CN115869778A

CN115869778A - PVDF nano-particle array porous membrane and preparation method and application thereof

Info

Publication number: CN115869778A
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: 2023-03-31
Anticipated expiration: 2043-03-02
Also published as: CN115869778B

Abstract

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

Description

PVDF nano-particle array porous membrane and preparation method and application thereof

Technical Field

The invention relates to the technical field of membrane materials, and particularly relates to a PVDF nano-particle array porous membrane, a preparation method and an application thereof.

Background

With the increasing global level of industrialization, plastics are discharged into the ecological environment every year, and the plastics are broken and degraded in nature to form micro plastics. The toxic effect of the micro plastic particles is more prominent because of the tiny micro plastic particles and the strong adsorption property.

The membrane separation technology is one of the processing technologies commonly used in the field of environmental protection, the technology drives fluid to transmit across a porous separation membrane by pressure, and because the inner pore ruler of the membrane is generally in the nanometer level and smaller than the size of micro plastic, the micro plastic in a water body can not transmit across the membrane and is intercepted under the driving of the pressure, thereby realizing the purpose of micro plastic separation. In order to realize the high-efficiency separation of the micro-plastics, the type and the structure of the separation membrane are very important. At present, the common commercial separation membrane is an organic separation membrane, and has the problems of low through degree of pore channels in the membrane, nonuniform arrangement of membrane pores, low porosity and the like, so that the permeation flux of the membrane is less than 1000 L.m ^-2 ·h ^-1 ·bar ^-1 It is difficult to meet the large-scale processing requirements.

To solve the above problems, it is necessary to construct regular and uniform pores in the membrane. At present, the construction method of regular uniform pore channels in the membrane mainly comprises the following three methods: 1. the sacrificial template method is that polymer is poured into an anodic alumina template, and then the template is etched to obtain a separation membrane with regular and uniform pore passages in the membrane; 2. an ice template method, which is to assemble the membrane along the growth direction of ice crystals by using a dispersion medium and then freeze-dry the membrane to obtain a separation membrane with uniformly distributed pores; 3. and growing the carbon nano tube vertical array by chemical vapor deposition. Although the method can realize regular and uniform construction of the pore canal, the method has the defects of complex preparation process, various and expensive used raw materials, unstable mechanical property of the prepared membrane, wide pore size distribution range of the membrane, difficulty in effectively retaining micro-plastics in sewage and the like because other substances are required to be used as templates, and the practical application and popularization of the membrane are limited.

In addition, although the prior art CN114835944A discloses a preparation method of a self-sufficient energy-consumption type high-efficiency photothermal evaporation nanoparticle porous membrane, the preparation purpose of the self-sufficient energy-consumption type high-efficiency photothermal evaporation nanoparticle porous membrane is mainly used for a photothermal conversion system to convert light energy into heat energy. The application scenario of the energy-self-contained efficient photothermal evaporation nanoparticle porous membrane disclosed in CN114835944A is natural illumination conditions, and the membrane cannot bear high pressure and high shear force generated in the membrane separation process, and has no capability of resisting mechanical shear force, so that it cannot be applied to the interception and recovery treatment of micro-plastics.

Therefore, it is urgently needed to develop an organic membrane material with simple raw material composition, uniform and regular pore channels, simple and controllable preparation, low cost, large flux, good mechanical property 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 nano-particle array porous membrane with uniform pore channels, which has simple process, practicality and low cost;

the invention also aims to provide a PVDF nano particle array porous membrane which has simple composition, regular interval of polymer particles, uniform pore channels and large flux and can efficiently treat sewage containing micro-plastics;

the invention also aims to provide application of the PVDF nano particle array porous membrane.

The invention conception of the invention is as follows: based on the dissolution characteristics of the crystalline polymer PVDF, firstly, the steps of mechanical shaking and swelling are utilized to realize the partial dissolution of the polymer PVDF and the uniform distribution of the PVDF rubbery seed crystals; 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. Due to the preparation process of mechanical shaking and swelling and uniform distribution of PVDF seed crystals, the films with the same distance between the nano particles formed after phase inversion are formed; in addition, since the concentration fluctuation in the phase inversion process has a fixed wavelength and the size of the nanoparticles is consistent with the wavelength, the formed nanoparticles have a regular size, and thus the PVDF nanoparticle array film can be formed.

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

in a first aspect, the invention provides a preparation method of 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 a polyvinylidene fluoride solution into a dispersion medium to obtain a polyvinylidene fluoride nanoparticle dispersion liquid;

and step 3: carrying out suction filtration on the polyvinylidene fluoride nanoparticle dispersion liquid to obtain a PVDF nanoparticle film; adding an organic solvent into the PVDF nano-particle membrane, and performing suction filtration to obtain a PVDF swelling membrane; adding a dispersion medium into the PVDF swelling membrane, and performing 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 for suction filtration is a nylon microfiltration membrane or a polytetrafluoroethylene microfiltration membrane.

Preferably, the preparation method of the PVDF nanoparticle array porous membrane further comprises: the PVDF nano-particle array porous membrane is placed in an eluent (for example, ethanol) for stripping, and then placed in a preservation solution for preservation.

Specifically, the PVDF nano-particle membrane is prepared by preparing high-molecular PVDF into PVDF nano-particle dispersion liquid, and then carrying out suction filtration by adopting a solvent-resistant commercial substrate (namely a filter membrane); then, a proper amount of organic solvent is added and suction filtration is carried out, so that the macromolecule is converted to a rubber-like state, and the uniform distribution of crystal seeds is realized through mechanical uniform mixing and swelling, so that a swelling membrane is obtained; adding a non-solvent (namely the dispersion medium, such as water) and performing suction filtration through PVDF seed crystal induction to perform phase transformation on the rubber-like PVDF polymer to obtain 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, then allowing the nanoparticle array membrane to fall off spontaneously, taking out the nanoparticle array membrane, and storing the nanoparticle array membrane in ethanol for later use (so as to obtain the PVDF nanoparticle array porous membrane).

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

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

Preferably, the demoulding time is 10-15 hours.

Further preferably, the time for demoulding is 12 hours.

Specifically, the time of placing in the eluent is designed to completely elute the PVDF nanoparticle array porous membrane on the filter membrane after suction filtration; and the PVDF nano-particle array porous membrane is placed in an eluent, so that the prepared regular pore channel structure is protected, and the porous membrane obtained by the preparation process does not need to be dried (the production energy consumption is saved), and is convenient to popularize and apply on a large scale.

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

Further preferably, the polyvinylidene fluoride of step 1 has an average molecular weight of 0.4 MDa.

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

Further preferably, the dissolving temperature of the step 1 is 55-65 ℃.

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

More preferably, the polyvinylidene fluoride solution in the step 1 has a polyvinylidene fluoride content of 0.5g/100mL to 0.7g/100mL.

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

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

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

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

Specifically, step 1 is to dissolve the high molecular weight polyvinylidene fluoride in the organic solvent under heating conditions (55-65 ℃), so as to be more beneficial to dissolving the polyvinylidene fluoride. If the high molecular 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 speed of the polyvinylidene fluoride solution in the step 2 is 4 mL/min-6 mL/min.

Further preferably, the dropping rate of the polyvinylidene fluoride solution in the step 2 is 5mL/min.

Preferably, the particle size of the polyvinylidene fluoride nanoparticles in the polyvinylidene fluoride nanoparticle dispersion liquid in the step 3 is 100 nm to 300nm.

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

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

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

Further preferably, the dosage of the polyvinylidene fluoride nanoparticle dispersion liquid in the step 3 is 150 mL-250 mL.

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

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

Preferably, the filter membrane is circular or square.

Preferably, the aperture of the filter membrane is 100 nm to 600 nm.

More preferably, the aperture 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 to 60mm.

Still more preferably, the filter membrane is a circular polytetrafluoroethylene commercial microfiltration membrane, the diameter of the membrane is 50mm, and the pore size of the membrane is 0.22 μm. Specifically, the manufacturer is Tianjin Jinteng laboratory equipments Ltd.

Preferably, the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid in the step 3 to the organic solvent 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 to 1.5).

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

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

Preferably, the thickness of the PVDF nano-particle membrane in the step 3 is 1-14 μm.

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

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

Specifically, the seed crystal induced phase transformation means that partial dissolution and mechanical uniform mixing of PVDF nano particles can be realized by adding different solvents and suction filtration, the seed crystals are uniformly distributed and swelled on a filter membrane to form rubber-like polyvinylidene fluoride nano seed crystals, so that a PVDF swelling membrane can be obtained, and then the PVDF nano particle array porous membrane is obtained under the action of seed crystal induced phase transformation, wherein the PVDF nano particle array porous membrane has a three-dimensional porous structure.

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

Preferably, the membrane pore diameter of the PVDF nano particle array porous membrane is 300nm to 500 nm.

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

In a third aspect, the invention provides an application of the PVDF nano particle array porous membrane in water treatment.

Preferably, the water treatment is sewage treatment containing micro-plastics.

Preferably, the particle size of the micro plastic in the micro plastic-containing sewage is 680nm to 1.5 μm.

Preferably, the micro plastic 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 650 L.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 the PVDF nano-particle array porous membrane is pretreated by ethanol, the pure water flux is set to 1733 +/-17 L.m ^-2 ·h ^-1 ·bar ^-1 ~14625±53 L·m ^-2 ·h ^-1 ·bar ^-1 And treating the sewage containing the micro-plastics with the concentration of 5-15 mg/L.

Specifically, the pretreatment is suction filtration.

The invention has the beneficial effects that: the preparation method of the PVDF nano-particle array porous membrane has the advantages of few raw material types, simple preparation process, controllability and low cost, can prepare the PVDF nano-particle array porous membrane with regular pore passages and high efficiency of retaining micro-plastics without using additional raw materials as a template, and is suitable for mass production and application. The method specifically comprises the following steps:

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

(2) Based on the dissolution characteristic of the crystalline polymer, the invention uses PVDF crystalline polymer nano particles on the surface of the membrane as the basis, and adopts a good polymer solvent to partially swell the nano particles, so as to excite the polymer chain segments to move synergistically on the premise of keeping the partial crystalline structure (seed crystal) in the nano particles, and further to uniformly distribute the seed crystal on the surface of the membrane through mechanical action. And then the concentration of the rubbery polymer fluctuates by using a non-solvent induced phase inversion technology induced by the seed crystal, the polymer in a region with higher concentration (rich phase) grows to form nano particles again through heterogeneous nucleation of the seed crystal, and the nano particles are mutually crosslinked by the polymer in a region with lower concentration (poor phase). Because the seed crystals are uniformly distributed in the swelling and mechanical processes, the distance between the nano-particles formed after phase inversion is the same; since the concentration fluctuation during the phase inversion has a fixed wavelength and the size of the nanoparticles coincides with the wavelength, the nanoparticles have a regular size, thereby forming a nanoparticle array film.

(3) Based on the mature phase transformation and heterogeneous nucleation theory, the invention designs a simple and practical PVDF nanoparticle array homogeneous pore membrane, and the retention rate of the membrane on micro-plastics can reach 99% or more.

Drawings

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

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

Fig. 3 is a schematic representation of the PVDF nanoparticle array porous membrane in example 1.

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

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

FIG. 6 is an SEM photograph of porous PVDF nanoparticle array membranes obtained by phase inversion in examples 1 and 3 to 5.

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

FIG. 8 is a SEM (scanning Electron microscope) view of the cross-sectional surface 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 comparative example 1 in which a swollen film is obtained during mechanical mixing and swelling.

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

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

FIG. 12 is a Fourier infrared spectrum of PVDF nanoparticle array porous membranes in example 1 and comparative example 1.

FIG. 13 is X-ray diffraction patterns of PVDF nanoparticle array porous membranes obtained in examples 1, 3 to 5 and comparative examples 1 to 4 and PVDF nanoparticle membranes obtained in comparative example 7.

FIG. 14 is a DSC chart of the porous PVDF nanoparticle array membranes of examples 1, 3 to 5 and comparative examples 1 to 4.

FIG. 15 is a graph showing a pore size distribution of a PVDF nanoparticle array porous membrane in examples 1 and 3 to 5.

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

Fig. 17 is a graph showing the performance of the PVDF nanoparticle array porous membrane 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.

It should be noted that the commercial basement membrane used in the examples and comparative examples was a commercial Polytetrafluoroethylene (PTFE) microfiltration membrane purchased from tianjingtze experimental facilities ltd, and the diameter of the microfiltration membrane was 50mm, and the pore size of the membrane was 0.22 μm; the mechanical mixing and swelling and the uniform distribution of the seed crystals are realized by the process of adding DMF solvent into the PVDF nano-particle membrane, and performing complete suction filtration to obtain the PVDF swelling membrane; the phase inversion and seed crystal induced film formation technology in the invention refer to the process of adding deionized water into the PVDF swelling film, and performing suction filtration to obtain the PVDF nano-particle array porous film.

If not specifically stated, the process of preparing the PVDF nano-particle array porous membrane by the conversion method can be carried out at room temperature, and the room temperature refers to 15-35 ℃; the ethanol content in the "ethanol soak" in the inventive examples and comparative examples was about 98wt%; the ethanol content "preserved in ethanol" in the inventive examples and comparative examples was about 75wt%.

Example 1

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

(1) And (3) synthesizing PVDF nano particles:

adding 0.6 g of polyvinylidene fluoride with the average molecular weight of 0.4 MDa into 100mL of N, N-Dimethylformamide (DMF) solvent, heating the mixture to 60 ℃ by using an oil bath, dissolving the mixture for 2 hours at the temperature of 60 ℃ and at the speed of 150 rpm, and cooling the mixture to room temperature to obtain a DMF solution of PVDF;

0.5mL of PVDF DMF solution is dripped into 200mL of deionized water, the dripping speed is controlled to be 5mL/min, and the stirring is continuously carried out at the same time, so as to obtain a PVDF nanoparticle dispersion liquid;

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

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

s2, adding 5mL of DMF solvent into the PVDF nano-particle membrane, and carrying out complete suction filtration to obtain a PVDF swelling membrane;

s3, adding 200mL of deionized water into the PVDF swelling membrane, and performing suction filtration to obtain a PVDF nano-particle array porous membrane with a commercial substrate (a commercial PTFE microfiltration membrane is used as the substrate);

s4, soaking the PVDF nano-particle array porous membrane with the commercial substrate in ethanol, standing for 12 hours to enable the PVDF nano-particle array average pore membrane to fall off spontaneously, and taking out to obtain the PVDF nano-particle array porous membrane (stored in the ethanol for later use);

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

The PVDF swollen membrane and the PVDF nanoparticle array porous membrane in this example both include a β crystal phase for the PVDF nanoparticles.

Example 2

This example provides a preparation method of PVDF nanoparticle array porous membrane, which is different from example 1 only in that: the amount of PVDF in DMF was replaced with 0.2mL, and the method comprises the following steps:

(1) And (3) synthesizing PVDF nano particles:

0.2mL of PVDF DMF solution is dripped into 200mL of deionized water, the dripping speed is controlled to be 5mL/min, and the stirring is continuously carried out at the same time, so as to obtain a PVDF nanoparticle dispersion liquid;

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

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

It should be noted that this example is provided for the purpose of comparison with example 1, but is described as an example since it also involves the processes of mechanical shaking and swelling, seed crystal induced phase inversion, and both the PVDF swollen membrane and the PVDF nanoparticle array porous membrane in this example include the PVDF nanoparticle in the β crystal phase.

Example 3

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

Example 4

This example provides a preparation method of PVDF nanoparticle array porous membrane, which is different from example 1 only in that: the amount of PVDF in DMF was replaced with 1.0 mL, and the procedure was the same as in example 1.

Example 5

This example provides a preparation method of PVDF nanoparticle array porous membrane, which is different from example 1 only in that: the amount of PVDF in DMF was replaced with 2.0mL, and the procedure was the same as in example 1.

Comparative example 1

This comparative example provides a method for preparing a PVDF nanoparticle array porous membrane, which is different from example 1 only in that: directly obtaining a PVDF swelling film, directly putting the film into a 60 ℃ blast oven to dry for 30 minutes to form a film, and storing the film in ethanol for later use after film formation, namely, the process does not carry out phase inversion, and comprises the following steps:

(1) And (3) synthesizing PVDF nano particles:

(2) PVDF nanoparticle array porous membrane process:

s1, taking a commercial PTFE microfiltration 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 nano-particle membrane, and performing complete suction filtration to obtain a PVDF swelling membrane with a commercial substrate (a commercial PTFE microfiltration membrane is used as a substrate);

s3, putting the PVDF swelling membrane into a 60 ℃ blast oven to dry for 30 minutes to form a membrane, and obtaining the PVDF nano-particle array porous membrane (after the membrane is formed, storing the membrane in ethanol for later use);

Comparative example 2

This comparative example provides a method for preparing a PVDF nanoparticle array porous membrane, which is different from example 3 only in that: and (2) directly obtaining a PVDF swelling membrane, directly putting the PVDF swelling membrane into a 60-DEG C forced air oven for drying for 30 minutes to form a membrane, and storing the membrane in ethanol for later use after membrane formation, namely, the process does not carry out phase inversion, and the rest steps are the same as those in the example 3.

Comparative example 3

This comparative example provides a method for preparing a PVDF nanoparticle array porous membrane, which is different from example 4 only in that: and (2) directly obtaining a PVDF swelling membrane, directly putting the PVDF swelling membrane into a 60-DEG C forced air oven for drying for 30 minutes to form a membrane, and storing the membrane in ethanol for later use after the membrane is formed, namely, the process does not carry out phase inversion, and the rest steps are the same as those in the example 4.

Comparative example 4

The present comparative example provides a preparation method of a PVDF nanoparticle array porous membrane, which is different from example 5 only in that: and (2) directly obtaining a PVDF swelling membrane, directly putting the PVDF swelling membrane into a 60-DEG C forced air oven for drying for 30 minutes to form a membrane, and storing the membrane in ethanol for later use after the membrane is formed, namely, the process does not carry out phase inversion, and the rest steps are the same as those in the example 5.

Comparative example 5

The present comparative example provides a preparation method of a PVDF nanoparticle array porous membrane, which is different from example 1 only in that: in the step (2), soaking the nanoparticle membrane in 5mL of DMF solvent for 10 minutes to obtain a PVDF swelling membrane; then, performing suction filtration (the vacuum pressure of suction filtration is 0.8 bar) on 200mL of deionized water by using a PVDF swelling membrane to obtain a PVDF membrane with a commercial substrate; and finally, soaking the PVDF membrane with the commercial substrate (PTFE commercial microfiltration membrane) into ethanol, standing for 12 h to enable the membrane to fall off spontaneously, taking out the membrane and storing the membrane in the ethanol for later use, namely, the process does not carry out the process of mechanically mixing the high polymers, and specifically comprises the following steps:

(1) And (3) synthesizing PVDF nano particles:

0.5mL of a PVDF DMF solution is dripped into 200mL of deionized water, the dripping speed is controlled to be 5mL/min, and the solution is continuously stirred at the same time to obtain a PVDF nanoparticle dispersion solution;

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

s4, soaking the PVDF nano-particle array porous membrane with the commercial substrate in ethanol, standing for 12 hours to enable the PVDF nano-particle array uniform pore membrane to fall off spontaneously, and taking out to obtain the PVDF nano-particle array porous membrane (stored in ethanol for later use);

Comparative example 6

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

(1) And (3) synthesizing PVDF nano particles:

dropwise adding 2.0mL of PVDF DMF solution into 200mL of deionized water, controlling the dropwise adding speed to be 5mL/min, and continuously stirring to obtain a PVDF nanoparticle dispersion liquid;

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

Comparative example 7

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

(1) And (3) synthesizing PVDF nano particles:

dropwise adding 2.0mL of PVDF DMF solution into 200mL of deionized water, controlling the dropwise adding rate to be 5mL/min, and continuously stirring to obtain a PVDF nanoparticle dispersion liquid;

(2) Preparation of PVDF nano-particle membrane:

and (3) carrying out suction filtration by using a commercial PTFE microfiltration membrane (the vacuum pressure of suction filtration is 0.8 bar) to obtain 200mL of the PVDF nanoparticle dispersion liquid prepared in the step (1), putting the PVDF nanoparticle dispersion liquid into a 60-DEG C forced air oven for drying for 30 minutes to form a film, and removing the commercial PTFE microfiltration membrane to obtain the PVDF nanoparticle film (which is stored in the air after the film is formed).

Characterization and performance analysis:

1. a Transmission Electron Microscope (TEM) image of the PVDF nanoparticle prepared in the example of the present invention is shown in fig. 5. A schematic flow chart of preparation of the PVDF nanoparticle array porous membrane in example 1 is shown in fig. 1; example 1 Scanning Electron Microscope (SEM) images of the PVDF nanoparticle membrane, the swollen membrane, and the phase-converted PVDF nanoparticle array porous membrane prepared in the preparation process are shown in fig. 2, wherein a in fig. 2 is an SEM image of the PVDF nanoparticle membrane in example 1, b in fig. 2 is an SEM image of the swollen membrane in example 1, and c and d in fig. 2 are SEM images of the phase-converted PVDF nanoparticle array porous membrane 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 the preparation procedure of example 1. Based on the dissolution characteristic of crystalline polymer PVDF, a PVDF nanoparticle membrane (see a in figure 2) formed by accumulating nanoparticles (see figure 5) is prepared by suction filtration of a commercial basement membrane and a PVDF nanoparticle dispersion liquid with proper concentration; then, N-Dimethylformamide (DMF) and suction filtration are added into the PVDF nano-particle membrane, so that partial PVDF particle dissolution and uniform distribution of macromolecular PVDF can be realized on one hand under the action of N, N-dimethylformamide (DMF, a good solvent of PVDF) and suction filtration, and further the mechanical uniform mixing and swelling process (see b in figure 2) are realized to prepare a swelling membrane, and partial dissolution can realize uniform distribution of PVDF small particles which can be used as seed crystals, namely, good conditions can be created for realizing the membrane formation of the seed crystal induced phase conversion technology; then, water is added into the swelling membrane, and in the process, the PVDF seed crystals are utilized to perform membrane formation through a seed crystal induced phase inversion technology under the action of low solubility and suction filtration in an aqueous solvent system, so that equidistant distribution and crosslinking of uniform-size nanoparticles in the membrane are realized, and the PVDF nanoparticle array membrane can be constructed (see c and d in figure 2).

It is emphasized that the mechanical mixing and swelling process, and the step of uniform distribution of the polymer seed crystal are very critical in the present invention, so that the distance between the nanoparticles formed after phase inversion is basically the same structure; 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 the final phase inversion and the seed crystal induction have regular size, and further the final PVDF nano particle array film is formed.

Example 1 Scanning Electron Microscope (SEM) images of the PVDF nanoparticle film, the swollen film, and the phase-inverted PVDF nanoparticle array porous film obtained in the preparation process are shown in fig. 2. Assembling nanoparticles on the surface of PFTE commercial nanofilm by suction filtration method, it can be found that nanoparticles are accumulated on the film surface (see a in fig. 2); after DMF (PVDF good solvent) is adopted for suction filtration of the PTFE commercial membrane surface nanoparticles (see b in figure 2), the membrane surface is smooth and uniform, and the structure of the previously observed membrane surface nanoparticles disappears, which indicates that the nanoparticles are swelled after DMF suction filtration; finally, the swollen nanoparticle membrane was suction filtered with water (a nonsolvent for PVDF) (c and d in fig. 2), and the membrane surface was found to produce a regularly arranged PVDF nanoparticle array.

Meanwhile, the finally prepared membrane in comparative example 1 can reflect the features of the morphology and material composition of the swollen membrane in example 1, so that the TEM image of the swollen membrane obtained in the test of comparative example 1 in the mechanical mixing and swelling process is shown in fig. 9, wherein a and b in fig. 9 are TEM images of the swollen membrane of comparative example 1 measured at different magnifications, respectively.

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

Meanwhile, although the surface of the swollen membrane prepared by the mechanical shaking and swelling processes is uniform and smooth, the high-power TEM representation can still find that a large number of nano particles are uniformly distributed on the surface and in the swollen membrane, and the nano particles are polyvinylidene fluoride nano crystal seeds with the diameter of about 5nm (see figure 9). The particles are seed crystals which appear in the membrane after mechanical shaking and swelling treatment, and the seed crystals enable the membrane to have certain crystallinity after swelling, and can lay a foundation for the subsequent phase inversion induced crystallization membrane forming.

Based on the characterization results, the preparation process of the PVDF nano-particle array porous membrane is consistent with the inventive concept of the invention, which shows that the PVDF nano-particle array porous membrane, even the PVDF nano-particle array homogeneous pore membrane, can be prepared by the control of the integral preparation method.

2. Fig. 3 and 4 show an entity diagram and an SEM diagram of the PVDF nanoparticle array porous membrane in example 1, respectively. SEM pictures of the PVDF nanoparticle array porous membranes after phase inversion in examples 1 and 3 to 5, as shown in fig. 6, a in fig. 6 is an SEM picture of the PVDF nanoparticle array porous membrane in example 1, b in fig. 6 is an SEM picture of the PVDF nanoparticle array porous membrane in example 3, c in fig. 6 is an SEM picture of the PVDF nanoparticle array porous membrane in example 4, and d in fig. 6 is an SEM picture of the PVDF nanoparticle array porous membrane in example 5; an SEM image of the PVDF nanoparticle array porous membrane after phase inversion in example 2 is shown in fig. 7. The cross-sectional SEM images of the PVDF nanoparticle array porous membranes after phase inversion in the examples 1 and 3 to 5 are shown in FIG. 8; wherein, a 'and a' are cross-sectional SEM images of the PVDF nano-particle 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 SEM images of the cross section of the PVDF nanoparticle array porous membrane obtained in example 5.

As can be seen from fig. 2, 3, 4, 6, 7 and 8: the size of the nano particles in the array porous film finally obtained in the embodiment 1 and the embodiments 3 to 5 is uniform, and the whole film is transparent, complete and round. Further, the thicknesses of the array porous films finally obtained in examples 1 and 3 to 5 were 1.94 μm,3.75 μm,5.41 μm and 11.33 μm, respectively, as can be seen from the sectional SEM photograph; the pore diameter of the membrane is about 400nm to 550nm.

Moreover, by testing the morphology of the PVDF nano-particle array porous membrane in different embodiments through SEM, it can be found that the surface morphology of the porous membrane is closely related to the volume of the polymer solution participating in phase inversion (abbreviated as participating in phase inversion volume, the same below); when the volume participating in phase inversion is small, the PVDF nanoparticle array porous membrane (i.e., the porous membrane in example 2, see fig. 7) has a large number of defects on the surface and the nanoparticles are not uniformly distributed; when the volume participating in phase inversion is large (examples 3 to 5, see fig. 8), the nanoparticles of the PVDF nanoparticle array porous membrane are located on the surface of the membrane and show a small amount of maldistribution, but the PVDF nanoparticle array porous membrane for water treatment can still be formed.

Further analysis shows the relationship between the volume of the polymer solution participating in the phase transformation and the film thickness in examples 1 and 3 to 5, as shown in FIG. 16.

As can be seen from fig. 16: because the invention adopts the suction filtration nano particles as a basic method, the invention can regulate the film thickness by regulating the amount of the nano particles. Meanwhile, the film thicknesses obtained in example 2, example 1 and examples 3 to 5 were 1.94 μm,3.75 μm,5.41 μm and 11.33 μm, respectively; by analysis, the linear fitting curve equation obtained by the analysis software is as follows:

y = -1.11623+6.25464x, and the correlation coefficient is R ² 0.99795, which indicates that the participating volume is approximately linear with the thickness of the PVDF nanoarray porous membrane (see fig. 16).

3. An SEM image of the PVDF nanoparticle array porous membrane in comparative example 5, as shown in fig. 10, wherein a and a' in fig. 10 represent SEM images of the PVDF nanoparticle array porous membrane in comparative example 5 at different magnifications; an SEM image of the PVDF nanoparticle array porous membrane in comparative example 6 is shown in fig. 11, where a and a' in fig. 11 are SEM images of the PVDF nanoparticle array porous membrane in comparative example 6 at different magnifications.

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

4. Fourier Transform ion conductivity response (FTIR) plots 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 film obtained in examples 1, 3 to 5 and 1 to 4 and the PVDF nanoparticle film in comparative example 7 are shown in FIG. 13, wherein a in FIG. 13 is the XRD pattern of the PVDF nanoparticle array porous film in example 5, the swollen film in comparative example 4 and the PVDF nanoparticle film in comparative example 7, b in FIG. 13 is the XRD pattern of the swollen film obtained in comparative examples 1 to 4, and c in FIG. 13 is the XRD pattern of the PVDF nanoparticle array porous film obtained in examples 1, 3 to 5 and the XRD pattern of the PVDF nanoparticle array porous film obtained in examples 1, 3 to 5.

The thermal Differential Scanning (DSC) graphs of the porous films of the PVDF nano-particle arrays in the examples 1, 3 to 5 and the comparative examples 1 to 4 are shown in FIG. 14; wherein, a in FIG. 14 shows that the film obtained in example 1 and comparative example 1 ranges from 130 to 220 ^O DSC curve under C, b in figure 14 shows that the films obtained in example 3 and comparative example 2 are in 130-220 ^O DSC chart under C, wherein C in figure 14 shows that the films obtained in example 4 and comparative example 3 are in 130-220 ^O DSC chart under C, and d in FIG. 14 represents that the films obtained in example 5 and comparative example 4 are in the range of 130 to 220 ^O DSC plot under C.

As can be seen from fig. 12, 13 and 14: the FTIR results show that: the PVDF nano-particle array porous membrane and the swelling membrane are 840 cm ^-1 There is an absorption peak, which is a characteristic peak of the beta crystal phase of typical PVDF. The alpha crystal phase characteristic absorption peak of PVDF should appear at 766 cm ^-1 At least one of (1) and (b); however, the FTIR results of the present invention show that the corresponding characteristic absorption peaks of both films are not found, thereby demonstrating that the PVDF nanoparticle array porous film and the swollen film of the present invention have crystalline structures, and both have a β crystalline phase.

XRD characterization test results show that: the crystallinity of the PVDF swollen membrane in the examples is reduced to a different degree compared to that of the PVDF nanoparticle (or PVDF nanoparticle membrane), and after the PVDF swollen membrane is phase-converted to form the nanoparticle array porous membrane, the crystallinity of the PVDF is greatly increased again.

Further DSC characterization results (see FIG. 14) confirm this conclusion by area integration of various membrane endotherms and using the crystallinity expression

Wherein Δ X _c Is the degree of PVDF crystallinity,. DELTA.H _f Is the enthalpy of fusion, Δ H, of the sample ₁₀₀ The melting enthalpy of the PVDF at 100% crystallinity is 104.6 J.g ^-1 (ii) a The calculation shows that the crystallinity of the PVDF swelling film is generally smaller than that of the PVDF nano-particle array porousAnd (3) a membrane.

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

TABLE 1 production parameters of PVDF nanoparticle array porous membranes in example 1 and examples 2 to 5

As can be seen from table 1 and fig. 15: the PVDF nano-particle array porous membrane finally prepared in the embodiment 1 and the embodiments 3 to 5 of the invention has centralized membrane aperture distribution, and the aperture is 450nm to 550nm. Moreover, the film thicknesses of the PVDF nano-particle array porous films finally prepared in the embodiments 1 and 3 to 5 are micron-sized, and the porosity is 19 to 43 percent.

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

further, as shown in FIGS. 9 to 11, in conjunction with FIG. 2, the results of FTIR, XRD and DSC characterization tests are analyzed: suction filtration with DMF did not lead to dissolution of the PVDF nanoparticles, but rather swelled them. In addition, as can be seen from the characterization results shown in fig. 9 to 11, the PVDF nanoparticle array film can be finally formed only by combining the swelling and mechanical mixing processes.

In fact, in the dissolving process of the crystalline polymer, firstly a macromolecule crystal phase is broken to swell, and then the crystalline phase and the solvent are mixed to form a macromolecule solution. In the following non-solvent phase inversion process (i.e. the process of adding water and filtering), the high-concentration (rich phase) polymer in the region where the concentration of the rubbery polymer on the surface of the membrane fluctuates grows to form the nanoparticles again through the heterogeneous nucleation of the seed crystal, and the nanoparticles are mutually crosslinked by the low-concentration (poor phase) polymer. Because the seed crystals can be uniformly distributed in the mechanical shaking and swelling processes, the distance between the nano-particles on a formed film after phase conversion is the same; because the concentration fluctuation in the phase inversion process has fixed wavelength, and the size of the nano particles is consistent with the wavelength, the finally formed nano particles have regular size, and further the nano particle array porous membrane can be finally formed.

The characterization results shown in fig. 6 to 8 and fig. 16 show that the preparation of the nanoparticle array film is sensitive to the volume of the polymer solution participating in phase inversion, and the reason is that when the volume of the nanoparticle array film is small, the nanoparticles cannot be tightly and uniformly accumulated 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 participating volume is large, the degree of DMF swelling nano particles is insufficient, the rubbery polymer cannot be completely mixed in the suction filtration process, the amplitude and orientation of the concentration fluctuation of a film surface micro-area are changed, and finally the phenomenon that the nano particles are unevenly distributed and are uneven along with the increase of the participating volume is more obvious.

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

(1) Respectively carrying out four-stage filtration on the finally prepared membranes in the embodiments 1, 3 to 5 and 1 to 5, and firstly running for 15 min by using deionized water under the pressure of 1.0 bar to ensure the stability of an operating system; then, the permeation amount of the membranes with respect to pure water was tested under a pressure of 1.0 bar (test time 10min, each membrane was averaged after 3 passes of the test at that pressure); finally, the pure water flux of the membrane was calculated by formula (I). The calculation formula of the actual value of pure water flux of the membrane is as follows:

in the formula:J _v pure water flux for the membrane, unit: l/(m) ² ·h)；

VIs pure water at deltatPermeate volume over time, unit: l;

Ais the effective separation area of the membrane, m ² 。

(2) Respectively testing the retention rate of the film finally prepared in examples 1, 3 to 5 and comparative examples 1 to 5 on polyethylene micro-plastic beads by using simulated sewage containing fluorescent-labeled 700nm polyethylene micro-plastic (microspheres with the concentration of 10 mg/L); wherein, the pretreatment of suction filtration of the membrane to be tested by 200mL of ethanol is required before the test. The calculation formula of the retention rate of the membrane to the micro plastic beads is shown as the formula (II):

in the formula:Rretention of membrane,%;

C ₁ the concentration of the micro-plastic on the raw material side, unit: mg/L;

C ₀ concentration of the micro-plastic on the permeate side, unit: mg/L;C ₁ andC ₀ were measured using a fluorescence spectrophotometer (model: RF-5301PC, manufactured by Shimadzu, manufactured by Kogyo, japan).

The results of the film properties test of the above porous film are shown in table 2 and fig. 17; fig. 17 a is a graph showing the results of testing the actual permeability coefficient of the membrane obtained in example 1, and the results of testing the actual and theoretical permeability coefficients of the membranes obtained in examples 3, 4 and 5, and fig. 17 b is a graph showing the results of testing the rejection rate of the membranes obtained in examples 1, 3, 4 and 5 to the micro plastic with a diameter of 700 nm.

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: the polymer solution in Table 2 refers to a DMF solution of PVDF; the porous film prepared in example 2 of table 2 had defects and was difficult to use for the film property test, and was therefore regarded as ineffective; comparative example 7 in table 2 produced a PVDF nanoparticle membrane, which was a powder packed structure and was unstable and difficult to use in testing the membrane performance, and was considered ineffective.

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

(whereinJ, ε,r _p ,ΔP,μ,LRespectively, permeate flux, porosity, membrane pore size, transmembrane pressure difference, liquid viscosity, and membrane thickness), the permeability coefficient of a membrane is directly related to the thickness, porosity, and pore size of the membrane. As provided in table 2, based on the actual flux of the membrane obtained in example 1, substituting these parameters into the calculation results revealed that the permeability coefficients of the membranes obtained in examples 3 to 5 were smaller than the theoretical permeability coefficients, and the fluxes of examples 3, 4, and 5 were smaller than 38.45%,33.8%, and 14.45%, respectively. This is due to the fact that the Hagen-Poiseuille equation treats the channels in the separation membrane as vertical cylindrical channels, whereas the channels in the membrane are generally tortuous and therefore closer to the theoretical value, the more uniform the channels of the membrane.

It should be further noted that, for the theoretical value a in fig. 17, the membrane materials in example 1 of the present invention are all PVDF, and the hydrophilicity and hydrophobicity of the PVDF are relatively consistent, and the porous membranes in examples 1 to 5 have certain tortuous channels, however, the influence of the tortuous channels cannot be quantitatively characterized in the prior art. Based on the above reasons, the flux of the membrane in the ideal case is adopted in example 1, that is, the tortuosity of the membrane in example 1 is regarded as the ideal case to reversely deduce whether the tortuosity of other examples has the same tortuosity as example 1, so that quantitative calculation of hydrophilicity and hydrophobicity and tortuosity can be avoided, and the embodiment form is more intuitive. Therefore, the theoretical flux of other membranes is obtained by reverse extrapolation by taking the flux obtained in example 1 as an ideal value, so as to illustrate that the pore channels in the PVDF nano-array porous membranes in examples 1 and 3 to 5 have similar or identical tortuosity.

Based on the membrane obtained in example 1, it can also be found that the pore size distribution of the nanoparticle array membrane gradually becomes uniform as the volume of the polymer solution participating in phase inversion decreases. Therefore, the preparation method can relatively controllably prepare a series of PVDF nano-particle array homogeneous-pore membranes with similar pore canal bending degrees. Because the mass transfer resistance of fluid in the membrane caused by the tortuous pore channels is effectively reduced, the measured value of the permeability coefficient of the membrane is up to 14625 +/-53 L.m ^-2 ·h ^-1 ·bar ^-1 (a of FIG. 17). Meanwhile, b of fig. 17 illustrates that the membranes obtained in examples 1 and 3 to 5 have about 99% rejection rate for the micro plastic with the average particle size of 700nm, which indicates that the PVDF nano array porous membrane of the invention can completely reject micro plastic pellets with the diameter of 700nm, and is suitable for water treatment, especially for the treatment of sewage containing the micro plastic.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a PVDF nano particle array porous membrane is characterized by comprising the following steps:

and 2, step: dripping a polyvinylidene fluoride solution into a dispersion medium to obtain a polyvinylidene fluoride nanoparticle dispersion liquid;

2. The method for preparing the PVDF nanoparticle array porous membrane as described in claim 1, wherein: the preparation method of the PVDF nano particle array porous membrane also comprises the following steps: and (3) placing the PVDF nano-particle array porous membrane in eluent for demoulding, and then placing the PVDF nano-particle array porous membrane in preserving fluid for preserving.

3. The method for preparing the PVDF nanoparticle array porous membrane as described in claim 1 or 2, wherein: the average molecular weight of the polyvinylidene fluoride in the step 1 is 0.3 MDa-0.5 MDa; the content of the polyvinylidene fluoride in the polyvinylidene fluoride solution in the step 1 is 0.3g/100mL to 0.8g/100mL.

4. The method for preparing the PVDF nanoparticle array porous membrane as described in claim 3, wherein: the dissolving temperature in the step 1 is 50-70 ℃.

5. The method for preparing the PVDF nanoparticle array porous membrane as described in claim 3, wherein: the volume ratio of the polyvinylidene fluoride solution in the step 2 to the dispersion medium is (0.2 to 1.25): 100; and (3) the dropping speed of the polyvinylidene fluoride solution in the step (2) is 4-6 mL/min.

6. The method for preparing the PVDF nanoparticle array porous membrane as described in claim 1 or 2, wherein: the particle size of the polyvinylidene fluoride nano particles in the polyvinylidene fluoride nano particle dispersion liquid in the step 3 is 100 nm to 300nm; and 3, the particle size of the polyvinylidene fluoride nano crystal seed in the swelling film is 1nm to 8nm.

7. The method for preparing the PVDF nanoparticle array porous membrane according to claim 1 or 2, wherein: the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid to the organic solvent in the step 3 is (50-20) to 1; the volume ratio of the polyvinylidene fluoride nanoparticle dispersion liquid to the dispersion medium in the step 3 is 1 (0.8-1.5).

8. A PVDF nanoparticle array porous membrane produced by the production method according to any one of claims 1 to 7.

9. The porous PVDF nanoparticle array membrane of claim 8, wherein: the PVDF nano particle array porous membrane comprises PVDF nano particles of a beta crystalline phase formed by polyvinylidene fluoride nano crystal seeds through seed crystal induced phase conversion, and the PVDF nano particles of the beta crystalline phase form a three-dimensional porous structure through seed crystal induction; the membrane aperture of the PVDF nano particle array porous membrane is 300 nm-500 nm.

10. Use of the PVDF nanoparticle array porous membrane of claim 8 or 9 in water treatment.