The most efficient method for synthesizing quantum dots with a narrow size distribution and high quantum yield using environmentally friendly solvents and non-toxic precursors is the aqueous synthesis method. This method involves the use of water as the primary solvent and non-toxic precursors, such as metal salts and thiols, to synthesize quantum dots.Aqueous synthesis of quantum dots typically involves the following steps:1. Preparation of precursors: Choose non-toxic metal salts, such as zinc acetate or cadmium chloride, and thiols, such as thioglycolic acid or cysteine, as the precursors for the synthesis of quantum dots.2. pH adjustment: Adjust the pH of the precursor solution to a suitable value usually around 7 using a non-toxic base, such as sodium hydroxide or potassium hydroxide.3. Temperature control: Heat the precursor solution to a specific temperature usually between 80-100C to initiate the nucleation and growth of quantum dots.4. Growth control: To achieve a narrow size distribution, carefully control the reaction time, temperature, and precursor concentration. This can be done by monitoring the reaction using UV-Vis spectroscopy and adjusting the parameters accordingly.5. Surface passivation: To improve the quantum yield of the synthesized quantum dots, surface passivation can be performed using non-toxic ligands, such as mercaptoacetic acid or polyethylene glycol.6. Purification: After the synthesis is complete, the quantum dots can be purified using techniques such as dialysis or size-exclusion chromatography to remove any unreacted precursors and byproducts.7. Characterization: The synthesized quantum dots can be characterized using techniques such as transmission electron microscopy TEM and photoluminescence spectroscopy to confirm their size, shape, and optical properties.The aqueous synthesis method offers several advantages, including the use of environmentally friendly solvents, non-toxic precursors, and relatively mild reaction conditions. Additionally, this method can produce quantum dots with high quantum yields and narrow size distributions, making it an efficient and sustainable approach for the synthesis of quantum dots.