Monodisperse Fe3O4 spheres: Large-scale controlled synthesis in the absence of surfactants and chemical kinetic process

Fe3O4 has attracted tremendous interest in vast areas of biomedicine and catalysis as well as environment engineering. However, it is highly desired to fully understand the chemical kinetic process and propose a general, surfactantfree, large-scale synthesis approach for Fe3O4 spheres. Herein, we developed a facile scalable solvothermal method in the absence of surfactants to produce Fe3O4 spheres with the yield of 5.1 g, which present tunable sizes from 107 to 450 nm by modulated molar ratio of Fe3+/COO- in the solution. Particularly, it is observed that the reactants undergo a redox process, composed of a precipitation-dissolution equilibrium combined with a coordination reaction (termed as RPC), to the final product based on the LaMer model. It is worth noting that the generation of di-carboxyl group and its coordination with iron cations determine the formation of Fe3O4 spheres. This work not only offers a strategy to precisely tailor the particle size in scalable synthesis process, but also gives the insight on the role of dihydric alcohol in the formation mechanism of Fe3O4 spheres in the absence of surfactants.