One-Step Synthesis of N-Doped Graphene Quantum Dots via Plasma Contacting Liquid for Multiple Heavy Metal Ion Detection

N doping is crucial to improving the properties of graphene quantum dots (GQDs) and broadening their application. However, the current routes for doping N into GQDs require high pressure, high temperature, and a long time. Here, we reported a simple and fast approach for synthesizing N-doped GQDs from glucosamine via plasma contacting liquid. The synthesis process operated in one step within minutes at atmospheric pressure and temperature lower than 80 °C. The synthesized N-doped GQDs featuring pyrrole, graphitic-N, and pyridine structures were confirmed with XPS, HRTEM, Raman, and FTIR spectroscopy. Our results showed that the atomic ratio of N/C in N-doped GQDs was about 0.14, in which 54% of N atoms doped in GQDs under pyrrole and graphitic-N structures. These N-doped GQDs contained many O-rich functional groups and surface defects such as Stone–Wales disorder and trivacancy defects. We found that N-doped GQDs synthesized via plasma contacting liquid were more sensitive to multiple metal ions than those synthesized by conventional methods. In detail, through the fluorescence quenching observation, we found that N-doped GQDs in this study were responsive to Fe3+, Cu2+, Pd2+, Hg2+, Pb2+, and Co2+. Our results indicated that N-doped GQDs via plasma contacting liquid could be used as fluorescent sensors to detect the presence of heavy metal ions in wastewater or pollutant aqueous environments.