CN111943172A - A method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition - Google Patents

Abstract

The invention relates to a method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, which is characterized by the following process: (1) forming a transition metal catalyst/passivation layer catalyst system on the surface of a planar substrate. (2) Place the flat substrate with the transition metal catalyst/passivation layer in a vacuum system, use hydrogen as the carrier gas, excite the metal wire with a certain power and deposit the second phase metal on the reduced metal catalyst to form a second phase metal. Phase metal/catalyst/passivation layer system. (3) introducing carbon source gas, and using chemical vapor deposition method to grow carbon nanotube arrays on the second-phase metal/catalyst/passivation layer system prepared above.

Description

A method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition

technical field

The invention relates to a preparation method for preparing carbon nanotube array carbon nanotube array by metal wire-assisted chemical vapor deposition.

Background technique

Carbon nanotubes (Carbon nanotubes, CNTs) can be understood as a vector curled hollow seamless nano-scale tube body formed by a single-layer or multi-layer graphite-like layer structure according to a certain method. Its unique structure endows it with large specific surface area, excellent mechanical properties, ultra-high electrical and thermal conductivity. Carbon nanotube arrays (CNTAs) not only inherit the advantages of CNTs, but also because of their regular orientation and arrangement, as well as optimized electron transport paths, CNTAs materials have great potential in field emission, catalysis, electrochemistry, sensors and other fields. application prospect and attracted strong attention. The diameter, orientation, and graphitization degree of CNTAs can significantly affect their physical and chemical properties, so it is of great significance to realize the controllable preparation of CNTA.

At present, using metal catalyst/passivation layer system as catalyst to prepare CNTAs by chemical vapor deposition (CVD) has become a widely recognized preparation method. The structure of CNTAs is controlled by the catalyst and growth atmosphere, and it is generally believed that the particle size of the catalyst plays a dominant role in the diameter of the carbon nanotubes in the array. The introduced passivation layer (such as Al ₂ O ₃ , MgO, etc.) can inhibit the migration, growth, and sintering of metal catalyst particles (such as Fe, Co, Ni, etc.) during high-temperature CVD, thereby ensuring the growth of CNTAs. However, for the preparation of single-walled, double-walled and few-walled CNTAs, not only the buffer of the passivation layer is required, but also other auxiliary methods need to be introduced to maintain the size structure, dispersion and catalytic activity of the catalyst. The introduction of second-phase metals (such as Mo, W, Ta, etc.) into the catalytically active metal particles inhibits the catalyst failure caused by the strong interaction between the catalyst metal and carbon or the migration and agglomeration of the catalyst metal, and then achieves the improvement of single-walled carbon nanotubes. effect of productivity. At present, the preparation methods of the second phase metal/catalyst/passivation layer system mainly include magnetron sputtering and electron beam evaporation coating. Although the reaction is highly controllable, the preparation cost is high, which is not conducive to single-wall, double-wall and less Low-cost production of wall CNTAs (Document 1: Noda S, Sugime H, Osawa T, et al. Carbon, 2006, 44(8): 1414-1419; Document 2: Wang X, Li Q, Xie J, Jin Z, et al. Nano Letters, 2009(9): 3137-3141; Literature 3: Sugime H, Sato T, Nakagawa R, et al. ACS Nano 2019, 13, 13208-13216).

In summary, it is of great research value and application significance to develop a low-cost and controllable preparation technology to introduce second-phase metals to realize the controllable preparation of high-quality single-wall and few-wall carbon nanotube arrays.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, which is simple and controllable in process, low in raw materials, and can greatly reduce the production cost of high-quality single-wall and few-wall carbon nanotube arrays . The invention adopts a chemical vapor deposition method, uses hydrogen as a carrier gas, transition metal/passivation layer as a catalyst, and uses a high-melting point metal wire as a second-phase metal deposition source, and adjusts the deposition of the second-phase metal by controlling the action power and time of the metal wire. The content of the phase metal is further reduced to form a second phase metal/catalyst/passivation layer system, thereby realizing the controllable preparation of carbon nanotube arrays. The technical scheme of the present invention is realized by the following scheme,

A method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition is characterized by the following process:

(1) A transition metal catalyst/passivation layer catalyst system is formed on the surface of the planar substrate.

(2) Place the flat substrate with the transition metal catalyst/passivation layer in a vacuum system, use hydrogen as the carrier gas, excite the metal wire with a certain power and deposit the second phase metal on the reduced metal catalyst to form a second phase metal. Phase metal/catalyst/passivation layer system.

(3) introducing carbon source gas, and using chemical vapor deposition method to grow carbon nanotube arrays on the second-phase metal/catalyst/passivation layer system prepared above.

In the method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, the required planar substrates can be polished silicon/silicon oxide wafers, quartz wafers, metal foils, and the like.

The described method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, the method for supporting transition metal catalyst/passivation layer can be spin coating or spraying solution, thermal evaporation deposition, magnetron sputtering, electron beam evaporation coating Wait for the method to complete.

In the method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, the transition metal catalyst can be one of metal iron (Fe), cobalt (Co), and nickel (Ni); the passivation layer can be oxidized One of aluminum (Al ₂ O ₃ ), magnesium oxide (MgO), zirconium oxide (CrO), silicon oxide (SiO ₂ ), and titanium dioxide (TiO ₂ ).

In the method for preparing carbon nanotube materials by metal wire-assisted chemical vapor deposition, the required melting point of the metal wire is not lower than 900 ° C, and can be metal tungsten (W) wire, molybdenum (Mo) wire, niobium (Nb) wire. ) wire, tantalum (Ta), gadolinium (Gd) wire, etc., the working power range is 5-500W, the processing time is 0.5-30min, the deposition content of the second-phase metal is regulated, and the second-phase metal/ Transition metal catalyst/passivation layer catalytic system to obtain catalyst with stable structure at high temperature.

In the method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, the pressure of the chemical vapor deposition system is 1-100 torr; the flow rate of the carrier gas hydrogen is 100-2000 sccm.

In the method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, the carbon source gas can be one of acetylene, methane, ethanol, and benzene, and the flow rate of the carbon source gas is 1-100 sccm.

In the method for preparing carbon nanotube arrays by metal wire-assisted chemical vapor deposition, the reaction temperature for preparing high-quality single-wall and few-wall carbon nanotube arrays by chemical vapor deposition is 600-900°C.

The beneficial effect of the present invention is that: using high melting point metal wire as the second phase metal source under vacuum and low pressure conditions, the second phase metal is deposited on the transition metal catalyst/passivation layer to form the second phase metal/catalyst/passivation layer catalysis The system significantly improved the structural stability of the catalyst at high temperature, and combined with the chemical vapor deposition method, carbon nanotube arrays were prepared by using the second phase metal/catalyst/passivation layer as the catalyst. The carbon nanotube array prepared by the invention has complete structure, less impurity content and high crystallinity. The invention prepares the carbon nanotube array based on the metal wire-assisted chemical vapor deposition method, and the method is simple and controllable, has low cost, simple equipment, and is easy to realize and popularize.

Description of drawings

FIG. 1 is a scanning electron microscope picture of the carbon nanotube array prepared in Example 1.

FIG. 2 is a low magnification transmission electron microscope picture and a corresponding element distribution diagram of the carbon nanotube array prepared in Example 1. FIG.

FIG. 3 is a high-magnification transmission electron microscope picture obtained in Example 1. FIG.

FIG. 4 is the Raman spectrum obtained in Example 1. FIG.

FIG. 5 is a scanning electron microscope picture of the carbon nanotube array prepared in Example 2. FIG.

FIG. 6 is a scanning electron microscope picture of the carbon nanotube array prepared in Example 3. FIG.

FIG. 7 is a scanning electron microscope picture of the carbon nanotube array prepared in Example 8. FIG.

Detailed ways

Example 1

7.5mM aluminum acetylacetonate and 7.5mM iron acetylacetonate were dissolved in 100mL dibenzyl ether solution and reacted at 200°C for 1h, the precipitate was taken out and dissolved in 50mL n-hexane solution to obtain iron oxide/alumina liquid phase catalyst. The iron oxide/alumina liquid phase catalyst was supported on the polished Si/SiO ₂ substrate surface by spin coating method at 2000 rpm/min. Select the tungsten wire as the required metal wire, heat the chemical vapor deposition system to 600 ° C, pass 500 sccm of hydrogen as the carrier gas, keep the system pressure at 7torr, and the working power of the tungsten wire is 80W. The Si/SiO ₂ was placed in a chemical vapor deposition system close to the tungsten wire, and after 0.5 min of treatment, 2 sccm of acetylene was introduced and kept for 2 min, then the sample was withdrawn and rapidly cooled.

The samples were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy:

Accompanying drawing 1 is the scanning electron microscope picture of the prepared carbon nanotubes, as can be seen from the figure, due to the high catalyst loading density, uniform dispersion, and stable structure at high temperature, the prepared carbon nanotubes have an array structure and are neatly arranged and uniform in diameter. There is no granular impurities on the surface of the nanotubes; Figure 2 is the transmission electron microscope picture of the prepared carbon nanotubes and the corresponding element distribution map, it can be seen that under the action of hydrogen, the iron oxide/alumina catalyst is first reduced to Fe/alumina. Al ₂ O ₃ catalyst, and then tungsten element acts on the surface of the catalyst through the tungsten wire and forms a W/Fe/Al ₂ O ₃ system, which ensures the size structure and activity of the catalyst at high temperature; Figure 3 shows the high-power transmission of the sample From the electron microscope photo, it can be seen that the tube wall of the prepared carbon nanotube is clear and straight, the tube wall is between 1 and 4 layers, with few structural defects and low impurity carbon content; in the Raman spectrum diagram (see Figure 4) The radial breathing vibration peak located at 100～300cm ^-1 further confirms that the prepared carbon nanotubes are composed of single-walled and few-walled carbon nanotubes, and the lower ID / _IG value ( _0.82 ) indicates that the prepared carbon nanotubes The nanotubes contain fewer defects, indicating that high-quality single-wall and few-wall carbon nanotubes are successfully prepared in this example.

Embodiment 2

The Al ₂ O ₃ /Co catalyst is deposited on the polished Si/SiO ₂ substrate by the method of electron beam evaporation coating, wherein the size of the Co nanoparticles is ~2nm, and the thickness of the Al _{2 O3} layer is ~5nm. Select molybdenum wire as the required metal wire, heat the chemical vapor deposition system to 800 ℃, pass 1000sccm of hydrogen as the carrier gas, keep the system pressure at 50torr, the working power of the molybdenum wire is 5W, and the Al ₂ O ₃ /Co The Si/SiO ₂ was placed in the chemical vapor deposition system and close to the molybdenum wire. After 2 min of treatment, 1 sccm of acetylene was introduced and kept for 10 min, and then the sample was withdrawn and rapidly cooled. Accompanying drawing 5 is the scanning electron microscope picture of the prepared carbon nanotubes. Due to the high catalyst loading density, uniform dispersion, and stable structure at high temperature, the prepared carbon nanotubes have an array structure and are neatly arranged and uniform in diameter, and the surface of the carbon nanotubes has no surface. Granular impurities.

Embodiment 3

The MgO/Co catalyst is deposited on the copper foil substrate by the method of magnetron sputtering, wherein the size of the Co nanoparticles is ~1 nm, and the thickness of the MgO layer is ~3 nm. Select the tantalum wire as the required metal wire, heat the chemical vapor deposition system to 900 ° C, pass 800sccm of hydrogen as the carrier gas, the working power of the tantalum wire is 100W, the system pressure is maintained at 4torr, and the copper foil with MgO/Co is attached. It was placed in a chemical vapor deposition system near the tantalum wire, and after 5 minutes of treatment, 20 sccm of ethanol was poured into it and kept for 30 minutes, and then the sample was drawn out and rapidly cooled to obtain a carbon nanotube array material.

Embodiment 4

A CrO/Ni catalyst is deposited on a quartz plate substrate by a magnetron sputtering method, wherein the size of the Ni nanoparticles is ∼5 nm, and the thickness of the CrO layer is ∼10 nm. Select the gadolinium wire as the required metal wire, heat the chemical vapor deposition system to 700 ° C, pass 2000sccm of hydrogen as the carrier gas, the working power of the gadolinium wire is 200W, the system pressure is kept at 2torr, and the quartz plate with CrO/Ni is attached. It was placed in a chemical vapor deposition system close to the rhenium wire, and after 10 minutes of treatment, 100 sccm of benzene was introduced for 30 minutes, and then the sample was withdrawn and rapidly cooled to obtain a carbon nanotube array material.

Embodiment 5

The TiO ₂ /Ni catalyst was deposited on the quartz flake substrate by magnetron sputtering, wherein the size of Ni nanoparticles was ∼5 nm, and the thickness of the TiO ₂ layer was ∼10 nm. Select the tungsten wire as the required metal wire, heat the chemical vapor deposition system to 800 ° C, pass 100sccm of hydrogen as the carrier gas, the working power of the tungsten wire is 200W, the system pressure is maintained at 100torr, the quartz with SiO ₂ /Fe is attached The sheet was placed in a chemical vapor deposition system close to the tungsten wire, and after 30 minutes of treatment, 2 sccm of methane was passed in and kept for 30 minutes, and then the sample was pulled out and rapidly cooled to obtain a carbon nanotube array material.

Embodiment 6

A SiO ₂ /Fe catalyst was deposited on a quartz plate substrate by magnetron sputtering, wherein the Fe nanoparticles were ˜20 nm in size and the SiO ₂ layer was ˜15 nm in thickness. Select the niobium wire as the required metal wire, heat the chemical vapor deposition system to 800 ° C, pass 2000sccm of hydrogen as the carrier gas, the working power of the niobium wire is 200W, the system pressure is maintained at 10torr, the quartz with SiO ₂ /Fe The sheet was placed in a chemical vapor deposition system close to the niobium wire, and after 30 min of treatment, 10 sccm of methane was fed for 30 min, and then the sample was pulled out and rapidly cooled to obtain a carbon nanotube array material.

Embodiment 7

7.5mM aluminum acetylacetonate and 7.5mM iron acetylacetonate were dissolved in 100mL dibenzyl ether solution and reacted at 200°C for 1h, the precipitate was taken out and dissolved in 50mL n-hexane solution to obtain iron oxide/alumina liquid phase catalyst. The iron oxide/alumina liquid phase catalyst was supported on the polished Si/SiO ₂ substrate surface by spin coating method at 2000 rpm/min. Select the silver wire as the required metal wire, heat the chemical vapor deposition system to 700 ° C, pass 500sccm of hydrogen as the carrier gas, keep the system pressure at 7torr, and the working power of the silver wire is 30W. The Si/SiO ₂ was placed in a chemical vapor deposition system close to the tungsten wire. After 2 min of treatment, 4 sccm of acetylene was introduced and kept for 5 min, and then the sample was withdrawn and rapidly cooled. Figure 7 is a scanning electron microscope picture of the carbon nanotubes prepared in Example 8.

Claims (10)

1. A method for preparing a carbon nanotube array by metal wire assisted chemical vapor deposition is characterized by comprising the following steps:

(1) a transition metal catalyst/passivation layer catalyst system is formed on the surface of the planar substrate.

(2) The planar substrate with the transition metal catalyst/passivation layer is placed in a vacuum system, hydrogen is used as carrier gas, the metal wire is excited at a certain power, and second phase metal is deposited on the reduced metal catalyst, so that a second phase metal/catalyst/passivation layer system is formed.

(3) Introducing carbon source gas, and growing a carbon nanotube array on the prepared second-phase metal/catalyst/passivation layer system by using a chemical vapor deposition method.

2. The method of claim 1, wherein the planar substrate is a polished silicon wafer, a silicon oxide wafer, a quartz wafer or a metal foil.

3. The method for preparing a carbon nanotube array according to claim 1, wherein the step (1) of loading the transition metal catalyst/passivation layer is performed by spin coating or spray coating solution, thermal evaporation deposition, magnetron sputtering or electron beam evaporation coating.

4. The method of claim 1, wherein the transition metal catalyst is one of iron (Fe), cobalt (Co) and nickel (Ni).

5. The method of claim 1, wherein the passivation layer is aluminum oxide (Al)₂O₃) Magnesium oxide (MgO), zirconium oxide (CrO), silicon oxide (SiO)₂) Titanium dioxide (TiO)₂) Or (2) to (d).

6. The method of claim 1, wherein the metal wire has a melting point of not less than 900 ℃ and is one of tungsten (W), molybdenum (Mo), niobium (Nb), tantalum (Ta), gadolinium (Gd), and the like.

7. The method for preparing a carbon nanotube array according to claim 5, wherein the working power of the metal wire is in a range of 5 to 500W, the treatment time is in a range of 0.5 to 30min, the deposition content of the second phase metal is controlled to form a second phase metal/transition metal catalyst/passivation layer catalyst system, and the catalyst having a stable structure at a high temperature is obtained.

8. The method of claim 1, wherein the carbon source gas is one of acetylene, methane, ethanol, and benzene.

9. The method of claim 1, wherein the reaction temperature for preparing the carbon nanotube array by chemical vapor deposition is 600-900 ℃.

10. The method of claim 1, wherein the pressure of the CVD system is 1-100 torr; the flow rate of the carrier gas hydrogen is 100-2000 sccm.

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