Synthesis of distinctly thiol-capped CdTe quantum dots under microwave heating: multivariate optimization and characterization

The present work reports a straightforward one-step synthetic route assisted by microwave irradiation for the aqueous preparation of highly luminescence CdTe quantum dots capped with different ligands, namely, 3-mercaptopropionic acid (MPA), l-glutathione reduced and 2-mercaptoethanesulfonate. Utilization of microwave heating instead of convective heating, prevailing in the conventional hydrothermal synthesis, allows for rapid, uniform and controlled nucleation and growth of nanoparticles. Moreover, the use of air-stable Na2TeO3 as Te precursor enables a more user-friendly synthetic process averting the need for handling reagents in vacuum or under inert atmosphere. The experimental synthesis conditions for each capping were optimized by using a response surface methodology. The variables used for the optimization were the molar ratios of reagents and pH, and the optimization output was the highest photoluminescence quantum yield (QY). The optimal settings were determined by using a central composite design comprising a complete 23-factorial design as cubic points, with six axial points at a distance of α = 1.682 from the design center and four center points. Additionally, the influence of the microwave irradiation time (2–90 min) and the reaction temperature (85–150 °C) on the nanoparticles growth kinetics were thoroughly investigated. Under the optimized synthetic conditions highly luminescent (QY values up to approximately 60%), crystalline and monodisperse CdTe quantum dots with suitable surface functionalities were successfully obtained. The surface passivation with the respective capping ligand was characterized by FT-IR while the size and the high crystallinity of the as-prepared nanocrystals were confirmed by HR-TEM.