Lignin-based fluorescence-switchable graphene quantum dots for Fe3+ and ascorbic acid detection.

ABSTRACT

The synthesis of lignin-based graphene quantum dots (GQDs) with excellent fluorescence stability, quantum yield, and biocompatibility for sensitive and selective detection of Fe3+ and ascorbic acid (AA) has remained a challenging endeavor. Using an acidolysis process with 17.5% nitric acid followed by hydrothermal treatment at 200 °C, this study provided an improved synthesis route for the production of high-quality GQDs from alkali lignin. The nitrogen-doped GQDs exhibit remarkable fluorescence stability under a wide range of pH (3-10), duration (1-12 h), and [NaCl] (0-1000 mM) conditions, and have a high quantum yield of 28%. The GQDs or GQDs/Fe3+ sensing systems ([GQDs] at 50 mg L-1, [Fe3+] at 500 µmol L-1, and UV excitation at 370 nm) for fluorescence sensing of Fe3+ or AA have excellent sensitivity, selectivity, and reproducibility. For Fe3+ and AA, the limit of detection is 1.49 and 1.62 µmol L-1, respectively. Mechanism investigation shows that photoluminescence quenching is caused by the formation of GQDs-Fe3+ complexes, whereas fluorescence recovery is due to Fe3+ reduction by AA.