Recent advancements towards the green synthesis of carbon quantum dots as an innovative and eco-friendly solution for metal ion sensing and monitoring

In recent years, the synthesis of carbon quantum dots (CQDs) through green methods for environmental remediation has gained significant interest owing to their benefits of reducing toxic by-products and minimising the usage of hazardous chemicals. CQDs are a new type of zero-dimensional carbon nanomaterials having a size less than 10 nm. They have attracted much attention considering their outstanding optical characteristics, non-toxicity, low-cost synthesis, biocompatibility, uniform particle size, high photostability and highly tuneable photoluminescence. The synthesis of CQDs from biodegradable and renewable resources, such as biowastes and biomass, provides an eco-friendly and sustainable alternative to conventional synthesis methods. The synthesized CQDs possess unique optical and electronic properties, including a high selectivity and sensitivity, making them promising for metal ion sensing. This review highlights the recent progress in the green synthesis of CQDs, including their synthesis methods, optical properties and potential use in sensing applications for the detection of heavy metal ions, such as iron(III), copper(II), mercury(II), chromium(IV), lead(II), silver(I), arsenic(III) and gold(III), which are considered as major environmental pollutants. A comparison based on the quantum yield, sensitivity, selectivity, detection limit, linear range concentration and sensing mechanisms is also presented. In addition, the effect of heteroatom doping on CQD performance for heavy metal detection is also discussed. In conclusion, this review emphasizes the importance of employing eco-friendly and sustainable methodologies for CQD synthesis, which not only benefits the environment but also makes these materials more accessible and cost-effective for widespread use in detecting harmful pollutants.