Engineered full-color-emissive lignin carbon dots enable selectively fluorescent sensing of metal ions

As a burgeoning luminescent unit, multifaceted carbon dots (CDs) from ideally sustainable and aromatic-like lignin biopolymer have been igniting the renaissance to alleviate the bimodal anxieties of carbon neutrality and ecological environment. However, the dilemma of synthesizing full-color-emissive CDs with a modulated solvent-engineering is hugely lopsided which severely impedes the illumination of linking their photoluminescence mechanism and selective metal-ion-sensing functions. Herein, the solvent-engineered, lignin-derived multicolor CDs (blue, green, yellow, and red light) with a distinctively well-defined nanostructure consisting of sp2/sp3-hybridized carbon skeleton and partially surface-functionalized domains (e.g., –OCH3, –OH, –COOH, and N, S co-doping) are proposed to maneuver the molecular-structure-sensing correlations. We found that full-color N, S co-doped CDs with a narrow size distribution of 2.13–2.63 nm have the rapidly selective quenching abilities to fluorometrically probe the explicit metal-ion systems of Fe3+, Ag+, Cu2+ and/or Al3+ under a wide response range (0–500 μM) with high accuracy. The factors of lignin molecular state, quantum size, zeta potential, electrostatic and cation-π interactions that endow their unique fluorescence, real-time and sensitive monitoring provoked by polar solvents are comprehensively highlighted. Hence the present attempt not only provides a scalable tactic to rationally nanoscale-design lignin valorization with a blueprint of expanding the biorefining toolbox, but also paves the avenue to forecast specific metal-ion recognition of multicolor CDs coordinating molecular structure and photophysical properties.