A carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane and a preparation method thereof

Abstract

The application discloses a carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane and a preparation method thereof. Carboxyl groups in carboxymethyl-beta-cyclodextrin are activated by using 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and activated carboxymethyl-beta-cyclodextrin is obtained. The activated carboxymethyl-beta-cyclodextrin aqueous solution and a COF nanosheet dispersion liquid are uniformly mixed, and the obtained precipitate is washed and dispersed in deionized water at room temperature, so that a CM-beta-CD@COF nanosheet dispersion liquid is obtained. The CM-beta-CD@COF nanosheet dispersion liquid and an ANF / water suspension liquid are uniformly mixed, so that a CM-beta-CD@COF / ANF composite dispersion liquid is obtained. The CM-beta-CD@COF / ANF composite nanofiltration membrane is obtained by assembling according to a vacuum filtration method. The carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane has no defects, high permeability and high selectivity, and balances the permeability and selectivity of the composite nanofiltration membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of preparation of composite nanofiltration membranes, and particularly relates to a carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] With the rapid development of industry and agriculture, freshwater resource shortage has become one of the important problems to be solved. Two-dimensional layered nanofiltration membranes formed by two-dimensional nanomaterials (such as graphene oxide, molybdenum disulfide, transition metal carbide, etc.) through stacking or self-assembly have a membrane structure with nanoscale layered channels, and are an important material newly emerging in the field of membrane separation technology in recent years, which has the characteristics of high selectivity, high flux, good stability and energy saving and environmental protection, and shows a wide application prospect in water treatment, food processing, medicine, chemical industry, environmental protection, energy, agriculture and other fields, and is therefore considered to have great potential in seawater, brackish water desalination and wastewater recovery.

[0003] Two-dimensional covalent organic framework nanosheets (COF) are a kind of emerging porous crystalline polymer nanomaterials formed by covalent bonding of organic monomers. Due to the characteristics of high, directional and ordered pore structure, rich nanofluidic channels, large specific surface area, excellent chemical stability and easy functionalization, COF has great application potential in the fields of material transmission and molecular separation.

[0004] At present, the preparation methods of two-dimensional COF mainly include a bottom-up interfacial polymerization method and a top-down exfoliation method, and the most commonly used method is the bottom-up interfacial polymerization method. Since COF membranes are inevitably formed in the interfacial polymerization process, the COF prepared by this method usually has a low lateral size (less than 100 nm), and the two-dimensional layered nanofiltration membrane assembled by the COF usually has many defects and shows low selectivity to target separation substances. SUMMARY

[0005] In view of the problems in the prior art, the application provides a carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane and a preparation method thereof, which is simple in method, low in raw material cost, easy to realize industrial application, defect-free, high in permeability and selectivity, and balances the permeability and selectivity of the composite nanofiltration membrane.

[0006] The application is realized by the following technical scheme:

[0007] A preparation method of a carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane, comprising the following steps:

[0008] S1, activating the carboxyl group in carboxymethyl-β-cyclodextrin with 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide to obtain activated carboxymethyl-β-cyclodextrin, which is used as a cross-linking agent to link several COF nanosheets when in contact with COF nanosheets to obtain CM-β-CD@COF nanosheets with high aspect ratio;

[0009] S2, mixing the activated carboxymethyl-β-cyclodextrin aqueous solution and the COF nanosheet dispersion liquid uniformly, wherein the mass ratio of COF to carboxymethyl-β-cyclodextrin in S1 is (1-9):(1-9), and then reacting at room temperature, washing the obtained precipitate and dispersing it in deionized water to obtain a CM-β-CD@COF nanosheet dispersion liquid;

[0010] S3, mixing the CM-β-CD@COF nanosheet dispersion liquid and the ANF / water suspension liquid uniformly, wherein the mass ratio of CM-β-CD@COF nanosheets to ANF is (99-90):(1-10) to obtain a CM-β-CD@COF / ANF composite dispersion liquid, and then assembling by vacuum filtration to obtain a carboxymethyl-β-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane.

[0011] Preferably, S1 first dissolves carboxymethyl-β-cyclodextrin, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide in deionized water in the ratio of (1-9) mg:(2-15) mg:(1-9) mg:(10-30) mL, respectively, and then stirs to obtain the activated carboxymethyl-β-cyclodextrin aqueous solution of S2.

[0012] Further, the stirring is performed for 0.5-2 h to obtain the activated carboxymethyl-β-cyclodextrin aqueous solution of S2.

[0013] Preferably, the COF nanosheet dispersion liquid of S2 is obtained by the following process:

[0014] Dissolve triformylphloroglucinol in n-octanoic acid, and then add dropwise to the top of the aqueous solution of diamino benzenesulfonic acid, wherein the mass ratio of triformylphloroglucinol to diamino benzenesulfonic acid is (20-60):(25-75), and after reacting for 3-5 days, dialyze with deionized water to obtain a COF nanosheet dispersion liquid.

[0015] Further, the ratio of triformylphloroglucinol to n-octanoic acid is (25-75) mg:(20-40) mL, and in the aqueous solution of diamino benzenesulfonic acid, the ratio of diamino benzenesulfonic acid to deionized water is (20-60) mg:(10-30) mL, and the concentration of the COF nanosheet dispersion liquid is 0.1-0.3 mg / mL.

[0016] Preferably, the reaction in S2 is carried out at room temperature for 12-24h.

[0017] Preferably, the ANF / water suspension in S3 is obtained by the following process:

[0018] The para-aramid fiber, potassium hydroxide and dimethyl sulfoxide are mixed uniformly in a ratio of 1g:1.5g:500mL, then stirred at room temperature for 7-14 days to obtain a deprotonated ANF dispersion, and then deionized water is added and stirred uniformly to obtain an ANF / water suspension.

[0019] Preferably, S3 mixes the CM-β-CD@COF nanosheet dispersion and the ANF / water suspension, the concentration of the CM-β-CD@COF nanosheet dispersion is 0.1-0.3mg / mL, and the concentration of the ANF / water suspension is 0.01-0.02mg / mL, then ultrasonic dispersion is carried out at 400-800W for 5-20min, and then stirring is carried out for 12-24h to obtain a CM-β-CD@COF / ANF composite dispersion.

[0020] Preferably, in S3, the CM-β-CD@COF / ANF composite dispersion is assembled on a polyether sulfone microfiltration membrane as a support layer by vacuum filtration, and a carboxymethyl-β-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane is formed on the support layer after room temperature drying for 12-24h.

[0021] A carboxymethyl-β-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane obtained by the preparation method of the carboxymethyl-β-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane according to any one of the above.

[0022] Compared with the prior art, the present application has the following beneficial technical effects:

[0023] The preparation method of the carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane of the application can activate the carboxyl group in CM-beta-CD by 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, so that CM-beta-CD can be used as a crosslinking agent, and then when in contact with COF nanosheets, several COF nanosheets can be bonded to obtain CM-beta-CD@COF nanosheets with high aspect ratio. On the other hand, the outer diameter of CM-beta-CD can match the vertical one-dimensional nanopore of the COF nanosheet, so that CM-beta-CD can easily enter the nanopore of the COF nanosheet, and by constructing a pore-in-pore structure, the CM-beta-CD@COF nanosheet has a sub-nanometer pore, which can improve the size screening capability of the nanofiltration membrane. By introducing a small amount of ANF as a reinforcing phase, the CM-beta-CD@COF / ANF composite nanofiltration membrane can be finally assembled according to the vacuum suction filtration method. In addition, the unique hydrophobic inner cavity of CM-beta-CD can promote the frictionless transport of water molecules, and finally the CM-beta-CD@COF / ANF composite nanofiltration membrane exhibits high flux, high selectivity and strong stability. The CM-beta-CD is introduced into the two-dimensional COF nanosheet by EDC / NHS (1-ethyl-(3-dimethylaminopropyl) carbodiimide) reaction to prepare CM-beta-CD@COF nanosheets with a pore-in-pore structure and high aspect ratio, and finally obtain a CM-beta-CD@COF / ANF composite nanofiltration membrane with no defects, high permeability and high selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 SEM image of the COF nanofiltration membrane described in Comparative Example 1 of the application.

[0025] Figure 2 SEM image of the CM-beta-CD@COF / ANF composite nanofiltration membrane obtained in Example 1 of the application.

[0026] Figure 3 UV absorption spectrum of the filtrate and the feed solution after the methylene blue solution (feed solution) with a concentration of 4 ppm is separated by the CM-beta-CD@COF / ANF composite nanofiltration membrane obtained in Example 1 of the application. DETAILED DESCRIPTION

[0027] The application will be further described in detail below with specific examples, which are an explanation of the application rather than a limitation.

[0028] The preparation method of the carboxymethyl-beta-cyclodextrin modified two-dimensional covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane of the application specifically includes the following steps:

[0029] Step (1), 20-60 mg of diaminobenzene sulfonic acid was added to 10-30 mL of deionized water, and ultrasonic was performed for 10-30 min to form solution A;

[0030] Step (1), 20-60 mg of diaminobenzene sulfonic acid was added to 10-30 mL of deionized water, and ultrasonic was performed for 10-30 min to form solution A;

[0031] Solution A and solution B were prepared for use.

[0032] Step (2), solution A obtained in step (1) was used as the lower layer, and solution B was used as the upper layer (by dropwise addition) and placed in a beaker, and then left to stand at room temperature for 3-5 days to allow the interfacial polymerization reaction to occur, and then the lower layer COF (TpPa-SO3H) nanosheet was taken out and placed in a dialysis bag for dialysis for 3-5 days to obtain a COF nanosheet dispersion liquid, and the concentration of COF in the COF nanosheet dispersion liquid was measured to be 0.1-0.3 mg / mL.

[0033] Step (3), 1-9 mg of carboxymethyl-β-cyclodextrin (abbreviated as CM-β-CD), 2-15 mg of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (abbreviated as EDC·HCl), and 1-9 mg of N-hydroxysuccinimide (abbreviated as NHS) were sequentially dissolved in 10-30 mL of deionized water, and stirred at room temperature for 0.5-2 h to activate the carboxyl group in CM-β-CD by reaction of 1-ethyl-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide.

[0034] Step (4), the above prepared 10-30 mL of activated CM-β-CD solution was mixed uniformly with 10-30 mL of the COF nanosheet dispersion liquid prepared in step (2), and reacted at room temperature for 12-24 h. The obtained precipitate was centrifuged and washed with deionized water, and then dispersed in deionized water to obtain a CM-β-CD@COF nanosheet dispersion liquid with a concentration of 0.1-0.3 mg / mL, wherein @ represents modification and cross-linking.

[0035] Step (5), para-aramid fiber, potassium hydroxide and dimethyl sulfoxide were mixed in a beaker at a ratio of 1 g:1.5 g:500 mL, and then continuously stirred at room temperature for 7-14 days to prepare a deprotonated aramid nanofiber (ANF) dispersion liquid, and then deionized water was added and stirred uniformly to perform secondary protonation, and a ANF / water suspension liquid with a concentration of 0.01-0.02 mg / mL was obtained.

[0036] Step (6), mixing the CM-β-CD@COF nanosheet dispersion obtained in step (4) and the ANF / water suspension, wherein the mass ratio of CM-β-CD@COF nanosheet and ANF is (99-90):(1-10), and then ultrasonic dispersion is carried out under the condition of 400-800 W power for 5-20 min, and then it is placed on a magnetic stirrer, and after stirring for 12-24 h, a CM-β-CD@COF / ANF composite dispersion is obtained.

[0037] Step (7), using a polyether sulfone microfiltration membrane as a support layer, the composite dispersion obtained in step (6) is assembled on the polyether sulfone microfiltration membrane by vacuum filtration, and after drying at room temperature for 12-24 h, a CM-β-CD@COF / ANF composite nanofiltration membrane is formed on the mechanical support layer.

[0038] Example 1

[0039] The application discloses a preparation method of a carboxymethyl-beta-cyclodextrin modified two-dimensional covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane.

[0040] Step (1), 40 mg of diaminobenzenesulfonic acid is added to 20 mL of deionized water, and ultrasonic treatment is carried out for 20 min, so as to form solution A;

[0041] 50 mg of tri-aldehyde-based phloroglucinol is added to 30 mL of n-octanoic acid, and ultrasonic treatment is carried out for 20 min, so as to form solution B;

[0042] Solution A and solution B are prepared.

[0043] Step (2), solution A obtained in step (1) is used as a lower layer, and solution B is used as an upper layer, which are placed in a beaker, and interfacial polymerization is carried out at room temperature for 3 days; the COF nanosheet in the lower layer is taken out and placed in a dialysis bag for dialysis for 3 days, so as to obtain a COF nanosheet dispersion; and the concentration of COF in the COF nanosheet dispersion is 0.2 mg / mL.

[0044] Step (3), 2 mg of carboxymethyl-beta-cyclodextrin (CM-β-CD), 3 mg of 1-ethyl-(3-dimethylaminopropyl) carbonyldiimidazole hydrochloride (EDC·HCl) and 2 mg of N-hydroxysuccinimide (NHS) are sequentially dissolved in 10 mL of deionized water, and stirring is carried out at room temperature for 1 h, so as to activate the carboxyl group in the CM-β-CD.

[0045] Step (4), 10 mL of the above prepared activated CM-β-CD solution was mixed with 10 mL of the COF nanosheet dispersion prepared in step (2) uniformly, and reacted at room temperature for 12 h. The obtained precipitate was separated by centrifugation and washed with deionized water, and then dispersed in deionized water to obtain a CM-β-CD@COF nanosheet dispersion with a concentration of 0.2 mg / mL.

[0046] Step (5), 1 g of para-aramid fiber, 1.5 g of potassium hydroxide and 500 mL of dimethyl sulfoxide were mixed uniformly in a beaker, and then placed at room temperature for continuous stirring for 12 days to prepare a deprotonated aramid nanofiber (ANF) dispersion. Then, deionized water was added and stirred uniformly to perform secondary protonation, and an ANF / water suspension with a concentration of 0.01 mg / mL was obtained.

[0047] Step (6), the CM-β-CD@COF nanosheet dispersion obtained in step (4) and the ANF / water suspension were mixed, and the mass ratio of CM-β-CD@COF nanosheet to ANF was 99:1. Then, it was ultrasonically dispersed at a power of 600 W for 10 min, and then placed on a magnetic stirrer and stirred for 12 h to obtain a CM-β-CD@COF / ANF composite dispersion.

[0048] Step (7), the composite dispersion obtained in step (6) was assembled on a polyether sulfone microfiltration membrane as a support layer by vacuum filtration, and a CM-β-CD@COF / ANF composite nanofiltration membrane was formed on the mechanical support layer after drying at room temperature for 12 h.

[0049] Comparative Example 1

[0050] The preparation method of the COF nanofiltration membrane specifically includes the following steps:

[0051] Step (1), 40 mg of diamino benzene sulfonic acid was added to 20 mL of deionized water, and ultrasonicated for 20 min to form solution A;

[0052] 50 mg of tri-aldehyde phloroglucinol was added to 30 mL of n-octanoic acid, and ultrasonicated for 20 min to form solution B;

[0053] Solution A and solution B were prepared.

[0054] Step (2), solution A obtained in step (1) was used as the lower layer and solution B was used as the upper layer, which were placed in a beaker and interfacially polymerized at room temperature for 3 days. The COF nanosheet in the lower layer was taken out and dialyzed in a dialysis bag for 3 days to obtain a COF nanosheet dispersion. The concentration of COF in the COF nanosheet dispersion was measured to be 0.2 mg / mL.

[0055] Step (3), the COF nanosheet dispersion obtained in step (2) is assembled on a polyether sulfone microfiltration membrane as a support layer by vacuum filtration, and a small amount of COF nanofiltration membrane is formed on the mechanical support layer after drying at room temperature for 12 hours.

[0056] Since the lateral size of the COF nanosheet is smaller than the pore size of the polyether sulfone microfiltration membrane, the COF nanosheet is almost not retained on the polyether sulfone microfiltration membrane, Figure 1 In the middle, only 2 COF nanosheets can be seen in the pores of the polyether sulfone microfiltration membrane, and the COF nanofiltration membrane produces a large number of voids and defects.

[0057] Since the CM-β-CD@COF has a larger lateral size, it can be seen that Figure 2 In the middle, the CM-β-CD@COF / ANF composite nanofiltration membrane is almost completely retained on the polyether sulfone microfiltration membrane, and the surface of the CM-β-CD@COF / ANF composite nanofiltration membrane is smooth and no cracks appear.

[0058] Figure 3 In the middle, the absorbance of 4 ppm methylene blue solution (feed liquid) at 664 nm is 0.72, and the absorbance of the filtrate after separation by the CM-β-CD@COF / ANF composite nanofiltration membrane obtained by the present application is 0.01 at 664 nm, and the separation efficiency is more than 98%.

[0059] In addition, the CM-β-CD@COF / ANF composite nanofiltration membrane also shows a permeation flux as high as 439 L·m –2 ·h –1 ·bar –1 .

[0060] Example 2

[0061] The present application is a preparation method of a carboxymethyl-β-cyclodextrin modified two-dimensional covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane, which specifically includes the following steps:

[0062] Step (1), 20 mg of diamino benzene sulfonic acid is added to 10 mL of deionized water, and ultrasonic treatment is performed for 10 min to form solution A;

[0063] 25 mg of tri-aldehyde phloroglucinol is added to 20 mL of n-octanoic acid, and ultrasonic treatment is performed for 10 min to form solution B;

[0064] Solution A and solution B are ready for use.

[0065] Step (2), solution A obtained in step (1) is used as the lower layer, and solution B is used as the upper layer, which is placed in a beaker and interfacial polymerization is performed at room temperature for 3 days. The COF nanosheet in the lower layer is taken out and placed in a dialysis bag for dialysis for 3 days to obtain a COF nanosheet dispersion.

[0066] Step (3), 6 mg of carboxymethyl-β-cyclodextrin (CM-β-CD), 9 mg of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC·HCl), and 5 mg of N-hydroxysuccinimide (NHS) were sequentially dissolved in 20 mL of deionized water, and stirred at room temperature for 1.5 h to activate the carboxyl group in CM-β-CD.

[0067] Step (4), the above prepared 20 mL of activated CM-β-CD solution was mixed with 20 mL of COF nanosheet dispersion prepared in step (2) and uniformly mixed at room temperature for 18 h. The obtained precipitate was centrifuged and washed with deionized water, and then dispersed in deionized water to obtain a CM-β-CD@COF nanosheet dispersion.

[0068] Step (5), 1 g of para-aramid fiber, 1.5 g of potassium hydroxide and 500 mL of dimethyl sulfoxide were uniformly mixed in a beaker, and then placed in a room temperature for continuous stirring for 7 days to obtain a deprotonated aramid nanofiber (ANF) dispersion. Then, deionized water was added and stirred uniformly to perform secondary protonation to obtain an ANF / water suspension.

[0069] Step (6), the CM-β-CD@COF nanosheet dispersion obtained in step (4) and the ANF / water suspension were mixed, and the mass ratio of CM-β-CD@COF nanosheet to ANF was 95:5. Then, it was ultrasonically dispersed for 5 min under the condition of 400 W power, and then placed on a magnetic stirrer and stirred for 18 h to obtain a CM-β-CD@COF / ANF composite dispersion.

[0070] Step (7), the composite dispersion obtained in step (6) was assembled on a polyether sulfone microfiltration membrane as a support layer by vacuum filtration, and a CM-β-CD@COF / ANF composite nanofiltration membrane was formed on the mechanical support layer after drying at room temperature for 18 h.

[0071] Example 3

[0072] The preparation method of the carboxymethyl-β-cyclodextrin modified two-dimensional covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane according to the present application specifically includes the following steps:

[0073] Step (1), 60 mg of diamino benzenesulfonic acid was added to 30 mL of deionized water and ultrasonically treated for 30 min to form solution A;

[0074] 75 mg of tri-aldehyde phloroglucinol was added to 40 mL of n-octanoic acid and ultrasonically treated for 30 min to form solution B;

[0075] Solution A and Solution B are standby.

[0076] Step (2), the solution A obtained in step (1) is placed in a beaker as the lower layer and solution B as the upper layer, and interfacial polymerization is carried out at room temperature for 5 days. The COF nanosheet in the lower layer is taken out and placed in a dialysis bag for dialysis for 5 days to obtain a COF nanosheet dispersion.

[0077] Step (3), 9 mg of carboxymethyl-β-cyclodextrin (CM-β-CD), 15 mg of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC·HCl), and 9 mg of N-hydroxysuccinimide (NHS) are sequentially dissolved in 30 mL of deionized water, and the carboxyl group in CM-β-CD is activated by stirring at room temperature for 2 h.

[0078] Step (4), the above prepared 30 mL of activated CM-β-CD solution is mixed with 30 mL of the COF nanosheet dispersion prepared in step (2) and uniformly mixed, and the reaction is carried out at room temperature for 24 h. The obtained precipitate is centrifuged and washed with deionized water, and then dispersed in deionized water to obtain a CM-β-CD@COF nanosheet dispersion.

[0079] Step (5), 1 g of para-aramid fiber, 1.5 g of potassium hydroxide, and 500 mL of dimethyl sulfoxide are uniformly mixed in a beaker, and then placed in a room temperature continuous stirring for 14 days to obtain a deprotonated aramid nanofiber (ANF) dispersion. Then, deionized water is added and stirred uniformly to perform secondary protonation to obtain an ANF / water suspension.

[0080] Step (6), the CM-β-CD@COF nanosheet dispersion obtained in step (4) and the ANF / water suspension are mixed, and the mass ratio of CM-β-CD@COF nanosheet to ANF is 90:10. Then, it is ultrasonically dispersed at a power of 800 W for 20 min, and then placed on a magnetic stirrer and stirred for 24 h to obtain a CM-β-CD@COF / ANF composite dispersion.

[0081] Step (7), the composite dispersion obtained in step (6) is assembled on a polyether sulfone microfiltration membrane as a support layer by vacuum filtration, and a CM-β-CD@COF / ANF composite nanofiltration membrane is formed on the mechanical support layer after drying at room temperature for 24 h.

Claims

1. A method for preparing a carboxymethyl-β-cyclodextrin modified covalent organic framework nanoplatelet / aramid nanofiber composite nanofiltration membrane, characterized in that, Comprise the following steps: S1, the carboxyl group in carboxymethyl-beta-cyclodextrin is activated by using 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, to obtain activated carboxymethyl-beta-cyclodextrin; S2, the activated carboxymethyl-beta-cyclodextrin aqueous solution and the COF nanosheet dispersion liquid are mixed uniformly, wherein the mass ratio of COF to carboxymethyl-beta-cyclodextrin in S1 is (1~9):(1~9), then the reaction is carried out at room temperature, the obtained precipitate is washed and dispersed in deionized water to obtain the CM-beta-CD@COF nanosheet dispersion liquid; The COF nanosheet dispersion liquid is obtained by the following process: Tri-aldehyde phloroglucinol is dissolved in n-octanoic acid, then added dropwise to the top of the aqueous solution of diamino benzenesulfonic acid, wherein the mass ratio of tri-aldehyde phloroglucinol to diamino benzenesulfonic acid is (20~60):(25~75), after reacting for 3~5 days, the COF nanosheet dispersion liquid is obtained by dialysis with deionized water; S3, the CM-beta-CD@COF nanosheet dispersion liquid and aramid nanofiber ANF / water suspension liquid are mixed uniformly, wherein the mass ratio of CM-beta-CD@COF nanosheet to ANF is (99~90):(1~10), the concentration of the CM-beta-CD@COF nanosheet dispersion liquid is 0.1~0.3 mg / mL, and the concentration of the ANF / water suspension liquid is 0.01~0.02 mg / mL, to obtain a CM-beta-CD@COF / ANF composite dispersion liquid, then the CM-beta-CD@COF / ANF composite dispersion liquid is assembled on a polyether sulfone microfiltration membrane as a support layer by vacuum filtration, and a carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane is formed on the support layer after drying at room temperature for 12~24 h, to obtain the carboxymethyl-beta-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane.

2. The method of claim 1, wherein the carboxymethyl-β-cyclodextrin modified covalent organic framework nanoplatelet / aramid nanofiber composite nanofiltration membrane is prepared by the following steps of: S1 is (1~9) mg:(2~15) mg:(1~9) mg:(10~30) mL in proportion, carboxymethyl-beta-cyclodextrin, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are dissolved in deionized water in turn, then stirred to obtain the activated carboxymethyl-beta-cyclodextrin aqueous solution of S2.

3. The method of claim 2, wherein the carboxymethyl-β-cyclodextrin modified covalent organic framework nanoplatelet / aramid nanofiber composite nanofiltration membrane is prepared by the following steps of: (1) preparing a covalent organic framework nanoplatelet / aramid nanofiber composite nanofiltration membrane; (2) modifying the covalent organic framework nanoplatelet / aramid nanofiber composite nanofiltration membrane with carboxymethyl-β-cyclodextrin. The stirring is carried out for 0.5~2 h to obtain the activated carboxymethyl-beta-cyclodextrin aqueous solution of S2.

4. The method for preparing the carboxymethyl-β-cyclodextrin-modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, The ratio of tri-aldehyde phloroglucinol to n-octanoic acid is (25~75) mg:(20~40) mL, and the ratio of diamino benzenesulfonic acid to deionized water in the aqueous diamino benzenesulfonic acid solution is (20~60) mg:(10~30) mL, and the concentration of the COF nanosheet dispersion liquid is 0.1~0.3 mg / mL.

5. The method for preparing the carboxymethyl-β-cyclodextrin-modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, The reaction in S2 is carried out at room temperature for 12~24 h.

6. The method of claim 1, wherein the carboxymethyl-β-cyclodextrin modified covalent organic framework nanoplatelet / aramid nanofiber composite nanofiltration membrane is prepared by the following steps of: The ANF / water suspension liquid in S3 is obtained by the following process: The para-aramid fiber, potassium hydroxide and dimethyl sulfoxide are mixed uniformly in a ratio of 1 g: 1.5 g: 500 mL, then stirred at room temperature for 7-14 days to obtain a deprotonated ANF dispersion, and then deionized water is added and stirred uniformly to obtain an ANF / water suspension.

7. The method for preparing the carboxymethyl-β-cyclodextrin-modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, S3 The CM-β-CD@COF nanosheet dispersion and the ANF / water suspension are mixed, then ultrasonically dispersed at 400-800 W for 5-20 min, and then stirred for 12-24 h to obtain a CM-β-CD@COF / ANF composite dispersion.

8. A carboxymethyl-β-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane obtained by the preparation method of the carboxymethyl-β-cyclodextrin modified covalent organic framework nanosheet / aramid nanofiber composite nanofiltration membrane according to any one of claims 1-7.

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