Size Control, Chemical Kinetics, and Theoretical Analysis for the Production of Fe₃O₄ Nanoparticles with a High Specific Absorption Rate

In this study, an industrial process is proposed to produce Fe₃O₄ nanoparticles with a high specific absorption rate. The analysis was focused on the theoretical study of the dynamic performance in a continuous stirred tank reactor system, using the chemical kinetics of the reaction, which was obtained experimentally in the present work. For this purpose, nanoparticles with different sizes were prepared varying the reaction time by the thermal decomposition method. Subsequently, their physical and chemical properties were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, transmission electron microscopy, and magnetic measurements. The results obtained suggested that this material could be used in magnetic hyperthermia; for this reason, the nanoparticles were functionalized with DMSA through a binder exchange reaction. Afterward, the specific absorption rate of the ferrofluid was determined under an applied AC magnetic field (17.5 kA/m, 153 kHz), obtaining a value of 109.75 W/g. To produce these nanoparticles industrially, the use of two CSTRs connected in series was considered because one was required for the nucleation zone and another for the growth zone. The heating in each of the reactors was carried out by a set of electrical resistances regulated by a feedback control system, using PI controllers, which were tuned minimizing the IAE through the stochastic method of simulated annealing. The preheating in each stream that fed each reactor and the cooling in the output stream of the second reactor were through heat exchangers. The results indicate that the proposed process is appropriate because the dynamic responses in both reactors do not present higher oscillations when the temperature is disturbed in each of the currents that feed to the reactors. Also, the stabilization time in the temperature of the CSTRs is not greater than 10 min, which leads to a reasonable control of the particle size during its production, since the size is a function of the reaction time and temperature. Therefore, these Fe₃O₄ nanoparticles are suitable to be applied in magnetic hyperthermia and produced by the proposed process.