A semi-arc-shaped one-dimensional carbon structure and its preparation method

Abstract

The present application relates to the field of nano-carbon material technology, more specifically, it relates to a kind of semi-arc one-dimensional carbon structure and preparation method thereof. The one-dimensional carbon structure is prepared using the polyacrylonitrile fiber coated with high-polymerization degree silica sol by high-temperature pyrolysis, by uniformly mixing polyacrylonitrile (PAN) and N, N-dimethylformamide (DMF) to obtain polyacrylonitrile spinning precursor solution, electrostatic spinning process is used to spin fiber precursor, using high-polymerization degree silica (SiO2) sol impregnation of the fiber precursor, then high-temperature sintering in a nitrogen environment, finally by etching, after deionized water cleaning, drying to obtain the one-dimensional carbon structure, the one-dimensional carbon structure is semi-arc. The semi-arc one-dimensional carbon structure obtained is well distributed, and the diameter size is uniform.

Description

Technical Field

[0001] The present application relates to the technical field of nano-carbon materials, and more specifically, to a semi-arc-shaped one-dimensional carbon structure and a preparation method thereof. Background Art

[0002] The construction of novel carbon nanostructures is crucial for the development of nanotechnology, electronics, optics, and biomedicine. Carbon, in various allotropes, is currently widely used in research in fields such as lithium-ion batteries, supercapacitors, sensors, solar cells, catalytic supports, and nanoelectronic devices. The synthesis and isolation of novel carbon structures with different dimensionalities has been a focus of research over the past two to three decades. Scientists have discovered new carbon allotropes such as three-dimensional fullerenes, one-dimensional carbon nanotubes, and two-dimensional graphene, all of which have become cutting-edge and hot topics in international academic research. Carbon materials can be classified by dimensionality, with carbon fibers, carbon nanotubes, and carbon nanowires belonging to the category of one-dimensional carbon materials. In 1991, Japanese scientists discovered a hollow tubular structure composed of graphene sheets while observing a sample under transmission electron microscopy. This material was later named carbon nanotube or Bucky tube. Carbon nanotubes are one-dimensional nanomaterials. Due to their unique hollow structure, high aspect ratio, chemical stability, and excellent mechanical, conductive, and optical properties, they are important targets for basic research and applied development. Over the past decade, carbon nanotube technology has rapidly developed worldwide.

[0003] Carbon nanotubes typically have a hollow, tubular structure, usually sealed at both ends. However, experimental studies have shown that the caps at the ends of carbon nanotubes exhibit a pentagonal structure and greater curvature, making them more mobile. The tube ends can be opened at low temperatures (around 400°C) using nitric acid in the presence of a catalyst (such as Pb), or by directly heating to 700°C in air to oxidize the top. Furthermore, two US research groups have demonstrated that graphene ribbons of various widths can be produced by longitudinally opening carbon nanotubes. A research team at Rice University used sulfuric acid and an oxidant to chemically create a pore in a carbon nanotube. This pore extends along one side of the carbon nanotube, opening it and forming a flat graphene ribbon. The width of the graphene ribbon depends on the diameter of the carbon nanotube. Researchers believe that this type of graphene ribbon could be used as a conductive or semiconducting thin film and could potentially become a low-cost alternative to single-crystalline silicon for photovoltaics. However, this preparation method makes it difficult to accurately place individual graphene ribbons on a substrate, making the fabrication of many devices extremely challenging. A research team at Stanford University placed carbon nanotubes on a silicon substrate, coated them with a polymer, and heated them. They then exfoliated the polymer and exposed the polymer-carbon nanotube material to argon plasma for a specified period of time. Some of the exposed carbon nanotubes were then cut into graphene ribbons. Longer exposure time allowed the carbon nanotubes to be cut deep within the polymer coating. Once the polymer dissolved, only the graphene ribbons remained. This heating and cutting method produced graphene ribbons with relatively sharp edges and fewer defects, resulting in optimized electrical conductivity.

[0004] The preparation of new carbon materials has always been a cutting-edge scientific issue in the field of materials. The discovery of each new carbon material has triggered a wave of research enthusiasm among materials scientists. At present, there are no reports on the discovery of semi-arc one-dimensional carbon structure and its preparation method. As a new form of carbon structure, it has significant anisotropy, and there is a correlation between its structure and physical properties. Summary of the Invention

[0005] The present disclosure provides a semi-arc-shaped one-dimensional carbon structure and a preparation method thereof. The main principle is to prepare the structure by high-temperature pyrolysis of polyacrylonitrile fiber coated with high-polymerization degree silica sol. First, high-polymerization degree silica sol is prepared by hydrothermal treatment with tetraethyl orthosilicate. A polyacrylonitrile spinning precursor solution is obtained by uniformly mixing polyacrylonitrile and N,N-dimethylformamide. The precursor polyacrylonitrile fiber is spun by an electrospinning process. The polyacrylonitrile fiber is impregnated with high-polymerization degree silica sol. After drying at room temperature, the polyacrylonitrile fiber is sintered at high temperature in a nitrogen environment. Finally, the silica on the surface is etched with hydrofluoric acid, washed with deionized water, and dried to obtain the one-dimensional carbon structure. The one-dimensional carbon structure is characterized as a semi-arc shape by scanning electron microscopy. The preparation method herein provides technical support for the structurally controlled synthesis of one-dimensional carbon materials.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions:

[0007] A semi-arc-shaped one-dimensional carbon structure and a preparation method thereof mainly comprise the following steps: mixing tetraethyl orthosilicate with a mixed solution of water and ethanol in a certain proportion, heating and refluxing, and obtaining a silica sol with a certain degree of polymerization after sufficient hydrolysis; dissolving polyacrylonitrile with a certain molecular weight in an N,N-dimethylformamide solution, stirring thoroughly and completely dissolving the mixture until it becomes colorless and transparent, thereby obtaining a polyacrylonitrile spinning solution; subjecting the polyacrylonitrile spinning solution to an electrostatic spinning process to obtain a polyacrylonitrile fiber precursor; impregnating the polyacrylonitrile fiber precursor with a high-polymerization-degree silica sol, and then sintering the mixture at a high temperature in nitrogen to obtain a sample coated with a silica ceramic layer; and immersing the sample coated with the silica ceramic layer in an etching solution, cleaning it with deionized water, and naturally drying it at room temperature to obtain the one-dimensional carbon structure.

[0008] In the technical solution of the present application, anhydrous ethanol, deionized water and ethyl orthosilicate are preferably taken in a volume ratio of 1:3:6, stirred to make them uniform, and hydrochloric acid is added to adjust the pH value to 3-4. The mass fraction of silica in the silica sol is 5-10%, preferably 7.8wt%.

[0009] In the technical solution of the present application, the mass ratio of polyacrylonitrile to N,N-dimethylformamide in the spinning solution is 1:8.5-9. The molecular weight of polyacrylonitrile is 50,000, 150,000 and 250,000, preferably 250,000;

[0010] In the technical solution of the present application, polyacrylonitrile fiber precursor is prepared by electrospinning. First, the prepared fiber spinning solution is extracted with a needle and placed on a syringe pump. The appropriate syringe pump propulsion rate is set, the positive electrode of the high-voltage power supply is connected to the liquid outlet, and the negative electrode of the high-voltage power supply is connected to an aluminum plate with a suitable receiving distance. The device connection is checked, the propulsion rate is set and the automatic propulsion button is pressed. The liquid outlet is observed, the power is turned on and the value is adjusted. After the device is stable, the fiber precursor is received. The electrospinning process parameters are: the polyacrylonitrile spinning solution outlet rate is 0.5-1ml / h, preferably 0.6ml / h, the voltage is 15-20kV, preferably 15kV, and the distance between the receiving plate and the nozzle is 15-20cm, preferably 15cm.

[0011] In the technical solution of the present application, the high-temperature sintering temperature of the polyacrylonitrile fiber sample wrapped with the silica ceramic layer is 900-1200° C., preferably 1200° C.; the high-temperature sintering time is 0.5-2 h, preferably 0.5 h.

[0012] In the technical solution of the present application, the etching solution is an acidic solution or an alkaline solution, the acidic solution is a hydrofluoric acid solution, and the alkaline solution is a NaOH solution, preferably a hydrofluoric acid solution, with a mass fraction of 10-40%, preferably 20%, and the etching time is 48h.

[0013] In the technical solution of the present application, the etched sample is cleaned with ionized water and the sample is naturally dried at room temperature.

[0014] In the technical solution of the present application, the reagents include deionized water, ethanol organic solvent, N,N-dimethylformamide, tetraethyl orthosilicate, and polyacrylonitrile powder.

[0015] In the technical solution of the present application, the polyacrylonitrile fiber is produced by an electrostatic spinning process.

[0016] In the technical solution of the present application, the one-dimensional carbon structure is semi-arc-shaped, has a clear structure, and a diameter of 200-400 nm.

[0017] In summary, this application has the following beneficial effects:

[0018] 1. This application utilizes high-temperature pyrolysis of high-polymerization silica sol-coated polyacrylonitrile fibers to fabricate a novel one-dimensional carbon structure. Electrospinning, a novel fiber preparation technique, can produce polyacrylonitrile fibers with adjustable fineness, ranging from a few nanometers to tens of microns, and exhibiting excellent fiber uniformity. Polyacrylonitrile can be dissolved in N,N-dimethylformamide solution through stirring, enabling the preparation of spinning solutions of varying molecular weights and concentrations. The polyacrylonitrile fiber membranes produced by electrospinning have a large specific surface area and high porosity, which facilitates silica sol coating.

[0019] 2. The preparation of the silica sol of the present application adopts a sol-gel method. TEOS is dispersed in a mixed solvent of ethanol and water. The molecular level uniformity can be obtained in a very short time, and only a low synthesis temperature is required to complete the polymerization reaction of silica. Moreover, the degree of polymerization of the silica sol can be controlled by adjusting the ratio of the starting reaction reagents. In addition, the prepared silica sol can be dissolved in different types of organic solvents for dilution, and can also be concentrated by evaporating the solvent. The concentration control range is large and has good fluidity, which is conducive to coating polyacrylonitrile fibers. The carbonization of the sample of the present application adopts high-temperature sintering in a tubular furnace, which has program temperature control and can effectively regulate the carbonization of the sample.

[0020] 3. This application presents a novel semi-arc-shaped one-dimensional carbon structure with significant anisotropy. Its appearance resembles a tube structure cut longitudinally in the middle. Currently, there are no reports on the discovery and preparation of semi-arc-shaped one-dimensional carbon structures. As a new form of carbon structure, this semi-arc-shaped one-dimensional carbon structure exhibits significant anisotropy. The correlation between its structure and physical properties is of great significance and is expected to provide more possibilities for the performance and application of carbon materials.

[0021] It should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory and are not intended to limit the scope of protection of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 1. Figure 1 This is a scanning electron microscope image of the polyacrylonitrile fiber precursor prepared in Example 1 of the present application (magnifications are 10,000 times and 50,000 times, respectively);

[0023] 2. Figure 2 These are scanning electron microscope photos of the polyacrylonitrile fiber precursor prepared in Example 1 of the present application after being treated with a high-polymerization SiO2 sol but not sintered (magnifications are 10,000 times and 100,000 times, respectively);

[0024] 3. Figure 3 These are scanning electron microscope photos (at different magnifications) of the semi-arc-shaped one-dimensional carbon structure prepared in Example 1 of the present application;

[0025] 4. Figure 4 These are scanning electron microscope photos (at different magnifications) of the samples prepared in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0026] The present application is further described in detail below in conjunction with the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0027] Example

[0028] Example 1

[0029] A method for preparing a semi-arc-shaped one-dimensional carbon structure comprises the following steps:

[0030] (1) Take 1.5 g of polyacrylonitrile (PAN) and 8.5 g of N,N-dimethylformamide (DMF), stir them thoroughly with a magnetic stirrer until they become colorless and transparent to obtain a polyacrylonitrile spinning solution.

[0031] (2) Take the polyacrylonitrile spinning solution prepared in (1), inject the prepared polyacrylonitrile spinning solution into an electrospinning machine, adjust the relevant electrospinning process parameters (spinning solution outlet speed is 0.6 ml / h, voltage is 15 kV, and the distance between the receiving plate and the nozzle is 15 cm), and obtain a polyacrylonitrile fiber precursor after electrospinning.

[0032] (3) The polyacrylonitrile fiber precursor prepared in (2) was impregnated with a high-polymerization silica sol (SiO2 mass fraction: 7.8 wt%) and sintered at a high temperature of 1100°C under nitrogen atmosphere (the initial temperature was 25°C, the temperature was heated to 1000°C at a heating rate of 5°C / min, then heated to 1100°C at a heating rate of 2°C / min, and then kept at a constant temperature of 1100°C for 30 minutes and naturally cooled) to obtain a sample wrapped with a ceramic layer.

[0033] (4) The sample wrapped with the SiO2 ceramic layer was immersed in a 40% by mass hydrofluoric acid solution for 48 hours, and the ceramic layer on the surface was etched to obtain a semi-arc one-dimensional carbon structure.

[0034] The scanning electron microscope image of the polyacrylonitrile fiber precursor prepared in this example is as follows Figure 1 As shown, from Figure 1 It can be seen that the fibers have no orientation and are arranged irregularly, with a relatively smooth surface, clear structure, good overall distribution, and no beading. The scanning electron microscope image of the polyacrylonitrile fiber precursor prepared in this embodiment after being treated with high-polymerization SiO2 sol but not sintered is as follows Figure 2 As shown, from Figure 2 It can be seen that the fiber before sintering and impregnated with ceramic sol has a good one-dimensional fiber morphology, but due to the high degree of SiO2 polymerization, cracks appear on the sol surface. This is why the degree of damage to the carbon nanotubes increases, which is conducive to the preparation of semi-arc-shaped one-dimensional carbon structures. The scanning electron microscope image of the semi-arc-shaped one-dimensional carbon structure prepared in this embodiment is shown in FIG. Figure 4 As shown, from Figure 4 It can be seen that the material after sintering and etching has a good semi-arc structure.

[0035] Example 2

[0036] 1.5g of 250,000 molecular weight polyacrylonitrile and 8.5g of N,N-dimethylformamide were stirred thoroughly with a magnetic stirrer until colorless and transparent to obtain a polyacrylonitrile spinning solution. The prepared polyacrylonitrile spinning solution was injected into an electrospinning machine at a spinning rate of 0.6ml / h, a voltage of 15kV, and a distance of 15cm between the receiving plate and the nozzle. After electrospinning, a polyacrylonitrile fiber precursor was obtained. The solution was impregnated with a high-polymerization silica sol (mass fraction: 7.8wt%) and sintered at 900°C under a nitrogen atmosphere (initial temperature: 25°C, heating to 900°C at a rate of 5°C / min, then holding at 900°C for 0.5h and cooling naturally) to obtain a sample coated with a ceramic layer. The sample coated with the silica ceramic layer was then immersed in a 20% hydrofluoric acid solution for 48h to etch the surface ceramic layer.

[0037] Example 3

[0038] 1.5g of 50,000 molecular weight polyacrylonitrile and 8.5g of N,N-dimethylformamide were stirred thoroughly with a magnetic stirrer until colorless and transparent to obtain a polyacrylonitrile spinning solution. The prepared polyacrylonitrile spinning solution was injected into an electrospinning machine at a spinning rate of 0.6ml / h, a voltage of 15kV, and a distance of 15cm between the receiving plate and the nozzle. After electrospinning, a polyacrylonitrile fiber precursor was obtained. The solution was impregnated with a high-polymerization silica sol (mass fraction: 7.8wt%) and sintered at 900°C under a nitrogen atmosphere (initial temperature: 25°C, heating to 900°C at a rate of 5°C / min, then holding at 900°C for 0.5h and cooling naturally) to obtain a sample coated with a ceramic layer. The sample coated with the silica ceramic layer was then immersed in a 20% hydrofluoric acid solution for 48h to etch the surface ceramic layer.

[0039] Example 4

[0040] 1.5g of 150,000 molecular weight polyacrylonitrile and 8.5g of N,N-dimethylformamide were stirred thoroughly with a magnetic stirrer until colorless and transparent to obtain a polyacrylonitrile spinning solution. The prepared polyacrylonitrile spinning solution was injected into an electrospinning machine at a spinning rate of 0.6ml / h, a voltage of 15kV, and a distance of 15cm between the receiving plate and the nozzle. After electrospinning, a polyacrylonitrile fiber precursor was obtained. The solution was impregnated with a high-polymerization silica sol (mass fraction: 7.8wt%) and sintered at 900°C under a nitrogen atmosphere (initial temperature: 25°C, heating to 900°C at a rate of 5°C / min, then holding at 900°C for 0.5h and cooling naturally) to obtain a sample coated with a ceramic layer. The sample coated with the silica ceramic layer was then immersed in a 20% hydrofluoric acid solution for 48h to etch the surface ceramic layer.

[0041] Comparative Example

[0042] Comparative Example 1

[0043] In order to verify the sintering temperature and the differences in sample morphology after removing the silicon dioxide layer by different methods, NaOH solution was used instead of hydrofluoric acid to etch silicon dioxide, including the following steps:

[0044] 1.5g of 250,000 molecular weight polyacrylonitrile and 8.5g of N,N-dimethylformamide were stirred thoroughly with a magnetic stirrer until colorless and transparent to obtain a polyacrylonitrile spinning solution. The prepared polyacrylonitrile spinning solution was injected into an electrospinning machine at a spinning rate of 0.6ml / h, a voltage of 15kV, and a distance of 15cm between the receiving plate and the nozzle. After electrospinning, a polyacrylonitrile fiber precursor was obtained. The solution was impregnated with a high-polymerization silica sol (mass fraction: 7.8wt%) and sintered at 900°C under a nitrogen atmosphere (initial temperature: 25°C, heating to 900°C at a rate of 5°C / min, then holding at 900°C for 0.5h and cooling naturally) to obtain a sample coated with a ceramic layer. The sample coated with the silica ceramic layer was then immersed in a 40% sodium hydroxide solution for 48h to etch the surface ceramic layer.

[0045] Result Analysis

[0046] The scanning electron microscope image of the polyacrylonitrile fiber precursor prepared in this example is as follows Figure 1 As shown, from Figure 1 It can be seen that the fibers have no orientation and are arranged irregularly, with a relatively smooth surface, clear structure, good overall distribution, and no beading. The scanning electron microscope image of the polyacrylonitrile fiber precursor prepared in this embodiment after being quenched by high-polymerization silica sol but not sintered is shown in FIG. Figure 2 As shown, from Figure 2 It can be seen that the fiber before sintering and impregnated with ceramic sol has a good one-dimensional morphology of the fiber, but due to the high degree of polymerization of silica, cracks appear on the surface of the sol. This is why the degree of damage to the carbon nanotubes is increased, which is conducive to the preparation of semi-arc-shaped one-dimensional carbon structures. The scanning electron microscope image of the semi-arc-shaped one-dimensional carbon structure prepared in this embodiment is shown in FIG. Figure 3 As shown in the figure, the sintered and etched material has a good semi-arc structure. The sample wrapped with the silicon dioxide ceramic layer was immersed in a 40% NaOH solution for 48 hours to etch the surface ceramic layer. Figure 4 It shows that no one-dimensional semi-arc structure appears during low-temperature sintering, the etching effect of NaOH solution is poor, and the carbonized product is in the silicon dioxide ceramic system.

[0047] The above description is merely an exemplary embodiment of the present disclosure, but the scope of protection of the present disclosure is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present disclosure should be included in the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be based on the scope of protection of the claims.

Claims

1. A semi-arc one-dimensional carbon structure, characterized in that: The one-dimensional carbon structure is prepared by high-temperature pyrolysis of polyacrylonitrile fiber coated with high-polymerization silica sol, by uniformly mixing polyacrylonitrile (PAN) with a molecular weight of 250K and N,N-dimethylformamide (DMF) to obtain a polyacrylonitrile spinning precursor solution, spinning a fiber precursor using an electrospinning process, impregnating the fiber precursor with high-polymerization silica (SiO2) sol, and then sintering at a temperature of 1100-1200°C in a nitrogen environment for 0.5-1h. Finally, the one-dimensional carbon structure is obtained by etching with a hydrofluoric acid solution with a mass fraction of 10-40%, washing with deionized water, and drying. The one-dimensional carbon structure is semi-arc-shaped; The mass ratio of the polyacrylonitrile to the N,N-dimethylformamide is 1:8.5-9; The high-polymerization silica refers to a silica sol in which the mass fraction of silica is 7.8 wt %.

2. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 1, characterized in that: The following steps are involved: (1) Preparation of spinning solution: polyacrylonitrile (PAN) and N,N-dimethylformamide (DMF) are mixed uniformly until they become colorless and transparent to prepare polyacrylonitrile spinning solution; (2) subjecting the polyacrylonitrile spinning solution to an electrospinning process to prepare a polyacrylonitrile fiber precursor; (3) impregnating the polyacrylonitrile fiber precursor with a high-polymerization SiO2 sol, and then sintering at a high temperature in nitrogen to obtain a sample coated with a SiO2 ceramic layer; (4) The sample wrapped with the SiO2 ceramic layer is immersed in an etching solution, cleaned with deionized water, and naturally dried at room temperature to obtain the one-dimensional carbon structure.

3. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 2, characterized in that: In the step (1), the mass ratio of the polyacrylonitrile to the N,N-dimethylformamide is 1:8.5-9.

4. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 2, wherein: In the step (1), the molecular weight of the polyacrylonitrile is 250K, and the diameter of the semi-arc-shaped one-dimensional carbon structure is 200-400 nm.

5. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 2, characterized in that: The step (2) specifically comprises: injecting the polyacrylonitrile spinning solution into an electrospinning machine, adjusting relevant electrospinning process parameters, and obtaining the polyacrylonitrile fiber precursor after electrospinning.

6. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 5, characterized in that: The electrospinning process parameters are as follows: the polyacrylonitrile spinning solution outlet speed is 0.5-1 ml / h, the voltage is 15-20 kV, and the distance between the receiving plate and the nozzle is 15-20 cm.

7. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 2, characterized in that: In the step (3), the mass fraction of SiO2 in the high-polymerization SiO2 sol is 7.8 wt%.

8. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 2, characterized in that: In the step (3), the temperature of the high-temperature sintering is 1100-1200° C., and the time of the high-temperature sintering is 0.5-1 h.

9. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 2, characterized in that: In the step (4), the etching solution is a hydrofluoric acid solution, and the etching time is 48 hours.

10. The method for preparing a semi-arc-shaped one-dimensional carbon structure according to claim 9, characterized in that: In the step (4), the mass fraction of the hydrofluoric acid solution is 10-40%.

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