A benchmark quantum chemical probe into the structural stability of various anchoring groups to form graphene oxides

Abstract

Graphene and graphene oxides (GO) are among the intriguing materials of this era, being widely used in many modern technologies. Many properties of GOs are owing to its more reactivity as compared with graphene. It is interesting to study the changes in chemical properties while changing graphene to GOs. There are commonly known three ways to change a graphene to GO by adding epoxy, hydroxyl and carboxyl groups. We used quantum chemical methods to systematically attach epoxy, hydroxyl and carboxyl groups on graphene surface. We designed GOs as hydroxyl (OH-GO), epoxy (O-GO), carboxyl (COOH-GO) derivatives of graphene and one derivative with all functional groups collectively (HEC-GO). In the current work, we have employed DFT method by using B3LYP functional along with 6-31G* basis set to calculate electronic properties computationally. The calculated band gap for GOs are less than pristine graphene (1.680 eV). Minimum band gap of 1.565 eV is shown by O-GO, while compound HEC-GO with collective functional groups shows 1.539 eV. Frontier molecular orbitals, molecular electrostatic potential maps and density of state analysis has been performed. Localized orbital locator (LOL) are drawn to check the charge transfer via topology visualization. Binding energy has been calculated using basis set superposition error (BSSE) correction. COOH-GO shows binding energy of −302.90 kcal/mol which is seen better than OH-GO and O-GO systems. NPA analysis showed that there is more ICT as functional groups are attached to the pristine graphene molecule because of the strong electron withdrawing nature of attached groups. TD-DFT with TD-B3LYP/6-31G* is employed to check the absorption properties of entitled compounds. Graphene shows maximum absorption at 341 nm, while GOs shows red shift, e.g., COOH-GO at 371 nm, OH-GO at 386 nm, HEC-GO at 409 nm and O-GO at 462 nm. The current investigation highlighted the molecular level insights about the stability and relative role of epoxy, hydroxyl and carboxyl groups on graphene surface during formation of GOs.