Synthesis of thickness-controlled cuboid WO3 nanosheets and their exposed facets-dependent acetone sensing properties

Thickness-controlled cuboid WO3 nanosheets with exposed (020) and (200) facets have been successively synthesized by a low temperature acid-assisted (HCl) hydrothermal process and the subsequent heating treatment. The average thickness of the WO3 nanosheet samples can be adjusted from about 10 to 110 nm by simply changing the oxalic acid and HCl content in the preparation solutions. A high exposure degree of (020) facets make WO3 nanosheets a very promising sensitive material for developing gas sensors with high acetone sensing performance, which can even make them easy to distinguish between acetone and ethanol. The gas responses of the WO3 nanosheet samples increased with the increase of the exposure degree of (020) facets, obvious facet-dependent gas sensing characteristic was found. A high response of 49.1, a lower detection limit of 0.5 ppm, and shorter response and recovery times (7 and 19 s, respectively) to 100 ppm acetone vapor were obtained for the WO3 nanosheet sample with the highest exposure degree of (020) facets. The gas sensing mechanism was discussed in detail. The content of dangling bonds and the local electric polarization on the exposed special facets could be the key factors for the highly acetone sensitivity and selectivity.