A molecular brush modified anti-pollution polyamide membrane and its preparation method and application

Abstract

The present invention belongs to the technical field of wastewater and sewage treatment, and specifically discloses a molecular brush modified anti-pollution polyamide membrane and its preparation method and application for sewage and wastewater treatment. The method comprises the following steps: S1. polyethyleneimine is covalently grafted on the surface of the polyamide membrane after activation to form an amino functional layer; the reaction concentration of polyethyleneimine is 0.05-1.5%; S2.α-bromoisobutyric acid reacts with the amino functional layer to form an initiator layer; S3. the initiator layer is sequentially grafted with a zwitterionic polymer and a fluoropolymer to form a zwitterionic hydrophilic layer and a low surface energy layer, and a molecular brush modified anti-pollution polyamide membrane is obtained. The polyamide membrane provided by the present invention has better water flux, excellent resistance to organic pollution and inorganic scaling performance, has more excellent stability, has excellent flux decay rate and flux recovery rate in simulated wastewater treatment, and can be used in devices such as sewage treatment equipment, seawater desalination equipment, industrial wastewater treatment and reuse equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater and sewage treatment, and more specifically, relates to a molecular brush modified anti-pollution polyamide membrane for sewage and wastewater treatment, and a preparation method and application thereof. Background Art

[0002] Sewage and wastewater treatment and resource utilization are key measures to address my country's freshwater resource crisis and a major national strategic need. Nanofiltration (NF) technology, due to its advantages such as small footprint, high effluent quality, and high treatment efficiency, is widely used in water softening, organic matter removal, heavy metal removal, wastewater treatment, and resource utilization. However, its practical application has long been constrained by membrane fouling. Currently, polyamide nanofiltration membranes, due to their comprehensive performance advantages and mature modification technology, account for 60%-70% of the global nanofiltration membrane market. Existing polyamide nanofiltration membranes are susceptible to adsorption of particulate matter, colloids, and organic matter in wastewater, forming a fouling layer that reduces flux and even causes irreversible membrane pore blockage.

[0003] To effectively alleviate the critical issue of membrane fouling, the most common method is to construct a hydrophilic antifouling buffer layer on the surface of the nanofiltration membrane to prevent the diffusion of pollutants to the membrane surface. This buffer layer is rich in hydrophilic functional groups, such as carboxyl, hydroxyl, sulfonic acid, and amino groups. These functional groups can form a unique network structure with water molecules through hydrogen bonding, thereby forming a dense hydration layer on the membrane surface, preventing the migration and aggregation of pollutants to the membrane surface.

[0004] The new method of grafting hydrophilic polymers onto membrane surfaces has gained widespread recognition in academia. Practice has demonstrated that, among various hydrophilic polymers, zwitterionic polymers offer unparalleled advantages over other hydrophilic compounds in improving membrane antifouling performance. This is due to their ability to bind water molecules through electrostatic interactions, with a binding force approximately 7-8 times stronger than that of ordinary hydrogen bonds. This facilitates the formation of a denser hydration layer, effectively preventing contaminant deposition on the membrane surface.

[0005] In the field of membrane science research, the SI-ATRP reaction (surface-initiated atom transfer radical polymerization) is used to trigger the polymerization of zwitterionic compound monomers on the membrane surface, allowing the polymer molecular chains to grow in situ on the membrane surface to form a brush-like buffer layer with appropriate density and height. This has become the most commonly used and effective method for grafting zwitterionic polymers on membrane surfaces.

[0006] This method successfully overcomes the problem of uneven grafting caused by steric hindrance in the traditional process of grafting long-chain polymers. The key step in implementing the SI-ATRP reaction is to precisely anchor α-bromoisobutyryl bromide as an initiator on the membrane surface. In practice, the surface of the polyamide nanofiltration membrane lacks functional groups that can form covalent bonds with acyl bromide groups. This prompted the researchers to adopt a specific strategy in practice: first, α-bromoisobutyryl bromide is blended with dopamine hydrochloride salt to combine the acyl bromide group and the phenolic hydroxyl group to form an ester bond, and with the help of dopamine hydrochloride salt, it self-polymerizes under alkaline conditions. The resulting polydopamine coating with a "mussel-like structure" can form hydrogen bonds with the surface of the polyamide nanofiltration membrane, thereby introducing α-bromoisobutyryl bromide to the membrane surface. For example, the document "Facile preparation of antifouling nanofiltration membrane by grafting zwitterions for reuse of shale gas wastewater" (Minli Hu, Separation and Purification Technology, https: / / doi.org / 10.1016 / j.seppur.2021.119310) discloses a method for modifying the surface of a polyamide nanofiltration membrane NF90 membrane. First, α-bromoisobutyryl bromide is mixed with dopamine hydrochloride salt as an initiator, and then a polydopamine coating is formed on the NF90 membrane. Subsequently, a zwitterionic polymer brush (PSBMA) is grafted on this basis through a SI-ATRP reaction.

[0007] However, the above method still has obvious defects, which limit its application in large-scale production. Specifically: (1) The stability of the polydopamine coating is relatively poor because there are a large number of non-covalent structures inside the coating, which makes the coating very unstable in acid, alkali and polar organic solvents; (2) The initiator α-bromoisobutyryl bromide and dopamine hydrochloride salt need to be blended in an organic solvent and a closed environment, and nitrogen needs to be used in advance to remove water and oxygen in the organic solvent, which is a relatively complicated operation; (3) The water flux of the modified polyamide nanofiltration membrane finally prepared is low, only 0.83 L / (m 2 ·h·bar), which is difficult to meet the needs of practical applications; (4) the initiator α-bromoisobutyryl bromide has high reactivity and is easily decomposed under light conditions. The acyl bromide group in its molecule is easily affected by water vapor in the air and hydrolyzed into a low-reactivity carboxyl group, which loses the ability to react with dopamine hydrochloride. The hydrobromic acid produced by hydrolysis is highly corrosive to equipment; (5) triethylamine needs to be added as an acid-binding agent in the reaction, and α-bromoisobutyryl bromide itself is volatile and has a strong pungent odor. The above problems indicate that the application of zwitterionic polymers in polyamide nanofiltration membranes still has many limitations. Summary of the Invention

[0008] In response to the above-mentioned existing technical problems, the primary objective of the present invention is to provide a method for preparing a molecular brush-modified anti-fouling polyamide membrane. This method is simple to operate and can be carried out at room temperature in aqueous solution and air. The reaction conditions are mild, and no air or water vapor isolation is required. Triethylamine as an acid-binding agent is required for the reaction, and no organic solvent is required. Furthermore, the reagents used are non-toxic and have no negative environmental impact. The resulting molecular brush-modified anti-fouling polyamide membrane exhibits improved water flux, excellent resistance to organic pollution and inorganic scaling, and superior stability, making it more suitable for long-term use. It can be used in membrane module equipment for sewage treatment, seawater desalination, and industrial wastewater treatment and reuse.

[0009] The second object of the present invention is to provide a molecular brush modified anti-pollution polyamide membrane prepared by the above preparation method.

[0010] The third object of the present invention is to provide the use of the molecular brush modified anti-pollution polyamide membrane in wastewater treatment.

[0011] The fourth object of the present invention is to provide the use of α-bromoisobutyric acid as an initiator in the preparation of polyamide membranes by surface-initiated atom transfer radical polymerization.

[0012] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0013] The present invention claims protection for a method for preparing a molecular brush modified anti-pollution polyamide membrane, comprising the following steps:

[0014] S1. Covalently grafting polyethyleneimine onto the surface of an activated polyamide membrane to form an amino-functionalized layer; the reaction concentration of polyethyleneimine is 0.05-1.5%;

[0015] S2. α-bromoisobutyric acid reacts with the amino-functionalized layer to form an initiator layer;

[0016] S3. The initiator layer is sequentially grafted with a zwitterionic polymer and a fluoropolymer to form a zwitterionic hydrophilic layer and a low surface energy layer, thereby preparing a molecular brush-modified anti-fouling polyamide membrane.

[0017] In step S1 of the present invention, polyethyleneimine is used, and its molecule contains multiple amino groups, wherein a part of the amino groups can be coupled with the carboxyl groups on the surface of the polyamide nanofiltration membrane through reaction to form multiple stable amide bonds, so that the polyethyleneimine is firmly bonded to the polyamide nanofiltration membrane, and the residual amino groups can serve as new active groups for further grafting initiators; the polyethyleneimine used in the present invention can replace the most commonly used polydopamine coating in the existing method, and from the perspective of coating stability, the method of forming a covalent bond with the substrate is more stable than the polydopamine coating that adheres to the substrate through hydrogen bonding, and is more conducive to long-term use.

[0018] Furthermore, the present invention uses α-bromoisobutyric acid as an initiator, which forms an amide bond with the amino groups on the polyethyleneimine cross-linked base layer, completing the grafting and forming an initiator layer. Subsequently, through two SI-ATRP reactions, a zwitterionic polymer (PSBMA) and a fluoropolymer (PHFBM) are grafted sequentially to form a hydrophilic hydration barrier and a low-surface-energy antifouling interface, resulting in a diblock molecular brush with both "pollution prevention" and "pollution release" functions.

[0019] Furthermore, the inventors discovered through research that for the amino-functionalized layer and the ultimately prepared molecular brush-modified anti-fouling polyamide membrane, the reaction concentration of polyethyleneimine in step S1 is crucial. A higher polyethyleneimine reaction concentration increases the amount of polyethyleneimine grafted to the membrane surface, thereby increasing the number of SI-ATRP reaction active sites and producing a denser molecular brush layer, which in turn reduces the pure water permeation flux. On the other hand, a lower polyethyleneimine reaction concentration results in less polyethyleneimine grafted to the membrane surface, which significantly affects the anti-fouling performance of the molecular brush-modified anti-fouling polyamide membrane. By controlling the polyethyleneimine reaction concentration within a specific range, the present invention enables the molecular brush-modified anti-fouling polyamide membrane to have both excellent water flux and excellent anti-fouling performance.

[0020] This paper proposes a method for covalently grafting zwitterionic polymers, which is superior to the traditional α-bromoisobutyryl bromide-polydopamine method in terms of environmental friendliness and ease of operation. This method innovatively utilizes α-bromoisobutyric acid as an environmentally friendly initiator, which is non-toxic and has excellent hydrolytic stability. Furthermore, the covalent grafting technique combined with polyethyleneimine (PEI) achieves permanent fixation of the initiator, avoiding the risk of delamination associated with traditional non-covalent coatings.

[0021] Compared with the traditional polydopamine coating method and α-bromoisobutyryl bromide initiator, the method provided by the present invention is simple in operation and can be carried out at room temperature, in aqueous solution and in air. The reaction conditions are mild, and there is no need to isolate air and water vapor. There is no need to use triethylamine as an acid-binding agent to participate in the reaction, and no organic solvent is required. In addition, the reagents used are non-toxic and have no negative impact on the environment.

[0022] The traditional α-bromoisobutyryl bromide initiator needs to be mixed with dopamine hydrochloride salt in an organic solvent (such as N,N-dimethylformamide) first, so that the acyl bromide group forms an ester group with the phenolic hydroxyl group, and then induces dopamine to self-polymerize on the membrane surface to form a polydopamine coating. It should be emphasized that the blending process needs to react for several hours under a nitrogen atmosphere to prevent α-bromoisobutyryl bromide from being hydrolyzed and losing its reaction effect when it encounters water vapor in the air. In addition, triethylamine, which also has a pungent odor, needs to be added as an acid binding agent to promote the reaction. This operation method requires air isolation conditions, and the reagents used are highly toxic and have a negative impact on the environment. Therefore, the method provided by the present invention is superior to traditional polydopamine coatings and α-bromoisobutyryl bromide initiators in terms of environmental protection and ease of operation.

[0023] Furthermore, the molecular brush-modified anti-fouling polyamide membrane prepared by the above-mentioned method of the present invention exhibits improved water flux, excellent resistance to organic fouling and inorganic scaling, and superior stability, making it more suitable for long-term use. After 24 hours of filtration in simulated wastewater, the flux decay rate (FDR) was only 8.8%, and the flux recovery rate (FRR) was 96.6%. In ultrafiltration tests of landfill leachate membrane bioreactor (MBR) effluent, the flux recovery rate (FRR) remained at 94.2% after three cycles of filtration. This invention provides another green, efficient, and simple solution for constructing molecular brush coatings on the surface of polyamide nanofiltration membranes.

[0024] Preferably, in step S1, the polyethyleneimine is grafted onto the surface of the polyamide membrane through an EDC / NHS reaction.

[0025] Further preferably, in step S1, the specific operation of covalently grafting polyethyleneimine onto the surface of the polyamide membrane is: immersing the polyamide membrane in an aqueous solution containing EDC (N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide hydrochloride), NHS (N-hydroxysuccinimide) and polyethyleneimine to react, thereby forming an amino functional layer on the surface of the polyamide membrane.

[0026] Preferably, the reaction concentration of NHS in the aqueous solution is 0.001-0.02 mol / L; further preferably, the reaction concentration of NHS in the aqueous solution is 0.008-0.015 mol / L.

[0027] Preferably, the reaction ratio of EDC to NHS is 1:2-4:1.

[0028] Preferably, in step S1, at least one of the following (a) to (c) is selected:

[0029] (a) the reaction concentration of polyethyleneimine is 0.1-1.5%; preferably, the reaction concentration is 0.8-1.3%; more preferably, the reaction concentration is 1-1.2%; most preferably, the reaction concentration is 1%;

[0030] (b) the reaction time in the aqueous solution is 30-300 min; preferably, the reaction time is 80-160 min; more preferably, the reaction time is 100-140 min; most preferably, the reaction time is 120 min;

[0031] (c) The reaction temperature in aqueous solution is 15-60°C; preferably, the reaction temperature is 20-30°C; most preferably, the reaction temperature is 25°C.

[0032] Preferably, the polyethyleneimine comprises one or more of linear polyethyleneimine and branched polyethyleneimine.

[0033] Preferably, the molecular weight of the polyethyleneimine is 100-750,000 Da. Further preferably, the molecular weight of the polyethyleneimine is 200-10,000 Da; more preferably, the molecular weight of the polyethyleneimine is 300-1,000 Da; and most preferably, the molecular weight of the polyethyleneimine is 400-800 Da. More specifically, the molecular weight of the polyethyleneimine can be 100 Da, 200 Da, 300 Da, 400 Da, 500 Da, 600 Da, 700 Da, 800 Da, 900 Da, 1000 Da, 2000 Da, 4000 Da, 6000 Da, 8000 Da, 10000 Da, 50000 Da, 100000 Da, 200000 Da, 400000 Da, 600000 Da, etc., or an interval range formed by any of the above values, such as 200-800 Da, 400-5000 Da, etc., but the present invention is not limited thereto.

[0034] Preferably, the polyamide membrane can be a polyamide membrane conventionally used in the art or commercially available, such as DuPont NF90. Preferably, the molecular weight cutoff of the polyamide membrane is 100-2000 Da; further preferably, the molecular weight cutoff is 120-1000 Da; more preferably, the molecular weight cutoff is 140-500 Da; more preferably, the molecular weight cutoff is 150-200 Da. More specifically, the molecular weight cutoff of the polyamide membrane can be 100 Da, 110 Da, 120 Da, 130 Da, 140 Da, 150 Da, 160 Da, 170 Da, 180 Da, 190 Da, 200 Da, 500 Da, 600 Da, 800 Da, 1000 Da, 1400 Da, 1800 Da, etc., or an interval range formed by any of the above values, such as 200-800 Da, 120-180 Da, etc., but the present invention is not limited thereto.

[0035] Preferably, in step S2, the specific operation of reacting α-bromoisobutyric acid with the amino-functionalized layer to form an initiator layer is: immersing the polyamide membrane having the amino-functionalized layer formed in step S1 into an aqueous solution containing EDC, NHS and α-bromoisobutyric acid to react, thereby forming an initiator layer.

[0036] Further preferably, in step S2, at least one of the following (d) to (f) is selected:

[0037] (d) the mass fraction of α-bromoisobutyric acid in the aqueous solution is 0.1-1.5%; preferably, the mass fraction of α-bromoisobutyric acid is 0.5-1.2%; more preferably, the mass fraction of α-bromoisobutyric acid is 0.8-1.0%;

[0038] (e) the reaction time in the aqueous solution is 30-300 min; preferably, the reaction time is 80-280 min; more preferably, the reaction time is 200-260 min; most preferably, the reaction time is 240 min;

[0039] (f) The reaction temperature in aqueous solution is 15-60°C; preferably, the reaction temperature is 20-30°C; most preferably, the reaction temperature is 25°C.

[0040] Preferably, in steps S1 and S2, the aqueous solution is a MES buffer solution. More specifically, the concentration of the MES buffer solution is 0.001-0.02 mol / L; further preferably, the concentration is 0.008-0.015 mol / L. More specifically, the pH of the MES buffer solution is 5.0-6.0; most preferably, the pH is 5.5.

[0041] Preferably, in some specific embodiments, the operation of step S3 is: immersing the polyamide membrane after the reaction in step S2 in an ATRP reaction solution 1 containing a zwitterionic polymer monomer, adding a reducing agent to initiate free radical polymerization to form a zwitterionic hydrophilic layer (i.e., a hydrophilic PSBMA layer); further, immersing the polyamide membrane after the reaction in an ATRP reaction solution 2 containing a fluorine-containing polymer monomer, adding a reducing agent to initiate free radical polymerization to form a low surface energy layer (i.e., a low surface energy PHFBM layer).

[0042] Preferably, the ATRP reaction solution 1 and the ATRP reaction solution need to be subjected to a bubbling deoxygenation operation. More specifically, the total time of the bubbling deoxygenation operation is 10-30 minutes; most preferably, the total time of the bubbling deoxygenation operation is 20 minutes.

[0043] Preferably, the monomer of the zwitterionic polymer is selected from one or more of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, and 2-methacryloyloxyethyl phosphorylcholine; and / or, the monomer of the fluorine-containing polymer is selected from one or more of hexafluorobutyl methacrylate, dodecafluoroheptyl methacrylate, and trifluoroethyl methacrylate.

[0044] Preferably, the ATRP reaction solution 1 and the ATRP reaction solution 2 further include: a solvent, copper chloride and tris(2-pyridylmethyl)amine.

[0045] Specifically, the solvent is a mixed solution of an alcohol solvent (such as isopropyl alcohol) and water; the volume ratio of the alcohol solvent to water is 1:1-1:3. Specifically, the concentration of copper chloride in the ATRP reaction solution 1 is 1-20 mmol / L; preferably, the concentration of copper chloride is 3-8 mmol / L; most preferably, the concentration of copper chloride is 5 mmol / L. Specifically, the concentration of tris(2-pyridylmethyl)amine in the ATRP reaction solution 1 is 0.01-0.12 mol / L; preferably, the concentration of tris(2-pyridylmethyl)amine is 0.02-0.06 mol / L; most preferably, the concentration of tris(2-pyridylmethyl)amine is 0.03 mol / L.

[0046] Preferably, the reducing agent can be a reducing agent commonly used in the art for SI-ATRP reactions. More specifically, the reducing agent includes, but is not limited to, L-ascorbic acid. Specifically, the reducing agent is added in an amount of 1-10 g per liter of reaction solution; preferably, the reducing agent is added in an amount of 4-8 g per liter of reaction solution; and most preferably, the reducing agent is added in an amount of 6 g per liter of reaction solution.

[0047] Preferably, the reaction time in the ATRP reaction solution 1 is 15-60 minutes; further preferably, the reaction time in the ATRP reaction solution 1 is 30-50 minutes; most preferably, the reaction time in the ATRP reaction solution 1 is 40 minutes. Preferably, the reaction temperature in the ATRP reaction solution 1 is 15-60°C. Most preferably, the reaction temperature is 25°C.

[0048] Preferably, the reaction time in ATRP reaction solution 2 is 15-120 min; more preferably, the reaction time in ATRP reaction solution 1 is 20-50 min; most preferably, the reaction time in ATRP reaction solution 1 is 30 min. Preferably, the reaction temperature in ATRP reaction solution 2 is 15-60°C. Most preferably, the reaction temperature is 25°C.

[0049] Furthermore, the present invention seeks to protect the molecular brush modified anti-pollution polyamide membrane prepared by the above preparation method.

[0050] Furthermore, the present invention seeks to protect the use of the above-mentioned molecular brush modified anti-fouling polyamide membrane in wastewater treatment.

[0051] Furthermore, the present invention claims protection for the use of α-bromoisobutyric acid as an initiator in the preparation of polyamide membranes by surface-initiated atom transfer radical polymerization.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The method provided by the present invention is simple in operation and can be carried out at room temperature, in aqueous solution and in air. The reaction conditions are mild, and there is no need to isolate the reaction from air and water vapor. There is no need to use triethylamine as an acid-binding agent to participate in the reaction, and no organic solvent is required. In addition, the reagents used are non-toxic and have no negative impact on the environment.

[0054] (2) The molecular brush modified anti-fouling polyamide membrane prepared by the above method of the present invention has better water flux, excellent resistance to organic pollution and inorganic scaling, better stability, and is more conducive to long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is the water contact angle of each polyamide film in Example 1.

[0056] Figure 2 The scanning electron microscope (SEM) characterization images of each polyamide membrane in Example 1 are shown.

[0057] Figure 3 The atomic force microscope (AFM) characterization images of each polyamide film in Example 1 are shown.

[0058] Figure 4For the membrane N in Example 1 Br X-ray photoelectron spectroscopy (XPS) high-resolution spectrum of Br 3d.

[0059] Figure 5 This is a membrane fouling curve diagram when each polyamide membrane in Example 1 is applied to humic acid simulated wastewater.

[0060] Figure 6 This is a membrane fouling curve diagram when each polyamide membrane in Example 1 is applied to the actual wastewater leachate MBR effluent deep treatment process.

[0061] Figure 7 This is a long-term membrane fouling curve diagram of the membrane D3 prepared in Example 1 when applied to the actual wastewater leachate MBR effluent deep treatment process.

[0062] Figure 8 The short-term pollution curves of the polyamide membranes prepared in Examples 1-3 and Comparative Examples 3 and 4 when applied to bovine serum albumin simulated wastewater are shown. DETAILED DESCRIPTION

[0063] The present invention will be further described below with reference to the accompanying drawings and specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0064] Example 1 Preparation of Molecular Brush Modified Anti-Pollution Polyamide Membrane

[0065] (1) DuPont's commercial polyamide film Fimtec TM NF90 was rinsed with deionized water several times to remove the preservative and membrane pore retention agent, and then soaked in deionized water for later use, which was marked as N0;

[0066] (2) Prepare a 0.1 mol / L MES buffer solution with a pH of 5.5, dissolve EDC and NHS in the MES buffer solution successively, with the concentrations of EDC and NHS both being 0.1 mol / L, and finally add polyethyleneimine (PEI) with an average molecular weight of 600 Da, with a mass fraction of PEI of 1%;

[0067] (3) Fix N0 in the reaction device and ensure that the selective layer of the membrane faces upward; pour the solution prepared in step (2) into the reaction device, place it on a shaker, and react at room temperature in the open air at a speed of 60 rpm for 2 h. After the reaction is completed, pour out the solution and wash away the remaining reactants with deionized water. Keep the membrane fixed in the reaction device and mark the PEI modified membrane as N PEI membrane;

[0068] (4) Prepare a 0.1 mol / L MES buffer solution with a pH of 5.5, dissolve EDC and NHS in the MES buffer solution successively, with the concentrations of both EDC and NHS being 0.1 mol / L, and finally add α-bromoisobutyric acid to fully dissolve them, with the mass fraction of α-bromoisobutyric acid being 1%;

[0069] (5) Pour the solution prepared in step (4) above into the PEI The membrane was placed on a shaker in a reaction device and reacted at 60 rpm in open air at room temperature for 4 h. After the reaction was completed, the solution was poured out and the remaining reactants were washed with deionized water and marked as N Br membrane;

[0070] (6) Prepare ATRP reaction solution 1 containing zwitterionic monomers. The solvent is a mixture of isopropanol and water in a volume ratio of 1:1. The solutes are 270 mmol / L [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide (SBMA), 5 mmol / L copper chloride and 0.03 mol / L tris(2-picolyl)amine (TPMA). Br The membrane was cut into appropriate size and added to the three-necked flask together with the above ATRP reaction solution 1, and nitrogen was continuously bubbled into the flask for 20 min;

[0071] (7) Prepare a reducing agent solution, the volume of which is 1 / 20 of the volume of the ATRP reaction solution 1 in step (6), the solvent is a mixture of isopropanol and water in a volume fraction ratio of 1:1, the solute is L-ascorbic acid, and the amount of L-ascorbic acid added is 6 g per liter of ATRP reaction solution 1;

[0072] (8) After the nitrogen bubbling time in step (6) is completed, the reducing agent solution in step (7) is poured into the three-necked flask, and then the three bottle openings of the three-necked flask are quickly sealed with rubber stoppers to place the reaction system in an oxygen-free environment. The total reaction time is 40 min. After the reaction is completed, the membrane is taken out, washed thoroughly with ultrapure water, soaked in ultrapure water, and stored in a refrigerator at 4°C. The membrane is marked as N1 membrane;

[0073] (9) A secondary ATRP reaction was performed to graft low surface energy fluorine-containing molecular brushes. The operation was the same as that in steps (6) to (8) above, except that ATRP reaction solution 2 was used, in which the monomer was replaced with hexafluorobutyl methacrylate (HFBM) at a concentration of 5 mmol / L; the reaction time in step (8) was 30 min, and a molecular brush-modified anti-fouling polyamide membrane was prepared, which was labeled as D3 membrane.

[0074] Example 2 Preparation of Molecular Brush Modified Anti-Pollution Polyamide Membrane

[0075] The difference between this embodiment and embodiment 1 is that the mass fraction of polyethyleneimine in step (2) is 0.1%, and the molecular brush modified anti-fouling polyamide membrane finally prepared is marked as D1.

[0076] Example 3 Preparation of Molecular Brush Modified Anti-Pollution Polyamide Membrane

[0077] The difference between this embodiment and embodiment 1 is that the mass fraction of polyethyleneimine in step (2) is 0.5%, and the molecular brush modified anti-fouling polyamide membrane finally prepared is marked as D2.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that ethylenediamine (EDA) is used in step (2) instead of polyethyleneimine, and the mass fraction is kept at 1%. The membrane grafted with ethylenediamine is marked as N EDA The molecular brush modified anti-fouling polyamide membrane finally prepared was labeled D6.

[0080] Comparative Example 2

[0081] This comparative example compares the stability of a polyethyleneimine coating and a polydopamine coating fixed with an initiator. The specific steps are as follows:

[0082] (1) After commercial polyamide membrane NF90 was rinsed with deionized water several times to remove preservatives and membrane pore retention agents, it was soaked in deionized water for later use;

[0083] (2) Prepare 1 mol / L Tris buffer with a pH of 8.5, add an appropriate amount of dopamine hydrochloride to dissolve it, and prepare a 4 g / L dopamine hydrochloride modified solution;

[0084] (3) Fix the membrane in the reaction device, ensuring that the selective layer of the membrane faces upward, pour the modified solution from step (2) on the membrane surface, and allow dopamine to self-polymerize on the membrane surface for 10 minutes. After the reaction is complete, pour out the activation solution and wash away the remaining reactants with deionized water. Keep the membrane fixed in the reaction device and mark the two prepared membranes as N and N respectively. PDA-1 and N PDA-2 ;

[0085] (4) According to steps (1) to (3) of Example 1, two PEI modified membranes were prepared and marked as N and PEI-1 and N PEI-2 ;

[0086] (5) Prepare hydrochloric acid solution with pH=2 and sodium hydroxide solution with pH=13 respectively, and PEI-1 and N PDA-1 At the same time, the membrane was immersed in hydrochloric acid. PEI-2 and N PDA-2The membranes were immersed in sodium hydroxide solution for 12 hours at the same time. The membranes after acid treatment were marked as N PEI-1A 、N PDA-1A , the membranes after alkali treatment were marked as N PEI-2B 、N PDA-2B Comparative film N PEI-1 、N PDA-1 、N PEI-2 and N PDA-2 The coating stability was evaluated by measuring the changes in pure water permeation flux and sodium sulfate and magnesium chloride retention performance before and after acid and alkali immersion.

[0087] Comparative Example 3 Preparation of Molecular Brush Modified Anti-Pollution Polyamide Membrane

[0088] The difference between this comparative example and Example 1 is that the mass fraction of polyethyleneimine in step (2) is 2.0%, and the molecular brush modified anti-fouling polyamide membrane finally prepared is marked as D4.

[0089] Comparative Example 4 Preparation of Molecular Brush Modified Anti-Pollution Polyamide Membrane

[0090] The difference between this comparative example and Example 1 is that the mass fraction of polyethyleneimine in step (2) is 3.0%, and the molecular brush modified anti-fouling polyamide membrane finally prepared is marked as D5.

[0091] Test Case

[0092] 1. Experimental Subjects

[0093] Polyamide nanofiltration membranes prepared using the examples and comparative examples.

[0094] 2. Experimental Methods

[0095] The prepared polyamide nanofiltration membrane was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and its hydrophilic and hydrophobic properties were measured. The pure water flux and salt retention rate were also measured. The anti-fouling performance during the filtration of simulated wastewater containing humic acid, simulated wastewater containing bovine serum albumin, and the ultrafiltration effluent of the membrane bioreactor (MBR) of actual wastewater leachate was also measured.

[0096] (1) Pure water flux measurement:

[0097] This experiment uses a cross-flow filtration device for measurement, and the effective area of the membrane is 16 cm 2 The filtration temperature was controlled at 25°C, the test pressure was 6 bar, and the membrane surface flow rate was controlled at 0.1 m / s. The polyamide nanofiltration membrane was pre-pressed with pure water. After the flux stabilized, the water permeability J of the polyamide nanofiltration membrane was recorded. The calculation formula is:

[0098]

[0099] in, V represents the volume of leachate (L), A Indicates the effective membrane area (m 2 ), Indicates the filtering time (h).

[0100] (2) Determination of membrane retention rate:

[0101] Determine the retention rate of polyamide nanofiltration membranes for 2000 mg / L MgCl2 and Na2SO4 solutions. The retention rate of polyamide nanofiltration membranes is calculated using the following formula:

[0102]

[0103] in, C F and C P Represent the conductivity of the concentrate and leachate respectively.

[0104] (3) Anti-pollution performance test:

[0105] The humic acid HA simulated wastewater simulates the composition of actual landfill leachate and is prepared with 6 g / L NaCl, 0.15 g / L CaCl2, and 0.1 g / L humic acid, with the pH adjusted to 7.0. Before the test, the polyamide nanofiltration membrane was pre-pressurized with 30 bar ultrapure water overnight and the initial flux was adjusted with 6 g / L NaCl solution. J 0 to 30 L·m -2 ·h -1 The pollution test lasted for 24 hours, during which the leachate was refluxed every hour to keep the overall osmotic pressure of the raw liquid constant and the membrane surface flow rate at 0.44 m·s -1 and temperature 25±3℃. After the test, rinse the membrane with ultrapure water for 30 minutes and test the flux after cleaning with NaCl solution with the same conductivity. J 2, and then evaluate the flux recovery rate (FRR). The flux decline ratio (FDR) and flux recovery ratio (FRR) are respectively calculated by the initial flux ( J 0), post-pollution flux ( J t ) and post-cleaning flux ( J 2) Calculation: The formula is as follows:

[0106]

[0107]

[0108] in, J 0 andJ t are the initial flux and final flux during the test, J 2 is the NaCl flux after physical cleaning after contamination filtration.

[0109] Bovine serum albumin (BSA) simulated wastewater was used to evaluate the treatment effects of wastewater treatment processes and equipment on protein-containing wastewater. It was prepared with 2 g / L NaCl, 0.15 g / L CaCl2, and 0.1 g / L BSA. Before testing, the polyamide nanofiltration membrane was pre-pressurized with 30 bar ultrapure water overnight and the initial flux was adjusted to 30 L·m with 2 g / L NaCl solution. -2 ·h -1 The pollution test lasted for 6 hours, during which the leachate was refluxed every hour to keep the overall osmotic pressure of the raw liquid constant and the transmembrane flow rate at 0.44 m·s -1 and temperature 25 ± 3 ° C. After the test, the membrane was rinsed with ultrapure water for 30 min, and the flux recovery rate (FRR) of the membrane was evaluated with NaCl solution with the same conductivity.

[0110] The actual wastewater was collected from the ultrafiltration effluent of the MBR treatment of a waste incineration plant in Guangzhou. The water sample was stored at 4 °C and the pretreatment included 0.22 μ m polyethersulfone microfiltration membrane filtration removed suspended particles, and ICP-OES and TOC analysis were used to detect metal ion and organic matter concentrations. During the test, sodium chloride solution with the same conductivity as actual water was first used for pre-pressure and the initial flux was adjusted to 40 ± 2 L·m -2 ·h -1 4.5 L of wastewater was used as the feed solution and continuous filtration was performed until the cumulative permeate volume reached 3 L or the FDR exceeded 80%. After the test, the membrane was rinsed with ultrapure water for 30 minutes, and the flux recovery rate (FRR) was evaluated using a NaCl solution with the same conductivity.

[0111] 3. Experimental Results

[0112] Table 1

[0113]

[0114] Table 1 is a summary of the pure water permeation flux and inorganic salt retention rate of the polyamide nanofiltration membranes prepared in Examples 1-3 and Comparative Examples 1-4 of the present application. As can be seen from the results in Table 1, after the original membrane was grafted with PEI, the pure water permeation flux decreased to 5.0 LMH / bar, the sodium sulfate retention rate decreased to 95.0%, and the magnesium chloride retention rate increased to 97.7%. This is mainly because the grafting of PEI shrinks the membrane pores, making the membrane pores denser, and the pure water permeation flux decreases. At the same time, the positive charge of the membrane is enhanced, resulting in a weakened rejection of sulfate ions and an enhanced rejection of magnesium ions. After the SI-ATRP reaction grafted with zwitterionic molecular brushes and diblock molecular brushes, the pure water permeation flux further decreased to 2.6 LMH / bar and 2.3 LMH / bar, the sodium sulfate retention rate increased to 97.6% and 98.6%, respectively, and the magnesium chloride retention rate decreased to 94.2% and 96.7%, respectively. This is because the dense molecular brush layer increases the resistance of water molecules to pass through the membrane, and at the same time the grafting of the initiator consumes the amino groups on the membrane surface, weakening the positive charge of the membrane. PEI Compared with N0, the changes in pure water permeation flux and salt rejection performance of N1, D3 membranes indicate that the new initiator and diblock molecular brush coating were successfully grafted on the membrane surface.

[0115] In addition, compared with the existing polyamide membrane synthesized by the method of dopamine hydrochloride salt + α-bromoisobutyryl bromide, its water flux is lower, only 0.83 L m -2 h -1 bar -1 The polyamide membrane prepared by the polyethyleneimine + α-bromoisobutyric acid scheme adopted in the present invention has excellent water flux, with a water flux of ≥2.3 L m -2 h -1 bar -1 . Significantly better than existing solutions.

[0116] The pure water permeation fluxes of membranes D1 to D5 obtained in Examples 1 to 3 and Comparative Examples 3 and 4 were 3.1, 2.7, 2.3, 1.8, and 1.3 L m, respectively. -2 h -1 bar -1 There are also differences in the inorganic salt retention rate, which shows that increasing the mass fraction of polyethyleneimine (reaction concentration) can increase the amount of polyethyleneimine grafted to the membrane surface, thereby increasing the number of SI-ATRP reaction active sites and obtaining a denser molecular brush layer, which in turn leads to a decrease in the pure water permeation flux.

[0117] The ethylenediamine modified membrane N prepared in Comparative Example 1 EDA The pure water permeation fluxes of the molecular brush modified membrane D6 were 5.3 and 1.6 L m -2 h -1 bar -1, the sodium sulfate rejection rate decreased slightly compared to the original membrane N0, while the magnesium chloride rejection rates increased significantly to 97.0% and 95.5%, respectively, demonstrating the successful grafting of ethylenediamine onto the membrane surface and the successful construction of the molecular brush. Furthermore, compared to membrane D3 prepared in Example 1, membrane D6 exhibited a lower pure water permeation flux. This is likely due to the molecular weight of ethylenediamine being only 60.1 Da, far lower than the 600 Da used in Example 1 for polyethyleneimine. Ethylenediamine with a smaller molecular weight is more easily grafted into the membrane pores, leading to the growth of molecular brushes within the membrane pores, which can block the pores and thus reduce the pure water permeation flux.

[0118] The membrane N of the grafted polyethyleneimine coating in Comparative Example 2 PEI-1 and N PEI-2 The pure water permeation fluxes were 4.5 and 4.6 L m -2 h -1 bar -1 , while the polydopamine-coated membrane N PDA-1 and N PDA-2 The pure water permeation fluxes were 3.8 and 4.0 L m -2 h -1 bar -1 This is mainly because the grafted polyethyleneimine forms a nano-scale coating, while the coating formed by dopamine self-polymerization has a certain thickness, so it has a greater resistance to water molecule transmission and a lower pure water permeation flux. After soaking in hydrochloric acid at pH = 2 for 12 hours, the membrane N PDA-1A The pure water permeation flux of N PDA-1 Significantly increased to 4.5 L m -2 h - 1 bar -1 The retention rates of sodium sulfate and magnesium chloride decreased to 97.4% and 93.6%, respectively, which indicated that the polydopamine coating was partially decomposed after acid immersion. PEI-1A Maintained with N PEI-1 Similar pure water permeation flux and inorganic salt retention rate, both 4.6 L m -2 h -1 bar -1 , the sodium sulfate and magnesium chloride rejection rates were 97.0% and 96.5% respectively. Similarly, after soaking in sodium hydroxide solution with pH = 13 for 12 hours, the membrane N PDA-2B The pure water permeation flux is compared with N PDA-2 Significantly increased to 4.5 L m -2 h - 1 bar -1 , the sodium sulfate rejection rate dropped to 97.1%, which indicates that the polydopamine coating was partially decomposed after alkali immersion. PEI-2BMaintained with N PEI-2 Similar pure water permeation flux and inorganic salt retention rate are 4.7 L m -2 h -1 bar -1 The retention rates of sodium sulfate and magnesium chloride were 96.2% and 97.1%, respectively. In conclusion, polyethyleneimine coating is more stable than polydopamine coating in both acidic and alkaline environments.

[0119] Figure 1 is the water contact angle of each polyamide film in Example 1. Figure 1 The results show that after the PEI hydrophilic layer was grafted on the membrane surface, the contact angle of the membrane did not change significantly. This may be because the base membrane has a strong hydrophilicity and the membrane surface still maintains good hydrophilicity after PEI modification. Br The water contact angle of N1 increased significantly to 50.9°, indicating the successful grafting of α-bromoisobutyric acid onto the PEI substrate. The hydrophobic methyl groups contained in the α-bromoisobutyric acid molecular structure enhance the membrane's hydrophobicity. After the zwitterionic brushes were grafted onto the membrane surface via SI-ATRP, the contact angle of N1 decreased to 24.9°, demonstrating the successful grafting of the superhydrophilic zwitterionic brushes onto the membrane surface. Further grafting of the fluorinated brushes increased the contact angle of D3 to 38.5°, primarily due to the hydrophobicity of the fluorinated brushes. Figure 1 The successful grafting of the novel initiator coating and molecular brushes was demonstrated.

[0120] Figure 2 Scanning electron microscopy (SEM) images of the polyamide membranes in Example 1 show no significant changes in surface morphology after PEI modification, indicating that PEI grafting is limited to the molecular level and does not stack to form a thick coating. However, after grafting with zwitterionic molecular brushes, more ridge-like protrusions appear on the surface, primarily due to clusters formed by the polyelectrolyte effect of the zwitterionic polymer brushes. Further grafting with fluorinated molecular brushes reveals large dark areas, indicating that the fluorinated molecular brushes have formed a dense coating on the surface.

[0121] Figure 3Figure 1 shows atomic force microscopy (AFM) images of the polyamide membranes used in Example 1. PEI modification of the membrane surface showed no significant change in surface roughness. This is primarily due to the fact that PEI grafting is limited to the molecular level, forming a nanometer-thick coating and therefore having minimal impact on the roughness of the original membrane. The introduction of zwitterionic molecular brushes also did not cause a significant change in roughness. Although the zwitterionic molecular brushes form clusters under dry conditions due to the polyelectrolyte effect, which could potentially increase roughness, some of the zwitterionic molecular brushes fill in some of the uneven areas of the original membrane, offsetting the effects of the two on roughness and maintaining the same roughness. Further grafting of fluorinated molecular brushes to the membrane resulted in a significant increase in roughness, primarily due to the formation of unevenly sized clusters between the fluorinated molecular brushes through hydrophobic interactions.

[0122] Figure 4 For the membrane N in Example 1 Br The X-ray photoelectron spectroscopy (XPS) high-resolution spectrum of Br 3d shows an obvious Br 3d corresponding absorption peak near the binding energy of 68 eV, indicating the successful grafting of the initiator α-bromoisobutyric acid (Biba) on the membrane surface and proving the feasibility of the new initiator in the present invention.

[0123] Table 2

[0124]

[0125] Table 2 is a summary table of FDR and FRR of the modified anti-pollution polyamide nanofiltration membranes prepared in Examples 1-3 and Comparative Examples 3 and 4 of the present application in short-cycle humic acid simulated wastewater, bovine serum albumin simulated wastewater and landfill leachate MBR ultrafiltration effluent filtration experiments. Figure 5 The membrane fouling curves of each polyamide membrane in Example 1 were applied to humic acid simulated wastewater. PEI As a control group, Figure 5 The molecular brush-modified nanofiltration membranes N1 and D3 exhibited excellent antifouling properties. After 24 hours of filtration, the flux reduction rates (FRR) were 23.7% and 8.8%, respectively, and the flux recovery rates after cleaning reached 82.6% and 96.6% (Table 2). These results demonstrate that the novel initiator coating proposed in this invention can be used to prepare modified nanofiltration membranes with significant antifouling properties.

[0126] Figure 6 The membrane fouling curves of each polyamide membrane in Example 1 when applied to the actual wastewater leachate MBR ultrafiltration effluent. PEI As a control group, Figure 6It can be seen that the nanofiltration membranes N1 and D3 modified with molecular brushes have excellent anti-fouling performance. When the membrane flux is reduced to less than 20% of the initial flux, the cumulative permeate volume can reach 2900 mL and 3000 mL, while the control N0 and N PEI The effluent volume is only 2600 mL. This result shows that the novel initiator coating proposed in the present invention can be used to prepare a modified nanofiltration membrane with significant anti-fouling effect and can be applied to actual wastewater treatment.

[0127] Table 3

[0128]

[0129] Table 3 is a summary table of the FDR and FRR of each cycle in the long-cycle landfill leachate MBR ultrafiltration effluent filtration experiment of the modified anti-pollution polyamide nanofiltration membrane prepared in Example 1 of the present application. Figure 7 The membrane D3 prepared in Example 1 is applied to the long-term membrane fouling curve of the actual wastewater landfill leachate MBR ultrafiltration effluent. As can be seen from the results, the flux decline rate of the membrane in each filtration cycle gradually increases. This is mainly due to the fact that the pollutant concentration in the raw liquid gradually increases with the continuous concentration of the wastewater, which gradually increases the rate at which pollutants migrate to the membrane surface. At the same time, the osmotic pressure also increases. Under the dual effects of concentration polarization and osmotic pressure increase, the membrane flux inevitably decreases. However, as shown in Table 3, after completing three cycles of anti-pollution tests, after simple pure water physical cleaning, the modified membrane can still achieve a flux recovery rate of 94.2%. This surface dual defense functional molecular brush coating can significantly prevent the formation of irreversible pollution and extend the service life of the membrane.

[0130] Figure 8 The short-term pollution curves of the polyamide membranes prepared in Examples 1-3, Comparative Examples 3 and 4 were applied to bovine serum albumin simulated wastewater. Figure 8 The flux of molecular brush-modified polyamide nanofiltration membranes D1-D5 decreased more slowly during filtration than that of the original membrane N0, indicating that the molecular brush-modified membranes possess superior antifouling properties. After 6 hours of contamination filtration, the flux decline rate (FDR) of the original membrane N0 reached 35.5%, while the flux recovery rate (FRR) was only 85.6%. With increasing polyethyleneimine grafting concentration, the FDR of membranes D1-D5 gradually decreased, while the flux recovery rate (FRR) gradually increased. This indicates that increasing the polyethyleneimine grafting concentration increases the molecular brush grafting density, thereby improving antifouling performance (Table 3). Table 1 indicates that there is a trade-off between the antifouling performance of molecular brush-modified membranes and the pure water permeation flux, which requires comprehensive consideration.

[0131] In summary, the new initiator coating proposed in the present invention, that is, the coating formed by combining polyethyleneimine and α-bromoisobutyric acid, is not only environmentally friendly and easy to operate, but also has excellent stability. This is mainly reflected in the fact that polyethyleneimine and α-bromoisobutyric acid are combined with the membrane surface through the formation of covalent bonds; at the same time, in the anti-pollution test, the molecular brush modified membrane has excellent anti-pollution performance, indicating that the new initiator coating can not only replace the traditional polydopamine initiator coating in the coating grafting method, but also can achieve similar effects as the polydopamine initiator coating in the subsequent process of anti-pollution modification of the membrane, and is also applicable.

[0132] The foregoing examples are merely illustrative, serving to illustrate some of the features of the method of the present invention. The appended claims are intended to claim the widest possible scope that can be envisioned, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the present invention. Some numerical ranges used in the claims also include subranges therein, and variations in these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for preparing a molecular brush modified anti-pollution polyamide membrane, characterized in that: The steps include: S1. Covalently grafting polyethyleneimine onto the surface of the activated polyamide membrane to form an amino-functionalized layer; the reaction concentration of polyethyleneimine is 0.05-1.5wt%; S2. α-bromoisobutyric acid reacts with the amino-functionalized layer to form an initiator layer; S3 initiator layer sequentially grafted zwitterionic polymer and fluorinated polymer to form a zwitterionic hydrophilic layer and a low surface energy layer to prepare a molecular brush modified anti-fouling polyamide membrane; In the step S1, the polyethyleneimine is grafted onto the surface of the polyamide membrane through an EDC / NHS reaction.

2. The preparation method according to claim 1, characterized in that In step S1, the specific operation of covalently grafting polyethyleneimine onto the surface of the polyamide membrane is: immersing the polyamide membrane in an aqueous solution containing EDC, NHS and polyethyleneimine to react, thereby forming an amino functional layer on the surface of the polyamide membrane.

3. The preparation method according to claim 2, characterized in that: At least one selected from the following (a)-(c): (a) The reaction concentration of polyethyleneimine is 0.1-1.2 wt%; (b) the reaction time in aqueous solution is 30-240 min; (c) The reaction temperature in aqueous solution is 15-60°C.

4. The preparation method according to claim 1, characterized in that In step S2, the specific operation of reacting α-bromoisobutyric acid with the amino-functionalized layer to form an initiator layer is as follows: immersing the polyamide membrane having the amino-functionalized layer formed in step S1 in an aqueous solution containing EDC, NHS and α-bromoisobutyric acid to react, thereby forming an initiator layer.

5. The preparation method according to claim 4, characterized in that: At least one selected from the following (d)-(f): (d) the mass fraction of α-bromoisobutyric acid in the aqueous solution is 0.1-1.5%; (e) the reaction time in aqueous solution is 30-300 min; (f) The reaction temperature in aqueous solution is 15-60°C.

6. The preparation method according to claim 1, characterized in that: The monomer of the zwitterionic polymer is selected from one or more of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, and 2-methacryloyloxyethyl phosphorylcholine; and / or The monomer of the fluorine-containing polymer is selected from one or more of hexafluorobutyl methacrylate, dodecafluoroheptyl methacrylate, and trifluoroethyl methacrylate.

7. The molecular brush modified anti-pollution polyamide membrane prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the molecular brush modified anti-pollution polyamide membrane according to claim 7 in wastewater treatment.

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