Effect of water on size-controllable synthesis of mesoporous Fe ₃O₄ 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 Fe₃O ₄. 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.