Growth Of Magnetite Crystals Research Articles

Effect of Ni2+, Zn2+, and Co2+ on green rust transformation to magnetite

In this study, we investigated Ni2+, Zn2+, and Co2+ mineralogical incorporation and its effect on green rust transformation to magnetite. Mineral transformation experiments were conducted by heating green rust suspensions at 85 °C in the presence of Ni2+, Zn2+, or Co2+ under strict anoxic conditions. Transmission electron microscopy and powder X-ray diffraction showed the conversion of hexagonal green rust platelets to fine grained cubic magnetite crystals. The addition of Ni2+, Zn2+, and Co2+ resulted in faster rates of mineral transformation. The conversion of green rust to magnetite was concurrent to significant increases in metal uptake, demonstrating a strong affinity for metal sorption/co-precipitation by magnetite. Dissolution ratio curves showed that Ni2+, Zn2+, and Co2+ cations were incorporated into the mineral structure during magnetite crystal growth. The results indicate that the transformation of green rust to magnetite is accelerated by metal impurities, and that magnetite is a highly effective scavenger of trace metals during mineral transformation. The implications for using diagenetic magnetite from green rust precursors as paleo-proxies of Precambrian ocean chemistry are discussed.Graphical

Oriented Attachment Crystal Growth Model in Hydrothermal Synthesis of Magnetite (Fe3O4) Nanoparticles

The magnetite nanoparticles (Fe3O4) are very promising nanomaterials to be applied as drug delivery due to their excellent superparamagnetic, biocompatibility and easily modified surface properties. Those properties are influenced by the structure and size of the material which can be controlled by studying the evolution of crystal growth. The purpose of this research is to study the evolution of crystal growth of magnetite nanoparticles in the hydrothermal system and determine the crystal growth kinetics using the Oriented Attachment Growth model. Magnetite nanoparticles were synthesized using a hydrothermal method from FeCl3, citrate, urea and polyethylene glycol at 210?C for 1 - 12 hours at a various concentration of FeCl3 (0.05 M, 0.10 M, and 0.15 M). The characterizations were conducted by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Particle size analyzer (PSA), and Vibrating Sample Magnetometer (VSM). The XRD difractogram indicated that the magnetite was begun to form at 3.5 hours synthesis. The crystallinity and the crystal size of magnetite rose with reaction time. The diameter of magnetite crystals was in the range of 9.4-30 nm. Characterization by TEM showed that the particles were formed from a smaller particles which were then agglomerated. The PSA characterization showed that the distribution of diameter size enlarged with the enhancement of concentrations. VSM result showed that the magnetite nanoparticle has superparamagnetic properties. The magnetite crystal growth can be fitted by the Oriented Attachment Growth model with an error of 29%.

Crystal formation and growth by slow cooling for recovery of magnetite particles from copper smelting slag

ABSTRACTCopper smelting produces large amounts of slag and new methods of handling this by-product are required. Considering copper smelting slag as metal resource, we studied the effects of a slow cooling process on the crystal growth of magnetite in smelting slag and the applicability of magnetic separation techniques. As the cooling rate was lowered, the weight fraction of magnetite increased together with the average magnetite grain size. Furthermore, slow cooling in an oxidising atmosphere and temperature holding during the slow cooling process promoted magnetite crystal growth. Magnetic separation tests showed that high separation efficiency was possible when the slow cooled slag was ground to a particle size of ≤20 μm owing to the high magnetite liberation ratio. Consequently, slow cooling was shown to effectively promote crystal growth of magnetite and improve magnetic recovery of magnetite.Abbreviations: EDS: Energy dispersive X-ray spectrometer; MLA: Mineral Liberation Analyzer; SEM: Scanning electron microscope; XRD: X-ray diffraction

Crystal-growth kinetics of magnetite (Fe3O4) nanoparticles with Ostwald Ripening Model approach

Magnetite (Fe3O4) nanoparticles is a magnetic nanomaterial that have potential properties to be applied as drug delivery The purpose of this study was to determine the influence of time and temperature synthesis of magnetie characteristics and determine its crystal growth kinetics model with Ostwald ripening model approach. Magnetite nanoparticles synthesized from FeCl3, citrate, urea and polyethylene glycol with hydrothermal method at 180, 200 and 220 °C for 1,3,5,7,9 and 12 hours. Characterization by X-ray Diffraction (XRD) indicated that magnetite formed at temperatures of 200 and 220 °C. Magnetite crystallite diameter obtained was 10-29 nm. Characterization by Transmission Electron Mycroscope (TEM) shows that magnetite nanoparticles have uniform size and non-agglomerated. Core-shell shaped particles formed at 200 °C and 220 °C for 3 hours. Irregular shape obtained at 220 °C for 12 hour synthesis with particle diameter about 120 nm. Characterization using Vibrating Sample Magnetometer (VSM) shown that magnetite has super paramagnetism behaviour with the highest saturation magnetization (Ms) was 70.27 emu/g. magnetite crystal growth data at temperature of 220 °C can be fitted by Ostwald ripening growth model with growth controlled by the dissolution of surface reaction (n≈4) with the percent error of 2.53%.

Localized iron accumulation precedes nucleation and growth of magnetite crystals in magnetotactic bacteria

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles that originate from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here we address the question: can iron transported inside MTB for the production of magnetite crystals be spatially mapped using electron microscopy? Cultured and uncultured MTB from brackish and freshwater lagoons were studied using analytical transmission electron microscopy in an attempt to answer this question. Scanning transmission electron microscopy was used at sub-nanometric resolution to determine the distribution of elements by implementing high sensitivity energy dispersive X-ray (EDS) mapping and electron energy loss spectroscopy (EELS). EDS mapping showed that magnetosomes are enmeshed in a magnetosomal matrix in which iron accumulates close to the magnetosome forming a continuous layer visually appearing as a corona. EELS, obtained at high spatial resolution, confirmed that iron was present close to and inside the lipid bilayer magnetosome membrane. This study provides important clues to magnetite formation in MTB through the discovery of a mechanism where iron ions accumulate prior to magnetite biomineralization.

Combined Experimental and Theoretical Approach to the Kinetics of Magnetite Crystal Growth from Primary Particles.

It is now recognized that nucleation and growth of crystals can occur not only by the addition of solvated ions but also by accretion of nanoparticles, in a process called nonclassical crystallization. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Here, we study the growth of magnetite nanoparticles from primary particles—nanometer-sized amorphous iron-rich precursors—in aqueous solution at different temperatures. We propose a theoretical framework to describe the growth of the nanoparticles and model both a diffusion-limited and a reaction-limited pathway to determine which of these best describes the rate-limiting step of the process. We show that, based on the measured iron concentration and the related calculated concentration of primary particles at the steady state, magnetite growth is likely a reaction-limited process, and within the framework of our model, we propose a phase diagram to summarize the observations.

ChemInform Abstract: Bioinspired Magnetite Synthesis via Solid Precursor Phases

AbstractReview: 106 refs.

Magnetizing of nano-materials on example of Degussa’s P-25 TiO2 photocatalyst: Synthesis of magnetic aggregates, characterization and possible use

This study deals with the production of a magnetic photocatalyst using a new magnetizing technique – growth of magnetite crystals onto P-25 TiO2 particles from Degussa. Magnetite (MT) crystals were grown via the synthesis of layered FeII–FeIII hydroxide sulfate (green rust) on the surfaces of TiO2. The magnetite/P-25 TiO2 aggregates (MT/P-25) were characterized with XRD and TEM. The structure of the P-25 TiO2 photocatalyst appeared to be unchanged by the treatment. The photocatalytic activity of MT/P-25 in aqueous suspensions were tested in the near neutral pH area where magnetite is stable and compared to the photoactivity of pure P-25 TiO2. Photooxidation of tartronic acid (TA) was first used to test the photooxidative efficiency of MT/P-25 followed by other more complex compounds: aqueous solution of 2,6 difluorobenzoic acid (2,6 DFBA) as well as the natural organic matter in water from the Hohloh Lake, Germany (NOM-HLW). For the TA photocatalytic oxidation with MT/P-25 similar oxidation rates were observed as for the P-25 TiO2, but for 2,6 DFBA and NOM-HLW the degradation rates were higher for pure P-25 TiO2. Two types of laboratory reactors were applied for photocatalytic degradation of 2,6 DFBA and NOM-HLW: a reactor (400mL) with an artificial UV radiation source and the other one (800mL) that was irradiated by natural solar radiation. Photonic efficiencies of organic substrates degradation processes for both types of the reactors were calculated and compared. The bigger reactor showed better results in degradation of organic substrates (photonic efficiency was more than 7 times higher for 2,6 DFBA).Magnetic separation using a simple separator (hand magnet, batch experiment) showed a mass loss less than 3% of MT/P-25 per experiment. However, using a high gradient magnetic separator (with continuous flow) less than 0.3% of MT/P-25 aggregates were lost with a suspension flow rate of 250mL/min. In both cases magnetically separated and reused MT/P-25 showed practically unchanged photoactivity.The mechanical stability of the MT/P-25 was checked comparing the photoactivity of MT/P-25 in TA solution without prior stirring and after stirring in the reactor “in the dark” for durations of 80 and 160h. No significant differences were observed in their photoactivity before and after stirring. However, ultrasonication of the MT/P-25 at 35kHz for 60min separated the MT/P-25 material into MT and TiO2. Nevertheless, for practical purposes the stability of the aggregates during the mechanical stirring and during the magnetic separation is of major importance.

A magnetosome-associated cytochrome MamP is critical for magnetite crystal growth during the exponential growth phase.

Magnetotactic bacteria use a specific set of conserved proteins to biomineralize crystals of magnetite or greigite within their cells in organelles called magnetosomes. Using Magnetospirillum magneticum AMB-1, we examined one of the magnetotactic bacteria-specific conserved proteins named MamP that was recently reported as a new type of cytochrome c that has iron oxidase activity. We found that MamP is a membrane-bound cytochrome, and the MamP content increases during the exponential growth phase compared to two other magnetosome-associated proteins on the same operon, MamA and MamK. To assess the function of MamP, we overproduced MamP from plasmids in wild-type (WT) AMB-1 and found that during the exponential phase of growth, these cells contained more magnetite crystals that were the same size as crystals in WT cells. Conversely, when the heme c-binding motifs within the mamP on the plasmid was mutated, the cells produced the same number of crystals, but smaller crystals than in WT cells during exponential growth. These results strongly suggest that during the exponential phase of growth, MamP is crucial to the normal growth of magnetite crystals during biomineralization.

Structural insight into magnetochrome-mediated magnetite biomineralization

Magnetotactic bacteria align along the Earth's magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(II) and iron(III) is clear, little is known about the biological mechanisms controlling their ratio. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(II) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(III) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization.

Phase Transformations and Structural Developments in the Radular Teeth of Cryptochiton Stelleri

AbstractDuring mineralization, the hard outer magnetite‐containing shell of the radular teeth of Cryptochiton stelleri undergoes four distinct stages of structural and phase transformations: (i) the formation of a crystalline α‐chitin organic matrix that forms the structural framework of the non‐mineralized teeth, (ii) the templated synthesis of ferrihydrite crystal aggregates along these organic fibers, (iii) subsequent solid state phase transformation from ferrihydrite to magnetite, and (iv) progressive magnetite crystal growth to form continuous parallel rods within the mature teeth. The underlying α‐chitin organic matrix appears to influence magnetite crystal aggregate density and the diameter and curvature of the resulting rods, both of which likely play critical roles in determining the local mechanical properties of the mature radular teeth.

The Major Magnetosome Proteins MamGFDC Are Not Essential for Magnetite Biomineralization inMagnetospirillum gryphiswaldensebut Regulate the Size of Magnetosome Crystals

Magnetospirillum gryphiswaldense and related magnetotactic bacteria form magnetosomes, which are membrane-enclosed organelles containing crystals of magnetite (Fe3O4) that cause the cells to orient in magnetic fields. The characteristic sizes, morphologies, and patterns of alignment of magnetite crystals are controlled by vesicles formed of the magnetosome membrane (MM), which contains a number of specific proteins whose precise roles in magnetosome formation have remained largely elusive. Here, we report on a functional analysis of the small hydrophobic MamGFDC proteins, which altogether account for nearly 35% of all proteins associated with the MM. Although their high levels of abundance and conservation among magnetotactic bacteria had suggested a major role in magnetosome formation, we found that the MamGFDC proteins are not essential for biomineralization, as the deletion of neither mamC, encoding the most abundant magnetosome protein, nor the entire mamGFDC operon abolished the formation of magnetite crystals. However, cells lacking mamGFDC produced crystals that were only 75% of the wild-type size and were less regular than wild-type crystals with respect to morphology and chain-like organization. The inhibition of crystal formation could not be eliminated by increased iron concentrations. The growth of mutant crystals apparently was not spatially constrained by the sizes of MM vesicles, as cells lacking mamGFDC formed vesicles with sizes and shapes nearly identical to those formed by wild-type cells. However, the formation of wild-type-size magnetite crystals could be gradually restored by in-trans complementation with one, two, and three genes of the mamGFDC operon, regardless of the combination, whereas the expression of all four genes resulted in crystals exceeding the wild-type size. Our data suggest that the MamGFDC proteins have partially redundant functions and, in a cumulative manner, control the growth of magnetite crystals by an as-yet-unknown mechanism.

Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: inorganic, abiotic formation by shock and thermal metamorphism.

Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe(3)O(4), reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered).

The synthesis and some properties of Co, Ni, Zn, Cu, Mn and Cd substituted magnetites

Abstract When magnetites were synthesised by oxidising two-thirds of the iron in a 0.51 m ferrous sulphate solution using potassium nitrate as an oxidising agent, the crystallization of magnetites occurred predominantly at pH 4.5. The presence of phosphate and citrate at a H 2 PO 4 − or citrate: Fe 2+ mole ratio of 0.4 inhibited the nucleation and crystal growth of magnetite. Acetate was ineffective in suppressing the nucleation or crystal growth of magnetite. The magnetite particles were present in a range of sizes and morphologies. The incorporation of small amounts ( 2+ and its ability to exhibit the Jahn-Teller effect and the larger ionic radii of Mn 2+ and Cd 2+ may be responsible for their non-uniform distribution in the magnetite crystals.

The growth of magnetite crystals

The growth of magnetite crystals