Quantitative determination of magnetite and maghemite in iron oxide nanoparticles using Mössbauer spectroscopy

Abstract

Iron oxide nanoparticles are available in two common phases, namely magnetite (Fe 3 O 4) and maghemite (Fe 2 O 3). Upon exposure to oxygen atoms, the magnetite phase readily oxidizes into the maghemite phase with the partial conversion of ferrous ions into ferric ions. We report on the approach to determine the ratio of magnetite and maghemite in iron oxide nanoparticles synthesized by the wet chemical route. X-ray diffraction studies and transmission electron microscopy observations confirmed the formation of highly crystalline nanoparticles of size (7 ± 2) nm. The average particle size is in the magnetic single-domain range suitable for the superparamagnetic behavior. The Mössbauer spectrum of the sample is composed of two six-line patterns in perfect agreement with the theoretically predicted model. The extracted Mössbauer parameters show contribution of two phases accounting for 47% magnetite and 53% maghemite. The hysteresis loops of the iron nanoparticles demonstrated the "S-shaped" pattern with negligible coercivity and remanence magnetization. This result reveals a promising method to synthesize and characterize magnetic nanoparticles of uniform size with a potential for biomedical applications.

Influence of Magnetite Nanoparticles Shape and Spontaneous Surface Oxidation on the Electron Transport Mechanism

“…When analyzing this type of nanoparticles, it can be seen that the low-frequency electron transport did not occur from the surface of one nanoparticle to the surface of the second one, but through the disordered γ-Fe 2 O 3 layer. Accordingly, the accumulation of charge carriers occurred on highly defected, more resistive γ-Fe 2 O 3 surfaces containing many different defects such as iron vacancies and dislocations [ 4 , 14 ].…”

“…It is well-known that the transport of electrons in magnetite is much easier than in maghemite and is related to the electrons hopping between Fe 3+ and Fe 2+ ions [ 41 ]. When the magnetite surface is blocked by other non-magnetic nanoparticles, high disordering, or γ-Fe 2 O 3 , in which only Fe 3+ and iron vacancies exist, the electron movement becomes slower [ 4 , 14 , 42 ]. In high-temperature regions, movement of electrons increases; however, negatively charged cation vacancies and thermal vibrations of the lattice structure appear.…”

“…The oxidation of a magnetite surface results in phase transformation, in which magnetite is transformed into maghemite [ 13 ]. In the magnetite structure, the tetrahedral sites (A-sites) are occupied by Fe 3+ ions and the octahedral sites (B-sites) are occupied by Fe 3+ and Fe 2+ ions, whereas in maghemite, all Fe 2+ ions convert into Fe 3+ ions with the formation of iron vacancies (2.5 per 21.5 Fe 3+ ions in the unit cell) as a result of Fe 3 O 4 NPs oxidation [ 4 , 14 ]. The magnetic response under AC-fields of magnetite and maghemite nanoparticles of the same size is also different, which has been confirmed by Morales et al [ 15 ].…”

Magnetically Functionalized Moss Biomass as Biosorbent for Efficient Co2+ Ions and Thioflavin T Removal

“…The average particle size of Fe 3 O 4 organized into micrometer-sized aggregates on the biomass surface calculated from diffraction peaks (see above) was ca 13 nm, which is consistent with previous results [ 2 ]. It is important to note that upon exposure to O atoms, magnetite oxidizes to maghemite with the partial conversion of Fe 2+ ions into Fe 3+ ions [ 18 ]. The as-synthetized iron oxide particles exhibited a good dispersibility on the biomass surface ( Figure 2 B), and thus, magnetically modified R. squarrosus shows a rapid magnetic response to an external magnetic field, enabling a rapid and selective separation of the biosorbent from aqueous solutions using a permanent magnet [ 19 ].…”

Modernistic and Emerging Developments of Nanotechnology in Glioblastoma-Targeted Theranostic Applications

“…Magnetic nanoparticles (MNPs) are highly enticing nanomaterials with greater proportions of accumulation within the brain tumors, which can be conveniently monitored through MRI. For example, iron oxide NPs (e.g., Fe 3 O 4 and Fe 2 O 3 ) can have promising properties, such as biodegradability, non-toxicity, and superparamagnetic features, which facilitate tumor imaging and targeting applications [87,88]. These SPIONs are believed to be the best MRI contrasting agents for glioma imaging, and the suitable therapeutic candidates for magnetism-dependent hyperthermia.…”