Efficient, Knowledge-Based Design of ZnO Nanoparticles < 10 nm in a Modular Microreaction Technology Setup

During the past years continuous synthesis concepts of colloids using microreaction technology (MRT) devices became more and more attractive. Especially the possibility of a controlled production of larger quantities at high quality is important. However, the modeling of particle formation in MRT based on the mechanistic understanding of nucleation, growth and ripening is still missing.

We use ZnO semiconductor nanoparticles due to their technical relevance and due to the fact that the dispersity of our product is easily derived from absorbance measurements.¹ However, the description of Ostwald ripening of small particles < 10 nm is highly challenging because of the strong size dependence of the solubility.² We addressed this issue by an implicit numerical scheme which enables a significant reduction of the applied time steps. In fact, several hours of ripening can be predicted within a few minutes on a standard workstation. The subsequent transfer of the batch simulation to the continuous MRT process was realized by means of the experimentally determined residence time distribution. For validation of our model, an excellent agreement with the experimental findings at the reactor outlet was proven. Our methodology is believed to be a very important step for a future process design that enables the continuous larger scale production of complex nanoparticles.