(521dq) A Sustainable Process for Continuous Synthesis and Separation of Silver Nanoparticles Using Segmented Flow with an Aqueous Two-Phase System

Continuous synthesis of metal nanoparticles enables good quality control, and supports process automation. For better control of particles size, the synthesis process is employed in slugs (segmented flow) as each slug acts as a well-mixed microreactor. The recent focus on nanoparticle synthesis in segmented flow regime using aqueous – organic two-phase system limits the nanoparticle uses in several biological applications. In this work, we overcome this problem by using a biocompatible aqueous two-phase system (ATPS) for continuous synthesis of nanoparticles. This work is first of its kind to report the dispersed flow with ATPS by using milli-channel pertaining low capillary number. We have shown how the advantages of both segmented flow for their mixing characteristics and ATPS for their eco-friendly biocompatibility can be exploited together. We report for the first time the continuous synthesis and separation of silver nanoparticles using ATPS as shown in Figure 1. Polyethylene glycol 6000 and tri-sodium citrate at high concentrations was used to form ATPS. We investigated six different operating procedure based on the occurrence of mass transfer process (ATPS formation) after, during and before the reaction (synthesis) in both batch and continuous mode of synthesis. The physico-chemical properties of the nanoparticle obtained from each procedure characterized using optical spectrophotometer and electron microscopy was compared. Continuous mode of operation resulted in shape-controlled synthesis of nanoparticle compared to batch process. Among all the synthesis procedure investigated, use of continuous single-phase flow with pure PEG as reducing agent resulted in sharp LSPR indicating narrow particle size distribution and smaller particle sizes (< 30 nm). Use of dispersed flow in continuous mode eliminated the additional downstream step required for nanoparticle separation. The present work for synthesizing nanoparticles in the ATPS using continuous process opens up a new scope for one-step synthesis and separation of nanoparticles.