Fluorescent Chitosan Hydrogels Based on Biomass-Derived Carbon Dots for Toxic Aromatic Detection

This study presents a sustainable method for synthesizing anionic carbon dots (CDs) from food waste, specifically almond peels (AP) and butternut peels (BP) and seeds (BS), using a microwave-ultrasound process. The novelty of this work lies in the systematic investigation of thermal pretreatment (torrefaction) and its influence on the photoluminescence (PL) properties of biomass-derived CDs. Torrefaction enhances PL intensity in CDs synthesized from almond peels and butternut seeds, while having a limited effect on those from butternut peels. The resulting CDs exhibit excitation-dependent, blue-emitting fluorescence and maintain over 85% PL stability across the environmentally relevant pH range of 5–9. To enable pollutant detection, the optimized CDs are embedded into chitosan-based hydrogels, forming water-stable, reusable fluorescent sensors. These composites detect aromatic contaminants, including pentachlorophenol (PCP) and 4-chloro-2-methylphenoxyacetic acid (MCPA), with detection limits of 1.45 ± 0.08 and 4.10 ± 0.10 nm, respectively. The combination of waste valorization, surface-state modulation, and soft-material integration supports the development of cost-effective, environmentally friendly sensors. This initiave contributes to Sustainable Development Goals focused on clean water and responsible consumption by transforming food waste into functional materials for environmental monitoring.