Fabrication of carbon dots from Siraitia grosvenorii shells and their fluorescent response for deep eutectic solvents

For the first time, the valorization of waste shells from the Siraitia grosvenorii industry involves their conversion into carbon dots (CDs) for the detection of deep eutectic solvents (DESs) concentrations through their fluorescence effect. The material composition of the fruit shells was first analyzed, revealing that lignin constitutes 29.8 % of their total mass. Then four types of DESs were prepared for the extraction of lignin from these shells; among them, choline chloride-lactic acid (ChCl-Lac) achieving the highest extraction rate of 92.49 %. The obtained lignin was characterized and subsequently used as a raw material to synthesize carbon dots possessing tunable fluorescent properties with a quantum yield of 5.73 %. Moreover, it was found that Fe 3 + could quench the fluorescence of the CDs, while the addition of certain DESs could restore the quenched fluorescence. The presence of DESs alone could also induce changes in fluorescence when interacting with the CDs. Based on this effect, a new system for the effective quantitation of the concentration of DESs in aqueous solutions using CDs was established, and DESs were used in several main steps and played multiple roles. This study provides not only a solution for the value-added utilization of solid waste from current fruit industry, but also a new approach for the concentration detection of DESs in aqueous solutions.