Preparation of Magnetic Nanoparticles Encapsulated by an Ultrathin Silica Shell via Transformation of Magnetic Fe-MCM-41

Sub-10-nm Fe 2 O 3 nanoparticles were successfully encapsulated within uniform-sized 10 nm silica nanospheres with ultrathin walls (ca. 1 nm) via the transformation of iron-loaded mesoporous MCM-41. This represents a new synthesis approach that involves the deposition of either an iron precursor (i.e., Fe 3+ ) or nanoparticles (i.e., maghemite/magnetite) within the mesopores of MCM-41 followed by solvothermal conversion that produces the encapsulated nanoparticles. The prepared SiO 2 -encapsulated Fe nanoparticles are superparamagnetic, with a diamagnetic contribution from the silica shell.