Cr-Doped Urchin-Like WO Hollow Spheres: The Cooperative Modulation of Crystal Growth and Energy-Band Structure for High-Sensitive Acetone Detection.

Acetone is a biomarker in the exhaled breath of diabetic patients; sensitive and selective detection of acetone in human exhaled breath plays an important role in noninvasive diagnosis. Tungsten oxide (especially for γ-WO) is a promising material for the detection of breath acetone. It is generally believed that the stable metastable phase of WO (ε-WO) is the main reason for the improved response to acetone detection. In this work, pure and Cr-doped urchin-like WO hollow spheres were synthesized by a facile hydrothermal approach. Analyses of the resulting materials via X-ray photoelectron spectroscopy (XPS) and Raman confirmed that they are mainly composed by γ-WO. The gas sensing performances of pure and Cr-doped WO to acetone were systematically tested. Results show that the sensor based on pure WO annealed at 450 °C has a high response of 20.32 toward 100 ppm acetone at a working temperature of 250 °C. After doped with Cr, the response was increased 3.5 times higher than the pure WO sensor. The pure and Cr-doped WO sensors both exhibit a tiny response to other gases, low detection limits (ppb-level) and an excellent repeatability. The improvement of gas sensing properties could be attributed to an optimized morphology of Cr-doped WO by regulating the crystal growth and reducing the assembled nanowires' diameter. The increasing number of oxygen vacancy and the introduction of impurity energy level with trap effect after Cr doping would lead to the wider depletion layer as well as a better gas sensing performance. This work will contribute to the development of new WO acetone sensors with a novel morphology and will explain the increased response after Cr doping from a new perspective.