Synthesis and Characterization of Carbon Dots Derived from Citrullus Lanatus Rinds in Solid and Liquid States

Abstract

Citrullus lanatus (watermelon) rinds, a major organic waste from fruit consumption, can serve as a sustainable precursor for carbon-based nanomaterials. This research presents the green synthesis and comparative characterization of carbon dots (CDs) derived from watermelon rinds in solid and liquid states. The rinds were dried, carbonized at 220 °C for two hours, and subjected to solvothermal synthesis. The synthesized CDs were characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS), Ultraviolet-Visible (UV-Vis) Spectroscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray (SEMEDX). The solid-state and liquid-state CDs displayed average particle sizes of 3.62 nm and 19.4 nm, respectively, with polydispersity indices of 0.245 and 0.247, indicating moderate dispersion. UV-Vis analysis revealed absorption peaks at 286 nm (solid) and 280 nm (liquid), while FTIR spectra confirmed the presence of C=C, O–H and C–H functional groups. XRD confirmed amorphous graphitic structures, and SEM-EDX showed high carbon and nitrogen content. The findings suggest that watermelon rind-derived carbon dots possess tunable optical and structural properties suitable for bioimaging, sensing, and optoelectronic applications, promoting waste valorization and sustainable nanomaterial production.