2D MOFs-based Composite For Nano-Lubricating

In recent years,two-dimensional(2D)layered nanomaterials with super-lubricated structure have become the focus of tribology.Traditional inorganic 2D layered nanomaterials exhibit excellent lubrication performance,but their practical application is limited by poor dispersion stability in lubricants.2D metal-organic frameworks(2D MOFs)could become an important research platform to solve the above technical bottlenecks due to the great interfacial interaction,elastic stiffness and significant super-lubrication structure.However,individual 2D MOFs as nano-lubricating additives in base oils shows poor tribological properties due to the instability of the skeleton.Therefore,this paper focused on desighing and constructuring a series of 2D MOFs-based nanocomposites to sol ve the above shortcomings,and investigated the lubrication performance of the prepared nanocomposite in lubricants.The specific works of this paper as follows:(1)Sliver nanowires/2D nickel-based metal-organic framework(Ag NWs/2D Ni-BDC)composites were successfully prepared by in-situ chemical reduction method.A series of characterizations confirmed that the glutathione-modified Ag nanoparticles(Ag NPs)selfassembled into Ag NWs and uniformly grew on the surface of 2D Ni-BDC nanosheets though bonding.The Ag NWs/2D Ni-BDC showed better dispersion and stability properties compared with the individual Ag NPs and 2D Ni-BDC in base oil(150SN).The tribological properties of the composite in base oil were investigated.The result showed that the average friction coefficient(COF)and wear scar diameter(AWSD)of lubricating oil contain 0.04wt.%composite reduced by 38.2%and 37%compared with pure base oil,and 17.39%and 12.26%lower than that of 2D Ni-BDC(0.04wt.%),respectively.In addition,the maximum non-seize load value(PB)of nanocomposites improved 22.62%and wear scar roughness(Ra)decreased by 45.83%compared with base oil,showing an excellent synergistic lubrication performance in base oil.(2)Nitrogen-doped carbon quantum dots/2D Ni-BDC(N-CDs/2D Ni-BDC)composites were synthesized by in-situ solvothermal method.Nitrogen-doped carbon quantum dots with particle size of about 3 nm were uniformly modified on the surface of 2D Ni-BDC nanosheets.The N-CDs/2D Ni-BDC showed great dispersibility with stably dispersing in castor oil for 12 days.The tribological properties of N-CDs/2D Ni-BDC composites in castor oil under ballon-ball contact and ball-on-slider contact were investigated.The results showed that the COF,AWSD and Ra value of the castor oil with 0.04wt.%nanocomposites decreased by 66.67%,30.64%and 52.63%compared with pure castor oil at the ball-on-ball contact,and 35.29%,25%and 43.75%lower than that of 2D Ni-BDC respectively.In the ball-on-slider contact,the COF,wear rate and Ra value of 0.04wt.%composites added to castor oil were reduced by 43.53%,34.68%and 51.9%compared with pure castor oil respectively,and 20%,12.3%and 17.39%lower than that of 2D Ni-BDC respectively.The N-CDs/2D Ni-BDC composites exhibited excellent lubricating properties in castor oil under different friction contacts.(3)The ZIF-7/2D Ni-BDC composites were prepared by in-situ synthesis,which the zerodimensional spherical ZIF-7 were uniformly covered on the surface of 2D Ni-BDC nanosheets through electrostatic adsorption and bongding effect.The ZIF-7/2D Ni-BDC(0.08wt.%)showed better dispersion than individual 2D Ni-BDC and ZIF-7 particles in liquid paraffin,and the precipitation was the least after 72 h of stabilization.The anti-friction and anti-wear properties of the three samples in liquid paraffin were test.The results showed that COF of liquid paraffin contain 0.08wt.%composite decreased 40.52%,35%and 15.74%respectively,and the corresponding AWSD were reducded by 18.03%,16.85%and 14.77%relative to pure liquid paraffin,2D Ni-BDC and ZIF-7.In addition,extreme pressure property and wear resistance of the ZIF-7/2D Ni-BDC in liquid paraffin also significantly improved.(4)Cacium borate/2D Ni-BDC(CB/2D Ni-BDC)composites were successfully synthesized through one-pot hydrothermal method.The interaction between the two synthetic solutions made the 2D Ni-BDC grow into a curly flower structure with about seven layers,while the CB was attached to its folded layer or surface with a smaller particle size.The test of the anti-friction and anti-wear properties of composite in base oil(150SN)showed that the COF and AWSD of the composites(0.15wt.%)were reduced by 37.42%and 28.13%compared with base oil.In addition,it exhibited the best wear resistance,which the PB of composite improve 23.15%and Ra value decreased by 56.25%compared with base oil.