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 °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.