CN110559859A - electrostatic spinning nanofiber-based double-skin forward osmosis membrane and preparation method thereof - Google Patents

Abstract

The invention discloses an electrospinning nanofiber base double-skin forward osmosis membrane and a preparation method thereof. The forward osmosis membrane comprises an electrospinning nanofiber base film layer in the middle and a polyamide skin layer located on the upper and lower sides of the base film layer. The preparation method is as follows: dissolving a high polymer in a solvent to prepare a spinning solution; electrospinning the spinning solution to obtain an electrospinning nanofiber base film; performing interfacial polymerization on the upper and lower surfaces of the electrospinning nanofiber base film , and finally an electrospun nanofiber-based double-skinned forward osmosis membrane with a double-skinned structure was obtained with electrospun nanofibers as the base membrane. The advantages of the present invention are that the high porosity and three-dimensional through-hole structure of the electrospinning nanofibers can effectively alleviate the internal concentration polarization phenomenon in the base membrane and improve the water flux of the forward osmosis membrane; and the double skin layer structure can effectively prevent the raw materials The solute in the liquid enters the base membrane layer, endows the membrane surface with excellent anti-fouling performance, thereby obtaining a forward osmosis membrane with both high flux and strong anti-fouling.

Description

Electrospinning nanofiber-based double-skinned forward osmosis membrane and preparation method thereof

technical field

The invention belongs to the technical field of forward osmosis membranes, and in particular relates to an electrospinning nanofiber-based double-skin forward osmosis membrane and a preparation method thereof.

Background technique

Forward osmosis (FO) is an osmotic pressure-driven membrane separation process, which has attracted the attention of many researchers because of its unique advantages such as no external pressure and relatively low degree of membrane fouling. Forward osmosis technology is known as the most promising new technology for desalination and water purification, and has broad application prospects in the field of water treatment, such as seawater desalination, drinking water purification, domestic sewage reuse, industrial wastewater treatment, landfill leachate treatment, Medicines and food concentrates, etc. Although forward osmosis technology has developed rapidly in recent years, it is still not perfect in practical application, and there are still a series of technical obstacles hindering its industrial development, and it is unlikely to replace the status of reverse osmosis (RO) technology at present. One of the main challenges in applying forward osmosis technology from the laboratory to industrial processes is that there is currently no high-performance forward osmosis membrane, so there are many problems to be solved in practical applications, such as: the current production of forward osmosis membranes The amount of water cannot be compared with the high water flux of reverse osmosis; the severe internal concentration polarization phenomenon (ICP) causes the filtration efficiency to be greatly reduced; in addition, although the forward osmosis process is not as serious as the membrane fouling problem in the pressure-driven membrane process, the membrane fouling The phenomenon is still unavoidable, and the resulting problems of membrane cleaning and shortening of membrane life cannot be ignored. Therefore, the research and development of high-performance forward osmosis membranes and the preparation of high-flux, strong anti-fouling forward osmosis membranes are still the focus of current research.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides an electrospinning nanofiber-based double-skinned forward osmosis membrane and a preparation method thereof. Through special structural design, an electrospinning nanofiber base with high flux and strong antifouling is prepared. Double-skinned forward osmosis membrane.

The electrospinning nanofiber-based double-skin forward osmosis membrane of the present invention includes a base membrane layer composed of electrospinning nanofibers and a polyamide skin layer located on the upper and lower sides of the base membrane layer (that is, there are two polyamide skin layers in total, forming a double skin layer). structure), the polyamide skin layer includes a dense first skin layer facing the drawing liquid side and a loose second skin layer facing the raw material liquid side during application.

The polyamide skin layers on both sides of the basement membrane have different densities, among which: the first skin layer is denser than the second skin layer, which can be used as a selective separation functional layer to intercept the solute ions in the extraction liquid; the second skin layer is looser than the first skin layer. , it can effectively prevent the solute in the raw material liquid from entering and depositing in the base film without significantly increasing the mass transfer resistance.

Further, the base film layer is an electrospinning nanofiber base film layer; the polyamide skin layer is composed of an aqueous phase solution of a polyamine compound and an organic phase solution of a polybasic acid chloride compound on the upper and lower surfaces of the base film layer. prepared by interfacial polymerization.

As a general technical concept, the present invention also provides a method for preparing the above-mentioned electrospinning nanofiber-based double-skinned forward osmosis membrane, comprising the following steps:

①Preparation of electrospinning solution: add the polymer into the solvent, stir the polymer at a specified temperature to dissolve the polymer in the solvent, and then let it stand for defoaming to obtain the spinning solution;

② Preparation of electrospinning nanofiber base film: put the spinning solution in step ① into a syringe, use electrospinning equipment to electrospin the spinning solution, and cover the collector with a layer of aluminum foil to Receive the nanofibers prepared by electrospinning, and finally remove the aluminum foil to obtain an electrospinning nanofiber base film;

3. Preparation of interfacial polymerization reaction solution: Dissolve two parts of polyamine compounds in two parts of deionized water respectively, stir evenly, and configure into a first aqueous phase solution and a second aqueous phase solution respectively, and the polyamine compound in the first aqueous phase solution is prepared. The mass concentration of the polybasic amine compound is greater than the mass concentration of the polyvalent amine compound in the second aqueous phase solution; two parts of the polybasic acid chloride compound are respectively dissolved in two parts of the organic solvent, stirred evenly, and respectively configured into the first organic phase solution and the second organic phase solution, And the mass concentration of the polybasic acid chloride compound in the first organic phase solution is greater than the mass concentration of the polybasic acid chloride compound in the second organic phase solution;

④ Preparation of double-skinned forward osmosis membrane: fix the electrospinning nanofiber base film prepared in step ② in a plate frame, pour the first aqueous phase solution on the upper surface of the electrospinning nanofiber base film, and then pour the first aqueous phase solution on the upper surface of the electrospinning nanofiber base film. After a specified time, pour the first aqueous phase solution and remove the excess solution on the upper surface of the electrospinning nanofiber base film, and then pour the first organic phase solution on the upper surface of the electrospinning nanofiber base film, and pour it after a second specified time. The first organic phase solution was removed and dried naturally in the air, and then placed in an oven for heat treatment to form the first skin layer on the upper surface of the electrospinning nanofiber base film; and then the electrospinning nanofibers were Pour the second aqueous phase solution on the lower surface of the base film, pour off the second aqueous phase solution after the third specified time and remove the excess solution on the lower surface of the electrospinning nanofiber base film, and then pour the second aqueous phase solution on the lower surface of the electrospinning nanofiber base film. Pour the second organic phase solution, pour out the second organic phase solution after the fourth fixed time, and dry it naturally in the air, and then place it in an oven for heat treatment, in the electrospinning nanofiber base film The second skin layer is formed on the lower surface of the electrospinning nanofiber, and an electrospinning nanofiber-based double skin layer forward osmosis membrane with a double skin layer structure is finally obtained.

Preferably, the high polymer is polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), polystyrene (PS), polyvinylidene fluoride (PVDF), polyethylene (PE), Polypropylene (PP), Cellulose Acetate (CA), Cellulose Triacetate (CTA), Polyethylene Terephthalate (PET), Polyimide (PI), Nylon (Nylon), Polyvinyl Alcohol (PVA), one or more of polyvinylpyrrolidone (PVP), the mass concentration of the high polymer is 12-25%; the solvent is a solvent capable of dissolving the high polymer, including N,N-Dimethylformamide (DMF), N,N-Dimethylacetamide (DMAc), N-Methylpyrrolidone (NMP), Dimethylsulfoxide (DMSO), 1,4 - one or more of dioxane, dichloromethane, chloroform, tetrahydrofuran, toluene, acetone, methanol, ethanol, formic acid, acetic acid, and water; the specified temperature in step ① is 25 to 95°C, The stirring time in the step ① is 6-24 h; the temperature of the static defoaming in the step ① is 25-95° C., and the static defoaming time in the step ① is 12-48 h.

Preferably, the collector is a cylindrical collecting roller, and the process conditions for electrospinning in step (2) are: the rotating speed of the roller of the collector is 100-500 rpm; The inner diameter of the needle is 0.6-1.0mm. During the electrospinning process, the flat-mouthed needle moves horizontally and reciprocatingly in the direction of the roller axis of the collector, and the moving speed is 0.5-2.0cm/s; the spinning voltage is 15-25kV; The receiving distance between the collectors is 8-20 cm; the extrusion rate of the spinning solution is 0.5-2 ml/h; the spinning temperature is 23-28° C., and the spinning humidity is 15-25% RH.

Preferably, the polyamine compound contains at least two reactive amino groups, including m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, trimesyltriamine, ethylenediamine, propylenediamine, hexamethylenediamine, 1 , any one or more of 4-cyclohexanediamine, 1,3-cyclohexanedimethylamine and piperazine;

The polybasic acid chloride compound contains at least two reactive acid chloride groups, including any one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride;

The organic solvent is an organic solvent that can dissolve acyl chloride monomers but not polyamides in aliphatic hydrocarbons, cycloaliphatic hydrocarbons, and aromatic hydrocarbons whose monomers contain 4 to 12 carbon atoms, including n-hexane, cyclohexane, n-heptane alkane, xylene, Isopar-G.

Preferably, the mass concentration of the polyamine compound in the first aqueous phase solution is 3.0% to 5.0%, and the mass concentration of the polyamine compound in the second aqueous phase solution is 1.0% to 3.0%; The mass concentration of the acid chloride compound is 0.1%-0.5%, and the mass concentration of the polybasic acid chloride compound in the second organic phase solution is 0.05%-0.3%.

Preferably, the first designated time is 2-5 min; the second designated time is 1-3 min; the third designated time is 1-3 min; the fourth designated time is 0.5-2 min; 2-5min; oven temperature is 40-80℃; heat treatment time is 5-15min.

Compared with the prior art, the advantages of the present invention are: the present invention prepares the electrospinning nanofiber-based double-skinned forward osmosis membrane by performing interfacial polymerization on the upper and lower surfaces of the electrospinning nanofiber base film, and this method can slow down the internalization of the base film. The phenomenon of internal concentration polarization can improve the flux of the membrane and can effectively prevent the solute in the raw material liquid from entering the porous base membrane layer, giving the membrane surface excellent anti-fouling performance. A polyamide skin layer is interfacially polymerized on both sides of the electrospinning nanofiber base film layer, which effectively improves the anti-fouling performance of the membrane surface. The internal concentration polarization phenomenon in the membrane makes up for the deficiency of the double-skinned structure in increasing the mass transfer resistance to a certain extent, so that the prepared forward osmosis membrane can have both high flux and strong anti-fouling performance. In addition, the double-skinned forward osmosis membrane of the present invention can also flexibly adjust the density of the second skin layer according to different conditions of the treated feed liquid.

Membrane performance test:

The indicators for evaluating the performance of forward osmosis membranes include water flux and reverse salt flux. Deionized water was used as the raw material solution, 1M NaCl solution was used as the extraction solution, and the temperature of the test solution was kept at 25±1°C. The tested forward osmosis membrane is loaded into the test membrane module, and the edges of the membrane are sealed with silicone gaskets. Adjust the speed of the peristaltic pumps on both sides of the feed solution and the draw solution to keep the liquid flow rates on both sides of the membrane consistent. The conductivity change of the raw material liquid side and the quality change of the drawn liquid side are collected online by a conductivity meter and a precision balance, and the water flux (J _w ) and reverse salt flux ( _Js ).

In the formula, J _w is the water flux of the membrane, L/m ² ·h or LMH; Δm is the mass change of the liquid side drawn during Δt, g; ρ is the density of water, g/cm ³ ; A _m is a positive The effective area of the permeable membrane, m ² ; Δt is the running time, h; J _s is the reverse salt flux, g/m ² ·h or gMH; V ₀ and C ₀ are the initial volume of the feed liquid side (L) and salt concentration (g/L); V _t and C _t are the volume (L) and salt concentration (g/L) of the raw material liquid side at time t.

The anti-fouling performance of the forward osmosis membrane is also an important index to evaluate the membrane performance. For the organic pollution in the forward osmosis process, three typical representative organic pollutants are selected, namely the polysaccharide pollutants sodium alginate (SA), Membrane fouling experiments were carried out for protein pollutants bovine serum albumin (BSA) and humic pollutants (HA). Using the forward osmosis device, the configured pollutant solution was injected into the raw material liquid tank, and the membrane fouling experiment was carried out with 1M NaCl solution as the drawing solution. The experiment was run for 2 hours, and the flux attenuation during the forward osmosis process was detected in real time. After the fouling experiment, the fouled membrane was cleaned. The specific cleaning conditions were as follows: using a cross-flow method, firstly rinse with 2L of deionized water for 30 minutes, then rinse with deionized water for 5 minutes, and then test the water flow after cleaning. to obtain the flux recovery rate.

Description of drawings

FIG. 1 is a SEM image of the cross-sectional structure of the electrospinning nanofiber-based double-skinned forward osmosis membrane of the present invention.

2 is a SEM image of the first skin layer of the electrospinning nanofiber-based double skin layer forward osmosis membrane of the present invention.

3 is a SEM image of the second skin layer of the electrospinning nanofiber-based double skin layer forward osmosis membrane of the present invention.

Legend description: 1. First skin layer; 2. Electrospinning nanofiber base film; 3. Second skin layer.

Detailed ways

The present invention is further described in detail below through specific embodiments.

Example 1

(1) Add 20g of PVDF to a mixed solvent of 64g of DMF and 16g of acetone, stir and dissolve at 25°C for 24h, and then stand at 25°C for 48h to completely deaerate, and finally obtain a spinning fiber with a mass concentration of 20%. liquid;

(2) Load the spinning solution into a syringe, and use a 0.8 mm flat-mouthed needle to perform electrospinning. The spinning solution extrusion rate is 1.0 ml/h, the spinning voltage is 15 kV, and the receiving distance from the tip of the needle to the collector is 15 cm, the speed of the collector is 300 rpm, the horizontal reciprocating speed of the flat needle head along the roller axis of the collector is 1.0 cm/s, the spinning temperature is 25 °C, and the relative humidity is 25% RH.

(3) m-phenylenediamine and ethylenediamine are dissolved in deionized water, the mass concentrations are respectively 3.0% and 0.5%, as the first aqueous solution, trimesic acid chloride is dissolved in n-hexane, and the mass concentrations are 0.20%, as the first organic phase solution; dissolve piperazine in water, the mass concentration is 3.0%, fully stir and dissolve as the second aqueous phase solution, and dissolve trimesoyl chloride in n-hexane, the mass concentration is 0.30%, as the second organic phase solution;

(4) Fix the PVDF nanofiber base membrane on the plate frame, pour the first aqueous phase solution on the upper surface, pour it out after 5 minutes and remove the excess solution on the surface with filter paper, and then pour the first organic phase solution on the upper surface, 2 minutes Then pour it out and dry it in the air for 2 minutes, and then place it in an oven at 80°C for 10 minutes to heat treatment to form a first skin layer on the upper surface of the PVDF nanofiber base film; then pour a second layer on the lower surface of the PVDF nanofiber base film. Aqueous phase solution, pour out the second aqueous phase solution after 3 minutes and remove excess solution on the lower surface with filter paper, then pour the second organic phase solution on the lower surface, take it out after 2 minutes and dry it in the air for 2 minutes, then place it in a 60°C oven Heat treatment for 5 min to form a second skin layer on the lower surface of the PVDF nanofiber base film.

(5) The PVDF electrospinning nanofiber-based double-skinned forward osmosis membrane prepared by the above method, using deionized water as the raw material solution, 1M NaCl solution as the drawing solution, and the measured water flux at 25 ° C is 24.7LMH , the salt reverse flux is 3.4 gMH. Contamination experiments were conducted with simulated pollutants of 1 g/L (that is, the concentrations of SA, BSA and HA were all 1 g/L), the flux attenuated by 17% in 2h, and the flux recovery rate after cleaning was 96%.

Comparative Example 1

The preparation method used in this comparative example is basically similar to that in Example 1, except that the base film in step (2) is prepared by the phase inversion method, and the specific steps are: using a doctor blade to cast the spinning solution onto a clean glass plate , after standing in the air for 30s, it was quickly and horizontally placed in deionized water to solidify, and the base film prepared by the phase inversion method was obtained.

The prepared phase inversion method-based double-skin forward osmosis membrane was prepared with deionized water as the raw material solution and 1M NaCl solution as the draw solution. The measured water flux at 25°C was 18.4LMH, and the salt reverse flux was 3.1 gMH. Contamination experiments were conducted with simulated pollutants of 1 g/L (that is, the concentrations of SA, BSA and HA were all 1 g/L), the flux attenuated by 15% in 2h, and the flux recovery rate after cleaning was 97%.

Example 1 is compared with Comparative Example 1. Except for the preparation method of the base film, other preparation and test conditions are the same. Example 1 is a nanofiber base film prepared by electrospinning, while Comparative Example 1 is a phase inversion method. prepared base film. The test results found that the water flux of Example 1 was higher than that of Comparative Example 1, which indicated that using electrospinning nanofibers as the base membrane could slow down the internal concentration polarization phenomenon in the base membrane layer, and the prepared forward osmosis membrane Has a higher water flux.

Example 2

(1) 12g of Nylon was added to 70.4g of formic acid and 17.6g of dichloromethane, heated and stirred for 12 hours at 50°C, and then allowed to stand at 50°C for 12 hours to make it completely defoamed, and finally obtained A spinning solution with a mass concentration of 12%;

(2) Put the spinning solution into the syringe, and use a 0.6mm flat needle for electrospinning. The spinning solution extrusion rate is 0.5ml/h, the spinning voltage is 25kV, and the receiving distance from the tip of the needle to the collector is 8 cm, the rotating speed of the collector is 100 rpm, the horizontal reciprocating speed of the flat needle along the roller axis of the collector is 0.5 cm/s, the spinning temperature is 23° C., and the relative humidity is 15% RH.

(3) m-phenylenediamine is dissolved in water, the mass concentration is 3.0%, after fully stirring, as the first aqueous solution, trimesic acid chloride is dissolved in n-heptane, the mass concentration is 0.10%, as the first organic Phase solution; dissolving m-phenylenediamine and piperazine in water, the mass concentration is 1.5% and 0.5% respectively, as the second aqueous phase solution, dissolving isophthaloyl chloride in n-heptane, the mass concentration is 0.10% , as the second organic phase solution;

(4) Fix the Nylon electrospinning nanofiber base film on the plate frame, pour the first aqueous phase solution on the upper surface, pour it out after 3 minutes and remove the excess solution on the surface with filter paper, and then pour the first organic phase solution on the upper surface. The phase solution was poured out after 2 minutes and air-dried for 5 minutes, and then placed in an oven at 80 °C for heat treatment for 5 minutes to form a first skin layer on the upper surface of the Nylon electrospinning nanofiber base film; The lower surface of the fiber base membrane 2 is poured into the second aqueous phase solution, and the second aqueous phase solution is poured out after 2 minutes and the excess solution on the lower surface is removed with filter paper, and then the second organic phase solution is poured into the lower surface. Dry in the air for 5 min, and then place it in an oven at 70° C. for heat treatment for 8 min to form a second skin layer on the lower surface of the Nylon electrospinning nanofiber base film 3 .

(5) the Nylon electrospinning nanofiber-based double-skin forward osmosis membrane prepared by the above method, with deionized water as the raw material solution, 1M NaCl solution as the drawing solution, and the measured water flux at 25 ° C is 35.2LMH , the salt reverse flux was 2.8 gMH. Contamination experiments were carried out with 5g/L of simulated pollutants (that is, the concentrations of SA, BSA and HA were all 5g/L), the flux attenuated by 36% in 2h, and the flux recovery rate after cleaning was 93%.

Comparative Example 2

The preparation method used in this comparative example is basically similar to that of Example 2, except that in step (4), the lower surface of the base membrane is no longer subjected to interfacial polymerization to obtain a Nylon electrospinning nanofiber-based single-skin forward osmosis membrane.

The prepared Nylon electrospinning nanofiber-based single-skin forward osmosis membrane was prepared with deionized water as the raw material solution, and 1M NaCl solution as the drawing solution. The amount was 6.1 gMH. The pollution experiment was carried out with 5g/L (that is, the concentrations of SA, BSA and HA were all 5g/L) of simulated pollutants, the flux attenuated by 55% in 2h, and the flux recovery rate after cleaning was 78%.

Example 2 is compared with Comparative Example 2. Except for the difference in the structure of the lower surface of the base film, the other preparation and testing conditions are the same. The lower surface of the base film did not undergo interfacial polymerization. The test results found that in the pollution experiment, the flux attenuation ratio of Example 2 was low, and the flux recovery rate was high, which indicated that the second skin layer facing the raw material liquid side could improve the anti-fouling performance of the membrane surface. The skin layer forward osmosis membrane has more excellent anti-pollution performance.

Example 3

(1) Add 15g of PVDF and 10g of PAN to 75g of DMAc, heat and stir to dissolve at 80°C for 6h, and then stand at 80°C for 12h to completely deaerate, and the final mass concentration is 25% the spinning solution;

(2) Load the spinning solution into the syringe, and use a 1.0 mm flat-mouthed needle for electrospinning. The spinning solution extrusion rate is 2.0 ml/h, the spinning voltage is 20 kV, and the receiving distance from the tip of the needle to the collector is 20 cm, the speed of the collector is 500 rpm, the horizontal reciprocating speed of the flat needle head along the roller axis of the collector is 2.0 cm/s, the spinning temperature is 28 °C, and the relative humidity is 20% RH.

(3) m-phenylenediamine and hexamethylene diamine are dissolved in water, the mass concentrations are respectively 4.0% and 1.0%, as the first aqueous phase solution, trimesoyl chloride is dissolved in n-hexane, the mass concentration is 0.50%, as The first organic phase solution; dissolving m-phenylenediamine in water, the mass concentration is 1.0%, as the second aqueous phase solution, dissolving trimesoyl chloride in n-hexane, the mass concentration is 0.05%, as the second organic phase solution solution;

(4) Fix the PVDF/PAN electrospinning nanofiber base film on the plate frame, pour the first aqueous phase solution on the upper surface, pour it out after 2 minutes and remove the excess solution on the surface with filter paper, and then pour the first aqueous phase solution on the upper surface. 1. The organic phase solution was poured out after 1 min and air-dried for 3 min, and then placed in a 60°C oven for heat treatment for 8 min to form a first skin layer on the upper surface of the PVDF/PAN electrospinning nanofiber base film; The second aqueous phase solution was poured into the lower surface of the /PAN electrospinning nanofiber base film. After 1 min, the second aqueous phase solution was poured out and the excess solution on the lower surface was removed with filter paper, and then the second organic phase solution was poured into the lower surface. After 0.5min, take it out and dry it in the air for 3min, then place it in a 40°C oven for 15min heat treatment, so that the lower surface of the PVDF/PAN electrospinning nanofiber base film forms a second skin layer.

(5) The PVDF/PAN electrospinning nanofiber-based double-skinned forward osmosis membrane prepared by the above method, using deionized water as the raw material solution, 1M NaCl solution as the drawing solution, and the measured water flux at 25°C is 28.1 LMH with a salt reverse flux of 2.6 gMH. Contamination experiments were carried out with 10g/L of simulated pollutants (that is, the concentrations of SA, BSA and HA were all 10g/L), the flux attenuated 64% in 2h, and the flux recovery rate after cleaning was 93%.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied to other related All technical fields are similarly included in the scope of patent protection of the present invention.

Claims (8)

1. An electrostatic spinning nanofiber-based double-skin forward osmosis membrane is characterized by comprising a base membrane layer consisting of electrostatic spinning nanofibers and polyamide skin layers respectively positioned on the upper side and the lower side of the base membrane layer; the polyamide skin layer comprises a dense first skin layer facing the draw solution side and a loose second skin layer facing the feed solution side during application.

2. The electrospun nanofiber-based double-skin forward osmosis membrane according to claim 1, wherein the base membrane layer is an electrospun nanofiber-based membrane layer; the polyamide skin layer is prepared by respectively carrying out interfacial polymerization reaction on the upper surface and the lower surface of the base film layer by using an aqueous phase solution of a polyamine compound and an organic phase solution of a polybasic acyl chloride compound.

3. A method of preparing the electrospun nanofiber-based double-skin forward osmosis membrane of claim 1 or 2, comprising the steps of:

Preparation of electrostatic spinning solution: adding a high polymer into a solvent, stirring at a specified temperature to dissolve the high polymer in the solvent, and standing for defoaming to prepare a spinning solution;

preparing an electrostatic spinning nanofiber base film: filling the spinning solution obtained in the step I into an injector, performing electrostatic spinning on the spinning solution by using electrostatic spinning equipment, covering a layer of aluminum foil on a collector to receive the nano-fibers prepared by electrostatic spinning, and finally removing the aluminum foil to obtain an electrostatic spinning nano-fiber base film;

Preparing interfacial polymerization reaction solution: respectively dissolving two parts of polyamine compound in two parts of deionized water, uniformly stirring, and respectively preparing a first aqueous phase solution and a second aqueous phase solution, wherein the mass concentration of the polyamine compound in the first aqueous phase solution is greater than that of the polyamine compound in the second aqueous phase solution; respectively dissolving two parts of polyacyl chloride compounds in two parts of organic solvents, uniformly stirring, and respectively preparing a first organic phase solution and a second organic phase solution, wherein the mass concentration of the polyacyl chloride compounds in the first organic phase solution is greater than that of the polyacyl chloride compounds in the second organic phase solution;

Preparing a double-skin forward osmosis membrane: fixing the electrostatic spinning nanofiber basement membrane prepared in the second step in a plate frame, pouring a first aqueous phase solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring the first aqueous phase solution after a first designated time, removing redundant solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring a first organic phase solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring the first organic phase solution after a second designated time, naturally drying in the air, then placing the electrostatic spinning nanofiber basement membrane in an oven for heat treatment, and forming a first skin layer on the upper surface of the electrostatic spinning nanofiber basement membrane; and then pouring a second aqueous phase solution on the lower surface of the electrostatic spinning nanofiber base film, pouring the second aqueous phase solution after a third designated time and removing redundant solution on the lower surface of the electrostatic spinning nanofiber base film, then pouring a second organic phase solution on the lower surface of the electrostatic spinning nanofiber base film, pouring the second organic phase solution after a fourth designated time, naturally drying in the air, then placing the film in an oven for heat treatment, forming a second skin layer on the lower surface of the electrostatic spinning nanofiber base film, and finally obtaining the electrostatic spinning nanofiber base double-skin layer forward osmosis film with the electrostatic spinning nanofiber as the base film and a double-skin layer structure.

4. The method for preparing the electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, wherein the high polymer is one or more of polysulfone (PSf), Polyethersulfone (PES), Polyacrylonitrile (PAN), Polystyrene (PS), polyvinylidene fluoride (PVDF), Polyethylene (PE), polypropylene (PP), Cellulose Acetate (CA), Cellulose Triacetate (CTA), polyethylene terephthalate (PET), Polyimide (PI), Nylon (Nylon), polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), and the mass concentration of the high polymer is 12-25%; the solvent is a solvent capable of dissolving the high polymer and comprises one or more of N, N-Dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), 1, 4-dioxane, dichloromethane, trichloromethane, tetrahydrofuran, toluene, acetone, methanol, ethanol, formic acid, acetic acid and water; the designated temperature in the first step is 25-95 ℃, and the stirring time in the first step is 6-24 hours; the temperature of the standing defoaming in the step I is 25-95 ℃, and the time of the standing defoaming in the step I is 12-48 hours.

5. The method for preparing the electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, wherein the collector is a cylindrical collecting roller, and the process conditions of the electrospinning in the step (II) are as follows: the rotating speed of a roller of the collector is 100-500 rpm; the electrostatic spinning method comprises the following steps that a plain needle head is used during electrostatic spinning, the inner diameter of the plain needle head is 0.6-1.0mm, the plain needle head horizontally reciprocates in a direction perpendicular to a rolling shaft of a collector in the electrostatic spinning process, and the moving speed is 0.5-2.0 cm/s; the spinning voltage is 15-25 kV; the receiving distance between the flat-mouth needle head and the collector is 8-20 cm; the extrusion rate of the spinning solution is 0.5-2 ml/h; the spinning temperature is 23-28 ℃, and the spinning humidity is 15-25% RH.

6. The method for preparing an electrospun nanofiber-based double skin forward osmosis membrane according to claim 3, characterized in that said polyamine compound contains at least two reactive amino groups, comprising any one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, s-phenylenediamine, ethylenediamine, propylenediamine, hexamethylenediamine, 1, 4-cyclohexanediamine, 1, 3-cyclohexanediamine, piperazine;

The polybasic acyl chloride compound at least contains two reactive acyl chloride groups, including one or more of trimesoyl chloride, paraphthaloyl chloride, isophthaloyl chloride and phthaloyl chloride;

The organic solvent is an organic solvent which can dissolve acyl chloride monomers but not polyamide in aliphatic hydrocarbons, cycloaliphatic hydrocarbons and aromatic hydrocarbons of which the monomers contain 4-12 carbon atoms, and comprises n-hexane, cyclohexane, n-heptane, xylene and Isopar-G.

7. The method for preparing an electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, characterized in that the mass concentration of the polyamine compound in the first aqueous phase solution is 3.0% to 5.0%, and the mass concentration of the polyamine compound in the second aqueous phase solution is 1.0% to 3.0%; the mass concentration of the polybasic acyl chloride compound in the first organic phase solution is 0.1-0.5%, and the mass concentration of the polybasic acyl chloride compound in the second organic phase solution is 0.05-0.3%.

8. The method for preparing an electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, wherein the first specified time is 2-5 min; the second designated time is 1-3 min; the third designated time is 1-3 min; the fourth designated time is 0.5-2 min; naturally airing in the air for 2-5 min; the temperature of the oven is 40-80 ℃; the heat treatment time is 5-15 min.