Gold nanoparticles green production using diethyl carbonate as continuum phase in a dripping regime microfluidic reactor

A dripping-regime segmented-flow microfluidic reactor for the continuous production of gold nanoparticles (Au NPs) was designed based on computational fluid dynamics calculations. A flow-focusing junction was applied. Diethyl carbonate (DEC) was used as a green material for the continuous phase. The dispersed aqueous phase consisted of HAuCl₄, NaBH₄, and PVA. Experimental dispersed phase droplet diameter as a function of Capillary number (Ca) corroborated with the CFD calculations. The effect of Ca (0.0013,0.0025 and 0.0050) and pH (1,3 and 11) on HAuCl₄ conversion and Au NPs particle size distribution (PSD) was investigated. Based on nanoparticle tracking analysis (NTA), average particle diameters as small as 1.73 nm with a sharp distribution (standard deviation of 0.27 nm) could be achieved. The apparent pseudo-first-order reduction reaction rate constant was found proportional to the average vorticity within the droplets. Particle growth was not dominated by coalescence processes. No leaching of Au³⁺ by DEC was detected.