CN114797864B - Preparation method of growth catalyst for small-diameter bulk single-walled carbon nanotubes - Google Patents

Preparation method of growth catalyst for small-diameter bulk single-walled carbon nanotubes Download PDF

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CN114797864B
CN114797864B CN202110082993.1A CN202110082993A CN114797864B CN 114797864 B CN114797864 B CN 114797864B CN 202110082993 A CN202110082993 A CN 202110082993A CN 114797864 B CN114797864 B CN 114797864B
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catalyst
carbon nanotubes
diameter
carbon
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CN114797864A (en
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李彦
张则尧
姚艺希
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Peking University Shenzhen Graduate School
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
    • 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
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/02—Single-walled nanotubes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/20—Nanotubes characterized by their properties
    • C01B2202/36—Diameter

Abstract

The invention provides a catalyst for growing small-diameter bulk single-walled carbon nanotubes, a preparation method thereof and a preparation method of the small-diameter bulk single-walled carbon nanotubes. The catalyst provided by the invention uses the complexing agent to effectively limit the size of metal catalyst particles, the catalyst carrier is easy to remove, the subsequent application of the carbon nano tube is convenient, the working procedure is simple, and the prepared carbon nano tube has smaller diameter and narrower tube diameter distribution.

Description

Preparation method of growth catalyst for small-diameter bulk single-walled carbon nanotubes
Technical Field
The invention relates to a preparation method of a carbon material growth catalyst, in particular to a preparation method of a small-diameter bulk single-wall carbon nano tube growth catalyst.
Background
The structure-controlled growth of single-walled carbon nanotubes is a key challenge for high-end applications in quantum devices, bioimaging, electronics, optoelectronics, etc. The band gap width of the semiconducting single-walled carbon nanotubes is directly related to the tube diameter size. The band gap can be regulated and controlled by controlling the diameter of the single-wall carbon nano tube so as to meet the requirements of corresponding application. For near infrared bioluminescence imaging, for example, single-walled carbon nanotubes with tube diameters in the range of 0.8-1.2nm can emit fluorescence in the near infrared 2 region window of biological tissue. For single photon light sources in quantum devices, single-wall carbon nanotubes with tube diameters of 0.9-1.2nm have suitable luminescence wavelengths. In single-walled carbon nanotube thin film field effect transistors, the size and uniformity of the carbon nanotube bandgap can directly affect device performance. In single-walled carbon nanotube-fullerene solar cells, the internal quantum efficiency of the cell decreases as the tube diameter of the carbon nanotubes increases, which means that only small diameter carbon nanotubes are suitable for use in such solar cells. Meanwhile, the bulk carbon nanotubes with small diameters are easier to disperse in the solution, so that the bulk carbon nanotubes are more suitable for being separated to obtain carbon nanotubes with different conductivities and chiral indexes by a solution phase separation means.
In the process of growing single-walled carbon nanotubes by Chemical Vapor Deposition (CVD), there are two main key factors controlling the diameter of carbon nanotubes, one is the regulation of the catalyst particle size distribution, and the other is the control of CVD conditions. First, the size distribution of the catalyst directly affects the diameter distribution of the carbon nanotubes. The zeolite, magnesia, alumina, mesoporous silica, etc. can synthesize nanometer particle with controllable size through solution chemical process and grow carbon nanotube with controllable diameter as catalyst or catalyst precursor. The size of the nano particles can be effectively controlled by using long-chain carboxylic acid or amine molecules as a protective agent or using deferiprone, dendritic polymers, block copolymers and the like as a nano reactor, so that uniform carbon nano tube catalyst precursors can be synthesized. The catalyst support may generally serve to stabilize the catalyst size and limit catalyst agglomeration.
In the prior art, porous materials such as zeolite, mesoporous silica and the like are commonly used as catalyst carriers, and the porous structure plays a role in limiting the size of the catalyst, but the zeolite and the mesoporous silica carriers are difficult to remove, so that certain inconvenience is brought to the preparation and application of the carbon nano tube.
Disclosure of Invention
Based on the above technical background, the present inventors have conducted intensive studies and as a result found that: the catalyst precursor is prepared by adopting the compound containing the element A, the catalyst carrier and the complexing agent, and then the metal catalyst prepared by burning and reducing can be used for growing bulk single-walled carbon nanotubes with small diameters, and the prepared single-walled carbon nanotubes have smaller diameters and narrower diameter distribution.
The first aspect of the invention is to provide a catalyst for growing small-diameter bulk single-walled carbon nanotubes, which is prepared from a compound containing an element A, a catalyst carrier and a complexing agent, wherein the element A is selected from one or more of iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium.
A second aspect of the present invention provides a method for preparing the catalyst according to the first aspect of the present invention, comprising the steps of:
step 1, preparing a catalyst precursor by adopting a compound containing an element A, a catalyst carrier and a complexing agent;
step 2, preparing a catalyst through burning and reduction;
the element A is one or more selected from iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium;
the compound containing the A element is selected from one or more of salts containing the A element and soluble in water;
the catalyst carrier is selected from oxides of magnesium, aluminum, silicon, calcium and the like or mixed oxides, carbonates, various zeolite, boron nitride and the like;
particularly, complexing agent molecules can coordinate metal ions of the element A, so that the metal ions are inhibited from hydrolyzing and the agglomeration is reduced, so that the prepared metal catalyst particles can keep smaller and uniform size, and the growth of the small-diameter single-wall carbon nanotubes is facilitated;
the complexing agent is one or more selected from ammonia water, methylamine, pyridine, oxalate, phenanthroline, ethylenediamine tetraacetic acid or its salt, sodium tripolyphosphate, triethanolamine and sodium pyrophosphate.
A third aspect of the present invention is to provide the use of the catalyst according to the first aspect of the present invention or the catalyst for growth of small diameter bulk single-walled carbon nanotubes produced by the production method according to the second aspect of the present invention, which can be used for production of small diameter bulk single-walled carbon nanotubes.
A fourth aspect of the present invention is to provide a method for preparing bulk single-walled carbon nanotubes having a small diameter, the method comprising the steps of:
step a, adding a catalyst into a tube furnace, and raising the furnace temperature to the growth temperature of the carbon nano tube;
and b, introducing a carbon source to prepare the carbon nano tube.
The invention provides a growth catalyst for small-diameter bulk single-walled carbon nanotubes and the small-diameter bulk single-walled carbon nanotubes prepared by the same, which have the following advantages: the catalyst carrier is simple to remove, the subsequent application of the carbon nano tube is convenient, the preparation efficiency is higher, and the prepared carbon nano tube has smaller diameter and narrower tube diameter distribution (the diameter distribution and 0.9-1.2 nm) and is suitable for being applied to the fields of near infrared bioluminescence imaging, quantum device single photon light sources and the like.
Drawings
FIG. 1 shows Raman spectra of the carbon nanotubes prepared in comparative example 2 and comparative example 3 of the present invention with laser wavelength of 532 nm;
FIG. 2 shows Raman spectra of carbon nanotubes prepared in comparative example 2 and comparative example 3 of the present invention with a laser wavelength of 633 nm;
FIG. 3 shows Raman spectra of 532nm laser wavelength carbon nanotubes prepared in comparative example 2, comparative example 4 and comparative example 5;
FIG. 4 shows Raman spectra of carbon nanotubes prepared in comparative example 2, comparative example 4 and comparative example 5 of the present invention with a laser wavelength of 633 nm;
FIG. 5 shows Raman spectra of the carbon nanotubes prepared in comparative examples 2, 6, 7, 8, 9, 10, 11 and 12 of the present invention with laser wavelength of 532 nm;
FIG. 6 shows Raman spectra of carbon nanotubes prepared in comparative examples 2, 6, 7, 8, 9, 10, 11 and 12 of the present invention, the laser wavelength of which is 633 nm;
FIG. 7 shows Raman spectra of the carbon nanotubes prepared in comparative example 2, comparative example 13, comparative example 14, comparative example 15 and comparative example 16 of the present invention with laser wavelength of 532 nm;
FIG. 8 shows Raman spectra of carbon nanotubes prepared in comparative examples 2, 13, 14, 15 and 16 of the present invention with a laser wavelength of 633 nm;
FIG. 9 shows Raman spectra of the carbon nanotubes prepared in comparative example 2 and example 2 of the present invention with laser wavelength of 532 nm;
FIG. 10 shows Raman spectra of carbon nanotubes prepared in comparative example 2 and example 2 of the present invention with a laser wavelength of 633 nm.
Detailed Description
The features and advantages of the present invention will become more apparent and evident from the following detailed description of the invention.
The first aspect of the invention is to provide a catalyst for growth of small-diameter bulk single-walled carbon nanotubes, which is prepared from an A-element-containing compound, a catalyst carrier and a complexing agent.
The compound containing the A element is selected from one or more of salts containing the A element which are soluble in water, preferably one or more of sulfates, nitrates and acetates containing the A element, more preferably from sulfates containing the A element.
The element A in the invention is selected from one or more of iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium, preferably one or more of iron, cobalt, nickel, copper, manganese and molybdenum, more preferably one or two of iron, cobalt and nickel.
The catalyst support is selected from one or more of magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, magnesium carbonate, aluminum carbonate, silicon carbonate, calcium carbonate, zeolite and boron nitride, preferably from one or more of magnesium oxide, Y-type zeolite and silicon oxide, more preferably magnesium oxide.
The mol ratio of the catalyst carrier to the compound containing the A element is (30-70): 1, preferably the molar ratio is (40 to 60): 1, more preferably the molar ratio is (45 to 55): 1. When a bimetal is used in the element A-containing compound, the molar ratio of the two metals is preferably 1:1.
The complexing agent is selected from one or more of ammonia water, methylamine, pyridine, oxalate, phenanthroline, ethylenediamine tetraacetic acid or salt thereof, sodium tripolyphosphate, triethanolamine and sodium pyrophosphate, preferably selected from one or more of oxalate, ethylenediamine tetraacetic acid or salt thereof and sodium tripolyphosphate, and more preferably ethylenediamine tetraacetic acid or ethylenediamine tetraacetic acid sodium salt.
The amount of the complexing agent to be added is 1 to 15 times, preferably 2 to 10 times, more preferably 4 to 7 times, for example 5 times, the molar amount of the compound containing the element A (the molar amount of the compound of the present invention).
The catalyst according to the invention is prepared by a process comprising the steps of:
step 1, preparing a catalyst precursor by adopting a compound containing an element A, a catalyst carrier and a complexing agent;
and 2, preparing the catalyst through burning and reduction.
A second aspect of the present invention is to provide a method for preparing the catalyst for growth of bulk single-walled carbon nanotubes having a small diameter according to the first aspect of the present invention, the method comprising the steps of:
step 1, preparing a catalyst precursor by adopting a compound containing an element A, a catalyst carrier and a complexing agent;
step 2, preparing a catalyst through burning and reduction;
this step is specifically described and illustrated below.
And step 1, preparing a catalyst precursor by adopting a compound containing an element A, a catalyst carrier and a complexing agent.
The catalyst precursor is prepared by mixing and post-treating a compound containing an element A and a catalyst carrier. Before mixing, the compound containing the element A and the catalyst carrier are dissolved in water and then mixed.
The molar concentration of the element A after the compound containing the element A is dissolved in water is 0.1-1 mmol/mL, preferably 0.1-0.5 mmol/mL, and more preferably 0.1-0.2 mmol/mL.
The compound containing the A element is selected from one or more of salts containing the A element which are soluble in water, preferably one or more of sulfates, nitrates and acetates containing the A element, more preferably from sulfates containing the A element.
In the preparation process, the compound containing the element A is dissolved in water to prepare a solution and then is mixed with the catalyst carrier, so that the compound containing the element A is water-soluble salt, the compound containing the element A is hydrolyzed in the later evaporation process after being dissolved in water, the more severe the hydrolysis degree is, the more serious the agglomeration degree is, the larger the size of the formed catalyst particles is, the diameter of the carbon nano tube is increased, the hydrolysis degree of sulfate is lower, and the diameter of the prepared carbon nano tube is smaller.
The element A in the invention is selected from one or more of iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium, preferably one or more of iron, cobalt, nickel, copper, manganese and molybdenum, more preferably one or two of iron, cobalt and nickel.
The inventors have found that the use of a bimetallic catalyst system, such as iron and cobalt, can effectively increase the growth efficiency of carbon nanotubes, while reducing the tube diameter and tube diameter distribution of the carbon nanotubes, as compared to a single metal catalyst.
The catalyst carrier is selected from one or more of magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, magnesium carbonate, aluminum carbonate, silicon carbonate, calcium carbonate, zeolite and boron nitride, preferably one or more of magnesium oxide, Y-type zeolite and silicon oxide, more preferably magnesium oxide.
The porous catalyst carrier can limit the size of the catalyst through nano-sized pore channels so as to control the pipe diameter of the carbon nano-tube, but porous structural carriers such as zeolite and the like are difficult to remove, so that certain inconvenience is brought to the subsequent application of the carbon nano-tube, magnesium oxide serving as the catalyst carrier can be removed by soaking with dilute acid, the catalyst carrier is very simple and convenient, the pipe diameter of the prepared carbon nano-tube is smaller, and meanwhile, the magnesium oxide can effectively control the sizes of iron and cobalt particles, so that the pipe diameter of the prepared carbon nano-tube is smaller and the distribution is narrower.
The catalyst carrier is dispersed in water, and the concentration of the catalyst carrier is 0.05 to 1g/mL, preferably 0.07 to 0.5g/mL, more preferably 0.1 to 0.2g/mL.
The mol ratio of the catalyst carrier to the compound containing the A element is (30-70): 1, preferably the molar ratio is (40 to 60): 1, more preferably the molar ratio is (45 to 55): 1. When the catalyst is a bimetallic catalyst, the molar ratio of the two metals is preferably 1:1.
According to a preferred embodiment of the present invention, a complexing agent is further added during the preparation of the catalyst precursor, and the inventors have found that the added complexing agent can coordinate with metal ions such as iron, cobalt, etc., thereby inhibiting the hydrolysis thereof, reducing the agglomeration thereof, and limiting the size of the catalyst particles so that the prepared metal catalyst particles remain small and uniform in size.
The complexing agent is selected from one or more of ammonia water, methylamine, pyridine, oxalate, phenanthroline, ethylenediamine tetraacetic acid or salt thereof, sodium tripolyphosphate, triethanolamine and sodium pyrophosphate, preferably selected from one or more of oxalate, ethylenediamine tetraacetic acid or salt thereof and sodium tripolyphosphate, and more preferably ethylenediamine tetraacetic acid or ethylenediamine tetraacetic acid sodium salt.
The amount of the complexing agent added is 1 to 15 times, preferably 2 to 10 times, more preferably 4 to 7 times the molar amount of the compound containing the element A.
The compound containing the a element and the catalyst support are preferably mixed with stirring for a period of preferably 5 to 20 minutes, more preferably 10 minutes.
After stirring, the mixture is heated and boiled for preferably 20 to 45 minutes, more preferably 30 minutes. And (5) carrying out post-treatment after cooling, wherein the post-treatment comprises suction filtration, washing and drying.
The detergent is preferably water and ethanol, and is washed a plurality of times, preferably 1 to 3 times, preferably 2 times, each of water and ethanol.
The washing is followed by drying at a temperature of 100-150 ℃ for 10-15 hours, preferably at a temperature of 110-130 ℃ for 11-13 hours, more preferably at a temperature of 120 ℃ for 12 hours.
And 2, preparing the catalyst through burning and reduction.
And (3) burning and reducing the catalyst precursor prepared in the step (1) in sequence to obtain the catalyst. Both firing and reduction were carried out in a tube furnace.
The firing is preferably performed under an air atmosphere at a firing temperature of 400 to 1200 ℃, preferably at a firing temperature of 600 to 800 ℃, more preferably at a firing temperature of 700 ℃.
The firing time is 1 to 60 minutes, preferably 2 to 10 minutes, more preferably 3 minutes.
Inert gas, preferably argon, is introduced into the tube furnace after firing at a rate of 100-300 sccm, preferably at a rate of 150-250 sccm, more preferably at a rate of 200sccm, to vent air from the tube furnace.
The aeration time is 2 to 15min, preferably 3 to 10min, more preferably 4min.
The reduction is preferably performed in a mixed atmosphere of an inert gas, preferably argon, and the inert gas is introduced at a rate of 50 to 200sccm, preferably 70 to 150sccm, more preferably 100sccm.
The hydrogen gas is introduced at a rate of 20 to 100sccm, preferably 40 to 70sccm, more preferably 50sccm.
The reduction temperature is 500 to 1200 ℃, preferably 800 to 1000 ℃, more preferably 900 ℃.
The reduction time is 1 to 60 minutes, preferably 2 to 5 minutes, more preferably 3 minutes.
A third aspect of the present invention is to provide the use of a catalyst according to the first aspect of the present invention or a catalyst prepared by the preparation method according to the second aspect of the present invention, which is useful for the preparation of bulk single-walled carbon nanotubes of small diameter.
A fourth aspect of the present invention is to provide a method for preparing small-diameter single-walled carbon nanotubes, the method comprising the steps of:
and a step a, adding a catalyst into the tubular furnace, and raising the furnace temperature to the growth temperature of the carbon nano tube.
The catalyst is the catalyst according to the first aspect of the invention or the catalyst prepared by the preparation method according to the second aspect of the invention, and the prepared catalyst is placed in a tube furnace.
The temperature of the tube furnace is adjusted to the growth temperature of the carbon nano tube, and the temperature adjusting process is carried out under the protection of inert gas, preferably argon.
The argon gas is introduced in an amount of 100 to 300sccm, preferably 150 to 250sccm, more preferably 200sccm.
The growth temperature of the carbon nanotubes is 600 to 1000 ℃, preferably 650 to 950 ℃, more preferably 700 to 900 ℃.
The growth temperature of the carbon nano tube is lower than 600 ℃ or higher than 1000 ℃, the growth efficiency of the carbon nano tube is obviously reduced, and the average tube diameter of the carbon nano tube is gradually increased along with the gradual increase of the temperature within the range of 600-1000 ℃.
The growth time of the carbon nano tube is 5-30 min, preferably 10-25 min. More preferably, the growth time is 15 to 20 minutes.
And b, introducing a carbon source to prepare the carbon nano tube.
In the present invention, the carbon source is selected from one or more of methanol, methane, carbon monoxide, ethanol, ethylene, acetylene, propanol, toluene and xylene, preferably from one or more of methanol, methane, carbon monoxide, ethanol and toluene, more preferably from one or more of methane and ethanol, for example ethanol.
The kind of carbon source has great influence on the diameter of the carbon nanotube, and experiments show that the diameter of the carbon nanotube grown by using ethanol as the carbon source is smaller than that of the carbon nanotube grown by using other carbon sources under the same condition.
In the invention, the growth of the carbon nano tube also needs to add a mixed gas of inert gas and hydrogen, and the inert gas is preferably argon.
The inert gas is introduced at a rate of 100 to 300sccm, preferably at a rate of 150 to 250sccm, more preferably at a rate of 200sccm.
The hydrogen gas is introduced at a rate of 10 to 50sccm, preferably 20 to 40sccm, more preferably 30sccm.
According to the present invention, when the carbon source is a gas, the carbon source is introduced into the tube furnace together with the inert gas and the hydrogen gas, and when the carbon source is a liquid, the liquid carbon source is preferably placed in a bubbler, the inert gas is introduced into the tube furnace after passing through the bubbler, and the inert gas serves as a carrier gas for the carbon source.
The ratio of the inert gas carrier gas inlet rate to the hydrogen inlet rate of the liquid carbon source is 200: (5-100), preferably the ratio of the feed rates is 200: (10-80), more preferably the ratio of the access rates is 200: (10-60).
The ratio of the carbon source to the hydrogen gas has an influence on the pipe diameter of the carbon nano-tube, the diameter of the carbon nano-tube gradually decreases along with the decrease of the ratio of the carbon source to the hydrogen gas, when the ratio of the carbon source to the hydrogen gas is too low, namely, the hydrogen gas is too high, the growth of the carbon nano-tube is inhibited, and if the ratio of the carbon source to the hydrogen gas is too high, the grown graphitized carbon layer quickly coats the catalyst to prevent the catalyst from contacting new carbon source molecules, so that the catalyst is deactivated, therefore, the growth preparation of the small-diameter carbon nano-tube is only facilitated by the proper ratio of the carbon source to the hydrogen gas.
The diameter of the small-diameter single-wall carbon nano tube is 0.9-1.2 nm. The method is suitable for being applied to the fields of near infrared bioluminescence imaging, quantum device single photon light sources and the like.
The invention has the beneficial effects that:
(1) The complexing agent is used in the preparation process of the small-diameter bulk single-walled carbon nanotube growth catalyst, and the catalyst can effectively limit the size of catalyst particles, so that the growth of the small-diameter bulk single-walled carbon nanotubes is realized;
(2) The method for removing the catalyst carrier in the small-diameter bulk single-walled carbon nanotube growth catalyst is simple, can be removed only by soaking with dilute acid, and is convenient for the subsequent application of the carbon nanotubes;
(3) The carbon nano tube prepared by the preparation method of the carbon nano tube has smaller diameter of 0.9-1.2nm, and is suitable for being applied to the fields of near infrared bioluminescence imaging, quantum device single photon light sources and the like.
Examples
The invention is further illustrated by the following specific examples, which are intended to be illustrative of the invention and are not intended to limit the scope of the invention.
Example 1 preparation of catalyst
Weighing 0.83mmolCo (SO) 4 ) 2 ·7H 2 O (purity 99.5%) and (NH) 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O (purity: 95%) was dissolved in 7.0mL of ultrapure water, and 3.33g (83 mmol) of light MgO was weighed into 33mL of ultrapure water, and the mixture was sonicated for 5 minutes until the mixture was uniformly dispersed. Under stirring, co (SO 4 ) 2 ·7H 2 O solution, (NH) 4 ) 2 Fe(SO 4 ) 2 ·6H 2 The O solution is dripped into MgO suspension (at the moment, the concentration of Fe and Co in the suspension is 0.16 mol/L), EDTA (ethylenediamine tetraacetic acid) which is 5 times of the sum of the molar amounts of Fe and Co is added, the suspension is stirred for 10min, boiled for 30min, cooled and filtered, washed twice by ultrapure water and absolute ethyl alcohol respectively, and then dried for 12h in an oven at 120 ℃ to obtain the FeCo/MgO catalyst precursor added with complexing agent, wherein the molar ratio of Mg to Fe to Co=100 to 1.
Weighing 50mg of the prepared catalyst precursor, pushing into a ceramic boat with the thickness of 7cm and 0.5cm, pushing into the center of a tubular furnace, heating to 700 ℃ in an air atmosphere, burning for 3min, introducing Ar gas 200sccm for 4min to discharge air in the tubular furnace, simultaneously heating the furnace to 900 ℃, introducing Ar gas 100sccm and H 2 And (3) keeping the temperature at 50sccm for 3min, and reducing to obtain the catalyst.
Example 2 preparation of carbon nanotubes
Placing the catalyst prepared in example 1 in a tube furnace, adjusting the furnace temperature to 900 ℃ under the protection of 200sccm Ar gas, leading 200sccm Ar gas into the tube furnace after passing through an ethanol (carbon source) bubbler (ice water bath constant temperature), and simultaneously leading H into 2 30sccm, maintaining at 900 deg.C for 15min, and finally heating with Ar gas and H 2 And the atmosphere is protected to be reduced to room temperature, so that the small-diameter single-walled carbon nanotube is obtained.
Comparative example
Comparative example 1
The procedure of example 1 was repeated, except that: no ethylenediamine tetraacetic acid was added.
Comparative example 2
The procedure of example 2 was repeated, with the only difference that: the catalyst prepared in comparative example 1 was used.
Comparative example 3
The procedure of comparative example 2 was repeated, with the only difference that: the carbon source adopts methane, and under the condition of introducing Ar gas of 200sccm, CH is simultaneously introduced 4 325sccm and H 2 The preparation of carbon nanotubes was performed at 30sccm.
Comparative example 4
The procedure of comparative example 2 was repeated, with the only difference that: weighing 0.83mmolCo (NO) 3 ) 2 ·6H 2 O (purity 98.5%) and Fe (NO) 3 ) 3 ·9H 2 O (purity 98.5%) was dissolved in 7.0mL of ultrapure water, respectively.
Comparative example 5
The procedure of comparative example 2 was repeated, with the only difference that: weighing 0.83mmolCo (CH) 3 COO) 2 ·4H 2 O (purity 95%) and (NH) 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O (purity: 99.5%) was dissolved in 7.0mL of ultrapure water, respectively.
Comparative example 6
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm Ar gas is introduced into a tube furnace after passing through an ethanol (carbon source) bubbler (ice water bath constant temperature), and H is introduced simultaneously 2 80sccm。
Comparative example 7
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm Ar gas is introduced into a tube furnace after passing through an ethanol (carbon source) bubbler (ice water bath constant temperature), and H is introduced simultaneously 2 60sccm。
Comparative example 8
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm Ar gas is introduced into a tube furnace after passing through an ethanol (carbon source) bubbler (ice water bath constant temperature), and H is introduced simultaneously 2 50sccm。
Comparative example 9
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm Ar gas is introduced into a tube furnace after passing through an ethanol (carbon source) bubbler (ice water bath constant temperature), and H is introduced simultaneously 2 40sccm。
Comparative example 10
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm Ar gas is introduced into a tube furnace after passing through an ethanol (carbon source) bubbler (ice water bath constant temperature), and H is introduced simultaneously 2 20sccm。
Comparative example 11
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm of Ar gas was passed through an ethanol (carbon source) bubbler (ice-water bath)Constant temperature) and then is fed into a tube furnace, and H is fed simultaneously 2 10sccm。
Comparative example 12
The procedure of comparative example 2 was repeated, with the only difference that: 200sccm of Ar gas was passed through an ethanol (carbon source) bubbler (ice water bath constant temperature) and then introduced into a tube furnace without introducing hydrogen gas.
Comparative example 13
The procedure of comparative example 2 was repeated, with the only difference that: the temperature of the grown carbon nanotubes was 1000 ℃.
Comparative example 14
The procedure of comparative example 2 was repeated, with the only difference that: the temperature of the grown carbon nanotubes was 900 ℃.
Comparative example 15
The procedure of comparative example 2 was repeated, with the only difference that: the temperature of the grown carbon nanotubes was 800 ℃.
Comparative example 16
The procedure of comparative example 2 was repeated, with the only difference that: the temperature of the grown carbon nanotubes was 600 ℃.
Experimental example
Experimental example 1 Raman test
The carbon nanotubes prepared in comparative examples 2 and 3 were subjected to raman tests at laser wavelengths of 532nm and 633nm, respectively, using a LabRAM anais raman spectrometer from Horiba Jobin-Yvon co, the test spectra of 532nm being shown in fig. 1, and the test spectra of 633nm being shown in fig. 2.
As can be seen from fig. 1 and 2, the RBM peak position of the carbon nanotubes grown using ethanol is significantly higher than that of the carbon nanotubes grown using methane, indicating that the diameter of the carbon nanotubes grown using methane is larger than that of the carbon nanotubes grown using ethanol.
The carbon nanotubes prepared in comparative examples 2, 4 and 5 were raman-tested at laser wavelengths of 532nm and 633nm, respectively, using a LabRAM anais raman spectrometer from Horiba Jobin-Yvon co, the test spectrum of 532nm being shown in fig. 3, and the test spectrum of 633nm being shown in fig. 4.
As can be seen from fig. 3 and 4, the RBM peak of the carbon nanotubes grown using the sulfate precursor (prepared in example 1) appears at a higher wavenumber, that is, the tube diameter of the carbon nanotubes is smaller, the acetate growth is inferior, and the tube diameter of the nitrate grown carbon nanotubes is largest.
The carbon nanotubes prepared in comparative examples 2, 6, 7, 8, 9, 10, 11 and 12 were raman-tested at laser wavelengths of 532nm and 633nm, respectively, using a LabRAM arais type raman spectrometer from Horiba Jobin-Yvon co, the test spectra at 532nm being shown in fig. 5, and the test spectra at 633nm being shown in fig. 6.
As can be seen from FIGS. 5 and 6, as the hydrogen flow rate gradually increases from 0, the Raman spectrum is 100-180 cm -1 The RBM peak of (a) gradually weakens or disappears (corresponding to a single-walled carbon nanotube with a diameter of 2.4-1.3 nm), and 200cm -1 The RBM peaks above were progressively enhanced (corresponding to single-walled carbon nanotubes having diameters less than 1.2 nm), indicating that the diameters of the grown carbon nanotubes progressively decreased as the carbon to hydrogen ratio in the CVD atmosphere was reduced. When the hydrocarbon ratio is too low, namely the hydrogen flow is too high, RBM peaks do not appear in the Raman spectrogram, and the growth of the carbon nano tube is inhibited.
The carbon nanotubes prepared in comparative examples 2, 13, 14, 15 and 16 were subjected to raman tests at laser wavelengths of 532nm and 633nm, respectively, using a LabRAM anais raman spectrometer from Horiba Jobin-Yvon co, the test spectra at 532nm being shown in fig. 7, and the test spectra at 633nm being shown in fig. 8.
In fig. 7 and fig. 8, as the growth temperature of the carbon nanotubes increases from 700 ℃ to 900 ℃, the intensity of RBM peak at lower wavenumber in the raman spectrum increases gradually, which means that as the temperature increases, the tube diameter of the carbon nanotubes increases gradually, and when the growth temperature is 600 ℃ and 1000 ℃, the growth efficiency of the carbon nanotubes decreases significantly, and RBM peak no longer appears in the raman spectrum.
The carbon nanotubes prepared in comparative example 2 and example 2 were subjected to raman tests at laser wavelengths of 532nm and 633nm, respectively, using a LabRAM anais raman spectrometer from Horiba Jobin-Yvon co, the test spectra of which are shown in fig. 9, and the test spectra of which are shown in fig. 10.
As can be seen from fig. 9 and 10, the RBM peak in the raman spectrum of the carbon nanotube obtained after EDTA addition is significantly blue shifted, indicating that the diameter of the carbon nanotube is reduced after EDTA addition, calculated from the RBM peak position (calculated from Zhang, d.; yang, j.; li, y. Small,2013,9,1284-1304.Doi: 10.1002/small, 201202986), and the diameter of the carbon nanotube grown after EDTA addition is in the range of 0.9 to 1.2nm.
The invention has been described in detail in connection with the specific embodiments and exemplary examples thereof, but such description is not to be construed as limiting the invention. It will be understood by those skilled in the art that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, and these fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (4)

1. A method for preparing small diameter bulk single-walled carbon nanotubes, the method comprising the steps of:
step a, adding a catalyst into a tube furnace, and raising the furnace temperature to the growth temperature of the carbon nano tube;
step b, introducing a carbon source to prepare the carbon nano tube;
the catalyst is prepared from a compound containing an element A, a catalyst carrier and a complexing agent, wherein the element A is one or more of iron, cobalt and nickel;
the catalyst is prepared by a method comprising the steps of:
step 1, preparing a catalyst precursor by adopting a compound containing an element A, a catalyst carrier and a complexing agent;
step 2, preparing a catalyst through burning and reduction;
in the step (1) of the process,
the compound containing the A element is selected from one or more of salts containing the A element and soluble in water;
the catalyst carrier is magnesium oxide;
the mol ratio of the catalyst carrier to the compound containing the A element is (30-70): 1;
the complexing agent is selected from ethylenediamine tetraacetic acid or salts thereof;
the diameter of the small-diameter single-wall carbon nano tube is 0.9-1.2 nm.
2. The method according to claim 1, wherein in step 1, the complexing agent is added in an amount of 1 to 15 times the molar amount of the compound containing the element a.
3. The method according to claim 1, wherein, in step 2,
the firing temperature is 400-1200 ℃, the firing atmosphere is air, and the firing time is 1-60 min;
the reduction temperature is 500-1200 ℃, the reduction atmosphere is the mixed gas of hydrogen and inert gas, and the reduction time is 1-60 min.
4. The method according to claim 1, wherein,
in the step a, the growth temperature of the carbon nano tube is 600-1000 ℃ and the growth time is 5-30 min;
in the step b, the carbon source is selected from one or more of methanol, methane, carbon monoxide, ethanol, ethylene, acetylene, propanol, toluene and xylene.
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