A Facile Method to Prepare Aligned Porous Magnetic Silica Monoliths from Directional Freeze-Drying

A facile method was developed to fabricate magnetic silica monoliths with aligned porous structure based on directional freeze-drying. Aligned porous silica monoliths were produced initially by directional freeze-drying and calcination. Then iron particles were immobilized into the silica monolith by impregnation in a FeCl3 solution and reduction with NaBH4 or H-2 to prepare the aligned porous magnetic silica monoliths. The reduction process played an important role on the morphologies of the formed iron particles. Iron networks composed of sheet structure with thickness of 20 nm were obtained from NaBH4, while iron particles from 1 to 3 mu m were produced in H-2 atmosphere. The loading amount of iron particles could be controlled by the FeCl3 concentration and silica monolith microstructures. Magnetic properties of the aligned porous magnetic monolith at room temperature were also investigated. All magnetic monoliths gave s-type hysteresis loops and exhibited soft magnetic properties. Saturated magnetization of the magnetic monolith prepared with H2 reduction was from 52 to 116 emu/g, which was higher than that from NaBH4, and it was attributed to a better crystalline structures. Compared with other methods, this work provided a simple and facile route to fabricate aligned porous magnetic monoliths.