Assembly of magnetitenanocrystals into spherical mesoporous aggregates with a 3-D wormhole-like pore structure

Abstract

Spherical mesoporous magnetite (Fe₃O₄) aggregates with a wormhole-like pore structure were successfully synthesized for the first time using a single iron precursor (iron(III) ethoxide) and an amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer (PEO₁₀₀–PPO₆₅–PEO₁₀₀) as a soft template. In this synthesis, the interaction between the iron precursor and the triblock copolymer self-assemblies in ethanol leads to the assembly of magnetite nanocrystals into spherical mesoporous aggregates. These aggregates were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, standard and high-resolution transmission electron microscopy, ⁵⁷Fe Mössbauer spectroscopy, and X-ray diffraction, confirming the formation of pure-phase Fe₃O₄ particles with monodisperse morphology (about 130 nm in diameter), three-dimensional wormhole-like mesopores, and highly crystalline spinel structure. In addition, a formation mechanism for this material in the present system is proposed, based on the analysis of results. The mesoporous magnetite has a high specific surface area of 165.6 m² g⁻¹, and relatively large pores with a mean size of 5.2 nm. The magnetic susceptibility data demonstrate that this material exhibits superparamagnetic behavior.