Molecular blueprints for cleaner air: theoretical insights into Cu(i)-decorated heterocycles for greenhouse gas (CO/CO2/CH4) capture

Abstract

This study presents a comprehensive DFT investigation on Cu(I)-decorated five-membered aromatic heterocycles—imidazole, pyrazole, thiazole, oxazole, isoxazole, and isothiazole—as molecular hosts for capturing key greenhouse gases (CO, CO₂, and CH₄). Geometry optimization and electronic-structure analyses (B3LYP/6-31+G(d,p)) were combined with adsorption-energy evaluation, CDFT descriptors, NBO charge distribution, NICS, PDOS, ELF, NCI analyses, ADMP dynamics, and Gibbs free-energy profiling to establish structure–property relationships governing gas uptake. Most Cu-heterocycle hosts accommodate up to four gas molecules, with adsorption strength following the consistent trend CO > CO₂ > CH₄. CO adsorption is strongly chemisorptive, supported by significant charge transfer and Cu → CO π-back donation, whereas CO₂ and CH₄ show progressively weaker interactions. Aromaticity is largely preserved after adsorption, and ADMP simulations confirm good kinetic stability of all hosts. Thermodynamic analysis reveals spontaneous CO binding, moderately favourable CO₂ capture, and marginal CH₄ adsorption at room temperature. Gravimetric storage capacities reach ∼39–46% (CO), ∼54–57% (CO₂), and ∼30–33% (CH₄). Among all systems, Cu(I)-decorated imidazole and oxazole frameworks emerge as the most efficient and stable hosts. These insights provide clear electronic and structural design rules for developing next-generation Cu-based adsorbents tailored for selective and high-capacity greenhouse-gas capture.