Adsorptive Removal of Nerve Agent Gases by Carbon Nanotubes: A Density Functional Theory Study

Density functional theory (DFT) studies were performed to evaluate the adsorption behavior and electronic response of (4,4) carbon nanotubes (CNTs) to the organophosphorus nerve agents 3,3-dimethylbutan-2-yl methyl phosphono fluoridate (Soman), pinacolyl methyl phosphonate (SOS), diethyl fluorophosphates (SAS-F) and diethyl chlorophosphate (SAS-Cl). The calculations were performed using the triple numerical plus polarization (TNP) as the basis set with an orbital cutoff of 4.5 angstrom. The electronic exchange and correlation effects were analyzed by generalized gradient approximation (GGA) with the BLYP parameterization. The studied systems were fully optimized and adsorption energy (E-ad), interaction distances, geometric and electronic structures were investigated. According to the obtained relatively high Ead, it was shown that Soman, SOS, SAS-Cl and SAS-F more likely to be absorbed on the CNTs surfaces, introducing an interesting candidate for chemisorption of the nerve agent gas molecules. As a result, the order of increasing of the E-ad values of the studied systems were vertical bar E-ad (SAS-F/CNT vertical bar) > vertical bar Ead SAS-Cl/CNT vertical bar > vertical bar E-ad SOS/CNT vertical bar > |E-ad Soman/CNT vertical bar systems. The calculated partial density of states (PDOS) of the adsorption systems confirmed the strong electrons interaction between the nerve agent molecules and the CNTs surfaces. The obtained results indicated the potential application of CNTs in the design and fabrication of protective low-cost gas filters against toxic odorless nerve agent gases.