Preparation method of hollow carbon sphere material with high loading capacity of manganese monoatom

Abstract

The invention discloses a preparation method of a hollow carbon sphere material with high loading capacity of manganese monoatoms, and belongs to the technical field of nano functional materials and monatomic catalytic materials. The method comprises the following steps: by taking silicon dioxide (SiO2) nanospheres synthesized by a # imgabs0 # method as a template, dispersing the silicon dioxide nanospheres into an ethanol-water mixed solution, introducing a nitrogen-containing organic ligand and a manganese source, and forming a precursor compound through self-assembly and polymerization reaction; and performing centrifugal separation, washing and freeze drying on the obtained intermediate, performing high-temperature carbonization in an inert atmosphere to form a manganese-doped nitrogen-carbon material (SiO2 (at) Mn-NC) coated on the surface of SiO2, and then removing a template through strong alkali etching to obtain the uniform HMn-NC material with a hollow spherical structure. The preparation method is simple and convenient and high in controllability, and the obtained material has the advantages that manganese is highly dispersed in a carbon matrix in a monatomic form; the whole material is of a hollow structure, and has high specific surface area, high metal loading capacity and excellent structural stability and function adjustability.

Description

Technical Field

[0001] The present invention focuses on the field of nanomaterial synthesis, and specifically relates to a method for preparing spherical hollow nanostructured materials with high specific surface area and high manganese single atom content. Background Art

[0002] Template technology is a controllable synthesis method for nanomaterials based on the confinement effect of templates. It can precisely control the morphology, size and structure of nanomaterials according to pre-designed templates. Compared with traditional synthesis methods, the template method can effectively achieve fine control of product morphology, particle size and structure by precisely controlling the nucleation and growth process of crystals. According to the difference in the properties of the template, the template method can be divided into hard template method (using rigid materials such as porous alumina and mesoporous silica) and soft template method (using molecular directing agents such as surfactants and block copolymers). The typical template synthesis process includes three key steps: first, preparing the template; second, achieving the directional growth of the target product in the confined space of the template through hydrothermal method, precipitation method or sol-gel method; third, removing the template. In this study, a hard template method was used to prepare porous materials using SiO2 as a template. SiO2 templates offer significant advantages, including high structural controllability, good chemical stability, and ease of specific removal. This allows for precise control of the pore size distribution and morphology of the product, resulting in the preparation of functional materials with high specific surface area and rich porous structures. This method offers advantages such as high reproducibility and easy control of product morphology, demonstrating significant potential applications in a variety of fields, including biomedicine, energy storage, and heterogeneous catalysis.

[0003] The material's spherical structure not only provides uniform pore distribution, a high specific surface area, and good mechanical strength, but its internal cavities also increase the density of active sites and improve mass transfer efficiency. In particular, the porous shell structure facilitates the diffusion of reactants, optimizing the reaction kinetics. This study aims to develop carbon spherical skeleton materials with high single-atom loading, excellent stability and controllable morphology by precisely controlling the material composition and microstructure to meet application needs in fields such as catalysis, energy storage and biomedicine.

[0004] Single-atom catalysts can achieve atomic utilization efficiencies close to the theoretical limit by fixing metal active centers on the support surface in an atomically dispersed manner, thereby significantly improving catalytic activity and reaction selectivity. Among them, manganese single-atom catalysts have significant advantages in biomedicine, catalysis, environment and other fields due to their unique 3D electronic configuration, controllable valence properties and rich coordination environment. However, existing preparation technologies have some key challenges, such as the easy agglomeration of metal atoms, the difficulty in controlling the support structure and the low single-atom content. These problems lead to insufficient catalyst stability and low utilization of active sites. To address these technical bottlenecks, the present invention proposes a novel preparation method. By precisely controlling the material's composition and microstructure, a single-atom-doped carbon spherical framework material with superior performance is successfully obtained, achieving uniform dispersion and stable immobilization of manganese atoms. Compared with existing preparation methods, this method can significantly increase the manganese atom content.

[0005] The present invention provides an HMn-NC material and a method for preparing the same. By anchoring single manganese atoms on a hierarchical porous carbon framework, this material achieves high single-atom dispersion, high specific surface area, high stability, and a high single-atom loading. Specifically, the present invention employs a template-assisted pyrolysis strategy, precisely controlling the precursor composition and pyrolysis parameters to successfully achieve uniform distribution of manganese atoms and precise control of the porous structure. The hollow structure significantly increases the specific surface area of ​​the material, maintains a stable structure at high temperatures, and achieves a high single-atom loading of manganese. This HMn-NC material combines the catalytic properties of manganese single atoms with the structural stability advantages of carbon materials, significantly improving dispersibility, loading capacity, and stability. This invention provides a new technical solution for the development of efficient and stable single-atom catalysts. Summary of the Invention

[0006] This invention discloses a method for preparing hollow carbon spheres with high manganese atom loadings. This approach aims to address the problems of metal atom aggregation, uneven distribution of active sites, and limited mass transfer efficiency in existing single-atom catalysts. Based on a silica hard template strategy, this method achieves high-density, uniform dispersion of manganese atoms within a carbon framework by precisely controlling the ratio of manganese and carbon source precursors and pyrolysis process parameters. Subsequently, the template is removed by selective etching, forming a composite structure with a hollow cavity and a porous shell. The resulting material possesses properties such as high specific surface area, high single-atom loading, and excellent structural stability. Its unique hollow porous structure helps improve mass transfer efficiency and accessibility of active sites. By optimizing the material's micromorphology and component distribution, the present invention significantly increases the content of single manganese atoms, enabling a synergistic effect between the manganese atoms and the carbon skeleton. This material exhibits potentially excellent catalytic activity and cyclic stability in fields such as catalysis, the environment, energy storage, and biomedicine, providing an effective solution for the development of high-performance single-atom catalysts.

[0007] In order to achieve the purpose of the invention, the technical solution of the present invention is as follows:

[0008] The present invention relates to a method for preparing a nano-scale hollow carbon sphere material with a high loading of manganese single atoms, and the specific steps are as follows:

[0009] First, under alkaline conditions, a silicon source is added to a mixed solution of ethanol and water and stirred at a constant speed to polymerize and form a nanoscale spherical template. The template is centrifuged and washed, then evenly dispersed in a mixture of ethanol and water in a certain proportion. Under continuous magnetic stirring, a mixed solution of a carbon source and a manganese salt, evenly dispersed in the same proportions of ethanol and water as mentioned above, is added. After sufficient polymerization, the mixed solution is centrifuged, washed, and freeze-dried to obtain an intermediate product. The dried product is ground into a powder and calcined at high temperature in a tubular furnace under a nitrogen atmosphere to obtain a single-atom manganese-doped carbon spherical nanomaterial. Next, the calcined powder is placed in an alkaline solution of a certain concentration and etched with stirring in an oil bath. After etching, the alkaline solution is centrifuged, washed using a specific method, and then freeze-dried to obtain a hollow carbon spherical nanomaterial with a high degree of single-atom manganese doping.

[0010] Preferably, when preparing the nanoscale spherical template, the volume ratio of ethanol to water is 5–9:1, the alkaline conditions are provided by aqueous ammonia, and the silicon source is an alkoxysilane compound. The stirring speed during the synthesis of SiO2 is 200–500 rpm, and the reaction time is 0.5–2 hours.

[0011] Preferably, the prepared SiO2 solid nanoparticles have a particle size of 100-120 nm.

[0012] Preferably, during the synthesis of the intermediate, the volume ratio of ethanol to water is 2-4:1, the carbon source is an amino-containing phenolic polymer, the manganese salt is manganese chloride, nitrate or acetate, and the mass ratio of the carbon source to the manganese salt is 4-6:3-5.

[0013] Preferably, the stirring speed during the synthesis of the intermediate is 300-600 rpm, and the reaction time is 12 to 36 hours.

[0014] Preferably, the calcination conditions are to heat to 700-900° C. at a heating rate of 2-10° C. / min in a tube furnace under inert atmosphere, and keep the temperature for 1-3 hours for high-temperature calcination.

[0015] Preferably, a 2-6 M strong alkaline solution is used during etching, the oil bath temperature is 60-90° C., the stirring speed is 200-500 rpm, and the reaction time is 2-8 hours.

[0016] Preferably, when washing the final product, first use a small amount of water for ultrasonic dispersion, then add a large amount of ethanol for dispersion washing, and the volume ratio of water to ethanol is 1:4-10.

[0017] The size of the prepared nanoscale hollow carbon sphere material with high loading of manganese single atoms is 100–200 nm.

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] The nanoscale hollow carbon sphere material with a high manganese atom loading prepared by the present invention has uniform size, good controllability and repeatability of the synthesis method, excellent high-temperature stability, higher manganese atom content, and a larger specific surface area that can expose more active sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 TEM image of the synthesis process of hollow carbon sphere materials with high loading of manganese single atoms.

[0021] Figure 2 XRD patterns of the prepared silica and hollow carbon sphere materials with high loading of manganese single atoms.

[0022] Figure 3 XPS graph of the prepared hollow carbon sphere material with high loading of manganese single atoms.

[0023] Figure 4 High-resolution O1s, Mn 2p, C 1s, and N1s spectra of the prepared hollow carbon sphere material with high manganese single atom loading.

[0024] Figure 5 Particle size diagram of the prepared hollow carbon sphere material with high manganese single atom loading.

[0025] Figure 6 Elemental distribution diagram of the prepared hollow carbon sphere material with high manganese single atom loading.

[0026] Figure 7 Thermogravimetric diagram of the prepared hollow carbon sphere material with high loading of manganese single atoms.

[0027] Figure 8HAADF-STEM image of the prepared hollow carbon sphere material with high loading of manganese single atoms.

[0028] Figure 9 ICP manganese content diagram of the prepared hollow carbon sphere material with high loading of manganese single atoms.

[0029] Figure 10 BET and pore size diagrams of the prepared hollow carbon sphere material with high manganese single atom loading before and after etching. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the embodiments and accompanying drawings.

[0031] Example 1

[0032] Preparation of SiO2: Mix 70 mL of ethanol and 10 mL of ultrapure water, and thoroughly remove bubbles by sonication. Add 1.5 mL of 25% ammonia solution at 500 rpm / min and thoroughly mix by sonication. Then, add 3 mL of tetraethyl silicate and continue stirring for 1 hour. This yields SiO2 nanoparticles approximately 120 nm in size. Centrifuge at 11,000 rpm / min for 5 minutes, and wash the precipitate twice with ethanol.

[0033] Preparation of the intermediate SiO2@Mn-PDA: Ultrasonically disperse the SiO2 nanoparticles homogeneously in 60 mL of ethanol and 20 mL of ultrapure water. Ultrasonically dissolve a mixture of 500 mg of DA and 400 mg (2 mmol) of manganese chloride tetrahydrate in 6 mL of ethanol and 2 mL of ultrapure water. Add the resulting mixture at 500 rpm and stir for 24 hours. After the reaction is complete, centrifuge at 12,000 rpm / min for 5 minutes and discard the supernatant. Wash the precipitate twice with ethanol and freeze-dry for 12 hours.

[0034] Preparation of SiO2@Mn-NC: The freeze-dried material was fully ground and placed in a tube furnace for high-temperature calcination. It was heated from room temperature to 800℃ (5℃min) under N2 protection. -1 ) and keep warm for 2h.

[0035] Preparation of HMn-NCs: Weigh 6.4 g of NaOH and dissolve it in 40 mL of ultrapure water to prepare a 4 M NaOH solution. Add the calcined material and stir in an oil bath at 80°C and 300 rpm for 6 hours. After the reaction, centrifuge and wash at 12,000 rpm / min for 10 minutes. Discard the supernatant. For subsequent washing, first disperse the material in a small amount of water (3 mL) and then in a large amount of ethanol (30 mL). Centrifuge at the same speed and time. Wash five times until the alkalinity is removed.

[0036] Figure 1This transmission electron micrograph shows the complete preparation process for this example. Monodisperse SiO2 nanospheres were synthesized, and then a manganese-doped dopamine (Mn-PDA) layer was in situ polymerized on the SiO2 surface. After high-temperature carbonization under a nitrogen atmosphere, the SiO2 template was selectively etched using a strong alkaline solution to produce a hollow-structured HMn-NC nanomaterial. The HMn-NC exhibited a well-defined hollow spherical structure with an average diameter of approximately 120 nm and a shell thickness of approximately 15 nm.

[0037] Figure 2 The XRD comparison of the hollow carbon sphere material prepared in this example before and after the template is etched shows that the characteristic SiO2 diffraction peak (20-22°) disappears completely after etching, indicating that the template and the amorphous nature of the material have been successfully removed. Figure 3 The XPS graph of the hollow carbon spherical material prepared in this example further confirms that the main components of the material are C, N, O and Mn. Figure 4 High-resolution O1s, Mn 2p, C 1s, and N 1s spectra reveal the presence of graphitic nitrogen, pyrrolic nitrogen, pyridinic nitrogen, and Mn-Nx bonds in HMn-NC. The Mn-Nx bonding environment suggests that manganese may exist in a single atomic form. Figure 5 Dynamic light scattering (DLS) of the hollow carbon spherical material prepared in this example characterized its hydrodynamic diameter, and the hydrated particle size of HMn-NC was 159 nm. Figure 6 Elemental distribution of the hollow carbon spherical material prepared in this example. Elemental mapping further confirmed the uniform distribution of Mn, N, C, and O elements in HMn-NC.

[0038] Figure 7 Thermogravimetric diagram of the hollow carbon spherical material prepared in this example. Thermogravimetric analysis (TGA) simulates the calcination process of the material under different conditions. Under a nitrogen atmosphere, the SiO2@Mn-PDA precursor lost 17.3% of its weight after calcination at 800°C, which was mainly attributed to the carbonization of organic components and the decomposition of volatile substances. The material showed excellent thermal stability below 300°C. Under an air atmosphere, HMn-NC showed significant weight loss in the range of 300-400°C, corresponding to the oxidation of amorphous carbon.

[0039] Figure 8 This is a HAADF-STEM image of the hollow carbon spheres prepared in this example. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observations at the atomic scale reveal the dispersion and robust anchoring of Mn atoms within the carbon framework. Clear, isolated bright spots, denoted by yellow circles, are visible, without the presence of metal clusters or nanoparticles, further confirming the successful construction of single-atom manganese sites. Figure 9This is the ICP manganese content diagram of the hollow carbon spherical material prepared in this example. Quantitative analysis by inductively coupled plasma mass spectrometry (ICP-MS) shows that the manganese content in HMn-NC is 12.74 wt.%.

[0040] Figure 10 The BET and pore size distribution diagrams of the hollow carbon spherical material prepared in this example before and after etching. The specific surface area of ​​the obtained material increased from 28.3m 2 / g increased to 361.7m 2 The resulting hollow structure increased the material's specific surface area by approximately 12 times. The pore diameter remained unchanged at 2.21 nm before and after etching. The 4M sodium hydroxide alkaline etching process maintained the original pore structure and selectively removed SiO2.

Claims

1. A method for preparing a high-load manganese single atom doped hollow carbon sphere material, characterized in that: The steps include: (1) adding a silicon source to a mixed solution of ethanol and water under alkaline conditions and stirring the mixture to form a nano-spherical template; (2) compounding the template with a mixed solution of a carbon source and a manganese salt to form a precursor intermediate; (3) After drying and grinding the intermediate, calcining it at high temperature under an inert atmosphere; heating it in a tube furnace under nitrogen protection at a heating rate of 2-10°C / min to 700-900°C, and holding it for 1-3 hours; (4) The calcined product is subjected to alkaline etching to remove the template, and the hollow structured manganese single atom-doped carbon sphere material is obtained after washing and drying.

2. The method according to claim 1, wherein the volume ratio of ethanol to water in step (1) is 5:1 to 9:1, the alkaline condition is provided by aqueous ammonia, the silicon source is an alkoxysilane compound, the stirring speed is 200-500 rpm, and the reaction time is 0.5-2 hours.

3. The method according to claim 1, wherein the volume ratio of ethanol to water in step (2) is 2:1 to 4:1, the carbon source is an amino-containing phenolic polymer, the manganese salt is manganese chloride, manganese nitrate or manganese acetate, the mass ratio of the carbon source to the manganese salt is 4-6:3-5, the stirring speed is 300-600 rpm, and the reaction time is 12-36 hours.

4. The method according to claim 1, wherein the etching solution in step (4) is a 2-6 M strong alkaline solution, the etching temperature is 60-90°C, the stirring speed is 200-500 rpm, and the reaction time is 2-8 hours.

5. The method according to claim 1, wherein the washing step comprises first ultrasonically dispersing with deionized water and then adding ethanol for washing, such washing can be repeated several times, and the volume ratio of water to ethanol is 1:4 to 1:10.

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