Carbon nanotube film surface treatment method

Abstract

The invention relates to a surface treatment method for a carbon nanotube film. The surface treatment method comprises the following steps: laying the carbon nanotube film on the surface of a substrate; carrying out annealing on the carbon nano tube film; carrying out acid treatment on the carbon nanotube film by using an inorganic acid, reacting the metal catalyst particles in the carbon nanotube film with the inorganic acid to generate an inorganic salt, and then cleaning the inorganic salt attached to the carbon nanotube film; and carrying out annealing treatment on the carbon nanotube film so as to remove the residual inorganic salt in the carbon nanotube film.

Description

Technical Field

[0001] The present invention relates to a method for surface treatment of a carbon nanotube film. Background Art

[0002] Due to the unique structure and excellent mechanical, electrical, and chemical properties of carbon nanotubes, they present broad application prospects, attracting great attention from many scientists in the fields of materials, physics, electronics, chemistry, etc., and becoming the research forefront and hot spot in the international new materials field. Carbon nanotube films containing multiple carbon nanotubes are also applied to various fields. For example, carbon nanotube films are applied to the field of growing epitaxial structures. It is adopted to lay a carbon nanotube film on a substrate, and then grow gallium nitride epitaxially on the carbon nanotube film. However, since the carbon nanotube film is obtained from a carbon nanotube array, and the carbon nanotube array is generally grown by chemical vapor deposition, a catalyst is deposited on the silicon substrate during the growth of the carbon nanotube array. Therefore, there are generally metal catalyst particles in the carbon nanotubes of the carbon nanotube film, which affects the quality of gallium nitride. When applying the carbon nanotube film to other technical fields, the quality and performance of the application will also be affected because there are generally metal catalyst particles in the carbon nanotubes of the carbon nanotube film. Summary of the Invention

[0003] In summary, it is indeed necessary to provide a method for surface treatment of a carbon nanotube film to remove the catalyst in the carbon nanotube film.

[0004] A method for surface treatment of a carbon nanotube film includes the following steps: laying the carbon nanotube film on the surface of a substrate; annealing the carbon nanotube film; performing acid treatment on the carbon nanotube film with an inorganic acid, wherein the metal catalyst particles in the carbon nanotube film react with the inorganic acid to form inorganic salts, and then washing the inorganic salts attached to the carbon nanotube film; performing annealing treatment on the carbon nanotube film to remove the residual inorganic salts in the carbon nanotube film.

[0005] Compared with the prior art, the method for surface treatment of a carbon nanotube film provided by the present invention can greatly reduce the content of catalyst metals in the carbon nanotube film in a relatively simple manner without damaging the structure of the carbon nanotube film, making the carbon nanotube film cleaner. Brief Description of the Drawings

[0006] Figure 1 It is a flowchart of the method for surface treatment of a carbon nanotube film.

[0007] Figure 2 It is a scanning electron microscope photo of a single-layer super-aligned carbon nanotube film.

[0008] Figure 3 It is a schematic structural diagram of a carbon nanotube segment in a single-layer super-aligned carbon nanotube film.

[0009] Figure 4 It is a scanning electron microscope photograph of the carbon nanotube flocculated film.

[0010] Figure 5 It is a scanning electron microscope photograph of the carbon nanotube rolled film.

[0011] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. Specific Embodiments

[0012] The technical solutions of the present invention will be further described in detail below according to the accompanying drawings of the specification and in conjunction with specific embodiments.

[0013] The present invention provides a method for surface treatment of a carbon nanotube film to remove metal catalyst particles in the carbon nanotube film. Please refer to Figure 1 , the method for surface treatment of the carbon nanotube film includes the following steps:

[0014] First, lay the carbon nanotube film on the surface of the substrate;

[0015] After that, anneal the carbon nanotube film;

[0016] Then, use an inorganic acid to perform acid treatment on the carbon nanotube film. The metal catalyst particles in the carbon nanotube film react with the inorganic acid to form inorganic salts, and then wash the inorganic salts attached to the carbon nanotube film;

[0017] Finally, perform annealing treatment on the carbon nanotube film to remove the residual inorganic salts in the carbon nanotube film.

[0018] Specific embodiments of the method for surface treatment of the carbon nanotube film are as follows:

[0019] First, lay the carbon nanotube film on the surface of the substrate. Specifically, lay at least one layer of carbon nanotube film on the cleaned substrate. The substrate can be selected from sapphire, silicon wafer, silicon oxide wafer, etc. If the thickness of the carbon nanotube film is too thick, it is not conducive to subsequent acid treatment and cleaning. Therefore, a carbon nanotube film with a reasonable thickness can be selected for surface treatment. Then, use volatile organic solvents such as ethanol, acetone, and isopropanol to shrink the carbon nanotube film and dry it at 50-80 °C.

[0020] In this embodiment, it is preferred to lay 6 layers of super-aligned carbon nanotube films on the silicon oxide wafer substrate.

[0021] The super-aligned carbon nanotube film is a carbon nanotube film obtained by pulling from a carbon nanotube array. Please refer to Figure 2 , the super-aligned carbon nanotube film includes a plurality of carbon nanotubes that are preferentially oriented in the same direction and arranged parallel to the surface of the super-aligned carbon nanotube film, and the carbon nanotubes are connected end to end by van der Waals forces.

[0022] Please refer to Figure 3 , each super-aligned carbon nanotube film includes a plurality of continuously and directionally arranged carbon nanotube segments 143. The plurality of carbon nanotube segments 143 are connected end to end by van der Waals forces. Each carbon nanotube segment 143 includes a plurality of mutually parallel carbon nanotubes 145, and the plurality of mutually parallel carbon nanotubes 145 are tightly connected by van der Waals forces. The carbon nanotube segment 143 has arbitrary width, thickness, uniformity and shape. The thickness of the super-aligned carbon nanotube film is 0.5 nanometers to 100 micrometers, the width is related to the size of the carbon nanotube array from which the super-aligned carbon nanotube film is drawn, and the length is not limited. For the super-aligned carbon nanotube film and its preparation method, please refer to the Chinese patent application "Carbon Nanotube Film Structure and Its Preparation Method" with the application number CN101239712A, which was applied on February 9, 2007 and published on August 13, 2008, applicant: Tsinghua University, Hon Hai Precision Industry (Shenzhen) Co., Ltd. For the sake of brevity, it is only cited here, but all the technical disclosures in the above application should also be regarded as part of the technical disclosures of the present invention application.

[0023] On the substrate, the multi-layer super-aligned carbon nanotube films are stacked on top of each other, and an intersection angle α is formed between the carbon nanotubes with preferred orientation arrangements in adjacent two-layer super-aligned carbon nanotube films, where α is greater than or equal to 0 degrees and less than or equal to 90 degrees (0°≤α≤90°).

[0024] In this embodiment, 6 super-aligned carbon nanotube films are orthogonally laid on a silicon oxide substrate, that is, the extending directions of the carbon nanotubes with preferred orientation arrangements in adjacent two-layer super-aligned carbon nanotube films among the 6 super-aligned carbon nanotube films are perpendicular to each other. Then, an ethanol solvent is used to shrink the super-aligned carbon nanotube film, and it is dried at 60°C.

[0025] It can be understood that the carbon nanotube film is not limited to the super-aligned carbon nanotube film in this embodiment, and can also be a carbon nanotube rolled film and a carbon nanotube flocculated film. Of course, the carbon nanotube film is not limited to this either.

[0026] The carbon nanotube flocculated film is a carbon nanotube film formed by a flocculation method. The carbon nanotube flocculated film includes carbon nanotubes that are intertwined and evenly distributed. The length of the carbon nanotubes is greater than 10 micrometers, preferably 200 to 900 micrometers. The carbon nanotubes attract and wind around each other by van der Waals forces to form a network structure. The carbon nanotube flocculated film is isotropic. The carbon nanotubes in the carbon nanotube flocculated film are evenly distributed and randomly arranged, forming a large number of pore structures, and the pore size is about less than 10 micrometers. The length and width of the carbon nanotube flocculated film are not limited. Please refer to Figure 4, in the carbon nanotube flocculated film, the carbon nanotubes are intertwined with each other. Therefore, the carbon nanotube flocculated film has good flexibility and is a self-supporting structure, which can be bent and folded into any shape without breaking. For the carbon nanotube flocculated film and its preparation method, please refer to the Chinese patent application "Preparation Method of Carbon Nanotube Film" with the application number CN101284662A, which was applied by Fan Shoushan et al. on April 13, 2007 and published on October 15, 2008. The applicants are Tsinghua University and Hon Hai Precision Industry (Shenzhen) Co., Ltd. For the sake of brevity, it is only cited here, but all the technical disclosures in the above application should also be regarded as part of the technical disclosures of this invention application.

[0027] The carbon nanotube rolled film is a carbon nanotube film formed by rolling a carbon nanotube array. The carbon nanotube rolled film includes uniformly distributed carbon nanotubes, and the carbon nanotubes are preferentially oriented in the same direction or different directions. The carbon nanotubes can also be isotropic. The carbon nanotubes in the carbon nanotube rolled film partially overlap each other and are attracted to each other by van der Waals forces and tightly combined, so that the carbon nanotube layer has good flexibility and can be bent and folded into any shape without breaking. And because the carbon nanotubes in the carbon nanotube rolled film are attracted to each other by van der Waals forces and tightly combined, the carbon nanotube rolled film is a self-supporting structure.

[0028] The carbon nanotube rolled film can be obtained by rolling a carbon nanotube array. The carbon nanotubes in the carbon nanotube rolled film form an angle β with the surface of the growth substrate on which the carbon nanotube array is formed, where β is greater than or equal to 0 degrees and less than or equal to 15 degrees (0 ≤ β ≤ 15°). This angle β is related to the pressure applied to the carbon nanotube array. The greater the pressure, the smaller the angle. Preferably, the carbon nanotubes in the carbon nanotube rolled film are arranged parallel to the growth substrate. Depending on the rolling method, the carbon nanotubes in the carbon nanotube rolled film have different arrangements. When rolling in the same direction, the carbon nanotubes are preferentially oriented in a fixed direction. Please refer to Figure 5, when rolling in different directions, the carbon nanotubes are preferentially oriented in different directions. When vertically rolling the carbon nanotube array from above the carbon nanotube array, the carbon nanotube rolled film is isotropic. The length of the carbon nanotubes in the carbon nanotube rolled film is greater than 50 microns. There is a certain gap between adjacent carbon nanotubes in the carbon nanotube rolled film, thereby forming a plurality of pores in the carbon nanotube rolled film, and the size of the pores is about less than 10 microns. For the carbon nanotube rolled film and its preparation method, please refer to the Chinese Patent Application Publication No. CN101314464A, "Preparation Method of Carbon Nanotube Film", filed on June 1, 2007 and published on December 3, 2008, by Fan Shoushan et al., Applicants: Tsinghua University, Hon Hai Precision Industry (Shenzhen) Co., Ltd. For the sake of brevity, only cited here, but all the technical disclosures in the above application should also be regarded as part of the technical disclosure of the present invention application.

[0029] After that, the carbon nanotube film is annealed. Specifically, the carbon nanotube film is annealed in air using a CVD tube furnace. This step is to slightly oxidize and open the closed ends of the carbon nanotubes to expose the catalyst particles inside. The laid carbon nanotube film sample is rapidly heated to 500 - 800 °C in an air atmosphere using a CVD tube furnace, maintained at this temperature for 10 - 30 minutes, and finally rapidly cooled to room temperature. It is advisable to heat at 600 °C for 15 minutes. A relatively high heating and cooling rate is used to avoid excessive heating time and uncontrollable oxidation. When the heating temperature is lower than 500 °C, the carbon nanotubes can still remain stable in air and are not easily oxidized.

[0030] Then, the carbon nanotube film is acid-treated with an inorganic acid. The metal catalyst particles in the carbon nanotube film react with the inorganic acid to form inorganic salts, and then the inorganic salts attached to the carbon nanotube film are washed. During the washing process, most of the inorganic salts are washed away. Generally, the carbon nanotube film is immersed in a mixed solution of an inorganic acid and volatile organic solvents such as ethanol, acetone, and isopropanol. Since the carbon nanotube film is hydrophobic and has a low mass, if volatile organic solvents are not used, the carbon nanotube film will float on the solution and cannot be immersed in the mixed solution of the inorganic acid and volatile organic solvents. If the content of volatile organic solvents in the mixed solution is relatively small, the carbon nanotube film cannot be completely wetted in the solution, and if it is relatively large, it will dilute the concentration of the acid. The acid can be an inorganic acid such as HCl, H2SO4, H3PO4, or a mixture of one of these acids or any two of them. During the acid treatment process, the metal catalyst particles in the carbon nanotubes react with the inorganic acid to form inorganic salts. In this embodiment, a mixed solution prepared by mixing 12 mol / L HCl with an equal volume of ethanol is used, and the carbon nanotube film is immersed in the mixed solution for 72 hours. The metal catalyst particles in the carbon nanotubes react with hydrochloric acid to form chlorides of the corresponding metals, such as iron chloride, etc.

[0031] Then, after taking out the carbon nanotube film sample, it is rinsed with a large amount of mixed solution of volatile organic solvent and water, and dried at 50 - 80 °C. During this process, most of the inorganic salts attached to the carbon nanotube film sample are rinsed off. In this embodiment, after taking out the carbon nanotube film sample, it is rinsed with a large amount of mixed solution of ethanol and water, and dried at 60 °C. Most of the chlorides attached to the carbon nanotube film sample are rinsed off.

[0032] The volatile organic solvent preferably used for cleaning the carbon nanotube film sample is the same as the volatile organic solvent used for acid treatment of the carbon nanotube film with inorganic acid. This can avoid introducing other substances into the carbon nanotube film and the types of solvents used are less, making the operation convenient.

[0033] Finally, the carbon nanotube film is annealed to remove the residual inorganic salts in the carbon nanotube film. Specifically, the carbon nanotube film is annealed in an inert gas or nitrogen atmosphere using a CVD tube furnace, with the temperature controlled between 300 °C and 500 °C, and the flow rate of the inert gas or nitrogen controlled between 50 - 500 sccm. Since the boiling point of inorganic salts is usually low, when annealing at a temperature higher than the boiling point of inorganic salts, the residual inorganic salts in the carbon nanotube film or inside the carbon nanotubes can sublimate and be carried away by the argon gas flow, further purifying the carbon nanotube film.

[0034] In this embodiment, the carbon nanotube film is annealed in an argon atmosphere using a CVD tube furnace. It is appropriate to anneal at 350 °C with an argon flow rate of 100 sccm for 2 h. The residual inorganic salts such as iron chloride in the carbon nanotube film sublimate and are carried away by the argon gas flow, further purifying the carbon nanotube film.

[0035] Comparative example:

[0036] Six layers of super-aligned carbon nanotube films are orthogonally laid on the surface of a silicon oxide substrate, shrunk with ethanol, dried at 60 °C, and no subsequent treatment is performed.

[0037] The carbon nanotube films of this embodiment and the comparative example are respectively detected by inductively coupled plasma mass spectrometry (ICP-MS). Only the content of Fe element in the carbon nanotube film is measured in this detection, and the ICP-MS detection results are shown in the following table.

[0038] Sample Fe (μg) Comparative example 0.25 This example 0.14

[0039] It can be seen that through the carbon nanotube film surface treatment method provided by the present invention, the iron element content in the carbon nanotube film can be reduced. Of course, the content of other metal elements can also be reduced.

[0040] It is understandable that during the process of acid-treating and cleaning the carbon nanotube film with an inorganic acid, it is not limited to hydrochloric acid, and a sulfuric acid ethanol solution with a mass percentage of 10% etc. can also be used.

[0041] The surface treatment method of the carbon nanotube film provided by the present invention can greatly reduce the content of catalyst metal in the carbon nanotube film in a relatively simple manner without damaging the structure of the carbon nanotube film, making the carbon nanotube film cleaner for application in various fields.

[0042] In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should all be included within the scope claimed by the present invention.

Claims

1. A method for surface treatment of a carbon nanotube film, comprising the following steps: Lay the carbon nanotube film on the surface of a substrate; Anneal the carbon nanotube film; Perform acid treatment on the carbon nanotube film using an inorganic acid. Metal catalyst particles in the carbon nanotube film react with the inorganic acid to form inorganic salts, and then wash the inorganic salts adhering to the carbon nanotube film; Perform annealing treatment on the carbon nanotube film to remove residual inorganic salts in the carbon nanotube film.

2. The method for surface treatment of the carbon nanotube film according to claim 1, characterized in that, In the step of performing acid treatment on the carbon nanotube film using an inorganic acid, where metal catalyst particles in the carbon nanotube film react with the inorganic acid to form inorganic salts, immerse the carbon nanotube film in a mixed solution of an inorganic acid and a volatile organic solvent.

3. The method for surface treatment of the carbon nanotube film according to claim 2, characterized in that The inorganic acid is any one or a mixture of any two or more of hydrochloric acid, sulfuric acid, and phosphoric acid.

4. The method for surface treatment of a carbon nanotube film according to claim 2, characterized in that, In the step of washing the inorganic salts adhering to the carbon nanotube film, take out the carbon nanotube film, rinse it with a mixed solution of a volatile organic solvent and water, and dry it at 50 - 80 °C.

5. The method for surface treatment of a carbon nanotube film according to claim 1, characterized in that, In the step of annealing the carbon nanotube film, use a CVD tube furnace to rapidly heat the laid carbon nanotube film to 500 - 800 °C in an air atmosphere, maintain heating for 10 - 30 minutes, and finally rapidly cool it to room temperature.

6. The method for surface treatment of a carbon nanotube film according to claim 1, wherein In the step of performing annealing treatment on the carbon nanotube film to remove residual inorganic salts in the carbon nanotube film, use a CVD tube furnace to anneal the carbon nanotube film in an inert gas or nitrogen atmosphere, control the temperature between 300 °C and 500 °C, and control the flow rate of the inert gas or nitrogen between 50 - 500 sccm.

7. The method for surface treatment of a carbon nanotube film according to claim 1, wherein, After laying the carbon nanotube film on the surface of the substrate, use a volatile organic solvent to shrink the carbon nanotube film and dry it at 50 - 80 °C.

8. The method for surface treatment of a carbon nanotube film according to claim 2 or 4, characterized in that, The volatile organic solvent is ethanol, acetone, or isopropanol.

9. The method for surface treatment of a carbon nanotube film according to claim 1, characterized in that, In the step of laying the carbon nanotube film on the surface of the substrate, the carbon nanotube film is a super-aligned carbon nanotube film, a carbon nanotube rolled film, or a carbon nanotube flocculated film.

10. The method for surface treatment of a carbon nanotube film according to claim 9, characterized in that, A single-layer super-aligned carbon nanotube film includes a plurality of carbon nanotubes that are preferentially oriented in the same direction and arranged parallel to the surface of the super-aligned carbon nanotube film, and the carbon nanotubes are connected end to end by van der Waals forces.

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