Single‐Precursor Derived NCQDs from o‐Phenylenediamine as Fluorescent Sensors for Highly Selective and Sensitive Detection of Fe³⁺ Ions in Environmental Water Samples

The development of cost-effective, highly sensitive and selective fluorescent probes for Fe³⁺ detection is essential both for environmental monitoring and water quality assessment. Herein, we report a one-step solvothermal synthesis of nitrogen-doped carbon quantum dots (NCQDs) using o-phenylenediamine as a single aromatic precursor. The inherent nitrogen-rich structure and conjugated backbone of o-phenylenediamine facilitate efficient N-doping and the formation of sp² carbon domains, yielding NCQDs with high photoluminescence and strong green emission. The synthesized NCQDs exhibited excellent photostability, high aqueous dispersibility, and a quantum yield (QY) of 14.2%. Structural and morphological characterization via TEM, XRD, and FTIR confirmed the formation of quasi-spherical particles (∼2.5 nm) with abundant surface functional groups. The fluorescence intensity exhibited a linear response to Fe³⁺ concentrations in the range of 0.196 µM to 1.667 µM, with a detection limit (LOD) of 0.296 µM and a quantification limit (LOQ) of 0.986 µM. Furthermore, the sensor was successfully applied to detect Fe³⁺ in tap and lake water samples, achieving recovery rates between 95.3 to 107%. This study demonstrates a facile single-precursor synthesis of stable, highly fluorescent NCQDs for selective Fe³⁺ detection, offering a low-cost and efficient platform for real-world environmental sensing.