Cr-doped WO3 nanosheets: Structural, optical and formaldehyde sensing properties

Co-precipitated undoped and Cr-doped WO3 nanosheets have been investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) in order to study the influence of Cr doping on their structural and morphological properties. XRD analyses confirm the monoclinic structure of nanocrystalline WO3, whereas the FESEM and TEM images exhibit nanosheet-like morphology of the as-synthesized WO3 materials. Among all the samples examined, the 1.5 at% Cr-doped WO3 nanosheets exhibit the selective maximum response (~82%) to formaldehyde over methanol, ethanol, propan-2-ol and acetone at the operating temperature of 200 °C for 50 ppm concentration in air. The sensing mechanism has been explained based on chemisorption of oxygen on the WO3 surface and the subsequent reaction between the adsorbed oxygen species and the formaldehyde molecules.