Mixed (Mo,W) oxide/sulfide composite nanostructures: synthesis and gas-sensing properties

Abstract

This work presents a study of heterostructured materials prepared by hydrothermal treatment of MoO3 seed materials in the presence of tungstate ions and a sulfur source (thioacetamide). Elemental analysis by SEM/EDS revealed the presence of Mo, W, O and S in the final products. Raman and XRD characterization show evidence for mixed (Mo1-xWxO3) and (Mo1-xWxS2) phases, indicating the formation of mixed metal oxide/transition metal sulfide (MOS/TMD) interfaces. The materials were tested for gas sensing properties, with a high response to NO2 and a significant lower limit of detection below 1 ppm at 150 °C. The structural properties of the materials and the sensor response were found to be dependent on the concentrations in the synthesis medium, with the optimal conditions observed for the materials prepared with 1 Mo: 0.5 W: 0.1 S molar ratios. To explain the dependence of the sensor response with the composition, we propose that electronic sensitization effects promoted by the (SMO/TMD) junctions together with electron trapping effects known to exist in mixed (Mo,W) oxide phases. Overall, this work introduces the use of mixed metal phases in oxide/sulfide nanostructures as a strategy to achieve materials sensitive to NO2 that can be used for the development of better sensors.