Adsorção de trihalometanos em nanotubos de carbono

Abstract

In this work we study the interaction of thihalomethanes (THM) with single wall carbon nanotubes using first principles calculations based on the Density Functional Theory (DFT), implemented in the SIESTA code which uses pseudopotentials to describe core electrons and localized basis to expand the valence wavefunctions. The adsorption of CHCl3 (the most important and abundant THM) on pristine, vacant and carboxylated carbon nanotubes is simulated aiming to understand the interaction process in different geometries and pursuing the best route for the potential application of carbon nanotubes as filters. The metallic (5,5) and semiconducting (8,0) nanotubes are used in all calculations. A complementary study involving bromated THMs (CHCl2Br, CHClBr2 and CHBr3) is also performed in order to investigate the influence of the bromine atoms on the interaction between THMs and pristine nanotubes. Based on the analysis of structural, electronic and energetic properties it is verified that THMs are adsorbed on the carbon nanotube surface through a physisorption process (binding energies in the range -0,06 eV to -0,21 eV) in all cases. This fact makes carbon nanotubes as promissing candidates to extract THMs from aqueous solutions. The calculations also predict the stability of chemical groups (COCCl3 and COOCCl3) bounded on the nanotube surface. These chemical groups can be derived from possible chemical reactions, through coupling agents, between CHCl3 and the carboxyl groups anchored to the nanotube wall. The binding energies of these groups and the nanotubes are found to be in the range -1,31 eV to -2,26 eV.