Quantum chemical investigation for enhanced electrochemical sensing of toxic gases by hexaazaphenH2†

Abstract

Strategies for sensing toxic gases have garnered significant attention for environmental monitoring and air pollution control. In this study, we investigated the adsorption behavior of hazardous gases (H₂S, SO₂, SO₃, N₂O, and NO₂) on an organic macrocyclic compound, hexaazaphenH₂ (HA), using a quantum chemical approach. Density functional theory (DFT) was employed to study the interactions of HA with the target gases. Optimized geometries, electronic parameters, and natural bond orbital (NBO) charge transfer analyses confirmed stable interactions between the gases and HA. The charge-transfer spectra (CTS) analysis shows distinct absorption features in HA complexes, influenced by the attached analyte, highlighting their potential for selective gas sensing. Non-covalent interaction analysis revealed electrostatic interactions, steric repulsion, and van der Waals dispersion forces, indicating physisorption. The interaction energies followed the trend SO₃@HA ≫ SO₂@HA > H₂S@HA > NO₂@HA > N₂O@HA, highlighting the significant adsorption of sulfur-containing analytes. Furthermore, the effect of an applied external electric field (EEF) ranging from −0.26 to 0.26 V Å⁻¹ was studied, revealing that increasing EEF enhances adsorption strength and polarization, with SO₃ showing the most significant changes. Additionally, electronic and charge transfer absorption spectroscopy indicated that the HA complexes exhibit distinct absorption peaks, which are influenced by the nature of the attached analyte. These findings suggest that HA is highly sensitive to harmful gases, making it a promising candidate for developing advanced environment-monitoring sensors.