An asymmetric flat sheet ultrafiltration membrane and a method for preparing the same

Abstract

The application discloses an asymmetric flat plate ultrafiltration membrane and a preparation method thereof. The asymmetric flat plate ultrafiltration membrane comprises an ultrafiltration separation layer and a heavy metal and micro-pollutant removal layer. The ultrafiltration separation layer is composed of a surface layer and a bottom layer. One outer surface of the bottom layer is close to the surface layer, and the other outer surface is connected with the heavy metal and micro-pollutant removal layer. The bottom layer and the heavy metal and micro-pollutant removal layer are combined through a chemical bond. The heavy metal and micro-pollutant removal layer exists in the bottom of the ultrafiltration membrane in a grafted manner, is more stable, and has a longer service life. Compared with the heavy metal and micro-pollutant removal layer existing in the surface and the membrane hole of the ultrafiltration membrane, when the heavy metal and micro-pollutant are adsorbed, the separation effect and the flow of the membrane itself are not affected. When the concentration of the heavy metal adsorbed Cd(NO3)2 is less than 5 ppb, the water volume of the membrane passing the standard solution can reach 5.7 L at most. When the concentration of the micro-pollutant adsorbed bisphenol A is less than 10 ppb, the water volume of the membrane passing the standard solution can reach 6.2 L at most.

Description

TECHNICAL FIELD

[0001] The present application relates to an asymmetric flat plate ultrafiltration membrane and a preparation method thereof. BACKGROUND

[0002] In recent years, the concept of healthy water has emerged. In low-hardness areas, ultrafiltration water purifiers can be used to retain minerals in water. However, the separation pore size of the ultrafiltration membrane, which is the main filter in the ultrafiltration water purifier, is 2-100 nm, which is much larger than the size of heavy metal ions and micro-pollutants. Therefore, the ultrafiltration membrane cannot remove heavy metal ions and micro-pollutants in water by size screening mechanism alone. Long-term drinking of water containing heavy metal ions and micro-pollutants will cause heavy metal and micro-pollutants to accumulate in human organs, which is harmful to the human body. At present, for the removal of heavy metal ions and micro-pollutants, membrane method, ion exchange, electrodialysis and activated carbon separation are generally used.

[0003] In recent years, in the field of drinking water, the most common method for removing heavy metals and micro-pollutants is to use activated carbon, reverse osmosis membrane or nanofiltration. Activated carbon mainly uses its own microporous adsorption to adsorb harmful substances, but it has a broad spectrum of adsorption, and the types of adsorbed substances are various, such as residual chlorine, humic acid, COD and other substances, so it is easy to reach adsorption saturation, and the removal effect is not good. Reverse osmosis removes heavy metals and micro-pollutants, but also removes beneficial mineral elements for the human body. Nanofiltration membrane has a certain effect on removing heavy metals and micro-pollutants, but cannot completely remove heavy metals in water. Other methods for removing heavy metals and micro-pollutants, such as ion exchange and electrodialysis, have the problems of poor removal effect and high cost.

[0004] Traditional ultrafiltration membranes have the advantages of low operating cost, retention of minerals in water, and objective treatment effect of viruses, high molecular organic matter, colloids and other pollutants, and have been widely used in practical engineering. However, based on the fact that the ultrafiltration membrane only uses size screening mechanism to remove heavy metal ions and micro-pollutants in water, the removal of these pollutants is particularly important in the process of wastewater advanced treatment. In order to solve this problem, new ultrafiltration membrane technology needs to be developed. SUMMARY

[0005] To solve the above technical problems, the purpose of the present application is to provide an asymmetric flat plate ultrafiltration membrane and a preparation method thereof. The heavy metal and micro-pollutant removal layer is introduced into the bottom layer of the ultrafiltration separation layer of the flat plate ultrafiltration membrane, which is more stable and has a longer service life. After adsorbing heavy metals and micro-pollutants, the separation effect and flow rate of the ultrafiltration membrane itself are not affected. The heavy metal and micro-pollutant removal layer is composed of β-cyclodextrin and amine substances, and the functions of removing heavy metals and micro-pollutants of the two are complementary.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] One of the technical solutions provided by the present application is an asymmetric flat ultrafiltration membrane, characterized in that the asymmetric flat ultrafiltration membrane comprises an ultrafiltration separation layer and a heavy metal and micro-pollutant removal layer, the ultrafiltration separation layer is composed of a surface layer and a bottom layer, one outer surface of the bottom layer is in close contact with the surface layer, and the other outer surface is connected with the heavy metal and micro-pollutant removal layer, and the bottom layer and the heavy metal and micro-pollutant removal layer are combined by a chemical bond. The asymmetric flat ultrafiltration membrane satisfies one or more of the following conditions:

[0008] a. The heavy metal and micro-pollutant removal layer and the ultrafiltration separation layer are connected by an amide bond; the heavy metal and micro-pollutant removal layer preferably contains an amino group, and the bottom layer in the ultrafiltration separation layer preferably contains a carboxyl group;

[0009] b. The thickness of the heavy metal and micro-pollutant removal layer is 50-1000 nm, for example, 100 nm, 300 nm or 600 nm;

[0010] c. The thickness of the ultrafiltration separation layer is 200-250 μm, for example, 100 μm, 150 μm or 200 μm;

[0011] d. The thickness of the surface layer in the ultrafiltration separation layer is 0.1-1.5 μm, for example, 1 μm;

[0012] e. The thickness of the bottom layer in the ultrafiltration separation layer is 50-250 μm, for example, 99 μm, 149.5 μm or 198.5 μm.

[0013] The asymmetric flat ultrafiltration membrane of the present application is a conventional ultrafiltration membrane in the field, and the membrane pore size is 1-100 nm.

[0014] The second technical solution provided by the present application is a method for preparing an asymmetric flat ultrafiltration membrane, which comprises the following steps: first, grafting an active group used to realize chemical bond combination to the bottom layer of the ultrafiltration separation layer, and then reacting with the heavy metal and micro-pollutant removal layer; the ultrafiltration separation layer is composed of a surface layer and a bottom layer, and one outer surface of the bottom layer is in close contact with the surface layer.

[0015] The grafting is performed by irradiation grafting method, preferably, the irradiation grafting method is to irradiate the bottom layer of the ultrafiltration separation layer upward under a UV lamp;

[0016] Further, the irradiation grafting satisfies one or more of the following conditions:

[0017] a. The power of the UV lamp is 20-200 W, for example, 50 W, 100 W or 180 W;

[0018] b. the main wavelength of the ultraviolet lamp is 290-400 nm, for example, 300 nm, 350 nm or 380 nm;

[0019] c. the distance between the ultraviolet lamp and the ultrafiltration separation layer is 5-20 cm, for example, 8 cm, 10 cm or 18 cm;

[0020] d. the time for the irradiation grafting is 5-30 min, for example, 15 min, 20 min or 25 min.

[0021] The active group is provided by a vinyl carboxylic acid substance;

[0022] And / or, the reaction includes the following steps, the ultrafiltration separation layer after grafting is reacted with a β-cyclodextrin aqueous solution and an amine substance aqueous solution in sequence, namely.

[0023] The operation of the reaction with the β-cyclodextrin aqueous solution meets one or more of the following conditions:

[0024] a. the concentration of β-cyclodextrin in the aqueous solution is 1-10 wt%, for example, 2 wt%, 4 wt% or 8 wt%;

[0025] b. the temperature of the reaction is 50-80℃, for example, 60℃, 70℃ or 80℃;

[0026] c. the time of the reaction is 5-12 h, for example, 6 h or 10 h.

[0027] The operation of the reaction with the amine substance aqueous solution meets one or more of the following conditions:

[0028] a. the amine substance is one or more of chitosan, polyethyleneimine, triethylenetetramine, tetraethylenetetramine and pentaethylenehexamine, preferably polyethyleneimine and / or chitosan;

[0029] b. the concentration of the amine substance in the aqueous solution is 1-10 wt%, for example, 2 wt%, 5 wt% or 9 wt%;

[0030] c. the temperature of the reaction is 60-90℃, for example, 70℃ or 90℃;

[0031] d. the time of the reaction is 10-24 h, for example, 15 h, 20 h or 24 h.

[0032] The method for preparing the asymmetric flat plate ultrafiltration membrane meets one or more of the following conditions:

[0033] a. the ultrafiltration separation layer is a polysulfone ultrafiltration membrane;

[0034] b. The vinyl carboxylic acid substance is one or more of acrylic acid, butenoic acid and pentenoic acid, preferably 2-butenoic acid or acrylic acid;

[0035] c. The solution concentration of the vinyl carboxylic acid substance is 2wt%-20wt%, for example 5wt%, 8wt% or 15wt%.

[0036] In the present application, the method for preparing the asymmetric flat plate ultrafiltration membrane further comprises cleaning the reacted ultrafiltration membrane and storing it in a 1wt%-3wt% sodium bisulfite solution, preferably a 3wt% solution, for standby use.

[0037] The third technical solution of the present application is an asymmetric flat plate ultrafiltration membrane prepared by the above-mentioned preparation method.

[0038] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0039] The reagents and raw materials used in the present application are commercially available.

[0040] The positive progress effect of the present application is that:

[0041] (1) The heavy metal and micro-pollutant removal layer exists in the ultrafiltration membrane bottom layer in a grafted manner, is more stable and has a longer service life; and compared to the heavy metal and micro-pollutant removal layer existing in the surface and pores of the ultrafiltration membrane, the separation effect and flow of the membrane itself are not affected after adsorbing heavy metals and micro-pollutants, and the flow of the membrane is basically unchanged after adsorbing heavy metals and micro-pollutants.

[0042] (2) The main function of β-cyclodextrin is to adsorb micro-pollutants, in addition, its cavity can also chelate heavy metals, and also has a certain heavy metal adsorption capacity; the main function of amine substances is to adsorb heavy metals, and since the amino group is easily protonated, it also has a certain removal capacity for negatively charged micro-pollutants, and the two complement each other, giving the membrane piece super strong heavy metal and micro-pollutant removal performance. When the concentration of the adsorbed Cd(NO3)2 is less than 5ppb, the water volume of the membrane piece passing the standard solution is highest and can reach 5.7L, and when the concentration of the adsorbed bisphenol A is less than 10ppb, the water volume of the membrane piece passing the standard solution is highest and can reach 6.2L. DETAILED DESCRIPTION

[0043] The present application will be further described by way of examples, but the present application is not limited to the examples. The experimental methods in the following examples are not specified, and are selected according to conventional methods and conditions, or according to the instructions of the goods.

[0044] Example 1

[0045] (1) 5wt% 2-butenoic acid solution was coated on the bottom layer of the polysulfone ultrafiltration separation layer, the thickness of the polysulfone ultrafiltration separation layer was 100 μm, and the thickness of the bottom layer of the polysulfone ultrafiltration separation layer was 99 μm;

[0046] (2) The bottom layer of the polysulfone ultrafiltration separation layer was placed upwards on the table surface directly below the ultraviolet lamp. A 100W ultraviolet lamp was turned on and irradiated for 20 min; the main wavelength of the ultraviolet lamp was 300 nm, and the distance between the ultraviolet lamp and the ultrafiltration separation layer was 8 cm.

[0047] (3) After the ultrafiltration separation layer was washed, it was placed in a 2wt% β-cyclodextrin (β-CD) aqueous solution, and reacted at 80°C for 6h;

[0048] (4) After the ultrafiltration membrane was washed, it was placed in a 2% polyethyleneimine aqueous solution, and reacted at 70°C for 20h, and the thickness of the heavy metal and micro-pollutant removal layer obtained was 100 nm;

[0049] (5) After the reaction was completed, the polysulfone ultrafiltration membrane was washed and stored in a 3wt% sodium bisulfite (NaHSO3) solution for standby.

[0050] (6) A flat plate ultrafiltration membrane with a diameter of 53 mm was placed in the test tool and pre-pressed at 0.2MPa for 30min, and the flow rate was measured to be 230LMH at 0.1MPa;

[0051] (6) A flat plate ultrafiltration membrane with a diameter of 53 mm was placed in the test tool and pre-pressed at 0.2MPa for 30min, and the flow rate was measured to be 230LMH at 0.1MPa;

[0052] (7) A flat plate nanofiltration membrane with a diameter of 53 mm was placed in the test tool and pre-pressed at 0.2MPa for 30min, and the flow rate was measured to be 230LMH at 0.1MPa;

[0053] Example 2

[0054] (1) 15wt% acrylic acid solution was coated on the bottom layer of the polysulfone ultrafiltration separation layer, the thickness of the polysulfone ultrafiltration separation layer was 150 μm, and the thickness of the bottom layer of the polysulfone ultrafiltration separation layer was 149.5 μm;

[0055] (2) Put the bottom layer of polysulfone ultrafiltration separation layer upside down on the table, directly below the ultraviolet lamp. Turn on the 180W ultraviolet lamp for 25 minutes; the main wavelength of the ultraviolet lamp is 350nm, and the distance between the ultraviolet lamp and the ultrafiltration separation layer is 10cm.

[0056] (3) After washing the ultrafiltration separation layer, put it into an 8wt% β-cyclodextrin (β-CD) aqueous solution, and react at 70°C for 10h;

[0057] (4) After washing the ultrafiltration membrane, put it into a 9wt% polyethyleneimine aqueous solution, and react at 90°C for 15h, and the thickness of the heavy metal and micro-pollutant removal layer obtained is 600nm;

[0058] (5) After the reaction is completed, the polysulfone ultrafiltration membrane is washed and stored in a 3wt% sodium bisulfite (NaHSO3) solution for standby.

[0059] (6) Take a flat plate ultrafiltration membrane with a diameter of 53mm and put it into the test tool, and pre-press it at 0.2MPa for 30min, and measure the flow rate at 0.1MPa to be 154LMH;

[0060] (6) Take a flat plate ultrafiltration membrane with a diameter of 53mm and put it into the test tool, and test its heavy metal adsorption performance, using a 25ppb cadmium nitrate (Cd(NO3)2) solution as a standard solution, and when the Cd(NO3)2 concentration in the solution passing through the membrane is greater than 5ppb, stop the test, and the final membrane passes through the standard solution The amount of water is 5.7L; After the heavy metal adsorption test is completed, the flow rate is measured at 0.1MPa to be 154LMH, and the flow rate does not change;

[0061] (7) Take a flat plate nanofiltration membrane with a diameter of 53mm and put it into the test tool, and test its micro-pollutant adsorption performance, using a 50ppb bisphenol A (BPA) solution as a standard solution, and when the BPA concentration in the solution passing through the membrane is greater than 10ppb, stop the test, and the final membrane passes through the standard solution The amount of water is 6.2L; After the micro-pollutant adsorption test is completed, the flow rate is measured at 0.1MPa to be 150LMH, and the flow rate changes little.

[0062] Example 3

[0063] (1) A 8% acrylic acid solution is coated onto the bottom layer of the polysulfone ultrafiltration separation layer, and the thickness of the polysulfone ultrafiltration separation layer is 200μm, and the thickness of the bottom layer of the polysulfone ultrafiltration separation layer is 198.5μm;

[0064] (2) Put the bottom layer of polysulfone ultrafiltration separation layer upside down on the table, directly below the ultraviolet lamp. Turn on the 50W ultraviolet lamp for 15 minutes; the main wavelength of the ultraviolet lamp is 380nm, and the distance between the ultraviolet lamp and the ultrafiltration separation layer is 18cm.

[0065] (3) After washing the ultrafiltration membrane, put it into a 4wt% β-cyclodextrin (β-CD) aqueous solution, react at 60°C for 10h;

[0066] (4) After washing the ultrafiltration membrane, put it into a 5wt% polyethyleneimine aqueous solution, react at 70°C for 24h, and the thickness of the heavy metal and micro-pollutant removal layer obtained is 300nm;

[0067] (5) After the reaction is completed, the polysulfone ultrafiltration membrane is washed and stored in a 3wt% sodium bisulfite (NaHSO3) solution for standby.

[0068] (6) Take a flat plate ultrafiltration membrane with a diameter of 53mm and put it into the test tool, pre-press for 30min under a pressure of 0.2MPa, and measure the flow rate under a pressure of 0.1MPa, which is 279LMH;

[0069] (6) Take a flat plate ultrafiltration membrane with a diameter of 53mm and put it into the test tool, and test its heavy metal adsorption performance, using a 25ppb cadmium nitrate (Cd(NO3)2) solution as a standard solution. When the concentration of Cd(NO3)2 in the solution that has passed through the membrane is greater than 5ppb, stop the test. The final water volume of the membrane that has passed through the standard solution is 3.5L. After the heavy metal adsorption test is completed, the flow rate under a pressure of 0.1MPa is 280LMH, and the flow rate changes little.

[0070] (7) Take a flat plate nanofiltration membrane with a diameter of 53mm and put it into the test tool, and test its micro-pollutant adsorption performance, using a 50ppb bisphenol A (BPA) solution as a standard solution. When the concentration of BPA in the solution that has passed through the membrane is greater than 10ppb, stop the test. The final water volume of the membrane that has passed through the standard solution is 3.7L. After the micro-pollutant adsorption test is completed, the flow rate under a pressure of 0.1MPa is 275LMH, and the flow rate changes little.

[0071] Comparative Example 1

[0072] (1) A 5wt% 2-butenoic acid solution is coated on the surface layer of the polysulfone ultrafiltration separation layer, the thickness of the polysulfone ultrafiltration separation layer is 100μm, and the thickness of the surface layer of the polysulfone ultrafiltration separation layer is 1μm;

[0073] (2) Put the surface layer of the polysulfone ultrafiltration separation layer upside down on the table, directly below the ultraviolet lamp. Turn on the 100W ultraviolet lamp for 20 minutes; the main wavelength of the ultraviolet lamp is 300nm, and the distance between the ultraviolet lamp and the ultrafiltration separation layer is 8cm.

[0074] (3) The ultrafiltration membrane was washed and placed in a 2 wt% aqueous solution of β-cyclodextrin (β-CD) at 80°C for 6 h;

[0075] (4) The ultrafiltration membrane was washed and placed in a 2% aqueous solution of polyethyleneimine at 70°C for 20 h. The thickness of the heavy metal and micro-pollutant removal layer was 100 nm;

[0076] (5) After the reaction was completed, the polysulfone ultrafiltration membrane was washed and stored in a 3 wt% sodium bisulfite (NaHSO3) solution for standby use.

[0077] (6) A flat plate ultrafiltration membrane with a diameter of 53 mm was placed in a test tool and pre-pressed at 0.2 MPa for 30 min. The flow rate was measured to be 230 LMH at 0.1 MPa;

[0078] (6) A flat plate ultrafiltration membrane with a diameter of 53 mm was placed in a test tool and tested for heavy metal adsorption performance. A 25 ppb cadmium nitrate (Cd(NO3)2) solution was used as a standard solution. When the Cd(NO3)2 concentration in the solution passing through the membrane was greater than 5 ppb, the test was stopped. The final membrane passed through the standard solution with a water volume of 3.9 L. After the heavy metal adsorption test was completed, the flow rate was measured to be 201 LMH at 0.1 MPa, and the flow rate decreased significantly;

[0079] (7) A flat plate nanofiltration membrane with a diameter of 53 mm was placed in a test tool and tested for micro-pollutant adsorption performance. A 50 ppb bisphenol A (BPA) solution was used as a standard solution. When the BPA concentration in the solution passing through the membrane was greater than 10 ppb, the test was stopped. The final membrane passed through the standard solution with a water volume of 4.3 L. After the micro-pollutant adsorption test was completed, the flow rate was measured to be 194 LMH at 0.1 MPa, and the flow rate decreased significantly.

Claims

1. A method for preparing an asymmetric flat-sheet ultrafiltration membrane, characterized in that, The process includes the following steps: first, grafting one of the active groups used to achieve chemical bonding onto the bottom layer of the ultrafiltration separation layer, and then reacting it with the heavy metal and micro-pollutant removal layer; the ultrafiltration separation layer consists of a surface layer and a bottom layer, with one outer surface of the bottom layer closely attached to the surface layer; The active group is provided by a vinyl carboxylic acid; The reaction includes the following steps: the grafted ultrafiltration separation layer is reacted sequentially with an aqueous solution of β-cyclodextrin and an aqueous solution of amine substances.

2. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The grafting was performed using the irradiation grafting method.

3. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 2, characterized in that, The irradiation grafting method involves irradiating the bottom layer of the ultrafiltration separation layer with the bottom layer facing upwards under an ultraviolet lamp.

4. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 3, characterized in that, The power of the ultraviolet lamp is 20~200W.

5. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 4, characterized in that, The power of the ultraviolet lamp is 50W, 100W or 180W.

6. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 3, characterized in that, The main wavelength of the ultraviolet lamp is 290~400nm.

7. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 6, characterized in that, The main wavelength of the ultraviolet lamp is 300nm, 350nm or 380nm.

8. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 3, characterized in that, The distance between the ultraviolet lamp and the ultrafiltration separation layer is 5~20cm.

9. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 8, characterized in that, The distance between the ultraviolet lamp and the ultrafiltration separation layer is 8cm, 10cm or 18cm.

10. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 3, characterized in that, The irradiation grafting time is 5-30 minutes.

11. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 10, characterized in that, The irradiation grafting time is 15 min, 20 min, or 25 min.

12. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The concentration of β-cyclodextrin in the aqueous solution is 1~10wt%.

13. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 12, characterized in that, The concentration of β-cyclodextrin in the aqueous solution is 2 wt%, 4 wt%, or 8 wt%.

14. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The reaction temperature with the β-cyclodextrin aqueous solution is 50~80℃.

15. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 14, characterized in that, The reaction temperature with the β-cyclodextrin aqueous solution is 60°C, 70°C, or 80°C.

16. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The reaction time with the β-cyclodextrin aqueous solution is 5-12 hours.

17. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 16, characterized in that, The reaction time with the β-cyclodextrin aqueous solution is 6 h or 10 h.

18. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The amine is one or more of chitosan, polyethyleneimine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

19. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 18, characterized in that, The amine is polyethyleneimine and / or chitosan.

20. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The concentration of amines in the aqueous solution is 1-10 wt%.

21. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 20, characterized in that, The concentration of amines in the aqueous solution is 2 wt%, 5 wt%, or 9 wt%.

22. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The reaction temperature with the aqueous solution of amines is 60~90℃.

23. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 22, characterized in that, The reaction temperature with the aqueous solution of the amine substance is 70°C or 90°C.

24. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The reaction time with the aqueous solution of amine substances is 10-24 hours.

25. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 24, characterized in that, The reaction time with the aqueous solution of the amine substance is 15h, 20h or 24h.

26. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The ultrafiltration separation layer is a polysulfone ultrafiltration membrane.

27. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The vinyl carboxylic acid is one or more of acrylic acid, butenoic acid, and pentenoic acid.

28. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 27, characterized in that, The vinyl carboxylic acid is 2-butenoic acid or acrylic acid.

29. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, The solution concentration of the vinyl carboxylic acid is 2wt%-20wt%.

30. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 29, characterized in that, The solution concentration of the vinyl carboxylic acid is 5 wt%, 8 wt%, or 15 wt%.

31. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 1, characterized in that, It also includes washing the ultrafiltration membrane after the reaction and storing it in 1wt%~3wt% sodium bisulfite for later use.

32. The method for preparing an asymmetric flat-sheet ultrafiltration membrane as described in claim 31, characterized in that, Store in a 3wt% solution for later use.

33. An asymmetric flat-sheet ultrafiltration membrane prepared by any one of claims 1-32.

34. The asymmetric flat-sheet ultrafiltration membrane as described in claim 33, characterized in that, The asymmetric flat-sheet ultrafiltration membrane includes an ultrafiltration separation layer and a heavy metal and micro-pollutant removal layer. The ultrafiltration separation layer consists of a surface layer and a bottom layer. One outer surface of the bottom layer is in close contact with the surface layer, and the other outer surface is connected to the heavy metal and micro-pollutant removal layer. The bottom layer and the heavy metal and micro-pollutant removal layer are chemically bonded together.

35. The asymmetric flat-sheet ultrafiltration membrane as described in claim 34, characterized in that, The heavy metals are connected to the micro-pollutant removal layer and the ultrafiltration separation layer via amide bonds.

36. The asymmetric flat-sheet ultrafiltration membrane as described in claim 35, characterized in that, The heavy metal and micro-pollutant removal layer contains amino groups.

37. The asymmetric flat-sheet ultrafiltration membrane as described in claim 35, characterized in that, The bottom layer of the ultrafiltration separation layer contains carboxyl groups.

38. The asymmetric flat-sheet ultrafiltration membrane as described in claim 34, characterized in that, The thickness of the heavy metal and micro-pollutant removal layer is 50~1000 nm.

39. The asymmetric flat-sheet ultrafiltration membrane as described in claim 38, characterized in that, The thickness of the heavy metal and micro-pollutant removal layer is 100nm, 300nm, or 600nm.

40. The asymmetric flat-sheet ultrafiltration membrane as described in claim 34, characterized in that, The thickness of the ultrafiltration separation layer is 200~250μm.

41. The asymmetric flat-sheet ultrafiltration membrane as described in claim 40, characterized in that, The thickness of the ultrafiltration separation layer is 100μm, 150μm or 200μm.

42. The asymmetric flat-sheet ultrafiltration membrane as described in claim 34, characterized in that, The thickness of the surface layer in the ultrafiltration separation layer is 0.1-1.5 μm.

43. The asymmetric flat-sheet ultrafiltration membrane as described in claim 42, characterized in that, The thickness of the surface layer in the ultrafiltration separation layer is 1 μm.

44. The asymmetric flat-sheet ultrafiltration membrane as described in claim 34, characterized in that, The thickness of the bottom layer in the ultrafiltration separation layer is 50-250 μm.

45. The asymmetric flat-sheet ultrafiltration membrane as described in claim 44, characterized in that, The thickness of the bottom layer in the ultrafiltration separation layer is 99 μm, 149.5 μm, or 198.5 μm.