Accelerated Nanopit Formation on MoS₂ Nanosheets through Photo-Fenton Reactions

Two-dimensional (2D) molybdenum disulfide (MoS2) is a nanomaterial of emerging interest with distinctive properties that are useful in water treatment and photochemical applications. For example, redox pathways driven by MoS2 nanosheets can facilely convert ferric ions to ferrous ions, improving Fenton and Fenton-like reactions. Here, we show how photo-Fenton/Fenton-like reactions influence the morphologies, chemical compositions, and photocatalytic activities of MoS2 nanosheets in aqueous environments. Under light illumination, aqueous iron promoted MoS2 nanosheet dissolution, increasing its thickness and creating circular pits on the basal surface. Furthermore, the fraction of oxidized Mo species in the MoS2 nanosheets continuously increased over the reaction. These results suggest that MoS2 is first oxidized, then nanopits form on its basal surface, and finally is penetrated as the pits are deepened and enlarged by dissolution. We also demonstrate that the photocatalytic activity of the MoS2 nanosheets generates reactive oxygen species (ROS) and electron holes, both of which facilitate the formation of circular pits in MoS2 nanosheets and their oxidation. Moreover, during a 1 h dissolution test, the MoS2 nanosheets' surfaces were significantly oxidized, which decreased their photocatalytic activity by ∼37% through photo-Fenton reactions. These findings emphasize that exposure to aqueous iron and light alters the properties of MoS2 nanosheets, changing their dissolution kinetics, pathways, and photocatalytic activity. These changes are all directly linked to their reliability in photochemical applications and their environmental fate.