α-Fe2O3 Nanocrystals Research Articles

Preparation and structural, optical, magnetic, and electrical characterization of Mn2+/Co2+/Cu2+ doped hematite nanocrystals

Pure and Mn2+ / Co2+ / Cu2+ doped (1 and 2 at.%) spherical hematite (α-Fe2O3)nanocrystals have been synthesized by a simple solvothermal method using a domestic microwave oven. XRD measurements confirm that all the seven nanocrystals prepared consist of nanocrystalline hematite phase without any other phases. The energy dispersive X-ray and Fourier transform infrared spectral analyses confirm the phase purity of the nanocrystals prepared. TEM analysis shows the average particle sizes within the range 33–51nm. Optical absorption measurements indicate that all the three dopants enhance the optical transmittance and reflectance. A red shift is observed in the bandgap energy values estimated from optical absorption and reflectance spectra. Results of magnetic measurements made at room temperature using a vibrating sample magnetometer indicate significant changes in the magnetic properties (coercivity, retentivity and saturationmagnetization) due to doping. Results of magnetic measurements indicate significant changes in the magnetic properties. Results of AC electrical measurements made at various temperatures in the range 40–130°C and frequencies in the range 100 Hz –1MHz indicate low dielectric constants and AC electrical conductivities and consequently show the occurrence of nanoconfined states.

WO3 nanoneedles/α-Fe2O3/cobalt phosphate composite photoanode for efficient photoelectrochemical water splitting

We report the fabrication of the WO3 nanoneedles/α-Fe2O3 heterojunction photoanodes for efficient photoelectrochemical water splitting. The high-aspect-ratio single crystalline WO3 nanoneedles (NNs) act as both the photoanode framework and the light harvester in the UV and blue visible region. The porous layer of small α-Fe2O3 nanocrystals act as a cooperative light harvester in the visible region. The WO3 NNs/α-Fe2O3 heterojunction photoanodes exhibit an extended light absorption band in the visible region and a significantly enhanced photocurrent density, which is ca. 1.6 times higher than that obtained on the pure WO3 NNs. Cobalt phosphate (Co-Pi) was employed as an oxygen evolving catalyst to modify the heterojunction electrode, and the resulting WO3 NNs/α-Fe2O3/Co-Pi composite photoanodes show an excellent photostability for oxygen evolution reaction.

Origin of Tunable Photocatalytic Selectivity of Well‐Defined α‐Fe2O3 Nanocrystals

Visible-light induced degradation of an aqueous mixture containing MO and RhB on well-defined α-Fe2 O3 nanocrystals shows that MO degradation is more favorable and such selectivity on the {012} facet is greater than that on {001}. The origin of selectivity is rationalized as the inherent surface structural difference and preferential molecular adsorption.

The effects of cerium doping on the size, morphology, and optical properties of α-hematite nanoparticles for ultraviolet filtration

Metal oxide nanoparticles have potential use in energy storage, electrode materials, as catalysts and in the emerging field of nanomedicine. Being able to accurately tailor the desirable properties of these nanoceramic materials, such as particle size, morphology and optical bandgap (Eg) is integral in the feasibility of their use. In this study we investigate the altering of both the structure and physical properties through the doping of hematite (α-Fe2O3) nanocrystals with cerium at a range of concentrations, synthesised using a one-pot co-precipitation method. This extremely simple synthesis followed by thermal treatment results in stable Fe2−xCexOy nanoceramics resulting from the burning of any unreacted precursors and transformation of goethite-cerium doped nanoparticle intermediate. The inclusion of Ce into the crystal lattice of these α-Fe2O3 nanoparticles causes a significantly large reduction in mean crystalline size and alteration in particle morphology with increasing cerium content. Finally we report an increase optical semiconductor bandgap, along with a substantial increase in the ultraviolet attenuation found for a 10% Ce-doping concentration which shows the potential application of cerium-doped hematite nanocrystals to be used as a pigmented ultraviolet filter for cosmetic products.

Oriented growth of α-Fe2O3 nanocrystals with different morphology and their optical behavior

Different morphologically varied α-Fe2O3 nanocrystals have been successfully synthesized by a solvothermal route. X-ray diffraction patterns, transmission electron microscopy and field emission scanning electron microscopy have been employed for structural and morphological characterization. Various unique shapes of the well crystalline α-Fe2O3 phase has been revealed and the evolution of crystal growth with different morphology is explained on the basis of oriented attachment mechanism controlled by different solvents used in the reaction. The effect of morphology of α-Fe2O3 nanocrystals on their optical absorption behavior has been observed and the absorptions were analyzed considering all the possible electronic transitions in such 3d5 systems.

Hydrothermal synthesis, characterization and optical properties of ellipsoid shape α-Fe2O3 nanocrystals

Abstract A facile hydrothermal method for the synthesis of α-Fe 2 O 3 nanocrystals is described. The crystalline structure and morphology of the as-prepared product were investigated by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Powder X-ray diffraction pattern exhibited pure rhombohedral structure. The SEM and TEM results showed that the average diameter of the highly crystalline ellipsoid shape α-Fe 2 O 3 nanocrystals was about 40–50 nm. The band gap energies were investigated by the UV–vis absorption studies.

Facile Size-Controllable Synthesis of Colorful Quasi-Cubic α-Fe2 O3 Materials from Nanoscale to Microscale and Their Properties Related to the Size Effect.

A facile and environmentally friendly hydrothermal approach has been employed to synthesize size-controllable quasi-cubic α-Fe2 O3 nanocrystals by using an aqueous solution of FeCl3 without any alkaline materials and stabilizing agent. The as-prepared products were carefully characterized and the growth mechanism is also discussed. This hydrothermal synthesis of such quasi-cubic structures implies a simple and low-cost route to prepare monodisperse nanomaterials on a large scale. The size-controllable synthesis of α-Fe2 O3 is the first achieved successfully from 80 nm to 2 μm with constant structures. The synthesized α-Fe2 O3 materials have different optical properties and stabilities in water, which are caused by the change of their band-gap energy and specific surface areas. Finally, the dielectric properties of synthesized α-Fe2 O3 cubes were also investigated, and the differences caused by the particle sizes are discussed.

Nickel ions inducing growth of high-index faceted α-Fe2O3 and their facet-controlled magnetic properties

In this study, single-crystalline α-Fe2O3 polyhedrons with high-indexed facets exposed were controllably synthesized through a simple hydrothermal route with Ni2+ ions as the structure-directing agent. The polyhedral crystals are quasi-cubic with an angle of approximately 86° and bound by (012), (10–2) and (1–12) facets. With insufficient Ni2+ ions added, only concave α-Fe2O3 crystals can be got while only irregular α-Fe2O3 crystals were obtained without the addition of Ni2+ ions. The growth process of α-Fe2O3 quasi-cubes was investigated and possible growth mechanism was proposed. Magnetic measurements confirm that the α-Fe2O3 nanocrystals with different morphologies display shape and surface-dependent magnetic behaviors. As the morphology of α-Fe2O3 crystals change from irregular particles to concave cube and then quasi-cubes with the increase of added Ni2+ amounts, the magnetism of the obtained α-Fe2O3 alters from spin-canted ferromagnetism, coexistent spin-canted and defect magnetism and then defect magnetism at room temperature.

Can hematite nanoparticles be an environmental indicator?

Environmental indicators play an important role in assessing the state of the environment and understanding the trend of environmental changes. Iron oxide nanostructures are widespread in multiple ecosystems, and are therefore suitable for providing environmental indicators with measurable physical or chemical properties that are sensitive to the environmental conditions. It has been found that the morphologies of natural hematite (α-Fe2O3) nanocrystals have large variations depending on thermodynamic and chemical conditions of their formation environments. To assess the applicability of nanomorphology as an environmental indicator, we construct a morphology map of hematite nanocrystals in hydrous environments, characterized with different temperatures, humidity and supersaturation of oxygen. Our model indicates that the fractional surface areas of morphologically significant facets change with humidity and temperature, and can be used to track the variation of these environmental conditions.

Single-crystalline α-Fe2O3 nanostructures: controlled synthesis and high-index plane-enhanced photodegradation by visible light

In this work, α-Fe2O3 oblique and truncated nanocubes were synthesized in the presence of oleylamine (OAm), acetylacetone (Hacac) and oleic acid (OA) through a facile one-step solvothermal method. The phase of iron oxide was precisely regulated through the volume ratio of OAm/Hacac, and confirmed by X-ray diffraction (XRD) and Raman imaging microscopy. The formation mechanism of α-Fe2O3 nanocrystals was discussed systematically and a schematic illustration of the probable formation of the morphologies in the whole of the synthetic process was also proposed. Furthermore, the truncated nanocubes exposing both the {012} and {104} dominant planes exhibit higher photocatalytic activity toward RhB compared with the oblique nanocubes surrounded by only the {012} dominant facet, which reveals that the high photocatalytic activity is attributed to the exposure of {104} high-index planes. The truncated nanocubes with high catalytic activity may potentially serve as effective and cheap catalysts for photodegradation.

Hierarchical hollow spheres composed of ultrathin Fe2O3 nanosheets for lithium storage and photocatalytic water oxidation

Hollow hierarchical spheres self-organized from the ultrathin nanosheets of α-Fe2O3 were prepared by a simple process. These ultrathin nanosheet subunits possess an average thickness of around 3.5 nm and show preferential exposure of (110) facets. Their Li ion storage and visible-light photocatalytic water oxidation performance are tested. Such hierarchical nanostructures show high Li storage properties with good cycling stability and excellent rate capabilities. The water oxidation catalytic activity is 70 μmol h−1 g−1 for O2 evolution under visible light irradiation and can be maintained for 15 hours. The structural features of these α-Fe2O3 nanocrystals are considered to be important to lead to the attractive properties in both Li storage and photocatalytic water oxidation, e.g. hollow interior, ultrathin thickness and largely exposed active facets.

Ge-doped hematite nanosheets with tunable doping level, structure and improved photoelectrochemical performance

Doping impurities and nanostructuring are two effective ways to modulate the photoelectrochemical properties of hematite materials. Ge-doped hematite (α-Fe2O3) nanocrystals were synthesized by combining laser ablation in liquid and hydrothermal synthesis. The doping level of Ge and morphology of hematite could be readily tuned through adjusting the ablation time. Hematite nanocrystals doped with 2at% Ge exhibited a morphology of ultra-thin circular nanosheets with a thickness of about 10nm and diameter of 200nm, while hematite doped with 5at.% Ge consisted of assembled nanosheets with a thickness of about 30–40nm. High-resolution transmission electron microscopy demonstrated that Ge presented randomly at the Fe sites in the hematite lattice of the 2at% doped hematite, but at a higher doping level of 5at%, Ge distributed orderly in the host lattice to result in doubling of the basal plane vector. The band gap of α-Fe2O3 can be reduced by Ge doping, leading to increased photocurrent density and improvement in the photoelectrochemical performance of α-Fe2O3.

Synthesis of a sugar-organometallic compound 1,1′-difurfurylferrocene and its microwave preparation of carbon/iron oxide nanocomposite

In order to synthesize a carbon–metal or metal oxide combination sphere, carbonaceous resource furfural 1 was introduced, which was nucleophilic treated with 1,1′-dilithioferrocene 2 to form a sugar-organometallic compound: ferrocenyl monosaccharide derivative 1,1′-difurfurylferrocene 3. 1,1′-Difurfurylferrocene 3 can be hydrothermally treated in a microwave reactor to give 300–500nm microspheres with the α-Fe2O3 or Fe3O4 nanocrystals formed on the surface, which may be favorable for new magnetic materials preparation or instead of iron with other metal ions, versatile carbon/metal composites will be possibly synthesized for catalysis, drug delivery and magnetic uses.

Controllable synthesis, magnetic and biocompatible properties of Fe3O4 and α-Fe2O3 nanocrystals

Iron oxide nanocrystals (NCs) with a series of well-controlled morphologies (octahedron, rod, wire, cube and plate) and compositions (Fe3O4 and α-Fe2O3) were synthesized via a facile hydrothermal process. The morphological and compositional control of various iron oxide NCs was based on the regulations of precursor thermolysis kinetics and surfactants. The obtained samples were characterized by XRD, SEM, TEM, SQUID and cytotoxicity test. These as-prepared iron oxide NCs showed excellent magnetic properties and good biocompatibility, paving the way for their high-efficiency bio-separation and bio-detection applications.

In situ growth of Au nanoparticles on Fe2O3 nanocrystals for catalytic applications

Gold nanoparticles are successfully grown in situ on α-Fe2O3 nanocrystals through a cysteine-linked seed-planting approach followed by photo-assisted growth. The size of the gold particles on α-Fe2O3 nanocrystals can be further tuned from 2 to 20 nm by using photoinduced seed-mediation strategy. The formed Au-α-Fe2O3 hetero-nanoparticles are highly dispersible in aqueous and alcohol solvents, and capable of efficient catalysis for 4-nitrophenol reduction. In addition, they also show promoted photocatalytic efficiencies for visible-light-driven dye degradation and water oxidation due to the enhancement by surface plasmon resonance of the attached gold nanoparticles. The present strategy gives a promising way to prepare hetero-nanostructures composed by metal oxide nanocrystals and metal nanoparticles with tailorable sizes for broad applications in catalysis and photocatalysis.

Controlled growth and magnetic properties of α-Fe2O3 nanocrystals: Octahedra, cuboctahedra and truncated cubes

A series of α-Fe2O3 crystalline materials with fascinating polyhedral morphologies, such as octahedral, cuboctahedral and truncated cubic structures, were prepared through a novel solid-phase sintering process. Our results demonstrated that the structural transformations among the polyhedra were easily controlled by the sintering times. This suggested that the Wulff polyhedra transformation could occur in a hexagonal crystal system. Furthermore, we found that the magnetic properties of the α-Fe2O3 crystals were associated with their size and shape.

Facile shape and size-controlled growth of uniform magnetite and hematite nanocrystals with tunable properties

Monodispersed magnetite Fe3O4 and hematite α-Fe2O3 nanocrystals have been grown in co-solvents of alcohol and water. Either the shape or the size of the nanocrystals could be easily controlled. Both the phases and nanostructures have been characterized by powder X-ray diffraction patterns and electron microscopy. The magnetic and catalytic properties of these products were investigated and compared with each other. The obtained results clearly demonstrate that these iron oxide nanocrystals are soft ferromagnetic at room temperature and α-Fe2O3 has a more effective catalytic property on the thermal decomposition of ammonium perchlorate than Fe3O4. Based on the experimental data, it is proposed that the magnetic and catalytic properties of these nanocrystals are dependent not only on the size and shape, but also on the surface structure of the nanocrystals. The nanoplates with significant anisotropic nanostructure demonstrate a highly enhanced performance as compared to nanoparticles.

Single-crystalline α-Fe2O3 oblique nanoparallelepipeds: High-yield synthesis, growth mechanism and structure enhanced gas-sensing properties

In this paper, single-crystalline α-Fe2O3 oblique nanoparallelepipeds are fabricated in high yield via a facile surfactant-free hydrothermal method, which involves oriented aggregation and Ostwald ripening. The obtained nanocrystals have exposed facets of {012}, {01-4} and {-210} with a rhombohedral α-Fe2O3 structure. The gas sensors based on the as-synthesized α-Fe2O3 nanostructures exhibit high sensitivity, short recovery time, and good reproducibility in ethanol and acetone. The superiority of the gas-sensing properties of the obtained nanostructures should be attributed to the surface structure of the nanocrystals. The as-prepared α-Fe2O3 nanocrystals are significant for exploiting their other applications in the future.

Reactivity Differences of Nanocrystals and Continuous Films of α-Fe2O3 on Au(111) Studied with In Situ X-ray Photoelectron Spectroscopy

The interaction of CO with nanocrystals and continuous films of α-Fe2O3 grown on Au(111) was investigated using in situ X-ray photoelectron spectroscopy (XPS) at near ambient pressure (200 mTorr) and scanning tunneling microscopy (STM). Adsorbed CO was detected by XPS when α-Fe2O3 nanocrystals (6−7 nm) grown on Au(111) were exposed to 200 mTorr of the gas at room temperature. Under a low H2O background, surface bound hydroxyl groups (adsorbed OH) were also noted on these α-Fe2O3 nanocrystals as a result of H2O dissociation on the edges of the particles. Adsorbed formate (HCOO−) was detected during heating to 373 K and believed to originate from the reaction of adsorbed CO with the OH groups. The adsorbed formate desorbed or decomposed above 473 K. Continuous α-Fe2O3 thin films on Au(111) were inert under the same conditions studied for nanocrystalline α-Fe2O3. Specifically, neither adsorbed CO nor OH groups were observed for the continuous films of α-Fe2O3. This reactivity difference can be explained by the presence of α-Fe2O3 crystal edges and the interface which exists between the α-Fe2O3 nanocrystals and the Au(111) substrate. These edges and interfaces are present for the nanocrystalline α-Fe2O3/Au(111) system but are not present in significant amounts for the continuous films of α-Fe2O3. The implications of these experimental results for the water-gas shift reaction will be also discussed.

Crystal plane effect of Fe2O3 with various morphologies on CO catalytic oxidation

Hematite (α-Fe2O3) nanocrystals with various morphologies (nanocubes and nanorods with different particle sizes) were synthesized by a facile hydrothermal process. The crystal plane effects of different Fe2O3 nanomaterials on the catalytic activity of CO oxidation were investigated. Besides the BET area of catalyst, the predominantly exposed planes have a significant influence on the catalytic activity for CO oxidation. Fe2O3 nanorods with more reactive crystal planes {110}, which have relative higher density of Fe atoms, showed a higher activity than the other samples.