Graphene oxide-based lubricating oil additive and preparation method thereof

Abstract

The invention discloses a graphene oxide-based lubricating oil additive and a preparation method thereof. Relates to the field of nano lubricating materials, and a preparation method comprises the following steps: modifying graphene oxide by adopting long-chain alkyl quaternary ammonium salt dissolved in a solvent to obtain a modified graphene oxide solution; the alkyl chain length of the long-chain alkyl quaternary ammonium salt is 14-18, and the number of the long-chain alkyl quaternary ammonium salt is 1-2; carrying out centrifugal treatment on the modified graphene oxide dispersion liquid by using a centrifugal machine to obtain a modified graphene oxide precipitate; mixing the modified graphene oxide precipitate with a dispersing agent and base oil, and uniformly dispersing to obtain a mixed solution; drying the mixed solution to remove a residual solvent; and dispersing the mixed solution from which the residual solvent is removed into the base oil. The graphene oxide-based lubricating oil additive disclosed by the invention has excellent stability and anti-friction and anti-attrition effects, and the method is simple to operate, stable in yield and excellent in product performance.

Description

Technical Field

[0001] The invention relates to the field of lubricating oil additives, and in particular to a method for preparing a graphene oxide lubricating oil anti-wear additive. Background Art

[0002] The molecular design of traditional lubricant additives is mainly to meet the performance of lubricants, and rarely considers factors such as the environment and health. Its use is increasingly restricted. In addition, with the rapid development of modern large-scale industries, traditional lubricant additives have been unable to adapt to increasingly harsh working conditions. Therefore, it is particularly important to develop new environmentally friendly and high-performance lubricant additives.

[0003] Graphene oxide has the characteristics of high specific surface area, weak interlayer interaction, good high temperature and chemical stability, and no corrosion. As a lubricant additive, it can theoretically show excellent tribological properties and high temperature resistance. Moreover, the use of graphene oxide as a lubricant additive fully meets its development requirements of green environmental protection, sustainability, chlorine-free, low sulfur and low phosphorus. The application of graphene lubricant additives in lubricating grease can form an effective inorganic protective film on the surface of the friction pair, thereby providing excellent gear and bearing protection performance, optimizing vibration noise, and also having excellent copper protection, stability and thermal conductivity. However, due to the poor compatibility of the oxygen-containing functional groups on graphene oxide with the base oil and the interlayer van der Waals force of graphene oxide, graphene oxide additives tend to agglomerate and then precipitate in lubricants. In addition, the poor compatibility of graphene oxide composite base oil with other additives further hinders its large-scale application. The current graphene oxide-based additives generally have the characteristics of high cost, complex technology, unstable products, and poor compatibility with other additives.

[0004] Chinese invention patent application CN 115895764 A discloses a graphene oxide lubricating oil additive prepared by a double modification method by modifying graphene oxide with an amino modifier and using titanium dioxide modified with a silane modifier. However, since the modified lubricating oil additive is a binary system of modified graphene oxide and modified titanium dioxide, it is extremely unstable when dispersed in a base oil system and is prone to agglomeration, and the dispersion stability needs to be improved.

[0005] Chinese invention patent CN 117887500 B discloses a lubricating oil additive and a preparation method thereof, wherein modified flake graphene and modified graphene microspheres are mixed, and a suitable mixing ratio of the two substances is further found, and the two substances act synergistically. However, the high-temperature dispersion of this technology is still not stable enough, and its extreme pressure bearing capacity is not strong, and the friction reduction and anti-wear effect is not obvious.

[0006] Chinese invention patent CN106350153B discloses a modified graphene oxide, an engine lubricant and an application thereof. The preparation steps of the modified graphene oxide of the technology include: dissolving a long-chain fatty amine in ethanol, mixing evenly, pouring it into an aqueous solution containing graphene oxide, heating for reaction, then naturally cooling to room temperature, filtering out the reaction solid, washing the solid with ethanol, drying the filter cake, and finally obtaining the modified graphene oxide; when the long-chain fatty amine is dissolved in ethanol, a silane coupling agent is added thereto; the silane coupling agent is selected from KH-550, KH-560 or KH-570; the graphene oxide is prepared by the Hummers method; the long-chain fatty amine is octadecylamine. However, due to the low reactivity of the oxygen-containing functional groups on the surface of graphene oxide, the modification of graphene oxide by long-chain fatty amines and silane coupling agents is not sufficient, and the long-chain alkyl density on the surface of modified graphene oxide is low, resulting in low compatibility with the base oil. This technology of using long-chain fatty amines and silane coupling agents to modify graphene oxide has the problem of instability of the modified graphene oxide in the base oil.

[0007] Chinese invention patent application CN106883900A discloses lubricant additives, lubricants and applications based on graphene oxide modified with nitrogen-containing compounds; the mass percentage of graphene oxide modified with nitrogen-containing compounds in lubricants is 0.01-0.9%; the reagent for surface modification of nitrogen-containing compounds is selected from long-chain alkylamines with 4-16 carbon atoms, and compounds with amide, imide, glucosamine, pyrrolyl or pyridine groups; the reagent for surface modification of nitrogen-containing compounds is ethylenediamine, hexamethylenediamine, acetamide or galactosamine. However, the modification step of this technology is carried out in a two-phase system, and is subsequently washed with a mixed solution of water and methanol, resulting in a low amount of grafting of the surface-modified long-chain alkylamine on the surface of graphene oxide, making it unstable in dispersion in the base oil. Summary of the invention

[0008] In view of the problems of unstable dispersion, easy agglomeration and insufficient lubrication performance of graphene oxide in base oil in the prior art, the present invention provides a graphene oxide-based lubricating oil additive with extremely strong dispersion stability and good anti-wear performance and a preparation method thereof.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a graphene oxide-based lubricating oil additive comprises the following steps: Step 1: modifying graphene oxide with a long-chain alkyl quaternary ammonium salt dissolved in a solvent to obtain a modified graphene oxide solution; wherein the alkyl chain length of the long-chain alkyl quaternary ammonium salt is 14-18, the number is 1-2, the number of quaternary ammonium cations is 1-2, and the coordinated anions are hydroxide, chloride, and bromide; Step 2: centrifuge the modified graphene oxide dispersion to obtain a modified graphene oxide precipitate; Step 3: mix the modified graphene oxide precipitate with a dispersant and a base oil to disperse uniformly to obtain a mixed solution; Step 4: Drying the mixed solution to remove residual solvent; Step 5: Disperse the mixed solution from which the residual solvent has been removed in the base oil.

[0011] To further achieve the purpose of the present invention, preferably, the long-chain alkyl quaternary ammonium salt is any one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium hydroxide, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, ethylenebis(hexadecyldimethylammonium chloride), ethylenebis(hexadecyldimethylammonium hydroxide), octadecylamine polyoxyethylene ether diquaternary ammonium salt, and tetradecylamine polyoxyethylene ether diquaternary ammonium salt.

[0012] Preferably, the solvent is any one or more of methanol and ethanol; the mass ratio of the long-chain alkyl quaternary ammonium salt to the solvent is 1:1-1:6.

[0013] Preferably, the dispersant is any one or more of monoalkenyl succinimide, bisalkenyl succinimide, polyalkenyl succinimide and polyisobutylene succinimide.

[0014] Preferably, the base oil is one of 150N base oil, 500N base oil, 75SN, 100SN, 250SN and PAO.

[0015] Preferably, the mass ratio of the graphene oxide to the long-chain alkyl quaternary ammonium salt is 1:10-1:25; the mass ratio of the dispersant to the graphene oxide is 1:1-10:1.

[0016] Preferably, the time for modifying graphene oxide by the long-chain alkyl quaternary ammonium salt dissolved in the solvent is 7-12 hours.

[0017] Preferably, the mass ratio of the modified graphene oxide precipitate to the dispersant and the base oil is 1:1-10:20-50.

[0018] Preferably, the drying is carried out in an oven; the drying temperature is 65-85 degrees Celsius and the drying time is 12-24 hours.

[0019] Preferably, the modified graphene oxide is added to the base oil in an amount of 0.025wt%-0.15wt%;

[0020] The single-layer sheet diameter of the graphene oxide in step 1 is 0.1-2 μm and the thickness is 0.5 nm-1.5 nm.

[0021] A graphene oxide-based lubricating oil additive is prepared by the above-mentioned preparation method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention prepares a graphene oxide-based lubricating oil additive by modifying graphene oxide with a long-chain quaternary ammonium salt. It is found that by controlling the alkyl chain length of the long-chain alkyl quaternary ammonium salt to 14-18, the number to 1-2, the number of quaternary ammonium cations to 1-2, and the coordinated anions to be hydroxide, chloride, and bromide, the dispersion stability of the lubricating oil additive can be significantly improved, and at the same time, the lubricating oil additive has better anti-wear performance.

[0024] 2) The quaternary amine on the long-chain quaternary ammonium salt of the present invention is positively charged, and the carboxyl group on the graphene oxide ionizes H + After that, it becomes negatively charged; through the mutual attraction between positive and negative charges, graphene oxide adsorbs a large number of positively charged long-chain quaternary amine structures on its surface. Under the action of the dispersant, the long-chain quaternary ammonium salt-modified graphene oxide is dispersed in the base oil, which helps to improve the dispersion stability of lubricating oil additives.

[0025] 3) Due to the interaction of ions, a large amount of long-chain alkyl quaternary ammonium salts are grafted onto the surface of graphene oxide in the present invention, and then the graphene oxide is mixed with a dispersant to make it have good compatibility with the base oil, thereby improving the dispersion stability of the lubricating oil additive.

[0026] 4) The preparation method disclosed in the present invention is simple, green and environmentally friendly, the raw materials are easily available and the equipment requirements are low, and batch preparation can be achieved, which is worthy of promotion and use.

[0027] 5) The drying process will cause the modified graphene oxide to agglomerate. The present invention first uses a small amount of base oil in combination with a dispersant to disperse the modified graphene oxide and then dries it, and then disperses the resulting product in the base oil, which can reduce the impact of agglomeration to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram of the oil sample of the hexadecyltrimethylammonium hydroxide (CTAOH) functionalized graphene oxide lubricating oil prepared in Example 1 of the present invention after standing for 300 days. DETAILED DESCRIPTION

[0029] In order to better understand the present invention, the present invention is further explained in conjunction with the following examples, but the examples do not constitute a limitation on the scope of protection of the claims of the present invention. Based on the examples, other examples obtained by those skilled in the art without making any creative work all fall within the scope of protection of the present invention.

[0030] Aiming at the problem that graphene oxide in the prior art is unstable in dispersion and prone to agglomeration in base oil, the present invention uses long-chain alkyl quaternary ammonium salt as a modifier, first dissolves the long-chain alkyl quaternary ammonium salt in methanol or ethanol, adds graphene oxide to the system, and stirs it magnetically to make it fully react. In this process, due to the interaction of ions, a large amount of long-chain alkyl quaternary ammonium salt is grafted on the surface of graphene oxide. Then, it is matched with a dispersant to make it have good compatibility with the base oil. The method of the present invention not only solves the problem that graphene oxide is unstable in dispersion in base oil, but also can bring extremely strong anti-wear and friction-reducing effects, thereby making it possible to use graphene oxide-based additives in lubricating oils. Among them, the core measure is to control the alkyl chain length of long-chain alkyl quaternary ammonium salts to 14-18, the number of alkyl chains to 1-2, the number of quaternary ammonium cations to 1-2, and the coordinated anions to be hydroxide, chloride, and bromide; when the alkyl chain length is lower than 14 or higher than 18, and the number of alkyl chains exceeds 3, the dispersion stability of lubricating oil additives and friction performance are significantly reduced after testing.

[0031] The present invention provides a method for preparing a graphene oxide-based lubricating oil additive, comprising the following steps: Step 1: modifying graphene oxide with a long-chain alkyl quaternary ammonium salt dissolved in a solvent to obtain a modified graphene oxide solution; the alkyl chain length of the long-chain alkyl quaternary ammonium salt is 14-18, the number is 1-2, the number of quaternary ammonium cations is 1-2, and the coordinated anions are hydroxide, chloride, and bromide; Step 2: centrifuging the modified graphene oxide dispersion using a centrifuge to obtain a modified graphene oxide precipitate; Step 3: Mixing and evenly dispersing the modified graphene oxide with the dispersant and the base oil; Step 4: Place the mixed solution in an oven to remove residual solvent; Step 5: Disperse the mixed solution from which the residual solvent has been removed in the base oil.

[0032] Wherein the long-chain alkyl quaternary ammonium salt can be preferably selected from any one or more of hexadecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium hydroxide, tetradecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium chloride, ethylene bis (hexadecyl dimethyl ammonium chloride), ethylene bis (hexadecyl dimethyl ammonium hydroxide), octadecylamine polyoxyethylene ether diquaternary ammonium salt, and tetradecylamine polyoxyethylene ether diquaternary ammonium salt on the basis of the above definition. Dispersant and base oil etc. can be selected according to the purpose of the present invention; the relevant raw material dosage and process conditions can also be obtained according to the purpose of the invention in combination with experiments.

[0033] The small-sized graphene oxide involved in the following examples and comparative examples is graphene oxide with a single-layer sheet diameter of 0.1-2 μm and a thickness of 0.5 nm-1.5 nm.

[0034] Example 1

[0035] Step 1: Mix hexadecyltrimethylammonium hydroxide and methanol in a mass ratio of 1:3.

[0036] Step 2: Mix the small-sized graphene oxide with the mixed solution of step 1 at a mass ratio of 1:100.

[0037] Step 3: The material obtained in step 2 was magnetically stirred at room temperature and a rotation speed of 300 rpm for 12 h.

[0038] Step 4: centrifuge the mixed solution obtained in step 3 at a speed of 8000 rpm for 30 min.

[0039] Step 5: Take the bottom sediment after centrifugation in step 4 and mix it with the dispersant polyisobutylene succinimide and 500N base oil in a mass ratio of 1:5:50.

[0040] Step 6: The mixed solution in step 5 was fully magnetically stirred at a speed of 300 rpm for 1 h.

[0041] Step 7: Place the mixed solution stirred thoroughly in step 6 into an oven to remove the residual solvent therein. The treatment conditions are: 70° C., 12 h.

[0042] Step 8: Disperse the lubricating oil concentrate processed in step 7 in 500N base oil according to the SGO mass fraction before modification being 0.075wt%.

[0043] Example 2

[0044] Step 1: Mix hexadecyltrimethylammonium bromide and methanol in a mass ratio of 1:4.

[0045] Step 2: Mix the small-sized graphene oxide with the mixed solution of step 1 at a mass ratio of 1:40.

[0046] Step 3: The material obtained in step 2 was magnetically stirred at room temperature and a speed of 400 rpm for 8 h.

[0047] Step 4: centrifuge the mixed solution obtained in step 3 at 6000 rpm for 50 min.

[0048] Step 5: Take the bottom sediment after centrifugation in step 4 and mix it with the dispersant polyisobutylene succinimide and 500N base oil in a mass ratio of 1:5:50.

[0049] Step 6: The mixed solution of step 5 is fully magnetically stirred, and the magnetic stirring conditions are: 3h, 100rpm.

[0050] Step 7: Place the mixed solution stirred thoroughly in step 6 into an oven to remove the residual solvent therein. The treatment conditions are: 80° C., 12 h.

[0051] Step 8: Disperse the lubricating oil concentrate processed in step 7 in 250SN base oil according to the SGO mass fraction before modification being 0.075wt%.

[0052] Example 3

[0053] Step 1: Mix hexadecyltrimethylammonium chloride and methanol in a mass ratio of 1:6.

[0054] Step 2: Mix the small-sized graphene oxide with the mixed solution of step 1 at a mass ratio of 1:70.

[0055] Step 3: The material obtained in step 2 was magnetically stirred at room temperature and a speed of 200 rpm for 18 h.

[0056] Step 4: centrifuge the mixed solution obtained in step 3 at 7000 rpm for 40 min.

[0057] Step 5: Take the bottom sediment after centrifugation in step 4 and mix it with the dispersant polyisobutylene succinimide and 500N base oil in a mass ratio of 1:5:50.

[0058] Step 6: The mixed solution of step 5 is fully magnetically stirred. The magnetic stirring conditions are: 1.5 h, 300 rpm.

[0059] Step 7: Place the mixed solution stirred thoroughly in step 6 into an oven to remove the residual solvent therein. The treatment conditions are: 70° C., 20 h.

[0060] Step 8: Disperse the lubricating oil concentrate processed in step 7 in 100SN base oil according to the SGO mass fraction before modification being 0.075wt%.

[0061] Example 4 Step 1, mixing hexadecyltrimethylammonium hydroxide and methanol in a mass ratio of 1:4; Step 2, mixing the small-sized graphene oxide with the mixed solution of step 1 at a mass ratio of 1:80; Step 3, the material obtained in step 2 was magnetically stirred at room temperature at a speed of 200 rpm for 12 h; Step 4: centrifuge the mixed solution obtained in step 3 at 9000 rpm for 20 min; Step 5, taking the bottom sediment after centrifugation in step 4, and mixing it with the dispersant polymonoolefin succinimide and 150N base oil in a mass ratio of 1:10:50; Step 6: The mixed solution of step 5 is fully magnetically stirred, and the magnetic stirring conditions are: 2h, 200rpm; Step 7: Place the mixed solution stirred thoroughly in step 6 into an oven to remove the residual solvent therein. The treatment conditions are: 80° C., 8 h; Step 8: Disperse the lubricating oil concentrate processed in step 7 in 150N base oil according to the SGO mass fraction before modification being 0.1wt%.

[0062] Example 5

[0063] Step 1: Mix ethylenebis(hexadecyldimethylammonium chloride) and methanol in a mass ratio of 1:1.

[0064] Step 2: Mix the small-sized graphene oxide with the mixed solution of step 1 at a mass ratio of 1:50.

[0065] Step 3: The material obtained in step 2 was magnetically stirred at room temperature and a speed of 300 rpm for 24 h.

[0066] Step 4: centrifuge the mixed solution obtained in step 3 at 10,000 rpm for 25 min.

[0067] Step 5: Take the bottom sediment after centrifugation in step 4 and mix it with the dispersant polyisobutylene succinimide and 250SN base oil in a mass ratio of 1:5:50.

[0068] Step 6: The mixed solution of step 5 is fully magnetically stirred, and the magnetic stirring conditions are: 1 h, 400 rpm.

[0069] Step 7: Place the mixed solution stirred thoroughly in step 6 into an oven to remove the residual solvent therein. The treatment conditions are: 100° C., 8 h.

[0070] Step 8: Disperse the lubricating oil concentrate processed in step 7 in 250SN base oil according to the SGO mass fraction before modification being 0.1 wt%.

[0071] Comparative Example 1 Different from Example 1, in Comparative Example 1, unmodified graphene oxide is directly dispersed in 500N base oil at a mass fraction of 0.075 wt%.

[0072] Comparative Example 2 The difference from Example 1 is that dodecyltrimethylammonium chloride is used as a modifier.

[0073] Comparative Example 3 The difference from Example 1 is that eicosyltrimethylammonium bromide is used as a modifier.

[0074] Comparative Example 4 The difference from Example 1 is that hexadecyltrimethylammonium hydrogen sulfate is used as a modifier.

[0075] Comparative Example 5 The difference from Example 1 is that trihexadecylmethylammonium bromide is used as a modifier.

[0076] Performance Testing

[0077] 1. Product dispersion stability test

[0078] Stable dispersion time test (natural sedimentation method) Common methods used to evaluate the stability of nanolubricants include natural sedimentation, ultraviolet-visible spectroscopy (UV-Vis), zeta potential, etc. Currently, the most widely used method is natural sedimentation. Compared with lubricating oil, lubricants dispersed in nanoparticles are visually different. This allows the occurrence of aggregation and subsequent deposition to be distinguished by visual inspection. The specific operation method is: place the prepared sample, observe the sample at regular intervals and take photos to record. When agglomerations appear at the bottom of the sample, its stable dispersion time can be recorded.

[0079] 2. Product tribological performance test The four-ball friction and wear test was carried out in accordance with the Petrochemical Industry Standard of the People's Republic of China SH / T0189-2017 "Determination of Anti-wear Performance of Lubricating Oils by Four-Ball Method". Sample preparation: Disperse the lubricating oil additives in the base oil. Specific test conditions: speed 1200±60rpm, load 392±2N, temperature 75±2℃, friction time 60±1min, and the steel ball is a CCr15 standard steel ball with a diameter of 12.7mm.

[0080] The wear spots were observed by using an optical microscope wear spot instrument, and the diameters of the wear spots formed on the three steel balls were tested respectively. The average value of the three wear spot diameters was taken as the wear spot diameter, and the average tribology coefficient during the wear process could be read on the four-ball friction and wear machine. The test results are shown in Table 1.

[0081] Table 1 Tribological performance test results

[0082] Chinese invention patent application CN 117363401 A mixes magnetized base oil and iron oxide intercalated graphite oxide and performs intercalation treatment to obtain graphene lubricant additive, whose stable dispersion time is 90 days. Since the storage time of industrial lubricants is mostly around 150 days, it is difficult to meet the storage time requirements in practical applications. The lubricant additive obtained by using long-chain alkyl quaternary ammonium salt to modify graphene oxide and compatibility with succinimide dispersant can be dispersed in base oil for more than 300 days, which can meet the storage time requirements of the lubricant industry. Figure 1 This is an optical picture of an oil sample after the hexadecyltrimethylammonium hydroxide (CTAOH) functionalized graphene oxide prepared in Example 1 of the present invention was dispersed in 500N base oil and allowed to stand for 300 days. Figure 1 The long-chain alkyl quaternary ammonium salt-modified graphene oxide obtained in Example 1 was dispersed in 500N base oil and allowed to stand for 300 days. Figure 1 It was found that the modified graphene oxide did not show any sedimentation after standing in 500N base oil for 300 days, indicating that multilayer graphene oxide modified with long-chain alkyl quaternary ammonium salt showed excellent stability in 500N base oil.

[0083] Chinese invention patent CN 115895764 B modifies graphene oxide with an amino modifier and uses titanium dioxide modified with a silane modifier to prepare a graphene oxide lubricating oil additive using a double modification method. The tribological properties of the graphene oxide lubricating oil additive are as follows: the average friction coefficient of the base oil is reduced by 10.9%, and the average wear spot diameter is reduced by 15.5%, and the friction reduction and anti-wear effect is not significant. The present invention uses a long-chain alkyl quaternary ammonium salt to modify graphene oxide and uses a succinimide dispersant to obtain a lubricating oil additive. The tribological properties are as follows: the average friction coefficient of the base oil is reduced by 46.3%, and the average wear spot diameter is reduced by 30.7%, which can meet the requirements for the tribological properties of lubricating oil additives in some industrial applications.

[0084] By comparing the stable dispersion days of Example 1 and Comparative Example 1, it can be seen that compared with the stratification after dispersion in the base oil for 1 day in Comparative Example 1, Example 1 can achieve stable dispersion for 300 days. This is because the modification of graphene oxide with alkyl quaternary ammonium salt can make a large number of long-chain alkyl groups grafted on the surface of graphene oxide, thereby improving its compatibility with the base oil. And the use of dispersants to treat the modified graphene oxide can further improve its dispersion stability in the base oil. By comparing the tribological properties of Example 1 and Comparative Example 1, it can be seen that the tribological coefficient and wear spot diameter of Comparative Example 1 are 0.093 and 0.774 mm, respectively, and the tribological performance of Example 1 is significantly better than that of Comparative Example 1, and its tribological coefficient and wear spot diameter are 0.058 and 0.617 mm, respectively. This is because the excellent dispersion stability can make the modified graphene oxide more evenly distributed on the friction interface, thereby bringing better tribological performance.

[0085] By comparing the stable dispersion days of Example 2 with those of Comparative Examples 2 and 3, it can be seen that compared with the stratification after dispersion in the base oil for 30 days and 60 days in Comparative Examples 2 and 3, Example 2 can achieve stable dispersion for 180 days. This is because the alkyl chain length of the quaternary ammonium salt has a significant effect on the dispersion stability of the modified graphene oxide. This is because when the number of carbon atoms on the alkyl chain is less than 14, sufficient steric hindrance cannot be generated when grafted on the surface of graphene oxide and the compatibility with the base oil is insufficient. When the number of carbon atoms on the alkyl chain is more than 18, the long alkyl chains grafted on the surface of graphene oxide will agglomerate in the base oil system due to mutual entanglement, thereby affecting its dispersion stability. By comparing the tribological properties of Example 2 with Comparative Examples 2 and 3, it can be seen that the tribological coefficients and wear spot diameters of Comparative Examples 2 and 3 are 0.098, 0.101 and 0.831 mm, 0.842 mm, respectively, while the tribological properties of Example 2 are significantly better than those of Comparative Examples 2 and 3, with the tribological coefficients and wear spot diameters being 0.068 and 0.621 mm, respectively. This is because the alkyl chain length affects the compatibility of the modified graphene oxide with the base oil, thereby affecting the formation of the lubricating oil film and the graphene friction protection film during the friction process.

[0086] Comparing the stable dispersion days of Example 1 and Comparative Example 4, it can be seen that compared with the stratification after dispersion in the base oil for 50 days in Comparative Example 4, Example 1 can achieve stable dispersion for 300 days. This is because the anion of the quaternary ammonium salt also has a significant effect on the dispersion stability of the modified graphene oxide. According to the analysis of its modification principle, the anion of hexadecyltrimethylammonium hydroxide is a hydroxide, which can undergo an acid-base neutralization reaction with the carboxyl group on the surface of graphene oxide, so that more quaternary ammonium salts can be grafted on the surface of graphene oxide, thereby making the modified graphene oxide have better dispersibility in the base oil. Comparing the tribological properties of Example 1 and Comparative Example 4, it can be seen that the tribological coefficient and wear spot diameter of Comparative Example 4 are 0.097 and 0.838 mm respectively, and the tribological performance of Example 1 is significantly better than that of Comparative Example 4, and its tribological coefficient and wear spot diameter are 0.058 and 0.617 mm respectively. This is because the grafting density of quaternary ammonium salt on the surface of graphene oxide will affect the renewal of the graphene friction protection film during the friction process, thereby affecting its tribological properties.

[0087] Comparing the stable dispersion days of Example 2 and Comparative Example 5, it can be seen that compared with the stratification after dispersion in the base oil for 60 days, Example 2 can achieve stable dispersion for 180 days. This is because the number of alkyl chains of the quaternary ammonium salt will also have a significant effect on the dispersion stability of the modified graphene oxide. According to the molecular structure analysis, when the number of alkyl chains in the quaternary ammonium salt structure increases, its polarity will be reduced, and it will be more difficult to react with graphene oxide, and the grafting density on the surface of graphene oxide will be low, thereby reducing its dispersion stability. Comparing the tribological properties of Example 2 and Comparative Example 5, it can be seen that the tribological coefficient and wear spot diameter of Comparative Example 5 are 0.096 and 0.835 mm, respectively, and the tribological performance of Example 2 is significantly better than that of Comparative Example 5, and its tribological coefficient and wear spot diameter are 0.068 and 0.621 mm, respectively. This is because the grafting density of the quaternary ammonium salt on the surface of graphene oxide will affect the renewal of the graphene friction protection film during the friction process, thereby affecting its tribological properties.

Claims

1. A method for preparing a graphene oxide-based lubricating oil additive, characterized in that: The following steps are involved: Step 1: modifying graphene oxide with a long-chain alkyl quaternary ammonium salt dissolved in a solvent to obtain a modified graphene oxide solution; wherein the alkyl chain length of the long-chain alkyl quaternary ammonium salt is 14-18, the number is 1-2, the number of quaternary ammonium cations is 1-2, and the coordinated anions are hydroxide, chloride, and bromide; Step 2: centrifuging the modified graphene oxide dispersion using a centrifuge to obtain a modified graphene oxide precipitate; Step 3: Mixing the modified graphene oxide precipitate with a dispersant and a base oil, and dispersing them evenly to obtain a mixed solution; Step 4: Drying the mixed solution to remove residual solvent; Step 5: Disperse the mixed solution from which the residual solvent has been removed in the base oil.

2. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The long-chain alkyl quaternary ammonium salt is any one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium hydroxide, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, ethylenebis(hexadecyldimethylammonium chloride), ethylenebis(hexadecyldimethylammonium hydroxide), octadecylamine polyoxyethylene ether diquaternary ammonium salt, and tetradecylamine polyoxyethylene ether diquaternary ammonium salt.

3. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The solvent is any one or more of methanol and ethanol; the mass ratio of the long-chain alkyl quaternary ammonium salt to the solvent is 1:1-1:

6.

4. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The dispersant is any one or more of monoalkenyl succinimide, bisalkenyl succinimide, polyalkenyl succinimide and polyisobutylene succinimide.

5. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The base oil is one of 150N base oil, 500N base oil, 75SN, 100SN, 250SN and PAO.

6. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The mass ratio of the graphene oxide to the long-chain alkyl quaternary ammonium salt is 1:10-1:25; the mass ratio of the dispersant to the graphene oxide is 1:1-10:

1.

7. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The time for modifying graphene oxide by the long-chain alkyl quaternary ammonium salt dissolved in the solvent is 7-12 hours; the mass ratio of the modified graphene oxide precipitate to the dispersant and the base oil is 1:1-10:20-50.

8. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The drying is carried out in an oven; the drying temperature is 65-85 degrees Celsius and the drying time is 12-24 hours.

9. The method for preparing a graphene oxide lubricant anti-wear additive according to claim 1, characterized in that: The modified graphene oxide is added in an amount of 0.025wt%-0.15wt% in the base oil; The single-layer sheet diameter of the graphene oxide in step 1 is 0.1-2 μm and the thickness is 0.5 nm-1.5 nm.

10. A graphene oxide-based lubricating oil additive, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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