CONICET | Buscador de Institutos y Recursos Humanos

There has been increasing interest, in recent years, in the applications of carbon nanotubes in areas such as gas storage and heterogeneous catalysis.1) The structure of the nanotube bundles, the degree of functionalization of the nanotubes, and the extent to which the ends of the tubes are uncapped, are all determinant factors in the performance of SWNTs in these applications. Here we report on the changes observed in the properties of SWNTs that result from subjecting them to acid treatments. The treatments were undertaken with the goals of increasing the microporosity of the samples2) and opening the ends of the tubes3). We studied the gas storage behavior of these samples. The nanotube samples were characterized with Scanning Electron Microscopy (SEM); Thermal Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA); Fourier Transform Infra-Red Spectroscopy (FT-IR) and X-Ray Photoelectronic Spectroscopy (XPS). Gas adsorption was used to investigate changes in the surface properties of the samples (including changes in their porosity), as well as changes in the adsorbate-substrate interactions, which occurred as a result of the acid treatments. The adsorption studies were conducted using H2 and N2 at 77 K and CH4 and CO2 at different temperatures between 190 and 298 K, over pressures ranging between 1x10-6 and 3-4 MPa. Different models for pore filling and gas-surface interactions have been applied to the adsorption data to determine the textural properties of the treated SWNTs. We have obtained values for the isosteric heats of adsorption for CH4 and CO2 and we have correlated the changes in the degree of porosity of the samples resulting from the acid treatments with changes in the adsorption thermodynamics for these gases.