Carbon quantum dots from sugar beet molasses: Synthesis, purification, characterization, and functional properties

Carbon dots (CDs) are nanoparticles smaller than 10 nm, which exhibit advantageous characteristics, such as high chemical stability, hydrophilicity, as well as antimicrobial, antioxidant, and biocompatible properties. Here, CDs were synthesized from sugar beet molasses via hydrothermal carbonization and subsequently purified using the cloud point extraction method. A preliminary study was conducted to evaluate the effect of synthesis and purification factors on the fluorescence intensity of CDs. The optimal conditions for the synthesis of CDs were a processing temperature of 171.2 °C for 7.18 h. Moreover, the ideal conditions for the purification of CDs involved using 4.4 mL of acetone, 1.6 g of sodium sulfate, and 18.1 mg of sodium dodecyl sulfate (SDS). The purified CDs exhibited an average size of 0.69 ± 0.1 nm and a zeta potential of -9.87 mV. The antioxidant activity of the CDs was approximately three times greater than that of a 10 % (w/v) sugar beet molasses solution. Additionally, the minimum inhibitory concentration (MIC) of CDs against Gram-positive bacteria ( Bacillus cereus, Listeria monocytogenes , and Staphylococcus aureus ) was four times greater than that of the Gram-negative bacteria ( Salmonella enterica and Pseudomonas aeruginosa ). The results of the cytotoxicity assay showed cell viability of more than 90 % after 24 and 48 h of exposure to CDs. In conclusion, our results highlight the potential of purified CDs as multifunctional agents with antioxidant and antibacterial activities for food preservation applications.