Fluorescent Sensing of Ferric Ions in Water Using Hydrothermally Derived Cu-Doped Dual-Emissive Carbon Dots

Iron is an important parameter in environmental water analysis, where its concentration strongly influences water quality and environmental behavior, thus necessitating its detection in aqueous samples. Herein, we report a simple, label-free fluorescent sensing platform based on copper-doped dual-emission carbon dots (CuCDs) for the rapid and quantitative detection of Fe3+ in aqueous media. CuCDs were synthesized via a one-step hydrothermal method using Cu (NO3)2·3H2O and tryptamine (C10H12N2) as precursors at 180 °C for 6 h. The resulting CuCDs exhibited two characteristic emission peaks at 336 nm and 395 nm under 290 nm excitation, and their fluorescence was selectively quenched by Fe3+. Under optimized conditions (MES buffer, pH 5, 60 °C, 10 min reaction time), the fluorescence intensity ratio (F0/F) showed a linear correlation with Fe3+ concentration in the range of 20–700 μM at both emission wavelengths, yielding limits of detection of 11.68 μM (336 nm) and 10.07 μM (395 nm). The sensor demonstrated good selectivity against eleven common coexisting metal ions at 100-fold concentrations. Practical applicability was validated through spiked recovery assays in Min River water samples, achieving recoveries of 84.4–119.5% with results consistent with those obtained via standard atomic absorption spectrometry. The method offers low cost, a 10 min response time, and operational simplicity, providing a proof-of-concept basis for environmental water screening and future portable implementation.