Characterization of Nanocrystalline γ–Fe₂O₃Prepared by Wet Chemical Method

Abstract

Homogeneous maghemite (γ–Fe2O3) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe2O3), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.

Carbon nanosphere–iron oxide nanocomposites as high-capacity adsorbents for arsenic removal

“…This should be ascribed to the existence of iron oxide nanoparticles on the surfaces of the carbon matrix which act as catalysts for the carbon combustion since their exothermic oxidation takes place at lower temperatures. 50 Different from the complete weight loss observed in the carbon samples, the composites show different residual char yield at 500 C (7, 13, 28, and 60 wt%, respectively), corresponding to the content of iron oxide within the nanocomposites. Consequently, these composites are termed as FeO x -CNS-#, with the number (#) representing the mass percentage of iron oxide in the composites.…”

Mössbauer Investigation of γ-Fe2O3 Nanocrystals in Silica Matrix Prepared by the Sol-gel Method

“…Its properties are enhanced when the size of the particles reaches the nanometer range [3,4]. Nanosized -Fe 2 O 3 transforms to -Fe 2 O 3 (hematite) at rather low temperatures ( 350 C) [5,6], but it can be stabilized by incorporating the nanoparticles into polymeric, glassy or ceramic matrices [5,7,8]. Moreover, a growing attention has recently been devoted to maghemite nanoparticles dispersed in a transparent matrix for their use in magneto-optical recording systems [7,9,10].…”

Zero-field and in-field Mössbauer spectroscopy as a tool for structural and magnetic characterization of maghemite (γ-Fe2O3) nanoparticles

“…As we know today there are four different crystalline polymorphs of iron(III) oxide [1,2]: a-Fe203, naturally occurring as hematite, showing a rhombohedrally centered hexagonal structure of a corundum type (space group R3c); /3-Fe203 having a body-centered cubic "bixbyite" structure (space group Ia3); 7-Fe203, known as maghemite, with a cubic spinel structure; and r exhibiting an orthorhombic structure (space group Pna21). Maghemite, a red-brown magnetic material that is structurally similar with magnetite and has the same chemical composition as hematite, is the most important and prosperous phase out of the above mentioned polymorphs because it is widely used in a plenty of applications such as magnetic pigments in recording and information-storage media [3,4], in catalysis [5], *) Presented at International Colloquium "M6ssbauer Spectroscopy in Materials Science", V~emina, Czech Republic, June 1-4, 2004. magnetic fluids [6], anticorrosion protective paints [7], gas sensors [8], magnetooptical devices [9] and in studies of macroscopic quantum tunneling effect [10]. It is also worthwhile to mention that maghemite has been found effective as an imageintensifying agent for nuclear magnetic resonance imaging [11], in bioprocessing [12], magnetic separations [13], magneto-caloric refrigeration [14], medical diagnosis [15], controlled drug delivery [16] and magnetic-induced cancer therapy [17].…”