Towards enhanced tribological performance as water-based lubricant additive: Selective fluorination of graphene oxide at mild temperature

It is still difficult to prepare hydrophilic fluorinated graphene with abundant oxygen functional groups and high F/C ratio.Herein, selective fluorination for graphene oxide (GO) was realized to prepare highly oxygen/fluorine dual functionalized graphene (OFG) under a mild temperature without damaging the sheet structure. Its O/C and F/C ratios came up to 0.58 and 0.19 respectively, which contained the intactly reserved oxygen functional groups from GO during fluorination and C-F bonds from addition reaction between aromatic region and F2, as demonstrated via X-ray photoelectron spectroscopy (XPS), thermo gravimetric analysis (TGA), Raman measurements and so on.Experiments and density functional theory (DFT) calculations revealed that oxygen functional groups in-situ promoted addition reaction between aromatic region and F2, and the critical point was confirmed that oxygen functional groups began to react with F2 by substitution reaction. As-prepared OFG presented a 47% and 31% decrease of wear rate compared with that of pure water and GO, respectively. During friction process, the abundant oxygen functional groups of OFG contributed to hydrophilic property and introduced fluorine played an important role in enhancing the tribological performance by self-lubricating behavior. Such mild and simple method is achieved to expand the application of fluorinated graphene in aqueous environment.