The transformation of lignin with natural aromatic structure into value-added carbon dots (CDs) achieves a win-win situation for low-cost production of novel nanomaterials and reasonable disposal of biomass waste. However, it remains challenging to produce multi-emission CDs from biomass for advanced applications. Herein, a green and facile approach to preparing multi-emission CDs from alkali lignin via N and B co-doping is developed. The obtained N and B co-doped CDs (NB-CDs) show multi-emission fluorescence centers at 346, 428 and 514 nm under different excitations. As the doping amount of N and B increases, the fluorescence emission band gradually shifts to 428 and 514 nm, while that at 346 nm decreases. The fluorescence mechanism is explored through the research of the structure, composition and optical performance of NB-CDs in combination with density functional theory (DFT) calculations. It demonstrates that the effect of doping with B-containing functional groups on the fluorescence emission behavior is multivariate, which may be the crucial contribution to the unique multi-emission fluorescence of CDs. The multi-emission NB-CDs with prominent stability are applied for multilevel anti-counterfeiting printing. It provides a promising direction for the sustainable and advanced application of biomass-derived CDs, and the theoretical results highlight a new insight into the deep understanding of the multi-emission fluorescence mechanism.
Keywords: B co-doped; N; carbon dots; density functional theory; lignin; multi-emission; multilevel anti-counterfeiting.