Transforming bio-waste lignin into amine functionalized carbon quantum dots for selective detection of trace Cu in aqueous system.

Developing carbon quantum dots (CQDs) from bio-waste lignin for effectively detecting Cu is of great significance for promoting the value-added utilization of lignin resources. However, the limited amount of surface-active groups and low quantum yield of lignin-based CQDs hinder their application in this regard. Herein, bio-waste lignin was converted into value-added amine functionalized CQDs using a facile two-step hydrothermal approach. The as-synthesized CQDs modified with amino groups exhibit bright green fluorescence, abundant surface functional groups, high water solubility and uniform particle size (3.9 nm). Systematic analysis demonstrates that the rich NH groups (~12.3 %) on the CQDs backbone improve their fluorescence properties (quantum yield increased from 3.4 % to 21.1 %) and specific detection ability for Cu. The developed NH-CQDs serve as an efficient fluorescent probe, displaying high sensitivity and selectivity towards Cu in aqueous system, with a detection limit of 2.42 μmol/L, which is lower than the maximum permitted amount of Cu in drinking water (20 μmol/L). The detection mechanism of NH-CQDs for Cu is attributed to the synergy of static quenching and photo-induced electron transfer. This study provides a valuable reference for the synthesis of high-quality fluorescent CQDs from lignin resources and the effective detection of trace Cu in aquatic environments.