J. P. A. Mendonça

Structural and vibrational study of graphene oxide via coronene based models: theoretical and experimental results

We use the Coronene (C24H12), a simple and finite molecule, to make a model to study the spectroscopic and structural alterations generated by oxygenated groups in graphene oxide (GO). Based on the Lerf–Klinowski model, we chose the hydroxyl [OH−], the carboxyl [COOH−] and the epoxy [the ring C2O inside the molecule] as our radicals of interest and study their collective and isolated effects. We perform geometry optimization, vibrational IR (via AM1 and DFT-B3LYP) and Raman spectra (via DFT-B3LYP) of a series of functionalized coronene molecules. As results, we obtain some useful data for the analysis of IR and Raman spectra of GO, which facilitate the understanding and identification of the peaks found in the experiment. Finally, we suggest a new model to study GO, producing an accurate signature when compared to our experimental data. Such molecule shows in more details of the structural effects caused by functionalization when compared to experimental data.

Enhancement of Nonlinear Optical Properties of Graphene Oxide-based Structures: Push-Pull Models

Through DFT calculations and the finite field approach, it is possible to identify some structural and electronic aspects that could lead to enhancement of the nonlinear optical (NLO) molecular properties of graphene oxide and its derivatives. We proposed a molecular design scheme of NLO response based on push–pull structures. The best NLO models contain –COOH at their edges, acting as electron acceptors, and –OH in the basal plane, acting as an electron donor.

Exploring the effect of substitutional doping on the electronic properties of graphene oxide

Through molecular and solid-state approaches, structural and electronic properties of graphene oxide (GO) using substitutional doping were studied. Nitrogen, boron, phosphorus, silicon, aluminum, arsenic, and germanium atoms were integrated to GO at various sites to search for a suitable candidate that can reduce the energy gap of GO. As per our molecular investigations, Si- and Ge-doped GO reduces nearly 10% of the gap compared to the undoped molecule, while P, As, and N doping enhance the gap more than 50%. B and mainly Al (more energetically favorable structures) were found to be a suitable choice to be doped in GO, as it causes up to a 60% reduction in the energy gap compared to that of pristine GO. Moreover, the periodic calculations revealed that the introduction of Al can turn the GO structure into a metallic one. In addition, our studies disclosed that not only the dopant type but also the dopant sites are crucial in order to alter the electronic properties of GO.