High-flux composite nanofiltration membrane and method for preparing the same

Abstract

The application relates to the technical field of nanofiltration membranes, in particular to a high-flux composite nanofiltration membrane and a preparation method thereof, wherein the preparation method comprises the following steps: adding metal precursors and high-molecular polymers into an organic solvent to prepare nanofiber casting solution, and preparing nanofiber membranes coated with the metal precursors by using an electrostatic spinning method; then generating nanorod structures on the nanofiber membranes in situ by using an ultrasonic-assisted growth method; and finally forming a wrinkle-shaped polyamide separation layer around the nanorod structures to obtain the high-flux composite nanofiltration membrane. The preparation method of the high-flux composite nanofiltration membrane provided by the application avoids the problems of poor combination between inorganic nanomaterials and support layers and easy falling-off in traditional methods, and simultaneously increases the surface area of the nanofiber membranes, forms a wrinkle-shaped polyamide separation layer, constructs rich water channels, and can significantly improve the permeation flux of the composite nanofiltration membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite nanofiltration membrane, and particularly relates to a high-flux composite nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] The composite nanofiltration membrane is composed of a porous base film support layer and an ultrathin polyamide separation layer, and has been proved to be capable of efficiently intercepting inorganic salts and low-molecular organic matters, and is widely applied in the fields of brackish water desalination and wastewater reuse. However, due to the trade-off effect between permeability and selectivity, the composite nanofiltration membrane with a dense polyamide separation layer usually has a relatively low permeation flux under the premise of ensuring high selectivity. How to obtain the composite nanofiltration membrane with high selectivity and high permeation flux is a long-term goal in the field of membrane technology.

[0003] At present, there are two main strategies for improving the flux of the composite nanofiltration membrane. One is to select a base film with a large pore size and high porosity. Compared with the base film prepared by the traditional phase inversion method, the nanofiber membrane has excellent properties such as large pore size, high porosity, interconnected pore structure and controllable pore size, and is an ideal support layer for effectively improving the permeation flux of the nanofiltration membrane. The other is to introduce some inorganic nanomaterials into the polyamide separation layer. There are a large number of reports on introducing inorganic nanomaterials such as silicon dioxide, carbon nanotubes (CNT), metal oxides and zeolite molecular sieves into the polyamide separation layer. By utilizing the interface gap between the inorganic nanomaterials and the polymer, as well as the pore structure, charge and functionality of the nanomaterials, the permeation flux of the composite nanofiltration membrane can be significantly improved. The patent with the application publication number CN110917906A disperses the modified iron nanoparticles in a piperazine aqueous solution to perform an interfacial polymerization reaction, thereby obtaining a composite nanofiltration membrane capable of improving the membrane flux, and expanding the upper limit of the permeability-selectivity balance. The patent with the application publication number CN110694493A adds porous copper-coated TiO2 nanoparticles into an aqueous phase or an organic phase, and the permeation flux of the porous copper-coated TiO2 nanoparticle composite nanofiltration membrane is 1.5 times that before the addition of the nanoparticles. In these studies, the method for introducing inorganic nanomaterials is to disperse the nanomaterials in an aqueous phase or an organic phase for interfacial polymerization. The poor compatibility and weak interfacial force between the inorganic nanomaterials and the base film result in poor combination and easy falling off of the nanomaterials and the base film. The falling off of the nanomaterials will cause defects in the separation layer, thereby affecting the stability of the membrane structure.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a high-flux composite nanofiltration membrane and a preparation method thereof, and to solve the problem of poor flux of the composite nanofiltration membrane due to poor interfacial compatibility between the inorganic nanomaterials and the support layer of the composite nanofiltration membrane.

[0006] The technical scheme of the present application is as follows:

[0007] A preparation method of a high-flux composite nanofiltration membrane, comprising the following steps:

[0008] A nanofiber casting solution is prepared by adding a metal precursor and a high-molecular polymer into an organic solvent, and the nanofiber casting solution is prepared into a nanofiber membrane coated with the metal precursor by using an electrospinning method.

[0009] The nanofiber membrane coated with the metal precursor is soaked in a reaction mother liquor A, and after being taken out, is placed in an oven for heat setting treatment to prepare a nanofiber membrane coated with metal nanoparticle seeds, and the reaction mother liquor A is a sodium hydroxide ethanol solution or an acetic acid ethanol mixed solution.

[0010] The nanofiber membrane coated with the metal nanoparticle seeds is placed in a stirring reaction mother liquor B, and at the same time, the reaction mother liquor B is subjected to ultrasonic pulse stimulation treatment to prepare a nanofiber membrane in which nanorod structures are grown in situ, and the reaction mother liquor B is a zinc nitrate urotropine mixed solution or a Ti(n-OBu)4 hydrochloric acid mixed solution.

[0011] The nanofiber membrane in which the nanorod structures are grown in situ is immersed in a water-phase monomer solution for a first predetermined time, taken out and then immersed in an oil-phase monomer solution for an interfacial polymerization reaction for a second predetermined time to prepare a high-flux composite nanofiltration membrane, and the water-phase monomer solution is a water-phase piperazine, water-phase polyethylene glycol or water-phase polyethylene imine solution; and the oil-phase monomer solution is an oil-phase phthaloyl dichloride, oil-phase terephthaloyl dichloride or oil-phase 1,3,5-benzene triformyl chloride solution.

[0012] The preparation method of the high-flux composite nanofiltration membrane, wherein the metal precursor is ZnCl2 or Ti(n-OBu)4; the high-molecular polymer is polysulfone, polyether sulfone, polyvinylidene fluoride, polyvinyl alcohol or polylactic acid; and the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide or styrene.

[0013] The preparation method of the high-flux composite nanofiltration membrane, wherein in the nanofiber casting solution, the mass fraction of the metal precursor is 5-15 wt%, the mass fraction of the high-molecular polymer is 10-30 wt%, and the mass fraction of the organic solvent is 55-85 wt%.

[0014] The preparation method of the high-flux composite nanofiltration membrane, wherein in the step of preparing the nanofiber membrane coated with the metal precursor by using the electrospinning method, the electrospinning voltage is 10-30 kV, the electrospinning distance is 5-20 cm, the spinning temperature is 15-35℃, and the relative humidity is 30-70%.

[0015] The preparation method of the high-flux composite nanofiltration membrane, wherein the concentration of the sodium hydroxide ethanol solution or the acetic acid ethanol solution is 1-3 g / L; in the sodium hydroxide ethanol solution, the volume ratio of sodium hydroxide to ethanol is 1:1-1:4; in the acetic acid ethanol solution, the volume ratio of acetic acid to ethanol is 1:1-1:4.

[0016] The preparation method of the high-flux composite nanofiltration membrane, wherein the temperature of the heat fixation treatment is 40-80 DEG C, and the time is 1-10 h.

[0017] The preparation method of the high-flux composite nanofiltration membrane, wherein the concentration of the reaction mother liquor B is 50-200 mmol / L.

[0018] The preparation method of the high-flux composite nanofiltration membrane, wherein in the step of placing the nanofiber membrane coated with metal nanoparticle seeds in the stirring reaction mother liquor B and simultaneously performing ultrasonic pulse stimulation treatment on the reaction mother liquor B, the frequency of the ultrasonic probe for the ultrasonic pulse stimulation treatment is 5 kHz-50 kHz, the time for the ultrasonic pulse stimulation treatment is 2-10 h, and the stirring speed of the reaction mother liquor B is 500 r / min-1000 r / min.

[0019] The preparation method of the high-flux composite nanofiltration membrane, wherein the first predetermined time is 1-10 minutes; and the second predetermined time is 1-10 minutes.

[0020] A high-flux composite nanofiltration membrane is prepared by the preparation method of the high-flux composite nanofiltration membrane.

[0021] Beneficial effects: the application provides a preparation method of a high-flux composite nanofiltration membrane with a metal oxide nanorod structure nanofiber membrane as a substrate, in which a nanorod structure is generated in situ on the fiber by an ultrasonic assisted growth method, thereby avoiding the problems of poor combination and easy falling off between the inorganic nanomaterial and the support layer in traditional methods, and increasing the surface area of the nanofiber membrane; a wrinkle morphology "ridge valley structure" formed by polyamide around the nanorod structure constructs rich water channels, which can significantly improve the permeation flux of the composite nanofiltration membrane. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A preparation method of a high-flux composite nanofiltration membrane is provided.

[0023] Figure 2 A scanning electron microscope image of the nanofiber membrane in Example 1 and Comparative Example 1.

[0024] Figure 3 A scanning electron microscope image of the composite nanofiltration membrane in Example 1 and Comparative Example 1.

[0025] Figure 4 The results of the membrane performance test of the composite nanofiltration membrane prepared for examples 1-4 and comparative example 1 are shown in the figure. DETAILED DESCRIPTION

[0026] The present application provides a high-flux composite nanofiltration membrane and a preparation method thereof. To make the purpose, technical scheme and effect of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0027] Please refer to Figure 1 , Figure 1 The preparation method of the high-flux composite nanofiltration membrane provided by the present application is shown in the flow chart, which includes the following steps:

[0028] S10, adding metal precursors and high molecular polymers into an organic solvent to prepare a nanofiber casting solution, and using electrospinning method to prepare a nanofiber membrane coated with metal precursors from the nanofiber casting solution;

[0029] S20, soaking the nanofiber membrane coated with metal precursors in a reaction mother liquor A, and then taking out and placing in an oven for heat setting treatment to prepare a nanofiber membrane coated with metal nanoparticle seeds, wherein the reaction mother liquor A is a sodium hydroxide ethanol solution or an acetic acid ethanol mixed solution;

[0030] S30, placing the nanofiber membrane coated with metal nanoparticle seeds in a stirring reaction mother liquor B, and at the same time, performing ultrasonic pulse stimulation treatment on the reaction mother liquor B to prepare a nanofiber membrane with nanorod structures grown in situ, wherein the reaction mother liquor B is a zinc nitrate urotropine mixed solution or a Ti(n-OBu)4 hydrochloric acid mixed solution;

[0031] S40, immersing the nanofiber membrane with nanorod structures grown in situ in a water phase monomer solution for a first predetermined time, then taking out and immersing in an oil phase monomer solution for an interfacial polymerization reaction for a second predetermined time to prepare a high-flux composite nanofiltration membrane, wherein the water phase monomer solution is a water phase piperazine, water phase polyethylene glycol or water phase polyethylene imine solution; and the oil phase monomer solution is an oil phase isophthaloyl chloride, oil phase terephthaloyl chloride or oil phase 1,3,5-benzene triformyl chloride solution.

[0032] The present application generates metal oxide nanorods in situ on the nanofiber membrane by a simple and economical growth method, which effectively improves the surface binding force between the metal oxide nanorods and the base membrane, overcomes the problem of poor interface compatibility between inorganic nanomaterials and the base membrane existing in the traditional method of introducing inorganic nanometer intermediate layer; at the same time, the surface area of the nanofiber membrane is also increased, and the wrinkle-shaped "ridge valley structure" formed by polyamide around the nanorod structure constructs rich water channels, which significantly improves the permeation flux of the composite nanofiltration membrane under the premise of ensuring high selectivity.

[0033] In some embodiments, the metal precursor is ZnCl2 or Ti(n-OBu)4, but is not limited thereto; the high molecular polymer is polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl alcohol or polylactic acid, but is not limited thereto; and the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide or styrene, but is not limited thereto.

[0034] The preparation method of the high-flux composite nanofiltration membrane, wherein the mass fraction of the metal precursor in the nanofiber casting solution is 5-15wt%, the mass fraction of the high molecular polymer is 10-30wt%, and the mass fraction of the organic solvent is 55-85wt%.

[0035] In some embodiments, in the step of preparing the nanofiber membrane coated with the metal precursor by electrospinning the nanofiber casting solution, the electrospinning voltage is 10-30kV, the electrospinning distance is 5-20cm, the spinning temperature is 15-35℃, and the relative humidity is 30-70%.

[0036] In some embodiments, the concentration of the sodium hydroxide ethanol solution or the acetic acid ethanol solution is 1-3g / L; the volume ratio of sodium hydroxide to ethanol in the sodium hydroxide ethanol solution is 1:1-1:4; and the volume ratio of acetic acid to ethanol in the acetic acid ethanol solution is 1:1-1:4.

[0037] In some embodiments, the temperature of the heat fixation treatment is 40-80℃, and the time is 1-10h.

[0038] In some embodiments, the concentration of the reaction mother liquor B is 50-200mmol / L.

[0039] In some embodiments, the nanofiber membrane coated with the metal nanoparticle seeds is placed in the stirring reaction mother liquor B, and the reaction mother liquor B is subjected to ultrasonic pulse stimulation treatment, so as to generate nanorods in situ under the assistance of an ultrasonic probe, thereby preparing the nanofiber membrane with the nanorod structure grown in situ. In this embodiment, if the metal precursor is ZnCl2, the added reaction mother liquor B is a zinc nitrate urotropine mixed solution; and if the metal precursor is Ti(n-OBu)4, the added reaction mother liquor B is a Ti(n-OBu)4 hydrochloric acid mixed solution. In this embodiment, the frequency of the ultrasonic probe for the ultrasonic pulse stimulation treatment is 5kHz-50kHz, the time for the ultrasonic pulse stimulation treatment is 2-10h, and the stirring speed of the reaction mother liquor B is 500rpm-1000rpm.

[0040] In some embodiments, the mass concentration of the water-phase monomer is 0.1wt%-10wt%, and the mass concentration of the oil-phase monomer is 0.1wt%-10wt%.

[0041] In some embodiments, the first predetermined time is 1-10 minutes; and the second predetermined time is 1-10 minutes.

[0042] In some embodiments, the high-flux composite nanofiltration membrane is prepared by the preparation method of the high-flux composite nanofiltration membrane.

[0043] The application will be further explained and described below by means of specific examples:

[0044] Example 1

[0045] 1.25g of ZnCl2 and 5g of polyvinylidene fluoride were weighed and dissolved in 18.75g of N,N-dimethylacetamide to prepare a polyvinylidene fluoride casting solution with a ZnO precursor mass fraction of 5wt%, which was heated and stirred at 70℃ for 5h and then left to stand at room temperature for 12h for sufficient defoaming;

[0046] The prepared casting solution was added to a syringe for electrospinning, and the electrospinning parameters were controlled as follows: electrospinning voltage 15kV, electrospinning distance 15cm, spinning temperature 25℃, and relative humidity 50%. After spinning, a nanofiber membrane coated with ZnCl2 was obtained. The membrane was immersed in a 1g / L sodium hydroxide ethanol solution for 1min, taken out, and placed in an oven at 135℃ for heating and curing for 1h to prepare a nanofiber membrane coated with ZnO nanoparticles;

[0047] The nanofiber membrane coated with ZnO nanoparticles was placed in a solution containing 150ml of a zinc nitrate urotropine mixed solution with a concentration of 50mmol / L, and stirred at a speed of 500r / min. Under the auxiliary action of an ultrasonic probe with a frequency of 10kHz, ZnO nanorods were generated in situ on the fibers to prepare a nanofiber membrane with nanorod structures grown in situ;

[0048] A certain amount of piperazine was dissolved in deionized water to prepare a 1.5wt% aqueous monomer solution, and a certain amount of 1,3,5-benzene tricarbonyl chloride was dissolved in n-hexane to prepare a 0.1wt% 1,3,5-benzene tricarbonyl chloride oil monomer solution. Under the conditions of normal pressure, 25℃ and 50% relative humidity, the nanofiber membrane with nanorod structure grown in situ was immersed in the aqueous monomer solution and stood for 2 minutes. The membrane was taken out and the excess solution on the surface of the membrane was removed with a roller. Then the membrane was immersed in the 0.1wt% 1,3,5-benzene tricarbonyl chloride oil monomer solution and stood for 1 minute. The membrane was taken out and placed in a 50℃ oven for drying for 3 minutes. The prepared composite nanofiltration membrane was stored in deionized water.

[0049] Example 2

[0050] A polyvinylidene fluoride casting solution with a ZnO precursor mass fraction of 1wt% was configured to prepare a nanorod micro-nano structure nanofiber membrane, and the remaining steps were the same as those in Example 1.

[0051] Example 3

[0052] A polyvinylidene fluoride casting solution with a ZnO precursor mass fraction of 3wt% was configured to prepare a nanorod micro-nano structure nanofiber membrane, and the remaining steps were the same as those in Example 1.

[0053] Example 4

[0054] A polyvinylidene fluoride casting solution with a ZnO precursor mass fraction of 9wt% was configured to prepare a nanorod micro-nano structure nanofiber membrane, and the remaining steps were the same as those in Example 1.

[0055] Comparative Example 1

[0056] 5g of polyvinylidene fluoride was dissolved in 20g of N,N-dimethylacetamide to prepare a polyvinylidene fluoride casting solution without a precursor and spun into a nanofiber membrane;

[0057] A certain amount of piperazine was dissolved in deionized water to prepare a 1.5wt% aqueous monomer solution, and a certain amount of 1,3,5-benzene tricarbonyl chloride was dissolved in n-hexane to prepare a 0.1wt% 1,3,5-benzene tricarbonyl chloride oil monomer solution. Under the conditions of normal pressure, 25℃ and 50% relative humidity, the nanofiber membrane with nanorod structure grown in situ was immersed in the aqueous monomer solution and stood for 2 minutes. The membrane was taken out and the excess solution on the surface of the membrane was removed with a roller. Then the membrane was immersed in the 0.1wt% 1,3,5-benzene tricarbonyl chloride oil monomer solution and stood for 1 minute. The membrane was taken out and placed in a 50℃ oven for drying for 3 minutes. The prepared composite nanofiltration membrane was stored in deionized water.

[0058] The composite nanofiltration membranes prepared in the above Examples 1-4 and Comparative Example 1 were used for desalination, and the desalination performance of the composite nanofiltration membranes was represented by the rejection rate and the water permeation flux. The performance test of the composite nanofiltration membranes was carried out in a cross-flow filtration mode, and the inorganic salt solution with a concentration of 1000 mg / L was used as the raw material, and the test was carried out under a pressure of 0.4 MPa.

[0059] The rejection rate formula is: wherein Cf represents the concentration of salt ions in the solution before treatment; and Cp represents the concentration of salt ions in the solution after treatment.

[0060] The water permeation flux formula is: wherein V represents the volume of the solution, in L; T represents time, in h; A represents the effective area, in m2; and P represents the operating pressure, in bar.

[0061] Figure 2 The right and left graphs in FIG. 2 are scanning electron microscope images of the nanofiber membranes in Example 1 and Comparative Example 1, respectively. Figure 2 As can be seen from FIG. 2, the right graph clearly shows the nanorods grown in situ on the surface of the nanofiber, and the left graph is the nanofiber membrane without the micro-nano structure of the nanorods grown in situ.

[0062] Figure 3 The right and left graphs in FIG. 3 are scanning electron microscope images of the composite nanofiltration membranes in Example 1 and Comparative Example 1, respectively. Figure 3 As can be seen from FIG. 3, the right graph shows that the membrane surface of Example 1 has more ridge-valley wrinkle structures than the membrane surface of Comparative Example 1.

[0063] The composite nanofiltration membranes prepared in Examples 1-4 and Comparative Example 1 were subjected to membrane performance test, and the results are shown in FIG. 4. Figure 4 As the mass fraction of ZnO precursor increased from 1 wt% to 5 wt%, the water flux of the prepared composite nanofiltration membranes gradually increased to a maximum, and as the mass fraction continued to increase to 9 wt%, the water flux of the prepared composite nanofiltration membranes gradually decreased. The water flux of the composite nanofiltration membranes prepared in Examples 1-4 was significantly improved compared with that of Comparative Example 1, and in particular, the water flux of the composite nanofiltration membrane prepared in Example 1 was 2.5 times that of the nanofiltration membrane of Comparative Example 1, because the nanorods grown in situ on the surface of the composite nanofiltration membrane fibers of Example 1 constructed many water channels between the selective layer and the support layer of the polyamide, significantly enhancing the permeation flux of the composite nanofiltration membrane.

[0064] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A method for preparing a high-flux composite nanofiltration membrane, characterized in that, The steps include: adding a metal precursor and a polymer to an organic solvent to prepare a nanofiber casting solution, and using electrospinning to prepare a nanofiber membrane coated with a metal precursor from the nanofiber casting solution. The nanofiber membrane coated with the metal precursor was immersed in the reaction mother solution A, and then placed in an oven for heat fixation to obtain the nanofiber membrane coated with metal nanoparticle seeds. The reaction mother solution A is a sodium hydroxide ethanol solution or an acetic acid ethanol mixture. A nanofiber membrane coated with metal nanoparticle seeds was placed in a stirring reaction mother liquor B, and the reaction mother liquor B was subjected to ultrasonic pulse stimulation treatment to obtain a nanofiber membrane with nanorod structure grown in situ. The reaction mother liquor B was a zinc nitrate and hexamethylenetetramine mixed solution or a Ti(n-OBu)4 and hydrochloric acid mixed solution. A nanofiber membrane with an in-situ grown nanorod structure is immersed in an aqueous monomer solution for a first predetermined time, then removed and immersed in an oil-phase monomer solution for a second predetermined time to carry out interfacial polymerization reaction, thereby obtaining a high-flux composite nanofiltration membrane. The aqueous monomer solution is an aqueous piperazine, aqueous polyethylene glycol, or aqueous polyethyleneimine solution; the oil-phase monomer solution is an oil-phase isophthaloyl chloride, an oil-phase phthaloyl chloride, or an oil-phase 1,3,5-trimethylpyridine chloride solution. In the step of placing the nanofiber membrane coated with metal nanoparticle seeds into the stirred reaction mother liquor B, and simultaneously subjecting the reaction mother liquor B to ultrasonic pulse stimulation, the ultrasonic probe frequency for ultrasonic pulse stimulation is 5kHz-50kHz, the ultrasonic pulse stimulation time is 2-10h, and the stirring speed of the reaction mother liquor B is 500 rpm-1000 rpm.

2. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, The metal precursor is ZnCl2 or Ti(n-OBu)4; the polymer is polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl alcohol, or polylactic acid. The organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide, or styrene.

3. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, In the nanofiber casting solution, the mass fraction of the metal precursor is 5-15 wt%, the mass fraction of the polymer is 10-30 wt%, and the mass fraction of the organic solvent is 55-85 wt%.

4. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, In the step of preparing a nanofiber membrane coated with a metal precursor from the nanofiber casting solution by electrospinning, the electrospinning voltage is 10-30kV, the electrospinning distance is 5-20cm, the spinning temperature is 15-35℃, and the relative humidity is 30-70%.

5. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, The concentration of the sodium hydroxide ethanol solution or the acetic acid ethanol mixture is 1-3 g / L.

6. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, The temperature for heat fixation is 40-80℃, and the time is 1-10h.

7. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, The concentration of the mother liquor B is 50-200 mmol / L.

8. The method for preparing the high-flux composite nanofiltration membrane according to claim 1, characterized in that, The first scheduled time is 1-10 minutes; the second scheduled time is 1-10 minutes.

9. A high-flux composite nanofiltration membrane, characterized in that, The high-flux composite nanofiltration membrane was prepared using the preparation method described in any one of claims 1-8.

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