CN115138220B - Anionic covalent organic framework film and preparation and application thereof - Google Patents
Anionic covalent organic framework film and preparation and application thereof Download PDFInfo
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- B01D67/0002—Organic membrane manufacture
- B01D67/0006—Organic membrane manufacture by chemical reactions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
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Abstract
The invention discloses an anionic covalent organic framework membrane, which consists of two types of reaction monomers, namely 1,3, 5-trihydroxybenzene tricarboxaldehyde and 1, 4-diamine benzoic acid, wherein the two types of reaction monomers firstly generate anionic covalent organic framework nano sheets through a pH-mediated oil-water-oil interfacial polymerization method, and then assemble the nano sheets on a porous substrate through a vacuum auxiliary assembly method to prepare the anionic covalent organic framework membrane; the membrane is integrally provided with an asymmetric structure and comprises a compact skin layer and a porous supporting layer, wherein the porous supporting layer is of a fiber staggered stacking structure. Because the covalent organic framework material has sub-nanometer aperture and easy cutting site, a hydration layer can be constructed in the channel, the screening function of monovalent cations is endowed to the membrane, the efficient separation process is realized, and the technical bottleneck of the microporous framework material for ion separation is broken through. In addition, by adjusting the conditions of the kind of the reaction monomer, the concentration of the dispersion liquid, and the like, the film properties can be further optimized.
Description
Technical Field
The invention belongs to the technical field of novel separation membrane materials, relates to membrane material development applied to the field of ion separation, and in particular relates to a preparation method of an anionic covalent organic framework membrane.
Background
The membrane separation technology is a novel separation technology, can realize selective separation of molecular mixtures with different characteristics on a molecular level, and has the characteristics of high efficiency, energy conservation, environmental protection, small occupied area and the like. At present, the membrane separation technology is widely applied to the fields of medicine, food, biology, chemical industry, environmental protection, electronic and water treatment and the like, and brings great economic and social benefits.
Na is widely present in salt lakes, seawater and brine + 、K + And Li (lithium) + And so on. With the wide application of monovalent metal ions in the fields of energy storage, metallurgy, agriculture and the like, efficient separation of monovalent cation mixtures is an important requirement. Currently, monovalent cation separationsMainly relies on comprehensive or combined technologies such as evaporation-precipitation-adsorption, evaporation-extraction, evaporation-calcination and the like, and has complex process and high energy consumption. Membrane technology has broad prospects in separation of monovalent cations due to its non-thermal, low carbon and low environmental footprint characteristics. However, sub-nanometer ion sizes (e.g., bare ionsHydrated ions) Difference in angstrom level->And the same charge valence state between the mixtures, making monovalent cation separation one of the most challenging separation tasks. So far, the use of membrane technology to achieve monovalent/monovalent cation separations has been rarely studied. Among these, some studies evaluate membrane performance using single ion permeability ratios, and the ideal selectivity is typically calculated to be between 1.0 and 10. Furthermore, the separation by membrane technology using binary monovalent ion mixtures has been reported in only two works [1-2] And the selectivity is only between 1.0 and 2.0, and the precision of the separation process is greatly improved.
COFs constructed from rigid covalent bonds, long range ordered frameworks, have received wide attention in the field of liquid mixture separations. The selection of the COF organic precursor and the directional assembly of the framework endow the aperture with controllable atomic scale, which enables the COF to have high flexibility and precision in the separation task of atomic/molecular scale. In addition, the rich chemical customization capability of COF gives it a high degree of freedom, and multiple chemical functions of the channel can be designed according to specific requirements of hydrophilicity, activity or polarity in separation applications to enhance multiple mechanisms of the separation process.
[ reference ]
[1]Z.Jia,W.Shi,Tailoring permeation channels of graphene oxide membranes for precise ion separation.Carbon,2016,101,290-295.
[2]Z.Jia,Y.Wang,W.Shi,J.Wang,Diamines cross-linked graphene oxide free-standing membranes for ion dialysis separation.Journal of Membrane Science,2016,520,139-144.
Disclosure of Invention
Aiming at the prior art, the invention provides an anionic covalent organic framework membrane and a preparation method thereof, and the invention designs and prepares a series of anionic covalent organic framework membranes. The hydration function and the domain limiting function of the anionic groups are utilized to control the selective transfer of monovalent cations, so that the high-efficiency monovalent ion separation is realized, and the technical bottleneck of the macroporous covalent organic framework material for the high-efficiency ion separation is broken through.
In order to solve the technical problems, the invention provides an anionic covalent organic framework membrane, which consists of two types of reaction monomers of 1,3, 5-trihydroxybenzoic acid and 1, 4-diamine benzoic acid, wherein the two types of reaction monomers firstly generate an anionic covalent organic framework nano sheet by a pH-mediated oil-water-oil interfacial polymerization method, and then prepare the nano sheet into the anionic covalent organic framework membrane by a vacuum auxiliary assembly method; the membrane integrally presents an asymmetric structure and comprises a compact cortex and a porous supporting layer, wherein the average pore diameter of the compact cortex is 1.3-1.5nm, and the thickness of the compact cortex is 0.1-5.0 mu m; the porous supporting layer is of a fiber staggered stacking structure, and the average pore diameter is 2.0 mu m. The preparation steps of the film are as follows:
step one, preparing an anionic covalent organic framework nano sheet by adopting an oil-water-oil interfacial polymerization method:
1,3, 5-trihydroxybenzene trimesic aldehyde is dissolved in methylene dichloride according to the concentration of 0.5-3mol/L, ultrasonic treatment is carried out for 15 minutes, and the obtained solution is recorded as oil phase solution A; 1, 4-diamine benzoic acid is dissolved in N, N-dimethylformamide according to the concentration of 0.75-4.5mol/L, ultrasonic treatment is carried out for 15 minutes, and the obtained solution is recorded as oil phase solution B; adding acetic acid or sodium bicarbonate into deionized water, regulating the pH to 4-12, and performing ultrasonic treatment for 15 minutes to obtain a water phase solution; slowly assembling the oil phase solution A, the water phase solution and the oil phase solution B in a sequence from bottom to top according to the volume ratio of (4-8): 1:2, reacting for 72 hours, extracting, separating liquid, and collecting the water phase solution therein to obtain the anionic covalent organic framework nano-sheet dispersion;
preparing an anionic covalent organic framework film by a vacuum assisted assembly method:
the concentration of the anionic covalent organic framework nano-sheet dispersion liquid prepared in the step one is regulated to be 0.1-0.5g/L, and the dispersion liquid is assembled on a porous substrate of a solvent filter device by suction filtration under the vacuum condition of 0.05-0.1MPa, so that an anionic covalent organic framework film is obtained; the porous substrate is polytetrafluoroethylene with an average pore diameter of 0.2 mu m, and the effective interception radius of the anionic covalent organic framework membrane is 0.6-1.0 cm.
Further, the preparation method of the invention, wherein the 1, 4-diamine-based benzoic acid is one of 1, 4-diamine-based phenylphosphonic acid, 1, 4-diamine-based benzenesulfonic acid and 1, 4-diamine-based phenylcarboxylic acid.
The 1, 4-diamine benzoic acid is 1, 4-diamine phenylphosphonic acid, and the pH value is 11.
The 1, 4-diaminobenzene acid is 1, 4-diaminobenzene sulfonic acid, and the pH value is 4.
The 1, 4-diaminobenzoic acid is 1, 4-diaminobenzene carboxylic acid, and the pH value is 7.
The concentration of the oil phase solution A is 0.5mol/L, and the concentration of the oil phase solution B is 0.75mol/L.
In the second step, the concentration of the anionic covalent organic framework nano-sheet dispersion liquid is 0.1g/L.
The anion covalent organic framework membrane prepared by the invention is used in monovalent cation separation process, and the potassium ion permeation rate is 0.010-0.016mol h -1 m -2 The selectivity of the binary mixture of potassium ions and lithium ions is 1.0-4.2, and the selectivity of the binary mixture of potassium ions and sodium ions is 0.8-2.5.
Compared with the prior art, the invention has the beneficial effects that:
the invention relates to an anionic covalent organic framework membrane, which strengthens the interlayer electrostatic interaction of an anionic covalent organic framework by a pH-mediated oil-water-oil interfacial polymerization method and promotes the in-plane growth of the covalent organic framework to obtain a nano-sheet so as to solve the problem of film forming property of the anionic covalent organic framework. And then processing into a film by using a vacuum auxiliary assembly method, wherein the film preparation method is convenient, simple, convenient and controllable and is convenient to operate. In the preparation process, the anionic covalent organic framework membrane structure is optimized by adjusting the reaction conditions in the preparation step, such as monomer types, monomer concentration, dispersion liquid concentration and the like. The abundant groups in the prepared anion covalent organic framework membrane endow the membrane with a stable limited-domain hydration structure, so that the selectivity of the membrane to monovalent cations is enhanced, and the membrane shows excellent monovalent cation separation performance.
Drawings
FIG. 1 is a surface and cross-sectional electron microscopy image and pore size distribution plot of the anionic covalent organic framework film of examples 1, 2 and 3, wherein:
(a), (b) and (c) are the surface, cross-sectional electron microscopy and pore size profiles, respectively, of the anionic covalent organic framework membrane of example 1;
(d) (e) and (f) are the surface, cross-sectional electron microscopy and pore size distribution maps, respectively, of the anionic covalent organic framework membrane of example 1;
(g) (h) and (i) are the surface, cross-sectional electron microscopy and pore size profiles, respectively, of the anionic covalent organic framework membrane of example 1;
fig. 2 is the ion permeation rate and binary ion mixture selectivity of the anionic covalent organic framework membranes of examples 1, 2 and 3.
Fig. 3 is the ion permeation rate and binary ion mixture selectivity of the anionic covalent organic framework membranes of examples 1,4 and 5.
Fig. 4 is the ion permeation rate and binary ion mixture selectivity of the anionic covalent organic framework membranes of examples 1, 6 and 7.
Detailed Description
The invention will now be further described with reference to the accompanying drawings and specific examples, which are in no way limiting.
The design concept of the anion covalent organic framework membrane provided by the invention is as follows: the membrane is composed of two types of reaction monomers, namely 1,3, 5-trihydroxybenzene tricaldehyde and 1, 4-diamine benzoic acid, wherein the two types of reaction monomers firstly generate anionic covalent organic framework nano-sheets through a pH-mediated oil-water-oil interfacial polymerization method, and then assemble the nano-sheets on a porous substrate through a vacuum auxiliary assembly method to prepare the anionic covalent organic framework membrane; the membrane integrally presents an asymmetric structure and comprises a compact cortex and a porous supporting layer, wherein the average pore diameter of the compact cortex is 1.3-1.5nm, and the thickness of the compact cortex is 0.1-5.0 mu m; the porous supporting layer is of a fiber staggered stacking structure, and the average pore diameter is 2.0 mu m. The anion covalent organic framework nano-sheet has high aspect ratio and good ductility, and is beneficial to preparing continuous, defect-free and thickness-controllable anion covalent organic framework films. Pore diameter smaller than 2 nanometers and easily controlled acidic groups in the membrane are beneficial to designing a hydration structure in the membrane, endowing the membrane with screening functions for different monovalent cations, and realizing an efficient monovalent cation separation process, thereby breaking through the technical bottleneck of microporous frame materials for ion separation. In addition, by adjusting the conditions of the monomer type, the monomer concentration, the dispersion concentration, and the like, the film performance can be further optimized.
The technical scheme of the present invention is further described in detail below with reference to the accompanying drawings and the specific embodiments, and the described specific examples are only for illustrating the present invention and are not intended to limit the present invention.
Example 1
The preparation of the anionic covalent organic framework film comprises the following steps:
step one, preparing an anionic covalent organic framework nano sheet by adopting an oil-water-oil interfacial polymerization method:
8.4g of 1,3, 5-trihydroxybenzene trimesic aldehyde is weighed and dissolved in 80mL of dichloromethane, and ultrasonic treatment is carried out for 15 minutes to obtain a solution with the concentration of 0.5mol/L, and the solution is recorded as an oil phase solution A; 7.1g of 1, 4-diaminobenzoic acid is weighed and dissolved in 50mL of N, N-dimethylformamide, and ultrasonic treatment is carried out for 15 minutes to obtain a solution with the concentration of 0.75mol/L, and the solution is recorded as an oil phase solution B; dissolving 0.8mg of acetic acid in 20mL of deionized water, and carrying out ultrasonic treatment for 15 minutes to obtain an aqueous phase solution with pH of 4;
slowly assembling the oil phase solution A, the water phase solution and the oil phase solution B in a sequence from bottom to top at a volume ratio of 4:1:2 at a speed of 0.5mL/s, reacting for 72 hours, extracting, separating liquid, and collecting the water phase solution to obtain an anionic covalent organic framework nano-sheet dispersion;
preparing an anionic covalent organic framework film by a vacuum assisted assembly method:
and (3) adjusting the concentration of the anionic covalent organic framework nano-sheet dispersion liquid prepared in the step (I) to 0.1g/L, taking 60mL of the anionic covalent organic framework nano-sheet dispersion liquid, and carrying out suction filtration on the anionic covalent organic framework nano-sheet dispersion liquid on a porous substrate of a solvent filter device under the vacuum condition of 0.075MPa to obtain an anionic covalent organic framework membrane, which is marked as a membrane 1. The porous substrate was polytetrafluoroethylene with an average pore size of 0.2 μm and the effective membrane rejection radius was 0.7 cm.
In fig. 1 (a) and (b), it can be observed that the membrane 1 has a continuous defect-free surface and a dense cross-sectional morphology, and the membrane as a whole exhibits an asymmetric structure comprising a dense skin layer having a thickness of about 2.0nm and a porous support layer having a fiber-staggered stack structure with an average pore size of 2.0 μm. In FIG. 1 (c), the dense cortex of the membrane 1 was found to have an average pore size of 1.4nm.
Membrane 1 was subjected to monovalent cation separation experiments: the experiment adopts a concentration diffusion device, 200mL of potassium chloride with the concentration of 0.1mol/L and 0.1mol/L of lithium chloride mixed solution are selected to be placed on the raw material side, 200mL of deionized water is selected to be placed on the permeation side, and the cation permeation rate and the ion selectivity of the membrane are evaluated. The potassium ion permeation rate of the membrane is 0.013mol h -1 m -2 The potassium ion/lithium ion binary mixture selectivity was 2.5 and the potassium ion/sodium ion binary mixture selectivity was 1.2, as shown in fig. 2.
Example 2
The preparation of an anionic covalent organic framework membrane, which is unchanged from the procedure in example 1 above, was accomplished by changing only one of the monomers used in step 1 from 1, 4-diaminobenzenesulfonic acid to 1, 4-diaminophenylphosphonic acid and adding sodium bicarbonate to change the pH of the aqueous phase from 4 to 8, and finally obtaining an anionic covalent organic framework membrane, designated membrane 2. Fig. 1 (d) and (e) show the surface and cross-sectional electron microscope images of the film. The membrane has an asymmetric structure as a whole, and comprises a dense cortex layer with a thickness of about 2.0nm and a fiber staggered stack structure with an average pore diameter of 2.0 μmIs provided. The dense cortex of membrane 2 was found to have an average pore size of 1.3nm in FIG. 1 (f). Membrane 2 was subjected to monovalent cation separation experiments, as a result of which: potassium ion permeation rate of 0.016mol h -1 m -2 The potassium ion/lithium ion binary mixture selectivity was 4.2 and the potassium ion/sodium ion binary mixture selectivity was 2.5, as shown in fig. 2.
Example 3
The preparation of an anionic covalent organic framework membrane, which is unchanged from the procedure in example 1 above, was accomplished by changing only one of the monomers C used in the procedure from 1, 4-diaminobenzenesulfonic acid to 1, 4-diaminobenzenecarboxylic acid, and adding sodium bicarbonate to change the pH of the aqueous solution from 4 to 12, and finally obtaining an anionic covalent organic framework membrane, designated as membrane 3. Fig. 1 (g) and (h) show surface and cross-sectional electron microscopic views of the film 3. The membrane as a whole exhibits an asymmetric structure comprising a dense skin layer having a thickness of about 2.0nm and a porous support layer having a fiber-interlaced stack structure with an average pore size of 2.0 μm. The average pore size of the dense cortex of the membrane 3 was found to be 1.4nm in FIG. 1 (i). The membrane prepared in example 3 was subjected to monovalent cation separation experiments, the result of which was: potassium ion permeation rate of 0.015mol h - 1 m -2 The potassium ion/lithium ion binary mixture selectivity was 1.0 and the potassium ion/sodium ion binary mixture selectivity was 0.8, as shown in fig. 2.
Example 4
The preparation of the anionic covalent organic framework film was unchanged from the procedure in example 1, and only the concentration of the oil phase solution in the first step was changed, namely, the concentration of the oil phase solution A was changed from 0.5mol/L to 1.0mol/L, and the concentration of the oil phase solution B was changed from 1.5mol/L to 4.5mol/L, to obtain the anionic covalent organic framework film, which was designated as film 4. The monovalent cation separation experiment was performed on membrane 4, as a result of which: potassium ion permeation rate of 0.012mol h -1 m -2 The potassium ion/lithium ion binary mixture selectivity was 2.1 and the potassium ion/sodium ion binary mixture selectivity was 1.1, as shown in fig. 3.
Example 5
Preparation of an anionic covalent organic framework film, as in example 1 above, the concentration of the oily phase solution was varied only in step one, i.eThe concentration of the oil phase solution A is changed from 0.5mol/L to 3mol/L, and the concentration of the oil phase solution B is changed from 0.75mol/L to 4.5mol/L, so that the anionic covalent organic framework membrane is obtained and is marked as a membrane 5. The monovalent cation separation experiment was performed on membrane 5, as a result of which: potassium ion permeation rate of 0.010mol h -1 m -2 The potassium ion/lithium ion binary mixture selectivity was 1.8 and the potassium ion/sodium ion binary mixture selectivity was 1.0, as shown in fig. 3.
Example 6
An anionic covalent organic framework film was prepared, as in the above example 1, by changing the concentration of the nanosheet dispersion in step two from 0.1g/L to 0.3g/L, and the film was designated as film 6. Membrane 6 was subjected to monovalent cation separation experiments, as a result of which: potassium ion permeation rate of 0.011mol h -1 m -2 The potassium ion/lithium ion binary mixture selectivity was 2.6 and the potassium ion/sodium ion binary mixture selectivity was 1.4, as shown in fig. 4.
Example 7
An anionic covalent organic framework film was prepared, as in example 1 above, with the concentration of the nanoplatelet dispersion in step two being changed from 0.1g/L to 0.5g/L, giving an anionic covalent organic framework film, designated film 7. The monovalent cation separation experiment was performed on membrane 7, as a result of which: potassium ion permeation rate of 0.010mol h -1 m -2 The potassium ion/lithium ion binary mixture selectivity was 2.8 and the potassium ion/sodium ion binary mixture selectivity was 1.5, as shown in fig. 4.
The monovalent cation permeation rates and monovalent cation binary mixture selectivities of membranes 1 through 7 are summarized in Table 1, where A represents 1, 4-diaminobenzenesulfonic acid, B represents 1, 4-diaminophenylphosphonic acid, and C represents 1, 4-diaminobenzenecarboxylic acid in the monomer species.
TABLE 1
In summary, the preparation method of the anionic covalent organic framework film provided by the invention strengthens the interlayer electrostatic interaction of the anionic covalent organic framework by utilizing the pH-mediated oil-water-oil interfacial polymerization method, and promotes the in-plane growth of the covalent organic framework to obtain the nano-sheet so as to solve the film forming problem of the anionic covalent organic framework. The anion covalent organic framework membrane prepared by the nano-sheet has pore diameter smaller than 2 nanometers and acid groups easy to modulate, a hydration structure can be created in the membrane, the screening function of different monovalent cations is obtained, and an efficient monovalent cation separation process is realized, as shown in fig. 2, 3, 4 and table 1, the potassium ion permeation rate and the ion selectivity of the membrane are both reduced along with the increase of the concentration of the oil phase solution, the potassium ion permeation rate of the membrane is reduced along with the increase of the dispersion concentration of the nano-sheet, and the ion selectivity of the membrane is increased along with the increase of the concentration of the nano-sheet dispersion. When 1, 4-diamine-based phenylphosphonic acid is selected as a monomer, the concentration of the oil phase solution A is 0.5mol/L, the concentration of the oil phase solution B is 0.75mol/L, and the concentration of the nano-sheet dispersion liquid is 0.1g/L, the finally prepared anion covalent organic framework membrane has better separation performance.
Although the invention has been described above with reference to the accompanying drawings, the invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many modifications may be made by those of ordinary skill in the art without departing from the spirit of the invention, which fall within the protection of the invention.
Claims (7)
1. The preparation method of the anionic covalent organic framework membrane for monovalent cation separation is characterized in that the membrane is composed of two types of reaction monomers of 1,3, 5-trihydroxybenzoic acid and 1, 4-diamine benzoic acid, wherein the two types of reaction monomers firstly generate anionic covalent organic framework nano sheets through a pH-mediated oil-water-oil interfacial polymerization method, and then assemble the nano sheets on a porous substrate through a vacuum auxiliary assembly method to prepare the anionic covalent organic framework membrane; the membrane integrally presents an asymmetric structure and comprises a compact cortex and a porous supporting layer, wherein the average pore diameter of the compact cortex is 1.3-1.5nm, and the thickness of the compact cortex is 0.1-5.0 mu m; the porous supporting layer is of a fiber staggered stacking structure, and the average pore diameter is 2.0 mu m; the anionic covalent organic framework film is prepared according to the following steps:
step one, preparing an anionic covalent organic framework nano sheet by adopting an oil-water-oil interfacial polymerization method:
1,3, 5-trihydroxybenzene trimesic aldehyde is dissolved in methylene dichloride according to the concentration of 0.5-3mol/L, ultrasonic treatment is carried out for 15 minutes, and the obtained solution is recorded as oil phase solution A;
1, 4-diamine benzoic acid is dissolved in N, N-dimethylformamide according to the concentration of 0.75-4.5mol/L, ultrasonic treatment is carried out for 15 minutes, and the obtained solution is recorded as oil phase solution B; the 1, 4-diamine benzoic acid is one of 1, 4-diamine benzene phosphonic acid, 1, 4-diamine benzene sulfonic acid and 1, 4-diamine benzene carboxylic acid;
adding acetic acid or sodium bicarbonate into deionized water, regulating the pH to 4-12, and performing ultrasonic treatment for 15 minutes to obtain a water phase solution;
slowly assembling the oil phase solution A, the water phase solution and the oil phase solution B in a sequence from bottom to top according to the volume ratio of (4-8): 1:2, reacting for 72 hours, extracting, separating liquid, and collecting the water phase solution therein to obtain the anionic covalent organic framework nano-sheet dispersion;
preparing an anionic covalent organic framework film by a vacuum assisted assembly method:
the concentration of the anionic covalent organic framework nano-sheet dispersion liquid prepared in the step one is regulated to be 0.1-0.5g/L, and the dispersion liquid is assembled on a porous substrate of a solvent filter device by suction filtration under the vacuum condition of 0.05-0.1MPa, so that an anionic covalent organic framework film is obtained; the porous substrate is polytetrafluoroethylene with an average pore diameter of 0.2 mu m, and the effective interception radius of the anionic covalent organic framework membrane is 0.6-1.0 cm.
2. The method according to claim 1, wherein the 1, 4-diaminobenzoic acid is 1, 4-diaminophenylphosphonic acid and has a pH of 11.
3. The method according to claim 1, wherein the 1, 4-diaminobenzoic acid is 1, 4-diaminobenzenesulfonic acid and the pH is 4.
4. The method according to claim 1, wherein the 1, 4-diaminobenzoic acid is 1, 4-diaminobenzene carboxylic acid and the pH is 7.
5. The preparation method according to claim 1, wherein the concentration of the oil phase solution A is 0.5mol/L and the concentration of the oil phase solution B is 0.75mol/L.
6. The method of claim 1, wherein in step two, the concentration of the anionic covalent organic framework nanoplatelet dispersion is 0.1g/L.
7. Use of an anionic covalent organic framework membrane for monovalent cation separation, characterized in that the anionic covalent organic framework membrane prepared by the preparation method according to any one of claims 1 to 6 is used in monovalent cation separation process, and the potassium ion permeation rate is 0.010-0.016mol h -1 m -2 The selectivity of the binary mixture of potassium ions and lithium ions is 1.0-4.2, and the selectivity of the binary mixture of potassium ions and sodium ions is 0.8-2.5.
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