Anomalous high adsorption energy of H2O on fluorinated graphenes: a first principles study

Abstract

Polytetrafluoroethylene (PTFE) has been well-known for the surface superhydrophobicity, while its two-dimensional stable analogues, CF and C₄F, possess distinct surface wettability. The CF inherits the hydrophobicity from PTFE since the van der Waals interaction is mitigated by the high electronegativity of fluorine. Surprisingly, a high adsorption energy (∼550 meV per molecule) of water has been unveiled on C₄F via density functional theory studies, implying anomalous superhydrophilicity of C₄F. The abrupt transition from hydrophobicity of CF to superhydrophilicity of C₄F can be reconciled with the difference in their molecular orbitals. The high adsorption energy of C₄F is mainly attributed to the Coulomb attraction among the non-bonding interactions, as proposed by our theoretical model. Since the surface chemical inertness of CF inhibits it from being widely adopted in device fabrication, the present finding suggests that C₄F can be a promising candidate in graphene-based electronic devices.