Graphene lubricating oil and preparation method thereof

Abstract

The invention provides graphene lubricating oil and a preparation method thereof.The preparation method of the graphene lubricating oil comprises the following steps that graphite powder is subjected to oxidation treatment firstly, then dimethyl octadecyl [3-(trimethoxysilyl) propyl] ammonium chloride and azodiisobutyronitrile are adopted for intercalation treatment, and intercalated graphene is obtained; mixing the intercalated graphene with an alpha-olefin monomer, and carrying out a polymerization reaction to obtain modified graphene; uniformly mixing the modified graphene with zirconium nitrate and an organic ligand, and reacting to obtain passivated graphene; and uniformly mixing the passivated graphene with base oil to obtain the graphene lubricating oil. According to the preparation method of the graphene lubricating oil, the obtained graphene lubricating oil is stable in antifriction performance and good in oxidation stability.

Description

Technical Field

[0001] This invention relates to the field of lubricating oil technology, and in particular to a graphene lubricating oil and its preparation method. Background Technology

[0002] With the diversification of mechanical motion conditions, lubricants used on various types of mechanical equipment to reduce friction and protect machinery and processed parts also need to be continuously improved to ensure service stability and durability under extreme working conditions.

[0003] Graphene, due to its excellent mechanical properties, chemical stability, and thermal conductivity, shows promising application prospects as a lubricant additive under extreme working conditions. However, graphene has poor compatibility with base oils and is prone to agglomeration and sedimentation. In particular, under the pressure of mechanical motion, prolonged shearing behavior generates a large amount of frictional heat, causing the temperature in the contact area to rise rapidly. This leads to poor dispersion stability of graphene, increased agglomeration rate, and a rapid decline in the friction-reducing performance of graphene lubricants. Furthermore, the presence of graphene can also easily reduce the oxidation stability of lubricants, negatively impacting their service life. Summary of the Invention

[0004] The purpose of this invention is to provide a graphene lubricating oil and its preparation method, so as to solve the problems of rapid decline in friction reduction performance and poor oxidation stability of graphene lubricating oil in the prior art.

[0005] This invention provides the following technical solution:

[0006] A method for preparing a graphene lubricating oil includes the following steps:

[0007] (1) The graphite powder is first oxidized, and then intercalated with dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile to obtain intercalated graphene;

[0008] (2) The intercalated graphene obtained in step (1) is mixed with α-olefin monomers and subjected to polymerization reaction to obtain modified graphene.

[0009] (3) Mix the modified graphene obtained in step (2) with zirconium nitrate and organic ligands evenly, and after the reaction, passivated graphene is obtained.

[0010] (4) Mix the passivated graphene obtained in step (3) with base oil to obtain graphene lubricating oil.

[0011] Preferably, in step (1), the oxidation treatment includes the following steps:

[0012] At 0-5℃, graphite powder is added to concentrated sulfuric acid, followed by sodium nitrate and potassium permanganate, and reacted at 25-35℃ for 1-3 hours. Deionized water is then added, and the mixture is stirred at 90-100℃ for 30-60 minutes. Hydrogen peroxide is then added, and the mixture is allowed to stand for 12-24 hours. The precipitate is then filtered and washed to obtain oxidized graphite.

[0013] Preferably, the particle size of the graphite powder is less than or equal to 100 μm;

[0014] Optionally, 0.4-0.6g of graphite powder is added to every 10ml of the concentrated sulfuric acid;

[0015] Optionally, the weight ratio of the graphite powder, the sodium nitrate, and the potassium permanganate is 1:(0.4-0.6):(2.5-3.5);

[0016] Optionally, the volume ratio of the deionized water, the concentrated sulfuric acid, and the hydrogen peroxide is (2-6):1:(0.1-0.3);

[0017] Optionally, the hydrogen peroxide has a mass fraction of 10-20 wt%.

[0018] Optionally, the washing process involves washing with a 5-12 wt% hydrochloric acid solution until no sulfate ions are present in the washing solution, followed by washing with water until the pH of the washing solution is greater than or equal to 6.8.

[0019] Preferably, the intercalation process specifically includes the following steps:

[0020] Oxidized graphite was added to N,N-dimethylformamide solvent and ultrasonically dispersed at 20-35℃ for 30-60 min to obtain a suspension. Then, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile were added to the suspension and mixed evenly. The mixture was stirred at 20-35℃ and 200-300 rpm for 4-6 h, filtered, and dried to obtain intercalated graphene.

[0021] Preferably, in the suspension, the concentration of oxidized graphite in N,N-dimethylformamide is 1-3 mg / ml;

[0022] Optionally, the weight ratio of the oxidized graphite, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and azobisisobutyronitrile is 1:(2-4):(0.2-0.5).

[0023] Preferably, step (2) specifically includes:

[0024] The intercalated graphene and α-olefin monomer obtained in step (1) are mixed evenly and stirred at a temperature of 60-80℃ and a speed of 300-500rpm for 4-6 hours to obtain modified graphene.

[0025] The weight ratio of the intercalated graphene to the α-olefin monomer is 1:(10-20).

[0026] Preferably, step (3) specifically includes:

[0027] Zirconium nitrate, organic ligand, and N,N-dimethylformamide were mixed evenly, and then the modified graphene obtained in step (2) was added. The mixture was stirred at 60-80℃ for 3-6 hours to obtain passivated graphene.

[0028] The organic ligand is one or more of dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid.

[0029] Preferably, the concentration of zirconium nitrate in N,N-dimethylformamide is 0.1-0.3 mol / L; the molar ratio of zirconium nitrate to the organic ligand is 1:(3.8-4.0).

[0030] Optionally, the concentration of the modified graphene in the N,N-dimethylformamide is 0.3-1.0 mg / ml;

[0031] Optionally, the organic ligand is a mixture of dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid in a molar ratio of 1:(8-12).

[0032] Preferably, in step (4), the base oil is a polyalphaolefin base oil;

[0033] Optionally, step (4) may also include the addition of a dispersant and / or an antioxidant.

[0034] Preferably, step (4) specifically includes: mixing the passivated graphene obtained in step (3) with base oil, antioxidant and dispersant to obtain graphene lubricating oil.

[0035] Preferably, the antioxidant is one or more of 2,6-di-tert-butyl-p-cresol and dioctyldiphenylamine; the weight ratio of the antioxidant to the base oil is (0.2-1.0):100.

[0036] Preferably, the dispersant is succinimide; the weight ratio of the dispersant to the base oil is (0.5-0.8):100.

[0037] Preferably, the weight ratio of the passivated graphene to the base oil is (0.3-1.5):100.

[0038] The present invention also provides a graphene lubricating oil, which is obtained by the preparation method of the graphene lubricating oil described above.

[0039] The above-described solution of the present invention has at least the following beneficial effects:

[0040] (1) The preparation method of the graphene lubricating oil of the present invention includes the following steps: First, graphite powder is oxidized, and then intercalated with dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile to obtain intercalated graphene; the intercalated graphene is mixed with α-olefin monomers and subjected to polymerization to obtain modified graphene; the modified graphene is mixed evenly with zirconium nitrate and organic ligands, and after reaction, passivated graphene is obtained; the passivated graphene is mixed evenly with base oil to obtain graphene lubricating oil. The graphene lubricating oil prepared by the method of the present invention has stable friction-reducing properties and good oxidation stability.

[0041] The method for preparing graphene lubricating oil according to the present invention first involves oxidizing graphite powder to introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups into the graphite sheets, thereby expanding the interlayer spacing. Then, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride is used for intercalation. As an intercalating agent, the quaternary ammonium cation at one end enters the interlayer of graphite through electrostatic interaction. The siloxy group stabilizes its position in the interlayer of graphite through covalent interaction with the hydroxyl group introduced after oxidation of the graphite. The long-chain alkyl group at the other end has a certain steric hindrance, which can effectively increase the distance between graphite layers and form a loose and easily dispersed structure. At the same time, the long-chain alkyl group can also bring the azobisisobutyronitrile into the interlayer through hydrophobic interaction and stabilize its residence. After intercalation, the intercalated graphene is mixed with α-olefin monomers, and polymerization is initiated using azobisisobutyronitrile (AIBN) between the graphene layers. Polymerization occurs in situ on the graphene surface to form polyα-olefin chains, resulting in modified graphene. This improves the problem of graphene's tendency to agglomerate and significantly enhances its compatibility with non-polar base oils, allowing it to disperse uniformly in the base oil and avoiding the decline in lubrication performance caused by agglomeration. Defects in graphene can lead to poor oxidation stability in the resulting lubricating oil. This is because graphene defects readily act as active reaction sites, accelerating oxidation. During oxidation, oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups are introduced into the graphene sheets, which readily act as highly active sites for hydrolysis, oxidation, or reactions with other substances, leading to structural damage. Therefore, reacting modified graphene with zirconium nitrate and organic ligands can passivate it. Specifically, zirconium ions from zirconium nitrate can form coordination bonds with oxygen-containing functional groups on the surface of modified graphene, introducing organic ligands to form a protective layer of organic-inorganic hybrid structure. This shields active reaction sites, improves the chemical stability of the modified graphene, and enhances the oxidative stability of the resulting lubricating oil. By uniformly mixing the passivated graphene with base oil, graphene lubricating oil can be obtained.

[0042] (2) The method for preparing the graphene lubricating oil of the present invention, wherein the organic ligand is one or more of dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid. The carboxyl group of the organic ligand forms a stable coordination bond with the zirconium ion, and the thiophene ring can form a protective layer with a high electron cloud density through sulfur atoms, thereby achieving a good passivation effect and improving the oxidation stability of the lubricating oil. Among them, the dibenzothiophene-4-carboxylic acid has a planar structure and can achieve good bonding with graphene through π-π interaction, effectively covering the defect sites on the graphene surface. The 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid has a flexible long alkyl chain that extends outward, and can form a flexible protective layer. When the dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid are used in combination, the passivation effect is good and the oxidation stability of the obtained lubricating oil is improved. Detailed Implementation

[0043] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products; different manufacturers and models of raw materials do not affect the implementation of the technical solution or the achievement of the technical effect of this invention.

[0044] In the following examples, the CAS number of the dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride is 27668-52-6. The CAS number of the octadecyltrimethylammonium chloride is 112-03-8.

[0045] The dibenzothiophene-4-carboxylic acid has the CAS number 2786-08-5 and has the following structure:

[0046]

[0047] The CAS number of the 3-undecylthiopheno[3,2-b]thiophene-2-carboxylic acid is 950223-96-8, and it has the following structure:

[0048]

[0049] The CAS number of the 4-phenylbenzoic acid is 92-92-2. The CAS number of the undecanoic acid is 112-37-8.

[0050] Example 1

[0051] The method for preparing graphene lubricating oil in this embodiment includes the following steps:

[0052] (1) Oxidation treatment: At 5°C, graphite powder is added to concentrated sulfuric acid, and sodium nitrate and potassium permanganate are added to it. The reaction is carried out at 25°C for 3 hours. Deionized water is added to it, and the reaction is carried out at 100°C for 45 minutes. Then, hydrogen peroxide is added to it, and the mixture is allowed to stand for 12 hours. The precipitate is filtered and washed to obtain the oxidized graphite.

[0053] The graphite powder has a particle size of less than or equal to 100 μm; 0.6 g of graphite powder is added to every 10 ml of concentrated sulfuric acid; the weight ratio of graphite powder, sodium nitrate, and potassium permanganate is 1:0.5:2.5; the volume ratio of deionized water, concentrated sulfuric acid, and hydrogen peroxide is 4:1:0.3; the mass fraction of hydrogen peroxide is 20 wt%; the washing process involves washing with a 12 wt% hydrochloric acid solution until no sulfate ions are present in the washing solution (e.g., barium chloride can be used for detection), followed by washing with water until the pH value of the washing solution is greater than or equal to 6.8.

[0054] Intercalation treatment: Oxidized graphite was added to N,N-dimethylformamide solvent and ultrasonically dispersed at 30°C for 30 min to obtain a suspension. Then, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile were added to the suspension, mixed evenly, and stirred at 35°C and 250 rpm for 6 h. After filtration and drying, intercalated graphene was obtained.

[0055] In the suspension, the concentration of oxidized graphite in N,N-dimethylformamide is 3 mg / ml; the weight ratio of oxidized graphite, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and azobisisobutyronitrile is 1:2:0.2.

[0056] (2) The intercalated graphene and α-olefin monomer obtained in step (1) are mixed evenly and stirred for 6 hours at a temperature of 80°C and a speed of 500 rpm to obtain modified graphene.

[0057] In this embodiment, the weight ratio of the intercalated graphene to the α-olefin monomer is 1:20. It should be noted that in this embodiment, the α-olefin monomer is 1-decene, but other α-olefin monomers, such as C8-C, can also be used. 12 α-olefins (the same applies below, and will not be repeated hereafter).

[0058] (3) Mix zirconium nitrate, organic ligand, and N,N-dimethylformamide evenly, then add the modified graphene obtained in step (2), and stir the reaction at 70°C for 6 hours to obtain passivated graphene.

[0059] The organic ligand is a mixture of dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid in a molar ratio of 1:12. The concentration of zirconium nitrate in N,N-dimethylformamide is 0.2 mol / L; the molar ratio of zirconium nitrate to the organic ligand is 1:4.0; and the concentration of modified graphene in N,N-dimethylformamide is 1.0 mg / ml.

[0060] (4) Mix the passivated graphene obtained in step (3) with base oil to obtain graphene lubricating oil.

[0061] The base oil is a polyalphaolefin base oil. The weight ratio of the passivated graphene to the base oil is 1.5:100.

[0062] Example 2

[0063] The method for preparing graphene lubricating oil in this embodiment includes the following steps:

[0064] (1) Oxidation treatment: At 1℃, graphite powder is added to concentrated sulfuric acid, and sodium nitrate and potassium permanganate are added to it. The reaction is carried out at 35℃ for 2 hours. Deionized water is added to it, and the reaction is carried out at 90℃ for 60 minutes. Then, hydrogen peroxide is added to it, and the mixture is allowed to stand for 24 hours. The precipitate is filtered and washed to obtain the oxidized graphite.

[0065] The graphite powder has a particle size of less than or equal to 100 μm; 0.5 g of graphite powder is added to every 10 ml of concentrated sulfuric acid; the weight ratio of graphite powder, sodium nitrate, and potassium permanganate is 1:0.6:3.5; the volume ratio of deionized water, concentrated sulfuric acid, and hydrogen peroxide is 6:1:0.1; the mass fraction of hydrogen peroxide is 15 wt%; the washing process involves washing with a 5 wt% hydrochloric acid solution until no sulfate ions are present in the washing solution, followed by washing with water until the pH value of the washing solution is greater than or equal to 6.8.

[0066] Intercalation treatment: Oxidized graphite was added to N,N-dimethylformamide solvent and ultrasonically dispersed at 20°C for 60 min to obtain a suspension. Then, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile were added to the suspension, mixed evenly, and stirred at 30°C and 300 rpm for 5 h. After filtration and drying, intercalated graphene was obtained.

[0067] In the suspension, the concentration of oxidized graphite in N,N-dimethylformamide is 1 mg / ml; the weight ratio of oxidized graphite, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and azobisisobutyronitrile is 1:4:0.3.

[0068] (2) The intercalated graphene and α-olefin monomer obtained in step (1) are mixed evenly and stirred for 5 hours at a temperature of 70°C and a speed of 300 rpm to obtain modified graphene.

[0069] The weight ratio of the intercalated graphene to the α-olefin monomer is 1:10.

[0070] (3) Mix zirconium nitrate, organic ligand, and N,N-dimethylformamide evenly, then add the modified graphene obtained in step (2), and stir the reaction at 80°C for 3 hours to obtain passivated graphene.

[0071] The organic ligand is a mixture of dibenzothiophene-4-carboxylic acid and 3-undecylthieno[3,2-b]thiophene-2-carboxylic acid in a molar ratio of 1:8. The concentration of zirconium nitrate in the N,N-dimethylformamide is 0.3 mol / L; the molar ratio of zirconium nitrate to the organic ligand is 1:3.8; and the concentration of modified graphene in the N,N-dimethylformamide is 0.6 mg / ml.

[0072] (4) Mix the passivated graphene obtained in step (3) with base oil to obtain graphene lubricating oil.

[0073] The base oil is a polyalphaolefin base oil. The weight ratio of the passivated graphene to the base oil is 0.9:100.

[0074] Example 3

[0075] The method for preparing graphene lubricating oil in this embodiment includes the following steps:

[0076] (1) Oxidation treatment: At 2℃, graphite powder is added to concentrated sulfuric acid, and sodium nitrate and potassium permanganate are added to it. The reaction is carried out at 30℃ for 1 hour. Deionized water is added to it, and the reaction is carried out at 95℃ for 30 minutes. Then, hydrogen peroxide is added to it, and the mixture is allowed to stand for 18 hours. The precipitate is filtered and washed to obtain the oxidized graphite.

[0077] The graphite powder has a particle size of less than or equal to 100 μm; 0.4 g of graphite powder is added to every 10 ml of concentrated sulfuric acid; the weight ratio of graphite powder, sodium nitrate, and potassium permanganate is 1:0.4:3.0; the volume ratio of deionized water, concentrated sulfuric acid, and hydrogen peroxide is 2:1:0.2; the mass fraction of hydrogen peroxide is 10 wt%; the washing process involves washing with an 8 wt% hydrochloric acid solution until no sulfate ions are present in the washing solution, followed by washing with water until the pH value of the washing solution is greater than or equal to 6.8.

[0078] Intercalation treatment: Oxidized graphite was added to N,N-dimethylformamide solvent and ultrasonically dispersed at 35°C for 45 min to obtain a suspension. Then, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile were added to the suspension, mixed evenly, and stirred at 20°C and 200 rpm for 4 h. After filtration and drying, intercalated graphene was obtained.

[0079] In the suspension, the concentration of oxidized graphite in N,N-dimethylformamide is 2 mg / ml; the weight ratio of oxidized graphite, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and azobisisobutyronitrile is 1:3:0.5.

[0080] (2) The intercalated graphene and α-olefin monomer obtained in step (1) are mixed evenly and stirred for 4 hours at a temperature of 60°C and a speed of 400 rpm to obtain modified graphene.

[0081] The weight ratio of the intercalated graphene to the α-olefin monomer is 1:15.

[0082] (3) Mix zirconium nitrate, organic ligand, and N,N-dimethylformamide evenly, then add the modified graphene obtained in step (2), and stir the reaction at 60°C for 5 hours to obtain passivated graphene.

[0083] The concentration of zirconium nitrate in N,N-dimethylformamide is 0.1 mol / L; the molar ratio of zirconium nitrate to organic ligand is 1:3.9; the concentration of modified graphene in N,N-dimethylformamide is 0.3 mg / ml; and the organic ligand is a mixture of dibenzothiophene-4-carboxylic acid and 3-undecylthieno[3,2-b]thiophene-2-carboxylic acid in a molar ratio of 1:10.

[0084] (4) Mix the passivated graphene obtained in step (3) with base oil to obtain graphene lubricating oil.

[0085] The base oil is a polyalphaolefin base oil. The weight ratio of the passivated graphene to the base oil is 0.3:100.

[0086] Example 4

[0087] The method for preparing graphene lubricating oil in this embodiment includes the following steps:

[0088] (1) Oxidation treatment: At 3°C, graphite powder is added to concentrated sulfuric acid, and sodium nitrate and potassium permanganate are added to it. The reaction is carried out at 30°C for 2 hours. Deionized water is added to it, and the reaction is carried out at 95°C for 45 minutes. Then, hydrogen peroxide is added to it, and the mixture is allowed to stand for 18 hours. The precipitate is filtered and washed to obtain the oxidized graphite.

[0089] The graphite powder has a particle size of less than or equal to 100 μm; 0.5 g of graphite powder is added to every 10 ml of concentrated sulfuric acid; the weight ratio of graphite powder, sodium nitrate, and potassium permanganate is 1:0.5:2.8; the volume ratio of deionized water, concentrated sulfuric acid, and hydrogen peroxide is 5:1:0.2; the mass fraction of hydrogen peroxide is 16 wt%; the washing process involves washing with an 8 wt% hydrochloric acid solution until no sulfate ions are present in the washing solution, followed by washing with water until the pH value of the washing solution is greater than or equal to 6.8.

[0090] Intercalation treatment: The oxidized graphite was added to N,N-dimethylformamide solvent and ultrasonically dispersed at 25°C for 60 min to obtain a suspension. Then, the dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile were added to the suspension, mixed evenly, and stirred at 25°C and 300 rpm for 5 h. After filtration and drying, the intercalated graphene was obtained.

[0091] In the suspension, the concentration of oxidized graphite in N,N-dimethylformamide is 2 mg / ml; the weight ratio of oxidized graphite, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and azobisisobutyronitrile is 1:3:0.3.

[0092] (2) The intercalated graphene and α-olefin monomer obtained in step (1) are mixed evenly, and stirred for 5 hours at 70°C and 400 rpm. After filtration and washing, modified graphene is obtained.

[0093] The weight ratio of the intercalated graphene to the α-olefin monomer is 1:16.

[0094] (3) Mix zirconium nitrate, organic ligand, and N,N-dimethylformamide evenly, then add the modified graphene obtained in step (2), and stir the reaction at 70°C for 5 hours to obtain passivated graphene.

[0095] The concentration of zirconium nitrate in N,N-dimethylformamide is 0.2 mol / L; the molar ratio of zirconium nitrate to organic ligand is 1:4.0; the concentration of modified graphene in N,N-dimethylformamide is 0.8 mg / ml; and the organic ligand is a mixture of dibenzothiophene-4-carboxylic acid and 3-undecylthieno[3,2-b]thiophene-2-carboxylic acid in a molar ratio of 1:10.

[0096] (4) Mix the passivated graphene obtained in step (3) with base oil to obtain graphene lubricating oil.

[0097] The base oil is a polyalphaolefin base oil. The weight ratio of the passivated graphene to the base oil is 1.0:100.

[0098] Example 5

[0099] The preparation method of the graphene lubricating oil in this embodiment is the same as that in Example 4, except that step (4) also includes the step of adding a dispersant.

[0100] In this embodiment, step (4) specifically includes: mixing the passivated graphene obtained in step (3) with base oil and dispersant evenly to obtain graphene lubricating oil.

[0101] The dispersant is succinimide; the weight ratio of the dispersant to the base oil is 0.65:100.

[0102] Example 6

[0103] The preparation method of the graphene lubricating oil in this embodiment is the same as that in Example 4, except that step (4) also includes the step of adding an antioxidant.

[0104] In this embodiment, step (4) specifically includes: mixing the passivated graphene obtained in step (3) with base oil and antioxidant to obtain graphene lubricating oil.

[0105] The antioxidant is 2,6-di-tert-butyl-p-cresol; the weight ratio of the antioxidant to the base oil is 0.6:100.

[0106] Example 7

[0107] The preparation method of the graphene lubricating oil in this embodiment is the same as that in Example 4, except that step (4) also includes the step of adding an antioxidant.

[0108] In this embodiment, step (4) specifically includes: mixing the passivated graphene obtained in step (3) with base oil and antioxidant to obtain graphene lubricating oil.

[0109] The antioxidant is dioctyldiphenylamine; the weight ratio of the antioxidant to the base oil is 0.6:100.

[0110] Example 8

[0111] The preparation method of the graphene lubricating oil in this embodiment is the same as that in Example 4, except that step (4) also includes the step of adding a dispersant and an antioxidant.

[0112] In this embodiment, step (4) specifically includes: mixing the passivated graphene obtained in step (3) with base oil, antioxidant and dispersant to obtain graphene lubricating oil.

[0113] The antioxidant is 2,6-di-tert-butyl-p-cresol; the weight ratio of the antioxidant to the base oil is 0.4:100. The dispersant is succinimide; the weight ratio of the dispersant to the base oil is 0.6:100.

[0114] Comparative Example 1

[0115] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that step (1) does not include the oxidation treatment step.

[0116] In this comparative example, step (1) specifically involves: adding graphite powder to N,N-dimethylformamide solvent, ultrasonically dispersing it at 25°C for 60 min to obtain a suspension, then adding the dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile to the suspension, mixing it evenly, and stirring it at 25°C and 300 rpm for 5 h, filtering and drying to obtain the intercalated graphene.

[0117] Comparative Example 2

[0118] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that: in step (1), the intercalation treatment step is not included, and in step (2), azobisisobutyronitrile is directly added.

[0119] In this comparative example, step (1) is as follows: at 3°C, graphite powder is added to concentrated sulfuric acid, and sodium nitrate and potassium permanganate are added to it, and the reaction is carried out at 30°C for 2 hours; deionized water is added to it, and the reaction is carried out at 95°C for 45 minutes; then hydrogen peroxide is added to it, and the mixture is allowed to stand for 18 hours. The precipitate is filtered and washed to obtain the oxidized graphite.

[0120] In this comparative example, step (2) specifically involves mixing the oxidized graphite, α-olefin monomer, and azobisisobutyronitrile obtained in step (1) evenly, and stirring the mixture at 70°C and 400 rpm for 5 hours to obtain modified graphene.

[0121] Comparative Example 3

[0122] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that: in step (1), azobisisobutyronitrile is not added during the intercalation treatment, but azobisisobutyronitrile is added directly in step (2).

[0123] In this comparative example, step (2) specifically involves mixing the intercalated graphene, α-olefin monomer, and azobisisobutyronitrile obtained in step (1) evenly, and stirring the mixture at 70°C and 400 rpm for 5 hours to obtain modified graphene.

[0124] Comparative Example 4

[0125] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that: in step (1), the dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride is not added during the intercalation process.

[0126] Comparative Example 5

[0127] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that in step (1), during the intercalation process, the dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride is replaced with octadecyltrimethylammonium chloride.

[0128] Comparative Example 6

[0129] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that no α-olefin monomer is added in step (2).

[0130] Comparative Example 7

[0131] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that step (3) is not included.

[0132] Comparative Example 8

[0133] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that the organic ligand is dibenzothiophene-4-carboxylic acid.

[0134] Comparative Example 9

[0135] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that the organic ligand is 3-undecylthiopheno[3,2-b]thiophene-2-carboxylic acid.

[0136] Comparative Example 10

[0137] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that the organic ligand is undecanoic acid.

[0138] Comparative Example 11

[0139] The preparation method of the graphene lubricating oil in this comparative example is the same as that in Example 8, except that the organic ligand is 4-phenylbenzoic acid.

[0140] Comparative Example 12

[0141] The lubricating oil used in this comparative example is the base oil used in Example 8.

[0142] Comparative Example 13

[0143] The lubricating oil in this comparative example is a mixture of the base oil from Example 8 and an antioxidant. The antioxidant is 2,6-di-tert-butyl-p-cresol; the weight ratio of the antioxidant to the base oil is 0.4:100.

[0144] Effect Experiment Example

[0145] To verify the technical effectiveness of the graphene lubricating oil preparation method described in this invention, the following experiments were conducted:

[0146] Graphene lubricating oils were prepared according to the methods in Examples 1-8 and Comparative Examples 1-11, respectively. 200 ml of each graphene lubricating oil and the lubricating oil in Comparative Examples 12-13 were taken as samples, and the initial acid value of each graphene lubricating oil was measured (denoted as S1). Then, a standard Feton reagent solution with a volume percentage of 55% was added to the sample, copper wire was placed in it, and after maintaining the oil temperature at 110°C for 480 h, samples were taken and their final acid value (denoted as S2) and sludge mass were measured. The increase in acid value was calculated according to the formula Δacid value = S2 - S1, and denoted as Δacid value.

[0147] Tribological properties were tested using a four-ball friction testing machine in point-to-point contact mode. The test friction couple consisted of Φ12.7mm GCr15 bearing steel balls (elastic modulus 210 GPa, surface roughness 0.08 μm). The normal load was 148 N, the rotational speed was 1200 r / min, and the test time was 1800 s. The coefficient of friction was measured at temperatures of 50℃ and 150℃, and denoted as f. 50℃ f 150℃ The rate of change of friction coefficient F, based on the friction coefficient at a test temperature of 50℃, is calculated using the following formula:

[0148] F = (f 150℃ -f 50℃ ) / f 50℃ .

[0149] The initial absorbance (A1) of each graphene lubricating oil was determined by ultraviolet spectrophotometry, and the absorbance (A2) of the graphene lubricating oil after standing at room temperature (25℃) for 30 days was also determined. The absorbance decrease value ΔA was calculated according to the formula ΔA = A1 - A2. A larger absorbance decrease value indicates that more graphene has settled and agglomerated; a smaller absorbance decrease value indicates that the lubricating oil has better dispersion stability.

[0150] The results of the experiment are as follows:

[0151]

[0152]

[0153] Based on the results of Examples 1-8 and Comparative Examples 1-13, it can be seen that the graphene lubricating oil prepared by the method of the present invention has stable friction-reducing properties and good oxidation stability.

[0154] Based on the results of Examples 1-4 and Examples 5 and 8, it can be seen that the addition of the dispersant can reduce the decrease in absorbance ΔA to a certain extent, and the quality of the sludge also decreases slightly. It can be seen that the dispersant helps to reduce the aggregation of graphene.

[0155] Based on the results of Examples 1-4 and Examples 6-8, it is evident that the antioxidant reduces the increase in acid value; that is, the addition of the antioxidant enhances the oxidative stability of the graphene lubricant. The effect is even better when the antioxidant is 2,6-di-tert-butyl-p-cresol.

[0156] Based on the results of Example 8 and Comparative Examples 1-6, it is evident that oxidation and intercalation treatments of graphite significantly reduce the absorbance decrease ΔA, thereby improving the dispersion stability of the graphene lubricant. Oxidation treatment prior to intercalation helps form a loose, easily dispersed structure, thus enhancing the dispersion stability of the graphene lubricant. Comparative Example 1, which only underwent oxidation treatment, showed limited effect on widening the interlayer spacing of graphite, resulting in a graphene lubricant with poor dispersion stability, although the Δacid value decreased. This indicates that the defects introduced by the oxidation treatment still have a certain impact on the oxidation stability of the graphene lubricant, even after passivation treatment.

[0157] When intercalating oxidized graphite, Comparative Example 3, which involved adding azobisisobutyronitrile (AIB) directly during the α-olefin monomer polymerization reaction without AIB, showed a larger decrease in absorbance (ΔA) and a larger sludge mass. This indicated that the polymerization reaction did not occur within the graphene interlayers, resulting in severe agglomeration and sedimentation problems. However, Comparative Example 3 was significantly better than Comparative Example 2. This demonstrates that the dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride intercalation treatment can improve the graphene agglomeration problem and also has a certain stabilizing effect on the friction-reducing properties at high temperatures.

[0158] In Comparative Example 4, which did not include dimethyloctadecyl[3-(trimethoxysilyl)propyl]chloride, the initiator azobisisobutyronitrile (AIBN) had difficulty fully penetrating the interlayer of graphene, resulting in severe agglomeration and sedimentation problems. Comparative Example 6, which did not include α-olefin monomers in the polymerization reaction, showed a slight improvement in dispersion stability compared to Comparative Example 3, but the effect was still unsatisfactory. It is evident that while dimethyloctadecyl[3-(trimethoxysilyl)propyl]chloride has a certain effect on dispersion stability during intercalation treatment, introducing the initiator azobisisobutyronitrile into the interlayer of graphene and then initiating the in-situ polymerization of α-olefin monomers can effectively inhibit graphene agglomeration and significantly improve the compatibility between graphene and base oil. In Comparative Example 5, where dimethyloctadecyl[3-(trimethoxysilyl)propyl]chloride was replaced with octadecyltrimethylammonium chloride, compared to Example 8, the rate of change in the coefficient of friction increased, and its high-temperature friction-reducing performance stability decreased significantly.

[0159] Based on the results of Examples 8 and Comparative Examples 7-11, the oxidation stability of Comparative Example 7, which did not undergo passivation treatment of the modified graphene, was significantly reduced, and was significantly worse than that of the base oil without added graphene (Comparative Example 12). Simultaneously, compared to Example 8, the rate of change in the coefficient of friction was larger, and the coefficient of friction at high temperatures increased significantly. Comparative Example 8, which used dibenzothiophene-4-carboxylic acid alone as the organic ligand, showed significantly improved oxidation stability compared to Comparative Example 7. Comparative Example 11, which used 4-phenylbenzoic acid alone as the organic ligand, showed little change in oxidation stability compared to Comparative Example 7. Comparative Example 9, which used 3-undecylthieno[3,2-b]thiophene-2-carboxylic acid alone as the organic ligand, showed better oxidation stability than Comparative Example 8, but its high-temperature coefficient of friction was poor. Comparative Example 10, which used undecanoic acid alone, showed a decrease in both oxidation stability and high-temperature coefficient of friction compared to Comparative Example 7. It is evident that both dibenzothiophene-4-carboxylic acid and 3-undecylthiopheno[3,2-b]thiophene-2-carboxylic acid, which possess thiophene rings, can improve the oxidation stability of graphene lubricating oil. The effect of dibenzothiophene-4-carboxylic acid on improving oxidation stability is relatively weak, while the effect of 3-undecylthiopheno[3,2-b]thiophene-2-carboxylic acid on improving oxidation stability is significant, but it will have an adverse effect on high-temperature friction performance. When the two are used in combination, the resulting graphene lubricating oil exhibits excellent performance in both oxidation stability and friction performance.

[0160] The results of Comparative Examples 12-13 show that the addition of antioxidants can improve the oxidation stability of lubricating oils. However, the results of Comparative Example 7 show that even with the addition of antioxidants, the oxidation stability of unpassivated graphene remains poor. Example 4, which passivated graphene without adding antioxidants, exhibited significantly better oxidation stability than Comparative Examples 12-13 and 7. This indicates that passivated graphene not only covers active sites, reducing oxidation reactions occurring at these active centers, but also actively inhibits oxidation reactions. This may be due to the presence of thiophene rings on the passivated graphene, whose sulfur atoms possess lone pairs of electrons, providing adsorption for free radicals. Examples 6-8, using passivated graphene combined with antioxidants, form a dual protection mechanism, resulting in lubricating oils with even higher oxidation stability. The effect is particularly good when the antioxidant is phenolic 2,6-di-tert-butyl-p-cresol.

[0161] The 3-undecylthiopheno[3,2-b]thiophene-2-carboxylic acid has two thiophene rings, and the presence of long alkyl chains may increase the steric hindrance of the molecule, forming a barrier to the active sites, thereby reducing oxidation reactions and providing better passivation. It significantly improves oxidation stability. However, the excessively dense flexible chains on the graphene surface can lead to a decrease in the frictional performance of the resulting lubricant under thermal conditions. The dibenzothiophene-4-carboxylic acid has a planar structure, which can cover defect sites and achieve good bonding with graphene through π-π interactions. However, its steric hindrance is smaller, and its passivation effect is weaker compared to that of the 3-undecylthiopheno[3,2-b]thiophene-2-carboxylic acid. When the two are combined, they can exert a synergistic effect, resulting in a graphene lubricant that exhibits excellent oxidation stability and frictional performance.

[0162] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative and not exhaustive. All modifications within the scope of this invention or its equivalents are encompassed by this invention.

Claims

1. A method for preparing a graphene lubricating oil, characterized in that, Includes the following steps: (1) The graphite powder is first oxidized, and then intercalated with dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile to obtain intercalated graphene; (2) The intercalated graphene obtained in step (1) is mixed with α-olefin monomers and subjected to polymerization reaction to obtain modified graphene. (3) Mix the modified graphene obtained in step (2) with zirconium nitrate and organic ligands evenly, and after the reaction, passivated graphene is obtained. (4) Mix the passivated graphene obtained in step (3) with base oil to obtain graphene lubricating oil.

2. The method for preparing graphene lubricating oil according to claim 1, characterized in that, In step (1), the oxidation treatment includes the following steps: At 0-5℃, graphite powder is added to concentrated sulfuric acid, followed by sodium nitrate and potassium permanganate, and reacted at 25-35℃ for 1-3 hours. Deionized water is then added, and the mixture is stirred at 90-100℃ for 30-60 minutes. Hydrogen peroxide is then added, and the mixture is allowed to stand for 12-24 hours. The precipitate is then filtered and washed to obtain oxidized graphite.

3. The method for preparing graphene lubricating oil according to claim 2, characterized in that, The particle size of the graphite powder is less than or equal to 100 μm; Optionally, 0.4-0.6 g of graphite powder is added to every 10 ml of the concentrated sulfuric acid; Optionally, the weight ratio of the graphite powder, the sodium nitrate, and the potassium permanganate is 1:(0.4-0.6):(2.5-3.5); Optionally, the volume ratio of the deionized water, the concentrated sulfuric acid, and the hydrogen peroxide is (2-6):1:(0.1-0.3); Optionally, the hydrogen peroxide has a mass fraction of 10-20 wt%. Optionally, the washing process involves washing with a 5-12 wt% hydrochloric acid solution until no sulfate ions are present in the washing solution, followed by washing with water until the pH of the washing solution is greater than or equal to 6.

8.

4. The method for preparing graphene lubricating oil according to claim 1, characterized in that, The intercalation process specifically includes the following steps: Oxidized graphite was added to N,N-dimethylformamide solvent and ultrasonically dispersed at 20-35℃ for 30-60 min to obtain a suspension. Then, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and azobisisobutyronitrile were added to the suspension and mixed evenly. The mixture was stirred at 20-35℃ and 200-300 rpm for 4-6 h, filtered, and dried to obtain intercalated graphene.

5. The method for preparing graphene lubricating oil according to claim 4, characterized in that, In the suspension, the concentration of oxidized graphite in N,N-dimethylformamide is 1-3 mg / ml; Optionally, the weight ratio of the oxidized graphite, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and azobisisobutyronitrile is 1:(2-4):(0.2-0.5).

6. The method for preparing graphene lubricating oil according to claim 1, characterized in that, Step (2) specifically includes: The intercalated graphene and α-olefin monomer obtained in step (1) are mixed evenly and stirred at a temperature of 60-80℃ and a speed of 300-500rpm for 4-6 hours to obtain modified graphene. The weight ratio of the intercalated graphene to the α-olefin monomer is 1:(10-20).

7. The method for preparing graphene lubricating oil according to claim 1, characterized in that, Step (3) specifically includes: Zirconium nitrate, organic ligand, and N,N-dimethylformamide were mixed evenly, and then the modified graphene obtained in step (2) was added. The mixture was stirred at 60-80℃ for 3-6 hours to obtain passivated graphene. The organic ligand is one or more of dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid.

8. The method for preparing graphene lubricating oil according to claim 7, characterized in that, The concentration of zirconium nitrate in N,N-dimethylformamide is 0.1-0.3 mol / L; the molar ratio of zirconium nitrate to the organic ligand is 1:(3.8-4.0). Optionally, the concentration of the modified graphene in the N,N-dimethylformamide is 0.3-1.0 mg / ml; Optionally, the organic ligand is a mixture of dibenzothiophene-4-carboxylic acid and 3-undecylthiophene[3,2-b]thiophene-2-carboxylic acid in a molar ratio of 1:(8-12).

9. The method for preparing graphene lubricating oil according to claim 8, characterized in that, In step (4), the base oil is a polyalphaolefin base oil; Optionally, step (4) may also include the addition of a dispersant and / or an antioxidant.

10. A graphene lubricating oil, characterized in that, The graphene lubricating oil is prepared using the method described in any one of claims 1-9.

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