Bionic zwitterionic polymer modified membrane as well as preparation method and application thereof

Abstract

The invention provides a bionic zwitterionic polymer which comprises a porous polymer base membrane, the surface of the porous polymer base membrane is loaded with polydopamine and a bionic zwitterionic polymer. According to the bionic zwitterionic polymer modified membrane disclosed by the invention, a dopamine monomer and a zwitterionic polymer containing dopamine and amine oxide structural units are utilized to carry out hydrophilic modification on a substrate; wherein the amine oxide zwitterions can form a hydration layer on the surface of the film through hydrogen bonds and electrostatic interaction to serve as a barrier, so that oil molecules are not easily adsorbed on the surface of the film, and the super-hydrophilic and underwater super-oil-transportation net film is prepared; in addition, zwitter-ions are firmly fixed on the surface of a substrate due to super-strong adhesiveness generated by oxidative auto-polymerization of catechol groups in the polydopamine particles and the zwitter-ion copolymer, and the coating prepared by co-deposition is more stable than a coating prepared by single dopamine, has good chemical stability, structural stability and recyclability, and can be applied to the field of chemical engineering. And the service life is longer.

Description

Technical Field

[0001] The invention relates to the technical field of separation membranes, and in particular to a bionic zwitterionic polymer modified membrane and a preparation method and application thereof. Background Art

[0002] The amount of oily wastewater generated by industrial emissions, oil spill accidents, and daily human activities has increased dramatically, posing a serious threat to the ecological environment and human health. Some traditional oil-water separation technologies, such as gravity separation, flotation separation, adsorption separation, and centrifugal separation, can effectively treat oily wastewater, but they have limitations such as low separation efficiency, high energy consumption, complex operation, and secondary pollution risks. In addition, these methods can rarely effectively separate highly emulsified oily wastewater, thus limiting their practical application.

[0003] In recent years, membrane separation technology has attracted much attention as a highly promising technology for continuous oil-water separation. This is due to its high separation efficiency, low energy consumption, less emissions and simple operation. Generally, organic polymer membranes such as polyvinylidene fluoride (PVDF) and polysulfone (PES) are widely used to treat oily wastewater due to their cost-effectiveness and chemical stability. However, due to the lipophilicity and hydrophobicity of these membranes themselves, during the separation process, oil can easily adhere to the surface and pores of the membrane, resulting in filter cake accumulation on the membrane surface and serious membrane fouling, thereby significantly reducing the separation performance of the membrane. In addition, the traditional single polydopamine modification method has limited hydrophilic modification of the separation membrane. Therefore, there is an urgent need to develop membranes that are resistant to oil pollution to efficiently treat oily wastewater. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, one of the purposes of the present invention is to provide a bionic zwitterionic polymer modified membrane. The second purpose of the present invention is to provide a method for preparing the above-mentioned bionic zwitterionic polymer modified membrane. The third purpose of the present invention is to provide the application of the above-mentioned bionic zwitterionic polymer modified membrane. The present invention adopts a bionic zwitterionic polymer containing both amine oxide and catechol groups, and can modify the porous polymer-based membrane by combining polydopamine with a mussel-like co-deposition loading method. The modified membrane exhibits excellent superhydrophilicity / underwater superoleophobicity, and has excellent antifouling performance and reusability, and can achieve efficient oil-water emulsion separation in a variety of harsh environments.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a biomimetic zwitterionic polymer modified membrane, characterized in that it comprises a porous polymer base membrane, the surface of the porous polymer base membrane is loaded with polydopamine particles and a biomimetic zwitterionic polymer; the biomimetic zwitterionic polymer has a structural formula as shown in Formula 1 below:

[0007]

[0008] Wherein, R1 and R4 are each independently H or CH3; R2 is selected from a single bond, C1-C5 alkylene or substituted C1-C5 alkylene, C1-C5 acyloxy, C1-C5 amide, phenyl; R3 is an alkyl chain consisting of 1-18 carbon atoms; R5 is selected from C1-C5 amide; x and y are the numbers of each monomer structural unit.

[0009] Preferably, x is selected from any integer between 10 and 3500, and y is selected from any integer between 10 and 1400.

[0010] Preferably, the molecular weight of the biomimetic zwitterionic polymer is 2000-300000.

[0011] More preferably, the molecular weight of the biomimetic zwitterionic polymer is 5000-50000.

[0012] Preferably, the biomimetic zwitterionic polymer is obtained by free radical polymerization of a monomer containing an amine oxide zwitterionic group and a monomer containing a dopamine group.

[0013] Preferably, the membrane material of the porous polymer-based membrane is selected from at least one of polypropylene, polysulfone, polyethersulfone and polyvinylidene fluoride.

[0014] Preferably, the pore size of the porous polymer-based membrane is 0.2-5 μm.

[0015] The second aspect of the present invention provides a method for preparing the biomimetic zwitterionic polymer modified membrane according to the first aspect, comprising the following steps:

[0016] The porous polymer base membrane is immersed in a mixed solution containing dopamine monomer and biomimetic zwitterionic polymer to react and obtain the biomimetic zwitterionic polymer modified membrane.

[0017] Preferably, the method further comprises pre-activating the porous polymer base membrane, and the specific steps include: immersing the porous polymer base membrane in an alcohol solution with a volume concentration greater than 50% for activation treatment, and washing with water to remove the alcohol after the treatment.

[0018] Preferably, the method for preparing the bionic zwitterionic polymer comprises the following steps: subjecting a monomer containing an amine oxide zwitterionic group, a monomer containing a dopamine group and an initiator to a polymerization reaction in a solvent to obtain the bionic zwitterionic polymer;

[0019] The structures of the monomer containing amine oxide zwitterionic groups and the monomer containing dopamine groups are shown in Formula 2 and Formula 3, respectively:

[0020]

[0021] Wherein, the definitions of R1, R2, R3, R4 and R5 are as described in the first aspect.

[0022] More preferably, the reaction temperature of the polymerization reaction is 60°C-80°C.

[0023] More preferably, the reaction time of the polymerization reaction is 20-30 hours.

[0024] More preferably, the polymerization reaction is carried out under an inert atmosphere.

[0025] More preferably, the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate and potassium persulfate.

[0026] More preferably, the dopamine group-containing monomer is selected from 3-methacryloyl dopamine or 3-acryloyl dopamine.

[0027] More preferably, the monomer containing amine oxide zwitterionic groups is prepared by the following preparation method: firstly, a diethylenetriaminepentaacetic acid solution is mixed with a hydrogen peroxide solution, and then a zwitterionic precursor is added to the mixed solution to react, so as to obtain a monomer containing amine oxide zwitterionic groups.

[0028] Further preferably, the zwitterionic precursor is selected from at least one of 2-(dimethylamino)ethyl methacrylate, (2-dimethylaminoethyl)methacrylate, 2-(dimethylamino)ethyl acrylate, N-[(3-(dimethylamino)propyl]methacrylamide, N-(3-dimethylaminopropyl)acrylamide, diethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, and N,N-dimethylvinylbenzylamine.

[0029] More preferably, the solvent is an alcohol solvent.

[0030] More preferably, the method for preparing the biomimetic zwitterionic polymer further comprises the following step: drying the polymerization product at -30 to -70°C.

[0031] Preferably, the method for preparing the mixed solution containing dopamine monomer and biomimetic zwitterionic polymer comprises the following steps: mixing dopamine monomer, biomimetic zwitterionic polymer and alkaline buffer to prepare a mixed solution.

[0032] More preferably, the alkaline buffer is a tris hydrochloride buffer.

[0033] More preferably, the alkaline buffer has a pH of 8.0-9.0.

[0034] More preferably, the concentration of the alkaline buffer is 10-50 mmol / L.

[0035] Preferably, the concentrations of dopamine monomer and biomimetic zwitterionic polymer in the mixed solution are independently 0.5-10 mg / mL.

[0036] More preferably, the concentration of dopamine monomer in the mixed solution is 2-4 mg / mL.

[0037] More preferably, the concentration of the biomimetic zwitterionic polymer in the mixed solution is 2-4 mg / mL.

[0038] Preferably, the impregnation is performed under shaking conditions.

[0039] Preferably, the immersion time is 20-30 hours.

[0040] Preferably, the temperature of the mixed solution during the immersion is 15-40°C.

[0041] The third aspect of the present invention provides the use of the bionic zwitterionic polymer modified membrane described in the first aspect in oil-water separation products.

[0042] Preferably, the oil-water separation product is used to separate at least one of kerosene, emulsified oil, dissolved oil and petroleum.

[0043] The beneficial effects of the present invention are:

[0044] The bionic zwitterionic polymer modified membrane of the present invention utilizes dopamine monomers and zwitterionic polymers containing dopamine and amine oxide structural units to perform hydrophilic modification on a substrate, wherein the amine oxide zwitterionic ions can form a hydration layer as a barrier on the film surface through hydrogen bonding and electrostatic action, so that oil molecules are not easily adsorbed on the film surface, thereby preparing a super-hydrophilic and underwater super-oil transport network membrane; in addition, the super-strong adhesion generated by the oxidative self-polymerization of catechol groups in polydopamine particles and zwitterionic copolymers firmly fixes the zwitterions on the substrate surface, and the coating prepared by co-deposition is more stable than the coating prepared by single dopamine, has good chemical stability, structural stability and recyclability, and has a longer service life.

[0045] The specific beneficial effects are as follows:

[0046] 1. The positive and negative charges in the amine oxide zwitterions of the biomimetic zwitterionic polymer modified membrane of the present invention are directly connected, and compared with other types of zwitterions, it has stronger hydrophilicity and underwater super oil transport performance, and has great potential in the field of oil-water separation. In addition, the introduction of amine oxide zwitterions not only prevents polydopamine from agglomerating into polydopamine particles and clogging the porous membrane, but also reduces the roughness of the membrane surface, and no pollutants adhere.

[0047] 2. The preparation method of the bionic zwitterionic polymer of the present invention is simple. The self-assembly of polydopamine and the introduction of the bionic zwitterionic polymer can be completed by immersing the porous polymer membrane in the reaction solution, and the method has good industrial application prospects.

[0048] 3. The bionic zwitterionic polymer modified PVDF oil-water separation membrane of the present invention exhibits high permeation flux in the oil-water separation process, and the flux of pure water is as high as 10357L m -2 h -1 bar -1 , in water-in-oil emulsion (mineral oil emulsion) the flux is 5634 L m -2 h -1 bar -1 , greatly improving the water flux of PVDF membrane. Compared with PVDF membrane, the modified PVDF membrane has achieved an excellent oil removal rate of over 99% for various emulsions (such as toluene, petroleum ether, vacuum pump oil, etc.), showing excellent oil-water separation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The hydrogen spectra of TMAO, DMA, PTODA-1 and PTODA-2; (a) is the hydrogen spectra of TMAO and DMA; (b) is the hydrogen spectra of PTODA-1 and PTODA-2

[0050] Figure 2 Scanning electron microscope (SEM) images of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, and PVDF / PDA / PTODA-2 membranes;

[0051] Figure 3 Atomic force microscopy (AFM) images of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, and PVDF / PDA / PTODA-2 membranes;

[0052] Figure 4 The dynamic water contact angles (WCA) of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1 and PVDF / PDA / PTODA-2 films; the inset is the initial water contact angle test diagram;

[0053] Figure 5 The hydrophilicity tests were performed for blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, PVDF / PDA / PTODA-2, PP / PDA / PTMAO and PES / DMA / TMAO.

[0054] Figure 6The underwater oil (n-hexane) contact angles (UOCA) of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, and PVDF / PDA / PTODA-2 membranes;

[0055] Figure 7 is the underwater oil contact angle of PVDF / PDA / PTODA-2 membrane for different oils;

[0056] Figure 8 is the pure water flux of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, PVDF / PDA / PTODA-2, PVDF / PDA / PTMAO, PVDF / PTODA-2, and PVDF / DMA / TMAO membranes;

[0057] Fig. 9 The mineral oil emulsion fluxes of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1 and PVDF / PDA / PTODA-2, PVDF / PDA / PTMAO, PVDF / PTODA-2, and PVDF / DMA / TMAO membranes;

[0058] Fig.10 The recovered water flux (FRR) and separation efficiency (R) of blank PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, PVDF / PDA / PTODA-2, PVDF / PDA / PTMAO, PVDF / PTODA-2 and PVDF / DMA / TMAO membranes for mineral oil emulsions;

[0059] Fig.11 The emulsion flux and separation efficiency of PVDF / PDA / PTODA-2 membrane for different emulsion separations;

[0060] Fig.12 The separation flux and separation efficiency of mineral oil emulsions of PVDF / PDA / PTODA-2 membrane in various complex environments;

[0061] Fig.13 The stability of PVDF / PDA / PTODA-2 membrane for multiple separations of mineral oil emulsions. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below through specific examples. The raw materials used in the following examples, unless otherwise specified, can be obtained from conventional commercial sources or prepared and separated by simple synthesis; the processes used, unless otherwise specified, are conventional processes in the art.

[0063] Example 1

[0064] This embodiment provides a biomimetic zwitterionic polymer modified membrane, and the preparation steps are as follows:

[0065] S1. Dissolve 0.7 g of diethylenetriaminepentaacetic acid in 20 mL of water to obtain a diethylenetriaminepentaacetic acid aqueous solution; drip 21.76 g of a 30% hydrogen peroxide aqueous solution into the diethylenetriaminepentaacetic acid aqueous solution; heat the temperature to 60°C; dissolve 20 g of N-[(3-(dimethylamino)propyl]methacrylamide in 10 mL of water and mix well to obtain an N-[(3-(dimethylamino)propyl]methacrylamide aqueous solution, and slowly drip the N-[(3-(dimethylamino)propyl]methacrylamide aqueous solution into the reaction solution; perform an oil bath reaction at a temperature of 60°C for 6 hours; wait for the reaction solution to be cooled to room temperature, drip into acetone for precipitation, and after removing the acetone, obtain a new zwitterion of amine oxide containing an unsaturated double bond, recorded as TMAO.

[0066] S2. After dissolving 1.032 g TMAO and 0.211 g 3-methacryloyl dopamine (DMA) in ethanol, a free radical polymerization reaction was carried out in an inert atmosphere under the action of 2% azobisisobutyronitrile (AIBN) initiator. The reaction temperature of the free radical polymerization reaction was 70° C. and the reaction time was 24 h. After the reaction, the polymer product was purified by a dialysis bag with a molecular weight cutoff of 6000 Da to 8000 Da, and then freeze-dried at -50° C. to obtain a polymer PTODA-1 containing amine oxide zwitterions and dopamine structural units.

[0067] S3. The polymer PTODA-1 and dopamine monomer prepared in S2 are simultaneously dissolved in 50 mM Tris-HCl buffer (pH = 8.5) to prepare solutions with a concentration of 2 mg / mL. The PVDF film is pretreated with ethanol and then immersed in the above solution. After 24 hours, it is taken out, cleaned, and dried to obtain a bionic zwitterionic polymer-modified PVDF oil-water separation membrane, recorded as PVDF / PDA / PTODA-1.

[0068] The hydrogen spectrum of TMAO prepared in this example is as follows Figure 1 As shown in (a), the multiple peaks at 6.10 ppm and 5.3 ppm correspond to the H absorption peaks of the unsaturated double bond C=C, and the single peak at 3.05 ppm corresponds to the absorption peaks of N + The H of the two methyl groups connected together, these characteristic peaks have successfully synthesized TMAO.

[0069] The characteristic peaks of the biomimetic zwitterionic polymer PTODA-1 (prepared from TMAO and DMA) involved in this embodiment are as follows: Figure 1 As shown in (b), the broad peak at 6.73-6.60 ppm corresponds to Figure 1The peak at 3.05 ppm in the DMA hydrogen spectrum of (a) corresponds to the hydrogen on the benzene ring Figure 1 (a) The hydrogen spectrum of TMAO and N + The H of the two connected methyl groups. In addition, a new characteristic peak appeared at 2.60 ppm after polymerization, while the hydrogen signal related to the C=C hydrogen bond disappeared. The hydrogen spectrum shows that the target biomimetic zwitterionic polymer PTODA-1 has been successfully synthesized.

[0070] Example 2

[0071] This embodiment provides a biomimetic zwitterionic polymer modified membrane. The specific preparation process is the same as that of Example 1, except that the reaction monomers and amounts in S2 are changed to 2.064 g TMAO and 0.211 g DMA. The prepared polymer is recorded as PTODA-2, and the prepared film is recorded as PVDF / PDA / PTODA-2.

[0072] The characteristic peaks of the biomimetic zwitterionic polymer PTODA-2 (prepared from TMAO and DMA) involved in this embodiment are as follows: Figure 1 As shown in (b), the broad peak at 6.73-6.60 ppm corresponds to Figure 1 The peak at 3.05 ppm corresponds to the hydrogen on the benzene ring in the bDMA hydrogen spectrum Figure 1 The hydrogen spectrum of TMAO in a and N + The H of two connected methyl groups. In addition, after polymerization, a new characteristic peak appeared at 2.60 ppm, while the hydrogen signal related to the C=C hydrogen bond disappeared. From the hydrogen spectrum, it can be seen that the product PTODA-2 has been successfully synthesized.

[0073] from Figure 2 From the SEM image, we can see that compared with the blank PVDF membrane, some particles on the dopamine-modified film are anchored on the surface of the PVDF / PDA membrane, which is the result of dopamine self-assembly. Figure 3 It can be seen that the deposition of such aggregates and the uneven stacking of polydopamine molecules caused the membrane surface roughness to increase from 210 nm of the original PVDF membrane to 257 nm. At the same time, no aggregates were observed on the surface of PVDF / PDA / PTODA-1 and PVDF / PDA / PTODA-2 membranes. This is because the amphoteric polymers contained in PTODA can act as a medium to promote the deposition of catechol fragments and weaken the hydrogen bonds between polydopamine through phenolic hydroxyl groups and amine oxides and the cation-π interactions between quaternary ammonium salts and aromatic benzene rings. Therefore, compared with the original PVDF and PVDF / PDA membranes, the roughness of the membranes modified by co-deposition of dopamine and PTODA is reduced, as shown in Figure 2. Figure 3The roughness of PVDF / PDA / PTODA-1 and the roughness of PVDF / PDA / PTODA-2 are shown to be reduced to 232 nm and 160 nm, respectively.

[0074] Example 3

[0075] This embodiment provides a biomimetic zwitterionic polymer modified membrane. The specific preparation process is the same as that of Example 2, except that the PVDF membrane is replaced by a polypropylene (PP) membrane, and the obtained modified membrane is recorded as PP / PDA / PTODA-2.

[0076] Example 4

[0077] This embodiment provides a biomimetic zwitterionic polymer modified membrane. The specific preparation process is the same as that of Example 2, except that the PVDF membrane is replaced by a polyethersulfone (PES) membrane, and the obtained modified membrane is recorded as PES / PDA / PTODA-2.

[0078] Comparative Example 1

[0079] This comparative example provides a biomimetic polymer modified PVDF oil-water separation membrane, and the preparation steps are as follows:

[0080] S1 is the same as Example 1, to obtain TMAO;

[0081] S2. After dissolving 2.064 g of TMAO in ethanol, a free radical polymerization reaction was carried out in an inert atmosphere under the action of 2% azobisisobutyronitrile (AIBN) initiator. The reaction temperature of the free radical polymerization reaction was 70° C. and the reaction time was 24 hours. After the reaction was completed, the polymer product was purified using a dialysis bag with a molecular weight cutoff of 6000 Da to 8000 Da, and then freeze-dried at -50° C. to obtain a polymer PTMAO containing amine oxide zwitterions.

[0082] S3. The polymer PTMAO and dopamine monomer prepared in S2 are simultaneously dissolved in 50 mM Tris-HCl buffer (pH = 8.5) to prepare solutions with a concentration of 2 mg / mL. The PVDF film is pretreated with ethanol and then immersed in the above solution. After 24 hours, it is taken out, cleaned, and dried to obtain a bionic zwitterionic polymer-modified PVDF oil-water separation membrane, recorded as PVDF / PDA / PTMAO.

[0083] Comparative Example 2

[0084] This comparative example provides a biomimetic polymer modified PVDF oil-water separation membrane, and the preparation steps are as follows:

[0085] S1 is the same as Example 2, to obtain TMAO;

[0086] S2 was the same as Example 2, and the product PTODA-2 was synthesized;

[0087] S3. The polymer PTODA-2 prepared in S2 was dissolved in 50 mM Tris-HCl buffer (pH = 8.5) to prepare a solution with a concentration of 2 mg / mL. The PVDF film was pretreated with ethanol and then immersed in the above solution. After 24 hours, it was taken out, cleaned, and dried to obtain a bionic zwitterionic polymer-modified PVDF oil-water separation membrane, recorded as PVDF / PTODA-1.

[0088] Comparative Example 3

[0089] This comparative example provides a polydopamine-modified PVDF oil-water separation membrane, and the preparation steps are as follows:

[0090] Dopamine monomer was dissolved in Tris-HCl (pH=8.5) buffer solution to prepare a solution with a concentration of 2 mg / mL. The PVDF film pretreated with ethanol was immersed in the above solution, taken out and cleaned after 24 hours to obtain an amine oxide homopolymer modified PVDF oil-water separation membrane, recorded as PVDF / PDA.

[0091] Comparative Example 4

[0092] This embodiment provides a modified PVDF oil-water separation membrane, and the specific process is as follows:

[0093] TMAO and DMA monomers were dissolved in Tris-HCl (pH = 8.5) buffer solution to prepare solutions with a concentration of 2 mg / mL. The PVDF film pretreated with ethanol was immersed in the above solution, taken out and cleaned after 24 hours to obtain an amine oxide homopolymer modified PVDF oil-water separation membrane, recorded as PVDF / DMA / TMAO.

[0094] Experimental analysis

[0095] Test Example The performance of the blank PVDF membrane, the modified polymer-based membranes prepared in the examples and the comparative examples was tested, and the specific process was as follows:

[0096] 1. Contact angle test: Water contact angle (WCA) and underwater oil contact angle (UOCA) were measured at room temperature (25°C). 3 μL and 5 μL water and oil droplets were used to test the polymer-based film, respectively, and at least three parallel measurements were performed, and the average value was calculated.

[0097] The wettability of the membrane surface is a key factor affecting the pure water flux and anti-oil adhesion ability. Figure 4As shown in the figure, the water contact angle of the membranes co-modified with dopamine (DA) and dopamine and biomimetic zwitterionic polymers decreased significantly. Although the surface roughness of the PVDF-PDA membrane is higher than that of the membrane co-modified with dopamine and PTODA, the latter shows better hydrophilicity due to the positive and negative charges directly connected to the NO zwitterionic groups. And as the zwitterion content in the polymer increases, the hydrophilicity also increases. In particular, the PVDF / PDA / PTODA-2 membrane shows significant hydrophilicity and achieves zero contact angle within 18 seconds. In addition, dopamine and PTODA-2 were co-deposited to modify the PP membrane and PES membrane, respectively. Both the PP / PDA / PTODA-2 membrane and the PES / PDA / PTODA-2 membrane showed excellent hydrophilicity, and the contact angle became 0 within 20s ( Figure 5 ).

[0098] Underwater super-oiling is crucial to achieve efficient separation of oil-water emulsions. Figure 6 As shown in the figure, the PVDF membranes modified by co-deposition of dopamine and biomimetic zwitterionic polymers all exhibit underwater superoleophobicity (the oil is n-hexane), and the underwater oleophobicity increases with the increase of the zwitterion content in the polymer. Among them, the PVDF / PDA / PTODA-2 membrane exhibits significant superoleophobicity in water, and its UOCA value is as high as 150°. In addition, as Figure 7 As shown, when the PVDF / PDA / PTODA-2 membrane comes into contact with various types of oil droplets such as dichloromethane, n-dodecane, and mineral oil, its UOCA value exceeds 150°, further highlighting its excellent performance in underwater superoleophobicity.

[0099] 2. Water flux test:

[0100] (1) Preparation of an emulsifier-stabilized oil-water emulsion: 5 ml of oil was added to 495 ml of pure water, and sodium dodecyl sulfate (SDS) was used as an emulsifier, followed by stirring at 10,000 rpm in a high-speed homogenizer (FSH-2A) for 20 min.

[0101] (2) Place the membrane sample to be tested (effective filtration area: 13.85 cm 2 ) was placed in the terminal filtration system and the flux of pure water and emulsion was tested at a pressure of 0.1Mpa (J, unit: L·m -2 ·h -1 bar -1 ), calculated as follows:

[0102] J = V / A×t (1)

[0103] Where V is the volume of filtrate passing through the effective area A within time t.

[0104] Use UV to test the oil content in water.

[0105] The calculation formula of membrane separation efficiency R (%) is:

[0106] Rejection(%)=(1 – C p / C f ) × 100% (2)

[0107] Among them C p is the oil content in the water after separation, C f is the oil content in water before separation.

[0108] The calculation formula of water flux recovery rate FRR (%) is:

[0109] FRR = J′ / J × 100% (3)

[0110] Where J is the flux of pure water before emulsion separation, and J' is the flux of pure water after five cycles of emulsion separation.

[0111] Figure 8 The separation performance of various membranes for pure water at a pressure of 0.1 MPa using a terminal filtration device was demonstrated. The pure water permeation of the original PVDF, PVDF / PDA, PVDF / PDA / PTODA-1, and PVDF / PDA / PTODA-2 membranes was 5041 L·m -2 ·h -1 bar -1 、6843L·m -2 ·h -1 bar -1 、8423L·m -2 ·h -1 bar -1 and 10357L·m -2 ·h -1 bar -1 The pure water flux of PVDF / PDA / PTMAO prepared from amine oxide homopolymer and dopamine in Comparative Example 1 is close to that of PVDF / PDA / PTODA-2 membrane, and the water flux of the membranes prepared in Comparative Examples 2 and 4 is close to that of the membrane in Comparative Example 3. The results show that the introduction of the amphoteric copolymer PTODA on the membrane surface can effectively improve the water permeability, thereby reducing the resistance to mass transfer.

[0112] Fig. 9The separation performance of various membranes for mineral oil emulsions at a pressure of 0.1 MPa using a terminal filtration device was demonstrated. The results of emulsion separation performance were similar to those of pure water permeation. With the introduction of zwitterionic copolymers, the emulsion permeation increased. Among them, the zwitterionic copolymer-modified PVDF / PDA / PTODA-2 membrane with the highest zwitterion content had excellent oil-water emulsion separation performance, and its emulsion permeation reached 5634 L m -2 h -1 bar -1 , which is nearly 4 times the emulsion permeation of the blank membrane.

[0113] Although from Figure 8 and Fig. 9 The data analysis in shows that the pure water flux and emulsion flux of PVDF / PDA / PTMAO are similar to those of PVDF / PDA / PTODA-2 membrane, but Fig.10 It shows that after 5 cycles of oil-water emulsion separation, the water flux recovery rate of PVDF / PDA / PTODA-2 membrane is as high as 90%, which is significantly higher than the original PVDF (67%), PVDF / PDA (78%), PVDF / PDA / PTODA-1 (85%), PVDF / PDA / PTMAO (82%), PVDF / PTODA-2 (79%), PVDF / DMA / TMAO (72%), which proves to a certain extent that the coating prepared by the PTODA-2 copolymer with the highest content of PDA and amine oxide has better stability, making the PVDF / PDA / PTODA-2 membrane have better repeatability. In addition, the oil-water separation efficiency of all membranes is as high as 99%. Because the PVDF / PDA / PTODA-2 membrane has the best oil-water separation performance, the modified membrane will continue to be used for the separation of other oil-water emulsions. Fig.11 It is proved that PVDF / PDA / PTODA-2 membrane has efficient separation performance for emulsions such as n-hexane, dichloromethane, dodecane, and petroleum ether.

[0114] 3. Membrane oil-water separation performance test under harsh environment:

[0115] The surface hydrophilicity / underwater hydrophobicity of the membrane was tested by immersing the membrane in hydrochloric acid solution (pH=2), sodium hydroxide solution (pH=12), 3.5% NaCl solution, 60°C hot water and 0°C ice bath for 2 hours. Then, the separation performance of the membrane for oil-water emulsion (mineral oil) was tested to evaluate the separation ability of the membrane in complex environments.

[0116] The stability of the membrane under different environments plays an important role in its practical application. Fig.12It was proved that when PVDF / PDA / PTODA-2 membrane was placed in challenging environments such as strong acid, strong alkali, high salt, cold and hot, it still had high oil-water emulsion separation performance. For mineral oil emulsion, its oil-water separation flux exceeded 3800L m -2 h -1 bar -1 , the oil-water separation efficiency is higher than 99%. Fig.13 The experimental results show that the water flux of PVDF / PDA / PTODA-2 membrane is still more than 5200 L m after 20 oil-water emulsion separation cycles. -2 h -1 bar -1 , the separation efficiency is still as high as 98%. However, the stability of the PVDF / PDA / PTMAO, PVDF / PTODA2, PVDF / PDA and PVDF / DMA / TMAO films prepared in Comparative Examples 1, 2, 3 and 4 is not as good as that of the PVDF / PDA / PTODA-2 membrane. When these membranes are placed in challenging environments such as strong acid, strong alkali, high salt, cold and hot, the oil-water separation performance is greatly reduced.

[0117] In addition, when the above-mentioned films are subjected to emulsion circulation, the separation performance is greatly reduced after the films are circulated 3-5 times. This is mainly because the hydrophilicity and underwater oleophobicity of PVDF / PDA / PTMAO, PVDF / PTODA2, PVDF / PDA and PVDF / DMA / TMAO membranes are not as good as those of PVDF / PDA / PTODA-2 membranes, resulting in poor oil-water separation performance; at the same time, the coatings of PVDF / PDA / PTMAO, PVDF / PTODA2, PVDF / PDA and PVDF / DMA / TMAO membranes are oxidized and self-polymerized and adhered to the surface of PVDF membranes by a single dopamine or a polymer containing dopamine fragments. The stability of the above-mentioned coatings is not as good as that of the PVDF / PDA / PTODA-2 membrane prepared by co-deposition of dopamine monomers and PTODA-2 containing dopamine structural units, because PVDF / PDA / PTMAO, PVDF / PTODA2, PVDF / PDA and PVDF / DMA / TMAO membranes have poor applicability in harsh environments.

[0118] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A biomimetic zwitterionic polymer modified membrane, characterized in that: It comprises a porous polymer base membrane, the surface of which is loaded with polydopamine and a biomimetic zwitterionic polymer; the structural formula of the biomimetic zwitterionic polymer is shown in the following formula 1: Wherein, R1 and R4 are each independently H or CH3; R2 is selected from a single bond, C1-C5 alkylene or substituted C1-C5 alkylene, C1-C5 acyloxy, C1-C5 amide, phenyl; R3 is an alkyl chain consisting of 1-18 carbon atoms; R5 is selected from C1-C5 amide; x and y are the numbers of each monomer structural unit.

2. The biomimetic zwitterionic polymer modified membrane according to claim 1, characterized in that: The x is selected from any integer between 10 and 3500, and the y is selected from any integer between 10 and 1400; And / or, the molecular weight of the biomimetic zwitterionic polymer is 2000-300000.

3. The biomimetic zwitterionic polymer modified membrane according to claim 1, characterized in that: The membrane material of the porous polymer-based membrane is selected from at least one of polypropylene, polysulfone, polyethersulfone and polyvinylidene fluoride.

4. The method for preparing the biomimetic zwitterionic polymer modified membrane according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: immersing a porous polymer base membrane in a mixed solution containing dopamine monomer and a bionic zwitterionic polymer, and reacting the mixture to obtain the bionic zwitterionic polymer modified membrane.

5. The method for preparing the biomimetic zwitterionic polymer modified membrane according to claim 4, characterized in that: The method also includes pre-activating the porous polymer base membrane, and the specific steps include: immersing the porous polymer base membrane in an alcohol solution with a volume concentration greater than 50% for activation treatment, and washing with water to remove the alcohol after the treatment.

6. The method for preparing the biomimetic zwitterionic polymer modified membrane according to claim 4, characterized in that: The preparation method of the bionic zwitterionic polymer comprises the following steps: subjecting a monomer containing an amine oxide zwitterionic group, a monomer containing a dopamine group and an initiator to a polymerization reaction in a solvent to obtain the bionic zwitterionic polymer; The structures of the monomer containing amine oxide zwitterionic groups and the monomer containing dopamine groups are shown in Formula 2 and Formula 3, respectively: Wherein, R1, R2, R3, R4 and R5 are defined as in claim 1.

7. The method for preparing the biomimetic zwitterionic polymer modified membrane according to claim 4, characterized in that: The method for preparing the mixed solution containing dopamine monomer and biomimetic zwitterionic polymer comprises the following steps: mixing dopamine monomer, biomimetic zwitterionic polymer and alkaline buffer to prepare a mixed solution; And / or, the concentrations of dopamine monomer and biomimetic zwitterionic polymer in the mixed solution are independently 0.5-10 mg / mL.

8. The method for preparing the biomimetic zwitterionic polymer modified membrane according to claim 4, characterized in that: The impregnation satisfies one or more of the following conditions: a) the impregnation is carried out under shaking conditions; b) the immersion time is 20-30h; c) The temperature of the mixed solution during the immersion is 15-40°C.

9. Use of the bionic zwitterionic polymer modified membrane according to any one of claims 1 to 3 in oil-water separation products.

10. The use according to claim 9, characterized in that: The oil-water separation product is used for separating at least one of kerosene, emulsified oil, dissolved oil and petroleum.

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