Amino ionic liquid grafted polyamide thin layer composite nanofiltration membranes and methods of making the same

Abstract

The application discloses an amino ionic liquid grafted polyamide thin layer composite nanofiltration membrane and a preparation method thereof. The preparation method comprises the following steps: (1) performing an interfacial polymerization reaction on the surface of a base film by using an aqueous phase solution and an oil phase solution to form a polyamide functional skin layer on the surface of the base film; and (2) rapidly coating an amino ionic liquid organic solution on the surface of the polyamide functional skin layer to graft the amino ionic liquid on the polyamide functional skin layer, and then removing the excessive amino ionic liquid organic solution, and washing, solidifying and drying to obtain the amino ionic liquid grafted polyamide thin layer composite nanofiltration membrane. The post-grafting reaction is performed in a water-free environment, so that the acyl chloride groups on the surface of the polyamide skin layer after the interfacial polymerization are prevented from being hydrolyzed by contacting with water, the ionic liquid grafting rate is improved, the charge regulation of the polyamide skin layer is improved, and the prepared polyamide thin layer composite nanofiltration membrane has super strong antibacterial property, high rejection performance for divalent anions and cations and high water flux.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation technology, and particularly relates to an amino ionic liquid grafted polyamide thin layer composite nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] Currently, the content of available fresh water resources on the earth is less, and with the development of industry, water resource shortage is still an important problem faced by human beings at present, so advanced water treatment technology is needed to alleviate the water resource shortage problem faced by human beings. Membrane separation technology is widely applied in the fields of seawater desalination, hard water softening, brackish water purification and sewage treatment due to high efficiency, low energy consumption and simple operation. Separation membrane is the core component of membrane separation technology, and the separation membrane can be divided into microfiltration membrane (10 4 ~ 50 nm), ultrafiltration membrane (50 ~ 2 nm), nanofiltration membrane (2 ~ 0.5 nm) and reverse osmosis membrane (below 0.5 nm) according to the pore size.

[0003] Nanofiltration membrane is a new type of membrane separation material, which originated in the 1980s, and is a new type of separation membrane after ultrafiltration membrane and reverse osmosis membrane. It has been widely and deeply studied due to small permeation resistance, low operation energy consumption, excellent separation performance and effective interception of divalent salt ions and most of organic matters in water. At present, the thin layer composite nanofiltration membrane composed of a porous substrate membrane and an ultra-thin polyamide separation layer has become a research hotspot due to wide selection range of substrate materials, easy accurate control of separation layer structure and properties.

[0004] At present, the interfacial polymerization method has become the most commonly used method for preparing polyamide skin layer due to simple operation process, mild reaction conditions and high synthesis efficiency. The interfacial polymerization method adopts two kinds of monomers with high reactivity to occur condensation polymerization to generate a polymer film at the interface of two incompatible phases. The water phase monomer is a polyamine such as piperazine, and the oil phase monomer is a polyacyl chloride, usually an aromatic acyl chloride. With the increasing popularization of industrial application of polyamide thin layer composite nanofiltration membrane, it is found that the polyamide skin layer still faces many challenges. First, the polyamide skin layer surface has unreacted acyl chloride groups after interfacial polymerization, which is easy to hydrolyze in the washing and drying process. Therefore, the polyamide skin layer is usually negatively charged, the interception of divalent anions is high, but the interception of divalent cations is generally low. The second key problem is that the surface properties and functionality are single, which restricts the high performance and multifunctionalization. The grafting modification of the polyamide skin layer after the unreacted acyl chloride groups after the interfacial polymerization can adjust the charge of the polyamide skin layer, and new functional groups can be grafted through the second reaction to endow the nanofiltration membrane with new functions.

[0005] Ionic liquids (ILs) are a class of liquid salts composed of organic cations and inorganic or organic anions, with a melting point generally below 100℃. Ionic liquids have the advantages of not being volatile and stable in properties. At the same time, the organic cations and anions of ionic liquids can be designed to have amino groups that can react with acyl chloride. By using the reactive ionic liquid as a grafting molecule and reacting with the residual acyl chloride groups after interfacial polymerization, the ionic liquid is grafted on the surface of the polyamide separation layer through an amide bond. On the one hand, by reacting the ionic liquid with the amino groups on the polyamide skin layer, the residual acyl chloride groups react with the amino ionic liquid, reducing the degree of hydrolysis of acyl chloride, thereby regulating the charge property of the polyamide skin layer. On the other hand, the charge property of the ionic liquid itself can also adjust the charge property of the polyamide skin layer. At the same time, the grafted ionic liquid can endow the polyamide skin layer with new functionality, making the polyamide composite membrane have more application possibilities. For example, the bonding of ionic liquid can regulate the thickness, wettability and roughness of the polyamide skin layer, and different thickness, charge-adjustable and antibacterial polyamide active layers can be prepared. However, the post-grafting solution used in the prior art is an ionic liquid aqueous solution. The presence of water causes a large amount of hydrolysis of the acyl chloride on the surface of the polyamide, resulting in a sharp decrease in the reaction sites with the functional ionic liquid, low grafting efficiency, and even grafting failure.

[0006] A related patent (CN115518532A) reports a method of post-grafting a polyamide separation layer with an ionic liquid aqueous solution. However, the aqueous solution easily causes the hydrolysis of acyl chloride in water, and the carboxylic acid groups generated after hydrolysis do not react with the amino groups of the ionic liquid. On the one hand, this results in low grafting efficiency of the amino ionic liquid. On the other hand, the carboxylic acid groups after hydrolysis make the membrane surface exhibit negative charge, limiting the regulation range of the charge property of the polyamide skin layer.

[0007] Among the many reports currently available, the use of ionic liquid post-grafting of the polyamide skin layer in a water-free environment to prepare a polyamide thin-layer composite nanofiltration membrane is still a blank in the technical field, and has important research value and application prospect. SUMMARY

[0008] The present application provides a kind of amino ionic liquid grafted polyamide thin-layer composite nanofiltration membrane and its preparation method, the amino ionic liquid grafting rate of the preparation method is high, the regulation range of surface charge of polyamide thin-layer composite nanofiltration membrane is wide, and it can also endow polyamide nanofiltration membrane with new functions, such as antibacterial property.

[0009] The technical scheme of the present application is as follows:

[0010] A preparation method of an amino ionic liquid grafted polyamide thin-layer composite nanofiltration membrane, comprising the following steps:

[0011] (1) interfacial polymerization reaction of aqueous solution and oil phase solution on the surface of the base film to form a polyamide functional skin layer on the surface of the base film;

[0012] (2) The amino ionic liquid organic solution is rapidly coated onto the surface of the polyamide functional skin generated in step (1), and the polyamide functional skin is grafted with amino ionic liquid. After the reaction is completed, the excess amino ionic liquid organic solution is removed, and the product is washed, cured and dried to obtain the final product.

[0013] In existing technologies, when grafting amino ionic liquids onto polyamide functional skins, an aqueous solution of the amino ionic liquid is used. This aqueous solution readily hydrolyzes acyl chlorides, and the resulting carboxylic acid groups do not react with the amino groups in the ionic liquid, resulting in low grafting efficiency and a narrow range of charge control. In this invention, an organic solution of the amino ionic liquid is used for grafting the polyamide functional skin. The anhydrous reaction environment prevents acyl chloride hydrolysis, allowing the acyl chloride groups remaining on the polyamide surface to react with the amino ionic liquid, enabling the ionic liquid to graft onto the polyamide skin surface via amide bonds. Using an organic solution of the amino ionic liquid for grafting avoids the problems of low grafting rate, grafting failure, and narrow range of surface charge control caused by the hydrolysis of acyl chlorides in aqueous solutions. The resulting polyamide thin-layer composite nanofiltration membrane exhibits high rejection rates and water flux for both positive and negative ions, and also possesses high antibacterial properties.

[0014] Preferably, the aqueous phase solution is an aqueous solution of piperazine and / or m-phenylenediamine; the oil phase solution is an organic solution of polyacrylamide chloride.

[0015] More preferably, the concentration of piperazine and / or m-phenylenediamine in the aqueous solution is 3-6 g / L; and the concentration of polyacrylamide in the oil solution is 2-5 g / L.

[0016] In step (1), the interfacial polymerization reaction time is 1-5 min.

[0017] Preferably, the substrate membrane is a polyethersulfone microfiltration membrane or ultrafiltration membrane, a polysulfone microfiltration membrane or ultrafiltration membrane, a polyvinyl acrylonitrile microfiltration membrane or ultrafiltration membrane, a polypropylene microfiltration membrane or ultrafiltration membrane, a polyvinylidene fluoride microfiltration membrane or ultrafiltration membrane, or a polytetrafluoroethylene microfiltration membrane or ultrafiltration membrane.

[0018] In the aforementioned amino ionic liquid organic solution, the organic solvent needs to be screened and its solubility is required; it must be able to dissolve the ionic liquid but not the substrate. Examples include N,N-dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and tetrahydrofuran, but are not limited to these solvents.

[0019] Amino ionic liquids are at least one of the following: monoamino ionic liquids with amino groups located on anions or cations, and diamino ionic liquids having amino groups on both anions and cations.

[0020] Preferably, the amino ionic liquid is at least one of 1-amino-3-methylimidazolium chloride, 1-hydroxypropyl-3-methylimidazolium glycinate, 1-aminoethyl-3-methylimidazolium glycinate, 1-aminopropyl-3-methylimidazolium glycinate, 1-aminobutyl-3-methylimidazolium glycinate, 1-butylmethoxy-3-methylimidazolium glycinate, 1-aminopropyl-3-methylimidazolium bromide, and 3-propylamino-tributylphosphonium glycinate.

[0021] Preferably, the concentration of the amino ionic liquid in the amino ionic liquid organic solution is 0.01-1 mol / L. The concentration of the ionic liquid can also be not limited to this concentration range.

[0022] Preferably, in step (2), the grafting reaction time of the amino ionic liquid is 1-2 h.

[0023] Further preferably, in step (2), the grafting reaction time of the amino ionic liquid is 0.5-1 h.

[0024] Preferably, in step (2), the solidification temperature is 50-70℃, and the solidification time is 5-10 min.

[0025] The application also provides the amino ionic liquid grafted polyamide thin-layer composite nanofiltration membrane prepared by the above preparation method.

[0026] The polyamide thin-layer composite nanofiltration membrane of the application has a high grafting rate of amino ionic liquid on the surface, a wide range of surface charge regulation, super-high antibacterial property, and adjustable thickness pore size and charge property, and has high rejection performance for divalent anions and high water flux. The application also provides the application of the amino ionic liquid grafted polyamide thin-layer composite nanofiltration membrane in seawater desalination, hard water softening, drug separation, or sewage purification.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] (1) The surface of the polyamide skin layer prepared by interfacial polymerization has unreacted acyl chloride groups, which are easy to hydrolyze in the washing and drying processes. Therefore, the polyamide skin layer is usually negatively charged and difficult to regulate. The post-grafting reaction of the application is carried out in a water-free environment to prevent the acyl chloride groups from being hydrolyzed by contacting with water, thereby retaining the acyl chloride groups on the surface of the polyamide skin layer after interfacial polymerization, improving the grafting rate of the ionic liquid, and improving the regulation of the charge of the polyamide skin layer.

[0029] (2) The application uses amino ionic liquid as the post-grafting molecule. The ionic liquid reacts with the acyl chloride groups on the surface of the skin layer through the amino groups to be bonded to the surface of the skin layer, thereby endowing the skin layer with new functionality, which provides the polyamide nanofiltration membrane with a wider application prospect. Compared with the traditional polyamide nanofiltration membrane, the amino ionic liquid modified polyamide skin layer has super-strong antibacterial property.

[0030] (3) The amino ionic liquid grafted polyamide thin layer composite nanofiltration membrane of the application has high rejection performance and high water flux for divalent anions. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 SEM images of the surface of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1-2 and Example 1-3, (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Example 1, (d) is Example 2, and (e) is Example 3;

[0032] Figure 2 Infrared spectra of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1, Comparative Example 2 and Example 1;

[0033] Figure 3 Zeta potential diagrams of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1, Comparative Example 2 and Example 1;

[0034] Figure 4 Rejection rate and water flux results of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1, Comparative Example 2 and Example 1 for salt solutions;

[0035] Figure 5 Bacteriostatic results of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1 and Example 1 for Escherichia coli and Staphylococcus aureus, wherein (a) is the bacteriostatic results of Comparative Example 1 for Escherichia coli, (b) is the bacteriostatic results of Comparative Example 1 for Staphylococcus aureus, (c) is the bacteriostatic results of Example 1 for Escherichia coli, and (d) is the bacteriostatic results of Example 1 for Staphylococcus aureus. DETAILED DESCRIPTION

[0036] The application will be further described in conjunction with the drawings and examples. It should be noted that the following examples are intended to facilitate the understanding of the application and do not limit the application in any way.

[0037] In order to better understand the technical solutions of the application, the application will be further described in conjunction with the examples. However, the content of the application is not limited to the following examples. The experimental methods used in the following examples are conventional methods unless otherwise specified. The reagents and materials used in the following examples can be obtained from commercial channels unless otherwise specified.

[0038] The following polytetrafluoroethylene (PTFE) microfiltration membranes were purchased from Haishan Xindongfang Plastic Co., Ltd. The pore size of the PTFE microfiltration membranes was 0.1 μm.

[0039] Comparative Example 1: Polyamide thin layer composite membranes were prepared by grafting polyamide without using ionic liquid afterwards

[0040] (1) The base membrane was fixed in the polymerization device, 2 mL of solution A was added and the surface of the base membrane was infiltrated for 30 s, and then the excess aqueous phase was removed. Solution A is a 5 g / L aqueous piperazine solution.

[0041] (2) Then 2 mL of organic phase solution B was added for polymerization reaction, and the organic phase was poured out after 2 min. Solution B is a 3 g / L 1,3,5-benzene tricarbonyl chloride solution in n-hexane.

[0042] (3) After drying, a polyamide thin layer composite nanofiltration membrane was obtained.

[0043] The chemical composition of the skin layer was characterized by infrared. The surface infrared spectrum is shown in Figure 2 .

[0044] Comparative Example 2: Polyamide thin layer composite membrane modified by grafting after using aqueous solution of amino ionic liquid

[0045] (1) The base membrane was fixed in the polymerization device, 2 mL of solution A was added and the surface of the base membrane was infiltrated for 30 s, and then the excess aqueous phase was removed. Solution A is a 5 g / L aqueous piperazine solution.

[0046] (2) Then 2 mL of organic phase solution B was added for polymerization reaction, and the organic phase was poured out after 2 min. Solution B is a 3 g / L 1,3,5-benzene tricarbonyl chloride solution in n-hexane.

[0047] (3) Then 2 mL of aqueous solution C containing 0.01 mol / L monoamino ionic liquid (1-amino-3-methyl imidazole chloride) was added on the surface of the formed polyamide skin layer, the reaction time was 2 h, and then the solution C was poured out, and then it was taken out after being placed in a 60°C oven for 5 min.

[0048] (4) After drying, a polyamide thin layer composite nanofiltration membrane was obtained by grafting after using aqueous solution of amino ionic liquid.

[0049] The chemical composition of the skin layer was characterized by infrared. The surface infrared spectrum is shown in Figure 2 .

[0050] Example 1: Preparation of polyamide thin layer composite membrane by grafting after using amino ionic liquid organic solution

[0051] (1) The base membrane was fixed in the polymerization device, 2 mL of solution A was added and the surface of the base membrane was infiltrated for 30 s, and then the excess aqueous phase was removed. Solution A is a 5 g / L aqueous piperazine solution.

[0052] (2) Then 2 mL of organic phase solution B was added for polymerization, and the organic phase was poured out after 2 min. Solution B was 3 g / L of 1,3,5-benzene tricarbonyl chloride in n-hexane.

[0053] (3) Then 2 mL of solution C containing 0.01 mol / L of a diamino ionic liquid (1-amino-3-methyl imidazole chloride) was added dropwise on the surface of the formed polyamide skin layer, and the reaction time was 2 h. Then solution C was poured out, and the sample was taken out after being placed in a 60°C oven for 5 min.

[0054] (4) After drying, a polyamide thin layer composite nanofiltration membrane grafted with an amino ionic liquid was obtained.

[0055] The chemical composition of the skin layer was characterized by infrared, and the surface infrared spectrum is shown in FIG. 1. Figure 2

[0056] Example 2: Preparation of a polyamide thin layer composite membrane grafted with an amino ionic liquid organic solution

[0057] (1) The base membrane was fixed in the polymerization device, 2 mL of solution A was added and soaked on the surface of the base membrane for 30 s, and then the excess aqueous phase was removed. Solution A was a 5 g / L piperazine aqueous solution.

[0058] (2) Then 2 mL of organic phase solution B was added for polymerization, and the organic phase was poured out after 2 min. Solution B was 3 g / L of 1,3,5-benzene tricarbonyl chloride in n-hexane.

[0059] (3) Then 2 mL of solution C containing 0.01 mol / L of a monoamino ionic liquid (1-hydroxypropyl-3-methyl imidazole glycine salt) was added dropwise on the surface of the formed polyamide skin layer, and the reaction time was 2 h. Then solution C was poured out, and the sample was taken out after being placed in a 60°C oven for 5 min.

[0060] (4) After drying, a polyamide thin layer composite nanofiltration membrane grafted with an amino ionic liquid was obtained.

[0061] Example 3: Preparation of a polyamide thin layer composite membrane grafted with an amino ionic liquid organic solution

[0062] (1) The base membrane was fixed in the polymerization device, 2 mL of solution A was added and soaked on the surface of the base membrane for 30 s, and then the excess aqueous phase was removed. Solution A was a 5 g / L piperazine aqueous solution.

[0063] (2) Then 2 mL of organic phase solution B was added for polymerization, and the organic phase was poured out after 2 min. Solution B was 3 g / L of 1,3,5-benzene tricarbonyl chloride in n-hexane.

[0064] ​(3) Immediately after the surface of the formed polyamide skin layer, 2 mL of solution C (1-aminopropyl-3-methyl imidazole glycine salt) containing 0.01 mol / L of a mono-amino ionic liquid was added dropwise, and the reaction time was 2 h. After that, the solution C was poured out, and the sample was taken out after being placed in an oven at 60°C for 5 min.

[0065] (4) After drying, a polyamide thin layer composite nanofiltration membrane grafted with an amino ionic liquid was obtained.

[0066] Figure 1 SEM images of the surfaces of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1, Comparative Example 2, and Examples 1-3. Figure 1 In Fig. (a), the surface of the membrane of Comparative Example 1 without grafting of an ionic liquid is shown, and the surface is obviously granular and has a large roughness; Figure 1 In Fig. (b), the surface of the membrane of Comparative Example 2 grafted with an ionic liquid aqueous solution is shown, and it is found that the surface has no obvious change compared with Comparative Example 1. However, the surfaces of the polyamide thin layer composite membranes grafted with the three kinds of amino ionic liquids in Examples 1-3 change obviously from ridge-like to wrinkle-like (as shown in Figs. (c)-(e)). Figure 1 This indicates that the grafting in an aqueous solution environment is prone to failure and has a low grafting rate.

[0067] Figure 2 Infrared spectra of the modified polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1, Comparative Example 2, and Example 1. It can be seen from the infrared spectra that Figure 2 the peak at a wavelength of 1625 cm-1 is the vibration peak of the carbonyl group on the amide bond, which can prove the existence of the polyamide skin layer on the base membrane of Comparative Examples 1 and 2 and Example 1; the peak at a wavelength of 1540 cm-1 is the absorption peak of the imidazole group in the ionic liquid, and it is found that no ionic liquid is detected in Comparative Example 1 and Comparative Example 2 grafted with an ionic liquid aqueous solution, while the ionic liquid is detected in Example 1 grafted with an ionic liquid organic solution, which indicates that the grafting with an ionic liquid organic solution has a high grafting rate of the ionic liquid. -1 -1

[0068] Figure 3 Zeta potential diagrams of the polyamide skin layers after no grafting (Comparative Example 1), grafting with an ionic liquid aqueous solution (Comparative Example 2), and grafting with an ionic liquid organic solvent (Example 1) can be found. It can be found that the grafting efficiency is low in the ionic liquid aqueous solution, and the charge of the skin layer changes little. However, the grafting efficiency is improved in the ionic liquid organic solvent, the amino group on the cation of the ionic liquid is bonded to the polyamide skin layer, and the positive charge of the skin layer is obviously enhanced.

[0069] Test Example 1: Test of rejection performance

[0070] The rejection performance of a composite membrane to a certain solute can be expressed by the rejection rate, which is specifically shown in formula (1):​​

[0071] R = (1 - C P / C f ) x 100% (1)

[0072] wherein R represents the rejection rate, C f (mg / L) represents the concentration of solute in the feed liquid, C p (mg / L) represents the concentration of solute in the permeate liquid.

[0073] The polyamide thin layer composite nanofiltration membranes prepared in Comparative Example 1 and Examples 1-3 were placed in a cross-flow device, and a Na2SO4 salt solution (1.0 g / L in concentration) was added to the feed side. The filtrate after filtration through the nanofiltration membrane was collected, and its conductivity was tested by a conductivity meter.

[0074] Test Example 2: Water flux test

[0075] The water flux represents the volume of flow per unit time through a unit membrane area under a certain pressure, and is calculated according to formula (2):

[0076] J = V / (A*T) (2)

[0077] wherein V (L) represents the volume of the filtrate, A (m 2 ) represents the test area of the sample, and T (h) represents the time used for collecting the filtrate with a volume of V.

[0078] Compared with the polyamide nanofiltration membrane without grafting of the ionic liquid, the polyamide thin layer composite nanofiltration membrane prepared in Examples 1-3 has a flux increased by two times without loss of the rejection rate, indicating that grafting of the amino ionic liquid can increase the flux of the polyamide nanofiltration membrane.

[0079] Figure 4 The rejection results of the polyamide skin layer after no grafting (Comparative Example 1), grafting of the ionic liquid aqueous solution (Comparative Example 2), and grafting of the ionic liquid organic solvent (Example 1) against a 1 g / L sodium sulfate solution were found. It was found that grafting of the ionic liquid organic solvent makes the water flux increased by two times without a decrease in the rejection rate.

[0080] Figure 5 The antibacterial results of the polyamide skin layer after no grafting (Comparative Example 1, Figure 5 (a) and (b)), and grafting of the ionic liquid organic solvent (Example 1, Figure 5 (c) and (d)) against Escherichia coli and Staphylococcus aureus were found. It was found that the grafting of the ionic liquid organic solvent to the polyamide skin layer has an antibacterial rate of 99.9% against Escherichia coli and Staphylococcus aureus, while the polyamide skin layer without grafting has no antibacterial effect against Escherichia coli and Staphylococcus aureus.

[0081] The above embodiments describe the technical solutions and advantages of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, supplement, and equivalent replacement within the principle range of the present application should be included in the protection scope of the present application.

Claims

1. A process for the preparation of an amino ionic liquid anhydrous grafted polyamide thin layer composite nanofiltration membrane characterized in that, The method comprises the following steps: (1) performing interfacial polymerization reaction on the surface of the base membrane with the aqueous phase solution and the oil phase solution to form a polyamide functional skin layer on the surface of the base membrane; (2) rapidly coating an amino ionic liquid organic solution on the surface of the polyamide functional skin layer formed in step (1) to graft the polyamide functional skin layer with the amino ionic liquid without water, removing the excess amino ionic liquid organic solution after the reaction, and washing, solidifying and drying to obtain the product; the type of the amino ionic liquid is related to the charge property of the polyamide skin layer; the amino ionic liquid is at least one of a mono-amino ionic liquid with an amino group on an anion, a di-amino ionic liquid with an amino group on both an anion and a cation; in the amino ionic liquid organic solution, the concentration of the amino ionic liquid is 0.01-1 mol / L, and the organic solvent is an organic solvent that can dissolve the ionic liquid and cannot dissolve the base membrane.

2. The process for the preparation of an aminic ionic liquid-free grafted polyamide thin layer composite nanofiltration membrane according to claim 1, characterized in that, the aqueous phase solution is a piperazine and / or m-phenylenediamine aqueous solution; and the oil phase solution is a polyacyl chloride organic solution.

3. The process for the preparation of an aminic ionic liquid-free grafted polyamide thin layer composite nanofiltration membrane according to claim 2, characterized in that, in the aqueous phase solution, the concentration of the piperazine and / or m-phenylenediamine is 3-6 g / L; and in the oil phase solution, the concentration of the polyacyl chloride is 2-5 g / L.

4. The process for the preparation of an aminic ionic liquid free grafted polyamide thin layer composite nanofiltration membrane according to claim 1, characterized in that, in step (1), the interfacial polymerization reaction time is 1-5 min.

5. The process for the preparation of an aminic ionic liquid free grafted polyamide thin layer composite nanofiltration membrane according to claim 1, characterized in that, in step (1), the base membrane is a polyether sulfone microfiltration membrane or ultrafiltration membrane, a polysulfone microfiltration membrane or ultrafiltration membrane, a polyvinyl acetate microfiltration membrane or ultrafiltration membrane, a polypropylene microfiltration membrane or ultrafiltration membrane, a polyvinylidene fluoride microfiltration membrane or ultrafiltration membrane, or a polytetrafluoroethylene microfiltration membrane or ultrafiltration membrane.

6. The process for the preparation of an aminic ionic liquid free grafted polyamide thin layer composite nanofiltration membrane according to claim 1, characterized in that, the amino ionic liquid is at least one of 1-hydroxypropyl-3-methylimidazole glycinate, 1-aminoethyl-3-yl imidazole glycinate, 1-aminopropyl-3-methylimidazole glycinate, 1-aminobutyl-3-methylimidazole glycinate, 1-butylmethoxy-3-methylimidazole glycinate, and 3-propylamino-t-butyl phosphonium glycinate.

7. The process for the preparation of an aminic ionic liquid free grafted polyamide thin layer composite nanofiltration membrane according to claim 1, characterized in that, the amino ionic liquid grafting reaction time is 0.5-1 h.

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