A polyamide composite membrane based on a positively charged support layer and its preparation method and application

Abstract

The invention discloses a polyamide composite membrane based on a positively charged support layer, a preparation method and application thereof, and belongs to the technical field of water treatment membranes. The preparation method of the polyamide composite membrane comprises: (1) using an amino monomer to perform amino modification on a porous support membrane to prepare an amino support membrane; (2) immersing the amino support membrane in a functional monomer solution to generate a Michael addition reaction or a nitrogen alkylation reaction to obtain a positively charged support membrane; (3) subjecting an aqueous phase solution containing a polyamine and an oil phase solution containing a polyacyl chloride to an interfacial polymerization reaction on the positively charged support membrane to obtain the polyamide composite membrane based on the positively charged support layer. The method of the invention has simple process and low equipment requirements. The prepared polyamide nanofiltration composite membrane has large water permeation flux, good ion selectivity and high antibiotic removal rate. The method has broad application prospects in the field of water treatment, especially in the removal of trace antibiotics in drinking water.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment membranes, and in particular to a polyamide composite membrane based on a positively charged support layer and a preparation method and application thereof. Background Art

[0002] Antibiotic pollution in water environments is one of the important environmental issues faced in recent years. Due to the incomplete metabolism of organisms and the long environmental half-life, about 30-90% of antibiotics enter and accumulate in water environments through various pathways, forming a "pseudo-persistent" water pollution phenomenon, which seriously interferes with the growth and reproduction of organisms, pollutes drinking water sources, and poses a serious threat to human health. Solving the problem of antibiotic pollution in water environments is crucial. However, due to the small molecular weight, low concentration, and difficulty in removal of antibiotics, the use of traditional adsorption methods is limited by the operational complexity and operating costs of adsorbent regeneration. Therefore, it is urgent to develop efficient and low-cost technologies for removing antibiotic micropollutants in water environments.

[0003] Nanofiltration (NF) is a new generation of ideal water purification technology, with its filtration accuracy, water production capacity, and operating pressure being between reverse osmosis and ultrafiltration. As the core of nanofiltration technology, the pore size of the nanofiltration membrane is about 1 nm, and the surface is charged, so its separation mechanism mainly includes the size screening effect generated by physical pores and the Donan effect generated by the membrane surface charge. This pore structure and surface characteristics determine that the nanofiltration membrane has unique separation performance: the removal rate of divalent and above ions and organic matter with a molecular weight between 200 and 1000 is high, and the removal rate of monovalent ions and small molecules is low, which can achieve the dual goals of "removing harm and retaining benefits" in drinking water treatment. At the same time, due to the selective permeability characteristics, nanofiltration still has high permeation flux and concentration capacity at low operating pressure, showing significant advantages such as large processing capacity, high concentration multiple, and low energy consumption. Therefore, nanofiltration has a strong competitive advantage in the removal of trace antibiotics in water.

[0004] Currently, commercial nanofiltration membrane materials are mostly composite membranes of aromatic polyamide, which are three-layer structures from top to bottom, including polyamide separation layer, porous support layer and non-woven fabric substrate. Among them, the polyamide separation layer is usually prepared by interfacial polymerization of aqueous polyamine and organic polyacyl chloride in water and oil phases. Existing nanofiltration membranes can basically achieve complete retention of antibiotics with molecular weight significantly higher than the membrane cut-off molecular weight (Mw>700), but the removal efficiency of medium and low molecular weight antibiotics is obviously insufficient.

[0005] A Chinese patent document with publication number CN117732245A discloses a degradable positively charged nanofiltration composite membrane and a preparation method and application thereof. The preparation method of the positively charged nanofiltration composite membrane is as follows: (1) filtering a nanocellulose aqueous dispersion onto a viscose fiber non-woven fabric, performing a first heat treatment and then immersing the dispersion into a crosslinking agent solution, taking the dispersion out and then performing a second heat treatment to obtain a crosslinked nanocellulose ultrafiltration membrane; (2) spin coating a chitosan-based casting solution onto the crosslinked nanocellulose ultrafiltration membrane, performing a third heat treatment and then immersing the dispersion into a crosslinking agent solution, taking the dispersion out and then performing a fourth heat treatment to obtain the positively charged nanofiltration composite membrane; and the test results show that the positively charged nanofiltration composite membrane is used to remove pollutants in water, and the removal rates of roxithromycin, erythromycin and sulpiride are 92.8%, 80.7% and 50.2%, respectively.

[0006] A Chinese patent document with publication number CN117258543A discloses a method for constructing an antibiotic desalination nanofiltration membrane based on doctor blade assisted interfacial polymerization. The antibiotic desalination nanofiltration membrane is a COFs separation membrane. The COFs separation membrane is prepared by uniformly coating a hydrophobic ionic liquid solution containing COFs A monomers on a hydrolyzed polymer membrane rich in an aqueous solution of COFs B monomers using a doctor blade, so that COFs A and COFs B monomers undergo a Schiff base reaction at the ionic liquid-water interface. The COFs separation membrane can achieve rapid and accurate separation of antibiotics / salts, with larger antibiotic molecules being retained by the COFs separation membrane, while smaller salts quickly passing through the COFs separation membrane.

[0007] In the above methods, new reaction monomers are introduced to prepare nanofiltration membranes in order to achieve better antibiotic removal effects, but the problem of insufficient removal efficiency of low and medium molecular weight antibiotics by existing polyamide nanofiltration membranes cannot be solved. Summary of the invention

[0008] In order to improve the water permeation flux of a polyamide composite membrane while increasing its antibiotic removal rate, the present invention provides a method for preparing a polyamide composite membrane based on a positively charged support layer. The method has a simple process and low equipment requirements. The prepared polyamide nanofiltration composite membrane has a large water permeation flux, good ion selectivity and a high antibiotic removal rate.

[0009] The specific technical solutions adopted are as follows:

[0010] A method for preparing a polyamide composite membrane based on a positively charged support layer comprises the following steps:

[0011] (1) using an amino monomer to modify the porous support membrane by amino modification to prepare an amino support membrane;

[0012] (2) immersing the amino support membrane in a functional monomer solution to cause Michael addition reaction or nitrogen alkylation reaction to obtain a positively charged support membrane;

[0013] (3) preparing the polyamide composite membrane based on the positively charged support layer by subjecting an aqueous solution containing polyamine and an oil solution containing polyacyl chloride to an interfacial polymerization reaction on a positively charged support membrane;

[0014] When the Michael addition reaction occurs, the functional monomer is selected from at least one of acryloyloxyethyl trimethyl ammonium chloride (DAC), methacryloyloxyethyl trimethyl ammonium chloride (DMC), methacryloyl propyl trimethyl ammonium chloride (MAPTAC), (3-acrylamide propyl) trimethyl ammonium chloride, acryloyloxyethyl dimethyl benzyl ammonium chloride (DABC), methacryloyloxyethyl dimethyl benzyl ammonium chloride, methacryloyl propyl dimethyl benzyl ammonium chloride, benzyl ethyl trimethyl ammonium chloride, and diallyl dimethyl ammonium chloride;

[0015] When the nitrogen alkylation reaction occurs, the functional monomer is selected from at least one of methyl chloride, ethyl chloride, methyl bromide, ethyl bromide, methyl iodide, ethyl iodide, benzyl chloride, chloroethanol, and chloroacetic acid.

[0016] The present invention introduces amino groups into the originally inert porous support membrane by aminated modification of the porous support membrane, and utilizes the high reactivity of the amino group to use the aminated support membrane as a carrier for subsequent further positive charging. Furthermore, the aminated support membrane is modified to be positively charged in situ, and the amino groups are converted into positively charged quaternary ammonium groups through two pathways: Michael addition or nitrogen alkylation: the former is a nucleophilic addition reaction, i.e., the addition is performed using amino groups and unsaturated hydrocarbons containing quaternary ammonium groups; the latter is a nucleophilic substitution reaction, i.e., the hydrogen atoms on the amino groups are replaced by alkyl groups. Using either Michael addition reaction or nitrogen alkylation reaction, all amino groups on the aminated support membrane can be replaced in situ with positively charged quaternary ammonium groups, thereby realizing directional regulation of the surface chemical properties of the inert support membrane.

[0017] The porous support membrane includes but is not limited to polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polytetrafluoroethylene ultrafiltration membrane, polypropylene ultrafiltration membrane, polyethylene ultrafiltration membrane, polystyrene ultrafiltration membrane, polyimide ultrafiltration membrane, polyvinyl chloride ultrafiltration membrane, hydrolyzed polyacrylonitrile ultrafiltration membrane, etc.

[0018] Preferably, in step (1), the porous support membrane is immersed in a reaction solution containing an amino monomer for amino modification, wherein the amino monomer is at least one of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine; and the content of the amino monomer in the reaction solution containing the amino monomer is 10-20wt%.

[0019] More preferably, the conditions for the amino modification are: temperature 90-160° C., time 24-48 h.

[0020] Preferably, in step (2), when Michael addition reaction occurs, the content of functional monomer in the functional monomer solution is 0.5-2wt%, and the reaction conditions are: temperature 20-30°C, time 6-24h; when nitrogen alkylation reaction occurs, the content of functional monomer in the functional monomer solution is 5-10wt%, and the reaction conditions are: temperature 20-30°C, time 6-12h.

[0021] In the aqueous phase solution, the aqueous phase monomer polyamine is at least one of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, m-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, xylene diamine, ethylenediamine, propylenediamine, tris(2-aminoethyl)amine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, and 1,4-diaminocyclohexane.

[0022] In the oil phase solution, the oil phase monomer polyacyl chloride is at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, pyromellitoyl chloride, malonyl chloride, glutaryl chloride, and fumaroyl chloride, and the solvent of the oil phase solution is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L, or isopar M.

[0023] More preferably, the content of the polyamine in the aqueous phase solution is 0.05-2 wt %, and the content of the polyacyl chloride in the oil phase solution is 0.05-2 wt %.

[0024] Preferably, in step (3), the interfacial polymerization method is:

[0025] 1) Pour the aqueous solution containing polyamine onto the surface of the positively charged support membrane, let it stand for 1-10 minutes, and then remove the excess liquid on the membrane surface;

[0026] 2) pouring the oil phase solution containing polyacid chloride onto the surface of the membrane obtained in step 1), leaving it in contact for 0.5-5 minutes, and then removing excess liquid on the membrane surface;

[0027] 3) The membrane obtained in step 2) is subjected to heat treatment to obtain the polyamide composite membrane based on the positively charged support layer.

[0028] The method of the present invention carries out interfacial polymerization reaction on a positively charged support membrane to prepare a polyamide composite membrane. The quaternary ammonium group introduced on the positively charged support membrane can promote the diffusion of aqueous phase monomers that are also positively charged, so that they enter the oil phase faster to react, promote the faster generation of the polyamide primary layer, and thus make the formed polyamide separation layer more compact. At the same time, since the diffusion of the monomer in the polyamide primary layer is much smaller than that in the solution, the rapid formation of the polyamide primary layer further inhibits the subsequent transmembrane diffusion of the aqueous phase monomers, limits the longitudinal growth of the polyamide separation layer, reduces the actual thickness of the separation layer, reduces the water permeation resistance, and improves the water permeation performance of the membrane.

[0029] Preferably, the heat treatment conditions in step 3) are 50-80°C for 10-20 min.

[0030] The present invention also provides a polyamide composite membrane based on a positively charged support layer prepared by the method for preparing the polyamide composite membrane based on a positively charged support layer.

[0031] The polyamide composite membrane based on the positively charged support layer comprises a non-woven fabric layer, a positively charged support layer and a polyamide separation layer, and the water flux is greater than 15 L·m -2 ·h -1 bar -1 , good ion selectivity, the removal rate of trace tetracycline, ofloxacin and other antibiotics in drinking water is >95%.

[0032] The present invention also provides the application of the polyamide composite membrane based on the positively charged support layer in the field of water treatment, especially in the fields of deep purification of drinking water, reuse of municipal sewage and the like.

[0033] The present invention also provides a method for treating wastewater containing antibiotics, using the polyamide composite membrane based on a positively charged support layer. Preferably, the antibiotics include tetracycline or ofloxacin, and the antibiotic concentration in the wastewater containing antibiotics is 1-10 ppm.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The method of the present invention uses a two-step method to in situ prepare a positively charged support membrane containing quaternary ammonium groups, thereby changing the surface properties of the originally uncharged inert porous support membrane, promoting the diffusion of aqueous phase monomers during interfacial polymerization, making the polyamide separation layer form faster and denser, and further preventing the subsequent longitudinal growth of the polyamide layer, reducing the actual thickness of the polyamide layer, and reducing the water permeation resistance. Therefore, the prepared polyamide composite membrane based on the positively charged support layer has high water permeation flux and separation selectivity, and has an effective antibiotic removal effect.

[0036] (2) The method of the present invention has low equipment requirements, the preparation method of the positively charged support membrane is simple, and there are few influencing factors. It is easy to improve on the basis of the traditional polyamide nanofiltration composite membrane preparation process to achieve scaled-up preparation and production. The prepared polyamide composite membrane based on the positively charged support layer has broad application prospects in the field of water treatment.

[0037] (3) The polyamide composite membrane based on the positively charged support layer provided by the present invention has excellent water permeation flux and ion selectivity, and the water flux is greater than 15 L·m -2 ·h -1 bar -1 The removal rate of trace tetracycline, ofloxacin and other antibiotics in drinking water is >95%.

[0038] (4) For the removal of trace antibiotics in water, conventional methods only modify the surface of the separation layer, which inevitably leads to an increase in separation resistance. While improving the antibiotic removal rate, it sacrifices water permeability, which seriously restricts the efficiency of the membrane during application. In contrast, the present invention optimizes the separation layer structure by adjusting the surface characteristics of the support layer, which can improve the antibiotic removal rate without affecting the resistance of the separation layer, and achieve a simultaneous improvement in the antibiotic removal rate and water permeability of the polyamide composite membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a SEM image of the surface of the polyamide composite membrane based on the positively charged support layer in Example 1.

[0040] Figure 2 This is a SEM image of the cross section of the polyamide composite membrane based on the positively charged support layer in Example 1. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the embodiments and drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] Example 1

[0043] A commercial polyethersulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 10wt% diethylenetriamine, and after being amino-modified at 90°C for 24 hours, the membrane surface is washed with anhydrous ethanol and deionized water in succession to obtain an amino-modified support membrane; subsequently, the amino-modified support membrane is immersed in an aqueous solution containing 1wt% methacryloyloxyethyltrimethylammonium chloride, and the Michael addition reaction occurs at a constant temperature of 20°C for 24 hours, and the membrane surface is washed with deionized water after being taken out to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 0.05wt% piperazine is poured on the surface of the positively charged support membrane, and after being in contact and standing for 1 minute, excess liquid on the membrane surface is removed; then a n-hexane solution containing 0.05wt% trimesoyl chloride is poured on the membrane surface, and after being in contact and standing for 0.5 minutes, excess liquid on the membrane surface is removed, and then heat-treated at 50°C for 10 minutes to obtain the polyamide composite membrane based on the positively charged support layer.

[0044] Example 2

[0045] A commercial polysulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 20wt% diethylenetriamine, and is amino-modified at 160°C for 48 hours, then taken out, and the membrane surface is rinsed with anhydrous ethanol and deionized water in succession to obtain an amino support membrane; subsequently, the amino support membrane is immersed in an aqueous solution containing 0.5wt% acryloyloxyethyltrimethylammonium chloride, and is constantly oscillated at 30°C for 6 hours to cause a Michael addition reaction, and the membrane surface is rinsed with deionized water after being taken out to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 2wt% piperazine is poured on the surface of the positively charged support membrane, and after being in contact and standing for 10 minutes, excess liquid on the membrane surface is removed; then a n-hexane solution containing 2wt% trimesoyl chloride is poured onto the membrane surface, and after being in contact and standing for 5 minutes, excess liquid on the membrane surface is removed, and then heat-treated at 80°C for 20 minutes to obtain the polyamide composite membrane based on the positively charged support layer.

[0046] Example 3

[0047] A commercial polyethersulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 10wt% diethylenetriamine, and after being amino-modified at 90°C for 48h, the membrane surface is washed with anhydrous ethanol and deionized water in succession to obtain an amino-supported membrane; subsequently, the amino-supported membrane is immersed in an aqueous solution containing 0.5wt% methacryloylpropyltrimethylammonium chloride, and the Michael addition reaction occurs at a constant temperature of 30°C for 24h, and the membrane surface is washed with deionized water after being taken out to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 0.05wt% 2-methylpiperazine is poured on the surface of the positively charged support membrane, and after being in contact and standing for 10min, excess liquid on the membrane surface is removed; then a n-hexane solution containing 0.05wt% trimesoyl chloride is poured on the membrane surface, and after being in contact and standing for 5min, excess liquid on the membrane surface is removed, and then heat-treated at 80°C for 10min to obtain the polyamide composite membrane based on the positively charged support layer.

[0048] Example 4

[0049] A commercial polysulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 20wt% diethylenetriamine, and after being amino-modified at 160°C for 24 hours, the membrane surface is washed with anhydrous ethanol and deionized water in succession to obtain an amino-supported membrane; subsequently, the amino-supported membrane is immersed in an aqueous solution containing 0.5wt% methacryloylpropyltrimethylammonium chloride, and the Michael addition reaction occurs at a constant temperature of 30°C for 24 hours, and the membrane surface is washed with deionized water after being taken out to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 0.05wt% piperazine is poured on the surface of the positively charged support membrane, and after being in contact and standing for 10 minutes, excess liquid on the membrane surface is removed; then a n-hexane solution containing 0.05wt% trimesoyl chloride is poured on the membrane surface, and after being in contact and standing for 5 minutes, excess liquid on the membrane surface is removed, and then heat-treated at 80°C for 10 minutes to obtain the polyamide composite membrane based on the positively charged support layer.

[0050] Example 5

[0051] A commercial polyacrylonitrile ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 10wt% hexamethylenediamine, and after being amino-modified at 90°C for 24 hours, the membrane surface is washed with anhydrous ethanol and deionized water in succession to obtain an amino-modified support membrane; subsequently, the amino-modified support membrane is immersed in an aqueous solution containing 0.5wt% methacryloyloxyethyltrimethylammonium chloride, and the Michael addition reaction occurs at a constant temperature of 20°C for 24 hours, and the membrane surface is washed with deionized water after being taken out to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 0.1wt% 2-methylpiperazine is poured on the surface of the positively charged support membrane, and after being in contact and standing for 1 minute, excess liquid on the membrane surface is removed; then a n-hexane solution containing 0.1wt% trimesoyl chloride is poured on the membrane surface, and after being in contact and standing for 0.5 minutes, excess liquid on the membrane surface is removed, and then heat-treated at 60°C for 20 minutes to obtain the polyamide composite membrane based on the positively charged support layer.

[0052] Example 6

[0053] A commercial polyethersulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 10wt% diethylenetriamine, and is amino-modified at 90°C for 24 hours, then taken out, and the membrane surface is rinsed with anhydrous ethanol and deionized water in succession to obtain an amino-modified support membrane; subsequently, the amino-modified support membrane is immersed in an aqueous solution containing 5wt% methyl iodide, and is constantly oscillated at 20°C for 6 hours to undergo a nitrogen alkylation reaction, and is taken out and the membrane surface is rinsed with deionized water to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 0.05wt% piperazine is poured on the surface of the positively charged support membrane, and after the contact is allowed to stand for 1 minute, excess liquid on the membrane surface is removed; then a n-hexane solution containing 0.05wt% trimesoyl chloride is poured onto the membrane surface, and after the contact is allowed to stand for 0.5 minutes, excess liquid on the membrane surface is removed, and then heat-treated at 50°C for 10 minutes to obtain the polyamide composite membrane based on the positively charged support layer.

[0054] Example 7

[0055] A commercial polysulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 20wt% diethylenetriamine, and is amino-modified at 160°C for 48 hours, then taken out, and the membrane surface is rinsed with anhydrous ethanol and deionized water in succession to obtain an amino support membrane; subsequently, the amino support membrane is immersed in an aqueous solution containing 10wt% methyl bromide, and is constantly oscillated at 30°C for 12 hours to cause a nitrogen alkylation reaction, and is taken out and rinsed with deionized water to obtain a positively charged support membrane; after completing the above steps, an aqueous solution containing 2wt% piperazine is poured on the surface of the positively charged support membrane, and after the contact is allowed to stand for 10 minutes, excess liquid on the membrane surface is removed; then a n-hexane solution containing 2wt% trimesoyl chloride is poured onto the membrane surface, and after the contact is allowed to stand for 5 minutes, excess liquid on the membrane surface is removed, and then heat-treated at 80°C for 20 minutes to obtain the polyamide composite membrane based on the positively charged support layer.

[0056] Comparative Example 1

[0057] A commercial polyethersulfone ultrafiltration membrane was used as the porous support membrane. An aqueous solution containing 0.05 wt% piperazine was poured on the surface of the porous support membrane. After the membrane was in contact and allowed to stand for 1 minute, excess liquid on the membrane surface was removed. Then, an n-hexane solution containing 0.05 wt% trimesoyl chloride was poured onto the membrane surface. After the membrane was in contact and allowed to stand for 0.5 minute, excess liquid on the membrane surface was removed. Subsequently, the membrane was heat treated at 50°C for 10 minutes to obtain a polyamide composite membrane based on traditional interfacial polymerization.

[0058] Comparative Example 2

[0059] A commercial polyethersulfone ultrafiltration membrane is used as a porous support membrane, and the porous support membrane is immersed in an aqueous solution containing 10wt% diethylenetriamine, and is amino-modified at 90°C for 24 hours, then taken out, and the membrane surface is rinsed with anhydrous ethanol and deionized water in succession to obtain an amino-modified support membrane; after completing the above steps, an aqueous solution containing 0.05wt% piperazine is poured on the surface of the positively charged support membrane, and after being in contact and standing for 1 minute, excess liquid on the membrane surface is removed; then a n-hexane solution containing 0.05wt% trimesoyl chloride is poured onto the membrane surface, and after being in contact and standing for 0.5min, excess liquid on the membrane surface is removed, and then a polyamide composite membrane based on an amino-modified support layer is obtained by heat treatment at 50°C for 10min.

[0060] Sample analysis

[0061] The microscopic morphology of the polyamide composite membrane based on the positively charged support layer prepared in Example 1 was analyzed. The surface SEM results and the cross-sectional SEM results were as follows: Figure 1 and Figure 2 As shown, the vesicle structure of the polyamide layer of the polyamide composite membrane based on the positively charged support layer is smaller and more uniform, and the thickness of the polyamide layer is thinner.

[0062] The performance of the polyamide composite membranes prepared in Examples 1 to 7 and Comparative Examples 1 and 2 was tested at room temperature using a cross-flow flat-plate membrane performance evaluation device. The pure water flux of the product membranes, the retention rate of a 2000 ppm Na2SO4 aqueous solution, the retention rate of a 2000 ppm NaCl aqueous solution, and a 10 ppm tetracycline aqueous solution were tested (the test temperature was 25°C and the pressure was 5 bar). The results are shown in Table 1.

[0063] Table 1 Performance test results of polyamide composite membranes prepared in Examples 1 to 7 and Comparative Examples 1 and 2

[0064]

[0065] As shown in Table 1, compared with the comparative example, the embodiment proves that the pure water flux of the polyamide composite membrane prepared by the method of the present invention is significantly improved. This is because the positively charged support layer promotes the diffusion of aqueous phase monomers, so that the polyamide primary layer is generated faster, and the further diffusion of subsequent monomers is inhibited, so that the interfacial polymerization reaction interval is controlled at a relatively small level, resulting in a decrease in the thickness of the polyamide separation layer and an improvement in water permeability. In addition, the polyamide composite membrane based on the positively charged support layer in the embodiment has a significantly improved tetracycline removal rate and better ion selectivity. This is because the polyamide separation layer of the product membrane in the embodiment is denser than that in the comparative example, so that the polyamide composite membrane in the embodiment has a smaller effective pore size, thereby improving the removal of trace small molecule antibiotics by the membrane.

[0066] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyamide composite membrane based on a positively charged support layer, characterized in that: The following steps are involved: (1) Using an amino monomer to modify the porous support membrane by amino modification to prepare an amino support membrane; (2) immersing the amino support membrane in a functional monomer solution to cause Michael addition reaction or nitrogen alkylation reaction to obtain a positively charged support membrane; (3) preparing the polyamide composite membrane based on the positively charged support layer by subjecting an aqueous solution containing polyamines and an oily solution containing polyacyl chlorides to an interfacial polymerization reaction on a positively charged support membrane; When the Michael addition reaction occurs, the functional monomer is selected from at least one of acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, methacryloyl propyl trimethyl ammonium chloride, (3-acrylamide propyl) trimethyl ammonium chloride, acryloyloxyethyl dimethyl benzyl ammonium chloride, methacryloyloxyethyl dimethyl benzyl ammonium chloride, methacryloyl propyl dimethyl benzyl ammonium chloride, benzyl ethyl trimethyl ammonium chloride, and diallyl dimethyl ammonium chloride; the content of the functional monomer in the functional monomer solution is 0.5-2 wt %, and the reaction conditions are: temperature 20-30 ° C, time 6-24 h; When the nitrogen alkylation reaction occurs, the functional monomer is selected from at least one of methyl chloride, ethyl chloride, methyl bromide, ethyl bromide, methyl iodide, ethyl iodide, benzyl chloride, chloroethanol, and chloroacetic acid; the content of the functional monomer in the functional monomer solution is 5-10 wt%, and the reaction conditions are: temperature 20-30 ° C, time 6-12 h; In the aqueous phase solution, the polyamine is at least one of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, m-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, xylene diamine, ethylenediamine, propylenediamine, tris(2-aminoethyl)amine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, and 1,4-diaminocyclohexane; In step (1), the porous support membrane is immersed in a reaction solution containing an amino monomer for amino modification, wherein the amino monomer is at least one of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine; and the content of the amino monomer in the reaction solution containing the amino monomer is 10-20 wt%.

2. The method for preparing a polyamide composite membrane based on a positively charged support layer according to claim 1, characterized in that: The conditions for amination modification are: temperature 90-160 ℃, time 24-48 h.

3. The method for preparing a polyamide composite membrane based on a positively charged support layer according to claim 1, characterized in that: In the oil phase solution, the polyacyl chloride is at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, pyromellitoyl chloride, malonyl chloride, glutaryl chloride and fumaroyl chloride.

4. The method for preparing a polyamide composite membrane based on a positively charged support layer according to claim 1, characterized in that: The content of the polyamine in the aqueous phase solution is 0.05-2wt%, and the content of the polyacyl chloride in the oil phase solution is 0.05-2wt%. 5 . A polyamide composite membrane based on a positively charged support layer obtained according to the method for preparing a polyamide composite membrane based on a positively charged support layer according to any one of claims 1 to 4 .

6. Application of the polyamide composite membrane based on the positively charged support layer according to claim 5 in the field of water treatment.

7. A method for treating antibiotic-containing wastewater, characterized in that: Utilize the polyamide composite membrane based on the positively charged support layer as described in claim 5.

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