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

Abstract

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 nanoparticle play a crucial role in inhibiting nanoparticles regrowth and promoting nanopaticles aggregation. At the subsequent stage Ostwald ripening contributes to the formation of the hollow microspheres. With further increasing hydrothermal duration, hollow magnetite microspheres can evolve into solid durian-like architectures with compact surface and numerous octahedral vertexes, which can be attributed to the further growth of magnetite nanocrystals on the wall. Moreover, we also measured the magnetic properties of the synthesized products. The saturation magnetizations (M s) of hollow and durian-like microspheres are 45.2 and 62.3 emu/g, respectively.

Synthesis of Well‐Dispersed Aqueous‐Phase Magnetite Nanoparticles and Their Metabolism as an MRI Contrast Agent for the Reticuloendothelial System

“…This broad peak also merges with that at 845 cm -1 , which represents the stretching vibration of CCO groups from MAH or TSC. [34] These results suggest that the Fe-O bond in the bare Fe 3 O 4 becomes indistinct, meaning that the interface between the surface of the NPs and the stabilizers becomes unclear due to the MAH incorporation, or that strong bonds are formed among the NPs and stabilizers. The peak at about 1651 cm -1 (Figure 1d) becomes extremely strong and broad, merging the vibrations of C=O bonds from all of the stabilizers, indicating the formation of strong bonds between the carboxylate groups in the stabilizers and the Fe 3 O 4 NPs after the addition of MAH.…”

Magnetic field induced controllable self-assembly of maghemite nanocrystals: From 3D arrays to 1D nanochains

“…Various superstructures based on iron oxides have been demonstrated, representative morphologies including flowerlike iron oxide nanostructures [19,20], porous or hollow Fe 3 O 4 nanospheres [21][22][23][24], durian-like magnetite architectures [25], monodisperse Fe 3 O 4 nanoflakes [26], spherical mesoporous magnetite aggregates with a 3-D wormhole-like pore structure [27], and magnetite nanoclusters [28]. Nonetheless, secondary assembly of iron oxide superstructures into 3D arrays is still rare, partially because of the lack of simple yet effective strategies to align such iron oxide superstructures with highly ordered arrangement.…”

Hollow Magnetic Nanoparticles: Synthesis and Applications in Biomedicine

“…Some highly soluble gases (such as CO 2 , NH 3 that decomposed from some soluble and labile ammonium salts were introduced into reaction system. [65][66] Hu et al prepared monodisperse Fe 3 O 4 hollow spheres with 400 nm average diameter and 60 nm shell thickness through a one-pot solvothermal process by using NH 4 Ac as the structure-directing agent. A novel gas-bubble-assisted Ostwald ripening process was proposed to explain the formation of hollow structures (the mechanism of formation process was shown in Fig.…”