Method for preparing carbon nanotubes through plasma pretreatment-dipping deposition

Abstract

The invention discloses a method for preparing a carbon nanotube through plasma pretreatment-dipping deposition, which comprises the following steps: carrying out plasma treatment on a substrate, dipping the substrate subjected to plasma treatment into a catalyst precursor solution, taking out and drying to obtain a pretreated substrate; and introducing a carbon source gas, and preparing the carbon nanotubes on the surface of the pretreated substrate by adopting a vapor deposition method. According to the method, the wettability of the catalyst solution is improved by processing the base material through the plasma, the surface of the base plate is rough, the migration potential barrier of catalyst atoms on the surface of the base plate in the high-temperature annealing process is increased, excessive agglomeration of the catalyst atoms is prevented, and formation of small catalyst particles which are uniformly distributed is promoted; therefore, the prepared carbon nano tube is relatively compact, and the obtained carbon nano tube is high in density, large in specific surface area, and relatively high in yield and purity.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon nanotubes, and particularly relates to a method for preparing carbon nanotubes by plasma pretreatment-immersion deposition. Background Art

[0002] Carbon nanotubes (CNTs) are tubular nanomaterials composed of carbon atoms. Their unique structure endows them with excellent mechanical, electrical, and thermal properties, making them widely used in electronics, energy, composite materials, and sensors. Vertically aligned CNTs (VACNTs), in particular, have become a research hotspot in recent years due to their outstanding advantages in applications such as field emission cathodes, supercapacitor electrodes, thermal interface materials, and reinforcements for high-performance composites.

[0003] The substrate-based method, a key approach to carbon nanotube growth, offers significant advantages. By preparing a catalyst layer on a specific substrate, the particle size, density, and distribution of the catalyst can be precisely controlled, resulting in highly ordered carbon nanotube growth and a well-consistent carbon nanotube array. This method is particularly well-suited for applications requiring precise array structures, such as electronics, optoelectronics, and sensor arrays.

[0004] Currently, catalytic chemical vapor deposition (CCVD) is commonly used to grow VACNTs on substrates, and the preparation of the catalyst is one of the key steps that determines the quality and yield of CNTs growth. Traditional methods usually use physical vapor deposition (PVD) technology, such as sputtering and evaporation, to deposit a thin layer of catalytic metal film (such as iron, nickel or cobalt) on the substrate surface, and then anneal it at high temperature to form catalyst nanoparticles. Although PVD technology can accurately control the thickness and composition of the catalyst film layer, its equipment is complex and usually requires an ultra-high vacuum environment. It is expensive and difficult to maintain. It is not suitable for large-scale and large-area continuous production in industry, and there are major bottlenecks in production efficiency and economy.

[0005] To overcome the shortcomings of PVD catalyst preparation, researchers have explored simpler and more economical chemical methods in recent years, such as impregnation, sol-gel, and co-precipitation. However, these traditional wet chemical methods suffer from problems such as insufficient wettability of the precursor solution and uneven distribution of catalyst particles. This results in the catalysts being difficult to achieve the desired activity and stability, thus limiting the large-scale and efficient preparation of VACNTs.

[0006] In view of the above-mentioned problems, there is an urgent need in the art to develop a catalyst preparation technology that is simple, low-cost, and can achieve highly dispersed catalyst particles to meet the needs of industrialized carbon nanotube production. The present invention addresses the shortcomings of the existing technology and proposes a new method for preparing carbon nanotube catalysts based on plasma pretreatment combined with chemical impregnation. This method does not require complex vacuum equipment, is simple to operate, and uses readily available raw materials. It can significantly improve the bonding strength between the catalyst and the substrate and the dispersion density of the catalyst, thereby providing a new technical approach for the large-scale, low-cost production of high-quality carbon nanotubes. Summary of the Invention

[0007] The present invention aims to overcome the existing technical deficiencies and provide a simple method for preparing a carbon nanotube catalyst. The catalyst has a simple preparation process, uses readily available and inexpensive raw materials, and has a low cost.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] Step S1: Before dipping, the surface of the silicon dioxide wafer is first subjected to plasma treatment with a treatment power of 10 to 120 W and a treatment time of 120 to 300 seconds;

[0010] Specifically, the plasma processing gas can be Ar or O2, the processing power can be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120W, or other values ​​within this range, and the processing time can be 120, 140, 160, 180, 200, 220, 240, 260, 280, 300s, or other values ​​within this range.

[0011] Step S2, preparing a catalyst precursor solution: the catalyst precursor solution includes, in addition to iron, cobalt or nickel salt precursors, one or more metal salt auxiliary agent precursors, and the auxiliary agent precursor includes at least one or more of aluminum salts, magnesium salts, titanium salts, zirconium salts, cerium salts, lanthanum salts and molybdenum salts.

[0012] Preferably, the auxiliary agent precursor includes at least one or more of magnesium nitrate, magnesium acetate, titanium tetrachloride, butyl titanate, zirconyl nitrate, zirconium chloride, cerium nitrate, lanthanum nitrate, ammonium molybdate or sodium molybdate.

[0013] Preferably, Fe is configured 3+ and Al 3+ A catalyst precursor solution, wherein the molar ratio of each metal ion Fe:Al=1:0.1-10, preferably, the molar ratio Fe:Al=1:0.8-5, more preferably, the molar ratio Fe:Al=1:(1-2);

[0014] Furthermore, Fe 3+ 、Al 3+Selected from nitrate compounds, such as Fe 3+ Provided by ferric nitrate nonahydrate, Al 3+ Provided by aluminum nitrate nonahydrate;

[0015] Ammonia water was added and mixed with stirring to adjust the pH value of the catalyst precursor solution to neutral to obtain a clear reddish-brown solution.

[0016] Step S3, immersing the silicon dioxide sheet in the solution;

[0017] Specifically, the immersion time may be 10 s, 20 s, 30 s, 40 s, or other proportional values ​​within this range.

[0018] Step S4: drying the impregnated silicon dioxide wafer at room temperature.

[0019] Step S5, placing the silicon wafer in a tube furnace, introducing a mixed gas with a gas flow rate ratio of (1-10) : (1-10) : (2-30) : (1-10) of water-carrying argon, carbon source gas, hydrogen and argon, and reacting at 570-1000°C for 10-20 minutes. Naturally cool to room temperature, remove the silicon wafer, and obtain carbon nanotubes. Specifically, the gas flow rate of the water-carrying argon gas can be 1, 2, 3, 4...10 in the total gas, the gas flow rate of the carbon source gas can be 1, 2, 3, 4...10 in the total gas, the gas flow rate of the hydrogen gas can be 2, 3, 4, 5...30 in the total gas, and the gas flow rate of the argon gas can be 1, 2, 3, 4...10 in the total gas.

[0020] Furthermore, the carbon source gas may be one of ethylene, propylene, methane, propane, and acetylene.

[0021] Compared with the prior art, the beneficial effects of the method of the present invention are as follows:

[0022] 1. The carbon nanotube catalyst provided by the present invention is Fe 3+ :Al 3+ is a metal ion, among which Fe 3+ Al is the active component of the catalyst. 3+As a catalyst adjuvant, it is used to provide more active sites. By adjusting the ratio of metal ions and adopting an impregnation method to prepare, the catalyst particles are clustered after calcination, and the surface is small stacked particles, which provide attachment sites for the growth of carbon nanotubes, thereby having good catalytic activity. It is conducive to combining with the cracked carbon source gas to grow carbon nanotubes according to the gas-solid mechanism. In the present invention, the plasma treatment substrate increases the wettability of the catalyst solution on the one hand, and at the same time makes the substrate surface rough, thereby increasing the migration barrier of the catalyst atoms on the substrate surface during the high-temperature annealing process, preventing the catalyst atoms from excessively agglomerating, and promoting the formation of evenly distributed small catalyst particles, thereby making the prepared carbon nanotubes denser, the obtained carbon nanotubes have a high density, a large specific surface area, and a high yield and purity.

[0023] Second, the present invention provides a method for preparing a carbon nanotube catalyst. By adjusting the catalyst ratio and other conditions, the resulting catalyst not only improves the catalytic efficiency but also reduces the energy consumption of carbon nanotube production. In the catalyst precursor solution of the present invention, the additive precursor can be used to inhibit the agglomeration and sintering of the iron, cobalt, or nickel salt catalyst particles, improve the thermal stability of the catalyst, optimize the adhesion between the catalyst particles and the substrate, enhance the catalytic activity, and regulate the diameter and morphology of the carbon nanotubes.

[0024] 3. The preparation method of the carbon nanotube catalyst provided by the present invention has a simple catalyst preparation process. Except for water vapor and a small amount of calcination waste gas, no other waste gas is generated, which is environmentally friendly. In addition, the raw materials are cheap and easily available, and the cost is low. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0026] Unless otherwise specified, all raw materials used in the following examples are commercially available products or can be prepared according to conventional methods in the art. Silicon dioxide wafers (thickness 500 ± 10 μm) were purchased from Shenzhen Lijing Electronics Co., Ltd.; ammonia was purchased from Source Test Standard (Quanzhou) Technology Co., Ltd.; and hydrogen peroxide was purchased from Huizhou Xiangsheng Industry and Trade Co., Ltd. Ferric nitrate nonahydrate was purchased from Guangdong Lin's Chemical Reagent Co., Ltd.; and aluminum nitrate nonahydrate was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0027] Example 1

[0028] The surface of a silicon dioxide wafer was first plasma-treated using O₂ gas at 10W for 120 seconds. Then, 1.01g of aluminum nitrate and 1.09g of ferric nitrate were dissolved in 20ml of deionized water in two small beakers, respectively, to obtain a clear, colorless solution and a clear, yellow solution. The dissolved ferric nitrate and aluminum nitrate solutions were then mixed with 100ml of 0.025mol / L ammonia in a new 250ml beaker and stirred thoroughly to obtain a clear, reddish-brown precursor solution. A silicon wafer (10mm x 10mm) was immersed in the solution for 20 seconds and then dried at room temperature. The wafer was then placed in a tube furnace and introduced with a mixture of water-carrying argon, ethylene, hydrogen, and argon at a flow rate ratio of (1-10):(1-10):(2-30):(1-10). The reaction was carried out at 570-1000°C for 10-20 minutes. The mixture was cooled naturally to room temperature, and the silicon wafer was taken out to obtain carbon nanotubes.

[0029] Example 2

[0030] The surface of a silicon dioxide wafer was first plasma-treated using O₂ gas at 120W for 300 seconds. Then, 1.01g of aluminum nitrate and 1.09g of ferric nitrate were dissolved in 20ml of deionized water in two small beakers, respectively, to obtain clear colorless and yellow solutions. The dissolved ferric nitrate and aluminum nitrate solutions were then mixed with 100ml of 0.5mol / L ammonia in a new 250ml beaker and stirred thoroughly to obtain a clear reddish-brown precursor solution. A silicon wafer (10mm x 10mm) was immersed in the solution for 30 seconds and then dried at room temperature. The wafer was then placed in a tube furnace and introduced with a mixture of water-carrying argon, ethylene, hydrogen, and argon at a flow rate ratio of (1-10):(1-10):(2-30):(1-10). The reaction was carried out at 570-1000°C for 10-20 minutes. The mixture was cooled naturally to room temperature, and the silicon wafer was taken out to obtain carbon nanotubes.

[0031] Example 3

[0032] A silicon dioxide wafer was first plasma-treated using O₂ gas at 120W for 300 seconds. Then, 1.39g of aluminum nitrate and 1.00g of ferric nitrate were dissolved in 20ml of deionized water in two small beakers, respectively, to obtain a clear, colorless solution and a clear, yellow solution. The dissolved ferric nitrate and aluminum nitrate solutions were then mixed with 100ml of 0.025mol / L ammonia in a new 250ml beaker and stirred thoroughly to obtain a clear, reddish-brown precursor solution. A silicon wafer (10mm x 10mm) was immersed in the solution for 10 seconds and then dried at room temperature. The wafer was then placed in a tube furnace and introduced with a mixture of water-carrying argon, ethylene, hydrogen, and argon at a flow rate ratio of (1-10):(1-10):(2-30):(1-10). The reaction was carried out at 570-1000°C for 10-20 minutes. The mixture was cooled naturally to room temperature, and the silicon wafer was taken out to obtain carbon nanotubes.

[0033] Comparative Example 1

[0034] The difference from Example 1 is that the surface of the silicon dioxide wafer is not subjected to plasma treatment, and the other conditions are the same as those in Example 1.

[0035] Comparative Example 2

[0036] The difference from Example 1 is that the gas type for plasma treatment on the surface of the silicon dioxide wafer is Ar, and the other conditions are the same as those in Example 1.

[0037] Comparative Example 3

[0038] A silicon dioxide wafer was first plasma-treated using Ar gas at 120W for 300 seconds. Then, 1.01g of aluminum nitrate and 1.09g of ferric nitrate were dissolved in 20ml of deionized water in two small beakers, respectively, to obtain a clear, colorless solution and a clear, yellow solution. The dissolved ferric nitrate and aluminum nitrate solutions were then mixed with 100ml of aqueous ammonia in a new 250ml beaker and stirred thoroughly to obtain a clear, reddish-brown precursor solution. A silicon wafer (10mm x 10mm) was immersed in the solution for 30 seconds in a humidity-controlled temperature chamber (25°C, RH = 50%). The immersed silicon dioxide wafer was then dried at room temperature for 1 hour. The wafer was then placed in a tube furnace and heated at a rate of 60°C / min to a calcination temperature of 500°C. During the reduction calcination, water-carrying argon gas was introduced at a flow rate of 3:8:12 between argon and hydrogen. The temperature was continuously raised to 750°C, and the hydrogen reduction time was 15 minutes. Then, water-carrying argon gas, ethylene gas, hydrogen gas, and argon gas were introduced at a flow rate ratio of 3:4:9:4, and the reaction was carried out at 750°C for 15 minutes. The tube furnace was then purged with argon gas for 5 minutes, and the mixture was naturally cooled to room temperature. The silicon wafer was removed to obtain carbon nanotubes.

[0039] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing carbon nanotubes by plasma pretreatment-immersion deposition, characterized in that: The method comprises the following steps: performing plasma treatment on the substrate, dipping the plasma-treated substrate into a catalyst precursor solution, taking out the substrate, and drying the substrate to obtain a pretreated substrate; A carbon source gas is introduced to prepare carbon nanotubes on the surface of the pretreated substrate by a vapor deposition method; Among them, the plasma treatment power is 10~120W, and the treatment time is 120~300s; The catalyst precursor solution includes one or more of iron salt, cobalt salt or nickel salt, and also includes an auxiliary agent precursor.

2. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1, characterized in that: The auxiliary agent precursor includes at least one or more of aluminum salt, magnesium salt, titanium salt, zirconium salt, cerium salt, lanthanum salt and molybdenum salt; and the pH value of the catalyst precursor solution is adjusted to be neutral.

3. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1, characterized in that: The material of the substrate includes silicon dioxide wafer, silicon wafer or steel wafer.

4. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1 or 2, characterized in that: The plasma treatment gas includes Ar or O2.

5. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1 or 2, characterized in that: The molar ratio of the iron salt, cobalt salt or nickel salt to the auxiliary agent precursor is 1:0.1-10.

6. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1 or 2, characterized in that: The plasma-treated substrate is immersed in a catalyst precursor solution for a time of 10s to 40s.

7. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1 or 2, characterized in that: The carbon source gas includes one or more of ethylene, propylene, methane, propane, and acetylene.

8. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1 or 2, characterized in that: The vapor deposition method includes introducing carbon source gas and a mixed gas of water-carrying argon, hydrogen and argon, heating the mixture to 570-1000° C., and preparing carbon nanotubes on the surface of a pretreated substrate.

9. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 8, characterized in that: The gas flow rate ratio of the water-carrying argon gas, the carbon source gas, the hydrogen gas and the argon gas is (1-10): (1-10): (2-30): (1-10).

10. The method for preparing carbon nanotubes by plasma pretreatment-immersion deposition according to claim 1 or 2, characterized in that: The step of adjusting the pH value of the catalyst precursor solution to be neutral includes adding an alkaline solution to adjust the pH value of the catalyst precursor solution to be neutral.