Effect of water on size-controllable synthesis of mesoporous Fe3O4 microspheres and their applications in waste water treatment

Monodispersed mesoporous Fe3O4 microspheres were synthesized by a simple solvothermal route using mixed solvent with different volume ratios of ethylene glycol to water (E/W). The investigation on the phase evolution reveals that trace amounts of water in the nonaqueous ethylene glycol solution are needed to trigger the crystallization of Fe3O4. The obtained Fe3O4 microspheres are composed of well-oriented primary nanocrystals with mesoporous structure. The particle sizes can be facilely controlled in the range from 553 to 68 nm by adjustment of the E/W. A novel quasi-reverse-emulsion formation mechanism was proposed for the monodispersed mesoporous Fe3O4 microspheres with tunable size. The obtained Fe3O4 microspheres exhibit size-dependent specific surface areas with excellent magnetic properties and are explored for efficient wastewater treatment. The comprehensive comparison and analysis of the adsorption capacity for Congo red (CR) are carried out, and a close relationship between the specific surface area and CR adsorption capacity is identified.