This study reports a facile and efficient one-step hydrothermal method for the synthesis of zinc oxide (ZnO) nanoflakes with exposed ZnO(101̅0) surfaces. The as-prepared nanoflakes exhibit excellent sensitivity, selectivity, and stability toward volatile n-butanol gas at the optimized operating temperature of 330 °C. The gas-sensing results further indicate that the chemisorbed oxygen species on the surfaces of the ZnO nanoflakes are dominated by O2– rather than O– ions at 330 °C. The molecular dynamics (MD) method was also employed to understand the underlying fundamentals through simulating the adsorption of different gas molecules onto various ZnO crystal surfaces, such as (101̅0), (112̅0), and (0001). The simulation results confirm the enhancing effect of the exposed (101̅0) surfaces toward n-butanol gas molecules because of their lower diffusion coefficient on (101̅0) compared to those on (112̅0) and (0001) surfaces. The findings will provide new physical insights into the adsorption behaviors of volatile reducing gases on various ZnO surfaces under different temperature and humidity conditions and will be useful for the design and construction of gas-sensing materials with specifically exposed surfaces.

The sensitivity of a metal oxide gas sensor is strongly dependent on the nature of the crystal surface exposed to the gas species. In this study, two types of zinc oxide (ZnO) nanostructures: nanoplates and nanorods with exposed (0001) and (10̄10) crystal surfaces, respectively, were synthesized through facile solvothermal methods. The gas-sensing results show that sensitivity of the ZnO nanoplates toward ethanol is two times higher than that of the ZnO nanorods, at an optimum operating temperature of 300 °C. This could be attributed to the higher surface area and the exposed (0001) crystal surfaces. DFT (Density Functional Theory) simulations were carried out to study the adsorption of ethanol on the ZnO crystal planes such as (0001), (10̄10), and (11̄20) with adsorbed O(-) ions. The results reveal that the exposed (0001) planes of the ZnO nanoplates promote better ethanol adsorption by interacting with the surface oxygen p (O2p) orbitals and stretching the O-H bond to lower the adsorption energy, leading to the sensitivity enhancement of the nanoplates. These findings will be useful for the fabrication of metal oxide nanostructures with specifically exposed crystal surfaces for improved gas-sensing and/or catalytic performance.