Flow synthesis of silver nanoparticles using water in supercritical CO2 emulsion

Abstract

Rapid and continuous synthesis of metal nanoparticles using green solvent system is still a serious challenge for both fundamental and practical research. In this work, we report a new flow process using water in supercritical CO2 (w/scCO2) emulsion and applied it to the synthesis of silver nanoparticles (AgNPs). To investigate the performance of our system, AgNPs were synthesized by batch, flow and w/scCO2 emulsion flow system at 40 ºC while using AgNO3, NaBH(OAc)3, trisodium citrate and Aerosol-OT as precursor, reducer, stabilizer and emulsifier. As a result, we demonstrated that water droplets in w/scCO2 emulsion significantly contribute to a rise in the size controllability and productivity (product yield). Additionally, w/scCO2 emulsion flow process allowed the control of mean size from 4.0 to 36.6 nm and yield from 25% to 65% by changing the CO2 pressure and Aerosol-OT concentration. Furthermore, synthesized AgNPs successfully gave citrate-modified surface with high zeta potential of –54 mV and the transparent water dispersion with unimodal size distribution, showing promising potential to allow various practical applications.