A single-walled carbon nanotube short tube, a preparation method thereof and a catalyst precursor

Abstract

The present application relates to the field of single-walled carbon nanotube structure control preparation, and particularly to a preparation method of a catalyst precursor for single-walled carbon nanotube short tubes, a quartz tube for preparing single-walled carbon nanotube short tubes, and a single-walled carbon nanotube short tube and a preparation method thereof. The preparation method of the single-walled carbon nanotube short tube comprises the following steps: dissolving cobalt nitrate hexahydrate and CTAB in deionized water, and then mixing and stirring with a 2-methyl imidazole aqueous solution; mixing and uniformly dispersing the prepared cobalt-based metal organic framework compound, ferrocene, thiophene and liquid-phase carbon source to form a dispersion liquid; and then injecting the dispersion liquid into a reaction furnace, and under the action of a gaseous carbon source, a reducing gas and a protective gas, a mixture containing single-walled carbon nanotube short tubes is prepared by a floating catalyst chemical vapor deposition method. The method has the advantage that direct controllable preparation of single-walled carbon nanotube short tubes is realized by using a chemical vapor deposition method.

Description

Technical Field

[0001] This invention relates to the field of controlled preparation of single-walled carbon nanotubes, specifically to a method for preparing single-walled carbon nanotubes, the single-walled carbon nanotubes obtained by the method, and a catalyst precursor used in the method. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) are one-dimensional nanomaterials with a unique hexagonal honeycomb lattice structure composed of a single layer of carbon atoms, typically with diameters between 0.4 and 2 nm. SWCNTs possess extremely high specific surface area and excellent mechanical and electrical properties. Their electronic properties are strongly dependent on chirality and tube diameter, exhibiting metallic or semiconducting characteristics. Therefore, they show broad application prospects in many cutting-edge fields such as electronic devices, energy storage, and sensors.

[0003] Compared to long single-walled carbon nanotubes with lengths of 5–30 micrometers, short single-walled carbon nanotubes with lengths of 1–3 micrometers exhibit significant advantages in specific applications. Short tubes are easier to uniformly disperse in composite matrices, coatings, or slurries, effectively suppressing agglomeration and thus ensuring the uniformity and stability of the material's electrical and thermal conductivity. This characteristic makes them particularly suitable for applications requiring high dispersion quality, such as electrode coatings and functional thin films. Furthermore, in size-sensitive applications such as micro / nanoelectronic devices, sensors, and thin-film batteries, short tubes, due to their smaller axial dimensions, are easier to integrate and less prone to structural defects or spatial conflicts, resulting in greater fabrication versatility.

[0004] In terms of preparation, the commonly used acid shearing method (such as ultrasonic treatment in mixed acid) can cut long tubes, but the process is prone to damage to the carbon nanotube structure and the generation of amorphous carbon impurities, as well as the increase of various functional groups on the surface, which affects the purity and performance of the product.

[0005] In contrast, chemical vapor deposition (CVD) has become the mainstream technology for preparing SWCNTs due to its simple equipment, low cost, and high product purity. Among these methods, floating catalyst CVD significantly improves the yield of short carbon nanotubes (SWCNTs) because of its sufficient gas-solid contact, continuous movement and collision of catalyst particles under turbulent gas flow, which promotes the detachment of carbon nanotubes from active sites. However, while current CVD methods can avoid structural damage to the product, they suffer from low yield, poor uniformity, and wide size distribution. The fundamental reason for this is the lack of effective synergistic control over the catalyst particle size and the fluid dynamics environment within the reaction chamber. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a single-walled carbon nanotube, a preparation method thereof, and a catalyst precursor for preparing single-walled carbon nanotubes. This involves using a cobalt-based metal-organic framework as a precursor for adsorbing ferrocene ions and thiophene, with the framework itself serving as the catalyst precursor. The reduction of metal ions is then completed at high temperature and in a reducing atmosphere to obtain a catalyst capable of catalyzing the production of single-walled carbon nanotubes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing single-walled carbon nanotubes, the specific steps of which are as follows:

[0009] S1. Preparation of cobalt-based metal-organic framework compound: Cobalt nitrate hexahydrate and hexadecyltrimethylammonium bromide are dissolved in deionized water, then mixed with an aqueous solution of 2-methylimidazole, reacted, the precipitate is collected, washed and dried to obtain the cobalt-based metal-organic framework compound; wherein, the amount of hexadecyltrimethylammonium bromide added is used to control the particle size of the cobalt-based metal-organic framework compound;

[0010] S2. Preparation of catalyst dispersion: The cobalt-based metal-organic framework compound obtained in step S1 is mixed with ferrocene, thiophene, and liquid carbon source and dispersed evenly to form a dispersion.

[0011] S3. Chemical vapor deposition growth: The dispersion is injected into a reactor. In the presence of a gaseous carbon source, reducing gas and protective gas, a floating catalyst chemical vapor deposition reaction is carried out in a quartz tube reaction chamber with nipple-shaped protrusions on the inner wall to disturb the airflow and increase the probability of catalyst particle collision. The reaction time is 0.5 to 20 minutes to obtain a product containing single-walled carbon nanotubes.

[0012] S4. Purification: The product obtained in step S3 is heat-treated in an oxygen-containing atmosphere, followed by acid washing and water washing to obtain purified single-walled carbon nanotubes.

[0013] More preferably, the mass ratio of cobalt nitrate hexahydrate, hexadecyltrimethylammonium bromide and 2-methylimidazole is 0.6:(0.01~0.06):9; the mass ratio of cobalt-based metal-organic framework compound, ferrocene and thiophene is (50~70):(5~7):(0.5~0.7).

[0014] More preferably, the liquid-phase carbon source is one or more of methanol, ethanol, benzyl alcohol, and toluene; the gas-phase carbon source is one or two of methane and ethylene; the reducing gas is hydrogen; and the protective gas is nitrogen.

[0015] More preferably, the dispersion is injected at a rate of 5-10 μL / min, the total flow rate of nitrogen and hydrogen is 5-10 L / min, the nitrogen / hydrogen flow ratio is 2-4, the methane / ethylene supply is 1-5 mL / min, and the reactor growth temperature is 1150-1250℃.

[0016] More preferably, the nipple-like protrusion is hemispherical, and the height of the protrusion is 1~4mm; and the ratio of the height (H) of the nipple-like protrusion to the inner diameter (D) of the quartz tube satisfies: 0.45% ≤ H / D ≤ 5.0%.

[0017] More preferably, the quartz tube is divided into an upstream region, a core growth region, and a downstream region along the airflow direction, and the number of the nipple-like protrusions in the upstream region, the core growth region, and the downstream region decreases sequentially; the nipple-like protrusions in the upstream region and the downstream region are distributed in a non-periodic manner, and the nipple-like protrusions in the core growth region are distributed in a regular arrangement of multiple rows in a ring on the inner wall of the tube, and the protrusions in adjacent rows are staggered in the circumferential direction.

[0018] More preferably, the length of the upstream region accounts for 20% to 30% of the total length of the quartz tube; the length of the core growth region accounts for 40% to 60% of the total length of the quartz tube; the length of the downstream region accounts for 20% to 30% of the total length of the quartz tube; and the ratio of the number of papillary protrusions in the upstream region, core growth region, and downstream region is (4 to 5): (2 to 3): (1 to 2).

[0019] More preferably, the number of papillary protrusions in the upstream region is 20-25, the number of papillary protrusions in the core growth region is 10-15, and the number of papillary protrusions in the downstream region is 5-10.

[0020] More preferably, the total projected area of ​​all the said papillary protrusions on the inner wall of the quartz tube accounts for 0.007% to 1.00% of the total projected area of ​​the inner wall of the tube.

[0021] The core of this method lies in the innovative design of two synergistic effects:

[0022] 1. Precise source control of catalyst size

[0023] This invention achieves precise control over the size of the catalyst support by introducing a specific amount of the surfactant cetyltrimethylammonium bromide (CTAB) during the preparation of cobalt-based metal-organic framework compounds (Co-MOFs). The mechanism is as follows:

[0024] (1) Steric hindrance effect: The long alkyl chain of CTAB forms an organic layer on the surface of Co-MOF crystal, which generates steric hindrance, preventing disordered aggregation and further fusion growth between crystal grains, thereby promoting the formation of small-sized, monodisperse nanocrystals.

[0025] (2) Competitive coordination: bromide ions (Br) in CTAB - ) is a relatively weak coordinating anion that can compete with 2-methylimidazole for coordination to Co. 2+ On the ionic side, this competitive coordination slows down the nucleation and growth rate of Co-MOF crystals. When nucleation and growth are slower, the reaction system has more time to generate more nucleation sites, rather than allowing existing nuclei to grow rapidly, ultimately resulting in smaller and more uniformly distributed products. In summary, the amount of CTAB is adjustable from 1.67% to 10% of the mass of cobalt nitrate hexahydrate. A higher CTAB content results in a greater number of Co-MOF seed crystals and a smaller Co-MOF particle size.

[0026] Using small-sized Co-MOF as a support to adsorb ferrocene and thiophene to form a catalyst precursor, high-density, small-sized active catalyst particles can be obtained after high-temperature reduction. Small-sized catalysts have two key advantages: First, small particles have extremely high specific surface area and surface energy, making them very unstable at high temperatures. The carbon source is more likely to undergo carbon encapsulation on the surface, encapsulating the catalyst and causing it to lose activity. Due to the premature and rapid deactivation of the catalyst particles, the growth of carbon nanotubes is forced to terminate within a short time. Therefore, the grown SWCNTs are shorter; the larger particle volume makes them less likely to be completely encapsulated by the carbon layer, effectively extending the catalyst's active lifetime and allowing SWCNTs to continue growing, resulting in longer SWCNTs. Second, for the same mass of Co-MOF catalyst, smaller-sized Co-MOF has a greater number of particles. The floating catalyst has a higher collision probability in the reactor tube, making it easier for the growing carbon nanotubes to detach from the catalyst surface, terminating growth and resulting in shorter tubes.

[0027] This is the first level of regulation for achieving the "shortening" of carbon nanotubes in this invention.

[0028] 2. Active intervention design for the fluid dynamics environment within the reaction chamber

[0029] This invention uses a quartz tube with specific nipple-like protrusions on its inner wall as the reaction chamber. The nipple-like protrusions are hemispherical; this shape effectively disturbs the airflow while avoiding carbon particle deposition and stress concentration caused by sharp edges. Taking a quartz tube with an inner diameter of 0.22 m and a length of 2.2 m as an example, the height of the nipple-like protrusions is 1–4 mm, and the bottom diameter is 2–8 mm. That is, the ratio of the protrusion height to the inner diameter of the quartz tube (height / inner diameter × 100%) is approximately 0.45%–1.8%. Taking a quartz tube with an inner diameter of 0.08 m and a length of 1 m as an example, the height of the nipple-like protrusions is 1–4 mm, and the bottom diameter is 2–8 mm; the ratio of the protrusion height to the inner diameter of the quartz tube (height / inner diameter × 100%) is approximately 1.25%–5%. The height of this protrusion is much smaller than the inner diameter of the quartz tube (the proportion is less than 5%). The protrusion has a very small effect on reducing the cross-sectional area of ​​the channel inside the tube. Its overall impact on fluid flow is more reflected in the surface roughness reflected by the projected area.

[0030] The arrangement of the papillae is carefully designed: divided into an upstream zone, a core growth zone, and a downstream zone along the airflow direction. The upstream zone has a dense distribution of papillae (20-25) to enhance turbulence and ensure thorough mixing of the carbon source, catalyst precursor, and carrier gas before they enter the growth zone. The core growth zone has a uniform distribution of papillae (10-15), whose main function is to continuously disturb the reaction boundary layer, greatly increasing the probability of collisions between catalyst particles and between particles and the tube wall. This actively "knocks" the growing carbon nanotubes off the active sites, forcibly terminating their axial growth—the most direct and effective physical means of obtaining short tubes. Simultaneously, the number of papillae in the core growth zone should not be too large to ensure gas-phase mass transfer, providing a continuous and stable carbon source and catalyst "supply" for the growing carbon nanotubes. The downstream zone has a sparse distribution of papillae (5-8) to stabilize the airflow and ensure smooth product transport.

[0031] The ratio of the projected area of ​​the papilla structure on the inner wall of the quartz tube to the total projected area of ​​the inner wall: The total projected area of ​​all papillae accounts for 0.007% to 1% of the total projected area of ​​the inner wall of the tube. This ratio is optimized to ensure effective disturbance while avoiding eddies or pressure fluctuations caused by excessive flow resistance, thereby suppressing the deposition of by-products (amorphous carbon) caused by these unfavorable flow states.

[0032] This is the second active regulation by which the present invention achieves the "shortening" of carbon nanotubes.

[0033] The synergistic effect of the aforementioned dual regulatory mechanisms enables efficient and controllable preparation of single-walled carbon nanotubes.

[0034] Secondly, the present invention provides a single-walled carbon nanotube prepared by the above method, wherein the average length of the single-walled carbon nanotube prepared by the above method is less than 6 micrometers; wherein the proportion of single-walled carbon nanotubes with a length in the range of 0.5 to 3 micrometers is greater than 40%; the Raman spectrum of the single-walled carbon nanotube is... G / I D The ratio is not less than 15. It has high crystallinity and excellent length uniformity.

[0035] Thirdly, the present invention provides a catalyst precursor for the above method, which is formed by adsorbing ferrocene and thiophene onto a cobalt-based metal-organic framework compound.

[0036] The cobalt-based metal-organic framework compound is prepared by a method comprising the following steps: dissolving cobalt nitrate hexahydrate and hexadecyltrimethylammonium bromide in deionized water, then mixing and reacting with an aqueous solution of 2-methylimidazole, collecting the precipitate and washing and drying it, wherein the amount of hexadecyltrimethylammonium bromide is 1.67% to 10% of the mass of cobalt nitrate hexahydrate.

[0037] Compared with the prior art, the present invention has the following significant advantages:

[0038] 1. This invention organically combines the "chemical regulation" of catalyst size with the "physical regulation" of reaction flow field. Through the synergistic effect of the two, it achieves active and precise control of carbon nanotube length from the growth mechanism, solving the problems of low yield and wide distribution of short tubes in traditional methods.

[0039] 2. Its mechanism is clear and highly designable. It clarifies the competitive coordination and steric hindrance mechanism of CTAB in regulating Co-MOF size, as well as the dual role of small-sized catalysts in deactivation and collision. It also elucidates the different functions of papillary structure partitioning design in mixing, collision, and flow field stabilization. The process parameters have a clear theoretical basis and can be customized for target lengths.

[0040] 3. Excellent product quality: The method avoids post-processing shearing, resulting in short tubes with complete structure, few defects, and high crystallinity, retaining excellent intrinsic properties and greatly improving the yield and proportion of single-walled carbon nanotubes.

[0041] 4. This method is based on existing CVD equipment, is easy to modify, and is easy to scale up, thus having good prospects for industrial application. Attached Figure Description

[0042] The above features and advantages of the present invention will become clearer and more readily understood from the following description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0043] Figure 1 This is a flowchart of the method for preparing single-walled carbon nanotubes using metal-organic frameworks according to the present invention;

[0044] Figure 2 This is the X-ray diffraction pattern of the cobalt-based metal-organic framework compound obtained in step (1) of Example 1;

[0045] Figure 3 These are scanning electron microscope images of the cobalt-based metal-organic framework compounds obtained in step (1) of Examples 1 (d1-d3 represent different magnifications), 2 (c1-c3 represent different magnifications), 3 (b1-b3 represent different magnifications), and 4 (a1-a3 represent different magnifications);

[0046] Figure 4 This is a scanning electron microscope image of the single-walled carbon nanotubes from Example 1.

[0047] Figure 5 This is a transmission electron microscope image of the single-walled carbon nanotubes from Example 1. Figure 5 (a1) is a low-magnification TEM image of the sample. Figure 5 (a2) is a high-magnification TEM image of the sample;

[0048] Figure 6 The image shows the Raman spectrum of a single-walled carbon nanotube from Example 1.

[0049] Figure 7 This is a schematic diagram of the quartz tube in Example 1. Detailed Implementation

[0050] 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.

[0051] Example 1

[0052] (1) 0.6 g of Co(NO3)2·6H2O was dissolved in 20 mL of deionized water containing 60 mg of CTAB. The solution was then rapidly injected into 150 mL of aqueous solution containing 9 g of 2-methylimidazole and stirred vigorously at room temperature for 30 minutes. The purple precipitate was collected by centrifugation, washed 6 times with ethanol, and dried to obtain a cobalt-based metal-organic framework compound.

[0053] (2) The Co-MOF, ferrocene, thiophene and ethanol prepared in the above steps are stirred and ultrasonically dispersed in a mass ratio of 50:5:0.5:200000 to obtain a mixed dispersion; the purpose is to make Co-MOF adsorb a small amount of ferrocene ions as a catalyst precursor and thiophene as a growth promoter.

[0054] See Figure 1 The dispersion was then injected into a floating catalyst chemical vapor deposition (VCVDC) tubular furnace using a microsyringe at a rate of 5 μL / min. Nitrogen was used as the protective gas, hydrogen as the reducing gas, and ethylene as the gaseous carbon source. The total flow rate of nitrogen and hydrogen was 5 L / min, the nitrogen / hydrogen flow ratio was 2, the ethylene supply was 5 mL / min, and the furnace growth temperature was 1200 °C. The reaction chamber of the furnace was a quartz tube with a papillary structure on the inner wall, and a mixture containing high-quality single-walled carbon nanotubes was prepared by floating catalyst VCVDC.

[0055] like Figure 7 As shown, the quartz tube used in this embodiment 1 has an inner diameter of 0.22 meters and a length of 2.2 meters.

[0056] Along the airflow direction, the quartz tube is divided into an upstream region, a core growth region, and a downstream region. The core growth region is 1 m long, while the upstream and downstream regions are each 0.6 m long. On the inner walls of the upstream, core growth, and downstream regions, there are nipple-like protrusions. These protrusions are identical in shape and size, all being hemispherical, with a height of 2 mm and a bottom diameter of 4 mm.

[0057] The number of papillary protrusions decreases sequentially in the upstream, core growth, and downstream regions. Specifically, there are 25 in the upstream region, 15 in the core growth region, and 8 in the downstream region. The papillary protrusions in the upstream and downstream regions are randomly distributed, while those in the central core region are arranged in multiple rows of regular rings on the inner wall of the tube, with adjacent rows of protrusions staggered circumferentially.

[0058] The projected area of ​​a single mastoid base is approximately 12.6 square millimeters, and the total projected area is approximately 603.8 square millimeters, accounting for approximately 0.04% of the total projected area of ​​the inner wall of the tube.

[0059] The height of the papillary protrusions is 0.91% of the inner diameter of the quartz tube.

[0060] (3) After reacting for 0.5 minutes, turn off the gas source and microsyringe, and stop heating. Allow the mixture to cool naturally to room temperature under argon protection, and collect the sample product. Place the prepared mixture in a conventional tube furnace and oxidize it in air at 350°C for 10 hours to remove the porous hard carbon material inside, thus purifying the mixture. After cooling to room temperature, remove the sample and soak it in a 7M hydrochloric acid solution. Wash it several times at 80°C until the hydrochloric acid solution no longer changes color. Finally, wash the sample with deionized water until the pH value is 7, and then vacuum dry the sample at 100°C to obtain the final single-walled carbon nanotubes.

[0061] The product was characterized as follows:

[0062] Figure 2 The XRD pattern of the cobalt-based metal-organic framework compound obtained in Example 1 is consistent with the characteristic peaks of the ZIF-67 fitting card. Figure 3 These are scanning electron microscope images of the cobalt-based metal-organic framework compounds obtained in step (1) of Examples 1 (d1-d3), 2 (c1-c3), 3 (b1-b3), and 4 (a1-a3). It can be seen that the product size gradually increases as the amount of CTAB added decreases. Figure 4 The image shows a SEM image of the single-walled carbon nanotube short tubes obtained in Example 1. After statistical analysis of the dimensions of 203 single-walled carbon nanotubes, 66% of them had a length in the range of 0.5 to 3 micrometers. Figure 5 The image shown is a TEM image of the single-walled carbon nanotube short tube obtained in Example 1, which proves that the sample is mainly composed of single-layer single-walled carbon nanotubes. Figure 6 The image shown is the Raman spectrum of the sample, I G / I D The ratio can be used to qualitatively determine the degree of graphitization and crystallinity of single-walled carbon nanotubes. After calculation, I... G / I D The ratio is 15.79, which shows that the sample has good crystallinity.

[0063] The average length of the carbon nanotubes obtained from the catalyst shows a positive correlation with the catalyst size; that is, the smaller the catalyst size, the smaller the corresponding average length of the carbon nanotubes. This is because smaller catalyst particles result in a higher collision frequency in the reaction chamber, making it more likely that the carbon nanotubes will detach from the catalyst surface in the early stages of short tube formation, thus ending their growth.

[0064] Example 2

[0065] (1) 0.6 g of Co(NO3)2·6H2O was dissolved in 20 mL of deionized water containing 40 mg of CTAB. Then, the solution was rapidly injected into 150 mL of aqueous solution containing 9 g of 2-methylimidazole and stirred vigorously at room temperature for 30 minutes. The purple precipitate was collected by centrifugation, washed 6 times with ethanol, and dried.

[0066] (2) Same as step (2) in Example 1.

[0067] (3) Same as step (3) in Example 1.

[0068] Example 3

[0069] (1) 0.6 g of Co(NO3)2·6H2O was dissolved in 20 mL of deionized water containing 20 mg of CTAB. Then, the solution was rapidly injected into 150 mL of aqueous solution containing 9 g of 2-methylimidazole and stirred vigorously at room temperature for 30 minutes. The purple precipitate was collected by centrifugation, washed 6 times with ethanol, and dried.

[0070] (2) Same as step (2) in Example 1.

[0071] (3) Same as step (3) in Example 1.

[0072] Example 4

[0073] (1) 0.6 g of Co(NO3)2·6H2O was dissolved in 20 mL of deionized water containing 10 mg of CTAB. Then, the solution was rapidly injected into 150 mL of aqueous solution containing 9 g of 2-methylimidazole and stirred vigorously at room temperature for 30 minutes. The purple precipitate was collected by centrifugation, washed 6 times with ethanol, and dried.

[0074] (2) Same as step (2) in Example 1.

[0075] (3) Same as step (3) in Example 1.

[0076] Example 5

[0077] (1) Same as step (1) in Example 1.

[0078] (2) Same as step (2) in Example 1.

[0079] (3) After reacting for 1 minute, turn off the gas source and micro-syringe, stop heating, and allow the sample to cool naturally to room temperature under argon protection. Collect the sample product.

[0080] Example 6

[0081] (1) Same as step (1) in Example 1.

[0082] (2) Same as step (2) in Example 1.

[0083] (3) After the reaction has been going on for 2 minutes, turn off the gas source and the micro-syringe, and stop heating. Allow the mixture to cool naturally to room temperature under argon protection and collect the sample product.

[0084] Example 7

[0085] (1) Same as step (1) in Example 1.

[0086] (2) Same as step (2) in Example 1.

[0087] (3) After the reaction has been going on for 3 minutes, turn off the gas source and the micro-syringe, and stop heating. Allow the mixture to cool naturally to room temperature under argon protection and collect the sample product.

[0088] Example 8:

[0089] The dimensions of the quartz tube in Example 8 are the same as in Example 1.

[0090] The papillary protrusion is 1 mm high and 2 mm in diameter at the base.

[0091] Twenty papillae were set in the upstream area, ten in the core growth area, and five in the downstream area.

[0092] The total projected area of ​​the mastoid process is approximately 109.96 square millimeters, accounting for about 0.007% of the total projected area of ​​the inner wall of the tube.

[0093] The height of the papillary protrusions is 0.45% of the inner diameter of the quartz tube.

[0094] Example 9:

[0095] In this embodiment, the quartz tube has an inner diameter D = 80 mm and a length L = 1000 mm; the total inner wall area is 251,327 mm². 2 .

[0096] The nipple-like protrusion is 4 mm high and has a base diameter of 8 mm.

[0097] There are 25 upstream zones, 15 core growth zones, and 10 downstream zones.

[0098] The total projected area of ​​the mastoid process is approximately 2513.27 square millimeters, accounting for about 1.00% of the total projected area of ​​the inner wall of the tube.

[0099] The height of the nipple-like protrusions is 5% of the inner diameter of the quartz tube.

[0100] Example 10:

[0101] The quartz tube in Example 4 is the same as in Example 3.

[0102] In this embodiment, the height of the nipple-like protrusion is 2 mm, and the bottom diameter is 4 mm.

[0103] There are 20 upstream zones, 15 core growth zones, and 10 downstream zones.

[0104] The total projected area of ​​the mastoid process is approximately 628.32 square millimeters, accounting for about 0.2% of the total projected area of ​​the inner wall of the tube.

[0105] The height of the papillary protrusions is 2.5% of the inner diameter of the quartz tube.

[0106] Comparative Example 1 (using a smooth quartz tube)

[0107] (1) Same as step (1) in Example 1.

[0108] (2) Cobalt-based metal-organic framework compound, ferrocene, thiophene and ethanol were stirred and ultrasonically dispersed in a mass ratio of 50:5:0.5:100 to obtain a mixed solution. The solution injection rate was 5 μL / min, the total flow rate of nitrogen and hydrogen was 5 L / min, the nitrogen / hydrogen flow rate ratio was 2, the ethylene supply was 5 mL / min, and the growth temperature was 1200℃.

[0109] The main difference lies in the use of conventional quartz tubes to prepare high-quality single-walled carbon nanotubes via floating catalyst chemical vapor deposition.

[0110] (3) Same as step (3) in Example 1.

[0111] Key data for each embodiment and comparative example are summarized in Table 1 below.

[0112]

[0113] Data Analysis

[0114] 1. Comparing Examples 1-4, it can be seen that under the same reaction time and quartz tube structure, the greater the amount of CTAB (i.e. the smaller the size of the catalyst precursor), the shorter the average length of the obtained carbon nanotubes and the higher the proportion of short tubes (0.5-3μm). This verifies that controlling the catalyst size through CTAB is an effective means to achieve the preparation of short tubes.

[0115] 2. Comparing Examples 1, 5, 6, and 7, it can be seen that the reaction time has a significant impact on the final length, and a shorter reaction time is beneficial for obtaining a short tube.

[0116] 3. The most important comparison is that Example 1 and Comparative Example 1 used the exact same catalyst precursor (10% CTAB) and reaction time (0.5 minutes). The only difference was the structure of the inner wall of the quartz tube. Example 1, using the papillary quartz tube of the present invention, had a product with an average length (1.7 μm) much shorter than Comparative Example 1 (6.8 μm) using a smooth quartz tube, and a significantly higher proportion of short tubes (66%) than Comparative Example 1 (37%). Although Comparative Example 1's I... G / I D The length is greater than that of Example 1, but this advantage comes from the longer average length of Example 1. The present invention aims at controllable preparation of short tubes, rather than simply pursuing the highest I. G / I D The above facts irrefutably demonstrate that the papillary quartz tube structure plays a decisive role in increasing collisions and forcibly terminating growth to obtain short tubes.

[0117] Based on the above data, the small-sized catalyst precursor and the papillary quartz tube reaction chamber work synergistically to constitute the core technical solution for the efficient and controllable preparation of single-walled carbon nanotubes of this invention, achieving superior results far exceeding those of any single technical method. The above embodiments have provided a detailed description of the inventive intent and implementation of this invention. However, those skilled in the art will understand that the above embodiments are merely preferred embodiments of this invention. Due to space limitations, not all embodiments can be listed here. Any implementation that embodies the technical solution of the claims of this invention is within the protection scope of this invention.

[0118] It should be noted that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and it should not be considered that the specific embodiments of the present invention are limited to this. Under the guidance of the above embodiments, those skilled in the art can make various improvements and modifications based on the above embodiments, and these improvements or modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing a single-walled carbon nanotube short, characterized by, The method comprises the following steps: S1. Preparing a cobalt-based metal organic framework compound: dissolving cobalt nitrate hexahydrate and cetyltrimethylammonium bromide in deionized water, then mixing and reacting with an aqueous 2-methylimidazole solution, collecting and washing the precipitate and drying to obtain the cobalt-based metal organic framework compound; wherein the addition amount of the cetyltrimethylammonium bromide is used to control the particle size of the cobalt-based metal organic framework compound; the mass ratio of the cobalt nitrate hexahydrate, the cetyltrimethylammonium bromide and the 2-methylimidazole is 0.6: (0.01 ~ 0.06): 9; S2. Preparing a catalyst dispersion liquid: mixing and uniformly dispersing the cobalt-based metal organic framework compound prepared in step S1 with ferrocene, thiophene and a liquid carbon source to form a dispersion liquid; S3. Chemical vapor deposition growth: injecting the dispersion liquid into a reaction furnace, and in the presence of a gaseous carbon source, a reducing gas and a protective gas, performing a floating catalyst chemical vapor deposition reaction in a quartz tube reaction chamber with a papillary protrusion on the inner wall for disturbing the airflow and increasing the collision probability of catalyst particles, the reaction time being 0.5 to 20 minutes, to obtain a product containing single-walled carbon nanometer short tubes; S4. Purification: performing heat treatment on the product obtained in step S3 in an oxygen-containing atmosphere, then performing acid washing and water washing to obtain purified single-walled carbon nanometer short tubes.

2. The method of claim 1, wherein the single-walled carbon nanotube is a short tube. The mass ratio of the cobalt-based metal organic framework compound, the ferrocene and the thiophene is (50 ~ 70): (5 ~ 7): (0.5 ~ 0.7).

3. The method of claim 1, wherein the single-walled carbon nanotube is a short tube. The liquid carbon source is one or more of methanol, ethanol, benzyl alcohol and toluene; the gaseous carbon source is one or both of methane and ethylene; the reducing gas is hydrogen; and the protective gas is nitrogen.

4. The method for preparing a single-walled carbon nanotube as described in claim 3, characterized in that: The injection speed of the dispersion liquid is 5 ~ 10 microliters / minute, the total flow rate of nitrogen and hydrogen is 5 ~ 10 liters / minute, the nitrogen / hydrogen flow rate ratio is 2 ~ 4, the methane / ethylene supply amount is 1 ~ 5 milliliters / minute, and the growth temperature of the reaction furnace is 1150 ~ 1250℃.

5. The method of claim 1, wherein the single-walled carbon nanotube is a short tube. The papillary protrusion is hemispherical, the height of the protrusion is 1 ~ 4 mm, and the ratio of the height (H) of the papillary protrusion to the inner diameter (D) of the quartz tube satisfies: 0.45% ≤ H / D ≤ 5.0%.

6. The method for preparing a single-walled carbon nanotube as described in claim 5, characterized in that: The quartz tube is divided into an upstream zone, a core growth zone and a downstream zone along the airflow direction, and the number of the papillary protrusions in the upstream zone, the core growth zone and the downstream zone decreases in turn; the distribution mode of the papillary protrusions in the upstream zone and the downstream zone is aperiodic distribution, and the distribution mode of the papillary protrusions in the core growth zone is a plurality of rows of annular regular arrangements on the inner wall of the tube, and the protrusions of adjacent rows are arranged in a staggered manner in the circumferential direction.

7. The method for preparing a single-walled carbon nanotube as described in claim 6, characterized in that: The length of the upstream zone accounts for 20% ~ 30% of the total length of the quartz tube; the length of the core growth zone accounts for 40% ~ 60% of the total length of the quartz tube; the length of the downstream zone accounts for 20% ~ 30% of the total length of the quartz tube; and the number ratio of the papillary protrusions in the upstream zone, the core growth zone and the downstream zone is (4 ~ 5): (2 ~ 3): (1 ~ 2).

8. The method for preparing a single-walled carbon nanotube as described in claim 7, characterized in that: The total area of the orthographic projections of all the papillary projections on the inner wall of the quartz tube accounts for 0.007% to 1.00% of the total projection area of the inner wall of the tube.

9. A single-walled carbon nanobucal, characterized by: Prepared by the method of any one of claims 1-8, having an average length of less than 6 microns; wherein the single-walled carbon nanotubes having a length in the range of 0.5-3 microns comprise greater than 40% of the total number of single-walled carbon nanotubes; and the single-walled carbon nanotubes having a length in the range of 0.5-3 microns have a Raman spectrum I G / I D ratio of not less than 15.

10. A catalyst precursor for catalyzing growth of single-walled carbon nanobucalcs, characterized by, The cobalt-based metal organic framework compound is adsorbed with ferrocene and thiophene; The cobalt-based metal organic framework compound is prepared by a method comprising the following steps: dissolving cobalt nitrate hexahydrate and cetyltrimethylammonium bromide in deionized water, then mixing and reacting with 2-methyl imidazole aqueous solution, collecting and washing the precipitate and drying, and the amount of the cetyltrimethylammonium bromide is 1.67% to 10% of the mass of the cobalt nitrate hexahydrate.

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