Carbon-based material with a ball-in-bowl structure and method for producing the same
By preparing carbon-based materials with a bowl-in-ball structure, the problems of insufficient specific surface area and morphology uniformity in the existing carbon material structure design are solved, and efficient catalysis, energy storage and biosensing applications are achieved.
Patent Information
- Application Number
- CN202311761447.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-20
- Publication Date
- 2025-10-17
- Estimated Expiration
- 2043-12-20
AI Technical Summary
The structural design of existing carbon materials has failed to effectively improve the specific surface area and morphology uniformity, limiting their application potential in catalysis, energy storage, and biosensing.
By adopting the method of template layer-by-layer coating and polymer modification, a double-layer hollow structure of bowl-in-ball carbon-based material consisting of an inner carbon bowl and an outer carbon hollow sphere was prepared. The inner bowl-shaped structure was formed by controlling the thickness and flexibility difference of the carbon wall.
Carbon-based materials with high specific surface area and uniform morphology have been achieved, which enriches the active sites and expands their application potential in catalysis, energy storage, biosensing and other fields.
Smart Images
Figure CN117735528B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a kind of nano composite structure carbon materials, especially it relates to a kind of carbon-based materials of bowl structure in ball and its preparation method. BACKGROUND
[0002] Nanostructure refers to the material structure with size at nanoscale, including particles, fibers, membranes and tubes and other morphologies. Because its size characteristic scale is equivalent to the interaction scale between atoms and molecules, therefore, nanostructure shows many unique properties and characteristics, such as high specific surface area, excellent optical, electrical, magnetic, mechanical and chemical properties, etc. The preparation methods of nanostructure are very diverse, including physical methods, chemical methods, biological methods, etc. Physical methods include sputtering, thermal evaporation, magnetron sputtering, etc. Chemical methods include sol-gel method, hydrothermal method, vapor deposition method, etc. Biological methods include biosynthesis method, biomineralization method, etc. These methods can realize the control of the morphology, size, structure, etc. of nanostructure by adjusting experimental conditions. Nanostructure has potential applications in biomedical, energy, environment, etc. In summary, nanostructure is a special material structure, with many unique properties and applications. With the development of nanotechnology, the preparation and application of nanostructure will get more attention and development.
[0003] Carbon material is a kind of very important functional material, its properties and performance are affected by its structural characteristics. Therefore, reasonable design of structure of carbon material is of great significance for developing new carbon materials, improving their performance and promoting their application. Reasonable design of structure can improve the mechanical, thermal, electrical, optical, etc. properties of carbon material by adjusting the physical, chemical structure and surface morphology, etc. characteristics of the material. For example, by precisely controlling the pore structure and surface properties of carbon material, its adsorption capacity and catalytic activity can be improved, thereby improving its application performance in environmental governance and energy conversion, etc. fields.
[0004] Reasonably designed carbon material can be widely used in various fields. For example, porous carbon material with appropriate pore size can be used in adsorption, separation and catalysis, etc. environmental and energy conversion fields; composite carbon material can be used for high strength, high conductivity and high wear resistance materials; ordered arrangement of nanometer carbon tube structure can be used for high-performance electronic devices and biomedical fields, etc. Reasonable design of structure of carbon material can reduce the production cost of material. By optimizing the synthesis process and designing the material structure, high-efficiency, low-cost, green production of carbon material can be realized, which provides technical support for large-scale preparation of carbon material.
[0005] In summary, reasonable design of structure of carbon material is of great significance for improving material performance, expanding application fields, reducing production cost and promoting the development of carbon material field. SUMMARY
[0006] The purpose of the present application is to provide a carbon-based material with a large specific surface area and a uniform bowl-in-ball structure.
[0007] Technical solution: The carbon-based material with a bowl-in-ball structure of the present application is a double-layer hollow structure composed of an inner "carbon bowl" (CB) and an outer "carbon hollow sphere" (CS). There is a gap between the inner "carbon bowl" and the outer shell. The inner "carbon bowl" is formed by the bending of the carbon wall due to its thinness and poor flexibility, and the outer shell has a hollow sphere structure due to its thicker carbon wall.
[0008] Preferably, the inner "carbon bowl" is formed by bending the hollow sphere, with a "bowl mouth" diameter of 200-250 nm, a depth of 85-110 nm, and a thickness of 15-25 nm.
[0009] The preparation method of the above-mentioned carbon-based material with a bowl-in-ball structure includes the following steps:
[0010] (1) Dissolve tetraethyl orthosilicate in an alkaline mixed solvent of water and ethanol, heat in a water bath, and stir to form a milky white turbidity. Add formaldehyde and resorcinol to the above solution and continue to stir to form a brownish yellow turbidity;
[0011] (2) Continue to add tetraethyl orthosilicate to the brownish yellow turbidity and heat in a water bath for a period of time. Add resorcinol, formaldehyde and styrene again and continue to stir to form a dark brown turbidity. Centrifuge and dry to obtain a dark brown powder;
[0012] (3) Calcine the dark brown powder in step (2) in argon to obtain a SiO2@C@SiO2@C composite material. Disperse the above material in an alkaline solution, stir at high temperature, and etch to form a carbon-based material with a bowl-in-ball structure.
[0013] In the alkaline mixed solvent of water and ethanol, tetraethyl orthosilicate is hydrolyzed to form silica nanospheres, which then serve as a hard template to cover a thin layer of phenol formaldehyde resin containing polystyrene (SiO2@RF-PS) on their surface. On this basis, SiO2 and RF coatings are successively added, followed by carbonization to form a SiO2@C@SiO2@C composite material.
[0014] Due to the thinness of the inner carbon sphere wall, bending occurs during the etching process, forming a bowl-shaped structure. The outer carbon sphere shell is thicker and still maintains a hollow sphere structure. The two are combined to form a bowl-in-ball structure.
[0015] In step (1), the mass ratio of tetraethyl orthosilicate, ammonia water, water and ethanol is 1:1-2:5-10:50-100, and the mass ratio of resorcinol, formaldehyde and styrene is 1:1-3:1-2.
[0016] In step (1), the first stirring time is 10-15 min, and the second stirring time is 20-28 h.
[0017] Preferably, in step (2), the mass ratio of tetraethyl orthosilicate, resorcinol and formaldehyde is 1:0.1-0.3:0.1-0.2.
[0018] In step (2), the first stirring time is 20-30 min, and the second stirring time is 30-42 h.
[0019] In step (3), the calcination temperature is 600-800℃, the heating rate is 2-5℃ / min, and the calcination time is 4-8 h.
[0020] In step (3), the alkaline solution is NaOH solution, and the concentration is 1M-2M.
[0021] In step (3), the etching stirring time is 4-8 h, and the stirring temperature is 60-80℃.
[0022] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: the ball-in-bowl structure carbon-based material in the present application has a regular structure, low density, high specific surface area and rich loading sites, and will be widely applied in the fields of catalysis, energy storage and biosensing. This method provides a new reference scheme for the design of carbon nano composite structures. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1 A scanning electron microscope image of SiO2 prepared in Example 1;
[0024] Figure 2 A transmission electron microscope image of SiO2 prepared in Example 1;
[0025] Figure 3 A scanning electron microscope image of SiO2@RF-PS prepared in Example 1;
[0026] Figure 4 A transmission electron microscope image of SiO2@RF-PS prepared in Example 1;
[0027] Figure 5 A scanning electron microscope image of SiO2@RF-PS@SiO2@RF prepared in Example 1;
[0028] Figure 6 A transmission electron microscope image of SiO2@RF-PS@SiO2@RF prepared in Example 1
[0029] Figure 7 Scanning electron microscope image of the ball-in-bowl structure composite material prepared in Example 1;
[0030] Figure 8 Transmission electron microscope image of the ball-in-bowl structure composite material prepared in Example 1;
[0031] Figure 9 Transmission electron microscope image of the ball-in-bowl structure composite material prepared in Example 2;
[0032] Figure 10 Transmission electron microscope image of the ball-in-bowl structure composite material prepared in Example 3;
[0033] Figure 11 Transmission electron microscope image of the ball-in-bowl structure composite material prepared in Example 4;
[0034] Figure 12 Transmission electron microscope image of the double-layer hollow structure carbon material prepared in Comparative Example 1;
[0035] Figure 13 Transmission electron microscope image of the hollow structure carbon material prepared in Comparative Example 2. DETAILED DESCRIPTION
[0036] The technical solutions of the present application will be further described below in combination with the drawings.
[0037] Example 1
[0038] (1) 100 g of anhydrous ethanol, 10 g of deionized water and 2 g of ammonia water were sequentially added into a beaker, followed by vigorous stirring. Then, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 15 minutes. Then, 0.3 g of resorcinol was taken, and 0.9 g of formaldehyde and 0.6 g of styrene were measured and sequentially added into the above mixed solution. Magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 28 h.
[0039] (2) 2 g of tetraethyl orthosilicate was continuously added, and magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 30 minutes. Next, 0.6 g of resorcinol was taken, and 0.4 g of formaldehyde was measured and sequentially added into the above mixed solution. Magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 42 h.
[0040] (3) After the reaction was completed, centrifugal washing was performed, and the solid phase was obtained and dried. The dried product was calcined at 700°C for 6 h under an argon atmosphere with a temperature increasing rate of 2°C / min, and then the high-temperature calcined product was etched with a 2M sodium hydroxide solution under a water bath condition at 70°C for 6 h. Finally, the etched product was centrifugally washed and dried.
[0041] The carbon material with the ball-in-bowl structure obtained in the present embodiment and the intermediate product were subjected to scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis, as shown in Figures 1-8 .
[0042] From Figure 1 ,2, it can be seen that the silica nanospheres have uniform morphology. The size is basically consistent. The diameter is 200-250 nm, and the surface is smooth, which has the necessary conditions for being used as a subsequent template.
[0043] From Figure 3 ,4, it can be seen that the surface of the silica is covered with a layer of phenol-aldehyde resin with polystyrene branches. The surface is uniformly covered, and the morphology is uniform, with a diameter of about 210-260 nm.
[0044] From Figure 5 ,6, it can be seen that the double-layer coated silica and phenol-aldehyde resin have obvious boundaries between each layer. The thickness of the inner phenol-aldehyde resin is smaller than that of the outer layer. The morphology is regular, with a diameter of about 350-400 nm, and the surface is slightly wrinkled.
[0045] From Figure 7 ,8, it can be seen that the carbon material with the ball-in-bowl structure has an intact outer shell, and the inner part presents a bowl structure with a cavity structure in the middle. The outer shell has a diameter of 450-500 nm and a thickness of 10-20 nm. The inner "bowl mouth" has a diameter of 200-250 nm, a depth of 85-110 nm, and a thickness of 15-25 nm.
[0046] Example 2
[0047] (1) 50 g of anhydrous ethanol, 5 g of deionized water, and 1 g of ammonia water were sequentially added to a beaker, followed by vigorous stirring. Then, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 10 minutes. Then, 0.3 g of resorcinol, 0.3 g of formaldehyde, and 0.3 g of styrene were sequentially added to the above-mentioned mixed solution. Magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 18 h.
[0048] (2) 2 g of tetraethyl orthosilicate was continuously added, and magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 20 minutes. Next, 0.2 g of resorcinol and 0.2 g of formaldehyde were sequentially added to the above-mentioned mixed solution. Magnetic stirring was performed in a water bath with a temperature maintained at 30°C for 30 h.
[0049] (3) After the reaction was completed, centrifugal washing was performed, and the solid phase was dried. The dried product was calcined at 700°C at a temperature increasing rate of 2°C / min for 8 h under argon protection, and then the high-temperature calcined product was etched with 1M sodium hydroxide solution at 60°C for 8 h. Finally, the etched product was centrifugally washed and dried.
[0050] Figure 9 The TEM morphology of the product is a bowl-shaped structure inside and a hollow sphere structure outside, with slight wrinkles on the shell.
[0051] Example 3
[0052] (1) 50 g of anhydrous ethanol, 5 g of deionized water, and 1 g of ammonia water were sequentially added to a beaker, followed by vigorous stirring. Next, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath maintained at 30°C for 10 minutes. Then, 0.3 g of resorcinol, 0.9 g of formaldehyde, and 0.6 g of styrene were sequentially added to the above-mentioned mixed solution. Magnetic stirring was performed in a water bath maintained at 30°C for 18 h.
[0053] (2) 1 g of tetraethyl orthosilicate was continuously added, and magnetic stirring was performed in a water bath maintained at 30°C for 30 minutes. Next, 0.3 g of resorcinol and 0.2 g of formaldehyde were sequentially added to the above-mentioned mixed solution. Magnetic stirring was performed in a water bath maintained at 30°C for 30 h.
[0054] (3) After the reaction was completed, centrifugal washing was performed, and the solid phase was obtained and dried. The dried product was calcined at 800°C at a temperature increase rate of 5°C / min for 8 h under argon protection, and then the high-temperature calcined product was etched with 2M sodium hydroxide solution at 80°C for 8 h. Finally, the etched product was centrifugally washed and dried.
[0055] Figure 10 The TEM morphology of the product is a bowl-shaped structure inside and a hollow sphere structure outside, with slight wrinkles on the shell.
[0056] Example 4
[0057] (1) 50 g of anhydrous ethanol, 5 g of deionized water, and 1 g of ammonia water were sequentially added to a beaker, followed by vigorous stirring. Next, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath maintained at 30°C for 15 minutes. Then, 0.3 g of resorcinol, 0.9 g of formaldehyde, and 0.3 g of styrene were sequentially added to the above-mentioned mixed solution. Magnetic stirring was performed in a water bath maintained at 30°C for 24 h.
[0058] (2) 1 g of tetraethyl orthosilicate was continuously added, and magnetic stirring was performed in a water bath maintained at 30°C for 20 minutes. Next, 0.1 g of resorcinol and 0.2 g of formaldehyde were sequentially added to the above-mentioned mixed solution. Magnetic stirring was performed in a water bath maintained at 30°C for 30 h.
[0059] (3) After the reaction is completed, the product is centrifuged and washed, dried, and calcined at 600°C for 4 hours at a temperature increasing rate of 2°C / min under argon protection. Then, the calcined product is etched with 1M NaOH solution in a water bath at 60°C for 4 hours. Finally, the etched product is centrifuged and washed, and dried.
[0060] The product obtained in the present comparative example is analyzed by TEM as shown in FIG. 4. As can be seen from the figure, the second carbon sphere is coated with a thinner layer of phenolic resin due to the adjustment of the mixing ratio and stirring time in step (2). The outer carbon layer of the material forming the bowl-shaped sphere is thinner, thus showing a more obvious wrinkle effect. Figure 11
[0061] Comparative Example 1
[0062] (1) 100 g of anhydrous ethanol, 10 g of deionized water, and 2 g of ammonia water were sequentially added to a beaker, followed by vigorous stirring. Then, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath maintained at 30°C for 10 minutes. Then, 0.3 g of resorcinol, 0.9 g of formaldehyde, and 0.1 g of styrene were sequentially added to the above mixture solution. Magnetic stirring was performed in a water bath maintained at 30°C for 28 hours.
[0063] (2) 2 g of tetraethyl orthosilicate was further added, and magnetic stirring was performed in a water bath maintained at 30°C for 20 minutes. Next, 0.6 g of resorcinol and 0.8 g of formaldehyde were sequentially added to the above mixture solution. Magnetic stirring was performed in a water bath maintained at 30°C for 42 hours.
[0064] (3) After the reaction was completed, the product was centrifuged and washed, dried, and calcined at 800°C for 8 hours at a temperature increasing rate of 2°C / min under argon protection. Then, the calcined product was etched with 1M NaOH solution in a water bath at 70°C for 6 hours. Finally, the etched product was centrifuged and washed, and dried.
[0065] The product obtained in the present comparative example is analyzed by TEM as shown in FIG. 4. As can be seen from the figure, the second carbon sphere is coated with a thinner layer of phenolic resin due to the adjustment of the mixing ratio and stirring time in step (2). The outer carbon layer of the material forming the bowl-shaped sphere is thinner, thus showing a more obvious wrinkle effect. Figure 12
[0066] Comparative Example 2
[0067] (1) In a beaker, 50 g of anhydrous ethanol, 5 g of deionized water and 1 g of ammonia water were added in sequence, followed by vigorous stirring. Next, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath maintained at 30°C for 10 minutes. Then, 0.3 g of resorcinol, 0.3 g of formaldehyde and 0.2 g of styrene were measured and added in sequence to the above mixture solution. Magnetic stirring was performed in a water bath maintained at 30°C for 18 h.
[0068] (2) 5 g of tetraethyl orthosilicate was further added, and magnetic stirring was performed in a water bath maintained at 30°C for 30 minutes. Next, 1.5 g of resorcinol and 2 g of formaldehyde were measured and added in sequence to the above mixture solution. Magnetic stirring was performed in a water bath maintained at 30°C for 42 h.
[0069] (3) After the reaction was completed, the product was washed by centrifugation, dried, and then calcined at 600°C for 4 h at a temperature increase rate of 5°C / min under argon atmosphere. Subsequently, the calcined product was etched with 2M sodium hydroxide solution at 70°C for 4 h. Finally, the etched product was washed by centrifugation and dried.
[0070] The product obtained in the present comparative example was subjected to transmission electron microscope analysis as shown in FIG. 1. As can be seen from the figure, due to the adjustment of the stirring time to 18 h and other ingredient ratios in step (1), the phenolic resin covering was thin, and the internal carbon content was reduced. The hollow carbon spheres with single-wall structure were formed, but there was still some carbon residue inside. Figure 13
[0071] Comparative Example 3
[0072] (1) In a beaker, 100 g of anhydrous ethanol, 10 g of deionized water and 2 g of ammonia water were added in sequence, followed by vigorous stirring. Next, 1 g of tetraethyl orthosilicate was added, and magnetic stirring was performed in a water bath maintained at 30°C for 15 minutes. Then, 0.3 g of resorcinol, 0.2 g of formaldehyde and 1 g of styrene were measured and added in sequence to the above mixture solution. Magnetic stirring was performed in a water bath maintained at 30°C for 24 h.
[0073] (2) 2 g of tetraethyl orthosilicate was further added, and magnetic stirring was performed in a water bath maintained at 30°C for 20 minutes. Next, 0.8 g of resorcinol and 1.0 g of formaldehyde were measured and added in sequence to the above mixture solution. Magnetic stirring was performed in a water bath maintained at 30°C for 36 h.
[0074] (3) After the reaction is completed, centrifugal washing is performed, the solid phase is obtained, and drying is performed. The dried product is calcined at 600 DEG C for 6h under the protection of argon at a temperature increasing rate of 2 DEG C / min. Subsequently, the calcined product is etched with 1M sodium hydroxide solution under the condition of a water bath at 60 DEG C for 8h. Finally, the etched product is centrifugally washed and dried.
[0075] The product obtained in the present comparative example is subjected to transmission electron microscope analysis, and no carbon material with regular morphology is obtained.
[0076] The present application adopts a method of template layer-by-layer coating and polymer modification, and first prepares a carbon-based material with a bowl-in-ball structure. Carbon materials are widely used in medical treatment, environment, energy storage and other fields due to their multifunctionality. Reasonable design of carbon materials is a hot field that researchers have been focusing on. The method used in the present application is simple, and the instrument and equipment are simple. The synthesized carbon-based material with a bowl-in-ball structure can effectively increase the specific surface area, enrich the active sites, and provide space for subsequent material compounding inside. Therefore, the present application has both innovation and practical application.
Claims
1. A carbon-based material with a bowl-in-ball structure, characterized in that: The carbon material presents a composite structure, namely, composed of an inner bowl-shaped carbon structure and an outer hollow sphere carbon structure. There is a gap between the inner "carbon bowl" and the outer "carbon hollow sphere", and both surfaces have mesopores. The preparation method of the carbon-based material with a bowl-in-sphere structure includes the following steps: (1) Primary coating: dissolve tetraethyl orthosilicate in a mixed solvent of water, ethanol and ammonia, heat in a water bath, and stir for a period of time to form a milky white turbid liquid; add formaldehyde, resorcinol and styrene to the above solution, continue stirring for a period of time to form a brownish yellow turbid liquid; (2) Secondary coating: Tetraethyl orthosilicate was added to the brown-yellow turbid solution for a second time, heated in a water bath, and stirred for a period of time; formaldehyde and resorcinol were added again, and stirring was continued for a period of time to form a dark brown turbid solution, which was centrifuged and dried to obtain dark brown powder SiO2@RF-PS@SiO2@RF; (3) The dark brown powder in step (2) was calcined in argon to obtain a SiO2@C@SiO2@C composite material; the above material was dispersed in an alkaline solution and stirred and etched to form a carbon-based material CBs@CSs with a bowl-in-ball structure.
2. The carbon-based material of the bowl-in-ball structure according to claim 1, characterized in that: The internal "carbon bowl" is formed by bending a hollow sphere. The diameter of the "bowl mouth" is 200~250 nm, the depth is 85-110 nm, and the thickness is 15~25 nm.
3. The carbon-based material of the bowl-in-ball structure according to claim 1, characterized in that: The diameter of the outer carbon hollow sphere is 400~500 nm, the carbon wall thickness is 10~15 nm, and the surface is wrinkled.
4. A method for preparing the carbon-based material of the bowl-in-ball structure according to claim 1, characterized in that: The steps include: (1) Primary coating: dissolve tetraethyl orthosilicate in a mixed solvent of water, ethanol and ammonia, heat in a water bath, and stir for a period of time to form a milky white turbid liquid; add formaldehyde, resorcinol and styrene to the above solution, continue stirring for a period of time to form a brownish yellow turbid liquid; (2) Secondary coating: Tetraethyl orthosilicate was added to the brown-yellow turbid solution for a second time, heated in a water bath, and stirred for a period of time; formaldehyde and resorcinol were added again, and stirring was continued for a period of time to form a dark brown turbid solution, which was centrifuged and dried to obtain dark brown powder SiO2@RF-PS@SiO2@RF; (3) The dark brown powder in step (2) was calcined in argon to obtain a SiO2@C@SiO2@C composite material; the above material was dispersed in an alkaline solution and stirred and etched to form a carbon-based material CBs@CSs with a bowl-in-ball structure.
5. The method for preparing a carbon-based material with a bowl-in-ball structure according to claim 4, characterized in that: In step (1), the mass ratio of tetraethyl orthosilicate, ammonia water, water and ethanol is 1:1-2:5-10:50-100, and the mass ratio of resorcinol, formaldehyde and styrene is 1:1-3:1-2.
6. The method for preparing a carbon-based material with a bowl-in-ball structure according to claim 4, characterized in that: In step (1), the first stirring time is 10-15 min, and the second stirring time is 20-28 h.
7. The method for preparing a carbon-based material with a bowl-in-ball structure according to claim 4, characterized in that: In step (2), the mass ratio of tetraethyl orthosilicate, resorcinol and formaldehyde is 1:0.1~0.3:0.1~0.
2.
8. The method for preparing a carbon-based material with a bowl-in-ball structure according to claim 4, characterized in that: In step (2), the first stirring time is 20-30 min, and the second stirring time is 30-42 h.
9. The method for preparing a carbon-based material with a bowl-in-ball structure according to claim 4, characterized in that: In step (3), the calcination temperature is 600~800℃, the heating rate is 2~5℃ / min, and the calcination time is 4~8h.
10. The method for preparing a carbon-based material with a bowl-in-ball structure according to claim 4, characterized in that: In step (3), the alkaline solution is a NaOH solution with a concentration of 1 M-2 M; the stirring etching time is 4-8 h, and the temperature is 60-80 °C.
Citation Information
Patent Citations
Multilayer porous hollow bowl-shaped carbon material and preparation method thereof
CN110171812A