CN117379993A

CN117379993A - High-strength composite film and preparation method thereof

Info

Publication number: CN117379993A
Application number: CN202311477146.0A
Authority: CN
Inventors: 赵凯; 牛青山; 赵盛超; 雷晶; 李鹏
Original assignee: Shenzhen University; Shenzhen Angel Drinking Water Equipment Co Ltd
Current assignee: Shenzhen University; Shenzhen Angel Drinking Water Equipment Co Ltd
Priority date: 2023-11-06
Filing date: 2023-11-06
Publication date: 2024-01-12

Abstract

The invention provides a high-strength composite membrane and a preparation method thereof, wherein the composite membrane comprises an ultrathin separating layer and a composite polymer substrate, and is characterized in that the ultrathin separating layer (1) is prepared by an interfacial polymerization method or a layer-by-layer self-assembly method or a coating method; the preparation method comprises the steps of compounding a single-layer or multi-layer polyolefin film with a non-woven fabric or a runner screen made of polymer materials by an ultrasonic welding method or an adhesive bonding method or a hot-press welding method so as to improve the integral strength of the independent polyolefin substrate; hydrophilizing modification is carried out on the high-strength composite polymer substrate so as to regulate and control compatibility among all layers of the thin-layer composite film; the performance of the composite membrane is regulated and controlled by using an additive for the ultrathin separation layer.

Description

High-strength composite film and preparation method thereof

Technical Field

The present invention relates to membrane separation technology, and more particularly, to thin layer composite (TFC) membrane materials and methods of making the same.

Background

The problems of environmental pollution, energy crisis and the like facing the world at present severely restrict the development of socioeconomic performance, and the membrane separation technology has been widely focused by various countries in the world. Compared with the traditional separation technologies such as extraction, adsorption, rectification and the like, the membrane separation technology is a more energy-saving and efficient separation technology, and has the advantages of being green, free of pollution, easy to operate and maintain and the like.

In high-precision pressure-driven membrane separation processes (mainly nanofiltration and reverse osmosis), thin-layer composite (TFC) membrane materials are widely studied and used for their better desalination performance and acid and alkali resistance (compared to earlier cellulose acetate membranes). However, high-end membrane materials (including nanofiltration and reverse osmosis membranes) currently used domestically are mostly derived from foreign sources, such as the companies of the dow, the eastern electricians and the eastern, etc. of japan in the united states. Therefore, the localization of high-end membrane materials is imperative.

TFC membranes are characterized by having an ultra-thin selective separation layer. Typical commercial composite membranes are usually three-layer structures, including a bottom nonwoven layer, a middle porous support layer (the two are often collectively referred to as the substrate), and a top ultrathin separating layer. The primary function of the nonwoven layer is to provide tensile strength to prevent deformation of the composite film during operation to form channels within the permeate spacer layer of the roll element. This layer may affect the performance of the composite membrane but is typically not to the same extent as the support or separation layer. The porous support layer is typically an asymmetric membrane prepared by a phase inversion process, with pore sizes typically ranging from 2 to 100 μm, with suitable pore sizes and surface properties providing preparation sites for the top separation layer. The separation layer is usually prepared by interfacial polymerization, i.e. two reactive monomers, which are dissolved in immiscible two phases, undergo polymerization at the phase interface to form a dense film. In addition, the separation layer may be prepared by layer-by-layer self-assembly of polyelectrolyte or polymer coating.

However, there are technical drawbacks in the preparation of TFC membranes in the market as follows: support layers such as polysulfones and polyethersulfones are costly and are poorly resistant to polar solvents; the cost of support layers resistant to organic solvents such as polyimide and polyacrylonitrile is too high, affecting the explosive development of the industry. Polyolefin membranes have a significantly lower cost, but there are also some adverse factors for the preparation of thin-layer composite membranes, such as inert surface properties and soft texture, which to some extent affect their affinity for polymer separation layers and the operability of the composite membrane preparation and subsequent membrane rolling processes, preventing their large-scale application in the field of thin-layer composite separation membranes.

Disclosure of Invention

Aiming at the technical defects, the application provides a high-strength composite membrane and a preparation method thereof, wherein the composite membrane has a structure shown in a figure 1, and (1) a layer is a compact ultrathin separating layer and is prepared by an interfacial polymerization method or a layer-by-layer self-assembly method or a coating method; the high-strength composite polymer substrate is a combination of a polyolefin film of the layer (2) and a non-woven fabric or a runner screen of the layer (3); namely, the middle part of the composite film is a polyolefin film, the lower part is a non-woven fabric or a runner screen, and the composite film is used as a composite material to improve the strength of a substrate and enhance the practicability and operability of the thin-layer composite film on the polyolefin substrate in the preparation, rolling and using processes.

The high-strength composite polyolefin material has a thickness of 60-600 mu m and is used as a substrate to prepare a novel thin layer composite film.

The high strength composite polymer substrate reduces cost compared to conventional substrates and improves strength and handleability during film preparation and winding compared to single layer polyolefin substrates. The thin-layer composite separation membrane can meet the requirements of different separation precision through substrate surface modification and separation layer formula adjustment.

The high-strength composite membrane comprises a compact ultrathin separating layer and a high-strength composite polymer substrate;

according to the invention, the single-layer or multi-layer polyolefin film and the non-woven fabrics or the runner separation net made of polymer materials are compounded by an ultrasonic welding method or an adhesive bonding method or a hot-press welding method so as to improve the integral strength of the independent polyolefin substrate, the operability is obviously improved in the preparation of the thin-layer composite film and the rolling process of the film, and the cost is obviously reduced compared with the traditional substrate prepared based on a phase inversion process.

The invention aims at the use of a high-strength polyolefin substrate in a thin-layer composite film, various optimization strategies for improving the performance of all layers except the substrate, the improvement of the specificity of the component design of the polyolefin-based thin-layer composite film and the application of the thin-layer composite film under special separation conditions.

The preparation method of the high-strength composite film comprises the following steps: the preparation process of the compact ultrathin separating layer is preferably an interfacial polymerization method, and is characterized by comprising the following preparation steps: (1) Coating an aqueous phase solution on a hydrophilization substrate for 1-30min, pouring out the aqueous phase solution, and removing surface residual aqueous solution by using a rubber roller or an air knife or absorbent paper, wherein the aqueous phase solution contains reactive monomers (such as polyamine or alcohol or phenol) and aqueous phase additives (such as surfactant, phase transfer catalyst, cosolvent, acid binding agent, nanofiller and the like); (2) Coating an alkane phase solution on the substrate treated in the step (1) for 10-180s, pouring out the alkane phase solution, cleaning the surface of the film by using pure alkane, and finally carrying out heat treatment for 1-20min in an oven at the temperature of 30-95 ℃, wherein the alkane phase solution contains a reactive monomer (such as polybasic acyl chloride or sulfonyl chloride or isocyanate and the like) and an oil phase additive (such as a cosolvent, a nanofiller and the like), and the alkane solvent is n-alkane, isoparaffin or a mixture of the n-alkane and the isoparaffin with the carbon chain length of six-thirteen.

The polyolefin film is a polyethylene film or a polypropylene film or a combination of the polyethylene film and the polypropylene film, and the polyolefin film is prepared by a dry method or a wet method.

The total thickness of the high-strength composite polymer substrate is 60-600 mu m, wherein the thickness of the polyolefin film layer is 5-50 mu m, and the thickness of the non-woven fabric or the runner separation net layer is 55-550 mu m.

The non-woven fabric is made of one or more of polyester, polypropylene, polyamide, polyacrylamide, polyethylene, polyvinyl chloride and viscose fiber, and has a pore diameter of 1-30 μm.

The manufacturing raw materials of the runner screen comprise one or more of polyester, polyethylene and polypropylene, and the aperture is 0.2-2mm.

The high-strength composite polymer substrate is prepared by compositing a lower non-woven fabric or a runner screen layer with a middle single-layer or multi-layer polyolefin film, and the compositing process is one or a plurality of combined treatment methods of ultrasonic welding, adhesive bonding or hot-press welding. Preferably, the compounding process of the high-strength composite polymer substrate is preferably an ultrasonic welding compounding process, and is characterized in that the working frequency is 20-40kHz, the ultrasonic amplitude is 30-90 mu m, the welding pressure is 0.2-0.6MPa, and the welding time is 1-10s.

The high-strength composite polymer substrate disclosed by the invention is subjected to proper treatment including physical or chemical modification on the surface before being used for preparing an ultrathin separating layer, optionally, physical methods including plasma treatment, ionizing radiation treatment, corona treatment and the like, and chemical methods including treatment technologies based on diazonium salt chemistry, based on phenolamine chemistry, based on coordination chemistry, based on a siloxane coupling agent, based on epoxy resin, based on hydroxyl acetalization, based on strong acid and alkali and the like or treatment technologies of various combinations of the above, and finally, the hydrophilized substrate is obtained, wherein the static water contact angle is 30-110 degrees.

Preferably, the surface treatment scheme of the polyolefin film can be a combined treatment technology based on diazonium salt chemistry and based on strong acid, specifically, the surface polarity of the polyolefin film is increased by coating para-aminodiazonium benzene and phenyl radical solution under the strong acid condition on the surface of the polyolefin film for 1-48 hours, so that the affinity of the high-strength composite polymer substrate and the compact ultrathin separating layer is improved.

The p-aminodiazobenzene and phenyl free radical solution under the strong acid condition is prepared by diazotizing p-phenylenediamine and nitrite and further reducing the p-aminodiazobenzene and phenyl free radical solution at the reaction temperature of 0-5 ℃ by adopting iron powder or zinc powder as a reducing agent.

The compact ultrathin separating layer is prepared by an interfacial polymerization method or a layer-by-layer self-assembly method or a coating method, and the thickness is 10nm-200 mu m, preferably by the interfacial polymerization method.

In the invention, the membrane flux and the desalination rate are evaluated by adopting cross-flow membrane performance evaluation equipment customized by a laboratory, the test temperature is 25+/-2 ℃, and the effective area of the membrane test is 28.27cm ² The composition of the feed liquid and the test pressure are adjusted according to the type of the composite membrane, the flux (F) of the composite membrane is calculated through a formula (1), and the desalination rate (R) of the composite membrane is calculated through a formula (2).

Formula (1): f=v/(p·a·t), where V is permeate volume per unit time, p is test pressure, a is filtration area, and t is permeate sampling time.

Formula (2): r=1 to C _P /C _F Wherein C _P For permeate concentration, C _F Is the concentration of the raw material liquid.

The beneficial effects of the invention are as follows:

1. the novel thin layer composite film prepared based on the high-strength composite polyolefin substrate can greatly reduce the film preparation cost (only the substrate material is considered, and the cost can be reduced to about one third of that of the traditional substrate) compared with the thin layer composite film prepared based on the traditional substrate; compared with a thin layer composite film prepared based on a common polyolefin substrate, the film-forming and film-rolling process has the advantage that the operability in the film-forming and film-using processes is obviously improved due to the improvement of the substrate strength;

2. hydrophilizing and modifying the substrate by a physical or chemical method to regulate and control the performance of the thin-layer composite film and enhance the compatibility between layers;

3. the performance of the thin-layer composite membrane is regulated and controlled by improving the preparation process of the top ultrathin compact separation layer, using novel additives, post-treatment and other strategies;

4. the filling area of the membrane in the unit volume membrane shell is increased by improving the assembly mode from the membrane to the membrane element, so that the water yield of the element is improved;

5. the novel thin layer composite membrane prepared based on the high-strength composite polyolefin substrate can be applied to the separation process of Jiang Suanjian and a polar organic solvent system.

Drawings

Fig. 1 is a schematic structural diagram of the present invention:

FIG. 2 is a schematic diagram of examples 1-3;

FIG. 3 is a schematic diagram of examples 4-6;

FIG. 4 is a schematic representation of examples 7-9.

The specific embodiment is as follows:

the invention relates to a preparation method of a thin layer composite separation membrane based on a high-strength composite polymer substrate for brackish water desalination, wherein the high-strength composite polymer substrate is formed by compositing a polyester non-woven fabric and a single-layer polypropylene membrane prepared based on a dry process through a preferred ultrasonic welding process, the substrate surface treatment scheme is a preferred combined treatment technology based on diazonium salt chemistry and based on strong acid, and the compact ultrathin separation layer is prepared through an interfacial polymerization method.

The thickness of the polyester non-woven fabric layer in the high-strength composite polymer substrate is preferably 120 mu m, the thickness of the polypropylene film layer is preferably 50 mu m, the working frequency of the ultrasonic welding process is preferably 32kHz, the ultrasonic amplitude is preferably 60 mu m, the welding pressure is preferably 0.3MPa, and the welding time is preferably 4s.

The concentration of m-phenylenediamine in the preferred polyolefin film surface treatment scheme is preferably 0.1%, the pH of the solution is adjusted by concentrated sulfuric acid, the concentration of nitrite is preferably sodium nitrite, the concentration of reducing agent is preferably iron powder, the coating time of the reaction liquid in examples 1-3 is respectively 1h, 2h and 4h, and the modified hydrophilized substrate is washed with ethanol for 30s to remove small molecular fragments which are not covalently bonded on the surface.

The static water contact angles of the modified hydrophilized substrates with the reaction liquid coating time of 1h, 2h and 4h are 73.2+/-4.3 degrees, 65.3+/-2.1 degrees and 55.2+/-2.3 degrees respectively.

The preparation scheme of the compact ultrathin separating layer comprises the steps of firstly coating an aqueous phase solution on a hydrophilization substrate in examples 1-3 for 1-30min, then pouring out and removing the surface residual aqueous solution by using a rubber roller; then coating alkane phase solution on the substrate treated by the aqueous phase solution for 10-180s, pouring out superfluous alkane solution and cleaning the surface of the membrane by pure alkane; finally, heat treatment is carried out for 1-20min in a baking oven at 30-95 ℃.

The aqueous solution is preferably coated for 5 minutes, the reactive monomer in the aqueous solution is preferably polyamine, more preferably m-phenylenediamine, the concentration is preferably 3%, the additive is preferably a combination of sodium dodecyl benzene sulfonate and triethylamine, and the concentration is respectively 0.1% and 1.1%.

The alkane phase solution is preferably Isopar G, the coating time is preferably 60s, the reactive monomer in the alkane phase solution is preferably polybasic acyl chloride, more preferably trimesoyl chloride, the concentration is preferably 0.2%, the additive is preferably acetone, and the concentration is 0.8%.

The temperature of the heat treatment oven is preferably 80 ℃, and the heat treatment time is preferably 2min.

Examples 1-3 were tested under the following conditions: the feed solution was 2000mg/L sodium chloride aqueous solution, the test pressure was 1.55MPa, and the desalting performance after two hours of stable operation was as shown in FIG. 2.

The result shows that the high-strength composite polymer substrate has good operability in the preparation process of the compact ultrathin separation layer, the thin-layer composite separation membrane based on the high-strength composite polymer substrate prepared by the interfacial polymerization method can withstand cross-flow pressure of 1.55MPa, the comprehensive performance of the composite membrane is better when the substrate is coated for 2 hours by the modifying liquid in advance, and the performance of the composite membrane can be regulated and controlled by changing the modifying degree of the substrate.

The invention relates to a preparation method of a thin layer composite separation membrane based on a high-strength composite polymer substrate for a household water purifier, wherein the high-strength composite polymer substrate is formed by compositing a polyester non-woven fabric and a polyethylene membrane prepared by a single-layer wet-process based process through a preferential ultrasonic welding process, the substrate surface treatment scheme is a preferential combined treatment technology based on diazonium salt chemistry and strong acid, and the compact ultrathin separation layer is prepared by an interfacial polymerization method.

The thickness of the polyester non-woven fabric layer in the high-strength composite polymer substrate is preferably 120 mu m, the thickness of the polypropylene film layer is preferably 15 mu m, the working frequency of the ultrasonic welding process is preferably 32kHz, the ultrasonic amplitude is preferably 45 mu m, the welding pressure is preferably 0.3MPa, and the welding time is preferably 2s.

The concentration of m-phenylenediamine in the preferred polyolefin film surface treatment scheme is preferably 0.1%, the pH of the solution is adjusted by concentrated sulfuric acid, the concentration of nitrite is preferably sodium nitrite, the concentration of reducing agent is preferably iron powder, the coating time of the reaction liquid in examples 4-6 is respectively 1h, 2h and 4h, and the modified hydrophilized substrate is washed with ethanol for 30s to remove small molecular fragments which are not covalently bonded on the surface.

The preparation scheme of the compact ultrathin separating layer comprises the steps of firstly coating an aqueous phase solution on a hydrophilized substrate of examples 4-6 for 1-30min, then pouring out and removing the surface residual aqueous solution by using a rubber roller; then coating alkane phase solution on the substrate treated by the aqueous phase solution for 10-180s, pouring out superfluous alkane solution and cleaning the surface of the membrane by pure alkane; finally, heat treatment is carried out for 1-20min in a baking oven at 30-95 ℃.

The aqueous solution is preferably coated for 2 minutes, the reactive monomer in the aqueous solution is preferably polyamine, more preferably m-phenylenediamine, the concentration is preferably 1.5%, the additive is preferably a combination of sodium dodecyl benzene sulfonate and triethylamine, and the concentrations are respectively 0.15% and 1.1%.

The alkane phase solution is preferably n-hexane, the coating time is preferably 30s, the reactive monomer in the alkane phase solution is preferably polybasic acyl chloride, more preferably trimesoyl chloride, the concentration is preferably 0.12%, the additive is preferably acetone, and the concentration is 1.0%.

The temperature of the heat treatment oven is preferably 60 ℃, and the heat treatment time is preferably 3min.

Examples 4-6 were tested under the following conditions: the feed liquid is prepared by referring to GB 34914-2021 Water efficiency Limit value and Water efficiency grade of Water purifier, and comprises calcium chloride, magnesium sulfate, sodium chloride, sodium bicarbonate and sodium hypochlorite, and pH of the feed liquid is adjusted to 7.0-7.5 by using sodium hydroxide solution or hydrochloric acid solution, the test pressure is 0.5MPa, and the desalination performance after two hours of stable operation is shown in figure 3.

The results show that the combination property of the thin-layer composite separation membrane based on the preparation by the interfacial polymerization method is better when the high-strength composite polymer substrate is previously coated with the modifying liquid for 2 hours.

The invention relates to a preparation method of a thin layer composite separation membrane based on a high-strength composite polymer substrate for removing dye molecules in a polar organic solvent, wherein the high-strength composite polymer substrate is formed by compositing a polyester non-woven fabric and a polyethylene membrane prepared by a single-layer wet-process-based process through a preferential ultrasonic welding process, the substrate surface treatment scheme is a preferential combined treatment technology based on diazonium salt chemistry and based on strong acid, and the compact ultrathin separation layer is prepared by coating.

The thickness of the polyester non-woven fabric layer in the high-strength composite polymer substrate is preferably 120 mu m, the thickness of the polyethylene film layer is preferably 15 mu m, the working frequency of the ultrasonic welding process is preferably 32kHz, the ultrasonic amplitude is preferably 35 mu m, the welding pressure is preferably 0.3MPa, and the welding time is preferably 2s.

The concentration of m-phenylenediamine in the preferred polyolefin film surface treatment scheme is preferably 0.1%, the pH of the solution is adjusted by concentrated sulfuric acid, the concentration of nitrite is preferably sodium nitrite, the concentration of reducing agent is preferably iron powder, the coating time of the reaction liquid in examples 7-9 is respectively 4h, 6h and 8h, and the modified hydrophilized substrate is washed with ethanol for 30s to remove small molecular fragments which are not covalently bonded on the surface.

The static water contact angles of the modified hydrophilized substrates with the reaction liquid coating time of 4h, 6h and 8h are 55.2+/-2.3 degrees, 43.6+/-2.2 degrees and 38.8+/-1.9 degrees respectively.

The preparation scheme of the compact ultrathin separating layer comprises the steps of firstly coating an aqueous phase solution on a hydrophilized substrate in the embodiment 1-3 for 1-30min, then pouring out and removing the surface residual aqueous solution by using a rubber roller; then coating alkane phase solution on the substrate treated by the aqueous phase solution for 10-180s, pouring out superfluous alkane solution and cleaning the surface of the membrane by pure alkane; finally, heat treatment is carried out for 1-20min in a baking oven at 30-95 ℃.

The aqueous solution is preferably applied for 2 minutes, the reactive monomer in the aqueous solution is preferably polyamine, more preferably piperazine, the concentration is preferably 1.5%, the additive is preferably a combination of sodium dodecyl sulfate and sodium hydroxide, and the concentrations are respectively 0.1% and 0.2%.

The alkane phase solution is preferably n-hexane, the coating time is preferably 30s, the reactive monomer in the alkane phase solution is preferably polybasic acyl chloride, more preferably trimesoyl chloride, the concentration is preferably 0.1%, the additive is preferably acetone, and the concentration is 0.05%.

The temperature of the heat treatment oven is preferably 60 ℃, and the heat treatment time is preferably 2min.

Examples 7-9 were tested under the following conditions: the feed solution was 500mg/L rhodamine B/methanol solution, the test pressure was 0.5MPa, and the desalting performance after two hours of stable operation was as shown in FIG. 4.

The results show that the thin-layer composite membrane prepared based on the high-strength composite polymer substrate shows good solvent resistance stability, and the thin-layer composite separation membrane prepared by the interfacial polymerization method has better comprehensive performance when the high-strength composite polymer substrate is coated with the modifying liquid for 6 hours in advance.

Claims

1. The high-strength composite membrane comprises an ultrathin separating layer and a composite polymer substrate, and is characterized in that the ultrathin separating layer is formed by a compact film formed by polymerization reaction of two active reaction monomers dissolved in immiscible two phases at a phase interface; the composite polymer substrate is a composite layer of a non-woven fabric or a runner screen layer and a polyolefin film.

2. The composite membrane of claim 1 wherein the ultra-thin separating layer is located in an upper portion of the composite membrane, the composite polymer substrate comprising a polyolefin membrane in a central portion and a nonwoven fabric or flow channel barrier in a lower portion.

3. The composite membrane of claim 2, wherein the composite polymer substrate is a single-layer or multi-layer polyolefin film composite with the nonwoven fabric or the flow channel barrier of polymer material.

4. The composite film of claim 2, wherein the polyolefin film is a polyethylene film or a polypropylene film or a combination of the polyethylene film or polypropylene film.

5. The composite film according to claim 2, wherein the polymer substrate has a thickness of 60 to 600 μm, the polyolefin film layer has a thickness of 5 to 50 μm, and the nonwoven fabric or the flow passage barrier layer has a thickness of 55 to 550 μm.

6. The composite membrane of claim 1, wherein the ultra-thin separation layer is prepared by an interfacial polymerization process.

7. The composite membrane of claim 1, wherein the ultra-thin separation layer is prepared by a layer-by-layer self-assembly process or a coating process.

8. The method of producing a composite film according to any one of claims 1 to 7, wherein the method comprises controlling compatibility between layers of a thin-layer composite film by hydrophilizing modification of the composite polymer substrate; the performance of the composite membrane is regulated and controlled by using an additive for the ultrathin separation layer.

9. The method of claim 8, wherein the membrane to membrane element is of a fabricated configuration.

10. The method of preparing a composite film according to claim 8, wherein the polyolefin film is prepared by a dry or wet process.

11. The method of preparing a composite membrane according to claim 8, wherein the method of preparing the ultra-thin separation layer is an interfacial polymerization method comprising coating an aqueous phase solution on a hydrophilized substrate, and then pouring out and removing a surface residual aqueous solution, wherein the aqueous phase solution contains a reactive monomer and an aqueous phase additive; and (3) coating an alkane phase solution on the treated substrate, pouring out the alkane phase solution, cleaning the surface of the film by pure alkane, and finally carrying out heat treatment.

12. The method of claim 11, wherein the alkane phase solution comprises a reactive monomer and an oil phase additive, and the alkane solvent is n-alkane, isoparaffin or a mixture thereof having a carbon chain length of six to thirteen.

13. The method of claim 11, wherein the reactive monomer in the aqueous solution is a polyamine, a polyol, or a polyphenol.

14. The method of claim 11, wherein the aqueous phase additive is one or more of sodium dodecyl sulfate, sodium hydroxide, and triethylamine.

15. The method of preparing a composite membrane according to claim 12, wherein the reactive monomer is a polyacyl chloride, a polysulfonyl chloride or a polyisocyanate, and the oil phase additive is a co-solvent, a nanofiller or a combination of both.

16. The method for preparing a composite membrane for a household water purifier according to any one of claims 1 to 7, wherein the composite polymer substrate is formed by compositing a polyester non-woven fabric and a polyethylene membrane prepared by a single-layer wet-process-based process through an ultrasonic welding process, the surface of the substrate is based on a combination treatment technology of diazonium salt chemistry and a strong acid, and the compact ultrathin separation layer is prepared by interfacial polymerization.

17. The method according to claim 16, wherein the polyolefin film is coated with a solution of p-aminodiazobenzene and phenyl radicals under strongly acidic conditions for 1 to 48 hours.

18. The preparation method according to claim 17, wherein the p-aminodiazobenzene and phenyl radical solution under the strong acid condition is prepared by diazotizing p-phenylenediamine and nitrite and further reducing the p-aminodiazobenzene and phenyl radical solution at the reaction temperature of 0-5 ℃.

19. The method for preparing a composite membrane based on a composite polymer substrate for removing dye molecules in a polar organic solvent according to any one of claims 1 to 7, wherein the composite polymer substrate is formed by compositing a polyester nonwoven fabric with a polyethylene film prepared by a single-layer wet process through an ultrasonic welding process, the surface of the substrate is based on a combined treatment technology of diazonium salt chemistry and a strong acid, and the compact ultrathin separating layer is prepared by a coating method.