CN115611268A

CN115611268A - Ultra-high yield preparation method of ultra-long carbon nanotube

Info

Publication number: CN115611268A
Application number: CN202211361272.5A
Authority: CN
Inventors: 张如范; 姜沁源; 汪菲; 李润
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-11-02
Filing date: 2022-11-02
Publication date: 2023-01-17

Abstract

The application discloses a method for preparing an ultra-long carbon nanotube with ultra-high yield. The method comprises the steps of arranging a substrate in a reactor, introducing mixed gas 1 into the reactor to replace air in the reactor with the mixed gas 1, and raising the temperature in the reactor until the reaction temperature is reached, wherein the mixed gas 1 comprises hydrogen and inert atmosphere gas; continuously introducing mixed gas 2 and a catalyst solution into the reactor, and reacting to obtain an ultra-long carbon nanotube; the mixed gas 2 comprises carbon source gas, hydrogen, the inert atmosphere gas and water vapor; the catalyst solution includes a catalyst precursor, a cocatalyst, and a solvent. The method for preparing the ultra-long carbon nano tube with ultra-high yield is called a substrate interception guiding strategy. The method uses the substrate placed in the tube furnace to intercept and guide the floating short tube generated by chemical vapor deposition, which can obviously prolong the growth time of the carbon nano tube and finally grow the carbon nano tube into the ultra-long carbon nano tube.

Description

Ultra-high yield preparation method of ultra-long carbon nanotube

Technical Field

The present disclosure relates to, but is not limited to, the field of nanomaterials and their preparation techniques, and more particularly, but not limited to, an ultra-high yield method for preparing ultra-long carbon nanotubes.

Background

The carbon nano tube as a one-dimensional Dirac nano material has excellent mechanical, electrical, optical and thermal properties, so that the carbon nano tube has wide application prospect in high-end fields of transparent conductive films, super-strong fibers, carbon-based integrated circuits and the like. However, the length, orientation degree, defect concentration, crystallinity, chirality, and other structural elements of the carbon nanotube have a very significant influence on the properties thereof, and the short plate in either aspect may significantly degrade the performance of the carbon nanotube. Among these structural elements, the length of the carbon nanotube is strongly correlated with basic physical properties such as tensile strength, elongation at break, electrical conductivity, thermal conductivity, and the like of the macroscopic fiber and the film. Therefore, in the preparation of carbon nanotubes, the length thereof should be increased as much as possible to ensure the intrinsic excellent properties thereof.

The carbon nanotubes can be classified into clustered carbon nanotubes, vertical array carbon nanotubes and horizontal array carbon nanotubes according to the difference of the length, the degree of orientation and the morphology of the carbon nanotubes. The length of the clustered carbon nanotubes and the vertical array carbon nanotubes is usually very short (within 1 mm), and the clustered carbon nanotubes and the vertical array carbon nanotubes contain many defects, so that all properties of the clustered carbon nanotubes and the vertical array carbon nanotubes are far lower than the theoretical predicted values. In contrast, horizontal arrays of carbon nanotubes, grown on flat substrates, have less tube-to-tube interaction, thus ensuring that the carbon nanotubes can grow relatively independently. Thus, horizontal arrays of carbon nanotubes generally have fewer defects, fewer wall counts, and superior properties. The horizontal array carbon nano tube can be divided into two subclasses of bottom growth and top growth according to different growth mechanisms. The horizontal array carbon nanotubes grown at the bottom end usually adopt materials such as single crystal quartz or sapphire and the like as a substrate, and the carbon nanotubes follow a creeping growth mode on the substrate. Since the carbon nanotubes are always limited by van der waals force from the substrate during the crawling growth process, and the mass transfer process at the wall surface is also limited, the horizontal array carbon nanotubes grown at the bottom end have the problems of short length (usually within 1 mm) and slow growth rate. In contrast, tip-grown carbon nanotubes follow a growth pattern similar to a kite: the catalyst nanoparticles are located on the top of the carbon nanotubes and the catalyst floats in the gas stream with the top of the carbon nanotubes. The growth mode enables the carbon nano-tube to grow freely and rapidly, and the final length can reach centimeter or even decimeter, so the horizontal array carbon nano-tube growing at the top end is also called as the super-long carbon nano-tube.

Although the ultra-long carbon nanotube has significant advantages in length, structural perfection and properties compared with other kinds of carbon nanotubes, the ultra-long carbon nanotube is still difficult to be put into practical use at present, and the fundamental reason is the low yield of the ultra-long carbon nanotube. First, the low yield of ultra-long carbon nanotubes is mainly due to the low catalyst utilization. The top growth mode similar to a kite puts more rigorous requirements on the growth conditions of the ultra-long carbon nano-tubes, and under the better growth conditions, only a part of the carbon nano-tubes can float to grow into the ultra-long carbon nano-tubes. Such low catalyst utilization results in an array density of ultra-long carbon nanotubes that is typically about three orders of magnitude lower than the bottom-grown horizontal array. Secondly, the coalescence of the catalyst particles further reduces the number of catalyst particles suitable for the growth of the ultra-long carbon nanotubes, thereby further reducing the yield of the ultra-long carbon nanotubes. In addition, the yield of ultra-long carbon nanotubes is also reduced due to the entanglement of the carbon nanotubes and the falling of the tips of the carbon nanotubes on the substrate during the growth process. Therefore, it is necessary to develop a novel method that is compatible with the top growth mode of the ultra-long carbon nanotube and improves the utilization rate of the catalyst, so as to achieve the purpose of improving the yield of the ultra-long carbon nanotube.

Disclosure of Invention

The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the present application.

The application provides a brand-new preparation method of the ultra-long carbon nano tube from the aspect of methodology, namely a substrate interception guiding strategy, and can realize batch preparation of the ultra-long carbon nano tube with ultrahigh yield. In the method, a substrate for intercepting and guiding the floating short pipe is introduced in the chemical vapor deposition process so as to achieve the purpose of prolonging the growth time of the carbon nano tube. By means of the substrate interception and guide strategy, the growth time of the carbon nano tube can be prolonged by about three orders of magnitude, and then the carbon nano tube can be efficiently grown into the ultra-long carbon nano tube. In the traditional method for growing the ultra-long carbon nano-tube, only a few carbon nano-tubes can float under the comprehensive action of the drag force, the thermal buoyancy, the van der waals force and the like to grow the ultra-long carbon nano-tubes; the rest carbon nano-tubes can only be distributed in the catalyst area in an orientation and disorderly way and can not grow into the super-long carbon nano-tubes. In comparison, the method can effectively utilize the intrinsic floating state of the carbon nano tube, so that most of the carbon nano tubes can meet the conditions of floating growth, and the problems of low catalyst utilization rate, easy coalescence of catalyst particles and the like in the traditional method for growing the ultra-long carbon nano tubes are successfully solved.

The application provides an ultra-high yield preparation method of an ultra-long carbon nanotube, which comprises the following steps:

arranging a substrate in a reactor, introducing mixed gas 1 into the reactor to replace air in the reactor with the mixed gas 1, and raising the temperature in the reactor until the reaction temperature is reached, wherein the mixed gas 1 comprises hydrogen and a first atmosphere gas;

continuously introducing mixed gas 2 and a catalyst solution into the reactor, and reacting to obtain an ultra-long carbon nanotube; the mixed gas 2 comprises carbon source gas, hydrogen, second inert atmosphere gas and water vapor;

the catalyst solution includes a catalyst precursor, a cocatalyst, and a solvent.

In one embodiment provided herein, the substrate is a substrate that can withstand a temperature of 300 ℃ to 2000 ℃, and the substrate fixes one end of the carbon nanotube during the growth of the ultra-long carbon nanotube.

In one embodiment provided herein, the substrate is made of one or more materials selected from silicon, quartz, ceramic, and metal.

In one embodiment provided herein, the substrate is placed in the center of the tube furnace reactor prior to growth.

In one embodiment provided herein, the substrate extends in a direction parallel to the gas flow direction; alternatively, the substrate extends perpendicular to the gas flow direction and has a through hole therein, the through hole allowing the end of the carbon nanotube not held by the substrate to grow therethrough.

In the description of the present application, "the extending direction of the substrate is parallel to the gas flow direction" means that the angle between the extending direction of the substrate and the gas flow direction is in the range of-10 ° to 10 °;

the "extending direction of the substrate is perpendicular to the gas flow direction" means that an angle between the extending direction of the substrate and the gas flow direction is in a range of 80 ° to 100 °.

In one embodiment provided herein, the substrate is a perforated frame substrate or a non-porous block substrate.

In one embodiment provided herein, the perforated frame substrate has a porosity of 0.001 to 0.999.

In one embodiment provided herein, the non-porous bulk substrate has a height that is between 0.1% and 90% of the reactor internal diameter.

In embodiments provided herein, the reaction temperature is from 300 ℃ to 2000 ℃, and the reaction time is from 1min to 2000min; in one embodiment provided herein, the reaction time of the reaction is 3min to 600min.

In one embodiment provided herein, the total flow rate of the mixed gas 1 is 0.01sccm to 100000sccm; in one embodiment, the total flow rate of the mixed gas 1 is 1sccm to 10000sccm.

In one embodiment provided herein, the concentration of hydrogen in the mixed gas 1 is 0.001vol.% to 99vol.%; in one embodiment provided herein, the concentration of hydrogen in the mixed gas 1 is 1vol.% to 99vol.%.

In one embodiment provided herein, the total flow rate of the mixed gas 2 is 0.01sccm to 100000sccm; in one embodiment, the total flow rate of the mixed gas 2 is 1sccm to 10000sccm.

In one embodiment provided herein, the flow rate of the catalyst solution is from 0.001 μ L/min to 10000 μ L/min; in one embodiment provided herein, the flow rate of the catalyst solution is from 0.01 μ L/min to 100 μ L/min.

In one embodiment provided herein, the carbon source gas is selected from any one or more of methane, ethane, ethylene, acetylene, methanol vapor, ethanol vapor, isopropanol vapor, acetone vapor, and carbon monoxide.

In one embodiment provided herein, the concentration of the carbon source gas in the mixed gas 2 is 0.00001vol.% to 99vol.%; in one embodiment provided herein, the concentration of the carbon source gas in the mixed gas 2 is 0.01vol.% to 80vol.%.

In one embodiment provided herein, the concentration of the hydrogen gas in the mixed gas 2 is 0.001vol.% to 99vol.%; in one embodiment provided herein, the concentration of the hydrogen in the mixed gas 2 is 1vol.% to 99vol.%.

In one embodiment provided herein, the concentration of the water vapor in the mixed gas 2 is 0.0001vol.% to 99vol.%.

In one embodiment provided herein, the concentration of the catalyst precursor in the catalyst solution is from 0.0001wt.% to 99wt.%; in one embodiment provided herein, the concentration of the catalyst precursor in the catalyst solution is from 0.01wt.% to 20wt.%.

In one embodiment provided herein, the concentration of the promoter in the catalyst solution is from 0.0001wt.% to 99wt.%; in one embodiment provided herein, the concentration of the promoter in the catalyst solution is from 0.01wt.% to 60wt.%.

In one embodiment provided herein, the catalyst precursor is a metallocene compound and the cocatalyst is thiophene.

In one embodiment provided herein, the metallocene compound is selected from any one or more of a group VIII element metallocene compound and a group IVB metal metallocene compound.

In one embodiment provided herein, the metallocene compound is selected from any one or more of ferrocene, cobaltocene, nickelocene, and dichlorotitanocene.

In one embodiment provided herein, the solvent is selected from any one or more of methanol, ethanol, isopropanol, acetone, benzene, toluene, ethylbenzene, xylene, n-hexane, and cyclohexane.

In one embodiment provided herein, formulating the catalyst solution comprises: dissolving a catalyst precursor and an auxiliary thiophene in a solvent, and performing ultrasonic treatment to obtain a clear solution. The prepared solution was extracted with a syringe and mounted on a syringe pump, and the syringe was connected to the reactor.

In one embodiment, the method for preparing ultra-long carbon nanotubes with ultra-high yield further comprises: and cooling under the protection of the mixed gas 1 after the growth of the ultra-long carbon nano tube is finished.

In one embodiment provided herein, the first inert gas and the second inert gas are each independently selected from any one or more of nitrogen, argon, and helium.

In another aspect, the present application provides an ultra-long carbon nanotube prepared by the above ultra-high yield preparation method of an ultra-long carbon nanotube;

in one embodiment provided herein, the ultra-long carbon nanotubes have a length of 1cm to 100cm.

In yet another aspect, the present application provides applications of the ultra-long carbon nanotubes in carbon-based chips, carbon nanotube fibers, and composite cables.

Introducing mixed gas of hydrogen and carrier gas into the reactor in the temperature rise process of the reactor, and slowly raising the temperature of the tubular furnace

The method can prepare the ultra-long carbon nano tube with ultra-high yield, the length of the obtained ultra-long carbon nano tube can reach a centimeter to meter level, and the growth speed of a single carbon nano tube can reach 2.37mm/min (calculated by the length of a horizontal array under different growth times). The ultra-long carbon nanotube prepared by the method also has the characteristics of perfect structure, less wall number (the number of the tube walls is one to three), excellent electrical property and the like.

A variety of substrates may be used for interception guidance in the methods described herein. If a flat substrate such as a monocrystalline silicon wafer, a monocrystalline quartz wafer and the like is used, a high-density ultra-long carbon nanotube horizontal array or film can be obtained; if a mesh-shaped substrate with a mesh is used, a fiber composed of ultra-long carbon nanotubes can be obtained.

The ultra-long carbon nanotube has excellent electrical properties, and the purity of the semiconductor type carbon nanotube can reach 95.7% (obtained by Raman spectrum data statistics).

Compared with the prior art, the method provided by the application adopts a substrate interception guide strategy to greatly improve the utilization rate of the catalyst and obviously inhibit the coalescence of catalyst particles, thereby realizing the controllable preparation of the high-yield ultra-long carbon nanotube. By using the substrate interception guiding strategy, the array density can be formed on a planar substrate by 10 ³ Root/mm to 10 ⁵ The root/mm horizontal array (2-4 orders of magnitude higher than the traditional method) can also use interception substrates (such as a frame with holes, a metal net and the like) with different shapes and sizes to realize the batch preparation of the ultra-long carbon nanotubes (such as films, fibers and the like) with different appearances and different aggregation modes so as to meet the requirements of various application scenes.

The carbon nanotube monomer of the ultra-long carbon nanotube prepared by the method has the length from centimeter level to meter level, high orientation degree, low defect concentration and excellent mechanical, thermal and electrical properties, and the ultra-long carbon nanotube aggregate prepared by the substrate interception guide strategy can fully exert the intrinsic excellent properties of the carbon nanotube and can be used in the fields of ultra-strong fibers, transparent conductive films, carbon-based chips and the like. The method also has the advantages of simplicity, easy implementation, wide operation window, low requirements on the material, shape and size of the substrate and the like.

Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the application. Other advantages of the present application can be realized and attained by the invention in the aspects illustrated in the description.

Drawings

The accompanying drawings are included to provide an understanding of the present disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the examples serve to explain the principles of the disclosure and not to limit the disclosure.

FIG. 1A is a schematic diagram of an apparatus for preparing a horizontal array of ultra-long carbon nanotubes with ultra-high yield. FIG. 1B is a schematic diagram of a growth process for preparing a horizontal array of ultra-long carbon nanotubes in ultra-high yield.

Fig. 2A is a schematic view of an apparatus for preparing ultra-long carbon nanotube fibers in ultra-high yield. FIG. 2B is a schematic diagram of the growth process for preparing ultra-long carbon nanotube fibers in ultra-high yield.

FIG. 3 is a schematic diagram of a process for preparing an ultra-long carbon nanotube film.

Fig. 4 is a water vapor-assisted optical visualization of the horizontal array of ultra-long carbon nanotubes prepared in example 3.

FIG. 5 is a scanning electron microscope photograph of the horizontal array of ultra-long carbon nanotubes prepared in example 2.

FIG. 6 is a scanning electron microscope image of the ultra-long carbon nanotube film obtained in example 5.

Fig. 7 is a scanning electron microscope image of the ultra-long carbon nanotube fiber prepared in example 1.

Fig. 8 is a transmission electron microscope photograph and a raman spectrum of a plurality of monomers of the ultra-long carbon nanotube prepared in example 2.

Fig. 9 is a graph of the length of the ultra-long carbon nanotube according to example 3 as a function of growth time.

Fig. 10 is a transfer characteristic curve of the ultra-long carbon nanotube prepared in example 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application are described in detail below. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.

The ultra-long carbon nanotube is defined as: carbon nanotubes having a length of 1cm or more.

The ultra-high yield is defined as: the ratio of carbon atoms in the carbon source to the ultra-long carbon nanotubes is more than 1% based on the amount of the carbon source supplied.

Different from the traditional chemical vapor deposition process, the method realizes the functions of dividing the flow field, intercepting the carbon nano tube and guiding by utilizing the substrate placed in the reactor; the catalyst nanoparticles formed by the cracking and reduction of the catalyst precursor grow short carbon nanotubes in a floating state in the mixed gas 2. The formed floating short pipe flows through the reactor continuously along with the gas flow, wherein a part of the floating short pipe is intercepted by the substrate arranged in the center of the reactor, one end of the floating short pipe is fixed by the substrate, the other end of the floating short pipe is guided by the drag force of the gas flow, and the ultra-long carbon nano-tube is obtained with ultra-high yield after a period of growth.

In the embodiments of the present application, the shape and size of the substrate are not limited (for example, the substrate may be plate-shaped or sheet-shaped) as the volume of the reactor allows; the arrangement mode (such as position, orientation and the like) of the substrate is not limited; the reactor used may be a tubular reactor, the internal diameter of which may be from 5mm to 1000mm, and the length of which may be from 20cm to 10000cm.

In the examples of the present application, the catalyst solution was contained in a syringe and connected to the reactor by a syringe pump.

Example 1

A benzene solution of 6wt.% cobaltocene and 2wt.% thiophene was prepared as a catalyst solution, which was then clarified by sonication. The prepared solution was extracted with a syringe and mounted on a syringe pump, and the syringe was connected to the reactor. The quartz plate with sieve holes (porosity of 0.6) was placed vertically in the center of the tube furnace reactor before growth (i.e. the quartz plate with sieve holes extended perpendicular to the gas flow direction, as shown in fig. 2A and 2B). Then, the reactor was charged with mixed gas 1 (500 sccm hydrogen and 50sccm argon, the volume fraction of hydrogen being (500/550 = 90.91vol.%), the volume fraction of argon being (50/550 = 9.09vol.%), while slowly raising the tube furnace temperature to 1400 ℃. After the temperature was stabilized, mixed gas 2 (20 sccm ethanol vapor, 100sccm hydrogen, 3000sccm helium, and 26.21sccm water vapor, the volume fraction of ethanol vapor being (20/3146.21= 0.64vol.%), the volume fraction of hydrogen being (100/3146.21= 3.18vol.%), the volume fraction of helium being (3000/3146.21 = 95.35vol.%), and the volume fraction of water vapor being 26.21/3146.21= 0.83vol.%) was fed. At the same time, the syringe pump was turned on and the catalyst solution was introduced at a flow rate of 0.5. Mu.L/min. After 80 minutes of growth, the reactor was cooled under the protection of the mixed gas 1. And cooling the reactor to room temperature, and taking out the quartz plate to obtain the ultra-long carbon nanotube fiber growing on the quartz plate with the sieve pores. The yield was 5.2% when the fiber was weighed.

As can be seen from fig. 2A and 2B, when interception is performed using a mesh substrate placed vertically, one end of the intercepted carbon nanotube passes through the mesh hole, and continues to grow as an ultra-long carbon nanotube as directed by the gas flow. After the reaction is finished, the ultra-long carbon nanotube fiber can be collected from the mesh substrate.

As can be seen from fig. 7, the carbon nanotube monomers in the ultra-long carbon nanotube fiber prepared in this embodiment are regularly arranged, and have a higher degree of orientation.

Example 2:

a cyclohexane solution of 2wt.% of titanium dichlorobis and 8wt.% of thiophene was prepared and then clarified by sonication. The prepared solution was extracted with a syringe and mounted on a syringe pump, and the syringe was connected to the reactor. A single crystal quartz plate (thickness 3.0% of the inner diameter of the reactor) was placed in the center of the tube furnace reactor before growth so that the extension direction of the single crystal quartz plate was parallel to the gas flow direction (as shown in fig. 1A and 1B). Subsequently, the reactor was started to be fed with mixed gas 1 (300 sccm hydrogen and 500sccm nitrogen, the volume fraction of hydrogen being (300/800 =37.5 vol.%), the volume fraction of nitrogen being (500/800 =62.5 vol.%), while slowly raising the tube furnace temperature to 800 ℃. After the temperature was stabilized, mixed gas 2 (10 sccm ethanol vapor, 500sccm hydrogen, 2000sccm helium and 0.30sccm water vapor, the volume fraction of ethanol vapor being (10/2510.3 =0.4 vol.%), the volume fraction of hydrogen being (500/2510.3 = 19.92vol.%), the volume fraction of helium being (2000/2510.3 = 79.67vol.%), and the volume fraction of water vapor being 0.3/2510.3= 0.01vol.%) was introduced. At the same time, the syringe pump was turned on and the catalyst solution was introduced at a flow rate of 10. Mu.L/min. After 80 minutes of growth, the reactor was cooled under the protection of the mixed gas 1. And cooling the reactor to room temperature, and taking out the quartz plate to obtain the ultra-long carbon nanotube horizontal array grown on the single crystal quartz plate. The yield was 1.3% (yield is the ratio of the mass of carbon nanotubes to the mass of carbon in the introduced reaction raw material carbon source) converted from the array density and the tube diameter of carbon nanotubes.

As can be seen from fig. 1A and 1B, when the interception is performed using a planar substrate, the floating short tubes grow into ultra-long carbon nanotubes under the guiding action of the airflow, and finally fall on the substrate to form a horizontal array with high degree of orientation.

As can be seen from fig. 5, the array density of the ultra-long carbon nanotubes prepared by the present embodiment is much higher than that of the conventional method, and has a good degree of orientation.

As can be seen from the transmission electron micrograph and raman spectrum of fig. 8, the ultra-long carbon nanotubes prepared in this example have a nearly perfect structure, a clean surface, a small number of walls (1 to 3 walls at most), and a high purity of the semiconducting carbon nanotubes (95.7% purity is obtained at an array length of 40 mm).

Example 3:

a toluene solution of 3wt.% ferrocene and 0.45wt.% thiophene was prepared and then clarified by sonication. The prepared solution was drawn up by a syringe and mounted on a syringe pump, and the syringe was connected to the reactor. A single crystal silicon wafer (having a thickness of 1.1% of the inner diameter of the reactor) was placed in the center of the tube furnace reactor before growth (as shown in fig. 1A and 1B). Then, the reactor was started to be charged with mixed gas 1 (100 sccm hydrogen and 100sccm argon, the volume fraction of hydrogen being (100/200 = 50vol.%), the volume fraction of argon being (100/200 = 50vol.%), and the temperature of the tube furnace was slowly raised to 1050 ℃. After the temperature was stabilized, mixed gas 2 (4 sccm ethylene, 330sccm hydrogen, 1390sccm argon and 8.28sccm steam, volume fraction of ethylene (4/1732.28 = 0.23vol.%), volume fraction of hydrogen (330/1732.28 = 19.05vol.%), volume fraction of argon (3000/1732.28 = 80.24vol.%), and volume fraction of steam (8.28/1732.28 = 0.48vol.%) was introduced. At the same time, the syringe pump was turned on and the catalyst solution was introduced at a flow rate of 1.8. Mu.L/min. After 60 minutes of growth, the reactor was cooled under the protection of the mixed gas 1. And cooling the reactor to room temperature, and taking out the substrate to obtain the high-density ultra-long carbon nanotube horizontal array grown on the monocrystalline silicon wafer. The yield is 2.2% converted from the array density and the tube diameter of the carbon nano tube.

As can be seen from fig. 1A and 1B, when the interception is performed by using a planar substrate, the floating short tubes grow into ultra-long carbon nanotubes under the guiding action of the airflow, and finally fall on the substrate to form a horizontal array with high orientation degree.

As shown in fig. 4, the bright line in the figure is the position of the ultra-long carbon nanotube. As can be seen from the figure, the horizontal array of the ultra-long carbon nanotubes prepared by the method can uniformly cover a silicon wafer substrate with the length of about 10 centimeters and has very high array density. A considerable part of the ultra-long carbon nanotubes can grow to a position of 10 cm, which shows that the catalyst has high activity, long service life and slow decay of array density. Theoretically, when the constant temperature area of the tube furnace is long enough, the carbon nano tube can continuously grow under a constant condition, so that the meter-level length is reached.

As can be seen from FIG. 9, the ultra-long carbon nanotubes prepared in this example have a growth rate as high as 2.37mm/min.

As can be seen from fig. 10, the ultra-long carbon nanotube prepared in this example can be used to prepare a field effect device, and exhibits excellent switching performance.

Example 4

A solution of 8wt.% nickelocene, 2wt.% cobaltocene, and 0.32wt.% thiophene in n-hexane was prepared and then clarified by sonication. The prepared solution was extracted with a syringe and mounted on a syringe pump, and the syringe was connected to the reactor. A stainless steel mesh (porosity 0.9) was placed vertically in the center of the tube furnace reactor before growth (as shown in fig. 2A and 2B). Then, the reactor was charged with mixed gas 1 (100 sccm hydrogen and 100sccm argon, the volume fraction of hydrogen being (100/200 = 50vol.%), the volume fraction of argon being (100/200 = 50vol.%), while slowly raising the tube furnace temperature to 950 ℃. After the temperature was stabilized, mixed gas 2 (50 sccm carbon monoxide, 600sccm hydrogen, 300sccm argon, and 9.12sccm steam, the volume fraction of carbon monoxide being (50/959.12 = 5.21vol.%), the volume fraction of hydrogen being (600/959.12 = 62.56vol.%), the volume fraction of argon being (300/959.12 = 31.28vol.%), and the volume fraction of steam being 9.12/959.12= 0.95vol.%) was fed. At the same time, the syringe pump was turned on and the catalyst solution was introduced at a rate of 26. Mu.L/min. After 180 minutes of growth, the reactor was cooled under the protection of the mixed gas 1. And cooling the reactor to room temperature, and taking out the stainless steel net to obtain the ultra-long carbon nanotube fiber growing on the stainless steel net. The yield was 6.5% calculated after weighing the fiber.

As can be seen from fig. 2A and 2B, when interception is performed using a mesh substrate placed vertically, one end of the intercepted carbon nanotubes passes through the mesh and continues to grow into ultra-long carbon nanotubes as directed by the gas flow. After the reaction is finished, the ultra-long carbon nanotube fibers can be collected from the mesh-shaped substrate.

Example 5:

a methanol solution of 3wt.% ferrocene, 3wt.% cobaltocene, 6wt.% nickelocene, and 9.5wt.% thiophene was prepared and then clarified by sonication. The prepared solution was drawn up by a syringe and mounted on a syringe pump, and the syringe was connected to the reactor. An alumina ceramic wafer (5% of the reactor internal diameter in thickness) was placed in the center of the tube furnace reactor prior to growth. Then, the reactor was started to be charged with mixed gas 1 (1000 sccm hydrogen and 1000sccm nitrogen, the volume fraction of hydrogen being (1000/2000 = 50vol.%), the volume fraction of nitrogen being (1000/2000 = 50vol.%), while slowly raising the temperature of the tube furnace to 1200 ℃. After the temperature was stabilized, mixed gas 2 (15 sccm acetylene, 800sccm hydrogen, 300sccm nitrogen, and 15.61sccm steam was introduced, the volume fraction of acetylene was (15/1130.61= 1.33vol.%), the volume fraction of hydrogen was (800/1130.61 = 70.76vol.%), the volume fraction of nitrogen was (300/1130.61 = 26.53vol.%), and the volume fraction of steam was 15.61/1130.61= 1.38vol.%). At the same time, the syringe pump was turned on and the catalyst solution was introduced at a rate of 14. Mu.L/min. After 80 minutes of growth, the reactor was cooled under the protection of the mixed gas 1. And cooling the reactor to room temperature, taking out the alumina ceramic wafer, rotating the alumina ceramic wafer by 68 degrees on the horizontal plane, putting the alumina ceramic wafer back into the reactor again, repeating the growth step, and taking out again to obtain the ultra-long carbon nanotube film grown on the alumina ceramic wafer. The yield is 1.9% converted from the array density and the tube diameter of the carbon nano tube.

As can be seen from fig. 3, if the orientations of the two growth steps of the ultra-long carbon nanotube are different but are respectively consistent with the airflow direction, the ultra-long carbon nanotube film with a certain crossing angle can be obtained after the two growth steps are mutually overlapped. The preparation of the super-long carbon nanotube film continues to use the device and the method for preparing the horizontal array, after the growth of the horizontal array is finished for one time, the substrate is taken out and horizontally rotated for a certain angle, and the film consisting of the staggered super-long carbon nanotubes can be obtained.

As can be seen from fig. 6, the ultra-long carbon nanotube film prepared in this example is composed of two sets of horizontal arrays with different orientations, and the array orientation is controlled by the airflow direction.

Comparative example 1:

as in the method for producing carbon nanotubes described in reference 1, a catalyst precursor (iron salt solution such as ferric chloride) is coated on the edge of a substrate before growing carbon nanotubes, and no additional catalyst precursor is introduced during the growth process. The yield of carbon nanotubes in reference 1 is low and the array density is usually less than 10 per mm. The yield and array density of the carbon nanotubes prepared by the method provided by the application are 2 to 4 orders of magnitude higher than those of the carbon nanotubes prepared by the prior art 1.

Reference 1: zhang R, zhang Y, wei F. Controlled synthesis of elongated carbon nanotubes with implementation structures and orthogonal properties [ J ]. Accounts of chemical resources, 2017,50 (2): 179-189.

According to the preparation method provided by the application, the catalyst precursor needs to be continuously introduced in the growth process, so that the prepared carbon nano tube has the effect of ultra-long and ultra-high yield, the length of the obtained ultra-long carbon nano tube can reach a centimeter to meter level, and the growth speed of a single carbon nano tube can reach 2.37mm/min. The ultra-long carbon nanotube prepared by the method also has the characteristics of perfect structure, less wall number (the number of the tube walls is one to three), excellent electrical property and the like.

Claims

1. A method for preparing ultra-long carbon nanotubes with ultra-high yield is characterized by comprising the following steps:

arranging a substrate in a reactor, introducing mixed gas 1 into the reactor to replace air in the reactor with the mixed gas 1, and raising the temperature in the reactor until the reaction temperature is reached, wherein the mixed gas 1 comprises hydrogen and first inert atmosphere gas;

2. The method for ultra-high yield production of ultra-long carbon nanotubes of claim 1, wherein the substrate is made of any one or more materials selected from the group consisting of silicon, quartz, ceramic and metal.

3. The ultra-high yield method of producing ultra-long carbon nanotubes of claim 2, wherein the extending direction of the substrate is parallel to the gas flow direction; alternatively, the substrate extends perpendicular to the gas flow direction and has a through hole therein, the through hole allowing the end of the carbon nanotube not held by the substrate to grow therethrough.

4. The ultra-high yield method for preparing ultra-long carbon nanotubes of claim 1 or 2, wherein the reaction temperature is 300 ℃ to 2000 ℃, and the reaction time is 1min to 2000min; optionally, the reaction time of the reaction is 3min to 600min;

optionally, the total flow rate of the mixed gas 2 is 0.01sccm to 100000sccm; optionally, the total flow rate of the mixed gas 2 is 1sccm to 10000sccm;

optionally, the flow rate of the catalyst solution is 0.001 μ L/min to 10000 μ L/min; optionally, the flow rate of the catalyst solution is 0.01 μ L/min to 100 μ L/min;

optionally, the carbon source gas is selected from any one or more of methane, ethane, ethylene, acetylene, methanol vapor, ethanol vapor, isopropanol vapor, acetone vapor, and carbon monoxide;

optionally, the concentration of the carbon source gas in the mixed gas 2 is 0.00001vol.% to 99vol.%; optionally, the concentration of the carbon source gas in the mixed gas 2 is 0.01vol.% to 80vol.%;

optionally, the concentration of the hydrogen in the mixed gas 2 is 0.001vol.% to 99vol.%; optionally, the concentration of the hydrogen in the mixed gas 2 is 1vol.% to 99vol.%;

optionally, the concentration of the water vapor in the mixed gas 2 is 0.0001vol.% to 99vol.%.

5. The ultra-high yield method for the production of ultra-long carbon nanotubes of claim 1 or 2, wherein the concentration of the catalyst precursor in the catalyst solution is 0.0001 to 99wt.%; optionally, the concentration of the catalyst precursor in the catalyst solution is from 0.01wt.% to 20wt.%;

optionally, the concentration of promoter in the catalyst solution is from 0.0001wt.% to 99wt.%; optionally, the concentration of the promoter in the catalyst solution is from 0.01wt.% to 60wt.%.

6. The ultra-high yield method of producing ultra-long carbon nanotubes of claim 1, wherein the catalyst precursor is a metallocene compound and the cocatalyst is thiophene;

optionally, the metallocene compound is selected from any one or more of a metallocene compound of a group VIII element and a metallocene compound of a group IVB metal;

still optionally, the metallocene compound is selected from any one or more of ferrocene, cobaltocene, nickelocene, and dichlorotitanocene;

optionally, the solvent is selected from any one or more of methanol, ethanol, isopropanol, acetone, benzene, toluene, ethylbenzene, xylene, n-hexane and cyclohexane.

7. The ultra-high yield method of producing ultra-long carbon nanotubes of claim 1, further comprising:

and cooling the ultra-long carbon nano tube under the protection of the mixed gas 1 after the growth of the ultra-long carbon nano tube is finished.

8. The ultra-high yield method of producing ultra-long carbon nanotubes of claim 1, wherein the first inert atmosphere gas and the second inert gas are each independently selected from any one or more of nitrogen, argon and helium.

9. The ultra-long carbon nanotubes prepared by the ultra-high yield preparation method of ultra-long carbon nanotubes according to any one of claims 1 to 8;

optionally, the length of the ultra-long carbon nanotube is 1cm to 100cm.

10. Use of the ultra-long carbon nanotubes of claim 9 in carbon-based chips, carbon nanotube fibers and composite cables.