Microwave-assisted hydrothermal synthesis of nitrogen-rich biomass carbon dots (CDs): B, N co-doped with enhanced luminescence and dual mode afterglow emitting properties

This study utilizes nitrogen-rich biomass, soybean meal, as a raw material to synthesize carbon dots (CDs) based dual-mode afterglow emission materials via microwave-assisted hydrothermal treatment (reaction temperature:180–220 °C, residence time: 15–60 min) through nitrogen-boron co-doping strategy. Boric acid was used as an acidic proton source to investigate the microwave-assisted hydrolysis of soymeal under varying temperatures and reaction times. The distribution and types of major organic compounds in the hydrothermal liquid phase were analyzed, and the formation of B–C covalent bonds in the hydrothermal system was induced. Under optimal reaction conditions, boron-doped carbon dots (S-BCDs) with a glassy structure were successfully synthesized, and melamine-doped carbon dots (S-BCDs@MA) were also prepared. The fluorescence properties and structural changes of S-BCDs and S-BCDs@MA were compared and analyzed under different reaction conditions, exploring the effect of nitrogen-boron co-doping on the transition from fluorescence to phosphorescence in S-BCDs@MA. To research the dual-mode afterglow emission mechanism in room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) of S-BCDs@MA under different reaction temperatures and residence times, and to obtain the optimal afterglow performance of S-BCDs@MA through the analyses of fluorescence spectra, afterglow spectra, and also time-resolved spectra. The biomass-carbon dots were applied in the field of information encryption.