Magnetic properties of hematite (α-Fe2O3) nanoparticles prepared by hydrothermal synthesis method

International audienceHematite (α-Fe2O3) nanoparticles are successfully synthesized by using the hydrothermal synthesis method. An X-ray powder diffraction (XRPD) of the sample shows formation of the nanocrystalline α-Fe2O3 phase. A transmission electron microscopy (TEM) measurements show spherical morphology of the hematite nanoparticles and narrow size distribution. An average hematite nanoparticle size is estimated to be about 8 nm by TEM and XRD. Magnetic properties were measured using a superconducting quantum interference device (SQUID) magnetometry. Investigation of the magnetic properties of hematite nanoparticles showed a divergence between field-cooled (FC) and zero-field-cooled (ZFC) magnetization curves below Tirr = 103 K (irreversibility temperature). The ZFC magnetization curve showed maximum at TB = 52 K (blocking temperature). The sample did not exhibit the Morin transition. The M(H) (magnetization versus magnetic field) dependence at 300 K showed properties of superparamagnetic iron oxide nanoparticles (SPION). The M(H) data were successfully fitted by the Langevin function and magnetic moment μp = 657 μB and diameter d = 8.1 nm were determined. Furthermore, magnetic measurements showed high magnetization at room temperature (MS = 3.98 emu/g), which is desirable for application in spintronics and biomedicine. Core–shell structure of the nanoparticles was used to describe high magnetization of the hematite nanoparticles

Annealing-dependent structural and magnetic properties of nickel oxide (NiO) nanoparticles in a silica matrix

We show that annealing at high temperatures has a significant effect on the structural and magnetic properties of NiO/SiO2 nanostructures synthesized by a sol-gel combustion method. Samples underwent heat treatments at 500 degrees C, 800 degrees C, 950 degrees C and 1100 degrees C. As compared to the 500 degrees C sample, the 800 degrees C sample showed the following magnetic properties: much higher irreversibility temperature, a significantly broadened zero-field-cooled (ZFC) magnetization maximum, a decrease of the ZFC magnetization, an increase of the coercivity, and weaker inter-particle interactions. These changes can be attributed to agglomeration of nanoparticles in part of the sample. We believe that this agglomeration can be explained by the removal of thin regions of silica that separate nanoparticles in close proximity during the annealing process at 800 degrees C. Magnetic measurements for the 1100 sample reveal both an abrupt increase in size of the NiO nanoparticles, which is confirmed by TEM and XRPD measurements, and an increase in inter-particle interaction strength. (C) 2015 Elsevier Ltd. All rights reserved

Hydrothermal synthesis of hematite (alpha-Fe2O3) nanoparticle forms: Synthesis conditions, structure, particle shape analysis, cytotoxicity and magnetic properties

In this work, we present the magnetic and structural properties of alpha-Fe2O3 nanoparticles synthesized by the hydrothermal synthesis method. XRD, FTIR and Raman spectroscopy indicate that the samples consist of single-phase alpha-Fe2O3 nanoparticles. A microstructural analysis by TEM and SEM shows: (i) irregular nanoparticles (similar to 50 nm), (ii) plate-like nanoparticles (with thickness t similar to 10 nm and diameter d similar to 50 -80 nm) and (iii) microsized ellipsoid 3D superstructures (with length l similar to 3.5 and diameter d similar to 1.5 mu m) composed of nanosized building blocks (similar to 50 nm). We used circularity, elongation and convexity measures to quantitatively analyze the shape of the particles. Irregular hematite nanoparticles were synthesized using a water solution of ferric precursor and sodium acetate during the hydrothermal reaction (reaction conditions: T = 180 degrees C, t = 12 h). The same hydrothermal reaction temperature, reaction duration and ferric precursor (without sodium acetate) were used for synthesizing hematite ellipsoid 3D superstructures. Addition of urea and glycine surfactants in hydrothermal reaction resulted in the formation of nanoplate hematite particles. The role of these surfactants on the structure and morphology of the particles was also investigated. Magnetic measurements at the room temperature displayed a wide range of coercivities, from H-C = 73 Oe for irregular nanoparticles, H-C = 689 Oe for nanoplates to H-C = 2688 Oe for hematite ellipsoid 3D superstructures. The measured coercivity for the ellipsoid superstructure was about 35 times higher than in the case of irregular hematite nanoparticles and about 4 times than the coercivity of hematite nanoplates. Magnetic properties of synthesized samples were related to their structure and morphology. We conclude that shape anisotropy influenced enhancement of the coercivity in hematite nanoplates whereas hematite ellipsoid 3D superstructure (nanoparticle clusters) induced the formation of multidomain magnetic structure and highest coercivity revealing its superior structure for enhanced magnetic properties. The synthesized hematite nanoparticle structures exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating a safe use of these nanoparticles for practical applications

High Energy/Power Supercapacitor Performances of Intrinsically Ordered Ruthenium Oxide Prepared through Fast Hydrothermal Synthesis

A simple one-step microwave-assisted and temperature-controlled hydrothermal synthesis was applied to prepare a nanocrystalline RuO2 dispersion from an aqueous solution of RuCl3 for supercapacitive applications. The obtained RuO2 dispersions were subjected to dynamic light scattering in order to analyze the particle size distribution, whereas morphology and structural properties of the solid phase were investigated by using AFM, SEM, EDX, TEM, and XRD techniques. Ellipsoidally shaped 100-500 nm-sized compact grains, joined into highly ordered prismatic agglomerates, are observed. Two types of grains are observed: more regular ones consisting of spherical, amorphous particles of a few nanometers in size, and irregular ones made of partially crystalline 10-80 nm-sized particles. Consequently, the most dominant structure is 250-nm grains. The particles tend to join tightly across their crystalline domains, which appears responsible for the formation of prismatic shapes of several micrometers. This arraying causes high capacitive activity - specific capacitances of up to 800 Fg(-1) are registered, which negligibly depend on the charging/discharging rate. The synthesized material is of highly accessible internal structure, and is an excellent candidate for both low- and high-power applications

Synthesis of core-shell hematite (alpha-Fe2O3) nanoplates: Quantitative analysis of the particle structure and shape, high coercivity and low cytotoxicity

Hematite core-shell nanoparticles with plate-like morphology were synthesized using a one-step hydrothermal synthesis. An XRPD analysis indicates that the sample consist of single-phase alpha-Fe2O3 nanoparticles. SEM and TEM measurements show that the hematite sample is composed of uniform core-shell nanoplates with 10-20 nm thickness, 80-100 nm landscape dimensions (aspect ratio 5) and 3-4 nm thickness of the surface shells. We used computational methods for the quantitative analysis of the core-shell particle structure and circularity shape descriptor for the quantitative shape analysis of the nanoparticles from TEM micrographs. The calculated results indicated that a percentage of the shell area in the nanoparticle area (share [%]) is significant. The determined values of circularity in the perpendicular and oblique perspective clearly show shape anisotropy of the nanoplates. The magnetic properties revealed the ferromagnetic-like properties at room temperature with high coercivity H-C = 2340 Oe, pointing to the shape and surface effects. These results signify core-shell hematite nanoparticles' for practical applications in magnetic devices. The synthesized hematite plate-like nanoparticles exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating the safe use of these nanoparticles for biomedical applications

Synthesis of core-shell hematite (alpha-Fe2O3) nanoplates: Quantitative analysis of the particle structure and shape, high coercivity and low cytotoxicity

Hematite core-shell nanoparticles with plate-like morphology were synthesized using a one-step hydrothermal synthesis. An XRPD analysis indicates that the sample consist of single-phase alpha-Fe2O3 nanoparticles. SEM and TEM measurements show that the hematite sample is composed of uniform core-shell nanoplates with 10-20 nm thickness, 80-100 nm landscape dimensions (aspect ratio 5) and 3-4 nm thickness of the surface shells. We used computational methods for the quantitative analysis of the core-shell particle structure and circularity shape descriptor for the quantitative shape analysis of the nanoparticles from TEM micrographs. The calculated results indicated that a percentage of the shell area in the nanoparticle area (share [%]) is significant. The determined values of circularity in the perpendicular and oblique perspective clearly show shape anisotropy of the nanoplates. The magnetic properties revealed the ferromagnetic-like properties at room temperature with high coercivity H-C = 2340 Oe, pointing to the shape and surface effects. These results signify core-shell hematite nanoparticles' for practical applications in magnetic devices. The synthesized hematite plate-like nanoparticles exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating the safe use of these nanoparticles for biomedical applications.Peer-reviewed manuscript: [http://cherry.chem.bg.ac.rs/handle/123456789/3094

NiO core–shell nanostructure with ferromagnetic-like behavior at room temperature

International audienceWe report on ferromagnetic-like magnetic properties, at room temperature, of spherical nickel oxide core–shell nanoparticles synthesized by sol–gel combustion method. The sample is characterized by using transmission electron microscopy (TEM), selected electron area diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS) and superconducting quantum interference device (SQUID) magnetometer. The SAED, EDX and RS show high quality and purity of the sample. The TEM images point to core–shell NiO nanostructure with a well crystallized NiO core and surface disorder shell. The size of the nanoparticles of about 5 nm and thickness of the surface shell below 1 nm are estimated from the TEM and HRTEM measurements. The measurements of the magnetization reveals ferromagnetic-like behavior of the sample at room temperature with remanent magnetization Mr = 0.0087 emu/g and coercive field HC = 115 Oe. These magnetic properties are quite different than in NiO bulk materials and uncommon for nanosized NiO materials. These results also indicate that the synthesized NiO core–shell nanostructure is suitable for spin-valve applications

Detection of ammonia by residual gas analysis in AUG and JET

Nitrogen seeding, necessary for divertor heat-load mitigation in ITER, has been shown to lead to ammonia formation which would be a severe operational and safety issue in ITER. Predictions of ammonia production in ITER are based on data from present day fusion devices. Ammonia is mainly detected by residual gas analysis (RGA). Detection of ammonia is impeded by the presence of water and methane which, in a mixed H-D system, leave signatures in the same range of the mass spectra. A statistical model is used to ascribe an average isotope ratio to each gaseous species. The model is tested with simulated RGA recordings with varying concentration of ammonia to evaluate the sensitivity to fitting parameter boundaries, noise in the recordings and mis-matching cracking patterns. The analysis shows that the fitting procedure may in some occasions substitute species among each other, resulting in faulty concentrations. Nevertheless, the right choice of parameter boundaries ensures correct fitting results. Finally, the fitting procedure is applied to experimental data from nitrogen-seeeded discharges at AUG and JET