Green Synthesis, Structural Characterization, and Solvent-Dependent Optical Properties of Moringa oleifera-Derived Carbon Dots for Selective Turn-On Detection of Co2+ 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 NaH2PO4-citric acid, 8:2, pH 7.4) was exposed to Co2+ ions, the fluorescence intensity of the MCDs increased significantly, showing ninefold enhancement, indicating high selectivity and sensitivity toward Co2+ ion detection. A good linear relationship was observed between the fluorescence intensity and varying Co2+ 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 Co2+ ions. Analysis using the Benesi-Hildebrand (B-H) method confirmed a 1:1 stoichiometry ratio of MCDs and Co2+ ions in real water samples. These results demonstrate the potential of Moringa-derived CDs as efficient fluorescent probes for Co2+ 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.