Rapid synthesis of highly photoluminescent nitrogen-doped carbon quantum dots via a microreactor with foamy copper for the detection of Hg2+ ions

A rapid synthetic method for highly photoluminescent (PL) nitrogen-doped carbon quantum dots (N-CQDs) was developed by using a microreactor with foamy copper having different porosities. By taking advantage of the foamy copper, we obtained a high quantum yield (QY) of 84.1%, which was more efficient than most of the previous reports. Compared to the procedure without adding foamy copper, the QY when foamy copper was used was two times higher. The formation mechanism of the N-CQDs, which involved molecular condensation and the formation of carbon cores, was demonstrated. To explore the relationship between the use of a microreactor with foamy copper having different porosities and the PL properties of the N-CQDs, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis was employed. The results show that the surface functional groups and elemental contents influence the PL emission. We further demonstrate the application of the N-CQDs as probes for heavy metal ion detection. The results indicated that N-CQDs are very suitable for use as nanoprobes for Hg 2+ ion detection and that the lowest detection limit (LOD) for Hg 2+ is 2.104   nM, which is superior to many other research studies. This method highlights that the value of microreactor synthetic system as a tool for the environmental and hazard detection.