Preparation method of ZIF-8-derived porous carbon nanofiber

Abstract

The invention belongs to the field of new materials, and particularly relates to a preparation method of ZIF-8-derived porous carbon nanofibers. The preparation method comprises the following steps: synthesizing ZIF-8 with different particle sizes through a solution mixing method, then mixing the ZIF-8 with polyacrylonitrile and polyvinylpyrrolidone to prepare a spinning solution, carrying out electrostatic spinning to obtain polymer fibers, and finally carrying out carbonization treatment on the polymer fibers in a nitrogen atmosphere to obtain the ZIF-8-derived porous carbon nanofibers. The porous carbon nanofiber prepared by the method has the characteristics of simple process, good electrolyte wettability, wide pore size distribution, large specific surface area, doping of various heteroatoms and the like, and has potential application prospects in the fields of catalysis, energy storage and the like.

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and particularly relates to a ZIF-8-derived porous carbon nanofiber and a preparation method thereof. Background Art

[0002] Metal organic Frameworks (MOFs for short) are coordination polymers formed by the reversible coordination bond between metal ions and organic ligands. The synthesis of MOFs starts from the coordination of metal ions. Generally, divalent or trivalent transition metal ions are selected, which have high coordination ability; while organic ligands generally contain two or more coordination groups. Metal ions generally form complexes with organic ligands through reversible reactions, and then construct secondary units to form a three-dimensional framework structure. The control of the framework structure can be achieved by controlling the conditions in the reaction process. MOFs have become one of the research hotspots due to their highly ordered pore structures and abundant active sites. In addition, the structural controllability of MOFs makes them have great application potential in many fields, such as gas storage and separation, catalysts, energy storage, and sensors.

[0003] Electrospinning is a simple method for preparing nanofibers. Its main structure includes a high-voltage power supply, a propeller, a syringe, and a collector. The principle of electrospinning is that when the spinning solution is extruded from the needle of the syringe, a liquid droplet is formed due to the action of surface tension. Applying a certain voltage to the liquid, the liquid deforms into a Taylor cone under the influence of electrostatic repulsion and ejects a charged jet. The jet is further stretched into finer fibers under the action of the electric field and lands on the collector. Finally, nanofibers are formed as the solvent volatilizes. The parameters in the electrospinning process will directly or indirectly affect the structure of the final nanofibers, such as voltage, propulsion amount, receiving distance, environmental temperature and humidity, viscosity and conductivity of the spinning solution, and so on.

[0004] As can be seen from the above, MOFs have the advantages of high porosity and high thermal stability, while nanofibers have a high aspect ratio and adjustable structure. Therefore, rationally incorporating MOFs into nanofibers can obtain composite nanofibers with specific structures, thus showing excellent properties and having greater advantages in many fields. However, it is difficult to incorporate MOFs into nanofibers by electrospinning, and factors such as the compatibility between MOFs and conductive polymers and the influence of the size of MOFs on the structure of nanofibers need to be considered. Therefore, it is of great significance to explore various influencing factors in the process of incorporating MOFs into nanofibers by electrospinning to obtain composite fibers with a reliable structure. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for preparing ZIF-8-derived porous carbon nanofibers, which solves the following problems: ① ZIF-8 is successfully introduced into carbon nanowire fibers, and a macroporous structure is introduced inside the fibers. This structure can increase the specific surface area of carbon fibers, enhance the wettability with the electrolyte, and shorten the ion transport distance; ② PAN can introduce N atom doping into carbon nanowire fibers, which can improve the wettability of the electrolyte. At the same time, the presence of graphitic N can also improve the conductivity of carbon fibers; ③ The decomposition of PVP not only introduces O heteroatoms inside carbon fibers, but also introduces micropores and mesopores into carbon fibers, further increasing the specific surface area of carbon fibers and enhancing the wettability between carbon materials and the electrolyte.

[0006] A method for preparing ZIF-8-derived porous carbon nanofibers, characterized in that the porous carbon nanofibers prepared by this method have irregular nano-protrusions on the surface, a hierarchical pore structure of micropores, mesopores and macropores inside the fibers, the carbon fibers are doped with O and N elements, and the doped N elements are presented in three types: pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen, and the pore diameter inside the carbon fibers is distributed between 1 and 200 nm.

[0007] A method for preparing ZIF-8-derived porous carbon nanofibers, and its specific preparation process is as follows: ① Weigh 1.64 g of anhydrous zinc acetate and dissolve it in 100 - 350 ml of methanol solution to form solution A. Weigh 1.0 - 14.8 g of 2-methylimidazole and dissolve it in 100 - 350 ml of methanol to form solution B. Rapidly add solution A to solution B and stir at room temperature for 1 h to form a white solution. Centrifuge the obtained white solution at a speed of 10000 r min-1 for 15 min at room temperature. Wash the centrifuged white precipitate with methanol three times. Dry the obtained white powder in a vacuum oven overnight at an oven temperature of 60 °C to collect white ZIF-8 nanocrystals with a diameter between 98 and 1150 nm. ② ZIF-8-PVP-PAN composite nanofibers: Take 0.2 - 1.0 g of the ZIF-8 nanocrystals prepared in step ① and disperse them in 3 - 10 ml of DMF solution. Then add 0.2 - 1.0 g of PAN and 0.2 - 0.8 g of PVP in sequence and stir to obtain a uniform spinning solution. Perform electrospinning at a voltage of 12 - 20 KV and a receiving distance of 18 cm to obtain ZIF-8-PVP-PAN composite nanofibers. ③ Preparation of porous carbon nanofibers: The IF-8-PVP-PAN composite nanofibers prepared in the above step ② were placed in a muffle furnace and heated in air at a heating rate of 1 °C min-1 to 270 °C and held for 2 h for pre-oxidation, and then heated to 1000 °C in a nitrogen atmosphere and carbonized for 2 h to obtain porous carbon nanofibers.

[0008] The present invention has the following beneficial technical effects: ① ZIF-8 was successfully introduced into carbon nanofibers, and a macroporous structure was introduced inside the carbon fibers, which can store the electrolyte and enhance the wettability between the carbon material and the electrolyte; ② The decomposition of PVP not only successfully introduced mesopores and micropores into the carbon fibers, but also introduced oxygen atom doping, improving the specific surface area of the material and the wettability of the electrolyte; ③ The pre-oxidation of PAN during the carbonization process can achieve the transformation of the chain skeleton from linear to ladder-shaped, thereby enhancing the stability of the carbon material. At the same time, the carbonization process can also introduce N atom doping, further improving the wettability and conductivity of the carbon material to the electrolyte. Description of the drawings

[0009] Figure 1 It is the scanning electron microscope image of the fiber membrane of Example 1.

[0010] Figure 2 It is the transmission electron microscope image of the fiber of Example 1.

[0011] Figure 3 It is the scanning electron microscope image of the fiber membrane of Example 2.

[0012] Figure 4 It is the scanning electron microscope image of the fiber membrane of Example 3.

[0013] Figure 5 It is the scanning electron microscope image of the fiber membrane of Comparative Example 1. Detailed implementation manners

[0014] The principles and features of the present invention are described below in conjunction with embodiments. The listed examples are only used to explain the present invention and do not limit the scope of the present invention.

[0015] Example 1 1) Preparation of ZIF-8 nanocrystals: Weigh 1.64 g of anhydrous zinc acetate and dissolve it in 100 ml of methanol solution to form solution A. Weigh 1.47 g of 2-methylimidazole and dissolve it in 100 ml of methanol to form solution B. Rapidly add solution A to solution B and stir at room temperature for 1 h to form a white solution. Centrifuge the obtained white solution at a speed of 10000 r / min for 15 min at room temperature. Wash the centrifuged white precipitate with methanol three times. Dry the obtained white powder in a vacuum oven overnight at an oven temperature of 60 °C to collect ZIF-8 nanocrystals with an average diameter of 780 nm; 2) Preparation of ZIF-8-PVP-PAN composite nanofibers: Take 0.4 g of the ZIF-8 nanocrystals prepared in step 1) and disperse them in 5.6 ml of DMF solution. Then, sequentially add 0.6 g of PAN and 0.4 g of PVP, and stir to obtain a homogeneous spinning solution. Perform electrospinning at a voltage of 12 - 20 KV and a receiving distance of 18 cm to obtain ZIF-8-PVP-PAN composite nanofibers; 3) Preparation of porous carbon nanofibers: Put the ZIF-8-PVP-PAN composite nanofibers prepared in the above step 2) into a muffle furnace, heat it to 270 °C at a heating rate of 1 °C / min in air and keep it for 2 h for pre-oxidation, and then heat it to 1000 °C in a nitrogen atmosphere and carbonize it for 2 h to obtain porous carbon nanofibers.

[0016] Example 2 1) Preparation of ZIF-8 nanocrystals: Weigh 1.64 g of anhydrous zinc acetate and dissolve it in 100 of methanol solution to form solution A. Weigh 7.4 g of 2-methylimidazole and dissolve it in 100 ml of methanol to form solution B. Rapidly add solution A to solution B and stir at room temperature for 1 h to form a white solution. Centrifuge the obtained white solution at a speed of 10000 r / min for 15 min at room temperature. Wash the centrifuged white precipitate with methanol three times. Dry the obtained white powder in a vacuum oven overnight at an oven temperature of 60 °C to collect ZIF-8 nanocrystals with an average diameter of 141 nm; 2) Preparation of ZIF-8-PVP-PAN composite nanofibers: Take 0.3 g of the ZIF-8 nanocrystals prepared in step 1) and disperse them in 4.2 ml of DMF solution. Then, sequentially add 0.45 g of PAN and 0.3 g of PVP, and stir to obtain a homogeneous spinning solution. Perform electrospinning at a voltage of 12 - 20 KV and a receiving distance of 18 cm to obtain ZIF-8-PVP-PAN composite nanofibers; 3) Preparation of porous carbon nanofibers: Follow Example 1.

[0017] Example 3 1) Preparation of ZIF-8 nanocrystals: Weigh 1.64 g of anhydrous zinc acetate and dissolve it in 100 mL of methanol solution to form solution A. Weigh 11.76 g of 2-methylimidazole and dissolve it in 100 mL of methanol to form solution B. Rapidly add solution A to solution B and stir at room temperature for 1 h to form a white solution. Centrifuge the obtained white solution at a speed of 10000 r / min for 15 min at room temperature. Wash the centrifuged white precipitate with methanol three times. Dry the obtained white powder in a vacuum oven overnight at an oven temperature of 60 °C to collect ZIF-8 nanocrystals with an average diameter of 98 nm; 2) Preparation of ZIF-8-PVP-PAN composite nanofibers: Take 0.54 g of the ZIF-8 nanocrystals prepared in step 1) and disperse them in 7.56 mL of DMF solution. Then, sequentially add 0.81 g of PAN and 0.54 g of PVP, and stir to obtain a uniform spinning solution. Electrospinning is carried out at a voltage of 12 - 20 KV and a receiving distance of 18 cm to obtain ZIF-8-PVP-PAN composite nanofibers; 3) Preparation of porous carbon nanofibers: Follow Example 1.

[0018] Comparative Example 1: 1) Preparation of PVP-PAN composite nanofibers: Add 0.6 g of PAN and 0.4 g of PVP to 5.6 mL of DMF and stir to obtain a uniform spinning solution. Electrospinning is carried out at a voltage of 12 - 20 KV and a receiving distance of 18 cm to obtain PVP-PAN composite nanofibers; 3) Preparation of carbon nanofibers: Follow Example 1.

[0019] Performance test: 1) Preparation of the working electrode: Cut the prepared carbon nanofiber film into circular pieces with the same diameter using a 9 mm stamping die, and weigh the mass of the circular pieces with a balance. Cut out a foam nickel with a diameter of 10 mm using a punching machine as the current collector of the electrode material. Subsequently, cut out a foam nickel strip with a length of 30 mm and a width of 6 mm using scissors. Ultrasonically wash the foam nickel in acetone, absolute ethanol, and deionized water step by step for 30 min to wash the oxide layer on the surface of the foam nickel, and finally dry it in an oven at 60 °C for 3 h. Take out the weighed carbon fiber circular pieces, place them between two pieces of foam nickel, and clamp the two foam nickel circular pieces with the notch of the long strip-shaped foam nickel. Press the assembled foam nickel with a press at a pressure of 10 MPa for 30 s to prepare a working electrode, and soak it in 6 M KOH solution for more than 8 h before use; 2) Electrochemical performance test: The electrochemical performance test under a three-electrode system was carried out on an electrochemical workstation. The reference electrode was a saturated calomel electrode, and the counter electrode was a platinum mesh electrode. The constant current charge-discharge method (GCD) was selected, and the mass specific capacitance of the electrode material was calculated according to the GCD curve. The calculation formula is as follows: ; where C: specific capacitance (F g -1 ); I: discharge current of the active material (A); m: mass of the active material (mg); ∆t: discharge time (s); ∆V (V): voltage window. The specific surface areas of the carbon nanofibers prepared in the examples and comparative examples and the specific capacitance values measured at a current density of 1 A g -1 are listed as follows.

[0020]

[0021] The above examples show that: The porous carbon nanofibers prepared in Example 3 have the largest specific capacitance. Compared with Comparative Example 1, the specific surface area and specific capacitance of each example are significantly increased, indicating that the materials prepared by the present invention have a relatively high specific surface area, and the prepared electrode materials have a relatively large specific capacitance.

[0022] The above examples are only for explaining the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of ZIF-8-derived porous carbon nanofibers, characterized in that, The surface of the porous carbon nanofibers prepared by this method contains irregular nano-protrusions, and the fibers contain a hierarchical pore structure of micropores, mesopores and macropores. The carbon fibers are doped with O and N elements, and the doped N elements present three types: pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen. The pore size inside the carbon fibers is distributed between 1 and 200 nm.

2. A method for preparing ZIF-8-derived porous carbon nanofibers according to claim 1, characterized in that, The preparation process includes the following steps: ① Preparation of ZIF-8 nanocrystals: Weigh 1.64 g of anhydrous zinc acetate and dissolve it in 100 - 350 ml of methanol solution to form solution A. Weigh 1.0 - 14.8 g of 2-methylimidazole and dissolve it in 100 - 350 ml of methanol to form solution B. Rapidly add solution A to solution B and stir at room temperature for 1 h to form a white solution. Centrifuge the obtained white solution at a speed of 10000 r min-1 for 15 min at room temperature. Wash the centrifuged white precipitate with methanol three times. Dry the obtained white powder overnight in a vacuum oven at a temperature of 60 °C to collect white ZIF-8 nanocrystals with a diameter between 98 and 1150 nm. ② Preparation of ZIF-8-PVP-PAN composite nanofibers: Take 0.2 - 1.0 g of the ZIF-8 nanocrystals prepared in step ① and disperse them in 3 - 10 ml of DMF solution. Then, successively add 0.2 - 1.0 g of PAN and 0.2 - 0.8 g of PVP, and stir to obtain a uniform spinning solution. Electrospin at a voltage of 12 - 20 KV and a receiving distance of 18 cm to obtain ZIF-8-PVP-PAN composite nanofibers. ③ Preparation of porous carbon nanofibers: Put the IF-8-PVP-PAN composite nanofibers prepared in the above step ② into a muffle furnace, heat it to 270 °C in air at a heating rate of 1 °C min -1 and keep it for 2 h for pre-oxidation, and then heat it to 1000 °C in a nitrogen atmosphere and carbonize it for 2 h to obtain porous carbon nanofibers.

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