Exposed crystal facets of WO3 nanosheets by phase control on NO2-sensing performance

WO3 is a traditional type of NO2-sensing material. There are still some problems in relevant studies, such as high detection limit, high working temperature, and complex process. In this paper, simple hydrothermal method was used to prepare monoclinic WO3 (M-WO3), triclinic WO3 (T-WO3), and hexagonal WO3 (H-WO3) nanosheets. The NO2-sensing performance of T-WO3 sensors is the best among these three phases. The response of T-WO3 toward 300 ppb NO2 at its optimum working temperature (100 degrees C) is 18.8. The selectivity and stability toward NO2 are also great. The differences of NO2-sensing performances existed between different phases of WO3, owing to different exposed crystal facets. The T-WO3 sensors have excellent ppb-level NO2-sensing performance at low working temperature, owing to more O-1c active sites on the main exposed crystal (200) facet, and NO2 molecules are easily adsorbed at O-1c active sites, which is the root cause of the better sensing performance of T-WO3 toward NO2. These results show that T-WO3 nanosheets sensor can be seen as a competitive candidate for low concentration NO2 detection, and this study can be regarded as a basic research on improving gas-sensing performance of sensitive materials by controlling the exposed crystal facets.