A metal organic framework derived porous carbon material, and a preparation method and application thereof

Abstract

This invention provides a metal-organic framework-derived porous carbon material, its preparation method, and its applications. The material has a hollow structure with a nitrogen-doped porous carbon framework. Layered MnO2 nanosheets are grown in situ on the inner and outer surfaces of the carbon framework. The carbon layers contain Fe-N4 and Cu-N4 bimetallic single-atom sites, and the material also contains Fe3O4 nanoparticles. The preparation method includes: preparing an Fe-doped ZIF-8 precursor, followed by high-temperature pyrolysis, selective oxidation, copper salt impregnation for thermal activation, and hydrothermal growth of MnO2 nanosheets to obtain the material. This material utilizes its hollow porous structure to enhance dye adsorption and enrichment capabilities. Through the triple synergistic activation of persulfate by the Fe-N4 / Cu-N4 dual single-atom sites and MnO2 nanosheets, dyes are efficiently degraded, and magnetic separation and recovery are achieved using Fe3O4. The material of this invention has advantages such as good adsorption-catalysis synergy, high free radical generation efficiency, and easy recovery, and can be used in the field of dye wastewater treatment.

Description

Technical Field

[0001] This invention relates to the fields of porous materials and wastewater treatment technology, specifically to a metal-organic framework-derived porous carbon material, its preparation method, and its application. Background Technology

[0002] With the rapid development of industries such as textiles and dyeing, the discharge of dye wastewater has been increasing year by year, becoming one of the main sources of water pollution. This type of wastewater is complex in composition, highly chromatic, and highly toxic, containing recalcitrant dyes such as methyl orange and rhodamine B. These dye molecules have good chemical stability and biological inertness, making them difficult to completely mineralize using traditional treatment processes. This not only reduces the light transmittance of water bodies and damages aquatic ecosystems, but also harms human health through the food chain. The efficient treatment of dye wastewater has become an urgent need and a research hotspot in the field of environmental protection.

[0003] Dye wastewater treatment methods mainly include adsorption, coagulation, biodegradation, and advanced oxidation processes. Traditional adsorption methods can only achieve the physical transfer of dyes and cannot completely degrade pollutants; moreover, adsorbent regeneration is difficult. Biodegradation methods have extremely low efficiency in treating highly toxic and recalcitrant dyes and have long reaction cycles. Among advanced oxidation processes, persulfate activation technology has attracted much attention due to its high degradation efficiency and wide applicability. However, the core of this technology lies in the performance of the catalyst. Existing catalysts suffer from problems such as single active sites, low activation efficiency, and difficulty in recovery, which limit their industrial application.

[0004] Metal-organic framework (MOF)-derived porous carbon materials have become preferred supports for wastewater treatment catalysts due to their advantages such as large specific surface area, tunable pore structure, and ease of doping with heteroatoms such as nitrogen and phosphorus. ZIF-8, a typical MOF material, possesses a well-defined hollow structure and abundant nitrogen-doped sites, enabling effective loading of active components. However, the catalytic activity of a single ZIF-8-derived carbon material is limited, making it difficult to meet the requirements for efficient degradation. Furthermore, MOF-derived carbon-based catalysts often suffer from drawbacks such as uneven loading of active components, poor adsorption-catalytic synergy, and difficulty in efficient catalyst recovery.

[0005] Therefore, developing a MOF-derived porous carbon material that combines high adsorption performance, excellent catalytic activity, good recyclability, and synergistic adsorption and catalysis is of great significance for promoting the upgrading of dye wastewater treatment technology. Summary of the Invention

[0006] The technical problem to be solved: The purpose of this invention is to provide a metal-organic framework-derived porous carbon material. Using hollow nitrogen-doped porous carbon derived from a metal-organic framework as a carrier, Fe-N4 and Cu-N4 bimetallic single-atom sites are sequentially constructed on the carbon framework through a temperature-separated preparation strategy. Layered MnO2 nanosheets are grown in situ on both the inner and outer surfaces, while Fe3O4 nanoparticles are contained within. This material enables integrated treatment of dyes in dye wastewater through efficient adsorption and enrichment, as well as persulfate activation and degradation, enhancing the material's adsorption-catalytic synergistic performance, free radical generation efficiency, and magnetic separation and recovery capabilities.

[0007] Technical solution: A metal-organic framework-derived porous carbon material, wherein the material has a hollow structure, the framework is nitrogen-doped porous carbon, layered MnO2 nanosheets are grown in situ on the inner and outer surfaces of the nitrogen-doped porous carbon framework, Fe-N4 and Cu-N4 bimetallic single-atom sites are on the carbon layers of the nitrogen-doped porous carbon framework, and the material also contains Fe3O4 nanoparticles inside.

[0008] The above-mentioned method for preparing metal-organic framework-derived porous carbon materials is characterized by comprising the following steps: S1. Zinc salt, iron salt and 2-methylimidazole were mixed in a solvent and stirred at room temperature for 1-2 h. Then, the mixture was centrifuged, washed and dried to obtain the Fe-doped ZIF-8 precursor. S2. The Fe-doped ZIF-8 precursor was subjected to high-temperature pyrolysis under an inert atmosphere to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 is kept at a temperature in an oxygen-containing atmosphere to obtain a hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Fe3O4. S4. The material obtained in S3 is dispersed in a copper salt solution, stirred and impregnated, then dried, and then heated under an inert atmosphere for thermal activation treatment to obtain a hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Cu-N4 / Fe3O4. S5. The material obtained in S4 was dispersed in a mixed aqueous solution of potassium permanganate and ethanol and subjected to hydrothermal reaction to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. S6. The product obtained in S5 is centrifuged, washed, and dried to obtain a metal-organic framework-derived porous carbon material.

[0009] Preferably, in step S1, the zinc salt is Zn(NO3)2·6H2O, the iron salt is FeCl3·6H2O or Fe(NO3)3·9H2O, wherein the molar ratio of Zn to Fe is (15~25):(1~3), and the molar ratio of 2-methylimidazole to total metal is (3~5):1; the solvent is methanol or water.

[0010] Preferably, in step S2, the inert atmosphere is nitrogen or argon, the heating rate is 3~8℃ / min, the pyrolysis temperature is 820~850℃, and the holding time is 1~3h.

[0011] Preferably, in step S3, the oxygen-containing atmosphere is air or a mixed gas with an oxygen volume fraction of 10-21%, the oxidation temperature is 200-300℃, and the holding time is 0.5-1h.

[0012] Preferably, in step S4, the copper salt is Cu(NO3)2·3H2O, the concentration of the copper salt solution is 5~20 mM, the impregnation time is 2~6 h, the inert atmosphere is nitrogen or argon, the heating rate is 3~8℃ / min, the pyrolysis temperature is 500~600℃, and the holding time is 1~2 h.

[0013] Preferably, in step S5, the concentration of potassium permanganate solution is 0.005~0.02 M, the volume fraction of ethanol in the mixed aqueous solution is 5~15%, the hydrothermal reaction temperature is 120~140℃, the time is 1~2h, and the loading of the layered MnO2 nanosheets is 10~20 wt%.

[0014] Preferably, in step S6, the centrifugal washing is performed by alternating washing with deionized water and ethanol until neutral, the drying temperature is 50~80℃, and the drying time is 8~12h.

[0015] The above-mentioned metal-organic framework-derived porous carbon material is applied in the treatment of dye wastewater. The material is added to the dye-containing wastewater, and after the dye is adsorbed, persulfate is added to degrade and remove the dye. After the reaction, the magnetic properties of Fe3O4 are used for magnetic separation and recovery.

[0016] Preferably, the dye is at least one of methyl orange, rhodamine B, methylene blue, and Congo red, the persulfate is permonosulfate or perdisulfate, the amount of the material added to the wastewater is 0.1~0.5 g / L, the amount of persulfate added is 0.2~1 mM, the pH of the wastewater is 3~10, and the treatment time is 20~60 min.

[0017] Beneficial effects: The metal-organic framework-derived porous carbon material of this invention has the following advantages: This invention utilizes a hierarchical porous carbon structure with hollow nitrogen doped to enhance the adsorption and enrichment capacity of dye wastewater, providing a high-concentration microenvironment for subsequent catalytic degradation. The material is prepared by high-temperature pyrolysis of Fe-doped ZIF-8. After zinc volatilization, a hollow cavity is formed, while a hierarchical porous structure is formed within the carbon framework. The hollow structure provides a containment space, rapidly capturing and enriching dye molecules from the water within the cavity. The micropores and mesopores further enhance the adsorption rate and capacity through capillary effects.

[0018] This invention employs a temperature-zone preparation strategy to sequentially construct Fe-N4 and Cu-N4 bimetallic single-atom sites on a carbon framework. These sites jointly activate persulfate, enhancing the free radical generation rate. The formation of Fe-N4 originates from the first step of high-temperature pyrolysis: Fe... 3 + The reducing gases (CO, H2, NH3) produced by carbonization in ZIF-8 are reduced to Fe. 0 Meanwhile, the pyridine nitrogen and pyrrole nitrogen in the skeleton and Fe 0 Coordination forms stable Fe-N4 single atoms; Cu-N4 originates from subsequent impregnation-thermal activation: loading Cu... 2+ The material is treated in a high-temperature inert atmosphere, Cu 2+ Reduced to Cu by carbon 0 It coordinates with nitrogen to form Cu-N4. Fe-N4 acts as the main activation center, efficiently breaking the OO bond of persulfate to generate sulfate radicals. Cu-N4 promotes the reduction of Fe³⁺ to Fe²⁺, enabling Fe-N4 to continuously generate reactive oxygen species.

[0019] In the first step of high-temperature pyrolysis, part of the Fe... 0 Fe was dispersed in the form of nanoparticles within a carbon framework, and then the material was cooled and introduced into an oxygen-containing atmosphere. 0 The surface of the nanoparticles is oxidized to form an Fe3O4 shell. After the reaction is complete, the catalyst can be separated from the wastewater by applying an external magnetic field.

[0020] This invention grows MnO2 nanosheets in situ on the inner and outer surfaces of a carbon skeleton. The surface of the MnO2 nanosheets is rich in hydroxyl groups and oxygen vacancies, and carries a negative charge at neutral pH. It has an electrostatic adsorption effect on cationic dyes such as Rhodamine B and methylene blue. The redox reaction on the MnO2 surface can directly break the OO bonds of persulfate to generate free radicals, which form a triple catalytic center with Fe-N4 / Cu-N4.

[0021] When the material of this invention is added to dye wastewater, it first rapidly adsorbs and enriches dye molecules through multi-level channels and hollow structure. Then, persulfate is added. The Fe-N4 and Cu-N4 double single-atom sites on the surface of the material and the layered MnO2 nanosheets activate the persulfate, continuously generating high concentrations of sulfate radicals and hydroxyl radicals. These radicals have extremely strong oxidizing power and can non-selectively attack conjugated aromatic rings, heterocycles and azo bonds in dye molecules, mineralizing them into CO2, H2O and inorganic ions. Attached Figure Description

[0022] Figure 1 The absorbance change curves for the adsorption degradation of methyl orange are shown in Example 5 and Comparative Examples 1-6. Figure 2The absorbance change curve of Example 5 after 5 cycles of adsorption and degradation of the dye; Figure 3 The absorbance curves for the adsorption and degradation of dyes in Example 5 are shown in the control groups with and without persulfate. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1

[0024] A method for preparing a metal-organic framework-derived porous carbon material includes the following steps: S1. 3.27 g Zn(NO3)2·6H2O, 0.54 g FeCl3·6H2O and 5.25 g 2-methylimidazole were mixed in 80 mL methanol and stirred at room temperature for 1 h. Then, the mixture was centrifuged, washed with methanol and dried at 60 °C to obtain the Fe-doped ZIF-8 precursor. S2. The Fe-doped ZIF-8 precursor was heated to 820℃ at a rate of 3℃ / min under a nitrogen atmosphere, and then held at that temperature for 3 hours for high-temperature pyrolysis to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 is kept in air atmosphere for 1 hour at a temperature of 200℃ to obtain Fe-N4 / Fe3O4 co-supported hollow nitrogen-doped porous carbon material; S4. The material obtained in S3 was dispersed in a Cu(NO3)2 solution with a concentration of 5 mM, stirred, impregnated for 6 h, dried at 60 °C, and then heated to 500 °C at 3 °C / min under a nitrogen atmosphere, and then held at the temperature for 2 h for thermal activation treatment to obtain hollow nitrogen-doped porous carbon material co-loaded with Fe-N4 / Cu-N4 / Fe3O4. S5. Mix 0.079 g potassium permanganate, 5 mL ethanol, and 95 mL water to obtain a mixed aqueous solution. Adjust the pH to 9 with 0.1 M NaOH solution. Disperse the material obtained in S4 in the mixed aqueous solution, transfer it to a reaction vessel, and perform a hydrothermal reaction at 120 °C for 2 h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. The loading of MnO2 nanosheets is 10 wt%. S6. Centrifuge the product obtained in S5, wash it alternately with deionized water and ethanol until neutral, and dry it at 50°C to obtain metal-organic framework-derived porous carbon materials.

[0025] Example 2

[0026] A method for preparing a metal-organic framework-derived porous carbon material includes the following steps: S1. 7.44 g Zn(NO3)2·6H2O, 0.81 g FeCl3·6H2O and 8.21 g 2-methylimidazole were mixed in 120 mL methanol and stirred at room temperature for 2 h. Then, the mixture was centrifuged, washed with methanol and dried at 60 °C to obtain the Fe-doped ZIF-8 precursor. S2. The Fe-doped ZIF-8 precursor was heated to 850℃ at a rate of 8℃ / min under an argon atmosphere, and then held at that temperature for 1 h for high-temperature pyrolysis to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 was kept in a mixed gas with an oxygen volume fraction of 21% for 0.5 h at a temperature of 300℃ to obtain a hollow nitrogen-doped porous carbon material co-supported with Fe-N4 / Fe3O4. S4. The material obtained in S3 was dispersed in a Cu(NO3)2 solution with a concentration of 20 mM, stirred, impregnated for 2 h, dried, and then heated to 600 °C at 8 °C / min under an argon atmosphere, followed by heat activation treatment for 1 h to obtain hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Cu-N4 / Fe3O4. S5. Mix 0.316 g potassium permanganate, 15 mL ethanol, and 85 mL water to obtain a mixed aqueous solution. Adjust the pH to 9 with 0.1 M NaOH solution. Disperse the material obtained in S4 in the mixed aqueous solution, transfer it to a reaction vessel, and perform a hydrothermal reaction at 140 °C for 1 h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. The loading of MnO2 nanosheets is 20 wt%. S6. Centrifuge the product obtained in S5, wash it alternately with deionized water and ethanol until neutral, and dry it at 50°C to obtain metal-organic framework-derived porous carbon materials.

[0027] Example 3

[0028] A method for preparing a metal-organic framework-derived porous carbon material includes the following steps: S1. Mix 5.36g Zn(NO3)2·6H2O, 0.54g Fe(NO3)3·9H2O and 6.98g 2-methylimidazole in 100mL methanol, stir at room temperature for 1h, then centrifuge, wash and dry to obtain Fe-doped ZIF-8 precursor; S2. The Fe-doped ZIF-8 precursor was heated to 835℃ at a rate of 5℃ / min under a nitrogen atmosphere, and then held at that temperature for 2 hours for high-temperature pyrolysis to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 is kept in a mixed gas with a volume fraction of 15% air or oxygen for 1 hour at a temperature of 250℃ to obtain a hollow nitrogen-doped porous carbon material co-supported with Fe-N4 / Fe3O4. S4. The material obtained in S3 was dispersed in a Cu(NO3)2 solution with a concentration of 12 mM, stirred, impregnated for 4 h, dried, and then heated to 550 °C at 5 °C / min under a nitrogen atmosphere, and then held at the temperature for 1.5 h for thermal activation treatment to obtain hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Cu-N4 / Fe3O4. S5. Mix 0.158 g potassium permanganate, 10 mL ethanol, and 90 mL water to obtain a mixed aqueous solution. Adjust the pH to 9 with 0.1 M NaOH solution. Disperse the material obtained in S4 in the mixed aqueous solution, transfer it to a reaction vessel, and perform a hydrothermal reaction at 130 °C for 1.5 h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. The loading of MnO2 nanosheets is 15 wt%. S6. Centrifuge the product obtained in S5, wash it alternately with deionized water and ethanol until neutral, and dry it at 65°C to obtain metal-organic framework-derived porous carbon materials.

[0029] Example 4

[0030] A method for preparing a metal-organic framework-derived porous carbon material includes the following steps: S1. 6.7g Zn(NO3)2·6H2O, 0.54g FeCl3·6H2O and 6.98g 2-methylimidazole were mixed in 100mL methanol and stirred at room temperature for 1h. Then, the mixture was centrifuged, washed and dried to obtain the Fe-doped ZIF-8 precursor. S2. The Fe-doped ZIF-8 precursor was heated to 825℃ at a rate of 6℃ / min under an argon atmosphere, and then held at that temperature for 2.5h for high-temperature pyrolysis to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 was kept in air at 280℃ for 0.5h to obtain a hollow nitrogen-doped porous carbon material co-supported with Fe-N4 / Fe3O4. S4. The material obtained in S3 was dispersed in a Cu(NO3)2 solution with a concentration of 8 mM, stirred, impregnated for 5 h, dried, and then heated to 520 °C at 4 °C / min under an argon atmosphere, followed by heat activation treatment for 2 h to obtain hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Cu-N4 / Fe3O4. S5. 0.118 g potassium permanganate, 12 mL ethanol, and 88 mL water were stirred until homogeneous to obtain a mixed aqueous solution. The pH was adjusted to 9 with 0.1 M NaOH solution. The material obtained in S4 was dispersed in the mixed aqueous solution and transferred to a reaction vessel. The reaction was carried out hydrothermally at 125 °C for 1.5 h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. The loading of MnO2 nanosheets was 12 wt%. S6. Centrifuge the product obtained in S5, wash it alternately with deionized water and ethanol until neutral, and dry it at 60°C to obtain metal-organic framework-derived porous carbon materials.

[0031] Example 5

[0032] A method for preparing a metal-organic framework-derived porous carbon material includes the following steps: S1. Mix 5.95g Zn(NO3)2·6H2O, 0.54g FeCl3·6H2O and 6.57g 2-methylimidazole in 100mL methanol, stir at room temperature for 1h, then centrifuge, wash and dry to obtain Fe-doped ZIF-8 precursor; S2. The Fe-doped ZIF-8 precursor was heated to 830℃ at a rate of 5℃ / min under an argon atmosphere, and then held at that temperature for 2 hours for high-temperature pyrolysis to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 is kept in air at 250℃ for 0.5h to obtain a hollow nitrogen-doped porous carbon material co-supported with Fe-N4 / Fe3O4. S4. The material obtained in S3 was dispersed in a Cu(NO3)2 solution with a concentration of 10 mM, stirred, impregnated for 4 h, dried, and then heated to 550 °C at 5 °C / min under an argon atmosphere, and then held at the temperature for 1.5 h for thermal activation treatment to obtain hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Cu-N4 / Fe3O4. S5. Mix 0.158 g potassium permanganate, 10 mL ethanol, and 90 mL water to obtain a mixed aqueous solution. Adjust the pH to 9 with 0.1 M NaOH solution. Disperse the material obtained in S4 in the mixed aqueous solution, transfer it to a reaction vessel, and perform a hydrothermal reaction at 130 °C for 1.5 h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. The loading of MnO2 nanosheets is 15 wt%. S6. Centrifuge the product obtained in S5, wash it alternately with deionized water and ethanol until neutral, and dry it at 60°C to obtain metal-organic framework-derived porous carbon materials.

[0033] Comparative Example 1 The difference between Comparative Example 1 and Example 5 is that no iron salt is added in S1 of Comparative Example 1; S1. Mix 5.95g Zn(NO3)2·6H2O and 6.57g 2-methylimidazole in 100mL methanol, stir at room temperature for 1h, then centrifuge, wash and dry to obtain ZIF-8 precursor; S2. The ZIF-8 precursor was dispersed in a 10 mM Cu(NO3)2 solution, stirred, impregnated for 4 h, dried, and then heated to 550 °C at 5 °C / min under an argon atmosphere, followed by heat activation treatment for 1.5 h to obtain Cu-N4 supported hollow nitrogen-doped porous carbon material. S3. 0.158 g potassium permanganate, 10 mL ethanol and 90 mL water were stirred evenly to obtain a mixed aqueous solution. The pH was adjusted to 9 with 0.1 M NaOH solution. The material obtained in S2 was dispersed in the mixed aqueous solution and transferred to a reaction vessel. The reaction was carried out hydrothermally at 130 °C for 1.5 h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. S4. Centrifuge the product obtained in S3, wash it alternately with deionized water and ethanol until neutral, and dry it at 60°C to obtain metal-organic framework-derived porous carbon materials.

[0034] Comparative Example 2 The difference between Comparative Example 2 and Example 5 is that Comparative Example 2 omits step S4 and does not perform copper salt impregnation treatment, while the remaining steps are the same as in Example 5.

[0035] Comparative Example 3 The difference between Comparative Example 3 and Example 5 is that potassium permanganate is not added in step S5 of Comparative Example 3, while the remaining steps are the same as in Example 5.

[0036] Comparative Example 4 The difference between Comparative Example 4 and Example 5 is that Comparative Example 4 does not undergo the S3 oxidation treatment, while the remaining steps are the same as in Example 5.

[0037] Comparative Example 5 The difference between Comparative Example 5 and Example 5 is that Fe / Cu bimetallic materials are simultaneously doped into the ZIF-8 precursor; S1. Mix 5.95g Zn(NO3)2·6H2O, 0.54g FeCl3·6H2O, 0.097g Cu(NO3)2·3H2O and 6.57g 2-methylimidazole in 100mL methanol, stir at room temperature for 1.5h, then centrifuge, wash and dry to obtain the precursor; S2. The precursor was heated to 830℃ at 5℃ / min under an argon atmosphere, and then held at that temperature for 2h to carry out high-temperature pyrolysis to obtain hollow nitrogen-doped porous carbon material. S3. The material obtained in S2 is kept in air at 250℃ for 0.5h to obtain co-loaded hollow nitrogen-doped porous carbon material; S4. Mix 0.158g potassium permanganate, 10mL ethanol and 90mL water to obtain a mixed aqueous solution. Adjust the pH to 9 with 0.1M NaOH solution. Disperse the material obtained in S3 in the mixed aqueous solution and transfer it to a reaction vessel. Perform hydrothermal reaction at 130℃ for 1.5h to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. S5. Centrifuge the product obtained in S4, wash it alternately with deionized water and ethanol until neutral, and dry it at 60°C to obtain metal-organic framework-derived porous carbon materials.

[0038] Comparative Example 6 The difference between Comparative Example 6 and Example 5 is that the pyrolysis temperature in S2 of Comparative Example 6 is 700°C, while the remaining steps are the same as in Example 5.

[0039] Application Example 1 The metal-organic framework-derived porous carbon materials prepared in Examples 5 and Comparative Examples 1-6 were used for the degradation of methyl orange. The specific steps are as follows: 100 mL of 50 mg / L methyl orange aqueous solution was prepared, and 20 mg of the sample to be tested was added. 3 mL of each solution was taken and labeled "original". Adsorption stage: The solution was placed under light-protected conditions and stirred at 500 rpm for 30 min. 3 mL samples were taken every 10 min and labeled "-30", "-20", "-10", and "0" to determine the adsorption removal rate. Catalytic degradation stage: Persulfate was added to a final concentration of 0.5 mM, and stirring was continued at 500 rpm for 60 min. 3 mL samples were taken every 10 min and labeled "10", "20", "30", "40", "50", and "60". The samples were centrifuged, and the supernatant was retained. The absorbance was measured using a UV-Vis spectrophotometer.

[0040] Application Example 2 The metal-organic framework-derived porous carbon materials prepared in Example 5, Comparative Example 1, and Comparative Example 4 were used for magnetic recovery performance testing. The specific steps are as follows: 100 mL of 50 mg / L methyl orange aqueous solution was prepared, 20 mg of the sample to be tested was added, and the mixture was stirred at 500 rpm for 30 min for adsorption. Persulfate was added to a final concentration of 0.5 mM, and stirring was continued for 60 min for catalytic degradation. After degradation, the reaction vessel was placed next to an external magnetic field, the recovered material was separated, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60 °C for 12 h. The mass of the recovered material was weighed, and the recovery rate was calculated.

[0041] Application Example 3 The metal-organic framework-derived porous carbon material prepared in Example 5 was used for multiple cyclic degradation of methyl orange. The specific steps are as follows: 100 mL of 50 mg / L methyl orange aqueous solution was prepared, 20 mg of the sample to be tested was added, and the mixture was stirred at 500 rpm for 30 min for adsorption. Persulfate was added to a final concentration of 0.5 mM, and stirring was continued for 60 min for catalytic degradation. After degradation, the material was separated and recovered using an external magnetic field, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60 °C for 12 h for the next cycle. The above steps were repeated to complete 5 cycles. After each cycle, the absorbance of methyl orange was measured.

[0042] Application Example 4 The metal-organic framework-derived porous carbon material prepared in Example 5 was used for the catalytic degradation of methyl orange. Two control groups were established: Group A (with persulfate) and Group B (without persulfate). The specific steps were as follows: 100 mL of a 50 mg / L methyl orange aqueous solution was prepared, and 20 mg of the sample was added to each group. All sample groups were stirred at 500 rpm for 30 min for adsorption. After adsorption, one group was treated with persulfate to a final concentration of 0.5 mM, and stirred for another 60 min for catalytic degradation. The other group was treated without persulfate, and stirred for another 60 min (adsorption only). Every 10 min, 3 mL of sample was taken, centrifuged, and the supernatant was retained. The absorbance was measured using a UV-Vis spectrophotometer.

[0043] Figure 1 The figures show the absorbance changes over time during the degradation of methyl orange in Example 5 and the comparative examples. The material in Example 5 has a hollow nitrogen-doped porous carbon framework with layered MnO2 nanosheets grown in situ on the inner and outer surfaces. Fe-N4 and Cu-N4 bimetallic single-atom sites are anchored on the carbon layers, and Fe3O4 nanoparticles are also present internally. During the adsorption stage, its hollow structure and hierarchical channels provide a high specific surface area and abundant adsorption sites. The capillary effect of micropores and mesopores rapidly captures and enriches dye molecules within the cavities, resulting in the most significant decrease in absorbance in Example 5. In the catalytic degradation stage after the addition of persulfate, Fe-N4, as the main activation center, efficiently breaks the O / O bonds of persulfate to generate sulfate radicals. Cu-N4 promotes the degradation of Fe... 3+ / Fe 2+The cycle allows Fe-N4 to continuously generate reactive oxygen species. The redox pairs on the surface of MnO2 nanosheets can directly activate persulfate and form a triple catalytic center with Fe-N4 / Cu-N4, exhibiting the best adsorption-catalytic synergy. Comparative Example 1, lacking iron salts and therefore containing neither Fe-N4 nor Fe3O4, relies on Cu-N4 and MnO2 to activate persulfate. The lack of Fe-N4 reduces the efficiency of free radical generation, resulting in a slow decrease in absorbance and the highest proportion of remaining dye, indicating that Fe-N4 is an indispensable active center in the entire catalytic system. Comparative Example 2, omitting the copper salt impregnation step and lacking Cu-N4, lacks the electron acceleration effect of Cu-N4, leading to Fe... 3+ Reduced to Fe 2+ The rate of absorption reduction is limited, and Fe-N4 cannot continuously and efficiently activate persulfate, resulting in a lower catalytic efficiency than in Example 5 and a slower rate of absorbance decrease. Comparative Example 3 did not grow MnO2 nanosheets and relied solely on Fe-N4 and Cu-N4 dual single-atom sites to activate persulfate, leading to reduced free radical production and decreased catalytic efficiency. Comparative Example 4 did not undergo oxidation treatment and therefore did not contain Fe3O4, but its Fe-N4, Cu-N4, and MnO2 catalytic components were completely retained, and its absorbance decrease rate was similar to that of Example 5. The final proportion of remaining dye was also similar, indicating that Fe3O4 does not participate in the catalytic reaction but only serves as a magnetic separation functional component. The catalytic degradation performance of the material is not affected. Comparative Example 5 uses a one-step pyrolysis method with simultaneous Fe / Cu bimetallic doping. Cu volatilization loss is severe at high temperature, and the Fe / Cu bimetallic synergistic effect is lost, resulting in a high proportion of residual dye. The temperature-zone preparation strategy of this invention can effectively avoid Cu volatilization and ensure the synergistic effect of bimetallic single-atom sites. The pyrolysis temperature of Comparative Example 6 is only 700℃, which is lower than the volatilization temperature of Zn. Zn failed to fully volatilize to form a hollow structure, and the material is a solid structure with a small specific surface area and reduced adsorption and enrichment capacity. This shows that a hollow structure is a basic prerequisite for efficient adsorption and enrichment and subsequent catalytic degradation.

[0044] In the magnetic recovery test of Application Example 2, Example 5, due to the presence of Fe3O4 nanoparticles, can aggregate to the magnet side under the influence of a magnetic field, causing the solution to gradually clarify and enabling rapid magnetic separation and recovery. During the high-temperature pyrolysis of S2, Fe... 3+ There are two parallel transformation paths: one for Fe 3+ Reduced to Fe 2+ or Fe 0 Subsequently, it is captured by pyridine nitrogen and pyrrole nitrogen on the carbon skeleton, forming stable Fe-N4 single-atom sites, while another part of Fe... 3+ Excessively reduced to Fe 0 It migrates and aggregates, entering S3. Fe-N4 remains stable in an oxygen-containing atmosphere at 200-300℃, while Fe... 0The nanoparticles undergo oxidation to form an Fe3O4 shell, imparting magnetism to the material. Comparative Example 4, which did not undergo oxidation and therefore contains no Fe3O4, showed no significant aggregation under the same magnetic field conditions, and the solution turbidity did not change significantly, making magnetic separation and recovery impossible. Comparative Example 1, lacking any iron components due to the absence of added iron salts, also lacked magnetic responsiveness and could not be separated by an external magnetic field. These results indicate that Fe3O4 does not participate in the catalytic degradation reaction but imparts excellent magnetic separation performance to the material.

[0045] Figure 2 The absorbance curves for Example 5 during multiple cycles of methyl orange degradation are shown. Because the material in Example 5 contains Fe3O4 nanoparticles, it can be easily separated and recovered using an external magnetic field after each cycle. In the first cycle, Example 5 utilizes its hollow structure and hierarchical channels to rapidly capture and enrich dye molecules during the adsorption stage. During the catalytic degradation stage, the triple synergistic effect of Fe-N4 and Cu-N4 metal single-atom sites and MnO2 nanosheets efficiently activates persulfate to generate sulfate radicals and hydroxyl radicals, degrading and mineralizing the dye molecules adsorbed in the cavities in situ, resulting in a decrease in absorbance. After multiple cycles, the absorbance remains low after degradation, indicating that the material has good cyclic stability and structural integrity. This is because the Fe-N4 and Cu-N4 single-atom sites are firmly anchored in the nitrogen-doped carbon framework, making them difficult to detach or aggregate; the Fe3O4 nanoparticles are encapsulated by the carbon matrix, maintaining stability during the reaction; the MnO2 nanosheets are tightly bound to the carbon framework through in-situ growth, making them difficult to peel off; at the same time, since the dye molecules are completely mineralized into CO2 and H2O, no pollutant intermediates accumulate on the surface of the active sites. Therefore, Example 5 can still maintain highly efficient adsorption-catalysis synergistic performance after multiple cycles.

[0046] Figure 3 The figures show the control curves for the two groups (with and without persulfate) in Application Example 4. During the adsorption stage, neither group had persulfate added. The material utilized its hollow structure and hierarchical pores to provide abundant adsorption sites, rapidly capturing and enriching dye molecules through the capillary effect of micropores and mesopores, as well as the containment capacity of the hollow cavity. The absorbance of both groups showed a decreasing trend during the adsorption stage, and the decrease was basically consistent, indicating that the material has excellent physical adsorption capacity. After adsorption, persulfate was added to group A. At this time, the Fe-N4 on the material surface acted as the main activation center, efficiently breaking the O0 bonds of the persulfate to generate sulfate radicals. Cu-N4 promoted the Fe... 3+ / Fe 2+The cycle allows Fe-N4 to continuously generate reactive oxygen species. The redox pairs on the surface of MnO2 nanosheets can directly activate persulfate and form a triple catalytic center with Fe-N4 / Cu-N4. The absorbance decreases rapidly during the catalytic stage, achieving complete mineralization of the dye. In Group B, no persulfate was added after adsorption. The material removed the dye solely through physical adsorption. The absorbance basically stopped decreasing after the adsorption stage and tended to stabilize, indicating that the material had reached adsorption saturation and could not further remove residual dye, thus failing to achieve mineralization.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A metal-organic framework-derived porous carbon material, characterized in that, The material has a hollow structure with a framework of nitrogen-doped porous carbon. Layered MnO2 nanosheets are grown in situ on the inner and outer surfaces of the nitrogen-doped porous carbon framework. Fe-N4 and Cu-N4 bimetallic single-atom sites are present on the carbon layers of the nitrogen-doped porous carbon framework. The material also contains Fe3O4 nanoparticles.

2. The method for preparing metal-organic framework-derived porous carbon materials according to claim 1, characterized in that, Includes the following steps: S1. Zinc salt, iron salt and 2-methylimidazole were mixed in a solvent and stirred at room temperature for 1-2 h. Then, the mixture was centrifuged, washed and dried to obtain the Fe-doped ZIF-8 precursor. S2. The Fe-doped ZIF-8 precursor was subjected to high-temperature pyrolysis under an inert atmosphere to obtain Fe-N4 / Fe. 0 Co-loaded hollow nitrogen-doped porous carbon materials; S3. The material obtained in S2 is kept at a temperature in an oxygen-containing atmosphere to obtain a hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Fe3O4. S4. The material obtained in S3 is dispersed in a copper salt solution, stirred and impregnated, then dried, and then heated under an inert atmosphere for thermal activation treatment to obtain a hollow nitrogen-doped porous carbon material co-supported by Fe-N4 / Cu-N4 / Fe3O4. S5. The material obtained in S4 was dispersed in a mixed aqueous solution of potassium permanganate and ethanol and subjected to hydrothermal reaction to grow layered MnO2 nanosheets in situ on the inner and outer surfaces of the hollow structure. S6. The product obtained in S5 is centrifuged, washed, and dried to obtain a metal-organic framework-derived porous carbon material.

3. The preparation method according to claim 2, characterized in that: In step S1, the zinc salt is Zn(NO3)2·6H2O, and the iron salt is FeCl3·6H2O or Fe(NO3)3·9H2O. The molar ratio of Zn to Fe is (15~25):(1~3), and the molar ratio of 2-methylimidazole to total metal is (3~5):

1. The solvent is methanol or water.

4. The preparation method according to claim 2, characterized in that: In step S2, the inert atmosphere is nitrogen or argon, the heating rate is 3~8℃ / min, the pyrolysis temperature is 820~850℃, and the holding time is 1~3h.

5. The preparation method according to claim 2, characterized in that: In step S3, the oxygen-containing atmosphere is air or a mixed gas with an oxygen volume fraction of 10-21%, the oxidation temperature is 200-300℃, and the holding time is 0.5-1h.

6. The preparation method according to claim 2, characterized in that: In step S4, the copper salt is Cu(NO3)2·3H2O, the concentration of the copper salt solution is 5~20 mM, the impregnation time is 2~6 h, the inert atmosphere is nitrogen or argon, the heating rate is 3~8℃ / min, the pyrolysis temperature is 500~600℃, and the holding time is 1~2 h.

7. The preparation method according to claim 2, characterized in that: In step S5, the concentration of potassium permanganate solution is 0.005~0.02 M, the volume fraction of ethanol in the mixed aqueous solution is 5~15%, the hydrothermal reaction temperature is 120~140℃, the time is 1~2h, and the loading of the layered MnO2 nanosheets is 10~20 wt%.

8. The preparation method according to claim 2, characterized in that: In step S6, centrifugal washing is performed by alternating washing with deionized water and ethanol until neutral, and the drying temperature is 50~80℃, and the drying time is 8~12h.

9. The application of the metal-organic framework-derived porous carbon material according to claim 1 in dye wastewater treatment, characterized in that: The material is added to wastewater containing dye to adsorb the dye. Then, persulfate is added to degrade and remove the dye. After the reaction, the magnetic properties of Fe3O4 are used for magnetic separation and recovery.

10. The application according to claim 9, characterized in that: The dye is at least one of methyl orange, rhodamine B, methylene blue, and Congo red. The persulfate is permonosulfate or perdisulfate. The amount of the material added to the wastewater is 0.1~0.5 g / L, the amount of persulfate added is 0.2~1 mM, the pH of the wastewater is 3~10, and the treatment time is 20~60 min.

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