Covalent functionalization of fluorinated graphene through activation of dormant radicals for water-based lubricants

Abstract

Targeted covalent functionalization of graphene derivatives and simultaneously preserving their intrinsic structure and property are an underexplored, urgent and challenging task in two-dimensional chemistry. Herein, we develop a novel and facile method to achieve lossless covalent functionalization of fluorinated graphene (FG) through activating dormant radicals, derived from stabilization from conjugation effect of surrounding aromatic regions/fluorine atoms and particular two-dimensional skeleton. The activated radicals under definite temperature initiate acrylic acid (AA) to be grafted onto FG surface without any catalyst, completely different from traditional nucleophilic substitution (SN) reaction through sacrificing fluorocarbon bonds. Compared to destructive self-lubricating ability of FG-PEI from SN reaction, obtained FG-AA improves water dispersibility of hydrophobic FG and simultaneously maintains intrinsic self-lubricating ability with limited commensurate stacking and week interlayer interactions. Therefore, FG-AA presents excellent tribological performance as water-based lubricant additive, regarded as eco-friendly and sustainable system, whose friction coefficient and wear rate have about 66% and 82% decrease compared to that of FG-PEI, respectively. Moreover, taking advantage of such FG chemistry, the activated radicals and originally reactive fluorocarbon bonds also offer two non-interfering routes to implement stepwise double functionalization of graphene. Designing this strategy in mind expands the applications of FG in aqueous environment and enriches graphene chemistry.