Method for driving in-situ formation of carbon dots based on shearing force

Abstract

The invention discloses a method for forming carbon dots in situ based on shearing force driving, which comprises the following steps: constructing a lubricant system based on aromatic acid, inducing aromatic acid molecules to break and perform recombination reaction through load (300-600N) and rotating speed (1000-1500rpm) in the friction process, generating carbon dots in situ in the friction process, and transferring the carbon dots to a friction interface in the friction process to form a lubricating film, the friction coefficient is obviously reduced; and friction heat is inhibited. According to the method, carbon dot nanoparticles do not need to be prepared in advance, the problem that the dispersion stability is poor due to the fact that the carbon dot nanoparticles are directly added into a traditional lubricant is solved, and meanwhile the method is easy to operate, can adapt to the high-load working condition and is suitable for high-precision lubrication scenes such as a mechanical transmission system and a precise instrument.

Description

Technical Field

[0001] The present invention relates to the field of nano-lubrication technology, and in particular to a method for in-situ formation of carbon dots driven by shear force. Background Art

[0002] Traditional lubricants rely on oil-based media, which poses challenges such as environmental pollution, biotoxicity, and failure at high temperatures. While existing nano-lubricant additives (such as graphene and molybdenum disulfide) can improve lubrication performance, their preparation is complex, their dispersion stability is poor, and they require pre-synthesis of nanomaterials, which is costly.

[0003] Chinese patent publication CN117343782A discloses a water-based lubricant that achieves ultra-lubricity under ultra-high contact pressures, as well as its preparation method and application. The lubricant comprises an aqueous base fluid comprising water and a polyol, and functional nanoparticles dispersed within the base fluid; the aqueous base fluid comprises water and a polyol; and the functional nanoparticles comprise phosphorus-containing carbon quantum dots. However, because the carbon quantum dots require a microwave reaction before being produced, the preparation method is complex and exhibits poor dispersion stability.

[0004] Reference 1 (Zhang Lixiu, Li Shuai, Rui Haibo, et al. Preparation and Tribological Properties of Carbon Quantum Dot / Graphene Composites. Mechanical Science and Technology, 1-7 [2025-04-09]. Doi:10.13433 / j.cnki.1003-8728.20240043.) discloses the preparation of carbon quantum dots (CQDs) by pyrolysis using citric acid as a precursor. These CQDs are then combined with graphene via a hydrothermal synthesis method to produce a CQDs / graphene composite. However, the resulting CQDs / graphene composite is not suitable for use under high-load conditions.

[0005] In recent years, technologies that utilize friction processes to generate lubricating films in situ have gained increasing attention. However, existing methods often rely on catalytic coatings or specific precursor molecules, limiting their applicability. Furthermore, the heat generated during friction accelerates lubricant decomposition, reducing equipment life. Therefore, there is an urgent need to develop a green, efficient lubrication method that simultaneously suppresses frictional heat. Based on this, the present invention proposes an in situ conversion of molecules into carbon dots driven by shear forces, which then self-assemble into nanoclusters through hydrogen bonding, achieving the dual goals of low friction coefficient and frictional heat suppression. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a method for in-situ formation of carbon dots based on shear force driving. During the friction process, high load and rotation speed are used to induce the breakage of aromatic acid molecules and undergo recombination reaction to generate carbon dots in situ.

[0007] A method for in-situ formation of carbon dots based on shear force driving comprises the following steps:

[0008] (1) preparing a lubricant containing an aromatic acid;

[0009] (2) The lubricant obtained in step (1) is subjected to in-situ generation of carbon dots under friction conditions of a load of 300 to 600 N and a rotation speed of 1000 to 1500 rpm.

[0010] In the present invention, a lubricant system is constructed based on aromatic acids. During the friction process, the load (300-600N) and rotation speed (1000-1500rpm) are used to induce the aromatic acid molecules to break and undergo a recombination reaction. Carbon dots are generated in situ during the friction process. The carbon dots can be transferred to the friction interface during the friction process to form a lubricating film, significantly reducing the friction coefficient and suppressing frictional heat. The method of the present invention does not require the pre-preparation of carbon dot nanoparticles, avoiding the problem of poor dispersion stability caused by directly adding carbon dot nanoparticles to traditional lubricants. At the same time, the method is simple to operate and can adapt to high-load conditions. It is suitable for high-precision lubrication scenarios such as mechanical transmission systems and precision instruments.

[0011] Preferably, in step (1), the method for preparing the aromatic acid-containing lubricant comprises the following steps: mixing the aromatic acid with a mixed solution of polyethylene glycol and water, and stirring to obtain the aromatic acid-containing lubricant.

[0012] In the present invention, a mixed solution of polyethylene glycol and water is used in the lubricant as a dispersant for aromatic acids. The carbon dots generated in situ during the friction process can self-assemble with water molecules and polyethylene glycol molecules in the lubricant through hydrogen bonds to form solid-liquid nanoclusters. The nanoclusters can form a continuous lubricating film at the friction interface, significantly reducing the friction coefficient and suppressing frictional heat.

[0013] More preferably, the aromatic acid is one of trimesic acid, terephthalic acid, phthalic acid, benzoic acid, gallic acid, salicylic acid, and phenylacetic acid.

[0014] In the present invention, aromatic acid is used as a carbon precursor, and the number of carboxyl groups on the aromatic ring is positively correlated with its anti-wear performance, that is, the more carboxyl groups at the same concentration, the better the anti-wear performance.

[0015] Further preferably, in step (1), the mass percentage of the aromatic acid in the lubricant is 1.0 to 2.5 wt%.

[0016] Further preferably, in the mixed solution of polyethylene glycol and water, the mass ratio of the polyethylene glycol to water is 1:1-5.

[0017] More preferably, the thermal decomposition starting temperature of the aromatic acid-containing lubricant is 180-220°C.

[0018] Preferably, in step (2), the friction time is 3 to 30 minutes.

[0019] Preferably, in step (2), the particle size of the carbon dots is 2 to 5 nm.

[0020] Further preferably, the carbon dots form solid-liquid nanoclusters with polyethylene glycol and water in the lubricant, and the particle size of the solid-liquid nanoclusters is 1000 to 2600 nm.

[0021] In the present invention, the surface of the carbon dots generated in situ by the above method is rich in hydroxyl and carboxyl groups, and forms solid-liquid nanoclusters with a core-shell structure through hydrogen bonds with polyethylene glycol molecules. The dynamic contact between nanoclusters or at the interface between nanoclusters reduces the resistance on the shear interface, thereby providing support for high loads.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention constructs a lubricant system based on aromatic acids. During the friction process, the load (300-600N) and rotation speed (1000-1500rpm) are used to induce the aromatic acid molecules to break and undergo a recombination reaction. Carbon dots are generated in situ during the friction process. The carbon dots can be transferred to the friction interface during the friction process to form a lubricating film, significantly reducing the friction coefficient and suppressing frictional heat. The method of the present invention does not require the pre-preparation of carbon dot nanoparticles, avoiding the problem of poor dispersion stability caused by directly adding carbon dot nanoparticles to traditional lubricants. At the same time, the method is simple to operate and can adapt to high-load conditions. It is suitable for high-precision lubrication scenarios such as mechanical transmission systems and precision instruments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The wear morphology and friction coefficient curves of the lubricants prepared in Examples 1 to 4 on the surface of the steel ball after friction, wherein (a) is the structure, wear scar image, three-dimensional height image and cross-sectional image from top to bottom, (b) to (d) are the friction coefficient images and average wear spot diameter images of the lubricants prepared in Examples 1 to 4 after friction, respectively.

[0025] Figure 2 The thermogravimetric curves of the lubricants prepared in Examples 1 to 4 in an air atmosphere at 0 to 800°C are shown.

[0026] Figure 3 Graphs illustrating the friction heat suppression effects of the lubricants prepared in Examples 1 to 4, wherein (a) is a viscosity-shear rate curve of the lubricants prepared in Examples 1 to 4, and (b) and (c) are temperature rise comparison graphs of the lubricants prepared in Examples 1 to 4 after 30 minutes of friction.

[0027] Figure 4The figures are transmission electron micrographs of carbon dots in the solution of the trimesic acid-containing lubricant prepared in Example 1 during the friction process and Raman spectra of the corresponding lower steel ball wear surface, wherein (a) is a schematic diagram of the in-situ generation route and operation process of carbon dots, (b) to (f) are transmission electron micrographs of carbon dots in the grinding solution of the trimesic acid-containing lubricant prepared in Example 1 at friction times of 0, 3, 7.5, 15, and 30 min, respectively, and (g) is a Raman spectra of the corresponding lower steel ball surface of the trimesic acid-containing lubricant prepared in Example 1 at friction times of 0, 3, 7.5, 15, and 30 min.

[0028] Figure 5 : These are analysis diagrams of the wear scar area on the surface of the lower steel ball after friction with the lubricant containing trimesic acid prepared in Example 1, wherein (a) and (b) are tribofilm images of the wear scar area after friction with the lubricant containing trimesic acid prepared in Example 1, (c) to (f) are cross-sectional HADDF images and EDS mapping result diagrams of the tribofilm after friction with the lubricant containing trimesic acid prepared in Example 1, (g) is an internal structure diagram of the tribofilm after friction with the lubricant containing trimesic acid prepared in Example 1, (h) and (i) are partial enlarged diagrams of Figure (g), and (j) to (m) are XPS data analysis images of C, O and Fe elements on the wear scar surface, respectively.

[0029] Figure 6 The infrared spectra and particle size analysis diagrams of the lubricants containing different aromatic acids prepared in Examples 1 to 4 are shown. (a) is the infrared spectra analysis diagram of the lubricants containing different aromatic acids, the mixed solution of polyethylene glycol and water (PEG-Water solution), and the mixed solution of trimesic acid and polyethylene glycol prepared in Examples 1 to 4, respectively; (b) is the infrared spectra analysis diagram of H3TMA solution, H3TMA-PEG solution, and Water at 2800-3750 cm -1 (c) is the infrared spectrum diagram within the range, and (c) is the particle size distribution diagram of the lubricant containing trimesic acid prepared in Example 1 at different friction stages.

[0030] Figure 7 Schematic diagram comparing traditional nano-additive lubrication and the shear force-driven in-situ formation of carbon dots method of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited to the following examples.

[0032] The raw materials used in the present invention are all commercially available.

[0033] Example 1

[0034] (1) 0.24 g of trimesic acid (H3TMA) was mixed with 15 g of a mixed solution of polyethylene glycol and water, and stirred for 5 h to obtain a lubricant containing trimesic acid (i.e., H3TMA solution), wherein the mass percentage of trimesic acid in the lubricant was 1.6 wt %;

[0035] (2) The lubricant obtained in step (1) was injected into the oil cup of a four-ball tribometer, and the load was set to 600 N and the speed was set to 1200 rpm, and the friction was carried out for 30 min.

[0036] Examples 2 to 7

[0037] The preparation method is the same as that of Example 1, with the differences shown in the following table:

[0038] Table 1: Preparation differences of Examples 1 to 7

[0039]

[0040] Sample analysis

[0041] 1. Friction performance and wear

[0042] The lubricants prepared in Examples 1 to 4 were subjected to a friction test for 30 minutes. The results are as follows: Figure 1 shown.

[0043] Figure 1 The wear morphology and friction coefficient curves of the lubricants prepared in Examples 1 to 4 on the surface of the steel ball after friction, wherein (a) is the structure, wear scar map, three-dimensional height map and cross-sectional map from top to bottom, (b) to (d) are the friction coefficient map and average wear scar diameter map of the lubricants prepared in Examples 1 to 4 after friction, respectively. In the figure, BA solution refers to a lubricant containing benzoic acid, CA solution refers to a lubricant containing citric acid, IA solution refers to a lubricant containing isophthalic acid, and H3TMA solution refers to a lubricant containing trimesic acid. Figure 1As shown in (a), it can be observed that after 30 minutes of friction test, the mixed solution of polyethylene glycol and water (i.e., PEG-Water solution) has a larger wear scar diameter (WSD) of 1037.5μm. The three-dimensional height and cross-sectional images also show that the surface of the steel ball lubricated by the mixed solution of polyethylene glycol and water has deep grooves and a rough surface. Similarly, the CA (citric acid) solution with three carboxyl groups shows similar wear performance, and the wear scar also shows plow-shaped grooves with a WSD of 1088.4μm. Comparing the two lubrication results, we found that adding CA to the mixed solution of polyethylene glycol and water did not improve the lubrication effect, but instead increased the wear scar, which may be due to the corrosive effect of CA on the steel ball surface. Similarly, we conducted tribological tests on lubricants containing aromatic acids (lubricants with different numbers of carboxyl groups) and found that under the same structural conditions as the aromatic ring, the number of carboxyl groups has a significant effect on the wear scar after lubrication. The WSD values of the steel balls lubricated with benzoic acid-containing lubricants, terephthalic acid-containing lubricants, and trimesic acid-containing lubricants were significantly reduced to 944.5 μm, 707.2 μm, and 663.8 μm, respectively. Therefore, we found that the number of carboxyl groups of acids with the same aromatic ring structure has a very significant positive effect on their wear properties, and the more carboxyl groups at the same concentration, the better the anti-wear properties. The friction coefficients and average wear spot diameters of the lubricants with different aromatic acids prepared in Examples 1 to 4 are significantly smaller than those of the mixed solution of polyethylene glycol and water ( Figure 1 (b) to (d) in the figure). 2. Thermogravimetric analysis and friction heat suppression effect

[0044] (1) Thermogravimetric analysis

[0045] The lubricants prepared in Examples 1 to 4 were subjected to thermogravimetric analysis in an air atmosphere at 0 to 800°C. The results are as follows: Figure 2 The thermal decomposition temperatures of lubricants containing benzoic acid, citric acid, isophthalic acid, and trimesic acid are all between 180 and 220°C.

[0046] (2) Frictional heat suppression

[0047] The stability of the lubricants prepared in Examples 1 to 4 under high shear conditions was tested using a rotational shear rheometer (e.g. Figure 3 (a) in the figure). We found that the viscosity of several lubricants remained essentially unchanged within the shear range of 0 to 200 rad / s. Rheological results showed that the addition of aromatic acid molecules and the strong shear environment had no significant effect on the original polyethylene glycol and water mixed solution system. This method directly reveals the film-forming ability and friction heat suppression characteristics of the lubrication system ( Figure 3(b) to (c) in Figure 1). Temperature sensor results show that during the friction process, the temperatures of the PEG and polyethylene glycol / water mixtures increased by 30.4°C and 50.3°C, respectively. In contrast, the temperature of the trimesic acid lubricant increased by only 6.5°C during lubrication, representing temperature increases that were 4.7 times and 7.7 times lower, respectively, than those of the control.

[0048] 3. Effect of Friction Time on Carbon Dots

[0049] The lubricant prepared in Example 1 was used to measure the transmission electron microscopy images of carbon dots at friction times of 0, 3, 7.5, 15, and 30 minutes, respectively, to observe the effect of friction time on the carbon dots.

[0050] Figure 4 Transmission electron microscopy (TEM) and Raman spectra of carbon dots during friction in the lubricant prepared in Example 1. (a) Schematic diagram of the in situ carbon dot generation route and process. These results suggest that PEG and H3TMA molecules may form carbon dots directly on the friction surface through the local high-temperature and high-pressure environment created by the friction process in the presence of water molecules. This in situ shear-driven carbon dot generation method not only avoids the complex carbon dot preparation process, saving significant time and energy, but also avoids the dispersion issues associated with using traditional nanomaterials as lubricant additives. Figure 4 (b) to (f) show transmission electron microscopy (TEM) images of carbon dots in solution at different friction times. Except for the absence of carbon dots at 0 min, spherical carbon dots with a diameter of 3.9 nm were formed within a very short time span (3 min). This rapid method for preparing carbon dots is significantly more efficient than most established carbon dot synthesis techniques. In addition, we also conducted Raman experiments on the wear scars of the lower steel ball at different friction times ( Figure 4 (g) in the figure. The results show that before friction, no D or G peaks appeared on the steel ball surface. However, starting from 3 minutes, D and G peaks characteristic of graphite-like carbon dots appeared on the steel ball surface. With increasing friction time, the D peak gradually intensified, while the G peak gradually decreased, reflecting the presence of numerous defects or disordered structures in the tribofilm formed by the carbon dots on the friction surfaces after friction.

[0051] 4. Tribofilm Analysis

[0052] A focused ion beam (FIB) was used to thin the wear scar area on the surface of the lower steel ball after friction with the lubricant prepared in Example 1, and the morphology and composition of the tribofilm were directly observed.

[0053] Figure 5 The figure is an analysis diagram of the wear scar area on the surface of the lower steel ball after friction with the lubricant prepared in Example 1, wherein Figure 5As shown in (a), a tribofilm can be observed. The cross-sectional transmission electron microscope image of the wear scar shows that the thickness of the tribofilm is about 65nm ( Figure 5 (b) in the figure. Figure 5 (c) to (f) show the cross-sectional HADDF images and EDS mapping results of the tribofilm, which is mainly composed of C, O and a small amount of Fe. In order to better observe the internal composition and structure of the tribofilm, we enlarged the internal structure of the tribofilm ( Figure 5 (g) in the figure, and two areas were selected for magnification. Figure 5 (h) shows the presence of ferric oxide and ferroferric oxide particles in the tribofilm. The inset is a high-resolution image of a single particle, which may be due to the oxidation of the contact surface and the formation of wear debris. The lattice spacing is 0.268nm and 0.148nm, corresponding to the (1, 0, 4) crystal plane of ferric oxide and the (4, 4, 0) crystal plane of ferroferric oxide, respectively. Figure 5 (i) in the figure shows the uniformly distributed carbon dots in the tribofilm. After data calibration and fitting, we obtained the XPS data images of C, O and Fe elements ( Figure 5 (j) to (m) in the figure). The C1s spectrum shows a peak at 284.8eV, which corresponds to the C-C / C=C bond of the carbon dots or PEG molecules. The peak at around 283eV is attributed to CO / C=O, which may be due to the oxidation of the precursor during the formation of carbon dots. The peak at around 282eV is related to the C-Fe bond, which is consistent with the presence of a small amount of Fe in the tribofilm. The O1s spectrum shows peaks at 529.7eV and 528.4eV, which are CO and Fe-O, respectively. The Fe 2p spectrum shows that Fe 0 、Fe 2+ and Fe 3+ The presence of ferric oxide and ferroferric oxide particles observed in the

[0054] 5. Infrared spectroscopy and particle size analysis of lubricants

[0055] The lubricants containing different aromatic acids, a mixed solution of polyethylene glycol and water (PEG-Water solution), and a mixed solution of trimesic acid and polyethylene glycol (H3TMA-PEG solution) prepared in Examples 1 to 4 were respectively subjected to infrared spectroscopy analysis, and the particle size of the lubricant (H3TMA solution) prepared in Example 1 at different friction stages was analyzed.

[0056] Figure 6The infrared spectra and particle size analysis diagrams of the lubricants containing different aromatic acids prepared in Examples 1 to 4 are shown. Among them, (a) is the infrared spectra analysis diagram of the lubricants containing different aromatic acids prepared in Examples 1 to 4, the mixed solution of polyethylene glycol and water (PEG-Water solution), and the mixed solution of trimesic acid and polyethylene glycol, respectively. 3370 cm -1 The peak at 2910 cm is due to the OH groups in water and PEG molecules, while the peak at 2910 cm -1 The peak at 1640 cm is due to the CC stretching vibration of PEG in solution. -1 The broad peaks on the left and right are characteristic of liquid water.

[0057] Figure 6 (b) shows the H3TMA solution, H3TMA-PEG solution and water at 2800-3750 cm -1 Infrared spectrum in the range. After peak fitting, H3TMA solution is at 3460cm -1 and 3240cm -1 The -OH peak at is displaced from the peaks in H3TMA-PEG solution and water, indicating that there are strong hydrogen bonds between molecules in the H3TMA solution, which can promote the good lubrication performance of the H3TMA solution under high load.

[0058] The particle size distribution of the solution at different friction stages was analyzed using a light scattering particle size analyzer ( Figure 6 In (c), initially, the H3TMA molecules, polyethylene glycol molecules, and water molecules in the solution aggregated into aggregates with diameters between 250 and 1000 nm through hydrogen bonding (I). These aggregates contained a large number of hydrogen bonds, with a span value of 0.82, indicating an uneven size distribution and low size consistency. After the start of friction, the in situ generated carbon dots had a large number of hydroxyl and carboxyl groups on their surfaces, forming more uniform carbon dot nanoclusters (II) with smaller and more consistent sizes, with a span value of 0.40. As the friction time increases, the nanoclusters will combine with the aggregates in the original solution to form larger aggregates (III). The nanoclusters remain uniformly distributed, with a span of 0.38. During the friction, due to the increase in iron oxides caused by friction, the iron ions contained in the solution and the aggregates are attracted to each other through electrostatic interaction, and the diameter of the nanoclusters increases to the micron level (IV), with a span of 0.48. This can prevent the aggregation of abrasive particles.

[0059] 6. Lubrication mechanism analysis

[0060] Figure 7This diagram compares traditional nano-additive lubrication and the present invention's shear-driven in-situ carbon dot formation method. Generally speaking, traditional lubricants (with long alkyl chains) or nanoparticles used as oil additives can form a carbonaceous or specialized tribofilm at the interface, reducing wear and friction coefficient during friction. The properties of the raw materials remain unchanged, and the friction process does not destroy or generate specific substances.

[0061] In contrast, the lubricant molecules in this study are directly transformed from molecules into specific nanoparticles, and their physical properties change, and they have different friction mechanisms. First, at the beginning of friction, a large number of trimesic acid molecules are adsorbed on the surface of the friction pair through coordination bonds. Water molecules promote the formation of hydrogen bonds between the hydroxyl groups of polyethylene glycol molecules and the carboxyl groups of trimesic acid molecules. These water molecules help assemble trimesic acid and polyethylene glycol molecules into a structure similar to a fat chain, forming a brush-like structure on the surface of the friction pair to resist shear. This layer of adsorbed water quickly provides hydration lubrication under shear force, generating outward hydrodynamic pressure and enhancing the ability to withstand external loads. At the same time, water molecules also combine with the polar groups of polyethylene glycol and trimesic acid through hydrogen bonds to form larger aggregates.

[0062] With prolonged friction, the molecules in these fatty chains fragment and rearrange under high load and rotational speed, transforming in situ into carbon dots at the interface. While most carbon dots contribute to the rolling, filling, and repairing processes at the interface, some escape into the solution. Under shear, carbon dots in the solution slowly adsorb onto the opposing surfaces, contributing to the tribofilm. These carbon dots, escaping from the interface, form nanoclusters of a certain size through hydrogen bonding with molecules in the solution. Dynamic contact between nanoclusters or at the interface between them reduces shear resistance, thereby supporting high loads. Simultaneously, water molecules within the nanoclusters exchange with water molecules in the solution, enabling nanoclusters to move across the interface. In summary, the in situ shear-driven formation of carbon dots not only contributes to the tribofilm formation through its own nanomaterial properties but also increases the size of the nanoclusters by binding to lubricant molecules and enhances their cohesion through hydrogen bonding, enabling them to withstand high loads.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for in-situ formation of carbon dots based on shear force drive, characterized in that: The following steps are involved: (1) preparing a lubricant containing an aromatic acid; (2) The lubricant obtained in step (1) is subjected to in-situ generation of carbon dots under friction conditions of a load of 300 to 600 N and a rotation speed of 1000 to 1500 rpm.

2. The method for in-situ formation of carbon dots based on shear force driving according to claim 1, characterized in that: In step (1), the method for preparing the lubricant containing aromatic acid is: mixing the aromatic acid with a mixed solution of polyethylene glycol and water, and stirring to obtain the lubricant containing aromatic acid.

3. The method for in-situ formation of carbon dots based on shear force driving according to claim 1 or 2, characterized in that: The aromatic acid is one of trimesic acid, terephthalic acid, phthalic acid, benzoic acid, gallic acid, salicylic acid and phenylacetic acid.

4. The method for in-situ formation of carbon dots based on shear force driving according to claim 1 or 2, characterized in that: The mass percentage of the aromatic acid in the lubricant is 1.0-2.5wt%.

5. The method for in-situ formation of carbon dots based on shear force driving according to claim 2, characterized in that: In the mixed solution of polyethylene glycol and water, the mass ratio of the polyethylene glycol to water is 1:1-5.

6. The method for in-situ formation of carbon dots based on shear force driving according to claim 1, characterized in that: The thermal decomposition temperature of the aromatic acid-containing lubricant is 180-220°C.

7. The method for in-situ formation of carbon dots based on shear force driving according to claim 1, characterized in that: In step (2), the friction time is 3 to 30 minutes.

8. The method for in-situ formation of carbon dots based on shear force driving according to claim 1, characterized in that: In step (2), the particle size of the carbon dots is 2 to 5 nm.

9. The method for in-situ formation of carbon dots based on shear force driving according to claim 2, characterized in that: The carbon dots form solid-liquid nanoclusters with polyethylene glycol and water in the lubricant. The particle size of the solid-liquid nanoclusters is 1000-2600 nm.

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