Method for specifically separating carbon nanotubes by using ammonium salt functionalized silicon oxide microspheres

Abstract

The invention discloses a method for carrying out specific separation on carbon nanotubes by using ammonium salt functionalized silicon oxide microspheres, and belongs to the technical field of carbon nanotube purification. The method comprises the following steps: firstly, carrying out surface modification on silicon oxide microspheres by using amino silane to graft amino groups, and then converting the amino groups into ammonium salt groups through acid liquor treatment to prepare functionalized silicon oxide microspheres with the ammonium salt groups on the surfaces; and contacting the microspheres with a carbon nanotube dispersion liquid, selectively adsorbing the metal type carbon nanotubes and the short carbon nanotubes in the dispersion liquid, and carrying out solid-liquid separation to obtain a long carbon tube enriched semiconductor type carbon nanotube solution. The method does not need to depend on ultra-high-speed centrifugation, metal type / semiconductor type high-purity separation of the carbon nanotubes and efficient separation of long / short carbon tubes can be synchronously achieved in a single process step, damage to the long carbon tubes can be reduced, meanwhile, the separation efficiency and the material length can be considered, the process is simple and flexible, and the method is suitable for industrial production. The preparation method is suitable for preparing a semiconductor type carbon nanotube material required by a high-performance carbon-based electronic device.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanotube purification technology, and particularly relates to a method for the specific separation of carbon nanotubes using ammonium salt-functionalized silica microspheres. Background Technology

[0002] Single-walled carbon nanotubes (SWNTs) are a typical class of one-dimensional nanomaterials exhibiting anisotropic and quasi-one-dimensional ballistic transport properties. Thanks to their extremely small diameter and excellent band structure, SWNTs can achieve weak scattering transport, high carrier mobility, and a long path of freedom under appropriate conditions, and can effectively suppress short-channel effects at relatively short channel lengths. These properties make SWNTs widely regarded as potential channel materials for next-generation high-performance field-effect transistors, flexible electronic devices, and other carbon-based electronic devices.

[0003] From the perspective of band structure, SWNTs can be classified into metallic single-walled carbon nanotubes (m-SWNTs) and semiconductor single-walled carbon nanotubes (s-SWNTs) based on their chirality and diameter. In switching devices such as field-effect transistors, s-SWNTs mainly perform channel conduction, while a small amount of residual m-SWNTs provides leakage paths in the off-state, leading to an increase in the off-state current and a decrease in the on / off ratio (I0). on / I off The decline in s-SWNT content severely impacts the subthreshold characteristics and circuit-level integration reliability of devices. Therefore, to fully leverage the performance advantages of SWNTs in logic devices and analog circuits, it is urgent to obtain s-SWNTs with extremely low metal content and extremely high semiconductor purity.

[0004] Besides the purity of the electrical type, the length distribution of SWNTs is also a crucial factor affecting device performance. For single or a few SWNT channels that need to cross the source and drain electrodes, excessively short s-SWNTs often fail to effectively bridge the electrodes, or multiple short transistors need to be connected in series to form a conductive path. This results in increased channel resistance, reduced effective mobility, and decreased transconductance (G). m ), On-state current (I) on The conductivity and noise level will be adversely affected. For thin-film devices that rely on network conductivity, if the proportion of long tubes in the network is low, a higher areal density is required to form a through path, which will also introduce additional scattering and device uniformity issues. Therefore, in practical applications, it is desirable not only to effectively remove m-SWNTs and improve the electrical purity of s-SWNTs, but also to retain and enrich long tubes as much as possible to balance conductivity and device controllability.

[0005] To address these needs, academia and industry have proposed various SWNT purification and separation techniques. These include density gradient ultracentrifugation (DGU), electrophoretic separation, aqueous two-phase extraction (ATPE), gel permeation chromatography, and selective separation methods based on surfactant or conjugated polymer coatings. These methods typically utilize differences in density, charge state, hydrophilicity / hydrophobicity, or interaction with functionalized media among SWNTs of different chirality / diameter to separate m-SWNTs from s-SWNTs. However, existing methods generally suffer from complex processes, high dependence on expensive equipment such as ultracentrifugation, narrow parameter windows, and difficulties in large-scale scale-up. For example, DGU requires a precisely configured density gradient system and long-term operation under ultracentrifugation conditions; while some gel permeation chromatography or aqueous two-phase systems require fine-tuning of formulations and temperatures, and process reproducibility is significantly affected by operating conditions.

[0006] On the other hand, many existing separation techniques, while achieving electrical purification, do not ideally maintain the length of SWNTs. To obtain better dispersion stability, strong ultrasonic treatment or repeated high-intensity centrifugation is usually required. These steps easily introduce cutting and defects, resulting in the destruction of a large number of long tubes, and the final product is dominated by short tubes. Even if this problem can be alleviated to some extent by adjusting the ultrasonic power, treatment time, or type of dispersant, a trade-off often needs to be made between separation efficiency, semiconductor purity, and average length, making it difficult to simultaneously meet the requirements of high-purity s-SWNTs and long tube enrichment.

[0007] In summary, while existing single-walled carbon nanotube (SWNT) separation technologies can achieve separation of m-SWNTs and s-SWNTs to some extent, they generally suffer from drawbacks such as complex processes, demanding equipment requirements, difficulty in scaling up, and severe damage to long SWNTs. Particularly for high-performance carbon-based device applications, there is a lack of a separation strategy that is simple, operates under mild conditions, is easy to scale up, and can efficiently and effectively remove metallic components while simultaneously achieving effective sorting of long / short SWNTs. This technological gap restricts the availability of high-quality s-SWNT materials and the performance of subsequent devices. Summary of the Invention

[0008] This invention aims to provide a method for the specific separation of carbon nanotubes using ammonium salt-functionalized silica microspheres, thereby overcoming the shortcomings of existing technologies. The technical problem to be solved by this invention is achieved through the following technical solution, including the following steps: a) Provide a carbon nanotube dispersion, the dispersion comprising metallic single-walled carbon nanotubes, semiconductor carbon nanotubes, and carbon nanotubes with different aspect ratios; b) Prepare ammonium salt functionalized silica microspheres, wherein the microspheres are obtained by functionalizing the silica core with aminosilane and then acidifying it, and the surface of the microspheres is functionalized with ammonium salt groups. c) Contact the carbon nanotube dispersion with the ammonium salt-functionalized silica microspheres to selectively adsorb the metallic single-walled carbon nanotubes and short carbon nanotubes onto the surface of the ammonium salt-functionalized silica microspheres; and d) Separate the ammonium salt-functionalized silica microspheres and the adsorbed carbon nanotubes from the remaining carbon nanotube dispersion to obtain a dispersion enriched with long semiconductor carbon nanotubes.

[0009] In a preferred embodiment, the ammonium salt functionalized silica microspheres comprise a silica core and ammonium salt groups covalently attached to the surface of the silica core.

[0010] In a preferred embodiment, the ammonium salt functionalized silica microspheres are formed by the following steps: S1: Silica microspheres are dispersed in a mixture of aminosilane and toluene and reacted to graft amino groups onto the surface of the silica microspheres. After solid-liquid separation and drying, amino-functionalized silica microspheres are obtained. S2: The amino-functionalized silica microspheres are placed in an acidic solution for surface modification, so that the amino groups on the surface are converted into ammonium salt groups. After solid-liquid separation and drying, ammonium salt-functionalized silica microspheres are obtained.

[0011] In a preferred embodiment, the aminosilane is N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0012] In a preferred embodiment, in step S1, the particle size of the silica microspheres is 100 μm to 150 μm; more preferably, the particle size of the silica microspheres is about 115 μm.

[0013] In a preferred embodiment, the specific process of step S2 is as follows: placing the silica microspheres in a mixture of aminosilane and toluene at a concentration of 10 mM, magnetically stirring for 2 hours at 60°C and 750 rpm, then centrifuging and vacuum drying at 120°C for 30 min.

[0014] In a preferred embodiment, the specific process of step S2 is as follows: the dried amino-functionalized silica microspheres are placed in a 3% dilute hydrochloric acid solution and reacted for 2 hours. After solid-liquid separation by centrifugation, isopropanol is used for solvent replacement. Solid-liquid separation is performed again by centrifugation and vacuum drying is carried out at 120°C.

[0015] In a preferred embodiment, the separation of the ammonium salt-functionalized silica microspheres and the adsorbed carbon nanotubes from the remaining carbon nanotube dispersion is performed by static adsorption or column filtration.

[0016] In a preferred embodiment, the static adsorption method involves adding 0.4 g of silica microspheres to every 3 mL of carbon nanotube solution, allowing the adsorption to proceed statically for 48 hours until dynamic equilibrium is reached, and then centrifuging to obtain the supernatant.

[0017] In a preferred embodiment, the column filtration method involves filling the column with the ammonium salt-functionalized silica microspheres, injecting the carbon nanotube solution into the column for filtration, and collecting the eluent.

[0018] The present invention has the following beneficial effects: This invention achieves high-purity separation of carbon nanotubes into "metallic / semiconductor" types and efficient sorting of "long / short" diameters simultaneously in a single process step. Existing separation methods (such as ultracentrifugation) often suffer from carbon nanotube breakage due to strong shear forces when pursuing purity, making it difficult to balance length. This invention utilizes the highly specific adsorption capacity of ammonium salt-functionalized silica microspheres for metallic single-walled carbon nanotubes, while simultaneously leveraging the kinetic difference that shorter carbon nanotubes have more intense Brownian motion and higher kinetic energy, making them more easily adsorbed. This results in carbon nanotubes remaining in solution being enriched with semiconductor properties while retaining their longer length.

[0019] This invention significantly expands the adsorption energy difference between metallic and semiconducting single-walled carbon nanotubes by converting amino acids on the surface of silica microspheres into ammonium salts and utilizing the strong interaction between cations and π bonds. First-principles calculations show that the adsorption energy difference increases from 0.24 eV to 0.60 eV after acidification, thereby greatly improving selectivity. Raman spectroscopy and field-effect transistor device testing confirm that the purity of the semiconducting single-walled carbon nanotube solution obtained by the method of this invention can reach over 99.999%, effectively solving the problem of insufficient semiconductor purity (usually below 99.9%) in existing technologies.

[0020] This invention effectively enriches long carbon nanotubes, significantly improving the performance of the material in electronic devices. Existing carbon nanotube solutions often consist mainly of short nanotubes, making direct bridging of source and drain electrodes difficult, leading to decreased transconductance and increased subthreshold swing. This invention utilizes large-diameter (e.g., 115 μm) silica microspheres, leveraging their smaller surface curvature to reduce the desorption probability of long nanotubes while simultaneously adsorbing and removing short nanotubes. Experimental data shows that after adsorption treatment, the average length of carbon nanotubes in the solution increases by 4-5 times compared to before treatment (e.g., from approximately 0.5-0.6 μm to approximately 2.4-2.8 μm). Field-effect transistors fabricated based on this long carbon nanotube-enriched solution exhibit excellent on / off current ratio (>10). 4 This meets the needs of high-performance carbon-based electronic devices.

[0021] The method of this invention offers flexibility and avoids reliance on expensive ultracentrifugation equipment. The ammonium salt-functionalized silica microspheres prepared by this invention can be used not only for static adsorption but also for packing into chromatographic columns. Unlike traditional methods that require ultracentrifugation at speeds exceeding 50,000 g, this invention, combined with gel chromatography, requires only low-speed centrifugation (e.g., 19,000 g) or even natural filtration to obtain high-purity long semiconductor carbon nanotube solutions. This not only reduces dependence on expensive equipment but also effectively avoids the physical damage caused by ultracentrifugation to the excellent aspect ratio of semiconductor single-walled carbon nanotubes, demonstrating broad prospects for industrial applications. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the method for achieving specific separation of carbon nanotubes using ammonium salt-functionalized silica microspheres according to the present invention; Figure 2 The UV-Vis absorption spectra of PCz-coated organic phase single-walled carbon nanotube dispersions before and after adsorption by amino / ammonium salt-functionalized silica microspheres. Figure 3 The UV-Vis absorption spectra of aqueous single-walled carbon nanotube dispersions before and after adsorption by amino / ammonium salt-functionalized silica microspheres; Figure 4 The results are based on the Raman spectra of single-walled carbon nanotubes before and after adsorption by silica microspheres excited by a 488nm laser.

[0023] Figure 5 It is C8H 22 N2O3Si and C8H 24 A schematic diagram of a ball-and-stick model of N2O3Si; Figure 6 It is C8H 22 N2O3Si and C8H 24Statistical results of adsorption energies between N2O3Si and semiconductor single-walled carbon nanotubes (13, 0) and metallic single-walled carbon nanotubes (10, 10); Figure 7 These are the chemical structural formulas of nine silanes; Figure 8 The UV-Vis absorption spectra of a single-walled carbon nanotube dispersion before and after adsorption by silica microspheres functionalized with nine silanes are shown. Figure 9 The results show a comparison between the removal rate of metal-type single-walled carbon nanotubes and the loss rate of semiconductor-type single-walled carbon nanotubes after adsorption by silica microspheres functionalized with nine silanes. Figure 10 The water contact angle measurement results are obtained from silicon wafers with a 285 nm silica top layer that have been functionalized with nine silanes under the same conditions. Figure 11 The length statistics of carbon nanotubes in solution before and after adsorption by silica microspheres functionalized with 9 silanes are measured by dynamic light scattering (left), and the length statistics of carbon nanotubes after adsorption by silica microspheres functionalized with silane 7 are based on scanning electron microscopy images (right). Figure 12 These are scanning electron microscope images of carbon nanotubes before and after adsorption onto silica microspheres functionalized with silane 7. Figure 13 The results are UV-Vis absorption spectra of PCz-coated organic phase single-walled carbon nanotube dispersions before and after adsorption of silica microspheres with different particle sizes (0.5 μm, 1 μm, 2 μm, 5 μm and 115 μm) functionalized with silane 7. Figure 14 The results show a comparison of the removal rate of metal-type single-walled carbon nanotubes and the loss rate of semiconductor-type single-walled carbon nanotubes after adsorption by silica microspheres with different particle sizes (0.5μm, 1μm, 2μm, 5μm and 115μm) functionalized with silane 7. Figure 15 The length statistics are obtained by dynamic light scattering after adsorption of silica microspheres with different particle sizes (0.5μm, 1μm, 2μm, 5μm and 115μm) functionalized with silane 7. Figure 16 The length statistics of silica microspheres with different particle sizes (0.5 μm, 1 μm, 2 μm, 5 μm and 115 μm) after adsorption by silane 7 functionalization are based on scanning electron microscope images. Figure 17 This is the UV-Vis absorption spectrum of single-walled carbon nanotubes after adsorption onto silane-7 functionalized silica microspheres with a particle size of 115 μm, in wavenumber coordinates. The reference wavenumber range for the initial single-walled carbon nanotubes is 7800 cm⁻¹. -1 Up to 14500cm -1 ; Figure 18 It is a scanning electron microscope image of the carbon nanotube network in the channel; Figure 19 These are Raman spectra of 115 μm silica microspheres functionalized with silane 7 before and after adsorption of single-walled carbon nanotubes. The purple region indicates the radial breathing pattern of the metallic single-walled carbon nanotubes. Figure 20 This is a schematic diagram of a bottom-gate field-effect transistor designed to verify purity. Figure 21 The field-effect transistor transfer characteristic curves using single-walled carbon nanotube networks as channel materials are shown: (left) adsorption of 115 μm silica microspheres without silane 7 functionalization, and (right) adsorption of 115 μm silica microspheres with silane 7 functionalization. Figure 22 The Raman spectra of the single-walled carbon nanotube solution after one filtration by a gel chromatography column are as follows: (left) without ultracentrifugation, (right) after ultracentrifugation. The purple area indicates the radial breathing pattern of the metallic single-walled carbon nanotubes. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] In this invention, short semiconductor carbon nanotubes (short carbon nanotubes) generally refer to carbon nanotubes with an average length of less than 0.5 μm, which are often produced by processes such as ultrasonic dispersion; long semiconductor carbon nanotubes (long carbon nanotubes) refer to carbon nanotube components with a larger aspect ratio or a longer average length compared to the carbon nanotubes in the initial dispersion. Typically, after enrichment by the method of this invention, their average length is more than three times the initial average length. Generally, it refers to carbon nanotubes with an average length greater than 1.5 μm. Preferably, the average length of the long carbon nanotubes is between 1.5 μm and 5.0 μm.

[0026] This embodiment proposes a method for efficiently sorting carbon nanotubes using ammonium salt surface-functionalized silica microspheres. This method is mainly achieved by preparing specific functionalized microspheres and utilizing their differentiated adsorption on metallic single-walled carbon nanotubes and short carbon nanotubes. Figure 1 This is a flowchart illustrating the entire method. First, it provides dispersions of metallic single-walled carbon nanotubes, semiconductor carbon nanotubes, and carbon nanotubes with different aspect ratios. Then, it provides ammonium salt-functionalized silica microspheres, obtained by functionalizing a silica core with aminosilanes followed by acidification, and functionalizing its surface with ammonium salt groups. In the acidification process, the acid's role is merely to provide protons to convert the amino group into an ammonium ion (-NH₃). 3+Therefore, any acid that does not damage the microsphere structure is suitable; in this embodiment, dilute hydrochloric acid can be used for acidification. The carbon nanotube dispersion is brought into contact with the ammonium salt-functionalized silica microspheres to selectively adsorb metallic single-walled carbon nanotubes and carbon nanotubes with relatively small aspect ratios onto the surface of the ammonium salt-functionalized silica microspheres. The ammonium salt-functionalized silica microspheres and the adsorbed carbon nanotubes are then separated from the remaining carbon nanotube dispersion, thereby obtaining a dispersion enriched with semiconductor-type carbon nanotubes with relatively large aspect ratios. The ammonium salt-functionalized silica microspheres comprise a silica core and ammonium salt groups covalently attached to the surface of the silica core. The specific process steps for the above-mentioned ammonium salt-functionalized silica microspheres are described in detail below.

[0027] Step S1: Preparation of amino-functionalized silica microspheres Silica microspheres with a particle size of 100 μm to 150 μm were selected as the substrate. In this embodiment, silica microspheres with a particle size of 115 μm were selected as the substrate and placed in a toluene mixture containing aminosilane. In this embodiment, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was used as the modifier because its dual-amino structure can provide a higher grafting density. The silane concentration in the mixture was set to 10 mM, and the reaction was carried out with magnetic stirring at 60 °C and 750 rpm for 2 h to successfully graft amino groups onto the surface of the silica microspheres. After the reaction, solid-liquid separation was achieved by centrifugation at 2000 g for 20 min, and the separated microspheres were dried in a vacuum oven at 120 °C for 30 min to obtain dried amino-functionalized silica microspheres.

[0028] Step S2: Preparation of ammonium salt functionalized silica microspheres The microspheres were modified by ammonium salt formation. A 3% acidic solution was prepared; in this embodiment, the acidic solution was dilute hydrochloric acid, but in other embodiments, the acidic solution could be dilute sulfuric acid or nitric acid. The dried amino-functionalized silica microspheres were immersed in this solution and reacted for 2 hours. The acidic environment protonated the amino groups on the surface of the microspheres, converting them into ammonium salt groups. This step significantly enhanced the interaction difference between the cations on the microsphere surface and the π-electron cloud of the carbon nanotubes, thereby greatly improving the selective adsorption capacity for metallic single-walled carbon nanotubes. After the reaction was completed, the microspheres were centrifuged at 2000g and immersed in isopropanol for 5 minutes to remove residual moisture and impurities. After centrifugation again, the microspheres were dried a second time in a vacuum oven at 120℃ for 30 minutes to obtain the dried ammonium salt-functionalized silica microspheres.

[0029] The specific steps for separating ammonium salt-functionalized silica microspheres and adsorbed carbon nanotubes from the remaining carbon nanotube dispersion are as follows: Carbon nanotubes are sorted using the prepared ammonium salt-functionalized silica microspheres. In this embodiment, a static adsorption method is employed. The ammonium salt-functionalized silica microspheres are added to the carbon nanotube solution to be purified in a specific ratio, preferably 0.4 g of microspheres per 3 mL of solution. The mixed system is allowed to stand for 48 h to reach adsorption dynamic equilibrium. At this point, the microspheres preferentially adsorb metallic single-walled carbon nanotubes and short carbon nanotubes with faster diffusion rates. After adsorption is complete, the solution is centrifuged at 2000 g for 20 min, and the supernatant is collected to obtain a high-purity semiconductor single-walled carbon nanotube solution enriched with long carbon nanotubes.

[0030] In another embodiment, column filtration is used to separate ammonium salt-functionalized silica microspheres and adsorbed carbon nanotubes from the remaining carbon nanotube dispersion. This method is more suitable for continuous processing. Approximately 2 g of ammonium salt-functionalized silica microspheres are packed into a column and rinsed with an appropriate amount of toluene. Subsequently, a carbon nanotube solution (e.g., 50 mL) that has been centrifuged at 19000 g to remove large particles is slowly injected into the column, allowing it to filter naturally. During this process, metallic single-walled carbon nanotubes and short tubes are retained by the packing medium, and the effluent is the target product. Compared to traditional methods, this approach eliminates the need for expensive ultra-high-speed centrifugation equipment and effectively avoids physical damage to long carbon nanotubes caused by strong centrifugal force. The carbon nanotube solution treated by the above method exhibits excellent performance indicators.

[0031] Figure 2 The figures show the UV-Vis absorption spectra of PCz-coated organic phase single-walled carbon nanotube dispersions before and after adsorption by amino / ammonium salt-functionalized silica microspheres. As can be seen from the figures, in the PCz-coated organic phase single-walled carbon nanotube dispersion, after adsorption by ammonium salt-functionalized silica microspheres, the M... 11 The characteristic absorption peaks of metallic single-walled carbon nanotubes all disappeared. Ammonium-functionalized silica microspheres exhibited stronger removal efficiency of metallic single-walled carbon nanotubes compared to amino-functionalized microspheres. Figure 3 The UV-Vis absorption spectra of sodium dodecyl sulfate-based aqueous single-walled carbon nanotube dispersions before and after adsorption by amino / ammonium salt-functionalized silica microspheres also show the aforementioned effects. Based on 488nm laser excitation, we compared the G / D and Go of the single-walled carbon nanotubes before and after adsorption. + / G - Ratio (see) Figure 4 After adsorption by microspheres, the G / D ratio G + / G -The ratios did not change significantly, indicating that the adsorption process of the ammonium salt-functionalized silica microspheres can selectively remove metallic single-walled carbon nanotubes without damaging the structural integrity of the semiconductor single-walled carbon nanotubes.

[0032] This invention proposes that single-walled carbon nanotubes (SWNTs) exhibit a strong affinity for amine-functionalized surfaces, an interaction related to the chiral structure of SWNTs. SWNTs can be viewed as quasi-one-dimensional cylindrical aromatic macromolecules. According to Hückel's rule, semiconducting SWNTs exhibit an electronic structure similar to [4n+2] cycloolefins (aromatic), while metallic SWNTs are closer to the [4n] system (anti-aromatic). Furthermore, semiconducting SWNTs possess an indirect band gap, while metallic SWNTs exhibit a continuous band structure and a higher density of states near the Fermi level. Due to the reduced aromaticity and smaller band gap, the reactivity of amine molecules with cycloolefins is enhanced, resulting in a stronger interaction between amine molecules and metallic SWNTs than with semiconducting SWNTs. This difference in chemical affinity provides a theoretical basis for the separation of metallic and semiconducting SWNTs.

[0033] To quantify the adsorption energies of amine molecules with metallic and semiconducting single-walled carbon nanotubes, we performed density functional theory calculations using DS-PAW, a first-principles calculation software integrated into Device Studio. 3-(2-aminoethylamino)propyltrimethoxysilane (C8H) was used as the adsorption energie. 22 Taking N2O3Si as an example, typical semiconductor single-walled carbon nanotubes (13,0) and metallic single-walled carbon nanotubes (10,10) are selected.

[0034] Figure 5 The ball-and-stick model before and after acidification of 3-(2-aminoethylamino)propyltrimethoxysilane (left: C8H) 22 N2O3Si, right: C8H 24 (N2O3Si). All plate models incorporate a 20 Å vacuum layer to eliminate proximity interactions, and the Brillouin zone integral uses a 1×1×1 Gamma-centered k-point grid. Geometric optimization convergence is conditional on energy changes less than 1×10⁻⁶. -4 The residual force is less than 0.05 eV / Å, and the cutoff energy is set to 580 eV. The adsorption energy is calculated using the following formula: Where E slab+mol E slab and E mol These represent the total energy of the adsorption system, the substrate, and the molecule, respectively. Figure 6 This is a statistical result of adsorption energy, C8H 22The adsorption energies of N₂O₃Si with metallic single-walled carbon nanotubes (10,10) and semiconductor single-walled carbon nanotubes (13,0) are -0.32 eV and -0.08 eV, respectively, with a difference of 0.24 eV, which is only about the thermodynamic energy scale kJ / L. BT The adsorption energy is approximately 8 times that of the amino group (approximately 0.0257 eV at 298 K). This small difference suggests that thermal fluctuations can significantly affect selectivity. It is known that cations interact more strongly with π bonds, potentially leading to more efficient selective adsorption. The adsorption energy is significantly enhanced by converting the amino group to an ammonium salt: C8H... 24 The adsorption energies of N₂O₃Si with metallic single-walled carbon nanotubes (10,10) and semiconductor single-walled carbon nanotubes (13,0) increased to -3.32 eV and -2.72 eV, respectively, representing increases of 3.00 eV and 2.64 eV. This enhancement widened the adsorption energy difference from 0.24 eV to 0.60 eV, thereby significantly improving the selective adsorption efficiency.

[0035] This invention uses nine amino-containing silanes to conduct a comparative experiment on the selective adsorption of metallic single-walled carbon nanotubes and semiconductor single-walled carbon nanotubes. The structural formulas of the nine silanes are as follows: Figure 7 As shown in the figure. In the comparative experiment, a representative system was used for selectivity evaluation: an organic phase single-walled carbon nanotube dispersion was encapsulated with poly[9-(1-octanoyl)-9H-carbazole-2,7-diyl] (hereinafter referred to as PCz) and silica microspheres with a particle size of 115 μm. The selective adsorption performance was evaluated by characterizing the purity and length distribution of the single-walled carbon nanotubes after adsorption by silica microspheres functionalized with nine silanes (acidified).

[0036] Two batches of single-walled carbon nanotube dispersions with high metallic single-walled carbon nanotube content were prepared using the same formulation (polymer:carbon nanotube = 8:1). Two sets of experiments were set up: the first set used silica microspheres functionalized with silane 1-4 (acidification), and the second set used silica microspheres functionalized with silane 5-9 (acidification). The first set underwent three adsorption cycles, and the second set underwent two adsorption cycles.

[0037] Figure 8 The UV-Vis absorption spectra of single-walled carbon nanotube dispersions before and after adsorption by silica microspheres functionalized with nine silanes (acidification) show that silica microspheres functionalized with silanes 2, 5, 7, and 8 (acidification) can achieve near-complete (>99%) removal of metallic single-walled carbon nanotubes. Figure 9 As shown, the silica microspheres functionalized with silane 7 (acidified) can remove nearly 100% of the metallic single-walled carbon nanotubes after adsorption, while maintaining the highest remaining proportion (35.9%) of the semiconductor single-walled carbon nanotubes in the solution. This superior performance stems from its higher silane surface modification density.

[0038] Further, under the same controlled conditions, a mixture of nine silanes and toluene at the same concentration (10 mM) was used to modify a silicon wafer with a 285 nm silicon dioxide layer. Figure 10 The results of contact angle measurements show that unmodified silicon wafers are highly hydrophilic (contact angle of deionized water is approximately 6.2°). After silane modification, the contact angle increases, with the silicon wafer modified with silane 7 (N-(2-aminoethyl)-3-aminopropyltrimethoxysilane) exhibiting the highest contact angle (63.6°), indicating the highest silane grafting density. The increased contact angle is attributed to the introduction of an organic molecular layer (silane), covering the originally highly hydrophilic silica surface. The increased density of the silane coating is directly related to the increase in the number of adsorption sites on the silica microsphere surface, thereby enhancing the overall adsorption capacity. Furthermore, compared to silanes 2, 5, and 8, the presence of diamino functional groups in the silane 7 molecular structure enhances its interaction with carbon nanotubes.

[0039] The length of carbon nanotubes is another key parameter determining their material quality and device performance. Short carbon nanotubes are difficult to bridge source and drain electrodes and introduce charge scattering centers, leading to degraded transport performance, specifically manifested as decreased transconductance, threshold voltage drift, and increased subthreshold swing. To evaluate the length selectivity of the adsorption process of silica microspheres functionalized with different silanes (acidification), dynamic light scattering was used to characterize the length of carbon nanotubes after adsorption by silica microspheres functionalized with silanes 2, 5, 7, and 8 (acidification).

[0040] Figure 11 The length of carbon nanotubes in the solution after adsorption by silica microspheres functionalized with silanes 2, 5, 7, and 8 (acidified) was statistically analyzed using dynamic light scattering and scanning electron microscopy (SEM) images. Silane 7 exhibited the best short carbon nanotube removal efficiency, with an average supernatant length of approximately 2.456 μm determined by dynamic light scattering. This result was corroborated by manual statistical analysis of over 200 carbon nanotubes in the SEM images, with a statistically average length of 2.85 ± 0.63 μm. SEM characterization confirmed the presence of a large number of short carbon nanotubes at the beginning of the ultrasonic dispersion process, such as... Figure 12 As shown in the left figure. This effective length screening is attributed to the stronger Brownian motion of short carbon nanotubes in solution, which promotes their faster adsorption onto the surface of silica microspheres, thereby achieving the enrichment of long carbon nanotubes in solution, such as... Figure 12 As shown in the figure on the right.

[0041] Meanwhile, the adsorption capacity of silane-functionalized silica microspheres is closely related to their particle size. To elucidate this effect, silica microspheres with particle sizes of 0.5 μm, 1 μm, 2 μm, 5 μm, and 115 μm were functionalized using a mixture of silane 7 (acidified) and toluene (10 mM) at the same concentration. Figure 13The results are UV-Vis absorption spectra of PCz-coated organic phase single-walled carbon nanotube dispersions before and after adsorption of silica microspheres of different particle sizes functionalized with silane 7 (acidification). All spectral baselines have been calibrated. Figure 14 This comparison examines the removal rates of metallic single-walled carbon nanotubes (SSWCNTs) and the loss rates of semiconductor SSWCNTs after adsorption by silica microspheres of different particle sizes functionalized with silane 7 (acidification). The results show that only silica microspheres with a particle size of 115 μm can achieve near-complete removal (>99%) of metallic SSWCNTs. Furthermore, dynamic light scattering was used to characterize the length distribution of carbon nanotubes before and after adsorption by silica microspheres of different particle sizes functionalized with silane 7 (acidification), as shown in the figure. Figure 15 As shown, the initial average length of PCz-encapsulated organic-phase carbon nanotubes was approximately 0.52 μm. After adsorption by silica microspheres with a particle size of 115 μm, the average length significantly increased to 2.44 μm. Figure 15 As shown, this achieves an improvement of approximately 4-5 times. This was further verified by manually measuring the length of over 200 carbon nanotubes. Figure 16 As shown, the results indicate that the initial average length of PCz-encapsulated organic phase carbon nanotubes was approximately 0.64 ± 0.39 μm, which increased to 2.49 ± 0.69 μm after adsorption by silica microspheres with a particle size of 115 μm. This particle size-dependent adsorption behavior can be attributed to the greater curvature of the surface of the small-sized silica microspheres, which makes it easier for the carbon nanotubes to desorb from the surface after adsorption in the liquid phase, ultimately reducing the overall adsorption capacity.

[0042] Furthermore, the purity of single-walled carbon nanotubes has a decisive influence on the performance of their field-effect transistors. This invention first uses ultraviolet-visible absorption spectroscopy to determine purity, and then evaluates it by calculating the spectral integral value φ in a wavenumber coordinate system, where φ is defined as:

[0043] Where A CNT With A B M respectively 11 and M 22 The integral area of ​​the regional absorption peak and the background absorption intensity. When φ > 0.42, it indicates that the purity of the single-walled carbon nanotubes is > 99.9%. Figure 17 This is the UV-Vis absorption spectrum of single-walled carbon nanotubes after adsorption onto 115 μm silica microspheres functionalized with silane 7 (acidification) in the wavenumber coordinate system, where the reference wavenumber range for the initial single-walled carbon nanotubes is 7800 cm⁻¹. -1 Up to 14500cm -1 The calculated φ=0.435 indicates that the purity of single-walled carbon nanotubes in the test sample is >99.9%. However, this purity assessment method has limitations due to the complexity of the UV-Vis absorption spectrum caused by the coexistence of multiple components in the single-walled carbon nanotube dispersion.

[0044] To further evaluate the technical effectiveness, Raman mapping was used as a supplementary characterization method. In Raman spectroscopy, 100 cm⁻¹ -1 Up to 400cm -1 The interval corresponds to the radial breathing mode of single-walled carbon nanotubes. For arc-grown single-walled carbon nanotubes with a diameter of approximately 1.4 nm, a significant resonant Raman enhancement effect is only observed under 785 nm laser excitation (spot diameter ≈ 1.06 μm). Under this condition, metallic single-walled carbon nanotubes exhibit a radial breathing mode at 160 cm⁻¹. -1 The surrounding area displays a characteristic radial breathing pattern. For example... Figure 18 As shown, the carbon nanotube network density, as determined by scanning electron microscopy, is approximately 67 nanotubes / μm. Assuming an average of 71 carbon nanotubes are detected per laser spot (calculation method: 67 × 1.06), the actual effective detection of 1024-point Raman mapping is approximately 72,704 individual carbon nanotubes (calculation method: 71 × 1024). Figure 19 The images show the Raman spectra of 115 μm silica microspheres functionalized with silane 7 (acidification) before and after adsorption of single-walled carbon nanotubes. The purple region indicates the radial breathing mode of metallic single-walled carbon nanotubes. The results show that no metallic single-walled carbon nanotube signal was found in the approximately 72,704 carbon nanotubes detected after adsorption, indicating that the purity of semiconductor single-walled carbon nanotubes exceeds 99.998% (calculated as 1 - 1 / 72704).

[0045] To further evaluate the current-to-onset ratio of the device to estimate the purity of the semiconductor-type single-walled carbon nanotubes, a bottom-gate field-effect transistor was fabricated in another embodiment, such as... Figure 20 As shown. Typically, the on-state current of a single metallic single-walled carbon nanotube is on the same order of magnitude as that of a semiconductor single-walled carbon nanotube, and their off-state currents are also in a similar range. Here, we define the on-state current and off-state current of a single semiconductor single-walled carbon nanotube as I0 and I1, respectively; the on-state current and off-state current of a single metallic single-walled carbon nanotube as I0; and the on-state current and off-state current of the entire field-effect transistor device as I... on with I off For a field-effect transistor device containing n0 semiconductor single-walled carbon nanotubes and n1 metallic single-walled carbon nanotubes, its on / off ratio parameter N can be estimated as follows:

[0046] For field-effect transistors fabricated entirely from semiconductor-type single-walled carbon nanotubes, the typical current on / off ratio exceeds 10. 3 This corresponds to N>2. In contrast, when a single metallic single-walled carbon nanotube exists in the channel, the value of N is approximately log((n0+n1) / n1)≈log(180)≈2.35. Therefore, N=2 can be set as the threshold for determining the presence of metallic single-walled carbon nanotubes in the channel of a field-effect transistor. Figure 21The following are the transfer characteristic curves of field-effect transistors using single-walled carbon nanotube networks as channel materials: the left graph shows the adsorption of 115 μm silica microspheres without silane 7 functionalization, and the right graph shows the adsorption of 115 μm silica microspheres with silane 7 functionalization. To prepare a solution rich in metallic single-walled carbon nanotubes, a purification process with a polymer:singan carbon nanotube ratio of 8:1 was used in the examples. The results show that devices fabricated from single-walled carbon nanotubes adsorbed onto 115 μm silica microspheres that had undergone centrifugation but were not functionalized with silane 7 (acidification) mostly exhibited low on / off current ratios (<10). 2 This indicates that the purity of the semiconductor-type single-walled carbon nanotubes is low. In contrast, 210 devices fabricated using single-walled carbon nanotubes adsorbed onto 115 μm silica microspheres functionalized with silane 7 (acidification) all exhibited on / off current ratios greater than 10. 4 According to statistical measurements, the average length of the single-walled carbon nanotubes used in this study is approximately 2.5 µm. In devices with a channel length of 1 µm, the probability of single-walled carbon nanotubes directly connecting to the source and drain is approximately 73.8% (calculated as 1 - 2arcsin(1 / 2.5) / π). Based on a single-walled carbon nanotube network density of 67 nanotubes / µm, the effective number of single-walled carbon nanotubes actually bridging the channel in each transistor is approximately 495 (calculated as 10 × 67 × 0.738). This study conducted statistical analysis on 210 devices, involving independent evaluation of 103,950 single-walled carbon nanotubes (calculated as 210 × 495). The results show that none of the devices exhibited metallic conductivity, indicating that the purity of the semiconducting single-walled carbon nanotubes is greater than 99.999% (calculated as 1 - 1 / 103950). Therefore, by combining the results of UV-Vis absorption spectroscopy and Raman spectroscopy, field-effect transistor tests confirmed the high efficiency of 115 μm diameter silica microspheres functionalized with silane 7 (acidification) for screening semiconductor single-walled carbon nanotubes.

[0047] Furthermore, by combining the technology of this invention with gel permeation chromatography, a column was packed with 2g of silane 7 (acidified)-functionalized silica microspheres with a particle size of 115μm. Then, 50mL of carbon nanotube solution, without high-speed centrifugation (only 19000g), was slowly poured into the column for permeation. The original solution was collected only once and filtered. The collected solution was divided into two portions: one portion was directly deposited into network tubes, and the other portion was first subjected to ultra-high-speed centrifugation (50000g, 2h) followed by network tube deposition. Scanning electron microscopy characterization showed that the density of both carbon nanotube networks was approximately 67 nanotubes / μm. Using the same Raman spectroscopy measurement method as described above, the measurement results are as follows... Figure 22 As shown, the original solution filtered once did not exceed 160 cm⁻¹ before or after ultracentrifugation. -1The presence of metallic single-walled carbon nanotube signals nearby indicates that the purity of the semiconductor single-walled carbon nanotubes exceeds 99.998%. This result confirms that combining the technology of this invention with gel chromatography columns has the potential to replace traditional ultra-high-speed centrifugation techniques, effectively reducing the loss of high aspect ratio semiconductor single-walled carbon nanotubes, and efficiently obtaining high-purity semiconductor single-walled carbon nanotube solutions enriched with long carbon nanotubes, with broad application prospects.

[0048] It should be noted that the above detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0051] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0052] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways, such as rotated 90 degrees or in other orientations, and the spatial relative descriptions used herein will be interpreted accordingly.

[0053] In the detailed description above, reference has been made to the accompanying drawings, which form part of this document. In the drawings, similar symbols typically identify similar parts unless the context otherwise indicates otherwise. The illustrated embodiments described in the detailed specification, drawings, and claims are not intended to be limiting. Other embodiments may be used and other changes may be made without departing from the spirit or scope of the subject matter presented herein.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for the specific separation of carbon nanotubes using ammonium salt-functionalized silica microspheres, characterized in that, Includes the following steps: a) Provide a carbon nanotube dispersion, the dispersion comprising metallic single-walled carbon nanotubes, semiconductor single-walled carbon nanotubes, and carbon nanotubes with different aspect ratios. b) Provide ammonium salt functionalized silica microspheres, wherein the microspheres are obtained by functionalizing silica microspheres with aminosilane and then acidifying them, and the surface of the microspheres is functionalized with ammonium salt groups; c) Contact the carbon nanotube dispersion with the ammonium salt functionalized silica microspheres to selectively adsorb the metallic single-walled carbon nanotubes and short semiconductor carbon nanotubes onto the surface of the ammonium salt functionalized silica microspheres, wherein the short semiconductor carbon nanotubes are carbon nanotubes with an average length of less than 0.5 μm. as well as d) Separate the ammonium salt-functionalized silica microspheres and the adsorbed carbon nanotubes from the remaining carbon nanotube dispersion to obtain a dispersion enriched with long semiconductor carbon nanotubes.

2. The method as described in claim 1, wherein, The ammonium salt functionalized silica microspheres comprise a silica core and ammonium salt groups covalently attached to the surface of the silica core.

3. The method as described in claim 2, wherein, The ammonium salt functionalized silica microspheres are formed through the following steps: S1: Silica microspheres are dispersed in a mixture of aminosilane and toluene and reacted to graft amino groups onto the surface of the silica microspheres. After solid-liquid separation and drying, amino-functionalized silica microspheres are obtained. S2: The amino-functionalized silica microspheres are placed in an acidic solution for surface modification, so that the amino groups on the surface are converted into ammonium salt groups. After solid-liquid separation and drying, ammonium salt-functionalized silica microspheres are obtained.

4. The method according to claim 3, characterized in that, The aminosilane is N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

5. The method according to claim 3, characterized in that, In step S1, the particle size of the silica microspheres is 100 μm to 150 μm; preferably, the particle size of the silica microspheres is 115 μm.

6. The method according to claim 3, characterized in that, The specific process of step S1 is as follows: place the silica microspheres in a mixture of aminosilane and toluene with a concentration of 10mM, stir magnetically for 2 hours at 60℃ and 750 rpm, then centrifuge and vacuum dry at 120℃ for 30 min.

7. The method according to claim 3, characterized in that, The specific process of step S2 is as follows: the dried amino-functionalized silica microspheres are placed in a 3% dilute hydrochloric acid solution and reacted for 2 hours. After solid-liquid separation by centrifugation, isopropanol is used for solvent replacement. Solid-liquid separation is performed again by centrifugation and vacuum drying is carried out at 120°C.

8. The method according to claim 1, characterized in that, The ammonium salt-functionalized silica microspheres and adsorbed carbon nanotubes are separated from the remaining carbon nanotube dispersion by static adsorption or column filtration.

9. The method according to claim 8, characterized in that, The static adsorption method involves adding 0.4 g of silica microspheres to every 3 mL of carbon nanotube solution, allowing the adsorption to proceed for 48 hours until dynamic equilibrium is reached, and then centrifuging to obtain the supernatant.

10. The method according to claim 8, characterized in that, The column filtration method involves filling the column with the ammonium salt-functionalized silica microspheres, injecting the carbon nanotube solution into the column for filtration, and collecting the eluent.

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