CN106564875A - Preparation method of monodisperse cobalt-nitrogen co-doped hollow carbon nano-particles - Google Patents

Abstract

The invention relates to a preparation method of monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles, using ZnO nanosphere template and Zn source, adding cobalt ions to form a double metal hybrid zeolite-like imidazolate skeleton compound shell, that is, ZnO@ Zn/Co-ZIF precursor; followed by high-temperature carbonization of the ZnO@Zn/Co-ZIF precursor to directly obtain cobalt-nitrogen co-doped hollow carbon nanoparticles with a specific surface area of 400-600m ² g ^‑1 . The synthesis method of the invention is simple, does not need to use pickling to remove the core layer template, and can realize an environment-friendly preparation process.

Description

A preparation method of monodisperse cobalt nitrogen co-doped hollow carbon nanoparticles

technical field

The invention belongs to the technical field of nanometer materials, in particular to a preparation method of monodisperse cobalt nitrogen co-doped hollow carbon nanoparticles.

Background technique

In recent years, porous carbon nanomaterials doped with heteroatoms (such as nitrogen, boron, phosphorus, sulfur, cobalt, etc.), especially hollow-structured carbon nanomaterials with special pore structures, have been , low density, and good physical and chemical stability, it has a wide range of applications in the fields of catalysis, adsorbents, electrode materials, and batteries. On the one hand, after heteroatoms are introduced into the carbon structure, due to the difference in bond length, valence electrons, and atomic size with carbon atoms, defects appear in sites near adjacent carbon atoms, the charge distribution is uneven, and the electrical neutrality of carbon materials is destroyed. It is more conducive to constructing the catalytic active center of carbon materials. On the other hand, carbon materials with hollow structures have unique macroporous hollow cores and porous carbon shells, which can greatly improve the migration and diffusion of electrons, thereby enhancing the catalytic activity of carbon materials. Therefore, the preparation of heteroatom-doped hollow carbon materials is of great research significance.

At present, the preparation methods of hollow carbon nanoparticles include: template method, vapor deposition method, arc discharge method, laser evaporation method and so on. Among them, the template method is the most widely used method for preparing hollow carbon particles. Template method can be divided into hard template method and soft template method. Most of the hard template methods use monodisperse silicon spheres, polymer spheres, etc. as templates, and then grow carbon source compounds on their surfaces to obtain core-shell structure composites. After carbonization, choose an appropriate method to remove the templates to obtain hollow carbon particles. Although the hollow carbon particles prepared by the hard template method are uniform in size and have high monodispersity, incomplete removal of the template during the template removal process will result in low purity, and even easily cause the carbon particles to break or collapse.

Vapor deposition is one of the commonly used methods for the synthesis of hollow carbon particles. The principle is that in a flowing atmosphere, organic gas is used as a carbon source, pyrolyzed under high temperature conditions, and the process of depositing and growing solid carbon on the surface of the catalyst. Since metal oxides are generally used as catalysts in the vapor phase deposition method, but there is little research on the mechanism of the catalysts, so by-products are generated during the synthesis process. Therefore, the purity of hollow carbon particles prepared by this method is not high.

The arc discharge method is also a method for preparing hollow carbon particles. According to the Chinese patent CN1454839, the specific implementation method is to pass an inert gas in an arc reaction chamber containing a graphite anode and a cathode, and apply a voltage between the two electrodes with a pulse current, thereby generating Arc discharge reaction, the product collected and deposited on the cathode is hollow carbon particles, the carbon particles have high purity, but the cost is also high.

In recent years, using metal-organic framework materials, especially the zeolite imidazolate framework material ZIF-67, as a precursor, high-temperature carbonization can directly obtain cobalt-nitrogen co-doped porous carbon materials. In the document "Well-definedcarbonpolyhedrons prepared from nano metal-organic frameworks for oxygenreduction.J.Mater.Chem.A, 2(2014) 11606–11613", Ruqiang Zou et al. reported cobalt-nitrogen co-doped porous with controllable particle size The disadvantage of carbon nanoparticles is that the specific surface area (100-400m ² g ^-1 ) of the prepared carbon material is relatively small. In the literature "From Bimetallic Metal-Organic Framework to Porous Carbon: High SurfaceArea and Multicomponent Active Dopants for Excellent Electrocatalysis. Adv. Mater., 27 (2015) 5010–5016", Hai-Long Jiang et al. reported that based on bimetallic hybrid metal- Porous carbon nanomaterials from organic framework (Zn/Co-ZIF) precursors. By adjusting the different molar ratios of Zn/Co in the reactant (0, 0.2, 5, 10, 20, 40, 100), the specific surface area of the carbon material can be greatly improved (270, 362, 550, 1090, 1225, 1480, 2184m ² g ^-1 ), and introduce abundant CoN _x active catalytic sites in carbon materials. Among them, when the Zn/Co molar ratio is 20, the obtained carbon material exhibits the best electrocatalytic performance. The carbon materials reported in the literature above are all monodisperse solid porous carbon nanoparticles without a hollow structure.

In order to overcome the shortcomings of the existing technology, it is of great significance to explore a simple and low-cost method for preparing heteroatom-doped hollow carbon particles to take advantage of its performance.

Contents of the invention

The purpose of the present invention is to provide a method for preparing monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles, which overcomes the shortcomings of the porous carbon nanoparticles prepared in the prior art that do not have a hollow structure and have a low specific surface area.

In the present invention, ZnO nanosphere template and Zn source are used to add cobalt ions to form a double metal hybrid zeolite imidazolate framework compound (Zn/Co-ZIF) shell, that is, ZnO@Zn/Co-ZIF precursor; then ZnO@ The Zn/Co-ZIF precursor is subjected to high-temperature carbonization to directly obtain cobalt-nitrogen co-doped hollow carbon nanoparticles without a template removal step.

The invention provides a method for preparing monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles, comprising the following steps:

1) Preparation of ZnO nanospheres:

Stir and mix 0.1 mol/L zinc acetate aqueous solution and 0.1 mol/L triethanolamine aqueous solution, then ultrasonically react in a water bath; then stand still for 10 hours; centrifuge, wash, and dry to obtain ZnO nanospheres with a particle size range of 150-250 nm;

2) Preparation of ZnO@Zn/Co-ZIF precursor:

Add the cobalt salt and the ZnO nanospheres obtained in step 1) to a mixed solution composed of N,N-dimethylformamide (DMF)/water, and ultrasonically diffuse fully at room temperature; then add 2-methylimidazole and mix well , after mixing, transfer the solution to a hydrothermal kettle, place the hydrothermal kettle in an oven at 50-70°C for 3-5 hours, after the reaction, centrifuge, wash and dry to obtain ZnO@Zn/Co-ZIF Precursor;

3) Carbonization step:

The ZnO@Zn/Co-ZIF precursor obtained in step 2) is placed in a tube furnace, heated and carbonized in an inert gas atmosphere, and then naturally cooled to room temperature to obtain monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles;

The volume ratio of zinc acetate aqueous solution to triethanolamine aqueous solution in the above step 1) is 1:5, the water bath temperature is 20-50°C, and the ultrasonic reaction time is 20-40min;

The molar ratio of 2-methylimidazole and ZnO nanospheres in the above step 2) is 4-32:1;

The mol ratio of ZnO and cobalt salt in above-mentioned step 2) is 14-35:1;

The cobalt salt described in the above step 2) is cobalt nitrate, cobalt acetate or cobalt chloride;

The volume ratio of DMF and water in the above step 2) is 1-3:1;

The flow rate of the inert gas in the above step 3) is 50-150mL/min, the carbonization temperature is 800-900°C, and the carbonization time is 1-3h;

The inert gas in the above step 3) is nitrogen or argon;

Compared with prior art, the present invention has following advantage:

1) The present invention prepares core-shell structure ZnO@Zn/Co-ZIF nanopolyhedron composites with different Co contents by adjusting the molar ratio of ZnO and Co salt;

2) The present invention uses ZnO@Zn/Co-ZIF as a precursor, controls the carbon consumption of ZnO in the carbonization process by controlling the particle size (150-250nm) of ZnO, and obtains macroporous hollow carbon nanometer after complete reaction of ZnO particles;

3) The hollow carbon nanoparticles prepared by the present invention can realize uniform co-doping of cobalt and nitrogen in the shell carbon material, and maintain the polyhedral morphology;

4) The hollow carbon nanoparticles prepared by the present invention have good monodispersity and high specific surface area (400-600m ² g ^-1 )

5) The synthesis method of the present invention is simple, does not need to use pickling to remove the core layer template, and can realize an environmentally friendly preparation process.

Description of drawings

Fig. 1 is the scanning electron microscope (SEM) picture (under 500nm scale) of the ZnO nanosphere prepared in embodiment 1.

FIG. 2 is a transmission electron microscope (TEM) photo (under 100 nm scale) of the ZnO@Zn/Co-ZIF precursor prepared in Example 1.

3 is a transmission electron microscope (TEM) photo (under 100 nm scale) of the cobalt-nitrogen co-doped hollow carbon nanoparticles prepared in Example 1.

4 is an X-ray diffraction (XRD) spectrum of the cobalt-nitrogen co-doped hollow carbon nanoparticles prepared in Example 1.

5 is a nitrogen adsorption curve (77K) of cobalt-nitrogen co-doped hollow carbon nanoparticles prepared in Example 1.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that these descriptions are exemplary only, and are not intended to limit the scope of the present invention.

Example 1

(1) Add 40 mL of 0.1 mol/L zinc acetate aqueous solution and 200 mL of 0.1 mol/L triethanolamine aqueous solution into an Erlenmeyer flask, stir at room temperature for 30 min, and then irradiate it ultrasonically in a water bath at 30°C for 20 min After that, let it stand for 10h. After centrifugation, washing and drying, ZnO nanospheres are obtained.

(2) Add 80.0 mg of ZnO nanospheres and 20.0 mg of cobalt nitrate obtained in step 1 to an Erlenmeyer flask containing a mixed solvent of DMF and water (64 mL, volume ratio 3:1), and ultrasonically 20 min at room temperature to fully diffuse , then add 0.660g of 2-methylimidazole, after ultrasonication for 5min, transfer it to a hot water kettle, place it in a 50°C oven for 5h, after the reaction, centrifuge, wash and dry to obtain ZnO@Zn /Co-ZIF precursor.

(3) The ZnO@Zn/Co-ZIF precursor obtained in step 2) was placed in a high-temperature furnace, and the temperature was raised to 800 °C at a rate of 5 °C/min in a nitrogen atmosphere with an inert gas flow rate of 50 mL/min. After carbonizing at 800° C. for 3 hours, it was naturally cooled to room temperature to obtain the monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles described in the present invention.

Fig. 1 is a scanning electron microscope (SEM) photograph (under 500nm scale) of ZnO nanosphere; Fig. 2 is a transmission electron microscope (TEM) photograph (under 100nm scale) of core-shell structure ZnO@Zn/Co-ZIF precursor; Fig. 3 is The transmission electron microscope (TEM) picture (under 100nm scale) of cobalt-nitrogen co-doped hollow carbon nanoparticles; Fig. 4 is the XRD spectrogram of gained cobalt-nitrogen co-doped hollow carbon nanoparticles; Fig. 4 is gained cobalt-nitrogen co-doped hollow carbon nanoparticles Nitrogen adsorption curve (77K) of carbon nanoparticles.

It can be seen from Figure 1 that the ZnO nanospheres prepared in step (1) have a uniform particle size (200±20nm). From Figure 2, it can be clearly seen that the core-shell structure ZnO@Zn/Co-ZIF nanoparticles are polyhedral in shape, the particle size of the ZnO core is 150±20nm, and the thickness of the shell ZnO-8 is 70±10nm. As shown in Figure 3, the hollow carbon obtained after carbonization maintains the original polyhedron shape, the hollow core diameter is 150±20nm, and the carbon wall thickness is 15±5nm. The black particles in the white circles in the figure are wrapped by graphite carbon. Cobalt nanoparticles. Figure 4 is the XRD spectrum of the obtained cobalt-nitrogen co-doped hollow carbon nanoparticles. The diffraction peak position is approximately at 2θ=26° corresponding to the (002) crystal plane of the graphite structure, and at 2θ=44° and 51° corresponding to face-centered cubic cobalt The (111) and (200) crystal planes of the crystal. Fig. 5 is the nitrogen adsorption curve (77K) of the obtained cobalt-nitrogen co-doped hollow carbon nanoparticles, and the calculated specific surface area (BET surface area) is 420 m ² g ^-1 .

Example 2

(1) Add 40 mL of 0.1 mol/L zinc acetate aqueous solution and 200 mL of 0.1 mol/L triethanolamine aqueous solution into an Erlenmeyer flask, stir at room temperature for 30 min, and then irradiate it ultrasonically in a water bath at 30°C for 20 min After that, let it stand for 10h. After centrifugation, washing and drying, ZnO nanospheres are obtained.

(2) Add 80.0 mg of ZnO nanospheres and 12.0 mg of cobalt nitrate obtained in step 1 to an Erlenmeyer flask containing a mixed solvent of DMF and water (64 mL, volume ratio 2:1), and ultrasonicate for 20 min at room temperature to fully diffuse , then add 0.660g of 2-methylimidazole, after ultrasonication for 5min, transfer it to a hot water kettle, put it in a 60°C oven for 4h, after the reaction, centrifuge, wash and dry to get ZnO@Zn /Co-ZIF precursor.

(3) The ZnO@Zn/Co-ZIF precursor obtained in step 2) was placed in a high-temperature furnace, and the temperature was raised to 900 °C at a rate of 5 °C/min in a nitrogen atmosphere, and the flow rate of the inert gas was 50 mL/min. After carbonization at 900° C. for 3 hours, it was naturally cooled to room temperature to obtain the monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles described in the present invention.

Example 3

(1) Add 40 mL of 0.1 mol/L zinc acetate aqueous solution and 200 mL of 0.1 mol/L triethanolamine aqueous solution into an Erlenmeyer flask, stir at room temperature for 30 min, and then irradiate it ultrasonically in a water bath at 30°C for 20 min After that, let it stand for 10h. After centrifugation, washing and drying, ZnO nanospheres are obtained.

(2) Add 80.0 mg of ZnO nanospheres and 8.0 mg of cobalt nitrate obtained in step 1 to an Erlenmeyer flask filled with DMF and water mixed solvent (64 mL, volume ratio 1:1), and ultrasonically 20 min at room temperature to make it fully diffuse , followed by adding 1.32g of 2-methylimidazole, after ultrasonication for 5 minutes, pour the solution in the conical flask into a hydrothermal kettle, place it in a 70°C oven for 3 hours, after the reaction, centrifuge, wash and dry to obtain ZnO@Zn/Co-ZIF precursor.

(3) The ZnO@Zn/Co-ZIF precursor obtained in step 2) was placed in a high-temperature furnace, and the temperature was raised to 900 °C at a rate of 5 °C/min in a nitrogen atmosphere, and the flow rate of the inert gas was 50 mL/min. After carbonization at 900° C. for 3 hours, it was naturally cooled to room temperature to obtain the monodisperse cobalt-nitrogen co-doped hollow carbon nanoparticles described in the present invention.

Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims (8)

1. a kind of preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt, comprises the steps：

1) preparation of ZnO nano ball：

After by the zinc acetate aqueous solution of 0.1mol/L and 0.1mol/L triethanolamine aqueous solution stirring and evenly mixings, in water-bath, ultrasound is anti- Should；Then stand 10h；It is centrifuged, washs, is dried to obtain the ZnO nano ball that particle size range is 150-250nm；

2) preparation of ZnO@Zn/Co-ZIF presomas：

By cobalt salt and step 1) in gained ZnO nano ball be added to DMF/ water composition mixed solution in, ultrasound is filled at room temperature Divide diffusion；2-methylimidazole mix homogeneously is subsequently adding, solution is transferred in water heating kettle after mixing, water heating kettle is placed in into 50- 3-5h is reacted in 70 DEG C of baking ovens, after reaction terminates, is centrifuged, washed, being dried, obtaining ZnO@Zn/Co-ZIF presomas；

3) carburising step：

By step 2) in gained ZnO@Zn/Co-ZIF presomas be placed in tube furnace, in the atmosphere of noble gases heat up carbonization, Then room temperature is naturally cooled to, the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt is obtained, the single dispersing cobalt is nitrogen co-doped hollow Carbon nano-particle specific surface area is 400-600m²g^-1。

2. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 1) in zinc acetate aqueous solution and triethanolamine aqueous solution volume ratio be 1:5, bath temperature is 20-50 DEG C, during ultrasonic reaction Between be 20-40min.

3. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 2) in the mol ratio of 2-methylimidazole and ZnO nano ball be 4-32:1.

4. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 2) in the mol ratio of ZnO and cobalt salt be 14-35:1.

5. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 2) described in cobalt salt be cobalt nitrate, cobaltous acetate or cobaltous chloride.

6. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 2) in the volume ratio of DMF and water be 1-3:1.

7. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 3) in noble gases flow be 50-150mL/min, carburizing temperature be 800-900 DEG C, carbonization time is 1-3h.

8. the preparation method of the nitrogen co-doped hollow carbon nano-particle of single dispersing cobalt according to claim 1, it is characterised in that： Step 3) in noble gases be nitrogen or argon.