Electronic and adsorption properties of extended chevron and cove-edged graphene nanoribbons

The electronic and adsorption properties of chevron and cove-edged graphene nanoribbons (GNRs) are studied using first principles calculations. The positive binding and adsorption energies in conjunction with the positive infrared frequencies insure the stability of the considered GNRs. The results show that the binding strength of coved-edged GNRs is higher than that of chevron ones because the morphology of the latter requires a higher number of C-atoms at the edges than the former. The edge atoms in chevron GNRs create interactive edge states that significantly decreases the energy gap (Eg = 0.03 eV) with respect to the wide gap between bulk states in cove-edged ones (Eg = 2.19 eV). The molecular orbitals distributions of these edge states are localized only on the arms of the nanoribbon making it a potential topological insulator. The energy gap between bulk states in cove-edged decreases by increasing the width due to quantum size effect, while in chevron GNRs the gap between edge states increases because of the interaction among these states. The adsorption of methylene blue shows interesting properties depending on the type of the nanoribbons, the interaction position, and the attached chemical group. The interactive edge states provide moderate adsorption on the arms of the nanoribbons and the attached chemical groups enhance the adsorption by adding new adsorption positions. The additional molecular orbitals from the physically adsorbed dye lower the band gap and create semimetal GNRs with zero or negative band gap.