Computational design of metal-doped carbon nanotubes as sensors for carbonyl sulfide: Implication for environmental gas monitoring

Abstract

The detection of carbonyl sulfide (COS), a toxic, flammable, and environmentally hazardous gas, is vital for industrial safety and aligns with several UN Sustainable Development Goals (SDGs), including SDG 3 (Good Health and Well-being), SDG 6 (Clean Water and Sanitation), SDG 9 (Industry, Innovation and Infrastructure), and SDG 13 (Climate Action). In this density functional theory (DFT)-based study, we investigated Sn- and multi-Si-substituted carbon nanotubes (Sn@SiCNT) functionalized with Co, Ir, and Rh as potential COS sensors. These dopants (Co, Rh, Ir) were chosen as representative of 3d, 4d and 5d transition metals in order to investigate how the d‐state–driven charge transfer and adsorption strength affect COS sensing performance. All simulations were performed at the UPW6B95D3/LANL2DZ level of theory and included geometry optimization, electronic structure analysis (frontier molecular orbital (FMO), molecular electrostatic potential (MESP), density of states (DOS), dipole moment, adsorption energy investigation, and bonding interaction evaluation using quantum theory of atoms in molecules (QTAIM), and non-covalent interaction (NCI) analyses. COS adsorption was explored at both oxygen and sulfur termini on each surface. Metal doping introduced minimal distortion, with Si–C bond elongations ranging from 2.8% to 4.7%, thereby preserving the nanotube’s structural integrity. Among the systems, Ir-doped surfaces exhibited the most favorable adsorption energies (–0.533 eV), reflecting a 65.6% improvement over pristine Sn@SiCNT (–0.321 eV), while Co-doped systems followed closely. Notably, Co-functionalization resulted in the highest electronic reactivity, reducing the highest occupied molecular orbital–lowest occupied molecular orbital gap (HOMO–LUMO gap) by 46.7% and increasing electron affinity by 45.5%. Upon COS binding, the dipole moment at the O-site increased by 29.4%, indicating strong polarization effects. Moreover, QTAIM revealed high electron density (ρ = 0.382 a.u.) and partially covalent bonding in Co and Ir systems, while NCI plots confirmed strong non-covalent interactions at both COS ends. Additionally, Shapley additive explanations (SHAP) and heatmap correlation analyses identified Fermi level and electronegativity as key factors influencing adsorption. Overall, Co- and Ir-functionalized Sn@SiCNTs demonstrate selective, reversible COS binding and hold strong promise for nanosensor development aligned with global sustainability efforts.