Silicon carbide-based janus film and preparation method and application thereof

Abstract

The application provides a silicon carbide-based Janus membrane and a preparation method and application thereof. The steps comprise: a) ultrasonic spraying of a silicon carbide separation layer slurry liquid on one side of a silicon carbide support body, and performing air sintering to obtain a silicon dioxide-bonded silicon carbide-based ceramic membrane; and b) then performing one-side super-hydrophobic modification on the silicon dioxide-bonded silicon carbide-based ceramic membrane obtained in step a) by using a graft polymerization method to obtain a silicon carbide-based Janus membrane. The super-hydrophobic / hydrophilic Janus membrane prepared by the application not only has excellent super-hydrophobic separation layers and hydrophilic supports, but also has excellent acid and alkali resistance, friction resistance, thermal stability and anti-fouling performance, and the membrane distillation flux is significantly improved. At the same time, a simple cleaning method is used, so that the membrane flux can maintain a recovery rate of 90% in the long-term cycle of vacuum membrane distillation. Therefore, the super-hydrophobic / hydrophilic composite Janus filter membrane prepared by the application has a high-efficiency, environmentally-friendly seawater desalination application prospect.

Description

Technical Field

[0001] This invention belongs to the field of functional membrane preparation technology, and relates to a silicon carbide-based Janus membrane, its preparation method and application. Background Technology

[0002] The increasing scarcity of freshwater resources has become a global challenge, and seawater desalination is considered an effective way to solve this problem. Among the many seawater desalination technologies, membrane distillation has attracted widespread attention due to its advantages such as low energy consumption, compact system design, and ease of operation.

[0003] However, in the commercialization of membrane distillation, some long-standing and prominent problems still need to be addressed, such as membrane fouling, pore wetting, and low permeation flux of its core component, the hydrophobic membrane. Current research on these issues mainly focuses on organic membrane materials. Patent CN107511081B provides a method for preparing an antifouling PTFE-CA / SiNPs composite membrane, specifically involving a method for preparing a composite membrane with an oil-resistant surface and a porous three-dimensional network structure using electrospinning. This invention constructs a superhydrophilic antifouling layer on the surface of a hydrophobic PTFE base membrane using electrospinning, thus preparing a PTFE-CA / SiNPs composite membrane. This method has a simple membrane formation process, is easy to operate, and is readily applicable to industrial production. Moreover, the prepared composite membrane exhibits good antifouling performance, high permeation flux, strong chemical stability, good mechanical properties, and high retention efficiency, showing broad application prospects. Patent CN115463554A discloses a method for preparing a PVDF-HFP / TPU multi-level structured nanofiber membrane using electrospinning and its membrane distillation application, belonging to the field of membrane distillation technology. The preparation method uses polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and thermoplastic polyurethane (TPU) as spinning polymer raw materials to prepare multi-level nanofiber composite membranes through electrospinning technology. PVDF-HFP nanofiber membranes exhibit excellent hydrophobic properties and low crystallinity; TPU possesses superior comprehensive performance, exhibiting flexibility, toughness, and antibacterial properties. Furthermore, its unique hard-soft segment microphase structure allows for the simultaneous presence of hydrophilic and hydrophobic groups on the molecular chain segments, resulting in excellent moisture permeability. By incorporating different proportions of TPU into the PVDF-HFP spinning solution using electrospinning technology to modify the membrane pores with hydrophilic groups, high-flux, mechanically strong multi-level nanofiber composite membranes can be prepared. The composite membrane prepared by this invention exhibits high permeate flux, rejection rate, and long-term stability during membrane distillation, showing broad application prospects in seawater desalination, brackish water treatment, and other water treatment fields.

[0004] However, the membranes provided by the above patents have some drawbacks: First, the bonding strength between the hydrophobic and hydrophilic layers of the membrane is relatively weak, and its mechanical properties are still inferior to those of ceramic membranes, resulting in a short service life. Second, the membrane has a low hydrophobic angle, making it prone to membrane wetting. In addition, the high porosity and nanofiber structure easily adsorb organic matter, microorganisms, or colloidal particles, leading to membrane fouling.

[0005] In recent years, hydrophobic ceramic membranes have attracted considerable attention due to their long service life and have been applied in scenarios such as vacuum membrane distillation (VMD), water-in-oil emulsion separation, CO2 capture, and waste heat recovery. Among them, porous silicon carbide ceramic membranes are a new type of ceramic membrane that has been gradually developed in recent years, with advantages such as high flux, strong antifouling ability, acid and alkali resistance, and corrosion resistance. Currently, hydrophobically modified silicon carbide ceramic membranes have been applied in the separation of oil-water emulsions. For example, the literature (Y.Wang, C.Yuan, K.Zhou, Q.Gu, W.Jing, Z.Zhong, W.Xing, Construction of Janus silicon carbidembranes with asymmetric wettability for enhanced antifouling in water-in-oil emulsification process[J]. Journal of Membrane Science, 2023, 671:121389) utilizes a silane coupling agent to hydrophobically modify one side of a pure silicon carbide membrane to prepare a SiC membrane with asymmetric wettability. This membrane can separate small-sized W / O emulsions and has good antifouling ability and regenerability. However, the application of pure silicon carbide hydrophobic membranes in membrane distillation has not yet been observed.

[0006] Studies have found that the limited application of silicon carbide ceramic membranes in membrane distillation may be mainly due to two factors: First, the scarcity of functional groups on the silicon carbide surface makes it difficult to achieve stable and robust hydrophobic modification. Second, the pore size of silicon carbide membranes is larger than that of inorganic membranes such as alumina, resulting in a low material retention rate in membrane distillation applications. Preparing a silicon carbide separation layer bonded to silica using air sintering technology, followed by hydrophobic modification, is a feasible solution.

[0007] Air sintering involves sintering silicon carbide in an air atmosphere to form a silicon carbide separation layer bonded with silica on its surface. This method was proposed and demonstrated in the applicant's previous patent (CN115845619A), proving its ability to effectively reduce the sintering temperature of silicon carbide. The resulting separation layer exhibits high mechanical integrity and smaller pore size. Furthermore, the silica-bonded silicon carbide separation layer obtained through this method is both robust and conducive to hydrophobic modification. However, the hydrophobic modification method in this patent is complex and fails to achieve a superhydrophobic state. Simultaneously, the prepared membrane is a fully hydrophobic membrane with a small pore size, leading to increased mass transfer resistance and consequently, lower membrane distillation flux. In addition, this membrane suffers from rapid fouling and difficult scaling and cleaning, shortening its service life. Therefore, there is an urgent need to develop a superhydrophobic membrane with controllable pore size, low mass transfer resistance, and easy cleaning to improve membrane distillation flux and extend the service life of the filter membrane. Summary of the Invention

[0008] In view of the current situation where there is a lack of superhydrophobic membranes with controllable pore size, low mass transfer resistance and easy cleaning in the existing technology, the present invention provides a silicon carbide-based Janus membrane, its preparation method and application.

[0009] This application is based on the air sintering technology in the previous patent (CN115845619A), and has made key improvements in both the control of the pore size of the separation layer and the hydrophobic modification.

[0010] First, the pore size of the separation layer was controlled, increasing the membrane flux by approximately two times while maintaining the vacuum membrane distillation rejection rate (>99%). Second, a superhydrophobic / hydrophilic asymmetric Janus structure was creatively introduced. This structure not only improves the membrane flux to a certain extent, but also allows for flux recovery through a simple cleaning procedure when membrane fouling occurs during operation, thus extending the service life of the filter membrane.

[0011] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0012] One of the technical solutions of this application provides a method for preparing a silicon carbide-based Janus film, comprising the following steps:

[0013] a) Prepare silicon carbide separation layer slurry; apply the silicon carbide separation layer slurry to one side of a silicon carbide support to obtain a single-sided coated silicon carbide preform; subject the single-sided coated silicon carbide preform to air sintering to obtain a silicon carbide-based ceramic film bonded with silicon dioxide.

[0014] b) Then, the silicon dioxide-bonded silicon carbide-based ceramic film obtained in step a) is subjected to single-sided hydrophobic modification by graft polymerization to obtain a silicon carbide-based Janus film.

[0015] Further, the silicon carbide separation layer slurry prepared in step a) is prepared by ball milling, and the steps are as follows: silicon carbide powder, binder, dispersant and RO water are mixed in a mass ratio of (5~15):(0.05~0.15):(1~2):(80~90) and then ground in a ball mill;

[0016] Further, the particle size of the silicon carbide powder in step a) is (4-6) μm, preferably 5 μm; the ball milling time is 1-5 hours, preferably 2.5 hours; the binder is selected from any one of hydroxypropyl methylcellulose, methylcellulose or sodium hexametaphosphate; the dispersant is selected from any one of polyethylene glycol, polyvinyl alcohol, polyacrylic acid.

[0017] Furthermore, the silicon carbide separation layer slurry prepared in step a) contains two particle sizes: small particles with a particle size of 59–220 nm and large particles with a particle size of 342–1032 nm. The particle size and the content of large and small particles are determined by the ball milling time. The solid content of the slurry in step a) is 5–15 wt%, preferably 10 wt%.

[0018] Further, the coating in step a) is preferably performed by using ultrasonic spraying to deposit the silicon carbide separation layer slurry on one side of the silicon carbide support.

[0019] Further, the purpose of air sintering in step a) is to bond the deposited particles to the silicon carbide support, thereby obtaining a silicon carbide-based ceramic film bonded with silicon dioxide; the air sintering is preferably carried out in a muffle furnace; the air sintering adopts the following process:

[0020] ① First, in an air atmosphere, heat the temperature from room temperature to 300℃ at a heating rate of 5℃ / minute, and then keep it at 300℃ for 15-25 minutes;

[0021] ②Then, in an air atmosphere, the temperature is increased from 300℃ to 600℃ at a rate of 5℃ / minute, and then held at 600℃ for 15 to 25 minutes;

[0022] ③Then, in an air atmosphere, the temperature is increased from 600℃ to 800℃ at a rate of 5℃ / minute, and then held at 800℃ for 15 to 25 minutes;

[0023] ④Then, in an air atmosphere, the temperature is increased from 800℃ to 1100-1300℃ at a heating rate of 5℃ / minute;

[0024] ⑥ Then sinter at 1100-1300℃ in air for 2 hours;

[0025] ⑦ Finally, allow it to cool naturally to room temperature in the air.

[0026] Furthermore, in one specific embodiment of this application, step b) includes the following specific operations:

[0027] b1) Prepare a 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) solution and stir until homogeneous;

[0028] b2) Spray the FOTS solution prepared in step b1) onto the separation layer side and dry it to obtain a silicon carbide-based Janus membrane.

[0029] Further, in step b1), the solvent of the 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) solution is any one of n-hexane, cyclohexane, hexadecane, and anhydrous ethanol, preferably n-hexane; the mass fraction of the FOTS solution is 0.4-1.6 vol%, preferably 1 vol%; and the stirring time is 15-25 min.

[0030] Furthermore, the 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) can be replaced with other silane coupling agents, and the specific operating methods will be different.

[0031] Further, the drying in step b2) is preferably carried out in a vacuum drying oven; the drying temperature is 100-200°C and the time is 0.5-1.5 hours.

[0032] Furthermore, the principle of the graft polymerization method involved in this step is as follows: FOTS is hydrolyzed in n-hexane solvent to generate silanol, which undergoes a condensation reaction with the silicon carbide separation layer bonded to silicon dioxide rich in hydroxyl groups to form Si-O-Si covalent bonds. At the same time, the silanol molecules undergo lateral cross-linking to form a dense and ordered perfluoroalkyl monolayer.

[0033] The second technical solution of this application provides a silicon carbide-based Janus membrane obtained by the above-mentioned technical solution. The silicon carbide-based Janus membrane uses a silicon carbide support as a substrate and has a superhydrophobic modified silicon carbide separation layer sprayed on one side; the pore size of the silicon carbide-based Janus membrane is 100nm to 1000nm; the pure water flux is 1418.82 to 4405.82 kg / (m³). 2 ·h).

[0034] The hydrophobic angle of the membrane separation layer side reaches 151.33° under preferred conditions (air sintering temperature of 1200°C; 1 vol% FOTS solution); the side of the support without the separation layer coating maintains excellent hydrophilicity, and water droplets can be completely immersed in a short time (0.12s). The silicon carbide-based Janus membrane has outstanding acid and alkali resistance, abrasion resistance, and thermal stability.

[0035] The third technical solution of this application provides an application of the silicon carbide-based Janus membrane obtained by the above technical solution. The silicon carbide-based Janus membrane is used to prepare membrane modules to achieve membrane distillation of seawater, converting seawater into desalinated water.

[0036] In vacuum membrane distillation applications using a 3.5 wt% NaCl solution as the feed solution, the silicon carbide-based Janus membrane exhibited high membrane flux, and the flux recovered to approximately 90% after simple cleaning. Furthermore, when using a NaCl solution containing supersaturated gypsum as the feed solution, the flux variation trend of the silicon carbide-based Janus membrane was essentially consistent with that of a gypsum-free NaCl solution, indicating that the silicon carbide-based Janus membrane possesses excellent anti-fouling properties.

[0037] Compared with the prior art, the present invention has the following significant advantages:

[0038] The superhydrophobic / hydrophilic Janus membrane prepared in this application not only possesses an excellent superhydrophobic separation layer and a hydrophilic support, but also exhibits superior performance in acid and alkali resistance, abrasion resistance, thermal stability, and scale prevention, while significantly improving membrane distillation flux. Furthermore, this invention employs a simple cleaning method, enabling the membrane flux to maintain a 90% recovery rate during long-term VMD cycling experiments. Therefore, the superhydrophobic / hydrophilic composite Janus filter membrane prepared by this method shows promising prospects for efficient and environmentally friendly seawater desalination applications. Attached Figure Description

[0039] Figure 1 This is a material comparison diagram of the silicon dioxide bonded silicon carbide separation layer and the silicon carbide support characterized by XRD in Example 1;

[0040] Figure 2 These are scanning electron microscope (SEM) images of the silicon dioxide-bonded silicon carbide film in Example 2 at different sintering temperatures. Figures (a), (c), and (e) are silicon dioxide-bonded silicon carbide films sintered at 1100°C, 1200°C, and 1300°C, respectively; Figures (b), (d), and (f) are corresponding magnified views.

[0041] Figure 3 This describes the particle size distribution in the slurry under different ball milling times in Example 3.

[0042] Figure 4 These are pore size distribution diagrams of the silicon dioxide-bonded silicon carbide films measured by different methods in Example 3, wherein... Figure 4 (a) and (b) are mercury porosimetry methods. Figure 4 (c) is the fluorescent probe method;

[0043] Figure 5These are physical images of a silicon carbide support, a silicon carbide film bonded to silicon dioxide, and a silicon carbide-based Janus film.

[0044] Figure 6 This is a wettability characterization of the silicon carbide-based Janus film in Example 4; Figure 6 (a) The wetting condition of silicon carbide-based ceramic membranes using 4 μL RO water droplets as the test solution; Figure 6 (b) shows the FTIR analysis results of the silicon carbide-based ceramic film samples before and after modification;

[0045] Figure 7 This is an investigation into the stability of the prepared silicon carbide-based Janus film in Example 4; Figure 7 (a) shows the change in hydrophobic angle of silicon carbide-based Janus films after heat treatment at 100°C, 120°C, 150°C and 200°C; Figure 7 (b) is the contact angle measurement using RO water, sulfuric acid (pH=1), and sodium hydroxide (pH=13) as test liquids; Figure 7 (c) shows the change in the hydrophobic angle of the silicon carbide-based Janus film before and after the sandpaper abrasion test;

[0046] Figure 8 This refers to the hydrophobic angle of the silicon carbide-based Janus film under different modifier concentrations in Example 5;

[0047] Figure 9 This is a comparison of the membrane distillation treatment effects of silicon carbide-based Janus membrane and double-sided hydrophobic modified silicon carbide-based ceramic membrane on brine in Example 6.

[0048] Figure 10 Example 7 compares the performance of silicon carbide-based ceramic membranes with three different pore sizes prepared in Example 3 after modification with reference to Example 4 in membrane distillation tests.

[0049] Figure 11 This is a comparison of the membrane flux change trends of the silicon carbide-based Janus membrane when the feed solutions are salt solutions containing gypsum and salt solutions without gypsum, respectively, in Example 8.

[0050] Figure 12 The changes in membrane flux and conductivity over time are shown in Example 9 after the silicon carbide-based Janus membrane was cleaned using the cleaning process described in Example 6 during the VMD long-term desalination test. Detailed Implementation

[0051] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0052] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0053] Example 1: A silicon carbide-based ceramic film bonded with silicon dioxide

[0054] In this embodiment, a silicon carbide-based ceramic film bonded with silicon dioxide is prepared. The specific steps are as follows:

[0055] a1) 5μm silicon carbide powder (Shandong Sailike Membrane Technology Co., Ltd.), hydroxypropyl methylcellulose (Shandong Sailike Membrane Technology Co., Ltd.), polyethylene glycol (Shandong Sailike Membrane Technology Co., Ltd.), and RO water (reverse osmosis water) were mixed in a mass ratio of 10:0.1:1.4:88.5 and added to a planetary ball mill jar. Then, a planetary ball mill (3S-T10, Beijing Tonglin Technology Co., Ltd.) was used with silicon carbide balls as the ball milling medium. The ball-to-material ratio was controlled at 5:1 and the ball milling speed was 380 rpm. The ball milling was carried out for 2.5 hours to obtain a silicon carbide separation layer slurry with a solid content of 10wt%.

[0056] The slurry was ultrasonically sprayed onto a silicon carbide support (Shandong Sailike Membrane Technology Co., Ltd.) using an ultrasonic thin-film spraying machine (UAM4000E, Hangzhou Chifei Ultrasonic Equipment Co., Ltd.). During ultrasonic spraying, the stage temperature was 90℃, the spraying pressure was 0.4MPa, the ultrasonic frequency was 40kHz, the spraying flow rate was 1.9mm / s, and the number of sprays was 20. The thickness of the silicon carbide separation layer was controlled at 31±2μm. Then, it was placed in a vacuum drying oven (DZF-6050, Shanghai Huitai Instrument Manufacturing Co., Ltd.) and dried at 100℃ for 4 hours to obtain a single-sided coated silicon carbide preform.

[0057] a2) The dried single-sided coated silicon carbide preform prepared in step a1) is placed in a muffle furnace (KSL-1400X-A1, Hefei Kejing Materials Technology Co., Ltd.) for air sintering to obtain a silicon carbide-based ceramic film bonded with silicon dioxide; the air sintering adopts the following process:

[0058] ① First, in an air atmosphere, heat the temperature from room temperature to 300℃ at a heating rate of 5℃ / minute, and then keep it at 300℃ for 20 minutes;

[0059] ②Then, in an air atmosphere, the temperature is increased from 300℃ to 600℃ at a rate of 5℃ / minute, and then held at 600℃ for 20 minutes;

[0060] ③Then, in an air atmosphere, the temperature is increased from 600℃ to 800℃ at a heating rate of 5℃ / minute, and then held at 800℃ for 20 minutes;

[0061] ④Then, in an air atmosphere, the temperature is increased from 800℃ to 1200℃ at a heating rate of 5℃ / minute;

[0062] ⑥ Then sinter at 1200℃ in air for 2 hours;

[0063] ⑦ Finally, allow it to cool naturally to room temperature in the air.

[0064] The silicon dioxide-bonded silicon carbide-based ceramic films obtained above were characterized as follows:

[0065] Figure 1 The image shown is a material-to-material comparison of the silica-bonded silicon carbide separation layer and the silicon carbide support, characterized by XRD. Figure 1 As shown, the characteristic peaks of the silicon dioxide-bonded silicon carbide separation layer and the silicon carbide support highly overlap, with the only difference being the characteristic peaks between 20° and 25° at the 2θ angle. Comparison with PDF card PDF#27-0605 shows that the characteristic peaks between 20° and 25° at the 2θ angle are amorphous silicon dioxide, indicating that the prepared ceramic film is a silicon dioxide-bonded silicon carbide film.

[0066] Example 2 investigates the sintering temperature for preparing silicon dioxide-bonded silicon carbide-based ceramic films.

[0067] This embodiment uses the method described in Example 1, except that the air sintering temperature is adjusted from 1200℃ to 1100℃ and 1300℃; then the strength of the separation layer of the silicon carbide-based ceramic membrane bonded with silicon dioxide and the pure water flux are tested at the three sintering temperatures.

[0068] The specific method for testing the firmness is as follows: First, pour 50mL of ultrapure water into the beaker, and then place a piece with dimensions of 0.025×0.025m... 2 The membrane separation layer was placed face down, flat at the bottom of the beaker. The beaker was then placed in an ultrasonic cleaner (KQ-3200, Kunshan Ultrasonic Instrument Co., Ltd.) and ultrasonicated continuously for 5 minutes at 100kW. After treatment, the solution was thoroughly mixed, and its turbidity value was measured using a turbidimeter (2100N, Hach Instruments, USA).

[0069] The pure water flux was measured using a self-built dead-end filtration system (a routine procedure for those skilled in the art). The specific method involved assembling the membrane sample into a well-sealed mold, then opening the pressure regulating valve to precisely control the filtration pressure at 1 bar. A high-precision electronic balance (ME204EJ02, Mettler Toledo Instruments Shanghai Co., Ltd.) was used to record the changes in filtrate mass in real time, and the flux was calculated using the flux formula. The pure water flux J was calculated as follows: J = M / (A×t); where J is the pure water flux, typically expressed in kg / (m³). 2 • h·MPa (kg / m² / hour / MPa); M: Mass of pure water permeating the membrane, in kilograms (kg); A: Effective area of ​​the membrane, in square meters (m²) 2 ); t: filtration time, in hours (h).

[0070] Figure 2 The image shown is a scanning electron microscope (SEM) image of a silicon carbide-based ceramic film bonded with silicon dioxide at different sintering temperatures. Figure 2 Images (a), (c), and (e) are silicon dioxide-bonded silicon carbide-based ceramic films sintered at 1100℃, 1200℃, and 1300℃, respectively. Figure 2 (b), 2(d), and 2(f) are the corresponding magnified views. Figure 2 As can be seen, the separation layer is smooth and defect-free, and the fine particles are bonded together by the formation of silica. As the sintering temperature increases, the separation layer particles gradually become rounded and more sintering necks are formed between the particles, which gradually increases the bonding strength between the separation layer particles.

[0071] Table 1 shows the turbidity and pure water flux data of silicon carbide-based ceramic membranes bonded with silica after ultrasonication at different sintering temperatures. The turbidity of the sample sintered at 1100℃ reached 283.9 NTU after ultrasonication, which is much higher than that of the membranes sintered at the other two temperatures. This indicates that the separation layer formed at low sintering temperatures has poor stability, resulting in severe powder detachment from the surface. The pure water flux of the sample sintered at 1300℃ was only 1418.82 ± 153.61 kg / (m³). 2 The sintering temperature at this temperature (·h) is much lower than the other two sintering temperatures. This is because the viscous flow of silica is enhanced at this temperature, forming a dense silica film, which increases the resistance to gas-liquid permeation. Therefore, 1200℃ was chosen as the sintering temperature for silica-bonded silicon carbide films in subsequent experiments.

[0072] Table 1. Turbidity and pure water flux after ultrasonication at different sintering temperatures.

[0073] 1100℃ 283.9 4405.82±924.4 1200℃ 56.56 3523.3±311.54 1300℃ 19.86 1418.82±153.61

[0074] Example 3 investigates the effect of ball milling time on the particle size distribution of the slurry and the pore size of silicon carbide-based ceramic membranes bonded with silica.

[0075] This embodiment uses the method described in Example 1, except that the ball milling time of 2.5 h in the silicon carbide separation layer slurry preparation method is adjusted to 2 h and 3 h. Then, the particle size distribution of the three slurries is detected, and the mercury porosimetry method (for specific operation, please refer to the literature: Y. Liu, Q. Jiang, K. Zhou, Q. Gu, Z. Zhong, W. Jing, Y. Fan, W. Xing, Tailored surface wettability and pore structure of hydrophobic SiO2 / SiC membranes for preparing monodisperse emulsion with high-efficiency, Applied Surface Science 2024, 665:160364) and the fluorescence probe method (for specific operation, please refer to the literature: J. Zhu, J. Wang, H. Zhong, Y. Hu, L. Hu, P. Rao, R. Liu, J. Zhu, G. Li, New method for measuring the pore sizes and pore size distributions of filter membranes—the fluorescence probe method, Microchim) are used. Acta, 2023, 190(12):469) measured the pore size of three silica-bonded silicon carbide-based ceramic films.

[0076] Figure 3 The particle size distribution in the slurry under different ball milling times is shown. It can be seen that as the ball milling time increases, the large particles gradually decrease in size and the fine particles increase in size.

[0077] Figure 4 Figures (a) and (b) show the pore size distribution of silicon carbide-supported silicon carbide-based ceramic films bonded with silicon dioxide, measured by mercury intrusion porosimetry. The pore size of the silicon carbide support is around 6600 nm. In the silicon dioxide-bonded silicon carbide films prepared under different ball milling times, the pore size of the separation layer decreases with the increase of ball milling time. Figure 4 (c) The same conclusion was obtained by fluorescence probe method (449nm~331nm). The pore size of the silica-bonded silicon carbide-based ceramic membrane prepared by this method is between 100nm and 1000nm, which is very suitable for the pore size requirements of membrane distillation applications.

[0078] Example 4: A silicon carbide-based Janus film

[0079] The silica-bonded silicon carbide-based ceramic film prepared in Example 1 was subjected to the following hydrophobic modification:

[0080] b1) Using hexane as a solvent, prepare a 1 vol% 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) solution and stir vigorously for 20 min using a magnetic stirrer (84-1A6S, Shanghai Sile Instruments Co., Ltd.);

[0081] b2) Cover the support side of the cleaned silica-bonded silicon carbide-based ceramic membrane completely with tape, spray the FOTS solution prepared in step b1) onto the separation layer side using a spray bottle, and then place it in a vacuum drying oven at 150°C for 1 hour to obtain a silicon carbide-based Janus membrane that can be used for membrane distillation.

[0082] The silicon carbide support used in Example 1, the silicon dioxide-bonded silicon carbide film prepared in Example 1, and the silicon carbide-based Janus film provided in Example 4 are shown in the following physical images. Figure 5 As shown.

[0083] The wettability of the silicon carbide-based Janus membrane obtained in this embodiment was characterized using a droplet shape analyzer (DSA30S, Krüger GmbH, Germany) to detect the contact angle of the membrane material. The specific measurement procedure is as follows: a 4 μL test droplet was precisely added to the horizontally placed membrane surface using a microsyringe. After the droplet stabilized, the droplet morphology was captured by the instrument's built-in high-speed camera system, and the contact angle value was calculated using the accompanying analysis software. The characterization results are as follows:

[0084] Figure 6 This is a characterization of the wettability of silicon carbide-based Janus films. Figure 6 (a) The wetting of silicon carbide-based ceramic membranes with 4 μL RO water droplets as test solution. The test results showed that the contact angle of the modified side (separation layer) of the silicon carbide-based Janus membrane prepared in this embodiment to water can be stably maintained above 150°, while the contact angle of the unmodified side (support) can be completely immersed within a short time (0.12s), indicating that the hydrophilicity is still well maintained. Figure 6 (b) shows the FTIR analysis results of the silicon carbide-based ceramic film samples before and after modification. The FTIR values ​​at 1240 cm⁻¹ on the modified side of the silicon carbide-based Janus film are also shown. -1 An absorption peak appeared nearby, corresponding to the characteristic peak of -CF3-, while the silicon carbide-based ceramic film bonded with silica before modification did not show the corresponding functional group, indicating that the FOTS modification was successful.

[0085] Figure 7 The stability of the prepared silicon carbide-based Janus film was investigated. Figure 7As shown in (a), after heat treatment at 100°C, 120°C, 150°C and 200°C for 10 hours, the hydrophobic angle of the silicon carbide-based Janus membrane did not change significantly. Figure 7 (b) shows the contact angle measurements using RO water, sulfuric acid (pH=1), and sodium hydroxide (pH=13) as test liquids. The decreases in WCA for the three test liquids within 10 minutes were 7.59°, 7.12°, and 10.93°, respectively. The primary reason for the contact angle decrease is likely due to liquid evaporation. Furthermore, the change in hydrophobic angle of the silicon carbide-based Janus membrane before and after the sandpaper abrasion test was characterized. Figure 7 As shown in (c), after 30 reciprocating wear cycles, the WCA only decreased by about 10°. The experimental results indicate that the hydrophobic separation layer of the silicon carbide-based Janus membrane prepared in this embodiment has excellent thermal stability, acid and alkali resistance, and wear resistance.

[0086] Example 5 investigates the effect of modifier concentration on the hydrophobicity of the obtained silicon carbide-based Janus film.

[0087] This embodiment uses the method described in Example 4, except that the mass fraction of the 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS) solution is adjusted from 1 vol% to 0.4 vol% to 1.6 vol%.

[0088] Hydrophobic angle of the membrane under different modifier concentrations, such as Figure 8 As shown, under the same conditions, with the increase of modifier concentration, the contact angle of the modified side of the silicon carbide-based Janus membrane shows a trend of first increasing and then decreasing, indicating that 1 vol% is the optimal concentration for the graft polymerization reaction, which can make the hydrophobic membrane have a contact angle of up to 151.33° with water.

[0089] Comparative Example 1: A double-sided hydrophobically modified silica-bonded silicon carbide-based ceramic membrane

[0090] This embodiment uses the modification method described in Example 4, except that in step b2), FOTS solution is sprayed on both the separation layer side and the support side instead of only spraying it on the separation layer side. After modification, the contact angle on the separation layer side is 150.67°, and the contact angle on the support side is 147.48°. It is evident that, under the same conditions, spraying FOTS solution only on the separation layer side results in a membrane with better hydrophobicity.

[0091] Example 6: Membrane distillation test of silicon carbide-based Janus membrane

[0092] The silicon carbide-based Janus membrane prepared in Example 4 and the double-sided hydrophobic modified silica-bonded silicon carbide-based ceramic membrane prepared in Comparative Example 1 were used for membrane distillation tests.

[0093] The test conditions for membrane distillation are as follows: 1) 3.5% NaCl solution; 2) feed flow rate of 0.225 m / s; 3) temperature of 80℃; 4) single test time of 1 hour.

[0094] After the membrane distillation test is completed, the membrane is cleaned using the following cleaning procedure: First, the pipeline is cleaned with 500 mL of 80℃ deionized water. Then, the feed side and the permeate side are exchanged, and a vacuum membrane distillation process is carried out with 80℃ deionized water for 1 hour. Finally, the filter membrane is dried.

[0095] Then, the membrane distillation effects of two different hydrophobic ceramic membranes on brine were compared using two indicators: membrane flux and salt rejection rate. The results are as follows: Figure 9 As shown; where: membrane flux is determined by the mass of the distillate; salt rejection rate is determined by the conductivity of the solution before and after distillation (conductivity method, a conventional measurement method in this field).

[0096] Depend on Figure 9 The results show that the silicon carbide-based Janus membrane prepared in Example 4 has a higher initial membrane flux, and the membrane flux can be recovered by about 90% after cleaning. This indicates that the membrane can not only be used for membrane distillation applications, but also has significant membrane distillation effects and obvious application value.

[0097] Example 7 investigates the effect of pore size of silica-bonded silicon carbide separation layer on membrane distillation performance.

[0098] The silica-bonded silicon carbide-based ceramic membranes with three different pore sizes prepared in Example 3 were modified according to Example 4 and used for membrane distillation tests. The results are as follows: Figure 10 As shown, the salt rejection rate of the filter membrane with an average pore size of 967 nm in the separation layer is only 7.13%, indicating that the membrane with this pore size is insufficient to withstand the vacuum membrane distillation operating conditions. Compared with the other two filter membranes, the membrane flux of the filter membrane with an average pore size of 810 nm in the separation layer is much higher than that of the filter membrane with 601 nm while ensuring the salt rejection rate.

[0099] Example 8 examines the anti-fouling properties of the silicon carbide-based Janus membrane prepared by the method of the present invention.

[0100] This embodiment uses the method described in Example 6, except that the 3.5% NaCl solution is replaced with a NaCl solution containing supersaturated gypsum (CaSO4, 20mM).

[0101] like Figure 11 As shown, the flux reduction trend of the silicon carbide-based Janus membrane is basically consistent with that of the gypsum-free salt solution when using a gypsum-containing salt solution as the feed solution, and the salt rejection rate reaches 99.9%. This indicates that the silicon carbide-based Janus membrane has excellent anti-fouling properties.

[0102] Example 9 examines the long-term stability of the silicon carbide-based Janus membrane prepared by the method of the present invention in vacuum membrane distillation applications.

[0103] This embodiment uses the VMD method described in Embodiment 6, except that the running time is changed from 1 hour to membrane cleaning after every 6 hours of continuous operation.

[0104] Figure 12 The results show the changes in membrane flux and salt rejection rate over time after cleaning the silicon carbide-based Janus membrane using the cleaning process described in Example 6 during a long-term desalination test in vacuum membrane distillation. It can be seen that after each membrane cleaning cycle, the membrane flux recovers to over 90% of its initial flux, while the salt rejection rate remains at approximately 99%, indicating that no pore wetting occurred throughout the operation. These experimental results demonstrate that the silicon carbide-based Janus membrane with its layered structure can improve the desalination performance and anti-wetting properties during vacuum membrane distillation, and that the vacuum membrane distillation process requires only a simple pure water cleaning process after each run.

[0105] In summary, this invention successfully prepared a silicon carbide-based ceramic membrane with controllable pore size using an oxidation sintering method, and a superhydrophobic / hydrophilic composite Janus ceramic membrane using a graft polymerization method. Furthermore, it was successfully applied to desalination experiments using a vacuum membrane distillation (VMD) method. This method not only yielded a superhydrophobic silicon carbide-based ceramic membrane but also exhibited excellent acid and alkali resistance, abrasion resistance, thermal stability, and scale prevention properties. Simultaneously, it achieved high flux in membrane distillation applications while maintaining a high rejection rate. Furthermore, a simple cleaning method was used, enabling the membrane flux to maintain a 90% recovery rate in long-term VMD cycling experiments. This demonstrates that the superhydrophobic / hydrophilic composite Janus ceramic membrane prepared by this method has promising prospects for efficient and environmentally friendly seawater desalination applications.

[0106] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a silicon carbide-based Janus film, characterized in that, The steps include the following: a) Prepare a silicon carbide separation layer slurry; coat the silicon carbide separation layer slurry onto one side of a silicon carbide support to obtain a single-sided coated silicon carbide preform; subject the single-sided coated silicon carbide preform to air sintering to obtain a silicon carbide-based ceramic film bonded with silicon dioxide. b) Then, the silica-bonded silicon carbide-based ceramic film obtained in step a) is subjected to single-sided hydrophobic modification by graft polymerization to obtain a silicon carbide-based Janus film. The silicon carbide separation layer slurry prepared in step a) is prepared by ball milling. The steps are as follows: silicon carbide powder, binder, dispersant and RO water are mixed in a mass ratio of 5~15:0.05~0.15:1~2:80~90 and then ground. The silicon carbide powder in step a) has a particle size of 4~6μm; the ball milling time is 2.5~3 hours; The silicon carbide separation layer slurry prepared in step a) contains two particle sizes: small particles (59-68 nm) and large particles (342-955 nm). The particle size and the content of large and small particles are determined by the ball milling time. The solid content of the slurry in step a) is 5-15 wt%. The coating in step a) is as follows: using ultrasonic spraying to deposit silicon carbide separation layer slurry on one side of the silicon carbide support; The purpose of air sintering in step a) is to bond the deposited particles to the silicon carbide support, thereby obtaining a silicon carbide-based ceramic film bonded with silicon dioxide; the air sintering adopts the following process: ① First, in an air atmosphere, heat the temperature from room temperature to 300℃ at a heating rate of 5℃ / minute, and then keep it at 300℃ for 15-25 minutes; ②Then, in an air atmosphere, the temperature is increased from 300℃ to 600℃ at a rate of 5℃ / minute, and then held at 600℃ for 15 to 25 minutes; ③Then, in an air atmosphere, the temperature is increased from 600℃ to 800℃ at a rate of 5℃ / minute, and then held at 800℃ for 15 to 25 minutes; ④Then, in an air atmosphere, the temperature is increased from 800℃ to 1200-1300℃ at a heating rate of 5℃ / minute; ⑤ Then sinter at 1100-1300℃ in air for 2 hours; ⑥ Finally, allow it to cool naturally to room temperature in the air. Step b) includes the following specific operations: b1) Prepare a 1H,1H,2H,2H-perfluorooctyltrichlorosilane solution and stir until homogeneous; b2) Spray the 1H,1H,2H,2H-perfluorooctyltrichlorosilane solution prepared in step b1) onto the separation layer side and dry it to obtain a silicon carbide-based Janus membrane. In step b1), the mass fraction of the 1H,1H,2H,2H-perfluorooctyltrichlorosilane solution is 0.4~1.6 vol%; the stirring time is 15~25 min. The drying temperature in step b2) is 100~200℃, and the time is 0.5~1.5 hours; The principle of the graft polymerization method involved in this step is as follows: 1H,1H,2H,2H-perfluorooctyltrichlorosilane is hydrolyzed in a solvent to generate silanol, which undergoes a condensation reaction with the silicon carbide separation layer bonded to silicon dioxide rich in hydroxyl groups to form Si-O-Si covalent bonds. At the same time, the silanol molecules undergo transverse cross-linking to form a dense and ordered perfluoroalkyl monolayer. The silicon carbide-based Janus membrane uses a silicon carbide support as the substrate and is coated with a superhydrophobic modified silicon carbide separation layer on one side; the pore size of the silicon carbide-based Janus membrane is 100 nm to 1000 nm; the pure water flux is 1418.82 to 3523.3 kg / (m³). 2 ·h); The membrane separation layer side has a high hydrophobic angle; the side of the support without the separation layer coating maintains excellent hydrophilicity, and water droplets can be completely immersed in a short time; the silicon carbide-based Janus membrane has outstanding acid and alkali resistance, abrasion resistance and thermal stability. The pore size of the separation layer was controlled, and a superhydrophobic / hydrophilic asymmetric Janus structure was introduced. While maintaining the rejection rate, the silicon carbide-based Janus membrane exhibited high membrane flux, and the membrane flux could be restored after simple cleaning, thus extending the service life of the filter membrane. The silicon carbide-based Janus membrane also has excellent anti-fouling properties.

2. The method for preparing a silicon carbide-based Janus film according to claim 1, characterized in that, The binder in step a) is selected from any one of hydroxypropyl methylcellulose, methylcellulose, or sodium hexametaphosphate; the dispersant is selected from any one of polyethylene glycol, polyvinyl alcohol, or polyacrylic acid.

3. The method for preparing a silicon carbide-based Janus film according to claim 1, characterized in that, The solvent for the 1H,1H,2H,2H-perfluorooctyltrichlorosilane solution in step b1) is any one of n-hexane, cyclohexane, hexadecane, or anhydrous ethanol.

4. An application of a silicon carbide-based Janus film obtained by the preparation method according to any one of claims 1 to 3, characterized in that, The silicon carbide-based Janus membrane is used to prepare membrane modules to achieve membrane distillation of seawater, converting seawater into desalinated water.

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