Carboxyl-directed hydrothermal synthesis of WO3 nanostructures and their morphology-dependent gas-sensing properties

Abstract

Three different morphologies of tungsten oxides, nanoparticles, nanosheets and hierarchical microspheres, have been successfully synthesized by a facile carboxyl-directed hydrothermal process. The chelation of carboxylic groups with W(OH)₆ nuclei is recognized to be the origin of the morphological change. Gas-sensing measurements reveal that the sensing performance varies with WO₃ morphology, and the hierarchical WO₃ not only exhibits high sensitivity and fast response but also has low operating temperature to toxic NO₂. The response of hierarchical WO₃ is nearly 2 times and 10 times higher than those of the nanosheets and nanoparticles, respectively. The maximum response of hierarchical WO₃ reaches 319 to 10 ppm NO₂ at 200 °C. A relationship between morphology and crystal defect is established based on photoluminescence analysis. It is demonstrated that the change in defect feature in crystalline WO₃ is responsible for its morphology-dependent gas-sensing properties.