CN110975645B

CN110975645B - Preparation method of composite film and composite film

Info

Publication number: CN110975645B
Application number: CN201911254896.5A
Authority: CN
Inventors: 李炜怡; 涂国权; 刘鑫; 刘格; 杜东宇
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology
Priority date: 2019-12-09
Filing date: 2019-12-09
Publication date: 2021-12-31
Anticipated expiration: 2039-12-09
Also published as: CN110975645A

Abstract

The invention relates to a preparation method of a composite film and the composite film. The preparation method of the composite film comprises the following steps: placing the hydrophobic base membrane subjected to alkali treatment in a polyelectrolyte solution to form a modified layer on the base membrane to obtain a composite membrane intermediate; and placing the composite film intermediate into the aqueous phase solution, and then placing the composite film intermediate into the organic phase solution, wherein the aqueous phase solution and the organic phase solution can generate interfacial polymerization reaction after contacting, so that a selection layer is formed on the modification layer, and the composite film is obtained. The composite film with higher forward osmosis efficiency can be prepared by adopting the preparation method of the composite film.

Description

Preparation method of composite film and composite film

Technical Field

The invention relates to the field of materials, in particular to a preparation method of a composite film and the composite film.

Background

The composite film is a high polymer material compounded by two or more layers of films made of different materials. Since the 80 s of the last century, the composite film plays an important role in applications including seawater desalination, ultrapure water production, advanced wastewater treatment and the like due to the selective separation performance of the composite film. To date, composite films have played a considerable role in a number of key areas of sustainable development. But also, therefore, the functional requirements of the market for composite films are becoming more and more demanding. The forward osmosis efficiency of the traditional composite film can not meet the actual requirement.

Disclosure of Invention

In view of the above, there is a need for a method for preparing a composite film with high forward osmosis efficiency and a composite film.

A preparation method of a composite film comprises the following steps:

placing the hydrophobic base membrane subjected to alkali treatment in a polyelectrolyte solution to form a modified layer on the base membrane to obtain a composite membrane intermediate; and

and placing the composite film intermediate into an aqueous phase solution, and then placing the composite film intermediate into an organic phase solution, wherein the aqueous phase solution and the organic phase solution can generate interfacial polymerization reaction after contacting, so that a selection layer is formed on the modification layer, and the composite film is obtained.

According to the preparation method of the composite film, the hydrophobic base film is subjected to hydrophilic modification through alkali treatment to improve the hydrophilicity of the base film, the base film subjected to hydrophilic modification is placed in a polyelectrolyte solution to form a modified layer on the base film, a composite film intermediate with high hydrophobicity is obtained, the composite film intermediate is placed in an aqueous phase solution firstly and then placed in an organic phase solution, so that the aqueous phase solution and an organic phase solution are contacted on the surface of the modified layer to generate interfacial polymerization reaction to form a selection layer, and the composite film with high positive permeation efficiency is prepared.

In one embodiment, the step of alkali treating comprises placing the hydrophobic base film in a strongly alkaline solution having a concentration of 1mol/L to 2 mol/L.

In one embodiment, the strongly alkaline solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.

In one embodiment, the hydrophobic base membrane is a polyacrylonitrile membrane, a polyethersulfone membrane, a polypropylene membrane, or a polyethylene membrane.

In one embodiment, the polyelectrolyte solution comprises a polycationic electrolyte.

In one embodiment, the polycationic electrolyte is polyallylamine hydrochloride, polyethyleneimine or polydiallyldimethylammonium chloride.

In one embodiment, the polyelectrolyte solution further comprises a neutral salt.

In one embodiment, the step of placing the composite film intermediate in the aqueous phase solution and then in the organic phase solution comprises:

placing the composite film intermediate into an aqueous phase solution, and then blowing off the composite film intermediate by using inert gas to obtain a composite film precursor; and

and placing the composite film precursor into an organic phase solution, and washing the composite film precursor by using an organic solvent to obtain the composite film.

In one embodiment, the aqueous solution comprises a first reactive monomer which is m-phenylenediamine, 1, 4-cyclohexanediamine, or piperazine; and/or the presence of a catalyst in the reaction mixture,

the organic phase solution comprises a second active monomer, wherein the second active monomer is trimesoyl chloride, 5-oxoformyl chloride-isopeptide acyl chloride or 5-isocyanate isopeptide acyl chloride; and/or the presence of a catalyst in the reaction mixture,

the organic solvent is the same as the organic solvent used in the organic phase solution.

The composite film prepared by the preparation method of the composite film.

Drawings

FIG. 1 is a flow chart of a composite film intermediate obtained by modifying a hydrophobic base film with polyelectrolyte after alkali treatment;

FIG. 2 is a mechanism diagram of a composite film intermediate obtained by modifying a hydrophobic base film with polyelectrolyte after alkali treatment;

FIG. 3 is a flow chart of the preparation of a composite film using the composite film intermediate;

FIG. 4 is a schematic diagram of a mechanism for preparing a composite film selective layer using a composite film intermediate;

FIG. 5 is a bar graph comparing the contact angles of the composite film of example 1 and the composite film of comparative example 1;

FIG. 6-a is a scanning electron microscope photograph of the surface of the composite film of comparative example 1; FIG. 6-b is a scanning electron microscope photograph of the surface of the composite film of example 1; FIG. 6-c is a scanning electron microscope photograph of a cross section of the composite film of comparative example 1; FIG. 6-d is a scanning electron microscope photograph of a cross-section of the composite film of example 1;

FIG. 7 is a bar graph comparing the pure water permeability of the composite film of example 1 and the composite film of comparative example 1;

FIG. 8 is a bar graph comparing salt rejection for the composite film of example 1 and the composite film of comparative example 1;

FIG. 9 is a schematic structural view of a homemade forward osmosis unit used in test example 4;

FIG. 10 is a bar graph comparing the water flux during forward osmosis for the composite membrane of example 1 and the composite membrane of comparative example 1;

FIG. 11 is a bar graph comparing the salt flux/water flux during forward osmosis for the composite membrane of example 1 and the composite membrane of comparative example 1;

fig. 12 is a bar graph comparing the forward osmosis efficiencies of the composite film of example 1 and the composite film of comparative example 1 during forward osmosis.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The method for preparing a composite film according to an embodiment can prepare a composite film having a high forward osmosis efficiency. Specifically, the preparation method comprises the following steps: placing the hydrophobic base membrane subjected to alkali treatment in a polyelectrolyte solution to form a modified layer on the base membrane to obtain a composite membrane intermediate (shown in figure 1); and placing the composite film intermediate into the aqueous phase solution, and then placing the composite film intermediate into the organic phase solution, wherein the aqueous phase solution and the organic phase solution can generate interfacial polymerization reaction after contacting, so that a selection layer is formed on the modification layer, and the composite film is obtained.

In one embodiment, the step of alkali treating comprises placing the hydrophobic base film in a strongly alkaline solution of 1mol/L to 2 mol/L. The arrangement is helpful to enable basic groups in the strong alkaline solution to react with nitrile groups in the hydrophobic base membrane, so that the nitrile groups are converted into carboxyl groups, and the carboxyl groups are hydrolyzed and negatively charged, so that the base membrane is negatively charged, and the hydrophilicity of the hydrophobic base membrane can be improved to a greater extent. Further, the step of alkali treatment includes placing the hydrophobic base film in a strongly alkaline solution of 1.5 mol/L. This arrangement contributes to increase the hydrophilicity of the hydrophobic base film. Further, the strongly alkaline solution is an aqueous sodium hydroxide solution. The strongly alkaline solution is not limited to a sodium hydroxide aqueous solution, and may be another strongly alkaline solution, for example, a potassium hydroxide aqueous solution.

In one embodiment, the hydrophobic base membrane is placed in a strong alkaline solution with the molar concentration of 1-2 mol/L at the temperature of 40-50 ℃ for 80-100 min. This arrangement contributes to increase the hydrophilicity of the hydrophobic base film. Specifically, the hydrophobic base film was placed in a strongly alkaline solution having a molar concentration of 1.5mol/L at 45 ℃ for 90 min.

In one embodiment, the hydrophobic base film is a Polyacrylonitrile (PAN) film. The polyacrylonitrile membrane has weaker hydrophobicity, and the hydrophilic modification by utilizing the polyacrylonitrile membrane is beneficial to obtaining a base membrane with stronger hydrophilicity so as to be beneficial to optimizing the performance of the composite film. The hydrophobic base film is not limited to the polyacrylonitrile film, and may be other hydrophobic base films, for example, a polyethersulfone film, a polypropylene film, a polyethylene film, or the like. Further, the preparation step of the hydrophobic base film comprises: weighing a high molecular polymer, a pore-forming agent and a solvent according to the mass ratio of (16-18) to (1-3) to (79-83), mixing to prepare a casting solution, pouring the casting solution on a clean and smooth plane to uniformly distribute the casting solution on the plane to form a liquid film with a certain thickness, and finally placing the plane coated with the liquid film in a water coagulation bath to perform phase conversion on the liquid film in water to obtain the hydrophobic base film. This arrangement contributes to obtaining a hydrophobic base film excellent in properties. In a specific example, polyacrylonitrile, lithium chloride (LiCl) and N, N-Dimethylformamide (DMF) are weighed according to a mass ratio of 18: 2: 80, and mixed to prepare a casting solution, the casting solution is poured onto a glass plate, the casting solution is uniformly distributed on the glass plate to form a liquid film with a certain thickness, and finally the glass plate coated with the liquid film is placed in a deionized water coagulation bath, and the liquid film is subjected to phase conversion in water to obtain the polyacrylonitrile film.

The pore-forming agent is not limited to lithium chloride, and may be other pore-forming agents, for example, polyethylene glycol, polyvinylpyrrolidone, gum arabic, and the like, and may be provided as needed.

The solvent is not limited to N, N-dimethylformamide, and may be other solvents, for example, N-dimethylacetamide and dimethylsulfoxide, and may be provided as needed.

The clean and smooth surface is not limited to a glass plate, but may be other clean and smooth surfaces, such as an iron plate. Further, the subsequent alkali treatment step is not limited to the step of using a flat-type base film made of a clean and smooth flat surface, and a base film of other configuration, such as a hollow fiber film or a tubular film, may be used, and may be provided as needed.

The water coagulation bath is not limited to the deionized water coagulation bath, and may be another water coagulation bath, for example, a purified water coagulation bath, and may be provided as needed.

It is understood that the method is not limited to placing the hydrophobic base film after the alkali treatment in the polyelectrolyte solution so that the modified layer is formed on the base film to obtain the intermediate of the composite film, but also can directly place the hydrophilic base film in the polyelectrolyte solution so that the modified layer is formed on the base film to obtain the intermediate of the composite film. Further, the hydrophilic base film is a base-treated polypropylene nitrile base film. The hydrophilic base film is not limited to the alkali-treated polypropylenitrile base film, and may be other hydrophilic base films, for example, a polyethersulfone/sulfonated polyethersulfone blend film, a dopamine/polyethyleneimine-modified polycarbonate film, or a graphene oxide-modified polysulfone film, and may be provided as needed.

In one embodiment, the polyelectrolyte solution comprises a polycationic electrolyte. As shown in fig. 2, the surface of the base membrane after the alkali treatment has carboxyl groups and is electronegative, when the base membrane is placed in a polycation electrolyte solution, the electrolyte with positive charges is deposited on the surface of the base membrane due to the bonding force such as electrostatic attraction, van der waals force and the like or the action of hydrogen bond, hydrophobic interaction, coordination and the like, so as to form a modified layer, and the introduction of the modified layer can change the hydrophilic and hydrophobic properties and the like of the base membrane. Further, the polycationic electrolyte is polyallylamine hydrochloride (PAH), polyethyleneimine or polydiallyldimethylammonium chloride. This arrangement helps to obtain a composite film intermediate with a relatively high hydrophobicity. Further, the polycationic electrolyte is polyallylamine hydrochloride. Specifically, the mass concentration of the polycation electrolyte in the polyelectrolyte solution is 1 g/L-2 g/L. The arrangement is beneficial to increasing the interaction force between the modification layer and the base film so as to obtain the composite film with excellent performance. More specifically, the mass concentration of the polycationic electrolyte in the polyelectrolyte solution is 1 g/L. The polycationic electrolyte is not limited to the above-mentioned examples, and may be other polycationic electrolytes, and may be provided as needed.

In one embodiment, the hydrophobic base membrane after alkali treatment is placed in a polyelectrolyte solution for 15min to 30 min. This arrangement helps to obtain a composite film intermediate with a relatively high hydrophobicity. Specifically, the hydrophobic base membrane after alkali treatment is placed in a polyelectrolyte solution for 15 min.

In one embodiment, the polyelectrolyte solution further comprises a neutral salt. The arrangement can change the components of the polyelectrolyte solution, is beneficial to increasing the electrostatic force combination between polycation and the surface of the base membrane with negative charge, and ensures that the modified layer is not easy to fall off from the base membrane, thereby being beneficial to obtaining a composite membrane intermediate with stronger hydrophobicity. Further, the neutral salt is sodium chloride, potassium chloride or magnesium chloride. This arrangement helps to increase the bonding force between the modified layer and the base film. Further, the neutral salt is sodium chloride. Specifically, the concentration of neutral salt in the polyelectrolyte solution is 0.5 mol/L-1.0 mol/L. This arrangement helps to increase the bonding force between the modified layer and the base film. More specifically, the concentration of the neutral salt in the polyelectrolyte solution was 0.5 mol/L. The neutral salt is not limited to the above-mentioned neutral salts, and may be other neutral salts, and may be provided as needed. It is also noted that the polyelectrolyte solution may not include a neutral salt, and may be set as desired.

In one embodiment, the step of placing the base-treated hydrophobic base film in a polyelectrolyte solution such that a modified layer is formed on the base film further comprises the steps of: placing the basement membrane in water for 5-10 min. Such an arrangement helps to remove excess, free polyelectrolyte. Specifically, the basement membrane was placed in water for 5 min.

In one embodiment, the step of obtaining the intermediate composite film further comprises storing the intermediate composite film in water. This arrangement helps to ensure the performance of the composite film intermediate. Further, the composite film intermediate was stored in deionized water. This arrangement helps to ensure the cleanliness of the composite film intermediate. Further, the composite film intermediate was stored in deionized water at 4 ℃. This arrangement helps prevent contamination of the composite film intermediate by microorganisms. The composite film intermediate is not limited to be stored in deionized water, and may be stored in distilled water or purified water, and may be provided as needed.

In a specific example, the method for preparing the composite film intermediate comprises the following steps: spreading the hydrophobic base membrane subjected to alkali treatment in a rectangular stainless steel iron plate, pouring the polyelectrolyte solution into the iron plate for soaking for 15min, pouring out the polyelectrolyte solution, soaking the modified base membrane for 5min by using deionized water, pouring out to obtain a composite film intermediate, and finally storing the composite film intermediate in the deionized water at normal temperature for later use.

As shown in fig. 3, the step of placing the composite film intermediate into the aqueous phase solution and then into the organic phase solution includes steps S1 to S2:

and S1, placing the composite film intermediate into the aqueous phase solution, and then blowing off the composite film intermediate by using inert gas to obtain the composite film precursor.

In one embodiment, the aqueous solution comprises a first reactive monomer, wherein the first reactive monomer is m-phenylene diamine (MPD), 1, 4-cyclohexanediamine, or piperazine. This arrangement helps to attach a thin aqueous phase to the modified layer. Further, the first reactive monomer is m-phenylenediamine. The first reactive monomer is not limited to the first reactive monomer listed above, and may be another first reactive monomer, and may be provided as needed. Specifically, the mass fraction of the first active monomer is 1% to 3%. This arrangement helps to attach a thin aqueous layer to the modified layer. More specifically, the mass fraction of the first reactive monomer was 2%, i.e., 2g of the first reactive monomer was dissolved in 98g of deionized water.

In one embodiment, the composite film intermediate is firstly placed in the aqueous phase solution for 5min to 10 min. This arrangement helps to attach a thin aqueous phase to the modified layer. Specifically, the composite film intermediate is firstly placed in an aqueous phase solution for 5 min.

In one embodiment, the inert gas is nitrogen. The arrangement is beneficial to blowing off the redundant first active monomer solution on the surface of the composite film intermediate body, so that the surface of the composite film intermediate body is not provided with obviously suspended first active monomer liquid drops, and a relatively uniform extremely thin liquid film of the first active monomer is formed. The inert gas is not limited to nitrogen, and may be another inert gas, for example, argon.

And S2, placing the composite film precursor into an organic phase solution, and washing the composite film precursor by using an organic solvent to obtain the composite film.

In one embodiment, the organic phase solution comprises a second reactive monomer, which is Trimesoyl chloride (TMC), 5-oxoformyl chloride-isopeptide chloride, or 5-isocyanatoisopeptide chloride. As shown in fig. 4, the second reactive monomer is contacted with the first reactive monomer to cause interfacial polymerization, thereby forming a selective layer on the modified layer. Still further, the second reactive monomer is trimesoyl chloride. The second reactive monomer is not limited to the above-mentioned examples, and may be another second reactive monomer, and may be provided as needed.

In one embodiment, the composite film precursor is placed in the organic phase solution for 1min to 2 min. This arrangement facilitates the formation of the selective layer. Specifically, the composite film precursor was placed in the organic phase solution for 1 min.

In one embodiment, the organic solvent is the same as the organic solvent used in the organic phase solution. This arrangement contributes to cost savings. Further, the organic solvent is n-hexane with the purity of 97-99%. This arrangement helps to ensure the cleanliness of the composite film. Further, the organic solvent was n-hexane having a purity of 98%.

The composite film prepared by the preparation method of the composite film plays an important role in the field of membrane separation. The performance of the composite film prepared by the hydrophilic modified base film through interfacial polymerization can be improved by performing hydrophilic modification on the hydrophobic base film. In the preparation method of the composite film, the hydrophobic base film is subjected to alkali treatment to enhance the hydrophilicity of the base film, and then the hydrophobicity of the surface of the base film is enhanced by introducing the polyelectrolyte modified layer on the surface of the base film, so that the selection layer generated through interfacial polymerization reaction is thinner and smoother and can be tightly combined with the base film, and the composite film with excellent performance is obtained. The composite film prepared by the preparation method shows higher selectivity, and in the forward osmosis process, the forward osmosis efficiency can be greatly improved on the premise of maintaining the selectivity of the composite film unchanged.

Membrane separation technology plays an important role in a number of key areas that are relevant to sustainable development. Due to its good separation performance and low resistance, the composite membrane plays an increasingly important role in various applications based on membrane separation, including seawater desalination, ultrapure water production, sewage deep treatment and the like, since the last 80 th century. The traditional preparation method of the composite film generally adopts a hydrophobic base film to prepare the composite film through interfacial polymerization. In order to further improve the permeability and the selectivity of the composite film, a great deal of optimization is carried out on the interfacial polymerization process. Researches show that the enhancement of the hydrophilicity of the base membrane is expected to improve the performance of the composite membrane selection layer and reduce the intramembrane concentration polarization and membrane pollution in the osmotic driving process, thereby improving the separation effect of the composite membrane. However, if the selective layer is directly prepared on the hydrophilic base film by interfacial polymerization, there is a problem in that the selective layer is easily peeled off from the hydrophilic base film or the prepared composite film has poor selectivity, so that it is difficult to obtain a stable composite film having a good separation effect.

The embodiment adopts a simple and easy method, the hydrophilic performance of the hydrophobic basement membrane is improved through alkali treatment, and the surface hydrophobicity of the basement membrane is improved by utilizing polyelectrolyte so that the selection layer can be stably formed on the surface of the basement membrane, thereby obtaining the high-performance composite membrane. The preparation method of the composite film expands the base film material and properties for interfacial polymerization, solves the problems that a polyamide selection layer generated by interfacial polymerization is easy to peel off from a hydrophilic base film and has low selectivity, and prepares the high-performance composite film. Specifically, the preparation method of the composite film innovatively utilizes polyelectrolyte to adjust the hydrophilic and hydrophobic properties and the like of the surface of the base film with strong hydrophilicity, and prepares a selection layer with tight combination on the surface of the base film with strong hydrophilicity by an interfacial polymerization method, thereby laying a foundation for the research and development and production of high-performance composite films.

Compared with the traditional method for changing the hydrophilic and hydrophobic properties of the surface of the base membrane by doping the nano material into the membrane casting solution, carrying out surface grafting or surface coating on the surface of the base membrane, plasma modification and the like, the preparation method of the composite membrane has the advantages of simplicity, strong operability, mild and controllable reaction conditions, good stability, low cost and more contribution to industrial application.

The preparation method of the composite film can further improve the performance of the composite film. Based on polyelectrolyte self-assembly, the properties of hydrophilicity, hydrophobicity and the like of the surface of the base membrane can be adjusted, and the formation of the selection layer can be influenced, so that the appearance of the selection layer is changed, the thickness of the selection layer is reduced, the permeability of the selection layer is improved, and the performance of the composite membrane is improved.

The composite film prepared by the preparation method of the composite film improves the water flux and the forward osmosis efficiency of the separation film in the forward osmosis process on the premise of maintaining the original selectivity of the separation film; thereby providing a forward osmosis separation membrane with more excellent performance and providing assistance for application and popularization of forward osmosis.

The preparation method of the composite film can overcome the problem that the base film with stronger hydrophilicity is difficult to prepare the high-performance composite film through interfacial polymerization, the prepared composite film has higher selectivity, and the excellent forward osmosis efficiency is shown in the forward osmosis process.

The following are specific examples:

unless otherwise specified, in the following examples: polyacrylonitrile available from sigma aldrich, cat # 181315; lithium chloride is available from sigma aldrich under the trade designation 746460; n, N-dimethylformamide was purchased from sigma aldrich, cat # 32293; the automatic film scraping machine is purchased from Jinan Annie Medit instruments, Inc., and has a product number of AT-TB-2100; the doctor blade is available from jennel, switzerland under the designation ZUA 2000; the freeze dryer is purchased from Ningbo Xinzhi Biotech Co., Ltd, with the product number of Scientz-12N; the contact angle measuring instrument is purchased from Kruss company of Germany, and has the product number of KRUSS DSA 25; scanning electron microscope purchased from carl zeiss, germany under the trade designation Merlin; the vacuum sputtering coater is purchased from Quorum corporation, UK, with a product number of Q150 TES; the triple high-pressure flat membrane pilot unit is purchased from Xiamen Fumei science and technology Limited, and has a product number of FlowMem-0021-HP.

Example 1

The preparation steps of the composite film of this example are as follows:

(1) the preparation raw materials comprise: polyacrylonitrile, lithium chloride and N, N-dimethylformamide.

(2) Preparation of hydrophobic base membrane: weighing 18g of polyacrylonitrile, 2g of lithium chloride and 80g of N, N-dimethylformamide by using an electronic balance, mixing, placing on a magnetic heating stirrer at 60 ℃, stirring at the rotating speed of 70rpm until the materials are completely dissolved to form a uniform and clear casting solution, then stopping heating, continuing stirring the casting solution at room temperature for 12h, and then standing and defoaming the casting solution for 12h for later use; finally, pouring the casting solution on a glass plate, and pushing a scraper with the fixed height of 150 microns at a constant speed by using an automatic film scraping machine to uniformly distribute the casting solution on the glass plate to form a liquid film with a certain thickness; and (3) quickly and stably immersing the glass plate coated with the casting solution into a deionized water coagulation bath, and carrying out phase conversion on the liquid film in water to obtain the hydrophobic base film.

(3) Preparation of a composite film intermediate: soaking the hydrophobic base membrane in 1.5mol/L sodium hydroxide aqueous solution at 45 ℃ for 90min, rinsing with deionized water (to remove residual sodium hydroxide on the surface of the base membrane), spreading in a rectangular stainless steel iron plate, dissolving 1g polyallylamine hydrochloride in 1L sodium chloride solution with the concentration of 0.5mol/L to prepare polyelectrolyte solution, pouring the polyelectrolyte solution into the iron plate for soaking for 15min, pouring out the polyelectrolyte solution, soaking the modified base membrane for 5min with deionized water, pouring out to obtain a composite membrane intermediate, and finally storing the composite membrane intermediate in deionized water at normal temperature for later use.

(4) Preparing a composite film: weighing 2g of m-phenylenediamine and dissolving the m-phenylenediamine in 98g of deionized water to obtain a m-phenylenediamine aqueous solution with the mass fraction of 2%, weighing 0.1g of trimesoyl chloride and dissolving the trimesoyl chloride in 100mL of pure hexane to obtain a trimesoyl chloride n-hexane solution with the mass fraction of 0.1%, paving the composite film intermediate in a stainless steel iron plate, pouring 50mL of m-phenylenediamine aqueous solution to infiltrate the composite film intermediate for 5 min; then pouring off the m-phenylenediamine aqueous solution, blowing off the redundant m-phenylenediamine aqueous solution on the surface of the composite film intermediate by using a nitrogen gun, so that no m-phenylenediamine liquid drop is obviously suspended on the surface of the composite film intermediate, and a relatively uniform m-phenylenediamine ultrathin liquid film is formed; then 50mL of trimesoyl chloride n-hexane solution is poured on the surface of the membrane, and the membrane and the trimesoyl chloride n-hexane solution react for 1min to form a polyamide selection layer; after the interfacial polymerization reaction is completed, pouring off the residual trimesoyl chloride normal hexane solution, and washing the surface of the membrane by using normal hexane with the purity of 98%; and after the n-hexane is completely volatilized, obtaining the composite film and storing the composite film in deionized water.

Comparative example 1

The preparation procedure of the composite film of this comparative example was as follows:

(3) Preparing a composite film: weighing 2g of m-phenylenediamine and dissolving the m-phenylenediamine in 98g of deionized water to obtain a m-phenylenediamine aqueous solution with the mass fraction of 2%, weighing 0.1g of trimesoyl chloride and dissolving the trimesoyl chloride in 100mL of pure hexane to obtain a trimesoyl chloride n-hexane solution with the mass volume fraction of 0.1%, paving the hydrophobic base film in a stainless steel iron disc, pouring 50mL of m-phenylenediamine aqueous solution to soak the composite film intermediate for 5 min; then pouring off the m-phenylenediamine aqueous solution, blowing off the redundant m-phenylenediamine aqueous solution on the surface of the hydrophobic basement membrane by using a nitrogen gun, so that no m-phenylenediamine liquid drop is obviously hung on the surface of the basement membrane, and a relatively uniform m-phenylenediamine extremely thin liquid membrane is formed; then 50mL of trimesoyl chloride n-hexane solution is poured on the surface of the membrane, and the membrane and the trimesoyl chloride n-hexane solution react for 1min to form a polyamide selection layer; after the interfacial polymerization reaction is completed, pouring off the residual trimesoyl chloride normal hexane solution, and washing the surface of the membrane by using normal hexane with the purity of 98%; and after the n-hexane is completely volatilized, obtaining the composite film and storing the composite film in deionized water.

And (3) testing:

test example 1

The hydrophilicity and hydrophobicity of the hydrophobic base film and the composite film intermediate of example 1 were tested by the pendant drop method using a contact angle measuring instrument. The results are detailed in table 1 and fig. 5. Table 1 shows the contact angles of the hydrophobic base film and the composite film intermediate of example 1, respectively measured by a contact angle measuring instrument, and the corresponding deviations, wherein the deviations represent the standard deviations of the contact angles measured at the same position in a plurality of times. Fig. 5 is a bar graph showing a comparison of contact angles between the hydrophobic base film and the intermediate composite film of example 1, respectively, measured by a contact angle measuring instrument.

The specific test process is as follows:

testing a sample: the hydrophobic base film and the composite film intermediate of example 1.

The testing process comprises the following steps: the test sample is placed in a freeze dryer, freeze-dried for about 12 hours under vacuum, then the dried test sample is cut to have a size of about 7.0cm in length and about 1.5cm in width and is flatly adhered on a glass slide, the test sample is placed under a contact angle measuring instrument for measurement, a profile image of the liquid drop (as shown in figure 5) is obtained through a microscope and a camera, and the contact angle of the liquid drop is calculated by digital image processing. In order to improve the accuracy and the representativeness of the test results, the obtained contact angle values are the average values obtained by taking 3 positions (namely 9 different positions) on 3 independently prepared test samples, and the deviation value in fig. 3 represents the standard deviation of the contact angle values measured at the 9 points.

TABLE 1

As can be seen from table 1 and fig. 5, the contact angle of the hydrophobic base film surface used in example 1 is 66.0 ± 6.7 °, which is more hydrophilic than the polysulfone base film commonly used in industry for preparing composite films; and the contact angle of the surface of the intermediate of the composite film obtained after polyelectrolyte modification is increased to 93.4 +/-6.4 degrees, which shows that the hydrophobicity of the surface of the intermediate of the composite film is obviously improved.

Test example 2

The surface and cross-sectional shapes of the freeze-dried composite film of example 1 and the composite film of comparative example 1 were observed with a scanning electron microscope. The results are shown in detail in FIGS. 6-a to 6-d. Wherein FIG. 6-a is a scanning electron microscope photograph of the surface of the composite film of comparative example 1; FIG. 6-b is a scanning electron microscope photograph of the surface of the composite film of example 1; FIG. 6-c is a scanning electron microscope photograph of a cross section of the composite film of comparative example 1; FIG. 6-d is a scanning electron microscope photograph of a cross-section of the composite film of example 1.

The specific test process is as follows:

testing a sample: the composite film of example 1 and the composite film of comparative example 1.

The testing process comprises the following steps: prior to testing, the test specimens were freeze-dried for 12h and the test specimen surfaces were platinized using a vacuum sputter coater to increase their conductivity. During the scanning, the test voltage was 5kV and the current was 100 pA.

And (3) testing results: as can be seen from FIG. 6, the surface of the composite film of comparative example 1 exhibited a typical "peak-valley" morphology, and the resulting selective layer was thicker (about 300nm, indicated by the arrow in FIG. 6-c) and had a rougher surface; whereas the surface of the composite film of example 1 was relatively flat, the obtained selective layer was thin (about 150nm, indicated by the arrows in FIG. 6-d) and its surface was smooth.

Test example 3

Pure water permeability and salt rejection of the composite film of example 1 and the composite film of comparative example 1 were tested using a triple high-pressure flat membrane pilot plant to explore water permeability and separation characteristics of the composite film in a pressure-driven mode. The results are shown in Table 2, FIG. 7 and FIG. 8. Table 2 shows pure water permeability, salt rejection and their corresponding deviations of the composite membrane of example 1 and the composite membrane of comparative example 1, respectively, measured using a triple high pressure flat sheet membrane pilot unit. FIG. 7 is a bar graph showing pure water permeability of the composite membrane of example 1 and the composite membrane of comparative example 1, respectively, measured using a triple high pressure flat sheet membrane pilot unit. FIG. 8 is a bar graph showing the salt rejection of the composite membrane of example 1 and the composite membrane of comparative example 1, respectively, using a triple high pressure flat sheet membrane pilot unit.

The specific test process is as follows:

The testing process comprises the following steps: the high-pressure pump applies a certain pressure on the feed liquid side, and under the pushing action of the pressure, water passes through the separation membrane due to the interception action of the separation membrane in the membrane component, and solute is intercepted. The pure water permeability of the composite film can be obtained by weighing the weight of the pure water which permeates through the separation film under a certain pressure within a certain test time (weighing the weight of the liquid in the percolate container); the salt rejection of the composite membrane can be determined by comparing the amounts of solutes in the feed solution and the leachate (which can be calculated from the conductivity values of the feed solution and the leachate). The feed solution used in the salt cut-off test was 20mmol/L aqueous sodium chloride solution.

TABLE 2

As can be seen from table 2, fig. 7 and fig. 8, the pure water permeability of the composite film of example 1 is not much different from that of the composite film of comparative example 1; however, compared with the salt rejection of the composite film of comparative example 1, the salt rejection of the composite film of example 1 is greatly improved from 62.3 ± 8.9% to 88.0 ± 1.4%, which indicates that the selectivity of the composite film prepared from the polyelectrolyte-modified base film is greatly improved.

Test example 4

The composite membrane of example 1 and the composite membrane of comparative example 1 were tested for water flux, salt flux/water flux and forward osmosis efficiency during forward osmosis using a home-made forward osmosis apparatus (shown in fig. 9). The results are shown in Table 3, FIG. 10, FIG. 11 and FIG. 12. In the present test, the forward osmosis apparatus 100 used includes a balance 110, a feed liquid bottle 120, a conductivity meter 130, two pumps 140, a separation membrane test assembly 150, and a draw liquid bottle 160. Table 3 shows the water flux, salt flux/water flux, forward osmosis efficiency and their corresponding deviations in the forward osmosis process of the composite membrane of example 1 and the composite membrane of comparative example 1, respectively, measured using a home-made forward osmosis apparatus. Fig. 10 is a bar graph showing the water flux during forward osmosis measured for the composite membrane of example 1 and the composite membrane of comparative example 1, respectively, using a home-made forward osmosis apparatus. Fig. 11 is a bar graph showing salt flux/water flux during forward osmosis of the composite membrane of example 1 and the composite membrane of comparative example 1, respectively, measured using a home-made forward osmosis apparatus. Fig. 12 is a bar graph showing forward osmosis efficiencies of the composite film of example 1 and the composite film of comparative example 1, respectively, in a forward osmosis process, measured using a home-made forward osmosis apparatus.

The specific test process is as follows:

The testing process comprises the following steps: a self-made forward osmosis device (shown in figure 9) is used for simultaneously measuring the water flux and the salt flux in the forward osmosis process, the drawing liquid used in the forward osmosis test is a 2mol/L sodium chloride aqueous solution, the feeding liquid is deionized water, the test temperature is 25 ℃, and the flow rates of the drawing liquid and the feeding liquid are both about 12 cm/s; in order to fully measure the performance of the separation membrane, the forward osmosis test procedure used two membrane orientations, i.e. membrane selection layer facing the draw solution and feed solution, respectively.

TABLE 3

As can be seen from table 3 and fig. 10, 11, 12, the water flux of the composite membrane of example 1 was increased by nearly one-fold in both membrane orientations, namely, 28.1 ± 5.1LMH (membrane selective layer toward draw solution) and 24.9 ± 1.8LMH (membrane selective layer toward feed solution), compared to the composite membrane of comparative example 1 (15.0 ± 2.8 LMH); the salt flux/water flux value of the composite film of example 1 is not significantly different from, or even slightly lower than, the composite film of comparative example 1, which indicates that the modification of the base film has no adverse effect on the selectivity of the prepared composite film; the forward osmosis efficiency results of both membranes also showed a similar trend to water flux, i.e., the forward osmosis efficiency of the composite membrane of example 1 was significantly improved. The above results demonstrate that under the same test conditions, the forward permeability of the composite film of example 1 is greatly improved compared to the composite film of comparative example 1, which is likely to benefit from the hydrophilicity of the base film and the adjustment of polyelectrolyte to the performance of the polyamide selective layer.

In conclusion, the composite film obtained by the embodiment has high forward osmosis efficiency and can meet the market demand.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The preparation method of the composite film is characterized by comprising the following steps:

placing the hydrophobic base membrane subjected to alkali treatment in a polyelectrolyte solution to form a modified layer on the base membrane to obtain a composite membrane intermediate; the solute of the polyelectrolyte solution consists of polycation electrolyte and neutral salt, the mass concentration of the polycation electrolyte is 1-2 g/L, and the concentration of the neutral salt is 0.5-1.0 mol/L; and

placing the composite film intermediate into an aqueous phase solution, and then placing the composite film intermediate into an organic phase solution, wherein the aqueous phase solution and the organic phase solution can generate interfacial polymerization reaction after being contacted, so that a selection layer is formed on the modification layer, and the composite film is obtained;

the step of placing the composite film intermediate into an aqueous phase solution and then into an organic phase solution comprises the following steps:

2. The method of producing the composite film according to claim 1, wherein the alkali treatment step comprises subjecting the hydrophobic base film to a strongly alkaline solution having a concentration of 1 to 2 mol/L.

3. The method for producing a composite film according to claim 2, wherein the strongly alkaline solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.

4. The method for preparing a composite film according to claim 1, wherein the hydrophobic base film is a polyacrylonitrile film, a polyethersulfone film, a polypropylene film or a polyethylene film.

5. The method for preparing a composite film according to claim 1, wherein the step of placing the hydrophobic base film after the alkali treatment in the polyelectrolyte solution is carried out for a period of 15 to 30 min.

6. The method of claim 1, wherein the polycationic electrolyte is polyallylamine hydrochloride, polyethyleneimine or polydiallyldimethylammonium chloride.

7. The method of claim 1, wherein the neutral salt is sodium chloride, potassium chloride or magnesium chloride.

8. The method for preparing a composite film according to claim 1, wherein the time period for placing the composite film intermediate in the aqueous solution is 5 to 10 min; the time for placing the composite film precursor in the organic phase solution is 1-2 min.

9. The method of claim 1, wherein the aqueous solution comprises a first reactive monomer, wherein the first reactive monomer is m-phenylenediamine, 1, 4-cyclohexanediamine, or piperazine; and/or the presence of a catalyst in the reaction mixture,

10. The composite film produced by the method for producing a composite film according to any one of claims 1 to 9.