Triatomic Catalyst and Its Preparation Method and Application

Abstract

The present invention discloses a tri - atomic catalyst. In this tri - atomic catalyst, three isolated transition metal single atoms are confined into a unit as the active component through a complexing agent, with carbon nitride as the carrier, and the mass fraction of the active component accounts for 0.5 wt.% to 3 wt.% of the total mass of the catalyst. The present invention also discloses a preparation method of the above - mentioned tri - atomic catalyst. The present invention further discloses the application of the above - mentioned tri - atomic catalyst in the photo - Fenton reaction. The tri - atomic catalyst, its preparation method and application disclosed by the present invention provide a unique configuration (simultaneous close - range adsorption) for the adsorption of pollutants and oxidants. At the same time, by combining photocatalysis technology with advanced oxidation technology, it exhibits higher visible - light absorption ability and carrier separation efficiency, and is more likely to activate PMS or O2 to generate reactive oxygen species.

Description

Technical Field

[0001] The present invention belongs to the technical field of new material catalyst synthesis methods, specifically relates to triatomic catalysts, and also relates to the preparation method and application of the above triatomic catalysts. Background Art

[0002] Traditional wastewater treatment strategies rely on the Fenton method, which uses the Fe 2+ / H2O2 system to degrade pollutants discharged into water bodies. In this system, Fe 2+ acts as a catalyst, activates H2O2 molecules, and promotes the generation of highly oxidizing hydroxyl radicals (·OH), which then gradually oxidize and decompose organic pollutants in the water into harmless small-molecule substances and even ultimately convert them into carbon dioxide (CO2). However, H2O2 itself has the disadvantages of limited mineralization ability and easy explosiveness, which significantly increases the complexity and cost of its transportation and storage.

[0003] To overcome these limitations, the scientific research community has developed a series of advanced oxidation technologies as alternative solutions, among which the new persulfate advanced oxidation technology is particularly remarkable. This technology stands out with its excellent oxidation performance and generates sulfate radicals (·SO4 - ) by activating persulfate. The redox potential of these radicals is as high as 2.5 - 3.1V, significantly superior to that of hydroxyl radicals at 1.8 - 2.7V, showing stronger oxidation ability. In addition, sulfate radicals also have the remarkable advantages of fast reaction rate, strong environmental adaptability, mild operating conditions, and high mineralization efficiency for organic pollutants, opening up a new way for the effective treatment of water pollutants.

[0004] In addition, photocatalysis is a new technology that can effectively utilize solar energy. Photocatalysis technology has the characteristics of being clean, pollution-free, and renewable. However, traditional photocatalysts have weak absorption ability for visible light and low carrier separation efficiency under visible light, which greatly limits the application of photocatalysis technology. Combining photocatalysis technology with Fenton oxidation technology, using the free electrons in the conduction band of semiconductor photocatalytic reactions, persulfate can be activated into ·SO4 - , and cooperate to generate ·OH, ·O2 - etc. to improve the ability to remove pollutants, which is a more promising new technology.

[0005] A single-atom catalyst refers to a catalyst in which when the size of the surface metal particles is reduced to the single-atom scale, it can coordinate with the atoms on the surface of the support to form a uniform local active site, constituting the single-atom catalyst. The improvement in the activity of the single-atom catalyst is because the reduction in the size of the surface metal particles can bring more unsaturated coordination environments and expose more active sites, thereby promoting the improvement of catalytic performance. However, single atoms also have limitations. A single single-atom site cannot simultaneously satisfy the adsorption of PMS and pollutants and the subsequent free radical generation process, resulting in a slow rate of catalytic degradation of pollutants. Summary of the Invention

[0006] The object of the present invention is to provide a three-atom catalyst, which solves the problem that the existing single-atom catalyst cannot simultaneously satisfy the adsorption of PMS and pollutants and the subsequent free radical generation process, resulting in a slow rate of catalytic degradation of pollutants.

[0007] The second object of the present invention is to provide a preparation method of the above three-atom catalyst.

[0008] The third object of the present invention is to provide the application of the above three-atom catalyst in the photo-Fenton reaction.

[0009] The first technical solution adopted by the present invention is: a three-atom catalyst, which uses a complexing agent to form three isolated transition metal single-atom constituent units as the active component, uses carbon nitride as the support, and the mass fraction of the active component accounts for 0.5 wt.% to 3 wt.% of the total mass of the catalyst.

[0010] The characteristics of the first technical solution adopted by the present invention also lie in:

[0011] Furthermore, the transition metal single atom is one or more of transition metals Fe, Co, Cu, Ni, and Mn.

[0012] The second technical solution adopted by the present invention is: a preparation method of a three-atom catalyst, which is prepared according to the following steps:

[0013] Step 1: Prepare a carbon nitride support by pyrolysis;

[0014] Step 2: Prepare a ternary metal single-atom catalyst precursor by complexation;

[0015] Step 3: Pyrolyze to obtain the three-atom catalyst.

[0016] The characteristics of the second technical solution adopted by the present invention also lie in:

[0017] Further, Step 1 is specifically as follows: Weigh 15 g to 30 g of melamine, transfer it to a crucible, and in an air atmosphere, heat it in a muffle furnace at a heating rate of 5 °C / min to 500 °C to 550 °C, and keep it warm for 3 h to 4 h to obtain a carbon nitride support.

[0018] Further, Step 2 is specifically as follows: Weigh 2.5 mg to 140 mg of one or more metal salts, add them to 7.5 mL - 10 mL of Solvent 1, and ultrasonically dissolve them completely to obtain Solution A; at the same time, add 50 μL to 300 μL of a ternary complexing agent to 1 mL to 3 mL of Solvent 2, and ultrasonically mix them evenly to obtain Solution B; mix Solution A and B evenly, transfer them to an oil bath at 70 °C to 90 °C, add 0.1 g to 0.5 g of the carbon nitride support, and stir the mixture at a rotation speed of 500 rpm for 30 min to 60 min; centrifuge to obtain a solid product, wash it with ethanol 2 to 3 times, and transfer it to a 60 °C oven to dry for 12 h.

[0019] Further, in Step 2, the metal salt precursor is any one or more of the chlorides, nitrates, or sulfates of transition metals Fe, Co, Cu, Ni, and Mn; Solvent 1 is any one or more of acetone, butanone, ethanol, ethylene glycol, isopropanol, and ethyl acetate; Solvent 2 is any one or more of acetonitrile, methanol, ethanol, isopropanol, and diisopropyl ether; the ternary complexing agent is triethanolamine or triethylamine.

[0020] Further, in Step 2, the drying method is any one of conventional drying, vacuum drying, and freeze drying.

[0021] Further, Step 3 is specifically as follows: Grind the dried ternary metal single-atom cluster catalyst precursor in a mortar for 10 min, transfer it to a tubular furnace, and heat it to 550 °C at a heating rate of 5 °C / min under a certain atmosphere and calcine it for 2 h to obtain it; the calcination atmosphere is any one or a mixture of two gases among air, nitrogen, and hydrogen.

[0022] The third technical solution adopted in the present invention is: the application of a tri-atom catalyst in the photo-Fenton reaction.

[0023] The characteristics of the third technical solution adopted in the present invention also lie in:

[0024] Further, use 50 mL of an organic pollutant solution with a concentration of 5 mg / L to 25 mg / L as the raw material liquid, the solvent is water, the catalyst dosage is 5 mg to 20 mg, the mass ratio of the oxidant to the catalyst dosage is 0.5 to 2:1, react at room temperature in the visible light range of a xenon lamp source, and the stirring rate is 300 rpm to 800 rpm; the organic pollutant is any one of dyes, antibiotics, and phenolic compounds, and the oxidant is any one of hydrogen peroxide, peroxymonosulfate PMS, and peroxydisulfate PDS.

[0025] The beneficial effects of the present invention are as follows:

[0026] The three-atom catalyst of the present invention confines three atoms, which can further make the best use of advantages and avoid disadvantages. Different transition metal single atoms between its active sites will produce a synergistic effect, activate PMS faster, and promote the generation of active free radicals. Compared with the single-atom catalyst, the catalytic performance of the catalyst will be further improved.

[0027] The three-atom catalyst of the present invention provides a unique configuration for the adsorption of pollutants and oxidants. At the same time, by combining photocatalysis technology with advanced oxidation technology, it shows higher visible light absorption ability and carrier separation efficiency.

[0028] The three-atom catalyst of the present invention provides a unique catalyst configuration that confines ternary metal single atoms. It not only shows a unique adsorption configuration (simultaneous close-range adsorption) for the adsorption of organic pollutants and oxidants in the photo-Fenton reaction, but also has a more negative conduction band energy level, making it easier to activate PMS or O2 to generate reactive oxygen species. At the same time, the three-atom structure of the catalyst promotes the visible light response of carbon nitride, provides multiple channels for carrier transport, and has more excellent photo-generated carrier separation and transport performance than single atoms. In addition, the preparation method of the present invention is unique, and ternary complexing agents are used to successfully anchor and confine transition metal triatoms on the surface of carbon nitride materials. Description of the Drawings

[0029] Figure 1 It is a graph showing the degradation efficiency of single atoms, single-metal triatoms, and double-metal triatoms catalysts of Example 1 of the present invention under visible light for 90 minutes;

[0030] Figure 2 It is a graph showing the degradation efficiency of triatom catalysts with different active components of Example 2 of the present invention under visible light for 90 minutes;

[0031] Figure 3 It is a graph showing the degradation efficiency under different activation conditions of Example 3 of the present invention;

[0032] Figure 4 It is a graph showing the degradation efficiency of triatom catalysts with different loadings of Example 4 of the present invention under visible light for 90 minutes;

[0033] Figure 5 It is a graph showing the 90-minute degradation efficiency with different amounts of oxidant added in Example 5 of the present invention;

[0034] Figure 6 It is a graph showing the 90-minute degradation efficiency with different amounts of catalyst added in Example 6 of the present invention;

[0035] Figure 7 It is a graph showing the degradation efficiency of the triatom catalyst of Example 7 of the present invention under different pollutants.

[0036] Figure 8 This is the degradation efficiency diagram of the three-atom catalysts with different carriers prepared by changing the carrier preparation conditions in Example 8 of the present invention.

[0037] Figure 9 This is the degradation efficiency diagram of the three-atom catalysts with different precursors prepared by changing the preparation conditions of the three-atom catalyst precursors in Example 9 of the present invention. Detailed implementation manners

[0038] The present invention will be further described below with reference to the accompanying drawings and specific implementation manners.

[0039] The present invention provides a three-atom catalyst. Three isolated transition metal single-atom building units are used as active components through a complexing agent, and carbon nitride is used as the carrier. The mass fraction of the active components accounts for 0.5 wt.% to 3 wt.% of the total mass of the catalyst; the single-atom active components are one or more of transition metals Fe, Co, Cu, Ni, and Mn, and the carrier is carbon nitride. The carbon nitride carrier is prepared by a pyrolysis method, and the organic matter is thermally decomposed to form a carrier precursor; a ternary metal single-atom cluster precursor is prepared by a complexing method, and metal ions are connected to the carrier by a ternary complexing agent to form a ternary metal single-atom cluster catalyst precursor; finally, the three-atom catalyst is prepared by a pyrolysis method, and the ternary metal single-atom cluster catalyst precursor is ground and calcined to prepare the three-atom catalyst.

[0040] The three-atom catalyst of the present invention confines three atoms within a certain range. Further leveraging strengths and avoiding weaknesses, the different transition metal single atoms between the active sites will produce a synergistic effect, activating PMS faster and promoting the generation of active free radicals. Compared with single-atom catalysts, the catalytic performance of the catalyst will be further improved.

[0041] The present invention also provides a preparation method of a three-atom catalyst, which is specifically prepared according to the following steps:

[0042] Step 1: Prepare the carbon nitride carrier by a pyrolysis method. Weigh 15 g to 30 g of melamine, transfer it to a crucible, and in an air atmosphere, heat it in a muffle furnace at a heating rate of 5 °C / min to 500 °C to 550 °C, and keep it warm for 3 h to 4 h to obtain the carbon nitride carrier;

[0043] Step 2: Prepare the ternary metal single-atom cluster catalyst precursor by the complexation method. Weigh 2.5 mg - 140 mg of one or two metal salts, add them to 7.5 mL - 10 mL of Solvent 1, and ultrasonically dissolve them to obtain Solution A. At the same time, add 50 μL - 300 μL of the ternary complexing agent to 1 mL - 3 mL of Solvent 2, and ultrasonically mix them evenly to obtain Solution B. Mix Solutions A and B evenly, transfer them to an oil bath at 70 °C - 90 °C, add 0.1 g - 0.5 g of the carbon nitride support, and stir the mixture at a speed of 500 rpm for 30 min - 60 min. Centrifuge to obtain the solid product, wash it with ethanol 2 - 3 times, and transfer it to an oven at 60 °C to dry for 12 h.

[0044] In Step 2, the metal salt precursor is any one of chloride salts, nitrate salts, and sulfate salts. Solvent 1 is any one or several of acetone, butanone, ethanol, ethylene glycol, isopropanol, and ethyl acetate. Solvent 2 is any one or several of acetonitrile, methanol, ethanol, isopropanol, and diisopropyl ether. The ternary complexing agent is any one of triethanolamine and triethylamine.

[0045] Step 3: Pyrolyze to obtain the triatomic catalyst. Grind the dried ternary metal single-atom cluster catalyst precursor in a mortar for 10 min, transfer it to a tube furnace, and heat it to 500 °C - 600 °C at a heating rate of 5 °C / min under a certain atmosphere, and calcine it for 1 h - 3 h to obtain it.

[0046] In Step 3, the drying method is any one of conventional drying, vacuum drying, and freeze drying. The calcination atmosphere is any one or a mixture of two gases among air, nitrogen, and hydrogen.

[0047] For the method of photocatalytic Fenton degradation of organic pollutants using the triatomic catalyst prepared in the present invention, 50 mL of an organic pollutant solution with a concentration of 5 mg / L - 25 mg / L is used as the raw material liquid, and the solvent is water. The catalyst dosage is 5 mg - 20 mg. The mass ratio of the oxidant to the catalyst dosage is 0.5 - 2:1. The reaction is carried out at room temperature in the visible light range of a xenon lamp source, and the stirring rate is 300 rpm - 800 rpm.

[0048] The organic pollutant is any one of dyes, antibiotics, and phenolic compounds.

[0049] The oxidant is any one of hydrogen peroxide, peroxymonosulfate (PMS), and persulfate (PDS).

[0050] The preparation and performance of the catalyst of the present invention will be further described below through specific examples.

[0051] Example 1

[0052] In this example, triatomic catalysts with different proportions of metal atoms are prepared:

[0053] First, weigh 15 g of melamine and transfer it to a crucible. Under an air atmosphere, heat it in a muffle furnace at a heating rate of 5 °C / min to 500 °C and hold for 3 h to obtain a carbon nitride support.

[0054] Then, weigh 3.5 mg of cobalt nitrate hexahydrate, 2.6 mg of iron nitrate nonahydrate, 1.8 mg of cobalt nitrate hexahydrate and 5.3 mg of iron nitrate nonahydrate, 7.8 mg of iron nitrate nonahydrate, 5.2 mg of cobalt nitrate hexahydrate, 2.6 mg of iron nitrate nonahydrate, and 1.7 mg of cobalt nitrate hexahydrate. Add them to 7.5 mL of acetone solution and ultrasonically dissolve them completely to obtain solution A. At the same time, add 200 μL of triethanolamine to 1 mL of acetonitrile solution and ultrasonically mix them evenly to obtain solution B. Mix solutions A and B evenly, transfer them to an oil bath at 70 °C, add 0.1 g of the carbon nitride support, and stir the mixture at a speed of 500 rpm for 40 min. Centrifuge to obtain a solid product, wash it 3 times with ethanol, and transfer it to an oven at 60 °C to dry for 12 h.

[0055] Finally, grind the dried ternary metal single-atom cluster catalyst precursor and the single-atom catalyst precursor in a mortar for 10 min, transfer them to a tube furnace, and heat them to 550 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and calcine for 2 h to obtain a tri-atom catalyst and a single-atom catalyst with a theoretical active component accounting for 1% of the catalyst, denoted as Fe1Co2-CN-1%, Fe2Co1-CN-1%, Fe3-CN-1%, Co3-CN-1%, Fe1-CN-1%, Co1-CN-1%. After ICP testing, the actual loadings of iron single atoms and cobalt single atoms in the Fe1Co2-CN-1% and Fe2Co1-CN-1% tri-atom catalysts are 0.29% and 0.59%, 0.63% and 0.25% respectively. The actual loading of iron atoms in the Fe3-CN-1% tri-atom catalyst is 0.98%. The actual loading of cobalt single atoms in the Co3-CN-1% tri-atom catalyst is 0.96%. The actual loading of iron atoms in the Fe1-CN-1% single-atom catalyst is 0.96%. The actual loading of iron atoms in the Co1-CN-1% single-atom catalyst is 0.93%.

[0056] Take 10 mg each of the above tri-atom catalysts and single-atom catalysts and add them to 50 mL of a phenol solution with a concentration of 15 mg / L respectively. Stir in the dark at a speed of 500 rpm for 30 min. At this time, the absorbance of the phenol solution is detected by ultraviolet-visible spectroscopy and denoted as C0, and the time is denoted as t0. Add 10 mg of potassium monopersulfate and continuously stir under a xenon lamp visible light (400 - 760 nm). Take samples for analysis and detection every 15 min, record the solution absorbance as C and the time as t to obtain a degradation efficiency graph.

[0057] AsFigure 1 As shown, after 90 min, the Fe1Co2-CN-1% catalyst has the best catalytic degradation performance for phenol, with a degradation rate of 100%. Compared with the carrier carbon nitride CN, the use of transition metal single-atom active components has significantly improved the oxidative degradation activity. Therefore, the transition metal single atom is the active center. At the same time, the catalytic performance of the tri-atom catalyst is significantly higher than that of the single-atom catalyst, and the catalytic performance of the tri-atom catalyst with two metal atoms is better than that of the tri-atom catalyst with one metal atom. This may be due to the synergistic effect generated between the three confined atoms, resulting in changes in the geometric and electronic structures. The tri-atom catalyst with two metals can adsorb and activate PMS while adsorbing phenol, further enhancing the catalytic performance of the catalyst.

[0058] Example 2

[0059] In this example, tri-atom catalysts with different active components were prepared:

[0060] First, 15 g of melamine was weighed and transferred to a crucible. Under an air atmosphere, it was heated in a muffle furnace at a heating rate of 5 °C / min to 500 °C and held for 3 h to obtain a carbon nitride support.

[0061] Then, 3.5 mg of cobalt nitrate hexahydrate and 2.6 mg of iron nitrate nonahydrate were weighed and added to 7.5 mL of acetone solution. It was ultrasonicated to dissolve completely to obtain solution A; at the same time, 200 μL of triethanolamine was added to 1 mL of acetonitrile solution and ultrasonicated to mix evenly to obtain solution B; solution A and B were mixed evenly, transferred to an oil bath at 70 °C, 0.1 g of carbon nitride support was added, and the mixture was stirred at a speed of 500 rpm for 40 min; the solid product was obtained by centrifugation, washed 3 times with ethanol, and transferred to an oven at 60 °C to dry for 12 h.

[0062] Finally, the dried ternary metal single-atom cluster catalyst precursor was ground in a mortar for 10 min, transferred to a tube furnace, and heated to 550 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and calcined for 2 h to obtain a tri-atom catalyst with a theoretical active component accounting for 1% of the catalyst. The actual loadings of iron single atoms and cobalt single atoms were measured by ICP to be 0.29% and 0.59% respectively, denoted as Fe1Co2-CN-1%.

[0063] In this example, different active transition metal precursors were also used to replace iron nitrate nonahydrate and cobalt nitrate hexahydrate to prepare tri-atom catalysts. Finally, tri-atom catalysts with a theoretical metal accounting for 1% of the total mass of the catalyst were obtained. The actual loadings of the tri-atoms were 0.29% and 0.59% respectively. The different catalysts were: Fe1Cu2-CN-1%, Fe1Ni2-CN-1%, Fe1Mn2-CN-1%.

[0064] Take 10 mg of each of the above three-atom catalysts and add them separately to 50 mL of a phenol solution with a concentration of 15 mg / L. Stir in the dark at a rotation speed of 500 rpm for 30 min. At this time, the absorbance of the phenol solution is detected using ultraviolet-visible spectroscopy and denoted as C0, and the time is denoted as t0. Add 10 mg of potassium monopersulfate, and continuously stir under visible light (400 - 760 nm) of a xenon lamp light source. Sample and analyze every 15 min, denote the absorbance of the solution as C and the time as t, and obtain the catalytic degradation efficiency graph.

[0065] As Figure 2 shown, after 90 min, when using different catalysts to degrade the phenol solution separately, the iron-cobalt three-atom catalyst has the best degradation performance, with a degradation rate of 100%, which is significantly better than the other two metal combinations. This may be because the three-atom catalyst formed by the combination of iron atoms and cobalt atoms is more conducive to adsorbing phenol and activating PMS, resulting in a more excellent synergistic effect.

[0066] Example 3

[0067] Take 10 mg of Fe1Co2-CN-1% prepared in Example 1 above and add it to 50 mL of a phenol solution with a concentration of 15 mg / L. Stir in the dark at a rotation speed of 500 rpm for 30 min. At this time, the absorbance of the phenol solution is detected using ultraviolet-visible spectroscopy and denoted as C0, and the time is denoted as t0. Conduct three groups of phenol degradation experiments of only adding 10 mg of potassium monopersulfate, only adding light, and the synergistic effect of potassium monopersulfate and light. Continuously stir, sample and analyze every 15 min, denote the absorbance of the solution as C and the time as t, and obtain the catalytic degradation graph.

[0068] As Figure 3 shown, after 90 min, when potassium monopersulfate and light are added simultaneously, the degradation effect of Fe1Co2-CN-1% on phenol is significant, and the degradation efficiency reaches 100%. At the same time, the catalytic performance of Fe1Co2-CN-1% is about 95% higher than that of only adding visible light and only adding PMS. This further illustrates that visible light and PMS have a synergistic effect in this catalytic system.

[0069] Example 4

[0070] In this example, three-atom catalysts with different loadings are prepared:

[0071] First, weigh 15 g of melamine, transfer it to a crucible, and in an air atmosphere, heat it in a muffle furnace at a heating rate of 5 °C / min to 500 °C and hold for 3 h to obtain a carbon nitride support.

[0072] Then, weigh 1.7 mg of cobalt nitrate hexahydrate, 1.3 mg of iron nitrate nonahydrate, 7.0 mg of cobalt nitrate hexahydrate and 5.2 mg of iron nitrate nonahydrate, and add them to 7.5 mL of acetone solution. Ultrasonically dissolve them completely to obtain solution A. At the same time, add 200 μL of triethanolamine to 1 mL of acetonitrile solution and ultrasonically mix them evenly to obtain solution B. Mix solution A and B evenly, transfer them to an oil bath at 70 °C, add 0.1 g of carbon nitride support, and stir the mixture at a speed of 500 rpm for 40 min. Centrifuge to obtain a solid product, wash it 3 times with ethanol, and transfer it to an oven at 60 °C to dry for 12 h.

[0073] Finally, grind the dried ternary metal single-atom cluster catalyst precursor in a mortar for 10 min, transfer it to a tube furnace, and heat it to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and calcine it for 2 h to obtain triatomic catalysts with theoretical active component contents of 0.5%, 2%, and 3% in the catalyst. The actual loadings of iron single atoms and cobalt single atoms measured by ICP are 0.14%, 0.52%, 0.91% and 0.32%, 1.31%, 1.92% respectively, denoted as Fe1Co2-CN-0.5%, Fe1Co2-CN-2%, Fe1Co2-CN-3%.

[0074] Take 10 mg of each of the above triatomic catalysts and add them to 50 mL of phenol solution with a concentration of 15 mg / L respectively. Stir them in the dark at a speed of 500 rpm for 30 min. At this time, the absorbance of the phenol solution is detected by ultraviolet-visible spectroscopy and denoted as C0, and the time is denoted as t0. Add 10 mg of potassium monopersulfate, and continuously stir under a xenon lamp visible light (400 - 760 nm). Take samples for analysis and detection every 15 min, and denote the solution absorbance as C and the time as t. After 90 min, as Figure 4 shown, the Fe1Co2-CN-1% catalyst has the best catalytic degradation performance for phenol, and the degradation rate is 100%.

[0075] Example 5

[0076] Take 10 mg of the Fe1Co2-CN-1% catalyst prepared in Example 1 in three groups and add them to 50 mL of phenol solution with a concentration of 15 mg / L respectively. Stir them in the dark at a speed of 500 rpm for 30 min. At this time, the absorbance of the phenol solution is detected by ultraviolet-visible spectroscopy and denoted as C0, and the time is denoted as t0. Add 5 mg, 10 mg, 15 mg, and 20 mg of potassium monopersulfate respectively, and continuously stir under a xenon lamp visible light (400 - 760 nm). Take samples for analysis and detection every 15 min, and denote the solution absorbance as C and the time as t. After 90 min, as Figure 5As shown, the degradation rates of phenol for the samples added with 5 mg, 10 mg, 15 mg, and 20 mg of potassium monopersulfate are 89.74%, 100%, 100%, and 100% respectively. Considering the economic benefits comprehensively, when the addition amount of potassium monopersulfate is 10 mg, it is the optimal addition amount.

[0077] Example 6

[0078] Take 5 mg, 10 mg, 15 mg, and 20 mg of the Fe1Co2-CN-1% catalyst prepared in Example 1 respectively, add them to 50 mL of phenol solution with a concentration of 15 mg / L, stir in the dark at a rotation speed of 500 rpm for 30 min. At this time, the absorbance of the phenol solution is detected by ultraviolet-visible spectroscopy and recorded as C0, and the time is recorded as t0. Add 10 mg of potassium monopersulfate respectively, and continuously stir under the visible light (400 - 760 nm) of the xenon lamp light source. Sampling and analysis are carried out every 15 min, and the solution absorbance is recorded as C, and the time is t. After 90 min, as Figure 6 shown, when the addition amount is 10 mg, phenol is preferentially completely degraded within 90 min. Considering comprehensively, the optimal addition amount of the catalyst is 10 mg.

[0079] Example 7

[0080] Take three groups of 10 mg of the Fe1Co2-CN-1% catalyst prepared in Example 1, and add them to 50 mL of tetracycline solution, rhodamine B solution, and bisphenol A solution with a concentration of 15 mg / L respectively. Stir in the dark at a rotation speed of 500 rpm for 30 min. At this time, the absorbance of each solution is detected by ultraviolet-visible spectroscopy and recorded as C0, and the time is recorded as t0. Add 10 mg of potassium monopersulfate respectively, and continuously stir under the visible light (400 - 760 nm) of the xenon lamp light source. Sampling and analysis are carried out every 15 min, and the solution absorbance is recorded as C, and the time is t. After 90 min, as Figure 7 shown, the catalytic degradation efficiency of the Fe1Co2-CN-1% catalyst for various pollutants can reach 100% within 90 min. Considering comprehensively, the Fe1Co2-CN-1% catalyst has universality in degrading pollutants.

[0081] Example 8

[0082] In this example, the preparation conditions of the carrier are changed to prepare triatomic catalysts with different carriers:

[0083] First, weigh 20 g of melamine and 30 g of melamine respectively, transfer them to a crucible, and in an air atmosphere, heat them to 520 °C and 550 °C at a heating rate of 5 °C / min in a muffle furnace, and keep them warm for 3.5 h and 4 h respectively to obtain carbon nitride carriers CN1 and CN2.

[0084] Then, weigh 3.5 mg of cobalt nitrate hexahydrate and 2.6 mg of iron nitrate nonahydrate, add them to 7.5 mL of acetone solution, and ultrasonically dissolve them to obtain solution A. At the same time, add 200 μL of triethanolamine to 1 mL of acetonitrile solution, and ultrasonically mix them evenly to obtain solution B. Mix solution A and B evenly, transfer them to an oil bath at 70 °C, add 0.1 g of CN1 and 0.1 g of CN2 carbon nitride carriers respectively, and stir the mixture at a speed of 500 rpm for 30 min. Centrifuge to obtain a solid product, wash it with ethanol 3 times, and transfer it to an oven at 60 °C to dry for 12 h.

[0085] Finally, grind the dried ternary metal single-atom cluster catalyst precursor in a mortar for 10 min, transfer it to a tube furnace, and heat it to 550 °C at a heating rate of 5 °C / min under a nitrogen atmosphere, and calcine it for 2 h to obtain a tri-atom catalyst with a theoretical active component accounting for 1% of the catalyst. The actual loadings of iron single atoms and cobalt single atoms measured by ICP are 0.26%, 0.25% and 0.54%, 0.55% respectively, denoted as Fe1Co2-CN1-1% and Fe1Co2-CN2-1%.

[0086] Take 5 mg each of the above tri-atom catalyst and Fe1Co2-CN-1% prepared in Example 1 and add them to 50 mL of a phenol solution with a concentration of 5 mg / L respectively. Stir them in the dark at a speed of 300 rpm for 30 min. At this time, the absorbance of the phenol solution is detected by ultraviolet-visible spectroscopy and denoted as C0, and the time is denoted as t0. Add 10 mg of potassium monopersulfate, and continuously stir under a xenon lamp visible light (400 - 760 nm). Take samples for analysis and detection every 15 min, and denote the absorbance of the solution as C and the time as t. As Figure 8 shown, the degradation efficiency of the prepared tri-atom catalysts all reaches 100% within 90 min, showing excellent catalytic degradation performance. And during the process of degrading the phenol solution with the prepared different tri-atom catalysts, there is no obvious difference in the degradation trend. This indicates that during the preparation of the tri-atom catalysts, when adding carriers with different preparation temperature conditions, the tri-atom catalysts still have excellent and similar catalytic degradation performance, further proving that different carriers do not have an obvious impact on the formation of stable and reliable active centers of transition metal atoms in the tri-atom catalysts.

[0087] Example 9

[0088] In this example, the preparation conditions of the tri-atom catalyst precursor are changed to prepare tri-atom catalysts with different precursors:

[0089] First, weigh 15 g of melamine, transfer it to a crucible, and heat it to 500 °C at a heating rate of 5 °C / min in a muffle furnace under an air atmosphere, and keep it warm for 3 h to obtain a carbon nitride carrier.

[0090] Then, weigh out two portions of 3.5 mg of cobalt nitrate hexahydrate and 2.6 mg of iron nitrate nonahydrate, and add them to 9 mL and 10 mL of acetone solution respectively. Ultrasonically dissolve them until completely dissolved to obtain solutions A1 and A2. At the same time, add 150 μL and 300 μL of triethanolamine to 2 mL and 3 mL of acetonitrile solution respectively, and ultrasonically mix them evenly to obtain solutions B1 and B2. Mix solutions A1 and B1, and A2 and B2 evenly, and transfer them to an oil bath at 80 °C and 90 °C respectively. Add 0.1 g of carbon nitride support, and stir the mixture at a speed of 500 rpm for 50 min and 60 min respectively. Centrifuge to obtain solid products, wash them three times with ethanol, and transfer them to an oven at 60 °C to dry for 12 h.

[0091] Finally, grind the dried ternary metal single-atom cluster catalyst precursor in a mortar for 10 min, transfer it to a tube furnace, and heat it to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere, and calcine it for 2 h to obtain a tri-atom catalyst with a theoretical active component accounting for 1% of the catalyst. The actual loading amounts of iron single atoms and cobalt single atoms measured by ICP are 0.27%, 0.29% and 0.57%, 0.54% respectively, denoted as Fe1Co2-CN-1%-1 and Fe1Co2-CN-1%-2.

[0092] Take 20 mg of each of the above tri-atom catalysts and add them to 50 mL of phenol solution with a concentration of 25 mg / L respectively. Stir in the dark at a speed of 800 rpm for 30 min. At this time, the absorbance of the phenol solution is detected by ultraviolet-visible spectroscopy, denoted as C0, and the time is denoted as t0. Add 10 mg of potassium monopersulfate, and continuously stir under visible light (400 - 760 nm) of a xenon lamp source. Take samples for analysis and detection every 15 min, and record the absorbance of the solution as C and the time as t. As Figure 9 shown, for the tri-atom catalysts prepared under the preparation conditions of different tri-atom catalyst precursors, the catalytic degradation efficiency of the catalyst reaches 100%, indicating that the tri-atom catalyst precursors prepared under different masses of solvents do not affect the final catalytic degradation performance of the tri-atom catalyst.

[0093] Combined with Example 8 and Example 9, the tri-atom catalysts prepared under different preparation conditions show excellent catalytic degradation performance for phenol solutions with different concentrations, and also show good preparation stability of the tri-atom catalyst under different preparation conditions.

[0094] A triatomic catalyst of the present invention is a catalyst in which one or several transition metal single atoms are formed into active sites in groups of three and confined on the surface of a carbon nitride support through a unique preparation method. All the metals of the catalyst of the present invention are dispersed on the surface of the support, with strong synergy and high intrinsic activity. When it is applied to the degradation of organic pollutants by the photo-Fenton reaction, excellent catalytic activity is obtained, and excellent universality is shown, which can reduce environmental pollution and production application costs.

Claims

1. A method for preparing a three-atom catalyst, characterized in that: The three-atom catalyst uses a complexing agent to make three isolated transition metal single-atom constituent units as active components, and uses carbon nitride as a carrier, and the mass fraction of the active components accounts for 0.5wt.%~3wt.% of the total mass of the catalyst; The transition metal single atom is one or more of transition metals Fe, Co, Cu, Ni, and Mn; Specifically prepared according to the following steps: Step 1: preparing a carbon nitride support by pyrolysis; Step 2: preparing a ternary metal single atom catalyst precursor by complexation; The step 2 is specifically as follows: weigh 2.5 mg to 140 mg of one or more metal salts, add them to 7.5 mL to 10 mL of solvent 1, and dissolve them completely by ultrasonication to obtain solution A; at the same time, add 50 μL to 300 μL of a ternary complexing agent to 1 mL to 3 mL of solvent 2, and mix them uniformly by ultrasonication to obtain solution B; mix solutions A and B uniformly, transfer to an oil bath at 70° C. to 90° C., add 0.1 g to 0.5 g of a carbon nitride carrier, and stir the mixture at a speed of 500 rpm for 30 min to 60 min; centrifuge to obtain a solid product, wash it with ethanol 2 to 3 times, and transfer it to a 60 o C oven drying for 12h; The drying method in step 2 is any one of vacuum drying and freeze drying; The ternary complexing agent is triethanolamine or triethylamine; Step 3: Pyrolysis to obtain the three-atom catalyst.

2. The method for preparing a three-atom catalyst according to claim 1, characterized in that: The step 1 is specifically as follows: 15 g to 30 g of melamine is weighed and transferred to a crucible, and in an air atmosphere, the temperature is increased to 500° C. to 550° C. at a heating rate of 5° C. / min in a muffle furnace, and the temperature is kept for 3 h to 4 h to obtain a carbon nitride carrier.

3. The method for preparing a three-atom catalyst according to claim 1, characterized in that: In step 2, the metal salt precursor is any one or more of chlorides, nitrates or sulfates of transition metals Fe, Co, Cu, Ni and Mn; solvent 1 is any one or more of acetone, butanone, ethanol, ethylene glycol, isopropanol and ethyl acetate; solvent 2 is any one or more of acetonitrile, methanol, ethanol, isopropanol and diisopropyl ether.

4. The method for preparing a three-atom catalyst according to claim 1, characterized in that: The specific steps of step 3 are as follows: the dried ternary metal single atom cluster catalyst precursor is ground in a mortar for 10 minutes, transferred to a tubular furnace, heated to 550°C at a heating rate of 5°C / min under a certain atmosphere, and calcined for 2 hours to obtain the catalyst; the calcination atmosphere is any one of air, nitrogen, and hydrogen, or a mixture of two gases.

5. Use of the three-atom catalyst prepared by the preparation method according to any one of claims 1 to 4 in a photo-Fenton reaction; 50 mL of an organic pollutant solution with a concentration of 5 mg / L to 25 mg / L is used as a raw material liquid, the solvent is water, the amount of the catalyst is 5 mg to 20 mg, the mass ratio of the oxidant to the catalyst is 0.5 to 2:1, the reaction is carried out in the visible light range of a xenon lamp light source at room temperature, and the stirring rate is 300 rpm to 800 rpm; the organic pollutant is any one of a dye, an antibiotic, and a phenolic compound, and the oxidant is any one of hydrogen peroxide, permonosulfate PMS, and peroxydisulfate PDS.

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