Supporting Information for
Trifluoromethylation of Graphene
Figure S1. Raman spectrum of pristine graphene and the same graphene sample after
immersing in a solution of 30 mM Togni reagent in anhydrous methanol under the
protection of argon gas.
Figure S2. Raman spectrum of the trifluoromethylated graphene shown in Figure 2c.
Figure S3. (a) High-resolution I 3d spectrum of the same region on the
trifluoromethylated graphene. The absence of I 3d peaks indicates that iodine element
does not exist in this area. (b) The low resolution XPS survey of the same
trifluoromethylated graphene supported by 300 nm SiO2 substrate, in which the Si,
and O peaks come from the SiO2 substrate. Thus, contaminations on graphene such as
CuCl, Togni can be excluded.
Figure S4. Raman spectra of graphene samples with different degree of
trifluoromethylation. The black, blue and red curves correspond to the same sample
shown in figure 4a.
Theoretical part:
To investigate the structure and properties of trifluoromethylated graphene, density
functional theory (DFT) calculations using the Vienna ab initio simulation package
(VASP) within the local density approximation (LDA) were performed on the
adsorption of CF3 groups on graphene with various coverages and arrangements. We
first simulated the adsorption configurations of two CF3 groups on 50 carbon atoms,
since the experimental coverage is nearly 4% deduced from the XPS result. Three
representative configurations are shown in Figure S6a. For two CF3 groups at para
sites in a hexagonal ring, the short distance between CF3 leads to repulsive force, and
increases the total energy to -0.22 eV. As the distance increases, the repulsive force
between CF3 groups decreases. The energetically favorable configure for this
coverage is shown in the right plane of Figure S6a, which corresponds to the uniform
distribution of CF3 groups on graphene (Eb = -0.54 eV, Eb=binding energy). Since CF3
groups prefer to uniformly adsorb on graphene, the binding energy per CF3 group for
the uniform configurations for various coverage were calculated (Figure S6b). The
binding energy is largest for the 4% coverage (C50(CF3)2), which is consistent with the
CF3 coverage observed in experiment. The band structure of this stable configuration
is shown in figure S6c. Interestingly, a band gap as large as 1.2 eV is expected to open
up after trifluoromethylation.
Figure S5.
(a) Adsorption of a CF3 dimer on graphene. (b) Calculated binding
energy of different CF3 adsorption configurations. (c) Band structure for
homogeneous CF3 adsorption pattern on graphene (C50(CF3)2).