Urea-choline chloride deep eutectic solvent-assisted synthesis of luminescent nitrogen-doped carbon dots from chitin and their photocatalytic application in decolourizing malachite green

Luminescent carbon dots (CDs) are emerging carbon nanomaterials whose tunable and exceptional optoelectronic properties have found applications as alternatives to traditional fluorophores and metal-based catalysts. Further, they can be easily prepared from biomass and using green solvents. Biomass sources of CDs, however, often result in the formation of thousands of products which are difficult to separate. In this study, CDs were synthesized using a urea-choline chloride deep eutectic solvent (DES) and shrimp shell-derived chitin as raw materials through a low temperature solvothermal treatment. This was followed by a facile liquid-liquid extraction with acetone to improve the optical properties and narrow the size distribution of the CDs. The acetone-extracted CDs (ACDs) showed good performance in photocatalytic degradation of the aquatic pollutant, malachite green. They also show good potential in monitoring various toxic water pollutants through the quenching effect of selected pesticides, antibiotics, heavy metals and anions on the fluorescence of ACDs.