Chiang Mai Journal of Science

       Gas sensors based on flame-synthesized WO₃ nanoparticles loaded with 0.2-5 wt% electrochemically exfoliated graphene were evaluated for NO₂ detection at ppb levels. The characterizations by X-Ray diffraction, nitrogen adsorption, electron microscopy and Raman spectrometry verified that multi-layer graphene sheets were well dispersed within spheroidal WO₃ nanoparticles. Sensing layers fabricated with different graphene loading levels were tested towards 50-5000 ppb NO₂ with varying operating temperatures from 100 to 350 °C in dry air. From the test results, the graphene-loaded WO₃ nanoparticles with the optimal graphene content of 2 wt% exhibited the highest sensor response of ~ 5061 to 5000 ppb NO₂ at the optimum working temperature of 150 °C. Furthermore, the sensor based on graphene/WO₃ composites displayed high NO₂ selectivity against various environmental gases and volatile organic compounds at 150 °C. The mechanistic roles of graphene on NO₂ gas-sensing performances were described based on reactive ohmic M-S heterointerfaces. Therefore, the combination of electrochemically exfoliated graphene and flame-made WO₃ nanoparticles could be an attractive mean to achieve highly sensitive and selective NO₂ sensors.