Dependence of fluorination intercalation for graphene toward high-quality fluorinated graphene formation

Direct gas-solid reaction between fluorine gas (F2) and graphene is expected to become an inexpensive, continuous and scalable production method to prepare fluorinated graphene. However, the dependence of fluorination intercalation for graphene is still poorly understood, which restricts the formation of high-quality fluorinated graphene. Herein, we demonstrated that chemical defects (oxygen groups defects) on graphene sheet played a leading role in promoting fluorination intercalation, whereas physical defects (point defects), widely considered to be an advantage due to more diffusion channels for F2, did not count as influential. Tracing origins, compared with point defects, the unstable hydroxyl and epoxy groups produced active radicals and the relatively stable carbonyl and carboxyl activated surrounding aromatic regions, thereby both facilitating fluorination intercalation, and the former was preferential and easier to react. Based on above investigations, we successfully prepared fluorinated graphene with an ultrahigh interlayer distance (9.7 A), the biggest value reported for fluorinated graphene, by customizing graphene with more hydroxyl and epoxy groups. It presented excellent self-lubricating ability with an ultralow interlayer interaction of 0.056 mJ m-2, thus possessing far lower friction coefficient compared with graphene as lubricants. Moreover, it was also easy to exfoliate by shearing, due to the diminutive interlayer friction and eliminated commensurate stacking. The exfoliated number of layers less than three exceeded 80% (monolayer rate≈40%), and no any surfactant was applied to avoid again stacking.