Chemical and Physical Viewpoints About the Bonding in Fullerene–Graphene Hybrid Materials: Interaction on Pristine and Fe-Doped Graphene

A DFT scheme was adopted to study the noncovalent/covalent attachment of fullerenes (C-60, Si24C36, and B24N36) to graphene and Fe-doped graphene nanosheets (FeG). Geometrical, energetic, and electronic properties related to the physical and chemical nature of the bonding were characterized. The results show that fullerenes are physisorbed on graphene with adsorption energies of 0.7-1.2 eV, while the chemisorption is reached on FeG by cycloadditions with adsorption energies of 1.6-4.4 eV and is depending on the topology of FeG. The origin of the stability was analyzed from chemical and physical viewpoints, applying methods such as atom-in-molecules (AIM), natural bond orbital (NBO), and energy decomposition analysis based on absolutely localized molecular orbitals (ALMO-EDA). It is shown that noncovalent graphene-fullerene hybrids are assembled by van der Waals interactions but are also governed by permanent electrostatic Coulombic interactions that contribute at least 31% to the binding stability and depending on the bond polarity of fullerenes. Otherwise, the cycloaddition of fullerenes with FeG is reached by the formation of highly polarized chemical bonds, which were described in a detailed orbital picture. The structural stability of the covalent complexes is dominated by the contribution of charge transfer and permanent electrostatic physical effects. Additionally, the polarizability is an intrinsic property of fullerenes that also determines its binding strength on graphene (up to 35%); in this way, the larger polarizability of fullerenes increases the interaction stability. Therefore, this work gives insights into the bonding properties governing the stability of hybrid materials formed by self-assembly of fullerenes onto emerging low-dimensional nanostructures.