Arc discharge equipment and preparation method of multi-walled carbon nanotube

Abstract

The invention discloses an improved arc discharge device for preparing materials. According to the device, a special substrate for agglomeration of a precursor is added in a vacuum chamber of a conventional arc discharge device. The invention also discloses a parameter optimization preparation method of the multi-walled carbon nanotube, and the multi-walled carbon nanotube is prepared under the nitrogen pressure of 40 kPa to 80 kPa by adopting an arc discharge technology and taking Fe, Ni and Mo as a catalyst according to a certain proportion.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of new electronic materials, and relates to an arc discharge device for preparing materials and application thereof, in particular, to the preparation of nanomaterials, such as zero-dimensional quantum dots, one-dimensional carbon nanotubes, etc., by using the device; and to a preparation method of multi-walled carbon nanotubes. BACKGROUND

[0002] The arc discharge device generally comprises a gas supply system, a gas extraction system, a cooling system, a vacuum reaction chamber, electrodes and an electric control system, etc. The gas supply system is composed of protective gas for growth deposition and pipelines. The gas extraction system is composed of a vacuum pump, gas extraction pipelines and vacuum measuring instruments. The cooling system is composed of cooling liquid and pipeline valves. The arc discharge device is used for preparing nanomaterials, and generally comprises one or more groups of conductive electrodes in the vacuum reaction chamber, and the reaction chamber is connected to the vacuum system to maintain low pressure. The electrodes are made of conductive materials, and the arc discharge dissociates the materials to generate precursors of the materials to be prepared, and then the precursors condense at different positions in the reaction chamber to form various products. The disadvantage of this device is that there is no uniform deposition substrate suitable for the growth mechanism of the precursors.

[0003] Carbon nanotubes have broad application prospects in many fields such as nanoelectronic devices, sensors, solar cells, etc. due to their unique electrical, mechanical, optical, thermal and other properties. The application of carbon nanotubes is usually determined by the structure of carbon nanotubes (number of walls, diameter, length, chirality angle, etc.), which endows them with specific properties. There are many methods for synthesizing carbon nanotubes, each of which has its own advantages and disadvantages.

[0004] The current mainstream methods for preparing carbon nanotubes include arc discharge method, laser ablation method and chemical vapor deposition method. The structure and performance of carbon nanotubes will vary greatly depending on the preparation method. Generally, the carbon nanotubes prepared by arc discharge method and laser ablation method have high crystallinity and tube straightness, but have the defect of low yield. The most widely studied method for carbon nanotubes is chemical vapor deposition method, which has the advantage of obtaining carbon nanotube arrays with high parallelism and good purity. Although chemical vapor deposition method has realized industrial production of carbon nanotubes, the prepared carbon nanotubes have poor graphitization degree due to the low growth temperature, and have many structural defects, which seriously limit the play of their excellent properties. Therefore, it is very meaningful to explore the preparation of high-quality and defect-free carbon nanotubes. Arc discharge belongs to the method of synthesizing carbon nanotubes using high-temperature technology, which has the advantages of simple operation, short time consumption and fewer structural defects of the synthesized carbon nanotubes.

[0005] In the process of synthesizing carbon nanotubes by arc discharge method, two high-purity graphite electrodes are usually used. In this configuration, the anode can be made of pure graphite, or a graphite electrode doped with a metal catalyst. When the anode contains metal, the metal is mixed with graphite powder and introduced into the hole in the center of the anode. After a voltage is applied to the electrodes, an arc is formed between the electrodes, which in turn forms a plasma between the electrodes, and the temperature in the region between the electrodes is high enough to sublimate and consume the carbon in the anode. By adjusting the distance between the electrodes, the arc between the anode and the cathode can be maintained for a long time, and the plasma can be stable for a long reaction time. Finally, a variety of products are formed in different parts of the reactor, so that carbon nanotubes can be synthesized in a controlled atmosphere composed of inert gas and / or reactant gas at low pressure. There are also amorphous carbon, encapsulated metal nanoparticles, polyhedral carbon, etc. in the product. When no catalyst is used, only soot and deposits are formed. The soot contains fullerenes, while the carbon deposits contain nanocarbon tubes and graphite nanoparticles. The commonly used metals are Fe, Ni, Co, Mo, Y or used alone or in combination [2019 foreign journal paper "Conductive nanomaterials for 2D and 3D printed flexible electronics"].

[0006] Many researchers have prepared carbon nanotubes (CNT) by arc method [2022 foreign journal paper "Nanosynthesis by atmospheric arc discharges excited with pulsed-DC power: a review"; 2020 foreign journal paper "Individual arc-discharge synthesized multiwalled carbon nanotubes probed with multiple measurement techniques"], plasma jet method, chemical vapor deposition (CVD) and solid phase pyrolysis. The arc chamber is often pressurized with air, nitrogen, hydrogen, helium or argon gas [2016 doctoral thesis "Preparation of petroleum residue-based carbon nanotubes by arc plasma method and its application"], or immersed in a liquid environment. Atmospheric pressure is an important factor affecting the quality of CNT in arc discharge technology [2013 doctoral thesis "Preparation method and application research of high-quality multi-walled carbon nanotubes"]. Zhao et al. [2012 foreign journal paper "Synthesis of straight multi-walled carbon nanotubes by arc discharge in air and their field emission properties"] used direct current arc discharge technology to prepare straight multi-walled carbon nanotubes (MWCNT) in low-pressure air. They also found that the yield of multi-walled carbon nanotubes (MWCNT) was highest at an air pressure of about 60 torr. Mehdi et al. [2023 foreign journal paper "Superior field emission characteristics of highly crystalline and thermally stable carbon nanotubes grown in N2 and O2 by arc discharge"] used arc discharge technology to manufacture multi-walled carbon nanotubes (MWCNT) in a nitrogen-oxygen mixture. The yield of multi-walled carbon nanotubes under different gas mixing ratios was studied. The results showed that when the ratio of nitrogen and oxygen was 9:1, high-density and high-quality multi-walled carbon nanotubes could be obtained. Chinese patent document CN102502583B describes that using thin air in the preparation of carbon nanotubes by arc discharge is beneficial to the large-scale production of high-quality carbon nanotubes, and Chinese patent document CN102502576A uses low-pressure air in the preparation of carbon nanotubes by arc discharge, with a gas pressure range of 6-12 KPa.

[0007] In summary, due to the defect scattering in carbon nanotubes, the migration of charge carriers is greatly reduced, so synthesizing defect-free carbon nanotubes is an important problem to be solved. SUMMARY

[0008] The present application provides an arc discharge device with a uniform deposition substrate suitable for precursor growth mechanism, which can solve the shortcomings of the prior art and prepare good nanomaterials.

[0009] The present application also provides an optimized method for preparing multi-walled carbon nanotubes. In view of the shortcomings of the prior art, an arc discharge technique is used to prepare multi-walled carbon nanotubes by using Fe, Ni and Mo as catalysts in a certain proportion under a gas pressure of 60 kPa. It is found by comparison that when Fe is used as a catalyst, the obtained multi-walled carbon nanotubes (MWCNT) are long and straight, and have high graphitization characteristics.

[0010] In order to achieve the above, the specific implementation technical solutions

[0011] The present application provides an improved arc discharge device for preparing materials, and the improved part of the device is specifically implemented as follows:

[0012] The present application provides an arc discharge device for preparing materials, and the improved part of the device is specifically implemented as follows:

[0013] The present application provides a method for preparing multi-walled carbon nanotubes, comprising the following steps:

[0014] (1) The synthesis of carbon nanotubes (CNTs) in this experiment is carried out in an improved arc discharge experimental device, in which two electrodes are vertically placed opposite to each other. The anode and cathode are made of pure graphite rods (99%), and a metal mesh (such as an iron mesh) is placed above the electrodes for auxiliary collection of carbon nanotubes. The experimental device uses a rod-shaped carbon anode with a size of 6 mm (diameter) x 100 mm (length) and an 80 mm (length) x 6 mm (diameter) rod-shaped carbon cathode.

[0015] (2) Iron powder and graphite powder are weighed according to the proportion, and the content of iron powder is 6at%, which is put into a ball mill tank for grinding for 48h, and then filled into the anode.

[0016] (3) The arc plasma is generated at a current of 150 to 160 A and a voltage of 20 to 25 V, and the discharge time is 6 minutes under an atmosphere with a pressure of 60 kPa. The buffer gas is nitrogen, and the experiments are carried out under conditions of 60 kPa, 25 kPa and 6.5 kPa, respectively.

[0017] (4) High quality multi-walled carbon nanotubes were synthesized by arc discharge method in nitrogen environment (pressure ranging from 40 kPa to 80 kPa). BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 An improved arc discharge device for synthesizing multi-walled carbon nanotubes.

[0019] Figure 2 Samples prepared under different nitrogen pressures (from left to right) 60 kPa, 6.5 kPa, 25 kPa, respectively.

[0020] Figure 3 Transmission electron microscope (TEM) images (a) multi-walled carbon nanotubes obtained under 25 kPa nitrogen, (b) multi-walled carbon nanotubes obtained under 6.5 kPa nitrogen.

[0021] Figure 4 Transmission electron microscope (TEM) image, multi-walled carbon nanotubes obtained under 60 kPa nitrogen.

[0022] Figure 5 Micro-Raman spectra of multi-walled carbon nanotubes synthesized under different conditions in the range of 1000-2000 cm-1.

[0023] Figure 1 An improved arc discharge experimental device is shown, in which two electrodes are placed vertically opposite to each other. The anode and cathode are made of conductive material, and a metal mesh (such as iron mesh) is placed above the electrodes, which serves as a precursor for condensing nanomaterials.

[0024] Figure 2 Samples prepared under different nitrogen pressures (from left to right) in the vacuum chamber (60 kPa, 6.5 kPa, 25 kPa, respectively).

[0025] Figures 3-4 Transmission electron microscope (TEM) image of multi-walled carbon nanotubes prepared. Figure 3 Multi-walled carbon nanotubes in are obtained under 25 kPa and 6.5 kPa nitrogen, respectively, using iron as a catalyst, Figure 4 Multi-walled carbon nanotubes obtained under 60 kPa nitrogen pressure. From the transmission electron microscope (TEM) characterization results, it can be seen that the morphological characteristics of multi-walled carbon nanotubes are affected by the buffer gas pressure. With the increase of gas pressure, the length of multi-walled carbon nanotubes becomes longer, and the boundary between the tube walls becomes more obvious.

[0026] Figure 5These are microscopic Raman spectra of multi-walled carbon nanotubes synthesized under different nitrogen pressures using iron as a catalyst, in the 1000-2000 cm⁻¹ range. Raman spectroscopy is typically based on two vibrational modes: the G mode and the D mode. The G mode gives characteristic peaks corresponding to graphitic carbon, while the D mode gives characteristic peaks corresponding to disordered carbon. According to... Figure 5 As shown, it is very clear that the G peak in all multi-walled carbon nanotubes is much higher than the D peak, indicating that there are fewer defects in the samples. With increasing gas pressure, the IG / ID value increases from 8.09 to 11.95. This indicates that the IG / ID values ​​of multi-walled carbon nanotubes synthesized under nitrogen pressure of 60 kPa are higher than those of other samples, demonstrating a higher degree of graphitization.

[0027] Beneficial effects of the present invention

[0028] 1. An improved arc discharge device of the present invention provides a uniform deposition substrate (metal mesh above or at both ends of the electrodes) with a suitable precursor growth mechanism, which can overcome the shortcomings of existing devices and prepare excellent nanomaterials.

[0029] 2. The multi-walled carbon nanotubes (MWCNTs) synthesized in this invention possess highly graphitized properties, providing a simple and low-cost method for producing high-quality MWCNTs. Experimental results show that, under a nitrogen atmosphere of 60 kPa, the MWCNTs synthesized using iron as a catalyst have an aspect ratio exceeding 1000, a diameter of approximately 12 nm, and a typical length of 25 μm. The center width of the MWCNTs is approximately 3 nm.

Claims

1. An arc discharge device for material preparation, wherein in order to provide a uniform deposition substrate suitable for the precursor growth mechanism, thereby enabling controllable material preparation, the technical solution is to provide a substrate for precursor aggregation by installing one or more metal meshes above or at both ends of the electrodes in the vacuum chamber of a conventional arc discharge device. The equipment consists of a gas supply system, a gas extraction system, a cooling system, a vacuum reaction chamber, a metal mesh substrate, electrodes, and an electrical control system. Its features are: In the above-mentioned device, the metal mesh substrate is installed above the vertical electrode pair or at both ends of the horizontal electrode pair; there can be one or more metal meshes, which can be meshes made of metal materials, such as iron mesh, nickel mesh, etc.

2. A method for preparing multi-walled carbon nanotubes using an arc discharge device, characterized in that, Includes the following steps: (1) The experimental synthesis of carbon nanotubes (CNTs) was carried out in an arc discharge device in which two electrodes were placed vertically or horizontally opposite each other. The anode and cathode were made of pure graphite rods. (2) Weigh metal powder and graphite powder in a certain proportion, mix them, and then fill them into the anode without grinding or grinding. (3) After installing the electrodes, evacuate the vacuum chamber and fill it with nitrogen gas until a certain vacuum level is reached. Apply a certain voltage to the electrodes at a set pressure (pressure range of 40 kPa to 80 kPa) to generate an electric arc discharge. The electric arc discharge lasts for a certain period of time, and various nanomaterials are obtained in different parts of the vacuum chamber. (4) High-quality multi-walled carbon nanotubes were also obtained.

3. The method for preparing multi-walled carbon nanotubes using the arc discharge device according to claim 2, characterized in that: The arc discharge device described herein may be an improved arc discharge device as described in claim 1.

4. The method for preparing multi-walled carbon nanotubes using the arc discharge device according to claim 2, characterized in that: The metal powder can be a mixture of several metal powders or a single metal powder, such as iron powder or nickel powder.

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