A method for in-situ extraction of high-activity single-atom catalysts from MOFs-derived metal oxides and applications

Abstract

The application belongs to the technical field of catalyst preparation and wastewater treatment, and particularly relates to a method for in-situ extraction of a high-activity single-atom catalyst from MOFs derived metal oxides and application thereof. A transition metal salt and an organic ligand are used to prepare a metal organic framework with N coordination through a precipitation method; then pyrolysis is carried out at 300-800 DEG C to obtain a metal single-atom catalyst loaded on a metal oxide and a carbon-nitrogen composite carrier; the organic ligand includes trimesic acid and a nitrogen-containing ligand. The catalyst couples the carrier effects of the metal oxide and the carbon, and realizes in-situ adjustment of the coordination environment of the single-atom metal site by introducing the nitrogen-containing ligand, effectively improving the efficiency of the catalyst in activating persulfate to degrade phenol, and showing good anti-interference and recycling characteristics. The catalyst preparation process is simple, the catalytic effect is excellent, the stability is high, the requirements for the treatment process and treatment equipment are low, there is no secondary pollution, and the catalyst has important significance for the field of wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and wastewater treatment technology, specifically relating to a method and application for in-situ extraction of highly active single-atom catalysts from MOF-derived metal oxides. Background Technology

[0002] Phenolic compounds pose a threat to the ecological environment and human health due to their difficulty in biodegradation and their tendency to bioaccumulate. Therefore, achieving low-carbon and efficient treatment of phenols has become a research hotspot in the field of water treatment. Among different water treatment technologies, persulfate advanced oxidation technology (PS-AOPs) has a high oxidant utilization rate, aligns with the concept of low-carbon treatment, and the reactive oxygen species (SO4) generated after activation... · -、·OH、O2 · -and 1 O2 (and other organic pollutants) can effectively remove organic pollutants. Currently, numerous homogeneous and heterogeneous catalysts have been developed for activating persulfate. Among them, heterogeneous catalysts, including carbon-based and metal-based materials, are highly sought after by environmental workers due to their good recyclability. However, because most heterogeneous catalysts have few surface reaction sites and high metal ion leaching, the efficiency of persulfate activation in removing pollutants needs further improvement. Therefore, there is an urgent need to develop a catalyst with higher activity to achieve efficient treatment of wastewater pollution using PS-AOPs.

[0003] Single-atom catalysts (SACs) have become a research hotspot in the field of catalysis due to their significant advantages, such as high activity, maximum atom utilization, and easily tunable electronic structure. To date, there are numerous strategies for preparing SACs, but their synthesis and reaction processes are prone to aggregation, making it difficult to maximize atom utilization and severely affecting catalytic stability. Therefore, improving the activity and stability of single atoms by changing the preparation method and the type of support has become a research focus. In the past decade, the synthesis of single atoms has mainly included wet chemical methods using metal oxide supports and pyrolysis methods using carbon-based supports. Although these methods are simple and easy to operate, single-atom loading on a single support still fails to overcome the limitations of persulfate oxidation kinetics. MOF derivatives, due to their advantages such as single metal sites, tunable functional ligands, and abundant pore structures, have been widely used in catalysis. On the one hand, numerous studies have shown that MOFs can derive various metal oxides through controllable pyrolysis conditions. On the other hand, the carbon structure of MOFs can tightly anchor target SACs, effectively preventing their migration and aggregation, which makes them widely used in the preparation of carbon-based SACs. Therefore, it is necessary to rationally design the synthesis process of MOFs derivatives to couple the support effect of metal oxides and carbon materials, realize the in-situ regulation of the coordination environment of SACs, and thus push the efficiency of SACs activating PS-AOPs to degrade organic pollutants to a higher level. Summary of the Invention

[0004] The purpose of this invention is to provide a method and application for in-situ extraction of highly active single-atom catalysts from MOF-derived metal oxides, in order to solve the problems of insufficient kinetics and poor degradation efficiency of existing single-atom catalysts in the degradation of organic pollutants by persulfate.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for in-situ extraction of highly active single-atom catalysts from MOF-derived metal oxides, comprising: preparing an N-coordinated metal-organic framework by precipitation of a transition metal salt and an organic ligand; and then pyrolyzing it at 300-800°C to obtain a single-atom metal catalyst supported on a metal oxide and a carbon-nitrogen composite support; wherein the organic ligand comprises pyromellitic acid and a nitrogen-containing ligand.

[0006] Furthermore, the molar ratio of the pyromellitic acid to the nitrogen-containing ligand is 1:(0.5-2).

[0007] Furthermore, the nitrogen-containing ligand includes one or more of melamine, urea, diethylenetriamine, ethylenediamine, 2-2'-bipyridine, ethylenediaminetetraacetic acid, and 2-aminoterephthalic acid, preferably 2-aminoterephthalic acid.

[0008] Furthermore, the precipitation method includes: mixing the transition metal salt and the organic ligand in a solution, then allowing the mixture to stand for 1-3 hours by precipitation, followed by centrifugation, washing, and drying to obtain the N-coordinated metal-organic framework;

[0009] Furthermore, the pyrolysis temperature is 300–800℃, the time is 2–4 h, and the heating rate is 5–10℃ / min.

[0010] Furthermore, the transition metal salt is one or more of copper salt, iron salt, cobalt salt, nickel salt, zinc salt, and manganese salt.

[0011] A second aspect of the present invention provides a highly active single-atom catalyst obtained by any of the methods described above.

[0012] A third aspect of the present invention provides an application of the above-described highly active single-atom catalyst in water purification.

[0013] Furthermore, the highly active metal single-atom catalyst and oxidant are added to the wastewater to purify the water by catalytically degrading organic pollutants in the wastewater.

[0014] Furthermore, the molar ratio of the oxidant to the organic pollutant is (1-2):1.

[0015] Furthermore, the dosage of the highly active metal single-atom catalyst in wastewater is 0.3-2.0 g / L.

[0016] Furthermore, the catalytic degradation is carried out under conditions of pH 4.0-10.0.

[0017] Furthermore, the organic pollutant includes aromatic compounds containing electron-rich groups, preferably including at least one of phenol, 4-chlorophenol, and sulfamethoxazole.

[0018] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0019] 1. This invention provides a method for in-situ extraction of highly active single-atom catalysts from MOF-derived metal oxides, using a metal-organic framework modified with N-ligands as a precursor, which is then obtained through high-temperature pyrolysis. This method effectively couples the support effect of metal oxides and carbon by efficiently constructing a nitrogen-containing carbon layer structure at the edge of the metal oxide, and utilizes nitrogen coordination to regulate the coordination environment of single atoms, promoting the in-situ extraction and dispersion of highly active metal single atoms. This not only achieves full utilization of the catalyst synthesis raw materials but also optimizes the spatial configuration and local coordination characteristics of the metal single atoms. It facilitates charge transport during the reaction, thus effectively promoting the oxidation kinetics of persulfate and improving the efficiency of organic pollutant degradation.

[0020] 2. This invention regulates the metal coordination environment by adjusting the type and ratio of nitrogen-containing ligands in the metal-organic framework and the pyrolysis temperature under air conditions, thereby obtaining a metal single-atom catalyst with better catalytic performance by metal oxide / carbon-nitrogen synergistic modification.

[0021] 3. The catalyst of this invention has a simple preparation process, good reproducibility, excellent catalytic effect, good anti-interference and cycle stability, and has broad practical application prospects, making it easy to promote and apply on a large scale. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process for achieving in-situ extraction of highly active single atoms on a metal oxide / carbon-nitrogen support, as provided in Example 1.

[0023] Figure 2 The images show: (a) XRD pattern of the CuO@CN single-atom catalyst obtained in Example 1; (be) elemental surface scan analysis results; (fg) transmission electron microscopy and high-resolution transmission electron microscopy; and (h) high-angle dark-field annular scanning transmission electron microscopy image.

[0024] Figure 3This is a graph showing the degradation activity of phenol (PhOH) obtained in Example 2, where a represents the change in degradation effect over time at different pyrolysis temperatures, b represents the change in degradation effect over time at different pH values, c represents the change in degradation effect over time for Comparative Examples 1 and 2 and Example 1, d represents the change in degradation rate over time for Comparative Examples 1 and 2 and Example 1, e represents the degradation effect of changing the molar ratio of pyromellitic acid to 2-aminoterephthalic acid, and f represents the degradation effect of changing the type of nitrogen-containing ligand.

[0025] Figure 4 These are the identification spectra of key active species in the reaction process obtained in Example 3, where ab are free radical electron paramagnetic resonance spectra in different reaction systems, c is the free radical quenching experiment, and d is the path proportion.

[0026] Figure 5 This refers to the results of the investigation into the source of active species in Example 4. (ab represents Fourier transform infrared spectroscopy in the range of 450-4000 cm⁻¹) -1 Spectra within the range of 1500-1800 cm⁻¹ -1 The magnified graph within the range shows the linear correlation between the -COOH peak intensity and the reaction rate (c).

[0027] Figure 6 In Figure a, we have a comparison of the resistance of CuO@CN to common anion interference, Figure b shows the removal performance of different pollutants, and Figure c shows the cycle stability. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] This invention provides a method for in-situ extraction of highly active single-atom catalysts from MOF-derived metal oxides, comprising: preparing an N-coordinated metal-organic framework by precipitation of a transition metal salt and an organic ligand; and then pyrolyzing it at 300-800℃ to obtain a metal single-atom catalyst supported on a metal oxide and a carbon-nitrogen composite support; wherein the organic ligand includes pyromellitic acid and a nitrogen-containing ligand.

[0030] This invention first synthesizes a nitrogen-coordinated metal-organic framework (MOF) via precipitation, and then synthesizes a metal single-atom catalyst (SACs) (i.e., a metal single-atom catalyst supported on a metal oxide and carbon-nitrogen composite support) by high-temperature pyrolysis. During pyrolysis, nitrogen coordination can provide different coordination environments to effectively anchor metal atoms, generating SACs sites; the MOF can form a metal oxide / carbon-nitrogen composite support, synergistically enhancing the activity of SACs and further influencing the catalytic mechanism and catalyst performance. Experiments show that the metal oxide / carbon-nitrogen co-modified single-atom catalyst can efficiently activate persulfate and degrade phenol, exhibiting high cycling stability. The catalyst preparation process of this invention is simple, with excellent catalytic performance and high system stability, showing great application potential.

[0031] The molar ratio of trimesic acid to nitrogen-containing ligand is 1:(0.5-2), preferably 1:1. Experiments of this invention show that the catalytic activity of the obtained single-atom catalyst can be adjusted by regulating the molar ratio of trimesic acid to nitrogen-containing ligand.

[0032] The nitrogen-containing ligand includes one or more of melamine, urea, diethylenetriamine, ethylenediamine, 2,2'-bipyridine, ethylenediaminetetraacetic acid, and 2-aminoterephthalic acid, preferably 2-aminoterephthalic acid. The effect is even better when the nitrogen-containing ligand contains both amino and carboxyl groups.

[0033] The pyrolysis temperature is 300–800℃, the time is 2–4 h, and the heating rate is 5–10℃ / min. Experimental results of this invention show that the pyrolysis temperature has a significant impact on the catalytic efficiency of the obtained single-atom catalyst, with the highest catalytic efficiency at 300℃.

[0034] The transition metal salt is one or more of copper, iron, cobalt, nickel, zinc, and manganese salts. By adjusting the type of organic ligand, the metal coordination structure can be modified, thereby regulating the structure of the metal oxide and nitrogen-containing carbon layer during pyrolysis, thus synergistically enhancing the activity of metal single atoms in the nitrogen-containing carbon layer.

[0035] The specific methods for preparing highly active single-atom catalysts include:

[0036] The first step is to prepare MOFs with N coordination.

[0037] 1.1) Disperse 2-8 mmol of pyromellitic acid and the nitrogen-containing ligand in 100-300 mL of methanol solution, stir and sonicate until completely dissolved to obtain solution A;

[0038] 1.2) Disperse 10-15 mmol of metal salt in 100-300 mL of methanol solution and stir at room temperature for 5-20 min to obtain solution B. Then add solution A to solution B and co-precipitate for 1-3 h to obtain N-coordinated MOF; wherein the volume ratio of solution A to solution B is 1:(0.5-3).

[0039] The second step involves preparing single-atom catalysts modified with metal oxides / carbon-nitrogen synergistic modification.

[0040] The product from the first step was placed in a muffle furnace for controlled-temperature pyrolysis and naturally cooled to room temperature to obtain a copper oxide / carbon-nitrogen co-modified Cu single-atom catalyst.

[0041] Specifically, this invention provides a Cu single-atom catalyst derived from a Cu-based metal-organic framework and modified with copper oxide / carbon-nitrogen synergistically. The N-coordinated Cu-MOF-derived Cu single-atom catalyst is labeled as CuO@CN. It is prepared by high-temperature pyrolysis using Cu-MOF obtained by co-precipitation of nitrogen-containing ligands, trimesic acid, and copper salt as a precursor.

[0042] The copper salt is selected from at least one of copper chloride trihydrate and copper nitrate pentahydrate; preferably copper nitrate pentahydrate. The high-temperature pyrolysis temperature is 300-800℃, specifically 300℃, 400℃, 500℃, 600℃, 700℃, or 800℃, preferably 300℃, and the heating rate is 10℃ / min.

[0043] The preparation method employed in this invention not only yields copper oxide crystals but also retains an amorphous carbon structure surrounding the copper oxide. The introduction of nitrogen-containing ligands for N coordination facilitates in-situ regulation of the coordination environment at the Cu sites, enabling the in-situ extraction of highly active single-atom Cu. Ultimately, the coupled support effect of metal oxides and carbon synergistically enhances the activity of single-atom Cu, thereby improving the efficiency of activated persulfate degradation of organic pollutants.

[0044] A copper salt with a preferred molar mass of 10–13 mmol, 4 mmol of trimesic acid, and 4 mmol of a nitrogen-containing ligand are each dispersed in 100 mL of methanol solution and thoroughly dissolved before mixing. The mixture is then allowed to stand for 1–3 hours using a precipitation method, specifically 1 hour, 2 hours, and 3 hours, preferably 2 hours. The precipitate is then washed twice with water and ethanol, respectively, and dried overnight at 60–80 °C, preferably 60 °C, to obtain a Cu-MOF precursor. The Cu-MOF is then placed in a crucible and calcined in a muffle furnace at a pyrolysis temperature for 2–4 hours, specifically 2 hours, 3 hours, and 4 hours, preferably 3 hours. The heating rate is 5–10 °C / min, specifically 5 °C / min and 10 °C / min, preferably 10 °C / min. This process oxidizes the Cu-MOF at high temperature to obtain CuO, and to a certain extent, carbonizes and recombines to form an ordered nitrogen-coordinated structure, resulting in Cu single atoms, denoted as CuO@CN.

[0045] This invention also provides an application of the above-mentioned highly active single-atom catalyst in water purification, specifically its application in the efficient activation of persulfate to degrade organic pollutants.

[0046] Furthermore, the highly active single-atom catalyst and oxidant are added to the wastewater (preferably, the highly active single-atom catalyst is added first for pre-adsorption for a preset time, and then the oxidant is added to improve degradation efficiency), thereby purifying the water by catalytically degrading organic pollutants in the wastewater. The oxidant is one or both of persulfate and perdisulfate, preferably persulfate.

[0047] The molar ratio of the oxidant to the organic pollutant is (1-2):1, preferably with a concentration of 300 mg / L. The dosage of the highly active single-atom catalyst in the wastewater is 0.3-2.0 g / L, preferably 0.5 g / L. The catalytic degradation is carried out at a pH of 4.0-10.0. Specifically, pH values ​​can be 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or 10.0, with a preferred pH of 6.0. The pH is preferably adjusted using 0.1 M NaOH.

[0048] The organic pollutant includes aromatic compounds containing electron-rich groups, preferably including at least one of phenol, 4-chlorophenol, and sulfamethoxazole, with phenol being more preferred. The concentration of the organic pollutant is 20–50 mg / L, preferably 30 mg / L.

[0049] After the catalytic degradation reaction is completed, when relevant tests are required, take 1 mL of the solution, filter it through a 0.22 μm polyethersulfone microporous membrane, add 50 μL of methanol and mix well to terminate any possible degradation reactions in the sample.

[0050] Comparative Example 1

[0051] The preparation of the copper oxide / carbon catalyst (CuO@C) involved the following steps: 13 mmol of copper nitrate pentahydrate and 4 mmol of trimesic acid were separately dispersed in 100 mL of methanol solution, dissolved thoroughly, and then mixed. The mixture was allowed to stand for 2 h using a precipitation method. The precipitate was then washed twice with water and ethanol, and dried overnight at 60 °C to obtain the Cu-MOF precursor. The Cu-MOF was then placed in a crucible and placed in a muffle furnace, where it was pyrolyzed at 300 °C for 3 h in air at a heating rate of 10 °C / min to obtain CuO@C.

[0052] Comparative Example 2

[0053] The preparation of copper oxide catalyst (CuO) involved the following steps: 13 mmol of copper nitrate pentahydrate and 4 mmol of trimesic acid were separately dispersed in 100 mL of methanol solution, dissolved thoroughly, and then mixed. The mixture was allowed to stand for 2 h using a precipitation method. The precipitate was then washed twice with water and ethanol, and dried overnight at 60 °C to obtain the Cu-MOF precursor. The Cu-MOF was then placed in a crucible and placed in a muffle furnace, where it was pyrolyzed at 800 °C for 3 h in air at a heating rate of 10 °C / min.

[0054] Example 1

[0055] Preparation of CuO@CN catalysts, such as Figure 1 As shown, the steps are as follows: 13 mmol of copper nitrate pentahydrate, 4 mmol of trimesic acid, and 4 mmol of 2-aminoterephthalic acid were dispersed in 100 mL of methanol solution, dissolved thoroughly, and mixed. The mixture was then allowed to stand for 2 hours using a precipitation method. The precipitate was then washed twice with water and ethanol, and dried overnight at 60 °C to obtain the Cu-MOF precursor. The Cu-MOF was placed in a crucible and placed in a muffle furnace, where it was pyrolyzed at 300 °C for 3 hours. This process oxidized the Cu-MOF at high temperature to obtain CuO crystals, and to a certain extent, carbonized and reorganized to form an ordered coordination structure, resulting in Cu single atoms, denoted as CuO@CN.

[0056] In addition, keeping a single variable in mind, the dosage of 2-aminoterephthalic acid was varied to 2 mmol, 6 mmol, and 8 mmol to adjust the molar ratio of trimesic acid to 2-aminoterephthalic acid to 1:0.5, 1:1.5, and 1:2. Keeping a single variable in mind, the type of nitrogen-containing ligand was varied to include melamine, urea, 2-2'-bipyridine, ethylenediaminetetraacetic acid, 5-amino-4-azolium, and ethylenediamine. The effects of the molar ratio of trimesic acid to nitrogen-containing ligand and the type of nitrogen-containing ligand on the performance of the single-atom catalyst were investigated. The experimental results are as follows: Figure 3 As shown in e and f.

[0057] Figure 2The XRD patterns of the catalysts prepared by CuO@CN and Comparative Examples 1 and 2 are shown. Compared with CuO, the widths of the diffraction peaks of the modified catalysts increased to varying degrees, which is related to the reduction of CuO crystallinity by the introduced amorphous carbon layer. Furthermore, CuC8 signal peaks appeared on CuO@C and CuO@CN, further demonstrating that a certain carbon structure is retained in both materials, and that nitrogen coordination is conducive to the formation of Cu-C bonds. Figure 2 The morphology of the catalyst was further characterized in bg, revealing that CuO@CN consists of copper oxide particles encapsulated with amorphous carbon structures. Furthermore, Figure 2 High-angle dark-field ring scanning transmission electron microscopy (H STEM) images revealed dispersed Cu single atoms in the thin carbon layer, indicating that the active metal on the carbon layer is dispersed as single atoms. This demonstrates that nitrogen coordination promotes the regulation of the coordination environment at the metal sites, enabling in-situ extraction of highly active single atoms. Based on these characterizations, we confirm the synthesis and preparation of Cu-based metal-organic framework-derived copper oxide / carbon-modified Cu single-atom composite catalysts.

[0058] Example 2

[0059] The effects of varying the pyrolysis temperature and pH value during the catalyst synthesis process in Example 1 on the degradation performance of phenol (PhOH) by activated persulfate (PMS) were investigated. The specific steps are as follows:

[0060] 25 mg of CuO@CN catalyst prepared by pyrolysis at 300℃, 400℃, 500℃, 600℃, 700℃, and 800℃ was weighed and dispersed in 50 mL of aqueous solution containing 30 mg / L PhOH. The solution was stirred evenly, 0.3 g / L PMS was added, and 0.1 M NaOH was added dropwise to adjust the initial pH to the range of 4.0-10.0. Samples were taken at regular intervals and filtered through a 0.22 μm disposable filter. The concentration change of residual PhOH was detected by high performance liquid chromatography. Figure 3 In this context, C represents the concentration during the degradation process, and C0 represents the initial concentration of PhOH. Figure 3 The reaction pH value corresponding to Figure a is 6.0. The catalyst corresponding to Figure b is obtained at a pyrolysis temperature of 300℃. In Figures c and d, CuO@CN is the catalyst obtained at a pyrolysis temperature of 300℃, and the reaction pH value is 6.0.

[0061] The effect of calcination temperature, such as Figure 3 As shown in Figure a, since the carbon layer content decreases with increasing temperature, the best phenol degradation performance is observed at 300℃, with near-complete degradation within 30 minutes. Furthermore, as... Figure 3 As shown in Figure b, a pH of 6.0, which is near neutral, is more conducive to the generation and action of active species. Therefore, the optimal reaction conditions were determined. Figure 3 The results showed that after 30 minutes of pre-adsorption (no oxidant was added during pre-adsorption, and PMS was added after pre-adsorption), at pH 6.0, Cu@CN achieved 100% removal of phenol within 5 minutes, while CuO@C required approximately 30 minutes for complete degradation, and CuO only achieved a 40% removal rate of PhOH within 30 minutes. Figure 3 The degradation rate of phenol in CuO@CN shows a 46.4-fold increase compared to CuO, and a further 3.7-fold increase compared to CuO@C. Furthermore, as... Figure 3 Tables e and f compare the catalytic performance of non-preferred embodiments with molar ratios of pyromellitic acid to 2-aminoterephthalic acid of 1:0.5, 1:1.5, and 1:2, respectively, and different nitrogen source ligands. It can be seen that the PhOH degradation rate is fastest when the molar ratio of pyromellitic acid to 2-aminoterephthalic acid is 1:1, and 2-aminoterephthalic acid exhibits a faster degradation rate than other nitrogen-containing ligands. This demonstrates that 1:1 is the optimal molar ratio and that 2-aminobenzoic acid is the optimal structure for nitrogen source. These experimental results indicate that the CuO@CN catalyst, due to the combined effect of copper oxide and carbon support, enhances the single-atom activity of Cu, effectively improving the performance of activated persulfate in degrading PhOH.

[0062] Example 3

[0063] This invention uses electron paramagnetic resonance (EPR) to compare the differences in active species generated during the degradation of organic matter in a persulfate system by CuO, CuO@C, and CuO@CN catalysts (prepared from Comparative Examples 1, 2, and Example 1, respectively). The results are as follows: Figure 4 As shown, where, Figure 4 In Figure c, Blank, MT, TBA, L-HIS, and PBQ represent CuO@CN catalytic systems without quenchers and with 50 mM methanol, tert-butanol, L-histidine, and p-benzoquinone quenchers, respectively. MT can quench sulfate radicals SO42-. · - and hydroxyl radicals ·OH, TBA can quench ·OH, L-HIS can quench singlet oxygen. 1 O2, PBQ can quench O2 · -

[0064] like Figure 4 As shown in Figures a and b, the addition of PMS to the CuO, CuO@C, and CuO@CN systems all resulted in the detection of ·OH signals and 1 Comparing the O2 signal intensity with that after the addition of PhOH, it was found that the system mainly consists of singlet oxygen. 1 O2-dominated non-radical system. Figure 4Quenching experiments in media c and d showed that both L-HIS and PBQ could almost completely inhibit the degradation of PhOH. Combined with the active species signal of EPR, the non-radical-dominated pathway of the system was determined, and the active species were... 1 O2.

[0065] Example 4

[0066] Further on the above 1 To explore the sources of O2, such as Figure 5 As shown, CuO@CN and CuO@CN 0.5 CuO@CN 1.5 CuO@C-N2 represents single-atom catalysts obtained by molar ratios of pyromellitic acid and 2-aminoterephthalic acid of 1:1, 1:0.5, 1:1.5, and 1:2, respectively.

[0067] Figure 5 Image a shows the infrared spectra of five materials at approximately 500 cm⁻¹. -1 All regions showed obvious CuO vibrational signals, and the catalyst also exhibited -OH vibrational signals from H2O adsorption (3300-3645 cm⁻¹). -1 The most significant change was at 1623cm. -1 This is attributed to the vibration of the carboxyl group -COOH. And in Figure 5 In step b, the signal location is further amplified, and the peak intensity is linearly fitted to the reaction rate, as shown below. Figure 5 The results showed a linear correlation of 0.9665 between the phenol degradation rate and the -COOH peak intensity, demonstrating that appropriate N coordination concentrations are beneficial for the in-situ extraction of active Cu single atoms. Simultaneously, the carbonyl group, as an activation site for PMS, promotes... 1 The generation of O2.

[0068] Example 5

[0069] Following the catalytic degradation experiment of PhOH in Example 2, the catalyst prepared in Example 1 was tested for interference resistance, universality, and cycle stability. The results are as follows... Figure 6 As shown in Figure a. Wherein, Figure 6 In the 'a' section, 'Control' refers to the absence of anions in the CuO@CN catalytic system. Cl - NO3 - SO4 2- and HCO3 - These refer to common anions in water that affect catalytic performance. During the experiment, sodium chloride, sodium nitrate, sodium sulfate, and sodium bicarbonate at a concentration of 100 mM were added to simulate the interference of actual water bodies on catalyst performance.

[0070] from Figure 6 As can be seen from a, in the anion Cl- NO3 - SO4 2- and HCO3 - Under the influence of [unspecified factor], the catalytic performance was slightly inhibited, indicating that the system has good anti-interference ability. Figure 6 Degradation experiments of different pollutants in sample b (PhOH, BA, SMX, and 4-CP represent phenol, benzoic acid, sulfamethoxazole, and 4-chlorophenol, respectively) showed that CuO@CN exhibited relatively high catalytic activity for organic pollutants with different structures, such as phenol (PhOH), sulfamethoxazole (SMX), and 4-chlorophenol (4-CP). Figure 6 The medium-cycle experiments showed that the CuO@CN catalyst could still maintain 70% of its catalytic activity after five cycles, proving that the strong interaction between Cu single atoms and CuO effectively enhanced the affinity of Cu sites for PMS and contaminants, thereby improving catalytic stability.

[0071] In summary, this invention first synthesizes a nitrogen-coordinated Cu-based metal-organic framework (Cu-MOF) via precipitation, and then synthesizes a metal oxide / carbon-nitrogen synergistic modified single-atom catalyst (CuO@CN) via high-temperature pyrolysis. During pyrolysis, nitrogen coordination can provide different coordination environments to effectively anchor metal atoms, generating SACs sites; the metal-organic framework can form a metal oxide / carbon-nitrogen composite support, synergistically enhancing the activity of SACs and further influencing the catalytic mechanism and catalyst performance. Persulfate activation and organic pollutant degradation experiments show that CuO@CN can efficiently activate persulfate and degrade phenol, exhibiting high cycling stability.

[0072] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of in-situ extraction of single atom catalysts from MOFs derived metal oxides characterized in that, The application relates to a method for in-situ extraction of a single-atom catalyst from MOFs derived metal oxides. The method comprises the following steps: preparing an N-coordinated metal organic framework by precipitating a transition metal salt and an organic ligand; and pyrolyzing the N-coordinated metal organic framework at 300-500 DEG C to obtain a single-atom catalyst loaded on a metal oxide and a carbon-nitrogen composite carrier; wherein the pyrolysis is carried out in an air atmosphere. The organic ligand comprises trimesic acid and a nitrogen-containing ligand. The molar ratio of the trimesic acid and the nitrogen-containing ligand is 1: (0.5-2). The nitrogen-containing ligand comprises one or more of melamine, urea, ethylenediamine, 2,2'-bipyridine, diethylenetriamine, ethylenediaminetetraacetic acid and 2-amino terephthalic acid. The precipitating method comprises the following steps: mixing the transition metal salt and the organic ligand in a solution, and then standing for 1-3 h by using the precipitating method, centrifuging, washing and drying to obtain the N-coordinated metal organic framework. The pyrolysis is carried out for 2-4 h, and the temperature rising rate is 5-10 DEG C / min.

2. The method for in-situ extraction of single-atom catalysts from MOF-derived metal oxides according to claim 1, characterized in that, The nitrogen-containing ligand is 2-amino terephthalic acid.

3. The method for in-situ extraction of single-atom catalysts from MOF-derived metal oxides according to claim 1, characterized in that, The transition metal salt is one or more of a copper salt, an iron salt, a cobalt salt, a nickel salt, a zinc salt and a manganese salt.

4. A metal monatomic catalyst characterized in that, The method for in-situ extraction of a single-atom catalyst from MOFs derived metal oxides is obtained by the method according to any one of claims 1-3.

5. The single-atom catalyst according to claim 4 is applied to water purification.

6. Use according to claim 5, characterized in that, The single-atom catalyst and an oxidant are put into sewage to realize water purification by catalytic degradation of organic pollutants in the sewage.

7. Use according to claim 6, characterized in that, The oxidant is a persulfate.

8. Use according to claim 6, characterized in that, The molar ratio of the oxidant to the organic pollutants is (1-2):

1. The single-atom catalyst is added into the sewage in an amount of 0.3-2.0 g / L. The catalytic degradation is carried out at a pH value of 4.0-10.

0.

9. Use according to claim 8, characterized in that, The organic pollutants comprise aromatic compounds containing electron-rich groups.

10. Use according to claim 9, characterized in that, The aromatic compounds containing electron-rich groups comprise at least one of phenol, 4-chlorophenol and sulfamethoxazole.

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