Size Of Hematite Nanoparticles Research Articles

Effect of Calcination Temperature on Activity of Fe2O3–Al2O3 Nanocomposite Catalysts in CO Oxidation

Nanocomposite Fe–Al oxide catalysts were prepared by the melting of iron and aluminum nitrates with the subsequent calcination in air at different temperatures. It was found that the catalysts calcined at 450 °C are more active in the oxidation of CO than the catalysts calcined at 700 °C. X-ray diffraction and X-ray photoelectron spectroscopy showed that all the catalysts consist of hematite, α-Fe2O3 nanoparticles, and Al2O3 in an amorphous state. Iron oxide is the active component, which provides the oxidation of CO, while alumina is a texture promoter. The increase in the calcination temperature leads to a minor increase in the average size of hematite nanoparticles and an insignificant decrease in the specific surface area. Kinetic measurements showed that the oxidation of CO over the Fe–Al catalysts calcined at 450 and 700 °C proceeds with the activation energy of 61–69 and 91 kJ/mol, respectively. This means that the low-temperature and high-temperature catalysts contain different active species. Temperature-programmed reduction with CO indicated that the decrease in the calcination temperature improves the reducibility of the Fe-Al nanocomposites. According to 57Fe Mossbauer spectroscopy, the low-temperature catalysts contain hydrated iron oxides (acagenite and ferrihydrite) and a significant amount of highly defective hematite, which is absent in the high-temperature catalyst. These species can provide the enhanced activity of the low-temperature catalysts in the oxidation of CO.

Structural, optical, magnetic and electrical properties of hematite (α-Fe2O3) nanoparticles synthesized by two methods: polyol and precipitation

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.

Influence of reducing agent concentration on the structure, morphology and ferromagnetic properties of hematite (α-Fe2O3) nanoparticles

Hematite (α-Fe2O3) nanoparticles are successfully synthesized by using the chemical reduction synthesis method. The obtained XRD results revealed the formation of rhombohedral crystal structure of hematite α-Fe2O3with R3c space group. Raman-forbidden LO Eu mode and E1g mode observed at 657, 409 and 285 are clearly revealed hematite α-Fe2O3 formation. The prominent PL peak observed at 576 nm is attributed to stronger 3d–4sp hybridization due to the impact of size and morphology effect on synthesized hematite (α-Fe2O3) nanoparticles. SEM analysis revealed that the estimated average hematite nanoparticle size is reduced to be about 600–300 nm with an increase in the concentration of the reducing agent. The investigation of the magnetic properties of hematite nanoparticles showed that the product synthesized at low NaBH4 concentration exhibited an extremely small hysteresis loop and low coercivity when compared to higher concentrations. The influence of reducing agent concentration on the structure, morphology and ferromagnetic properties of hematite (α-Fe2O3) nanoparticles are discussed comprehensively.

Considering the formation of hematite spherules on Mars by freezing aqueous hematite nanoparticle suspensions

The enigmatic and unexpected occurrence of coarse crystalline (gray) hematite spherules at Terra Meridiani on Mars in association with deposits of jarosite-rich sediments fueled a variety of hypotheses to explain their origin. In this study, we tested the hypothesis that freezing of aqueous hematite nanoparticle suspensions, possibly produced from low-temperature weathering of jarosite-bearing deposits, could produce coarse-grained hematite aggregate spherules. We synthesized four hematite nanoparticle suspensions with a range of sizes and morphologies and performed freezing experiments. All sizes of hematite nanoparticles rapidly aggregate during freezing. Regardless of the size or shape of the initial starting material, they rapidly collect into aggregates that are then too big to push in front of a stable advancing ice front, leading to incohesive masses of particles, rather than solid spherules. We also explored the effects of “seed” silicates, a matrix of sand grains, various concentrations of NaCl and CaCl2, and varying the freezing temperature on hematite nanoparticle aggregation. However, none of these factors resulted in mm-scale spherical aggregates. By comparing our measured freezing rates with empirical and theoretical values from the literature, we conclude that the spherules on Mars could not have been produced through the freezing of aqueous hematite nanoparticle suspensions; ice crystallization front instability disrupts the aggregation process and prevents the formation of mm-scale continuous aggregates.

Structural Characterization of Ferrihydrite/Hematite Nanocomposites and Their Arsenic Adsorption Properties

A rich variety of ferrihydrite/hematite nanocomposites (NCs) with specific size, composition and properties were obtained in transformation reactions of 2-line ferrihydrite. Transmission electron microscopy observations showed that the NCs consist of clusters of strongly aggregated nanoparticles (NPs) similarly to a “plum pudding”, where hematite NPs “raisins” are surrounded by ferrihydrite “pudding”. The arsenic adsorption performance of the NCs can be modified for As(III) and As(V) removal, which depends on the NCs composition and the size of hematite NPs. It was found that adequate ferrihydrite/hematite NCs adsorb As(III) faster than ferrihydrite. Otherwise, for As(V), the adsorption exhibited by NCs is slower that for pure ferrihydrite. The data of adsorption isotherms fitted better to the Freundlich model for both As(III) and As(V) adsorption. For all the samples, the model revealed that chemical adsorption is the favorable adsorption process. Additionally, for the ferrihydrite/hematite NCs, the capa...

Influence of hydrothermal synthesis conditions on size, morphology and colloidal properties of Hematite nanoparticles

The synthesis, morphological characterization, and colloidal properties of Hematite nanoparticles (hemNP) with different sizes and shapes were presented. To prepare hemNP we used hydrothermal synthesis with different combinations of reaction conditions. Various characterization techniques involving XRD, TEM, AFM and DLS were employed to describe the dependence of the hemNP size, charge and morphology on different synthesis conditions. Spheroidal Hematite nanoparticles from 20 to 60 nm were obtained by varying the rate of addition of iron precursor solutions and the aging time (Δt) at ca. 100∘C. The transformation from Ferrihydrite to Hematite (α-Fe2O3) started with a burst nucleation of nanosized crystallites, followed by a first-order kinetic growth of primary grains up to a final threshold size of ca 30 nm. Colloidal behavior was also checked at pH 4 and 7, finding interparticle aggregation at circumneutral pH only for hemNP obtained for Δt<2 h. Electrophoretic ζ potential measurements yield positive values at pH 4 and negative at pH 7. The shifts in (IEP) at lower values depended on the adsorption of appreciable counterions on the particle surface and reduced at pH 7 the charge–charge repulsion, whereas the attractive forces became predominant. The results confirmed that the particle size of the Hematite nanoparticle critically affected their colloidal behavior with significant consequences for sorption and aggregation processes. Particularly for low particle sizes of the order of 10–20 nm, the surface charge and surface reactivity also could differ in important ways compared to 40–60 nm size particles.

Formation of complexes between hematite nanoparticles and a non-conventional galactomannan gum. Toward a better understanding on interaction processes

The physicochemical characteristics of hematite nanoparticles related to their size, surface area and reactivity make them useful for many applications, as well as suitable models to study aggregation kinetics. For several applications (such as remediation of contaminated groundwater) it is crucial to maintain the stability of hematite nanoparticle suspensions in order to assure their arrival to the target place. The use of biopolymers has been proposed as a suitable environmentally friendly option to avoid nanoparticle aggregation and assure their stability. The aim of the present work was to investigate the formation of complexes between hematite nanoparticles and a non-conventional galactomannan (vinal gum — VG) obtained from Prosopis ruscifolia in order to promote hematite nanoparticle coating with a green biopolymer. Zeta potential and size of hematite nanoparticles, VG dispersions and the stability of their mixtures were investigated, as well as the influence of the biopolymer concentration and preparation method. DLS and nanoparticle tracking analysis techniques were used for determining the size and the zeta-potential of the suspensions. VG showed a polydispersed size distribution (300–475nm Z-average diameter, 0.65Pdi) and a negative zeta potential (between −1 and −12mV for pH2 and 12, respectively). The aggregation of hematite nanoparticles (3.3mg/L) was induced by the addition of VG at lower concentrations than 2mg/L (pH5.5). On the other hand, hematite nanoparticles were stabilized at concentrations of VG higher than 2mg/L. Several phenomena between hematite nanoparticles and VG were involved: steric effects, electrostatic interactions, charge neutralization, charge inversion and polymer bridging. The process of complexation between hematite nanoparticles and the biopolymer was strongly influenced by the preparation protocols. It was concluded that the aggregation, dispersion, and stability of hematite nanoparticles depended on biopolymer concentration and also on the way of preparation and initial physicochemical properties of the aqueous system.

Hematite nanoparticles in aquathermolysis: A desulfurization study of thiophene

The potential usage of hematite nanoparticles as heterogeneous catalysts in aquathermolysis was investigated in this work. The desulfurization of thiophene was studied to investigate the catalytic activity of hematite in the aquathermolysis of heavy oil. It was found that reaction conditions, e.g., reaction time and temperature, ratio between thiophene and water, hematite nanoparticle size, catalyst concentration, and the presence of hydrogen donors, influenced the ability of hematite nanoparticles to decompose thiophene. Experimental results showed that thiophene conversion was increased with reaction time, temperature and catalyst concentration but decreased with thiophene/water ratio and particle size. Further analysis showed that the activity of the hematite nanocatalyst was also reduced in the presence of hydrogen donors. This is because hydrogen donors occupy the catalyst surface and block the catalytic sites. Furthermore, FTIR and XRD analyses revealed that thiophene underwent oxidative desulfurization to produce maleic acid, SO2 and CO2, whereas some areas of the hematite surface were transformed into magnetite. However, this magnetite was re-oxidized back into hematite in the presence of water as the source of active oxygen.

Magnetic properties of hematite (α-Fe2O3) nanoparticles prepared by hydrothermal synthesis method

Hematite (α-Fe2O3) nanoparticles are successfully synthesized by using the hydrothermal synthesis method. An X-ray powder diffraction (XRPD) of the sample shows formation of the nanocrystalline α-Fe2O3 phase. A transmission electron microscopy (TEM) measurements show spherical morphology of the hematite nanoparticles and narrow size distribution. An average hematite nanoparticle size is estimated to be about 8nm by TEM and XRD. Magnetic properties were measured using a superconducting quantum interference device (SQUID) magnetometry. Investigation of the magnetic properties of hematite nanoparticles showed a divergence between field-cooled (FC) and zero-field-cooled (ZFC) magnetization curves below Tirr=103K (irreversibility temperature). The ZFC magnetization curve showed maximum at TB=52K (blocking temperature). The sample did not exhibit the Morin transition. The M(H) (magnetization versus magnetic field) dependence at 300K showed properties of superparamagnetic iron oxide nanoparticles (SPION). The M(H) data were successfully fitted by the Langevin function and magnetic moment μp=657μB and diameter d=8.1nm were determined. Furthermore, magnetic measurements showed high magnetization at room temperature (MS=3.98emu/g), which is desirable for application in spintronics and biomedicine. Core–shell structure of the nanoparticles was used to describe high magnetization of the hematite nanoparticles.

Control of hematite nanoparticle size and shape by the chemical precipitation method

Hematite (α-Fe2O3) nanoparticles were synthesized from the ferrihydrite precursor via a simple chemical precipitation method with trace amounts of Fe(II) as the catalyst under nitrogen atmosphere. The characteristic of the synthesized hematite particles were evaluated by XRD, FT-IR, and FE-SEM. The magnetic and electrical properties were studied by a vibrating sample magnetometer (VSM) and an electrometer, respectively. The synthesized products were of a single phase of the hexagonal structure hematite without any other impurities. The physical morphology of the synthesized hematite appears to be composed of a large number of very small particles appearing as the “raspberry shape”. The particle size of the synthesized hematite can be successfully controlled at 50–150nm, appearing as three different morphologies: the spherical-like, the cubic-like, and the ellipsoidal shape, through adjusting the synthesis conditions. The smallest particle possesses the highest electrical conductivity of 5.2×10−3s/cm. On the other hand, the largest particle exhibits weak ferromagnetism and the highest saturation magnetization (Ms) of 1.94emu/g, is higher than that of the smaller particle, which possesses the super-paramagnetic behavior. Furthermore, the different particle shapes are shown here to critically affect the electrical and magnetic properties of the nanoparticles.

Syntheses of Hematite (α-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;) Nanoparticles Using Microwave-Assisted Calcination Method

Hematite (α-Fe2O3) nanoparticles were synthesized from the solution of FeCl3.6H2O and NaOH in water using microwave-assisted calcination method. The syntheses were initially carried out by microwave heating and completed by a calcination process using a simple heating method. The effect of microwave heating time, calcination temperature, and calcination time were investigated. The XRD patterns demonstrated that the obtained nanoparticles are pure hematite. Using the Scherrer method, the average crystallite sizes of hematite nanoparticles were in the range of 35.6 to 54.4 nm. The obtained hematite nanoparticles were spherical with the average particle sizes ranging from 91 to 116 nm as confirmed by the SEM images.

Modeling temperature and reaction time impacts on hematite nanoparticle size during forced hydrolysis of ferric chloride

On the hypothesis that a mathematical relationship exists between synthesis conditions and hematite nanoparticle (NP) sizes, an empirical model was developed by synthesizing hematite NPs at different temperatures and hydrolysis times, and then correlating them with the obtained NP sizes. We found that the hematite NP sizes can be described by a simple relationship, dP=(0.49×T−26.4)×t0.33. The predictive capabilities of the model were validated by synthesizing NPs at randomly selected experimental conditions and comparing them to the model predictions. The experimental findings suggested that the model may be limited to predicting NP sizes smaller than 50nm because of a possible shift from a slow, hydrolysis-driven growth mechanism to a mechanism characterized by rapid aggregation of the existing NPs.

Human intestinal epithelial cells exhibit a cellular response indicating a potential toxicity upon exposure to hematite nanoparticles

This study examined the effects of different-sized nanoparticles on potential cytotoxicity in intestinal epithelia. Three sizes of hematite nanoparticles were used for the study at a 10ppm concentration: 17, 53, and, 100nm. Results indicate that, of the hematite nanoparticles tested, 17nm was more toxic to the epithelial integrity than 53 or 100nm. In addition, the epithelial integrity was affected by disruption of epithelial structures such as apical microvilli, and by disruption of the cell-cell junctions leading to reduction in transepithelial electrical resistance measurements (TEER). The drop in TEER was caused by disruption of the adhering junctions not by cell death, as determined by immunocytochemistry, and by using a cell viability assay. Epithelial integrity was also affected at the molecular level as shown by differential expression of genes related to cell junction maintenance, which was assessed by microarray analysis. In conclusion, the 17- and 100-nm hematite nanoparticles caused significant structural changes in the epithelium but not the 53nm nanoparticles. Also, different-sized hematite nanoparticles each had different effects both at the cellular level and genetic level.

Size-Dependent Pb Sorption to Nanohematite in the Presence and Absence of a Microbial Siderophore

This study focused on the effects of particle size (40, 8.6, and 3.6 nm) and the presence of the microbial ligand desferrioxamine B (DFOB) on Pb(II) sorption to hematite, based on sorption edge experiments (i.e., sorption as a function of pH). Effects of hematite nanoparticle size on sorption edges, when plotted either as sorption density or as % Pb uptake, depended on whether the experiments were normalized to account for differences in specific surface area within the reaction vessels or postnormalized after the fact. Accounting for specific surface area within reaction vessels is needed to maintain comparable ratios of sorbate to sorbent surface sites. When normalized for BET specific surface area (A(s,BET)) within the reaction vessels, the Pb(II) sorption edge shifted ∼0.5 pH units to the left for <10 nm hematite particles, but maximum sorption density (at pH ≥ 6) was unaffected by particle size. DFOB had little or no effect on Pb(II) sorption to <10 nm particles, but DFOB decreased Pb(II) sorption to the 40 nm particles at pH ≥ 6 by ∼20%. Hematite (nano)particle size thus exerts subtle effects on Pb(II) sorption, but the effects may be more pronounced in the presence of a metal complexing agent.

A magnetic zeolitic nanocomposite from occlusion of silica-coated iron species by crystalline titanosilicate-1

This paper examines the preparation of novel magnetic zeolitic nanocomposites from the occlusion of silica-coated iron species by crystalline titanosilicate-1. The results revealed that well-crystallized TS-1 could be synthesized in the presence of silica-hematite nanoparticles. Each as-made nanocomposite particle exhibited a compact and monolithic ‘brick-like’ morphology with a size of ca. 400 nm × 200 nm × 200 nm. The non-magnetic hematite (iron oxide) in such an as-made nanocomposite can be reduced by hydrogen to produce ferrimagnetic iron oxides and ferromagnetic elemental iron. The resultant nanocomposite consists of TS-1 as outer shell, which occludes a small portion of silica-iron species as the core with a total magnetization value of 3.7 emu/g. The silica coating and size of hematite nanoparticles, the presence of ammonium carbonate as the crystallization-mediating agent for nucleation and growth of TS-1 are critical factors when preparing such nanocomposites.

Microbial Reduction of Fe(III) in Hematite Nanoparticles by Geobacter sulfurreducens

The rates of microbial Fe(III) reduction of three sizes of hematite nanoparticles by Geobacter sulfurreducens were measured under two H2 partial pressures (0.01 and 1 atm) and three pH (7.0, 7.5, and 8.0) conditions. Hematite particles with mean primary particle sizes of 10, 30, and 50 nm were synthesized by a novel aerosol method that allows tight control of the particle size distribution. The mass-normalized reduction rates of the 10 and 30 nm particles were comparable to each other and higher than the rate for the 50 nm particles. However, the surface area-normalized rate was highest for the 30 nm particles. Consistent with a previously published model, the reduction rates are likely to be proportional to the bacteria-hematite contact area and not to the total hematite surface area. Surface area-normalized iron reduction rates were higher than those reported in previous studies, which may be due to the sequestration of Fe(II) through formation of vivianite. Similar initial reduction rates were observed under all pH and H2 conditions studied.