Manufacturing method of metal-organic structures

Abstract

When adjusting the function and performance of a metal-organic structure by substituting some of its organic ligands with different ones, this method suppresses the decrease in purity and performance of the metal-organic structure caused by the formation of by-products due to the presence of different organic ligands. [Solution] In a method for producing a metal-organic structure, a raw material mixture is prepared, which includes a first ligand having two or more functional groups for coordination, a second ligand that is insoluble in the raw material mixture, and a solvent. When producing a metal-organic structure using the raw material mixture by solvothermal synthesis, a treatment is performed prior to the solvothermal synthesis to improve the uniform dispersion of the second ligand in the raw material mixture.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a metal-organic structure. [Background technology]

[0002] Metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs), are complex crystals formed by the coordination bonding of metal ions and organic ligands. They possess a highly regular, porous coordination network structure formed by the metal ions and organic ligands, containing countless nanospaces within. These nanospaces allow MOFs to be used as materials for the absorption and separation of various substances such as water vapor and other gases, or as catalytic materials. Various types of metal-organic frameworks are known; for example, Patent Document 1 discloses various porous metal complexes containing MIL-101(Cr) and MIL-101(Fe). Furthermore, attempts have been made to impart additional functions and performance to MOFs by substituting some of the organic ligands in the metal-organic framework with different organic ligands (see, for example, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-196677 [Non-patent literature]

[0004] [Non-Patent Document 1] Nakeun Ko et al., J. Mater. Chem. A 3 (2015) 2057-2064 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, when substituting some of the organic ligands of a metal-organic structure with different organic ligands, there was a possibility of a decrease in the purity of the metal-organic structure due to the generation of by-products caused by the presence of the different organic ligands. However, when adjusting the function and performance of a metal-organic structure by substituting some of its organic ligands with different organic ligands, sufficient consideration had not been given to techniques to suppress the decrease in purity of the metal-organic structure and the decrease in performance of the metal-organic structure due to the generation of by-products caused by the presence of different organic ligands. [Means for solving the problem]

[0006] This disclosure can be implemented in the following forms: (1) According to one embodiment of the present disclosure, a method for producing a metal-organic structure is provided. In this method for producing a metal-organic structure, a raw material mixture is prepared, which includes a first ligand having two or more functional groups for coordination, a second ligand that is insoluble in the raw material mixture, and a solvent. When producing the metal-organic structure using the raw material mixture by solvothermal synthesis, a treatment is performed prior to the solvothermal synthesis to improve the uniform dispersion of the second ligand in the raw material mixture. In this method for producing metal-organic structures, when synthesizing a metal-organic structure by adding a second ligand, which is insoluble in the raw material mixture, to a first ligand, a treatment is performed to improve the uniform dispersion of the second ligand in the raw material mixture prior to solvothermal synthesis. Therefore, during the synthesis reaction, when the raw material mixture is heated to the synthesis temperature, the second ligand can dissolve more rapidly in the raw material mixture, and the occurrence of regions in the raw material mixture where the synthesis reaction is progressing that have a higher concentration of the second ligand compared to other regions is suppressed. In regions with a relatively high concentration of the second ligand, the growth of crystal structures using the second ligand proceeds more easily, and by-products with different crystal particle shapes are more likely to be generated. By suppressing the occurrence of regions with a relatively high concentration of the second ligand during the synthesis of metal-organic structures, the generation of by-products is suppressed, and it becomes possible to obtain metal-organic structures with the desired crystalline phase more efficiently. As a result, the purity of the metal-organic structure is improved, and the performance of the metal-organic structure can be improved. (2) In the method for manufacturing the metal-organic structure described above, the treatment to improve uniform dispersion may be a treatment to prepare particles with a smaller particle size as the particles of the second ligand. With such a configuration, by using a second ligand with a smaller particle size, the uniform dispersion of the second ligand in the raw material mixture can be improved more easily. (3) In the method for manufacturing the metal-organic structure described above, the treatment to improve uniform dispersion may be a treatment to pulverize the particles of the second ligand. With such a configuration, it is possible to easily prepare a second ligand with a smaller particle size. (4) In the method for manufacturing the metal-organic structure described above, the treatment to improve uniform dispersion may be a treatment in which the particles of the second ligand are crushed by ultrasonic treatment. With such a configuration, a second ligand with a smaller particle size can be easily prepared. (5) In the method for producing the metal-organic structure described above, the process for improving uniform dispersion may be a process of selecting particles of the second ligand with smaller particle size by classification prior to the preparation of the raw material mixture. With such a configuration, the second ligand with smaller particle size can be easily prepared. (6) In the method for producing the metal-organic structure described above, the treatment to improve uniform dispersion may be a treatment to prepare particles with a particle size of 1000 μm or less as the particles of the second ligand. With such a configuration, the uniform dispersion of the second ligand in the raw material mixture can be further improved. (7) In the method for producing the metal-organic structure described above, the treatment for improving uniform dispersion may be a treatment in which the raw material mixture is held at a temperature higher than the temperature at which heating begins when performing solvothermal synthesis using the raw material mixture, but lower than the synthesis temperature during solvothermal synthesis. With such a configuration, the uniform dispersion of the second ligand in the raw material mixture can be easily improved by increasing the dissolution state of the second ligand in the raw material mixture. (8) In the method for manufacturing a metal-organic structure according to the above embodiment, a MIL-type metal-organic structure may be manufactured as the metal-organic structure. With this configuration, since MIL-type metal-organic structures are generally synthesized by hydrothermal synthesis, it is possible to manufacture a metal-organic structure that is difficult to decompose in water and is relatively stable. (9) In the method for manufacturing the metal-organic structure described above, the metal-organic structure may be a MIL-based metal-organic structure having a cubic crystal structure. With such a configuration, a metal-organic structure that is difficult to decompose in water and is relatively stable can be manufactured. (10) In the method for manufacturing the metal-organic structure described above, MIL-101 may be manufactured in which a portion of the ligand is replaced with the second ligand as the metal-organic structure. With such a configuration, it is possible to manufacture a metal-organic structure that is difficult to decompose in water, is relatively stable, and has excellent water vapor adsorption performance. (11) In the method for manufacturing the metal-organic structure described above, MIL-101(Cr) in which a portion of the ligand is replaced with the second ligand may be manufactured as the metal-organic structure. With such a configuration, it is possible to manufacture a metal-organic structure that is difficult to decompose in water, is relatively stable, and has excellent water vapor adsorption performance. (12) In the method for manufacturing a metal-organic structure according to the above embodiment, a ligand containing a benzene ring may be used as the second ligand. With such a configuration, a metal-organic structure can be suitably manufactured in combination with the first ligand having a benzene ring. Furthermore, when using a second ligand having a benzene ring, it becomes easier to adjust the hydrophilicity and hydrophobicity of the metal-organic structure, as well as the pore size of the micropores formed inside the metal-organic structure, by changing the amount of the second ligand in the metal-organic structure. (13) In the method for producing the metal-organic structure described above, benzoic acid may be used as the second ligand. With this configuration, the metal-organic structure can be suitably produced in combination with the first ligand having a benzene ring. Furthermore, since benzoic acid can easily satisfy the property of being insoluble in the raw material mixture, the effect of producing the metal-organic structure while suppressing the generation of by-products can be obtained more significantly. This disclosure can be implemented in various forms other than those described above, for example, in the form of a method for suppressing by-products during the manufacture of metal-organic structures, a method for improving the purity of metal-organic structures, or metal-organic structures themselves. [Brief explanation of the drawing]

[0007] [Figure 1] A flowchart illustrating the general method for manufacturing a metal-organic structure according to the first embodiment. [Figure 2] A flowchart illustrating the general method for manufacturing the metal-organic structure according to the second embodiment. [Figure 3] An explanatory diagram summarizing the characteristics and evaluation results of each sample. [Figure 4]Explanatory diagram showing the XRD charts of each sample arranged side by side. [Figure 5] Explanatory diagram showing the SEM image of sample S1. [Figure 6] Explanatory diagram showing the SEM image of sample S2. [Figure 7] Explanatory diagram showing the SEM image of sample S3. [Figure 8] Explanatory diagram showing the SEM image of sample S4. [Figure 9] Explanatory diagram showing the SEM image of sample S5. [Figure 10] Explanatory diagram showing the SEM image of sample S6.

Mode for Carrying Out the Invention

[0008] A. First Embodiment: (A-1) Structure of the Metal-Organic Framework: The metal-organic framework obtained by the production method of the metal-organic framework of the first embodiment includes a first ligand having two or more functional groups for coordination and a second ligand different from the first ligand.

[0009] Here, the metal-organic structure is a porous metal complex obtained by utilizing the self-assembly of metal ions and organic ligands. It is a crystalline material that forms a highly regular arrangement structure and exhibits excellent properties as an adsorbent due to having countless nanospaces within the arrangement structure. Generally, the metal-organic structure is equipped with organic ligands (corresponding to the first ligand in this embodiment) that have two or more functional groups for coordination, arranged to surround the metal ions and form coordination bonds with the metal ions. As a result, the crystal structure grows three-dimensionally via the organic ligands, forming a crystalline structure as a three-dimensional structure in which each constituent element is regularly arranged in three dimensions. In other words, "functional groups for coordination" can be said to be functional groups involved in crystal growth. In this embodiment, the metal-organic structure includes a second ligand having only one functional group for coordination, in addition to a first ligand having two or more functional groups for coordination. This suppresses three-dimensional crystal growth and facilitates one-dimensional crystal growth, resulting in a partial change in the regularity of the crystal structure.

[0010] The first ligand of the metal-organic structure of this embodiment is not particularly limited as long as it has two or more functional groups for coordination. For example, it can be a carboxylic acid having a carboxyl group as a functional group for coordination, or an amine having an amino group. In particular, it is preferable to have two or more carboxyl groups as functional groups for coordination. The first ligand can have a benzene ring, for example, and ligands having a single benzene ring, such as aromatic dicarboxylic acids containing terephthalic acid, or aromatic tricarboxylic acids containing trimesic acid, can be suitably used. Since metal-organic structures having ligands with carboxyl groups are generally synthesized by hydrothermal synthesis, by using ligands with carboxyl groups as ligands, it is possible to obtain a metal-organic structure that is difficult to decompose in water and has relatively high stability.

[0011] The second ligand in the metal-organic structure of this embodiment contains one functional group for coordination. However, if the first ligand has a benzene ring, the second ligand can also have a benzene ring, similar to the first ligand, and it is desirable that it has a single benzene ring. When using a second ligand having a benzene ring, it becomes easy to adjust the hydrophilicity and hydrophobicity of the metal-organic structure, as well as the pore size of the micropores formed inside the metal-organic structure, by changing the amount of the second ligand in the metal-organic structure. By changing the properties of the metal-organic structure in this way, it becomes possible to adjust the adsorption and desorption characteristics, such as the amount of water vapor and other gases adsorbed by the metal-organic structure, the adsorption and desorption rate, or the adsorption and desorption initiation pressure.

[0012] Furthermore, the second ligand is preferably a monocarboxylic acid having a carboxyl group as a functional group for coordination. Examples of monocarboxylic acids used as the second ligand include benzoic acid or benzoic acid derivatives. Among these, benzoic acid is preferable. Benzoic acid or benzoic acid derivatives readily satisfy the property described later that they are "insoluble in the raw material mixture used in the production of metal-organic structures," and when benzoic acid or benzoic acid derivatives are used as the second ligand, the metal-organic structure production method in this embodiment can be employed to obtain a metal-organic structure with suppressed by-product formation, which is a significant advantage.

[0013] Furthermore, it is desirable that the coordination functional group of the second ligand be the same as the coordination functional group of the first ligand. For example, when a dicarboxylic acid is used as the first ligand, it is desirable to use a monocarboxylic acid as the second ligand. This makes it possible to simplify the manufacturing process of the metal-organic structure by performing crystal growth via the first ligand and crystal growth via the second ligand in a common process. In addition, because the first ligand and the second ligand have the same coordination functional group, good coordination bonding can be achieved between them and the metal ions contained in the metal-organic structure.

[0014] Thus, the metal-organic framework of this embodiment contains a second ligand in addition to the first ligand, and by adjusting the combination of the first ligand and the second ligand and the content ratio of the second ligand, various performances and functions as a metal-organic framework, such as the performance related to the occlusion and separation of various substances such as water vapor and other gases, can be adjusted.

[0015] Hereinafter, a metal-organic framework similar to the metal-organic framework of this embodiment, which is different only in that it does not have a second ligand and has only the first ligand as a ligand, is referred to as a "basic structure MOF". The metal-organic framework produced by the production method of the metal-organic framework of this embodiment has a second ligand, so that a part of the regularity of the crystal structure is changed with respect to the basic structure MOF, but the generation of by-products having different crystal structures is suppressed. Therefore, when a metal-organic framework is produced by the production method of the metal-organic framework of this embodiment, a metal-organic framework that shows an XRD pattern similar to that of the basic structure MOF by powder XRD analysis and does not show a peak corresponding to a by-product can be obtained.

[0016] The metal ion as the complex metal constituting the metal-organic framework of this embodiment may be appropriately selected in consideration of the combination with the ligand according to the use of the metal-organic framework (for example, uses such as gas occlusion and separation, and the type of the target gas, etc.), and is not particularly limited. For example, zirconium ion (Zr 3+ , 2+ , 2+ , 3+ , , 3+ , , 3+ ,

[0017] , 2+ ), zinc ion (Zn 2+ ), copper ion (Cu 2+ ), aluminum ion (Al 3+ ), iron ion (Fe 3+ ), cobalt ion (Co 3+ ), nickel ion (Ni 2+ ), magnesium ion (Mg 2+ ), chromium ion (Cr 3+ ), manganese ion (Mn 2+ ) can be at least one selected therefrom.

[0017] As previously described, the metal-organic structure of this embodiment can be constructed by various combinations of the first ligand, the second ligand, and the metal ion, but the basic structure MOF can be constructed, for example, with one type of first ligand and one type of metal. Examples of the metal-organic structure of this embodiment include, for example, metal-organic structures having a benzene ring and a ligand having two or more carboxyl groups, such as MIL-101, MIL-100, MIL-125, MIL-88, HKUST-1, or metal-organic structures with UiO-66-BDC as the basic structure MOF. Furthermore, it is desirable that the metal-organic structure of this embodiment be a MIL-type metal-organic structure. This is because MIL-type metal-organic structures are generally synthesized by hydrothermal synthesis and therefore have relatively high stability and are not easily decomposed in water. MIL-type metal-organic structures are those containing a trivalent metal ion (for example, Cr 3+ , Al 3+ Fe 3+ ) or tetravalent metal ions (e.g., Ti 4+ This refers to a metal-organic structure composed of terephthalic acid or trimesic acid, and their derivatives. Specifically, it is a structure with a cubic crystal structure, and is preferably such as the MIL-100 system having trimesic acid as the first ligand, or the MIL-101 system having terephthalic acid as the first ligand. Among these, MIL-101 is preferred. MIL-101 is represented by the following empirical formula (1).

[0018] [ka]

[0019] (However, Me is a metallic element, and X represents an element or group of atoms that can be changed depending on the raw materials used, such as halogens like Cl or F.)

[0020] MIL-101 is known as a metal-organic structure with a relatively high water adsorption capacity, and because the raw material cost for its manufacture is relatively low, metal-organic structures with MIL-101 as the basic MOF structure are particularly preferred as metal-organic structures used for water vapor adsorption and separation. Specifically, MIL-101(Cr) can be suitably adopted as the basic MOF structure.

[0021] (A-2) Method for manufacturing metal-organic structures: Figure 1 is a flowchart illustrating the method for manufacturing a metal-organic structure according to the first embodiment. When manufacturing the metal-organic structure according to this embodiment, first, raw materials for synthesizing the metal-organic structure are prepared (step T100). Specifically, raw materials containing a compound that will serve as a metal ion source for the metal-organic structure, a first ligand, a second ligand, and a solvent are prepared. The types and combinations of these raw materials can be appropriately selected according to the composition of the metal-organic structure to be manufactured.

[0022] As a metal ion source, metal salts such as nitrates, chlorides, oxides, etc. that produce the desired metal ions can be used. For example, when producing a metal-organic structure whose basic structure MOF is MIL-101(Cr), metal salts, chlorides, oxides, etc. that produce trivalent metal ions such as chromium should be prepared. As the first ligand, for example, aromatic dicarboxylic acids containing terephthalic acid, or aromatic tricarboxylic acids containing trimesic acid, etc., can be suitably used. As the second ligand, for example, benzoic acid or benzoic acid derivatives can be suitably used.

[0023] As solvents, for example, water, methanol, ethanol, N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), or mixtures thereof can be used, and should be appropriately selected depending on the types of other raw materials containing the first and second ligands. In step T130 described later, if hydrothermal synthesis (hydrothermal synthesis) is performed as solvothermal synthesis, water is used as the solvent.

[0024] Here, the second ligand in this embodiment has the property of being "insoluble in the raw material mixture used in the production of the metal-organic structure." The raw material mixture refers to the mixture used in the synthesis reaction of the metal-organic structure described later, and includes the compound described above as a metal ion source, the first ligand, the second ligand, and the solvent. A specific solid component being "insoluble in the raw material mixture" means that the solid component remains undissolved even after the raw material mixture has been stirred at room temperature for 24 hours. Whether or not a solid component remains can be determined by whether or not it can be recovered as a residue when the stirred raw material mixture is filtered. Whether or not it can be recovered as a residue can be determined by identifying the components of the residue using XRD (X-ray diffraction), IR (infrared absorption spectroscopy), or NMR (nuclear magnetic resonance spectroscopy). For example, when preparing a raw material mixture using terephthalic acid as the first ligand, benzoic acid as the second ligand, and water as the solvent, and appropriately adjusting the concentrations of the particles of the first and second ligands, both the first ligand (terephthalic acid) and the second ligand (benzoic acid) are determined to be insoluble.

[0025] After step T100, the second ligand is subjected to a treatment to improve its uniform dispersion in the raw material mixture (hereinafter also referred to as the "high dispersion treatment") (step T110).

[0026] The high-dispersion treatment in step T110 can be, for example, a process to prepare particles with a smaller particle size as the second ligand particles. Specifically, for example, it can be a process to grind the second ligand particles prepared in step T100. Grinding of the second ligand particles can be done using a mortar and pestle or a grinder (mill). In addition to grinding, another process to prepare second ligands with a smaller particle size is to select second ligand particles with a smaller particle size by classification. In any case, the particle size of the second ligand particles after the high-dispersion treatment is preferably, for example, 1 mm (1000 μm) or less, and more preferably 500 μm or less. Note that the above "particle size" refers to the maximum distance between any two points on the outer circumference of the particle in the microscope image of the second ligand, i.e., the "absolute maximum length". Furthermore, the statement above that "the particle size of the second ligand is 1 mm or less" means that in a microscope image containing 50 or more particles, the proportion of particles with a particle size exceeding 1 mm is 10% or less.

[0027] After step T110, the second ligand, which has undergone high-dispersion treatment in step T110, is mixed with other raw materials to prepare a raw material mixture (step T120). At this time, because the second ligand has undergone high-dispersion treatment as described above, the uniform dispersion of the second ligand in the raw material mixture can be further improved.

[0028] The mixing ratio of the first ligand to the second ligand in the raw material mixture should be set appropriately according to the type of metal-organic structure to be synthesized (combination of the basic structure MOF and the second ligand), such that the addition of the second ligand alters some of the regularity of the crystal structure to the basic structure MOF to the extent that desirable functions and performance are imparted to the crystal structure, while suppressing the formation of by-products with different crystal structures. For example, consider the case where the basic structure MOF is MIL-101(Cr), and a metal-organic structure is produced using terephthalic acid, a dicarboxylic acid, as the first ligand, and benzoic acid, a monocarboxylic acid, as the second ligand. Here, when producing a basic MOF structure (MIL-101(Cr)) containing only the first ligand (terephthalic acid) as a ligand, the amount of the first ligand used (charge amount) is set to 100%. In this embodiment, to partially substitute the first ligand with the second ligand (benzoic acid) in the metal-organic structure, the percentage of reduction (molar ratio) of the amount of the first ligand used, in proportion to the amount of the second ligand used, is called the "substitution ratio of the amount of the first ligand." This "substitution ratio (molar ratio) of the amount of the amount of the first ligand" is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. Furthermore, it is preferably less than 40%, more preferably 38% or less, and even more preferably 35% or less.

[0029] After step T120, solvothermal synthesis is performed using the prepared raw material mixture (step T130). For example, the metal-organic structures having the MIL-type crystal structure described above are generally suitable for hydrothermal synthesis (hydrothermal synthesis) using water as the 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 "-CO2 -The ligand coordinates to the metal ion in the form of ", and the crystal structure grows, synthesizing a metal-organic structure. In this embodiment, as previously described, the second ligand is subjected to a highly dispersible treatment prior to the synthesis reaction. Therefore, during the synthesis reaction in step T120, the second ligand, which has the property of being "insoluble in the raw material mixture," dissolves more rapidly in the raw material mixture when the raw material mixture is heated to the synthesis temperature, thereby improving its dispersibility in the raw material mixture.

[0030] After the synthesis reaction is complete, the liquid containing the synthesized metal-organic structure is cooled from the synthesis temperature to near room temperature and then filtered (step T140) to recover the solid component containing the metal-organic structure. Subsequently, components other than the metal-organic structure, specifically residual insoluble raw materials, in the solid component recovered in step T140 are dissolved (step T150). For example, when terephthalic acid is used as the first ligand and benzoic acid as the second ligand, and the metal-organic structure is synthesized by hydrothermal synthesis using water as the solvent, the solubility of terephthalic acid and benzoic acid in water is relatively low. Therefore, terephthalic acid and benzoic acid that are not used in the synthesis reaction and remain can be recovered as unwanted components in the solid component. In such cases, by using a suitable solvent such as dimethylformamide (DMF), the residual insoluble raw materials can be dissolved without dissolving the metal-organic structure.

[0031] After dissolving the remaining insoluble raw materials, the liquid containing the dissolved insoluble raw materials is filtered (step T160) to recover a solid component containing a highly purified metal-organic structure. The solid component recovered in step T160 is dried to remove the solvent (step T170) to obtain the metal-organic structure.

[0032] In the method for manufacturing a metal-organic structure of this embodiment, configured as described above, when a metal-organic structure is synthesized by adding a second ligand having the property of being "insoluble in the raw material mixture" to a first ligand, a process is performed prior to the synthesis operation to improve the uniform dispersion of the second ligand in the raw material mixture. Therefore, during the synthesis reaction, when the raw material mixture is heated to the synthesis temperature, the second ligand can dissolve more quickly in the raw material mixture, and the occurrence of regions with a higher concentration of the second ligand compared to other regions in the raw material mixture during the synthesis reaction is suppressed. In regions with a high concentration of the second ligand, for example, the growth of a one-dimensional crystal structure by the second ligand proceeds more easily, and metal-organic structures as impurities (by-products) with different crystal structures and particle shapes from the basic MOF structure are more likely to be generated. In the method for manufacturing a metal-organic structure of this embodiment, the occurrence of such high-concentration regions of the second ligand is suppressed, thereby suppressing the generation of by-products and making it possible to obtain a metal-organic structure having the desired crystalline phase more efficiently. As a result, the purity of the metal-organic structure is improved, leading to enhanced performance, reduced refining costs, and easier quality control of the metal-organic structure.

[0033] B. Second Embodiment: Figure 2 is a flowchart illustrating the manufacturing method of the metal-organic structure according to the second embodiment. Compared to the manufacturing method of the metal-organic structure according to the first embodiment shown in Figure 1, steps T100 and T130-T170 in Figure 1 correspond to steps T200 and T230-T270 in Figure 2, but differ in that step T210 is performed instead of step T110, and step T220 is performed instead of step T120. Specifically, in the manufacturing method of the metal-organic structure according to the second embodiment, a high-dispersion treatment is performed prior to carrying out the synthesis reaction of the metal-organic structure. This differs from the first embodiment in that after preparing the raw material mixture (step T210), a treatment to improve the uniform dispersion of the second ligand in the raw material mixture (high-dispersion treatment) is performed (step T220).

[0034] In step T210 of the second embodiment, the second ligand prepared in step T200 is mixed with other raw materials to create a raw material mixture without undergoing a high-dispersion treatment. Then, the raw material mixture is subjected to a treatment to improve the uniform dispersion of the second ligand (step T220). The high-dispersion treatment performed in the second embodiment can be, for example, a treatment to prepare particles with a smaller particle size as the particles of the second ligand. Specifically, the high-dispersion treatment in step T220 can be, for example, ultrasonic treatment of the raw material mixture. The ultrasonic treatment is preferably performed so that the particle size of the second ligand after the high-dispersion treatment becomes, for example, 1 mm or less, and more preferably 500 μm or less, similar to the grinding treatment in the first embodiment. With such a configuration, it is possible to suppress the generation of by-products and obtain a metal-organic structure having the desired crystalline phase more efficiently, similar to the first embodiment.

[0035] C. Third Embodiment: In the second embodiment, ultrasonic treatment is performed as the high-dispersion treatment in step T220 shown in Figure 2, but other high-dispersion treatments may also be employed. In the manufacturing method of the metal-organic structure of the third embodiment, the high-dispersion treatment in step T220 is "a treatment in which the raw material mixture is held at a temperature that is higher than the temperature at which heating begins when performing solvothermal synthesis using the raw material mixture, but lower than the synthesis temperature during solvothermal synthesis." Specifically, the raw material mixture is held at an intermediate temperature during the process of heating to start the synthesis of the metal-organic structure and raising the temperature to the synthesis conditions. The temperature and time when performing such treatment can be appropriately set depending on the type of metal-organic structure to be produced and the ease with which the second ligand dissolves in the solvent. From the viewpoint of sufficiently improving the uniform dispersion of the second ligand, the time for holding the raw material mixture at the above intermediate temperature conditions is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 1 hour or more. Furthermore, from the viewpoint of ensuring the manufacturing efficiency of the metal-organic structure, it is preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 5 hours or less. For example, when using terephthalic acid as the first ligand and benzoic acid as the second ligand to produce a metal-organic structure by hydrothermal synthesis, the above-mentioned high-dispersion treatment can be performed at 80-150°C for approximately 30 minutes to 5 hours. After such treatment in step T220, the raw material mixture can be heated and pressurized without lowering its temperature until the synthesis conditions are reached.

[0036] By performing this process, the dissolution of the second ligand into the solvent in the raw material mixture progresses, and the uniform dispersion of the second ligand in the raw material mixture is improved. Therefore, as in the first embodiment, the formation of by-products is suppressed, and it becomes possible to obtain a metal-organic structure having the desired crystalline phase more efficiently.

[0037] D. Other Embodiments In the second embodiment, ultrasonic treatment was performed on the raw material mixture as a highly dispersed treatment to pulverize the particles of the second ligand as step T220, but a different configuration is also possible. For example, instead of mixing all the raw materials to prepare a raw material mixture and then ultrasonically treating the resulting raw material mixture, ultrasonic treatment may be performed on a liquid obtained by mixing the particles of the second ligand with a portion of the other raw materials (hereinafter also referred to as the "partial raw material mixture"). Specifically, for example, in step T110 in Figure 1, the particles of the second ligand are mixed with only at least a portion of the solvent to prepare a partial raw material mixture, and ultrasonic treatment is performed on the obtained partial raw material mixture. Then, in step T120, the remaining raw materials are mixed with the ultrasonically treated partial raw material mixture to prepare a raw material mixture. Even with such a configuration, the same effects as in the first and second embodiments can be obtained. [Examples]

[0038] <Fabrication of metal-organic structures> As metal-organic structures, we prepared MIL-101(Cr) containing only terephthalic acid as a ligand, and a metal-organic structure in which benzoic acid was added to MIL-101(Cr) in a certain proportion, thereby substituting a portion of the first ligand, terephthalic acid, with the second ligand, benzoic acid. For the metal-organic structures with the added second ligand, various metal-organic structures were prepared by varying the presence or absence of high-dispersion treatment of the second ligand, or by varying the type of high-dispersion treatment, using the methods shown in Figure 1 or Figure 2. The manufactured metal-organic structures are represented by the following compositional formula (2).

[0039] [ka]

[0040] In equation (2) above, x represents the "percentage of reduction (molar ratio) of the amount of the first ligand added in proportion to the amount of the second ligand" when the second ligand (benzoic acid) is added, when the "amount of the first ligand added when producing the basic structure MOF (MIL-101(Cr))" is set to 100%, and corresponds to the "substitution ratio of the amount of the first ligand" described above. Note that 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 of equation (2) (where x=0). Below, we show the results of preparing five types of samples with the "substitution ratio (molar ratio) x of the amount of the first ligand" set to 20% and one type of sample with the "substitution ratio (molar ratio) x of the amount of the first ligand" set to 0%. Since changing the "substitution ratio (molar ratio) x of the amount of the first ligand" is thought to change the ease with which impurities (by-products) are formed during the production of the metal-organic structure, the above substitution ratio for the second ligand was kept constant as described above for comparison. Samples with a "substitution ratio (molar ratio) x of the amount of the first ligand" of 0% correspond to the basic structure MOF. When reducing the amount of the first ligand, which is a dicarboxylic acid, by an amount equivalent to the above-mentioned molar ratio x% compared to the basic structure MOF, the amount of the second ligand, which is a monocarboxylic acid, is set to an amount equivalent to twice the above-mentioned molar ratio x%.

[0041] Figure 3 is an explanatory diagram summarizing the composition and manufacturing conditions of the six types of samples prepared, as well as the evaluation results regarding the presence or absence of by-products, which will be described later. As shown in Figure 3, samples S1 to S5 are samples in which the "substitution ratio (molar ratio) x of the amount of the first ligand" is 20%, and sample S6 is a sample in which the "substitution ratio (molar ratio) x of the amount of the first ligand" is 0%. Furthermore, samples S1 to S3 are examples of cases in which "high dispersion treatment" was performed during the manufacturing process, while samples S4 to S5 are samples in which "high dispersion treatment" was not performed. In other words, samples S4 to S6 are comparative examples.

[0042] Samples S1 and S2 were manufactured using the method for manufacturing metal-organic structures shown in Figure 1. For sample S1, as a high-dispersion treatment in step T110, the particles of the second ligand were crushed using a mortar and pestle until the particle size was 1 mm or less. For sample S2, as a high-dispersion treatment in step T110, benzoic acid particles with a particle size of 1 mm or less were obtained as sub-sieve particles by classification using a sieve with a mesh size of 1 mm. For sample S3, as a high-dispersion treatment in step T220, the raw material mixture was held at 100°C for 3 hours, which is below the synthesis temperature during the solvothermal synthesis in step T230.

[0043] Sample S4 is a sample in which no special treatment was applied to the benzoic acid particles, which are the second ligand, prepared in the process corresponding to process T100. Sample S5 was manufactured by the method for manufacturing metal-organic structures shown in Figure 1, and instead of the high-dispersion treatment in process T110, a classification using a sieve with a mesh size of 1 mm was performed to obtain benzoic acid particles with a particle size greater than 1 mm as particles on the sieve. Obtaining particles with a particle size greater than 1 mm from the benzoic acid particles, which are the second ligand, prepared in process T100, and using only such relatively large particles as the second ligand particles is thought to make it easier for the second ligand to be partially localized in the raw material mixture, and is considered a treatment that suppresses the uniform dispersion of the second ligand in the raw material mixture. As described above, Sample S6 is a sample corresponding to the basic structure MOF without the addition of benzoic acid, which is the second ligand.

[0044] When preparing each of the above samples, chromium nitrate (Cr(NO3)3), terephthalic acid, benzoic acid, and hydrochloric acid (HCl) were used as raw materials. When preparing a sample as a metal-organic structure in which the "substitution ratio (molar ratio) of the amount of the first ligand" is x%, the amount of each raw material [mmol] in the raw material mixture should be (Cr(NO3)3:terephthalic acid:benzoic acid:HCl) = (8.0:8.0 × (1-x / 100):8.0 × (x / 100) × 2:3.95). Therefore, when preparing samples S1 to S5, in which the "substitution ratio (molar ratio) of the amount of the first ligand" is 20%, the amount of each raw material [mmol] in the raw material mixture was set to (Cr(NO3)3:terephthalic acid:benzoic acid:HCl) = (8.0:8.0 × (1 - 20 / 100):8.0 × (20 / 100) × 2:3.95) = (8.0:6.40:3.20:3.95). Also, when preparing sample S6, in which the "substitution ratio (molar ratio) of the amount of the first ligand" is 0%, the amount of each raw material [mmol] in the raw material mixture was set to (Cr(NO3)3:terephthalic acid:benzoic acid:HCl) = (8.0:8.0:0:3.95). When preparing the raw material mixture, 42 mL of pure water was added to the above raw materials.

[0045] In preparing each sample, in the processes corresponding to steps T130 and T230, the raw material mixture was placed in a 100 mL container made of PTFE (polytetrafluoroethylene), which was then sealed in a stainless steel container and hydrothermally synthesized at 220°C for 8 hours. Subsequently, in the filtration steps of steps T140 and T240, three washes with methanol were performed. In steps T150 and T250, the solid components recovered in step T140, etc., were stirred in N,N-dimethylformamide (DMF) at room temperature for 12 hours or more to dissolve the remaining insoluble raw materials, terephthalic acid and benzoic acid. Subsequently, in the filtration steps of steps T160 and T260, three washes with methanol were performed. In steps T170 and T270, the solid components recovered in step T160, etc., were dried at 80°C for 12 hours or more to obtain each sample, which is a metal-organic structure.

[0046] <Powder X-ray diffraction> Powder X-ray diffraction patterns were obtained for each of the samples S1 to S6 prepared as described above using the following method. First, each sample was pre-treated by vacuuming at 125°C for more than 6 hours. Then, powder XRD analysis was performed using an X-ray diffractometer (MiniFlex600 (manufactured by Rigaku Corporation)). XRD was measured using a CuKα source, with a tube voltage of 40kV and a tube current of 15mA during measurement.

[0047] Figure 4 is an explanatory diagram showing the XRD charts of samples S1 to S6 side by side. In Figure 4, the XRD pattern of the CIF file of the basic structure MOF, MIL-101(Cr), is also shown (data obtained by single-crystal X-ray structure analysis, and the XRD pattern included in the crystal structure data registered in accordance with the Common Crystallographic Information Data Format (CIF) format). As shown in Figure 4, the XRD patterns of samples S1 to S3 and sample S6 matched the peak pattern of the XRD chart of the MIL-101(Cr) CIF file. In contrast, the XRD patterns of samples S4 and S5 included the peak pattern of the MIL-101(Cr) CIF file XRD chart, and also had peaks that were not present in the peak pattern of the MIL-101(Cr) CIF file XRD chart. In Figure 4, these peaks that are not present in the peak pattern of the MIL-101(Cr) CIF file XRD chart are indicated by black arrows as peaks indicating impurities (by-products).

[0048] <Observation of particle shape> Particles in each of the prepared samples S1 to S6 were observed using a scanning electron microscope (SEM). Prior to observation using a scanning electron microscope (SEM), each of the above samples was pre-treated by vacuuming at 125°C for more than 6 hours.

[0049] Figures 5 to 10 are explanatory diagrams showing SEM images of each of the samples S1 to S6, respectively. As shown in Figure 10, in sample S6, which corresponds to the basic structure MOF MIL-101(Cr), the particle shape of the metal-organic structure was octahedral. This result is consistent with the previously known literature information regarding the particle shape of MIL-101 (Mahmoud Y. Zorainy et al., J. Mater. Chem. A, 2021, 9, 22159-22217, S. Yu et al., Chem. Eng. Sci., 2015, 135, 479-488). Furthermore, as shown in Figures 5 to 7, in samples S1 to S3, particles with the same particle shape as sample S6 were observed throughout each sample. In contrast, as shown in Figures 8 and 9, samples S4 and S5 contained particles with a particle shape completely different from that of MIL-101(Cr) (hereinafter also referred to as "irregularly shaped particles"). Specifically, elongated, particulate irregularly shaped particles were observed. In Figures 8 and 9, irregularly shaped particles are indicated by white dashed circles. Such irregularly shaped particles are considered to be impurities (by-products) with a different crystal structure from MIL-101(Cr). Figure 3 shows the results of determining the presence or absence of particles considered to be by-products for each of samples S1 to S6. Here, if one or more irregularly shaped particles were found in an SEM image containing 50 or more particles of the metal-organic structure, it was determined that "by-products were present," and only samples S4 and S5 were determined to have by-products. Irregularly shaped particles were determined to be particles with an aspect ratio (short axis diameter / long axis diameter) of 0.3 or less.

[0050] <Evaluation Results> As described above, in metal-organic structures prepared by adding a second ligand in addition to the first ligand, it was confirmed that the generation of impurities (by-products) with different crystal structures can be suppressed by performing a high-dispersion treatment on the second ligand during the preparation process, as in samples S1 to S3.

[0051] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-mentioned problems, or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0052] This disclosure can also be implemented in the following forms: [Application Example 1] A method for manufacturing a metal-organic structure, A raw material mixture is prepared, comprising a first ligand having two or more functional groups for coordination, a second ligand insoluble in the raw material mixture, and a solvent. The method is characterized in that, when producing the metal-organic structure using the raw material mixture by solvothermal synthesis, a treatment is performed prior to the solvothermal synthesis to improve the uniform dispersion of the second ligand in the raw material mixture. Method for producing metal-organic frameworks. [Application Example 2] A method for manufacturing a metal-organic structure as described in Application Example 1, The process for improving uniform dispersion is characterized by preparing particles with smaller particle sizes as the particles of the second ligand. Method for producing metal-organic frameworks. [Application Example 3] A method for manufacturing a metal-organic structure as described in Application Example 2, The process for improving uniform dispersion is characterized by being a process for grinding the particles of the second ligand. Method for producing metal-organic frameworks. [Application Example 4] A method for manufacturing a metal-organic structure as described in Application Example 3, The process for improving uniform dispersion is characterized by a process of pulverizing the particles of the second ligand by ultrasonic treatment. Method for producing metal-organic frameworks. [Application Example 5] A method for manufacturing a metal-organic structure as described in Application Example 2, The process for improving uniform dispersion is characterized by being a process of selecting particles of the second ligand with smaller particle sizes by classification prior to the preparation of the raw material mixture. Method for producing metal-organic frameworks. [Application Example 6] A method for manufacturing a metal-organic structure as described in Application Example 2, The process for improving uniform dispersion is characterized by preparing particles with a particle size of 1000 μm or less as the particles of the second ligand. Method for producing metal-organic frameworks. [Application Example 7] A method for manufacturing a metal-organic structure as described in Application Example 1, The process for improving uniform dispersion is characterized by holding the raw material mixture at a temperature higher than the temperature at which heating begins when performing solvothermal synthesis using the raw material mixture, but lower than the synthesis temperature during solvothermal synthesis. Method for producing metal-organic frameworks. [Application Example 8] A method for manufacturing a metal-organic structure as described in any one of the application examples 1 to 7, The aforementioned metal-organic structure is characterized by the production of a MIL-type metal-organic structure. Method for producing metal-organic frameworks. [Application Example 9] A method for manufacturing a metal-organic structure as described in Application Example 8, The aforementioned metal-organic structure is characterized by the production of a MIL-based metal-organic structure having a cubic crystal structure. Method for producing metal-organic frameworks. [Application Example 10] A method for manufacturing a metal-organic structure as described in Application Example 9, The method for producing the aforementioned metal-organic structure is characterized by manufacturing MIL-101 in which a portion of the ligand is replaced with the second ligand. Method for producing metal-organic frameworks. [Application Example 11] A method for manufacturing a metal-organic structure as described in Application Example 10, The method for producing the aforementioned metal-organic structure is characterized by manufacturing MIL-101(Cr) in which a portion of the ligand is replaced with the second ligand. Method for producing metal-organic frameworks. [Application Example 12] A method for manufacturing a metal-organic structure as described in any one of the application examples 1 to 11, The second ligand is characterized by using a ligand containing a benzene ring. Method for producing metal-organic frameworks. [Application Example 13] A method for manufacturing a metal-organic structure as described in Application Example 12, The present invention is characterized by using benzoic acid as the second ligand. Method for producing metal-organic frameworks.

Claims

1. A method for manufacturing a metal-organic structure, A raw material mixture is prepared, comprising a first ligand having two or more functional groups for coordination, a second ligand insoluble in the raw material mixture, and a solvent. The method is characterized in that, when producing the metal-organic structure using the raw material mixture by solvothermal synthesis, a treatment is performed prior to the solvothermal synthesis to improve the uniform dispersion of the second ligand in the raw material mixture. Method for producing metal-organic frameworks.

2. A method for producing a metal-organic structure according to claim 1, The process for improving uniform dispersion is characterized by preparing particles with smaller particle sizes as the particles of the second ligand. Method for producing metal-organic frameworks.

3. A method for producing a metal-organic structure according to claim 2, The process for improving uniform dispersion is characterized by being a process for grinding the particles of the second ligand. Method for producing metal-organic frameworks.

4. A method for manufacturing a metal-organic structure according to claim 3, The process for improving uniform dispersion is characterized by a process of pulverizing the particles of the second ligand by ultrasonic treatment. Method for producing metal-organic frameworks.

5. A method for producing a metal-organic structure according to claim 2, The process for improving uniform dispersion is characterized by being a process of selecting particles of the second ligand with smaller particle sizes by classification, prior to the preparation of the raw material mixture. Method for producing metal-organic frameworks.

6. A method for producing a metal-organic structure according to claim 2, The process for improving uniform dispersion is characterized by preparing particles with a particle size of 1000 μm or less as the particles of the second ligand. Method for producing metal-organic frameworks.

7. A method for producing a metal-organic structure according to claim 1, The process for improving uniform dispersion is characterized by holding the raw material mixture at a temperature higher than the temperature at which heating begins when performing solvothermal synthesis using the raw material mixture, but lower than the synthesis temperature during solvothermal synthesis. Method for producing metal-organic frameworks.

8. A method for producing a metal-organic structure according to claim 1, The aforementioned metal-organic structure is characterized by the production of a metal-organic structure of the MIL type. Method for producing metal-organic frameworks.

9. A method for producing a metal-organic structure according to claim 8, The aforementioned metal-organic structure is characterized by the production of an MIL-based metal-organic structure having a cubic crystal structure. Method for producing metal-organic frameworks.

10. A method for producing a metal-organic structure according to claim 9, The method for producing MIL-101 is characterized by having a portion of the ligand replaced with the second ligand as the metal-organic structure. Method for producing metal-organic frameworks.

11. A method for producing a metal-organic structure according to claim 10, The method for producing the aforementioned metal-organic structure is characterized by manufacturing MIL-101(Cr) in which a portion of the ligand is replaced with the second ligand. Method for producing metal-organic frameworks.

12. A method for producing a metal-organic structure according to claim 1, The second ligand is characterized by using a ligand containing a benzene ring. Method for producing metal-organic frameworks.

13. A method for producing a metal-organic structure according to claim 12, The present invention is characterized by using benzoic acid as the second ligand. Method for producing metal-organic frameworks.

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