One-pot hydrothermal synthesis of highly monodisperse water-dispersible hollow magnetic microspheres and construction of photonic crystals

Water-dispersible monodisperse hollow Fe₃O₄ microspheres were prepared via a one-pot hydrothermal process based on FeCl₃·6H₂O, sodium citrate, urea and sodium polyacrylate (PAAS). Different alkali sources and FeCl₃·6H₂O amounts were added to investigate the formation mechanism, and a gas-bubble-assisted Ostwald ripening process was possibly responsible for the formation of hollow structure. In the process, the particle size and morphology could be effectively controlled by the slight change of FeCl₃·6H₂O addition amount. Meanwhile, monodisperse solid microspheres were obtained when sodium acetate was added to offer alkaline environment. The microspheres exhibited superparamagnetic properties with high saturation magnetization value about 76.7emug^-1 at room temperature, and the BET surface area of the sample was 50.04m²g^-1. Besides, it was found that the particles could be used for constructing photonic crystals. Such monodisperse hollow Fe₃O₄ microspheres have a great application potential in biomedicine, MRI agents and color display areas.