Preparation method of ceramic composite nanofiltration membrane with controllable polyamide layer thickness and application thereof

Abstract

The application discloses a kind of polyamide ceramic composite nanofiltration membranes, and nanofiltration membrane is composed of ceramic carrier and selective separation layer, wherein one side of ceramic carrier is hydrophobic, and one side is hydrophilic, wherein the thickness of hydrophilic layer is controllable.The application controls the thickness of hydrophilic layer of ceramic carrier, adjusts the adsorption amount and diffusion speed of water phase monomer in ceramic carrier, realizes the thickness adjustment of polyamide separation layer, reduces the mass transfer resistance of composite membrane, and improves permeability while ensuring the rejection performance of composite membrane.

Description

Technical Field

[0001] This invention belongs to the field of ceramic membrane technology, specifically relating to a method for preparing a ceramic composite nanofiltration membrane with controllable polyamide layer thickness and its application. Background Technology

[0002] Overcoming water scarcity remains a critical issue due to the increasing global population and dwindling freshwater resources. The chemical, food, and pharmaceutical industries are experiencing a growing demand for the separation and recovery of small molecules from aqueous and organic solutions. Membrane separation technology, with its high productivity, energy efficiency, and simple operation, has become a widely adopted industrial water treatment process (Chem.Eng.J.421(2021),127773). In recent years, non-fluidized membrane (NF) and non-fluidized membrane (OSNF) technologies have been extensively studied in dye and drug separation (J.Membr.Sci.645(2022),120241). However, the permeability-selectivity trade-off and poor solvent resistance of membrane materials are currently the main bottlenecks limiting their application (J.Membr.Sci.641(2022),119911), making them difficult to adapt to complex and variable industrial application environments. Therefore, designing a membrane with high permeability, solvent resistance, and versatility to realize its industrial application in the separation and recovery of small molecules is of great significance.

[0003] Nanofiltration has become an important membrane technology for water softening, wastewater treatment, pharmaceutical processing, and food production (Sep. Purif. Technol. 216 (2019), 115-125). Compared with reverse osmosis, nanofiltration membranes typically have a lower or larger pore size, and the separation process is less limited by osmotic pressure, allowing them to operate at lower pressures. Their molecular weight cutoff (MWCO) is between 200 and 1000 Da, effectively separating small organic molecules and various inorganic salts. Solute repulsion is primarily based on size repulsion and electrostatic interactions. Interfacial polymerization (IP) technology is widely used due to its simple operation, high efficiency, and stable film formation. Nanofiltration membranes prepared by this process are called thin film composite (TFC) nanofiltration membranes, consisting of a selective layer and a support layer, with the selective layer having a pore size range of 1–50 nm (Sep. Purif. Technol. 293 (2022), 121096). They possess characteristics such as high stability, high water flux, and ease of industrial production.

[0004] Traditional interfacial polymerization technology involves the condensation reaction of polyamine monomers and acyl chloride monomers dissolved in oil-water phases on the surface of a base membrane to form a dense polyamide (PA) film. This film is solidified on the base membrane surface and plays a selective separation role, becoming a key factor determining the performance of nanofiltration membranes. Currently, two main aspects affect the performance of the polyamide separation layer: first, the pore structure and chemical properties of the carrier. The pore structure of the carrier affects monomer diffusion and reaction sites during interfacial polymerization, which in turn affects the formation of the polyamide layer. Furthermore, the chemical stability, high mechanical strength, and strong thermal stability of the carrier itself limit the further application of nanofiltration membranes (J.Membr.Sci.678(2023),121687). Second, the surface properties and cross-linking structure of the polyamide layer. Currently available commercial PA layers have weak surface hydrophilicity and low surface charge (J.Membr.Sci.608(2020),1182020), which is insufficient to attract water molecules. At the same time, they have the disadvantages of dense cross-linked structure and thick separation layer (J.Membr.Sci.657(2022),120673). The combination of these two factors leads to a significant increase in mass transfer resistance, which severely limits the application of polyamide nanofiltration membranes.

[0005] Because NF membranes have a unique and independent preparation process, the polyamide layer and the base membrane can be optimized separately, thereby effectively changing the performance of the composite membrane. To improve the performance of polyamide nanofiltration membranes, researchers have started from two aspects: first, optimizing the base membrane. Some researchers have used polysulfone (PSF) base membranes with different pore sizes as carriers for interfacial polymerization (Sep. Purif. Technol. 212 (2019), 438–448). However, these polymer membranes usually have some problems, such as low solvent resistance, poor mechanical strength, weak acid and alkali resistance, and weak oxidation or heat resistance. Second, modifying the interfacial polymerization to reduce mass transfer resistance. The mass transfer resistance of the composite membrane is mainly determined by the thickness and cross-linking degree of the selective layer. Some researchers have introduced nanoparticles during interfacial polymerization, such as zeolite imidazole framework-8 (ZIF-8) (Colloid Surface A.612(2021),125971), ortho-hydroxy porous organic polymers (o-POP) (J.Memb.Sci.585(2019),19–28), and silica (SiO2) (J.Memb.Sci.565(2018),145–156) are used to improve the surface roughness and crosslinking degree of the membrane. However, since the thickness of the polyamide layer has not been improved significantly, the flux improvement is not significant. At the same time, the nanoparticles will show uneven distribution and agglomeration, which will reduce the selectivity of the composite membrane. Therefore, reducing the thickness of the polyamide layer while ensuring its integrity and absence of defects is the key to improving the membrane flux. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a polyamide ceramic composite nanofiltration membrane. The surface of the inorganic ceramic carrier is first hydrophobically modified, and then unilaterally hydrophilic modified. By controlling the thickness of the unilateral hydrophilic layer, the adsorption amount and diffusion rate of aqueous monomers in the ceramic carrier are improved, thereby achieving the adjustment of the thickness of the polyamide separation layer and reducing the mass transfer resistance of the composite membrane.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A ceramic composite nanofiltration membrane with controllable polyamide layer thickness is disclosed. The nanofiltration membrane is composed of a ceramic carrier and a selective separation layer. The ceramic carrier is hydrophobically modified as a whole before interfacial polymerization, and then one side of the hydrophobically modified ceramic carrier is hydrophilically modified. The selective separation layer is made of polyamide and is formed by interfacial polymerization on the hydrophilically modified side of the ceramic carrier.

[0009] Preferably, the side of the ceramic carrier that is hydrophilically modified is the side of the ceramic carrier with a relatively small pore size.

[0010] A method for preparing a ceramic composite nanofiltration membrane with controllable polyamide layer thickness as described in claim 1, characterized by comprising the following steps:

[0011] S1. Provide a ceramic carrier;

[0012] S2. Hydrophobic modification of the ceramic carrier;

[0013] S3. Perform hydrophilic modification on one side of the hydrophobically modified ceramic carrier;

[0014] S4. A selective separation layer of polyamide material is prepared by interfacial polymerization on the hydrophilically modified side of the ceramic carrier.

[0015] Preferably, in step S1, the ceramic carrier is one of alumina ultrafiltration membrane, zirconium oxide ultrafiltration membrane, titanium dioxide ultrafiltration membrane or silicon carbide ultrafiltration membrane; the ceramic carrier needs to be hydroxyl activated before use, and the ceramic carrier is immersed in water to allow water to enter the membrane pores, and then the water on the surface is removed.

[0016] Preferably, the hydrophobic modification method in step S2 includes one or more of the following: oil immersion method, chemical vapor deposition, and sol-gel method; wherein the oil immersion method involves immersing the ceramic support in an active organosilane solution and shaking it in a gas bath constant temperature shaker for a period of time, then rinsing it with an ethanol-water solution and subsequently drying it in a vacuum drying oven; the chemical vapor deposition method involves placing the organosilane solution and the ceramic support in a sealed container, then heating it at the boiling point of the reactive organosilane, and finally removing and sealing it after the reaction is complete; the sol-gel method involves aging the prepared organosilane sol for one week to generate a gel. Then, the ceramic membrane support is immersed in the gel sol solution at room temperature, removed, and dried in an oven.

[0017] Preferably, the concentration of the active organosilane solution in the oil immersion method is 1-5 wt%, and the solvent used is one or a mixture of water, alcohol, or hexane; the organosilane is one or more of methyltrimethoxysilane, polydimethylsiloxane, perfluorooctyltrichlorosilane, perfluorodecyltriethoxysilane, hexadecylthiol, or hexadecyltrimethoxysilane; the oscillation time in the gas bath constant temperature shaker is 40-300 min; the mass fraction of the ethanol aqueous solution is 25-100 wt%; the drying temperature in the vacuum drying oven is 40-100℃; and the drying time is 30-300 min. The active organosilane solution in the chemical vapor deposition method is the same as that in the oil immersion method. The active organosilane solution in the sol-gel method is the same as that in the oil immersion method; the drying temperature is 60-120℃; and the drying time is 10-120 min.

[0018] Preferably, the method for unilateral hydrophilic modification in step S3 is one or more of plasma etching, oxidant coating, and surfactant wetting, and the specific operation is as follows:

[0019] (1) Plasma etching, wherein one side of the ceramic carrier is irradiated with plasma for 1 to 5 minutes, wherein the plasma is one or more of oxygen plasma, nitrogen plasma, and argon plasma.

[0020] (2) Strong oxidant coating, in which alkylsilane compounds are stereoselectively oxidized to the corresponding alcohols by peroxy acid, the concentration of peroxy acid is 0.5-8 g / L, the coating time is 40-300 s, wherein the peroxy acid is selected from one or more of performic acid, peracetic acid, perbenzoic acid or m-chloroperbenzoic acid;

[0021] (3) Surfactant wetting: The hydrophobically modified ceramic carrier is wetted by surface-induced wetting for 10–120 s, followed by coating the wetted layer with a polyphenolic compound. The surfactant is one or more of sodium dodecylbenzenesulfonate, polyethylene glycol ether, polyethylene glycol sulfate, or glycerin, and the concentration of the polyphenolic compound is 1–6 g / L. The polyphenolic compound is one or more of dopamine, tannic acid, catechol, and catechin.

[0022] Preferably, step S4 includes the following steps:

[0023] (1) Immerse the hydrophilically modified side of the unilateral hydrophilically modified ceramic carrier in an aqueous solution, then remove and dry it;

[0024] (2) The dried ceramic support and the organic phase monomer solution were subjected to interfacial polymerization reaction;

[0025] (3) Take out the ceramic carrier after the reaction and heat treat it to obtain a polyamide ceramic composite nanofiltration membrane with controllable separation layer thickness.

[0026] Preferably, in step (1), the aqueous phase solution is a mixed solution of aqueous monomer and alkaline solution with a mass concentration of 0.1-6 wt%, the aqueous phase monomer is an organic compound containing polyamino groups, selected from one or more of piperazine, m-phenylenediamine, ethylenediamine, diethylenetriamine, or dopamine, and the alkaline solution is NaOH solution with a mass concentration of 0.05-0.6 wt%; in step (2), the organic phase monomer solution is a mixed solution of organic phase monomer and organic solvent with a mass concentration of 0.05-0.5 wt%, the organic phase monomer is an organic compound containing polyacrylamide chloride groups, selected from one or more of trimesoyl chloride, phthaloyl chloride, or trimesoyl tetramethyl chloride, and the organic solvent is one of n-hexane, cyclohexane, or n-heptane; the interfacial polymerization reaction time is 10-600 s; in step (3), the heat treatment temperature is 5-100 °C, and the heat treatment time is 10-30 min.

[0027] Application of polyamide ceramic composite nanofiltration membrane in the separation and recovery of small molecules in organic solutions.

[0028] The advantages of this invention are:

[0029] 1. This invention modifies the ceramic carrier by hydrophobic modification followed by unilateral hydrophilic modification. By controlling the thickness of the unilateral hydrophilic layer, the storage and diffusion of aqueous monomers in the ceramic carrier can be controlled, thereby adjusting the thickness of the polyamide layer in the subsequent interfacial polymerization process. This is beneficial for forming a thinner separation layer and reducing mass transfer resistance.

[0030] 2. Since the ceramic substrate itself is hydrophilic, it is impossible to directly regulate the storage of aqueous monomers on the ceramic substrate. Therefore, the ceramic substrate is first completely hydrophobically modified, and then hydrophilically modified on one side. The hydrophobic modification provides conditions for subsequent hydrophilic layer adjustment, making one side of the ceramic substrate hydrophilic and the other side oleophilic. Due to the presence of the hydrophilic layer, when treating organic wastewater, oil in the wastewater cannot directly contact the hydrophobic layer of the membrane, thus avoiding membrane fouling caused by oil.

[0031] 3. Ceramic carriers have high chemical stability, high mechanical strength and strong thermal stability. Using ceramic carriers as base films ensures the working efficiency of composite films in harsh environments.

[0032] 4. The structure of the polyamide separation layer can be adjusted directly by controlling the thickness of the hydrophilic layer on the ceramic carrier, thus eliminating the need for an intermediate layer. This not only simplifies the operation but also saves costs. Attached Figure Description

[0033] Figure 1 These are photographs of water droplets just coming into contact with the surface of a polyamide ceramic composite nanofiltration membrane: (a) hydrophilic side of the ceramic carrier after unilateral hydrophobic modification; (b) hydrophilic side of the composite membrane.

[0034] Figure 2 The dynamic contact angle test of the polyamide ceramic composite nanofiltration membrane: (a) hydrophilic side of the ceramic carrier after hydrophobic modification on one side; (b) hydrophilic side surface of the composite membrane.

[0035] Figure 3 This is an organic solvent resistance test for polyamide ceramic composite nanofiltration membranes;

[0036] Figure 4 It is the molecular weight cutoff of the polyamide ceramic composite nanofiltration membrane. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] A method for preparing a polyamide ceramic composite nanofiltration membrane includes the following specific preparation steps:

[0040] 1. Preparation of unilateral hydrophilic ceramic carriers

[0041] (1) After performing hydroxyl activation on the ceramic carrier, the ceramic substrate film is immersed in deionized water for 3 hours, then removed and dried in a vacuum drying oven for 5 hours. After removal, it is stored in a sealed plastic bag.

[0042] (2) The ceramic support was hydrophobically modified using methyltrimethoxysilane (MTMS). A certain volume of MTMS was dissolved in anhydrous ethanol to prepare a 5% MTMS solution. The ceramic support described in step (1) was immersed in the MTMS solution and placed in a constant temperature oscillator (25°C) for 60 min. After removal, the unreacted MTMS on the membrane surface was removed with an ethanol aqueous solution, and then dried in a vacuum drying oven. After removal, the ceramic support described in step (2) was coated with 0.5 g / L peracetic acid and placed in an oven at 45°C for 300 s. After removal, it was washed 2-3 times with deionized water and then dried in air to obtain a one-sided hydrophilic ceramic support.

[0043] 2. Preparation of polyamide ceramic composite nanofiltration membrane

[0044] (1) Immerse the single-sided hydrophilic ceramic carrier in a solution of 6 wt% aqueous piperazine monomer and 0.6 wt% NaOH for 5 min, then pour out the aqueous solution and remove the ceramic carrier at the same time. Dry it in the air for 15 min and let the moisture on the inner surface of the membrane air dry naturally.

[0045] (2) The dried membrane is soaked again in a solution of 0.05 wt% organic phase monomer pyromellitic acid chloride and poured into the device. After the interfacial polymerization reaction is carried out for 10 seconds, the ceramic carrier is removed. The surface of the residual organic phase solution is rinsed with deionized water.

[0046] (3) Heat treatment of the ceramic carrier in an oven at 60°C for 10 minutes to obtain a polyamide ceramic composite membrane with unilateral hydrophilicity.

[0047] Example 2

[0048] The difference between this embodiment and Example 1 is that the concentration of peracetic acid in the unilateral hydrophilic modification is 8 g / L, and the time spent in the oven at 45°C is 40 s. In the preparation of the polyamide ceramic composite nanofiltration membrane, the interfacial polymerization reaction time is 600 s, the heat treatment temperature is 100°C, and the heat treatment time is 30 min.

[0049] Example 3

[0050] The difference between this embodiment and Example 1 is that the unilateral hydrophilic modification is carried out by oxygen plasma irradiation for 1 minute, and the mass concentration of the aqueous piperazine monomer solution is 0.1 wt% and contains 0.05 wt% NaOH solution when preparing the polyamide ceramic composite nanofiltration membrane.

[0051] Example 4

[0052] The preparation steps in this embodiment are the same as in Example 1, except that the unilateral hydrophilic modification is carried out by oxygen plasma irradiation for 5 minutes, and the organic phase phenyltrimethylammonium chloride has a mass concentration of 0.5 wt% when preparing the polyamide ceramic composite nanofiltration membrane.

[0053] Example 5

[0054] The difference between this embodiment and Example 1 is that, during the unilateral hydrophilic modification, the membrane was coated with tannic acid (1 g / L) after glycerol-induced wetting for 10 seconds, and the heat treatment temperature was 5°C during the preparation of the polyamide ceramic composite nanofiltration membrane.

[0055] Example 6

[0056] Compared with Example 1, the difference in this embodiment is that when the unilateral hydrophilic modification is performed, the membrane is coated with tannic acid (6 g / L) after glycerol-induced wetting for 120 s, while the interfacial polymerization reaction time is 600 s when preparing the polyamide ceramic composite nanofiltration membrane.

[0057] Comparative Example

[0058] Compared with Example 1, no hydrophobic modification or unilateral hydrophilic modification was performed on the surface of the ceramic carrier; instead, interfacial polymerization was performed directly on the surface of the ceramic carrier.

[0059] (1) Immerse the ceramic support in an aqueous phase of piperazine monomer with a mass concentration of 0.1wt% and a solution containing 0.1wt% NaOH for 5 minutes, then pour out the aqueous phase solution and remove the ceramic support at the same time. Dry it in the air for 15 minutes and let the moisture on the inner surface of the membrane air dry naturally.

[0060] (2) The dried membrane is soaked again in a solution of 0.05 wt% organic phase monomer pyromellitic acid chloride and poured into the device. After the interfacial polymerization reaction is carried out for 10 seconds, the ceramic carrier is removed. The surface of the residual organic phase solution is rinsed with deionized water.

[0061] (3) Heat treatment of the ceramic carrier in an oven at 90°C for 30 minutes to obtain the polyamide ceramic composite film.

[0062] Test methods

[0063] Test conditions: The feed solution is an aqueous solution containing 5 mg / mL of inorganic salt or anhydrous ethanol; the feed flow rate is 40 L / h; the test is conducted at room temperature and pre-pressurized at 0.5 MPa for 1 h, followed by testing at 0.4 MPa. The inorganic salt includes any one or more combinations of sodium sulfate, sodium chloride, magnesium sulfate, and magnesium chloride.

[0064] (1) Permeation flux (J): The permeability of the reactive membrane is calculated using the following formula:

[0065]

[0066] Where V is the volume of the collected permeate (L), and A is the effective area of ​​the membrane (m²). 2 ), where t is the time (h) required to collect V volume of permeate.

[0067] (2) The membrane rejection rate (R) reflects the membrane's separation performance, and the calculation formula is as follows:

[0068]

[0069] Among them, C p With C f These represent the concentrations of the solute components in the feed solution and the permeate, respectively.

[0070] Test Results

[0071] 1. Membrane retention performance and permeation flux testing

[0072] (1) The retention rate and permeation flux of the composite nanofiltration membranes prepared in Examples 1-6 and the comparative examples were tested, and the results are shown in Table 1 and Table 2, respectively:

[0073] Table 1. Retention rate test results of composite nanofiltration membranes

[0074] Sodium sulfate rejection rate (%) Calcium chloride retention rate (%) Sodium chloride retention rate (%) Magnesium sulfate retention rate (%) Example 1 / / 35.33 / Example 2 52.73 / / / Example 3 / 27.88 / / Example 4 / / / 81.96 Example 5 / / 27.11 / Example 6 78.31 / / / Comparative Example 1 58.44 / / /

[0075] Table 2. Permeation flux test results of composite nanofiltration membranes

[0076] As can be seen from Tables 1 and 2, although the ceramic support underwent hydrophobic modification, the final composite nanofiltration membrane still...

[0077] Ethanol flux (LMH / bar) Pure water flux (LMH / bar) Example 1 / 36.59 Example 2 / 21.52 Example 3 24.63 / Example 4 / 15.72 Example 5 27.33 / Example 6 / 21.14 Comparative Example / 24.63

[0078] The high pure water flux can be maintained because the thickness of the hydrophilic layer is controlled during the unilateral hydrophilic modification, which ultimately limits the amount of aqueous piperazine monomer stored in the base film during interfacial polymerization, resulting in a reduction in the thickness of the final polyamide layer.

[0079] 2. Contact Angle Test

[0080] Contact angle tests were conducted on the ceramic carriers after unilateral hydrophilic modification and the composite membranes after interfacial polymerization in Examples 1, 3, 5, and 6, as well as the comparative examples. The test results are as follows: Figure 1 and Figure 2 As shown, from Figure 1 (a) It can be seen that the surface water contact angle of the composite nanofiltration membranes in the embodiments all changed to varying degrees, indicating that unilateral controllable hydrophilic modification of the ceramic carrier surface was achieved. However, compared with the comparative example, the hydrophilicity of the ceramic carrier in the embodiments still decreased due to hydrophobic modification. Figure 1(b) It can be seen that the surface hydrophilicity of the composite film has the same characteristics as that before interfacial polymerization, but the hydrophilicity is improved. This may be due to the formation of carboxyl groups by the hydrolysis of oil phase monomers on the surface. Figure 2 The dynamic contact angle shows that the water contact angle on the ceramic carrier surface in the embodiment does not tend to decrease with the extension of measurement time after a certain period. This means that water droplets cannot diffuse well on the substrate, indicating that the thickness of the hydrophilic layer of the base film is limited. Similarly, it can be seen that the thickness of the hydrophilic layer is also different, indicating that unilateral controllable hydrophilic modification has been achieved.

[0081] 3. Membrane resistance to organic solvents test

[0082] Example 6 and the comparative example were tested for resistance to organic solvents by immersing the ceramic composite membrane in acetone solution and measuring its rejection rate and flux to sodium sulfate solution every hour. The results are as follows. Figure 3 As shown in the figure, we can see that the performance of the composite membrane in the comparative example decreased significantly with increasing immersion time in the organic solvent, while the performance of the composite membrane in the embodiment remained essentially unchanged. This is because the ceramic carrier in the embodiment underwent hydrophobic modification, which improved the organic solvent resistance of the composite membrane.

[0083] 4. Membrane molecular weight cutoff test

[0084] The molecular weight cutoff of the composite nanofiltration membranes in Examples 1, 6, and the comparative example were tested respectively, and the test results are as follows: Figure 4 As shown in the figure, the molecular weight cutoffs of the composite membranes in Example 6 and the comparative example are not significantly different (528 Da and 594 Da respectively), while the molecular weight cutoff of the composite membrane in Example 1 is 806 Da. This is because the different thicknesses of the hydrophilic layer of the base membrane have different effects on the storage and diffusion of aqueous monomers, ultimately leading to changes in the structure and thickness of the polyamide layer.

[0085] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A ceramic composite nanofiltration membrane with controllable polyamide layer thickness, characterized in that, The nanofiltration membrane is composed of a ceramic carrier and a selective separation layer. The ceramic carrier is first hydrophobically modified as a whole before interfacial polymerization, and then one side of the hydrophobically modified ceramic carrier is hydrophilically modified. The selective separation layer is made of polyamide and is formed by interfacial polymerization on the hydrophilically modified side of the ceramic carrier. The hydrophilically modified side of the ceramic carrier is the side with a relatively small pore size.

2. A method for preparing a ceramic composite nanofiltration membrane with controllable polyamide layer thickness as described in claim 1, characterized in that, Includes the following steps: S1. Provide a ceramic carrier; S2. Hydrophobic modification of the ceramic carrier; S3. Perform hydrophilic modification on one side of the hydrophobically modified ceramic carrier; S4. A selective separation layer of polyamide material is prepared by interfacial polymerization on the hydrophilically modified side of the ceramic carrier.

3. The method according to claim 2, characterized in that, In step S1, the ceramic carrier is one of alumina ultrafiltration membrane, zirconium oxide ultrafiltration membrane, titanium dioxide ultrafiltration membrane or silicon carbide ultrafiltration membrane; before use, the ceramic carrier needs to be activated by hydroxyl groups and then immersed in water to allow water to enter the membrane pores, and then the water on the surface is removed.

4. The method according to claim 3, characterized in that, The hydrophobic modification method in step S2 includes one or more of the following: oil immersion method, chemical vapor deposition, and sol-gel method. The oil immersion method involves immersing the ceramic support in an active organosilane solution and then oscillating it in a constant-temperature air bath for a period of time. After removal, it is rinsed with an ethanol-water solution and subsequently dried in a vacuum drying oven. The chemical vapor deposition method involves placing the organosilane solution and the ceramic support in a sealed container and then heating it at the boiling point of the reactive organosilane. After the reaction is complete, the container is removed and sealed for storage. The sol-gel method involves aging the prepared organosilane sol for one week to generate a gel. Then, the ceramic support is immersed in the sol-gel solution at room temperature, removed, and dried in an oven.

5. The method according to claim 4, characterized in that: The concentration of the active organosilane solution in the oil immersion method is 1-5 wt%, and the solvent used is one or a mixture of water, alcohol, or hexane; the active organosilane in the active organosilane solution is one or more of methyltrimethoxysilane, polydimethylsiloxane, perfluorooctyltrichlorosilane, perfluorodecyltriethoxysilane, hexadecylthiol, or hexadecyltrimethoxysilane; the oscillation time in the gas bath constant temperature shaker is 40-300 min; the mass fraction of the ethanol aqueous solution is 25-100 wt%; the drying temperature in the vacuum drying oven is 40-100℃; and the drying time is 30-300 min. The active organosilane solution in the chemical vapor deposition method is the same as that in the oil immersion method. The active organosilane solution in the sol-gel method is the same as that in the oil immersion method; the drying temperature is 60-120℃; and the drying time is 10-120 min.

6. The method according to claim 2, characterized in that, The hydrophilic modification method in step S3 is one or more of plasma etching, oxidant coating, and surfactant wetting, and the specific operation is as follows: Plasma etching involves irradiating one side of a ceramic substrate with plasma for 1 to 5 minutes. The plasma can be one or more of oxygen plasma, nitrogen plasma, and argon plasma. A strong oxidizing agent is used to coat the alkylsilane compound stereoselectively to the corresponding alcohol by peroxy acid. The concentration of peroxy acid is 0.5~8 g / L and the coating time is 40~300 s. The peroxy acid is selected from one or more of performic acid, peracetic acid, perbenzoic acid or m-chloroperbenzoic acid. Surfactant impregnation involves surface-induced wetting of one side of the hydrophobically modified ceramic carrier for 10-120 seconds, followed by coating the wetted layer with a polyphenolic compound. The surfactant is one or more of sodium dodecylbenzenesulfonate, polyethylene glycol ether, polyethylene glycol sulfate, or glycerin, and the concentration of the polyphenolic compound is 1-6 g / L. The polyphenolic compound is one or more of dopamine, tannic acid, catechol, and catechin.

7. The method according to claim 2, characterized in that, Step S4 includes the following steps: (1) Immerse the hydrophilic modified side of the ceramic carrier after step S3 into an aqueous solution, and then remove and dry it; (2) The dried ceramic carrier and the organic phase monomer solution are subjected to interfacial polymerization reaction; (3) Take out the ceramic carrier after the reaction and heat treat it to obtain a polyamide ceramic composite nanofiltration membrane with controllable separation layer thickness.

8. The method according to claim 7, characterized in that: In step (1), the aqueous solution is a mixture of aqueous monomer and alkaline solution with a mass concentration of 0.1-6 wt%. The aqueous monomer is an organic compound containing polyamino groups, selected from one or more of piperazine, m-phenylenediamine, ethylenediamine, diethylenetriamine, or dopamine. The alkaline solution is NaOH solution with a mass concentration of 0.05-0.6 wt%. In step (2), the organic monomer solution is a mixture of organic monomer and organic solvent with a mass concentration of 0.05-0.5 wt%. The organic monomer is an organic compound containing polyacrylamide chloride groups, selected from one or more of trimesoyl chloride, phthaloyl chloride, or trimesoyl tetramethyl chloride. The organic solvent is one of n-hexane, cyclohexane, or n-heptane. The interfacial polymerization reaction time is 10-600 s. In step (3), the heat treatment temperature is 5-100℃ and the heat treatment time is 10-30 min.

9. The application of the ceramic composite nanofiltration membrane with controllable polyamide layer thickness according to claim 1 in the separation and recovery of small molecules in water or organic solutions.

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