Unveiling the gas-sensing potential of methylene-bridged [6]cycloparaphenylene nanobelt: a DFT perspective

The rapid expansion of industrialization has led to the release of numerous toxic gases into the atmosphere, posing significant environmental and health risks even at low concentrations. This has created an urgent need for novel carbon-based nanostructures capable of detecting gases selectively and efficiently. In this study, we systematically investigate the adsorption behavior and sensing performance of the methylene-bridged [6]cycloparaphenylene ([6]MCPP) nanobelt for detecting hazardous gases, including hydrogen sulfide (H₂S), carbon monoxide (CO), ammonia (NH₃), ozone (O₃), sulfur dioxide (SO₂), and nitrogen dioxide (NO₂), using density functional theory (DFT)-based electronic structure analysis. The [6]MCPP nanobelt demonstrated excellent structural robustness, with a cohesive energy of − 301.22 kcal/mol, confirming its intrinsic stability for gas-sensing applications. Among the gases examined, NO₂ exhibited the most pronounced interaction-induced electronic modulation, reflected by a 67.17% reduction in the HOMO–LUMO energy gap (from 2.62 to 0.84 eV) and a sharp rise in electrical conductivity (up to 239 S/m). Its rapid recovery time of 978 µs (9.78 × 10⁻⁴ s) at 298 K suggests both high sensitivity and excellent reusability. Although SO₂ showed the strongest adsorption energy (-20.8 kcal/mol), the moderate binding strength of -12.33 kcal/mol for NO₂, combined with its large band gap variation and short recovery time, highlights an optimal balance between selectivity and reversibility. Density of states (DOS) analysis revealed significant redistribution of electronic states near the Fermi level, confirming enhanced charge transfer upon gas adsorption. Additionally, quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and non-covalent interaction (NCI) analyses identified van der Waals forces as the dominant stabilizing interactions, with notably strong attractive regions for [6]MCPP@O₃, [6]MCPP@SO₂, and [6]MCPP@NO₂ complexes. These findings not only establish [6]MCPP as a stable and reusable nanobelt sensor but also reveal its superior selectivity and sensitivity toward NO₂, positioning it as a next-generation candidate for efficient environmental monitoring applications.