Journal of Molecular Liquids
Adsorption, DFT calculations, Fluorographene nanosheet, Ionic liquid, Non-covalent interactions, Optical properties
In the present study, we investigate the adsorption characteristics of six different ionic liquids (ILs) on a fully-fluorinated graphene (fluorographene, FG) surface using electronic structure studies and associated analysis methods. A systematic comparison of differences in IL binding energies (ΔEb) with fluorographene, graphene and hexagonal boron nitride surfaces indicates that fluorination strongly decreases the binding energy compared to the other two surfaces, hence resulting in the binding energetics: ΔEb (Graphene…IL) > ΔEb (Hexagonal boron-nitride…IL) > ΔEb (Fluorographene…IL). To probe the reasons for this difference, quantum theory of atoms in molecules (QTAIM) analysis and non-covalent interactions (NCI) analyses were carried out. Results indicate that the stability of complexes of FG surface with ILs (FG…IL) arises only due to the presence of the expected weak non-covalent intermolecular interactions. The calculation of charge transfers by employing the ChelpG method shows that the interaction of ILs with FG surface generally induces a negative charge on the FG surface. Furthermore, these interactions lead to a decrease of the HOMO-LUMO energy gap (Eg) of the FG surface, enhancing its electrical conductivity. In addition, a detailed analysis of the global molecular descriptors including the Fermi energy level (EFL), work function (WF), electronic chemical potential (μ), chemical hardness (η), global softness (S) and electrophilicity index (ω) was carried out for both the FG surface alone and the adsorbed complexes showing that there are small, but meaningful, differences in the reactivity of the surface depending on the nature of the IL. Finally, time-dependent DFT (TD-DFT) calculations of the optical properties of FG surface and FG…IL complexes reveal that the absorption spectrum of the FG surface undergoes a red shift following IL adsorption. This study demonstrates that FG provides a useful complementary tool to graphene and boron nitride materials, allowing for the fine-tuning of the optoelectronic properties of these monolayer materials. These results will assist in the development of these types of ILs for applications in optoelectronics.
Shakourian-Fard, Mehdi; Maryamdokht Taimoory, S.; Semeniuchenko, Volodymyr; Kamath, Ganesh; and Trant, John F.. (2018). The effect of ionic liquid adsorption on the electronic and optical properties of fluorographene nanosheets. Journal of Molecular Liquids, 268, 206-214.