A method for preparing three-dimensional hollow carbon spheres

Abstract

The application discloses a preparation method of three-dimensional hollow carbon spheres. The three-dimensional hollow carbon spheres are prepared by one-step pyrolysis method through the three-dimensional network structure of melamine foam and the compounding of MOFs materials. The method is simple in process, environment-friendly, low in cost and capable of industrial production. The three-dimensional hollow carbon spheres prepared by the method have uniform and good micro-morphology, the carbon spheres are hollow in the inside, each carbon sphere has four branches connected with other carbon spheres, and multiple carbon spheres are connected to form a three-dimensional network structure.

Description

Technical Field

[0001] This invention belongs to the field of carbon material preparation technology, specifically relating to a method for preparing three-dimensional hollow carbon spheres. Background Technology

[0002] Hollow carbon spheres, as a high-performance carbon micro / nanomaterial, have broad application prospects in catalysis, adsorption, energy storage, and biomedicine due to their unique cavity structure, high specific surface area, and porosity. Currently, the main methods for preparing hollow carbon spheres include the sol-gel method, hydrothermal method, solvothermal method, and template method. The template method, being the most widely used, generally involves coating a carbon precursor onto the surface of a silica sphere template, followed by high-temperature carbonization and template removal to obtain hollow carbon spheres.

[0003] Several methods exist for preparing hollow carbon spheres, and relatively mature processes exist for preparing different types and requirements of hollow carbon spheres. However, the preparation of three-dimensional carbon sphere networks is currently not feasible. Since carbon spheres are generally obtained through water bath or template etching, it is difficult to achieve one-step direct preparation of three-dimensional carbon sphere networks. Carbon spheres with a three-dimensional network structure not only possess the properties of a hollow shell structure, but also exhibit perfect interconnection between carbon spheres, greatly enhancing their specific surface area and internal cavity. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a method for preparing three-dimensional hollow carbon spheres using MOFs composite melamine foam, aiming to obtain hollow carbon spheres with a three-dimensional network structure.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing three-dimensional hollow carbon spheres includes the following steps:

[0007] Step 1: Add zinc nitrate to a methanol solution and stir at a constant temperature until dissolved to obtain solution A; add 2-methylimidazole to a methanol solution and stir at a constant temperature until dissolved to obtain solution B;

[0008] Step 2: Slowly add solution A to solution B, stir and react for 1-4 hours, centrifuge, dissolve the resulting white precipitate in ethanol solution to obtain MOFs solution;

[0009] Step 3: The MOFs solution is impregnated into melamine foam by ultrasonication or stirring, and then dried to obtain the precursor;

[0010] Step 4: Pyrolyze the precursor at high temperature under an inert atmosphere to obtain three-dimensional hollow carbon spheres.

[0011] Preferably, in step 1, the concentration of zinc nitrate in solution A is 0.05-0.5 mol / L, and the concentration of 2-methylimidazole in solution B is 0.4-2.0 mol / L.

[0012] Preferably, in step 1, the temperature of the constant temperature stirring is 20-50℃, the stirring method is magnetic stirring, and the speed is 50-500 rpm.

[0013] Preferably, in step 2, the volume ratio of solution A to solution B is 1:1-5.

[0014] Preferably, in step 2, the centrifugation speed is 5000-8000 rpm.

[0015] Preferably, in step 3, the amount of MOF solution coated on melamine foam is controlled by adjusting the concentration of the MOF solution, thereby controlling the thickness of the carbon coating layer in the precursor and ultimately controlling the size of the carbon spheres.

[0016] Preferably, in step 3, the time for ultrasonication or stirring is 0.1 to 1 hour.

[0017] Preferably, in step 3, the drying is performed under a constant temperature of 60-80°C for 2-6 hours.

[0018] Preferably, in step 4, the high-temperature pyrolysis uses high-purity argon as a protective gas with a gas flow rate of 0.005 L / min to 0.05 L / min, and is carried out at 700-1000℃ for 30-180 min.

[0019] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0020] 1. This invention utilizes the three-dimensional network structure of melamine foam and avoids the etching process by composite with MOF materials, and obtains three-dimensional hollow carbon spheres through a one-step pyrolysis method, which is economical and environmentally friendly.

[0021] 2. The three-dimensional hollow carbon spheres prepared by this invention have uniform and good microstructure. The interior of the carbon spheres is hollow, and each carbon sphere has four branches that connect with other carbon spheres. Multiple carbon spheres form pentagonal rings and are further interconnected to form a three-dimensional network structure. Furthermore, the size of the carbon spheres can be controlled by adjusting the concentration of the MOF solution.

[0022] 3. The method of the present invention uses inexpensive raw materials, has an environmentally friendly process route, is simple to operate, has an easy-to-control reaction process, a short production cycle, and low requirements for experimental conditions. It does not require special instruments and reagents, does not involve complex processing steps, and can be prepared on a large scale. It is a simple, environmentally friendly, low-cost method for preparing three-dimensional hollow carbon spheres that can be industrially produced. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0024] Figure 1 (a) to (e) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 1 of the present invention at different magnifications, and (f) is its TEM image.

[0025] Figure 2 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 2 of this invention at different magnifications.

[0026] Figure 3 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 3 of the present invention at different magnifications.

[0027] Figure 4 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 4 of this invention at different magnifications.

[0028] Figure 5 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 5 of this invention at different magnifications. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0030] Example 1

[0031] Step 1: Add 0.005 mol of zinc nitrate (Zn(NO3)2·6H2O) (analytical grade) to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution A; add 0.046 mol of 2-methylimidazole to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution B.

[0032] Step 2: Slowly add solution A to solution B, stir and react for 2 hours, centrifuge at 6000 rpm, dissolve the resulting white precipitate in 50 mL of ethanol solution, and sonicate for 15 minutes to obtain MOFs solution.

[0033] Step 3: Pour the MOFs solution into melamine foam, sonicate at room temperature for 15 min, and then dry in an oven at 80°C for 4 h to obtain the precursor.

[0034] Step 4: The precursor is directly loaded into a graphite crucible and placed in a high-temperature tube furnace. High-purity argon (Ar≥99.999%) is used as the protective gas at a flow rate of 0.01 L / min. The temperature is increased from room temperature to 900℃ at a rate of 5℃ / min, held at that temperature for 120 min, and finally naturally cooled to room temperature to obtain three-dimensional hollow carbon spheres.

[0035] Example 2

[0036] Step 1: Add 0.01 mol of zinc nitrate (Zn(NO3)2·6H2O) (analytical grade) to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution A; add 0.068 mol of 2-methylimidazole to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution B.

[0037] Step 2: Slowly add solution A to solution B, stir and react for 1 hour, centrifuge at 6000 r / min, dissolve the resulting white precipitate in 50 mL of ethanol solution, and sonicate for 15 min to obtain MOFs solution.

[0038] Step 3: Pour the MOFs solution into melamine foam, sonicate at room temperature for 15 min, and then dry in an oven at 80°C for 4 h to obtain the precursor.

[0039] Step 4: The precursor is directly loaded into a graphite crucible and placed in a high-temperature tube furnace. High-purity argon (Ar≥99.999%) is used as the protective gas at a flow rate of 0.01 L / min. The temperature is increased from room temperature to 700℃ at a rate of 5℃ / min, held at that temperature for 180 min, and finally naturally cooled to room temperature to obtain three-dimensional hollow carbon spheres.

[0040] Example 3

[0041] Step 1: Add 0.005 mol of zinc nitrate (Zn(NO3)2·6H2O) (analytical grade) to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution A; add 0.02 mol of 2-methylimidazole to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution B.

[0042] Step 2: Slowly add solution A to solution B, stir and react for 2 hours, centrifuge at 6000 r / min, dissolve the resulting white precipitate in 100 mL of ethanol solution, and sonicate for 15 min to obtain MOFs solution.

[0043] Step 3: Pour the MOFs solution into melamine foam, sonicate at room temperature for 30 min, and then dry in an oven at 80℃ for 4 h to obtain the precursor.

[0044] Step 4: The precursor is directly loaded into a graphite crucible and placed in a high-temperature tube furnace. High-purity argon (Ar≥99.999%) is used as the protective gas at a flow rate of 0.05 L / min. The temperature is increased from room temperature to 900℃ at a rate of 5℃ / min, held at that temperature for 60 min, and finally naturally cooled to room temperature to obtain three-dimensional hollow carbon spheres.

[0045] Example 4

[0046] Step 1: Add 0.0025 mol of zinc nitrate (Zn(NO3)2·6H2O) (analytical grade) to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution A; add 0.046 mol of 2-methylimidazole to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution B.

[0047] Step 2: Slowly add solution A to solution B, stir and react for 1 hour, centrifuge at 6000 r / min, dissolve the resulting white precipitate in 50 mL of ethanol solution, and sonicate for 15 min to obtain MOFs solution.

[0048] Step 3: Pour the MOFs solution into melamine foam, sonicate at room temperature for 15 min, and then dry in an oven at 60°C for 6 h to obtain the precursor.

[0049] Step 4: The precursor is directly loaded into a graphite crucible and placed in a high-temperature tube furnace. High-purity argon (Ar≥99.999%) is used as the protective gas, with a gas flow rate of 0.005 L / min. The temperature is increased from room temperature to 1000℃ at a rate of 5℃ / min, and calcined for 120 min. Finally, it is naturally cooled to room temperature to obtain three-dimensional hollow carbon spheres.

[0050] Example 5

[0051] Step 1: Add 0.015 mol of zinc nitrate (Zn(NO3)2·6H2O) (analytical grade) to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution A; add 0.068 mol of 2-methylimidazole to 50 mL of methanol solution, and stir magnetically at 500 rpm at room temperature until clear to obtain solution B.

[0052] Step 2: Slowly add solution A to solution B, stir and react for 1 hour, centrifuge at 6000 r / min, dissolve the resulting white precipitate in 50 mL of ethanol solution, and sonicate for 15 min to obtain MOFs solution.

[0053] Step 3: Pour the MOFs solution into melamine foam, sonicate at room temperature for 15 min, and then dry in an oven at 80°C for 4 h to obtain the precursor.

[0054] Step 4: The precursor is directly loaded into a graphite crucible and placed in a high-temperature tube furnace. High-purity argon (Ar≥99.999%) is used as the protective gas at a flow rate of 0.03 L / min. The temperature is increased from room temperature to 900℃ at a rate of 5℃ / min, and calcined for 120 min. Finally, it is naturally cooled to room temperature to obtain three-dimensional hollow carbon spheres.

[0055] The morphology of the three-dimensional hollow carbon spheres prepared in Examples 1-5 of this invention was observed, and the following results were obtained:

[0056] Figure 1 Images (a) to (e) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 1 of the present invention at different magnifications. It can be seen that the average diameter of the carbon spheres is about 10-15 μm and the wall thickness is 100-200 nm. Each carbon sphere has four branches that are connected to other carbon spheres. Multiple carbon spheres form pentagonal rings and are further connected to each other to form a three-dimensional network structure. Figure 1 Image (f) is a TEM image of the three-dimensional hollow carbon sphere prepared in Example 1 of the present invention, showing that the carbon sphere has a hollow structure inside.

[0057] Figure 2 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 2 of this invention at different magnifications. It can be seen that the average diameter of the carbon spheres is approximately 5-15 μm. Compared to Example 1, the decrease in calcination temperature resulted in a smaller size of the carbon spheres and an increase in the number of individual carbon spheres.

[0058] Figure 3Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 3 of the present invention at different magnifications. It can be seen that the average diameter of the carbon spheres is about 10-15 μm, the size of each carbon sphere is uniform, and each carbon sphere has four branches around it that are connected to other carbon spheres to form a three-dimensional network structure. The interior of the carbon spheres is hollow.

[0059] Figure 4 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 4 of this invention at different magnifications. It can be seen that the average diameter of the carbon spheres is approximately 10-15 μm, the individual carbon spheres are uniform in size, and there is internal fragmentation within the carbon spheres. Each carbon sphere has four branches connecting it to other carbon spheres, and the interior of the carbon spheres is hollow. The results indicate that higher calcination temperatures accelerate the formation of carbon spheres but also disrupt their hollow structure.

[0060] Figure 5 Images (a) to (c) are FESEM images of the three-dimensional hollow carbon spheres prepared in Example 5 of the present invention at different magnifications. It can be seen that the average diameter of the carbon spheres is about 15-25 μm and the wall thickness is 400-700 nm. The size of each carbon sphere is uniform. Each carbon sphere has four branches around it that are connected to other carbon spheres, forming a three-dimensional network structure. The interior of the carbon spheres is hollow.

[0061] In summary, this invention prepares three-dimensional hollow carbon spheres using MOFs composite melamine foam by adjusting the concentration of the MOF solution and the preparation process. The method of this invention is simple, does not involve complex reaction processes, and can be prepared with a short cycle and low raw material costs. Furthermore, the three-dimensional hollow carbon spheres prepared by this invention have good morphology and uniform size, meeting the three-dimensional structural requirements of different materials, providing a technological foundation and commercial potential for energy storage, catalysis, and thermal material management.

[0062] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing three-dimensional hollow carbon spheres, characterized in that, Includes the following steps: Step 1: Add zinc nitrate to the methanol solution and stir magnetically at a constant temperature of 20-50℃ with a speed of 50-500 rpm until dissolved to obtain solution A with a zinc nitrate concentration of 0.05-0.5 mol / L; 2-Methylimidazole was added to a methanol solution and magnetically stirred at a constant temperature of 20-50℃ with a speed of 50-500 rpm until dissolved, to obtain solution B with a 2-methylimidazole concentration of 0.4-2.0 mol / L. Step 2: According to the volume ratio of solution A to solution B of 1:1-5, slowly add solution A to solution B, stir and react for 1-4 hours, centrifuge at 5000-8000 rpm, dissolve the resulting white precipitate in ethanol solution to obtain MOFs solution. Step 3: The MOFs solution is impregnated into melamine foam by ultrasonication or stirring, and then dried to obtain the precursor; the ultrasonication or stirring time is 0.1-1 h; the drying is carried out at a constant temperature of 60-80℃ for 2-6 h. Step 4: Using high-purity argon as a protective gas, the precursor is calcined at 700-1000℃ for 30-180 minutes to obtain three-dimensional hollow carbon spheres; the carbon spheres have an average diameter of 10-15μm and a wall thickness of 100-200nm. Each carbon sphere has four branches that are connected to other carbon spheres. Multiple carbon spheres form pentagonal rings and are further connected to each other to form a three-dimensional network structure. In step 3, the amount of MOF solution coated on melamine foam is controlled by adjusting the concentration of MOF solution, thereby controlling the thickness of the carbon coating layer in the precursor and ultimately controlling the size of the carbon spheres.

2. A three-dimensional hollow carbon sphere prepared by the method of claim 1.

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