Salt-responsive nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses a composite nanofiltration membrane with salt response characteristic, the composite nanofiltration membrane comprises a modified porous support base membrane and a separation layer compounded on the modified porous support base membrane, the modified porous support base membrane is obtained by carrying out surface modification treatment on the porous support base membrane by adopting a modifier, and the separation layer is prepared from the modified porous support base membrane. The modifier is a chemical modifier with oxidability or alkalinity. And the functional separation layer is constructed by adopting an interfacial polymerization reaction to form a cross-linked network structure with an ion response characteristic. The salt-responsive nanofiltration membrane disclosed by the invention can quickly respond under high salt concentration, effectively improve membrane flux and inorganic salt permeability, enhance the separation effect of small molecular organic matters and salt, has excellent salt concentration response characteristic, is especially suitable for high-salt wastewater treatment and resource recovery, and has wide application prospect. And an innovative solution with high-efficiency separation performance and working condition adaptability is provided for zero discharge of industrial wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a salt-responsive nanofiltration membrane and a preparation method thereof. In particular, the present invention also relates to the application of a salt-responsive nanofiltration membrane. Background Art

[0002] The high salinity and high organic matter concentration in textile wastewater pose a serious threat to environmental safety and human health. There is an urgent need to develop efficient treatment technologies to address this challenge. Nanofiltration (NF) technology has received extensive attention due to its low energy consumption, high separation efficiency, and environmental friendliness. In particular, polyamide thin-film composite nanofiltration membranes (TFC membranes) prepared by interfacial polymerization have become the mainstream products in the fields of desalination and wastewater recycling. However, for traditional polyamide composite nanofiltration membranes (TFC nanofiltration membranes), based on the process that aqueous-phase amino monomers diffuse into the oil phase and rapidly react with acyl chloride monomers to form a membrane within seconds, the controllability of the microstructure and physicochemical properties of the nanofiltration membrane after preparation and molding is poor. Especially when dealing with complex working conditions such as dynamic salinity and pH fluctuations in actual treatment, the adaptability is insufficient, and it is difficult to overcome the "Trade-off" effect between permeation flux and rejection rate, resulting in generally low water fluxes. In addition, due to the easy occurrence of concentration polarization in high-salt systems, leading to a sudden drop in flux, and irreversible fouling caused by organic matter adsorption, it is particularly prominent in the desalination of complex systems such as dyes / inorganic salts. Therefore, developing intelligent nanofiltration membranes with salt-responsive characteristics has become a key strategy to break through the existing technical barriers. Summary of the Invention

[0003] The present invention is based on the inventors' discovery and recognition of the following facts and problems: Under the positive stimulation of the change in the external solution salinity, the salt-responsive nanofiltration membrane can achieve intelligent regulation of membrane pore size / charge with the change in salt concentration by constructing a dynamic salt-responsive separation layer: expanding the pore size to increase the flux under high-salt conditions, and at the same time enhancing the pollutant rejection through the Donnan effect; shrinking the pore size in a low-salt environment to maintain selectivity. This self-adaptive characteristic can not only alleviate membrane fouling, but also significantly improve the system operation efficiency, providing a new generation of separation membrane solution with high flux, anti-fouling property, and long-term stability for textile wastewater treatment.

[0004] Currently, the preparation of salt-responsive nanofiltration membranes mainly adopts methods such as grafting on the surface of the TFC membrane separation layer, surface coating, layer-by-layer self-assembly on the surface of the support substrate membrane, and adding zwitterionic polymers to the aqueous phase of interfacial polymerization. However, the addition of intermediate organic compounds (such as zwitterionic polymers or polyelectrolytes) not only increases the peeling between the support substrate membrane and the separation layer, but also increases the complexity and cost of membrane preparation, and is insufficient in environmental friendliness. Therefore, it is necessary to develop a salt-responsive nanofiltration membrane with a green and environmentally friendly preparation method and simple operation, which can maintain a large membrane flux and excellent anti-fouling performance in high-salt solutions and achieve efficient separation of dyes and salts.

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, an embodiment of the present invention provides a salt-responsive nanofiltration membrane and a preparation method thereof. The nanofiltration membrane has a rapid membrane flux salt concentration responsiveness when filtering high-salt solutions, can effectively improve the membrane flux, while reducing the salt rejection rate, has excellent inorganic salt permeation performance, and effectively improves the separation effect of small molecule organic matters and salts.

[0006] The salt-responsive nanofiltration membrane of the embodiment of the present invention includes a modified porous support membrane and a separation layer composite on the modified porous support membrane. Among them, the modified porous support membrane is obtained by surface modification of the porous support membrane with a modifier, and the modifier is a chemical modifier with oxidizing or alkaline properties.

[0007] The advantages and technical effects brought by the salt-responsive nanofiltration membrane of the embodiment of the present invention are as follows: 1. In the embodiment of the present invention, after the porous support membrane is treated with a modifier, not only the bonding degree between the base membrane and the separation layer is enhanced, but also the negative charge and hydrophilicity of the surface of the nanofiltration membrane are effectively improved, solving the mutually restrictive relationship between the membrane flux and the membrane performance where one increases while the other decreases, realizing the improvement of the membrane flux while reducing the salt rejection rate, effectively improving the separation effect of small molecule organic matters and salts, and having excellent anti-fouling performance; 2. The salt-responsive nanofiltration membrane of the embodiment of the present invention has excellent salt concentration response characteristics, and the membrane water flux will increase with the increase of the salt concentration in the filtered solution, and can be used to treat high-concentration saline wastewater, and has great industrial application potential in the fields of dye desalination or high-salt wastewater treatment.

[0008] In some embodiments, the porous support membrane is poly(m-phenylene isophthalamide).

[0009] In some embodiments, the thickness of the porous support membrane is 0.10 - 0.25 mm.

[0010] In some embodiments, the separation layer includes polyamide.

[0011] In some embodiments, the modifier includes at least one of sodium hypochlorite, potassium hydroxide, sodium hydroxide, and hydrogen peroxide.

[0012] In some embodiments, the concentration of the modifier is 0.5 - 2.5 mol / L.

[0013] The embodiment of the present invention also provides a preparation method of a salt-responsive nanofiltration membrane, including the following steps:

[0014] a. Immerse the porous support membrane in the modifier for modification treatment to obtain a modified porous support membrane;

[0015] b. Immerse the modified porous support membrane obtained in step a in an aqueous phase reaction monomer solution;

[0016] c. Take out the modified porous support membrane impregnated with the aqueous phase reaction monomer solution in step b and immerse it in an organic phase reaction monomer solution to carry out an interfacial polymerization reaction to prepare a salt-responsive nanofiltration membrane.

[0017] The advantages and technical effects brought by the preparation method of the salt-responsive nanofiltration membrane of the embodiment of the present invention are as follows: 1. In the method of the embodiment of the present invention, the porous support membrane is first impregnated in a modifier for modification treatment. After the porous support membrane is modified, not only the bonding degree between the base membrane and the aqueous monomer and the separation layer formed by the interfacial polymerization reaction is enhanced, but also the negative charge and hydrophilicity on the surface of the nanofiltration membrane are effectively improved, realizing the improvement of the membrane flux while reducing the salt rejection rate, effectively improving the separation effect of small molecule organic matter and salt, and significantly improving the anti-fouling performance of the nanofiltration membrane; 2. The method of the embodiment of the present invention prepares a nanofiltration membrane with excellent salt concentration response characteristics. The membrane water flux increases with the increase of the salt concentration in the filtration solution and can be used to treat high-concentration saline wastewater, and has great industrial application potential in the fields of dye desalination or high-salt wastewater treatment.

[0018] In some embodiments, in step a, the temperature of the modification treatment is 20-80 °C, and the time of the modification treatment is 0.5-5 hours.

[0019] In some embodiments, in step a, the preparation method of the porous support membrane includes: mixing poly(m-phenylene isophthalamide), an additive and a solvent to obtain a casting solution, coating the casting solution on a substrate, and curing to obtain a porous support membrane. Preferably, the additive includes at least one of polyvinylpyrrolidone, lithium chloride, polyethylene glycol, ethylene glycol, dipropylene glycol monomethyl ether, tetrahydrofuran, acetone; the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone; in the casting solution, the mass percentage content of poly(m-phenylene isophthalamide) is 12%-18%, and the mass percentage content of the additive is 4%-18%.

[0020] In some embodiments, in step b, the aqueous phase reaction monomer includes at least one of piperazine, polyethyleneimine, m-phenylenediamine, o-phenylenediamine, triethanolamine, N,N-diaminopiperazine, 1,4-bis(3-aminopropyl)piperazine, N-(3-aminopropyl)piperazine. Preferably, the mass-volume concentration of the aqueous phase reaction monomer in the aqueous phase reaction monomer solution is 0.01-5.0 w / v%, and the unit is g / ml.

[0021] In some embodiments, in step b, the impregnation time is 1-5 minutes.

[0022] In some embodiments, in step c, the oil-phase reaction monomer includes at least one of trimellitic acid chloride, phthalic acid chloride, isophthalic acid chloride, and terephthalic acid chloride, and the solvent in the oil-phase reaction monomer solution includes at least one of cyclohexane, n-hexane, and heptane; preferably, the mass-volume concentration of the oil-phase reaction monomer in the oil-phase reaction monomer solution is 0.01-2.0 w / v%, with the unit of g / ml.

[0023] In some embodiments, in step c, the time of the interfacial polymerization reaction is 10-120 seconds.

[0024] The embodiments of the present invention also provide an application of the salt-responsive nanofiltration membrane in dye desalination or high-salt wastewater treatment. The nanofiltration membrane of the embodiments of the present invention has a rapid membrane flux salt concentration responsiveness when filtering a high-concentration salt-containing solution, can more efficiently separate small-molecule organic substances and salts, and can be used for dye desalination and refining or effective separation and treatment of high-salt wastewater. Description of the Drawings

[0025] Figure 1 is the water flux of the nanofiltration membranes of Example 3 and Comparative Example 1 in aqueous NaCl solutions with different concentrations;

[0026] Figure 2 is the water flux and rejection rate of the nanofiltration membrane of Example 3 in mixed solutions of different concentrations of NaCl and congo red. Detailed Embodiments

[0027] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0028] The salt-responsive nanofiltration membrane of the embodiments of the present invention includes a modified porous support membrane and a separation layer composite on the modified porous support membrane, wherein the modified porous support membrane is obtained by surface modification of the porous support membrane with a modifier, and the modifier is a chemical modifier with oxidizing or basic properties. Preferably, the modifier includes at least one of sodium hypochlorite, potassium hydroxide, sodium hydroxide, and hydrogen peroxide.

[0029] In the salt-responsive nanofiltration membrane of the embodiment of the present invention, after the porous support substrate membrane is treated with a modifier, not only the bonding degree between the substrate membrane and the separation layer is enhanced, but also the negative charge and hydrophilicity on the surface of the nanofiltration membrane are effectively improved, solving the mutually restrictive relationship between the membrane flux and the membrane performance where one increases while the other decreases. It realizes the improvement of the membrane flux while reducing the salt rejection rate, effectively improves the separation effect of small-molecule organic matters and salts, and has excellent anti-fouling performance; the salt-responsive nanofiltration membrane of the embodiment of the present invention has excellent salt concentration response characteristics, and the membrane water flux increases with the increase of the salt concentration in the filtration solution, and can be used for treating high-concentration saline wastewater, and has great industrial application potential in the fields of dye desalination or high-salt wastewater treatment.

[0030] In some embodiments, the porous support substrate membrane is poly(m-phenylene isophthalamide). In the embodiment of the present invention, poly(m-phenylene isophthalamide) is preferably used as the porous support substrate membrane, which is beneficial to microscopically and precisely regulating its pore size range, charge distribution, and hydrophilic characteristics, and precisely constructing a high-performance nanofiltration membrane separation layer.

[0031] In some embodiments, the thickness of the porous support substrate membrane is 0.10 - 0.25 mm. In the embodiment of the present invention, there is no special limitation on the thickness of the porous support substrate membrane, and the thickness of the substrate membrane in the commonly used nanofiltration membranes in the prior art can all be applicable to the present invention.

[0032] In some embodiments, the separation layer includes polyamide. In the embodiment of the present invention, there is no special limitation on the separation layer, and the commonly used separation layers in the prior art can all be applicable to the present invention.

[0033] In some embodiments, the concentration of the modifier is 0.5 - 2.5 mol / L. In the embodiment of the present invention, the concentration of the modifier is further optimized, which is not only beneficial to improving the salt-responsive performance of the nanofiltration membrane, but also helps to reduce the occurrence of side reactions during the membrane preparation process. If the concentration of the modifier is too high, it will cause the separation layer structure to be loose and the crosslinking degree to be insufficient, resulting in membrane defects and reducing the permeability and selectivity of the membrane; if the concentration of the modifier is too low, it will cause the formation and distribution of functional groups to be uneven and unable to effectively improve the salt-responsive performance of the membrane.

[0034] The embodiment of the present invention also provides a preparation method of a salt-responsive nanofiltration membrane, including the following steps:

[0035] a. Immerse the porous support substrate membrane in the modifier for modification treatment to obtain a modified porous support substrate membrane;

[0036] b. Immerse the modified porous support substrate membrane obtained in step a in an aqueous phase reaction monomer solution;

[0037] c. Take out the modified porous support membrane impregnated with the aqueous phase reaction monomer solution in step b and immerse it in the oil phase reaction monomer solution to carry out an interfacial polymerization reaction to obtain a salt-responsive nanofiltration membrane.

[0038] In the preparation method of the salt-responsive nanofiltration membrane according to the embodiment of the present invention, the porous support membrane is first impregnated in a modifier for modification treatment. After the porous support membrane is modified, not only the bonding degree between the base membrane and the aqueous monomer and the separation layer formed by the interfacial polymerization reaction is enhanced, but also the negative charge and hydrophilicity on the surface of the nanofiltration membrane are effectively improved, realizing the improvement of the membrane flux while reducing the salt rejection rate, effectively improving the separation effect of small molecule organic matters and salts, and significantly improving the anti-fouling performance of the nanofiltration membrane; the method of the embodiment of the present invention produces a nanofiltration membrane with excellent salt concentration response characteristics, and the membrane water flux will increase with the increase of the salt concentration in the filtration solution, and it can be used to treat high-concentration saline wastewater, and has great industrial application potential in the fields of dye desalination or high-salt wastewater treatment.

[0039] In some embodiments, in step a, the temperature of the modification treatment is 20-80 °C, and the time of the modification treatment is 0.5-5 hours. In the embodiment of the present invention, the temperature and time of the modification treatment are further optimized to improve the performance of the nanofiltration membrane. If the temperature of the modification treatment is too high, it will be unfavorable to the stability of the membrane structure, which may cause degradation of the membrane material or damage to functional groups, thereby reducing the mechanical strength and separation performance of the membrane; if the temperature is too low, it will be unfavorable to the sufficient reaction between the modifier and the base membrane, resulting in uneven distribution of functional groups or incomplete reaction, affecting the performance of the separation layer. If the time of the modification treatment is too long, it will be unfavorable to the integrity and uniformity of the formation of the separation layer, and at the same time, due to excessive reaction, defects in the separation layer will reduce the permeability and selectivity of the membrane; if the time of the modification treatment is too short, the modification effect cannot be effectively exerted, which is not conducive to the effective combination of the base membrane and the separation layer, and may cause insufficient adhesion of the separation layer, affecting the long-term stability and anti-peeling performance of the membrane.

[0040] In some embodiments, in step a, the porous support base membrane is prepared by a phase inversion method. Preferably, the preparation method includes: mixing poly(m-phenylene isophthalamide), an additive, and a solvent to obtain a casting solution, coating the casting solution on a substrate, and curing to obtain the porous support base membrane. Preferably, the additive includes at least one of polyvinylpyrrolidone, lithium chloride, polyethylene glycol, ethylene glycol, dipropylene glycol, tetrahydrofuran, and acetone; the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; in the casting solution, the mass percentage content of poly(m-phenylene isophthalamide) is 12% to 18%, and the mass percentage content of the additive is 4% to 18%. In the embodiments of the present invention, there is no particular limitation on the preparation method of the porous support base membrane, and the methods commonly used in the prior art for preparing poly(m-phenylene isophthalamide) porous membranes can all be applicable to the present invention.

[0041] In some embodiments, in step b, the aqueous phase reaction monomer includes at least one of piperazine, polyethyleneimine, m-phenylenediamine, o-phenylenediamine, triethanolamine, N,N-diaminopiperazine, 1,4-bis(3-aminopropyl)piperazine, and N-(3-aminopropyl)piperazine. Preferably, the mass-volume concentration of the aqueous phase reaction monomer in the aqueous phase reaction monomer solution is 0.01 to 5.0 w / v%, with the unit of g / ml.

[0042] In some embodiments, in step b, the impregnation time is 1 to 5 minutes.

[0043] In some embodiments, in step c, the oil phase reaction monomer includes at least one of trimesoyl chloride, phthaloyl chloride, isophthaloyl chloride, and terephthaloyl chloride, and the solvent in the oil phase reaction monomer solution includes at least one of cyclohexane, n-hexane, and heptane; preferably, the mass-volume concentration of the oil phase reaction monomer in the oil phase reaction monomer solution is 0.01 to 2.0 w / v%, with the unit of g / ml.

[0044] In some embodiments, in step c, the time for the interfacial polymerization reaction is 10 to 120 seconds.

[0045] In the embodiments of the present invention, the separation layer is prepared by an interfacial polymerization method, and the aqueous phase reaction monomers and oil phase reaction monomers commonly used in the prior art can all be applicable to this application.

[0046] The embodiments of the present invention also provide an application of the salt-responsive nanofiltration membrane in dye desalination or high-salt wastewater treatment. The nanofiltration membrane of the embodiments of the present invention has a rapid membrane flux salt concentration responsiveness when filtering high-concentration salt-containing solutions, can more efficiently separate small-molecule organic substances and salts, and can be used for dye desalination and purification or effective separation and treatment of high-salt wastewater.

[0047] The present invention will be described in detail below in conjunction with embodiments and the accompanying drawings.

[0048] Example 1

[0049] Preparation of porous support substrate membrane: Dissolve 16 g of poly(m-phenylene isophthalamide), 5 g of anhydrous lithium chloride, and 5 g of polyvinylpyrrolidone in 74 g of N,N-dimethylacetamide. After complete dissolution, degas under vacuum for 8 hours to obtain a homogeneous casting solution. Using polyester non-woven fabric as the support substrate, coat the casting solution on the substrate with a doctor blade, control the thickness of the doctor blade to be 0.15 mm. After uniformly scraping the casting solution, directly immerse it in water to cure into a porous support substrate membrane.

[0050] Modification treatment: Immerse the dried substrate membrane in a 1 mol / L potassium hydroxide solution and perform modification treatment at 25 °C for 1 hour. Subsequently, rinse with tap water until the pH value of the cleaning solution is neutral to obtain a modified porous support substrate membrane.

[0051] Interfacial polymerization: Immerse the modified porous support substrate membrane in a 0.2 w / v% aqueous piperazine solution (i.e., the mass ratio of piperazine to the volume of the solution is 0.2 g:100 ml), and take it out after 2 minutes. When there are no obvious droplets on the surface of the modified porous support substrate membrane, immerse the surface of the modified porous support substrate membrane again in a n-hexane solution containing 0.1 w / v% trimesoyl chloride (i.e., the mass ratio of trimesoyl chloride to the volume of the solution is 0.1 g:100 ml) for 60 seconds of interfacial polymerization reaction to obtain a nanofiltration membrane with salt responsiveness, denoted as NF1.

[0052] Example 2

[0053] The method is the same as that in Example 1, except that the modifier used in the modification treatment is a 2 mol / L potassium hydroxide solution.

[0054] Example 3

[0055] The method is the same as that in Example 2, except that the time of the modification treatment is 3 hours.

[0056] Example 4

[0057] The method is the same as that in Example 1, except that the modifier used in the modification treatment is a 1 mol / L sodium hypochlorite solution.

[0058] Example 5

[0059] The method is the same as that in Example 1, except that the modifier used in the modification treatment is a 1 mol / L hydrogen peroxide solution.

[0060] Example 6

[0061] The method is the same as that of Example 1, except that the modification treatment is carried out at 40 °C during the modification treatment.

[0062] Comparative Example 1

[0063] The method is the same as that of Example 1, except that the modification treatment step is cancelled, and the subsequent interfacial polymerization step is directly carried out on the poly(m-phenylene isophthalamide) porous support membrane to prepare a nanofiltration membrane.

[0064] Comparative Example 2

[0065] The method is the same as that of Example 1, except that the porous support membrane used is a polyethersulfone (PES) ultrafiltration membrane with a molecular weight of 100,000 to prepare a nanofiltration membrane.

[0066] Performance tests were carried out on the nanofiltration membranes prepared in each example and comparative example, and the test results are shown in Figure 1-2 and Table 1-2.

[0067] The calculation formula for the water flux (J) is: J = V / (A·t·ΔP), where V is the volume of the permeate (L), A is the effective area of the membrane (m 2 ), t is the filtration time (h), and ΔP is the operating pressure (bar).

[0068] The calculation formula for the rejection rate (R) of inorganic salts and dyes is: R = (1 - C p / C f ) × 100%, where C p and C f are the concentrations of the permeate and the feed solution (mg / L), respectively.

[0069] The rejection rates of the inorganic salts sodium chloride (NaCl) and sodium sulfate (Na2SO4) were calculated using the conductivity values of the raw material solution and the membrane permeate.

[0070] The rejection rate of the dye Congo Red (molecular weight: 696.68 daltons) was determined by measuring the absorbance of the raw material solution and the membrane permeate using a UV-visible spectrophotometer, and calculating the corresponding concentration through a standard absorbance curve.

[0071] All nanofiltration membranes were tested 3 times, and the average value was taken as the final test result.

[0072] I. The water flux tests of the nanofiltration membranes prepared in each example and comparative example were carried out in pure water and 1 g / L Na2SO4 solution at 25 °C and 0.3 MPa, and the test results are shown in Table 1.

[0073] Table 1

[0074]

[0075] As can be seen from Table 1, the nanofiltration membranes prepared in Examples 1-6 of the present invention have excellent salt-responsive performance, and the water flux in the saline solution is significantly greater than that in pure water, which is suitable for the treatment of high-salt wastewater. However, the nanofiltration membranes prepared in Comparative Example 1 without modification treatment, and Comparative Example 2, the nanofiltration membrane without using poly(m-phenylene isophthalamide) as the support matrix membrane, do not have salt-responsive performance, and the water flux in the salt water shows varying degrees of decline.

[0076] II. Performance tests were carried out on the nanofiltration membranes of Example 3 and Comparative Example 1 in aqueous NaCl solutions with different concentrations. The test results are shown in Figure 1 .

[0077] Under normal circumstances, the higher the salt content in the feed liquid, the more the water flux of the membrane will decrease due to the increase in hydrodynamic resistance and the occurrence of concentration polarization on the membrane surface during filtration. And it can be seen from Figure 1 that compared with Comparative Example 1, for the nanofiltration membrane of Example 3, the water flux increases with the increase of salt concentration, showing obvious and rapid salt concentration response characteristics.

[0078] III. Performance tests were carried out on the nanofiltration membrane prepared in Example 3 in a mixed solution of 0.1 g / L Congo red and different concentrations of NaCl. The test results are shown in Figure 2 .

[0079] As Figure 2 shown, when the nanofiltration membrane prepared in Example 3 is used to treat the dye / inorganic salt mixed solution system, it still shows excellent salt concentration response characteristics, and at the same time can completely retain Congo red dye. Moreover, as the NaCl concentration in the mixed solution increases from 0.5 g / L to 10 g / L, the rejection rate of the nanofiltration membrane for NaCl decreases from 25.0% to 2.0%, having excellent inorganic salt permeation performance and realizing the effective separation of dyes and inorganic salts. It can be seen that the salt-responsive nanofiltration membrane prepared by the present invention shows excellent performance in the efficient separation of salts and small molecule organic substances (such as dyes).

[0080] IV. Performance tests were carried out on the nanofiltration membranes prepared in each example and comparative example in a mixed solution of 0.1 g / L Congo red and 5 g / L NaCl. The test results are shown in Table 2.

[0081] Table 2

[0082] Dye rejection rate (%) Salt rejection rate (%) <![CDATA[Water flux (L / m 2 ·h·bar)]]> Example 1 99.8 7.3 23.6 Example 2 99.4 6.2 35.3 Example 3 99.2 4.6 43.8 Example 4 99.5 7.7 29.3 Example 5 99.8 9.5 22.5 Example 6 99.4 4.4 34.7 Comparative Example 1 99.8 25.2 15.0 Comparative Example 2 99.6 22.8 12.8

[0083] As can be seen from Table 2, the nanofiltration membranes prepared in each example of the present invention have excellent water flux in high-concentration saline wastewater, and at the same time have high salt permeation ability, and can realize the effective separation of dyes and inorganic salts.

[0084] In the present invention, terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0085] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A salt-responsive nanofiltration membrane, characterized in that, It includes a modified porous support membrane and a separation layer composite on the modified porous support membrane. Among them, the modified porous support membrane is obtained by surface modification of the porous support membrane with a modifier, and the modifier is a chemical modifier with oxidizing or alkaline properties.

2. The salt-responsive nanofiltration membrane according to claim 1, wherein The porous support membrane is poly(m-phenylene isophthalamide); and / or, the thickness of the porous support membrane is 0.10 - 0.25 mm; and / or, the separation layer includes polyamide; and / or, the modifier includes at least one of sodium hypochlorite, potassium hydroxide, sodium hydroxide, and hydrogen peroxide; and / or, the concentration of the modifier is 0.5 - 2.5 mol / L.

3. A method for preparing the salt-responsive nanofiltration membrane according to claim 1 or 2, characterized in that, It includes the following steps: a. Immerse the porous support membrane in the modifier for modification treatment to obtain a modified porous support membrane; b. Immerse the modified porous support membrane obtained in step a in an aqueous phase reaction monomer solution; c. Take out the modified porous support membrane impregnated with the aqueous phase reaction monomer solution in step b and immerse it in an organic phase reaction monomer solution for interfacial polymerization reaction to prepare a salt-responsive nanofiltration membrane.

4. The preparation method of the salt-responsive nanofiltration membrane according to claim 3, characterized in that, In step a, the temperature of the modification treatment is 20 - 80 °C, and the time of the modification treatment is 0.5 - 5 hours.

5. The method for preparing the salt-responsive nanofiltration membrane according to claim 3, wherein, In step a, the preparation method of the porous support membrane includes: mixing poly(m-phenylene isophthalamide), an additive, and a solvent to obtain a casting solution, coating the casting solution on a substrate, and curing to obtain a porous support membrane; Preferably, the additive includes at least one of polyvinylpyrrolidone, lithium chloride, polyethylene glycol, ethylene glycol, dipropylene glycol, tetrahydrofuran, and acetone; Preferably, the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; Preferably, in the casting solution, the mass percentage content of poly(m-phenylene isophthalamide) is 12% - 18%, and the mass percentage content of the additive is 4% - 18%.

6. The preparation method of the salt-responsive nanofiltration membrane according to claim 3, characterized in that, In step b, the aqueous phase reaction monomer includes at least one of piperazine, polyethyleneimine, m-phenylenediamine, o-phenylenediamine, triethanolamine, N,N-diaminopiperazine, 1,4-bis(3-aminopropyl)piperazine, and N-(3-aminopropyl)piperazine. Preferably, the mass volume concentration of the aqueous phase reaction monomer in the aqueous phase reaction monomer solution is 0.01 - 5.0 w / v%, and the unit is g / ml.

7. The method for preparing a salt-responsive nanofiltration membrane according to claim 3 or 6, characterized in that, In step b, the impregnation time is 1 - 5 minutes.

8. The preparation method of the salt-responsive nanofiltration membrane according to claim 3, wherein, In step c, the organic phase reaction monomer includes at least one of trimesoyl chloride, phthaloyl chloride, isophthaloyl chloride, and terephthaloyl chloride. The solvent in the organic phase reaction monomer solution includes at least one of cyclohexane, n-hexane, and heptane; preferably, the mass volume concentration of the organic phase reaction monomer in the organic phase reaction monomer solution is 0.01 - 2.0 w / v%, and the unit is g / ml.

9. The method for preparing a salt-responsive nanofiltration membrane according to claim 3 or 8, characterized in that, In step c, the time of the interfacial polymerization reaction is 10 - 120 seconds.

10. Use of the salt-responsive nanofiltration membrane according to claim 1 or 2, or the salt-responsive nanofiltration membrane prepared by the method according to any one of claims 3-9, in dye desalination or high-salt wastewater treatment.

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