Preparation and application of monatomic catalyst for phenol degradation
By preparing single-atom catalysts of Fe, Co, Mn, Cu and nitrogen-doped porous carbon supports, the problems of reduced active sites and low metal utilization after recycling of nanocatalysts were solved, and efficient phenol degradation and low-cost industrial wastewater treatment were achieved.
Patent Information
- Application Number
- CN202510878819.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-27
- Publication Date
- 2025-10-10
AI Technical Summary
Existing nanocatalysts in phenol wastewater treatment have problems such as reduced active sites after recycling, low metal atom utilization and high cost. The homogeneous Fenton system requires strict pH control and produces iron sludge hazardous waste.
A single-atom catalyst composed of transition metal active central atoms (M=Fe, Co, Mn, Cu) and nitrogen-doped porous carbon supports is formed through atomic-level dispersion of the M-N4 coordination configuration, combined with gradient confined pyrolysis and acid washing purification steps, to form a catalytic material with high dispersion stability and wide pH adaptability.
Under neutral conditions, persulfate is efficiently activated to generate strong oxidizing free radicals, achieving a phenol degradation efficiency of ≥92% and an activity retention rate of ≥85% after 5 cycles, reducing engineering costs.
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Figure CN120754889A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of nanocatalytic materials, in particular to the preparation and application of a single-atom catalyst for phenol degradation. Background Art
[0002] Heterogeneous catalytic technologies are currently attracting attention for phenol wastewater treatment due to their potential to avoid secondary pollution. However, they still suffer from fundamental drawbacks: nanocatalysts (such as Fe₃O₄ / CeO₂) aggregate due to surface free energy, resulting in a >50% reduction in active sites after recycling, and metal atom utilization is generally <30%. While homogeneous Fenton systems offer high activity, they require a pH of ≤3.0 and generate hazardous iron sludge, increasing sludge treatment costs by over 40%. Single-atom catalysts (SACs) theoretically offer the potential to surpass this atomic utilization limit, but existing preparation methods inevitably form metal clusters at loadings >3 wt%, and persulfate activation efficiency under neutral conditions is less than 45% of that of conventional systems. Therefore, the development of novel catalytic materials with high dispersion stability, wide pH adaptability, and low engineering costs is urgently needed. Summary of the Invention
[0003] In order to solve the problems raised in the above background technology, the purpose of the present invention is to provide a preparation and application of a single-atom catalyst for phenol degradation.
[0004] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a single-atom catalyst for phenol degradation. The single-atom catalyst is composed of a transition metal active center atom (M) and a nitrogen-doped porous carbon support. The transition metal atoms (M = at least one of Fe, Co, Mn, and Cu) are atomically dispersed on the support via a planar M-N4 coordination configuration, and the metal loading is 0.5-5.0 wt% (verified by ICP-OES).
[0005] Furthermore, the nitrogen content of the single-atom catalyst is 5-15 at% (measured by XPS), the proportion of pyridinic nitrogen in the total nitrogen is ≥80%, and the specific surface area is 800-1200 m 2 / g, (BET method), pore volume 0.8~1.2 cm 3 / g (BJH method).
[0006] The present invention also provides a method for preparing a single-atom catalyst for phenol degradation, which specifically comprises the following steps: (1) Precursor coordination self-assembly: Metal acetylacetonate (M(acac)3, M=Fe / Co / Mn / Cu), 2-methylimidazole, and melamine were dissolved in ethanol and ultrasonically dispersed for 20-30 min to form a homogeneous solution; the solution was stirred and refluxed in an oil bath at 60-80 °C for 5-7 h to allow the metal ions to coordinate with the nitrogen of imidazole and triazine to self-assemble; the reaction solution was centrifuged to collect the solid, which was washed with anhydrous ethanol to remove the unreacted monomers and finally dried in vacuum to obtain the precursor.
[0007] (2) Gradient confined pyrolysis: The precursor is placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow: the first stage: the temperature is raised to 220-250 °C at a certain rate and kept at this temperature for 2-3 h; the second stage: the temperature is raised to 700-800 °C at a certain rate, the carbon skeleton condenses to form nitrogen-doped confined cavities, and the migration and agglomeration of metal atoms are inhibited; the third stage: the temperature is kept constant at 700-800 °C for 1-3 h to complete the M-N4 coordination reconstruction.
[0008] (3) Acid washing and purification: Add H2SO4 solution to the pyrolysis product and mechanically stir it in a water bath at 50-60℃ for a period of time; after acid washing, centrifuge and wash with deionized water, then rinse with NaHCO3 solution 2-5 times to neutralize trace acid; finally, vacuum dry the solid at a certain temperature for a period of time to obtain a single-atom catalyst.
[0009] Furthermore, in step (1), the metal in the metal acetylacetonate is one of Fe, Co, Mn, and Cu.
[0010] Furthermore, in the homogeneous solution of step (1), the concentrations of metal acetylacetonate, 2-methylimidazole, and melamine are 0.015-0.025 mol / L, 0.042-0.075 mol / L, and 0.072-0.125 mol / L, respectively.
[0011] Furthermore, in step (1), the reaction solution is centrifuged at 8000-10000 rpm for 8-10 min to collect the solid, which is then washed three times with anhydrous ethanol to remove unreacted monomers, and finally vacuum dried at 55-65° C. for 10-12 h to obtain the precursor.
[0012] Furthermore, in step (2), in the first stage, the temperature is raised to 220-250°C at a rate of 2-5°C / min and kept at that temperature for 2-3 h to allow the acetylacetone ligand to evaporate slowly to avoid pore collapse; in the second stage, the temperature is raised to 700-800°C at a rate of 2-5°C / min.
[0013] Furthermore, in step (3), the concentration of the H2SO4 solution is 0.5~1 M, the concentration of the NaHCO3 solution is 0.1~0.4 M, and the vacuum drying temperature is 60~80°C and the time is 18~24 h.
[0014] The present invention also provides the use of the above-mentioned single-atom catalyst in phenol degradation. The single-atom catalyst is added to phenol-containing wastewater to a concentration of 0.1-1.0 g / L; a persulfate oxidant is added to a concentration of 0.5-5.0 mM; the reaction is stirred at a pH of 3-9 and a temperature of 10-40°C for 10-30 minutes. After the reaction, the catalyst is separated and recovered, regenerated with NaOH, and then recycled.
[0015] Furthermore, the persulfate oxidant is peroxymonosulfate (PMS) or peroxydisulfate (PDS).
[0016] Furthermore, under neutral conditions, the degradation rate of 10~200 mg / L phenol was ≥92% in 30 minutes, and the TOC removal rate was ≥85.7%.
[0017] Furthermore, after regeneration with 0.1~0.5 M NaOH and recycling, the phenol removal rate was ≥85% after 5 cycles. Compared with the prior art, the present invention has the following beneficial effects: The planar M-N4 active center, through atomic-level dispersion, provides uniform and highly exposed catalytic sites, efficiently activating persulfate to generate strong oxidizing free radicals or non-radical active species, significantly improving the kinetics of phenol degradation. The high proportion of pyridinic nitrogen not only stabilizes the M-N4 coordination structure but also synergistically modulates the electron cloud density of the metal center, enhancing persulfate adsorption and electron transfer capabilities, and achieving dual-site synergistic catalysis. A gradient confined pyrolysis strategy forms a rigid nitrogen-doped carbon framework and its microporous / mesoporous confined cavities, effectively inhibiting the migration and agglomeration of metal atoms and ensuring structural stability. In a persulfate activation system, the catalyst of this invention degrades 10-200 mg / L of phenol under neutral conditions with a removal rate of ≥92% in 30 minutes and an activity retention rate of ≥85% after five cycles. It is suitable for advanced industrial wastewater treatment and has the advantages of high atom utilization, wide pH adaptability, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 HAADF-STEM image of Fe single-atom catalyst supported on nitrogen-doped porous carbon; Figure 2 HAADF-STEM image of Co single-atom catalyst supported on nitrogen-doped porous carbon. DETAILED DESCRIPTION
[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1
[0020] Preparation of single atom catalysts: (1) Precursor coordination self-assembly: 0.02 mol / L Fe(acac)3, 0.06 mol / L 2-methylimidazole, and 0.1 mol / L melamine were dissolved in ethanol and ultrasonically dispersed for 25 min to form a homogeneous solution. The mixture was stirred and refluxed in a 70°C oil bath for 6 h to allow the iron ions to coordinate with the nitrogen of imidazole and triazine to self-assemble. The reaction solution was centrifuged at 9000 rpm for 9 min to collect the solid, which was then washed three times with anhydrous ethanol to remove unreacted monomers. Finally, the precursor was dried in a vacuum at 60°C for 11 h to obtain the precursor.
[0021] (2) Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow. In the first stage, the temperature was raised to 230°C at a rate of 3°C / min and held for 2.5 h. In the second stage, the temperature was raised to 750°C at a rate of 3°C / min to allow the carbon skeleton to condense into nitrogen-doped confined cavities, inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 750°C for 2 h to complete the Fe-N4 coordination reconstruction.
[0022] (3) Acid washing and purification: The pyrolysis product was added to a 0.75 M H2SO4 solution and mechanically stirred in a 55°C water bath for a period of time. After acid washing, the product was centrifuged, washed with deionized water, and then rinsed three times with a 0.25 M NaHCO3 solution to neutralize trace acid. The final solid was vacuum dried at 70°C for 20 h to obtain a single-atom catalyst. The HAADF-STEM image of the Fe single-atom catalyst is shown in Figure 2. Figure 1 As shown in the figure, it can be seen that there are some dispersed metal bright spots in the catalyst, indicating that the metal exists in the form of atomic dispersion. The nitrogen content of the catalyst is 12 at%, of which pyridinic nitrogen accounts for 87%, and the specific surface area is 1200 m 2 / g, pore volume 1.2 cm 3 / g.
[0023] Phenol degradation applications: The prepared catalyst was added to wastewater containing phenol (initial concentration 100 mg / L) to a concentration of 0.5 g / L. Permonosulfate (PMS) oxidant was then added to a concentration of 2.5 mM. The reaction was stirred at pH 7 and 25°C for 30 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.3 M NaOH, and then recycled. Testing showed a phenol removal rate of 95%, and after five cycles, the phenol removal rate reached 90%. Example 2
[0024] Preparation of single-atom catalysts (1) Precursor coordination self-assembly: 0.015 mol / L Co(acac)3, 0.042 mol / L 2-methylimidazole, and 0.072 mol / L melamine were dissolved in ethanol and ultrasonically dispersed for 20 min to form a homogeneous solution. The mixture was stirred and refluxed in an oil bath at 60°C for 5 h to allow the cobalt ions to coordinate with the nitrogen of imidazole and triazine to self-assemble. The reaction solution was centrifuged at 8000 rpm for 8 min to collect the solid, which was then washed three times with anhydrous ethanol to remove unreacted monomers. Finally, the precursor was dried in a vacuum at 55°C for 10 h to obtain the precursor.
[0025] (2) Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow. In the first stage, the temperature was raised to 220°C at a rate of 2°C / min and held for 2 h. In the second stage, the temperature was raised to 700°C at a rate of 2°C / min to allow the carbon skeleton to condense and form nitrogen-doped confined cavities, thereby inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 700°C for 1 h to complete the Co-N4 coordination reconstruction.
[0026] (3) Acid washing and purification: The pyrolysis product was added to a 0.5 M H2SO4 solution and mechanically stirred in a 50°C water bath for a period of time. After acid washing, the product was centrifuged, washed with deionized water, and then rinsed twice with a 0.1 M NaHCO3 solution to neutralize trace acid. The final solid was vacuum dried at 60°C for 18 h to obtain a single-atom catalyst. The HAADF-STEM image of the Co single-atom catalyst is shown in Figure 2. Figure 2 As shown in the figure, there are dispersed metal bright spots, indicating that the Co in the catalyst is atomically dispersed. The nitrogen content of the catalyst is 10 at%, of which pyridinic nitrogen accounts for 85%, and the specific surface area is 900 m 2 / g, pore volume 0.8 cm 3 / g.
[0027] Phenol degradation application: The prepared catalyst was added to wastewater containing phenol (initial concentration 10 mg / L) to a concentration of 0.1 g / L. Peroxydisulfate (PDS) oxidant was then added to a concentration of 0.5 mM. The reaction was stirred at pH 3 and 10°C for 10 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.1 M NaOH, and then recycled. Testing showed a phenol removal rate of 90%, and after five cycles, the phenol removal rate reached 87%. Example 3
[0028] Preparation of single-atom catalysts (1) Precursor coordination self-assembly: 0.025 mol / L Mn(acac)3, 0.075 mol / L 2-methylimidazole, and 0.125 mol / L melamine were dissolved in ethanol and ultrasonically dispersed for 30 min to form a homogeneous solution. The solution was stirred and refluxed in an 80°C oil bath for 7 h to allow the manganese ions to coordinate with the nitrogen of imidazole and triazine to self-assemble. The reaction solution was centrifuged at 10,000 rpm for 10 min to collect the solid, which was then washed three times with anhydrous ethanol to remove unreacted monomers. Finally, the precursor was dried in a vacuum at 65°C for 12 h to obtain the precursor.
[0029] (2) Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow. In the first stage, the temperature was raised to 250°C at a rate of 5°C / min and held for 3 h. In the second stage, the temperature was raised to 800°C at a rate of 5°C / min to allow the carbon skeleton to condense and form nitrogen-doped confined cavities, thereby inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 800°C for 3 h to complete the Mn-N4 coordination reconstruction.
[0030] (3) Acid washing and purification: The pyrolysis product was added to a 1 M H2SO4 solution and mechanically stirred in a 60°C water bath for a period of time. After acid washing, the product was centrifuged, washed with deionized water, and then rinsed five times with a 0.4 M NaHCO3 solution to neutralize trace acid. The final solid was vacuum dried at 80°C for 24 h to obtain a single-atom catalyst. The catalyst nitrogen content was 8 at%, of which pyridinic nitrogen accounted for 82%, and the specific surface area was 1000 m 2 / g, pore volume is 1 cm 3 / g.
[0031] Phenol degradation application: The prepared catalyst was added to wastewater containing phenol (initial concentration 200 mg / L) to a concentration of 1.0 g / L. Permonosulfate (PMS) oxidant was then added to a concentration of 5.0 mM. The reaction was stirred at pH 9 and 40°C for 30 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.5 M NaOH, and then recycled. Testing showed a phenol removal rate of 92%, and an activity retention rate of 87% after five cycles. Example 4
[0032] Preparation of single-atom catalysts Precursor coordination self-assembly: 0.018 mol / L Cu(acac)3, 0.05 mol / L 2-methylimidazole, and 0.08 mol / L melamine were dissolved in ethanol and ultrasonically dispersed for 22 minutes to form a homogeneous solution. The mixture was stirred and refluxed in a 65°C oil bath for 5.5 hours to allow the copper ions to coordinate with the nitrogen atoms of imidazole and triazine to self-assemble. The reaction solution was centrifuged at 8500 rpm for 8.5 minutes to collect the solid, which was then washed three times with anhydrous ethanol to remove unreacted monomers and finally dried in a vacuum at 58°C for 10.5 hours to obtain the precursor.
[0033] Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage temperature ramp under a high-purity nitrogen flow. In the first stage, the temperature was raised to 225°C at a rate of 2.5°C / min and held for 2.2 hours. In the second stage, the temperature was raised to 720°C at a rate of 2.5°C / min to condense the carbon skeleton into nitrogen-doped confined cavities, inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 720°C for 1.5 hours to complete the Cu-N4 coordination reconstruction.
[0034] Acid washing and purification: The pyrolysis product was added to a 0.6 M H2SO4 solution and mechanically stirred in a 52°C water bath for a period of time. After acid washing, the product was centrifuged, washed with deionized water, and then rinsed three times with a 0.15 M NaHCO3 solution to neutralize trace acid. The final solid was vacuum dried at 62°C for 19 h to obtain a single-atom catalyst. The catalyst had a nitrogen content of 11 at%, of which pyridinic nitrogen accounted for 85%, and a specific surface area of 800 m2. 2 / g, pore volume is 1 cm 3 / g.
[0035] Phenol degradation application: The prepared catalyst was added to wastewater containing phenol (initial concentration 50 mg / L) to a concentration of 0.3 g / L. Peroxydisulfate (PDS) oxidant was then added to a concentration of 1.5 mM. The reaction was stirred at pH 5 and 15°C for 20 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.2 M NaOH, and then recycled. Testing showed a phenol removal rate of 92%. After five cycles of use, the activity retention rate was 89%. Example 5
[0036] S01. Preparation of single-atom catalysts (1) Precursor coordination self-assembly: 0.022 mol / L Co(acac)3, 0.065 mol / L 2-methylimidazole, and 0.11 mol / L melamine were dissolved in ethanol and ultrasonically dispersed for 30 min to form a homogeneous solution. The mixture was stirred and refluxed in an 80°C oil bath for 7 h to allow the cobalt ions to coordinate with the nitrogen of imidazole and triazine to self-assemble. The reaction solution was centrifuged at 10,000 rpm for 10 min to collect the solid, which was then washed three times with anhydrous ethanol to remove unreacted monomers. Finally, the precursor was dried in a vacuum at 65°C for 12 h to obtain the precursor.
[0037] (2) Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow. In the first stage, the temperature was raised to 250°C at a rate of 5°C / min and held for 3 h. In the second stage, the temperature was raised to 800°C at a rate of 5°C / min to allow the carbon skeleton to condense and form nitrogen-doped confined cavities, thereby inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 800°C for 3 h to complete the Co-N4 coordination reconstruction.
[0038] (3) Acid washing and purification: The pyrolysis product was added to a 1 M H2SO4 solution and mechanically stirred in a 60°C water bath for a period of time. After acid washing, the product was centrifuged, washed with deionized water, and then rinsed five times with a 0.4 M NaHCO3 solution to neutralize trace acid. The final solid was vacuum dried at 80°C for 24 h to obtain a single-atom catalyst. The catalyst nitrogen content was 7 at%, of which pyridinic nitrogen accounted for 81%, and the specific surface area was 800 m 2 / g, pore volume 0.8 cm 3 / g.
[0039] Phenol degradation application: The prepared catalyst was added to wastewater containing phenol (initial concentration 150 mg / L) to a concentration of 0.8 g / L. Peroxydisulfate (PDS) oxidant was then added to a concentration of 4.0 mM. The reaction was stirred at pH 8 and 35°C for 30 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.4 M NaOH, and then recycled. Testing demonstrated a phenol removal rate of 90%, and an activity retention rate of ≥88% after five cycles. Example 6
[0040] Preparation of single-atom catalysts (1) Precursor coordination self-assembly: 0.025 mol / L Fe(acac)3, 0.045 mol / L 2-methylimidazole, and 0.1 mol / L melamine were dissolved in ethanol. The other conditions were the same as those in Example 1.
[0041] (2) Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow. In the first stage, the temperature was raised to 220°C at a rate of 2°C / min and held for 2 h. In the second stage, the temperature was raised to 700°C at a rate of 2°C / min to allow the carbon skeleton to condense and form nitrogen-doped confined cavities, thereby inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 700°C for 1 h to complete the Fe-N4 coordination reconstruction.
[0042] (3) Acid washing and purification: This process is the same as in Example 1. The obtained catalyst has a nitrogen content of 8 at%, of which pyridine nitrogen accounts for 85%, and a specific surface area of 1100 m 2 / g, pore volume 1.2 cm 3 / g.
[0043] Phenol degradation application: The prepared catalyst was added to wastewater containing phenol (initial concentration 80 mg / L) to a concentration of 0.2 g / L. Permonosulfate (PMS) oxidant was then added to a concentration of 1.0 mM. The reaction was stirred at pH 6 and 18°C for 25 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.2 M NaOH, and then recycled. Testing showed a phenol removal rate of 94%, and an activity retention of 90% after five cycles. Example 7
[0044] S01. Preparation of single-atom catalysts (1) Precursor coordination self-assembly: same as Example 1.
[0045] (2) Gradient confined pyrolysis: The precursor was placed in a porcelain boat and subjected to a three-stage programmed temperature increase under a high-purity nitrogen flow. In the first stage, the temperature was raised to 250°C at a rate of 5°C / min and held for 3 h. In the second stage, the temperature was raised to 800°C at a rate of 5°C / min to allow the carbon skeleton to condense into nitrogen-doped confined cavities, inhibiting the migration and aggregation of metal atoms. In the third stage, the temperature was maintained at 800°C for 3 h to complete the Fe-N4 coordination reconstruction.
[0046] (3) Acid washing and purification: The pyrolysis product was added to a 0.5 M H2SO4 solution and mechanically stirred in a 60°C water bath for a period of time. The remaining conditions were the same as those in Example 1. The obtained catalyst had a nitrogen content of 12 at%, of which pyridinic nitrogen accounted for 86%, and a specific surface area of 900 m 2 / g, pore volume 0.7 cm 3 / g.
[0047] Phenol degradation application: The prepared catalyst was added to wastewater containing phenol (initial concentration 150 mg / L) to a concentration of 0.8 g / L. Peroxydisulfate (PDS) oxidant was then added to a concentration of 4.0 mM. The reaction was stirred at pH 8 and 35°C for 30 minutes. After the reaction, the catalyst was separated and recovered, regenerated with 0.4 M NaOH, and then recycled. Testing demonstrated a phenol removal rate of 92%, with an activity retention rate of ≥89% after five cycles.
[0048] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.
[0049] It should be noted that the above content merely illustrates the technical idea of the present invention and cannot be used to limit the scope of protection of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications all fall within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing a single-atom catalyst for phenol degradation, characterized in that: The following steps are involved: Dissolve the metal acetylacetonate, 2-methylimidazole, and melamine in ethanol and ultrasonically disperse for 20-30 minutes to form a homogeneous solution. Stir and reflux in an oil bath at 60-80°C for 5-7 hours. Collect the solid by centrifugation, wash with anhydrous ethanol to remove unreacted monomers, and finally vacuum dry to obtain the precursor. The precursor is placed in a porcelain boat and subjected to a three-stage temperature ramp under a high-purity nitrogen flow: the first stage is 220-250°C for 2-3 hours; the second stage is 700-800°C, where the carbon skeleton condenses to form nitrogen-doped confined cavities, inhibiting the migration and aggregation of metal atoms. The third stage: constant temperature at 700-800℃ for 1-3 hours to obtain pyrolysis products; The pyrolysis product was added to H2SO4 solution, stirred and acid washed at 50-60℃, centrifuged, washed with deionized water, and then rinsed with NaHCO3 solution 2-5 times to neutralize trace acid; After vacuum drying, the single-atom catalyst was obtained.
2. The method for preparing a single-atom catalyst for phenol degradation according to claim 1, wherein: In step (1), the metal in the metal acetylacetonate is one of Fe, Co, Mn and Cu.
3. The method for preparing a single-atom catalyst for phenol degradation according to claim 1, wherein: In the homogeneous solution of step (1), the concentrations of metal acetylacetonate, 2-methylimidazole, and melamine are 0.015-0.025 mol / L, 0.042-0.075 mol / L, and 0.072-0.125 mol / L, respectively.
4. The method for preparing a single-atom catalyst for phenol degradation according to claim 1, wherein: In step (1), the reaction solution is centrifuged at 8000-10000 rpm for 8-10 min to collect the solid, which is then washed three times with anhydrous ethanol and finally dried under vacuum at 55-65°C for 10-12 h to obtain the precursor.
5. The method for preparing a single-atom catalyst for phenol degradation according to claim 1, wherein: In step (2), in the first stage, the temperature is raised to 220-250°C at a rate of 2-5°C / min and kept at this temperature for 2-3 h; in the second stage, the temperature is raised to 700-800°C at a rate of 2-5°C / min.
6. The method for preparing a single-atom catalyst for phenol degradation according to claim 1, characterized in that: In step (3), the concentration of H2SO4 solution is 0.5~1 M, the concentration of NaHCO3 solution is 0.1~0.4 M, and the vacuum drying temperature is 60~80℃ for 18~24 h.
7. A single-atom catalyst for phenol degradation prepared by the preparation method according to any one of claims 1 to 6.
8. The single-atom catalyst for phenol degradation according to claim 7, characterized in that: The metal loading of the single-atom catalyst is 0.5-5.0 wt%, the nitrogen content of the single-atom catalyst is 5-15 at%, the proportion of pyridinic nitrogen in the total nitrogen is ≥80%, and the specific surface area is 800-1200 m 2 / g, pore volume of 0.8~1.2 cm 3 / g.
9. Use of the single-atom catalyst prepared by the preparation method according to any one of claims 1 to 6 in the degradation of phenol.
10. The use according to claim 9, characterized in that A single-atom catalyst was added to phenol-containing wastewater to a concentration of 0.1-1.0 g / L; a persulfate oxidant was added to a concentration of 0.5-5.0 mM; the reaction was stirred at a pH of 3-9 and a temperature of 10-40°C for 10-30 min. After the reaction, the catalyst was separated and recovered, regenerated with NaOH, and then recycled.