Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

Superparamagnetic Iron Oxide Nanoparticles with Variable Size and an Iron Oxidation State as Prospective Imaging Agents

Abstract: Magnetite nanoparticles in the size range of 32-75 nm were synthesized in high yields under variable reaction conditions using high-temperature hydrolysis of the precursor iron(II) and iron(III) alkoxides in diethylene glycol solution The average sizes of the particles were adjusted by changing the reaction temperature and time and by using a sequential growth technique To obtain γ-iron(III) oxide particles in the same range of sizes, magnetite particles were oxidized with dry oxygen in diethylene glycol at room temperature The products were characterized by DLS, TEM, X-ray powder diffractometry, TGA, chemical analysis, and magnetic measurements NMR r(1) and r(2) relaxivity measurements in water and diethylene glycol (for OH and CH(2) protons) have shown a decrease in the r(2)/r(1) ratio with the particle size reduction, which correlates with the results of magnetic measurements on magnetite nanoparticles Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe(3)O(4) with the same particle size, but their r(1) relaxivities are similar Because the oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor and therefore may be a better prospective imaging agent because of its chemical stability

Oxidation of magnetite nanoparticles: impact on surface and crystal properties

Abstract: Iron oxide nanoparticles are of great scientific interest due to their huge versatility of applications. The oxidation process of magnetite to maghemite is difficult to monitor as both iron oxide polymorphs possess connatural chemical properties. Especially the surface composition and reactivity of these nanosystems, which are most relevant for interactions with their environment, are not completely understood. Here, the oxidation of magnetite is investigated under mild and harsh conditions in order to understand the oxidation behaviour and the chemical stability of transition forms. Therefore, the oxidation process, is investigated with Raman, Mossbauer and X-ray photoelectron spectroscopy as well as X-ray diffraction and magnetometry. The multi-analytical approach allows new insights into surface composition and rearrangement according to respective different depth profiles. For both conditions investigated, the ferrous iron components are oxidised prior to structural changes in the Fe–O vibrations and crystal structure. The process starts from the outer layers and is acid catalysed. Oxidation leads to a decrease of magnetisation which still remains higher than 54 emu g−1. The charge and surface reactivity can be affected by the different oxidation methods and the irreversible adsorption of acid molecules. Biocompatibility and catalytic properties of iron oxide nanoparticles open doors to future applications.

Tunable synthesis of carboxyl-functionalized magnetite nanocrystal clusters with uniform size

Abstract: It is essential to tune the physicochemical properties of magnetic nanomaterials for their biomedical applications. Herein we report a facile polyol method to synthesize the carboxyl-functionalized magnetite nanocrystal cluster (CMNC) with tunable size and high magnetization. Through introduction of urea as a homogeneous precipitator, the formation of magnetite nanocrystal clusters is facilitated compared to the previous reports. These magnetic clusters, with uniform size and good colloidal stability in water, have a magnetization over 70 emu g−1. The effect of the stabilizer (sodium citrate) on the physicochemical properties of clusters is studied systematically in the polyol process. By simply changing the concentration of sodium citrate in the reaction from 0.001 M to 0.1 M, the diameter of the CMNC can be tuned from approximately 300 nm to 40 nm. The variation of the concentration of sodium citrate also gave rise to a change of the size of the subunits, the surface charge and the magnetization of the clusters due to the adsorption of the citrate molecules on the magnetite nanocrystal clusters. The tuning effect of sodium citrate on the size of CMNCs was attributed to the interaction of different forces in the polyol process: the electrostatic repulsion and the surface tension.

Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles

Abstract: In this study, magnetite–maghemite nanoparticles were used to treat arsenic-contaminated water. X-ray photoelectron spectroscopy (XPS) studies showed the presence of arsenic on the surface of magnetite–maghemite nanoparticles. Theoretical multiplet analysis of the magnetite–maghemite mixture (Fe3O4-γFe2O3) reported 30.8% of maghemite and 69.2% of magnetite. The results show that redox reaction occurred on magnetite–maghemite mixture surface when arsenic was introduced. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on contact time and initial concentration of arsenic. Equilibrium was achieved in 3 h in the case of 2 mg/L of As(V) and As(III) concentrations at pH 6.5. The results further suggest that arsenic adsorption involved the formation of weak arsenic-iron oxide complexes at the magnetite–maghemite surface. In groundwater, arsenic adsorption capacity of magnetite–maghemite nanoparticles at room temperature, calculated from the Langmuir isotherm, was 80 μmol/g and Gibbs free energy (∆G0, kJ/mol) for arsenic removal was −35 kJ/mol, indicating the spontaneous nature of adsorption on magnetite–maghemite nanoparticles.