Nitrogen dioxide gas-sensing properties of hydrothermally synthesized WO₃ · nH₂O nanostructures

Nitrogen dioxide (NO₂) has been identified as a serious air pollutant that threats to our environment, human life and world ecosystems. Therefore, detection of this air pollutant is crucial. Metal oxide semiconductor is one of the best approaches frequently used to detect NO₂ at relatively low temperatures. Hydrated tungsten trioxide (WO₃ · H₂O), an n-type semiconductor, is regarded to be a promising material for fabricating gas sensors, which are widely used in environmental and safety monitoring. In this work, WO₃ · nH₂O nanoparticles have been synthesized using a polyfunctional surfactant-mediated hydrothermal approach in the addition of H₂C₂O₄ and K₂SO₄ at a molar ratio of 1 : 1. This paper has also reported the effect of reaction temperature (120°C to 200°C) on morphological changes and gas-sensing performance. The characterization of these synthesized nanostructures was carried out by UV-Vis absorption spectroscopy, X-ray diffraction and field-emission scanning electron microscopy (FESEM). The UV absorption peak was obtained around 300 nm. FESEM analysis showed sheet-like structures come together to form flower-type morphology. The synthesized WO₃ · nH₂O flower-like structures was then used for NO₂ gas-sensing application. The prepared sensors showed considerably better sensor response (R _g/R _a = 17.48) at 185°C for 25 ppm NO₂.