A self-supporting MXene hollow fiber membrane, its preparation method and application

Abstract

The present invention relates to a self-supporting MXene hollow fiber membrane and its preparation method and application. Each single fiber of the hollow fiber membrane consists of an internal support layer and an external functional layer. The support layer is a three-dimensional stereoscopic structure support layer formed by MXene, and the functional layer is an MXene layer. The inner pore diameter of each single fiber is 350 - 450 μm; the outer pore diameter is 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer pore diameter and the inner pore diameter of each single fiber; the thickness of the functional layer is 70 - 150 nm. In the present invention, MXene is mixed with a polymer and formed into a membrane by dry-wet spinning, and then heat-treated under a nitrogen or argon atmosphere. On the one hand, the high temperature decomposes the polymer, and on the other hand, the hydroxyl groups (-OH) on the surface of MXene in the support layer and the functional layer undergo self-crosslinking to form new chemical bonds (-O- bonds), crosslinking the two-dimensional materials to construct a three-dimensional stereoscopic membrane structure, and finally obtaining a hollow fiber membrane completely composed of MXene. The self-supporting MXene hollow fiber membrane prepared by the present invention has good structural stability while also possessing hydrophilicity and conductivity.

Description

Technical Field

[0001] The present invention relates to the field of membrane technology, and in particular to a self-supporting MXene hollow fiber membrane, a preparation method thereof and an application thereof. Background Art

[0002] Membrane separation technology has the characteristics of stable operation, low cost and environmental friendliness, and is an ideal solution to solve the shortage and pollution of fresh water resources. The selection and design of separation membrane materials determine the separation performance and efficiency. Two-dimensional materials represented by graphene, with nano-gaps generated by interlayer stacking, have received extensive attention in membrane technology. As a new two-dimensional material emerging in 2011, MXene has better electrical conductivity and hydrophilicity compared with graphene. Theoretical research and experimental data on these two characteristics show that MXene membranes have excellent water treatment effects, so it is a new membrane material with great development potential.

[0003] However, at present, the research on MXene materials in membrane technology mainly focuses on improving selectivity and permeability, and there are few reports on the exploration of membrane preparation processes and membrane structure stability. Since membrane fouling inevitably occurs during the separation process in the membrane, backwashing is required to regenerate the membrane performance after continuous use. However, in the current MXene membrane preparation methods (such as Liu, G.Z., et al., Chinese Journal of Chemical Engineering, 2022.41: p.260-266. Sun, Y.Q., et al., 2D Materials, 2018.5(4)), conventional membranes are used as the support substrate, and MXene is filtered or coated on its surface as the functional layer. The connection between the functional layer and the substrate of these membranes relies on hydrogen bonds and van der Waals forces. Under the influence of various external forces including backwashing during operation, the functional layer will fall off and be damaged. Moreover, if a rigid substrate is used, the MXene layer will also crack and fall off during storage in a dry environment. The reason is that traditional preparation is carried out in a liquid phase, at this time MXene is in a swollen state, and when stored dry, the deformation of MXene and the substrate is inconsistent, resulting in cracking and falling off. Although introducing other chemical drugs to crosslink between MXene and the substrate can enhance the binding force, this method will have a negative impact on electrical conductivity and hydrophilicity, losing the advantages of MXene itself. These problems greatly limit the application of MXene membranes. Therefore, developing a new preparation method for MXene membranes has important value and significance. Summary of the Invention

[0004] Aiming at the problems of existing MXene membranes, that is, the functional layer and the support substrate are not well-matched, the purpose of the present invention is to provide a self-supporting MXene hollow fiber membrane, a preparation method thereof and an application thereof.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] A self-supporting MXene hollow fiber membrane. The basic idea is to use dry-wet spinning technology to produce an MXene / polymer hybrid membrane blank, and then perform high-temperature self-crosslinking in an inert gas atmosphere to finally obtain a self-supporting MXene hollow fiber membrane.

[0007] The present invention provides a self-supporting MXene hollow fiber membrane, characterized in that a single fiber of the hollow fiber membrane is composed of an internal support layer and an external functional layer. The support layer is a three-dimensional support layer formed by MXene, and the functional layer is paved with MXene flakes. The functional layer adheres to the surface of the support layer.

[0008] Further, in the above technical solution, the inner diameter of the single fiber is 350-450 μm; the outer diameter is 550-650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer diameter and the inner diameter of the single fiber; the thickness of the functional layer is 70-140 nm.

[0009] The present invention provides a method for preparing a self-supporting MXene hollow fiber membrane, comprising the following steps:

[0010] (1) Prepare the raw materials for the support layer; dissolve the polymer in a solvent and add MXene to the solution;

[0011] (2) Prepare the raw materials for the functional layer; disperse MXene in deionized water;

[0012] (3) Use dry-wet spinning technology to produce an MXene / polymer hybrid membrane blank;

[0013] (4) Treat the MXene / polymer hybrid membrane blank obtained in step (3).

[0014] Further, in the above technical solution, in steps (1) and (2), the MXene is Ti3C2T x , Ti2CT x , Ti3CNT x , V2CT x , Ti4N3T x or Nb2CT x or one of them.

[0015] Further, in the above technical solution, in step (1), the polymer is polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polypropylene (PP), polyacrylonitrile (PAN), or polyethersulfone (PES).

[0016] Further, in the above technical solution, in step (3), a three-channel coaxial spinning head is used for the dry-wet spinning.

[0017] Still further, in the above technical solution, the three-channel spinning solutions are respectively deionized water core liquid (inner channel), MXene / polymer mixed liquid of the support layer (middle channel), and MXene aqueous dispersion of the functional layer (outer channel); the flow rate ratio (ml / h) of the inner layer, middle layer, and outer layer is 1:(2 - 4):(3 - 6).

[0018] Further, in the above technical solution, in step (1), the solvent is one of DMF, DMAC, and DMSO.

[0019] Further, in the above technical solution, in step (1), the mass-volume ratio of MXene, polymer, and solvent is 1 g:(0.2 - 0.6) g:(10 - 20) mL; the concentration of the MXene aqueous dispersion in the outer functional layer liquid is 0.5 - 2 g / L, and more preferably 1 - 1.5 g / L.

[0020] Further, in the above technical solution, in step (4), the high-temperature self-crosslinking heat treatment is carried out in an inert gas atmosphere, placed in a tube furnace at a temperature of 400 - 700 °C, with a heating rate of 5 - 20 °C / min and a time of 90 - 240 min.

[0021] The present invention provides a self-supporting MXene hollow fiber membrane prepared by the preparation method described in the above solution.

[0022] The present invention provides the application of the self-supporting MXene hollow fiber membrane described in the above solution as an MXene rigid separation membrane in water treatment.

[0023] Advantages of the present invention

[0024] The present invention uses the co-extrusion method to prepare a support layer film blank by mixing MXene and polymer through dry-wet spinning. The MXene in the aqueous dispersion adheres to the surface of the support layer film blank to form a functional layer. The polymer in the support layer film blank decomposes during the high-temperature treatment in an inert gas atmosphere. At the same time, the hydroxyl groups (-OH) on the surface of MXene in the support layer and the functional layer undergo self-crosslinking to form new chemical bonds (-O- bonds), enhancing the structural stability, and finally obtaining an integral hollow fiber membrane composed entirely of MXene. The self-supporting MXene hollow fiber membrane prepared by the present invention has good structural stability, hydrophilicity, and conductivity. Description of the drawings

[0025] Figure 1 SEM image of the self-supporting MXene hollow fiber membrane for Example 1;

[0026] Figure 2 SEM image of the self-supporting MXene hollow fiber membrane of Example 1;

[0027] Figure 3 SEM image of the MXene / PVB hollow fiber membrane of Example 1;

[0028] Figure 4 TG curve of the self-supporting MXene hollow fiber membrane of Example 1;

[0029] Figure 5 XPS of the self-supporting MXene hollow fiber membrane of Example 1;

[0030] Figure 6 Hydrophilic angle test result of the self-supporting MXene hollow fiber membrane of Example 1;

[0031] Figure 7 Mechanical strength test result of the self-supporting MXene hollow fiber membrane of Example 1. Detailed implementation mode

[0032] The present invention provides a preparation method of a self-supporting MXene hollow fiber membrane, comprising the following steps: using the dry-wet spinning technology to produce a membrane blank mixed with MXene and a polymer, and then performing high-temperature treatment in an argon atmosphere. On the one hand, the polymer is volatilized and burned off, and on the other hand, the hydroxyl functional groups (-OH) on the surface of MXene are thermally crosslinked into oxygen functional groups (-O-) to enhance the binding force, and finally a self-supporting MXene hollow fiber membrane is obtained.

[0033] In the present invention, unless otherwise specified, the raw materials used are commercially available products well-known in the art, and the specifications of the three-channel coaxial spinning head are inner needle 25G, middle needle 18G, and outer needle 15G.

[0034] Example 1

[0035] Slowly pour 0.4 g of PVB powder into 10 ml of DMF solution, stir until completely dissolved, and then add 1 g of Ti3C2T x , stir for 2 h and then let stand for 4 h to defoam, as the raw material for the support layer; Disperse Ti3C2T x in deionized water (1 g / L) as the raw material for the functional layer. Using a three-channel coaxial spinning head, the inner channel is deionized water, the middle channel is the Ti3C2T x support layer solution, and the outer channel is Ti3C2T xAqueous dispersion. Each raw material solution was connected to a spinneret with a polytetrafluoroethylene tube, and the flow rate of each channel was controlled separately with a micro-injection pump. Then the spinneret was fixed about 0.5 cm above the liquid level of the coagulation bath. The flow rate of the inner channel was controlled at 6 ml / h, the middle channel at 16 ml / h, and the outer channel at 24 ml / h. A membrane was formed by co-extrusion in the coagulation bath, transferred to a washing bath, dried and shaped after 6 h to obtain a PVB / MXene hollow fiber membrane. After drying, it was placed in a tube furnace and heated to 500 °C at a rate of 5 °C / min in an Ar atmosphere to obtain a self-supporting MXene hollow fiber membrane. During this process, functional groups were cross-linked and PVB decomposed. The inner pore diameter of the single fiber was 350 - 450 μm; the outer pore diameter was 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer was the difference between the outer and inner pore diameters of the single fiber; the thickness of the functional layer was 70 - 150 nm; the functional layer was formed by laying MXene flakes.

[0036] The self-supporting MXene hollow fiber membrane prepared by the above method was characterized by scanning electron microscopy, as Figure 1 and Figure 2 are the scanning electron micrographs of the self-supporting MXene hollow fiber membrane of Example 1, showing a typical hollow fiber structure. The MXene flakes on the outer surface were laid flat to form a functional layer, and the internal MXene formed a honeycomb-like support layer; Figure 3 is the SEM image of the MXene / PVB membrane of Example 1. PVB was filled in the support layer. Due to the insulation of the material, the membrane conductivity was low, at 79.1 S / m; Figure 4 is the thermogravimetric curve of PVB in Example 1. It can be seen that it completely decomposed when the temperature exceeded 400 °C; Figure 5 is the XPS spectrum of the self-supporting MXene hollow fiber membrane of Example 1. By analyzing the decrease in the content of hydroxyl functional groups and the increase in the proportion of oxygen functional groups, it was proved that a cross-linking reaction occurred at high temperature; Figure 6 shows that the hydrophilic angle measured by the contact angle meter in Example 1 was 44.8°, Figure 7 shows the dry (storage) and wet (working) states of Example 1, and the structure remained intact. The dry-state conductivity measured by using a four-probe resistance measuring instrument in Example 1 was 347.3 S / m. The above examples show that the self-supporting MXene hollow fiber membrane has excellent conductivity and hydrophilicity;

[0037] Example 2

[0038] 0.6 g of PVDF powder was slowly poured into 10 ml of DMF solution, stirred until completely dissolved, and then 1 g of Ti2CT x , was added. After stirring for 2 h, it was left to stand for 4 h to defoam, as the raw material for the support layer; Ti2CT xDispersed in deionized water (1.5 g / L) as the raw material for the functional layer. Using a three-channel coaxial spinning needle, the inner channel is deionized water, the middle channel is Ti2CT x support layer solution, and the outer channel is Ti2CT x aqueous dispersion. Each raw material solution is connected to the spinning head with a polytetrafluoroethylene tube, and the flow rate of each channel is controlled separately with a micro-injection pump. Then the spinning head is fixed about 0.5 cm above the liquid level of the coagulation bath. The flow rate of the inner channel is controlled at 10 ml / h, the middle channel at 20 ml / h, and the outer channel at 40 ml / h. A membrane is formed by co-extrusion in the coagulation bath, transferred to the washing bath for 6 h and then dried and shaped to obtain a PVB / MXene hollow fiber membrane. After drying, it is placed in a tubular furnace and heated to 700 °C at a rate of 5 °C / min in an Ar atmosphere to obtain a self-supporting MXene hollow fiber membrane. The inner pore diameter of the single fiber is 350 - 450 μm; the outer pore diameter is 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer and inner pore diameters of the single fiber; the thickness of the functional layer is 100 - 200 nm.

[0039] Example 3

[0040] 0.5 g of PVA powder was slowly poured into 15 ml of DMSO solution. After stirring until completely dissolved, 1 g of Ti3C2T x was added, and after stirring for 2 h, it was left to stand for 4 h to defoam, as the raw material for the support layer; Ti3C2T x was dispersed in deionized water (1 g / L) as the raw material for the functional layer. Using a three-channel coaxial spinning needle, the inner channel is deionized water, the middle channel is Ti3C2T x support layer solution, and the outer channel is Ti3C2T x aqueous dispersion. Each raw material solution is connected to the spinning head with a polytetrafluoroethylene tube, and the flow rate of each channel is controlled separately with a micro-injection pump. Then the spinning head is fixed about 0.3 cm above the liquid level of the coagulation bath. The flow rate of the inner channel is controlled at 5 ml / h, the middle channel at 10 ml / h, and the outer channel at 15 ml / h. A membrane is formed by co-extrusion in the coagulation bath, transferred to the washing bath for 6 h and then dried and shaped to obtain a PVB / MXene hollow fiber membrane. After drying, it is placed in a tubular furnace and heated to 600 °C at a rate of 10 °C / min in an Ar atmosphere to obtain a self-supporting MXene hollow fiber membrane. The inner pore diameter of the single fiber is 350 - 450 μm; the outer pore diameter is 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer and inner pore diameters of the single fiber; the thickness of the functional layer is 50 - 100 nm.

[0041] Comparative Example 1

[0042] Slowly pour 0.4 g of PVB powder into 10 ml of DMF solution, stir until completely dissolved, and then add 1 g of Ti3C2T x , stir for 2 h and then let stand for 4 h to defoam, which is used as the raw material for the support layer; Disperse Ti3C2T x in deionized water (1 g / L), which is used as the raw material for the functional layer. Using a three-channel coaxial spinning head, the inner channel is deionized water, the middle channel is the Ti3C2T x support layer solution, and the outer channel is the Ti3C2T x aqueous dispersion. Connect each raw material solution to the spinning head with a polytetrafluoroethylene tube, and use a micro-injection pump to control the flow rate of each channel respectively. Then fix the spinning head about 0.5 cm above the liquid surface of the coagulation bath, with an inner channel flow rate of 6 ml / h, a middle channel flow rate of 16 ml / h, and an outer channel flow rate of 24 ml / h. Form a membrane by co-extrusion in the coagulation bath, transfer it to the washing bath for 6 h and then dry and shape it to obtain a PVB / MXene hollow fiber membrane. After drying, place it in a tubular furnace and heat it to 200 °C at a rate of 5 °C / min in an Ar atmosphere. The inner pore diameter of the single fiber is 350 - 450 μm; the outer pore diameter is 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer pore diameter and the inner pore diameter of the single fiber; the thickness of the functional layer is 70 - 150 nm. At this time, PVB still exists, with a low conductivity of 82.3 S / m and a water contact angle of 54.7°.

[0043] Comparative Example 2

[0044] Slowly pour 0.4 g of PVB powder into 10 ml of DMF solution, stir until completely dissolved, and then add 1 g of Ti3C2T x , stir for 2 h and then let stand for 4 h to defoam, which is used as the raw material for the support layer; Disperse Ti3C2T x in deionized water (1 g / L), which is used as the raw material for the functional layer. Using a three-channel coaxial spinning head, the inner channel is deionized water, the middle channel is the Ti3C2T x support layer solution, and the outer channel is the Ti3C2T xA water dispersion. The flow rate of the inner channel is controlled at 6 ml / h, the middle channel at 16 ml / h, and the outer channel at 6 ml / h. A film is formed by coextrusion in a coagulation bath and transferred to a washing bath, where it is dried and shaped after 6 h. After drying, it is placed in a tubular furnace and heated to 400 °C at a rate of 5 °C / min in an Ar atmosphere to obtain a self-supporting MXene hollow fiber membrane. During this process, functional groups are crosslinked and PVB decomposes. The inner pore diameter of the single fiber is 350 - 450 μm; the outer pore diameter is 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer and inner pore diameters of the single fiber; the thickness of the functional layer is 30 - 60 nm. At this time, the concentration of the functional layer is low and the conductivity is low, with a conductivity of 168.4 S / m and a water contact angle of 46.4°.

[0045] Comparative Example 3

[0046] Slowly pour 1 g of PVB powder into 10 ml of DMF solution, stir until completely dissolved, and then add 1 g of Ti3C2T x , stir for 2 h and then let stand for 4 h to defoam, as the raw material for the support layer; Disperse Ti3C2T x in deionized water (1 g / L) as the raw material for the functional layer. Using a three-channel coaxial spinning head, the inner channel is deionized water, the middle channel is the 3Ti3C2T x support layer solution, and the outer channel is the Ti3C2T x water dispersion. Each raw material solution is connected to the spinning head with a PTFE tube, and the flow rate of each channel is controlled separately with a micro-injection pump. Then fix the spinning head about 0.5 cm above the liquid level of the coagulation bath. The flow rate of the inner channel is controlled at 6 ml / h, the middle channel at 16 ml / h, and the outer channel at 24 ml / h. A film is formed by coextrusion in a coagulation bath and transferred to a washing bath, where it is dried and shaped after 6 h. After drying, it is placed in a tubular furnace and heated to 400 °C at a rate of 5 °C / min in an Ar atmosphere to obtain a self-supporting MXene hollow fiber membrane. During this process, functional groups are crosslinked and PVB decomposes. The inner pore diameter of the single fiber is 350 - 450 μm; the outer pore diameter is 550 - 650 μm; the sum of the thicknesses of the support layer and the functional layer is the difference between the outer and inner pore diameters of the single fiber; the thickness of the functional layer is 70 - 150 nm. Due to the increased PVB content, after burning out, there are too many pores and the conductivity is low. At this time, the conductivity is 213.3 S / m and the water contact angle is 45.7°.

[0047] The above embodiments are only the preferred experimental methods of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting MXene hollow fiber membrane, characterized in that, It includes the following steps: (1) Prepare the raw materials for the support layer; dissolve the polymer in a solvent, and add MXene to the solution; (2) Prepare the raw materials for the functional layer; disperse MXene in deionized water; (3) Produce the MXene / polymer hybrid film blank by dry-wet spinning technology; the dry-wet spinning uses a three-channel coaxial spinneret; in the three channels, the spinning solution in the inner channel is the deionized water core liquid, the spinning solution in the middle channel is the MXene / polymer mixture obtained in step (1), and the spinning solution in the outer channel is the MXene aqueous dispersion obtained in step (2); (4) Perform high-temperature self-crosslinking treatment on the MXene / polymer hybrid film blank obtained in step (3); the high-temperature self-crosslinking treatment is placed in a tube furnace under an argon or nitrogen atmosphere, and the temperature is 400 - 700 °C; The single fiber of the self-supporting MXene hollow fiber membrane is composed of an inner support layer and a functional layer attached to the outside of the support layer. The support layer is a three-dimensional structure support layer formed by MXene, and the functional layer is a MXene sheet layer.

2. The preparation method according to claim 1, characterized in that, The inner diameter of a single fiber is 350 - 450 μm; the outer diameter is 550 - 650 μm; the thickness of the functional layer is 70 - 150 nm.

3. The preparation method according to claim 1, wherein In steps (1) and (2), the MXene is Ti3C2T x , Ti2CT x , Ti3CNT x , V2CT x , Ti4N3T x or Nb2CT x among them.

4. The preparation method according to claim 1, characterized in that In step (1), the polymer is one of polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinylidene fluoride, polypropylene, polyacrylonitrile or polysulfone.

5. The preparation method according to claim 1, wherein In step (3), the flow rate ratio of the inner channel, the middle channel and the outer channel is 1:(2 - 4):(3 - 6).

6. According to the preparation method described in claim 1, in step (1), the solvent is one of N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide; the mass-volume ratio of MXene, polymer and solvent is 1 g:(0.2 - 0.6) g:(10 - 20) mL; in step (2), the concentration of the MXene aqueous dispersion is 0.5 - 2 g / L.

7. According to the preparation method described in claim 1, in step (4), the heating rate of the tube furnace is 5 - 20 °C / min, and the time is 90 - 240 min.

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