Lignin-derived green-emitting carbon quantum dots for sensitive fluorometric detection of water in ethanol

Efficient utilization of lignin, an abundant yet underutilized biomass resource, is essential for sustainable development and advancing functional material innovation. However, strategies for transforming lignin into practical sensing materials remain limited. In this study, carbon quantum dots (CQDs) were synthesized using lignin as a carbon source through a simple one-pot hydrothermal method. The CQDs exhibited a fluorescence quantum yield of 15.28 % and significant solvent-dependent optical properties. Upon exposure to varying water content in ethanol, the CQDs showed a red shift in emission spectra and a decrease in fluorescence intensity due to hydrogen bonding-induced aggregation. Leveraging these properties, the CQDs were used as a sensitive fluorescent probe for detecting water content in ethanol, demonstrating a good linear correlation (R 2  = 0.989) and a detection limit as low as 0.288 %. To further validate the practicality of the CQDs, their anti-interference ability was evaluated by testing the fluorescence response in the presence of common interfering solvents, including methanol, acetone, isopropanol, ethyl acetate, n-hexane, and DMSO. The results demonstrated high sensitivity and minimal interference, particularly from non-polar solvents. Furthermore, the sensing platform was converted into a portable paper-based sensor for convenient, real-time detection of water content in ethanol under UV light. This study presents a sustainable approach for lignin utilization and offers a promising tool for monitoring water content in ethanol and potentially other organic solvents, even in complex environments.