La-mof-cooh / pei-pvdf composite membrane material for removing phosphorus, preparation method and application

Abstract

The application belongs to the technical field of water treatment and new material, and discloses a La-MOF-COOH / PEI-PVDF composite membrane material for removing phosphorus, a preparation method and application, which comprises the following steps: (1) preparation of PVDF; (2) preparation of La-MOF-COOH; (3) preparation of La-MOF-COOH / PEI-PVDF composite membrane, to obtain the La-MOF-COOH / PEI-PVDF composite membrane material. The interface compatibility of the La-MOF-COOH / PEI-PVDF composite membrane material can significantly improve the mechanical properties, chemical stability, thermal stability, filtration performance, recyclability and reusability, uniform dispersibility and adsorption performance of the composite membrane. These advantages not only improve the comprehensive performance of the composite membrane, but also expand the application range of the composite membrane in the field of water treatment and the like, and have important practical significance.

Description

Technical Field

[0001] This invention belongs to the fields of water treatment and new materials technology, and in particular to a La-MOF-COOH / PEI-PVDF composite membrane material for phosphorus removal, its preparation method and application. Background Technology

[0002] Phosphorus is an essential nutrient for aquatic life, but excessive phosphorus levels in water can lead to the overgrowth of phytoplankton such as algae. Excessive algal growth can cause algal blooms or red tides, reducing water transparency and hindering sunlight penetration, thus affecting photosynthesis in aquatic plants. Simultaneously, the decomposition of dead algae consumes large amounts of dissolved oxygen, leading to oxygen depletion in the water, causing fish and other aquatic organisms to suffocate and die, disrupting the balance of the aquatic ecosystem. Long-term consumption of water with excessive phosphorus content may adversely affect human organs such as bones and kidneys. Furthermore, the concentration of phosphates in actual surface water is one to two orders of magnitude lower than the concentrations of other coexisting anions and cations, making selective phosphate removal more difficult. Therefore, developing efficient and highly selective phosphate adsorption materials is of great significance for water pollution control.

[0003] Adsorption technology has attracted widespread attention due to its selective and efficient adsorption of phosphates. In particular, lanthanum-based metal-organic frameworks (La-MOFs) adsorbents can form stable inner-sphere complexes with phosphates, thereby enhancing their selectivity for phosphates. However, La-MOF adsorbents, typically used in powder form, face significant challenges in practical applications, including non-recyclability and potential secondary pollution. Membrane materials, with their large specific surface area and ease of synthesis, have become attractive carriers for adsorbents, facilitating the recovery of powdered adsorbents. Composite membrane materials containing La-MOF adsorbents offer a novel solution for phosphate removal. Although composite membrane materials effectively address the non-recyclability issue of powdered MOF adsorbents, poor interfacial compatibility between MOFs and polymers leads to MOF detachment and decreased membrane performance. Therefore, it is necessary to improve the interfacial compatibility between polymers and MOF particles.

[0004] Chinese patent publication CN112007527A discloses a gas separation membrane containing MOF composite material and its preparation method. MOF-801 IL composite material is added as a filler to a PIM-1 polymer matrix to form a hybrid membrane. This membrane exhibits good permeability. However, the compatibility between the MOF filler and the polymer was not considered in the preparation of this membrane material, which may lead to MOF aggregation and detachment during actual use. Specifically, poor compatibility between the MOF filler and the polymer matrix leads to a series of limitations, mainly in the following aspects:

[0005] Poor interfacial compatibility between MOF filler and the polymer matrix can lead to reduced chemical stability of the composite material. Poor interfacial compatibility can cause MOF particles to detach from the polymer matrix, which not only affects material performance but may also lead to secondary pollution and damage to aquatic ecosystems. The detachment of MOF particles and secondary pollution issues impact the sustainability of the material and fail to meet environmental protection requirements. In membrane materials, MOF particle detachment alters the membrane's pore structure, affecting filtration performance and selectivity, and reducing phosphorus removal efficiency.

[0006] Poor interfacial compatibility increases the processing difficulty of composite materials. Poor dispersion of MOF particles in the polymer matrix may lead to agglomeration of the material during processing, affecting the uniformity of the material.

[0007] Poor interfacial compatibility between MOF fillers and the polymer matrix can lead to a decline in the mechanical properties of the composite material. This is because insufficient adhesion between the MOF particles and the polymer matrix prevents effective stress transfer, making the material prone to fracture at the interface under stress. Poor interfacial compatibility may also shorten the material's service life, requiring more frequent replacements and thus increasing costs.

[0008] The poor compatibility between MOF fillers and polymer matrices mainly manifests in decreased physical properties, reduced chemical stability, interfacial stability issues, processing and application limitations, and cost and sustainability concerns. These limitations severely impact the performance and application effectiveness of composite materials. Therefore, improving the interfacial compatibility between MOF fillers and polymer matrices is crucial for enhancing the performance of composite materials. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a La-MOF-COOH / PEI-PVDF composite membrane material for phosphorus removal, its preparation method, and its application.

[0010] The technical solution adopted by this invention to solve its technical problem is:

[0011] A method for preparing a La-MOF-COOH / PEI-PVDF composite membrane material for phosphorus removal includes the following steps:

[0012] (1) Preparation of casting solution: Polyvinylidene fluoride (PVDF) powder and pore-forming agent are added to an organic solvent, heated and stirred evenly in a water bath, then polyethyleneimine (PEI) is added to the above solution, a dispersant is added and stirred evenly, and the mixture is allowed to stand to remove bubbles to obtain the casting solution.

[0013] (2) Preparation of La-MOF-COOH: Weigh the metal salt and organic ligand and add them to the organic solvent. Transfer the mixed solution to the high-pressure reactor and place it in the oven for hydrothermal reaction. Cool and discard the supernatant. Centrifuge to collect the precipitate, wash and dry it to obtain La-MOF-COOH powder.

[0014] (3) Preparation of La-MOF-COOH / PEI-PVDF composite membrane

[0015] 1) Preparation of La-MOF-COOH dispersion

[0016] Weigh the La-MOF-COOH powder from step (2) into an organic solvent, place the mixture in a magnetic stirrer, and stir at room temperature for initial dispersion; then place it in a probe for ultrasonic treatment at 500W, and cool it in an ice bath to prevent overheating, to obtain the La-MOF-COOH dispersion.

[0017] 2) Activation of La-MOF-COOH

[0018] The activator is slowly added to the La-MOF-COOH dispersion in step 1), and stirred to fully dissolve the activator and form a homogeneous solution, thereby activating the carboxyl groups to obtain a mixed solution;

[0019] 3) Phase transformation and interfacial strengthening reactions

[0020] Slowly pour the mixture from step 2) into the casting solution from step (1), stir evenly, and scrape the film to obtain the La-MOF-COOH / PEI-PVDF composite membrane material.

[0021] Furthermore, in step (1), the pore-forming agent is either polyvinylpyrrolidone or polyethylene glycol;

[0022] Alternatively, in step (1), the ratio of polyvinylidene fluoride (PVDF) powder: pore-forming agent: organic solvent (g: g: mL) is 10~18:5~20:100;

[0023] Alternatively, the organic solvent in step (1) is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0024] Alternatively, in step (1), the heating temperature in the water bath is 45℃~75℃, and the heating time is 4h~12h.

[0025] Furthermore, in step (1), the ratio of polyethyleneimine (PEI): polyvinylidene fluoride (PVDF) powder: dispersant (mL): g: g is 0.1~6: 10~18; 0.1~10;

[0026] Alternatively, the dispersant in step (1) may be either lithium chloride or sodium tripolyphosphate;

[0027] Alternatively, in step (1), the dispersant can be stirred and dispersed for 0.5h to 4h.

[0028] Furthermore, in step (2), the ratio of metal salt: organic ligand: organic solvent in g: g: mL is 1~4:2~6:100;

[0029] Alternatively, the metal salt in step (2) is either lanthanum chloride heptahydrate or lanthanum nitrate hexahydrate;

[0030] Alternatively, the organic ligand in step (2) may be one of terephthalic acid, pyromellitic acid, or pyromellitic tetracarboxylic acid.

[0031] Alternatively, the conditions for the hydrothermal reaction in step (2) are a heating temperature of 80~150℃ and a reaction time of 6~24h;

[0032] Alternatively, the drying conditions in step (2) are a temperature of 50~80℃ and a heating time of 6h~24h.

[0033] Further, in step (3), the organic solvent in step 1) is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0034] Alternatively, the activator in step (3) 2) is one or two of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride EDC, N-hydroxysuccinimide NHS, and dicyclohexylcarbodiimide DCC.

[0035] Alternatively, the stirring time in step (3) 2) is 30-60 min.

[0036] Alternatively, the stirring time in step (3) is 0.5-3h.

[0037] Furthermore, in step (3), the ratio of La-MOF-COOH powder to organic solvent in step 1) is 0.001~0.5:2~10 (g:mL).

[0038] Alternatively, in step (3) 2), the ratio of La-MOF-COOH dispersion to activator in mL to g is 1~20:0.001~1;

[0039] Alternatively, in step (3), the volume ratio of the mixture in step 2) to the casting solution in step (1) is 1~20:5~50.

[0040] Further, the specific steps in step (3) are as follows: slowly pour the mixture from step 2) into the casting solution from step (1), continue heating at 60°C in a water bath for 1 hour, stir evenly, pour it onto a glass plate and scrape it, expose the coated glass plate to a water or ethanol coagulation bath, so that the solvent is quickly replaced by water or ethanol, complete the phase separation and solidification, and obtain the La-MOF-COOH / PEI-PVDF composite membrane material.

[0041] The La-MOF-COOH / PEI-PVDF composite membrane material was prepared by the method described above.

[0042] The application of the La-MOF-COOH / PEI-PVDF composite membrane material in phosphate adsorption, as described above.

[0043] The application of the La-MOF-COOH / PEI-PVDF composite membrane material in phosphate removal, as described above.

[0044] The advantages and positive effects of this invention are as follows:

[0045] 1. This invention uses the amidating reagent EDC / NHS to activate the carboxyl functional groups in La-MOF-COOH; PEI is grafted onto the surface of a PVDF membrane to prepare a La-MOF-COOH / PEI-PVDF composite membrane material. In this invention, the amino groups on the surface of the PEI-grafted PVDF membrane undergo an amidation reaction with the activated carboxyl groups in La-MOF-COOH, generating a stable amide bond structure. This avoids the aggregation of La-MOF-COOH filler, significantly enhances the dispersibility of MOF filler in the polymer, and improves the interfacial compatibility, stability, and functionality of the MOF filler with the polymer matrix, giving the composite membrane of this invention good application prospects.

[0046] 2. After the interfacial compatibility of the composite membrane material of the present invention is improved, the adhesion between La-MOF-COOH particles and PEI-PVDF matrix is ​​enhanced, which can more effectively transfer stress and thus improve the tensile strength of the composite membrane. The bond between La-MOF-COOH particles and PEI-PVDF matrix is ​​tighter, which can maintain better structural stability at high temperatures, thereby improving the thermal stability of the composite membrane.

[0047] Better interfacial compatibility reduces the shedding of La-MOF-COOH particles, maintains the stability of the membrane's pore structure, and thus improves the membrane's adsorption performance. Improved interfacial compatibility also leads to better dispersion of La-MOF-COOH particles in the PEI-PVDF matrix, resulting in a more uniform distribution within the membrane and improved overall membrane performance. Aggregation of La-MOF-COOH particles in the polymer matrix, however, degrades membrane performance.

[0048] 3. The shedding of La-MOF-COOH particles can lead to secondary pollution, especially in water treatment applications. The composite membrane material of this invention improves interfacial compatibility, thus reducing this phenomenon and enhancing the membrane's environmental performance. With improved interfacial compatibility, the bond between the La-MOF-COOH particles and the PEI-PVDF matrix is ​​stronger, allowing the composite membrane to maintain good performance even after multiple uses. This improves the membrane's recyclability and reusability, reducing replacement frequency and lowering operating costs.

[0049] 4. After the improved interfacial compatibility between the La-MOF-COOH particles and the PEI-PVDF matrix in the composite membrane material of this invention, the La-MOF-COOH particles can more effectively form stable complexes with phosphates, thereby improving the phosphate adsorption capacity of the membrane. Better interfacial compatibility can enhance the exposure of active sites of La-MOF-COOH particles, thereby improving the membrane's phosphate adsorption selectivity.

[0050] 5. The improved interfacial compatibility of the La-MOF-COOH / PEI-PVDF composite membrane by the composite membrane material of this invention can significantly enhance the mechanical properties, chemical stability, thermal stability, filtration performance, recyclability and reusability, uniform dispersion, and adsorption performance of the composite membrane. These advantages not only improve the overall performance of the composite membrane but also expand its application range in water treatment and other fields, which has important practical significance. Attached Figure Description

[0051] Figure 1 The Fourier transform infrared spectrum of the PEI-PVDF film prepared in Example 1 of this invention;

[0052] Figure 2 This is an electron scanning image of the La-MOF-COOH / PEI-PVDF membrane prepared in Example 1 of this invention;

[0053] Figure 3 This is a graph showing the phosphate removal rate of Example 1 and the comparative example in this invention;

[0054] Figure 4 This is a graph showing the phosphate removal rate of Example 1 and the comparative example after 5 cycles in this invention;

[0055] Figure 5 This is a graph showing the phosphate removal rates of Example 1 and the comparative example under the interference of competing substances in this invention;

[0056] Figure 6 This is a glass transition temperature diagram for Example 1 and the comparative example in this invention;

[0057] Figure 7This is an electron scanning image of the La-MOF / PVDF membrane prepared in Comparative Example 1 of this invention;

[0058] Figure 8 This is an electron scanning image of the La-MOF-COOH / PVDF membrane prepared in Comparative Example 2 of this invention;

[0059] Figure 9 The Fourier transform infrared spectrum of the PEI-PVDF film prepared in Comparative Example 3 of this invention is shown below.

[0060] Figure 10 This is an electron scanning image of the La-MOF / PEI-PVDF membrane prepared in Comparative Example 3 of this invention. Detailed Implementation

[0061] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0062] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0063] A method for preparing a La-MOF-COOH / PEI-PVDF composite membrane material for phosphorus removal includes the following steps:

[0064] (1) Preparation of casting solution: Polyvinylidene fluoride (PVDF) powder and pore-forming agent are added to an organic solvent, heated and stirred evenly in a water bath, then polyethyleneimine (PEI) is added to the above solution, a dispersant is added and stirred evenly, and the mixture is allowed to stand to remove bubbles to obtain the casting solution.

[0065] (2) Preparation of La-MOF-COOH: Weigh the metal salt and organic ligand and add them to the organic solvent. Transfer the mixed solution to the high-pressure reactor and place it in the oven for hydrothermal reaction. Cool and discard the supernatant. Centrifuge to collect the precipitate, wash and dry it to obtain La-MOF-COOH powder.

[0066] (3) Preparation of La-MOF-COOH / PEI-PVDF composite membrane

[0067] 1) Preparation of La-MOF-COOH dispersion

[0068] Weigh the La-MOF-COOH powder from step (2) into an organic solvent, place the mixture in a magnetic stirrer, and stir at room temperature for initial dispersion; then place it in a probe for ultrasonic treatment at 500W, and cool it in an ice bath to prevent overheating, to obtain the La-MOF-COOH dispersion.

[0069] 2) Activation of La-MOF-COOH

[0070] The activator is slowly added to the La-MOF-COOH dispersion in step 1), and stirred to fully dissolve the activator and form a homogeneous solution, thereby activating the carboxyl groups to obtain a mixed solution;

[0071] 3) Phase transformation and interfacial strengthening reactions

[0072] Slowly pour the mixture from step 2) into the casting solution from step (1), stir evenly, and scrape the film to obtain the La-MOF-COOH / PEI-PVDF composite membrane material.

[0073] Preferably, the pore-forming agent in step (1) is either polyvinylpyrrolidone or polyethylene glycol;

[0074] Alternatively, in step (1), the ratio of polyvinylidene fluoride (PVDF) powder: pore-forming agent: organic solvent (g: g: mL) is 10~18:5~20:100;

[0075] Alternatively, the organic solvent in step (1) is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0076] Alternatively, in step (1), the heating temperature in the water bath is 45℃~75℃, and the heating time is 4h~12h.

[0077] Preferably, in step (1), the ratio of polyethyleneimine (PEI):polyvinylidene fluoride (PVDF) powder:dispersant in mL:g:g is 0.1~6:10~18; 0.1~10;

[0078] Alternatively, the dispersant in step (1) may be either lithium chloride or sodium tripolyphosphate;

[0079] Alternatively, in step (1), the dispersant can be stirred and dispersed for 0.5h to 4h.

[0080] Preferably, in step (2), the ratio of metal salt: organic ligand: organic solvent in g: g: mL is 1~4:2~6:100;

[0081] Alternatively, the metal salt in step (2) is either lanthanum chloride heptahydrate or lanthanum nitrate hexahydrate;

[0082] Alternatively, the organic ligand in step (2) may be one of terephthalic acid, pyromellitic acid, or pyromellitic tetracarboxylic acid.

[0083] Alternatively, the conditions for the hydrothermal reaction in step (2) are a heating temperature of 80~150℃ and a reaction time of 6~24h;

[0084] Alternatively, the drying conditions in step (2) are a temperature of 50~80℃ and a heating time of 6h~24h.

[0085] Preferably, in step (3), the organic solvent in step 1) is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0086] Alternatively, the activator in step (3) 2) is one or two of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride EDC, N-hydroxysuccinimide NHS, and dicyclohexylcarbodiimide DCC.

[0087] Alternatively, the stirring time in step (3) 2) is 30-60 min.

[0088] Alternatively, the stirring time in step (3) is 0.5-3h.

[0089] Preferably, in step (3), the ratio of La-MOF-COOH powder to organic solvent in step 1) is 0.001~0.5:2~10 (g:mL).

[0090] Alternatively, in step (3) 2), the ratio of La-MOF-COOH dispersion to activator in mL to g is 1~20:0.001~1;

[0091] Alternatively, in step (3), the volume ratio of the mixture in step 2) to the casting solution in step (1) is 1~20:5~50.

[0092] Preferably, the specific steps in step (3) are as follows: slowly pour the mixture from step 2) into the casting solution from step (1), continue heating at 60°C in a water bath for 1 hour, stir evenly, pour it onto a glass plate and scrape it, expose the coated glass plate to a water or ethanol coagulation bath, so that the solvent is quickly replaced by water or ethanol, complete the phase separation and solidification, and obtain the La-MOF-COOH / PEI-PVDF composite membrane material.

[0093] The La-MOF-COOH / PEI-PVDF composite membrane material was prepared by the method described above.

[0094] The application of the La-MOF-COOH / PEI-PVDF composite membrane material in phosphate adsorption, as described above.

[0095] The application of the La-MOF-COOH / PEI-PVDF composite membrane material in phosphate removal, as described above.

[0096] Specifically, the relevant preparation and testing methods are as follows:

[0097] Example 1

[0098] The synthesis and preparation steps of a La-MOF-COOH / PEI-PVDF composite membrane material are as follows:

[0099] 1. Preparation of PVDF membrane: Dissolve 15g of PVDF powder and 15g of polyvinylpyrrolidone in 50mL of N,N-dimethylformamide, place in a water bath and heat at 60℃ for 5h to obtain casting solution, pour onto a glass plate and scrape, expose the coated glass plate in a water coagulation bath to allow the solvent to be quickly replaced by water, complete phase separation and solidification, and form PVDF membrane.

[0100] 2. Preparation of PEI-PVDF membrane: Dissolve 15g PVDF powder and 15g polyvinylpyrrolidone in 50mL N,N-dimethylformamide, place in a water bath and heat at 60℃ with stirring for 3h. Add 0.5mL PEI (polyethyleneimine) and 0.5g lithium chloride, and stir for 2h to obtain casting solution. Pour the solution onto a glass plate and coat it. Expose the coated glass plate to a water coagulation bath to allow the solvent to be rapidly replaced by water, completing phase separation and solidification to form a PEI-PVDF membrane.

[0101] 3. Preparation of La-MOF-COOH: Weigh 3.73g of lanthanum chloride heptahydrate and 2.54g of pyromellitic acid and add them to 100mL of N,N-dimethylformamide solvent. Transfer the mixture to a reaction vessel and place it in an oven at 120℃ for 12h. Centrifuge, wash, collect the precipitate and dry it at 80℃ for 12h to obtain La-MOF-COOH powder.

[0102] 4. Preparation of La-MOF-COOH / PEI-PVDF membrane

[0103] 1) Preparation of La-MOF-COOH dispersion

[0104] Accurately weigh 0.15 g of the La-MOF-COOH powder obtained in step 3 into 20 mL of N,N-dimethylformamide solvent. Place the mixture in a magnetic stirrer and initially disperse it at 500 rpm for 15 min at room temperature. Then, sonicate it at 500 W for 30 min in a probe sonicator, followed by 10 min intervals of ice bath cooling to prevent overheating, to obtain the La-MOF-COOH dispersion.

[0105] 2) Activation of La-MOF-COOH

[0106] Add 0.5g EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 0.5g NHS (N-hydroxysuccinimide) to the La-MOF-COOH dispersion in step 1), and continue to sonicate at 500W for 30min to fully dissolve the activator and activate the carboxyl groups in La-MOF-COOH to obtain a mixed solution;

[0107] 3) Phase transformation and interfacial strengthening reactions

[0108] Slowly pour the activated mixture from step 2) into the casting solution prepared in step 2, continue heating in a water bath at 60°C for 1 hour, stir evenly, pour it onto a glass plate and scrape it, expose the coated glass plate to a water coagulation bath, so that the solvent is quickly replaced by water, complete phase separation and solidification, and form La-MOF-COOH / PEI-PVDF composite membrane material.

[0109] The Fourier transform infrared spectra of the PVDF film and PEI / PVDF film prepared in Example 1 are as follows: Figure 1 As shown, by Figure 1 It can be seen that for the Fourier transform infrared spectrum of PVDF, in PEI-PVDF, 760 cm⁻¹ -1 The absorption band at 1560 cm⁻¹ (flexural vibration of FCF) weakens, attributed to the partial dehydrohalogenation grafting reaction of PVDF. New peaks include those from the NH bending vibration (1560 cm⁻¹). -1 ), C=N vibration (1660 cm) -1 This demonstrates the successful grafting of PEI into the PVDF membrane. Example 1 successfully prepared a PEI / PVDF membrane.

[0110] The compatibility of the La-MOF-COOH and PEI-PVDF membranes was determined by scanning electron microscopy (SEM). The SEM image of the La-MOF-COOH / PEI-PVDF membrane prepared in Example 1 is shown below. Figure 2As shown, the La-MOF-COOH filler particles exhibit good bonding with the PEI-PVDF polymer matrix, indicating good interfacial compatibility. SEM images reveal a smooth transition region between the filler particles and the matrix, without significant separation or voids, suggesting a tight bond. The covalent bonds between the activated carboxyl groups and the grafted PEI promote this bonding. The covalent bonds formed between the carboxyl groups of La-MOF-COOH and PEI-PVDF firmly and uniformly anchor the MOF within the membrane matrix, inhibiting particle aggregation and detachment. The formation of these covalent bonds eliminates interfacial defects, ensuring the composite membrane maintains good structural stability under tensile and bending stresses.

[0111] Initial phosphorus removal efficiency: The La-MOF-COOH / PEI-PVDF membrane was placed in a phosphate solution for performance testing. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined by spectrophotometry. Figure 3 As shown, the La-MOF-COOH / PEI-PVDF membrane achieved a phosphate removal rate of 99.89%. In contrast, the phosphorus removal efficiencies of the composite membranes in Comparative Examples 1, 2, and 3 were 83.21%, 85.68%, and 89.52%, respectively, all lower than that of Example 1. The high phosphorus removal rate of the La-MOF-COOH / PEI-PVDF membrane demonstrates that La-MOF-COOH is well dispersed and stably bound on the PEI-PVD membrane. This strong interfacial interaction keeps the La-MOF-COOH particles stable in a dynamic environment, preventing the detachment of adsorption active sites and ensuring efficient phosphate removal. The phosphorus removal performance of the La-MOF-COOH / PEI-PVDF composite membrane directly depends on the stability of the interfacial binding and the retention rate of the La-MOF-COOH adsorbent. The strong binding dominated by amide bonds is key to inhibiting MOF loss.

[0112] Changes in phosphorus removal efficiency during cycling: To better understand the membrane's performance during long-term cycling, the membrane was exposed to a phosphorus-containing aqueous solution during cycling. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined spectrophotometrically. Five repeated cycles were performed. The membrane was then shaken in 0.02 mmol / L NaOH solution for 2 hours to ensure sufficient contact and separation of adsorbed phosphate from the membrane; subsequently, it was washed with 0.01 mmol / L HNO3 and deionized water; finally, the washed membrane was reused. Figure 4As shown, after 5 cycles, the phosphorus removal efficiency of the La-MOF-COOH / PEI-PVDF membrane was measured to be 94.56%. Improved interfacial compatibility enhanced particle immobilization on the membrane. Therefore, the phosphate removal efficiency of the La-MOF-COOH / PEI-PVDF membrane decreased by 5.33% after 5 cycles compared to the first use, exhibiting a low loss rate and excellent stability. In contrast, the phosphorus removal efficiencies of the composite membranes in Comparative Examples 1, 2, and 3 decreased by 13.04%, 17.03%, and 19.32% respectively after 5 cycles compared to the first use, with loss rates all higher than that of Example 1. This indicates that the long-term stability of the membrane in Example 1 is far superior to that of the comparative membranes, proving that it can work effectively for a long time in practical applications, reducing the frequency of replacement and maintenance, and lowering costs.

[0113] The composite membrane's selectivity for phosphates: selecting several common anions, namely Cl... - NO3 - SO4 2- The concentration of phosphate was 100 mg / L. Common organic compounds, namely humic acid and sodium alginate, were selected. The concentration of sodium alginate was 20 mg / L. The selectivity of the composite membrane for phosphate was studied in a mixed system with a phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined spectrophotometrically. Figure 5 As shown, the phosphorus removal efficiency of the La-MOF-COOH / PEI-PVDF membrane in the presence of interfering substances was 96.35%, a decrease of 3.54% compared to the phosphorus removal efficiency without competing substances, indicating a low loss rate. In contrast, the phosphorus removal efficiencies of the composite membranes in Comparative Examples 1, 2, and 3 in the presence of interfering substances decreased by 16.93%, 19.70%, and 25.27% respectively compared to the phosphorus removal efficiency without competing substances, with loss rates all higher than in Example 1. When there is a good chemical bond between the PEI-PVDF membrane substrate and the La-MOF-COOH particles, the La-MOF-COOH particles can be uniformly dispersed in the membrane substrate, forming a stable pore structure. Such a structure typically has small and uniform pores, which can effectively screen molecules of specific sizes (such as phosphates), thereby improving the membrane selectivity.

[0114] The glass transition temperature (Tg) was calculated using differential scanning calorimetry (DSC). g Tg, or T-g, is commonly used to reflect the chain mobility of polymers to understand the filler-polymer interface in membranes. Tg is closely related to the intermolecular forces of polymer molecules. The stronger the intermolecular forces, the greater the energy barrier that chain segment motion must overcome, and the higher the Tg. g The higher the value, the better. Figure 6 As shown, the T of La-MOF-COOH / PEI-PVDFg The temperature was 178.54℃, while the T values ​​of the composite membranes in Comparative Examples 1, 2, and 3 were... g The temperatures were 178.06℃, 178.13℃, and 178.18℃, respectively, all lower than the T in Example 1. g This indicates that a chemical bond has formed between the La-MOF-COOH filler and PEI-PVDF. An amide bond is formed between the carboxyl groups of La-MOF-COOH and the amino groups of PEI-PVDF. This strong interaction further restricts the movement of polymer chain segments, leading to T... g The increase was significant, indicating that the interfacial compatibility between the filler and the polymer was improved after activating the carboxyl groups and adding PEI.

[0115] La-MOF-COOH contains carboxyl functional groups, while PEI-grafted PVDF is rich in amino functional groups. After activation by an amidating agent, the carboxyl groups in La-MOF-COOH can form amide bonds with the amino groups on the PEI-grafted PVDF, enhancing the immobilization of La-MOF-COOH on PEI / PVDF and strengthening the interfacial compatibility between La-MOF-COOH and PEI / PVDF. This molecular-level design strategy provides a theoretical basis for developing high-performance membranes.

[0116] Comparative Example 1

[0117] The synthesis and preparation steps of a La-MOF / PVDF composite membrane material are as follows:

[0118] 1. Preparation of PVDF casting solution: Dissolve 15g of PVDF powder and 15g of polyvinylpyrrolidone in 50mL of N,N-dimethylformamide, place in a water bath and heat at 60℃ for 5h to obtain the casting solution.

[0119] 2. Preparation of La-MOF: Weigh 3.73g of lanthanum chloride heptahydrate and 2.54g of terephthalic acid and add them to 100mL of N,N-dimethylformamide solvent. Transfer the mixture to a reaction vessel and place it in an oven at 120℃ for 12h. Centrifuge, wash, collect the precipitate and dry it at 80℃ for 12h to obtain La-MOF powder.

[0120] 3. Preparation of La-MOF / PVDF membranes

[0121] 1) Preparation of La-MOF dispersion

[0122] Accurately weigh 0.15 g of the powder from step 2 into 20 mL of N,N-dimethylformamide solvent. Place the mixture in a magnetic stirrer and stir at 500 rpm for 15 min at room temperature for initial dispersion. Then, place it in a probe sonicator and sonicate at 500 W for 30 min, followed by 10 min intervals of ice bath cooling to prevent overheating, to obtain the La-MOF dispersion.

[0123] 2) Activation of La-MOF

[0124] Add 0.5g EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 0.5g NHS (N-hydroxysuccinimide) to the dispersion in step 1), and continue to sonicate at 500W for 30min to fully dissolve the activator to obtain a mixture.

[0125] 3) Phase transformation and interfacial strengthening reactions

[0126] Slowly pour the activated mixture from step 2) into the casting solution prepared in step 1, and continue heating in a water bath at 60°C for 1 hour. Stir until homogeneous, pour onto a glass plate and scrape. Expose the coated glass plate to a water coagulation bath so that the solvent is quickly replaced by water, completing phase separation and solidification to form a La-MOF / PVDF composite membrane.

[0127] The compatibility of La-MOF and PVDF films was determined by scanning electron microscopy (SEM). The SEM image of the La-MOF / PVDF film prepared in Comparative Example 1 is shown below. Figure 7 As shown in the figure, some MOF particle agglomerates can be observed. The formation of agglomerates usually leads to a decrease in material performance. Interfacial incompatibility results in weak adhesion between particles and the matrix, which cannot effectively transfer stress, thereby reducing the mechanical strength of the composite material. Poor particle dispersion in the matrix leads to an inhomogeneous internal structure of the material.

[0128] Initial phosphorus removal efficiency: The La-MOF / PVDF membrane was placed in a phosphate solution for performance testing. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined by spectrophotometry. Figure 3As shown, the La-MOF / PVDF membrane achieved a phosphate removal rate of 83.21%, while the composite membrane in Example 1 achieved a phosphorus removal efficiency of 99.89%, significantly lower than that of Example 1. The lower phosphorus removal rate of the La-MOF / PVDF membrane is attributed to the poor compatibility between the MOF and the polymer, leading to irregular interfacial voids within the membrane. These voids allow the liquid to bypass the adsorption sites of the MOF, thus reducing the phosphorus removal efficiency. Furthermore, due to the poor interaction between the MOF and the polymer, MOF particles tend to aggregate within the polymer matrix. Aggregated MOF particles reduce the number of adsorption sites, further decreasing the phosphorus removal efficiency.

[0129] Changes in phosphorus removal efficiency during cycling: To better understand the membrane's performance during long-term cycling, the membrane was exposed to a phosphorus-containing aqueous solution during cycling. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined spectrophotometrically. Five repeated cycles were performed. The membrane was then shaken in 0.02 mmol / L NaOH solution for 2 hours to ensure sufficient contact and separation of adsorbed phosphate from the membrane; subsequently, it was washed with 0.01 mmol / L HNO3 and deionized water; finally, the washed membrane was reused. Figure 4 As shown, after 5 cycles, the phosphorus removal efficiency of the La-MOF / PVDF membrane was measured to be 70.17%. Therefore, the phosphorus removal efficiency of Comparative Example 1 decreased by 13.04% after 5 cycles compared to the first use, indicating a higher loss rate. In contrast, the phosphorus removal efficiency of Example 1 decreased by 5.33% after 5 cycles compared to the first use, with a lower loss rate than the Comparative Example. The rapid decline in phosphorus removal efficiency indicates that the shedding of MOF particles from the membrane is the main cause of performance degradation.

[0130] The composite membrane's selectivity for phosphates: selecting several common anions, namely Cl... - NO3 - SO4 2- The concentration of phosphate was 100 mg / L, using common organic compounds such as humic acid and sodium alginate at a concentration of 20 mg / L, and phosphate at a concentration of 5 mg / L. The pH was 7, the experimental time was 2 hours, the temperature was 25℃, and the shaking rate was 100 rpm. The residual phosphate concentration was determined spectrophotometrically. The selectivity of the composite membrane for phosphate was studied in a mixed system. Figure 5As shown, the phosphorus removal efficiency of the La-MOF / PVDF membrane was 66.28%, a decrease of 16.93% compared to the phosphorus removal efficiency without competing substances, indicating a high loss rate. In Example 1, the phosphorus removal efficiency in the presence of interfering substances was only 3.54% lower than that without competing substances, with a lower loss rate than the comparative example. Poor interfacial compatibility and weak bonding between La-MOF particles and the PVDF matrix meant that La-MOF particles might aggregate on the membrane surface or form large clumps within the membrane, resulting in irregular pore morphology and large pore size. This irregular pore structure affects the membrane's screening performance and reduces its selectivity for specific phosphates.

[0131] The glass transition temperature (Tg) of Comparative Example 1 was calculated by differential scanning calorimetry (DSC). g ), like Figure 6 As shown, the T of La-MOF / PVDF g The temperature is 178.06 °C, which is lower than the 178.54 °C of La-MOF-COOH / PEI-PVDF. g A smaller value may indicate weaker interfacial interactions between the filler and the polymer. A lack of interfacial interaction leads to a looser bond between the filler and the polymer, resulting in less resistance to chain segment movement and thus lower T. g The filler may not form strong hydrogen bonds, covalent bonds, or other chemical bonds with the polymer, or the filler may have poor dispersion in the polymer matrix, resulting in a small contact area and weak interaction between the filler and the polymer.

[0132] Comparative Example 2

[0133] The synthesis and preparation steps of a La-MOF-COOH / PVDF composite membrane material are as follows:

[0134] 1. Preparation of PVDF casting solution: Dissolve 15g of PVDF powder and 15g of polyvinylpyrrolidone in 50mL of N,N-dimethylformamide, place in a water bath and heat at 60℃ for 5h to obtain the casting solution.

[0135] 2. Preparation of La-MOF-COOH: Weigh 3.73g of lanthanum chloride heptahydrate and 2.54g of pyromellitic acid and add them to 100mL of N,N-dimethylformamide solvent. Transfer the mixture to a reaction vessel and place it in an oven at 120℃ for 12h. Centrifuge, wash, collect the precipitate and dry it at 80℃ for 12h to obtain La-MOF-COOH powder.

[0136] 3. Preparation of La-MOF-COOH / PVDF membranes

[0137] 1) Preparation of La-MOF-COOH dispersion

[0138] Accurately weigh 0.15 g of the powder from step 2 into 20 mL of N,N-dimethylformamide solvent. Place the mixture in a magnetic stirrer and stir at 500 rpm for 15 min at room temperature for initial dispersion. Then, place it in a probe sonicator and sonicate at 500 W for 30 min, followed by 10 min intervals of ice bath cooling to prevent overheating, to obtain a La-MOF-COOH dispersion.

[0139] 2) Activation of La-MOF-COOH

[0140] Add 0.5g EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 0.5g NHS (N-hydroxysuccinimide) to the dispersion in step 1), and continue to sonicate at 500W for 30min to fully dissolve the activator and activate the carboxyl groups to obtain a mixture;

[0141] 3) Phase transformation and interfacial strengthening reactions

[0142] Slowly pour the activated mixture from step 2) into the casting solution prepared in step 1, and continue heating in a water bath at 60°C for 1 hour. Stir until homogeneous, pour onto a glass plate and scrape. Expose the coated glass plate to a water coagulation bath so that the solvent is quickly replaced by water, completing phase separation and solidification to form a La-MOF-COOH / PVDF composite membrane.

[0143] The compatibility of La-MOF-COOH with PVDF membranes was determined by scanning electron microscopy (SEM). The SEM image of the La-MOF-COOH / PVDF membrane prepared in Comparative Example 2 is shown below. Figure 8 As shown in the figure, some MOF particle agglomerates can be observed. When MOF particles agglomerate in the membrane, their specific surface area and pore structure are disrupted, leading to a reduction in the effective active sites involved in separation. Uniform dispersion of MOF particles is crucial for ensuring the homogeneity of the composite membrane structure. Agglomeration results in uneven particle aggregation regions on the membrane surface and cross-section, compromising the membrane's homogeneity. Furthermore, the interfacial bonding between agglomerated La-MOF-COOH particles and the PVDF matrix is ​​weak, making them prone to detachment or cracking during membrane use, leading to membrane instability and shortened lifespan. When physical interactions between MOF and polymer dominate, MOF particles are prone to agglomeration due to a lack of chemical anchoring, forming aggregates of uneven size. The contact area between the agglomerates and the matrix is ​​much smaller than that of the dispersed particles, resulting in interfacial stress concentration.

[0144] Initial phosphorus removal efficiency: The La-MOF-COOH / PVDF membrane was placed in a phosphate solution for performance testing. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined by spectrophotometry. Figure 3 As shown, the measured phosphate removal rate of the La-MOF-COOH / PVDF membrane was 85.68%, while the phosphorus removal efficiency of the composite membrane in Example 1 was 99.89%, significantly lower than that of Example 1. The lower phosphorus removal rate of the La-MOF-COOH / PVDF membrane is due to the poor interfacial compatibility caused by the lack of interaction forces between MOF and the polymer. This makes it difficult for MOF to be uniformly dispersed in the polymer matrix. Uneven dispersion leads to uneven distribution of adsorption sites, with some areas having too few adsorption sites to fully exert their adsorption effect, thus reducing the overall adsorption and phosphorus removal efficiency.

[0145] Changes in phosphorus removal efficiency during cycling: To better understand the membrane's performance during long-term cycling, the membrane was exposed to a phosphorus-containing aqueous solution during cycling. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined spectrophotometrically. Five repeated cycles were performed. The membrane was then shaken in 0.02 mmol / L NaOH solution for 2 hours to ensure sufficient contact and separation of adsorbed phosphate from the membrane; subsequently, it was washed with 0.01 mmol / L HNO3 and deionized water; finally, the washed membrane was reused. Figure 4 As shown, after 5 cycles, the phosphorus removal efficiency of the La-MOF-COOH / PVDF membrane was measured to be 68.65%. After cycling, the phosphate removal efficiency of Comparative Example 2 decreased by 17.03% compared to the first cycle, indicating a higher loss rate. In contrast, the phosphorus removal efficiency of Example 1 after 5 cycles decreased by 5.33% compared to the first cycle, with a lower loss rate than the Comparative Example. The significant decrease in phosphorus removal efficiency after cycling is due to poor interfacial compatibility between the particles and the polymer, making the particles prone to detachment during use. This leads to a reduction in the effective phosphorus removal surface area of ​​the membrane, uneven distribution of the filler within the membrane, and ultimately affects the overall performance of the membrane.

[0146] The composite membrane's selectivity for phosphates: selecting several common anions, namely Cl... - NO3 - SO4 2-The concentration of phosphate was 100 mg / L, using common organic compounds such as humic acid and sodium alginate at a concentration of 20 mg / L, and phosphate at a concentration of 5 mg / L. The pH was 7, the experimental time was 2 hours, the temperature was 25℃, and the shaking rate was 100 rpm. The residual phosphate concentration was determined spectrophotometrically. The selectivity of the composite membrane for phosphate was studied in a mixed system. Figure 5 As shown, the phosphorus removal efficiency of the La-MOF-COOH / PVDF membrane was 65.98%, a decrease of 19.70% compared to the phosphorus removal efficiency without competing substances, indicating a high loss rate. In Example 1, the phosphorus removal efficiency in the presence of interfering substances was only 3.54% lower than that without competing substances, with a lower loss rate than the comparative example. Poor interfacial compatibility leads to the aggregation or uneven distribution of La-MOF-COOH particles, resulting in uneven or excessively large membrane pores. These larger pores not only allow larger ions or molecules in the water to pass through but may also render the membrane's screening function ineffective, leading to a decrease in phosphate selectivity. Phosphate molecules may flow through these large pores along with other large molecules, thus affecting the membrane's selectivity and reducing its phosphate removal capacity.

[0147] The glass transition temperature (T2) of Comparative Example 2 was calculated by differential scanning calorimetry (DSC). g ),like Figure 6 As shown, the T of La-MOF-COOH / PVDF g The temperature was 178.13 °C, lower than the 178.54 °C of La-MOF-COOH / PEI-PVDF. g A smaller value does indeed indicate a weaker interaction force between the polymer and the filler. In this case, the polymer chain segments can begin to move at lower temperatures, and the thermal stability and mechanical properties of the material may be poorer.

[0148] Comparative Example 3

[0149] The synthesis and preparation steps of a La-MOF / PEI-PVDF composite membrane material are as follows:

[0150] 1. Preparation of PVDF casting solution: Dissolve 15g of PVDF powder and 15g of polyvinylpyrrolidone in 50mL of N,N-dimethylformamide, place in a water bath and heat at 60℃ for 5h to obtain the casting solution.

[0151] 2. Preparation of PEI-PVDF membrane: Dissolve 15g of PVDF powder and 15g of polyvinylpyrrolidone in 50mL of N,N-dimethylformamide, place in a water bath and heat at 60℃ for 3h. Add 0.5mL of PEI (polyethyleneimine) and 0.5g of lithium chloride, and stir for 2h. Pour the resulting casting solution onto a glass plate and scrape it. Expose the coated glass plate to a water coagulation bath to allow the solvent to be rapidly replaced by water, completing phase separation and solidification to form a PEI-PVDF composite membrane.

[0152] 3. Preparation of La-MOF: Weigh 3.73g of lanthanum chloride heptahydrate and 2.54g of terephthalic acid and add them to 100mL of N,N-dimethylformamide solvent. Transfer the mixture to a reaction vessel and place it in an oven at 120℃ for 12h. Centrifuge, wash, collect the precipitate and dry it at 80℃ for 12h to obtain La-MOF powder.

[0153] 4. Preparation of La-MOF / PEI-PVDF membranes

[0154] 1) Preparation of La-MOF dispersion

[0155] Accurately weigh 0.15 g of the powder from step 3 into 20 mL of N,N-dimethylformamide solvent. Place the mixture in a magnetic stirrer and stir at 500 rpm for 15 min at room temperature for initial dispersion. Then, place it in a probe sonicator and sonicate at 500 W for 30 min, followed by 10 min intervals of ice bath cooling to prevent overheating, to obtain the La-MOF dispersion.

[0156] 2) Activation of La-MOF

[0157] Add 0.5g EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) and 0.5g NHS (N-hydroxysuccinimide) to the dispersion in step 1), and continue to sonicate at 500W for 30min to fully dissolve the activator to obtain a mixture.

[0158] 3) Phase transformation and interfacial strengthening reactions

[0159] Slowly pour the activated mixture from step 2) into the casting solution from step 2, and continue heating in a water bath at 60°C for 1 hour. Stir until homogeneous, pour onto a glass plate and scrape. Expose the coated glass plate to a water coagulation bath so that the solvent is quickly replaced by water, completing phase separation and curing to form a La-MOF / PEI-PVDF composite membrane.

[0160] The Fourier transform infrared spectrum of the PEI-PVDF film prepared in Comparative Example 3 is shown below. Figure 9 As shown, by Figure 9As can be seen from the Fourier transform infrared spectrum, this comparative example 3 successfully prepared a PEI-PVDF film.

[0161] The compatibility of La-MOF and PEI-PVDF films was determined by scanning electron microscopy (SEM). The SEM image of the La-MOF / PEI-PVDF film prepared in Comparative Example 3 is shown below. Figure 10 As shown in the figure, some MOF particle agglomerates can be observed. These agglomerates can disrupt the synergistic effect between the PEI-PVDF matrix and the MOF. Uniformly dispersed MOF particles can enhance the mechanical strength of the membrane by increasing the crystallinity of the matrix or forming a physical cross-linking network. However, agglomerated MOF particles are prone to cracking under external forces, leading to a decline in the membrane's mechanical properties.

[0162] Initial phosphorus removal efficiency: The La-MOF / PEI-PVDF membrane was placed in a phosphate solution for performance testing. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined by spectrophotometry. Figure 3 As shown, the La-MOF / PEI-PVDF membrane achieved a phosphate removal rate of 89.52%, while the composite membrane in Example 1 achieved a phosphorus removal efficiency of 99.89%, significantly lower than that of Example 1. The lower phosphorus removal rate of the La-MOF / PEI-PVDF membrane is due to poor interfacial compatibility. Poor interfacial compatibility results in weaker interactions between the MOF and the polymer, potentially preventing the MOF particles from fully exposing their adsorption sites within the polymer matrix. This reduction in adsorption sites directly leads to a decrease in phosphorus removal efficiency. Poor interfacial compatibility may also degrade the membrane's mechanical properties and thermal stability. During use, the membrane may be damaged due to insufficient mechanical properties or undergo structural changes due to poor thermal stability, further reducing its phosphorus removal efficiency.

[0163] Changes in phosphorus removal efficiency during cycling: To better understand the membrane's performance during long-term cycling, the membrane was exposed to a phosphorus-containing aqueous solution during cycling. The test conditions were: phosphate concentration of 5 mg / L, pH=7, experimental time of 2 hours, temperature of 25℃, and shaking rate of 100 rpm. The residual phosphate concentration was determined spectrophotometrically. Five repeated cycles were performed. The membrane was then shaken in 0.02 mmol / L NaOH solution for 2 hours to ensure sufficient contact and separation of adsorbed phosphate from the membrane; subsequently, it was washed with 0.01 mmol / L HNO3 and deionized water; finally, the washed membrane was reused. Figure 4As shown, after 5 cycles, the phosphorus removal efficiency of the La-MOF / PEI-PVDF membrane was measured to be 70.20%. After 5 cycles, the phosphorus removal efficiency of Comparative Example 2 decreased by 19.32% compared to the first cycle, indicating a higher loss rate. In contrast, the phosphorus removal efficiency of Example 1 after 5 cycles decreased by 5.33% compared to the first cycle, with a lower loss rate than the Comparative Example. The significant loss in phosphorus removal efficiency is attributed to the shedding of filler particles or the uneven distribution of MOF particles on the membrane surface, indicating that particle shedding is the main reason for the decrease in phosphorus removal efficiency.

[0164] The composite membrane's selectivity for phosphates: selecting several common anions, namely Cl... - NO3 - SO4 2- The concentration was 100 mg / L, and common organic compounds, namely humic acid and sodium alginate, were selected at a concentration of 20 mg / L. The selectivity of the composite membrane for phosphate was studied in a mixed system. Figure 5 As shown, the phosphorus removal efficiency of the La-MOF / PEI-PVDF membrane was 64.25%, a decrease of 25.27% compared to the phosphorus removal efficiency without competing substances, indicating a high loss rate. In contrast, Example 1, with the presence of interfering substances, showed a phosphorus removal efficiency that was only 3.54% lower than that without competing substances, with a lower loss rate than the comparative example. The surface changes in the membrane were caused by poor interfacial compatibility. Good interfacial compatibility contributes to the formation of a tight, uniform membrane surface, while poor interfacial compatibility can lead to a rough, uneven surface, and even particle shedding or aggregation. These surface irregularities result in non-uniformity in water flow through the membrane, causing uneven distribution of ions, including phosphates, in the water, thereby reducing the membrane's phosphorus removal efficiency and selectivity.

[0165] The glass transition temperature (Tg) of Comparative Example 3 was calculated by differential scanning calorimetry (DSC). g ),like Figure 6 As shown, the T of La-MOF / PEI-PVDF g The temperature is 178.18 °C, which is lower than the 178.54 °C of La-MOF-COOH / PEI-PVDF. g A smaller value indicates that the polymer chain segments can begin to move at a lower temperature. This suggests that the energy required for chain segment movement is lower, meaning there is less resistance to chain segment movement. In this case, the interaction force between the polymer and the filler is weaker, allowing the chain segments to move relatively freely.

[0166] Meanwhile, by comparing Example 1 and Comparative Examples 1-3, it can be seen that the activation of carboxyl groups and the PEI-PVDF membrane in the method of the present invention have a synergistic effect, which can synergistically improve the relevant performance of the prepared La-MOF-COOH / PEI-PVDF composite membrane material.

[0167] Meanwhile, by comparing Example 1 and Comparative Examples 1-3, it can be seen that pyromellitic acid and PEI-PVDF membrane have a synergistic effect in the method of the present invention, which can synergistically improve the relevant performance of the prepared La-MOF-COOH / PEI-PVDF composite membrane material.

[0168] Comparison between the present invention and existing technologies:

[0169] 1. Interfacial Compatibility Comparison: In traditional membrane materials, the interfacial interaction between the filler and the matrix may be insufficient, leading to poor filler dispersion and interfacial stress concentration. This affects the mechanical properties and durability of the membrane and may also cause particle shedding and secondary pollution during use. For example, the patent technology CN119708565A prepared a chitosan-MOF composite membrane, but it did not consider the interfacial compatibility between Co-MOF and chitosan, and neglected the interaction between particles and the polymer carrier. This invention enhances the interfacial interaction between the filler and the matrix through the activation of carboxyl groups and the use of PEI-PVDF membrane. The activated carboxyl groups can form stronger chemical bonds with PEI, thereby improving interfacial compatibility and adhesion. This upgraded synergistic mechanism helps to improve the overall performance of the composite material.

[0170] 2. Comparison of Simplification Levels: Chinese patent publication CN120115030A describes the preparation of MOF-808 using a solvothermal method. MOF-808 is then grafted with carboxyl groups via reaction with citric acid to obtain MOF-808-CA, which is then reacted with melamine to obtain MOF-808-CA-Me. This is then uniformly mixed with Pebax 1657 casting solution and poured onto a substrate. The target membrane material is obtained via solvent evaporation. The modification and preparation process of this membrane material involves multiple complex steps, such as multiple surface modifications, complex mixing and processing, various equipment, and various condition parameters.

[0171] 3. Cost Comparison: Complex steps increase production costs and may also affect product consistency and quality. This invention simplifies the reaction steps and reduces additional surface treatment steps through carboxyl group activation and the use of a PEI-PVDF membrane. This simplified reaction process helps improve production efficiency and reduce costs.

[0172] In summary, this invention, through the activation of carboxyl groups and the use of PEI-PVDF membranes, not only upgrades the interfacial interaction mechanism and improves the compatibility and adhesion between the filler and the matrix, but also enables higher phosphorus removal efficiency at lower dosages and simplifies the reaction steps, thereby improving production efficiency and reducing costs. These advantages make this invention highly competitive in relevant applications.

[0173] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing a La-MOF-COOH / PEI-PVDF composite membrane material for phosphorus removal, characterized in that: Includes the following steps: (1) Preparation of casting solution: 15g of polyvinylidene fluoride (PVDF) powder and 15g of polyvinylpyrrolidone were dissolved in 50mL of N,N-dimethylformamide, placed in a water bath and heated at 60℃ for 3h with stirring. 0.5mL of polyethyleneimine (PEI) and 0.5g of lithium chloride were added and stirred for 2h to obtain the casting solution. (2) Preparation of La-MOF-COOH: Weigh 3.73g of lanthanum chloride heptahydrate and 2.54g of pyromellitic acid and add them to 100mL of N,N-dimethylformamide solvent. Transfer the mixture to a reaction vessel and place it in an oven at 120℃ for 12h. Centrifuge, wash, collect the precipitate and dry it at 80℃ for 12h to obtain La-MOF-COOH powder. (3) Preparation of La-MOF-COOH / PEI-PVDF composite membrane material 1) Preparation of La-MOF-COOH dispersion Accurately weigh 0.15g of the La-MOF-COOH powder obtained in step (2) into 20mL of N,N-dimethylformamide solvent. Place the mixture in a magnetic stirrer and stir at 500rpm for 15min at room temperature for initial dispersion. Then place it in a probe sonicator and sonicate at 500W for 30min. Cool it in an ice bath every 10min to prevent overheating, and obtain the La-MOF-COOH dispersion. 2) Activation of La-MOF-COOH Add 0.5g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 0.5g of N-hydroxysuccinimide (NHS) to the La-MOF-COOH dispersion in step 1), and continue to sonicate at 500W for 30 minutes to fully dissolve the activator and activate the carboxyl groups in La-MOF-COOH to obtain a mixed solution; 3) Phase transformation and interfacial strengthening reactions Slowly pour the activated mixture from step 2) into the casting solution prepared in step (1), continue heating in a water bath at 60°C for 1 hour, stir evenly, pour it onto a glass plate and scrape it, expose the coated glass plate to a water coagulation bath, so that the solvent is quickly replaced by water, complete phase separation and solidification, and form La-MOF-COOH / PEI-PVDF composite membrane material.

2. The La-MOF-COOH / PEI-PVDF composite membrane material prepared by the preparation method described in claim 1.

3. The application of the La-MOF-COOH / PEI-PVDF composite membrane material as described in claim 2 in phosphate adsorption.

4. The application of the La-MOF-COOH / PEI-PVDF composite membrane material as described in claim 2 in phosphate removal.

Images