Ultrafast magneto-inductive synthesis of carbon dots from plant-based precursors using deep eutectic solvents: A comparative study with traditional hydrothermal methods

The batch hydrothermal synthesis of carbon dots (CDs) has limitations in terms of yields and production capacity. This work aimed to develop an efficient and rapid technique to synthesize CDs through magneto- induction from natural plant-based precursors. Firstly, the influence of temperature and duration in a batch hydrothermal method was studied, using lignin, palm empty fruit bunch (EFB), glucose, sucrose, and xylose as the precursors. Green and sustainable deep eutectic solvents (DESs), specifically choline chloride (ChCl)/lactic acid (ChLa), ChCl/urea (ChUr), ChCl/1,3 butanediol (ChBu), and ChCl/oxalic acid (ChOx), were utilized in the batch hydrothermal synthesis of CDs. This study demonstrated that the CDs derived from ChLa and ChOx showed a high quantum yield (%QY) when lignin was the precursor. In contrast, the CDs from ChLa and ChBu demonstrated a high %QY for biomass EFB precursor, and the CDs from ChUr and ChBu achieved a high %QY for glucose, sucrose, and xylose precursors, respectively. ChBu demonstrated a well-balanced %QY and promising CD characteristics alongside a notably higher mass yield across all precursors, making it the ideal choice for the magneto-inductive synthesis study. Magnetic hyperthermia (MHT) stands out by producing superior CDs with an impressive QY of 23.44 % and a remarkable mass yield of 28.85 %. The MHT method generated the highest CD productivity of 62.72 mg CDs/g Lig/h from lignin in ChBu solvent at 25 wt% Fe3O4 in only 180 sec (ChBuLig25wtFe180s). This was 11.18 times higher than the conventional hydrothermal method, which required an exogenous heat source at 220 degrees C for 10 h. The MHT method cut production costs by 13.41 times compared to traditional hydrothermal methods. This significant cost-saving stems primarily from its ability to dramatically shorten processing times, enhance heat transfer efficiency to the carbon nanostructures, and reduce overall expenses. These advantages culminate in a more efficient, streamlined, and practical production process, delivering superior CD productivity.