Universal Fluorination-Created Edge C–F Groups in Networks of Multidimensional Carbon Materials

Abstract

Fluorination can significantly change the physical and chemical properties of carbon materials (CMs). Common sense for the fluorination mechanism for CMs indicates that one basal-plane C−F group (CF group) can form as one fluorine atom bonded to one carbon atom along the out-of-plane carbon networks without creating edge C−F groups (including CF 2 and CF 3 groups) at vacancies in carbon networks. We report that fluorination can generally create edge C−F groups in multidimensional CMs such as graphite, graphene, carbon nanotubes, and fullerene, and the concentration of edge C−F groups is dependent on both the crystallinity of starting CMs and the fluorination pressure and temperature. As an example, we show the significant differences in the band gap opening, photoluminescence, and magnetic properties between two half-fluorinated graphenes with different concentrations of edge C−F groups. Our findings highlight the importance of fluorination in creating edge C−F groups in the structure and properties and introduce new insight into fluorinated CMs.

Non-clustering of sp 3 fluorine adatoms on pristine graphene surface

“…It is found that the spectrum at 280-296 eV exhibits two strong combined with two weak characteristic peaks. As to the two strong peaks, one peak at ∼285.8 eV is attributed to the C-CF bonds for carbons adjacent to CF bonds, and the other peak at ∼288.8 eV to the CF bonds for carbons to CF covalent bonds [3,10,[41][42][43]. As mentioned above, if fluorine clustering is present, the CF peak should be much stronger than C-CF peak.…”

“…Reasonably, a fluorine cluster consists of two parts, the outermost fluorine shell and the inner fluorine core, as illustrated in figure 1(a). In the C 1s XPS spectrum of FG, the great difference in the binding energy of the sp 2 C-C peak, C-CF peak (for carbons adjacent to CF bonds), and CF peak (for CF covalent bonds) due to the strong binding energy shift relative to each other [3,10,[41][42][43], affords one to obtain the exact R [3,41]. In principle, the C-CF peak mainly results from the fluorinated carbons of the shell of the cluster, whilst, the CF peak mainly results from the fluorinated carbons of the core.…”

“…By contrast, slightly FG with F/C much lower than 0.5 has enough bare carbons for fluorine adatoms to migrate. Previous study revealed that fluorination generating vacancies is universal for defective graphene, whilst is difficult for pristine graphene [43]. To exclude the effect of both such fluorinationgenerated vacancies on the fluorination pattern, we choose freestanding pristine monolayer graphene as the starting material [46].…”

“…X-ray photoelectron spectrum (XPS) is widely used to quantitatively characterize the element stoichiometry and probe the nature of chemical bonds of graphene derivatives [38][39][40][41][42][43]. Nevertheless, this spectrum, which can effectively detect fluorine adatoms, cannot detect hydrogen adatoms due to that the photoionization cross section of H 1s spectrum is 5000 times smaller than that of C 1s XPS spectrum [44].…”

“…Especially, the fluorination degree of F/C atomic ratio can be tuned from 0 to 1 for the highest electronegativity of fluorine atoms [19][20][21][22][23][24][25][26], which is favorable to investigate the functionalization degree-dependent evolution of sp 3 pattern. Furthermore, due to the great difference in binding energy for C-CF and CF peaks in C 1s XPS spectrum of FG, the intensity ratio of C-CF peak to CF peak (R) can be obtained [3,10,[41][42][43], which can be used to evaluate the size of fluorine cluster.…”