Synergistic Effects of PdO<i>_x</i>–CuO<i>_x</i> Loadings on Methyl Mercaptan Sensing of Porous WO₃ Microspheres Prepared by Ultrasonic Spray Pyrolysis

Abstract

In this work, PdO<i>_x</i>-CuO<i>_x</i> co-loaded porous WO₃ microspheres were synthesized with varying loading levels by ultrasonic spray pyrolysis (USP) using polymethyl methacrylate (PMMA) microspheres as a vehicle template. The as-prepared sensing materials and their fabricated sensor properties were characterized by X-ray analysis, nitrogen adsorption, and electron microscopy. The gas-sensing properties were studied toward methyl mercaptan (CH₃SH), hydrogen sulfide (H₂S), dimethyl sulfide (CH₃SCH₃), nitric oxide (NO), nitrogen dioxide (NO₂), methane (CH₄), ethanol (C₂H₅OH), and acetone (C₃H₆O) at 0.5 ppm under atmospheric conditions with different operating temperatures ranging from 100 to 400 °C. The results showed that the CH₃SH response of USP-made WO₃ microspheres was collaboratively enhanced by the creation of pores in the microsphere and co-loading of CuO<i>_x</i> and PdO<i>_x</i> at low operating temperatures (≤200 °C). More importantly, the CH₃SH selectivity against H₂S was significantly improved and high selectivity against CH₃SCH₃, NO, NO₂, CH₄, C₂H₅OH, and CH₃COCH₃ were upheld by the incorporation of PdO<i>_x</i> to CuO<i>_x</i>-loaded WO₃ sensors. Therefore, the co-loading of PdO<i>_x</i>-CuO<i>_x</i> on porous WO₃ structures could be promising strategies to achieve highly selective and sensitive CH₃SH sensors, which would be practically useful for specific applications including biomedical and periodontal diagnoses.