Co-Sensitization of ZnCo₂O₄ Hierarchical Microspheres with MoO₃ and Ag Nanoparticles for Chemiresistive Detection of Acetone

Recently, the detection of acetone by using a gas sensor fabricated with metal oxide semiconductors has stimulated intense research enthusiasm, owing to its promising application in the noninvasive diagnosis of diabetes by monitoring human exhaled breath. In this work, a potential acetone sensor was fabricated by comodification of the nanosheets-assembled ZnCo₂O₄ hierarchical microspheres (HMSs) with MoO₃ and Ag nanoparticles (NPs). The ZnCo₂O₄ HMSs were synthesized via a solvothermal route and then sequentially modified with MoO₃ and Ag NPs via immersion, calcination, and photoreduction routes. The results of gas sensing measurement indicated that after modification with MoO₃ and Ag, a continuous improvement of acetone sensitivity was realized on the ZnCo₂O₄ sensor. At the optimal working temperature of 260 °C, the response of the best Ag/MoO₃/ZnCo₂O₄ sensor to 50 ppm of acetone was 7.23, which was about 3.3 and 1.4 times higher than that of ZnCo₂O₄ and MoO₃/ZnCo₂O₄, respectively. Apart from the higher response, the selectivity and response speed of the Ag/MoO₃/ZnCo₂O₄ sensor were also improved. The results of density functional theory calculations showed that the enhanced absorbability of ZnCo₂O₄ for acetone after modification with MoO₃ and Ag should be responsible for the improved acetone sensitivity and selectivity of the Ag/MoO₃/ZnCo₂O₄ sensor.