An anion exchange membrane for separating nitrogen and phosphorus ions in water and a preparation method thereof

Abstract

The application discloses a selective anion exchange membrane for separating nitrogen and phosphorus ions in water and a preparation method thereof. A solution of polyamine monomers, anion functional group-containing amine monomers and dopamine is blended on the surface of a commercial anion exchange membrane to form a deposition layer of negatively charged polydopamine nanoparticles loaded with polyamine monomers, and then a selective anion exchange membrane is obtained through nano-limit interface polymerization. The preparation method is simple, controllable and easy to scale up, and the obtained membrane has excellent anion separation selectivity, and has a good application prospect for effectively separating and concentrating nitrogen and phosphorus ions in water.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation, and particularly relates to a selective anion exchange membrane for separating nitrogen and phosphorus ions in water and its preparation method. Background Technology

[0002] Eutrophication has become a major environmental problem in my country that urgently needs to be addressed. Its main cause is the accumulation of nutrients such as nitrogen and phosphorus, which enter water bodies through industrial and agricultural wastewater discharge. Phosphorus content is a particularly important controlling factor; as the total phosphorus content in water increases, cyanobacteria and other microorganisms proliferate, leading to reduced oxygen levels, severe water pollution, and environmental degradation. The nitrogen cycle is an important biogeochemical cycle. The industrialization of ammonia synthesis technology has increased ammonia production and has a wide range of applications, but it inevitably results in ammonia loss and waste. Therefore, there is an urgent need to treat nitrogen- and phosphorus-rich wastewater, remove phosphates, and recover nitrogen ions to achieve efficient wastewater treatment and resource recovery.

[0003] Currently, the main treatment processes for nitrogen and phosphorus-containing wastewater include physical adsorption, chemical precipitation, electrochemical methods, and microbial degradation. However, these methods typically suffer from low removal efficiency, generation of secondary solid waste, and environmental pollution. Electrodialysis membrane separation technology, due to its low energy consumption, high efficiency, lack of secondary pollution, and continuous operation capabilities, is increasingly being applied to seawater and brackish water desalination, high-salinity wastewater treatment, and resource recovery. Ion exchange membranes are a crucial component of electrodialysis devices, allowing ions with opposite charges (counterions) to pass through while blocking ions with similar charges (like ions). Ion exchange membranes achieve ion separation through electrostatic repulsion, pore size sieving, and differences in the Gibbs free energy of hydrated ions. However, existing anion exchange membranes (AEMs) typically only separate anions / cations, making effective separation of different types of anions with similar sizes difficult.

[0004] In recent years, the preparation of selective anion exchange membranes (AEMs) has become a research hotspot in the field of electrodialysis membrane separation. Selective anion exchange membranes can be prepared by developing novel AEMs and by surface modification of existing commercial AEMs. Developing novel AEMs requires synthesizing new polymers and obtaining selective AEMs through in-situ crosslinking and quaternization treatments; however, the membrane preparation process is complex, time-consuming, and requires stringent conditions, resulting in high costs. On the other hand, surface modification of commercial AEMs using methods such as surface coating crosslinking, in-situ growth, and electrostatic layer-by-layer self-assembly can improve membrane separation selectivity. However, selective AEMs prepared by these methods still suffer from problems such as thick surface modification layers leading to high mass transfer resistance, unstable interlayer structures, and a trade-off between ion permeability and separation selectivity. Interfacial polymerization is a membrane preparation method that uses polyamine monomers and acyl chloride monomers at the interface between the aqueous and organic phases to obtain polyamide thin layers. This method offers mild reaction conditions and rapid membrane formation, and is expected to be used for surface modification of AEMs to improve the membrane's selectivity for different anions. However, how to control the interfacial polymerization film formation process through simple methods, and simultaneously adjust the pore structure, charge, and interfacial stability of the polyamide surface functional layer, thereby improving the ion permeation selectivity and stability of AEMs to achieve effective separation of nitrogen and phosphorus ions in water, remains a key problem that urgently needs to be solved.

[0005] This invention proposes a method of solution-blending polyamine monomers, anion-functionalized amine monomers, and dopamine onto the surface of a commercially available anion exchange membrane to form a negatively charged polydopamine nanoparticle deposition layer loaded with polyamine monomers. Selective anion exchange membranes are then obtained through nano-confined interfacial polymerization. The negatively charged polydopamine nanoparticles, formed by the oxidative polymerization of dopamine and anion-functionalized amine monomers in an alkaline aqueous solution, can alter the interfacial diffusion rate of the polyamine monomers and the degree of interfacial polymerization reaction with the polyacrylamide monomers, thereby controlling the pore structure and surface charge intensity of the polyamide layer and improving the membrane's selectivity for anion permeation. Simultaneously, the negatively charged polydopamine nanoparticles can adhere to the AEM surface, improving the interlayer stability between the polyamide layer and the AEM, thus ensuring long-term service stability of the membrane under an electric field. This membrane preparation method is simple, controllable, and easily scaled up. The resulting membrane exhibits excellent anion separation selectivity and shows promising application prospects for the effective separation and concentration of nitrogen and phosphorus ions in water. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an anion exchange membrane for the separation of nitrogen and phosphorus ions in water, as well as its preparation method. A negatively charged polydopamine nanoparticle deposition layer loaded with polyamine monomers is formed on the surface of a commercial anion exchange membrane by solution blending of polyamine monomers, anion-functionalized amine monomers, and dopamine. This layer is then polymerized through a nano-confined interface to obtain a selective anion exchange membrane. The negatively charged polydopamine nanoparticles enhance the negative charge on the membrane surface by controlling the pore size of the polyamide surface functional layer, significantly improving the separation selectivity of the anion exchange membrane for different nitrogen and phosphorus ions in water. Simultaneously, it effectively improves the interaction between the polyamide functional layer and the commercial anion exchange membrane layer, giving the membrane long-term service stability under an electric field. This membrane preparation method is simple, controllable, and easy to scale up. The resulting membrane exhibits excellent anion separation selectivity and shows promising application prospects for the effective separation and concentration of nitrogen and phosphorus ions in water.

[0007] The technical solution of this invention is as follows:

[0008] A method for preparing an anion exchange membrane for separating nitrogen and phosphorus ions in water, characterized by comprising the following steps:

[0009] 1) Dissolve 0.1 to 1.0 parts by weight of polyamine monomer, 0.02 to 1.0 parts by weight of amine monomer containing anionic functional groups and 0.005 to 0.5 parts by weight of dopamine in 100 parts by weight of alkaline aqueous solution, stir until completely dissolved, immerse the above mixed aqueous solution on the surface of a commercial anion exchange membrane for a certain period of time, remove the residual aqueous solution on the membrane surface, and form a negatively charged polydopamine nanoparticle deposition membrane loaded with polyamine monomer;

[0010] 2) Pour the organic phase solution containing polyacrylamide chloride monomers onto the surface of the above-mentioned negatively charged polydopamine nanoparticle deposition membrane loaded with polyamine monomers, carry out nano-confined interfacial polymerization reaction, remove the residual organic phase solution on the membrane surface, and heat treat at 30-70°C for 5-30 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water.

[0011] The polyamine monomer mentioned in step 1) is one of m-phenylenediamine, p-phenylenediamine, piperazine, diethylenetriamine, triethylenetetramine, or N-aminoethylpiperazine; the amine monomer containing anionic functional groups mentioned in step 1) is one of sodium 2,4-diaminobenzenesulfonate, 3,5-diaminobenzoic acid, 2,4-diaminophenol hydrochloride, 2,5-diaminobenzenesulfonic acid, 2,5-diaminoterephthalic acid, or 2,2′-bis(sulfonic acid)benzidine; the commercially available anion exchange membrane mentioned in step 1) is one of homogeneous anion exchange membrane or heterogeneous anion exchange membrane; the polyacrylamide chloride monomer mentioned in step 2) is one of phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, toluenedioxyl chloride, cyanuric chloride, or biphenyltetracarboxylic acid chloride; the solvent of the organic phase solution mentioned in step 2) is one of n-hexane, cyclohexane, or heptane.

[0012] Preferably, the alkaline aqueous solution in step 1) is an aqueous solution of sodium hydroxide or potassium hydroxide with a mass percentage concentration of 0.01 to 0.1%.

[0013] Preferably, the stirring conditions described in step 1) are stirring at 400-800 rpm and 10-40°C for 10-40 minutes.

[0014] Preferably, the mixed aqueous solution described in step 1) is immersed on the surface of a commercial anion exchange membrane under the following conditions: immersion at 15–40°C for 0.5–4 hours.

[0015] Preferably, the mass percentage concentration of the polyacrylamide chloride monomer in the organic phase solution in step 2) is 0.05-1.0%.

[0016] Preferably, the nano-confined interface polymerization reaction conditions described in step 2) are: reaction at 15–35°C for 0.5–5 minutes.

[0017] Another technical solution of the present invention is an anion exchange membrane prepared by the above method.

[0018] The selective anion exchange membrane prepared by the method described above, used for the separation of nitrogen and phosphorus ions in water, can be used for the separation of different types of anions in the field of electrodialysis.

[0019] Selective anion exchange membranes are produced by solution blending polyamine monomers, amine monomers containing anionic functional groups, and dopamine onto the surface of commercial anion exchange membranes to form a negatively charged polydopamine nanoparticle deposition layer loaded with polyamine monomers. This layer is then polymerized through a nano-confined interface to obtain the selective anion exchange membrane. By controlling the pore size of the polyamide surface functional layer, the negative charge on the membrane surface is enhanced, improving the pore size sieving and electrostatic repulsion of different anions, thus achieving the separation of nitrogen and phosphorus ions in water. Compared with commercial anion exchange membranes, at 10 mA·cm⁻¹, [the membrane exhibits superior performance]. -2Under the specified operating current, the modified anion exchange membrane exhibits significantly improved selectivity for separating nitrogen and phosphorus ions in water, providing an effective method for the separation and concentration of nitrogen and phosphorus ions in water, with promising application prospects. Attached Figure Description

[0020] Figure 1 This is a surface morphology diagram of the selective anion exchange membrane for separating nitrogen and phosphorus ions in water prepared in Example 3 of the present invention. Detailed Implementation

[0021] The following are examples of implementation of the present invention, but the present invention is not limited to these examples.

[0022] In the following embodiments, the selective separation performance test method of the selective anion exchange membrane is as follows: The selective anion exchange membrane is placed in a conventional electrodialysis apparatus in the art, a 0.2 mol / L sodium sulfate solution is circulated in the electrode chamber, and a mixed salt solution of sodium nitrate and sodium phosphate with a concentration of 0.05 mol / L is added to the two test chambers respectively, at a current density of 10 mA·cm⁻¹. -2 The test lasts for 2 hours. The calculation formula is as follows: in, - Nitrate ion flux of the modified membrane, mol·m -2 h -1 , - Phosphate ion flux of the modified membrane, mol·m -2 h -1 ; - Nitrate ion concentration in the concentration chamber, mol / L - Phosphate ion concentration in the concentrate chamber, mol / L; P- Separation selectivity; The separation selectivity of the modified anion exchange membrane is calculated by measuring the ion concentration on one side of the dilute chamber.

[0023] Example 1:

[0024] 0.1 parts by mass of piperazine monomer, 0.02 parts by mass of sodium 2,4-diaminobenzenesulfonate monomer, and 0.005 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% sodium hydroxide aqueous solution. The solution was stirred at 400 rpm and 10°C for 10 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercial homogeneous anion exchange membrane at 15°C for 0.5 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A 0.05% solution of trimesoyl chloride in n-hexane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A nano-confined interfacial polymerization reaction was carried out at 15°C for 0.5 minutes. The residual organic phase solution on the membrane surface was removed. The membrane was then heat-treated at 30°C for 5 minutes to obtain a selective anion exchange membrane suitable for the separation of nitrogen and phosphorus ions in water.

[0025] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 2.20 after running for 2 hours at the operating current.

[0026] Example 2:

[0027] 1.0 parts by weight of piperazine monomer, 1.0 parts by weight of sodium 2,4-diaminobenzenesulfonate monomer, and 0.5 parts by weight of dopamine were dissolved in 100 parts by weight of a 0.1% sodium hydroxide aqueous solution. The solution was stirred at 800 rpm and 40°C for 40 minutes until completely dissolved. The above mixed aqueous solution was then immersed in the surface of a commercial homogeneous anion exchange membrane at 40°C for 4 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A 1.0% (w / w) solution of trimesoyl chloride and hexane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A nano-confined interfacial polymerization reaction was carried out at 35°C for 5 minutes. The residual organic phase solution on the membrane surface was removed. The membrane was then heat-treated at 70°C for 30 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water.

[0028] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 2.79 after running for 2 hours at the operating current.

[0029] Example 3:

[0030] 0.3 parts by mass of piperazine monomer, 0.1 parts by mass of sodium 2,4-diaminobenzenesulfonate monomer, and 0.5 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% sodium hydroxide aqueous solution. The solution was stirred at 600 rpm and 20°C for 30 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercial homogeneous anion exchange membrane at 30°C for 1.5 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A 0.25% by mass solution of trimesoyl chloride n-hexane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A nano-confined interfacial polymerization reaction was carried out at 15°C for 5 minutes. The residual organic phase solution on the membrane surface was removed, and the membrane was heat-treated at 60°C for 15 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water.

[0031] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 3.63 after running for 2 hours at the operating current.

[0032] Comparative Example 1

[0033] Referring to the steps in Example 3, without preparing a negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer, a polyamide-modified anion exchange membrane was prepared directly by interfacial polymerization of piperazine and trimesoyl chloride monomer (preparation conditions as described in Example 3).

[0034] Comparative Example 2

[0035] Referring to the steps in Example 3, without preparing negatively charged polydopamine nanoparticles, a polydopamine nanoparticle deposition film loaded with piperazine monomer was directly formed by oxidative polymerization of piperazine and dopamine. Then, it was subjected to interfacial polymerization with trimesoyl chloride (preparation conditions as described in Example 2) to prepare a polyamide modified anion exchange membrane containing polydopamine nanoparticles.

[0036] Table 1. Comparison of separation selectivity of anion exchange membranes prepared in Example 3 and Comparative Examples 1-2

[0037]

[0038] The results in Table 1 show that all three methods can prepare selective anion exchange membranes, but they have significant differences in ion flux and separation selectivity for nitrate / phosphate ions. This is because the chemical composition and microstructure of the membranes used to prepare the selective anion exchange membranes are different.

[0039] In Comparative Example 1, a polyamide modified layer was prepared by interfacial polymerization of polyamine monomers and polyacrylamide chloride monomers. The membrane had high density and low ion permeation flux. Although the negative charge on the membrane surface caused electrostatic repulsion of phosphate ions, the interaction between the polyamide modified layer and the commercial anion exchange membrane was weak, resulting in low anion selectivity. In Comparative Example 2, a polyamide modified anion exchange membrane containing polydopamine nanoparticles was prepared by interfacial polymerization of polyamine monomers, dopamine, and polyacrylamide chloride monomers. The introduction of polydopamine nanoparticles improved the interfacial interaction between the modified layer and the commercial anion exchange membrane, resulting in higher anion selectivity compared to the polyamide selective anion exchange membrane.

[0040] In Example 3, negatively charged polydopamine nanoparticles loaded with polyamine monomers regulate the pore size of the polyamide surface functional layer, enhance the negative charge on the membrane surface, improve the membrane's pore size sieving and electrostatic repulsion of different anions, and significantly improve the membrane's selectivity for anion separation. At the same time, the strong adhesion of the negatively charged polydopamine nanoparticles can improve the interaction between the polyamide functional layer and the commercial anion exchange membrane layer, enabling the membrane to have long-term service stability under the action of an electric field, and achieving effective separation and concentration of nitrogen and phosphorus ions in water.

[0041] Example 4:

[0042] 0.7 parts by mass of piperazine monomer, 0.35 parts by mass of sodium 2,4-diaminobenzenesulfonate monomer, and 0.25 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% potassium hydroxide aqueous solution. The solution was stirred at 800 rpm and 40°C for 30 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercially available heterogeneous anion exchange membrane at 25°C for 3.5 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A 0.35% by mass solution of isophenyltrimethylol chloride n-hexane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane loaded with piperazine monomer. A nano-confined interfacial polymerization reaction was carried out at 20°C for 4 minutes. The residual organic phase solution on the membrane surface was removed, and the membrane was heat-treated at 70°C for 10 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water.

[0043] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 2.68 after running for 2 hours at the operating current.

[0044] Example 5:

[0045] 0.5 parts by mass of m-phenylenediamine monomer, 0.2 parts by mass of 3,5-diaminobenzoic acid, and 0.15 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% potassium hydroxide aqueous solution. The solution was stirred at 500 rpm and 20°C for 30 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercial homogeneous anion exchange membrane at 20°C for 2 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane supported on m-phenylenediamine monomer. A 0.2% phthaloyl chloride cyclohexane solution was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane supported on m-phenylenediamine monomer. A nano-confined interfacial polymerization reaction was carried out at 20°C for 5 minutes. The residual organic phase solution on the membrane surface was removed, and the membrane was heat-treated at 60°C for 15 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water.

[0046] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 2.78 after running for 2 hours at the operating current.

[0047] Example 6:

[0048] 0.4 parts by mass of p-phenylenediamine monomer, 0.3 parts by mass of 2,4-diaminophenol hydrochloride, and 0.2 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% sodium hydroxide aqueous solution. The solution was stirred at 400 rpm and 25°C for 40 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercial homogeneous anion exchange membrane at 15°C for 3 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane supported on p-phenylenediamine monomer. A 0.25% (w / w) terephthaloyl chloride n-hexane solution was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane supported on p-phenylenediamine monomer. A nano-confined interfacial polymerization reaction was carried out at 20°C for 3 minutes. The residual organic phase solution on the membrane surface was removed. The membrane was then heat-treated at 50°C for 25 minutes to obtain a selective anion exchange membrane suitable for the separation of nitrogen and phosphorus ions in water.

[0049] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 2.79 after running for 2 hours at the operating current.

[0050] Example 7:

[0051] 0.8 parts by mass of diethylenetriamine monomer, 0.4 parts by mass of 2,5-diaminobenzenesulfonic acid, and 0.3 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% sodium hydroxide aqueous solution. The solution was stirred at 400 rpm and 20°C for 30 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercially available heterogeneous anion exchange membrane at 20°C for 4 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane loaded with diethylenetriamine monomer. A 0.15% (w / w) solution of cyanuric chloride heptane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane loaded with diethylenetriamine monomer. A nano-confined interfacial polymerization reaction was carried out at 25°C for 2 minutes. The residual organic phase solution on the membrane surface was removed, and the membrane was heat-treated at 40°C for 30 minutes to obtain a selective anion exchange membrane suitable for the separation of nitrogen and phosphorus ions in water.

[0052] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 3.02 after running for 2 hours at the operating current.

[0053] Example 8:

[0054] 0.6 parts by mass of N-aminoethylpiperazine monomer, 0.2 parts by mass of 2,5-diaminoterephthalic acid, and 0.35 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% sodium hydroxide aqueous solution. The solution was stirred at 500 rpm and 40°C for 15 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercially available heterogeneous anion exchange membrane at 40°C for 0.5 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane supported on N-aminoethylpiperazine monomer. A 0.2% by mass solution of toluenedicarboxychlorocyclohexane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane supported on N-aminoethylpiperazine monomer. A nano-confined interfacial polymerization reaction was carried out at 30°C for 1 minute. The residual organic phase solution on the membrane surface was removed, and the membrane was heat-treated at 60°C for 20 minutes to obtain a selective anion exchange membrane suitable for the separation of nitrogen and phosphorus ions in water.

[0055] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 2.86 after running for 2 hours at the operating current.

[0056] Example 9:

[0057] 0.6 parts by mass of triethylenetetramine monomer, 0.2 parts by mass of benzidine 2,2′-disulfonic acid, and 0.3 parts by mass of dopamine were dissolved in 100 parts by mass of a 0.01% potassium hydroxide aqueous solution. The solution was stirred at 600 rpm and 25°C for 10 minutes until completely dissolved. The resulting aqueous solution was then immersed in a commercial homogeneous anion exchange membrane at 20°C for 2.5 hours. The residual aqueous solution on the membrane surface was removed to form a negatively charged polydopamine nanoparticle deposition membrane loaded with triethylenetetramine monomer. A 0.3% by mass solution of biphenyltetracarboxylic acid chloride hexane was poured onto the surface of the negatively charged polydopamine nanoparticle deposition membrane loaded with triethylenetetramine monomer. A nano-confined interfacial polymerization reaction was carried out at 20°C for 5 minutes. The residual organic phase solution on the membrane surface was removed. The membrane was then heat-treated at 60°C for 10 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water.

[0058] Selective anion exchange membrane at 10 mA·cm -2 The separation coefficient for a 0.05 mol / L sodium nitrate / sodium phosphate mixed salt solution was 3.16 after running for 2 hours at the operating current.

Claims

1. A method for preparing an anion exchange membrane for separating nitrogen and phosphorus ions in water, characterized in that: Includes the following steps: 1) Dissolve 0.1 to 1.0 parts by weight of polyamine monomer, 0.02 to 1.0 parts by weight of amine monomer containing anionic functional groups and 0.005 to 0.5 parts by weight of dopamine in 100 parts by weight of alkaline aqueous solution, stir until completely dissolved, immerse the above mixed aqueous solution on the surface of a commercial anion exchange membrane for a certain period of time, remove the residual aqueous solution on the membrane surface, and form a negatively charged polydopamine nanoparticle deposition membrane loaded with polyamine monomer; 2) Pour the organic phase solution containing polyacrylamide chloride monomers onto the surface of the above-mentioned negatively charged polydopamine nanoparticle deposition membrane loaded with polyamine monomers, carry out nano-confined interfacial polymerization reaction, remove the residual organic phase solution on the membrane surface, and heat treat at 30-70°C for 5-30 minutes to obtain a selective anion exchange membrane that can be used for the separation of nitrogen and phosphorus ions in water. The polyamine monomer mentioned in step 1) is one of m-phenylenediamine, p-phenylenediamine, piperazine, diethylenetriamine, triethylenetetramine, or N-aminoethylpiperazine; the amine monomer containing anionic functional groups mentioned in step 1) is one of sodium 2,4-diaminobenzenesulfonate, 3,5-diaminobenzoic acid, 2,4-diaminophenol hydrochloride, 2,5-diaminobenzenesulfonic acid, 2,5-diaminoterephthalic acid, or 2,2′-bis(sulfonic acid)benzidine; the commercially available anion exchange membrane mentioned in step 1) is one of homogeneous anion exchange membrane or heterogeneous anion exchange membrane; the polyacrylamide chloride monomer mentioned in step 2) is one of phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, toluenedioxyl chloride, cyanuric chloride, or biphenyltetracarboxylic acid chloride; the solvent of the organic phase solution mentioned in step 2) is one of n-hexane, cyclohexane, or heptane.

2. The method for preparing anion exchange membrane for separating nitrogen and phosphorus ions in water as described in claim 1, characterized in that: The alkaline aqueous solution mentioned in step 1) is a sodium hydroxide or potassium hydroxide aqueous solution with a mass percentage concentration of 0.01 to 0.1%.

3. The method for preparing anion exchange membrane for separating nitrogen and phosphorus ions in water as described in claim 1, characterized in that: The stirring conditions described in step 1) are: stirring at 400–800 rpm and 10–40°C for 10–40 minutes.

4. The method for preparing anion exchange membrane for separating nitrogen and phosphorus ions in water as described in claim 1, characterized in that: The mixed aqueous solution described in step 1) is immersed on the surface of a commercial anion exchange membrane under the following conditions: at 15–40°C for 0.5–4 hours.

5. The method for preparing anion exchange membrane for separating nitrogen and phosphorus ions in water as described in claim 1, characterized in that: The mass percentage concentration of polyacrylamide chloride monomer in the organic phase solution described in step 2) is 0.05–1.0%.

6. The method for preparing anion exchange membrane for separating nitrogen and phosphorus ions in water as described in claim 1, characterized in that: The nano-confined interface polymerization reaction conditions described in step 2) are: reaction at 15–35°C for 0.5–5 minutes.

7. The anion exchange membrane prepared by the method according to any one of claims 1-6.

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