Continuous Synthesis and Separation of Silver Nanoparticles Using an Aqueous Two-Phase System

Continuous synthesis of metal nanoparticles enables good control on quality and supports process automation. In this work,
we have used a biocompatible aqueous two-phase system (ATPS) for the continuous synthesis of nanoparticles. We propose the use of a milli-channel to lower the capillary number. This ensures the dominance of interfacial forces and the system exhibits segmented flow in ATPS. The chaotic advection-based mixing within each slug is
exploited for nanoparticle synthesis. Herein, we report for the first time the continuous synthesis and separation of silver nanoparticles using ATPS formed by polyethylene glycol 6000 and tri-sodium citrate. The phase separation in ATPS was explored for nanoparticle trapping at the
interface. We investigated six different operating procedures based on the occurrence of mass transfer (ATPS formation) after, during, and before the reaction (synthesis) in both batch and continuous modes of synthesis. We believe the dominance of Van der Waals force
over convective force is responsible for nanoparticle trapping at the interface. The physico-chemical properties of the nanoparticle obtained from different synthesis modes were characterized using localized surface plasma resonance and electron microscopy. The continuous mode of operation resulted in the shape-controlled synthesis of a nanoparticle compared to the batch process. The use of two-phase flow in the continuous mode eliminated the additional downstream step for particle separation. This has the potential for high-throughput nanoparticle production at the commercial scale.