Marine composite lubricating material with multi-fuel compatibility as well as preparation method and application of marine composite lubricating material

Abstract

The invention provides a marine composite lubricating material with multi-fuel compatibility and a preparation method and application thereof, and relates to the technical field of lubricating materials. The preparation method of the composite lubricating material comprises the following steps: S1, stirring and dissolving a carbon source and a nitrogen source in deionized water, and carrying out hydrothermal reaction to prepare NCDs; s2, dissolving NCDs in a Tris-HCl buffer system, adding dopamine hydrochloride, and stirring in a dark place to prepare NCDs / PDA (Personal Digital Assistant); s3, the NCDs / PDA is dissolved in deionized water, a molybdenum source and a sulfur source are added, and after a hydrothermal reaction, the NCDs / PDA / MoS2 composite lubricating material is prepared. According to the prepared composite lubricating material, through the nano filling effect of the NCDs, the interface coating regulation and control effect of the PDA and the synergistic effect between interlayer slippage mechanisms of the vertically-growing MoS2 nanoflowers, the lubricating performance under a multi-fuel system is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lubricating materials, and in particular to a marine composite lubricating material with multi-fuel compatibility, a preparation method thereof, and applications thereof. Background Art

[0002] With stricter sulfur oxide emissions limits and the advancement of low-carbon fuel policies, low-sulfur fuel oil, biodiesel, and methanol fuel have become the primary fuel options for ocean-going shipping. However, the physical and chemical properties of these three fuels pose significant challenges to the friction and wear performance of the cylinder liner-piston ring assembly of main engine engines. Low-sulfur fuel oil significantly reduces its natural lubrication properties due to desulfurization. Its low viscosity, coupled with its difficulty forming a stable oil film, can easily lead to boundary lubrication failure under high-load conditions. Furthermore, traditional highly alkaline cylinder oils are poorly compatible with low-sulfur fuel oils, and residual alkaline substances can easily cause the oil film on the cylinder liner surface to break down, further exacerbating wear. Biofuels have a high oxygen content and are highly hygroscopic, but the free fatty acids and glycerides produced during their combustion can cause acidic corrosion. Their low viscosity further weakens lubrication performance, leading to abnormal wear of plunger components and injector sticking. Methanol fuel combustion produces highly corrosive products such as formic acid. Its extremely low viscosity reduces the load-bearing capacity of the oil film, easily causing severe boundary lubrication failure.

[0003] The above-mentioned issues place higher demands on existing lubrication systems. However, current lubricant additive technology still has significant drawbacks: traditional additives (such as calcium alkyl salicylate and zinc dialkyl dithiophosphate) have limited functionality and lack multi-fuel compatibility. While high-alkalinity detergents can effectively neutralize sulfuric acid, their excessive ash content can easily clog the DPF (Diesel Particulate Filter) and does not match the alkalinity requirements of low-sulfur fuels. Furthermore, the oxidation byproducts of biodiesel and the highly corrosive nature of methanol fuel accelerate lubricant degradation, resulting in nonlinear degradation of lubrication performance. Especially when dealing with methanol fuel, existing additives offer little effective protection against issues such as boundary lubrication failure caused by formic acid.

[0004] Therefore, there is an urgent need to develop a composite additive that has high environmental adaptability, multi-scale lubrication mechanism and dynamic response function. Summary of the Invention

[0005] In view of this, the present invention proposes a marine composite lubricating material with multi-fuel compatibility, its preparation method and application. By self-assembling nitrogen-doped carbon quantum dots (NCDs) and polydopamine (PDA) to form a core-shell structure, and vertically growing MoS2 nanoflowers on its surface, a heterogeneous composite system with a synergistic lubrication effect is constructed, which significantly improves its lubrication stability and corrosion resistance in marine low-sulfur fuel, marine biofuel and marine methanol (fuel).

[0006] The technical solution of the present invention is achieved as follows:

[0007] In a first aspect, the present invention provides a method for preparing a marine composite lubricating material having multi-fuel compatibility, comprising the following steps:

[0008] S1. Dissolve the carbon source and nitrogen source in deionized water with stirring, perform hydrothermal reaction, cool, centrifuge, filter, dialysis purification, and freeze-dry to obtain NCDs.

[0009] S2, dissolving NCDs in a Tris-HCl buffer system, adding dopamine hydrochloride, stirring in the dark, washing, and drying to prepare NCDs / PDA;

[0010] S3. Dissolve NCDs / PDA in deionized water, add a molybdenum source and a sulfur source, perform a hydrothermal reaction, cool, centrifuge, wash, and dry to obtain an NCDs / PDA / MoS2 composite lubricating material.

[0011] By adopting the above technical solution, the present invention realizes the precise control of the three-dimensional structure and interfacial chemical bonding between NCDs, PDA and MoS2 based on the gradient hydrothermal coupling and in-situ self-assembly strategy. Specifically, first, glucose and urea are used as carbon sources and nitrogen sources, and high NCDs are synthesized through a one-step hydrothermal carbonization reaction. The rich hydroxyl and amino functional groups on the surface provide a large number of active anchoring sites for subsequent PDA coating; then, dopamine hydrochloride is added to the Tris-HCl buffer system, and dopamine is induced to self-polymerize in situ under a weakly alkaline environment. Through π-π conjugation and hydrogen bond interaction, a uniform and dense PDA coating layer is formed on the surface of NCDs, effectively avoiding the problem of component interface peeling in traditional physical mixing methods; finally, under hydrothermal conditions at 200°C, thiourea is used as a sulfur source and structure directing agent to decompose the H2S and MoO4 2- A topological transformation reaction occurs, and MoS2 nanoflower structures with abundant edge sulfur active sites grow vertically on the NCDs / PDA surface.

[0012] The preparation method of the present invention can achieve strong interactions between multi-component heterogeneous interfaces, including the formation of chemical bonds such as Mo-N bonds and CS bonds, without the need to introduce complex templates or inert gas protection. It significantly improves the structural stability of the composite lubricating material and overcomes the problems of loose components and weak interface bonding commonly seen in traditional step-by-step synthesis methods. It has good application prospects.

[0013] Furthermore, in step S1, the carbon source is glucose, the nitrogen source is urea, and the mass ratio of the glucose to the urea is 1:1.

[0014] Furthermore, the stirring time is 15 to 30 minutes.

[0015] Furthermore, the conditions of the hydrothermal reaction include: temperature of 190° C. and time of 10 to 12 hours.

[0016] Furthermore, the centrifugal conditions include: a rotation speed of 8000 to 10000 rpm and a time of 15 to 20 minutes.

[0017] Furthermore, the dialysis purification conditions include: a molecular weight cut-off of 1000 Da and a time of 24 to 30 hours.

[0018] Furthermore, the freeze-drying time is 48 to 72 hours.

[0019] Furthermore, the particle size of the NCDs is 2 to 10 nm.

[0020] Furthermore, in step S2, the pH value of the Tris-HCl buffer system is 8.5.

[0021] Furthermore, the mass ratio of the NCDs to the dopamine hydrochloride is 1:2.

[0022] Furthermore, the conditions for stirring in the dark include: a temperature of 20 to 30° C. and a time of 24 to 48 hours.

[0023] Furthermore, the drying temperature is 60-80° C., and the drying time is 24-48 hours.

[0024] Furthermore, in step S3, the molybdenum source is ammonium molybdate, the sulfur source is thiourea, and the ratio of the number of molybdenum atoms in the ammonium molybdate to the number of sulfur atoms in the thiourea is 1:4.

[0025] Furthermore, the usage ratio of the NCDs / PDA, the ammonium molybdate and the thiourea is 0.16g-0.2g:2.4g:4.5g.

[0026] Furthermore, the conditions of the hydrothermal reaction include: temperature of 200° C. and time of 20 to 24 hours.

[0027] Furthermore, the centrifugal conditions include: a rotation speed of 3000 to 5000 rpm and a time of 15 to 30 minutes.

[0028] Furthermore, the drying temperature is 60-80° C., and the drying time is 24-48 hours.

[0029] In the second aspect, the present invention relates to a marine composite lubricating material with multi-fuel compatibility prepared by the above-mentioned preparation method, wherein the composite lubricating material includes NCDs / PDA with a core-shell structure, and MoS2 nanoflowers vertically grown on the surface of the NCDs / PDA with a core-shell structure.

[0030] In a third aspect, the present invention relates to the use of the above-mentioned marine composite lubricating material with multi-fuel compatibility in a marine power system using low-sulfur fuel, biofuel and methanol fuel as driving energy.

[0031] By adopting this technical solution, the strong adhesion and chemical stability of PDA effectively enhances the dispersion stability of NCDs / MoS2 in oxygenated biofuels and low-viscosity methanol. Furthermore, the PDA coating isolates MoS2 from direct contact with oxygen, inhibiting its oxidation at high temperatures to form the non-lubricating phase MoO3, thereby maintaining the high-temperature lubrication properties of the layered structure. Furthermore, the nanofilling effect of NCDs dynamically repairs microcracks on the friction surface. The interlayer slip mechanism of MoS2 nanoflowers synergizes with the rolling bearing effect of NCDs to reduce the friction coefficient. Furthermore, the nitrogen-containing functional groups on the NCDs surface preferentially adsorb acidic substances, reducing the direct corrosion of the metal matrix by formic acid, a methanol combustion product. This allows for integrated control of long-term friction reduction, anti-wear, and anti-corrosion functions under complex operating conditions with multiple fuel types.

[0032] Specifically, the NCDs / PDA / MoS2 composite lubricating material prepared by the present invention achieves efficient friction reduction and anti-wear effects through the synergistic effect of multiple components. Its core mechanism is that the active edge sites exposed by the vertically grown MoS2 nanoflowers form a low shear strength transfer film through the interlayer slip effect during the friction process, thereby significantly reducing the friction coefficient; at the same time, NCDs, with their high hardness and nanometer size characteristics, play a dual role of "nano-balls" and "filling and repairing" at the micro-defects on the surface of the friction pair, effectively reducing the sliding resistance through the rolling bearing effect, and utilizing the nitrogen functional groups (such as pyridinic nitrogen) enriched on its surface to preferentially adsorb acidic corrosion products, thereby inhibiting the corrosion of substances such as formic acid on the metal matrix. The PDA coating layer enhances the interfacial bonding force between NCDs and MoS2 through covalent bonds, avoiding the agglomeration and shedding of nanomaterials during use; at the same time, its excellent adhesion properties can induce the directional arrangement of MoS2 nanoflowers during dynamic friction, thereby forming a dense and stable composite lubricating film at the friction interface. In addition, the sulfur vacancies of MoS2 and the carbon defects of NCDs can synergistically capture free radicals generated on the friction pair surface, inhibiting the degradation of the lubricating film caused by biodiesel oxidation byproducts, thereby achieving integrated optimization of long-term friction reduction, corrosion resistance and self-repairing functions under high temperature, high shear and multi-fuel complex working conditions.

[0033] The multi-fuel compatible marine composite lubricating material of the present invention, its preparation method, and its application have the following beneficial effects compared with the prior art:

[0034] The NCDs / PDA / MoS2 composite lubricating material provided by the present invention significantly improves the lubrication performance in a multi-fuel system through the synergistic effect of the nanofilling effect of NCDs, the interface coating regulation effect of PDA, and the interlayer slip mechanism of vertically grown MoS2 nanoflowers.

[0035] In the composite lubricating material prepared by the present invention, the PDA coating layer enhances the interfacial adhesion between NCDs and MoS2 through chemical bonding, effectively inhibiting the oxidative deactivation of the MoS2 nanoflowers at high temperatures. Its excellent adhesion effectively improves the dispersion stability of the nanomaterial in low-sulfur fuel, biofuel, and methanol fuel. Furthermore, the vertically grown MoS2 nanoflower structure exposes more active edge sites. Combined with the preferential adsorption properties of the nitrogen functional groups of the NCDs for acidic corrosion products and the synergistic free radical capture effect of the NCDs' defect sites and MoS2 sulfur vacancies, this effectively inhibits the damage of biodiesel oxidation byproducts to the lubricating film, achieving long-term anti-wear and dynamic self-repair functions under various fuel operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a scanning electron microscope image of the NCDs / PDA / MoS2 composite lubricating material prepared in Example 1 of the present invention;

[0038] Figure 2 This is a transmission electron micrograph of the NCDs / PDA / MoS2 composite lubricating material prepared in Example 1 of the present invention;

[0039] Figure 3 The XRD patterns of the products obtained in each step of Example 2 of the present invention are as follows;

[0040] Figure 4 Element distribution diagram of the NCDs / PDA / MoS2 composite lubricating material prepared in Example 3 of the present invention;

[0041] Figure 5 These are test results of the cylinder liner-piston ring friction test of the NCDs / PDA / MoS2 composite lubricating material of the present invention under different fuel working conditions; in the figure, a is a test result diagram of the NCDs / PDA / MoS2 composite lubricating material of the present invention in marine low-sulfur fuel, b is a test result diagram of the NCDs / PDA / MoS2 composite lubricating material of the present invention in marine biofuel, c is a test result diagram of the NCDs / PDA / MoS2 composite lubricating material of the present invention in marine methanol, and d is a comparison diagram of the changes in friction coefficient under different fuel working conditions. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] The present invention will be further described below with reference to specific examples, but the scope of protection of the present invention is not limited by the following examples. Unless otherwise specified, the materials mainly involved in the following examples are conventional commercial products.

[0044] Example 1

[0045] The method for preparing a marine composite lubricating material with multi-fuel compatibility provided in this embodiment comprises the following steps:

[0046] S1. Disperse glucose and urea in a 1:1 mass ratio in 60 mL of deionized water and stir for 15 minutes until completely dissolved. Pour the dispersion into a Teflon-lined container and place it in a hydrothermal reactor. Place the reactor in an oven at 190°C for 10 hours. After the reaction is complete and allowed to cool naturally, remove the reaction solution and centrifuge it in a high-speed centrifuge at 10,000 rpm for 10 minutes to obtain the supernatant. Filter the supernatant through a 0.22 μm filter membrane and dialysis the filtrate against pure water (dialysis bag, 1000 Da molecular weight) for 30 hours. After purification, freeze-dry for 72 hours to obtain NCDs with a particle size of 2 to 10 nm.

[0047] S2. Disperse the NCDs prepared in step S1 in a Tris-HCl (pH = 8.5) buffer system, add dopamine hydrochloride twice the mass of the NCDs, and stir at 20°C in the dark for 48 hours. After the reaction, wash the mixture three times with anhydrous ethanol and deionized water, and dry it at 80°C for 24 hours to obtain NCDs / PDA.

[0048] S3. Disperse 0.2 g of NCDs / PDA in 70 mL of deionized water. Add 2.4 g of ammonium molybdate and 4.5 g of thiourea to the NCDs / PDA dispersion. Pour the dispersion into a Teflon-lined container and place it in a hydrothermal reactor. Place the reactor in an oven at 200°C for 24 hours. After the reaction is complete and allowed to cool naturally, remove the reaction solution and centrifuge it in a high-speed centrifuge at 3000 rpm for 10 minutes. Wash the mixture three times with alternating ethanol and deionized water, and dry it at 80°C for 24 hours to obtain the NCDs / PDA / MoS2 composite lubricant.

[0049] The surface morphology of the composite lubricating material prepared in Example 1 was characterized by scanning electron microscopy (SEM). Figure 1 As shown; the structure of the composite lubricating material prepared in Example 1 was standardized by transmission electron microscopy (TEM), as shown Figure 2 shown.

[0050] Depend on Figure 1 、 2 It can be seen that the NCDs / PDA / MoS2 composite lubricating material prepared in Example 1 presents a nanoflower-core-shell structure, with the surface being a nanoflower structure grown in situ by MoS2, and the core-shell being spherical polydopamine formed by self-polymerization of dopamine.

[0051] Example 2

[0052] The method for preparing a marine composite lubricating material with multi-fuel compatibility provided in this embodiment comprises the following steps:

[0053] S1. Disperse glucose and urea in a 1:1 mass ratio in 60 mL of deionized water and stir for 20 minutes until completely dissolved. Pour the dispersion into a Teflon-lined container and place it in a hydrothermal reactor. Place the reactor in an oven at 190°C for 12 hours. After the reaction is complete and allowed to cool naturally, remove the reaction solution and centrifuge it in a high-speed centrifuge at 8000 rpm for 20 minutes to obtain the supernatant. Filter the supernatant through a 0.22 μm filter membrane and dialysis the filtrate against pure water (dialysis bag, 1000 Da molecular weight) for 24 hours. After purification, freeze-dry for 54 hours to obtain NCDs with a particle size of 2 to 10 nm.

[0054] S2. Disperse the NCDs prepared in step S1 into a Tris-HCl (pH = 8.5) buffer system, add dopamine hydrochloride twice the mass of the NCDs, and stir at 25°C in the dark for 36 hours. After the reaction, wash the mixture three times with anhydrous ethanol and deionized water, and dry it at 70°C for 36 hours to obtain NCDs / PDA.

[0055] S3. Disperse 0.16 g of NCDs / PDA in 70 mL of deionized water. Add 2.4 g of ammonium molybdate and 4.5 g of thiourea to the NCDs / PDA dispersion. Pour the dispersion into a Teflon-lined container and place it in a hydrothermal reactor. Place the reactor in an oven at 200°C for 22 hours. After the reaction is complete and allowed to cool naturally, remove the reaction solution and centrifuge it in a high-speed centrifuge at 4000 rpm for 20 minutes. Wash the mixture three times with alternating ethanol and deionized water, and dry it at 70°C for 36 hours to obtain the NCDs / PDA / MoS2 composite lubricant.

[0056] The NCDs obtained in S1, the NCDs / PDA obtained in S2, and the NCDs / PDA / MoS2 composite lubricating materials obtained in S3 were analyzed by X-ray diffractometer. Figure 3 shown.

[0057] Depend on Figure 3 It can be seen that: in the XRD pattern of NCDs, a broad diffraction peak at around 22° corresponds to the (002) crystal plane of graphene. In the XRD pattern of NCDs / PDA / MoS2, a three-dimensional flower-like structure of 1T / 2H multiphase MoS2 can be seen in the MoS2 synthesized by the hydrothermal method. The peaks at 9.8°, 32.9°, and 7.8° point to the (002), (100), and (110) planes of MoS2, respectively, indicating that a MoS2 nanoflower structure has grown on its surface.

[0058] Example 3

[0059] The method for preparing a marine composite lubricating material with multi-fuel compatibility provided in this embodiment comprises the following steps:

[0060] S1. Disperse glucose and urea in a 1:1 mass ratio in 60 mL of deionized water and stir for 20 minutes until completely dissolved. Pour the dispersion into a Teflon-lined container and place it in a hydrothermal reactor. Place the reactor in an oven at 190°C for 12 hours. After the reaction is complete and allowed to cool naturally, remove the reaction solution and centrifuge it in a high-speed centrifuge at 8000 rpm for 20 minutes to obtain the supernatant. Filter the supernatant through a 0.22 μm filter membrane and dialysis the filtrate against pure water (dialysis bag, 1000 Da molecular weight) for 24 hours. After purification, freeze-dry for 48 hours to obtain NCDs with a particle size of 2 to 10 nm.

[0061] S2. Disperse the NCDs prepared in step S1 in a Tris-HCl (pH = 8.5) buffer system, add dopamine hydrochloride twice the mass of the NCDs, and stir at 30°C in the dark for 24 hours. After the reaction, wash the mixture three times with anhydrous ethanol and deionized water, and dry it at 60°C for 48 hours to obtain NCDs / PDA.

[0062] S3. Disperse 0.16 g of NCDs / PDA in 70 mL of deionized water. Add 2.4 g of ammonium molybdate and 4.5 g of thiourea to the NCDs / PDA dispersion. Pour the dispersion into a Teflon-lined container and place it in a hydrothermal reactor. Place the reactor in an oven, set the temperature to 200°C, and react for 24 hours. After the reaction is complete and allowed to cool naturally, remove the reaction solution and centrifuge it in a high-speed centrifuge at 3000 rpm for 30 minutes. Wash it three times with alternating ethanol and deionized water, and dry it at 60°C for 48 hours to obtain the NCDs / PDA / MoS2 composite lubricant.

[0063] The EDS mapping analysis of the NCDs / PDA / MoS2 composite lubricating material prepared in this embodiment is shown in the following figure: Figure 4 shown.

[0064] Depend on Figure 4 It can be seen that the composite lubricating material prepared in this embodiment is composed of four main elements: C, N, O, Mo, and S. Among them, C and N come from NCDs and PDA respectively, and Mo and S come from molybdenum disulfide.

[0065] Taking the NCDs / PDA / MoS2 composite lubricating material prepared in Example 1 as an example, a cylinder liner-piston ring friction test was carried out under different fuel working conditions. The specific steps are as follows:

[0066] 0.125 wt% of the NCDs / PDA / MoS2 composite lubricant prepared in Example 1 was uniformly dispersed in marine low-sulfur fuel oil, marine biofuel, and marine methanol using ultrasonic and magnetic stirring. Samples without the composite lubricant were used as controls. Samples were prepared using commonly used materials for marine diesel engine cylinder liners and piston rings. The cylinder liner samples were machined to dimensions of 120 mm x 15 mm x 5 mm. The piston rings were cut into arc-shaped strips with a circumferential length of 8 mm.

[0067] The friction and wear behavior of the cylinder liner-piston ring friction pair was studied using a 600N, 100rpm load to simulate the heavy-load, low-speed operation of a ship. The experiment was conducted indoors, with each experiment lasting 1.5 hours. Before the experiment began, three NCDs / PDA / MoS f The experimental fuel of the composite lubricant was dripped onto the cylinder liner sample. The friction coefficient was continuously recorded using an MWF-10 reciprocating friction and wear tester, and each test was conducted for 90 minutes. After the friction test, all cylinder liner samples were cleaned with anhydrous ethanol and weighed using a precision analytical balance. Specifically, the cylinder liner-piston ring tribology test results were conducted using marine fuel, marine biofuel, and methanol as lubricants, as well as additives added thereto. Table 1 shows the test results. Figure 5 As shown:

[0068] Table 1 Test results

[0069] test Average friction coefficient Wear amount (mg) Marine low-sulfur fuel 0.113 8.5 Marine low sulfur fuel + composite lubricating materials 0.082 5.7 Marine biofuel 0.109 4.1 Marine biofuel + composite lubricating materials 0.096 2.5 Marine methanol 0.097 10.3 Marine methanol + composite lubricating materials 0.088 6.4

[0070] Combined with Table 1 and Figure 5 As shown in a-d, adding the composite lubricant prepared in this invention to the three fuels significantly reduces both the friction coefficient and wear rate. The maximum reduction in friction coefficient reached 27.4% in a marine low-sulfur fuel environment, and the maximum reduction in wear rate reached 37.9% in a marine methanol fuel environment, demonstrating the excellent wear-reducing and anti-wear properties of the composite lubricant prepared in this invention.

[0071] 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, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a marine composite lubricating material with multi-fuel compatibility, characterized in that: The following steps are involved: S1. Dissolve the carbon source and nitrogen source in deionized water with stirring, perform hydrothermal reaction, cool, centrifuge, filter, dialysis purification, and freeze-dry to obtain NCDs. S2, dissolving NCDs in a Tris-HCl buffer system, adding dopamine hydrochloride, stirring in the dark, washing, and drying to prepare NCDs / PDA; S3. Dissolve NCDs / PDA in deionized water, add a molybdenum source and a sulfur source, perform a hydrothermal reaction, cool, centrifuge, wash, and dry to obtain an NCDs / PDA / MoS2 composite lubricating material.

2. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 1, characterized in that: In step S1, the carbon source is glucose, the nitrogen source is urea, and the mass ratio of the glucose to the urea is 1:

1.

3. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 2, characterized in that: The stirring time is 15 to 30 minutes; The conditions of the hydrothermal reaction include: temperature of 190° C., time of 10 to 12 h; The centrifugal conditions include: a rotation speed of 8000 to 10000 rpm and a time of 10 to 20 minutes; The dialysis purification conditions include: a molecular weight cut-off of 1000 Da, a time of 24 to 30 h; The freeze-drying time is 48 to 72 hours.

4. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 3, characterized in that: The particle size of the NCDs is 2 to 10 nm.

5. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 1, characterized in that: In step S2, the pH value of the Tris-HCl buffer system is 8.5; The mass ratio of the NCDs to the dopamine hydrochloride is 1:2; The conditions for stirring in the dark include: temperature of 20 to 30° C. and time of 24 to 48 hours; The drying temperature is 60-80° C., and the drying time is 24-48 hours.

6. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 1, characterized in that: In step S3, the molybdenum source is ammonium molybdate, the sulfur source is thiourea, and the ratio of the number of molybdenum atoms in the ammonium molybdate to the number of sulfur atoms in the thiourea is 1:

4.

7. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 6, characterized in that: The usage ratio of the NCDs / PDA, the ammonium molybdate and the thiourea is 0.16g-0.2g:2.4g:4.5g.

8. The method for preparing a marine composite lubricating material with multi-fuel compatibility according to claim 7, characterized in that: The conditions of the hydrothermal reaction include: temperature of 200°C and time of 20 to 24 hours; The centrifugal conditions include: a rotation speed of 3000 to 5000 rpm and a time of 10 to 30 minutes; The drying temperature is 60-80° C., and the drying time is 24-48 hours.

9. A marine composite lubricating material with multi-fuel compatibility prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The composite lubricating material includes NCDs / PDA with a core-shell structure and MoS2 nanoflowers vertically grown on the surface of the NCDs / PDA with the core-shell structure.

10. The marine composite lubricating material with multi-fuel compatibility according to claim 9, characterized in that: Used in ship power systems that use low-sulfur fuel, biofuel and methanol fuel as driving energy.

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