CQDs-based Optical Sensors for the Detection of Metal ions: Preparation and Mechanism of Detection

One of the major challenges of the recent decades is environmental pollution, particularly in water and wastewater. Several solutions have been proposed for their treatment. Furthermore, an important issue is the identification of environmental contaminants and quantifying their levels to inform further actions. Therefore, monitoring pollutant concentrations is a key strategy for identifying and removing these contaminants. Heavy metals are among the pollutants that pose significant dangers to living organisms. Optical sensors, which can detect metal pollutants through colorimetry and fluorescence, are among the easily fabricated and employed sensors for this purpose. In recent decades, the unique optical properties of CQDs have led to considerable investigation into their use as sensors for detecting metals. Due to their stability, high water solubility, environmental compatibility, low toxicity, affordability, and availability, CQDs are a suitable choice for developing optical sensors. This review explores the synthesis methods for CQDs, focusing on both bottom-up and top-down approaches. Additionally, it will discuss the origins of CQDs preparation and detection mechanisms of metal ions.