The α-Fe2O3/Ag2S p-n heterojunction has been prepared via a facile room temperature successive ionic layer adsorption and reaction (SILAR) method. The heterojunction exhibits higher photoelectrochemical property compared to bare α-Fe2O3. The amount of Ag2S has a significant effect on the PEC performance, which could be controlled by varying the number of SILAR cycles. The α-Fe2O3/Ag2S p-n heterojunction prepared via 6 cycles of SILAR processes displays the best photoelectrochemical performance, which exhibits 1.8 times enhancement of photocurrent density and 70 mV cathodic shift of onset potential compared to bare α-Fe2O3. The improved PEC performance could be attributed to the formation of p-n junction between Ag2S and α-Fe2O3, which not only enhanced the optical absorption ability, but also facilitated the separation efficiency of photogenerated charge carriers and passivized the surface state. 相似文献
The influence of interaction between anisotropic γ-Fe2O3 nanoparticles on their coercive force Hc is studied. In samples where the degree of homogenization of anisotropic γ-Fe2O3 nanoparticles is high owing to mechanical, ultrasonic, and magnetic dispersion with subsequent filtering of resulting suspensions,
Hc is almost independent of volume concentration η of the particles when η varies between 4 × 10−4 and 10−1. In samples homogenized only mechanically, the Hc versus logη dependence is linear. 相似文献
Direct comparison of the properties of a thin surface layer and the bulk of macroscopic hematite (α-Fe2O3) crystals was used to study the magnetic structure of the surface layer and the bulk and the processes attendant on spin-reorientation phase transition (SRT). The investigation tool was simultaneous γ-ray, X-ray, and electronic Mössbauer spectroscopy, which enabled us to study the bulk and surface properties of macroscopic samples simultaneously and to compare them directly. Direct evidence of the existence of a surface “transition layer” on hematite crystals is obtained. The existence of this layer was suggested and described by Krinchik and Zubov [JETP 69, 707 (1975)]. The study in the SRT region showed that (1) the Morin SRT in the crystal bulk occurs in a jump (as a first-order phase transition), whereas in the surface layer of about 200 nm thick, some smoothness appears in the mechanism of magnetic-moment reorientation; (2) SRT in the surface layer, as in the bulk, involves an intermediate state in which low-and high-temperature phases coexist; and (3) SRT in the surface layer occurs at a temperature several degrees higher than in the bulk. Our experimental evidence on the SRT mechanism in the surface layer correlates with the inferences from phenomenological theory developed by Kaganov [JETP 79, 1544 (1980)]. 相似文献
The superparamagnetism of an ensemble of ?-Fe2O3 nanoparticles with a mean size of 3.9 nm dispersed in a xerogel SiO2 matrix is studied by the Mössbauer spectroscopy method. It is shown that most nanoparticles at room temperature are in the superparamagnetic (unblocked) state. As the temperature decreases, the progressive blocking of the magnetic moments of the particles occurs, which is manifested in the Mössbauer spectra as the transformation of the quadrupole doublet into a Zeeman sextet. The analysis of the relative intensity of the superparamagnetic (quadrupole doublet) and magnetically split (sextets) spectral components in the range of 4–300 K provides the particle size distribution, which is in agreement with the transmission electron microscopy data. The values of the effective magnetic anisotropy constants (Keff) are determined, and the contribution of surface anisotropy (KS) is estimated for particles of various sizes. It is shown that the quantity Keff is inversely proportional to the particle size, which indicates the significant contribution of the surface to the magnetic state of the ?-Fe2O3 nanoparticles with the size of several nanometers. 相似文献
Nearly monodisperse hollow α-Fe2O3 microspheres composed of nanoparticles have been successfully synthesized through a facile template-free hydrothermal method.
The products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It
is shown that the hollow α-Fe2O3 microspheres consist of well-aligned α-Fe2O3 nanoparticles with a mean diameter of about 15 nm. This facile reaction route presents an efficient method for mass production
of monodisperse hollow magnetic nanomaterials. The final α-Fe2O3 microspheres exhibit special magnetic properties with a small remnant magnetization of 0.09 emu g−1 and a high coercivity of 1121.67 Oe at room temperature. 相似文献
-Fe2O3 particles with an average size of 10 nm were prepared by heating the precipitates obtained from a homogeneous solution of stearic acid and hydrated iron (III) nitrate. The compositional and thermal characteristics of the precipitates were studied with the aid of Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Presence of -Fe2O3 nanoparticles in the heat treated product was established by X-ray diffraction (XRD) investigations. The average particle size was estimated from the XRD patterns by single line profile analysis and directly from transmission electron microscopic (TEM) images. Kinetic analysis of the calorimetric data revealed that nucleation and growth type kinetic law remain operative during the process and the activation energy of the process is 115 kJ/mol. 相似文献
CdS/α-Fe2O3 hierarchical nanostructures, where the CdS nanorods grow irregularly on the side surface of α-Fe2O3 nanorods, were synthesized via a three-step process. The diameters and lengths of CdS nanorods can be tuned by changing the
ethylenediamine (EDA) and Cd ion concentrations. The magnetic investigations by superconducting quantum interference device
indicate that the hierarchical nanostructures have an Morin transition at lower temperature (230 K) than that of the single
bulk α-Fe2O3 materials (263 K). Importantly, the hierarchical nanostructures exhibit weakly ferromagnetic characteristics at 300 K. A
sharp peak assigned to the surface trap induced emission are observed in room temperature PL spectra. Combining with the optoelectronic
properties of CdS, the CdS/α-Fe2O3 hierarchical nanostructures may be used as multi-functional materials for optoelectronic and magnetic devices.
Supported by the National Natural Science Foundation of China (Grant Nos. 50772025 and 50872159), the Ministry of Science
and Technology of China (Grant No. 2008DFR20420), the China Postdoctoral Science Foundation (Grant Nos. 20060400042 and 200801044),
the Natural Science Foundation of Heilongjiang Province, China (Grant No. F200828), the Specialized Research Fund for the
Doctoral Program of Higher Education of China (Grant No. 20070217002), and the Innovation Foundation of Harbin City (Grant
No. RC2006QN017016) 相似文献
The production of low-dimensional nanoparticles (NPs) with appropriate surface modification has attracted increasing attention
in biological, biochemical, and environmental applications including chemical sensing, photocatalytic degradation, separation,
and purification of toxic molecules from the matrices. In this study, iron oxide NPs have been prepared by hydrothermal method
using ferric chloride and urea in aqueous medium under alkaline condition (pH 9 ~ 10). As-grown low-dimensional NPs have been
characterized by UV–vis spectroscopy, FT-IR, X-ray diffraction, Field emission scanning electron microscopy, Raman spectroscopy,
High-resolution Transmission electron microscopy, and Electron Diffraction System. The uniformity of the NPs size was measured
by the scanning electron microscopy, while the single phase of the nanocrystalline β-Fe2O3 was characterized using powder X-ray diffraction technique. As-grown NPs were extensively applied for the photocatalytic
degradation of acridine orange (AO) and electrochemical sensing of ammonia in liquid phase. Almost 50% photo-catalytic degradation
with AO was observed in the presence of UV sources (250 W) with NPs. β-Fe2O3 NP-coated gold electrodes (GE, surface area 0.0216 cm2) have enhanced ammonia-sensing performances in their electrical response (I–V characterization) for detecting ammonia in liquid phase. The performances of chemical sensor were investigated, and the results
exhibited that the sensitivity, stability, and reproducibility of the sensor improved significantly using β-Fe2O3 NPs on GE surface. The sensitivity was approximately 0.5305 ± 0.02 μAcm−2mM−1, with a detection limit of 21.8 ± 0.1 μM, based on a signal/noise ratio of 3 with short response time. 相似文献
A method has been developed for fabricating nanoporous matrices based on anodic aluminum oxide for the deposition of ferromagnetic nanoparticles in them. The modes of deposition of strontium ferromolybdate thin films prepared by the ion-plasma method have been worked out, and the magnetic and magnetoresistive properties, structure, and composition of the films have been investigated. It has been revealed that the microstructure and properties of the strontium ferromolybdate films deposited by ionplasma sputtering depend on the deposition rate and the temperature of the substrate. Based on the measurement of the electrical resistivity of nanoheterostructures in a magnetic field, it has been found that the magnetoresistance reaches 14% at T = 15 K and B = 8 T, which is due to the manifestation of tunneling magnetoresistance. 相似文献
The structural characteristics, valence states, and distribution of cerium ions between the components in In2O3–CeO2 and SnO2–CeO2 nanocomposites fabricated using the impregnation method were studied. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were used to show that, during impregnation, cerium ions are not included into In2O3 crystals and are disposed only on their surface in the form of nano-sized crystallites or amorphous clusters. On the other side, under the contact of CeO2 clusters with a surface of SnO2 matrix crystals, cerium ions penetrate into the surface layer of these crystals. In contrast to an In2O3–CeO2 system, where the addition of CeO2 does not affect the conduction activation energy, where cerium oxide is added to SnO2, the observed increase in the resistance of a SnO2–CeO2 composite is accompanied by a sufficient increase in activation energy. These data and the XPS spectra confirm the modification of the surface layers of conductive SnO2 crystals as, a result of the penetration of cerium ions into these layers. 相似文献
Composite solid electrolytes in the system (1???x)Li2CO3–xAl2O3, with x?=?0.0–0.5 (mole), were synthesized by a sol–gel method. The synthesis carried out at low temperature resulted in voluminous and fluffy products. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy/energy-dispersive X-ray, Fourier transform infrared spectroscopy and AC impedance spectroscopy. Structural analysis of the samples showed an amorphous feature of Li2CO3 and traces of α-LiAlO2, γ-LiAlO2 and LiAl5O8. The prepared composite samples possess high ionic conductivities at 130–180 °C on account of the presence of lithium aluminates as well as the formation of a high concentration of an amorphous phase of Li2CO3 via this sol–gel preparative technique. 相似文献
Laboratory vapor phase condensation experiments systematically yield amorphous, homogeneous, nanoparticles with unique deep
metastable eutectic compositions. They formed during the nucleation stage in rapidly cooling vapor systems. These nanoparticles
evidence the complexity of the nucleation stage. Similar complex behavior may occur during the nucleation stage in quenched-melt
laboratory experiments. Because of the bulk size of the quenched system many of such deep metastable eutectic nanodomains
will anneal and adjust to local equilibrium but some will persist metastably depending on the time–temperature regime and
melt/glass transformation. 相似文献
We have investigated the role of the grain boundary on the resistive magnetodielectric property of polycrystalline γ-Fe2O3 through impedance spectroscopy measurements. Depending on the sample preparation temperature, the dielectric constant of
γ-Fe2O3 is significantly different especially at low frequencies (<104 Hz) and high temperatures (>200 K). The value of the magnetodielectric effect at a specific frequency and the resonance frequency
for the maximized magnetodielectric effect are different, although polycrystalline γ-Fe2O3 samples show a quite similar magnetoresistance. Through the experimentally obtained resistance ratio between the grain and
the grain boundary, we can reproduce the magnetodielectric curves based on the Maxwell–Wagner model and the measured magnetoresistance. 相似文献
In this paper, single-crystalline hexahedron hematite is successfully obtained by a simple hydrothermal approach with assistance of PVP as surfactant. SEM and XRD results show that the as-obtained α-Fe2O3 has a nanohexahedron shape with high uniformity and high crystallinity. The effects of a few factors influencing the morphology of α-Fe2O3, such as PVP amount, reaction temperature, etc., are investigated carefully. More importantly, time-dependent experiments are carried out to have in-depth insight into the formation of the single-crystalline α-Fe2O3 nanohexahedron. Based on the full characterization of as-obtained α-Fe2O3, it is concluded that PVP as surfactant plays an important role in the formation of the hexahedron shape of α-Fe2O3. Besides, the proposed formation mechanism of α-Fe2O3 nanohexahedron is that the shape of α-Fe2O3 evolves from the nuclei, needle-like shapes, and urchin-like aggregates to the hexahedron shape, driven by minimization of surface energy and Ostwald ripening. When used as an anode material for lithium-ion batteries, nanohexahedron α-Fe2O3 shows a high rate capability. Moreover, after 150 cycles, the storage capacity of α-Fe2O3 is still up to 680 mAh g?1 and almost remains unchanged, suggesting high cyclability.
Theoretical investigations of adsorption of 3d-metals from Ti to Cu on the α-Al2O3 (0001) surface are presented. The influence of adsorbates on the atomic and electronic structure of the aluminum oxide surface
is considered. Values of the adsorption energy are calculated, and the equilibrium adatom positions on the surface are determined.
A comparative analysis of the properties and mechanisms of 3d-metal interaction with atoms of the substrate is performed. 相似文献
Features of the formation of lead-ferroniobate compounds in the xBaCO3–(1 – x)PbO–Fe2O3–Nb2O5 system by solid-phase synthesis are investigated. For perovskite-type lead-ferroniobate solid solution, a single-phase concentration region is revealed at 1233 K. The crystalline structures of the synthesized compounds are refined using Rietveld analysis and the Pm3?m and R3m space groups. Ceramic samples of lead ferroniobate are studied by scanning electron microscopy. 相似文献
The α-Fe2O3/TiO2 bi-functional composites with hierarchical and hollow structures are fabricated through a hydrothermal route. The adsorption performance and photocatalytic activity of the composites towards Pb2+ are investigated in this work. Different adsorption kinetics models and equilibrium models are used to explore the adsorption behavior of hierarchical α-Fe2O3/TiO2 hollow spheres. Experimental data show that adsorption kinetics of the hierarchical α-Fe2O3/TiO2 hollow spheres can be fitted well by the pseudo-second-order model, while the isothermal data can be perfectly described by the Langmuir adsorption model. The maximum adsorption capacity of the hierarchical α-Fe2O3/TiO2 hollow spheres is 32.36 mg g?1. Moreover, the hierarchical α-Fe2O3/TiO2 hollow spheres possess photocatalytic oxidation character under simulated solar light irradiation. The results demonstrate that the hierarchical α-Fe2O3/TiO2 hollow spheres, as effective and cheap materials, can be applied to the removal of heavy metal ions from wastewater. 相似文献
The structural and the thermodynamic properties of potassium nitrate KNO3 and its composites with nanosized aluminum oxide Al2O3 have been studied by differential scanning calorimetry. It has been found that an amorphous phase forms in composites (1–x)KNO3–xAl2O3. The thermal effect corresponding to this phase has been observed at 316°C. It has been found that the phase transition heats of potassium nitrate decreased as the aluminum oxide fraction increased. 相似文献