Self-supporting MOF ceramic membrane with self-repairing function and preparation method and application thereof

Abstract

The application discloses a self-supporting MOF ceramic membrane with a self-repairing function and a preparation method and application thereof, and belongs to the technical field of ceramic membranes; the preparation method comprises the following steps: (1) preparation of defect-engineered MOF seed crystals; (2) inoculation of defect-activated seed crystals; (3) pressure reverse diffusion self-repairing secondary growth; (4) defect-mediated in-situ repair of coordination polymer glass melting impregnation; and (5) construction of a hydroxyl-bridged self-supporting MOF ceramic membrane. According to the functional progressive logic of "interface activation, large defect closure, micro-leakage repair and self-supporting formation", the application is systematically integrated, and a MOF ceramic membrane with high interface compatibility, double-mode self-repairing capability and intrinsic self-supporting characteristics is cooperatively constructed.

Description

Technical Field

[0001] This invention belongs to the field of ceramic membrane technology, and in particular relates to a self-supporting MOF ceramic membrane with self-healing function, its preparation method and application. Background Technology

[0002] Ceramic membranes are widely used in water treatment due to their high mechanical strength, corrosion resistance, and resistance to microbial degradation. However, their separation accuracy is limited by the lower limit of pore size, making it difficult to efficiently retain emerging pollutants. Combining metal-organic frameworks (MOFs) with ceramic membranes holds promise for overcoming this bottleneck, but current technologies still face three major challenges.

[0003] First, the chemical inertness of the ceramic substrate surface makes it difficult for MOFs to grow uniformly and firmly. Existing strategies such as polydopamine modification can improve the interface, but they introduce additional mass transfer resistance and the risk of detachment. While one-step deposition methods can improve adhesion, they rely on binders and have complex processes.

[0004] Secondly, intergranular defects and non-selective leakage channels within the polycrystalline MOF film severely restrict separation selectivity. Existing research has proposed using melt-processable coordination polymer glass (CP glass) to seal grain boundary defects, thus preparing GUM composite membranes with self-healing capabilities. However, this strategy is mainly aimed at organic solvent nanofiltration and gas separation, and its long-term stability in water treatment pressure differential driven systems has not been verified.

[0005] Third, fabricating MOFs into self-supporting macroscopic continuous membranes is a recognized challenge. Existing research uses a hydroxyl bridging strategy to "weld" defect-rich MOF nanocrystals into self-supporting ceramic-like membranes, preserving the crystalline structure and intrinsic pores. However, its applications are mainly limited to proton conduction in high-humidity environments and have not yet been extended to pressure differential-driven separation systems in water treatment.

[0006] In summary, there is an urgent need to develop a MOF ceramic membrane that combines high interfacial compatibility, graded in-situ self-healing of defects, intrinsic self-support of the membrane layer, and suitability for hydraulic drive applications. Summary of the Invention

[0007] To address the technical problems in existing technologies, this invention provides a self-supporting MOF ceramic membrane with self-healing capabilities, its preparation method, and its applications. This invention is the first to systematically integrate four major technical modules—intracrystalline defect engineering, pressurized reverse diffusion self-healing secondary growth, coordination polymer glass melt infiltration, and hydroxyl-bridged cold pressing densification—according to a functional progression logic of "interface activation → large defect sealing → micro-leakage repair → self-supporting molding," synergistically constructing a MOF ceramic membrane with high interfacial compatibility, dual-mode self-healing capabilities, and intrinsic self-supporting properties. Notably, the coordination polymer glass melt infiltration strategy and the hydroxyl-bridged cold pressing strategy are both applied for the first time in a water treatment differential pressure-driven system, and have been systematically adapted for the aqueous environment, solving the long-standing technical bottlenecks in intercrystalline defect repair and macroscopic self-supporting molding of existing MOF ceramic membranes.

[0008] To achieve the above-mentioned objectives, the present invention employs the following technical solution: a method for preparing a self-supporting MOF ceramic membrane with self-healing function, comprising the following steps: Preparation of defect-engineered MOF seed crystals: Zinc nitrate hexahydrate and 2-methylimidazole were added to DMF, and then pyridine was added to regulate crystal plane defects. The molar ratio of pyridine to 2-methylimidazole was x, where 0 < x ≤ 0.15. After dissolution, the mixture was transferred to a reactor for reaction. After the reaction was completed, the product was collected by centrifugation, washed with DMF and methanol respectively, and then vacuum dried. In order to introduce controllable intracrystalline defects to expose the coordination unsaturated metal sites, pyridine was added as a coordination competition regulator during the hydrothermal synthesis process. The intracrystalline defect density was controlled by changing the ratio of regulator to ligand, and defect-type seed crystals were obtained, denoted as ZIF-8-x. Defect-activated seeding: The ceramic substrate was ultrasonically cleaned with deionized water and ethanol in sequence, and then dried for later use. The ZIF-8-x seed crystals from step (1) were dispersed in deionized water to prepare a seed dispersion with a mass fraction of 0.2-1.0%. The ZIF-8-x seed crystals were uniformly loaded onto the surface of the ceramic substrate by vacuum filtration or dip-coating method. The seed distribution density was adjusted by controlling the concentration of the seed solution and the number of loading times. After drying at 60-80℃ for 10-20 min, the substrate was activated by heating at 120℃ for 1-4 h. The abundant coordination unsaturated metal sites on the seed surface were used to form strong coordination bonds with the residual hydroxyl groups on the surface of the ceramic substrate, thereby achieving the directional fixation of the seed crystals on the inert ceramic surface and obtaining a defect-loaded seed substrate, denoted as ZIF-8-x@Al2O3. Pressure reverse diffusion self-healing secondary growth: Precursor solution A and precursor solution B were prepared respectively; wherein solution A is an aqueous solution of zinc nitrate hexahydrate and solution B is an aqueous solution of 2-methylimidazole; the ceramic substrate ZIF-8-x@Al2O3 with seed crystals obtained in step (2) was fixed in the dead end filter membrane pool, and the membrane pool was divided into an upper chamber and a lower chamber by a sealing ring. Precursor solution A was placed on one side of the membrane, and precursor solution B was placed on the other side. An inert gas was used to apply a pressure difference between the two sides, causing the precursor solution to diffuse to the opposite side driven by the pressure difference, and to nucleate and grow in situ in the intergranular gaps within the seed layer. The reaction temperature was 50-90℃ and the time was 0.5-4h. Under the pressure difference, the precursor penetrated into the interior of the intergranular defects and underwent in-situ crystallization. The non-selective intergranular defects were sealed and repaired in situ through the Ostwald ripening mechanism. After the reaction was completed, the composite membrane was taken out, washed with deionized water and methanol, and then vacuum dried at 60℃ to obtain a pressure-reverse diffusion secondary growth membrane, denoted as PCD-ZIF-8@Al2O3. In-situ repair of defects mediated by fusion infiltration of coordination polymer glass: The coordination polymer glass powder was mixed with the PCD-ZIF-8@Al2O3 film from step (3) and placed in a quartz tube, which was then vacuum sealed. The tube furnace was heated to the melting temperature of the coordination polymer glass at a rate of 2-10℃ / min, and fusion infiltration was performed for 10-60 min. The molten ligands wetted the intergranular residual defects of the MOF film under capillary action and formed a dense amorphous barrier layer after cooling, which sealed the microporous leakage channels without blocking the intrinsic pores of the MOF. The film was naturally cooled to room temperature under argon protection to obtain a glass-modified composite film, denoted as GUM-ZIF-8@Al2O3. Construction of hydroxyl-bridged self-supporting MOF ceramic film: The GUM-ZIF-8@Al2O3 film prepared in step (4) was immersed in an alkaline solution and etched at 50-90℃ for 0.5-4h. Some MOF ligands were selectively dissolved and removed to generate gradient distribution of intracrystalline defects. After etching, the film was dried and activated at 60-120℃ and transferred to a high-pressure mold. A unidirectional pressure of 20-100MPa was applied at room temperature or under heating to densify the film. The ligand-deficient sites generated by etching exposed the hydroxyl coordination ability of the metal nodes. A dense and hydrophilic grain boundary bonding network was formed between the nanoparticles inside the MOF film through metal-hydroxyl-metal bridging (OH-bridging), thereby improving the mechanical strength and structural integrity of the film. The hydroxyl-bridged self-supporting MOF ceramic film was obtained and denoted as OHB-MOF-ceramic.

[0009] Furthermore, the reaction temperature in step (1) is 120°C and the time is 24h; the washing with DMF and methanol is performed 3 times each, and the drying temperature is 60°C.

[0010] Furthermore, in step (1), the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:3.45.

[0011] Furthermore, the pressure difference in step (3) is 0.05-0.5 MPa.

[0012] Furthermore, in step (3), the mass ratio of zinc nitrate hexahydrate to deionized water is 1:50.

[0013] Further, in step (3), the mass ratio of 2-methylimidazole to deionized water is 1.1:50.

[0014] Further, the mass ratio of the glass powder to the PCD-ZIF-8@Al2O3 film in step (4) is (2-5):1.

[0015] Further, the alkaline solution in step (5) is a sodium hydroxide solution with a concentration of 0.1-1.0 mol / L.

[0016] A self-supporting MOF ceramic membrane with self-healing function is prepared by any one of the preparation methods described in 1-8 above.

[0017] The self-supporting MOF ceramic membrane with self-healing function described above can be used in the field of water treatment.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is the first to integrate four major technologies—intracrystalline defect engineering, pressurized reverse diffusion secondary growth, coordination polymer glass melt infiltration, and hydroxyl-bridged cold pressing densification—in a logical system of "interface activation → large defect sealing → microleakage repair → self-supporting molding." The prepared self-supporting MOF ceramic membrane achieves a methylene blue rejection rate of 99% and a pure water flux of 72 Lm³. -2 h -1 bar -1 The flux recovery rate after 10 cycles is 92%, and its overall performance is significantly better than that of existing MOF-ceramic composite membranes.

[0019] The introduction of coordination polymer glass in this invention endows the membrane with excellent in-situ self-healing ability, and the rejection rate after scratch damage can be restored from 60% to 99%. At the same time, hydroxyl bridging densification greatly improves the mechanical strength of the membrane, realizing self-supporting molding of pure MOF components. This invention provides a full-chain solution for the water treatment field that combines high selectivity, high throughput, high stability and self-healing. Attached Figure Description

[0020] Figure 1 The graphs show the membrane performance test results of Examples 1-3 and Comparative Examples 1-3.

[0021] Figure 2The graph shows the change in methylene retention rate before and after scratch repair of the self-supporting membrane in Example 1 and Comparative Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Example 1

[0024] (1) Preparation of defect-engineered ZIF-8-0.10 seed crystals Zinc nitrate hexahydrate (2.0 g, 6.72 mmol) and 2-methylimidazole (1.9 g, 23.2 mmol) were dissolved in 50 mL of DMF. 0.18 mL of pyridine (approximately 2.32 mmol, pyridine / 2-methylimidazole molar ratio 0.10) was added, and the mixture was sonicated and transferred to a high-pressure reactor. The reaction was carried out at 120 °C for 24 h. After the reaction was complete, the product was collected by centrifugation, washed three times each with DMF and methanol, and dried under vacuum at 60 °C to obtain ZIF-8-0.10 seed crystals.

[0025] (2) Seed seeding for defect activation A porous α-Al₂O₃ ceramic substrate (average pore size 0.1-1 μm) was ultrasonically cleaned sequentially with deionized water and ethanol, and then dried at 60 °C for later use. ZIF-8-0.10 seed crystals (0.5% by mass) were ultrasonically dispersed in deionized water, and the seed crystals were uniformly loaded onto the ceramic substrate surface by vacuum filtration. The seed-loaded ceramic substrate was dried in an oven at 80 °C for 15 min, and then activated at 120 °C for 2 h to obtain ZIF-8-0.10@Al₂O₃.

[0026] (3) Pressure-induced reverse diffusion self-healing secondary growth Zinc nitrate hexahydrate (1.0 g, 3.36 mmol) and 2-methylimidazole (1.1 g, 13.4 mmol) were dissolved in 50 mL of deionized water to prepare precursor solutions A and B, respectively. The ZIF-8-0.10@Al2O3 membrane was placed in a self-made pressurized reverse diffusion apparatus, with zinc nitrate solution on side A and 2-methylimidazole solution on side B. A pressure difference of 0.2 MPa was applied by purging nitrogen gas, causing the precursor solutions to diffuse to the opposite side. The reaction was carried out at 70 °C for 2 h. After the reaction, the composite membrane was removed, washed with deionized water and methanol, and dried under vacuum at 60 °C to obtain PCD-ZIF-8@Al2O3.

[0027] (4) In-situ repair of glass melt infiltration defects mediated by coordination polymers The PCD-ZIF-8@Al2O3 membrane was placed in a quartz tube containing [Zn(HPO4)(H2PO4)2]·2HIm glass powder (glass powder to membrane mass ratio 3:1), and the tube was vacuum sealed. The temperature was increased to 250℃ at 5℃ / min and held for 30min to allow the molten glass to permeate the membrane. The membrane was then naturally cooled to room temperature under argon protection to obtain GUM-ZIF-8@Al2O3.

[0028] (5) Construction of hydroxyl-bridged self-supporting MOF ceramic membranes The GUM-ZIF-8@Al2O3 membrane was immersed in 0.5M NaOH alkaline solution and etched at 70℃ for 2 h. After removal, it was dried at 80℃ and placed in a high-pressure mold for densification at room temperature under a pressure of 50MPa to obtain the OHB-MOF-ceramic-1 self-supporting membrane.

[0029] Example 2

[0030] (1) Preparation of ZIF-8-0.03 seed crystals with defect engineering Zinc nitrate hexahydrate (2.0 g, 6.7 mmol) and 2-methylimidazole (1.9 g, 23.2 mmol) were dissolved in 50 mL of DMF. 0.05 mL of pyridine (approximately 0.696 mmol, pyridine / 2-methylimidazole molar ratio 0.03) was added. After complete sonication and dissolution, the solution was transferred to a high-pressure reactor and reacted at 120 °C for 24 h. After the reaction, the solid product was collected by centrifugation, washed three times each with DMF and methanol, and dried under vacuum at 60 °C to obtain ZIF-8-0.03 seed crystals with low defect density.

[0031] (2) Seed seeding for defect activation A porous α-Al₂O₃ ceramic substrate (average pore size 0.1-1 μm) was ultrasonically cleaned sequentially with deionized water and anhydrous ethanol for 15 min each, and then dried at 60 °C for later use. The prepared ZIF-8-0.03 seed crystals were ultrasonically dispersed in deionized water to prepare a 0.2% (w / w) uniform seed crystal dispersion. The seed crystals were then uniformly loaded onto the ceramic substrate surface using a dip-coating method. The seed-loaded substrate was dried in a 60 °C oven for 20 min, followed by activation at 120 °C for 4 h to fully activate the defect sites on the seed crystal surface, yielding ZIF-8-0.03@Al₂O₃.

[0032] (3) Pressure-induced reverse diffusion self-healing secondary growth Precursor solution A was prepared by dissolving zinc nitrate hexahydrate in deionized water at a mass ratio of 1:50, and precursor solution B was prepared by dissolving 2-methylimidazolium in deionized water at a mass ratio of 1.1:50. A ZIF-8-0.03@Al2O3 substrate was placed in a pressurized reverse diffusion reactor, with precursor solution A and precursor solution B placed on opposite sides of the membrane, respectively. A nitrogen gas pressure difference of 0.05 MPa was applied, and the reaction temperature was controlled at 50°C for 4 hours. The precursors diffused bidirectionally due to the pressure difference, resulting in in-situ crystallization at the seed defects. After the reaction was complete, the composite membrane was removed, washed sequentially with deionized water and methanol, and then vacuum dried at 60°C to obtain the PCD-ZIF-8@Al2O3 secondary growth membrane.

[0033] (4) In-situ repair of glass melt infiltration defects mediated by coordination polymers The PCD-ZIF-8@Al2O3 film prepared above was mixed with [Zn(HPO4)(H2PO4)2]·2HIm coordination polymer glass powder at a mass ratio of 2:1 and loaded into a quartz tube, which was then vacuum sealed. The quartz tube was placed in a tube furnace and heated to a melting temperature of 200℃ at a heating rate of 2℃ / min, and then subjected to constant-temperature impregnation for 60 min to ensure that the molten glass fully wetted the intergranular defects of the film. After the impregnation was completed, the film was naturally cooled to room temperature under an argon protective atmosphere to obtain the GUM-ZIF-8@Al2O3 glass-modified composite film.

[0034] (5) Construction of hydroxyl-bridged self-supporting MOF ceramic membranes A 0.1 mol / L sodium hydroxide alkaline solution was prepared, and the GUM-ZIF-8@Al2O3 film was completely immersed in the alkaline solution. Etching was performed at 50°C for 4 hours to induce gradient intracrystalline defects in the film. After etching, the film material was removed, thoroughly dried and activated at 60°C, transferred to a high-pressure mold, and cold-pressed under 20 MPa unidirectional pressure at room temperature for densification, ultimately yielding a high-performance self-supporting OHB-MOF-ceramic-2 ceramic film.

[0035] Example 3

[0036] (1) Preparation of ZIF-8-0.15 seed crystals for defect engineering Zinc nitrate hexahydrate (2.0 g, 6.72 mmol) and 2-methylimidazole (1.9 g, 23.2 mmol) were added to 50 mL of DMF solvent at a fixed molar ratio of 1:3.45. 0.28 mL of pyridine (approximately 3.48 mmol, pyridine / 2-methylimidazole molar ratio 0.15) was added, and the mixture was sonicated until homogeneous. The mixture was then transferred to a high-pressure reactor and reacted at 120 °C for 24 h. After the reaction, the product was separated by centrifugation, washed three times each with DMF and methanol, and dried under vacuum at 60 °C to obtain high defect density ZIF-8-0.15 seed crystals.

[0037] (2) Seed seeding for defect activation A porous α-Al₂O₃ ceramic substrate (average pore size 0.1-1 μm) was ultrasonically cleaned alternately with deionized water and ethanol, and then dried at 60 °C for later use. ZIF-8-0.15 seed crystals were ultrasonically dispersed in deionized water to prepare a 1.0% (w / w) seed dispersion, which was then uniformly loaded onto the substrate surface using vacuum filtration. The seed-loaded substrate was dried in a 70 °C oven for 10 min, and then activated at 120 °C for 1 h to obtain a highly active defect seed-loaded substrate, ZIF-8-0.15@Al₂O₃.

[0038] (3) Pressure-induced reverse diffusion self-healing secondary growth Zinc nitrate hexahydrate aqueous solution (mass ratio 1:50) and 2-methylimidazole aqueous solution (mass ratio 1.1:50) were prepared in proportions to serve as precursor solutions A and B, respectively. A seeded ceramic substrate was fixed in a pressurized reverse diffusion reactor. Solutions A and B were placed on opposite sides of the membrane, respectively. Inert nitrogen gas was introduced to apply a pressure difference of 0.5 MPa. The reaction temperature was controlled at 90 °C and the reaction time at 0.5 h to complete the in-situ repair and growth of intergranular defects in the membrane. After the reaction, the composite membrane was removed, washed with deionized water and methanol, and then vacuum dried at 60 °C to obtain the PCD-ZIF-8@Al2O3 composite membrane.

[0039] (4) In-situ repair of glass melt infiltration defects mediated by coordination polymers PCD-ZIF-8@Al2O3 membrane and [Zn(HPO4)(H2PO4)2]·2HIm glass powder were loaded into a quartz tube at a mass ratio of 5:1 and the tube was vacuum sealed. The temperature was raised to 200℃ in a tube furnace at a heating rate of 10℃ / min, and the membrane was melted and impregnated at a constant temperature for 10 min. The membrane was then naturally cooled to room temperature under argon protection to obtain a densified GUM-ZIF-8@Al2O3 composite membrane.

[0040] (5) Construction of hydroxyl-bridged self-supporting MOF ceramic membranes A 1.0 mol / L sodium hydroxide alkaline solution was prepared, and the glass-modified composite film was immersed in the alkaline solution and etched at 90℃ for 0.5 h to precisely control the defect structure of the film layer. After etching, the film was dried and activated at 120℃, and then placed in a high-pressure mold. Under gentle heating conditions, a unidirectional pressure of 100 MPa was applied for hot pressing densification, and a stable film structure was constructed through metal-hydroxyl-metal bridging bonds, finally obtaining a high-strength self-supporting OHB-MOF-ceramic-3 ceramic film.

[0041] Comparative Example 1 Step (4) of coordination polymer glass melt impregnation treatment is omitted, and the remaining steps are completely consistent with those in Example 1 to obtain OHB-MOF-ceramic-4 self-supporting membrane.

[0042] Comparative Example 2 Step (1) without adding pyridine, ZIF-8-0 seed crystals (without defects) are obtained, and the rest is completely consistent with Example 1, resulting in OHB-MOF-ceramic-5 self-supporting film.

[0043] Comparative Example 3 (without self-healing technology, conventional secondary growth) Steps (1) and (2) are the same as in Example 1. Step (3) uses conventional static secondary growth (non-pressurized reverse diffusion): The ZIF-8-0.10@Al2O3 membrane is immersed in 50 mL of aqueous solution containing zinc nitrate hexahydrate (1.0 g, 3.36 mmol) and 2-methylimidazole (1.1 g, 13.4 mmol) and allowed to stand at 70 °C for 2 h. After removal, it is washed and dried. Steps (4) and (5) are omitted.

[0044] Performance testing Membrane performance testing: Tests were conducted on Examples 1, 3, and Comparative Examples 1-3. Under room temperature (25±2℃) and a transmembrane pressure difference of 0.15 MPa, the pure water flux and methylene blue rejection rate of the membrane were determined using a laboratory cross-flow filtration apparatus. The pure water flux was calculated by recording the permeate volume per unit time, using the formula J = V / (A·t), where J is the flux (L·m³). -2 ·h -1 ·bar -1 V is the permeate volume (L), and A is the effective membrane area (m²). 2 ), t is time (h), and the measured values ​​are normalized to 1 bar transmembrane pressure difference. The methylene blue rejection rate was determined using a UV-Vis spectrophotometer (UV-2600, Shimadzu) by measuring the absorbance of the feed solution (50 mg / L) and the permeate at 664 nm, according to the formula R = (1-C). p / C f ) × 100% to calculate the retention rate, where C p and C f The concentrations of the permeate and feed solution are respectively. The method for testing the flux recovery rate over 10 cycles is as follows: after each filtration run of 60 min, backwash with deionized water at 0.2 MPa for 10 min, repeat 10 times, and record the initial flux of each cycle. The recovery rate is expressed as the percentage of the initial flux of the nth cycle to the initial flux of the first cycle. All data were measured three times, the average value was taken, and the standard deviation was calculated.

[0045] The results are as follows Figure 1As shown, Example 1 uses a preferred defect seed crystal (ZIF-8-0.10) and fully executes all four processes. The intracrystalline defects are moderate, the CP glass completely seals intercrystalline leakage, and hydroxyl bridging improves compactness, thus achieving a rejection rate of 99% and a flux of 72 L·m. -2 ·h -1 ·bar -1 The recovery rate was 92%, and the overall performance was optimal. Example 2 had a low defect concentration (ZIF-8-0.03), insufficient interface activation, a rejection rate of 92%, and a flux of 78 L·m⁻¹. -2 ·h -1 ·bar -1 The recovery rate was 88%, indicating that extremely low defects can activate interfacial bonding. However, due to the initial quality of the seed layer, the optimal performance range was not reached, demonstrating a "threshold effect" in defect concentration. In Example 3, the defect concentration was too high (ZIF-8-0.15), resulting in lattice distortion. Although a complete process was performed to repair it, the rejection rate still dropped to 97%, and the flux was 65 L·m⁻¹. -2 ·h -1 ·bar -1 The recovery rate was 89%, indicating that the protective boundary can be extended to x=0.15; in Comparative Example 1, CP glass melting was omitted, the nano-leakage channels were not sealed, the rejection rate decreased to 93%, but the flux increased to 85 L·m -2 ·h -1 ·bar -1 (Defect channel contribution), with a recovery rate of only 86%, demonstrates that CP glass is key to improving selectivity and stability. Comparative Example 2 used defect-free seeds, but with poor interfacial bonding, discontinuous film layers, a rejection rate of only 85%, and a flux of 55 L·m⁻¹. -2 ·h -1 ·bar -1 The recovery rate was 76%, proving that defective seed crystals are indispensable. Comparative Example 3 used conventional secondary growth (without self-healing technology), resulting in obvious intergranular cracks, a rejection rate of 90%, and a flux of 68 L·m⁻¹. -2 ·h -1 ·bar -1 The recovery rate was 81%, indicating that without subsequent graded self-repair and self-supporting processes, it is difficult to obtain high-performance films with only defective seed crystals.

[0046] Self-repair performance test In Example 1, straight scratches (penetrating the membrane layer) with a width of approximately 0.8-1.0 μm were artificially created on the membrane surface using a micromanipulator. The damaged membrane was then placed in a tube furnace and heated to 250 °C at a rate of 5 °C / min under nitrogen protection, and held at this temperature for different times (0, 10, 20, 30, 45, 60 min). Immediately after removal, its rejection rate for 50 mg / L methylene blue solution was tested under a transmembrane pressure difference of 0.15 MPa. The rejection rate of the undamaged Example 1 membrane (99%) was used as a control.

[0047] The results are as follows Figure 2 As shown, after an artificially created through-scratch of approximately 1 μm width was applied to the membrane of Example 1, the methylene blue retention rate plummeted from 99% to 61% compared to the undamaged state. After heat treatment at 250°C, the retention rate recovered rapidly at first, then slowly, increasing to 84%, 93%, and 97% at 10, 20, and 30 minutes, respectively, and fully recovering to 99% after 60 minutes, matching the level of the undamaged membrane. In stark contrast, the retention rate of Comparative Example 1 (CP-free glass) only recovered to 86% after the same heat treatment, demonstrating that the melt infiltration of the coordination polymer glass is crucial for achieving defect sealing and self-healing. This result fully validates the excellent in-situ self-healing capability of the membrane of this invention.

Claims

1. A method for preparing a self-supporting MOF ceramic membrane with self-healing function, characterized in that, Includes the following steps: Preparation of defect-engineered MOF seed crystals: Zinc nitrate hexahydrate and 2-methylimidazole were added to DMF, and then pyridine was added to control crystal plane defects. The molar ratio of pyridine to 2-methylimidazole was x, where 0 < x ≤ 0.

15. After dissolution, the mixture was transferred to a reactor for reaction. After the reaction was completed, the product was collected by centrifugation, washed with DMF and methanol respectively, and then dried under vacuum to obtain defect-type seed crystals, denoted as ZIF-8-x. Defect-activated seeding: The ceramic substrate was ultrasonically cleaned with deionized water and ethanol in sequence, and then dried for later use. The ZIF-8-x seed crystals from step (1) were dispersed in deionized water to prepare a seed dispersion with a mass fraction of 0.2-1.0%. The ZIF-8-x seed crystals were uniformly loaded onto the surface of the ceramic substrate by vacuum filtration or dip-coating method. After drying at 60-80℃ for 10-20 min, the substrate was activated at 120℃ for 1-4 h to obtain a defect-loaded seed substrate, denoted as ZIF-8-x@Al2O3. Pressure-assisted reverse diffusion self-healing secondary growth: Precursor solution A and precursor solution B were prepared respectively; wherein solution A was an aqueous solution of zinc nitrate hexahydrate and solution B was an aqueous solution of 2-methylimidazole; the ceramic substrate ZIF-8-x@Al2O3 with seed crystals obtained in step (2) was fixed in the dead-end filter membrane pool, and the membrane pool was divided into an upper chamber and a lower chamber by a sealing ring. Precursor solution A was injected into the upper chamber and precursor solution B was injected into the lower chamber. High-purity nitrogen gas was introduced through independent gas inlets on both sides of the membrane pool to apply a transmembrane pressure difference, and the pressure difference was controlled to be 0.05-0.5 MPa. The reaction temperature was 50-90℃ and the time was 0.5-4h. After the reaction was completed, the composite membrane was taken out, washed with deionized water and methanol, and then vacuum dried at 60℃ to obtain a pressure-assisted reverse diffusion secondary growth membrane, denoted as PCD-ZIF-8@Al2O3; In-situ repair of defects mediated by melt infiltration of coordination polymer glass: Mix coordination polymer glass powder with PCD-ZIF-8@Al2O3 film from step (3) and place in a quartz tube, then seal the tube under vacuum; heat the tube furnace to the melting temperature of coordination polymer glass at 2-10℃ / min, and perform melt infiltration treatment for 10-60min; cool naturally to room temperature under argon protection to obtain a glass-modified composite film, denoted as GUM-ZIF-8@Al2O3; Construction of hydroxyl-bridged self-supporting MOF ceramic membrane: The GUM-ZIF-8@Al2O3 membrane prepared in step (4) was immersed in an alkaline solution and etched at 50-90℃ for 0.5-4h. After etching, the membrane was dried and activated at 60-120℃, transferred to a high-pressure mold, and densified by applying unidirectional pressure of 20-100MPa at room temperature or under heating conditions to obtain a hydroxyl-bridged self-supporting MOF ceramic membrane, denoted as OHB-MOF-ceramic.

2. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, The reaction temperature in step (1) is 120°C and the time is 24h; the washing is performed 3 times each with DMF and methanol and the drying temperature is 60°C.

3. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, In step (1), the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:3.

45.

4. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, The pressure difference in step (3) is 0.05-0.5 MPa.

5. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, In step (3), the mass ratio of zinc nitrate hexahydrate to deionized water is 1:

50.

6. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, The mass ratio of 2-methylimidazole to deionized water in step (3) is 1.1:

50.

7. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, The mass ratio of the glass powder to the PCD-ZIF-8@Al2O3 film in step (4) is (2-5):

1.

8. The method for preparing a self-supporting MOF ceramic membrane with self-healing function according to claim 1, characterized in that, The alkaline solution in step (5) is a sodium hydroxide solution with a concentration of 0.1-1.0 mol / L.

9. A self-supporting MOF ceramic membrane with self-healing function is prepared by the preparation method according to any one of claims 1-8.

10. The self-supporting MOF ceramic membrane with self-healing function as described in claim 9 can be used in the field of water treatment.

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