Phase Manipulation of Two-Dimensional MoS2 Nanostructures

Simple hydrothermal process was used to successfully produce two-dimensional (2D) MoS2 powder flower-like nanosheets. The structure of the end product 2D-MoS2 is altered by changing the preparation conditions of reaction time and pH value with a constant autoclave temperature. Via annealing at 500°C, all samples transfer into 2H-MoS2 instead of 1T-MoS2. X-ray diffraction patterns showed that the peaks along (002) planes shifted dramatically from 14.2° to 9.4°. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images revealed that the prepared samples have a flower-like structure composed of spheres of nanosheets with a good polycrystalline structure. The energy gap for pristine and annealed samples is calculated from diffuse reflectance measurements and found to be 1.3 and 0.68 eV, respectively. Differential scanning calorimeter curves showed an impressive exothermic peak at 318°C, suggesting a structural to the stable 2H-MoS2 phase. The Brunauer–Emmett–Teller technique showed rapid decreases in the samples surface area at nearly 48 m2 g–1 with the structural transformation.