Pharmaceutical Waste‐Derived Carbon Quantum Dots via Microwave Method for Selective Au³⁺ Ion Detection

Heavy metals released in various ways into water bodies is a key concern for environmental protection. Their nonbiodegradability and the health risks associated with these heavy metals in the environment exacerbate the problem. Scientists worldwide are addressing the issue through various approaches. Among them, the fluorescence approach is unique in its simplicity and rapid results. In this study, carbon quantum dots (CQDs) were synthesized from an expired vitamin B12 tablet using a simple microwave‐assisted approach. The resulting CQDs showed sustainability, good photostability with quantum yield (30.08%), water solubility, prolonged storage stability, and produced a brilliant blue emission when exposed to UV light. These CQDs exhibited stable photoluminescence attributes across a wide range of ionic strengths and pH levels. Au 3+ ions effectively quenched the PL intensity of CQDs in a linear, selective, and sensitive approach. We demonstrated Au 3+ sensing in aqueous conditions utilizing CQDs as the fluorescent probe, with a limit of detection of 41 nM. This work has been demonstrated to create an efficient and cost‐effective method for detecting auric ions in wastewater effluents.