Rational synthesis of superparamagnetic core-shell structured mesoporous microspheres with large pore sizes

Core-shell structured porous materials combining the functionalities of the core and shell have great application potential in various fields. Here, we report the synthesis of superparamagnetic core-shell structured microspheres which possess a core of nonporous silica-protected magnetite particle and an outer shell of ordered mesoporous silica with large pores. The synthesis adopts a co-surfactant templating approach under acidic conditions, with triblock-copolymer Pluronic P123 as a primary surfactant and a trace amount of cationic surfactant CTAB as an assistant template. The obtained magnetic mesoporous silica microspheres have uniform large pore size (4.5 nm), tuneable shell thickness (15-50 nm), high specific surface area (190-250 m² g^-1), large pore volume (0.17-0.38 cm³ g^-1) and high magnetization (29.3 emu g^-1). By using the obtained microspheres as an advanced magnetic absorbent, a fast, convenient, and efficient removal of large-size toxic microcystins in water solution was achieved in 60 seconds. The superparamagnetic properties and unique nanostructure enable the core-shell microspheres to be not only a novel absorbent for large size molecules, but also an ideal carrier for nanocatalysts like noble metallic nanoparticles and tools for peptide purification.