Preparation method of single-walled carbon nanotube

Abstract

The invention relates to the technical field of rice tube preparation, and discloses a single-walled carbon nanotube preparation method, which comprises the following steps: arranging a stirring device in a reactor to provide a uniform dispersion environment, applying an electric field to realize directional control, carrying out temperature periodic change according to a preset program, and carrying out a thermal shock-stabilization-slow cooling circulation process to obtain a single-walled carbon nanotube. And a fluid dynamic pulse is generated by changing a stirring mode at a specific time point to form a transient stress induction effect. Precise regulation and control on the spatial configuration, the crystallinity and the orientation of the single-walled carbon nanotube are realized through the synergistic effect of various physical fields, the single-walled carbon nanotube product with a special curvature structure, high crystallinity and high-orientation arrangement is prepared, and the application requirements in the fields of high-end electronic devices, supercapacitors and the like are met.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanotube preparation, and more specifically, to a method for preparing single-walled carbon nanotubes. Background Art

[0002] Single-walled carbon nanotubes have broad application prospects in many high-tech fields due to their excellent mechanical, electrical and thermal properties. However, the existing single-walled carbon nanotube preparation methods have the following major technical problems: First, the spatial configuration of the prepared single-walled carbon nanotubes is difficult to accurately control, especially it is difficult to obtain carbon nanotubes with specific curvature structures (such as Y-type, Z-type or spiral type); second, the product crystallinity is not high and there are a large number of defects, which affect its mechanical and electrical properties; third, it is difficult to achieve precise control of the growth orientation of single-walled carbon nanotubes, resulting in disordered product arrangement, affecting its enhancement effect in applications such as composite materials. Although the existing technology uses a variety of preparation methods, such as chemical vapor deposition, arc discharge and laser ablation, these methods often only focus on the action of a single physical field and lack a systematic method for the coordinated regulation of multiple physical fields. Therefore, it is difficult to solve the above-mentioned multiple technical problems at the same time. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for preparing single-walled carbon nanotubes.

[0004] A method for preparing single-walled carbon nanotubes comprises the following steps: Establishing a stirring system, including a stirring device that can switch between mechanical stirring and pulse stirring modes; Establishing an electric field system, including an electrode device and a programmable DC power supply for forming a uniform electric field in the reactor; Establish a temperature cycle change system to achieve temperature cycle changes of thermal shock-stabilization-slow cooling; A transient stress induction system is established to generate fluid dynamic pulses by changing the stirring mode, thus forming transient mechanical stress on growing carbon nanotubes; Through a computer control unit, the synergistic effects of the above physical fields are coordinated according to a preset time sequence to achieve precise control of the structure and performance of single-walled carbon nanotubes; Preparation of single-walled carbon nanotubes.

[0005] Preferably: the establishment of the stirring system includes: constructing a variable mode stirring device including a stirring paddle, a variable speed motor and a control unit; Determine the stirring parameters. In the mechanical stirring mode, the speed is 200-600 rpm. In the pulse stirring mode, the speed increases from the normal speed to 800-1200 rpm within 0.1-0.5 seconds. Arrange the stirring mode timing, including the uniform dispersion stage in the initial stage of the reaction, the stable growth stage in the middle stage and the pulse impact stage at a predetermined time point.

[0006] Preferably: the establishment of the electric field system includes: Parallel plate electrodes are installed in the reactor to form a uniform electric field, and the electrodes are connected to a programmable DC power supply; Determine the electric field parameters. In the liquid phase reaction system, the electric field strength is 50-500 V / cm; in the gas phase reaction system, the electric field strength is 500-2000 V / cm; A pulsed electric field is applied to adjust the electric field strength and direction at different stages of temperature change.

[0007] Preferably: the establishment of the temperature cycle change system includes: Using a temperature control system including a heating element, a temperature sensor and a temperature controller; Determine the temperature cycle, including three stages: thermal shock stage, raising the temperature from room temperature to 600-900°C within 30-60 seconds; stabilization stage, maintaining the high temperature of 600-900°C for 10-30 minutes; slow cooling stage, cooling to 400-600°C at a cooling rate of 1-5°C / min; Through the configuration of heating elements and control algorithms, the temperature distribution in the reaction area is uniform and the temperature gradient is <10℃ / cm.

[0008] Preferably: the establishment of the transient stress inducing system includes: By rapidly changing the stirring mode, a hydrodynamic pulse is generated to form a transient shear force field; Determine the transient stress induction method according to the type of curvature structure of the carbon nanotube to be prepared; The timing of transient stress induction is precisely coordinated with temperature cycling and electric field application.

[0009] Preferably: the transient stress induction method comprises: For the Y-type structure: in the middle of the stable phase of the temperature cycle, a single strong pulse stirring shock is applied, and the shock direction is 60-90 degrees to the electric field direction; For the Z-type structure: in the middle and late stages of the stable phase of the temperature cycle, two pulse stirring shocks of similar intensity are applied respectively, and the two shocks are in opposite or nearly opposite directions; For spiral structures: During the stable phase of the temperature cycle, apply multiple (3-5) medium-intensity pulse stirring shocks at equal time intervals, with each shock direction forming an angle of 45-60 degrees with the previous one.

[0010] Preferably, the process of preparing single-walled carbon nanotubes includes the following stages: Dispersion and activation stage: start conventional stirring, evenly disperse the catalyst at a speed of 200-300rpm, and enter the thermal shock stage and apply a strong electric field; Directed growth stage: Entering the stable stage of the temperature cycle, adjusting the electric field strength to a medium level, and adding a carbon source to start the growth of carbon nanotubes; Curvature control stage: at a predetermined time point in the temperature cycle stabilization phase, a transient stress induction operation is performed and the electric field parameters are adjusted simultaneously; Structural improvement stage: Enter the slow cooling stage of the temperature cycle, slowly reduce the electric field strength, and maintain low-speed conventional stirring; Post-processing stage: collect the product, wash, dry and purify it.

[0011] Preferably, the catalyst is selected from metal salts containing iron group elements, and the carbon source is selected from carbon-containing gas or liquid carbon source.

[0012] Preferably, when the carbon source is a liquid carbon source, the carbon source / catalyst mass ratio is 50-200:1; when the carbon source is a carbon-containing gas, the carbon source flow rate is 50-200 ml / min, and the catalyst loading is 0.5-2 wt %.

[0013] Preferred: Single-walled carbon nanotubes have the following characteristics: The branching angle of the Y-shaped carbon nanotubes is controlled within the range of 30-45 degrees, with a deviation of <5 degrees; The turning angle of Z-shaped carbon nanotubes is controlled within the range of 100-140 degrees, with a deviation of <10 degrees; The pitch of the helical carbon nanotubes is controlled within the range of 20-100nm, and the uniformity deviation of the helical structure per unit length is <15%; The intensity ratio of the G peak to the D peak of the carbon nanotubes (IG / ID) is 8-12, and the orientation degree reaches 85-95%. The beneficial effect of the present invention is that the present invention realizes precise control of the curvature structure of carbon nanotubes by means of the synergistic effect of electric field orientation and transient stress induction. According to different transient stress induction schemes, Y-type, Z-type or spiral single-walled carbon nanotubes can be selectively prepared. Among them, the branching angle of the Y-type carbon nanotube can be controlled within the range of 30-45 degrees, with a deviation of <5 degrees; the turning angle of the Z-type carbon nanotube can be controlled within the range of 100-140 degrees, with a deviation of <10 degrees; the pitch of the spiral carbon nanotube can be controlled within the range of 20-100nm, and the uniformity deviation of the spiral structure per unit length is <15%.

[0014] The crystallinity of carbon nanotubes was significantly improved through the synergistic effect of temperature cycle changes and electric fields, especially the structural repair process in the slow cooling stage. Raman spectroscopy showed that the intensity ratio of G peak to D peak (IG / ID) was increased to 8-12, which was significantly higher than that of carbon nanotubes prepared by traditional methods (IG / ID is usually 3-5), indicating that the structural defects of carbon nanotubes were greatly reduced.

[0015] Through the coordination of the electric field orientation and the stirring system, the carbon nanotubes are highly oriented during the growth process. The orientation degree of the product (determined by polarizing microscope or X-ray diffraction) reaches 85-95%, which is much higher than the randomly arranged carbon nanotubes prepared by traditional methods.

[0016] Due to the precise control of the structure and high crystallinity, the single-walled carbon nanotubes prepared by this method have excellent comprehensive properties. The electrical conductivity is increased by 30-50%, the thermal conductivity is increased by 40-60%, and the mechanical strength is increased by 20-40%. Compared with similar products prepared by traditional methods, the comprehensive performance is significantly improved.

[0017] This method can customize the preparation of single-walled carbon nanotubes with different structural characteristics according to different application requirements by adjusting various physical field parameters and timing relationships, and has wide adaptability and scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the preparation effect of single-walled carbon nanotubes with various curvature structures in the present invention; Figure 2 It is a comparison of the crystallinity of single-walled carbon nanotubes prepared by different experimental groups in the present invention; Figure 3 It is a comparison of the orientation degree of single-walled carbon nanotubes prepared by different experimental groups in the present invention; Figure 4 It is the performance comparison data of two groups of samples in the present invention; Figure 5 It is the performance test result of the nanocomposite material in the present invention; Figure 6 It is the adaptability of different catalysts in the present invention to the multi-physical field collaborative preparation method; Figure 7 It is the adaptability of different carbon sources in the present invention to the multi-physical field collaborative preparation method; Figure 8 It is the influence of the key process parameters in the present invention on the product characteristics; Fig. 9 It is the customized preparation result for different applications in the present invention. DETAILED DESCRIPTION

[0019] The subject matter described herein will now be discussed with reference to example implementations. It should be understood that the discussion of these implementations is only to enable those skilled in the art to better understand and implement the subject matter described herein, and the functions and arrangements of the elements discussed may be changed without departing from the scope of protection of the present specification. Various examples may omit, replace, or add various processes or components as needed. In addition, the features described in some examples may also be combined in other examples.

[0020] At least one embodiment of the present invention discloses a method for preparing single-walled carbon nanotubes, comprising the following steps: Select catalyst and carbon source raw materials.

[0021] In this embodiment, the catalyst is a metal salt containing an iron group element (iron, cobalt, nickel or a combination thereof), and the carbon source raw material is a carbon-containing gas (methane, acetylene or carbon monoxide) or a liquid carbon source (ethanol, benzene or toluene). The catalyst precursor is dissolved in a solvent to prepare a catalyst solution or suspension.

[0022] 1. Establishment of stirring system Stirring device construction: A variable mode stirring device is made, which can switch between conventional mechanical stirring and pulse stirring according to the control signal. The stirring device includes a stirring paddle, a variable speed motor and a control unit. The variable speed motor can achieve a sharp change in speed in a short time (<0.5 seconds), and the control unit controls the stirring mode switching according to the program.

[0023] Determination of stirring parameters: Determine the stirring speed range according to the viscosity, density and catalyst properties of the reaction system. In the conventional stirring mode, the speed is a fixed value of 200, 400 or 600 rpm to ensure uniform dispersion of the reactants; in the pulse stirring mode, the speed increases from the conventional speed to 800, 1000 or 1200 rpm within 0.1, 0.3 or 0.5 seconds, and then returns to the conventional speed, forming a pulse stirring impact.

[0024] In this embodiment, the rotation speed is fixed at 400 rpm in the normal stirring mode to ensure uniform dispersion of the reactants; in the pulse stirring mode, the rotation speed is increased from the normal speed to 1000 rpm within 0.3 seconds. Stirring mode timing arrangement: The stirring process is divided into multiple stages, including the uniform dispersion stage at the initial stage of the reaction, the stable growth stage in the middle stage, and the pulse impact stage at a predetermined time point. The stirring mode control program is compiled to coordinate it with the timing of temperature change and electric field application to achieve multi-physical field timing coordination.

[0025] 2. Electric field system establishment Electric field generating device: Install electrodes in the reactor. The electrode materials are made of high temperature resistant and chemically stable conductive materials such as graphite, stainless steel or platinum. The electrodes are arranged in parallel plates to form a uniform electric field. The electrodes are connected to a programmable DC power supply to achieve programmable control of the electric field intensity and application time.

[0026] Determination of electric field parameters: The electric field strength range is determined according to the dielectric properties of the reaction medium and the response characteristics of the catalyst. In a liquid phase reaction system, the electric field strength is 50, 300 or 500 V / cm; in a gas phase reaction system, the electric field strength is 500, 1200 or 2000 V / cm.

[0027] In this embodiment, the electric field strength is 300 V / cm; in the gas phase reaction system, the electric field strength is 1200 V / cm.

[0028] Electric field application method: Pulsed electric field application is used to adjust the electric field strength and direction at different stages of temperature change. A strong electric field (close to the upper limit of the set range) is applied during the thermal shock stage to promote the directional arrangement of catalytic active sites; a medium-intensity electric field is maintained during the stable growth stage to guide the carbon nanotubes to grow along the direction of the electric field; the electric field strength is gradually reduced during the slow cooling stage to reduce interference with carbon atom rearrangement, which is conducive to the repair of structural defects.

[0029] 3. Establishment of temperature cycle change system Temperature control device: Use a temperature control system, including heating elements, temperature sensors and temperature controllers. The heating elements achieve rapid heating and constant temperature, and the temperature controller adjusts the temperature change process according to the program.

[0030] Temperature cycle determination: Establish a temperature cycle mode of thermal shock-stabilization-slow cooling. A complete cycle includes three stages: Thermal shock stage: Raise the temperature from room temperature to 600, 750 or 900°C within 30, 45 or 60 seconds, with a heating rate ≥ 10°C / second.

[0031] Stabilization stage: Keep at a high temperature of 600, 750 or 900°C for 10, 20 or 30 minutes to maintain a constant temperature.

[0032] Slow cooling stage: cooling to 400, 500 or 600°C at a cooling rate of 1, 3 or °C / min, and then naturally cooling to room temperature.

[0033] In this embodiment, the following is adopted: thermal shock stage: the temperature is increased from room temperature to 750° C. within 45 seconds, and the heating rate is ≥10° C. / second.

[0034] Stabilization stage: Keep at 750℃ for 20 minutes to maintain a constant temperature.

[0035] Slow cooling stage: cool to 500°C at a cooling rate of 3°C / min, and then cool naturally to room temperature.

[0036] Temperature distribution uniformity: Through the configuration of heating elements and control algorithms, the temperature distribution in the reaction area is uniform, and the temperature gradient is <10℃ / cm. Combined with the stirring system, the fluid circulation is used to enhance heat transfer and improve the uniformity of the temperature field.

[0037] 4. Establishment of transient stress induction system Principle of transient stress induction: At the critical stage of single-walled carbon nanotube growth, fluid dynamic pulses are generated by rapidly changing the stirring mode to form a transient shear force field, which applies directional mechanical stress to the growing carbon nanotubes. This transient stress affects the arrangement of carbon atoms and induces the carbon nanotubes to form a curvature structure.

[0038] Transient stress induction method: According to the type of curvature structure of the carbon nanotubes to be prepared (Y-type, Z-type or spiral type), a transient stress induction method is formulated: For the Y-type structure: In the middle of the stable phase of the temperature cycle (after the initial phase of growth is completed), a single strong pulse stirring shock is applied, with the shock direction forming an angle of 60, 75 or 90 degrees with the electric field direction.

[0039] In this embodiment, the impact direction and the electric field direction form an angle of 75 degrees.

[0040] For the Z-type structure: in the middle and late stages of the stable phase of the temperature cycle, two pulse stirring shocks of similar intensity are applied respectively, and the two shocks are in opposite or nearly opposite directions.

[0041] For the spiral structure: in the stable stage of the temperature cycle, 3, 4 or 5 medium-intensity pulse stirring shocks are applied continuously at equal time intervals, and the direction of each shock is 45, 52 or 60 degrees to the previous one; in this embodiment, 4 medium-intensity pulse stirring shocks are applied continuously at equal time intervals, and the direction of each shock is 52 degrees to the previous one.

[0042] Synergy between transient stress induction and other physical fields: The timing of transient stress induction is precisely coordinated with the temperature cycle and electric field application. While applying transient stress, the intensity and direction of the electric field are adjusted to enhance the control effect on the growth direction of carbon nanotubes. This synergy of multiple physical fields is the key to preparing single-walled carbon nanotubes with curvature structures.

[0043] 5. Multi-field collaborative preparation process Preparation process integration: Integrate the above physical field systems into a reaction device, including a stirring device, an electric field generation system, a temperature control system and a computer control unit. The computer control unit controls the intensity, direction and time changes of all physical fields according to a preset program.

[0044] Reaction feed: The catalyst solution or suspension and the carbon source raw material are fed into the reactor in a certain ratio.

[0045] When the carbon source is a liquid carbon source, it is recorded as a liquid phase system, and the mass ratio of the liquid phase system carbon source / catalyst is 50 or 100 or 150 or 200:1; in this embodiment, the mass ratio of the liquid phase system carbon source / catalyst is 150:1.

[0046] When the carbon source is a carbon-containing gas, it is recorded as a gas phase system, the gas phase system carbon source flow rate is 50 or 150 or 200 ml / min, and the catalyst loading is 0.5 or 1.2 or 2 weight %; in this embodiment: the gas phase system carbon source flow rate is 150 mL / min, and the catalyst loading is 1.2 weight %.

[0047] Confirmation of preparation conditions: Before starting the program, confirm the physical field parameters, including stirring mode and speed, electric field strength and direction, temperature cycle parameters, transient stress induction time point, etc. Ensure that the control system operates normally and the data of each sensor is read correctly.

[0048] Synergistic preparation of single-walled carbon nanotubes by multiple fields: The first stage (dispersion and activation stage): Start conventional stirring, and evenly disperse the catalyst under constant low-speed stirring (200-300rpm). At the same time, start the temperature control system, enter the thermal shock stage, quickly heat up to 700℃±50℃, and apply an electric field with an intensity of 80-90% of the upper limit of the set range to promote catalyst activation and active site arrangement.

[0049] The second stage (directional growth stage): Enter the stable stage of the temperature cycle and maintain a constant temperature. Adjust the electric field strength to a medium level (50-70% of the setting range) and maintain regular stirring. Add a carbon source to start the carbon nanotube growth process.

[0050] The third stage (curvature control stage): At a predetermined time point in the temperature cycle stabilization stage, the corresponding transient stress induction operation is performed according to the type of curvature structure to be prepared. At the same time, the electric field strength and direction are adjusted to coordinately control the growth curvature of the carbon nanotubes.

[0051] The fourth stage (structural improvement stage): Enter the slow cooling stage of the temperature cycle, and cool down at a rate of 1-5℃ / minute. Slowly reduce the electric field strength and finally turn off the electric field. Maintain low-speed conventional stirring (100-200rpm), which is conducive to carbon atom rearrangement and structural defect repair.

[0052] The fifth stage (post-processing stage): After the temperature drops to room temperature, all physical fields are turned off. The product is collected, washed, dried and purified to obtain the final single-walled carbon nanotube product.

[0053] In order to verify the technical effect of the present invention, experiments and tests were carried out, as follows: Experiment 1: Verification of curvature structure control effect 1. Purpose of the experiment Verify whether the curvature structure of carbon nanotubes can be precisely controlled through the synergistic effect of electric field orientation and transient stress induction, and whether Y-shaped, Z-shaped and spiral single-walled carbon nanotubes can be effectively prepared.

[0054] 2. Experimental Materials Catalyst: ferric nitrate, cobalt nitrate, nickel nitrate (mass ratio is 3:2:1); Carbon source: acetylene gas (purity 99.9%); Carrier gas: argon (purity 99.999%); Reaction device: A self-assembled multi-physical field coordinated control device, including a stirring system, an electric field system, a temperature control system and a computer control unit.

[0055] 2. Experimental Procedure Catalyst preparation: Mix ferric nitrate, cobalt nitrate and nickel nitrate in a mass ratio of 3:2:1 and dissolve in deionized water to a concentration of 0.1 mol / L.

[0056] Reactor preparation: Add the catalyst solution into the reactor and set up the electric field system, temperature control system and stirring system.

[0057] Preparation of Y-shaped carbon nanotubes: Set the electric field strength to 1000 V / cm, with the direction perpendicular to the bottom of the reactor; Set the temperature cycle: heat up to 800°C in 40 seconds, hold for 20 minutes, and then cool to 500°C at 2°C / min; The transient stress induction parameters were set as follows: in the middle of the stable phase (about 10 minutes), a single strong pulse stirring shock (1000 rpm) was applied, and the shock direction was 70 degrees to the electric field direction.

[0058] Preparation of Z-type carbon nanotubes: Set the electric field strength to 1200 V / cm, with the direction perpendicular to the bottom of the reactor; Set the temperature cycle: heat to 850°C in 40 seconds, hold for 25 minutes, then cool to 500°C at 2°C / min; Set the transient stress induction parameters: in the middle (about 8 minutes) and late (about 20 minutes) of the stable stage, apply two pulse stirring shocks (1100 rpm) of similar intensity, respectively, and the two shocks are in opposite directions.

[0059] Preparation of helical carbon nanotubes: Set the electric field strength to 800 V / cm, with the direction perpendicular to the bottom of the reactor; Set the temperature cycle: heat to 750°C in 35 seconds, hold for 30 minutes, then cool to 500°C at 3°C / min; Set the transient stress induction parameters: in the stable stage (5th, 10th, 15th, 20th, and 25th minutes), apply 5 medium-intensity pulse stirring shocks (900 rpm), and the direction of each shock is 50 degrees to the previous one; Product collection and treatment: After the reaction is completed, wait for the reactor to cool to room temperature, collect the product and wash it with hydrochloric acid (3 mol / L) to remove the catalyst, then wash it with deionized water for 3 times and dry it at 60°C for 12 hours.

[0060] Structural characterization: Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the morphology and structure of carbon nanotube samples.

[0061] 3. Experimental results See Figure 1 Preparation effects of single-walled carbon nanotubes with various curvature structures.

[0062] It can be seen that the carbon nanotubes prepared by the method of the present invention have clear curvature structural characteristics, and the formation ratio is much higher than that of the traditional method (the control group uses conventional chemical vapor deposition method without multi-physical field synergy). The structural parameter measurement results show that the Y-type branch angle, Z-type turning angle and spiral pitch all meet the design goals, and the structural deviation is small, which proves the ability of the present invention to accurately control the curvature structure of carbon nanotubes.

[0063] Experiment 2: Verification of the effect of improving crystallinity 1. Purpose of the experiment Verify whether the synergistic effect of temperature cycle changes and electric fields, especially the structural repair process in the slow cooling stage, can significantly improve the crystallinity of carbon nanotubes and reduce structural defects.

[0064] 2. Experimental Materials Catalyst: ferric nitrate (purity 99.5%); Carbon source: methane gas (purity 99.9%); Carrier gas: a mixture of hydrogen (purity 99.999%) and argon (purity 99.999%) (volume ratio 1:9); Reaction apparatus: Same as experiment 1 2. Experimental Procedure Catalyst preparation: Dissolve ferric nitrate in anhydrous ethanol at a concentration of 0.05 mol / L.

[0065] Experimental group settings: Experimental group A (method of the present invention): a temperature cycle process was used, including a thermal shock stage (heating to 850°C within 45 seconds), a stabilization stage (maintaining 850°C for 20 minutes) and a slow cooling stage (cooling to 450°C at a rate of 3°C / min), while applying an electric field of 200-400V / cm; Experimental group B (control group 1): using conventional constant temperature process, directly reacting at 850°C for 20 minutes, followed by rapid cooling, without applying an electric field; Experimental group C (control group 2): using conventional constant temperature process, directly reacting at 850°C for 20 minutes, then rapidly cooling, and applying a constant electric field of 300 V / cm; Experimental group D (control group 3): temperature cycle change process was adopted without applying electric field.

[0066] 3. Experimental process: The catalyst solution is dripped onto the silicon substrate and placed into the reactor; According to the parameter settings of each experimental group, the temperature change process and the application of the electric field are controlled; In the stable stage, a mixture of methane and carrier gas was introduced at a flow rate of 50 ml / min of methane and 150 ml / min of mixed carrier gas; After the reaction is completed, turn off the methane gas source, continue to introduce the carrier gas, and cool according to the set cooling method; Product collection and processing: The silicon substrate was taken out and ultrasonically cleaned with acetone and anhydrous ethanol to obtain the carbon nanotube sample.

[0067] Crystallinity Characterization: Raman spectroscopy analysis: The intensity ratio (IG / ID) of the G peak (~1580cm-1) and the D peak (~1350cm-1) was measured using a Raman spectrometer with a 532nm laser. High-resolution transmission electron microscopy (HRTEM) observation: measuring the integrity and defect density of the carbon nanotube wall; X-ray diffraction (XRD) analysis: Determination of the crystallinity of carbon nanotubes.

[0068] 4. Experimental Results See Figure 2 Comparison of crystallinity of single-walled carbon nanotubes prepared in different experimental groups.

[0069] High-resolution TEM observation and defect site statistics show that the carbon nanotubes (experimental group A) prepared by the method of the present invention have fewer fractures, deformations and vacancy defects in the tube wall structure. Raman spectroscopy analysis shows that the IG / ID ratio of experimental group A reaches 10.8, which is much higher than that of the control group, indicating that it has higher crystallinity and fewer structural defects. XRD test results also confirm that experimental group A has higher lattice integrity (95.7%).

[0070] The results show that the synergistic effect of temperature cycle change process and electric field (experimental group A) has a significant effect on improving the crystallinity of carbon nanotubes, among which the slow cooling stage plays a key role in the rearrangement of carbon atoms and the repair of structural defects. Control experiments show that the use of temperature cycle change alone (experimental group D) or the application of electric field alone (experimental group C) can also improve the crystallinity to a certain extent, but the synergistic effect (experimental group A) is the most significant, confirming the technical advantages of the present invention.

[0071] Experiment 3: Verification of the effect of orientation control 1. Purpose of the experiment Verify whether the coordinated cooperation of the electric field orientation effect and the stirring system can achieve highly oriented arrangement of carbon nanotubes during the growth process, and measure their orientation degree.

[0072] 2. Experimental Materials Catalyst: cobalt nitrate (purity 99.5%); Carbon source: acetylene gas (purity 99.9%); Carrier gas: nitrogen (purity 99.999%); Reaction substrate: silicon substrate (100nm oxide layer); Reaction apparatus: Same as experiment 1, equipped with a polarizing microscope and an X-ray diffractometer with an image acquisition system.

[0073] 3. Experimental Procedure Catalyst preparation: Dissolve cobalt nitrate in anhydrous ethanol at a concentration of 0.08 mol / L.

[0074] Preparation of reaction substrate: After cleaning the silicon substrate, the catalyst solution is evenly coated on its surface by spin coating to form a catalyst film with a thickness of about 50 nm.

[0075] Experimental group settings: Experimental group E (method of the present invention): applying an electric field of 350 V / cm, with the direction of the electric field parallel to the substrate surface, and using multi-physics field synergy (including temperature cycle change and stirring system); Experimental group F (control group 1): 350 V / cm electric field was applied, but temperature cycle change and stirring system were not used; Experimental group G (control group 2): no electric field was applied and conventional synthesis method was used; Experimental group H (control group 3): 350 V / cm electric field was applied, temperature cycle was used, but no stirring system was used.

[0076] Carbon nanotube growth process: Experimental group E adopted the method of the present invention, placing the substrate into the reactor, setting up the electric field system (350 V / cm), the temperature cycle change system (raising the temperature to 800 °C within 45 seconds, maintaining it for 15 minutes, and then cooling it to 500 °C at 2 °C / min), and the stirring system (conventional stirring at 300 rpm); During the stable phase, acetylene gas (80 ml / min) and carrier gas (200 ml / min) were introduced; The other experimental groups were operated according to their respective parameter settings.

[0077] Orientation characterization: Polarized light microscope observation: observe the arrangement direction of carbon nanotubes under polarized light, and calculate the percentage of carbon nanotubes that are consistent with the main direction (deviation <15°); X-ray diffraction (XRD) analysis: The orientation degree was determined by scanning the azimuth angle of the (002) diffraction peak; Field emission scanning electron microscopy (FESEM) observation: Directly observe the arrangement direction and uniformity of carbon nanotubes.

[0078] 4. Experimental Results See Figure 3 Comparison of orientation degree of single-walled carbon nanotubes prepared in different experimental groups.

[0079] FESEM image analysis shows that the carbon nanotubes prepared by experimental group E (method of the present invention) present a highly consistent arrangement direction, and more than 90% of the carbon nanotubes are arranged along the main direction (electric field direction), forming a highly ordered parallel structure. Polarized light microscopy observation shows that the orientation degree of experimental group E reaches 92.3%, and XRD azimuth scanning analysis also confirms that it has a high orientation degree of 90.6%.

[0080] The comparison results of each experimental group show that the application of electric field alone (experimental group F) can achieve a certain degree of orientation control (orientation degree of about 65-68%), but compared with the synergistic effect of temperature cycle change and stirring system (experimental group E), the orientation degree and uniformity are significantly lower than the method of the present invention. Experimental group G without the application of electric field shows almost no orientation, and the carbon nanotubes are randomly arranged. The orientation degree of experimental group H with electric field and temperature cycle synergy but no stirring is between experimental groups E and F, which further proves the importance of multi-physical field synergy in improving orientation.

[0081] The experimental results confirm that the method of the present invention can effectively achieve highly oriented arrangement of carbon nanotubes through the coordinated cooperation of the electric field orientation effect and the stirring system, with an orientation degree of more than 90%, which is much higher than the traditional method, and provides an effective way to prepare highly oriented carbon nanotube materials.

[0082] Experiment 4: Verification of comprehensive performance improvement effect 1. Purpose of the experiment The improvement effect of the single-walled carbon nanotubes prepared by the method of the present invention in terms of comprehensive properties such as electrical conductivity, thermal conductivity and mechanical strength was verified.

[0083] 2. Experimental Materials Single-walled carbon nanotube samples prepared by the method of the present invention (experimental group I); Single-walled carbon nanotube samples prepared by conventional chemical vapor deposition (control group J); Testing equipment: four-probe conductivity test system, laser flash thermal conductivity analyzer, nanoindentation tester, tensile testing machine; 3. Experimental Procedure Sample preparation: Experimental group I: single-walled carbon nanotubes were prepared by the method of the present invention (multi-physical field synergy), with the specific conditions of electric field strength of 300 V / cm, temperature cycle of heating to 800°C within 40 seconds, holding for 20 minutes, and then cooling to 500°C at 2°C / min, and stirring speed of 300 rpm; Control group J: Single-walled carbon nanotubes were prepared by conventional chemical vapor deposition, with a fixed temperature of 800°C and a reaction time of 20 minutes; Sample processing: Both groups of samples underwent the same purification process, including acid washing, filtration and drying, to ensure that the sample purity was basically consistent.

[0084] Performance Testing: Conductivity test: Use a four-probe conductivity test system to measure the conductivity of two groups of samples at room temperature; Thermal conductivity test: Use a laser flash thermal conductivity analyzer to measure the thermal conductivity of the two groups of samples; Mechanical properties test: Young's modulus was measured using a nanoindentation tester, and tensile strength was measured using a tensile testing machine; Cyclic voltammetry test: Using a three-electrode electrochemical workstation, the electrochemical properties of the two groups of samples as electrode materials were measured; Nanocomposite material preparation and testing: The two groups of carbon nanotube samples were mixed with epoxy resin in the same proportion (3wt%) to prepare nanocomposites; The tensile strength, elastic modulus and electrical conductivity of the composite materials were tested.

[0085] 4. Experimental Results See Figure 4 Performance comparison data of two groups of samples; See Figure 5 Nanocomposite material performance test results.

[0086] The experimental data analysis shows that the single-walled carbon nanotubes prepared by the method of the present invention (experimental group I) are significantly better than those prepared by the traditional method (control group J) in all key performance indicators. The electrical conductivity is increased by 50.0%, the thermal conductivity is increased by 60.9%, and the mechanical properties (Young's modulus and tensile strength) are increased by more than 30%.

[0087] The nanocomposite materials prepared by respectively compounding the two groups of carbon nanotubes with epoxy resin also showed a similar trend. The composite materials containing carbon nanotubes prepared by the method of the present invention were significantly superior to the composite materials containing carbon nanotubes prepared by the traditional method in terms of mechanical properties and conductive properties.

[0088] The significant improvement in comprehensive performance is attributed to the three key effects brought about by the method of the present invention: higher crystallinity reduces structural defects and improves the transmission efficiency of electrons and phonons; the precisely controlled curvature structure enhances the three-dimensional mechanical properties of carbon nanotubes; and the highly oriented arrangement improves the reinforcement effect and anisotropic conduction properties in the composite material. These experimental results fully demonstrate the significant effect of the present invention in improving the comprehensive performance of carbon nanotubes.

[0089] Experiment 5: Verification of the universality of controllable preparation 1. Purpose of the experiment Verify whether the method of the present invention has wide adaptability and scalability, and whether it can customize the preparation of single-walled carbon nanotubes with different structural characteristics according to different application requirements by adjusting various physical field parameters and timing relationships.

[0090] 2. Experimental Materials Catalysts: iron-based catalysts (ferric nitrate, ferric chloride), cobalt-based catalysts (cobalt nitrate, cobalt chloride), nickel-based catalysts (nickel nitrate, nickel chloride) and combinations thereof; Carbon source: methane, acetylene, ethanol, benzene and other types of carbon sources; Reaction device: Same as experiment 1, with a multi-physical field collaborative device that can be precisely controlled.

[0091] 3. Experimental Procedure Catalyst universality test: Three different catalysts, iron-based, cobalt-based, and nickel-based, and their combinations are used respectively; For each catalyst, the multi-physical field collaborative preparation method of the present invention is applied; Keeping other conditions the same, record the effects of different catalysts on the growth of carbon nanotubes.

[0092] Carbon source universality test: Gaseous carbon sources (methane, acetylene) and liquid carbon sources (ethanol, benzene) were used respectively; For each carbon source, the multi-physical field collaborative preparation method of the present invention is applied; Keeping other conditions the same, record the effects of different carbon sources on the growth of carbon nanotubes.

[0093] Parameter control experiment: Electric field intensity control: set different electric field intensities (100-1500V / cm) to observe the effects on the structure and performance of carbon nanotubes; Temperature cycle control: set different thermal shock rates, stable temperatures and cooling rates to observe the impact on the product; Transient stress induced regulation: Set different stirring impact intensities, time points and directions to observe the impact on the product curvature structure.

[0094] Application Customization Experiments: Customized for electronic device applications: Adjust process parameters to prepare carbon nanotubes with high conductivity and high crystallinity; Customized for supercapacitor applications: Adjust process parameters to prepare carbon nanotubes with specific curvature structures (increase specific surface area); Tailored for composite reinforcement applications: Adjust process parameters to produce highly oriented, high-strength carbon nanotubes.

[0095] 4. Experimental Results See Figure 6 The adaptability of different catalysts to multi-physics field collaborative preparation methods; See Figure 7 The adaptability of different carbon sources to the multi-physics field collaborative preparation method; See Figure 8 The impact of key process parameters on product characteristics; See Fig. 9 Customized preparation results for different applications.

[0096] Experimental results show that the method of the present invention has broad universality: it shows good adaptability to different types of catalysts and carbon sources, and various catalysts and carbon sources can be efficiently prepared in this method by simply adjusting the process parameters; by precisely controlling the electric field intensity, temperature cycle parameters and transient stress induction parameters, the structural characteristics and performance indicators of the product can be controlled in a targeted manner; single-walled carbon nanotube products that meet specific performance requirements can be customized according to the needs of different application fields, and various key performance indicators are significantly better than traditional methods.

[0097] These experimental results fully demonstrate the universality and scalability of the method of the present invention in controllable preparation, and provide an effective technical path for the customized production of single-walled carbon nanotubes in a variety of high-end application fields.

[0098] Experimental Summary Through the above five sets of systematic experiments, the key technical effects of the single-walled carbon nanotube preparation method of the present invention were fully verified. The experimental results show that: Curvature structure control effect: The method of the present invention achieves precise control of the curvature structure of carbon nanotubes through the synergistic effect of electric field orientation and transient stress induction, and can selectively prepare Y-shaped, Z-shaped or helical single-walled carbon nanotubes, with a formation ratio of 78-86%, which is much higher than the 2-5% of traditional methods. The structural parameters are precisely controlled, and the deviations of the Y-shaped branch angle, Z-shaped turning angle and helical pitch are all within the design target range.

[0099] Crystallinity improvement effect: The synergistic effect of temperature cycle change process and electric field significantly improves the crystallinity of carbon nanotubes, and the IG / ID ratio reaches 10.8, which is 1.5-2.5 times higher than the traditional method. The defect density is reduced by about 75%, the lattice integrity is increased to 95.7%, and the structural integrity of the product is greatly improved.

[0100] Orientation control effect: The synergy of the electric field orientation and the stirring system achieves a high degree of orientation of carbon nanotubes, with an orientation degree of more than 90%, which is about 25% higher than using the electric field alone and about 80% higher than the traditional method. The orientation uniformity is also greatly improved, providing a basis for high-performance anisotropic materials.

[0101] Comprehensive performance improvement effect: The single-walled carbon nanotubes prepared by the present invention are significantly better than traditional methods in key performance indicators such as electrical conductivity, thermal conductivity and mechanical strength, with an improvement of 30-60%. When applied to nanocomposites, they also show obvious performance advantages, laying the foundation for the application of high-performance materials.

[0102] Universality of controllable preparation: The method of the present invention has good adaptability to different types of catalysts and carbon sources. By adjusting various physical field parameters and timing relationships, single-walled carbon nanotubes with different structural characteristics can be customized for different application requirements. Both process versatility and product adaptability are excellent.

[0103] In summary, the experimental verification results fully demonstrate the innovation and practicality of the present invention in the field of single-walled carbon nanotube preparation. Through the synergistic effect of four physical fields, namely stirring, electric field, temperature cycle change and transient stress induction, the precise control of the structure and performance of single-walled carbon nanotubes is achieved, and the technical problems of the prior art in spatial configuration control, crystallinity improvement and orientation arrangement are solved, providing a new technical solution for the preparation of high-performance single-walled carbon nanotube materials.

[0104] The above describes an embodiment of the present invention, but this embodiment is not limited to the above-mentioned specific implementation mode. The above-mentioned specific implementation mode is merely illustrative and not restrictive. Under the guidance of this embodiment, ordinary technicians in this field can also make more forms of equivalent embodiments, all of which are within the protection of this embodiment.

Claims

1. A method for preparing single-walled carbon nanotubes, characterized in that: The following steps are involved: Establishing a stirring system, including a stirring device that can switch between mechanical stirring and pulse stirring modes; Establishing an electric field system, including an electrode device and a programmable DC power supply for forming a uniform electric field in the reactor; Establish a temperature cycle change system to achieve temperature cycle changes of thermal shock-stabilization-slow cooling; A transient stress induction system is established to generate fluid dynamic pulses by changing the stirring mode, thus forming transient mechanical stress on growing carbon nanotubes; Through a computer control unit, the synergistic effects of the above physical fields are coordinated according to a preset time sequence to achieve precise control of the structure and performance of single-walled carbon nanotubes; Preparation of single-walled carbon nanotubes.

2. The method according to claim 1, characterized in that The establishment of the stirring system includes: constructing a variable mode stirring device including a stirring paddle, a variable speed motor and a control unit; Determine the stirring parameters. In the mechanical stirring mode, the speed is 200-600 rpm. In the pulse stirring mode, the speed increases from the normal speed to 800-1200 rpm within 0.1-0.5 seconds. Arrange the stirring mode timing, including the uniform dispersion stage in the initial stage of the reaction, the stable growth stage in the middle stage and the pulse impact stage at a predetermined time point.

3. The method according to claim 1, characterized in that The establishment of the electric field system includes: Parallel plate electrodes are installed in the reactor to form a uniform electric field, and the electrodes are connected to a programmable DC power supply; Determine the electric field parameters. In the liquid phase reaction system, the electric field strength is 50-500 V / cm; in the gas phase reaction system, the electric field strength is 500-2000 V / cm; A pulsed electric field is applied to adjust the electric field strength and direction at different stages of temperature change.

4. The method according to claim 1, characterized in that: The establishment of the temperature cycle change system includes: Using a temperature control system including a heating element, a temperature sensor and a temperature controller; Determine the temperature cycle, including three stages: thermal shock stage, raising the temperature from room temperature to 600-900°C within 30-60 seconds; stabilization stage, maintaining the high temperature of 600-900°C for 10-30 minutes; slow cooling stage, cooling to 400-600°C at a cooling rate of 1-5°C / min; Through the configuration of heating elements and control algorithms, the temperature distribution in the reaction area is uniform and the temperature gradient is <10℃ / cm.

5. The method according to claim 1, characterized in that The establishment of the transient stress inducing system includes: By rapidly changing the stirring mode, a hydrodynamic pulse is generated to form a transient shear force field; Determine the transient stress induction method according to the type of curvature structure of the carbon nanotube to be prepared; The timing of transient stress induction is precisely coordinated with temperature cycling and electric field application.

6. The method according to claim 5, characterized in that The transient stress inducing method comprises: For the Y-type structure: in the middle of the stable phase of the temperature cycle, a single strong pulse stirring shock is applied, and the shock direction is 60-90 degrees to the electric field direction; For the Z-type structure: in the middle and late stages of the stable phase of the temperature cycle, two pulse stirring shocks of similar intensity are applied respectively, and the two shocks are in opposite or nearly opposite directions; For spiral structures: During the stable phase of the temperature cycle, apply several medium-intensity pulse stirring shocks continuously at equal time intervals, with the direction of each shock being 45-60 degrees to the previous one.

7. The method according to claim 1, characterized in that The process for preparing single-walled carbon nanotubes includes the following stages: Dispersion and activation stage: start conventional stirring, evenly disperse the catalyst at a speed of 200-300rpm, and enter the thermal shock stage and apply a strong electric field; Directed growth stage: Entering the stable stage of the temperature cycle, adjusting the electric field strength to a medium level, and adding a carbon source to start the growth of carbon nanotubes; Curvature control stage: at a predetermined time point in the temperature cycle stabilization phase, a transient stress induction operation is performed and the electric field parameters are adjusted simultaneously; Structural improvement stage: Enter the slow cooling stage of the temperature cycle, slowly reduce the electric field strength, and maintain low-speed conventional stirring; Post-processing stage: collect the product, wash, dry and purify it.

8. The method according to claim 7, characterized in that The catalyst is selected from metal salts containing iron group elements, and the carbon source is selected from carbon-containing gas or liquid carbon source.

9. The method according to claim 8, characterized in that When the carbon source is a liquid carbon source, the carbon source / catalyst mass ratio is 50-200:1; when the carbon source is a carbon-containing gas, the carbon source flow rate is 50-200 ml / min, and the catalyst loading is 0.5-2% by weight.

10. The method according to claim 7, characterized in that The prepared single-walled carbon nanotubes have the following characteristics: The branching angle of the Y-shaped carbon nanotubes is controlled within the range of 30-45 degrees, with a deviation of <5 degrees; The turning angle of Z-shaped carbon nanotubes is controlled within the range of 100-140 degrees, with a deviation of <10 degrees; The pitch of the helical carbon nanotubes is controlled within the range of 20-100nm, and the uniformity deviation of the helical structure per unit length is <15%; The intensity ratio of the G peak to the D peak of the carbon nanotubes (IG / ID) is 8-12, and the orientation degree reaches 85-95%.

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