Rapid Synthesis of Highly Fluorescent Nitrogen-Doped Graphene Quantum Dots for Effective Detection of Ferric Ions and as Fluorescent Ink

Graphene quantum dots (GQDs) have attracted much attention of many researchers because of their low cytotoxicity, good optical stability, and excellent photoluminescence property, which make them novel nanostructured materials in many application fields ranging from energy to biomedicine and the environment. In this work, highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) were synthesized through microwave heating using sodium citrate and triethanolamine as raw materials. The as-prepared N-GQDs showed considerable bright blue fluorescence with a quantum yield of 8% and excellent uniform dispersion with an average diameter of approximately 5.6 nm; they also exhibited excellent stability and pH-sensitive properties. Furthermore, we demonstrated the application of N-GQDs as probes for metal ion detection. The results indicated that N-GQDs responded rapidly toward Fe3+ because of the static quenching mechanism. A detection method was proposed, with detection linear in two ranges from 20 to 70 nM (F = -0.9666 CFe3+ (nM) + 608.85 (R = 0.9740)) and from 1 to 100 μM (F = -12.04 CFe3+ (μM) + 1191.94 (R = 0.9541)); the lowest detection limit of 9.7 nM for Fe3+ was obtained. The results obtained in this work lay the foundation for the development of high-performance and robust metal ion detection sensors. Moreover, it can also possibly be used as a new type of fluorescent ink.