A molybdenum disilicide-re-crystallized silicon carbide ceramic composite ultrafiltration membrane and a preparation method thereof

Abstract

The application provides a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane and a preparation method thereof, and belongs to the technical field of silicon carbide ceramic materials. The recrystallized silicon carbide ceramic membrane is subjected to activation treatment to obtain an activated membrane material; molybdenum disilicide powder, silicon sol, a dispersing agent and a solvent are mixed to obtain a molybdenum disilicide suspension; the molybdenum disilicide suspension is coated on the surface of the activated membrane material, and a composite membrane material is obtained after drying; and the composite membrane material is sequentially subjected to heat treatment, etching treatment and hydrophilization treatment to obtain the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane. The pore diameter of the molybdenum disilicide-based ultrafiltration coating layer in the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared by the method is 10-20 nm, and the fine filtration requirement can be met.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramic materials technology, and in particular to a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane and its preparation method. Background Technology

[0002] Silicon carbide (SiC) ceramic membranes exhibit great application potential in high-temperature flue gas purification, chemical product separation, and filtration of strong acid and alkali media due to their excellent thermal stability, chemical inertness, mechanical strength, and high throughput. Recrystallized silicon carbide (R-SiC) is a classic SiC ceramic preparation technology. It achieves sintering through evaporation-condensation mass transfer on the surface of SiC particles at high temperatures (>2400℃), obtaining high-purity, corrosion-resistant SiC sintered bodies without the addition of traditional sintering aids.

[0003] However, the pore size of recrystallized silicon carbide ceramic membranes in current related technologies is usually above 50nm, which cannot meet the filtration requirements of the Drinking Water Quality Guidelines (4th Edition, 2017). Summary of the Invention

[0004] The purpose of this invention is to provide a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane and its preparation method. The molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared by the method of this invention has a pore size of 10~20nm in the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane, which can meet the requirements of fine filtration.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane, comprising the following steps:

[0007] The recrystallized silicon carbide ceramic film was activated to obtain the activated film material;

[0008] Molybdenum disilicide powder, silica sol, dispersant, and solvent are mixed to obtain a molybdenum disilicide suspension. The particle size of the molybdenum disilicide powder is 50-100 nm, the content of nano-silica in the silica sol is 30-40 wt%, the content of molybdenum disilicide powder in the molybdenum disilicide suspension is 15-20 wt%, and the content of silica sol is 3-5 wt%.

[0009] The molybdenum disilicide suspension was coated onto the surface of the activated membrane material and dried to obtain a composite membrane material.

[0010] The composite membrane material was subjected to heat treatment, etching treatment and hydrophilic treatment in sequence to obtain the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane.

[0011] Preferably, the activation treatment includes: immersing the recrystallized silicon carbide ceramic membrane in a silane coupling agent solution; the concentration of the silane coupling agent solution is 4~7wt%, the activation treatment temperature is 20~30℃, and the time is 0.5~1.5h.

[0012] Preferably, the dispersant comprises polyvinylpyrrolidone and / or phosphate ester; the solvent is water and ethanol, and the volume ratio of water to ethanol is 8:1.5~2.5; the content of dispersant in the molybdenum disilicide suspension is 0.5~1wt%.

[0013] Preferably, the coating is applied 2 to 5 times, and each coating is dried afterward; the coating is sprayed, and the conditions for each spraying are independent, including: the temperature of the activated film material is 58 to 62°C, the spraying pressure is 1.0 to 1.5 bar, and the nozzle diameter is 0.3 mm.

[0014] Preferably, the heat treatment includes performing a first stage heat treatment, a second stage heat treatment, and a third stage heat treatment sequentially;

[0015] The temperature of the first stage heat treatment is 180~200℃, the holding time is 25~30min, the first stage heat treatment is carried out in an air atmosphere, and the heating rate from room temperature to the temperature of the first stage heat treatment is 0.8~1℃ / min.

[0016] The temperature of the second stage heat treatment is 380~400℃, the holding time is 1~2h, the second stage heat treatment is carried out in an air atmosphere, and the heating rate from the temperature of the first stage heat treatment to the temperature of the second stage heat treatment is 1~3℃ / min.

[0017] The temperature of the third stage heat treatment is 1600~1700℃, the holding time is 1~2h, the third stage heat treatment is carried out in a protective atmosphere, and the heating rate from the temperature of the second stage heat treatment to the temperature of the third stage heat treatment is 2~5℃ / min.

[0018] The third stage of heat treatment also includes cooling in a protective atmosphere.

[0019] Preferably, the etching process includes immersing the heat-treated composite film obtained after heat treatment in an HF solution; the concentration of the HF solution is 0.08~0.1mol / L, the etching temperature is 20~30℃, and the etching time is 8~10s.

[0020] Preferably, the hydrophilization treatment includes: immersing the etched composite film obtained after etching treatment in an H2O2 solution; the concentration of the H2O2 solution is 28~30wt%, the temperature of the hydrophilization treatment is 20~30℃, and the time is 50~60min.

[0021] Preferably, the pore size of the recrystallized silicon carbide ceramic membrane is 50~70nm; the recrystallized silicon carbide ceramic membrane is a tubular membrane or a flat membrane.

[0022] The present invention provides a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared by the preparation method described above, comprising a recrystallized silicon carbide ceramic membrane and a molybdenum disilicide-based ultrafiltration coating coated on the surface of the recrystallized silicon carbide ceramic membrane, wherein the pore size of the molybdenum disilicide-based ultrafiltration coating is 10~20 nm.

[0023] Preferably, the thickness of the molybdenum disilicide-based ultrafiltration coating is 2.5~5.0 μm.

[0024] Beneficial effects: Currently, the filtration accuracy of recrystallized silicon carbide ceramic membranes is typically above 50 nm. This invention activates the membrane and coats its surface with a suspension containing molybdenum disilicide powder and silica sol (i.e., molybdenum disilicide suspension). By selecting molybdenum disilicide powder of appropriate particle size and using appropriate amounts of molybdenum disilicide powder and silica sol, and after drying, heat treatment is performed. During this heat treatment, molybdenum disilicide and silica in the silica sol can form a eutectic phase, enabling nanoscale pore size control, ultimately forming a molybdenum disilicide-based ultrafiltration coating with a pore size of 10-20 nm. This achieves the preparation of a sub-nanofiltration membrane, meeting the requirements for fine filtration. Furthermore, the interface between the molybdenum disilicide-based ultrafiltration coating and the recrystallized silicon carbide ceramic membrane is bonded by Si-O-Si bonds, exhibiting strong adhesion and avoiding thermal expansion mismatch. This ensures the excellent stability of the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane, which is beneficial for improving its service life. Attached Figure Description

[0025] Figure 1 The image shows a cross-sectional SEM image of the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared in Example 1. Detailed Implementation

[0026] This invention provides a method for preparing a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane, comprising the following steps:

[0027] The recrystallized silicon carbide ceramic film was activated to obtain the activated film material;

[0028] Molybdenum disilicide powder, silica sol, dispersant, and solvent are mixed to obtain a molybdenum disilicide suspension. The particle size of the molybdenum disilicide powder is 50-100 nm, the content of nano-silica in the silica sol is 30-40 wt%, the content of molybdenum disilicide powder in the molybdenum disilicide suspension is 15-20 wt%, and the content of silica sol is 3-5 wt%.

[0029] The molybdenum disilicide suspension was coated onto the surface of the activated membrane material and dried to obtain a composite membrane material.

[0030] The composite membrane material was subjected to heat treatment, etching treatment and hydrophilic treatment in sequence to obtain the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane.

[0031] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or prepared using methods well known to those skilled in the art.

[0032] This invention utilizes recrystallized silicon carbide ceramic membranes to prepare molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membranes. In one embodiment of this invention, the pore size of the recrystallized silicon carbide ceramic membrane can be 50-70 nm, more specifically 50-60 nm, and in this embodiment, 50 nm. The recrystallized silicon carbide ceramic membrane can be a tubular membrane or a flat sheet membrane. Specifically, the recrystallized silicon carbide ceramic membrane prepared in Preparation Example 1 is used in this embodiment.

[0033] After obtaining the recrystallized silicon carbide ceramic membrane, the present invention activates the recrystallized silicon carbide ceramic membrane to obtain an activated membrane material. In one embodiment of the present invention, the recrystallized silicon carbide ceramic membrane is preferably cleaned before activation. The cleaning includes sequential alkaline washing, acid washing, water washing, and drying. The alkaline reagent used for alkaline washing is specifically NaOH solution, the concentration of which can be 0.8~1 mol / L, and the alkaline washing method can be ultrasonic cleaning, the ultrasonic cleaning time can be 15~20 min. The acid reagent used for acid washing is nitric acid, the concentration of which can be 0.08~0.1 mol / L, and the present invention does not have a specific limitation on the acid washing method. The water used for water washing is deionized water, and the water washing method can be rinsing, ensuring that the pH value of the recrystallized silicon carbide ceramic membrane surface is neutral. The drying temperature can be 110~120℃, and the present invention does not have a specific limitation on the drying time, as long as it is sufficiently dried.

[0034] In one embodiment of the present invention, the activation treatment includes: immersing the recrystallized silicon carbide ceramic membrane in a silane coupling agent solution; the concentration of the silane coupling agent solution is 4-7 wt%, specifically 5 wt%; the silane coupling agent in the silane coupling agent solution can be KH550, and the solvent in the silane coupling agent solution can be ethanol. In another embodiment of the present invention, the activation treatment temperature can be 20-30°C, specifically room temperature (25°C); the time can be 0.5-1.5 h, specifically 1 h. The present invention enhances the hydrophilicity and interfacial bonding effect of the recrystallized silicon carbide ceramic membrane through activation treatment.

[0035] This invention involves mixing molybdenum disilicide powder, silica sol, dispersant, and solvent to obtain a molybdenum disilicide suspension. In this invention, molybdenum disilicide powder is used as the main coating material. Through subsequent processes, a molybdenum disilicide-based ultrafiltration coating can be formed on the surface of a recrystallized silicon carbide ceramic membrane. Molybdenum disilicide can form Mo-Si-C chemical bonds with the recrystallized silicon carbide ceramic membrane, enhancing the adhesion between the coating and the membrane. Furthermore, the molybdenum disilicide powder can act as a liquid-phase sintering aid to promote the rearrangement of silicon carbide particles, thereby promoting densification while avoiding the adverse effects of traditional liquid-phase sintering aid residues on the material's high-temperature performance and chemical stability. The silica sol acts as an inorganic binder, playing a cross-linking role. The silica sol can form Si-O-Si chemical bonds with the recrystallized silicon carbide ceramic membrane, enhancing the adhesion between the coating and the membrane. Using silica sol also helps prevent cracking in the coating and can form a hydrophilic layer in situ, thus improving hydrophilicity. The dispersant prevents the agglomeration of molybdenum disilicide powder in the molybdenum disilicide suspension. The solvent is the dispersion medium for the molybdenum disilicide suspension.

[0036] In this invention, the particle size of the molybdenum disilicide powder can be 50~100nm, specifically 75±20nm; the purity is >99.5wt%; the silica sol is specifically SiO2 sol, and the content of nano-silica in the silica sol is 30~40wt%, further 30~35wt%; the dispersant can include polyvinylpyrrolidone (PVP) and / or phosphate ester, specifically PVP; the solvent is water and ethanol, and the volume ratio of water to ethanol can be 8:1.5~2.5, specifically 8:2. In this invention, the molybdenum disilicide suspension contains 15-20 wt% molybdenum disilicide powder, specifically 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%; the silica sol contains 3-5 wt%, specifically 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%; and the dispersant contains 0.5-1 wt%, specifically 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%.

[0037] In one embodiment of the present invention, the mixing of molybdenum disilicide powder, silica sol, dispersant, and solvent may include: mixing the dispersant and solvent, and ultrasonically treating for 5-10 minutes; adding molybdenum disilicide powder to the resulting first mixture, and ball milling at 150-200 rpm for 20-24 hours; adding silica sol to the resulting second mixture, and stirring for 1.5-2 hours. In another embodiment of the present invention, the mixture preferably further includes sieving to remove any potentially larger particles; the sieve used for sieving may have a mesh size of 500. In one embodiment of the present invention, the pH value of the molybdenum disilicide suspension can be 9-10, specifically 9.5. The above pH range is beneficial to enhance the electrostatic stability of the molybdenum disilicide suspension, making the absolute value of the Zeta potential of the molybdenum disilicide suspension >30mV, thus preventing sedimentation. When the pH value of the molybdenum disilicide suspension does not meet the above requirements, a pH adjuster can be used to adjust its pH value. The pH adjuster can be ammonia or nitric acid. The present invention does not have a special limitation on the concentration of the pH adjuster, as long as the pH value of the molybdenum disilicide suspension is adjusted to meet the above requirements.

[0038] After obtaining the molybdenum disilicide suspension and the activated film material, the present invention coats the molybdenum disilicide suspension onto the surface of the activated film material, and obtains a composite film material after drying. In one embodiment of the present invention, the coating can be applied 2 to 5 times, specifically based on ensuring a coating of the target thickness; drying is preferably performed after each coating; the coating can be spraying, and the conditions for each spraying independently include: the temperature of the activated film material can be 58 to 62°C, specifically 60°C; the spraying pressure can be 1.0 to 1.5 bar, specifically 1.3 bar; and the nozzle diameter can be 0.3 mm. The present invention controls the temperature of the activated film material within the above range, which helps to reduce coating cracking. In one embodiment of the present invention, the thickness of the wet film formed by the molybdenum disilicide suspension on the surface of the activated film material during each coating is preferably ≤1 μm; the drying temperature after each coating can be independently 70 to 80°C, and the drying time can be independently 5 to 10 minutes. The spraying method used in the present invention facilitates precise control of the coating thickness.

[0039] After obtaining the composite membrane material, the present invention sequentially performs heat treatment, etching treatment, and hydrophilication treatment on the composite membrane material to obtain the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane. As one embodiment of the present invention, the heat treatment may include sequentially performing a first-stage heat treatment, a second-stage heat treatment, and a third-stage heat treatment, which will be described in detail below.

[0040] In one embodiment of the present invention, the temperature of the first stage heat treatment can be 180~200℃, specifically 180℃, 185℃, 190℃, 195℃, or 200℃; the holding time can be 25~30 minutes; the first stage heat treatment can be carried out in an air atmosphere; and the heating rate from room temperature to the temperature of the first stage heat treatment can be 0.8~1℃ / min. Under the above conditions, the first stage heat treatment of the present invention can further remove moisture from the material; and controlling the slow heating can prevent coating cracking.

[0041] In one embodiment of the present invention, the temperature of the second stage heat treatment can be 380~400℃, specifically 380℃, 385℃, 390℃, 395℃, or 400℃; the holding time can be 1~2 hours, specifically 1.5 hours; the second stage heat treatment can be carried out in an air atmosphere, and the heating rate from the temperature of the first stage heat treatment to the temperature of the second stage heat treatment can be 1~3℃ / min, specifically 2℃ / min. Under the above conditions, the second stage heat treatment of the present invention can decompose and remove organic matter from the material; and controlling the slow heating can prevent coating cracking.

[0042] In one embodiment of the present invention, the temperature of the third-stage heat treatment can be 1600~1700℃, specifically 1600℃, 1625℃, 1650℃, 1675℃, or 1700℃; the holding time can be 1~2 hours, specifically 1.5 hours; the third-stage heat treatment can be carried out in a protective atmosphere, specifically an argon atmosphere, wherein the oxygen content is <10ppm; the heating rate from the temperature of the second-stage heat treatment to the temperature of the third-stage heat treatment can be 2~5℃ / min, further 3~4℃ / min. Under the above conditions, the third-stage heat treatment of the present invention can promote the densification of MoSi2 and SiO2 into a eutectic phase, ultimately forming MoSi2-SiO2. x Eutectic treatment and recrystallization of the silicon carbide ceramic film reduce its pore size to meet the requirement of 10-20 nm; and controlled slow heating can prevent coating cracking. As one embodiment of the invention, the third-stage heat treatment preferably further includes cooling in a protective atmosphere; specifically, the protective atmosphere can be a nitrogen atmosphere, wherein the oxygen content is <10 ppm; the cooling method can specifically be furnace cooling to room temperature. The third-stage heat treatment and cooling process of the present invention are carried out in a protective atmosphere, which can prevent MoSi2 from being oxidized by contact with air at high temperatures to form MoO3 (volatile) and SiO2.

[0043] After heat treatment, a heat-treated composite film is obtained. This invention then etches the heat-treated composite film. In one embodiment, the etching process may include: immersing the heat-treated composite film obtained after heat treatment in an HF solution; the concentration of the HF solution may be 0.08~0.1 mol / L; the etching temperature may be 20~30℃, specifically room temperature, and the etching time may be 8~10 seconds. This invention removes loose particles from the material surface through etching, which helps to prevent the loose particles from falling off and causing contamination during use.

[0044] After the etching process, an etched composite film is obtained. This invention further hydrophilicates the etched composite film. In one embodiment, the hydrophilication treatment may include immersing the etched composite film obtained after the etching process in an H2O2 solution; the concentration of the H2O2 solution may be 28-30 wt%, the temperature of the hydrophilication treatment may be 20-30°C (specifically room temperature), and the time may be 50-60 minutes. This invention adds -OH groups to the material surface through hydrophilication treatment, which is beneficial for improving the hydrophilicity of the film surface.

[0045] The present invention provides a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared by the preparation method described above, comprising a recrystallized silicon carbide ceramic membrane and a molybdenum disilicide-based ultrafiltration coating coated on the surface of the recrystallized silicon carbide ceramic membrane, wherein the pore size of the molybdenum disilicide-based ultrafiltration coating is 10~20 nm.

[0046] The molybdenum disilicide-based ultrafiltration coating of this invention is defect-free and of high quality. In one embodiment of this invention, the thickness of the molybdenum disilicide-based ultrafiltration coating can be 2.5~5.0 μm, specifically 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5.0 μm; if the molybdenum disilicide-based ultrafiltration coating is too thick, it will reduce the flux of the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane.

[0047] The molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane of this invention exhibits high rejection rate (rejection rate of >95% for substances with molecular weight of 100,000~150,000 Da), high flux (>150 LMH / bar), good resistance to acid and solvent corrosion, and excellent long-term operational stability. Furthermore, the molybdenum disilicide-based ultrafiltration coating on the surface of the recrystallized silicon carbide ceramic membrane enables the inorganic ceramic membrane to be charged, laying the foundation for the electro-assisted function of the ceramic membrane.

[0048] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0049] Preparation Example 1

[0050] The recrystallized silicon carbide ceramic membrane used in the following experiments is a tubular membrane with a pore size of 50 nm; the method for preparing the recrystallized silicon carbide ceramic membrane includes the following steps:

[0051] Step 1, Preparation of the support:

[0052] The raw materials were mixed according to the following mass percentages: 70% silicon carbide, 6% cellulose, 3% dextran, 1% vegetable oil (specifically rice bran oil), 19% water, and 1% glycerol. The mixture was then subjected to a series of processes including kneading (room temperature, 4 hours), extrusion, degumming (150℃, 10 hours), and first sintering. The mixture was cooled to room temperature at a rate of 2-5℃ / min to obtain a support with a filter pore size of 10μm. The first sintering process was as follows: heating from room temperature to 600℃ at a rate of 1-2℃ / min and holding for 1 hour; heating from 600℃ to 1600℃ at a rate of 5-10℃ / min and holding for 1 hour; heating from 1600℃ to 2200℃ at a rate of 3-5℃ / min and holding for 2 hours; and heating from 2200℃ to 2450℃ at a rate of 3-5℃ / min and holding for 3 hours. The first sintering was carried out under argon atmosphere.

[0053] Step 2: Preparation of microfilters with a support / transition layer structure:

[0054] Silicon carbide powder (7 μm particle size), vegetable oil, water, and glycerol were mixed in a mass ratio of 60:10:25:5 to obtain a transition coating. The transition coating was applied to a support, and a second sintering was performed to obtain a transition film with a pore size of 1 μm. The second sintering process was as follows: heating from room temperature to 600℃ at a rate of 1–2℃ / min and holding for 1 hour; heating from 600℃ to 1600℃ at a rate of 5–10℃ / min and holding for 1 hour; heating from 1600℃ to 2200℃ at a rate of 3–5℃ / min and holding for 2 hours; cooling from 2200℃ to room temperature at a rate of 2–5℃ / min; the second sintering was carried out under argon atmosphere.

[0055] Step 3: Preparation of recrystallized silicon carbide ceramic membrane with support-transition layer-ultrafiltration layer:

[0056] Silicon carbide powder (0.7 μm particle size), vegetable oil, water, and glycerol were mixed in a mass ratio of 60:10:25:5 to obtain an ultrafiltration coating. This ultrafiltration coating was coated onto a transition layer and subjected to a third sintering process to obtain a recrystallized silicon carbide ceramic membrane with a pore size of 0.05 μm. The third sintering process consisted of: heating from room temperature to 600 °C at a rate of 1–2 °C / min and holding for 1 hour; heating from 600 °C to 1600 °C at a rate of 5–10 °C / min and holding for 1 hour; heating from 1600 °C to 2200 °C at a rate of 3–5 °C / min and holding for 1 hour; and cooling from 2200 °C to room temperature at a rate of 2–5 °C / min. The third sintering was carried out under argon atmosphere.

[0057] Example 1

[0058] The recrystallized silicon carbide ceramic membrane was ultrasonically cleaned with a 1 mol / L NaOH solution for 20 min, then washed with a 0.1 mol / L nitric acid solution, rinsed with deionized water until neutral, and then dried at 120 °C. The dried recrystallized silicon carbide ceramic membrane was then immersed in an ethanol solution of a 5 wt% silane coupling agent KH550 and activated at room temperature (25 °C) for 1 h to obtain the activated membrane material.

[0059] The solvent (a mixture of deionized water and anhydrous ethanol at a volume ratio of 8:2) was ultrasonically mixed with polyvinylpyrrolidone (PVP) for 10 min. MoSi2 powder (particle size 75±20 nm, purity >99.5 wt%) was added to the resulting material and ball-milled at 200 rpm for 24 h. Silica sol (nano-silica content 30 wt%, specifically ZW-30 silica sol from Henan Zhuangwei New Materials Co., Ltd.) was added to the resulting material and stirred for 2 h. The mixture was then passed through a 500-mesh sieve, and the sieve-passing liquid was collected and the pH was adjusted to 9.5 with ammonia to obtain a MoSi2 suspension (Zeta potential absolute value >30 mV). The MoSi2 suspension contained 15 wt% MoSi2 powder, 3 wt% silica sol, and 0.8 wt% PVP.

[0060] The MoSi2 suspension was sprayed onto the activated membrane material three times. The conditions for each spraying were: pressure of 1.2 bar, activated membrane material temperature of 60°C, and nozzle diameter of 0.3 mm. After each spraying, the membrane material was dried at 80°C for 10 minutes to obtain the final composite membrane material.

[0061] In an air atmosphere, the composite membrane material is heated from room temperature to 200°C at a rate of 1°C / min and held for 30 min. Then, in an air atmosphere, it is heated from 200°C to 400°C at a rate of 2°C / min and held for 1.5 h. Next, in an argon atmosphere (oxygen content <10 ppm), it is heated from 400°C to 1650°C at a rate of 3°C / min and held for 1.5 h. Finally, in a nitrogen atmosphere (oxygen content <10 ppm), it is cooled to room temperature in the furnace to obtain the heat-treated composite membrane.

[0062] The heat-treated composite film was immersed in a 0.1 mol / L HF solution and etched at room temperature for 10 seconds to obtain an etched composite film.

[0063] The etched composite membrane was immersed in a 30wt% H2O2 solution and subjected to hydrophilication treatment at room temperature for 1 hour to obtain a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane. The molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane includes a recrystallized silicon carbide ceramic membrane and a molybdenum disilicide-based ultrafiltration coating coated on the surface of the recrystallized silicon carbide ceramic membrane. The pore size of the molybdenum disilicide-based ultrafiltration coating is 10~20nm, and the thickness of the molybdenum disilicide-based ultrafiltration coating is 3.5μm.

[0064] Figure 1 The image shows a cross-sectional SEM image of the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared in Example 1. The results show that the molybdenum disilicide phase partially penetrates into the recrystallized silicon carbide ceramic composite ultrafiltration membrane, and the interfacial lattice bonding is tight. The density of the molybdenum disilicide membrane is significantly higher than that of the recrystallized silicon carbide ceramic composite ultrafiltration membrane.

[0065] Example 2

[0066] The procedure was performed in accordance with the method in Example 1, except that the MoSi2 suspension was sprayed 5 times, and the thickness of the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane was 5 μm.

[0067] Comparative Example 1

[0068] The procedure was carried out in accordance with the method of Example 1, except that the content of MoSi2 powder in the MoSi2 suspension was adjusted to 10wt%, and the thickness of the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane was 2μm.

[0069] Comparative Example 2

[0070] The procedure is the same as in Example 1, except that the content of nano-silica in the silica sol is adjusted to 20wt%, and the content of silica sol in the MoSi2 suspension is 2wt%.

[0071] Comparative Example 3

[0072] The procedure is the same as in Example 1, except that the silica sol is replaced with other non-silicone adhesives, and the adhesive is a polyvinyl alcohol (PVA-124) solution with a concentration of 2 wt% (polyvinyl alcohol decomposes completely upon heating, leaving only carbon, which cannot perform the functions of bonding, filling pores, and densification).

[0073] Comparative Example 4

[0074] The procedure was performed in accordance with the method in Example 1, except that the particle size of the MoSi2 powder was adjusted to 150±20nm (purity >99.5wt%).

[0075] Test Example 1

[0076] The performance of the composite ultrafiltration membranes prepared in the examples and comparative examples was tested, as follows:

[0077] 1. Surface pore size: Bubble point method: GB / T32361-2015 "Test method for pore size of separation membranes: bubble point and average flow rate method", using a bubble point meter from Best Instrument Technology (Beijing) Co., Ltd.

[0078] 2. Pure water flux: GBT32360-2015 "Test Methods for Ultrafiltration Membranes", Dead End Filtration (1 bar, 25℃).

[0079] 3. Acid resistance: The sample was immersed in 1 mol / L hydrochloric acid at room temperature for 48 hours, and the weight change was tested.

[0080] 4. Long-term operation effect: The sample throughput was tested after continuous filtration of wastewater for 72 hours at room temperature; the wastewater was a humic acid aqueous solution with a concentration of 20 mg / L.

[0081] The specific experimental test results are shown in Tables 1-3. Table 1 shows that the surface pore size of the composite ultrafiltration membranes prepared in Examples 1 and 2 is 10-20 nm, and the pure water flux is 200 ± 15 LMH / bar. In contrast, the surface pore size distribution of the membrane materials prepared in Comparative Examples 1-4 ranges from 15-25 nm and 20-30 nm, respectively, which cannot meet the requirements for fine filtration. Table 2 shows that the composite ultrafiltration membranes prepared in Examples 1 and 2 exhibit excellent acid resistance; after soaking in 1 mol / L hydrochloric acid for 48 hours, the sample weight decreases by less than 10%. Table 3 shows that the composite ultrafiltration membranes prepared in Examples 1 and 2 demonstrate excellent long-term operational stability; after 72 hours of continuous wastewater filtration, the sample flux exceeds 85% of the initial flux.

[0082] Table 1. Surface pore size and pure water flux test results of the composite ultrafiltration membranes prepared in the examples and comparative examples.

[0083]

[0084] Table 2. Acid resistance test results of the composite ultrafiltration membranes prepared in the examples and comparative examples.

[0085]

[0086] Table 3. Long-term operational test results of the composite ultrafiltration membranes prepared in the examples and comparative examples.

[0087]

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane, characterized in that, Includes the following steps: The recrystallized silicon carbide ceramic film was activated to obtain the activated film material; The pore size of the recrystallized silicon carbide ceramic membrane is 50~70nm; the activation treatment includes: immersing the recrystallized silicon carbide ceramic membrane in a silane coupling agent solution; Molybdenum disilicide powder, silica sol, dispersant, and solvent are mixed to obtain a molybdenum disilicide suspension. The particle size of the molybdenum disilicide powder is 50-100 nm, the content of nano-silica in the silica sol is 30-40 wt%, the content of molybdenum disilicide powder in the molybdenum disilicide suspension is 15-20 wt%, and the content of silica sol is 3-5 wt%. The molybdenum disilicide suspension was coated onto the surface of the activated membrane material and dried to obtain a composite membrane material. The composite membrane material was subjected to heat treatment, etching treatment and hydrophilization treatment in sequence to obtain the molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane. The heat treatment includes sequentially performing a first-stage heat treatment, a second-stage heat treatment, and a third-stage heat treatment. The temperature of the first stage heat treatment is 180~200℃, the holding time is 25~30min, the first stage heat treatment is carried out in an air atmosphere, and the heating rate from room temperature to the temperature of the first stage heat treatment is 0.8~1℃ / min. The temperature of the second stage heat treatment is 380~400℃, the holding time is 1~2h, the second stage heat treatment is carried out in an air atmosphere, and the heating rate from the temperature of the first stage heat treatment to the temperature of the second stage heat treatment is 1~3℃ / min. The temperature of the third stage heat treatment is 1600~1700℃, the holding time is 1~2h, the third stage heat treatment is carried out in a protective atmosphere, and the heating rate from the temperature of the second stage heat treatment to the temperature of the third stage heat treatment is 2~5℃ / min. The third stage of heat treatment also includes cooling in a protective atmosphere.

2. The preparation method according to claim 1, characterized in that, The concentration of the silane coupling agent solution is 4~7wt%, and the activation treatment temperature is 20~30℃, and the time is 0.5~1.5h.

3. The preparation method according to claim 1, characterized in that, The dispersant includes polyvinylpyrrolidone and / or phosphate ester; the solvent is water and ethanol, and the volume ratio of water to ethanol is 8:1.5~2.5; the content of dispersant in the molybdenum disilicide suspension is 0.5~1wt%.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The coating is applied 2 to 5 times, and each coating is dried afterward. The coating is sprayed, and the conditions for each spraying are independent, including: the temperature of the activated film material is 58 to 62°C, the spraying pressure is 1.0 to 1.5 bar, and the nozzle diameter is 0.3 mm.

5. The preparation method according to claim 1, characterized in that, The etching process includes immersing the heat-treated composite film obtained after heat treatment in an HF solution; the concentration of the HF solution is 0.08~0.1mol / L, the etching temperature is 20~30℃, and the etching time is 8~10s.

6. The preparation method according to claim 1 or 5, characterized in that, The hydrophilization treatment includes immersing the etched composite film obtained after etching treatment in an H2O2 solution; the concentration of the H2O2 solution is 28~30wt%, the temperature of the hydrophilization treatment is 20~30℃, and the time is 50~60min.

7. The preparation method according to claim 1, characterized in that, The recrystallized silicon carbide ceramic membrane is a tubular membrane or a flat sheet membrane.

8. The molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It includes a recrystallized silicon carbide ceramic membrane and a molybdenum disilicide-based ultrafiltration coating coated on the surface of the recrystallized silicon carbide ceramic membrane, wherein the pore size of the molybdenum disilicide-based ultrafiltration coating is 10~20nm.

9. The molybdenum disilicide-recrystallized silicon carbide ceramic composite ultrafiltration membrane according to claim 8, characterized in that, The thickness of the molybdenum disilicide-based ultrafiltration coating is 2.5~5.0 μm.

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