Hierarchical ZnO nanoflower assembled by well-connected nanograins with highly exposed {0001} facet for enhanced NOx sensing

Multilayer ZnO nanoflowers constructed by many nanograins with highly exposed {0001} facet have been prepared. The grain size and exposed {0001} facet is adjusted by hydrothermal condition and citrate-assisted steric hindrance, respectively. Subsequently, the gas sensing performances of the as-prepared ZnO sensors with various hydrothermal temperatures and times were investigated. The detailedly sensing experiments demonstrated that when the hydrothermal temperature and time are 120 °C and 9h, respectively, the obtained ZnO nanoflower sensor (ZnO-120-9) possesses optimal response of 80.3 towards 100 ppm NO x gas concentration at 180 °C. Meanwhile, ZnO-120-9 exhibits excellent selectivity, rapid response and recovery time, and also shows an obvious response signal at 0.5 ppm NO x exposure, which manifests that the lower concentration detection is also attainable. The superior performance of ZnO-120-9 towards NO x is due to the highly exposed {0001} facet and the size comparable to Debye length. As a result, such structure is conducive to the adsorption of more oxygen species and significant reduction of resistance, and they improve the sensitivity of a sensor.