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.