High Temperature Stable Maghemite Nanoparticles Sandwiched between Hectorite Nanosheets

Maghemite (γ‐Fe 2 O 3 ) is a metastable iron oxide phase and usually undergoes fast phase transition to hematite at elevated temperatures (>350 °C). Maghemite nanoparticles were synthesized by the polyol method and then intercalated into a highly swollen (>100 nm separation) nematic phase of hectorite. A composite of maghemite nanoparticles sandwiched between nanosheets of synthetic hectorite was obtained. The confinement of the nanoparticles hampered Ostwald ripening up to 700 °C and consequently the phase transition to hematite is suppressed. Only above 700 °C γ‐Fe 2 O 3 nanoparticles started to grow and undergo phase transition to α‐F 2 O 3 . The structure and the phase transition of the composite was evaluated using X‐ray diffraction, TEM, SEM, physisorption, TGA/DSC, and Mößbauer spectroscopy.