Composite conductive separation membrane with stable conductive skin layer as well as preparation method and application of composite conductive separation membrane

Abstract

The invention provides a composite conductive separation membrane with a stable conductive skin layer and a preparation method and application thereof, and belongs to the technical field of conductive separation membranes. The preparation method comprises the following steps: blending polyvinylpyrrolidone, functionalized carbon nanotubes and a membrane matrix polymer material to prepare a membrane casting solution; by adjusting the molecular weight of polyvinylpyrrolidone and the surface groups of the carbon nanotubes, the synergistic segregation behavior of the polyvinylpyrrolidone and the carbon nanotubes in the phase inversion process is regulated and controlled, and electric field induction is combined to promote the polyvinylpyrrolidone and the carbon nanotubes to form a continuous conductive network structure on the skin layer of the composite separation membrane; therefore, the prepared conductive composite separation membrane not only can break through the trade-off effect between selectivity and permeability in electric auxiliary filtration, but also has excellent anti-pollution performance and long-term stability performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive separation membranes, and in particular relates to a composite conductive separation membrane with a stable conductive skin layer, a preparation method and an application thereof. Background Art

[0002] The conductive separation membrane preparation process integrates membrane separation technology and electrochemical technology. It has the advantages of low cost and easy structure control. It has shown significant advantages and huge potential in the field of wastewater purification and treatment.

[0003] The preparation process of conductive separation membranes mainly includes blending modification method and vacuum filtration method. Among them: the blending modification method is simple, but the easy agglomeration characteristics of the conductive particles and the insulating properties of the membrane matrix polymer result in the prepared composite membrane having low conductivity; the vacuum filtration method can form a deposition layer with high conductivity on the surface of the polymer membrane matrix, but due to the weak bonding force between the deposition layer and the membrane matrix, this makes the membrane unstable during long-term operation and easy to fall off.

[0004] Therefore, it is necessary to provide a composite conductive separation membrane with a stable conductive skin layer and its preparation method and application to solve the above problems. Summary of the Invention

[0005] The present invention provides a composite conductive separation membrane with a stable conductive skin layer, a preparation method and application thereof, by blending polyvinyl pyrrolidone and functionalized carbon nanotubes with a membrane matrix polymer material, and utilizing non-solvent-induced phase separation technology to simply and large-scale prepare the composite conductive separation membrane with a stable conductive skin layer, thereby effectively solving at least one technical problem involved in the background technology.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows: A method for preparing a composite conductive separation membrane having a stable conductive skin layer comprises the following steps: Step S1, dissolving the polymer, functionalized carbon nanotubes, and polyvinyl pyrrolidone in dimethylacetamide in a mass ratio of (10-18): (1-3): (1-5) to obtain a uniform casting solution; In step S2, the casting liquid is degassed and then coated on the electrode plate, and an electric field is immediately induced. The casting liquid is then placed in a coagulation bath for phase exchange to obtain a composite membrane. The obtained composite membrane is taken out of the coagulation bath and placed in distilled water for cleaning to obtain a composite separation membrane with a stable conductive skin.

[0007] As a preferred improvement, the polymer is one of polyvinylidene fluoride, polysulfone and polyethersulfone.

[0008] As a preferred improvement, the functionalized carbon nanotubes are one of carboxylated carbon nanotubes, hydroxylated carbon nanotubes, and amino carbon nanotubes.

[0009] As a preferred improvement, the molecular weight of polyvinyl pyrrolidone is 8000-58000 g / mol.

[0010] As a preferred improvement, the dissolution temperature is 70-100°C and the dissolution time is 24-48h.

[0011] As a preferred improvement, the electric field induction time is 1-5 minutes, and the electrode spacing is 1-2 mm.

[0012] As a preferred improvement, the electrode plate is one of a copper plate, an iron plate, and a graphene plate.

[0013] As a preferred improvement, the degassing time of the casting solution is 3-10 hours; and the phase exchange time is 12-48 hours.

[0014] A composite conductive separation membrane with a stable conductive skin layer is prepared by adopting the above-mentioned method for preparing a composite conductive separation membrane with a stable conductive skin layer.

[0015] An application of the composite conductive separation membrane with a stable conductive skin as described above is used as a separation membrane in a wastewater purification process.

[0016] The beneficial effects of the present invention are: (1) The present invention uses polyvinyl pyrrolidone and functionalized carbon nanotubes to blend with membrane matrix polymer materials, and utilizes non-solvent-induced phase separation technology to simply and large-scale prepare a composite conductive separation membrane with a stable conductive skin layer. By adjusting the molecular weight of polyvinyl pyrrolidone and the surface groups of carbon nanotubes, their cooperative segregation behavior during the phase transformation process is regulated, and combined with electric field induction, they are prompted to form a continuous conductive network structure in the skin layer of the composite separation membrane, thereby enhancing the responsiveness of the membrane surface structure and groups to electric field stimulation; (2) The composite conductive separation membrane prepared by the present invention can break through the trade-off effect between selectivity and permeability in electrically assisted filtration, and at the same time has excellent permeability, separation performance and anti-pollution performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive work, among which: Figure 1A schematic diagram showing the separation process of the composite conductive separation membrane provided by the present invention under electrical assistance; Figure 2 The figure shows the surface morphology of the composite conductive separation membrane prepared in Example 7. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] This embodiment provides a method for preparing a composite conductive separation membrane having a stable conductive skin layer, comprising the following steps: Step S1, dissolving the polymer, functionalized carbon nanotubes, and polyvinyl pyrrolidone in dimethylacetamide in a mass ratio of (10-18): (1-3): (1-5) to obtain a uniform casting solution; In step S2, the casting liquid is degassed and then coated on the electrode plate, and an electric field is immediately induced. The casting liquid is then placed in a coagulation bath for phase exchange to obtain a composite membrane. The obtained composite membrane is taken out of the coagulation bath and placed in distilled water for cleaning to obtain a composite separation membrane with a stable conductive skin.

[0020] The polymer is one of polyvinylidene fluoride, polysulfone, and polyethersulfone; the dissolution temperature in step S1 is 70-100° C., and the dissolution time is 24-48 hours.

[0021] In step S2, the degassing time of the casting solution is 3-10 hours; and the phase exchange time is 12-48 hours.

[0022] In the non-solvent-induced phase separation membrane formation process, the commonly used porogen polyvinylpyrrolidone not only exhibits excellent hydrophilic properties and strong segregation behavior, but also forms hydrogen bonds with carboxyl, hydroxyl, and amino groups on the surface of functionalized carbon nanotubes. The present invention blends polyvinylpyrrolidone, functionalized carbon nanotubes, and a membrane matrix polymer. During the subsequent phase inversion process, these may synergistically segregate through strong hydrogen bonding, enriching them on the membrane surface to form a stable conductive cortex. The resulting composite separation membrane is not only suitable for large-scale production but also exhibits high conductivity.

[0023] During the preparation process, the molecular weight of polyvinyl pyrrolidone and the surface groups of carbon nanotubes were adjusted to control their cooperative segregation behavior during phase transformation. The molecular weight of polyvinyl pyrrolidone significantly affects its hydrophilicity. Low-molecular-weight polyvinyl pyrrolidone has short chains, flexible conformations, and high freedom of movement in solution. The polar amide groups (-C=O and -N-) on the molecular chains are more easily exposed, fully contacting water molecules and quickly forming hydrogen bonds, exhibiting higher "hydration efficiency" and faster dissolution / wetting speeds, resulting in better hydrophilicity. High-molecular-weight polyvinyl pyrrolidone, on the other hand, has long chains and is prone to intramolecular and intermolecular entanglement in solution. This entanglement restricts the conformational changes and mobility of the molecular chains. Some amide groups may be "wrapped" inside the entangled chain segments or in the contact area between chains, reducing their chances of direct contact with water molecules and forming hydrogen bonds, which leads to slower dissolution. In addition, its long chain structure and strong entanglement tendency lead to a significant increase in solution viscosity, hindering the diffusion of water molecules and the movement of polymer chain segments. This kinetic limitation greatly delays and hinders the process of hydrophilic groups exerting their ability to bind to water or improve interfacial wetting, making high molecular weight polyvinyl pyrrolidone less hydrophilic than low molecular weight polyvinyl pyrrolidone.

[0024] The hydrophilic low molecular weight polyvinyl pyrrolidone has better hydrogen bonding ability with carbon nanotubes, thereby promoting their cooperative segregation behavior during phase transformation. Therefore, in this embodiment, the molecular weight of polyvinyl pyrrolidone is 8000-58000 g / mol.

[0025] Furthermore, adjusting the type and content of functional groups on the carbon nanotube surface can also modulate the carbon nanotube's hydrogen bonding ability and cooperative segregation behavior with polyvinyl pyrrolidone. Specifically, different types and contents of functional groups combine with the amide groups in the polyvinyl pyrrolidone molecule to form hydrogen bonds with varying strengths, numbers, and stability, thereby adjusting the hydrogen bonding ability and cooperative segregation behavior between the carbon nanotubes and polyvinyl pyrrolidone. Functionalized carbon nanotubes are selected from carboxylated carbon nanotubes, hydroxylated carbon nanotubes, and amino-treated carbon nanotubes.

[0026] The electric field induction method can promote the functionalized carbon nanotubes and polyvinyl pyrrolidone to form a continuous conductive network structure in the cortex of the composite separation membrane. In the electric field, free electrons are redistributed on the surface of the carbon tubes to generate a dipole moment, which will generate a translational force and a rotational force to promote the movement of the carbon nanotubes. In addition, the surface of the carbon nanotubes has charged groups, so they can be promoted to enrich on the membrane surface to form a highly conductive cortex by adjusting the direction of the electric field. As a result, the conductive composite separation membrane prepared by the present invention can not only break through the trade-off effect between selectivity and permeability in electrically assisted filtration, but also have excellent anti-pollution performance and long-term stability. The electric field induction time is 1-5 minutes, and the electrode spacing is 1-2 mm; the electrode plate is one of a copper plate, an iron plate, and a graphene plate.

[0027] This embodiment also provides a composite conductive separation membrane with a stable conductive skin layer, which is prepared using the above-mentioned preparation method.

[0028] like Figure 1 As shown, this embodiment also provides an application of a composite conductive separation membrane with a stable conductive cortex, which is used as a separation membrane in a wastewater purification process. Since the composite conductive separation membrane has a stable conductive cortex, after being energized, the conductive cortex is charged. Based on the principle of electrical repulsion, it can strongly repel pollutants with the same charge in the wastewater. At the same time, it can also slightly decompose some nearby pollutants based on electrochemical reactions, greatly enhancing the ability of the composite conductive separation membrane to block pollutants, making it anti-clogging, durable, and having good separation effects. Through the electrostatic effect that can be adjusted by screening the coupled electric field, for example, in electrically assisted filtration, by adjusting the applied voltage, the electrostatic interaction strength between the surface of the composite conductive separation membrane and the charged substance can be adjusted, thereby achieving the adjustment and control of the separation capacity.

[0029] Example 1 This embodiment provides a method for preparing a composite conductive separation membrane having a stable conductive skin layer, comprising the following steps: 15 wt% polyvinylidene fluoride, 1 wt% carboxylated carbon nanotubes, and 2 wt% polyvinyl pyrrolidone were dissolved in 82 wt% dimethylacetamide at 70°C for 24 hours to obtain a uniform casting solution; The casting liquid was degassed for 4 hours, coated on a copper plate using an automatic scraper, and immediately subjected to electric field induction for 1 minute. It was then placed in a coagulation bath for phase exchange. After 12 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0030] Example 2 This embodiment provides a method for preparing a composite conductive separation membrane having a stable conductive skin layer, comprising the following steps: 15 wt% polyvinylidene fluoride, 2.5 wt% carboxylated carbon nanotubes, and 4 wt% polyvinylpyrrolidone were dissolved in 78.5 wt% dimethylacetamide at 75°C for 36 h to obtain a uniform casting solution; The casting liquid was degassed for 6 hours, coated on a copper plate using an automatic scraper, and immediately subjected to electric field induction for 2 minutes. It was then placed in a coagulation bath for phase exchange. After 24 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0031] Example 3 11 wt% polysulfone, 2.5 wt% amino carbon nanotubes, and 4 wt% polyvinylpyrrolidone were dissolved in 82.5 wt% dimethylacetamide at 80°C for 36 h to obtain a uniform casting solution. The casting liquid was degassed for 8 hours, coated on an iron plate using an automatic scraper, and immediately subjected to electric field induction for 3 minutes. It was then placed in a coagulation bath for phase exchange. After 36 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0032] Example 4 11 wt% polysulfone, 3 wt% amino-modified carbon nanotubes, and 4 wt% polyvinylpyrrolidone were dissolved in 82 wt% dimethylacetamide at 90°C for 24 h to obtain a uniform casting solution. The casting liquid was degassed for 10 hours, coated on an iron plate using an automatic scraper, and immediately subjected to electric field induction for 5 minutes. It was then placed in a coagulation bath for phase exchange. After 48 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0033] Example 5 18 wt% polyethersulfone, 2.5 wt% hydroxylated carbon nanotubes, and 4 wt% polyvinylpyrrolidone were dissolved in 75.5 wt% dimethylacetamide at 80°C for 24 h to obtain a uniform casting solution; The casting liquid was degassed for 6 hours, coated on a graphite plate using an automatic scraper, and immediately subjected to electric field induction for 2 minutes. It was then placed in a coagulation bath for phase exchange. After 24 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0034] Example 6 18 wt% polyethersulfone, 2.5 wt% carboxylated carbon nanotubes, and 4 wt% polyvinylpyrrolidone were dissolved in 75.5 wt% dimethylacetamide at 80°C for 24 h to obtain a uniform casting solution; The casting liquid was degassed for 6 hours, coated on a graphite plate using an automatic scraper, and immediately subjected to electric field induction for 3 minutes. It was then placed in a coagulation bath for phase exchange. After 36 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0035] Example 7 18 wt% polyethersulfone, 2.5 wt% amino carbon nanotubes, and 4 wt% polyvinylpyrrolidone were placed in 75.5 wt% dimethylacetamide at 80°C for 24 h to obtain a uniform casting solution; The casting liquid was degassed for 6 hours, coated on a copper plate using an automatic scraper, and immediately subjected to electric field induction for 1 minute. It was then placed in a coagulation bath for phase exchange. After 24 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0036] Comparative Example 1 15 wt% of polyvinylidene fluoride, 2.5 wt% of carboxylated carbon nanotubes, and 82.5 wt% of dimethylacetamide were mixed and dissolved at 75°C for 36 hours to obtain a uniform casting solution; The casting liquid was degassed for 6 hours, coated on a copper plate using an automatic scraper, and immediately subjected to electric field induction for 2 minutes. It was then placed in a coagulation bath for phase exchange. After 24 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0037] Comparative Example 2 Step 1, preparation of casting solution; 11 wt% polysulfone, 2.5 wt% amino carbon nanotubes, and 86.5 wt% dimethylacetamide were mixed and dissolved at 80°C for 36 hours to obtain a uniform casting solution. The casting liquid was degassed for 8 hours, coated on an iron plate using an automatic scraper, and immediately subjected to electric field induction for 3 minutes. It was then placed in a coagulation bath for phase exchange. After 36 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0038] Comparative Example 3 18 wt% polyethersulfone, 2.5 wt% amino carbon nanotubes, and 79.5 wt% dimethylacetamide were mixed and dissolved at 80°C for 24 hours to obtain a uniform casting solution; The casting liquid was degassed for 6 hours, coated on a copper plate using an automatic scraper, and immediately subjected to electric field induction for 1 minute. It was then placed in a coagulation bath for phase exchange. After 24 hours, the obtained composite membrane was taken out of the coagulation bath and placed in distilled water for cleaning to remove residual solvent, thereby obtaining a composite separation membrane sample with a stable conductive skin.

[0039] The conductivity, separation performance and anti-fouling performance of the membrane samples obtained in Examples 1-7 and Comparative Examples 1-3 were tested respectively.

[0040] The test method is as follows: Conductivity test: The test was conducted using a four-probe resistivity tester, the ST2258C multifunctional digital four-probe tester produced by Suzhou Jingge Electronics Co., Ltd. Separation performance test: A laboratory-made membrane pool with electrodes was used to simulate the filtration process of Congo red and methyl green wastewater. During the filtration process, a voltage of ±1V was applied, the filtration pressure was 0.1MPa, the filtration time was 1h, and the effective membrane area was 22.1 cm 2 , test the permeability and retention rate of membrane samples to Congo red and methyl green.

[0041] Flux J w Calculated as follows: ; Where, V represents the volume of filtrate; A represents the effective membrane area; Δt represents the filtration time; ΔP represents the filtration pressure; The retention rate R is calculated as follows: ; Where C p Indicates the concentration of the filtrate; C f Indicates the concentration of the feed liquid.

[0042] Anti-pollution performance test: Pure water and Congo red wastewater were used alternately as the filtrate. The dye-contaminated separation membrane was cleaned with deionized water and then filtered again with pure water. The flux recovery rate was calculated according to the following formula to evaluate the anti-pollution performance.

[0043] ; Where, J w1 is the permeation flux of the first filtration of pure water, J w2 is the permeate flux of the second filtered pure water.

[0044] The test results are shown in Table 1: Table 1 Membrane sample performance test table As can be seen from Table 1, the amount of carbon nanotubes added and the type of surface groups greatly affect the conductivity of the constructed composite separation membrane and the permeation flux, retention rate and anti-pollution performance in electrical assisted filtration. Compared with hydroxylated carbon nanotubes, amino and carboxyl carbon nanotubes have stronger hydrogen bonding with polyvinyl pyrrolidone, so they can more effectively segregate through their synergistic effect to form a dense continuous conductive network and enhance the conductivity, separation performance and anti-pollution performance of the separation membrane. It can be seen from Examples 2, 3, 7 and Comparative Examples 1, 2, 3 that in the absence of polyvinyl pyrrolidone, the conductivity of the prepared composite separation membrane is significantly reduced, resulting in a decrease in the responsiveness of the membrane to electric field stimulation, and a decrease in separation and anti-pollution performance. The above results show that functionalized carbon nanotubes and polyvinyl pyrrolidone can form a continuous conductive network in the membrane cortex through electric field induction, thereby improving the conductivity, separation performance and anti-pollution performance of the separation membrane.

[0045] Finally, the membrane sample of Example 7 was taken separately and its surface morphology was observed using SEM. The results are as follows: Figure 2 As shown, from Figure 2 It can be seen that a continuous network structure formed by amino-modified carbon nanotubes and polyvinyl pyrrolidone appeared on the surface of the membrane sample, proving the successful formation of the conductive cortex.

[0046] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for preparing a composite conductive separation membrane having a stable conductive skin layer, characterized in that: The steps include: Step S1, dissolving the polymer, functionalized carbon nanotubes, and polyvinyl pyrrolidone in dimethylacetamide in a mass ratio of (10-18): (1-3): (1-5) to obtain a uniform casting solution; In step S2, the casting liquid is degassed and then coated on the electrode plate, and an electric field is immediately induced. The casting liquid is then placed in a coagulation bath for phase exchange to obtain a composite membrane. The obtained composite membrane is taken out of the coagulation bath and placed in distilled water for cleaning to obtain a composite separation membrane with a stable conductive skin.

2. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, characterized in that: The polymer is one of polyvinylidene fluoride, polysulfone and polyethersulfone.

3. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, wherein: The functionalized carbon nanotube is one of carboxylated carbon nanotube, hydroxylated carbon nanotube and amino carbon nanotube.

4. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, wherein: The molecular weight of polyvinylpyrrolidone is 8000-58000 g / mol.

5. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, wherein: The dissolution temperature is 70-100°C and the dissolution time is 24-48h.

6. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, characterized in that: The electric field induction time is 1-5 minutes, and the electrode spacing is 1-2 mm.

7. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, characterized in that: The electrode plate is one of a copper plate, an iron plate and a graphene plate.

8. The method for preparing a composite conductive separation membrane having a stable conductive skin layer according to claim 1, wherein: The degassing time of the casting solution is 3-10 hours; the phase exchange time is 12-48 hours.

9. A composite conductive separation membrane having a stable conductive skin layer, characterized in that: The composite conductive separation membrane is prepared by the method for preparing a composite conductive separation membrane with a stable conductive skin layer according to any one of claims 1 to 8.

10. Use of the composite conductive separation membrane with a stable conductive skin layer as claimed in claim 9, characterized in that: Used as a separation membrane in wastewater purification processes.

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