Two-line Ferrihydrite Research Articles

Ultrastructure and potential sub-seafloor evidence of bacteriogenic iron oxides from Axial Volcano, Juan de Fuca Ridge, north-east Pacific Ocean

Iron oxides from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge, were found to consist predominantly of microbial structures in hydrated whole mounts examined using an environmental scanning electron microscope. Novel observations were made of the iron oxides revealing the spatial relationships of the bacteria within to be more consistent with microbial mats than mineral precipitates. The bacterial structures are attributed to the sheaths of Leptothrix ochracea, the stalks of Gallionella ferruginea, and the filaments of a novel iron oxidizing PV-1 strain, based on the distinctive morphological characteristics of these three bacteria. Energy dispersive X-ray spectroscopy revealed the presence and distribution of Fe, Si, and Cl on the bacterial sheaths, stalks and filaments. The iron oxides were identified by X-ray diffraction to be two-line ferrihydrite, a poorly ordered iron oxyhydroxide. Adsorption of Si in particular to two-line ferrihydrite likely contributes to its stability on the seafloor, and might also be a preservation mechanism creating microfossils of the bacterial structures encrusted with ferrihydrite. Presumptive evidence of the sub-seafloor presence of L. ochracea, G. ferruginea and PV-1 at Axial Volcano was obtained from the presence of these bacteria on a trap that had been placed within an active vent, and also in a vent fluid sample. If indeed these bacteria are present in the sub-seafloor, it may be an indication that the surface expression of iron oxide deposits at Axial Volcano is minimal in comparison to what exists beneath the seafloor.

Magnetic study of iron sorbitol

A magnetic study of iron sorbitol, an iron-containing drug to treat the iron deficiency anemia is presented. Transmission electron microscopy reveals that the system contains nanometric particles with an average diameter of 3 nm whose composition is close to two-line ferrihydrite. The characterisation by magnetisation and AC susceptibility measurements indicates superparamagnetic behaviour with progressive magnetic blocking starting at 8 K. The quantitative analysis of the magnetic results indicates that the system consists of an assembly of very small magnetic moments, presumably originated by spin uncompensation of the antiferromagnetic nanoparticles, with Arrhenius type magnetic dynamics.

Adsorption of arsenate and arsenite on ferrihydrite in the presence and absence of dissolved organic carbon.

The adsorption of As(V) and As(III) on synthetic two-line ferrihydrite in the presence and absence of a peat humic acid (HAp), Suwannee River fulvic acid (FA), or citric acid (CA) was investigated. Previous work with goethite has demonstrated the ability of dissolved organic carbon (DOC) to decrease As(V) and As(III) adsorption. The results obtained demonstrate that As(V) adsorption on ferrihydrite was decreased only in the presence of CA. Arsenate decreased the adsorption of all organic acids except HAp. Both FA and CA reduced As(III) adsorption on ferrihydrite, while HAp had no effect. Fulvic and citric acid adsorption on ferrihydrite was decreased in the presence of As(III); however, FA and CA adsorption increased at lower pH, which was consistent with decreased As(III) adsorption. Peat humic acid did not decrease As(III) adsorption, and we believe that the adsorption process of HAp and As(III) and As(V) on ferrihydrite are independent of each other. Previously, we observed that As(V) adsorption on goethite decreased in the presence of HAp > FA > CA, while As(III) adsorption on goethite was decreased similarly to that on ferrihydrite in the presence of CA > FA approximately HAp, yet As(III) adsorption on ferrihydrite was greater than on goethite. The observed differences between this study and the earlier study on goethite are believed to be an intricate function of ferrihydrite's surface characteristics, which affect the mechanisms of adsorption and hence the affinity of organic acids such as HAp, FA, and CA for the ferrihydrite surface. As such, the adsorption of DOCs to ferrihydrite are assumed to be less favorable and to occur with a fewer number of ligands, resulting in lower surface coverage of weaker bond strength.

Biomineralization of Poorly Crystalline Fe(III) Oxides by Dissimilatory Metal Reducing Bacteria (DMRB)

Dissimilatory metal reducing bacteria (DMRB) catalyze the reduction of Fe(III) to Fe(II) in anoxic soils, sediments, and groundwater. Two-line ferrihydrite is a bioavailable Fe(III) oxide form that is exploited by DMRB as a terminal electron acceptor. A wide variety of biomineralization products result from the interaction of DMRB with 2-line ferrihydrite. Here we describe the state of knowledge on the biotransformation of synthetic 2-line ferrihydrite by laboratory cultures of DMRB using select published data and new experimental results. A facultative DMRB is emphasized ( Shewanella putrefaciens ) upon which most of this work has been performed. Key factors controlling the identity of the secondary mineral suite are evaluated including medium composition, electron donor and acceptor concentrations, ferrihydrite aging/recrystallization status, sorbed ions, and co-associated crystalline Fe(III) oxides. It is shown that crystalline ferric (goethite, hematite, lepidocrocite), ferrous (siderite, vivianite), and mixed valence (magnetite, green rust) iron solids are formed in anoxic, circumneutral DMRB incubations. Some products are well rationalized based on thermodynamic considerations, but others appear to result from kinetic pathways driven by ions that inhibit interfacial electron transfer or the precipitation of select phases. The primary factor controlling the nature of the secondary mineral suite appears to be the Fe(II) supply rate and magnitude, and its surface reaction with the residual oxide and other sorbed ions. The common observation of end-product mineral mixtures that are not at global equilibrium indicates that microenvironments surrounding respiring DMRB cells or the reaction-path trajectory (over Eh-pH space) may influence the identity of the final biomineralization suite.

Intracellular iron minerals in a dissimilatory iron-reducing bacterium.

Among prokaryotes, there are few examples of controlled mineral formation; the formation of crystalline iron oxides and sulfides [magnetite (Fe3O4) or greigite (Fe3S4)] by magnetotactic bacteria is an exception. Shewanella putrefaciens CN32, a Gram-negative, facultative anaerobic bacterium that is capable of dissimilatory iron reduction, produced microscopic intracellular grains of iron oxide minerals during growth on two-line ferrihydrite in a hydrogen-argon atmosphere. The minerals, formed at iron concentrations found in the soil and sedimentary environments where these bacteria are active, could represent an unexplored pathway for the cycling of iron by bacteria.

Effect of Si doping on the electron spin resonance properties of ferrihydrite nanoparticles

Electron spin resonance investigations at 9.24 GHz in Si-doped two-line ferrihydrite (Si/FeOOH/spl middot/nH/sub 2/O) nanoparticles of size /spl sime/4 nm are reported for x=Si/(Si+Fe)=0, 0.02, 0.05, 0.10 and 0.15. For all samples, a single broad resonance near g/spl sime/2 is observed; however with increase in x, both the resonance field H/sub r/ and linewidth /spl Delta/H increase but integrated intensity I of the line decreases, similar to the observed decrease in magnetization with x. These observations suggest that the observed resonance is due to uncompensated Fe/sup 3+/ surface spins. Temperature variation (300 K to 80 K) of H/sub r/ and /spl Delta/H for x=0.05 shows a downward shift (/spl delta/H/sub r/) of the line with a rapid increase in /spl Delta/H so that /spl delta/H/sub r//spl prop/(/spl Delta/H)/sup 3/ predicted for randomly oriented nanoparticles is observed.

Atrazine, isoproturon, mecoprop, 2,4-D, and bentazone adsorption onto iron oxides.

Iron oxides are important components influencing the adsorption of various inorganic and organic compounds in soils and sediments. In this study the adsorption on iron oxides of nonionic and ionic pesticides was determined as a function of solution pH, ionic strength, and pesticide concentration. The investigated iron oxides included two-line ferrihydrite, goethite, and lepidocrocite. Selected pesticides comprised atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine), isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea)], mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propionic acid], 2,4-D (2,4-dichlorophenoxyacetic acid), and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. The adsorption of the nonionic pesticides (atrazine and isoproturon) was insignificant, whereas the adsorption of the acidic pesticides (mecoprop, 2,4-D, and bentazone) was significant on all investigated iron oxides. The adsorption capacity increased with decreasing pH, with maximum adsorption reached close to the pKa values. The addition of CaCl2 in concentrations from 0.0025 to 0.01 M caused the adsorption capacity to diminish. The adsorption of bentazone was significantly lower than the adsorption of mecoprop and 2,4-D, illustrating the importance of a carboxyl group in the pesticide structure. The adsorption capacity on the iron oxides increased in the order: lepidocrocite < goethite < two-line ferrihydrite. The maximum adsorption capacities of meco-prop and 2,4-D on goethite were found to be equivalent to the site density of singly coordinated hydroxyl groups on the faces of the dominant (110) form, suggesting that singly coordinated hydroxyl groups are responsible for adsorption. Differences in adsorption capacities between iron oxides can be explained by differences in the surface site density of singly coordinated hydroxyl groups. The maximum measured adsorption capacity of mecoprop on two-line ferrihydrite was equivalent to 0.2 mol/mol Fe.

Structure of synthetic 6-line ferrihydrite by electron nanodiffraction

Single-crystal electron diffraction patterns of nanocrystals in two samples of synthetic six-line ferrihydrite (6LFh) were obtained using electron nanodiffraction to produce diffraction patterns from areas between ~0.7 and 5 nm across. One of the samples was synthesized at 75 °C by a conventional method; the other was synthesized by a recently developed room-temperature technique. Structures of individual nanocrystals were investigated by comparing experimental and simulated electron-diffraction patterns. The most common structure in each sample is based on double-hexagonal (ABAC) stacking of close-packed oxygen layers, and is similar to the “defect-free ferrihydrite” structure proposed by Drits and co-workers. Nanocrystals with maghemite- or magnetite-like structures and structures similar to those in two-line ferrihydrite (2LFh) occur less commonly in both samples. The sample synthesized at room temperature has a small amount of hematite, which was not found in nanodiffraction patterns from the 75 °C sample. The most common structure in 6LFh is distinct from those previously determined by nanodiffraction of 2LFh, indicating that 6LFh is not simply a more crystalline form of 2LFh.

The effect of clay minerals on the formation of goethite and hematite from ferrihydrite after 16 years’ ageing at 25°C and pH 4 – 7

AbstractIn soils and other weathering environments, hematite and goethite are usually formed in the presence of clay minerals. Two-line ferrihydrite was aged in the presence of six different clay minerals in aqueous suspension at 25°C and pH 4, 5, 6 and 7 for 16 years. The transformation into hematite/goethite mixtures was complete in the systems with gibbsite, kaolinite, illite and smectite, but incomplete in those with soil smectite and allophane. Soil smectite and allophane, as well as increasing pH, favoured hematite over goethite. The grainy and multi-domainic hematite crystals in the allophane system contained Si and Al (EDX) and showed a Si – O vibration at ∼920 cm– 1(FTIR). The unit-cell contraction due to structural Al was counteracted by structural OH, which was removed at 200°C. Heating also increased the magnetic hyperfine field at RT by 1.2 – 1.6 T. Hematite crystals with irregular shape and grainy interior have also been observed in soils.

Structure of synthetic 2-line ferrihydrite by electron nanodiffraction

Comparison of experimental single-crystal electron diffraction patterns of synthetic two-line ferrihydrite (2LFh) with simulated single-crystal electron-diffraction patterns indicates that a synthetic 2LFh sample contains highly disordered material and nanocrystals with structures based on hexagonal (ABAB) and cubic (ABC) stacking of close-packed layers of O 2 - and OH- ions. An apparently continuous variation in ordering exists between the highly disordered material and each of the crystalline structures, suggesting that both nanocrystalline structures represent local extremes of three-dimensional ordering. Experimental diffraction patterns were obtained using electron nanodiffraction, a technique in which the finely focused beam from a field-emission gun in an electron microscope can be used to produce diffraction patterns from areas &lt;1 nm across. Nanodiffraction patterns from the highly disordered material have diffuse streaks rather than distinct reflections, and are consistent with a two-dimensional structure that consists of close-packed anionic layers with essentially complete stacking disorder and nearly random distribution of Fe atoms. The structure with cubic stacking is similar to maghemite and has ~25% of the Fe in tetrahedral sites. The structure with hexagonal stacking consists of double chains of face-sharing Fe octahedra; each octahedron shares one face, two edges, and three corners with adjacent octahedra. Previous results from transmission electron microscopy, powder X-ray and electron diffraction, and synchrotron-based techniques reflect the overall high degree of structural disorder rather than the characteristics of the maghemite-like and double-chain structures

Synthesis of CoFe2O4 Nanoparticles via the Ferrihydrite Route

ABSTRACTNanoparticles of CoFe2O4 in the size range of 5 nm to 36 nm have been synthesized by first producing two-line Co-doped ferrihydrite and annealing it at temperatures between 573 and 1073 K. Co-doped ferrihydrite is produced by reacting appropriate amounts of FeCl3/CoCl2 solutions with NH4OH at pH = 7. Thermogravimetric measurements provide evidence for the ferrihydrite to CoFe2O4 conversion between 500 and 700 K and x-ray diffraction is used to confirm the transformation to CoFeO4 and determine the particle size. The lattice constant increases initially with the increase in particle size approaching a constant value above 20 nm. The measured Tc equals 788 K for the 36 nm particles. Measurements of magnetization as a function of temperature and magnetic field confirm that the precursor Co-ferrihydrite is a superparamagnet with T ≃ 40 K, whereas for the 30 nm CoFe2O4, the coercivity Hc ≃ 7 kOe at 20 K, decreasing to Hc ≃ 800 Oe with Ms ≃ 60 emu/g at 300 K.

Trace Metal Adsorption onto an Acid Mine Drainage Iron(III) Oxy Hydroxy Sulfate

The adsorption properties of Fe-rich precipitates in acid mine drainage (AMD) systems differ from those of pure hydrous iron(III) oxides, and this can lead to inaccurate predictions of trace metal adsorption and attenuation. Adsorption edges for Cu, Pb, Zn and Cd adsorption onto a poorly ordered, goethite-bearing iron(III) oxy hydroxy sulfate, precipitated in an AMD system in New Zealand, have been compared to those for adsorption onto synthetic schwertmannite and two-line ferrihydrite. Adsorp tion of Cu and Zn onto the AMD iron(III) oxy hydroxy sulfate was greater than onto synthetic schwertmannite, which was in turn greater than onto two-line ferrihydrite. The two factors considered most likely to enhance Cu and Zn adsorption on the AMD iron(III) oxy hydroxy sulfate were (i) the formation of ternary complexes between the oxide surface, adsorbed SO4 and the metal ion and (ii) bacterially mediated formation of the AMD precipitate. Cd adsorption was similarly enhanced on AMD iron(III) oxy hydroxy sulfate b...

95/05783 Catalytic systems for hydrogenation of brown coal under 6-MPa hydrogen pressure

Two-line ferrihydrite was prepared by two different procedures. In procedure 1, which is widely used, ferrihydrite (named as ferrihydrite-1) was prepared by droping NaOH solution into Fe(III) solution. In procedure 2, which is rarely reported, ferrihydrite (named as ferrihydrite-2) was prepared by adding Fe(III) and NaOH solutions into a certain volume of water simultaneously. The results showed that mixing procedures of Fe(III) and alkaline were critical in the sub-microstructures and the conversion mechanisms of ferrihydrites in the presence or absence of trace Fe(II). The sub-microstructure of ferrihydrite-1 favored the mechanism of its dissolution re-crystallization and hematite nanoparticles with rough surface were obtained. The sub-microstructure of ferrihydrite-2 favored the solid state transformation from ferrihydrite to hematite and hematite nanoparticles with smooth surface were formed. These research results will be helpful for us to control the synthesis of hematite nanoparticles with different surface state.

Nanophase iron-based liquefaction catalysts: synthesis, characterization, and model compound reactivity

Ultrafine nanometer-scale iron-based catalyst precursor powders were generated using two novel technologies, the rapid thermal decomposition of precursors in solution (RTDS) and the modified reverse micelle (MRM) processes. The powders were characterized according to their phase and crystallite size and were evaluated for activity toward C-C bond scission using the model compound, naphthylbibenzylmethane, in the presence of elemental sulfur and 9,10-dihydrophenanthrene. The catalytic activities of the powders were found to be strongly dependent on their crystallographic phase. RTDS magnetite, six-line ferrihydrite, and ferric oxyhydroxysulfate were found to have very high activity toward conversion of the model compound whereas two-line ferrihydrite and hematite were determined to be poor or mediocre catalyst precursors

Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate

EXAFS spectra were collected on both the As and Fe K-edges from samples of two-line ferrihydrite with adsorbed (ADS) and coprecipitated (CPT) arsenate prepared over a range of conditions and arsenate surface coverages. Spectra also were collected for arsenate adsorbed on the surfaces of three FeOOH crystalline polymorphs, α (goethite), β (akaganeite), and γ (lepidocrocite), and as a free ion in aqueous: solution. Analyses of the As EXAFS show clear evidence for inner sphere bidentate (bridging) arsenate complexes on the ferrihydrite surface and on the surfaces of the crystalline FeOOH polymorphs. The bridging arsenate is attached to adjacent apices of edge-sharing Fe oxyhydroxyl octahedra. The arsenic-iron distance at the interface ( 3.28 ±0.01 A ̊ ) is close to that expected for this geometry on the FeOOH polymorph surfaces, but is slightly shorter on the ferrihydrite surfaces ( 3.25 ± 0.02 A ̊ ). Mono-dentate arsenate linkages ( 3.60 ± 0.03 A ̊ ) also occur on the ferrihydrite, but are not generally observed on the crystalline FeOOH polymorphs. The proportion of monodentate bonds appears largest for adsorption samples with the smallest As Fe molar ratio. In all cases the arsenate tetrahedral complex is relatively undistorted with As-O bonds of 1.66 ± 0.01 A ̊ . Precipitation of arsenate or scorodite-like phases was not observed for any samples, all of which were prepared at a pH value of 8. The Fe EXAFS results confirm that the Fe-Fe correlations in the ferrihydrite are progressively disrupted in the CPT samples as the As Fe ratio is increased. Coherent crystallite size is probably no more than 10 Å in diameter and no Fe oxyhydroxyl octahedra corner-sharing linkages (as would be present in FeOOH polymorphs) are observed at the largest As Fe ratios. Comparison of the number and type of Fe-Fe neighbors with the topological constraints imposed by the arsenate saturation limit in the CPT samples (about 0.7 As Fe ) indicates ferrihydrite units consisting mainly of Fe oxyhydroxyl octahedra arranged in short dioctahedral chains with minimal interchain linking by octahedra corners. This is consistent with an enlarged surface area and a larger proportion of sites for bidentate arsenate bonding in CPT samples as compared to the ADS samples, which saturate with arsenate at lower As Fe ratios. The latter samples have larger crystallite sizes and a definite proportion of ferric octahedra sharing corners. The ratio of corner-sharing to edge-sharing Fe oxyhydroxyl octahedra in the ADS samples, and CPT samples with small As loadings, is very similar to what would be present in very small particles of goethite or akaganeite. The difference in the polymeric structure of ADS and CPT samples at higher As Fe ratios is due to strong arsenate bidentate adsorption that poisons the surface of particles of ferrihydrite precipitated in the presence of substantial arsenate, limiting their normal crystallization, and preventing further Fe-O-Fe polymerization. If the arsenate is applied after precipitation much less adsorption occurs since polymerization has already progressed. In both ADS and CPT samples, Fe-O-Fe polymerization increases with age, though at different rates for each type of sample.

Structural and Magnetic Properties of Ferrihydrite

Abstract57Fe Mössbauer spectra of two synthetic samples of ferrihydrite, recorded at 4.2 K in applied fields of up to 9 T, have been analysed by a mean-field model. The samples exhibit two and six X-ray diffraction peaks. It is shown that only one ferric ion site is present in the mineral, and that in this site the ions are octahedrally coordinated. The spectra show the presence of different magnetic states: ferrimagnetism in two-line ferrihydrite, and antiferromagnetism in six-line ferrihydrite. The ferrimagnetism in two-line ferrihydrite is analysed in terms of random fluctuations arising from the small numbers of ferric ions per particle, and it is shown that the different magnetic states may arise purely as a result of these fluctuations.