Adsorption and Dissociation Energy Barriers of H2O, H2, CO, CO2, NH3, CH4, NO, and NO2 on (ZnO)12 Nanobubbles by First-Principles Calculations.

The adsorption and dissociation of H2O, H2, CO, CO2, NH3, CH4, NO, and NO2 on the (ZnO)12 nanobubble were systematically investigated using first-principles density functional theory at the B3LYP, PBE, and HSE levels. The (ZnO)12 cluster, identified as a representative and energetically stable model of active sites in larger ZnO nanoparticles, enabled fundamental insight into gas-surface interactions at the nanoscale. Molecular hydrogen (H2) undergoes spontaneous dissociation at room temperature, while H2O dissociates under similar conditions, forming stable Zn-H, O-H, and Zn-O species. Carbon monoxide (CO) is readily oxidized to CO2, and CO2 undergoes further activation on the (ZnO)12 cluster to form CO3 species, indicating potential catalytic activity in small-molecule redox transformations. Nitric oxide exhibits moderate chemisorption without dissociation, with a NO dissociation barrier of about 3.25 eV, whereas NO2 binds more strongly through electron-acceptor interactions. Ammonia is one of the most strongly adsorbed via Lewis acid-base Zn-N bonding, while CH4 is best described as a strongly polarized interaction. The remaining molecules are adsorbed without dissociation. Additionally, O2 and N2 exhibit physisorption on (ZnO)12, with a predominance of dispersion interactions. Preliminary findings suggest that air does not compete with or inhibit the adsorption or reactivity of other analytes, including H2. However, further coadsorption studies are required for confirmation. Overall, the adsorption trend CO2 ≳ NH3 > H2O > NO2 > CO > CH4 is obtained. These findings provide a theoretical foundation for the rational design of ZnO-based catalysts and sensors, particularly for applications in hydrogen activation, CO oxidation, CO2 capture, and gas detection under ambient conditions.