Effect of noble metal element on microstructure and NO2 sensing properties of WO3 nanoplates prepared from a low-grade scheelite concentrate

To break the limitation of raw materials for preparing functional WO3 nanomaterials, a low-grade scheelite concentrate was selected as the tungsten source, and WO3 nanoplates doped with Ag, Pd, Au and Pt were synthesized through three combined processes including NaOH leaching, chemical precipitation and acidification. The microstructure and NO2 sensing properties of pure and noble metal-doped WO3 nanoplates were investigated. The microstructure characterization demonstrated that all WO3 products were composed of interlaced and irregular nanoplates with the thickness of 10-30 nm, and the length and width of these nanoplates were in the range of several hundred nanometers. NO2 sensing properties indicated that WO3 nanoplates doped with noble metal nanoparticles exhibited obviously higher responses and shorter response times than pure WO3 nanoplates. Especially, noble metal-doped WO3 nanoplates exhibited distinct behaviors in terms of the enhancement of sensing properties. Pd-doped WO3 nanoplates exhibited highest response to NO2, and Ag-doped WO3 nanoplates exhibited fastest response speed. Additionally, Ag-, Pd- and Pt-doped WO3 nanoplates exhibited a relatively lower optimal operating temperature. The enhanced NO2 sensing performance can be ascribed to the large specific surface area of WO3 nanoplates, the catalytic activities of noble metal nanoparticles, and the varied work function energies together with the lower activation energies. (C) 2019 Elsevier B.V. All rights reserved.