Stable lignin-based afterglow materials with ultralong phosphorescence lifetimes in solid-state and aqueous solution

Nowadays, afterglow materials with long-lifetime phosphorescence are mainly prepared from metal-containing substances. It is necessary and challenging to find a simple, green and feasible approach to generate afterglow materials with excellent phosphorescence from biomass materials. Herein, a facile strategy is proposed to construct afterglow materials via confining fluorescence carbon dots from lignin into silica (SiO2). Specifically, a microwave-assisted carboxymethylation process was adopted for the lignin precursor, which endowed the lignin with abundant carboxyl groups (3.69 mmol g(-1)) and maintained its benzene ring structure. Subsequently, N-doped lignin-based carbon dots (NL-CDs) with nanoscale size (6.07 nm) and excellent fluorescence (quantum yield = 30.6%) were prepared through the hydrothermal treatment of carboxymethylated lignin. Finally, the NL-CDs were confined in SiO2 and the generated NL-CDs@SiO2 exhibited excellent phosphorescence behavior in both solid-state and aqueous solution. The obtained afterglow materials achieved 5.97% of phosphorescence quantum yield and 834 ms of lifetime, which could be observed for 6 s by the naked eye. Meanwhile, a multi-modal information encryption strategy was designed based on the phosphorescence characteristics of the afterglow materials. The proposed strategy in this paper will pave the way to generate afterglow materials from lignin biomass and provide guidance for high-value utilization of lignin.