Converting waste Chrysanthemi Flos residues into high-value fluorescent carbon dots for rapid and selective detection of mercury (II) ions in aqueous environments

Chrysanthemi Flos (CF) is widely used as an edible and medicinal crop, resulting in large amounts of residue production annually. The discarded CF residues (CFR) cause environmental pollution and wastage of resources. Converting CFR into functional carbon dots (CDs) is an important strategy to achieve its “waste-to-wealth” goal. Here, a CFR-derived CDs (CFR-CDs) based fluorescent sensor was successfully developed for the rapid and selective detection of mercury (Ⅱ) ions in aqueous environments, and its sensing mechanism for detecting Hg 2+ was elucidated. First, the CFR was used as a precursor to extract fluorescent CDs via a simple and green hydrothermal method. The prepared CFR-CDs possessed a typical graphite-like structure with an average size of 2.23 nm, and exhibited good hydrophilicity, excellent photostability, and excitation-dependence fluorescence behavior, while emitting blue fluorescence. Interestingly, the CFR-CDs were highly selective towards Hg 2+ , and their fluorescence was rapidly quenched by Hg 2+ (within 1 min). The prepared CFR-CDs were then used as a fluorescent sensor for efficient detection of Hg 2+ in the range of 0.3–10 μmol/L with a low limit of detection (LOD) of 0.129 μmol/L. The recovery of the Hg 2+ in actual water environments ranged between 98.60 % and 104.00 % with a relative standard deviation < 5.0 %, demonstrating the reliability of the developed sensor. Additionally, the detection mechanism was revealed to be the synergistic action of the static quenching effect (SQE), inner filter effect (IFE) and photo-induced electron transfer (PET), generating CFR-CDs/Hg 2+ complexes through the formation of surface chemical bonds and promoting the rapid shutdown of the sensor signal. This study demonstrates, for the first time, the application of CFR towards producing green and low-cost CDs as promising fluorescent sensor for the detection of Hg 2+ in actual environmental samples, and is therefore helpful for improving the utilization efficiency of CFR and promoting the realization of carbon peak and carbon neutrality goals. • Waste Chrysanthemi Flos residues derived carbon dots (CFR-CDs) were developed by one-step hydrothermal method. • CFR-CDs were innovatively used as a fluorescent sensor for efficient detection of Hg 2+ in real samples . • Detection mechanism of CFR-CDs-based Hg 2+ sensor was systematically clarified. • Achieve the value-added utilization of CFR and turn it into treasure.