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

Abstract 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 n m , 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.