Thermal stability of C-F/C(-F)2 bonds in fluorinated graphene detected by in situ heating infrared spectroscopy

The thermal stability of fluorinated graphene (FG) plays an important role in its application and research, and thus it is necessary to conduct in-depth research on the thermal stability of the C-F bond in FG. Herein, FG with different types and distributions of C-F/C(-F)₂ bonds were synthesized, and the correlation between the C-F/C(-F)₂ bonds and thermal stability of these FG samples was monitored via in situ heating infrared spectroscopy (in situ FTIR). The stability of the different types and distributions of C-F/C(-F)₂ bonds in FG and the temperatures at which these C-F/C(-F)₂ bonds were eliminated were determined. In terms of C-F bonds in FG, the most stable type is that in C(-F)₂ of perfluorinated FG, followed by the C-F bonds in perfluorinated FG. The thermal stability of isolated C-F bonds and C(-F)₂ bonds adjacent to the conjugated structure was the worst, which would be detached from FG at low temperature (≤82 °C). Furthermore, the evolution of the conjugated structures in FG during thermal annealing was also affected by the type and distribution of the C-F bonds.

Radical mechanism of a nucleophilic reaction depending on a two-dimensional structure

The mechanism of nucleophilic substitution deserves more investigation to include more reaction systems such as two-dimensional (2D) materials. In this study, we used fluorinated graphene (FG) as a representative 2D material to reveal the in-depth mechanism of its defluorination and nucleophilic substitution reaction under attack of common nucleophiles to explore the chemistry of 2D materials and enrich the research on the nucleophilic substitution reaction. DFT calculations and electron paramagnetic resonance spectroscopy (EPR) demonstrated that defluorination of FG occurred via a radical mechanism after a single electron transfer (SET) reaction between the nucleophile and C-F bond, and a spin center was generated on the nanosheet and fluorine anion. Moreover, neither the S_N1 nor S_N2 mechanism was suggested to be appropriate for the substitution reaction of FG with a 2D structure due to the corresponding kinetics or thermodynamics disadvantage; hence, its nucleophilic substitution was proved to occur via a radical mechanism initiated by the defluorination step. The proposed substitution mechanism of FG demonstrates that nucleophilic substitution via a radical mechanism can also be applied to the attacking process of common nucleophiles without any particular conditions. Furthermore, it has been discovered that triethylamine without active hydrogen can be covalently attached to graphene nanosheets via a nucleophilic substitution reaction with FG; this further indicates a radical process for the nucleophilic substitution of FG rather than an S_N1 or S_N2 mechanism. The detailed process of the nucleophilic substitution reaction of FG was revealed to occur via a radical mechanism depending on the 2D structure of FG, which could also represent the typical characteristic of 2D chemistry.

Tuning the Reactivity of Graphene by Surface Phase Orientation

Tuning the local reactivity of graphene is a subject of paramount importance. Among the available strategies, the activation/passivation of graphene by copper substrate is very promising because it enables the properties of graphene to be influenced without any transfer procedure, since graphene can be grown directly on copper. Herein, it is demonstrated that the reactivity of graphene towards fluorination is strongly influenced by the face of the surface of the copper substrate. Graphene on the copper foil was probed and grain orientations were identified. The results of the reactivity were evaluated by means of X-ray photo electron and Raman spectroscopy. Graphene on the grains with a surface orientation close to the (111) face is the most reactive, whereas graphene on the grains close to the (110) surface is least reactive. The long-term stability test showed that the decomposition of fluorinated graphene was slowest on the grains with a surface orientation close to the (111) face. The results are consistent with the variation of the mechanical strain of graphene on different faces of copper. In contrast, no clear correlation of the graphene reactivity with doping induced by different facets was found.

Characterization of the thermal/thermal oxidative stability of fluorinated graphene with various structures

The thermal/thermal oxidative stability of various fluorinated graphene depends on the differences in their corresponding C–F bonds, CF_n defects and spin centers on the nanosheets.

Defluorination and covalent grafting of fluorinated graphene with TEMPO in a radical mechanism

The work innovatively reveals the radical mechanism of derivative reactions of fluorinated graphene including its defluorination and covalent grafting, meanwhile first confirming the destination of deciduous fluorine atoms after defluorination.