Green synthesis of carbon quantum dots from biomass with down and upconversion luminescence for methylene blue degradation

Water pollution, driven by the discharge of synthetic dyes from industries like textiles, remains a global threat to human health. Methylene blue, a common dye in the textile sector, exacerbates this issue. In response, this study presents a novel approach to mitigate water pollution by synthesizing nanomaterials using biomass-derived (grapes and watermelon) carbon quantum dots (CQDs). Employing the hydrothermal method at temperatures ranging from 80°C to 160°C for 1 to 24 hours, CQDs were successfully synthesized using watermelon shell and grape pomace as organic precursors. Characterization techniques, including UV-Visible spectra, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and luminescence spectroscopy, verified the quality of the CQDs. Degradation tests on methylene blue were conducted separately under sunlight and incandescent focus light irradiation, assessing catalytic activity at 20-minute intervals over a 2-hour period. The CQDs (1-10 nm) exhibit optical properties including upconversion and downconversion luminescence. This CQDs shown an effective photocatalytic activity in methylene blue degradation under sunlight. The straightforward and cost-effective synthesis process suggests the potential for scalable production of catalytic nanomaterials for synthetic dye degradation.