Showing papers on "Hematite published in 2017"

Control of the shape and size of iron oxide (α-Fe2O3) nanoparticles synthesized through the chemical precipitation method

Abstract: Hematite (α-Fe 2 O 3 ) nanoparticles were synthesized via a simple chemical precipitation method. The impact of varying the concentration of precursor on the crystalline phase, size and morphology of α-Fe 2 O 3 products was explored. The characteristic of the synthesized hematite nanoparticles were evaluated by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FT-IR) spectroscopy, Raman spectroscopy, Differential Thermal Analysis (DTA), Thermo Gravimetric Analysis (TGA), Ultraviolet–Visible (UV–Vis) analysis and Photoluminescence (PL). XRD data revealed a rhombohedral (hexagonal) structure with the space group R -3 c in all samples. Uniform spherical like morphology was confirmed by TEM and SEM. The result revealed that the particle sizes were varied between 21 and 82 nm and that the increase in precursor concentration (FeCl 3 , 6H 2 O) is accompanied by an increase in the particle size of 21 nm for pure α-Fe 2 O 3 synthesized with [Fe 3+ ] = 0.05 M at 82 nm for pure α-Fe 2 O 3 synthesized with [Fe 3+ ] = 0.4 M. FT-IR confirms the phase purity of the nanoparticles synthesized. The Raman spectroscopy was used not only to prove that we have synthesized pure hematite but also to identify their phonon modes. The thermal behavior of compound was studied by using TGA/DTA results: The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. Besides, the optical investigation revealed that samples have an optical gap of about 2.1 eV and that this value varies as a function of the precursor concentration.

Morphology and Doping Engineering of Sn-Doped Hematite Nanowire Photoanodes

Abstract: High-temperature activation has been commonly used to boost the photoelectrochemical (PEC) performance of hematite nanowires for water oxidation, by inducing Sn diffusion from fluorine-doped tin oxide (FTO) substrate into hematite. Yet, hematite nanowires thermally annealed at high temperature suffer from two major drawbacks that negatively affect their performance. First, the structural deformation reduces light absorption capability of nanowire. Second, this “passive” doping method leads to nonuniform distribution of Sn dopant in nanowire and limits the Sn doping concentration. Both factors impair the electrochemical properties of hematite nanowire. Here we demonstrate a silica encapsulation method that is able to simultaneously retain the hematite nanowire morphology even after high-temperature calcination at 800 °C and improve the concentration and uniformity of dopant distribution along the nanowire growth axis. The capability of retaining nanowire morphology allows tuning the nanowire length for opt...

Ascorbate-Promoted Surface Iron Cycle for Efficient Heterogeneous Fenton Alachlor Degradation with Hematite Nanocrystals

Abstract: This study reports the H2O2 activation with different hematite nanocrystals and ascorbate ions for the herbicide alachlor degradation at pH 5. We found that hematite nanoplates (HNPs) exposed with {001} facets exhibited better catalytic performance than hematite nanocubes (HNCs) exposed with {012} facets, which was attributed to the formation of inner-sphere iron–ascorbate complexes on the hematite facets. The 3-fold undercoordination Fe cations of {001} facet favors the formation of inner-sphere iron–ascorbate complexes, while the 5-fold undercoordination Fe cations of {012} facet has stereo-hindrance effect, disfavoring the complex formation. The surface area normalized alachlor degradation rate constant (23.3 × 10–4 min–1 L m–2) of HNPs–ascorbate Fenton system was about 2.6 times that (9.1 × 10–4 min–1 L m–2) of HNCs–ascorbate counterpart. Meanwhile, the 89.0% of dechlorination and 30.0% of denitrification in the HNPs–ascorbate Fenton system were also significantly higher than those (60.9% and 13.1%) o...

Structural, optical, magnetic and electrical properties of hematite (α-Fe 2 O 3 ) nanoparticles synthesized by two methods: polyol and precipitation

Abstract: Hematite (α-Fe2O3) nanoparticles have been successfully synthesized via two methods: (1) polyol and (2) precipitation in water. The influence of synthesis methods on the crystalline structure, morphological, optical, magnetic and electrical properties were investigated using X-ray diffraction, RAMAN spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), superconducting quantum interference device and impedance spectroscopy. The structural properties showed that the obtained hematite α-Fe2O3 nanoparticles with two preparation methods exhibit hexagonal phase with high crystallinity and high-phase stability at room temperature. It was found that the average hematite nanoparticle size is estimated to be 36.86 nm for the sample synthesized by precipitation and 54.14 nm for the sample synthesized by polyol. Moreover, the optical properties showed that the band gap energy value of α-Fe2O3 synthesized by precipitation (2.07 eV) was higher than that of α-Fe2O3 synthesized by polyol (1.97 eV) and they showed a red shift to the visible region. Furthermore, the measurements of magnetic properties indicated a magnetization loop typical of ferromagnetic systems at room temperature. Measurements of electrical properties show higher dielectric permittivity (5.64 × 103) and relaxation phenomenon for α-Fe2O3 issued from the precipitation method than the other sample.

Scandium speciation in a world-class lateritic deposit

Abstract: Scandium (Sc) has unique properties, highly valued for many applications. Future supply is expected to rely on unusually high-grade (up to 1000 ppm) lateritic Sc ores discovered in Eastern Australia. To understand the origin of such exceptional concentrations, we investigated Sc speciation in one of these deposits. The major factors are unusually high concentrations in the parent rock together with lateritic weathering over long time scales in a stable tectonic context. At microscopic and atomic scales, by combining X-ray absorption near edge structure spectroscopy, X-ray diffraction and microscopic and chemical analyses, we show that Sc-rich volumes are associated with iron oxides. In particular, Sc adsorbed on goethite accounts for ca 80 % of the Sc budget in our samples. The remaining is incorporated in the crystal structure of hematite, substituting for Fe3+. Scandium grades reflect the high capacity of goethite to adsorb this element. In contrast, the influence of hematite is limited by the low levels of Sc that its structure can incorporate. These crystal-chemical controls play a major role in lateritic Sc deposits developed over ultramafic–mafic rocks.

New insight into the roles of oxygen vacancies in hematite for solar water splitting

Abstract: Oxygen vacancies play an important role in the performance improvement of oxide semiconductors as photoanodes for water splitting, such as TiO2, WO3, and Fe2O3 Conductivity improvement due to the presence of oxygen vacancies was reported to be the main reason for the enhanced performance However, oxygen vacancies may also affect light absorption and charge transfer through the solid/electrolyte interface The roles of oxygen vacancies have not been thoroughly discussed in the past Herein, with hematite as an example, the effects of oxygen vacancies on bulk charge transport and surface catalysis are quantitatively analyzed by decoupling photon absorption, interfacial charge transfer and charge separation processes Oxygen vacancies improve the charge separation of both pristine and Ti-doped hematite However, opposite observations are found in the charge transfer process for pristine and Ti-doped hematite: the positive effect in pristine hematite but the negative effect in the Ti-doped one An electrochemical technique is used to analyze the different influences on pristine and Ti-doped hematite to unravel the mechanism of the opposite observations caused by oxygen vacancies The current study sheds lights on how oxygen vacancies affect various aspects of important factors behind PEC performance, which is helpful to the development of more efficient photoanodes in the future

Microwave-assisted ammonia decomposition reaction over iron incorporated mesoporous carbon catalysts

Abstract: Microwave-assisted ammonia decomposition reaction was investigated to produce COx free hydrogen, for fuel cell applications. Iron incorporated mesoporous carbon catalysts were prepared at different metal loadings, following an impregnation procedure. Mesoporous carbon acted as the catalyst support, as well as the microwave receptor. Complete conversion of ammonia was achieved at 450 °C over the catalyst having 7.7 wt% Fe, when the reaction was carried out in the microwave reactor system, using pure ammonia (GHSV of 36000 ml/h gcat). However, in the case of using the conventionally heated reactor, complete conversion of ammonia was achieved only at 600 °C. Iron oxides, namely maghemite (γ-Fe2O3), magnetite (Fe3O4) and hematite (α-Fe2O3) simultaneously appeared in the structure of the synthesized catalysts, after their calcination at 450 °C, under pure N2 flow. Iron oxides present in the calcined catalytic materials then were reduced to metallic iron at 500 °C. Formation of iron carbide crystals was observed in the structure of spent catalysts that were used in microwave reactor system, while metallic iron crystals were still present in the catalysts that were tested in conventionally heated system.

Synthesis, characterization, and catalytic applications of hematite (α-Fe2O3) nanoparticles as reusable nanocatalyst

Abstract: A novel magnetically recoverable hematite nanoparticles (α-Fe2O3 NPs) was fabricated by a simple, one pot, and green method using the rhizome of Cyperus rotundus L., as a reducing and stabilizing agent. The prepared nanoparticles were well characterized by all parameters. TEM showed that the hematite nanoparticles had a rhombohedral shape and ranged in size from 80 to 100 nm. The phase study of the α-Fe2O3 nanoparticles was confirmed by Raman spectroscopy. In addition, the synthesized nanoparticles shows good photocatalytic activity in degradation of highly toxic Congo red dye within 25 min, and the same NPs exhibits higher catalytic activity for the reduction of 4-nitro-o-phenylenediamine (4-NPD) to 1,2,4-benzenetriamine in the presence of NaBH4 within 12 min. After the reaction, the catalyst was recovered and reused three times without significant loss of catalytic activity.

Optimization of charge transport in a Co–Pi modified hematite thin film produced by scalable electron beam evaporation for photoelectrochemical water oxidation

Abstract: Hematite (α-Fe2O3) is an attractive candidate for photoelectrochemical (PEC) hydrogen generation by oxidation of water due to its low cost, earth-abundance and appropriate bandgap. However, large scale production of hematite thin films with efficient PEC performance is a challenging problem in the field. In this article, based on an electron beam evaporation method, we provide a scalable route for preparation of a Co–Pi modified hematite thin film with efficient solar water oxidation properties. To our knowledge, no work has been done on photoelectrochemical characterization of Co–Pi modified hematite films prepared based on electron beam evaporation. We show that by optimization of deposition conditions including the film thickness and annealing temperature and performing the deposition in an oxygen medium, an efficient PEC performance is achieved from the produced pristine hematite photoanode. By various characterizations including XRD, EDX, SEM, transient photocurrent and I–V measurements, and impedance spectroscopy, it is shown that the efficient performance is attributed to the improved crystalline structure and suppression of recombination centres originated from the defects in bulk and surface of the hematite layer. Also with deposition of different thicknesses of Co–Pi electro-catalysts on the hematite layer, the optimum structure for fast water oxidation and charge transfer kinetics across the interface of the photoanode and electrolyte is obtained. The most efficient photoanode delivers up to 1.5 (mA cm−2) at the potential of 1.5 V versus the reversible hydrogen electrode (RHE), which is among the large value photocurrents attained from a hematite-based photoanode, but with the advantage of large scale production capability of the proposed method of this work.

Ascorbate Induced Facet Dependent Reductive Dissolution of Hematite Nanocrystals

Abstract: The interaction between ascorbate and hematite facets was systematically investigated with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, density functional theory (DFT) calculation, and kinetics model. Results of ATR-FTIR spectroscopy and DFT calculation suggested formation of nonprotonated inner-sphere bidentate mononuclear and monodentate mononuclear iron–ascorbate complexes on the hematite {001} and {012} facets, respectively. The estimated reductive dissolution rate constants at pH 5.0 were (4.04 ± 0.16) × 10–4 and (1.59 ± 0.14) × 10–4 min–1 for hematite nanoplates and nanocubes, respectively, indicating that the bidentate mononuclear iron–ascorbate complexes on the {001} facets favored the hematite reductive dissolution process than the monodentate mononuclear iron–ascorbate counterparts on the {012} facets. These results also revealed that the hematite facet reduction with ascorbate was strongly dependent on the iron–ascorbate complexes formed on the hematite facet...

Synergistic effect of co-existence of hematite (α-Fe2O3) and magnetite (Fe3O4) nanoparticles on graphene sheet for dye adsorption

Abstract: Graphene oxide (GO) functionalized with hematite (α-Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) nanoparticles (rGO-Fe 2 O 3 –Fe 3 O 4 ) was prepared using a facile one-step co-precipitation technique. It shows superior performance towards methylene blue (MB) adsorption for water purification, compared to GO functionalized with hematite (rGO-Fe 2 O 3 ) or magnetite (rGO-Fe 3 O 4 ) nanoparticles. It also shows better performance compared to a composite mixture of rGO-Fe 2 O 3 and rGO-Fe 3 O 4 (rGO-M). It has been postulated that the co-existence of hematite and magnetite nanoparticles on graphene sheet causes the synergistic effect towards MB adsorption. The adsorption behaviour of GO, reduced graphene oxide (rGO), rGO-Fe 2 O 3 , rGO-Fe 3 O 4 , rGO-Fe 2 O 3 –Fe 3 O 4 and rGO-M was studied. These materials were characterized using XRD, XPS, Raman spectroscopy, TGA, TEM, VSM and BET surface area analyzer. The phases present in the as-synthesized adsorbents were identified by XRD, Raman and XPS techniques. TGA studies confirmed the strong bonding between iron oxide particles and graphene sheet. TEM characterization was used for nanoparticles morphology and size distribution studies. Kinetics of MB adsorption was well described by the pseudo second order model. Langmuir adsorption isotherm better fits the equilibrium adsorption behaviour of rGO-Fe 2 O 3 –Fe 3 O 4 as compared to Freundlich isotherm and the maximum adsorption capacity was determined to be 72.8 ± 2.7 mg/g. Regeneration and reusability studies performed on rGO-Fe 2 O 3 –Fe 3 O 4 revealed that it retains more than 65% of the original adsorption capacity even after 3 cycles thus making it a potential candidate for water treatment.