Some interesting insights into the acetone sensing characteristics of monoclinic WO3

Abstract

Considering the importance of tungsten oxide (WO₃) in fabricating acetone sensors for the non-invasive diagnosis of diabetes, it has become pertinent to understand the critical reasons behind the diverse and interesting acetone sensing behaviour of WO₃ nanomaterials. To find a solution for our quest to understand the effect of particle morphology and crystallographic modifications on the acetone sensing behaviour of WO₃, we have synthesized γ-monoclinic WO₃ nanoparticles by a hydrothermal technique and fibers by an electrospinning technique. The fabricated tubular-type sensor utilizing the synthesized WO₃ exhibited a distinct difference in the response towards different concentrations of acetone in the lower range, such as 10, 5, 2, 1, 0.8 and 0.5 parts per million (ppm). In contrast to the 84% sensing response of the WO₃ particle-based sensor towards 10 ppm acetone at an operating temperature of 200 °C, the fiber-based sensor exhibited a much better response of more than 90% at a lower operating temperature of 150 °C with improved recovery time. Based on various characterization techniques, it has been confirmed that both the synthesized materials exhibit an interesting crystallographic texture with preferred orientation along the 002 crystal facet, which is expected to chemisorb more oxygen molecules on the surface leading to the observed higher sensing performance at a lower temperature. Moreover, the excellent gas sensing performances of the WO₃ fiber-based sample could be attributed to the charge confinement and electron transfer ability of a one-dimensional (1D) structure with high surface-to-volume ratio, and the exposed highly reactive (002) plane with improved crystallinity which facilitates more chemisorbed oxygen molecules at a lower temperature (150 °C). We have also demonstrated the performance of the sensor at different humidity levels and acetone concentrations to prove its potential use in breath analysis. This study further envisages the potential of the WO₃-fibers for developing next-generation solid-state gas sensors for the non-invasive detection of diabetes.