NANOTUBOS DE CARBONO CARBOXILADOS E SUA INTERACÃO COM MOLÉCULAS DE ÁGUA: UMA ABORDAGEM EMPÍRICA E DE PRIMEIROS PRINCÍPIOS

• Autor(a) principal: Lara, Ivi Valentini
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional Universidade Franciscana
• Texto Completo: http://tede.universidadefranciscana.edu.br:8080/handle/UFN-BDTD/273; http://www.tede.universidadefranciscana.edu.br:8080/handle/UFN-BDTD/353
• topic: nanotubo de carbono; carboxilação; solubilidade em água; funcionalização; carbon nanotube; carboxilation; water solubulity; functionalization; CNPQ::ENGENHARIAS

This dissertation studied the interaction of carboxyl groups -COOH with (8,0) and (16,0) single wall carbon nanotubes, both semiconductors, by ab initio calculation based on the formalism of the Density Functional Theory using the SIESTA code, in which were adopted localized bases to the electronic wave functions description and Troullier- Martins pseudopotentials for describing the interaction between valence electrons and core electrons. As the -COOH group is taken as default when the purpose of the carbon nanotubes functionalization is to make them hydrophilic, this interaction was studied by different positions of the carboxyl on the nanotubes walls with different concentrations of those seeking to verify the influence of these parameters in the electronic character of the carbon nanotubes. By analyzing the energetic, structural and electronic properties of all patterns, it is observed that the carboxyl groups interact with the nanotubes through covalent bonds (binding energies between −3.39 and −0.73 eV , with the smallest for the case of carboxyl confined within the nanotube), nanotubes (16,0) are more flexible than the (8,0) (when connected to the same number of carboxyl groups), and a behavior, very interesting, is presented when the concentration of carboxylation is varied: the character of the system can be modulated from a semiconductor to semiconductor with a halffilled level over the Fermi level (methalic character tendency). It is still studied in this work, the dynamics of water molecules around pure and carboxylated carbon nanotubes, obtained from ab initio calculations, through classic molecular dynamics simulations, using empirical parameters with the GROMACS program. The structural analysis of water around the tubes indicated the already expected hydrophobic character of the pure nanotubes and the hydrophilic character of the carboxylated nanotubes with which the water molecules interactions are greater with its walls, a fact confirmed by energy analysis, which shows a higher interaction energy in this system. This work has, in addition to contributing to the understanding and analysis of related experimental results, pointing out also the possibility to modulate the electronic behavior of these systems at the nanoscale.