CN110872741B

CN110872741B - Composite nanofiber membrane simultaneously used for emulsion separation and dye adsorption and preparation method thereof

Info

Publication number: CN110872741B
Application number: CN201910865214.8A
Authority: CN
Inventors: 杨浩; 张庆霞; 洪汉火; 廖腾飞; 唐其金; 吕中
Original assignee: Wuhan Institute of Technology
Current assignee: Wuhan Institute of Technology
Priority date: 2019-09-12
Filing date: 2019-09-12
Publication date: 2023-01-13
Anticipated expiration: 2039-09-12
Also published as: CN110872741A

Abstract

The invention discloses a composite nanofiber membrane material simultaneously used for latex separation and dye adsorption, which comprises a polyacrylonitrile nanofiber membrane and a polyvinyl alcohol-chitosan nanofiber membrane, wherein the polyvinyl alcohol-chitosan nanofiber membrane is formed by polyvinyl alcohol nanofiber filaments and a chitosan spherical nodular structure. The invention adopts the electrostatic spinning technology to prepare the polyacrylonitrile fiber membrane at first, then continues to spin on the membrane to obtain PAN/PVA-CS composite nanofiber membrane, and finally cross-links and solidifies by glutaraldehyde to obtain the final product; the related preparation method is simple, low in cost and low in energy consumption, and is beneficial to industrial large-scale production; the obtained composite nanofiber membrane has both underwater super-oleophobic property and in-oil super-hydrophobic property, can selectively treat oil-in-water type emulsion and water-in-oil type emulsion, can simultaneously adsorb and remove organic dye in the process of emulsion separation, can be used for wastewater treatment of a complex system, and has wide applicability.

Description

Composite nanofiber membrane simultaneously used for emulsion separation and dye adsorption and preparation method thereof

Technical Field

The invention belongs to the technical field of functional membrane materials, and particularly relates to a composite nanofiber membrane simultaneously used for emulsion separation and dye adsorption and a preparation method thereof.

Background

With the establishment of the national ecological environment department, the national monitoring and treatment of water pollution is more and more intensive, and oil stains and water-soluble organic pollutants (such as dyes) in wastewater are a great problem in sewage treatment. For the treatment of oil-containing sewage, the treatment methods mainly include chemical methods (including combustion method, emulsifier method and oil condensing agent method), biological methods (activated sludge method, biofilm method and immobilized cell method) and physical methods (fence method, adsorption method and membrane filtration method), wherein the membrane separation technology in the physical method is widely applied to the treatment of various kinds of sewage due to the advantages of simple method, high separation efficiency, no secondary pollution, low energy consumption and the like.

Recently, researches find that a membrane material with the underwater super-oleophobic property can separate an oil-water mixture under the action of gravity, and the material has the advantages of high separation efficiency, large flux, no need of external force, remarkable reduction of energy consumption and important application potential. Particularly, underwater super oleophobic membrane materials with fiber net structures have good separation effect on oil-water emulsion which is difficult to separate. For example, ge et al [ ACS Applied Materials & Interfaces 2018,10,16183-16192] reported an underwater super-oleophobic multilayer fiber membrane, two layers of fiber membranes are obtained through electrostatic spinning, and then organic oligomer and silicon dioxide nanofiber are added for polymerization reaction, so that a bionic fiber membrane with a multilevel structure is constructed, and the membrane has efficient separation and purification effects on emulsified oily wastewater; zang et al [ Journal of Materials Chemistry A2017,5,19398-19405] hydrogel nanofiber membranes with core-shell structure prepared by electrospinning method also have emulsion separation ability. Patent CN108889140A reports an electrospun fibrous membrane of asymmetric wettability, one side of which is superhydrophobic in air and the other side of which is superhydrophilic in air, which can be selectively used for the separation of water-in-oil or oil-in-water type emulsions. Both reports only separate insoluble oil stains in wastewater, but have no obvious effect on removing water-soluble organic pollutants. In contrast, cao et al [ ACS Applied Materials & Interfaces 2016,8,3333-3339] prepared polydopamine and polyethylenepolyamine co-deposited films (PDA/PEPA) that can be loaded on different substrates, which exhibit ultra-oleophobic properties under water, when deposited on the surface of a microfiltration membrane, both to separate oil-in-water emulsions and to adsorb organic dyes in water; however, the technology is closely related to the choice of substrate, and when the substrate is replaced with a stainless steel mesh or sponge, the properties of emulsion separation and dye adsorption are lost. Graphene/nanofiber aerogels prepared by Xiao et al [ Chemical Engineering Journal 2018,338,202-210 ]. Firstly, obtaining cellulose acetate nanofibers by using an electrostatic spinning method, stirring the cellulose acetate nanofibers with a graphene oxide solution at a high speed to obtain a suspension, and then carrying out freeze drying for 48 hours at the temperature of minus 50 ℃ to obtain the graphene/nanofiber aerogel (GNA). If GNA can be used for emulsion separation, dopamine (PDA) and Polyethyleneimine (PEI) coprecipitation are also adopted to modify GNA, so that the underwater super-oleophobic property is obtained. The material exists in the form of aerogel, does not belong to the field of membrane material preparation, and has a complex preparation process and high energy consumption.

In summary, the following technical problems exist in the present wastewater treatment of complex systems, especially in the field of membrane materials for simultaneously treating emulsion separation and dye adsorption: for example, some membrane materials can only be used for emulsion separation, but cannot realize dye adsorption; some membrane materials can be used for emulsion separation and dye adsorption, but can only process oil-in-water emulsions, but cannot process water-in-oil emulsions. Therefore, the functional membrane material which can separate the water-in-oil emulsion and the oil-in-water emulsion and can adsorb the organic dye in water is designed, and has important research value and wide application prospect.

Disclosure of Invention

The invention mainly aims to provide a composite nanofiber membrane material for emulsion separation and dye adsorption, which has the performance of super-hydrophobicity in oil and super-oleophobicity under water and can adsorb organic dye simultaneously, aiming at the defects of the prior art; effectively expands the application range of the membrane material in the emulsion separation, solves the technical problem that most of the membrane materials can only be used for the emulsion separation at present, and has important promoting significance on the wastewater treatment technology of a complex system.

In order to realize the purpose, the invention adopts the technical scheme that:

the composite nanometer fiber membrane for both emulsion separation and dye adsorption includes nanometer polyacrylonitrile fiber membrane and nanometer PVA-chitosan fiber membrane, which consists of nanometer polyacrylonitrile fiber filament and nanometer PVA-chitosan fiber filament and has spherical chitosan nodule structure.

In the scheme, the diameter of the nanofiber filaments in the polyacrylonitrile nanofiber membrane is 300-500nm; the diameter of the nano-fiber filament in the polyvinyl alcohol-chitosan nano-fiber membrane is 20-100nm.

In the scheme, the polyacrylonitrile nanofiber membrane is formed by performing electrostatic spinning on a polyacrylonitrile solution.

In the scheme, the polyvinyl alcohol-chitosan nanofiber membrane is formed by performing electrostatic spinning on a medium polyvinyl alcohol-chitosan mixed solution.

Preferably, the composite nanofiber membrane for both emulsion separation and dye adsorption is prepared by performing electrostatic spinning on a polyacrylonitrile solution to prepare the polyacrylonitrile nanofiber membrane, then performing electrostatic spinning on the surface of the polyacrylonitrile nanofiber membrane by using a polyvinyl alcohol-chitosan mixed solution to prepare a PAN/PVA-CS composite fiber membrane, and finally soaking the obtained composite fiber membrane into a glutaraldehyde solution for crosslinking treatment.

The preparation method of the composite nanofiber membrane for simultaneously separating the emulsion and adsorbing the dye comprises the following steps:

1) Dissolving polyacrylonitrile in an organic solvent, and uniformly stirring to prepare a polyacrylonitrile solution; dissolving chitosan in an acetic acid aqueous solution, uniformly stirring, then adding polyvinyl alcohol powder, continuously stirring, standing and defoaming to obtain a uniform PVA-CS solution;

2) Spinning a polyacrylonitrile solution by adopting an electrostatic spinning technology to obtain a polyacrylonitrile fiber membrane, continuously spinning a PVA-CS solution on the surface of the polyacrylonitrile fiber membrane to obtain a PAN/PVA-CS composite fiber membrane, soaking the PAN/PVA-CS composite fiber membrane in a glutaraldehyde solution for a crosslinking reaction, taking out, drying and finally obtaining the composite nanofiber membrane.

In the scheme, the molecular weight of the polyacrylonitrile is 7,000-100,000.

In the above scheme, the organic solvent is one of dimethyl sulfoxide, dimethylformamide and dimethylacetamide.

In the scheme, the mass concentration of the polyacrylonitrile solution is 8-15%.

In the above scheme, the molecular weight of the polyvinyl alcohol is 10,000-100,000.

In the scheme, the mass ratio of the polyvinyl alcohol to the chitosan is 2-20.

In the scheme, the mass concentration of the polyvinyl alcohol in the PVA-CS solution is 3-6%.

In the scheme, the viscosity of the chitosan is 200-400 mPa.

In the scheme, the electrostatic spinning conditions of the polyacrylonitrile solution are as follows: the voltage is 13-20kV, the humidity is 40% -50%, the sample introduction rate is 0.6-1.5mL/h, the distance between the needle point and the receiving plate is 15-25cm, and the electrospinning time is 4-10h.

In the above scheme, the conditions of the electrostatic spinning of the PVA-CS solution are as follows: the voltage is 18-25kV, the humidity is 30% -40%, the sample injection rate is 0.5-1.0mL/h, the distance between the needle point and the receiving plate is 10-20cm, and the electrospinning time is 4-10h.

In the scheme, the mass concentration of the glutaraldehyde solution is 4% -10%.

In the scheme, the crosslinking reaction time is 15-60min.

The principle of the invention is as follows:

1) The invention adopts an electrostatic spinning method, firstly, the polyacrylonitrile solution is subjected to spinning under the action of a high-voltage electric field to obtain a fiber mat with a certain thickness, so that the membrane material has good mechanical properties; meanwhile, because polyacrylonitrile shows hydrophilicity changing along with time in the air, when the film is immersed in oil, the film shows super-hydrophobic property in the oil, so that water-in-oil type emulsion can be separated; then, spinning PVA/CS solution on a polyacrylonitrile fiber membrane to obtain nano fibers (the diameter is 20-100 nm) with smaller scale and a spherical nodular structure, thereby constructing a multi-scale microstructure and increasing the surface roughness of the membrane, wherein the structure is favorable for enhancing the wettability of the surface of the material and realizing the functions of underwater super-oleophobic property and oil-in-water emulsion separation; in addition, the PAN/PVA-CS composite fiber membrane is further subjected to cross-linking treatment by glutaraldehyde to form a cross-linked network structure, so that the membrane is prevented from being dissolved in water, meanwhile, a large amount of hydroxyl and amino active groups on the cross-linked polyvinyl alcohol and chitosan are fixed on the surface of the membrane, and the dye is adsorbed by the action of hydrogen bonds, ion exchange and the like and the characteristics of the internal network structure of the polymer; meanwhile, the formed cross-linked network structure can further enhance the roughness of the membrane and further effectively improve the performance of super-hydrophobicity in oil and super-lipophobicity in water.

2) The polyacrylonitrile liquid drop injected slowly is charged under the external voltage, in a high-voltage electrostatic field, when the charge repulsion force of the polyacrylonitrile surface exceeds the surface tension, polyacrylonitrile jet flow is jetted out at a high speed on the surface of a Taylor cone at the tail end of a spray head, and the polyacrylonitrile jet flow is finally deposited on a receiving plate after the high-speed stretching of the electric field force, solvent volatilization and solidification, so that the polyacrylonitrile fiber film with the porous structure is formed.

3) The mixed solution of polyvinyl alcohol and chitosan has an electrospray effect under the action of high pressure, and a spherical nodular structure is formed on the surface of the membrane, so that the roughness of the surface of the membrane is enhanced, and the underwater super-oleophobic performance is promoted to be realized.

Compared with the prior art, the invention has the beneficial effects that:

1) The nano-fiber membrane material prepared by the invention can simultaneously separate emulsion and adsorb organic dye;

2) The nanofiber membrane prepared by the method has underwater super-oleophobic property and oil-in-water super-hydrophobic property, and can selectively separate oil-in-water type emulsion and water-in-oil type emulsion;

3) The preparation process is simple, the fiber continuity is good, the fiber film-forming post-treatment is simple, the efficiency is high, and the energy consumption is low;

4) By utilizing the electrospray effect of the mixed solution of the polyvinyl alcohol and the chitosan under the action of high pressure, microstructures with different scales can be obtained on the surface of the membrane, and the problems of easy aggregation, easy falling and the like caused by adding inorganic nano materials are avoided.

Drawings

FIG. 1 is an SEM photograph of PVA-CS plane of the composite nanofiber membrane obtained in example 1.

FIG. 2 is an SEM photograph of a polyacrylonitrile side of the composite nanofiber membrane obtained in example 1.

FIG. 3 is a chart of underwater hexane contact angle of the composite nanofiber membrane obtained in example 3.

FIG. 4 is a graph of the underwater petroleum ether contact angle of the composite nanofiber membrane obtained in example 4.

FIG. 5 is a graph showing the water contact angle in hexane of the composite nanofiber membrane obtained in example 5.

FIG. 6 is a graph showing the effect of separating an O/W emulsion in application example 1.

FIG. 7 is a graph showing the effect of separation of an emulsion containing a dye in application example 2.

FIG. 8 is a graph showing the effect of W/O emulsion separation in application example 3.

Detailed Description

For better understanding of the present invention, the following examples are given for further illustration of the present invention, but the present invention is not limited to the following examples.

Example 1

A composite nanofiber membrane for both emulsion separation and dye adsorption is prepared by the following steps:

1) Dissolving polyacrylonitrile (Mw =90,000) in dimethyl sulfoxide, and uniformly stirring to prepare a polyacrylonitrile solution with the mass concentration of 8%; dissolving chitosan (with the viscosity of 200-400mPa & s) in 10wt% acetic acid solution, then adding polyvinyl alcohol (Mw =80,000) powder, uniformly stirring, preparing PVA/CS solution with the mass ratio of polyvinyl alcohol to chitosan being 1.5, wherein the mass concentration of polyvinyl alcohol is 6%, standing and removing bubbles for later use;

2) Sucking 20mL of polyacrylonitrile solution by using a syringe, setting the injection rate to be 1.5mL/h, the electrospinning voltage to be 20kV, the distance between an electrospinning receiver and a needle to be 20cm, controlling the humidity to be 45%, spinning the polyacrylonitrile solution for 10h at room temperature, and airing overnight under the environmental condition to completely volatilize the solvent to obtain a polyacrylonitrile fiber membrane;

3) Then setting the injection rate of the prepared PVA/CS solution to be 1.0mL/h, setting the electrospinning voltage to be 25kV, setting the distance between an electrospinning receiver and a needle head to be 15cm, controlling the humidity to be 35%, spinning for 8h on the surface of the polyacrylonitrile fiber membrane under the room temperature condition, and airing overnight under the environmental condition after the electrospinning is finished to completely volatilize the solvent to obtain the PAN/PVA-CS composite fiber membrane;

4) And after the electrospinning is finished, soaking the obtained PAN/PVA-CS composite fiber membrane in 8% glutaraldehyde acetone solution for 20min, and drying to obtain the composite nanofiber membrane (PAN/PVA-CS membrane).

FIG. 1 is an SEM image of PVA-CS surface of the nanofiber membrane obtained in example 1, and it can be seen that the PVA-CS surface nanofibers are distributed in a staggered manner with spherical nodular structures; wherein the spherical particles have an average diameter of about 400nm and the nanofibers have an average diameter of 80nm.

FIG. 2 is an SEM image of polyacrylonitrile side of the nanofiber membrane obtained in example 1, and it can be seen that the nanofibers on the polyacrylonitrile side are randomly arranged, wherein the average diameter of the nanofibers is 300nm.

Example 2

1) Dissolving polyacrylonitrile (Mw =30,000) in dimethyl sulfoxide, and uniformly stirring to prepare a polyacrylonitrile solution with a mass concentration of 10%; dissolving chitosan (with the viscosity of 200-400mPa & s) in 10wt% acetic acid solution, then adding polyvinyl alcohol (Mw =100,000) powder, uniformly stirring, preparing a PVA/CS solution with the mass ratio of polyvinyl alcohol to chitosan being 1.03, wherein the mass concentration of polyvinyl alcohol is 3%, standing and removing bubbles for later use;

2) Sucking 20mL of polyacrylonitrile solution by using a syringe, setting the injection rate to be 1.1mL/h, setting the electrospinning voltage to be 16kV, setting the distance between an electrospinning receiver and a needle head to be 25cm, controlling the humidity to be 40%, spinning the polyacrylonitrile solution for 8h at room temperature, and airing overnight under the environmental condition to completely volatilize the solvent to obtain a polyacrylonitrile fiber membrane;

3) Then setting the injection rate of the prepared PVA/CS solution to be 0.6mL/h, setting the electrospinning voltage to be 25kV, setting the distance between an electrospinning receiver and a needle head to be 15cm, controlling the humidity to be 30%, spinning for 8h on the surface of the polyacrylonitrile fiber membrane under the room temperature condition, and airing overnight under the environmental condition after the electrospinning is finished to completely volatilize the solvent to obtain the PAN/PVA-CS composite fiber membrane;

4) And after the electrospinning is finished, soaking the obtained PAN/PVA-CS membrane in a 4% glutaraldehyde acetone solution for 60min, and drying to obtain the composite nanofiber membrane (PAN/PVA-CS membrane).

Example 3

1) Dissolving polyacrylonitrile (Mw =60,000) in dimethylformamide, and uniformly stirring to prepare a polyacrylonitrile solution with the mass concentration of 15%; dissolving chitosan (with the viscosity of 200-400mPa & s) in a 15wt% acetic acid solution, adding polyvinyl alcohol (Mw =50,000) powder, uniformly stirring, preparing a PVA/CS solution with the mass ratio of polyvinyl alcohol to chitosan being 1.3, wherein the mass concentration of polyvinyl alcohol is 4%, standing and removing bubbles for later use;

2) Sucking 20mL of polyacrylonitrile solution by using a syringe, setting the injection rate to be 1.2mL/h, setting the electrospinning voltage to be 18kV, setting the distance between an electrospinning receiver and a needle head to be 22cm, controlling the humidity to be 48%, spinning the polyacrylonitrile solution for 4h at room temperature, and airing overnight under the environmental condition to completely volatilize the solvent to obtain a polyacrylonitrile fiber membrane;

3) Setting the injection rate of the prepared PVA/CS solution to be 0.9mL/h, setting the electrospinning voltage to be 20kV, setting the distance between an electrospinning receiver and a needle head to be 20cm, controlling the humidity to be 34%, spinning the surface of the polyacrylonitrile fiber membrane for 10h at room temperature, and airing the polyacrylonitrile fiber membrane overnight under the environmental condition after the electrospinning is finished to completely volatilize the solvent to obtain the PAN/PVA-CS composite fiber membrane;

4) And after the electrospinning is finished, soaking the obtained PAN/PVA-CS composite fiber membrane in 6% glutaraldehyde acetone solution for 40min, and drying to obtain the composite nanofiber membrane (PAN/PVA-CS membrane).

Fig. 3 is an underwater hexane contact angle diagram of the composite nanofiber membrane obtained in the embodiment, and the result shows that the underwater oil contact angle of the surface of the obtained double-layer nanofiber membrane material is 155.7 degrees, so that the underwater super-oleophobic property is achieved.

Example 4

1) Dissolving polyacrylonitrile (Mw =100,000) in dimethylacetamide, and uniformly stirring to prepare a polyacrylonitrile solution with a mass concentration of 12%; dissolving chitosan (with the viscosity of 200-400mPa & s) in 20wt% acetic acid solution, then adding polyvinyl alcohol (Mw =10,000) powder, uniformly stirring, preparing PVA/CS solution with the mass ratio of polyvinyl alcohol to chitosan being 1.08, wherein the mass concentration of polyvinyl alcohol is 5%, standing and removing bubbles for later use;

2) Sucking 20mL of polyacrylonitrile solution by using a syringe, setting the injection rate to be 1.0mL/h, the electrospinning voltage to be 15kV, the distance between an electrospinning receiver and a needle to be 15cm, controlling the humidity to be 50%, spinning the polyacrylonitrile solution for 10h at room temperature, and airing overnight under the environmental condition to completely volatilize the solvent to obtain a polyacrylonitrile fiber membrane;

3) Setting the injection rate of the prepared PVA/CS solution to be 0.5mL/h, setting the electrospinning voltage to be 18kV, setting the distance between an electrospinning receiver and a needle head to be 15cm, controlling the humidity to be 37%, spinning the surface of the polyacrylonitrile fiber membrane for 4h at room temperature, and airing the polyacrylonitrile fiber membrane overnight under the environmental condition after the electrospinning is finished to completely volatilize the solvent to obtain the PAN/PVA-CS composite fiber membrane;

4) And after the electrospinning is finished, soaking the PAN/PVA-CS composite fiber membrane in a 10% glutaraldehyde acetone solution for 15min, and drying to obtain the composite nanofiber membrane.

Fig. 4 is an underwater petroleum ether contact angle diagram of the composite nanofiber membrane obtained in the embodiment, and the result shows that the underwater oil contact angle of the surface of the composite nanofiber membrane is 159.2 degrees, and the underwater super-oleophobic property is achieved.

Example 5

1) Dissolving polyacrylonitrile (Mw =85,000) in dimethyl sulfoxide, and uniformly stirring to prepare a polyacrylonitrile solution with a mass concentration of 10%; dissolving chitosan (with the viscosity of 200-400mPa & s) in 20wt% acetic acid solution, adding polyvinyl alcohol (Mw =70,000) powder, uniformly stirring, preparing PVA/CS solution with the mass ratio of polyvinyl alcohol to chitosan being 1.2, wherein the mass concentration of polyvinyl alcohol is 5%, standing and removing bubbles for later use;

2) Sucking 20mL of polyacrylonitrile solution by using a syringe, setting the injection rate to be 0.6mL/h, setting the electrospinning voltage to be 13kV, setting the distance between an electrospinning receiver and a needle head to be 20cm, controlling the humidity to be 44%, spinning the polyacrylonitrile solution for 8h at room temperature, and airing overnight under the environmental condition to completely volatilize the solvent to obtain a polyacrylonitrile fiber membrane;

3) Setting the injection rate of the prepared PVA/CS solution to be 0.9mL/h, setting the electrospinning voltage to be 25kV, setting the distance between an electrospinning receiver and a needle head to be 10cm, controlling the humidity to be 40%, spinning the surface of the polyacrylonitrile fiber membrane for 6h at room temperature, and airing the polyacrylonitrile fiber membrane overnight under the environmental condition after the electrospinning is finished to completely volatilize the solvent to obtain the PAN/PVA-CS composite fiber membrane;

4) And after the electrospinning is finished, soaking the obtained PAN/PVA-CS composite fiber membrane in 5% glutaraldehyde acetone solution for 30min, and drying to obtain the composite nanofiber membrane (PAN/PVA-CS membrane).

Fig. 5 is a hexane water contact angle diagram of the PAN/PVA-CS film obtained in this example, and the result shows that the oil water contact angle of the surface of the obtained composite nanofiber film is 153.0 °, which achieves the property of superhydrophobicity in oil.

Application example 1

The PAN/PVA-CS composite nanofiber membrane prepared in example 2 is used for emulsion separation, and the specific steps are as follows: adding 1mL of hexane into 99mL of deionized water, and carrying out ultrasonic treatment for 30min to obtain turbid emulsion; pouring the obtained emulsion onto a PAN/PVA-CS membrane which is wetted by water in advance, wherein a PVA-CS layer is a contact layer, and separating to obtain a clear and transparent aqueous solution.

FIG. 6 is a graph showing the effect of separating an O/W emulsion in application example 1, wherein the left graph shows the emulsion before separation, and the right graph shows the emulsion after separation, and the emulsion after separation turns from a milky turbid state to a clear transparent state.

Application example 2

The PAN/PVA-CS composite nanofiber membrane prepared in example 3 is simultaneously used for emulsion separation and dye adsorption, and the specific steps are as follows: adding 1mL of hexane into 99mL of Congo red dyed deionized water, carrying out ultrasonic treatment for 30min to obtain uniform pink emulsion, pouring the uniform pink emulsion onto a PAN/PVA-CS membrane which is wetted with water in advance, wherein the PVA-CS layer is a contact layer, and separating to obtain a clear and transparent aqueous solution.

FIG. 7 is a graph showing the separation effect of an emulsion containing a dye in application example 2, wherein the left graph shows the emulsion containing the dye before separation, and the right graph shows the filtrate after separation, wherein the emulsion after separation changes from a pink turbid state to a clear transparent state.

Application example 3

The PAN/PVA-CS composite nanofiber membrane prepared in example 5 is used for emulsion separation, and the specific steps are as follows: adding 1mL of water into 99mL of edible oil, carrying out ultrasonic treatment for 2h to obtain turbid emulsion, pouring the obtained emulsion onto a PAN/PVA-CS membrane which is wetted by the edible oil in advance, wherein a polyacrylonitrile layer is a contact layer, and separating to obtain clear and transparent edible oil.

FIG. 8 is a graph showing the effect of separating a W/O emulsion in application example 3, wherein the right graph shows the emulsion before separation, and the left graph shows the emulsion after separation, and the emulsion of vegetable oil and water after separation becomes a clear vegetable oil.

The foregoing is a further description of the invention with reference to specific embodiments thereof, and it is not intended that the scope of the invention be limited by these descriptions. Numerous derivations or substitutions may be made without departing from the spirit of the invention and are intended to fall within the scope of the invention.

Claims

1. A composite nanofiber membrane used for both latex separation and dye adsorption comprises a polyacrylonitrile nanofiber membrane and a polyvinyl alcohol-chitosan nanofiber membrane, wherein the polyvinyl alcohol-chitosan nanofiber membrane consists of polyvinyl alcohol nanofiber filaments and chitosan spherical nodular structures; simultaneously has underwater super oleophobic property and super hydrophobic property in oil;

the diameter of the nanofiber filaments in the polyacrylonitrile nanofiber membrane is 300-500nm; the diameter of the nano fiber filament in the polyvinyl alcohol-chitosan nano fiber membrane is 20-100nm;

the preparation method comprises the following steps:

1) Dissolving polyacrylonitrile in an organic solvent, and uniformly stirring to prepare a polyacrylonitrile solution; dissolving chitosan in acetic acid aqueous solution, stirring uniformly, then adding polyvinyl alcohol, continuing stirring, standing and defoaming to obtain a uniform PVA-CS solution;

2) Spinning a polyacrylonitrile solution by adopting an electrostatic spinning technology to obtain a polyacrylonitrile fiber membrane, continuously spinning a PVA-CS solution on the surface of the polyacrylonitrile fiber membrane to obtain a PAN/PVA-CS composite fiber membrane, soaking the obtained composite fiber membrane in a glutaraldehyde solution to perform a crosslinking reaction, taking out and drying to finally obtain the composite nanofiber membrane;

the mass ratio of the polyvinyl alcohol to the chitosan is 2-20;

the electrostatic spinning conditions of the PVA-CS solution are as follows: the voltage is 18-25kV, the humidity is 30% -40%, the sample injection rate is 0.5-1.0mL/h, the distance between the needle point and the receiving plate is 10-20cm, and the electrospinning time is 4-10h;

the crosslinking reaction time is 15-60min.

2. The method for preparing the composite nanofiber membrane for both emulsion separation and dye adsorption as claimed in claim 1, comprising the steps of:

1) Dissolving polyacrylonitrile in an organic solvent, and uniformly stirring to prepare a polyacrylonitrile solution; dissolving chitosan in acetic acid aqueous solution, stirring uniformly, then adding polyvinyl alcohol, continuing stirring, standing and defoaming to obtain uniform PVA-CS solution;

2) Spinning a polyacrylonitrile solution by adopting an electrostatic spinning technology to obtain a polyacrylonitrile fiber membrane, continuously spinning a PVA-CS solution on the surface of the polyacrylonitrile fiber membrane to obtain a PAN/PVA-CS composite fiber membrane, soaking the obtained composite fiber membrane in a glutaraldehyde solution for a crosslinking reaction, taking out, drying and finally obtaining the composite nanofiber membrane.

3. The method according to claim 2, wherein the mass ratio of the polyvinyl alcohol to the chitosan is 2 to 20.

4. The method according to claim 2, wherein the mass concentration of the polyvinyl alcohol in the PVA-CS solution is 3-6%.

5. The preparation method according to claim 2, wherein the electrostatic spinning conditions of the polyacrylonitrile solution are as follows: the voltage is 13-20kV, the humidity is 40% -50%, the sample introduction rate is 0.6-1.5mL/h, the distance between the needle point and the receiving plate is 15-25cm, and the electrospinning time is 4-10h.