Modified carbon nanotube-polyimide composite nanofiltration membrane, preparation method and application thereof

Abstract

The application relates to the technical field of nanofiltration separation, and discloses a modified carbon nanotube-polyimide composite nanofiltration membrane as well as a preparation method and application thereof. The composite nanofiltration membrane comprises a support layer and a modified carbon nanotube-polyimide layer; and the orientation degree of the modified carbon nanotube in the modified carbon nanotube-polyimide layer is 60-80%. The composite nanofiltration membrane has high salt rejection rate and water flux, excellent solvent resistance, and the modified carbon nanotube in the composite nanofiltration membrane has high orientation degree.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration separation technology, specifically to a modified carbon nanotube-polyimide composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration (NF) was first used in the mid-1980s to describe a pressure-driven membrane separation process that lies between reverse osmosis and ultrafiltration. Nanofiltration membranes typically have an average pore size between 0.5 and 2 nm. NF membranes can effectively separate small molecules and high-valence salt ions with molecular weights between 200 and 1000 Da, and also exhibit some separation performance for monovalent salt ions. NF membranes have great potential for separating organic matter and are widely used in food, petrochemical, pharmaceutical, and fine chemical industries. Polyimide (PI), as a polymer material with excellent heat resistance, mechanical properties, and solvent resistance, is widely used in the field of nanofiltration membranes. Interfacial polymerization has become one of the most common and effective methods for preparing nanofiltration membranes due to its ability to produce ultrathin separation layers. Nanofiltration membranes prepared by interfacial polymerization reduce the resistance caused by the thickness of the separation layer during separation, which is beneficial to improving the separation performance of NF membranes. However, the solvent-resistant nanofiltration membranes prepared from polymer materials are not chemically stable enough in organic solvents, which affects the flux of the NF membrane. To address the contradiction between the increased permeation flux and the decreased separation efficiency of existing nanofiltration membranes, organic-inorganic hybrid modification can be carried out on the PI-NF membrane.

[0003] Carbon nanotubes (CNTs) possess properties such as low density, low coefficient of friction, π-π stacking interactions with aromatic compounds, and a large number of nanochannels. Therefore, adding them as nanofillers to separation membranes can improve separation performance. However, CNTs are not easily dispersed uniformly in solvents.

[0004] Reports often suggest that CNTs are functionalized by grafting groups such as -COOH or -NH2 onto their surface to improve the performance of nanofiltration membranes. However, the problem of disordered arrangement of functionalized carbon nanotubes during interfacial polymerization remains to be solved.

[0005] Therefore, it is of great significance to develop a functionalized carbon nanotube-polyimide nanofiltration membrane with directional alignment. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low salt rejection rate, low water flux, and poor solvent resistance of modified carbon nanotube-polyimide nanofiltration membranes in the prior art, and to provide a modified carbon nanotube-polyimide composite nanofiltration membrane, its preparation method, and its application. This composite nanofiltration membrane has high salt rejection rate and water flux, excellent solvent resistance, and the modified carbon nanotubes in the composite nanofiltration membrane have high orientation.

[0007] To achieve the above objectives, the first aspect of the present invention provides a modified carbon nanotube-polyimide composite nanofiltration membrane, characterized in that the composite nanofiltration membrane comprises a support layer and a modified carbon nanotube-polyimide layer;

[0008] The degree of orientation of the modified carbon nanotubes in the modified carbon nanotube-polyimide layer is 60-80%.

[0009] A second aspect of the present invention provides a method for preparing a modified carbon nanotube-polyimide composite nanofiltration membrane, characterized in that the method comprises:

[0010] S1. The modified carbon nanotubes are mixed with an aqueous solution containing amine monomers to obtain a mixture, and the support layer is immersed in the mixture to obtain the modified support layer.

[0011] S2. The modified support layer is immersed in an organic phase solution containing acyl chloride monomer to carry out an interfacial polymerization reaction, thereby obtaining a polyamic acid film supported on the modified support layer.

[0012] S3. In the presence of a magnetic field, after the polyamic acid membrane loaded with the modified support layer is subjected to a first array treatment, the polyamic acid membrane after the first array is subjected to an imidization treatment in the presence of a chemical imid reagent to obtain the modified carbon nanotube-polyimide composite nanofiltration membrane.

[0013] The first array treatment results in the modified carbon nanotubes in the modified carbon nanotube-polyimide composite nanofiltration membrane having an orientation degree of 60-80%.

[0014] A third aspect of the present invention provides a modified carbon nanotube-polyimide composite nanofiltration membrane prepared by the above method.

[0015] The fourth aspect of this invention provides the application of the modified carbon nanotube-polyimide composite nanofiltration membrane provided in the first and third aspects of this invention, and the method for preparing the modified carbon nanotube-polyimide composite nanofiltration membrane provided in the second aspect, in nanofiltration treatment.

[0016] Through the above technical solutions, the modified carbon nanotube-polyimide composite nanofiltration membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0017] (1) The modified carbon nanotube-polyimide composite nanofiltration membrane has a high water flux, specifically, a water flux of not less than 10.3 L / (m²). -2 ·h -1 •bar)) maintains a high rejection rate (not less than 85%) for salt solutions;

[0018] (2) The modified carbon nanotube-polyimide composite nanofiltration membrane has good solvent resistance. After being soaked in organic solution, it still maintains high rejection rate and high water flux for salt solution. Attached Figure Description

[0019] Figure 1 This is a surface morphology image of the magnetized hydrophilic thiolized carbon nanotube-polyimide nanofiltration membrane prepared in Example 4 of this invention.

[0020] Figure 2 This is a cross-sectional morphology diagram of the magnetized hydrophilic thiolized carbon nanotube-polyimide nanofiltration membrane prepared in Example 4 of the present invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of the present invention provides a modified carbon nanotube-polyimide composite nanofiltration membrane, characterized in that the composite nanofiltration membrane comprises a support layer and a modified carbon nanotube-polyimide layer;

[0023] The degree of orientation of the modified carbon nanotubes in the modified carbon nanotube-polyimide layer is 60-80%.

[0024] In this invention, when the orientation degree of the modified carbon nanotubes in the modified carbon nanotube-polyimide layer meets the above-mentioned range, the composite nanofiltration membrane has the characteristic of directional arrangement, thereby improving its water flux and the rejection rate of salt solutions.

[0025] According to the present invention, the orientation degree of the modified carbon nanotubes in the modified carbon nanotube-polyimide layer is 70-80%.

[0026] According to the present invention, the pore size of the support layer is 0.1-0.3 μm.

[0027] In this invention, when the pore size of the support layer meets the above-mentioned range, the composite nanofiltration membrane can meet the mechanical properties required in the field while having high water flux and salt rejection rate, thus improving its service life.

[0028] In this invention, the thickness of the support layer is 0.1-0.4 mm.

[0029] In this invention, the support layer is selected from at least one of polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), and polysulfone (PSF).

[0030] According to the present invention, the thickness of the modified carbon nanotube-polyimide layer is 1-5 μm, based on the thickness of the composite nanofiltration membrane.

[0031] In this invention, the thickness of the modified carbon nanotube-polyimide layer meets the above-mentioned range, which enables the composite nanofiltration membrane to have high water flux and high salt solution rejection rate.

[0032] According to the present invention, the thickness of the modified carbon nanotube-polyimide layer is 1-3 μm, based on the thickness of the composite nanofiltration membrane.

[0033] According to the present invention, the modified carbon nanotubes are selected from magnetized carbon nanotubes.

[0034] Furthermore, the modified carbon nanotubes are selected from at least one functionalized carbon nanotube selected from magnetized amino carbon nanotubes, magnetized thiol carbon nanotubes, magnetized carboxyl carbon nanotubes, and magnetized hydrophilic thiolized carbon nanotubes.

[0035] In this invention, the modified carbon nanotube can be a modified multi-walled carbon nanotube or a modified single-walled carbon nanotube.

[0036] In this invention, the magnetized amino carbon nanotubes are prepared using amino carbon nanotubes, and the magnetized hydrophilic thiolized carbon nanotubes are prepared using thiolized carbon nanotubes.

[0037] In this invention, the sources of the aminated carbon nanotubes and thiolized carbon nanotubes are not particularly limited; they can be commercially available or obtained in-house, for example, through the following methods:

[0038] Preparation of aminated carbon nanotubes:

[0039] (1) Add multi-walled carbon nanotubes to a mixed acid solution (volume ratio: H2SO4 / HNO3=3 / 1), sonicate at 50-70℃ for 2-6h, dilute with water, centrifuge, wash, filter with a water-based membrane, wash until pH is 6.5-7.5, and vacuum dry at 40-60℃ for 10-30h to obtain carboxylated carbon nanotubes;

[0040] (2) After thoroughly mixing the above carboxylated carbon nanotubes and thionyl chloride, N,N-dimethylformamide (DMF) was added dropwise, and the mixture was refluxed at 60-80℃ for 10-30 h. The mixture was then subjected to a solution of tetrahydrofuran and alcohol (V... 醇 V 水The mixture of 1:1 was centrifuged and washed, and the product was filtered through an organic microporous membrane and vacuum dried to obtain acyl chloride carbon nanotubes.

[0041] (3) After mixing acyl chloride carbon nanotubes, 4-dimethylaminopyridine and organic solvent, ethylenediamine was slowly added and refluxed at 90-110℃ for 7-9h. The product was filtered and the filter cake was washed with ethanol and ultrapure water respectively. Finally, it was vacuum dried at 40-60℃ for 10-30h to obtain aminated carbon nanotubes.

[0042] Preparation of thiolized carbon nanotubes:

[0043] (1) The preparation of carboxylated carbon nanotubes is the same as the preparation steps of aminated carbon nanotubes (1);

[0044] (2) After mixing carboxylated carbon nanotubes, γ-mercaptopropyltriethoxysilane (MTS) and an alcohol solution, the mixture was refluxed at 60-80℃ for 7-9 hours to obtain a mixture. The mixture was then rinsed with an alcohol solution (V 乙醇 :V 去离子水 The mixture was centrifuged (1:1 ratio), washed, and then vacuum filtered through a 0.2-0.3 μm nylon 6 membrane. Finally, it was vacuum dried at 30-50℃ for 10-30 h to obtain thiolized carbon nanotubes.

[0045] According to the present invention, based on the total weight of the modified carbon nanotubes, the functional group grafting rate of the modified carbon nanotubes is 8-50%, preferably 9-45%.

[0046] According to the present invention, the method for preparing the magnetized hydrophilic thiolized carbon nanotubes includes:

[0047] 1) Under sealed and light-protected conditions, thiol-based carbon nanotubes, hydrophilic polymers, photoinitiators, and solvents are mixed to obtain a mixture;

[0048] 2) The mixture was subjected to ultraviolet radiation and then separated to obtain hydrophilic thiolized carbon nanotubes;

[0049] 3) In the presence of a surfactant, hydrophilic thiolated carbon nanotubes and magnetic iron oxide nanoparticles are stirred to obtain a mixture, and then the magnetized hydrophilic thiolated carbon nanotubes are separated.

[0050] In this invention, the mass ratio of the thiol-based carbon nanotubes, the hydrophilic polymer compound, and the initiator is 1-3:2-5:1-4.

[0051] In this invention, the hydrophilic polymer compound is selected from at least one of terminal alkyne-terminated poly(polyethylene glycol methacrylate) block polymethyl methacrylate (P(PEGMA)-b-PMMA-alkynyl), terminal alkyne-terminated 2-phenoxyethyl acrylate grafted polymethyl methacrylate (PHEA-g-PMMA-alkynyl), poly(N-isopropylacrylamide) (PNIPAM), and polyethylene glycol (PEG), preferably P(PEGMA)-b-PMMA-alkynyl.

[0052] In this invention, the hydrophilic polymer compound is preferably P(PEGMA)-b-PMMA-alkynyl, which enables the alkynylated PMMA-bP(PEGMA) block copolymer to be grafted onto thiolated carbon nanotubes to prepare hydrophilic thiolated carbon nanotubes, ultimately resulting in uniform dispersion of carbon nanotubes in the composite nanofiltration membrane.

[0053] In this invention, there is no particular limitation on the type of photoinitiator, which can be a conventional photoinitiator in the art, such as 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173).

[0054] In this invention, before subjecting the mixture to ultraviolet radiation, it is preferable to fill the system containing the mixture with a protective gas to ensure that the reaction environment is free of oxygen.

[0055] In this invention, there is no particular limitation on the type of protective gas; for example, it can be N2 and / or an inert gas. In step 1), it is preferable to use N2 to fill 2-3 times.

[0056] In this invention, the conditions for ultraviolet radiation include: using ultraviolet radiation at 30-40°C for 5-6 hours.

[0057] In this invention, there is no particular limitation on the wavelength of the ultraviolet light, as long as it can initiate the polymerization of the amine monomer and the acyl chloride monomer by the photoinitiator.

[0058] In this invention, there is no particular limitation on the separation method; for example, it can be centrifugal separation, filtration, etc.

[0059] In this invention, to further obtain pure hydrophilic thiolized carbon nanotubes, it is preferable to centrifuge and purify the heated mixture, and then vacuum filter it through a 0.2-0.3 μm nylon 6 membrane. Finally, the mixture is removed by Soxhlet extraction with THF (tetrahydrofuran) for 30-50 h, and then vacuum dried at 30-50 °C for 10-30 h to obtain hydrophilic thiolized carbon nanotubes.

[0060] In this invention, the mass ratio of the surfactant, hydrophilic thiolized carbon nanotubes, and magnetic particles is 3-8:2-7:3-9.

[0061] In this invention, the surfactant is not particularly limited and can be a conventional surfactant in the art, such as sodium dodecyl sulfate (SDS) used in the embodiments of this invention.

[0062] In this invention, there are no particular limitations on the type and method of addition of magnetic particles. Those skilled in the art can adjust them as needed. In order to make the magnetic particles evenly dispersed, it is preferred to add magnetic iron oxide nanoparticles in a stable solution.

[0063] In this invention, there is no particular limitation on the separation method; for example, it can be centrifugal separation, filtration, etc.

[0064] In this invention, the vacuum drying conditions are all conventional drying conditions in the art, such as vacuum drying at 30-50°C for 10-30 hours.

[0065] In this invention, the magnetized amino carbon nanotubes are prepared using amino carbon nanotubes, and the magnetized hydrophilic thiolated carbon nanotubes are prepared using hydrophilic thiolated carbon nanotubes.

[0066] In this invention, the preparation methods of the magnetized aminated carbon nanotubes and magnetized thiolized carbon nanotubes are the same as the magnetization method of magnetized hydrophilic thiolized carbon nanotubes, and will not be repeated here.

[0067] A second aspect of the present invention provides a method for preparing a modified carbon nanotube-polyimide composite nanofiltration membrane, characterized in that the method comprises:

[0068] S1. The modified carbon nanotubes are mixed with an aqueous solution containing amine monomers to obtain a mixture, and the support layer is immersed in the mixture to obtain the modified support layer.

[0069] S2. The modified support layer is immersed in an organic phase solution containing acyl chloride monomer to carry out an interfacial polymerization reaction, thereby obtaining a polyamic acid film supported on the modified support layer.

[0070] S3. In the presence of a magnetic field, after the polyamic acid membrane loaded with the modified support layer is subjected to a first array treatment, the polyamic acid membrane after the first array is subjected to an imidization treatment in the presence of a chemical imid reagent to obtain the modified carbon nanotube-polyimide composite nanofiltration membrane.

[0071] The first array treatment results in the modified carbon nanotubes in the modified carbon nanotube-polyimide composite nanofiltration membrane having an orientation degree of 60-80%.

[0072] In this invention, the polyamic acid membrane prepared by the above method has a suitable thickness, and the modified carbon nanotubes in the final modified carbon nanotube-polyimide composite nanofiltration membrane have a high degree of orientation, which is beneficial to improving the separation performance.

[0073] In this invention, the properties and types of the support layer are the same as those of the support layer described in the first aspect, and will not be repeated here.

[0074] According to the present invention, the modified carbon nanotubes are selected from magnetized carbon nanotubes.

[0075] Furthermore, the modified carbon nanotubes are selected from at least one of magnetized amino carbon nanotubes, magnetized thiol carbon nanotubes, magnetized carboxyl carbon nanotubes, and magnetized hydrophilic thiolized carbon nanotubes.

[0076] In this invention, the sources of the aminated carbon nanotubes and thiolized carbon nanotubes are not particularly limited. They can be purchased commercially or obtained by self-production. The self-production method is the same as that in the first aspect of this invention, and will not be described again.

[0077] In this invention, the preparation methods of the hydrophilic thiolized carbon nanotubes, magnetized aminated carbon nanotubes, magnetized thiolized carbon nanotubes, and magnetized hydrophilic thiolized carbon nanotubes are also consistent with the method in the first aspect, and will not be repeated here.

[0078] In this invention, the polyamic acid film loaded with the modified support layer is subjected to a first array treatment, which can further improve the orientation degree of the modified carbon nanotubes.

[0079] According to the present invention, the amount of the amine monomer is 1-10 wt%, based on the total weight of the mixture.

[0080] Furthermore, based on the total weight of the mixture, the amount of the amine monomer is 3-7 wt%.

[0081] According to the present invention, the amine monomer is selected from at least one of m-phenylenediamine, ethylenediamine, and piperazine.

[0082] According to the present invention, the mixing conditions include a temperature of 20-40°C and a time of 20-100 seconds.

[0083] According to the present invention, the amount of modified carbon nanotubes is 0.1-0.5 wt%, preferably 0.15-0.35 wt%, based on the total weight of the mixture.

[0084] According to the present invention, the method further includes: in step S1, the obtained modified support layer is subjected to a second array processing.

[0085] In this invention, the modified support layer is subjected to a second array treatment, which can further improve the orientation degree of the modified carbon nanotubes.

[0086] In this invention, to achieve better results, it is preferable to remove excess aqueous solution from the surface of the modified support layer.

[0087] According to the present invention, the amount of the acyl chloride monomer is 0.1-0.5 wt%, based on the total mass of the organic phase solution.

[0088] Furthermore, based on the total mass of the organic phase solution, the amount of the acyl chloride monomer used is 0.1-0.3 wt%.

[0089] According to the present invention, the acyl chloride monomer is selected from pyromellitic methyl methacrylate (PMMA) and / or benzoyl chloride.

[0090] According to the present invention, the organic phase solution further contains 0.02-0.1 wt% of a crosslinking agent based on the total weight of the organic phase solution.

[0091] In this invention, the amounts of crosslinking agent and acyl chloride monomer in the organic phase solution meet the above-mentioned range, which can improve the degree of crosslinking.

[0092] Furthermore, based on the total weight of the organic phase solution, the organic phase solution contains 0.06-0.09 wt% of a crosslinking agent.

[0093] According to the present invention, the crosslinking agent is selected from at least one of pyromellitic chloroformyl chloride, ethylenediamine and hexamethylenediamine.

[0094] In this invention, when both the crosslinking agent and the amine monomer are selected from ethylenediamine, the amount of ethylenediamine used is calculated independently as when it is used as an amine monomer and as a crosslinking agent.

[0095] According to the present invention, the mass ratio of the amine monomer to the acyl chloride monomer is 20-30:1.

[0096] According to the present invention, the conditions for the interfacial polymerization reaction include: a temperature of 20-40°C and a time of 20-100 s.

[0097] In this invention, it is preferable to immerse the polyamic acid film loaded with the modified support layer in an organic solvent to remove unreacted acyl chloride monomers on the surface.

[0098] In this invention, there is no particular limitation on the amount of organic solvent used, as long as it is sufficient to remove unreacted acyl chloride monomers.

[0099] Furthermore, there is no particular limitation on the type of organic solvent, which can be a conventional organic solvent in the art, such as n-hexane, n-pentane, 1,4-dioxane, etc.

[0100] According to the present invention, the conditions for the first array processing and the second array processing are independent of each other, including: magnetic field strength of 0.4-0.6T and array time of 20-40s.

[0101] In this invention, when the conditions of the first array processing and the second array processing meet the above-mentioned range, the orientation degree of the modified carbon nanotubes can be further improved.

[0102] In this invention, the conditions for the first array processing and the second array processing are independent of each other, including: magnetic field strength of 0.5-0.6T and array time of 30-40s.

[0103] According to the present invention, the conditions for the imidization treatment include: treatment at 20-40°C for 2-12 hours.

[0104] According to the present invention, the molar ratio of the chemical imine reagent to the amine monomer is 20-50:1.

[0105] In this invention, when the molar ratio of the chemical imine reagent to the amine monomer meets the above-mentioned range, polyamic acid can be fully converted into polyimide, thereby improving film-forming properties and the degree of crosslinking.

[0106] According to the present invention, the chemical imine reagent contains acetic anhydride, triethylamine, and acetone.

[0107] Furthermore, the volume ratio of acetic anhydride, triethylamine, and acetone in the chemical imine reagent is (2-5):(1-3):(7-12).

[0108] In this invention, it is preferable to soak the product in distilled water after the imidization treatment to remove excess chemical imidizing reagents from its surface.

[0109] A third aspect of the present invention provides a modified carbon nanotube-polyimide composite nanofiltration membrane prepared by the above method.

[0110] The fourth aspect of this invention provides the application of the modified carbon nanotube-polyimide composite nanofiltration membrane provided in the first and third aspects of this invention, and the method for preparing the modified carbon nanotube-polyimide composite nanofiltration membrane provided in the second aspect, in nanofiltration treatment.

[0111] The present invention will be described in detail below through embodiments. In the following embodiments,

[0112] The grafting rate of functional groups in functionalized carbon nanotubes was determined by thermogravimetric analysis.

[0113] The orientation degree of the modified carbon nanotubes was calculated using XRD peak area;

[0114] In the composite nanofiltration membrane, the thicknesses of the modified carbon nanotube-polyimide layer and the support layer were measured by scanning electron microscopy.

[0115] The retention rate is calculated using the following formula (1):

[0116]

[0117] Where R is the rejection rate (%); C1 is the salt concentration in the original solution (g / L); and C2 is the salt concentration in the permeate (g / L).

[0118] Water flux is calculated using the following formula (2):

[0119]

[0120] Where J is the transmission flux, L / (m 2 (·h·bar); S is the effective membrane area, m -2 V is the volume of liquid permeated, in L; t is the time required for a certain volume of pure water to permeate, in h.

[0121] The salt rejection rate was analyzed using a conductivity meter.

[0122] All other raw materials used in the experiment were commercially available products.

[0123] The following preparation examples and comparative preparation examples are used to illustrate the preparation of modified carbon nanotubes.

[0124] Preparation Example 1

[0125] Preparation of magnetized aminated carbon nanotubes

[0126] (1) Weigh 1g of multi-walled carbon nanotubes and add them to 60mL of mixed acid solution (volume ratio: H2SO4 / HNO3=3 / 1), and sonicate at 60℃ for 4h. Add 20ml of water to dilute, centrifuge and wash, then filter and wash with an aqueous membrane until the pH is 7, and then vacuum dry at 50℃ for 24 hours to obtain carboxylated carbon nanotubes;

[0127] (2) Weigh 1g of carboxylated carbon nanotubes and 50ml of sulfoxide, ultrasonically disperse until the system is homogeneous, then add 1ml of LDMF dropwise, reflux at 70℃ for 24h, and then react with tetrahydrofuran and a mixed solution (V 乙醇 V 水 : 1:1) Centrifugation and washing, the product was filtered through an organic microporous membrane and vacuum dried to obtain acyl chloride carbon nanotubes;

[0128] (3) Weigh 0.5g of acyl chloride carbon nanotubes, 1.0g of 4-dimethylaminopyridine, and 100mL of toluene, mix them, slowly add 25m of ethylenediamine, reflux at 100℃ for 8h, filter, wash the filter cake with ethanol and ultrapure water respectively, and finally vacuum dry it at 50℃ for 24h to obtain aminated carbon nanotubes.

[0129] (4) Weigh 1g of aminated carbon nanotubes and 0.1g of SDS into a 250mL round-bottom flask. Add 5mL of a stable solution of 0.02mol / L magnetic iron oxide nanoparticles dropwise with ultrasonic-assisted rapid stirring at 40℃, and continue stirring for 2h. Transfer the product to a solution (V... 乙醇 V 去离子水 After centrifugation, filtration, and washing (1:1 ratio), the mixture was vacuum dried at 40°C for 24 hours and then ground to obtain magnetized amino carbon nanotubes S2.

[0130] Preparation Example 2

[0131] Preparation of magnetized hydrophilic thiolized carbon nanotubes

[0132] (1) Weigh 1g of carboxylated carbon nanotubes, 2mL of LMTS, and 100mL of ethanol into a round-bottom flask equipped with a stir bar, and reflux at 70℃ for 8h. Then, rinse the mixture with solution (V... 乙醇 V 去离子水 =1:1) Centrifuge, wash, then vacuum filter through a 0.22μm nylon 6 membrane, and then vacuum dry at 40℃ for 24h before grinding to obtain mercapto-based carbon nanotubes;

[0133] (2) 0.1 g of thiol-modified carbon nanotubes, 0.2 g of P(PEGMA)-b-PMMA-alkynyl, 0.1 g of photoinitiator 1173, and 25 mL of THF were sealed in a Schlenk flask equipped with a magnetic stirrer and a 50 mL container. The mixture was then filled three times with N2, and heated at 30 °C under UV radiation for 6 hours. After the reaction, the mixture was centrifuged for purification and then vacuum filtered through a 0.22 μm nylon 6 membrane. Finally, the mixture was Soxhlet extracted with THF for 48 hours to remove impurities, and then vacuum dried at 40 °C for 24 hours to obtain hydrophilic thiol-modified carbon nanotubes.

[0134] (3) Weigh 1g of hydrophilic thiolized carbon nanotubes and 0.1g of SDS into a 250mL round-bottom flask. Add 5mL of a stable solution of magnetic iron oxide nanoparticles dropwise with ultrasonic-assisted rapid stirring at 40℃, and continue stirring for 2 hours. Dissolve the product in solution (V... 乙醇 :V 去离子水 =1:1) After centrifugation, filtration and washing, the mixture was vacuum dried at 40℃ for 24h and then ground to obtain magnetized hydrophilic thiolized carbon nanotubes S1.

[0135] Preparation Example 3

[0136] Similar to Preparation Example 2, except that P(PEGMA)-b-PMMA-alkynyl was replaced with an equimolar amount of PHEA-g-PMMA-alkynyl to obtain magnetized hydrophilic thiolized carbon nanotubes S3.

[0137] Preparation Example 4

[0138] Similar to Preparation Example 2, except that 0.2 g P(PEGMA)-b-PMMA-alkynyl was replaced with 0.14 g P(PEGMA)-b-PMMA-alkyny to obtain magnetized hydrophilic thiolized carbon nanotubes S4.

[0139] Preparation Example 5

[0140] Similar to Preparation Example 2, except that 5 mL of magnetic iron oxide nanoparticles were replaced with 2 mL of magnetic iron oxide nanoparticles to obtain magnetized hydrophilic thiolized carbon nanotubes S5.

[0141] Preparation Example 6

[0142] Similar to Preparation Example 1, except that the aminated carbon nanotubes were replaced with an equal amount of carboxylated carbon nanotubes to obtain magnetized carboxylated carbon nanotubes S6.

[0143] Preparation Example 7

[0144] Similar to Preparation Example 1, except that the aminated carbon nanotubes were replaced with an equal amount of thiolized carbon nanotubes to obtain magnetized thiolized carbon nanotubes S7.

[0145] Preparation Example 8

[0146] Similar to Preparation Example 1, except that the amount of ethylenediamine used was 10 mL, and magnetized aminated carbon nanotubes S8 were finally obtained.

[0147] Preparation Example 9

[0148] Similar to Preparation Example 2, except that the photoinitiator 1173 was replaced with azobisisobutyronitrile, and magnetized hydrophilic thiolated carbon nanotubes S9 were finally prepared.

[0149] Comparative Preparation Example 1

[0150] Following the same steps (1) as in Preparation Example 1, carboxylated carbon nanotubes DS1 were obtained.

[0151] Comparative Preparation Example 2

[0152] Aminated carbon nanotubes DS2 were obtained by following steps (1), (2), and (3) of Preparation Example 1.

[0153] Comparative preparation example 3

[0154] The preparation method is the same as step (1) of preparation example 1, to obtain thiolized carbon nanotubes DS3.

[0155] Comparative preparation example 4

[0156] (1) Weigh 1g of carboxylated carbon nanotubes, 2mL of LMTS, and 100mL of ethanol into a round-bottom flask equipped with a stir bar, and reflux at 70℃ for 8h. Then, rinse the mixture with solution (V... 乙醇 V 去离子水 =1:1) Centrifuge, wash, then vacuum filter through a 0.22μm nylon 6 membrane, and then vacuum dry at 40℃ for 24h before grinding to obtain mercapto-based carbon nanotubes;

[0157] (2) 0.1 g of thiol-modified carbon nanotubes, 0.2 g of P(PEGMA)-b-PMMA-alkynyl, 0.1 g of photoinitiator 1173, and 25 mL of THF were sealed in a Schlenk flask equipped with a magnetic stirrer and a 50 mL container. The mixture was then filled three times with N2, and heated at 30 °C under UV radiation for 6 hours. After the reaction, the mixture was centrifuged for purification and then vacuum filtered through a 0.22 μm nylon 6 membrane. Finally, the mixture was Soxhlet extracted with THF for 48 hours to remove impurities, and then vacuum dried at 40 °C for 24 hours to obtain hydrophilic thiol-modified carbon nanotubes DS4.

[0158] Table 1

[0159]

[0160]

[0161] The following examples and comparative examples illustrate the preparation of modified carbon nanotube-polyimide composite nanofiltration membranes.

[0162] Example 1

[0163] Preparation of solution

[0164] (1) Carbon nanotube-m-phenylenediamine aqueous solution: Dissolve m-phenylenediamine in 50 ml of water to prepare an aqueous solution containing 0.023 mol of m-phenylenediamine (m-phenylenediamine mass concentration is 5 wt%); add aminated carbon nanotubes S1 to the above aqueous solution of m-phenylenediamine, sonicate for 30 min to obtain carbon nanotube-m-phenylenediamine aqueous solution, wherein the content of magnetized aminated carbon nanotubes S1 is 0.25 wt%;

[0165] (2) Pyromellitic tetracarboxylate chloride organic phase solution: Pyromellitic tetracarboxylate chloride and pyromellitic tricarboxylate chloride were dissolved in 30 ml of n-hexane solution to prepare a solution containing 1.2 × 10⁻⁶ ppm. -3A mol pyromellitic tetracarboxylic acid chloride organic phase solution (pyromellitic tetracarboxylic acid chloride mass concentration is 0.2 wt%), wherein the content of pyromellitic tricarboxylic acid chloride is 6 × 10⁻⁶. -5 mol (the mass concentration of pyromellitic methyl chloride is 0.08 wt%);

[0166] (3) Chemical imidizing reagent: The volume ratio of acetic anhydride, triethylamine and acetone is 3:1:10.

[0167] Preparation of modified carbon nanotube-polyimide composite nanofiltration membrane

[0168] S1. Immerse a PTFE support with a pore size of 0.22 μm and a thickness of 0.16 mm in the above carbon nanotube-m-phenylenediamine aqueous solution for 10 min. After removing it, remove the excess aqueous solution from the surface to obtain the modified support layer.

[0169] S2. Place the modified support layer in a magnetic field with a magnetic field strength of 0.5T and array it for 30s;

[0170] S3. The modified support layer obtained in step S2 is immersed in the above pyromellitic tetracarboxylate organic phase solution to carry out an interfacial polymerization reaction. The mass ratio of m-xylene to pyromellitic tetracarboxylate is 25:1, the reaction temperature is 25℃, and the reaction time is 90s. After the reaction is completed, the polyamic acid film loaded with the modified support layer is prepared by immersing it in n-hexane to remove the unreacted pyromellitic tetracarboxylate on the surface.

[0171] S4. Place the polyamic acid film loaded with the modified support layer into a magnetic field with a magnetic field strength of 0.5T and array it for 30s.

[0172] S5. The polyamic acid membrane loaded with the modified support layer obtained in step S4 is immersed in the chemical imine reagent prepared in step (3) at 25°C for 8 hours. (The molar ratio of the chemical imine reagent to the amine monomer is 38:1) It is then immersed in distilled water for 2 hours to remove the chemical imine reagent on its surface, thereby obtaining the modified carbon nanotube-polyimide composite nanofiltration membrane, denoted as M1.

[0173] Examples 2-9

[0174] The method is consistent with that in Example 1, except that the aminated carbon nanotubes S1 are replaced with modified carbon nanotubes S2-S9.

[0175] The remaining steps are the same as in Example 1, and the modified carbon nanotube-polyimide composite nanofiltration membrane M2-M9 is prepared.

[0176] Examples 10-14

[0177] The method is consistent with that in Example 2, except that carbon nanotube-m-phenylenediamine aqueous solutions are prepared separately, with modified carbon nanotube contents of 0.1wt%, 0.15wt%, 0.35wt%, 0.45wt%, and 0.5wt%, respectively, to prepare magnetized hydrophilic thiolized carbon nanotubes S10-14.

[0178] The remaining steps are the same as in Example 2, and modified carbon nanotube-polyimide composite nanofiltration membranes M10-M14 are prepared.

[0179] Example 15

[0180] The method is consistent with that in Example 2, except that the modified support layer is not arrayed, but only the polyamic acid film loaded on the modified support layer is arrayed.

[0181] The remaining steps are the same as in Example 2, and the modified carbon nanotube-polyimide composite nanofiltration membrane M15 is prepared.

[0182] Example 16

[0183] The method is consistent with that in Example 2, except that the modified support layer is placed in a magnetic field with a magnetic field strength of 0.4T and arrayed for 20s.

[0184] The remaining steps are the same as in Example 2, and the modified carbon nanotube-polyimide composite nanofiltration membrane M16 is prepared.

[0185] Example 17

[0186] The method is consistent with that in Example 2, except that the molar ratio of the imidization solution to the amine monomer is 15:1.

[0187] The remaining steps are the same as in Example 2, and the modified carbon nanotube-polyimide composite nanofiltration membrane M17 is prepared.

[0188] Comparative Examples 1-4

[0189] The method is consistent with that in Example 2, except that S2 is replaced with DS1-DS3 to prepare modified carbon nanotube-polyimide composite nanofiltration membranes DM1-DM4.

[0190] Comparative Examples 5-6

[0191] The method is consistent with that in Example 2, except that carbon nanotube-m-phenylenediamine aqueous solutions with modified carbon nanotube contents of 0 wt% and 0.75 wt% are prepared respectively.

[0192] The remaining steps are the same as in Example 2, and the modified carbon nanotube-polyimide composite nanofiltration membrane DM5-DM6 is prepared.

[0193] Table 2 shows the types, orientation degrees, contents, and thicknesses of the modified carbon nanotube-polyimide composite nanofiltration membranes prepared in Examples 1-17 and Comparative Examples 1-6.

[0194] Table 2

[0195] Composite nanofiltration membrane Modified carbon nanotubes Orientation degree / % <![CDATA[Content a / wt%]]> Thickness / μm M1 S1 79.7 0.25 2 M2 S2 76.4 0.25 2 M3 S3 76.1 0.25 2 M4 S4 76 0.25 2 M5 S5 71.3 0.25 2 M6 S6 72.3 0.25 2 M7 S7 73.1 0.25 2 M8 S8 10.1 0.25 2 M9 S9 75.1 0.25 2 M10 S10 75.9 0.1 2 M11 S11 76.1 0.15 2 M12 S12 76 0.35 2 M13 S13 75.7 0.45 2 M14 S14 75.8 0.5 2 M15 S2 60.3 0.25 2 M16 S2 40.2 0.25 2 M17 S2 60 0.25 DM1 DS1 8.6 0.25 2 DM2 DS2 10 0.25 2 DM3 DS3 9.5 0.25 2 DM4 DS4 9.2 0.25 2 DM5 S2 8 0 1 DM6 S2 55.9 0.75 3

[0196] Note: Content a This refers to the content of modified carbon nanotubes based on the total weight of the mixture.

[0197] As can be seen from the results in Table 2, the modified carbon nanotubes in Examples 1-7 and 9-15 of this invention have a high degree of orientation and good magnetic field response. The modified carbon nanotubes are arranged in a relatively regular manner. Among them, Examples 1, 2, and 11-12 have an even higher degree of orientation and the modified carbon nanotubes are arranged in a more regular manner, which ensures the high water flux of the modified carbon nanotube-polyimide composite nanofiltration membrane.

[0198] Combination Figure 1 It can be seen that the magnetized hydrophilic thiolized carbon nanotubes S2 are relatively uniformly dispersed, and the membrane surface exhibits a porous network structure. Figure 2 It can be seen that the thickness of the separation layer of the modified carbon nanotube-polyimide composite nanofiltration membrane is appropriate, which ensures the high rejection rate of the modified carbon nanotube-polyimide composite nanofiltration membrane.

[0199] Test case

[0200] The separation performance of the modified carbon nanotube-polyimide composite nanofiltration membranes M1-M17 and DM1-DM6 prepared above was tested. The solution used was 0.5 g / L CaSO4 solution, and the operating pressure was 4 bar. The test results are shown in Table 2.

[0201] Table 3

[0202]

[0203]

[0204] The above results show that Embodiments 1-17 of the present invention have good technical effects, with a water flux reaching 10.3 L / (m²). -2 ·h -1 The concentrations of CaSO4 were 85% and above, and the retention rates of CaSO4 were 85% and above.

[0205] Among them, embodiments 1, 2, and 11-12, which satisfy the preferred technical solutions of the present invention, have significantly better effects, with water flux reaching 20 L / (m²). -2 ·h -1·bar) and above, with a CaSO4 retention rate of 93% and above.

[0206] Solvent resistance tests were conducted on the modified carbon nanotube-polyimide composite nanofiltration membranes M2 and M10: The modified carbon nanotube-polyimide composite nanofiltration membranes M2 and M10 were immersed in tetrahydrofuran, N,N-dimethylacetamide, and methanol for 48 hours, followed by separation performance tests. The results are shown in Table 4.

[0207] Table 4

[0208] Composite nanofiltration membrane <![CDATA[Water flux / L / (m -2 ·h -1 ·bar)]]> <![CDATA[CaSO4 rejection rate (%)]]> M2 (after solvent soaking) 25.4 93 M10 (after solvent soaking) 20.1 93

[0209] As can be seen above, the composite nanofiltration membranes M2 and M10, even after being soaked in organic solvents, still exhibit good performance, with water flux reaching 20 L / (m²). -2 ·h -1 At ·bar) and above, the CaSO4 retention rate reaches 93%.

[0210] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified carbon nanotube-polyimide composite nanofiltration membrane, characterized in that, The composite nanofiltration membrane comprises a support layer and a modified carbon nanotube-polyimide layer; The degree of orientation of the modified carbon nanotubes in the modified carbon nanotube-polyimide layer is 60-80%. The modified carbon nanotubes are selected from at least one of magnetized amino carbon nanotubes, magnetized thiol carbon nanotubes, magnetized carboxyl carbon nanotubes, and magnetized hydrophilic thiolized carbon nanotubes. Based on the total weight of the modified carbon nanotubes, the functional group grafting rate of the modified carbon nanotubes is 8-50%.

2. The composite nanofiltration membrane according to claim 1, wherein, The degree of orientation of the modified carbon nanotubes in the modified carbon nanotube-polyimide layer is 70-80%.

3. The composite nanofiltration membrane according to claim 1 or 2, wherein, The pore size of the support layer is 0.1-0.3 μm.

4. The composite nanofiltration membrane according to claim 1 or 2, wherein, Based on the total weight of the modified carbon nanotubes, the functional group grafting rate of the modified carbon nanotubes is 9-45%.

5. The composite nanofiltration membrane according to claim 4, wherein, The preparation method of the magnetized hydrophilic thiolized carbon nanotubes includes: 1) Under sealed and light-protected conditions, thiol-based carbon nanotubes, hydrophilic polymers, photoinitiators, and solvents are mixed to obtain a mixture; 2) The mixture was subjected to ultraviolet radiation and then separated to obtain hydrophilic thiolized carbon nanotubes; 3) In the presence of a surfactant, hydrophilic thiolized carbon nanotubes and magnetic particles are stirred to obtain a mixture, and then magnetized hydrophilic thiolized carbon nanotubes are separated.

6. A method for preparing the modified carbon nanotube-polyimide composite nanofiltration membrane according to any one of claims 1-5, characterized in that, The method includes: S1. The modified carbon nanotubes are mixed with an aqueous solution containing amine monomers to obtain a mixture, and the support layer is immersed in the mixture to obtain the modified support layer. S2. The modified support layer is immersed in an organic phase solution containing acyl chloride monomer to carry out an interfacial polymerization reaction, thereby obtaining a polyamic acid film supported on the modified support layer. S3. In the presence of a magnetic field, after the polyamic acid membrane loaded with the modified support layer is subjected to a first array treatment, the polyamic acid membrane after the first array is subjected to an imidization treatment in the presence of a chemical imid reagent to obtain the modified carbon nanotube-polyimide composite nanofiltration membrane. The first array treatment results in the modified carbon nanotubes in the modified carbon nanotube-polyimide composite nanofiltration membrane having an orientation degree of 60-80%. The modified carbon nanotubes are selected from at least one of magnetized amino carbon nanotubes, magnetized thiol carbon nanotubes, magnetized carboxyl carbon nanotubes, and magnetized hydrophilic thiolized carbon nanotubes. Based on the total weight of the mixture, the amount of modified carbon nanotubes used is 0.1-0.5 wt%.

7. The method according to claim 6, wherein, Based on the total weight of the mixture, the amount of the amine monomer is 1-10 wt%; And / or, the amine monomer is selected from at least one of m-phenylenediamine, ethylenediamine, and piperazine; And / or, the mixing conditions include: a temperature of 20-40°C and a time of 20-100 seconds; And / or, the method further includes, in step S1, performing a second array processing on the obtained modified support layer.

8. The method according to claim 7, wherein, Based on the total weight of the mixture, the amount of the amine monomer is 3-7 wt%; And / or, based on the total weight of the mixture, the amount of modified carbon nanotubes is 0.1-0.35 wt%.

9. The method according to claim 6 or 7, wherein, Based on the total weight of the organic phase solution, the amount of the acyl chloride monomer used is 0.1-0.5 wt%. And / or, the acyl chloride monomer is selected from pyromellitic methyl methacrylate chloride and / or phthaloyl chloride; And / or, based on the total weight of the organic phase solution, the organic phase solution further contains 0.02-0.1 wt% of a crosslinking agent; And / or, the crosslinking agent is selected from at least one of pyromellitic methyl chloride, ethylenediamine, and hexamethylenediamine; And / or, the mass ratio of the amine monomer to the acyl chloride monomer is 20-30:1; And / or, the conditions for the interfacial polymerization reaction include: a temperature of 20-40°C and a time of 20-100 s.

10. The method according to claim 9, wherein, Based on the total weight of the organic phase solution, the amount of the acyl chloride monomer used is 0.1-0.3 wt%. And / or, based on the total weight of the organic phase solution, the organic phase solution further contains 0.06-0.09 wt% of a crosslinking agent.

11. The method according to claim 6 or 7, wherein, The conditions for the first array processing and the second array processing are independent of each other, including: magnetic field strength of 0.4-0.6T and array time of 20-40s; And / or, the conditions for the imidization treatment include: treatment at 20-40°C for 2-12 hours; And / or, the molar ratio of the chemical imine reagent to the amine monomer is 20-50:1; And / or, the chemical imine reagent contains acetic anhydride, triethylamine, and acetone.

12. The method according to claim 11, wherein, The volume ratio of acetic anhydride, triethylamine, and acetone in the chemical imine reagent is (2-5):(1-3):(7-12).

13. The modified carbon nanotube-polyimide composite nanofiltration membrane prepared by the method according to any one of claims 6-12.

14. The application of the modified carbon nanotube-polyimide composite nanofiltration membrane according to any one of claims 1-5 and 13, and the method according to any one of claims 6-12, in nanofiltration treatment.

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