A fully exposed single-atom catalyst and its preparation method and application

Abstract

The present invention provides a fully exposed single-atom catalyst and its preparation method and application, which belongs to the field of catalyst technology. The present invention uses tubular graphite phase carbon nitride as a carrier, wherein the nitrogen atoms in the graphite phase carbon nitride have fixed sites, so that the environment around the transition metal single atoms is uniform, which is conducive to the uniform distribution of the transition metal single atoms on the carrier; since the transition metal single-atom sites of the fully exposed single-atom catalyst provided by the present invention are all exposed on the surface of the carrier, the transition metal single-atom active center can be directly in contact with the reactant, thereby significantly improving the catalytic activity of the catalyst; in the fully exposed single-atom catalyst provided by the present invention, the mass of the transition metal single atom is 5 to 28% of the fully exposed single-atom catalyst, and the catalyst has a higher transition metal single-atom content. And since the active sites of these single atoms are all exposed on the surface of the carrier, the catalytic activity of the catalyst can be significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and in particular to a fully exposed single-atom catalyst and a preparation method and application thereof. Background Art

[0002] Single-atom catalysts have attracted widespread attention in various catalytic fields such as environment, energy, and chemical industry due to their advantages such as high atom utilization, high selectivity, and high efficiency. However, when the atomic loading of the single-atom catalyst is low, the catalyst space gain and mass gain are low, and the catalyst activity is low. Therefore, with the development of single-atom catalyst preparation technology, the current research direction is mainly to improve the catalytic activity of the catalyst by increasing the loading of single atoms. However, since single-atom catalysts are all heterogeneous reactions, the reactants need to be in direct contact with the catalytic active sites. However, the current high-loaded single-atom catalysts often have the problem that the single-atom active centers are not exposed on the catalyst surface, resulting in the catalyst efficiency not being significantly improved despite the high content of single atoms loaded in the catalyst. Therefore, it is necessary to provide a fully exposed single-atom catalyst with a high loading of single atoms to improve the catalytic activity of the catalyst. Summary of the Invention

[0003] The purpose of the present invention is to provide a fully exposed single-atom catalyst with a high loading of single atoms, and its preparation method and application. The fully exposed single-atom catalyst provided by the present invention has a high catalytic efficiency when degrading organic pollutants.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a fully exposed single-atom catalyst, comprising a carrier and a transition metal single atom supported on the surface of the carrier; the carrier is tubular graphite phase carbon nitride; the sites of the transition metal single atom are all exposed on the surface of the carrier; the mass of the transition metal single atom is 5 to 28% of the mass of the fully exposed single-atom catalyst.

[0006] Preferably, the length of the tubular graphite phase carbon nitride is 1 to 30 μm; and the diameter of the tubular graphite phase carbon nitride is 0.1 to 10 μm.

[0007] Preferably, the transition metal single atom includes an Fe atom, a Cu atom or an Ag atom.

[0008] The present invention also provides a method for preparing the fully exposed single-atom catalyst described in the above technical solution, comprising the following steps:

[0009] Melamine, cyanuric acid and deionized water are mixed and subjected to self-assembly reaction to obtain a supramolecular suspension;

[0010] Mixing the supramolecular suspension, a soluble transition metal salt and an organic ligand, and stirring at room temperature for 2 to 24 hours to obtain a precursor;

[0011] pyrolyzing the precursor to obtain a fully exposed single-atom catalyst;

[0012] The molar ratio of the organic ligand, the metal ions in the soluble transition metal salt, cyanuric acid and melamine is (0.1-0.5):(0.05-0.4):(0.5-1.0):1.

[0013] Preferably, the temperature of the self-assembly reaction is room temperature, and the time of the self-assembly reaction is 5 to 60 minutes.

[0014] Preferably, the soluble transition metal salt comprises ferrous chloride, ferrous sulfate, cupric chloride, cupric nitrate, cupric acetate or silver nitrate.

[0015] Preferably, the organic ligand is one of ethylenediaminetetraacetic acid, citric acid and oxalic acid.

[0016] Preferably, the pyrolysis temperature is 500-700° C.; and the pyrolysis time is 1-4 hours.

[0017] Preferably, the pyrolysis is carried out under a protective atmosphere.

[0018] The present invention also provides the fully exposed single-atom catalyst described in the above technical solution, or the present invention also provides the use of the fully exposed single-atom catalyst prepared by the preparation method described in the above technical solution in catalytic degradation of organic pollutants.

[0019] The present invention provides a fully exposed single-atom catalyst, comprising a support and transition metal atoms supported on the support surface. The support is a tubular graphite-phase carbon nitride, wherein the sites of the transition metal atoms are all exposed on the support surface; the mass of the transition metal atoms is 5-28% of the mass of the fully exposed single-atom catalyst. The present invention uses the tubular graphite-phase carbon nitride as the support, wherein the nitrogen atoms in the graphite-phase carbon nitride have fixed sites, making the environment around the transition metal atoms uniform, thereby facilitating the uniform distribution of the transition metal atoms on the support. Since the transition metal atoms in the fully exposed single-atom catalyst provided by the present invention are all exposed on the support surface, the active centers of the transition metal atoms can directly contact the reactants, thereby significantly improving the catalytic activity of the catalyst. In the fully exposed single-atom catalyst provided by the present invention, the mass of the transition metal atoms is 5-28% of the mass of the fully exposed single-atom catalyst, and the catalyst has a high single-atom content. Moreover, since the active sites of these atoms are all exposed on the support surface, the catalytic activity of the catalyst can be significantly improved. Therefore, the fully exposed single-atom catalyst provided by the present invention has excellent catalytic activity when degrading organic pollutants. The results of the example show that pure CN has almost no effect on the degradation of BPA by activating PDS. However, the fully exposed single-atom catalyst Cu1CN provided by the present invention can activate PDS to rapidly degrade BPA. In the presence of Cu1CN, BPA can be degraded by more than 90% in 5 minutes, the degradation rate reaches 98% in 20 minutes, and almost complete degradation in 40 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of Cu1CN prepared in Example 1 of the present invention and CN prepared in Comparative Example 1;

[0021] Figure 2 FT-IR images of Cu1CN prepared in Example 1 of the present invention and CN prepared in Comparative Example 1;

[0022] Figure 3 This is a SEM image of Cu1CN prepared in Example 1 of the present invention;

[0023] Figure 4 TEM image of Cu1CN prepared in Example 1 of the present invention;

[0024] Figure 5 Element distribution diagram of Cu1CN prepared in Example 1 of the present invention;

[0025] Figure 6 This is a spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of Cu1CN prepared in Example 1 of the present invention;

[0026] Figure 7TEM image of Ag1CN prepared in Example 2 of the present invention;

[0027] Figure 8 TEM image of Fe1CN prepared in Example 3 of the present invention;

[0028] Figure 9 This is a graph showing the degradation efficiency of BPA catalyzed by the catalysts prepared in Examples 1 to 3 of the present invention and Comparative Example 1;

[0029] Figure 10 This is a diagram showing the experimental results of the catalyst prepared in Example 1 of the present invention degrading BPA and capturing free radicals;

[0030] Figure 11 This is a diagram showing the experimental results of the catalyst prepared in Example 1 of the present invention degrading BPA and capturing singlet oxygen. DETAILED DESCRIPTION

[0031] The present invention provides a fully exposed single-atom catalyst, comprising a carrier and transition metal single atoms supported on the surface of the carrier; the carrier is tubular graphite phase carbon nitride; the sites of the transition metal single atoms are all exposed on the surface of the carrier; the mass of the single atoms is 5 to 28% of that of the fully exposed single-atom catalyst.

[0032] The fully exposed single-atom catalyst provided by the present invention includes a carrier, and the carrier is tubular graphite-phase carbon nitride. In the present invention, the length of the tubular graphite-phase carbon nitride is preferably 1 to 30 μm, more preferably 10 to 20 μm; the diameter of the tubular graphite-phase carbon nitride is preferably 0.1 to 10 μm, more preferably 0.2 to 6 μm. In the present invention, the tubular graphite-phase carbon nitride has good stability and a large specific surface area, and the nitrogen atoms in the graphite-phase carbon nitride have fixed sites, which makes the environment around the transition metal single atoms uniform, thereby facilitating the uniform distribution of the single atoms on the carrier; when the length and diameter of the tubular graphite-phase carbon nitride are within the above range, it is more conducive to fully increasing the loading amount of the transition metal single atoms.

[0033] The fully exposed single-atom catalyst provided by the present invention comprises a transition metal single atom supported on the surface of a support, with the sites of the transition metal single atom fully exposed on the support surface. In the present invention, the transition metal single atom is bound to the support surface through coordination between the metal and nitrogen atoms in the support, thereby securing the single atom to the support surface. Furthermore, the transition metal single atom is the active atom of the catalyst. When the sites of the transition metal single atom are fully exposed on the support surface, the catalytic effect of the transition metal single atom can be fully exerted even with a high loading, thereby significantly improving the catalytic activity of the catalyst.

[0034] In the present invention, the mass of the transition metal single atoms is 5 to 28%, preferably 10 to 27.47%, of the mass of the fully exposed single atom catalyst. In the present invention, when the mass content of the transition metal single atoms is within the above range, a high transition metal single atom loading is achieved. Furthermore, since all the transition metal single atom sites are exposed on the support surface, the catalytic activity of the fully exposed single atom catalyst can be significantly improved.

[0035] In the present invention, the transition metal single atom preferably includes an Fe atom, a Cu atom or an Ag atom. In the present invention, when the transition metal is of the above type, it has excellent catalytic activity.

[0036] The present invention also provides a method for preparing the fully exposed single-atom catalyst described in the above technical solution, comprising the following steps:

[0037] Melamine, cyanuric acid and deionized water are mixed and subjected to self-assembly reaction to obtain a supramolecular suspension;

[0038] Mixing the supramolecular suspension, a soluble transition metal salt and an organic ligand, and stirring at room temperature for 2 to 24 hours to obtain a precursor;

[0039] pyrolyzing the precursor to obtain a fully exposed single-atom catalyst;

[0040] The molar ratio of the organic ligand, the metal ions in the soluble transition metal salt, cyanuric acid and melamine is (0.1-0.5):(0.05-0.4):(0.5-1.0):1.

[0041] The invention mixes melamine, cyanuric acid and deionized water and then performs self-assembly reaction to obtain a supramolecular suspension.

[0042] The present invention does not specifically limit the method for mixing melamine, cyanuric acid, and deionized water; it only requires that the components be uniformly mixed. In the present invention, the method for mixing melamine, cyanuric acid, and deionized water is preferably as follows: melamine and cyanuric acid are separately mixed with deionized water, heated to 80-85°C to dissolve the melamine and cyanuric acid in the deionized water, respectively, to obtain a melamine solution and a cyanuric acid solution; and then the melamine solution and cyanuric acid are poured into the melamine solution. In the present invention, the heating promotes the dissolution of melamine and cyanuric acid in the deionized water, respectively. The present invention does not specifically limit the heating time; it only requires that the melamine or cyanuric acid be dissolved in the deionized water. The present invention does not specifically require the stirring rate; it can be adjusted as needed.

[0043] The present invention has no particular limitation on the amount of deionized water used, and the amount can be adjusted according to the amounts of melamine and cyanuric acid so as to be able to dissolve melamine and cyanuric acid respectively.

[0044] In the present invention, the temperature of the self-assembly reaction is preferably room temperature, more preferably 10-30°C; the time of the self-assembly reaction is preferably 5-60 minutes, more preferably 30-60 minutes. During the self-assembly reaction, melamine and cyanuric acid can self-assemble to form a supramolecular compound, thereby obtaining a supramolecular suspension. When the temperature and time of the self-assembly reaction are within the above ranges, melamine and cyanuric acid can fully react to form a supramolecular compound.

[0045] After obtaining the supramolecular suspension, the present invention mixes the supramolecular suspension, a soluble transition metal salt and an organic ligand, and stirs the mixture at room temperature for 2 to 24 hours to obtain a precursor.

[0046] In the present invention, the soluble transition metal salt preferably includes ferrous chloride, ferrous sulfate, cupric chloride, cupric nitrate, cupric acetate or silver nitrate. In the present invention, when the soluble transition metal salt is of the above type, it provides transition metal single atoms for the fully exposed single atom catalyst.

[0047] In the present invention, the organic ligand is preferably one of ethylenediaminetetraacetic acid, citric acid, and oxalic acid. In the present invention, the organic ligand can undergo a complex reaction with a soluble transition metal salt to fix the transition metal ion. When the organic ligand is of the above type, it is more conducive to the full progress of the complex reaction.

[0048] In the present invention, the molar ratio of the organic ligand, the metal ion in the soluble transition metal salt, cyanuric acid, and melamine is (0.1-0.5):(0.05-0.4):(0.5-1.0):1, preferably (0.2-0.4):(0.2-0.3):(0.6-0.8):1. In the present invention, when the molar ratio of the organic ligand, the metal ion in the soluble transition metal salt, cyanuric acid, and melamine is within the above ranges, a sufficient amount of transition metal atoms can be loaded into the fully exposed single atom catalyst, and the mass of the transition metal atoms can be 5-28% of the mass of the fully exposed single atom catalyst.

[0049] In the present invention, by mixing the supramolecular suspension, a soluble transition metal salt and an organic ligand, a complex formed by the transition metal and the organic ligand can be coated on the supramolecular surface. The present invention does not particularly limit the method for mixing the supramolecular suspension, the soluble transition metal salt and the organic ligand, and a mixing method well known to those skilled in the art can be used to mix the above components evenly. In the present invention, the method for mixing the supramolecular suspension, the soluble transition metal salt and the organic ligand is preferably: dissolving the soluble transition metal salt and the organic ligand in deionized water respectively to obtain a soluble transition metal salt solution and an organic ligand solution, and then adding the soluble transition metal salt solution and the organic ligand solution to the supramolecular suspension. In the present invention, when the supramolecular suspension, the soluble transition metal salt and the organic ligand are mixed according to the above method, the three can be mixed more evenly.

[0050] In the present invention, during the stirring process, the transition metal salt and the organic ligand undergo a complex reaction to form a transition metal-organic complex. At the same time, the nitrogen atoms in the supramolecular suspension can combine with the transition metal-organic complex through coordination, so that the transition metal-organic complex is coated on the surface of the supramolecular compound.

[0051] In the present invention, the stirring temperature is room temperature, preferably 10 to 30°C; and the stirring time is 2 to 24 hours, preferably 4 to 12 hours. In the present invention, when the stirring temperature and time are within the above ranges, the transition metal salt and the organic ligand can fully react to form a transition metal-organic complex, and the transition metal-organic complex can be combined with the supramolecular compound.

[0052] After stirring at room temperature for 2 to 24 hours, the product obtained by stirring is preferably subjected to solid-liquid separation, washing and drying in sequence to obtain a precursor.

[0053] The present invention does not particularly limit the methods for solid-liquid separation, washing, and drying; methods of filtration, washing, and drying well known to those skilled in the art may be used. In the present invention, the solid-liquid separation is preferably filtration; the washing agent is preferably water; and the drying temperature is preferably 80°C.

[0054] After obtaining the precursor, the present invention pyrolyzes the precursor to obtain a fully exposed single-atom catalyst.

[0055] In the present invention, the pyrolysis temperature is preferably 500-700°C, more preferably 550-650°C; the pyrolysis time is preferably 1-4 hours, more preferably 2-3 hours; the heating rate to the pyrolysis temperature is preferably 2-15°C / min, more preferably 5-10°C / min; and the pyrolysis is preferably carried out under a protective atmosphere, preferably argon or nitrogen. During the pyrolysis process, the supramolecular compound formed by melamine and cyanuric acid undergoes thermal polymerization to form tubular graphitic carbon nitride, and transition metal atoms are anchored to the tubular graphitic carbon nitride to form single atoms. When the pyrolysis temperature and time are within the above ranges, excessive decomposition of the tubular graphitic carbon nitride caused by excessively high pyrolysis temperatures or prolonged pyrolysis times can be prevented. When the heating rate is within the above range, the tubular graphitic carbon nitride is more likely to have a larger specific surface area. The present invention does not particularly limit the pyrolysis apparatus; a pyrolysis apparatus familiar to those skilled in the art can be used. In the present invention, the pyrolysis device is preferably a tube furnace.

[0056] The preparation method provided by the present invention comprises the following steps: first preparing a supramolecular suspension, then mixing the supramolecular suspension with a soluble transition metal salt and an organic ligand, and stirring the soluble transition metal salt and the organic ligand to undergo a complex reaction to form a transition metal-organic ligand complex. Simultaneously, the transition metal-organic ligand complex is bound to the surface of the supramolecular compound. Through the pyrolysis process, not only tubular graphite phase carbon nitride is formed, but also transition metal single atoms are anchored on the surface of the tubular graphite phase carbon nitride rather than being anchored inside the tubular graphite phase carbon nitride, thereby exposing all transition metal single atom sites on the carrier surface.

[0057] The present invention also provides the use of the fully exposed single-atom catalyst described in the above technical solution or the fully exposed single-atom catalyst prepared by the preparation method described in the above technical solution in catalytic degradation of organic pollutants.

[0058] The present invention does not particularly limit the method for applying the fully exposed single-atom catalyst in the catalytic degradation of organic pollutants. The method for applying the single-atom catalyst in the catalytic degradation of organic pollutants well known to those skilled in the art can be used.

[0059] In the present invention, the method for using the fully exposed single atom catalyst in catalytic degradation of organic pollutants preferably comprises: mixing the fully exposed single atom catalyst, persulfate and the organic pollutants to be treated, and performing degradation.

[0060] In the present invention, the organic pollutant to be treated is preferably one or more of phenol, parachlorophenol, and bisphenol A. In the present invention, the persulfate preferably includes potassium peroxymonosulfate and / or potassium peroxydisulfate. In the present invention, when the persulfate is of the above type, it can work together with the fully exposed single-atom catalyst to catalytically degrade the organic pollutant.

[0061] In the present invention, the mass ratio of the fully exposed single atom catalyst to the persulfate is preferably 1:0.5 to 4, more preferably 1:1.78. In the present invention, the mass ratio of the fully exposed single atom catalyst to the organic pollutant to be treated is preferably 1:0.25 to 1, more preferably 1:0.5. In the present invention, when the mass ratio of the fully exposed single atom catalyst to the persulfate and the mass ratio of the fully exposed single atom catalyst to the organic pollutant to be treated are within the above ranges, the organic pollutants to be treated can be fully degraded.

[0062] In the present invention, the degradation temperature is preferably room temperature, and the degradation time is preferably 20 to 60 minutes, more preferably 40 minutes. In the present invention, when the degradation temperature and time are within the above ranges, the organic pollutants to be treated can be fully degraded.

[0063] The fully exposed single-atom catalyst provided by the present invention has all the transition metal single-atom sites exposed on the support surface, so that the transition metal single atoms can fully contact with organic pollutants, thereby degrading organic pollutants in the presence of persulfate, and can significantly improve the degradation efficiency of organic pollutants.

[0064] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. 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.

[0065] Example 1

[0066] A fully exposed single-atom catalyst comprises a carrier and copper single atoms supported on the carrier surface, wherein the carrier is tubular graphite-phase carbon nitride, the length of the tubular graphite-phase carbon nitride is 1 to 30 μm, and the diameter of the tubular graphite-phase carbon nitride is 0.1 to 6 μm. The copper single-atom sites are all exposed on the carrier surface, and the mass of the copper single atoms is 27.47% of the mass of the fully exposed single-atom catalyst.

[0067] The preparation method of the fully exposed single-atom catalyst comprises the following steps:

[0068] 2.46 g of cyanuric acid was weighed, added to 350 mL of deionized water, and heated at 80° C. to dissolve to obtain a cyanuric acid solution; 3.00 g of melamine was weighed, added to 350 mL of deionized water, and heated at 80° C. to dissolve to obtain a melamine solution; the cyanuric acid solution was added to the melamine solution and stirred at room temperature for 30 minutes to perform a self-assembly reaction to obtain a supramolecular suspension;

[0069] The supramolecular suspension, a soluble transition metal salt (copper acetate) and an organic ligand (citric acid) were mixed, stirred at room temperature for 4 hours, and then filtered. The solid obtained by filtration was washed with water and dried at 80° C. for 12 hours to obtain a precursor;

[0070] The method for mixing the supramolecular suspension, copper acetate and citric acid is as follows: 1.00 g of citric acid is weighed and added to 50 mL of deionized water to dissolve to obtain a citric acid solution; 960 mg of copper acetate is weighed and added to 50 mL of deionized water to dissolve to obtain a copper acetate solution; and then the citric acid solution and the copper acetate solution are added to the supramolecular suspension;

[0071] The precursor was placed in a tube furnace, heated to 600°C at 5°C / min under argon atmosphere and kept at this temperature for 4 h. The fully exposed single-atom catalyst obtained was recorded as Cu1CN (Cu content 27.47%).

[0072] In this embodiment, the molar ratio of the organic ligand, the metal ion in the soluble transition metal salt, cyanuric acid, and melamine is 0.22:0.2:0.8:1.

[0073] Example 2

[0074] A fully exposed single-atom catalyst comprises a carrier and silver single atoms supported on the carrier surface, wherein the carrier is tubular graphite-phase carbon nitride, the length of the tubular graphite-phase carbon nitride is 1 to 10 μm, and the diameter of the tubular graphite-phase carbon nitride is 0.1 to 0.6 μm. The silver single-atom sites are all exposed on the carrier surface, and the mass of the silver single atoms is 11.21% of the mass of the fully exposed single-atom catalyst.

[0075] The preparation method of the fully exposed single-atom catalyst comprises the following steps:

[0076] 0.83 g of cyanuric acid was weighed, added to 100 mL of deionized water, and heated at 80° C. to dissolve to obtain a cyanuric acid solution; 1.00 g of melamine was weighed, added to 100 mL of deionized water, and heated at 80° C. to dissolve to obtain a melamine solution; the cyanuric acid solution was added to the melamine solution and stirred at room temperature for 30 minutes to perform a self-assembly reaction to obtain a supramolecular suspension;

[0077] The supramolecular suspension, a soluble transition metal salt (silver nitrate) and an organic ligand (citric acid) were mixed, stirred at room temperature for 4 hours, and then filtered. The solid obtained by filtration was washed with water and dried at 80° C. for 12 hours to obtain a precursor;

[0078] The method for mixing the supramolecular suspension, copper acetate and citric acid is as follows: 0.336 g of citric acid is weighed and added to 20 mL of deionized water to dissolve to obtain a citric acid solution; 68 mg of silver nitrate is weighed and added to 20 mL of deionized water to dissolve to obtain a silver nitrate solution; and then the citric acid solution and the silver nitrate solution are added to the supramolecular suspension;

[0079] The precursor was placed in a tube furnace, and the temperature was raised to 600°C at 5°C / min under argon atmosphere and kept at this temperature for 4 h. The fully exposed single-atom catalyst obtained was recorded as Ag1CN (Ag content 11.21%).

[0080] In this embodiment, the molar ratio of the organic ligand, the metal ion in the soluble transition metal salt, cyanuric acid, and melamine is 0.22:0.05:0.81:1.

[0081] Example 3

[0082] A fully exposed single-atom catalyst comprises a carrier and iron single atoms supported on the carrier surface, wherein the carrier is tubular graphite-phase carbon nitride, the length of the tubular graphite-phase carbon nitride is 1 to 5 μm, the diameter of the tubular graphite-phase carbon nitride is 0.1 to 0.5 μm, the iron single-atom sites are all exposed on the carrier surface, and the mass of the iron single atoms is 21.44% of the mass of the fully exposed single-atom catalyst.

[0083] The preparation method of the fully exposed single-atom catalyst comprises the following steps:

[0084] 2.46 g of cyanuric acid was weighed, added to 350 mL of deionized water, and heated at 80° C. to dissolve to obtain a cyanuric acid solution; 3.00 g of melamine was weighed, added to 350 mL of deionized water, and heated at 80° C. to dissolve to obtain a melamine solution; the cyanuric acid solution was added to the melamine solution and stirred at room temperature for 30 minutes to perform a self-assembly reaction to obtain a supramolecular suspension;

[0085] The supramolecular suspension, a soluble transition metal salt (ferric nitrate) and an organic ligand (oxalic acid) were mixed, stirred at room temperature for 4 hours, and then filtered. The filtered solid was washed with water and dried at 80° C. for 12 hours to obtain a precursor;

[0086] The method for mixing the supramolecular suspension, ferric nitrate and oxalic acid is as follows: 0.432 g of oxalic acid is weighed and added to 50 mL of deionized water to dissolve to obtain an oxalic acid solution; 1.939 g of ferric nitrate is weighed and added to 50 mL of deionized water to dissolve to obtain a ferric nitrate solution; and then the oxalic acid solution and the ferric nitrate solution are added to the supramolecular suspension;

[0087] The precursor was placed in a tube furnace, and the temperature was raised to 600°C at 5°C / min under argon atmosphere and kept at this temperature for 4 h. The fully exposed single-atom catalyst obtained was recorded as Fe1CN (Fe content 21.44%).

[0088] In this embodiment, the molar ratio of the organic ligand, the metal ion in the soluble transition metal salt, cyanuric acid, and melamine is 0.2:0.33:0.79:1.

[0089] Comparative Example 1

[0090] A method for preparing a catalyst comprises the following steps:

[0091] 2.46 g of cyanuric acid was weighed, added to 350 mL of deionized water, and heated at 80° C. to dissolve to obtain a cyanuric acid solution; 3.00 g of melamine was weighed, added to 350 mL of deionized water, and heated at 80° C. to dissolve to obtain a melamine solution; the cyanuric acid solution was added to the melamine solution and stirred at room temperature for 30 minutes to perform a self-assembly reaction to obtain a supramolecular suspension;

[0092] The supramolecular suspension was mixed with an organic ligand (citric acid), stirred at room temperature for 4 hours, and then filtered. The solid obtained by filtration was washed with water and dried at 80° C. for 12 hours to obtain a precursor.

[0093] The method of mixing the supramolecular suspension with citric acid is as follows: 1.00 g of citric acid is weighed and added to 50 mL of deionized water to dissolve to obtain a citric acid solution; then the citric acid solution is added to the supramolecular suspension;

[0094] The precursor was placed in a tube furnace, and the temperature was raised to 600° C. at a rate of 5° C. / min under argon atmosphere and kept at this temperature for 4 hours to obtain graphite-phase carbon nitride, which was recorded as CN.

[0095] Test Example 1

[0096] The Cu1CN prepared in Example 1 and the CN prepared in Comparative Example 1 were tested using an X-ray single crystal diffractometer, and the XRD patterns were as follows: Figure 1 As shown. Figure 1It can be seen that Cu1CN and CN have two XRD diffraction peaks at 13.1° and 27.8°, which correspond to the (100) and (002) crystal plane diffraction characteristic peaks of graphitic carbon nitride, respectively, and there are no diffraction peaks of copper and its compounds.

[0097] The Cu1CN prepared in Example 1 and the CN prepared in Comparative Example 1 were tested by infrared spectrometer, and the FT-IR images were as follows: Figure 2 As shown. Figure 2 It can be seen that at 1700~1200cm -1 The characteristic absorption peaks corresponding to the CN heterocyclic stretching vibration and aromatic stretching vibration modes appeared at 807 cm -1 The peak corresponds to the stretching vibration of the heptazine ring.

[0098] Depend on Figure 1 and Figure 2 It can be seen that the support of the Cu1CN sample is graphite carbon nitride, and there are no copper nanoparticles and their oxides.

[0099] The Cu1CN prepared in Example 1 was tested using a scanning electron microscope, and the SEM image was obtained as shown in FIG. Figure 3 The Cu1CN prepared in Example 1 was tested using a transmission electron microscope, and the TEM image was as shown. Figure 4 The Cu1CN prepared in Example 1 was tested by X-ray energy dispersive spectroscopy (EDS), and the element distribution diagram was obtained as shown in FIG. Figure 5 The Cu1CN prepared in Example 1 was tested using a spherical aberration corrected high-angle annular dark field scanning transmission electron microscope, and the spherical aberration corrected high-angle annular dark field scanning transmission electron microscope image was shown in Figure 6. Figure 4 It can be seen that no nanoparticles and clusters were observed. Figure 5 It can be seen that C, N, S and Cu are uniformly dispersed throughout the sample. This indicates that copper may be distributed in the support in the form of single atoms. Figure 6 It can be seen that copper is uniformly dispersed on the support in the form of single atoms. The above results indicate that Cu is loaded on the support in the form of single atoms, that is, the Cu single-atom catalyst is successfully prepared.

[0100] The TEM image of Ag1CN prepared in Example 2 of the present invention was tested using a projection electron microscope, and the TEM image was as follows: Figure 7 The TEM image of Fe1CN prepared in Example 3 of the present invention was tested using a projection electron microscope, and the TEM image was as shown. Figure 8 shown.

[0101] Application Example 1

[0102] In a 50 mL beaker, 10 mg (0.2 g / L) of CuCN prepared in Example 1 was dispersed as a catalyst in 50 mL of a 20 ppm bisphenol A solution. The catalyst was ultrasonically dispersed to uniformly distribute the catalyst. The catalyst was adsorbed for 30 minutes without the addition of peroxydisulfate. Then, 17.8 mg (1.5 mM) of sodium peroxydisulfate was added to generate active species to degrade bisphenol A. The remaining amount of bisphenol A was sampled and tested. The test results are shown in FIG. Figure 8 As shown;

[0103] Among them, the mass ratio of the fully exposed single atom catalyst to persulfate is 1:1.78, and the mass ratio of the fully exposed single atom catalyst to the organic pollutants to be treated is 2:1.

[0104] Application Example 2

[0105] The only difference from Application Example 1 is that the catalyst is replaced with Ag1CN prepared in Example 2.

[0106] Application Example 3

[0107] The only difference from Application Example 1 is that the catalyst is replaced with Fe1CN prepared in Example 2.

[0108] Comparative Application Example 1

[0109] The only difference from Application Example 1 is that the catalyst is replaced with CN prepared in Comparative Example 1.

[0110] Test Example 2

[0111] from Figure 9 It can be seen that pure CN has almost no effect on the activation of peroxydisulfate (PDS) to degrade BPA, but the addition of the catalysts prepared in Examples 1 to 3 can degrade BPA. In particular, Cu1CN can activate PDS to rapidly degrade BPA. It is worth noting that Cu1CN can degrade BPA by more than 90% in 5 minutes, the degradation rate reaches 98% in 20 minutes, and almost complete degradation in 40 minutes.

[0112] Figure 10 This is the experimental result of the fully exposed single atom catalyst prepared by the present invention for degrading BPA and capturing free radicals. Figure 10 It can be seen that when the quenching agents isopropanol, chloroform, ethanol, tert-butanol, benzoquinone and methanol are added to the catalyst prepared by the present invention, the degradation rate is not affected, which indicates that when the catalyst prepared by the present invention degrades organic pollutants, there are almost no free radicals in the system participating in the reaction.

[0113] Figure 11 The results of the singlet oxygen capture experiment of the catalyst prepared by the present invention when sodium carbonate, L-tryptophan, 4-hydroxy-2,2,6,6-tetramethylpiperidine, L-histidine and furfuryl alcohol are added to degrade BPA. Figure 11 It can be seen that different quenchers 1 O2 quenching has a good inhibitory effect, indicating that the main active species in the system is 1 O2.

[0114] It can be seen from the above experimental results that the fully exposed single-atom catalyst provided by the present invention has a high transition metal single atom loading, which can reach 5 to 28%; and the transition metal single atom sites are all exposed on the surface of the carrier, so that when the catalyst provided by the present invention is used to degrade organic polluted wastewater, it has a higher catalytic effect with a smaller addition amount, can significantly improve the degradation efficiency of the catalyst in catalyzing the degradation of organic pollutants, and has strong anti-interference ability and good stability.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that 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 should also be regarded as within the scope of protection of the present invention.

Claims

1. A fully exposed single-atom catalyst comprising a support and transition metal atoms supported on the support surface; the support is tubular graphite-phase carbon nitride; the transition metal atoms are all exposed on the support surface; the mass of the transition metal atoms is 21.44-28% of the mass of the fully exposed single-atom catalyst; the transition metal atoms comprise Fe atoms, Cu atoms, or Ag atoms; The method for preparing the fully exposed single-atom catalyst comprises the following steps: Melamine, cyanuric acid and deionized water are mixed and subjected to self-assembly reaction to obtain a supramolecular suspension; The supramolecular suspension, the soluble transition metal salt and the organic ligand are mixed and stirred at room temperature for 2 to 24 hours to obtain a precursor; pyrolyzing the precursor to obtain a fully exposed single-atom catalyst; The molar ratio of the organic ligand, the metal ion in the soluble transition metal salt, cyanuric acid and melamine is (0.1-0.5):(0.05-0.4):(0.5-1.0):1; The organic ligand is one of ethylenediaminetetraacetic acid, citric acid and oxalic acid.

2. The fully exposed single-atom catalyst according to claim 1, characterized in that The length of the tubular graphite phase carbon nitride is 1 to 30 μm; the diameter of the tubular graphite phase carbon nitride is 0.1 to 10 μm.

3. The method for preparing the fully exposed single-atom catalyst according to any one of claims 1 to 2, comprising the following steps: Melamine, cyanuric acid and deionized water are mixed and subjected to self-assembly reaction to obtain a supramolecular suspension; The supramolecular suspension, the soluble transition metal salt and the organic ligand are mixed and stirred at room temperature for 2 to 24 hours to obtain a precursor; pyrolyzing the precursor to obtain a fully exposed single-atom catalyst; The molar ratio of the organic ligand, the metal ions in the soluble transition metal salt, cyanuric acid and melamine is (0.1-0.5):(0.05-0.4):(0.5-1.0):

1.

4. The preparation method according to claim 3, characterized in that The temperature of the self-assembly reaction is room temperature, and the time of the self-assembly reaction is 5 to 60 minutes.

5. The preparation method according to claim 3, characterized in that The soluble transition metal salt includes ferrous chloride, ferrous sulfate, cupric chloride, cupric nitrate, cupric acetate or silver nitrate; The organic ligand is one of ethylenediaminetetraacetic acid, citric acid and oxalic acid.

6. The preparation method according to claim 3, characterized in that The pyrolysis temperature is 500-700° C., and the pyrolysis time is 1-4 h.

7. The preparation method according to claim 3, characterized in that The pyrolysis is carried out under a protective atmosphere.

8. Use of the fully exposed single-atom catalyst according to any one of claims 1 to 2 or the fully exposed single-atom catalyst prepared by the preparation method according to any one of claims 3 to 7 in the catalytic degradation of organic pollutants.

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