Microwave synthesis of carbon dots in ten choline chloride-based deep eutectic solvents: Effect of solvent molecular structure on carbon dots fluorescence and sensing properties

Deep eutectic solvents (DESs) have showed great interest in carbon dots synthesis. Surface and optical characteristics of carbon dots (CDs) can be influenced by solvent during the synthesis. In this study, microwave method was used for CDs synthesis in ten choline chloride based DESs. Glucose was used as a cheap carbon source. Surface functional groups, optical and fluorescence properties of ten CDs were compared. Quantum yield (QY) of the prepared CDs in choline chloride/urea, choline chloride/glycerol and choline chloride/thiourea DESs were 41.3, 38.7 and 35.5%, respectively. Doping of nitrogen and sulfur atoms in the CDsDES1, CDsDES2 and CDsDES4 enhanced the photoluminescence performance. TEM, FT-IR, EDXS and fluorescence spectroscopy were used for CDs characterization. Results showed that molecular structure of hydrogen bond donor (HBD) had important influence on the CDs properties and doping. The hydrogen bond strength and hydrogen donor ability of DES reduce by the increase of carbon chain length of HBD. DESs with short carbon chain and high content of –NH2 and –OH produce CDs with higher QYs. Some of these CDs were also used as fluorescent nano-probes.