Method for purifying carbon nanotubes by using eutectic solvent

Abstract

The invention discloses a method for purifying a carbon nano tube by using a deep eutectic solvent. The method comprises the following steps: drying carbon nanotube powder prepared on a supported catalyst by adopting a chemical vapor deposition method; the method comprises the following steps: mixing a hydrogen bond donor and a hydrogen bond acceptor according to a fixed molar ratio, and stirring at a set temperature to obtain a homogeneous eutectic solvent; adding the dried carbon nanotube powder into a deep-eutectic solvent, and dissolving the supported catalyst particles by regulating and controlling the temperature and the time; and carrying out vacuum filtration, cleaning and drying treatment on the reacted liquid to obtain the high-quality carbon nanotube. Compared with a traditional strong acid purification process, the method has the advantages of being simple, environmentally friendly, low in cost and the like, the intrinsic structure and surface characteristics of the carbon nanotubes can be effectively kept, and the method has important industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of carbon nanotube materials, and particularly to a method for purifying carbon nanotubes using a deep eutectic solvent. Background Art

[0002] Carbon nanotubes are typical quasi-one-dimensional nano-carbon materials. Their unique tubular structure and excellent physical and chemical properties make them have broad application prospects in many fields such as composite materials, electronic devices, biomedicine, energy storage and conversion, and aerospace. Therefore, carbon nanotubes are included in the first batch of 15 kinds of frontier materials in the "Key Development Guidance Catalog for the Industrialization of Frontier Materials" issued by the Ministry of Industry and Information Technology in 2023. For example, carbon nanotubes, with their excellent electrical conductivity and the characteristic of less addition amount (only 1 / 6 - 1 / 2) compared with traditional conductive agents, can be used as conductive agents for lithium-ion batteries and significantly improve the energy density of the batteries. In addition to being used as battery conductive agents, they are also widely used in fields such as conductive plastic filling, semiconductor chips, and electromagnetic wave shielding.

[0003] Growing carbon nanotubes on a supported catalyst using chemical vapor deposition technology is a mature technology with advantages such as low cost, high yield, and scalability. Among them, the supported catalyst is composed of a high specific surface area support and metal nanoparticles. Commonly used supports are mainly some oxides with high stability and high specific surface area (such as silica, alumina, magnesia, layered double hydroxide), and commonly used metal catalysts are mainly some iron-based metals with high carbon solubility (such as iron, cobalt, nickel). However, the carbon nanotube powder prepared by chemical vapor deposition often remains impurities such as the support, metal catalyst particles, and amorphous deposited carbon, which seriously affect its electrical, mechanical, and thermal properties and limit its further application in high-end fields.

[0004] The traditional strong acid (such as concentrated nitric acid, sulfuric acid or mixed acid) purification process removes impurities in the powder through oxidative corrosion. Combining centrifugation or filtration technology can obtain high-purity carbon nanotube materials. However, this method also has significant defects: the strong acid oxidation destroys the graphitization structure of carbon nanotubes, resulting in tube wall fracture and performance degradation, and introducing excessive oxygen-containing functional groups; metal particles are easily wrapped by graphite and remain, affecting high-purity demand scenarios; the process produces toxic waste liquid, with high treatment costs and environmental hazards, and at the same time, the multi-step process is complex and energy-consuming. In addition, acid treatment easily leads to excessive oxidation on the surface of carbon tubes, resulting in aggravated agglomeration phenomenon, and additional dispersants need to be added to achieve stable dispersion, increasing the difficulty of subsequent applications. In the future, green, efficient, and highly selective purification technologies need to be developed to balance environmental protection, economy, and maintain the integrity of the carbon tube structure to meet the needs of high-end applications.

[0005] Deep eutectic solvents are a class of compounds with special metal oxide dissolution capabilities. These solvents are composed of eutectic mixtures of hydrogen bond donors and acceptors, and their raw materials usually have the characteristics of low cost, simple preparation, relatively non-toxic and biodegradable. Multiple studies have confirmed that deep eutectic solvents can effectively dissolve common oxides and metals, and the dissolution performance of some formulations can even be comparable to that of strong acids. Compared with the traditional strong acid purification process, the main advantage of using deep eutectic solvents is that there is no need to add additional reducing agents and / or expensive solvent extractants, which conforms to the development concept of environmental protection, and at the same time can protect the intrinsic structure and surface properties of carbon nanotubes. Summary of the Invention

[0006] Object of the Invention: Aiming at the problems existing in the traditional strong acid purification process of carbon nanotubes, the present invention applies the advantages of deep eutectic solvents to the carbon nanotube material purification process. By regulating the ratio of hydrogen bond donors to acceptors, the metal ion complexing ability and carbon material wettability of the solvent are optimized directionally. Selectively dissolve the support, metal and amorphous carbon impurities under mild reaction conditions, effectively avoid the damage of the intrinsic structure of carbon nanotubes caused by strong acid oxidation, and achieve the efficient separation of the solvent and carbon nanotubes through solid-liquid separation technology, providing a green and sustainable solution for large-scale purification of high-quality carbon nanotubes.

[0007] Technical Solution: A method for purifying carbon nanotubes using deep eutectic solvents according to the present invention includes the following steps:

[0008] (1) After drying the carbon nanotube powder prepared by chemical vapor deposition, add a deep eutectic solvent prepared by a hydrogen bond donor and a hydrogen bond acceptor in a fixed molar ratio, dissolve the supported catalyst particles by regulating the reaction conditions, and obtain high-quality carbon nanotubes through vacuum filtration, washing and drying.

[0009] Further, in step (1), the carbon nanotube powder is any one or a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0010] Further, in step (1), the hydrogen bond acceptor is any one or a combination of choline chloride, betaine, polyethylene glycol, tetrabutylammonium bromide.

[0011] Further, in step (1), the hydrogen bond donor is any one or a combination of urea, thiourea, ethylene glycol, lactic acid.

[0012] Further, in step (1), the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is (1-2):(1-2).

[0013] Further, in step (1), the regulation of the reaction conditions includes the reaction temperature and the reaction time. The reaction temperature is 60-80°C, and the reaction time is 12-24h.

[0014] Further, in step (1), the supported catalyst is composed of a support and metal nanoparticles. The support includes any one or a combination of silica, alumina, magnesia, and layered double hydroxides. The metal nanoparticles include any one or a combination of iron, cobalt, nickel, copper, ruthenium, manganese, zinc, rhodium, and palladium.

[0015] Further, in step (1), the high-quality carbon nanotubes have a purity ≥ 98 wt%.

[0016] Beneficial effects: Compared with the traditional strong acid purification process, the present invention has the following remarkable effects: 1) The deep eutectic solvent is composed of low-toxic and biodegradable compounds, significantly reducing the environmental pollution risk. 2) The deep eutectic solvent has extremely strong solubility for metal oxides, and its performance can be comparable to that of acidic solvents, without relying on strongly corrosive chemicals. 3) The raw materials for synthesizing the deep eutectic solvent are cheap and easily available, and the synthesis process is simple, without the need for complex equipment or high-purity reagents, being suitable for large-scale applications. 4) This method effectively maintains the intrinsic structure and surface characteristics of carbon nanotubes, providing an innovative solution for large-scale clean production, and is expected to promote the application breakthrough of carbon nanotube materials in industrial production. Description of the Drawings

[0017] Figure 1 is the Raman spectrum of the multi-walled carbon nanotube powder before separation and purification in Example 1, with the excitation laser being 633 nm;

[0018] Figure 2 is the scanning electron microscope image of the multi-walled carbon nanotube powder before separation and purification in Example 1;

[0019] Figure 3 is the Raman spectrum of the multi-walled carbon nanotube after separation and purification in Example 1, with the excitation laser being 633 nm;

[0020] Figure 4 is the transmission electron microscope image of the multi-walled carbon nanotube after separation and purification in Example 1; Detailed Embodiments

[0021] To make the content of the invention of this application easier to understand, the following further explains it in conjunction with specific examples and drawings.

[0022] Example 1: A method for purifying carbon nanotubes using a deep eutectic solvent, comprising the following steps:

[0023] (1) A layered double hydroxide-supported iron-cobalt bimetallic catalyst was prepared by the impregnation method. Using ethylene as a carbon source, multi-walled carbon nanotube powder was prepared by chemical vapor deposition technology, and the powder was dried in an oven at 100 °C for 24 h. Figure 1 The Raman spectrum in Figure 2The scanning electron microscope images in prove to be multi-walled carbon nanotubes.

[0024] (2) Mix polyethylene glycol and thiourea in a beaker at a molar ratio of 2:1, and stir at a constant temperature of 50 °C for 1 h to obtain a clear and transparent homogeneous eutectic solvent.

[0025] (3) Take 5.0 g of multi-walled carbon nanotube powder and add it to the eutectic solvent. Stir and dissolve at a constant temperature of 80 °C for 24 h, and then vacuum filter the dissolved mixture to obtain the final product. Figure 3 The Raman spectra in and Figure 4 The transmission electron microscope images in prove to be high-purity multi-walled carbon nanotubes.

[0026] Example 2: A method for purifying carbon nanotubes using a eutectic solvent, comprising the following steps:

[0027] (1) Prepare a layered double hydroxide-supported iron metal catalyst by the impregnation method. Using ethylene as a carbon source, multi-walled carbon nanotube powder is prepared by chemical vapor deposition technology, and the powder is dried in an oven at 100 °C for 24 h.

[0028] (2) Mix polyethylene glycol and thiourea in a beaker at a molar ratio of 2:1, and stir at a constant temperature of 50 °C for 1 h to obtain a clear and transparent homogeneous eutectic solvent.

[0029] (3) Take 5.0 g of multi-walled carbon nanotube powder and add it to the eutectic solvent. Stir and dissolve at a constant temperature of 80 °C for 24 h, and then vacuum filter the dissolved mixture to obtain the final product.

[0030] Example 3: A method for purifying carbon nanotubes using a eutectic solvent, comprising the following steps:

[0031] (1) Prepare a porous magnesium oxide-supported cobalt metal catalyst by the impregnation method. Using methane as a carbon source, multi-walled carbon nanotube powder is prepared by chemical vapor deposition technology, and the powder is dried in an oven at 100 °C for 24 h.

[0032] (2) Mix choline chloride and ethylene glycol in a beaker at a molar ratio of 1:2, and stir at room temperature for 1 h to obtain a clear and transparent homogeneous eutectic solvent.

[0033] (3) Take 3.0 g of multi-walled carbon nanotube powder and add it to the eutectic solvent. Continuously introduce a nitrogen protection atmosphere, stir and dissolve at a constant temperature of 80 °C for 24 h, and then vacuum filter the dissolved mixture to obtain high-quality multi-walled carbon nanotubes.

[0034] Example 4: A method for purifying carbon nanotubes using a eutectic solvent, comprising the following steps:

[0035] (1) An iron metal catalyst supported on alumina was prepared by the impregnation method. Using carbon monoxide as a carbon source, single-walled carbon nanotube powders were prepared by chemical vapor deposition technology. The powders were placed in an oven at 100 °C and dried for 24 h.

[0036] (2) Polyethylene glycol and thiourea were mixed in a beaker at a molar ratio of 2:1 and stirred at a constant temperature of 50 °C for 1 h to obtain a clear and transparent homogeneous eutectic solvent.

[0037] (3) 5.0 g of single-walled carbon nanotube powders were added to the eutectic solvent and stirred at a constant temperature of 80 °C for 24 h to dissolve. After dissolution, the mixed solution was vacuum filtered to obtain high-quality single-walled carbon nanotubes.

Claims

1. A method for purifying carbon nanotubes using a deep eutectic solvent, characterized in that, After drying the carbon nanotube powder prepared by chemical vapor deposition, a deep eutectic solvent configured with a hydrogen bond donor and a hydrogen bond acceptor in a fixed molar ratio is added, and the supported catalyst particles are dissolved by regulating the reaction conditions. High-quality carbon nanotubes are obtained through vacuum filtration, washing, and drying.

2. The method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, wherein The carbon nanotube powder described above is any one or a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes.

3. A method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, wherein, The hydrogen bond acceptor described above is any one or a combination of choline chloride, betaine, polyethylene glycol, and tetrabutylammonium bromide.

4. A method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, characterized in that, The hydrogen bond donor described above is any one or a combination of urea, thiourea, ethylene glycol, and lactic acid.

5. A method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, characterized in that, The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is (1-2):(1-2).

6. The method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, characterized in that, The regulation of the reaction conditions includes the reaction temperature and reaction time. The reaction temperature is 60-80 °C, and the reaction time is 12-24 h.

7. A method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, characterized in that, The supported catalyst described above consists of a support and metal nanoparticles. The support includes any one or a combination of silica, alumina, magnesia, and layered double hydroxides. The metal nanoparticles include any one or a combination of iron, cobalt, nickel, copper, ruthenium, manganese, zinc, rhodium, and palladium.

8. A method for purifying carbon nanotubes using a deep eutectic solvent according to claim 1, characterized in that, For the high-quality carbon nanotubes described above, their purity is ≥98 wt%.

Images