Iron-molybdenum-based catalyst and its preparation method and application in the preparation of single-walled carbon nanotubes

Abstract

The present invention discloses an iron-molybdenum-based catalyst, a preparation method thereof, and an application thereof in the preparation of single-walled carbon nanotubes. The preparation method of the iron-molybdenum-based catalyst comprises: inputting an easily decomposable catalyst precursor and a sulfur promoter into a plasma arc device, and then obtaining a sulfur-modified iron-molybdenum-based catalyst under the action of hydrogen and plasma arc; wherein the easily decomposable catalyst precursor comprises a metallocene. The present invention utilizes the transient reaction advantage of plasma rapidly cracking carbon sources to form carbon atoms and combining with iron-molybdenum-based catalysts to efficiently grow single-walled carbon nanotubes; at the same time, the introduction of molybdenum plays a role in refining iron particles, which is beneficial to the formation of single-walled carbon nanotubes, and realizes the efficient preparation of single-walled carbon nanotubes with high crystallinity and high purity.

Description

Technical Field

[0001] The invention belongs to the technical field, and specifically relates to an iron-molybdenum-based catalyst and a preparation method thereof and an application thereof in preparing single-walled carbon nanotubes. Background Art

[0002] Single-walled carbon nanotubes can be regarded as geometric structures formed by curling up a single layer of graphene. Due to the full carbon-carbon covalent bond characteristics in the structure, it exhibits excellent thermodynamic, electrical and other properties, and is therefore also regarded as an industrial universal additive. With the rapid development of my country's new energy vehicles and energy storage battery industries, the use of single-walled carbon nanotubes with excellent conductive properties will increase significantly. At present, only Russia's OCSIAL company has the ability to mass-produce single-walled carbon nanotubes on a large scale in the world. Therefore, achieving domestic substitution of single-walled carbon nanotube materials in my country is of great significance to the development of my country's new energy and high-tech.

[0003] The methods that have been studied more in the preparation of single-walled carbon nanotubes are chemical vapor deposition, laser evaporation, and plasma arc. However, these methods are still insufficient and generally cannot meet the requirements of large-scale mass production. Among them, the plasma arc method is considered to be a very promising method. This method can provide very high temperatures and ionize high-energy particles, reduce the reaction barrier, and thus quickly crack the carbon source, which is conducive to the formation of high-crystallinity single-walled carbon nanotubes. However, the problem is that its efficiency in decomposing carbon sources is too high, resulting in the commonly used solid catalysts with high decomposition temperatures (mainly iron, cobalt, nickel, and their oxides) and sulfur additives (mainly sulfur powder, iron sulfide and ferrous sulfide) not being able to keep up with the supply speed of carbon atoms, which results in carbon atoms coating the catalyst particles, poisoning the catalyst, and low yield and purity, and cannot be prepared continuously on a large scale. At the same time, high temperatures tend to make iron atoms grow further, which is not conducive to the formation of single-walled carbon nanotubes. Summary of the invention

[0004] The main purpose of the present invention is to provide an iron-molybdenum-based catalyst and a preparation method thereof and an application in the preparation of single-walled carbon nanotubes to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0006] The embodiment of the present invention provides a method for preparing an iron-molybdenum-based catalyst, which comprises:

[0007] An easily decomposable catalyst precursor and a sulfur promoter are introduced into a plasma arc device, and then a sulfur-modified iron-molybdenum-based catalyst is obtained under the action of hydrogen and plasma arc; wherein the easily decomposable catalyst precursor includes a metallocene.

[0008] The embodiment of the present invention also provides an iron-molybdenum-based catalyst prepared by the aforementioned preparation method.

[0009] The embodiment of the present invention also provides the use of the aforementioned iron-molybdenum-based catalyst in the preparation of single-walled carbon nanotubes by a plasma method.

[0010] The embodiment of the present invention also provides a method for preparing single-walled carbon nanotubes by a plasma method, which comprises:

[0011] An easily decomposable catalyst precursor, a sulfur promoter, and a carbon source gas are input into a plasma arc device, and then under the action of hydrogen and plasma arc, a sulfur-modified iron-molybdenum-based catalyst and single-walled carbon nanotubes grown on the catalyst surface are obtained; wherein the easily decomposable catalyst precursor includes a metallocene.

[0012] The embodiment of the present invention also provides single-walled carbon nanotubes prepared by the aforementioned method.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The synthesis process of the iron-molybdenum-based catalyst in the present invention is simple and does not require an additional synthesis process. It is generated in situ during the plasma arc process of preparing carbon nanotubes. In addition, the raw material source is wide, the preparation cycle is extremely short, the repeatability is good, and it can be mass-produced;

[0015] (2) The iron-molybdenum-based catalyst of the present invention selects a catalyst precursor and a sulfur promoter that are extremely easy to decompose, and the two are synchronously matched with a rapidly decomposing carbon source, forming a synchronous coordinated reaction of the catalyst, the sulfur promoter, and the carbon source, thereby solving the problem that the current plasma arc has the advantages of high temperature and ionization of high-energy particles, thereby providing the high energy required for the high reaction barrier, but due to the lack of a more matching catalyst, carbon-coated catalyst particles are formed, resulting in catalyst deactivation, low yield, poor quality, and inability to be mass-produced;

[0016] (3) The catalyst of the present invention selects an easily decomposable molybdenum alkene compound as a molybdenum source, which can react with the decomposed iron atoms in time to form an active substance similar to an iron-molybdenum alloy. The introduction of molybdenum can further inhibit the aggregation and growth of iron atoms under high temperature of the arc, which is beneficial to the formation of single-walled carbon nanotubes;

[0017] (4) The method provided by the present invention realizes the continuous and regular preparation of high-quality single-walled carbon nanotubes, the Raman IG / ID ratio of the product is not less than 38, the product purity is above 85%, and has great commercial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is a scanning electron microscope image of the carbon nanotubes prepared in Example 1 of the present invention;

[0020] Figure 2 This is a Raman spectrum of the carbon nanotubes prepared in Example 1 of the present invention;

[0021] Figure 3 This is a transmission electron microscope image of the carbon nanotubes prepared in Example 1 of the present invention;

[0022] Figure 4 This is a thermogravimetric test curve of the carbon nanotubes prepared in Example 1 of the present invention;

[0023] Figure 5 This is a scanning electron microscope image of the carbon nanotubes prepared in Example 2 of the present invention;

[0024] Figure 6 This is a Raman spectrum of the carbon nanotubes prepared in Example 2 of the present invention;

[0025] Figure 7 This is a thermogravimetric test curve of carbon nanotubes prepared in Example 2 of the present invention;

[0026] Figure 8 This is a transmission electron microscope image of the product prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In view of the defects of the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution utilizes easily decomposable metallocenes and sulfur promoters to decompose transiently under the high temperature and high-energy particle impact of the plasma arc, and are reduced to iron and molybdenum metal atoms by hydrogen, and further combine with sulfur atoms to form a sulfur-modified iron-molybdenum-based catalyst. The formed catalyst violently collides and reacts with the carbon atoms produced by the high-speed decomposition of the gaseous carbon source under the plasma arc, and rapidly grows single-walled carbon nanotubes. The advantages of the transient reaction of the plasma rapidly cracking the carbon source to form carbon atoms and combining with the catalyst are fully explored and utilized, and single-walled carbon nanotubes are efficiently grown. At the same time, the introduction of molybdenum plays a role in refining the iron particles, which is beneficial to the formation of single-walled carbon nanotubes, thereby realizing the efficient preparation of single-walled carbon nanotubes with high crystallinity and high purity.

[0028] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Specifically, as one aspect of the technical solution of the present invention, a method for preparing an iron-molybdenum-based catalyst involves:

[0030] An easily decomposable catalyst precursor and a sulfur promoter are introduced into a plasma arc device, and then a sulfur-modified iron-molybdenum-based catalyst is obtained under the action of hydrogen and plasma arc; wherein the easily decomposable catalyst precursor includes a metallocene.

[0031] In some preferred embodiments, the preparation method specifically comprises:

[0032] The easily decomposable catalyst precursor, the sulfur promoter and the solvent are mixed and ultrasonically dispersed to form a catalyst precursor mixture; wherein the easily decomposable catalyst precursor includes an iron source and a molybdenum source;

[0033] And, the plasma arc device is evacuated, and then an inert gas is introduced to start the arc so that the temperature of the device rises to 2000-4000°C, and then hydrogen is introduced and the catalyst precursor mixture is input to react to obtain a sulfur-modified iron-molybdenum-based catalyst.

[0034] Furthermore, the reaction is an instantaneous in-situ reaction.

[0035] Further, the iron source includes ferrocene and / or ethylferrocene, but is not limited thereto.

[0036] Further, the molybdenum source includes dihydrogenated molybdenumocene and / or dichloromolybdenumocene, but is not limited thereto.

[0037] Furthermore, the sulfur promoter includes any one or more combinations of thiourea, thioamide, and ethyl mercaptan, but is not limited thereto.

[0038] Furthermore, the solvent includes any one or more combinations of ethanol, ethylene glycol, and glycerol, but is not limited thereto.

[0039] Furthermore, the inert gas includes any one or more combinations of argon, nitrogen, and helium, but is not limited thereto.

[0040] Furthermore, the molar ratio of the iron source, the molybdenum source and the sulfur additive is 1:0.05-0.1:0.3-0.7.

[0041] Furthermore, the ultrasonic dispersion time is 30-90 min.

[0042] Furthermore, the speed of inputting the catalyst precursor mixture into the plasma arc device is 0.2-0.6 mL / min.

[0043] Furthermore, the inert gas has an inlet flow rate of 20-40 L / min.

[0044] Furthermore, the hydrogen gas has an inlet flow rate of 3-6 L / min.

[0045] Furthermore, the parameters adopted by the plasma arc device include: arc power supply power ≥ 10kW, voltage 30-200V, and current 75-500A.

[0046] Another aspect of the embodiments of the present invention further provides an iron-molybdenum-based catalyst prepared by the aforementioned preparation method.

[0047] Another aspect of the embodiments of the present invention further provides the use of the aforementioned iron-molybdenum-based catalyst in the preparation of single-walled carbon nanotubes by a plasma method.

[0048] Another aspect of the embodiments of the present invention further provides a method for preparing single-walled carbon nanotubes by a plasma method, which comprises:

[0049] An easily decomposable catalyst precursor, a sulfur promoter, and a carbon source gas are input into a plasma arc device, and then under the action of hydrogen and plasma arc, a sulfur-modified iron-molybdenum-based catalyst and single-walled carbon nanotubes grown on the catalyst surface are obtained; wherein the easily decomposable catalyst precursor includes a metallocene.

[0050] In some preferred embodiments, the method specifically comprises:

[0051] The easily decomposable catalyst precursor, the sulfur promoter and the solvent are mixed and ultrasonically dispersed to form a catalyst precursor mixture; wherein the easily decomposable catalyst precursor includes an iron source and a molybdenum source;

[0052] Furthermore, the plasma arc device is evacuated, and then an inert gas is introduced to strike the arc so that the temperature of the device rises to 2000-4000°C, and then hydrogen and carbon source gas are introduced and the catalyst precursor mixture is input for reaction, thereby obtaining a sulfur-modified iron-molybdenum-based catalyst and single-walled carbon nanotubes grown on the catalyst surface.

[0053] Further, the iron source includes ferrocene, but is not limited thereto.

[0054] Further, the molybdenum source includes dihydrogenated molybdenumocene and / or dichloromolybdenumocene, but is not limited thereto.

[0055] Furthermore, the sulfur promoter includes any one or more combinations of thiourea, thioamide, and ethyl mercaptan, but is not limited thereto.

[0056] Furthermore, the solvent includes any one or more combinations of ethanol, ethylene glycol, and glycerol, but is not limited thereto.

[0057] Furthermore, the inert gas includes any one or more combinations of argon, nitrogen, and helium, but is not limited thereto.

[0058] Furthermore, the carbon source gas includes any one or more combinations of methane, ethane, and acetylene, but is not limited thereto.

[0059] Furthermore, the molar ratio of the iron source, the molybdenum source and the sulfur additive is 1:0.05-0.1:0.3-0.7.

[0060] Furthermore, the ultrasonic dispersion time is 30-90 min.

[0061] Furthermore, the speed of inputting the catalyst precursor mixture into the plasma arc device is 0.2-0.6 mL / min.

[0062] Furthermore, the inert gas has an inlet flow rate of 20-40 L / min.

[0063] Furthermore, the hydrogen gas has an inlet flow rate of 3-6 L / min.

[0064] Furthermore, the carbon source gas has an inlet flow rate of 6-10 L / min.

[0065] Furthermore, the parameters adopted by the plasma arc device include: arc power supply power ≥ 10kW, voltage 30-200V, and current 75-500A.

[0066] In some more specific embodiments, the method for preparing single-walled carbon nanotubes by plasma method comprises:

[0067] The easily decomposable catalyst precursor (iron source and molybdenum source) and the sulfur additive are dissolved in a solvent and ultrasonically dispersed. The plasma arc furnace is then evacuated and an inert gas is introduced therein to initiate an arc. When the temperature in the arc furnace rises to a certain value, hydrogen and carbon source gases are introduced therein. At the same time, the ultrasonically treated catalyst and sulfur additive mixture is delivered to the arc region through an injection pump. Under the high temperature of the plasma arc and the impact of high-energy particles, the carbon source, the easily decomposable catalyst and the additive are instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms bound to the surface act as catalysts to adsorb carbon atoms, thereby completing the growth of single-walled carbon nanotubes.

[0068] Furthermore, the iron source is ferrocene; the molybdenum source is at least one of dihydrogenated molybdenumcene or dichloromolybdenumcene; and the sulfur promoter is at least one of thiourea, thioamide and ethanethiol.

[0069] Furthermore, the solvent is at least one of ethanol, ethylene glycol and glycerol, wherein the volume of the solvent is 100 times the mass of the iron source; the ultrasonic dispersion time is 30-90 minutes, and the catalyst injection speed is 0.2-0.6 mL / min.

[0070] Furthermore, the molar ratio of the iron source, the molybdenum source and the sulfur additive is 1:0.05-0.1:0.3-0.7.

[0071] Furthermore, the inert gas is at least one of argon, nitrogen and helium, and the carbon source gas is at least one of methane, ethane and acetylene.

[0072] Furthermore, the introduction rates of the carbon source gas, the inert gas and the hydrogen are 6-10 L / min, 20-40 L / min and 3-6 L / min respectively.

[0073] Furthermore, the reaction temperature of the electric arc furnace is 2000-4000° C. The power of the electric arc furnace is not less than 10 kW, the voltage is 30-200 V, and the current is 75-500 A.

[0074] Another aspect of the embodiments of the present invention further provides single-walled carbon nanotubes prepared by the aforementioned method.

[0075] Furthermore, the Raman spectroscopy of the single-walled carbon nanotubes G / I D The ratio is above 38.

[0076] Furthermore, the purity of the single-walled carbon nanotubes is greater than 85%.

[0077] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0078] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0079] Example 1

[0080] 0.016mol ferrocene, 0.0016mol dichloromolybdenum cyclopentadienyl and 0.008mol thiourea were dissolved in 300mL ethanol and ultrasonically dispersed for 30min. The plasma arc furnace was then vacuumed, and argon gas was introduced into the furnace at a gas flow rate of 20L / min to start the arc. At this time, the power supply voltage and current were set to 40V and 300mA, respectively. When the temperature in the arc furnace was raised to 2200°C, hydrogen and methane were introduced into the furnace at a gas flow rate of 3L / min and 8L / min, respectively. At the same time, the ultrasonic catalyst and sulfur additive mixture were sent into the arc region at an injection rate of 0.3mL / min by a syringe pump. Under the high temperature and high-energy particle impact of the plasma arc, the carbon source, catalyst and additive were instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms adsorbed on the surface were used as catalysts to adsorb carbon atoms and grow single-walled carbon nanotubes. Figure 1 The electron microscope image of the carbon nanotube product; the Raman spectrum is as follows Figure 2 As shown in the figure, it can be seen that in the range of 100-300cm -1 There is an obvious RBM characteristic peak of single-walled carbon nanotubes between the two, and the calculated I G / I D The ratio is 55, indicating that the product has high crystallinity; transmission electron microscopy Figure 3 It also shows that the product is single-walled carbon nanotubes; the product thermogravimetric test curve Figure 4 This indicated that the impurity residue was 14.1%, i.e., the product purity was 85.9%.

[0081] Example 2

[0082] 0.016mol ferrocene, 0.0016mol dichloromolybdenum cyclopentadienyl and 0.008mol ethanethiol were dissolved in 300mL ethanol and ultrasonically dispersed for 30min. The plasma arc furnace was then vacuumed, and argon gas was introduced into the furnace at a gas flow rate of 20L / min for arc initiation. At this time, the power supply voltage and current were 40V and 300mA, respectively. When the temperature in the arc furnace was raised to 2200°C, hydrogen and methane were introduced into the furnace at gas flows of 3L / min and 6L / min, respectively. At the same time, the ultrasonic catalyst and sulfur additive mixture were sent into the arc region at an injection rate of 0.3mL / min by a syringe pump. Under the high temperature and high-energy particle impact of the plasma arc, the carbon source, catalyst and additive were instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms adsorbed on the surface were used as catalysts to adsorb carbon atoms and grow single-walled carbon nanotubes. Figure 5 The electron microscope image of the carbon nanotube product; the Raman spectrum is as follows Figure 6 As shown in the figure, it can be seen that in the range of 100-300cm -1 There is an obvious RBM characteristic peak of single-walled carbon nanotubes between the two, and the calculated IG / I D The ratio is 38, indicating that the product has high crystallinity; the product thermogravimetric test curve Figure 7 This indicated that the impurity residue was 13.7%, i.e., the product purity was 86.3%.

[0083] Example 3

[0084] 0.016mol ferrocene, 0.001mol dichloromolybdenum cyclopentadienyl, and 0.008mol thioamide were dissolved in 300mL ethanol and ultrasonically dispersed for 30min. The plasma arc furnace was then vacuumed, and argon was introduced into the furnace at a gas flow rate of 20L / min to start the arc. At this time, the power supply voltage and current were 45V and 300mA, respectively. When the temperature in the arc furnace was raised to 2400°C, hydrogen and methane were introduced into the furnace at gas flows of 3L / min and 8L / min, respectively. At the same time, the ultrasonic catalyst and sulfur additive mixture were sent into the arc region at an injection rate of 0.3mL / min by a syringe pump. Under the high temperature and high-energy particle impact of the plasma arc, the carbon source, catalyst, and additive were instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms adsorbed on the surface were used as catalysts to adsorb carbon atoms and grow single-walled carbon nanotubes. The I of the obtained carbon nanotube product G / I D The ratio was 42, indicating that the product had high crystallinity; the product purity was 87.7%.

[0085] Example 4

[0086] 0.016mol ferrocene, 0.001mol dihydrogenated molybdenum cyclopentadienyl, and 0.008mol thiourea were dissolved in 300mL ethanol and ultrasonically dispersed for 30min. The plasma arc furnace was then vacuumed, and argon gas was introduced into the furnace at a gas flow rate of 20L / min to start the arc. At this time, the power supply voltage and current were 45V and 300mA, respectively. When the temperature in the arc furnace was raised to 2400°C, hydrogen and methane were introduced into the furnace at gas flows of 3L / min and 6L / min, respectively. At the same time, the ultrasonic catalyst and sulfur additive mixture were sent into the arc region at an injection rate of 0.3mL / min by an injection pump. Under the high temperature and high-energy particle impact of the plasma arc, the carbon source, catalyst, and additive were instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms adsorbed on the surface were used as catalysts to adsorb carbon atoms and grow single-walled carbon nanotubes. The I of the obtained carbon nanotube product G / I D The ratio was 44, indicating that the product had high crystallinity; the product purity was 88.3%.

[0087] Example 5

[0088] 0.016mol ferrocene, 0.0016mol dihydrogenated molybdenum cyclopentadienyl, and 0.008mol ethanethiol were dissolved in 300mL ethanol and ultrasonically dispersed for 30min. The plasma arc furnace was then vacuumed, and argon was introduced into the furnace at a gas flow rate of 30L / min to start the arc. At this time, the power supply voltage and current were 40V and 300mA, respectively. When the temperature in the arc furnace was raised to 2200°C, hydrogen and methane were introduced into the furnace at a gas flow rate of 4L / min and 8L / min, respectively. At the same time, the ultrasonic catalyst and sulfur additive mixture were sent into the arc region at an injection rate of 0.3mL / min by a syringe pump. Under the high temperature and high-energy particle impact of the plasma arc, the carbon source, catalyst, and additive were instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms adsorbed on the surface were used as catalysts to adsorb carbon atoms and grow single-walled carbon nanotubes. The I of the obtained carbon nanotube product G / I D The ratio was 47, indicating that the product had high crystallinity; the product purity was 88.9%.

[0089] Example 6

[0090] 0.016mol ferrocene, 0.0016mol dihydrogenated molybdenum, and 0.006mol thiourea were dissolved in 300mL ethanol and ultrasonically dispersed for 30min. The plasma arc furnace was then vacuumed, and argon was introduced into the furnace at a gas flow rate of 30L / min to start the arc. At this time, the power supply voltage and current were 45V and 300mA, respectively. When the temperature in the arc furnace was raised to 2400°C, hydrogen and methane were introduced into the furnace at a gas flow rate of 4L / min and 6L / min, respectively. At the same time, the ultrasonic catalyst and sulfur additive mixture were sent into the arc region by an injection pump at an injection rate of 0.3mL / min. Under the high temperature and high-energy particle impact of the plasma arc, the carbon source, catalyst, and additive were instantly cracked and reduced by hydrogen. The reduced iron and molybdenum atoms and the sulfur atoms adsorbed on the surface were used as catalysts to adsorb carbon atoms and grow single-walled carbon nanotubes. The I of the obtained carbon nanotube product G / I D The ratio was 53, indicating that the product had high crystallinity; the product purity was 91.2%.

[0091] Comparative Example 1

[0092] The method is the same as in Example 1, except that dichlorodicyclopentadienyl molybdenum is absent. The transmission electron microscopy image of the product is as follows: Figure 8 As shown, it can be seen from the figure that in the absence of dichloromolybdenumcyclopentadienyl, the carbon nanotubes are multi-walled tubes, which is not conducive to the formation of single-walled carbon nanotubes.

[0093] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0094] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing single-walled carbon nanotubes by plasma method, characterized in that: include: The easily decomposable catalyst precursor, the sulfur promoter and the solvent are mixed and ultrasonically dispersed to form a catalyst precursor mixture; wherein the easily decomposable catalyst precursor comprises an iron source and a molybdenum source; the iron source is selected from ferrocene; the molybdenum source is selected from dihydrogenated molybdenumcene and / or dichloro molybdenumcene; the sulfur promoter is selected from any one or more combinations of thiourea, thioamide and ethanethiol; Furthermore, the plasma arc device is evacuated, and then an inert gas is introduced to strike the arc so that the temperature of the device rises to 2000-4000°C, and then hydrogen and carbon source gas are introduced and the catalyst precursor mixture is input for reaction, thereby obtaining a sulfur-modified iron-molybdenum-based catalyst and single-walled carbon nanotubes grown on the catalyst surface.

2. The method according to claim 1, characterized in that: The solvent is selected from any one or more combinations of ethanol, ethylene glycol and glycerol.

3. The method according to claim 1, characterized in that: The inert gas is selected from any one or more combinations of argon, nitrogen and helium.

4. The method according to claim 1, characterized in that: The carbon source gas is selected from any one or more combinations of methane, ethane and acetylene.

5. The method according to claim 1, characterized in that: The molar ratio of the iron source, the molybdenum source and the sulfur additive is 1:0.05-0.1:0.3-0.

7.

6. The method according to claim 1, characterized in that: The ultrasonic dispersion time is 30-90 min.

7. The method according to claim 1, characterized in that: The catalyst precursor mixture is fed into the plasma arc device at a rate of 0.2-0.6 mL / min.

8. The method according to claim 1, characterized in that: The inert gas flow rate is 20-40 L / min.

9. The method according to claim 1, characterized in that: The hydrogen gas has an inlet flow rate of 3-6 L / min; and / or the carbon source gas has an inlet flow rate of 6-10 L / min.

10. The method according to claim 1, characterized in that: The parameters adopted by the plasma arc device include: arc power supply power ≥ 10kW, voltage 30-200V, and current 75-500A.

11. A single-walled carbon nanotube prepared by the method according to any one of claims 1 to 10, characterized in that: The Raman I G / I D The ratio is above 38; the purity of the single-walled carbon nanotubes is greater than 85%.

Images