Microfluidic assisted synthesis of silver nanoparticles: coupled PBM-CFD simulations and experimental study*

The implementation of microfluidic approaches alongside a computational "digital twin" can be used to extend the knowledge of the formation of silver nanoparticles (AgNPs) and decrease the cost and ecological impact, by minimising trials and waste. In this work, the synthesis of AgNPs is investigated via a coupled population balance model and computational fluid dynamics (PBM-CFD) approach which aims to predict the final mean particle size and particle size distribution (PSD) for different operating conditions in a microfluidic T-mixer. Three synthesis steps are considered: the reduction of silver ions to silver atoms, nucleation, and growth of AgNPs. The nucleation and growth kinetic constants were calculated from UV-vis measurements through the Finke-Watzky two-step mechanism, generally used to describe metal-nanoparticles synthesis. PBM-CFD results are validated against experiments, in terms of silver ion concentration and PSD at different outlet channel lengths. It is shown that mass diffusivity and reaction kinetics have a significant effect on the species concentrations, as well as PBM parameters such as critical nucleus size and aggregation efficiency.