Array of carbon nanotubes and method for preparing same

Abstract

This application relates to the technical field of carbon nanotubes, and provides an array of carbon nanotubes and a preparation method thereof, including the following steps: providing an initial flaky catalyst; performing activation treatment on the initial flaky catalyst to obtain an activated flaky catalyst; placing the activated flaky catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas to perform the first fluidized growth of carbon nanotubes, and then performing the second fluidized growth of carbon nanotubes to obtain an array of carbon nanotubes; wherein, the rate of the first fluidized growth is greater than the rate of the second fluidized growth. The preparation method of the array of carbon nanotubes provided by this application first rapidly grows an array of carbon nanotubes with a certain length on the surface of the activated flaky catalyst, and then enables the array of carbon nanotubes on the surface of the activated flaky catalyst to continue to grow slowly, which is beneficial to the growth of carbon nanotubes along the initial growth direction, thereby preventing the carbon nanotubes from growing randomly and forming long array carbon nanotubes.

Description

Technical Field

[0001] This application belongs to the technical field of carbon nanotubes, and particularly relates to an array of carbon nanotubes and a preparation method thereof. Background Art

[0002] In chemical vapor deposition, a fluidized bed reactor is a commonly used device for batch and continuous production of carbon nanotubes. The fluidized bed is often used to produce entangled carbon nanotubes, but the entangled carbon nanotubes are prone to agglomeration and difficult to disentangle, which has a great impact on their applications. Array carbon nanotubes have better orientation and dispersion properties compared to entangled carbon nanotubes, and array carbon nanotubes have a larger specific surface area and more excellent electrical conductivity. To prepare array carbon nanotubes using the existing fluidized bed process, a flake catalyst is required. However, the active components loaded on the existing flake catalyst carriers are few and the active component particles are large, and the flake catalysts are prone to stacking in the fluidized state, which affects the growth of carbon nanotubes on the surface of the active components and easily causes problems such as uneven length and low growth rate of the array carbon nanotubes.

[0003] Therefore, it is necessary to develop a preparation method that can prepare array carbon nanotubes with uniform length and high growth rate. Summary of the Invention

[0004] The purpose of this application is to provide an array of carbon nanotubes and a preparation method thereof, aiming to solve the problems of uneven length and low growth rate of the array carbon nanotubes prepared by the existing preparation methods of array carbon nanotubes.

[0005] To achieve the above application purpose, the technical solution adopted in this application is as follows:

[0006] In the first aspect, this application provides a preparation method for an array of carbon nanotubes, including the following steps:

[0007] Provide an initial flake catalyst;

[0008] Perform activation treatment on the initial flake catalyst to obtain an activated flake catalyst;

[0009] Place the activated flake catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas for the first fluidized growth of carbon nanotubes, and then perform the second fluidized growth of carbon nanotubes to obtain an array of carbon nanotubes; wherein, the rate of the first fluidized growth is greater than the rate of the second fluidized growth.

[0010] In the second aspect, this application provides an array of carbon nanotubes, which is prepared by the preparation method for an array of carbon nanotubes provided in this application.

[0011] Compared with the prior art, this application has the following beneficial effects:

[0012] The preparation method of the array carbon nanotubes provided in the first aspect of the present application is to carry out the first fluidized growth of carbon nanotubes by placing an activated flaky catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas, and then carry out the second fluidized growth of carbon nanotubes. The rate of the first fluidized growth is greater than that of the second fluidized growth. In this way, a certain length of array carbon nanotubes can be rapidly grown on the surface of the activated flaky catalyst, and then the array carbon nanotubes on the surface of the activated flaky catalyst continue to grow slowly, which is beneficial to the growth of carbon nanotubes along the initial growth direction, thereby preventing the chaotic growth of carbon nanotubes and forming long array carbon nanotubes.

[0013] The array carbon nanotubes provided in the second aspect of the present application are prepared by the preparation method of the array carbon nanotubes of the present application. Therefore, the array carbon nanotubes of the present application have a long diameter and are arranged in parallel, are easy to disperse, and have good product quality. Brief Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 It is the preparation flow chart of the preparation method of the array carbon nanotubes provided in the embodiment of the present application;

[0016] Figure 2 It is the SEM image with a low magnification of the array carbon nanotubes prepared in Example 3 of the present application;

[0017] Figure 3 It is the SEM image with a high magnification of the array carbon nanotubes prepared in Example 3 of the present application;

[0018] Figure 4 It is the SEM image of the carbon nanotubes prepared in Comparative Example 1 of the present application. Detailed Description of the Embodiments

[0019] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer, the following further details the present application in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0020] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Here, A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0021] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following items" or its similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0022] It should be understood that in various embodiments of this application, the magnitude of the sequence numbers of the above processes does not mean the order of execution. Some or all of the steps can be executed in parallel or successively. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0023] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application. The singular forms of "a", "the", and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0024] The weight of the relevant components mentioned in the specification of the embodiments of this application not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the specification of the embodiments of this application is scaled up or down proportionally, it is within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass described in the specification of the embodiments of this application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0025] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of this application, the first XX can also be referred to as the second XX. Similarly, the second XX can also be referred to as the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features. [[ID=()]]

[0026] The first aspect of the embodiments of this application provides a method for preparing an array of carbon nanotubes, such asFigure 1 as shown, including the following steps:

[0027] S01: Provide an initial flaky catalyst;

[0028] S02: Activate the initial flaky catalyst to obtain an activated flaky catalyst;

[0029] S03: Place the activated flaky catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas for the first fluidized growth of carbon nanotubes, and then conduct the second fluidized growth of carbon nanotubes to obtain arrayed carbon nanotubes; wherein, the rate of the first fluidized growth is greater than that of the second fluidized growth.

[0030] The method for preparing arrayed carbon nanotubes provided by the embodiments of the present application, by placing the activated flaky catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas for the first fluidized growth of carbon nanotubes, and then conducting the second fluidized growth of carbon nanotubes, and the rate of the first fluidized growth is greater than that of the second fluidized growth, so that a certain length of arrayed carbon nanotubes can be rapidly grown on the surface of the activated flaky catalyst, and then the arrayed carbon nanotubes on the surface of the activated flaky catalyst continue to grow slowly, which is beneficial to the growth of carbon nanotubes along the initial growth direction, thereby preventing the carbon nanotubes from growing randomly and forming long arrayed carbon nanotubes.

[0031] In the above step S01, the preparation steps of the flaky catalyst include: preparing a metal salt solution; adding an alkaline precipitant solution, a complexing agent solution and the metal salt solution into a solution containing a layered porous mineral in a co-current manner for coprecipitation reaction, and then performing separation treatment and calcination treatment to obtain the flaky catalyst. In a specific embodiment, under a stirring state, the alkaline precipitant solution, the complexing agent solution and the metal salt solution are added into the solution containing the layered porous mineral in a co-current manner for coprecipitation reaction, and then the flaky catalyst precipitate is separated, and then placed in an oven for drying.

[0032] In the embodiment, the molar ratio of the alkaline precipitant solution, the complexing agent solution and the metal salt solution is (1.05 - 1.2):(1.05 - 1.2):1, such as 1.05:1.05:1, 1.1:1.1:1, 1.15:1.15:1, 1.2:1.2:1, etc. The dosages of the alkaline precipitant solution and the complexing agent solution are slightly larger than that of the metal salt solution, which is beneficial to adjusting the particle size of the catalytic active particles formed on the surface of the layered porous mineral, making the catalytic active particles have a small particle size, a large number and good uniformity, thereby being beneficial to improving the growth magnification of arrayed carbon nanotubes growing on the surface of the layered porous mineral.

[0033] In an embodiment, the metal salt solution is selected from nickel cobalt iron salt solutions with a molar ratio of nickel, cobalt, and iron of 0.6∶(0.9 - 1)∶(0.9 - 1). The preparation of the metal salt solution can be achieved by dissolving nickel salt, cobalt salt, and iron salt in an appropriate amount of pure water, or by dissolving iron cobalt salt and nickel salt in an appropriate amount of pure water to obtain the metal salt solution. Among them, the nickel salt can be selected from at least one of nickel nitrate, nickel chloride, and nickel sulfate; the cobalt salt can be selected from at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate; the iron salt can be selected from at least one of iron nitrate, iron chloride, and iron sulfate.

[0034] In an embodiment, the alkaline precipitant solution is selected from at least one of ammonium carbonate solution, ammonium bicarbonate solution, urea solution, and ammonia water.

[0035] In an embodiment, the complexing agent solution is selected from at least one of oxalic acid, citric acid, and sorbic acid. The layered porous mineral is selected from at least one of vermiculite, kaolinite, and illite. Vermiculite is preferred. For example, the layered porous mineral is selected from vermiculite or expanded vermiculite, and the complexing agent solution is selected from citric acid. Adding citric acid in the embodiment of the present application is beneficial to promoting the ion exchange process between metal ions such as Fe 3+ , Co 3+ , Ni 3+ in the metal salt solution and cations such as Ca 2+ , Na + , K + , Mg 2+ in the interlayer of vermiculite, so as to form catalytically active particles uniformly distributed in the interlayer and on the surface of vermiculite during the calcination process. In addition, citric acid can also complex with the alkaline precipitant and the metal salt solution, can better control the reaction process, accelerate the precipitation of the metal salt and its attachment to the surface of expanded vermiculite, reduce the size of the attached catalytically active particles, increase the number of catalytically active particles, and thus improve the growth rate of the array of carbon nanotubes grown on the surface of the flaky catalyst.

[0036] In an embodiment, the dosage of vermiculite can be selected according to actual production requirements and is not limited herein.

[0037] In an embodiment, the temperature of the coprecipitation reaction is 80 - 100 °C, such as 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, etc., and the time is 4 - 6 h, such as 4 h, 4.5 h, 5 h, 5.5 h, 6 h.

[0038] In an embodiment, the separation treatment can adopt conventional separation treatment as long as it can separate the flaky catalyst from the reaction system. For example, filtration and other methods can be used for separation.

[0039] In the research process, the inventors of the present application found that the calcination temperature not only affects the interlayer spacing between the layered porous minerals, affects the growth length of the array carbon nanotubes, but also affects the dispersion uniformity of the catalytic active particles on the surface of the layered porous minerals. During the high-temperature calcination process, dehydration dissociation and expansion will occur between the layers of the layered porous minerals. Therefore, the calcination temperature is closely related to the expansion state. In the embodiment, the temperature of the calcination treatment is 600-1000 °C, preferably 800 °C. Within this calcination temperature range, it is beneficial to the uniform expansion degree of the layered porous minerals, and thus beneficial to the uniform dispersion of the catalytic active particles on the surface of the layered porous minerals.

[0040] In the above step S02, the activation treatment steps include: introducing a mixed gas of hydrogen and a second protective gas with a volume ratio of (1-2):1 at a flow rate of 150-200 L / min, and performing activation for 5-10 min at a temperature of 300-400 °C. The reducing property of hydrogen is used to reduce the metal oxides on the surface of the layered porous minerals to active metals. However, since using hydrogen reduction easily causes sintering and agglomeration of transition metal elements, resulting in a decrease in the activity of the flaky catalyst and also affecting the diameter uniformity of the grown array carbon nanotubes, in the embodiment of the present application, by introducing a second protective gas and controlling the volume ratio of hydrogen to the second protective gas to be (1-2):1, the balance between the activation and agglomeration of the flaky catalyst can be regulated. At the same time, introducing the second protective gas can increase the gas pressure, which can achieve the effects of crushing and dispersing the flaky catalyst, so that the catalytic activity of the flaky catalyst is good. In the embodiment, the second protective gas is selected from at least one of nitrogen, argon, and helium.

[0041] In the above step S03, the step of placing the activated flaky catalyst in an ambient atmosphere containing a carbon source gas and a first protective gas for the first fluidized growth of carbon nanotubes and then performing the second fluidized growth of carbon nanotubes includes: introducing the carbon source gas at a first flow rate and the first protective gas at a second flow rate into the environment where the activated flaky catalyst is placed for the first fluidized growth of carbon nanotubes to form a preset array of carbon nanotubes; introducing the carbon source gas at a third flow rate and the first protective gas at a fourth flow rate into the environment containing the preset array of carbon nanotubes for the second fluidized growth of carbon nanotubes. Wherein, the first flow rate is greater than the third flow rate, the second flow rate is greater than the fourth flow rate, and the temperature of the first fluidized growth is higher than the temperature of the second fluidized growth. In the embodiments of the present application, the growth rate of the fluidized carbon nanotubes can be jointly determined by the flow rate of the carbon source gas, the flow rate of the first protective gas, and the temperature. Therefore, by controlling the flow rate of the carbon source gas for the first fluidized growth to be greater than the flow rate of the carbon source gas for the second fluidized growth, at the same time controlling the flow rate of the first protective gas for the first fluidized growth to be greater than the flow rate of the first protective gas for the second fluidized growth, and at the same time controlling the temperature of the first fluidized growth to be higher than the temperature of the second fluidized growth, the growth rate of the first fluidized growth can be made greater than the growth rate of the second fluidized growth, so that it is possible to ensure that a certain length of array carbon nanotubes grows rapidly on the surface of the activated flaky catalyst, and then let the array carbon nanotubes on the surface of the activated flaky catalyst continue to grow slowly, which is beneficial to the growth of carbon nanotubes along the initial growth direction to form long array carbon nanotubes. Moreover, by controlling process conditions such as the flow rates of the carbon source gas and the first protective gas and the temperature, the fluidization state of the activated flaky catalyst during the reaction can be enhanced, preventing the stacking of the activated flaky catalyst, thereby preventing the stacking and entanglement of carbon nanotubes and further reducing the probability of the disordered growth of carbon nanotubes.

[0042] In the embodiment, it can be realized by using a reaction furnace device with a primary reactor and a secondary reactor connected in series. The reaction furnace can be a large-capacity fluidized bed device, which can be understood as that it can be realized by using a large-capacity fluidized bed device with a primary reactor and a secondary reactor connected in series. Specifically, the carbon source gas is introduced at a first flow rate and the first protective gas is introduced at a second flow rate into the primary reactor containing the activated flaky catalyst for the first fluidized growth of carbon nanotubes to form a preset array of carbon nanotubes; the carbon source gas is introduced at a third flow rate and the first protective gas is introduced at a fourth flow rate into the secondary reactor containing the preset array of carbon nanotubes for the second fluidized growth of carbon nanotubes to obtain an array of carbon nanotubes.

[0043] In an embodiment, the first flow rate is 550 - 650 L / min; the second flow rate is 600 - 700 L / min; the third flow rate is 400 - 500 L / min; the fourth flow rate is 550 - 600 L / min; the temperature for the first fluidized growth is 660 - 700 °C, and the time is 20 - 30 min; the temperature for the second fluidized growth is 600 - 650 °C, and the time is 20 - 30 min. By designing the unique two-stage reaction of the present application, that is, a larger carbon source gas flow rate, a first protective gas flow rate, and a higher temperature are adopted during the first fluidized growth of carbon nanotubes to improve the reaction activity, and an array of carbon nanotubes with a certain length is rapidly grown on the surface of the flaky catalyst first. Then, it enters the second fluidized growth of carbon nanotubes. By reducing the flow rates of the carbon source gas and the first protective gas and lowering the growth temperature, the reaction activity is reduced, and the array of carbon nanotubes on the surface of the flaky catalyst continues to grow slowly, which is beneficial to the growth of carbon nanotubes along the initial growth direction and prevents the chaotic growth of carbon nanotubes, thereby forming long-array carbon nanotubes.

[0044] In an embodiment, the carbon source gas includes at least one of propylene, ethylene, hexane, acetylene, methane, butane, carbon monoxide, benzene, and ethanol. The first protective gas is selected from at least one of nitrogen, argon, and helium.

[0045] In an embodiment, a method for preparing an array of carbon nanotubes includes the following steps:

[0046] S001: A basic precipitant solution, a complexing agent solution, and a metal salt solution with a molar ratio of (1.05 - 1.2)∶(1.05 - 1.2)∶1 are added in parallel to a solution containing a layered porous mineral, and a coprecipitation reaction is carried out at a temperature of 80 - 100 °C for 4 - 6 h. After filtration and separation, it is calcined at a temperature of 600 - 1000 °C to obtain a flaky catalyst; wherein, the metal salt solution includes a nickel-cobalt-iron salt solution with a molar ratio of nickel, cobalt, and iron of 0.6∶(0.9 - 1)∶(0.9 - 1), the basic precipitant solution is selected from at least one of ammonium carbonate solution, ammonium bicarbonate solution, urea solution, and ammonia water, the complexing agent solution is selected from at least one of oxalic acid, citric acid, and sorbic acid; the layered porous mineral is selected from at least one of vermiculite, kaolinite, and illite.

[0047] S002: The flaky catalyst is placed in a catalyst reduction and activation device, and a mixed gas of hydrogen and a second protective gas with a volume ratio of (1 - 2)∶1 is introduced at a flow rate of 150 - 200 L / min, and activation is carried out at a temperature of 300 - 400 °C for 5 - 10 min to obtain an activated flaky catalyst;

[0048] S003: Feed the carbon source gas at a flow rate of 550 - 650 L / min and the first protective gas at a flow rate of 600 - 700 L / min into the first-stage reactor filled with the activated flaky catalyst, and carry out the first fluidized growth of carbon nanotubes for 20 - 30 min at a temperature of 660 - 700 °C to form the preset array of carbon nanotubes; then feed the carbon source gas at a flow rate of 400 - 500 L / min and the first protective gas at a flow rate of 550 - 600 L / min into the second-stage reactor filled with the preset array of carbon nanotubes, and carry out the second fluidized growth of carbon nanotubes for 20 - 30 min at a temperature of 600 - 650 °C to obtain the array of carbon nanotubes; wherein, the carbon source gas includes at least one of propylene, ethylene, hexane, acetylene, methane, butane, carbon monoxide, benzene, and ethanol, and the first protective gas is selected from at least one of nitrogen, argon, and helium.

[0049] In the second aspect of the embodiments of the present application, an array of carbon nanotubes is provided, which is prepared by the method for preparing an array of carbon nanotubes provided by the present application.

[0050] The array of carbon nanotubes provided by the embodiments of the present application is prepared by the method for preparing an array of carbon nanotubes of the present application. Therefore, the carbon nanotubes of the present application have a long diameter and are arranged in parallel, are easy to disperse, and have good product quality.

[0051] In the embodiment, the length of the array of carbon nanotubes is 50 - 100 μm, and the specific surface area is 100 - 200 m 2 / g. The array of carbon nanotubes in the embodiments of the present application has a long length and a small specific surface area, so it has good dispersion performance and conductivity.

[0052] The following is illustrated with specific embodiments.

[0053] Example 1

[0054] This embodiment provides a method for preparing an array of carbon nanotubes, including the following steps:

[0055] S11: Prepare the flaky catalyst:

[0056] Screen expanded vermiculite, remove impurities, and add it to an aqueous solution to obtain a solution containing expanded vermiculite;

[0057] According to the molar ratio of Fe, Co, and Ni of 1:1:0.6, dissolve ferric nitrate, cobalt nitrate, and nickel nitrate in water to form a nitrate solution of nickel, cobalt, and iron;

[0058] According to the molar ratio of urea, citric acid, and nickel, cobalt, and iron nitrate solutions being 1.05∶1.05∶1, urea, citric acid, and nickel, cobalt, and iron nitrate solutions are added in parallel to a solution containing expanded vermiculite, stirred and reacted at a temperature of 80 °C for 6 hours, filtered and dried, and then calcined at a temperature of 800 °C for 2 h to obtain a flaky catalyst;

[0059] S12: Activation treatment of the flaky catalyst:

[0060] The flaky catalyst is added to a catalyst reduction and activation device, and a mixed gas of hydrogen and nitrogen with a volume ratio of 1∶1 is introduced at a flow rate of 150 L / min, and reduced and activated at a temperature of 400 °C for 8 min to obtain an activated flaky catalyst;

[0061] S13: Preparation of array carbon nanotubes by secondary reaction:

[0062] The activated flaky catalyst is added to a fluidized bed primary reactor, a carbon source gas is introduced at a flow rate of 550 L / min, nitrogen is introduced at a flow rate of 600 L / min, and the first fluidized growth of carbon nanotubes is carried out at a temperature of 700 °C for 25 min to form a preset array of carbon nanotubes;

[0063] The carbon source gas is introduced into a fluidized bed secondary reactor containing the preset array of carbon nanotubes at a flow rate of 400 L / min and nitrogen is introduced at a flow rate of 550 L / min, and the second fluidized growth of carbon nanotubes is carried out at a temperature of 600 °C for 25 min to obtain an array of carbon nanotubes.

[0064] Example 2

[0065] This example provides a method for preparing an array of carbon nanotubes, including the following steps:

[0066] S11: Preparation of a flaky catalyst:

[0067] Screen expanded vermiculite, remove impurities, and add it to an aqueous solution to obtain a solution containing expanded vermiculite;

[0068] According to the molar ratio of Fe, Co, and Ni being 1∶1∶0.6, ferric sulfate, cobalt sulfate, and nickel sulfate are dissolved in water to form a nickel, cobalt, and iron sulfate solution;

[0069] According to the molar ratio of ammonium bicarbonate solution, citric acid, and nickel, cobalt, and iron sulfate solution being 1.1∶1.1∶1, the ammonium bicarbonate solution, citric acid, and nickel, cobalt, and iron sulfate solution are added in parallel to the solution containing expanded vermiculite, stirred and reacted at a temperature of 100 °C for 5 hours, filtered and dried, and then calcined at a temperature of 700 °C for 2.5 h to obtain a flaky catalyst;

[0070] S12: Activation treatment of the flaky catalyst:

[0071] Add the flaky catalyst into the catalyst reduction and activation device, and introduce a mixed gas of hydrogen and nitrogen with a volume ratio of 2:1 at a flow rate of 200 L / min. Reduce and activate it at 350 °C for 10 min to obtain the activated flaky catalyst;

[0072] S13: Prepare array carbon nanotubes through a secondary reaction:

[0073] Add the activated flaky catalyst into the first-stage fluidized bed reactor, introduce the carbon source gas at a flow rate of 650 L / min, introduce nitrogen at a flow rate of 700 L / min, and carry out the first fluidized growth of carbon nanotubes at 700 °C for 20 min to form the preset array carbon nanotubes;

[0074] Introduce the carbon source gas at a flow rate of 500 L / min and nitrogen at a flow rate of 600 L / min into the second-stage fluidized bed reactor filled with the preset array carbon nanotubes, and carry out the second fluidized growth of carbon nanotubes at 600 °C for 20 min to obtain the array carbon nanotubes.

[0075] Example 3

[0076] This example provides a method for preparing array carbon nanotubes, including the following steps:

[0077] S11: Prepare the flaky catalyst:

[0078] Screen vermiculite, remove impurities, and add it to the aqueous solution to obtain a solution containing vermiculite;

[0079] According to the molar ratio of Fe, Co, and Ni of 1:1:0.6, dissolve ferric chloride, cobalt chloride, and nickel chloride in water to form a hydrochloric acid salt solution of nickel, cobalt, and iron;

[0080] According to the molar ratio of ammonium carbonate, citric acid, and the hydrochloric acid salt solution of nickel, cobalt, and iron of 1.2:1.2:1, add ammonium carbonate, citric acid, and the hydrochloric acid salt solution of nickel, cobalt, and iron into the solution containing vermiculite in parallel flow, stir and react at 90 °C for 5 hours, filter and dry, and then calcine at 750 °C for 2 h to obtain the flaky catalyst;

[0081] S12: Activate the flaky catalyst:

[0082] Add the flaky catalyst into the catalyst reduction and activation device, and introduce a mixed gas of hydrogen and nitrogen with a volume ratio of 1.5:1 at a flow rate of 180 L / min. Reduce and activate it at 350 °C for 10 min to obtain the activated flaky catalyst;

[0083] S13: Prepare array carbon nanotubes through a secondary reaction:

[0084] Add the activated flaky catalyst into the first-stage fluidized bed reactor, introduce the carbon source gas at a flow rate of 600 L / min, introduce nitrogen at a flow rate of 650 L / min, and carry out the first fluidized growth of carbon nanotubes at 700 °C for 30 min to form a preset array of carbon nanotubes.

[0085] Introduce the carbon source gas at a flow rate of 450 L / min and nitrogen at a flow rate of 560 L / min into the second-stage fluidized bed reactor filled with the preset array of carbon nanotubes, and carry out the second fluidized growth of carbon nanotubes at 650 °C for 30 min to obtain an array of carbon nanotubes.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing carbon nanotubes, which includes the following steps:

[0088] S11: Prepare the flaky catalyst:

[0089] Screen expanded vermiculite, remove impurities, and add it to an aqueous solution to obtain a solution containing expanded vermiculite.

[0090] According to the molar ratio of Fe, Co, and Ni of 1:1:0.6, dissolve ferric chloride, cobalt chloride, and nickel chloride in water to form a hydrochloric acid salt solution of nickel, cobalt, and iron.

[0091] According to the molar ratio of ammonium carbonate and the hydrochloric acid salt solution of nickel, cobalt, and iron of 1.2:1, add ammonium carbonate and the hydrochloric acid salt solution of nickel, cobalt, and iron in parallel to the solution containing expanded vermiculite, stir and react at 90 °C for 5 hours, filter and dry, and then calcine at 750 °C for 2 h to obtain the flaky catalyst.

[0092] S12: Activation treatment of the flaky catalyst:

[0093] Add the flaky catalyst into the catalyst reduction and activation device, introduce a mixed gas of hydrogen and nitrogen with a volume ratio of 1.5:1 at a flow rate of 180 L / min, and carry out reduction and activation at 350 °C for 10 min to obtain the activated flaky catalyst.

[0094] S13: Prepare an array of carbon nanotubes:

[0095] Add the activated flaky catalyst into the fluidized bed reactor, introduce the carbon source gas at a flow rate of 550 L / min, introduce nitrogen at a flow rate of 600 L / min, and carry out the fluidized growth of carbon nanotubes at 700 °C for 60 min to obtain an array of carbon nanotubes.

[0096] Relevant performance test and analysis:

[0097] The morphologies of the array carbon nanotubes prepared in Example 3 and the carbon nanotubes prepared in Comparative Example 1 were tested using a scanning electron microscope.

[0098] From Figure 2 the low-magnification SEM images and Figure 3 the high-magnification SEM images of the array carbon nanotubes prepared in Example 3 of the present application, it can be seen that the carbon nanotubes grown on the surface of vermiculite have long diameters and are arranged in parallel, which are array carbon nanotubes. However, from Figure 4 the SEM images of the carbon nanotubes prepared in Comparative Example 1 of the present application, it can be seen that the carbon nanotubes are significantly entangled. It shows that through the unique secondary reaction of the present application, a larger carbon source gas flow rate, a first protective gas flow rate, and a higher temperature are used in the first fluidized growth process of the carbon nanotubes, while the carbon source gas flow rate and the first protective gas flow rate are reduced, and the temperature is lowered in the second fluidized growth process of the carbon nanotubes. This can first rapidly grow a certain length of array carbon nanotubes on the surface of the flaky catalyst, and then let the array carbon nanotubes on the surface of the flaky catalyst continue to grow slowly, enabling the carbon nanotubes to grow along the initial growth direction, thereby obtaining array carbon nanotubes with long diameters and parallel arrangements. In addition, it can also be shown that adding citric acid when preparing the flaky catalyst by the coprecipitation method in the examples of the present application can well control the reaction process, reduce the precipitate particles precipitated during the coprecipitation process, increase the number of precipitate particles, and thus improve the growth rate of the array carbon nanotubes grown on the surface of the flaky catalyst.

[0099] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an array of carbon nanotubes, characterized in that, It includes the following steps: Provide an initial flaky catalyst; Perform activation treatment on the initial flaky catalyst to obtain an activated flaky catalyst; Place the activated flaky catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas to perform the first fluidized growth of carbon nanotubes, so as to rapidly grow an array of carbon nanotubes with a certain length on the surface of the flaky catalyst, and then perform the second fluidized growth of the carbon nanotubes to make the array of carbon nanotubes on the surface of the flaky catalyst continue to grow slowly, obtaining an array of carbon nanotubes; wherein, the rate of the first fluidized growth is greater than that of the second fluidized growth, the temperature of the first fluidized growth is higher than that of the second fluidized growth, the time of the first fluidized growth is 20-30 min, the time of the second fluidized growth is 20-30 min, the length of the array of carbon nanotubes is 50-100 μm, and the specific surface area is 100-200 m 2 / g.

2. The preparation method according to claim 1, wherein The step of placing the activated flaky catalyst in an environmental atmosphere containing a carbon source gas and a first protective gas for the first fluidized growth of carbon nanotubes and then performing the second fluidized growth of the carbon nanotubes includes: Introduce the carbon source gas at a first flow rate and the first protective gas at a second flow rate into the environment where the activated flaky catalyst is placed to perform the first fluidized growth of the carbon nanotubes, forming a preset array of carbon nanotubes; Introduce the carbon source gas at a third flow rate and the first protective gas at a fourth flow rate into the environment containing the preset array of carbon nanotubes to perform the second fluidized growth of the carbon nanotubes.

3. The preparation method according to claim 2, wherein, The first flow rate is greater than the third flow rate, and the second flow rate is greater than the fourth flow rate.

4. The preparation method according to claim 3, characterized in that, The first flow rate is 550 - 650 L / min; and / or The second flow rate is 600 - 700 L / min; and / or The third flow rate is 400 - 500 L / min; and / or The fourth flow rate is 550 - 600 L / min; and / or The temperature of the first fluidized growth is 660 - 700 °C; and / or The temperature of the second fluidized growth is 600 - 650 °C.

5. The preparation method according to any one of claims 1 to 4, characterized in that The preparation steps of the flaky catalyst include: Prepare a metal salt solution; Add the alkaline precipitant solution, the complexing agent solution, and the metal salt solution in parallel flow into the solution containing the layered porous mineral for coprecipitation reaction, and then perform separation treatment and calcination treatment to obtain a flaky catalyst.

6. The preparation method according to claim 5, characterized in that, The molar ratio of the alkaline precipitant solution, the complexing agent solution, and the metal salt solution is (1.05 - 1.2)∶(1.05 - 1.2)∶1; and / or The metal salt solution is selected from a nickel-cobalt-iron salt solution with a molar ratio of nickel, cobalt, and iron of 0.6∶(0.9 - 1)∶(0.9 - 1); and / or The alkaline precipitant solution is selected from at least one of ammonium carbonate solution, ammonium bicarbonate solution, urea solution, and ammonia water; and / or The complexing agent solution is selected from at least one of oxalic acid, citric acid, and sorbic acid; and / or The layered porous mineral is selected from at least one of vermiculite, kaolinite, and illite; and / or The temperature of the coprecipitation reaction is 80 - 100 °C, and the time is 4 - 6 h; and / or The temperature of the calcination treatment is 600 - 1000 °C.

7. The preparation method according to claim 5, characterized in that, The activation treatment steps include: introducing a mixed gas of hydrogen and a second protective gas with a volume ratio of (1 - 2)∶1 at a flow rate of 150 - 200 L / min, and activating the initial flaky catalyst for 5 - 10 min at a temperature of 300 - 400 °C; and / or The layered porous mineral is selected from vermiculite.

8. The preparation method according to claim 7, characterized in that, The carbon source gas includes at least one of propylene, ethylene, hexane, acetylene, methane, butane, carbon monoxide, benzene, and ethanol; and / or The first protective gas is selected from at least one of nitrogen, argon, and helium; and / or The second protective gas is selected from at least one of nitrogen, argon, and helium.

9. An array of carbon nanotubes, characterized in that, The array of carbon nanotubes is prepared by the method for preparing an array of carbon nanotubes according to any one of claims 1 to 8.

10. The array of carbon nanotubes according to claim 9, wherein The length of the arrayed carbon nanotubes is 50 to 100 μm, and the specific surface area is 100 to 200 m 2 / g.

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