Regulating the Bonding Nature and Location of C–F Bonds in Fluorinated Graphene by Doping Nitrogen Atoms

Enhanced directional transfer of charge carriers and optimized electronic structure in fluorine doped polymeric carbon nitride nanosheets for efficient photocatalytic water splitting

The high photogenerated charge carrier recombination and sluggish oxygen evolution reaction (OER) kinetics of polymeric carbon nitride (PCN) photocatalysts limit their application in photocatalytic water splitting. Herein, fluorine (F) doped PCN (PCNF-x) nanosheets with high crystallinity were prepared using dicyandiamide (C2H4N4) and ammonium hydrogen fluoride (NH4HF2) through high temperature thermal polymerization. This process not only resulted in PCNF-x nanosheets with a large number of pores, but also improved the crystallinity of PCNF-x nanosheets. Under illumination, the PCNF-0.5 nanosheets exhibited an excellent photocatalytic water splitting activity with a comparable H2 evolution rate of 135.30 μmol h-1 g-1 and O2 evolution rate of 63.75 μmol h-1 g-1, which were 2.3-fold, 3.3-fold, and 25-fold as compared to those of PCNF-1, PCNF-0.2, and pristine PCN nanosheets, respectively. Photoluminescence (PL) spectra and density functional theory (DFT) calculations indicate that F doping of PCN nanosheets brings two changes in PCNF-x nanosheets, one is the increase in crystallinity after F doping effectively weakens the bulk defects of PCNF nanosheets, which is conducive to the directional transfer of charge carriers; the other is the modulation of the electronic structure after F doping, which optimizes the reaction mechanism of the OER in PCNF-x nanosheets. Both the enhancement in charge carrier transfer and the optimization of the reaction mechanism significantly contribute to the improved photocatalytic performance of water splitting in the fluorine doped PCN nanosheets.

Recent Advances in Fluorinated Graphene from Synthesis to Applications: Critical Review on Functional Chemistry and Structure Engineering

Fluorinated graphene (FG), as an emerging member of the graphene derivatives family, has attracted wide attention on account of its excellent performances and underlying applications. The introduction of a fluorine atom, with the strongest electronegativity (3.98), greatly changes the electron distribution of graphene, resulting in a series of unique variations in optical, electronic, magnetic, interfacial properties and so on. Herein, recent advances in the study of FG from synthesis to applications are introduced, and the relationship between its structure and properties is summarized in detail. Especially, the functional chemistry of FG has been thoroughly analyzed in recent years, which has opened a universal route for the functionalization and even multifunctionalization of FG toward various graphene derivatives, which further broadens its applications. Moreover, from a particular angle, the structure engineering of FG such as the distribution pattern of fluorine atoms and the regulation of interlayer structure when advanced nanotechnology gets involved is summarized. Notably, the elaborated structure engineering of FG is the key factor to optimize the corresponding properties for potential applications, and is also an up-to-date research hotspot and future development direction. Finally, perspectives and prospects for the problems and challenges in the study of FG are put forward.