An Axially Asymmetric MOF Ceramic Catalytic Material, Its Preparation Method and Application

Abstract

This invention discloses an axially asymmetric MOF ceramic catalytic material, its preparation method, and its applications. The catalytic material includes a porous ceramic tube and a catalytically active layer supported on the inner and outer surfaces of the porous ceramic tube. Along the axial direction of the porous ceramic tube, the catalytically active layer has an asymmetric structure. This invention prepares an axially asymmetric MOF ceramic catalytic material by synergistically constructing a catalytic activity gradient distribution along the axial direction of the porous ceramic tube through matrix pretreatment, in-situ MOF growth, and axial gradient calcination. This asymmetric structure can form differentiated electronic environments and metal coordination states in different sections, achieving synergistic generation of free radical and non-free radical pathways. This overcomes the limitation of a single active site in homogeneous catalytic membranes, thereby significantly improving the degradation efficiency and mineralization degree of various recalcitrant pollutants such as benzene compounds, phenols, nitrogen-containing heterocycles, and organic amines.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment catalytic materials technology, and in particular to an axially asymmetric MOF ceramic catalytic material, its preparation method, and its application. Background Technology

[0002] Coal chemical industry is an important component of modern energy and chemical engineering, but its production process generates large amounts of high-concentration, complex wastewater. This type of wastewater typically contains benzene compounds, phenols, nitrogen-containing heterocycles, organic amines, and various recalcitrant organic compounds. It may also accumulate inorganic pollutants such as cyanide and sulfur, exhibiting high chemical oxygen demand (COD), high total organic carbon (TOC), deep color, and poor biodegradability. Due to the stable molecular structure and strong antioxidant capacity of these pollutants, conventional biological treatment or physicochemical methods are insufficient for effective degradation. Advanced oxidation processes (AOPs), as a highly efficient water treatment method, generate reactive oxygen species (ROS) such as hydroxyl radicals (•OH) and sulfate radicals (SO4•-). - Singlet oxygen () 1 Catalytic radicals, such as O2, utilize strong oxidizing properties to achieve ring-opening and chain scission of recalcitrant organic compounds, gradually becoming a research hotspot in the treatment of recalcitrant wastewater. How to fully regulate the distribution of active sites and electron transfer pathways during the catalytic process to efficiently and sustainably generate various free radicals is the main technical challenge facing this field.

[0003] In recent years, ceramic catalytic materials have been widely used in advanced oxidation systems due to their excellent mechanical stability and chemical inertness. For example, patent document CN115608403A discloses a nitrogen-doped metal-based carbon-based composite ceramic catalytic membrane. This technology uses a two-step in-situ growth-calcination process to load a metal-organic framework (MOF)-derived nitrogen-doped carbon-based catalyst onto the surface and interior of a ceramic substrate membrane. The aim is to activate persulfate (PMS) to generate a high proportion of singlet oxygen to address high-salt wastewater environments. Its advantages include a singlet oxygen molar ratio of over 80%, selective degradation capability for electron-rich pollutants, and enhanced catalyst stability through confined growth.

[0004] However, existing technologies still have the following shortcomings: While the uniform loading strategy of the catalytic membrane results in a uniform distribution of catalyst nanoparticles on the ceramic substrate, leading to efficient singlet oxygen generation, it lacks a synergistic mechanism between free radical and non-free radical pathways. For example, its ROS generation is primarily singlet oxygen, resulting in insufficient synergistic degradation of diverse pollutants in coal chemical wastewater (such as the coexistence of benzene series compounds and phenols), leading to the accumulation of intermediate products and limited mineralization efficiency. Insufficient mass transfer motive force: the uniform structure cannot form a chemical potential gradient, and pollutants and oxidants rely on passive diffusion, resulting in a significant boundary layer effect. Especially when treating high-concentration wastewater, membrane flux is prone to decline, and catalytic performance decreases after long-term operation, exhibiting weak anti-fouling ability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to overcome the bottlenecks of existing homogeneous catalytic materials in the synergistic degradation of multiple pollutants, mass transfer optimization, and long-term stability, and to provide a more efficient solution for advanced oxidation water treatment.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an axially asymmetric MOF ceramic catalytic material, comprising the following steps: S1. Matrix pretreatment: The porous ceramic tube is surface modified by introducing amino or hydroxyl functional groups on its inner and outer surfaces. S2. In-situ growth of metal-organic frameworks: The pretreated porous ceramic tube is immersed in a metal-organic framework precursor solution, and a metal-organic framework layer is formed on the substrate surface through in-situ reaction. S3. Axial gradient calcination: The porous ceramic tube loaded with the metal-organic framework layer is divided into a first section and a second section along the axial direction. The first section and the second section are calcined at different temperatures to form a catalytic active layer with an axially asymmetric structure.

[0007] This invention prepares axially asymmetric MOF ceramic catalytic materials. Through the synergistic effect of matrix pretreatment, in-situ MOF growth, and axial gradient calcination, a catalytic activity gradient distribution is constructed axially within a porous ceramic tube. This asymmetric structure enables the formation of differentiated electronic environments and metal coordination states in different sections, facilitating free radical pathways (such as •OH, SO4•). - ) and non-radical pathways (such as 1 The synergistic generation of O2 breaks through the limitation of a single active site in homogeneous catalytic membranes, thereby significantly improving the degradation efficiency and mineralization degree of various recalcitrant pollutants such as benzene series compounds, phenols, nitrogen-containing heterocycles and organic amines.

[0008] In some preferred or optional embodiments, the calcination temperature of the first section is 600-700℃, the calcination temperature of the second section is 300-450℃, and the difference between the calcination temperatures of the first and second sections is 200-350℃. By setting differentiated calcination temperature ranges, a significant temperature gradient is formed along the axial direction of the catalytic material, causing different sections to undergo different degrees of thermal conversion. The high-temperature region promotes the deep carbonization of the metal-organic framework material and the high-valence state conversion of metal sites, while the low-temperature region retains more organic ligand structures and functional groups, thereby constructing complementary catalytic active centers within the material and enhancing the synergistic degradation ability of multiple pollutants.

[0009] In some preferred or optional embodiments, the length ratio of the first section and the second section along the axial direction of the porous ceramic tube is 1:4 to 4:1. By adjusting the length ratio of different temperature sections, the mass transfer path and reaction residence time of pollutants in the catalytic material are optimized. An appropriate section ratio can balance the two processes of rapid oxidation and deep mineralization, ensuring that large molecular pollutants are effectively broken down in the inlet region and intermediate products are fully degraded in the outlet region, thereby improving the overall treatment efficiency.

[0010] In some preferred or optional embodiments, in step S3, the calcination time is 2-4 hours, and the calcination atmosphere is air or an inert gas. Controlling the calcination time ensures that the metal-organic framework material can be fully converted into a stable catalytically active phase, while avoiding the loss of specific surface area due to over-sintering.

[0011] In some preferred or optional embodiments, step S1 specifically includes: immersing the porous ceramic tube in a 1-5 vol% 3-aminopropyltriethoxysilane ethanol solution or a 0.5-2 mol / L hydrochloric acid aqueous solution, treating it at 50-70°C for 0.5-2 hours, and then rinsing it with ethanol and deionized water and drying it. Through specific surface modification treatment, active functional groups are introduced onto the surface of the ceramic matrix, providing effective anchoring points for the subsequent in-situ growth of metal-organic framework materials; this treatment enhances the bonding force between the catalyst layer and the matrix, prevents the loss of catalytic components during use, and improves the stability of the material.

[0012] In some preferred or optional embodiments, in step S2, the metal-organic framework precursor is selected from one or more of the ZIF series, MIL series, CPL series, PCN series, and HKUST series. The metal-organic framework precursor solution includes a metal salt and an organic ligand, wherein the organic ligand is selected from one or more of 2-methylimidazole, terephthalic acid, pyrazine, polycarboxylic acid ligands, and trimesic acid, and the molar ratio of the metal salt to the organic ligand is 1:1 to 1:10. By selecting a specific type of metal-organic framework precursor and controlling its composition ratio, the pore structure, active site types, and distribution of the derived catalytic material can be tuned; this design enables the material to adapt to pollutants with different characteristics, achieving efficient removal of a variety of recalcitrant organic compounds.

[0013] In some preferred or optional embodiments, in step S2, the in-situ reaction temperature is 25-200°C, and the reaction time is 1-72 hours. Optimizing the reaction conditions for in-situ growth ensures that the metal-organic framework crystals can grow uniformly and densely on the substrate surface, forming a continuous catalytic layer.

[0014] A second aspect of the present invention provides an axially asymmetric MOF ceramic catalytic material prepared by the above preparation method, comprising a porous ceramic tube and a catalytic active layer supported on the inner and outer surfaces of the porous ceramic tube, wherein the catalytic active layer has an asymmetric structure along the axial direction of the porous ceramic tube.

[0015] The present invention provides a catalytic material with an axially asymmetric structure. Its unique gradient design enables the material to exhibit differentiated catalytic properties in different sections, and can simultaneously initiate multiple degradation pathways, thus solving the problem of insufficient efficiency of homogeneous catalytic materials in treating complex wastewater.

[0016] In some preferred or optional embodiments, the porous ceramic tube is made of alumina and / or zirconium oxide, with a pore size of 0.1-1 μm and a length of 15-100 cm, and the thickness of the catalytic active layer is 5-50 μm. By limiting the physical parameters of the matrix material, the catalytic material is ensured to possess good mechanical strength, suitable mass transfer channels, and sufficient active site loading.

[0017] The third aspect of this invention provides the application of the aforementioned axial asymmetric MOF ceramic catalytic material for advanced oxidation treatment of industrial wastewater. Applying the asymmetric catalytic material of this invention to advanced oxidation treatment of industrial wastewater fully leverages its advantages in multi-mechanism synergistic degradation, exhibiting particularly excellent adaptability in treating complex, high-salinity, and recalcitrant wastewater. This provides a reliable technical solution for the deep treatment of industrial wastewater from coal chemical, petrochemical, pharmaceutical, and dyeing industries.

[0018] In summary, compared with the prior art, the present invention has the following beneficial effects: (1) Synergistic effect of multiple mechanisms significantly improves degradation efficiency: Through axial partition design, the synergistic effect of free radical pathway and non-free radical pathway is integrated in the same catalytic layer. The strong oxidizing free radicals generated in the first section rapidly attack and break the stable structure of macromolecular pollutants (such as benzene series and phenols). The second section selectively degrades intermediate products such as nitrogen-containing heterocycles and organic amines through non-free radical pathway, forming a multi-level oxidative degradation chain, realizing comprehensive deep oxidation of complex pollutant system, and improving COD and TOC removal rates simultaneously.

[0019] (2) Enhanced mass transfer dynamics and excellent anti-fouling ability: The chemical potential difference formed by the axial catalytic activity gradient spontaneously drives pollutant molecules and oxidants to migrate directionally from the high-activity region to the low-activity region, effectively weakening the boundary layer effect and improving mass transfer efficiency; the multi-stage oxidation process avoids the local enrichment of intermediate products, significantly reducing the risk of membrane surface blockage and pollution, and ensuring the stability and processing efficiency of the system in the long term.

[0020] (3) Stable active sites and long service life: MOF is grown in situ on the ceramic tube substrate through chemical bonding and is transformed into a firmly bonded composite catalyst layer through gradient calcination, which effectively prevents the dissolution and loss of active metal components under harsh reaction conditions; the catalyst material exhibits excellent mechanical strength and chemical stability in continuous flow operation, and its service life is significantly extended.

[0021] (4) The function is adjustable and the application is flexible: By adjusting parameters such as MOF type, partition ratio and calcination temperature, the oxidation characteristics of the catalytic material can be precisely adjusted, so that it can be customized and optimized for specific wastewater quality in coal chemical, petrochemical, printing and dyeing industries, showing strong engineering application potential. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the catalytic active layer in the catalytic material of Example 1 of the present invention.

[0023] Figure 2 This is a diagram showing the experimental results of the catalytic material degrading phenol in Example 5 of the present invention.

[0024] Figure 3 This is a diagram showing the experimental results of the catalytic material degrading pyridine in Example 6 of the present invention.

[0025] Figure 4 The figure shows the experimental results of the catalytic material in Comparative Example 2 of this invention degrading phenol.

[0026] Figure 5 The figure shows the experimental results of phenol degradation by ceramic tube in Comparative Example 3 of this invention. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0030] The present invention provides an axially asymmetric MOF ceramic catalytic material and its preparation and application method. The preparation method consists of three steps: matrix pretreatment, in-situ MOF growth, and axial gradient calcination. The specific steps are as follows: We provide porous ceramic tube substrates, MOF precursor solutions, and calcination equipment. The porous ceramic tubes can be made of alumina, zirconium oxide, or a mixture of both, with pore sizes ranging from 0.1-1 μm, wall thicknesses from 0.5-5 mm, and lengths from 15-100 cm to suit the needs of reactors of different sizes. The MOF precursors are selected from one or more of the ZIF, MIL, CPL, PCN, and HKUST series. The calcination equipment must have independent temperature control for multiple zones, such as a zoned tube furnace.

[0031] In the matrix pretreatment step, the ceramic tube is immersed in a 1-5 vol% 3-aminopropyltriethoxysilane ethanol solution or a 0.5-2 M hydrochloric acid aqueous solution and treated at 50-70°C for 0.5-2 hours. After treatment, it is rinsed with ethanol and deionized water and dried. This step introduces amino or hydroxyl functional groups on the surface of the ceramic tube, providing anchoring sites for in-situ MOF growth.

[0032] In the MOF in-situ growth step, precursor solutions containing metal salts and organic ligands are prepared separately. The metal salts are selected from one or more of cobalt, iron, and copper salts, and the organic ligands are selected from one or more of 2-methylimidazole, terephthalic acid, pyrazine, polycarboxylic acid ligands, and trimesic acid. The molar ratio of metal salt to organic ligand is controlled at 1:1 to 1:10, and the reaction solvent is one or more of methanol, ethanol, and N,N-dimethylformamide. The pretreated ceramic tube is immersed in the precursor solution and reacted at 25-200℃ for 1-72 hours to allow MOF crystals to grow uniformly on the substrate surface.

[0033] In the axial gradient calcination step, the MOF-loaded ceramic tube is placed in a multi-zone tube furnace, dividing the furnace into a first section and a second section along the axial direction. The calcination temperature of the first section is set at 600-700℃, and that of the second section at 300-450℃, with a temperature difference of 200-350℃ between the two sections. The calcination time is 2-4 hours, and the atmosphere is air or an inert gas. The length ratio of the first to the second section is controlled within the range of 20:80 to 80:20, preferably 30:70 to 70:30. During the calcination process, refractory fiber cotton is used to insulate the junctions of the sections to reduce heat conduction interference.

[0034] The above method constructs an asymmetric structure through axial gradient calcination, overcoming the bottlenecks of traditional technology: in the pretreatment step, the introduction of surface functional groups ensures that the MOF crystal is firmly bonded to the matrix; in the in-situ growth step, the concentration of precursors and reaction conditions are controlled to form a dense catalytic layer; in the gradient calcination step, differentiated temperature treatment causes the MOF to undergo different degrees of thermal transformation, with fully carbonized high-valence metal sites forming in the high-temperature region and more coordination functional groups retained in the low-temperature region, ultimately obtaining an asymmetric structure with a gradient of catalytic functions.

[0035] The axially asymmetric MOF ceramic catalytic material prepared by the above method comprises a porous ceramic tube matrix and a catalytic active layer supported on its inner surface, with a thickness of 5-50 μm. Along the axial direction, the catalytic active layer exhibits an asymmetric structural feature, forming a catalytic activity distribution through axial gradient design. The first segment dominates the radical generation pathway, rapidly attacking large molecular pollutants; the second segment dominates the non-radical pathway, selectively degrading intermediate products. In this synergistic catalytic system design, the asymmetric structure not only provides differentiated active sites but also enhances mass transfer kinetics through chemical potential gradients.

[0036] The above-mentioned axially asymmetric MOF ceramic catalyst was applied to the advanced oxidation treatment of industrial wastewater. The specific operation is as follows: A continuous flow reactor was provided, and the catalyst was installed inside the reactor, connected to the inlet and outlet water systems. Recalcitrant industrial wastewater was introduced into the reactor, and an oxidant such as persulfate was added at the inlet. The wastewater flowed through a porous ceramic tube at a certain velocity, contacting the active sites on the surface of the catalyst active layer to undergo a catalytic oxidation reaction.

[0037] In specific embodiments, the wastewater types include coal chemical wastewater, petrochemical wastewater, pharmaceutical wastewater, or dyeing and printing wastewater, and the target pollutants include benzene compounds, phenols, nitrogen-containing heterocyclic compounds, and organic amines. The oxidant dosage is controlled at 0.5-2.0 mmol / L, the hydraulic retention time is 10-60 minutes, and the operating temperature is room temperature, without the need for additional heating.

[0038] In some embodiments, by adjusting parameters such as MOF type, partition ratio, and calcination temperature, the characteristics of the catalytic active layer can be customized for specific wastewater qualities. For example, ZIF-67 derived catalytic active layer is preferred when treating phenol-containing wastewater, and CPL-1 derived catalytic active layer is preferred when treating nitrogen-containing heterocyclic wastewater.

[0039] The application of axially asymmetric catalytic materials in advanced oxidation wastewater treatment offers significant advantages over traditional homogeneous catalytic membranes: the chemical potential gradient formed by the asymmetric structure spontaneously drives the directional migration of pollutants, enhancing mass transfer efficiency; the multi-stage oxidation pathway avoids the accumulation of intermediate products, reducing the risk of membrane fouling; and the MOF-derived layer firmly bonds to the substrate, preventing the loss of active components. This catalytic material exhibits excellent stability in continuous flow operation and is suitable for the advanced treatment and reuse of high-salt, high-concentration, and recalcitrant industrial wastewater.

[0040] The technical effects of the present invention will be described below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the embodiments of this application were all purchased through commercial channels.

[0041] Example 1 In this embodiment, a Co-based asymmetric MOF ceramic catalytic material was constructed using ZIF-67 as a precursor. The specific preparation process is as follows: Matrix pretreatment: A porous Al2O3 ceramic tube with a pore size of 0.5 μm and a length of 20 cm was ultrasonically cleaned with deionized water and ethanol for 30 minutes in sequence to remove surface impurities, and then dried in an oven at 60℃. The cleaned ceramic tube was then immersed in a 3 vol% 3-aminopropyltriethoxysilane (APTES) ethanol solution and treated in a constant temperature water bath at 60℃ for 1 hour to introduce amino functional groups.

[0042] In-situ MOF growth: ZIF-67 precursor solutions were prepared. Solution A was a 0.2 mol / L Co(NO3)2·6H2O methanol solution, and solution B was a 0.8 mol / L 2-methylimidazolium methanol solution. Solutions A and B were mixed at a molar ratio of metal salt to organic ligand of 1:4. The pretreated ceramic tube was completely immersed in the mixture and reacted at a constant temperature of 30℃ for 12 hours to allow ZIF-67 crystals to uniformly nucleate and grow on the ceramic substrate surface. After the reaction, the tube was washed three times with methanol to remove unreacted precursors and dried at 60℃ to obtain a ZIF-67-loaded ceramic tube. The thickness of the MOF layer formed in this step was approximately 20-30 μm.

[0043] Axial gradient calcination: The ZIF-67-loaded ceramic tube was horizontally placed in a dual-temperature zone tube furnace, and asymmetric calcination zones were defined along the axial direction. The first zone, approximately 1 / 3 of the total length, was located near the inlet end; the second zone, approximately 2 / 3 of the total length, was located near the outlet end. The calcination temperature for the first zone was set at 650℃, and the calcination temperature for the second zone was set at 400℃. Calcination was carried out under a nitrogen atmosphere for 3 hours. During the calcination process, the ZIF-67 in the first zone was fully carbonized into Co3O4 nanoparticles encapsulated by nitrogen-doped carbon material, generating high-valence Co. 3+ The dominant free radical active site; the second segment partially retains the coordination structure of ZIF-67, forming an enriched Co. 2+The non-radical active centers are used to obtain an asymmetric catalytic active layer with an axial catalytic gradient distribution. The microstructures of the first and second segments are as follows: Figure 1 As shown in (a) and (b).

[0044] Example 2 In this embodiment, Fe-based asymmetric MOF ceramic catalytic materials were constructed using MIL-53(Fe) as a precursor. The specific preparation process is as follows: Matrix pretreatment: Take the same porous Al2O3 ceramic tube as in Example 1 and perform the same pretreatment steps to introduce amino functional groups.

[0045] In-situ MOF growth: A MIL-53(Fe) precursor solution was prepared. Solution A was a 0.05 mol / L FeCl3·6H2O N,N-dimethylformamide (DMF) solution, and solution B was a 0.05 mol / L terephthalic acid DMF solution. Solutions A and B were mixed at a molar ratio of metal salt to organic ligand of 1:1. The pretreated ceramic tube was completely immersed in the mixture and subjected to a solvothermal reaction at 100℃ for 24 hours to allow MIL-53(Fe) crystals to uniformly nucleate and grow on the ceramic substrate surface. After the reaction, the tube was washed three times alternately with DMF and ethanol to remove unreacted precursor. After drying at 60℃, the MIL-53(Fe)-loaded ceramic tube was obtained. The MOF layer formed in this step had a thickness of approximately 15-25 μm.

[0046] Axial gradient calcination: A ceramic tube loaded with MIL-53(Fe) was horizontally placed in a dual-temperature zone tube furnace, and asymmetric calcination zones were defined along the axial direction: the first zone, approximately half the total length, was located near the inlet; the second zone, approximately half the total length, was located near the outlet. The calcination temperature of the first zone was set at 600℃, and the calcination temperature of the second zone was set at 350℃. Calcination was carried out in air for 2 hours to obtain an asymmetric catalytic active layer with an axial catalytic gradient distribution.

[0047] Example 3 In this embodiment, a Cu-based asymmetric MOF ceramic catalyst was constructed using HKUST-1 as a precursor. The specific preparation process is as follows: Matrix pretreatment: Take the same porous Al2O3 ceramic tube as in Example 1 and perform the same pretreatment steps to introduce amino functional groups.

[0048] In-situ MOF growth: HKUST-1 precursor solutions were prepared. Solution A was a 1:1 volume ratio (0.1 mol / L Cu(NO3)2·3H2O in ethanol / water) and solution B was a 0.05 mol / L ethanol solution of trimesic acid. Solutions A and B were mixed at a molar ratio of metal salt to organic ligand of 1:2. The pretreated ceramic tube was completely immersed in the mixture and reacted at 80°C for 8 hours to allow HKUST-1 crystals to nucleate and grow uniformly on the ceramic substrate surface. After the reaction, the tube was washed three times with ethanol to remove unreacted precursors and dried at 60°C to obtain a ceramic tube loaded with HKUST-1. The thickness of the MOF layer formed in this step was approximately 10-20 μm.

[0049] Axial gradient calcination: The ceramic tube loaded with HKUST-1 was placed horizontally in a dual-temperature zone tube furnace, and asymmetric calcination zones were divided along the axial direction: the first zone, approximately 1 / 3 of the total length, was located near the inlet end; the second zone, approximately 2 / 3 of the total length, was located near the outlet end. The calcination temperature of the first zone was set at 620℃, and the calcination temperature of the second zone was set at 380℃. Under a nitrogen atmosphere, the calcination was maintained at this temperature for 4 hours to obtain an asymmetric catalytic active layer with an axial catalytic gradient distribution.

[0050] Example 4 In this embodiment, Cu-based asymmetric MOF ceramic catalytic material was constructed using CPL-1 as a precursor. The specific preparation process is as follows: Matrix pretreatment: Take the same porous Al2O3 ceramic tube as in Example 1 and perform the same pretreatment steps to introduce amino functional groups.

[0051] In-situ MOF growth: A CPL-1 precursor solution was prepared. Solution A was a 1:1 volume ratio (0.1 mol / L Cu(NO3)2·3H2O in ethanol and water), and solution B was a 1:1 mol / L ethanol solution of pyrazine-2,3-dicarboxylic acid. Solutions A and B were mixed at a 1:1 molar ratio of metal salt to organic ligand. The pretreated ceramic tube was completely immersed in the mixture and reacted at 70°C for 10 hours to allow CPL-1 crystals to nucleate and grow uniformly on the ceramic substrate surface. After the reaction, the tube was washed three times with ethanol to remove unreacted precursors and dried at 60°C to obtain a CPL-1-loaded ceramic tube. The MOF layer thickness formed in this step was approximately 15-25 μm.

[0052] Axial gradient calcination: The ceramic tube loaded with CPL-1 was placed horizontally in a dual-temperature zone tube furnace, and asymmetric calcination zones were divided along the axial direction: the section near the inlet was designated as the first section, accounting for approximately 1 / 3 of the total length; the section near the outlet was designated as the second section, accounting for approximately 2 / 3 of the total length. The calcination temperature of the first section was set at 630℃, and the calcination temperature of the second section was set at 380℃. Under a nitrogen atmosphere, the calcination was maintained at this temperature for 3 hours to obtain an asymmetric catalytic active layer with an axial catalytic gradient distribution.

[0053] Example 5 This embodiment uses the axially asymmetric MOF ceramic catalyst material prepared in Example 1 to treat phenol-containing simulated wastewater. The specific process is as follows: Target pollutant: Phenol (50 mg / L), used as a model compound for typical phenolic pollutants in coal chemical wastewater. The ZIF-67-derived asymmetric ceramic catalyst prepared in Example 1 was placed in a continuous flow reactor. Simulated wastewater (initial phenol concentration 50 mg / L, pH = 6.5) was pumped into the membrane tube at a flow rate of 10 mL / min, while persulfate (PMS) was continuously injected at the inlet to an initial concentration of 0.5 mM. The reaction was carried out at room temperature.

[0054] The processing result is as follows Figure 2 As shown, within a 30-minute hydraulic retention time, the phenol concentration in the effluent was below the detection limit, with a removal rate >99.9%. At 60 minutes, the mineralization rate of total organic carbon (TOC) reached 75%, indicating that phenol was effectively decomposed into CO2 and H2O. The asymmetric structure enabled synergistic degradation: the high-temperature inlet zone rapidly broke down the phenol molecular structure, while the low-temperature outlet zone further oxidized the intermediates generated from ring-opening (such as small-molecule carboxylic acids), thus achieving a high mineralization rate.

[0055] Example 6 This embodiment uses the axially asymmetric MOF ceramic catalyst material prepared in Example 4 to treat nitrogen-containing heterocyclic simulated wastewater. The specific process is as follows: Target pollutant: Pyridine (50 mg / L), used as a model compound for typical nitrogen-containing heterocyclic compounds in coal chemical wastewater. The CPL-1-derived asymmetric ceramic catalyst prepared in Example 4 was placed in a continuous flow reactor. Simulated wastewater (initial pyridine concentration 50 mg / L, pH = 6.5) was pumped into the membrane tube at a flow rate of 10 mL / min, while persulfate (PMS) was continuously injected at the inlet to an initial concentration of 1.0 mmol / L. The reaction was carried out at room temperature.

[0056] The processing result is as follows Figure 3As shown, the pyridine removal rate reached 98% within a 45-minute hydraulic retention time. At 120 minutes, the TOC mineralization rate reached 65%, demonstrating the membrane's efficient ability to disrupt stable heterocyclic structures. The catalytic material exhibited good stability. After five consecutive cycles (a total of 10 hours), the pyridine removal rate remained above 95%, indicating its long catalytic lifetime.

[0057] Comparative Example 1 This comparative example uses ZIF-67 as a precursor to construct a Co-based symmetric MOF ceramic catalytic material. The difference between this example and Example 1 is that the homogeneous ZIF-67-derived catalytic active layer is obtained by calcining the ZIF-67-loaded ceramic tube at a single temperature (500°C). Other steps and conditions are the same.

[0058] Comparative Example 2 The ZIF-67-derived symmetric ceramic catalytic material prepared in Comparative Example 1 was used to treat phenol-containing simulated wastewater, and the conditions and steps were the same as in Example 5.

[0059] The processing result is as follows Figure 4 As shown, the phenol removal rate was only about 85% at 30 minutes. The TOC mineralization rate was only about 50% at 60 minutes. The homogeneous catalytic active layer, due to its single active site, could not form a multi-level oxidation pathway, leading to the accumulation of intermediate products and a mineralization efficiency significantly lower than that of the asymmetric catalytic active layer in Example 1.

[0060] Comparative Example 3 The same porous Al2O3 ceramic tube as in Example 1 was used, and the same pretreatment steps were performed to introduce amino functional groups. The pretreated ceramic tube was then used to treat simulated phenol-containing wastewater, under the same conditions and steps as in Example 5.

[0061] The processing result is as follows Figure 5 As shown, the phenol removal rate was less than 5% within 60 minutes, and it was mainly due to physical adsorption. This comparison proves that the ceramic tube substrate itself has almost no catalytic activity, and the high performance of the catalytic material of this invention comes entirely from the catalytically active layer formed by in-situ growth on its surface and gradient calcination.

[0062] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A method of preparing an axially asymmetric MOF ceramic catalytic material, characterized in that, Includes the following steps: S1. Matrix pretreatment: The porous ceramic tube is surface modified by introducing amino or hydroxyl functional groups on its inner and outer surfaces. S2. In-situ growth of metal-organic frameworks: The pretreated porous ceramic tube is immersed in a metal-organic framework precursor solution, and a metal-organic framework layer is formed on the substrate surface through in-situ reaction. S3. Axial gradient calcination: The porous ceramic tube loaded with the metal-organic framework layer is divided into a first section and a second section along the axial direction. The first section and the second section are calcined at different temperatures to form a catalytic active layer with an axially asymmetric structure.

2. The production method according to claim 1, characterized by, The calcination temperature of the first section is 600-700℃, the calcination temperature of the second section is 300-450℃, and the difference between the calcination temperatures of the first section and the second section is 200-350℃.

3. The production method according to claim 1, characterized by, The length ratio of the first section and the second section along the axial direction of the porous ceramic tube is 1:4 to 4:

1.

4. The production method according to any one of claims 1 to 3, characterized by, In step S3, the calcination time is 2-4 hours, and the calcination atmosphere is air or an inert gas.

5. The preparation method according to claim 1, characterized in that, Step S1 specifically includes: immersing the porous ceramic tube in a 1-5 vol% 3-aminopropyltriethoxysilane ethanol solution or a 0.5-2 mol / L hydrochloric acid aqueous solution, treating it at 50-70°C for 0.5-2 hours, and then rinsing it with ethanol and deionized water and drying it.

6. The preparation method according to claim 1, characterized in that, In step S2, the metal-organic framework precursor is selected from one or more of the ZIF series, MIL series, CPL series, PCN series, and HKUST series. The metal-organic framework precursor solution includes a metal salt and an organic ligand. The organic ligand is selected from one or more of 2-methylimidazole, terephthalic acid, pyrazine, polycarboxylic acid ligand, and trimesic acid. The molar ratio of the metal salt to the organic ligand is 1:1 to 1:

10.

7. The preparation method according to claim 6, characterized in that, In step S2, the in-situ reaction temperature is 25-200℃ and the reaction time is 1-72 hours.

8. An axially asymmetric MOF ceramic catalytic material prepared by any one of the preparation methods described in claims 1-7, characterized in that, It includes a porous ceramic tube and a catalytic active layer supported on the inner and outer surfaces of the porous ceramic tube. Along the axial direction of the porous ceramic tube, the catalytic active layer has an asymmetric structure.

9. The axially asymmetric MOF ceramic catalytic material according to claim 8, characterized in that, The porous ceramic tube is made of alumina and / or zirconium oxide, with a pore size of 0.1-1 μm and a length of 15-100 cm. The thickness of the catalytic active layer is 5-50 μm.

10. An application characterized in that, The axially asymmetric MOF ceramic catalyst material as described in claim 8 or 9 is used for advanced oxidation treatment of industrial wastewater.

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