Monatomic and nanoparticle composite catalyst, preparation and use

Abstract

The present application relates to a kind of metal single atom and nanoparticle composite catalyst and its preparation method.By the reasonable proportioning of metal salt, dicyanediamine and urea dosage, high loading single atom and nanoparticle composite catalyst is prepared by simple two-step pyrolysis method, the preparation method is simple, metal loading can be controlled, with good reproducibility and applicable to a variety of metal salt (such as Co, Cu, Ni, Fe, Mn, etc.).Single atom and nanoparticle composite catalyst obtained by the present application can construct a large number of active sites, significantly improve the catalytic activity and stability of catalyst, for degrading sulfonamide organic pollutants, quinolone organic pollutants and tetracycline organic pollutants, or for depolymerization lignin, all of which show excellent catalytic activity, and the degradation or depolymerization effect is higher than that of currently reported catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, and more specifically relates to a composite catalyst of metal single atoms and nanoparticles and its preparation method. Background Technology

[0002] Catalysts play a crucial role in chemical reactions, significantly increasing reaction rates and lowering activation energies, thereby achieving more efficient energy utilization and material conversion. Metal-supported catalysts are the most practical and common, with metal particle size significantly influencing catalyst performance. As metal particle size decreases to the atomic level, the active atomic centers are uniformly dispersed on the support through chemical bonding, maximizing the utilization of metal atoms and ensuring stability under many harsh reaction conditions, while also enhancing the catalyst's selectivity and reactivity. However, single-atom catalysts also have limitations. Because they contain only one specific type of active site, when the reaction involves multiple steps with multiple intermediates, single-atom catalysts struggle to break the linear scale relationship between different intermediates. Furthermore, to maintain the single-atom configuration, the loading of metal sites on the single-atom catalyst must be limited to prevent spatial aggregation, which may result in high activity of individual atoms at the expense of the overall catalytic performance.

[0003] Recently, single-atom catalysts modified with nanoscale metal particles (such as nanoparticles or nanoclusters) have emerged as a potential solution to overcome the aforementioned limitations, particularly in reactions requiring multiple active sites of metal atoms. Compared to single-atom catalysts, single-atom and nanoparticle composite catalysts exhibit different electronic and geometric structures. Notably, when loaded onto a support, single-atom and nanoparticle composite catalysts typically exhibit irregular polyhedral shapes, with varying coordination environments at these sites leading to different adsorption strengths of reactants. Meanwhile, single-atom metal catalysts, due to their highly dispersed metal atoms, exhibit extremely high atom utilization and unique electronic structure and surface properties, demonstrating excellent catalytic activity; while nanoparticle catalysts, with their large specific surface area and abundant active sites, enable catalytic reactions to proceed efficiently at the nanoscale.

[0004] Current methods for preparing composite catalysts of metal single atoms and nanoparticles mainly include physical synthesis, chemical synthesis, and biosynthesis. These methods often suffer from problems such as complex operation, high cost, and poor catalyst stability. Among these methods, physical synthesis typically requires high temperature and high pressure conditions; chemical synthesis involves cumbersome synthesis steps and complex residue problems; and while biosynthesis is environmentally friendly, the preparation process is time-consuming and difficult to control. Furthermore, existing literature reports that composite catalysts of metal single atoms and nanoparticles prepared by existing methods are prone to aggregation and deactivation during the reaction process, reducing their long-term stability and catalytic performance.

[0005] For example, some methods require expensive equipment and high-purity raw materials, which increases preparation costs; other methods require high temperature or high pressure, which not only increases the difficulty of operation but may also affect the structure and performance of the catalyst. Furthermore, due to the special properties of metal single atoms and nanoparticles, they are prone to aggregation or loss during preparation, leading to a decrease in catalyst activity.

[0006] Therefore, developing a new method for preparing composite catalysts of highly stable and highly active metal single atoms and nanoparticles that is simple to operate, low in cost, and capable of producing such catalysts is of great significance for promoting the development of catalyst technology and improving the efficiency of catalytic reactions. Summary of the Invention

[0007] In view of the above-mentioned technical problems, this application provides a single-atom and nanoparticle composite catalyst to solve the problems of high preparation cost, unstable catalytic activity, poor catalytic performance, and low support loading in the prior art. The preparation method of the single-atom and nanoparticle composite catalyst provided in this application should have the advantages of simple operation steps, conventional equipment, low raw material cost, and no need for washing and separation, easily meeting the needs of large-scale industrial production. The single-atom and nanoparticle composite catalyst provided in this application should be applicable to the degradation of certain typical organic pollutants and the depolymerization of some high-molecular organic compounds, so as to promote its widespread application in energy conversion, resource utilization, and environmental governance.

[0008] To achieve the above objectives, in a first aspect, the inventors provide a method for preparing a composite catalyst of single atoms and nanoparticles, comprising the following steps:

[0009] Preparation of the metal complex: 0.1-2 mmol of metal salt, 1-8 mmol of dicyandiamine and 0.1-10 mmol of urea were dissolved in ultrapure water by weight, thoroughly mixed and then subjected to heat treatment to obtain the metal complex.

[0010] Preparation of single-atom and nanoparticle composite catalyst: The metal composite is thoroughly ground and then calcined and naturally cooled to obtain the single-atom and nanoparticle composite catalyst.

[0011] This invention employs two main preparation processes. First, a metal composite is prepared by low-temperature hydrothermal calcination of metal salts, dicyandiamine, and urea to adsorb a large number of metal atoms around the nitrogen atoms of a nitrogen-carbon support. Second, high-temperature pyrolysis, accompanied by an increase in calcination temperature and the introduction of reducing gases, allows the adsorbed metal species around the nitrogen atoms to generate in-situ single-atom and nano-metal sites, thus preparing a composite catalyst loaded with metal single atoms and nanoparticles. The preparation method provided by this invention does not involve the addition of any other external support; the metal single atoms, metal nanoparticles, and nitrogen-doped carbon support are generated from the above-mentioned raw materials through reaction.

[0012] In a preferred embodiment, the heat treatment temperature is 100–400°C, and the heat treatment time is 1–6 hours. In these embodiments, the metal salt, dicyandiamine, and urea are heat-treated according to the above-mentioned molar ratio. The heat treatment temperature of 100–400°C is chosen based on the consideration of sufficient adsorption of Co atoms and avoiding the evaporation loss of N elements at excessively high temperatures. Below 100°C, Co atoms cannot achieve sufficient adsorption, and above 400°C, N elements are easily evaporated, leading to loss. The heat treatment time of 1–6 hours is mainly to take into account the adsorption saturation process of Co atoms under lower temperature conditions.

[0013] In some preferred embodiments, the metal salt is at least one of cobalt, copper, nickel, iron, and manganese, existing as at least one salt of nitrate, sulfate, hydrochloride, and acetate. These metal elements are all transition metals located in the d-block of the periodic table, where metals are widely used in catalyst preparation, and the aforementioned metal salt forms are all common metal salt forms that can readily provide transition metal ions.

[0014] In other preferred embodiments, the calcination temperature is 300–800°C, and the calcination time is 2–6 hours. The calcination temperature affects the in-situ conversion efficiency of metal species and the formation of metal clusters. The calcination temperature of 300–800°C is chosen primarily because calcination temperatures below 300°C result in excessively low in-situ conversion efficiencies, failing to meet production requirements; while temperatures above 800°C improve the in-situ conversion efficiency but easily lead to further aggregation of metal nanosites into metal clusters, a result clearly undesirable to the applicant. Therefore, the preferred calcination temperature is determined to be 300–800°C.

[0015] In some other preferred embodiments, the calcination is carried out at a temperature of 1–10 °C·min. -1The temperature is increased at a rate of 300–800°C.

[0016] In some preferred embodiments, the calcination is carried out in an atmosphere of hydrogen, nitrogen, and / or an inert gas. More preferably, it is carried out in a reducing gas atmosphere of hydrogen to ensure the formation of metal nanoparticles.

[0017] In a second aspect, the inventors provide a single-atom and nanoparticle composite catalyst, which is prepared using the preparation method provided in the first aspect of the present invention.

[0018] In a third aspect, the inventors provide a method for using a single-atom and nanoparticle composite catalyst prepared by the preparation method provided in the first aspect of the invention to oxidatively degrade organic pollutants.

[0019] Preferably, the organic pollutants include sulfonamide organic pollutants, quinolone organic pollutants, and / or tetracycline organic pollutants.

[0020] In a fourth aspect, the inventors provide a method for using a single-atom and nanoparticle composite catalyst prepared by the preparation method provided in the first aspect of the invention for the catalytic depolymerization of lignin.

[0021] Unlike existing technologies, the above-mentioned technical solution prepares a high-load single-atom and nanoparticle composite catalyst by rationally proportioning the amounts of metal salt, dicyandiamine, and urea using a simple two-step pyrolysis method. This preparation method is simple, the metal loading is controllable, it has good reproducibility, and it is applicable to various metal salts (such as Co, Cu, Ni, Fe, Mn, etc.). Furthermore, the single-atom and nanoparticle composite catalyst obtained using the method of this invention can construct a large number of active sites, significantly improving the catalytic activity and stability of the catalyst.

[0022] The single-atom and nanoparticle composite catalyst provided by this invention exhibits excellent catalytic activity in degrading sulfonamide, quinolone, and tetracycline organic pollutants, as well as in catalyzing the depolymerization of lignin. Under similar reaction conditions, its catalytic activity is higher than that of currently reported catalysts. Due to its advantages such as simple preparation process, low raw material cost, no need for washing and separation, and recyclability, this catalyst holds broad industrial application prospects in energy conversion, resource utilization, and environmental remediation.

[0023] The above description of the invention is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the description and drawings, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and drawings of this application. Attached Figure Description

[0024] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of this application and other related content, and should not be considered as limitations on this application.

[0025] In the accompanying drawings of the instruction manual:

[0026] Figure 1 This is a SEM image of the metal composite prepared by the low-temperature hydrothermal method in Example 1 of the present invention;

[0027] Figure 2 Here is a SEM image of the single-atom and nanoparticle composite catalyst in Example 1 of this invention;

[0028] Figure 3 This is a TEM image of the single-atom and nanoparticle composite catalyst in Example 1 of the present invention;

[0029] Figure 4 This is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the single-atom and nanoparticle composite catalyst in Example 1 of the present invention.

[0030] Figure 5 This is a surface scan distribution map of the single-atom and nanoparticle composite catalyst prepared in Example 1 of the present invention, wherein... Figure 5 (a) is the corresponding EDS layered image. Figure 5 (b) is the corresponding C element distribution image. Figure 5 (c) is the corresponding N-element distribution image. Figure 5 (d) shows the distribution of the corresponding metallic elements;

[0031] Figure 6 The image shows the EXAFS (Extended X-ray Absorbed Fine Structure) spectrum of the single-atom and nanoparticle composite catalyst prepared in Example 1 of this invention.

[0032] Figure 7 The graph shows the correlation between different amounts of Co salt added and the Co loading in the composite catalyst in Example 1.

[0033] Figure 8 The inset shows the N2 adsorption-desorption isotherm of the nitrogen-doped carbon support of the present invention (the inset shows its pore size distribution characteristics).

[0034] Figure 9 The degradation curves of sulfonamide organic pollutants, quinolone organic pollutants, and tetracycline organic pollutants by the single-atom and nanoparticle composite catalyst prepared in Example 1 of the present invention are shown.

[0035] Figure 10 This is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Ni single-atom and nanoparticle composite catalyst in Example 2 of the present invention.

[0036] Figure 11 This is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Fe single-atom and nanoparticle composite catalyst in Example 3 of the present invention.

[0037] Figure 12 This is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Cu single-atom and nanoparticle composite catalyst in Example 4 of the present invention.

[0038] Figure 13 This is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark field scanning transmission electron microscope) image of the Mn single-atom and nanoparticle composite catalyst in Example 5 of the present invention. Detailed Implementation

[0039] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0040] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0041] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0042] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0043] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0044] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0045] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0046] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0047] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0048] In this invention, "single-atom and nanoparticle composite catalyst" refers to a composite catalyst formed by supporting metals on a support in the form of coexisting single atoms and nanoparticles.

[0049] The metal salts, dicyandiamine, urea, persulfate, and other materials and reagents used in the embodiments of this invention are all from commercial sources.

[0050] The crucibles, muffle furnaces, tube furnaces, SEM, TEM, EDS spectrometers, and other instruments and equipment used in the embodiments of this invention are all commonly used instruments and equipment in the field.

[0051] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0052] Example 1

[0053] This embodiment provides a single-atom and nanoparticle composite catalyst, its preparation, and its application.

[0054] 1) Dissolve 1 mmol of Co(NO3)2·6H2O, 2 mmol of dicyandiamine and 1 mmol of urea (total mass 0.519 g) in 50 ml of ultrapure water. After thorough stirring, place the mixture in a covered crucible and heat-treat it at 220 °C for 4 hours in an air atmosphere in a muffle furnace to obtain the metal complex.

[0055] Please see Figure 1 The image shown is a SEM image of the metal composite obtained by field emission scanning electron microscopy. The image shows that the metal composite exhibits a petal-like stacked structure.

[0056] 2) The metal composite obtained in step 1) is thoroughly ground, passed through a 100-mesh sieve, and placed in a covered quartz boat. It is then heated in a tube furnace at 5°C / min. -1 The heating rate was increased to 600℃ under a specific atmosphere (hydrogen) for 4 hours, and after natural cooling, the CoNPs-SAs@NC composite catalyst with metal single atoms and nanoparticles coexisting was collected.

[0057] Please refer to the following documents separately. Figure 2 and Figure 3 The SEM and TEM images of the CoNPs-SAs@NC composite catalyst obtained by field emission scanning electron microscopy and high-resolution transmission electron microscopy are shown. From the SEM images ( Figure 2 As can be seen, the composite material exhibits an irregular granular structure, which may provide a favorable catalyst structure for the subsequent adsorption of PMS (persulfate) and pollutants on the catalyst surface and the resulting high degradation efficiency; in addition, TEM images ( Figure 3 The composite catalyst exhibits a layered structure, and cobalt nanoparticles can be seen to be coated with graphite carbon, which verifies the existence of Co nanosites.

[0058] Please see Figure 4 The image shown is a HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) image of the CoNPs-SAs@NC composite catalyst obtained by aberration-corrected high-angle annular dark-field scanning transmission electron microscope. The image shows the coexistence of cobalt single atoms (bright spots) and cobalt nanoparticles (stripes).

[0059] In addition, please refer to the following: Figure 5 The EDS (energy dispersive spectroscopy) layered image shown is a surface elemental distribution map of the CoNPs-SAs@NC composite catalyst. The image shows the coexistence of cobalt single atoms and cobalt nanoparticles, and also indicates that the cobalt element is uniformly distributed on the catalyst surface.

[0060] Further, please refer to Figure 6 The EXAFS (Extended X-ray Absorption Spectrum) spectrum in R space shown in the figure reveals the presence of Co-N and Co-Co bonds in the composite material, further demonstrating the coexistence of cobalt single atoms and cobalt nanoparticles.

[0061] Therefore, from Figure 5 and Figure 6 The information shown further illustrates that the composite catalyst prepared by the method of the present invention has a high loading of metal species and abundant active sites.

[0062] Please see Figure 7 The correlation analysis diagram shown is based on the relationship between the Co loading and the Co salt addition in the composite catalyst. Figure 7 As can be seen from the figure, the CoNPs-SAs@NC composite catalyst obtained in this embodiment has a high loading capacity, and the mass fraction of Co in the CoNPs-SAs@NC composite catalyst can be controlled by the amount of Co salt added. The correlation R between the Co loading and the amount of Co salt added is shown in the figure. 2 =0.987.

[0063] Please see Figure 8The N2 adsorption-desorption isotherm diagram of the nitrogen-doped carbon support shown in the figure shows that the N2 adsorption-desorption of the composite catalyst provided by the preparation method of the present invention exhibits a type IV adsorption-desorption isotherm and an H3 hysteresis loop. Combined with the pore size distribution characteristics in the inset, it is indicated that the composite catalyst has a mesoporous structure.

[0064] The nitrogen-doped carbon-supported cobalt single atoms and cobalt nanoparticles synergistic CoNPs-SAs@NC composite catalyst prepared in this embodiment was applied to the catalytic degradation reaction of organic pollutants. The specific implementation steps were as follows: three 5 mg portions of CoNPs-SAs@NC composite catalyst and 25 mg of sodium persulfate were weighed in parallel and mixed with 50 mL of 20 mg L⁻¹ sodium persulfate solution. -1 Solutions containing sulfonamides, quinolones, and tetracyclines were placed in three separate 100 mL beakers and magnetically stirred until homogeneous. The pH of the system was adjusted to 9 using either 0.1 M sodium hydroxide or 0.1 M sulfuric acid. Every 2 minutes, 1.5 mL of the reaction solution was extracted, filtered through a 0.22 μm filter membrane, and finally, 200 μL of sodium thiosulfate (Na₂S₂O₃) was injected to quench the reaction. The residual pollutants were analyzed using high-performance liquid chromatography (HPLC20AT). The degradation efficiency of the CoNPs-SAs@NC composite catalyst prepared in this embodiment of the invention for the above three organic pollutants is as follows: Figure 9 As shown. From Figure 9 As can be seen from the present invention, the CoNPs-SAs@NC composite catalyst prepared in the embodiments of the present invention exhibits extremely high degradation efficiency for three typical organic pollutants.

[0065] Comparative Example 1

[0066] After thoroughly mixing 1 mmol of Co(NO3)2·6H2O, 2 mmol of dicyandiamine, and 1 mmol of urea, the mixture was placed directly into a covered quartz boat and heated in a tube furnace at 5 °C·min. -1 The temperature was increased to 600℃ and pyrolyzed in a hydrogen atmosphere for 4 hours. After natural cooling, the Co@NC composite catalyst prepared by one-step pyrolysis was collected.

[0067] The Co@NC composite catalyst prepared by the above method was applied to the catalytic degradation reaction of organic pollutants. The specific implementation steps were as follows: three 5 mg Co@NC composite catalysts and 25 mg sodium persulfate were weighed in parallel and mixed with 50 mL of 20 mg L⁻¹ sodium persulfate solution. -1Solutions containing sulfonamides, quinolones, and tetracyclines were placed in three separate 100mL beakers and magnetically stirred until homogeneous. The pH of the system was adjusted to 9 using either 0.1M sodium hydroxide or 0.1M sulfuric acid. Every 2 minutes, 1.5mL of the reaction solution was extracted, filtered through a 0.22μm filter membrane, and finally, 200µL of sodium thiosulfate (Na₂S₂O₃) was injected to quench the reaction. Analysis of the residual pollutants using high-performance liquid chromatography (HPLC 20AT) revealed that the degradation efficiency of the Co@NC composite catalyst for each of the aforementioned typical organic pollutants was less than 50% after ten minutes, significantly lower than that of the CoNPs-SA@NC composite catalyst in Example 1 of this invention.

[0068] Comparative Example 2

[0069] 1 mmol of Co(NO3)2·6H2O and 10 g of urea were dissolved in ultrapure water, placed in a 50 ml corundum crucible, and ultrasonically treated for 1 hour. The mixture was then dried at 70 °C for 24 hours to obtain the precursor. Subsequently, it was heated at 520 °C for 2 hours at a heating rate of 5 °C / min. -1 The obtained product was cooled to room temperature and then ground into powder. The powder product was washed three times with 0.1M sulfuric acid, ethanol (EtOH), and ultrapure water, respectively, and then dried at 70°C for 24 h to obtain the SA-CoCNs single-atom catalyst prepared by urea composite.

[0070] The SA-CoCNs single-atom catalyst was applied to the catalytic degradation reaction of organic pollutants. The specific implementation steps were as follows: three 5 mg portions of SA-CoCNs composite catalyst and 25 mg of sodium persulfate were weighed in parallel and mixed with 50 mL of 20 mg L⁻¹ sodium persulfate solution. -1 Solutions containing sulfonamides, quinolones, and tetracyclines were placed in three separate 100mL beakers and magnetically stirred until homogeneous. The pH of the system was adjusted to 9 using either 0.1M sodium hydroxide or 0.1M sulfuric acid. Every 2 minutes, 1.5mL of the reaction solution was extracted, filtered through a 0.22μm filter membrane, and finally, 200µL of sodium thiosulfate (Na₂S₂O₃) was injected to quench the reaction. The residual pollutants were analyzed using high-performance liquid chromatography (HPLC 20AT). The results showed that the SA-CoCNs single-atom catalyst achieved a degradation efficiency of 99% for various typical organic pollutants within 40 minutes, significantly lower than the CoNPs-SAs@NC composite catalyst in Example 1. This indicates that the nano- and single-atom site composite catalyst provided by this invention exhibits superior performance compared to single-atom catalysts.

[0071] Comparative Example 3

[0072] 30 mL of ethanol and 90 mL of N,N-dimethylformamide were mixed, and then 0.6 g of polyvinylpyrrolidone K30 was added until fully dissolved. Then, 0.291 g of Co(NO3)2·6H2O and 0.843 g of 1,3,5-trimeric acid were added and stirred for 20 min. The mixture was then poured into a 100 mL high-pressure autoclave and kept at 120 °C for 12 h. After cooling to room temperature, purple crystals were collected using a centrifuge at 3900 rpm and washed at least three times with ethanol. After drying in an oven at 60 °C, the dried sample was placed in a porcelain boat and then placed in a high-temperature tubular furnace for one-step high-temperature carbonization under a N2 atmosphere. The heating rate was 5 °C / min, and the temperature was maintained at 900 °C for 2 h. After natural cooling to room temperature, Co@DC nanocatalyst was obtained.

[0073] The Co@DC nanocatalyst prepared by pyrolysis was applied to the catalytic degradation reaction of organic pollutants. The specific implementation steps were as follows: three 5 mg Co@DC composite catalysts and 25 mg sodium persulfate were weighed in parallel and mixed with 50 mL of 20 mg L⁻¹ sodium persulfate solution. -1 Solutions containing sulfonamides, quinolones, and tetracyclines were placed in three separate 100mL beakers and magnetically stirred until homogeneous. The pH of the system was adjusted to 9 using either 0.1M sodium hydroxide or 0.1M sulfuric acid. Every 2 minutes, 1.5mL of the reaction solution was extracted, filtered through a 0.22μm filter membrane, and finally, 200µL of sodium thiosulfate (Na₂S₂O₃) was injected to quench the reaction. The residual pollutants were analyzed using high-performance liquid chromatography (HPLC 20AT). The degradation efficiency for various typical organic pollutants reached 99% within 20 minutes, which is shorter than the CoNPs-SAs@NC composite catalyst in Example 1. This indicates that the nano- and single-atom site composite catalyst provided by this invention has superior performance compared to nano-catalysts.

[0074] Example 2

[0075] This embodiment provides a single-atom and nanoparticle composite catalyst, its preparation, and its application.

[0076] 1) Dissolve 1 mmol of Ni(NO3)2·6H2O, 2 mmol of dicyandiamine and 1 mmol of urea in 50 ml of ultrapure water. After stirring thoroughly, place the mixture in a covered crucible and heat-treat it at 220 °C for 4 hours in an air atmosphere in a muffle furnace to obtain the metal complex.

[0077] 2) Grind the metal composite obtained in the previous step thoroughly, pass it through a 100-mesh sieve, place it in a covered quartz boat, and heat it in a tube furnace at 5°C / min. -1The heating rate was increased to 600℃ under a specific atmosphere (nitrogen) for 4 hours. After natural cooling, a NiNPs-SAs@NC composite catalyst with high loading of metal single atoms and nanoparticles was collected.

[0078] Please see Figure 10 The image shown is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Ni single-atom and nanoparticle composite catalyst in Example 2 of the present invention. The image shows the coexistence of nickel single atoms (bright spots) and nickel nanoparticles (stripes).

[0079] The nitrogen-doped carbon-supported NiNPs-SAs@NC composite catalyst prepared in this embodiment was applied to the catalytic depolymerization reaction of lignin. The specific steps were as follows: 0.2 g of the NiNPs-SAs@NC composite catalyst, 0.4 g of bamboo lignin, and 20 ml of isopropanol were added to a hydrothermal reactor, stirred until homogeneous, heated to 220°C, and reacted for 5 h. The product was then collected and analyzed by GC-MS. Experimental results showed that the lignin conversion rate was 91.2%, and the yield of phenolic compounds was 12.62%. Specific products are shown in Table 1. This indicates that the NiNPs-SAs@NC composite catalyst provided in this embodiment can promote the cleavage of CO bonds in lignin structural units and the hydrogenation conversion of lignin, demonstrating good application performance in catalyzing lignin depolymerization.

[0080] Table 1. GC-MS analysis results of lignin depolymerization products

[0081]

[0082]

[0083] Example 3

[0084] This embodiment provides a single-atom and nanoparticle composite catalyst and its preparation method.

[0085] 1) Dissolve 1 mmol of Fe(NO3)3·9H2O, 2 mmol of dicyandiamine and 1 mmol of urea in 50 ml of ultrapure water. After stirring thoroughly, place the mixture in a covered crucible and heat-treat it at 220 °C for 4 hours in an air atmosphere in a muffle furnace to obtain the metal complex.

[0086] 2) After thoroughly grinding the metal composite obtained in the previous step through a 100-mesh sieve, place it in a covered quartz boat and heat it in a tube furnace at 5°C / min. -1The heating rate was increased to 600℃ under a specific atmosphere (inert gas) for 4 hours. After natural cooling, a FeNPs-SAs@NC composite catalyst with high loading of metal single atoms and nanoparticles was collected.

[0087] Please see Figure 11 The image shown is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Fe single-atom and nanoparticle composite catalyst in Example 3 of the present invention. The image shows the coexistence of iron single atoms (bright spots) and iron nanoparticles (stripes) in the FeNPs-SAs@NC composite catalyst.

[0088] Example 4

[0089] This embodiment provides a single-atom and nanoparticle composite catalyst and its preparation method.

[0090] 1) Dissolve 1 mmol of Cu(NO3)2·6H2O, 2 mmol of dicyandiamine and 1 mmol of urea in 50 ml of ultrapure water. After stirring thoroughly, place the mixture in a covered crucible and heat-treat it at 220 °C for 4 hours in an air atmosphere in a muffle furnace to obtain the metal complex.

[0091] 2) After thoroughly grinding the metal composite obtained in the previous step through a 100-mesh sieve, place it in a covered quartz boat and heat it in a tube furnace at 5°C / min. -1 The heating rate was increased to 600℃ under a specific atmosphere (hydrogen) for 4 hours. After natural cooling, CuNPs-SAs@NC composite catalyst with high loading of metal single atoms and nanoparticles was collected.

[0092] Please see Figure 12 The image shown is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Cu single-atom and nanoparticle composite catalyst in Example 4 of the present invention. The image shows the coexistence of copper single atoms (bright spots) and copper nanoparticles (stripes) in the CuNPs-SAs@NC composite catalyst.

[0093] Example 5

[0094] This embodiment provides a single-atom and nanoparticle composite catalyst and its preparation method.

[0095] 1) Dissolve 1 mmol of Mn(NO3)2·6H2O, 2 mmol of dicyandiamine and 1 mmol of urea in 50 ml of ultrapure water. After stirring thoroughly, place the mixture in a covered crucible and heat it in a muffle furnace at 220 °C for 4 hours under an air atmosphere to obtain the metal complex.

[0096] 2) After thoroughly grinding the metal composite obtained in the previous step through a 100-mesh sieve, place it in a covered quartz boat and heat it in a tube furnace at 5°C / min. -1 The heating rate was increased to 600℃ under a specific atmosphere (nitrogen) for 4 hours. After natural cooling, a high-load MnNPs-SAs@NC composite catalyst with coexisting metal single atoms and nanoparticles was collected.

[0097] Please see Figure 13 The image shown is an AC-HAADF-STEM (spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope) image of the Mn single-atom and nanoparticle composite catalyst in Example 5 of the present invention. The image shows the coexistence of manganese single atoms (bright spots) and manganese nanoparticles (stripes) in the MnNPs-SAs@NC composite catalyst.

[0098] In summary, this invention provides a composite catalyst of metal single atoms and nanoparticles and its preparation method. The preparation method is simple, and the resulting product exhibits an irregular layered morphology with a surface rich in highly active metal single atoms and nanoparticle active sites, possessing excellent catalytic oxidation ability and highly active multifunctional sites. The nitrogen-doped carbon support easily exposes more active sites and enhances the catalyst's electron transfer capability (see reference). Figure 8 Furthermore, the combination of metal single atoms and nanoparticles is beneficial for increasing synergistic catalytic activity. These characteristics make the single-atom and nanoparticle composite catalyst of this invention have great potential application value in the fields of micro-nano reactors and synergistic catalysis.

[0099] This invention also investigated the catalytic activity of the prepared metal single-atom and nanoparticle composite catalyst in the catalytic activation of sodium persulfate for the degradation of organic pollutants and in the catalytic depolymerization of lignin. These application results also demonstrate the significant development potential of the metal single-atom and nanoparticle composite catalyst provided by this invention in photothermal catalysis and synergistic catalysis. Furthermore, the catalyst preparation process is simple, applicable to various metal salts, and easily scalable for large-scale industrial production by adjusting the raw material ratio.

[0100] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A method for preparing a composite catalyst of single atoms and nanoparticles, characterized in that, Includes the following steps: Preparation of metal complex: 0.1-2 mmol of metal salt, 1-8 mmol of dicyandiamine and 0.1-10 mmol of urea are dissolved in ultrapure water by weight, thoroughly mixed and then subjected to heat treatment at a temperature of 100-400°C for 1-6 h to obtain the metal complex. Preparation of single-atom and nanoparticle composite catalyst: The metal composite is thoroughly ground and then calcined in a hydrogen atmosphere at a temperature of 300–800°C for 2–6 hours, followed by natural cooling to obtain the single-atom and nanoparticle composite catalyst.

2. The preparation method according to claim 1, characterized in that, The metal salt is at least one of the metals selected from cobalt, copper, nickel, iron, and manganese, and exists in the form of at least one salt selected from nitrate, sulfate, hydrochloride, and acetate.

3. The preparation method according to claim 1, characterized in that, The calcination is carried out at 1-10℃·min -1 The temperature is increased at a rate of 300–800°C.

4. A composite catalyst of single atoms and nanoparticles, characterized in that, It is prepared by any one of the preparation methods described in claims 1-3.

5. A method for using the single-atom and nanoparticle composite catalyst prepared by any one of the preparation methods described in claims 1-3 for the oxidative degradation of organic pollutants.

6. The method according to claim 5, characterized in that, The organic pollutants include sulfonamide organic pollutants, quinolone organic pollutants and / or tetracycline organic pollutants.

7. A method for using the single-atom and nanoparticle composite catalyst prepared by any one of the preparation methods described in claims 1-3 for the catalytic depolymerization of lignin.

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