A La-MOF-COOH / AO-PAN composite membrane material, its preparation method and application

Abstract

The present invention belongs to the technical fields of membrane material preparation and water treatment, and discloses a La-MOF-COOH / AO-PAN composite membrane material, a preparation method thereof and an application thereof. The preparation of the membrane comprises the following steps: preparation of a PAN membrane; preparation of an AO-PAN membrane; preparation of La-MOF-COOH; preparation of a La-MOF-COOH / AO-PAN membrane. The composite membrane material of the present invention is composed of modified polyacrylonitrile fibers, lanthanum metal and organic ligands. In the present invention, the amino groups and hydroxyl groups in amidoximated PAN participate in hydrogen bonding and covalent interactions, improving the interfacial compatibility and stability between La-MOF-COOH and AO-PAN, avoiding the agglomeration of La-MOF-COOH fillers, enhancing the structural uniformity, stability and functionality of the La-MOF-COOH / AO-PAN composite membrane, and endowing the composite membrane of the present invention with good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical fields of membrane material preparation and water treatment, and in particular relates to a La-MOF-COOH / AO-PAN composite membrane material, a preparation method thereof and an application thereof. Background Art

[0002] Phosphorus pollution is one of the main sources of surface water pollution and poses a serious threat to the water ecosystem. Phosphorus is one of the key limiting elements for the growth of aquatic plants and algae. Excessive phosphorus content in water bodies can lead to abnormal reproduction of algae and phytoplankton, forming water blooms or red tides, and destroying the ecological balance of water bodies. Excessive phosphorus mainly comes from agricultural fertilization, domestic wastewater and industrial wastewater, etc. The ecological degradation caused by phosphorus pollution may damage related industries such as fisheries, tourism and agriculture, and increase the operating costs of water treatment facilities.

[0003] Metal-Organic Frameworks (MOF) are porous materials assembled from metal ions or organic clusters. They have the functions of adjustable pore size structure, and diverse and adjustable metal nodes and organic ligands. MOF has attracted much attention when applied to phosphorus removal in water treatment due to its excellent structural characteristics and functionalization potential. Most MOF materials exist in the form of powders, which have limitations such as inconvenient recycling and are difficult to be used on a large scale in water treatment. Polyacrylonitrile membrane (PAN) has advantages in water treatment including excellent chemical and mechanical stability, low cost and easy functionalization modification. These characteristics make PAN an excellent substrate material for MOF material deposition.

[0004] Chinese patent publication CN 118179449A discloses a preparation method and application of a porous lanthanum-based metal-organic framework La MOF-X-C adsorbent and filter membrane. The MOF mixed dispersion is vacuum filtered onto a glass fiber filter membrane to obtain a LaMOF-X-C filter membrane, avoiding secondary pollution caused by powder materials in actual water bodies. However, in the preparation of this membrane material, there is a lack of interaction between the MOF filler and the glass fiber filter membrane, which may lead to the shedding of MOF during long-term use, limiting its practical application.

[0005] Chinese patent publication CN 108310985A discloses a MOF-199@PVDF matrix blend membrane with high anti-pollution performance and a preparation method thereof. The membrane material is prepared by phase inversion from a blend including PVDF, metal-organic framework material MOF-199 and a pore former. The pure water flux of this blend membrane has been greatly improved. However, due to poor interfacial compatibility between the filler and the polymer in direct blending, the filler aggregates, reducing the stability of MOF on the membrane.

[0006] Specifically, the following deficiencies still exist in the prior art:

[0007] Insufficient interfacial binding force leads to the detachment of MOF particles. This is because there is no interaction between the MOF filler and the membrane matrix, relying only on physical coating or weak van der Waals forces, lacking chemical bonding or strong anchoring mechanisms, and it is difficult to form a continuous interfacial binding network. As a result, the interface is prone to slip or fracture. This weak binding interface is prone to slip under dynamic water flow scouring or mechanical stress, causing the MOF particles to gradually detach from the membrane surface. The MOF particles are fixed only through surface physical contact, and the particles at the pore edges are more susceptible to hydraulic shear and fall off. During long-term use, the detachment rate may increase significantly with the accumulation of interfacial fatigue.

[0008] Poor interfacial compatibility between the filler and the polymer, caused by filler agglomeration, sedimentation, and weak interactions, will damage the adsorption performance. If the filler is unevenly dispersed, it will lead to a reduction in effective adsorption sites and affect the overall performance. The interfacial compatibility between inorganic particles and the polymer is crucial for ensuring the high performance of the composite material. Due to the poor interfacial compatibility between MOF and the polymer, performance improvement is often not achieved, which leads to interfacial defects. The filler surface is only bound to the polymer through physical interactions such as van der Waals forces or hydrogen bonds and is prone to debonding under thermal / mechanical stress.

[0009] Defects in long-term stability pose a risk of secondary pollution. Fluctuations in pH, temperature changes, or the presence of organic solvents in the water treatment environment will weaken the interaction between MOF and the membrane interface. Under temperature fluctuations, humidity changes, or mechanical stress, the composite membrane will cause the interfacial binding to relax. The long-term stability of the MOF membrane material in the water environment is insufficient, reducing the adsorption performance. The detached MOF particles may diffuse through the water body, causing secondary pollution.

[0010] Therefore, due to the poor interfacial compatibility between the filler and the polymer, the filler is difficult to disperse in its polymer membrane and forms no force or weak force with the polymer membrane, seriously damaging the stability of the composite membrane and reducing the practical feasibility of the composite membrane. Summary of the Invention

[0011] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a La-MOF-COOH / AO-PAN composite membrane material, its preparation method, and application.

[0012] The technical solution adopted by the present invention to solve its technical problems is:

[0013] A preparation method of a La-MOF-COOH / AO-PAN composite membrane material, comprising the following steps:

[0014] (1)Preparation of PAN membrane: Add polyacrylonitrile (PAN) powder and porogen into an organic solvent, heat and stir evenly in a water bath, then let it stand for degassing, pour it on a glass plate and scrape it, and carry out phase inversion in a coagulation bath to form a PAN membrane;

[0015] (2)Preparation of AO-PAN membrane: Dissolve hydroxylamine hydrochloride in water and methanol solvents, adjust the pH with a basic reagent, put the membrane obtained in step (1) into this solution and heat it for reaction, then rinse it with deionized water to obtain the AO-PAN membrane;

[0016] (3)Preparation of La-MOF-COOH: Weigh metal salts and organic ligands and add them into an organic solvent, transfer the mixed solution to a high-pressure reaction kettle, carry out hydrothermal reaction in an oven, cool and discard the supernatant, centrifuge to collect the precipitate, wash it, dry it, and collect the La-MOF-COOH powder;

[0017] (4)Preparation of La-MOF-COOH / AO-PAN membrane

[0018] 1) Preparation of La-MOF-COOH dispersion

[0019] Weigh the La-MOF-COOH powder obtained in step (3) into the dispersion, put the above mixed solution on a magnetic stirrer, stir at room temperature for preliminary dispersion; then put it into a probe ultrasonic bath and carry out ultrasonic treatment at 500 W, and carry out ice bath cooling to prevent overheating to obtain the La-MOF-COOH dispersion;

[0020] 2) Stabilization

[0021] Weigh a surfactant and put it into the dispersion in step 1), stir and disperse evenly to avoid secondary aggregation to obtain a mixed solution;

[0022] 3) Vacuum filtration loading

[0023] Lay the AO-PAN membrane obtained in step (2) flat on the surface of the filter membrane, soak it in deionized water for 5 min for pre-wetting; then slowly pour the mixed solution in step 2), control the flow rate at 1 mL / min, load it in 3 cycles, drain it every 5 min; after loading, suck the residual liquid drops on the membrane surface with filter paper to obtain a composite membrane;

[0024] 4) Post-treatment and interface strengthening

[0025] Prepare an activator and put it into a buffer solution, adjust the pH of the buffer solution, soak the composite membrane in step 3) in the above buffer solution to activate carboxyl and amino groups; then rinse it with deionized water to obtain the La-MOF-COOH / AO-PAN composite membrane material.

[0026] Further, in step (1), the pore-forming agent is one of polyvinylpyrrolidone, polyethylene glycol, or silicon dioxide;

[0027] Alternatively, in step (1), the ratio of PAN powder, pore-forming agent, and organic solvent is 15 - 18:5 - 15:100 in g:g:mL;

[0028] Alternatively, in step (1), the organic solvent is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide;

[0029] Alternatively, in step (1), the heating temperature in the water bath is 50°C - 70°C, and the heating time is 6h - 10h;

[0030] Alternatively, in step (1), the phase inversion coagulation bath condition is one of water or ethanol solvents.

[0031] Further, in step (2), the ratio of hydroxylamine hydrochloride, water, and methanol solvent is 2 - 8:30 - 75:30 - 75 in g:mL:mL;

[0032] Alternatively, in step (2), the basic reagent is one of sodium carbonate, sodium hydroxide, or sodium bicarbonate;

[0033] Alternatively, in step (2), the pH is adjusted to 7 - 8 with the basic reagent;

[0034] Alternatively, in step (2), the heating temperature is 30°C - 80°C, and the heating time is 2h - 6h.

[0035] Further, in step (3), the ratio of metal salt, organic ligand, and organic solvent is 2 - 4:2 - 3:100 in g:g:mL.

[0036] Further, in step (3), the metal salt is one of lanthanum chloride heptahydrate or lanthanum nitrate hexahydrate;

[0037] Alternatively, in step (3), the organic ligand is one of terephthalic acid or pyromellitic acid;

[0038] Alternatively, in step (3), the hydrothermal condition is a heating temperature of 80 - 150°C and a reaction time of 8 - 24h;

[0039] Alternatively, in step (3), the drying condition is a temperature of 30 - 80°C and a heating time of 8h - 24h.

[0040] Further, in step (4), the dispersion liquid in 1) is one of water or ethanol;

[0041] Alternatively, in step (4), the surfactant is one of sodium dodecylbenzenesulfonate or sodium dodecyl diphenyl ether disulfonate;

[0042] Alternatively, 0.01 - 0.2 g of surfactant is added to every 50 - 200 mL of the dispersion in step (1);

[0043] Alternatively, the stirring and dispersion time in step (4) is 10 - 60 min.

[0044] Furthermore, the activator in step (4) is one or two of EDC (1 - ethyl - 3 - (3 - dimethylaminopropyl)carbodiimide hydrochloride), NHS (N - hydroxysuccinimide), and DCC (dicyclohexylcarbodiimide);

[0045] Alternatively, the activator concentration in step (4) is 0.5 - 5 mM;

[0046] Alternatively, the buffer solution in step (4) is one of PBS (phosphate buffer solution) or borate buffer solution;

[0047] Alternatively, the pH of the buffer solution is adjusted to 5 - 8;

[0048] Alternatively, the soaking time in step (4) is 0.5 - 3 h.

[0049] Furthermore, the ratio of the dispersion to the La - MOF - COOH powder in step (4)(1) is 100 - 200 mL : 0.3 g.

[0050] The La - MOF - COOH / AO - PAN composite membrane material prepared by the preparation method as described above.

[0051] Application of the La - MOF - COOH / AO - PAN composite membrane material as described above in phosphate adsorption and / or removal.

[0052] The advantages and positive effects achieved by the present invention are:

[0053] 1. Improvement in interfacial compatibility and structural uniformity

[0054] In the present invention, La - MOF - COOH forms covalent bonds with the amino groups in AO - PAN, and at the same time, the amino and hydroxyl groups in AO - PAN participate in hydrogen bonding, enhancing the interfacial bonding between the filler and the matrix. This prevents the agglomeration of La - MOF - COOH fillers and ensures the structural uniformity of the membrane. The structural uniformity improves the mechanical strength and durability of the membrane, ensuring the uniform distribution of functional groups (such as adsorption sites). It ensures the consistency and reliability of the membrane in practical applications. Traditional methods mostly rely on single actions (such as physical dispersion or surface modification), while the present invention significantly reduces the risk of filler phase separation through the synergistic effect of covalent bonds and hydrogen bonds.

[0055] 2. Enhancement of stability and durability

[0056] In the present invention, the strong binding of covalent bonds and hydrogen bonds improves the chemical and physical stability of the membrane, especially in complex environments (such as acid-base solutions, high temperatures, or high humidity). It extends the service life of the membrane, reduces maintenance costs, and is suitable for continuous industrial operation. The stability ensures the performance maintenance of the membrane during long-term use, especially suitable for the field of water treatment. The dynamic reversibility of hydrogen bonds implies self-healing potential. When the local structure is damaged, the hydrogen bond network may reform to maintain the overall performance of the membrane.

[0057] 3. Improvement in adsorption performance

[0058] In the present invention, in addition to forming inner-sphere complexes with phosphates, the carboxyl groups of La-MOF-COOH bind to phosphates through hydrogen bonds, enhancing the adsorption sites and improving the adsorption selectivity for phosphates. Additionally, the electrostatic interaction between amino groups and phosphates further stabilizes the hydrogen bond network, improving the adsorption selectivity and capacity. This makes the membrane more efficient in adsorbing target substances (such as phosphates). This multiple interaction mechanism can be applied to adsorb trace pollutants (such as low-concentration phosphates in surface water), providing new solutions for high-difficulty fields such as surface water remediation. The adsorption performance not only depends on traditional coordination chemistry but also combines the "dual-drive" mode of electrostatic interaction and hydrogen bonds.

[0059] 4. Simple operation, mild preparation conditions, environmental friendliness, and economy

[0060] In the present invention, the preparation process emphasizes simple operation and mild conditions, without the need for extreme conditions. It reduces the energy consumption and technical threshold during the production process. At the same time, it reduces the impact on the environment, conforming to the development trend of green chemistry. The mild preparation conditions and multifunctionality imply the environmental friendliness and cost-effectiveness of the membrane during production and use. It reduces the use of high-energy-consuming processes and toxic solvents, reducing production costs. The high-efficiency adsorption performance reduces subsequent treatment steps, enhancing economic efficiency. The membrane may achieve circular economy by recycling and reusing the La-MOF-COOH filler. For example, after adsorption saturation, the filler can be desorbed and regenerated through simple chemical treatment for the next round of membrane preparation.

[0061] 5. Multifunctionality and expansion of application prospects

[0062] In the present invention, the membrane integrates structural uniformity, stability, and excellent adsorption performance, possessing multifunctional characteristics. The functional groups can be adjusted according to requirements to meet the customized needs of different scenarios such as water treatment, gas separation, and catalytic carriers. It expands the application scope. The prepared La-MOF-COOH / AO-PAN membrane has excellent comprehensive performance. Description of the drawings

[0063] Figure 1 It is the Fourier transform infrared spectrum of the AO-PAN membrane prepared in Example 1 of the present invention;

[0064] Figure 2 This is the Fourier transform infrared spectrum of the La-MOF-COOH / AO-PAN membrane prepared in Example 1 of the present invention;

[0065] Figure 3 This is the electron scanning image of the La-MOF-COOH / AO-PAN composite membrane prepared in Example 1 of the present invention before ultrasonic treatment;

[0066] Figure 4 This is the electron scanning image of the La-MOF-COOH / AO-PAN composite membrane prepared in Example 1 of the present invention after ultrasonic treatment;

[0067] Figure 5 This is the electron scanning image of the La-MOF / PAN composite membrane prepared in Comparative Example 1 of the present invention before ultrasonic treatment;

[0068] Figure 6 This is the electron scanning image of the La-MOF / PAN composite membrane prepared in Comparative Example 1 of the present invention after ultrasonic treatment;

[0069] Figure 7 This is the electron scanning image of the La-MOF-COOH / PAN composite membrane prepared in Comparative Example 2 of the present invention before ultrasonic treatment;

[0070] Figure 8 This is the electron scanning image of the La-MOF-COOH / PAN composite membrane prepared in Comparative Example 2 of the present invention after ultrasonic treatment;

[0071] Figure 9 This is the Fourier transform infrared spectrum of the AO-PAN composite membrane prepared in Comparative Example 3 of the present invention;

[0072] Figure 10 This is the electron scanning image of the La-MOF / AO-PAN composite membrane prepared in Comparative Example 3 of the present invention before ultrasonic treatment;

[0073] Figure 11 This is the electron scanning image of the La-MOF / AO-PAN composite membrane prepared in Comparative Example 3 of the present invention after ultrasonic treatment. Detailed implementation manners

[0074] The following further illustrates the present invention in conjunction with embodiments. The following embodiments are narrative and not restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0075] All the various experimental operations involved in the specific embodiments are conventional techniques in the art. For the parts not specifically annotated in this article, those of ordinary skill in the art can refer to various commonly used reference books, scientific and technical literatures, or relevant specifications, manuals, etc. before the filing date of this invention application for implementation.

[0076] A preparation method of a La-MOF-COOH / AO-PAN composite membrane material comprises the following steps:

[0077] (1) Preparation of PAN membrane: Add polyacrylonitrile PAN powder and a pore-forming agent into an organic solvent, heat and stir evenly in a water bath, then stand for defoaming, pour it on a glass plate for scraping, and carry out phase inversion in a coagulation bath to form a PAN membrane;

[0078] (2) Preparation of AO-PAN membrane: Dissolve hydroxylamine hydrochloride in water and methanol solvents, adjust the pH with a basic reagent, put the membrane obtained in step (1) into this solution and heat for reaction, then rinse with deionized water to obtain an AO-PAN membrane;

[0079] (3) Preparation of La-MOF-COOH: Weigh metal salts and organic ligands and add them into an organic solvent, transfer the mixed solution to a high-pressure reaction kettle, carry out hydrothermal reaction in an oven, cool and discard the supernatant, centrifuge to collect the precipitate, wash, dry, and collect La-MOF-COOH powder;

[0080] (4) Preparation of La-MOF-COOH / AO-PAN membrane

[0081] 1) Preparation of La-MOF-COOH dispersion

[0082] Weigh the La-MOF-COOH powder obtained in step (3) into a dispersion, put the obtained mixed solution on a magnetic stirrer, stir at room temperature for preliminary dispersion; then put it into a probe ultrasonic wave for ultrasonic treatment at 500 W, and carry out ice bath cooling to prevent overheating to obtain a La-MOF-COOH dispersion;

[0083] 2) Stabilization

[0084] Weigh a surfactant and put it into the dispersion obtained in step 1), stir and disperse evenly to avoid secondary aggregation to obtain a mixed solution;

[0085] 3) Vacuum filtration loading

[0086] Lay the AO-PAN membrane obtained in step (2) flat on the surface of a filter membrane, soak it in deionized water for 5 min for pre-wetting; then slowly pour the mixed solution obtained in step 2), control the flow rate at 1 mL / min, load it in 3 cycles, drain for 5 min at intervals each time; after loading, suck the residual liquid drops on the membrane surface with filter paper to obtain a composite membrane;

[0087] 4) Post-treatment and interface strengthening

[0088] Prepare an activator and put it into a buffer solution. Adjust the pH of the buffer solution. Immerse the composite membrane obtained in step 3) in the buffer solution with adjusted pH to activate the carboxyl and amino groups. Then rinse with deionized water to obtain the La-MOF-COOH / AO-PAN composite membrane material.

[0089] Preferably, in step (1), the pore-forming agent is one of polyvinylpyrrolidone, polyethylene glycol, or silicon dioxide;

[0090] Alternatively, in step (1), the ratio of PAN powder, pore-forming agent, and organic solvent is 15 - 18:5 - 15:100 in g:g:mL;

[0091] Alternatively, in step (1), the organic solvent is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide;

[0092] Alternatively, in step (1), the heating temperature in the water bath is 50°C - 70°C, and the heating time is 6h - 10h;

[0093] Alternatively, in step (1), the phase inversion coagulation bath condition is one of water or ethanol solvent.

[0094] Preferably, in step (2), the ratio of hydroxylamine hydrochloride, water, and methanol solvent is 2 - 8:30 - 75:30 - 75 in g:mL:mL;

[0095] Alternatively, in step (2), the basic reagent is one of sodium carbonate, sodium hydroxide, or sodium bicarbonate;

[0096] Alternatively, in step (2), the pH is adjusted to 7 - 8 with the basic reagent;

[0097] Alternatively, in step (2), the heating temperature is 30°C - 80°C, and the heating time is 2h - 6h.

[0098] Preferably, in step (3), the ratio of metal salt, organic ligand, and organic solvent is 2 - 4:2 - 3:100 in g:g:mL.

[0099] Preferably, in step (3), the metal salt is one of lanthanum chloride heptahydrate or lanthanum nitrate hexahydrate;

[0100] Alternatively, in step (3), the organic ligand is one of terephthalic acid or pyromellitic acid;

[0101] Alternatively, in step (3), the hydrothermal condition is a heating temperature of 80 - 150°C and a reaction time of 8 - 24h;

[0102] Alternatively, in step (3), the drying conditions are a temperature of 30-80°C and a heating time of 8h-24h.

[0103] Preferably, in step (4), 1) the dispersion liquid is one of water or ethanol;

[0104] Alternatively, in step (4), the surfactant is one of sodium dodecylbenzenesulfonate or sodium dodecyldiphenyloxide disulfonate;

[0105] Alternatively, 0.01-0.2 g of surfactant is added to every 50-200 mL of the dispersion liquid in step 1);

[0106] Alternatively, in step (4), the stirring and dispersion time is 10-60 min.

[0107] Preferably, in step (4), the activator is one or two of EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride), NHS (N-hydroxysuccinimide), and DCC (dicyclohexylcarbodiimide);

[0108] Alternatively, in step (4), the activator concentration is 0.5-5 mM;

[0109] Alternatively, in step (4), the buffer solution is one of PBS, i.e., phosphate buffer solution or borate buffer solution;

[0110] Alternatively, the pH of the buffer solution is adjusted to 5-8;

[0111] Alternatively, in step (4), the soaking time is 0.5-3 h.

[0112] Preferably, in step (4), the ratio of the dispersion liquid in 1) to the La-MOF-COOH powder is mL:g = 100-200:0.3.

[0113] The La-MOF-COOH / AO-PAN composite membrane material prepared by the preparation method as described above.

[0114] The application of the La-MOF-COOH / AO-PAN composite membrane material as described above in phosphate adsorption and / or removal.

[0115] Specifically, the relevant preparation and detection are as follows:

[0116] Example 1

[0117] A La-MOF-COOH / AO-PAN composite membrane material, and its synthesis and preparation steps are as follows:

[0118] 1. Preparation of PAN (polyacrylonitrile) membrane: Dissolve 15 g of PAN (polyacrylonitrile) powder and 15 g of polyvinylpyrrolidone in 100 mL of N,N-dimethylformamide, place it in a water bath at 60 °C, heat and stir for 8 h, let it stand for defoaming, then pour it on a glass plate and scrape it to form a PAN membrane by water coagulation bath phase inversion.

[0119] 2. Preparation of AO-PAN membrane: Dissolve 5 g of hydroxylamine hydrochloride in 50 mL of water and 50 mL of methanol solvent, adjust the pH to 8 with sodium hydroxide reagent, put the membrane obtained in step 1 into this solution, heat at 60 °C for 4 h, and rinse with deionized water to obtain the AO-PAN membrane.

[0120] 3. Preparation of La-MOF-COOH: Weigh 3.73 g of lanthanum chloride heptahydrate and 2.54 g of pyromellitic acid and add them to 100 mL of N,N-dimethylformamide solvent. Transfer the mixed solution to a reaction kettle, place it in an oven and react at 120 °C for 12 h, centrifuge, wash, collect the precipitate and dry it at 80 °C for 12 h to obtain La-MOF-COOH powder.

[0121] 4. Preparation of La-MOF-COOH / AO-PAN membrane

[0122] (1) Preparation of La-MOF-COOH dispersion

[0123] Accurately weigh 20 mg of the powder obtained in step 3 into 100 mL of ethanol solvent. Place the above mixed solution on a magnetic stirrer and rotate it at 300 rpm for 30 min at room temperature for preliminary dispersion. Then put it into a probe ultrasonic device and perform ultrasonic treatment at 500 W for 30 min, and perform ice bath cooling every 5 min to prevent overheating to obtain the La-MOF-COOH dispersion.

[0124] (2) Stabilization

[0125] Weigh 0.1 g of sodium dodecylbenzenesulfonate and put it into 100 mL of the dispersion obtained in step (1), stir for 10 min to disperse evenly and avoid secondary aggregation.

[0126] (3) Vacuum filtration loading

[0127] Lay the membrane obtained in step 2 flat on the surface of the filter membrane, soak it in deionized water for 5 min for pre-wetting. Then slowly pour the dispersion obtained in step (2), control the flow rate at 1 mL / min, load it in 3 cycles, and drain it every 5 min. After loading, gently press the surface of the membrane with filter paper to absorb the residual liquid drops to obtain the composite membrane.

[0128] (4) Post-treatment and interface strengthening

[0129] Prepare a PBS buffer containing 5 mM EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 2 mM NHS (N-hydroxysuccinimide), adjust the pH of the buffer to 7, soak the composite membrane in step (3) in the buffer for 2 h to activate carboxyl and amino groups. Then rinse with deionized water to obtain the La-MOF-COOH / AO-PAN composite membrane material.

[0130] The Fourier transform infrared spectrum of the AO-PAN membrane prepared in this example is as Figure 1 shown. As can be seen from Figure 1 , for the Fourier transform infrared spectrum of PAN, the peak intensity of the -CN group decreases significantly, which means that the conversion of the -CN bond to the amidoxime group is feasible. In the wavelength range of 3000 - 3500 cm -1 , the peak is significantly broadened and enhanced, which is mainly due to the increase in the amounts of -OH and -NH2 after the amidoxime reaction of PAN. This further proves the existence of the amidoxime group. The AO-PAN membrane was successfully prepared in this example.

[0131] The Fourier transform infrared spectrum of the La-MOF-COOH / AO-PAN membrane prepared in this example is as Figure 2 shown. The Fourier transform infrared spectrum shows a band between 3000 - 3500 cm -1 , which is caused by the stretching vibrations of -OH and -NH2. Compared with La-MOF-COOH and AO-PAN, the peaks of the La-MOF-COOH / AO-PAN membrane become broader, indicating that the formation of hydrogen bond networks or covalent networks is promoted on the surface, thus improving the interfacial compatibility.

[0132] Characterize the binding stability of La-MOF-COOH and AO-PAN membranes by electron scanning images. The SEM image of the La-MOF-COOH / AO-PAN membrane prepared in this example is as Figure 3 shown. The thickness of the composite membrane is 4.14 ± 0.5 μm. Place the La-MOF-COOH / AO-PAN membrane in a 70W water bath and ultrasonicate for 10 min. The SEM image of the composite membrane after ultrasonication is as Figure 4 shown. The thickness of the composite membrane after ultrasonication is 3.29 ± 0.5 μm. The results show that ultrasonication removes the loosely adsorbed La-MOF-COOH layer and retains the chemically bonded / deeply embedded La-MOF-COOH.

[0133] The synergistic effect of hydrogen bonds and covalent bonds is the core driving force. The covalent bonds activated by EDC / NHS provide the main binding force, while hydrogen bonds, as secondary interactions, help disperse stress and enhance interfacial compatibility. The synergistic force between La-MOF-COOH and AO-PAN membrane improves the interfacial stability. The covalent bonds formed by EDC / NHS activation and the hydrogen bond network work together to anchor MOF particles in the polymer matrix. SEM shows that the MOF is evenly distributed after ultrasonic treatment and the thickness only fluctuates slightly, verifying the strong interfacial binding characteristics. The results shown demonstrate the fixation of the sample La-MOF-COOH in Example 1 on the surface of the AO-PAN membrane. This process proves the stable binding between La-MOF-COOH and AO-PAN membrane.

[0134] The La-MOF-COOH / AO-PAN membrane after ultrasonic treatment was placed in a phosphate solution for performance testing. The test conditions were as follows: the phosphate concentration was 2 mg / L and pH = 7. The phosphate removal rate of the La-MOF-COOH / AO-PAN membrane was measured to be 99.09%. The high phosphate removal rate of the La-MOF-COOH / AO-PAN membrane proves the stable binding of La-MOF-COOH on the AO-PAN membrane. The MOF in the modified membrane is evenly dispersed to form continuous pores, providing a fast diffusion path for phosphates. This strong interfacial binding keeps the MOF particles stable in a dynamic environment, avoiding the shedding of adsorption active sites and ensuring a phosphate removal rate of 99.09%. The phosphorus removal performance of the La-MOF-COOH / PAN composite membrane directly depends on the interfacial stability and the MOF retention rate. The strong binding dominated by covalent bonds and the dynamic repair assisted by hydrogen bonds are the keys to inhibiting the shedding of MOF.

[0135] The organic ligand pyromellitic acid has good stability and modifiable carboxyl functional groups, which can form interaction forces with the modified PAN, helping the uniform loading of La-MOF-COOH on AO-PAN and improving the interfacial compatibility between La-MOF-COOH and AO-PAN. Pyromellitic acid forms a covalent and hydrogen bond synergistic interface with the amino / hydroxyl groups of AO-PAN through the dual characteristics of multidentate coordination and modifiable carboxyl groups, solving the problems of dispersion and stability of MOF in polymers. This molecular-level design strategy provides a theoretical basis for the development of high-performance composite membranes.

[0136] Comparative Example 1

[0137] A La-MOF / PAN composite membrane material, which is a La-MOF / PAN composite membrane. The synthesis and preparation steps are as follows:

[0138] 1. Preparation of PAN (polyacrylonitrile) membrane: Dissolve 15 g of PAN (polyacrylonitrile) powder and 15 g of polyvinylpyrrolidone in 100 mL of N,N-dimethylformamide, place it in a water bath at 60 °C, heat and stir for 8 h, let it stand for degassing, then pour it on a glass plate and scrape it to form a PAN membrane by water coagulation bath phase inversion.

[0139] 2. Preparation of La-MOF: Weigh 3.73 g of lanthanum chloride heptahydrate and 1.66 g of terephthalic acid, add them to 100 mL of N,N-dimethylformamide solvent, transfer the mixture to a reaction kettle, place it in an oven and react at 120 °C for 12 h, centrifuge, wash, collect the precipitate and dry it at 80 °C for 12 h to obtain La-MOF powder.

[0140] 3. Preparation of La-MOF / PAN membrane

[0141] (1) Preparation of La-MOF dispersion

[0142] Accurately weigh 20 mg of the powder from step 2 into 100 mL of ethanol solvent. Place the above mixture on a magnetic stirrer and rotate it at 300 rpm for 30 min at room temperature for preliminary dispersion. Then place it in a probe sonicator and perform sonication at 500 W for 30 min, with ice bath cooling every 5 min to prevent overheating, to obtain La-MOF dispersion.

[0143] (2) Stabilization

[0144] Weigh 0.1 g of sodium dodecylbenzenesulfonate and put it into 100 mL of the dispersion from step (1), stir for 10 min to disperse evenly and avoid secondary aggregation.

[0145] (3) Vacuum filtration loading

[0146] Lay the membrane from step 1 flat on the surface of the filter membrane, soak it in deionized water for 5 min for pre-wetting. Then slowly pour the dispersion from step (2), control the flow rate at 1 mL / min, load it in 3 cycles, drain it every 5 min. After loading, gently press the surface of the membrane with filter paper to absorb the residual droplets. Obtain La-MOF / PAN membrane.

[0147] (4) Post-treatment and interface strengthening

[0148] Prepare a PBS buffer solution containing 5 mM EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 2 mM NHS (N-hydroxysuccinimide), adjust the pH of the buffer solution to 7, soak the composite membrane from step (3) in the buffer solution for 2 h to activate carboxyl and amino groups. Then rinse it with deionized water to obtain La-MOF / PAN composite membrane material.

[0149] The binding stability of La-MOF and PAN membrane was determined by electronic scanning image characterization. The SEM image of the La-MOF / PAN membrane prepared in Comparative Example 1 is as follows Figure 5 shown. The thickness of the composite membrane is 4.10 ± 0.5 μm. The La-MOF / PAN membrane was placed in a 70W water bath and ultrasonically treated for 10 min. The SEM image of the composite membrane after ultrasonication is as follows Figure 6 shown. The thickness of the composite membrane after ultrasonication is 351.0 ± 0.5 nm. La-MOF detached from the surface of the PAN membrane, and the overall thickness of the membrane decreased accordingly. A large number of La-MOF particles were shaken off by ultrasonication, and the membrane thickness was significantly lower than the initial range of 4.10 ± 0.5 μm. The mechanical vibration and cavitation effect generated by the water bath ultrasonication would damage the interaction force between La-MOF and PAN membrane. The two are mainly combined by physical adsorption. The ultrasonic energy causes the La-MOF particles to detach from the surface of the PAN membrane, resulting in a decrease in binding stability. It was observed that the distribution of La-MOF on the surface of the PAN membrane became sparse, and some areas that were originally covered by La-MOF but are now exposed appeared. The results show that the La-MOF in the sample of Comparative Example 1 is unstable on the surface of the PAN membrane.

[0150] The ultrasonically treated La-MOF / PAN composite membrane was placed in a phosphate solution for performance testing. The test conditions were as follows: the phosphate concentration was 2 mg / L and pH = 7. The measured removal rate of the La-MOF / PAN composite membrane performance was 26.22%. The removal rate of phosphate by the composite membrane after ultrasonication decreased. The detachment of MOF led to a reduction in the effective adsorption surface area and the loss of adsorption active sites. The exposed PAN matrix (without MOF modification) has low affinity for phosphate. At the same time, the interfacial defects hinder the mass transfer of the solution to the MOF pores, resulting in a decrease in the kinetic adsorption capacity.

[0151] Comparative Example 2

[0152] A La-MOF-COOH / PAN composite membrane material, which is a La-MOF-COOH / PAN composite membrane. The synthesis and preparation steps are as follows:

[0153] 1. Preparation of PAN (polyacrylonitrile) membrane: Dissolve 15 g of PAN (polyacrylonitrile) powder and 15 g of polyvinylpyrrolidone in 100 mL of N,N-dimethylformamide, heat in a water bath at 60 °C and stir for 8 h. After standing and defoaming, pour it on a glass plate and scrape it to form a PAN membrane by water coagulation bath phase inversion.

[0154] 2. Preparation of La-MOF-COOH: Weigh 3.73 g of lanthanum chloride heptahydrate and 2.54 g of pyromellitic acid and add them to 100 mL of N,N-dimethylformamide solvent. Transfer the mixed solution to a reaction kettle, place it in an oven and react at 120 °C for 12 h. Then centrifuge, wash, collect the precipitate and dry it at 80 °C for 12 h to obtain La-MOF-COOH powder.

[0155] 3. Preparation of La-MOF-COOH / PAN membrane

[0156] (1) Preparation of La-MOF-COOH dispersion

[0157] Accurately weigh 20 mg of the powder from step 2 into 100 mL of ethanol solvent. Place the above mixed solution on a magnetic stirrer and rotate it at 300 rpm for 30 min at room temperature for preliminary dispersion. Then place it in a probe ultrasonic device and perform ultrasonic treatment at 500 W for 30 min, and perform ice bath cooling every 5 min to prevent overheating to obtain La-MOF-COOH dispersion.

[0158] (2) Stabilization

[0159] Weigh 0.1 g of sodium dodecylbenzenesulfonate and put it into 100 mL of the dispersion from step (1), stir for 10 min to disperse evenly and avoid secondary aggregation.

[0160] (3) Vacuum filtration loading

[0161] Lay the membrane from step 1 flat on the surface of the filter membrane, soak it in deionized water for 5 min for pre-wetting. Then slowly pour the dispersion from step (2), control the flow rate at 1 mL / min, load it in 3 cycles, drain for 5 min each time. After loading, gently press the surface of the membrane with filter paper to remove the residual liquid drops. Obtain La-MOF-COOH / PAN membrane.

[0162] (4) Post-treatment and interface strengthening

[0163] Prepare a PBS buffer solution containing 5 mM EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 2 mM NHS (N-hydroxysuccinimide), adjust the pH of the buffer solution to 7, soak the composite membrane from step (3) in the buffer solution for 2 h to activate carboxyl and amino groups. Then rinse with deionized water to obtain La-MOF-COOH / PAN composite membrane material.

[0164] Characterize the binding stability of La-MOF-COOH and PAN membrane by electron scanning image measurement. The SEM image of the La-MOF-COOH / PAN membrane prepared in this comparative example 2 is as Figure 7As shown, the thickness of the composite film is 4.08 ± 0.5 μm. The La-MOF-COOH / PAN film was placed in a 70W water bath and sonicated for 10 min. The SEM image of the composite film after sonication is as Figure 8 shown. After sonication, the thickness of the composite film is 1.68 ± 0.5 μm. The sonication affects the binding force between La-MOF-COOH particles and the PAN matrix. The binding force is weakened by sonication. Separation is observed between La-MOF-COOH particles and the PAN matrix, with signs of particles detaching from the matrix surface, which appears as obvious voids around the particles in the image. Sonication causes the originally uniformly distributed La-MOF-COOH particles to agglomerate. Larger agglomerates formed by the aggregation of particles can be seen in the SEM image. The results shown indicate that La-MOF-COOH is peeled off from the surface of the PAN film after sonication of the sample in Comparative Example 2. This process proves that the binding between La-MOF-COOH and the PAN film is unstable.

[0165] The sonicated La-MOF-COOH / PAN composite film was placed in a phosphate solution for performance testing. The test conditions were as follows: the phosphate concentration was 2 mg / L and pH = 7. The removal rate of the La-MOF-COOH / PAN composite film performance was measured to be 29.75%. Phosphate is captured by the MOF through mechanisms such as coordination (La-O-P), and the detachment of La-MOF-COOH directly weakens these effects. The shedding of the MOF directly affects the phosphate capture ability. The shedding of the MOF directly leads to a decrease in the effective La 3+ active sites, and the exposed PAN matrix has no affinity for phosphate.

[0166] Comparative Example 3

[0167] A La-MOF / AO-PAN composite membrane material, its preparation method and application. The material is a La-MOF / AO-PAN composite membrane, and the synthesis preparation steps are as follows:

[0168] 1. Preparation of PAN (polyacrylonitrile) membrane: Dissolve 15 g of PAN (polyacrylonitrile) powder and 15 g of polyvinylpyrrolidone in 100 mL of N,N-dimethylformamide, heat in a water bath at 60 °C and stir for 8 h, let it stand for defoaming and then pour it on a glass plate for scraping, and convert it into a PAN membrane by a water coagulation bath phase conversion.

[0169] 2. Preparation of AO-PAN membrane: Dissolve 5 g of hydroxylamine hydrochloride in 50 mL of water and 50 mL of methanol solvent, adjust the pH to 8 with sodium hydroxide reagent, put the membrane from step 1 into this solution and heat at 60 °C for 4 h, and rinse with deionized water to obtain the AO-PAN membrane.

[0170] 3. Preparation of La-MOF: Weigh 3.73 g of lanthanum chloride heptahydrate and 1.66 g of terephthalic acid, and add them to 100 mL of N,N-dimethylformamide solvent. Transfer the mixed solution to a reaction kettle, place it in an oven and react at 120 °C for 12 h. Then centrifuge, wash, collect the precipitate and dry it at 80 °C for 12 h to obtain La-MOF powder.

[0171] 4. Preparation of La-MOF / AO-PAN membrane

[0172] (1) Preparation of La-MOF dispersion

[0173] Accurately weigh 20 mg of the powder from step 3 into 100 mL of ethanol solvent. Place the above mixed solution on a magnetic stirrer and rotate it at 300 rpm for 30 min at room temperature for preliminary dispersion. Then place it in a probe sonicator and perform sonication at 500 W for 30 min, with ice bath cooling every 5 min to prevent overheating, to obtain La-MOF dispersion.

[0174] (2) Stabilization

[0175] Weigh 0.1 g of sodium dodecylbenzenesulfonate and put it into 100 mL of the dispersion from step (1), stir for 10 min to disperse evenly and avoid secondary aggregation.

[0176] (3) Vacuum filtration loading

[0177] Lay the membrane from step 2 flat on the surface of the filter membrane, soak it in deionized water for 5 min for pre-wetting. Then slowly pour the dispersion from step (2), control the flow rate at 1 mL / min, load it in 3 cycles, drain for 5 min each time. After loading, gently press the surface of the membrane with filter paper to remove the residual droplets. Obtain the La-MOF / AO-PAN composite membrane.

[0178] (4) Post-treatment and interface strengthening

[0179] Prepare a PBS buffer solution containing 5 mM EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 2 mM NHS (N-hydroxysuccinimide), adjust the pH of the buffer solution to 7, soak the composite membrane from step (3) in the buffer solution for 2 h to activate carboxyl and amino groups. Then rinse with deionized water to obtain the La-MOF / AO-PAN composite membrane material.

[0180] The Fourier transform infrared spectrum of the AO-PAN membrane prepared in Comparative Example 3 is as Figure 9 shown. It can be seen from Figure 9 the Fourier transform infrared spectrum that the presence of amidoxime groups is proved. In this Comparative Example 3, the AO-PAN membrane was successfully prepared.

[0181] Characterize the binding stability of La-MOF and AO-PAN membranes by electronic scanning image measurement. The SEM image of the La-MOF / AO-PAN membrane prepared in Comparative Example 3 is as Figure 10 shown. The thickness of the composite membrane is 3.77 ± 0.5 μm. The La-MOF / AO-PAN membrane was placed in a 70W water bath and ultrasonically treated for 10 min. The SEM image of the composite membrane after ultrasonication is as Figure 11 shown. The thickness of the composite membrane after ultrasonication is 2.09 ± 0.5 μm. Ultrasonic treatment caused the MOF particles to fall off, and the lack of covalent bonds could not provide sufficient binding force, resulting in the failure of binding relying only on physical interactions. Ultrasonic treatment led to a decrease in the thickness of the La-MOF / AO-PAN composite membrane, indicating that a large number of MOF particles were peeled off from the substrate surface. SEM comparison showed that the unmodified MOF and the membrane were only bound by physical adsorption, lacking chemical bonding anchoring. The interface between the unmodified MOF and the polymer was prone to slip and fall off under dynamic stress. The results shown indicate that the ultrasonication of the sample in Comparative Example 3, La-MOF, is unstable on the surface of the AO-PAN membrane.

[0182] The ultrasonically treated La-MOF / AO-PAN composite membrane was placed in a phosphate solution for performance testing. The test conditions were as follows: the phosphate concentration was 2 mg / L and pH = 7. The measured removal rate of the La-MOF / modified PAN composite membrane performance was 31.16%. The thickness of the La-MOF / AO-PAN membrane decreased after ultrasonication, and SEM showed that the MOF particles fell off, resulting in a decrease in adsorption performance. The weak binding characteristics dominated by physical adsorption led to the fall off of MOF particles. When the material interface relied only on van der Waals forces or physical coating, the dynamic water shear force would break the binding. The MOF particles were only fixed by surface contact, and the particles at the pore edges were preferentially shed under hydraulic scouring. Insufficient interfacial binding force led to physical shedding, affecting mass transfer efficiency and structural stability.

[0183] At the same time, by comparing Example 1 and Comparative Examples 1-3, it can be seen that there is a synergistic effect between pyromellitic acid and the AO-PAN membrane in the method of the present invention, which can synergistically improve the relevant properties of the prepared La-MOF-COOH / AO-PAN composite membrane material.

[0184] Comparison between the present invention and the prior art:

[0185] 1. Comparison of interface action mechanism upgrades: The present invention is a stable adsorption dominated by chemical bonding (breaking through the limitations of physical adsorption). The patented technology of traditional MOF composite membranes (such as Chinese Patent CN118179449A, a preparation method and application of a porous lanthanum-based metal-organic framework La MOF-X-C adsorbent and filter membrane) only relies on physical loading (vacuum filtration) and ignores the synergistic effect between particles and polymer carriers. The present invention creatively combines La-MOF-COOH with AO-PAN to simultaneously improve the adsorption capacity and interface stability. The film-forming technology utilizes chemical actions (hydrogen bonding and covalent bonding assist vacuum filtration).

[0186] 2. Comparison of the relationship between dosage and phosphorus removal efficiency: The present invention has made a breakthrough in optimizing the relationship between dosage and phosphorus removal efficiency, and the critical dosage threshold has been reduced. The patented technology (Chinese Patent CN114870823A, a lanthanum-based metal-organic framework phosphorus removal composite material and its preparation method and application) requires a dosage of 2 g / L to achieve a 95% phosphorus removal rate (taking 480 minutes). However, in the present invention, by stabilizing La-MOF-COOH with high phosphorus removal performance on the AO-PAN carrier, a large number of adsorption sites are retained. Through the La 3+ -O-P coordination bond with phosphate, the dosage is reduced to 0.01 - 0.04 g / L, and the removal rate reaches 99.09% (taking 60 minutes).

[0187] 3. Comparison of the simplification degree of reaction steps: In the patented technology (Chinese Patent CN113262651A, a modified polyacrylonitrile ultrafiltration membrane for removing phosphate in water and its preparation method), aminized iron oxide is obtained by modifying iron oxide with a silane coupling agent, then grafting allyl groups, copolymerizing with acrylonitrile, and finally forming a film to improve dispersibility and interface compatibility. The whole process involves multiple chemical reactions, requires different reaction conditions and equipment, and multiple purification steps. The steps are numerous and complex. After preparing La-MOF-COOH and AO-PAN in the present invention, EDC / NHS activates the carboxyl group and amino group to directly form a covalent bond, eliminating the intermediate grafting and copolymerization steps. Only simple solution treatment and conventional equipment are needed, greatly simplifying the process. At the same time, the equipment investment and energy consumption are significantly reduced.

[0188] In summary, the present invention has significant advantages compared with the prior art.

[0189] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments.

Claims

1. A preparation method of a La-MOF-COOH / AO-PAN composite membrane material, characterized in that: It includes the following steps: (1) Preparation of PAN membrane: Add polyacrylonitrile (PAN) powder and a pore-forming agent into an organic solvent, heat and stir evenly in a water bath, then stand for defoaming, pour it on a glass plate and scrape it, and carry out phase inversion in a coagulation bath to form a PAN membrane; (2) Preparation of AO-PAN membrane: Dissolve hydroxylamine hydrochloride in water and methanol solvents, adjust the pH with a basic reagent, put the PAN membrane in step (1) into this solution and heat for reaction, then rinse with deionized water to obtain an AO-PAN membrane; (3) Preparation of La-MOF-COOH: Weigh metal salts and organic ligands and add them into an organic solvent, transfer the mixed solution to a high-pressure reaction kettle, carry out hydrothermal reaction in an oven, after cooling, discard the supernatant, centrifuge to collect the precipitate, wash and dry to collect La-MOF-COOH powder; (4) Preparation of La-MOF-COOH / AO-PAN membrane 1) Preparation of La-MOF-COOH dispersion Weigh the La-MOF-COOH powder in step (3) into a dispersion, put the obtained mixed solution on a magnetic stirrer, stir at room temperature for preliminary dispersion; then put it into a probe ultrasonic for ultrasonic treatment at 500 W, and carry out ice bath cooling to prevent overheating to obtain a La-MOF-COOH dispersion; 2) Stabilization Weigh a surfactant and put it into the dispersion in step 1), stir and disperse evenly to avoid secondary aggregation to obtain a mixed solution; 3) Vacuum filtration loading Lay the AO-PAN membrane in step (2) flat on the surface of the filter membrane, soak it in deionized water for 5 min for pre-wetting; then slowly pour the mixed solution in step 2), control the flow rate at 1 mL / min, load it in 3 cycles, drain for 5 min at intervals each time; after loading, suck the residual liquid droplets on the membrane surface with filter paper to obtain a composite membrane; 4) Post-treatment and interface strengthening Prepare an activator and put it into a buffer solution, adjust the pH of the buffer solution, soak the composite membrane in step 3) in the buffer solution with adjusted pH to activate carboxyl and amino groups; then rinse with deionized water to obtain a La-MOF-COOH / AO-PAN composite membrane material.

2. The preparation method according to claim 1, characterized in that: In step (1), the pore-forming agent is one of polyvinylpyrrolidone, polyethylene glycol or silica; In step (1), the ratio of PAN powder, pore-forming agent and organic solvent is 15-18 g: 5-15 g: 100 mL; In step (1), the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide; In step (1), the heating temperature in the water bath is 50°C-70°C, and the heating time is 6 h-10 h; In step (1), the coagulation bath conditions for phase inversion are one of water or ethanol solvents.

3. The preparation method according to claim 1, characterized in that: In step (2), the ratio of hydroxylamine hydrochloride, water and methanol solvent is 2-8 g: 30-75 mL: 30-75 mL; In step (2), the basic reagent is one of sodium carbonate, sodium hydroxide or sodium bicarbonate; In step (2), use the basic reagent to adjust the pH to 7-8; In step (2), the heating temperature is 30°C-80°C, and the heating time is 2 h-6 h.

4. The preparation method according to claim 1, characterized in that: In step (3), the ratio of metal salt, organic ligand, and organic solvent is 2 - 4 g : 2 - 3 g : 100 mL.

5. The preparation method according to claim 1, characterized in that: In step (3), the metal salt is one of lanthanum chloride heptahydrate or lanthanum nitrate hexahydrate; In step (3), the organic ligand is one of terephthalic acid or pyromellitic acid; In step (3), the hydrothermal conditions are a heating temperature of 80 - 150 °C and a reaction time of 8 - 24 h; In step (3), the drying conditions are a temperature of 30 - 80 °C and a heating time of 8 h - 24 h.

6. The preparation method according to claim 1, characterized in that: In step (4), 1), the dispersion liquid is one of water or ethanol; In step (4), the surfactant is one of sodium dodecylbenzenesulfonate or sodium dodecyl diphenyl ether disulfonate; 0.01 - 0.2 g of surfactant is added to every 50 - 200 mL of the dispersion liquid in step 1) of step (4); In step (4), the stirring and dispersion time is 10 - 60 min.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step (4), the activator is one or two of EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride), NHS (N-hydroxysuccinimide), and DCC (dicyclohexylcarbodiimide); In step (4), the activator concentration is 0.5 - 5 mmol / L; In step (4), the buffer solution is one of phosphate buffer solution or borate buffer solution; Adjust the pH of the buffer solution to 5 - 8; In step (4), the soaking time is 0.5 - 3 h.

8. The preparation method according to claim 7, characterized in that: In step (4), in step 1), the ratio of the dispersion liquid to the La-MOF-COOH powder is 100 - 200 mL : 0.3 g.

9. The La-MOF-COOH / AO-PAN composite membrane material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the La-MOF-COOH / AO-PAN composite membrane material according to claim 9 in phosphate adsorption and / or removal.

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