Transforming bio-waste lignin into amine functionalized carbon quantum dots for selective detection of trace Cu²⁺ in...

Developing carbon quantum dots (CQDs) from bio-waste lignin for effectively detecting Cu²⁺ 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 NH₂ 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 Cu²⁺. The developed NH₂-CQDs serve as an efficient fluorescent probe, displaying high sensitivity and selectivity towards Cu²⁺ in aqueous system, with a detection limit of 2.42 μmol/L, which is lower than the maximum permitted amount of Cu²⁺ in drinking water (20 μmol/L). The detection mechanism of NH₂-CQDs for Cu²⁺ 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 Cu²⁺ in aquatic environments.