Structural and Electronic Properties of Carbon Nanotubes and Graphenes Functionalized with Cyclopentadienyl–Transition Metal Complexes: A DFT Study

Abstract

In order to explore possible ways of using metallocene compounds in heterogeneous catalysis and in sensor applications, we present a theoretical characterization of cyclopentadienyl (Cp) + transition metal (TM) complexes adsorbed on boron-doped carbon nanotubes (B-CNTs) and boron-doped graphenes. Using spin-polarized density functional theory calculations, we present a systematic study of the geometries, energetics, and electronic properties of CpTM (where TM = Fe, Ni, Co, Cr, Cu) adsorbed on both pristine and boron-doped carbon supports. Our work reveals significant increases of the binding energies between CpTM and boron-doped CNTs and graphenes (versus pristine carbon supports), surpassing even the adsorption strength of the isolated metals atoms (by about 2 eV). According to our electronic structure analysis, both the delocalization of the TM-d state by the presence of the Cp ring and the interactions between the Cp ring and the carbon substrate are responsible for the enhancement of the binding energies. This stabilization may play an important role in immobilizing ferrocene-based catalysts. Moreover, tunable metallicities of CpTMs adsorbed on pristine and on B-CNTs are observed, indicating potential applications of CpTM/B-CNT complexes in nanoelectronics and as sensors. Using these complexes, we also probed the adsorption of O2 molecules, as an initial indicator of catalytic performance. Both chemisorption (with an elongated O–O bond) and dissociative chemisorption were found on CpFe/B-CNT (8,0) complexes.