Continuous supercritical synthesis of high quality UV-emitting ZnO nanocrystals for optochemical applications

ZnO nanocrystals (NCs) are of increasing interest in many industrial applications especially in the field of optochemical sensors. We recently demonstrated the synthesis of excitonic luminescent ZnO NCs using the perfectly controlled environment offered by supercritical microfluidics. However, the limited production rates of such a microscale synthesis approach make it essential to develop scaled-up continuous supercritical synthesis processes. Here, we investigate the influence of the scale-up effect from continuous microfluidic up to millifluidic systems over the synthesized ZnO NCs' optical properties. We also propose to discuss the influence of reactor's dimensions, as a consequence of different hydrodynamics regimes, on the characteristics of ZnO NCs. The obtained ZnO NCs have various shapes depending on the considered set-up. A strong excitonic-only emission in the UV region in room temperature photoluminescence (PL) spectra is obtained from all types of reactors, demonstrating the success of the scale-up process for higher production rates (up to 100 mg per hour).