Formation of Hollow Magnetite Microspheres and Their Evolution into Durian-like Architectures

Hollow magnetite microspheres with a diameter of ca. 1 μm have been successfully synthesized in aqueous medium by use of triblock copolymer F127 (PEO106PPO70PEO106) as capping and assembly reagents and aspartic acid (Asp, HOOCCH(NH2)CH2COOH) as a reductant. The products were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy, transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Brunauer−Emmett−Teller (BET) gas sorptometry, and vibrating sample magnetometer (VSM). These hollow microspheres are hierarchically assembled by hundreds of tiny magnetite nanoparticles. The time-dependent experiments unveil that the magnetite nanoparticles first aggregate into spherolites, then the spherolites develop into hollow microspheres. The in-depth investigations, based on control experiments and FT-IR spectrum analyses, reveal that at the stage of nanopaticles assembling, F127 molecules capping to the surface of individual ...