Surface-Dependent Isotopic Adsorption of CO on α-AlO: Role of Weak Interactions and Zero-Point Energy.

Carbon isotopes, particularly C, are critical for applications in food authentication, biomedical diagnostics, and metabolic research; however, their efficient separation remains challenging due to their low natural abundance. This study investigates the adsorption behavior of CO and CO on various low-index α-AlO surfaces as a strategy for isotope separation. Density functional theory (DFT) calculations with D3 (BJ) dispersion corrections were employed to optimize surface models for five representative α-AlO facets. Nine adsorption configurations were systematically evaluated by optimizing geometric structures, computing adsorption enthalpies with zero-point energy corrections, and performing Bader charge and charge density difference analyses to elucidate interfacial interactions. The results reveal that CO preferentially adsorbs in a vertical configuration via its carbon end at Al sites, with the (0001) surface exhibiting the lowest surface energy and most favorable adsorption characteristics. Furthermore, we found that facets with lower surface energy not only facilitate stronger CO adsorption but also demonstrate pronounced adsorption enthalpy differences between CO and CO, driven by vibrational zero-point energy disparities. These findings highlight the potential of low adsorption enthalpy surfaces, particularly (0001), (011¯2), and (112¯0), for enhancing isotope separation efficiency, providing valuable insights for the design of advanced separation materials.