A method for preparing a superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane

Abstract

This invention discloses a method for preparing a superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane, comprising the following steps: a) adding at least two types of hydrophilic silica nanoparticles of different particle sizes to water to obtain a suspension with a silica nanoparticle content of 1-3 wt%; b) immersing an unoxidized silicon carbide ceramic membrane in the suspension for modification, removing it, drying it at 55-65°C for 10-12 hours, and then placing it in a muffle furnace for calcination at 590-610°C for 25-35 minutes. The preparation method of this invention is not only simple and easy to scale up, but also produces silicon carbide ceramic membranes with excellent comprehensive properties, including small pore size, good durability, high oil-water separation efficiency, good abrasion resistance, and good corrosion resistance. It can be used for oil-water separation caused by oil spills and industrial oily wastewater discharge in fields such as food, textiles, metal processing, pharmaceutical manufacturing, and the oil and gas industry.

Description

Technical Field

[0001] This invention relates to a method for preparing a superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane, belonging to the field of silicon carbide ceramic membrane preparation technology. Background Technology

[0002] With the continuous development of industry, oil spills and the discharge of oily substances into industrial wastewater have led to serious environmental pollution. Against this backdrop, the effective recycling of water faces significant challenges. Emulsified oil / water mixtures are key to treatment. As relatively stable colloidal dispersions, their small droplet size increases the challenge of separation. Traditional methods for separating emulsified oil / water mixtures employ chemical treatment, solvent extraction, microwave radiation, oxidation, and other methods for demulsification followed by further separation. These methods consume significant energy, leading to increased separation costs; the separation equipment is complex, requiring substantial installation space; the use of toxic compounds during the separation process poses potential risks; and for crude oil, gasoline, and diesel, the separation efficiency is low, making effective recovery difficult and potentially causing secondary pollution. To overcome these problems, innovative solutions are needed to improve the efficiency and environmental friendliness of oil-water mixture separation.

[0003] In recent years, ultrafiltration and microfiltration membrane separation technologies have become highly efficient and effective methods for treating oil-water emulsions of varying concentrations. Compared with traditional methods, membrane separation technology offers advantages such as low cost, high emulsification efficiency, strong selectivity, environmental friendliness, and ease of operation, and has been widely applied in industrial and other fields. While organic membrane separation technology has been widely used in research and commercial fields for treating industrial oily wastewater, organic membranes are limited by material properties, resulting in disadvantages such as low flux, short lifespan, susceptibility to fouling, aging, damage, difficulty in backwashing, and high pretreatment requirements. In contrast, inorganic ceramic membranes possess numerous advantages over organic membranes, such as excellent chemical stability, high temperature resistance, fouling resistance, pressure resistance, good mechanical stability, and long service life, making them a current hot topic in membrane material development.

[0004] Silicon carbide ceramic membranes are a type of inorganic ceramic membrane with good hydrophilic-oversea oleophobic properties and are currently widely used in oil-water separation. Industrially, post-oxidized silicon carbide ceramic membranes are mainly used for oil-water separation. These membranes are created by calcining unoxidized silicon carbide ceramic membranes at high temperatures to form a thin SiO2 layer on their surface, achieving superhydrophilic-oversea superoleophobic properties and thus achieving oil-water separation. However, post-oxidized silicon carbide ceramic membranes have relatively large pore sizes, which not only leads to poor separation of emulsified oil / water mixtures but also makes the pores prone to oil clogging, resulting in poor durability, difficult cleaning, and easy scaling, hindering continuous and effective oil-water separation. Furthermore, the SiO2 layer on the surface of post-oxidized silicon carbide ceramic membranes is susceptible to wear and damage, exhibiting poor abrasion resistance, which reduces its superhydrophilic-oversea superoleophobic properties and thus affects oil-water separation efficiency. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the purpose of this invention is to provide a method for preparing a superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane with small pore size, good durability, high oil-water separation efficiency, and good abrasion resistance.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a superhydrophilic-underwater superoleophobic silicon carbide ceramic film includes the following steps:

[0008] a) Add at least two kinds of hydrophilic silica nanoparticles with different particle sizes to water and mix them evenly to obtain a suspension with a silica nanoparticle content of 1 to 3 wt%.

[0009] b) The unoxidized silicon carbide ceramic film is immersed in the suspension obtained in step a) for modification, taken out, dried at 55-65°C for 10-12 hours, and then placed in a muffle furnace and calcined at 590-610°C for 25-35 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0010] In one embodiment, the suspension in step a) includes at least one small-diameter silica nanoparticle with a particle size of 10-50 nm and at least one large-diameter silica nanoparticle with a particle size of 100-300 nm.

[0011] In a preferred embodiment, the small-diameter silica nanoparticles include at least one of 12nm silica nanoparticles and 20-50nm silica nanoparticles; the large-diameter silica nanoparticles include at least one of 100nm silica nanoparticles and 300nm silica nanoparticles.

[0012] In a preferred embodiment, the mass ratio between the small-diameter silica nanoparticles and the large-diameter silica nanoparticles is 1:(1-3).

[0013] In a preferred embodiment, when the small-diameter silica nanoparticles include 12nm silica nanoparticles and 20-50nm silica nanoparticles, the mass ratio between the small-diameter silica nanoparticles is 1:1; when the large-diameter silica nanoparticles include 100nm silica nanoparticles and 300nm silica nanoparticles, the mass ratio between the large-diameter silica nanoparticles is 1:1.

[0014] In a preferred embodiment, in step a), the mass ratio of 12nm silica nanoparticles or 20-50nm silica nanoparticles to 100nm silica nanoparticles or 300nm silica nanoparticles is 1:3; the mass ratio of 12nm silica nanoparticles to 20-50nm silica nanoparticles to 100nm silica nanoparticles or 300nm silica nanoparticles is 1:1:2.

[0015] In one embodiment, the content of silica nanoparticles in the suspension described in step a) is 2 wt%.

[0016] In one embodiment, in step b), the unoxidized silicon carbide ceramic film is washed sequentially with ethanol and water, dried at 55-65°C for 10-12 hours, and then immersed in the suspension obtained in step a) for modification.

[0017] In one embodiment, in step b), the unoxidized silicon carbide ceramic membrane is immersed in the suspension obtained in step a) and ultrasonically treated for 15 to 25 minutes.

[0018] In a preferred embodiment, in step b), the ultrasonic frequency is 30–50 kHz.

[0019] In one embodiment, in step b), during calcination, the temperature is increased to 600°C at a rate of 4°C / minute, and calcined at 600°C for 25–35 minutes.

[0020] In a preferred embodiment, step b) is performed as follows: the unoxidized silicon carbide ceramic film is washed sequentially with ethanol and water, dried at 55-65°C for 10-12 hours, then immersed in the suspension obtained in step a), ultrasonically treated for 15-25 minutes, removed, dried at 55-65°C for 10-12 hours, then placed in a calcination apparatus, heated to 600°C at a heating rate of 4°C / min, and calcined at 600°C for 25-35 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0021] Compared with the prior art, the present invention has the following significant advantages:

[0022] This invention uses a suspension containing 1-3 wt% of at least two different types of hydrophilic silica nanoparticles to inorganically modify unoxidized silicon carbide ceramic membranes. The superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane is obtained by low-temperature calcination at 590-610℃. This method is not only simple, mild, and uses readily available and inexpensive raw materials, making it easy to scale up production, but also produces silicon carbide ceramic membranes with excellent superhydrophilic and underwater superoleophobic properties, small pore size, good durability, high oil-water separation efficiency, good abrasion resistance, and good corrosion resistance. It can be used in the food, textile, metal processing, pharmaceutical manufacturing, and oil and gas industries for oil spills and for oily wastewater discharge from industries requiring oil-water separation (especially for emulsified oil / water mixtures), showing great application potential. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope (SEM) image of the superhydrophilic-underwater superoleophobic silicon carbide ceramic film prepared in Example 1 of the present invention.

[0024] Figure 2 The figures show the oil removal rates of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membranes prepared in Examples 1-6 and the comparative silicon carbide ceramic membranes prepared in Comparative Examples 1-5 for different emulsified oil / water mixtures.

[0025] Figure 3 The permeation flux test diagrams for the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in Example 1 of the present invention and the comparative silicon carbide ceramic membrane prepared in Comparative Example 1 for emulsified oil / water mixtures are shown.

[0026] Figure 4 The permeation flux test diagrams for the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in Example 1 of the present invention and the comparative silicon carbide ceramic membrane prepared in Comparative Example 3 for emulsified oil / water mixtures are shown.

[0027] Figure 5 The graphs show the permeation flux test results of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in Example 1 of this invention and the comparative silicon carbide ceramic membrane prepared in Comparative Example 5 for emulsified oil / water mixtures. Detailed Implementation

[0028] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments.

[0029] Example 1

[0030] a) Add 12nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0031] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the superhydrophilic-underwater superoleophobic silicon carbide ceramic film prepared in this embodiment; (The image is from...) Figure 1 As can be seen, the pores of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment are filled by 12nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles, resulting in a reduction in pore size.

[0033] The superhydrophilic-underwater superoleophobic silicon carbide ceramic film prepared in this embodiment was tested. Specifically, the dynamic water contact angle and underwater oleophobic angle of the superhydrophilic-underwater superoleophobic silicon carbide ceramic film prepared in this embodiment were tested using a contact angle meter. The test results are shown in Table 1 and Table 2, respectively.

[0034] The corrosion resistance of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment was tested. Specifically, the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane was immersed in an acid solution with pH=1 for 2 hours and then a hydrophilicity test was performed. The test results are shown in Table 3. The measured data were compared with the initial immersion time and dynamic water contact angle data in Table 1 to evaluate the corrosion resistance.

[0035] The abrasion resistance of the superhydrophilic-underwater superoleophobic silicon carbide ceramic film prepared in this embodiment was tested. Specifically, the superhydrophilic-underwater superoleophobic silicon carbide ceramic film was polished back and forth with sandpaper 30 times and then the underwater superoleophobic performance was tested. The test results are shown in Table 4. The measured data were compared with the initial underwater superoleophobicity in Table 2 to evaluate the abrasion resistance.

[0036] The pore size of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment was tested. Specifically, the retention rate of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment for fluorescent microspheres of different sizes was tested, and the test results are shown in Table 5.

[0037] The oil-water separation efficiency of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment was tested, specifically as follows:

[0038] First, 0.5 mg of surfactant SDS was added to 450 mL of water with magnetic stirring to obtain a surfactant aqueous solution. Then, 50 mL each of edible oil, olive oil, and hexadecane were mixed with the surfactant aqueous solution obtained above and ultrasonically treated to obtain an emulsified oil / water mixture.

[0039] The superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment is placed as a filter membrane in the filter of a vacuum filtration device. A general-purpose vacuum filtration device can be used. The emulsified oil / water mixture is poured into the filter above the vacuum filtration device and filtered. After filtration, the emulsified oil / water mixture flows into a filter flask below the vacuum filtration device. The filtrate in the filter flask is taken out, and the turbidity of the filtrate is tested using a turbidity meter. The oil removal rate is calculated based on the measured turbidity. The oil removal rate result is as follows: Figure 2 As shown, the oil-water separation efficiency of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane is evaluated by the oil removal rate.

[0040] The permeation flux of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment was tested. The permeation flux of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane to the emulsified oil / water mixture was tested at different cycles. The test results are as follows: Figure 3 , 4 As shown in Figure 5.

[0041] Example 2

[0042] a) Add 20nm-50nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0043] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0044] The test results of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment, including its superhydrophilic-underwater superoleophobic properties, corrosion resistance, abrasion resistance, pore size, and oil-water separation efficiency, are shown in Tables 1, 2, 3, 4, and 5, respectively. Figure 2 As shown.

[0045] Example 3

[0046] a) Add 12nm hydrophilic silica nanoparticles, 20nm-50nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles to water at a mass ratio of 1:1:2, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0047] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0048] The test results of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment, including its superhydrophilic-underwater superoleophobic properties, corrosion resistance, abrasion resistance, pore size, and oil-water separation efficiency, are shown in Tables 1, 2, 3, 4, and 5, respectively. Figure 2 As shown.

[0049] Example 4

[0050] a) Add 12nm hydrophilic silica nanoparticles and 100nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0051] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0052] The test results of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment, including its superhydrophilic-underwater superoleophobic properties, corrosion resistance, abrasion resistance, pore size, and oil-water separation efficiency, are shown in Tables 1, 2, 3, 4, and 5, respectively. Figure 2 As shown.

[0053] Example 5

[0054] a) Add 20nm-50nm hydrophilic silica nanoparticles and 100nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0055] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0056] The test results of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment, including its superhydrophilic-underwater superoleophobic properties, corrosion resistance, abrasion resistance, pore size, and oil-water separation efficiency, are shown in Tables 1, 2, 3, 4, and 5, respectively. Figure 2 As shown.

[0057] Example 6

[0058] a) Add 12nm hydrophilic silica nanoparticles, 20nm-50nm hydrophilic silica nanoparticles and 100nm hydrophilic silica nanoparticles to water at a mass ratio of 1:1:2, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0059] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

[0060] The test results of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membrane prepared in this embodiment, including its superhydrophilic-underwater superoleophobic properties, corrosion resistance, abrasion resistance, pore size, and oil-water separation efficiency, are shown in Tables 1, 2, 3, 4, and 5, respectively. Figure 2 As shown.

[0061] Comparative Example 1

[0062] Unoxidized silicon carbide ceramic film was placed in a muffle furnace and heated to 900°C at a heating rate of 5°C / min, and calcined at 900°C for 30 minutes to obtain a comparative silicon carbide ceramic film.

[0063] The test results of the superhydrophilic-underwater superoleophobic properties, corrosion resistance, abrasion resistance, pore size, oil-water separation efficiency, and permeation flux of the comparative silicon carbide ceramic membrane prepared in this example are shown in Tables 1 and 2, 3, 4, and 5, respectively. Figure 2 , Figure 3 As shown.

[0064] Comparative Example 2

[0065] a) Add 12nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 2wt%.

[0066] b) The unoxidized silicon carbide ceramic film was washed sequentially with ethanol and water, dried at 60°C for 11 hours, then immersed in the suspension obtained in step a), and ultrasonically treated for 20 minutes at a frequency of 40 kHz. After removal, it was dried at 60°C for 11 hours, then placed in a muffle furnace and heated to 550°C at a heating rate of 3.7°C / min, and calcined at 550°C for 30 minutes to obtain the comparative silicon carbide ceramic film.

[0067] The test results of the superhydrophilic-underwater superoleophobic properties and oil-water separation efficiency of the comparative silicon carbide ceramic membrane prepared in this example are shown in Tables 1 and 2, respectively. Figure 2 As shown.

[0068] Comparative Example 3

[0069] a) Add 100nm hydrophilic silica nanoparticles to water and stir for 2 hours to mix them evenly, to obtain a suspension with a silica nanoparticle content of 2wt%.

[0070] b) The unoxidized silicon carbide ceramic film was washed with ethanol and water in sequence, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After being removed, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain the comparative silicon carbide ceramic film.

[0071] The test results of the superhydrophilic-underwater superoleophobic properties, oil-water separation efficiency, and permeation flux of the comparative silicon carbide ceramic membrane prepared in this example are shown in Tables 1 and 2, respectively. Figure 2 , Figure 4 As shown.

[0072] Comparative Example 4

[0073] a) Add 12nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 0.5wt%.

[0074] b) The unoxidized silicon carbide ceramic film was washed with ethanol and water in sequence, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After being removed, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain the comparative silicon carbide ceramic film.

[0075] The test results of the superhydrophilic-underwater superoleophobic properties and oil-water separation efficiency of the comparative silicon carbide ceramic membrane prepared in this example are shown in Tables 1 and 2, respectively. Figure 2 As shown.

[0076] Comparative Example 5

[0077] a) Add 12nm hydrophilic silica nanoparticles and 300nm hydrophilic silica nanoparticles to water at a mass ratio of 1:3, stir for 2 hours to mix evenly, and obtain a suspension with a silica nanoparticle content of 5wt%.

[0078] b) The unoxidized silicon carbide ceramic film was washed with ethanol and water in sequence, dried at 60°C for 11 hours, and then immersed in the suspension obtained in step a). It was ultrasonically treated for 20 minutes at a frequency of 40 kHz. After being removed, it was dried at 60°C for 11 hours and then placed in a muffle furnace. The temperature was increased to 600°C at a rate of 4°C / min and calcined at 600°C for 30 minutes to obtain the comparative silicon carbide ceramic film.

[0079] The test results of the superhydrophilic-underwater superoleophobic properties, oil-water separation efficiency, and permeation flux of the comparative silicon carbide ceramic membrane prepared in this example are shown in Tables 1 and 2, respectively. Figure 2 , Figure 5 As shown.

[0080] Table 1. Hydrophilicity data of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membranes prepared in Examples 1-6 and the comparative silicon carbide ceramic membranes prepared in Comparative Examples 1-5.

[0081]

[0082] In Table 1, immersion time refers to the time required for water droplets to completely immerse the tested silicon carbide ceramic membrane during the test. Generally, the shorter the immersion time, the better the hydrophilicity of the tested silicon carbide ceramic membrane, the higher the permeation flux, and the faster the separation speed during oil-water separation.

[0083] As can be seen from Table 1, although the silicon carbide ceramic membranes of Examples 1-6 and Comparative Examples 1-5 of the present invention all have superhydrophilicity, the immersion time of Comparative Examples 2, 4 and 5 is longer than that of Examples 1-6.

[0084] Table 2 shows the underwater superoleophobic silicon carbide ceramic films prepared in Examples 1-6 and the comparative silicon carbide ceramic films prepared in Comparative Examples 1-5.

[0085] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Underwater oleophobic angle 165.4° 162.7° 165.1° 163.3° 162.9° 164.5° Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Underwater oleophobic angle 161.6° 145.9° 159.4° 117.4° 161.1°

[0086] As can be seen from Table 2, the silicon carbide ceramic films of Examples 1-6 of the present invention have excellent oleophobicity; the oleophobicity of Comparative Examples 1 and 5 is similar to that of Examples 1-6, the oleophobicity of Comparative Examples 2 and 4 is poor, and the oleophobicity of Comparative Example 3 is slightly poor.

[0087] Table 3 shows the hydrophilicity data of the superhydrophilic-underwater superoleophobic silicon carbide ceramic membranes prepared in Examples 1-6 and the comparative silicon carbide ceramic membrane prepared in Comparative Example 1 after immersion in an acidic solution at pH=1 for 2 hours.

[0088] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Immersion time 0.35s-0.6s 0.4s-0.6s 0.4s-0.6s 0.4s-0.6s 0.4s-0.6s 0.6s-0.8s 0.3s-0.5s Dynamic water contact angle 0° 0° 0° 0° 0° 0° 0°

[0089] As can be seen from Tables 1 and 3, after the silicon carbide ceramic membranes of Examples 1-6 of the present invention are immersed in an acidic solution with pH=1 for 2 hours, the immersion time changes very little, and the dynamic water contact angle is 0°, indicating that they are still superhydrophilic. This shows that the silicon carbide ceramic membranes of Examples 1-6 of the present invention have excellent corrosion resistance.

[0090] Table 4 shows the underwater superoleophobicity data of the superhydrophilic-underwater superoleophobic silicon carbide ceramic films prepared in Examples 1-6 and the silicon carbide ceramic film prepared in Comparative Example 1 after being polished back and forth with sandpaper 30 times.

[0091] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Underwater oleophobic angle 163.9° 161.7° 163.3° 161.4° 161.2° 163.5° 137.4°

[0092] As can be seen from Tables 2 and 4, the silicon carbide ceramic films of Examples 1-6 of the present invention showed very little change in underwater superoleophobicity after being polished back and forth with sandpaper 30 times, indicating that the silicon carbide ceramic films of Examples 1-6 of the present invention have excellent abrasion resistance. In contrast, the silicon carbide ceramic film of Comparative Example 1 showed a significant decrease in underwater superoleophobicity after being polished back and forth with sandpaper 30 times, indicating that the silicon carbide ceramic film of Comparative Example 1 had poor abrasion resistance.

[0093] Table 5 shows the retention rates of fluorescent microspheres of different sizes for the superhydrophilic-underwater superoleophobic silicon carbide ceramic membranes prepared in Examples 1-6 and the comparative silicon carbide ceramic membrane prepared in Comparative Example 1.

[0094] fluorescent beads Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 A-20nm 99.14％ 99.24％ 99.48％ 99.26％ 99.19％ 99.11％ 22.22％ M-100nm 99.36％ 99.78％ 99.64％ 99.33％ 99.69％ 99.46％ 3.99％ E-200nm 99.63％ 99.85％ 99.83％ 99.80％ 99.78％ 99.61％ 31.47％

[0095] As can be seen from Table 5, the average pore size of the silicon carbide ceramic membranes in Examples 1-6 of the present invention is less than 20 nm, while the average pore size of the silicon carbide ceramic membrane in Comparative Example 1 is greater than 200 nm. This indicates that the method described in the present invention can effectively reduce the pore size of the silicon carbide ceramic membrane and improve the oil-water separation effect.

[0096] Depend on Figure 2 It can be seen that when the silicon carbide ceramic membranes of Examples 1-6 of the present invention are used for the separation of emulsified oil / water mixtures, they have higher oil removal rates for edible oil, olive oil, and hexadecane, and the oil removal rates are all higher than those of the post-oxidized silicon carbide ceramic membrane of Comparative Example 1. This indicates that the silicon carbide ceramic membranes of Examples 1-6 of the present invention have excellent oil-water separation efficiency, and the oil-water separation efficiency is higher than that of Comparative Example 1.

[0097] Depend on Figure 3 It can be seen that when the silicon carbide ceramic membrane of Example 1 of the present invention is used for oil-water separation, it still has a certain permeation flux after 6 cycles of use, and the permeation flux decreases relatively slowly. In contrast, the silicon carbide ceramic membrane of Comparative Example 1 has a larger pore size, which results in a higher permeation flux when used for the first time. However, it becomes clogged after the 6th cycle of use, resulting in a significant decrease in permeation flux. This shows that the silicon carbide ceramic membrane of Example 1 of the present invention is not easily clogged, has good durability, and can be used sustainably when used for oil-water separation.

[0098] Combined with Table 1-5, Figure 2 , Figure 3 As can be seen from Examples 1-6 and Comparative Example 1, the silicon carbide ceramic membrane obtained by modifying the suspension with hydrophilic silica nanoparticles and then calcining it has the following advantages over the silicon carbide ceramic membrane obtained by directly calcining without modification with the suspension of hydrophilic silica nanoparticles: it can effectively reduce the calcination temperature (from 900℃ to 600℃), effectively reduce the pore size of the silicon carbide ceramic membrane, and improve the wear resistance. Most importantly, it effectively improves the oil-water separation efficiency and durability of the silicon carbide ceramic membrane.

[0099] Combining Table 1 and Table 2, Figure 2 As can be seen from Examples 1-6 and Comparative Example 2, the silicon carbide ceramic membrane obtained by calcination after modification with a suspension of hydrophilic silica nanoparticles at 550°C in Comparative Example 2 exhibits poorer superhydrophilic-underwater superoleophobicity and oil-water separation efficiency compared to the silicon carbide ceramic membrane obtained by calcination after modification with a suspension of hydrophilic silica nanoparticles at 600°C in Examples 1-6. This indicates that the calcination temperature has a significant impact on the performance of the obtained silicon carbide ceramic membrane.

[0100] Combining Table 1 and Table 2, Figure 2 , Figure 4As can be seen from Examples 1-6 and Comparative Example 3, the silicon carbide ceramic membrane obtained by modifying the suspension of hydrophilic silica nanoparticles of a single particle size in Comparative Example 3, although only slightly inferior in superhydrophilic-underwater superoleophobicity and oil-water separation efficiency compared to the silicon carbide ceramic membranes obtained by modifying the suspension of hydrophilic silica nanoparticles of multiple particle sizes in Examples 1-6, has poor permeation flux and decreases significantly with increasing number of cycles. When used for oil-water separation, it not only has a longer separation time but also poor durability. This indicates that the modification effect of hydrophilic silica nanoparticles of multiple particle sizes is better than that of hydrophilic silica nanoparticles of a single particle size.

[0101] Combining Table 1 and Table 2, Figure 2 As can be seen from Examples 1-6 and Comparative Example 4, the silicon carbide ceramic membrane obtained by modification with a suspension containing 0.5 wt% hydrophilic silica nanoparticles in Comparative Example 4 exhibits poorer superhydrophilic-underwater superoleophobicity and oil-water separation efficiency compared to the silicon carbide ceramic membrane obtained by modification with a suspension containing 2 wt% hydrophilic silica nanoparticles in Examples 1-6. This indicates that the concentration of hydrophilic silica nanoparticles in the suspension has a significant impact on the performance of the obtained silicon carbide ceramic membrane, and the concentration of hydrophilic silica nanoparticles should not be too low.

[0102] Combining Table 1 and Table 2, Figure 2 , Figure 5 As can be seen from Examples 1-6 and Comparative Example 5, the silicon carbide ceramic membrane obtained in Comparative Example 5 after modification with a suspension containing 5 wt% hydrophilic silica nanoparticles has a similar oil-water separation efficiency compared to the silicon carbide ceramic membrane obtained in Examples 1-6 after modification with a suspension containing 2 wt% hydrophilic silica nanoparticles. The superhydrophilic-underwater superoleophobicity is only slightly inferior. However, the permeation flux of the silicon carbide ceramic membrane in Comparative Example 5 is very poor, and it is blocked during the fourth cycle, resulting in a permeation flux of 0. When used for oil-water separation, it not only has a long separation time but also poor durability. This indicates that the concentration of hydrophilic silica nanoparticles in the suspension has a significant impact on the performance of the obtained silicon carbide ceramic membrane, and the concentration of hydrophilic silica nanoparticles should not be too high.

[0103] In summary, the silicon carbide ceramic membrane prepared by this invention not only possesses excellent superhydrophilic and underwater superoleophobic properties, but also has advantages such as small membrane pore size, good durability, high oil-water separation efficiency, good abrasion resistance, and good corrosion resistance. Its comprehensive performance is excellent, and it has great application prospects in the field of oil-water separation. Furthermore, the preparation method of this invention is simple, the conditions are mild, the raw materials are readily available, and the cost is low, making it easy to achieve large-scale production.

[0104] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a superhydrophilic-underwater superoleophobic silicon carbide ceramic film, characterized in that, Includes the following steps: a) At least two types of hydrophilic silica nanoparticles with different particle sizes are added to water and mixed evenly to obtain a suspension with a silica nanoparticle content of 1-3 wt%; the suspension includes at least one small-diameter silica nanoparticle with a particle size of 10-50 nm and at least one large-diameter silica nanoparticle with a particle size of 100-300 nm, wherein the small-diameter silica nanoparticles include at least one of 12 nm silica nanoparticles and 20-50 nm silica nanoparticles; and the large-diameter silica nanoparticles include at least one of 100 nm silica nanoparticles and 300 nm silica nanoparticles; and the mass ratio of the small-diameter silica nanoparticles to the large-diameter silica nanoparticles is 1:(1-3). b) The unoxidized silicon carbide ceramic film is immersed in the suspension obtained in step a) for modification, taken out, dried at 55-65°C for 10-12 hours, and then placed in a muffle furnace and calcined at 590-610°C for 25-35 minutes to obtain a superhydrophilic-underwater superoleophobic silicon carbide ceramic film.

2. The preparation method according to claim 1, characterized in that: In the suspension described in step a), the content of silica nanoparticles is 2 wt%.

3. The preparation method according to claim 1, characterized in that: In step b), the unoxidized silicon carbide ceramic film is washed with ethanol and water in sequence, dried at 55-65°C for 10-12 hours, and then immersed in the suspension obtained in step a) for modification.

4. The preparation method according to claim 1, characterized in that: In step b), the unoxidized silicon carbide ceramic film is immersed in the suspension obtained in step a) and ultrasonically treated for 15 to 25 minutes.

5. The preparation method according to claim 1, characterized in that: In step b), during calcination, the temperature is increased to 600°C at a rate of 4°C / minute, and then calcined at 600°C for 25–35 minutes.

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