Continuous microwave-assisted gas–liquid segmented flow reactor for controlled nucleation and growth of nanocrystals

Hot-injection techniques are currently the state-of-the-art method for the synthesis of high-quality colloidal nanocrystals (NCs) but have typically been limited to small batch reactors. The nature of this method leads to local fluctuations in temperature and concentration where inhomogeneity due to mixing makes precise control of reaction conditions very challenging at a large scale. Therefore, development of methods to produce high-quality colloidal NCs with high-throughput is necessary for many technological applications. Herein, we report a high-quality and high-throughput NC synthesis method via a continuous microwave-assisted flow reactor where separation of nucleation and growth is demonstrated. A significant issue of microwave heating in a single-phase continuous flow microwave reactor is the deposition of in situ generated NCs on the inner wall of the reactor in the microwave zone. This deposited material leads to significantly enhanced microwave absorption and rapid heating and can result in sparking in the reactor. A gas–liquid segmented flow is used to avoid this problem and also results in improved residence time distributions. The use of this system allows for finely tuned parameters to achieve a high level of control over the reaction by separating the nucleation and growth stages.