Fan Kun, Fu Jiemin, Liu Xikui, Liu Yang, Lai Wenchuan, Liu Xiangyang, Wang Xu
College of Polymer Science and Engineering , State Key Laboratory of Polymer Material and Engineering , Sichuan University , Chengdu 610065 , People's Republic of China . Email:
Chem Sci. 2019 Apr 30;10(21):5546-5555. doi: 10.1039/c9sc00975b. eCollection 2019 Jun 7.
A direct gas-solid reaction between fluorine gas (F) and graphene is expected to become an inexpensive, continuous and scalable production method to prepare fluorinated graphene. However, the dependence of the fluorination intercalation of graphene is still poorly understood, which prevents the formation of high-quality fluorinated graphene. Herein, we demonstrate that chemical defects (oxygen group defects) on graphene sheets play a leading role in promoting fluorination intercalation, whereas physical defects (point defects), widely considered to be an advantage due to more diffusion channels for F, were not influential. Tracing the origins, compared with the point defects, the unstable hydroxyl and epoxy groups produced active radicals and the relatively stable carbonyl and carboxyl groups activated the surrounding aromatic regions, thereby both facilitating fluorination intercalation, and the former was a preferential and easier route. Based on the above investigations, we successfully prepared fluorinated graphene with an ultrahigh interlayer distance (9.7 Å), the largest 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, thus possessing a far lower friction coefficient compared with graphene, when acting as a lubricant. Moreover, it was also easy to exfoliate by shearing, due to the diminutive interlayer friction and eliminated commensurate stacking. The exfoliated number of layers of less than three exceeded 80% (monolayer rate ≈ 40%), and no surfactant was applied to prevent further stacking.
氟气（F₂）与石墨烯之间的直接气固反应有望成为一种廉价、连续且可扩展的制备氟化石墨烯的生产方法。然而，石墨烯氟化插层的依赖性仍未得到充分理解，这阻碍了高质量氟化石墨烯的形成。在此，我们证明了石墨烯片上的化学缺陷（氧基团缺陷）在促进氟化插层方面起主导作用，而物理缺陷（点缺陷），尽管通常认为因其为氟提供了更多扩散通道而具有优势，但实际上并无影响。追溯其根源，与点缺陷相比，不稳定的羟基和环氧基团会产生活性自由基，而相对稳定的羰基和羧基则会活化周围的芳香区域，从而都促进了氟化插层，且前者是更优先、更易实现的途径。基于上述研究，我们通过制备具有更多羟基和环氧基团的石墨烯，成功制备出了层间距高达9.7 Å的氟化石墨烯，这是报道的氟化石墨烯的最大层间距值。它表现出优异的自润滑能力，层间相互作用超低，仅为0.056 mJ/m²，因此在作为润滑剂时，其摩擦系数远低于石墨烯。此外，由于层间摩擦力小且消除了相应的堆叠，它也易于通过剪切进行剥离。剥离出的层数小于三层的比例超过80%（单层率约为40%），且未使用表面活性剂来防止进一步堆叠。
