Evaluation of Process Variables in the Continuous Flow Synthesis of Quantum Dot Nanoparticles

Abstract

Cadmium selenide (CdSe) quantum dots (QDs) have attracted considerable attention due to their size-tunable optical properties, enabling applications in areas including biomedical imaging and energy harvesting. Developing continuous and lower-toxicity synthesis routes is important to improve process reproducibility and broaden application potential. This study investigated the continuous synthesis of CdSe QDs using a phosphine-free formulation to reduce toxicity while maintaining strong optical responses. The effects of synthesis temperature (240, 250, and 260°C), Cd:Se molar ratio (1:1, 1:5, and 5:1), and residence time (60, 90, and 120 s) on QD optical characteristics and estimated particle size were evaluated using fluorescence spectroscopy and ultraviolet–visible (UV–Vis) spectroscopy. The combined influence of these parameters was subsequently assessed using response surface analysis based on three empirical particle size estimation approaches. Statistical analysis showed that Cd:Se molar ratio exhibited the strongest observed influence on estimated QD size (p < 0.001), whereas temperature and residence time demonstrated comparatively weaker effects within the investigated operating range. Preferred synthesis conditions for producing CdSe QDs with an estimated particle size of approximately 2 nm were identified as a Cd:Se ratio of 1:5 under fixed conditions of 240°C and 60 s residence time. Although particle size was estimated from optical measurements rather than direct structural characterisation, the findings provide useful insight into synthesis parameter effects and demonstrate the potential of combining optical-property-based screening with continuous-flow processing for preliminary optimisation of CdSe QD synthesis.