A nanofiltration membrane, a preparation method and application thereof

Abstract

The present application relates to a kind of temperature response nanofiltration membrane for mixed molecular separation and its preparation method and application.The present application obtains MXene-g-PNIPAm by covalently grafting PNIPAm on MXene, the solution of the obtained MXene-g-PNIPAm is vacuumed and filtered into film, and MX-PN membrane can be obtained after drying, wherein PNIPAm has temperature response, when temperature is higher than the lowest critical phase inversion temperature (LCST), the segment of PNIPAm changes from stretched state to shrinkage state, MX-PN membrane can spontaneously adjust the interlayer spacing of MXene according to the change of external temperature, thereby adjusting the effective pore size of membrane, the MXene membrane has excellent temperature response, and excellent separation performance is shown to three different molecular diameter mixed substances.The present application can realize the change from positive correlation to negative correlation of temperature and flux compared with existing temperature response membrane.The nanofiltration membrane of the present application has great market prospect and development potential in the field of water purification, molecular separation, drug separation, organic synthesis and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of separation membrane preparation, and particularly relates to a temperature-responsive nanofiltration membrane for mixed molecular separation and a preparation method thereof. TECHNICAL BACKGROUND

[0002] Organic micro-pollutants in water resources, such as drugs and pesticides, have potential negative effects on humans and ecological systems due to their small molecular size, low concentration, and high chemical stability. Compared with traditional separation methods, membrane separation technology has the advantages of low energy consumption, simple operation, high efficiency, and environmental protection, and has a wide application in water purification. With the continuous improvement of separation requirements, traditional functional single separation membranes have been unable to meet the needs of production. Intelligent response membranes respond to changes in external stimuli, such as pH, humidity, electric field, magnetic field, light, and temperature, and produce a series of structural changes (permeability, pore size, hydrophilic / hydrophobic properties, etc.). Compared with traditional membrane separation, intelligent response membranes can spontaneously respond to changes in the external environment, expanding the application field of membrane separation technology.

[0003] MXene is a new type of layered two-dimensional metal-based carbide material. It has attracted special interest due to its strong structure, rich surface functional groups (such as -O-, -OH, and -F, etc.) and unique physical and chemical properties. In recent years, MXene-based separation membranes can exhibit excellent selectivity for molecules and ions in solution and gas mixtures. In order to improve the separation performance of MXene-based separation membranes, researchers have conducted a lot of research, such as compounding MXene with Fe(OH)3 nanoparticles to prepare a separation membrane with high flux and high retention rate (Ding L, Wei Y, Wang Y, et al. A two-dimensional lamellar membrane: MXene nanosheet stacks. Angewandte Chemie International Edition, 2017, 56). Although the separation membrane obtained by compounding MXene with different organic / inorganic materials can improve the permeability and retention rate of the separation membrane, the interlayer spacing of the membrane prepared by MXene stacking is usually small and difficult to change, which greatly limits its application. SUMMARY

[0004] The application aims to provide a temperature-responsive MXene separation membrane capable of effectively separating mixed molecules of different sizes and a preparation method thereof. By covalently grafting PNIPAm (poly-N-isopropyl acrylamide) onto MXene, a smart polymer composite MXene-g-PNIPAm nanosheet is obtained, and then a temperature-responsive MX-PN membrane is successfully prepared by vacuum filtration, which can spontaneously adjust the interlayer spacing of MXene and thus the effective pore size of the membrane according to the change of external temperature.

[0005] The application provides a preparation method of a temperature-responsive MXene nanofiltration membrane for mixed molecule separation, which comprises the following steps:

[0006] (1) LiF solid powder and Ti3AlC2 are stirred in an HCl solution, centrifuged and washed, then added into water, ultrasonically treated under an inert gas, centrifuged, and the supernatant is taken to obtain MXene; the obtained MXene is added into a lye solution to react and obtain MXene-OH; then the MXene-OH is added into a mixed solution of ethanol and deionized water, the pH value is adjusted, and γ-methacryloxypropyltrimethoxysilane is added and stirred at room temperature; after centrifugation and washing, the product is ultrasonically dispersed in DMF to obtain a vinylated MXene;

[0007] (2) The vinylated MXene obtained in step (1) is mixed with DMF, N-isopropyl acrylamide monomer is added, and an initiator azobisisobutyronitrile is added to polymerize and obtain poly-N-isopropyl acrylamide grafted MXene;

[0008] (3) The poly-N-isopropyl acrylamide grafted MXene obtained in step (2) is dispersed in water to prepare a dispersion liquid with a concentration of 0.1-2 mg / mL, and a temperature-responsive nanofiltration membrane is prepared by vacuum filtration with a microfiltration membrane as a substrate.

[0009] In step (1), the stirring temperature is 25-40℃, the stirring time is 12-48 h, the ultrasonic treatment time at room temperature is 30-60 min, the centrifugal speed is 1500-3500 rpm, and the centrifugal time is 30-60 min; the inert gas is argon or nitrogen.

[0010] In step (1), the lye is a commonly used lye in the art, which can be NaOH or KOH, etc.; when the lye is NaOH or KOH, the concentration of the NaOH or KOH solution is 2-5 mol / L, and the reaction time is preferably 2-4 h.

[0011] In step (1), the pH is adjusted to 3-4.5 with acetic acid; stirring is carried out at room temperature for 6-10 h; the mass ratio of MXene to gamma-methacryloxypropyltrimethoxysilane is 1:1-2; and the volume ratio of ethanol to water in the mixed solution of ethanol and water is 6-9:1-4.

[0012] In step (2), the mass ratio of the vinylated MXene to DMF is 1:950-1900; and the mass ratio of the vinylated MXene to N-isopropylacrylamide is 1:100-250.

[0013] In step (2), the mass ratio of the azobisisobutyronitrile to N-isopropylacrylamide is 1:50-100.

[0014] In step (2), the polymerization temperature is 55-70℃, and the reaction time is 6-24 h.

[0015] In step (3), the pressure during vacuum filtration is 0.01-0.1 MPa.

[0016] In step (3), the base microfiltration membrane used is one of cellulose acetate membrane, nylon membrane, polyvinylidene fluoride membrane and anodic aluminum oxide.

[0017] The application also comprises an application of the temperature-responsive nanofiltration membrane prepared by the preparation method for mixed molecular separation, which can be used in the fields of water treatment, molecular separation of various different molecular sizes, drug separation and the like.

[0018] The advantages or beneficial effects of the application are as follows:

[0019] (1) By simply regulating the external temperature, the interlayer spacing of MXene can be effectively controlled, and a MXene nanofiltration membrane with adjustable pore size can be prepared.

[0020] (2) By adjusting the grafting rate, MXene membranes with different response behaviors can be prepared, which can realize the change from positive correlation to negative correlation between temperature and flux, and expand the application range.

[0021] (3) Since MXene has good optical and electrical properties, the MXene separation membrane can realize multiple responses such as photo-thermal and electro-thermal responses at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The pure water fluxes of the membranes MX, MX-PN-1, MX-PN-2 and MX-PN-3 obtained for the examples and comparative examples at 25℃ and 50℃.

[0023] Figure 2The retention rates of the membranes MX, MX-PN-3 obtained for the examples and comparative examples for various small molecules at 25°C and 50°C.

[0024] Figure 3 Schematic diagram of the temperature-responsive MX-PN membrane for separating mixed molecules regulated by temperature.

[0025] Figure 4 Retention effect of the membrane MX-PN-3 obtained for the example for separating mixed molecules.

[0026] Figure 5 UV spectrum of the separation product of the membrane MX-PN-3 obtained for the example for separating mixed molecules.

[0027] Figure 6 Photo-thermal conversion effect of the membrane MX-PN-3 obtained for the example. DETAILED DESCRIPTION

[0028] Example 1

[0029] (1) Preparation of vinylated MXene

[0030] 30 mL of HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After 3.2 g of LiF solid powder was completely dissolved, 2 g of Ti3AlC2 powder was slowly added, and magnetic stirring was performed at 35°C for 24 h. After washing with deionized water and centrifugation (3500 rpm, 5 min), surface residual impurities were removed until the pH value of the washing liquid was not less than 6. Then 200 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was performed at room temperature for 60 min. After centrifugation (3500 rpm, 60 min), the upper clear liquid was taken to obtain MXene. Then, the MXene was added to a 5 mol / L NaOH solution, stirred at room temperature for 2 h, and then centrifuged and washed to neutral to obtain MXene-OH. Then, 20 mL of deionized water was mixed with 180 mL of ethanol solution, and then 120 mg of MXene-OH was added. The pH value was adjusted to 3.5 with acetic acid solution, and then 0.24 g of γ-methacryloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the vinylated MXene was obtained by centrifugal washing with ethanol for 3 times.

[0031] (2) Preparation of temperature-responsive MXene

[0032] The 40 mg of ethylenated MXene obtained in step (1) was dispersed in 37.95 g of DMF to obtain a DMF dispersion of MXene-Si, and then 4.526 g of NIPAm monomer and 0.0452 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and after three subcooling-freezing-vacuum-thawing cycles, the oxygen in the system was removed. The reaction was carried out at 65°C for 12 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene, thereby obtaining poly-N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm).

[0033] (3) Temperature-responsive nanofiltration membrane

[0034] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion of 2 mg / mL. A 0.22 μm nylon membrane was used as a substrate, and 5 mL of the dispersion was filtered under 0.1 MPa to prepare a MX-PN-1 separation membrane, i.e., a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0035] Example 2

[0036] (1) Preparation of ethylenated MXene

[0037] 30 mL of HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 35°C for 24 h. The surface residue impurities were removed by washing with deionized water and centrifugation (3500 rpm, 5 min) until the pH value of the washing liquid was not less than 6. Then 200 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was performed at room temperature for 60 min. After centrifugation (3500 rpm, 60 min), the upper clear liquid was obtained to obtain MXene. Then, the MXene was added to a 5 mol / L NaOH solution, stirred at room temperature for 2 h, and then centrifuged and washed to neutral. Then, 20 mL of deionized water was mixed with 180 mL of ethanol solution, and 120 mg of MXene-OH was added. The pH value was adjusted to 3.5 with acetic acid solution, and 0.24 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the mixture was washed with ethanol three times by centrifugation to obtain ethylenated MXene.

[0038] (2) Preparation of temperature-responsive MXene

[0039] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 37.95 g of DMF to obtain a DMF dispersion of MXene-Si, and then 6.78 g of NIPAm monomer and 0.0678 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles. The reaction was carried out at 65°C for 12 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene, thereby obtaining poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm).

[0040] (3) Temperature-responsive nanofiltration membrane

[0041] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL. A 0.22-μm nylon membrane was used as a substrate, and 5 mL of the dispersion liquid was filtered under a pressure of 0.1 MPa to prepare a MX-PN-2 separation membrane, that is, a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0042] Example 3

[0043] (1) Preparation of vinylated MXene

[0044] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 35°C for 24 h. The surface residual impurities were removed by washing with deionized water and centrifugation (3500 rpm, 5 min) until the pH value of the washing liquid was not less than 6. Then, 200 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was performed at room temperature for 60 min. After centrifugation (3500 rpm, 60 min), the upper clear liquid was obtained to obtain MXene. Then, the MXene was added to a 5 mol / L NaOH solution, stirred at room temperature for 2 h, and then centrifuged and washed to neutral. Then, 20 mL of deionized water was mixed with 180 mL of an ethanol solution, and 120 mg of MXene-OH was added. The pH value was adjusted to 3.5 with an acetic acid solution, and 0.24 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the vinylated MXene was obtained by centrifugation and washing with ethanol three times.

[0045] (2) Preparation of temperature-responsive MXene

[0046] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 37.95 g of DMF to obtain a DMF dispersion of MXene-Si, and then 9.052 g of NIPAm monomer and 0.0905 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles. The reaction was carried out at 65°C for 12 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene. Thus, poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm) was obtained.

[0047] (3) Temperature-responsive nanofiltration membrane

[0048] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion with a concentration of 2 mg / mL. A 0.22 μm nylon membrane was used as a substrate, and 5 mL of the dispersion was filtered under a pressure of 0.1 MPa to prepare a MX-PN-3 separation membrane, i.e., a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0049] Example 4

[0050] (1) Preparation of vinylated MXene

[0051] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 25°C for 24 h. The surface residue impurities were removed by washing with deionized water and centrifugation (3500 rpm, 5 min) until the pH value of the washing liquid was not less than 6. Then, 200 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was performed at room temperature for 60 min. After centrifugation (1500 rpm, 30 min), the upper clear liquid was obtained, and MXene was obtained. Then, the MXene was added to a 5 mol / L KOH solution, stirred at room temperature for 2 h, and then centrifuged and washed to neutral. Then, 40 mL of deionized water was mixed with 160 mL of an ethanol solution, and 120 mg of MXene-OH was added. The pH value was adjusted to 3.5 with an acetic acid solution, and 0.12 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the vinylated MXene was washed with ethanol three times by centrifugation.

[0052] (2) Preparation of temperature-responsive MXene

[0053] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 37.95 g of DMF to obtain a DMF dispersion of MXene-Si, and then 4.526 g of NIPAm monomer and 0.0452 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles. The reaction was carried out at 65°C for 24 h, and then the unreacted NIPAm monomer and the PNIPAm not grafted to the surface of the MXene were removed by centrifugal (7800 rpm, 10 min) washing with deionized water three times. Finally, poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm) was obtained.

[0054] (3) Temperature-responsive nanofiltration membrane

[0055] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL. A MX-PN-4 separation membrane was prepared by filtering 5 mL of the dispersion liquid under a pressure of 0.05 MPa using a polyvinylidene fluoride substrate with a pore size of 0.22 μm. The MX-PN-4 separation membrane is a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0056] Example 5

[0057] (1) Preparation of vinylated MXene

[0058] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added. The mixture was stirred at 25°C for 48 h, washed with deionized water and centrifuged (3500 rpm, 5 min) to remove surface residue impurities until the pH value of the washing liquid was not less than 6. Then, 200 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was carried out at room temperature for 60 min. After centrifugation (1500 rpm, 60 min), the upper clear liquid was taken to obtain MXene. Then, the MXene was added to a 2 mol / L KOH solution, stirred at room temperature for 4 h, and then centrifuged and washed to neutral. Finally, 60 mL of deionized water was mixed with 140 mL of an ethanol solution, and then 120 mg of MXene-OH was added. The pH value was adjusted to 4.0 with an acetic acid solution, and then 0.12 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the mixture was washed with ethanol three times by centrifugation to obtain vinylated MXene.

[0059] (2) Preparation of temperature-responsive MXene

[0060] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 75.9 g of DMF to obtain a DMF dispersion of MXene-Si, and then 6.78 g of NIPAm monomer and 0.0678 g of azobisisobutyronitrile were added and completely dissolved, and then the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles, and the reaction was carried out at 70°C for 12 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene. Poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm) was obtained.

[0061] (3) Temperature-responsive nanofiltration membrane

[0062] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL, and 5 mL of the dispersion liquid was filtered under a pressure of 0.1 MPa using a polyvinylidene fluoride substrate with a pore size of 0.22 μm to prepare a MX-PN-5 separation membrane, i.e., a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0063] Example 6

[0064] (1) Preparation of vinylated MXene

[0065] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker, 3.2 g of LiF solid powder was completely dissolved, and then 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 35°C for 12 h, and then washed with deionized water and centrifuged (3500 rpm, 5 min) to remove surface residual impurities until the pH value of the washing liquid was not less than 6, and then 200 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was carried out at room temperature for 60 min, and then the upper clear liquid was taken by centrifugation (1500 rpm, 45 min) to obtain MXene; then 5 mol / L NaOH solution was added, and the mixture was stirred at room temperature for 2 h, and then centrifuged and washed to neutral to obtain MXene-OH; 80 mL of deionized water was mixed with 120 mL of an ethanol solution, and then 120 mg of MXene-OH was added, and the pH value was adjusted to 3.0 with an acetic acid solution, and then 0.18 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added, and the mixture was stirred at room temperature for 6 h, and then washed with ethanol by centrifugation three times to obtain vinylated MXene.

[0066] (2) Preparation of temperature-responsive MXene

[0067] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 75.9 g of DMF to obtain a DMF dispersion of MXene-Si, and then 9.052 g of NIPAm monomer and 0.0905 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles. The reaction was carried out at 60°C for 36 h, and then the unreacted NIPAm monomer and the PNIPAm not grafted to the surface of the MXene were removed by centrifugal (7800 rpm, 10 min) washing with deionized water three times. Finally, poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm) was obtained.

[0068] (3) Temperature-responsive nanofiltration membrane

[0069] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL. A MX-PN-6 separation membrane was prepared by vacuum filtration of 5 mL of the dispersion liquid on a polyvinylidene fluoride substrate with a pore size of 0.22 μm at a pressure of 0.05 MPa. The MX-PN-6 separation membrane is a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0070] Example 7

[0071] (1) Preparation of vinylated MXene

[0072] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added. The mixture was stirred at 35°C for 48 h, washed with deionized water and centrifuged (3500 rpm, 5 min) to remove surface residue impurities until the pH value of the washing liquid was not less than 6. Then, 150 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was carried out at room temperature for 60 min. After centrifugation (2500 rpm, 45 min), the upper clear liquid was obtained, and MXene was obtained. Then, the MXene was added to a 5 mol / L NaOH solution, stirred at room temperature for 4 h, and then centrifuged and washed to neutral. Then, 20 mL of deionized water was mixed with 180 mL of an ethanol solution, and 120 mg of MXene-OH was added. The pH value was adjusted to 3.5 with an acetic acid solution, and 0.18 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the vinylated MXene was obtained by centrifugal washing with ethanol three times.

[0073] (2) Preparation of temperature-responsive MXene

[0074] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 75.9 g of DMF to obtain a DMF dispersion of MXene-Si, and then 9.052 g of NIPAm monomer and 0.0453 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and after three subcooling-freezing-vacuum-thawing cycles, the oxygen in the system was removed. The reaction was carried out at 55°C for 24 h, and then the unreacted NIPAm monomer and the PNIPAm not grafted to the surface of the MXene were removed by centrifugal (7800 rpm, 10 min) washing with deionized water three times. Finally, poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm) was obtained.

[0075] (3) Temperature-responsive nanofiltration membrane

[0076] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL. A MX-PN-7 separation membrane was prepared by using an anodized aluminum with a pore size of 0.22 μm as a substrate and by suction filtering 5 mL of the dispersion liquid at 0.1 MPa. The MX-PN-7 separation membrane is a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0077] Example 8

[0078] (1) Preparation of vinylated MXene

[0079] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added. The mixture was stirred at 40°C for 48 h, and then washed with deionized water and centrifuged (3500 rpm, 5 min) to remove surface residue impurities until the pH value of the washing liquid was not less than 6. Then, 150 mL of ultrapure water was added, argon was filled, and ultrasonic stripping was performed at room temperature for 30 min. After centrifugation (3500 rpm, 60 min), the upper clear liquid was taken to obtain MXene. Then, the MXene was added to a 5 mol / L KOH solution, stirred at room temperature for 3 h, and then centrifuged and washed to neutral. Then, 20 mL of deionized water was mixed with 180 mL of an ethanol solution, and then 120 mg of MXene-OH was added. The pH value was adjusted to 3.0 with an acetic acid solution, and then 0.12 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added. After stirring at room temperature for 10 h, the mixture was washed with ethanol three times by centrifugation to obtain vinylated MXene.

[0080] (2) Preparation of temperature-responsive MXene

[0081] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 57 g of DMF to obtain a DMF dispersion of MXene-Si, and then 6.78 g of NIPAm monomer and 0.0339 g of azobisisobutyronitrile were added and completely dissolved, and then the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles, and the reaction was carried out at 70°C for 12 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene, thereby obtaining poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm).

[0082] (3) Temperature-responsive nanofiltration membrane

[0083] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL, and a cellulose acetate with a pore size of 0.22 μm was used as a substrate, and 5 mL of the dispersion liquid was filtered under a pressure of 0.01 MPa to prepare a MX-PN-8 separation membrane, i.e., the temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0084] Example 9

[0085] (1) Preparation of vinylated MXene

[0086] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker, 3.2 g of LiF solid powder was completely dissolved, and then 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 40°C for 24 h, and then washed with deionized water and centrifuged (3500 rpm, 5 min) to remove surface residual impurities until the pH value of the washing liquid was not less than 6, and then 150 mL of ultrapure water was added, nitrogen was filled, and ultrasonic stripping was carried out at room temperature for 30 min, and then centrifugation (1500 rpm, 45 min) was carried out to obtain the upper clear liquid, thereby obtaining MXene; then the MXene was added to a 5 mol / L NaOH solution, stirred at room temperature for 2 h, and then centrifuged and washed to neutral, thereby obtaining MXene-OH; 20 mL of deionized water was mixed with 180 mL of an ethanol solution, and then 120 mg of MXene-OH was added, and the pH value was adjusted to 4.0 with an acetic acid solution, and then 0.24 g of γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added, and the mixture was stirred at room temperature for 8 h, and then washed with ethanol by centrifugation three times, thereby obtaining the vinylated MXene.

[0087] (2) Preparation of temperature-responsive MXene

[0088] The 40 mg of the vinylated MXene obtained in step (1) was dispersed in 757 g of DMF to obtain a DMF dispersion of MXene-Si, and then 4.526 g of NIPAm monomer and 0.0226 g of azobisisobutyronitrile were added and completely dissolved, and then the mixture was transferred to a Schlenk flask, and after three subcooling-freezing-vacuum-thawing cycles, the oxygen in the system was removed, and the reaction was carried out at 70°C for 24 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene, thereby obtaining poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm).

[0089] (3) Temperature-responsive nanofiltration membrane

[0090] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion liquid with a concentration of 2 mg / mL, and 5 mL of the dispersion liquid was suction filtered under a pressure of 0.1 MPa using cellulose acetate with a pore size of 0.22 μm as a substrate, thereby obtaining a MX-PN-9 membrane, i.e., a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0091] Example 10

[0092] (1) Preparation of vinylated MXene

[0093] 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker, 3.2 g of LiF solid powder was completely dissolved, and then 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 35°C for 24 h, and then washed with deionized water and centrifuged (3500 rpm, 5 min) to remove surface residual impurities until the pH value of the washing liquid was not less than 6, and then 150 mL of ultrapure water was added, nitrogen was filled, and ultrasonic stripping was carried out at room temperature for 30 min, and then the upper clear liquid was taken by centrifugation (2000 pm, 30 min) to obtain MXene; then the MXene was added to a 4 mol / L KOH solution, stirred at room temperature for 3 h, and then centrifuged and washed to neutral, thereby obtaining MXene-OH; 20 mL of deionized water was mixed with 180 mL of an ethanol solution, and then 120 mg of MXene-OH was added, and the pH value was adjusted to 3.0 with an acetic acid solution, and then 0.24 of a γ-methacryloyloxypropyltrimethoxysilane (KH570) solution was slowly added, and the mixture was stirred at room temperature for 6 h, and then washed with ethanol by centrifugation three times, thereby obtaining vinylated MXene.

[0094] (2) Preparation of temperature-responsive MXene

[0095] The 40 mg of the vinylated MXene obtained in step (1) was dispersed into 57 g of DMF to obtain a DMF dispersion of MXene-Si, and then 9.052 g of NIPAm monomer and 0.6789 g of azobisisobutyronitrile were added. After complete dissolution, the mixture was transferred to a Schlenk flask, and the oxygen in the system was removed after three sub-cooling-freezing-vacuum-thawing cycles. The reaction was carried out at 65°C for 12 h, and then centrifuged (7800 rpm, 10 min) and washed with deionized water three times to remove unreacted NIPAm monomer and PNIPAm not grafted to the surface of MXene. Thus, poly N-isopropyl acrylamide grafted MXene (MXene-g-PNIPAm) was obtained.

[0096] (3) Temperature-responsive nanofiltration membrane

[0097] The obtained MXene-g-PNIPAm was added to deionized water to prepare a dispersion with a concentration of 2 mg / mL. A 5 mL dispersion was filtered under a pressure of 0.01 MPa using a cellulose acetate membrane with a pore size of 0.22 μm as the substrate to obtain a MX-PN-10 membrane, i.e., a temperature-responsive MXene nanofiltration membrane for mixed molecular separation.

[0098] Comparative Example 1

[0099] In this comparative example, a pure MXene nanofiltration membrane was prepared. 30 mL of an HCl solution and 10 mL of deionized water were measured and added to a polytetrafluoroethylene beaker. After complete dissolution of 3.2 g of LiF solid powder, 2 g of Ti3AlC2 powder was slowly added, and the mixture was stirred at 35°C for 24 h. The surface residue impurities were removed by washing and centrifuging (3500 rpm, 5 min) several times until the pH value of the washing liquid was not less than 6. Then, 200 mL of ultrapure water was added, argon was filled, and ultrasonic exfoliation was carried out at room temperature for 60 min. The upper clear liquid was obtained by centrifugation (3500 rpm, 60 min). The obtained MXene was added to deionized water to prepare a dispersion with a concentration of 2 mg / mL. A 5 mL dispersion was filtered under a pressure of 0.1 MPa using a nylon membrane with a pore size of 0.22 μm as the substrate to obtain a MX separation membrane.

[0100] Test Example:

[0101] (1) The determination results of water flux involved: a laboratory separation device was used, and the effective test membrane area was 9.62 cm 2 250 mL of deionized water was continuously poured from the top of the device to the surface of the nanofiltration membrane. The water flux was calculated by the formula:

[0102]

[0103] In the formula, v is the volume of water that permeates through the membrane; A is the effective filtration area of ​​the membrane; and Δt is the permeation time.

[0104] (2) Results of the separation efficiency determination: A laboratory separation apparatus was used, and the separation test was conducted at a stable temperature and a transmembrane pressure of 0.1 MPa. After a certain period of time, the filtrate was collected. Its absorbance was measured using a UV spectrophotometer. The separation efficiency was calculated using the formula:

[0105] R = 1 - (c p / c o )×100%

[0106] In the formula, c p and c o These are the concentrations of the filtrate and the feed solution, respectively.

[0107] Flux, photothermal conversion, and separation of dye and mixed molecules were tested at different temperatures on the temperature-responsive nanofiltration membrane prepared in Example 1.2.3. Compared with the MX separation membrane, the MX-PN separation membrane exhibited significant temperature response performance. The MX-PN-1 and MX-PN-2 separation membranes showed a positive correlation; when the temperature changed from 25°C to 50°C, the pure water flux increased from 44.1 L / m³ to 63.8 L / m³. -2 h -1 bar -1 Increased to 72.4 and 90.2 L m -2 h -1 bar -1 The MX-PN-3 separation membrane showed a negative correlation, with the pure water flux decreasing from 95.6 L / m³. -2 h -1 bar -1 Reduced to 68.7 L m -2 h -1 bar -1 -( Figure 1 When MX and MX-PN-3 separation membranes are used for dye separation, compared with MX separation membranes, MX-PN-3 separation membranes can effectively improve the retention rate when the temperature increases. Figure 2 When the MX-PN-3 separation membrane was used for the separation of mixed molecules, at 25°C, the largest molecules were retained while the two smaller molecules permeated; at 50°C, the smallest molecules permeated while the medium-sized molecules were retained, indicating good performance in separating mixed molecules. Figure 3 , Figure 4 , Figure 5 Irradiating the MX-PN-3 separation membrane with an 808nm point light source demonstrated its excellent photothermal conversion performance. Figure 6 ).

Claims

1. A nanofiltration membrane, characterized in that, The preparation method of the nanofiltration membrane comprises the following steps: (1) stirring LiF solid powder and Ti3AlC2 in an HCl solution, centrifuging, washing, adding water, ultrasonicating under an inert gas, centrifuging, and taking the supernatant to obtain MXene; adding the obtained MXene into a lye solution to obtain MXene-OH through reaction; adding the MXene-OH into a mixed solution of ethanol and deionized water, adjusting the pH value, adding γ-methacryloxypropyltrimethoxysilane, stirring at room temperature, centrifuging, washing, and ultrasonicating and dispersing in DMF to obtain a vinylated MXene; (2) mixing the vinylated MXene obtained in step (1) with DMF, adding N-isopropyl acrylamide monomers, and then adding an initiator azobisisobutyronitrile to obtain a poly-N-isopropyl acrylamide grafted MXene through polymerization; (3) dispersing the poly-N-isopropyl acrylamide grafted MXene obtained in step (2) into water to configure a dispersion liquid with a concentration of 0.1-2 mg / mL, and using a microfiltration membrane as a substrate to prepare a temperature-responsive nanofiltration membrane through vacuum filtration.

2. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the stirring temperature is 25-40℃, the stirring time is 12-48 h, the ultrasonicating time at room temperature is 30-60 min, the centrifuging speed is 1500-3500 rpm, and the centrifuging time is 30-60 min, and the inert gas is argon or nitrogen.

3. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the mass ratio of MXene to γ-methacryloxypropyltrimethoxysilane is 1:1-2, and the volume ratio of ethanol to water in the mixed solution of ethanol and water is 6-9:1-4.

4. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the lye is NaOH or KOH, the concentration of NaOH or KOH is 2-5 mol / L, the reaction time is 2-4 h, the pH value is adjusted to 3-4.5 with acetic acid, and the stirring time at room temperature is 6-10 h.

5. The nanofiltration membrane according to claim 1, characterized in that, In step (2), the mass ratio of the vinylated MXene to DMF is 1:950-1900, and the mass ratio of the vinylated MXene to N-isopropyl acrylamide is 1:100-250.

6. The nanofiltration membrane according to claim 1, characterized in that, In step (2), the mass ratio of azobisisobutyronitrile to N-isopropyl acrylamide is 1:50-100, the polymerization reaction temperature is 55-70℃, and the reaction time is 6-24 h.

7. The nanofiltration membrane according to claim 1, characterized in that, In step (3), the pressure in the vacuum filtration process is 0.01-0.1 MPa.

8. The nanofiltration membrane according to claim 1, characterized in that, In step (3), the substrate microfiltration membrane used is one of cellulose acetate membrane, nylon membrane, polyvinylidene fluoride membrane, and anodic aluminum oxide.

9. A preparation method of the nanofiltration membrane according to claim 1, characterized in that, The preparation method of the separation membrane comprises the following steps: (1) stirring LiF solid powder and Ti3AlC2 in an HCl solution, centrifuging and washing, adding water, ultrasonicating under an inert gas, centrifuging, and taking the supernatant to obtain MXene; adding the obtained MXene into a lye solution to obtain MXene-OH through reaction; adding the MXene-OH into a mixed solution of ethanol and deionized water, adjusting the pH value, adding γ-methacryloxypropyltrimethoxysilane, stirring at room temperature, centrifuging and washing, and ultrasonicating and dispersing in DMF to obtain vinylated MXene; (2) mixing the vinylated MXene obtained in step (1) with DMF, adding N-isopropyl acrylamide monomers, and adding an initiator azobisisobutyronitrile to obtain poly-N-isopropyl acrylamide grafted MXene through polymerization; (3) dispersing the poly-N-isopropyl acrylamide grafted MXene obtained in step (2) into water to configure a dispersion liquid with a concentration of 0.1-2 mg / mL, taking a microfiltration membrane as a substrate, and preparing a temperature-responsive nanofiltration membrane through vacuum suction filtration.

10. The application of the nanofiltration membrane according to claims 1-8, characterized in that the nanofiltration membrane is used for the application of a temperature-responsive nanofiltration membrane for mixed molecular separation. The application of the nanofiltration membrane according to claims 1-8, characterized in that the nanofiltration membrane is used for the application of a temperature-responsive nanofiltration membrane for mixed molecular separation.

Images