Green Synthesis, Structural Characterization, and Solvent‐Dependent Optical Properties of Moringa oleifera –Derived Carbon Dots for Selective Turn‐On Detection of Co 2+ Ions

Moringa carbon dots (MCDs) were prepared in a green and sustainable way using Moringa oleifera leaves as a natural carbon source through a sand bath reflux method. The resulting MCDs showed strong fluorescence, moderate solubility in DMSO, and lower solubility in water. The as‐prepared MCDs were characterized using high‐resolution transmission electron microscopy (HR‐TEM), Fourier transform infrared spectroscopy (FT‐IR), x‐ray diffraction (XRD), UV–vis absorption, and fluorescence spectroscopy. Additionally, when MCD solution (10 mM NaH 2 PO 4 –citric acid, 8:2, pH 7.4) was exposed to Co 2+ ions, the fluorescence intensity of the MCDs increased significantly, showing ninefold enhancement, indicating high selectivity and sensitivity toward Co 2+ ion detection. A good linear relationship was observed between the fluorescence intensity and varying Co 2+ ions concentration in the range of 1–9 μmol L −1 . The LOD and LOQ with 0.162 × 10 −5 M and 0.54 × 10 −5 M, respectively, were found. The fluorescence quantum yield of MCDs enhanced from 29.5% to 93% upon the addition of Co 2+ ions. Analysis using the Benesi–Hildebrand (B‐H) method confirmed a 1:1 stoichiometry ratio of MCDs and Co 2+ ions in real water samples. These results demonstrate the potential of Moringa‐derived CDs as efficient fluorescent probes for Co 2+ ion sensing in environmental applications. GC‐MS analysis was also carried out to identify the organic fragments present in the synthesized MCDs, providing additional information about their chemical composition.