Oxidation of Molybdenum Disulfide Sheet in Water under in Situ Atomic Force Microscopy Observation

Abstract

In situ observation of molybdenum disulfide (MoS2) sheet exposed to water was performed using atomic force microscopy (AFM) to obtain a better understanding for the preparation and application of two-dimensional molybdenum disulfide. It was found that the MoS2 sheet underwent chemical reactions in water, leading to the partial etching of the surface layer and the formation of needlelike protrusions on the surfaces. X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) analyses showed that this behavior might arise from the oxidation of MoS2 into Mo(VI) and SO42–. The oxidative product Mo(VI) was present in the form of either MoO3·H2O crystals on the MoS2 surface or molybdate ions in aqueous solution, whereas SO42– was present in the solution, resulting in the etching of the surface layer and the formation of needlelike protrusions. These findings might be significant in terms of applications of two-dimensional MoS2 and the concentration of molybdenite.