Estudo e aplicações de nanomateriais multifuncionais: propriedades de transporte de nanotubos de titanato e novos materiais baseados em óxido de grafeno

Abstract

In this work, we investigate the properties and applications of two multifunctional nanomaterials; titanate nanotubes (TNTs) and graphene oxide (GO). In the first part, TNTs were applied as hydrogen gas sensor and presented sensitivity in a range 50 - 5000 ppm at low operating temperature (100 - 150 oC), which was associated with the modulation of protonic transport at the TNTs surface. The transport properties of TNTs were further investigated by impedance spectroscopy. The study of TNT conductivity with temperature dependence in the range of 25-250 oC revealed that TNT samples have two transport regimes: for T < 150 oC, a regime whereby protonic conduction is dominant, which is associated with physisorbed and/or structural water molecules; and for T >150 oC, a regime whereby thermally activated electronic conduction is dominant. The activation energy of the electronic transport varied with the previous thermal treatment of the samples, indicating that such treatment causes changes in defect structure of TNTs. In the second part, we show that copper nanoparticles supported by reduced GO (rGO) is an efficient catalyst system for the electrochemical reduction of CO2. We observed about 0;34 V of reduction in the overpotential, good electrochemical stability after several cycles of operation and high corrent density, about four times better as compared as simple copper catalyst. Furthermore, we demonstrate a route for chemical hydrogenation of GO. Raman spectroscopy of the produced material showed the appearance of two unusual peaks that suggest that the hydrogen atoms were incorporated into the structure of the GO being covalently bonded to carbon atoms in a configuration similar to trans-polyacetylene chains.