Quartz tube and tube furnace for preparing single-walled carbon nano short tube

Abstract

The invention discloses a quartz tube and a tube furnace for preparing a single-walled carbon nano short tube, and belongs to the field of nano material preparation equipment. A plurality of hemispherical mastoid protrusions are arranged on the inner wall of the quartz tube, the height of the protrusions ranges from 1 mm to 4 mm, and the ratio of the height (H) to the inner diameter (D) of the quartz tube meets the condition that H / D is larger than or equal to 0.45% and smaller than or equal to 5.0%. The inner wall is divided into an upstream area, a core growth area and a downstream area in the airflow direction, the number of protrusions in all the areas is sequentially decreased, and the protrusions in the core growth area are annularly and regularly arranged. According to the structure, a flow field is physically disturbed, so that the collision probability of a catalyst is increased, and the carbon nanotubes are promoted to fall off in an early stage, so that the single-walled carbon nano short tubes with concentrated length distribution are directly prepared. The invention also provides a tubular furnace comprising the quartz tube.

Description

Technical Field

[0001] This invention relates to the field of controlled fabrication of single-walled carbon nanotubes, specifically a quartz tube and a floating catalyst chemical vapor deposition tube furnace for fabricating single-walled carbon nanotubes. 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 control over 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 quartz tube specifically for preparing single-walled carbon nanotubes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a quartz tube for preparing single-walled carbon nanotubes, wherein the inner wall of the quartz tube is provided with a plurality of nipple-shaped protrusions for disturbing the airflow and increasing the probability of catalyst particle collision. The nipple-shaped protrusions are hemispherical and the height of the protrusions is 1~4mm; and the ratio of the height (H) of the nipple-shaped protrusions to the inner diameter (D) of the quartz tube satisfies: 0.45% ≤ H / D ≤ 5.0%.

[0008] 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.

[0009] 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; and the length of the downstream region accounts for 20% to 30% of the total length of the quartz tube.

[0010] More preferably, the ratio of the number of papillary protrusions in the upstream region, the core growth region, and the downstream region is (4~5):(2~3):(1~2).

[0011] 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.

[0012] 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.

[0013] Secondly, the present invention provides a floating catalyst chemical vapor deposition tube furnace, wherein a quartz tube as described above is disposed therein.

[0014] Compared with the prior art, the present invention has the following significant advantages: 1. In-situ physical control of carbon nanotube length is achieved: The quartz tube of this invention actively intervenes in the flow field within the reaction chamber through hemispherical nipple-like protrusions of specific size and spaced intervals on its inner wall. The protruding structure continuously disturbs the gas flow boundary layer, significantly increasing the collision frequency between floating catalyst particles and between the particles and the tube wall. This forces the growing carbon nanotubes to detach from the catalyst active sites at an early stage, achieving direct and effective control over the length of single-walled carbon nanotubes. A high proportion of short tubes (0.5-3 μm > 40%) can be obtained without subsequent shearing or purification damage steps.

[0015] 2. Scientific flow field design with clearly defined functions: The papilla structure adopts a zoned functional design: dense protrusions in the upstream region promote thorough mixing of reactants; regularly arranged protrusions in the core growth region continuously provide controllable collision disturbances, which is the key area for terminating carbon nanotube growth; sparse protrusions in the downstream region are used to stabilize airflow. This design takes into account mixing efficiency, growth intervention, and transport stability, and the process parameters have a clear theoretical basis in fluid mechanics, which can be customized according to the target product length.

[0016] 3. Synergistic Effect and Superior Product Performance: When used in conjunction with specific small-sized catalyst precursors (such as Co-MOF supported catalysts), the quartz tubes of this invention exhibit a significant synergistic effect. The small-sized catalysts provide more collision "hosts" and a shorter intrinsic growth window, while the papillary quartz tubes provide a highly efficient collision "environment." The combination of these two technologies results in short tube yields and length uniformity far exceeding those of single techniques. The prepared single-walled carbon nanotubes exhibit high crystallinity (Raman spectroscopy). G / I D (≥15), with few structural defects, retaining excellent intrinsic electrical and mechanical properties.

[0017] 4. Simple equipment modification and strong practicality: This quartz tube structure can directly replace the conventional quartz tube in the existing floating catalyst CVD system without complex modifications to the entire equipment. The device is simple, low-cost, and has good process compatibility, making it easy to achieve large-scale and stable preparation of single-walled carbon nanotubes, and has good prospects for industrial application. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a flowchart of the method for preparing single-walled carbon nanotubes using metal-organic frameworks according to the present invention; Figure 2 This is the X-ray diffraction pattern of the cobalt-based metal-organic framework compound obtained in step (1) of Example 1; Figure 3 This is a scanning electron microscope image of the single-walled carbon nanotubes from Example 1. Figure 4 This is a transmission electron microscope image of the single-walled carbon nanotubes from Example 1. Figure 4 (a1) is a low-magnification TEM image of the sample. Figure 4 (a2) is a high-magnification TEM image of the sample; Figure 5 The image shows the Raman spectrum of a single-walled carbon nanotube from Example 1. Figure 6 This is a schematic diagram of the quartz tube in Example 1. Detailed Implementation

[0020] 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.

[0021] Example 1 like Figure 6 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The height of the papillary protrusions is 0.91% of the inner diameter of the quartz tube.

[0026] See Figure 1 Using the aforementioned quartz tube structure, single-walled carbon nanotubes are prepared via a floating catalyst chemical vapor deposition tube furnace. The specific steps are as follows: (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.

[0027] (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.

[0028] The dispersion was then injected into the reactor 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 reactor growth temperature was 1200 °C. The reactor chamber used a quartz tube with a papillary structure on its inner wall, and a mixture containing high-quality single-walled carbon nanotubes was prepared by floating catalyst chemical vapor deposition.

[0029] (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.

[0030] The product was characterized as follows: 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 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 4 This is a transmission electron microscope image of the single-walled carbon nanotubes from Example 1. Figure 4 (a1) is a low-magnification TEM image of the sample. Figure 4 (a2) is a high-magnification TEM image of the sample, which proves that the sample is mainly composed of single-layer single-walled carbon nanotubes. Figure 5 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.

[0031] Example 2: The dimensions of the quartz tube in Example 2 are the same as those in Example 1.

[0032] The papillary protrusion is 1 mm high and 2 mm in diameter at the base.

[0033] Twenty papillae were set in the upstream area, ten in the core growth area, and five in the downstream area.

[0034] 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.

[0035] The height of the papillary protrusions is 0.45% of the inner diameter of the quartz tube.

[0036] Example 3: 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 .

[0037] The nipple-like protrusion is 4 mm high and has a base diameter of 8 mm.

[0038] There are 25 upstream zones, 15 core growth zones, and 10 downstream zones.

[0039] 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.

[0040] The height of the nipple-like protrusions is 5% of the inner diameter of the quartz tube.

[0041] Example 4: The quartz tube in Example 4 is the same as in Example 3.

[0042] In this embodiment, the height of the nipple-like protrusion is 2 mm, and the bottom diameter is 4 mm.

[0043] There are 20 upstream zones, 15 core growth zones, and 10 downstream zones.

[0044] 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.

[0045] The height of the papillary protrusions is 2.5% of the inner diameter of the quartz tube.

[0046] Comparative Example 1 (using a smooth quartz tube) (1) Same as step (1) in Example 1.

[0047] (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℃.

[0048] The main difference lies in the use of conventional quartz tubes of the size of Example 1, with high-quality single-walled carbon nanotubes prepared by floating catalyst chemical vapor deposition.

[0049] (3) Same as step (3) in Example 1.

[0050] Key data for each embodiment and comparative example are summarized in Table 1 below.

[0051]

[0052] A comparison of Comparative Example 1 and Example 1 shows that both used the exact same catalyst precursor (10% CTAB) and reaction time (0.5 minutes), the only difference being the structure of the inner wall of the quartz tube. Example 1, using the papillary quartz tube of the present invention, had a significantly shorter average product length (1.7 μm) than the Comparative Example (6.8 μm) using a smooth quartz tube, and a much 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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 quartz tube for preparing single-walled carbon nanotubes, used in a floating catalyst chemical vapor deposition tube furnace, characterized in that: The inner wall of the quartz tube is provided with a plurality of nipple-shaped protrusions for disturbing the airflow and increasing the probability of catalyst particle collision. The nipple-shaped protrusions are hemispherical and the height of the protrusions is 1~4mm. The ratio of the height (H) of the nipple-shaped protrusions to the inner diameter (D) of the quartz tube satisfies: 0.45% ≤ H / D ≤ 5.0%.

2. The quartz tube for preparing single-walled carbon nanotubes as described in claim 1, characterized in that: 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, while the nipple-like protrusions in the core growth region are distributed in multiple rows of regular rings on the inner wall of the tube, and the protrusions in adjacent rows are staggered in the circumferential direction.

3. A quartz tube for preparing single-walled carbon nanotubes as described in claim 2, characterized in that: The upstream region accounts for 20% to 30% of the total length of the quartz tube; the core growth region accounts for 40% to 60% of the total length of the quartz tube; and the downstream region accounts for 20% to 30% of the total length of the quartz tube.

4. A quartz tube for preparing single-walled carbon nanotubes as described in claim 2, characterized in that: The ratio of the number of papillary protrusions in the upstream region, core growth region and downstream region is (4~5):(2~3):(1~2).

5. A quartz tube for preparing single-walled carbon nanotubes as described in claim 4, characterized in that: The upstream region has 20-25 papillary protrusions, the core growth region has 10-15 papillary protrusions, and the downstream region has 5-10 papillary protrusions.

6. A quartz tube for preparing single-walled carbon nanotubes as described in claim 1, characterized in that: The total projected area of ​​all the aforementioned 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.

7. A floating catalyst chemical vapor deposition tube furnace, wherein a quartz tube as described in any one of claims 1-6 is disposed therein.

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