Room-temperature methane sensors based on ZnO with different exposed facets: A combined experimental and first-principle study

Methane is a flammable and explosive gas, which is difficult to detect at room temperature. In this work, the photo-activation route was explored to realize the monitoring of methane at room temperature, and the strategy of surface morphology engineering was used to boost excellent methane gas-sensing performance. Three types of ZnO structures: rods, plates, and spheres with exposed (001) and (100) crystal facets in different ratios, were obtained using solvothermal methods. Such characteristics of samples were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption analyzer. The gas-sensing performances of sensors based on as-prepared materials were tested under UV light and in the dark. The results indicate that sensors exhibit excellent gas-sensing performances toward methane under UV light at room temperature. ZnO spheres showed a much better response of 20.577 toward 5000 ppm methane and a faster response time of 6 s compared to ZnO plates and rods. The enhanced gas sensing properties were ascribed to high-energy exposed facets and unique hollow structures. In addition, density functional theory (DFT) was investigated to support the effect of crystal facets