Conductive composite film, method for preparing the same, and use thereof

Abstract

The present application relates to the technical field of membrane, in particular to a kind of conductive composite membrane and its preparation method and use.Conductive composite membrane includes carbon nanotube and polymer deposited on the surface of carbon-based substrate, the surface of carbon nanotube is crosslinked with first binder, the surface of carbon-based substrate is crosslinked with second binder, the mass ratio of polymer and carbon nanotube is 20:1-9, and the mass ratio of carbon nanotube and first binder is 3-6:1.The porosity of conductive composite membrane reaches more than 60%, and the pore size is 1.32-5.26nm.The conductive composite membrane of the present application has the characteristics of high porosity, high conductivity, strong selective separation performance, not easy to delaminate, high flux recovery rate and the like.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, and more specifically, to a conductive composite membrane, its preparation method, and its applications. Background Technology

[0002] Conductive composite membranes have attracted widespread attention in electric field-assisted separation, fouling-resistant membranes, and smart response membrane systems due to their dual functions of separation and conductivity. Existing technologies generally employ a phase inversion method to prepare conductive separation membranes by blending conductive fillers such as carbon nanotubes (CNTs) with film-forming polymers such as polyvinylidene fluoride (PVDF) and polyethersulfone (PES). However, this method suffers from several insurmountable drawbacks in practical applications: First, CNTs readily aggregate in the polymer matrix, making it difficult to form a continuous conductive network. To address the seepage problem, the CNT addition amount typically needs to exceed 10 wt%, leading to membrane pore blockage, a water flux reduction of over 50%, and decreased retention performance. Second, due to the instantaneous phase separation of polymers such as PVDF in the coagulation bath, CNTs are completely encapsulated within the polymer matrix, resulting in high surface resistivity, which cannot meet the high conductivity requirements of electric field-assisted membrane processes. Furthermore, existing conductive membranes have narrow pore size distributions and low porosity, making it difficult to simultaneously achieve high water flux and selective separation, and research on separation processes for heat-sensitive active ingredients in traditional Chinese medicine and food is lacking.

[0003] Therefore, there is an urgent need for a method to prepare conductive composite films that can construct a continuous conductive network while maintaining large pore size and high flux at ultra-low CNT content (<5wt%), in order to solve the technical bottlenecks of poor conductivity, weak interfacial bonding and easy pore blockage in existing conductive films.

[0004] Carbon-based substrates possess excellent electrical conductivity, but in current technologies, they are only used as gas diffusion layers (GDL) in fuel cells or as cathodes in electro-Fenton systems. Their function is limited to conductivity, gas conduction, and mechanical support, and they have never been considered as substrates for liquid-phase separation membranes. Compared to traditional nonwoven substrates, carbon-based substrates can overcome the limitations of traditional substrate insulation, directly utilizing their continuous conductive framework to construct electro-assisted separation systems. Simultaneously, their large-pore three-dimensional structure can significantly reduce transmembrane resistance and increase permeate flux. However, compared to nonwoven fabrics, carbon-based substrates have strong hydrophobicity, excessively large pore sizes (typically micrometer-scale), and lack a selective skin layer. This makes it difficult for the casting solution to fully wet and anchor during membrane preparation, easily leading to interfacial delamination, functional layer peeling, and contaminant leakage during filtration or electrochemical processes. Furthermore, the weak physical entanglement between the carbon cloth and the polymer separation layer makes it difficult to withstand long-term liquid-phase shear forces, severely limiting their application in conductive membrane separation. Therefore, the key to realizing the application of conductive separation films on carbon cloth substrates is to strengthen the interfacial bonding between carbon cloth and separation layer through surface modification or interface engineering, and to construct a thin and dense skin layer with selective separation function on its surface. Summary of the Invention

[0005] To address the problems of weak interfacial bonding, easy peeling and leakage of functional skin, and lack of selective separation layer in existing carbon-based conductive substrates during liquid phase membrane separation, this invention provides a conductive composite film, its preparation method, and its applications.

[0006] In a first aspect, the present invention provides a conductive composite film comprising carbon nanotubes and a polymer deposited on the surface of a carbon-based substrate, wherein a first binder is cross-linked on the surface of the carbon nanotubes, a second binder is cross-linked on the surface of the carbon-based substrate, the mass ratio of the polymer to the carbon nanotubes is 20:1-9, and the mass ratio of the carbon nanotubes to the first binder is 3-6:1.

[0007] Preferably, the porosity of the conductive composite film is 60% or more and the pore size is 1.32-5.26 nm; more preferably, the porosity of the conductive composite film is 60%-80%.

[0008] Preferably, the area occupied by the carbon nanotubes on the surface of the carbon-based substrate is greater than 1%; more preferably, the area occupied by the carbon nanotubes on the surface of the carbon-based substrate is 1%-9%.

[0009] Preferably, the thickness of the second adhesive crosslinked on the surface of the carbon-based substrate is less than the thickness of the first adhesive crosslinked on the surface of the carbon nanotubes.

[0010] Preferably, the thickness ratio of the second adhesive crosslinked on the surface of the carbon substrate to the thickness of the first adhesive crosslinked on the surface of the carbon nanotube is 1-5:5-30; more preferably, the thickness of the second adhesive crosslinked on the surface of the carbon substrate is 10-50 nm, and the thickness of the first adhesive crosslinked on the surface of the carbon nanotube is 50-300 nm.

[0011] Preferably, the flux recovery rate of the conductive composite film is >95%; more preferably, the flux recovery rate of the conductive composite film is >98%.

[0012] Preferably, the conductive composite film has a plant polysaccharide retention rate of >98%; more preferably, the conductive composite film has a plant polysaccharide retention rate of >99%.

[0013] Preferably, the carbon nanotubes include single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes, and the carbon includes carbon black nanotubes, graphene oxide, micene, or carbon derivatives.

[0014] Preferably, the carbon-based substrate comprises carbon fiber cloth, activated carbon cloth, or carbon paper.

[0015] Preferably, the polymer includes polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PSF), or polypropylene (PP).

[0016] Preferably, in the first adhesive and the second adhesive, the adhesive comprises a copolymer containing vinyl and acrylic acid.

[0017] Preferably, the adhesive comprises a vinyl styrene copolymer.

[0018] Preferably, the carbon-based substrate has a porosity of 50%-85% and a bulk density of 0.1-0.5 g / cm³. 3 The carbon nanotubes have an outer diameter of 2-40 nm and a length of 1-30 μm.

[0019] Preferably, the conductive composite film has a surface resistivity of <0.5Ω / sq, a water flux of >100LMH / bar, a plant polysaccharide rejection rate of >98%, and a peel strength of ≥8N / m.

[0020] Secondly, the present invention provides a method for preparing a conductive composite film, comprising the following steps:

[0021] A binder is mixed and stirred with an organic solvent to obtain a solution; a portion of the solution is mixed and stirred with carbon nanotubes to obtain a dispersion; the solution, polymer, and pore-forming agent are mixed and stirred to obtain a casting solution.

[0022] The remaining solutions are coated onto the surface of a carbon-based substrate and dried to obtain a carbon-based substrate with covalent ester bonds;

[0023] The casting solution is coated on the surface of the carbon-based substrate having covalent ester bonds, and after phase transformation, a conductive composite film of polymer and carbon nanotubes is formed on the surface of the carbon-based substrate having covalent ester bonds.

[0024] Preferably, the temperature for mixing the adhesive and the organic solvent is 70-110°C, and the mixing time is 1-3 hours.

[0025] Preferably, the content of the binder in the solution is 0.5-2.5 wt%.

[0026] Preferably, the content of carbon nanotubes in the dispersion is 0.5-5 wt%.

[0027] Preferably, the solids content of the polymer is 15-25 wt%.

[0028] Preferably, the temperature for mixing the solution with the carbon nanotubes is 30-110℃, the stirring time is 1-3h, and the solution is ultrasonicated for 5-30min to obtain a dispersion.

[0029] Preferably, the power of the ultrasound is 10-60kW.

[0030] Preferably, the mass ratio of the polymer to the porogen is 3-10:1.

[0031] Preferably, the temperature for mixing and stirring the solution, polymer, and pore-forming agent is 60-80°C, and the stirring time is 8-16 hours.

[0032] Preferably, after the solution is coated on the surface of the carbon-based substrate, the binder in the solution is crosslinked with the carbon-based substrate at a temperature of 80-120°C for 0.5-2 hours, and then the drying is performed.

[0033] Preferably, the drying temperature is 30-60°C.

[0034] Preferably, the phase transformation is carried out in a coagulation bath at a temperature of 20-50°C, and the phase transformation time is 10-30 min.

[0035] Preferably, the coagulation bath is deionized water or a mixed solution of organic solvent and water, wherein the volume ratio of organic solvent to water in the mixed solution is 1:3-1:5.

[0036] Preferably, the organic solvent includes N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), or dimethyl sulfoxide (DMSO).

[0037] Preferably, the pore-forming agent includes polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), or Tween 80.

[0038] Preferably, the carbon nanotubes are obtained by ball milling under an inert atmosphere. The ball milling is performed using agate balls with a ball-to-material mass ratio of 10-20:1, a milling speed of 250-500 rpm, and a milling time of 6-8 hours.

[0039] Preferably, the thickness ratio of the solution coated on the surface of the carbon-based substrate to the casting solution coated on the surface of the carbon-based substrate having covalent ester bonds is 10-50:0.1-0.2.

[0040] Preferably, the thickness ratio of the solution coated on the surface of the carbon-based substrate to the casting solution coated on the surface of the carbon-based substrate having covalent ester bonds is 20:0.15.

[0041] Preferably, the thickness of the solution coated on the surface of the carbon-based substrate is 10-50 nm, and the thickness of the casting solution coated on the surface of the carbon-based substrate having covalent ester bonds is 100-200 μm.

[0042] Preferably, the thickness of the solution coated on the surface of the carbon-based substrate is 50 nm, and the thickness of the casting solution coated on the surface of the carbon-based substrate having covalent ester bonds is 150 μm.

[0043] Thirdly, the present invention provides the use of a conductive composite membrane as described above in the selective separation of thermosensitive active ingredients in traditional Chinese medicine or food.

[0044] Preferably, under the conditions of transmembrane pressure difference ≤2 bar and optional application of DC voltage of 0.5-1V, selective separation of target substances is achieved, with a separation factor >60. At the same time, self-cleaning can be achieved with electric field assistance, and flux recovery rate >95%.

[0045] Preferably, the traditional Chinese medicines include, but are not limited to, Astragalus membranaceus, Ganoderma lucidum, Lycium barbarum, Ginseng, Angelica sinensis, Scutellaria baicalensis, Glycyrrhiza uralensis, Shiitake mushroom, Poria cocos, or Tremella fuciformis; the foods include, but are not limited to, fruits and vegetables (such as blueberries, Lycium barbarum, tomatoes, and prickly pears), plant proteins (such as milk and fermented whey), tea, or honey; and the heat-sensitive active ingredients include, but are not limited to, vitamins (vitamin C, B vitamins), natural pigments (anthocyanins, carotenoids, chlorophyll), polyphenols (tea polyphenols, flavonoids, resveratrol), proteins and polypeptides (whey protein, collagen peptides, enzyme preparations), volatile essential oils (menthol, eucalyptus oil, limonene), active polysaccharides (plant polysaccharides), or microbial active ingredients (probiotics, active enzymes).

[0046] Preferably, the polysaccharide has a molecular weight of 5-2500 kDa.

[0047] To address the technical bottlenecks of weak interfacial adhesion of conductive films on carbon-based substrates, easy pore clogging under high load of conductive fillers, difficulty in anti-fouling regeneration, and poor selectivity in the separation of thermosensitive active substances, this invention has the following advantages:

[0048] 1. By crosslinking the adhesive onto the surface of the carbon-based substrate of carbon cloth or carbon paper fiber to generate covalent ester bonds, carbon nanotubes can be fixed to the carbon-based substrate by the adhesive, which significantly improves the peel strength between the functional layer and the substrate, ensuring that the conductive composite film maintains its structural integrity under long-term liquid phase shear force, and fundamentally solves the technical defects of carbon-based substrates being prone to delamination and peeling.

[0049] 2. By using a three-dimensional porous framework of carbon cloth / carbon paper as a conductive channel carrier, only a small amount of carbon nanotubes are needed to form a continuous three-dimensional conductive permeation network. This breaks through the limitation of traditional blend membranes that require high load of conductive fillers to form conductive pathways, effectively avoiding the problem of a sharp drop in permeation flux caused by "high filler pore blockage". While significantly reducing raw material costs, it maintains the high permeability of the membrane.

[0050] 3. The conductive composite membrane of this invention serves as the anode, which can electro-oxidize organic pollutants (such as proteins, polysaccharides, and humic acids) in situ in a short time under low voltage and weak electric field. The circulation flux recovery rate can reach more than 95%, and no chemical cleaning agent is required, thus avoiding secondary pollution and realizing the synergistic coupling of membrane separation and electrochemical regeneration.

[0051] 4. In the field of selective separation of functional components of traditional Chinese medicine or food, this invention can achieve efficient separation of target active substances (such as polysaccharides of traditional Chinese medicine, plant polyphenols, and active peptides) and impurities (inorganic salts, monosaccharides, and pigments) under mild operating conditions (transmembrane pressure difference ≤ 0.2 bar, optional coupling of 0.5-1.0V DC electric field), by utilizing the synergistic mechanism of size sieving-electrophoretic migration-Donnan effect. The separation factor is > 60, while avoiding the loss of activity caused by thermal concentration. The retention rate of heat-sensitive components is increased by more than 30% compared with traditional processes. Attached Figure Description

[0052] Figure 1 A scanning electron microscope (SEM) image of the conductive composite film of Example 1 is shown.

[0053] Figure 2 The scanning electron microscope (SEM) image of the conductive composite film of Example 2 is shown.

[0054] Figure 3 A scanning electron microscope (SEM) image of the conductive composite film of Example 3 is shown.

[0055] Figure 4 A scanning electron microscope (SEM) image of the conductive composite film of Example 4 is shown.

[0056] Figure 5 A scanning electron microscope (SEM) image of the conductive composite film of Comparative Example 1 is shown.

[0057] Figure 6 The scanning electron microscope (SEM) image of the conductive composite film in Comparative Example 2 is shown. Detailed Implementation

[0058] The present disclosure will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and thus implement the present disclosure, and are not intended to imply any limitation on the scope of the disclosure.

[0059] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment". The term "another embodiment" is to be interpreted as "at least one other embodiment". Furthermore, the terms "first", "second", etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific kind and construction) and are not intended to indicate or imply the relative importance or number of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0060] Example 1

[0061] A method for preparing a conductive composite film on a carbon-based substrate includes the following steps:

[0062] Step 1: Grind the CNTs raw material in a ball mill at 280 rpm for 8 hours. The outer diameter of the ball-milled CNTs is 20-40 nm and the length is 1-2 μm.

[0063] Step 2: Weigh 2g of EAA and place it in 68g of DMAC. Stir and dissolve it at 70℃ for 2 hours. Divide the solution into two equal portions of EAA solution. Add 2.5g of CNTs to one portion of the EAA solution and continue stirring at 70℃ for 1 hour. Then sonicate at 60kW for 5 minutes to prepare a dispersion.

[0064] Step 3: Transfer the dispersion to a three-necked flask, add 18g of PVDF and 6g of PEG (10k) powder, and continue stirring for 12 hours to prepare a conductive casting solution;

[0065] Step 4: The second portion of EAA solution is dipped into the carbon paper surface with a thickness of 50 nm, crosslinked at 80°C for 1 h, and dried at 50°C to obtain a chemically bonded reinforced carbon paper substrate. The chemically bonded reinforced carbon paper substrate is a carbon-based substrate with covalent ester bonds on its surface.

[0066] Step 5: Fix the chemically bonded reinforced carbon paper substrate onto a smooth glass plate, pour on the conductive casting solution, and use a scraper to evenly spread the casting solution onto the carbon cloth to a thickness of 100 μm. Then, place the glass plate together in a deionized water coagulation bath at 30°C for phase transformation and remove excess organic solvents and pore-forming agents to obtain a conductive composite film. The conductive composite film is stored in deionized water at room temperature.

[0067] The conductive composite membrane obtained in this embodiment has a porosity of 68.53%, an average pore size of 2.75 nm, a peel strength of 9.26 N / m, a surface resistivity of 0.48 Ω / sq, and a water flux of 182.65 LMH / bar. Under the synergistic effect of a pressure of 1 bar and an electric field of 1 V, the conductive composite membrane achieves a separation factor of 62.13 for a mixed solution of 1000 ppm traditional Chinese medicine polysaccharides or salts. Among these, the retention rate of traditional Chinese medicine polysaccharides by the conductive composite membrane reaches 98.23%, and the flux recovery rate of the conductive composite membrane after reverse energization is 95.82%.

[0068] Example 2

[0069] A method for preparing a conductive composite film on a carbon-based substrate includes the following steps:

[0070] Step 1: Grind the CNTs raw material in a ball mill at 280 rpm for 8 hours. The outer diameter of the ball-milled CNTs is 20-40 nm and the length is 1-2 μm.

[0071] Step 2: Weigh 1g of EAA and place it in 68g of DMAC. Stir and dissolve it at 70℃ for 2 hours. Divide the solution into two equal portions of EAA solution. Add 2.5g of CNTs to one portion of the EAA solution and continue stirring at 70℃ for 1 hour. Then sonicate at 60kW for 10 minutes to prepare a dispersion.

[0072] Step 3: Transfer the dispersion to a three-necked flask, add 18g of PVDF and 4g of PEG (10k) powder, and continue stirring for 12 hours to prepare a conductive casting solution;

[0073] Step 4: The second portion of EAA solution is dipped into the carbon paper surface at a thickness of 30 nm, crosslinked at 80°C for 1 h, and dried at 60°C to obtain a chemically bonded reinforced carbon paper substrate. The chemically bonded reinforced carbon paper substrate is a carbon-based substrate with covalent ester bonds on its surface.

[0074] Step 5: Fix the chemically bonded reinforced carbon paper substrate onto a smooth glass plate, pour on the conductive casting solution, and use a scraper to evenly spread the casting solution onto the carbon cloth to a thickness of 120 μm. Then, place the glass plate together in a deionized water coagulation bath at 30°C for phase transformation and remove excess organic solvents and pore-forming agents to obtain a conductive composite film. The conductive composite film is stored in deionized water at room temperature.

[0075] The conductive composite membrane obtained in this embodiment has a porosity of 77.32%, an average pore size of 3.86 nm, a peel strength of 9.25 N / m, a surface resistivity of 0.41 Ω / sq, and a water flux of 192.17 LMH / bar. Under the synergistic effect of a pressure of 1 bar and an electric field of 1 V, the conductive composite membrane achieves a separation factor of 65.21 for a mixed solution of 1000 ppm traditional Chinese medicine polysaccharides or salts. Among these, the retention rate of traditional Chinese medicine polysaccharides by the conductive composite membrane reaches 99.21%, and the flux recovery rate of the conductive composite membrane after reverse energization is 96.21%.

[0076] Example 3

[0077] A method for preparing a conductive composite film on a carbon-based substrate includes the following steps:

[0078] Step 1: Grind the CNTs raw material in a ball mill at 280 rpm for 8 hours. The outer diameter of the ball-milled CNTs is 1-2 nm and the length is 5-30 μm.

[0079] Step 2: Weigh 2g of EAA and place it in 68g of DMAC. Stir and dissolve it at 70℃ for 2 hours. Divide the solution into two equal portions of EAA solution. Add 5.5g of CNTs to one portion of the EAA solution and continue stirring at 70℃ for 1 hour. Then sonicate at 60kW for 5 minutes to prepare a dispersion.

[0080] Step 3: Transfer the dispersion to a three-necked flask, add 18g of PVDF and 6g of PEG (10k) powder, and continue stirring for 12 hours to prepare a conductive casting solution;

[0081] Step 4: The second portion of EAA solution is dipped into the carbon paper surface at a thickness of 20 nm, crosslinked at 80°C for 1 h, and dried at 50°C to obtain a chemically bonded reinforced carbon paper substrate. The chemically bonded reinforced carbon paper substrate is a carbon-based substrate with covalent ester bonds on its surface.

[0082] Step 5: Fix the chemically bonded reinforced carbon paper substrate onto a smooth glass plate, pour on the conductive casting solution, and use a scraper to evenly spread the casting solution onto the carbon cloth to a thickness of 120 μm. Then, place the glass plate together in a deionized water coagulation bath at 30°C for phase transformation and remove excess organic solvents and pore-forming agents to obtain a conductive composite film. The conductive composite film is stored in deionized water at room temperature.

[0083] The conductive composite membrane obtained in this embodiment has a porosity of 64.25%, an average pore size of 2.72 nm, a peel strength of 10.19 N / m, a surface resistivity of 0.35 Ω / sq, and a water flux of 172.43 LMH / bar. Under the synergistic effect of a pressure of 1 bar and an electric field of 1 V, the conductive composite membrane achieves a separation factor of 72.18 for a mixed solution of 1000 ppm traditional Chinese medicine polysaccharides or salts. Among these, the retention rate of traditional Chinese medicine polysaccharides by the conductive composite membrane reaches 99.62%, and the flux recovery rate of the conductive composite membrane after reverse energization is 96.82%.

[0084] Example 4

[0085] A method for preparing a conductive composite film on a carbon-based substrate includes the following steps:

[0086] Step 1: Grind the CNTs raw material in a ball mill at 280 rpm for 8 hours. The outer diameter of the ball-milled CNTs is 1-2 nm and the length is 5-30 μm.

[0087] Step 2: Weigh 2g of EAA and place it in 68g of DMAC. Stir and dissolve it at 70℃ for 2 hours. Divide the solution into two equal portions of EAA solution. Add 3.5g of CNTs to one portion of the EAA solution and continue stirring at 70℃ for 1 hour. Then sonicate at 60kW for 5 minutes to prepare a dispersion.

[0088] Step 3: Transfer the dispersion to a three-necked flask, add 18g of PVDF and 6g of PEG (10k) powder, and continue stirring for 12 hours to prepare a conductive casting solution;

[0089] Step 4: The second portion of EAA solution is dipped into the carbon paper surface with a thickness of 50 nm, crosslinked at 80°C for 1 h, and dried at 50°C to obtain a chemically bonded reinforced carbon paper substrate. The chemically bonded reinforced carbon paper substrate is a carbon-based substrate with covalent ester bonds on its surface.

[0090] Step 5: Fix the chemically bonded reinforced carbon paper substrate onto a smooth glass plate, pour on the conductive casting solution, and use a scraper to evenly spread the casting solution onto the carbon cloth to a thickness of 150 μm. Then, place the glass plate together in a deionized water coagulation bath at 30°C for phase transformation and remove excess organic solvents and pore-forming agents to obtain a conductive composite film. The conductive composite film is stored in deionized water at room temperature.

[0091] The conductive composite membrane obtained in this embodiment has a porosity of 62.13%, an average pore size of 4.21 nm, a peel strength of 9.26 N / m, a surface resistivity of 0.21 Ω / sq, and a water flux of 152.31 LMH / bar. Under the synergistic effect of a pressure of 1 bar and an electric field of 1 V, the conductive composite membrane achieves a separation factor of 78.21 for a mixed solution of 1000 ppm traditional Chinese medicine polysaccharides or salts. Among these, the retention rate of traditional Chinese medicine polysaccharides by the conductive composite membrane reaches 99.62%, and the flux recovery rate of the conductive composite membrane after reverse energization is 98.12%.

[0092] Comparative Example 1

[0093] A method for preparing a conductive composite film on a carbon-based substrate includes the following steps:

[0094] Step 1: Grind the CNTs raw material in a ball mill at 280 rpm for 8 hours. The outer diameter of the ball-milled CNTs is 1-2 nm and the length is 5-30 μm.

[0095] Step 2: Weigh 2g of EAA and place it in 68g of DMAC. Stir and dissolve it at 70℃ for 2 hours. Add 3g of CNTs and continue stirring at 70℃ for 1 hour. Then sonicate at 60kW for 5 minutes to prepare a dispersion.

[0096] Step 3: Transfer the dispersion to a three-necked flask, add 18g of PVDF and 6g of PEG (10k) powder, and continue stirring for 12 hours to prepare a conductive casting solution;

[0097] Step 4: Fix the carbon paper onto a smooth glass plate, pour on the conductive casting solution, and use a scraper to evenly spread the casting solution onto the carbon paper to a thickness of 20μm. Then, place the glass plate together in a deionized water coagulation bath at a temperature of 30℃ for phase inversion and removal of excess solvent to obtain a conductive composite film. The conductive composite film is stored in deionized water at room temperature.

[0098] The conductive composite membrane obtained in this comparative example has a porosity of 45.21%, an average pore size of 4.55 nm, and a peel strength of 0.72 N / m. Its surface resistivity is 0.54 Ω / sq, and its water flux is 321.42 LMH / bar. Under the synergistic effect of a 1 bar pressure and a 1 V electric field, the separation factor of the conductive composite membrane for a mixed solution of 1000 ppm traditional Chinese medicine polysaccharides or salts is only 11.23. Specifically, the retention rate of the conductive composite membrane for traditional Chinese medicine polysaccharides reaches 72.12%, and after reverse energization, the flux recovery rate of the conductive composite membrane is 85.43%.

[0099] Comparative Example 2

[0100] Step 1: Weigh 2g of EAA and place it in 68g of DMAC. Stir and dissolve at 70℃ for 2h. Divide the solution into two equal parts. Add 4g of untreated CNTs raw material to one part of the EAA solution. Continue stirring at 70℃ for 1h. Then sonicate at 60kW for 5min to prepare a dispersion. The outer diameter of the CNTs raw material is 20-40nm and the length is 1-2μm.

[0101] Step 2: Transfer the dispersion to a three-necked flask, add 18g of PVDF and 6g of PEG (10kDa) powder, and continue stirring for 12 hours to prepare a conductive casting solution;

[0102] Step 3: The second portion of EAA solution is dipped into the carbon paper surface at a thickness of 50 nm, crosslinked at 80°C for 1 h, and dried to obtain a chemically bonded reinforced carbon paper substrate.

[0103] Step 4: Fix the chemically bonded reinforced carbon paper substrate onto a smooth glass plate, pour on the conductive casting solution, and use a scraper to evenly spread the casting solution onto the carbon cloth to a thickness of 200 μm. Then, place the glass plate together in a deionized water coagulation bath at a temperature of 30°C to remove excess solvent. After that, take out the composite film and store it at room temperature with deionized water to obtain the conductive composite film.

[0104] The conductive composite membrane obtained in this comparative example has a porosity of 57.83%, an average pore size of 6.21 nm, and a peel strength of 9.12 N / m. Its surface resistivity is 1.23 Ω / sq, and its water flux is 152.42 LMH / bar. Under the synergistic effect of a 1 bar pressure and a 1 V electric field, the separation factor of the conductive composite membrane for a mixed solution of 1000 ppm traditional Chinese medicine polysaccharides or salts is only 32.12. Specifically, the retention rate of the conductive composite membrane for traditional Chinese medicine polysaccharides reaches 78.92%, and after reverse energization, the membrane flux recovery rate is 88.32%.

[0105] TEM images of the conductive composite films of Examples 1-4 and Comparative Examples 1-2 are shown below. Figure 1-6 As shown. By Figure 1-4 It can be seen that the conductive composite film of Examples 1-4 has a porous structure on the surface, with relatively uniform pore size, good interface continuity, and basically no cracks. The carbon nanotubes with binder on the surface are not completely embedded by the polymer.

[0106] and Figure 5 and Figure 6 In the comparison, the conductive composite film surfaces of Comparative Example 1 and Comparative Example 2 exhibit an uneven, groove-like structure, and the conductive composite film surface of Comparative Example 2 shows obvious crack structures.

[0107] A comparison of the surface morphology images of the conductive composite films in the examples and comparative examples shows that the carbon-based substrate significantly affects the surface microstructure of the conductive composite film. Using a carbon-based substrate to prepare the conductive composite film promotes the formation of micropores on the surface, thereby improving the pure water flux of the conductive composite film and achieving cost reduction and efficiency improvement in engineering applications. The comparison also demonstrates the fundamental differences in surface chemical properties, microstructure characteristics, and thermophysical properties between carbon-based substrates (carbon paper / carbon cloth) and non-carbon-based substrates (traditional nonwoven fabric / polymer mesh), leading to significant differences in solvent-non-solvent exchange kinetics and interfacial stress distribution during the phase transformation film formation process. In the examples, upon immersion in the coagulation bath, the solvent in the casting solution forms hydrogen bonds or dipole interactions with the functional groups on the surface of the carbon-based substrate, promoting the migration of solvent molecules to the matrix interface, inducing local transient liquid-liquid phase separation, optimizing interfacial stability and mass transfer kinetics during the phase transformation process, and thus preparing a high-performance conductive composite film with uniform surface micropores and a continuous, crack-free interface.

[0108] This invention achieves the connection between the carbon-based substrate and the separation layer through chemical bonding by grafting an ultrathin ethylene-acrylic acid copolymer skin onto the fiber surface of a carbon-based substrate. This improves the effect of fixing the separation layer to the carbon-based substrate and solves the problem of delamination between the carbon-based substrate and the separation layer during long-term use of the composite film. At the same time, the carbon-based substrate and carbon nanotubes work together to enhance the conductivity of the conductive composite film.

[0109] This invention utilizes COC ester bonds and physical anchors formed on the surface of a carbon-based substrate by cross-linking an ethylene-acrylic acid copolymer binder with the carbon-based substrate, thereby transforming the carbon-based substrate used for the "gas diffusion layer of a fuel cell" into a "liquid phase separation membrane," achieving a functional leap from electrode to separation for the carbon-based substrate.

[0110] This invention constructs a three-dimensional surface conductive network, rather than a traditional bulk blend conductive network, by coating a casting solution onto the surface of a carbon-based substrate with covalent ester bonds, allowing the EAA binder to pre-anchor carbon nanotubes to the surface of carbon cloth / carbon paper fibers. In the subsequent phase transformation film formation process, carbon nanotubes, as a pre-fabricated conductive framework, remain at the interface between the carbon substrate and the polymer functional layer, avoiding the risk of being completely embedded in the polymer matrix. Part of their tube walls are exposed on the membrane surface or in the interfacial micropores, maintaining an effective electron transport channel with the external circuit and providing electrochemical active sites for in-situ oxidation and anti-fouling. The prepared highly conductive separation membrane, acting as an in-situ anode, can electro-oxidize organic pollutants in situ under the synergistic effect of electric field and pressure, with a flux recovery rate >95%. This enables the conductive composite membrane to continuously and efficiently separate the heat-sensitive active ingredients of traditional Chinese medicine or food, with a selective separation factor >60. This solves the problems in the field of conductive membranes, such as discontinuous conductive networks and pore blockage caused by carbon nanotube aggregation in the polymer matrix, weak and easily peeled-off bonding between the conductive layer and the carbon substrate interface, conductivity loss due to carbon nanotube embedding in the polymer during phase transformation, and the inability to simultaneously achieve high flux and selectivity. This invention achieves synergistic optimization of flux and selectivity, and the conductive composite membrane of this invention has excellent prospects for industrial application.

[0111] Meanwhile, in this invention, ethylene-acrylic acid copolymer (EAA) acts as a macromolecular binder. Its ethylene segments can be tightly bonded to the surface of carbon nanotubes (CNTs) through π-π stacking, while the side chain carboxyl groups (-COOH) form a hydrogen bond network with CNT surface defects and oxygen-containing groups. The steric hindrance effect effectively prevents the aggregation and re-entanglement of CNTs in the dispersion. More importantly, EAA acts as a "molecular medium" between the carbon-based substrate and the functional polymer. Its hydrophobic ethylene backbone has good affinity with the graphitized surface of carbon cloth / carbon paper, while the polar carboxyl groups can generate dipole-dipole interactions or hydrogen bonds with polar polymers in the casting solution (such as fluorine atoms in PVDF and sulfone groups in PES), which significantly improves the interfacial compatibility between the hydrophobic carbon-based substrate and the polar polymer casting solution. During the phase transformation film formation process, the carboxyl groups of EAA preferentially adsorb onto the surface of the carbon substrate to form a hydrophilic transition layer, reducing the contact angle between the casting solution and the carbon cloth surface, and promoting the uniform spreading and capillary penetration of the casting solution in the three-dimensional porous carbon framework. At the same time, as a physical anchoring point, the molecular chains of EAA can penetrate into the interior of the functional polymer skin to form an interpenetrating network structure or covalent cross-linking points. This allows the separation layers such as PVDF to not only form a skin through phase separation during the curing process, but also to form a mechanical bond with the carbon substrate through the "bridging" effect of EAA. This effectively avoids the common problems of interface debonding, blistering, and delamination leakage during long-term operation in traditional physical coating, ensuring the structural integrity of the conductive composite membrane under high-throughput filtration and electrochemical conditions.

[0112] The conductive composite membrane of this invention has the characteristics of large pore size, high conductivity and strong selective separation performance.

[0113] Those skilled in the art will understand that the above embodiments are specific examples of implementing this disclosure, and in practical applications, various changes can be made in form and detail without departing from the scope of this disclosure.

Claims

1. A conductive composite film, characterized in that, The invention comprises carbon nanotubes and polymers deposited on the surface of a carbon-based substrate, wherein the surface of the carbon nanotubes is cross-linked with a first binder and the surface of the carbon-based substrate is cross-linked with a second binder, the mass ratio of the polymer to the carbon nanotubes is 20:1-9, and the mass ratio of the carbon nanotubes to the first binder is 3-6:

1.

2. The conductive composite film according to claim 1, characterized in that, The carbon-based substrate includes carbon fiber cloth, activated carbon cloth, or carbon paper.

3. The conductive composite film according to claim 1, characterized in that, The polymer includes polyvinylidene fluoride, polyethersulfone, polysulfone, or polypropylene.

4. The conductive composite film according to claim 1, characterized in that, In the first adhesive and the second adhesive, the adhesive comprises a copolymer containing vinyl and acrylic acid.

5. The method for preparing a conductive composite film according to claim 1, characterized in that, The conductive composite film has a porosity of 60%-80% and a pore size of 1.32-5.26 nm.

6. The conductive composite film according to claim 1, characterized in that, The carbon-based substrate has a porosity of 50%-85% and a bulk density of 0.1-0.5 g / cm³. 2 The carbon nanotubes have an outer diameter of 2-40 nm and a length of 1-30 μm.

7. The conductive composite film according to claim 1, characterized in that, The conductive composite film has a surface resistivity of <0.5Ω / sq, a water flux of >100LMH / bar, a plant polysaccharide rejection rate of >98%, and a peel strength of ≥8N / m.

8. A method for preparing a conductive composite film according to any one of claims 1-7, characterized in that, Includes the following steps: A binder is mixed and stirred with an organic solvent to obtain a solution; a portion of the solution is mixed and stirred with carbon nanotubes to obtain a dispersion; the solution, polymer, and pore-forming agent are mixed and stirred to obtain a casting solution. The remaining solutions are coated onto the surface of a carbon-based substrate and dried to obtain a carbon-based substrate with covalent ester bonds; The casting solution is coated on the surface of the carbon-based substrate having covalent ester bonds, and after phase transformation, a conductive composite film of polymer and carbon nanotubes is formed on the surface of the carbon-based substrate having covalent ester bonds.

9. The method for preparing a conductive composite film according to claim 8, characterized in that, The thickness ratio of the solution coated on the carbon substrate surface to the casting solution coated on the substrate layer surface is 10-50:0.1-0.

2.

10. The use of a conductive composite membrane as described in any one of claims 1-9 in the selective separation of thermosensitive active ingredients in traditional Chinese medicine or food.

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