• • Hydrothermal synthesis from biomass yields C-dots with quantum yields up to 30% and high aqueous solubility, enabling scalable production for photocatalytic dye degradation with >90% efficiency within 60 minutes under visible light.
• • Microwave-assisted synthesis reduces reaction time to minutes (e.g., 5-10 min) compared to hours for hydrothermal, achieving particle sizes below 5 nm with narrow distribution, critical for uniform performance in DSSCs and photocatalysis.
• • Surface passivation with nitrogen doping increases photoluminescence quantum yield by up to 50% (from 20% to 30%) and enhances electron transfer, improving solar cell efficiency by 15% relative to undoped C-dots.
• • C-dots derived from waste coffee residues exhibit excellent stability over 100 cycles in photocatalytic applications, retaining 95% of initial activity, demonstrating cost-effective waste valorization for industrial wastewater treatment.