Hydrothermally Synthesized Carbon Quantum Dots from Watermelon Peel for Fluorescent Ink and selective Sensing of Fe³⁺, Pb²⁺, and Ag⁺ Ions

Natural product-derived carbon quantum dots (CQDs) have recently drawn much attention owing to their excellent optical and electrical properties. This study aims to develop CQDs that can be applied to fluorescent inks and detect Fe3+ metal ions in aqueous solutions. Watermelon peel waste was converted into CQDs using a one-step, straightforward, environmentally friendly, and efficient hydrothermal process. The resulting CQDs were analyzed with various techniques, including UV-Visible absorbance spectroscopy, spectrofluorometric, X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy. According to the available literature, the CQDs exhibit strong blue fluorescence that is very photostable, good enough to allow their possible use in a fluorescent ink application. The CQDs were examined regarding their potential as sensors to detect metal ions by studying how much their fluorescence was quenched when mixed with several different metal ions in solution. Examination of the data indicates that the only metal ions that significantly quenched the fluorescence of the CQDs were the Fe3+ metal ions, and these caused about an 80% reduction in the amount of fluorescence that was observable from the CQDs. This study suggests that these watermelon peel-derived carbon dots are probably good candidates for both fluorescent inks and sensors for detecting metal ions.