A nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, its preparation method, and its application.

Abstract

This invention discloses a nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, its preparation method, and its application, belonging to the field of nanocomposite material technology. This invention employs a combination of mechanical liquid-phase ultrasonic exfoliation and hydrothermal method to anchor zero-dimensional nitrogen- and boron co-doped carbon quantum dots onto a few-layer molybdenum disulfide substrate plane, thereby obtaining the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material. The preparation method of this invention includes: (1) preparation of few-layer molybdenum disulfide nanosheets; (2) preparation of the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material. The composite material of this invention exhibits excellent structural stability. When used as a lubricating oil additive, it demonstrates excellent dispersibility and long-term dispersion stability in base oils, significantly improving the tribological properties of the base oil.

Description

[0001] This invention belongs to the field of nanocomposite materials technology, specifically relating to a nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, its preparation method, and its application. Background Technology

[0002] In mechanical systems, lubricating oil effectively reduces friction and wear between components, thereby lowering energy consumption and preventing component failure. Polyethylene glycol (PEG) possesses excellent lubricating properties and good biodegradability, making it widely used as a base oil in applications such as metalworking fluids, compressor lubricants, gear oils, and bearing oils. However, PEG base oils have limited lubrication performance under high temperature and high load conditions. Furthermore, nano-additives in PEG oils tend to agglomerate and exhibit poor dispersion stability, leading to a decrease in extreme pressure performance and even causing lubrication failure, which severely restricts the industrial application of PEG base oils.

[0003] To improve the tribological properties of polyethylene glycol base oils under harsh operating conditions, researchers have developed a variety of novel lubricant additives. Among them, zero-dimensional carbon quantum dots (CQDs), as promising nanomaterials, can penetrate to micro-damage on metal surfaces and repair worn areas through the rolling effect, thereby achieving surface polishing and repair to enhance lubrication performance. However, CQDs as additives still suffer from poor compatibility with base oils, insufficient long-term dispersion stability, and limited extreme pressure performance. Currently, surface chemical modification and elemental doping are commonly used to functionalize CQDs. Heteroatom doping (such as N, S, P, B, F, etc.) can adjust their electronic structure and surface properties, improving their catalytic activity, wettability, and reaction affinity on friction surfaces, thus expanding their applications in lubrication and other fields. In particular, while nitrogen doping can improve the lubrication performance of CQDs, the strong adsorption of nitrogen atoms on the friction surface easily leads to agglomeration, resulting in unstable lubrication. Furthermore, single-element doping strategies often fail to achieve synergistic improvement in tribological properties. For example, patent CN 113897235 A discloses a method for preparing a nitrogen-doped carbon quantum dot / 2D Ni-BDC nanocomposite lubricating material. This method uniformly loads a large number of nitrogen-doped carbon quantum dots onto the surface of 2DNi-BDC nanosheets to improve the tribological performance of 2D Ni-BDC as a lubricant. However, this method only uses nitrogen-doped carbon quantum dots and fails to introduce elements that can further enhance extreme pressure performance, thus it is still insufficient in terms of synergistic enhancement of extreme pressure performance and wear resistance. At the same time, the Ni-BDC used is a metal-organic framework material, which, although having high porosity, has weak mechanical stability and is prone to structural collapse in the early stages of friction, thereby affecting the durability of lubrication effect. The introduction of boron can form a strong and tough boron-based chemical reaction film at the friction interface, significantly improving extreme pressure and wear resistance. Therefore, N and B co-doped carbon quantum dots, by leveraging the synergistic doping effect of nitrogen and boron, can both enhance extreme pressure performance and alleviate the adsorption and aggregation problem caused by nitrogen, becoming an effective strategy for improving lubrication performance. However, single N,B co-doped carbon quantum dots still suffer from poor dispersibility in base oils and tend to over-accumulate on friction surfaces to form uneven films, which limits their practical application.

[0004] Molybdenum disulfide (MoS2), a typical two-dimensional layered material, exhibits excellent anti-friction properties due to its weak interlayer van der Waals forces, low shear strength, and strong adsorption capacity. However, when used as a lubricant additive, MoS2 is prone to agglomeration and lacks sufficient interlayer sliding durability during long-term friction, leading to uneven dispersion in the oil and accumulation on the friction surface, which exacerbates wear. Furthermore, MoS2's insufficient elasticity makes it prone to breakage during long-term operation, disrupting the protective film formation and ultimately causing a decline in lubrication performance. Current improvement methods mainly include surface chemical modification, process optimization, and composite material development. While surface chemical modification can improve dispersibility, the introduced surfactants are prone to decomposition under extreme conditions. Process optimization, such as preparing few-layer MoS2 nanosheets, can reduce agglomeration, making it easier to enter the friction interface and form a high-quality lubricating film; however, this process requires precise control of exfoliation parameters to avoid material structural damage. The construction of composite materials achieves a synergistic enhancement effect of "1+1>2" by integrating the performance advantages of different materials. Therefore, combining CQDs with MoS2 can both inhibit the agglomeration of CQDs by leveraging the layered structure of MoS2 and prevent the stacking of MoS2 sheets by the rolling effect of CQDs, thereby jointly improving the lubrication performance, structural stability and adaptability of the composite material.

[0005] Based on the above, in order to simultaneously solve the problems of insufficient lubrication performance of PEG base oil under harsh working conditions and poor dispersibility and stability of existing nano-additives, this invention uses mechanical liquid phase ultrasonic exfoliation combined with hydrothermal method to prepare a nitrogen and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material with a "sphere-on-sheet" heterostructure, and uses it as an additive for PEG base oil. Summary of the Invention

[0006] To address the above problems, this invention provides a nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, its preparation method, and its applications. By employing a combination of mechanical liquid-phase ultrasonic exfoliation and hydrothermal method, the nitrogen- and boron co-doped carbon quantum dots are anchored onto the substrate plane of the few-layer molybdenum disulfide, effectively solving the problem of easy agglomeration of carbon quantum dots and molybdenum disulfide nanomaterials. When used as a lubricating oil additive, this composite material exhibits excellent dispersibility and long-term dispersion stability in base oils, significantly improving the tribological properties of the base oil.

[0007] This invention is achieved through the following technical solution: A nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material is obtained by using a combination of mechanical liquid-phase ultrasonic exfoliation and hydrothermal method to anchor the nitrogen- and boron co-doped carbon quantum dots onto the substrate plane of few-layer molybdenum disulfide.

[0008] Furthermore, in the nitrogen and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, the spherical nitrogen and boron co-doped carbon quantum dots are grown on nanosheet-like few-layer molybdenum disulfide to form an on-sheet sphere heterojunction structure. The water contact angle of the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material is 0°.

[0009] A method for preparing the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material as described above includes the following steps: (1) Preparation of few-layer molybdenum disulfide nanosheets: molybdenum disulfide, cellulose nanocrystals and methanol were placed in a ball mill jar and ball milled at room temperature. The mixture after ball milling was dissolved in water and subjected to water bath ultrasonic treatment to obtain a dispersion of few-layer molybdenum disulfide nanosheets. The precipitate was collected by centrifugation and dried to obtain few-layer molybdenum disulfide nanosheets. (2) Preparation of nitrogen and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material: Citric acid, urea, boric acid and the few-layer molybdenum disulfide nanosheets obtained in step (1) were added to water and magnetically stirred until completely dissolved to obtain a uniform mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, precipitated and dried to obtain nitrogen and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material.

[0010] Further, in step (1), the mass ratio of molybdenum disulfide to cellulose nanocrystals is 5 to 15:1; the mass ratio of cellulose nanocrystals to methanol is 1 g: 5 to 15 mL.

[0011] Further, in step (1), the water bath ultrasonic treatment is performed for 1 to 3 hours at a temperature of 25 to 28°C, a power of 350 to 400W, and a frequency of 35 to 40KHz.

[0012] Further, in step (1), the ball milling speed is 100-300 rpm and the time is 30-60 min.

[0013] Further, in step (2), the mass ratio of citric acid, urea, boric acid and few-layer molybdenum disulfide nanosheets is 0.1-0.3:0.1-0.3:0.1-0.3:1.

[0014] Furthermore, in step (2), the temperature of the hydrothermal reaction is 170-190°C and the time is 11-13 hours.

[0015] Furthermore, in step (2), the magnetic stirring speed is 500-700 rpm and the time is 3-5 h.

[0016] The application of the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material described above as a lubricating oil additive. Applying this lubricating oil additive to base oils such as polyethylene glycol (PEG) and polyalphaolefin (PAO) can effectively reduce the tribological properties of the base oil.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention constructs a nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material with a "sphere-on-sheet" heterostructure via mechanical liquid-phase ultrasonic exfoliation combined with a hydrothermal method. In this composite material, zero-dimensional nitrogen- and boron co-doped carbon quantum dots are uniformly anchored to the substrate plane of the few-layer molybdenum disulfide, forming a stable composite structure. This composite material exhibits excellent structural stability, and when used as a lubricating oil additive, it demonstrates excellent dispersibility and long-term dispersion stability in base oils, significantly improving the tribological properties of the base oil. Furthermore, the preparation method of this invention is environmentally friendly, low-cost, and simple, suitable for large-scale application, and is expected to generate significant economic and social benefits in the field of lubricating materials.

[0018] 2. The composite material prepared in this invention exhibits a multi-stage synergistic effect during lubrication, significantly enhancing lubrication performance. In the initial stage, few-layer molybdenum disulfide nanosheets form a continuous protective film through interlayer sliding under shear force, isolating direct contact between friction pairs and regulating the rolling behavior of nitrogen- and boron-doped carbon quantum dots to prevent local aggregation. Entering the synergistic stage, the rolling effect of nitrogen- and boron-doped carbon quantum dots further enhances the sliding friction of the few-layer molybdenum disulfide nanosheets, significantly reducing frictional resistance and stabilizing the friction coefficient. In the dynamic repair stage, frictional heat triggers a chemical reaction on the metal surface, generating oxides such as Fe2O3 and Fe3O4, which, together with the formed metal nitrides (Fe-N) and organic components (CN), construct a stable composite protective film. Under external load, the composite material can decompose into finer particles, promoting the synergistic release of the few-layer molybdenum disulfide nanosheets and nitrogen- and boron-doped carbon quantum dots, rapidly filling surface micro-damage and reducing surface roughness. This multi-stage mechanism, which combines rolling-sliding synergy, tribochemical film formation, and dynamic repair filling, significantly improves the anti-friction and anti-wear properties of PEG base oil under high pressure and high speed conditions.

[0019] 3. The composite material of this invention, as a lubricating oil additive, features low dosage and significant lubrication effect, exhibiting good dispersion stability in various base oils. When applied to polyethylene glycol (PEG) and polyalphaolefin (PAO) base oils, the average wear scar diameters are only 0.48 mm and 0.36 mm, respectively, and the average friction coefficients are as low as 0.033 and 0.067, respectively. Extreme pressure performance is also significantly improved, effectively enhancing the tribological properties of the base oils. The raw materials used in the preparation method of this invention are safe, environmentally friendly, and pollution-free. The preparation process is simple and the production cost is low. The resulting composite material has excellent practical application value and is suitable for large-scale promotion and application. Attached Figure Description

[0020] Figure 1 The images show the XRD patterns of MoS2, C-MoS2, and N,B-CQDs / C-MoS2 obtained in Comparative Examples 1-2 and Example 1, respectively; wherein, (a) is the XRD pattern of MoS2, C-MoS2, and N,B-CQDs / C-MoS2, and (b) is a magnified view of the XRD pattern of MoS2, C-MoS2, and N,B-CQDs / C-MoS2.

[0021] Figure 2 The FT-IR images are of C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 2-3 and Example 1, respectively.

[0022] Figure 3 XPS plots of C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 2-3 and Example 1, respectively.

[0023] Figure 4 XPS spectra of C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 materials prepared in Comparative Examples 2-3 and Example 1, respectively; where (a), (b), (c), and (d) are XPS spectra of C 1s, N 1s, O 1s, and B 1s for N,B-CQDs and N,B-CQDs / C-MoS2, respectively, and (e) and (f) are XPS spectra of S 2p and Mo 3d for C-MoS2 and N,B-CQDs / C-MoS2, respectively.

[0024] Figure 5 The images show SEM images of MoS2, C-MoS2, and N,B-CQDs / C-MoS2 obtained in Comparative Examples 1-2 and Example 1, respectively; where (a), (b), and (c) are SEM images of MoS2, C-MoS2, and N,B-CQDs / C-MoS2, respectively.

[0025] Figure 6 The images show the AFM diagrams of MoS2, C-MoS2, and N,B-CQDs / C-MoS2 obtained in Comparative Examples 1-2 and Example 1, respectively; where (a), (b), and (c) are the AFM diagrams of MoS2, C-MoS2, and N,B-CQDs / C-MoS2, respectively.

[0026] Figure 7 The images show TEM images of MoS2, C-MoS2, and N,B-CQDs / C-MoS obtained in Comparative Examples 1-2 and Example 1, respectively; where (a), (b), and (c) are TEM images of MoS2, C-MoS2, and N,B-CQDs / C-MoS2, respectively.

[0027] Figure 8 The image shows the elemental surface distribution of C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 obtained in Comparative Examples 2-3 and Example 1, respectively.

[0028] Figure 9 The images show the dispersion and dispersion analysis of MoS2, C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-3 and Example 1, respectively. Among them, (a), (b), (c), (d), and (e) are dispersion diagrams for 0h, 5h, 7d, 14d, and 21d, respectively, and ①, ②, ③, and ④ are MoS2, C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2, respectively.

[0029] Figure 10 The contact angle diagrams are for MoS2, C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-3 and Example 1, respectively; where (a), (b), (c), and (d) are the contact angle diagrams for MoS2, C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2, respectively. Detailed Implementation

[0030] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0031] Example 1 Preparation of nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposites: (1) Place 5.0 g of molybdenum disulfide, 0.5 g of cellulose nanocrystals, and 3 mL of methanol in a ball mill jar, add agate beads, and ball mill at 200 rpm for 30 min at room temperature. Then, let the ball-milled mixture stand overnight to allow the residual solvent to evaporate completely. Dissolve the mixture in 100 mL of deionized water, and treat it with ultrasonic treatment in a water bath (temperature 25℃, power 400 W, frequency 40 kHz) for 2 h to obtain a molybdenum disulfide nanosheet dispersion. Centrifuge at 10000 rpm to collect the precipitate, and dry at 80℃ for 8 h to obtain few-layer molybdenum disulfide nanosheets.

[0032] (2) Take 0.2g citric acid, 0.2g urea, 0.2g boric acid and 1.0g few-layer molybdenum disulfide nanosheets, add 120mL deionized water, and stir magnetically at 600rpm for 3h until completely dissolved to obtain a homogeneous mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave and react at 180℃ for 12h. After the reaction is completed, cool naturally to room temperature, filter, wash, precipitate and collect the product, and dry the obtained solid in an oven at 80℃ for 8h to obtain nitrogen and boron co-doped carbon quantum dots / few-layer molybdenum disulfide nanocomposite material (denoted as N,B-CQDs / C-MoS2).

[0033] Example 2 Preparation of nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposites: (1) 5.0 g of molybdenum disulfide, 0.4 g of cellulose nanocrystals, 5 mL of methanol and agate beads were placed in a ball mill jar, and the agate beads were added. The mixture was ball milled at 300 rpm for 30 min at room temperature. The mixture was then left to stand overnight to allow the residual solvent to evaporate completely. The mixture was dissolved in 100 mL of deionized water and treated with ultrasonic treatment in a water bath (temperature 25℃, power 400 W, frequency 40 kHz) for 1 h to obtain a molybdenum disulfide nanosheet dispersion. The precipitate was collected by centrifugation at 9000 rpm and dried at 80℃ for 8 h to obtain few-layer molybdenum disulfide nanosheets.

[0034] (2) Take 0.2g citric acid, 0.1g urea, 0.3g boric acid and 1.0g few-layer molybdenum disulfide nanosheets, add 100mL deionized water, and stir magnetically at 500rpm for 4h until completely dissolved to obtain a homogeneous mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave and react at 190℃ for 12h. After the reaction is completed, allow it to cool naturally to room temperature. After filtration, washing and precipitation, collect the product. Dry the obtained solid in an oven at 80℃ for 8h to obtain nitrogen and boron co-doped carbon quantum dots / few-layer molybdenum disulfide nanocomposite material.

[0035] Example 3 Preparation of nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposites: (1) 6.0 g of molybdenum disulfide, 0.5 g of cellulose nanocrystals, 6 mL of methanol and agate beads were placed in a ball mill jar, and the agate beads were added. The mixture was ball milled at 100 rpm for 30 min at room temperature. The mixture was then left to stand overnight to allow the residual solvent to evaporate completely. The mixture was dissolved in 100 mL of deionized water and treated with ultrasonic treatment in a water bath (temperature 25℃, power 400 W, frequency 40 kHz) for 3 h to obtain a molybdenum disulfide nanosheet dispersion. The precipitate was collected by centrifugation at 11000 rpm and dried at 80℃ for 8 h to obtain few-layer molybdenum disulfide nanosheets.

[0036] (2) Take 0.2g citric acid, 0.3g urea, 0.1g boric acid and 1.0g few-layer molybdenum disulfide nanosheets, add 130mL deionized water, and stir magnetically at 700rpm for 2h until completely dissolved to obtain a homogeneous mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave and react at 180℃ for 13h. After the reaction is completed, allow it to cool naturally to room temperature. After filtration, washing and precipitation, collect the product. Dry the obtained solid in an oven at 80℃ for 7h to obtain nitrogen and boron co-doped carbon quantum dots / few-layer molybdenum disulfide nanocomposite material.

[0037] Example 4 Preparation of nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposites: (1) 4.0 g of molybdenum disulfide, 0.6 g of cellulose nanocrystals, 3 mL of methanol and agate beads were placed in a ball mill jar, and the agate beads were added. The mixture was ball milled at 200 rpm for 30 min at room temperature. The mixture was then left to stand overnight to allow the residual solvent to evaporate completely. The mixture was dissolved in 100 mL of deionized water and treated with ultrasonic treatment in a water bath (temperature 25℃, power 400 W, frequency 40 kHz) for 2 h to obtain a molybdenum disulfide nanosheet dispersion. The precipitate was collected by centrifugation at 11000 rpm and dried at 80℃ for 8 h to obtain few-layer molybdenum disulfide nanosheets.

[0038] (2) Take 0.1g citric acid, 0.2g urea, 0.3g boric acid and 1.0g few-layer molybdenum disulfide nanosheets, add 120mL deionized water, and stir magnetically at 600rpm for 3h until completely dissolved to obtain a homogeneous mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave and react at 170℃ for 11h. After the reaction is completed, allow it to cool naturally to room temperature. After filtration, washing and precipitation, collect the product. Dry the obtained solid in an oven at 80℃ for 9h to obtain nitrogen and boron co-doped carbon quantum dots / few-layer molybdenum disulfide nanocomposite material.

[0039] Comparative Example 1 Comparative Example 1 used only raw bulk molybdenum disulfide (MoS2) without any experimental preparation.

[0040] Comparative Example 2 Preparation of few-layer molybdenum disulfide nanosheets: 5.0 g of molybdenum disulfide, 0.5 g of cellulose nanocrystals, and 3 mL of methanol were placed in a ball mill jar, and agate beads were added. The mixture was ball-milled at 200 rpm for 30 min at room temperature, and then left to stand overnight to allow the residual solvent to evaporate completely. The mixture was dissolved in 100 mL of deionized water and treated with ultrasonic treatment in a water bath (temperature 25℃, power 400W, frequency 40 kHz) for 2 h to obtain a molybdenum disulfide nanosheet dispersion. The precipitate was collected by centrifugation at 10000 rpm and dried at 80℃ for 8 h to obtain few-layer molybdenum disulfide nanosheets (denoted as C-MoS2).

[0041] Comparative Example 3 Preparation of nitrogen- and boron co-doped carbon quantum dots: Take 0.2g of citric acid, 0.2g of urea, and 0.2g of boric acid, add 120mL of deionized water, and stir magnetically at 600rpm for 3h until completely dissolved to obtain a homogeneous mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave and react at 180℃ for 12h. After the reaction is complete, allow it to cool naturally to room temperature. After filtration, washing, and precipitation, collect the product. Dry the obtained solid in an oven at 80℃ for 8h to obtain nitrogen- and boron-doped carbon quantum dots (denoted as N,B-CQDs).

[0042] Material characterization (a) X-ray diffraction (XRD) analysis X-ray diffraction (XRD) was used to characterize MoS2, C-MoS2, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-2 and Example 1, respectively, to explore the phase information of the materials. The characterization results are as follows: Figure 1 As shown.

[0043] Figure 1 (a) Both the bulk MoS2 and the exfoliated C-MoS2 samples exhibit distinct diffraction peaks (JCPDS #37-1492) at characteristic angles 2θ≈14.5°(002), 29.1°(004), 32.7°(100), 39.6°(103), 44.3°(006), 49.8°(105), and 58.4°(110), with no significant peak shift, indicating that mechanical liquid-phase exfoliation did not alter the 2H phase structure of MoS2. Notably, the intensity of the (002) peak in C-MoS2 is significantly reduced, indicating a decrease in grain size along the crystal plane and a reduction in the number of stacked MoS2 nanosheets.

[0044] also, Figure 1 (b) Displays (002) peak shifting towards a lower angle region (2) θ (Decrease). According to Bragg's equation (2d sin θ =λ), indicating an increase in interlayer spacing. Characterization results show that the introduction of N,B-CQDs did not alter the crystal structure of C-MoS2, and the material retained its few-layer lamellar structure. Combined XRD results show that bulk MoS2 has been successfully exfoliated into nanosheet structures with fewer layers and smaller dimensions.

[0045] (II) Fourier Transform Infrared Spectroscopy (FT-IR) Analysis Fourier transform infrared spectroscopy (FT-IR) was used to characterize C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 2-3 and Example 1, respectively, to determine the functional groups of the materials. The characterization results are as follows: Figure 2 As shown.

[0046] Figure 2 The Fourier transform infrared spectra of N,B-CQDs, C-MoS2, and N,B-CQDs / C-MoS2 are shown. The N,B-CQDs spectrum is at 3250 cm⁻¹. -1 A broad and strong absorption band is observed at 2920 cm⁻¹, attributed to the OH / NH stretching vibration. -1 With 1382cm -1 The absorption peaks at 1671 cm⁻¹ are attributed to the CH stretching vibration and CN bending vibration in the amide structure, respectively. -1 With 1581cm -1 The peaks at 1354 cm⁻¹ originate from the stretching vibrations of NC=O and C=C, respectively, indicating the presence of oxygen-containing functional groups such as carboxyl groups. -1 The CN stretching vibration peak at 1022 cm⁻¹ is similar to that at 1022 cm⁻ -1 The CB vibrational peaks at 1242, 1095, and 459 cm⁻¹ confirm the successful incorporation of nitrogen and boron atoms into the carbon framework structure. Furthermore, the peaks at 1242, 1095, and 459 cm⁻¹ further confirm this. -1 The absorption peaks at 1160 and 642 cm⁻¹ are attributed to the BN, BO, and -B(4)-O vibrations, respectively, further confirming the presence of boron-containing functional groups. Compared with C-MoS₂ and N,B-CQDs, the N,B-CQDs / C-MoS₂ composite material exhibits higher absorption peaks at 1160 and 642 cm⁻¹. -1 The N,B-CQDs / C-MoS2 composite exhibits new characteristic peaks, corresponding to the S=O stretching vibration and Mo-O vibration, respectively. These spectral features indicate that the N,B-CQDs / C-MoS2 composite effectively retains and integrates the water solubility of both components, thereby optimizing its dispersion stability and dispersibility in PEG base oil. Simultaneously, the covalent bond structure formed between N,B-CQDs and C-MoS2 effectively reduces the aggregation tendency of N,B-CQDs, promotes the formation of a stable friction film at the interface, and thus significantly improves lubrication performance.

[0047] (III) X-ray photoelectron spectroscopy (XPS) analysis The surface chemical states of C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 2-3 and Example 1 were analyzed using X-ray photoelectron spectroscopy (XPS). The analytical results are as follows: Figure 3 and Figure 4 As shown. XPS spectra provided detailed information on surface chemistry using Thermo Avantage fitting software.

[0048] XPS analysis revealed the elemental composition and chemical state of C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2, as shown in the following results. Figure 3 As shown, the presence of C, N, O, and B elements in the N,B-CQDs sample confirms the successful incorporation of nitrogen and boron into the carbon matrix.

[0049] exist Figure 4 In the C 1s spectrum of (a), N,B-CQDs exhibit characteristic peaks at 284.8, 286.7, and 288.4 eV, corresponding to CC / C=C, CN / CB, and OC=O bonds, respectively. Notably, the OC=O functional group at 288.4 eV significantly enhances the hydrophilicity of the material, aiding its dispersion in PEG base oils, a finding consistent with FT-IR results. In the C 1s spectrum of the N,B-CQDs / C-MoS2 composite, the characteristic peaks remain clearly visible, but the intensity of the OC=O peak is slightly reduced. This attenuation may stem from the low loading of N,B-CQDs in the composite. The significantly enhanced peak at 286.7 eV (CN / CB) indicates successful integration of N,B-CQDs onto the C-MoS2 surface. Figure 4 In the N 1s spectrum of (b), the peaks at 399.6 eV and 401.4 eV correspond to CN and BN bonds, respectively, confirming the co-doping of N and B in the carbon framework. For the N,B-CQDs / C-MoS2 system, a new peak at 398.5 eV appears in the N 1s spectrum, attributed to Mo-N bonds, indicating the formation of chemical interface bonds between N,B-CQDs and C-MoS2. Figure 4 In the O 1s spectrum of (c), peaks related to OC=O, CO, and BO appear at 533.1, 533.8, and 534.7 eV, respectively, in the N,B-CQDs. Figure 4In the B 1s spectrum (d), the BO peak at 192.3 eV further confirms that boron atoms are embedded in the carbon framework. For the N,B-CQDs / C-MoS2 composite material, in addition to the characteristic peaks of oxygen and boron, a Mo-O bond peak at 531.8 eV appears in the O 1s spectrum, and a Mo-B bond peak at 186.3 eV appears in the B 1s spectrum. These results further indicate that N,B-CQDs and C-MoS2 form a stable heterostructure through chemical bonds, consistent with the results observed by transmission electron microscopy. The characteristic peaks of C-MoS2 are also present in both the Mo 3d and S 2p XPS spectra. The stable heterostructure formed between N,B-CQDs and C-MoS2 through chemical bonds is consistent with the transmission electron microscopy (TEM) results. Figure 4 (e) of S 2p and Figure 4 In the Mo 3d spectra shown in (f), characteristic peaks corresponding to C-MoS2 were observed, indicating that the structure of MoS2 in N,B-CQDs / C-MoS2 remains stable. The surface of this material is rich in oxygen-containing functional groups (such as OC=O), which endows it with excellent hydrophilicity. The interfacial structure formed by N,B-CQDs and C-MoS2 enhances interfacial stability, thereby synergistically optimizing lubrication performance.

[0050] (iv) Scanning electron microscopy (SEM) analysis The MoS2, C-MoS2, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-2 and Example 1 were characterized and analyzed using scanning electron microscopy (SEM). The analytical results are as follows: Figure 5 As shown.

[0051] Figure 5 (a) shows that the original bulk MoS2 exhibits a typical tightly packed layered structure. After mechanical liquid-phase ultrasonic exfoliation, Figure 5 (b) shows that C-MoS2 is transformed into nanosheets with significantly reduced size and thickness, a result consistent with XRD analysis data. Figure 5 (c) shows that after being combined with N,B-CQDs, the material still maintains a clear small-sized layered structure.

[0052] Figure 8 The elemental surface distribution results show that C, O, N, B, Mo, and S elements are uniformly distributed in the N,B-CQDs / C-MoS2 nanocomposite, confirming the successful loading of N,B-CQDs onto the few-layer C-MoS2 surface. However, some larger-sized few-layer MoS2 surfaces are covered with fine fragments, which is attributed to its high surface energy properties.

[0053] (v) Atomic force microscopy (AFM) analysis The MoS2, C-MoS2, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-2 and Example 1 were characterized and analyzed using atomic force microscopy (AFM). The analytical results are as follows: Figure 6 As shown.

[0054] Figure 6 (a) shows that the original bulk MoS2 has a lateral dimension of approximately 1000 nm and a thickness of 63.4 nm. After mechanical liquid-phase ultrasonic ablation, Figure 6 (b) shows that its lateral dimension is reduced to approximately 500 nm, and its thickness is significantly reduced to 6.3 nm, only 10% of the original sample. Furthermore, after recombination with nitrogen, Figure 6 (c) shows that the material thickness was further reduced to approximately 2.7 nm, equivalent to a stacked structure of approximately 4-5 layers of MoS2. This micron-scale thin film has a lateral dimension of only 50% and a thickness of only 10% of the original material, exhibiting a significant size effect. Figure 6 The analysis results in (c) show that after N,B-CQDs composite treatment, the material thickness was further reduced to about 2.7 nm, equivalent to a stacked structure of 4-5 layers of MoS2. This micro-sized few-layer structure can reduce the shear resistance during the friction process, allowing the material to quickly enter the friction contact area and form a high-quality protective lubricating film, significantly improving the tribological properties.

[0055] (vi) Transmission electron microscopy (TEM) analysis Transmission electron microscopy (TEM) was used to characterize and analyze the MoS2, C-MoS2, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-2 and Example 1, respectively. The analytical results are as follows: Figure 7 As shown.

[0056] Figure 7 (a) shows that the bulk MoS2 exhibits clear lattice diffraction fringes with a lattice spacing of 0.24 nm, corresponding to the (105) crystal plane of MoS2. Figure 7 (b) shows that, compared to bulk MoS2, the lattice spacing of the exfoliated C-MoS2 extends to 0.64 nm, indicating successful exfoliation into nanosheets with fewer layers and increased interlayer spacing. Furthermore, Figure 7 (b) shows diffraction fringes with a diameter less than 10 nm and a lattice spacing of 0.22 nm, corresponding to nitrogen-boron-carbon quantum dots attached to the C-MoS2 surface. Figure 7As shown in (c), a clear boundary (red dashed line) exists between C-MoS2 and N,B-CQDs, confirming the successful construction of the "sphere-on-sheet" heterojunction structure in N,B-CQDs / C-MoS2. The sheet-like structures are C-MoS2 after mechanical ultrasonic exfoliation, and the spherical structures are "quasi-spherical" N,B-CQDs. The spherical quantum dots of N,B-CQDs grow on the sheet-like C-MoS2 to form the "sphere-on-sheet" heterojunction structure.

[0057] Figure 8 The elemental surface distribution results showed that the C-MoS2 surface was enriched with carbon atoms, while the N,B-CQDs region was enriched with nitrogen atoms. XRD, SEM and AFM characterization results jointly showed that the bulk MoS2 had been successfully exfoliated into C-MoS2 nanosheets with few layers and small size, while quasi-spherical N,B-CQDs were uniformly distributed on its surface to form a "sphere-on-sheet" heterostructure. (VII) Water Contact Angle (WCA) Analysis and Dispersion and Dispersion Stability Analysis The water contact angle (WCA) was used to characterize and analyze the MoS2, C-MoS2, N,B-CQDs, and N,B-CQDs / C-MoS2 prepared in Comparative Examples 1-3 and Example 1, respectively. The test results are as follows: Figure 9 and Figure 10 As shown, the long-term dispersion stability of the N,B-CQDs / C-MoS2 composite material in base oil has a significant impact on its tribological properties.

[0058] Figure 9 The dispersion stability and dispersibility of MoS2, C-MoS2, N,B-CQDs and N,B-CQDs / C-MoS2 composites in PEG base oils were shown as changes over time (0h, 5h, 7d, 14d, 21d). Figure 9 (a) shows that the dispersion stability of the composite material in the base oil gradually decreases over time. The dispersion stability and dispersibility of N,B-CQDs / C-MoS2 in PEG base oil vary with time (0h, 5h, 7d, 14d and 21d). Figure 9 (a) In the initial stage, all four materials were well dispersed in PEG oil after ultrasonic treatment, mainly due to the van der Waals forces between the particles and the oil phase. After 5 hours, Figure 9 (b) The bulk MoS2 particles, due to their hydrophobicity and larger particle size, have clearly settled. In contrast, Figure 9 (c) The C-MoS2 nanosheets remained stably dispersed after 7 days, but showed obvious stratification by 14 days (due to...). Figure 9 (d) shows that N,B-CQDs / C-MoS2 remained well dispersed after 14 days, with slight stratification only appearing at 21 days (due to...). Figure 9 (e) is shown.

[0059] Figure 10 (a) shows that the contact angle of bulk MoS2 is 125°, which is due to its inherent hydrophobicity. In contrast, the contact angle of C-MoS2 obtained by mechanical ultrasonic exfoliation decreases to 61° (due to...). Figure 10 (b) shows that it has changed from hydrophobic to hydrophilic. This change is due to the exfoliation process exposing a large number of active edge sites and introducing oxygen-containing defects, thereby forming polar functional groups. In addition, the surface of N,B-CQDs is rich in strongly polar groups (such as NH and OH), exhibiting superhydrophilicity, with a contact angle close to 0° (as shown in (b)). Figure 10 (c) shows). Correspondingly, the N,B-CQDs / C-MoS2 composite also exhibits a 0° contact angle (as shown in (c)). Figure 10 (d) illustrates that the introduction of N,B-CQDs further enhances the hydrophilicity of the material surface. This enhanced hydrophilicity helps achieve uniform and stable dispersion in polar PEG base oils, playing a crucial role in maintaining long-term lubrication performance.

[0060] Application Example 1 The 1-N,B-CQDs / C-MoS2 prepared in Example 1 was added to 0.2wt% PEG, and its tribological properties were investigated using a four-ball friction tester. The conditions for the four-ball friction test were: test load 392N, operating speed 1200 r / min, and operating time 60min. The average wear scar diameter was 0.48mm, and the average coefficient of friction was 0.033. The extreme pressure test was conducted according to GB / T 3142-82, with the test conditions being: time 10s and speed 1450rpm. The average extreme pressure value obtained was 932N.

[0061] The same test was performed with PEG replaced by PAO using the same method. The average wear scar diameter was 0.36 mm, the average coefficient of friction was 0.067, and the average extreme pressure was 821 N.

[0062] Application Comparative Example 1 MoS2 from Comparative Example 1 was added to 0.2 wt% PEG, and its tribological properties were investigated using a four-ball friction tester. The conditions for the four-ball friction test were: test load 392 N, operating speed 1200 r / min, and operating time 60 min. The average wear scar diameter obtained was 1.10 mm, and the average coefficient of friction was 0.086. The extreme pressure test was conducted according to GB / T 3142-82, with the test conditions being: time 10 s and speed 1450 rpm. The average extreme pressure value obtained was 600 N.

[0063] The same test was performed with PEG replaced by PAO using the same method. The average wear scar diameter was 1.15 mm, the average coefficient of friction was 0.089, and the average extreme pressure was 512 N.

[0064] Application Comparative Example 2 The C-MoS2 prepared in Comparative Example 2 was added to PEG with a concentration of 0.2 wt%, and its tribological properties were investigated using a four-ball friction tester. The conditions for the four-ball friction test were: test load 392 N, operating speed 1200 r / min, and operating time 60 min. The average wear scar diameter obtained was 1.03 mm, and the average coefficient of friction was 0.078. The extreme pressure test was conducted according to GB / T3142-82, with the test conditions being: time 10 s and speed 1450 rpm. The average extreme pressure value obtained was 650 N.

[0065] The same test was performed with PEG replaced by PAO using the same method. The average wear scar diameter was 0.67 mm, the average coefficient of friction was 0.088, and the average extreme pressure was 531 N.

[0066] Application Comparative Example 3 The N,B-CQDs prepared in Comparative Example 3 were added to 0.2 wt% PEG, and their tribological properties were investigated using a four-ball friction tester. The conditions for the four-ball friction test were: test load 392 N, operating speed 1200 r / min, and operating time 60 min. The average wear scar diameter was 0.65 mm, and the average coefficient of friction was 0.052. The extreme pressure test was conducted according to GB / T3142-82, with the test conditions being: time 10 s and speed 1450 rpm. The average extreme pressure value obtained was 710 N.

[0067] The same test was performed with PEG replaced by PAO using the same method. The average wear scar diameter was 0.79 mm, the average coefficient of friction was 0.068, and the average extreme pressure was 660 N.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, characterized in that, A combination of mechanical liquid-phase ultrasonic exfoliation and hydrothermal method was used to anchor nitrogen- and boron-co-doped carbon quantum dots onto a few-layer molybdenum disulfide substrate, resulting in a nitrogen- and boron-co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material.

2. The nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material according to claim 1, characterized in that, In the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material, spherical nitrogen- and boron co-doped carbon quantum dots are grown on nanosheet-like few-layer molybdenum disulfide, forming an on-sheet sphere heterojunction structure. The water contact angle of the nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material is 0°.

3. A method for preparing a nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of few-layer molybdenum disulfide nanosheets: molybdenum disulfide, cellulose nanocrystals and methanol were placed in a ball mill jar and ball milled at room temperature. The mixture after ball milling was dissolved in water and subjected to water bath ultrasonic treatment to obtain a dispersion of few-layer molybdenum disulfide nanosheets. The precipitate was collected by centrifugation and dried to obtain few-layer molybdenum disulfide nanosheets. (2) Preparation of nitrogen and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material: Citric acid, urea, boric acid and the few-layer molybdenum disulfide nanosheets obtained in step (1) were added to water and magnetically stirred until completely dissolved to obtain a uniform mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, precipitated and dried to obtain nitrogen and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material.

4. The method for preparing nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite materials according to claim 3, characterized in that, In step (1), the mass ratio of molybdenum disulfide to cellulose nanocrystals is 5-15:1; the mass ratio of cellulose nanocrystals to methanol is 1g:5-15mL.

5. The method for preparing nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite materials according to claim 3, characterized in that, In step (1), the water bath ultrasonic treatment is performed at a temperature of 25-28℃, a power of 350-400W, and a frequency of 35-40KHz for 1-3 hours.

6. The method for preparing nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite materials according to claim 3, characterized in that, In step (1), the ball mill rotates at a speed of 100-300 rpm for 30-60 min.

7. The method for preparing nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite materials according to claim 3, characterized in that, In step (2), the mass ratio of citric acid, urea, boric acid and few-layer molybdenum disulfide nanosheets is 0.1-0.3:0.1-0.3:0.1-0.3:

1.

8. The method for preparing nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite materials according to claim 3, characterized in that, In step (2), the temperature of the hydrothermal reaction is 170-190°C and the time is 11-13 hours.

9. The method for preparing nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite materials according to claim 3, characterized in that, In step (2), the magnetic stirring speed is 500-700 rpm and the time is 3-5 h.

10. The application of a nitrogen- and boron co-doped carbon quantum dot / few-layer molybdenum disulfide nanocomposite material as described in claim 1 or 2 as a lubricating oil additive.

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