Modelagem de processos de oxidação de nanotubos de carbono de parede única em meio ácido

Abstract

This work is divided in two parts; the first one consisted on the analysis of the interaction process between carbon nanotubes (CNT) and the oxidant agent nitronium ion (NO2+). The second part addressed the analysis of structure and energy of the cluster formed between the nitronium ion and its first solvation shell. In the first part we used the density functional theory (DFT) with B3LYP functional and basis set 6-31G and 6-31G(d) to evaluate the three CNT isomers with molecular formula C110H20, including two with topological defect in different arrangements. Geometry optimization and vibrational frequency calculations for isolated molecules were carried out. It was observed that the systems with topological defects led to a rearrangement of electronic charges in the CNT surface, resulting in positive and negative carbon atoms, which are more susceptible to nucleophilic and electrophilic attack, respectively. The nitronium ion adsorption on the CNT surface was also evaluated showing that the systems containing defects are more reactive then the pristine isomer. In addition, a proposal for the oxidation mechanism was made, leading to an epoxide group on the CNT surface and releasing a NO molecule. In the second part, the cluster NO2+(H2O)n, with n = 1,2,3 and 4, was analyzed in order to explore the structural and energy properties, as well as to assess the different methodologies. DFT approach with B3LYP, B972 and M062X functionals, and MP2 and MP4with distinct basis sets, from 6-31G+(d) to aug-cc-pVTZ were used. The results showed that positive charge is concentrated on the nitrogen with increasing number of water and the average hydration energy were -19.0±0.4 kcal/mol, -36.0±0.7 kcal/mol, -50.6±0.8 kcal/mol e 63.3±0.8 kcal/mol for n=1,2,3 e 4 respectively.