Efeito de funcionalizações nas propriedades eletrônicas de pontos quânticos de grafeno visando aplicações em sensores químicos: Contribuições teóricas e experimentais.

Abstract

In this study, a theoretical and experimental study was performed to evaluate the performance of graphene quantum dots (GQDs) for the detection of trimethylamine (TMA). Firstly, the influence of each oxygen functional group, i.e., hydroxyl, carboxyl and epoxy groups, in the hydrothermally obtained GQDs structures for the detection of TMA. To achieve this, three representative GQDs models were proposed to evaluate the individual effect of each group in the stabilization of the GQD···TMA complex. For this end, potential energy curves were built at the M06-2X/6-31+G(d,p) level of theory, between TMA and the GQDs models. The difference on the interaction for each model was explained by a topology analysis, based on the atoms in molecules theory and non-covalent interaction index analysis. GQDs based electrical sensors, with different proportions of oxygen functional groups, were also obtained, in which the sensing measurements exhibited a good correlation with the theoretical results. The obtained electrical responses showed good correlation with the computational results. In a second moment, the effect of doping with nitrogen and/or sulfur was considered, to achieve enhanced optical detection towards TMA. To achieve this, other than the undoped GQDs, nitrogen doped GQDs (N-GQDs) and codoped nitrogen and sulfur GQDs (N,S-GQDs) were obtained. These products were synthesized by means of a pyrolysis method, and characterized by spectroscopic techniques (FTIR, UV-Vis, Fluorescence and XPS) and thermal analysis (TGA and DTG). The doped GQDs exhibited a higher quantum yield and sensibility towards TMA, if compared with the undoped GQDs. Besides, preliminary tests, aiming to obtain a optical gas sensor, were performed by the functionalization of cellulose nanofibers, and indicated the potential of the N,S-GQDs as a gas sensor for TMA detection.