Gas separation membrane and method for manufacturing the same

Abstract

The present invention provides a gas separation membrane that has N2 / O2 gas selectivity and / or gas permeation rate equivalent to or better than conventional gas separation membranes, while also having N2 / CO2 (nitrogen / carbon dioxide) gas selectivity and / or gas permeation rate, as well as a method for manufacturing the same. [Solution] Some aspects of the present invention relate to a ferroelectric gas separation membrane comprising graphene oxide and / or graphene and ferroelectric fine particles.

Description

Technical Field

[0001] Some aspects of the present invention relate to gas separation membranes and methods for manufacturing the same.

Background Art

[0002] Conventionally, various studies have been conducted on gas separation membranes. For example, Patent Document 1 discloses a zeolite separation membrane formed by bonding zeolite microcrystals to each other, wherein the surface of each zeolite microcrystal is coated with graphene oxide, and the zeolite microcrystals are bonded without gaps through the graphene oxide, and a zeolite separation membrane formed by bonding zeolite microcrystals to each other, wherein the surface of each zeolite microcrystal is coated with graphene, and the zeolite microcrystals are bonded without gaps through the graphene.

[0003] Patent Document 2 discloses a composite characterized by containing graphene oxide and a porous polymer metal complex.

[0004] Patent Document 3 discloses a coating step of coating zeolite microcrystals with graphene oxide in an aqueous dispersion (I) containing zeolite microcrystals, graphene oxide, and a charge adjuster, and a method for manufacturing a zeolite gas separation membrane, wherein the zeta potential of an aqueous dispersion (II) containing graphene oxide and a charge adjuster having the same concentration as the aqueous dispersion (I) is -5 mV to 8 mV.

[0005] Patent Document 4 discloses a zeolite gas separation membrane produced using graphene oxide and zeolite microcrystals, wherein the interlayer distance (d 001 ) measured by X-ray diffraction is 0.88 to 0.94 nm.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] Separating gases from the atmosphere offers significant industrial advantages. For example, high concentrations of oxygen can improve the combustion efficiency of boilers and other machinery, and increase the output of internal combustion engines and fuel cells. Enriching the atmosphere with high concentrations of carbon dioxide (around 800 ppm) can improve plant growth.

[0008] In other words, the industrial sector desires materials that can separate N2 / O2 gas for oxygen enrichment and N2 / CO2 gas for carbon dioxide enrichment.

[0009] Therefore, some aspects of the present invention aim to provide a gas separation membrane having N2 / CO2 (nitrogen / carbon dioxide) gas selectivity and / or gas permeation rate that is equal to or better than that of conventional gas separation membranes, as well as a method for manufacturing the same. [Means for solving the problem]

[0010] Therefore, the inventors investigated various means to solve the above problems. The inventors found that by using barium titanate, a ferroelectric material, instead of zeolite, which was conventionally used as a material, in a gas separation membrane, the resulting gas separation membrane has an N2 / O2 gas selectivity and / or gas permeation rate that is equal to or better than that when zeolite is used, as well as an excellent N2 / CO2 gas selectivity and / or gas permeation rate, and thus completed several embodiments of the present invention.

[0011] In other words, the gist of some aspects of the present invention is as follows: (1) A ferroelectric gas separation membrane comprising graphene oxide and / or graphene and ferroelectric nanoparticles. (2) The ferroelectric gas separation membrane according to (1), wherein the content of graphene oxide and / or graphene is in the range of 10% by mass or more and 70% by mass or less with respect to the total mass of the ferroelectric gas separation membrane. (3) The ferroelectric gas separation membrane according to (1) or (2), wherein the surface of the ferroelectric fine particles is coated with graphene oxide and / or graphene, and the ferroelectric fine particles are bonded to each other via graphene oxide and / or graphene. (4) The ferroelectric gas separation membrane according to any one of (1) to (3), wherein the ferroelectric fine particles contain barium titanate. (5) A method for producing a ferroelectric gas separation membrane, comprising the steps of: (i) preparing a dispersion A by dispersing ferroelectric fine particles and graphene oxide in an aqueous solution; (ii) depositing graphene oxide on the surface of ferroelectric fine particles in dispersion A to obtain a dispersion B of ferroelectric fine particles coated with graphene oxide; (iii) separating the ferroelectric fine particles coated with graphene oxide from dispersion B to obtain a ferroelectric gas separation membrane in which the ferroelectric fine particles are interconnected via graphene oxide; (iii') separating the ferroelectric fine particles coated with graphene oxide from dispersion B and reducing the graphene oxide to obtain a ferroelectric gas separation membrane in which the ferroelectric fine particles are interconnected via graphene; or (iii'') obtaining a dispersion C by reducing the ferroelectric fine particles coated with graphene oxide in dispersion B to ferroelectric fine particles coated with graphene, and then separating the graphene-coated ferroelectric fine particles from dispersion C to obtain a ferroelectric gas separation membrane in which the ferroelectric fine particles are interconnected via graphene. A method for producing a ferroelectric gas separation membrane as described in (5), wherein a charge adjusting agent is added in step (6)(ii). [Effects of the Invention]

[0012] According to some aspects of the present invention, there are provided a gas separation membrane having an N2 / O2 gas selectivity and / or gas permeation rate equal to or higher than those of a conventional gas separation membrane and an N2 / CO2 gas selectivity and / or gas permeation rate, and a method for producing the same.

Brief Description of the Drawings

[0013] [Figure 1] It is an optical microscope image of a barium titanate dispersion liquid that has been subjected to pretreatment of untreated, grinding in a mortar, ultrasonic irradiation, or grinding in a mortar and ultrasonic irradiation with respect to barium titanate. [Figure 2] It is a SEM image of barium titanate that has been ground in a mortar and then subjected to ultrasonic irradiation for 10 minutes. [Figure 3] It is a graph showing the relationship between the apparent number of graphene layers and the selectivity (N2 / O2) and N2 permeation rate. [Figure 4] It is a graph showing the relationship between the N2 permeation rate and the selectivity (N2 / O2) (A) or the selectivity (N2 / CO2) (B).

Modes for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of some aspects of the present invention will be described in detail. In this specification, the features of some aspects of the present invention will be described with reference to the drawings as appropriate. Note that the gas separation membrane and the method for producing the same according to some aspects of the present invention are not limited to the following embodiments, and various forms in which those skilled in the art can make changes, improvements, etc. without departing from the gist of some aspects of the present invention can be implemented.

[0015] (Ferroelectric gas separation membrane) The ferroelectric gas separation membrane according to some embodiments of the present invention generally has a structure in which the surface of ferroelectric fine particles is coated with graphene oxide and / or graphene, and the ferroelectric fine particles are bonded to each other (both in the planar direction and in the stacking direction) via the graphene oxide and / or graphene. The ferroelectric gas separation membrane according to some embodiments of the present invention has a function of separating a mixed gas or the like by utilizing the minute pore structure provided in the ferroelectric fine particles, and is formed in a sheet-like form in which the ferroelectric fine particles are bonded without gaps.

[0016] Ferroelectric fine particles are fine particles composed of a ferroelectric material and are not limited. Examples of the ferroelectric fine particles include barium titanate (BaTiO3), lead zirconate titanate Pb(Zr,Ti)O3, strontium bismuth tantalate (SrBi2Ta2O9), and the like. The ferroelectric fine particles may be a mixture of two or more of the materials listed above.

[0017] The average particle diameter of the ferroelectric fine particles is not limited. The ferroelectric fine particles are coated with a plurality of graphene oxide and / or graphene (having a size of about 10 nm to several tens of nm) as described in detail below. Therefore, the average primary particle diameter measured by SEM of the powder of the ferroelectric fine particles is usually in the range of 20 nm or more and 3 μm or less, in one embodiment in the range of 30 nm or more and 1 μm or less, in one embodiment in the range of 40 nm or more and 500 nm or less, and in one embodiment in the range of 50 nm or more and 300 nm or less. The ferroelectric fine particles may be a mixture of separate ferroelectric fine particle powders having an average particle diameter within the above range.

[0018] The ferroelectric gas separation membrane according to some embodiments of the present invention generally includes an inclusion body having a structure in which ferroelectric fine particles are included in graphene oxide and / or graphene. The ferroelectric fine particles included in graphene oxide and / or graphene are usually obtained by including the ferroelectric fine particles in graphene oxide and then optionally reducing the graphene oxide after the inclusion. [[ID=1,13]] [[ID=2,14]]

[0019] [[ID=3,15]] The graphene oxide and / or graphene in some embodiments of the present invention are not limited. The graphene oxide (graphene compounds) may be commercially available graphene oxide (graphene compounds), or it may be prepared by the improved Hammers method, for example, the method disclosed in "Daniela C. Marcano, Dmitry V. Kosynkin, Jacob M. Berlin, Alexander Sinitskii, Zhengzong Sun, Alexander Slesarev, Lawrence B. Alemany, Wei Lu, and James M. Tour Improved Synthesis of Graphene Oxide. ACS Nano 2010, 4, 8, 4806-4814" or by the method disclosed in the examples. Furthermore, a negatively charged state of graphene oxide is necessary for coating the surface of ferroelectric nanoparticles, as described later, but this negatively charged state varies greatly depending on the type and amount of oxygen functional groups (hydroxyl groups, epoxy groups, carbonyl groups, carboxylic acid groups, etc.) that constitute the graphene oxide. Therefore, it is preferable to appropriately adjust the type and amount of oxygen functional groups in graphene oxide according to the charged state of the ferroelectric nanoparticles. For example, the modified Brodie's method described in "Tatsuki Tsugawa, Kazuto Hatakeyama, Junko Matsuda, Michio Koinuma, and Shintaro Ida. Synthesis of Oxygen Functional Group-Controlled Monolayer Graphene Oxide. Bulletin of the Chemical Society of Japan, Volume 94, Issue 9, September 2021, Pages 2195-2201" is a method that can selectively produce graphene oxide containing many epoxy groups with a low negative charge, and such graphene oxide may be used. Graphene (graphene compounds) are compounds obtained by reducing graphene oxide (graphene compounds). The reduction method is well known in the art and will be described in detail below.

[0020] The content of graphene oxide and / or graphene is not limited, but is typically in the range of 10% to 70% by mass, and in one embodiment, in the range of 20% to 55% by mass, relative to the total mass of the ferroelectric gas separation membrane.

[0021] A ferroelectric gas separation membrane according to some aspects of the present invention may consist only of ferroelectric fine particles and graphene oxide and / or graphene.

[0022] Furthermore, the graphene oxide and / or graphene are not arranged continuously between the ferroelectric nanoparticles. The graphene oxide and / or graphene are smaller than the ferroelectric nanoparticles, and the surface of the ferroelectric nanoparticles is coated with multiple layers of graphene oxide and / or graphene.

[0023] Furthermore, the graphene oxide and / or graphene coating the ferroelectric nanoparticles are far larger than the pores of the ferroelectric nanoparticles and do not affect the molecular separation effect based on the pore structure of the ferroelectric nanoparticles. In addition, the ferroelectric gas separation membrane may be used supported on a support such as alumina that has pores larger in diameter than the pores of the ferroelectric gas separation membrane.

[0024] The apparent number of graphene oxide and / or graphene layers coating the ferroelectric nanoparticles is not limited. "Apparent number of layers" refers to the apparent number of layers of graphene oxide and / or graphene coating on the surface of the ferroelectric nanoparticles, calculated by the method described below. The apparent number of layers is typically in the range of 1 to 50 layers, in one embodiment in the range of 2 to 35 layers, in one embodiment in the range of 5 to 30 layers, and in one embodiment in the range of 10 to 25 layers.

[0025] Ferroelectric gas separation membranes according to some embodiments of the present invention have superior nitrogen permeability compared to oxygen, and can therefore be used to separate oxygen and nitrogen from a mixed gas containing oxygen and nitrogen, such as air. Furthermore, ferroelectric gas separation membranes have few defects such as cracks, resulting in high separation efficiency. The phrase "ferroelectric nanoparticles are bonded" means that the ferroelectric nanoparticles are densely bonded via graphene oxide and / or graphene, maintaining the separation function based on the pore structure of the ferroelectric nanoparticles, that is, the separation membrane is constructed in a state where defects such as cracks that impair the separation function of the ferroelectric nanoparticles are eliminated.

[0026] A membrane capable of separating oxygen and nitrogen, which have similar molecular sizes, and moreover, a membrane capable of separating them by allowing the larger nitrogen molecule to pass through, is extremely difficult to realize with conventional technology. Therefore, ferroelectric gas separation membranes in several embodiments of the present invention are highly useful. The reason for this is not clear, but the inventors believe that coated graphene obtained by reducing graphene oxide has many holes (nanopus windows), and that polar functional groups present around the holes (edges) cause a charge imbalance within the holes. There is a difference in the quadrupole moment related to electrostatic interaction between nitrogen molecules and oxygen molecules, and the instantaneous polarization (instantaneous dipole) is larger for nitrogen molecules. For this reason, it is presumed that nitrogen molecules can more easily pass through the holes in graphene where the charge imbalance exists.

[0027] The gas permeability of ferroelectric gas separation membranes according to some embodiments of the present invention can be evaluated, for example, by measuring the amount of gas permeation using a ferroelectric gas separation membrane formed into a flat plate shape (for example, a flat plate with a thickness of typically 100 μm to 200 μm). By flowing nitrogen and oxygen through the separation membrane individually and measuring the permeation time when a unit amount of gas permeates through the separation membrane, the permeation rate (e.g., transmittance, permeation coefficient) of each gas type can be calculated.

[0028] Furthermore, the selectivity of the permeate gas in a ferroelectric gas separation membrane according to some embodiments of the present invention can be calculated by the following formula. The selectivity of the permeate gas is also referred to as "gas selectivity" or simply "selectivity". The gas selectivity (N2 / O2) of a ferroelectric gas separation membrane is calculated as follows: [permeation rate of nitrogen] / [permeation rate of oxygen] The gas selectivity (N2 / CO2) of a ferroelectric gas separation membrane is calculated as follows: [permeation rate of nitrogen] / [permeation rate of carbon dioxide]

[0029] (Method for manufacturing ferroelectric gas separation membranes) A method for producing a ferroelectric gas separation membrane according to some aspects of the present invention includes the steps of: (i) preparing a dispersion A by dispersing ferroelectric fine particles and graphene oxide in water; (ii) depositing graphene oxide on the surface of ferroelectric fine particles in dispersion A to obtain a dispersion B of ferroelectric fine particles coated with graphene oxide; (iii) separating the graphene oxide-coated ferroelectric fine particles from dispersion B to obtain a ferroelectric gas separation membrane in which the ferroelectric fine particles are bonded to each other via graphene oxide; (iii') separating the graphene oxide-coated ferroelectric fine particles from dispersion B and reducing the graphene oxide to obtain a ferroelectric gas separation membrane in which the ferroelectric fine particles are bonded to each other via graphene; or (iii'') obtaining a dispersion C by reducing the graphene oxide-coated ferroelectric fine particles in dispersion B to graphene-coated ferroelectric fine particles, and then separating the graphene-coated ferroelectric fine particles from dispersion C to obtain a ferroelectric gas separation membrane in which the ferroelectric fine particles are bonded to each other via graphene.

[0030] Before performing the coating step in (ii), a step to eliminate aggregation of ferroelectric nanoparticles may be included. For example, commercially available ferroelectric nanoparticles may be aggregated (secondary aggregation), but in such cases, the aggregates can be loosened. For example, by adding a small amount of water to commercially available ferroelectric nanoparticles and irradiating them with ultrasound, aggregation can be suitably eliminated and a dispersion of ferroelectric nanoparticles can be obtained. When irradiating with ultrasound, the ultrasonic intensity can be set to about 100W to 200W and the irradiation time to about 5 to 20 minutes, depending on the amount of ferroelectric nanoparticles.

[0031] The coating step in (ii) can be carried out, for example, by adding graphene oxide and optionally a charge modifier to the ferroelectric microparticle dispersion obtained by the ultrasonic treatment described above, and then mixing and stirring. The content of ferroelectric microparticles in the ferroelectric microparticle dispersion is not limited, but is usually in the range of 0.1% to 50% by weight, and in one embodiment, in the range of 1% to 30% by weight, relative to the total mass of the ferroelectric microparticle dispersion. Over time after addition, graphene oxide coats the ferroelectric microparticles. In this coating step, the homogenization of the graphene oxide coating state and the apparent number of layers can be adjusted by adjusting the amount of ferroelectric microparticles, the amount of graphene oxide added, and optionally the amount of charge modifier added. The apparent number of layers of graphene oxide can be calculated using the following formula. The aforementioned "homogenization of the coating state" refers to a state in which graphene oxide is evenly coated over the entire surface of the ferroelectric microparticles without any aggregation of graphene oxide on a part of the surface of the ferroelectric microparticles.

[0032] Apparent number of layers = S GO / S 強誘電体微粒子 S GO : Surface area of ​​graphene oxide S GO =[Amount of graphene oxide added (g)] / [Graphene density (2.05 g / cm³)] 3 ) × Graphene layer thickness (0.35nm)] S 強誘電体微粒子 : Outer surface area of ​​ferroelectric nanoparticles

[0033] In some embodiments of the present invention, in step (ii), a charge modifier may be added to dispersion A as described above. The charge modifier is not limited. Examples of charge modifiers include water-soluble salts, specifically inorganic salts such as ammonium chloride, sodium chloride, and potassium chloride, and organic salts such as sodium acetate, ammonium acetate, and sodium oxalate. The concentration of the charge modifier is not limited. The concentration of the charge regulator is typically in the range of 0.001 mol (charge regulator) / g (graphene oxide) to 0.5 mol (charge regulator) / g (graphene oxide) when a charge regulator is added. In one embodiment, the range is 0.01 mol (charge regulator) / g (graphene oxide) to 0.5 mol (charge regulator) / g (graphene oxide). In another embodiment, the range is 0.02 mol (charge regulator) / g (graphene oxide) to 0.1 mol (charge regulator) / g (graphene oxide). In yet another embodiment, the range is 0.03 mol (charge regulator) / g (graphene oxide) to 0.08 mol (charge regulator) / g (graphene oxide).

[0034] In conventional manufacturing methods for zeolite separation membranes, charge modifiers are used. These agents prevent electrostatic repulsion between negatively charged zeolite microcrystals and similarly negatively charged graphene oxide or graphene, thereby facilitating the coating of graphene oxide or graphene on the surface of the zeolite microcrystals. On the other hand, ferroelectric nanoparticles composed of ferroelectric materials according to some embodiments of the present invention, such as barium titanate, possess a slight positive charge in acidic aqueous solutions. Therefore, in the case of ferroelectric nanoparticles, such as barium titanate, the surface of the ferroelectric nanoparticles can be coated with graphene oxide and / or graphene without the use of a charge modifier. Consequently, the use of a charge modifier is not essential in some manufacturing methods of the present invention. However, the use of a charge modifier can contribute to homogenization of the graphene oxide coating on the ferroelectric nanoparticles, stabilization of the resulting inclusion complex, and its role as an inclusion between the surface of the ferroelectric nanoparticles, such as barium titanate, and the graphene oxide and / or graphene.

[0035] In some aspects of the present invention, ferroelectric nanoparticles are coated with graphene oxide by electrostatic interactions between the particles, so that ferroelectric nanoparticles that do not bond (integrate) with each other on their own will bond with each other via graphene oxide.

[0036] In some embodiments of the present invention, a method for producing a ferroelectric gas separation film may be performed in step (iii) after the coating step in (ii), or in step (iii') after separation and then reduction of graphene oxide to graphene, or in step (iii'') after reduction and then separation. By performing the reduction step, graphene-coated ferroelectric nanoparticles (graphene-encapsulated ferroelectric nanoparticles) can be obtained.

[0037] Methods for reducing graphene oxide back to graphene include, for example, the dry method in step (iii') and the wet method in step (iii''), both of which involve exposing ferroelectric nanoparticles coated with graphene oxide to a reducing atmosphere to reduce graphene.

[0038] In the dry method, the graphene oxide-encapsulated ferroelectric nanoparticles (ferroelectric nanoparticles coated with graphene oxide) obtained in the coating process are dried, and then reduced by heat treatment. The atmosphere during heat treatment is preferably a vacuum or an inert gas (nitrogen, noble gas, e.g., argon), but any low oxygen level is acceptable, and heating may be performed while flowing dry air to prevent the graphene from burning or disappearing. The heating temperature is usually 300°C to 400°C, and in one embodiment it is 340°C to 380°C. Furthermore, the drying treatment before reduction should be performed to reduce the bulk density so that the reduction reaction in the reduction treatment can proceed easily, for example, by freeze-drying or spray-drying.

[0039] In the wet process, a reducing agent is added to a dispersion of graphene oxide inclusion ferroelectric fine particles obtained in the coating process. The reducing agent added to the dispersion can be an organic substance such as hydrazine, formic acid, oxalic acid, or gallic acid, or an inorganic substance such as sodium borohydride or diisobutylaluminum hydride.

[0040] In some embodiments of the present invention, a method for producing a ferroelectric gas separation membrane may be obtained by forming graphene-encapsulated ferroelectric fine particles after the reduction step.

[0041] There are no particular limitations on the method for forming graphene-encapsulated ferroelectric nanoparticles, and they can be formed into desired shapes by various molding methods. For example, the dried graphene-encapsulated ferroelectric nanoparticles can be compressed directly to form a flat plate, or the dispersion can be filtered through a porous support (filter) such as filter paper to form a sheet.

[0042] Alternatively, in some embodiments of the present invention, a graphene-encapsulated ferroelectric gas separation membrane can be formed by first forming graphene oxide-encapsulated ferroelectric fine particles into a sheet on a support (filter) before reduction, and then performing a reduction treatment. [Examples]

[0043] The following describes some embodiments of the present invention, but it is not intended to limit the embodiments of the present invention to those shown in these embodiments.

[0044] 1. Preparation of barium titanate inclusion of graphene oxide 1-1. Preparation of barium titanate The particle size of barium titanate should be small. This is because smaller particle sizes result in a greater number of barium titanate / graphene interfaces within the barium titanate gas separation membrane, which facilitates the gas separation mechanism and increases the permeability of gas molecules.

[0045] Figure 1 shows optical microscope images of barium titanate dispersions pretreated with grinding in an agate mortar and / or ultrasonic irradiation. Untreated barium titanate was in a state where dozens of particles were aggregated, but grinding dissolved the aggregates to a certain extent, and further irradiation with ultrasound for 10 minutes resulted in aggregates of only a few particles, and the proportion of single particles increased.

[0046] Figure 2 shows SEM images of barium titanate after grinding in an agate mortar and subsequent 10 minutes of ultrasonic irradiation. The primary particles of barium titanate were approximately 300 nm in size with clearly defined crystal corners, and had a structure resembling a stacking of partially plate-like particles.

[0047] 1-2. Preparation of graphene oxide Graphene oxide was produced using graphite from Madagascar, following the modified Hammers process. 1. Put graphite (2g) into a beaker. 2. Sulfuric acid (98%, 80 mL) and phosphoric acid (9 mL) were added to a beaker. 3. Add potassium permanganate (10g) to the beaker. 4. Stirred at approximately 38°C for 4 hours at 250 rpm. 5. After stirring, it was diluted with water. 6. Hydrogen peroxide (15%, 40 mL) was added. It was washed five times with 7.5% hydrochloric acid solution. 8. Washed with water five times. 9. The graphene oxide dispersion (GO dispersion) (GOD) in the supernatant was collected.

[0048] 1-3. Preparation of barium titanate inclusion of graphene oxide By adding a predetermined amount of graphene oxide to an aqueous dispersion containing barium titanate powder and dispersing it, the barium titanate could be coated with graphene oxide. Similarly, by adding the aforementioned charge adjusting agent, barium titanate coated with graphene oxide could also be prepared.

[0049] 2. Evaluation of barium titanate inclusion of graphene oxide 2-1. Zeta potential of dispersion of graphene oxide-encapsulated barium titanate particles To evaluate the inclusion state of barium titanate by graphene oxide (GO), the properties of a GO-inclusionated barium titanate dispersion were assessed. Table 1 shows the inclusion conditions, the pH of the dispersion, and the zeta potential of the GO-inclusionated barium titanate complex.

[0050] [Table 1]

[0051] The pH of the dispersion decreased as the amount of GO added increased. The addition of ammonium chloride had little effect because the amount added was small. The zeta potential of the GO-clad barium titanate inclusion complex did not depend on the amount of GO added, but the absolute value of the zeta potential increased when ammonium chloride was added. In particular, the zeta potential was large, around -50mV, in the dispersion sample where a homogeneous precipitate had formed. It is thought that the addition of ammonium chloride increased the absolute value of the zeta potential of the GO-clad barium titanate particles, making aggregation less likely. The zeta potential of the GO-clad barium titanate dispersion did not change with pH even after several days, suggesting that the inclusion complex was in a stable colloidal state.

[0052] 2-2. Measurement of gas permeation rate and selectivity As measurement samples, dried barium titanate inlaid with graphene oxide, prepared according to the method described in "1-3. Preparation of Graphene Oxide-Inlaid Barium Titanate" and the conditions described in Table 2 below, was subjected to reduction treatment. The resulting barium titanate powder was compressed by hand press, and the resulting flat plate-shaped film was fixed to an acrylic plate with fine holes using adhesive. In Examples 1 to 14, as mentioned above, barium titanate with an average primary particle diameter of about 300 nm was used, while in Examples 15 to 18, barium titanate with an average primary particle diameter of about 50 nm was used. Comparative Examples 1 and 2 used the examples described in Japanese Patent Application Publication No. 2024-6292, and Comparative Example 3 was prepared in the same manner as the examples, using dried graphene-inlaid zeolite prepared according to the conditions described in Table 3 below, referencing the N2 and CO2 permeation test example described in Science Advances Vol 8, Issue 20.

[0053] Nitrogen, oxygen, or carbon dioxide were flowed individually through the gas separation membranes of the examples and comparative examples, and the permeation time for a unit amount of gas to permeate the separation membrane was measured to calculate the permeability and permeation coefficient of each gas type. The temperature of the measurement atmosphere (15-25°C in the examples) and atmospheric pressure were also measured, and the area of ​​the gas separation membrane was measured. From these, the gas permeability and permeation coefficient were calculated. The selectivity of the permeated gas was calculated using the following formula. The gas selectivity of a gas separation membrane (N2 / O2) = [nitrogen permeation rate] / [oxygen permeation rate] The gas selectivity of a gas separation membrane (N2 / CO2) = [permeation rate of nitrogen] / [permeation rate of carbon dioxide]

[0054] [Table 2]

[0055] [Table 3]

[0056] Figure 3 shows the relationship between the apparent number of layers of graphene, the selectivity (N2 / O2), and the N2 permeation rate. From Figure 3, it was found that the apparent number of layers, the selectivity (N2 / O2), and the N2 permeation rate change depending on the amount of ammonium chloride (Am) added as a charge modifier (0, 0.05 mol (NH4Cl) / g (GO), or 0.1 mol (NH4Cl) / g (GO)). From Figure 3, it was found that the N2 permeation rate tends to decrease as the number of layers increases. On the other hand, it was found that the selectivity (N2 / O2) can have a maximum value at a specific number of layers. Since it is preferable to have both a high selectivity (N2 / O2) and a high N2 permeation rate, it was found that it is preferable to appropriately adjust the number of layers according to the amount of charge modifier added.

[0057] Figure 4A shows the relationship between N2 permeation rate and selectivity (N2 / O2). From Figure 4A, it can be seen that the graphene-clad barium titanate of the examples has an N2 permeation rate and selectivity (N2 / O2) equivalent to that of graphene-clad zeolite. It was found that the nitrogen permeation rate can be further increased when the number of graphene layers is set to 12 to 24, especially 12 to 18, and / or when the amount of charge adjusting agent added (effective ammonium chloride amount Am, unit mol(NH4Cl) / g(GO)) is 0.05 to 0.2.

[0058] Figure 4B shows the relationship between N2 permeation rate and selectivity (N2 / CO2). From Figure 4B, it was found that the graphene-clad barium titanate in the examples had a higher selectivity (N2 / CO2) compared to the graphene-clad zeolite. Therefore, it was found that graphene-clad barium titanate is more effective at inhibiting carbon dioxide permeation than graphene-clad zeolite.

Claims

1. A ferroelectric gas separation membrane comprising graphene oxide and / or graphene and ferroelectric nanoparticles.

2. The ferroelectric gas separation membrane according to claim 1, wherein the content of graphene oxide and / or graphene is in the range of 10% by mass or more and 70% by mass or less, based on the total mass of the ferroelectric gas separation membrane.

3. The ferroelectric gas separation membrane according to claim 1, wherein the surface of the ferroelectric fine particles is coated with graphene oxide and / or graphene, and the ferroelectric fine particles are bonded to each other via graphene oxide and / or graphene.

4. The ferroelectric gas separation membrane according to any one of claims 1 to 3, wherein the ferroelectric fine particles include barium titanate.

5. (i) A step of preparing dispersion A by dispersing ferroelectric fine particles and graphene oxide in an aqueous solution, (ii) A step of depositing graphene oxide onto the surface of ferroelectric nanoparticles in dispersion A to obtain dispersion B of ferroelectric nanoparticles coated with graphene oxide, (iii) A step of separating ferroelectric nanoparticles coated with graphene oxide from dispersion B and obtaining a ferroelectric gas separation film in which the ferroelectric nanoparticles are interconnected via graphene oxide, (iii') A step of separating ferroelectric nanoparticles coated with graphene oxide from dispersion B and reducing the graphene oxide to obtain a ferroelectric gas separation film in which the ferroelectric nanoparticles are mutually bonded via graphene, or (iii'') A process to obtain dispersion C by reducing graphene oxide-coated ferroelectric nanoparticles in dispersion B to graphene-coated ferroelectric nanoparticles, and then separating the graphene-coated ferroelectric nanoparticles from dispersion C to obtain a ferroelectric gas separation membrane in which the ferroelectric nanoparticles are interconnected via graphene, and A method for manufacturing a ferroelectric gas separation membrane, including the method described above.

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