CN113511645B - Method for preparing carbon nano tube - Google Patents

Method for preparing carbon nano tube Download PDF

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CN113511645B
CN113511645B CN202110370018.0A CN202110370018A CN113511645B CN 113511645 B CN113511645 B CN 113511645B CN 202110370018 A CN202110370018 A CN 202110370018A CN 113511645 B CN113511645 B CN 113511645B
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separation
solid
solution
acid
washing
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CN113511645A (en
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马伟斌
张权
杨锦
张洋岳
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Jiaozuo Jiyue Nano Material Technology Co ltd
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Jiaozuo Jiyue Nano Material Technology Co ltd
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    • C—CHEMISTRY; METALLURGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Abstract

The invention relates toThe technical field of carbon nanotube preparation, and discloses a preparation method of a carbon nanotube, which comprises the following steps: the catalyst precursor Fe 3 O 4 @NiFe‑LDH、Fe 3 O 4 @ CoFe-LDH or Fe 3 O 4 The @ CoFeNi-LDH is placed in a vacuum tube furnace and is reduced in a reducing atmosphere to obtain a catalyst; introducing carbon source gas and hydrogen gas to carry out cracking reaction to obtain a solid material containing carbon nano tubes; carrying out multi-step treatment such as primary acid washing on the solid material, mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, carrying out tertiary ultrasonic dispersion, and then carrying out centrifugal separation to obtain the quintic separation liquid and the quintic separation solid; and (4) performing microporous filtration on the five times of separated liquid under ultrasonic oscillation, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The carbon nano tube prepared by the preparation method has high yield and high purity.

Description

Method for preparing carbon nano tube
Technical Field
The invention belongs to the technical field of carbon nanotube preparation, and particularly relates to a preparation method of a carbon nanotube.
Background
Carbon Nanotubes (CNTs) are a hollow tubular structure made of carbon elements, also known as buckytubes, which are one-dimensional quantum materials with special structures (diameters between a few nanometers to tens of nanometers, lengths up to several micrometers, and substantially sealed ends at both ends of the tube).
The carbon nano tube is used as a one-dimensional nano material, has light weight, perfect connection of a hexagonal structure, and has a plurality of excellent mechanical, electrical and chemical properties: 1) Mechanical properties: the tensile strength of the carbon nano tube reaches 50-200 GPa, which is 100 times of that of steel, the density is only 1/6 of that of the steel, the hardness is equivalent to that of diamond, and the carbon nano tube has good flexibility and stretchability, the length-diameter ratio is generally above 1000: 1, and is an ideal high-strength fiber material; 2) Electrical properties: the carbon nano tube has the same structure as the graphite sheet structure, so the carbon nano tube has good electrical property; 3) Thermal properties: the carbon nano tube has very large length-diameter ratio, so the heat exchange performance along the length direction is very high, the carbon nano tube can synthesize a heat conduction material with high anisotropy through proper orientation, and in addition, the carbon nano tube has higher heat conductivity, so the heat conductivity of the composite material can be greatly improved. Besides, the carbon nano tube has other good performances such as optics, hydrogen storage and the like, and the excellent performances enable the carbon nano tube to be considered as an ideal reinforcing material of the polymer composite material.
In view of the excellent physicochemical and mechanical properties of carbon nanotubes, great potential application values are receiving wide attention. The application research of the carbon nano tube mainly focuses on the fields of composite materials, hydrogen storage, electronic devices, batteries, super capacitors, field emission displays, quantum wire template electron guns, sensors, microscope probes and the like.
The preparation method of the carbon nano tube comprises the following steps: an arc method, a Chemical Vapor Deposition (CVD) method, a catalytic thermal decomposition method, a hydrothermal method, and the like, wherein the CVD method has advantages of low cost, convenient operation, and the like, and has been widely used for the preparation of CNTs. In the process of preparing the CNT, the catalyst with better performance is selected, so that the yield of the carbon nano tube can be improved.
Disclosure of Invention
In view of the above-mentioned situation existing in the prior art, the present invention aims to provide a method for preparing carbon nanotubes by selecting magnetic material Fe 3 O 4 The catalyst prepared by combining the hydrotalcite can improve the yield of the carbon nano tube and is convenient for solid-liquid separation in the purification process of the carbon nano tube.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a first aspect of the present invention provides a method for preparing a carbon nanotube, the method comprising the steps of:
1) The catalyst precursor Fe 3 O 4 @NiFe-LDH、Fe 3 O 4 @ CoFe-LDH or Fe 3 O 4 @ CoFeNi-LDH is placed in a vacuum tube furnace and is reduced in a reducing atmosphere to obtain a catalyst;
2) Introducing carbon source gas and hydrogen gas at the temperature of 500-800 ℃ to carry out cracking reaction to obtain a solid material containing carbon nano tubes;
3) Carrying out primary acid washing on the solid material obtained in the step 2), and then carrying out permanent magnet separation to obtain primary separated liquid and primary separated solid;
4) Performing primary ultrasonic dispersion on the primary separated solid, and then performing permanent magnet separation to obtain secondary separated liquid and secondary separated solid;
5) Carrying out secondary acid washing on the secondary separated solid, and then carrying out permanent magnet separation to obtain a tertiary separated liquid and a tertiary separated solid;
6) Performing secondary ultrasonic dispersion on the third separation solid, and then performing permanent magnet separation to obtain fourth separation liquid and fourth separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, performing tertiary ultrasonic dispersion, and performing centrifugal separation to obtain a fifth separation liquid and a fifth separation solid;
8) And (4) performing microporous filtration on the five times of separated liquid under ultrasonic oscillation, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube.
In the present invention, the catalyst precursor Fe 3 O 4 The preparation of @ NiFe-LDH includes: preparation of Fe 3 O 4 A magnetic core; mixing Fe 3 O 4 Magnetic nuclei are dispersed in methanol, the Fe 3 O 4 The mass ratio of the sodium hydroxide to the methanol is 2.5-5 g: 1L, salt solution and alkali solution are simultaneously dripped into the solution under stirring, the salt solution is mixed solution of nickel nitrate and ferric nitrate, the molar ratio of the nickel nitrate to the ferric nitrate is 1-3: 1, the solvent of the salt solution is mixed solvent of methanol and water, the volume ratio of the methanol to the water is 1: 19, the total concentration of cations in the salt solution is 0.1mol/L, the alkali solution is mixed solution of sodium hydroxide and sodium carbonate, the concentration of the sodium hydroxide in the alkali solution is 0.1mol/L, the concentration of the sodium carbonate in the alkali solution is 0.2mol/L, and Fe is added into the solution 3 O 4 The mol ratio of the nickel nitrate to the nickel nitrate is 1: 5, the temperature is controlled to be 60 ℃ and the pH value is 8-9 in the dripping process, the crystallization is continued for 36 hours after the salt solution is dripped, the permanent magnet is adopted for separation, and then CO is removed 2 Washing with deionized water for three times, separating with permanent magnet during washing, drying the obtained solid at 65 deg.C for 24 hr to obtain Fe 3 O 4 @NiFe-LDH。
According to the invention, the catalyst precursor Fe 3 O 4 The preparation of @ CoFe-LDH includes: preparation of Fe 3 O 4 A magnetic core; mixing Fe 3 O 4 Magnetic nuclei are dispersed in methanol, the Fe 3 O 4 The mass ratio of the sodium hydroxide to the methanol is 2.5-5 g: 1L, salt solution and alkali solution are simultaneously dripped into the solution under stirring, the salt solution is mixed solution of cobalt nitrate and ferric nitrate, the molar ratio of the cobalt nitrate to the ferric nitrate is 2-5: 1, the solvent of the salt solution is mixed solvent of methanol and water, the volume ratio of the methanol to the water is 1: 19, the total concentration of cations in the salt solution is 0.1mol/L, the alkali solution is mixed solution of sodium hydroxide and sodium carbonate, the concentration of the sodium hydroxide in the alkali solution is 0.1mol/L, the concentration of the sodium carbonate in the alkali solution is 0.2mol/L, and Fe is added into the solution 3 O 4 The mol ratio of the cobalt salt to the solution is 1: 5, the temperature is controlled at 70 ℃ and the pH value is 8-8.5 in the dripping process, crystallization is continued for 36 hours after the salt solution is dripped, permanent magnet is adopted for separation, and CO is removed 2 Washing with deionized water for three times, separating with permanent magnet during washing, drying the obtained solid at 65 deg.C for 24 hr to obtain Fe 3 O 4 @CoFe-LDH。
In the present invention, the catalyst precursor Fe 3 O 4 The preparation of @ CoFeNi-LDH includes: preparation of Fe 3 O 4 A magnetic core; mixing Fe 3 O 4 Magnetic nuclei are dispersed in methanol, the Fe 3 O 4 The mass ratio of the sodium hydroxide to the methanol is 2.5-5 g: 1L, a salt solution and an alkali solution are simultaneously dripped into the mixed solution under stirring, the salt solution is a mixed solution of cobalt nitrate, nickel nitrate and ferric nitrate, the molar ratio of the cobalt nitrate, the ferric nitrate and the nickel nitrate is 6: 3: 1, the solvent of the salt solution is a mixed solvent of methanol and water, the volume ratio of the methanol to the water is 1: 19, the total concentration of cations in the salt solution is 0.1mol/L, the alkali solution is a mixed solution of sodium hydroxide and sodium carbonate, the concentration of the sodium hydroxide in the alkali solution is 0.1mol/L, and the concentration of the sodium carbonate in the alkali solution is 0.2mol/L; fe 3 O 4 The mol ratio of the cobalt salt to the total amount of the nickel salt is 1: 5, the temperature is controlled to be 60 ℃ and the pH value is 10.5 in the dripping process, the crystallization is continued for 36 hours after the dripping of the salt solution is finished, a permanent magnet is adopted for separation, and then CO is removed 2 Washing with deionized water for three times, wherein permanent magnet is adopted in the washing processSeparating, drying the obtained solid at 65 ℃ for 24 hours to obtain Fe 3 O 4 @CoFeNi-LDH。
In the present invention, fe 3 O 4 The magnetic core may be prepared by methods conventional in the art. Preferably, fe is prepared 3 O 4 The magnetic core comprises: dissolving ferric trichloride solution with the molar concentration of 0.1mol/L and sodium acetate in ethylene glycol to form solution, wherein the molar ratio of ferric trichloride to sodium acetate is 1: 5, the ratio of the amount of ferric trichloride to the volume of ethylene glycol is 1 mol: 10L, carrying out crystallization reaction on the solution at 200 ℃ for 8 hours, cooling a reaction product to 10-30 ℃, then respectively washing the reaction product with ethanol and deionized water for 2-3 times, simultaneously separating by adopting a permanent magnet in the washing process, separating to obtain a solid, drying the solid at 65 ℃ for 24 hours, and grinding to obtain Fe 3 O 4 A magnetic core.
Fe prepared by the method of the invention 3 O 4 The magnetic core has good spherical appearance and strong magnetism. The invention is realized by adding Fe 3 O 4 NiFe-LDH, coFe-LDH and CoFeNi-LDH are coated and grown on the magnetic core, so that on one hand, the surface area of the carrier can be increased, and the dispersity of the active center is improved, thereby improving the activity of the catalyst; on the other hand, each hydrotalcite contains ions capable of serving as active centers, so that the hydrotalcite has high activity, and each ion also has magnetism and is Fe 3 O 4 The combined action is beneficial to the solid-liquid separation in the purification process of the carbon nano tube.
Preferably, in the step 1), the reducing atmosphere is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 1-20, and the reduction space velocity is 0.1-0.2hr -1 (mass space velocity: mass ratio of reducing gas to catalyst precursor), the reduction temperature is 500-800 ℃.
Preferably, in the step 2), the carbon source gas is methane, ethylene or propylene, and the flow ratio of the carbon source gas to the hydrogen gas is 1: 1-6: 1; the flow rate of the carbon source gas is 0.1-1m per gram of the catalyst precursor 3 H; the time of the cracking reaction is 20-60min.
Preferably, the conditions of the primary pickling and the secondary pickling comprise: the method comprises the steps of carrying out acid washing by using a mixed acid solution of nitric acid and hydrochloric acid, wherein the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 2M-5M, the concentration of the hydrochloric acid is 2M-8M, the volume ratio of the mass of the solid material or the secondary separation solid to the mixed acid solution is 1g/50-200mL, dispersing the solid material or the secondary separation solid in the mixed acid solution, and refluxing for 0.5-2h.
In the invention, the conditions of the primary ultrasonic dispersion and the secondary ultrasonic dispersion comprise: dispersing the first separation solid or the third separation solid in deionized water, and performing ultrasonic treatment for 15-50min;
the third ultrasonic dispersion is to directly carry out ultrasonic treatment on the mixed liquid for 15-50min.
Preferably, the pore size of the filter membrane used for microfiltration is 0.2 to 1 μm.
The method adopts the combination of primary acid washing, primary ultrasonic dispersion, secondary acid washing, secondary ultrasonic dispersion, tertiary ultrasonic dispersion and microporous filtration to purify the carbon nano tube, can dissolve reduced metal and remove carbon covering the surface of the carbon nano tube through simple acid washing and ultrasonic dispersion, can separate the carbon nano tube from an undissolved carrier, can separate the carrier from liquid through permanent magnet separation, and is simple and convenient to operate, and can remove carbon on the surface of the carbon nano tube through the tertiary ultrasonic dispersion and then separate the carbon nano tube through the microporous filtration, thereby improving the yield and the purity of the carbon nano tube. The purification steps of the invention are simple and convenient to operate, and particularly, the operation is simpler by carrying out solid-liquid separation by virtue of magnetism.
The parameters which are not limited in the invention are the conventional parameters in the prior art.
The preparation method of the invention adopts specific catalyst, the catalyst activity is high, the yield of the prepared carbon nano tube is high, in addition, in the purification process of the carbon nano tube, the magnetism of the catalyst is utilized, the solid-liquid separation is convenient, and the purity of the obtained carbon nano tube is high.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, belong to the scope of the present invention.
Example 1
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 3 times respectively, separating the reaction product by using a permanent magnet in the washing process, drying the reaction product for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction product to obtain Fe 3 O 4 A magnetic core; 0.87g of Fe to be obtained 3 O 4 Ultrasonic dispersing magnetic core in 200mL methanol, adding salt solution and alkali solution dropwise while stirring, wherein the salt solution is prepared by adding 5.45g Ni (NO) 3 ) 2 ·6H 2 O and 2.53gFe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature at 60 ℃ and the pH value at 8.5 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, separating by using a permanent magnet, and removing CO by using a CO removing method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ NiFe-LDH; mixing Fe 3 O 4 The @ NiFe-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 10, and the reduction space velocity is 0.1hr -1 And the reduction temperature is 600 ℃, thus obtaining the catalyst.
2) Introducing methane and hydrogen at the temperature of 600 ℃ to carry out cracking reaction, wherein the flow ratio of the methane to the hydrogen is 1: 1; the flow rate of methane per gram of catalyst precursor was 0.2m 3 /h；The time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 4M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/100mL, the solid material is dispersed in the mixed acid liquor, refluxing is carried out for 1h, and then permanent magnet separation is carried out, so that primary separation liquid and primary separation solid are obtained.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by adopting mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 4M, the mass of the secondary separation solid and the volume ratio of the mixed acid liquor is 1g/100mL, the secondary separation solid is dispersed in the mixed acid liquor and refluxed for 1h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Example 2
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 3 times respectively, separating the reaction product by using a permanent magnet in the washing process, drying the reaction product for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction product to obtain Fe 3 O 4 A magnetic core; 0.77g of Fe to be obtained 3 O 4 The magnetic core was ultrasonically dispersed in 200mL of methanol, and a salt solution prepared by adding 4.85g of Ni (NO) and an alkali solution to the mixture simultaneously dropwise under stirring 3 ) 2 ·6H 2 O and 3.37g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare 250mL of salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare the mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature to be 60 ℃ and the pH value to be 8.5 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, separating by adopting a permanent magnet, and removing CO by adopting a CO removing method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ NiFe-LDH; mixing Fe 3 O 4 The @ NiFe-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 20, and the reduction space velocity is 0.2hr -1 The reduction temperature is 650 ℃, and the catalyst is obtained.
2) Introducing methane and hydrogen for cracking reaction at 650 ℃, wherein the flow ratio of the methane to the hydrogen is 1: 1; the flow rate of methane per gram of catalyst precursor was 0.2m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: the method comprises the steps of carrying out acid washing by using a mixed acid solution of nitric acid and hydrochloric acid, wherein the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 4M, the volume ratio of the mass of a solid material to the volume of the mixed acid solution is 1g/100mL, dispersing the solid material in the mixed acid solution, refluxing for 1h, and then carrying out permanent magnet separation to obtain a primary separation liquid and a primary separation solid.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 4M, the mass ratio of the secondary separation solid to the volume ratio of the mixed acid liquor is 1g/100mL, the secondary separation solid is dispersed in the mixed acid liquor and refluxed for 1h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, separating by a permanent magnet to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Example 3
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 20 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 3 times respectively, separating the reaction kettle with a permanent magnet during washing, drying the reaction kettle for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction kettle to obtain Fe 3 O 4 A magnetic core; 0.58g of Fe to be obtained 3 O 4 The magnetic nuclei were ultrasonically dispersed in 200mL of methanol, and a salt solution prepared by adding 3.63g of Ni (NO) and an alkali solution simultaneously dropwise thereto under stirring 3 ) 2 ·6H 2 O and 5.05g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare 250mL of salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare the mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature to be 60 ℃ and the pH value to be 9 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, separating by adopting a permanent magnet, and removing CO by adopting a CO removing method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ NiFe-LDH; mixing Fe 3 O 4 The @ NiFe-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere, the reducing atmosphere is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 1, and the reduction space velocity is 0.15hr -1 And the reduction temperature is 700 ℃, thus obtaining the catalyst.
2) Introducing methane and hydrogen for cracking reaction at 650 ℃, wherein the flow ratio of the methane to the hydrogen is 1: 1; the flow rate of methane per gram of catalyst precursor was 0.2m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 4M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/100mL, the solid material is dispersed in the mixed acid liquor, refluxing is carried out for 1h, and then permanent magnet separation is carried out, so that primary separation liquid and primary separation solid are obtained.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: the method comprises the steps of carrying out acid washing by using a mixed acid solution of nitric acid and hydrochloric acid, wherein the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 4M, the volume ratio of the mass of the secondary separation solid to the volume of the mixed acid solution is 1g/100mL, dispersing the secondary separation solid in the mixed acid solution, refluxing for 1h, and then carrying out permanent magnet separation to obtain a tertiary separation liquid and a tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, separating by a permanent magnet to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a fifth separation liquid and a fifth separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
Example 4
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Made of O0.1mol/L ferric trichloride solution, adding 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 2 times respectively, separating the reaction kettle by using a permanent magnet in the washing process, drying the reaction kettle for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction kettle to obtain Fe 3 O 4 A magnetic core; 0.77g of Fe to be obtained 3 O 4 Ultrasonic dispersing magnetic core in 200mL methanol, adding salt solution and alkali solution dropwise while stirring, wherein the salt solution is prepared by adding 4.85g Co (NO) in the solution 3 ) 2 ·6H 2 O and 3.37g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature to be 70 ℃ and the pH value to be 8 in the dropping process, continuing crystallizing for 36h after the dropping of the salt solution is finished, separating by using a permanent magnet, and removing CO by using a CO removal method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ CoFe-LDH; mixing Fe 3 O 4 The @ CoFe-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 1, and the reduction space velocity is 0.1hr -1 And the reduction temperature is 700 ℃, thus obtaining the catalyst.
2) Introducing ethylene and hydrogen at the temperature of 700 ℃ to carry out cracking reaction, wherein the flow ratio of the ethylene to the hydrogen is 2: 1; the ethylene flow rate was 0.1m per gram of procatalyst 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M, the concentration of hydrochloric acid is 5M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/150mL, the solid material is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain primary separation liquid and primary separation solid.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 35min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by adopting mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 2M, the concentration of the hydrochloric acid is 5M, the mass of the secondary separation solid and the volume ratio of the mixed acid liquor is 1g/150mL, the secondary separation solid is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 35min; then, separating by a permanent magnet to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a fifth separation liquid and a fifth separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Example 5
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 O dissolved in 320mL of ethylene glycolTransferring the solution into a 500mL reaction kettle, performing crystallization reaction at 200 ℃ for 8h, cooling the reaction kettle in water bath to 30 ℃, washing with ethanol and deionized water for 3 times respectively, separating by using a permanent magnet in the washing process, drying in a vacuum drying oven at 65 ℃ for 24h, and grinding to obtain Fe 3 O 4 A magnetic core; 0.87g of Fe to be obtained 3 O 4 The magnetic core was ultrasonically dispersed in 200mL of methanol, and a salt solution prepared by adding 5.46g of Co (NO) and an alkali solution to the mixture simultaneously dropwise under stirring 3 ) 2 ·6H 2 O and 2.53g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature at 70 ℃ and the pH value at 8.2 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, separating by using a permanent magnet, and removing CO by using a CO removing method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ CoFe-LDH; mixing Fe 3 O 4 The @ CoFe-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 10, and the reduction space velocity is 0.2hr -1 And the reduction temperature is 750 ℃, thus obtaining the catalyst.
2) Introducing ethylene and hydrogen at the temperature of 700 ℃ to carry out cracking reaction, wherein the flow ratio of the ethylene to the hydrogen is 2: 1; the flow rate of ethylene per gram of procatalyst was 0.1m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M, the concentration of hydrochloric acid is 5M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/150mL, the solid material is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain primary separation liquid and primary separation solid.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 35min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by adopting mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 2M, the concentration of the hydrochloric acid is 5M, the mass of the secondary separation solid and the volume ratio of the mixed acid liquor is 1g/150mL, the secondary separation solid is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 35min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration under ultrasonic oscillation on the five times of separated liquid, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration and the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Example 6
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, performing crystallization reaction for 8 hours at 200 ℃, cooling the reaction kettle to 20 ℃ in water bath, and usingWashing with ethanol and deionized water for 3 times, respectively, separating with permanent magnet during washing, drying at 65 deg.C for 24 hr in vacuum drying oven, and grinding to obtain Fe 3 O 4 A magnetic core; 0.96g of Fe to be obtained 3 O 4 Ultrasonic dispersing magnetic core in 200mL methanol, adding salt solution and alkali solution dropwise while stirring, wherein the salt solution is prepared by adding 6.06g Co (NO) in the solution 3 ) 2 ·6H 2 O and 1.68g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature at 70 ℃ and the pH value at 8.5 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, separating by using a permanent magnet, and removing CO by using a CO removing method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ CoFe-LDH; mixing Fe 3 O 4 The @ CoFe-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 20, and the reduction space velocity is 0.2hr -1 And the reduction temperature is 800 ℃, thus obtaining the catalyst.
2) Introducing ethylene and hydrogen at 750 ℃ to carry out cracking reaction, wherein the flow ratio of the ethylene to the hydrogen is 2: 1; the ethylene flow rate was 0.1m per gram of procatalyst 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M, the concentration of hydrochloric acid is 5M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/150mL, the solid material is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain primary separation liquid and primary separation solid.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 35min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M, the concentration of hydrochloric acid is 5M, the mass ratio of the secondary separated solid to the volume ratio of the mixed acid liquor is 1g/150mL, the secondary separated solid is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain tertiary separated liquid and tertiary separated solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 35min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
Example 7
A preparation method of carbon nanotubes comprises the following steps:
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing with ethanol and deionized water for 2 times respectively, separating by adopting a permanent magnet in the washing process, then in a vacuum drying oven,drying at 65 ℃ for 24h, grinding to obtain Fe 3 O 4 A magnetic core; 0.81g of Fe obtained 3 O 4 The magnetic core is ultrasonically dispersed in 200mL methanol, and under stirring, a salt solution and an alkali solution are simultaneously added dropwise, wherein the salt solution is prepared by adding 4.37g Co (NO) 3 ) 2 ·6H 2 O、3.03g Fe(NO 3 ) 3 ·9H 2 O and 0.73g Ni (NO) 3 ) 2 ·6H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature at 60 ℃ and the pH value at 10.5 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, separating by using a permanent magnet, and removing CO by using a CO removing method 2 Washing with deionized water for three times, separating with permanent magnet during washing, and drying at 65 deg.C for 24 hr to obtain Fe 3 O 4 @ CoFeNi-LDH; mixing Fe 3 O 4 The @ CoFeNi-LDH is placed in a vacuum tube furnace and reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 10, and the reduction space velocity is 0.1hr -1 And the reduction temperature is 700 ℃, thus obtaining the catalyst.
2) At the temperature of 650 ℃, introducing propylene and hydrogen for cracking reaction, wherein the flow ratio of the propylene to the hydrogen is 1: 1; the flow rate of propylene per gram of procatalyst was 0.1m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 5M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/150mL, the solid material is dispersed in the mixed acid liquor, refluxing is carried out for 1h, and then permanent magnet separation is carried out, so that primary separation liquid and primary separation solid are obtained.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: the method comprises the steps of carrying out acid washing by using a mixed acid solution of nitric acid and hydrochloric acid, wherein the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 5M, the volume ratio of the mass of the secondary separation solid to the volume of the mixed acid solution is 1g/150mL, dispersing the secondary separation solid in the mixed acid solution, refluxing for 1h, and then carrying out permanent magnet separation to obtain a tertiary separation liquid and a tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a fifth separation liquid and a fifth separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Comparative example 1
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 2 times respectively, separating the reaction kettle with a permanent magnet during washing, drying the reaction kettle for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction kettle to obtain Fe 3 O 4 A magnetic core; preparation of NiFe-LDH, with Fe in example 1 3 O 4 The preparation of @ NiFe-LDH differsThe method comprises the following steps: does not contain Fe 3 O 4 The dispersing step of (1), directly adding dropwise to 200mL of methanol, while stirring, a salt solution prepared by adding 5.45g of Ni (NO) and an alkali solution 3 ) 2 ·6H 2 O and 2.53g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature at 60 ℃ and the pH value at 8.5 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, filtering and separating, and removing CO 2 Washing with deionized water for three times, and drying at 65 ℃ for 24 hours to obtain NiFe-LDH; 0.87gFe 3 O 4 Mixing magnetic core and NiFe-LDH, placing the mixture in a vacuum tube furnace, and reducing in a reducing atmosphere of a mixture of hydrogen and argon at a volume ratio of 1: 10 and a reduction space velocity of 0.1hr -1 The reduction temperature was 600 ℃ to obtain comparative catalyst 1.
2) Introducing methane and hydrogen at the temperature of 600 ℃ to carry out cracking reaction, wherein the flow ratio of the methane to the hydrogen is 1: 1; the flow rate of methane per gram of catalyst precursor was 0.2m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 4M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/100mL, the solid material is dispersed in the mixed acid liquor, refluxing is carried out for 1h, and then permanent magnet separation is carried out, so that primary separation liquid and primary separation solid are obtained.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: the method comprises the steps of carrying out acid washing by using a mixed acid solution of nitric acid and hydrochloric acid, wherein the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 4M, the volume ratio of the mass of the secondary separation solid to the volume of the mixed acid solution is 1g/100mL, dispersing the secondary separation solid in the mixed acid solution, refluxing for 1h, and then carrying out permanent magnet separation to obtain a tertiary separation liquid and a tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 20min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
Comparative example 2
1) Fe obtained in comparative example 1 3 O 4 0.87g is reduced in a reducing atmosphere which is a mixed gas of hydrogen and argon, the volume ratio of the hydrogen to the argon is 1: 10, and the reduction space velocity is 0.1hr -1 The reduction temperature was 600 ℃ to obtain comparative catalyst 2.
2) Introducing methane and hydrogen at the temperature of 600 ℃ to carry out cracking reaction, wherein the flow ratio of the methane to the hydrogen is 1: 1; the flow rate of methane was 0.2m per g of catalyst precursor 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 4M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/100mL, the solid material is dispersed in the mixed acid liquor, refluxing is carried out for 1h, and then permanent magnet separation is carried out, so that primary separation liquid and primary separation solid are obtained.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by adopting mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 4M, the mass of the secondary separation solid and the volume ratio of the mixed acid liquor is 1g/100mL, the secondary separation solid is dispersed in the mixed acid liquor and refluxed for 1h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration under ultrasonic oscillation on the five times of separated liquid, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration and the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Comparative example 3
1) The NiFe-LDH prepared in comparative example 1 was placed in a vacuum tube furnace and reduced in a reducing atmosphere of a mixture of hydrogen and argon at a volume ratio of 1: 10 and a reduction space velocity of 0.1hr -1 The reduction temperature is 600 ℃ to obtainTo comparative catalyst 3.
2) Introducing methane and hydrogen at the temperature of 600 ℃ to carry out cracking reaction, wherein the flow ratio of the methane to the hydrogen is 1: 1; the flow rate of methane per gram of catalyst precursor was 0.2m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 3M, the concentration of hydrochloric acid is 4M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/100mL, the solid material is dispersed in the mixed acid liquor, refluxing is carried out for 1h, and then permanent magnet separation is carried out, so that primary separation liquid and primary separation solid are obtained.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by adopting mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 4M, the mass of the secondary separation solid and the volume ratio of the mixed acid liquor is 1g/100mL, the secondary separation solid is dispersed in the mixed acid liquor and refluxed for 1h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration on the five times of separated liquid under ultrasonic oscillation, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
Comparative example 4
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 2 times respectively, separating the reaction kettle with a permanent magnet during washing, drying the reaction kettle for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction kettle to obtain Fe 3 O 4 A magnetic core; preparation of CoFe-LDH, corresponding to Fe in example 4 3 O 4 The preparation of @ CoFe-LDH differs: does not contain Fe 3 O 4 To 200mL of methanol were added dropwise, while stirring, a salt solution obtained by adding 4.85g of Co (NO) and an alkali solution simultaneously 3 ) 2 ·6H 2 O and 3.37g Fe (NO) 3 ) 3 ·9H 2 Dissolving O in a mixed solvent of water and methanol to prepare 250mL of salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in the aqueous alkali to prepare the mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the aqueous alkali are respectively 0.1mol/L and 0.2mol/L, controlling the temperature to be 70 ℃ and the pH value to be 8 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, filtering and separating, and removing CO by adopting 2 Washing with deionized water for three times, and drying at 65 ℃ for 24 hours to obtain CoFe-LDH; 0.77gFe 3 O 4 Mixing magnetic core and CoFe-LDH, placing the mixture in a vacuum tube furnace, and reducing in a reducing atmosphere of a mixture of hydrogen and argon at a volume ratio of 1: 1 and a reduction space velocity of 0.1hr -1 The reduction temperature was 700 ℃ to obtain comparative catalyst 4.
2) Introducing ethylene and hydrogen at the temperature of 700 ℃ to carry out cracking reaction, wherein the flow ratio of the ethylene to the hydrogen is 2: 1; in terms of per gram of catalyst precursorThe flow rate of the ethylene is 0.1m 3 H; the time of the cracking reaction is 40min, and the solid material containing the carbon nano tube is obtained.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M, the concentration of hydrochloric acid is 5M, the mass ratio of the solid material to the volume ratio of the mixed acid liquor is 1g/150mL, the solid material is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain primary separation liquid and primary separation solid.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 35min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M, the concentration of hydrochloric acid is 5M, the volume ratio of the mass of the secondary separation solid to the volume of the mixed acid liquor is 1g/150mL, the secondary separation solid is dispersed in the mixed acid liquor and reflows for 1.5h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 35min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (3) performing microfiltration under ultrasonic oscillation on the five times of separated liquid, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration and the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
Comparative example 5
1) Preparation of the catalyst precursor: 8.66g FeCl was weighed 3 ·6H 2 Preparing 0.1mol/L ferric trichloride solution from O, mixing the ferric trichloride solution with 21.77g CH 3 COONa·3H 2 Dissolving O in 320mL of glycol to form a solution, transferring the solution into a 500mL reaction kettle, carrying out crystallization reaction for 8h at 200 ℃, cooling the reaction kettle to 30 ℃ in water bath, washing the reaction kettle with ethanol and deionized water for 2 times respectively, separating the reaction kettle with a permanent magnet during washing, drying the reaction kettle for 24h at 65 ℃ in a vacuum drying oven, and grinding the reaction kettle to obtain Fe 3 O 4 A magnetic core; preparation of CoFeNi-LDH, with Fe in example 7 3 O 4 The preparation of @ CoFeNi-LDH differs in that: does not contain Fe 3 O 4 The dispersing step of (1), to 200mL of methanol were added dropwise, simultaneously, with stirring, a salt solution obtained by mixing 4.37g of Co (NO) 3 ) 2 ·6H 2 O、3.03g Fe(NO 3 ) 3 ·9H 2 O and 0.73g Ni (NO) 3 ) 2 ·6H 2 Dissolving O in a mixed solvent of water and methanol to prepare a 250mL salt solution, wherein the volume ratio of the methanol to the water is 1: 19, dissolving sodium hydroxide and sodium carbonate in water to prepare a mixed solution, the concentration of the sodium hydroxide and the concentration of the sodium carbonate in the alkali solution are respectively 0.1mol/L and 0.2mol/L, controlling the temperature at 60 ℃ and the pH value at 10.5 in the dropping process, continuing to crystallize for 36h after the dropping of the salt solution is finished, filtering and separating, and removing CO 2 Washing with deionized water for three times, and drying at 65 ℃ for 24 hours to obtain CoFeNi-LDH; 0.81gFe 3 O 4 Mixing magnetic core and CoFeNi-LDH, placing the mixture in a vacuum tube furnace, and reducing in a reducing atmosphere of a mixture of hydrogen and argon at a volume ratio of 1: 10 and a reduction space velocity of 0.1hr -1 The reduction temperature was 700 ℃ to obtain comparative catalyst 5.
2) At the temperature of 650 ℃, introducing propylene and hydrogen for cracking reaction, wherein the flow ratio of methane to hydrogen is 1: 1; the flow rate of methane per gram of catalyst precursor was 0.1m 3 H; the cracking reaction time is 40min to obtain solid containing carbon nanotubeAnd (4) feeding.
3) Carrying out primary acid washing on the solid material obtained in the step 2), wherein the conditions of the primary acid washing comprise: the method comprises the steps of carrying out acid washing by using a mixed acid solution of nitric acid and hydrochloric acid, wherein the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 5M, the volume ratio of the mass of a solid material to the volume of the mixed acid solution is 1g/150mL, dispersing the solid material in the mixed acid solution, refluxing for 1h, and then carrying out permanent magnet separation to obtain a primary separation liquid and a primary separation solid.
4) Performing primary ultrasonic dispersion on the primary separated solid, dispersing the primary separated solid in deionized water, and performing ultrasonic treatment for 30min; then the permanent magnet is separated to obtain secondary separated liquid and secondary separated solid.
5) And carrying out secondary acid washing on the secondary separated solid, wherein the conditions of the secondary acid washing comprise: acid washing is carried out by adopting mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of the nitric acid to the hydrochloric acid is 1: 1, the concentration of the nitric acid is 3M, the concentration of the hydrochloric acid is 5M, the mass of the secondary separation solid and the volume ratio of the mixed acid liquor is 1g/150mL, the secondary separation solid is dispersed in the mixed acid liquor and refluxed for 1h, and then permanent magnet separation is carried out to obtain tertiary separation liquid and tertiary separation solid.
6) Performing secondary ultrasonic dispersion on the three-time separated solid, dispersing the three-time separated solid in deionized water, and performing ultrasonic treatment for 30min; then, permanent magnet separation is carried out to obtain four times of separation liquid and four times of separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, and performing tertiary ultrasonic dispersion, wherein the tertiary ultrasonic dispersion is to directly perform ultrasonic treatment on the mixed liquid for 40min, and then performing centrifugal separation to obtain a fifth separation liquid and a fifth separation solid;
8) And (3) performing microfiltration under ultrasonic oscillation on the five times of separated liquid, wherein the aperture of a filter membrane used in the microfiltration is 0.5 mu m, and mixing the solid obtained by filtration and the five times of separated solid to obtain the carbon nano tube. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
Comparative example 6
In comparison with example 1, comparative example 6 does not include step 8), and the five separated solids obtained are the prepared carbon nanotubes in the same manner as in example 1. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Comparative example 7
In contrast to example 1, comparative example 7 did not include step 5) and step 6), and the primary separation liquid and the secondary separation liquid were directly mixed in step 7) and subjected to the ultrasonic dispersion three times. The rest is the same as in example 1. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in table 1.
Comparative example 8
In comparison with example 1, comparative example 8 did not include the third ultrasonic dispersion, and the first separation liquid, the second separation liquid, the third separation liquid, and the fourth separation liquid were mixed and centrifuged to obtain the fifth separation liquid and the fifth separation solid. The rest is the same as in example 1. The conditions for the preparation of carbon nanotubes and the parameters for the preparation of carbon nanotubes are shown in Table 1.
TABLE 1
Figure RE-GDA0003089106600000311
As can be seen from the data in Table 1, the present invention is achieved by adding Fe 3 O 4 NiFe-LDH, coFe-LDH and CoFeNi-LDH are coated and grown on magnetic cores, compared with simple physical mixing, due to Fe 3 O 4 The synergistic effect of the magnetic core and the LDH can improve the activity of the catalyst and the yield of the carbon nano tube, and the magnetic catalyst is beneficial to the solid-liquid separation of the carbon nano tube in the purification process.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the illustrated embodiments.

Claims (7)

1. The preparation method of the carbon nano tube is characterized by comprising the following steps:
1) The catalyst precursor Fe 3 O 4 @NiFe-LDH、Fe 3 O 4 @ CoFe-LDH or Fe 3 O 4 @ CoFeNi-LDH is put in a vacuum tube furnace and reduced in a reducing atmosphere to obtain a catalyst,
catalyst precursor Fe 3 O 4 The preparation of @ NiFe-LDH includes: preparation of Fe 3 O 4 A magnetic core; mixing Fe 3 O 4 Magnetic nuclei are dispersed in methanol, the Fe 3 O 4 The mass ratio of the sodium hydroxide to the methanol is 2.5-5 g: 1L, a salt solution and an alkali solution are simultaneously dripped into the solution under stirring, the salt solution is a mixed solution of nickel nitrate and ferric nitrate, the molar ratio of the nickel nitrate to the ferric nitrate is 1-3: 1, the solvent of the salt solution is a mixed solvent of methanol and water, the volume ratio of the methanol to the water is 1: 19, the total concentration of cations in the salt solution is 0.1mol/L, the alkali solution is a mixed solution of sodium hydroxide and sodium carbonate, the concentration of the sodium hydroxide in the alkali solution is 0.1mol/L, the concentration of the sodium carbonate in the alkali solution is 0.2mol/L, and Fe is 3 O 4 The mol ratio of the nickel nitrate to the nickel nitrate is 1: 5, the temperature is controlled to be 60 ℃ and the pH value is 8-9 in the dripping process, the crystallization is continued for 36 hours after the salt solution is dripped, the permanent magnet is adopted for separation, and then CO is removed 2 Washing with deionized water for three times, separating with permanent magnet during washing, drying the obtained solid at 65 deg.C for 24 hr to obtain Fe 3 O 4 @NiFe-LDH，
Catalyst precursor Fe 3 O 4 The preparation of @ CoFe-LDH includes: preparation of Fe 3 O 4 A magnetic core; mixing Fe 3 O 4 Magnetic nuclei are dispersed in methanol, the Fe 3 O 4 The mass ratio of the salt solution to the methanol is 2.5-5 g: 1L, a salt solution and an alkali solution are simultaneously dripped into the solution under stirring, the salt solution is a mixed solution of cobalt nitrate and ferric nitrate, the molar ratio of the cobalt nitrate to the ferric nitrate is 2-5: 1, the solvent of the salt solution is a mixed solvent of methanol and water, the volume ratio of the methanol to the water is 1: 19, the total concentration of cations in the salt solution is 0.1mol/L, and the alkali solution is sodium hydroxideAnd sodium carbonate, the concentration of sodium hydroxide in the alkali solution is 0.1mol/L, the concentration of sodium carbonate is 0.2mol/L, fe 3 O 4 The molar ratio of the cobalt salt to the solution is 1: 5, the temperature is controlled at 70 ℃ and the pH value is 8-8.5 in the dripping process, the crystallization is continued for 36 hours after the dripping of the salt solution is finished, a permanent magnet is used for separation, and then CO is removed 2 Washing with deionized water for three times, separating with permanent magnet during washing, drying the obtained solid at 65 deg.C for 24 hr to obtain Fe 3 O 4 @CoFe-LDH，
Catalyst precursor Fe 3 O 4 The preparation of @ CoFeNi-LDH includes: preparation of Fe 3 O 4 A magnetic core; mixing Fe 3 O 4 Magnetic nuclei are dispersed in methanol, the Fe 3 O 4 The mass ratio of the sodium hydroxide to the methanol is 2.5-5 g: 1L, under stirring, a salt solution and an alkali solution are simultaneously dripped into the mixed solution, the salt solution is a mixed solution of cobalt nitrate, nickel nitrate and ferric nitrate, the molar ratio of the cobalt nitrate, the ferric nitrate and the nickel nitrate is 6: 3: 1, the solvent of the salt solution is a mixed solvent of methanol and water, the volume ratio of the methanol to the water is 1: 19, the total concentration of cations in the salt solution is 0.1mol/L, the alkali solution is a mixed solution of sodium hydroxide and sodium carbonate, the concentration of the sodium hydroxide in the alkali solution is 0.1mol/L, and the concentration of the sodium carbonate is 0.2mol/L; fe 3 O 4 The mol ratio of the cobalt salt to the nickel salt is 1: 5, the temperature is controlled at 60 ℃ and the pH value is 10.5 in the dripping process, crystallization is continued for 36 hours after the dripping of the salt solution is finished, permanent magnets are used for separation, and then CO is removed 2 Washing with deionized water for three times, separating with permanent magnet during washing, drying the obtained solid at 65 deg.C for 24 hr to obtain Fe 3 O 4 @CoFeNi-LDH；
2) Introducing carbon source gas and hydrogen gas at the temperature of 500-800 ℃ to carry out cracking reaction to obtain a solid material containing carbon nano tubes;
3) Carrying out primary acid washing on the solid material obtained in the step 2), and then carrying out permanent magnet separation to obtain primary separated liquid and primary separated solid;
4) Performing primary ultrasonic dispersion on the primary separated solid, and then performing permanent magnet separation to obtain secondary separated liquid and secondary separated solid;
5) Carrying out secondary acid washing on the secondary separated solid, and then carrying out permanent magnet separation to obtain a tertiary separated liquid and a tertiary separated solid;
6) Performing secondary ultrasonic dispersion on the third separation solid, and then performing permanent magnet separation to obtain fourth separation liquid and fourth separation solid;
7) Mixing the primary separation liquid, the secondary separation liquid, the tertiary separation liquid and the quaternary separation liquid, performing tertiary ultrasonic dispersion, and performing centrifugal separation to obtain a quintic separation liquid and a quintic separation solid;
8) And (4) performing microporous filtration on the five times of separated liquid under ultrasonic oscillation, and mixing the solid obtained by filtration with the five times of separated solid to obtain the carbon nano tube.
2. The method for producing carbon nanotubes according to claim 1, wherein Fe is produced 3 O 4 The magnetic core comprises: dissolving ferric trichloride solution with the molar concentration of 0.1mol/L and sodium acetate into ethylene glycol to form solution, wherein the molar ratio of the ferric trichloride to the sodium acetate is 1: 5, the amount of ferric trichloride and the volume of the ethylene glycol are 1 mol: 10L, carrying out crystallization reaction on the solution at 200 ℃ for 8 hours, cooling a reaction product to 10-30 ℃, then respectively washing the reaction product with ethanol and deionized water for 2-3 times, simultaneously adopting permanent magnet separation in the washing process, separating to obtain a solid, drying the solid at 65 ℃ for 24 hours, and grinding to obtain Fe 3 O 4 。
3. The method of claim 1, wherein in step 1), the reducing atmosphere is a mixture of hydrogen and argon, the volume ratio of hydrogen to argon is 1: 1-20, and the reduction space velocity is 0.1-0.2hr -1 The reduction temperature is 500-800 ℃.
4. The method of claim 1, wherein in the step 2), the carbon source gas is methane, ethylene or propylene, and the flow ratio of the carbon source gas to the hydrogen gas is 1: 1-6: 1; the carbon source gas is calculated by per gram of catalyst precursorThe flow rate of the body is 0.1-1m 3 H; the time of the cracking reaction is 20-60min.
5. The method for producing carbon nanotubes according to claim 1, wherein the conditions of the primary acid washing and the secondary acid washing include: acid washing is carried out by using mixed acid liquor of nitric acid and hydrochloric acid, the volume ratio of nitric acid to hydrochloric acid is 1: 1, the concentration of nitric acid is 2M-5M, the concentration of hydrochloric acid is 2M-8M, the mass ratio of the solid material or secondary separation solid to the volume ratio of the mixed acid liquor is 1g/50-200mL, the solid material or secondary separation solid is dispersed in the mixed acid liquor, and refluxing is carried out for 0.5-2h.
6. The method for producing carbon nanotubes according to claim 1, wherein: the conditions of the primary ultrasonic dispersion and the secondary ultrasonic dispersion comprise: dispersing the first separation solid or the third separation solid in deionized water, and performing ultrasonic treatment for 15-50min;
the third ultrasonic dispersion is to directly carry out ultrasonic treatment on the mixed liquid for 15-50min.
7. The method for producing carbon nanotubes according to claim 1, wherein: the aperture of the filter membrane used for the micro-filtration is 0.2-1 μm.
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