Oxidation of 2D-WS2 nanosheets for generation of 2D-WS2/WO3 heterostructure and 2D and nanospherical WO3.

The oxidation behaviour of tungsten disulphide (WS2) nanosheet powder with an average thickness of about 10 nm was studied in the temperature range of 25-700 °C. The samples were subjected to exposure in air in a short continuous mode as well as extended isothermal holding. It was observed that WS2 nanosheets were stable below 350 °C in air for short exposure times. A two-dimensional WS2/WO3 heterostructure evolved at 350 °C on short exposures to the oxidising atmosphere. Complete oxidation of WS2 nanosheets was observed at a temperature of about 450 °C in the continuous heating mode and at 350 °C under isothermal holding for an extended exposure time. During oxidation, WS2 nanosheets were initially transformed to 2D-WO3 nanosheets with an average thickness of about 10 nm. Significant distortion in the monoclinic structure of 2D-WO3 was observed. At higher temperatures, the WO3 nanosheets disintegrated initially to rod-shaped WO3 particles, which were subsequently transformed to thermodynamically stable spherical shaped WO3 nanoparticles.