CN111924826A - Preparation method of narrow-diameter distribution and high-purity metallic single-walled carbon nanotube - Google Patents

Preparation method of narrow-diameter distribution and high-purity metallic single-walled carbon nanotube Download PDF

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CN111924826A
CN111924826A CN202010709224.5A CN202010709224A CN111924826A CN 111924826 A CN111924826 A CN 111924826A CN 202010709224 A CN202010709224 A CN 202010709224A CN 111924826 A CN111924826 A CN 111924826A
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walled carbon
catalyst
carbon nanotube
metallic single
carbon nanotubes
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CN111924826B (en
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刘畅
李鑫
张峰
侯鹏翔
成会明
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Abstract

The invention relates to the field of controllable preparation of metallic single-walled carbon nanotubes, in particular to a preparation method of a narrow-diameter-distribution high-purity metallic single-walled carbon nanotube. The preparation method comprises the steps of controllably preparing catalyst nano particles with uniform size by using a block copolymer self-assembly method, and designing components of the catalyst and regulating and controlling oxidation and reduction conditions of the catalyst to obtain bimetal solid solution nano particles with uniform size, monodispersity, close-packed hexagonal structure and high melting point; and then the dynamic reaction conditions of low temperature, low carbon source, low hydrogen and low carrier gas flow rate are controlled to realize the quasi-static chemical vapor deposition process, and metallic single-walled carbon nanotubes with the diameter of 1.1 +/-0.3 nm and the purity of 80 wt% are directly grown. The invention combines the design of the catalyst with growth thermodynamics and kinetics control, realizes the direct controllable growth of the metallic single-walled carbon nanotube with narrow diameter distribution and high purity, improves the structure control precision of the metallic single-walled carbon nanotube and lays a material foundation for promoting the application of the metallic single-walled carbon nanotube.

Description

Preparation method of narrow-diameter distribution and high-purity metallic single-walled carbon nanotube
Technical Field
The invention relates to the field of controllable preparation of metallic single-walled carbon nanotubes, in particular to a preparation method of a narrow-diameter-distribution high-purity metallic single-walled carbon nanotube.
Background
Single-walled carbon nanotubes with different chiral angles and diameters can behave as metallic and semiconducting. The metallic single-walled carbon nanotube has ultrahigh electric transport property due to quantum transport effect, and is an excellent electrode material in future nano-electronic devices, and the semiconductor single-walled carbon nanotube has high carrier mobility and a one-dimensional structure, and is an ideal material for constructing a field effect transistor channel. Therefore, obtaining single-walled carbon nanotubes (metallic or semiconducting) with high purity and single conductive properties is a necessary premise for realizing the application thereof in the above fields, and is of great significance.
At present, although the controllable preparation work of the single-walled carbon nanotube is greatly advanced, most of the single-walled carbon nanotubes utilize the characteristic that the semiconductor single-walled carbon nanotube has lower chemical reaction activity than the metallic single-walled carbon nanotube, and the metallic carbon nanotube is removed by introducing etching gas in situ to obtain the semiconductor-enriched single-walled carbon nanotube. In contrast, metallic single-walled carbon nanotubes are more difficult to prepare and less selective preparation has been reported. The only representative work is as follows: (1) by controlling the nucleation stage of the single-walled carbon nanotube, the method comprises the following steps: controlling the surface state and morphology of the catalyst during nucleation to preferentially grow metallic single-walled carbon nanotubes (literature I: Harutyunyan A.R.; Cheng, G., Sumanasekera, G.U.et.al.science,2009,326,116); (2) the high-temperature stability of the catalyst and the control of the crystal phase exposing a specific crystal face are realized, and the matching of the catalyst with the specific crystal face and the single-walled carbon nanotube with a specific structure is realized (document II: Yang, F.; Wang, X.; Li, Y.et al.Nature 2014,510,7506); (3) symmetry control of a specific crystal face of the catalyst is carried out, and symmetry matching of the catalyst and a carbon nanotube with specific properties is realized (three documents: Zhang, S.C.; Kang, L.X.; Zhang, J.et al.Nature 2017,543,7644); (4) the size of the high-melting-point non-metal oxide catalyst nano particles and the oxygen content in the growth process are controlled, and the direct growth of the narrow-diameter distribution and metallic single-walled carbon nano tubes is realized (four documents: Zhang, L.L.; Sun, D.M.; Liu, C.et al. advanced Materials,2017,29, 32).
However, there are still many problems with the current preparation of metallic single-walled carbon nanotubes: (1) the traditional metal catalysts such as iron, cobalt, nickel and the like are easy to agglomerate and Ostwald ripening in the chemical vapor deposition process at high temperature (>600 ℃) due to low melting point, and the particle size distribution is widened, so that the diameter distribution of the carbon nano tube is wide; (2) the regulation and control difficulty of the components and the structure of the bimetallic catalyst is high, and high-melting-point bimetallic catalyst nano-particles with uniform size and controllable components and structures cannot be obtained; (3) the low activity of the non-metallic catalyst causes low efficiency of metallic carbon nanotube growth; (4) the mechanism of controlled growth of metallic single-walled carbon nanotubes remains unclear.
Therefore, the main problems facing today are: how to develop a method for controllably growing narrow-diameter distribution metallic single-walled carbon nanotubes on the basis of understanding the controllable growth mechanism.
Disclosure of Invention
The invention aims to provide a preparation method of a narrow-diameter-distribution high-purity metallic single-walled carbon nanotube, which solves the problem of wide diameter distribution of a growing carbon nanotube caused by unstable high-temperature and easy agglomeration of common metal nanoparticles through the design of the size, the components and the structure of a catalyst; the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate are selected to directly grow the metallic single-walled carbon nanotube with narrow diameter distribution, high purity and high quality.
The technical scheme of the invention is as follows:
a preparation method of a narrow-diameter-distribution high-purity metallic single-walled carbon nanotube is characterized in that catalyst nanoparticles with uniform size are controllably prepared by utilizing a block copolymer self-assembly method, and bimetallic solid solution nanoparticles with uniform size, monodispersity, close-packed hexagonal structure and high melting point are obtained by designing components of a catalyst and regulating and controlling oxidation and reduction conditions of the catalyst, so that a thermodynamic basis is provided for nucleation and growth of the single-walled carbon nanotube; and then realizing a quasi-static chemical vapor deposition process by controlling the dynamic reaction conditions of low temperature, low carbon source, low hydrogen and low carrier gas flow rate, and directly growing metallic single-walled carbon nanotubes with the diameter of 1.1 +/-0.3 nm and the content of 75-85 wt%, wherein the method specifically comprises the following steps:
(1) preparation of block copolymer micelle film: soaking a silicon wafer substrate in a piranha solution for cleaning and hydrophilic treatment, then performing oxygen plasma treatment, and spin-coating a block copolymer micelle solution to form a block copolymer micelle film;
(2) preparation of catalyst nanoclusters: immersing the substrate with the micelle film on the surface in NaReO4And K3[Co(CN)6]Adsorbing two metal anions ReO in a catalyst precursor salt solution4 -And [ Co (CN)6]3-Assembling into nanoclusters; the control of cluster components is realized by adjusting the concentrations of two catalyst precursors in the solution;
(3) preparation of catalyst nanoparticles: carrying out high-temperature oxidation and reduction treatment on the catalyst nanocluster by using hydrogen and argon mixed gas to obtain CoRexSolid solution nanoparticles; the technological parameters are as follows: oxidizing at high temperature of 700-750 ℃ for 1-5 min, introducing 500-800 sccm argon for 1-5 min, and switching to 75-250 sccm Ar and 5-40 sccm H2Reducing the mixed gas for 2-5 min;
(4) preparing single-walled carbon nanotubes: with CoRexThe nano particles are used as a catalyst, and the single-walled carbon nano tubes with narrow diameter distribution and dominant metallicity directly grow under the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate; the technological parameters are as follows: using 30-40 sccm argon gas to load ethanol molecule as carbon source, 2-15 sccm H2And (3) as an etching gas for controlling the growth rate during the reduction of the nano particles and the growth of the carbon nano tubes, regulating the flow rate of the gas and the concentration of a carbon source and hydrogen by using Ar of 75-115 sccm, keeping the total flow of the gas at 115-200 sccm, and performing chemical vapor deposition to grow the single-walled carbon nano tubes for 1-10 min.
The preparation method of the narrow-diameter distribution and high-purity metallic single-walled carbon nanotube comprises the following steps of structural characterization of a catalyst and the single-walled carbon nanotube: measuring and counting the diameter and density of the catalyst nano particles by using an atomic force microscope, and representing the crystal structure and component distribution of the catalyst by using a transmission electron microscope; and measuring and counting the density and the length of the single-walled carbon nanotube by using a scanning electron microscope, measuring the diameter of the single-walled carbon nanotube by using a transmission electron microscope, counting the distribution of the single-walled carbon nanotube, and estimating the purity of the metallic single-walled carbon nanotube by using a multi-wavelength Raman spectrum.
The catalyst prepared by the method for preparing the narrow-diameter-distribution high-purity metallic single-walled carbon nanotube has a structure of close-packed hexagonal CoRexThe solid solution particles have a particle size distribution within a range of 1.5-3.5 nm, an atomic ratio of Co to Re of 1: 1-1: 9, a melting point of 2000 ℃ or higher as seen from an alloy phase diagram, and are high-melting-point catalysts.
According to the preparation method of the narrow-diameter-distribution high-purity metallic single-walled carbon nanotube, the length of the grown single-walled carbon nanotube is 1-10 mu m.
The preparation method of the narrow-diameter-distribution high-purity metallic single-walled carbon nanotube regulates the diameter and the conductive property of the single-walled carbon nanotube by regulating and controlling the thermodynamic nucleation condition and the kinetic growth condition, including catalyst components, size, structure, growth temperature, carbon source, hydrogen concentration and flow rate.
In the preparation method of the narrow-diameter-distribution high-purity metallic single-walled carbon nanotube, in the step (1), a toluene and tetrahydrofuran solution of a polystyrene-b-poly (4-vinylpyridine) block copolymer with the concentration of 0.01-0.25 wt% is adopted as a block copolymer micelle solution, the mass ratio of toluene to tetrahydrofuran is 2-4: 1, and the block copolymer micelle height is 6-15 nm.
The preparation method of the narrow-diameter-distribution high-purity metallic single-walled carbon nanotube comprises the step (2) of NaReO4And K3[Co(CN)6]The catalyst precursor salt solution is a hydrochloric acid solution with the molar concentration of 0.01-1M, NaReO4And K3[Co(CN)6]In a molar ratio of x: (0.5-x), wherein x is 0.1-0.3.
The narrow diameter distribution and high purity metallic single-wall carbon nano-meterMethod for producing tube, step (3), CoRexThe particle size of the solid solution nano particles is 0.5-3.5 nm.
The design idea of the invention is as follows:
the invention uses high melting point bimetallic solid solution CoRexIs used as catalyst for directly and selectively growing metallic single-wall carbon nanotube. The method designs and prepares the monodisperse, uniform-size and hexagonal close-packed CoRe high-melting-point catalyst, thereby not only avoiding the high-temperature agglomeration of the catalyst, but also solving the problem of controlling the nucleation of the metallic carbon nanotube and obtaining the carbon cap with uniform and stable size; CoRe because of the stronger affinity of Co to H than Rex(e.g., CoRe)4Etc.) more hydrogen atoms are adsorbed on the surface, the decomposition and diffusion of a carbon source are inhibited, and the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate are adopted, so that the carbon atoms are slowly diffused and grown on the surface of the catalyst in a quasi-static state, the maximization of the growth rate difference of the metallic single-walled carbon nanotube and the semiconductor single-walled carbon nanotube is further realized, and the preferential growth of the metallic single-walled carbon nanotube is realized.
The invention has the advantages and beneficial effects that:
1. the invention realizes the preparation of the high-melting-point bimetallic catalyst nano-particles with uniform size and controllable components and structure, and solves the problem of high-temperature agglomeration of the catalyst;
2. the invention directly grows the single-walled carbon nanotube with high purity metallic enrichment, and the method is simple and has strong applicability;
3. the diameter distribution of the metallic single-walled carbon nanotube prepared by the invention is narrow;
4. the invention clarifies the main factors influencing the growth of the metallic single-walled carbon nanotube and the controllable growth mechanism thereof, and provides a new idea for the controllable growth of the carbon nanotube.
In conclusion, the invention takes the catalyst which plays a decisive role in controlling the nucleation stage of the single-walled carbon nanotube as a starting point, breaks through the bottleneck of controlling and preparing the metallic single-walled carbon nanotube at the present stage by regulating and controlling the thermodynamic conditions such as the high melting point and the structural component of the bimetallic catalyst and the kinetic conditions in the process of growing the carbon nanotube by chemical vapor deposition, and provides new knowledge for the controllable growth of the single-walled carbon nanotube with a specific structure.
Drawings
FIG. 1.CoRexThe preparation of bimetallic catalyst nano-particles and the process of growing narrow-diameter distribution metallic single-walled carbon nano-tubes are shown in the figure.
FIG. 2.CoRexSchematic diagram of principle of bimetallic catalyst nano-particle growth narrow diameter distribution metallic single-wall carbon nano-tube.
FIG. 3.CoRe4Morphology and structure of nanoparticles. Wherein (a) an atomic force microscope photograph of the nanoparticles; (b) transmission electron micrographs of nanoparticles; (c) a particle size distribution histogram of transmission electron microscopy statistics; (d-e) high resolution transmission electron micrographs of nanoparticles; (f-g) high resolution Fourier transform photographs of nanoparticles.
FIG. 4.CoRe4And (4) characterizing the components of the nanoparticles. Wherein (a) a high angle annular dark field image; (b) the point scanning elements of the energy spectrum in the transmission electron microscope are distributed, and the position of the abscissa is the distance from the beginning to the end of the grain marking line of the circle in the step (a); (c-d) elemental content distribution of the area scan.
FIG. 5.CoRe4The morphology and structure of the carbon nanotubes prepared by the catalyst. Wherein, (a) the scanning electron microscope photo of the carbon nano tube on the surface of the silicon chip; (b-c) transmission electron micrograph of single-walled carbon nanotube; (d) and (4) carrying out statistics on the diameter distribution histogram of the carbon nano tube based on the transmission electron microscope photo.
FIG. 6.CoRe4Multi-wavelength Raman spectrum of single-wall carbon nano tube grown by using nano particles as catalyst. Wherein, (a) a 633nm wavelength laser-excited breathing mode; (b) a breathing mode excited by laser with a wavelength of 532 nm; (c)785nm wavelength laser-excited breathing mode; (d) d, G mode excited by 532nm laser.
Figure 7 morphology and structure characterization of Co nanoparticle catalysts. Wherein (a) an atomic force microscope photograph of the nanoparticles; (b) transmission electron micrographs of nanoparticles; (c) a particle size distribution histogram of transmission electron microscopy statistics; (d-e) high resolution transmission electron micrographs of nanoparticles; (f-g) high resolution Fourier transform photographs of nanoparticles.
FIG. 8.Co and CoRe1Scanning photos of single-walled carbon nanotubes prepared for the catalyst and corresponding multi-wavelength Raman spectrum RBM mode. Wherein, (a) Co is a scanning photo of the single-walled carbon nanotube grown by the catalyst; (b) co is a 532nm wavelength laser RBM mode of the single-walled carbon nanotube grown by the catalyst; (c) co is a single-walled carbon nanotube 633nm wavelength laser RBM mode grown by a catalyst; (d) scanning photos of the single-walled carbon nanotubes grown by the catalyst with the Co/Re atomic ratio of 1: 1; (e) CoRe is a 532nm wavelength laser RBM mode of the single-walled carbon nanotube grown by the catalyst; (f) CoRe is laser RBM mode with 633nm wavelength of single-wall carbon nanotube grown by catalyst.
Detailed Description
As shown in FIG. 1, CoRe is used in the inventionxThe method for preparing the narrow-diameter-distribution high-purity metallic single-walled carbon nanotube by using the high-melting-point bimetallic solid solution nano particles as the catalyst comprises the following specific preparation and growth processes:
the method is used for preparing monodisperse CoRe with narrow diameter distribution by regulating and controlling the self-assembly process of the block copolymer and the method for forming nano particles by post-treatmentx(X ═ 1 to 9) bimetallic nanoparticle catalysts; obtaining uniform-sized block copolymer micelles by adopting a block copolymer self-assembly method, wherein each block copolymer micelle is subjected to spin coating, dipping and chemical adsorption of quantitative bimetallic anions, so that uniform-sized metal nanoclusters are obtained; by controlling the composition ratio of bimetal and the conditions of low-temperature oxidation and reduction, the CoRe with monodisperse, close-packed hexagonal structure and high melting point is obtainedxCatalyst nanoparticles; and then the quasi-static chemical vapor deposition is realized by controlling the growth kinetic conditions of low temperature, low carbon source, low hydrogen and low flow rate, so that carbon atoms are slowly diffused and assembled on the surface of the catalyst, the maximization of the difference of the growth rates of the metallic single-walled carbon nano-tubes and the semiconductor single-walled carbon nano-tubes is realized, and the metallic single-walled carbon nano-tubes with narrow diameter distribution (the diameter is 1.1 +/-0.3 nm) and high purity (the purity reaches 80 wt%) can be directly and controllably grown.
The invention combines the design of the catalyst with growth thermodynamics and kinetics control, realizes the direct controllable growth of the metallic single-walled carbon nanotube with narrow diameter distribution and high purity, improves the structure control precision of the metallic single-walled carbon nanotube and lays a material foundation for promoting the application of the metallic single-walled carbon nanotube.
As shown in fig. 2, the mechanism for controlling the growth of narrow diameter distribution metallic single-walled carbon nanotubes is as follows:
first, thermodynamically, the catalyst CoRexCompared with Co, the cobalt-rhenium alloy has a higher melting point, a cobalt face-centered cubic melting point of 1495 ℃, and a close-packed cubic melting point of the cobalt-rhenium alloy>2000 ℃, can effectively inhibit catalyst agglomeration, high-temperature Oswald ripening, nanoparticle high-temperature melting and thermal vibration, thereby stabilizing the structure of the carbon cap in the nucleation stage, so that the prepared particles have smaller and more uniform size, are beneficial to growth of single-walled carbon nanotubes with narrow diameter distribution, and CoRexThe structure of (A) is a close-packed hexagonal structure, which is beneficial to the nucleation of metallic carbon nanotubes;
secondly, in terms of kinetics, since Co has a stronger affinity with H than Re, the Co surface can adsorb 5 hydrogen atoms ([ CoH ]5]4-) Or 4 hydrogen atoms ([ CoH ]4]5-) The Re surface can adsorb 9 hydrogen atoms ([ ReH ]9]2-) Or 6 hydrogen atoms ([ ReH ]6]5-) Thus CoRe4More hydrogen atoms are adsorbed on the surface, so that the active sites adsorbed on the metal surface are occupied, and the adsorption, catalytic cracking and surface diffusion of a carbon source on the surface of the catalyst are inhibited. Therefore, on the basis of obtaining the metallic carbon cap with uniform and stable size, the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate are adopted, so that carbon atoms are slowly diffused and assembled on the surface of the catalyst in a quasi-static manner, the maximization of the growth rate difference of the metallic single-walled carbon nanotube and the semiconductor single-walled carbon nanotube is further realized, and finally, the long preferential growth of the metallic single-walled carbon nanotube is realized through the control of the growth time.
The present invention will be described in more detail below with reference to examples.
Example 1.
In this example, the preparation and characterization of narrow diameter distribution, high purity metallic single-walled carbon nanotubes are as follows:
(1)CoRexdouble goldThe preparation of the catalyst comprises the following steps:
soaking 10mm × 10mm silicon wafer in piranha solution for 15min for cleaning, washing with deionized water, and treating with oxygen plasma at power of 32W. The method comprises the steps of spin-coating a toluene and tetrahydrofuran solution (the mass ratio of toluene to tetrahydrofuran is 3:1) of polystyrene-b-poly (4-vinylpyridine) block copolymer (PS50000-b-P4VP13000) with the concentration of 0.01-0.25 wt% on the surface of a silicon wafer subjected to hydrophilic treatment at the rotating speed of 2000-7000 rpm to form a block copolymer micelle film, wherein the height of a block copolymer micelle is 6-15 nm. Then, the silicon wafer is immersed in a hydrochloric acid solution with a solvent of 0.01-1M (mol/L), wherein the solute is a bimetallic catalyst precursor salt (x mM (mmol/L) NaReO4And (0.5-x) mM (mmol/L) K [ Co (CN)6]3X is 0.1-0.3), the time is 1-3 min, and ReO is adsorbed4 -And [ Co (CN)6]3-Two metal anions are assembled into nanoclusters, and cluster components can be controlled by adjusting the concentrations of two catalyst precursors in a bimetallic catalyst precursor salt solution. And taking out, washing with deionized water, drying at 50-60 ℃ for 15-20 min, and performing oxygen plasma treatment for 1-5 min.
And (3) placing the treated silicon wafer into a quartz boat of a tube furnace, oxidizing for 1-5 min at 700-750 ℃, pushing out the quartz boat, and cooling to room temperature. Then, introducing 500-800 sccm argon gas into the tube furnace for 4min, and switching to 75-250 sccm Ar and 5-40 sccm H2Pushing the quartz boat carrying the silicon wafers into a constant temperature area for reduction for 2-5 min to obtain CoRexThe particle size of the solid solution nano-particles is 1.5-3.5 nm, and the prepared nano-particles are subjected to structural characterization.
As shown in fig. 3(a), the atomic force microscope characterization result indicates that the nanoparticles are uniformly dispersed on the surface of the silicon substrate. As shown in fig. 3(b), the transmission electron microscopy characterization results indicated that the nanoparticles were uniform in size. The diameters of 150 particles were counted at random, and the results are shown in FIG. 3(c), where the particle size distribution of the nanoparticles was 1.5 to 3.5 nm. FIG. 3(d-e) is a high resolution TEM image of nanoparticles, the corresponding Fourier transform is shown in FIG. 3(f-g), it can be seen that the particles are typical hexagonal close-packed structures, the lattice fringe spacing is 0.20-0.27 nm for the a-axis, and 0.32-0.44 nm for the b-axis.
As shown in fig. 4(a), the size and the composition distribution thereof were further characterized by HADDF, and the composition distribution thereof was uniform. As shown in fig. 4(b), from the EDS statistics of the particles, the atomic ratio Co corresponding to the element content of the particles: re is 1: 4. as shown in FIGS. 4(c-d), the particles both contained Co and Re.
(2) Preparing and characterizing the narrow-diameter distribution and high-purity metallic single-walled carbon nanotube:
growing single-walled carbon nanotubes on the basis of the step (1) by using CoRe4The nanoparticles are used as a catalyst, 30-40 sccm argon gas is loaded into ethanol molecules to be used as a carbon source, and 2-15 sccm H2And (3) as an etching gas for controlling the growth rate during the reduction of the nano particles and the growth of the carbon nano tubes, regulating the flow rate of the gas and the concentration of a carbon source and hydrogen by using Ar of 75-115 sccm, keeping the total flow of the gas at 115-200 sccm, and performing chemical vapor deposition to grow the single-walled carbon nano tubes for 5 min. And after the growth is finished, closing the carbon source, pushing the quartz boat out of the constant temperature area under the protection of argon, cooling to room temperature, and taking out the sample. Therefore, the single-walled carbon nanotube with narrow diameter distribution and dominant metallic property can be directly grown under the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate.
The structures of the catalyst and the single-walled carbon nanotubes are characterized: measuring and counting the diameter and density of the catalyst nano particles by using an atomic force microscope, and representing the crystal structure and component distribution of the catalyst by using a transmission electron microscope; and measuring and counting the density and the length of the single-walled carbon nanotube by using a scanning electron microscope, measuring the diameter of the single-walled carbon nanotube by using a transmission electron microscope, counting the distribution of the single-walled carbon nanotube, and estimating the purity of the metallic single-walled carbon nanotube by using a multi-wavelength Raman spectrum.
As shown in fig. 5(a), the scanning electron micrograph of the prepared single-walled carbon nanotube shows that the single-walled carbon nanotube has a relatively straight wall and a length of about 5 μm. As shown in FIG. 5(b-c), the TEM image of the single-walled carbon nanotube shows that the single-walled carbon nanotube has excellent crystallinity as the wall is flat. As shown in FIG. 5(d), the diameters of 150 carbon nanotubes were randomly counted, and it was found that the diameter distribution was very narrow, mainly focusing on 0.8 to 1.4 nm.
As shown in FIGS. 6(a-c), in the respiratory mode of the multi-wavelength (532nm,633nm,785nm) laser Raman spectrum, it can be seen that most of the excited single-walled carbon nanotubes are located in the metallic region. As shown in FIG. 6(d), the single-walled carbon nanotube is 1200-1800 cm-1Raman spectrum in the range of 1350cm-1There is no distinct D peak to the left or right, again demonstrating high crystallinity, with the G mode being a typical metallic BWF type peak. The content of the metallic single-walled carbon nanotube is estimated to be about 80 wt% according to the Katarula plots diagram and the number of breathing mode peaks in the corresponding interval.
Comparative example 1: co catalyst grown single-wall carbon nano-tube
A thin film of spin-on block copolymer (PS50000-b-P4VP13000) was immersed at a molar concentration of 0.5mM K3[Co(CN)6]In the solution, the heat treatment conditions were the same, the morphology and size distribution of the obtained particles were as shown in FIG. 7(a-c), and it can be seen that the diameter distribution thereof was within the range of 0.5 to 5.5nm, and the ratio of the average size of the particles to the distribution range of the diameter was CoRexIs large. As shown in fig. 7(d-g), the high resolution transmission electron micrograph and the corresponding fourier transform micrograph show that the particles are typical of the cobalt FCC structure.
The Co nanoparticles prepared in the comparative example were used as a catalyst to prepare single-walled carbon nanotubes under the same conditions as in example 1, and the morphology of Co-grown carbon nanotubes was shown in fig. 8(a), which indicates that a long and dense carbon nanotube network had grown on the surface of the silicon wafer. As shown in fig. 8(b-c), raman spectroscopy analyzed the conductive properties of the carbon nanotubes, and found that the diameter distribution of the carbon nanotubes was broad, the content of the metallic carbon nanotubes was about 35 wt%, and there was no selectivity of the conductive properties.
Comparative example 2: CoRe catalyst grown single-wall carbon nanotube
A thin film of spin-on block copolymer (PS50000-b-P4VP13000) was immersed in a molar concentration of 0.25mM K3[Co(CN)6]+ molarity 0.25mM NaReO4In the solution, the heat treatment conditions are the same, the diameter range of the obtained CoRe nano-particles is 0.5-4.5 nm, the average particle size is 2.9nm, the atomic content ratio of Co to Re is 1:1, and the average size and diameter distribution range ratio of the particles is CoRe4Large and smaller than the diameter of the Co particles, and has an HCP structure.
CoRe prepared in the above comparative example1Nanoparticles as a catalyst, single-walled carbon nanotubes were prepared under the same conditions as in example (1) and their scanning and raman are shown in fig. 8 (d-f). Multi-wavelength raman characterization revealed that the metallic single-walled carbon nanotubes were present at about 50 wt%.
Comparative example 3: dynamic condition control-temperature
CoRe prepared as in example 1xThe nanoparticles are a catalyst, and the effect of temperature on the growth of carbon nanotubes is studied by increasing the growth temperature in example 1, and when the temperature is lower than that in example 1, the amount of carbon nanotubes obtained is small. With the increase of temperature, the density, length and growth rate of the carbon nano tube are all obviously improved, and the distribution range of the diameter and the conductive property of the carbon nano tube is widened. The temperature conditions of example 1 were also demonstrated to favor the controlled growth of narrow diameter and metallic carbon nanotubes.
Comparative example 4: kinetic Condition control-carbon Source concentration
CoRe prepared as in example 1xThe nanoparticles were used as catalysts, and the effect of the carbon source concentration on the growth of carbon nanotubes was investigated by increasing the concentration of the carbon source for growth in example 1. The result shows that with the increase of the carbon source concentration, the density, the length and the growth rate of the carbon nano tube are all obviously improved, and the diameter and the conductive property distribution range of the carbon nano tube are widened. When the carbon source concentration is too high, the catalyst is deactivated due to carbon supersaturation, and the ability to grow carbon nanotubes is reduced. This further confirms that the carbon source concentration used in example 1 is suitable for narrow diameter distribution and controlled growth of metallic carbon nanotubes.
Comparative example 5: dynamic condition control-influence of hydrogen flow rate on growth morphology and structure of carbon nano tube
CoRe prepared as in example 1xNanoparticles as catalyst by varying H in example 12And (4) concentration, and researching the influence of the hydrogen concentration on the growth of the carbon nano tube. The prepared single-walled carbon nano-tube is subjected to characterization of scanning electron microscope appearance and multi-wavelength Raman spectrum, and is found to be free of hydrogenUnder the condition, the decomposition capability of the carbon source is very strong, the grown carbon nano tube has higher density and longer length, and the Raman spectrum representation shows that the diameter distribution range is widened and the conductive property selection is not carried out; when H is present2When the flow rate of (2) is increased to more than 6sccm, the inhibition effect of hydrogen on the decomposition of the carbon source is enhanced, the growth rate of the carbon nanotube is reduced, the metallic carbon nanotube having a small diameter is etched, and the diameter of the carbon nanotube moves in the direction of a large diameter. This further confirms that the appropriate hydrogen concentration of example 1 facilitates the controlled growth of narrow diameter and metallic carbon nanotubes.
The results of the examples and comparative examples show that higher Re content, relatively lower growth temperature, lower carbon source concentration, hydrogen concentration and low flow rate are beneficial to the enrichment growth of metallic carbon nanotubes. The invention realizes the control of the size, the components and the structure of the bimetallic high-melting-point catalyst nano particles and solves the problem of high-temperature agglomeration of the catalyst; the method is simple and has strong applicability; the diameter distribution of the prepared metallic single-walled carbon nanotube is narrow; the main factors influencing the growth of the metallic carbon nano-tube and the growth mechanism thereof are clarified, and a new thought is provided for the controllable growth of the nano-carbon material. The accuracy of controlling the structure of the metallic single-walled carbon nanotube is improved, and a material foundation is laid for exploring the application of the metallic single-walled carbon nanotube with a specific structure. The present invention is not limited to the above-mentioned embodiments and comparative examples, and various modifications and improvements made to the present invention by those skilled in the art within the spirit of the present invention should be protected by the claims of the present invention.

Claims (8)

1. A preparation method of a narrow-diameter-distribution high-purity metallic single-walled carbon nanotube is characterized in that a segmented copolymer self-assembly method is utilized to controllably prepare catalyst nanoparticles with uniform size, and bimetallic solid solution nanoparticles with uniform size, monodispersity, close-packed hexagonal structure and high melting point are obtained by designing components of a catalyst and regulating and controlling oxidation and reduction conditions of the catalyst, so that a thermodynamic basis is provided for nucleation and growth of the single-walled carbon nanotube; and then realizing a quasi-static chemical vapor deposition process by controlling the dynamic reaction conditions of low temperature, low carbon source, low hydrogen and low carrier gas flow rate, and directly growing metallic single-walled carbon nanotubes with the diameter of 1.1 +/-0.3 nm and the content of 75-85 wt%, wherein the method specifically comprises the following steps:
(1) preparation of block copolymer micelle film: soaking a silicon wafer substrate in a piranha solution for cleaning and hydrophilic treatment, then performing oxygen plasma treatment, and spin-coating a block copolymer micelle solution to form a block copolymer micelle film;
(2) preparation of catalyst nanoclusters: immersing the substrate with the micelle film on the surface in NaReO4And K3[Co(CN)6]Adsorbing two metal anions ReO in a catalyst precursor salt solution4 -And [ Co (CN)6]3-Assembling into nanoclusters; the control of cluster components is realized by adjusting the concentrations of two catalyst precursors in the solution;
(3) preparation of catalyst nanoparticles: carrying out high-temperature oxidation and reduction treatment on the catalyst nanocluster by using hydrogen and argon mixed gas to obtain CoRexSolid solution nanoparticles; the technological parameters are as follows: oxidizing at high temperature of 700-750 ℃ for 1-5 min, introducing 500-800 sccm argon for 1-5 min, and switching to 75-250 sccm Ar and 5-40 sccm H2Reducing the mixed gas for 2-5 min;
(4) preparing single-walled carbon nanotubes: with CoRexThe nano particles are used as a catalyst, and the single-walled carbon nano tubes with narrow diameter distribution and dominant metallicity directly grow under the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate; the technological parameters are as follows: using 30-40 sccm argon gas to load ethanol molecule as carbon source, 2-15 sccm H2And (3) as an etching gas for controlling the growth rate during the reduction of the nano particles and the growth of the carbon nano tubes, regulating the flow rate of the gas and the concentration of a carbon source and hydrogen by using Ar of 75-115 sccm, keeping the total flow of the gas at 115-200 sccm, and performing chemical vapor deposition to grow the single-walled carbon nano tubes for 1-10 min.
2. The method of making narrow diameter distribution, high purity metallic single-walled carbon nanotubes of claim 1 wherein the catalyst and single-walled carbon nanotubes are structurally characterized by: measuring and counting the diameter and density of the catalyst nano particles by using an atomic force microscope, and representing the crystal structure and component distribution of the catalyst by using a transmission electron microscope; and measuring and counting the density and the length of the single-walled carbon nanotube by using a scanning electron microscope, measuring the diameter of the single-walled carbon nanotube by using a transmission electron microscope, counting the distribution of the single-walled carbon nanotube, and estimating the purity of the metallic single-walled carbon nanotube by using a multi-wavelength Raman spectrum.
3. The method of claim 1 wherein the catalyst structure is hexagonal close packed CoRexThe solid solution particles have a particle size distribution within a range of 1.5-3.5 nm, an atomic ratio of Co to Re of 1: 1-1: 9, a melting point of 2000 ℃ or higher as seen from an alloy phase diagram, and are high-melting-point catalysts.
4. The method for preparing narrow diameter distribution, high purity metallic single-walled carbon nanotubes according to claim 1, wherein the length of the grown single-walled carbon nanotubes is 1 to 10 μm.
5. The method for preparing narrow diameter distribution, high purity metallic single-walled carbon nanotubes of claim 1 wherein the diameter and conductivity properties of single-walled carbon nanotubes are manipulated by manipulating thermodynamic nucleation conditions and kinetic growth conditions, including catalyst composition, size, structure, and growth temperature, carbon source, hydrogen concentration and flow rate.
6. The method for preparing narrow diameter distribution, high purity metallic single-walled carbon nanotubes according to claim 1, wherein in the step (1), the block copolymer micelle solution is a solution of polystyrene-b-poly (4-vinylpyridine) block copolymer in toluene and tetrahydrofuran at a concentration of 0.01 to 0.25 wt%, the mass ratio of toluene to tetrahydrofuran is 2-4: 1, and the block copolymer micelle height is 6-15 nm.
7. The method for preparing narrow diameter distribution, high purity metallic single-walled carbon nanotubes as claimed in claim 1 wherein in step (2), NaReO4And K3[Co(CN)6]The catalyst precursor salt solution is a hydrochloric acid solution with the molar concentration of 0.01-1M, NaReO4And K3[Co(CN)6]In a molar ratio of x: (0.5-x), wherein x is 0.1-0.3.
8. The method for preparing narrow diameter distribution, high purity metallic single-walled carbon nanotubes of claim 1 wherein in step (3), CoRexThe particle size of the solid solution nano particles is 0.5-3.5 nm.
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