Hierarchical 3D flower-like MoS2 spheres: Post-thermal treatment in vacuum and their NO2 sensing properties

• MoS2 spheres were post annealed in vacuum to prevent its oxidation.
• n-type MoS2 spheres behaves as a p-type semiconductor when it was exposed to an oxidizing gas NO2.
• the NO2 sensing mechanisms of the MoS2 spheres were proposed.

Hierarchical 3D flower-like MoS2 spheres were first synthesized by a facile hydrothermal process. Afterwards, MoS2 spheres were annealed in vacuum under an Ar atmosphere to prevent MoS2 partial oxidation in the MoO3 form. As-prepared MoS2 samples were characterized by XRD, EDS, SEM, TEM and BET. SEM images showed that the flower-like spheres were about 1–2 µm in diameter and built up with MoS2 thin sheets. Moreover, there were many mesoporous structures consisting of nanosheets on the surface of the MoS2 spheres. The resulting NO2 gas sensor displayed a high sensitivity, good reproducibility and selectivity. A possible NO2 gas sensing mechanism of MoS2 spheres was preliminarily proposed.