Porous metal complex-containing film and method for manufacturing the same

Abstract

To provide: a porous metal complex-containing film with a low content of impurities; and a method for manufacturing the film.SOLUTION: A porous metal complex-containing film includes: a filter having a cavity therein and having light permeability and gas permeability; and a porous metal complex stabilized in the cavity. The porous metal complex contains a metal ion and an organic ligand subjected to coordination bond with the metal ion, and has an impurity content of 200 wtppm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a porous metal complex-containing film and a method for producing the porous metal complex-containing film.

Background Art

[0002] A porous metal complex (also referred to as a porous organic metal framework material, a metal organic framework, Metal Organic Framework, etc. Hereinafter, it may be referred to as MOF for short.) is a polymer-like metal complex obtained by crosslinking metal ions with organic ligands.

[0003] Patent Document 1 discloses a porous membrane containing a porous organic metal framework material (MOF), a composition for preparing this membrane, and a method for using the same. This porous membrane is, based on the total mass of this membrane, at least one porous organic metal framework material of 51% by mass to 99.9% by mass, and contains a material containing at least one kind of at least bidentate organic compound coordinated to at least one metal ion. Based on the total mass of this membrane, it contains at least one kind of fibrillated fluoropolymer of 0.1% by mass to 49% by mass and an additive component of 0% by mass to 48.9% by mass based on the total mass of this membrane. As a method for using this membrane, use as a sensor, a conductive membrane, a storage or separation device is disclosed. This membrane is produced, for example, by mixing a commercially available porous metal complex and a fluoropolymer powder to obtain a powder mixture, then kneading the fluoropolymer contained in the powder mixture with a pestle to fibrillate it, and thinning the obtained paste-like mass into a thin film by calendering.

[0004] Patent Document 2 discloses a metal-organic framework (MOF), a phosphor film, and a molecule detection device. This MOF is a metal-organic framework that emits fluorescence and is deformed by interaction with a target molecule. It has a pillared layer structure and contains metal ions, a tetrahedral ligand bonded to the metal ions, and a bidentate ligand bonded to the metal ions. The pillared layer structure has a plurality of two-dimensional layered structures formed from metal ions and a first ligand having a carboxyl group, and the layered structures are crosslinked by a second ligand having a pyridyl group, an imidazole group, or an amino group to form a three-dimensional structure. This MOF is excited by light from a light source to emit fluorescence and is deformed by interaction with a target molecule that is a guest molecule. The emission spectrum of the fluorescence of the MOFs changes according to the above deformation. Patent Document 2 discloses that by utilizing the above phenomenon, a molecule detection device such as a VOC sensor or an explosive sensor can be configured. Also, it is said that the pillared layer structure enables highly sensitive detection of target molecules.

[0005] Patent Document 3 discloses a selective gas permeation membrane having a metal-organic framework (MOF) layer and a method for producing the same. This selective gas permeation membrane has gas permeation membranes adhered to both sides of a layer of metal-organic framework (MOF) particles having gas selectivity. Patent Document 3 exemplifies Cu(bim)2 as an MOF capable of selectively separating and recovering CO2 from a CH4 / CO2 mixed gas. As a method for synthesizing Cu(bim)2 particles, 30 mg of terephthalic acid and 30 mg of copper(II) nitrate trihydrate are added with stirring to a mixed solution of 4 ml of dimethylformamide and 4 ml of acetonitrile, then placed in a thermostatic bath and left standing at 40 °C for 24 h, and then centrifuged to obtain 50 mg of Cu(bim)2 particles having an average particle diameter of about 100 nm.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] When a porous metal complex-containing film is used as a moisture sensor, if it contains a large amount of impurities, it may not exhibit sufficient function as a moisture sensor. However, in the method for producing a porous metal complex-containing film as disclosed in the above patent documents, there is room for further improvement in controlling the impurities in the porous metal complex-containing film, specifically, reducing the impurities.

[0008] The present invention has been made in view of such a situation, and an object thereof is to provide a porous metal complex-containing film having a low impurity content and a method for producing the same. MEANS FOR SOLVING THE PROBLEMS

[0009] The porous metal complex-containing film according to the present invention for achieving the above object comprises: a filter having voids inside and having light permeability and gas permeability; and a porous metal complex immobilized in the voids, and the porous metal complex contains metal ions and an organic ligand that coordinates with the metal ions, and the impurity content is 200 wtppm or less.

[0010] The method for producing a porous metal complex-containing film according to the present invention for achieving the above object is: the method for producing a porous metal complex-containing film described above, comprising: a solution preparation step of mixing a first polar solvent, the organic ligand, and a metal salt to prepare a precursor solution of the porous metal complex; an impregnation step of impregnating the filter with the precursor solution to obtain a precursor-impregnated film; A heating step of heat-treating the precursor-impregnated film; A washing step of washing the precursor-impregnated film after the heating step with a second polar solvent to obtain a washed film; An adsorption / desorption step of adsorbing and desorbing moisture to and from the washed film, and the like.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a porous metal complex-containing film with a low impurity content and a method for producing the same.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0013] With reference to the drawings, a porous metal complex-containing film according to the present embodiment, a sensing element including the same, and a method for producing the porous metal complex-containing film will be described.

[0014] First, an outline of the porous metal complex-containing film and the method for producing the porous metal complex-containing film according to the present embodiment will be described.

[0015] The porous metal complex-containing film according to this embodiment includes a filter having voids inside and having light permeability and gas permeability, and a porous metal complex immobilized in the voids. The porous metal complex includes metal ions and an organic ligand that coordinates with the metal ions. The content of impurities in this porous metal complex-containing film is 200 wtppm (weight ppm) or less.

[0016] The content of impurities in the porous metal complex-containing film according to this embodiment is controlled to be low. The porous metal complex-containing film according to this embodiment is suitable for use, for example, as a sensing element of a moisture sensor that detects water contained in a gas or measures the concentration of water.

[0017] As an example, this porous metal complex-containing film can be produced by the following production method. That is, the production method of the porous metal complex-containing film according to this embodiment includes a solution preparation step of mixing a first polar solvent, an organic ligand, and a metal salt to prepare a precursor solution of a porous metal complex, an impregnation step of impregnating a filter with the precursor solution to obtain a precursor-impregnated film, a heating step of heat-treating the precursor-impregnated film, a washing step of washing the precursor-impregnated film after the heating step with a second polar solvent to obtain a washed film, and an adsorption / desorption step of adsorbing and desorbing moisture to and from the washed film.

[0018] Hereinafter, the porous metal complex-containing film and the production method of the porous metal complex-containing film according to this embodiment will be described in detail.

[0019] The porous metal complex-containing film according to this embodiment includes a filter having voids inside and a porous metal complex (MOF) immobilized in the voids. The porous metal complex-containing film according to this embodiment can be suitably used, for example, as a sensing element that detects water contained in a gas or measures the concentration of water.

[0020] The filter is a base material for forming the porous metal complex-containing film according to this embodiment.

[0021] The filter has light permeability and gas permeability. The material of the filter is not particularly limited. An example of the material of the filter is metal, ceramic, glass, wood, resin, paper, or cloth. The material of the filter is preferably cellulose fiber, glass fiber, or polytetrafluoroethylene fiber. In particular, polytetrafluoroethylene fiber is suitable as the material of the filter.

[0022] The filter may be formed in a plate shape or a film shape. The thickness of the filter is not particularly limited, but it may be formed in a thin plate shape. The thickness of the filter may be, for example, 100 μm or more and 5 mm or less.

[0023] As described above, the filter has voids inside. The filter may be, for example, porous. The porosity of the filter may be determined in consideration of the physical properties of the porous metal complex-containing membrane, such as flexibility and mechanical strength, required when this filter is used as the base material for the porous metal complex-containing membrane. The porosity of the filter may be 50% or more and 95% or less on a volume basis.

[0024] Fine particles of the porous metal complex described later are immobilized in the voids of the filter. In this embodiment, immobilization means that the fine particles of the porous metal complex are captured in the voids of the filter and do not desorb from the filter (porous metal complex-containing membrane) when the porous metal complex-containing membrane is used as a sensing element. As a mode in which the fine particles of the porous metal complex are immobilized in the voids of the filter, cases where the fine particles of the porous metal complex do not desorb from the voids due to steric hindrance in the voids, and cases where the fine particles of the porous metal complex are supported on the surface without voids by adhesion, bonding, spreading, etc. are included. The size of the voids of the filter may be such that spherical particles with a diameter of 10 μm or more cannot pass through (are trapped).

[0025] A porous metal complex is a polymeric metal complex obtained by crosslinking metal ions with organic ligands. A porous metal complex is a porous substance having a plurality of pores communicating with the outside inside. In the present embodiment, the porous metal complex may be a structure in which metal ions or metal atoms and an organic ligand having a bidentate or higher coordinating functional group are continuously bonded.

[0026] Examples of the metal ions or metal atoms constituting the porous metal complex are transition metals, aluminum, and magnesium. The metal ions or metal atoms constituting the porous metal complex are not limited to one type. Two or more metal ions or metal atoms may constitute the porous metal complex.

[0027] The metal ions constituting the porous metal complex are particularly preferably copper ions.

[0028] The functional group of the organic ligand needs to be capable of coordinating to the above metal ions or metal atoms. Examples of the functional group of the organic ligand capable of coordinating to the above metal ions or metal atoms are a hydroxy group, an imidazole group, a sulfonic acid group, an amino group, a carboxyl group, an amide group, and the like.

[0029] The organic ligand is particularly preferably benzene-1,3,5-tricarboxylic acid (1,3,5-benzenetricarboxylate in the coordinated state).

[0030] In the porous metal complex-containing film according to the present embodiment, the content of the porous metal complex is preferably 0.5% or more and 50% or less, more preferably 1% or more and 30% or less, and still more preferably 1% or more and 15% or less on a mass basis.

[0031] The particle diameter of the porous metal complex preferably has a median diameter (cumulative 50% particle diameter) of 0.1 μm or more and 3 μm or less when viewed on a volume basis. The median diameter of the porous metal complex is more preferably 0.1 μm or more and 2 μm or less. The particle diameter of the porous metal complex may be appropriately adjusted in consideration of the viewpoint of ensuring the response intensity at the time of detection or detection when the porous metal complex-containing film is used as a detection element, and the viewpoint of maintaining the crystallinity of the porous metal complex particles.

[0032] The porous metal complex-containing film according to the present embodiment can be manufactured, for example, by a manufacturing method including a solution preparation step, an impregnation step, a heating step, a washing step, a drying step, and an adsorption / desorption step. In this manufacturing method, the solution preparation step, the impregnation step, the heating step, the washing step, the drying step, and the adsorption / desorption step are executed in this order.

[0033] As described above, the solution preparation step is a step of preparing a precursor solution of a porous metal complex by mixing a polar solvent (an example of a first polar solvent, hereinafter referred to as the first polar solvent), an organic ligand, and a metal salt.

[0034] The precursor solution is prepared by adding an organic ligand and a metal salt to a polar solvent and dissolving them. At the time of this dissolution, the order of adding the organic ligand and the metal salt to the polar solvent, the order of dissolving, and the order of mixing are not limited. For example, after dissolving the organic ligand in the polar solvent, the metal salt may be dissolved. Also, after dissolving the metal salt in the polar solvent, the organic ligand may be dissolved. Further, a solution obtained by dissolving the organic ligand in the polar solvent and a solution obtained by dissolving the metal salt in the polar solvent may be mixed to obtain a porous metal complex precursor solution.

[0035] The first polar solvent is not limited as long as it can dissolve the organic ligand and the metal salt. An example of the first polar solvent is tetrahydrofuran, acetonitrile, N,N-dimethylformamide, acetone, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and dimethyl sulfoxide. The first polar solvent is preferably an organic solvent.

[0036] In particular, when copper nitrate is used as the metal salt and 1,3,5-benzenetricarboxylic acid is used as the organic ligand, the first polar solvent is preferably methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, or 2-butanol.

[0037] In particular, to obtain crystals of a porous metal complex with a small particle size distribution (little variation in particle diameter), the first polar solvent is preferably methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, or 2-butanol. In this case, it is preferable that there is one type of the first polar solvent.

[0038] As described above, the impregnation step is a step of impregnating a filter with a precursor solution to obtain a precursor-impregnated membrane.

[0039] The precursor-impregnated membrane is produced by impregnating a filter with a precursor solution. The method of impregnating the filter with the precursor solution is not particularly limited. As an example, the container may be filled with the precursor solution, and the filter may be immersed in the precursor solution in the container to impregnate the filter with the precursor solution. Alternatively, the precursor solution may be dropped onto the filter to impregnate the filter with the precursor solution. Further, during impregnation, the atmosphere may be depressurized or heated. Further, it may be heated while depressurizing during impregnation.

[0040] When it is difficult for the precursor solution to penetrate into the voids of the filter, after previously impregnating the filter with a precursor solution and another polar solvent (for example, one selected from the above first polar solvents, hereinafter sometimes referred to as the third polar solvent), the precursor solution may be impregnated into the filter.

[0041] The heating step is a step of heat-treating the precursor-impregnated film. In the heating step, the precursor-impregnated film is heated to 40°C or higher and 100°C or lower. In the heating step, in the precursor-impregnated film, the porous metal complex precipitates and aggregates. The heating in the heating step may be performed under the flow of a carrier gas that exhausts volatiles generated by heating to the outside of the system. An example of the carrier gas in this case is hydrogen, nitrogen, argon, oxygen, helium, carbon dioxide, hydrocarbon, or clean dry air. Further, the heating step may be performed under reduced pressure such as making the atmosphere in which the precursor-impregnated film is heated a vacuum.

[0042] The heating step preferably includes a first heating step in which the heating of the precursor-impregnated film is performed under the flow of a carrier gas, and a second heating step that is performed after the first heating step and in which the heating of the precursor-impregnated film is performed under reduced pressure such as a vacuum. In the first heating step, the precursor-impregnated film may be heated to 60°C or higher and 80°C or lower. In the second heating step, the precursor-impregnated film may be heated to 40°C or higher and 100°C or lower.

[0043] FIG. 1 shows an example of the flow of the porous metal complex crystallization apparatus 100 that realizes the steps from the heating step to the drying step. The porous metal complex crystallization apparatus 100 includes, for example, a gas supply unit 11 such as a gas cylinder that supplies a carrier gas, a crystallization unit 12 that has a processing chamber in which the precursor-impregnated film is accommodated and to which the carrier gas is supplied from the gas supply unit 11, a heating unit 13 that has a heating mechanism such as a heater or an oil bath that heats the precursor-impregnated film accommodated in the processing chamber of the crystallization unit 12, and a pump unit 14 that reduces the internal atmosphere of the processing chamber of the crystallization unit 12 to a reduced pressure.

[0044] The washing step is a step of washing the precursor-impregnated film after the heating step (hereinafter sometimes referred to as the heat-treated film) with a polar solvent (an example of a second polar solvent, hereinafter referred to as the second polar solvent) to obtain a washed film. The washing step is preferably performed in a state where no first polar solvent remains in the precursor-impregnated film after the heating step.

[0045] The cleaning of the post-heat-treatment film is performed with a second polar solvent. By cleaning the post-heat-treatment film, fine particles of the porous metal complex not immobilized in the pores of the filter and raw materials (metal ions and organic ligands) of the non-crystallized porous metal complex can be removed.

[0046] The second polar solvent may be selected from those exemplified above as an example of the first polar solvent. The second polar solvent may be the same as or different from the solvent used as the first polar solvent. The second polar solvent is preferably ethanol, methanol or acetone.

[0047] The cleaning of the post-heat-treatment film may be performed by immersing the post-heat-treatment film in the second polar solvent, dropping the second polar solvent onto the post-heat-treatment film, or passing the second polar solvent through the post-heat-treatment film. During the cleaning of the post-heat-treatment film, the second polar solvent may be warmed or heated. For example, the post-heat-treatment film may be cleaned while refluxing with the second polar solvent heated.

[0048] The drying step is a step of drying the post-cleaning film. In the drying step, any method for drying the precursor-impregnated film may be used. The drying of the post-cleaning film in the drying step may be performed, for example, under reduced pressure or by heating the precursor-impregnated film to 80°C or higher and 100°C or lower (80°C as an example). Hereinafter, the dried post-cleaning film may sometimes be referred to as a dried film.

[0049] The adsorption / desorption step is a step of performing an adsorption / desorption treatment (hereinafter sometimes simply referred to as an adsorption / desorption treatment) for adsorbing and desorbing moisture to and from the post-cleaning film. In the adsorption / desorption step, moisture is adsorbed to the post-cleaning film and then desorbed. In the adsorption / desorption step, the cycle of the adsorption / desorption treatment for adsorbing and desorbing moisture to and from the post-cleaning film is performed two or more times. By the adsorption / desorption step, the amount of impurities in the porous metal complex-containing film is reduced. The post-cleaning film may be the one before the drying step or a dried film.

[0050] Here, an example of the impurities in the porous metal complex-containing film is the raw material of the porous metal complex remaining in the pores of the porous metal complex in the porous metal complex-containing film, and by-products generated during the manufacturing process of the porous metal complex-containing film. Specific examples of the components of these impurities are ethanol, benzene-1,3,5-tricarboxylic acid, copper nitrate, hydrogen, carbon monoxide, and carbon dioxide.

[0051] In the adsorption / desorption step, for example, the washed film may be exposed to water vapor accompanied by a carrier gas to adsorb moisture. In the adsorption / desorption step, it is preferable that the time for exposing the washed film to water vapor accompanied by a carrier gas to adsorb water vapor is 3 minutes or more (as an example, 10 minutes).

[0052] In the adsorption / desorption step, for example, the washed film that has adsorbed moisture may be exposed to a dry carrier gas that does not contain water vapor or contains almost no water vapor to desorb the moisture. In the adsorption / desorption step, it is preferable that the time for exposing the washed film to a dry carrier gas to desorb water vapor is 30 minutes or more (as an example, 1 day).

[0053] In the adsorption / desorption step, hydrogen, nitrogen, argon, oxygen, helium, neon, carbon dioxide, hydrocarbon, clean dry air, etc. can be used as the carrier gas.

[0054] In the adsorption / desorption step, it is preferable to repeat the adsorption / desorption treatment cycle 20 times or more (as an example, 50 times).

[0055] FIG. 2 shows an example of the flow of the porous metal complex impurity removal device 200 that realizes the adsorption / desorption process. The porous metal complex impurity removal device 200 has, for example, a processing space for accommodating the post-washing film, and includes a processing unit 25 such as an eggplant-shaped flask that performs the adsorption / desorption process, a gas supply unit 21 such as a gas cylinder that supplies a carrier gas to the processing unit 25, and a water vapor supply unit 22 such as a pure water vapor generator that supplies water vapor to the processing unit 25. The porous metal complex impurity removal device 200 may further include a dilution mixing unit 24 and a water vapor valve unit 23 in addition to the gas supply unit 21, the water vapor supply unit 22, and the processing unit 25. The dilution mixing unit 24 is a gas mixing mechanism that dilutes and mixes the water vapor supplied from the water vapor supply unit 22 with the carrier gas supplied from the gas supply unit 21 and supplies the mixture to the processing unit 25. The water vapor valve unit 23 is a valve device such as a regulator or a control valve that adjusts the amount of water vapor supplied from the water vapor supply unit 22 to the dilution mixing unit 24 or switches between the supply and prohibition of water vapor supply. The water vapor valve unit 23 may be disposed between the water vapor supply unit 22 and the dilution mixing unit 24.

[0056] The particle size distribution of the porous metal complex immobilized in the voids of the filter may be determined by image analysis using a scanning electron microscope (SEM).

[0057] The particle size distribution and median diameter (so-called d50, cumulative 50% particle diameter) of the porous metal complex in the present embodiment are obtained by measuring the maximum diameter of the crystals of the porous metal complex present in the image captured using a scanning electron microscope and obtaining the volume-based particle size distribution based on this maximum diameter.

[0058] An example of an apparatus that can use the porous metal complex-containing film according to the present embodiment as a sensing element is a device for measuring the trace moisture concentration in a gas.

[0059] FIG. 3 shows an example of a trace moisture concentration measuring device 300 that can use the porous metal complex-containing film according to the present embodiment as a sensing element. In FIG. 3, for the purpose of explaining the internal structure, a schematic cross-sectional configuration of the measurement unit 30 of the measuring device 300 is shown.

[0060] The measurement unit 30 is composed of three metal blocks: a central block 33 that forms a sample gas path C through which the sample gas G to be measured flows, a light source side block 31 disposed on one side of the sample gas path C, and a light receiving side block 32 disposed on the other side of the sample gas path C.

[0061] The central block 33 is provided with a sample gas inflow path C1 for introducing the sample gas G, a sample gas outflow path C2 for discharging the sample gas G, and a sensor element holding portion 35 for holding a sensor element 36 which is a porous metal complex-containing film.

[0062] The light source side block 31 has a measurement light path P provided with a light source 37 at the open end. The light receiving side block 32 has a light receiving path L provided with a light receiving element 38 which is a light receiving portion at the open end, and the light receiving path L is axially arranged with respect to the measurement light path P. Between the light source side block 31 and the central block 33, a convex light transmissive member 43 is sandwiched together with an annular packing 44.

[0063] Between the light receiving side block 32 and the central block 33, a flat light transmissive member 41 is sandwiched together with an annular packing 42. The convex light transmissive member 43 and the flat light transmissive member 41 have light transmissibility and gas impermeability, and by arranging the annular packings 42 and 44 between them and the central block 33, airtightness can be obtained to prevent leakage of the sample gas G from the sample gas path C to the outside and intrusion of external gas into the sample gas path C.

[0064] As an example, the light source 37 can be one that can irradiate measurement light with a wavelength of 200 nm or more and 800 nm or less. The light source 37 may be an LED light source or a laser light source.

[0065] The light receiving element 38 measures the intensity of the measurement light that has passed through the detection element 36 from the sample gas path C and reached the light receiving path L, converts it into a voltage signal, and outputs the voltage signal. As the light receiving element 38, any light receiving element capable of measuring the intensity of the measurement light can be adopted. An example of the light receiving element 38 is a photodiode or a photomultiplier tube.

[0066] A voltmeter 51 for measuring the voltage signal output from the light receiving element 38 is connected to the light receiving element 38. An arithmetic unit 52 for performing various arithmetic processes based on the measured voltage signal is connected to the voltmeter 51. The arithmetic unit 52 calculates the amount of change over time in the optical properties of the detection element 36 based on the amount of change in the intensity of the measurement light that has passed through the detection element 36 and reached the light receiving path L, and uses this amount of change over time to calculate the concentration of the gaseous impurity component (for example, the moisture concentration) accurately.

[0067] When detecting the concentration of the gaseous impurity component in the sample gas G using the measuring device 300, a sample gas inflow path C1 is connected to the upstream side of the sample gas path C through which the sample gas G flows, and a sample gas outflow path C2 is connected to the downstream side of the sample gas path C. As a result, the sample gas G flowing in from the upstream gas path into the sample gas inflow path C1 is introduced into the sample gas path C, and the sample gas G that has passed through the detection element 36 is led out from the sample gas outflow path C2 to the downstream gas path, so that the sample gas G always flows through the sample gas path C.

[0068] With the sample gas G flowing, the light source 37 is activated to irradiate the measurement light of a preset intensity in the sample gas path C from the measurement optical path P through the convex light-transmitting member 43. At the same time, the measurement light that has passed through the detection element 36 and the flat light-transmitting member 41 is received by the light-receiving element 38, converted into a measurement voltage corresponding to the intensity of the received measurement light, and output to the voltage measurement unit 51. The voltage measurement unit 51 outputs voltage information to the calculation unit 52. Based on this voltage information, the calculation unit 52 outputs the concentration of the gaseous impurity component (detection result) to a display device (not shown) such as a monitor or a printer. The calculation unit 52 can calculate the accurate concentration of the gaseous impurity component by using the relational expression between the intensity (voltage) of the measurement light at the light-receiving element 38 and the concentration of the gaseous impurity component (for example, moisture concentration) created in advance.

Example

[0069] Hereinafter, based on the examples, the manufacturing method of the porous metal complex-containing film according to the present embodiment will be described.

[0070] (Example 1) The precursor solution was prepared as follows.

[0071] First, 25 mL of ethanol manufactured by Tokyo Chemical Industry Co., Ltd. as the first polar solvent was weighed into a container (made of perfluoroalkoxyalkane), and trimesic acid (benzene-1,3,5-tricarboxylic acid) manufactured by Kanto Chemical Co., Inc. was added and stirred to dissolve. Next, copper nitrate trihydrate manufactured by Kanto Chemical Co., Inc. was further added and stirred to dissolve to prepare a precursor solution. The amount of copper nitrate trihydrate added was such that the molar ratio of copper nitrate trihydrate to benzene-1,3,5-tricarboxylic acid was 1.81.

[0072] Next, the filter was cut into a predetermined shape, and the cut filter was impregnated with the precursor solution. First, a circular polytetrafluoroethylene filter (PF100 manufactured by ADVANTEC) with a thickness of 1 mm and a diameter of 70 mm was punched out with a 7-mm diameter punching punch to obtain a circular filter with a diameter of 7 mm. Then, after impregnating the cut filter with acetone, which is the same as the first polar solvent, as the third polar solvent, the precursor solution was impregnated to obtain a precursor-impregnated membrane.

[0073] Next, with the precursor-impregnated membrane placed stationary in a glass petri dish, this petri dish was placed in a heating furnace capable of supplying gas from the outside and heated at 80 °C for 2 hours.

[0074] After this heat treatment, the precursor-impregnated membrane was transferred to a 100-mL glass eggplant flask. Then, the mouth of this eggplant flask was closed with a silicon stopper connected to a vacuum tube, and the vacuum tube was connected to a rotary pump. Thereafter, while heating the eggplant flask to 100 °C in an oil bath, suction was performed with a vacuum pump to evacuate the inside of the eggplant flask, and vacuum heating (vacuum drying) was performed for 8.5 hours to obtain a post-heat-treatment membrane.

[0075] Furthermore, 20 ml of ethanol was added to the eggplant flask containing the post-heat-treatment membrane, a Dimroth condenser was installed, and the operation of refluxing while heating to 40 °C was performed for 1 hour to wash the post-heat-treatment membrane. The ethanol after heating and refluxing was discarded from the eggplant flask. This washing operation was repeated 3 times to obtain a post-washing membrane. The post-washing membrane was further dried in an eggplant flask set at 80 °C for 24 hours to obtain a dried membrane.

[0076] When the particle size distribution of the porous metal complex contained in this dried membrane was determined by image observation using a scanning electron microscope, d50 was 0.1 μm. Also, d20 (cumulative 20% particle size) was 0.05 μm and d80 (cumulative 80% particle size) was 0.25 μm. Thus, it was found that the porous metal complex-containing membrane according to this example contains fine crystals with d50 of 0.1 μm. Also, it was found that it contains a porous metal complex with a narrow (sharp) particle size distribution with a small difference between d20 and d80.

[0077] Furthermore, this dry film was subjected to an adsorption / desorption process to obtain the porous metal complex-containing film according to this example. In this example, as the adsorption / desorption process, the dry film was exposed to 10 vppm (volume ppm) of water vapor accompanied by helium gas for 10 min, and then, the adsorption / desorption treatment cycle of exposing it to helium gas not containing water vapor for 1 day was repeated 50 times.

[0078] The impurity content in this porous metal complex-containing film was 150 wtppm, which was extremely low. The amount of impurities in the porous metal complex-containing film was measured as follows using an inductively coupled plasma mass spectrometer (ICP-MS, manufactured by Agilent Technologies, model: 7500cs), an inductively coupled plasma optical emission spectrometer (ICP-OES, manufactured by Thermo Fisher Scientific, model: iCAP-3000), a flame atomic absorption spectrophotometer (FAAS, manufactured by PerkinElmer, model: PinAAcle 500), a high-performance liquid chromatograph analyzer (HPLC, manufactured by Dionex, model: Ultimate 3000), a liquid chromatography-mass spectrometer (LC-MS, manufactured by Shimadzu Corporation, model: LCMS-2050), a gas chromatography-mass spectrometer (GC-MS, manufactured by Shimadzu Corporation, model: GC-2010), a gas chromatograph equipped with a thermal conductivity detector (GC-TCD, manufactured by Shimadzu Corporation, model: GC-8A), a gas chromatograph equipped with a pulsed discharge detector (GC-PDD, manufactured by Shimadzu Corporation, model: GC-14B), and a thermogravimetric differential thermal analyzer (TG-DTA, manufactured by Shimadzu Corporation, model: DTG-60). The gas components and organic solvent components were released as gas components by heat-treating the porous metal complex-containing film. Also, the metal components and ion components were dissolved from the porous metal complex-containing film with an acid and an organic solvent and separated as a solution. Then, the content of each component in the gas and the content of each component in the solution were quantified using the above-mentioned respective devices. As impurities, ethanol, benzene-1,3,5-tricarboxylic acid, copper nitrate, hydrogen, carbon monoxide, and carbon dioxide were detected. Copper nitrate was detected by FAAS. Benzene-1,3,5-tricarboxylic acid was detected by a liquid chromatograph analyzer. Ethanol was detected by TG-DTA. The other gas components were detected by GC-MS.

[0079] Next, the performance was evaluated when 30 porous metal complex-containing films according to this example were used as a detection element (humidity sensor) for measuring the moisture concentration in gas. This performance evaluation was performed based on the amount of variation in the baseline over one month and the amount of variation in the response intensity. In this performance evaluation, the smaller these amounts of variation, the better, and it is determined that the performance is high.

[0080] In addition, for the test for this evaluation (hereinafter simply referred to as the evaluation test), a measuring device according to the measuring device 300 shown in FIG. 3 was used. Then, the variation over one month of the baseline and response intensity of the sensing element was confirmed when the porous metal complex-containing film according to this example was used as the sensing element for detecting the trace moisture concentration in the sample gas.

[0081] Other conditions for this evaluation test were determined as follows.

[0082] An LED lamp (OSB5XNE1C1E, manufactured by OptoSupply) was used as the light source, and a photosensor (TSL-257, manufactured by AMS-TAOS USA) was used as the light-receiving element.

[0083] As the sample gas, high-purity nitrogen gas (moisture concentration < 1 vppb (volume ppb)) and standard gas (nitrogen as the base gas and moisture concentration 1 vppm: manufactured by Taiyo Nippon Sanso JFP) were used.

[0084] In this evaluation test, while supplying high-purity nitrogen gas as the sample gas to the measurement unit, the absorbance value of the sensing element using the porous metal complex-containing film according to this embodiment was confirmed, and this was used as the baseline value.

[0085] Also, in this evaluation test, while supplying the above-mentioned standard gas as the sample gas to the measurement unit, the voltage value of the sensing element using the porous metal complex-containing film according to this embodiment was confirmed, and this was used as the response intensity.

[0086] In this evaluation test, the baseline value and the response intensity value were confirmed every 24 hours (at an interval of once a day). In this evaluation test, this confirmation was continued for 30 days (one month). The results are shown in FIGS. 4 and 5. Note that FIG. 4 shows a graph indicating the variation of the baseline value with respect to the number of elapsed days over one month. Also, FIG. 5 shows a graph indicating the variation of the response intensity with respect to the number of elapsed days over one month. In FIGS. 4 and 5, the baseline and the response intensity are shown as relative values with the value on the first day being 100%.

[0087] In the sensor element using the porous metal complex-containing film according to this example, the amount of variation in the baseline over one month was 0.1%. Also, the amount of variation in the response intensity at a moisture concentration of 1 vppm was 1.4%.

[0088] (Comparative Example 1) In this comparative example, it differed from Example 1 in that the adsorption / desorption step was omitted, and in other respects, a porous metal complex-containing film was obtained in the same manner as in Example 1 and evaluated.

[0089] The content of impurities in the porous metal complex-containing film according to this comparative example was 10,000 wtppm.

[0090] Graphs showing the variation in the baseline and the variation in the response intensity in the sensor element using the porous metal complex-containing film according to this comparative example are shown together in FIGS. 4 and 5, respectively. In the sensor element using the porous metal complex-containing film according to this comparative example, the amount of variation in the baseline over one month exceeded 6%. Also, the amount of variation in the response intensity at a moisture concentration of 1 vppm exceeded 18%.

[0091] As is clear from the comparison of the results of the variation in the baseline and the variation in the response intensity between the example and the comparative example, the sensor element using the porous metal complex-containing film according to the example has less variation in the baseline over time and less variation in the response intensity over time compared to that according to the comparative example, is good, and it can be seen that the performance is high from the viewpoint of stability. Thus, it was found that the porous metal complex-containing film described in this example, since the content of impurities is controlled to a small amount of 200 wtppm or less, can be a highly stable sensor element with little variation in the baseline and the response intensity when used as a sensor element such as a moisture sensor.

[0092] As described above, it is possible to provide a porous metal complex-containing film with a low content of impurities and a method for producing the same.

[0093] Note that the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope not departing from the object of the present invention.

Industrial Applicability

[0094] The present invention can be applied to a porous metal complex-containing film, a sensing element including the same, and a method for producing a porous metal complex-containing film.

Explanation of Signs

[0095] 100: Porous metal complex crystallization apparatus 11: Gas supply unit 12: Crystallization unit 13: Heating unit 14: Pump unit 200: Porous metal complex impurity removal apparatus 21: Gas supply unit 22: Steam supply unit 23: Steam valve unit 24: Dilution mixing unit 25: Treatment unit 30: Measurement unit 300: Measuring device 31: Light source side block 32: Light receiving side block 33: Central block 35: Sensing element holding unit 36: Sensing element 37: Light source 38: Light receiving element 41: Flat light transmissive member 42: Annular packing 43: Convex light transmissive member 44: Annular packing 51: Voltage measurement unit 52: Calculation unit C: Sample gas path C1: Sample gas inflow path C2: Sample gas outflow path G: Sample gas L: Light receiving path P: Measurement light path

Claims

1. A filter having voids inside and having light permeability and gas permeability, and a porous metal complex immobilized in the voids, wherein the porous metal complex includes metal ions and an organic ligand that coordinates with the metal ions, a porous metal complex-containing film having an impurity content of 200 wtppm or less.

2. The porous metal complex-containing film according to Claim 1, wherein the metal ions are copper ions, and the organic ligand is benzene-1,3,5-tricarboxylic acid.

3. The porous metal complex-containing film according to Claim 1, wherein the filter is cellulose fiber, glass fiber or polytetrafluoroethylene fiber.

4. The porous metal complex-containing film according to Claim 1, wherein the median diameter of the porous metal complex on a volume basis is 0.1 μm or more and 3 μm or less.

5. A method for producing a porous metal complex-containing film according to any one of Claims 1 to 4, comprising: a solution preparation step of mixing a first polar solvent, the organic ligand, and a metal salt to prepare a precursor solution of the porous metal complex; an impregnation step of impregnating the filter with the precursor solution to obtain a precursor-impregnated film; a heating step of heat-treating the precursor-impregnated film; a washing step of washing the precursor-impregnated film after the heating step with a second polar solvent to obtain a washed film; and an adsorption / desorption step of adsorbing and desorbing moisture to / from the washed film.

6. The method for producing a porous metal complex-containing film according to Claim 5, wherein the first polar solvent is methanol, ethanol, 1-propanol, 2-propanol, 1-butanol or 2-butanol.

7. The method for producing a porous metal complex-containing film according to Claim 5, wherein the metal salt is copper nitrate.

8. The method for producing a porous metal complex-containing film according to Claim 5, wherein the adsorption / desorption step performs a cycle of adsorbing and desorbing moisture to / from the washed film two or more times.

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