Continuous production of magnetic iron oxide nanocrystals by oxidative precipitation

Abstract Continuous processes are always preferred over batch ones when reproducible and scalable industrial procedures are needed. This work illustrates the production of magnetite nanoparticles by oxidative precipitation in aqueous media, following a continuous approach that offers additional advantages. Particularly, the developed reaction setup succeeds (i) the complete separation of the green rust’s precipitation from Fe3O4 nucleation, (ii) the achievement of constant concentrations in all ionic and solid forms throughout the production line when steady-state is reached, what means constant supersaturation from both the formation of green rust and Fe3O4, and (iii) the possibility to control critical parameters, such as OH− excess over the initial stoichiometric Fe(OH)2 precipitation, through on-line regulation of synthesis parameters such as the reactor’s pH and redox potential. Importantly, continuous flow synthesis of Fe3O4 nanoparticles enables high production capacities, low energy consumption and proportional scale-up at any volume. As a proof of concept, obtained nanoparticles were evaluated according to their magnetic response as potential magnetic hyperthermia agents indicating significant improvement of heating efficiency that goes up to 1.5–2 kW/gFe3O4 for both smaller (~40 nm) and larger (~200 nm) particles.