Preparation method of double-wall and three-wall mixed carbon nanotubes and obtained carbon nanotubes

Abstract

The invention relates to a preparation method of a double-wall and three-wall mixed carbon nano tube and the obtained carbon nano tube, in particular to the field of carbon nano tube preparation, and the preparation method comprises the following steps: growing by adopting a floating catalyst vapor deposition method to obtain a carbon nano tube product; in the growth process, i reaction gas flows are adopted for reaction, i is larger than or equal to 2, and at least two reaction gas flows in the i reaction gas flows collide with each other at an acute angle; the reaction gas flow comprises a carbon source, a catalyst and an accelerant in a mass ratio of 100: (7.5-8.2): (0.9-6). According to the preparation method provided by the invention, the distribution behavior of the catalyst in the reaction process is optimized by virtue of collision of reaction gas flow, the nucleation effect of the catalyst is improved, and the double-wall and three-wall mixed carbon nanotubes are favorably generated, so that one-step preparation of the double-wall and three-wall mixed carbon nanotubes is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of carbon nanotube preparation, in particular to a preparation method of double-wall and triple-wall mixed carbon nanotubes and the obtained carbon nanotubes, and especially to a preparation method of double-wall and triple-wall mixed carbon nanotubes with a mass percentage of ≥80% and a low specific surface area and the obtained carbon nanotubes. BACKGROUND

[0002] In the field of carbon materials, great progress has been made in the study of "single-wall carbon nanotubes", but the single-wall carbon nanotubes prepared by industrialization are usually a mixture of single-wall carbon nanotubes (50-90%) and double-wall carbon nanotubes (10-50%).

[0003] Although single-wall carbon nanotubes have the best physical and chemical properties according to various indicators, the larger BET (1300 m 2 / g) and stronger mechanical properties of single-wall carbon nanotubes make it more difficult to use in application, while double-wall and triple-wall mixed carbon nanotubes have relatively small BET and similar mechanical strength and electrical conductivity, which can make up for the shortcomings of single-wall carbon nanotubes in application.

[0004] At the same time, studies have shown that the outer wall of double-wall carbon nanotubes protects the inner wall, and even if the outer wall is functionalized to a certain extent, the inner carbon nanotube can still maintain good mechanical strength and electrical conductivity, and has better application advantages in structural modification.

[0005] Therefore, it is of great significance to the current industrial application and the development of carbon nanotube preparation technology to study and prepare double / triple-wall carbon nanotubes with a high proportion.

[0006] At present, oxidation post-treatment is an effective method to obtain high-proportion double / triple-wall carbon nanotubes from industrialized mixed products. For example, CN110040720A removes amorphous carbon and single-wall carbon nanotubes in the product by oxidation at 500-540°C to obtain double-wall carbon nanotubes with a purity of 95%. This method is simple and effective, but it will cause a certain amount of loss or damage.

[0007] In the floating catalyst deposition method, due to the process characteristics, the catalyst needs to be in gaseous or liquid form, and the catalyst usually only contains active substances and additives that are easy to sublimate or dissolve, such as combinations of ferrocene, thiophene, and elemental sulfur. The active substance goes through three stages of free decomposition, clustering, and nucleation growth of carbon nanotubes after being introduced into a high-temperature reactor. During this process, the catalyst particles are in a self-growth and uncontrolled state due to the absence of carrier constraints. Therefore, the particle size distribution of the final catalyst particles is wide. Since the tube diameter or layer number of carbon nanotubes is directly related to the size of the catalyst particles, the existing floating catalyst deposition method cannot easily control the size of the catalyst particles, ultimately resulting in a mixture of single-walled, double-walled, and triple-walled carbon nanotubes with an uncontrollable proportion.

[0008] Therefore, how to control the size of active substance particles in a reaction system without a carrier and prepare a mixture of double-walled and triple-walled carbon nanotubes with a controllable proportion is a major problem in the floating catalyst deposition method. SUMMARY

[0009] In view of the problems in the prior art, the purpose of the present application is to provide a preparation method of double-walled and triple-walled mixed carbon nanotubes and the obtained carbon nanotubes, which realizes the one-step preparation of high-content double-walled and triple-walled mixed carbon nanotubes by the floating catalyst deposition method, and the mass content of double-walled and triple-walled carbon nanotubes in the obtained product is ≥80%.

[0010] To achieve this purpose, the present application adopts the following technical solutions:

[0011] In a first aspect, the present application provides a preparation method of double-walled and triple-walled mixed carbon nanotubes, which comprises:

[0012] obtaining a carbon nanotube product by floating catalyst gas phase deposition;

[0013] In the growth, i reaction gas streams are used for reaction, i≥2, and at least two of the i reaction gas streams collide at an acute angle; the reaction gas streams include: carbon source, catalyst, and promoter with a mass ratio of 100:(7.5-8.2):(0.9-6).

[0014] The preparation method provided by the present application optimizes the distribution behavior of the catalyst and the proportion of the reaction gas streams in the reaction process by means of the collision of the reaction gas streams, improves the nucleation effect of the catalyst, and is conducive to the generation of double-walled and triple-walled mixed carbon nanotubes, thereby realizing the one-step preparation of double-walled and triple-walled mixed carbon nanotubes.

[0015] As a preferred technical solution of the present application, all reaction gas streams in the i reaction gas streams collide at an acute angle.

[0016] Preferably, the acute angle is 30-60°.

[0017] As a preferred technical scheme of the present application, the carbon source comprises: a liquid-phase carbon source and / or a gas-phase carbon source.

[0018] Preferably, the liquid-phase carbon source comprises: one or a combination of at least two of toluene, ethanol, methanol, acetone or xylene.

[0019] Preferably, the gas-phase carbon source comprises: one or a combination of at least two of methane, ethylene or propylene.

[0020] As a preferred technical scheme of the present application, the catalyst comprises: one or a combination of at least two of an iron catalyst, a cobalt catalyst or a nickel catalyst.

[0021] As a preferred technical scheme of the present application, the promoter comprises: elemental sulfur and / or a sulfur compound.

[0022] As a preferred technical scheme of the present application, the growth temperature is 1200-1250℃.

[0023] Preferably, the carrier gas used in the growth comprises: hydrogen and an inert gas in a volume flow ratio of 1:(4-10).

[0024] As a preferred technical scheme of the present application, the carbon nanotube product is subjected to oxidation and acid washing in sequence to obtain a finished carbon nanotube product.

[0025] As a preferred technical scheme of the present application, the oxidation comprises: oxidation in an atmosphere of air and an inert gas in a volume ratio of 1:(1.5-2.5).

[0026] Preferably, the oxidation temperature is 350-450℃.

[0027] Preferably, the holding time of the oxidation is 30-60min.

[0028] As a preferred technical scheme of the present application, the acid washing comprises: cleaning with an acid solution with a mass concentration of 8-20%.

[0029] Preferably, the acid washing temperature is 80-90℃.

[0030] Preferably, the holding time of the acid washing is 12-15h.

[0031] In a second aspect, the present application provides a double-wall and triple-wall mixed carbon nanotube, which is prepared by the preparation method of the first aspect, and has a BET specific surface area <1000m 2 / g and a Raman RBM main peak <180cm-1 , Raman IG / ID>50, tube diameter distribution is 2.0-2.6nm.

[0032] Compared with prior art solutions, the present application has the following beneficial effects:

[0033] (1) The present application uses the floating method to prepare carbon nanotubes, through catalyst design and feed mode control, a crude product of carbon nanotubes with a mixed mass percentage of ≥80% of double-walled and triple-walled carbon nanotubes can be directly obtained, compared with the method of increasing the proportion of double-walled and triple-walled carbon nanotubes by oxidation, this method has no destructive effect on the structure of carbon nanotubes, and is easy to operate.

[0034] (2) The double-walled and triple-walled mixed carbon nanotubes prepared by the present application have uniform tube diameter distribution (2.0-2.6nm), and at the same time have low BET (750-950m 2 / g) and high IG / ID>50 characteristics, so the carbon nanotube conductive paste prepared therefrom has lower paste viscosity than single-walled carbon nanotube conductive paste, which is beneficial to paste storage. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a transmission electron microscope photo of the carbon nanotube product obtained in Example 1 of the present application;

[0036] Figure 2 is a transmission electron microscope photo of the carbon nanotube product obtained in Comparative Example 1 of the present application;

[0037] Figure 3 is a Raman RBM main peak spectrum of the carbon nanotube product obtained in Example 2 of the present application;

[0038] Figure 4 is a Raman RBM main peak spectrum of the carbon nanotube product obtained in Comparative Example 5 of the present application;

[0039] Figure 5 is a transmission electron microscope photo of the carbon nanotube product obtained in Comparative Example 7 of the present application.

[0040] The present application will be further described below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims. DETAILED DESCRIPTION

[0041] In order to better illustrate the present application and facilitate understanding of the technical solutions of the present application, the typical but non-limiting embodiments of the present application are as follows:

[0042] At present, the outer wall of the double-walled tube protects the inner wall, and even if the outer wall is functionalized to a certain extent, the inner carbon tube can still maintain good mechanical strength and electrical conductivity, and has better application advantages in structural modification. Therefore, the preparation of a high proportion of double-walled and triple-walled mixed carbon nanotubes has promoting significance for the current industrial application end and the development of carbon nanotube preparation technology. However, the current carbon nanotube preparation method can only prepare a mixture of single-walled carbon nanotubes and double-walled carbon nanotubes due to process limitations during preparation. Even after further processing, only double-walled carbon nanotubes with a mass content of more than 90% can be obtained, and the preparation of double-walled and triple-walled mixed carbon nanotubes cannot be achieved. Based on this, the present application realizes the preparation of high-content double-walled and triple-walled mixed carbon nanotubes by optimizing the preparation process, as follows:

[0043] One, the embodiment provides a preparation method of double-walled and triple-walled mixed carbon nanotubes, and the preparation method comprises:

[0044] The carbon nanotube product is grown by using a floating catalyst vapor deposition method;

[0045] In the growth, i reaction gas streams are used for reaction, i>=2, and at least two reaction gas streams in the i reaction gas streams collide at an acute angle; the reaction gas stream comprises: carbon source, catalyst and promoter with a mass ratio of 100:(7.5-8.2):(0.9-6).

[0046] In the application, the reaction gas streams collide at an acute angle, which can be selected by means of a Y-shaped reactor, or a nozzle arranged in the shape of Y, etc., that is, it is only necessary to ensure that the reaction gas streams introduced in the application collide, and when multiple gaseous catalysts converge in the Y-shaped structure at high temperature, the collision between iron atom clusters is increased, and it is easier to form larger size catalyst active particles; at the same time, the collision is also easy for the combination of S element and iron atom clusters, forming a process condition easy for the growth of double-walled and triple-walled mixed carbon nanotubes, and preferably, all reaction gas streams in the i reaction gas streams collide at an acute angle.

[0047] In the application, when the i reaction gas streams collide at an acute angle, the collision can be a planar acute angle or a three-dimensional space. For example, the collision is a planar acute angle, such as an acute angle of 45°, and the required number of reaction gas streams is arranged in the region of 45°, and the direction of the reaction gas streams is ensured to intersect at the vertex of the acute angle; if the collision is in a three-dimensional space, the acute angle is selected to be 60°, and the required number of reaction gas streams is arranged in a conical body with a vertex angle of 60°, and the direction of the reaction gas streams is ensured to intersect at the vertex of the cone.

[0048] The acute angle is 30-60°, for example, it can be 30°, 33°, 36°, 39°, 42°, 45°, 48°, 51°, 54°, 57° or 60°, etc., but is not limited to the listed values, and other values not listed in the range are also required. If the angle is too large, the degree of collision increases, the catalyst is adsorbed in the inner pipeline, causing the pipeline to be quickly blocked, which is not conducive to production, and at the same time, the catalyst particles may be deactivated due to being too large; if the angle is too small, the Y-shaped two-way feed tends to be parallel, and the effect of increasing the active particles is reduced.

[0049] The mass ratio of the carbon source, the catalyst and the promoter in the reaction gas flow is 100:(7.5-8.2):(0.9-6), for example, it can be 100:7.5:0.9, 100:7.57:1.32, 100:7.64:1.84, 100:7.71:2.36, 100:7.78:2.88, 100:7.85:3.4, 100:7.92:3.92, 100:7.99:4.44, 100:8.06:4.96, 100:8.13:5.48 or 100:8.2:6, etc., but is not limited to the listed values, and other values not listed in the range are also required.

[0050] In the present application, by controlling the Fe-S ratio in the reaction gas flow: in the carbon nanotube nucleation stage, the promoter S will form FeS x The local liquid phase region reduces the binding energy between graphene and the catalyst, is conducive to the generation of nucleation sites for CNT growth, promotes the lifting and growth of the carbon cap; at the same time, FeS x The larger the size of the local liquid phase region, the more conducive to the generation of double-walled carbon nanotubes or large-diameter triple-walled carbon nanotubes at the nucleation site with appropriate carbon source supply. If the amount of sulfur in the system is greater than 6, the sulfur element will completely wrap the catalyst when the catalyst nucleates, causing catalyst poisoning and affecting the reaction output; if it is less than 0.8, the reaction yield is reduced, and at the same time, the content of single-walled tubes in the product will increase appropriately.

[0051] The carbon source includes a liquid phase carbon source and / or a gas phase carbon source.

[0052] The liquid phase carbon source includes one or a combination of at least two of toluene, ethanol, methanol, acetone or xylene.

[0053] Exemplarily, the combination of the liquid phase carbon source can be selected as: a combination of toluene and ethanol, a combination of ethanol and methanol, a combination of methanol and acetone, a combination of acetone and xylene, etc.

[0054] The gas phase carbon source includes one or a combination of at least two of methane, ethylene or propylene.

[0055] Exemplarily, the combination of the gaseous carbon source can be selected as: a combination of methane and ethylene, a combination of methane and propylene, a combination of ethylene and propylene, etc.

[0056] The catalyst comprises one of iron catalyst, cobalt catalyst or nickel catalyst, or a combination of at least two thereof.

[0057] In the present application, the iron catalyst can be selected as ferrocene, ferrous chloride, ferric chloride, ferric sulfate, etc.

[0058] In the present application, the cobalt catalyst can be selected as cobalt chloride, cobalt sulfate, etc.

[0059] In the present application, the nickel catalyst can be selected as nickel chloride, nickel sulfate, etc.

[0060] The promoter comprises elemental sulfur and / or sulfur compound.

[0061] In the present application, the sulfur compound can be selected as thiophene, dimethyl sulfoxide, thiourea, sodium sulfide, ferric sulfate, etc.

[0062] In the present application, when the carbon source is selected as liquid phase carbon source, in order to meet the requirement of vapor deposition, the liquid phase carbon source needs to be gasified first, exemplarily, the carbon source, catalyst and thiophene are mixed and then high-temperature gasification is carried out, and then the reaction gas flow is fed, wherein the temperature of high-temperature gasification is 400-800 DEG C, and the heat source supply at this temperature can be realized by self-thermal radiation or thermal convection in the reaction furnace.

[0063] In the present application, when the reaction material is gasified, it can be selected to be gasified separately or to be uniformly gasified after mixing, such as the liquid phase carbon source, catalyst and promoter are respectively gasified, and then mixed according to the mass ratio or volume ratio to obtain the reaction gas flow for growth.

[0064] The growth temperature is 1200-1250 DEG C, for example, it can be 1200 DEG C, 1205 DEG C, 1210 DEG C, 1215 DEG C, 1220 DEG C, 1225 DEG C, 1230 DEG C, 1235 DEG C, 1240 DEG C, 1245 DEG C or 1250 DEG C, etc., but not limited to the listed values, other values not listed in this range also meet the requirements.

[0065] The carrier gas used in the growth comprises hydrogen and inert gas with a volume flow ratio of 1:(4-10), for example, it can be 1:4, 1:4.6, 1:5.2, 1:5.8, 1:6.4, 1:7, 1:7.6, 1:8.2, 1:8.8, 1:9.4 or 1:10, etc., but not limited to the listed values, other values not listed in this range also meet the requirements.

[0066] In the present application, the inert gas is a gas that does not affect the processing process, such as nitrogen, helium, neon, argon, etc.

[0067] The carbon nanotube product is sequentially subjected to oxidation and acid washing to obtain a finished carbon nanotube product.

[0068] In the present application, the purpose of oxidation and acid washing is to remove amorphous carbon and impurities such as iron in the carbon nanotube product.

[0069] The oxidation includes: oxidation in an atmosphere of air and inert gas in a volume ratio of 1:(1.5-2.5), for example, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5, etc., but not limited to the listed values, other unlisted values within the range are also required.

[0070] The temperature of the oxidation is 350-450℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃ or 450℃, etc., but not limited to the listed values, other unlisted values within the range are also required.

[0071] The holding time of the oxidation is 30-60min, for example, 30min, 33min, 36min, 39min, 42min, 45min, 48min, 51min, 54min, 57min or 60min, etc., but not limited to the listed values, other unlisted values within the range are also required.

[0072] The acid washing includes: cleaning with an acid solution with a mass concentration of 8-20%, for example, 8%, 9.2%, 10.4%, 11.6%, 12.8%, 14%, 15.2%, 16.4%, 17.6%, 18.8% or 20%, etc., but not limited to the listed values, other unlisted values within the range are also required.

[0073] In the present application, the acid solution used in the acid washing can be selected from hydrochloric acid, sulfuric acid, nitric acid and other commonly used acid pickling agents in the art.

[0074] The temperature of the acid washing is 80-90℃, for example, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, etc., but not limited to the listed values, other unlisted values within the range are also required.

[0075] The holding time of the pickling is 12-15h, for example, 12h, 12.3h, 12.6h, 12.9h, 13.2h, 13.5h, 13.8h, 14.1h, 14.4h, 14.7h or 15h, but is not limited to the listed values, and other values not listed in the range are also acceptable.

[0076] In the present application, the product after pickling can be washed with water to a reasonable pH value to ensure that the subsequent use is not affected, and can be further functionalized to further improve the use effect.

[0077] Secondly, the present application provides a double-wall and triple-wall mixed carbon nanotube, which is prepared by the preparation method of the first aspect, and has a BET specific surface area of <1000m 2 / g, a Raman RBM main peak of <180cm -1 , a Raman IG / ID of >50, and a tube diameter distribution of 2.0-2.6nm.

[0078] Thirdly, in order to illustrate the excellent performance of the carbon nanotube product prepared by the preparation method of the present application, the following actual examples are used for illustration, as follows:

[0079] In a specific implementation case, the present application uses a mixture of hydrogen and argon as a carrier gas, toluene as a carbon source, ferrocene as a catalyst, and thiophene as a promoter, adjusts the iron-sulfur ratio, and uses Y-type feeding, thereby increasing the FeS x local liquid phase region and the size of the active catalyst particles, so as to realize the enrichment and growth of the double-wall and triple-wall mixed carbon nanotube. Such double-wall and triple-wall mixed carbon nanotube has a uniform tube diameter distribution (2.0-2.6nm), and has the characteristics of low BET (750-950m 2 / g) and high IG / ID>50.

[0080] <Carbon nanotube yield>

[0081] The mass of the collected carbon nanotube is divided by the mass of the carbon source to calculate the formula as follows:

[0082] Carbon nanotube yield (%) = (collected carbon nanotube mass / total carbon source mass of the system) x 100%

[0083] <Raman RBM peak>

[0084] The laser Raman microscope with a laser wavelength of 532nm is used for measurement, and the G / D ratio is 1590cm -1 and 1350cm -1The peak intensity ratio at the wave number; the radial breathing mode (RBM) peak is one of the key features representing the structure of carbon nanotubes, and the peak value in the low wave number range of 100-300 cm⁻¹ is mainly counted. In this paper, the first RBM peak value is the main peak.

[0085] Example 1

[0086] Under the protection of argon, a tubular furnace with an outer diameter of 60 mm and a length of 150 mm was heated to 1250℃, and toluene, ferrocene and thiophene were configured into a mixed solution with a mass ratio of 100:8:1. The material decomposed by gasification at high temperature was used as a reaction gas stream, which was introduced into the tubular furnace through a Y-shaped feeding pipe with an internal angle of 45°. The two reaction gas streams collided at the Y-shaped converging port, and hydrogen gas 2 slm and argon gas 10 slm were introduced simultaneously for the growth of carbon nanotubes. The reaction time was set to 6h.

[0087] After the reaction was completed, the hydrogen and the feed were turned off, and the temperature was lowered to room temperature under the protection of argon. The black cloth-like carbon nanotube accumulation was collected from the carbon tube recovery device, and the carbon tube yield and the proportion of double-walled and triple-walled mixed carbon nanotubes were analyzed. The results are shown in Table 1.

[0088] Then the obtained carbon tube accumulation was sequentially subjected to oxidation and acid washing treatment, and the oxidation was carried out in an atmosphere of air and inert gas (nitrogen) with a volume ratio of 1:2. The oxidation temperature was controlled at 400℃, and the oxidation holding time was 45 min. Then, the acid washing was carried out using a hydrochloric acid solution with a mass concentration of 12%, and the acid washing temperature was 85℃, and the acid washing holding time was 13.5h. After drying, the finished product carbon nanotube product was obtained, and its BET and carbon tube diameter were analyzed. The results are shown in Table 1.

[0089] Example 2

[0090] The difference from Example 1 is only that the mass ratio of toluene, ferrocene and thiophene is 100:8:1.82, and the results are shown in Table 1.

[0091] Example 3

[0092] The difference from Example 1 is only that the mass ratio of toluene, ferrocene and thiophene is 100:8:5.46; the volume ratio of air and inert gas (argon) in oxidation is 1:1.5, the oxidation temperature is 350℃, and the oxidation holding time is 60 min; the mass concentration of hydrochloric acid solution in acid washing is 8%, the acid washing temperature is 90℃, and the acid washing holding time is 12h, and the results are shown in Table 1.

[0093] Comparative Example 1

[0094] The difference from Example 1 is only that the mass ratio of toluene, ferrocene and thiophene is 100:8:0.8, and the results are shown in Table 1.

[0095] Comparative Example 2

[0096] The difference from Example 1 is only that the mass ratio of toluene, ferrocene and thiophene is 100:8:7, and the results are shown in Table 1.

[0097] The samples obtained in Example 1 and Comparative Example 1 were characterized by transmission electron microscopy, as shown in Figure 1 and Figure 2 It can be seen from the analysis that, under the condition that the Y-shaped angle is 45°, when the mass fraction of thiophene is in the range of 1-5.46, the samples in Example 1 ( Figure 1 ) are mostly double-walled and triple-walled mixed carbon nanotubes 80%, while in Comparative Example 1 ( Figure 2 ) most of them are single-walled carbon nanotubes, and statistics show that double-walled and triple-walled mixed carbon nanotubes only account for 20%; this conclusion is consistent with the BET results of carbon nanotube products, that is, the BET of carbon nanotube products decreases with the increase of the content of double-walled and triple-walled mixed carbon nanotubes, for example, the BET of the product prepared in Comparative Example 1 containing 20% double-walled and triple-walled mixed carbon nanotubes is 1100 m 2 / g, while the BET of the product prepared in Example 1 containing 80% double-walled and triple-walled mixed carbon nanotubes has decreased to 830 m 2 / g. Therefore, the increase of thiophene content combined with Y-shaped feeding can obtain high content of double-walled and triple-walled mixed carbon nanotubes.

[0098] Table 1

[0099]

[0100] Example 4

[0101] Under the protection of argon, a tubular furnace with an outer diameter of 60 mm and a length of 150 mm was heated to 1250℃, and toluene, ferrocene and thiophene were configured into a mixed solution with a mass ratio of 100:8:1.82, which was used as a reaction gas stream after gasification or sublimation at high temperature, and was introduced into the tubular furnace through a Y-shaped feeding pipe with an internal angle of 30°. Two reaction gas streams were introduced into the tubular furnace, and hydrogen gas 2 slm and argon gas 10 slm were introduced at the same time for the growth of carbon nanotubes, and the reaction time was set to 6 h.

[0102] After the reaction was completed, the hydrogen and the feed were turned off, and the temperature was lowered to room temperature under the protection of argon. The black cloth-like carbon nanotube accumulation was collected from the carbon tube collector, and the carbon nanotube yield and the proportion of double-walled and triple-walled mixed carbon nanotubes were analyzed, and the results are shown in Table 2.

[0103] The obtained carbon tube accumulation is then subjected to oxidation and acid washing treatment in turn, and is subjected to oxidation in an atmosphere of air and inert gas (nitrogen) at a volume ratio of 1:2.5, the oxidation temperature is controlled at 450°C, and the oxidation holding time is 30 min; then the carbon tube accumulation is cleaned by using a hydrochloric acid solution with a mass concentration of 20%, the acid washing temperature is 80°C, the acid washing holding time is 15 h, and the obtained product is dried to obtain a finished product of carbon nanotube, and the product is subjected to BET and carbon tube diameter analysis, and the results are shown in Table 2.

[0104] Example 5

[0105] The difference from Example 4 is that the internal included angle of the Y-shaped structure is 60°, and the results are shown in Table 2.

[0106] Comparative Example 3

[0107] The difference from Example 4 is that the internal included angle of the Y-shaped structure is 90°, and the results are shown in Table 2.

[0108] Comparative Example 4

[0109] The difference from Example 4 is that the internal included angle of the Y-shaped structure is 120°, and the results are shown in Table 2.

[0110] Comparative Example 5

[0111] The difference from Example 4 is that the internal included angle of the Y-shaped structure is 0°, and the results are shown in Table 2.

[0112] Comparative Example 6

[0113] The difference from Example 4 is that the mass ratio of toluene, ferrocene and thiophene in the reaction gas flow is 100:4:1.82, and the results are shown in Table 2.

[0114] Comparative Example 7

[0115] The difference from Example 4 is that the mass ratio of toluene, ferrocene and thiophene in the reaction gas flow is 100:9:1.82, and the results are shown in Table 2.

[0116] Comparative Example 8

[0117] The difference from Example 4 is that the mass ratio of toluene, ferrocene and thiophene in the reaction gas flow is 100:4:0.5, and the results are shown in Table 2.

[0118] Comparative Example 9

[0119] The difference from Example 4 is that the first gas flow is only toluene, and the second gas flow is ferrocene and thiophene, that is, the reactants are fed separately, and the mass ratio of toluene, ferrocene and thiophene is 100:8:1.82, and the results are shown in Table 2.

[0120] Generally, the diameter of carbon nanotubes increases with the number of nanotube layers. Raman spectroscopy was performed on the samples obtained in Example 2 and Comparative Example 5, and the results are as follows: Figure 3 and Figure 4 As shown, it can be observed that when the Y-angle is 0°, the main Raman RBM peak of the sample is located at 180 cm⁻¹. -1 Nearby, and when the Y-shaped angle is 45°, the main peak of the Raman RBM is 180cm. -1 Shift to the left by 145cm -1 Nearby, according to the formula d=248 / ω, where ω is the RBM peak value, the reaction products passing through the Y-shaped angle can be obtained, having a larger diameter. Simultaneously, combined with... Figure 1 As can be seen from the transmission results of Example 1, the carbon nanotube products prepared by this method are mainly mixtures of double-walled and triple-walled carbon nanotubes.

[0121] Meanwhile, as shown in Examples 4, 6, and 8, when the proportion of ferrocene catalyst in the reaction system was significantly reduced to 4 parts under the condition of 100 parts toluene carbon source reaction, the carbon nanotube yield would be further reduced due to the excessive carbon source concentration, leading to catalyst deactivation and a decrease in carbon nanotube yield to 50-60%, thus reducing its production and application value. Therefore, no further research was conducted on the carbon nanotubes. However, as shown in Comparative Example 7, a slight increase in the amount of catalyst resulted in a small increase in the carbon nanotube yield due to the increased catalyst usage, but this increase was less than the 12.5% ​​increase due to the catalyst. Therefore, although the carbon nanotubes in Comparative Example 7 met the requirements in all data, their sample contained a larger amount of iron particles. Figure 5 As shown in the figure, the back-end purification may bring some problems. Therefore, in the preparation process of this invention, under the condition of fixed carbon source mass, the proportion of ferrocene and sulfur in the system has an important correlation with the yield of carbon nanotubes obtained from the reaction or their subsequent use.

[0122] Finally, to further demonstrate the beneficial effects of catalyst collision, in Comparative Example 9, the first gas stream in the reaction gas flow consisted only of toluene, and the second gas stream consisted of ferrocene and thiophene. This meant there was no catalyst collision process. As shown in Table 2, the proportion of double-walled and triple-walled mixed carbon nanotubes in the sample was only 45%, a result close to that of Comparative Example 5 where the Y-feed angle was 0°. Furthermore, when the Y-feed angle increased to 120°, although interparticle collision and fusion were sufficient, experiments in Comparative Example 4 showed that the catalyst easily formed carbon deposits inside the pipes, which could clog the pipes in severe cases, hindering the reaction.

[0123] In summary, the collision effect requires proper collision between catalysts to achieve the effect of this invention.

[0124] Table 2

[0125]

[0126] In conclusion, the carbon nanotubes are prepared by the floating method, and through the design of the catalyst and the regulation of the feeding mode, the carbon nanotube crude product with the mixed mass percentage of double-wall and triple-wall carbon nanotubes being greater than or equal to 80% can be directly obtained.

[0127] The above describes the preferred embodiments of the present application, but the present application is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0128] In addition, it should be noted that each specific technical feature described in the above-described specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combination manners.

[0129] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A method for preparing double-walled and triple-walled mixed carbon nanotubes, characterized by, The preparation method comprises: The carbon nanotube product is obtained by using a floating catalyst vapor deposition method to grow; In the growing, i reaction gas streams are used for reaction, i>=2, and at least two of the i reaction gas streams collide at an acute angle; the reaction gas streams comprise: carbon source, catalyst and promoter with a mass ratio of 100:(7.5-8.2):(0.9-6).

2. The production method according to claim 1, wherein All the reaction gas streams in the i reaction gas streams collide at an acute angle; Preferably, the acute angle is 30-60°.

3. The production method according to claim 1, wherein The carbon source comprises: liquid-phase carbon source and / or gas-phase carbon source; Preferably, the liquid-phase carbon source comprises: one or a combination of at least two of toluene, ethanol, methanol, acetone or xylene; Preferably, the gas-phase carbon source comprises: one or a combination of at least two of methane, ethylene or propylene.

4. The production method according to claim 1, wherein The catalyst comprises: one or a combination of at least two of iron catalyst, cobalt catalyst or nickel catalyst.

5. The production method according to claim 1, wherein The promoter comprises: elemental sulfur and / or sulfur compound.

6. The production method according to claim 1, wherein The growing temperature is 1200-1250℃; Preferably, the carrier gas used in the growing comprises: hydrogen and inert gas with a volume flow ratio of 1:(4-10).

7. The production method according to claim 1, wherein The carbon nanotube product is sequentially subjected to oxidation and acid washing to obtain a finished carbon nanotube product.

8. The production method according to claim 7, wherein The oxidation comprises: oxidation in an atmosphere of air and inert gas with a volume ratio of 1:(1.5-2.5); Preferably, the oxidation temperature is 350-450℃; Preferably, the holding time of the oxidation is 30-60min.

9. The production method according to claim 7, wherein The acid washing comprises: cleaning with an acid solution with a mass concentration of 8-20%; Preferably, the acid washing temperature is 80-90℃; Preferably, the holding time of the acid washing is 12-15h.

10. A double-walled and triple-walled hybrid carbon nanotube, characterized by, The double- and triple-walled mixed carbon nanotubes are prepared by the method of any one of claims 1-9, and have a BET specific surface area < 1000 m 2 / g, a Raman RBM main peak < 180 cm -1 , a Raman IG / ID > 50, and a tube diameter distribution of 2.0-2.6 nm.

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