Method for in-situ extraction of high-activity monatomic catalyst from MOFs-derived metal oxide and application of high-activity monatomic catalyst

Abstract

The invention 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 monatomic catalyst from MOFs derived metal oxides and application. Preparing an N-coordinated metal organic framework from transition metal salt and an organic ligand through a precipitation method; then pyrolyzing at 300 to 800 DEG C to obtain a metal monatomic catalyst loaded on the metal oxide and the carbon-nitrogen composite carrier; the organic ligand comprises trimesic acid and a nitrogen-containing ligand. According to the catalyst, the carrier effect of metal oxide and carbon is coupled, in-situ regulation of a monatomic metal site coordination environment is realized by introducing a nitrogen-containing ligand, the efficiency of catalyzing and activating persulfate to degrade phenol is effectively improved, and meanwhile, good anti-interference and cyclic utilization characteristics are shown. The catalyst disclosed by the invention is simple in preparation process, excellent in catalytic effect, high in stability, low in requirements on a treatment process and treatment equipment and free of secondary pollution, and has important significance in the field of wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation and wastewater treatment, and specifically relates to a method and application of in-situ extraction of high-activity single-atom catalysts from MOFs-derived metal oxides. Background Art

[0002] Phenolic compounds are difficult to biodegrade and easy to bioaccumulate, posing a threat to the ecological environment and human health. 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, which is in line with the concept of low-carbon treatment, and the active oxygen species (SO4 · -、OH、O2 · -and 1 O2, etc.) can effectively remove organic pollutants. At present, a large number of homogeneous and heterogeneous catalysts have been developed for activating persulfate. Among them, heterogeneous catalysts include carbon-based and metal-based materials, which are sought after by environmental workers due to their good recyclability. However, due to the small number of surface reaction sites and high metal ion leaching of most heterogeneous catalysts, the efficiency of activating persulfate to remove pollutants needs to be further improved. Based on this, it is urgent to develop a catalyst with higher activity to achieve PS-AOPs to efficiently treat wastewater pollution.

[0003] Single atom catalysts (SACs) have become a hot topic in the field of catalysis due to their significant advantages such as high activity, maximum atomic utilization and easily adjustable electronic structure. So far, the preparation strategies of SACs have been very rich, but they are easy to agglomerate during the synthesis and reaction process, making it difficult to maximize the utilization of atoms, which seriously affects the stability of the catalysis. Therefore, improving the activity and stability of single atoms by changing the preparation method and carrier type has become a hot topic in research. In the past decade, the synthesis of single atoms mainly includes wet chemical methods on metal oxide carriers and pyrolysis methods on carbon-based carriers. Although these methods are simple and easy to operate, single-carrier-loaded single atoms still fail to break the dilemma of insufficient persulfate oxidation kinetics. MOFs derivatives are widely used in the field of catalysis due to their advantages such as single metal sites, adjustable functional ligands and rich pore structures. On the one hand, a large number of 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 the target SACs, effectively avoiding 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 effects of metal oxides and carbon materials and realize the in situ regulation of the SACs coordination environment, thereby pushing the efficiency of the SACs-activated PS-AOPs degradation system of organic pollutants to a higher level. Summary of the invention

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

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

[0006] Furthermore, the molar ratio of trimesic 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] Further, the precipitation method comprises: mixing a transition metal salt and an organic ligand in a solution, then standing for 1-3 hours by a precipitation method, centrifuging, washing, and drying to obtain an N-coordinated metal organic framework;

[0009] Furthermore, the pyrolysis temperature is 300-800°C, the time is 2-4h, and the heating rate is 5-10°C / 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] The second aspect of the present invention provides a highly active single-atom catalyst obtained by any of the methods described above.

[0012] The third aspect of the present invention provides an application of the above-mentioned high-activity single-atom catalyst in water purification.

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

[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 sewage is 0.3-2.0 g / L.

[0016] Furthermore, the catalytic degradation is carried out at a pH value of 4.0-10.0.

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

[0018] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0019] 1. The method provided by the present invention for in-situ extraction of highly active single-atom catalysts from MOFs-derived metal oxides is prepared by high-temperature pyrolysis using a metal organic framework modified with a N-ligand as a precursor. This method effectively couples the carrier effect of metal oxides and carbon by effectively constructing a nitrogen-containing carbon layer structure at the edge of the metal oxide, and uses nitrogen coordination to regulate the coordination environment of single atoms, thereby promoting the in-situ extraction and dispersion of highly active metal single atoms. Not only can the full utilization of the raw materials for catalyst synthesis be achieved, but also the spatial configuration and local coordination characteristics of metal single atoms are optimized. It is beneficial to charge transfer during the reaction process, thereby effectively promoting the oxidation kinetics of persulfate and improving the efficiency of degrading organic pollutants.

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

[0021] 3. The catalyst of the present invention has a simple preparation process, good reproducibility, excellent catalytic effect, good system anti-interference and cycle stability, has broad practical application prospects, and is easy to promote and apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the process for achieving in-situ extraction of highly active single atoms on a metal oxide / carbon-nitrogen carrier provided in Example 1.

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

[0024] Figure 3is the degradation activity diagram of phenol (PhOH) obtained in Example 2, wherein a is the degradation effect changing with time at different pyrolysis temperatures, b is the degradation effect changing with time at different pH values, c is the degradation effect changing with time of Comparative Examples 1 and 2 and Example 1, d is the degradation rate changing with time of Comparative Examples 1 and 2 and Example 1, e is the degradation effect of changing the molar ratio of trimesic acid to 2-aminoterephthalic acid, and f is the degradation effect of changing the type of nitrogen-containing ligand.

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

[0026] Figure 5 is the result of the investigation of the active species sources in Example 4, ab is the Fourier transform infrared at 450-4000cm -1 Spectrum in the range of 1500-1800cm -1 The enlarged diagram within the range, c is the linear correlation between the -COOH peak intensity and the reaction rate.

[0027] Figure 6 (a) is a comparison chart of CuO@CN's ability to resist common anion interferences, (b) is the removal performance of different pollutants, and (c) is a cyclic stability chart. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The present invention provides a method for in-situ extraction of highly active single-atom catalysts from MOFs-derived metal oxides, comprising: preparing a N-coordinated metal organic framework from a transition metal salt and an organic ligand by a precipitation method; then pyrolyzing at 300-800°C to obtain a metal single-atom catalyst supported on a metal oxide and a carbon-nitrogen composite carrier; wherein the organic ligand comprises trimesic acid and a nitrogen-containing ligand.

[0030] The present invention first synthesizes a N-coordinated metal organic framework (MOF) by a precipitation method, and then synthesizes a metal oxide / carbon-nitrogen synergistically modified metal single atom catalyst (i.e., a metal single atom catalyst supported on a metal oxide and carbon-nitrogen composite carrier) by high-temperature pyrolysis. During the pyrolysis process, nitrogen coordination can provide different coordination environments to effectively anchor metal atoms and generate SACs (single atom catalyst) sites; the metal organic framework can form a metal oxide / carbon-nitrogen structure composite carrier, synergistically enhance the activity of SACs, and further affect the catalytic mechanism and the performance of the catalyst. Experiments show that the metal oxide / carbon-nitrogen synergistically modified single atom catalyst can efficiently activate persulfate and degrade phenol, and shows high cyclic stability. The catalyst of the present invention has a simple preparation process, excellent catalytic performance, and high system stability, and has great application potential.

[0031] The molar ratio of trimesic acid to the nitrogen-containing ligand is 1:(0.5-2), preferably 1: 1. The experiment of the present invention shows that the catalytic activity of the obtained single atom catalyst can be adjusted by regulating the molar ratio of trimesic acid to the 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. When the nitrogen-containing ligand contains both amino and carboxyl groups, the effect is better.

[0033] The pyrolysis temperature is 300-800°C, the time is 2-4h, and the heating rate is 5-10°C / min. The experimental results of the present invention show that the pyrolysis temperature has a great influence on the catalytic efficiency of the obtained single atom catalyst, and the catalytic efficiency is the highest at 300°C.

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

[0035] The preparation method of the highly active single-atom catalyst specifically includes:

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

[0037] 1.1) Disperse 2-8 mmol of trimesic acid and nitrogen-containing ligand in 100-300 mL of methanol solution respectively, 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, stir at room temperature for 5-20 min to obtain solution B, then add solution A to solution B, 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 is to prepare metal oxide / carbon-nitrogen coordinated modified single atom catalysts

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

[0041] Specifically, the present invention provides a Cu-based metal organic framework-derived copper oxide / carbon-nitrogen co-modified Cu single-atom catalyst. The N-coordinated Cu-MOF-derived Cu single-atom catalyst is marked as: CuO@CN, and 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 temperature of the high temperature pyrolysis is 300-800°C, specifically 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, preferably 300°C, and the heating rate is 10°C / min.

[0043] The preparation method adopted by the present invention can not only obtain copper oxide crystals, but also retain an amorphous carbon structure around the copper oxide, which is beneficial to the in-situ regulation of the coordination environment of the Cu site under the effect of the introduction of N coordination by the nitrogen-containing ligand, and realizes the in-situ extraction of highly active single-atom Cu. Ultimately, the carrier effect of the coupled metal oxide and carbon synergistically enhances the activity of the single-atom Cu, thereby improving the efficiency of the activated persulfate in degrading organic pollutants.

[0044] The preferred molar mass of 10-13 mmol copper salt, 4 mmol trimesic acid, and 4 mmol nitrogen-containing ligand are dispersed in 100 mL of methanol solution and fully dissolved and mixed. The precipitation method is used to stand for 1-3 hours, specifically 1 hour, 2 hours, 3 hours, preferably 2 hours. Then the above precipitate is washed with water and ethanol twice and dried overnight, the drying temperature is 60-80°C, preferably 60°C, to obtain a Cu-MOF precursor; the Cu-MOF is loaded into a crucible and placed in a muffle furnace, and the pyrolysis temperature is adjusted to calcine for 2-4 hours, specifically 2 hours, 3 hours, 4 hours, preferably 3 hours. The heating rate is 5-10°C / min, specifically 5°C / min, 10°C / min, preferably 10°C / min. This process oxidizes Cu-MOF at high temperature to obtain CuO, and carbonizes and reorganizes to a certain extent to form an ordered nitrogen coordination structure to obtain Cu single atoms, and the material is recorded as CuO@CN.

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

[0046] Furthermore, the highly active single-atom catalyst and the oxidant are added to the sewage (preferably, the highly active single-atom catalyst is first added for pre-adsorption for a preset time, and then the oxidant is added, which can improve the degradation efficiency), and the water body is purified by catalytic degradation of organic pollutants in the sewage. The oxidant is one or both of peroxymonosulfate and peroxydisulfate, preferably peroxymonosulfate.

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

[0048] The organic pollutants include aromatic compounds containing electron-rich groups, preferably include at least one of phenol, 4-chlorophenol and sulfamethoxazole, preferably include phenol. The concentration of the organic pollutants is 20-50 mg / L, preferably 30 mg / L.

[0049] After the catalytic degradation reaction is completed, if relevant tests are required, 1 mL of the solution is filtered through a 0.22 μm polyethersulfone microporous filter membrane, and 50 μL of methanol is added and mixed evenly to terminate possible degradation reactions in the sample.

[0050] Comparative Example 1

[0051] The preparation of copper oxide / carbon catalyst (CuO@C) comprises the following steps: 13 mmol of copper nitrate pentahydrate and 4 mmol of trimesic acid are dispersed in 100 mL of methanol solution, fully dissolved and mixed, and allowed to stand for 2 hours by precipitation method. The above precipitate is then washed twice with water and ethanol respectively and dried overnight at 60°C to obtain a Cu-MOF precursor; the Cu-MOF is loaded into a crucible and placed in a muffle furnace, and pyrolyzed at 300°C for 3 hours in an air atmosphere, with a heating rate of 10°C / min to obtain CuO@C.

[0052] Comparative Example 2

[0053] The preparation of copper oxide catalyst (CuO) comprises the following steps: 13 mmol of copper nitrate pentahydrate and 4 mmol of trimesic acid are dispersed in 100 mL of methanol solution, fully dissolved and mixed, and allowed to stand for 2 hours by precipitation method. The above precipitate is then washed twice with water and ethanol respectively and dried overnight at 60°C to obtain a Cu-MOF precursor; the Cu-MOF is loaded into a crucible and placed in a muffle furnace, and pyrolyzed at 800°C for 3 hours in an air atmosphere, with a heating rate of 10°C / min.

[0054] Example 1

[0055] Preparation of CuO@CN catalyst, such as Figure 1 As shown, the steps are as follows: 13mmol of copper nitrate pentahydrate, 4mmol of trimesic acid, and 4mmol of 2-aminoterephthalic acid are dispersed in 100mL of methanol solution, fully dissolved, mixed, and allowed to stand for 2h by precipitation method. Then the above precipitate is washed twice with water and ethanol respectively and dried overnight at 60°C to obtain a Cu-MOF precursor; the Cu-MOF is loaded into a crucible and placed in a muffle furnace, and pyrolyzed at 300°C for 3h. This process causes Cu-MOF to be oxidized at high temperature to obtain CuO crystals, and to carbonize and reorganize to a certain extent to form an ordered coordination structure to obtain Cu single atoms, and the material is recorded as CuO@CN.

[0056] In addition, keeping a single variable, the dosage of 2-aminoterephthalic acid was changed to 2mmol, 6mmol and 8mmol respectively to adjust the molar ratio of trimesic acid to 2-aminoterephthalic acid to 1:0.51:1.5 and 1:2. Keeping a single variable, the types of nitrogen-containing ligands were changed to melamine, urea, 2-2'bipyridine, ethylenediaminetetraacetic acid, 5-amino-4-nitrogenazole and ethylenediamine. The effects of the molar ratio of trimesic acid and nitrogen-containing ligands and the types of nitrogen-containing ligands on the performance of single-atom catalysts were explored. The experimental results are as follows: Figure 3 As shown in e and f.

[0057] Figure 2The XRD patterns of CuO@CN and the catalysts prepared in Comparative Examples 1 and 2 are shown. Compared with the CuO material, the width of the diffraction peaks of the modified catalysts increased to varying degrees, which is related to the fact that the introduced amorphous carbon layer reduced the crystallinity of CuO. In addition, the signal peak of CuC8 appeared on CuO@C and CuO@CN, further proving that a certain carbon structure was retained on the two materials and that nitrogen coordination was conducive to the formation of Cu-C bonds. Figure 2 The morphology of the catalyst was further characterized in bg, and it was found that CuO@CN was an amorphous carbon structure wrapped around copper oxide particles. Figure 2 In the h STEM (high-angle dark field annular scanning transmission electron microscope) image, it was observed that dispersed Cu single atoms were detected in the thin carbon layer, and it can be seen that the active metal on the carbon layer is dispersed as single atoms. This shows that nitrogen coordination promotes the regulation of the coordination environment of the metal site and realizes the in-situ extraction of highly active single atoms. Based on the above characterization, we confirmed the synthesis and preparation of Cu-based metal-organic framework-derived copper oxide / carbon-modified Cu single-atom composite catalyst.

[0058] Example 2

[0059] The pyrolysis temperature during the catalyst synthesis process and the pH value during the catalytic reaction process in Example 1 were changed to explore their effects on the performance of activated peroxymonosulfate (PMS) in degrading phenol (PhOH), and the specific steps were as follows:

[0060] Weigh 25 mg of the CuO@CN catalyst prepared by pyrolysis at 300°C, 400°C, 500°C, 600°C, 700°C, and 800°C, respectively, disperse it in 50 mL of an aqueous solution containing 30 mg / L PhOH, stir evenly, add 0.3 g / L PMS, and drop 0.1 M NaOH to adjust the initial pH to within the range of 4.0-10.0. Take samples at regular intervals and filter with a 0.22 μm disposable filter. Detect changes in the concentration of residual PhOH with high performance liquid chromatography. Figure 3 In the equation, C is the concentration during the degradation process, and C0 is the initial concentration of PhOH. Figure 3 The reaction pH value corresponding to Figure a is 6.0, Figure b corresponds to the catalyst obtained at a pyrolysis temperature of 300°C, and the CuO@CN in Figures c and d are catalysts obtained at a pyrolysis temperature of 300°C, and the reaction pH value is 6.0.

[0061] The influence of calcination temperature on Figure 3 As shown in Figure a, since the carbon layer content decreases with increasing temperature, the best phenol degradation performance is shown at 300°C, and the degradation is basically complete within 30 minutes. Figure 3 As shown in b, a pH of 6.0, i.e. a neutral environment, is more conducive to the generation and action of active species. Therefore, the optimal reaction conditions were determined. Figure 3 Figure c shows that after 30 minutes of pre-adsorption (no oxidant was added during the pre-adsorption period, and the oxidant PMS was added after the pre-adsorption), at pH = 6.0, Cu@CN can achieve 100% removal of phenol within 5 minutes, CuO@C can only be completely degraded in about 30 minutes, and the PhOH removal rate of CuO at 30 minutes is only 40%. Figure 3 It can be seen from the phenol degradation rate in Figure d that the phenol degradation rate of CuO@CN is 46.4 times higher than that of CuO and 3.7 times higher than that of CuO@C. Figure 3 Figures e and f respectively compare the catalytic performance of non-preferred embodiments with a molar ratio of trimesic acid to 2-aminoterephthalic acid of 1:0.5, 1:1.5 and 1:2 and different nitrogen source ligands. It can be seen that when the molar ratio of trimesic acid to 2-aminoterephthalic acid is 1:1, the degradation rate of PhOH is the fastest, and the degradation rate of 2-aminoterephthalic acid is faster than that of other nitrogen-containing ligands. It is proved that 1:1 is the optimal molar ratio and 2-aminobenzoic acid is the optimal structure of the nitrogen source. The above experimental results show that the CuO@CN catalyst enhances the single-atom activity of Cu due to the combined action of copper oxide and carbon carrier, and effectively improves the performance of activated persulfate in degrading PhOH.

[0062] Example 3

[0063] The present invention uses electron paramagnetic resonance (EPR) to compare the differences in active species generated by CuO, CuO@C and CuO@CN catalysts (prepared by Comparative Examples 1, 2 and Example 1, respectively) during the degradation of organic matter in a persulfate system. The results are as follows Figure 4 As shown, Figure 4 In Figure c, Blank, MT, TBA, L-HIS, and PBQ represent the CuO@CN catalytic system without quencher, with 50 mM methanol, tert-butyl alcohol, L-histidine, and p-benzoquinone quencher, respectively. MT can quench sulfate radicals SO4 · - 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 a and b, the ·OH signal and 1 O2 signal, compared with the signal intensity after adding PhOH, it is found that the system is mainly singlet oxygen 1 O2-dominated non-radical system. Figure 4The quenching experiment results in c and d show that L-HIS and PBQ can almost completely inhibit the degradation of PhOH. Combined with the active species signal of EPR, the non-radical dominant pathway of the system is determined, and the active species is 1 O2.

[0065] Example 4

[0066] Further to the above 1 The source of O2 is explored, such as Figure 5 As shown, CuO@CN, CuO@CN 0.5 、CuO@CN 1.5 , CuO@C-N2 represent single atom catalysts obtained when the molar ratios of trimesic acid and 2-aminoterephthalic acid are 1:1, 1:0.5, 1:1.5, and 1:2, respectively.

[0067] Figure 5 Figure a shows the infrared spectra of five materials. -1 The CuO vibration signals are obvious at all locations, and the catalyst has the -OH vibration signal of H2O adsorption (3300-3645cm -1 ), the most significant change is 1623cm -1 It is attributed to the vibration of carboxyl -COOH. Figure 5 In b, the signal position is further enlarged, and the peak intensity is linearly fitted with the reaction rate. Figure 5 The results show that the phenol degradation rate is linearly correlated with the -COOH peak intensity of 0.9665, proving that appropriate concentration of N coordination is conducive to the in-situ extraction of active Cu atoms. At the same time, carbonyl groups as activation sites of PMS promote 1 Production of O2.

[0068] Example 5

[0069] According to the catalytic degradation experiment of PhOH in Example 2, the catalyst prepared in Example 1 was tested for anti-interference, universality and cyclic stability. Figure 6 As shown in a. Among them, Figure 6 In a, Control means that no anions are added to the CuO@CN catalytic system. - 、NO3 - 、SO4 2- and HCO3 - It refers to the common anions in water that affect catalytic performance. During the experiment, sodium chloride, sodium nitrate, sodium sulfate and sodium bicarbonate with a concentration of 100mM were added to simulate the interference of actual water on catalyst performance.

[0070] from Figure 6 As can be seen in a, in the anion Cl- 、NO3 - 、SO4 2- and HCO3 - Under the influence of , the catalytic performance was slightly inhibited, and the results showed that the system had good anti-interference ability. Figure 6 The degradation experiments of different pollutants in b (PhOH, BA, SMX and 4-CP represent phenol, benzoic acid, sulfamethoxazole and 4-chlorophenol, respectively) show that CuO@CN has 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 experiment 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 with PMS and pollutants, thereby improving the catalytic stability.

[0071] In summary, the embodiment of the present invention first synthesizes a N-coordinated Cu-based metal organic framework (Cu-MOF) by precipitation method, and then synthesizes a metal oxide / carbon-nitrogen synergistically modified single atom catalyst (CuO@CN) by high temperature pyrolysis. During the pyrolysis process, nitrogen coordination can provide different coordination environments to effectively anchor metal atoms and generate SACs sites; the metal organic framework can form a metal oxide / carbon-nitrogen structure composite carrier, synergistically enhance the activity of SACs and further affect the catalytic mechanism and the performance of the catalyst. Persulfate activation and organic pollutant degradation experiments show that CuO@CN can efficiently activate persulfate and degrade phenol, and shows high cyclic stability.

[0072] It will be easily understood by those skilled in the art that the above description is only 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 in the protection scope of the present invention.

Claims

1. A method for in-situ extraction of single-atom catalysts from MOFs-derived metal oxides, characterized in that: include: The N-coordinated metal organic framework is prepared by a precipitation method using a transition metal salt and an organic ligand; Then, the catalyst is pyrolyzed at 300-800°C to obtain a metal single atom catalyst supported on a metal oxide and a carbon-nitrogen composite support; Wherein, the organic ligand includes trimesic acid and a nitrogen-containing ligand.

2. The method for in-situ extraction of single-atom catalysts from MOFs-derived metal oxides according to claim 1, characterized in that: The molar ratio of the trimesic acid to the nitrogen-containing ligand is 1:(0.5-2).

3. The method for in-situ extraction of single-atom catalysts from MOFs-derived metal oxides according to claim 1, characterized in that: The nitrogen-containing ligand includes one or more of melamine, urea, ethylenediamine, 2-2'bipyridine, diethylenetriamine, ethylenediaminetetraacetic acid and 2-aminoterephthalic acid, preferably 2-aminoterephthalic acid.

4. The method for in-situ extraction of single-atom catalysts from MOFs-derived metal oxides according to claim 1, characterized in that: The precipitation method specifically comprises: mixing a transition metal salt and an organic ligand in a solution, then standing for 1-3 hours by a precipitation method, centrifuging, washing, and drying to obtain a N-coordinated metal organic framework; And / or, the pyrolysis time is 2-4 hours, and the heating rate is 5-10°C / min.

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

6. A metal single atom catalyst, characterized in that: Obtained by the method according to any one of claims 1 to 5.

7. Use of the metal single atom catalyst according to claim 6 in water purification.

8. The use according to claim 7, characterized in that: The metal single atom catalyst and the oxidant are added into sewage to purify the water by catalytically degrading the organic pollutants in the sewage; the oxidant is preferably persulfate.

9. The use according to claim 8, characterized in that: The molar ratio of the oxidant to the organic pollutant is (1-2):1; And / or, the dosage of the metal single atom catalyst in the sewage is 0.3-2.0 g / L; And / or, the catalytic degradation is carried out at a pH value of 4.0-10.

0.

10. The use according to claim 7, characterized in that: The organic pollutants include aromatic compounds containing electron-rich groups, preferably at least one of phenol, 4-chlorophenol and sulfamethoxazole.

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