2D MOFs Nano-Lubricating Materials Based On Interface Interaction

Friction and wear were common phenomena in nature,and lubricating materials and lubricating additives were the most effective measures to reduce the harm caused by friction and wear and save energy consumption.Two-dimensional(2D)nanomaterials with special layered structure exhibit excellent mechanical properties,anti-friction and anti-wear properties.It is the most promising lubricating materials to replace traditional organic lubricant additives(zinc dialkyl dithiophosphate).Two-dimensional metal-organic frameworks(2D MOFs),ultra-thin thickness and the natural interfacial interaction with lubricants,has excellent dispersibility and stability in lubricants.Therefore,this article was mainly to optimize the preparation methods of 2D Zn-MOFs composed of different organic ligands,and to investigate the tribological properties of the prepared 2D Zn-MOFs lubricating materials.The specific work of this thesis were as follows:(1)2D Zn(Bim)(OAc)MOFs(Bim=benzimidazole,OAc=acetate)with a thickness of ca.3-4 nm were prepared by a simple ultrasonic-assisted peeling method in a solvent,and the yield was 21%.The dispersion and tribological properties of 2D Zn(Bim)(OAc)MOFs nanosheets dispersed in oils of different polarities were explored.The results showed that the 2D Zn(Bim)(OAc)MOFs nanosheets exhibit excellent dispersion properties in glycerol,while it exhibit better anti-friction properties and wear resistance in liquid paraffin.(2)The few-layer 2D ZnBDC MOFs nanosheets(BDC=1,4-phthalic acid)with a thickness of ca.5 nm were successfully prepared by surfactant-mediated.The friction behavior of 2D MOFs based on 2D ZnBDC under two friction modes(reciprocating ball-to-slider and ball-to-ball)has been comprehensively studied.Since the potential structural advantages of 2D MOFs effectively promote their good interfacial compatibility and dispersibility in oil,the dispersion and friction properties of 2D ZnBDC in base oils was studied.The results showed that the optimal addition amount of 2D ZnBDC-base oil in the ball-to-slider mode was 1.0 wt.%,and the corresponding wear amount was reduced by 29%;the optimal addition amount in the ball-to-ball mode was 0.05 wt.%,The friction coefficient and wear scar diameter were reduced by 16.7%and 20%,respectively.The effect of addition amount,load and friction speed on the tribological properties showed that it more obvious differences in the effects of the two modes on the tribological properties.By detecting the change of the contact angle between the ZnBDC and the friction pair,the possible friction mechanisms in two modes were proposed.(3)A new oil/water system was developed for the interface synthesis of 2D Zn(Bim)(OAc)nanosheets.This method was to disperse the two initial raw materials(metal salt and organic ligand)of MOF in an immiscible two-phase system of base oil and water respectively,and then form a 2D Zn(Bim)(OAc)nanosheets with uniform thickness at the interface between oil and water.A series of characterizations were used to determine the structure and composition of 2D Zn(Bim)(OAc)nanosheets.At the same time,the organic interface and 2D layered structure of 2D Zn(Bim)(OAc)nanosheets could solved the dispersibility and stability of anti-friction additives in the base oil.By compared the dispersibility and stability of 2D Zn(Bim)(OAc)nanosheets in three oils(base oil,castor oil and grease),an in-depth discussion of 2D Zn(Bim)(OAc)nanosheets and oil interaction between the interface.(4)The dispersibility and tribological behavior of zeolite imidazole salt skeleton-8(ZIF-8)with mixed morphology in lubricating oil were studied,and the possible anti-friction and anti-wear mechanism of the zeolite imidazole frameworks-8(ZIF-8)as a lubricant additive was proposed.Secondly,an oil-in-water emulsion based on 2D MOFs was successfully prepared by the self-assembly interface method.The emulsification results showed that 2D MOFs could stably form a self-assembled interface on the surface of oil droplets.In addition,the 2D ZIF-11-based emulsion exhibited the most excellent anti-friction,anti-wear performance and extreme pressure performance.Its friction coefficient and wear volume were reduced by 16.7%and 38.7%,respectively,while the PB value was increased by 11.3%.