A biomass-based ionic liquid modified carbon quantum dots and preparation method thereof

Abstract

The present invention discloses a biomass-based ionic liquid-modified carbon quantum dots, a preparation method thereof, and a composite lubricant. The preparation method of the biomass-based ionic liquid-modified carbon quantum dots uses biomass raw materials, choline chloride, and amino acids to prepare carbon quantum dots and choline amino acid ionic liquid. The choline amino acid ionic liquid is used to modify the carbon quantum dots to produce a biomass composite lubricant. This uses renewable biomass resources instead of traditional petrochemical resources, is environmentally friendly, can be decomposed by nature, achieves clean production, and eliminates environmental pollution. The CQDs / ILs composite lubricant can function as "nanoballs," thereby improving its load-bearing capacity and reducing wear. In addition to having good lubricating properties, the choline amino acid ionic liquid also has good solubility. Modifying the carbon quantum dots with the choline amino acid ionic liquid not only improves the dispersibility of the carbon quantum dots but also further enhances their tribological properties.

Description

Technical Field

[0001] The invention belongs to the technical field of lubricant development and relates to biomass-based ionic liquid modified carbon quantum dots and a preparation method thereof. Background Art

[0002] With the rapid development of modern industry, mechanical equipment consumes most of its energy due to friction during operation, and at the same time shortens the service life of mechanical parts. Therefore, lubricants are needed in mechanical movement. Lubrication is one of the important means to improve the friction state of friction pairs. Lubricants form a lubricating oil film on the friction surface, which isolates the direct contact between the two friction surfaces and reduces the friction and wear between the friction pairs, thereby achieving the purpose of saving energy and extending the service life of the machinery. At present, lubricants can be divided into solid lubricants, semi-solid lubricants and fluid lubricants. Among them, liquid lubricants belong to fluid lubricants, which are more widely used in practical applications. Among liquid lubricating materials, petroleum-based lubricants such as mineral oil have excellent lubricating properties, can effectively reduce the friction and wear of mechanical equipment, and increase the service life of the equipment, so they are widely used in the industrial field.

[0003] However, with the substantial increase in mechanical power, traditional petroleum-based lubricants also have disadvantages such as low flash points and flammability under certain high-temperature, high-pressure, and explosive conditions, posing potential risks. Furthermore, the limited lubricating performance and poor load-bearing capacity of lubricants in these operating conditions significantly shorten their service life, requiring frequent lubricant additions and replacements, increasing production costs. Furthermore, their low biodegradability makes them susceptible to ecological pollution upon discharge, and the non-renewable raw materials do not meet national environmental protection requirements. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a biomass-based ionic liquid-modified carbon quantum dots and a preparation method thereof, thereby solving the technical problems of the prior art petroleum-based lubricants in limited lubrication performance and poor load-bearing capacity under high temperature, high pressure, and explosive conditions, as well as poor biodegradability.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing biomass-based ionic liquid-modified carbon quantum dots comprises the following steps:

[0007] The biomass raw material is placed in an air atmosphere for carbonization and grinding, and the ground product is placed in water for ultrasonic treatment, centrifuged to obtain the supernatant, and the supernatant is freeze-dried to obtain biomass carbon quantum dots;

[0008] Dissolving choline chloride and hydroxide base in anhydrous ethanol, stirring to react, to prepare choline hydroxide, and adding the choline hydroxide aqueous solution dropwise to an amino acid aqueous solution, stirring to react, to prepare a choline amino acid ionic liquid;

[0009] The biomass carbon quantum dots are added to the choline amino acid ionic liquid, stirred and mixed evenly, and then a catalyst is added. After stirring for reaction, the product is vacuum freeze-dried to obtain the biomass-based ionic liquid modified carbon quantum dots.

[0010] Preferably, the biomass raw material is tea leaves or tea leaves residue; the tea leaves are one or more of black tea, green tea, dark tea, white tea, yellow tea or scented tea.

[0011] Preferably, the temperature during the carbonization process is 330-360° C., and the time is 2-4 hours.

[0012] Preferably, when the ground product is placed in water for ultrasonic treatment, the ratio of the ground product to water is (0.1~1):(10~100) by mass; when the supernatant is centrifuged, the centrifugal speed is 12000~18000 r / min.

[0013] Preferably, the hydroxide base is one or more of potassium hydroxide, sodium hydroxide, calcium hydroxide or magnesium hydroxide; and the amino acid is one or more of citrulline, arginine, glutamic acid, glycine and alanine.

[0014] Preferably, the ratio of the choline chloride, hydroxide base and anhydrous ethanol is (10-20):(10-20):(120-150) in parts by mass.

[0015] Preferably, the ratio of the biomass carbon quantum dots to the choline amino acid ionic liquid is (0.1-1):(1-10) in parts by mass.

[0016] Preferably, the catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and / or 1-(3-dimethylaminopropylbenzene)-3-ethylcarbodiimide.

[0017] A biomass-based ionic liquid modified carbon quantum dot is prepared by the above method.

[0018] A composite lubricant comprising the above-mentioned biomass-based ionic liquid modified carbon quantum dots; the friction coefficient of the composite lubricant is ≤0.1, and the wear rate is ≤1.90×10 -12 cm 3 / (N·m), fluorescence intensity ≥6.0×10 6 .

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] This invention discloses a method for preparing biomass-based ionic liquid-modified carbon quantum dots. The method first prepares the carbon quantum dots using biomass raw materials, then prepares the ionic liquid using choline chloride, a hydroxide base, and an amino acid. Finally, the biomass carbon quantum dots are modified with a choline amino acid ionic liquid to produce biomass-based ionic liquid-modified carbon quantum dots (CQDs / ILs). The biomass carbon quantum dots produced in this method have a unique quasi-spherical structure. When used as a lubricant, they can function as "nanoballs," changing the friction type between components from sliding friction to rolling friction, thereby improving their load-bearing capacity and reducing wear. In addition, choline amino acid ionic liquid has good lubrication properties, non-flammability, good chemical stability and thermal stability. In addition to reducing friction, the good solubility of choline amino acid ionic liquid is utilized to modify carbon quantum dots using choline amino acid ionic liquid. On the one hand, the dispersion of tea carbon quantum dots can be improved. On the other hand, the amino group of choline amino acid ionic liquid interacts with the carboxyl group on the surface of carbon quantum dots to form a strong chemical bond, constructing a special chemically bonded core-shell structure, forming a stable "shell" structure on the surface of carbon quantum dots, further improving the tribological properties and lubrication durability. In addition, CQDs will emit blue fluorescence under ultraviolet light. When in use, the fluorescence intensity can be used to monitor the service life of the lubricant and whether there is leakage. Furthermore, the use of biomass raw materials to prepare carbon quantum dots and the use of biomass choline chloride and amino acids to prepare choline amino acid ionic liquids have the advantages of wide distribution, abundant reserves, renewability and waste utilization. At the same time, the use of biomass renewable resources instead of traditional petrochemical resources to prepare carbon quantum dots and choline amino acid ionic liquids is environmentally friendly and can be decomposed by nature, achieving the concept of environmentally friendly chemistry, realizing clean production, and fundamentally eliminating environmental pollution, which is of great significance to the realization of the "dual carbon" goal. The present invention is convenient to prepare, has a reasonable process design, is green and environmentally friendly, and the obtained biomass-based ionic liquid modified carbon quantum dots have good high temperature resistance and lubrication properties, which has important theoretical value and practical significance for improving the lubrication performance and product service life of mechanical lubricants and expanding their scope of use.

[0021] Furthermore, another inventive point of the present invention is that the biomass raw material is tea leaves or tea leaves residue; the tea leaves are one or more of black tea, green tea, dark tea, white tea, yellow tea or scented tea. First, tea leaves are rich in polyphenol compounds, amino acids and sugars. These components can generate smaller and more uniform carbon quantum dots during pyrolysis and have good fluorescence properties. At the same time, the carbon content of tea leaves is relatively high, which enables it to produce more carbon quantum dots during pyrolysis. Tea leaves and their residues are by-products produced during the tea production process and are usually regarded as waste. However, these wastes are rich in organic matter and various nutrients. Through reasonable utilization, they can be converted into valuable materials. Using tea leaves or tea leaves residues as biomass raw materials not only realizes the recycling of resources, but also reduces environmental pollution. The dispersibility, stability and functionality of biomass carbon quantum dots can be further improved through the modification effect of choline amino acid ionic liquid.

[0022] Furthermore, another inventive point of the present invention is that the temperature during the carbonization process is 330-360°C and the time is 2-4 hours. First, within this temperature range, the organic components in the biomass feedstock can undergo moderate pyrolysis and carbonization reactions, producing carbonaceous materials with specific structures and properties. Too low a temperature leads to incomplete carbonization, while too high a temperature destroys the structure of the carbonaceous material, affecting the performance of the final product. Second, an appropriate temperature helps reduce the generation of impurities during the carbonization process. Excessively high temperatures can trigger unnecessary side reactions, generating impurities that are detrimental to subsequent applications. Within this temperature range, the reaction path can be better controlled, reducing the generation of impurities. Within this temperature range, the organic components in the biomass feedstock can be more efficiently converted into carbonaceous particles, thereby increasing product yield. Setting the carbonization time to 2-4 hours can ensure that the organic components in the biomass feedstock are fully carbonized. Shorter times lead to incomplete carbonization, while longer times increase energy consumption and costs, and may also trigger unnecessary side reactions. An appropriate carbonization time helps optimize the structure of the carbon quantum dots. Within this time range, the carbonaceous particles can form a relatively uniform and stable structure, thereby improving product performance.

[0023] Furthermore, another inventive point of the present invention is that when the ground product is placed in water for ultrasonic treatment, the ratio of the ground product to water is (0.1~1):(10~100) by mass; when the supernatant is centrifuged, the centrifugal speed is 12000~18000 r / min, wherein the appropriate ratio helps to uniformly disperse the ground product in water, and too high a concentration of the ground product causes particle aggregation, affecting the effect of the ultrasonic treatment; the appropriate ratio enables the ultrasonic wave to produce a more uniform and stronger cavitation effect in the suspension, thereby more effectively crushing and refining the ground product particles. High-speed centrifugation can generate a larger centrifugal force, so that the large particles in the suspension quickly settle to the bottom of the centrifuge tube, thereby achieving the separation of larger solids and smaller quantum dots, which helps to obtain a pure, impurity-free biomass carbon quantum dot solution. Under the premise of ensuring the separation effect, a higher centrifugal speed can shorten the centrifugation time and improve the processing efficiency.

[0024] Furthermore, another inventive point of the present invention is that the hydroxide base is one or more of potassium hydroxide, sodium hydroxide, calcium hydroxide or magnesium hydroxide; and the amino acid is one or more of citrulline, arginine, glutamic acid, glycine and alanine. First, these hydroxide bases all have strong alkalinity and can effectively react with raw materials such as choline chloride to produce the corresponding choline hydroxide. These hydroxide bases have good solubility in solvents such as water and ethanol, which is conducive to the uniform progress of the reaction and the purification of the product. Amino acids such as citrulline, arginine, glutamic acid, glycine and alanine have different structural and functional characteristics. After combining with choline, they can give ionic liquids different physical and chemical properties and biological activities. These amino acids are naturally occurring biomolecules with good biocompatibility and degradability.

[0025] Further, another invention point of the present invention is that in parts by mass, the ratio of the choline chloride, hydroxide base and anhydrous ethanol is (10-20): (10-20): (120-150), which ensures sufficient contact and mixing between the reactants, so that the reaction of choline chloride and hydroxide base can be carried out evenly, avoiding incomplete reaction or side reaction caused by excessively high or low local concentration, and appropriate reactant ratio helps to maximize the utilization of raw materials, reduce the residue of unreacted materials, thereby improving the yield of the product. Anhydrous ethanol, as a solvent, not only helps the dissolution and mixing of the reactants, but also can regulate the rate and selectivity of the reaction to a certain extent. An appropriate amount of anhydrous ethanol can also reduce side reactions that may occur during the reaction, such as hydrolysis, oxidation, etc., thereby protecting the structure and properties of the target product.

[0026] Furthermore, another inventive point of the present invention is that the ratio of the biomass carbon quantum dots to the choline amino acid ionic liquid is (0.1-1): (1-10) by mass. First, the addition amount of the choline amino acid ionic liquid is relatively large, which can effectively achieve effective surface modification of the biomass carbon quantum dots and improve the overall stability of the material. There is a synergistic effect between the biomass carbon quantum dots and the choline amino acid ionic liquid, that is, the combination of the two can produce better performance than when used alone. The appropriate ratio can maximize this synergistic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is a particle size diagram of tea carbon quantum dots (CQDs) prepared in Example 1 of the present invention;

[0029] Figure 2 TEM image of tea carbon quantum dots (CQDs) in Example 1 of the present invention;

[0030] Figure 3 The zeta potential diagrams of tea carbon quantum dots (CQDs), choline amino acid ionic liquids (ILs), and choline amino acid ionic liquid-modified tea carbon quantum dots (CQDs / ILs) in Example 1 of the present invention are shown;

[0031] Figure 4 This is a graph showing the dispersion stability of choline amino acid ionic liquid modified tea carbon quantum dots (CQDs / ILs) in water at different time points in Example 1 of the present invention;

[0032] Figure 5 This is a test graph of the friction coefficient of the composite lubricant modified with choline amino acid ionic liquid and tea carbon quantum dots (CQDs / ILs) in Example 1 added to water in different amounts. DETAILED DESCRIPTION

[0033] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0034] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0035] All features, such as values, amounts, contents, and concentrations, described herein as numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0036] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0037] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0038] The present invention provides a method for preparing biomass-based ionic liquid-modified carbon quantum dots, which specifically comprises the following steps:

[0039] 1) Biomass carbon quantum dots

[0040] First, 0.1-1 parts of biomass feedstock was calcined in a muffle furnace at 330-360°C under air for 2-4 hours to produce a dark black solid product, which was then ground. Next, 0.1-1 parts of the black solid powder was added to 10-100 parts of water and ultrasonically treated for 1-3 hours. Finally, the supernatant was centrifuged and freeze-dried for 12-14 hours to produce a pale yellow powder, the tea-based carbon quantum dots.

[0041] The biomass raw material is tea leaves or tea leaves residue; the tea leaves are one or more of black tea, green tea, dark tea, white tea, yellow tea, or scented tea. The high-speed centrifuge has a rotation speed of 12,000 to 18,000 r / min.

[0042] 2) Preparation of choline amino acid ionic liquid

[0043] First, 10-20 parts of choline chloride and 10-20 parts of a hydroxide base are dissolved in 120-150 parts of anhydrous ethanol. The mixture is stirred at 60-90°C for 6-8 hours. After completion, the ethanol is removed using a rotary evaporator to produce choline hydroxide. Next, 10-30 parts of choline hydroxide are dissolved in 20-50 parts of water to produce an aqueous choline hydroxide solution. Simultaneously, 0.1-1 parts of an amino acid are dissolved in 40-400 parts of water at room temperature. This aqueous choline hydroxide solution is added dropwise to the aqueous amino acid solution. After the addition is complete, the mixture is reacted at 50-90°C for 10-12 hours. After completion of the reaction, the water is removed from the reaction solution by distillation under reduced pressure. Then, 100-200 parts of an ethanol / acetonitrile mixture (in 50% saturation) is added to the distilled product, stirred for 1-2 hours, and allowed to stand for 0.5-1 hour to precipitate the excess amino acid. Finally, the filtrate is separated by filtration, and the obtained filtrate is subjected to reduced pressure distillation to obtain a light yellow to yellow viscous liquid, which is then dried in a vacuum oven at 70-100° C. for 6-8 hours to obtain a choline amino acid ionic liquid.

[0044] Wherein, the hydroxide base is one or more of potassium hydroxide, sodium hydroxide, calcium hydroxide, and magnesium hydroxide;

[0045] The amino acid is one or more of citrulline, arginine, glutamic acid, glycine, and alanine.

[0046] In the dropping process, the dropping time of the choline hydroxide aqueous solution is 10 to 15 minutes.

[0047] The ethanol / acetonitrile mixture is calculated by weight, and the ratio of ethanol to acetonitrile is (10~100):(90~900).

[0048] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0049] First, 0.1–1 parts of tea-based carbon quantum dots (CQDs) and 1–10 parts of choline amino acid ionic liquid (ILs) were mixed and stirred uniformly. Then, 0.2–0.6 parts of a catalyst was added and stirred at 20–30°C for 8–12 hours. After the reaction, the solution was freeze-dried in a vacuum for 10–14 hours to obtain a choline amino acid ionic liquid-modified tea-based carbon quantum dot composite lubricant.

[0050] The catalyst may be one or more of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) and 1-(3-dimethylaminopropylbenzene)-3-ethylcarbodiimide (EDC).

[0051] In addition, the present invention also discloses a biomass-based ionic liquid modified carbon quantum dot composite lubricant prepared by the above method. After testing, the friction coefficient of the lubricant prepared by the present invention is ≤0.1, and the wear rate is ≤1.90×10 -12 cm 3 / (N·m), fluorescence intensity ≥6.0×10 6 , it can be seen that the biomass-based ionic liquid modified carbon quantum dot composite lubricant has excellent lubricity and wear reduction capabilities. After experiencing a series of variable load and variable frequency friction, the friction coefficient changes very little and still does not lose lubrication performance. The average friction coefficient of the lubricant refers to the ratio of the friction force between the surfaces to the vertical force acting on the same surface under a certain external force. The wear rate is the amount of material wear under a certain pressure within a certain time (or a certain stroke, each movement, etc.). The wear rate of this application is benchmarked against 45 steel, and the wear test is carried out under the conditions of 100 N and 200r. The fluorescence intensity is the fluorescence intensity of the carbon quantum dot solution under an excitation wavelength of 380 nm-800 nm. The smoother the sliding surface, the smaller the friction coefficient, which is beneficial to energy saving and extending the life of the machine.

[0052] In the present invention, the MMUD-1B ultra-high temperature friction and wear tester produced by Jinan Hengxu Testing Machine Technology Co., Ltd. was used to conduct friction and wear experiments. The material was 45# steel, the test conditions were 100 N, 200 r / min, end-face friction pair, and the measurement time was 1 hour. The change curve of the friction coefficient over time was measured. Before each measurement, the tinplate and the friction pair were polished with 1000 mesh sandpaper and then wiped with acetone. The mass of the tinplate was weighed before and after the friction test, and its volume wear rate was calculated. The calculation formula is as follows:

[0053]

[0054] ω - volume wear rate, mm 3 / (N m);

[0055] m1—mass of the sample before testing, g;

[0056] m2—mass of the sample after testing, g;

[0057] ρ—density of the sample, g / mm 3 ;

[0058] L - sliding distance, m.

[0059] This invention discloses a method for preparing a biomass-based ionic liquid-modified carbon quantum dot composite lubricant. This method first prepares carbon quantum dots from biomass raw materials, then uses choline chloride and amino acids to prepare an ionic liquid. Finally, the biomass carbon quantum dots are modified with a choline amino acid ionic liquid to form a CQDs / ILs composite lubricant. Biomass tea carbon quantum dots are prepared from biomass raw materials, and the choline amino acid ionic liquid is prepared from biomass choline chloride and amino acids. The tea carbon quantum dots and choline amino acid ionic liquid, prepared from renewable biomass resources instead of traditional fossil energy, are environmentally friendly and can be decomposed by nature. This embodies the concept of environmentally friendly chemistry, enables clean production, and fundamentally eliminates environmental pollution, significantly contributing to the achievement of the "dual carbon" goals. Furthermore, the unique quasi-spherical structure of tea carbon quantum dots (CQDs) enables them to function as "nanoballs" in the CQDs / ILs composite lubricant, changing the friction type between components from sliding to rolling friction, thereby reducing wear. Moreover, CQDs emit blue fluorescence under ultraviolet light, and the fluorescence intensity can be used to monitor the service life of the lubricant and whether there is leakage during use. Secondly, choline amino acid ionic liquid has good lubrication properties, non-flammability, good chemical stability and thermal stability. In addition to reducing friction, by utilizing the good solubility of choline amino acid ionic liquid itself, modifying biomass carbon quantum dots with choline amino acid ionic liquid can not only improve the dispersibility of biomass carbon quantum dots, but also form a special core-shell structure with biomass carbon quantum dots, further improving tribological properties. In addition, the lubricant has the advantages of mild preparation process conditions, simple and easy control, low cost, and easy scale-up preparation.

[0060] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0061] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0062] Example 1

[0063] 1) Preparation of tea carbon quantum dots

[0064] First, 0.1 parts of Pu'er tea residue was calcined in a muffle furnace at 330°C for 2 hours under air to produce a dark black solid product, which was then ground. Next, 0.1 parts of the black solid powder was added to 10 parts of water and sonicated for 1 hour. Finally, the supernatant was centrifuged at 12,000 rpm and freeze-dried for 12 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0065] 2) Preparation of choline amino acid ionic liquid

[0066] First, 10 parts of choline chloride and 10 parts of sodium hydroxide were dissolved in 120 parts of anhydrous ethanol and stirred at 60°C for 6 hours. After the reaction, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 10 parts of choline hydroxide was dissolved in 20 parts of water to obtain a choline hydroxide aqueous solution. Simultaneously, 0.1 parts of citrulline was dissolved in 40 parts of water at room temperature. This choline hydroxide aqueous solution was added dropwise to the citrulline aqueous solution over 10 minutes. After the addition was complete, the reaction was continued at 50°C for 10 hours. After the reaction was completed, the water in the reaction solution was removed by vacuum distillation. Then, 100 parts of an ethanol / acetonitrile mixture was added to the distilled product, stirred for 1 hour, and allowed to stand for 0.5 hours to precipitate the excess citrulline. Finally, the filtrate was separated by filtration and vacuum distilled to obtain a pale yellow to yellow viscous liquid. This was then dried in a vacuum oven at 70°C for 8 hours to obtain the choline amino acid ionic liquid.

[0067] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0068] First, 0.1 parts of tea-based carbon quantum dots (CQDs) and 1 part of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added and stirred at 20°C for 8 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 10 hours to obtain a choline amino acid ionic liquid-modified tea-based carbon quantum dot composite lubricant.

[0069] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to water at a minimum ratio of 0.2 wt% for tribological performance testing. The results showed that the friction coefficient was 0.1, the wear rate was 1.90×10 -12 cm 3 / (N·m), fluorescence intensity = 6.0×10 6 .

[0070] Figure 1This is a particle size diagram of tea carbon quantum dots (CQDs) prepared in Example 1 of the present invention. As can be seen from the figure, its hydration dynamic size is about 2nm, its peak distribution range is narrow, the particle size is uniform, and the stability is good.

[0071] Figure 2 This is a TEM image of tea carbon quantum dots (CQDs) in Example 1 of the present invention. As can be seen from the figure, the CQDs sample is composed of evenly dispersed small dots, showing a spherical or quasi-spherical morphology. When used as a lubricant, it can effectively convert sliding friction into rolling friction, thereby improving lubrication efficiency.

[0072] Figure 3 This is the zeta potential diagram of tea carbon quantum dots (CQDs), choline amino acid ionic liquids (ILs) and choline amino acid ionic liquid modified tea carbon quantum dots (CQDs / ILs) in Example 1 of the present invention. Under normal circumstances, the higher the Zeta potential value, the more stable the system. It can be seen from the figure that the absolute value of the potential of the CQDs / ILs composite filler of this patent is 37.9 mV, indicating that the composite filler has good stability in water.

[0073] Figure 4 This is a dispersion stability diagram of choline amino acid ionic liquid modified tea carbon quantum dots (CQDs / ILs) in water at different time points in Example 1 of the present invention. It can be seen from the figure that CQDS / ILS can be evenly dispersed in water, and no precipitation occurs after 24 hours of standing, which shows that CQDS / ILS has good stability in water.

[0074] Figure 5 Figure 1 shows the friction coefficient of the choline amino acid ionic liquid-modified tea carbon quantum dot (CQDs / ILs) composite lubricant (Example 1) added to water at varying concentrations. Compared to pure water, the friction coefficient of the water-based lubricant containing the CQDs / ILs composite lubricant decreased, reaching its lowest value at 0.3 wt%. This is primarily due to the synergistic lubrication between the CQDs and ILs during the friction process, forming a continuous, uniform, dense, and robust self-lubricating transfer film on the surface of the metal friction pair. This effectively prevents direct contact between the friction pair and the counter-wearing part, reducing friction.

[0075] Example 2

[0076] 1) Preparation of tea carbon quantum dots

[0077] First, one part of Pu'er tea residue was calcined in a muffle furnace at 360°C in air for 4 hours to produce a dark black solid product, which was then ground. Next, one part of the black solid powder was added to 100 parts of water and ultrasonically treated for 3 hours. Finally, the supernatant was centrifuged at 18,000 rpm and freeze-dried for 14 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0078] 2) Preparation of choline amino acid ionic liquid

[0079] First, 20 parts of choline chloride and 20 parts of sodium hydroxide were dissolved in 150 parts of anhydrous ethanol and stirred at 90°C for 8 hours. After the reaction was complete, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 30 parts of choline hydroxide was dissolved in 50 parts of water to produce an aqueous choline hydroxide solution. Simultaneously, 1 part of arginine was dissolved in 400 parts of water at room temperature. This aqueous choline hydroxide solution was added dropwise to the aqueous arginine solution over 15 minutes. After the addition was complete, the reaction was continued at 90°C for 12 hours. After the reaction was complete, the water in the reaction solution was removed by vacuum distillation. Then, 200 parts of an ethanol / acetonitrile mixture was added to the distilled product, stirred for 2 hours, and allowed to stand for 1 hour to precipitate the excess arginine. Finally, the filtrate was separated by filtration and vacuum distilled to produce a pale yellow to yellow viscous liquid. The filtrate was then dried in a vacuum oven at 100°C for 6 hours to produce the choline amino acid ionic liquid.

[0080] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0081] First, 1 part of the prepared tea carbon quantum dots (CQDs) and 10 parts of choline amino acid ionic liquids (ILs) were mixed and stirred uniformly. Then, 0.2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added and stirred at 0°C for 12 hours. After the reaction, the reaction solution was freeze-dried in a vacuum to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0082] First, 0.1 parts of tea carbon quantum dots (CQDs) and 1 part of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added and stirred at 20°C for 8 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 14 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0083] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to water at a minimum ratio of 0.2 wt% for tribological performance testing. The results showed that the friction coefficient was 0.04, the wear rate was 1.20×10-12 cm 3 / (N·m), fluorescence intensity = 12.0×10 6 .

[0084] Example 3

[0085] 1) Preparation of tea carbon quantum dots

[0086] First, 0.2 parts of Lapsang Souchong tea residue was calcined in a muffle furnace at 340°C for 3 hours under air to produce a dark black solid product, which was then ground. Next, 0.2 parts of the black solid powder was added to 30 parts of water and sonicated for 2 hours. Finally, the supernatant was centrifuged at 15,000 rpm and freeze-dried for 13 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0087] 2) Preparation of choline amino acid ionic liquid

[0088] First, 15 parts of choline chloride and 15 parts of potassium hydroxide were dissolved in 130 parts of anhydrous ethanol and stirred at 70°C for 7 hours. After the reaction was complete, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 15 parts of choline hydroxide was dissolved in 25 parts of water to produce a choline hydroxide aqueous solution. Simultaneously, 0.2 parts of glutamic acid was dissolved in 90 parts of water at room temperature. This choline hydroxide aqueous solution was added dropwise to the glutamic acid aqueous solution over 11 minutes. After the addition was complete, the reaction was continued at 60°C for 11 hours. After the reaction was completed, the water in the reaction solution was removed by vacuum distillation. Then, 120 parts of an ethanol / acetonitrile mixture was added to the distilled product, stirred for 1.5 hours, and allowed to stand for 0.5 hours to precipitate the excess amino acid. Finally, the filtrate was separated by filtration and vacuum distilled to produce a pale yellow to yellow viscous liquid. The filtrate was then dried in a vacuum oven at 80°C for 7 hours to produce the choline amino acid ionic liquid.

[0089] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0090] First, 0.2 parts of tea carbon quantum dots (CQDs) and 3 parts of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.3 parts of 1-(3-dimethylaminopropylbenzene)-3-ethylcarbodiimide (EDC) was added and stirred at 25°C for 9 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 11 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0091] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to water at a minimum ratio of 0.2 wt% for tribological performance testing. The results showed that the friction coefficient was 0.08 and the wear rate was 1.30×10 -12 cm 3 / (N·m), fluorescence intensity = 8.0×10 6 .

[0092] Example 4

[0093] 1) Preparation of tea carbon quantum dots

[0094] First, 0.3 parts of Biluochun tea residue was calcined in a muffle furnace at 350°C for 3 hours under air to produce a dark black solid product, which was then ground. Next, 0.3 parts of the black solid powder was added to 40 parts of water and sonicated for 2 hours. Finally, the supernatant was centrifuged at 15,000 rpm and freeze-dried for 12 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0095] 2) Preparation of choline amino acid ionic liquid

[0096] First, 17 parts of choline chloride and 17 parts of potassium hydroxide were dissolved in 140 parts of anhydrous ethanol and stirred at 80°C for 7 hours. After the reaction, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 20 parts of choline hydroxide were dissolved in 30 parts of water to obtain a choline hydroxide aqueous solution. Simultaneously, 0.4 parts of glycine were dissolved in 200 parts of water at room temperature. This choline hydroxide aqueous solution was added dropwise to the glycine aqueous solution over 12 minutes. After the addition was complete, the reaction was continued at 70°C for 11 hours. After the reaction was completed, the water in the reaction solution was removed by vacuum distillation. Then, 130 parts of an ethanol / acetonitrile mixture was added to the distilled product, stirred for 1.5 hours, and allowed to stand for 0.8 hours to precipitate the excess glycine. Finally, the filtrate was separated by filtration and vacuum distilled to obtain a pale yellow to yellow viscous liquid. This was then dried in a vacuum oven at 80°C for 6.5 hours to obtain the choline amino acid ionic liquid.

[0097] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0098] First, 0.3 parts of tea carbon quantum dots (CQDs) and 3 parts of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.3 parts of 1-(3-dimethylaminopropylbenzene)-3-ethylcarbodiimide (EDC) was added and stirred at 28°C for 10 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 12 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0099] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to water at a minimum ratio of 0.2 wt% for tribological performance testing. The results showed that the friction coefficient was 0.06 and the wear rate was 1.40×10 -12 cm 3 / (N·m), fluorescence intensity = 8.5×10 6 .

[0100] Example 5

[0101] 1) Preparation of tea carbon quantum dots

[0102] First, 0.4 parts of Xinyang Maojian tea residue was calcined in a muffle furnace at 350°C in air for 2.5 hours to produce a dark black solid product, which was then ground. Next, 0.4 parts of the black solid powder was added to 40 parts of water and sonicated for 2.5 hours. Finally, the supernatant was centrifuged at 16,000 rpm and freeze-dried for 13 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0103] 2) Preparation of choline amino acid ionic liquid

[0104] First, 16 parts of choline chloride and 16 parts of calcium hydroxide were dissolved in 140 parts of anhydrous ethanol and stirred at 75°C for 7 hours. After the reaction, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 20 parts of choline hydroxide were dissolved in 40 parts of water to obtain a choline hydroxide aqueous solution. Simultaneously, 0.4 parts of alanine were dissolved in 220 parts of water at room temperature. The resulting choline hydroxide aqueous solution was added dropwise to the alanine aqueous solution over 12 minutes. After the addition was complete, the reaction was continued at 80°C for 10 hours. After the reaction was completed, the water in the reaction solution was removed by vacuum distillation. Then, 150 parts of an ethanol / acetonitrile mixture was added to the distilled product, stirred for 1.2 hours, and allowed to stand for 0.5 hours to precipitate the excess alanine. Finally, the filtrate was separated by filtration and vacuum distilled to obtain a pale yellow to yellow viscous liquid. This was then dried in a vacuum oven at 90°C for 7 hours to obtain the choline amino acid ionic liquid.

[0105] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0106] First, 0.4 parts of tea carbon quantum dots (CQDs) and 4 parts of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added and stirred at 27°C for 11 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 13 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0107] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to water at a minimum ratio of 0.2 wt% for tribological performance testing. The results showed that the friction coefficient was 0.05, the wear rate was 1.50×10 -12 cm 3 / (N·m), fluorescence intensity = 9.0×10 6 .

[0108] Example 6

[0109] 1) Preparation of tea carbon quantum dots

[0110] First, 0.5 parts of Longjing tea residue was calcined in a muffle furnace at 340°C under air for 3 hours to produce a dark black solid product, which was then ground. Next, 0.5 parts of the black solid powder was added to 50 parts of water and sonicated for 2.5 hours. Finally, the supernatant was centrifuged at 14,000 rpm and freeze-dried for 12-14 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0111] 2) Preparation of choline amino acid ionic liquid

[0112] First, 15 parts of choline chloride and 15 parts of magnesium hydroxide were dissolved in 14 parts of anhydrous ethanol and stirred at 80°C for 7.5 hours. After the reaction, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 20 parts of choline hydroxide were dissolved in 50 parts of water to obtain an aqueous choline hydroxide solution. Simultaneously, 0.1–1 part of glutamic acid was dissolved in 40–400 parts of water at room temperature. This aqueous choline hydroxide solution was added dropwise to the aqueous glutamic acid solution over 12 minutes. After the addition was complete, the reaction was continued at 70°C for 12 hours. After the reaction was completed, the water in the reaction solution was removed by vacuum distillation. Then, 150 parts of an ethanol / acetonitrile mixture (in proportions) was added to the distilled product, stirred for 1.5 hours, and allowed to stand for 0.5 hours to precipitate the excess glutamic acid. Finally, the filtrate was separated by filtration and vacuum distilled to obtain a pale yellow to yellow viscous liquid. This was then dried in a vacuum oven at 85°C for 6.5 hours to obtain the choline amino acid ionic liquid.

[0113] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0114] First, 0.5 parts of tea carbon quantum dots (CQDs) and 6 parts of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.3 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added and stirred at 25°C for 10 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 12 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0115] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to PAO-10 synthetic oil at a minimum ratio of 0.2wt% for tribological performance testing. The results showed that the friction coefficient was 0.045 and the wear rate was 1.70×10 - 12 cm 3 / (N·m), fluorescence intensity = 8.5×10 6 .

[0116] Example 7

[0117] 1) Preparation of tea carbon quantum dots

[0118] First, 0.8 parts of Tieguanyin tea residue was calcined in a muffle furnace at 360°C in air for 2 hours to produce a dark black solid product, which was then ground. Next, 0.8 parts of the black solid powder was added to 80 parts of water and sonicated for 1.5 hours. Finally, the supernatant was centrifuged at 16,000 rpm and freeze-dried for 12 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0119] 2) Preparation of choline amino acid ionic liquid

[0120] First, 19 parts of choline chloride and 19 parts of sodium hydroxide were dissolved in 145 parts of anhydrous ethanol and stirred at 85°C for 7.5 hours. After the reaction, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 25 parts of choline hydroxide were dissolved in 45 parts of water to obtain an aqueous choline hydroxide solution. Simultaneously, 0.8 parts of arginine were dissolved in 300 parts of water at room temperature. This aqueous choline hydroxide solution was added dropwise to the aqueous amino acid solution over 14 minutes. After the addition was complete, the solution was reacted at 80°C for 12 hours. After the reaction was complete, the water in the reaction solution was removed by vacuum distillation. Then, 180 parts of an ethanol / acetonitrile mixture (in 5% ethanol / acetonitrile ratio) was added to the distilled product, stirred for 2 hours, and allowed to stand for 1 hour to precipitate the excess arginine. Finally, the filtrate was separated by filtration and vacuum distilled to obtain a pale yellow to yellow viscous liquid. This was then dried in a vacuum oven at 80°C for 8 hours to obtain the choline amino acid ionic liquid.

[0121] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0122] First, 0.8 parts of tea carbon quantum dots (CQDs) and 8 parts of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.5 parts of 1-(3-dimethylaminopropylbenzene)-3-ethylcarbodiimide was added and stirred at 28°C for 11 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 13 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0123] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to PAO-10 synthetic oil at a minimum ratio of 0.2 wt% for tribological performance testing. The results showed that the friction coefficient was 0.41 and the wear rate was 1.30×10 -12 cm 3 / (N·m), fluorescence intensity = 9.5×10 6 .

[0124] Example 8

[0125] 1) Preparation of tea carbon quantum dots

[0126] First, 0.6 parts of oolong tea leaves were calcined in a muffle furnace at 350°C for 3 hours under air to produce a dark black solid product, which was then ground. Next, 0.6 parts of the black solid powder was added to 60 parts of water and sonicated for 3 hours. Finally, the supernatant was centrifuged at 15,000 rpm and freeze-dried for 14 hours to produce a pale yellow powder, the tea carbon quantum dots.

[0127] 2) Preparation of choline amino acid ionic liquid

[0128] First, 14 parts of choline chloride and 14 parts of potassium hydroxide were dissolved in 140 parts of anhydrous ethanol and stirred at 70°C for 7 hours. After the reaction, the anhydrous ethanol was removed using a rotary evaporator to produce choline hydroxide. Next, 24 parts of choline hydroxide were dissolved in 40 parts of water to obtain a choline hydroxide aqueous solution. Simultaneously, 0.6 parts of citrulline were dissolved in 350 parts of water at room temperature. This aqueous choline hydroxide solution was added dropwise to the citrulline aqueous solution over 12 minutes. After the addition was complete, the reaction was continued at 70°C for 10 hours. After the reaction was completed, the water in the reaction solution was removed by vacuum distillation. Then, 140 parts of an ethanol / acetonitrile (in 5% saturated ratio) mixture was added to the distilled product, stirred for 1 hour, and allowed to stand for 0.5 hours to precipitate the excess citrulline. Finally, the filtrate was separated by filtration and vacuum distilled to obtain a pale yellow to yellow viscous liquid. This was then dried in a vacuum oven at 90°C for 7 hours to obtain the choline amino acid ionic liquid.

[0129] 3) Preparation of choline amino acid ionic liquid modified tea carbon quantum dot composite lubricant

[0130] First, 0.6 parts of tea carbon quantum dots (CQDs) and 6 parts of choline amino acid ionic liquid (IL) were mixed and stirred uniformly. Then, 0.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride was added and stirred at 25°C for 10 hours. After the reaction, the reaction solution was freeze-dried in a vacuum for 12 hours to obtain a choline amino acid ionic liquid-modified tea carbon quantum dot composite lubricant.

[0131] The obtained biomass-based ionic liquid modified carbon quantum dot composite lubricant was added to PAO-10 synthetic oil at a minimum ratio of 0.2wt% for tribological performance testing. The results showed that the friction coefficient was 0.047 and the wear rate was 1.70×10 - 12 cm 3 / (N·m), fluorescence intensity = 7.5×10 6 .

[0132] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing biomass-based ionic liquid-modified carbon quantum dots, characterized in that: The following steps are involved: The biomass raw material is placed in an air atmosphere for carbonization and grinding, and the ground product is placed in water for ultrasonic treatment, centrifuged to obtain the supernatant, and the supernatant is freeze-dried to obtain biomass carbon quantum dots; Dissolving choline chloride and hydroxide base in anhydrous ethanol, stirring to react, to prepare choline hydroxide, and adding the choline hydroxide aqueous solution dropwise to an amino acid aqueous solution, stirring to react, to prepare a choline amino acid ionic liquid; The biomass carbon quantum dots are added to the choline amino acid ionic liquid, stirred and mixed, and then a catalyst is added. After stirring and reacting, the product is vacuum freeze-dried to obtain the biomass-based ionic liquid modified carbon quantum dots; The biomass raw material is tea leaves or tea leaves residue; The amino acid is one or more of citrulline, arginine, glutamic acid, glycine and alanine; In parts by mass, the ratio of choline chloride, hydroxide base and anhydrous ethanol is (10-20):(10-20):(120-150); In parts by mass, the ratio of the biomass carbon quantum dots to the choline amino acid ionic liquid is (0.1-1):(1-10); The catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and / or 1-(3-dimethylaminopropylbenzene)-3-ethylcarbodiimide.

2. The method for preparing biomass-based ionic liquid-modified carbon quantum dots according to claim 1, wherein: The tea leaves are one or more of black tea, green tea, dark tea, white tea, yellow tea or scented tea.

3. The method for preparing biomass-based ionic liquid-modified carbon quantum dots according to claim 1, wherein: The temperature during the carbonization process is 330-360° C. and the time is 2-4 hours.

4. The method for preparing biomass-based ionic liquid-modified carbon quantum dots according to claim 1, wherein: When the ground product is placed in water for ultrasonic treatment, the ratio of the ground product to water is (0.1-1):(10-100) by mass; when the supernatant is obtained by centrifugation, the centrifugal speed is 12000-18000 r / min.

5. The method for preparing biomass-based ionic liquid-modified carbon quantum dots according to claim 1, wherein: The hydroxide base is one or more of potassium hydroxide, sodium hydroxide, calcium hydroxide or magnesium hydroxide.

6. A biomass-based ionic liquid modified carbon quantum dots, characterized in that: Prepared by the method according to any one of claims 1 to 5.

7. A composite lubricant, characterized in that: The composite lubricant comprises a biomass-based ionic liquid modified carbon quantum dot as claimed in claim 6; the friction coefficient of the composite lubricant is ≤0.1, and the wear rate is ≤1.90×10 -12 cm 3 / (N·m), fluorescence intensity ≥6.0×10 6 .

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