A method for preparing and applying a covalent organic framework lubricating additive

Abstract

This invention discloses a method for preparing and applying a covalent organic framework lubricating additive, belonging to the field of lubricating materials and nano-additives technology. This invention utilizes the abundant pyridine nitrogen atoms in the framework of a specific covalent organic framework material to form strong coordination adsorption with the metal surface, allowing individual covalent organic framework particles to firmly adhere to the friction interface through a multi-toothed anchoring effect, significantly enhancing the shear resistance and retention of the lubricating film. Simultaneously, the porous structure of the covalent organic framework can store lubricating oil molecules, which are slowly released during friction, achieving self-replenishing lubrication. The additive of this invention can reduce the coefficient of friction by more than 50% at extremely low addition levels, significantly improving the friction-reducing and anti-wear properties, reliability, and service life of lubricating oil.

Description

Technical Field

[0001] This invention relates to the field of lubricating materials and nano-additives, and particularly to a method for preparing and applying a covalent organic framework lubricating additive. Background Technology

[0002] Lubricating oil additives are key components for improving the lubrication performance of base oils and are widely used in friction pairs of mechanical equipment such as internal combustion engines, gearboxes, and hydraulic systems. Traditional lubricating additives mainly include organosulfur compounds, organophosphorus compounds, and organomolybdenum compounds, which can form chemical reaction films or physical adsorption films on friction surfaces, thereby reducing the coefficient of friction and wear rate. However, these additives have many limitations: First, elements such as sulfur and phosphorus are prone to decomposition at high temperatures, producing corrosive gases that cause chemical corrosion to metal surfaces; second, traditional additives have limited functions and cannot simultaneously meet multiple requirements such as friction reduction, wear resistance, and oxidation resistance; third, some additives have poor compatibility with base oils, easily agglomerating or precipitating, leading to lubrication failure.

[0003] In recent years, nanomaterials have shown great application potential in the field of tribology due to their unique size effect, surface effect, and structural tunability. For example, nanographene, molybdenum disulfide, nanodiamond, and metal oxides have been widely studied as lubricant additives, which can significantly improve lubrication performance. However, existing nano-additives still face problems such as poor dispersion stability, weak interaction with metal surfaces, and difficulty in achieving long-term lubrication. There is an urgent need to develop novel nano-lubricating materials with well-defined structures, designable functions, and good compatibility with base oils.

[0004] Covalent organic frameworks (COFs) are a class of crystalline porous polymers composed of lightweight elements (such as C, H, O, N, and B) linked by strong covalent bonds. Since their first report in 2005, COFs have attracted widespread attention in fields such as gas adsorption, catalysis, sensing, and energy storage due to their extremely high specific surface area, tunable pore size, and abundant functional groups. In the field of lubrication, COFs have the following potential advantages: First, the porous structure of these materials can store lubricating oil molecules, which are slowly released during friction, achieving self-replenishing lubrication; second, the structure of COFs can be precisely designed, and their functional properties can be regulated by selecting different building blocks; third, heteroatoms can be introduced into the framework, and the hypercoordination interactions of these heteroatoms enhance adsorption capacity.

[0005] For example, Chinese invention patent CN118515831A discloses the use of a lubricating oil additive and a covalent organic framework material in the preparation of a lubricating oil additive. This lubricating oil additive is a crystalline porous polymer material formed by two compounds with specific structures linked by hydrogen bonds and covalent bonds. This material has limited compatibility with the oil phase of the lubricant. To address the difficulty in dispersing this covalent organic framework material in the lubricating oil additive, the aforementioned patent provides a scheme to modify it using amine salts or dopamine. However, further modification reactions with amine salts or dopamine tend to occur within the pores of the covalent organic framework material. Furthermore, dopamine modification is sensitive to reaction conditions, and its monomers are prone to self-polymerization, leading to partial pore blockage or uneven modification, significantly reducing the specific surface area and porosity of the material, thereby weakening its core function as a porous material. Furthermore, amine salt functional group modifications are prone to decomposition, hydrolysis, or ion exchange in the high-shear, high-temperature working environment of lubricating oils, leading to modification layer failure or the generation of corrosive byproducts. While dopamine groups possess strong adhesion, their long-term thermal stability is insufficient to meet the high-temperature operating conditions of high-end lubricating oils, posing a risk of degradation. Additional modification processes involve multi-step reactions, separation, and purification, increasing the complexity and cost of the production process and affecting the feasibility of large-scale industrial applications. Moreover, in this field, lubricating oil additives typically account for 2% to 30% of finished lubricating oils, while the concentration of the covalent organic framework material in the aforementioned patent in lubricating oil additives is 0.08 to 0.20 mg / mL, indicating that the addition amount needs further optimization. As the most expensive component of lubricating oil, additives are crucial for improving friction reduction and anti-wear performance with minimal dosage, directly reducing the total cost of the finished oil—a critical technical problem that urgently needs to be addressed in cost control.

[0006] In summary, this invention provides a novel covalent organic framework lubricant additive that exhibits good dispersibility and stability in base oils, and significantly reduces the coefficient of friction and wear volume with extremely low addition amounts. This is of great significance for improving the overall performance and application range of lubricants. Summary of the Invention

[0007] In view of the aforementioned deficiencies in the prior art, the present invention aims to provide an application of a covalent organic framework lubricating additive. Utilizing the high specific surface area, abundant coordination sites, and good oil phase dispersibility of a specific covalent organic framework lubricating additive, it achieves a significant reduction in the coefficient of friction and wear volume at extremely low addition levels, thereby improving the overall performance of the lubricating oil. The present invention also provides a method for preparing the aforementioned covalent organic framework lubricating additive.

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect of the invention, an application of a covalent organic framework lubricant is provided, comprising: Covalent organic framework lubricating additives are added to base oils as additives to reduce friction and wear in lubricating oils; The covalent organic framework lubricant additive is a covalent organic framework material (denoted as BTT-Bpy-COF) formed by the condensation of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde (BTT-CHO) and 5,5'-diamino-2,2'-bipyridine (Bpy-NH2) via a Schiff base reaction.

[0009] Preferably, the base oil includes one or more of polyalphaolefins, mineral oils, and ester oils.

[0010] Preferably, the amount of the covalent organic framework lubricant additive added is 0.05 wt.% to 1.0 wt.% of the base oil.

[0011] Preferably, the covalent organic framework lubricant additive has a two-dimensional layered structure, with the layers connected by covalent bonds and ordered channels formed between the layers by π-π stacking.

[0012] In this field, lubricating oil components include base oils and additives. The covalent organic framework lubricating additive selected in this invention exhibits excellent chemical stability, remaining stable above 350 °C in air. It is insoluble in common organic solvents (such as toluene, tetrahydrofuran, and acetone), making it suitable for conventional base oil systems in this field. It also demonstrates excellent compatibility with polyalphaolefins (such as PAO8 and PAO10), mineral oils, and ester oils. In these applications, the covalent organic framework lubricating additive itself possesses excellent oil-phase dispersibility. Those skilled in the art can add it to the base oil and disperse it using appropriate methods according to actual conditions or requirements. For example, in practical operation, ultrasonic dispersion can be used, with ultrasonic treatment at a frequency of 40–60 kHz for 30–60 min to obtain a uniformly dispersed and stable lubricating oil.

[0013] In a second aspect of the invention, a method for preparing a covalent organic framework lubricating additive used in the first aspect of the invention is provided, comprising the following steps: (1) Mix benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde, 5,5'-diamino-2,2'-bipyridine with an organic solvent to form a suspension; (2) Add an acidic catalyst to the suspension, degas it and seal it to obtain a pre-reaction solution; (3) The pre-reaction solution is subjected to Schiff base reaction at a certain temperature. After the reaction is completed, the crude product is collected, purified and dried to obtain a covalent organic framework lubricant additive.

[0014] Preferably, in step (1), the molar ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde to 5,5'-diamino-2,2'-bipyridine is 1:1.2 to 1:1.8.

[0015] Preferably, in step (1), the organic solvent comprises a mixed solvent of o-dichlorobenzene (o-DCB) and N,N-dimethylacetamide (DMAC); the amount of the organic solvent is 0.8 to 1.2 mL based on the amount of 0.042 mmol of the benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde.

[0016] More preferably, in the mixed solvent, the volume ratio of o-dichlorobenzene to N,N-dimethylacetamide is 2:1 to 4:1.

[0017] Preferably, in step (2), the acidic catalyst includes an aqueous acetic acid solution; the concentration of the aqueous acetic acid solution is 3~9 mol / L; and the amount of the aqueous acetic acid solution added is 0.05~0.2 mL, based on the amount of the organic solvent used being 0.8~1.2 mL.

[0018] Degassing of the mixed system is used to remove oxygen from the system, prevent oxidation side reactions, and ensure the smooth progress of the reaction. In actual operation, this degassing step can be completed by a cycle of freezing, evacuation, and thawing. For example, the mixed system can be frozen in liquid nitrogen at -196 °C, and after three cycles of freezing, evacuation, and thawing, it can be sealed with a flame.

[0019] Preferably, in step (3), the temperature of the Schiff base reaction is 100~150 ℃ and the reaction time is 48~96 h.

[0020] Under the preferred Schiff base reaction parameters, it is beneficial to obtain products with high crystallinity and large specific surface area. After the Schiff base reaction is complete, those skilled in the art can also select appropriate collection, purification, and drying methods based on actual conditions. For example, the crude solid product can be collected by filtration, followed by multiple washes with N,N-dimethylformamide (DMF) and acetone, and then Soxhlet extraction with tetrahydrofuran at 80-90 °C for at least 16 h to remove residual template and impurities in the pores, ensuring complete pore cleanliness.

[0021] Based on the above technical solutions, the design concept and principle of this invention are as follows: This invention is the first to use BTT-Bpy-COF, a specific covalent organic framework material containing pyridine nitrogen functional groups, as a lubricating oil additive, utilizing its high specific surface area (>1600 m²).2 The material ( / g) provides numerous adsorption sites. Compared to other covalent organic framework materials used as lubricant additives, the material selected in this invention is designed to possess abundant pyridine nitrogen functional groups (nitrogen content approximately 8 wt.%~12 wt.%), utilizing the lone pair electrons on the pyridine nitrogen atoms to form coordinate bonds with empty d orbitals on metal surfaces (such as iron, chromium, etc.), achieving strong chemisorption. This adsorption allows the covalent organic framework particles to firmly adhere to the surface of friction pairs (such as steel-iron friction pairs), forming a stable boundary lubrication film and significantly improving lubrication performance.

[0022] Furthermore, the BTT-Bpy-COF particles synthesized in this invention contain tens of thousands of pyridine units on their surface. Their design aims to enable a "multidentate coordination" effect when a single covalent organic framework sheet contacts a metal surface; that is, a covalent organic framework particle simultaneously binds to surface metal atoms through multiple pyridine sites. This multi-point anchoring effect is several orders of magnitude stronger than monomolecular adsorption, significantly enhancing the retention and erosion resistance of the covalent organic framework material at the friction interface, making it less prone to detachment under high shear stress, thereby maintaining long-term lubrication.

[0023] The BTT-Bpy-COF material prepared in this invention has a regular two-dimensional pore structure (pore size of approximately 2.7 nm), which can store base oil molecules. During friction, due to the local high temperature and pressure, the oil molecules in the pores are slowly released and replenished to the friction interface, forming an "oil storage-release" self-lubricating mechanism, which further reduces the coefficient of friction and delays wear.

[0024] As presented in one or more embodiments of the present invention, tribological tests show that adding only 0.1 wt.% of BTT-Bpy-COF to the base oil can reduce the coefficient of friction of gray cast iron surfaces from 0.35 to below 0.16, a reduction of more than 50%; simultaneously, the wear volume is reduced by approximately 60%. When the addition amount is increased to 0.5 wt.%, the coefficient of friction is further reduced to 0.12, and the wear volume is reduced by approximately 80%. Compared with traditional zinc dialkyl dithiophosphate additives or existing covalent organic framework materials used in lubricants, the covalent organic framework lubricant additive of the present invention is free of sulfur and phosphorus elements, environmentally friendly and non-toxic, and exhibits superior friction-reducing and anti-wear properties at extremely low addition amounts.

[0025] It should be noted that existing technologies (such as CN115646545A) include a technical solution for synthesizing BTT-Bpy-COF in an intermediate step, but its application of this material is as a carrier for photocatalytic water splitting, which is significantly different from the design concept and principle of this invention for lubrication and friction reduction.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention provides a method for preparing and applying a covalent organic framework lubricant additive. It utilizes the abundant pyridine nitrogen atoms in the framework of a specific covalent organic framework material to form strong coordination adsorption with the metal surface. This allows individual covalent organic framework particles to firmly adhere to the friction interface through a multi-toothed anchoring effect, significantly enhancing the shear resistance and retention of the lubricating film. Simultaneously, the porous structure of the covalent organic framework can store lubricating oil molecules, which are slowly released during friction, achieving self-replenishing lubrication. The additive of this invention can reduce the coefficient of friction by more than 50% at extremely low dosages, significantly improving the friction-reducing and anti-wear properties, reliability, and service life of the lubricating oil. Attached Figure Description

[0027] Figure 1 A schematic diagram of the synthesis process of BTT-Bpy-COF; Figure 2 Images of BTT-Bpy-COF obtained using a scanning electron microscope (SEM). Figure 3 The X-ray diffraction (XRD) pattern of BTT-Bpy-COF; Figure 4 In the figure, (a) is the nitrogen adsorption-desorption curve of BTT-Bpy-COF, and (b) is the pore size distribution diagram of BTT-Bpy-COF. Figure 5 The curves showing the change of friction coefficient over time for each oil sample in Examples 1, 2, and Comparative Example 1 are shown. Detailed Implementation

[0028] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0029] Example 1 This embodiment provides the application of the covalent organic framework lubricant additive BTT-Bpy-COF in lubricating oil and the corresponding preparation method of this material.

[0030] In this embodiment, 10 mg of BTT-Bpy-COF powder was added to 10 g of PAO8 base oil and placed in an ultrasonic cleaner (power 100 W, frequency 40 kHz) for ultrasonic treatment for 45 min to obtain a uniformly dispersed oil sample, which was denoted as COF-0.1%.

[0031] like Figure 1 As shown, the preparation method of the above-mentioned covalent organic framework lubricant additive BTT-Bpy-COF is as follows: (1) Weigh BTT-CHO (14.2 mg, 0.042 mmol) and Bpy-NH2 (15.3 mg, 0.062 mmol) and place them in a Pyrex glass tube (outer diameter 10 mm, inner diameter 8 mm, length 15 cm), add 1 mL of mixed solvent (o-DCB / DMAC, volume ratio 3:1), sonicate for 5 min, and obtain an orange-yellow suspension; (2) Then add 0.1 mL of acetic acid aqueous solution (6 mol / L) to the tube, immerse the glass tube in liquid nitrogen and freeze until the contents are completely solidified, evacuate the tube until the pressure inside the tube is lower than 5 Pa, close the vacuum valve, heat the tube with a flame to thaw the contents, repeat the above freezing-evacuation-thawing cycle three times; finally, seal the glass tube with a flame under vacuum. (3) The sealed glass tube was placed in an oven at 120 °C and allowed to stand for 72 h. After the reaction was completed, the glass tube was removed and allowed to cool naturally to room temperature. The glass tube was opened and the contents were transferred to a sintered glass funnel and filtered. The solid was washed with DMF (10 mL × 3) and acetone (10 mL × 3) in sequence. The solid was then transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 h to remove residual small organic molecules in the pores. After the extraction was completed, the solid was placed in a vacuum drying oven and dried at 100 °C overnight to obtain an orange-yellow powder, which is BTT-Bpy-COF, with a yield of about 85%.

[0032] The microstructure of BTT-Bpy-COF was observed using scanning electron microscopy, and the results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the synthesized BTT-Bpy-COF is a multi-level dendritic rod-shaped nano / micro structure with an uneven surface.

[0033] BTT-Bpy-COF was characterized by X-ray diffraction, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the synthesized BTT-Bpy-COF has good crystallinity. The XRD pattern shows obvious diffraction peaks at around 2.8° and 5.0°, corresponding to the (100) and (110) crystal planes, respectively. The simulated diffraction positions and experimentally measured diffraction peak positions and relative intensities of Bpy-IM-BTT-COF were compared using the Pawley refinement method. The experimentally measured diffraction data are in good agreement with the simulated AA stacking mode XRD pattern, proving that BTT-Bpy-COF conforms to the AA stacking mode.

[0034] The nitrogen adsorption-desorption curves and pore size distribution diagrams of BTT-Bpy-COF are shown below. Figure 4As shown in (a) and (b), the specific surface area of ​​BTT-Bpy-COF is 1642 m². 2 / g, with pore size distribution concentrated at 2.7 nm.

[0035] Example 2 This embodiment provides the application of the covalent organic framework lubricant additive BTT-Bpy-COF in lubricating oil. The BTT-Bpy-COF used in this embodiment is the same as that in Example 1, the difference being that its application in this embodiment is as follows: Weigh 50 mg of BTT-Bpy-COF powder and add it to 10 g of PAO8 base oil. Disperse the mixture ultrasonically for 45 min to obtain a COF-0.5% oil sample.

[0036] Those skilled in the art can also adjust the corresponding application or preparation parameters under preferred conditions according to actual conditions or needs to achieve the purpose of this invention.

[0037] Example 3 This embodiment investigates the effect of different solvent ratios on the structure of BTT-Bpy-COF during its preparation.

[0038] Following the synthesis steps provided in Example 1, only the volume ratio of the mixed solvent in step (1) was changed to prepare samples with o-DCB / DMAC ratios of 2:1 and 4:1, respectively, denoted as COF-2:1 and COF-4:1, with other step parameters remaining the same. X-ray diffraction characterization was performed on the products obtained with different volume ratios, and the highest crystallinity was observed when the ratio was 3:1. To achieve better application results, a solvent ratio of 3:1 is preferred for preparing the BTT-Bpy-COF mixed solution.

[0039] Example 4 This example investigated the effect of different reaction times on the structure of BTT-Bpy-COF during its preparation.

[0040] Following the synthesis steps of Example 1, only the reaction time in step (3) was changed, setting it to 48 h, 72 h, and 96 h respectively. Product characterization showed that the sample obtained at 72 h had the highest crystallinity, the change was not significant when extended to 96 h, and the crystallinity decreased when shortened to 48 h. To achieve better application results, the preferred reaction time for preparing BTT-Bpy-COF is 72 h.

[0041] Example 5 This embodiment investigates the stability of different amounts of BTT-Bpy-COF added during application.

[0042] The COF-0.1% and COF-0.5% oil samples prepared in Examples 1 and 2 were placed in transparent glass bottles, sealed, and observed for any precipitation or stratification. The results showed that all oil samples maintained a uniform dispersion state and no obvious precipitation was observed, indicating that BTT-Bpy-COF has good dispersion stability in base oils.

[0043] Comparative Example 1 This comparative example uses pure PAO8 base oil without any additives. It is used as a blank control in tribological testing.

[0044] Test Example 1 The practical application effect of the BTT-Bpy-COF invention was tested. A reciprocating friction and wear testing machine (model: MFT-5000, Rtec Corporation, USA) was used for testing. The upper sample was a GCr15 bearing steel ball (diameter 6.35 mm, hardness HRC61), and the lower sample was a gray cast iron plate (30 mm × 10 mm). Before the test, the samples were ultrasonically cleaned with petroleum ether for 10 min and dried before installation. Oil samples containing 0.1% COF, 0.5% COF, and Comparative Example 1 were added to the contact area of ​​the friction pair. The test parameters were set as follows: load 50 N, reciprocating stroke 10 mm, sliding speed 40 mm / s, test time 30 min, and ambient temperature 25 ℃. The friction coefficient was automatically recorded by computer during the test. After the test, the samples were removed, ultrasonically cleaned with anhydrous ethanol, dried, and the depth and width of the wear marks were measured using a three-dimensional optical profilometer to calculate the wear volume. Each test was repeated three times, and the average value was taken.

[0045] Figure 5 The curves showing the change in the coefficient of friction of each oil sample over time are presented. The coefficient of friction of pure PAO8 (Comparative Example 1) was relatively high in the initial stage (about 0.4), then gradually decreased and stabilized at around 0.35, indicating that the lubricating performance of the base oil itself was limited. After adding 0.1 wt.% BTT-Bpy-COF, the coefficient of friction rapidly decreased to about 0.16 and remained stable; when adding 0.5 wt.% BTT-Bpy-COF, the coefficient of friction was as low as 0.12, and the curve was stable without fluctuations, indicating that the covalent organic framework lubricating additive selected in this invention formed a stable and robust lubricating film at the friction interface.

[0046] Based on the structural characteristics of BTT-Bpy-COF and the results of tribological tests, the working mechanism of this invention is as follows: (1) Chemical adsorption: The pyridine nitrogen atoms in the BTT-Bpy-COF framework contain lone pairs of electrons, which form coordinate bonds with iron atoms on the surface of the friction pair, so that BTT-Bpy-COF is firmly adsorbed on the metal surface; (2) Multi-tooth anchoring: Each covalent organic framework sheet contains a large number of pyridine units, which significantly enhance the adsorption strength and shear resistance through multi-point coordination; (3) Oil storage effect: The nanopores of BTT-Bpy-COF store the base oil, which is slowly released under the action of frictional heat and pressure, replenishing the lubricating film and achieving self-repairing lubrication. The synergistic effect of the three gives BTT-Bpy-COF excellent friction reduction and anti-wear properties.

[0047] In summary, this invention utilizes the specific covalent organic framework material BTT-Bpy-COF as an additive in lubricating oils. This material has a simple synthesis method, a well-defined structure, and stable performance. The additive exhibits excellent dispersibility in base oils, and even extremely low addition levels (0.1~0.5 wt.%) can significantly reduce the coefficient of friction and wear volume. This invention provides a new approach for developing efficient and environmentally friendly lubricating additives, possessing significant application value and industrialization prospects.

[0048] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. Use of a covalent organic framework lubricating additive, characterized in that, include: Covalent organic framework lubricating additives are added to base oils as additives to reduce friction and wear in lubricating oils; The covalent organic framework lubricant additive is a covalent organic framework material formed by the condensation of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 5,5'-diamino-2,2'-bipyridine via a Schiff base reaction.

2. The application of the covalent organic framework lubricant additive according to claim 1, characterized in that: The base oil includes one or more of polyalphaolefins, mineral oils, and ester oils, or a mixture thereof.

3. The application of the covalent organic framework lubricant additive according to claim 1, characterized in that: The covalent organic framework lubricant additive is added at an amount of 0.05 wt.% to 1.0 wt.% of the base oil.

4. The application of the covalent organic framework lubricant additive according to claim 1, characterized in that: The covalent organic framework lubricant additive has a two-dimensional layered structure, with covalent bonds connecting the layers and ordered channels formed between the layers through π-π stacking.

5. A method for preparing a covalent organic framework lubricating additive according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Mix benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde, 5,5'-diamino-2,2'-bipyridine with an organic solvent to form a suspension; (2) Add an acidic catalyst to the suspension, degas it and seal it to obtain a pre-reaction solution; (3) The pre-reaction solution is subjected to Schiff base reaction at a certain temperature. After the reaction is completed, the crude product is collected, purified and dried to obtain a covalent organic framework lubricant additive.

6. The method for preparing the covalent organic framework lubricating additive according to claim 5, characterized in that: In step (1), the molar ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde to 5,5'-diamino-2,2'-bipyridine is 1:1.2 to 1:1.

8.

7. The method for preparing the covalent organic framework lubricant additive according to claim 5, characterized in that: In step (1), the organic solvent includes a mixed solvent of o-dichlorobenzene and N,N-dimethylacetamide; the amount of the organic solvent used is 0.8~1.2 mL based on the amount of 0.042 mmol of the benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde.

8. The method for preparing the covalent organic framework lubricating additive according to claim 7, characterized in that: In the mixed solvent, the volume ratio of o-dichlorobenzene to N,N-dimethylacetamide is 2:1 to 4:

1.

9. The method for preparing the covalent organic framework lubricant additive according to claim 5, characterized in that: In step (2), the acidic catalyst includes an aqueous acetic acid solution; the concentration of the aqueous acetic acid solution is 3~9 mol / L; based on the amount of organic solvent used being 0.8~1.2 mL, the amount of the aqueous acetic acid solution added is 0.05~0.2 mL.

10. The method for preparing the covalent organic framework lubricant additive according to claim 5, characterized in that: In step (3), the Schiff base reaction temperature is 100~150 ℃ and the reaction time is 48~96 h.

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