Structure and electronic characterization of pristine and functionalized single wall carbon nanotube interacting with sulfide ion: A density functional theory approach

Abstract

Density functional theory (DFT) and Time Dependent Density functional theory (TD-DFT) calculations were performed to study the interaction of sulfide ion with pristine and edge/sidewall covalently functionalized single wall carbon nanotube (SWCNT, OH+NH2-SWCNT and COOH+NH2-SWCNT). NBO and Mulliken charge transfer between sulfide ion and pristine, edge/sidewall functionalized SWCNT (OH+NH2-SWCNT and COOH+NH2-SWCNT) was analyzed and a greater effect of charge transfer from analyte (sulfide ion) to SWCNT was calculated for sidewall functionalized carbon nanotube (COOH+NH2-SWCNT-S2-). Further, the electronic properties like ionization potential (IPs), electron affinities (EAs), and frontier molecular orbitals analysis were computed. Upon interaction appreciable decrease in energy gap is observed in all studied systems, however, the least energy gap is obtained in case of sidewall functionalized COOH+NH2-SWCNT-S2-. The simulated vibrational frequencies of both pristine and functionalized SWCNT interacting with sulfide ion were in good correlations with the reported literature. Similarly, the UV–Vis–NIR spectral bands for SWCNT-S2-, OH+NH2-SWCNT-S2- and COOH+NH2-SWCNT-S2- have been analyzed at TD-DFT-ωB97XD/6-31G (d,p). DFT study has revealed that the sidewall functionalized COOH+NH2-SWCNT has a greater sensing ability towards sulfide ion over the pristine SWCNT.