An innovative chalcogenide transfer agent for improved aqueous quantum dot synthesis

Abstract

An innovative approach to chalcogenide precursor synthesis and their subsequent use for the production of CdX (X = S, Se, Te) quantum dots (QDs) in water under scalable and intensified continuous flow conditions is introduced. Herein, tris(2-carboxyethyl)phosphine (TCEP) is identified as a novel, efficient and water-soluble vehicle for chalcogenide transfer to form CdX QDs under aqueous conditions. A comprehensive exploration of critical process parameters, including pH, chalcogen excess, and residence time, utilizing a Design of Experiments (DoE) approach is reported. Reaction kinetics are investigated in real-time using a combination of in situ Raman spectroscopy and in-line ³¹P NMR spectroscopy. The conversion of TCEP into TCEPX (X = S, Se, Te) species is seamlessly adapted to continuous flow conditions. TCEPX precursors are subsequently employed in the synthesis of CdX QDs. Scalability trials are successfully demonstrated, with experiments conducted at flow rates of up to 80 mL min⁻¹ using a commercially available mesofluidic flow reactor with favorable metrics. Furthermore, biocompatible and aqueous CdSe/ZnS core–shell QDs are for the first time prepared in flow within a fully concatenated process. These results emphasize the potential for widespread biological or industrial applications of this novel protocol.