Room-Temperature Gas Adsorption on Standing and Zigzag ZnO Nanowires: A ReaxFF-MD Study

Gas adsorption is intrinsically governed by the surface structure of sensing materials, where a large surface area and a high reactivity are critical for optimal performance. Nanostructured materials, with their exceptional surface-to-volume ratios, offer enhanced sensing capabilities. In this study, we designed two distinct ZnO nanowire morphologies (standing and zigzag) and used reactive force field molecular dynamics (ReaxFF-MD) simulations to evaluate their adsorption performance for O2, H2, Cl2, CH2O, C2H6O, and C3H6O at 300 K with an initial gas level of 200 molecules per system. The results show that all molecules fully adsorb on the ZnO nanowire surfaces, O2 dissociates into O atoms, and C2H6O dissociates into C2H5O and H atoms, both attached to the surface. Energy analysis shows that standing nanowires exhibit more negative adsorption energies for nonpolar gases (O2, -10317.26 kcal/mol; H2, -385.67 kcal/mol; Cl2, -19000 kcal/mol), whereas zigzag nanowires favor polar molecules (CH2O, -9380 kcal/mol; C2H6O, -8568.58 kcal/mol; C3H6O, -6897.73 kcal/mol). Both morphologies display a two-stage adsorption process, with adsorption numbers in the second stage decreasing in the following order: O2 > C2H6O > CH2O > C3H6O > Cl2 > H2. Compared to zigzag nanowires, standing nanowires adsorb 136 O2, 9 H2, 15 Cl2, 38 CH2O, 53 C2H6O, and 29 C3H6O molecules, whereas zigzag nanowires adsorb 129 O2, 10 H2, 18 Cl2, 37 CH2O, 44 C2H6O, and 27 C3H6O molecules. In both morphologies, O2 adsorption leads to a strong improvement in sensitivity. These results pave the way for smarter nanoscale designs in next-generation gas sensors.