Full-value preparation of biochar and 2D N-doped CDs@ZIF-L from fermentation residues for sensitive sensing tetracyclines in food samples

The use of thermal conversion to convert Chinese patent medicines (CPM) residues into porous carbon-based materials and carbon dots (CDs) has effectively resolved the challenges associated with resource waste and environmental pollution while enhancing the added value of CPM residues. In this study, biochar and N-doped CDs with high quantum yield (QY) were simultaneously prepared from fermentation residues by employing a hydrothermal carbonization method without any chemical reagents . The obtained biochar had remarkable adsorption capacity, with an iodine adsorption value of 693.22 mg g –1 . The QY of N-doped CDs could reach to 36.17 % by the mean of self-doping due to the high nitrogen content of the fermentation residues. Considering the structural integrity and permeable porous structure of the two-dimensional leaf-like zeolitic imidazole framework (ZIF-L), N-doped CDs were encapsulated into ZIF-L to form novel fluorescent composites (N-doped CDs@ZIF-L). Moreover, N-doped CDs@ZIF-L as a novel fluorescent probe could be efficiently quenched in the presence of tetracycline (TC), doxycycline (DOC), and chlortetracycline (CTC) by static quenching and the inner filter effect . Notably, the fluorescent probe exhibited a good linear relationship with the TC, DOC, and CTC at 0–50, 0–50, and 0–45 μM, respectively, with limits of detection of 0.025, 0.033, and 0.027 μM, respectively. This probe could be employed to detect TC antibiotics in honey and milk, suggesting that it had the great potential for applications in environmental monitoring and food safety.