Continuous-flow purification of silver nanoparticles and its integration with flow synthesis

Purification of nanoparticles is an important step during preparation of nanoparticles in order to remove impurities and excess ligands. Such excess ligands in the solution may have unfavorable effects on downstream processing such as ligand exchange and shell growth. Most purification methods are batchwise and time-consuming. In this work, we developed an extraction system with a membrane separation to continuously purify nanoparticles. Here, silver nanoparticles (AgNPs) in an aqueous solution were used as a case study. AgNPs were synthesized with sodium dodecyl sulfate (SDS) as capping ligands, and ethyl acetate was used as an extraction solvent to remove the ligands. This novel method showed more 56.73% removal of the ligands while maintaining the morphology of the AgNPs. In addition, the AgNPs from this method was compared with those from conventional methods such as precipitation-redissolution in terms of purity well as catalytic activity. The integration of flow synthesis of AgNPs and continuous-flow purification was also demonstrated.