Calcination effects of 2D molybdenum disulfides

Designing earth abundant, cost effective 2D-layered materials capable replace graphene and precious metal nanoparticulated arrays in optoelectronic and catalytically working devices are among global challenges. The key factor for these applications is thermostability of MoS2 layered nanostructures. Herein, calcination effects of hydrothermally synthesized MoS2 and commercial MoS2 crystal as well as 1.7 and 6.0 μm-sized MoS2 powders were studied in the synthetic air and argon gas environments by thermogravimetric and differential thermal analysis, mass spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. Markedly lower thermal stability of hydrothermally synthesized 2D MoS2 species both in the synthetic air and Ar environments compared to MoS2 crystal and commercial powders have been established and transformations up to 1000 °C estimated. It was determined that oxidation of hydrothermally synthesized MoS2 films in the synthetic air starts below 200 °C and results in a transformation of nanoplatelet-shaped films to MoO3 sheets and nanowires at higher temperatures. The annealing in argon atmosphere, however, resulted in the MoS2 crystallinity increase, S/Mo ratio reduction, and temperature-dependent transition of 3R-MoS2 phase to 2H-MoS2 no influencing markedly the morphology of nanoplatelets up to 520 °C.