratio for "50FA" was 80%, and the ratio for "60FA" was 63%, and the ratios for "40FA", "50FA", and "60FA" were all less than 84%.

[0057] <Measurement of nitrogen adsorption isotherm and oxygen adsorption isotherm> For each of the samples "0FA" and "30FA", a nitrogen adsorption isotherm per unit mass was measured using Belsorp mini X (manufactured by Microtrac-Bell Co., Ltd.). First, each of the above samples was placed in a dedicated sample cell, and a pretreatment was carried out by evacuating at 250°C for 12 hours or more. At this time, the amount of metal-organic framework put into the sample cell was set to an amount that would be about 100 mg after the above pretreatment. Then, for each of the samples "0FA" and "30FA", the relative pressure (P / P ０ : P is the equilibrium pressure (kPa), and P ０ The adsorption isotherms on the adsorption side and the desorption side were measured in the range of 0 to 0.995 (where the pressure was set to 101.325 (kPa)).

[0058] When measuring the nitrogen adsorption isotherm, data was recorded at a change in adsorption amount of 50 cm per unit mass. ３ (STP)g －１ When measuring the nitrogen adsorption isotherm, equilibrium was judged to have occurred when the pressure change was less than 0.3% at 25°C for 300 seconds. In the leak check, the evacuation time was 30 minutes, and the pressure rise allowance was 1.0 x 10 0 The nitrogen adsorption isotherm per unit mass measured as above and the bulk density calculated by the method described below were used to determine the nitrogen adsorption isotherm per unit volume.

[0059] Furthermore, for each sample of "0FA" and "30FA", an oxygen adsorption isotherm per unit mass was measured using a Belsorp mini X (manufactured by Microtrac-Bell Corporation). The measurement of the oxygen adsorption isotherm was carried out in the same manner as the measurement of the nitrogen adsorption isotherm. First, each of the above samples was placed in a dedicated sample cell, and a pretreatment was carried out by evacuating at 250°C for 12 hours or more. At this time, the amount of metal-organic framework put into the sample cell was set to an amount that would be about 100 mg after the above pretreatment. Then, for each of the samples of "0FA" and "30FA", the relative pressure (P / P) was measured under a temperature condition of 25°C. ０ : P is the equilibrium pressure (kPa), and P ０The adsorption isotherms on the adsorption side and the desorption side were measured in the range of 0 to 0.995 (where the pressure was set to 101.325 (kPa)).

[0060] When measuring the oxygen adsorption isotherm, data was recorded at a change in adsorption amount per unit mass of 50 cm ３ (STP)g －１ When measuring the oxygen adsorption isotherm, equilibrium was judged to have occurred when the pressure change was less than 0.3% at 25°C for 300 seconds. In the leak check, the evacuation time was 30 minutes, and the pressure rise allowance was 1.0 x 10 ０ The oxygen adsorption isotherm per unit mass measured as above and the bulk density calculated by the method described below were used to determine the oxygen adsorption isotherm per unit volume.

[0061] FIG. 9 is an explanatory diagram showing the nitrogen adsorption isotherm per unit volume measured at 298 K for each sample of "0FA" and "30FA". FIG. 10 is an explanatory diagram showing the oxygen adsorption isotherm per unit volume measured at 298 K for each sample of "0FA" and "30FA". In FIG. 9, the horizontal axis represents pressure, and the vertical axis represents the nitrogen adsorption amount per unit volume. In FIG. 10, the horizontal axis represents pressure, and the vertical axis represents the oxygen adsorption amount per unit volume. As shown in FIGS. 9 and 10, "30FA", in which a second ligand (formic acid) is added to the basic structure MOF, shows a greater increase in the nitrogen adsorption amount per unit volume than the increase in the oxygen adsorption amount per unit volume when compared with "0FA" corresponding to the basic structure MOF MIL-101(Cr). Therefore, it was confirmed that the metal organic framework powder in which a second ligand is added to the basic structure MOF is suitable for use in an oxygen concentrator that extracts oxygen from a mixed gas of nitrogen and oxygen.

[0062] <Evaluation of Packing Ability> The packing ability was evaluated for each of the prepared samples "0FA," "20FA," "30FA," and "40FA." Specifically, the metal-organic framework powder of each sample was passed through a sieve with a mesh size of 100 μm to remove aggregated particles with a particle size of 100 μm or more, which were formed by agglomeration of primary particles. The sample was then placed in a borosilicate glass tube with an inner diameter of 5.7 mm, and then subjected to a pretreatment of evacuating the tube at 125°C for 6 hours or more. The amount of metal-organic framework powder placed in the glass tube was set to an amount that would result in 50 mg after the drying. The glass tube was then tapped until the thickness of the packed layer of the metal-organic framework powder no longer changed.

[0063] 11A and 11B are explanatory diagrams showing the results of an evaluation of the packing property of the metal-organic framework powder, in which Fig. 11A shows the state after the metal-organic framework powder is packed into a glass tube and tapped as described above, and Fig. 11B shows the results of calculating the bulk density.

[0064] The bulk density of each sample was calculated based on the volume of each sample after the metal organic framework powder was filled into a glass tube and tapped as described above. The volume of each sample was derived based on the thickness of the packed layer of the metal organic framework powder after tapping the glass tube as described above. The volume of each sample based on the packed layer thickness was derived by comparing the packed layer thickness of each sample with the thickness of the liquid phase of ethanol poured into the same type of glass tube as the one filled with the metal organic framework powder. Specifically, ethanol with a known density was weighed to various masses and poured into the glass tube, and the thickness of each liquid layer was measured. Then, the weighed mass and the density of ethanol (0.789 g cm －３) and derived the relationship between the volume of ethanol and the thickness of the ethanol liquid layer. Based on the relationship between the volume and thickness of the sample in the glass tube derived in this way, the volume of each sample was derived from the thickness of the packed layer of each metal-organic framework powder sample, and the bulk density of each sample was calculated. Figure 11(A) also shows how 1.0 mL and 0.5 mL of ethanol are placed in the glass tube, and Figure 11(B) also shows the theoretical density value of MIL-101(Cr), a basic structure MOF corresponding to the "0FA" sample (X. Liu et al., Chem. Rev. 120 (2020) 8303-8377).

[0065] As shown in Figure 11, it was confirmed that the volume of the metal-organic framework powder after tapping and packing decreases, the packing efficiency improves, and the bulk density increases in the order of "0FA," "20FA," and "30FA" in which the blending ratio of the second ligand increases. In this way, the packing efficiency of the metal-organic framework powder increases, and as described above, the water vapor adsorption amount per unit volume of the metal-organic framework powder increases (see Figure 8). Therefore, it can be said that the adsorption and desorption properties of the metal-organic framework powder are improved in the samples "20FA" and "30FA" in which the second ligand is blended. However, in "40FA," which has an even higher blending ratio of the second ligand, the volume of the metal-organic framework powder after tapping and packing was larger than that of "30FA," and the bulk density was similar to that of "0FA," so no effect of improving the packing efficiency was observed. Furthermore, as shown in Figure 8 described above, the water vapor adsorption amount per unit volume measured at 298 K was lower than that of "0FA." One of the reasons for this result is thought to be that the compounding ratio of the second ligand becomes excessive, which causes greater deformation of the particle shape of the metal-organic framework powder, or the formation of by-products with significantly different particle shapes, such as the particles ND ( FIG. 6 ), which are aggregates of nanorod-shaped particles as described above, making it impossible to obtain the effect of improving the packing efficiency due to the change in shape of the crystal particles caused by the addition of the second ligand.

[0066] <Measurement of particle size distribution> For each of the prepared samples of "0FA", "20FA", and "30FA", the particle size distribution was measured in a wet state using a laser diffraction / scattering particle size distribution analyzer (MT3000II, manufactured by Microtrac-Bell Co., Ltd.). Specifically, a 0.2% aqueous solution of sodium hexametaphosphate was used as the solvent, and each sample was subjected to a dispersion treatment for 3 minutes using an external homogenizer. The measurement was performed under the conditions of a sample refractive index of 1.6, a solvent refractive index of 1.3, and three measurements.

[0067] FIG. 12 is an explanatory diagram showing the results of particle size distribution measurement. In FIG. 12, the horizontal axis represents particle diameter, and the vertical axis represents frequency. For each of the samples "0FA," "20FA," and "30FA" whose particle size distributions were measured, the primary particles observed in SEM images all had particle sizes of 1 μm or less, specifically, 0.5 μm or less, as shown in FIGS. 3, 4, and 5. The white scale bars shown at the bottom of the SEM images in FIGS. 3, 4, and 5 represent 0.1 μm. When the particle size distributions of these samples were measured, as shown in FIG. 12, the metal-organic framework powders "20FA" and "30FA," which are metal-organic framework powders in which a second ligand (formic acid) is added to a basic structure MOF, had the strongest frequency peaks in the particle size distribution in the particle size range of 1 μm or more. In contrast, for "0FA," which corresponds to the basic structure MOF, the strongest frequency peak in the particle size distribution was present in the particle size range of less than 1 μm. Specifically, the particle diameters at which the strongest peaks were present for each sample were 0.578 μm for "0FA," 5.500 μm for "20FA," and 6.541 μm for "30FA." These results confirm that the addition of a second ligand to the basic structure MOF promotes particle aggregation. This particle aggregation is believed to have contributed to the aforementioned improvements in bulk density and packing efficiency.

[0068] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0069] The present disclosure can also be realized in the following forms: [Application Example 1] A metal-organic framework powder which is an aggregate of metal-organic framework particles, wherein, based on the results of powder XRD analysis of the metal-organic framework powder, when a metal-organic framework having only ligands having two or more functional groups for coordination among the ligands constituting the metal-organic framework is identified as a basic structure MOF, the basic structure MOF has an octahedral particle shape, and in an SEM image of the metal-organic framework powder including 10 or more primary particles each having a particle diameter of 0.1 μm or more and in which at least one or more particle faces can be entirely observed, when ridges of the primary particles each having a length of 20 nm or less are assumed to be points, the ratio of the number of primary particles whose observed faces are all triangular to the total number of the observed primary particles is less than 40%, A metal-organic framework powder, characterized in that in a water vapor adsorption isotherm at 298 K, the ratio of the water vapor adsorption amount per unit volume for the metal-organic framework powder at a relative pressure of 0.95 to the water vapor adsorption amount per unit volume for the basic structure MOF at a relative pressure of 0.95 is 84% ​​or more. [Application Example 2] The metal-organic framework powder according to Application Example 1, characterized in that the basic structure MOF has a MIL-type crystal structure. [Application Example 3] The metal-organic framework powder according to Application Example 1 or 2, characterized in that the basic structure MOF is MIL-101. [Application Example 4] The metal-organic framework powder according to Application Example 3, characterized in that the primary particle size observed in an SEM image of the metal-organic framework powder is 1 μm or less, and the particle size distribution of the metal-organic framework powder, measured by a laser diffraction particle size distribution measurement method, has a strongest frequency peak in a particle size region of 1 μm or more. [Application Example 5] The metal organic structure powder according to any one of Application Examples 1 to 4, characterized in that it has a monocarboxylic acid as a part of the ligand. [Application Example 6] The metal organic structure powder according to any one of Application Examples 1 to 5, characterized in that the monocarboxylic acid is formic acid.

Claims

1. A metal organic framework powder which is an aggregate of metal organic framework particles, wherein, based on the results of powder XRD analysis of the metal organic framework powder, when a metal organic framework having only ligands having two or more functional groups for coordination among the ligands constituting the metal organic framework is identified as a basic structure MOF, the basic structure MOF has an octahedral particle shape, and in an SEM image of the metal organic framework powder, the SEM image includes 10 or more primary particles having a particle diameter of 0.1 μm or more and at least one or more particle surfaces of which can be observed in their entirety, when ridges of the primary particles having a length of 20 nm or less are assumed to be points, the ratio of the number of primary particles whose observed surfaces are all triangular to the total number of the observed primary particles is less than 40%; A metal organic framework powder, characterized in that in a water vapor adsorption isotherm at 298 K, the ratio of the water vapor adsorption amount per unit volume for the metal organic framework powder at a relative pressure of 0.95 to the water vapor adsorption amount per unit volume for the basic structure MOF at a relative pressure of 0.95 is 84% ​​or more.

2. The metal organic framework powder according to claim 1, wherein the basic structure MOF has an MIL-type crystal structure.

3. The metal organic framework powder according to claim 1 or 2, wherein the basic structure MOF is MIL-101.

4. The metal organic framework powder according to claim 3, wherein the primary particle size observed in an SEM image of said metal organic framework powder is 1 μm or less, and the particle size distribution of said metal organic framework powder measured by a laser diffraction particle size distribution measurement method has the strongest peak of frequency in a region where the particle size is 1 μm or more.

5. The metal organic framework powder according to any one of claims 1 to 4, characterized in that it contains a monocarboxylic acid as part of the ligand.

6. The metal organic framework powder according to any one of claims 1 to 5, wherein the monocarboxylic acid is formic acid.

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