WO2006007760A1

WO2006007760A1 - Double-walled carbon nanotubes and the preparing method of same

Info

Publication number: WO2006007760A1
Application number: PCT/CN2004/000828
Authority: WO
Inventors: Lingyong Kong; Haiyan Yang
Original assignee: Lingyong Kong; Haiyan Yang
Priority date: 2004-07-19
Filing date: 2004-07-19
Publication date: 2006-01-26

Abstract

The present invention relates to a method for producing dour e-walled carbon nanotubes, comprising: a) a step of gas phase reducing reaction and deposition, wherein the liquefied petroleum gas or methane is used as carbon source, reducing agent is selected from the group of hydrogen, carbon monoxide, or the mixture thereof, the carbon source is reacted with the reducing agent under catalyst at the temperature of 600°C to 1000°C by chemical gas-phase deposition, thereby the primary product of the double-walled carbon is obtained; and b) a step of purification, wherein carbon dioxide and oxides of transition metal are used as combined catalyst, and the amorphous carbon in the carbon nanotubes is purified under the combined catalyst at the temperature of 600°C to 900°C. The present invention also relates to the double-walled carbon nanotubes produced according the method, which has a high purity (90%), a high yield (1~g/h), and can be produced in large scale.

Description

Double-walled carbon nanotubes and preparation method thereof

The present invention relates to a carbon material and a process for the preparation thereof, and more particularly to a method for preparing high-purity double-walled carbon nanotubes in large quantities and a double-walled carbon nanotube product produced by the method. Background technique

Carbon nanotubes show great potential for their excellent performance, while double-walled carbon nanotubes not only show many properties of single-walled carbon nanotubes. Moreover, since double-walled carbon nanotubes have a larger interlayer spacing (greater than 0.34 nm), they exhibit more excellent performance. For example, it is more conducive to hydrogen storage than a single-walled tube; in addition, the double-walled carbon nanotube inner layer can function as a single-walled carbon nanotube, and the outer layer can be modified to expand its application range. Reports show that double-walled carbon nanotubes are equivalent to an excellent wire, the outer layer is insulated, and the inner layer has a superconducting effect. At present, the research on the preparation of double-walled carbon nanotubes has attracted much attention.

Double-walled carbon nanotubes can be obtained by arc-discharge, chemical vapor deposition (Chemical Vapor Deposition), etc., but the existing methods are low in cost and low in yield (only a few grams or even milligrams). ), low purity (only about 40%), process control is not conducive to large-scale production. Zhu Hongwei et al. reported in "Science, 2002, 296: 884~886" and "Carbon, 2002, 40: 2021~2025": using n-hexane solution as carbon source, ferrocene as catalyst, thiophene as accelerator, Double-walled carbon nanotubes were prepared, but the process parameters were difficult to control, and the yield was also low, less than 5 wt%.

Ci Lijie et al., "Chemical Physics Letters, 2002, 359: 63~67" reported the synthesis of double-walled carbon nanotubes using acetylene as a carbon source, but the daily production is less than lg, and the product is coated with a large amount of amorphous carbon (amorphous). Carbon) and catalyst impurities, purity is not high.

Wei Jinquan et al., in Chinese Patent Application No. 03143102.X, introduced a method for synthesizing double-walled carbon nanotubes: n-butylene as a carbon source, ferrocene as a catalyst precursor, argon and hydrogen. The mixed gas is used as a carrier gas and sulfur is used as an additive to synthesize double-walled carbon nanotubes using a horizontal resistance furnace. Since the mixture must carry a process from low temperature to enthalpy after carrying the catalyst, the obtained product will be more complicated, the purity is not high, and the yield is not bad. Summary of the invention

Accordingly, it is an object of the present invention to provide a method for mass production of high-purity double-walled carbon nanotubes at low cost.

In order to achieve the above object, the inventors of the present invention conducted intensive studies and found that the preparation of double-walled carbon nanotubes by using a specific catalyst formulation and CVD method (chemical vapor deposition) can not only greatly reduce the cost. The yield is also greatly improved (up to 1 kg/h), and the process is stable. High-purity (more than 90%) double-walled nanotubes can be obtained by catalytic oxidation of amorphous carbon impurities by carbon dioxide.

Thus, the present invention provides the following aspects:

A method for producing double-walled carbon nanotubes, comprising:

a) using a chemical vapor deposition method using petroleum liquefied gas or formamidine as a reaction carbon source under a catalyst and a reducing agent selected from hydrogen, carbon monoxide or a mixture thereof at 600 ° C to 100 (TC) for gas phase reduction reaction and deposition a step of obtaining a crude double-walled carbon nanotube; and

b) a purification step for purifying amorphous carbon in a carbon nanotube at 600-90 CTC using a combination of carbon dioxide and a transition metal oxide as a catalyst.

2. The method for producing double-walled carbon nanotubes according to aspect 1, wherein the catalyst used in the reduction reaction is a supported catalyst formed by mixing cobalt, iron, or cobalt and iron in a certain ratio and supporting the magnesium oxide. .

3. The production method according to aspect 1, wherein the hydrogen gas has a volume percentage of at least 80% in a carrier gas stream composed of a reaction carbon source and hydrogen.

4. The production method according to aspect 1, wherein the transition metal oxide is at least one selected from the group consisting of oxides of chromium, iron, cobalt, and manganese.

5. The double-walled carbon nanotube product prepared according to the production method of any one of aspects 1-4, wherein the hollow carbon nanotube having an outer diameter of 10 - 35 A and an inner diameter of 5 - 30 A accounts for more than 90% of the total number of carbon nanotubes .

6. The double-walled carbon nanotube product according to aspect 5, wherein more than 90% of the carbon nanotubes are bundled, and the bundled carbon nanotubes are substantially double-walled carbon nanotubes composed of double walls. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a scanning electron microscope (SEM) photograph of the double-walled carbon nanotube obtained in the double wall tube purification example 1 of the present invention.

Figure 2 is a high resolution transmission electron microscope (HRTEM) photograph obtained in the double wall tube purification example 2 of the present invention. Fig. 3 is a Raman spectrum obtained in the second embodiment of the double wall tube of the present invention.

Fig. 4 is a HRTEM electron micrograph of a double-walled carbon nanotube bundle in the process of purification of the double-walled tube in the comparative example 1 of the present invention without carbon dioxide plus catalyst. detailed description

The invention provides a method for producing double-walled carbon nanotubes, which comprises the steps of performing gas phase reduction reaction and deposition with a reducing agent by a chemical vapor deposition method using petroleum liquefied gas or methane as a reaction carbon source under the action of a catalyst.

Among them, the reducing agent includes, but is not limited to, carbon monoxide, hydrogen, preferably hydrogen.

According to a preferred embodiment of the present invention, MgAO _x (A is used in combination with one or more of iron, cobalt and nickel salts) as a catalyst main body, through a combustion agent (EDTA, malic acid, glucose, citric acid, etc.) One or more of the organic substances are mixed and uniformly fired to form nano-sized oxide particles, and then fired at 300 ° C to 1000 ° C in a muffle furnace to form a catalyst powder.

The prepared catalyst is laid in a constant temperature zone of the reactor, such as a hydrocarbon gas (such as methane, natural gas, petroleum liquefied gas, acetylene, ethylene, etc.), an oxygen compound (methanol, ethanol, methyl formate, etc.), carbon monoxide or carbon dioxide. One or more of the combinations are used as a carbon source, combined with hydrogen (a carrier gas stream composed of a carbon source and hydrogen), and heated to 600 ° C ~ lOOO 'C reaction 10rain ~ 60min. Collect the product after cooling.

After the crude product is initially pickled, the transition metal element oxide powder is added to the carbon nanotubes, and after thorough mixing, carbon dioxide is introduced, the reaction time is 10 min to 50 min, and the temperature is controlled at 60 (TC~900 ° C, and then acid. Washing, the final method of synthesizing more than 90% of the product into bundles of fibers.

In one embodiment, the carrier gas stream preferably contains at least 80% by volume.

In another embodiment, more than 90% of the product has hollow carbon nanotubes having an outer diameter of 10A to 35A and an inner diameter of 5 to 30 Å.

In still another embodiment, the bundled product bundle is comprised primarily of carbon nanotubes constructed from double walls.

In the following, various stages of the invention are described in more detail by way of example:

1. Preparation of catalyst

Weigh a certain amount of magnesium oxide dissolved in nitric acid, weigh an appropriate amount of iron or cobalt-containing nitrate dissolved in water, and add one or more selected from ethylenediaminetetraacetic acid (EDTA), malic acid, and glucose. As a complexing agent, ammonia water was added as an additive. The resulting solution was concentrated to a viscous state, and then placed in a muffle furnace to be fired (300 ° C to 100 (TC) lh to 4 h, and cooled to prepare a catalyst powder. 2. Preparation of carbon nanotubes

The catalyst was placed in a tube-type resistance furnace controlled at 60 (TC~1000O), and the temperature was increased (from 600 至 to 1000 ° C, the heating rate was 15 ° C/min), and the carbon source was cracked [methyl hydrazine, petroleum liquefaction). Gas (propane accounts for 75% by volume, Ding 垸 accounts for 20% by volume)], controls the flow rate of hydrogen and carbon source, so that the volume ratio is greater than 2: 1, and the reaction is 20min~60min to obtain crude double-walled carbon nanotubes.

3. Purification of carbon nanotubes

The crude double-walled carbon nanotubes just prepared include impurities such as catalyst particles and amorphous carbon.气Using gas-liquid flexible oxidation method, the crude carbon nanotubes are first soaked with, for example, 25% hydrochloric acid (for example, 10 min), washed with deionized water until neutral, and added to the carbon nanotubes as lwt%~5 wt of the weight of the carbon nanotubes. % transition metal oxide (preferably one or several oxides of chromium, iron, cobalt, manganese) powder, after being thoroughly mixed, put into the reaction furnace and pass carbon dioxide, the temperature is controlled at 500 ° C ~ 900 ° C, reaction time 10min~50min, after the reaction is completed, it is cooled and taken out, and the product is dissolved in nitric acid (preferably 10% nitric acid), filtered and dried to obtain a finished carbon nanotube, and passed SEM (Scanning Electron Microscopy JEM-2010) It was observed that the purity of carbon nanotubes was greater than 95%.

As can be seen from Fig. 1, the carbon nanotubes obtained by the method of the present invention are mainly composed of bundles of carbon nanotubes entangled with each other, and the defined ends of the bundles of carbon nanotubes are not seen, and the bundles are clean and dense. Figure 1 shows that after purification, the purity of the carbon nanotubes exceeds 95% (no amorphous carbon impurities are observed under electron microscope, a small amount of catalyst particles are present, and the catalyst impurity is 1.6 wt% after ash analysis.)

As can be seen from the transmission electron microscope (produced by JEOL: [EM-2010) in Fig. 2, the sample mainly consists of a bundle of double-walled carbon nanotubes. The pipe diameter is about 2 nm.

It can be seen from Fig. 3 that the characteristic vibrational peaks of typical double-walled carbon nanotubes appear between 100 cm' SOOcm- ¹ , and the two peaks differ by 120 cm- ¹ .

As can be seen from Fig. 2 and Fig. 4, the surface of the carbon nanotubes which have not been subjected to purification by carbon dioxide plus catalyst is covered with a large amount of amorphous carbon.

As can be seen from the drawings and the following examples, the present invention creatively utilizes the CVD method and creatively utilizes liquefied petroleum gas to synthesize carbon nanotubes, which can be produced at a very low production cost in large quantities (e.g., lkg/h). High purity double-walled carbon nanotubes.

It can be seen from the following catalyst preparation examples that the present invention adds ammonia water during the preparation of the catalyst, and can convert a large amount of toxic excess nitric acid and nitrate decomposition gas generated during the combustion into nitrogen and water vapor discharge, thereby achieving environmental friendliness. the goal of. Example

Catalyst preparation example

60 g of magnesium oxide was dissolved in nitric acid, and 50 g of cobalt nitrate was weighed and dissolved in water. 30 g of each of EDTA, malic acid and glucose was used as a complexing agent, and ammonia water was used as an additive. The resulting solution was concentrated by heating to a thick state, placed in a muffle furnace, and dried for 3 hours, and cooled to prepare a catalyst 1 in which metallic cobalt was supported on magnesium oxide. Catalyst Preparation Example 2:

60 g of magnesium oxide was weighed and dissolved in nitric acid, and 60 g of iron nitrate was weighed and dissolved in water. 30 g of each of EDTA, malic acid and glucose was used as a complexing agent, and ammonia was used as an additive. The resulting solution was concentrated by heating to a thick state, placed in a muffle furnace at 1000 Torr for 4 hours, and cooled to prepare a catalyst in which metal iron was supported on magnesium oxide. Catalyst Preparation Example 3:

60 g of magnesium oxide was dissolved in nitric acid, and 30 g of cobalt and 25 g of iron nitrate were weighed and dissolved in water, and 30 g of each of EDTA, malic acid, and glucose was used as a complexing agent, and ammonia water was used as an additive. The resulting solution was concentrated by heating to a thick state, placed in a muffle furnace at 600 Torr for 2.5 h, and cooled to prepare a catalyst 3 in which both metallic iron and metallic cobalt were supported on magnesium oxide. Double wall tube synthesis example

210 g of the prepared catalyst 1 was plated in a quartz tube (tube diameter: 300 mm) to control a hydrogen flow rate of 0 m ³ /h, formazan 0.5 m ³ /h, and the reaction furnace temperature was between 600 Ό 〜: LOOO 'C , the reaction was stopped after 30 minutes, and the product was collected.

Double wall tube synthesis example 2:

150 g of the prepared catalyst 2 was placed in a quartz tube (300 mm diameter) to control the hydrogen flow rate of 2.0 la ³ /h, methane 0.5 m ³ /h, and the reactor temperature was 600 ° C to 1000 ° C. Between 30 minutes after the reaction, stop, collect the product

Double wall tube synthesis example 3:

270 g of the prepared catalyst 3 was placed in a quartz tube (300 mm diameter), and the hydrogen flow rate was controlled to be 2. OmVh, methane was 0.5 m ³ /h, and the temperature of the reaction furnace was between 600 ° C and 1000 ° C. Stop after 30 minutes of reaction, collect the product Double wall tube synthesis example 4:

The catalyst 3 was placed in a quartz tube (300 mm diameter), and the hydrogen flow rate was controlled to be 2.0 m ³ /h, and the flow rate of the petroleum liquefied gas was 0. 5 m ³ /h, and the temperature of the reaction furnace was 600 ° C. Between 950 ° C, the reaction was stopped after 30 min, and the product was collected 1310 _g . Double wall tube synthesis example 5:

The catalyst 3 is placed in a quartz tube (300 mm diameter), and the hydrogen flow rate is controlled to be 2. 5 m ³ /h, and the flow rate of the formazan is 0. 5 m ³ /h, and the temperature of the reaction furnace is 600 ° C to 1000 Between ° C, the reaction was stopped after 30 min, and 1010 g of product was collected. Double wall tube synthesis example 6:

The catalyst 3 is placed in a quartz tube (300 mm diameter), and the hydrogen flow rate is controlled to be 2.0 m ³ /h, methane is 0.5 m ⁷ h, and the temperature of the reaction furnace is between 600 ° C and 1000 ° C. After the reaction was stopped for 60 min, the product was collected 880 g. Double wall tube purification example 1

The crude product (obtained in Example 1) was immersed in a 25% by volume hydrochloric acid for 10 minutes, and then added to the carbon nanotubes to have a weight of 2 wt. The chromium oxide powder is thoroughly mixed and put into the reaction furnace, and carbon dioxide is introduced into the reaction furnace. The temperature is controlled at 500 ° C, the reaction time is 40 min, the reaction is completed, and then cooled and taken out, and the product is dissolved in 10% by volume of nitric acid. 6wt%。 The ash content of the product is 1. 6wt%. See Figure 1 for SEM electron micrographs. Double wall tube purification example 2

The crude product obtained in Example 1 was immersed in a 25% by volume hydrochloric acid solution for 10 minutes, and then chromic oxide powder containing 2% by weight of the carbon nanotubes was added to the carbon nanotubes, and the mixture was uniformly mixed and placed in a reaction furnace. The ash content of the product is 1. 5wt. The ash content of the product is 1. 00wt. %. See Figure 2 for HRTEM electron micrographs of the product. Double wall tube purification example 3

In the first embodiment, 800 g of the crude product was immersed in 25% hydrochloric acid for 10 min, and then iron oxide powder containing 2% by weight of the carbon nanotubes was added to the carbon nanotubes, and after fully mixing, the carbon dioxide was introduced into the reaction furnace. The temperature was controlled at 900 ° C and the reaction time was 20 min. After the completion of the reaction, the mixture was cooled and taken out, and the product was dissolved in 10% nitric acid, and dried by filtration to obtain 483 g of a finished carbon nanotube. After Ash analysis, the product ash content was 1. 5wt%. Double wall tube purification Example 4 'In Example 2, 800 g of crude product was immersed in 25% hydrochloric acid for 10 min, and then added to the carbon nanotubes, iron oxide and oxide complex accounted for 1 wt% of the weight of the carbon nanotubes (mass ratio 1:1) Powder, fully mixed, put into the reaction furnace and pass carbon dioxide, the temperature is controlled at 750 ° C, the reaction time is 20 min, after the reaction is completed, it is cooled and taken out, the product is dissolved in 10% nitric acid, and dried by filtration to obtain carbon nanotubes. Finished product 525g. After Ash analysis, the product ash content was 1. 8wt%. . Double wall tube purification example 5

In the second embodiment, the crude product 800g was immersed in 25% hydrochloric acid for 10 minutes, and then the manganese oxide powder which accounts for 4% by weight of the carbon nanotubes was added to the carbon nanotubes, and after being uniformly mixed, the carbon dioxide was introduced into the reaction furnace, and the temperature was controlled. At 750 ° C, the reaction time was 20 min. After the completion of the reaction, the mixture was cooled and taken out, and the product was dissolved in 10% nitric acid, and dried by filtration to obtain 485 g of a carbon nanotube product. After Ash analysis, the product has an ash content of 1.4% by weight. Comparative purification example 1

For example, the double wall tube is purified in Example 2, but the transition metal oxide is added as a catalyst reaction process, the carbon nanotubes are directly dissolved in nitric acid, and finally 716 g of the product is obtained. After ash analysis (Ash) analysis, the product ash content is 20 %. The surface is covered with a large amount of amorphous carbon, as shown in Figure 4. This is because a large amount of amorphous carbon is not removed and covers the surface of the catalyst so that the acid cannot enter the dissolved catalyst, so that the purity of the obtained product is low.

Claims

A method for producing double-walled carbon nanotubes, comprising:

a) using chemical vapor deposition with petroleum liquefied gas or formamidine as the reaction carbon source under the action of a catalyst with a reducing agent selected from hydrogen, carbon monoxide or a mixture thereof at 60 (TC~100 (rC for gas phase reduction reaction and deposition) a step of obtaining a crude double-walled carbon nanotube; and

b) a purification step of purifying the amorphous carbon in the carbon nanotubes at 600-900 Torr with carbon dioxide and a combination of the transition metal oxide powder as a catalyst.

2. The method for producing double-walled carbon nanotubes according to claim 1, wherein the catalyst used in the reduction reaction is a load formed by mixing cobalt, iron, or cobalt and iron in a certain ratio on a magnesium oxide. catalyst.

The production process according to claim 1, wherein said hydrogen gas has a volume percentage of at least 80% in a carrier gas stream composed of a reaction carbon source and hydrogen.

The production method according to claim 1, wherein said transition metal oxide is at least one selected from the group consisting of oxides of chromium, iron, cobalt, and manganese.

The double-walled carbon nanotube product produced by the production method according to any one of claims 1 to 4, wherein hollow carbon nanotubes having an outer diameter of 10 - 35 A and an inner diameter of 5 - 30 A account for 90% of the total number of carbon nanotubes the above.

6. The double-walled carbon nanotube product according to claim 5, wherein more than 90% of the carbon nanotubes are bundled, and the bundled carbon nanotubes are substantially double-walled carbon nanotubes composed of double walls.