Silver nanoparticles synthesis in microfluidic and well-mixed reactors: A combined experimental and PBM-CFD study

We investigate the production of silver nanoparticles (AgNPs) under different operating conditions of pH, inlet flow rates, and reactants concentration via a combination of population balance modelling and computational fluid dynamics (PBM-CFD) to elucidate our experimental observations in a well-mixed batch reactor and a T-junction microfluidic device. The synthesis process considered herein is based on a reduction protocol involving silver nitrate as precursor and a mixture of tannic acid/trisodium citrate as reducing/stabilising agents. Our novel PBM-CFD framework expands the current kinetic models developed for well-mixed reactors to explicitly account for the spatio-temporal dependence of mixing dynamics for microfluidic reacting flows in order to predict the final particle size distribution of the produced AgNPs. Nucleation and growth models are based on the Finke-Watzky (F-W) two-step mechanism and are directly coupled to the reduction reaction kinetics and the convection–diffusion equations of each species. The T-junction results suggest that the higher residence times involved in operations with lower flow rates are responsible for a cascade of kinetic/reactive and hydrodynamic events, unveiled by our simulations, that lead to higher outlet particle sizes and volume fraction of the particles in the dispersion. The simulation results also provide a characterisation of the radial heterogeneous concentration of particles and particle sizes across the channel typical of continuous-flow microfluidics. Limitations and advantages of our novel modelling approach are discussed in the context of future lines of research.