Preparation method of silicon carbide film with cobweb structure

Abstract

The invention discloses a preparation method of a silicon carbide film with a cobweb structure. The method comprises the following steps: firstly preparing polycarbosilane solutions with different concentrations, then soaking a prepared silicon carbide membrane tube in the solution, and forming silicon carbide with a cobweb structure in membrane pores under the action of high-temperature calcination, thereby achieving the effect of reducing the pore diameter of the silicon carbide membrane. According to the structure, the rejection rate of the silicon carbide film is improved under the condition that the flux is not sacrificed, and a new thought is provided for preparing the silicon carbide film layer.

Description

Technical Field

[0001] This invention belongs to the field of porous ceramic membrane material preparation technology, and relates to a method for preparing a spider web structure silicon carbide membrane. Background Technology

[0002] Silicon carbide membranes are non-oxide ceramic materials with stronger hydrophilicity and antifouling capabilities. They maintain good stability under harsh conditions such as high temperature, corrosion, and organic solvents, and have become one of the fastest-growing new membrane materials in recent years, attracting increasing attention from academia and industry. Compared with polymers (such as PVDF) and inorganic materials (such as Al2O3 and ZrO2), silicon carbide membranes have higher hydrophilicity and higher efficiency in oil-water emulsion separation.

[0003] To further improve the retention accuracy of silicon carbide membranes, a common method is to construct a silicon carbide membrane layer with smaller particle sizes on its surface, thus shrinking its pore size. For example, Chinese invention patent CN102633531B reports a gradient-pore pure silicon carbide membrane tube and its preparation method, which forms a membrane layer by stacking fine silicon carbide particles, resulting in a silicon carbide membrane layer with a pore size of 0.1–20 μm. Chinese invention patent CN118255592A reports a two-step co-firing method for preparing a silicon carbide ceramic support and membrane layer, producing a microfiltration membrane with a pore size of approximately 220 nm and a thickness of 21 µm, achieving a retention rate of 94.3% for oil-in-water emulsions, but its pure water permeability is only 1920 L·m⁻¹. -2 ·h -1 ·bar -1 It is evident that while preparing membranes with smaller pore sizes improves retention accuracy, it inevitably reduces flux, resulting in a trade-off effect.

[0004] To address the trade-off effect between flux and rejection rate, Chinese invention patent CN114432898B proposed composite carbon nanotube membranes onto porous polylactic acid membranes. This increased the surface area and significantly improved the water flux of the composite membrane, while maintaining a good rejection rate for water-in-oil emulsions. However, this method essentially improves water flux by increasing the filtration area, resulting in a decrease in flux per unit area. Therefore, it does not truly overcome the trade-off effect between flux and rejection rate.

[0005] This invention utilizes the transformation of polycarbosilane into spider web-structured β-silicon carbide at high temperature to construct silicon carbide fibers in the pores of the silicon carbide membrane, achieving the effect of "pore shrinkage" and thus increasing the retention rate of the silicon carbide membrane without reducing the flux. Summary of the Invention

[0006] This invention utilizes the conversion of polycarbosilane into β-silicon carbide with a spider web structure at high temperature, achieving both high throughput and high oil rejection rate.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a spider web-structured silicon carbide film, characterized by the following specific steps: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then graded and sieved through a standard sieve to obtain fine powder with uniform particle size distribution. Next, different masses of polycarbosilane powder are accurately weighed and dissolved in a certain amount of n-hexane solvent (100 g per portion) in sequence. The powder is then fully dissolved by magnetic stirring to finally prepare a series of polycarbosilane solutions of different concentrations. (2) Select tubular silicon carbide membranes with different pore sizes as substrate materials, and immerse them in polycarbosilane solutions of various concentrations prepared in step (1). Then, transfer the entire immersion system to a vacuum container, start the vacuum pump to remove the gas from the membrane pores and the surrounding environment, so that the solution can fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure; (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1200~1400 °C under an inert atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0008] The preferred step (1) is to weigh 10-30 g of polycarbosilane.

[0009] The tubular silicon carbide used in step (2) has an average pore size of 0.8 to 3 μm.

[0010] In step (3), the oven temperature is preferably 40-80 °C and the drying time is preferably 8-24 h.

[0011] In the preferred step (4), the heating rate is controlled at 1~2 °C / min, and the sintering atmosphere is argon or nitrogen.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention constructs a spider web structure in silicon carbide within the pores of the silicon carbide film, thereby improving the retention rate of the silicon carbide film.

[0013] 2. The present invention constructs a spider web structure in silicon carbide within the pore size of the silicon carbide membrane, which avoids the increase of filtration resistance and maintains a high flux while improving the rejection rate. Attached Figure Description

[0014] Figure 1 The image shows an electron microscope image of the silicon carbide film prepared in Example 2.

[0015] Figure 2 The pure water flux and oil rejection rate of the silicon carbide membranes prepared in Examples 1-4 are shown. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0017] Example 1 A method for preparing a spider web-structured silicon carbide film, the specific steps of which are as follows: (1) Weigh out 100 g of n-hexane; (2) Select a tubular silicon carbide membrane with an average pore size of 1 μm as the substrate material and immerse it in the solution prepared in step (1). Then, transfer the entire immersion system to a vacuum container, start the vacuum pump to remove the gas from the membrane pores and the surrounding environment, so that the solution can fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure; (3) After the solution has fully soaked the silicon carbide film sample, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1400 °C under the protection of argon atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0018] The prepared tubular silicon carbide membrane has a pure water permeability of approximately 6510 L·m⁻¹. -2 ·h -1 ·bar -1 Under conditions of a transmembrane pressure difference of 1 bar and a membrane surface flow rate of 1 m / s, the rejection rate of a 500 ppm oil-in-water emulsion reached 92.3%, and the oil content in the filtered permeate was 38.5 ppm.

[0019] Example 2 A method for preparing a spider web-structured silicon carbide film, the specific steps of which are as follows: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then sieved through a standard sieve to obtain fine powder with uniform particle size distribution. Next, 10 g of polycarbosilane powder is dissolved in a certain amount of n-hexane solvent (100 g), and magnetic stirring is used to fully dissolve it, finally preparing a polycarbosilane solution of a certain concentration; (2) A tubular silicon carbide membrane with an average pore size of 1 μm was selected as the substrate material and immersed in the polycarbosilane solution prepared in step (1). Subsequently, the entire immersion system was transferred to a vacuum container, and a vacuum pump was started to remove the gas from the membrane pores and the surrounding environment, so that the solution could fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure. (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1400 °C under the protection of argon atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0020] The prepared tubular silicon carbide film electron microscope, such as Figure 1 As shown, there is a clear spiderweb-like structure connecting the silicon carbide particles, and the pure water permeability is approximately 6372 L·m. -2 ·h -1 ·bar -1 Under conditions of a transmembrane pressure difference of 1 bar and a membrane surface flow rate of 1 m / s, the rejection rate of a 500 ppm oil-in-water emulsion reached 97.3%, and the oil content in the filtered permeate was only 13.5 ppm.

[0021] Example 3 A method for preparing a spider web-structured silicon carbide film, the specific steps of which are as follows: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then graded and sieved through a standard sieve to obtain fine powder with uniform particle size distribution. Next, 20 g of polycarbosilane powder is accurately dissolved in a certain amount of n-hexane solvent (100 g), and magnetic stirring is used to fully dissolve it, and finally a polycarbosilane solution of a certain concentration is prepared. (2) A tubular silicon carbide membrane with an average pore size of 1 μm was selected as the substrate material and immersed in the polycarbosilane solution prepared in step (1). Subsequently, the entire immersion system was transferred to a vacuum container, and a vacuum pump was started to remove the gas from the membrane pores and the surrounding environment, so that the solution could fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure. (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1400 °C under the protection of argon atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0022] The prepared tubular silicon carbide membrane has a pure water permeability of approximately 6219 L·m⁻¹. -2 ·h -1 ·bar -1 Under conditions of a transmembrane pressure difference of 1 bar and a membrane surface flow rate of 1 m / s, the rejection rate of a 500 ppm oil-in-water emulsion reached 98.6%, and the oil content in the filtered permeate was only 7.0 ppm.

[0023] Example 4 A method for preparing a spider web-structured silicon carbide film, the specific steps of which are as follows: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then graded and sieved through a standard sieve to obtain fine powder with uniform particle size distribution. Next, 30 g of polycarbosilane powder is accurately dissolved in a certain amount of n-hexane solvent (100 g), and magnetic stirring is used to fully dissolve it, finally preparing a polycarbosilane solution of a certain concentration; (2) A tubular silicon carbide membrane with an average pore size of 1 μm was selected as the substrate material and immersed in the polycarbosilane solution prepared in step (1). Subsequently, the entire immersion system was transferred to a vacuum container, and a vacuum pump was started to remove the gas from the membrane pores and the surrounding environment, so that the solution could fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure. (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1400 °C under the protection of argon atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0024] The prepared tubular silicon carbide membrane has a pure water permeability of approximately 6283 L·m⁻¹. -2 ·h -1 ·bar -1Under conditions of a transmembrane pressure difference of 1 bar and a membrane surface flow rate of 1 m / s, the rejection rate of a 500 ppm oil-in-water emulsion reached 99.2%, and the oil content in the filtered permeate was only 4.0 ppm.

[0025] Example 5 A method for preparing a spider web-structured silicon carbide film, the specific steps of which are as follows: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then sieved through a standard sieve to obtain fine powder with uniform particle size distribution. Next, 10 g of polycarbosilane powder is dissolved in a certain amount of n-hexane solvent (100 g), and magnetic stirring is used to fully dissolve it, finally preparing a polycarbosilane solution of a certain concentration; (2) A tubular silicon carbide membrane with an average pore size of 0.8 μm was selected as the substrate material and immersed in the polycarbosilane solution prepared in step (1). Subsequently, the entire immersion system was transferred to a vacuum container, and a vacuum pump was started to remove the gas from the membrane pores and the surrounding environment, so that the solution could fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure. (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1300 °C under a nitrogen atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0026] The prepared tubular silicon carbide membrane has a pure water permeability of approximately 6063 L·m⁻¹. -2 ·h -1 ·bar -1 Under conditions of a transmembrane pressure difference of 1 bar and a membrane surface flow rate of 1 m / s, the rejection rate of a 500 ppm oil-in-water emulsion reached 96.2%, and the oil content in the filtered permeate was only 19.0 ppm.

[0027] Example 6 A method for preparing a spider web-structured silicon carbide film, the specific steps of which are as follows: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then graded and sieved through a standard sieve to obtain fine powder with uniform particle size distribution. Next, 20 g of polycarbosilane powder is accurately dissolved in a certain amount of n-hexane solvent (100 g), and magnetic stirring is used to fully dissolve it, and finally a polycarbosilane solution of a certain concentration is prepared. (2) A tubular silicon carbide membrane with an average pore size of 3 μm was selected as the substrate material and immersed in the polycarbosilane solution prepared in step (1). Subsequently, the entire immersion system was transferred to a vacuum container, and a vacuum pump was started to remove the gas from the membrane pores and the surrounding environment, so that the solution could fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure. (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1200 °C under a nitrogen atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

[0028] The prepared tubular silicon carbide membrane has a pure water permeability of approximately 8620 L·m⁻¹. -2 ·h -1 ·bar -1 Under conditions of a transmembrane pressure difference of 1 bar and a membrane surface flow rate of 1 m / s, the rejection rate of a 500 ppm oil-in-water emulsion reached 91.6%, and the oil content in the filtered permeate was only 42.0 ppm.

Claims

1. A method for preparing a spiderweb-structured silicon carbide film, characterized in that, The specific steps are as follows: (1) First, the polycarbosilane raw material is mechanically ground and pulverized, and then graded and sieved through a standard sieve to obtain fine powder with uniform particle size distribution; then, different masses of polycarbosilane powder are accurately weighed and dissolved in a certain amount of n-hexane solvent (100 g per portion) in sequence, and the powder is fully dissolved by magnetic stirring to finally prepare a series of polycarbosilane solutions of different concentrations. (2) Select tubular silicon carbide membranes with different pore sizes as substrate materials and immerse them in polycarbosilane solutions of various concentrations prepared in step (1); then, transfer the entire immersion system to a vacuum container, start the vacuum pump to remove the gas in the membrane pores and the surrounding environment, so that the solution can fully penetrate and fill the micro-pore structure of the silicon carbide membrane under negative pressure. (3) After the solution has fully soaked the silicon carbide film sample loaded with polycarbosilane solution, take it out and place it in an oven to dry until it is completely dry; (4) Place the thoroughly dried silicon carbide film sample from step (3) into a high-temperature muffle furnace and heat it to the target temperature of 1200~1400 °C under an inert atmosphere. Maintain the temperature within this range for 2 hours. After the sintering process is completed, control the sample to cool slowly to room temperature with the furnace.

2. The method for preparing a spiderweb-structured silicon carbide film according to claim 1, characterized in that, In step (1), the mass of polycarbosilane weighed is 10~30 g.

3. The method for preparing a spiderweb-structured silicon carbide film according to claim 1, characterized in that, The average pore size of the tubular silicon carbide used in step (2) is 0.8~3 μm.

4. The method for preparing a spiderweb-structured silicon carbide film according to claim 1, characterized in that, In step (3), the oven temperature is 40~80 °C and the drying time is 8~24 h.

5. The method for preparing a spiderweb-structured silicon carbide film according to claim 1, characterized in that, Step (4) The heating rate is controlled at 1~2 °C / min, and the sintering atmosphere is argon or nitrogen.

Images