A ZIF-L(Co) derived Co-NC / Al2O3 catalyst, and a preparation method and application thereof

Abstract

This invention discloses a ZIF-L(Co)-derived Co-NC / Al2O3 catalyst, its preparation method, and its applications. The preparation method utilizes a self-assembly-carbonization process as its basic technology. PEI-functionalized Al2O3 is used as a support, and cobalt salt and dimethylimidazole are used as precursors to achieve in-situ growth of ZIF-L(Co) on the Al2O3 support surface. Pyrolysis then forms a highly dispersed cobalt-based active center and a nitrogen-containing carbon framework, resulting in a Co-NC / Al2O3 ternary composite structure. This invention also provides the application of the Co-NC / Al2O3 composite catalyst in activating PMS to degrade antibiotic pollutants. This invention employs an in-situ growth combined with pyrolysis derivatization preparation route, with clear process steps, mild conditions, and readily available raw materials, facilitating mass production and engineering applications. Simultaneously, it achieves highly efficient PMS activation and antibiotic pollutant degradation performance.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional material preparation and advanced oxidation water treatment technology, and relates to a ZIF-L(Co) derived Co-NC / Al2O3 catalyst, its preparation method and application. Specifically, it relates to a method for preparing a Co-NC / Al2O3 composite catalyst by using the two-dimensional layered Co-based metal-organic framework precursor ZIF-L(Co) as a template and cobalt source through in-situ loading and pyrolysis derivatization, and its application in the degradation of antibiotic pollutants by activated persulfate. Background Technology

[0002] With the increasing detection of antibiotic pollutants in industrial wastewater and surface water, traditional biological and conventional physicochemical methods face challenges in treating these pollutants, including low removal efficiency, insufficient mineralization, and weak resistance to shock loads. Based on SO4... •− Advanced oxidation technologies have attracted widespread attention in recent years due to their advantages such as fast reaction rates, strong oxidizing power, and wide applicable pH range. Among them, persulfate (PMS) is an important oxidant that can generate sulfate radicals, hydroxyl radicals, singlet oxygen, and surface electron transfer active sites under the action of a catalyst, thereby achieving efficient removal of various organic pollutants.

[0003] Co-based materials exhibit strong activation capabilities for PMS, but Co salt catalysts still suffer from limitations such as limited dispersion of active sites, susceptibility to metal agglomeration and activity decay during the reaction, high risk of Co ion leaching in some systems, and difficulties in separating and recovering powdered catalysts. Metal-organic frameworks (MOFs), due to their designable composition, tunable pore structure, and relatively uniform metal site distribution, have become important precursors for the preparation of Co-based derivatized catalysts. ZIF-L(Co) possesses a two-dimensional lamellar morphology and abundant imidazole ligand framework, which, upon pyrolysis, facilitates the formation of Co-based active centers coated with a nitrogen-carbon framework.

[0004] However, existing ZIF-derived Co-based catalysts mostly exist as independent powders, which are prone to problems such as particle agglomeration, insufficient utilization of the active phase, limited mass transfer efficiency, and separation difficulties. While in-situ growth of MOF precursors on the surface of an Al2O3 support can improve recoverability and mechanical stability, simply combining ZIF-L(Co), an Al2O3 support, in-situ growth, and pyrolysis derivatization does not necessarily guarantee a stable interfacial active structure. This is because Co... 2+ It readily undergoes homogeneous nucleation with imidazole ligands in solution to form free MOF crystals; during pyrolysis, the Co component is prone to migration, aggregation, or formation of CoOx particles; the supported layer may also block Al2O3 channels, leading to a decrease in specific surface area and pore volume.

[0005] Therefore, there is a need for a method that can preferentially confine the Co precursor to the Al2O3 support interface, induce ZIF-L(Co) heterogeneous nucleation, and form stable Co–N after pyrolysis. X A method for preparing nitrogen-containing carbon interface structures to simultaneously improve PMS activation efficiency, structural stability, and operability in engineering applications. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the problems of easy agglomeration of active components, easy blockage of support pores by the supported layer, insufficient stability of active sites, and difficulty in catalyst separation and recovery in existing Co-based PMS activated catalysts. The present invention provides a ZIF-L(Co) derived Co-NC / Al2O3 catalyst, its preparation method and application.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a ZIF-L(Co)-derived Co-NC / Al2O3 catalyst, comprising the following steps: 1) PEI surface functionalization of Al2O3 support: Weigh Al2O3 support, wash it with deionized water or anhydrous ethanol by ultrasonication, dry it and then immerse it in a polyethyleneimine (PEI) aqueous solution for surface functionalization treatment; after immersion, take out the solid, wash it with deionized water to remove unbound PEI, and dry it to obtain PEI modified Al2O3 support. 2) Co 2+ Pre-adsorption and ZIF-L(Co) in-situ growth: The support was added to a cobalt salt solution for Co growth. 2+ Pre-adsorption, utilizing the amino sites on the PEI surface to enrich Co 2+ This process enhances the heterogeneous nucleation density and adhesion strength of ZIF-L(Co) on the Al2O3 surface. After adsorption, an equal volume of dimethylimidazole solution to the cobalt salt solution is added dropwise while stirring, allowing the ZIF-L(Co) precursor to grow in situ on the Al2O3 support surface, thus constructing a ZIF-L(Co) precursor layer on the Al2O3 support surface. After completion, the mixture is filtered or centrifuged several times to remove unreacted metal salts, free ligands, and weakly adsorbed crystals. The washed solid is then dried to obtain the ZIF-L(Co) / Al2O3 precursor.

[0008] 3) Pyrolysis Derivatization: The ZIF-L(Co) / Al2O3 precursor obtained above was placed in a tube furnace and heat-treated under an inert atmosphere. During pyrolysis, the imidazole ligands in the ZIF-L(Co) precursor carbonized to form a nitrogen-containing carbon layer, and the cobalt component was converted into highly dispersed Co–N. x The active sites simultaneously form a stable interfacial coupling structure with the Al2O3 support, and after cooling, the Co-NC / Al2O3 composite catalyst is finally obtained.

[0009] In step 1), the PEI is preferably branched polyethyleneimine with a number-average molecular weight of 600-1800 Da, a concentration of 0.5-5.0 mg / mL, an impregnation temperature of 20-40℃, and an impregnation time of 2-12 h; in step 2), the cobalt salt is cobalt nitrate or cobalt acetate. 2+ Concentration of 10-200 mM, Co 2+ The molar ratio with dimethylimidazole is 1:8-1:16. Based on elemental composition, Co... 2+ The mass ratio of Al2O3 modified with PEI is 1:3-1:25; the inert atmosphere mentioned in step 3) is nitrogen, argon or a mixture thereof, the gas flow rate is 20-300 mL / min, the heat treatment temperature is 500-900 ℃, the heating rate is 1-10℃ / min, and the holding time is 0.5-5 h.

[0010] As a preferred embodiment of the present invention, the PEI in step 1) is branched polyethyleneimine with a number average molecular weight of 600-1800 Da, the mass concentration of the PEI aqueous solution is 0.5-5.0 mg / mL, the impregnation temperature is 20-40℃, and the impregnation time is 2-12 h.

[0011] As a preferred embodiment of the present invention, the Al2O3 carrier in step 1) is alumina powder, alumina microspheres, or porous alumina particles, the ultrasonic time is 10-40 min, and the drying time is 6-24 h; the mass ratio of PEI to Al2O3 carrier is 1:3-1:40, preferably 1:5-1:20.

[0012] As a preferred embodiment of the present invention, the cobalt salt in step 2) is cobalt nitrate or cobalt acetate; the Co in the cobalt salt solution... 2+ The concentration is 10-200 mM, preferably 50-100 mM; Co 2+ Pre-adsorption time is 0.5-6 h; Co 2+ The molar ratio of Co to dimethylimidazole is 1:8-1:16, preferably 1:10-1:14; based on elemental Co, Co 2+ The mass ratio of the PEI-modified Al2O3 support to the PEI-modified Al2O3 support is 1:3-1:25, preferably 1:5-1:20.

[0013] As a preferred embodiment of the present invention, in step 2), the dimethylimidazole is added at a dropping rate of 0.1-5 mL / min with a stirring rate of 0-750 rpm, and then allowed to stand or react for 1-8 h while maintaining the same stirring rate. The washing solution is at least one of deionized water, methanol, or ethanol. The drying temperature is 60-80℃, and the drying time is 6-12 h.

[0014] As a preferred embodiment of the present invention, in step 3), the heat treatment temperature is 500-700℃; the heating rate is 1-5℃ / min; the holding time is 1-5 h; and the inert gas flow rate is 50-150 mL / min.

[0015] This invention also provides a Co-NC / Al2O3 composite catalyst prepared by the above method. In the composite catalyst, the Al2O3 support surface is supported with a nitrogen-containing carbon layer formed by the pyrolysis of ZIF-L(Co), and the nitrogen-containing carbon layer contains Co–N. x The active sites, Co, N, and C, are dispersed on the surface of the Al2O3 support. The catalyst is named Co-NC / Al2O3-XY. X represents the support type: alumina powder (1), alumina microspheres (2), and porous alumina particles (3); Y represents the heat treatment temperature, 500-700℃.

[0016] This invention also provides the application of the Co-NC / Al2O3 composite catalyst in the degradation of antibiotic pollutants by activating PMS. The antibiotic pollutants are one or more of tetracycline, ofloxacin, norfloxacin, or ciprofloxacin; the pollutant concentration is 5-20 mg / L, the catalyst dosage is 0.05-0.3 g / L, the PMS concentration is 0.5-3 mM, the pH of the reaction system is 3-9, and the reaction temperature is 15-35℃.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention does not simply superimpose the ZIF-L(Co) precursor, Al2O3 support, and pyrolysis derivatization steps, but first performs surface functionalization of Al2O3 via PEI, and then performs Co... 2+ Pre-adsorption, so that Co 2+ ZIF-L(Co) is enriched at the Al2O3 interface, followed by the addition of dimethylimidazole to induce preferential heterogeneous nucleation of ZIF-L(Co) on the support surface. This sequence reduces the formation of free ZIF-L(Co) crystals in solution, improves the adhesion of the precursor layer, and enhances the interfacial dispersion of Co species.

[0018] (2) In this invention, a nitrogen-containing carbon layer and Co–Nx active sites are formed in situ from ZIF-L(Co) during pyrolysis. The nitrogen-containing carbon layer has coordination, confinement and coating effects on the Co sites, while the Al2O3 support provides mechanical support and interfacial anchoring. The two work together to inhibit Co migration and aggregation. Characterization results show that no obvious CoOx particles or CoOx lattice fringes were observed in Co-NC / Al2O3, and the elements Co, C, N, O and Al were dispersed.

[0019] (3) Conventional supported active phases may reduce the specific surface area and pore volume of porous supports. However, after in-situ growth and pyrolysis at the ZIF-L(Co) interface, the BET specific surface area of ​​Co-NC / Al2O3 in this invention is reduced from 210.21 m² of the Al2O3 support. 2 / g increased to 280.64 m 2 / g, pore volume from 0.26 cm 3 / g increased to 0.37 cm 3 / g; remains at 271.50 m after use. 2 BET specific surface area / g and 0.37 cm² 3 The / g pore volume indicates the stability of its open mesoporous structure and interfacial loading structure. This effect reflects the performance of PEI / Co. 2+ Synergistic effect between pre-adsorption-induced interfacial nucleation and pyrolysis-derived porous structure.

[0020] (4) The Co-NC / Al2O3 composite catalyst prepared in this invention can efficiently activate PMS to degrade antibiotic pollutants. In the tetracycline system, simple adsorption contributes less than 10% to the removal, and PMS self-decomposition contributes weakly. However, the Co-NC / Al2O3 / PMS system can achieve a tetracycline removal rate of 96.67% within 40 min, with an apparent rate constant of 0.085 min. −1 It can maintain good degradation performance within the pH range of 3-9. Attached Figure Description

[0021] Figure 1 Morphology study results of the catalytic material prepared in Example 1 SEM images of ZIF-L(Co) (a), ZIF-L(Co) / Al2O3 (b), ZIF-L(Co) / Al2O3 surface details (c), and Co-NC / Al2O3 (d); TEM image (e), HRTEM image (f), and EDS-mapping image (g) of Co-NC / Al2O3. (The average particle size of the Al2O3 microspheres is 2-4 mm.) Figure 2 Effects of precursor concentration (a), catalyst dosage (b), TC concentration (c), PMS dosage (d), pH (e), and temperature (f) on tetracycline degradation performance. (Except for the factors under investigation, the other conditions were fixed as follows: catalyst dosage = 0.2 g / L, persulfate = 2.0 mM, tetracycline concentration = 10 mg / L, pH = 7.0, and temperature = 25.0 ℃) Figure 3Cyclic experiment of TC degradation by Co-NC / Al2O3-1-500 (a); XRD patterns of Co-NC / Al2O3- before and after use (b); SEM image of Co-NC / Al2O3- after use (c); Co 2p spectra of Co-NC / Al2O3- before and after use (d) Figure 4 SEM images of Al2O3 without PEI modification (a), SEM images of ZIF-67 grown on Al2O3 without PEI modification (b), and SEM images of ZIF-67 free on the surface of Al2O3 (c, d).

[0022] Figure 5 The catalytic performance evaluation diagrams of the materials prepared using PEI-modified and unmodified Al2O3 as supports, respectively, are shown in Example 3. (Except for the factors under investigation, the other conditions were fixed as follows: catalyst dosage = 0.2 g / L, persulfate = 2.0 mM, tetracycline concentration = 10 mg / L, pH = 7.0, temperature = 25.0 ℃) Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. The PMS mentioned in the embodiments is persulfate.

[0024] Example 1 Al₂O₃ microspheres (2-4 mm) were weighed, ultrasonically washed with deionized water for 20 min, dried, and then added to a branched PEI aqueous solution (1 mg / mL, 800 Da), with an Al₂O₃ concentration of 10 mg / mL. The mixture was impregnated at 25 °C for 4 h, filtered, and the solid was washed 6 times with anhydrous ethanol and dried for 12 h to obtain PEI-modified Al₂O₃ microspheres. The obtained PEI-modified Al₂O₃ microspheres (29.12 g / L) were then added to a cobalt nitrate solution (50 mM) for adsorption for 2 h. Subsequently, an equal volume of dimethylimidazole solution was added dropwise at 1 mL / min with a stirring rate of 250 rpm. After this, the mixture was allowed to stand for 4 h. The microspheres were then washed 3 times with anhydrous ethanol and dried at 60 °C for 12 h to obtain the ZIF-L(Co) / Al₂O₃ microsphere precursor. The obtained ZIF-L(Co) / Al2O3 microsphere precursor was placed in a tube furnace and heated to 600℃ at 1℃ / min under a nitrogen atmosphere (100 mL / min) and held for 4 h. After cooling, the Co-NC / Al2O3 composite catalyst was finally obtained.

[0025] like Figure 1 As shown, the morphology of the prepared catalytic material was studied by SEM and TEM. The morphology of ZIF-L(Co) was... Figure 1a) It exhibits a smooth, elliptical lamellar morphology (average size 8.66 μm). The ZIF-L(Co) / Al2O3 support displays typical layered stacking. The rough surface of Al2O3 provides numerous anchoring sites for the in-situ growth of the ZIF-L(Co) precursor, which is beneficial for the uniform dispersion of the active component Co. Figure 1 bc). No obvious particle distribution or agglomeration was observed in the TEM image of Co-NC / Al2O3. Figure 1 e), and no lattice diffraction fringes belonging to CoOx were observed in the HR-TEM image. Figure 1 f) indicates that Co is anchored to the CN framework in atomic form rather than as a metal oxide. TEM-EDS mapping of Co-NC / Al2O3 ( Figure 1 The results of g) and the distribution of each element show that Al, Co, C, N and O are highly dispersed, and no obvious metal agglomeration was observed.

[0026] Example 2 Material Synthesis: Al2O3 powder was weighed, ultrasonically washed with deionized water for 10 min, dried, and then added to a branched PEI aqueous solution (1 mg / mL, 600 Da) with an Al2O3 concentration of 5 mg / mL. The mixture was impregnated at 25℃ for 4 h, filtered to remove the solid, washed 5 times with deionized water, and dried for 8 h to obtain PEI-modified Al2O3 powder. The obtained PEI-modified Al2O3 powder (14.56 g / L) was then added to a cobalt nitrate solution (50 mM) for adsorption for 1 h. Subsequently, under static conditions, an equal volume of dimethylimidazole solution (400 mM) was added dropwise at 1 mL / min, followed by standing for 3 h. The mixture was then filtered and washed 3 times with deionized water, and dried at 80℃ for 12 h to obtain the ZIF-L(Co) / Al2O3 precursor. The obtained ZIF-L(Co) / Al2O3 precursor was placed in a tube furnace and heated to 500℃ at 2℃ / min under a nitrogen atmosphere (100 mL / min) and held for 3 h. After cooling, the Co-NC / Al2O3 composite catalyst was finally obtained and named Co-NC / Al2O3-1-500.

[0027] The Co-NC / Al2O3-1-500 catalyst prepared above was used to activate PMS for tetracycline degradation. The reaction conditions were: catalyst dosage of 0.2 g / L, PMS dosage of 2 mM, tetracycline concentration of 10 mg / L, pH of 7, and temperature of 20℃. The tetracycline degradation efficiency reached 96.7% and the mineralization rate reached 45.3% within 40 min.

[0028] Example 3 Material Synthesis: Al2O3 microspheres (2-4 mm) were weighed, ultrasonically washed with deionized water for 20 min, dried, and then added to a branched PEI aqueous solution (1 mg / mL, 1000 Da) with an Al2O3 concentration of 10 mg / mL. After impregnation at 25 °C for 4 h, the solid was filtered out, washed five times with methanol, and dried for 6 h to obtain PEI-modified Al2O3 microspheres. Subsequently, the obtained PEI-modified Al2O3 microspheres (29.12 g / L) were added to a cobalt nitrate solution (50 mM) for adsorption for 2 h. Then, under static conditions, an equal volume of dimethylimidazole solution (600 mM) was added dropwise at 1 mL / min and allowed to stand for 4 h. Afterward, the microspheres were filtered and washed three times with anhydrous ethanol and dried at 60 °C for 12 h to obtain the ZIF-L(Co) / Al2O3 microsphere precursor. The obtained ZIF-L(Co) / Al2O3 microsphere precursor was placed in a tube furnace and heated to 600℃ at 1℃ / min under a nitrogen atmosphere (100 mL / min) and held for 4 h. After cooling, the Co-NC / Al2O3 composite catalyst was finally obtained and named Co-NC / Al2O3-2-600.

[0029] The Co-NC / Al2O3-2-600 catalyst prepared above was used to activate PMS for the degradation of ofloxacin. The reaction conditions were: catalyst dosage of 0.2 g / L, PMS dosage of 1 mM, ofloxacin concentration of 10 mg / L, pH of 7, and temperature of 20℃. Within 40 min, the degradation efficiency of ofloxacin reached 93.4%, and the mineralization rate reached 41.6%.

[0030] Example 4 Material Synthesis: Al2O3 microspheres (1-2 mm) were weighed and ultrasonically washed with anhydrous ethanol for 30 min each time. After drying, they were added to a branched PEI aqueous solution (1 mg / mL, 1200 Da), with an Al2O3 concentration of 15 mg / mL. After impregnation at 25℃ for 6 h, the solid was filtered out and washed 6 times with anhydrous ethanol and dried for 8 h to obtain PEI-modified Al2O3 microspheres. Subsequently, the obtained PEI-modified Al2O3 microspheres (43.65 g / L) were added to a cobalt nitrate solution (50 mM) for adsorption for 3 h. Then, a dimethylimidazole solution (800 mM) of the same volume as the cobalt nitrate solution was added dropwise at a stirring rate of 400 rpm at a stirring rate of 2 mL / min. After completion, stirring was continued at 400 rpm for 3 h. Then, the microspheres were filtered and washed 4 times with anhydrous ethanol and dried at 60℃ for 12 h to obtain the ZIF-L(Co) / Al2O3 microsphere precursor. The obtained ZIF-L(Co) / Al2O3 microsphere precursor was placed in a tube furnace and heated to 700℃ at 1℃ / min under a nitrogen atmosphere (150 mL / min) and held for 4 h. After cooling, the Co-NC / Al2O3 composite catalyst was finally obtained and named Co-NC / Al2O3-2-700.

[0031] The Co-NC / Al2O3-2-700 catalyst prepared above was used to activate PMS for the degradation of norfloxacin. The reaction conditions were: catalyst dosage of 0.2 g / L, PMS dosage of 2 mM, norfloxacin concentration of 20 mg / L, pH of 7, and temperature of 20℃. The norfloxacin degradation efficiency reached 87.2% and the mineralization rate reached 32.3% within 40 min.

[0032] Example 5 Material Synthesis: Porous alumina particles were weighed and ultrasonically washed with anhydrous ethanol and deionized water for 30 min each. After drying, they were added to a branched PEI aqueous solution (1 mg / mL, 1600 Da) with an Al2O3 concentration of 20 mg / mL. After impregnation at 25℃ for 8 h, the solid was filtered out and washed 6 times with anhydrous ethanol, then dried for 6 h to obtain PEI-modified Al2O3 microspheres. Subsequently, the obtained PEI-modified Al2O3 microspheres (54.2 g / L) were added to a cobalt nitrate solution (50 mM) for 2 h of adsorption. Then, a dimethylimidazole solution (500 mM) of the same volume as the cobalt nitrate solution was added dropwise at a stirring rate of 600 rpm at a stirring rate of 4 mL / min. After completion, stirring was continued at 600 rpm for 3 h. Subsequently, the microspheres were filtered and washed 6 times with anhydrous ethanol, and dried at 60℃ for 8 h to obtain the ZIF-L(Co) / Al2O3 porous particle precursor. The obtained ZIF-L(Co) / Al2O3 microsphere precursor was placed in a tube furnace and heated to 500℃ at 10℃ / min under a nitrogen atmosphere (150 mL / min) and held for 5 h. After cooling, the Co-NC / Al2O3 composite catalyst was finally obtained and named Co-NC / Al2O3-3-500.

[0033] The Co-NC / Al2O3-3-500 catalyst prepared above was used to activate PMS for the degradation of ciprofloxacin. The reaction conditions were: catalyst dosage of 0.2 g / L, PMS dosage of 1 mM, ciprofloxacin concentration of 10 mg / L, pH of 7, and temperature of 20℃. Within 40 min, the degradation efficiency of ciprofloxacin reached 91.8%, and the mineralization rate reached 43.9%.

[0034] Example 6 The stability performance of the catalyst prepared in Example 2 was tested. The Co-NC / Al2O3-1-500 catalyst prepared above was used to activate PMS to degrade tetracycline. The reaction conditions were: catalyst dosage of 0.2 g / L, PMS dosage of 2 mM, tetracycline concentration of 10 mg / L, pH of 7, and temperature of 20°C. Figure 3 As shown, after 5 cycles of testing, the degradation efficiency of TC still reached 88.15%, and the leaching concentration of Co was only 2.5 μg·L⁻¹. –1 XRD, SEM, and XPS characterization results of the catalyst after use indicate that the catalyst still possesses relatively stable structure and surface properties.

[0035] Example 7 A series of catalysts were prepared using the catalyst preparation route described in Example 2. The effects of precursor concentration (0-100 mM), catalyst dosage (0.05-0.3 g·L⁻¹), initial TC concentration (5-40 mg·L⁻¹), PMS concentration (0.25-3 mM), pH (2.98-9.04), and temperature (10-40℃) were systematically investigated.

[0036] like Figure 2 As shown, the effects of precursor concentration (0-100 mM), catalyst dosage (0.05-0.3 g·L⁻¹), initial TC concentration (5-40 mg·L⁻¹), PMS concentration (0.25-3 mM), pH (2.98-9.04), and temperature (10-40℃) were systematically investigated. The experiments showed that simple adsorption (<10%) and PMS self-decomposition contributed little to TC removal, while the Co-NC / Al₂O₃ / PMS system achieved a high removal rate of 96.67% within 40 min. k obs Up to 0.085 min –1 ). Optimization results show that, with the synthesis process, Co 2+ The catalytic activity reached its peak at a concentration of 100 mM. Increasing the catalyst dosage from 0.05 to 0.2 g·L⁻¹ significantly accelerated the formation of active species, but excessive catalyst (0.3 g·L⁻¹) and excessive PMS (>2.0 mM) resulted in only minor improvements due to active site saturation or the self-scavenging effect of free radicals. With increasing initial TC concentration, limited free radicals and competitive adsorption of intermediate products led to a decrease in degradation efficiency. The system maintained excellent performance within a pH range of 3-9 (optimal pH=7.0), and under acidic conditions, H₂O… + PMS activation is inhibited, and low-activity SO5 is easily generated under alkaline conditions. 2- Or surface passivation. Kinetic analysis revealed an activation energy (Ea) of 6.26 kJ·mol⁻¹, indicating that the reaction is controlled by chemical activation rather than mass transfer.

[0037] To quantitatively evaluate the effects of different reaction systems and different single-factor conditions on the degradation rate of tetracycline (TC), a pseudo-first-order kinetic model was used to fit the TC degradation process. The equations are as follows:

[0038] In the formula, kobs is the pseudo-first-order kinetic rate constant, min–1; t is the reaction time, min.

[0039] The thermodynamic equation is as follows:

[0040] In the formula k obs Let min be the pseudo-first-order kinetic reaction rate constant. –1 ; Ea The apparent activation energy is kJ·mol⁻¹. –1 ; A R is the pre-exponential factor; R is the gas constant, 8.314 J·mol⁻¹. –1 ·K –1 ; T K represents absolute temperature.

[0041] Comparative Example 1 The effect of different precursor concentrations on tetracycline degradation efficiency is as follows: Figure 2 As shown in Figure a, the activation effect of Al2O3 microspheres alone on PMS is limited, with a removal rate of only 55.2% for tetracycline within 40 min. In contrast, Co-NC / Al2O3-1-500 achieved a maximum removal rate of 96.7%, indicating that constructing a Co-NC layer on the outer surface of Al2O3 can effectively improve the activation effect of PMS.

[0042] Comparative Example 2 A comparison of N2 adsorption-desorption test data between Co-NC / Al2O3-1-500 material and pristine Al2O3 microspheres. Table 1 shows the N2 adsorption-desorption test data for Al2O3 microspheres (S... BET =210.21 m 2 / g, pore volume = 0.26 cm³ 3 / g) After a Co-NC layer is attached to the surface, both the specific surface area and pore volume are increased to a certain extent. The S of Co-NC / Al2O3 BET =280.64 m 2 / g, pore volume = 0.37 cm³ 3 / g. Furthermore, the pore size of Co-NC / Al2O3 (5.30 nm) is slightly larger than that of Al2O3 (5.04 nm). This indicates that the carbon skeleton formed by ZIF-L(Co) after high-temperature carbonization not only did not block the support pores, but also, by constructing new pore structures, enabled Co-NC / Al2O3 to maintain or even expand its large specific surface area, pore volume, and pore size after loading the active component. It is worth noting that the Co-NC / Al2O3 maintained extremely high structural stability (S) after use. BET =271.50 m 2 / g, pore volume = 0.37 cm³ 3 The catalyst (with an average pore size of 5.48 nm) maintained pore parameters similar to the original catalyst material. This open and stable mesoporous structure will be more conducive to the full exposure of catalytic sites and accelerate the mass transfer of reactants within the pores and the PMS activation rate.

[0043] Table 1. BET specific surface area, pore size, and pore volume data of the materials.

[0044] Comparative Example 3: Comparison of the microstructure of ZIF-L(Co) grown directly on Al2O3 without PEI modification.

[0045] like Figure 4 As shown in b, the Al2O3 surface on the catalyst synthesized using the same method as in Example 1 on unmodified Al2O3 exhibits a distinct prismatic dodecahedral structure belonging to ZIF-67. Figure 1 During synthesis on PEI-premodified Al2O3, a ZIF-L(Co) layered structure was positioned. Furthermore, in... Figure 4 In sample c, a single, free ZIF-67 layer was observed. At this point, the ZIF-67 did not form a heterojunction with Al₂O₃ but remained free in the aqueous phase. Furthermore, the TEM image of the material clearly shows that the formed ZIF-67 layer is attached to a free carbon layer structure. Figure 1 and Figure 4 The comparison shows that the PEI modification mentioned in this invention has a significant impact on the molding of ZIF and can also significantly promote the effective loading of active components.

[0046] Comparative Example 4: Performance comparison of catalysts synthesized using Al2O3 as a support with and without PEI modification. like Figure 5 As shown, when Al2O3 modified with PEI was used as the support, the synthesized catalyst achieved a tetracycline degradation efficiency of 96.67% within 40 min, while the catalyst synthesized with unmodified Al2O3 as the support only achieved a tetracycline removal rate of 34.38%. This result indicates that PEI functionalization has a significant effect on improving catalytic performance.

Claims

1. A method for preparing a ZIF-L(Co)-derived Co-NC / Al2O3 catalyst, characterized in that, Includes the following steps: 1) PEI surface functionalization of Al2O3 support: Weigh Al2O3 support, wash it with deionized water or anhydrous ethanol by ultrasonication, dry it and then immerse it in a polyethyleneimine (PEI) aqueous solution for surface functionalization treatment; after immersion, take out the solid, wash it with deionized water to remove unbound PEI, and dry it to obtain PEI-modified Al2O3 support. 2) Co 2+ Pre-adsorption and ZIF-L(Co) in-situ growth: The support was added to a cobalt salt solution for Co growth. 2+ Pre-adsorption, utilizing the amino sites on the PEI surface to enrich Co 2+ After adsorption is complete, a dimethylimidazole solution of the same volume as the cobalt salt solution is added dropwise while stirring, and stirring is continued to allow the ZIF-L(Co) precursor to grow in situ on the Al2O3 support surface, so as to construct a ZIF-L(Co) precursor layer on the Al2O3 support surface. After the process is completed, the sample is filtered or centrifuged and washed several times to remove unreacted metal salts, free ligands and weakly adsorbed crystals. The washed solid is dried to obtain the ZIF-L(Co) / Al2O3 precursor. 3) Pyrolysis Derivatization: The ZIF-L(Co) / Al2O3 precursor obtained above was placed in a tube furnace and heat-treated under an inert atmosphere. During pyrolysis, the imidazole ligands in the ZIF-L(Co) precursor carbonized to form a nitrogen-containing carbon layer, and the cobalt component was converted into highly dispersed Co–N. x The active sites are simultaneously formed with the Al2O3 support to create a stable interfacial coupling structure. After cooling, the Co-NC / Al2O3 composite catalyst is finally obtained. In step 1), the PEI is branched polyethyleneimine with a number-average molecular weight of 600-1800 Da, a concentration of 0.5-5.0 mg / mL, an impregnation temperature of 20-40℃, and an impregnation time of 2-12 h; in step 2), the cobalt salt is cobalt nitrate or cobalt acetate. 2+ Concentration of 10-200 mM, Co 2+ The molar ratio of Co to dimethylimidazole is 1:8-1:

16. Based on the elemental composition of Co, Co... 2+ The mass ratio of Al2O3 modified with PEI is 1:3-1:25; the inert atmosphere mentioned in step 3) is nitrogen, argon or a mixture thereof, the gas flow rate is 20-300 mL / min, the heat treatment temperature is 500-900 ℃, the heating rate is 1-10℃ / min, and the holding time is 0.5-5h.

2. The preparation method according to claim 1, characterized in that, The Al2O3 carrier mentioned in step 1) is alumina powder, alumina microspheres, or porous alumina particles. The ultrasonic time is 10-40 min, and the drying time is 6-24 h. The ratio of PEI to Al2O3 carrier by mass is 1:3-1:

40.

3. The preparation method according to claim 2, characterized in that, In step 1), the ratio of PEI to Al2O3 carrier by mass is 1:5-1:

20.

4. The preparation method according to claim 1, characterized in that, The cobalt salt mentioned in step 2) is cobalt nitrate or cobalt acetate; the cobalt salt solution contains Co 2+ Concentration of 50-100 mM; Co 2+ Pre-adsorption time is 0.5-6 h; Co 2+ The molar ratio with dimethylimidazole is 1:10-1:14; based on elemental Co, Co 2+ The mass ratio of the PEI-modified Al2O3 support to the PEI-modified Al2O3 support is 1:5-1:

20.

5. The preparation method according to claim 1, characterized in that, In step 2), the dropping rate of dimethylimidazole is 0.1-5 mL / min, and after the addition is completed with a stirring rate of 0-750 rpm, the mixture is allowed to stand or the reaction is maintained at the same stirring rate for 1-8 h. The washing solution is at least one of deionized water, methanol or ethanol, the drying temperature is 60-80℃, and the drying time is 6-12 h.

6. The preparation method according to claim 1, characterized in that, In step 3), the heat treatment temperature is 500-700℃; the heating rate is 1-5℃ / min; the holding time is 1-5 h; and the inert gas flow rate is 50-150 mL / min.

7. A Co-NC / Al2O3 composite catalyst prepared by the method described in any one of claims 1-6.

8. The Co-NC / Al2O3 composite catalyst according to claim 7, characterized in that, In the composite catalyst, the surface of the Al2O3 support is loaded with a nitrogen-containing carbon layer formed by the pyrolysis of ZIF-L(Co), and the nitrogen-containing carbon layer contains Co–N. x The active sites, Co, N, and C, are dispersed on the surface of the Al2O3 support.

9. The application of the Co-NC / Al2O3 composite catalyst according to claim 7 or 8 in the degradation of antibiotic pollutants by activated persulfate.

10. The application according to claim 9, characterized in that, The antibiotic contaminant is one or more of tetracycline, ofloxacin, norfloxacin, or ciprofloxacin, with a contaminant concentration of 5-20 mg / L, a catalyst dosage of 0.05-0.3 g / L, a persulfate concentration of 0.5-3 mM, a reaction system pH of 3-9, and a temperature of 15-35℃.

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