CN101618868B - Method for removing amorphous carbon in carbon nanotubes - Google Patents
Method for removing amorphous carbon in carbon nanotubes Download PDFInfo
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- CN101618868B CN101618868B CN 200810045458 CN200810045458A CN101618868B CN 101618868 B CN101618868 B CN 101618868B CN 200810045458 CN200810045458 CN 200810045458 CN 200810045458 A CN200810045458 A CN 200810045458A CN 101618868 B CN101618868 B CN 101618868B
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Abstract
The invention discloses a method for removing amorphous carbon in carbon nanotubes, which comprises the following steps: suspending the carbon nanotubes into molten salt solution, and introducing oxygen or air into the molten salt solution. The oxidation reaction of the amorphous carbon and oxygen in the oxygen or the air is performed to generate carbon dioxide at a temperature of between 400 and 600 DEG C, while the oxidation reaction of the carbon nanotubes of crystal structures is almost not performed at the temperature. Because a molten salt solution system has uniform temperature without the phenomenon of local overheating, the carbon nanotubes are prevented from being oxidized because of local high temperature. Simultaneously, because the nanotubes are in the molten salt solution all the time, the carbon nanotubes are not easy to bring out from access environment by air flow so as to reduce the loss of the carbon nanotubes and avoid environmental pollution. After a period of time, the amorphous carbon is oxidized and removed; the molten salt solution blocks after being cooled; molten salt blocks are taken out and put into pure water to dissolve molten salt completely to obtain the carbon nanotubes of which the amorphous carbon is removed through filtration or centrifugal sedimentation.
Description
Technical field
The invention belongs to the carbon nanomaterial preparation field, be particularly suitable for the purification of carbon nanotube or carbon nano fiber.
Background technology
No matter be the carbon nanotube of arc process, laser ablation method or catalytic chemical vapor deposition technique preparation, all contain to some extent amorphous carbon, particularly Single Walled Carbon Nanotube and double-walled carbon nano-tube product, the weight content of amorphous carbon reaches more than 98% sometimes, generally also more than 90%.Obtain the higher carbon nanotube of purity, all must be through removing the process of amorphous carbon.Remove at present amorphous carbon kinds of processes is arranged, such as gas phase systems such as the liquid-phase systems such as potassium bichromate-sulfuric acid system, concentrated nitric acid-sulfuric acid system, hydrogen peroxide-sodium hydroxide system and atmospheric oxidation, carbonic acid gas oxidation, steam oxidation, hydrogen methanations, wherein atmospheric oxidation is considered to most economical and the most eco-friendly technique.Because liquid-phase system relates to the use of a large amount of chemical reagent, must produce a large amount of wastes, contaminate environment, simultaneously a large amount of chemical reagent also need very high cost.The deacration oxidation can be beyond (～400 ℃) carry out under the lower temperature in the gas phase system, other process all at high temperature (＞700 ℃) carry out.Operation on the one hand will expend mass energy under the high temperature, the on the other hand carbon nanotube loss that also reacts easily under this temperature.Although atmospheric oxidation can be carried out at a lower temperature, the oxidation of amorphous carbon is an exothermic process, and near the temperature oxidizing reaction can cause rises rapidly, and carbon nanotube also can raise and oxidized loss by Yin Wendu.In addition, the hot gas flow that produces in the oxidising process also can be taken the dust of carbon nanotube out of, has both caused the loss of carbon nanotube, also contaminate environment.In sum, also there is not up till now desirable technique to remove amorphous carbon in the carbon nanotube.
Summary of the invention
The method that the purpose of this invention is to provide a kind of desirable removal amorphous carbon in carbon nanotubes is farthest removed amorphous carbon and carbon nanotube is not oxidized, simultaneously environment is not polluted.
Purpose of the present invention is by following process implementation: carbon nanotube is suspended in the liquid fused salt, passes into oxygen or air in liquid fused salt.Under 350～600 ℃ of temperature, amorphous carbon at first generates carbonic acid gas with oxygen or airborne oxygen generation oxidizing reaction, and oxidizing reaction occurs under this temperature the carbon nanotube of crystalline structure hardly.Because there is not the local superheating phenomenon in liquid fused salt system temperature uniformity, avoided the generation of carbon nanotube because of the high oxidized situation of local temperature.Because carbon nanotube is in the liquid fused salt always, be not easy to be taken out of entered environment by air-flow simultaneously, not only reduced the loss of carbon nanotube, also avoided the pollution of environment simultaneously.After for some time, the oxidized removal of amorphous carbon.Stopped heating, molten salt solution blocks after being cooled.The taking-up of fused salt piece is placed pure water, and fused salt dissolves fully, and filtration or centrifugal settling obtain to remove the carbon nanotube of amorphous carbon.
Compared with prior art, the present invention combine liquid-phase system without local superheating, temperature evenly and without the advantage of dust from flying and gas phase system without a large amount of chemical reagent uses, no waste discharge, advantage simple to operate, not only can go down except the amorphous carbon in the carbon nanotube in relatively gentle condition, and can effectively avoid occurring because local superheating causes the oxidized situation of carbon nanotube.
Another advantage of the present invention is can accurately control the temperature of reaction system, even the higher amorphous carbon of degree of crystallinity as long as have any different with the oxidizing temperature of carbon nanotube, just can adopt present method to remove, and carbon nanotube can not lose in a large number.The temperature of oxidizing reaction is higher in the inventive method, and amorphous carbon is removed more thoroughly.But when the oxidizing temperature of temperature of reaction and carbon nanotube near the time, carbon nanotube also has certain loss.Optimal reaction temperature is 580 ℃ among the present invention.
In technical solution of the present invention, the adding mode of carbon nanotube is also very crucial.If add after forming liquid fused salt, then carbon nanotube enters relatively difficulty of liquid fused salt, need to pass through strong stirring.Research finds, the raw material of carbon nanotube and fused salt mixed just be easy to realize the suspension of carbon nanotube in liquid fused salt.Simultaneously, adopt this feed way, be easy to increase the add-on of carbon nanotube, particularly in the larger situation of the amount of carbon nanotube.Generally speaking, carbon nanotube will absorb the liquid fused salt that is equivalent to more than ten times of weight of own wt.If after forming liquid fused salt, add, then the add-on of carbon nanotube can not reach 1/10th of liquid fused salt weight, because when the carbon nanotube amount is abundant, liquid fused salt and carbon nanotube form paste, the carbon nanotube of follow-up adding can only be piled up at the paste outside surface, liquid fused salt can not be realized to the infiltration of carbon nanotube, thereby the generation of local superheating situation in the oxidising process can not be avoided.If the raw material of carbon nanotube and fused salt is mixed, although the amount of carbon nanotube is larger, liquid fused salt is more fortunately carbon nano tube surface distribution also.Even oxidation heat liberation, liquid fused salt also can shift heat absorption very soon.Under this carbon nanotube adding mode, the weight ratio of carbon nanotube and liquid fused salt is the highest can to reach 1: 1.
If the weight ratio of carbon nanotube and liquid fused salt is higher, temperature of reaction system fast rise phenomenon then can appear in oxidising process, and the flow that passes into oxygen or air by control can be controlled oxidation rate, avoids the rising of temperature of reaction system.
Fused salt used in the present invention should have following features: the temperature that 1, forms liquid fused salt is lower than 600 ℃, is preferably lower than 200 ℃; 2,300-700 ℃ of lower stablizing, without obviously decomposing or the generation of volatilization phenomenon; 3, in water, can dissolve.
Fused salt used in the present invention can recycle.Behind the end of processing of oxidation removal amorphous carbon, liquid fused salt is poured out liquid fused salt cooling caking in the liquid fused salt from reactor.The fused salt piece is dropped in the deionized water, the fused salt dissolving, carbon nanotube is suspended in the fused salt aqueous solution.Filtration or centrifugal settling obtain the not fused salt aqueous solution of carbon nanotubes, and the carbon nanotube that will contain amorphous carbon is suspended in this aqueous solution, obtain the mixture of carbon nanotube and fused salt raw material after the spraying drying.Continue this mixture of oxide treatment according to method of the present invention, realize recycling of fused salt.
Be fit to fused salt of the present invention and comprise lithium chloride-KCl system, aluminum chloride-KCl system etc.
Reactor used in the present invention is stainless steel reactor, corundum reactor.
The said amorphous carbon of the present invention also is known as decolorizing carbon, is mainly particle on the form.
The present invention is equally applicable to the removal of amorphous carbon in carbon nano fiber and other graphite crystallization product.
The present invention realizes by following means:
Remove amorphous carbon in the carbon nanotube by following process implementation: 1. a certain proportion of carbon nanotube and fused salt raw material that contains amorphous carbon mixed; 2. the material that mixes is transferred in the reactor, be warmed up to 350～600 ℃, make the fused salt raw material form liquid fused salt (being liquid fused salt); 3. pass into oxygen or air in the liquid fused salt and come amorphous carbon in the oxide/carbon nanometer tube, the control gas flow is to keep temperature of molten salt to be no more than 580 ℃; 4. stop to pass into oxygen or air, liquid fused salt is poured out from reactor, formed fused salt piece is put into the container that pure water is housed, and makes the fused salt dissolving, and the carbon nanotube except amorphous carbon is separated in filtration or centrifugal settling.
The fused salt raw material is lithium chloride and Repone K, and the weight ratio of lithium chloride and Repone K is W
LiCl: W
KCl=1～2.5: 1; The weight ratio of fused salt raw material and carbon nanotube is W
The fused salt raw material: W
Carbon nanotube=1～200: 1; The weight ratio of fused salt raw material and carbon nanotube is W
The fused salt raw material: W
Carbon nanotube=10～100: 1;
Described carbon nanotube is multi-walled carbon nano-tubes, Single Walled Carbon Nanotube or the double-walled carbon nano-tube of pipe with small pipe diameter; The reaction of oxidation removal amorphous carbon is carried out between 400～580 ℃.
Description of drawings
Fig. 1 is the TEM photo that contains the Single Walled Carbon Nanotube of amorphous carbon;
Fig. 2 is for removing behind the amorphous carbon outside diameter less than the TEM photo of 8nm multi-walled carbon nano-tubes;
Fig. 3 is the TEM photo of Single Walled Carbon Nanotube behind the removal amorphous carbon.
Embodiment:
Embodiment 1 takes by weighing the thick product of 5g Single Walled Carbon Nanotube (amorphous carbon content is greater than 90%), 110g analytical pure Lithium chloride (anhydrous) and 90g Repone K and be pulverized and mixed 5 minutes in soybean milk maker, mixed material is transferred in the stainless steel reaction pipe of internal diameter 35mm, high 500mm, end sealing, jolt ramming, the reaction tubes opening end passes into nitrogen and gets rid of the interior air of reaction tubes with the soft rubber ball sealing with inlet pipe and escape pipe.The stainless steel reaction pipe is placed well formula resistance furnace, be warming up to 450 ℃ constant, liquid fused salt forms after 30 minutes.Change nitrogen into pure oxygen, the control flow guarantees that the maximum temperature amplitude of reaction system rises to 480 ℃ between 10-16L/hr.React and finish reaction after 2 hours, under continuing logical oxygen situation, airway is taken out from liquid fused salt, subsequently the stainless steel reaction pipe is taken out from well formula resistance furnace, rapidly liquid fused salt is poured in the Stainless Steel Disc.Liquid fused salt cooling caking.Take out interior remaining fused salt piece and the fused salt piece in the Stainless Steel Disc of stainless steel reaction pipe and put in the 600mL deionized water, under stirring fused salt is all dissolved, filter the Single Walled Carbon Nanotube filter cake that also washing obtains.The Single Walled Carbon Nanotube filter cake is transferred in the there-necked flask of 500mL, added 100mL deionized water and 200mL concentrated hydrochloric acid, the lower processing 2 hours of refluxing, cooled and filtered, washing are until filtrate is neutral.Take out 120 ℃ of oven dry of filter cake 6 hours.Be weighed as 0.4g, calculated yield is 8.0%.Heat analysis data shows that gained Single Walled Carbon Nanotube combustion initiation temperature in air is 559 ℃.
Embodiment 2 takes by weighing the 100g outside diameter and is pulverized and mixed 10 minutes less than the thick product of multi-walled carbon nano-tubes, 120g analytical pure Lithium chloride (anhydrous) and the 80g Repone K of 8nm in the soybean milk maker discontinuous, press the step operation of embodiment 1, temperature of reaction is constant in 480 ℃, top temperature is no more than 510 ℃, 4 hours reaction times.Finally obtain product 89g, yield is 89%.Heat analysis data shows that gained pipe with small pipe diameter multi-walled carbon nano-tubes combustion initiation temperature in air is 587 ℃.The tem study result of gained sample as shown in Figure 2.
Embodiment 3 takes by weighing the thick product of 50g Single Walled Carbon Nanotube (amorphous carbon content is greater than 90%), 100g analytical pure Lithium chloride (anhydrous) and 100g Repone K and is pulverized and mixed 5 minutes in the soybean milk maker discontinuous, press the step operation of embodiment 1, temperature of reaction is constant in 550 ℃, top temperature is no more than 580 ℃, 4 hours reaction times.Finally obtain product 1.6g, yield is 3.2%.Heat analysis data shows that gained Single Walled Carbon Nanotube combustion initiation temperature in air is 609 ℃.The transmission electron microscope photo of gained Single Walled Carbon Nanotube as shown in Figure 3.
Claims (5)
1. method of removing amorphous carbon in carbon nanotubes, adopt oxygen or contain the mixed gas oxidation of molecular oxygen, the reaction that it is characterized in that the oxidation removal amorphous carbon is carried out in liquid fused salt, by following process implementation: 1. a certain proportion of carbon nanotube and fused salt raw material that contains amorphous carbon mixed, the fused salt raw material is lithium chloride and Repone K, and the weight ratio of lithium chloride and Repone K is W
LiCl: W
KCl=1～2.5: 1, the weight ratio of fused salt raw material and carbon nanotube is W
The fused salt raw material: W
Carbon nanotube=10～100: 1; 2. the material that mixes is transferred in the reactor, be warmed up to 350～600 ℃, make the fused salt raw material form liquid fused salt, i.e. liquid fused salt; 3. pass into oxygen or air in the liquid fused salt and come amorphous carbon in the oxide/carbon nanometer tube, the control gas flow is to keep temperature of molten salt to be no more than 580 ℃; 4. stop to pass into oxygen or air, liquid fused salt is poured out from reactor, formed fused salt piece is put into the container that pure water is housed, and makes the fused salt dissolving, and the carbon nanotube except amorphous carbon is separated in filtration or centrifugal settling.
2. method according to claim 1 is characterized in that described fused salt is stable in 300-700 ℃ of scope, without obviously decomposition or volatilization phenomenon occur.
3. method according to claim 1 is characterized in that described carbon nanotube is multi-walled carbon nano-tubes, Single Walled Carbon Nanotube or the double-walled carbon nano-tube of pipe with small pipe diameter.
4. method according to claim 2 is characterized in that the reaction of described oxidation removal amorphous carbon is carried out between 400～580 ℃.
5. method according to claim 2 is characterized in that described reactor is stainless steel reactor or corundum reactor.
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| CN109650379B (en) * | 2019-02-19 | 2020-08-18 | 厦门大学 | Single-walled carbon nanotube gradient oxidation purification method |
| CN111235637A (en) * | 2020-02-21 | 2020-06-05 | 哈尔滨工业大学 | Method for removing amorphous carbon on surface of CVD diamond |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1475438A (en) * | 2003-07-18 | 2004-02-18 | 清华大学 | Purification method of carbon nano pipe and its device |
| CN1807233A (en) * | 2006-01-26 | 2006-07-26 | 上海交通大学 | Chemical shearing method for preparing high dispersion short carbon nanometer tube |
| CN1868870A (en) * | 2006-06-07 | 2006-11-29 | 西北工业大学 | Purification method of carbon nanometer pipe |
| CN101164874A (en) * | 2007-09-26 | 2008-04-23 | 合肥工业大学 | Method for purifying multi-wall carbon nano pipe |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1475438A (en) * | 2003-07-18 | 2004-02-18 | 清华大学 | Purification method of carbon nano pipe and its device |
| CN1807233A (en) * | 2006-01-26 | 2006-07-26 | 上海交通大学 | Chemical shearing method for preparing high dispersion short carbon nanometer tube |
| CN1868870A (en) * | 2006-06-07 | 2006-11-29 | 西北工业大学 | Purification method of carbon nanometer pipe |
| CN101164874A (en) * | 2007-09-26 | 2008-04-23 | 合肥工业大学 | Method for purifying multi-wall carbon nano pipe |
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Application publication date: 20100106 Assignee: Chengdu Zhongke Purui Purifying Equipment Co., Ltd. Assignor: Chengdu Organic Chemicals Co., Ltd., Chinese Academy of Sciences Contract record no.: 2015510000086 Denomination of invention: Method for removing amorphous carbon in carbon nanotubes Granted publication date: 20130313 License type: Exclusive License Record date: 20150629 |
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