Production of carbon dots during the liquid phase exfoliation of MoS2 quantum dots

N-methyl-2-pyrrolidone (NMP) has been widely used as a solvent for preparing two-dimensional quantum dots (2D-QDs) by probe sonication. Here we found that carbon dots (CDs) are simultaneously produced by the carbonization of NMP when preparing MoS2 QDs in a NMP solvent by probe sonication. These two kinds of QDs are similar in color, crystal structure, excitation wavelength dependent photoluminescence (PL), and have overlaps in their absorption spectra and coincidence of PL peaks. As a result, the co-production of CDs has not previously been recognized. The CDs show strong optical interactions with the MoS2 QDs, which leads to a dramatic decrease in the fluorescence intensity of the CDs/MoS2 QDs. Moreover, we found that the carbonization also occurs for the commonly used organic solvents. These findings suggest that associated production of CDs should be considered when preparing 2D-QDs by probe sonication, and the resulting hybrid CDs/2D-QDs will provide opportunities to design their properties and uses.