Preparation method of zwitterionic-fluorinated functionalized antifouling polyamide composite membrane

Abstract

This invention discloses a method for preparing a zwitterionic-fluorine functionalized antifouling polyamide composite membrane, comprising the following steps: (1) modifying a porous base membrane with a polyphenol-polyethyleneimine interlayer modification solution, denoted as PSF membrane; (2) preparing a polyamide layer on the PSF membrane by interfacial polymerization reaction using organic amines and organic acyl chlorides, denoted as TFC membrane; (3) grafting a tetramethylolphosphine sulfate aqueous solution onto the TFC membrane, denoted as TFC-P membrane; (4) grafting a fluorinated acyl chloride-containing oil phase solution onto the surface of the TFC-P membrane at a uniform rate, denoted as TFC-P-F membrane; (5) heat-treating the TFC-P-F membrane in an oven to obtain a crosslinked and stable antifouling polyamide composite membrane. This invention utilizes tetramethylolphosphine sulfate and fluorinated acyl chlorides to modify the polyamide composite membrane, which improves the oleophobicity of the membrane surface without sacrificing its hydrophilicity, thus ensuring the permeation flux of the composite membrane while endowing it with excellent resistance to pollutants and pollutant release capabilities.

Description

Technical Field

[0001] This invention relates to the field of antifouling polyamide composite membrane technology, specifically to a method for preparing a zwitterionic-fluorine functionalized antifouling polyamide composite membrane. Background Technology

[0002] In the field of wastewater treatment, polyamide membrane (NF) separation technology has broad application prospects due to its low energy consumption and wide applicability. However, polyamide membranes suffer from serious membrane fouling problems in practical applications. Pollutants adhere to the membrane surface, leading to a significant reduction in membrane flux, shortened lifespan, increased energy consumption, and frequent cleaning. The main influencing factor of membrane fouling is membrane performance. Surface modification to prepare antifouling polyamide membranes can mitigate membrane fouling during wastewater treatment, fundamentally overcoming the bottleneck in the industrial application of polyamide membranes.

[0003] The mechanisms for preparing antifouling membranes typically include: resisting contaminants, releasing contaminants, and degrading contaminants. Resisting contaminants refers to preventing bacteria, algae, and proteins from adhering to the membrane surface, which can be achieved by increasing the surface hydrophilicity. Releasing contaminants refers to releasing them through hydrodynamic shearing or simple mechanical cleaning; efficient contaminant release can also be achieved using materials with low surface energy or low modulus. Compared to resisting and releasing contaminants, degrading contaminants aims to disrupt their adhesion mechanisms. When contaminants approach a functionalized surface, they can be degraded by oxidants or killed by bactericidal action to kill (attached) bacteria and other microorganisms. Currently, most antifouling membranes resist contaminants by increasing the hydrophilicity of composite membranes. This method has a limited effect and narrow applicability, and because it only achieves antifouling through one mechanism, its antifouling efficiency is relatively low. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane. The method utilizes zwitterionic tetrahydroxymethylphosphonic acid sulfate and fluorinated acyl chloride for modification, which improves the oleophobicity of the membrane surface without sacrificing its hydrophilicity. This method ensures the permeation flux of the composite membrane while endowing it with excellent resistance to pollutants and the ability to prevent pollutant release.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for preparing an amphoteric-fluorine functionalized antifouling polyamide composite membrane, characterized by comprising the following steps:

[0007] (1) Add polyphenol to NaOH solution, stir to dissolve, then add polyethyleneimine, stir continuously until polyethyleneimine dissolves to obtain polyphenol-polyethyleneimine intermediate layer modification solution, apply polyphenol-polyethyleneimine intermediate layer modification solution to the surface of porous support base membrane for soaking modification, after modification, pour out excess modification solution, and then wash thoroughly with deionized water to remove the modification solution remaining on the membrane surface and in the membrane pores to obtain intermediate layer modified porous base membrane, denoted as PSF membrane;

[0008] (2) Fix the PSF membrane prepared in step (1) on the plate frame, cover the membrane surface with the organic amine aqueous solution and let it stand, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife; then pour the organic acyl chloride oil phase solution onto the membrane surface at a uniform speed to carry out the interfacial polymerization reaction to form a polyamide layer. After the reaction is completed, wash the unreacted organic acyl chloride monomer with an organic solvent to obtain a polyamide composite membrane, which is called TFC membrane.

[0009] (3) Pour the tetrahydroxymethylphosphoric acid aqueous solution onto the TFC membrane prepared in step (2) for grafting, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife to obtain a zwitterionic modified polyamide composite membrane, denoted as TFC-P membrane.

[0010] (4) The oil phase solution containing fluorinated acyl chloride is poured at a constant speed onto the surface of the TFC-P membrane prepared in step (3) for grafting. After the reaction is completed, the membrane surface is rinsed with an organic solvent to obtain a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane, denoted as TFC-PF membrane.

[0011] (5) The TFC-PF membrane prepared in step (4) is heat-treated in an oven to obtain a cross-linked and stable anti-fouling polyamide composite membrane.

[0012] In the above technical solution, step (1) is to modify the intermediate layer of the porous base membrane. By constructing a hydrophilic intermediate layer with polyphenols and polyethyleneimine, the surface of the base membrane is adjusted to form a PA active layer with a highly uniform pore size distribution, which allows it to have more aqueous monomers and provide more amine groups, thus promoting the smooth progress of the subsequent interfacial polymerization reaction and fluorinated acyl chloride grafting. Step (3) is to modify the membrane with tetrahydroxymethylphosphoric acid (THPS) monomer, which has zwitterionic properties. The multiple hydrogen bonds of THPS have a high water bonding ability and can build a hydration layer on the surface of the composite membrane, which is equivalent to a physical barrier and can resist the adhesion of pollutants. Step (4) is to modify the membrane with fluorinated acyl chloride. The amidation between the acyl chloride group and the amino group in the fluorinated acyl chloride allows the low surface energy perfluoroalkyl chain to be embedded in the polyamide membrane. The fluorinated acyl chloride can build low surface energy micro-regions on the membrane surface, reduce the molecular interaction force between the membrane surface and pollutants, and facilitate the release of pollutants. Therefore, pollutants can be released through water shear force, reducing the reversible pollution of the composite membrane.

[0013] Further, in step (1), the polyphenol is at least one of hydroquinone, catechol, resorcinol, hydroquinone, pyrogallol, and pyrogallol;

[0014] In step (1), the mass concentration of polyphenol in the polyphenol-polyethyleneimine intermediate modified solution is 0.5-3%, and the mass concentration of polyethyleneimine is 1-5%.

[0015] Furthermore, the modification time of the polyphenol-polyethyleneimine intermediate layer in step (1) is 1 to 10 minutes.

[0016] Furthermore, in step (1), the porous supporting membrane is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyimide ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polyethylene microfiltration membrane, and polypropylene microfiltration membrane.

[0017] Further, in step (2), the organic amine aqueous solution is obtained by dissolving the organic amine in water, and the organic amine is at least one of piperazine, m-phenylenediamine, phenylenediamine, p-phenylenediamine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, ethylenediamine, N,N-bis(2-aminoethyl)ethylenediamine, divinyltriamine, or polyethyleneimine;

[0018] In step (2), the organic acyl chloride oil phase solution is obtained by dissolving the organic acyl chloride in an organic solvent. The organic acyl chloride is at least one of pyromellitic tricarboxylic acid chloride, terephthaloyl chloride, phthaloyl chloride, pyromellitic tetracarboxylic acid chloride, cyclohexyl tricarboxylic acid chloride, cyclobutyrate tetracarboxylic acid chloride, cyclopentyl tetracarboxylic acid chloride, malonyl chloride, glutaryl chloride, and fumarate chloride. The organic solvent is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L, or isopar M.

[0019] In step (2), the mass concentration of the organic amine aqueous solution is 0.1–5%; and the mass concentration of the organic acyl chloride oil solution is 0.01–2%.

[0020] Furthermore, in step (2), during the process of rinsing unreacted organic acyl chloride monomers with an organic solvent, the organic solvent used is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L, or isopar M.

[0021] Furthermore, the polymerization reaction time in step (2) is 10–90 s.

[0022] Furthermore, the mass concentration of the tetrahydroxymethylphosphoric acid aqueous solution in step (3) is 0.05–1.0%.

[0023] Furthermore, the grafting reaction in step (3) lasts for 0.5 to 5 minutes.

[0024] Further, in step (4), the mass concentration of the fluorinated acyl chloride oil phase solution is 0.2-1.0%, and the fluorinated acyl chloride oil phase solution is obtained by dissolving the fluorinated acyl chloride in an organic solvent, the organic solvent being at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L or isopar M.

[0025] The fluorinated acyl chloride is at least one of perfluorooctanoyl chloride, perfluoroundecanoyl chloride, perfluorooctanesulfonyl chloride, nonafluoropentanoyl chloride, perfluorooctanoic acid, heptadecanoyl chloride, and heptafluorobutyryl chloride.

[0026] Furthermore, in step (4), during the process of rinsing the membrane surface with an organic solvent, the organic solvent used is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L, or isopar M.

[0027] Furthermore, the grafting reaction time in step (4) is 30 to 120 seconds.

[0028] Furthermore, in step (5), the heat treatment temperature is 50-80℃ and the heat treatment time is 0.5-5min.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention provides a method for preparing a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane. The method utilizes tetramethylolphosphine sulfate (THPS) monomer, which possesses zwitterionic properties, for hydrophilic modification. The multiple hydrogen bonds of THPS exhibit high water bonding capacity, enabling the construction of a hydrated layer on the composite membrane surface, acting as a physical barrier to resist pollutant adhesion. Furthermore, the THPS grafting process results in a denser separation layer and a narrower pore size distribution, thus constructing a thicker and denser separation layer to efficiently delay pollutant accumulation. In addition, this invention further grafts fluorinated acyl chlorides onto the THPS graft. The amidation between the acyl chloride groups and amino groups in the fluorinated acyl chloride allows low-surface-energy perfluoroalkyl chains to embed into the polyamide membrane. The fluorinated acyl chloride can construct low-surface-energy microregions on the membrane surface, reducing the molecular forces between the membrane surface and pollutants. Therefore, pollutants can be released through water shear force, reducing reversible fouling of the composite membrane. This invention utilizes zwitterionic tetrahydroxymethylphosphonic acid and fluorinated acyl chloride for modification, which improves the oleophobicity of the membrane surface without sacrificing its hydrophilicity, thereby giving the composite membrane excellent resistance to and release of pollutants while ensuring its permeation flux. Attached Figure Description

[0031] To clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart illustrating the preparation process of the antifouling polyamide composite membrane prepared according to the present invention.

[0033] Figure 2 The infrared and XPS spectra of zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 of this invention before and after THPS grafting;

[0034] Figure 3 The images show the surface SEM images, fluorine distribution map, and cross-sectional SEM images of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 of the present invention and the fluorinated functionalized antifouling polyamide composite membrane of Comparative Example 1.

[0035] Figure 4 The water-oil contact angle and underwater oil contact angle of the composite membranes with different THPS concentrations according to the present invention;

[0036] Figure 5 The surface energy of the composite membranes with different THPS concentrations in this invention;

[0037] Figure 6The pore size distribution and molecular weight cut-off of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 of the present invention and the fluorinated functionalized antifouling polyamide composite membrane of Comparative Example 1 are shown.

[0038] Figure 7 The normalized flux and antifouling performance of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 of the present invention and the fluorinated functionalized antifouling polyamide composite membrane in Comparative Example 1 are compared during the pump oil emulsion filtration process.

[0039] Figure 8 The normalized flux and flux reduction rate in the gypsum scaling experiment of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 of the present invention and the fluorinated functionalized antifouling polyamide composite membrane in Comparative Example 1 are shown.

[0040] Figure 9 This is a comparison chart showing the separation selectivity test of zwitterionic-fluorinated functionalized antifouling polyamide composite membranes (numbered 1-3) in the embodiments of the present invention with that of the fluorinated functionalized antifouling polyamide composite membrane of Comparative Example 1 and the commercial membrane NF270 for mono / divalent anions. Detailed Implementation

[0041] This invention provides a method for preparing a zwitterionic-fluorine-functionalized antifouling polyamide composite membrane. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0042] The present invention will now be described in detail with reference to the accompanying drawings.

[0043] Example 1

[0044] This embodiment provides a method for preparing an amphoteric ion-fluorine functionalized antifouling polyamide composite membrane, including the following steps:

[0045] (1) Add 1g of Noria to 100mL of 0.25mol·L⁻¹ -1 In a NaOH solution, after stirring and dissolving, 3g of polyethyleneimine (PEI) was added. PEI reacted with Noria in a Schiff base reaction. After continuous stirring until the polyethyleneimine dissolved, a polyphenol-polyethyleneimine intermediate layer modification solution was obtained. The polyphenol-polyethyleneimine intermediate layer modification solution was applied to the surface of the rinsed polyphenol-polyethyleneimine membrane for immersion modification. The modification time was 7min. After the modification was completed, the excess modification solution was poured off, and then the membrane was thoroughly washed with deionized water to remove the residual modification solution on the membrane surface and in the membrane pores, thus obtaining an intermediate layer modified porous membrane, denoted as N-PSF membrane.

[0046] (2) Fix the N-PSF membrane prepared in step (1) on a plate frame, cover the membrane surface with 1 wt% piperazine (PIP) aqueous solution and let it stand for 5 min, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife; then pour 1.0 wt% trimesoyl chloride (TMC) n-hexane oil solution onto the membrane surface at a uniform speed to carry out the polymerization reaction to form a polyamide layer. After reacting for 30 s, rinse the unreacted trimesoyl chloride with n-hexane to obtain a polyamide composite membrane, denoted as N-TFC membrane;

[0047] (3) 0.05wt%, 0.2wt%, 0.8wt%, and 1.6wt% tetrahydroxymethylphosphoric acid (THPS) aqueous solutions were poured onto the N-TFC membrane prepared in step (2) and grafted for 0.5 min respectively. Then, the excess aqueous solution was poured out and the water droplets on the surface were blown off with an air knife to obtain a zwitterionic modified polyamide composite membrane, denoted as N-TFC-P membrane.

[0048] (4) A 0.6 wt% hexane oil phase solution of perfluorooctanoyl chloride (PFOC) was uniformly poured onto the surface of the N-TFC-P membrane prepared in step (3) for 90 s to graft. After the reaction was completed, the membrane surface was rinsed with the organic solvent hexane to obtain a zwitterionic-fluorine functionalized antifouling polyamide composite membrane, denoted as N-TFC-PF membrane.

[0049] (5) The N-TFC-PF membranes prepared in the above four steps (4) are heat-treated in an oven at 60°C for 0.5 min, 1 min, 2 min and 4 min respectively to obtain four cross-linked stable anti-fouling polyamide composite membranes, namely cross-linked stable N-TFC-PF membranes.

[0050] The performance of the above four groups of antifouling polyamide composite membranes was tested, as shown in Table 1 below. Test conditions: The separation performance of the composite membranes was evaluated using Na2SO4 solution. First, the composite membranes were pre-pressed at 10 bar for 1 hour at 25℃ to reach a stable state. Then, the separation performance was tested. The permeate was collected, weighed to calculate the flux, and its conductivity was tested to calculate the rejection rate.

[0051] Table 1

[0052]

[0053] Example 2

[0054] This embodiment provides a method for preparing an amphoteric ion-fluorine functionalized antifouling polyamide composite membrane, including the following steps:

[0055] (1) Add 1g of Noria to 100mL of 0.25mol·L⁻¹ -1In a NaOH solution, after stirring and dissolving, 3g of polyethyleneimine (PEI) was added. PEI reacted with Noria in a Schiff base reaction. After continuous stirring until the polyethyleneimine dissolved, a polyphenol-polyethyleneimine intermediate layer modification solution was obtained. The polyphenol-polyethyleneimine intermediate layer modification solution was applied to the surface of the rinsed polyphenol-polyethyleneimine membrane for immersion modification. The modification time was 7min. After the modification was completed, the excess modification solution was poured off, and then the membrane was thoroughly washed with deionized water to remove the residual modification solution on the membrane surface and in the membrane pores, thus obtaining an intermediate layer modified porous membrane, denoted as N-PSF membrane.

[0056] (2) Fix the N-PSF membrane prepared in step (1) on a plate frame, cover the membrane surface with 1 wt% piperazine (PIP) aqueous solution and let it stand for 5 min, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife; then pour 1.0 wt% trimesoyl chloride (TMC) n-hexane oil solution onto the membrane surface at a uniform speed to carry out the polymerization reaction to form a polyamide layer. After reacting for 30 s, rinse the unreacted trimesoyl chloride with n-hexane to obtain a polyamide composite membrane, denoted as N-TFC membrane;

[0057] (3) Pour 1.6wt% tetrahydroxymethylphosphoric acid (THPS) aqueous solution onto the N-TFC membrane prepared in step (2) and perform grafting for 0.5min, 1min, 2min and 4min respectively. Then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife to obtain a zwitterionic modified polyamide composite membrane, denoted as N-TFC-P membrane.

[0058] (4) A 0.6 wt% hexane oil phase solution of perfluorooctanoyl chloride (PFOC) was uniformly poured onto the surface of the N-TFC-P membrane prepared in step (3) for 90 s to graft. After the reaction was completed, the membrane surface was rinsed with the organic solvent hexane to obtain a zwitterionic-fluorine functionalized antifouling polyamide composite membrane, denoted as N-TFC-PF membrane.

[0059] (5) The N-TFC-PF membranes prepared in the above four steps (4) are heat-treated in an oven at 70°C for 4 min, 2 min, 1 min and 0.5 min respectively to obtain four cross-linked stable anti-fouling polyamide composite membranes, namely cross-linked stable N-TFC-PF membranes.

[0060] The performance of the above four groups of antifouling polyamide composite membranes was tested, as shown in Table 2 below. Test conditions: The separation performance of the composite membranes was evaluated using Na2SO4 solution. First, the composite membranes were pre-pressed at 10 bar at 25℃ for 1 hour to reach a stable state, and then the separation performance was tested.

[0061] Table 2

[0062]

[0063] Example 3

[0064] This embodiment provides a method for preparing an amphoteric ion-fluorine functionalized antifouling polyamide composite membrane, including the following steps:

[0065] (1) Add 1g of Noria to 100mL of 0.25mol·L⁻¹ -1 In a NaOH solution, after stirring and dissolving, 3g of polyethyleneimine (PEI) was added. PEI reacted with Noria in a Schiff base reaction. After continuous stirring until the polyethyleneimine dissolved, a polyphenol-polyethyleneimine intermediate layer modification solution was obtained. The polyphenol-polyethyleneimine intermediate layer modification solution was applied to the surface of the rinsed polyphenol-polyethyleneimine membrane for immersion modification. The modification time was 7min. After the modification was completed, the excess modification solution was poured off, and then the membrane was thoroughly washed with deionized water to remove the residual modification solution on the membrane surface and in the membrane pores, thus obtaining an intermediate layer modified porous membrane, denoted as N-PSF membrane.

[0066] (2) Fix the PSF membrane prepared in step (1) on the plate frame, cover the membrane surface with 1 wt% piperazine (PIP) aqueous solution and let it stand for 5 min, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife; then pour 1.0 wt% trimesoyl chloride (TMC) n-hexane oil solution onto the membrane surface at a uniform speed to carry out the polymerization reaction to form a polyamide layer. After reacting for 30 s, rinse the unreacted trimesoyl chloride with n-hexane to obtain a polyamide composite membrane, denoted as N-TFC membrane;

[0067] (3) Pour 0.8wt% tetrahydroxymethylphosphoric acid (THPS) aqueous solution onto the N-TFC membrane prepared in step (2) for 1 min, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife to obtain a zwitterionic modified polyamide composite membrane, denoted as N-TFC-P membrane.

[0068] (4) 0.2wt%, 0.4wt%, 0.6wt%, and 1.0wt% of hexane oil phase solutions of perfluorooctanoyl chloride (PFOC) were uniformly poured onto the surface of the N-TFC-P membrane prepared in step (3) for grafting. The grafting times were 90s, 120s, 30s, and 60s, respectively. After the reaction was completed, the membrane surface was rinsed with the organic solvent hexane to obtain a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane, denoted as N-TFC-PF membrane.

[0069] (5) The N-TFC-PF membranes prepared in the above 4 groups of steps (4) are heat-treated in an oven at 60°C for 2 minutes to obtain 4 groups of cross-linked stable anti-fouling polyamide composite membranes, namely cross-linked stable N-TFC-PF membranes.

[0070] The performance of the above four groups of antifouling polyamide composite membranes was tested, as shown in Table 3 below. Test conditions: The separation performance of the composite membranes was evaluated using Na2SO4 solution. First, the composite membranes were pre-pressed at 10 bar at 25℃ for 1 hour to reach a stable state, and then the separation performance was tested.

[0071] Table 3

[0072]

[0073] Example 4

[0074] This embodiment provides a method for preparing an amphoteric ion-fluorine functionalized antifouling polyamide composite membrane, including the following steps:

[0075] (1) Add 0.5g of catechol and resorcinol to 100mL of 0.5mol·L⁻¹ -1 In a NaOH solution, after stirring and dissolving, 1g of polyethyleneimine (PEI) was added. PEI reacted with Noria in a Schiff base reaction. After continuous stirring until the polyethyleneimine dissolved, a polyphenol-polyethyleneimine intermediate layer modification solution was obtained. The polyphenol-polyethyleneimine intermediate layer modification solution was applied to the surface of the rinsed polyphenol-polyethyleneimine membrane for immersion modification. The modification time was 1min. After the modification was completed, the excess modification solution was poured off, and then the membrane was thoroughly washed with deionized water to remove the residual modification solution on the membrane surface and in the membrane pores, thus obtaining an intermediate layer modified porous membrane, denoted as PSF membrane.

[0076] (2) Fix the PSF membrane prepared in step (1) on the plate frame, cover the membrane surface with 0.1wt% aqueous solution of 2-methylpiperazine and 2,5-dimethylpiperazine and let it stand for 5 min. Then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife. Then pour 0.05wt% terephthaloyl chloride cyclohexane oil phase solution on the membrane surface at a uniform speed to form a polyamide layer. After reacting for 60 s, rinse the unreacted trimesoyl chloride with cyclohexane to obtain a polyamide composite membrane, which is called TFC membrane.

[0077] (3) Pour 0.8wt% tetrahydroxymethylphosphoric acid (THPS) aqueous solution onto the TFC membrane prepared in step (2) for 1 min, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife to obtain a zwitterionic modified polyamide composite membrane, denoted as TFC-P membrane.

[0078] (4) A cyclohexane oil phase solution of 0.6 wt% perfluorooctanoyl chloride (PFOC) was uniformly poured onto the surface of the TFC-P membrane prepared in step (3) for 90 s to graft. After the reaction was completed, the membrane surface was rinsed with the organic solvent cyclohexane to obtain a zwitterionic-fluorinated antifouling polyamide composite membrane, denoted as TFC-PF membrane.

[0079] (5) The TFC-PF membrane prepared in step (4) above is heat-treated in an oven at 80°C for 2 min to obtain a cross-linked stable anti-fouling polyamide composite membrane, namely a cross-linked stable TFC-PF membrane.

[0080] The performance of the above-mentioned antifouling polyamide composite membrane was tested, and its flux was 17.2 L·m. -2 ·h -1 ·bar -1 The retention rate was 98.6%.

[0081] Example 5

[0082] The difference between this embodiment and embodiment 1 is that in this embodiment, the fluorinated acyl chloride used in step (4) to prepare the TFC-PF membrane is perfluoroundecyl chloride.

[0083] Example 6

[0084] The difference between this embodiment and embodiment 1 is that, in step (4) of this embodiment, the fluorinated acyl chloride used to prepare the TFC-PF membrane is perfluorooctane sulfonyl chloride and heptafluorobutyryl chloride.

[0085] Comparative Example 1

[0086] This comparative example provides a method for preparing a fluorinated functionalized antifouling polyamide composite film, including the following steps:

[0087] (1) Add 1g of Noria to 100mL of 0.25mol·L⁻¹ -1 In a NaOH solution, after stirring and dissolving, 3g of polyethyleneimine (PEI) was added. PEI reacted with Noria in a Schiff base reaction. After continuous stirring until the polyethyleneimine dissolved, a polyphenol-polyethyleneimine intermediate layer modification solution was obtained. The polyphenol-polyethyleneimine intermediate layer modification solution was applied to the surface of the rinsed polyphenol-polyethyleneimine membrane for immersion modification. The modification time was 7min. After the modification was completed, the excess modification solution was poured off, and then the membrane was thoroughly washed with deionized water to remove the residual modification solution on the membrane surface and in the membrane pores, thus obtaining an intermediate layer modified porous membrane, denoted as N-PSF membrane.

[0088] (2) Fix the N-PSF membrane prepared in step (1) on a plate frame, cover the membrane surface with 1 wt% piperazine (PIP) aqueous solution and let it stand for 5 min, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife; then pour 1.0 wt% trimesoyl chloride (TMC) n-hexane oil solution onto the membrane surface at a uniform speed to carry out the polymerization reaction to form a polyamide layer. After reacting for 30 s, rinse the unreacted trimesoyl chloride with n-hexane to obtain a polyamide composite membrane, denoted as N-TFC membrane;

[0089] (3) A 0.6 wt% hexane oil phase solution of perfluorooctanoyl chloride (PFOC) was uniformly poured onto the surface of the N-TFC membrane prepared in step (2) for 90 s to graft. After the reaction was completed, the membrane surface was rinsed with the organic solvent hexane to obtain a fluorinated antifouling polyamide composite membrane, denoted as N-TFC-F membrane.

[0090] (4) The N-TFC-F membrane prepared in step (3) above is heat-treated in an oven at 60°C for 2 min to obtain a cross-linked stable anti-fouling polyamide composite membrane, i.e., a cross-linked stable N-TFC-F membrane.

[0091] The performance of the aforementioned antifouling polyamide composite membrane was tested. The separation performance was evaluated using Na₂SO₄ solution. First, the membrane was pre-compressed at 10 bar for 1 hour at 25°C to reach a stable state, and then the separation performance was tested. The measured flux was 9.5 L·m⁻¹. -2 ·h -1 ·bar -1 The retention rate was 97.2%.

[0092] Comparing the performance of the antifouling polyamide composite membranes of Examples 1-4 with that of Comparative Example 1, the flux of the zwitterionic-fluorinated antifouling polyamide composite membranes obtained in Examples 1-4 is significantly improved, that is, the antifouling polyamide composite membranes of Examples 1-4 have both high flux and high rejection rate.

[0093] The zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 above and the fluorinated functionalized antifouling polyamide composite membrane (denoted as N-TFC-PF) of Comparative Example 1 were subjected to the following tests to analyze the reasons for the performance differences between the two and to test their antifouling performance.

[0094] (I) Surface Chemical Properties of Composite Membranes

[0095] Infrared characterization was performed on the zwitterionic-fluorine-functionalized antifouling polyamide composite membranes (numbered 1-3 in Example 1) before and after THPS grafting. Figure 2 As shown. Among them, Figure 2 (a) shows the infrared spectra of zwitterionic-fluorinated functionalized antifouling polyamide composite membranes (numbered 1-3) in Example 1 before and after THPS grafting. It can be seen that the composite membranes after THPS grafting exhibit high spectral density at 1650-1700 cm⁻¹. -1 The enhanced FTIR is caused by the presence of C=O in the ester bond formed by the esterification reaction of the "acyl chloride group-hydroxyl group"; Figure 2 (b) shows the broad scan spectrum of surface XPS of the composite film before and after THPS grafting. It can be seen that the P element signal appears at 132eV, which proves that the THPS grafting was successful.

[0096] (II) Surface morphology and cross-sectional structure of composite membrane

[0097] The surface morphology and cross-sectional morphology of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 and the fluorinated functionalized antifouling polyamide composite membrane of Comparative Example 1 were examined. Figure 3 As shown. Among them, Figure 3 (a1) and (a2) are SEM images of the membrane surface of the composite membrane of Comparative Example 1 and the composite membranes numbered 1-3 in Example 1, respectively. It can be seen that the surface of the composite membrane of Comparative Example 1 has wrinkled morphology. The composite membrane in Example 1, after being modified by THPS, fills in the wrinkled morphology to a certain extent. The nodular and wrinkled morphologies coexist, and the roughness is reduced, which is conducive to achieving better anti-fouling under the condition of ensuring flux. Figure 3 (b1) and (b2) are fluorine element distribution maps detected by EDX mapping on the composite membrane of Example 1 and the composite membranes numbered 1-3 in Example 1, respectively. The yellow spots on the black background represent the distribution of element F in the separation layer. It can be seen that the fluorine element distribution of the composite membrane of Example 1 is more uniform. Figure 3 (c1) and (c2) are cross-sectional SEM images of the composite membrane of Comparative Example 1 and the composite membranes numbered 1-3 in Example 1, respectively. It can be seen that the bonding between the separation layer and the support layer of the composite membrane in Example 1 is tighter. This is because the polyamide layer in Comparative Example 1 is prepared only through interfacial polymerization, exhibiting incomplete network cross-linking characteristics. In subsequent processing, the loose membrane structure that has not undergone thermal cross-linking is rearranged. In the example, THPS solution is poured onto the surface of the TFC membrane, which can undergo a modification reaction on the surface of the polyamide membrane (i.e., the hydroxyl groups of THPS undergo esterification with the acyl chloride groups on the surface of the polyamide membrane, and THPS is grafted onto the membrane surface), and induce structural rearrangement downward along the membrane layer, thereby making the obtained composite membrane more stable.

[0098] (III) Surface wettability and surface energy of composite membranes

[0099] In studying the surface wetting properties and surface energy of composite films, based on the composite films (THPS concentration of 0.8 wt%) numbered 1-3 in Examples 1, composite films with THPS concentrations of 0.1 wt%, 0.2 wt%, 0.4 wt%, and 1.6 wt% were prepared under the same reaction conditions. The effect of different THPS concentrations on the surface wetting properties and surface energy of the composite films was investigated. Figure 4 As shown. Among them, Figure 4(a) shows the water-oil contact angle of the composite membrane with different THPS concentrations. It can be seen that compared with Comparative Example 1, the hydrophilicity of the THPS-grafted composite membrane is improved, and the oleophobic performance can be basically maintained due to the grafting of PFOC. When the THPS concentration reaches 0.2wt%, the membrane surface can be both hydrophilic and oleophobic. When the THPS concentration reaches 0.8wt%, the hydrophilic and oleophobic properties are most obvious. Figure 4 (b) shows the underwater oil contact angle of the composite membrane with different THPS concentrations. It can be seen that compared with the ungrafted THPS in Comparative Example 1, the THPS-grafted composite membrane has good hydrophilicity and oleophobicity in the underwater environment, which is most beneficial for achieving the antifouling performance of the composite membrane.

[0100] Based on the above contact angle data, the surface energy (γ) of the composite film was calculated. SV ),like Figure 5 As shown in the figure, it can be seen that with the increase of THPS concentration, the polar component (γ) in the surface energy... P SV The PFOC content also increases, which helps enhance the hydrophilicity of the membrane surface. Maintaining surface hydrophilicity helps resist the adhesion of pollutants; at the same time, the post-grafted PFOC reduces the dispersion component (γ). d SV This allows the prepared composite membrane to maintain low surface energy, thus maintaining the interaction force between the membrane and water molecules, reducing the interaction force between the composite membrane and pollutants, and endowing the composite membrane with anti-pollution ability to resist and release pollutants, without affecting its water flux.

[0101] Additionally, it should be noted that the surface energy of the TFC membrane prepared in step (2) of Comparative Example 1 is 72.1 mJ·m. -2 After grafting PFOC, low surface energy perfluorooctanoic acid (PFOC) is introduced onto the surface of the polyamide membrane to construct a hydrophobic and oleophobic membrane surface, reducing the molecular interaction force between the membrane surface and pollutants, and using water shear force to complete the release of pollutants.

[0102] (iv) Pore size distribution and molecular weight cutoff of composite membranes

[0103] The pore size distribution and molecular weight cutoff of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 above and the fluorinated functionalized antifouling polyamide composite membrane of Comparative Example 1 were detected. Figure 6 As shown. Among them, Figure 6 (a) is a pore size distribution diagram of the composite membrane of Comparative Example 1 and the composite membranes numbered 1-3 in Example 1. It can be seen from the figure that: compared with the ungrafted THPS of Comparative Example 1, the THPS-grafted composite membrane forms a strong interaction during the in-situ polymerization process through THPS grafting, which can reduce the pore size distribution of the membrane. The average effective pore size is reduced from 0.386 nm to 0.292 nm, and the pore size distribution is reduced. Figure 6 (b) is a molecular weight cutoff (MWCO) graph for the composite membrane of Comparative Example 1 and the composite membranes numbered 1-3 in Example 1. The MWCO of the composite membrane is defined as the molecular weight of PEG when PEG retention reaches 90%. The graph shows that the MWCO of the THPS-grafted composite membrane is also smaller than that of the ungrafted THPS in Comparative Example 1. This indicates that the membrane of Example 1 has a denser and more uniform separation layer (smaller geometric standard deviation), and that reducing the pore size distribution can significantly improve the separation selectivity of the polyamide membrane. The uniformity of the separation layer can effectively reduce the non-uniformity of the permeate flux distribution on the membrane surface during filtration, thereby slowing down the accumulation of contaminants. In contrast, the polyamide membrane in Comparative Example 1, with its wider pore size distribution, is more susceptible to fouling due to potential severe pore blockage and cake layer formation in localized permeate flux.

[0104] (V) Anti-pollution performance

[0105] In addition, the antifouling performance of the zwitterionic-fluorinated functionalized antifouling polyamide composite membranes numbered 1-3 in Example 1 above and the fluorinated functionalized antifouling polyamide composite membrane of Comparative Example 1 were tested, including tests for resistance to organic pollutants and tests for resistance to inorganic pollutants.

[0106] For the organic pollutant resistance test, pump oil (100 ppm) was selected as the model pollutant for the antifouling performance test. The test conditions were as follows: the membrane was initially pre-pressed with deionized water at 4 bar for 2 hours to reach a stable state. Based on this, the pure water flux (J) was measured every 0.5 hours. w0 Subsequently, pump oil contaminant solution was added for testing, and the water flux (J) was measured every hour during the test. p After the contamination experiment, the membrane was repeatedly washed three times with deionized water at low pressure and high cross-flow velocity, each time for about 15 minutes, to remove reversible deposits and adsorbed pollutants from the membrane surface. Finally, the pure water flux (J) of the composite membrane after washing was measured. w ).

[0107] The normalized composite membrane flux was monitored during the testing process as a function of operating time to study the membrane's antifouling effect. The results are as follows: Figure 7 As shown, where, Figure 7 (a) represents the normalized flux of the N-TFC-F and N-TFC-PF membranes during pump oil emulsion filtration. Figure 7 (b) represents the antifouling performance indicators of N-TFC-F and N-TFC-PF membranes during pump oil emulsion filtration, where FRR is the flux recovery rate, Rt is the flux decline rate, DRr is the reversible flux decline rate, and DRir is the irreversible flux decline rate. The calculation formulas are as follows:

[0108]

[0109] In the formula, J w0 The initial pure water flux is expressed in L·m. -2 ·h -1 ·bar -1 J w The pure water flux after cleaning, in L·m -2 ·h -1 ·bar -1 J p Stable permeation flux (L·m) of the composite membrane during the fouling stage -2 ·h -1 ·bar -1 .

[0110] pass Figure 7 It can be seen that the N-TFC-PF membrane exhibits significantly better antifouling performance than the N-TFC-F membrane. This is because zwitterionic ions (THPS) increase hydrophilicity, and the hydrophilic membrane tends to adsorb water molecules, thus forming a hydration layer between the membrane surface and the pollutants. This hydration layer helps increase the Gibbs free energy of pollutants during deposition, thereby inhibiting their adhesion to the membrane surface. Furthermore, the N-TFC-PF composite membrane has a smaller average pore size and a more concentrated distribution, forming a denser separation layer. This density effectively avoids uneven distribution of permeate flux during separation, thus slowing down fouling. The thick and dense separation layer also efficiently delays pollutant accumulation.

[0111] For the inorganic pollutant resistance test, a gypsum scaling experiment was conducted using a cross-flow test apparatus. The test conditions were as follows: the experimental solution contained 2840 mg / L (30 mM) sodium sulfate and 2220 mg / L (30 mM) calcium chloride, the pH was adjusted to 6, and the test was conducted in full circulation mode at 25.0 ± 1.0℃. The membrane was pre-pressurized for 1 hour to reach a stable state, and then the water flux was measured every 0.5 hours for 14 consecutive hours. The test results are as follows. Figure 8 As shown, where, Figure 8 (a) Normalized flux in gypsum scaling experiments of N-TFC-F and N-TFC-PF membranes. Figure 8 (b) represents the flux decline rate. From Figure 8As can be seen, the normalized flux of both N-TFC-F and N-TFC-PF membranes initially decreased slowly, then rapidly. After 13 hours of experimentation, until the end of the experiment, the flux decay rate of the N-TFC-PF membrane was lower than that of the N-TFC-F membrane. This is because the hydrophilic properties of THPS are unfavorable to the nucleation process of gypsum on the membrane surface, and the phosphate functional groups in the THPS molecule also have a certain impact on anti-fouling performance. The solubility product constant (pKsp) is a key parameter for measuring the solubility of a substance and the binding ability of ions at a specific concentration. The pKsp value of calcium phosphate is 28.70, which means that calcium ions have a strong complexing ability with the functional groups on the membrane surface. Therefore, during the experiment, the THPS-grafted membrane showed superior anti-fouling performance.

[0112] (vi) Anti-pollution testing of actual refining wastewater

[0113] The zwitterionic-fluorinated functionalized antifouling polyamide composite membranes (numbered 1-3 in Example 1), the composite membrane of Comparative Example 1, and the commercial membrane NF270 were tested using actual refining wastewater. The test results are shown in Table 4. Figure 9 As shown, Table 4 shows the wastewater composition before and after composite membrane treatment. Figure 9 This is a comparison diagram of the molecular selectivity of the composite membrane for monovalent / divalent anions.

[0114] Table 4

[0115]

[0116] As shown in Table 4, the quality of the treated wastewater was improved in all cases and met the wastewater reuse standard (GB / T41016-2021), but the water quality from the N-TFC-PF membrane was even better; in addition, from Figure 9 It can be seen that the composite membrane of Example 1 has a high SO4 content. 2- Retention rate, lower Cl - The rejection rate and ion selectivity of the composite membrane in Example 1 were three times that of the composite membrane in Comparative Example 1, indicating that the composite membrane in Example 1 exhibited better characteristics in terms of chloride and sulfate ion selectivity. Such high ion selectivity is beneficial for maintaining a high rejection rate for polyvalent ions while monovalent ions pass through the membrane.

[0117] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0118] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a zwitterionic-fluorine functionalized antifouling polyamide composite membrane, characterized in that, Including the following steps: (1) Add polyphenol to NaOH solution, stir to dissolve, then add polyethyleneimine, stir continuously until polyethyleneimine dissolves to obtain polyphenol-polyethyleneimine intermediate layer modification solution, apply polyphenol-polyethyleneimine intermediate layer modification solution to the surface of porous support base membrane for soaking modification, after modification, pour out excess modification solution, and then wash thoroughly with deionized water to remove the modification solution remaining on the membrane surface and in the membrane pores to obtain intermediate layer modified porous base membrane, denoted as PSF membrane; (2) Fix the PSF membrane prepared in step (1) on the plate frame, cover the membrane surface with the organic amine aqueous solution and let it stand, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife; then pour the organic acyl chloride oil phase solution onto the membrane surface at a uniform speed to carry out the polymerization reaction to form a polyamide layer. After the reaction is completed, wash the unreacted organic acyl chloride monomer with an organic solvent to obtain a polyamide composite membrane, which is called TFC membrane. (3) Pour the tetrahydroxymethylphosphoric acid aqueous solution onto the TFC membrane prepared in step (2) for grafting, then pour out the excess aqueous solution and blow away the water droplets on the surface with an air knife to obtain a zwitterionic modified polyamide composite membrane, denoted as TFC-P membrane; (4) The oil phase solution containing fluorinated acyl chloride is poured at a constant speed onto the surface of the TFC-P membrane prepared in step (3) for grafting. After the reaction is completed, the membrane surface is rinsed with an organic solvent to obtain a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane, which is denoted as TFC-PF membrane. (5) Heat-treat the TFC-PF membrane prepared in step (4) in an oven to obtain a cross-linked and stable anti-fouling polyamide composite membrane.

2. The method for preparing an amphoteric-fluorinated functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, In step (1), the polyphenol is at least one of hydroquinone, catechol, resorcinol, hydroquinone, pyrogallol, and pyrogallol. In step (1), the mass concentration of polyphenol in the polyphenol-polyethyleneimine intermediate modified solution is 0.5-3%, and the mass concentration of polyethyleneimine is 1-5%.

3. The method for preparing an amphoteric-fluorinated functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, The modification time of the polyphenol-polyethyleneimine intermediate layer in step (1) is 1~10 min.

4. The method for preparing an amphoteric-fluorinated functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, The organic amine aqueous solution in step (2) is obtained by dissolving an organic amine in water. The organic amine is at least one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, ethylenediamine, N,N-bis(2-aminoethyl)ethylenediamine, divinyltriamine, or polyethyleneimine. In step (2), the organic acyl chloride oil phase solution is obtained by dissolving the organic acyl chloride in an organic solvent. The organic acyl chloride is at least one of the following: trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, trimesoyl chloride, cyclohexyl chloride, cyclobutanetetracarboxylate chloride, cyclopentanetetracarboxylate chloride, malonyl chloride, glutaryl chloride, and fumarate chloride. The organic solvent is at least one of the following: n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L, or isopar M. In step (2), the mass concentration of the organic amine aqueous solution is 0.1-5%; the mass concentration of the organic acyl chloride oil solution is 0.01-2%.

5. The method for preparing a zwitterionic-fluorine functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, The polymerization reaction time in step (2) is 10~90s.

6. The method for preparing a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, The mass concentration of the tetrahydroxymethylphosphoric acid aqueous solution in step (3) is 0.05~2.0%.

7. The method for preparing a zwitterionic-fluorine functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, The grafting reaction in step (3) lasts for 0.5 to 5 minutes.

8. The method for preparing an amphoteric-fluorinated functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, In step (4), the mass concentration of the fluorinated acyl chloride oil phase solution is 0.2~1.0%; The fluorinated acyl chloride is at least one of perfluorooctanoyl chloride, perfluoroundecanoyl chloride, perfluorooctanesulfonyl chloride, nonafluoropentanoyl chloride, heptadecanoyl chloride, and heptafluorobutyryl chloride.

9. The method for preparing a zwitterionic-fluorine functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, The grafting reaction time in step (4) is 30~120s.

10. The method for preparing a zwitterionic-fluorinated functionalized antifouling polyamide composite membrane according to claim 1, characterized in that, In step (5), the heat treatment temperature is 50~80℃ and the heat treatment time is 0.5~5min.

Images