Adsorption of toxic gases chlorine, phosgene, and mustard on tetrahexcarbon: DFT and semi-empirical MD studies

This study demonstrates that tetrahexcarbon (THC) serves as an effective substrate for detecting toxic gases chlorine, phosgene, and mustard through non-covalent interactions. Density functional theory (DFT) calculations reveal excellent agreement with reference structures and size-dependent morphology (planar C₆₀H₂₈ vs. saddle-shaped C₉₈H₃₆). The THC substrate maintains a 3.83 eV band gap with $<$12 % reduction upon adsorption, while DOS, NBO, and ELF analyses confirm physisorption with minimal electronic perturbation. Adsorption energies follow reasonable pattern: mustard (-24.75 kcal mol^-1) $>$ phosgene (-13.18 kcal mol^-1) $>$ chlorine (-10.56 kcal mol^-1), supported by QTAIM showing 2-11 bond critical points with positive ${\nabla }^2\rho$. Chlorine exhibits superior sensitivity (9.11 × 10¹⁸ electrons/m³) and fast recovery (1.84 ns), enabling reusable detection, while mustard’s slow recovery (46.1 s) suggests single-use applications. Thermodynamics confirm spontaneous adsorption ($\Delta G<0$) with entropy trends reflecting molecular complexity, consistent with water interactions. Semi-empirical molecular dynamics (MD) simulations confirm the DFT-optimized configuration as the global minimum, with all sampled states showing higher energies and no chemical reactions, further validating THC’s physisorption capability for these toxic gases. These results position THC as a versatile platform for both real-time monitoring and one-time detection of chemical threats. Future work will investigate doping techniques to further optimize the properties of THC for applications in sensing, adsorption, and catalysis.