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

Abstract

Considering practical applications, the thermal/thermal oxidative stability of fluorinated graphene should be given sufficient attention. Herein, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were used to investigate in detail the differences in the thermal stabilities of two types of fluorinated samples, fluorinated graphene (FG) and fluorinated porous graphene (FPG) with various fluorine contents, respectively, as well as the reasons for these differences. It was demonstrated that the thermal stability of FG and FPG was improved upon increasing the fluorine content, which was mainly caused by the enhancement of bond energy of the covalent C-F bonds. Moreover, compared to that of the raw graphene samples, the thermal oxidative stability of FG was reduced due to the defects brought by fluorination, while the thermal oxidative stability of FPG was improved, originating from the inflaming retarding effect of the fluorine element. Interestingly, the thermal oxidative stability of the fluorinated samples was even better than their thermal stability. Using a comparison of the two types of fluorinated samples and support from the computational simulations of the model molecules, it was suggested that a greater amount of CF (n = 2, 3) groups or defects in the FG samples resulted in its relatively worse thermal stabilities. Furthermore, electron paramagnetic resonance (EPR) spectroscopy was introduced to analyze the thermal stabilities of the fluorinated graphene samples as a novel method. The changes in the spin centers in samples after thermal treatment were studied, which indicated that the lower amount of the more stable spin centers of FPG was another reason leading to its more outstanding thermal stabilities in comparison to FG samples.

Thermally reduced fluorographenes as efficient electrode materials for supercapacitors

“…A similar trend was observed for the FG samples prepared at different temperatures 79,80 and also for the FG samples pre-pared at a constant temperature but different pressures, as reported previously. 81 Fig . 3a shows a survey spectrum of the FG-20H sample and its elemental composition (inset of Fig.…”

Novel Synthesis of Slightly Fluorinated Graphene Quantum Dots with Luminescent and Paramagnetic Properties through Thermal Cutting of Fluorinated Graphene

“…Figure 2 a gives the survey XPS of FG and GQDs-F. For FG, there exist two prominent peaks at 688.8 and 833.8 eV corresponding to photoemission of the F 1s core level and Auger electron [ 31 , 33 ]. After being annealed at 810 K, it is seen from the survey XPS of GQDs-F sample that the F signals decrease obviously, along with the increasing C 1s signals at ca.…”

“…Figure 2 b,c gives the typical C 1s XPS spectra of FG and GQDs-F, which were fine-scanned and deconvoluted into several components. The locations of C 1s XPS peaks corresponding to different chemical groups are also given in Table 1 [ 31 , 33 ]. When compared to FG, GQDs-F show an obvious increase in the percent of sp 2 C–C bonds, as well as a decrease in the intensity of the CF n peaks, manifesting the reformation of sp 2 bonds and an evident defluorination.…”

“…The contents of chemical groups of the samples determined from the deconvolution of C 1s spectra are shown in Table 1 . Notably, for the FG sample, there is a non-negligible formation of CF n ( n = 2, 3) bonds (CF 2 : 23.9%, terminal CF 3 : 8.4%), generally located at graphene defects and edges [ 31 , 33 , 34 ]. It owes to the violent reaction of the direct fluorination of GO with excess of XeF 2 at the high fluorination temperature, and oxygenic groups in GO greatly accelerate fluorination reaction by activating the adjacent aromatic regions and participating in the substitution reaction with fluorine radicals [ 34 ].…”

“…Although perfect graphene fluoride is known as a two-dimensional counterpart of Teflon [ 28 ], the prepared fluorinated graphene in this work with high percent of structure defects is fragile [ 29 ]. Strikingly, we found that the CF n ( n = 2, 3) groups near structure defects are like scissors in thermal defluorination, which can evaporate as C 2 F 4 product and greatly enlarge the structure defects of fluorinated graphene [ 30 , 31 ]. The fluorinated graphene can be thermally cut into GQDs-F with a low F/C atomic ratio of ca.…”