Preparation method and application of carbon-defect type iron single-atom catalyst with high efficiency in degrading organic dyes

Abstract

The application belongs to the field of catalysts and preparation technology thereof, and relates to a carbon-defect type iron monatomic catalyst for efficiently degrading organic dyes as well as a preparation method and application thereof, and comprises the following steps: 1) mixing zinc nitrate hexahydrate, 2-methyl imidazole and a methanol solution; 2) further processing to obtain ZIF-8 solid; 3) dispersing the ZIF-8 solid in a methanol solution containing tannic acid, and processing to obtain hollow ZIF-8 solid; 4) dispersing the hollow ZIF-8 solid in a buffer solution, then adding dopamine hydrochloride, and processing to obtain a pyrolysis precursor; and 5) calcining the iron source and the pyrolysis precursor under an inert atmosphere to obtain a target product. The iron monatomic catalyst prepared by modifying polydopamine on the surface of the hollow ZIF-8 has a high specific surface area and is rich in carbon defects, can realize efficient degradation of organic dye wastewater in a natural environment or even a dark environment, has low treatment cost, a simple treatment process and a wide pH application range.

Description

Technical Field

[0001] This invention belongs to the field of catalyst and its preparation technology, and relates to a carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes, its preparation method and application. Background Technology

[0002] In recent years, environmental pollution has become one of the major issues of global concern. Organic dyes are widely used in industrial technologies such as food, textiles, and papermaking, and a large amount of dye wastewater generated each year urgently needs to be treated. Organic dyes have complex structures and are highly stable in wastewater. Therefore, it is very urgent to develop a low-cost and environmentally friendly dye degradation technology.

[0003] Existing dye degradation technologies mainly focus on the preparation of photocatalysts, but these catalysts almost all require external light sources such as visible light or ultraviolet light for excitation, which limits their application to some extent. In recent years, researchers have been committed to the development of photo-excitation-free catalysts. Single-atom catalysts have been extensively studied due to their ultra-high atomic utilization and well-defined structure. For example, patent document CN116651483A discloses a method for preparing α or γ-Fe modified Fe-NC materials and their applications. Fe-NC exhibits high activity in a wide pH range of 3.0 to 9.0 and has excellent resistance to anions and natural organic matter, showing good prospects in practical wastewater treatment. When both Fe-NC-1 and PMS are present in solution, the degradation efficiency increases to 82.8% within 40 minutes. This indicates that existing catalysts still require external oxidants such as persulfate and hydrogen peroxide to degrade dyes when degrading organic pollutants. These oxidants not only have certain biotoxicity but also undoubtedly increase production costs and process complexity. In addition, current catalysts for degrading pollutants almost all have stringent requirements on the pH of the aquatic environment. The pH of the wastewater needs to be adjusted before degradation. The catalyst disclosed in patent document CN116651483A can be used in acidic and weakly alkaline ranges. For strongly alkaline wastewater, secondary pH adjustment of the wastewater is still required. This secondary pH adjustment of the wastewater significantly increases the complexity of the process and may cause water pollution again. Summary of the Invention

[0004] To address the technical problems of high treatment costs and complex treatment processes caused by the above-mentioned catalysts requiring external photoexcitation, external oxidants, or strict pH requirements for wastewater degradation, this invention provides a carbon-deficient iron single-atom catalyst for the degradation of organic dyes, its preparation method, and its application.

[0005] This invention prepares a high specific surface area and carbon-defect-rich iron single-atom catalyst, Vc-Fe-NC@NC, by modifying the surface of hollow ZIF-8 with polydopamine. The prepared catalyst requires no external light source or oxidant and can directly and efficiently degrade pollutants in organic dye wastewater in natural or even dark environments. This reduces treatment costs, simplifies the process, and the catalyst has a wide pH application range. The technical solution adopted in this invention is as follows:

[0006] A method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes includes the following steps:

[0007] 1) A mixed solution is prepared using zinc nitrate hexahydrate, 2-methylimidazole, and methanol solution; the mass ratio of zinc nitrate hexahydrate to 2-methylimidazole is 0.5–1.5:1;

[0008] 2) The mixed solution from step 1) is centrifuged, washed, and dried to obtain ZIF-8 solid;

[0009] 3) Disperse ZIF-8 solid in a methanol solution containing tannic acid, and obtain hollow ZIF-8 solid by stirring, centrifugation, washing and drying in sequence; the mass ratio of ZIF-8 solid to tannic acid is 0.1 to 0.5:1, and the mass ratio of tannic acid to methanol is 0.005 to 0.02:1;

[0010] 4) Disperse the hollow ZIF-8 solid from step 3) in a buffer solution, sonicate for 5 min to 30 min, add dopamine hydrochloride and stir until homogeneous, then centrifuge, wash and dry sequentially to obtain the hollow ZIF-8@PDA pyrolysis precursor; the mass ratio of the hollow ZIF-8 solid to dopamine hydrochloride is 5 to 0.05:1, and the mass ratio of the hollow ZIF-8 solid to the buffer solution is 0.02 to 0.0003:1;

[0011] 5) Under an inert atmosphere, the iron source and the hollow ZIF-8@PDA pyrolysis precursor from step 4) are calcined together at a mass ratio of 0.5 to 1.5:1 to obtain a black solid, namely the target product Vc-Fe-NC@NC.

[0012] Further specifying, in step 1), the stirring temperature is room temperature and the stirring time is 4h to 8h.

[0013] Further specifying, the stirring time in step 3) is 1 min to 10 min.

[0014] Further specifying, in step 4), the stirring time is 3h to 15h, and the pH of the buffer solution is 8 to 10.

[0015] Further specifying, in step 5), the inert gas is nitrogen or argon; the iron source is ferrocene, ferric chloride, or ferrous chloride; and the calcination includes a first stage of calcination and a second stage of calcination.

[0016] Further specified, the first stage calcination conditions are: temperature of 100℃~200℃, holding time of 1h~3h, and heating rate of 1℃ / min~5℃ / min; the second stage calcination conditions are: temperature of 800℃~1000℃, holding time of 1h~3h, and heating rate of 1℃ / min~10℃ / min.

[0017] The carbon-deficient iron single-atom catalyst prepared by the method described above for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes.

[0018] The application of carbon-deficient iron single-atom catalysts in the degradation of organic dye wastewater, as described above.

[0019] Further specifying, the application involves directly adding a carbon-defective iron single-atom catalyst to organic dye wastewater to catalytically degrade organic dyes without an external light source.

[0020] Further specifying, the degraded organic dye is Rhodamine B, methyl orange, or methylene blue.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention prepares a high specific surface area and carbon-defect-rich iron single-atom catalyst Vc-Fe-NC@NC by modifying the surface of hollow ZIF-8 with polydopamine, thereby significantly improving its ability to activate dissolved oxygen in water. The prepared catalyst does not require an external light source or oxidant and can directly and efficiently degrade pollutants in organic dye wastewater in natural environments or even in dark environments. The treatment cost is reduced and the treatment process is simple, showing broad application prospects in dye wastewater treatment.

[0023] 2. This invention modifies the surface of hollow ZIF-8 with polydopamine. During high-temperature carbonization, the polydopamine layer on the surface of the pyrolysis precursor prevents the escape of Zn, thereby increasing the residence time of Zn in the pyrolysis precursor. This results in a sharp increase in the pore size of the prepared catalyst from micropores to mesopores. In other words, by increasing the residence time of Zn in hollow ZIF-8@PDA during thermal carbonization, the pore size of ZIF-8 derived carbon is expanded, thereby obtaining an iron single-atom catalyst Vc-Fe-NC@NC with high specific surface area and rich carbon defects. The increased specific surface area increases the surface area of ​​contact between reactants and catalyst, thereby accelerating the reaction rate. The increased pore size facilitates the transport of reactants and products to the active sites inside the catalyst, improving the utilization rate of the active sites. In addition, carbon defects themselves can also serve as new active sites, thus significantly improving catalytic performance. The 0.1 g / L catalyst can achieve a degradation rate of over 99% for Rhodamine B and methyl orange and over 97% for methylene blue within 10 min, demonstrating rapid degradation and good degradation effect.

[0024] 3. The Vc-Fe-NC@NC single-atom catalyst prepared by this invention does not require the addition of an oxidant when degrading organic wastewater, thereby reducing the biotoxicity of the oxidant during the degradation process. The degradation process is green, environmentally friendly and safe.

[0025] 4. When degrading organic dye wastewater, the catalyst prepared by this invention exhibits excellent degradation effects on organic dyes in a wide pH range of 3 to 11. It can achieve efficient and rapid degradation of organic matter in both strong acid and strong alkaline systems, overcoming the shortcomings of existing catalysts that have strict requirements on the pH of the water environment during degradation. In application, there is no need to adjust the pH of the organic dye wastewater twice; the catalyst can be directly added to the wastewater to complete the degradation, which is beneficial for industrial applications.

[0026] 5. The carbon-deficient iron single-atom catalyst prepared by this invention has a simple preparation process, readily available raw materials, low preparation cost, and is environmentally friendly. Attached Figure Description

[0027] Figure 1 The XRD pattern of the highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes prepared in Example 1 is shown below.

[0028] Figure 2 XPS C1s spectrum of the highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes prepared in Example 1;

[0029] Figure 3 ESR spectrum of the highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes prepared in Example 1;

[0030] Figure 4The UV-Vis absorption spectrum of the carbon-deficient iron single-atom catalyst for the degradation of Rhodamine B by the highly efficient organic dye degradation method prepared in Example 1 is shown.

[0031] Figure 5 The UV-Vis absorption spectrum of methyl orange degradation by the carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes prepared in Example 1 is shown.

[0032] Figure 6 The UV-Vis absorption spectrum of methylene blue degradation by the carbon-deficient iron single-atom catalyst prepared in Example 1 for the efficient degradation of organic dyes is shown below.

[0033] Figure 7 The degradation performance of the carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes prepared in Example 1 on Rhodamine B solution at different concentrations;

[0034] Figure 8 The degradation performance of the carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes prepared in Example 1 in Rhodamine B solutions at different pH values.

[0035] Figure 9 The degradation performance of the carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes prepared in Example 1 in methyl orange solutions at different pH values;

[0036] Figure 10 The degradation performance of the carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes prepared in Example 1 in methylene blue solutions at different pH values;

[0037] Figure 11 N2 adsorption-desorption isotherms of the carbon-defective iron single-atom catalysts prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0038] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] This invention provides a method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes, comprising the following steps:

[0040] 1) A mixed solution was prepared using zinc nitrate hexahydrate, 2-methylimidazole and methanol solution.

[0041] During preparation, zinc nitrate hexahydrate and methanol solution are mixed to obtain a mixed solution, namely zinc nitrate hexahydrate solution, denoted as solution A; 2-methylimidazole and methanol solution are mixed to obtain a mixed solution, namely 2-methylimidazole solution, denoted as solution B; finally, the two solutions are mixed to obtain a mixed solution, thus completing the preparation.

[0042] The mass ratio of zinc nitrate hexahydrate to 2-methylimidazole is 0.5–1.5:1; the mass ratio of zinc nitrate hexahydrate to methanol is 0.02–0.08:1; and the mass ratio of 2-methylimidazole to methanol is 0.02–0.08:1.

[0043] In this step, the stirring temperature is room temperature, and the stirring time is 4 to 8 hours.

[0044] 2) The mixed solution from step 1) was centrifuged, washed, and dried to obtain a white ZIF-8 solid.

[0045] 3) Disperse the white ZIF-8 solid in a methanol solution containing tannic acid, and then stir, centrifuge, wash and dry to obtain a light yellow hollow ZIF-8 solid; the mass ratio of ZIF-8 solid to tannic acid is 0.1 to 0.5:1; the mass ratio of tannic acid to methanol is 0.005 to 0.02:1.

[0046] The stirring time in this step is 1 min to 10 min. For example, the stirring time is 1 min, 3 min, 5 min, 8 min, or 10 min.

[0047] 4) The pale yellow hollow ZIF-8 solid from step 3) was dispersed in a buffered methanol solution and sonicated for 5-30 minutes. Then, dopamine hydrochloride was added and stirred for 3-15 hours. The mixture was then centrifuged, washed, and dried to obtain a gray hollow ZIF-8@PDA pyrolysis precursor. The mass ratio of hollow ZIF-8 solid to dopamine hydrochloride was 5-0.05:1, and the mass ratio of hollow ZIF-8 solid to buffer solution was 0.02-0.0003:1.

[0048] In this step, methanol is used as the solvent in the synthesis of ZIF-8. If water is used to prepare the buffer solution, it will cause partial dissolution and destruction of ZIF-8. Therefore, methanol is used as the solvent when preparing the buffer solution.

[0049] In this embodiment, the buffer solution is a mixed solution composed of Tris-HCl and methanol, with a pH of 8 to 10 and a concentration of 10 mmol / L to 50 mmol / L. In the following embodiments, mmol / L is denoted as mM.

[0050] 5) Under an inert atmosphere, ferrocene and the hollow ZIF-8@PDA pyrolysis precursor from step 4) are calcined together at a mass ratio of 0.5 to 1.5:1. The resulting black solid is the carbon-defective iron single-atom catalyst Vc-Fe-NC@NC.

[0051] In this step, the inert gas is nitrogen or argon; calcination includes a first stage of calcination and a second stage of calcination.

[0052] Specifically, the first stage of calcination conditions are: temperature of 100℃~200℃, holding time of 1h~3h, and heating rate of 1℃ / min~5℃ / min; the second stage of calcination conditions are: temperature of 800℃~1000℃, holding time of 1h~3h, and heating rate of 1℃ / min~10℃ / min.

[0053] The iron source used in the above synthesis method of the present invention is represented by ferrocene. However, other iron sources, such as ferric chloride and ferrous chloride, can also be used to prepare catalysts and obtain carbon-deficient iron single-atom catalysts with the same structure as those of the present invention for degrading organic dyes.

[0054] This invention prepares a high specific surface area and carbon-defect-rich iron single-atom catalyst, Vc-Fe-NC@NC, by modifying the surface of hollow ZIF-8 with polydopamine. This significantly improves the catalyst's ability to activate dissolved oxygen in water. This highly active catalyst has advantages such as simple preparation, low cost, and environmental friendliness. It can be applied to the degradation of organic dyes in wastewater. During the degradation process, no external conditions (light source and oxidant) are required for activation or stimulation, and efficient degradation of organic dyes can be achieved. In addition, the prepared catalyst can efficiently degrade organic wastewater within a wide pH range of 3 to 11 without the need for secondary pH adjustment, making it more convenient to use.

[0055] The application of the carbon-deficient iron single-atom catalyst prepared in this invention in the degradation of organic dye wastewater.

[0056] In practical applications, carbon-defective iron single-atom catalysts are directly added to organic dye wastewater to catalyze the degradation of organic dyes without an external light source.

[0057] Preferably, the amount of carbon-deficient iron single-atom catalyst used is 0.1 g / L, and the degradation time is 10 min.

[0058] Preferably, the organic dye in the organic dye wastewater is Rhodamine B, methyl orange, or methylene blue.

[0059] The following examples illustrate the preparation method and performance of the catalyst of the present invention, but these should not be construed as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes provided in this embodiment includes the following steps:

[0062] (1) Weigh 2.38g of zinc nitrate hexahydrate and dissolve it in 60mL of methanol solution. Then add 30mL of methanol solution containing 2.6g of 2-methylimidazole to the above solution. Mix and stir for 6h to obtain a mixed solution.

[0063] (2) Centrifuge the obtained mixed solution, wash it three times with methanol, and dry it overnight under vacuum at 60°C to obtain a white solid, which is denoted as ZIF-8.

[0064] (3) Disperse 1g of white ZIF-8 solid in 400mL of methanol solution containing 3.2g of tannic acid, stir for 5min, centrifuge to collect the pale yellow hollow ZIF-8, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain a pale yellow solid.

[0065] (4) Disperse 0.5g of pale yellow solid in 250mL of 25mM buffer solution and sonicate for 15min. The pH of the buffer solution is 8.5. Then add 0.1g of dopamine hydrochloride and stir for 6h. Centrifuge to collect gray hollow ZIF-8@PDA, wash three times with methanol, and dry under vacuum at 60℃ overnight to obtain gray hollow ZIF-8@PDA pyrolysis precursor.

[0066] (5) Place 0.24g of ferrocene and 0.3g of hollow ZIF-8@PDA pyrolysis precursor at both ends of a ceramic boat, with the ferrocene and hollow ZIF-8@PDA pyrolysis precursor placed sequentially along the airflow direction. Heat to 150℃ in a tube furnace under N2 atmosphere and hold for 2h at a heating rate of 2℃ / min. Then continue heating to 900℃ and hold for 2h at a heating rate of 5℃ / min. Allow to cool naturally to room temperature to obtain a carbon defect type iron single-atom catalyst.

[0067] Example 2

[0068] The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes provided in this embodiment includes the following steps:

[0069] (1) Weigh 2.38g of zinc nitrate hexahydrate and dissolve it in 60mL of methanol. Then add 30mL of methanol solution containing 1.19g of 2-methylimidazole to the above solution and mix and stir for 4h to obtain a mixed solution.

[0070] (2) Centrifuge the obtained mixed solution, wash it three times with methanol, and dry it overnight under vacuum at 60°C to obtain a white solid, which is denoted as ZIF-8.

[0071] (3) Disperse 1g of white ZIF-8 solid in 400mL of methanol solution containing 10g of tannic acid, stir for 1min, centrifuge to collect the pale yellow hollow ZIF-8, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain a pale yellow solid.

[0072] (4) Disperse 3g of pale yellow solid in 200mL of 30mM buffer solution and sonicate for 5min. The pH of the buffer solution is 8. Then add 1g of dopamine hydrochloride and stir for 10h. Centrifuge to collect gray hollow ZIF-8@PDA, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain gray hollow ZIF-8@PDA pyrolysis precursor.

[0073] (5) Place 0.24g of ferrocene and 0.12g of hollow ZIF-8@PDA pyrolysis precursor at both ends of a ceramic boat, with the ferrocene and hollow ZIF-8@PDA pyrolysis precursor placed sequentially along the direction of the gas flow. Heat to 100℃ in a tube furnace under N2 atmosphere and hold for 1h at a heating rate of 1℃ / min. Then continue heating to 800℃ and hold for 2h at a heating rate of 1℃ / min. Allow to cool naturally to room temperature to obtain a carbon defect type iron single-atom catalyst.

[0074] Example 3

[0075] The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes provided in this embodiment includes the following steps:

[0076] (1) Weigh 2.38g of zinc nitrate hexahydrate and dissolve it in 60mL of methanol. Then add 30mL of methanol solution containing 2.6g of 2-methylimidazole to the above solution and mix and stir for 8h to obtain a mixed solution.

[0077] (2) Centrifuge the obtained mixed solution, wash it three times with methanol, and dry it overnight under vacuum at 60°C to obtain a white solid, which is denoted as ZIF-8.

[0078] (3) Disperse 1g of white ZIF-8 solid in 400mL of methanol solution containing 4g of tannic acid, stir for 10min, centrifuge to collect the pale yellow hollow ZIF-8, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain a pale yellow solid.

[0079] (4) Disperse 0.03g of pale yellow solid in 300mL of 40mM buffer solution and sonicate for 30min. The pH of the buffer solution is 9. Then add 1g of dopamine hydrochloride and stir for 3h. Centrifuge to collect gray hollow ZIF-8@PDA, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain gray hollow ZIF-8@PDA pyrolysis precursor.

[0080] (5) Place 0.24g of ferrocene and 0.16g of hollow ZIF-8@PDA pyrolysis precursor at both ends of a ceramic boat, with the ferrocene and hollow ZIF-8@PDA pyrolysis precursor placed sequentially along the airflow direction. Heat to 150℃ in a tube furnace under N2 atmosphere and hold for 3h at a heating rate of 5℃ / min. Then continue heating to 900℃ and hold for 3h at a heating rate of 10℃ / min. Allow to cool naturally to room temperature to obtain a carbon defect type iron single-atom catalyst.

[0081] Example 4

[0082] The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes provided in this embodiment includes the following steps:

[0083] (1) Weigh 2.38g of zinc nitrate hexahydrate and dissolve it in 60mL of methanol. Then add 30mL of methanol solution containing 1.59g of 2-methylimidazole to the above solution and mix and stir for 8h to obtain a mixed solution.

[0084] (2) Centrifuge the obtained mixed solution, wash it three times with methanol, and dry it overnight under vacuum at 60°C to obtain a white solid, which is denoted as ZIF-8.

[0085] (3) Disperse 1g of white ZIF-8 solid in 400mL of methanol solution containing 2g of tannic acid, stir for 10min, centrifuge to collect the pale yellow hollow ZIF-8, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain a pale yellow solid.

[0086] (4) Disperse 0.05g of pale yellow solid in 150mL of 50mM buffer solution and sonicate for 15min. The pH of the buffer solution is 10. Then add 1g of dopamine hydrochloride and stir for 15h. Centrifuge to collect the gray hollow ZIF-8@PDA, wash three times with methanol, and dry under vacuum at 60℃ overnight to obtain the gray hollow ZIF-8@PDA pyrolysis precursor.

[0087] (5) Place 0.24g of ferrocene and 0.16g of hollow ZIF-8@PDA pyrolysis precursor at both ends of a ceramic boat, with the ferrocene and hollow ZIF-8@PDA pyrolysis precursor placed sequentially along the direction of the gas flow. Heat to 200℃ in a tube furnace under N2 atmosphere and hold for 3h at a heating rate of 5℃ / min. Then continue heating to 1000℃ and hold for 2h at a heating rate of 10℃ / min. Allow to cool naturally to room temperature to obtain a carbon defect type iron single-atom catalyst.

[0088] To further illustrate the catalytic performance of the carbon-defective iron single-atom catalyst prepared in this invention, the following experiments were conducted for verification. Simultaneously, the following comparative examples were designed, with the catalysts obtained in the comparative examples used as control samples for comparison with the catalyst of this invention.

[0089] Comparative Example 1

[0090] The method for preparing the carbon-deficient iron single-atom catalyst provided in this comparative example includes the following steps:

[0091] (1) Weigh 2.38g of zinc nitrate hexahydrate and dissolve it in 60mL of methanol solution. Then add 30mL of methanol solution containing 2.6g of 2-methylimidazole to the above solution. Mix and stir for 6h to obtain a mixed solution.

[0092] (2) Centrifuge the obtained mixed solution, wash it three times with methanol, and dry it overnight under vacuum at 60°C to obtain a white solid, which is denoted as ZIF-8.

[0093] (3) Disperse 1g of white ZIF-8 solid in 400mL of methanol solution containing 3.2g of tannic acid, stir for 5min, centrifuge to collect the pale yellow hollow ZIF-8, wash three times with methanol, and dry overnight under vacuum at 60℃ to obtain a pale yellow solid.

[0094] (4) Place 0.24g of ferrocene and 0.3g of hollow ZIF-8 pale yellow solid at both ends of a ceramic boat, with the ferrocene and hollow ZIF-8 placed sequentially along the direction of the airflow. Heat to 150℃ in a tube furnace under N2 atmosphere and hold for 2h at a heating rate of 2℃ / min. Then continue heating to 900℃ and hold for 2h at a heating rate of 5℃ / min. Allow to cool naturally to room temperature to obtain Vc-Fe-NC carbon defect type iron single atom catalyst.

[0095] Specifically, the catalyst prepared in Example 1 (Vc-Fe-NC@NC) and the catalyst prepared in Comparative Example 1 (Vc-Fe-NC) were used as examples to verify the catalyst performance.

[0096] Experiment 1 XRD spectrum

[0097] The XRD pattern of the carbon-defective iron single-atom catalyst prepared in Example 1 was determined using an X-ray diffractometer, as shown below. Figure 1 As shown.

[0098] from Figure 1 The XRD pattern of the carbon-defective iron single-atom catalyst shows two broad peaks at 43.9° and 25.2°, which belong to the (002) and (101) crystal planes of graphite carbon, respectively. No diffraction peaks of iron or iron oxide were observed, which proves that the iron atoms in the catalyst exist in an isolated state.

[0099] Experiment 2 XPS C 1s spectrum

[0100] The XPS C1s spectrum of the carbon-defect iron single-atom catalyst prepared in Example 1 was determined using X-ray photoelectron spectroscopy. Test conditions: Target material: Al target (1486.6 eV); Vacuum: better than 5 × 10⁻⁶ eV. -9 Torr power: 75W; resolution: 160eV; step size (meV): 1000.0.

[0101] from Figure 3 XPS C1s spectra of carbon-defective iron single-atom catalysts clearly show sp1 atoms representing carbon defects in carbon materials. 3 The peak carbon content is 47.88%, which indicates the degree of graphitization in the carbon material (sp). 2 The peak carbon content was 28.79%, indicating the introduction of a large number of carbon defects into the catalyst. On the one hand, carbon defects themselves can serve as new active sites; on the other hand, they facilitate the contact of reactants and products with the active sites inside the catalyst, improving the utilization rate of the active sites and thus significantly enhancing its catalytic performance.

[0102] Experiment 3 ESR spectrum

[0103] The ESR spectrum of the carbon-defective iron single-atom catalyst prepared in Example 1 was determined using electron spin resonance spectroscopy.

[0104] Sample preparation: Mix 5 μL of 15 mM 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO), 200 μL of ultrapure water, and 100 μL of 0.1 mg / mL (prepared with ultrapure water) Vc-Fe-NC@NC and shake well. Pipette the mixed solution to a height of about 2 cm to 3 cm using a capillary tube with an inner diameter of 0.9 mm to 1.1 mm. Seal the bottom of the capillary tube with a small amount of petroleum jelly. Wipe the capillary tube with lens paper and then place it in a paramagnetic tube to test for superoxide anion free radicals.

[0105] Test conditions: Microwave band: X-band; Modulation frequency: 100.00kHz; Modulation amplitude: 1.000G; Scan width: 100.0G; Scan range: 3306.4G-3406.4G. Results are as follows: Figure 3 As shown.

[0106] from Figure 3 The ESR spectrum of the carbon-deficient iron single-atom catalyst clearly shows that the catalyst can activate dissolved oxygen in water and generate a large number of superoxide anion radicals.

[0107] Experiment 4 Catalytic performance

[0108] The carbon-deficient iron single-atom catalysts prepared in Example 1 (Vc-Fe-NC@NC) and Comparative Example 1 (Vc-Fe-NC) were used for the catalytic degradation of organic dyes Rhodamine B, methyl orange and methylene blue. The specific experimental procedures are as follows.

[0109] (1) Prepare 50 mL of each of the following solutions using ultrapure water, with a concentration of 10 mg / L: Rhodamine B solution, methyl orange solution, and methylene blue solution. Prepare three portions of Rhodamine B solution, and one portion each of methyl orange solution and methylene blue solution.

[0110] (2) Three Rhodamine B solutions were prepared. The first solution contained 0.1 g / L of the catalyst from Comparative Example 1, the second contained 0.2 g / L of the catalyst from Comparative Example 1, and the third contained 0.1 g / L of the catalyst from Example 1. All solutions were continuously stirred in the dark to degrade the dye. Samples were taken at 0 min, 2 min, 5 min, 8 min, and 10 min of reaction time. After centrifugation, the absorbance of the supernatant was measured using a UV-Vis spectrophotometer. The degradation abilities of Rhodamine B by the samples of Example 1 (Vc-Fe-NC@NC) and Comparative Example 1 (Vc-Fe-NC) are shown in Table 1 and... Figure 4 As shown.

[0111] (3) 0.1 g / L of the catalyst from Example 1 was added to both methyl orange and methylene blue solutions. The mixture was continuously stirred in the dark to degrade the dye. Samples were taken at 0 min, 2 min, 5 min, 8 min, and 10 min of reaction time. After centrifugation, the absorbance of the supernatant was measured using a UV-Vis spectrophotometer. The degradation ability of methyl orange by Example 1 (Vc-Fe-NC@NC) is shown below. Figure 5 As shown; the degradation results of methylene blue in Example 1 are as follows. Figure 6 As shown.

[0112] Table 1 Comparison of Rhodamine B degradation between Example 1 and Comparative Example 1

[0113] Vc-Fe-NC 0.1 10 83 Vc-Fe-NC 0.2 10 99 Vc-Fe-NC@NC 0.1 10 99

[0114] The degradation effects in Table 1 were calculated as follows:

[0115] Degradation efficiency (%) = (C0 - C) t ) / C0×100%=(A0-A t ) / A0×100%

[0116] Where C0 is the initial concentration of the organic dye; C t Let A be the concentration of the organic dye solution at time t; A0 be the initial absorbance of the organic dye; A t Let t be the absorbance of the organic dye solution at time t.

[0117] from Figure 4The UV-Vis absorption spectra of the catalysts used to degrade Rhodamine B show that the catalyst of Example 1, at a concentration of 0.1 g / L, achieved a degradation rate of over 99% for Rhodamine B within 10 minutes. Table 1 shows that when the concentrations of Example 1 (Vc-Fe-NC@NC) and Comparative Example 1 (Vc-Fe-NC) are both 0.1 g / L, the catalyst of Example 1 exhibits a higher degradation efficiency of over 99% for Rhodamine B within the same 10-minute timeframe, while the catalyst of Comparative Example 1 achieves only 83% degradation. When the catalyst of Comparative Example 1 achieves a 99% degradation efficiency for Rhodamine B within 10 minutes, the required catalyst concentration is 0.2 g / L, which is twice the amount used in Example 1. Therefore, the catalyst of Example 1 demonstrates better degradation performance. This indicates that modifying the surface of hollow ZIF-8 with polydopamine can significantly improve the degradation capacity of carbon-deficient iron single-atom catalysts.

[0118] from Figure 5 The UV-Vis absorption spectrum of methyl orange degradation by the catalyst shows that the catalyst provided in Example 1 can achieve a degradation rate of over 99% for methyl orange within a dosage of 0.1 g / L and a degradation time of 10 min.

[0119] from Figure 6 The UV-Vis absorption spectrum of the catalyst for the degradation of methylene blue shows that the catalyst provided in Example 1 can achieve a degradation rate of over 97% for methylene blue within a dosage of 0.1 g / L and a degradation time of 10 min.

[0120] It is evident that, compared to the existing degradation conditions (light and external oxidant) and degradation effects of organic dye wastewater, the catalyst prepared in this invention does not require an external light source or external oxidant during degradation, and has a fast degradation rate, high efficiency, simple conditions, and low treatment cost.

[0121] Experiment 5 Catalyst Dosage

[0122] Taking the degradation of Rhodamine B by the catalyst in Example 1 as an example, the effect of the amount of carbon-deficient iron single-atom catalyst on the degradation effect was investigated. The specific experimental process is as follows.

[0123] (1) Prepare a Rhodamine B solution with a concentration of 10 mg / L using ultrapure water.

[0124] (2) Take five equal volumes of the above-mentioned Rhodamine B solution, with corresponding catalyst concentrations of 0, 0.05 g / L, 0.1 g / L, 0.2 g / L, and 0.3 g / L. Stir continuously in the dark to degrade the dye. Take samples every 2 minutes, centrifuge, and measure the absorbance of the supernatant using a UV-Vis spectrophotometer. Determine the change in solution concentration based on the change in absorbance. The results are as follows: Figure 7 As shown.

[0125] from Figure 7 It can be seen that the degradation rate increases with the increase of catalyst dosage. However, when the catalyst concentration is 0.1 g / L, 0.2 g / L, and 0.3 g / L, and the degradation time is 10 min or more, the degradation trend is slow and the degradation effect does not change much. A degradation time of 10 min is appropriate. Moreover, the degradation effect of catalyst dosages of 0.2 g / L and 0.3 g / L at 10 min is not much different from that of catalyst dosage of 0.1 g / L. Preferably, the catalyst dosage is 0.1 g / L.

[0126] pH of the catalytic system in Experiment 6

[0127] Taking the catalyst prepared in Example 1 for the degradation of Rhodamine B, methyl orange and methylene blue as an example, the effect of system pH on the degradation effect was investigated. The specific experimental process is as follows.

[0128] (1) Prepare Rhodamine B solution, methyl orange solution and methylene blue solution with a concentration of 10 mg / L respectively.

[0129] (2) Take five equal volumes of the above-mentioned Rhodamine B solution, with corresponding pH values ​​of 3, 5, 7, 9, and 11, respectively. Stir continuously in a dark environment to degrade the dye. Take samples every 2 minutes, centrifuge, and measure the absorbance of the supernatant using a UV-Vis spectrophotometer. The results are as follows: Figure 8 As shown.

[0130] from Figure 8 This indicates that the catalyst has a good degradation effect on Rhodamine B in a wide pH range (3-11).

[0131] (3) Referring to the method in step (2), the catalyst prepared in Example 1 was used to degrade methyl orange and methylene blue, and the results are as follows. Figure 9 and Figure 10 As shown.

[0132] from Figure 9 It can be seen that the catalyst has a good degradation effect on methyl orange within a wide pH range (3-11); from Figure 10 It can be seen that the catalyst has a good degradation effect on methylene blue in a wide pH range (3-11).

[0133] Experiment 7 N2 adsorption-desorption isotherm curve

[0134] The N2 adsorption-desorption isotherms of the carbon-defective iron single-atom catalysts prepared in Example 1 (Vc-Fe-NC@NC) and Comparative Example 1 (Vc-Fe-NC) were determined using a fully automated specific surface area and pore size analyzer.

[0135] Test conditions: (1) Pore structure parameters: a. Specific surface area, b. Mesopore distribution; (2) Data processing methods: a. Brunauer-Emmett-Teller specific surface area detection method, b. Barret-Joyner-Halenda mesoporous analysis model. Automatic degassing: √; Analytical adsorption: nitrogen; Analytical bath temperature approximately -195℃; Thermal correction: ×; Measurement equilibrium interval: 20s or 30s; Low-pressure dose: 3.000cm 3 / g.

[0136] 1. Sample information: The sample mass is 0.1g to 0.2g.

[0137] 2. Sample tube: Use of isothermal jacket: √; Vacuum seal type: Use of stopper.

[0138] 3. Degassing conditions: Vacuuming stage: heating rate 10℃ / min, target temperature 90℃, vacuuming rate 5.0 mmHg / s, vacuum degree 500 μmHg, vacuuming time 60 min. Heating stage: heating rate 10.0℃ / min, final degassing temperature 200℃, degassing time 480 min. Vacuuming and heating stages: maintaining pressure at 100 mmHg.

[0139] 4. Analysis conditions: Intake volume is 3.0000 cm³. 3 / g, Nitrogen gas backfill: √.

[0140] The N2 adsorption-desorption isotherm curve of the catalyst is shown in the figure. Figure 11 As shown. Figure 11 In the figure, (a) shows the specific surface area distribution; (b) shows the pore size distribution.

[0141] from Figure 11 (a) The N2 adsorption-desorption isotherm of the carbon-deficient iron single-atom catalyst shows that the specific surface area of ​​the catalyst in Example 1 (Vc-Fe-NC@NC) is 1897 m². 2 / g, significantly larger than the specific surface area of ​​790m² of the catalyst in Comparative Example 1 (Vc-Fe-NC). 2 / g, the catalyst in Example 1 has a significantly increased specific surface area, allowing reactants to contact a larger catalyst surface and thus significantly improving the reaction rate. From Figure 11As clearly seen in (b), the average pore size of the catalyst in Example 1 is 6.19 nm, which is larger than the average pore size of the catalyst in Comparative Example 1 (5.73 nm). Furthermore, the mesopore size of the catalyst in Example 1 increases sharply at 3.82 nm, and the proportion of this pore size in the catalyst of Example 1 is significantly greater than that in Comparative Example 1. This increase in pore size facilitates mass transport during the reaction process and exposes the active sites within the catalyst, thereby improving the utilization rate of the active sites. Therefore, the degradation ability of the catalyst in Example 1 is significantly higher than that of Comparative Example 1.

[0142] It should also be noted that the degradation test of organic matter in wastewater by the catalyst of the present invention was conducted in a dark environment. However, this does not mean that the catalyst of the present invention must be used in a dark environment. It only indicates that the catalyst of the present invention does not require external light source (such as visible light or ultraviolet light) for excitation like existing catalysts. It can directly achieve efficient degradation of organic dye wastewater in natural environment or even in extreme environmental conditions such as darkness. It is more convenient to use and has a lower degradation cost.

[0143] The above results show that the carbon-deficient iron single-atom catalyst for the efficient degradation of organic dyes prepared in this invention can directly degrade organic dyes without external light or oxidant, and the degradation is completed within 10 minutes. It has a fast degradation rate, high degradation efficiency, and low degradation cost. The catalyst has a wide applicable pH range (3-11). Therefore, during catalytic degradation, there is no need to adjust the pH of the organic dye wastewater twice, which is beneficial to the industrial application of the catalyst.

[0144] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes, characterized in that, Includes the following steps: 1) Prepare a mixed solution using zinc nitrate hexahydrate, 2-methylimidazole, and methanol solution; the mass ratio of zinc nitrate hexahydrate to 2-methylimidazole is 0.5~1.5:1; 2) The mixed solution from step 1) is centrifuged, washed, and dried to obtain ZIF-8 solid; 3) Disperse ZIF-8 solid in a methanol solution containing tannic acid, and obtain hollow ZIF-8 solid by stirring, centrifugation, washing and drying in sequence; the mass ratio of ZIF-8 solid to tannic acid is 0.1~0.5:1, and the mass ratio of tannic acid to methanol is 0.005~0.02:1; 4) Disperse the hollow ZIF-8 solid from step 3) in a buffer solution, sonicate for 5 min to 30 min, add dopamine hydrochloride and stir until homogeneous, then centrifuge, wash and dry sequentially to obtain the hollow ZIF-8@PDA pyrolysis precursor; the mass ratio of the hollow ZIF-8 solid to dopamine hydrochloride is 5 to 0.05:1, and the mass ratio of the hollow ZIF-8 solid to the buffer solution is 0.02 to 0.0003:1; 5) Under an inert atmosphere, the iron source and the hollow ZIF-8@PDA pyrolysis precursor from step 4) are calcined together at a mass ratio of 0.5~1.5:1 to obtain a black solid, namely the target product Vc-Fe-NC@NC; Calcination includes a first stage of calcination and a second stage of calcination; The first stage of calcination conditions are: temperature of 100℃~200℃, holding time of 1h~3h, and heating rate of 1℃ / min~5℃ / min; the second stage of calcination conditions are: temperature of 800℃~1000℃, holding time of 1h~3h, and heating rate of 1℃ / min~10℃ / min.

2. The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes according to claim 1, characterized in that, The stirring time in step 3) is 1 min to 10 min.

3. The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes according to claim 1, characterized in that, In step 4), the stirring time is 3h to 15h, and the pH of the buffer solution is 8 to 10.

4. The method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes according to claim 1, characterized in that, In step 5), the inert gas is nitrogen or argon; the iron source is ferrocene, ferric chloride or ferrous chloride.

5. The carbon-deficient iron single-atom catalyst prepared by the method for preparing a highly efficient carbon-deficient iron single-atom catalyst for degrading organic dyes as described in claim 1.

6. The application of the carbon-deficient iron single-atom catalyst as described in claim 5 in the degradation of organic dye wastewater.

7. The application according to claim 6, characterized in that, The application involves directly adding a carbon-defective iron single-atom catalyst to organic dye wastewater to catalyze the degradation of organic dyes without an external light source.

8. The application according to claim 7, characterized in that, The degraded organic dyes are Rhodamine B, methyl orange, or methylene blue.

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