Synthesis of Magnetic Fe3O4@hierarchical Hollow Silica Nanospheres for Efficient Removal of Methylene Blue from Aqueous Solutions

Magnetic Fe3O4@hierarchical hollow silica spheres (Fe3O4@HHSS) with high specific surface area (S-BET) were successfully synthesized by the microemulsification method. The microstructure and properties of Fe3O4@HHSS were studied by SEM, HRTEM, XRD, BET, and VSM techniques. The inner wall of Fe3O4@HHSS is composed of small hollow nanospheres and Fe3O4 nanoparticles, and the small hollow nanospheres and Fe3O4 nanoparticles are covered with an external silica wall. As a magnetic material, the Fe3O4@HHSS showed good magnetic response and could be easily recovered by an external magnet. The Fe3O4@HHSS exhibited an excellent ability to adsorb methylene blue (MB) from aqueous solutions with maximum MB adsorption capacity of 71.45 mg/g. The adsorption process was chemisorption in nature, while the adsorption isotherm data were well fitted to the Langmuir model and the kinetic data were well fitted to the pseudo-second-order kinetic model. Furthermore, the dye saturated Fe3O4@HHSS could be regenerated by using acidic ethanol solution, and the Fe3O4@HHSS showed excellent reusability.