KR102480878B1 - Nanofiber composite material, manufacturing method thereof, and ion exchange membrane including the same - Google Patents

Abstract

One embodiment of the present invention provides a nanofiber composite material. The nanofiber composite material includes a nanofiber support, which is an assembly of nanofibers prepared using a mixture of a hydrophilic polymer and MXene; and an ionomer filled in the pores between the nanofibers of the nanofiber support. Another embodiment of the present invention provides an ion exchange membrane in which a nanofiber composite material is formed in a sheet shape. Another embodiment of the present invention provides a method for manufacturing a nanofiber composite material including a nanofiber support and an ionomer. In the manufacturing method of the nanofiber composite material, first, the Maxine-phase material is prepared from the Maxine-phase material (M _n+1 AX _n ). Thereafter, a solution in which the hydrophilic polymer material and the material of the MXene phase are mixed is prepared. Next, a nanofiber scaffold is formed through electrospinning using the solution. Then, the ionomer is filled in the nanofiber support.

Description

Nanofiber composite material, manufacturing method thereof, and ion exchange membrane having the same

The present invention relates to a nanofiber composite material, a manufacturing method thereof, and an ion exchange membrane including the same, and more particularly, to a nanofiber composite material having both excellent mechanical strength and electrochemical properties, a manufacturing method thereof, and an ion exchange membrane having the same will be.

Almost all minerals dissolved in water are ionized. When an electrode is inserted here and direct current flows, positive ions move to the negative electrode and negative ions move to the positive electrode. At this time, by using a cation and anion exchange membrane that selectively passes cations or anions, it is possible to separate ionic components and water, and this unit operation is called electrodialysis (ED). That is, by the permselective membrane of ions, one side of the membrane is diluted with a salt component and the other side is increased in concentration of the salt component. Such a permselective membrane mainly uses an ion exchange resin. However, since only charged substances (mainly ionic components) are removed in the electrodialysis method, there is an advantage in that relatively strict pretreatment is not required.

Reverse Electro-Dialysis (RED) is a blue energy technology that uses the difference in salinity between seawater and freshwater to generate electricity. As opposed to the electrodialysis process that uses electricity to treat solutions, it goes through the reverse process of desalination. It is a technology that produces energy.

1 is a diagram illustrating an example of a RED system.

In RED, an anion exchange membrane and a cation exchange membrane are alternately arranged between two electrodes (anode and cathode). A gasket and a spacer are inserted between the cation exchange membrane and the anion exchange membrane. As a result, a space between the membrane and the membrane is created, and seawater and freshwater flow along this space. At this time, as Na+ and Cl- ions present in seawater pass through the anion exchange membrane and the cation exchange membrane and move toward fresh water, current is generated.

The ion exchange membrane used in RED is slightly different from the ion exchange membrane used in general electrodialysis devices. In general electrodialysis (ED), the ion exchange membrane acts as a kind of resistor. If the ion exchange membrane acts as a resistor in a device for generating energy, the power that can be produced will be reduced. Therefore, in RED, a specially designed ion exchange membrane is used to minimize resistance in the ion exchange membrane.

2 is a view showing the structure of a general ion exchange membrane.

A general ion exchange membrane composed of a conventional ion exchange material/support layer structure or a thick membrane composed of a composite of a polymer and an ion exchange resin having a specific charge (see FIG. 2) is a device such as reverse electrodialysis (RED), fuel cells, etc. When ions have to move in a specific direction through the ion exchange membrane during operation, serious performance degradation may occur because the membrane has a structure in which it is physically difficult for ions to pass through.

In order to solve the above problem, simply removing the support from the layered ion exchange membrane or reducing the thickness of the polymer and ion exchange resin complex can improve the mobility of ions, but the basic mechanical properties are seriously deteriorated, resulting in poor practical usability. do.

Therefore, there is a need for a material or ion exchange membrane capable of preventing or suppressing deterioration of mechanical properties while having electrochemical properties and shapes suitable for applications such as RED.

A technical problem to be achieved by the present invention is to provide a nanofiber composite material having excellent mechanical properties while having electrochemical properties such as improved ion mobility, a manufacturing method thereof, and an ion exchange membrane including the same.

In addition, the technical problem to be achieved by the present invention is a functional cation exchange membrane having a structure suitable for the case where ions are exchanged and passed through an ion exchange membrane, rather than an ion exchange membrane in which exchanged ions are removed while adsorbed on the membrane, and the same It is to provide a manufacturing method.

In addition, the technical problem to be achieved by the present invention is to provide a new type of cellulose acetate/Maxene nanofiber-based ion exchange membrane different from the structure of conventional typical ion exchange membranes.

The technical problem to be achieved by the present invention is not limited to the above-mentioned technical problem, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In order to achieve the above technical problem, one embodiment of the present invention provides a nanofiber composite material. The nanofiber composite material includes a nanofiber support, which is an assembly of nanofibers prepared using a mixture of a hydrophilic polymer and MXene; and an ionomer filled in the pores between the nanofibers of the nanofiber support.

In an embodiment of the present invention, the nanofiber support may be formed in the form of a film as an aggregate of nanofibers formed by electrospinning a mixture of a hydrophilic polymer and MXene.

In an embodiment of the present invention, the nanofiber support is formed by randomly assembling the nanofibers, and due to the pores, interference with the movement of ions can be suppressed.

In an embodiment of the present invention, the hydrophilic polymer is cellulose acetate, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP) And it may include at least one of polysulfone (PSf).

In an embodiment of the present invention, the ionomer may include Nafion.

In an embodiment of the present invention, the nanofibers may have ion exchange properties by having a structure in which MXene particles or MXene nanosheets form chemical and physical bonds with each other to the hydrophilic polymer.

In an embodiment of the present invention, the total composition ratio of the MXene and the hydrophilic polymer in the nanofibrous scaffold may be 100 wt%, and the composition ratio of the MXene may be 1 wt% to 10 wt%.

In an embodiment of the present invention, the nanofibers include a material represented by M _n+1 X _n T _x , M is an early transition metal, Sc, Ti, V, Cr, Mn, At least one of Y, Zr, Nb, Mo, Hf, and Ta, X is at least one of carbon and nitrogen (n is an integer from 1 to 4), and T _x is It may be an oxygen functional group or a fluorine functional group.

In order to solve the technical problem of the present invention, another embodiment of the present invention provides an ion exchange membrane in which the nanofiber composite material is formed in a sheet shape.

In order to solve the technical problem of the present invention, another embodiment of the present invention provides a method for manufacturing a nanofiber composite material including a nanofiber support and an ionomer. In the manufacturing method of the nanofiber composite material, first, the Maxine-phase material is prepared from the Maxine-phase material (M _n+1 AX _n ). Thereafter, a solution in which the hydrophilic polymer material and the material of the MXene phase are mixed is prepared. Next, a nanofiber scaffold is formed through electrospinning using the solution. Then, the ionomer is filled in the nanofiber support.

In an embodiment of the present invention, the step of preparing the Maxine phase material from the Maxine phase material (M _n+1 AX _n ) is a mixed solution of hydrochloric acid (HCl), hydrofluoric acid (HF), hydrochloric acid and nitric acid (HNO ₃ ) , sodium hydroxide (NaOH), and lithium fluoride (LiF) using a solution of at least one of: etching a layer corresponding to element A from a material on Max (M _n+1 AX _n ); A Max powder from which the elemental layer was removed was mixed with dimethyl sulfoxide (DMSO), dichloromethane (DCM), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and ethyl acetate. Supported in at least one solvent (polar aprotic solvent) of (ethyl acetate, EtOAc), acetone, dimethylformamide (DMF), acetonitrile (ACN), and propylene carbonate (PC) weakening the bonding force between the layers made of a combination of M and X elements; and exfoliating each layer composed of a combination of M and X elements by applying physical energy to the material whose bonding force is weakened.

In an embodiment of the present invention, in the material of the Max (M _{n + 1} AX _n ) phase, M is a transition metal Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf, and Ta At least one of, A is one of group A elements including Al, Si, P, Ga, Ge, As, Cd, In, Sn, Sb, Tl, and Pb, and X (n is 1 to 3 integer) is one of carbon and nitrogen, and the material of the MXene phase is a material expressed as M _{n + 1} X _n T _x , M is an early transition metal, Sc, Ti, V, Cr, Mn , Y, Zr, Nb, Mo, Hf, at least one of Ta, X is at least one of carbon and nitrogen (n is an integer from 1 to 4), T _x is It may be an oxygen functional group or a fluorine functional group.

In an embodiment of the present invention, the manufacturing of the _MXene phase material may include removing a layer composed of group A elements from the _Maxene phase material; delamination of the layered structure by inserting a first molecule into the material from which the layer composed of the group A element is removed; and dispersing the material having a broken layer structure in a first solvent, and obtaining MXene nanosheets as a material on MXene from which the layers are separated (exfoliation) through a purification process after sonication treatment.

In an embodiment of the present invention, in the step of forming the nanofiber support through electrospinning, the concentration of the solution, the scanning speed of the solution, the diameter of the nozzle, and the gap between the nozzle and the collector during the electrospinning process. A solution in which the hydrophilic polymer material and the MXene phase material are mixed may be spun by adjusting the distance and the applied voltage.

In an embodiment of the present invention, in the step of forming the nanofiber support through electrospinning, the thickness of the nanofiber support film may be controlled according to the concentration and total amount of the spinning solution.

In an embodiment of the present invention, the step of forming the nanofiber support,

vacuum-drying the film made of the nanofiber support after the spinning is completed on the collector at a set temperature; and drying in vacuum, spraying and wetting the solvent on the membrane made of the nanofiber support, and separating the nanofiber support from the surface of the collector.

In an embodiment of the present invention, in the step of filling the nanofiber support with the ionomer, the ionomer includes Nafion, and the ionomer dissolved in alcohol is cast or dip coated. It can be filled in the pores of the nanofiber support.

According to an embodiment of the present invention, it is possible to provide a nanofiber composite material having excellent mechanical properties while having electrochemical properties such as improved ion mobility, a manufacturing method thereof, and an ion exchange membrane including the same.

According to an embodiment of the present invention, after forming MXene with high hydrophilicity, MXene is mixed with cellulose acetate, the mixture is electrospun to form a nanofiber scaffold, and the nanofiber scaffold is impregnated with ionomer to form a nanofiber composite. By manufacturing a material or an ion exchange membrane, a method for manufacturing a nanofiber composite material having an efficient and simple manufacturing process can be provided.

According to an embodiment of the present invention, a nanofiber composite material or ion exchange membrane having high water uptake and high mechanical strength due to nanofibers can be provided by applying the low sheet resistance and high hydrophilic properties of MXene to an ion exchange membrane.

The cation exchange membrane according to an embodiment of the present invention has a shape that mimics the concrete structure of a general building, can maintain minimum mechanical strength while making the thickness of the ion exchange membrane thin, and the structure of the nanofiber support itself is physically resistant to the movement of ions. changed so as not to interfere. Accordingly, the ionic conductivity was effectively improved, and excellent ion exchange amount and permselectivity were exhibited. This type of ion exchange membrane can be expected to have various applications in fields related to electrochemical energy production in the future.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a diagram illustrating an example of a RED system.
2 is a view showing the structure of a general ion exchange membrane.
3 is a view for explaining a nanofiber composite material or an ion exchange membrane including the same according to an embodiment of the present invention.
Figure 4 is a flow chart showing a method for manufacturing a nanofiber composite material according to an embodiment of the present invention.
5 is a schematic diagram showing a process of manufacturing Maxine (Ti ₃ C ₂ T _X ) nanosheets from Maxine (Ti ₃ AlC ₂ ) through continuous etching and exfoliation processes.
6 is a view showing an example of an electrospinning apparatus used when fabricating nanofibers using a cellulose acetate solution or a cellulose acetate/maxene solution.
7 is a view showing the results of physical property analysis of MXene nanosheets.
8 is a view showing the results of scanning electron microscopy of the actual appearance and arbitrary parts of a cellulose acetate nanofibrous membrane and a cellulose acetate/maxene nanofibrous membrane.
9 is a view showing the results of analyzing the binding characteristics between cellulose acetate and MXene by X-ray photoelectron spectroscopy (XPS).
10 is a view showing the tensile test results for CA nanofibrous membranes and CA / MXene nanofibrous membranes for each MXene content.
11 is a table comparing and analyzing basic physical properties and electrochemical properties of CA nanofibrous membranes and CA / MXene nanofibrous membranes by MXene content.
12 is a runner electron micrograph of a sample dried by filling Nafion as an ion exchange filler in a CA/MXene nanofibrous membrane.
13 is a diagram showing the tensile strength of a cellulose acetate/Maxene nanofiber composite membrane filled with Nafion and its control group.
14 is a diagram showing the surface zeta potential of Nafion-filled cellulose acetate/Maxene nanofiber composite membranes and their controls.
15 is a comparative analysis table of physical/electrochemical properties between a cellulose acetate/Maxene nanofiber composite membrane filled with Nafion and its control group.

Since the present invention may have various changes and various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals have been used for like elements throughout the description of each figure.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail.

3 is a view for explaining a nanofiber composite material or an ion exchange membrane including the same according to an embodiment of the present invention.

The nanofiber composite material 10 includes a nanofiber support 20 and an ionomer 30 filled in the nanofiber support 20 .

The nanofiber support 20 may be formed by randomly gathering the nanofibers 21 . For example, nanofibers 21 may be randomly formed by electrospinning to form a kind of skeleton. The ionomer 30 may be filled in the voids 22 between the nanofibers of the nanofiber 21 scaffold (nanofiber support).

In this embodiment, the nanofiber support 20 may be formed through electrospinning using a cellulose acetate/MXene material. Accordingly, in the nanofiber composite material, due to the MXene characteristics, the nanofiber 21 itself may basically have ion exchange characteristics.

In this embodiment, Nafion, which has been verified to have excellent cationic properties, is used as the ionomer 30. A film may be formed by filling the pores 22 of the nanofiber support 20 with the ionomer 30 .

Since it is formed by filling the ionomer 30 in such a nanofiber support 20, the nanofiber composite material 10 of this embodiment may have the same shape as a concrete structure of a general building. Accordingly, the nanofiber composite material 10 has excellent basic mechanical properties such as tensile strength, and also has excellent ionic conductivity because it has a form in which the movement of ions is not physically hindered.

For example, an ion exchange membrane may be formed by forming the nanofiber composite material 10 in a sheet form. Such an ion exchange membrane has excellent mechanical and electrochemical properties and can be applied to the RED system illustrated in FIG. 1 .

Existing ion exchange membranes are too thick or have a structure in which the ion exchange material and the support 20 overlap, so that they are simply suitable for use for ion adsorption. However, the ion exchange membrane of this embodiment has a single structure in which the ionomer 30 is filled in the nanofiber support 20, which is a random assembly of nanofibers 21. Therefore, according to the ion exchange membrane of this embodiment, the thickness of the ion exchange membrane can be effectively reduced while maintaining basic mechanical properties and ion movement can be facilitated.

Such ion exchange membranes can be effectively used for reverse electrodialysis or fuel cells, for which conventional ion exchange membranes have not met sufficient requirements.

In particular, the ion exchange membrane of this embodiment has a structure that prevents the most important flow of ions from being hindered by the ion exchange membrane in the entire process of generating current. Specifically, the nanofiber scaffold 20 has ion exchange characteristics by being formed by MXene addition. Due to this, when the ionomer 30 is filled in the nanofiber support 20, the nanofibers present in the middle can act so that the characteristics of the ionomer 30 are not deteriorated.

In addition, when comparing the ion exchange membrane of this embodiment with each individual component (cellulose acetate/maxene nanofiber support 20, membrane made of ionomer), the ion exchange membrane of this embodiment has mechanical properties such as tensile strength that are higher than each individual component. It can be seen that it has a synergistic effect by having better performance in electrochemical properties such as and ionic conductivity.

Figure 4 is a flow chart showing a method for manufacturing a nanofiber composite material according to an embodiment of the present invention. 5 is a schematic diagram showing a process of manufacturing Maxine (Ti ₃ C ₂ T _X ) nanosheets from Maxine (Ti ₃ AlC ₂ ) through continuous etching and exfoliation processes.

In the manufacturing method of the nanofiber composite material, first, Maxine is manufactured using the material on Max (M _n+1 AX _n ) (S10).

MXene used in this embodiment was manufactured through a series of processes of etching the layer corresponding to element A using the material on Max (M _n+1 AX _n ) and peeling off each layer composed of a combination of M and X elements. (See Fig. 5).

Specifically, after removing the A layer of Max with a hydrofluoric acid (HF) solution using the material on Max, Maxine can be manufactured through continuous dimethyl sulfoxide (DMSO) support treatment and bath water ultrasonic treatment.

In general, when removing the element A layer, a solution such as hydrochloric acid (HCl), hydrofluoric acid, a mixed solution of hydrochloric acid and nitric acid (HNO ₃ ), sodium hydroxide (NaOH), lithium fluoride (LiF), or the like may be used.

Hydrofluoric acid can remove the element A layer more reliably than hydrochloric acid or a mixed solution of hydrochloric acid and nitric acid, and there is no severe formation of residue or poor cleaning after a chemical reaction, as in the case of using sodium hydroxide or lithium fluoride. There are advantages to the process. In addition, lithium fluoride also has an excellent removal ability of the element A layer, but has a disadvantage in that it must be performed in an inert gas atmosphere until the first washing process after completion of the reaction with Max.

In addition, the MAX powder from which the A layer was removed was treated with dimethyl sulfoxide or dichloromethane (DCM), methylpyrrolidone (NMP), tetrahydrofuran (THF), and ethyl acetate having similar properties. Supported in polar aprotic solvents such as (ethyl acetate, EtOAc), acetone, dimethylformamide (DMF), acetonitrile (ACN), and propylene carbonate (PC) Doing so can weaken the bonding force between the layers made of the combination of M and X elements (delamination). Afterwards, when appropriate physical energy is applied (sonication), MXene nanosheets can be obtained while exfoliating into individual layers.

As described above, the MXene nanosheet included in the composition of the present invention can be directly prepared by using a Maxine material through a continuous etching and exfoliation process. In the etching process, hydrochloric acid, hydrofluoric acid, a mixed solution of hydrochloric acid and nitric acid, sodium hydroxide, lithium fluoride, etc. can be used and is not limited by the type of specific solution. In the peeling process, dimethyl sulfoxide, dichloromethane, methylpyrrolidone, Tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, propylene carbonate, etc. can be used and is not limited by the type of specific solution. In this process, hydroxyl groups (-OH), epoxy groups (-O-), and fluorinated groups (-F) are formed on the surface and edge of MXene nanosheets, so that covalent bonds or hydrogen bonds with hydrophilic polymers such as cellulose acetate are formed. can be compounded with

Subsequently, a cellulose acetate/MXene composite solution is prepared using the prepared MXene nanosheets (S20).

After washing and drying the peeled MXene nanosheets, a MXene/polymer composite solution may be prepared by reacting with a solution in which cellulose acetate is dissolved.

6 is a view showing an example of an electrospinning apparatus used when fabricating nanofibers using a cellulose acetate solution or a cellulose acetate/maxene solution.

Next, nanofibers are formed using the composite solution by the electrospinning apparatus illustrated in FIG. 6 to prepare a nanosheet support (S30).

A nanofiber scaffold can be fabricated through electrospinning with a composite solution. Electrospinning is a technique in which, when a high voltage is applied to a solution, a polymer solution is spun in the direction of a collector charged with an opposite charge when a certain charge exceeds a certain threshold in the process of accumulating in the solution. Fibers produced by the electrospinning method have a diameter of about several hundred nm to several um, and the size of pores formed in the entire membrane structure is about several hundred nm to several um. Fibers produced by electrospinning are characterized by a very high specific surface area, and even for materials that have already been sufficiently developed, the membrane structure or surface characteristics can be changed through electrospinning, so functional fibers, industrial filters, medical and semiconductors It can be applied to various fields such as process and energy.

The present inventors fabricated a porous membrane (nanofiber structure) composed of nanofibers in order to prevent the support layer from structurally interfering with the movement of ions, and filled the voids 22 with ionomer to prepare an ion exchange membrane that secured basic mechanical properties. .

The nanofiber scaffold of this embodiment can be obtained by electrospinning after dissolving cellulose acetate in a mixed solvent of acetone-dimethylacetamide (DMAc). When a voltage difference is applied between the solution part and the collector, a specific charge is accumulated in the solution, and when the limit is exceeded, it is rapidly radiated in the direction of the oppositely charged collector, and the shape of the nanofiber is naturally obtained.

As the solvent, in addition to acetone and dimethylacetamide, solvents such as dimethylformamide, dichloromethane, acetic acid, and trifluoroacetic acid may be applied. Not limited.

In the manufacturing method of the nanofiber composite material of this embodiment, the porosity and thickness of the nanofiber membrane (nanofiber support) can be controlled by adjusting the concentration and amount of the cellulose acetate solution during electrospinning. In addition, when MXene nanosheets are included in the cellulose acetate nanofiber membrane, tensile strength, elongation, ion exchange capacity, ionic conductivity, etc. of the nanofibrous membrane can be controlled according to the amount of MXene added.

In one embodiment of the present invention, when preparing the cellulose acetate / MXene nanofiber membrane, the composition can be adjusted in the range of 10 - 20 wt% of cellulose acetate (relative to solvent) and 1 - 10 wt% of MXene (compared to cellulose acetate), thereby Accordingly, the tensile strength, elongation, ion exchange capacity, and ion conductivity of the cellulose acetate nanofiber/Maxene membrane itself before filling Nafion are changed.

Next, the ionomer is filled in the nanosheet support (S40) to prepare a nanofiber composite material.

A non-porous composite ion exchange membrane may be fabricated by filling the cellulose acetate/maxene nanofiber scaffold prepared by the electrospinning method with an arbitrary ionomer.

Conventional ion exchange membranes are in the form of coating a material having ion exchange characteristics on a support membrane in the form of a two-dimensional flat sheet made of a material having excellent mechanical properties (material having no or very weak ion exchange characteristics), or having ion exchange characteristics without a support. It is in the form of a thick film composed of a composite of polymer and resin. There is no problem with these types of ion exchange membranes when they are used for the purpose of adsorbing or displacing specific ions by supporting the ion exchange membrane in a solution. In a situation in which only certain types of ions must pass in a direction and ions of opposite characteristics must be rejected, there is a limit in that the performance cannot be fully exhibited due to the presence of a support or the physical properties of a membrane that is too thick.

A slightly more advanced form is an ion exchange membrane in which an ion exchange layer is applied on a mesh spacer without a flat sheet support. This form is also bulky for applications such as reverse electrodialysis and fuel cells, which require stacking of several ion exchange membranes due to the thick spacer layer. It is also disadvantageous in terms of ion mobility.

The ion exchange membrane (composite ion exchange membrane) presented in this embodiment does not exist in the form of a two-dimensional flat sheet, which hinders the physical movement of ions, but is formed in the form of a random collection of nanofibers, and the pores of the nanofibers The ionomer may be filled to have a film form as a whole. Therefore, in the ion exchange membrane of this embodiment, it is easier for ions to move in a direction perpendicular to the membrane surface than in the conventional ion exchange membrane.

In addition to this, since the ionomer is filled in the cellulose acetate/maxene nanofiber scaffold by casting or supported coating, mechanical properties are improved on the same principle as filling cement in the steel frame in modern buildings. Therefore, it is possible to solve the problem that it is difficult to apply various applications due to poor mechanical properties when the membrane is manufactured using only ionomer materials.

In addition, in the ion exchange membrane of this embodiment, the nanofibers themselves may have ion exchange characteristics by combining MXene particles or nanosheets with cellulose acetate nanofibers. As a result, the cellulose acetate/Maxene nanofibers form a skeleton in the ion exchange membrane and at the same time have ion exchange characteristics to a certain extent.

From a microscopic point of view, MXene nanosheets have a two-dimensional planar structure, which is very advantageous for ion transmission, and theoretically, when an interface is formed by contacting cellulose acetate, ion movement can be further improved on this interface.

In addition to this, the zeta potential of the ion exchange membrane filled with ionomer is finally further strengthened by the presence of MXene included in the nanofiber support, thereby improving the permselectivity.

In addition, MXene nanosheets supplement ion exchange characteristics that cellulose acetate lacks and at the same time improve the binding force between cellulose acetate and ionomer when the ionomer is finally filled in the pores.

As the hydrophilic polymer, in addition to cellulose acetate, materials having similar physical properties such as polyvinyl alcohol, polyacrylonitrile, polyvinylpyrrolidone, polysulfone, etc. may be used without limitation, and similar graphene or 2 2D transition metal chalcogenide (transition metal dichalcogenide) series compounds can be used without limitation.

As the ionomer, Nafion, a representative cation exchange material, was used, and various other materials having cation exchange properties can be applied.

Examples will be described below.

Example

<Preparation of MXene nanosheets>

First, Maxine was manufactured using the material on Max (M _n+1 AX _n ) (S10).

0.5 g of Ti ₃ AlC ₂ powder on Max as a starting material and 15 ml of hydrofluoric acid were mixed and stirred at 100 RPM for 24 hours (Al removal process). After completion of the reaction, 100 ml of distilled water is added to dilute, and centrifugation is performed at 3500 RPM for 30 minutes (washing process). Repeat the same centrifugation process 3 times. After the last centrifugation, the precipitate is collected and vacuum dried at room temperature for 2 to 3 days or dried at 50 °C for 1 day. The dried sample is dispersed in dimethyl sulfoxide and stirred at 300 RPM for 24 hours (delamination process). 85 ml of distilled water was added to the reaction-completed sample to dilute, and centrifuged at 8000 RPM for 10 minutes. Remove the supernatant, add 20 ml of distilled water to the precipitate, and vacuum filter through an anodic aluminum oxide membrane filter. Dry the sample at 35 °C for sufficient time. After mixing the dried powder sample and the solvent to be used in the experiment at a weight ratio of 1:500, ultrasonic treatment is performed for 5 hours (exfoliation process).

5 may refer to a schematic diagram of the MXene nanosheet manufacturing process.

7 is a view showing the results of physical property analysis of MXene nanosheets.

In FIG. 7, the left figure shows the Raman spectroscopy method for confirming the MXene nanosheet state, the middle figure shows the ultraviolet-visible light-infrared spectroscopy method, and the right figure shows the X-ray diffraction analysis result.

As a result of analyzing the state of MXene by Raman spectroscopy, ultraviolet-visible-infrared spectroscopy, and X-ray diffraction analysis, it was confirmed that the Maxine material was exfoliated into MXene nanosheets by showing the same or similar results as those reported in the existing MXene-related literature. could

<Preparation of Cellulose Acetate/Maxene Nanofiber Support>

A cellulose acetate/MXene solution is prepared using the prepared MXene nanosheets (S20). This is as described above.

Thereafter, nanofibers were formed using this solution by the electrospinning apparatus shown in FIG. 6 to prepare a nanosheet support (S30).

When preparing a cellulose acetate nanofiber membrane, prepare a mixture of acetone and dimethylacetamide at a volume ratio of 2: 1, add cellulose acetate powder to the mixed solution so that the weight-to-volume ratio (w / v%) is 15%, and run at 300 RPM and stirred for 24 hours (the ratio of cellulose acetate can be adjusted in the range of 10 - 20 w/v%). In the case of fabricating a cellulose acetate/MXene nanofiber membrane, prepare a solution in which the required amount of MXene nanosheets are dispersed in a mixture of acetone/dimethylacetamide with a volume ratio of 2:1, add cellulose acetate, and heat to 50 °C for 24 Stir for an hour. When the prepared solution is filled in an injection device, injected at a constant speed through a nozzle, and a high voltage is applied between the collector and the nozzle, the solution is spun to obtain a nanofiber film on the collector (see FIG. 6). During electrospinning, the applied voltage (13 - 20 kV) and the amount of spinning solution (10 - 40 ml) can be adjusted according to the conditions of the diameter of the nanofiber and the thickness of the film to be finally manufactured. In addition, the concentration of a suitable spinning solution may vary depending on the spinning conditions, and accordingly, the distance between the nozzle and the collector should also vary, which may be optimized between 13 and 20 cm.

In FIG. 8, it can be seen the actual shapes of the cellulose acetate nanofiber membrane and the cellulose acetate/maxene nanofiber membrane and the shapes observed with a scanning electron microscope. It can be seen from the XPS analysis of FIG. 9 that a bond is formed between cellulose acetate and MXene, and the tensile test results of FIG. 10 show that the cellulose acetate nanofiber membrane containing 5 wt% of MXene has optimal mechanical properties. there is. 11 is a comparison of the water absorption capacity, ion exchange capacity, and ion conductivity of the cellulose acetate nanofiber membrane and the cellulose acetate/MXene composite nanofibrous membrane by MXene content, and showed optimal performance when the MXene content was 5 wt%.

8 is a view showing the results of scanning electron microscopy of the actual appearance and arbitrary parts of a cellulose acetate nanofibrous membrane and a cellulose acetate/maxene nanofibrous membrane.

The photograph of FIG. 8 (a) shows the actual appearance of the cellulose acetate nanofiber membrane and the result of photographing an arbitrary part with a scanning electron microscope (SEM). The photograph of FIG. 8 (B) shows the actual appearance of the cellulose/maxene nanofiber membrane and the result of photographing an arbitrary part with a scanning electron microscope. Due to the presence of MXene, a clear color difference can be confirmed with the naked eye, and it can be seen that both membranes are well formed in the form of nanofibers and have a porous structure.

Referring to FIG. 8 (a), the actual appearance of the free-standing cellulose acetate nanofiber membrane can be confirmed, and as a result of photographing an arbitrary part with a scanning electron microscope (SEM), the nanofiber structure was able to confirm

Referring to FIG. 8 (B), the actual appearance of the free-standing cellulose acetate / Maxene nanofiber membrane can be confirmed, and as a result of photographing an arbitrary part with a scanning electron microscope, the nanofiber structure can be confirmed as described above. there was. Due to the presence of MXene, a clear color difference was observed compared to FIG. 8 (a).

9 is a view showing the results of analyzing the binding characteristics between cellulose acetate and MXene by X-ray photoelectron spectroscopy (XPS).

Basically, peaks of F 1s and Ti 2p, which do not appear in the results of pristine CA, were observed in the case of CA/MXene in the survey spectrum. Since F and Ti are components of MXene nanosheets, the existence of MXene can be inferred. In the C 1s spectrum, the C-O peak of CA/MXene shifted compared to CA, and the O-Ti/C-Ti-Ox peak observed in CA/MXene, which was not observed in the case of CA in the O 1s spectrum, is cellulose. This means that a chemical bond has been formed between the oxygen or carbon of the ace acetate and Ti constituting MXene. In addition, Ti-O(sp3), Ti-C(sp3), and Ti(II)(2p3) in the Ti 2p spectrum of CA/MXene appeared more distinctly than the generally known XPS result of MXene, indicating the bonding between cellulose acetate and MXene. means that it has been formed. And the fact that the F 1s spectrum was detected in CA/MXene itself is a result confirming once again that MXene exists.

10 is a view showing the tensile test results for CA nanofibrous membranes and CA / MXene nanofibrous membranes for each MXene content. 11 is a table comparing and analyzing basic physical properties and electrochemical properties of CA nanofibrous membranes and CA / MXene nanofibrous membranes by MXene content.

Referring to the comparison results of the tensile properties of the cellulose acetate nanofiber membrane and the cellulose acetate / MXene nanofiber membrane by MXene content shown in FIGS. 10 and 11, the elongation rate as the MXene content increased from 1 to 5 wt% Both the tensile strength and tensile strength were improved. In addition, when the content of MXene was increased to 10wt%, the tensile strength was improved, but the elongation was decreased. Therefore, the optimal MXene content can be set at 5 wt%.

When the basic physical properties and electrochemical properties of the cellulose acetate nanofiber membrane and the cellulose acetate/MXene nanofiber scaffold by MXene content were compared and analyzed, the hydrophilic properties were improved when MXene was added compared to the cellulose acetate nanofiber membrane, and the water absorption capacity (water uptake) was improved, and ion exchange capacity (IEC) and ionic conductivity were improved due to the functional groups on the surface of MXene and the two-dimensional shape that facilitates the movement of ions.

<Filling of ionomer>

Next, the ionomer was filled in the nanosheet support (S40) to prepare a nanofiber composite material.

The cellulose acetate/Maxene nanofiber membrane prepared by the above method is supported in an appropriate amount of the Nafion dispersion solution and dried at 60 °C for 24 hours and then dried at 80 °C for 4 hours. In some cases, sulfuric acid treatment can be performed at 60 - 80 °C for 1 - 4 hours to further maximize the cation exchange characteristics of the finished membrane.

12 is a runner electron micrograph of a sample dried by filling Nafion as an ion exchange filler in a CA/MXene nanofibrous membrane.

Referring to FIG. 12, in FIG. 12, the appearance of the surface of the Nafion@cellulose acetate/Maxene nanofiber composite film observed with a scanning electron microscope can be confirmed. Nafion is filled between the empty spaces of the cellulose acetate/maxene nanofiber membrane, and it has a structure similar to the concrete structure of a general building (reinforcing bar + cement ≒ nanofiber + Nafion).

13 is a diagram showing the tensile strength of a cellulose acetate/Maxene nanofiber composite membrane filled with Nafion and its control group.

13 shows tensile test results for CA nanofibrous membranes, CA/MXene nanofibrous membranes, nanofibrous membranes filled with Nafion (Nafion@CA/MXene), and recasted Nafion membranes.

Referring to FIG. 13, the membrane made of the nanofiber composite material of this example in which Nafion was filled in the cellulose acetate/Maxene nanofiber membrane showed much improved tensile strength and structural stability compared to other control membranes.

14 is a diagram showing the surface zeta potential of Nafion-filled cellulose acetate/Maxene nanofiber composite membranes and their controls.

14 shows surface zeta potential values of CA nanofibrous membranes, CA/MXene nanofibrous membranes, nanofibrous membranes filled with Nafion (Nafion@CA/MXene), and recasted Nafion membranes.

In addition, referring to FIG. 14 , when the surface zeta potential values of the membranes were compared, negative zeta potentials of cellulose acetate, MXene, and recast Nafion were shown as previously known. In particular, the absolute value of the zeta potential of the cellulose acetate nanofiber membrane was further increased when MXene was added, and the absolute value of the zeta potential of the cellulose acetate/MXene nanofiber composite membrane filled with Nafion was increased compared to the recast Nafion membrane. was able to check Therefore, the surface zeta potential value of the membrane was further improved by MXene, and as a result, the permselectivity of the membrane could be improved.

More specifically, referring to FIG. 14 , the effect of improving the absolute value of the surface zeta potential by the addition of MXene can be confirmed. The cellulose acetate nanofibrous membrane showed a stronger negative zeta potential after MXene was added, and the recast Nafion membrane also showed a stronger negative zeta potential value when mixed with MXene-added nanofibrous membrane. The higher ionic conductivity of the Nafion@cellulose acetate/Maxene nanofiber composite membrane than the recast Nafion membrane is the result of structural engineering of the support material so that the movement of ions is not hindered, and the recast Nafion membrane Although both the membrane and the Nafion@cellulose acetate/Maxene nanofiber composite membrane are non-porous, and Nafion is the main ion exchange material, the reason for the difference in permselectivity is that the zeta potential of the entire surface of the membrane is higher due to the presence of MXene. because it has a strong negative value.

15 is a comparative analysis table of physical/electrochemical properties between a cellulose acetate/Maxene nanofiber composite membrane filled with Nafion and its control group.

15 shows physical/electrochemical properties of CA nanofibrous membrane, CA/MXene nanofibrous membrane, recast Nafion membrane, and Nafion@CA/MXene nanofibrous membrane.

Referring to FIG. 15 , it can be seen that the cellulose acetate/Maxene nanofiber composite membrane filled with Nafion has a basic water absorption capacity. In addition, the ionic conductivity was improved by making the nanofiber support into a nanofibrous structure so that the movement of ions was not hindered, and the synergistic effect of Maxine and Nafion showed improved ion exchange amount and permselectivity compared to other control groups.

That is, in FIG. 15, the Nafion@cellulose acetate/Maxene nanofiber composite membrane has a non-porous structure, so the water absorption capacity is slightly reduced compared to the porous nanofiber membrane. @It can be confirmed that the cellulose acetate/Maxene nanofiber composite membrane is superior to the nanofiber membrane or the recast Nafion membrane.

When ions must pass through an ion exchange membrane to move in a specific direction during the operation of a device such as reverse electrodialysis or a fuel cell, a typical ion exchange membrane composed of a layered structure of an existing ion exchange material/support causes serious performance degradation.

The nanofiber composite material of this embodiment is prepared by manufacturing a cellulose acetate/maxene material in the form of nanofibers through electrospinning to form a skeleton and at the same time impart basic ion exchange characteristics, and can be prepared by filling the ionomer. As a result, the nanofiber composite material of this embodiment, its manufacturing method, and the ion exchange membrane having the same are materials that overcome the problems of the existing ion exchange membranes, and can suppress the deterioration of mechanical properties while having a form suitable for the application field.

In this embodiment, a material having low mechanical strength, such as cellulose acetate, but having a hydrophilic and biodegradable advantage, is used without using previously known materials with excellent mechanical properties. Nanofiber composite material is manufactured through the introduction of nanomaterials and structural engineering By doing so, it is possible to further expand the field of application of the ion exchange membrane while improving the chronic disadvantages of the existing ion exchange membrane.

As a key element of the present invention, it is possible to apply reverse electrodialysis, fuel cells, etc. by fabricating an ion exchange membrane in which the ionomer is filled in the pores using cellulose acetate/maxene nanofibers as a skeleton, rather than simply overlapping the support and ionomer. there is.

The above description of the present invention is for illustrative purposes, and those skilled in the art can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be interpreted as being included in the scope of the present invention.

10: nano fiber composite material
20: nanofiber support
21: nanofiber
22: air gap
30: ionomer

Claims (17)

In the nanofiber composite material,
A nanofiber support, which is an aggregate of nanofibers prepared using a mixture of a hydrophilic polymer and MXene; and
Characterized in that it comprises an ionomer filled in the pores between the nanofibers of the nanofiber support, nanofiber composite material.
The method of claim 1,
The nanofiber support is a nanofiber composite material, characterized in that formed in the form of a film as an aggregate of nanofibers formed by electrospinning a mixture of a hydrophilic polymer and MXene.
The method of claim 1,
The nanofiber support is formed by randomly assembling the nanofibers, and due to the voids, the movement of ions is suppressed, characterized in that, nanofiber composite material.
The method of claim 2,
The hydrophilic polymer,
Contains at least one of cellulose acetate, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP) and polysulfone (PSf) Characterized in that, nanofiber composite material.
The method of claim 4,
The ionomer is a nanofiber composite material, characterized in that it comprises Nafion (Nafion).
The method of claim 4,
The nanofibers have a structure in which MXene particles or MXene nanosheets form chemical and physical bonds with each other to the hydrophilic polymer, characterized in that they have ion exchange properties, nanofiber composite material.
According to claim 4,
The nanofiber composite material, characterized in that the total composition ratio of the MXene and the hydrophilic polymer in the nanofiber support is 100 wt%, and the composition ratio of the MXene is 1 wt% to 10 wt%.
According to claim 4,
The nanofibers include a material represented by M _{n + 1} X _n T _x ,
M is an early transition metal and is at least one of Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf, and Ta;
X is at least one of carbon and nitrogen (n is an integer from 1 to 4);
T _x is Characterized in that it is an oxygen functional group or a fluorine functional group, a nanofiber composite material.
An ion exchange membrane formed of the nanofiber composite material of claim 1 in a sheet shape.
In the manufacturing method of a nanofiber composite material comprising a nanofiber support and an ionomer,
Manufacturing a material on Maxine from a material on Max (M _n+1 AX _n );
preparing a solution in which a hydrophilic polymer material and a material of the MXene phase are mixed;
Forming a nanofiber scaffold through electrospinning using the solution; and
Characterized in that it comprises the step of filling the ionomer in the nanofiber support, the manufacturing method of the nanofiber composite material.
The method of claim 10,
The step of manufacturing the material on Maxine from the material on Max (M _n+1 AX _n ),
Using at least one solution of hydrochloric acid (HCl), hydrofluoric acid (HF), a mixed solution of hydrochloric acid and nitric acid (HNO ₃ ), sodium hydroxide (NaOH), and lithium fluoride (LiF) Max (M _n+1 AX _n ) Etching a layer corresponding to element A from the upper material;
A Max powder from which the elemental layer was removed was mixed with dimethyl sulfoxide (DMSO), dichloromethane (DCM), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and ethyl acetate. Supported in at least one solvent (polar aprotic solvent) of (ethyl acetate, EtOAc), acetone, dimethylformamide (DMF), acetonitrile (ACN), and propylene carbonate (PC) weakening the bonding force between the layers made of a combination of M and X elements; and
Characterized in that it comprises the step of peeling each layer composed of a combination of M and X elements by applying physical energy to the material whose bonding force is weakened, the manufacturing method of the nanofiber composite material.
The method of claim 10,
In the material of the Max (M _{n + 1} AX _n ) phase, M is at least one of Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf, and Ta as a transition metal, and A is Al , Si, P, Ga, Ge, As, Cd, In, Sn, Sb, Tl, and one of group A elements including Pb, and X (n is an integer from 1 to 3) is one of carbon and nitrogen is,
The material on MXene is a material represented by M _{n + 1} X _n T _x , where M is an early transition metal, Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf , at least one of Ta, X is at least one of carbon and nitrogen (n is an integer from 1 to 4), T _x is Characterized in that it is an oxygen functional group or a fluorine functional group, a method for producing a nanofiber composite material.
The method of claim 12,
The step of manufacturing the material on the Maxine,
removing a layer composed of group A elements from the material on the Max (M _n+1 AX _n );
delamination of the layered structure by inserting a first molecule into the material from which the layer composed of the group A element is removed; and
Characterized in that it comprises the step of dispersing the layered structure broken material in a first solvent and obtaining a MXene nanosheet as a material on MXene from which the layers are separated (exfoliation) through a purification process after sonication treatment, nanofibers. Manufacturing method of composite material.
The method of claim 12,
In the step of forming the nanofiber support through the electrospinning,
A solution in which the hydrophilic polymer material and the MXene material are mixed by adjusting the concentration of the solution, the injection speed of the solution, the diameter of the nozzle, the distance between the nozzle and the collector, and the applied voltage during the electrospinning process. Characterized in that by spinning, a method for producing a nanofiber composite material.
The method of claim 10,
In the step of forming the nanofiber support through the electrospinning,
A method for producing a nanofiber composite material, characterized in that the thickness of the membrane made of the nanofiber support is controlled according to the concentration and total amount of the spinning solution.
The method of claim 14,
Forming the nanofiber support,
vacuum-drying the film made of the nanofiber support after the spinning is completed on the collector at a set temperature; and
The method of manufacturing a nanofiber composite material, characterized in that it further comprises the step of spraying and wetting the solvent on the membrane made of the nanofiber support after vacuum drying and separating the nanofiber support from the surface of the collector.
According to claim 16,
In the step of filling the ionomer in the nanofiber support,
The ionomer includes Nafion, and the ionomer dissolved in alcohol is filled in the pores of the nanofiber support by casting or dip coating method, manufacturing a nanofiber composite material. method.

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