Preparation method and application of pom-pei nanofiltration membrane

Abstract

The application discloses a preparation method and application of a POMs-PEI nanofiltration membrane and belongs to the nanofiltration membrane preparation and application field. 12 The preparation method of the nanofiltration membrane is as follows: step 1, performing first soaking treatment on a PAN membrane in a PMo 12 solution to obtain a POMs modified membrane; and step 2, performing second soaking treatment on the POMs modified membrane in a PEI solution and then performing third soaking treatment on the POMs modified membrane in a glutaraldehyde solution to obtain the POMs-PEI nanofiltration membrane. The application solves the problem of low dye and salt ion separation efficiency of traditional polymer membrane treatment industrial printing and dyeing wastewater, the prepared nanofiltration membrane has excellent dye and salt separation performance and chemical stability, the preparation process is simple, and the nanofiltration membrane is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane preparation and application, specifically relating to a method for preparing and applying a POMs-PEI nanofiltration membrane. Background Technology

[0002] According to incomplete statistics, my country's current annual dye production exceeds 700,000 tons, and the annual discharge of textile dyeing and printing wastewater reaches 10 billion tons. However, dye molecules in dyeing and printing wastewater typically possess stable aromatic structures, making them difficult to degrade and exhibiting poor biodegradability. Furthermore, high-chroma dye wastewater flowing into ecological watersheds reduces water transparency, severely impacting the photosynthetic processes of aquatic plants. In addition, long-term exposure to certain dyes may damage human organs, the digestive system, and the central nervous system, and may even lead to cancer. Therefore, removing dyes from dyeing and printing wastewater before discharge is imperative.

[0003] To date, experts and scholars both domestically and internationally have developed a variety of physical, chemical, and biological technologies for the treatment of dyeing and printing wastewater, mainly including membrane separation, sedimentation, adsorption, photocatalytic degradation, chemical flocculation, and aerobic and anaerobic biological treatment. Among these technologies, membrane separation technology has gradually become dominant due to its advantages such as simple operation, low energy consumption, no secondary pollutants, and high separation efficiency.

[0004] The key to membrane separation technology lies in selective permeation membranes. Nanofiltration (NF) membranes, with their unique pore size range (0.5-5.0 nm), can easily achieve efficient retention of dye molecules and partial permeation of inorganic salts, playing a vital role in the treatment of dyeing and printing wastewater. However, the performance of NF membranes is severely limited by membrane fouling and concentration polarization. In the process of dyeing and printing wastewater treatment, the adsorption and accumulation of dyes in the membrane pore structure, mainly caused by electrostatic interactions, leads to irreversible fouling of the membrane matrix, resulting in a sharp decrease in permeate flux and a decline in wastewater treatment efficiency. Therefore, to maintain the stability of NF membrane performance, it is necessary to increase the cleaning frequency, which can easily lead to membrane structure damage and shorten membrane lifespan. In addition, dyeing and printing wastewater usually contains a large amount of inorganic salts, while traditional nanofiltration membranes often have a high rejection rate for divalent ions. Therefore, when using traditional nanofiltration methods to treat dyeing and printing wastewater, dyes and salts are usually removed simultaneously, making dye recovery difficult and resulting in resource waste. Meanwhile, excessively high salt rejection will lead to concentration polarization at the membrane-wastewater interface, increasing local osmotic pressure and solution resistance, thereby reducing permeate flux and wastewater treatment efficiency. Therefore, there is an urgent need to develop a novel nanofiltration membrane that combines high dye rejection rate, high salt solution permeability (i.e., low salt ion rejection rate), and excellent chemical stability to achieve efficient separation of dyes and salts. Summary of the Invention

[0005] To address the problem of low separation efficiency of dyes and salt ions in traditional polymer membrane treatment of industrial dyeing and printing wastewater, a method for preparing a POMs-PEI nanofiltration membrane is proposed. Furthermore, this POMs-PEI nanofiltration membrane is used to initially achieve the separation of salts and the recovery of dye molecules in dyeing and printing wastewater.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a POM-PEI nanofiltration membrane includes the following steps: Step 1, preparing a POM-modified membrane: Pretreated PAN membrane is subjected to PMo... 12 Step 1: The POMs modified membrane is prepared by first soaking in an aqueous solution; Step 2: Prepare POMs-PEI nanofiltration membrane: The POMs modified membrane prepared in step 1 is cleaned, and then subjected to a second soaking in a PEI aqueous solution and a third soaking in a glutaraldehyde aqueous solution to obtain the POMs-PEI nanofiltration membrane.

[0008] Furthermore, the pretreatment described in step 1 involves immersing the PAN film in deionized water at room temperature for 12 hours.

[0009] Further, the PMo mentioned in step 1 12 The concentration of the aqueous solution is 10-100 g / L, the pH is 1.5-2.0, the temperature of the first soaking treatment is 45-85℃, and the time is 10 min.

[0010] Furthermore, in step 2, the molecular weight of PEI is 600 Da, the concentration of the PEI aqueous solution is 2 mg / mL, and the second soaking treatment time is 10 min.

[0011] Furthermore, the concentration of the glutaraldehyde aqueous solution in step 2 is 50%, and the temperature of the third soaking treatment is 50°C for 20 minutes.

[0012] Furthermore, in step 2, the POMs modified membrane after the second immersion treatment is cleaned and dried before the third immersion treatment is performed.

[0013] The POMs-PEI nanofiltration membrane obtained by the above preparation method.

[0014] The application of the above-mentioned POMs-PEI nanofiltration membrane in the treatment of dyeing and printing wastewater.

[0015] This invention, based on in-situ modification of PAN membranes with POMs, sequentially immerses the membrane in PEI solution and glutaraldehyde (GA) solution. Utilizing electrostatic adsorption between POMs and PEI and chemical cross-linking between PEI and GA, polymers are adsorbed and deposited on the membrane surface to prepare a nanofiltration membrane. This invention designs PMo... 12In-situ modification of PAN membrane reaction temperature to control PMo on membrane surface 12 The amount, and then utilize PMo 12 The charge-induced deposition of PEI on the membrane surface is promoted, and finally, GA is cross-linked with the deposited PEI to reduce the pore size. Published studies mainly utilize polymers such as dopamine or tannic acid to modify PAN membranes. This modification process leads to pore size reduction, and the pore size of the nanofiltration membrane obtained after co-deposition is further reduced, resulting in lower permeability. Simultaneously, due to the excessively small pore size, the selectivity of the nanofiltration membrane for dyes and salt ions needs further improvement. In comparison, this invention uses soluble PMo 12 Modifying the PAN membrane can maximize the preservation of the initial pore size. Simultaneously, through PMo... 12 It can optimize the deposition amount of PEI, thereby controlling the pore size of the membrane. This not only enables the nanofiltration membrane to exhibit higher permeability, but also allows for the full retention of large molecular dyes and the rapid permeation of small-sized salt ions by controllably optimizing the membrane pore size.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] (1) The present invention prepares nanofiltration membranes by three immersion treatments. The preparation process is simple, the resulting membranes are environmentally friendly and have stable performance, and are suitable for large-scale industrial production.

[0018] (2) PMo is introduced by in-situ modification on PAN film. 12 The formation of POMs-modified membranes facilitates the electrostatic adsorption deposition of PEI on the membrane surface to enhance the cross-linking effect, thereby further improving the separation performance of nanofiltration membranes.

[0019] (3) The nanofiltration membrane of the present invention has excellent dye-salt separation efficiency, can completely retain dye macromolecules, and allows more salt ions to permeate. Compared with the blank membrane, the dye-salt separation efficiency of the nanofiltration membrane prepared by the present invention can be improved by up to 7.6 times. Attached Figure Description

[0020] Figure 1 These are scanning electron microscope (SEM) images of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention.

[0021] Figure 2 These are atomic force microscopy (AFM) images of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention.

[0022] Figure 3 These are the Fourier Transform Infrared (FTIR) spectra of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention.

[0023] Figure 4This is a water contact angle (WCA) diagram of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention;

[0024] Figure 5 These are the X-ray photoelectron spectroscopy (XPS) spectra of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention;

[0025] Figure 6 This is a zeta potential diagram of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention;

[0026] Figure 7 This is a graph showing the test results of the permeation flux of the POMs-PEI nanofiltration membrane to a single inorganic salt solution in this invention;

[0027] Figure 8 This is a graph showing the test results of the retention rate of inorganic salts in a single inorganic salt solution by the POMs-PEI nanofiltration membrane in this invention;

[0028] Figure 9 This is a graph showing the test results of the separation performance of the POMs-PEI nanofiltration membrane in a single dye solution in this invention;

[0029] Figure 10 This is a graph showing the salt separation test results of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention.

[0031] Example 1

[0032] A POM-PEI nanofiltration membrane is prepared by the following steps:

[0033] Step 1: Preparation of POMs modified membrane: At room temperature, the PAN membrane was immersed in deionized water for 12 hours, and then PMo was used at 45°C. 12 Step 1: The POMs-modified membrane was prepared by first soaking in an aqueous solution for 10 minutes. Step 2: Preparation of POMs-PEI nanofiltration membrane: The POMs-modified membrane prepared in step 1 was washed and soaked in deionized water for 12 hours. Then, it was soaked in a 2 mg / mL PEI aqueous solution for 10 minutes to clean the membrane surface. Subsequently, it was soaked in a 50% GA aqueous solution at 50°C for 20 minutes to obtain the POMs-PEI nanofiltration membrane. The prepared membrane is designated as PAN-45P-PG membrane.

[0034] Example 2

[0035] Same as Example 1, except that the PAN film is coated with PMo. 12 The temperature for the first immersion treatment in the aqueous solution was 65°C. The prepared membrane was designated as PAN-65P-PG membrane.

[0036] Example 3

[0037] Same as Example 1, except that the PAN film is coated with PMo. 12 The temperature for the first immersion treatment in the aqueous solution was 85°C. The prepared membrane was designated as PAN-85P-PG membrane.

[0038] Comparative Example 1

[0039] The PAN membrane was soaked in deionized water for 12 hours, then soaked in a 2 mg / mL PEI aqueous solution for 10 minutes to clean the membrane surface. Subsequently, it was soaked in a 50% GA aqueous solution at 50°C for 20 minutes to obtain the PAN-PEI nanofiltration membrane. The prepared membrane is designated as the PAN-PG membrane.

[0040] The methods for determining various evaluation indicators of PAN blank film, PAN-PG film, PAN-45P-PG film, PAN-65P-PG film and PAN-85P-PG film in this invention are as follows:

[0041] (1) Surface roughness was measured by AFM, and the results are as follows: Figure 2 As shown.

[0042] (2) The WCA was measured using a water contact angle meter. A 3μL water droplet was placed on the membrane surface, and the angle formed between the water droplet and the membrane surface was measured after 20 seconds. The results are as follows: Figure 4 As shown.

[0043] (3) The separation performance of the membrane in a single inorganic salt solution was tested using the following method. The membrane was pre-pressurized for 30 minutes at a flow rate of 0.6 m / s under a pressure of 1.1 bar using deionized water. A 1 g / L Na₂SO₄ solution (or a NaCl solution, MgSO₄ solution, or MgCl₂ solution of the same concentration) was used as the feed solution. The permeation flux (J, L·m⁻¹) of the membrane to the single inorganic salt solution was tested under a pressure of 1 bar. -2 ·h -1 The retention rate (R, %) is calculated using the following formula:

[0044]

[0045]

[0046] Where V is the permeation volume (L) and S is the effective filtration area (m²). 2 ), Δt is the filtering time (h), σp The conductivity of the leachate (μS / cm, measured using a conductivity meter), σ f The conductivity of the feed liquid (μS / cm, measured using a conductivity meter) is shown below. Figure 7 , Figure 8 As shown.

[0047] (4) The membrane separation performance in a single dye solution was tested using the following method. The membrane was pre-pressurized for 30 minutes with deionized water at a pressure of 1.1 bar and a flow rate of 0.6 m / s. Using 0.1 g / L Congo red (CR) solution as the feed solution, the membrane permeate flux (J, L·m⁻¹) to the single dye solution was tested at 1 bar. -2 ·h -1 The retention rate (R, %) is calculated using the following formula:

[0048]

[0049]

[0050] Where V is the permeation volume (L) and S is the effective filtration area (m²). 2 ), Δt is the filtering time (h), C p The concentration of CR in the leachate (g / L, measured by a UV-Vis spectrophotometer at an absorbance of 496 nm), C f The concentration of CR in the feed solution (g / L, measured by a UV-Vis spectrophotometer at 496 nm absorbance). Test results are as follows... Figure 9 As shown.

[0051] (5) The present invention tests the salt separation effect of PAN blank membrane and POMs-PEI nanofiltration membrane. The test method is as follows: Deionized water is used to pre-press the membrane for 30 minutes at a flow rate of 0.6 m / s under a pressure of 1.1 bar. A mixed solution of 1 g / L Na2SO4 and 0.1 g / L CR is used as the feed liquid. Under a pressure of 1 bar, the membrane rejection rate of Na2SO4 (R1,%), the membrane rejection rate of CR (R2,%), and the separation factor α are tested. The calculation formula is as follows:

[0052]

[0053]

[0054]

[0055] Where, σ p and σ f The conductivity (μS / cm, measured using a conductivity meter) of the leachate and feed liquid, respectively, is shown in C.p and C f The concentration of CR in the leachate (g / L, determined by a UV-Vis spectrophotometer at 496 nm absorbance). Test results are as follows... Figure 10 As shown.

[0056] (6) The elements of the PAN blank membrane and the POMs-PEI nanofiltration membrane were analyzed by X-ray photoelectron spectroscopy, and the results are shown in Table 1.

[0057] Figure 1 These are scanning electron microscope (SEM) images of the PAN blank membrane and the POMs-PEI nanofiltration membrane used in this invention. Figure 1 In the image, (a), (b), (c), (d), and (e) are SEM images of the surfaces of the blank PAN film, PAN-PG film, PAN-45P-PG film, PAN-65P-PG film, and PAN-85P-PG film, respectively. Figure 1 As can be seen from (a) and (b), the pore size on the membrane surface is slightly reduced, indicating that the copolymer PEI-GA is deposited on the membrane surface. Figure 1 (be) It can be seen that particulate matter is deposited on the membrane surface, and with the increase of PMo 12 The increase in content with increasing concentration indicates the introduction of PMo into the membrane matrix. 12 It effectively promotes particulate matter deposition, thereby producing a pore-blocking effect and reducing the membrane pore size.

[0058] Figure 2 These are atomic force microscopy (AFM) images of the PAN blank membrane and the POMs-PEI nanofiltration membrane used in this invention. Figure 2 In the image, (a), (b), (c), (d), and (e) are the AFM images of the blank PAN film, PAN-PG film, PAN-45P-PG film, PAN-65P-PG film, and PAN-85P-PG film, respectively. Figure 2 As can be seen from (a) and (b), the surface roughness of the membrane gradually increases from 7.2 ± 1.4 nm for the blank PAN membrane to 10.1 ± 2.7 nm for the PAN-PG membrane, indicating that the introduction of PEI-GA can increase the surface roughness of the membrane. Figure 2 (be) It can be seen that the surface roughness of the membrane gradually increases from 10.1±2.7 nm for the PAN-PG membrane to 24.4±3.9 nm for the PAN-85P-PG membrane, indicating that the introduction of PMo 12 This can further improve the surface roughness.

[0059] Figure 3 These are the Fourier Transform Infrared (FTIR) spectra of the PAN blank membrane and the POMs-PEI nanofiltration membrane used in this invention. Figure 3It can be seen that the characteristic peaks of the PAN blank membrane and the POMs-PEI nanofiltration membrane are basically the same. Compared with the PAN blank membrane, the PAN-PG membrane shows a different peak at 1660 cm⁻¹. -1 The enhanced intensity of nearby peaks is due to the introduction of the copolymer PEI-GA into the film matrix, resulting in an increase in CN bonds. The introduction of PMo... 12 POMs-PEI nanofiltration membrane at 794 cm⁻¹ -1 952cm -1 and 1073cm -1 A new characteristic peak appears. 794cm -1 The characteristic peak at that location can be attributed to PMo. 12 The redshift of Mo-O due to coordination assembly with the nitrile groups of the PAN film. 952 cm⁻¹ -1 and 1073cm -1 The characteristic peak at that location can be attributed to PMo. 12 At 957cm -1 (v(Mo=O)) and 1057cm -1 The presence of a strong absorption peak in (PO) causes a shift in the characteristic peaks of the POMs-PEI nanofiltration membrane, indicating that PMo 12 Successfully introduced into the membrane. Meanwhile, with PMo... 12 With the increase of content, the POMs-PEI nanofiltration membrane at 1660 cm⁻¹ -1 The increasing intensity of the nearby peaks indicates that PMo 12 The introduction of [the substance] facilitated the deposition of PEI-GA copolymers on the film surface.

[0060] Figure 4 This is a water contact angle (WCA) diagram of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention. Figure 4 It can be seen that the WCA decreased from 64° in the blank PAN membrane to 44.6° in the PAN-PG membrane, indicating that the introduction of PEI-GA is beneficial to improving the hydrophilicity of the membrane surface. Combined with... Figure 2 Analysis suggests that introducing PEI-GA increases the membrane surface roughness, thereby increasing the contact area between the membrane and water molecules and improving hydrophilicity. Comparing PAN-PG and PAN-45P-PG membranes, the WCA (water absorption capacity) increases from 44.6° in the PAN-PG membrane to 56.7° in the PAN-45P-PG membrane. This is due to the introduction of a small amount of PMo (poly(ethylene glycol)) onto the membrane surface. 12 PMo 12 It coordinates with PEI, consuming some of the active sites of the hydrophilic groups in PEI. Comparing PAN-45P-PG and PAN-65P-PG membranes, the WCA decreases to 47.1°. This is due to PMo... 12 -Electrostatic adsorption exists between PEI and PMo 12The increased content leads to the adsorption of more hydrophilic PEI onto the membrane surface. Comparing PAN-65P-PG and PAN-85P-PG membranes, the WCA increases to 50.4°. This is due to the increase in PMo... 12 Further increases in PEI content lead to excessive PEI content on the membrane surface, resulting in particle aggregation and severe pore blockage. This, in turn, increases the mass transfer resistance of water diffusion into the membrane, thus reducing the membrane's hydrophilicity.

[0061] Figure 5 These are the X-ray photoelectron spectroscopy (XPS) spectra of the PAN blank membrane and the POMs-PEI nanofiltration membrane used in this invention. Figure 5 It can be seen that PAN-45P-PG, PAN-65P-PG, and PAN-85P-PG films all produce obvious Mo characteristic peaks, indicating that PMo 12 It was successfully introduced into the membrane and the content was relatively high.

[0062] Figure 6 This is a zeta potential diagram of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention. The zeta potential of the membrane was tested using 1 mM KCl as the electrolyte, measuring the charge characteristics of the membrane between pH 3 and 10. Figure 6 It can be seen that the PAN-PG membrane exhibits increased charge compared to the blank PAN membrane. This is due to the deposition of PEI-GA on the membrane surface, resulting in an increase in surface charge. With increasing pH, the electronegativity of the PAN-45P-PG and PAN-65P-PG membranes significantly increases. This can be attributed to the presence of PMo in the POMs-PEI nanofiltration membrane. 12 The increased content leads to a greater generation of negative charges on the membrane surface. However, with the increase of PMo... 12 With further increases in content, under the same pH conditions, the electronegativity of the PAN-85P-PG membrane is lower than that of the PAN-45P-PG and PAN-65P-PG membranes. This can be attributed to the aggregation of PEI-GA copolymer on the membrane surface, PMo 12 The number of exposure sites is reduced.

[0063] Figure 7 and 8 This is a graph showing the test results of the separation performance of the POMs-PEI nanofiltration membrane in a single inorganic salt solution in this invention. Figure 7 This is a graph showing the test results of the permeation flux of the POMs-PEI nanofiltration membrane to a single inorganic salt solution in this invention. Figure 7 It can be seen that, compared with PAN-PG membranes, the introduction of PMo 12 Subsequently, the permeation flux of the POMs-PEI nanofiltration membrane to different salt solutions increased with PMo. 12 The content decreases as it increases. Figure 8This is a graph showing the test results of the retention rate of the composite membrane in a single inorganic salt solution according to the present invention. Figure 8 It can be seen that nanofiltration membranes exhibit extremely low rejection rates (<2%) for different salt solutions. This phenomenon is caused by several factors. Firstly, combined with... Figure 1 Research on membrane pore structure and Figure 4 Analysis of the hydrophilicity of the membrane surface can infer the effect of PMo 12 Increased concentration leads to PEI-GA deposition on the membrane surface, causing pore blockage and hindering water molecule permeation, thus reducing permeation flux. Secondly, combined with... Figure 6 Analysis of the zeta potential on the membrane surface can infer the PMo content. 12 As the concentration increases, the electronegativity of the membrane surface increases. Due to the electrostatic repulsion, the resistance of negatively charged ions to passing through the membrane increases, which in turn slightly increases the rejection rate.

[0064] Figure 9 This is a graph showing the separation performance test results of the POMs-PEI nanofiltration membrane in a single dye solution according to the present invention. Figure 9 It can be seen that the water flux is 300.58±15.66 L·m for the PAN-PG membrane. -2 ·h -1 ·bar -1 The CR rejection rate of the POMs-PEI nanofiltration membrane decreased to 181.68±4.37 LMH / bar compared to the PAN-85P-PG membrane, while the CR rejection rate of the POMs-PEI nanofiltration membrane increased from 89.18±0.81% for the PAN-PG membrane to 99.54±0.04% for the PAN-85P-PG membrane.

[0065] Figure 10 This is a graph showing the salt separation test results of the PAN blank membrane and the POMs-PEI nanofiltration membrane in this invention. Figure 10 It can be seen that the water flux decreased from 212.4 LMH / bar for the blank PAN membrane to 136.7 LMH / bar for the PAN-85P-PG membrane, while the membrane's CR rejection rate increased from 87.40% for the blank PAN membrane to 98.45% for the PAN-85P-PG membrane, and its Na2SO4 rejection rate increased from 3.06% for the blank PAN membrane to 13.03% for the PAN-85P-PG membrane. Calculations showed that the separation factor α increased from 7.69 for the blank PAN membrane to 59.18 for the PAN-65P-PG membrane, indicating a more than 7-fold improvement in salt separation performance. With the increase in PMo... 12 With further increases in content, the efficiency of salt separation decreases slightly.

[0066] Table 1 shows the elemental contents of the blank PAN membrane and the POMs-PEI nanofiltration membrane. As can be seen from Table 1, the amount of Mo, the element in situ modified on the PAN membrane, increases with increasing reaction temperature. Analysis of the C / N ratio indicates a lower degree of crosslinking at 45℃, possibly due to the introduction of PMo onto the PAN membrane. 12 The occupation of some active sites of PEI affected the crosslinking effect; when the temperature was 65℃, the PMo on the membrane surface... 12 The increased amount of PMo, with its strong negative charge, promotes the deposition of positively charged PEI, which in turn facilitates further cross-linking on the nanofiltration membrane surface, ultimately improving the separation efficiency of the nanofiltration membrane; when the temperature is 85℃, a large amount of PMo is introduced onto the membrane surface. 12 This causes excessive PEI to be electrostatically adsorbed onto the membrane surface, leading to an excessive reduction in the pore size of the nanofiltration membrane after the crosslinking reaction.

[0067] Table 1. Element content of PAN blank membrane and POMs-PEI nanofiltration membrane in this invention.

[0068]

Claims

1. A method for preparing a POMs-PEI nanofiltration membrane, characterized in that, The method comprises the following steps: Step 1, Preparation of POMs modified membrane: The pretreated PAN membrane was subjected to the first soaking treatment in PMo 12 aqueous solution to obtain the POMs modified membrane; Step 2, preparation of POMs-PEI nanofiltration membrane: the POMs modified membrane prepared in step 1 is cleaned, and then subjected to second soaking treatment in PEI aqueous solution and third soaking treatment in glutaraldehyde aqueous solution, to obtain the POMs-PEI nanofiltration membrane.

2. The method for preparing POMs-PEI nanofiltration membranes according to claim 1, characterized in that, The pretreatment in step 1 is soaking treatment of the PAN membrane in deionized water at room temperature, and the treatment time is 12 h.

3. The method of claim 1, wherein the POMs-PEI nanofiltration membrane is prepared by the steps of: PMo described in step 1 12 The concentration of the aqueous solution is 10-100 g / L, the pH is 1.5-2.0, the temperature of the first soaking treatment is 45-85°C, and the time is 10 min.

4. The method of claim 1, wherein the POMs-PEI nanofiltration membrane is prepared by the steps of: In step 2, the molecular weight of PEI is 600 Da, the concentration of the PEI aqueous solution is 2 mg / mL, and the second soaking treatment time is 10 min.

5. The method of claim 1, wherein the POMs-PEI nanofiltration membrane is prepared by the steps of: In step 2, the concentration of the glutaraldehyde aqueous solution is 50%, the third soaking treatment temperature is 50°C, and the treatment time is 20 min.

6. The method of claim 1, wherein the POMs-PEI nanofiltration membrane is prepared by the steps of: In step 2, the POMs modified membrane after the second soaking treatment is cleaned and dried, and then subjected to the third soaking treatment.

7. The POMs-PEI nanofiltration membrane prepared by the method of any one of claims 1-6.

8. The application of the POMs-PEI nanofiltration membrane of claim 7 in treatment of printing and dyeing wastewater.

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