One-Step Green Hydrothermal-Assisted Synthesis of Carbon Quantum Dots From Robinia hispida L. Flowers, and Flourimetric Detection of Au3+ Ions in Aqueous Media

Water-soluble fluorescent carbon quantum dots (CQDs) were synthesized via a single-step, eco-friendly hydrothermal process using Robinia hispida L. flowers as a novel carbon source. Advanced characterization techniques (HRTEM, XRD, XPS, FTIR, UV–vis, and fluorescence spectroscopy) revealed spherical CQDs with an average size of 3.96 ± 0.83 nm and a quantum yield of 5.13%. Under 365 nm UV light, the CQDs emitted blue fluorescence. Fluorescence quenching studies with various metal ions showed a significant 93.5% reduction in FL intensity with 500 μM Au3+ ions. At pH 7.0, a linear detection range of 0.5–3.5 μM was achieved, with limits of detection (LOD) and quantification (LOQ) of 0.4 and 1.2 μM, respectively. The non-functionalized CQDs effectively detected Au3+ ions in tap, drinking, and river water, acidic mine drainage (sludge), and a standard reference material (CRMSA-C Sandy Soil C), achieving spike recoveries of 96.06%–101.71% with variability below 4.13%.