Selective sensing property of triclinic WO₃ nanosheets towards ultra-low concentration of acetone

Uniform triclinic and monoclinic tungsten oxide (WO₃) nanosheets were synthesized by facile hydrothermal process and thermal annealing at 250 and 450 °C, respectively. Acetone-sensing properties of the as-synthesized WO₃ nanosheets were investigated with the aim of disease diagnose and environment detection. Triclinic WO₃ nanosheets exhibited superior acetone selective and sensing performances (response ~ 2.04 to 1 ppm of acetone at 230 °C) to that of monoclinic WO₃ nanosheets (response ~ 1.37 to 1 ppm of acetone and negligible selectivity). The mechanisms of acetone selective and sensing properties of triclinic WO₃ were discussed in detail. Photoluminescence results and surface structure study revealed that the triclinic WO₃ nanosheets exhibited higher defect level and more unsaturated coordinated O atoms than monoclinic WO₃ nanosheets on their surfaces. These defects and O atoms can act as chemical adsorption sites where acetone molecules could be adsorbed and react directly. Meanwhile, triclinic WO₃ exhibit lower symmetry and larger extent of polarization in comparison with monoclinic WO₃. The induced large dipole moment contributes to strong interaction at these chemisorption sites between triclinic WO₃ nanosheets and acetone molecules with a larger dipole moment than the other tested gases.