Green Synthesis of Carbon Quantum Dots from Cadaba fruticosa Flower for Photocatalytic Degradation of Methylene Blue, Rose Bengal, and Bromophenol Blue Dyes
Keywords:
Carbon quantum dots, Cadaba fruticosa, Rose Bengal, bromophenol blue, wastewater treatmentAbstract
Synthetic dyes discharged from textile, printing, and cosmetic industries are a major source of aquatic pollution, and there is a pressing need for low-cost, eco-friendly remediation photocatalysts. In this study, fluorescent carbon quantum dots (CQDs) were green-synthesized from Cadaba fruticosa flowers by a rapid, single-step microwave-assisted route and evaluated as visible-light photocatalysts for the degradation of three structurally distinct dyes: methylene blue (MB, cationic thiazine), Rose Bengal (RB, anionic xanthene), and bromophenol blue (BPB, halogenated sulfonphthalein). The CQDs were characterized by UV-Visible absorption spectroscopy (absorption maxima at 239 and 277 nm, assigned to π–π* and n–π* transitions), Fourier-transform infrared (FTIR) spectroscopy (C–H, C≡C, C=N and C–Br surface functionalities), powder X-ray diffraction (broad amorphous carbon halo with an average crystallite size of 21.26 ± 8.91 nm by the Debye–Scherrer equation), dynamic light scattering (DLS; principal population 1–10 nm, PDI 0.474), zeta potential (−3.56 mV), and fluorescence spectroscopy (stable emission at 538, 576 and 621 nm). Under visible-light irradiation, the CQDs degraded MB most effectively, reaching 85% and 66% removal at 50 and 100 µg/mL CQD loading, respectively, within 90 minutes, while RB (16–20%) and BPB (9–11%) were degraded to a much lower extent, reflecting the influence of dye charge, structure, and halogenation on adsorption and reactive-oxygen-species-mediated breakdown. These results establish Cadaba fruticosa flower-derived CQDs as a sustainable, low-cost nanomaterial with selective photocatalytic activity toward cationic dye pollutants and provide a mechanistic basis for further optimization toward broader-spectrum dye remediation.
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