Multi-layer composite film based on PAI-SiO2 / UIO-66-NH2 mixed matrix film and carboxyl carbon nanofiber enhanced Nb alloy and preparation process of multi-layer composite film

Abstract

The invention discloses a multi-layer composite membrane based on a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and carboxyl carbon nanofiber enhanced Nb alloy and a preparation process of the multi-layer composite membrane, and relates to the technical field of separation membranes. A mixed matrix membrane and a hydrogen filtering alloy membrane are made into a double-layer structure in a stacking mode, the mixed matrix membrane adopts high-purity polyamide-imide (PAI) and hydrophilic vapor-phase nano SiO2 as high-molecular organic matter filler, UIO-66-NH2 as main filler and is doped with NH2-MIL-53 (Fe) to form composite filler, and hydrogen filtering membrane alloy is prepared from Nb-Ni-Mo-V-Ag alloy, and a carboxyl-modified multi-wall carbon nanofiber channel is used as an alloy micro-stent. The mechanical properties, including strength, flexibility and ductility, of the hydrogen filtering film can be remarkably improved; the efficiency of filtering and purifying hydrogen can be further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membranes, and specifically to a multi-layer composite membrane based on a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and a carboxyl carbon nanofiber-reinforced Nb alloy, and a preparation process thereof. Background Art

[0002] A mixed matrix membrane is a composite membrane material formed by dispersing inorganic fillers into a polymer matrix. This kind of membrane combines the high selectivity of inorganic fillers and the good processability of polymers, aiming to overcome the limitations of traditional polymer membranes in applications such as gas separation and water treatment. Currently, most mixed matrix membranes use polyimide (an organic polymer material) as the polymer matrix and use zeolites, metal-organic frameworks, etc. as fillers. Inorganic fillers provide efficient selective adsorption or sieving capabilities, while polymers ensure the overall mechanical strength and formability of the membrane, which is a very promising development direction for membranes.

[0003] However, there are still many limitations in the existing technologies and materials. Currently, most patents on mixed matrix membranes use PI and ZIF-8, ZIF-67 as the materials for preparing membranes. Although this kind of mixed matrix membrane (PI-MOF mixed matrix membrane) has high efficiency, its mechanical properties are still insufficient, and the filtration accuracy has also reached a bottleneck, urgently needing to make relevant breakthroughs.

[0004] In recent methods for filtering hydrogen, hydrogen filtering alloy membranes have also been on the rise. Alloy membranes represented by noble metal palladium show excellent performance in filtering hydrogen, but the price of palladium is expensive and the cost is too high. Therefore, alloy membranes such as titanium-based alloys and nickel-based alloys, which also have good hydrogen filtering properties, have also been studied one after another, greatly reducing the cost. However, these alloys still have some problems: compared with palladium-based alloys, the hydrogen permeability of titanium-based alloys is usually lower, which means that under the same conditions, the speed of hydrogen transmission through the titanium-based alloy membrane is slower; the selectivity of nickel-based alloys for hydrogen is relatively low, which means that they can not only allow hydrogen to pass through, but also allow other gas molecules to pass through together, which limits their use in applications that require high-purity hydrogen.

[0005] Therefore, we have proposed a multi-layer composite membrane based on a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and a carboxyl carbon nanofiber-reinforced Nb alloy, and a preparation process thereof, in order to solve the problems mentioned above.

[0006] The above information disclosed in this background art is only used to increase the understanding of the background art of the present invention. Therefore, it may include prior art that is not known to those of ordinary skill in the art. Summary of the Invention

[0007] The object of the present invention is to provide a multi-layer composite membrane based on a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and a carboxyl carbon nanofiber-reinforced Nb alloy, and a preparation process thereof, so as to solve the problems put forward in the above-mentioned background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: A multi-layer composite membrane based on a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and a carboxyl carbon nanofiber-reinforced Nb alloy, which is made into a double-layer structure by stacking the mixed matrix membrane and the hydrogen filtration alloy membrane. The mixed matrix membrane uses high-purity polyamideimide (PAI) and hydrophilic fumed nano-SiO2 as polymer organic fillers, UIO-66-NH2 as the main filler, and doped with NH2-MIL-53(Fe) to form a composite filler. The hydrogen filtration membrane alloy is prepared from a Nb-Ni-Mo-V-Ag alloy, and a multi-walled carbon nanofiber channel modified with carboxyl is used as the alloy micro scaffold.

[0009] The preparation process of the multi-layer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy includes the following steps:

[0010] Step 1. Prepare the mixed matrix membrane:

[0011] 1.1: First, add PAI to the DMAc solvent, and stir with a magnetic stirrer at room temperature for 24 hours until the PAI is completely dissolved to form a uniform mixed solution;

[0012] 1.2: Secondly, put the mixed solution of 1.1 into an ultrasonic cleaner and perform ultrasonic treatment for 30 minutes to ensure the uniform dispersion of the silica nanoparticles;

[0013] 1.3: Mix UIO-66-NH2 and NH2-MIL-53(Fe) nanoparticles in a ratio of 7:3 and add them to the DMAc solvent;

[0014] 1.4: Put the mixed solution of 1.3 into an ultrasonic cleaner and perform ultrasonic treatment for 30 minutes to ensure the uniform dispersion of the NiO-66-NH2 and NH2-MIL-53(Fe) nanoparticles;

[0015] Step 2. Prepare the alloy:

[0016] 2.1: Use high-energy ball milling to mix Nb, Ni, Mo, and V in proportion, where Nb:Ni:Mo:V = 35:15:10:35, and ball milling makes the powder uniformly mixed and forms composite particles;

[0017] 2.2: Compress the composite particles into a green body under a pressure of 200 - 300 MPa, adding a small amount of organic binder PVA to prevent powder separation and improve the strength of the green body;

[0018] 2.3: First sintering, under the protection of an inert / reducing gas, sinter the Nb-Ni-Mo-V system at 1200 - 1400 °C to promote the diffusion of high-melting-point components. The sintering time is 2 - 4 hours to promote the solid-state diffusion of Nb-Ni-Mo-V and form a multi-porous structure;

[0019] 2.4: Uniformly sprinkle a mixed powder of Ag powder and carboxylated carbon nanofiber channels (CCNF) on the surface of the pre-sintered Nb-Ni-Mo-V porous green body, and use pressure assistance to cover the surface and pores of the green body with the mixed powder of Ag powder and carboxylated carbon nanofiber channels (CCNF);

[0020] 2.5: Second sintering, rapidly heat to above the melting point of Ag for liquid-phase sintering. Use 980 °C, 0.5 - 1 hour, argon protection, and a heating rate of 10 °C / min. Use liquid Ag to fill the pores to form a dense alloy. At the same time, liquid Ag wets the interface of high-melting-point metal particles to enhance the bonding strength. Use the hydrodynamic energy generated when the melted liquid Ag fills the pores to carry CCNF into the pores for filling together to achieve physical anchoring;

[0021] 2.6: Finally, perform post-treatment, use hot isostatic pressing (HIP) to eliminate residual pores, and annealing treatment to optimize the microstructure;

[0022] Step 3. Addition of surface hydroxyl groups to the enhanced Nb alloy:

[0023] 3.1: Make the alloy prepared in Step 2 into alloy flakes. Ultrasonically clean the alloy flakes with acetone, ethanol, and deionized water for 10 minutes in sequence to remove surface contaminants. Treat the surface of the alloy flakes with dilute nitric acid (5% HNO3) or hydrogen peroxide (H2O2) at room temperature for 30 minutes to generate surface hydroxyl groups, and then treat them in oxygen or air plasma for 5 - 10 minutes to enhance the hydroxyl density;

[0024] 3.2: Disperse the carboxylated carbon nanofiber channels (CCNF) in a polymer PVA solution, stir to make it evenly distributed. Take a certain amount of the carboxylated CNF dispersion and drop it on the treated alloy flakes, use a coater to disperse and coat it evenly, and place it under high-temperature conditions to evaporate the organic solvent, so that CCNF forms hydrogen bonds with the surface hydroxyl groups of the alloy flakes through carboxyl groups and binds tightly. Add a certain amount of binder to improve its stability;

[0025] Step 4. Assembly of each part:

[0026] 4.1: Use the mixed matrix membrane prepared in Step 1 as the substrate, and cover the strengthened membrane prepared in Step 3. The thickness of the mixed matrix membrane is 200 nm, and the thickness of the strengthened membrane is 50 μm. An adhesive is added between the two layers to form a composite membrane with a double-layer structure of a mixed matrix-CCNF reinforced Nb alloy membrane. Then, apply medium-temperature rolling with external pressure to closely bond the two-layer structure, and roll the thin sheet into a 50-μm strengthened membrane, thereby preparing a multi-layer composite membrane of a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and a carboxyl carbon nanofiber-reinforced Nb alloy.

[0027] Preferably, in Step 1.1, during the ultrasonic treatment, keep the solution temperature not exceeding 40 °C to prevent nanoparticle aggregation. Use a high-speed centrifuge to centrifuge at a speed of 8500 - 9500 rpm for 8 - 10 minutes to remove the undispersed aggregated particles.

[0028] Preferably, in Step 1.4, after the ultrasonic treatment, use a high-speed centrifuge to centrifuge at a speed of 8000 rpm for 10 minutes to remove the undispersed aggregated particles.

[0029] Preferably, in Step 2.2, the shape of the green body is blocky or sheet-like.

[0030] Preferably, in Step 2.4, Nb:Ni:Mo:V:Ag = 35:15:10:35:5.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] The present invention can significantly improve the mechanical properties of the hydrogen filtration membrane, including strength, flexibility, and ductility; and can further improve the efficiency of filtering and purifying hydrogen. This will be further elaborated in detail in the specific embodiments below.

[0033] The above summary is only for the purpose of the specification and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the present invention will be readily apparent by reference to the drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the electron microscopy analysis diagram of the membrane surface;

[0035] Figure 2 It is the SEM of the alloy membrane surface;

[0036] Figure 3 It is the detection data table of the gas chromatograph for the filtered gas;

[0037] Figure 4 It is the peak diagram of the gas chromatograph;

[0038] Figure 5 Schematic diagram of the hydrogen filtration composite membrane structure and the hydrogen permeation mechanism mediated by the hydrogen bond network. Specific implementation manners

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] Based on the multi-layer composite membrane of PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and carboxyl carbon nanofiber-reinforced Nb alloy, a double-layer structure is formed by stacking the mixed matrix membrane and the hydrogen filtration alloy membrane. The mixed matrix membrane uses high-purity polyamideimide (PAI) and hydrophilic gas-phase nano-SiO2 as polymer organic fillers, UIO-66-NH2 as the main filler, and doped with NH2-MIL-53(Fe) to form a composite filler. The hydrogen filtration membrane alloy is prepared from Nb-Ni-Mo-V-Ag alloy, and the carboxyl-modified multi-walled carbon nanofiber channels are used as alloy micro scaffolds.

[0041] The preparation process of the multi-layer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy is characterized by including the following steps:

[0042] Step 1. Prepare the mixed matrix membrane:

[0043] 1.1: First, add PAI to the DMAc solvent, and stir with a magnetic stirrer at room temperature for 24 hours until the PAI is completely dissolved to form a uniform mixed solution (during the stirring process, regularly check the transparency of the solution to ensure that there are no undissolved particles and avoid filler agglomeration); during the ultrasonic treatment, keep the solution temperature not exceeding 40 °C to prevent nanoparticle agglomeration, and use a high-speed centrifuge to centrifuge at a speed of 8500-9500 rpm for 8-10 minutes to remove undispersed agglomerated particles;

[0044] 1.2: Secondly, put the mixed solution in 1.1 into an ultrasonic cleaner and perform ultrasonic treatment for 30 minutes to ensure the uniform dispersion of the silica nanoparticles;

[0045] 1.3: Mix UIO-66-NH2 and NH2-MIL-53(Fe) nanoparticles in a ratio of 7:3 and add them to the DMAc solvent;

[0046] 1.4: Put the mixture in Step 1.3 into an ultrasonic cleaner and perform ultrasonic treatment for 30 minutes to ensure the uniform dispersion of NiO-66-NH2 and NH2-MIL-53(Fe) nanoparticles; use a high-speed centrifuge to centrifuge at a speed of 8000 rpm for 10 minutes to remove undispersed agglomerated particles;

[0047] Step 2. Prepare the alloy: The alloy film is prepared by powder metallurgy. However, the melting point of Ag is lower than that of the other three metals, and the difference is large. Therefore, a step-by-step sintering method is adopted. First, sinter the high-melting-point components (Nb, V, Ni, Mo), and then use liquid-phase sintering to assist in infiltrating Ag.

[0048] 2.1: Use high-energy ball milling to mix Nb, Ni, Mo, and V in proportion, where Nb:Ni:Mo:V = 35:15:10:35. Ball milling makes the powder uniformly mixed and forms composite particles;

[0049] 2.2: Press the composite particles into a green body at a pressure of 200-300 MPa. The shape of the green body is blocky or sheet-like. Add a small amount of organic binder PVA to prevent powder separation and improve the strength of the green body;

[0050] 2.3: First sintering, under the protection of an inert / reducing gas, sinter the Nb-Ni-Mo-V system at 1200-1400 °C to promote the diffusion of high-melting-point components. The sintering time is 2-4 hours to promote the solid-state diffusion of Nb-Ni-Mo-V and form a multi-porous structure (Nb and V are easily oxidized at high temperatures and require inert / reducing gas protection);

[0051] 2.4: Uniformly sprinkle the mixed powder of Ag powder and carboxylated carbon nanofiber channels (CCNF) on the surface of the pre-sintered Nb-Ni-Mo-V porous green body. Through pressure assistance, the mixed powder of Ag powder and carboxylated carbon nanofiber channels (CCNF) covers the surface and pores of the green body; Nb:Ni:Mo:V:Ag = 35:15:10:35:5;

[0052] 2.5: Second sintering, quickly raise the temperature to above the melting point of Ag for liquid-phase sintering. Use 980 °C, 0.5-1 hour, argon protection, and a heating rate of 10 °C / min. Use liquid Ag to fill the pores to form a dense alloy. At the same time, liquid Ag wets the interface of high-melting-point metal particles to enhance the bonding strength. Use the hydrodynamic energy generated when the melted liquid Ag fills the pores to carry CCNF into the pores for filling together to achieve physical anchoring;

[0053] 2.6: Finally, perform post-treatment. Use hot isostatic pressing (HIP) to eliminate residual pores and annealing treatment to optimize the microstructure;

[0054] Step 3. Add surface hydroxyl groups to the enhanced Nb alloy:

[0055] 3.1: Make the alloy prepared in Step 2 into alloy flakes. Ultrasonically clean the alloy flakes successively with acetone, ethanol, and deionized water for 10 minutes to remove surface contaminants. Treat the surface of the alloy flakes with dilute nitric acid (5% HNO3) or hydrogen peroxide (H2O2) at room temperature for 30 minutes to generate surface hydroxyl groups, and then treat them in oxygen or air plasma for 5 - 10 minutes to enhance the hydroxyl density;

[0056] 3.2: Disperse the carboxylated carbon nanofiber channels (CCNF) in the polymer PVA solution and stir to make it evenly distributed. Take a certain amount of the carboxylated CNF dispersion and drop it on the treated alloy flakes, and use a coater to disperse and coat it evenly. Place it under high-temperature conditions to evaporate the organic solvent, so that the CCNF forms hydrogen bonds with the surface hydroxyl groups of the alloy flakes through carboxyl groups and binds tightly. Add a certain amount of binder to improve its stability;

[0057] Step 4. Assembly of each part:

[0058] 4.1: Use the mixed matrix membrane prepared in Step 1 as the substrate, and cover the strengthened membrane prepared in Step 3 on the second layer. The thickness of the mixed matrix membrane is 200 nm, and the thickness of the strengthened membrane is 50 μm. Add an adhesive between the two layers to form a composite membrane with a double-layer structure of the mixed matrix - CCNF reinforced Nb alloy membrane. Then, make the two-layer structure tightly combined by medium-temperature rolling with external pressure, and roll the flakes into a 50-μm strengthened membrane, thereby preparing a multi-layer composite membrane of the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxylated carbon nanofiber-reinforced Nb alloy.

[0059] Next, to further verify the effect of the multi-layer composite membrane of the present invention, gas chromatography detection is carried out. The detection conditions are: the temperature is 473 K, the total flow rate of the mixed gas is 300 mL / min, and the mixed gas before filtration is: 15.0243% H2, 66.0251% N2, 18.4121% CO2, 0.5385% CH4.

[0060] The detection results are as follows:

[0061] 1. The hydrogen permeability is: 1600 barrer;

[0062] 2. The selectivities are respectively:

[0063] H2 / CO2 = 88.724;

[0064] H2 / N2 = 150.131;

[0065] H2 / CH4 = 93.080;

[0066] 3. The mechanical strength: the tensile strength is 80 Mpa; the elongation at break is 18.792%;

[0067] 4. Maximum operating temperature: 400 °C;

[0068] 5. Hydrogen embrittlement resistance (HEI): The loss rate of mechanical properties after hydrogen exposure < 5%;

[0069] The test data of the filtered gas by gas chromatograph is as Figure 3 shown.

[0070] It can be seen from the experimental results that the present invention can significantly improve the mechanical properties of the hydrogen filtration membrane, including strength, flexibility and ductility; at the same time, it can further improve the efficiency of filtering and purifying hydrogen.

[0071] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0072] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A multi-layer composite membrane based on a PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and a carboxyl carbon nanofiber-reinforced Nb alloy, characterized in that: A bilayer structure is made by stacking a mixed matrix membrane and a hydrogen filtering alloy membrane. The mixed matrix membrane uses high-purity polyamideimide (PAI) and hydrophilic fumed nano-SiO₂ as polymer organic fillers, UIO-66-NH₂ as the main filler, and doped with NH₂-MIL-53(Fe) to form a composite filler. The hydrogen filtering alloy membrane is prepared from Nb-Ni-Mo-V-Ag alloy, and uses carboxyl-modified multi-walled carbon nanofiber channels as the alloy micro scaffold.

2. The preparation process of the multilayer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy according to claim 1, characterized in that, It includes the following steps: Step 1. Prepare the mixed matrix membrane: 1.1: First, add PAI into the DMAc solvent and stir with a magnetic stirrer at room temperature for 24 hours until the PAI is completely dissolved to form a uniform mixed solution; 1.2: Secondly, put the mixed solution of 1.1 into an ultrasonic cleaner and perform ultrasonic treatment for 30 minutes to ensure the uniform dispersion of silica nanoparticles; 1.3: Mix UIO-66-NH₂ and NH₂-MIL-53(Fe) nanoparticles in a ratio of 7:3 and add them into the DMAc solvent; 1.4: Put the mixed solution of 1.3 into an ultrasonic cleaner and perform ultrasonic treatment for 30 minutes to ensure the uniform dispersion of NiO-66-NH₂ and NH₂-MIL-53(Fe) nanoparticles; Step 2. Prepare the alloy: 2.1: Use high-energy ball milling to mix Nb, Ni, Mo, and V in proportion, where Nb:Ni:Mo:V = 35:15:10:

35. Ball milling makes the powder uniformly mixed and forms composite particles; 2.2: Press the composite particles into a green body under a pressure of 200 - 300 MPa, add a small amount of organic binder PVA to prevent powder separation and improve the strength of the green body; 2.3: First sintering, sinter the Nb-Ni-Mo-V system at 1200 - 1400 °C under the protection of inert / reducing gas to promote the diffusion of high-melting-point components. The sintering time is 2 - 4 hours to promote the solid-state diffusion of Nb-Ni-Mo-V and form a multi-microporous structure; 2.4: Uniformly sprinkle the mixed powder of Ag powder and carboxylated carbon nanofiber channels (CCNF) on the surface of the pre-sintered Nb-Ni-Mo-V porous green body, and use pressure assistance to make the mixed powder of Ag powder and carboxylated carbon nanofiber channels (CCNF) cover the surface and pores of the green body; 2.5: Second sintering, quickly heat up to above the melting point of Ag for liquid-phase sintering. Use 980 °C, 0.5 - 1 hour, argon protection, and a heating rate of 10 °C / min. Use liquid Ag to fill the pores to form a dense alloy. At the same time, liquid Ag wets the interface of high-melting-point metal particles to enhance the bonding strength. Use the hydrodynamic energy generated when the melted liquid Ag fills the pores to carry CCNF into the pores for filling together to achieve physical anchoring; 2.6: Finally, perform post-treatment, use hot isostatic pressing (HIP) to eliminate residual pores and annealing treatment to optimize the microstructure; Step 3. Add surface hydroxyl groups to the enhanced Nb alloy: 3.1: Make the alloy prepared in Step 2 into alloy thin sheets. Ultrasonically clean the alloy thin sheets with acetone, ethanol, and deionized water in sequence for 10 minutes to remove surface contaminants. Treat the surface of the alloy thin sheets with dilute nitric acid (5% HNO3) or hydrogen peroxide (H2O2) at room temperature for 30 minutes to generate surface hydroxyl groups, and then treat them in oxygen or air plasma for 5 - 10 minutes to enhance the hydroxyl density; Step 4. Assembly of each part: 4.1: Use the mixed matrix membrane prepared in Step 1 as the substrate, and cover the second layer with the strengthened membrane prepared in Step 3. The thickness of the mixed matrix membrane is 200 nm, and the thickness of the strengthened membrane is 50 μm. Add an adhesive between the two layers to form a composite membrane with a double-layer structure of the mixed matrix - CCNF reinforced Nb alloy membrane. Then, make the two-layer structure closely combined by medium-temperature rolling with an external pressure, and roll the thin sheet into a 50-μm strengthened membrane, thereby preparing a multi-layer composite membrane of the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy.

3. The preparation process of the multi-layer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy according to claim 1, characterized in that: In Step 1.1, during the ultrasonic treatment process, keep the solution temperature not exceeding 40 °C to prevent nanoparticle aggregation. Use a high-speed centrifuge to centrifuge at a speed of 8500 - 9500 rpm for 8 - 10 minutes to remove undispersed aggregated particles.

4. The preparation process of the multilayer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy according to claim 1, characterized in that: In Step 1.4, after the ultrasonic treatment, use a high-speed centrifuge to centrifuge at a speed of 8000 rpm for 10 minutes to remove undispersed aggregated particles.

5. The preparation process of the multilayer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy according to claim 1, characterized in that: In Step 2.2, the shape of the green body is blocky or flaky.

6. The preparation process of the multilayer composite membrane based on the PAI-SiO2 / UIO-66-NH2 mixed matrix membrane and the carboxyl carbon nanofiber-reinforced Nb alloy according to claim 1, characterized in that: In Step 2.4, Nb:Ni:Mo:V:Ag = 35: 15：10：35：5。

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