In-situ preparation method of high-purity single-walled carbon nanotubes based on field-assisted growth

Abstract

The application discloses an in-situ preparation method of high-purity single-wall carbon nanotubes based on field-assisted growth, and belongs to the technical field of nanometer material preparation. The method integrates catalyst injection, pyrolysis, field-assisted purification growth, in-situ separation and powder collection steps in a floating catalyst chemical vapor deposition process; a coupled non-uniform electric field and a temperature gradient field with high temperature in the center and low temperature at the edge are constructed in a reaction zone, and the synergistic effect of dielectrophoresis force and thermophoresis force is utilized to make metal catalyst particles deviate from the center airflow and be deposited and removed, while single-wall carbon nanotubes continue to move with the center high-temperature airflow, so that the synchronous completion of growth and purification is realized. The application avoids structural damage to carbon tubes caused by offline purification, and the metal impurity content of the obtained product can be reduced to below 5wt.%, G / I D The ratio is high, the process is green and environmentally friendly, controllable, easy to continuous production, and suitable for multiple fields such as composite materials and conductive paste.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, and relates to an in-situ preparation method of high-purity single-walled carbon nanotubes based on field-assisted growth. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) possess excellent electrical, mechanical, and thermal properties, showing broad application prospects in composite materials, conductive pastes, electronic devices, and energy storage. Currently, floating catalyst chemical vapor deposition (FCCVD) is the mainstream technology for the mass production of SWCNTs, characterized by its simple process and high production efficiency, making it suitable for industrial production.

[0003] However, crude single-walled carbon nanotubes prepared by FCCVD typically contain a large number of residual metal catalyst particles (such as Fe and Co) and carbon impurities. These impurities severely restrict the intrinsic properties of single-walled carbon nanotubes and cannot meet the purity requirements of high-end applications. To remove these impurities, existing technologies all employ an offline processing mode of growth followed by purification. Common methods include gas-phase oxidation-acid treatment, liquid-phase oxidation purification-acid treatment, and supercritical fluid extraction. However, these offline purification methods have many inherent drawbacks: 1. Structural damage: Subsequent chemical steps such as oxidation and acid treatment will inevitably introduce defects into the sidewalls of single-walled carbon nanotubes, which can easily cause carbon nanotubes to break and shorten in length, destroying the integrity of the carbon nanotube structure and leading to a significant decrease in its performance. 2. Efficiency and cost issues: Multi-step offline operation will reduce the yield of single-walled carbon nanotubes, and the process is complicated, increasing production time and operating costs. 3. Environmental pollution: The pickling process generates a large amount of acidic waste liquid, which not only requires additional waste liquid post-treatment costs, but also easily causes environmental pollution.

[0004] Therefore, developing an integrated preparation method that can simultaneously remove metal impurities during the growth of single-walled carbon nanotubes and directly obtain high-purity, high-structural-integrity single-walled carbon nanotube powder products has become the key to breaking through the current bottleneck of single-walled carbon nanotube preparation technology, and is also a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an in-situ preparation method for high-purity single-walled carbon nanotubes based on field-assisted growth. This invention aims to simultaneously realize the growth and purification processes of single-walled carbon nanotubes, utilizing the synergistic effect of a physical field to efficiently remove metal catalyst impurities during carbon nanotube generation. This eliminates the need for subsequent offline chemical purification, directly yielding high-purity, high-crystallinity single-walled carbon nanotube powder products, thus solving problems such as structural damage, low efficiency, and environmental pollution associated with existing methods.

[0006] To achieve the above objectives, the present invention provides an in-situ preparation method for high-purity single-walled carbon nanotubes based on field-assisted growth, comprising the following steps: Step S1: Catalyst injection and pyrolysis: A carbon source solution containing catalyst precursor and growth promoter is injected into a vertical high-temperature reactor through a carrier gas. The catalyst precursor is pyrolyzed to form nano-metal catalyst particles, which catalyze the growth of single-walled carbon nanotubes. Step S2: Field-assisted purification and growth: A mixed gas flow containing the nano-metal catalyst particles and growing single-walled carbon nanotubes is passed through a composite field region coupled with a non-uniform electric field and a temperature gradient field; the non-uniform electric field is a radially non-uniformly distributed electric field perpendicular to the gas flow direction, and the temperature gradient field is a temperature gradient field with a high temperature at the center and a low temperature at the edge in the radial direction perpendicular to the gas flow direction. Step S3: In-situ separation: In the composite field region, the nano-metal catalyst particles are deviated from the central airflow and deposited and removed into the low-temperature zone of the vertical high-temperature reactor tube wall by the synergistic effect of dielectric force and thermophoresis force, and the single-walled carbon nanotubes are moved downstream with the central high-temperature airflow to achieve in-situ separation of single-walled carbon nanotubes and metal catalyst particles. Step S4: Powder collection: The airflow containing single-walled carbon nanotubes after in-situ separation is guided to the powder collection device to collect high-purity single-walled carbon nanotube powder.

[0007] Preferably, in step S1, the catalyst precursor is one or more of ferrocene and cobalt nitrate, or a combination of ferrocene and molybdenum acetylacetonate; the growth promoter is thiophene; the carbon source is toluene; and the carrier gas is hydrogen.

[0008] Preferably, in step S1, the vertical high-temperature reactor is a vertical high-temperature tube furnace; the injection rate of the carbon source solution is 5 μL / min; the carrier gas injection rate is 4000 sccm; and ethylene can also be introduced into the vertical high-temperature reactor as an auxiliary carbon source at an ethylene injection rate of 48 sccm.

[0009] Preferably, in step S1, the heating temperature of the reaction zone of the vertical high-temperature tubular furnace is 1000℃.

[0010] Preferably, in step S2, the non-uniform electric field is constructed by setting a rod-cylinder electrode in the rear section of the reaction zone of the vertical high-temperature reactor and applying AC high voltage; the temperature gradient field is constructed by setting a cooling device in the rear section of the reaction zone; the rear section is downstream of the airflow direction.

[0011] Preferably, the rod-cylinder electrode includes a high-voltage electrode rod disposed at the axial center of the vertical high-temperature reactor and a cylindrical grounding electrode attached to the reaction tube wall; the cooling device is a water-cooled jacket.

[0012] Preferably, in step S2, the voltage of the AC high voltage is 1~3kV and the frequency is 300Hz.

[0013] Preferably, in step S2, the center temperature of the temperature gradient field is 1000℃, and the temperature of the edge low-temperature zone is 300℃.

[0014] Preferably, in step S4, the powder collecting device is a filter bag dust collector.

[0015] Preferably, the high-purity single-walled carbon nanotube powder has a metal impurity content reduced to below 5 wt.%, and its Raman spectrum is [missing information]. G / I D If the ratio is greater than 70, the oxidation temperature in air is higher than 700℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In-situ integrated, non-destructive purification: The purification step is completely integrated into the growth process of single-walled carbon nanotubes (SUVs). Metal catalyst impurities are removed simultaneously with carbon nanotube formation, completely avoiding damage to the carbon nanotube structure caused by oxidation and acid treatment steps in traditional offline purification, such as tube breakage and defect introduction. This maximizes the preservation of the original length and structural integrity of the SUVs, resulting in a superior Raman spectrum of the powder product. G / I D It has a high ratio and extremely low defect content.

[0017] 2. Green and environmentally friendly, with high purification efficiency and low cost: This invention utilizes the synergistic effect of physical fields to achieve separation and purification without consuming any chemical reagents (acids, oxidants, etc.). The entire process generates no waste liquid or waste gas, making it green and environmentally friendly. At the same time, the equipment integration of the preparation process is high, and growth and purification are completed in one step, which is easy to realize continuous production, greatly reducing the time and cost of post-processing steps, and effectively ensuring the yield of single-walled carbon nanotubes.

[0018] 3. High product purity and wide applicability: High-purity single-walled carbon nanotube powder can be directly obtained through the method of this invention. The content of metal impurities can be reduced to below 5 wt.%, and to below 2 wt.% under some process parameters. Moreover, the product has an oxidation temperature in air above 700℃ and high crystallinity. It can directly meet the stringent purity requirements of composite materials, conductive pastes, energy storage, electronic devices and other fields without the need for additional purification treatment.

[0019] 4. Strong process controllability and good adaptability: By adjusting the intensity and frequency of the non-uniform electric field, the temperature difference of the temperature gradient field, and process parameters such as airflow velocity and carbon source solution injection rate, the separation efficiency of metal catalyst particles can be precisely controlled, and the purity of the final product can be flexibly controlled. At the same time, the method of this invention has good applicability to various catalyst systems such as ferrocene, cobalt nitrate, and ferrocene-molybdenum acetylacetonate, and can effectively remove impurities from various metal catalysts, adapting to different single-walled carbon nanotube growth requirements. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating an in-situ preparation method for high-purity single-walled carbon nanotubes according to a preferred embodiment of the present invention. Figure 2 A schematic diagram of an in-situ preparation process apparatus for high-purity single-walled carbon nanotubes according to a preferred embodiment of the present invention; Figure 3 Thermogravimetric analysis diagram of single-walled carbon nanotubes of preferred embodiment 1 of the present invention; Figure 4 I under different applied voltages in embodiments of the present invention G / I D Ratio change trend graph; In the diagram, 1. Vertical high-temperature reactor; 2. Carbon source solution inlet; 3. Carrier gas / auxiliary carbon source inlet; 4. Rod-cylinder electrode; 41. High-voltage electrode rod; 42. Cylindrical grounding electrode; 5. Cooling device (water-cooled jacket); 6. Composite field area; 7. Powder collection device (bag filter); 8. Exhaust port. Detailed Implementation

[0021] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The terms used in this specification, such as "front," "back," "left," "right," "inner," and "outer," are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered within the scope of the invention.

[0023] In the description of the following embodiments, unless otherwise expressly specified and limited, the term "connection" and other such terms should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an indirect connection through an intermediate medium; it can be the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] Figure 1 The flowchart shows the in-situ preparation method of high-purity single-walled carbon nanotubes based on field-assisted growth according to the present invention. The preparation method of the present invention mainly includes steps such as catalyst injection and pyrolysis, field-assisted purification and growth, in-situ separation and powder collection. Figure 2 This is a schematic diagram of the fabrication process apparatus. Figure 2 As shown, the process apparatus for implementing the in-situ preparation method of the present invention mainly includes a vertical high-temperature reactor 1, a carbon source solution inlet 2 and a carrier gas / auxiliary carbon source inlet 3 located at the top of the vertical high-temperature reactor 1, a rod-cylinder electrode 4 located at the rear section of the reaction zone of the vertical high-temperature reactor 1, a water-cooled jacket 5 located at the rear section of the reaction zone, a composite field region 6 formed by the rod-cylinder electrode 4 and the water-cooled jacket 5, a bag filter dust collector 7 located at the bottom of the vertical high-temperature reactor 1, and an exhaust port 8 located at the end of the bag filter dust collector 7. The rod-cylinder electrode 4 includes a high-voltage electrode rod 41 located at the axial center of the vertical high-temperature reactor 1 and a cylindrical grounding electrode 42 attached to the reaction tube wall, used to form a non-uniformly distributed electric field from the center to the tube wall.

[0025] The following combination Figure 1 , 2 The technical solution of the present invention will be described in detail through specific embodiments. Experimental methods that do not specify specific conditions in the embodiments are carried out in accordance with conventional methods and conditions, or selected in accordance with the product instructions.

[0026] Example 1: In-situ preparation of high-purity SWCNTs powder In this embodiment, a non-uniform electric field is constructed using rod-cylinder electrodes, a temperature gradient field is constructed using a water-cooled jacket, and ferrocene is used as the catalyst precursor. The specific steps are as follows: 1. Preparation of catalyst solution 3g of ferrocene (catalyst precursor) and 0.5g of thiophene (growth promoter) were dissolved in 100g of toluene (carbon source) and stirred at room temperature for 30min until completely dissolved to obtain a homogeneous catalyst precursor solution.

[0027] 2. FCCVD growth system setup A 4-inch vertical tube furnace is used as the vertical high-temperature reactor 1, and the constant temperature zone of the reaction tube is 60cm long (upper middle section of the reaction tube). A rod-cylinder electrode 4 is set in the rear section (lower section) of the reaction zone. The electrode 4 includes a 2mm diameter high-voltage electrode rod 41 set at the axial center of the tube furnace and a cylindrical grounding electrode 42 attached to the wall of the reaction tube. A water-cooled jacket 5 (cooling device) is set on the outside of the tube wall in the rear section of the reaction zone to establish a temperature gradient field in the radial direction of the airflow. The rod-cylinder electrode 4 and the water-cooled jacket 5 together form a composite field region in the rear section of the reaction tube. A filter bag dust collector 7 is connected at the outlet of the vertical tube furnace 1 as a powder collection device.

[0028] 3. Purification growth and in-situ separation process The reaction zone of the vertical tube furnace 1 is heated to 1000℃ and held at that temperature. 4000 sccm of hydrogen (carrier gas) and 48 sccm of ethylene (auxiliary carbon source) are introduced through the carrier gas / auxiliary carbon source inlet 3 to purge the reaction tube for 5 min. Then, the prepared catalyst precursor solution is injected into the reaction tube at a rate of 5 μL / min through the carbon source solution injection port 2. The catalyst precursor is pyrolyzed at 1000℃ to form nano-Fe catalyst particles, which catalyze the decomposition of toluene and ethylene, and begin to grow single-walled carbon nanotubes.

[0029] A mixed gas flow containing nano-Fe catalyst particles and growing single-walled carbon nanotubes moves downstream and enters the composite field region 6. A high-frequency alternating current of 2kV and 300Hz is applied to both ends of the rod-tube electrode 4, forming a non-uniformly distributed electric field in the radial direction (radial direction of the tube diameter) perpendicular to the gas flow direction. Simultaneously, cooling water is introduced through the water-cooling jacket 5, reducing the temperature of the reaction tube wall to approximately 300℃, forming a temperature gradient field with a center temperature of approximately 1000℃ and an edge temperature of approximately 300℃ in the radial direction perpendicular to the gas flow direction. In other words, on the cross-section of the furnace tube perpendicular to the gas flow direction, the temperature in the central region of the cross-section is approximately 1000℃, and the temperature near the edge of the tube wall is approximately 300℃, forming a temperature gradient along the radial direction of the tube diameter.

[0030] In the composite field region 6, the nano-Fe catalyst particles are polarized and, under the combined effect of dielectric and thermophoretic forces, deviate from the central high-temperature gas flow, migrate to the low-temperature region of the reaction tube wall and deposit on the tube wall, losing their catalytic activity; the single-walled carbon nanotubes are subjected to minimal forces from the composite field and continue to move downstream with the central high-temperature gas flow, achieving in-situ separation from the Fe catalyst particles.

[0031] 4. Powder collection Single-walled carbon nanotubes moving with the central airflow enter the bag filter dust collector 7. Through the filtration effect of the filter bag, the single-walled carbon nanotube powder is collected, and the purified gas is discharged from the exhaust port 8.

[0032] The properties of the single-walled carbon nanotube powder obtained in Example 1 were characterized, and the results are as follows: Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the residual Fe metal content in the single-walled carbon nanotube powder was 1.58 wt.%, lower than 2 wt.%; Raman spectroscopy analysis showed that the I content of the powder was... G / I D The ratio is 105, which is greater than 100, indicating that the single-walled carbon nanotubes have high crystallinity and extremely low defect content. Thermogravimetric analysis shows that the oxidation temperature of the sample in air is higher than 700℃, proving that the product has excellent purity and thermal stability, as shown in Figure 2.

[0033] The effects of different electric field strengths on product purity are examined below through examples and comparative examples.

[0034] Example 2: Using the same method and process parameters as in Example 1, only the AC high voltage applied to the rod-tube electrode was changed to 1kV.

[0035] Example 3: Using the same method and process parameters as in Example 1, only the AC high voltage applied to the rod-tube electrode was changed to 3kV.

[0036] Comparative Example 1: Using the same method and process parameters as in Example 1, only the AC high voltage applied to the rod-tube electrode was changed. The applied voltage was 0kV, with no electric field effect.

[0037] The results and data of the above embodiments and comparative examples were analyzed, and the results are shown in Table 1.

[0038] Table 1. Effect of different applied voltages on product properties I under different applied voltages G / I D The trend of the ratio is as follows Figure 3 As shown in Table 1, the results indicate that: 1. Without the influence of an electric field (Comparative Example 1), the residual metal content is 4.30 wt.%, I G / I D The ratio is only 70, indicating low product purity and crystallinity; 2. As the applied voltage increases, the amount of residual metal gradually decreases, and the purification effect improves; when the applied voltage is 2kV (Example 1), the residual metal is 1.58wt.%, and the product's I...G / I D When the ratio reaches 105, the crystallinity of carbon nanotubes is at its highest, achieving the best purification effect and carbon nanotube quality; 3. When the applied voltage is increased to 3kV (Example 3), although the metal residue further decreases to 0.96wt.%, I G / I D The ratio dropped to 98, indicating that excessively high voltage would cause a discharge phenomenon, which would have a slight adverse effect on the structure of single-walled carbon nanotubes, resulting in a slight decrease in crystallinity.

[0039] Therefore, when constructing a non-uniform electric field in this invention, the preferred voltage for AC high voltage is around 2kV.

[0040] The applicability of the method of the present invention to different catalyst systems will be examined by changing the catalyst.

[0041] Example 4: Using the same method and process parameters as in Example 1 (applying AC voltage of 2kV, 300Hz), only the type of catalyst precursor was changed to ferrocene + molybdenum acetylacetonate (Fe-Mo).

[0042] Example 5: Using the same method and process parameters as in Example 1 (applying AC voltage of 2kV, 300Hz), only the type of catalyst precursor was changed to cobalt nitrate (Co).

[0043] The results and data from the above embodiments were analyzed, and the results are shown in Table 2.

[0044] Table 2. Effects of different catalyst systems on product performance As shown in Table 2, the in-situ preparation method of this invention has good applicability to both monometallic catalyst systems (Fe, Co) and bimetallic composite catalyst systems (Fe-Mo), and can control the residual amount of metal impurities to about 2 wt.% in both cases. Furthermore, the resulting single-walled carbon nanotubes exhibit high Ig content. G / I D The ratios are all greater than 97, indicating excellent crystallinity; among them, product I prepared by the Fe-Mo composite catalyst system G / I D The ratio reaches 118, indicating higher crystallinity, which shows that the method of the present invention can be adapted to different catalyst systems and meet different growth requirements of single-walled carbon nanotubes.

[0045] In summary, in the multiple embodiments corresponding to different process parameters and different catalyst systems in this application, the highest residual metal impurity content was 3.85 wt.%, which was significantly lower than 5 wt.%. The metal impurity content of the product can be stably controlled below 5 wt.%, thereby obtaining high-purity single-walled carbon nanotube products.

[0046] This invention is not limited to the above-described embodiments. Any changes in shape or structure shall fall within the protection scope of this invention. The protection scope of this invention is defined by the appended claims. Those skilled in the art may make various changes, modifications, substitutions, combinations, and simplifications to these embodiments without departing from the principles and essence of this invention. All such changes and simplifications shall be considered equivalent substitutions and shall fall within the protection scope of this invention.

Claims

1. A method for in-situ preparation of high-purity single-walled carbon nanotubes based on field-assisted growth, characterized in that, Includes the following steps: Step S1: Catalyst injection and pyrolysis: A carbon source solution containing catalyst precursor and growth promoter is injected into a vertical high-temperature reactor through a carrier gas. The catalyst precursor is pyrolyzed to form nano-metal catalyst particles, which catalyze the growth of single-walled carbon nanotubes. Step S2: Field-assisted purification and growth: A mixed gas flow containing the nano-metal catalyst particles and growing single-walled carbon nanotubes is passed through a composite field region coupled with a non-uniform electric field and a temperature gradient field; the non-uniform electric field is a radially non-uniformly distributed electric field perpendicular to the gas flow direction, and the temperature gradient field is a temperature gradient field with a high temperature at the center and a low temperature at the edge in the radial direction perpendicular to the gas flow direction. Step S3: In-situ separation: In the composite field region, the nano-metal catalyst particles are deviated from the central airflow and deposited and removed into the low-temperature zone of the vertical high-temperature reactor tube wall by the synergistic effect of dielectric force and thermophoresis force, and the single-walled carbon nanotubes are moved downstream with the central high-temperature airflow to achieve in-situ separation of single-walled carbon nanotubes and metal catalyst particles. Step S4: Powder collection: The airflow containing single-walled carbon nanotubes after in-situ separation is guided to the powder collection device to collect high-purity single-walled carbon nanotube powder.

2. The in-situ preparation method according to claim 1, characterized in that, In step S1, the catalyst precursor is one or more of ferrocene and cobalt nitrate, or a combination of ferrocene and molybdenum acetylacetonate; the growth promoter is thiophene; the carbon source is toluene; and the carrier gas is hydrogen.

3. The in-situ preparation method according to claim 1, characterized in that, In step S1, the vertical high-temperature reactor is a vertical high-temperature tube furnace; the injection rate of the carbon source solution is 5 μL / min; the carrier gas injection rate is 4000 sccm; and ethylene can also be introduced into the vertical high-temperature reactor as an auxiliary carbon source at an ethylene injection rate of 48 sccm.

4. The in-situ preparation method according to claim 3, characterized in that, In step S1, the heating temperature of the reaction zone of the vertical high-temperature tubular furnace is 1000℃.

5. The in-situ preparation method according to claim 1, characterized in that, In step S2, the non-uniform electric field is constructed by setting a rod-cylinder electrode in the rear section of the reaction zone of the vertical high-temperature reactor and applying AC high voltage; the temperature gradient field is constructed by setting a cooling device in the rear section of the reaction zone; the rear section is downstream of the airflow direction.

6. The in-situ preparation method according to claim 5, characterized in that, The rod-cylinder electrode includes a high-voltage electrode rod disposed at the axial center of the vertical high-temperature reactor and a cylindrical grounding electrode attached to the reaction tube wall; the cooling device is a water-cooled jacket.

7. The in-situ preparation method according to claim 5, characterized in that, In step S2, the voltage of the AC high voltage is 1~3kV and the frequency is 300Hz.

8. The in-situ preparation method according to claim 5, characterized in that, In step S2, the center temperature of the temperature gradient field is 1000℃, and the temperature of the edge low-temperature zone is 300℃.

9. The in-situ preparation method according to claim 1, characterized in that, In step S4, the powder collection device is a filter bag dust collector.

10. The in-situ preparation method according to any one of claims 1-9, characterized in that, The metal impurity content of the obtained high-purity single-walled carbon nanotube powder was reduced to below 5 wt.%, and the Raman spectrum I... G / I D If the ratio is greater than 70, the oxidation temperature in air is higher than 700℃.

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