Rapid continuous aqueous production of copper indium sulfide quantum dots via a microwave-assisted microfluidic technique

Ternary copper indium sulfide (CIS) quantum dots (QDs) have been emerging as attractive alternatives to Cd- and Pb-based QDs in various applications owing to their favorable optical properties and low toxicity. However, methods allowing continuous production of CIS QDs in an easy-to-perform and/or organic-solvent-free way are yet to be realized. Here, we report a facile, rapid, continuous, and aqueous synthetic approach for CIS QDs based on a microwave-assisted microfluidic (MAM) technique with easy scale-up of production. Typically, CIS QDs and CIS@ZnS QDs are continuously produced with a flow rate of 30 mL h⁻¹ at a moderate temperature (∼95 °C) in an open-air system with a continuous flow of water as the reaction medium. This continuous synthesis process circumvents the requirements of batch operation, a degassed/inert atmosphere, high temperatures, organic solvents, and complex/expensive equipment. The resulting water-soluble CIS@ZnS QDs show a photoluminescence quantum yield of 44%. This work provides an efficient and green synthetic route for the scalable production of fluorescent nanomaterials.