Microflowers Composed of VO₂ Nanoflakes for Selective Detection of Acetone and Ammonia

As a typical phase-transition material, VO₂ could show great potential in the process of precise modulation of gas-sensing selectivity. However, the effect and mechanism of the phase transition on its gas sensitivity have not yet been clearly elucidated. In this paper, a temperature-controlled VO₂ gas sensor capable of phase change has been created using a one-step solvothermal method. With controllable transition of VO₂ from the monoclinic phase to the rutile phase by adjusting the operating temperature, the corresponding VO₂ sensor shows obvious changes in gas-sensing selectivity from acetone to ammonia. At room temperature (∼25 °C), the monoclinic VO₂ sensor produces response values of 93 and 29% to 10 ppm of acetone vapor and ammonia gas, respectively. Comparatively, the response values for the sensor based on rutile-phase VO₂ that operates at 100 °C are 41 and 95% for 10 ppm of acetone vapor and ammonia gas. Based on the first-principles mortise–tenon-style construction as well as Lewis acid–base theory, the mechanism of dual selectivity generated with the phase transition of VO₂ is demonstrated in terms of crystal structure, electronic orbitals, and adsorption energy calculations. The unique characteristic of adjustable dual-phase detectability of VO₂ contributes to the selective capability of gas sensing. It thus presents an effective strategy for developing gas sensors with regulated selectivity by phase transition of certain special semiconductor oxides.