Oxygen accelerated scalable synthesis of highly fluorescent sulfur quantum dots

Here, we report a facile and efficient approach for the large-scale synthesis of highly fluorescent sulfur quantum dots (SQDs) from inexpensive elemental sulfur under a pure oxygen (O₂) atmosphere. The important finding of this work is that the polysulfide (S ^2-) ions could be oxidized to zero-valent sulfur (S[0]) by O₂, which is the accelerator of the reaction. The SQDs prepared by this method possess nearly monodisperse size (1.5-4 nm), high fluorescence quantum yield (21.5%), tunable emission, and stable fluorescence against pH change, ionic strength variation and long-term storage. Moreover, the reaction yield of SQDs reached as high as 5.08% based on the content of S element in SQDs, which is much higher than other reported approaches (generally <1%). The prepared SQDs could be easily processed for widespread applications thanks to their low toxicity and superior dispersibility both in water and common organic solvents. These high-quality SQDs may find applications similar to or beyond those of carbon QDs and silicon QDs.