CN115869778B

CN115869778B - PVDF nanoparticle array porous membrane and preparation method and application thereof

Info

Publication number: CN115869778B
Application number: CN202310189422.7A
Authority: CN
Inventors: 马宇; 贺斌
Original assignee: Institute of Eco Environmental and Soil Sciences of Guangdong Academy of Sciens
Current assignee: Institute of Eco Environmental and Soil Sciences of Guangdong Academy of Sciens
Priority date: 2023-03-02
Filing date: 2023-03-02
Publication date: 2023-05-16
Anticipated expiration: 2043-03-02
Also published as: CN115869778A

Abstract

The invention discloses a PVDF nanoparticle array porous membrane, and a preparation method and application thereof. The preparation method of the PVDF nanoparticle array porous membrane comprises the following steps: 1) Dissolving polyvinylidene fluoride in an organic solvent to obtain a polyvinylidene fluoride solution; 2) Dripping polyvinylidene fluoride solution into a dispersion medium to obtain polyvinylidene fluoride nanoparticle dispersion liquid; 3) Performing suction filtration on the polyvinylidene fluoride nanoparticle dispersion liquid to obtain a PVDF nanoparticle film; adding an organic solvent into the PVDF nanoparticle membrane, and carrying out suction filtration to obtain a PVDF swelling membrane; and adding a dispersion medium into the PVDF swelling membrane, and carrying out suction filtration to obtain the PVDF nanoparticle array porous membrane. The method has the advantages of simple and controllable preparation process and low cost, can prepare the PVDF nanoparticle array porous membrane with regular pore channels and high efficiency of intercepting microplastic, and is suitable for large-scale production and application.

Description

PVDF nanoparticle array porous membrane and preparation method and application thereof

Technical Field

The invention relates to the technical field of membrane materials, in particular to a PVDF nanoparticle array porous membrane, and a preparation method and application thereof.

Background

With the increasing global industrialization, plastics are discharged into the ecological environment every year, and the plastics are continuously crushed and degraded in the nature to form microplastic. The micro plastic particles are tiny and have strong adsorption performance, so that the toxic effect is more prominent.

The membrane separation technology is one of the treatment technologies commonly used in the field of environmental protection, and the technology is to drive fluid to pass across a porous separation membrane through pressure, and as the pore size of the membrane is generally in the nanometer level and smaller than the size of microplastic, the microplastic in a water body cannot pass across the membrane to be trapped under the drive of the pressure, so that the purpose of separating the microplastic is realized. In order to realize efficient separation of microplastic, the type and structure of the separation membrane are important. At present, the common commercial separation membrane is an organic separation membrane, and has the problems of low penetration degree of the pore canal in the membrane, uneven arrangement of the membrane pores, low porosity and the like, thereby leading to membrane permeation flux of less than 1000L m ^-2 ·h ^-1 ·bar ^-1 It is difficult to meet the large-scale processing requirements.

To solve the above problems, regular and uniform pore paths are required to be constructed in the membrane. At present, the method for constructing regular and uniform pore channels in the membrane mainly comprises the following three steps: 1. the sacrificial template method is that polymer is poured into an anodic aluminum oxide template, and then the template is etched to obtain a separation membrane with regular and uniform pore channels in the membrane; 2. the ice template method is to assemble the ice template along the growth direction of ice crystals by using a dispersion medium, and then to obtain a separation membrane with uniform pore distribution by freeze drying; 3. a vertical array of carbon nanotubes is grown by chemical vapor deposition. The method can realize regular and uniform construction of pore channels, but has the defects of needing to use other substances as templates, having complex preparation process, using various and expensive raw materials, unstable mechanical properties of the prepared membrane, wider pore size distribution range of the membrane, being difficult to effectively intercept microplastic in sewage and the like, so that the practical application and popularization of the method are limited.

In addition, although the prior art CN114835944a discloses a method for preparing an energy-consumption self-contained type efficient photo-thermal evaporation nanoparticle porous membrane, the purpose of preparing the energy-consumption self-contained type efficient photo-thermal evaporation nanoparticle porous membrane is mainly used for a photo-thermal conversion system to convert light energy into heat energy. The application scene of the self-contained energy consumption efficient photo-thermal evaporation nano-particle porous membrane disclosed in CN114835944A is natural illumination condition, and the membrane cannot bear high pressure and high shearing force generated in the membrane separation process and has no capability of resisting mechanical shearing force, so that the membrane cannot be applied to interception and recovery treatment of micro-plastics.

Therefore, there is a need to develop an organic membrane material with simple and regular composition raw materials, uniform pore channels, simple and controllable preparation, low cost, large flux, better mechanical properties and high micro-plastic retention rate.

Disclosure of Invention

In order to overcome the problems in the prior art, one of the purposes of the invention is to provide a preparation method of PVDF nanoparticle array porous membrane with uniform pore channels, which has simple process, practicality and low cost;

the second purpose of the invention is to provide a PVDF nanoparticle array porous membrane which has simple composition, regular polymer particle interval, uniform pore canal and large flux and can efficiently treat sewage containing microplastic;

The invention further aims to provide an application of the PVDF nanoparticle array porous membrane.

The invention is characterized in that: based on the dissolution characteristic of the crystalline polymer PVDF, the steps of mechanical shaking and swelling are firstly utilized, and meanwhile, partial dissolution of the polymer PVDF and uniform distribution of PVDF rubbery crystal seeds are realized; and then forming a film by using a seed crystal induced phase inversion technology, and realizing equidistant distribution and crosslinking of nano particles with uniform size in the film, thereby constructing the PVDF nano particle array film. The membrane with the same distance between the nano particles formed after phase inversion is formed due to the preparation process of mechanical shaking and swelling and uniform distribution of PVDF seed crystals; in addition, since concentration fluctuation has a fixed wavelength in the phase inversion process and the size of the nano particles is consistent with the wavelength, the formed nano particles have a regular size, and thus the PVDF nano particle array film can be formed.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

in a first aspect, the invention provides a method for preparing a PVDF nanoparticle array porous membrane, comprising the following steps:

step 1: dissolving polyvinylidene fluoride in an organic solvent to obtain a polyvinylidene fluoride solution;

Step 2: dripping polyvinylidene fluoride solution into a dispersion medium to obtain polyvinylidene fluoride nanoparticle dispersion liquid;

step 3: performing suction filtration on the polyvinylidene fluoride nanoparticle dispersion liquid to obtain a PVDF nanoparticle film; adding an organic solvent into the PVDF nanoparticle membrane, and carrying out suction filtration to obtain a PVDF swelling membrane; adding a dispersion medium into the PVDF swelling membrane, and carrying out suction filtration to obtain a PVDF nanoparticle array porous membrane;

wherein the organic solvent in the step 1 and the step 3 is at least one of N, N-dimethylformamide, N-methylpyrrolidone, dimethylacetamide and dimethyl sulfoxide; the dispersion medium in the step 2 and the step 3 is at least one of water, ethanol and acetone; and 3, the filter membrane used in the suction filtration is a nylon micro-filter membrane or a polytetrafluoroethylene micro-filter membrane.

Preferably, the preparation method of the PVDF nanoparticle array porous membrane further comprises the following steps: and (3) putting the PVDF nanoparticle array porous membrane into an eluent (such as ethanol) for membrane removal, and then putting into a preservation solution for preservation.

Specifically, the PVDF nanoparticle dispersion liquid is prepared from high polymer PVDF, and then a solvent-resistant commercial substrate (i.e. a filter membrane) is adopted for suction filtration to obtain a PVDF nanoparticle membrane; then, a proper amount of organic solvent is added and suction filtration is carried out, so that the high polymer is converted into a rubber-like state, and the seed crystals are uniformly distributed by mechanical uniform mixing and swelling, thus obtaining a swelling film; adding a non-solvent (namely the dispersion medium, such as water) and carrying out suction filtration through PVDF seed crystal induction so as to enable the rubbery PVDF polymer to undergo phase inversion, thus obtaining the nanoparticle array porous membrane with the substrate (namely the filter membrane); and finally, soaking the membrane into an ethanol solvent, standing for a certain time, and then spontaneously falling off the nanoparticle array membrane, taking out the nanoparticle array membrane and storing the nanoparticle array membrane in ethanol for standby (namely obtaining the PVDF nanoparticle array porous membrane).

Preferably, the eluent and the preservation solution are 70 wt% -98.5% -wt% ethanol.

Further preferably, the eluent is 95 wt% -98 wt% ethanol, and the preservation solution is 70 wt% -78 wt% ethanol.

Preferably, the demolding time is 10-15 hours.

Further preferably, the time for the demolding is 12 hours.

Specifically, the time for placing the PVDF nanoparticle array porous membrane in the eluent is in order to completely elute the PVDF nanoparticle array porous membrane on the filter membrane after suction filtration; and the PVDF nanoparticle array porous membrane is placed in the eluent to be beneficial to protecting the prepared regular pore canal structure, so that the porous membrane prepared by the preparation process does not need to be dried (is beneficial to saving the production energy consumption), and is convenient for large-scale popularization and application.

Preferably, the average molecular weight of the polyvinylidene fluoride in the step 1 is 0.3 MDa-0.5 MDa.

It is further preferred that the polyvinylidene fluoride of step 1 has an average molecular weight of 0.4 MDa.

Preferably, the dissolution temperature in the step 1 is 50-70 ℃.

Further preferably, the dissolution temperature in the step 1 is 55 ℃ to 65 ℃.

Preferably, the polyvinylidene fluoride content in the polyvinylidene fluoride solution in the step 1 is 0.3g/100 mL-0.8 g/100mL.

Further preferably, the polyvinylidene fluoride content in the polyvinylidene fluoride solution in the step 1 is 0.5g/100mL to 0.7g/100mL.

Preferably, the volume ratio of the polyvinylidene fluoride solution to the dispersion medium in the step 2 is (0.2-1.25): 100.

Further preferably, the volume ratio of the polyvinylidene fluoride solution and the dispersion medium in the step 2 is (0.25-1): 100.

Preferably, the temperature of the polyvinylidene fluoride solution in the step 2 is 15-35 ℃ during dropwise adding.

Further preferably, the temperature of the polyvinylidene fluoride solution in the step 2 is 24-27 ℃ during dropwise addition.

Specifically, in the step 1, high molecular polyvinylidene fluoride is dissolved in an organic solvent under the heating condition (55-65 ℃), so that the dissolution of the polyvinylidene fluoride is facilitated. If the high polymer polyvinylidene fluoride is dissolved under the heating condition, the obtained polyvinylidene fluoride solution can be dripped into the dispersion medium only after being cooled to 15-35 ℃.

Preferably, the dropping rate of the polyvinylidene fluoride solution in the step 2 is 4 mL/min-6 mL/min.

It is further preferred that the dropping rate of the polyvinylidene fluoride solution in step 2 is 5mL/min.

Preferably, the particle size of the polyvinylidene fluoride nano particles in the polyvinylidene fluoride nano particle dispersion liquid in the step 3 is 100 nm-300 nm.

Preferably, the particle size of the polyvinylidene fluoride nano seed crystal in the swelling film in the step 3 is 1 nm-8 nm.

Further preferably, the particle size of the polyvinylidene fluoride nano seed crystal in the swelling film in the step 3 is 3 nm-7 nm.

Preferably, the dosage of the polyvinylidene fluoride nanoparticle dispersion liquid in the step 3 is 100-mL mL-500 mL.

Further preferably, the dosage of the polyvinylidene fluoride nanoparticle dispersion liquid in the step 3 is 150-mL mL.

Preferably, the ratio of the amount of polyvinylidene fluoride nanoparticle dispersion liquid used in step 3 to the area of the filter membrane used for suction filtration is 0.5 mL/1 mm ² ~2mL:1mm ² 。

Preferably, the filter membrane used in the suction filtration in the step 3 is a nylon micro-filter membrane or a polytetrafluoroethylene micro-filter membrane.

Preferably, the filter membrane is circular or square.

Preferably, the pore diameter of the filter membrane is 100 nm-600 nm.

Further preferably, the pore diameter of the filter membrane is 200 nm-500 nm.

Further preferably, the filter membrane is circular, and the diameter of the filter membrane is 30 mm-60 mm.

Still more preferably, the filter is a round polytetrafluoroethylene commercial microfiltration membrane having a diameter of 50mm and a membrane pore size of 0.22 μm. Specifically, the manufacturer is Tianjin Jinteng laboratory equipment Co., ltd.

Preferably, the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid and the organic solvent in the step 3 is (50-20): 1.

Preferably, the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid and the dispersion medium in the step 3 is 1 (0.8-1.5).

Preferably, the vacuum gauge value of the suction filtration in the step 3 is 0.5 bar to 1.0 bar.

Further preferably, the vacuum gauge value of the suction filtration in step 3 is 0.8bar.

Preferably, the thickness of the PVDF nanoparticle film in the step 3 is 1-14 μm.

In a second aspect, the present invention provides a porous membrane of PVDF nanoparticle array made by the method of the first aspect.

Preferably, the PVDF nanoparticle array porous membrane comprises PVDF nanoparticles of beta crystalline phase formed by seed induced phase inversion of polyvinylidene fluoride nano seed crystals, and the PVDF nanoparticles of beta crystalline phase form a three-dimensional porous structure by seed induction.

Specifically, the seed crystal induced phase inversion refers to that PVDF nano particle partial dissolution can be realized by adding different solvents and suction filtration, mechanical mixing is carried out, seed crystals are uniformly distributed and swelled on a filter membrane, and rubber-like polyvinylidene fluoride nano seed crystals are formed, so that a PVDF swelling membrane can be obtained, and then a PVDF nano particle array porous membrane is obtained under the seed crystal induced phase inversion effect, and the PVDF nano particle array porous membrane has a three-dimensional porous structure.

Preferably, the thickness of the PVDF nanoparticle array porous membrane is 1-20 μm.

Preferably, the membrane pore diameter of the PVDF nanoparticle array porous membrane is 300-500 nm.

Preferably, the porosity of the PVDF nanoparticle array porous membrane is 19% -50%.

In a third aspect, the present invention provides the use of the PVDF nanoparticle array porous membrane described above in water treatment.

Preferably, the water treatment is a microplastic-containing sewage treatment.

Preferably, the particle size of the microplastic in the sewage containing the microplastic is 680 nm-1.5 mu m.

Preferably, the microplastic comprises at least one of Polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET), nylon (PA).

Preferably, the flux of the water treatment is 650L m ^-2 ·h ^-1 ·bar ^-1 ~15000 L·m ^-2 ·h ^-1 ·bar ^-1 。

Further preferably, the flux of the water treatment is 5300L m ^-2 ·h ^-1 ·bar ^-1 ~14800 L·m ^-2 ·h ^-1 ·bar ^-1 。

Preferably, the application comprises the steps of:

after pretreatment of PVDF nanoparticle array porous membrane by ethanol, setting pure water flux to 1733+ -17L m ^-2 ·h ^-1 ·bar ^-1 ~14625±53 L·m ^-2 ·h ^-1 ·bar ^-1 And (3) treating the sewage containing the microplastic with the concentration of 5mg/L to 15 mg/L.

Specifically, the pretreatment is suction filtration.

The beneficial effects of the invention are as follows: the preparation method of the PVDF nanoparticle array porous membrane has the advantages of few raw material types, simple and controllable preparation process and low cost, can prepare the PVDF nanoparticle array porous membrane with regular pore channels and high efficiency of intercepting microplastic without using extra raw materials as templates, and is suitable for large-scale production and application. The method comprises the following steps:

(1) The invention adopts seed crystal induced phase inversion technology to prepare the polyvinylidene fluoride (PVDF) nanoparticle array uniform pore membrane. Compared with the prior uniform pore membrane preparation, the method has the problems of complex process, expensive raw materials and the like, and is simple, practical and low in cost. Because the PVDF nanoparticle array uniform pore membrane has a uniform pore structure and controllable membrane thickness, compared with the traditional commercial PVDF membrane, the membrane flux is improved by 1 order of magnitude, and the retention rate of the membrane to micro plastics is close to 100%.

(2) Based on the dissolution characteristic of crystalline polymer, the invention adopts polymer good solvent to partially swell the nano particles based on PVDF crystalline polymer nano particles on the surface of the film, so as to realize the aim of exciting the polymer chain segment to cooperatively move on the premise of keeping partial crystalline structure (seed crystal) in the nano particles, and further uniformly distribute the seed crystals on the surface of the film through mechanical action. And then the concentration of rubbery polymers is fluctuated by using a non-solvent induced phase inversion technology induced by the seed crystal, the high concentration region (rich phase) polymers grow into nano particles again through heterogeneous nucleation of the seed crystal, and the low concentration region (lean phase) polymers crosslink the nano particles with each other. The distance between the nano particles formed after phase inversion is the same because the seed crystals are uniformly distributed in the swelling and mechanical process; since concentration fluctuations have a fixed wavelength during phase inversion and nanoparticle sizes coincide with the wavelength, the nanoparticles have a regular size, thereby forming a nanoparticle array film.

(3) Based on the mature phase inversion and heterogeneous nucleation theory, the invention designs a simple and practical PVDF nanoparticle array pore-balancing film, and the interception rate of the PVDF nanoparticle array pore-balancing film to micro plastics can reach 99% or more.

Drawings

FIG. 1 is a schematic illustration of the preparation flow of a porous membrane of PVDF nanoparticle array in example 1.

Fig. 2 is an SEM image of PVDF nanoparticle film, swollen film and PVDF nanoparticle array porous film after phase inversion prepared in the preparation process of example 1.

Fig. 3 is a physical diagram of a PVDF nanoparticle array porous membrane in example 1.

Fig. 4 is an SEM image of a PVDF nanoparticle array porous membrane in example 1.

Fig. 5 is a TEM image of PVDF nanoparticles prepared in the examples of the invention.

Fig. 6 is an SEM image of a PVDF nanoparticle array porous membrane after phase inversion in example 1 and examples 3 to 5.

Fig. 7 is an SEM image of a PVDF nanoparticle array porous membrane after phase inversion in example 2.

Fig. 8 is a cross-sectional SEM image of the PVDF nanoparticle array porous membrane after phase inversion in example 1 and examples 3 to 5.

Fig. 9 is a TEM image of the swollen film obtained in the mechanical mixing and swelling process of comparative example 1.

Fig. 10 is an SEM image of a PVDF nanoparticle array porous membrane in comparative example 5.

Fig. 11 is an SEM image of a PVDF nanoparticle array porous membrane in comparative example 6.

Fig. 12 is a fourier infrared spectrum of a PVDF nanoparticle array porous film in example 1 and comparative example 1.

FIG. 13 is an X-ray diffraction pattern of PVDF nanoparticle array porous films prepared in example 1, examples 3 to 5, comparative examples 1 to 4, and PVDF nanoparticle film in comparative example 7.

FIG. 14 is a DSC graph of porous membranes of PVDF nanoparticle arrays of examples 1, 3-5 and comparative examples 1-4.

FIG. 15 is a graph showing pore size distribution of porous membranes of PVDF nanoparticle arrays of examples 1 and 3-5.

FIG. 16 is a graph showing the relationship between the volume of the polymer solution participating in phase inversion and the film thickness in examples 1 and 3 to 5.

Fig. 17 is a graph showing the performance of porous membranes of PVDF nanoparticle arrays in example 1, example 3, example 4, and example 5.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

The commercial base membrane used in examples and comparative examples was a commercial Polytetrafluoroethylene (PTFE) microfiltration membrane available from Tianjin's laboratory equipment Co., ltd., and had a diameter of 50mm and a membrane pore size of 0.22. Mu.m; the mechanical mixing and swelling and the uniform distribution of the seed crystals are realized by adding DMF solvent into the PVDF nano particle membrane, and obtaining the PVDF swelling membrane after complete suction filtration; the phase inversion and seed crystal induced film forming technology in the invention refer to the process of adding deionized water into the PVDF swelling film and carrying out suction filtration to obtain the PVDF nanoparticle array porous film.

Unless otherwise specified, the conversion method of the invention can be used for preparing the PVDF nanoparticle array porous membrane at room temperature, and the room temperature in the invention is 15-35 ℃; the ethanol content of the "soaked in ethanol" in the examples and comparative examples of the present invention was about 98wt%; the ethanol content "stored in ethanol" in the examples and comparative examples of the present invention was about 75wt%.

Example 1

The embodiment provides a preparation method of a PVDF nanoparticle array porous membrane, which comprises the following steps:

(1) Synthesis of PVDF nanoparticles:

polyvinylidene fluoride with an average molecular weight of 0.6. 0.6 g MDa was added to 100 mL of N, N-Dimethylformamide (DMF) solvent, heated to 60℃by means of an oil bath, dissolved for 2 hours at 60℃and 150 rpm, and cooled to room temperature to obtain a DMF solution of PVDF;

dropwise adding 0.5mL of PVDF DMF solution into 200mL of deionized water, controlling the dropwise adding rate to be 5mL/min, and continuously stirring to obtain PVDF nanoparticle dispersion;

(2) The process for preparing PVDF nanoparticle array porous membrane by phase inversion method comprises the following steps:

s1, taking a commercial PTFE micro-filtration membrane, and carrying out suction filtration on the PVDF nanoparticle dispersion liquid prepared in the step 1 of 200mL to obtain a PVDF nanoparticle membrane;

S2, adding 5 mL of DMF solvent into the PVDF nanoparticle membrane, and performing complete suction filtration to obtain a PVDF swelling membrane;

s3, adding 200 mL deionized water into the PVDF swelling membrane, and carrying out suction filtration to obtain a PVDF nanoparticle array porous membrane with a commercial substrate (commercial PTFE microfiltration membrane is taken as a substrate);

s4, soaking the PVDF nanoparticle array porous membrane with the commercial substrate in ethanol, standing for 12-h to enable the PVDF nanoparticle array porous membrane to spontaneously fall off, and taking out to obtain the PVDF nanoparticle array porous membrane (stored in ethanol for standby);

wherein the vacuum pressure of the suction filtration in S1, S2 and S3 is 0.8 bar; s2 is a process of mechanically mixing and swelling the polymer.

The PVDF swelling membrane and the PVDF nanoparticle array porous membrane in the embodiment comprise PVDF nanoparticles which are beta crystalline phases.

Example 2

This example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 1 only in that: the DMF solution usage of PVDF was replaced with 0.2 mL, comprising the steps of:

(1) Synthesis of PVDF nanoparticles:

Dropwise adding 0.2mL of PVDF DMF solution into 200mL of deionized water, controlling the dropwise adding rate to be 5mL/min, and continuously stirring to obtain PVDF nanoparticle dispersion;

s2, adding 5mL of DMF solvent into the PVDF nanoparticle film, and carrying out complete suction filtration to obtain a PVDF swelling film, wherein the process is a process of mechanically mixing and swelling polymers;

s3, adding 200mL deionized water into the PVDF swelling membrane, and carrying out suction filtration to obtain a PVDF nanoparticle array porous membrane with a commercial substrate (commercial PTFE microfiltration membrane is taken as a substrate);

wherein the vacuum pressure for suction filtration in S1, S2 and S3 is 0.8 bar.

It should be noted that the purpose of this example is to compare with example 1, but the PVDF swollen membrane and PVDF nanoparticle array porous membrane in this example are described as examples because they also involve the process of mechanical shaking and swelling, and seed induced phase inversion, and the PVDF nanoparticles are both beta crystalline phases.

Example 3

This example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 1 only in that: the PVDF DMF solution was replaced by 0.8. 0.8 mL and the rest of the procedure was the same as in example 1.

Example 4

This example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 1 only in that: the PVDF DMF solution was replaced by 1.0. 1.0 mL and the rest of the procedure was the same as in example 1.

Example 5

This example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 1 only in that: the PVDF DMF solution was replaced by 2.0mL and the rest was the same as in example 1.

Comparative example 1

This comparative example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 1 only in that: step (2) is to directly obtain PVDF swelling film, then directly put the film into a blast oven at 60 ℃ to dry for 30 minutes to form a film, and store the film in ethanol for standby after film formation, namely the process does not carry out phase inversion, and the method comprises the following steps:

(1) Synthesis of PVDF nanoparticles:

(2) The process of the PVDF nanoparticle array porous membrane:

s1, taking a commercial PTFE micro-filtration membrane, and carrying out suction filtration on 200mL of PVDF nanoparticle dispersion liquid prepared in the step 1 to obtain a PVDF nanoparticle membrane;

s2, adding 5mL of DMF solvent into the PVDF nanoparticle membrane, and performing complete suction filtration to obtain a PVDF swelling membrane with a commercial substrate (commercial PTFE microfiltration membrane is taken as a substrate);

s3, drying the PVDF swelling film in a blast oven at 60 ℃ for 30 minutes to form a film, thus obtaining a PVDF nanoparticle array porous film (after film formation, the film is stored in ethanol for standby);

wherein the vacuum pressure for suction filtration in S1, S2 and S3 is 0.8 bar.

Comparative example 2

This comparative example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 3 only in that: and (2) directly obtaining a PVDF swelling film, directly putting the film into a blast oven at 60 ℃ for drying for 30 minutes to form a film, and storing the film in ethanol for standby after film formation, wherein the process does not carry out phase inversion, and the rest steps are the same as those of the example 3.

Comparative example 3

This comparative example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 4 only in that: and (2) directly obtaining a PVDF swelling film, directly putting the film into a blast oven at 60 ℃ for drying for 30 minutes to form a film, and storing the film in ethanol for standby after film formation, wherein the process does not carry out phase inversion, and the rest steps are the same as those of the example 4.

Comparative example 4

This comparative example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 5 only in that: and (2) directly obtaining a PVDF swelling film, directly putting the film into a blast oven at 60 ℃ for drying for 30 minutes to form a film, and storing the film in ethanol for standby after film formation, wherein the process does not carry out phase inversion, and the rest steps are the same as those of the example 5.

Comparative example 5

This comparative example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 1 only in that: in the step (2), soaking the nano-particle membrane in 5 mL of DMF solvent for 10 minutes to obtain a PVDF swelling membrane; then, adopting a PVDF swelling membrane to carry out suction filtration (the suction filtration vacuum pressure is 0.8 bar) on 200 mL deionized water to obtain a PVDF membrane with a commercial substrate; finally, soaking the PVDF film with the commercial substrate (PTFE commercial micro-filtration film) into ethanol, standing for 12 h to enable the film to spontaneously fall off, taking out the film and storing the film in the ethanol for standby, namely, the process does not carry out a process of mechanically and uniformly mixing the polymers, and specifically comprises the following steps of:

(1) Synthesis of PVDF nanoparticles:

s2, soaking the PVDF nano particle membrane in 5mL of DMF solvent to obtain a PVDF swelling membrane;

Wherein the vacuum pressure for suction filtration in S1, S2 and S3 is 0.8 bar.

Comparative example 6

This comparative example provides a method for preparing a porous membrane of PVDF nanoparticle array, which differs from example 5 only in that: in the step (2), the nano particle film is soaked in 5mL of DMF solvent for 10 minutes to obtain the PVDF swelling film, namely, the process does not carry out high polymer mechanical mixing, and the method comprises the following steps:

(1) Synthesis of PVDF nanoparticles:

2.0mL of PVDF DMF solution is taken and added into 200mL of deionized water dropwise, the dropping speed is controlled to be 5mL/min, and the dispersion liquid of PVDF nano particles is obtained by continuously stirring;

s2, soaking the PVDF nano particle membrane into 5mL of DMF solvent for 10 minutes to obtain a PVDF swelling membrane;

wherein the vacuum pressure for suction filtration in S1, S2 and S3 is 0.8 bar.

Comparative example 7

This comparative example provides a PVDF nanoparticle film differing from example 5 only in: step (2) is different and comprises the following steps:

(1) Synthesis of PVDF nanoparticles:

(2) Preparation of PVDF nanoparticle film:

And (3) carrying out suction filtration (the suction filtration vacuum pressure is 0.8 bar) on the PVDF nanoparticle dispersion liquid prepared in the step (1) by adopting a commercial PTFE microfiltration membrane, drying the dispersion liquid in a blast oven at 60 ℃ for 30 minutes to form a membrane, and removing the commercial PTFE microfiltration membrane to obtain the PVDF nanoparticle membrane (after the membrane is formed, storing the membrane in the air).

Characterization and performance analysis:

1. a transmission electron microscope (Transmission Electron Microscope, TEM for short) image of PVDF nanoparticles prepared in the embodiment of the invention is shown in FIG. 5. Schematic of the preparation flow of porous membrane of PVDF nanoparticle array in example 1, as shown in fig. 1; example 1 a scanning electron microscope (Scanning Electron Microscope, abbreviated SEM) image of the PVDF nanoparticle film, the swollen film and the phase-converted PVDF nanoparticle array porous film prepared in the preparation process is shown in fig. 2, wherein a in fig. 2 is an SEM image of the PVDF nanoparticle film in example 1, b in fig. 2 is an SEM image of the swollen film in example 1, and c and d in fig. 2 are SEM images of the phase-converted PVDF nanoparticle array porous film measured at different magnifications, respectively.

As can be seen from fig. 1, 2 and 5: the inventive concept of the present invention is illustrated by taking the preparation process of example 1 as an example. The invention is based on the dissolution characteristic of crystalline polymer PVDF, and a PVDF nanoparticle film (see a in figure 2) formed by stacking nanoparticles (see figure 5) is prepared by suction filtration of a commercial substrate film and PVDF nanoparticle dispersion liquid with proper concentration; then, adding N, N-Dimethylformamide (DMF) and suction filtration into the PVDF nanoparticle film, so that the PVDF nanoparticles can be dissolved and uniformly distributed in a part of PVDF particles under the action of the N, N-dimethylformamide (DMF, a good solvent of PVDF) and suction filtration, and further the mechanical mixing and swelling process (see b in fig. 2) is realized, a swelling film is prepared, and on the other hand, the uniform distribution of PVDF small particles can be obtained by partial dissolution, and the small particles can be used as seed crystals, namely, the conditions can be created for the realization of the film formation by the seed crystal induced phase inversion technology; then, by adding water into the swelling film, the PVDF nano particle array film can be constructed by utilizing the PVDF seed crystal to form a film through the seed crystal induced phase inversion technology under the action of low solubility in an aqueous solvent system and suction filtration in the process, so that uniform-size nano particles in the film are equidistantly distributed and crosslinked (see c and d in figure 2).

It should be emphasized that the mechanical mixing and swelling process and the step of uniformly distributing the polymer seed crystals are very critical, so that the structure that the distances among the nano particles formed after phase inversion are basically the same; meanwhile, concentration fluctuation in the phase inversion process has fixed wavelength, and the size of the nano particles is consistent with the wavelength, so that the nano particles formed by final phase inversion and seed crystal induction have regular size, and the final PVDF nano particle array film is formed.

Example 1 a scanning electron microscope (Scanning Electron Microscope, abbreviated SEM) image of a PVDF nanoparticle film, a swollen film, and a PVDF nanoparticle array porous film after phase inversion, which were prepared in the preparation process, is shown in fig. 2. Assembling nano particles on the surface of the PFTE commercial nano film by a suction filtration method, wherein the nano particles can be found to be accumulated on the surface of the film (see a in figure 2); after the PTFE commercial membrane surface nano particles are subjected to suction filtration by adopting DMF (PVDF good solvent) (see b in fig. 2), the membrane surface is smooth and uniform, and the structure of the previously observed membrane surface nano particles disappears, which indicates that the nano particles swell after the DMF suction filtration; finally, the swollen nanoparticle film was suction filtered with water (non-solvent for PVDF) (c and d in fig. 2), and it was found that the film surface produced a regularly arranged array of PVDF nanoparticles.

Meanwhile, the film finally produced in comparative example 1 can reflect the morphology and the material composition characteristics of the swollen film in example 1, so that the test comparative example 1 gives a TEM image of the swollen film during mechanical mixing and swelling, as shown in fig. 9, wherein a and b in fig. 9 are TEM images of the swollen film of comparative example 1, respectively, measured at different magnifications.

As can be seen from fig. 9 and 2: from a in fig. 2, it can be illustrated that the particle size of the polyvinylidene fluoride nanoparticles in the PVDF nanoparticle film and the polyvinylidene fluoride nanoparticle dispersion is 100 nm to 300nm.

Meanwhile, although the surface of the swelling film prepared through the mechanical shaking and swelling processes is uniform and smooth, the phenomenon that a large number of nano particles are uniformly distributed on the surface and inside of the swelling film can still be found through high-power TEM characterization, and the nano particles are polyvinylidene fluoride nano seed crystals with the diameter of about 5 nm (see figure 9). The particles are seed crystals which appear in the membrane after mechanical shaking and swelling treatment, and the seed crystals still have certain crystallinity after membrane swelling, and lay a foundation for subsequent phase inversion induced crystallization membrane formation.

Based on the characterization result, the preparation process of the PVDF nanoparticle array porous membrane is consistent with the inventive concept, which shows that the PVDF nanoparticle array porous membrane, even the PVDF nanoparticle array uniform pore membrane, can be prepared by controlling the whole preparation method.

2. A physical view and an SEM view of the PVDF nanoparticle array porous membrane in example 1 are shown in fig. 3 and 4, respectively. As shown in fig. 6, a in fig. 6 is a SEM image of the PVDF nanoparticle array porous film of example 1, b in fig. 6 is a SEM image of the PVDF nanoparticle array porous film of example 3, c in fig. 6 is a SEM image of the PVDF nanoparticle array porous film of example 4, and d in fig. 6 is a SEM image of the PVDF nanoparticle array porous film of example 5; SEM images of the PVDF nanoparticle array porous membrane after phase inversion in example 2 are shown in fig. 7. Cross-sectional SEM images of the PVDF nanoparticle array porous membrane after phase inversion in example 1 and examples 3 to 5 are shown in fig. 8; wherein a, a' and a "are cross-sectional SEM images of the PVDF nanoparticle array porous membrane obtained in example 1; b. b' and b "are cross-sectional SEM images of the PVDF nanoparticle array porous membrane obtained in example 3; c. c' and c "are cross-sectional SEM images of the PVDF nanoparticle array porous membrane obtained in example 4; d. d' and d "are cross-sectional SEM images of porous membranes of PVDF nanoparticle arrays obtained in example 5.

As can be seen from fig. 2, 3, 4, 6, 7 and 8: the nano particles in the array porous membrane finally obtained in the embodiment 1 and the embodiment 3-5 have uniform sizes, and the whole membrane is transparent and complete round. Further, it can be found from the sectional SEM pictures that the thicknesses of the array porous films finally obtained in examples 1, 3 to 5 are 1.94 μm, 3.75 μm, 5.41 μm and 11.33 μm, respectively; the pore diameter of the membrane is about 400 nm-550 nm.

Moreover, the morphology of the PVDF nanoparticle array porous membrane in different embodiments is tested by SEM, and the surface morphology of the porous membrane is closely related to the participation phase inversion volume (abbreviated as participation phase inversion volume, hereinafter the same) of the high polymer solution; when the participating phase inversion volume is small, there are a large number of defects on the surface of the PVDF nanoparticle array porous membrane (i.e., the porous membrane in example 2, see fig. 7) and the nanoparticles are unevenly distributed; when the participating phase inversion volume is large (examples 3-5, see fig. 8), the nanoparticles of the PVDF nanoparticle array porous membrane are located on the membrane surface to show a small amount of maldistribution, but the PVDF nanoparticle array porous membrane for water treatment can still be formed.

Further analysis, the polymer solutions of examples 1 and 3 to 5 are shown in FIG. 16 as a graph of the volume of the phase inversion and the film thickness.

As can be seen from fig. 16: because the invention adopts the suction filtration nano particles as a basic method, the film thickness can be regulated by regulating the amount of the nano particles. Meanwhile, the film thicknesses obtained in examples 1 and 3 to 5 were 1.94 μm,3.75 μm,5.41 μm and 11.33 μm, respectively; the linear fit curve equation obtained by the analysis software was analyzed as:

y= -1.11623+6.25460 x, the correlation coefficient is R ² 0.99795, this illustrates that the participating volume is approximately linear with the thickness of the PVDF nanoarray porous membrane (see fig. 16).

3. SEM images of the PVDF nanoparticle array porous film of comparative example 5 are shown in fig. 10, in which a and a' in fig. 10 represent SEM images of the PVDF nanoparticle array porous film of comparative example 5 at different magnifications; SEM images of the PVDF nanoparticle array porous film of comparative example 6 are shown in fig. 11, wherein a and a' in fig. 11 are SEM images of the PVDF nanoparticle array porous film of comparative example 6 at different magnifications.

As can be seen from fig. 9, 10 and 11: in the embodiment, the surface of the swelling film prepared by mechanical shaking and swelling processes is uniform and smooth, and a large number of uniformly distributed polyvinylidene fluoride nano seed crystals with the diameter of about 5nm can be found on the surface and in the swelling film, and the nano particles still have a certain crystallinity after the swelling film is swelled and can be used as seed crystals for induced crystallization film formation. In contrast, in comparative examples 5 and 6, the mechanical mixing process of PVDF polymer was not performed, that is, the suction filtration operation (mechanical mixing operation) was not performed during the swelling of nanoparticles, and the surface morphology of the porous membrane obtained after the phase inversion was not significantly different from that of the PVDF nanoparticle membrane obtained initially in the preparation process, thus confirming that the mechanical mixing (i.e., suction filtration) is also a key factor for preparing the nanoparticle array membrane.

4. Fourier infrared spectra (Fourier Transform Ioncyclotron Resonance, i.e., FTIR) of the PVDF nanoparticle array porous membranes of example 1 and comparative example 1 are shown in fig. 12.

X-Ray Diffraction (XRD) patterns of the PVDF nanoparticle array porous films prepared in examples 1, 3-5 and comparative examples 1-4 and the PVDF nanoparticle film prepared in comparative example 7 are shown in FIG. 13, wherein a in FIG. 13 is the PVDF nanoparticle array porous film prepared in example 5, the swelling film prepared in comparative example 4 and the PVDF nanoparticle film prepared in comparative example 7, b in FIG. 13 is the XRD pattern of the obtained swelling film prepared in comparative examples 1-4, and c in FIG. 13 is the XRD pattern of the PVDF nanoparticle array porous films prepared in examples 1 and 3-5.

Thermal differential scanning (Differential Scanning Calorimetry, i.e., DSC) profiles of the PVDF nanoparticle array porous films of examples 1, 3-5 and comparative examples 1-4 are shown in fig. 14; wherein a in FIG. 14 is 130-220 of the films obtained in example 1 and comparative example 1 ^O DSC plot under C, b in FIG. 14 is the film obtained in example 3 and comparative example 2 at 130-220 ^O DSC plot at C, C in FIG. 14 being 130-220 for the films obtained in example 4 and comparative example 3 ^O DSC plot at C, d in FIG. 14 is the film obtained in example 5 and comparative example 4 at 130-220 ^O DSC profile under C.

As can be seen from fig. 12, 13 and 14: FTIR results showed: PVDF nanoparticle array porous and swollen membranes at 840 cm ^-1 There is an absorption peak, which is a characteristic peak of the beta crystalline phase of typical PVDF. The characteristic absorption peak of the alpha-crystalline phase of PVDF should appear at 766 cm ^-1 A place; however, the FTIR results of the present invention showed that the corresponding characteristic absorption peaks were not found for both films, thereby proving that the PVDF nanoparticle array porous film and the swollen film of the present invention have crystalline structures and are both beta-crystalline phases.

XRD characterization test results showed that: the crystallinity of the PVDF swelling film in the examples is reduced to a different extent than that of the PVDF nanoparticles (or PVDF nanoparticle film), but after phase inversion to form a nanoparticle array porous film, the crystallinity of PVDF is greatly increased again.

Further DSC characterization results (see FIG. 14) corroborate this conclusion by the various film endotherm peaks in the area integral plot and using the crystallinity expression

Wherein DeltaX _c For PVDF crystallinity, ΔH _f For melting enthalpy of the sample ΔH ₁₀₀ The melting enthalpy at a PVDF crystallinity of 100% was 104. J.g ^-1 The method comprises the steps of carrying out a first treatment on the surface of the As can be seen from the calculation, the crystallinity of PVDF swollen membranes is generally smaller than that of PVDF nanoparticle array porous membranes.

5. The membrane pore diameters, membrane thicknesses, membrane porosities and pore size distribution results of the PVDF nanoparticle array porous membranes in example 1 and examples 3 to 5 were tested, as shown in table 1; the pore size distribution of the membrane of the PVDF nanoparticle array porous membrane of example was tested using a capillary flow pore size analyzer, as shown in fig. 15, where a in fig. 15 is the pore size distribution of the membrane of the PVDF nanoparticle array porous membrane of example 5, b in fig. 15 is the pore size distribution of the membrane of the PVDF nanoparticle array porous membrane of example 4, c in fig. 15 is the pore size distribution of the membrane of the PVDF nanoparticle array porous membrane of example 3, and d in fig. 15 is the pore size distribution of the membrane of the PVDF nanoparticle array porous membrane of example 1.

TABLE 1 product parameters of PVDF nanoparticle array porous membranes in example 1, examples 3-5

As can be seen from table 1 and fig. 15: the PVDF nanoparticle array porous membrane finally prepared in the embodiment 1 and the embodiment 3-5 has concentrated membrane pore diameter distribution, and the pore diameters are 450-550 nm. And, the film thickness of the PVDF nanoparticle array porous membranes finally prepared in the embodiment 1 and the embodiment 3-5 is in the micron level, and the porosity is 19% -43%.

6. And (3) analyzing the characterization result, wherein the analysis process and the analysis result are as follows:

further, as shown in fig. 9 to 11, and in combination with fig. 2, FTIR, XRD, and DSC characterization test result analysis, it can be seen that: suction filtration with DMF does not result in dissolution of PVDF nanoparticles, but rather swelling thereof. In addition, as can be seen from the characterization results of fig. 9 to 11, the PVDF nanoparticle array film can be finally formed by combining the swelling and mechanical mixing processes.

In fact, the dissolution process of the crystalline polymer needs to firstly break the high molecular crystal phase to swell the high molecular crystal phase, and then the high molecular crystal phase and the solvent phase can be mixed to form the high molecular solution. In the next non-solvent phase conversion process (namely the process of adding water and suction filtration), the high-concentration region (rich phase) polymer with higher fluctuation concentration on the surface of the membrane generates heterogeneous nucleation growth of the seed crystal to form nano particles again, and the low-concentration region (lean phase) polymer cross links the nano particles with each other. The mechanical shaking and swelling process can lead the seed crystals to be evenly distributed, so that the distances among the nano particles on the formed film after the phase transformation are the same; since concentration fluctuations have a fixed wavelength during phase inversion and nanoparticle sizes are consistent with the wavelength, the finally formed nanoparticles have a regular size, and thus the nanoparticle array porous membrane can be finally formed.

As can be seen from the characterization results of fig. 6 to 8 and fig. 16, the preparation of the nanoparticle array film is sensitive to the participation of the high polymer solution in the phase inversion volume, and the reason is that when the participation volume is small, the nanoparticles cannot be closely and uniformly stacked on the surface of the film through suction filtration to form original defects, so that the finally formed array film has a large number of defects. When the participation volume is more, the DMF swelling nano particles are insufficient, the rubber state polymer cannot be completely mixed in the suction filtration process, the amplitude and the orientation of the concentration fluctuation of the membrane surface micro-area are changed, the nano particles are finally unevenly distributed, and the uneven phenomenon is more obvious along with the participation volume.

7. The membrane materials finally prepared in examples 1, 3 to 5 and comparative examples 1 to 5 were subjected to membrane performance test, and the specific membrane separation performance test method is as follows:

(1) The membranes finally prepared in examples 1, 3-5 and comparative examples 1-5 were subjected to four-stage filtration, and were run with deionized water for 15 min under a pressure of 1.0 bar to ensure the stability of the operating system; then, the membrane was tested for permeation with respect to pure water at a pressure of 1.0 bar (test time is 10min, each membrane was averaged after 3 passes at this pressure); finally, the pure water flux of the membrane is calculated by formula (I). The calculation formula of the actual value of pure water flux of the membrane is as follows:

Wherein:J _v pure water flux as membrane, unit: l/(m) ² ·h)；

VFor pure water at deltatOsmotic volume in time, unit: l is;

Afor effective separation area of membrane, m ² 。

(2) The entrapment rate of the film finally prepared in examples 1 to 5 on polyethylene microplastic pellets was tested in examples 3 to 5 by using simulated sewage containing fluorescence-labeled 700nm polyethylene microplastic (microsphere, concentration of 10 mg/L) respectively; wherein, the membrane to be tested needs to be pretreated by suction filtration with 200mL of ethanol before testing. The formula of the retention rate of the film to the micro plastic pellets is shown as formula (II):

wherein:Rrejection rate of the membrane,%;

C ₁ the concentration of the microplastic on the raw material side is as follows: mg/L;

C ₀ concentration of microplastic on permeation side, unit: mg/L;C ₁ andC ₀ all were obtained by a fluorescence spectrophotometer (model: RF-5301PC, manufacturer: shimadzu, origin: japan).

The results of the test of the membrane properties of the above porous membrane are shown in table 2 and fig. 17; a in fig. 17 is a graph of the results of the test of the actual permeability coefficient of the film obtained in example 1, and the results of the test of the actual and theoretical permeability coefficients of the films obtained in example 3, example 4 and example 5, and b in fig. 17 is a graph of the results of the test of the rejection rate of the film obtained in example 1, example 3, example 4 and example 5 against the 700nm diameter microplastic.

Table 2 preparation parameters and properties of PVDF nanoparticle array porous membranes in examples 1 to 5 and comparative examples 1 to 6, and PVDF nanoparticle membranes in comparative example 7

Note that: the polymer solution in Table 2 refers to DMF solution of PVDF; the porous film prepared in example 2 in table 2 had defects, was difficult to use for testing film properties, and was considered ineffective; comparative example 7 in table 2 produced PVDF nanoparticle films that were powder-packed structures and unstable and difficult to use for film performance testing, and were considered ineffective.

As can be seen from table 2 and fig. 17: from the Hagen-Poiseuille equation

(whereinJ, ε,r _p ,ΔP,μ,LPermeate flux, porosity, membrane pore size, transmembrane pressure difference, liquid viscosity and membrane thickness, respectively), the permeability coefficient of a membrane is directly related to the thickness, porosity, pore size of the membrane. Based on the actual flux of the membranes obtained in example 1, substituting these parameters into the calculations provided in table 2, it was found that the actual membrane permeation coefficients and theoretical results obtained in examples 3 to 5 were smaller, and the fluxes in examples 3, 4, and 5 were smaller by 38.45%,33.8%, and 14.45%, respectively. The reason for this is that the Hagen-Poiseuille equation treats the separation membrane channels as vertical cylindrical channels, whereas in reality the membrane channels are typically tortuous channels, thus the closer to theoretical the more uniform the membrane channels are.

For the theoretical value of a in fig. 17, it should also be noted that, because the membrane materials in the embodiment 1 of the present invention are PVDF, the hydrophilicity and hydrophobicity are relatively consistent, and the porous membranes in the embodiments 1 to 5 have certain tortuous pore paths, however, the influence caused by the tortuous pore paths cannot be quantitatively characterized in the prior art. For the above reasons, the membrane flux in the ideal case of example 1 is adopted, that is, the tortuosity degree of the membrane in example 1 is regarded as the ideal case, and whether other examples have the same tortuosity degree as that of example 1 is reversely deduced, so that the quantized calculation of the hydrophile-hydrophobic and tortuosity degree can be avoided, and the embodiment form is more visual. Therefore, the theoretical flux of other membranes is obtained by reversely pushing the flux obtained in the embodiment 1 as an ideal value, so as to illustrate that the pore channels in the PVDF nano-array porous membranes in the embodiment 1 and the embodiments 3-5 have similar or identical tortuosity.

Based on the film obtained in example 1, it was also found that the pore size distribution of the nanoparticle array film gradually became uniform as the volume of the polymer solution participating in phase inversion was reduced. From this, it can be proved that the preparation method of the invention can relatively controllably prepare a series of PVDF nano-particles with similar pore bending degree The rice grain array is a uniform pore membrane. Because the mass transfer resistance of the fluid in the membrane caused by the pore path tortuosity is effectively reduced, the actual measurement value of the permeability coefficient of the membrane is up to 14625 +/-53L m ^-2 ·h ^-1 ·bar ^-1 (a of FIG. 17). Meanwhile, fig. 17 b illustrates that the rejection rate of the membranes obtained in examples 1 and 3-5 on the microplastic with the average particle diameter of 700nm is about 99%, which shows that the PVDF nano-array porous membrane provided by the invention can completely reject microplastic pellets with the diameter of 700nm, and is suitable for water treatment, in particular for sewage treatment containing microplastic.

The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.

Claims

1. The preparation method of the PVDF nanoparticle array porous membrane is characterized by comprising the following steps of:

the preparation method of the PVDF nanoparticle array porous membrane further comprises the following steps: placing the PVDF nanoparticle array porous membrane in eluent for membrane removal, and then placing the PVDF nanoparticle array porous membrane in preservation solution for preservation;

wherein, the average molecular weight of the polyvinylidene fluoride in the step 1 is 0.3 MDa-0.5 MDa; the content of polyvinylidene fluoride in the polyvinylidene fluoride solution in the step 1 is 0.3g/100 mL-0.8 g/100mL;

the volume ratio of the polyvinylidene fluoride solution to the dispersion medium in the step 2 is (0.2-1.25) 100; the dropping speed of the polyvinylidene fluoride solution in the step 2 is 4-6 mL/min;

the organic solvent in the step 1 and the step 3 is at least one of N, N-dimethylformamide, N-methylpyrrolidone, dimethylacetamide and dimethyl sulfoxide; the dispersion medium in the step 2 and the step 3 is at least one of water, ethanol and acetone; and 3, the filter membrane used in the suction filtration is a nylon micro-filter membrane or a polytetrafluoroethylene micro-filter membrane.

2. The method for preparing the porous membrane of the PVDF nanoparticle array according to claim 1, wherein: the dissolution temperature in the step 1 is 50-70 ℃.

3. The method for preparing the porous membrane of the PVDF nanoparticle array according to claim 1, wherein: step 3, the particle size of the polyvinylidene fluoride nano particles in the polyvinylidene fluoride nano particle dispersion liquid is 100 nm-300 nm; and 3, the particle size of the polyvinylidene fluoride nano seed crystal in the swelling film is 1 nm-8 nm.

4. The method for preparing the porous membrane of the PVDF nanoparticle array according to claim 1, wherein: the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid to the organic solvent in the step 3 is (50-20) 1; and 3, the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid to the dispersion medium is 1 (0.8-1.5).

5. A PVDF nanoparticle array porous membrane made by the method of any of claims 1 to 4.

6. The PVDF nanoparticle array porous membrane of claim 5, wherein: the PVDF nanoparticle array porous membrane comprises beta-crystalline phase PVDF nanoparticles formed by the phase inversion of polyvinylidene fluoride nano seed crystals through seed crystal induction, and the beta-crystalline phase PVDF nanoparticles form a three-dimensional porous structure through seed crystal induction; the pore diameter of the PVDF nanoparticle array porous membrane is 300-500 nm.

7. Use of the PVDF nanoparticle array porous membrane of claim 5 or 6 in water treatment.