Comparative study on formic acid sensing properties of flame-made Zn₂SnO₄ nanoparticles and its parent metal oxides

In this work, the formic acid (CH₂O₂)-sensing properties of flame-made inverse spinel Zn₂SnO₄ nanostructures were systematically studied by comparing with its parent oxides, namely ZnO and SnO₂. All nanoparticles were synthesized via single nozzle flame spray pyrolysis (FSP) in one step and verified by electron microscopy, X-ray analysis, and nitrogen adsorption to exhibit high phase purity and high specific surface area. From gas-sensing measurements, the flame-made Zn₂SnO₄ sensor displayed the highest response of 1829 towards 1000 ppm CH₂O₂ at the optimal working temperature of 300 °C compared with ZnO and SnO₂. In addition, the Zn₂SnO₄ sensor presented a moderately low humidity sensitivity and high formic acid selectivity against several volatile organic acids, volatile organic compounds, and environmental gases. The enhanced CH₂O₂-sensing of Zn₂SnO₄ was attributed to very fine FSP-derived nanoparticles with a high surface area and unique crystal structure, which could induce the creation of a large number of oxygen vacancies useful for CH₂O₂ sensing. Moreover, the CH₂O₂-sensing mechanism with an atomic model was proposed to describe the surface reaction of the inverse spinel Zn₂SnO₄ structure to CH₂O₂ adsorption in comparison with that of the parent oxides. The results suggest that Zn₂SnO₄ nanoparticles derived from the FSP process could be a promising alternative material for CH₂O₂ sensing.