CN111924826B - A kind of preparation method of narrow diameter distribution, high-purity metallic single-wall carbon nanotube - Google Patents

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 the metallic single-walled carbon nanotube with the diameter of 1.1 +/-0.3 nm and the purity of 80 wt% is 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

A kind of preparation method of narrow diameter distribution, high-purity metallic single-wall 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 narrow diameter distribution and high-purity metallic single-walled carbon nanotubes.

Background technique

Single-walled carbon nanotubes with different chiral angles and diameters can exhibit metallic and semiconducting properties. Metallic single-walled carbon nanotubes have ultra-high electrical transport properties due to quantum transport effects, and are excellent electrode materials for future nanoelectronic devices, while semiconducting single-walled carbon nanotubes have high carrier mobility and One-dimensional structures are ideal materials for constructing field effect transistor channels. Therefore, obtaining high-purity single-walled carbon nanotubes (metallic or semiconducting) with single conductive properties is a necessary prerequisite for its application in the above-mentioned fields, and is of great significance.

At present, although great progress has been made in the controllable preparation of single-walled carbon nanotubes, most of them take advantage of the lower chemical reactivity of semiconducting single-walled carbon nanotubes than metallic single-walled carbon nanotubes. In situ introduction of etching gas removes metallic carbon nanotubes to obtain semiconducting enriched single-walled carbon nanotubes. In contrast, the preparation of metallic single-walled carbon nanotubes is more difficult, and there are fewer reports on their selective preparation. The only representative works are as follows: (1) Preferential growth of metallic SWNTs by controlling the nucleation stage of SWNTs, such as controlling the surface state and morphology of the catalyst during nucleation (Reference 1: Harutyunyan A.R.; Cheng, G., Sumanasekera, G.U.et.al.Science, 2009, 326, 116); (2) High temperature stability of catalysts and crystal phase control of exposing specific crystal planes, realizing catalysts with specific crystal planes and specific structures (Li, Y. et al. Nature 2014, 510, 7506); (3) Symmetry control on specific crystal planes of catalysts, Achieve symmetry matching between catalysts and carbon nanotubes with specific properties (Literature 3: Zhang, S.C.; Kang, L.X.; Zhang, J. et al. Nature2017, 543, 7644); (4) For high melting point non-metal oxide catalyst nano Control of particle size and oxygen content during growth to achieve direct growth of narrow diameter distribution and metallic single-walled carbon nanotubes (Literature 4: Zhang, L.L.; Sun, D.M.; Liu, C. et al. Advanced Materials, 2017 , 29, 32).

However, there are still many problems in the preparation of metallic single-walled carbon nanotubes: (1) The traditional metal catalysts such as iron, cobalt and nickel used are prone to agglomeration during high temperature (>600°C) chemical vapor deposition due to their low melting points. After aging with Oswald, the particle size distribution becomes wider, resulting in a wide diameter distribution of carbon nanotubes; (2) The composition and structure of bimetallic catalysts are difficult to control, and it is impossible to obtain a high melting point with uniform size and controllable composition and structure. Bimetallic catalyst nanoparticles; (3) the low activity of non-metallic catalysts leads to low efficiency of growing metallic CNTs; (4) the mechanism of controllable growth of metallic SWNTs is still unclear.

Therefore, the main problem currently faced is: how to develop a method for the controllable growth of narrow diameter distribution, metallic single-walled carbon nanotubes on the basis of understanding the controllable growth mechanism.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes, through the design of catalyst size, composition and structure, to overcome the high temperature instability of general metal nanoparticles and easy agglomeration to lead to the growth of carbon nanometers The problem of wide distribution of tube diameters; the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate are used to directly grow metallic single-wall carbon nanotubes with narrow diameter distribution, high purity and high quality.

Technical scheme of the present invention:

A method for preparing a narrow diameter distribution, high-purity metallic single-walled carbon nanotube, utilizing a block copolymer self-assembly method to controllably prepare catalyst nanoparticles of uniform size, by designing the composition of the catalyst and regulating its oxidation and reduction conditions, The bimetallic solid solution nanoparticles with uniform size, monodispersion, close-packed hexagonal structure and high melting point were obtained, which provided the thermodynamic basis for the nucleation and growth of single-walled carbon nanotubes; The dynamic reaction conditions of the gas flow rate realize the quasi-static chemical vapor deposition process, and directly grow metallic single-wall carbon nanotubes with a diameter of 1.1±0.3nm and a content of 75-85wt%, which specifically includes the following steps:

(1) Preparation of block copolymer micelle film: first, the silicon wafer substrate was immersed in piranha solution for cleaning and hydrophilic treatment, then oxygen plasma treatment was performed, and then the block copolymer micelle solution was spin-coated to form a block copolymer. segmented copolymer micelle film;

(2) Preparation of catalyst nanoclusters: The substrate covered with micellar film was immersed in NaReO ₄ and K ₃ [Co(CN) ₆ ] catalyst precursor salt solution to adsorb two metal anions ReO ₄ ^- and [ Co(CN) ₆ ] ^3- assembles into nanoclusters; by adjusting the concentration of the two catalyst precursors in the solution, the control of the cluster composition is realized;

(3) Preparation of catalyst nanoparticles: The catalyst nanoclusters are subjected to high temperature oxidation and hydrogen and argon mixed gas reduction treatment successively to obtain CoRe _x solid solution nanoparticles; the process parameters are as follows: high temperature oxidation is 700 ~ 750 ℃ oxidation 1 ~ 5min, pass 500～800sccm argon gas for 1～5min, switch to the mixed gas of 75～250sccm Ar and 5～40sccm H ₂ , and reduce for 2～5min;

(4) Preparation of single-walled carbon nanotubes: using _CoRex nanoparticles as catalysts, under the conditions of quasi-static chemical vapor deposition at low temperature, low carbon source, low hydrogen and low flow rate, the direct growth of narrow diameter distribution and dominant metallicity The process parameters are as follows: 30-40 sccm argon is loaded with ethanol molecules as the carbon source, 2-15 sccm H ₂ is used as an etchant gas to control the growth rate during nanoparticle reduction and carbon nanotube growth, Ar of 75-115 sccm adjusts the gas flow rate, carbon source and hydrogen concentration, the total gas flow is maintained at 115-200 sccm, and chemical vapor deposition is performed to grow single-walled carbon nanotubes, and the growth time is 1-10 min.

The preparation method of the described narrow diameter distribution, high-purity metallic single-walled carbon nanotubes, and the structural characterization of the catalyst and the single-walled carbon nanotubes: using atomic force microscopy to measure and count the diameter and density of catalyst nanoparticles, and transmission electron microscopy to characterize the catalyst The crystal structure and composition distribution of single-walled carbon nanotubes were measured and counted by scanning electron microscopy, the diameter and distribution of single-walled carbon nanotubes were measured and counted by transmission electron microscopy, and the metallic single-walled carbon nanotubes were estimated by multi-wavelength Raman spectroscopy. Purity of walled carbon nanotubes.

In the method for preparing a narrow diameter distribution, high-purity metallic single-walled carbon nanotube, the prepared catalyst structure is hexagonal close-packed _CoRex solid solution particles, and the particle size distribution is in the range of 1.5-3.5 nm, and Co and Re are in the range of 1.5 to 3.5 nm. The atomic ratio is 1:1~1:9, and the melting point is above 2000 ℃ from the alloy phase diagram, which is a high melting point catalyst.

In the method for preparing a narrow diameter distribution, high-purity metallic single-wall carbon nanotube, the length of the grown single-wall carbon nanotube is 1-10 μm.

The preparation method of the narrow diameter distribution, high-purity metallic single-walled carbon nanotubes, by regulating the thermodynamic nucleation conditions and kinetic growth conditions, includes catalyst composition, size, structure, growth temperature, carbon source, hydrogen concentration and flow rate to control the diameter and conductivity properties of single-walled carbon nanotubes.

In the method for preparing metallic single-walled carbon nanotubes with narrow diameter distribution and high purity, in step (1), the block copolymer micelle solution adopts polystyrene-b-poly(4) with a concentration of 0.01-0.25wt% -vinylpyridine) block copolymer in toluene and tetrahydrofuran solution, the mass ratio of toluene and tetrahydrofuran is 2-4:1, and the block copolymer micelle height is 6-15nm.

In the method for preparing metallic single-walled carbon nanotubes with narrow diameter distribution and high purity, in step (2), the NaReO ₄ and K ₃ [Co(CN) ₆ ] catalyst precursor salt solution has a molar concentration of 0.01-1M In the hydrochloric acid solution, the molar ratio of NaReO ₄ and K ₃ [Co(CN) ₆ ] is x: (0.5-x), and x=0.1-0.3.

In the method for preparing a narrow diameter distribution, high-purity metallic single-walled carbon nanotube, in step (3), the particle size of the _CoRex solid solution nanoparticles is 0.5-3.5 nm.

The design idea of the present invention is:

In the invention, the high melting point bimetallic solid solution CoRex _is used as a catalyst to directly and selectively grow metallic single-walled carbon nanotubes. The method designs and prepares a monodisperse, uniform size, hexagonal close-packed CoRe high melting point catalyst, which not only avoids the high temperature agglomeration of the catalyst, but also solves the problem of controlling the nucleation of metallic carbon nanotubes, and can obtain uniform and stable carbon cap; since Re has a stronger affinity for H than Co, the surface of CoRe _x (such as CoRe ₄ , etc.) adsorbs more hydrogen atoms, which inhibits the decomposition and diffusion of carbon sources. , The quasi-static chemical vapor deposition conditions of low flow rate make carbon atoms diffuse and grow slowly on the catalyst surface in a quasi-static manner, thereby maximizing the growth rate difference between metallic SWNTs and semiconducting SWNTs, Achievement of preferential growth of metallic single-walled carbon nanotubes.

The advantages and beneficial effects of the present invention are:

1. The present invention realizes the preparation of high melting point bimetallic catalyst nanoparticles with uniform size, controllable composition and structure, and solves the problem of catalyst agglomeration at high temperature;

2. The present invention directly grows high-purity metallic-enriched single-walled carbon nanotubes, and the method is simple and has strong applicability;

3. The diameter distribution of the metallic single-walled carbon nanotubes prepared by the present invention is narrow;

4. The present invention clarifies the main factors affecting the growth of metallic single-walled carbon nanotubes and the controllable growth mechanism thereof, and provides a new idea for the controllable growth of carbon nanotubes.

In a word, the present invention starts from the catalyst that plays a decisive role in controlling the nucleation stage of single-walled carbon nanotubes, and controls the thermodynamic conditions such as the high melting point and structural components of the bimetallic catalyst and the kinetics in the process of chemical vapor deposition growth of carbon nanotubes. It breaks through the current bottleneck of the controlled preparation of metallic SWCNTs and provides a new understanding for the controllable growth of SWCNTs with specific structures.

Description of drawings

Figure 1. The preparation of _CoRex bimetallic catalyst nanoparticles and the schematic diagram of the process of growing narrow diameter distribution metallic single-walled carbon nanotubes.

Figure 2. Schematic diagram of the principle of narrow diameter distribution metallic single-walled carbon nanotubes grown _{by CoRex} bimetallic catalyst nanoparticles.

Figure 3. Morphology and structure of CoRe ₄ nanoparticles. Among them, (a) AFM photo of nanoparticles; (b) TEM photo of nanoparticles; (c) histogram of particle size distribution of TEM statistics; (de) high-resolution TEM photo of nanoparticles; (fg) High-resolution Fourier transform photographs of nanoparticles.

Figure 4. Compositional characterization of CoRe ₄ nanoparticles. Among them, (a) high-angle annular dark field image; (b) point scanning element distribution of energy spectrum in transmission electron microscope, the position of abscissa is the distance between the beginning and end of the particle scribe in the circle in (a); (cd) element content of surface scanning distributed.

Figure 5. Morphology and structure of carbon nanotubes prepared by CoRe ₄ catalyst. Among them, (a) SEM photo of carbon nanotubes on the surface of silicon wafer; (bc) TEM photo of single-walled carbon nanotube; (d) histogram of carbon nanotube diameter distribution based on TEM photo statistics.

Figure 6. Multiwavelength Raman spectra of single-walled carbon nanotubes grown with CoRe ₄ nanoparticles as catalyst. Among them, (a) breathing mode excited by 633nm laser; (b) breathing mode excited by 532nm laser; (c) breathing mode excited by 785nm laser; (d) D and G modes excited by 532nm laser.

Figure 7. Morphology and structural characterization of Co nanoparticle catalysts. Among them, (a) AFM photo of nanoparticles; (b) TEM photo of nanoparticles; (c) histogram of particle size distribution of TEM statistics; (d-e) high-resolution TEM photos of nanoparticles; (f-g) High-resolution Fourier transform photographs of nanoparticles.

Figure 8. Scanning photos of single-walled carbon nanotubes prepared by Co and CoRe ₁ as catalysts and the corresponding RBM modes of multi-wavelength Raman spectroscopy. Among them, (a) Co is the scanning photo of the catalyst-grown single-walled carbon nanotubes; (b) Co is the 532 nm laser RBM mode of the catalyst-grown single-walled carbon nanotubes; (c) Co is the catalyst-grown single-walled carbon nanotubes 633nm wavelength laser RBM mode of the tube; (d) Co:Re atomic ratio=1:1 is the scanning photo of the catalyst-grown SWNT; (e) CoRe is the 532nm wavelength laser RBM of the catalyst-grown SWNT mode; (f) CoRe is the 633 nm wavelength laser RBM mode of the catalyst-grown single-walled carbon nanotubes.

Detailed ways

As shown in Figure 1, the present invention uses CoRe _x high melting point bimetallic solid solution nanoparticles as catalysts to prepare a method for narrow diameter distribution, high-purity metallic single-walled carbon nanotubes, and the specific preparation and growth process are as follows:

The method prepares monodisperse, narrow diameter distribution _CoRex (X=1-9) bimetallic nanoparticle catalyst by regulating the self-assembly process of block copolymer and its post-processing to form nanoparticles; The assembly method obtains block copolymer micelles with uniform size, and each block copolymer micelle is subjected to spin coating, dipping, and chemical adsorption of quantitative bimetal anions, thereby obtaining uniform size metal nanoclusters; by controlling the composition of bimetals Proportion and low temperature oxidation and reduction conditions to obtain monodisperse, close-packed hexagonal structure, high melting point _CoRex catalyst nanoparticles; and then by controlling the growth kinetics conditions of low temperature, low carbon source, low hydrogen and low flow rate to achieve quasi-static chemistry Vapor deposition makes carbon atoms diffuse and assemble slowly on the catalyst surface, maximize the difference in growth rate of metallic and semiconducting single-walled carbon nanotubes, and directly controllable growth of narrow diameter distribution (diameter is 1.1±0.3nm) , High-purity (purity up to 80wt%) metallic single-walled carbon nanotubes.

The invention realizes the direct and controllable growth of metallic single-walled carbon nanotubes with narrow diameter distribution and high-purity through catalyst design combined with growth thermodynamics and kinetic control, improves the structural control precision of metallic single-walled carbon nanotubes, and promotes the The application of metallic single-walled carbon nanotubes lays the material foundation.

As shown in Figure 2, the mechanism controlling the growth of narrow diameter distribution metallic SWNTs is as follows:

First of all, in terms of thermodynamics, the catalyst _CoRex has a higher melting point than Co, the face-centered cubic melting point of cobalt is 1495 °C, and the cobalt-rhenium alloy close-packed cubic melting point is >2000 °C, which can effectively inhibit catalyst agglomeration and high-temperature Oswald ripening. , high temperature melting and thermal vibration of nanoparticles, thus stabilizing the structure of the carbon cap in the nucleation stage, so the prepared particle size is smaller and more uniform, which is conducive to the growth of single-walled carbon nanotubes with narrow diameter distribution, and the structure of CoRe _x is Close-packed hexagonal, which is conducive to the nucleation of metallic carbon nanotubes;

Secondly, in terms of kinetics, since Re has a stronger affinity for H than Co, the surface of Co can adsorb 5 hydrogen atoms ([CoH ₅ ] ^4- ) or 4 hydrogen atoms ([CoH ₄ ] ^5- ) , the surface of Re can adsorb 9 hydrogen atoms ([ReH ₉ ] ^2- ) or 6 hydrogen atoms ([ReH ₆ ] ^5- ), so the surface of CoRe ₄ adsorbs more hydrogen atoms, thus occupying the adsorption capacity of the surface of the metal. The active site inhibits the adsorption, catalytic cracking and surface diffusion of carbon sources on the catalyst surface. Therefore, on the basis of obtaining uniform and stable metallic carbon caps, the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate are used to make carbon atoms diffuse and assemble slowly on the surface of the catalyst in a quasi-static manner, and then The difference between the growth rates of metallic single-walled carbon nanotubes and semiconducting single-walled carbon nanotubes is maximized. Finally, by controlling the growth time, the long-preferred growth of metallic single-walled carbon nanotubes is realized.

Hereinafter, the present invention will be further described in detail through examples.

Example 1.

In this embodiment, the preparation and characterization of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes are as follows:

(1) Preparation of CoRe _x bimetallic catalyst:

The 10mm×10mm silicon wafer was soaked in piranha solution for 15min for cleaning treatment, washed with deionized water, and then treated with oxygen plasma with a power of 32W. The concentration of 0.01 ~ 0.25wt% polystyrene-b-poly (4-vinylpyridine) block copolymer (PS50000-b-P4VP13000) in toluene and tetrahydrofuran solution (the mass ratio of toluene and tetrahydrofuran 3:1), Spin coating on the surface of the hydrophilic treated silicon wafer at a rotational speed of 2000-7000 rpm to form a block copolymer micelle film, and the block copolymer micelle height is 6-15nm. The silicon wafer is then immersed in a hydrochloric acid solution with a solvent of 0.01-1M (mol/L), wherein the solutes are bimetallic catalyst precursor salts (x mM (mmol/L) NaReO ₄ and (0.5-x) mM (mmol/ L)K[Co(CN) ₆ ] ₃ , x=0.1～0.3), for 1～3min, adsorb ReO ₄ ^- and [Co(CN) ₆ ] ^3- two metal anions and assemble into nanoclusters. The control of the cluster composition can be achieved by adjusting the concentrations of the two catalyst precursors in the bimetallic catalyst precursor salt solution. After taking out, it is washed with deionized water, dried at 50-60° C. for 15-20 minutes, and treated with oxygen plasma for 1-5 minutes.

The above-treated silicon wafers are placed in a quartz boat in a tube furnace, oxidized at 700-750° C. for 1-5 minutes, and cooled to room temperature after the quartz boat is pushed out. Then, 500-800 sccm argon gas was introduced into the tube furnace for 4 min, switched to a mixed gas of 75-250 sccm Ar and 5-40 sccm H ₂ , and the quartz boat loaded with silicon wafers was pushed into the constant temperature zone for reduction for 2-5 min to obtain CoRe _x solid solution nanoparticles, the particle size of which is 1.5-3.5 nm, and the structure of the prepared nanoparticles is characterized.

As shown in Fig. 3(a), AFM characterization results showed that the nanoparticles were uniformly dispersed on the surface of the silicon substrate. As shown in Fig. 3(b), the results of TEM characterization indicated that the nanoparticles were uniform in size. The diameters of 150 particles were randomly counted, and the results are shown in Figure 3(c), and the particle size distribution of the nanoparticles is 1.5-3.5 nm. Figures 3(d-e) are high-resolution TEM images of the nanoparticles, and the corresponding Fourier transforms are shown in Figures 3(f-g). nm, b-axis 0.32 to 0.44 nm.

As shown in Figure 4(a), the size and composition distribution were further characterized by HADDF, and the composition distribution was uniform. As shown in Fig. 4(b), from the particle EDS statistics, the atomic ratio Co:Re of the element content corresponding to the particle is 1:4. As shown in Fig. 4(c-d), both Co and Re are contained in the particles.

(2) Preparation and characterization of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes:

On the basis of step (1), single-walled carbon nanotubes are grown, using CoRe ₄ nanoparticles as catalyst, 30-40 sccm argon loaded with ethanol molecules as carbon source, 2-15 sccm _H2 as nano-particle reduction and carbon nanotubes Etching gas to control the growth rate during growth, 75-115 sccm Ar to adjust the gas flow rate, carbon source and hydrogen concentration, the total gas flow is kept at 115-200 sccm, and chemical vapor deposition is used to grow single-walled carbon nanotubes. Growth time for 5min. After the growth, the carbon source was turned off, the quartz boat was pushed out of the constant temperature zone under the protection of argon, cooled to room temperature, and the samples were taken out. Thus, under the quasi-static chemical vapor deposition conditions of low temperature, low carbon source, low hydrogen and low flow rate, single-walled carbon nanotubes with narrow diameter distribution and dominant metallicity are directly grown.

Characterize the structure of catalysts and single-walled carbon nanotubes: use atomic force microscopy to measure and count the diameter and density of catalyst nanoparticles, and use transmission electron microscopy to characterize the crystal structure and composition distribution of catalysts; use scanning electron microscopy to measure and count single-walled carbon nanotubes The density and length of the tube, the diameter of single-walled carbon nanotubes were measured by transmission electron microscopy and their distribution was calculated, and the purity of metallic single-walled carbon nanotubes was estimated by multi-wavelength Raman spectroscopy.

As shown in Figure 5(a), the scanning electron microscope photo of the prepared single-walled carbon nanotubes shows that the tube walls of the single-walled carbon nanotubes are relatively straight and the length is about 5 μm. As shown in Fig. 5(b-c), the transmission electron microscope pictures of single-walled carbon nanotubes are single single-walled carbon nanotubes, and the tube wall is straight, indicating that it has good crystallinity. As shown in Fig. 5(d), the diameters of 150 carbon nanotubes were randomly counted, and it can be seen that the diameter distribution is very narrow, mainly concentrated in 0.8-1.4 nm.

As shown in Figure 6(ac), the breathing mode of the multi-wavelength (532nm, 633nm, 785nm) laser Raman spectrum shows that most of the excited SWNTs are located in the metallic region. As shown in Figure 6(d), the Raman spectrum of single-walled carbon nanotubes in the range of 1200-1800 cm ^-1 has no obvious D peak around 1350 cm ^-1 , which again proves that its crystallinity is high, and the G mode is typical Metallic BWF-type peaks. According to the Katarula plots and the number of breathing mode peaks in the corresponding interval, it is estimated that the content of metallic single-walled carbon nanotubes is about 80wt%.

Comparative Example 1: Co-catalyst growth of single-walled carbon nanotubes

The spin-coated block copolymer (PS50000-b-P4VP13000) film was immersed in a 0.5 mM K ₃ [Co(CN) ₆ ] solution with the same heat treatment conditions. The morphology and size distribution of the obtained particles are shown in Figure 7 ( ac), it can be seen that its diameter distribution is in the range of 0.5-5.5 nm, and the average particle size and diameter distribution range are larger than those of CoRe _x . As shown in Fig. 7(dg), the high-resolution TEM image and the corresponding Fourier transform image show that the particles are of a typical cobalt FCC structure.

Using the Co nanoparticles prepared in the above comparative example as catalysts, single-walled carbon nanotubes were prepared under the same conditions as in Example 1. The morphology of the carbon nanotubes grown by Co is shown in Figure 8(a). dense carbon nanotube network. As shown in Figure 8(b-c), Raman spectroscopy analysis of its conductive properties shows that the diameter distribution of carbon nanotubes is wide, the content of metallic carbon nanotubes is about 35wt%, and there is no selectivity of conductive properties.

Comparative example 2: CoRe catalyst growth of single-walled carbon nanotubes

The thin film of the spin-coated block copolymer (PS50000-b-P4VP13000) was immersed in a solution with a molar concentration of 0.25 mM K ₃ [Co(CN) ₆ ] + a molar concentration of 0.25 mM NaReO ₄ , and the heat treatment conditions were the same to obtain CoRe The diameter of the nanoparticles ranges from 0.5 to _4.5 nm, the average particle size is 2.9 nm, and the atomic content ratio of Co and Re elements is 1:1. Small, HCP structure.

Using the CoRe ₁ nanoparticles prepared in the above comparative example as a catalyst, single-walled carbon nanotubes were prepared under the same conditions as in Example (1). The scan and Raman are shown in Figure 8(df). The multi-wavelength Raman characterization showed that the content of metallic SWCNTs was about 50wt%.

Comparative Example 3: Kinetic Condition Control - Temperature

Using the _CoRex nanoparticles prepared in Example 1 as a catalyst, by increasing the growth temperature in Example 1, the effect of temperature on the growth of carbon nanotubes was studied. When the temperature was lower than the temperature in Example 1, the amount of carbon nanotubes was obtained. rare. With the increase of temperature, the density, length and growth rate of carbon nanotubes increased significantly, and the distribution range of diameter and conductive properties of carbon nanotubes became wider. It is also confirmed that the temperature conditions of Example 1 are favorable for the controlled growth of narrow diameter and metallic carbon nanotubes.

Comparative Example 4: Kinetic Condition Control - Carbon Source Concentration

Using the CoRe _x nanoparticles prepared in Example 1 as a catalyst, the effect of the carbon source concentration on the growth of carbon nanotubes was studied by increasing the growth carbon source concentration in Example 1. The results show that with the increase of carbon source concentration, the density, length and growth rate of carbon nanotubes are significantly improved, and the distribution range of diameter and conductivity properties of carbon nanotubes is broadened. 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: Control of Kinetic Conditions—Influence of Hydrogen Flow Rate on Growth Morphology and Structure of Carbon Nanotubes

The _CoRex nanoparticles prepared in Example 1 were used as catalysts to study the effect of hydrogen concentration on the growth of carbon nanotubes by changing the _H2 concentration in Example 1. The characterization of the prepared single-walled carbon nanotubes by scanning electron microscopy and multi-wavelength Raman spectroscopy shows that under the condition of no hydrogen, the decomposition ability of the carbon source is very strong, and the grown carbon nanotubes have a higher density, longer length, and higher tensile strength. Mann spectroscopic characterization shows that the diameter distribution range is widened and there is no choice of conductive properties; when the flow rate of _H2 increases to more than 6 sccm, the inhibition effect of hydrogen on the decomposition of carbon source is enhanced, the growth rate of carbon nanotubes is reduced, and the metallicity of small diameters is increased. The carbon nanotubes are etched, and the diameter of the carbon nanotubes is shifted toward the larger diameter. This further confirms that the suitable hydrogen concentration of Example 1 is beneficial for the controlled growth of narrow diameter and metallic carbon nanotubes.

The results of 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, composition and structure of the bimetallic high melting point catalyst nano-particles, solves the problem of catalyst agglomeration at high temperature; directly grows high-purity metallic-enriched single-wall carbon nanotubes, the method is simple and the applicability is strong ; The diameter distribution of the prepared metallic single-walled carbon nanotubes is narrow; the main factors affecting the growth of metallic carbon nanotubes and the growth mechanism are clarified, which provides a new idea for the controllable growth of nanocarbon materials. The precision of structural control of metallic single-walled carbon nanotubes is improved, and a material foundation is laid for exploring the application of metallic single-walled carbon nanotubes with specific structures. The present invention is not limited to the above-mentioned embodiments and comparative examples, and involves various modifications and improvements made by engineers and technicians in the field to this scheme under the idea of the present invention, which shall belong to the protection of the claims of the present invention.

Claims (8)

1. a kind of preparation method of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes, it is characterized in that, utilizes block copolymer self-assembly method to controllably prepare the catalyst nanoparticles of uniform size, by designing the composition of catalyst and regulating and controlling Its oxidation and reduction conditions can obtain bimetallic solid solution nanoparticles with uniform size, monodispersion, close-packed hexagonal structure and high melting point, which provide a thermodynamic basis for the nucleation and growth of single-walled carbon nanotubes. , the kinetic reaction conditions of low hydrogen and low carrier gas flow rate to realize the quasi-static chemical vapor deposition process, and the direct growth of metallic single-wall carbon nanotubes with a diameter of 1.1±0.3nm and a content of 75-85wt% includes the following steps: (1) Preparation of block copolymer micelle film: first, the silicon wafer substrate was immersed in piranha solution for cleaning and hydrophilic treatment, then oxygen plasma treatment was performed, and then the block copolymer micelle solution was spin-coated to form a block copolymer. segmented copolymer micelle film; (2) Preparation of catalyst nanoclusters: The substrate covered with micellar film was immersed in NaReO ₄ and K ₃ [Co(CN) ₆ ] catalyst precursor salt solution to adsorb two metal anions ReO ₄ ^- and [ Co(CN) ₆ ] ^3- assembles into nanoclusters; by adjusting the concentration of the two catalyst precursors in the solution, the control of the cluster composition is realized; (3) Preparation of catalyst nanoparticles: The catalyst nanoclusters are subjected to high temperature oxidation and hydrogen and argon mixed gas reduction treatment successively to obtain CoRe _x solid solution nanoparticles; the process parameters are as follows: high temperature oxidation is 700 ~ 750 ℃ oxidation 1 ~ 5min, pass 500～800sccm argon gas for 1～5min, switch to the mixed gas of 75～250sccm Ar and 5～40sccm H ₂ , and reduce for 2～5min; (4) Preparation of single-walled carbon nanotubes: using _CoRex nanoparticles as catalysts, under the conditions of quasi-static chemical vapor deposition at low temperature, low carbon source, low hydrogen and low flow rate, the direct growth of narrow diameter distribution and dominant metallicity The process parameters are as follows: 30-40 sccm argon is loaded with ethanol molecules as the carbon source, 2-15 sccm H ₂ is used as an etchant gas to control the growth rate during nanoparticle reduction and carbon nanotube growth, Ar of 75-115 sccm adjusts the gas flow rate, carbon source and hydrogen concentration, the total gas flow is maintained at 115-200 sccm, and chemical vapor deposition is performed to grow single-walled carbon nanotubes, and the growth time is 1-10 min. 2. according to the preparation method of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes according to claim 1, it is characterized in that, the structural characterization of catalyst and single-walled carbon nanotubes: utilize atomic force microscope to measure and count catalyst nanoparticles The crystal structure and composition distribution of the catalyst were characterized by transmission electron microscopy; the density and length of single-walled carbon nanotubes were measured and counted by scanning electron microscopy, and the diameter of single-walled carbon nanotubes was measured by transmission electron microscopy and its distribution was counted, Estimation of the purity of metallic single-walled carbon nanotubes using multi-wavelength Raman spectroscopy. 3. according to the preparation method of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes according to claim 1, it is characterized in that, prepared catalyst structure is the _CoRex solid solution particle of close-packed hexagonal, and particle size is distributed in 1.5 Within the range of ~3.5nm, the atomic ratio of Co and Re is 1:1 to 1:9, and the melting point is above 2000 ℃ from the alloy phase diagram, which is a high melting point catalyst. 4 . The method for preparing metallic single-walled carbon nanotubes with narrow diameter distribution and high purity according to claim 1 , wherein the grown single-walled carbon nanotubes have a length of 1-10 μm. 5 . 5. according to the preparation method of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes according to claim 1, it is characterized in that, by regulating and controlling thermodynamic nucleation condition and kinetic growth condition, comprise catalyst composition, size, structure, As well as growth temperature, carbon source, hydrogen concentration and flow rate, the diameter and conductivity properties of single-walled carbon nanotubes can be regulated. 6. The preparation method of narrow diameter distribution and high-purity metallic single-walled carbon nanotubes according to claim 1, wherein in step (1), the concentration of the block copolymer micelle solution is 0.01 to 0.25wt wt % polystyrene-b-poly(4-vinylpyridine) block copolymer in toluene and tetrahydrofuran solution, the mass ratio of toluene and tetrahydrofuran is 2-4:1, and the block copolymer micelle height is 6-15nm. 7. The preparation method of narrow diameter distribution, high-purity metallic single-walled carbon nanotubes according to claim 1, characterized in that, in step (2), NaReO ₄ and K ₃ [Co(CN) ₆ ] catalyst precursors The body salt solution is a hydrochloric acid solution with a molar concentration of 0.01-1 M, the molar ratio of NaReO ₄ and K ₃ [Co(CN) ₆ ] is x: (0.5-x), and x=0.1-0.3. 8 . The method for preparing metallic single-walled carbon nanotubes with narrow diameter distribution and high purity according to claim 1 , wherein in step (3), the particle size of the _CoRex solid solution nanoparticles is 0.5-3.5 nm. 9 .

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