Tubular Superstructures Composed of α-Fe2O3 Nanoparticles from Pyrolysis of Metal–Organic Frameworks in a Confined Space: Effect on Morphology, Particle Size, and Magnetic Properties

While preparation of metal oxide from metal organic frameworks (MOFs) has been widely studied, crystal growth via thermal decomposition of MOFs in a confined space is rarely investigated. We demonstrate a confinement effect on the crystal growth via pyrolysis of MOFs at high temperature. Iron containing MOF (Fe-MIL-88A) was calcined inside a SiO2. The crystalline phase, particle size, morphology, and magnetic properties of the synthesized iron oxide were characterized; α-Fe2O3 tubular structures that consisted of nanoparticles (around 10 nm) were observed. Studies of the magnetic properties show enhanced magnetization with superparamagnetic behavior. These results indicate that space confinement during the thermal treatment in air at high temperature allows the synthesis of small nanoparticles and the preservation of initial morphology of MOF precursors, which cannot be obtained via heating of MOFs without shell under identical conditions.