Watermelon Peel-Based Fluorescent Carbon Quantum Dot Synthesis, Characterization, and Applications

The development of nanomaterials from renewable resources has emerged as a sustainable approach for producing low-cost and environmentally safe functional materials. In this study, carbon quantum dots (CQDs) were fabricated from watermelon peel using a one-step hydrothermal route. The as-prepared CQDs were uniformly dispersed in aqueous medium, exhibited nanoscale dimensions, and displayed strong blue?green fluorescence under ultraviolet illumination. Characterization through transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), UV?Vis absorption, and photoluminescence (PL) analyses verified their amorphous carbon structure, excitation-dependent luminescence, and high photostability across a wide pH range. Application experiments demonstrated that the CQDs served as selective fluorescent probes for Pb²⁺ and Hg²⁺ ions, exhibiting significant quenching effects while retaining stability in the presence of other competing metal ions. These findings highlight the potential of watermelon peel?derived CQDs as cost-efficient, sustainable nanomaterials for environmental sensing applications.