Magnetically controllable mesoporous α -Fe 2 O 3

Abstract Hematite ( α -Fe 2 O 3 ) is a low-cost, environmentally benign, and non-toxic material that can be used in various applications, such as catalytic systems, batteries, sensors, etc. To broaden the range of its applications, we propose a template-based approach for synthesizing a mesoporous, magnetically responsive α -Fe 2 O 3 (hematite) material in the form of a plate, enabling precise control over the particle size of the resulting phase. The nucleation and growth rate of the hematite phase are controlled by carrying out precipitation reactions within nanoscale pores of a commercial polyethylene film, which are generated via stretching in an n-heptane medium through an intercrystalline crazing mechanism. A comprehensive set of advanced characterization techniques was used to identify and analyze the synthesized materials, including transmission electron microscopy, x-ray diffraction, thermogravimetric analysis, Raman, and Mössbauer spectroscopy, as well as low-temperature nitrogen adsorption measurements. The stabilizing and confining effects of the polymer-matrix pores resulted in the formation of polydisperse α -Fe 2 O 3 nanoparticles with an average crystallite size of approximately 30 nm, interconnected into a continuous phase, and separated by nanoscale pores of comparable dimensions. Due to the presence of a fraction of hematite particles smaller than 20 nm, the resulting soft magnetic materials exhibit superparamagnetic behavior, with a relatively high saturation magnetization of about 50 emu g −1 and a low coercive field of approximately 70 Oe. It was found that the synthesized mesoporous α -Fe 2 O 3 undergoes complete transformation into porous γ -Fe 2 O 3 upon aging in an aqueous environment for more than 1.5 years. Nevertheless, the material retains its magnetic responsiveness and may be valuable for applications as a sorbent, a component of catalytic systems, or a carrier for magnetically guided targeted drug delivery systems.