Adsorption of SO2 molecules on Fe-doped carbon nanotubes: the first principles study

In this paper, the first-principles method has been employed to study the adsorption behavior of SO2 molecules on pristine carbon nanotubes (CNTs) and Fe-doped CNTs with or without the existence of vacancy defects. Through the analysis of geometric structure, adsorption energy, charge transfer, and electron density, our calculation illustrates that the adsorption of SO2 molecules is only a weak physical adsorption on both pristine CNTs and vacancy-defected CNTs. After doping with Fe, however, a much stable chemical adsorption is formed between SO2 and CNTs, where the adsorption distance decreases by a maximum of 44.8%, and the adsorption energy and charge transfer increase by a maximum of 1513.3% and 373.9%, respectively. Calculations of front orbit and density of states reveal that Fe-doping narrows the band gap and increases the electrical conductivity of the CNTs. The density of states of Fe-doped CNTs and SO2 molecules are clearly reinforced at the Fermi level, implicating that there is stronger coupling between Fe atoms and SO2 molecules and this enhances the adsorption of SO2 molecules on these CNTs. The study provides useful guidance on how to improve the interactions between air pollutant SO2 molecules and CNTs and illustrates that Fe-doped CNTs could be potentially applied as a next-generation SO2 gas sensor and collector.