CN1696052A - A method for preparing carbon nanotubes - Google Patents

Abstract

A process for preparing carbon nanotubes by chemical vapor deposition method features that the metallic catalyst (Fe, Co, or Ni) is carried by SiO2 as carrier, and the acetylene, propene, or methane is used as carbon source.

Description

A method for preparing carbon nanotubes

Technical field

The invention belongs to the field of synthesis of inorganic functional materials, and more specifically relates to a catalyst preparation method and a method for preparing carbon nanotubes by cracking carbon source gas (methane, ethylene or propylene, etc.) at high temperature as raw materials.

Background technique

Since the Japanese scientist Iijiam discovered carbon nanotubes (CNTs) in 1991, they have attracted great attention from scientists and technicians from various countries because of their unique physical and chemical properties and good application prospects. Scientists predict that carbon nanotubes will become the most promising one-dimensional nanomaterials in the 21st century. Carbon nanotubes are cylindrical structures based on hexagonal lattices formed by carbon atoms. Those with a single-layer structure are called single-walled carbon nanotubes (SWNTs), and those with a multi-layered structure are called multi-walled carbon nanotubes (MWNTs). ). Theoretical predictions and experimental studies have found that carbon nanotubes have very peculiar electrical properties, which are closely related to their structures, and can be used to make nanoelectronic devices such as transistors. Carbon nanotubes are a good heat-conducting material, relying on ultrasonic waves to transmit heat energy. Carbon nanotubes have high strength and toughness. The Young's modulus of carbon nanotubes can reach up to 3.7Tpa. The density of carbon nanotubes is only 1/7 of that of steel, but its tensile strength is 100 times that of steel. . Carbon nanotubes have a large specific surface area and are ideal hydrogen storage materials. In addition, carbon nanotubes are resistant to acid, alkali and high temperature, but can be derivatized, and because of their good mechanical strength and excellent electrical conductivity, they can be used to prepare composite materials, chemical sensing materials and artificial muscles.

Since the discovery of carbon nanotubes, their preparation process has been extensively studied. There are many preparation methods, such as arc discharge method, laser ablation, electrolysis, low-temperature solid cracking, catalytic decomposition of hydrocarbons or chemical vapor deposition. Among them, the chemical vapor deposition method is currently a widely used method for preparing carbon nanotubes. Generally, Fe, Co, Ni and their alloys are used as catalysts, clay, silica, diatomaceous earth, alumina and magnesia are used as carriers, acetylene, propylene and methane are used as carbon sources, hydrogen, nitrogen, helium, argon Gas or ammonia as diluent gas, in the range of 530°C to 1130°C, the free carbon ions produced by the cracking of hydrocarbons can generate single-wall or multi-wall carbon nanotubes under the action of the catalyst. The required equipment and process conditions are relatively simple, and are suitable for large-scale preparation of carbon nanotubes. However, its size is uneven, its length is different, and it has defects. The key is the preparation and dispersion of catalysis. At present, the rough products of disordered and non-oriented multi-walled carbon nanotubes contain a large amount of impurities such as amorphous carbon, nano-carbon particles and catalyst particles, and there are many crystal defects, which are not easy to disperse, often bend and deform, and graphitize. To a lesser extent, these shortcomings will have a negative impact on the mechanical properties and physical and chemical properties of carbon nanotubes. In the preparation process of carbon nanotubes, the composition of the catalyst, the type of raw gas, and the reaction temperature all affect the yield, quality and microstructure of carbon nanotubes to varying degrees. Therefore, the development of a carbon nanotube preparation method with high yield, good quality and good use effect has become one of the key technologies to be solved in the development of catalytic decomposition of hydrocarbons.

Contents of Invention

The object of the present invention is to provide a low-cost, simple and easy preparation method with good quality and high yield of carbon nanotubes.

The technical solution is as follows:

Fe, Co, Ni and their alloys are selected as catalysts, clay, silica, diatomaceous earth, alumina and magnesium oxide are used as carriers, acetylene, propylene and methane are used as carbon sources, hydrogen, nitrogen, helium, argon Or ammonia as a diluent gas, in the range of 530 ° C ~ 1130 ° C, the free carbon ions produced by the cracking of hydrocarbons can generate single-walled or multi-walled carbon nanotubes under the action of a catalyst;

(1) Prepare catalyst by sol-gel method: Silicate (AR), ethanol ((AR) and (0.5-2M) nitrate (AR) aqueous solution are mixed with 1: 1: 1 (volume ratio), fully stirred Evenly, then add a few drops of acid or alkali as a catalyst to speed up the hydrolysis reaction and promote the formation of the gel; dry the wet gel at a constant temperature of 40-60°C to obtain a xerogel; then grind the xerogel into particles as catalyst;

(2) Spread the prepared powdered catalyst on a quartz boat, put it into the constant temperature zone of the tubular heating furnace, raise the temperature to 400-800°C under the protection of nitrogen, and pass in hydrogen for 20-40 minutes to reduce The catalyst is then heated to 600-1000° C., passed through acetylene, reacted for 30-120 minutes, cooled to normal temperature under nitrogen atmosphere, and the carbon nanotubes are prepared.

The silicate is methyl orthosilicate Si(OCH ₃ ) ₄ (TMOS) or ethyl orthosilicate Si(OC ₂ H ₅ ) ₄ (TEOS).

Described nitrate is ferric nitrate, cobalt nitrate and nickel nitrate.

The acid catalyst is a protonic acid, and the base catalyst is ammonia water or a buffer solution of ammonia water and ammonium fluoride.

The process of preparing carbon nanotubes by using the experimental method of the invention is simple, easy to operate, low in cost and high in yield; a large number of carbon nanotubes with uniform diameters are produced, with an inner diameter of 5-20nm and an outer diameter of 20-50nm.

The impurity content in the carbon nanotube product prepared by this method is small, the degree of graphitization is high, the tube diameter of the carbon nanotube is relatively uniform, and the surface is relatively smooth, and the purified carbon nanotube can be directly used to develop composite materials or used as Gas storage materials.

Description of drawings

Fig. 1 is to implement a transmission electron microscope photograph adopting the carbon nanotube prepared by the present invention;

Fig. 2 is a scanning electron micrograph of implementing a carbon nanotube prepared by the present invention;

Fig. 3 is the transmission electron micrograph of the carbon nanotube prepared by the present invention;

Fig. 4 is a partial transmission electron micrograph of carbon nanotubes prepared by the present invention in Embodiment 4.

Detailed ways

The content of the present invention is further illustrated by the following examples and accompanying drawings, but does not limit the scope of the present invention.

Embodiment one

Mix 10ml of 2M ferric nitrate (AR), 10ml of ethyl orthosilicate (AR) and 10ml of ethanol (AR), and stir thoroughly for about 30 minutes. Then slowly add about 0.3ml of hydrofluoric acid (AR), and further stir evenly. The wet gel was prepared, dried at a constant temperature of 60° C. for 7 days, and ground into uniform particles as a catalyst. Spread 100mg of powdered catalyst on a quartz boat, put it in the constant temperature zone of the tube furnace, raise the temperature to 400°C under nitrogen atmosphere (flow rate: 500ml/min), feed hydrogen gas, flow rate: 300ml/min, and reduce for 25min , the temperature was raised to 600° C., acetylene was passed through at a flow rate of 50 ml/min, the reaction was carried out for 60 min, and the mixture was cooled under nitrogen atmosphere. That is, carbon nanotubes were prepared, and the yield of the obtained product was 133 mg.

Embodiment two

The other conditions and steps were the same as in Example 1, but the reaction temperature of acetylene was changed to 800° C., and the yield of carbon nanotubes was 156 mg.

Embodiment Three

The other conditions and steps were the same as in Example 1, but the reaction temperature of acetylene was changed to 1000° C., and the yield of carbon nanotubes obtained was 189 mg.

Embodiment Four

The other conditions and steps are the same as in Example 1, changing the hydrogen reaction temperature to 750° C., and the acetylene feeding time to 30 minutes. The yield of the obtained carbon nanotubes was 76.6 mg.

Embodiment five

The other conditions and steps are the same as in Example 1, changing the flow rate of hydrogen to 100ml/min. The yield of carbon nanotubes obtained was 162 mg.

Embodiment six

The other conditions and steps are the same as in Example 1, changing the flow rate of hydrogen to 100ml/min, and the temperature of acetylene to 800°C. The yield of the obtained carbon nanotubes was 171.1 mg.

Embodiment seven

Other conditions and steps are the same as in Example 1, 10ml of 0.5M ferric nitrate (AR) is mixed with 10ml of ethyl orthosilicate (AR) and 10ml of ethanol (AR). The yield of carbon nanotubes obtained was 156 mg.

Embodiment Eight

Other conditions and steps were the same as in Example 1, 10 ml of 0.5M cobalt nitrate (AR) was used to prepare the catalyst, and the yield of the obtained carbon nanotubes was 178.5 mg.

Claims (4)

1. A method for preparing carbon nanotubes, using Fe, Co, Ni and their alloys as catalysts, clay, silicon dioxide, diatomaceous earth, aluminum oxide and magnesia as carriers, acetylene, propylene and methane as carbon Source, hydrogen, nitrogen, helium, argon or ammonia as diluent gas, in the range of 530 ° C ~ 1130 ° C, the free carbon ions produced by the cracking of hydrocarbons can generate single-walled or multi-walled carbon nanotubes under the action of a catalyst ; characterized by: (1) Prepare catalyst by sol-gel method: Silicate (AR), ethanol ((AR) and (0.5-2M) nitrate (AR) aqueous solution are mixed with 1: 1: 1 (volume ratio), fully stirred Evenly, then add a few drops of acid or alkali as a catalyst to speed up the hydrolysis reaction and promote the formation of the gel; dry the wet gel at a constant temperature of 40-60°C to obtain a xerogel; then grind the xerogel into particles as catalyst; (2) Spread the prepared powdered catalyst on a quartz boat, put it into the constant temperature zone of the tubular heating furnace, raise the temperature to 400-800°C under the protection of nitrogen, and pass in hydrogen for 20-40 minutes to reduce The catalyst is then heated to 600-1000° C., passed through acetylene, reacted for 30-120 minutes, cooled to normal temperature under nitrogen atmosphere, and the carbon nanotubes are prepared. 2. The method for preparing carbon nanotubes as claimed in claim 1, wherein the silicate is methyl orthosilicate Si(OCH ₃ ) ₄ (TMOS) or ethyl orthosilicate Si(OC ₂ H ₅ ) ₄ (TEOS). 3. The method for preparing carbon nanotubes as claimed in claim 1, wherein said nitrate is iron nitrate, cobalt nitrate and nickel nitrate. 4. The method for preparing carbon nanotubes as claimed in claim 1, wherein the acid catalyst is a protonic acid, and the base catalyst is ammonia or a buffer solution of ammonia and ammonium fluoride.

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