Microfluidic Synthesis of Cobalt Nanoparticles

Co nanoparticles with three different crystal structures were synthesized in a microfluidic reactor through manipulation of reaction times, flow rates, and quenching procedures. Cobalt nanoparticles of face-centered cubic (β) phase were obtained from a high flow rate of the reactants followed by in situ quenching of the reaction. hcp and ε-cobalt nanoparticles were obtained at a low flow rate of the reactants followed by in situ quenching and delayed quenching, respectively. The crystal structures were characterized using Co K-edge X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction (XRD), and selected area electron diffraction (SAED). In situ XANES measurements on Co nanoparticles coming out of the outlet of the microfluidic reactor at different flow rates seem to indicate that the difference in flow rate influences the nucleation process in a critical way and that particle growth occurs mainly outside the reactor. The magnetic properties of the cobalt nanoparticles, measured using a SQUID magnetometer system, showed significant differences among the samples and are consistent with the three different crystal structures.