Green synthesis of boron-doped carbon dots from Chinese herbal residues for Fe3+ sensing, anti-counterfeiting, and photodegradation applications

Carbon dots (CDs), especially from biomass doped with heteroatoms, have drawn increasing attention owing to their versatility in potential applications. In this work, boron-doped CDs derived from Chinese herbal residues (B@HRCDs) were fabricated through a simple, green, one-step solvothermal method, resulting in B@HRCDs with a uniform size of 2.8 nm. The synthesized B@HRCDs were characterized using Fourier transform infrared spectroscopy, UV–visible spectroscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, and Fluorescence techniques. As prepared, the B@HRCDs demonstrated a bright fluorescence with a quantum yield of 4.0% and displayed exceptional selectivity towards Fe3+. In vitro experiments, they did not exhibit cytotoxicity against BV2 cells. The synthesized B@HRCDs were used as a sensitive nanoprobe for the detection of free Fe3+ in the range of 0–80 μM with a minimum limit of detection (LOD) of 1.08 μM. Based on their biocompatibility and negligible cytotoxicity, B@HRCDs were also shown to be useful for intracellular Fe3+ detection applications. When fluorescent ink was applied to bond paper, the patterns were clearly visible under UV light, indicating that B@HRCDs can be used for message encryption. Finally, it was further shown that the degradation rate of indigo carmine after 5 h of sunlight irradiation was 91% in the presence of B@HRCDs and decreased to 61% after 5 cycles, which indicates that the B@HRCDs have favorable photocatalytic activity and photostability. It is thus believed that this strategy achieves the reuse of herbal residues and proposes a low-cost, green method for the synthesis of CDs with Fe3+ sensing, anti-counterfeiting, and photodegradation functions.