Modified filtration membranes, methods of making and using the same

Abstract

The application discloses a modified filter membrane and a preparation method and application thereof. The preparation method comprises the following steps: S1, contacting a polyacrylonitrile membrane containing carboxyl on the surface with a first solution to obtain filter membrane I; the solute of the first solution comprises cationic modified guar gum and chitosan quaternary ammonium salt; S21, contacting the filter membrane I with a second solution to obtain filter membrane II; the solute of the second solution comprises sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate; S31, carrying out a cross-linking reaction of the filter membrane II with a cross-linking agent to obtain the modified filter membrane. The prepared modified filter membrane has the advantages of good oxidation resistance and long service life, can reduce the pretreatment requirement of a water purification system, and is economical and convenient to use.

Description

TECHNICAL FIELD

[0001] The present application relates to a modified filter membrane and a preparation method and application thereof. BACKGROUND

[0002] The residual chlorine in tap water has a bacteriostatic effect, but since the selection of the separation layer of the nanofiltration membrane and the reverse osmosis membrane material in the current water purification treatment field is mostly polyamide, the material has poor tolerance to residual chlorine, and is easily oxidized by residual chlorine during the purification treatment process, thereby reducing the service life of the membrane.

[0003] In the prior art, in order to avoid the influence of oxidizing substances such as residual chlorine on the filter membrane, an additional activated carbon filter core is usually added at the front end of the membrane filter core to remove residual chlorine, so as to avoid the influence of residual chlorine on the membrane assembly. However, such a method removes residual chlorine in front of the nanofiltration or reverse osmosis membrane, which may cause bacteria to breed in the water in the membrane assembly, produce harmful disinfection by-products to human health, and even cause the membrane assembly to have a foul smell. Furthermore, such a configuration leads to frequent replacement of the core of the water purification equipment, increases the use cost, and makes the user experience poor. SUMMARY

[0004] In order to overcome the defects of poor oxidation resistance of the filter membrane in the prior art, easy oxidation by residual chlorine in tap water, and reduction of the service life, the present application provides a modified filter membrane and a preparation method and application thereof. The modified filter membrane has the advantages of good oxidation resistance and long service life, can reduce the requirements of the water purification system on pretreatment, and is economical and convenient to use.

[0005] The present application provides a preparation method of a modified filter membrane, which comprises the following mode one or mode two:

[0006] Mode one:

[0007] S1. A polyacrylonitrile membrane containing carboxyl on the surface is contacted with a first solution to obtain a filter membrane I; the solute of the first solution comprises cationic modified guar gum and chitosan quaternary ammonium salt;

[0008] S21. The filter membrane I is contacted with a second solution to obtain a filter membrane II; the solute of the second solution comprises sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate;

[0009] S31. The filter membrane II is subjected to a crosslinking reaction with a crosslinking agent to obtain the modified filter membrane;

[0010] Mode two:

[0011] S1. A polyacrylonitrile membrane containing carboxyl on the surface is contacted with a first solution to obtain a filter membrane I; the solute of the first solution comprises cationic modified guar gum and chitosan quaternary ammonium salt;

[0012] S22. The filter membrane I is subjected to a cross-linking reaction with a cross-linking agent to obtain a filter membrane I';

[0013] S32. The filter membrane I' is contacted with a second solution to obtain the modified filter membrane; the solute of the second solution comprises sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate.

[0014] In the present application, the "cation-modified guar gum and quaternary ammonium salt of chitosan" and the "sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate" are self-assembled on the surface of the polyacrylonitrile membrane by electrostatic interaction to construct a selective separation layer, and the electrostatic force is not easily affected by oxidants such as residual chlorine in water, thereby bringing good antioxidant effect.

[0015] In the present application, the polyacrylonitrile membrane can be commercially available or prepared by a conventional preparation method in the art, and the preparation method preferably comprises the following steps: preparing a casting solution into a membrane, and then performing a hydrolysis reaction; the casting solution comprises polyacrylonitrile and a solvent.

[0016] Preferably, the mass fraction of the polyacrylonitrile is 10%-30%, for example, 18%; and the solvent is preferably N-methyl pyrrolidone.

[0017] Preferably, the polyacrylonitrile is first subjected to a drying treatment; the temperature of the water bath is preferably 75°C; the time of the water bath is preferably 5-7h; the degassing is preferably performed at a temperature of 50°C; and the time of the degassing is preferably 12h.

[0018] Preferably, the method for preparing the casting solution into a membrane is a phase inversion method by immersion, and specifically can be as follows: the casting solution is sequentially subjected to blade coating, phase inversion and removal of the solvent;

[0019] Preferably, the process of blade coating is to adjust the micrometer on the blade coating device to accurately control the distance between the blade and the glass plate, so that the distance is maintained at 200μm, then the casting solution is poured near the blade, and the blade is uniformly slid to spread the casting solution on the glass plate.

[0020] Preferably, the process of phase inversion is to immerse the material obtained by blade coating into a coagulation bath after pre-evaporation, so that the membrane is peeled off from the glass plate and solidified; and the coagulation bath is preferably water.

[0021] Preferably, the process of removing the solvent is to immerse the membrane material obtained by solidification in distilled water; and the time of the immersion is preferably more than 24h, and the distilled water is replaced every 12h.

[0022] The hydrolysis reaction is preferably carried out by first treating the film with a base and then treating the film with an acid. After the above treatment, the cyan group on the surface of the film is converted into a carboxyl group, which is negatively charged in water.

[0023] The base treatment is preferably carried out in an aqueous solution, and the concentration of the base in the aqueous solution is preferably 10%. The base treatment is preferably carried out using sodium hydroxide, and the base treatment is preferably carried out for 30 min at a temperature of 40°C. After the base treatment, the surface of the film is yellow.

[0024] The acid treatment is preferably carried out in an aqueous solution, and the concentration of the acid in the aqueous solution is preferably 0.2 mol / L. The acid treatment is preferably carried out using hydrochloric acid, and the acid treatment is preferably carried out for 3 h at room temperature. After the acid treatment, the surface of the film is changed from yellow to milky white, and active groups such as carboxyl groups are generated on the surface of the film.

[0025] After the base treatment, the film is preferably washed with distilled water before the acid treatment. The purpose of the washing is to remove the residual base on the surface of the film.

[0026] After the acid treatment, the film is preferably washed with distilled water, and then the polyacrylonitrile film is placed in distilled water for use. If the film is not used for a long time, potassium bisulfite can be added to the distilled water to prevent bacteria from growing on the surface of the film.

[0027] In the present application, the cationic modified guar gum (CGG) is obtained by modifying natural polysaccharide guar gum by a method commonly used in the art, and is a quaternary ammonium salt, the chemical name of which is guar gum hydroxypropyl trimethyl ammonium chloride. The cationic modified guar gum is named polyquaternium-55 by the CTFA in the United States.

[0028] In the present application, the chitosan quaternary ammonium salt (HACC) is a chitosan senior derivative obtained by modifying natural polysaccharide chitosan by a method commonly used in the art, and is a chitosan hydroxypropyl trimethyl ammonium chloride.

[0029] Chitosan and guar gum are natural polysaccharides, and their production is huge. Modification of the two natural polysaccharides can obtain quaternary ammonium salt. CGG is a natural polyelectrolyte, which can ionize chloride ions in water, and itself has a positive charge on the chain. HACC is a product obtained by quaternizing the free amino group on the sugar residue of the chitosan molecular chain. Quaternization of chitosan improves the water solubility of chitosan. The two substances are positively charged in aqueous solution, and can be combined to the surface of the polyacrylonitrile membrane through electrostatic interaction to form a separation layer.

[0030] In the present application, the cross-linking agent can be a substance that can cause cross-linking reaction of CGG and HACC in the art, preferably glutaraldehyde and / or ethylene glycol. The cross-linking agent can cause cross-linking reaction of cationic modified guar gum and chitosan quaternary ammonium salt.

[0031] In step S1, the concentration of the first solution can be 3%-8%, for example 5%.

[0032] In step S1, the mass ratio of the cationic modified guar gum and the chitosan quaternary ammonium salt can be (0.5-3):1, preferably (1-2.5):1, for example 0.5:1, 2:1 or 3:1.

[0033] In step S1, the mass ratio of the polyacrylonitrile membrane and the solute of the first solution can be (2-4):1, for example 3:1.

[0034] In step S1, the operation of the contact can be soaking the polyacrylonitrile membrane in the first solution; or coating the first solution on the polyacrylonitrile membrane; in the process of contact, CGG and HACC are adsorbed on the carboxyl group of the surface of the polyacrylonitrile membrane by electrostatic action, and self-assembly is constructed to build the separation layer structure.

[0035] In step S1, the time of the contact can be 20-120min, preferably 30min-90min, for example 30min, 60min or 90min.

[0036] In step S1, the temperature of the system of the contact can be 20℃-40℃, for example 25℃.

[0037] In the present application, the filter membrane I is a polyacrylonitrile membrane with positive groups introduced on the surface.

[0038] In the present application, the filter membrane I' is the filter membrane I on which the cationic modified guar gum and chitosan quaternary ammonium salt have cross-linking reaction with the cross-linking agent.

[0039] In step S21 or step S32, the concentration of the second solution can be 0.5%-1.5%, for example 0.5%, 1.0% or 1.5%.

[0040] In step S21 or step S32, the operation of the contact can be soaking the filter membrane I or the filter membrane I' in the second solution; or coating the second solution on the filter membrane I or the filter membrane I'; in the process of contact, "sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate" as negative electrolyte is adsorbed on the positive groups on the surface of the filter membrane II or the filter membrane I' by electrostatic action, and self-assembly is constructed to build the separation layer structure.

[0041] The contacting time in step S21 or step S32 can be 20-120 min, preferably 30-90 min, for example 30 min, 60 min or 90 min.

[0042] The temperature of the system in the contacting in step S21 or step S32 can be 20-40℃, for example 25℃.

[0043] The mass ratio of the polyacrylonitrile film to the solute in step S21 or step S32 can be (1-3):1, for example 3:1.

[0044] In the present application, the filter membrane II is a filter membrane I with negative groups introduced on the surface thereof.

[0045] The mass ratio of the crosslinking agent to the polyacrylonitrile film in step S31 or step S22 can be (0.1-1):100, for example 0.1:100, 0.8:100, 0.9:100 or 1:100.

[0046] The crosslinking reaction in step S31 or step S22 is preferably carried out in an aqueous solution; the concentration of the crosslinking agent in the raw material system of the crosslinking reaction is preferably 2%-5%, for example 5%.

[0047] In some embodiments, the mass ratio of the solution of the crosslinking agent to the polyacrylonitrile film is 1:10.

[0048] The time of the crosslinking reaction in step S31 or step S22 can be 20-40 min, for example 30 min.

[0049] The temperature of the crosslinking reaction in step S31 or step S22 can be 20-40℃, for example 25℃.

[0050] The present application also provides a modified filter membrane prepared by the preparation method as described above.

[0051] The present application also provides a modified filter membrane, which comprises a polyacrylonitrile base film and a selective separation layer; the polyacrylonitrile base film and the selective separation layer are combined by electrostatic interaction; wherein the surface of the polyacrylonitrile base film contains carboxyl groups; the selective separation layer is combined by the "cationic modified guar gum and quaternary ammonium salt of chitosan" and "sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate" through electrostatic interaction.

[0052] The present application also provides the use of the modified filter membrane as described above in the field of water treatment.

[0053] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0054] The reagents and raw materials used in the present application are commercially available.

[0055] The positive progress effect of the present application is that:

[0056] The present application constructs a selective separation layer on the surface of the polyacrylonitrile membrane by electrostatic layer-by-layer self-assembly, so that the modified filter membrane has good overall oxidation resistance, can withstand the influence of higher concentration of residual chlorine without losing the calcium and magnesium ion removal effect, and has a magnesium sulfate removal rate of 98.2% after passing 8000L of water, a flow rate of 1.38L / min, and the magnesium sulfate removal rate is equivalent to the effect when the flow rate and water passing amount are zero. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 Effect test device schematic diagram of the modified filter membrane prepared in Examples 1-13 and Comparative Examples 1-3 of the present application (1-nitrogen steel cylinder, 2-buffer tank, 3-nanofiltration cup, 4-magnetic stirrer, 5-liquid inlet, 6-modified filter membrane). DETAILED DESCRIPTION

[0058] The present application will be further described by way of examples, but the present application is not limited in the scope of the examples. The experimental methods in the following examples without specific conditions are selected according to conventional methods and conditions, or according to the product instructions.

[0059] The polyacrylonitrile used in the present application is purchased from Qilu Chemical Industry Co., Ltd., and has a viscosity average molecular weight of 5200;

[0060] The cationic modified guar gum used in the present application is purchased from Araldin Reagent (Shanghai) Co., Ltd.

[0061] The chitosan quaternary ammonium salt used in the present application is purchased from Araldin Reagent (Shanghai) Co., Ltd.

[0062] Example 1

[0063] (1) Stir the polyacrylonitrile in a 75°C water bath for 6h to dissolve it in N-methyl pyrrolidone, then de-bubble treat at 50°C for 12h to obtain a casting solution; then adjust the micrometer on the film casting device to accurately control the distance between the doctor blade and the glass plate, so that the distance is kept at 200μm, then pour the casting solution near the doctor blade, slide the doctor blade at a constant speed to spread the casting solution on the glass plate, then pre-evaporate for 30s, immerse in water to solidify the film and separate it from the glass plate, wash the solidified film with distilled water, then place it in distilled water for at least 24h, change the water every 12h during the soaking process to completely remove the solvent NMP from the film; then place the obtained film in a 10% sodium hydroxide solution at 40°C for 30min, at this time the surface of the PAN turns yellow, after multiple washings, treat it with a 0.2mol / L hydrochloric acid solution at room temperature for 3h to produce active groups such as carboxyl groups on the surface of the PAN, at this time the surface of the PAN turns milky white, then wash it with distilled water and place it in distilled water for use;

[0064] (2) Soak the PAN in the CGG / HACC solution for a certain period of time to obtain filter membrane I;

[0065] (3) Soak the filter membrane I obtained in step (2) in a sodium dodecyl sulfonate solution for a certain period of time to obtain filter membrane II;

[0066] (4) Crosslink the filter membrane II in a glutaraldehyde solution, after a period of time, wash away the unreacted glutaraldehyde with distilled water to obtain a modified filter membrane.

[0067] The amount of the substances and the process conditions of Examples 1-13 and Comparative Examples 1-3 are shown in Tables 1 and 2, and the conditions of other examples and comparative examples not listed are the same as those of Example 1.

[0068] Example 14

[0069] (1) Polyacrylonitrile is dissolved in N-methyl pyrrolidone by stirring for 6 h in a water bath at 75°C, and then deaerated at 50°C for 12 h to obtain a casting solution. The distance between the doctor blade and the glass plate is accurately controlled to 200 μm by adjusting the micrometer on the film casting device, and then the casting solution is poured near the doctor blade, and the doctor blade is slid at a uniform speed to spread the casting solution on the glass plate. After pre-evaporation for 30 s, the film is immersed in water to solidify and separate from the glass plate. The solidified film is washed with distilled water, and then immersed in distilled water for at least 24 h. The water is changed every 12 h during the immersion to completely remove the solvent NMP from the film. The obtained film is treated in a 10% sodium hydroxide solution at 40°C for 30 min, and the surface of the PAN turns yellow. After washing several times, the PAN is treated with a 0.2 mol / L hydrochloric acid solution at room temperature for 3 h to produce active groups such as carboxyl groups on the surface of the PAN. The surface of the PAN turns milky white. After washing with distilled water, the PAN is ready for use.

[0070] (2) The PAN is immersed in a CGG / HACC solution for a certain period of time to obtain a filter membrane I;

[0071] (3) The filter membrane I is crosslinked in a glutaraldehyde solution, and after a period of time, the unreacted glutaraldehyde is washed away with distilled water to obtain a filter membrane I';

[0072] (4) The filter membrane I' obtained in step (3) is immersed in a sodium dodecyl sulfonate solution for a certain period of time to obtain a modified filter membrane.

[0073] The specific amounts of substances and process parameters are shown in Tables 1 and 2.

[0074] Table 1

[0075]

[0076] Table 2

[0077]

[0078] Effect Examples

[0079] 1. Magnesium ion removal rate

[0080] A certain area of the modified filter membranes obtained in Examples 1-13 and Comparative Examples 1-3 is fixed in a nanofiltration testing device, as shown in Figure 1 , a certain concentration of magnesium sulfate solution is configured, and the TDS value (denoted as TDS0) is tested. The nanofiltration membrane is compacted with a solvent for 45 min at room temperature and 0.5 MPa (N2), and the TDS of the solution passing through the membrane (denoted as TDS1) is tested. Before each test, the solvent flow is substantially stabilized before the test is performed.

[0081] Magnesium ion removal rate = 1 - (TDS1 / TDS0)

[0082] 2. Membrane flux

[0083] A certain area of ​​the modified filter membranes prepared in Examples 1-13 and Comparative Examples 1-3 was fixed in a nanofiltration testing device, such as... Figure 1 As shown, the nanofiltration membrane was compacted with solvent for 45 min at room temperature and 0.5 MPa (N2). The mass m of water passing through the membrane was measured, and the volume V was calculated. Each test was conducted after the solvent flow rate had stabilized. That is, the volume V of solvent permeating the nanofiltration membrane was measured over a certain time t while maintaining a constant pressure. The formulas for calculating the flux F and permeation flux P of the modified filter membrane are:

[0084]

[0085]

[0086] Where: ΔP is the operating pressure, in bar;

[0087] V is the volume of solvent dropped out within time t, in L;

[0088] A represents the effective area of ​​the membrane module, in meters (m²). 2 ;

[0089] t represents the sampling time, in hours (h).

[0090] The test results for the above effects are shown in Table 3.

[0091] Table 3

[0092]

[0093]

[0094] As can be seen from the data in Table 3, the modified filter membrane prepared by this invention, when used as a membrane module, can achieve a flux of 6 L / m³. 2 •h, with an optimal flux of 7.6 L / m 2 • h or more; the removal rate of magnesium sulfate reaches more than 73%, and even more than 92%.

[0095] Comparative Example 1-2 and Example 1 are different in that only one of CGG and HACC is used in the comparative example, and the flux of the membrane module made of the modified filter membrane is only 6.6 or 6.8, which is reduced by more than 17% compared with Example 1, and the removal rate of magnesium sulfate is also reduced by more than 15% compared with Example 1. It can be seen that CGG and HACC must be combined, and the carboxyl groups on PAN are combined by electrostatic force, and then other characteristics are combined to achieve the good flux and the efficiency of the removal rate of magnesium sulfate of the present application. This may be because CGG and HACC are cross-linked under the action of the cross-linking agent to form an interpenetrating polymer network structure, and the structure of the membrane is enhanced by intertangling between the polymer networks, so the performance of the membrane is better when the two are used together.

[0096] Comparative Example 3 and Example 1 are different in that sodium dodecyl sulfonate is replaced by sodium pentadecyl sulfonate. Although a flux comparable to the example can be obtained, the removal effect on magnesium sulfate is poor, and the measured removal rate of magnesium sulfate is only 58%, which is reduced by 26% compared with Example 1. This may be because the molecular chain of sodium pentadecyl sulfonate is long, the proportion of the charged functional group is low, the electrostatic binding force is insufficient, and it is easy to separate during the use of the membrane.

[0097] Examples 1-9 and Examples 12-13 show the effect of the time for treating PAN membrane with CGG / HACC solution and the time for treating filter membrane I with sodium dodecyl sulfonate solution. It can be seen that the longer the treatment time is, the better the effect is not.

[0098] Examples 10-11 and Example 1 show the effect of the mass ratio of CGG and HACC. When the proportion of CGG increases, the flux and the removal rate of magnesium sulfate of the modified filter membrane first increase and then decrease, so a suitable proportion needs to be selected to obtain good results.

[0099] Table 4

[0100] Residual chlorine concentration (ppm) Membrane module flow rate (L / min) Magnesium sulfate removal rate (%) Water permeation amount (L) 2 1.42 98.5 0 2 1.40 98.4 2000 2 1.40 98.6 4000 2 1.39 98.4 6000 2 1.38. 98.2 8000

[0101] As can be seen from Table 4, the membrane module can withstand the influence of 2 ppm residual chlorine concentration, and the flux and the removal rate of sulfate do not change much after passing 8000 L of water. The residual chlorine concentration in tap water is usually 0.2-0.4 ppm, which is lower than the test concentration of the present application. It can be seen that the modified filter membrane of the present application has good oxidation resistance when applied to water treatment.

Claims

1. A method for preparing a modified filter membrane, characterized by, It comprises the following mode one or mode two: Mode one: S1. Contact the polyacrylonitrile membrane containing carboxyl on the surface with a first solution to obtain filter membrane I; the solute of the first solution comprises cationic modified guar gum and chitosan quaternary ammonium salt; S21. Contact the filter membrane I with a second solution to obtain filter membrane II; The solute of the second solution comprises sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate; S31. Mix the filter membrane II with a crosslinking agent to occur crosslinking reaction to obtain the modified filter membrane; Mode two: S1. Contact the polyacrylonitrile membrane containing carboxyl on the surface with a first solution to obtain filter membrane I; the solute of the first solution comprises cationic modified guar gum and chitosan quaternary ammonium salt; S22. Mix the filter membrane I with a crosslinking agent to occur crosslinking reaction to obtain filter membrane I'; S32. Contact the filter membrane I' with a second solution to obtain the modified filter membrane; The solute of the second solution comprises sodium dodecyl sulfonate and / or sodium dodecyl benzene sulfonate.

2. The method for preparing a modified filter membrane according to claim 1, wherein In step S1, the concentration of the first solution is 3%-8%; And / or, in step S1, the mass ratio of the cationic modified guar gum and the chitosan quaternary ammonium salt is (0.5-3):1; And / or, in step S1, the mass ratio of the polyacrylonitrile membrane and the solute of the first solution is (2-4):

1.

3. The method for preparing a modified filter membrane according to claim 2, wherein In step S1, the concentration of the first solution is 5%; And / or, in step S1, the mass ratio of the cationic modified guar gum and the chitosan quaternary ammonium salt is (1-2.5):1; And / or, in step S1, the mass ratio of the polyacrylonitrile membrane and the solute of the first solution is 3:

1.

4. The method for preparing a modified filter membrane according to claim 3, wherein In step S1, the mass ratio of the cationic modified guar gum and the chitosan quaternary ammonium salt is 2:

1.

5. The method for preparing the modified filter membrane as described in claim 1, characterized in that, In step S21 or step S32, the concentration of the second solution is 0.5%-1.5%; And / or, in step S21 or step S32, the mass ratio of the polyacrylonitrile membrane and the solute is (1-3):1; And / or, in step S31 or step S22, the mass ratio of the crosslinking agent and the polyacrylonitrile membrane is (0.1-1):

100.

6. The method for preparing a modified filter membrane according to claim 5, wherein In step S21 or step S32, the concentration of the second solution is 0.5%, 1.0% or 1.5%; And / or, in step S21 or step S32, the mass ratio of the polyacrylonitrile membrane and the solute is 3:1; And / or, in step S31 or step S22, the mass ratio of the crosslinking agent and the polyacrylonitrile membrane is 0.1:100, 0.8:100, 0.9:100 or 1:

100.

7. The method for preparing the modified filter membrane as described in claim 1, characterized in that, In step S1, the contacting time is 20-120min; And / or, in step S1, the temperature of the contacting system is 20℃-40℃; And / or, in step S1, the contacting operation is to immerse the polyacrylonitrile membrane in the first solution; or, to coat the first solution on the polyacrylonitrile membrane; And / or, in step S21 or step S32, the contacting time is 20-120min; And / or, in step S21 or step S32, the temperature of the system in contact is 20-40℃; And / or, in step S21 or step S32, the operation of the contact is to immerse the filter membrane I in step S21 or the filter membrane I' in step S32 in the second solution; or, to coat the second solution on the filter membrane I or the filter membrane I'.

8. The method for preparing a modified filter membrane according to claim 7, wherein In step S1, the time of the contact is 30-90min; And / or, in step S1, the temperature of the system in contact is 25℃; And / or, in step S21 or step S32, the time of the contact is 30-90min; And / or, in step S21 or step S32, the temperature of the system in contact is 25℃.

9. The method for preparing a modified filter membrane according to claim 8, wherein In step S1, the time of the contact is 30min, 60min or 90min; And / or, in step S21 or step S32, the time of the contact is 30min, 60min or 90min.

10. The method for preparing the modified filter membrane as described in claim 1, characterized in that, In step S31 or step S22, the cross-linking reaction is carried out in an aqueous solution; And / or, the cross-linking agent is glutaraldehyde and / or ethylene glycol; And / or, in step S31 or step S22, the time of the cross-linking reaction is 20-40min; And / or, in step S31 or step S22, the temperature of the cross-linking reaction is 20-40℃.

11. The method for preparing the modified filter membrane as described in claim 1, characterized in that, In step S31 or step S22, the cross-linking reaction is carried out in an aqueous solution; in the raw material system of the cross-linking reaction, the concentration of the cross-linking agent is 2-5%; And / or, in step S31 or step S22, the time of the cross-linking reaction is 30min; and / or, in step S31 or step S22, the temperature of the cross-linking reaction is 25℃.

12. The method for preparing the modified filter membrane as described in claim 11, characterized in that, The concentration of the cross-linking agent is 5%.

13. The method for preparing the modified filter membrane as described in claim 1, characterized in that, The preparation method of the polyacrylonitrile membrane with carboxyl on the surface comprises the following steps: preparing a casting solution into a membrane, and then carrying out a hydrolysis reaction; the casting solution comprises polyacrylonitrile and a solvent.

14. The method for preparing the modified filter membrane as described in claim 13, characterized in that, The mass fraction of the polyacrylonitrile is 10-30%; And / or, the solvent is N-methyl pyrrolidone; And / or, the preparation method of the casting solution is to stir the polyacrylonitrile under water bath conditions, so that it is dissolved in the solvent, and then to carry out defoaming treatment; And / or, the method of preparing the casting solution into a membrane is to make the casting solution pass through a doctor blade, a phase inversion and a solvent removal in sequence; And / or, the step of the hydrolysis reaction is to carry out alkali treatment first, and then acid treatment.

15. The method for preparing the modified filter membrane as described in claim 14, characterized in that, The mass fraction of the polyacrylonitrile is 18%; And / or, the polyacrylonitrile is subjected to drying treatment first; And / or, the temperature of the water bath is 75℃; And / or, the time of the water bath is 5-7h; And / or, the defoaming is carried out at 50℃; And / or, the time of the defoaming is 12h.

16. The method for preparing a modified filter membrane according to claim 14 or 15, wherein The process of the doctor blade is to adjust a micrometer on the doctor blade device to control the distance between the doctor blade and the glass plate to be kept at 200μm, then the casting solution is poured near the doctor blade, the doctor blade is slid at a uniform speed to spread the casting solution on the glass plate, and the process is completed. and / or, the phase inversion process is that the material obtained by the blade coating is pre-evaporated and then immersed in a coagulation bath, so that the film is solidified and peeled off from the glass plate; and / or, the solvent removal process is that the solidified film material is immersed in distilled water; and / or, the alkali treatment is carried out in an aqueous solution; and / or, the acid treatment is carried out in an aqueous solution; and / or, after the alkali treatment, distilled water is used for washing; and / or, after the acid treatment, distilled water is used for washing.

17. The method for preparing the modified filter membrane as described in claim 16, characterized in that, the phase inversion process is that the material obtained by the blade coating is pre-evaporated and then immersed in a coagulation bath, so that the film is solidified and peeled off from the glass plate, and the coagulation bath is water; and / or, the solvent removal process is that the solidified film material is immersed in distilled water, and the immersion time is more than 24 h, and the distilled water is replaced every 12 h; and / or, the alkali treatment is carried out in an aqueous solution, and the concentration of the alkali in the aqueous solution is 10%; and / or, the alkali treatment is carried out in an aqueous solution, and the alkali treatment uses sodium hydroxide; and / or, the alkali treatment is carried out in an aqueous solution, and the time of the alkali treatment is 30 min; and / or, the alkali treatment is carried out in an aqueous solution, and the temperature of the alkali treatment is 40℃; and / or, the acid treatment is carried out in an aqueous solution, and the concentration of the acid in the aqueous solution is 0.2 mol / L; and / or, the acid treatment is carried out in an aqueous solution, and the acid treatment uses hydrochloric acid; and / or, the acid treatment is carried out in an aqueous solution, and the time of the acid treatment is 3 h; and / or, the acid treatment is carried out in an aqueous solution, and the temperature of the acid treatment is 20-40℃.

18. The method for preparing the modified filter membrane as described in claim 17, characterized in that, the temperature of the acid treatment is 25℃.

19. A modified filtration membrane, characterized by, which is prepared by the preparation method as claimed in any one of claims 1-18.

20. Use of the modified filter membrane as claimed in claim 19 in the field of water treatment.

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