Nitrogen-rich carbon quantum dots (N-CQDs) based on natural deep eutectic solvents: Simultaneous detection and treatment of trace Co2+ under saline conditions

Trace Co2+, when present in large quantities, is harmful to the environment and therefore cannot be ignored. Inductively coupled plasma mass spectrometry (ICP-MS) is a standard method used to detect metal ions, however, detecting trace Co2+ under high saline conditions can be challenging. Similarly, existing Co2+ treatment methods are prone to secondary pollution and have high energy consumption. Therefore, it is necessary to find an efficient and non-polluting method for Co2+ detection and treatment. This study successfully synthesized nitrogen-rich carbon quantum dots (N-CQDs) based on natural deep eutectic solvents (NADES) using a one-step solvothermal method. The prepared N-CQDs exhibited excellent fluorescence and high salt tolerance. The simultaneous detection and treatment of trace Co2+ in water under high salinity conditions were achieved for the first time. The response of the N-CQDs to Co2+ under saline condition was linear in the range of 5-250 μM with a limit of detection (LOD) of 1.2269 μM. Feasibility of practical application was assessed by quantitative detection of Co2+ in real water samples. Furthermore, the N-CQDs can treat Co2+, and the removal rate was 99.98%.