CN113772659B - Method for preparing carbon nanotubes by coal tar pitch in-situ pyrolysis method - Google Patents

Method for preparing carbon nanotubes by coal tar pitch in-situ pyrolysis method Download PDF

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CN113772659B
CN113772659B CN202011228745.5A CN202011228745A CN113772659B CN 113772659 B CN113772659 B CN 113772659B CN 202011228745 A CN202011228745 A CN 202011228745A CN 113772659 B CN113772659 B CN 113772659B
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coal tar
tar pitch
cnts
temperature
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CN113772659A (en
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卢翠英
曹元甲
张智文
冯磊
王震
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Yulin University
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Yulin University
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    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/16—Preparation
    • C01B32/162—Preparation characterised by catalysts

Abstract

The invention provides a method for preparing carbon nanotubes by a coal tar pitch in-situ pyrolysis method, which comprises the following steps: 1) Ball milling and crushing coal tar pitch, placing in an oven, drying at 130-150 ℃ for 2.5-3.5h, naturally cooling, and sieving with 100 meshes; 2) Adding coal tar pitch into nickel acetate absolute ethanol solution, performing ultrasonic treatment for 20-40min, drying in a constant-temperature water bath at 75deg.C for 2-4h, grinding, placing into crucible, placing into a temperature-controlled tube furnace, and heating at flow rate of 40-60mL/min N 2 Heating to a preset temperature at a speed of 1.5-2.5 ℃/min under the atmosphere, preserving heat for 1.5-3h, and cooling to room temperature to obtain CNTs samples; wherein the preset temperature is 850-1000 ℃. The invention provides a beneficial way for preparing high-quality CNTs by using the green and environment-friendly low-cost coal tar pitch, improves the CNTs production effect and saves the production cost.

Description

Method for preparing carbon nanotubes by coal tar pitch in-situ pyrolysis method
Technical Field
The invention relates to the technical field of carbon nanotube preparation, in particular to a method for preparing carbon nanotubes by a coal tar pitch in-situ pyrolysis method.
Background
Since the first unexpected discovery of Carbon Nanotubes (CNTs), carbon nanotubes have been widely studied because of their many unique mechanical, electrical, magnetic and chemical properties, and have potential application prospects in numerous fields such as electrode materials, supercapacitors, energy storage and composite materials, and the like, and carbon nanotubes can be further improved in material properties by modification or compounding to expand their application range. Under the background, both theoretical research and application research of the carbon nanotubes have been developed. In many CNTs growing methods, catalytic Pyrolysis (CP) is considered to be the most likely process for realizing industrial CNTs production due to the advantages of low growth temperature (600-1100 ℃), easily controlled growth conditions, high yield and the like, but the growth process with high cost becomes a brake for mass production. The main reasons for this are the relatively expensive or toxic gases (methane, acetylene, ethylene, etc.), volatile liquids (benzene, toluene, xylene, etc.), sublimable solids (camphor, naphthalene, etc.) used. Therefore, the need for inexpensive, nontoxic, low energy consumption and readily available carbon sources is an important issue for CVD growth of CNTs. For this reason, some students have explored the study of growth of CNTs using biomass, waste plastics, coal tar pitch as carbon sources. And B, pyrolyzing palm oil at 700 ℃ by using ferrocene as a catalyst, and growing the oriented carbon nano tubes with the tube diameter of 50-100nm and the tube diameter of 300nm on a silicon (100) substrate. The Mukul Kumar uses high-content silicon molecular sieve to load Fe-Co, and makes it implement catalytic pyrolysis at 600-700 deg.C to make plant carbohydrate camphor, so that it can grow into uniform CNTs whose pipe diameter is about 10nm, when the temperature is raised to 850-900 deg.C, the SWCNTs content in the sample is up to 30wt%, and its diameter is 0.86-1.23nm, and the transmission electron microscope and Raman spectrum characterization show that the CNTs grown by camphor have good field emission property.
At present, coal tar pitch is mainly used as engineering material, and is not well utilized comprehensively at high value, so that high-quality resources are wasted seriously; although coal tar pitch often contains hydrogen and oxygen elements, which are not essential elements for generating CNTs, many studies show that the presence of the hydrogen and oxygen elements is beneficial to the formation of CNTs, and no additional hydrogen is required to be input into a pyrolysis atmosphere, so that the coal tar pitch is one of the advantages of the coal tar pitch as a carbon source material. Meanwhile, researches show that the CNTs manufactured by using the pitch as a carbon source have the advantages of higher activity and the like, which are two advantages of using the coal tar pitch as a carbon material. However, the direct coal growth CNTs do not accord with the quality-dividing, environment-friendly and green sustainable development concept, but the research on the coal tar pitch growth CNTs by an in-situ pyrolysis method is reported in a few cases, and many theoretical and practical problems are to be developed and perfected.
Disclosure of Invention
In order to solve the defects, the invention provides a method for preparing the carbon nanotubes by using the coal tar pitch in-situ pyrolysis method, which can provide a beneficial way for preparing high-quality CNTs from the green and environment-friendly low-cost coal tar pitch, improve the CNTs production effect and save the production cost.
In a first aspect, a method for preparing carbon nanotubes by in situ pyrolysis of coal tar pitch comprises the steps of: 1) Ball milling and crushing coal tar pitch, placing in an oven, drying at 130-150 ℃ for 2.5-3.5h, naturally cooling, and sieving with 100 meshes; 2) Adding nickel acetate absolute ethanol solutionAdding coal tar pitch, ultrasonic treating for 20-40min, drying in a constant temperature water bath at 75deg.C for 2-4 hr, grinding, placing into crucible, placing into temperature-controlled tube furnace, and heating at flow rate of 40-60mL/min N 2 Heating to a preset temperature at a speed of 1.5-2.5 ℃/min under the atmosphere, preserving heat for 1.5-3h, and cooling to room temperature to obtain CNTs samples; wherein the preset temperature is 850-1000 ℃.
In one embodiment of the invention, the weight ratio between the nickel acetate and the coal tar pitch is (0.75-3): (99.25-97).
In one embodiment of the invention, the mass fraction of the nickel acetate in the metal absolute ethyl alcohol solution is 20% -30%.
In one embodiment of the present invention, the preset temperature is 900-950 ℃.
In a second aspect, the present invention provides a carbon nanotube obtained by the method for preparing a carbon nanotube by the coal tar pitch in-situ pyrolysis method.
In summary, the invention provides a method for preparing carbon nanotubes by a coal tar pitch in-situ pyrolysis method, which has the following beneficial effects:
according to the invention, CNTs can be obtained by mixing the nickel salt precursor with the coal tar pitch under a high temperature condition, nickel acetate is an effective catalyst precursor for pyrolysis of the coal tar pitch to form CNTs, and the nickel acetate is a proper temperature range for growing CNTs within a temperature range of 900-950 ℃; when the nickel acetate content is less than 1%, CNTs production increases with increasing Ni content; the prolongation of pyrolysis time is favorable for generating CNTs with larger length-diameter ratio, and the maximum length-diameter ratio is up to 5650; the top and bottom growth mechanisms coexist in the pyrolysis growth CNTs process. The invention can provide a beneficial way for preparing high-quality CNTs from green, environment-friendly and low-cost coal tar pitch, improves the CNTs production effect and saves the production cost.
Drawings
Fig. 1 is an SEM image of coal tar pitch growth CNTs samples in the presence of the three catalysts comprising iron, cobalt, nickel in examples 1 to 3.
Figure 2 is an XRD and Raman plot of samples of coal tar pitch grown CNTs in the presence of the nickel-containing catalyst of example 1.
FIG. 3 is an SEM photograph of corresponding CNTs samples obtained for Ni-catalyzed pitch of examples 1, 4-6 at a temperature of 50℃per increase in the range of 850-1000 ℃; wherein, fig. 3a:850 ℃; fig. 3b:900 ℃; fig. 3c:950 ℃; fig. 3d:1000 ℃.
FIG. 4 is a thermal decomposition DTG/T plot in air of four CNTs samples obtained in examples 1, 4 to 6.
FIG. 5 is a Raman diagram and I of four CNTs samples obtained in examples 1, 4 to 6 D1 /I G A drawing.
FIG. 6 is an SEM image of four samples of CNTs obtained as a function of pyrolysis time for examples 1,7 to 9; wherein, fig. 6a: for 90min; fig. 6b:120min; fig. 6c:140min; fig. 6d:180min.
Fig. 7 is an XRD pattern of four CNTs samples obtained in examples 1, 4 to 6.
FIG. 8 is an SEM image of CNTs samples obtained with different amounts of nickel catalyst added.
FIG. 9 is a transmission plot of CNTs samples obtained with a nickel addition of 0.75% and a pyrolysis temperature of 950℃and a pyrolysis time of 2 h.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, based on the embodiments of the invention, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the invention. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, based on the embodiments of the invention, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the invention.
The invention provides a method for preparing carbon nanotubes by a coal tar pitch in-situ pyrolysis method, which comprises the following steps:
1) Raw material and reagent preparation
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
2) Adding coal tar pitch into nickel acetate absolute ethanol solution (mass fraction is 20% -30%), performing ultrasonic treatment for 20-40min, drying in a constant-temperature water bath at 75deg.C for 2-4h, grinding, placing into crucible, placing into a temperature-controlled tube furnace, and heating at flow rate of 40-60mL/min N 2 Heating to a preset temperature at a speed of 1.5-2.5 ℃/min under the atmosphere, and preserving heat until the furnace temperature is reduced to room temperature to obtain a CNTs sample.
Wherein the preset temperature is 850-1000 ℃. Further preferably, the preset temperature is 900-950 ℃. In an embodiment, the preset temperature is 850 ℃, 900 ℃, 950 ℃, 1000 ℃.
The weight ratio of the nickel acetate to the coal tar pitch is (0.25-3): (99.25-97). In the embodiment, the weight ratio between the nickel acetate and the coal tar pitch is selected to be 0.75:99.25,1.5:98.5,2.26:96.74,3:97.
the mass fraction of nickel acetate in the metal absolute ethyl alcohol solution is 20% -30%, and in an embodiment, the mass fraction of nickel acetate in the metal absolute ethyl alcohol solution is 20%.
The incubation time is 1.5-3 hours, and more preferably, the incubation time is 2-2.5 hours. In the embodiment, the heat preservation time is 90min,120min,140min and 180min.
Further, to select the catalyst, two comparative experiments were performed by adding cobalt acetate, ferric chloride instead of nickel acetate under the same conditions. In the comparative test, the weight of the cobalt acetate accounts for 0.75 percent of the sum of the cobalt acetate and the coal tar pitch; the weight of ferric chloride is 0.75% of the sum of ferric chloride and coal tar pitch.
The following is a description of specific examples.
Example 1
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of the nickel acetate absolute ethanol solution is 20%) for 30min by ultrasound, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a solution of 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 2
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of cobalt acetate absolute ethanol solution (the mass fraction of cobalt acetate in the cobalt acetate absolute ethanol solution is 20 percent) for ultrasonic treatment for 30min, drying for 3 hours in a constant-temperature water bath kettle at 75 ℃, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at a concentration of 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 3
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of ferric chloride absolute ethanol solution (the iron chloride weight fraction in the ferric chloride absolute ethanol solution is 20 percent), ultrasonically drying for 3 hours in a constant-temperature water bath kettle at 75 ℃, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at a concentration of 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 4
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at 50mL/min N 2 Heating to a preset temperature of 850 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 5
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at 50mL/min N 2 Heating to a preset temperature of 950 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 6
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at 50mL/min N 2 Heating to a preset temperature of 1000 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 7
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: to a solution of 3.75 parts by weight of nickel acetate in absolute ethanol(20% of nickel acetate mass fraction in nickel acetate absolute ethanol solution) adding 99.25 parts of coal tar pitch, performing ultrasonic treatment for 30min, drying in a constant-temperature water bath at 75deg.C for 3 hr, grinding, placing into a corundum crucible, placing into a temperature-controlled tube furnace, and adding into a solution of 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 90min, and cooling to room temperature to obtain the target CNTs sample.
Example 8
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 140min, and cooling to room temperature to obtain the target CNTs sample.
Example 9
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 99.25 parts of coal tar pitch into 3.75 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, and placing into a corundum crucibleFeeding into a temperature-controlled tube furnace, and heating at 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 180min, and cooling to room temperature to obtain the target CNTs sample.
Example 10
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 98.5 parts of coal tar pitch into 7.5 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 11
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 96.74 parts of coal tar pitch into 11.3 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3 hours, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Example 12
1. Raw materials and reagents
Coal tar pitch (CP) is provided by the elm market coal chemical industry upgrade technology development center. The coal tar pitch is not pretreated, ball-milled and crushed, then placed in an oven to be dried for 3 hours at 130 ℃, naturally cooled, screened by 100 meshes and sealed in a wide-mouth bottle for Standby (SCP). The other chemicals used were all analytically pure and purchased from the company Miou chemical reagent Co., tianjin.
CNTs preparation: adding 97 parts of coal tar pitch into 15 parts (weight parts) of nickel acetate absolute ethanol solution (the mass fraction of nickel acetate in the nickel acetate absolute ethanol solution is 20%) for ultrasonic treatment for 30min, drying in a constant-temperature water bath kettle at 75 ℃ for 3h, grinding and placing into a corundum crucible, placing into a temperature-controlled tubular furnace, and adding into a stirring tank at a concentration of 50mL/min N 2 Heating to a preset temperature of 900 ℃ at a speed of 2 ℃/min under the atmosphere, preserving heat for 2 hours, and cooling to room temperature to obtain the target CNTs sample.
Results and discussion
Composition and structural characterization: testing the target CNTs sample obtained in each example, and tracking the asphalt decomposition process by a thermogravimetric analyzer (TG-MS, NETZSCH, germany) and measuring the CNTs content in the sample; carrying out phase composition analysis on the sample by adopting an X' pertpro X-ray diffraction (XRD, netherlands); the degree of graphitization of the sample was characterized by a French Horiba Jobin-Yvon Labram-HR800 laser confocal Raman spectrometer (using a helium-neon laser generator, excitation wavelength 534 nm). The microscopic morphology and structure of the product was examined using a Nova400 Nano-type field emission Scanning Electron Microscope (SEM) and a JEM-2100UHR high resolution transmission electron microscope (FEI G2F 20).
1.1 selection of catalysts
When CNTs are produced by an arc method or a plasma method, CNTs can be grown without adding any catalyst at high temperature, but the key of whether CNTs can be grown by a catalytic pyrolysis method (CT) is closely related to the catalyst. For this reason, the present study was pyrolyzed at 900 ℃ for 2 hours, and examined the effect of coal tar pitch growth CNTs in the presence of three catalysts commonly used for transition metals including Fe, co, ni, etc., and SEM results of the corresponding samples are shown in fig. 1. From Co-and Fe-containing catalystsSEM photographs of the samples obtained with the chemoattractant (fig. 1a, 1b, respectively) showed flat surfaces with no CNTs observed, whereas Ni-catalyzed samples (fig. 1 c) showed clearly visible rod-like products by high magnification scanning electron microscopy, as shown in fig. 2, with corresponding XRD showing 2θ=25.94 ℃ peak and 1600cm in Raman -1 Characteristic peaks are shown, and the samples obtained by Ni catalysis have typical graphite structures, so that the feasibility of preparing CNTs by taking Ni as a catalyst and the rule of influencing products by preparation conditions are further explored.
1.2 Effect of pyrolysis temperature on CNTs formation Performance
1.2.1 Effect of pyrolysis temperature on CNTs morphology and yield
Pyrolysis temperature is a key factor for determining the rate, quality, crystallinity, length/diameter ratio, and number of layers of CNTs, and it can affect the degree of decomposition of carbon source, intermediate matters (C 2 Hy) in the catalyst, the solubility and diffusion rate of the catalyst, the structural state of the catalyst, and the electronic state, ultimately affecting the performance of CNTs. FIG. 3 is an SEM photograph of a corresponding sample obtained in examples 1, 4 to 6 for Ni (0.5%) catalyzed pitch at a temperature of 50℃per increase in 850-1000 ℃. As can be seen, the uniformity of sample formation, length/diameter ratio and distribution increases significantly with increasing temperature. Under the pyrolysis condition of 850 ℃ (figure 3 a), the generated amount is small and short, and more small nano carbon balls can be obviously observed to be connected in series in a high-power enlarged picture to form a bamboos shape. The result is consistent with the appearance of the CNTs prepared by the nickel-based catalyst. Under pyrolysis conditions at 900 ℃ (fig. 3 b), the amount of product increased significantly, giving rise to a certain fibrous product. When the pyrolysis temperature is raised to 950 ℃ (fig. 3 c) and 1000 ℃ (fig. 3 d), the product formation amount is more remarkable and the obvious fiber morphology feature is presented, which is an extremely important parameter for determining the application of the product, and the product is used as an electromagnetic interference shielding material, an invisible material, a hydrogen storage material, an information storage, a catalyst carrier, a flame retardant or an information storage, and the large length-diameter ratio is favorable for enhancing the conductivity, reducing the energy consumption in the transmission process and prolonging the service life. It can be seen that the temperature of the nickel-catalyzed coal tar pitch for CNTs is preferably controlled between 900-950 ℃.
In fact, the products of different morphologies in SEM photographs contain the metal catalyst and the corresponding carbon material. Among these are potentially Amorphous Carbon (AC), short range graphitic structural carbon and CNTs. The pyrolysis temperature of amorphous carbon is lower, typically around 650 ℃, while the crystalline structure of CNTs determines that its thermal stability is higher than amorphous carbon, typically around 750 ℃. FIG. 4 is a graph of the pyrolysis DTG/T of the four samples of FIG. 3 in air. As shown in fig. 4, the sample underwent two distinct weightings at 600-750 ℃ and both peaks moved toward the high temperature direction. It can be determined that the low Wen Shichong peak in FIG. 4 is probably from AC and the high Wen Shichong peak is from CNTs. Here, the area ratio of the two peaks is taken as representing the relative content of the two peaks, S 2 /S 1 The ratio increased from 0.151 at 850 ℃ to 1.19 at 950 ℃ and then decreased to 0.957 at 1000 ℃. I.e., as the temperature increases, the CNTs content of the sample tends to increase and then decrease.
1.2.2 Effect of pyrolysis temperature on CNTs defects
SEM, TG and TEM can represent the morphology, content and other relevant properties of CNTs, but the crystallization degree and defect condition cannot be well illustrated. Raman spectroscopy is an effective means of characterizing CNT defects, and its spectral data is processed by gaussian deconvolution to obtain 5 typical fitted curves. FIG. 5a shows a Roman spectrum of a sample obtained under pyrolysis temperature conditions of 850-1000℃in examples 1, 4 to 6, 1325cm -1 Peak (D) 1 Peak) represents a defect in the lattice of the material, 1592cm -1 The peak (G peak) represents the sp of C 2 Hybrid in-plane stretching vibration, D 4 And D 3 Bits 1189 and 1442, respectively, which indicate that the two peaks contain disordered graphite structure and C aromatic -C alkyl A bond and an aromatic ester. I D1 /I G The ratio indicates the degree of lattice defect of the MWCNT, and the larger the ratio, the more lattice defect of the MWCNT. FIGS. 5b and 5c show the Raman spectra and analysis results of samples at different temperatures in examples 1, 4 to 6, and it can be seen from the figures that the Raman spectra of the samples obtained at four temperatures appear to be 1325cm -1 And 1592cm -1 Two characteristic peaks. Indicating that all four samples had MWCNTs, I D1 /I G Increasing and decreasing with increasing temperature. At 850℃ byAt too low a temperature C 2 Hy has a low molecular weight and does not form ordered SP 2 A carbon atom structure; at 900 ℃, not only I D1 /I G Large and I D1 And I G The absolute intensity of the peak is strongest, and defects in CNTs increase with increasing temperature and high temperature damage.
1.2 mechanism of coal tar pitch growth of CNTs
1.2.1 Effect of catalyst variation on CNTs Performance
Typically, catalytic action is not a catalyst precursor species, but rather nano-sized active elemental particles produced by thermal decomposition thereof. Researches show that when nickel acetate is heated, crystallization water is lost at 118-137 ℃, meanwhile, partial acetic acid groups on the surface are decomposed into substances such as acetic acid and the like, and the solid phase remainder is (1-x) Ni (CH) 3 COO) 2 ·xNi(OH) 2 )(R 1 ) The method comprises the steps of carrying out a first treatment on the surface of the At 330-400 ℃, nickel acetate is pressed according to R 2 -R 5 The reaction proceeds to a final conversion to metallic nickel.
Ni(CH 3 COO) 2 ·4H 2 O＝0.86Ni(CH 3 COO) 2 ·0.14Ni(OH 2 )+0.28CH 3 COOH+3.72H 2 O(R 1 )
It is currently generally accepted that only nano-sized transition metal particles are catalytically active, the size of which determines the diameter of the CNTs, the larger the particles the larger the diameter of the CNTs grown. From the XRD (FIG. 2) characterization, the diameter of the active catalytic particles nickel at different temperatures can be calculated according to the formula Debye-scherer (d (hkl) =kλ/. Beta.cos θ) to be about 0.2nm, and the (111) crystal face is dominant, so that the (111) face of the metallic nickel which may be about 0.2nm is presumed to be catalytic. TEM-mapping (FIG. 9 b) uses nanomeasure software to count about 0.2nm size of dispersed metallic nickel particles, but some nano nickel particles are clustered together to form clusters of tens of nanometers size due to extremely large surface energy and are wrapped in CNTs, so that the inner diameter of CNTs is tens of nanometers, and the sizes of the metallic nickel clusters are different, thereby affecting the thickness and the diameter non-uniformity of CNTs. Instead, the grown CNTs increase in diameter.
1.2.2 influence of catalyst content on CNT
The content, size and microscopic electronic structure state of the catalyst have important influence on CNTs, and the catalyst content is proper to achieve the ideal catalytic effect, namely, the content has a critical value. In general, nano-active particles playing a role in catalysis are generated by thermal decomposition of a catalyst precursor, when the catalyst precursor is lower than a critical value, the yield of CNTs is low due to insufficient active content generated by pyrolysis of the catalyst precursor, and the yield of CNTs is increased along with the increase of the content of the catalyst precursor, but when the catalyst content is higher than the critical value, the catalytic activity is reduced due to accelerated migration and combination of active particles in a pyrolysis state, and the yield of CNTs is reduced. To determine the optimum catalyst addition, the microscopic properties of CNTs of the pyrolysis 2h sample at 900℃were studied in this experiment. Fig. 8 is an SEM image of samples obtained by proportional pyrolysis at 900 ℃ for 2h of different nickel contents, and it can be seen from fig. 8 that no CNTs are generated without catalyst addition, that CNTs are obviously generated when catalyst addition occurs, and that the yield of CNTs increases with increasing catalyst content in the range < 1%.
1.2.3 Effect of pyrolysis time on CNTs
Pyrolysis time may reflect CNTs formation, long pyrolysis time provides sufficient time rearrangement and long length for the C atoms. The longer the pyrolysis time, the greater the aspect ratio of the CNTs and the higher the crystallinity. The effect of different growth times on CNTs in the samples at 900℃was designed for this experiment and the results are shown in FIG. 6. When the growth time is only 90min (fig. 6 a), single carbon sphere or a plurality of carbon spheres with the size of about 200nm are observed to be combined together into a big sphere, and a local place has obvious tendency that a plurality of small spheres are overlapped into a line and are in a typical bamboo shape; when the growth time was extended for 30min (FIG. 6 b), the number of CNTs generated was increased, the length was about 1um, the bamboo-like signs were weakened, the growth time was further extended to 140min (FIG. 6 c), most CNTs were fully grown and matured, and not only the CNTs generated were dense but also the tubes were elongated, and when the growth time was 180min, the CNTs generated were as long as millimeter scale, but a sharp decrease in CNTs density could be observed.
Catalytic pyrolysis methodThe essential process of growing CNTs is: when the temperature of the system rises to a certain extent, the catalyst precursor is reduced to particles (R 1 ) At the same time, chemical bonds such as C-C, C-O, C-H and the like in the carbon source substances are broken by heating and decomposed into micromolecules C 2 Hy, these small molecules adsorb on the surface of the active catalyst and dissolve, precipitate from the other side of the catalyst when the carbon content reaches saturation, and are reduced (R 2 ，R 3 ) CNTs are produced by structural reforming. Pyrolysis temperature is the most critical factor in the ability to produce CNTs and in its performance. When the temperature is too low, the pyrolysis speed of the carbon source substance is too slow, C 2 Since the concentration of Hy is small, the CNTs can be easily blocked and the growth is stopped, CNTs grown at a low temperature are generally short, and the amount of CNTs grown at 850 ℃ and 900 ℃ is small. When the temperature is increased, the asphalt and the catalyst precursor acquire enough energy to be fully decomposed, C 2 The solubility of Hy molecules in the active catalyst is increased, the diffusion is accelerated, and the CNTs yield is increased suddenly and simultaneously is long.
Ni(CH 3 COOH) 2 →NiO→Ni R 1
C 2 H 2 +CO 2 →2C+H 2 O+CO R 2
C 2 H 2 +CO 2 →2C+H 2 +2CO R 3
Fig. 9 is a transmission diagram of the sample. As can be seen from the graph, CNTs have nonuniform diameters, but are all in a nanoscale range, the tube wall thickness is about 10nm, each layer is almost not broken and cracked near the 2/3 part of the inner wall, the arrangement is quite regular, the interplanar spacing is 0.33nm, the layer spacing is uniform and is close to 0.338nm of graphene, the continuity of the layers is weakened near the part of the outer wall, the arrangement of the layers is slightly misplaced, and the carbon tube is firstly grown from the inside, and then the outer layer grows layer by layer. FIGS. 9a and 9d show that one end of CNTs is open, indicating growth into WMCNTs through the bottom end. While fig. 9b shows that the nano nickel particle clusters are wrapped in the CNT and located at the top, indicating that the CNT grows following the growth of nano Ni particles, following the top growth mechanism, it can be considered that coal tar pitch grows both at the bottom and at the top during the growth of CNT by nickel catalytic pyrolysis. Due to steric hindrance, CNTs are straighter in the short range, become curved and grow dendritic in the long range.
The reduction in carbon nanotube growth sites at high temperatures is indicative of catalyst deactivation, which may be due to: (1) the combined growth of nano nickel particles weakens the catalytic activity; (2) The nano nickel particle clusters are wrapped by the carbon layer, so that the decomposition of the coal tar pitch, the deactivation of the catalyst and the stop growth of the CNTs are inhibited; (3) CO generated by thermal decomposition of the carbon source material reacts with metallic nickel to generate tetra-carbonyl compound (R) 4 )。
In summary, nickel acetate, which is an effective catalyst precursor for pyrolysis of coal tar pitch to form CNTs, can be obtained from a mixture of nickel acetate and coal tar pitch at high temperature. Is a suitable temperature range for growing CNTs within the temperature range of 900-950 ℃; when the nickel acetate content is less than 1%, CNTs production increases with increasing Ni content; the prolongation of pyrolysis time is favorable for generating CNTs with larger length-diameter ratio, and the maximum length-diameter ratio is up to 5650; the top and bottom growth mechanisms coexist in the pyrolysis growth CNTs process. The invention can provide a beneficial way for preparing high-quality WMCNTs from green, environment-friendly and low-cost coal tar pitch, improves the CNTs production effect and saves the production cost.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (3)

1. The method for preparing the carbon nano tube by the coal tar pitch in-situ pyrolysis method is characterized by comprising the following steps of:
1) Ball milling and crushing coal tar pitch, placing in an oven, drying at 130-150 ℃ for 2.5-3.5h, naturally cooling, and sieving with 100 meshes;
2) Adding coal tar pitch into nickel acetate absolute ethanol solution, performing ultrasonic treatment for 20-40min, drying in a constant-temperature water bath at 75deg.C for 2-4h, grinding, placing into crucible, placing into a temperature-controlled tube furnace, and heating at flow rate of 40-60mL/min N 2 Heating to a preset temperature at a speed of 1.5-2.5 deg.C/min under atmosphere and keepingHeating for 1.5-3h, and cooling to room temperature to obtain CNTs sample; wherein the preset temperature is 850-1000 ℃; the weight ratio of the nickel acetate to the coal tar pitch is (0.75-3): (99.25-97); the mass fraction of the nickel acetate in the nickel acetate absolute ethyl alcohol solution is 20% -30%.
2. The method for preparing carbon nanotubes by the in situ pyrolysis of coal tar pitch according to claim 1, wherein the preset temperature is 900-950 ℃.
3. A carbon nanotube obtained by the method for preparing a carbon nanotube by the coal tar pitch in situ pyrolysis method of any one of claims 1 to 2.
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