Hematite α-Fe2O3 Research Articles

Advanced hematite nanomaterials for newly emerging applications.

Because of the combined merits of rich physicochemical properties, abundance, low toxicity, etc., hematite (α-Fe2O3), one of the most chemically stable compounds based on the transition metal element iron, is endowed with multifunctionalities and has steadily been a research hotspot for decades. Very recently, advanced α-Fe2O3 materials have also been developed for applications in some cutting-edge fields. To reflect this trend, the latest progress in developing α-Fe2O3 materials for newly emerging applications is reviewed with a particular focus on the relationship between composition/nanostructure-induced electronic structure modulation and practical performance. Moreover, perspectives on the critical challenges as well as opportunities for future development of diverse functionalities are also discussed. We believe that this timely review will not only stimulate further increasing interest in α-Fe2O3 materials but also provide a profound understanding and insight into the rational design of other materials based on transition metal elements for various applications.

TRANSIÇÕES ELETRÔNICAS EM α-Fe2O3: MODELOS TEÓRICOS E LIMITAÇÕES

ELECTRONIC TRANSITIONS IN α-FE2O3: THEORETICAL MODELS AND LIMITATIONS. Addressing electronic transitions of hematite (α-Fe2O3) is still considered a topic in active debate, even though it is one of the most widely used compounds from ancient times to the present and also one of the most extensively investigated iron oxides. In this review, a general analysis of the approaches and theoretical models which had been used to explain the electronic absorption spectrum of α-Fe2O3, from the first proposal presented by Tandon and Gupta (1970) to the more recent results obtained by quantum mechanical calculations, is presented. The analysis of the already published studies is made pointing out the main factors that must be considered to allow a more reliable understanding of the UV-Vis-NIR spectra of α-Fe2O3. Furthermore, controversies in the calculated results are discussed, analysing the suitability of each of the approaches used. Reasons for differences observed in the experimental data reported in the literature are also discussed.

Development of ceramic grade red iron oxide pigment from waste iron source

Ceramic grade red iron oxide (α-Fe2O3) nanoparticles pigments have been synthesized from waste condensed milk containers which contain a prominent amount of iron (93.2%). The synthesis method comprised of two steps: in the first step ferrous sulfate was prepared following an acid leaching method; while the second step was oxidation and calcination of ferrous sulfate to produce desired α-Fe2O3 in nano form. The structure, functional groups, chemical state, morphology, particle size, surface area, elemental, thermal analysis and magnetic properties of the samples were investigated using XRD, FTIR, XPS, SEM, BET, EDS, TG-DT and VSM respectively. Pure hematite (α-Fe2O3) phase was confirmed by XRD and the average crystal sizes were in the range 34–126 nm have been performed by Debye-Scherer's formula, which are consistent with the results as achieved from SEM images. Agglomerated irregular spherical nanoparticles (45–149 nm) were found in SEM image. The surface chemistry and the chemical state (Fe3+) of the hematite nanoparticles was also confirmed by XPS. The mesoporous nature of the nanoparticles with high surface area were measured by BET and it has been revealed that the BET specific surface area (33.55 m2/g) was marginally higher than the commercial one. The magnetic nature of the nanoparticles was portrayed by VSM and the nanoparticles showed the ferromagnetic behavior. Moreover, particle size distributions and zeta potential values have been also measured by DLS.

Characterization of Iron Oxide Samples Using Mössbauer Spectroscopy and Hysteresis Loops

In this work, we used Mössbauer spectroscopy and magnetometry at room temperature to investigate the magnetic properties of four different iron oxide samples (α-FeOOH, γ-Fe2O3, or Fe3O4 and α-Fe2O3) before and after annealing at 1000°C for one hour. We found that after annealing, all four samples exhibited the same properties as hematite (α-Fe2O3). These results show that the iron oxides in this study underwent phase transformations from an initial phase of either α-FeOOH, γ-Fe2O3, or Fe3O4 to a single final phase of α-Fe2O3.

Key modification strategies for the rational design of hematite to promote photoelectrochemical water oxidation: a review of recent advances

In this review article, multiple modification strategies for hematite, including controlling the morphology, heterojunction engineering, doping engineering, modification of co-catalyst and other modifications are proposed.

Structural, optical and magnetic properties of chitosan mediated α-Fe2O3 nanoparticles

The environmentally-safe, copious, inexpensive, non-toxic and thermally stable α-Fe2O3 (Hematite) nanoparticles attracted more attention in the recent times. In the present work, we have made an attempt to develop α-Fe2O3 nanoparticles using chitosan (a naturally available biodegradable polymer) as a medium and iron nitrate as precursors. The chitosan gel is first prepared and then solubilized under pressure in water using CO2. Herein, we study the effects of the aqueous chitosan medium on the properties of α-Fe2O3 in terms of size, shape, crystallinity, optical, and magnetic properties. The developed nanoparticles have been characterized for their structural, morphological, thermal, magnetic, and optical properties using XRD, Raman Spectroscopy, HR-TEM, Thermogravimetric analysis, Vibrating sample magnetometer, FTIR, and UV–visible spectroscopy techniques. All the studies confirm the formation of hexagonal crystal structure with a space group R -3 c with polygonal shaped nanoparticles with size ranging from 10 to 30 nm. UV–Visible Spectroscopy shows a standard band gap of 3.34 eV, which is surprisingly much higher in comparison to the existing reports. Magnetic properties reveal the presence of antiferromagnetic nature at room temperature coupled with a ferromagnetic/superparamagnetic behavior.

Effect of Camellia sinensis Origin and Heat Treatment in the Iron Oxides Nanomaterials Composition and Fenton Degradation of Methyl Orange

Sustainable and environmentally friendly methods for nanomaterials synthesis have been emerging recently. The use of extracts of polyphenol-rich plants with high reducing and chelating power is advantageous because the polyphenol can protect the nanomaterial from agglomeration and deactivation. Green nanomaterials have been applied in several areas, including remediation of toxic organic pollutants from contaminated effluents. Herein, we describe the preparation of green iron oxide nanoparticles (IONPs) with extracts of the plant Camellia sinensis as black tea for dye removal application. The as-prepared IONPs were composed of amorphous FeOOH and FeII/III-polyphenol complexes. To obtain crystalline and pure iron-based nanomaterials, the amorphous precursor was annealed at 900 ºC. Samples of black tea from different regions were used to verify the reproducibility of the iron phases formed. The same iron phases were obtained for all black tea samples, α-Fe2O3 (hematite), FePO4, and Fe3PO7, but in different proportions. The materials were applied as heterogeneous-Fenton catalysts for the removal of the dye methyl orange. The amorphous as-prepared IONPs were more active than the respective annealed IONPs due to the proton release from the polyphenol into the reaction medium, setting the pH to around 3, which is the optimum pH for the Fenton system.

SYNTHESIS AND CHARACTERIZATION OF BARIUM MHEXAFERRITE BaFe12-2xCoxZnxO19 (0 ≤ X ≤ 1) PREPARED FROM CO-PRECIPITATION

Barium hexaferrite (BaFe12O19) has attracted research attention due to its diverse applications. This study reports the synthesis of barium M-hexaferrite (BaFe12-2xCoxZnxO19) powder using co-precipitation of BaCO3 and FeCl3.6H2O powder, Co and Zn powder as a dopant material on the variation of x = 0, 0.2, 0.4, 0.6, 0.8, and 1. Results show that co-precipitation is an effective method for the synthesis of nanomaterial barium M-hexaferrites (BaFe12-2xCoxZnxO19) containing >89% of Fe elements and an average particle size of 50 nm. The DTA/TGA analyses show phase transformation at T ≤ 285°C and T = 750-840°C. The results of refinement using the Rietveld method show that the barium M-hexaferrite phase begins to form at low temperatures, with the best yield at x = 0.4. At high temperatures T > 740°C, it tends to form single-phase α-Fe2O3 (hematite). Substitution ion dopant Co/Zn only slightly changes the lattice parameters of the hexagonal basic crystal structure

Surface passivation of hematite photoanodes using iron phosphate

Deposition of passive layers containing covalently bonded oxygen is an effective strategy to suppress the surface states of α-Fe2O3 (hematite).

Исследование наноразмерного порошка оксида железа в качестве биологически активного материала

A polydisperse nanopowder of iron oxide, consisting of hematite α-Fe2O3 and magnetite Fe3O4, was obtained by the method of solid-phase reduction of iron hydroxide Fe(OH)3. On the basis of the obtained iron oxide nanopowder, aqueous suspensions were prepared in the concentration range of 0.25 – 1.25 mg/l with a particle dispersion of 100 – 400 nm. To assess the biological activity of iron oxide nanopowder, pre-sowing treatment of corn seeds Zéa máys was carried out. It has been established that the treatment with nanoparticles has a stimulating effect on the development of the plant organism, making it possible to achieve an increase in germination by 15% and root mass by 23%. Determination of the quantitative content of iron in different parts of the plant was carried out using atomic emission and atomic absorption spectroscopy. It was shown that as a result of treatment of plants with iron nanoparticles, its accumulation in the root mass with subsequent redistribution to the leaves to stimulate the process of photosynthesis is observed.

From doping to composites: zirconia (ZrO2) modified hematite photoanodes for water splitting.

Herein, a ZrO2 added α-Fe2O3 photoanode that can split water at low applied potential is reported. First, the pristine hematite α-Fe2O3 photoanode was synthesized using an aerosol-assisted chemical vapour deposition (AACVD) method followed by modification with various amounts of ZrO2 (2 to 40%) in the form of thin films on conducting glass substrate. The XRD, Raman spectroscopy and scanning electron microscopy (SEM) analyses confirmed the presence of the monoclinic phase of ZrO2 in the composites with multifaceted particles of compact morphology. The optical analysis showed an increase in the absorbance and variation in band gap of the composites ascribed to the heterogeneity of the material. The photoelectrochemical studies gave a photocurrent density of 1.23 mA cm-2 at 1.23 V vs. RHE for the pristine hematite and remarkably higher value of 3.06 mA cm-2 for the optimized amount of ZrO2 in the modified α-Fe2O3 photoanode. To the best of our knowledge, this is the highest photocurrent reported for a ZrO2 containing photoanode. The optimized composite electrode produced nine times more oxygen than that produced by pristine hematite.

Effect of the laser-synthesized γ-Al2O3 support on the activity of Fe/γ-Al2O3 nanopowders in dehydrogenation of isobutane

The study shows that two types of the γ-Al2O3 supports synthesized using laser vaporization and precipitation methods essentially differ in their morphology and pore structure. The first type of support is represented by weakly agglomerated spherical particles with the diameter of 3–10 nm, whereas the second type consists of strongly aggregated and disordered nanocrystallites with the diameter of 10–15 nm. The indicated supports were used to obtain Fe/γ-Al2O3 catalysts with different Fe content by incipient wetness impregnation. In the catalyst supported on the laser-synthesized γ-Al2O3, the pore size distribution is narrow and pore sizes are close to the particle sizes. HAADF-STEM made it possible to observe highly dispersed locally isolated regions of iron oxide with the size of 0.5–2.0 nm in the maghemite (γ-Fe2O3) phase, which are not detected by XRD. On the contrary, according to XRD, the deposition of iron on the γ-Al2O3 obtained by precipitation leads to the distinct hematite (α-Fe2O3) phase with the crystallite size of ∼33 nm. Distinctive features of the catalysts were found also by H2-TPR and NH3-TPD. Comparative testing of the catalysts with the iron content of 5.0 wt.% revealed that the system obtained using the γ-Al2O3 synthesized by laser vaporization is by 6–10% more active in the fixed-bed dehydrogenation of isobutane.

Fabrication of r-GO/GO/α-Fe2O3/Fe2TiO5 Nanocomposite Using Natural Ilmenite and Graphite for Efficient Photocatalysis in Visible Light

Hematite (α-Fe2O3) and pseudobrookite (Fe2TiO5) suffer from poor charge transport and a high recombination effect under visible light irradiation. This study investigates the design and production of a 2D graphene-like r-GO/GO coupled α-Fe2O3/Fe2TiO5 heterojunction composite with better charge separation. It uses a simple sonochemical and hydrothermal approach followed by L-ascorbic acid chemical reduction pathway. The advantageous band offset of the α-Fe2O3/Fe2TiO5 (TF) nanocomposite between α-Fe2O3 and Fe2TiO5 forms a Type-II heterojunction at the Fe2O3/Fe2TiO5 interface, which efficiently promotes electron-hole separation. Importantly, very corrosive acid leachate resulting from the hydrochloric acid leaching of ilmenite sand, was successfully exploited to fabricate α-Fe2O3/Fe2TiO5 heterojunction. In this paper, a straightforward synthesis strategy was employed to create 2D graphene-like reduced graphene oxide (r-GO) from Ceylon graphite. The two-step process comprises oxidation of graphite to graphene oxide (GO) using the improved Hummer's method, followed by controlled reduction of GO to r-GO using L-ascorbic acid. Before the reduction of GO to the r-GO, the surface of TF heterojunction was coupled with GO and was allowed for the controlled L-ascorbic acid reduction to yield r-GO/GO/α-Fe2O3/Fe2TiO5 nanocomposite. Under visible light illumination, the photocatalytic performance of the 30% GO/TF loaded composite material greatly improved (1240 Wcm-2). Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) examined the morphological characteristics of fabricated composites. X-ray photoelectron spectroscopy (XPS), Raman, X-ray diffraction (XRD), X-ray fluorescence (XRF), and diffuse reflectance spectroscopy (DRS) served to analyze the structural features of the produced composites.

Deep surface reconstruction of Co-based cocatalyst on Ti-doped α-Fe2O3 photoanode for highly efficient water oxidation

Transition metal-based cocatalysts play important roles in promoting the surface kinetics of hematite (α-Fe2O3) photoanode. However, their performances are restricted by the shallow reconstruction process for generating highly efficient metal oxyhydroxides, where the oxygen evolution reaction (OER) occurs. Therefore, a Brnsted base-regulated strategy is developed to promote the in situ surface reconstruction of cocatalysts on Ti-doped α-Fe2O3 (Ti–Fe2O3) under photoelectrochemical conditions. After deep surface reconstruction by electrochemical activation, the CoWO4 cocatalyst decorated Ti–Fe2O3 photoanode (a-CoWO4/Ti–Fe2O3) delivers a photocurrent density of 0.88 mA cm−2 at 1.23 VRHE, which is about 3.0 times of activated Ti–Fe2O3 (a-Ti-Fe2O3) and 1.5 times of activated CoOx/Ti–Fe2O3. Tungstate promotes the surface reconstruction of cobalt-based cocatalyst, resulting in a significant increase in bulk charge separation efficiency (ηsep) and surface charge injection efficiency (ηinj). Moreover, the type-II heterojunction between CoWO4-derived CoOOH and a-Ti-Fe2O3 drives the rapid separation and transfer of photogenerated electron-hole pairs, and enhances the performance of Ti–Fe2O3 photoanode.

Design of electrical pathways on insulator materials by laser processing

The application of laser technology for surface modification is well known in several application fields, with very high versatility. In this work, the viability of using laser irradiation to promote electrically conductive pathways on the surface of insulator materials is demonstrated. This was performed through the laser-induced conversion of hematite (α-Fe2O3) into magnetite (Fe3O4). The results show the optimal feed rates and laser powers that promote larger magnetite pathway widths, depths and grain sizes and therefore higher electrical conductivity. The optimization of the laser processing parameters allowed magnetite pathway widths of 218 ± 8 µm and depths of 66 ± 2 µm. The electrical conductivity measurements of the irradiated regions, confirmed the effectiveness of the laser surface treatment to promote the local phase transformation of hematite into magnetite. A maximum conductivity of 1062 ± 6 mS/m was reached for a laser power of 90 W, which corresponds to the highest magnetite grain size. The results evidence the ability of laser technology to transform an electric insulator phase (α-Fe2O3) into a conductive material (Fe3O4), being possible to promote a localized electrical pathway. This study allows foreseeing applications in other oxide systems to promote localized electrical pathways on insulator surfaces, to be applied as future ceramic sensors.

Sequential modifications of the surface of hematite (α-Fe2O3) photoanodes with amorphous nickel iron oxide (NiFeOx) and cobalt phosphate (Co-Pi)

We prepared Hematite (α-Fe2O3)-based photoanodes, treated by either an amorphous NiFeOx coating or a cobalt-phosphate co-catalyst (Co-Pi) or both, and investigated the role of each treatment in the improvement of the PEC performances. We found that the PEC performances of the films in which both Co-Pi or NiFeOx were deposited on the surface of Hematite were much higher than that of bare Hematite regardless of the order of the treatments, which could be attributed to the synergistic effect on the enhancement of the charge transfer efficiency. Particularly, the film in which the surface of hematite was coated with NiFeOx, then Co-Pi was loaded on it, showed the excellent long-term stability, alleviating the shortcoming of the NiFeOx coating. In addition, we found that the treatments of either Co-Pi or NiFeOx resulted in the enhancement of the charge transfer efficiencies and the generation of the additional component arising from the trapped holes in Co-Pi (NiFeOx), separated from the surface states in hematite, which are beneficial for the enhancement of the PEC performance.

Structural, optical, and magnetic properties of submicron hematite (α-Fe2O3) particles synthesized from industrial steel waste

Hematite submicron particles were synthesized using oil-contaminated ferric oxide precursor obtained from the hot-rolled steel industry in Colombia. The samples received are difficult to recycle for the steel industry, which, due to their poor disposal, causes irreparable environmental damage. Here we propose a synthetic route to obtain functional magnetic particles with this residue. First, a series of washes with solvent and alcohols were proposed, thus achieving the total removal of the oil. X-ray diffraction and Mössbauer spectroscopy show that the as received sample consists of different iron phases, with wüstite being the majority phase. After the synthesis process, the hematite phase was present as the majority phase with ∼92 wt%. FTIR, UV–Vis, and SQUID measurements was carried out to study the structural, optical and magnetic properties of the samples. This methodology is a viable alternative to give added value to this waste to improve the management of this by-product.

Study of Phase Transformations and Hyperfine Interactions in Fe3O4 and Fe3O4@Au Nanoparticles

The paper presents the results of a study of iron oxide nanoparticles obtained by chemical coprecipitation, coated (Fe3O4@Au) and not coated (Fe3O4) with gold, which were subjected to thermal annealing. To characterize the nanoparticles under study, scanning and transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy on 57Fe nuclei were used, the combination of which made it possible to establish a sequence of phase transformations, changes in morphological and structural characteristics, as well as parameters of hyperfine interactions. During the studies, it was found that thermal annealing of nanoparticles leads to phase transformation processes in the following sequence: nonstoichiometric magnetite (Fe3-γO4) → maghemite (γ-Fe2O3) → hematite (α-Fe2O3), followed by structural ordering and coarsening of nanoparticles. It is shown that nanoparticles of nonstoichiometric magnetite with and without gold coating are in the superparamagnetic state with a slow relaxation rate. The magnetic anisotropy energy of nonstoichiometric magnetite is determined as a function of the annealing temperature. An estimate was made of the average size of the region of magnetic ordering of Fe atoms in nonstoichiometric magnetite, which is in good agreement with the data on the average sizes of nanoparticles determined by scanning electron microscopy.

Surface selective passivation and FexNi1-xOOH co-modified Fe2O3 photoanode toward high-performance water oxidation

Improving the water-splitting performance of hematite (α-Fe2O3) is still hindered due to its severe charge recombination and poor water oxidation kinetics. Herein, borate-treated Ti–Fe2O3 combined with a FexNi1-xOOH cocatalyst (FexNi1-xOOH/B/Ti–Fe2O3) greatly improved the performance of Ti–Fe2O3, and reached a notable photocurrent density of 3.39 mA/cm2 at 1.23 V vs. RHE. Transient surface photovoltage spectroscopy (TPV) directly reveals that [B(OH)4]− as a Lewis base can selectively passivate acceptor surface states on Ti–Fe2O3 photoanode surface, efficiently enhancing the charge separation efficiency. Moreover, the FexNi1-xOOH thin layer is devoted to further facilitate holes injection into the electrolyte, accelerating the water oxidation kinetics of Ti–Fe2O3 photoanode. The synergetic integration of acceptor surface states passivation and FexNi1-xOOH cocatalyst provides a novel strategy for the construction of efficient photoanodes by surface engineering.

Photoelectrochemical Detection of Calcium Ions Based on Hematite Nanorod Sensors.

α-Fe2O3 (hematite) thin films have been shown to be a robust sensor substrate for photoelectrochemical imaging with good stability and high spatial resolution. Herein, one-dimensional (1D) hematite nanorods (NRs) synthesized via a simple hydrothermal method are proposed as a substrate which provides nanostructured surfaces with enhanced photocurrent responses compared to previously described hematite films, good stability, and excellent spatial resolution for potential imaging applications. The photoelectrochemical sensing capability of hematite NRs was demonstrated by a high pH sensitivity without modification. The modification of the hematite NRs with a thin poly(vinyl chloride) (PVC)-based ion-selective film allowed highly reversible amperometric detection of calcium ions with sensor materials traditionally employed in potentiometric devices.