Biowaste‐Derived Nitrogen‐Doped Carbon Dots for Real‐Time Detection of Fe3+ and DFT Mechanistic Study

Nitrogen‐doped carbon dots (N‐CDs) are emerging as materials for advancing technologies in fields such as environmental analysis, biosensing, and fluorescent probes due to their outstanding fluorescence and excellent biofriendliness. The synthesis of N‐CDs involved a facile hydrothermal treatment of agricultural waste bagasse and urea, which acted as the carbon and nitrogen source, respectively. The as‐synthesized dots were thoroughly characterized to elucidate the structure and properties, demonstrating that the N‐CDs possessed well‐defined particle sizes, rich surface functional groups, and promising luminescent characteristics. Specifically, the measured quantum yield was 27.8%. N‐CDs exhibit an immediate fluorescence quenching response toward Fe3+, and based on this property, a novel sensing platform for real‐time Fe3+ detection was constructed, achieving a limit of detection (LOD) of 0.17 μM. Mechanistic investigations, including fluorescence lifetime decay analysis, temperature‐dependent Stern–Volmer studies, and DFT simulations, collectively reveal that the quenching process is primarily governed by dynamic electron transfer from the excited state of N‐CDs to the 3d orbital of Fe3+. This work not only presents a sustainable and effective fluorescent sensor for Fe3+ detection but also provides deeper insight into the photophysical interactions between heteroatom‐doped carbon dots and metal ions.