Design and optimization of novel vortex microreactors for ultrasound-assisted synthesis of high-performance Fe₃O₄ nanoparticles

Microreactors excel in nanomaterial preparation but are limited by microchannel clogging for sustained long-term use. This study reports an innovative design of an ultrasound-assisted vortex microreactor for the continuous synthesis of high-performance nano-Fe₃O₄ particles. Combining visual experiments with computational fluid dynamics (CFD) simulations, four vortex microreactors were designed, and their mixing and heat transfer processes were investigated. Through comprehensive analysis, the microreactor-4 was identified as the optimal configuration, with an optimal flow rate of 1 mL/min and a temperature of 70 °C. By coupling the microreactor with ultrasound, a continuous preparation method for nano-Fe₃O₄ was realized. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses revealed that the synthesized nano-Fe₃O₄ particles exhibit a spherical crystal morphology with an average particle size of approximately 6.68 nm, which is 24.4 % and 20.5 % smaller than those prepared by the beaker method and by a stirred-field coupled microreactor reported in the literature, respectively. Vibrating sample magnetometry (VSM) measurements indicated a saturation magnetization of 45.75 emu/g for the nano-Fe₃O₄, representing a 32.3 % increase over the beaker method and demonstrating excellent superparamagnetic properties. This study provides a novel and effective pathway for the continuous preparation of nanoscale magnetic materials.