A method for preparing continuous and pure carbon nanotube fibers based on floating catalytic CVD method

Abstract

The application discloses a method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method, which can effectively remove amorphous carbon and micron-sized impurity particles in the wall of the carbon nanotube fibers, has high orientation of the carbon nanotube, dense fiber structure, and can realize thousands of kilometers of continuous pure carbon nanotube fibers, and the continuous and pure carbon nanotube fibers have higher tensile strength and conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon material preparation, and in particular relates to a method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method. Background Art

[0002] Carbon nanotubes (CNTs) are nanomaterials with single- or multi-layered coaxial circular tube structures composed of sp2 carbon atoms, exhibiting excellent mechanical and electrical properties. Carbon nanotube fibers, consisting of a large number of CNTs, are considered one of the most promising high-performance carbon-based fibers due to their high strength, toughness, conductivity, and flexibility.

[0003] Carbon nanotube fibers are typically produced using wet spinning, array spinning, or floating catalytic CVD. The floating catalytic CVD method holds the greatest promise for industrial production due to its high mechanical strength, continuous spinning properties, ease of operation, low cost, safety, and environmental friendliness. However, carbon nanotube fibers produced using the floating catalytic CVD method still suffer from structural challenges, including a high amorphous carbon content and numerous micron-sized impurity particles. The fracture mechanism of carbon nanotube fibers primarily relies on relative slip between carbon nanotube bundles, and the high amorphous carbon content reduces sp2 interfacial contact and van der Waals forces. During the high-temperature fiber production process, the carbon-coated iron catalyst easily aggregates into impurity particles hundreds of nanometers or even micrometers in size. These particles become trapped between carbon nanotubes, which are tens of microns in diameter, reducing stress transfer and network connectivity between the carbon nanotube bundles. Consequently, the high amorphous carbon content and the high number of micron-sized impurity particles reduce the mechanical and electrical properties of carbon nanotube fibers, hindering their application in biomedicine, electronics, and nanocomposites.

[0004] So far, there has been some progress in the research on the purification of carbon nanotube fibers. CN101187094A discloses a desolvable continuous carbon nanotube fiber and a preparation process, which mentions adding 1 to 10% by mass of water to the spinning raw material. Water can remove amorphous carbon from the fiber. The Korea Institute of Science and Technology (Lee S.H. et al. Chemical Engineering Science 2018, 192, 655-664) reported that spraying a trace amount of water (36.3 mol / min) in the middle of a floating catalytic CVD device for growing carbon nanotube fibers can oxidize and etch the amorphous carbon on the carbon nanotube wall. However, the crystallinity of the carbon nanotube fibers prepared by this method is still not high (the highest IG / ID characterized by Raman spectroscopy is only 4.33). CN107541809B discloses an effective method for purifying carbon nanotube fibers. This involves first subjecting 1-20 cm carbon nanotube fibers to an electrical treatment, then soaking them in hydrogen peroxide and acid, respectively. This method effectively removes carbon-coated iron catalyst particles. However, this method is not suitable for the continuous production of large quantities of purified carbon nanotube fibers, and its impurity removal effect is inconsistent for highly dense, highly oriented carbon nanotube fibers.

[0005] Therefore, developing a floating catalytic CVD method to prepare continuous and pure carbon nanotube fibers is currently an important research hotspot. Summary of the Invention

[0006] The present invention aims to address the shortcomings of existing technologies by providing a method for producing continuous and pure carbon nanotube fibers using a floating catalytic CVD process. This method, based on the floating catalytic CVD process for growing continuous carbon nanotube fibers, involves adding an oxygen etchant to a raw material solution to produce continuous carbon nanotube fibers with a dense structure, high orientation, and low amorphous carbon content. This method then undergoes post-processing to remove impurities, ultimately yielding continuous and pure carbon nanotube fibers.

[0007] The present invention aims to provide a method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method, which is characterized by comprising the following steps:

[0008] S1, mixing the carbon source, catalyst, and promoter to form a clear solution;

[0009] S2, adding an oxygen etchant to the clarified solution and mixing to obtain a uniform spinning solution;

[0010] S3, injecting the spinning solution into a CVD reactor, introducing a carrier gas, and producing carbon nanotube aggregates;

[0011] S4, sequentially passing the carbon nanotube aggregate through water densification treatment, continuous collection of a winding collector, heating and drying to obtain a primary continuous carbon nanotube fiber;

[0012] S5, sequentially oxidizing and then acidizing the primary continuous carbon nanotube fiber, washing and drying to obtain the continuous and pure carbon nanotube fiber.

[0013] According to an embodiment of the present application, in step S1, the carbon source is a liquid carbon source, preferably one or more of acetone, ethanol, butanol, cyclohexane, benzene; more preferably ethanol and / or acetone.

[0014] The carbon source used in the present application must be a liquid carbon source, so as to first mix with the catalyst and the promoter to form a clear solution, thereby facilitating the preparation of pure and continuous carbon nanotube fiber.

[0015] According to an embodiment of the present application, in step S1, the catalyst is ferrocene.

[0016] According to an embodiment of the present application, in step S1, the promoter is one or more of thiophene, elemental sulfur, carbon disulfide; preferably thiophene.

[0017] According to an embodiment of the present application, in step S2, the oxygen etchant is hydrogen peroxide aqueous solution or a large amount of water.

[0018] Among them, the mass fraction of hydrogen peroxide aqueous solution in the spinning solution is 1% to 20%, the mass fraction of hydrogen peroxide in the hydrogen peroxide aqueous solution is 1% to 30%, and the mass fraction of the large amount of water in the spinning solution is 10.5wt% to 40wt%.

[0019] Compared with the prior art of adding a small amount of water (i.e. 10wt% or less), the present application adds hydrogen peroxide aqueous solution or a large amount of water (water accounts for 10.5wt% to 40wt% of the mass fraction of the spinning solution) as an oxygen etchant, which can reduce the generation of byproduct amorphous carbon, facilitate the removal of the catalyst later, and prepare carbon nanotube fibers with finer diameter.

[0020] According to an embodiment of the present application, in step S3, the carrier gas is a mixture of hydrogen and inert gas; preferably, the inert gas is one or more of argon and nitrogen.

[0021] According to an embodiment of the present application, in step S3, the reaction temperature is 1000-1500℃, preferably 1300℃; the reaction time is 1 second to 20 seconds.

[0022] According to one embodiment of the present application, the step specifically comprises: the carbon nanotube aggregate is subjected to water densification treatment in a water tank; and the water-densified fiber is continuously collected by a winding collector outside the water tank to obtain a continuous wet fiber with a length of thousands of meters.

[0023] According to one embodiment of the present application, in step S4, the drying temperature is 300-500°C, preferably 400°C.

[0024] The length of the obtained primary continuous carbon nanotube fiber is 1-10000 m, and the diameter is 5-30 μm.

[0025] According to one embodiment of the present application, in step S5, the oxidation treatment method comprises one or more of the following methods: soaking the primary continuous carbon nanotube fiber in a hydrogen peroxide solution, annealing treatment, and electric treatment.

[0026] According to one embodiment of the present application, the oxidation treatment is first annealing treatment, and then soaking in a H2O2 solution.

[0027] Preferably, the H2O2 solution used for the oxidation treatment is a 30 wt% H2O2 solution.

[0028] According to one embodiment of the present application, the annealing atmosphere is air.

[0029] The annealing treatment removes the amorphous carbon impurities in the fiber.

[0030] According to one embodiment of the present application, the annealing temperature is 300-500°C, preferably 400°C; and the annealing time is 10-14 h, preferably 12 h.

[0031] According to one embodiment of the present application, step S5 specifically comprises uniformly winding the primary continuous carbon nanotube fiber on a corrosion-resistant and high-temperature-resistant spinning spindle, preferably made of quartz, and then performing annealing treatment in a muffle furnace.

[0032] According to one embodiment of the present application, the acidification treatment method comprises soaking the carbon nanotube fiber after the oxidation treatment in an acid solution.

[0033] According to one embodiment of the present application, the acid solution is one or more of a hydrochloric acid solution, a nitric acid solution, or a sulfuric acid solution.

[0034] According to one embodiment of the present application, the soaking time in the H2O2 solution is 10-14 h, preferably 12 h; the soaking time in the HCl solution is 10-14 h, preferably 12 h; and the soaking temperature in the HCl solution is 60-80°C, preferably 70°C.

[0035] The purpose of the present invention's two-step treatment method of first oxidation and then acidification is to remove the carbon wrapped around the surface of the iron particles and oxidize them into iron oxide by oxidation, and then wash away the iron oxide by acidification.

[0036] Beneficial effects:

[0037] The preparation method of continuous and pure carbon nanotube fibers based on the floating catalytic CVD method provided by the present invention can effectively remove amorphous carbon and micron-sized impurity particles from the carbon nanotube walls in the fibers compared with the existing technology. The carbon nanotubes have a high degree of orientation and a dense fiber structure. The pure carbon nanotube fibers can be continuous at the kilometer level, and the resulting continuous and pure carbon nanotube fibers have higher tensile strength and electrical conductivity.

[0038] The preparation method for preparing continuous and pure carbon nanotube fibers based on the floating catalytic CVD method is simple, easy to implement, low in cost, high in yield, and suitable for industrial-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a scanning electron microscope image of the continuous and pure carbon nanotube fibers in Example 1.

[0040] Figure 2A This is a transmission electron microscope image of the continuous and pure carbon nanotube fibers in Example 1.

[0041] Figure 2B Transmission electron microscope images of different positions of the continuous and pure carbon nanotube fibers in Example 1.

[0042] Figure 3 These are Raman spectra of the carbon nanotube fibers of Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0043] Figure 4 1 and 2 are tensile stress-strain curves of the carbon nanotube fibers of Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0044] Figure 5 This is a scanning electron microscope image of the continuous and pure carbon nanotube fibers in Example 2.

[0045] Figure 6 This is a transmission electron microscope image of the continuous and pure carbon nanotube fibers in Example 2.

[0046] Figure 7 This is a scanning electron microscope image of the continuous carbon nanotube fiber in Comparative Example 1.

[0047] Figure 8 This is a transmission electron microscope image of the continuous carbon nanotube fiber in Comparative Example 1.

[0048] Figure 9 This is a scanning electron microscope image of the continuous carbon nanotube fiber in Comparative Example 2.

[0049] Figure 10 This is a transmission electron microscope image of the continuous carbon nanotube fiber in Comparative Example 2. DETAILED DESCRIPTION

[0050] In order to make the technical problems and technical solutions solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0051] Example 1

[0052] (1) Acetone, ethanol, ferrocene, and thiophene were prepared into a solution with a mass ratio of 93.4%, 4.1%, 0.6%, and 1.9%, and ultrasonically treated for 10 minutes to form a clear solution. Acetone, ethanol, ferrocene, and thiophene were used as carbon sources, catalysts, and promoters for preparing carbon nanotube fibers, respectively. Deionized water was added to the solution in an amount of 33.2% by mass, and ultrasonically treated for 10 minutes to obtain a uniform spinning solution.

[0053] (2) The spinning solution is sprayed through an ultrasonic atomizer and injected into a vertical reactor at 1300°C. A mixed carrier gas of argon and hydrogen at a flow rate of 2L / min and 3L / min is introduced into the furnace tube to grow cylindrical carbon nanotube aggregates. The carbon nanotube aggregates are densely packed in a water tank to form primary continuous carbon nanotube fibers. The fibers are continuously collected by a winding collector outside the water tank, and several kilometers of continuous wet fibers can be collected. The wet fibers are continuously dried in a 400°C heating furnace to obtain primary continuous carbon nanotube fibers.

[0054] (3) The primary continuous carbon nanotube fibers were wound onto a quartz spool and annealed in an air atmosphere at 400°C in a muffle furnace for 12 hours. After being removed from the muffle furnace, the fibers were immersed in a 30 wt.% H2O2 solution for 12 hours, and then immersed in a 1 M HCl solution at 70°C for 12 hours. After being removed from the HCl solution, the fibers were repeatedly rinsed with deionized water and then dried in an oven at 60°C to obtain continuous and pure carbon nanotube fibers with a fiber diameter of 10 to 20 μm.

[0055] (4) The scanning electron microscope image of the obtained continuous and pure carbon nanotube fibers is as follows Figure 1 , transmission electron microscope images at different positions are shown in Figure 2.Figure 2A and Figure 2B As shown, the Raman spectrum is Figure 3 The stress-strain curve of the fiber is shown in Figure 4 As shown. From the scanning electron microscope image, it can be seen that the surface structure of the continuous and pure carbon nanotube fiber is dense and the carbon nanotube bundles are highly oriented. From the transmission electron microscope image, it can be seen that the thickness of the carbon nanotubes in the carbon nanotube fiber is relatively uniform, there is no amorphous carbon outside the tube wall, and no catalyst agglomerated particles are observed. From the Raman spectrum, it can be seen that the ratio of the carbon nanotube G peak intensity to the D peak intensity is as high as 7.8, indicating that the carbon nanotube fiber has few intrinsic defects. From the stress-strain curve of the fiber, it can be seen that the continuous and pure carbon nanotube fiber has a higher strength of ~3.3GPa. The conductivity tested by the four-probe method is ~9.0×10 5 S / m.

[0056] Example 2

[0057] This embodiment provides a method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method.

[0058] (1) Acetone, ethanol, ferrocene, and thiophene were prepared into a solution with a mass ratio of 93.4%, 4.1%, 0.6%, and 1.9%, and ultrasonically treated for 10 minutes to form a clear solution. Acetone, ethanol, ferrocene, and thiophene were used as carbon sources, catalysts, and promoters for preparing carbon nanotube fibers, respectively. A hydrogen peroxide solution was added to the solution with a concentration of 30 wt.%, and the added mass of the hydrogen peroxide solution accounted for 10.9 wt.% of the total mass. The solution was ultrasonically treated for 10 minutes to obtain a uniform spinning solution.

[0059] (2) The spinning solution is sprayed through an ultrasonic atomizer and injected into a vertical reactor at 1300°C. A mixed carrier gas of argon and hydrogen at a flow rate of 2L / min and 3L / min is introduced into the furnace tube to grow cylindrical carbon nanotube aggregates. The carbon nanotube aggregates are densely packed in a water tank to form primary continuous carbon nanotube fibers. The fibers are continuously collected by a winding collector outside the water tank, and several kilometers of continuous wet fibers can be collected. The wet fibers are continuously dried in a 400°C heating furnace to obtain primary continuous carbon nanotube fibers.

[0060] (3) The primary continuous carbon nanotube fibers were wound onto a quartz spool and annealed in an air atmosphere at 400°C in a muffle furnace for 12 hours. After being removed from the muffle furnace, the fibers were immersed in a 30 wt.% H2O2 solution for 12 hours, and then immersed in a 1 M HCl solution at 70°C for 12 hours. After being removed from the HCl solution, the fibers were repeatedly rinsed with deionized water and then dried in an oven at 60°C to obtain continuous and pure carbon nanotube fibers with a fiber diameter of 15 to 25 μm.

[0061] (4) From the scanning electron microscope images (such as Figure 5 ) It can be seen that the carbon nanotube bundles on the surface of continuous and pure carbon nanotube fibers are highly oriented and have a relatively uniform thickness, but with large gaps. From the transmission electron microscopy images (such as Figure 6 ) It can be seen that the thickness of the carbon nanotubes in the carbon nanotube fiber is relatively uniform, there is little amorphous carbon outside the tube wall, and there are few catalyst agglomerated particles. From the Raman spectrum (such as Figure 3 ) can be seen from the carbon nanotube G peak intensity to D peak intensity ratio is as high as 5.3, indicating that the carbon nanotube fiber has few intrinsic defects. From the stress-strain curve of the fiber (such as Figure 4 ) It can be seen that the continuous and pure carbon nanotube fibers have a higher strength of ~2.7GPa. The conductivity measured by the four-probe method is ~7.0×10 5 S / m.

[0062] Comparative Example 1

[0063] This embodiment provides a method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method.

[0064] (1) Other conditions were the same as those in Example 1, except that deionized water was not added to the spinning solution.

[0065] (2) The spinning solution is sprayed through an ultrasonic atomizer and injected into a vertical reactor at 1300°C. A mixed carrier gas of argon and hydrogen at a flow rate of 2L / min and 3L / min is introduced into the furnace tube to grow cylindrical carbon nanotube aggregates. The carbon nanotube aggregates are densely packed in a water tank to form primary continuous carbon nanotube fibers. The fibers are continuously collected by a winding collector outside the water tank, and several kilometers of continuous wet fibers can be collected. The wet fibers are continuously dried in a 400°C heating furnace to obtain primary continuous carbon nanotube fibers.

[0066] (3) The primary continuous carbon nanotube fibers were wound onto a quartz reel and annealed in an air atmosphere at 400°C in a muffle furnace for 12 hours. After being removed from the muffle furnace, the fibers were immersed in a 30 wt.% H2O2 solution for 12 hours, and then immersed in a 1 M HCl solution at 70°C for 12 hours. After being removed from the HCl solution, the fibers were repeatedly rinsed with deionized water and then dried in an oven at 60°C to obtain continuous carbon nanotube fibers with a fiber diameter of 25 to 35 μm.

[0067] (4) From the scanning electron microscope images (such as Figure 7 ) It can be seen that the surface structure of continuous carbon nanotube fibers is relatively dense, and the orientation of carbon nanotube bundles is relatively disordered and contains many impurities. From the transmission electron microscopy images (such as Figure 8) It can be seen that the thickness of the carbon nanotubes in the carbon nanotube fiber is relatively uneven, the outer wall of the tube contains amorphous carbon, and there are many catalyst agglomerated particles. From the Raman spectrum (such as Figure 3 ) can be seen from the carbon nanotube G peak intensity to D peak intensity ratio is 2.3, indicating that the carbon nanotube fiber has many intrinsic defects. From the stress-strain curve of the fiber (such as Figure 4 ) It can be seen that the continuous carbon nanotube fiber has a tensile strength of ~1.2GPa. The conductivity measured by the four-probe method is ~2.7×10 5 S / m.

[0068] Comparative Example 2

[0069] This embodiment provides a method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method.

[0070] (1) Other conditions were the same as those in Example 1, except that the amount of deionized water added to the spinning solution was 7.5 wt%.

[0071] (2) The spinning solution is sprayed through an ultrasonic atomizer and injected into a vertical reactor at 1300°C. A mixed carrier gas of argon and hydrogen at a flow rate of 2L / min and 3L / min is introduced into the furnace tube to grow cylindrical carbon nanotube aggregates. The carbon nanotube aggregates are densely packed in a water tank to form primary continuous carbon nanotube fibers. The fibers are continuously collected by a winding collector outside the water tank, and several kilometers of continuous wet fibers can be collected. The wet fibers are continuously dried in a 400°C heating furnace to obtain primary continuous carbon nanotube fibers.

[0072] (3) The primary continuous carbon nanotube fibers were wound onto a quartz reel and annealed in an air atmosphere at 400°C in a muffle furnace for 12 hours. After being removed from the muffle furnace, the fibers were immersed in a 30 wt.% H2O2 solution for 12 hours, and then immersed in a 1 M HCl solution at 70°C for 12 hours. After being removed from the HCl solution, the fibers were repeatedly rinsed with deionized water and then dried in an oven at 60°C to obtain continuous carbon nanotube fibers with a fiber diameter of 25 to 35 μm.

[0073] (4) From the scanning electron microscope images (such as Figure 9 ) It can be seen that the surface structure of continuous carbon nanotube fibers is dense and the orientation of carbon nanotube bundles is disordered. From the transmission electron microscopy (such as Figure 10 ) It can be seen that the thickness of the carbon nanotubes in the carbon nanotube fiber is relatively uneven, the outer wall of the tube contains amorphous carbon, and there are many catalyst agglomerated particles. From the Raman spectrum (such as Figure 3 ) can be seen from the carbon nanotube G peak intensity to D peak intensity ratio is 3.2, indicating that the carbon nanotube fiber has many intrinsic defects. From the stress-strain curve of the fiber (such as Figure 4) It can be seen that the continuous carbon nanotube fiber has a tensile strength of ~1.4GPa. The conductivity measured by the four-probe method is ~3.5×10 5 S / m.

Claims

1. A method for preparing continuous and pure carbon nanotube fibers based on a floating catalytic CVD method, characterized in that: The following steps are involved: S1, mixing the carbon source, catalyst, and promoter to form a clear solution; S2, adding an oxygen etchant to the clarified solution and mixing to obtain a uniform spinning solution; S3, injecting the spinning solution into a CVD reactor, introducing a carrier gas, and producing carbon nanotube aggregates; S4, sequentially subjecting the carbon nanotube aggregates to water densification treatment, continuous collection by a winding collector, and heating and drying to obtain primary continuous carbon nanotube fibers; S5, subjecting the primary continuous carbon nanotube fibers to oxidation treatment and then acidification treatment, washing, and drying to obtain the continuous and pure carbon nanotube fibers; Wherein, in step S1, the carbon source is a liquid carbon source; In step S2, the oxygen etchant is a hydrogen peroxide aqueous solution or a large amount of water; the hydrogen peroxide aqueous solution accounts for 1% to 20% of the mass of the spinning solution, and the hydrogen peroxide accounts for 1% to 30% of the mass of the hydrogen peroxide aqueous solution; the large amount of water accounts for 10.5wt% to 40wt% of the mass of the spinning solution.

2. The method according to claim 1, characterized in that In step S1, the carbon source is one or more of acetone, ethanol, butanol, cyclohexane, and benzene.

3. The method according to claim 2, characterized in that The carbon source is ethanol and / or acetone.

4. The method according to claim 1, wherein In step S1, the catalyst is ferrocene.

5. The method according to claim 1, wherein In step S1, the accelerator is one or more of thiophene, elemental sulfur, and carbon disulfide.

6. The method according to claim 1, characterized in that In step S3, the carrier gas is a mixture of hydrogen and an inert gas.

7. The method according to claim 6, characterized in that The inert gas is one or more of argon and nitrogen.

8. The method according to claim 1, characterized in that In step S3, the reaction temperature is 1000-1500° C.; and the reaction time is 1 second to 20 seconds.

9. The method according to claim 8, characterized in that The reaction temperature is 1300°C.

10. The method according to claim 1, characterized in that Step S4 includes: the carbon nanotube aggregates are subjected to water densification treatment in a water tank; and then the fibers subjected to water densification treatment are continuously collected by a winding collector outside the water tank to obtain several kilometers of continuous wet fibers.

11. The method according to claim 1, characterized in that In step S5, the oxidation treatment method includes soaking the primary continuous carbon nanotube fibers in a hydrogen peroxide solution, annealing, soaking in nitric acid, or applying electricity, or more of the above methods; The acid treatment method includes soaking the oxidized carbon nanotube fibers in an acid solution.

12. The method according to claim 11, characterized in that The oxidation treatment is to first perform annealing treatment and then soak in H2O2 solution.

Images