Adsorption characteristics of pristine and defective SWCNTs towards F and Cl species: A density functional theory investigation towards water quality monitoring applications

Abstract

To keep drinking water safe and of high quality, levels of fluorine and chlorine must be continuously monitored. In this study, we have used density functional theory (DFT) simulations to evaluate the mono/di fluorine and chlorine sensing ability of pristine and defective armchair (5, 5) and zigzag (10, 0) single-walled carbon nanotubes (SWCNTs) in different sites and orientations. Water molecules are taken into consideration as co-adsorbents to assess their impact on the halogenated SWCNTs. Specifically, the potent chemisorption of F and the dissociative adsorption of F2 on armchair/zigzag SWCNTs (ASWCNTs/ZSWCNTs) indicate that CNTs may be useful in the desalination of water. According to the computed adsorption energies, Cl/Cl2 adsorbed on SWCNTs appears to be advantageous, which qualifies them as sensor candidates. Water interaction studies have shown that chlorinated SWCNTs have shown higher interaction with it when compared to fluorinated counterparts. Hence, water may act as a co-player to improve SWCNTs’ ability to sense chlorine. Finally, it has been demonstrated by ab initio molecular dynamics (AIMD) simulations that the co-adsorbed systems of water molecules and halogens are stable at ambient temperature. Overall, our results demonstrate that both ASWCNTs and ZSWCNTs can be used as room-temperature chlorine sensors for water quality monitoring applications.