Oxidative etching of MoS₂/WS₂ nanosheets to their QDs by facile UV irradiation

Oxidative etching has been proved to be an efficient top-down method to prepare quantum dots (QDs) of layered transition-metal dichalcogenides which possess unique properties and have potential applications in various areas. Here, one facile and green oxidative etching method induced by UV irradiation is reported to prepare the QDs of MoS₂/WS₂ in aqueous solution, respectively. A prominent morphology change occurred to the nanosheets of MoS₂/WS₂ after irradiation and finally they were etched to ultrasmall nanoparticles which were proved to be the QDs. Insight into the etching mechanism was discussed in detail and hydroxyl free radicals (˙OH) were conclusively demonstrated to play the main role in etching nanosheets. From another point of view, this work also proves the crucial long-term photo instability of MoS₂/WS₂ since there are increasing photo-related applications of them and points out an easy way to degrade their nanosheets.