Graphene composite lubricating additive and preparation method thereof

Abstract

The invention discloses a graphene composite lubricating additive and a preparation method thereof.The preparation method comprises the steps that a graphite rod serves as an anode, molybdenum disulfide serves as a cathode, and electrochemical intercalation is conducted in a fluorine-containing electrolyte solution; the mixture obtained through electrolysis is subjected to high-pressure homogenization treatment, and stripping and superfine grinding are achieved; and after washing and freeze-drying, calcining in an inert atmosphere to finally obtain the product. The preparation of nano graphene and molybdenum disulfide, fluorine functional group surface modification and composite assembly are realized in one step through a synergistic process of electrochemical intercalation, high-pressure homogenization and calcination; the method is simple in process, green, environment-friendly and pollution-free; in the prepared composite lubricating additive, the molybdenum disulfide nanosheets are loaded on the surface of the fluorine-functionalized graphene, the molybdenum disulfide nanosheets and the fluorine-functionalized graphene have a synergistic effect, and the obtained additive has excellent friction performance and high temperature resistance and is suitable for lubrication under severe working conditions such as high speed, heavy load and high temperature.

Description

Technical Field

[0001] This invention relates to the field of graphite material processing technology, specifically to a graphene composite lubricant and its preparation method. Background Technology

[0002] Lubricating additives are key components for improving the friction-reducing, anti-wear, and extreme pressure properties of lubricating oils (greases). Graphite, as a traditional solid lubricant, has carbon atoms arranged in an sp... 2 Hybridization forms a layered structure, with the layers bonded together by relatively weak van der Waals forces. During friction, these layered structures readily undergo shear slip, effectively reducing the coefficient of friction and improving the lubricating performance of the lubricating oil. Molybdenum disulfide (MoS2) is a two-dimensional layered material with a structure similar to graphite. It is also widely used as a lubricating additive due to its easy interlayer slip properties, exhibiting excellent friction-reducing and anti-wear effects.

[0003] However, the aforementioned materials also face numerous challenges in practical applications. Firstly, MoS2 exhibits poor dispersion stability in commonly used base oils, readily agglomerating and settling. This not only affects its lubricating performance but can also lead to oil passage blockage. More importantly, as modern industrial equipment evolves towards extreme operating conditions such as high speed, heavy load, and high temperature and pressure, more stringent requirements are placed on the performance of lubricating materials. Lubricating oil additives not only need to possess lower coefficients of friction and higher wear resistance but also excellent thermal stability and certain functionalities (such as electrical conductivity) to adapt to complex working environments. Single conventional additives, such as pure graphite or pure molybdenum disulfide, are insufficient to simultaneously meet all these comprehensive performance requirements.

[0004] To overcome these limitations, researchers have attempted to combine two or more materials or modify their surfaces to construct composite lubricants with novel structures and surface properties through synergistic effects. Combining graphene with molybdenum disulfide is considered an effective strategy. Graphene, with its extremely high strength and unique two-dimensional sheet structure, serves as an ideal supporting substrate, while loading molybdenum disulfide onto it fully leverages the synergistic lubricating advantages of both. Currently, common preparation methods in this field typically involve first preparing graphene oxide (GO) using strong oxidation processes such as the Hummers method, and then growing or loading MoS2 on GO using hydrothermal or solvothermal methods. However, these existing technical routes have significant drawbacks: firstly, the preparation process is lengthy and complex, involving multiple reaction steps; secondly, it usually uses hazardous chemicals such as strong acids and strong oxidants, generating large amounts of toxic and harmful wastewater, which is environmentally unfriendly; finally, the prepared composite materials often suffer from numerous structural defects, poor crystallinity, and limited surface modification effects, resulting in limited improvements in their thermal stability and lubrication performance.

[0005] Therefore, this invention provides a graphene composite lubricant and its preparation method, which uses chemical methods to modify the surface or load MoS2 to develop a simple, environmentally friendly method that can efficiently prepare a high-performance, highly dispersible graphene / molybdenum disulfide composite lubricant with excellent thermal stability. Summary of the Invention

[0006] The purpose of this invention is to provide a graphene composite lubricant and its preparation method, so as to develop a simple, environmentally friendly method that can efficiently prepare a high-performance, highly dispersible, and thermally stable graphene / molybdenum disulfide composite lubricant.

[0007] The objective of this invention is achieved through the following technical solution: A method for preparing a graphene composite lubricant includes the following steps: (1) Add electrolyte to the electrolytic cell, then insert the graphite rod anode and molybdenum disulfide cathode, and apply a DC voltage of 5~10V for electrolysis; (2) The electrolytic mixture obtained in step (1) is fed into a high-pressure homogenizer and homogenized for 5 to 10 cycles at a pressure of 1000 to 1500 bar. (3) The homogenized mixture from step (2) was filtered, washed with deionized water until neutral, and then freeze-dried to obtain the graphene / molybdenum disulfide composite precursor. (4) Place the precursor obtained in step (3) in a tube furnace, and under nitrogen atmosphere protection, heat it to 300-500°C at a rate of 2-5°C / min, keep it at the temperature for 1-3 hours, and cool it naturally to room temperature to obtain the graphene composite lubricant.

[0008] Preferably, in step (1), the electrolyte is a lithium tetrafluoroborate solution, a lithium hexafluorophosphate solution, or a mixture thereof with a concentration of 0.5~2 mol / L.

[0009] Preferably, in step (1), the electrolysis time is 2 to 6 hours.

[0010] Preferably, in step (2), the homogenization temperature of the high-pressure homogenizer is 10~30℃.

[0011] Preferably, in step (3), the freeze-drying conditions are: pre-freezing to below -50°C and freeze-drying for 24 to 48 hours.

[0012] Preferably, the flow rate of nitrogen gas in step (4) is 50~200 mL / min.

[0013] This application also claims a graphene composite lubricant prepared by the above-mentioned method for preparing graphene composite lubricants, wherein the graphene composite lubricant is a composite of graphene and molybdenum disulfide, and the graphene surface is grafted with fluorine-containing functional groups.

[0014] Preferably, in the graphene composite lubricant, molybdenum disulfide is loaded on the graphene surface in the form of nanosheets with a sheet size of 50~500nm.

[0015] Preferably, the fluorine-containing functional group includes at least one of -CF3, -CF2- or -F.

[0016] Preferably, the graphene composite lubricant has a coefficient of friction of less than 0.05 and a thermal decomposition temperature of more than 500°C.

[0017] Working mechanism of this invention: Using an electrolytic process and a suitable electrolyte, anions are inserted into the graphite layers of the anode, and cations are inserted into the molybdenum disulfide layers of the cathode. Then, through high-voltage homogenization, the graphite and molybdenum disulfide sheets are exfoliated and ultra-finely pulverized to obtain nano-graphene and nano-molybdenum disulfide. Simultaneously, during this process, fluorine-containing functional groups are grafted onto the graphene surface to achieve fluorine functionalization, and the graphene self-assembles with molybdenum disulfide to form a graphene / molybdenum disulfide composite structure, ultimately yielding a surface-modified graphene composite lubricant.

[0018] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention combines electrochemical intercalation with high-voltage homogeneous exfoliation technology to simultaneously realize the preparation of nano-graphene, in-situ fluorine functionalization modification of the surface, and composite assembly with molybdenum disulfide nanosheets in a coherent process system. The method is simple and avoids the cumbersome separation, purification and multiple reaction processes in traditional multi-step methods. It has high production efficiency and is easy to prepare on a large scale. 2. The entire preparation process of this invention does not require the use of strong acids, strong oxidants or other toxic and harmful chemical reagents, thus avoiding the generation of hazardous waste liquids containing acids and manganese from the source. It solves the problem of serious environmental pollution when preparing graphene composite materials by traditional redox methods, which is in line with the development direction of green chemistry. 3. This invention achieves synergistic and enhanced composite lubrication performance. The composite additive is not a simple physical mixture of graphene and molybdenum disulfide, but forms a stable composite structure through self-assembly. The two play a synergistic lubrication effect during friction, significantly reducing the coefficient of friction and exhibiting superior friction reduction and anti-wear performance compared to single components. 4. The product of this invention has excellent performance and high degree of functionalization. By introducing a fluorinated electrolyte during the electrolysis process, in-situ fluorine functional group grafting modification was successfully achieved on the graphene surface. This fluorination treatment not only greatly improves the dispersion stability of the composite additive in the base oil and prevents agglomeration and sedimentation, but also significantly improves the thermal stability and oxidation resistance of the material itself, enabling it to adapt to harsh working conditions at higher temperatures. 5. The product of this invention has a unique structure and broad application prospects. The nano-graphene and nano-molybdenum disulfide sheets prepared by this method have complete structures with few defects and a high degree of compositeness. The final product has excellent lubricity, high thermal conductivity and certain electrical conductivity. It can not only be used as a high-performance lubricating additive, but also provides a new option for the preparation of multifunctional composite materials. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be made based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the preparation process of the graphene composite lubricant in Example 1 of the present invention; Figure 2 This is a schematic diagram of the dispersion of the graphene composite lubricant in Example 1 of the present invention; Figure 3 This is a microstructure diagram of the graphene composite lubricant in Example 1 of the present invention. Detailed Implementation

[0021] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0022] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0023] Example 1 See appendix Figure 1 ~Appendix Figure 3 This embodiment provides a method for preparing a graphene composite lubricant, comprising the following steps: (1) Add a lithium tetrafluoroborate solution with a concentration of 0.5 mol / L to the electrolytic cell as the electrolyte, then insert a graphite rod anode and a molybdenum disulfide cathode, and apply a DC voltage of 5V for electrolysis for 3 hours; (2) The electrolytic mixture obtained in step (1) is fed into a high-pressure homogenizer. The homogenization temperature of the high-pressure homogenizer is 20°C, and the homogenization process is carried out 10 times under a pressure of 1200 bar. (3) The homogenized mixture from step (2) was filtered, washed with deionized water until neutral, and then freeze-dried for 24 hours to obtain the graphene / molybdenum disulfide composite precursor. (4) Place the precursor obtained in step (3) in a tube furnace, and under the protection of nitrogen atmosphere (nitrogen flow rate of 100 mL / min), heat it to 300°C at a rate of 3°C / min, keep it at the temperature for 2 hours, and cool it naturally to room temperature to obtain the graphene composite lubricant.

[0024] Example 2 This embodiment provides a method for preparing a graphene composite lubricant, comprising the following steps: (1) Add a lithium tetrafluoroborate solution with a concentration of 0.5 mol / L to the electrolytic cell as the electrolyte, then insert a graphite rod anode and a molybdenum disulfide cathode, and apply a DC voltage of 10V for electrolysis for 3 hours; (2) The electrolytic mixture obtained in step (1) is fed into a high-pressure homogenizer. The homogenization temperature of the high-pressure homogenizer is 20°C, and the homogenization process is carried out 8 times under a pressure of 1200 bar. (3) The homogenized mixture from step (2) was filtered, washed with deionized water until neutral, and then freeze-dried for 24 hours to obtain the graphene / molybdenum disulfide composite precursor. (4) Place the precursor obtained in step (3) in a tube furnace, and under the protection of nitrogen atmosphere (nitrogen flow rate of 100 mL / min), heat it to 400°C at a rate of 3°C / min, keep it at the temperature for 1 hour, and cool it naturally to room temperature to obtain the graphene composite lubricant.

[0025] Example 3 This embodiment provides a method for preparing a graphene composite lubricant, comprising the following steps: (1) Add a lithium hexafluorophosphate solution with a concentration of 0.5 mol / L to the electrolytic cell as the electrolyte, then insert a graphite rod anode and a molybdenum disulfide cathode, and apply a DC voltage of 5V for electrolysis for 3 hours; (2) The electrolytic mixture obtained in step (1) is fed into a high-pressure homogenizer. The homogenization temperature of the high-pressure homogenizer is 20°C, and the homogenization process is carried out 8 times under a pressure of 1500 bar. (3) The homogenized mixture from step (2) was filtered, washed with deionized water until neutral, and then freeze-dried for 24 hours to obtain the graphene / molybdenum disulfide composite precursor. (4) Place the precursor obtained in step (3) in a tube furnace, and under the protection of nitrogen atmosphere (nitrogen flow rate of 100 mL / min), heat it to 400°C at a rate of 3°C / min, keep it at the temperature for 2 hours, and cool it naturally to room temperature to obtain the graphene composite lubricant.

[0026] Example 4 This embodiment provides a method for preparing a graphene composite lubricant, comprising the following steps: (1) Add a mixture of lithium tetrafluoroborate solution and lithium hexafluorophosphate solution with a concentration of 0.5 mol / L to the electrolytic cell as the electrolyte (the volume ratio of lithium tetrafluoroborate solution to lithium hexafluorophosphate solution is 2:1), then insert the graphite rod anode and molybdenum disulfide cathode, and apply a DC voltage of 6V for electrolysis for 3 hours. (2) The electrolytic mixture obtained in step (1) is fed into a high-pressure homogenizer. The homogenization temperature of the high-pressure homogenizer is 20°C, and the homogenization process is carried out 5 times under a pressure of 1300 bar. (3) The homogenized mixture from step (2) was filtered, washed with deionized water until neutral, and then freeze-dried for 24 hours to obtain the graphene / molybdenum disulfide composite precursor. (4) Place the precursor obtained in step (3) in a tube furnace, and under the protection of nitrogen atmosphere (nitrogen flow rate of 100 mL / min), heat it to 350°C at a rate of 3°C / min, keep it at the temperature for 2 hours, and cool it naturally to room temperature to obtain the graphene composite lubricant.

[0027] Comparative Example 1 This comparative example is based on Example 1 above, and the similarities with Example 1 above will not be repeated. In this comparative example, a 0.5 mol / L lithium sulfate solution was added to the electrolytic cell as the electrolyte, and then a high-purity graphite rod anode and a high-purity molybdenum disulfide block cathode were inserted. Electrolysis was carried out for 3 hours with a voltage of 5V applied (using a fluorine-free electrolyte).

[0028] Comparative Example 2 In this comparative example, commercially available few-layer graphene nanosheets and commercially available molybdenum disulfide nanopowder were used. The graphene nanosheets and molybdenum disulfide nanopowder were weighed at a mass similar to that of the final product in Example 1. The two powders were placed in a beaker, ethanol solvent was added, and the mixture was sonicated for 2 hours to allow it to be initially dispersed and mixed. The mixture was filtered and dried to obtain a physically mixed graphene / molybdenum disulfide sample.

[0029] Comparative Example 3 This comparative example uses a commercially available graphene additive.

[0030] Comparative Example 4 This comparative example is a commercially available molybdenum disulfide additive.

[0031] 1.0% of the additives from Examples 1 to 4 and Comparative Examples 1 to 4 were added to the base oil, and the performance of the lubricating grease was tested under the same conditions. The test results are shown in Table 1.

[0032] Table 1 Test item Grinding marks / mm Drop point / °C Base oil 0.83 176 Example 1 0.56 236 Example 2 0.51 244 Example 3 0.54 230 Example 4 0.55 238 Comparative Example 1 0.57 206 Comparative Example 2 0.67 196 Comparative Example 3 0.64 204 Comparative Example 4 0.72 178

[0033] Wear marks are an important indicator of the anti-wear properties of grease; the smaller the wear marks, the better the anti-wear properties. Dropping point is an important indicator of the high-temperature resistance of grease; the higher the dropping point, the better the temperature resistance. As can be seen from Examples 1 to 4, the grease prepared using the additives of this invention has smaller wear marks and a higher dropping point; this indicates that the technical solution of this invention can significantly reduce the coefficient of friction of grease and enhance its anti-wear and high-temperature resistance properties.

[0034] As can be seen from Example 1 and Comparative Example 1 (physical mixing), the binding force between graphene and molybdenum disulfide in the physically mixed sample is weak, consisting only of van der Waals forces. This makes it extremely easy to separate during use, failing to produce a stable and continuous synergistic lubrication effect. Its dispersion stability and friction-reducing and anti-wear performance are expected to be far worse than all other examples. As can be seen from Example 1 and Comparative Example 2 (fluorine-free electrolyte), although the use of lithium sulfate electrolyte can achieve electrochemical intercalation and exfoliation, the product surface lacks fluorine-containing functional group grafts. Its anti-wear performance is significantly lower than that of Example 1 using a fluorine-containing electrolyte, thus demonstrating the necessity of fluorine functionalization for improving the overall performance of the product. As can be seen from Examples 1-4 and Comparative Examples 3-4, compared to single additives, the graphene composite additive of this invention has significantly better performance indicators in all aspects; and after fluorine functionalization modification, its high-temperature resistance is greatly improved.

[0035] In summary, this invention combines electrochemical intercalation with high-voltage homogeneous exfoliation technology, simultaneously achieving the preparation of nano-graphene, in-situ fluorine functionalization modification of its surface, and composite assembly with molybdenum disulfide nanosheets in a coherent process system. This method is simple, avoiding the cumbersome separation, purification, and multiple reaction processes of traditional multi-step methods, resulting in high production efficiency and ease of large-scale preparation. The entire preparation process of this invention does not require the use of strong acids, strong oxidants, or other toxic and harmful chemical reagents, thus avoiding the generation of hazardous waste liquids containing acids or manganese, solving the problem of severe environmental pollution in the preparation of graphene composite materials using traditional redox methods, and aligning with the development direction of green chemistry. This invention achieves synergistic composite lubrication performance; the resulting composite additive is not a simple physical mixture of graphene and molybdenum disulfide, but rather forms a stable composite structure through self-assembly. This invention exhibits a synergistic lubrication effect during friction, significantly reducing the coefficient of friction and demonstrating superior friction-reducing and anti-wear properties compared to single-component products. The product boasts excellent performance and a high degree of functionalization. By introducing a fluorinated electrolyte during electrolysis, in-situ grafting modification of fluorine functional groups onto the graphene surface was successfully achieved. This fluorination treatment not only greatly improves the dispersion stability of the composite additive in base oil, preventing agglomeration and sedimentation, but also significantly enhances the material's thermal stability and oxidation resistance, enabling it to withstand harsher operating conditions at higher temperatures. The product possesses a unique structure and broad application prospects. The nano-graphene and nano-molybdenum disulfide sheets prepared by this method have complete structures with few defects and a high degree of compositeness. The final product combines excellent lubricity, high thermal conductivity, and a certain degree of electrical conductivity, making it not only a high-performance lubricating additive but also a new option for preparing multifunctional composite materials.

[0036] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a graphene composite lubricant, characterized in that, Includes the following steps: (1) Add electrolyte to the electrolytic cell, then insert the graphite rod anode and molybdenum disulfide cathode, and apply a DC voltage of 5~10V for electrolysis; (2) The electrolytic mixture obtained in step (1) is fed into a high-pressure homogenizer and homogenized for 5 to 10 cycles at a pressure of 1000 to 1500 bar. (3) The homogenized mixture from step (2) was filtered, washed with deionized water until neutral, and then freeze-dried to obtain the graphene / molybdenum disulfide composite precursor. (4) Place the precursor obtained in step (3) in a tube furnace, and under nitrogen atmosphere protection, heat it to 300-500°C at a rate of 2-5°C / min, keep it at the temperature for 1-3 hours, and cool it naturally to room temperature to obtain the graphene composite lubricant.

2. The preparation method of the graphene composite lubricant according to claim 1, characterized in that, In step (1), the electrolyte is a lithium tetrafluoroborate solution, a lithium hexafluorophosphate solution, or a mixture of both with a concentration of 0.5~2 mol / L.

3. The preparation method of the graphene composite lubricant according to claim 1, characterized in that, In step (1), the electrolysis time is 2 to 6 hours.

4. The preparation method of the graphene composite lubricant according to claim 1, characterized in that, In step (2), the homogenization temperature of the high-pressure homogenizer is 10~30℃.

5. The method for preparing the graphene composite lubricant according to claim 1, characterized in that, In step (3), the freeze-drying conditions are: pre-freezing to below -50°C and freeze-drying for 24 to 48 hours.

6. The method for preparing the graphene composite lubricant according to claim 1, characterized in that, The flow rate of nitrogen gas in step (4) is 50~200 mL / min.

7. A graphene composite lubricant, characterized in that, The graphene composite lubricant is prepared by any one of claims 1 to 6, wherein the graphene composite lubricant is a composite of graphene and molybdenum disulfide, and the graphene surface is grafted with fluorine-containing functional groups.

8. The graphene composite lubricant according to claim 7, characterized in that, In the graphene composite lubricant, molybdenum disulfide is loaded onto the graphene surface in the form of nanosheets with a sheet size of 50~500nm.

9. The graphene composite lubricant according to claim 7, characterized in that, The fluorine-containing functional group includes at least one of -CF3, -CF2- or -F.

10. The graphene composite lubricant according to claim 7, characterized in that, The graphene composite lubricant has a friction coefficient of less than 0.05 and a thermal decomposition temperature of more than 500℃.

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