Intermolecular interaction of Al8O12 oxymetallic clusters in the detection of atmospheric pollutants: a DFT exploration of CO, CO2, H2, N2, NO, NO2, O2, and SO2, binding mechanisms

Abstract

Due to the lack of inherent geometric symmetry present in the structures of aluminum oxide clusters, determining their stable configuration becomes an exceedingly formidable task computationally. In this comprehensive analysis, we first propose the most stable state of Al₈O₁₂, determined through Density Functional Theory calculations at ωB97XD/Def2-TZVP level of theory. Multiple structural isomers were scrutinized for their stability and spin state, with the optimal structure determined using the bee colony algorithm for global optimization. Furthermore, we investigated the intermolecular interactions between various atmospheric gases (CO, CO₂, H₂, N₂, NO, NO₂, O₂, and SO₂) and this oxymetallic cluster. The interactions were evaluated through adsorption energy (E_ads) calculations and characterized using multiple analytical frameworks: quantum theory of atoms in molecules, total density of states, natural bond orbital analysis (including bond orders, natural charges, and natural electron configurations), and non-covalent interaction analysis with reduced density gradient. The findings reveal robust interactions between the gas molecules and the cluster structure, with the cluster exhibiting remarkable potential for monitoring various atmospheric gases. Adsorption energy calculations reveal a decreasing trend in binding strength for various gases on the Al₈O₁₂ cluster, with values of SO₂ (−1.283 eV) > CO (−0.669 eV) > CO₂ (−0.579 eV) > NO₂ (−0.573 eV) > O₂ (−0.521 eV) > NO (−0.486 eV) > N₂ (−0.432 eV) > H₂ (−0.239 eV), indicating the cluster's potential for selective gas adsorption in applications like sensing and environmental monitoring. The calculated adsorption energies suggest this cluster holds great promise for the development of gas sensing and removal devices, particularly for environmental monitoring applications.