A method for preparing carbon nanotubes using a deep eutectic solvent

Abstract

The application provides a method for preparing carbon nanotubes by using a eutectic solvent, and belongs to the technical field of carbon nanomaterial preparation. The method for preparing the carbon nanotubes comprises the following steps: mixing a hydrogen bond donor and a hydrogen bond acceptor to obtain a eutectic solvent; mixing the eutectic solvent and biomass to perform a reaction, thereby obtaining a cellulose sample; mixing the cellulose sample and a microwave absorber, and performing a reaction by microwave heating, thereby obtaining the carbon nanotubes. The application discloses a method for preparing carbon nanotubes, which is simple in process and mild in reaction condition, and effectively solves the problems that the existing methods for preparing carbon nanotubes are relatively complex, high in cost and may cause environmental pollution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon nanomaterial preparation, and particularly relates to a method for preparing carbon nanotubes by using a eutectic solvent. BACKGROUND

[0002] Carbon nanotubes (CNTs) are one of the most studied carbon nanomaterials, which are composed of graphite-like tubes with nanometer diameter and millimeter length. CNTs are mainly divided into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The structure of SWCNTs is similar to that of a tube structure seamlessly rolled by graphene. The structure of MWCNTs is similar to that of a concentric tube structure formed by concentric arrangement of multiple single-walled carbon nanotubes. CNTs have unique electronic, chemical and mechanical properties. These properties make CNTs applied to energy storage, sensors, composite materials, field emission displays, semiconductor devices, building fields, aerospace technology, biotechnology and nanoelectronic devices, and many other fields.

[0003] Since CNTs were discovered, they have attracted extensive attention from the scientific community due to their special physical and chemical properties, and greatly promoted the development of nanomaterials and electrochemistry. The preparation method of CNTs determines its properties, structure and application field. At present, the main preparation methods of CNTs include plasma arc discharge, laser evaporation and chemical vapor deposition. The plasma arc discharge method requires a high temperature, and the laser evaporation method is expensive and complex in structure. Although the CNTs prepared by the two methods have high crystallinity, the yield is relatively low. The chemical vapor deposition method has shown superiority in the preparation of CNTs, and can realize industrialized mass production, but the CNTs prepared by the method often have structural defects, and the catalyst impurities are also difficult to remove, which causes difficulties in the characterization and application of CNTs. Therefore, it is of great significance to develop a simple and low-cost CNTs preparation method.

[0004] Biomass has been considered as a traditional material for synthesizing CNTs due to its abundant reserves, renewability, low price and low greenhouse gas emission. The principle of microwave heating is the interaction between polar molecules in the material and the microwave electromagnetic field, which is a process of converting electromagnetic energy into heat. Compared with traditional heating methods, microwave heating has the advantages of uniform heating, fast heating speed, selective heating, timely control, reaction sensitivity, strong penetration, green environmental protection and no pollution. Microwave pyrolysis is a new green technology for synthesizing carbon materials. Compared with traditional heating methods, microwave heating can shorten the reaction time and produce more functionalized CNTs and nanocellulose (CNF). Ikeda et al. first studied the synthesis of fullerene by microwave-induced pyrolysis in a cylindrical coaxial cavity using naphthalene plasma, which was the first carbon nanostructure produced by microwave. Fidalgo B et al. successfully prepared carbon nanowires by microwave-assisted heating method, using methane as carbon source and activated carbon and carbon fiber as wave absorber, and found that no carbon nanowires were generated under the same experimental conditions when traditional electric heating method was used. Mubarak et al. prepared MWCNTs by microwave CVD method using ferrocene and acetylene / hydrogen mixture as catalyst and carbon source gas, respectively, and the diameter of MWCNTs was between 16-23 nm. However, these methods all need to use catalyst, which will have adverse effects on the environment. Although the patent CN104787747A “Method for preparing multi-walled carbon nanotubes by microwave-enhanced rapid pyrolysis of biomass and / or carbon-containing organic waste” discloses the use of microwave to pyrolyze biomass or carbon-containing organic waste or a mixture of the two to prepare MWCNTs with an average diameter of 3-200 nm, but transition metals and their metal oxides are used as catalysts in the preparation process, and the preparation and separation process is still relatively complex, which is not conducive to industrial production. In the invention patent with application number 202010952403.1, a method for preparing ultra-long CNTs by two-step microwave treatment of biomass is disclosed, which requires two microwave heat treatments of the cellulose sample, first low-temperature microwave heat treatment and then high-temperature microwave heat treatment, and the high-temperature microwave heat treatment temperature is 1000-1500℃, which requires high temperature and high equipment requirements, high energy consumption and high cost of finished products, which is not easy to realize large-scale production and application. How to provide a method for preparing carbon nanotubes with simple operation, low reaction temperature, low cost and batch production is a problem to be solved by those skilled in the art. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing carbon nanotubes using a eutectic solvent, to solve the problems of complex preparation and separation process of existing carbon nanotubes, high production cost, not conducive to industrial production, and the need to add catalyst in the reaction process, which will have adverse effects on the environment.

[0006] To achieve the above-mentioned object of the present application, the present application provides the following technical solutions.

[0007] A method for preparing carbon nanotubes by using a deep eutectic solvent, comprising the following steps:

[0008] 1) mixing a hydrogen bond donor with a hydrogen bond acceptor to obtain a deep eutectic solvent;

[0009] 2) mixing the deep eutectic solvent obtained in step 1) with biomass to perform a reaction, thereby obtaining a cellulose sample;

[0010] 3) mixing the cellulose sample obtained in step 2) with a microwave absorber to perform a reaction by microwave heating, thereby obtaining carbon nanotubes.

[0011] Preferably, the hydrogen bond donor in step 1) comprises one of oxalic acid, lactic acid and urea; and the hydrogen bond acceptor comprises one of choline chloride, tetrabutylphosphonium bromide and tetrabutylammonium bromide.

[0012] The mass ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1-5:1.

[0013] Preferably, the temperature for mixing in step 1) is 70-100°C, and the mixing time is 20-40 min.

[0014] Preferably, the biomass in step 2) is lignocellulosic biomass, and the lignocellulosic biomass comprises one or more of poplar, palm shell, water hyacinth and corn cob; and the particle size of the biomass is 180-250 μm.

[0015] Preferably, the temperature for reaction in step 2) is 80-120°C, and the reaction time is 1-4 h.

[0016] The mass ratio of the biomass to the deep eutectic solvent is 1:10-20.

[0017] Preferably, the mass ratio of the cellulose sample to the microwave absorber in step 3) is 1.5-2.5:1.

[0018] The microwave absorber comprises one or more of silicon carbide, activated carbon, graphite and acetylene black.

[0019] The reaction in step 3) is performed under an inert atmosphere.

[0020] Preferably, the temperature for reaction in step 3) is 500-700°C, the reaction time is 30-45 min, the heating rate during the reaction is 50-100°C / min, the microwave heating power is 1800-2200 W, and the microwave heating frequency is 2.20-2.55 GHz.

[0021] Preferably, the length of the carbon nanotubes obtained in step 3) is greater than or equal to 1 cm, and the diameter is 50-100 nm.

[0022] The present application has at least the following advantages:

[0023] 1. The present application overcomes the problems of traditional methods such as plasma arc discharge, laser evaporation and chemical vapor deposition for preparing carbon nanotubes, which need to use metal catalysts (Fe, Co, Ni, etc.), substrates and carbon sources (methane, ethane, acetylene, etc.), and have complex process, high cost, structural defects of prepared carbon nanotubes, etc. The present application uses biomass as raw material, and prepares high-quality carbon nanotubes by eutectic solvent and microwave pyrolysis, which is a method for preparing high-quality carbon nanotubes with simple preparation process, low cost and large-scale production. Microwave heating has the advantages of fast heating rate and uniform heating, etc. And carbon nanotubes are only observed under microwave heating, and no carbon nanotubes are observed under the same pyrolysis conditions using traditional heating methods.

[0024] 2. The inventors have found that cellulose is the main source of biomass components for preparing carbon nanotubes, and the higher the cellulose content of the biomass, the better the quality of the prepared carbon nanotubes. Traditional chemical pretreatment methods for separating cellulose components have the defects of high energy consumption and destruction of component structure. The present application creatively proposes to use the cellulose component in biomass as raw material, separate the cellulose component in biomass by eutectic solvent pretreatment method, and then prepare carbon nanotubes by microwave pyrolysis, which has a length greater than or equal to 1 cm and a diameter of 50-100 nm. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The process flow chart for preparing carbon nanotubes by using eutectic solvent according to the present application is shown in the figure.

[0026] Figure 2 The schematic diagram of the device for preparing carbon nanotubes by using eutectic solvent according to the present application is shown in the figure.

[0027] Wherein 1 is a flow meter, 2 is a microwave oven, 3 is a temperature control system, 4 is a quartz reactor, 5 is a thermocouple, 6 is a sample, 7 is a quartz connecting tube, and 8 is a condenser.

[0028] Figure 3 The low-magnification scanning electron microscope (SEM) image of the carbon nanotubes prepared in Example 1 is shown in the figure.

[0029] Figure 4 The high-magnification scanning electron microscope (SEM) image of the carbon nanotubes prepared in Example 1 is shown in the figure. DETAILED DESCRIPTION

[0030] The present application provides a method for preparing carbon nanotubes by using eutectic solvent, which comprises the following steps:

[0031] 1) mixing the hydrogen bond donor with the hydrogen bond acceptor to obtain a deep eutectic solvent;

[0032] 2) mixing the deep eutectic solvent obtained in step 1) with biomass to perform a reaction to obtain a cellulose sample;

[0033] 3) mixing the cellulose sample obtained in step 2) with a microwave absorber to perform a reaction by microwave heating to obtain carbon nanotubes.

[0034] In the present application, the hydrogen bond donor in step 1) comprises one of oxalic acid, lactic acid and urea; and the hydrogen bond acceptor comprises one of choline chloride, tetrabutylphosphonium bromide and tetrabutylammonium bromide.

[0035] The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1-5:1, preferably 2-4:1, and further preferably 3:1.

[0036] In the present application, the temperature for mixing in step 1) is 70-100°C, preferably 75-85°C, and further preferably 80°C; and the mixing time is 20-40 min, preferably 25-35 min, and further preferably 28-30 min.

[0037] In the present application, the mixing in step 1) is preferably stirring mixing, and the stirring rate is 500-1000 r / min, preferably 600-800 r / min, and further preferably 650-750 r / min.

[0038] In the present application, the biomass in step 2) is lignocellulosic biomass, and the lignocellulosic biomass comprises one or more of poplar, palm shell, water hyacinth and corn cob; and the particle size of the biomass is 180-250 μm, preferably 200-220 μm, and further preferably 210 μm.

[0039] In the present application, the biomass is preferably dried biomass; the drying temperature is 90-110°C, preferably 95-105°C, and further preferably 100-105°C; and the drying time is 18-26 h, preferably 20-24 h, and further preferably 22-23 h.

[0040] In the present application, the temperature for the reaction in step 2) is 80-120°C, preferably 90-110°C, further preferably 100-105°C, and again further preferably 103°C; and the reaction time is 1-4 h, preferably 2-3 h, and again further preferably 2.5 h.

[0041] The mass ratio of the biomass to the deep eutectic solvent is 1:10-20, preferably 1:13-18, further preferably 1:14-16, and again further preferably 1:15.

[0042] In the present application, the step 2) further comprises the following steps:

[0043] After the reaction, the mixed system is filtered and separated, the solid residue is washed with anhydrous ethanol for 2-3 times, then washed with water for 2-3 times, and dried at a temperature of 75-85℃ until the weight is constant to obtain the cellulose sample.

[0044] In the present application, the drying temperature is preferably 78-82℃, further preferably 80℃; the drying time is 20-30h, preferably 23-28h, further preferably 24-26h.

[0045] In the present application, the purpose of mixing the deep eutectic solvent with the biomass in the step 2) is to hydrolyze or dissolve hemicellulose and lignin.

[0046] In the present application, the mass ratio of the cellulose sample to the microwave absorber in the step 3) is 1.5-2.5:1, preferably 1.8-2.1:1, further preferably 1.9-2.0:1.

[0047] In the present application, the microwave absorber comprises one or more of silicon carbide, activated carbon, graphite and acetylene black; the particle size of the microwave absorber is 300-500μm, preferably 350-450μm, further preferably 380-420μm.

[0048] In the present application, the step 3) requires that the mixture of the microwave absorber and the cellulose sample is first placed in a reactor, and then the reactor is placed in a microwave heating device, wherein the reactor is one of a quartz reactor and a corundum tube.

[0049] In the present application, the reaction in the step 3) is carried out in an inert atmosphere to exclude air in the device; the inert atmosphere comprises a nitrogen atmosphere and / or a noble gas atmosphere; the noble gas atmosphere comprises one or more of a helium atmosphere, a neon atmosphere and an argon atmosphere.

[0050] In the present application, the temperature of the reaction in the step 3) is 500-700℃, preferably 500-600℃, further preferably 525-575℃; the reaction time is 30-45min, preferably 35-40min; the heating rate during the reaction is 50-100℃ / min, preferably 60-85℃ / min, further preferably 65-75℃ / min; the power of the microwave heating is 1800-2200W, preferably 1900-2100W, further preferably 1950-2000W; the frequency of the microwave heating is 2.20-2.55GHz, preferably 2.30-2.50GHz, further preferably 2.35-2.45GHz.

[0051] In the present application, the length of the carbon nanotubes obtained in step 3) is ≥1 cm, and the diameter is 50-100 nm.

[0052] In the present application, the process flow chart for preparing the carbon nanotubes by using the eutectic solvent is shown in Figure 1 The schematic diagram of the device is shown in Figure 2 The flow meter 1, the microwave oven 2, the temperature control system 3, the quartz reactor 4, the thermocouple 5, the sample 6, the quartz connecting tube 7, and the condenser 8.

[0053] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0054] Example 1

[0055] 1) 4.5 g of oxalic acid and 5 g of choline chloride (molar ratio 1:1) were heated and stirred in a constant temperature water bath at 75°C, the stirring rate was 750 r / min, and the stirring time was 20 min, forming a colorless transparent liquid, obtaining the eutectic solvent;

[0056] 2) The poplar biomass with a particle size of 200 μm was placed in a vacuum drying oven and dried at 100°C for 20 h to remove water; the dried poplar biomass was added with the prepared eutectic solvent (the mass ratio of biomass to eutectic solvent was 1:15), and continuously stirred at 100°C for 3 h, hydrolyzing or dissolving the hemicellulose and lignin; the pretreated sample was filtered and separated, the solid residue was washed with anhydrous ethanol for 2 times, then washed with deionized water for 3 times, and finally transferred to an oven at 80°C and dried to constant weight for 26 h, obtaining the cellulose sample;

[0057] 3) The cellulose sample obtained in step 2) was mixed with silicon carbide with a particle size of 380 μm according to a mass ratio of 2.0:1, and placed in a quartz reactor and in a microwave heating device; nitrogen was introduced into the quartz reactor to remove the air inside, and nitrogen was continuously introduced at a flow rate of 350 mL / min during the reaction; the microwave heating device was heated at a rate of 65°C / min to 525°C, and then kept at constant temperature for 30 min to obtain the carbon nanotubes. The power of the microwave heating was 2000 W, and the frequency of the microwave heating was 2.45 GHz.

[0058] The SEM images of the carbon nanotubes obtained in this example at different magnifications are shown in Figure 3 and Figure 4 Figure 3 and Figure 4 ​It can be seen that after the microwave high-temperature heat treatment, the carbon order degree in the carbon nanofiber is increased, the content of graphene crystal is increased, and the length is obviously increased, which is directly converted into super-long multi-walled carbon nanotubes with perfect carbon structure. The length of the obtained carbon nanotubes is ≥1 cm, and the diameter is 50-100 nm.

[0059] Example 2

[0060] 1) 9 g of lactic acid and 5 g of choline chloride (molar ratio 2:1) were heated and stirred in a constant temperature water bath at 80°C, the stirring rate was 800 r / min, and the stirring time was 25 min, a colorless transparent liquid was formed, and a eutectic solvent was obtained;

[0061] 2) The water hyacinth biomass with a particle size of 220 μm was placed in a vacuum drying oven and dried at 90°C for 26 h to remove water; the dried water hyacinth biomass was added with the prepared eutectic solvent (the mass ratio of biomass to eutectic solvent was 1:13), and continuously stirred at 110°C for 2 h, and the hemicellulose and lignin were hydrolyzed or dissolved out, and the pretreated sample was filtered and separated, the solid residue was washed with anhydrous ethanol for 3 times, then washed with deionized water for 3 times, and finally transferred to an oven at 83°C and dried for 24 h to constant weight, to obtain a cellulose sample;

[0062] 3) The cellulose sample obtained in step 2) was mixed with silicon carbide with a particle size of 420 μm according to a mass ratio of 1.5:1, and was placed in a quartz reactor and placed in a microwave heating device, nitrogen was introduced into the quartz reactor to remove the air inside, and nitrogen was continuously introduced at a flow rate of 380 mL / min during the reaction; the microwave heating device was heated at a rate of 75°C / min to 550°C, and then constant temperature reaction was carried out for 38 min to obtain carbon nanotubes. The power of microwave heating is 1900 W, and the frequency of microwave heating is 2.30 GHz. The length of the obtained carbon nanotubes is ≥1 cm, and the diameter is 30-130 nm.

[0063] Example 3

[0064] 1) 18 g of urea and 10 g of choline chloride (molar ratio 3:1) were heated and stirred in a constant temperature water bath at 90°C, the stirring rate was 1000 r / min, and the stirring time was 30 min, a colorless transparent liquid was formed, and a eutectic solvent was obtained;

[0065] 2) Put the palm shell biomass with particle size of 250 μm into a vacuum drying oven, dry at 105 °C for 24 h to remove water; add the prepared deep eutectic solvent (mass ratio of biomass to deep eutectic solvent is 1:18) to the dried palm shell biomass, continuously stir at 120 °C for 1 h to hydrolyze or dissolve hemicellulose and lignin, filter and separate the pretreated sample, wash the solid residue with anhydrous ethanol for 3 times, then wash with deionized water for 2 times, finally transfer to a 78 °C oven and dry to constant weight for 28 h to obtain a cellulose sample;

[0066] 3) Mix the cellulose sample obtained in step 2) with silicon carbide with particle size of 500 μm according to the mass ratio of 1.8:1, put it into a corundum tube and place it in a microwave heating device, introduce helium into the corundum tube to remove the air inside, and continuously introduce helium at a flow rate of 450 mL / min during the reaction; the microwave heating device is heated at a rate of 50 °C / min to 700 °C, and then kept at constant temperature for 45 min to obtain carbon nanotubes. The power of microwave heating is 2100 W, and the frequency of microwave heating is 2.50 GHz. The length of the obtained carbon nanotubes is ≥1 cm, and the diameter is 20-110 nm.

[0067] Example 4

[0068] 1) Heat and stir 18 g of lactic acid with 5 g of choline chloride (molar ratio 4:1) in a constant temperature water bath at 95 °C, the stirring rate is 650 r / min, the stirring time is 35 min, a colorless transparent liquid is formed, and a deep eutectic solvent is obtained;

[0069] 2) Put the poplar biomass with particle size of 180 μm into a vacuum drying oven, dry at 110 °C for 22 h to remove water; add the prepared deep eutectic solvent (mass ratio of biomass to deep eutectic solvent is 1:20) to the dried poplar biomass, continuously stir at 80 °C for 4 h to hydrolyze or dissolve hemicellulose and lignin, filter and separate the pretreated sample, wash the solid residue with anhydrous ethanol for 3 times, then wash with deionized water for 2 times, finally transfer to an 80 °C oven and dry to constant weight for 23 h to obtain a cellulose sample;

[0070] 3) The cellulose sample obtained in step 2) is mixed with silicon carbide with a particle size of 350 μm at a mass ratio of 2.5:1, placed in a corundum tube and placed in a microwave heating device, argon is introduced into the corundum tube to remove the air inside, and argon is continuously introduced at a flow rate of 320 mL / min during the reaction; the microwave heating device is heated at a rate of 100 ℃ / min to 600 ℃, and then kept at a constant temperature for 35 min to obtain carbon nanotubes. The power of microwave heating is 1950 W, and the frequency of microwave heating is 2.35 GHz. The length of the obtained carbon nanotubes is ≥1 cm, and the diameter is 15-90 nm.

[0071] Example 5

[0072] 1) 11.25 g of oxalic acid and 2.5 g of choline chloride (molar ratio 5:1) are heated and stirred in a constant temperature water bath at 100 ℃, the stirring rate is 600 r / min, and the stirring time is 40 min, a colorless transparent liquid is formed, and a eutectic solvent is obtained;

[0073] 2) The corn cob biomass with a particle size of 200 μm is placed in a vacuum drying oven and dried at 95 ℃ for 23 h to remove water; the prepared eutectic solvent is added to the dried corn cob biomass (the mass ratio of biomass to eutectic solvent is 1:10), and the mixture is continuously stirred at 90 ℃ for 3 h to hydrolyze or dissolve hemicellulose and lignin. The pretreated sample is filtered and separated, the solid residue is washed with anhydrous ethanol twice, then with deionized water twice, and finally transferred to a 75 ℃ oven for drying for 20 h to constant weight to obtain a cellulose sample;

[0074] 3) The cellulose sample obtained in step 2) is mixed with silicon carbide with a particle size of 300 μm at a mass ratio of 2.1:1, placed in a quartz reactor and placed in a microwave heating device, neon is introduced into the quartz reactor to remove the air inside, and neon is continuously introduced at a flow rate of 300 mL / min during the reaction; the microwave heating device is heated at a rate of 60 ℃ / min to 500 ℃, and then kept at a constant temperature for 40 min to obtain carbon nanotubes. The power of microwave heating is 1800 W, and the frequency of microwave heating is 2.20 GHz. The length of the obtained carbon nanotubes is ≥1 cm, and the diameter is 40-130 nm.

[0075] Example 6

[0076] 1) 15 g of urea and 5 g of choline chloride (molar ratio 5:1) are heated and stirred in a constant temperature water bath at 100 ℃, the stirring rate is 500 r / min, and the stirring time is 40 min, a colorless transparent liquid is formed, and a eutectic solvent is obtained;

[0077] 2) Put palm shell biomass with a particle size of 210 μm into a vacuum drying oven, dry at 105 °C for 20 h to remove water; add the prepared eutectic solvent (mass ratio of biomass to eutectic solvent is 1:16) to the dried palm shell biomass, continuously stir at 105 °C for 2 h to hydrolyze or dissolve hemicellulose and lignin, filter the pretreated sample, wash the solid residue with anhydrous ethanol for 3 times, then wash with deionized water for 2 times, finally transfer to an oven at 85 °C and dry to constant weight for 30 h to obtain a cellulose sample;

[0078] 3) Mix the cellulose sample obtained in step 2) with silicon carbide with a particle size of 450 μm at a mass ratio of 1.9:1, put into a corundum tube and place in a microwave heating device, introduce argon into the corundum tube to remove the air inside, and continuously introduce argon at a flow rate of 500 mL / min during the reaction; the microwave heating device is heated at a rate of 85 °C / min to 575 °C, then kept at constant temperature for 43 min to obtain carbon nanotubes. The power of microwave heating is 2200 W, and the frequency of microwave heating is 2.55 GHz. The length of the obtained carbon nanotubes is ≥1 cm, and the diameter is 35-130 nm.

[0079] From the above examples, it can be seen that the present application provides a method for preparing carbon nanotubes using a eutectic solvent, which has a simple preparation process, only one step of microwave treatment is needed to obtain carbon nanotubes with good morphology, and the required temperature during microwave treatment is low, which can be suitable for large-scale production.

[0080] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing carbon nanotubes using a deep eutectic solvent, characterized by, The method comprises the following steps: 1) mixing a hydrogen bond donor with a hydrogen bond acceptor to obtain a deep eutectic solvent; 2) mixing the deep eutectic solvent obtained in step 1) with biomass to perform a reaction, and after the reaction, filtering and separating the mixed system, washing the solid residue with anhydrous ethanol for 2-3 times, then washing with water for 2-3 times, and drying at a temperature of 75-85 ℃ until constant weight to obtain a cellulose sample; 3) mixing the cellulose sample obtained in step 2) with a microwave absorber, and performing a reaction by microwave heating to obtain carbon nanotubes; The hydrogen bond donor in step 1) comprises one of oxalic acid, lactic acid and urea; the hydrogen bond acceptor is choline chloride; and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1-5:1; The mixing temperature in step 1) is 70-100 ℃, and the mixing time is 20-40 min; The reaction temperature in step 2) is 80-120 ℃, and the reaction time is 1-4 h; The biomass in step 2) is lignocellulosic biomass, which comprises one or more of poplar, palm shell, water hyacinth and corn cob; and the mass ratio of the biomass to the deep eutectic solvent is 1:10-20; The reaction temperature in step 3) is 500-550 ℃, the reaction time is 30-45 min, the heating rate during the reaction is 50-100 ℃ / min, the microwave heating power is 1800-2200 W, and the microwave heating frequency is 2.20-2.55 GHz; The length of the carbon nanotubes obtained in step 3) is ≥1 cm, and the diameter is 50-100 nm. 2.The method for preparing carbon nanotubes using a deep eutectic solvent according to claim 1, characterized in that, The particle size of the biomass in step 2) is 180-250 μm.

3. The method for preparing carbon nanotubes using a eutectic solvent according to claim 1, characterized in that, The mass ratio of the cellulose sample to the microwave absorber in step 3) is 1.5-2.5:1; The microwave absorber comprises one or more of silicon carbide, activated carbon, graphite and acetylene black; The reaction in step 3) is performed in an inert atmosphere.

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