Mxene-based composite nanofiltration membrane, preparation method and application thereof

Abstract

The application discloses a kind of based on Mxene composite nanofiltration membrane and its preparation method and application.The method is that Mxene nanometer sheet dispersion liquid is mixed with tea polyphenol solution and is carried out adsorption reaction, and Mxene-TP precipitate is obtained;The Mxene-TP precipitate is mixed with silver salt solution and is carried out stirring reaction after solid-liquid separation, and solid is obtained, namely obtained.The composite nanofiltration membrane has high water flux and rejection capacity, and can effectively filter and remove organic pollutants in wastewater.The preparation method is simple, low in cost, and suitable for industrial scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to a nanofiltration membrane, in particular to a composite nanofiltration membrane based on Mxene, and a preparation method and application thereof, and belongs to the technical field of membrane materials. BACKGROUND

[0002] With the rapid development of industrialization, the demand for water resources by humans is expanding. Wastewater reuse and water purification are necessary conditions to meet the growing demand for water. At present, the mainstream water purification technology is still cost-intensive and energy-intensive, therefore, simple, energy-saving and environmentally friendly membrane-based technology has attracted widespread attention. Nanofiltration (NF) can reject small molecules (200-1000 Da) and separate salts with high water permeability at low pressure, and has been widely used in the field of water purification.

[0003] The key to nanofiltration technology is membrane material. However, it is still challenging to develop the most advanced nanofiltration membrane with high permeability and selectivity. In recent years, MXene has been tried to be used to prepare nanofiltration membranes with clear laminar flow structure due to its excellent physical and chemical properties and unique water molecule channel.

[0004] The MXene nanofiltration membrane often swells in the water environment, and there is an unbreakable trade-off effect between permeability and selectivity. Therefore, it is necessary to find a suitable modification method to improve the membrane water flux while maintaining high retention capacity, so as to promote the research and application of nanofiltration membranes. SUMMARY

[0005] In view of the deficiencies of the prior art, the first object of the present application is to provide a composite nanofiltration membrane based on Mxene. The composite nanofiltration membrane has high membrane water flux and filtration capacity.

[0006] The second object of the present application is to provide a preparation method of a composite nanofiltration membrane based on Mxene. The method is simple, low in cost, and suitable for industrial scale production.

[0007] The third object of the present application is to provide an application of a composite nanofiltration membrane based on Mxene. When used for treating sewage, it can efficiently filter and remove organic pollutants in water.

[0008] In order to achieve the above technical purposes, the present application provides a preparation method of a composite nanofiltration membrane based on Mxene, which comprises the following steps: mixing a Mxene nanosheet dispersion liquid with a tea polyphenol solution to perform an adsorption reaction, to obtain a Mxene-TP precipitate; mixing the Mxene-TP precipitate with a silver salt solution to perform a stirring reaction, and then performing solid-liquid separation to obtain a solid, namely.

[0009] The tea polyphenol can be adsorbed on the edge of the Mxene nanosheet, effectively prevent the nanosheet from being adsorbed on each other, and reduce the size of the nanosheet; after the Mxene is modified by the tea polyphenol, the silver salt cannot be reduced on the edge of the nanosheet in the compounding process, which can effectively prevent the nanosheet from being aggregated and being wrinkled, and can make the prepared nanofiltration membrane surface smooth, improve the organic matter filtration capacity and water flux of the membrane. In addition, the tea polyphenol itself has a sterilization effect, and the sterilization effect of the Mxene modified by the tea polyphenol is improved, which improves the anti-fouling ability of the membrane.

[0010] As a preferred scheme, the Mxene nanosheet is Ti3C2T x nanosheet.

[0011] As a preferred scheme, the Ti3C2T x nanosheet is obtained by etching Ti3AlC2 with hydrochloric acid and lithium fluoride.

[0012] As a preferred scheme, the solvent in the Mxene nanosheet dispersion liquid is water.

[0013] As a preferred scheme, the mass of the tea polyphenol in the tea polyphenol solution is not more than 10 times the mass of the Mxene nanosheet. Further preferably, the mass of the tea polyphenol in the tea polyphenol solution is 3-9 times the mass of the Mxene nanosheet.

[0014] As a preferred scheme, the mass ratio of the tea polyphenol to the Mxene nanosheet in the tea polyphenol solution is 2-10:1. The tea polyphenol can effectively reduce the size of the nanosheet, and controlling the amount of the tea polyphenol in a suitable range is beneficial to improve the performance of the composite membrane. If the amount of the tea polyphenol is too low, the nanosheet modification will not be sufficient, and if the amount of the tea polyphenol is too high, it will cause resource waste.

[0015] As a preferred scheme, the mass concentration of the Mxene nanosheet dispersion liquid is 3-5 mg / ml.

[0016] As a preferred scheme, the adsorption reaction is carried out at room temperature for 3-24 h.

[0017] As a preferred scheme, the silver salt is silver nitrate.

[0018] As a preferred scheme, the mass of the silver salt in the silver salt solution is not more than the mass of the Mxene nanosheet.

[0019] As a preferred scheme, the mass ratio of the silver salt in the silver salt solution to the Mxene nanosheet is 0.1-1:1, and further preferably 0.2-0.97:1. Controlling the silver salt dosage in a suitable range is beneficial to obtain a composite nanofiltration membrane with excellent performance. When the silver salt dosage is too high, the formation of excessive silver nanoparticles will cause the reduction of tea polyphenols, resulting in the continued aggregation of nanosheets, the loss of tea polyphenol effect, and the decrease of the filtration capacity of the prepared nanofiltration membrane; when the silver salt dosage is too low, the reduced silver nanoparticles will be too few, so that the prepared nanofiltration membrane cannot obtain a large enough water flow channel, resulting in the decrease of water flux.

[0020] As a preferred scheme, the concentration of the silver salt solution is 0.1-1 mg / mL.

[0021] As a preferred scheme, the stirring reaction condition is that the temperature is room temperature, and the time is 0.2-3 h.

[0022] As a preferred scheme, the solid-liquid separation mode is vacuum filtration.

[0023] The application further provides a Mxene-based composite nanofiltration membrane prepared by the above method.

[0024] The application further provides an application of the Mxene-based composite nanofiltration membrane, which is applied to filter organic pollutants in a water body.

[0025] As a preferred scheme, the organic pollutants are dyes.

[0026] As a preferred scheme, the concentration of the organic pollutants in the water body is ≤20 ppm.

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

[0028] (1) The composite nanofiltration membrane has excellent filtration capacity, while maintaining a high membrane water flux;

[0029] (2) By modifying the Mxene nanosheet with tea polyphenol, the size of the nanosheet is reduced, the stacking is more compact, the membrane surface state is effectively changed, the membrane surface is more smooth, and due to the reduction of the size of the nanosheet, the number of water flow channels after stacking is increased, and the water flux is improved;

[0030] (3) When the composite nanofiltration membrane is used for treating sewage, it can efficiently filter and remove organic pollutants in the water body;

[0031] (4) The preparation method is simple, the cost is low, and it is suitable for industrial scale production. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1Particle size distribution of the composite nanosheet dispersion liquid and SEM image of the film surface in Comparative Examples 1-2, wherein (a) is the Mxene nanosheet dispersion liquid and Mxene composite film of #5 in Comparative Example 1, and (b) is the Mxene-TP nanosheet dispersion liquid and Mxene-TP composite film of #7 in Comparative Example 2.

[0033] Figure 2 Particle size distribution of the composite nanosheet dispersion liquid and TEM image in Comparative Example 1 and Example 1, wherein (a) is the Mxene@Ag nanosheet dispersion liquid of #3 in Comparative Example 1, and (b) is the Mxene-TP@Ag nanosheet dispersion liquid of Example 1.

[0034] Figure 3 SEM image of the surface of the composite film prepared in Comparative Example 1 and Example 1, wherein (a) is the Mxene@Ag nanosheet dispersion liquid of #3 in Comparative Example 1, (b) is the Mxene-TP@Ag nanosheet dispersion liquid of Example 1, (c) is the Mxene@Ag composite film prepared from #3 in Comparative Example 1, and (d) is the Mxene-TP@Ag composite film prepared from Example 1.

[0035] Figure 4 XRD image of the composite film prepared in Comparative Examples 1-2 and Example 1 before and after wetting, wherein (a) is the Mxene composite film prepared from #5 in Comparative Example 1, (b) is the Mxene-TP composite film prepared from #7 in Comparative Example 2, (c) is the Mxene@Ag composite film prepared from #3 in Comparative Example 1, and (d) is the Mxene-TP@Ag composite film prepared from Example 1.

[0036] Figure 5 Comparison chart of the surface antibacterial ability of the composite film prepared in Comparative Examples 1-2, Example 1 paper, and PVDF filter paper, wherein (a) is the PVDF filter paper, (b) is the Mxene composite film prepared from #5 in Comparative Example 1, (c) is the Mxene-TP composite film prepared from #7 in Comparative Example 2, (d) is the Mxene@Ag composite film prepared from #3 in Comparative Example 1, and (e) is the Mxene-TP@Ag composite film prepared from Example 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be described in further detail below with reference to the drawings.

[0038] Comparative Example 1

[0039] The preparation of the Mxene composite film and the Mxene@Ag composite film is as follows:

[0040] (1) 10 mL of 9M HCl and 1 g of LiF were added to a PTFE beaker containing 1 g of Ti3AlC2, stirred and heated at 35°C for 24 hours to prepare an accordion-like Mxene. After that, the dispersion was washed with deionized water and centrifuged at 3500 rpm until pH > 6. Finally, the precipitate was removed by centrifugation at 5000 rpm for 30 minutes to obtain single-layer Ti3C2T x Mxene nanosheets.

[0041] (2) A 5 mg / mL Mxene nanosheet dispersion was prepared with water as the solvent, 300 μL of the Mxene nanosheet dispersion was added to 20 mL of deionized water to form a dilute dispersion containing 1.5 mg of Mxene nanosheets, and then a 1 mg / mL silver nitrate aqueous solution was prepared. Different volumes of silver nitrate solution were added to the above dilute dispersion according to the required silver nitrate content in Table 1, stirred for 1 h to obtain a Mxene@Ag nanosheet dispersion, and a Mxene@Ag composite membrane was prepared on a PVDF filter paper using a vacuum replication suction filtration method, numbered #1, #2, #3, #4.

[0042] In addition, in step (2), a dilute dispersion containing 1.5 mg of Mxene was directly prepared into a Mxene composite membrane on a PVDF filter paper using a vacuum replication suction filtration method, numbered #5.

[0043] Table 1

[0044]

[0045]

[0046] The Mxene composite membranes and Mxene@Ag composite membranes prepared in the above comparative examples were tested for performance, and the water flux J = V / AtP and the dye filtration capacity of the membranes were the most reflective parameters of the performance of the membranes. Among them, with the increase of silver nitrate, the fluxes of #1, #2, #3, #4, #5 membranes for 20 ppm rhodamine B solution were 80.6 L·m -2 ·h -1 ·bar -1 , 103.3 L·m -2 ·h -1 ·bar -1 , 135.8 L·m -2 ·h -1 ·bar -1 , 366.4 L·m -2 ·h -1 ·bar -1 , 26.6 L·m -2 ·h -1 ·bar -1, the dye filtration capacities were 82.3%, 79.8%, 76.9%, 62.4%, 96.95%, respectively. The results showed that the content of silver nitrate would directly affect the number of silver nanoparticles produced, and different contents of silver nanoparticles had a great influence on the membrane flux and the dye filtration capacity, therefore, the comprehensive performance of #3 membrane was the best.

[0047] Comparative Example 2

[0048] The preparation of Mxene-TP composite membrane, the specific steps are as follows:

[0049] (1) Mxene nanosheets were prepared by the method of Comparative Example 1;

[0050] (2) A 5mg / mL Mxene nanosheet dispersion was prepared with water as the solvent, 300μL of the Mxene nanosheet dispersion was added to 20mL of deionized water to form a diluted dispersion containing 1.5mg of Mxene nanosheets. A 3mg / mL tea polyphenol solution was prepared, and different volumes of tea polyphenol solution were taken according to the required tea polyphenol mass in Table 2, and added dropwise to the diluted dispersion containing 1.5mg of Mxene nanosheets, stirred for 12h, then the Mxene-TP dispersion was taken out and added to a 50mL centrifuge tube, centrifuged at a speed of 8500rpm / min for 5min, then the supernatant was sucked out with a rubber bulb dropper, 20mL of deionized water was added, and the operation was repeated 3 times, the last time the centrifugal precipitate was added to 20mL of deionized water, shaken and dispersed, and a Mxene-TP composite membrane #6, #7, #8 was prepared on a PVDF filter paper by vacuum replication filtration method.

[0051] Table 2

[0052] No. Mxene (mg) Tea polyphenol (mg) Silver nitrate (mg) #6 1.5 3 0 #7 1.5 9 0 #8 1.5 15 0

[0053] The membrane flux performance test was carried out on the Mxene composite membrane and the Mxene-TP composite membrane prepared in the above comparative examples, wherein the water fluxes of #5, #6, #7, #8 membranes were 45.6L·m -2 ·h -1 ·bar -1 , 52.3L·m -2 ·h -1 ·bar -1 , 56.8L·m -2 ·h -1 ·bar -1 , 56.9L·m -2 ·h -1 ·bar -1 The results showed that the introduction of tea polyphenol could reduce the average particle size of Mxene nanosheets, thereby increasing the two-dimensional flow channel of the membrane and improving the water flux.

[0054] The zeta particle size analysis was performed on the Mxene nanoplatelet (#5) solution prepared in the comparative example and the Mxene-TP nanoplatelet (#7) solution, and the surface morphology of the Mxene composite film and the Mxene-TP composite film formed thereby was analyzed, as shown in FIGS. 1(a) and 1(b), wherein (a) is the #5 film and (b) is the #7 film. As can be seen from the figures, the average particle size of the Mxene-TP nanoplatelet (#7) modified by tea polyphenol is significantly reduced, and the surface of the #7 film is more flat than that of the #5 film after the film is prepared. It can be seen that smaller nanoplatelets can provide more water flow channels to improve water flux. Figure 1

[0055] Example 1

[0056] Preparation of the Mxene-TP@Ag composite film, the specific steps are as follows:

[0057] (1) Mxene nanoplatelets were prepared by the method of Comparative Example 1;

[0058] (2) A 5 mg / mL Mxene nanoplatelet dispersion was prepared using water as the solvent, 300 μL of the dispersion was added to 20 mL of deionized water to form a diluted dispersion containing 1.5 mg of Mxene nanoplatelets. A 3 mg / mL tea polyphenol aqueous solution was prepared, 3 mL of the tea polyphenol aqueous solution with a concentration of 3 mg / mL was added dropwise to the diluted dispersion containing 1.5 mg of Mxene nanoplatelets, and stirred for 12 h. Then the Mxene-TP dispersion was taken out and added to a 50 mL centrifuge tube, centrifuged at a speed of 8500 rpm / min for 5 min, and then the supernatant was sucked out using a rubber bulb dropper. 20 mL of deionized water was added and the operation was repeated 3 times. The last time the centrifugal precipitate was added to 20 mL of deionized water and dispersed by shaking. Then, 500 μL of 1 mg / mL silver nitrate aqueous solution was added and stirred for 1 h to obtain a mixed solution containing Mxene-TP@Ag nanomaterials. A Mxene-TP@Ag composite film was prepared on a PVDF filter paper by vacuum replication suction filtration, and was numbered #9.

[0059] Example 2

[0060] The Mxene-TP@Ag composite film was prepared by the method of Example 1, except that in step (2), 300 μL and 1500 μL of 1 mg / mL silver nitrate solution were added according to the amount of silver nitrate required in Table 3, and stirred for 1 h to obtain a mixed solution containing Mxene-TP@Ag nanomaterials, respectively. A Mxene-TP@Ag composite film was prepared on a PVDF filter paper by vacuum replication suction filtration, and was numbered #10 and #11, respectively.

[0061] Table 3

[0062] ​ No. Mxene (mg) Tea polyphenol (mg) Silver nitrate (mg) #9 1.5 9 0.5 #10 1.5 9 0.3 #11 1.5 9 1.5

[0063] The performance of the Mxene-TP@Ag composite membranes (#9, #10, and #11) prepared in Examples 1 and 2 was tested. The flux of membrane #9 for 20 ppm Rhodamine B was 88.1 L·m⁻¹. -2 ·h -1 ·bar -1 The water rejection capacity is 95.8%, which is 1 / 4 higher than that of the comparative example #3 membrane. Meanwhile, the water flux is 3.3 times that of the comparative example #5 membrane. The fluxes of membranes #10 and #11 are 72.5 L·m³. -2 ·h -1 ·bar -1 and 307.6 L·m -2 ·h -1 ·bar -1 The retention capacities were 97.5% and 72.0%, respectively. The overall performance of the #9 membrane was higher than that of the #10 and #11. This is because the amount of silver nanoparticles was reduced, which could not expand the channel size sufficiently. Excessive silver nanoparticles would reduce the tea polyphenols, causing the nanosheets to partially aggregate and lose the effect of tea polyphenols, resulting in a relatively lower retention capacity.

[0064] Figure 2 The images show zeta particle size analysis and TEM images of nanosheets in solutions of membrane #3 and membrane #9, respectively. The top image shows the solution of membrane #3, and the bottom image shows the solution of membrane #9. It can be seen that the nanosheets in solution #3 showed obvious agglomeration, resulting in an increase in size, while the nanosheets in solution #9 were dispersed, with an average size significantly smaller than that in solution #3. Furthermore, the solution did not settle after 14 days, indicating that tea polyphenols can enhance the antioxidant capacity of the nanosheets.

[0065] Figure 3 SEM images of the nanosheets used to prepare films #3 and #9, and surface morphology images of films #3 and #9, show that the nanosheets used to prepare film #3 exhibit significant agglomeration, while film #9 does not. Film #3 has more wrinkles on its surface, while film #9 has a flat surface. This also results in the comparative film #3 having a significantly lower retention capacity than film #9 in example.

[0066] The Mxene-TP@Ag composite membrane #9 prepared in Example 1 and the Mxene@Ag composite membrane #3, Mxene composite membrane #5, and Mxene-TP composite membrane #7 prepared in the comparative example were vacuum dried and XRD tested. They were then soaked in deionized water for 24 hours and XRD tested again. The changes in characteristic peaks before and after were compared.

[0067] like Figure 4As shown in the XRD diagram, the (002) peaks of the #5 film (Mxene), the #7 film (Mxene-TP), and the #3 film (Mxene@Ag) have a large displacement in the dry and wet states, while the #9 film (Mxene-TP@Ag) has almost no displacement, indicating that there is a cross-linking effect between the Mxene, tea polyphenol, and silver nanoparticles, which can effectively improve the anti-swelling ability of the film.

[0068] Example 3

[0069] The Mxene-TP@Ag composite film was prepared by the method of Example 1, except that in step (2), 1 mL and 5 mL of 1 mg / mL nitro tea polyphenol solution were added according to the required amount of tea polyphenol in Table 4, and stirred for 12 h to obtain a mixed solution containing Mxene-TP@Ag nanomaterials. The Mxene-TP@Ag composite film was prepared on a PVDF filter paper by vacuum replication filtration, and was numbered as #12 and #13, respectively.

[0070] Table 4

[0071] No. Mxene (mg) Tea polyphenol (mg) Silver nitrate (mg) #12 1.5 3 0.5 #13 1.5 15 0.5

[0072] The Mxene-TP@Ag composite films (#9, #12, and #13) prepared in Examples 1 and 3 were tested for performance, wherein the flux of the prepared #9 film for 20 ppm rhodamine B was 88.1 L·m -2 ·h -1 ·bar -1 , the rejection ability was 95.8%, the fluxes of the #12 film and the #13 film were 92.3 L·m -2 ·h -1 ·bar -1 and 86.3 L·m -2 ·h -1 ·bar -1 , and the rejection abilities were 94.2% and 95.1%, respectively. The comprehensive performance of the #9 film was higher than that of the #12 and #13 films, because the tea polyphenol content was reduced, and the nanosheets still partially aggregated, affecting the rejection ability of the film to the dye. When the amount of tea polyphenol added exceeds a certain amount, it will not further improve the filtration performance of the film.

[0073] Example 4 (antibacterial performance test)

[0074] (1) Take 10 g, 5 g, 15 g, and 10 g of tryptone, yeast extract, agar, and sodium chloride, respectively, and dissolve them in 1 L of deionized water to prepare the culture medium. Use a high-pressure sterilization pot to fully dissolve the above reagents and sterilize the culture medium. Take 1 mL and plate the culture dish before the agar coagulates.

[0075] (2) Take tryptone, yeast extract powder, sodium chloride into 10 g, 5 g, 10 g respectively, dissolved in 1 L deionized water to prepare the medium. The above reagents were dissolved by high pressure sterilization pot, and the test tubes were sterilized at the same time to prepare the liquid medium.

[0076] (3) A small amount of slant bacteria was picked and added to the liquid medium for 24 hours of culture for activation. Then the bacteria solution was diluted to a concentration of 3000 CFU / mL, and #9 membrane (Mxene-TP@Ag), #5 membrane (Mxene), #7 membrane (Mxene-TP), #3 membrane (Mxene@Ag) and PVDF filter paper were placed in the solid medium prepared before. 50 μL of liquid medium was used to coat the surface of each membrane, and then the culture dishes were placed in an incubator at 37°C for 24 h.

[0077] As shown in Figure 5 , the growth of E. coli on the pure Mxene surface was reduced compared to the PVDF surface, and the antibacterial ability of the Mxene-TP membrane surface was improved compared to the Mxene membrane surface. The antibacterial ability of the Mxene-TP@Ag and Mxene@Ag membrane surfaces reached 100%.

Claims

1. A method for preparing a composite nanofiltration membrane based on Mxene, characterized in that: The Mxene nanosheet dispersion liquid is mixed with a tea polyphenol solution to perform an adsorption reaction to obtain a Mxene-TP precipitate; The Mxene-TP precipitate is mixed with a silver salt solution to perform a stirring reaction, and then solid-liquid separation is performed to obtain a solid, thereby obtaining the product.

2. The method for preparing a Mxene composite nanofiltration membrane according to claim 1, characterized in that: The Mxene nanoplatelets are Ti3C2T x nanoplatelets.

3. The preparation method of the Mxene-based composite nanofiltration membrane according to claim 1 or 2, characterized in that: The mass of tea polyphenols in the tea polyphenol solution is not more than 10 times the mass of the Mxene nanosheets; The mass concentration of the Mxene nanosheet dispersion liquid is 0.05-0.1 mg / ml.

4. The method of claim 1, wherein the method is characterized by: The silver salt is silver nitrate.

5. The method for preparing a Mxene-based composite nanofiltration membrane according to claim 1 or 4, characterized in that: The mass of the silver salt in the silver salt solution is not more than the mass of the Mxene nanosheets.

6. The method of claim 1 or 4, wherein the method is characterized by: The concentration of the silver salt solution is 0.1-1 mg / mL.

7. The method of claim 1, wherein the method is characterized by: The stirring reaction is performed at room temperature for 0.2-3 h, and the solid-liquid separation is performed by vacuum filtration.

8. A composite nanofiltration membrane based on Mxene, characterized in that: Prepared by the method of any one of claims 1-7.

9. The use of a composite nanofiltration membrane based on Mxene according to claim 8, characterized in that: Applied to filtering organic pollutants in water bodies.

10. The use of a composite nanofiltration membrane based on Mxene according to claim 9, characterized in that: The organic pollutants are dyes, and the concentration of the organic pollutants in the water bodies is ≤20 ppm.

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