Green Synthesis of Carbon Quantum Dots and Their Environmental Application for the Detection of Heavy Metal Ions

The increased spotlight on Sustainable Chemistry has progressively drawn attention to the greener synthesis of Carbon Dots. Among the endless production pathways, the evolution of green synthetic methods is uplifted by the abundance availability of natural precursors. This greener approach is attempted in the production of Carbon Dots (CDs) that flourished in the past two decades. Carbon Dots are crowned in the carbon family for their astonishing features. Owing to their tuneable optical properties, large surface area to volume ratio, and effective photon harvesting in the short-wavelength region, they serve as excellent choices for heavy metal detection. Industrial operations over the centuries tremendously increased the heavy metal ion concentration. The most prominent commercial heavy metals disrupting biological functions are mercury, chromium, cadmium, lead, and arsenic. Despite the high consciousness of heavy metal risks, the frequency of poisoning continues, demanding proactive and efficient management. Hence, designing viable, selective, and dependable sensors beneficial over conventional techniques that request complex instrumentation and sample preparation is vital. The emergence of fluorescent Carbon Dots with exceptional photoluminescent properties and simplicity of functionalization makes them a valuable tool for innocuous metal detection by fluorescence quenching. Certain suggested mechanisms for metal ion sensing by CDs include Complexation, Inner Filter Effect (IFE), Light induced Electron Transfer (LET), ion binding, and aggregation. Among these, the most widely recognized is the static fluorescence inhibition, which implies the development of a non-nuclear interaction between the CDs and the metal cation, thereby enabling the detection of metals. This chapter presents an outlook on the role of green synthesized CDs in sensing heavy metal ions shedding light on future studies.