Discovery of natural water-dispersible MoS₂ quantum dots in bulk powder

In contrast to laborious efforts to gain quantum dots (QDs) of two-dimensional (2D) layered materials, less attention has been given to the discovery of natural QDs present in the powder sample. In this study, we discovered that a considerable quantity of natural QDs are present in 2D powders and demonstrated a simple way to obtain MoS₂ QDs from a bulk powder without any chemical and severe ultrasonication. The natural MoS₂ QDs were obtained by filtering the MoS₂ powders dispersed in ethanol. The separated QDs resulted in a stable blue suspension in deionized water which exhibited the absorption spectra at a wavelength of 320 nm, supporting that MoS₂ QDs were successfully separated from the bulk powder. And, the maximum photoluminescence intensity appeared in the ultraviolet region under the excitation of 320 nm. Also, the doping effect of MoS₂ QDs on MoS₂ flakes led to the enhancement of photoluminescence spectra due to a hole carrier from MoS₂ QDs. Our finding paves the way to explore natural QDs from a powder sample of other 2D materials.