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

Continuoussynthesis of metal nanoparticles enables good controlon quality and supports process automation. In this work, we haveused a biocompatible aqueous two-phase system (ATPS) for the continuoussynthesis of nanoparticles. We propose the use of a milli-channelto lower the capillary number. This ensures the dominance of interfacialforces and the system exhibits segmented flow in ATPS. The chaoticadvection-based mixing within each slug is exploited for nanoparticlesynthesis. Herein, we report for the first time the continuous synthesisand separation of silver nanoparticles using ATPS formed by polyethyleneglycol 6000 and tri-sodium citrate. The phase separation in ATPS wasexplored for nanoparticle trapping at the interface. We investigatedsix different operating procedures based on the occurrence of masstransfer (ATPS formation) after, during, and before the reaction (synthesis)in both batch and continuous modes of synthesis. We believe the dominanceof Van der Waals force over convective force is responsible for nanoparticletrapping at the interface. The physico-chemical properties of thenanoparticle obtained from different synthesis modes were characterizedusing localized surface plasma resonance and electron microscopy.The continuous mode of operation resulted in the shape-controlledsynthesis of a nanoparticle compared to the batch process. The useof two-phase flow in the continuous mode eliminated the additionaldownstream step for particle separation. This has the potential forhigh-throughput nanoparticle production at the commercial scale.

Automated summary

Continuous synthesis of metal nanoparticles using a biocompatible aqueous two-phase system (ATPS) is achieved through the use of a milli-channel to control capillary number, resulting in segmented flow. Chaotic advection-based mixing is exploited for the synthesis of silver nanoparticles in ATPS, which is separated at the interface. Various operating procedures are investigated in batch and continuous modes, and Van der Waals force is found to be responsible for trapping the nanoparticles at the interface. The continuous mode allows shape-controlled synthesis and eliminates the need for downstream particle separation, making it suitable for high-throughput nanoparticle production.