A layered catalyst electrode based on plasma arc method for preparing single-walled carbon nanotubes and its preparation method.

Abstract

This invention relates to a layered catalyst electrode for preparing single-walled carbon nanotubes using a plasma arc method and its preparation method. This method, by designing a layered catalyst electrode with an outer catalyst layer, an intermediate controlled-release layer, and an inner support layer, precisely controls the time-space release of the catalyst, optimizing the catalyst supply process. By adjusting the arc parameters and reaction atmosphere, the initial instantaneous release peak of the catalyst is effectively reduced, catalyst agglomeration is suppressed, the yield and quality of single-walled carbon nanotubes are significantly improved, and metal residue is reduced. This method is suitable for continuous production; the layered electrode can improve service life and operational stability, demonstrating strong engineering feasibility and industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation, specifically relating to a layered catalyst electrode for preparing single-walled carbon nanotubes based on the plasma arc method and its preparation method. Background Technology

[0002] Single-walled carbon nanotubes (SUVs) are one-dimensional tubular nanomaterials formed by rolling up a single layer of graphene sheets. They possess excellent electrical, mechanical, and thermal properties and have significant application value in fields such as electronic devices, energy storage, composite materials, and biomedicine. Preparing high-purity SUVs with low metal residue and controllable diameter is one of the core challenges for industrialization.

[0003] Currently, commonly used methods for preparing single-walled carbon nanotubes include chemical vapor deposition (CVD), plasma arc discharge (PAD), and laser evaporation. Among these, CVD is the mainstream method for industrialization due to its cost and controllability, while PAD still holds advantages in producing high-quality samples due to its ability to generate high carbon vapor density and highly crystalline products. The PAD method differs significantly from CVD in its mechanism and process control. In the arc environment, the gaseous processes, the evaporation and condensation behavior of the metal, and the thermal field-gas flow coupling determine the carbon nucleation and growth kinetics.

[0004] In traditional electric arc methods, catalysts are typically obtained by mixing metal powder with graphite to form a consumable anode, or by sprinkling / coating catalyst precursors onto the electrode surface. However, existing technologies suffer from the following problems: the catalyst is often rapidly evaporated in the initial stage of discharge, leading to uncontrollable catalyst release rates; catalyst agglomeration and high metal residue affect product purity; and product quality fluctuates significantly over time during continuous preparation. To improve continuous production, various device improvements have been adopted, such as catalyst-in-crucible and catalyst-carbon source partitioning. However, these solutions still have shortcomings in controlling the timing of catalyst supply, avoiding initial release peaks, and suppressing agglomeration.

[0005] In chemical vapor deposition systems, the strategy of dispersing catalysts on supports such as MgO / Al2O3 / carbon-based porous materials to control particle size and slow metal release has been widely adopted. Supports such as MgO are soluble in acid, facilitating post-processing and promoting high single-walled carbon nanotube yields. Referring to similar design concepts, this invention proposes directly constructing a layered catalyst structure as an electrode, and provides a matching device and method to achieve time-space release control of the catalyst in a plasma arc environment. This results in a stable increase in the yield and quality of single-walled carbon nanotubes, reduced metal residue, and compatibility with continuous operation. Summary of the Invention

[0006] The purpose of this invention is to provide a layered catalyst electrode and a method for preparing single-walled carbon nanotubes using a plasma arc method. By introducing a layered catalyst structure into the electrode and coordinating it with arc parameters and atmosphere control, the invention solves the problems of uncontrollable catalyst release, catalyst agglomeration, product quality fluctuations over time, and difficulty in achieving continuous production in the prior art.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing a layered catalyst electrode of single-walled carbon nanotubes based on a plasma arc method, characterized by comprising the following steps:

[0009] (1) A layered catalyst electrode is provided as an anode, wherein the electrode comprises an outer catalyst layer, an intermediate slow-release layer and an inner conductive support layer in sequence along its axial or radial direction;

[0010] (2) Start the vacuum system, remove the air from the reaction chamber, switch to introduce carrier gas to establish a protective atmosphere, and ignite the plasma arc between the anode and cathode by applying electricity;

[0011] (3) A carbon-containing gas mixture is introduced into the reaction chamber, and the carbon-containing gas is decomposed in the electric arc zone under the action of high temperature of electric arc to generate carbon active species.

[0012] (4) During the discharge process, by controlling the arc parameters and reaction atmosphere, the layered catalyst electrode is driven to release the catalyst in a programmed manner, thereby catalyzing the growth of the carbon active species into single-walled carbon nanotubes.

[0013] (5) The generated carbon products are captured in the collection unit and post-processed to obtain high-purity single-walled carbon nanotube products.

[0014] Furthermore, the carbon-containing gas mixture includes organic carbon-containing gases and carrier gases.

[0015] Further, the carbon-containing gas is one or more of methane, ethylene, acetylene, or propane; the carrier gas is a mixture of an inert gas and hydrogen; and the inert gas is one or more of nitrogen, argon, or helium.

[0016] Furthermore, the volume fraction of carbon-containing gas accounts for 5-60% of the total flow rate of the reaction gas; the volume fraction of hydrogen gas accounts for 0.1-20% of the total flow rate of the reaction gas, with the remainder being inert gases; the flow rate of the reaction gas is 1-300 L / min.

[0017] Furthermore, the plasma arc furnace has a power of 10-300 kW, a voltage of 100-1000 V, a current of 100-1000 A, and an arc gap of 1-5 mm.

[0018] Furthermore, the preparation process is divided into a nucleation stage and a growth stage, using different discharge parameters; the current in the nucleation stage is preferably 300-1000 A, with a duration of 0.5-30 min; the current in the growth stage is preferably 100-800 A, with a duration of 0.5-24 h.

[0019] Furthermore, the device is equipped with an automatic clamping or pushing mechanism for holding or pushing the electrode at a low speed to maintain the stability of the arc gap; the pushing rate is preferably 0.01-5 mm / min.

[0020] Furthermore, a layered electrode for a layered catalyst electrode based on the plasma arc method for preparing single-walled carbon nanotubes is provided, wherein the electrode is provided with an outer catalyst layer, an intermediate slow-release layer and an inner support layer in a radial or axial direction.

[0021] Furthermore, the outer catalyst layer comprises one of iron, cobalt, nickel and their alloy nanoparticles or a metal precursor; the average particle size of the nanoparticles is preferably 2-20 nm; the metal content in the outer layer is preferably 1-20 wt% of the outer layer mass; and the thickness of the outer layer is preferably 10-200 μm.

[0022] Furthermore, the intermediate sustained-release layer is composed of one or more of MgO, Al2O3, SiO2 or carbon-based porous materials; the pore size of the intermediate sustained-release layer is preferably 5-200 nm; the porosity of the intermediate sustained-release layer is preferably 10%-60%; and the thickness of the intermediate sustained-release layer is preferably 50-500 μm.

[0023] Furthermore, the inner support layer is a high-density graphite or carbon-metal composite; the thickness of the inner support layer is ≥1 mm.

[0024] Furthermore, the layered electrode can be a solid or hollow cylindrical rod with a diameter of 6-50 mm and a length of 50-500 mm.

[0025] The beneficial effects of this invention are:

[0026] This invention achieves concentrated initial catalyst supply and continuous subsequent replenishment by constructing an outer-middle-inner layer design within the electrode. This smooths the metal supply curve over time, reduces the initial instantaneous release peak of the catalyst, and inhibits metal agglomeration. The method is compatible with continuous production and adaptable to the continuous supply of carbon-containing gases. The optimized layered electrodes have a long service life, and combined with an automatic electrode propulsion mechanism, it improves the reliability of continuous operation and the stability of product quality. The layered structure design is engineering-feasible, and the material selection and preparation process can be flexibly adjusted according to the equipment scale and preparation purpose. Without significantly changing the main structure of the arc device, the technology can be upgraded by replacing the electrodes, facilitating engineering scale-up and industrialization. Attached Figure Description

[0027] The invention will now be further described with reference to the accompanying drawings.

[0028] Figure 1 This is a schematic diagram of the layered catalyst electrode adapted to plasma arc for preparing single-walled carbon nanotubes in this application.

[0029] Figure 2 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of this application. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Equivalent adjustments made without departing from the spirit and essence of the present invention should also be considered to fall within the protection scope of the present invention.

[0031] Example 1:

[0032] (1) Preparation of layered catalyst electrode: The inner support layer is a high-density graphite rod with a diameter of 20 mm and a length of 200 mm; the graphite rod is coated with MgO as an intermediate slow-release layer with an average pore size of about 100 nm, a porosity of about 30%, and a thickness of about 200 μm; the outer catalyst layer is a metallic iron layer deposited on the slow-release layer by magnetron sputtering with a thickness of about 30 μm and a metal content of 5 wt% of the outer layer mass; the layered catalyst electrode is installed as an anode in a plasma arc furnace.

[0033] (2) Reacting gas: The carbon-containing mixed gas consists of methane (25%), argon (70%) and hydrogen (5%), with a total gas flow rate of 50 L / min.

[0034] (3) Implement two-stage current control: The plasma arc furnace power is 50 kW; firstly, in the nucleation stage (0-5 min), a high current of 800 A is set to promote the rapid release of the outer catalyst and form high-density nucleation sites; then, in the growth stage (5-180 min), the current is reduced to 400 A to maintain stable growth and slow down excessive evaporation of the catalyst. The arc gap is maintained at 2 mm by an automatic propulsion system.

[0035] (4) Product collection and characterization: Black flocculent precipitate was collected downstream of the reaction chamber and acid-washed with hydrochloric acid (5 wt%) at 60°C for 1 hour to remove metal catalyst particles. After washing with deionized water and drying, the final product was obtained. Samples were taken for morphology observation by scanning electron microscopy, followed by Raman spectroscopy and thermogravimetric analysis to evaluate product quality.

[0036] Example 2:

[0037] (1) Preparation of layered catalyst electrode: The inner support layer is a high-density graphite rod with a diameter of 20 mm and a length of 200 mm; the graphite rod is coated with Al2O3 as an intermediate slow-release layer with an average pore size of about 120 nm, a porosity of about 30%, and a thickness of about 300 μm; the outer catalyst layer is a metallic iron-cobalt alloy (Fe60% Co40%) deposited on the slow-release layer by magnetron sputtering, with a thickness of about 50 μm and a metal content of 10 wt% of the outer layer mass; the layered catalyst electrode is installed as an anode in a plasma arc furnace.

[0038] (2) Reacting gas: The carbon-containing mixed gas consists of methane (40%), argon (50%) and hydrogen (10%), with a total gas flow rate of 100 L / min.

[0039] (3) Implement two-stage current control: The plasma arc furnace power is 50 kW; firstly, in the nucleation stage (0-10 min), a high current of 800 A is set to promote the rapid release of the outer catalyst and form high-density nucleation sites; then, in the growth stage (10-180 min), the current is reduced to 500 A to maintain stable growth and slow down excessive catalyst evaporation. The arc gap is maintained at 2 mm by an automatic propulsion system.

[0040] (4) Product collection and characterization: Black flocculent precipitate was collected downstream of the reaction chamber and acid-washed with hydrochloric acid (5 wt%) at 60°C for 1 hour to remove metal catalyst particles. After washing with deionized water and drying, the final product was obtained. Samples were taken for morphology observation by scanning electron microscopy, followed by Raman spectroscopy and thermogravimetric analysis to evaluate product quality.

[0041] Comparative Example 1:

[0042] (1) Preparation of conventional catalyst electrode: Iron and cobalt catalyst micro powders with a total amount equivalent to that in Example 2 were uniformly mixed with graphite powder and pressed into electrodes of the same size. The electrode has no layered structure and the catalyst is uniformly distributed.

[0043] (2) Reacting gas: The carbon-containing mixed gas consists of methane (25%), argon (70%) and hydrogen (5%), with a total gas flow rate of 50 L / min.

[0044] (3) A constant current discharge mode was adopted, with the current set at 500 A for 180 minutes. Due to uneven electrode consumption, the arc gap fluctuated significantly during the process.

[0045] (4) Product collection and characterization: Black flocculent precipitate was collected downstream of the reaction chamber and acid-washed with hydrochloric acid (5 wt%) at 60°C for 1 hour to remove metal catalyst particles. After washing with deionized water and drying, the final product was obtained. Samples were taken for morphology observation by scanning electron microscopy, followed by Raman spectroscopy and thermogravimetric analysis to evaluate product quality.

[0046] Table 1. Characterization test results of the examples and comparative examples.

[0047] sample Current / A <![CDATA[Raman spectrum I G / I D > purity Example 1 800、400 96 69.2% Example 2 800、500 108 78.3% Comparative Example 1 500 55 42.1%

[0048] As shown in Table 1, when using a traditional uniform catalyst electrode in the comparative example, the proportion of single-walled carbon nanotubes in the product was low, with a large number of multi-walled carbon nanotubes and amorphous carbon present. In the examples using the layered catalyst electrode and segmented current of the present invention, the proportion of single-walled carbon nanotubes in the product was significantly increased, the nanotube walls were clean, and there were fewer amorphous carbon impurities. Raman spectroscopy also showed that the product had a high degree of graphitization and few structural defects. In the embodiments of the present invention, the high-current nucleation stage causes the outer surface metal or precursor to evaporate rapidly, forming a large number of nanoscale metal particles. These fine metal particles provide a large number of active nucleation sites in the downstream cooling zone and promote the formation of carbon caps and single-walled nuclei; therefore, the nucleation density is increased, which is beneficial for obtaining more single-walled nuclei. The intermediate porous support releases the metal precursor or nanoparticles slowly through physical adsorption or support immobilization, avoiding excessive release from the outer layer that leads to aggregation, and continuously releases or maintains small-particle-size catalyst during the growth stage, thereby maintaining the catalyst concentration and activity during the growth stage and slowing down aggregation and metal particle growth. The inner high-density graphite layer provides electro-thermal-mechanical support and serves as a supplementary carbon source during high-discharge ablation. In realizations dominated by gas-phase carbon sources, the inner layer primarily functions as support rather than the main carbon source, thereby reducing the engineering impact of rapid anode consumption.

Claims

1. A method for preparing a layered catalyst electrode based on single-walled carbon nanotubes using a plasma arc method, characterized in that, Includes the following steps: (1) A layered catalyst electrode is provided as an anode, wherein the electrode comprises an outer catalyst layer, an intermediate slow-release layer and an inner conductive support layer in sequence along its axial or radial direction; (2) Start the vacuum system, remove the air from the reaction chamber, switch to introduce carrier gas to establish a protective atmosphere, and ignite the plasma arc between the anode and cathode by applying electricity; (3) A carbon-containing gas mixture is introduced into the reaction chamber, and the carbon-containing gas is decomposed in the electric arc zone under the action of high temperature of electric arc to generate carbon active species. (4) During the discharge process, by controlling the arc parameters and reaction atmosphere, the layered catalyst electrode is driven to release the catalyst in a programmed manner, thereby catalyzing the growth of the carbon active species into single-walled carbon nanotubes. (5) The generated carbon products are captured in the collection unit and post-processed to obtain high-purity single-walled carbon nanotube products.

2. The method for preparing a layered catalyst electrode based on a plasma arc method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, The carbon-containing gas mixture in step (3) includes organic carbon-containing gas and carrier gas.

3. A method for preparing a layered catalyst electrode based on a plasma arc method for preparing single-walled carbon nanotubes according to claim 1 or 2, characterized in that, The carbon-containing gas is one or more of methane, ethylene, acetylene, or propane; the carrier gas is a mixture of an inert gas and hydrogen; and the inert gas is one or more of nitrogen, argon, or helium.

4. A method for preparing a layered catalyst electrode based on a plasma arc method for preparing single-walled carbon nanotubes according to claim 1 or 2, characterized in that, The volume fraction of the carbon-containing gas accounts for 5-60% of the total flow rate of the reaction gas; the volume fraction of the hydrogen gas accounts for 0.1-20% of the total flow rate of the reaction gas, with the remainder being inert gases; the flow rate of the reaction gas is 1-300 L / min.

5. The method for preparing a layered catalyst electrode based on a plasma arc method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, The power of the plasma arc furnace in step (4) is 10-300 kW, the voltage is 100-1000 V, the current is 100-1000 A, and the arc gap is 1-5 mm.

6. The method for preparing a layered catalyst electrode based on a plasma arc method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, The preparation process is divided into a nucleation stage and a growth stage, using different discharge parameters; the current in the nucleation stage is preferably 300-1000 A, with a duration of 0.5-30 min; the current in the growth stage is preferably 100-800 A, with a duration of 0.5-24 h.

7. The method for preparing a layered catalyst electrode based on a plasma arc method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, The device is equipped with an automatic clamping or pushing mechanism to hold or push the electrode at a low speed to maintain the stability of the arc gap; the pushing rate is preferably 0.01-5 mm / min.

8. A layered electrode for a layered catalyst electrode prepared from single-walled carbon nanotubes using a plasma arc method, characterized in that, The electrode is provided with an outer catalyst layer, a middle slow-release layer and an inner support layer in a radial or axial direction.

9. The layered electrode of the layered catalyst electrode prepared by plasma arc method for single-walled carbon nanotubes according to claim 8, characterized in that, The outer catalyst layer comprises one of iron, cobalt, nickel and their alloy nanoparticles or metal precursors; the average particle size of the nanoparticles is preferably 2-20 nm; the metal content in the outer layer is preferably 1-20 wt% of the outer layer mass; and the thickness of the outer layer is preferably 10-200 μm.

10. The layered electrode of a layered catalyst electrode prepared by plasma arc method for single-walled carbon nanotubes according to claim 8, characterized in that, The intermediate sustained-release layer is composed of one or more of MgO, Al2O3, SiO2, or carbon-based porous materials; the pore size of the intermediate sustained-release layer is preferably 5-200 nm; the porosity of the intermediate sustained-release layer is preferably 10%-60%; the thickness of the intermediate sustained-release layer is preferably 50-500 μm; the inner support layer is high-density graphite or carbon-metal composite; the thickness of the inner support layer is 1-3 mm; the layered electrode can be a solid or hollow cylindrical rod with a diameter of 6-50 mm and a length of 50-500 mm.

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