Showing papers on "Hematite published in 2020"

Sulfurized oolitic hematite as a heterogeneous Fenton-like catalyst for tetracycline antibiotic degradation

Abstract: A sulfurized oolitic hematite (SOH-600) was prepared successfully via annealing oolitic hematite in hydrogen sulfide and was investigated as a heterogeneous Fenton catalyst for the degradation of tetracycline. The physicochemical properties of SOH-600 before and after reaction were characterized by XRF, XRD, XPS, SEM and FT-IR. The influence of the experimental parameters on the performance of SOH-600, including SOH-600 dosage, initial H2O2 concentration, and initial solution pH, was systematically investigated. The results showed that the degradation process of TC followed the second-order kinetic model and that the degradation efficiency increased along with increasing SOH-600 dosage, increasing initial H2O2 concentration, and decreasing initial solution pH under the experimental conditions. Moreover, SOH-600 exhibited an excellent recycling performance and a high catalytic efficiency (>90%) after five cycles. UV–vis, TOC, ESR, and HPLC-MS analyses were used to reveal that the OH formed in the SOH-600/H2O2 system was mainly responsible for the degradation of TC, and the degradation pathway of TC was proposed.

Mineralogy of Vera Rubin Ridge From the Mars Science Laboratory CheMin Instrument

Abstract: Vera Rubin ridge (VRR) is an erosion‐resistant feature on the northwestern slope of Mount Sharp in Gale crater, Mars, and orbital visible/short‐wave infrared measurements indicate it contains red‐colored hematite The Mars Science Laboratory Curiosity rover performed an extensive campaign on VRR to study its mineralogy, geochemistry, and sedimentology to determine the depositional and diagenetic history of the ridge and constrain the processes by which the hematite could have formed X‐ray diffraction (XRD) data from the CheMin instrument of four samples drilled on and below VRR demonstrate differences in iron, phyllosilicate, and sulfate mineralogy and hematite grain size Hematite is common across the ridge, and its detection in a gray‐colored outcrop suggested localized regions with coarse‐grained hematite, which commonly forms from warm fluids Broad XRD peaks for hematite in one sample below VRR and the abundance of FeO_T in the amorphous component suggest the presence of nano‐crystalline hematite and amorphous Fe oxides/oxyhydroxides Well‐crystalline akaganeite and jarosite are present in two samples drilled from VRR, indicating at least limited alteration by acid‐saline fluids Collapsed nontronite is present below VRR, but samples from VRR contain phyllosilicate with d(001) = 96 A, possibly from ferripyrophyllite or an acid‐altered smectite The most likely cementing agents creating the ridge are hematite and opaline silica We hypothesize late diagenesis can explain much of the mineralogical variation on the ridge, where multiple fluid episodes with variable pH, salinity, and temperature altered the rocks, causing the precipitation and crystallization of phases that are not otherwise in equilibrium

Hematite and Magnetite Nanostructures for Green and Sustainable Energy Harnessing and Environmental Pollution Control: A Review

Abstract: The optoelectrical and magnetic characteristics of naturally existing iron-based nanostructures, especially hematite and magnetite nanoparticles (H-NPs and M-NPs), gained significant research inter...

Introduction of magnetic and supermagnetic nanoparticles in new approach of targeting drug delivery and cancer therapy application

Abstract: In this article, the recent applications of different types of magnetic nanoparticles such as α-Fe2O3 (hematite), γ-Fe2O3 (maghemite), Fe3O4 (magnetite), hexagonal (MFe12O19), garnet (M3Fe5...

Synthesis and characterization of biogenic iron oxides of different nanomorphologies from pomegranate peels for efficient solar hydrogen production

Abstract: An eco-friendly green synthesis of mesoporous iron oxide (hematite) using pomegranate peels through a low-cost and massive product method was investigated. The mass of pomegranate peels was varied to control the morphology of the produced hematite (Fe2O3). The structures, textures and optical properties of the products were investigated by FTIR, XRD, FE-SEM, and UV–Vis spectroscopy. Three different Fe2O3 morphologies were obtained; Fe2O3(I) nanorod like shape, Fe2O3(II) nanoparticles, and Fe2O3(III) nanoporous structured layer. The bandgap values for Fe2O3 (I), (II) and (III) were 2.71, 2.95, and 2.29 eV, respectively. The newly hematite samples were used as promising photoelectrodes supported on graphite substrate for the photoelectrochemical (PEC) water splitting toward the efficient production of solar hydrogen. The number of generated hydrogen moles was calculated per active area to be 50 μmol h−1 cm−2 for electrode III, which decreased to 15.3 μmol h−1 cm−2 for electrode II. The effects of temperature (30–70 °C) on the PEC behavior of the three electrodes were addressed. Different thermodynamic parameters were calculated for the three electrodes, which showed activation energies of 13.4, 16.8, and 15.2 kJ mol−1, respectively. The electrode stability was addressed as a function of the number of runs and exposure time in addition to electrochemical impedance study. Finally, the conversion efficiency of the incident photon-to-current (IPCE) was estimated under the monochromatic illumination. The optimum value was ∼11% @ 390 nm for Fe2O3(III) electrode.

Zn Doped α-Fe2O3: An Efficient Material for UV Driven Photocatalysis and Electrical Conductivity

Abstract: Zinc (Zn) doped hematite (α-Fe2O3) nanoparticles with varying concentrations (pure, 2%, 4% and 6%) were synthesized via sol-gel method. The influence of divalent Zn ions on structural, optical and dielectric behavior of hematite were studied. X-ray diffraction (XRD) pattern of synthesized samples were indexed to rhombohedral R3c space group of hematite with 14–21 nm crystallite size. The lattice parameter (a and c) values increase upto Zn 4% and decrease afterwards. The surface morphology of prepared nanoparticles were explored using transmission electron microscopy (TEM). The band gap measured from Tauc’s plot, using UV-Vis spectroscopy, showed reduction in its values upto Zn 4% and the reverse trend was obtained in higher concentrations. The dielectric properties of pure and Zn doped hematite were investigated at room temperature and followed the same trends as that of XRD parameters and band gap. Photocatalytic properties of nanoparticles were performed for hazardous Rose bengal dye and showed effective degradation in the presence of UV light. Hence, Zn2+ doped hematite can be considered as an efficient material for the potential applications in the domain of photocatalysis and also higher value of dielectric constant at room temperature makes them applicable in high energy storage devices.

Synthesis of two-dimensional hematite and iron phosphide for hydrogen evolution

Abstract: Facile and scalable synthesis of two-dimensional (2D) non-layered materials is highly desirable for novel applications. Iron compounds including hematite (α-Fe2O3) and iron phosphide (FeP) are an important group of semiconductors but their 2D ultrathin morphology has been rarely reported. Here, we develop a water dissolvable template-based synthesis route to produce free-standing ultrathin iron compounds. Such a method also enables the tunability of morphology from mesoporous nanosheet to meso-macroporous hierarchical nanonet utilizing the aging process, while its corresponding surface active area is reduced simultaneously. Ultrathin hematite is relatively inert to electrochemical hydrogen evolution reaction (HER). However, FeP exhibits excellent catalytic performances with a relatively low overpotential of 117 mV and a Tafel slope of 56 mV dec−1, which is as a whole improved over those of reported free-standing binary transition-metal phosphide nanostructures. This work extends the possibility to produce high-quality 2D non-layered materials, which are expected to exhibit unique properties compared to their bulk counterparts.

Hematite iron oxide nanoparticles (α-Fe2O3): Synthesis and modelling adsorption of malachite green

Abstract: To study themalachite green(MG) removal from aqueous solution, iron oxide was prepared from iron(III) nitrate nonahydrate (Fe(NO3)3, 9H2O) and ammonium hydroxide (NH4OH). The Fe2O3characterizationwas examined by X-ray diffraction spectroscopy (XRD), Brunauer Emmett- Teller (BET) specific surface area measurements and Fourier transform infrared (FT-IR) spectroscopy. The data of malachite green Kinetics adsorptions, show that the adsorption followed pseudo-second order kinetics. For concentrations below 6.10−4 mol/l, MG solution was almost completely decolorized after 45 min. The elimination percentage reached 86.13% for the concentration 6.10−4 mol/l and 25 mg of the Hematite. The experimental isotherms were analyzed with Langmuir, Freundlich and Redlich–Peterson using non-linear regression. The results showed that the Freundlich isotherms best-fit the equilibrium data. The thermodynamic study has shown that MG adsorption on Hematite is endothermic (ΔH°>0); it increases with temperature. The negative ΔG° values showed that the MG adsorption process on the Hematite is spontaneous. However, the positive value of ΔS° indicates the increase in Hematite-solution interface disorder at the time of MG fixation.

Ultra‐Narrow Depletion Layers in a Hematite Mesocrystal‐Based Photoanode for Boosting Multihole Water Oxidation

Abstract: Significant charge recombination that is difficult to suppress limits the practical applications of hematite (α-Fe2 O3 ) for photoelectrochemical water splitting. In this study, Ti-modified hematite mesocrystal superstructures assembled from highly oriented tiny nanoparticle (NP) subunits with sizes of ca. 5 nm were developed to achieve the highest photocurrent density (4.3 mA cm-2 at 1.23 V vs. RHE) ever reported for hematite-based photoanodes under back illumination. Owing to rich interfacial oxygen vacancies yielding an exceedingly high carrier density of 4.1×1021 cm-3 for super bulk conductivity in the electrode and a large proportion of ultra-narrow depletion layers (<1 nm) inside the mesoporous film for significantly improved hole collection efficiency, a boosting of multihole water oxidation with very low activation energy (Ea =44 meV) was realized.

Conduction Band of Hematite Can Mediate Cytochrome Reduction by Fe(II) under Dark and Anoxic Conditions

Abstract: While it was recently reported that the conduction band of iron minerals can mediate electron transfer between Fe(II) and different Fe(III) lattice sites during Fe(II)-catalyzed mineral transformation, it is unclear whether such a conduction band mediation pathway occurs in the microbial Fe(II) oxidation system under dark and anoxic subsurface conditions. Here, using cytochrome c (c-Cyts) as a model protein of microbial Fe(II) oxidation, the in vitro kinetics and thermodynamics of c-Cyts reduction by Fe(II) were studied. The results showed that the rates of c-Cyts reduction were greatly enhanced in the presence of the semiconducting mineral hematite (Hem, α-Fe2O3). The electrochemical experiments separating Fe(II) and c-Cyts demonstrated that electrons from Fe(II) to the electrode or from the electrode to c-Cyts could directly penetrate hematite, resulting in enhanced current. Independent photochemical and photoluminescence experiments indicated that c-Cyts could be directly reduced by the conduction band electrons of hematite which were generated under light illumination. In c-Cyts+Fe(II)+Hem, the redox potential of Fe(II)-Hem was shifted from -0.15 to -0.18 V and that of c-Cyts+Hem changed slightly from -0.05 to -0.04 V. For the bulk hematite, Mott-Schottky plots illustrated that the flat band was shifted negatively and positively in the presence of Fe(II) and oxidized c-Cyts, respectively, and the surface electron/charge density was higher in the presence of Fe(II)/c-Cyts. As a consequence, the redox gradients from adsorbed Fe(II) to adsorbed c-Cyts allow electron transfer across the conduction band of hematite and facilitate c-Cyts reduction. This mechanistic study on conduction band-mediating electron transfer could help interpret the role of semiconducting minerals in the microbial Fe(II) oxidation process under dark anoxic conditions.

Iron Mobility during Diagenesis at Vera Rubin ridge, Gale Crater, Mars

Abstract: The Curiosity rover investigated a topographic structure known as Vera Rubin ridge, associated with a hematite signature in orbital spectra. There, Curiosity encountered mudstones interpreted as lacustrine deposits, conformably overlying the 300 m‐thick underlying sedimentary rocks of the Murray formation at the base of Mount Sharp. While the presence of hematite (α‐Fe₂O₃) was confirmed in‐situ by both Mastcam and ChemCam spectral observations and by the CheMin instrument, neither ChemCam nor APXS observed any significant increase in FeO_T (total iron oxide) abundances compared to the rest of the Murray formation. Instead, Curiosity discovered dark‐toned diagenetic features displaying anomalously high FeO_T abundances, commonly observed in association with light‐toned Ca‐sulfate veins but also as crystal pseudomorphs in the host rock. These iron‐rich diagenetic features are predominantly observed in “grey” outcrops on the upper part of the ridge, which lack the telltale ferric signature of other Vera Rubin ridge outcrops. Their composition is consistent with anhydrous Fe‐oxide, as the enrichment in iron is not associated with enrichment in any other elements, nor with detections of volatiles. The lack of ferric absorption features in the ChemCam reflectance spectra and the hexagonal crystalline structure associated with dark‐toned crystals points toward coarse “grey” hematite. In addition, the host rock adjacent to these features appears bleached and show low‐FeO_T content as well as depletion in Mn, indicating mobilization of these redox‐sensitive elements during diagenesis. Thus, groundwater fluid circulations could account for the remobilization of iron and recrystallization as crystalline hematite during diagenesis on Vera Rubin ridge.

Diagenesis of Vera Rubin Ridge, Gale Crater, Mars, From Mastcam Multispectral Images.

Abstract: Images from the Mars Science Laboratory (MSL) mission of lacustrine sedimentary rocks of Vera Rubin ridge on "Mt. Sharp" in Gale crater, Mars, have shown stark color variations from red to purple to gray. These color differences crosscut stratigraphy and are likely due to diagenetic alteration of the sediments after deposition. However, the chemistry and timing of these fluid interactions is unclear. Determining how diagenetic processes may have modified chemical and mineralogical signatures of ancient Martian environments is critical for understanding the past habitability of Mars and achieving the goals of the MSL mission. Here we use visible/near-infrared spectra from Mastcam and ChemCam to determine the mineralogical origins of color variations in the ridge. Color variations are consistent with changes in spectral properties related to the crystallinity, grain size, and texture of hematite. Coarse-grained gray hematite spectrally dominates in the gray patches and is present in the purple areas, while nanophase and fine-grained red crystalline hematite are present and spectrally dominate in the red and purple areas. We hypothesize that these differences were caused by grain-size coarsening of hematite by diagenetic fluids, as observed in terrestrial analogs. In this model, early primary reddening by oxidizing fluids near the surface was followed during or after burial by bleaching to form the gray patches, possibly with limited secondary reddening after exhumation. Diagenetic alteration may have diminished the preservation of biosignatures and changed the composition of the sediments, making it more difficult to interpret how conditions evolved in the paleolake over time.

Highly sensitive NO2 gas sensor based on hematite nanoparticles synthesized by sol–gel technique

Abstract: The sol–gel technique was utilized to synthesize α-Fe2O3 nanoparticles in supercritical conditions of ethanol. The morphology and microstructure were investigated by scanning and transmission electron microscopy (SEM and TEM) analysis and X-ray diffraction (XRD).The average crystallite size estimated by sherrer’s equation was 60 nm. TEM images show that the obtained powder is composed of agglomeration of irregular shaped (between oval and spherical) grains. The prepared nanomaterial was used as sensing layer in gas sensing device. The sensor has been tested towards low concentrations in air of NO2 at different temperatures from 200 to 350 °C. We noticed that 225 °C was the best operating temperature. At this temperature, the obtained results indicated that the realized sensor has a high response towards 1 ppm of NO2 gas. The response and recovery times are 26 and 48 s, respectively. To show the selectivity of the sensor, we have tested it with different gases such as CO, CO2, and NH3. We found that hematite sensor exhibits high selectivity towards NO2 gas.

Adsorption of polymers onto iron oxides: Equilibrium isotherms

Abstract: The interactions of polymers (corn starch, dextrin from maize starch, humic acid sodium salt and sodium carboxymethyl cellulose) with iron oxides (hematite and magnetite) have been investigated by measuring adsorption isotherms and by electrophoresis. According to the electrophoresis measurements at pH 7 both iron oxides present negative surface charge and positive at pH 5. The equilibrium adsorption isotherms were then determined at pH 7 for all the adsorbates except for humic acid which was studied at pH 5, due to its anionic characteristics. The equilibrium data of both iron oxides were studied using Freundlich and Langmuir models and it was found to best fit to the Freundlich one. The values for Freundlich constants indicate that the mechanism that contributes most to the adsorption process in all experiments was the hydrogen bonding. However, the coexistence of more than one adsorption mechanism is what best explains the process itself, in addition to explaining the differences found amongst theories over the years.