Mnh2-mil-101-fe / pa-pan composite film, preparation method and application

Abstract

The application belongs to the technical field of water treatment and new material, and discloses a MNH2-MIL-101(Fe) / PA-PAN composite film, a preparation method and application, which comprises the following steps: preparation of NH2-MIL-101(Fe); preparation of MNH2-MIL-101(Fe); preparation of a PAN film; preparation of a PA-PAN film; and preparation of the MNH2-MIL-101(Fe) / PA-PAN composite film. The material improves the positive electric property of the adsorbent surface, increases the active sites, improves the adsorption capacity, improves the compatibility and stability of the MNH2-MIL-101(Fe) and the PA-PAN, avoids the agglomeration of the MOF on the film, greatly improves the uniformity and stability of the structure of the composite film under crosslinking, and has excellent adsorption performance, is easy to recover and easy to operate, and has a good application prospect when applied to the recovery of phosphorus resources in phosphorus-containing surface water.

Description

Technical Field

[0001] This invention belongs to the fields of water treatment and new materials technology, and in particular to an MNH2-MIL-101(Fe) / PA-PAN composite membrane, its preparation method and application. Background Technology

[0002] Phosphorus (P), an essential element for life, plays a crucial role in modern industrial and agricultural production and human societal development. With the global population exceeding 7.7 billion, the demand for phosphate fertilizers in agriculture continues to rise, leading to unprecedented mining pressure on phosphate rock resources. Even more serious is the fact that soil erosion, predatory mining, and inefficient phosphorus recycling practices are accelerating the global phosphorus crisis. Most of the phosphorus lost from the terrestrial environment ultimately enters surface waters, causing water quality problems (such as eutrophication). Therefore, it is necessary to efficiently recover phosphorus from natural water bodies.

[0003] Metal-organic frameworks (MOFs) based on iron (Fe2O3) are suitable for phosphate adsorbents due to their large specific surface area, high porosity, sufficient hydrothermal stability in aqueous solutions, and good selectivity, making them ideal for phosphorus recovery. However, most MOF adsorbents exhibit reduced selectivity and adsorption capacity in complex aqueous systems, and the predominantly powder form of MOF materials limits their recovery and hinders large-scale utilization. Polyacrylonitrile (PAN), with its excellent film-forming properties, ease of modification, antifouling properties, chemical stability, low cost, and modifiability, is a superior substrate for MOF powders in water treatment.

[0004] NH2-MIL-101(Fe) enhances the positive charge on the adsorbent surface due to the amino group (-NH2) in the ligand. The amino group is protonated in solution to form a positively charged -NH3 group. + It adsorbs negatively charged phosphate ions through electrostatic attraction; the introduction of amino groups can increase the isoelectric point (pHPZC) of the MOF adsorbent, so that it maintains positive charge over a wider pH range, thus improving its application over a wide pH range; the introduction of amino groups increases the number of active sites, which can adsorb phosphorus by forming hydrogen bonds.

[0005] Specifically, the existing technology still has the following shortcomings:

[0006] How to modify existing NH2-MIL-101(Fe) metal-organic framework materials to increase the content of amino groups and thus improve their selectivity and adsorption capacity is a problem that needs to be overcome in the field of adsorption technology at present.

[0007] The compatibility and bonding strength between the MOF filler and the polymer membrane substrate are crucial to the stability of the composite membrane structure. Insufficient interfacial bonding can lead to MOF particle detachment; relying solely on physical forces, this detachment will become increasingly pronounced with long-term use. Poor compatibility between the MOF and the base membrane can cause large-scale agglomeration of the filler, resulting in a significant reduction in adsorption sites and affecting the adsorption performance of the MOF. Poor stability can lead to secondary pollution. The instability of the MOF membrane material results in poor adsorption performance, leading to large-scale MOF detachment into the water. Adsorbed phosphorus returns to the water body, and the detached MOF particles diffuse and flow through the water, causing secondary pollution.

[0008] Therefore, to solve the existing problems, it is necessary to increase the active sites of Fe-MOF and add amino groups to improve the adsorption performance of MOF; to facilitate recycling, it is necessary to improve the interfacial compatibility and stability between MOF and membrane. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide an MNH2-MIL-101(Fe) / PA-PAN composite membrane, its preparation method, its application, and its application.

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

[0011] A method for preparing an MNH2-MIL-101(Fe) / PA-PAN composite membrane is disclosed. The method involves secondary amino modification of NH2-MIL-101(Fe) with melamine and epichlorohydrin to enhance its surface charge and phosphate adsorption capacity; polyamine treatment of a polyacrylonitrile membrane with ethylenediamine to obtain an amino-rich PA-PAN membrane substrate; loading a modified MOF onto the PA-PAN membrane via vacuum filtration and chemically crosslinking with a crosslinking agent to form covalent and hydrogen bonds between the MOF and the membrane substrate, thereby preparing the MNH2-MIL-101(Fe) / PA-PAN composite membrane.

[0012] Furthermore, it includes the following steps:

[0013] (1) Preparation of NH2-MIL-101(Fe): The hydrothermal synthesis method was adopted. The organic solution of metal salt and organic ligand was weighed and reacted in a high-pressure reactor. After the reaction product was cooled, it was collected by centrifugation and then washed and dried in sequence to obtain NH2-MIL-101(Fe) powder.

[0014] (2) Preparation of MNH2-MIL-101(Fe): Weigh the NH2-MIL-101(Fe) powder and crosslinking agent obtained in step (1) and add them to the organic solution and stir the reaction at room temperature; collect by centrifugation, wash, dry and collect MNH2-MIL-101(Fe) powder.

[0015] (3) Preparation of PAN film: Weigh polyacrylonitrile powder and pore-forming agent and add them to organic solvent. Heat and stir the mixed solution in a water bath, then let it stand to degas, scrape it, and the phase is transformed into PAN film.

[0016] (4) Preparation of PA-PAN membrane: Dissolve ethylenediamine in water and ethylene glycol solvent to obtain a mixed solution. Place the PAN membrane obtained in step (3) into the mixed solution, heat to react, and then take it out and wash until the solution is neutral to obtain PA-PAN membrane.

[0017] (5) Preparation of MNH2-MIL-101(Fe) / PA-PAN membrane

[0018] 1) Preparation of MNH2-MIL-101(Fe) dispersion

[0019] Weigh the MNH2-MIL-101(Fe) powder obtained in step (2) into the dispersion to obtain a mixture. Stir the mixture and after stirring and dispersing, place it in an ultrasonic machine for ultrasonic treatment. Cool it in an ice bath during ultrasonication to obtain the MNH2-MIL-101(Fe) dispersion.

[0020] 2) Vacuum filtration load

[0021] The PA-PAN membrane obtained in step (4) is laid flat on the filter membrane and pre-wetted with deionized water to activate the membrane surface and promote the uniform distribution of the subsequent solution. Then, the MNH2-MIL-101(Fe) dispersion obtained in step (1) is slowly poured in while controlling the flow rate. The membrane is poured in slowly in two batches, with a 3-minute interval between each batch. The membrane is then filtered dry and fixed layer by layer on the membrane substrate. After loading, the membrane is drawn for another 1 minute to remove the remaining water and obtain the composite membrane.

[0022] 3) Crosslinking treatment

[0023] The composite membrane obtained in step 2) is immersed in a crosslinking agent mixture solution, which is obtained by uniformly mixing crosslinking agent and deionized water, so that the amino and polyamine (PA) groups of MOF on the composite membrane react with the crosslinking agent respectively; then it is washed with deionized water to remove the crosslinking agent mixture solution, and the MNH2-MIL-101(Fe) / PA-PAN composite membrane material is obtained.

[0024] Furthermore, in step (1), the metal salt is ferric chloride hexahydrate;

[0025] Alternatively, the organic ligand in step (1) is 2-aminoterephthalic acid;

[0026] Alternatively, the organic solution of the organic ligand in step (1) is prepared using an organic solvent; the ratio of metal salt, organic ligand, and organic solvent in step (1) is 1.5~3:1.5~2.5:100~150 (g:g:mL); and the organic solution is N,N-dimethylformamide (DMF).

[0027] In step (1), the hydrothermal conditions for the hydrothermal synthesis method are 80~130℃ and the reaction time is 12~20h;

[0028] The drying temperature in step (1) is 60~100℃ and the drying time is 10h~20h.

[0029] Further, in step (2), the crosslinking agent is melamine and epichlorohydrin, wherein the ratio of melamine, NH2-MIL-101(Fe) powder obtained in step (1), and epichlorohydrin (g:g:uL) is 0.1~0.6:0.1~0.5:300~700;

[0030] The stirring time in step (2) is 8~16 hours;

[0031] In step (2), the drying temperature is 30~60℃ and the heating time is 8~16h.

[0032] Furthermore, in step (3), the pore-forming agent is polyvinylpyrrolidone, and the organic solvent is N,N-dimethylformamide;

[0033] In step (3), the ratio of polyacrylonitrile powder, pore-forming agent, and organic solution is 10~20:5~15:70 (g:g:mL).

[0034] In step (3), the water bath temperature for heating and stirring is 50~70℃, and the heating time is 5~8h;

[0035] The phase transformation condition in step (3) is either deionized water or ethanol solution.

[0036] Furthermore, in step (4), the volume ratio of ethylenediamine, water, and ethylene glycol (mL:mL:mL) is 10~50:50~75:50~75; and the ratio of PAN film to ethylenediamine (g:mL) obtained in step (3) is 0.5~1:10~50.

[0037] In step (4), the heating temperature is 70~100℃ and the heating time is 3~5h.

[0038] Furthermore, in step (5), the dispersion is either water or ethanol;

[0039] Alternatively, in step (5), the ratio of dispersion to MNH2-MIL-101(Fe) powder in step 1) is 100~150:0.1~0.3 (mL:g).

[0040] Alternatively, the conditions for ultrasonic treatment in step (5) 1) are 500W ultrasonic treatment for 1.5~2 hours;

[0041] Alternatively, the crosslinking agent in step (5) 3) is either glutaraldehyde or epichlorohydrin;

[0042] Alternatively, in step (5) 3), the mass ratio of crosslinking agent to deionized water is 1:1;

[0043] Alternatively, the soaking time in step (5) 3) is 5 hours.

[0044] The MNH2-MIL-101(Fe) / PA-PAN composite membrane was prepared by the method described above.

[0045] The application of the MNH2-MIL-101(Fe) / PA-PAN composite membrane as described above in phosphorus resource recovery from phosphorus-containing wastewater.

[0046] Furthermore, the characteristic pollutant of the phosphorus-containing wastewater is phosphorus, with a concentration of 2-3 mg / L.

[0047] The advantages and positive effects of this invention are as follows:

[0048] 1. The composite membrane material of this invention is composed of modified polyacrylonitrile, metallic iron, and organic ligands. The NH2-MIL-101(Fe) modification adds amino groups to the original amino-modified MOF, increasing the surface charge of the adsorbent, increasing active sites, and improving adsorption capacity. The amino groups in the polyamined PAN and the MOF form hydrogen bonds and covalent bonds through crosslinking, improving the compatibility and stability of MNH2-MIL-101(Fe) and PA-PAN, preventing MOF aggregation on the membrane. The structural uniformity and stability of the composite membrane are greatly improved under crosslinking. This composite material is suitable for phosphorus resource recovery from phosphorus-containing surface water, exhibiting excellent adsorption performance, easy recovery, and simple operation, showing promising application prospects.

[0049] 2. The preparation method of MNH2-MIL-101(Fe) adsorbent provided by the present invention involves preparing NH2-MIL-101(Fe) and melamine under the crosslinking of epichlorohydrin. The MNH2-MIL-101(Fe) adsorbent can be obtained by stirring at room temperature. The -NH2 group in NH2-MIL-101(Fe) undergoes an addition reaction with the epoxy group in epichlorohydrin, and the -NH2 group in melamine undergoes a substitution reaction with the Cl group at the other end of epichlorohydrin, thereby increasing the number of -NH2 groups and improving the adsorption capacity.

[0050] 3. The performance of the MNH2-MIL-101(Fe) adsorbent of this invention is superior to most previously reported adsorbents, achieving a maximum adsorption capacity of 234 mg / g. Furthermore, it exhibits low sensitivity to ionic strength within a pH range of 3 to 11 and strong selectivity for phosphates in the presence of competing ions.

[0051] 4. In this invention, the amino groups in MNH2-MIL-101(Fe) and PA-PAN form covalent and hydrogen bonds under the action of glutaraldehyde, enhancing the interfacial bonding between the MOF material and the membrane. This prevents the aggregation of MOF material on the membrane, ensures its uniform dispersion on the membrane, improves the mechanical properties of the membrane, and better exposes the adsorption sites of the MOF.

[0052] 5. The PAN membrane selected in this invention exhibits excellent resistance to most chemicals, oils, and solvents, especially biodegradability. This makes it perform exceptionally well in treating complex industrial wastewater, as the membrane is not easily degraded or corroded. The covalent and hydrogen bonds formed by the cross-linking of amino groups and PA groups on the MOF further enhance the chemical and physical stability of the membrane, extending its service life and facilitating better industrial applications, building upon the existing advantages of PAN membranes.

[0053] 6. The method of this invention is simple to operate, has mild modification conditions, and requires minimal equipment, making it a simple preparation method. It also reduces the possibility of secondary pollution, aligning with the trend of green development. The MOF and membrane used are among the most inexpensive combinations in existing technologies, reducing production costs. Its high adsorption performance, coupled with the ability to recover and reuse modified MNH2-MIL-101(Fe) through the membrane, better recovers phosphorus resources and reuses MOF, achieving a circular economy and improving industrial economics. Attached Figure Description

[0054] Figure 1 This is an electron scanning schematic diagram of MNH2-MIL-101(Fe) prepared in Example 2 of this invention;

[0055] Figure 2This is a partially enlarged electron scan diagram of MNH2-MIL-101(Fe) prepared in Example 2 of this invention;

[0056] Figure 3 The energy spectrum of NH2-MIL-101(Fe) prepared in Example 2 of this invention is shown below; the mapping spectrum is as follows;

[0057]

[0058] Figure 4 The energy spectrum of MNH2-MIL-101(Fe) prepared in Example 2 of this invention is shown below; the mapping spectrum is as follows;

[0059]

[0060] Figure 5 Fourier transform infrared spectra of NH2-MIL-101(Fe) and MNH2-MIL-101(Fe) obtained in Examples 1-2 of this invention;

[0061] Figure 6 The Fourier transform infrared spectra of the PAN film and PA-PAN film prepared in Example 3 of this invention are shown below.

[0062] Figure 7 Fourier transform infrared spectra of the MNH2-MIL-101(Fe) / PA-PAN composite films prepared in Example 4 of this invention;

[0063] Figure 8 This is a schematic diagram (surface) of the electron scanning electron microscope (ESB) scan of the MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Example 4 of this invention before ultrasound.

[0064] Figure 9 This is a cross-sectional view of the electron scanning diagram (section) of the MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Example 4 of this invention before ultrasound.

[0065] Figure 10 This is a schematic diagram (surface) of the electron scanning electron microscope (ESB) of the MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Example 4 of this invention after ultrasonication.

[0066] Figure 11 This is a cross-sectional view of the electron scanning diagram of the MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Example 4 of this invention after ultrasonication.

[0067] Figure 12This is a schematic diagram (surface) of the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Comparative Example 1 of this invention before ultrasound.

[0068] Figure 13 This is a cross-sectional view of the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Comparative Example 1 of this invention before ultrasound.

[0069] Figure 14 This is a schematic diagram (surface) of the electron scanning electron microscope (ESB) of the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Comparative Example 1 of this invention after ultrasonication.

[0070] Figure 15 This is a cross-sectional view of the electron scanning diagram (section) of the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in Comparative Example 1 of this invention after ultrasonication.

[0071] Figure 16 This is a schematic diagram (surface) of the electron scanning of the MNH2-MIL-101(Fe) / PAN composite membrane prepared in Comparative Example 2 of this invention before ultrasound.

[0072] Figure 17 This is a schematic diagram (surface) of the electron scanning of the MNH2-MIL-101(Fe) / PAN composite membrane prepared in Comparative Example 2 of this invention after ultrasonication. Detailed Implementation

[0073] 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.

[0074] 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.

[0075] A method for preparing an MNH2-MIL-101(Fe) / PA-PAN composite membrane is disclosed. The method involves secondary amino modification of NH2-MIL-101(Fe) with melamine and epichlorohydrin to enhance its surface charge and phosphate adsorption capacity; polyamine treatment of a polyacrylonitrile membrane with ethylenediamine to obtain an amino-rich PA-PAN membrane substrate; loading a modified MOF onto the PA-PAN membrane via vacuum filtration and chemically crosslinking with a crosslinking agent to form covalent and hydrogen bonds between the MOF and the membrane substrate, thereby preparing the MNH2-MIL-101(Fe) / PA-PAN composite membrane.

[0076] Furthermore, it includes the following steps:

[0077] (1) Preparation of NH2-MIL-101(Fe): The hydrothermal synthesis method was adopted. The organic solution of metal salt and organic ligand was weighed and reacted in a high-pressure reactor. After the reaction product was cooled, it was collected by centrifugation and then washed and dried in sequence to obtain NH2-MIL-101(Fe) powder.

[0078] (2) Preparation of MNH2-MIL-101(Fe): Weigh the NH2-MIL-101(Fe) powder and crosslinking agent obtained in step (1) and add them to the organic solution and stir the reaction at room temperature; collect by centrifugation, wash, dry and collect MNH2-MIL-101(Fe) powder.

[0079] (3) Preparation of PAN film: Weigh polyacrylonitrile powder and pore-forming agent and add them to organic solvent. Heat and stir the mixed solution in a water bath, then let it stand to degas, scrape it, and the phase is transformed into PAN film.

[0080] (4) Preparation of PA-PAN membrane: Dissolve ethylenediamine in water and ethylene glycol solvent to obtain a mixed solution. Place the PAN membrane obtained in step (3) into the mixed solution, heat to react, and then take it out and wash until the solution is neutral to obtain PA-PAN membrane.

[0081] (5) Preparation of MNH2-MIL-101(Fe) / PA-PAN membrane

[0082] 1) Preparation of MNH2-MIL-101(Fe) dispersion

[0083] Weigh the MNH2-MIL-101(Fe) powder obtained in step (2) into the dispersion to obtain a mixture. Stir the mixture and after stirring and dispersing, place it in an ultrasonic machine for ultrasonic treatment. Cool it in an ice bath during ultrasonication to obtain the MNH2-MIL-101(Fe) dispersion.

[0084] 2) Vacuum filtration load

[0085] The PA-PAN membrane obtained in step (4) is laid flat on the filter membrane and pre-wetted with deionized water to activate the membrane surface and promote the uniform distribution of the subsequent solution. Then, the MNH2-MIL-101(Fe) dispersion obtained in step (1) is slowly poured in while controlling the flow rate. The membrane is poured in slowly in two batches, with a 3-minute interval between each batch. The membrane is then filtered dry and fixed layer by layer on the membrane substrate. After loading, the membrane is drawn for another 1 minute to remove the remaining water and obtain the composite membrane.

[0086] 3) Crosslinking treatment

[0087] The composite membrane obtained in step 2) is immersed in a crosslinking agent mixture solution, which is obtained by uniformly mixing crosslinking agent and deionized water, so that the amino and polyamine (PA) groups of MOF on the composite membrane react with the crosslinking agent respectively; then it is washed with deionized water to remove the crosslinking agent mixture solution, and the MNH2-MIL-101(Fe) / PA-PAN composite membrane material is obtained.

[0088] Preferably, the metal salt in step (1) is ferric chloride hexahydrate;

[0089] Alternatively, the organic ligand in step (1) is 2-aminoterephthalic acid;

[0090] Alternatively, the organic solution of the organic ligand in step (1) is prepared using an organic solvent; the ratio of metal salt, organic ligand, and organic solvent in step (1) is 1.5~3:1.5~2.5:100~150 (g:g:mL); and the organic solution is N,N-dimethylformamide (DMF).

[0091] In step (1), the hydrothermal conditions for the hydrothermal synthesis method are 80~130℃ and the reaction time is 12~20h;

[0092] The drying temperature in step (1) is 60~100℃ and the drying time is 10h~20h.

[0093] Preferably, in step (2), the crosslinking agent is melamine and epichlorohydrin, wherein the ratio of melamine, NH2-MIL-101(Fe) powder obtained in step (1), and epichlorohydrin (g:g:uL) is 0.1~0.6:0.1~0.5:300~700;

[0094] The stirring time in step (2) is 8~16 hours;

[0095] In step (2), the drying temperature is 30~60℃ and the heating time is 8~16h.

[0096] Preferably, in step (3), the pore-forming agent is polyvinylpyrrolidone and the organic solvent is N,N-dimethylformamide;

[0097] In step (3), the ratio of polyacrylonitrile powder, pore-forming agent, and organic solution is 10~20:5~15:70 (g:g:mL).

[0098] In step (3), the water bath temperature for heating and stirring is 50~70℃, and the heating time is 5~8h;

[0099] The phase transformation condition in step (3) is either deionized water or ethanol solution.

[0100] Preferably, in step (4), the volume ratio of ethylenediamine, water, and ethylene glycol (mL:mL:mL) is 10~50:50~75:50~75; and the ratio of PAN film to ethylenediamine (g:mL) obtained in step (3) is 0.5~1:10~50.

[0101] In step (4), the heating temperature is 70~100℃ and the heating time is 3~5h.

[0102] Preferably, the dispersion in step (5) is either water or ethanol;

[0103] Alternatively, in step (5), the ratio of dispersion to MNH2-MIL-101(Fe) powder in step 1) is 100~150:0.1~0.3 (mL:g).

[0104] Alternatively, the conditions for ultrasonic treatment in step (5) 1) are 500W ultrasonic treatment for 1.5~2 hours;

[0105] Alternatively, the crosslinking agent in step (5) 3) is either glutaraldehyde or epichlorohydrin;

[0106] Alternatively, in step (5) 3), the mass ratio of crosslinking agent to deionized water is 1:1;

[0107] Alternatively, the soaking time in step (5) 3) is 5 hours.

[0108] The MNH2-MIL-101(Fe) / PA-PAN composite membrane was prepared by the method described above.

[0109] The application of the MNH2-MIL-101(Fe) / PA-PAN composite membrane as described above in phosphorus resource recovery from phosphorus-containing wastewater.

[0110] Preferably, the characteristic pollutant of the phosphorus-containing wastewater is phosphorus, with a concentration of 2-3 mg / L.

[0111] Specifically, the relevant preparation and testing methods are as follows:

[0112] Example 1

[0113] The preparation method of NH2-MIL-101(Fe) includes the following steps:

[0114] (1) Dissolve FeCl3·6H2O (1.323g) and NH2-BDC (2-aminoterephthalic acid) (0.423g) in 15mL of DMF respectively. Then sonicate the mixture for 20 minutes, transfer it to a hydrothermal reactor, place it in an oven, heat it at 110℃ for 20h, and then let it cool to room temperature.

[0115] (2) The mixture was washed three times by centrifugation with DMF and ethanol respectively.

[0116] (3) Finally, the solid was placed in a vacuum drying oven at 60°C and dried for 12 hours to obtain the NH2-MIL-101(Fe).

[0117] Example 2

[0118] The preparation method of MNH2-MIL-101(Fe) includes the following steps:

[0119] (1) The NH2-MIL-101(Fe) (0.3g) and melamine (0.36mmol) prepared in Example 1 were dispersed in 18mL LDM solution, and after sonication for 15min, the two mixtures were mixed. Epichlorohydrin (500uL) was added to the mixed solution and stirred at room temperature for 24 hours.

[0120] (2) The mixture was washed three times by centrifugation with DMF and ethanol respectively.

[0121] (3) Finally, the solid was placed in a vacuum drying oven at 60°C and dried for 12 hours. The Mel-NH2-MIL-101(Fe) adsorbent was obtained, namely MNH2-MIL-101(Fe).

[0122] The SEM image of MNH2-MIL-101(Fe) obtained in this embodiment is shown below. Figure 1 , Figure 2 As shown, the synthesized MNH2-MIL-101(Fe) exhibits a typical cubic octahedral structure with a rough surface and uniform distribution. The addition of melamine makes the adsorbent surface rough. The addition of melamine does not significantly affect the shape of the adsorbent.

[0123] The energy spectrum of MNH2-MIL-101(Fe) obtained in this embodiment is as follows: Figure 4 As shown above, the results indicate that MNH2-MIL-101(Fe) contains a significant amount of nitrogen (N) element, as shown in the elemental energy spectrum diagram of NH2-MIL-101(Fe) in Example 1. Figure 3 In comparison, the N content of the unmodified MOF was 9.26%, while that of the modified MOF was 12.88%, indicating a higher N content. These results suggest that MNH2-MIL-101(Fe) has more amino functional groups.

[0124] The Fourier transform infrared spectra of MNH2-MIL-101(Fe) and NH2-MIL-101(Fe) prepared in Examples 1-2 are as follows: Figure 5As shown, the characteristics of the two infrared spectra mainly reflect the phenylcarboxylate and amino groups: the band of NH2-MIL-101(Fe) at 1575.56 cm⁻¹ and the band of MNH2-MIL-101(Fe) at 1577.49 cm⁻¹. -1 The spectral band at 1060.17 cm⁻¹ is correlated with the C=O bond in the carboxylate, while NH₂-MIL-101(Fe) is located at 1060.17 cm⁻¹. -1 The spectral band and MNH2-MIL-101(Fe) are located at 1061.62 cm⁻¹. -1 The band at this location is attributed to the C-C vibrational mode of aromatic carbons. Due to the substitution of the benzene ring with an amino group, NH₂-MIL-101(Fe) was observed at 1250.13 cm⁻¹. -1 And MNH2-MIL-101(Fe) at 1253.02 cm -1 The band at 1652.21 cm⁻¹ represents the CN stretching mode of aromatic carbons. NH₂-MIL-101(Fe) and MNH₂-MIL-101(Fe) are also present at 1652.21 cm⁻¹. -1 The band at this point belongs to the NH shear vibration. Furthermore, NH₂-MIL-101(Fe) shows bands at 3460.15 and 3341.07 cm⁻¹. -1 The double peaks at 3456.37 and 3326.14 cm⁻¹, and the MNH₂-MIL-101(Fe) peaks at 3456.37 and 3326.14 cm⁻¹. -1 The appearance of the double peaks at the point proves the asymmetric and symmetric stretching of the amine group. The intensity of these peaks in Mel-NH2-MIL-101(Fe) is greater than that in MNH2-MIL-101(Fe), showing a good amine stretching mode, indicating that the amino group in the sample has a high degree of crystallinity.

[0125] Example 3

[0126] The preparation method of PA-PAN film includes the following steps:

[0127] (1) Preparation of PAN membrane: 10g of polyacrylonitrile PAN powder and 10g of polyvinylpyrrolidone were placed in 80mL of N,N-dimethylamide, heated in a water bath at 70℃ and stirred for 8h, and left to stand overnight for degassing treatment. Then, it was poured onto a glass plate and scraped, and phase inversion was carried out in a coagulation bath to obtain PAN membrane.

[0128] (2) Preparation method of PA-PAN membrane: Dissolve ethylenediamine in a mixed solvent of water and ethylene glycol, put the PAN membrane from step (1) into the solution and heat at 70°C for 3 hours, then wash with deionized water until neutral to obtain PA-PAN membrane; wherein, the ratio of ethylenediamine:water:ethylene glycol:PAN membrane mL:mL:mL:g is 30:50:50:0.75.

[0129] The Fourier transform infrared spectrum of the PA-PAN film prepared in this embodiment is as follows: Figure 6 As shown, by Figure 6 It can be seen that the infrared spectra all exhibit a distinct broad absorption peak of -CN at approximately 2242 cm⁻¹. For the Fourier transform infrared spectrum of PAN, the absorption band intensity of the -CN group is significantly weakened, proving that the conversion of the -CN bond into a polyamine group is feasible. In the 3000–3500 cm⁻¹ range... -1 Within the wavelength range, the peak intensity significantly increases, which is due to the introduction of a large number of -NH2 groups by the polyamine reaction of PAN; at 1636 cm⁻¹ -1 A new -NH2 absorption peak appeared, further demonstrating that a cross-linked structure was formed between the PAN molecular chains, and primary amine (-NH2) and secondary amine (-NH) functional groups were introduced. This example successfully prepared a PA-PAN membrane.

[0130] Example 4

[0131] The preparation method of MNH2-MIL-101(Fe) / PA-PAN composite membrane includes the following steps:

[0132] (1) Preparation of MNH2-MIL-101(Fe) dispersion

[0133] Weigh 0.02g of the MNH2-MIL-101(Fe) powder prepared in Example 2 into 100mL of ethanol solvent, stir the resulting mixture, disperse it, and then place it in an ultrasonic probe for ultrasonic treatment at 500W for 1h. Cool it in an ice bath during ultrasonication, and then obtain the MNH2-MIL-101(Fe) dispersion.

[0134] (2) Vacuum filtration load

[0135] The PA-PAN membrane prepared in Example 3 was laid flat on the filter membrane and pre-wetted with deionized water for 3 min to activate the membrane surface and promote the uniform distribution of the subsequent solution. Then, it was slowly poured into the MNH2-MIL-101(Fe) dispersion obtained in step (1) and the flow rate was controlled. It was slowly poured in twice, with a 3 min interval between each pour, and filtered dry. The membrane was then fixed layer by layer and uniformly on the membrane substrate. After loading, it was filtered for 1 min to remove the remaining water and obtain the composite membrane.

[0136] (3) Crosslinking treatment

[0137] The composite membrane obtained in step (2) was immersed in a mixture of 20 mL of glutaraldehyde and 20 mL of deionized water to allow the amino and polyamine (PA) groups of the MOF on the composite membrane to react with glutaraldehyde. After immersion for 5 h, the membrane was washed with deionized water to remove the glutaraldehyde mixture and obtain the MNH2-MIL-101(Fe) / PA-PAN composite membrane material.

[0138] Fourier transform infrared spectrum of the MNH2-MIL-101(Fe) / PA-PAN composite film prepared in this embodiment. Figure 7 As shown, the Fourier transform infrared spectrum reveals that in the wavelength range of 3000–3500 cm⁻¹, compared to the spectra of MOF, PAN, and PA-PAN, the peak broadens due to the stretching vibration of -NH₂. This is because the introduction of MOF results in more amino groups compared to PA-PAN films. However, after crosslinking, the -NH₂ absorption peak at 1636 cm⁻¹ weakens. This is because the aldehyde group of glutaraldehyde reacts with the amino group to form -C=N groups. This indicates successful crosslinking, which promotes the formation of hydrogen bond networks or covalent bonds on the surface, thereby improving interfacial compatibility.

[0139] The bonding stability of the MNH2-MIL-101(Fe) and PA-PAN membranes was determined by scanning electron microscopy (SEM). The SEM image of the MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in this example is shown below. Figure 8 As shown, MNH2-MIL-101(Fe) is uniformly distributed and has a compact structure on PA-PAN. Figure 9 As shown, the thickness of the composite membrane is 4.23 ± 0.5 μm. The MNH2-MIL-101(Fe) / PA-PAN membrane was subjected to ultrasonic treatment in a 60 W water bath for 15 min. The SEM image of the composite membrane after ultrasonication is shown below. Figure 10 As shown, MNH2-MIL-101(Fe) remains uniformly distributed on PA-PAN. Figure 11 The thickness of the composite film after ultrasonication is shown to be 3.98 ± 0.5 μm. The results indicate that ultrasonication removes the loosely adsorbed MNH2-MIL-101(Fe) layer while retaining the chemically bonded / deeply embedded MNH2-MIL-101(Fe).

[0140] The performance of the ultrasonically modified MNH2-MIL-101(Fe) / PA-PAN composite membrane was tested under the following conditions: phosphate concentration 2 mg / L, pH 7.5. The results showed that the MNH2-MIL-101(Fe) / PA-PAN membrane achieved a phosphate removal rate of 98.87%. The good removal effect of the MNH2-MIL-101(Fe) / PA-PAN membrane demonstrates the successful modification of NH2-MIL-101(Fe), resulting in better adsorption performance. It also proves the stable loading of MNH2-MIL-101(Fe) on the PA-PAN membrane. The modified NH2-MIL-101(Fe) contains more amino groups, which enhances electrostatic attraction, increases diffusion rate, strengthens intramolecular complexation, and results in a more uniform distribution of MOF on the membrane, increasing the diffusion pathways for phosphate. This interfacial compatibility and stability ensures the stability of the MOF on the membrane in dynamic water, preventing the detachment of adsorption active sites and thus ensuring efficient phosphate removal. The phosphorus removal performance of the MNH2-MIL-101(Fe) / PA-PAN membrane depends on the adsorption performance of the MOF. Improving the adsorption performance of the MOF while ensuring its stability and retention rate on the membrane is crucial. Increasing the number of amino groups on the MOF and the strong covalent bonds are key to preventing MOF detachment.

[0141] Comparative Example 1 (omitting step (3) of Example 4, i.e., the crosslinking treatment step)

[0142] A method for preparing an uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane includes the following steps:

[0143] (1) Preparation of MNH2-MIL-101(Fe) dispersion

[0144] Weigh 0.02g of the MNH2-MIL-101(Fe) powder prepared in Example 2 into 100mL of ethanol solvent, stir the resulting mixture, disperse it, and then place it in an ultrasonic probe for ultrasonic treatment at 500W for 1h. Cool it in an ice bath during ultrasonication, and then obtain the MNH2-MIL-101(Fe) dispersion.

[0145] (2) Vacuum filtration load

[0146] The PA-PAN membrane prepared in Example 3 was laid flat on the filter membrane and pre-wetted with deionized water for 3 min to activate the membrane surface and promote the uniform distribution of the subsequent solution. Then, it was slowly poured into the MNH2-MIL-101(Fe) dispersion prepared in step (1) and the flow rate was controlled. It was slowly poured in twice, with a 3 min interval between each pour, and filtered dry. The membrane was fixed layer by layer and uniformly on the membrane substrate. After loading, it was filtered for 1 min to remove the remaining water and obtain an uncrosslinked composite membrane.

[0147] The bonding stability of the uncrosslinked MNH2-MIL-101(Fe) and PA-PAN membranes was determined by scanning electron microscopy (SEM). The SEM images of the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane prepared in this comparative example are shown below. Figure 12 As shown, MNH2-MIL-101(Fe) is unevenly distributed on PA-PAN, exhibiting agglomeration. For example... Figure 13 As shown, the thickness of the composite membrane is 8.03 ± 0.5 μm. The MNH2-MIL-101(Fe) / PA-PAN membrane was subjected to ultrasonic treatment in a 60 W water bath for 15 min. The SEM image of the composite membrane after ultrasonication is shown below. Figure 14 As shown, MNH2-MIL-101(Fe) is distributed and accumulated on PA-PAN, with a large amount detaching and producing large cracks. Figure 15 The thickness of the composite film after adsorption is shown to be 4.03 ± 0.5 μm. The results indicate that the MOF particles detach significantly due to physical action alone, without the support of chemical bonds. Ultrasonic treatment reduced the thickness of the MNH2-MIL-101(Fe) / PA-PAN composite film, indicating that a large number of MOF particles were peeled off from the substrate surface. SEM comparison with Example 4 shows that in the uncrosslinked composite film, the MOF and the film are only physically adsorbed, lacking chemical bonding. In the uncrosslinked film, the MOF-polymer interface is prone to slippage and detachment under dynamic stress. The results show that the ultrasonically adsorbed MNH2-MIL-101(Fe) in Comparative Example 1 sample is unstable on the PA-PAN film surface.

[0148] The performance of the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN composite membrane after ultrasonication was tested under the following conditions: phosphate concentration 2 mg / L, pH 7.5. The results showed that the uncrosslinked MNH2-MIL-101(Fe) / PA-PAN membrane achieved a phosphate removal rate of 42.3%. This is because after ultrasonication, MNH2-MIL-101(Fe) is unstable on the PA-PAN membrane surface, leading to the detachment of a large amount of MOF, resulting in a decrease in adsorption performance. MOFs are loaded onto the membrane solely through physical action, exhibiting weak binding forces. Under dynamic water flow, they are easily detached, especially edge particles, thus affecting mass transfer efficiency.

[0149] The comparison between Comparative Example 1 and Example 4 shows that in order to realize the adsorption performance of MOF, the interfacial compatibility and stability of MOF on the membrane must be ensured. Under the crosslinking of glutaraldehyde, MNH2-MIL-101(Fe) and PA-PAN membrane have a good synergistic effect, which can improve the relevant performance of the prepared MNH2-MIL-101(Fe) / PA-PAN composite membrane.

[0150] Comparative Example 2

[0151] A method for preparing an MNH2-MIL-101(Fe) / PAN composite membrane includes the following steps:

[0152] (1) Preparation of PAN membrane: 10g of PAN powder and 10g of polyvinylpyrrolidone were placed in 80mL of N,N-dimethylamide, heated in a water bath at 70℃ and stirred for 8h, and left to stand overnight for degassing treatment. Then, it was poured onto a glass plate and scraped, and phase inversion was carried out in a coagulation bath to obtain PAN membrane.

[0153] (2) Preparation of MNH2-MIL-101(Fe) dispersion

[0154] Weigh 0.02g of the MNH2-MIL-101(Fe) powder prepared in Example 2 into 100mL of ethanol solvent, stir the resulting mixture, disperse it, and then place it in an ultrasonic probe for ultrasonic treatment at 500W for 1h. Cool it in an ice bath during ultrasonication, and then obtain the MNH2-MIL-101(Fe) dispersion.

[0155] (3) Vacuum filtration load

[0156] The PAN membrane from step (1) is laid flat on the filter membrane and pre-wetted with deionized water for 3 min to activate the membrane surface and promote the uniform distribution of the subsequent solution. Then, it is slowly poured into the MNH2-MIL-101(Fe) dispersion obtained in step (2) while controlling the flow rate. It is poured in slowly in two batches, with a 3 min interval between each batch, and filtered dry. The membrane is then fixed layer by layer and uniformly on the membrane substrate. After loading, it is filtered for 1 min to remove the remaining water and obtain the composite membrane.

[0157] (4) Crosslinking treatment

[0158] The composite membrane obtained in step (3) was immersed in a mixture of 20 mL of glutaraldehyde and 20 mL of deionized water for 5 h. Then it was washed with deionized water to remove the glutaraldehyde mixture and obtain the MNH2-MIL-101(Fe) / PAN composite membrane material.

[0159] The bonding stability of crosslinked MNH2-MIL-101(Fe) with the PAN membrane was determined by scanning electron microscopy (SEM). The SEM image of the MNH2-MIL-101(Fe) / PAN composite membrane prepared in this comparative example is shown below. Figure 16 As shown, MNH2-MIL-101(Fe) is unevenly distributed on the PAN membrane, exhibiting agglomeration. However, physical loading can be achieved through vacuum filtration. The MNH2-MIL-101(Fe) / PAN membrane was subjected to ultrasonic treatment in a 60W water bath for 15 minutes. The SEM image of the composite membrane after ultrasonication is shown below. Figure 17 As shown, MNH2-MIL-101(Fe) is scattered and piled up on the PAN, and a large amount of MOF is detached. This is because the amino groups on the MOF cannot form Schiff base bonds with the PAN film under the action of glutaraldehyde, resulting in no chemical bond action and only physical action, thus leading to the detachment of a large amount of MOF.

[0160] The performance of the ultrasonicated MNH2-MIL-101(Fe) / PAN composite membrane was tested under the following conditions: phosphate concentration 2 mg / L, pH 7.5. The results showed that the uncrosslinked MNH2-MIL-101(Fe) / PAN membrane achieved a phosphate removal rate of 26.7%. This is because after ultrasonication, the MNH2-MIL-101(Fe) on the PAN membrane surface becomes unstable, leading to the shedding of a large amount of MOF and a decrease in adsorption performance. The exposed PAN matrix (without MOF modification) has a low affinity for phosphate. Simultaneously, interfacial defects hinder mass transfer from the solution to the MOF channels, resulting in a decrease in kinetic adsorption capacity.

[0161] Meanwhile, by comparing Example 4, Comparative Example 1 and Comparative Example 2, it can be seen that the steps "(3) crosslinking treatment" and "(2) crosslinking treatment" in the method of the present invention are synergistic, which can synergistically improve the relevant performance of the prepared MNH2-MIL-101(Fe) / PA-PAN composite membrane. The steps "(2) PA-PAN membrane preparation method: dissolve ethylenediamine in a mixed solvent of water and ethylene glycol, put the PAN membrane of step (1) into the solution and heat it at 70°C for 3 hours, then wash it with deionized water until neutral, and obtain PA-PAN membrane" have a synergistic effect.

[0162] Comparison between the present invention and existing technologies:

[0163] 1. Comparison of Adsorption Efficiency and Dosage: This invention significantly optimizes the relationship between dosage and adsorption efficiency, and can effectively treat low-concentration phosphorus-containing solutions. The patented technology (Chinese Patent Publication CN119100504A, a method for preparing a supported Fe / La-MOF bimetallic-based metal-organic framework adsorbent for high-phosphorus wastewater, its products and applications) requires a dosage of 2 g / L to achieve an 87.3% phosphorus removal rate. In contrast, this invention, by immobilizing the highly efficient phosphorus-removing MNH2-MIL-101(Fe) on a PA-PAN membrane, achieves a stable interface, exposes numerous adsorption sites, and forms Fe-OP coordination bonds, resulting in a dosage as low as 0.01~0.03 g / L, achieving a very high removal rate.

[0164] 2. Comparison of Interfacial Compatibility and Stability: This invention focuses on interfacial compatibility and stability primarily through the chemical bond of the Schiff base. Traditional composite membranes in patented technologies (Chinese Patent Publication CN118179449A, a method for preparing and applying a porous lanthanum-based metal-organic framework LaMOF-XC adsorbent and filter membrane) rely solely on vacuum filtration to load the MOF, resulting in only physical interactions between the material and the base membrane, neglecting the chemical interactions between them. This invention combines MNH2-MIL-101(Fe) with a PA-PAN membrane through crosslinking, thereby improving interfacial compatibility and stability.

[0165] 3. Comparison of Economic Costs: This invention uses MIL-101 as the base MOF for modification. The composite material in the patented technology (Chinese Patent Publication CN120022761A, A La-MOF-COOH / AO-PAN Composite Membrane Material and its Preparation Method and Application) is synthesized using La, a relatively expensive metal. That invention uses hydroxylamine hydrochloride for PAN modification, while this invention uses ethylenediamine. Comparatively, Fe-based MOFs have a much lower economic cost than La-based MOFs. This invention is superior in terms of economic cost.

[0166] 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 an MNH2-MIL-101-Fe / PA-PAN composite membrane, characterized in that: The method employs melamine and epichlorohydrin to perform secondary amino modification on NH2-MIL-101-Fe, thereby enhancing its surface positive charge and phosphate adsorption capacity. Polyamine treatment is then applied to the polyacrylonitrile membrane to obtain an amino-rich PA-PAN membrane substrate. Modified MOF is loaded onto the PA-PAN membrane via vacuum filtration, and chemical crosslinking is performed using a crosslinking agent to form covalent and hydrogen bonds between the MOF and the membrane substrate, thus preparing the MNH2-MIL-101-Fe / PA-PAN composite membrane.

2. The preparation method according to claim 1, characterized in that: Includes the following steps: (1) Preparation of NH2-MIL-101-Fe: The hydrothermal synthesis method was adopted. The organic solution of metal salt and organic ligand was weighed and reacted in a high-pressure reactor. After the reaction product was cooled, it was collected by centrifugation and then washed and dried in sequence to obtain NH2-MIL-101-Fe powder. (2) Preparation of MNH2-MIL-101-Fe: Weigh the NH2-MIL-101-Fe powder and crosslinking agent obtained in step (1) and add them to the organic solution. Stir and react at room temperature. Collect by centrifugation, wash, dry and collect MNH2-MIL-101-Fe powder. (3) Preparation of PAN film: Weigh polyacrylonitrile powder and pore-forming agent and add them to organic solvent. Heat and stir the mixed solution in a water bath, then let it stand to degas, scrape it, and the phase is transformed into PAN film. (4) Preparation of PA-PAN membrane: Dissolve ethylenediamine in water and ethylene glycol solvent to obtain a mixed solution. Place the PAN membrane obtained in step (3) into the mixed solution, heat to react, and then take it out and wash until the solution is neutral to obtain PA-PAN membrane. (5) Preparation of MNH2-MIL-101-Fe / PA-PAN membrane 1) Preparation of MNH2-MIL-101-Fe dispersion Weigh the MNH2-MIL-101-Fe powder obtained in step (2) into the dispersion to obtain a mixture. Stir the mixture and after stirring and dispersing, place it in an ultrasonic machine for ultrasonic treatment. Cool it in an ice bath during ultrasonication, and then obtain the MNH2-MIL-101-Fe dispersion. 2) Vacuum filtration load The PA-PAN membrane obtained in step (4) was laid flat on the filter membrane and pre-wetted with deionized water to activate the membrane surface and promote the uniform distribution of the subsequent solution. Then, the MNH2-MIL-101-Fe dispersion obtained in step (1) was slowly poured in, and the flow rate was controlled. It was poured in slowly in two batches, with a 3-minute interval between each batch, and filtered dry. The membrane was then fixed layer by layer and uniformly on the membrane substrate. After loading, the membrane was drawn for another 1 minute to remove the remaining water and obtain the composite membrane. 3) Crosslinking treatment The composite membrane obtained in step 2) is immersed in a crosslinking agent mixture solution, which is obtained by uniformly mixing crosslinking agent and deionized water, so that the amino and polyamine groups of MOF on the composite membrane react with the crosslinking agent respectively; then it is washed with deionized water to remove the crosslinking agent mixture solution, and the MNH2-MIL-101-Fe / PA-PAN composite membrane material is obtained.

3. The preparation method according to claim 2, characterized in that: In step (1), the metal salt is ferric chloride hexahydrate; Alternatively, the organic ligand in step (1) is 2-aminoterephthalic acid; Alternatively, the organic solution of the organic ligand in step (1) is prepared using an organic solvent; the ratio of metal salt, organic ligand, and organic solvent in step (1) is 1.5~3:1.5~2.5:100~150 (g:g:mL); the organic solution is N,N-dimethylformamide. In step (1), the hydrothermal conditions for the hydrothermal synthesis method are 80~130℃ and the reaction time is 12~20h; The drying temperature in step (1) is 60~100℃ and the drying time is 10h~20h.

4. The preparation method according to claim 2, characterized in that: In step (2), the crosslinking agent is melamine and epichlorohydrin, wherein the ratio of melamine, NH2-MIL-101-Fe powder obtained in step (1), and epichlorohydrin (g:g:uL) is 0.1~0.6:0.1~0.5:300~700. The stirring time in step (2) is 8~16 hours; In step (2), the drying temperature is 30~60℃ and the heating time is 8~16h.

5. The preparation method according to claim 2, characterized in that: In step (3), the porogen is polyvinylpyrrolidone and the organic solvent is N,N-dimethylformamide; In step (3), the ratio of polyacrylonitrile powder, pore-forming agent, and organic solution is 10~20:5~15:70 (g:g:mL). In step (3), the water bath temperature for heating and stirring is 50~70℃, and the heating time is 5~8h; The phase transformation condition in step (3) is either deionized water or ethanol solution.

6. The preparation method according to claim 2, characterized in that: In step (4), the volume ratio of ethylenediamine, water, and ethylene glycol (mL:mL:mL) is 10~50:50~75:50~75; and the ratio of PAN film to ethylenediamine (g:mL) obtained in step (3) is 0.5~1:10~50. In step (4), the heating temperature is 70~100℃ and the heating time is 3~5h.

7. The preparation method according to claim 2, characterized in that: In step (5), the dispersion is either water or ethanol; Alternatively, in step (5), the ratio of dispersion to MNH2-MIL-101-Fe powder in step 1) is 100~150:0.1~0.3 (mL:g). Alternatively, the conditions for ultrasonic treatment in step (5) 1) are 500W ultrasonic treatment for 1.5~2 hours; Alternatively, the crosslinking agent in step (5) 3) is either glutaraldehyde or epichlorohydrin; Alternatively, in step (5) 3), the mass ratio of crosslinking agent to deionized water is 1:1; Alternatively, the soaking time in step (5) 3) is 5 hours.

8. The MNH2-MIL-101-Fe / PA-PAN composite membrane prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the MNH2-MIL-101-Fe / PA-PAN composite membrane as described in claim 8 in phosphorus resource recovery from phosphorus-containing wastewater.

10. The application according to claim 9, characterized in that: The characteristic pollutant of the phosphorus-containing wastewater is phosphorus, with a concentration of 2-3 mg / L.

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