A carbon quantum dot / molybdenum disulfide composite lubricant additive, its preparation method and application

Abstract

This invention provides a carbon quantum dot / molybdenum disulfide composite lubricant additive, its preparation method, and its application. Sodium hydroxide is slowly added to acetaldehyde, and after stirring, the reaction mixture is ultrasonically treated with dilute hydrochloric acid until it becomes flocculent. The flocculent product is washed with water until the washing liquid is neutral, and then freeze-dried to obtain carbon quantum dots. 1-Hexadecyl-3-methylimidazole bromide and molybdenum disulfide are added to deionized water to obtain a molybdenum disulfide dispersion. The carbon quantum dots and molybdenum disulfide dispersion are mixed at a mass ratio of (1~3):1, and then placed in an autoclave for hydrothermal reaction at 150~180℃ to obtain an initial suspension. After centrifugation, the supernatant is collected and freeze-dried to obtain the carbon quantum dot / molybdenum disulfide composite lubricant additive. It rapidly forms a continuous, dense, and self-healing lubricating film in liquid environments such as water and oil. Through the synergistic effect of the layered slip of MoS2 and the "nano-ball" effect of carbon quantum dots, it achieves a short break-in period, low coefficient of friction, and excellent wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and relates to composite materials and their preparation methods, specifically to a carbon quantum dot / molybdenum disulfide composite lubricant additive, its preparation method and application. Background Technology

[0002] As modern industrial equipment develops towards higher precision, higher load, and more complex operating conditions, the demand for mechanical systems operating under high loads, high speeds, and extreme temperature and humidity environments is increasing. Under these conditions, friction and wear problems become particularly prominent. In liquid lubrication systems, a long break-in period at the lubrication interface often leads to a high initial friction coefficient, accelerated surface wear, and a slow lubricating film nucleation rate. This not only reduces lubrication efficiency but also accelerates fatigue and failure of component surfaces. Related research indicates that the interfacial reaction process and film evolution characteristics during the break-in period have a decisive impact on the long-term stability of the lubrication system. Therefore, there is an urgent need to develop a high-efficiency lubricating material that can achieve rapid lubrication film formation and stable maintenance within a short break-in period to improve the energy efficiency and service reliability of mechanical systems.

[0003] Carbon quantum dots (CDs) are typical zero-dimensional carbon-based nanomaterials that have emerged in recent years, possessing ultra-small particle size, excellent water solubility, tunable surface functional groups, and good chemical stability. Their surface polar functional groups, such as hydroxyl and carboxyl groups, enhance their dispersion stability in polar media and can bind to metal surfaces through hydrogen bonding, electrostatic adsorption, or coordination to form a dense lubricating film, significantly reducing the coefficient of friction and wear rate. However, carbon quantum dots used alone lack physical support and self-healing capabilities. Under complex frictional environments (such as water-based, high-speed, or high-load conditions), they are easily squeezed out of the friction interface, leading to a decrease in friction-reducing and wear-resistant effects, making it difficult to simultaneously achieve both a low coefficient of friction and long-life stable wear resistance.

[0004] Molybdenum disulfide (MoS2) is a typical two-dimensional layered material, with weak van der Waals forces binding the layers together. During friction, interlayer slip easily occurs, resulting in excellent friction reduction and wear resistance. Simultaneously, the surface of MoS2 is rich in active sites, allowing it to form composite structures with various functional materials. However, it is prone to agglomeration and sedimentation in liquid lubrication and is limited by oxidation failure. Therefore, combining carbon quantum dots (CDs) with molybdenum disulfide (MoS2) can fully leverage the structural advantages of both: the surface active sites of CDs can inhibit the lamellar agglomeration of MoS2 and slow down its oxidation, while the surface functional groups can enhance the interfacial bonding and dispersibility of the composite system. The layered structure of MoS2 provides CDs with low-shear slip channels and mechanical support, thereby achieving a short break-in period and more stable friction reduction and wear resistance in a liquid lubrication environment.

[0005] Patent CN112316958A discloses a carbon quantum dot / titanium dioxide / molybdenum disulfide composite optical material. Although this material exhibits uniform composite structure and good stability, its preparation process involves multiple organic solvent changes and pH adjustments, resulting in high production costs. Patent CN112056310A discloses a DFNS-loaded carbon quantum dot / molybdenum disulfide quantum dot composite material, its preparation method, and its applications. While this improves the stability of the composite material, DFNS, being a porous silicon structure, is prone to cracking or wear under high-load friction, leading to a higher risk of quantum dot desorption. Furthermore, the preparation conditions are stringent and the process is complex. Summary of the Invention

[0006] The present invention aims to provide a carbon quantum dot / molybdenum disulfide composite material lubricant additive, its preparation method and application, which can rapidly form a continuous, dense and self-healing lubricating film in liquid environments such as water and oil. Through the synergistic effect of the layered slip of MoS2 and the "nanoball" effect of carbon quantum dots, it achieves a short break-in period, low coefficient of friction and excellent wear resistance.

[0007] This invention is achieved through the following technical solution: This invention provides an application of a carbon quantum dot / molybdenum disulfide composite lubricant additive in lubricating materials.

[0008] The present invention also provides a carbon quantum dot / molybdenum disulfide composite lubricant additive, wherein the structure of the carbon quantum dot / molybdenum disulfide composite lubricant additive is that carbon quantum dots with a particle size of 2.4-2.6 nm are loaded on molybdenum disulfide nanosheets with a lateral size of 100-300 nm.

[0009] This invention also provides a method for preparing a carbon quantum dot / molybdenum disulfide composite lubricant, comprising the following steps: Step 1: Weigh 5-7 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath until it becomes flocculent. Wash the flocculent product with water until the washing solution is neutral. Freeze-dry to obtain carbon quantum dots. Step 2: Weigh 200-400 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water, then perform ultrasonic dispersion to obtain molybdenum disulfide dispersion; Step 3: Disperse the freeze-dried carbon quantum dots and molybdenum disulfide dispersion by ultrasonication at a mass ratio of (1~3):1, then place them in an autoclave and carry out a hydrothermal reaction at 150~180℃ to obtain an initial suspension. After centrifugation, take the supernatant and freeze-dry it to obtain a carbon quantum dot / molybdenum disulfide composite lubricant additive.

[0010] Furthermore, the ultrasonic treatment time in step 1 is 25-30 minutes.

[0011] Furthermore, the ultrasonic dispersion time in step 2 is 40-45 minutes.

[0012] Furthermore, the ultrasonic dispersion time in step 3 is 15-20 minutes.

[0013] Furthermore, the hydrothermal reaction time in step 3 is 18-24 hours.

[0014] Furthermore, the centrifugation speed in step 3 is 2500~3000 rpm, and the centrifugation time is 20~30 min.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention prepares CDs through conjugation and disproportionation reactions. The CDs have branched chains and abundant oxygen-containing functional groups such as hydroxyl and carboxyl groups on their surface. These polar groups form stable physical adsorption and chemical anchoring with MoS2 sheets, effectively filling interlayer gaps and inhibiting nanosheet aggregation, thus significantly improving dispersibility in polar or weakly polar media. Simultaneously, S-vacancies and other defect sites on the surface and edges of MoS2 sheets can bind to functional groups on the CDs surface, further enhancing interfacial bonding. The layered structure of MoS2 provides low-shear slip channels and mechanical support for the CDs. The spherical structure of the CDs exerts a "nanoball" effect at the friction interface. The synergistic effect of both generates a continuous, dense, and self-healing lubricating film during friction, significantly reducing the coefficient of friction and enhancing wear resistance. This composite material exhibits short break-in periods and long-lasting lubrication in water, oil, and other liquid environments, possessing multiple advantages such as green preparation, excellent performance, and industrial application. The preparation method of this invention is simple, requires no extra impurity removal steps, uses green, environmentally friendly and pollution-free solvents throughout the process, is easy to control, has low preparation cost, and is suitable for industrial production. Attached Figure Description

[0016] Figure 1 The image shows the XRD patterns of carbon quantum dots, molybdenum disulfide, and the prepared composite lubricant additive in Example 1. Figure 2 Raman diagrams of carbon quantum dots, molybdenum disulfide, and the prepared composite lubricant additive in Example 1; Figure 3 The friction coefficient curves of the carbon quantum dot / molybdenum disulfide composite lubricant additives prepared in Examples 1-3 under pure water friction environment are shown. Figure 4 The friction coefficient curves of the carbon quantum dot / molybdenum disulfide composite lubricating additives prepared in Examples 1-3 under oil friction environment are shown. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. These descriptions are intended to explain the invention and not to limit it.

[0018] Example 1: A method for preparing a carbon quantum dot / molybdenum disulfide composite lubricant, comprising the following steps: Step 1: Weigh 5 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath for 25 min until it becomes flocculent. Wash the flocculent product with water until the washing solution is neutral. Freeze dry to obtain carbon quantum dots. Step 2: Weigh 200 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water. Then, ultrasonically disperse the mixture for 40 min to obtain a molybdenum disulfide dispersion. Step 3: The freeze-dried carbon quantum dots and molybdenum disulfide dispersion were ultrasonically dispersed for 15 min at a mass ratio of 1:1. Then, they were placed in an autoclave and subjected to hydrothermal reaction at 180°C for 18 h to obtain an initial suspension. After centrifugation at 2500 rpm for 30 min, the supernatant was collected and freeze-dried to obtain a carbon quantum dot / molybdenum disulfide composite lubricant additive.

[0019] X-ray diffraction (XRD) analysis was performed on the carbon quantum dots, molybdenum disulfide, and their composite lubricant additives in Example 1 to observe the crystal information and elemental composition of the samples, such as... Figure 1 As shown, MoS2 retains all the typical hexagonal phase MoS2 diffraction characteristic peaks in the XRD pattern, indicating that the method did not destroy its crystal structure. The (002) crystal plane peak at 14.4° is significantly shifted to the right; this interlayer spacing expansion is attributed to the successful embedding of CDs. The expanded interlayer space is beneficial for the stable loading of CDs. It can be seen that the characteristic diffraction peaks of both MoS2 and CDs appear in the XRD pattern, indicating that the composite is composed of molybdenum disulfide and carbon quantum dots.

[0020] Raman spectroscopy analysis of the carbon quantum dots, molybdenum disulfide, and their composite lubricant additives in Example 1 further verified the formation of the composite structure, such as... Figure 2 As shown, it can be seen that the MoS2 and CDs@MoS2 samples are at approximately 373 cm⁻¹ -1 With 401cm -1 The locations correspond to E respectively 2g 1 and A 1g The vibrational peaks are derived from in-plane vibrations of Mo and S atoms, and from out-of-plane vibrations of CDs@MoS2 at 1158 cm⁻¹. -1With 1592 cm -1 The presence of distinct D and G band characteristic peaks at the point corresponds to the defect structure of sp³ hybrid carbon and the graphitization domain of sp² carbon in CDs, respectively, further confirming the successful recombination of CDs on the MoS2 surface.

[0021] Example 2: A method for preparing a carbon quantum dot / molybdenum disulfide composite lubricant, comprising the following steps: Step 1: Weigh 7 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath for 28 min until it becomes flocculent. Wash the flocculent product with water until the washing solution is neutral. Freeze dry to obtain carbon quantum dots. Step 2: Weigh 300 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water. Then, ultrasonically disperse the mixture for 43 min to obtain a molybdenum disulfide dispersion. Step 3: Disperse carbon quantum dots and molybdenum disulfide dispersion by ultrasonication for 18 min at a mass ratio of 2:1, then place them in an autoclave and carry out hydrothermal reaction at 165℃ for 20 h to obtain an initial suspension. After centrifugation at 3000 rpm for 20 min, take the supernatant and freeze-dry it to obtain carbon quantum dots / molybdenum disulfide composite lubricant additive.

[0022] Example 3: A method for preparing a carbon quantum dot / molybdenum disulfide composite lubricant, comprising the following steps: Step 1: Weigh 6 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath for 30 min until it becomes flocculent. Wash the flocculent product with water until the washing solution is neutral. Freeze dry to obtain carbon quantum dots. Step 2: Weigh 400 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water. Then, ultrasonically disperse the mixture for 45 min to obtain a molybdenum disulfide dispersion. Step 3: Disperse carbon quantum dots and molybdenum disulfide dispersion by ultrasonication for 20 min at a mass ratio of 3:1, then place them in an autoclave and carry out hydrothermal reaction at 150℃ for 24 h to obtain an initial suspension. After centrifugation at 2800 rpm for 25 min, take the supernatant and freeze-dry it to obtain a carbon quantum dot / molybdenum disulfide composite lubricant additive.

[0023] To evaluate the tribological properties of the prepared carbon quantum dot / molybdenum disulfide composite lubricant, friction and wear tests were conducted in pure water and PAO10 base oil, respectively. Figure 3As shown, in a pure water environment, the average friction coefficients of the carbon quantum dot / molybdenum disulfide composite lubricant additives prepared in Examples 1-3 were 0.134, 0.096, and 0.086, respectively. Figure 4 As shown, in PAO10 base oil, the average friction coefficients of the carbon quantum dot / molybdenum disulfide composite lubricant additives prepared in Examples 1-3 were 0.071, 0.048, and 0.032, respectively. The break-in period was significantly shortened from the traditional hundreds of seconds to less than 60 seconds. This is because carbon quantum dots exert a "nanoball" effect at the interface, rolling between micro-dimples to disperse contact stress and significantly reduce shear energy loss caused by moving friction. The two-dimensional layered structure of molybdenum disulfide provides low-shear slip channels, effectively reducing interlayer shear strength during moving friction. Carbon quantum dots and molybdenum disulfide synergistically construct a continuous and dense lubricating film. This synergistic mechanism not only shortens the break-in period but also achieves a dual friction reduction effect of sliding and rolling friction. This composite lubricant additive has excellent lubrication performance and can effectively reduce friction and wear.

[0024] Example 4: A method for preparing a carbon quantum dot / molybdenum disulfide composite lubricant, comprising the following steps: Step 1: Weigh 6 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath for 30 min until it becomes flocculent. Wash the flocculent product with water until the washing solution is neutral. Freeze dry to obtain carbon quantum dots. Step 2: Weigh 250 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water. Then, ultrasonically disperse the mixture for 42 min to obtain a molybdenum disulfide dispersion. Step 3: Disperse carbon quantum dots and molybdenum disulfide dispersion by ultrasonication for 15 min at a mass ratio of 1.5:1. Then, place them in an autoclave and carry out hydrothermal reaction at 160℃ for 21 h to obtain an initial suspension. After centrifugation at 3000 rpm for 28 min, take the supernatant and freeze-dry it to obtain carbon quantum dots / molybdenum disulfide composite lubricant additive.

[0025] Example 5: A method for preparing a carbon quantum dot / molybdenum disulfide composite lubricant, comprising the following steps: Step 1: Weigh 6 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath for 30 min until it becomes flocculent. Wash the flocculent product with water until the washing solution is neutral. Freeze dry to obtain carbon quantum dots. Step 2: Weigh 350 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water. Then, ultrasonically disperse the mixture for 45 min to obtain a molybdenum disulfide dispersion. Step 3: Disperse carbon quantum dots and molybdenum disulfide dispersion by ultrasonication for 20 min at a mass ratio of 2.5:1. Then, place them in an autoclave and carry out hydrothermal reaction at 180℃ for 22 h to obtain an initial suspension. After centrifugation at 3000 rpm for 25 min, take the supernatant and freeze-dry it to obtain a carbon quantum dot / molybdenum disulfide composite lubricant additive.

Claims

1. Application of a carbon quantum dot / molybdenum disulfide composite lubricant additive in lubricating materials.

2. The carbon quantum dot / molybdenum disulfide composite lubricant additive as described in claim 1, characterized in that, The structure of the carbon quantum dot / molybdenum disulfide composite lubricant additive is that carbon quantum dots with a particle size of 2.4-2.6 nm are loaded on molybdenum disulfide nanosheets with a lateral size of 100-300 nm.

3. The preparation method of the carbon quantum dot / molybdenum disulfide composite lubricant additive as described in claim 1, characterized in that, Includes the following steps: Step 1: Weigh 5-7 g of sodium hydroxide and slowly add it to 20 mL of acetaldehyde. Stir and mix evenly to obtain a reaction mixture. Use dilute hydrochloric acid to sonicate the obtained reaction mixture in a water bath until it becomes flocculent. Wash the flocculent product with water until it is neutral and freeze-dry to obtain carbon quantum dots. Step 2: Weigh 200-400 mg of 1-hexadecyl-3-methylimidazole bromide and 500 mg of molybdenum disulfide and add them to 40 mL of deionized water, then perform ultrasonic dispersion to obtain molybdenum disulfide dispersion; Step 3: Disperse the freeze-dried carbon quantum dots and molybdenum disulfide dispersion by ultrasonication at a mass ratio of (1~3):1, then place them in an autoclave and carry out a hydrothermal reaction at 150~180℃ to obtain an initial suspension. After centrifugation, take the supernatant and freeze-dry it to obtain a carbon quantum dot / molybdenum disulfide composite lubricant additive.

4. The preparation method of the carbon quantum dot / molybdenum disulfide composite lubricant additive according to claim 3, characterized in that, The ultrasonic treatment time in step 1 is 25-30 minutes.

5. The preparation method of the carbon quantum dot / molybdenum disulfide composite lubricant additive according to claim 3, characterized in that, The ultrasonic dispersion time in step 2 is 40~45 min.

6. The preparation method of the carbon quantum dot / molybdenum disulfide composite lubricant additive according to claim 3, characterized in that, The ultrasonic dispersion time in step 3 is 15-20 min.

7. The preparation method of a carbon quantum dot / molybdenum disulfide composite lubricant additive according to claim 3, characterized in that, The hydrothermal reaction in step 3 takes 18-24 hours.

8. The preparation method of the carbon quantum dot / molybdenum disulfide composite lubricant additive according to claim 3, characterized in that, The centrifugation speed in step 3 is 2500~3000 rpm, and the centrifugation time is 20~30 min.

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