Imidazole type ionic liquid composite MCNTs based solvent-free nanofluid and preparation method thereof

Abstract

The application provides an imidazole type ionic liquid composite MCNTs based solvent-free nanofluid and a preparation method thereof, wherein acidified MCNTs-OH is used as a core, combined with ionic liquid, cross-linking occurs between the ionic liquid and the π electron on the surface of the carbon nanotube in the form of cation-π or π-π, so that the carbon nanotube can be dispersed, the prepared MCNTs based solvent-free nanofluid composition comprises 5-15% of MCNTs and 85-95% of imidazole type ionic liquid in mass fraction, the mass percentage of the MCNTs and the imidazole type ionic liquid is 100%, and the MCNTs is used as a core, and the ionic liquid is used as a neck-shaped layer and a crown-shaped layer. The ionic liquid with high stability, low toxicity and low volatility is introduced to serve as the "neck crown" structure, and is covalently grafted to the surface of the acidified carbon nanotube "core", so that the advantages of adjustable viscosity, high thermal conductivity, zero volatility and stable performance are achieved.

Description

Technical Field

[0001] This invention belongs to the field of carbon-based nanofluid materials and relates to a solvent-free nanofluid based on multi-walled carbon nanotubes (MCNTs). Background Technology

[0002] Solvent-free nanofluids possess diverse ionic structures and unique room-temperature solvent-free flowability, thus demonstrating broad application prospects in polymer-based composites, lithium-ion batteries, reaction media, nanoparticle self-assembly, and high-temperature lubricants. As a universal surface engineering technology, solvent-free nanofluid technology can not only endow macromolecules and multidimensional nanomaterials with special solvent-free flowability, but also flexibly select modification strategies based on the surface chemical structure characteristics of materials at different scales to achieve effective control over the microstructure, chemical structure, and function of materials. Therefore, it is of great significance for the efficient utilization of various functional materials and the preparation and device assembly of composite materials based on various functional structures.

[0003] Solvent-free nanofluids are surface-functionalized nanoparticle hybrid materials with unique room-temperature liquid-like properties. Their basic structure can be divided into two parts: a "core" and a "shell." Theoretically, the "core" structure can be zero-dimensional nanoparticles, one-dimensional nanofibers, two-dimensional nanosheets, or even macromolecular materials; the "shell" structure is an organic bilayer. The inner layer of this organic bilayer, called the "corona," connects the internal nanostructures to the outer organic molecules. It is covalently anchored to the "core" and is an ionic compound with specific chemical functional groups. The outer layer of the organic bilayer, called the "canopy," provides the "flow medium." It is ionicly grafted onto the inner organic molecules and is typically a flexible long-chain ion.

[0004] Currently, widely used nanoparticles mainly include metal and metal oxide nanoparticles and non-metallic nanoparticles. These nanoparticles, commonly used in the preparation of nanofluids, have thermal conductivity hundreds or thousands of times higher than that of liquid-based fluids. Carbon nanotubes and graphene, for example, have thermal conductivity more than 5000 times that of pure water. Furthermore, their production processes are relatively mature and can be mass-produced. Therefore, the development of solvent-free carbon-based nanofluids can significantly improve the thermal conductivity of traditional nanofluids. Tongji University's patent CN102618350A describes "a method for preparing a novel core-shell-crown structure solvent-free nanofluid," which produces molybdenum disulfide nanoparticles. These nanoparticles are then sulfonated with a surface modifier containing sulfonic acid groups. This method is simple to produce, but it is mainly used as a lubricant, and the core particles have a relatively low thermal conductivity, limiting its application. Currently, no methods for preparing MCNT-based solvent-free nanofluids have been reported.

[0005] The physical modification of carbon materials by ionic liquids (ILs), also known as non-covalent modification, mainly utilizes the π-π bonds or cation-π interactions formed between the organic cations in the ionic liquid and the carbon atom layer on the surface of the carbon material. This allows ionic liquid molecules or their polymers to be fixed on the carbon material surface in a relatively stable manner, dispersing carbon nanotubes without agglomeration, forming a gel-like substance that is easy to process and has strong stability. It can maintain its physical properties at low temperatures, providing possibilities for further functionalization of carbon nanotubes.

[0006] In summary, due to the relatively low surface energy of ionic liquids, they can encapsulate nanoparticles, ensuring their stability and preventing aggregation, thus achieving individual dispersion of nanoparticles. This solves the biggest problem faced by nanoparticles in applications. Therefore, synthesizing novel solvent-free nanofluids and exploring their applications in new fields is of great significance for the development of solvent-free nanofluids. Developing a carbon nanofluid working fluid with adjustable viscosity, high thermal conductivity, zero volatility, and stable performance is urgently needed. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides an imidazole-type ionic liquid composite MCNTs-based solventless nanofluid, which uses acidified MCNTs-OH as the core and combines it with an ionic liquid. The ionic liquid crosslinks with the π electrons on the surface of carbon nanotubes in the form of cation-π or π-π, which enables the carbon nanotubes to be dispersed and solves the problem of their aggregation. It has the advantages of adjustable viscosity, high thermal conductivity, zero volatility, and stable performance.

[0008] The technical solution adopted by the present invention to solve its technical problem is: an imidazole-type ionic liquid composite MCNTs-based solvent-free nanofluid, the components of which include 5-15% MCNTs and 85-95% imidazole-type ionic liquid by mass, the total mass percentage of MCNTs and imidazole-type ionic liquid is 100%, with MCNTs as the core and ionic liquid as the neck layer and coronal layer.

[0009] The MCNTs have an average outer diameter of 5 nm to 15 nm and a length of 10 to 30 μm.

[0010] The neck layer is a silane coupling agent, such as 3-chloropropyltriethylsilane (3CI), 3-chloropropyltrimethoxysilane, (3-chloropropyl)tris(trimethylsiloxy)silane, or (3-bromopropyl)triethoxysilane.

[0011] The coronal layer is an imidazole salt, specifically 1-methylimidazolium (1MI), 1-(2-hydroxyethyl)imidazolium, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac), or 1-allyl-3-methylimidazolium chloride ([AMIM]Cl).

[0012] This invention also provides a method for preparing the above-mentioned imidazole-type ionic liquid composite MCNTs-based solventless nanofluid, comprising the following steps:

[0013] (1) Add H2SO4 and HNO3 to MCNTs to prepare an acid solution of MCNTs. Stir the solution under heating. After the solution cools to room temperature, a black suspension is obtained. Pour the black suspension into deionized water and stir thoroughly. After standing and cooling, filter to obtain a black substance. Wash the black substance until neutral, dry it under vacuum, and grind it to obtain a black powder, i.e., acidified MCNTs-OH.

[0014] (2) The neck layer silane coupling agent and the coronal layer imidazole salt were heated and stirred under a nitrogen atmosphere to obtain the imidazole ionic liquid IL1; after cooling, the impurities in the imidazole ionic liquid IL1 were washed away, and then vacuum dried under heating conditions to obtain a light yellow viscous liquid.

[0015] (3) Add acidified MCNTs-OH to the pale yellow viscous liquid obtained in step (2), stir, dialyze, and vacuum dry under heating conditions to obtain solvent-free nanofluid based on MCNTs.

[0016] In step (1), H2SO4 and HNO3 with a mass ratio of (1-5):1 are added to MCNTs while stirring to prepare an acid solution with an MCNTs content of 0.3wt%. The obtained solution is refluxed and stirred in an oil bath at 50℃-70℃ for 3-6 hours. After the solution cools to room temperature, a black suspension is obtained. The black suspension is poured into deionized water at a rate of 20ml / min-60ml / min, with a volume ratio of black suspension to deionized water of 1:10. The mixture is stirred thoroughly, allowed to stand and cool, and then filtered through a 0.1μm microfiltration membrane to obtain a black substance. The black substance is washed with deionized water until neutral, then vacuum dried and ground to obtain a black powder, i.e., acidified MCNTs-OH.

[0017] In step (2), equimolar amounts of neck-layer silane coupling agent and coronal-layer imidazole salt are stirred under a nitrogen atmosphere for 12-36 hours at a reaction temperature of 40-100°C to obtain imidazole-type ionic liquid IL1. After cooling, imidazole-type ionic liquid IL1 is washed three times with diethyl ether to remove impurities, and then dried in a vacuum drying oven at 40-70°C for 12-36 hours to obtain a pale yellow viscous liquid.

[0018] In step (3), the acidified MCNTs-OH is added to the pale yellow viscous liquid obtained in step (2), and stirred for 12h to 36h. After the reaction is completed, the liquid is dialyzed for 24h to 84h using a dialysis bag, and then vacuum dried at 40℃ to 70℃ for 12h to 36h to obtain a black solvent-free MCNTs-based nanofluid that can flow at room temperature.

[0019] In step (3), the acidified MCNTs-OH is dispersed in methanol to prepare a methanol solution of 1-10% wt; then it is added to the pale yellow viscous liquid obtained in step (2).

[0020] The dialysis bag is a dialysis bag with a relative molecular mass Mw = 5000.

[0021] The beneficial effects of this invention are: by introducing a highly stable, low-toxicity, and non-volatile ionic liquid as the "crown" structure and covalently grafting it onto the surface of the acidified carbon nanotube "core," it possesses advantages such as adjustable viscosity, high thermal conductivity, zero volatility, and stable performance. Specifically, compared to other preparation methods, it has the following advantages:

[0022] 1) Selecting MCNTs with high thermal conductivity as the "core" greatly enhances the thermal conductivity of solvent-free nanofluids.

[0023] 2) The organic shell structure ("neck, crown") on the surface of nanoparticles is designed. The solvent-free nanomaterials prepared using ionic liquids have a stable fluid structure that is not prone to agglomeration, while retaining the intrinsic thermal conductivity of the core structure MCNTs.

[0024] 3) The prepared imidazole-type ionic liquid composite MCNTs-based solvent-free nanofluid can achieve flow under solvent-free and room temperature conditions.

[0025] 4) MCNTs-based solvent-free nanofluids can greatly enhance the thermal conductivity of thermally conductive fluids. This invention proposes to modify MCNTs with imidazole-type ionic liquids to prepare highly stable nanofluids. Combining carbon-based materials with ionic liquids provides a new method for the research and development of stable, low-viscosity, and high-thermal-conductivity solvent-free nanofluids, and provides technical support for their application in the defense field. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the preparation of solvent-free nanofluids based on ionic MCNTs, using 3CI and 1MI as examples of the neck and coronal layers.

[0027] Figure 2These are physical images and TEM images of the solvent-free MCNTs-based nanofluid prepared in Example 1 of the present invention, wherein a) is a physical image of the solvent-free nanofluid; b) is a TEM image of the surface morphology; and c) is a magnified TEM image. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. The present invention includes, but is not limited to, the following embodiments.

[0029] This invention uses an ionic liquid as the "crown" structure, which moderates the reaction conditions and simplifies the preparation process. It grafts an imidazole-type ionic liquid onto the surface of carbon nanotubes using pre-acidification and modification, with silane as a bridging agent. Finally, through hydrolysis, cross-linking, and dialysis, a solvent-free nanofluid that can flow at room temperature is obtained.

[0030] This invention provides a solvent-free nanofluid based on MCNTs and an imidazole-type ionic liquid composite, exhibiting macroscopic flow behavior at room temperature. The composition comprises 5–15% MCNTs and 85–95% imidazole-type ionic liquid by mass fraction. A core-shell structure consisting of a core, a neck layer, and a crown layer is prepared (MCNTs as the core, and the ionic liquid as the neck and crown layers). The silane coupling agent, referred to as the "neck layer," is covalently anchored to the "core," connecting the internal nanostructure "core" to the outer organic structure "crown." The outer layer, referred to as the "crown layer," provides the "flow medium" and is grafted onto the inner organic molecules via ionic or covalent bonds.

[0031] The neck layer is 3-chloropropyltriethylsilane (3CI), 3-chloropropyltrimethoxysilane, (3-chloropropyl)tris(trimethylsiloxy)silane, or (3-bromopropyl)triethoxysilane.

[0032] The coronal layer imidazole salt is 1-methylimidazolium (1MI), 1-(2-hydroxyethyl)imidazolium, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac), or 1-allyl-3-methylimidazolium chloride ([AMIM]Cl).

[0033] The MCNTs have an average outer diameter of 5 nm to 15 nm and a length of 10 to 30 μm.

[0034] The MCNTs-based solvent-free nanofluids exhibit macroscopic flow behavior at room temperature.

[0035] This invention also provides a method for preparing an imidazole-type ionic liquid composite MCNTs-based solvent-free nanofluid, comprising the following steps:

[0036] (1) Acidification of MCNTs: A certain amount of MCNTs was weighed and placed in a round-bottom flask. While stirring, H2SO4 and HNO3 with a mass ratio of 1:1 to 5:1 were added to the MCNTs to prepare an acid solution with an MCNTs content of 0.5 to 0.6 wt%. The solution was refluxed and stirred in an oil bath at 50℃ to 70℃ for 3 to 6 hours. After the solution cooled to room temperature, a black suspension was obtained. This suspension was poured into 1000 ml of deionized water at a rate of 20 ml / min to 60 ml / min, with a volume ratio of 1:10. The mixture was stirred thoroughly, allowed to stand and cool, and then filtered through a 0.1 μm microfiltration membrane to obtain a black substance. After washing with deionized water until neutral, the substance was vacuum dried and ground to obtain a black powder, i.e., acidified MCNTs-OH.

[0037] (2) Preparation of flexible organic chains as a flow medium by reacting the neck layer and the coronal layer: Equimolar amounts of neck layer silane coupling agent and coronal layer imidazole salt were added. Under a nitrogen atmosphere, the reaction temperature was 40℃~100℃, and the mixture was refluxed and magnetically stirred for 12h~36h to obtain imidazole ionic liquid IL1. After cooling, the ionic liquid (IL1) was washed three times with diethyl ether to remove impurities. Then, it was dried in a vacuum drying oven at 40℃~70℃ for 12h~36h to obtain a pale yellow viscous liquid. The mass ratio of the silane coupling agent to the imidazole salt was 1:1~1:10.

[0038] (3) Disperse the acidified MCNTs-OH in methanol to prepare a 1-10% wt methanol solution; sonicate for 10 min-40 min to make the MCNTs-OH evenly dispersed, and then add it to the product obtained in step (2), stir for 12 h-36 h, after the reaction is completed, dialyze using a dialysis bag for 24 h-84 h, and then vacuum dry at 40℃-70℃ for 12 h-36 h to obtain a black solvent-free MCNTs-based nanofluid that can flow at room temperature;

[0039] All the dialysis bags mentioned are dialysis bags with a relative molecular mass Mw = 5000.

[0040] Example 1: ① Weigh 0.2 g of carbon nanotubes (MCNTs) and place them in a three-necked round-bottom flask. Then, weigh 15 ml of H2SO4 and 5 ml of HNO3 in a volume ratio of 3:1 and add them to the MCNTs. Cool and reflux at 60°C, and mechanically stir for 6 hours. After the solution cools to room temperature, a black suspension is obtained. Pour it into 1000 ml of deionized water at a rate of 20 ml / min, stir thoroughly with a magnetic stirrer, and allow it to stand and cool. Filter the solution using a 0.1 μm microfiltration membrane to obtain a black substance. Then wash it with deionized water until neutral (pH = 7), and dry it in a vacuum drying oven at 100°C for 12 hours. Grind it thoroughly to obtain a black powder, namely the acidified carbon nanotubes (MCNTs-OH). ② Weigh 0.1 mol (24.08 g) of 3-chloropropyltriethylsilane and 0.1 mol (8.21 g) of 1-methylimidazole into a three-necked round-bottom flask. Under a nitrogen atmosphere, the reaction temperature is 80 °C, and the mixture is refluxed and magnetically stirred for 24 h to obtain the imidazole-type ionic liquid IL1. After cooling, the ionic liquid (IL1) is washed multiple times with diethyl ether to remove impurities until it no longer separates after stirring. Then, it is dried in a vacuum drying oven at 50 °C for 24 h to obtain a pale yellow viscous liquid. ③ Disperse the acidified MCNTs-OH in methanol to prepare a 2% wt methanol solution. Sonicate for 30 min to ensure uniform dispersion of MCNTs-OH. Then, add the solution to the pale yellow viscous liquid product obtained in step ② and stir at 60 °C for 24 h to obtain a black mixture. ④ Take a dialysis bag with a relative molecular mass Mw = 5000, boil it in boiling water for 15-20 minutes, add the black mixed MCNTs nanofluid obtained in step ③ to the dialysis bag and dialyze for 48 hours. Dry the resulting solution in a vacuum drying oven to constant weight, obtaining a black, viscous, flowing liquid. This is an ionic, solvent-free MCNTs-based nanofluid with the organosilane 3-chloropropyltriethylsilane as the neck layer and 1-methylimidazole as the crown layer.

[0041] Example 2: ① Weigh 0.2 g of carbon nanotubes (MCNTs) into a three-necked round-bottom flask. Then, weigh 15 ml of H2SO4 and 5 ml of HNO3 in a volume ratio of 3:1 and add them to the MCNTs. Cool and reflux at 60°C, and mechanically stir for 6 hours. After the solution cools to room temperature, a black suspension is obtained. Pour the suspension into 1000 ml of deionized water at a rate of 50 ml / min, stir thoroughly with a magnetic stirrer, and allow it to stand and cool. Filter the solution using a 0.1 μm microfiltration membrane to obtain a black substance. Wash the substance with deionized water until neutral (pH = 7), and dry it in a vacuum drying oven at 100°C for 12 hours. Grind the solution thoroughly to obtain a black powder, i.e., acidified carbon nanotubes (MCNTs-OH). ② Weigh 0.1 mol (24.08 g) of 3-chloropropyltriethylsilane and 0.1 mol (11.2 g) of 1-(2-hydroxyethyl)imidazole into a three-necked round-bottom flask. Under a nitrogen atmosphere, the reaction temperature is 80 °C, and the mixture is refluxed and magnetically stirred for 24 h to obtain the imidazole-type ionic liquid IL2. After cooling, the ionic liquid (IL2) is washed multiple times with diethyl ether to remove impurities until it no longer separates after stirring. Then, it is dried in a vacuum drying oven at 50 °C for 24 h to obtain a pale yellow viscous liquid. ③ Disperse the acidified MCNTs-OH in methanol to prepare a 2% wt methanol solution. Sonicate for 30 min to ensure uniform dispersion of MCNTs-OH. Then, add the solution to the pale yellow viscous liquid product obtained in step ② and stir at 60 °C for 24 h to obtain a black mixture. ④ Take a dialysis bag with a relative molecular mass Mw = 5000, boil it in boiling water for 15-20 minutes, add the black mixed MCNTs nanofluid obtained in step ③ into the dialysis bag and dialyze for 48 hours. Dry the resulting solution in a vacuum drying oven to constant weight to obtain a black, viscous, flowing liquid. This is an ionic MCNTs-based solvent-free nanofluid with the organosilane 3-chloropropyltriethylsilane as the neck layer and 1-(2-hydroxyethyl)imidazolium as the crown layer.

[0042] Example 3: ① Weigh 0.2 g of carbon nanotubes (MCNTs) into a three-necked round-bottom flask. Then, weigh 15 ml of H2SO4 and 5 ml of HNO3 (volume ratio 3:1) and add them to the MCNTs. Cool and reflux at 60°C, and mechanically stir for 6 h. After the solution cools to room temperature, a black suspension is obtained. Pour it into 1000 ml of deionized water at a rate of 20 ml / min, stir thoroughly with a magnetic stirrer, and after standing and cooling, filter it through a 0.1 μm microfiltration membrane to obtain a black substance. Then wash it with deionized water until neutral (pH = 7), and dry it in a vacuum drying oven at 100°C for 12 h. Grind it thoroughly to obtain a black powder, namely the acidified carbon nanotubes (MCNTs-OH). ② Weigh 3-chloropropyltrimethoxysilane (0.1 mol 19.9 g) and 1-methylimidazole (0.1 mol 8.21 g) into a three-necked round-bottom flask. Under a nitrogen atmosphere, the reaction temperature is 80 °C, and the mixture is refluxed and magnetically stirred for 24 h to obtain the imidazole-type ionic liquid IL3. After cooling, the ionic liquid (IL3) was washed multiple times with diethyl ether to remove impurities until it no longer separated into layers after stirring. Then, it was dried in a vacuum drying oven at 50°C for 24 hours to obtain a pale yellow viscous liquid. ③ The acidified MCNTs-OH was dispersed in methanol to prepare a 2% wt methanol solution. The solution was sonicated for 30 minutes to ensure uniform dispersion of the MCNTs-OH. This solution was then added to the pale yellow viscous liquid product obtained in step ② and stirred at 60°C for 24 hours to obtain a black mixture. ④ A dialysis bag with a relative molecular mass Mw = 5000 was boiled in boiling water for 15–20 minutes. The black mixture of MCNTs nanofluid obtained in step ③ was added to the dialysis bag and dialyzed for 48 hours. The resulting solution was dried in a vacuum drying oven to constant weight to obtain a black viscous flowing liquid. This is an ionic MCNTs-based solvent-free nanofluid with the organosilane 3-chloropropyltriethylsilane as the neck layer and 1-methylimidazole as the crown layer.

[0043] Example 4: ① Weigh 0.2 g of carbon nanotubes (MCNTs) into a three-necked round-bottom flask. Then, weigh 15 ml of H2SO4 and 5 ml of HNO3 in a volume ratio of 3:1 and add them to the MCNTs. Cool and reflux at 60°C, and mechanically stir for 6 h. After the solution cools to room temperature, a black suspension is obtained. Pour it into 1000 ml of deionized water at a rate of 50 ml / min, stir thoroughly with a magnetic stirrer, and after standing and cooling, filter it through a 0.1 μm microfiltration membrane to obtain a black substance. Then wash it with deionized water until neutral (pH = 7), and dry it in a vacuum drying oven at 100°C for 12 h. Grind it thoroughly to obtain a black powder, namely the acidified carbon nanotubes (MCNTs-OH). ② Weigh 3-chloropropyltrimethoxysilane (0.1 mol 19.9 g) and 1-(2-hydroxyethyl)imidazole (0.1 mol 11.2 g) into a three-necked round-bottom flask. Under a nitrogen atmosphere, the reaction temperature is 80 °C, and the mixture is refluxed and magnetically stirred for 24 h to obtain the imidazole-type ionic liquid IL4. After cooling, the ionic liquid (IL4) was washed multiple times with diethyl ether to remove impurities until it no longer separated into layers after stirring. Then, it was dried in a vacuum drying oven at 50°C for 24 hours to obtain a pale yellow viscous liquid. ③ The acidified MCNTs-OH was dispersed in methanol to prepare a 2% wt methanol solution. The solution was sonicated for 30 minutes to ensure uniform dispersion of the MCNTs-OH. This solution was then added to the pale yellow viscous liquid product obtained in step ② and stirred at 60°C for 24 hours to obtain a black mixture. ④ A dialysis bag with a relative molecular mass Mw = 5000 was boiled in boiling water for 15–20 minutes. The black mixture of MCNTs nanofluid obtained in step ③ was added to the dialysis bag and dialyzed for 48 hours. The resulting solution was dried in a vacuum drying oven to constant weight to obtain a black viscous flowing liquid. This is an ionic MCNTs-based solvent-free nanofluid with the organosilane 3-chloropropyltrimethoxysilane as the neck layer and 1-(2-hydroxyethyl)imidazolium as the crown layer.

[0044] In summary, Example 1 differs from Example 3 in its neck layer, while Example 2 and Example 4 differ only in their coronal layers; that is, the types of neck and coronal layers are different. The advantages of this invention compared to existing technologies are: it combines the excellent physicochemical properties of MCNTs with the high stability and fluidity of ionic liquids, representing a novel method for preparing solvent-free carbon nanotube nanofluidic materials.

Claims

1. A solvent-free nanofluid based on MCNTs and an imidazole-type ionic liquid composite, characterized in that, The components include 5-15% MCNTs and 85-95% imidazole ionic liquid, with the total mass percentage of MCNTs and imidazole ionic liquid being 100%. The MCNTs form the core, and the ionic liquid forms the neck and coronal layers. The MCNTs have an average outer diameter of 5 nm to 15 nm and a length of 10 to 30 μm. The neck layer is a silane coupling agent, specifically 3-chloropropyltriethylsilane, 3-chloropropyltrimethoxysilane, (3-chloropropyl)tris(trimethylsiloxy)silane, or (3-bromopropyl)triethoxysilane. The coronal layer is an imidazole salt, specifically 1-methylimidazolium, 1-(2-hydroxyethyl)imidazolium, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, or 1-allyl-3-methylimidazolium chloride.

2. A method for preparing the MCNTs-based solvent-free nanofluid composite of the imidazole-type ionic liquid as described in claim 1, characterized in that, Includes the following steps: (1) Add H2SO4 and HNO3 to MCNTs to prepare an acid solution of MCNTs. Stir the solution under heating conditions and obtain a black suspension after the solution cools to room temperature. The black suspension was poured into deionized water and stirred thoroughly. After standing and cooling, it was filtered to obtain the black substance. After washing the black substance to neutral, it was vacuum dried and ground to obtain a black powder, namely acidified MCNTs-OH. (2) The neck layer silane coupling agent and the coronal layer imidazole salt were heated and stirred under a nitrogen atmosphere to obtain the imidazole ionic liquid IL1; after cooling, the impurities in the imidazole ionic liquid IL1 were washed away, and then vacuum dried under heating conditions to obtain a light yellow viscous liquid. (3) Add acidified MCNTs-OH to the pale yellow viscous liquid obtained in step (2), stir, dialyze, and vacuum dry under heating conditions to obtain solvent-free nanofluid based on MCNTs.

3. The method for preparing the MCNTs-based solventless nanofluid composited with the imidazole-type ionic liquid according to claim 2, characterized in that, In step (1), H2SO4 and HNO3 with a mass ratio of (1~5):1 are added to MCNTs while stirring to prepare an acid solution with an MCNTs content of 0.3 wt%. The obtained solution is refluxed and stirred in an oil bath at 50℃~70℃ for 3h~6h. After the solution cools to room temperature, a black suspension is obtained. The black suspension is poured into deionized water at a rate of 20ml / min~60ml / min, with a volume ratio of black suspension to deionized water of 1:

10. After stirring thoroughly and allowing to stand and cool, it is filtered through a 0.1μm microfiltration membrane to obtain a black substance. The black substance is washed with deionized water until neutral, then vacuum dried and ground to obtain a black powder, namely acidified MCNTs-OH.

4. The method for preparing the MCNTs-based solvent-free nanofluid composited with the imidazole-type ionic liquid according to claim 2, characterized in that, In step (2), equimolar amounts of neck-layer silane coupling agent and coronal-layer imidazole salt are stirred under a nitrogen atmosphere for 12-36 hours at a reaction temperature of 40-100°C to obtain imidazole-type ionic liquid IL1. After cooling, imidazole-type ionic liquid IL1 is washed three times with diethyl ether to remove impurities, and then dried in a vacuum drying oven at 40-70°C for 12-36 hours to obtain a pale yellow viscous liquid.

5. The method for preparing the MCNTs-based solvent-free nanofluid composited with the imidazole-type ionic liquid according to claim 2, characterized in that, In step (3), the acidified MCNTs-OH is added to the pale yellow viscous liquid obtained in step (2), and stirred for 12h~36h. After the reaction is completed, the mixture is dialyzed for 24h~84h using a dialysis bag, and then vacuum dried at 40℃~70℃ for 12h~36h to obtain a black solvent-free MCNTs-based nanofluid that can flow at room temperature.

6. The method for preparing the MCNTs-based solventless nanofluid composited with the imidazole-type ionic liquid according to claim 5, characterized in that, In step (3), the acidified MCNTs-OH is dispersed in methanol to prepare a methanol solution of 1~10% wt; then it is added to the pale yellow viscous liquid obtained in step (2).

7. The method for preparing the MCNTs-based solventless nanofluid composited with the imidazole-type ionic liquid according to claim 5, characterized in that, The dialysis bag is a dialysis bag with a relative molecular mass Mw = 5000.

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