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Size and shape control of precipitated magnetite nanoparticles

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Abstract

Magnetite nanoparticles are ubiquitous in soils, sediments and mine wastes, and are also used in nanotechnological applications. We studied the influence of synthesis conditions on the size and shape of magnetite nanoparticles that were produced in inorganic co-precipitation processes. Variable parameters included the types of reagents and their concentrations, the pH, the temperature (from 9 to 90 °C) and the atmosphere (O2 and N2). The mineral phases, the morphologies, size and shape distributions of the resulting magnetite particles were characterised using transmission electron microscopy and X-ray powder diffraction. We managed to produce magnetite nanoparticles between ∼11 and 120 nm and to control the mean sizes of the crystals within this range. The morphologies of the magnetite nanocrystals were also affected by the synthesis conditions and varied according to grain size. Crystals with diameters between 10 and 25 nm have irregular or round morphologies, whereas crystals larger than 50 nm are octahedral. Various nucleation and growth processes are invoked to explain the influence of synthesis conditions on the sizes and shapes of the product magnetite nanoparticles.

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... It is common for the magnetite crystals formed in this manner to be of several different morphologies (within the same reaction mixture) including cubic, rounded, octahedral and/or irregular (Figures 2a and 2b). However, different morphologies, sizes and size distributions can be obtained by varying the conditions in the reaction mixture [e.g., Nyirö-Kósa et al., 2009]. For instance, the mean crystal size of the magnetite crystals formed can be adjusted over a large range at the nanometer scale (1.5-12.5 nm) by controlling the pH and the ionic strength of the iron solutions. ...
... Smaller magnetite particles can be obtained through higher pH values and higher ionic strengths of the iron solutions [Vayssières et al., 1998]. Nyirö-Kósa et al. [2009] studied in great detail the influence of synthesis conditions on the size and shape of magnetite nanoparticles that were produced in inorganic coprecipitation processes. Parameters examined included the types of reagents used and their concentrations, pH, temperature (from 9 to 90°C) and the presence and absence of oxygen (oxic versus anoxic under N 2 ). ...
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Over the years, nanometer-sized magnetite (Fe3O4) crystals have been recovered from many modern and ancient environments including sediments and soils and even meteorites. In some cases these crystals have been used as ``magnetofossils'' for evidence of the past presence of specific microbes. Magnetite nanocrystals can be formed by a number of different biological and inorganic mechanisms resulting in crystals with different physical and magnetic characteristics. Prokaryotes (bacteria) biomineralize magnetite through two methods that differ mechanistically, including: biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). Magnetite nanocrystals produced by BIM are known to be synthesized by the dissimilatory iron-reducing bacteria, are deposited external to the cell, and generally are physically indistinguishable from magnetite particles formed inorganically. BCM magnetites, in contrast, are synthesized by the magnetotactic bacteria and some higher organisms and are precipitated intracellularly as membrane-bounded structures called magnetosomes. These magnetites appear to have unique crystal morphologies and a narrow size range leading to their original use as magnetofossils. Because of the discovery of nanometer-sized crystals of magnetite in the Martian meteorite ALH84001, the use of these criteria for the determination of whether magnetite crystals could constitute a prokaryotic biomarker was questioned. Thus, there is currently great debate over what criteria to use in the determination of whether specific magnetite crystals are biogenic or not. In the last decade, additional criteria have been established (e.g., the Magnetite Assay for Biogenicity), and new tools and technologies have been developed to determine the origin of specific types of magnetite crystals.
... Most of the procedures involving the precipitation of magnetite from bulk solution follow the so-called "coprecipitation" method, in which a variety of salts of Fe 2+ and Fe 3+ mixtures (mainly as chlorides or nitrates) are introduced as starting solutions under anaerobic conditions. In order to maintain the conditions necessary for the thermodynamic stability field for magnetite, different compounds are used to increase and maintain alkaline conditions during magnetite precipitation including the following: NH 3 at 85 • C [24,25], NaOH at 25 • C in agarose gel [26], NaOH at 25-45 • C in solution [24], NH 3 and/or NaOH at 9-90 • C [27]. NH 4 OH at 25 • C [28], and N(CH 3 ) 4 OH [24]. ...
... It is also interesting that the size of our crystals could be modified just varying the time for the incubation, so the longer the incubation time, the bigger the crystals. Regarding coprecipitation methods, Nyirő-Kósa et al., [27] precipitated magnetite from solutions based on chloride salts, added with NH 4 and NaOH, at temperatures ranging from 9 to 90 • C. These authors obtained magnetite crystals within a size range from 11 to 120 nm, depending on the pH values (from 3.8 to 13.1). ...
Article
An easy, low-cost coprecipitation method to inorganically produce magnetite nanoparticles from solutions, in free-drift experiments, under anoxic conditions, at 25 °C and 1atm pressure is here presented. By using this method, pure magnetite is obtained as the final solid, which shows the typical magnetic properties and thermal stability behavior of magnetite produced by other methods. The size of the magnetite crystals produced by the present method varies from relatively big sizes (200–300nm), to sizes within the single magnetic domain range, just depending on the incubation time. The solution from which magnetite precipitates may be representative of certain natural environments where bacteria that produce magnetite may live and, thus, our magnetite may be used as an inorganic reference to compare to biologically produced magnetites. KeywordsMagnetite–Coprecipitation–Biomarker–Mineral synthesis–Magnetitc nanoparticles
... In the investigated synthesis procedure, the base was added in abrupt way (i.e., pH quickly increases from 2 to 9.2), resulting in significant pH gradient leading to the formation of lepidocrocite(γ-FeOOH) at pH 7−8 [44][45][46][47],then transformed into spinel iron oxide at higher pH. Moreover, the presence of oxygen in a reaction medium is a key factor in promoting the oxidation of Fe 2+ to Fe 3+ [48,49]. In our case, the produced nanoparticles under different synthesis conditions(O 2 /N 2 ) show different particles shape. ...
... 2021, 11, x FOR PEER REVIEW 6 of 12 lepidocrocite(γ-FeOOH) at pH 7−8 [44][45][46][47],then transformed into spinel iron oxide at higher pH. Moreover, the presence of oxygen in a reaction medium is a key factor in promoting the oxidation of Fe 2+ to Fe 3+ [48,49]. In our case, the produced nanoparticles under different synthesis conditions(O2/N2) show different particles shape. ...
Article
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Synthesis atmosphere (i.e., air and nitrogen) effects on the physical properties and formation mechanism of spinel iron oxide nanoparticles prepared via the co-precipitation method have been investigated using a multi-technique approach. The obtained magnetic nanoparticles (MNPs) were characterized using the X-ray diffraction, transmission electron microscopy (TEM), SQUID magnetometry, Mössbauer spectroscopy and X-ray absorption near-edge Structure spectroscopy techniques. The synthesis procedure leads to the formation of a spinel structure with an average crystallite size of 9.0(9) nm. The morphology of the particles synthetized under an inert atmosphere was quasi-spherical, while the nanoparticles prepared in air present a faceted shape. The small differences observed in morphological properties are explained by the influence of the reaction atmosphere on the formation mechanism of the MNPs. The magnetic characterization indicates that both samples exhibit superparamagnetic behavior at 300 K. The investigation by means of the Langevin approach at 300 K also leads to equal values for the mean size of the magnetic cores (Dm). Additionally, the analysis of the Mössbauer spectra revealed the lack of spin disorder for both samples, resulting in a high saturation magnetization. The fit of XANES spectrum suggests that about 2/3 of the iron ions reside in a local environment close to that of γ-Fe2O3 and about 1/3 close to that of Fe3O4 for the sample synthetized in inert atmosphere.
... As described above, in order to prevent oxidation of ferrous ions, the initial reaction temperature was set to 25 • C. As Nyirokosa et al. [29] reported, at constant ionic strength, increasing temperature from 25 to 90 • C had no effect on crystal size, but Hosono et al. [30] showed that at reaction temperatures above 50 • C, a single phase magnetite can be obtained. Also, Guang et al. [12] reported that as the reaction time increased to 4 h, the size of magnetite nanoparticles decreased. ...
... Fe-A1 and Fe-A2 samples showed the smallest size and the highest aggregation. Increasing the concentration of Fe salts causes the increase in particle size likely due to the nucleation and growth phenomena that happens in supersaturation state [10,29,32]. This means that in supersaturation state more nuclei are produced. ...
Article
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Abstract In this study, superparamagnetic iron oxide nanoparticles (SPION) were synthesized by coprecipitation of FeSO4•7H2O and FeCl3•6H2O with NH4OH at different temperatures and iron salt concentrations. The results showed that magnetite nanoparticles synthesized at elevated temperature (70 °C) and moderate salt concentration (0.012 M for FeCl3) had the highest saturation magnetization (67.8 emu/g) with the size of about 9 nm. The optimal magnetite nanoparticles with the lowest aggregation and highest magnetic behaviour were coated by polyamidoamine (PAMAM) dendrimer. The samples were characterized with X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy, fluorescent spectroscopy and magnetization measurements (VSM). The coated materials illustrated strong magnetic behaviour and XRD pattern like magnetite. The presence of Fe-O-Si bond in FTIR spectra confirmed the formation of thin APTS layer on the surface of magnetite nanoparticles. Energy-dispersive X-ray spectroscopy (EDS) and thermogravimetric analysis (TGA) indicated that the modification of core synthesis technique can raise the efficiency of aminosilane coating reaction (as an initiator for PAMAM dendrimer) up to 98% with the production of about 610 dendritic arms. TGA and FTIR spectra of PAMAM-grafted nanoparticles also verified the perfection of repetitive Michael addition and amidation reactions. The fluorescence spectrum displayed the excitation and emission peaks around 298 and 328 nm, respectively for PAMAM-grafted nanoparticles. We believe the resultant material showed the fluorescent properties which could be an applicable and powerful tool for biomedical diagnostic applications.
... Complex abiotic mineral structures can also be produced, and it is essential to be able to distinguish these from biological structures. The difficulty in achieving this is most clearly demonstrated by the controversy surrounding the assignment of magnetite crystals within Martian meteorite ALH84001 to biological activity [52,53]. Some minerals do not produce distinctive biologically induced morphologies, but their production is normally thermodynamically unfavourable and their discovery in the environment might indicate biological processes [54]. ...
Article
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Geomicrobiology investigates the interactions of microorganisms with geological substrates, and this branch of microbiology has enormous potential in the exploration and settlement of space. Microorganisms can be used to extract useful elements from extraterrestrial materials for industrial processes or for use as nutrients in life support systems. In addition, microorganisms could be used to create soil from lunar and Martian rocks. Furthermore, understanding the interactions of microorganisms with rocks is essential for identifying mineral biomarkers to be used in the search for life on other planetary bodies. Increasing space exploration activities make geomicrobiology an important applied science beyond Earth.
... Particle Synthesis. Magnetite particles of three distinct size ranges (90 (±42) nm, 44 (±11) nm, and 6 (±2) nm, see Supporting Information (SI)) were synthesized using established methods 35,36,23 as detailed in the SI. Following synthesis, magnetite particles were magnetically separated, washed a minimum of three times to remove excess salts, and then stored in an anaerobic chamber. ...
Article
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Logistic challenges make direct comparisons between laboratory and field based investigations into the size-dependent reactivity of nanomaterials difficult. This investigation sought to compare the size-dependent reactivity of nanoparticles in a field setting to a laboratory analog using the specific example of magnetite dissolution. Synthetic magnetite nanoparticles of three size intervals, ~6nm, ~44 nm, and ~90 nm were emplaced in the subsurface of the USGS Norman Landfill Site for up to 30 days using custom-made subsurface nanoparticle holders (SNHs). Laboratory analog dissolution experiments were conducted using synthetic groundwater. Reaction products were analyzed via TEM and SEM and compared to initial particle characterizations. Field results indicated that an organic coating developed on the particle surfaces largely inhibiting reactivity, although limited dissolution occurred displaying a largest to smallest size-dependent trend (~90 nm > ~44 nm > ~6 nm). Conversely, the laboratory analogs without organics revealed greater dissolution of the ~44 nm and ~6 nm particles. These results showed that the presence of dissolved organics led to a nearly complete reversal in the size-dependent reactivity trends displayed between the field and laboratory experiments indicating that size-dependent trends observed in laboratory investigations may not be relevant in organic-rich natural systems.
... Fe 3 O 4 nanoparticles were synthesized by co-precipitation method in alkaline medium [25,26]. The iron salts were dissolved in aqueous HCl (0.16 M) where the mole fraction of Fe 2+ to Fe 3+ was adjusted to 0.5. ...
... ?d (448) = 0.25565 nm in maghemite Reference vector[uwv] denotes the crystal orientation with respect to[110] in maghemite. b Calculated from powder XRD of maghemite, a = 0.83494 nm.40 ...
Article
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The origin of growth defects and epitaxial layers in nanocrystalline magnetite (Fe3O4) and its oxidation product, maghemite (gamma-Fe2O3), was studied. In magnetite, two types of planar defects are identified, (111) spinel-law twin boundaries and (110) stacking faults (SF). The twinning in magnetite is related to magnetic-field-assisted self-assembly and the growth of octahedral nanocrystals throughout their crystallization period. Simple contact twins of crystals sharing common octahedral faces, or even plate-like twins develop when two adjoined crystals continue their growth as a unit. Crystallographically, twinned domains are related by 180° rotation about the [111]-axis and with the (111) plane as the interface, producing local hcp stacking in the oxygen sub-lattice. SFs are present in both single and twinned magnetite crystals, where they are pinned to (111) twin boundaries and are present only in one domain. The displacement vector corresponding to the observed translation is R(SF) = 1/4[110], pointing normal to the (110) plane of the SF. After the thermal treatment at 250°C both types of planar defects are retained. In addition to planar defects, originating from magnetite, we identified a new formation of few-nanometers-thick epitaxial layers, of a hexagonal Fe(III)-oxide–hydroxide, feroxyhyte (d-FeOOH), covering the octahedral faces of the maghemite crystals. The crystallographic relationship between maghemite and feroxyhyte is described by [110](222)mag || [010](002)fer.
... Considering that chemical composition and morphology controls for these magnetic nanoparticles appear to be crucial for their applications, a specific interest has been dedicated to control the particle size dispersion [23][24][25][26]. Small sizes and uniform morphology are typically required for the applications of magnetic nanoparticles because of the dependence of magnetic properties on the morphologies of nanoparticles. ...
Article
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Magnetite (Fe3O4) nanoparticles prepared by microwave-assisted hydrothermal synthesis have been characterized in terms of morphological and structural features. Electron micrographs collected in both scanning (SEM) and transmission (TEM) modes and evaluations of X-ray powder diffraction (XRD) patterns have indicated the achievement of a monodispersed crystallite structure with particles having an average size around 15–20 nm. Structural investigations by Micro-Raman spectroscopy highlighted the obtainment of magnetite nanocrystals with a partial surface oxidation to maghemite (γ-Fe3O4). Preliminary attention has been also paid to the use of these magnetite nanoparticles as filler for a commercial polymethylmethacrylate resin. Hybrid formulations containing up to 3 wt% of nanoparticles were prepared by melt blending and characterized by calorimetric and thermogravimetric tests. For sake of comparison, same formulations containing commercial Fe3O4 nanoparticles are also reported. Calorimetric characterization indicates an increase of both glass transition temperature and thermal stability of the nanocomposite systems when loaded with the synthesized magnetite nanoparticles rather then loaded with the same amount of commercial Fe3O4. This first observation represents just one aspect of the promising potentiality offered by the novel magnetic nanoparticles when mixed with PMMA.
... The aspect ratio, defined as the length of the perimeter of a boundary divided by the area of the same boundary, can be derived from the combination of size, shape and the pure parameters. The statistics of size, shape and aspect ratio are widely adopted in nano science and engineering to characterize the morphology of NPs, and are believed to strongly affect the physical or chemical properties of the NPs [El-Sayed (2001), Nyiro-Kosa, Nagy and Posfai (2009)]. For example, the aspect ratio is considered as an important parameter relevant to certain macro-level material properties because physical and chemical reactions are believed to frequently occur on the surface of molecules so that as the aspect ratio of a nanoparticle gets larger, those reactions are more active. ...
Article
The properties of materials synthesized with nanoparticles (NPs) are highly correlated to the sizes and shapes of the nanoparticles. The transmission electron microscopy (TEM) imaging technique can be used to measure the morphological characteristics of NPs, which can be simple circles or more complex irregular polygons with varying degrees of scales and sizes. A major difficulty in analyzing the TEM images is the overlapping of objects, having different morphological properties with no specific information about the number of objects present. Furthermore, the objects lying along the boundary render automated image analysis much more difficult. To overcome these challenges, we propose a Bayesian method based on the marked-point process representation of the objects. We derive models, both for the marks which parameterize the morphological aspects and the points which determine the location of the objects. The proposed model is an automatic image segmentation and classification procedure, which simultaneously detects the boundaries and classifies the NPs into one of the predetermined shape families. We execute the inference by sampling the posterior distribution using Markov chain Monte Carlo (MCMC) since the posterior is doubly intractable. We apply our novel method to several TEM imaging samples of gold NPs, producing the needed statistical characterization of their morphology.
... These particles generally have several different morphologies (even within the same reaction mixture) including cubic, rounded, octahedral and/or irregular shapes. Differences in composition, morphology, grain size, and crystal-size distribution depend on the pathways, the precursors as well as the reaction conditions, such as the different species activities, time, T, pH, and the atmosphere (O 2 and N 2 ) (e.g., Nyiro-Kosa et al., 2009;Usman et al., 2012). ...
Article
Abstract Fossil biominerals and fossils of microorganisms in ancient rocks contain important biogeochemical signals. Decoding this record may reveal crucial information about the evolution of life on Earth and terrestrial paleoenvironments. However, the identification of traces of life especially in very old rocks is extremely challenging because the morphological and chemical signatures of biominerals and microfossils are subtle, of microscopic size and inevitably altered with aging. In this review, we stress on the fact that biomineralization is often the first step of fossilization and produces particular chemical, structural and morphological features that can be preserved in fossil biominerals or microfossils, with a special focus on Fe-biomineralization. The taphonomic processes affecting biominerals and microfossils and altering their morphology and/or chemical composition over time are then discussed in the light of experimental fossilization simulations and field sample analyses. We suggest that taxonomic biases observed in the fossil record may be related to differential abilities of species to trigger biomineralization. This calls for studies of the effective biomineralizing activity and fossilization potential of each species present in highly diverse natural microbial communities. Finally, recent analytical developments leave little doubt that very substantial progress in the study of biomineralization processes and ancient biostructures will be achieved in the near future.
... Attempts to produce nanoparticles within the single stable domain by low temperature process in aqueous solutions have failed [22,23] Baumgartner et al, reported that controlling the pH tunes the growth of particles to the range of single stable domain using a low temperature co-precipitation of ferrous and ferric iron under alkaline conditions [24]. Some authors have developed synthesis routes using low temperatures, generally in the superparamagnetic range, thus very low grain size [20,[25][26][27][28][29][30][31][32]. ...
Article
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The oxidation of methylamine by permanganate ion in aqueous phosphate buffers is autocatalyzed by a soluble form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ions on its surface. The dependence of the rate constants of both the noncatalytic and catalytic mechanisms on the concentrations of both methylammonium and hydroxyl ions and on temperature has been determined. The activation parameters have been obtained. Mechanisms in agreement with the experimental data are proposed.
... The purity of product was confirmed by strict control of pH, the AA measurement, classical titrimetric analyses, and EDX spectrum of product. The average particle size of Fe 3 O 4 suspension in n-hexane was found by LLS to be 5.2 nm, which is smaller than reported value, 14 nm (Enzel et al. 1999), 36.19 nm , 25.3 nm (Horng et al. 2006), and 11 nm (Ilona et al. 2009). The use of ammonium hydroxide and linoleic acid produce finer particles in comparison with sodium hydroxide and palmitoleic acid, respectively. ...
Article
In this study, highly pure magnetite nanoparticle dispersed in water and an organic solvent (n-hexane) and its powder form were prepared in laboratory scale by the fractional precipitation using ammonium hydroxide and microwave heating in the presence of linoleic acid as capping agent. In order to overcome the oxidation of Fe2+ during magnetite formation ferrous ammonium sulfate, sodium azide, and fractional precipitation technique were used. The Fe3O4 products were investigated by XRD, LLS, EDX, TEM, viscosity measurements, and chemical analysis. The effects of seven main factors on the average diameter of magnetite particles were studied by a screening design. The analysis of the samples showed that this new modified method is able to produce pure magnetite particles in the range of 1–15 nm. The most important factors on the particle size reduction of magnetite were found to be the capping agent used and the pH of solution at the end of precipitation process. Data analysis was performed using Qualitek-4 and Minitab softwares.
... A very promising application of magnetic nanoparticles is as drug carriers, in drug delivery, as proposed in the late 1970s by Widder et al. [151]. Based on previous studies he show the possibility to accumulate small iron particles that were intravenously injected into the leg vein of dogs, using a Using different kinds and amounts of polyols [129], precursors ratio, pH, temperature [130][131][132] or applying magnetic field [133][134][135] or ultrasonication [136][137][138] various types of particle morphologies and nanocrystal textures can be produced, including spherical, cubic hexagonal-shaped clusters of elongated crystals and porous and dense, rounded or sharp edged mono-or polycrystalline aggregates [129,[139][140][141][142][143]. This method is widely used for synthesis of magnetite because is cheap, easy, versatile, do not involve special reagents and conditions; permit "one pot" functionalization (even during the synthesis of magnetic core), etc. ...
Article
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In this review the synthesis, functionalization and some applications of magnetite nanoparticles (MNPs) were highlighted. It is our intention to highlight the correlations between the synthesis routes, related synthesis parameters, functionalization strategies and the properties expected for the materials containing MNPs. The uses of MNPs are strongly influenced by the properties of the materials. Therefore this review is trying to discuss the applications of the magnetite and magnetite based nanomaterials by taking into account all the factors that can influence the properties of the final materials and consequently their potential applications.
... Fe 2+ , Co 2+ , Cu 2+ , Ni 2+ , Mn 2+ ) in aqueous solution by the addition of a base. The characteristics of the particles formed depend on various experimental parameters including the concentration and type of salts and base used, the pH, ionic strength and temperature of the medium, the rate and order of addition of the reagents as well as the aging period of the crystallites (Babes et al., 1999;Massart, 1981;Nedkov et al., 2006;Nyirő-Kósa et al., 2009). Furthermore, the presence of oxidizing or chelating agents, surfactants, saccharides and polymers has been found to influence the characteristic of the particles Jiang et al., 2010;Lee et al., 1996). ...
... To produce particles with SSD properties or even larger MD particles, generally methods that involve elevated temperatures are required[11]. Attempts to produce nanoparticles within the SSD domain by low temperature processes in aqueous solution have failed until now[12,13]. Therefore, it is a synthetic challenge to develop new and optimize existing procedures to obtain SSD particles under milder chemical conditions. ...
Article
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The room temperature co-precipitation of ferrous and ferric iron under alkaline conditions typically yields superparamagnetic magnetite nanoparticles below a size of 20 nm. We show that at pH = 9 this method can be tuned to grow larger particles with single stable domain magnetic (> 20-30 nm) or even multi-domain behavior (> 80 nm). The crystal growth kinetics resembles surprisingly observations of magnetite crystal formation in magnetotactic bacteria. The physicochemical parameters required for mineralization in these organisms are unknown, therefore this study provides insight into which conditions could possibly prevail in the biomineralizing vesicle compartments (magnetosomes) of these bacteria.
... Depending on reaction time, the diffusion and growth process of samples could be completed. At elevated temperature and prolonged time, the reaction condition set to be completed and samples with less crystal defects and smaller particle size (about 9.5 nm) were produced [20][21]. With increase of ingredient (alkaline media) concentration more material is available on the growth phase and thus particles with higher diameter could be obtained (Fig. 3). ...
Conference Paper
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By controlling of two significant parameters mainly alkaline media concentration and temperature, magnetite nanoparticles were produced via coprecipitation method. Effect of named parameters on the particle size, size distribution and magnetic behaviour of particles were analyzed by means of X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). To the best of our knowledge, there is no report on evaluation of sample preparation at room temperature and then post stirring at higher temperature on particle size and its magnetic properties. Results show the particles synthesized at elevated temperature (70 degrees C) and lower alkaline concentration (0.9 M) have highest saturation magnetization, about 68 emu/gr at 70 degrees C, compared with 63 emu/gr at 25 degrees C and smallest particle size. (C) 2012 Published by Elsevier B. V. Selection and/or peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society
... [23] As some separate articles recommended, in order to produce tiny nuclei, the initial temperature of this study set to 25°C and after 1 hour group 1 was purified which resulted in particles with larger size (average diameter is about 14 nm). Depending on reaction time, the diffusion and growth process of samples could be completed [24]- [25]. At elevated temperature and prolonged time, the reaction condition set to be completed and samples with less crystal defects and smaller particle size (average diameter is about 10 nm) were produced. ...
... However, it has not been until quite recently, when attempts to produce magnetite nanoparticles at low temperatures, using aqueous solutions, have proven successful (e.g. Nyiro-Kosa et al., 2009;Perez-Gonzalez et al., 2011). An alternative way to conventional co-precipitation methods is the so-called Green Synthesis which involves organisms such as bacteria, fungi and plants, as directing or guiding agents in the formation of the magnetic phases (Bharde et al., 2005 andPhilip 2009;Cai et al., 2010;Foba-Tendo et al., 2013 among others). ...
Article
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This work presents a preliminary rock magnetic characterization of four Fe-oxides samples (MDaloe, MDpectin, P1 and P2 samples). The study was performed in order to know the nature, oxidation state, particle sizes and approximate shapes of these oxides, synthesized at room temperature via co-precipitation of Fe salts in pectin from Aloe vera. All the rock magnetic measurements were carried out in a versatile, highly sensitive (5x10-6 Am 2 /kg) and unique Variable Field Translation Balance (VFTB). The analysis of the thermomagnetic (high and low temperatures), thermosusceptibility and isothermal remanent magnetization (IRM) curves, reveal the presence of magnetite, largely oxidized to maghemite. Hysteresis parameters for MDaloe and MDpectin samples indicate that they contain non-stoichiometric multidomain (MD) magnetite. On the other hand, P1 and P2 samples seem to have maghemitized fine-grained magnetites of about 10 nm of diameter (superparamagnetic / single domain threshold), with cubic (P1) and acicular (P2) shapes. The mmol total Fe/meq COO ratios in the biomass (pectin), used in the synthesis of these samples, might have conditioned the growth, ordering and geometry of the magnetite particles.
... Once the magnetite nuclei are produced, ion-to-ion attachment, particle aggregation or Ostwald ripening (growth of larger particle at the expense of dissolving smaller one) cause the particle growth. [23] As some separate articles recommended, in order to produce tiny nuclei, the initial temperature of this study set to 25°C and after 1 hour group 1 was purified which resulted in particles with larger size (average diameter is about 14 nm). Depending on reaction time, the diffusion and growth process of samples could be completed [24]- [25]. ...
... Figures 1A & 1B show respectively the slight decrease of particle size and increase of saturation magnetization of SPIONs at elevated temperature because of loss of surface defects. Given that the completeness of diffusion and growth processes of samples are influenced by the reaction time [43,44], in our case, this was achieved at an elevated temperature of 70ºC and prolonged time where the samples with less crystal defects and smaller particle size (average diameter is about 10 nm) were produced. With increase of ingredient (alkaline media) concentration more materials are available on the growth phase and thus particles with higher diameter could be obtained ( Figure 1B). ...
Article
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An optimal sample was selected as those synthesized at 70ºC with particle size of about 10 nm << exchange length of 27 nm and a saturation magnetization of 67.8 emu/g. The samples were characterized with X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, fluorescent spectroscopy (LIF) and magnetization measurements (VSM). The coated materials illustrated strong magnetic behaviour and XRD pattern like magnetite. The presence of Fe-O-Si bond in FTIR spectra confirmed the formation of thin APTS layer on the surface of magnetite nanoparticles. Thermogravimetric analysis (TGA) indicated that the modification of core synthesis technique can raise the efficiency of aminosilane coating reaction (as an initiator for PAMAM dendrimer) up to 98% with the production of about 610 dendritic arms. UV-vis spectrum of both SPIONs and ID-NPs was measured in the range of 340-380 nm with the maximum peak at about 350 nm. The fluorescence properties of ID-NPs distributed in a collagenous substrate and MCF 7 cells was studied by fluorescence microscopy. The results showed that the viability of L 929 and MCF 7 cells decreased from 100% and 90% to 53% and 23% respectively between 10 μg/mL and 1 mg/mL for ID-NPs. The rate of uptake increased with time and it was higher for ID-NPs than SPIONs.
... From Figure 4(a), round shaped particles with an average particle size of 15.5 nm ± 3.5 nm were observed for the uncoated MNPs. Nyirő-Kósa and coresearchers claimed that the shape changes correlated with the crystallite size and the samples with crystal size of smaller than ∼25 nm are said to contain irregular and round shaped particles [18]. Nevertheless, addition of sufficient amount of PEG could act as a stabilizer and dispersing agent; hence MNPs of well-defined and homogeneous shape with smaller particle size, about 14.1 nm ± 2.3 nm (Figure 4(b)), were produced. ...
Article
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Polyethylene glycol (PEG) is one of the most frequently used synthetic polymers for surface modifications of magnetite nanoparticles (MNPs) to provide a new opportunity for constructing high colloidal stability. Herein, a facile in situ coprecipitation technique is described for the synthesis of PEG coated MNPs using ammonium hydroxide as the precipitating agent. The structure and morphology of the prepared PEG coated MNPs samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray spectroscopy, thermogravimetric analysis (TGA), and the high resolution transmission electron microscopy (HRTEM). In this study, all samples demonstrated hydrodynamic size in the range of 32 to 43 nm with narrow size distribution. In addition, the magnetic properties of resultant samples were investigated using a vibrating sample magnetometer (VSM) to reveal the superparamagnetic behaviour with saturation magnetization. The saturation magnetization of PEG coated MNPs samples was in the range of 63 to 66 emu/g at 300 K. Interestingly, it was found that 1.0 g of PEG coated MNPs exhibited high colloidal stability in a basic solution (pH = 10) and nitrile (NBR) latex up to 21 days as compared to the unmodified MNPs during the sedimentation test.
... Attempts to produce nanoparticles within the single stable domain by low temperature process in aqueous solutions have failed [22,23] Baumgartner et al, reported that controlling the pH tunes the growth of particles to the range of single stable domain using a low temperature co-precipitation of ferrous and ferric iron under alkaline conditions [24]. Some authors have developed synthesis routes using low temperatures, generally in the superparamagnetic range, thus very low grain size [20,[25][26][27][28][29][30][31][32]. ...
Research
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This work reports a simple process for preparation of stable and uniform magnetite nanoparticles (Fe3O4) at low temperature.
... The as-synthesized nanoparticles had inverse spinel structure, with particle size ranging 3-20 nm. In 2009 Nyiro-Kosa managed to produce magnetite nanoparticles between 11 and 120 nm and to control the mean size and morphologies of the crystals within this range [19]. Crystals with diameters between 10 and 25 nm had irregular or round morphologies, whereas crystals larger than 50 nm were octahedral. ...
... A general drawback of the aqueous co-precipitation method is that particle growth usually results in broad size distributions [50], [51]. Consistent to this aspect, the particles obtained are ranging from a ferrihydrite-like precursor phase [20] (1 -2 nm) over SP particles (MD < 20 nm) up to large particles of > 100 nm in size. ...
Thesis
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Magnetite is an iron oxide, which is ubiquitous in rocks and is usually deposited as small nanoparticulate matter among other rock material. It differs from most other iron oxides because it contains divalent and trivalent iron. Consequently, it has a special crystal structure and unique magnetic properties. These properties are used for paleoclimatic reconstructions where naturally occurring magnetite helps understanding former geological ages. Further on, magnetic properties are used in bio- and nanotechnological applications –synthetic magnetite serves as a contrast agent in MRI, is exploited in biosensing, hyperthermia or is used in storage media. Magnetic properties are strongly size-dependent and achieving size control under preferably mild synthesis conditions is of interest in order to obtain particles with required properties. By using a custom-made setup, it was possible to synthesize stable single domain magnetite nanoparticles with the co-precipitation method. Furthermore, it was shown that magnetite formation is temperature-dependent, resulting in larger particles at higher temperatures. However, mechanistic approaches about the details are incomplete. Formation of magnetite from solution was shown to occur from nanoparticulate matter rather than solvated ions. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Synthesis of magnetite nanoparticles at different temperatures was performed and the Arrhenius plot was used determine an activation energy for crystal growth of 28.4 kJ mol-1, which led to the conclusion that nanoparticle diffusion is the rate-determining step. Furthermore, a study of the alteration of magnetite particles of different sizes as a function of their storage conditions is presented. The magnetic properties depend not only on particle size but also depend on the structure of the oxide, because magnetite oxidizes to maghemite under environmental conditions. The dynamics of this process have not been well described. Smaller nanoparticles are shown to oxidize more rapidly than larger ones and the lower the storage temperature, the lower the measured oxidation. In addition, the magnetic properties of the altered particles are not decreased dramatically, thus suggesting that this alteration will not impact the use of such nanoparticles as medical carriers. Finally, the effect of biological additives on magnetite formation was investigated. Magnetotactic bacteria¬¬ are able to synthesize and align magnetite nanoparticles of well-defined size and morphology due to the involvement of special proteins with specific binding properties. Based on this model of morphology control, phage display experiments were performed to determine peptide sequences that preferably bind to (111)-magnetite faces. The aim was to control the shape of magnetite nanoparticles during the formation. Magnetotactic bacteria are also able to control the intracellular redox potential with proteins called magnetochromes. MamP is such a protein and its oxidizing nature was studied in vitro via biomimetic magnetite formation experiments based on ferrous ions. Magnetite and further trivalent oxides were found. This work helps understanding basic mechanisms of magnetite formation and gives insight into non-classical crystal growth. In addition, it is shown that alteration of magnetite nanoparticles is mainly based on oxidation to maghemite and does not significantly influence the magnetic properties. Finally, biomimetic experiments help understanding the role of MamP within the bacteria and furthermore, a first step was performed to achieve morphology control in magnetite formation via co-precipitation.
... Complex abiotic mineral structures can also be produced, and it is essential to be able to distinguish these from biological structures. The difficulty in achieving this is most clearly demonstrated by the controversy surrounding the assignment of magnetite crystals within Martian meteorite ALH84001 to biological activity [52,53]. Some minerals do not produce distinctive biologically induced morphologies, but their production is normally thermodynamically unfavourable and their discovery in the environment might indicate biological processes [54]. ...
... Generally, the preparation methods of Fe 3 O 4 nanoparticles include thermal decomposition [15], hydrothermal synthesis [16][17][18][19][20] and co-precipitation [21][22][23], etc., among which hydrothermal synthesis is usually regarded to be a simple and controllable way to synthesize Fe 3 O 4 nanoparticles with diverse morphologies and sizes. In recent studies of hydrothermal synthesis, there have been many reports on changing various experimental parameters to control the morphology of Fe 3 O 4 nanoparticles, such as altering the reaction temperature and reaction time in a one-pot solvothermal synthesis [24], changing the types of precursors [25], varying the amount of surfactant or solvent in the solution [26][27][28][29][30][31]. ...
Article
It has been known that morphology and size could affect the properties of crystalline magnetite (Fe3O4). However, specific principle for a simple and predictable way to control them was still absent. Alkali concentration has been demonstrated to be an influential factor on the morphology changes in an ethylene glycol/diethylene glycol (EG/DEG) binary solvothermal system. In this work, crystalline Fe3O4 nanoparticles with a variety of morphologies including clusters, solid spheres, octahedron, truncated-octahedrons, tetrakaidecahedrons and truncated-cubes were prepared in a facile way. Furthermore, first principle calculation based on density functional theory was carried out to calculate the adsorption energies of OH⁻ on different crystal planes of Fe3O4. The calculation results interpreted the crystal morphology changes accordingly, despite of the simplicity of the calculation model. The agreement between the theoretical calculation and the experimental data indicates the promising benefit of using first principle calculation to predict and design crystal morphologies in the future. On the other hand, size of the anisotropic octahedral Fe3O4 nanoparticles could be regulated from 30 nm to 115 nm by changing the volume ratio of EG/DEG with a certain OH⁻ concentration.
... The proportion of the reactants involved during the synthesis of NPs determine the final particle size, shape, dispersity, and surface chemistry. Diverse techniques and routes have been proposed in the last years to synthesize magnetite iron oxide nanoparticles [9], like sonochemical [10], reverse micelles [11], pyrolysis [12], electrochemical [13], co-precipitation [14], high-temperature reaction [15], and thermal decomposition [16]. Among the different chemical routes reported for the synthesis of magnetic NPs, high-temperature decomposition of organometallic precursors in a supersaturated solution has demonstrated the best outcomes in terms of particle size homogeneity [4]. ...
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Given the central role that nanoparticle size and shape play in many fundamental applications for designing functional materials, fine control of the synthesis has been intensively pursued. A simple one-step method for obtaining monodisperse nanoparticles over a large size range with shape control has not yet been reported. Here, we propose a simple method to control the morphology of magnetite nanoparticles by regulating the amount of non-selective binding surfactant by simply altering the ratio of oleylamine and fatty acid. With this approach, we were able to synthesize magnetite nanoparticles with sizes ranging between 6 ± 1 and 176 ± 20 nm and to select between more rounded or faceted shapes.
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This paper presents a multi-stage, semi-automated procedure that can expedite the morphology analysis of nanoparticles. Material scientists have long conjectured that morphology of nanoparticles has a profound impact on the properties of the hosting material but a bottleneck is the lack of a reliable and automated morphology analysis of the particles based on their image measurements. This paper attempts to fill in this critical void. One particular challenge in nano morphology analysis is how to analyze the overlapped nanoparticles, a problem not well addressed by the existing methods but effectively tackled by our proposed method. Our proposed method entails multiple stages of operations, executed sequentially, and is considered semi-automated due to the inclusion of a semi-supervised clustering step. Our method was applied to several images of nanoparticles, producing the needed statistical characterization of their morphology.
Article
Mục đích chính của nghiên cứu này là tổng hợp và đánh giá tính chất hóa lý, từ tính của vật liệu nano Fe3O4 và Fe3O4@SiO2 có cấu trúc lõi−vỏ, với quá trình thực hiện đơn giản, tiết kiệm. Vật liệu Fe3O4@SiO2 được tổng hợp từ hạt nano Fe3O4 được tạo thành bằng phương pháp đồng kết tủa và bao phủ bởi lớp SiO2 bằng cách sử dụng các phân tử silane từ tetraethyl orthosilicate (TEOS) làm tác nhân chuyển pha và môi trường phủ là một base mạnh (NaOH). Kết quả phân tích nhiễu xạ tia X cho thấy hạt nano Fe3O4 có độ kết tinh cao. Kết quả phân tích hiển vi điện tử quét và hiển vi điện tử truyền qua chỉ ra rằng hạt nano sắt từ thu được có hình khối bát giác với kích thước khá đồng đều khoảng 25 nm kể cả lớp phủ SiO2. Phân tích hồng ngoại biến đổi Fourier cho vật liệu Fe3O4@SiO2 thấy được các mũi Si-O-Si, O-Si-O, Fe-O, Fe-O-Si xuất hiện trên phổ đã minh chứng cho sự tồn tại của silica trên bề mặt hạt nano Fe3O4. Tính siêu thuận từ của vật liệu được khẳng định thông qua kết quả từ kế mẫu rung và độ từ hóa (VSM) của Fe3O4 và Fe3O4@SiO2 lần lượt là 90,54 emu/g và 68,42 emu/g.
Article
Two-dimensional plate-like Fe3O4 nanocrystals and nanoparticles could be synthesized by a simple one-step sonochemical method through ultrasonic irradiation in reverse co-precipitation solution at low temperature. This technique provided a facile and rapid way to prepare Fe3O4nanocrystals with different morphology and size. Magnetite nanoplates were synthesized with only ferrous salt adding into alkali solution, and adding ferric ions with low molar ratio in the metal salts solution would lead to the formation of very small magnetite nanoparticles (∼10 nm). The size of as-prepared magnetite nanoparticles increased with increasing reaction temperature and showed narrow size distribution, the standard deviation less than 2 nm. This investigation indicated that ferric ions had significant influence on the morphology of Fe3O4 nanocrystals. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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The iron pivalate clusters [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu (), [Fe(8)(OH)(4)(O(2)C(t)Bu)(12)(OC(6)H(4)C(6)H(5))(8)] () and [Fe(3)O(O(2)C(t)Bu)(6)(C(5)H(5)N)(3)] () have been used as single source precursors to synthesise iron oxide nanoparticles by a hot injection thermal decomposition method in oleylamine, hexadecanol, oleic acid, oleylamine/oleic acid with dodecanol or octyl ether as solvent. The effect of the different reaction parameters such as temperature, reaction time and capping agents on the phase and morphology were studied. The reaction time was studied for () by thermolysis in a mixture of oleylamine, oleic acid, hexadecanol and dodecanol (solvent) at 260 °C. The results obtained showed that a mixture of maghemite-C (Fe(2)O(3)) and magnetite (Fe(3)O(4)) were obtained for aliquots withdrawn for reaction times of less than 30 minutes whilst only magnetite was obtained after one hour. The nanoparticles were characterised by p-XRD, TEM and magnetic measurements. TEM showed that monodispersed magnetite particles were obtained when the precursor was injected at the boiling point of the solvent. The diameter of the monodispersed nanoparticles obtained by the thermolysis of [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu () in oleylamine, hexadecanol, oleic acid with dodecanol or octyl ether as solvent were 4.3 ± 0.4 and 4.9 ± 0.5 nm respectively. Magnetic measurements revealed that all the particles are superparamagnetic.
Article
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Magnetic (nano)particles are intensively studied in the last years due to their multiple applications. The purpose of this paper is the synthesis of rod-like magnetite by magnetically assisted co-precipitation. The synthesized magnetite nanoparticles were characterized by XRD, DSC-TG and TEM from compositional and especially morphological point of view. The use of 0.5T magnetic field induces a preferential growth of magnetite nanoparticles on the 400 direction while this preferential growth cannot be identified in the absence of the magnetic field proving that the synthesis of rod-like magnetite is due to the applied magnetic field. The mechanism of synthesis was explained based on the magnetite particles behaviour in magnetic field.
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In the present study, oleic acid (OA)-decorated magnetite nanoparticles (MNPs) were synthesized via in situ co-precipitation method using ammonium hydroxide as a precipitating agent. This study aims to determine the optimum loading amount of OA for improving the MNPs colloidal stability. Based on our results obtained, it was found that the zeta potential values of MNPs increased from −29.8 to −58.1 mV after modification of MNPs with 1.2 wt.% of OA. Indeed, results obtained clearly to show that a maximum colloidal stability of MNPs in a basic medium could be significantly improved. As a result, this resultant colloidal suspension performance was approximately 7 times higher (21 days-high colloidal stability against precipitation and agglomeration) than that of the undecorated MNPs sample (3 days). Based on vibrating sample magnetometer (VSM) analysis, the resultant OA-decorated MNPs exhibited superparamagnetic behavior with slightly lower saturation magneti-zation (51–69 emu/g) than that of undecorated MNPs sample (80 emu/g) at room temperature. This behavior was attributed to the sufficient carboxylate ions from the outer layer of the bilayer of OA-decorated MNPs, which promoted the high colloidal stability performance.
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Synthesis of magnetite nanoparticles has attracted increasing interest due to their importance in biomedical and technological applications. Tunable magnetic properties of magnetite nanoparticles to meet specific requirements will greatly expand the spectrum of applications. Tremendous efforts have been devoted to studying and controlling the size, shape and magnetic properties of magnetite nanoparticles. Here we investigate gadolinium (Gd) doping to influence the growth process as well as magnetic properties of magnetite nanocrystals via a simple co-precipitation method under mild conditions in aqueous media. Gd doping was found to affect the growth process leading to synthesis of controllable particle sizes under the conditions tested (0–10 at.% Gd³⁺). Typically, undoped and 5 at.% Gd-doped magnetite nanoparticles were found to have crystal sizes of about 18 and 44 nm, respectively, supported by X-ray diffraction and transmission electron microscopy. Our results showed that Gd-doped nanoparticles retained the magnetite crystal structure, with Gd³⁺ randomly incorporated in the crystal lattice, probably in the octahedral sites. The composition of 5 at.% Gd-doped magnetite was Fe(3-x)GdxO4 (x=0.085±0.002), as determined by inductively coupled plasma-mass spectrometry. Gd-doped nanoparticles exhibited ferrimagnetic properties with small coercivity (~65 Oe) and slightly decreased magnetization at 260 K in contrast to the undoped, superparamagnetic magnetite nanoparticles. Templation by the bacterial biomineralization protein Mmm6 did not appear to affect the growth of the Gd-doped magnetite particles synthesized by this method.
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This work aims at developing a novel method for fabricating 1D magnetite nanostructures with the help of mutagenized flagellar filaments. We constructed four different flagellin mutants displaying magnetite-binding motifs. Two of the mutants contained fragments of magnetosome-associated proteins from magnetotactic bacteria (MamI and Mms6), whereas for the other two mutants synthetic sequences were used. A magnetic selection procedure identified the mutant incorporating the loop segment from MamI to have the highest binding affinity towards magnetite. Filaments built from MamI loop-containing flagellin subunits were used as templates to form chains of magnetite nanoparticles along the filament by capturing them from suspension. Our study presents a proof of concept that flagellar filaments can be engineered to facilitite formation of 1D magnetite nanostructures under ambient conditions. In addition, it proves the interaction between MamI and magnetite, with implications for the role of the protein in magnetotactic bacteria.
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In this study, nanomagnetite particles have been successfully prepared via the coprecipitation method. The effect of the key explanatory variables on the saturation magnetization of synthetic nanomagnetite particles was investigated using the response surface methodology (RSM). The correlation of the involved parameters with the growth process was examined by employing the central composite design method through designating set up experiments that will determine the interaction of the variables. The vibrating sample magnetometer (VSM) was used to confirm the statistical analysis. Furthermore, the regression analysis monitors the priority of the variables' influence on the saturation magnetization of nanomagnetite particles by developing the statistical model of the saturation magnetization. According to the investigated model, the highest interaction of variable belongs to the pH and temperature with the optimized condition of 9–11, and 75–85 °C, respectively. The response obtained by VSM suggests that the saturation magnetization of nanomagnetite particles can be controlled by restricting the effective parameters.
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There is an increasing technological demand for magnetic nanocrystals with special morphologies and controlled sizes. Several approaches are used for the synthesis of magnetite crystals with irregular or octahedral shapes; however, the room-temperature synthesis of nanocrystals with specific morphologies is not yet established. Here, we describe the synthesis of magnetite crystals (100–300 nm) at a relatively low temperature (~70 °C) from organic precursors, including Fe(II) oxalate or Fe(II) sulfate, and study the effects of ethylene glycol and tetraethylene glycol on the final physical and chemical properties of the crystals. The magnetite crystals formed from different precursor materials (sulfate or oxalate green rust) show specific morphological and textural features. We show that octahedral magnetite crystals can be produced from Fe(II) oxalate via a simple co-precipitation process. Using different kinds and amounts of polyols, various types of particle morphologies and nanocrystal textures can be produced, including hexagonal-shaped clusters of elongated crystals and porous and solid, large, rounded polycrystalline aggregates.
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In this work, we aimed to develop a feasible method for in situ preparation of a magnetite ionic polymer nanocomposite at room temperature. For this purpose, acrylonitrile (AN) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers were copolymerized and crosslinked using different monomer mol ratios in the presence of N,N-methylenebisacrylamide (MBA) as crosslinker to produce ionic crosslinked polymers P(AN-co-AMPS. The nitrile groups were converted to amine amidoxime by reacting with hydroxylamine to increase the adsorption characteristics of the ionic polymers. The produced polymers were swelled in iron cations produced from the reaction of ferric chloride and potassium iodide, followed by reaction with an ammonium hydroxide solution to produce magnetite nano-polymer composites. We performed FT-IR and XRD analysis to determine the chemical and crystalline structures, and assessed the morphologies and magnetite content using SEM, TEM and TGA analyses. We investigated the adsorption capacity and mechanism of the prepared magnetite nano-composites as adsorbents for methylene blue, Co2+ and Ni2+ cations from water.
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Nanotechnology is an engineering science in which the aim is to develop novel procedures and structures at the nanoscale that might offer solutions to many current problems. In this article, we describe the synthesis of superparamagnetic iron oxide (Fe3O4) nanoparticles in biochar obtained from the condensed tannin extract of Acacia mearnsii, using a single-step process that is compliant with the principles of green chemistry. Characterization of this material (acronym: SPMIOBNs) was performed using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The porous particles produced contained iron oxide nanoparticles with average sizes in the range 20-35nm. The magnetic properties revealed that the SPMIOBNPs were superparamagnetic, with a saturation magnetization of 3.2memu/g at 300K.
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Various uses of ferrofluids for technical applications continuously raise interest in the improvement and optimization of the preparation methods. This paper deals with the preparation of finely granulated magnetite particles coated with oleic acid in hydrocarbon suspensions following either chemical co-precipitation from iron salt precursors or wet milling of micron size magnetite powder with the goal to compare the benefits and disadvantages of each method. Microstructural measurements showed that both methods gave similarsized magnetite particles of 10-15 nm. The wet-milled magnetite suspension had a higher saturation magnetization than that obtained in the relatively rapid co-precipitation synthesis. The different efficacies of ferrophase incorporation into kerosene could be related to the different mechanisms of oleic acid bonding to the surface of the nanoparticles. Comparative data showed that wet milling represents a viable alternative to the traditional co-precipitation method since despite of longer processing time, the impact of chemicals on the environment and remnant water in the final product could be avoided.
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Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from the Martian meteorite. In contrast to previous accounts, we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars.
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We studied intracellular magnetite particles produced by several morphological types of magnetotactic bacteria including the spirillar (helical) freshwater species, Magnetospirillum magnetotacticum, and four incompletely characterized marine strains: MV-1, a curved rodshaped bacterium; MC-1 and MC-2, two coccoid (spherical) microorganisms; and MV-4, a spirillum. Particle morphologies, size distributions, and structural features were examined using conventional and high-resolution transmission electron microscopy. The various strains produce crystals with characteristic shapes. All habits can be derived from various combinations of the isometric {111}, {110}, and {100} forms. We compared the size and shape distributions of crystals from magnetotactic bacteria with those of synthetic magnetite grains of similar size and found the biogenic and synthetic distributions to be statistically distinguishable. In particular, the size distributions of the bacterial magnetite crystals are narrower and have a distribution asymmetry that is the opposite of the nonbiogenic sample. The only deviation from ideal structure in the bacterial magnetite seems to be the occurrence of spinel-law twins. Sparse multiple twins were also observed. Because the synthetic magnetite crystals contain twins similar to those in bacteria, in the absence of characteristic chains of crystals, only the size and shape distributions seem to be useful for distinguishing bacterial from nonbiogenic magnetite.
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The aim of the present research is to determine the kinetics of the transformation from hematite (alpha-Fe2O3) to magnetite (Fe3O4). The procedure consisted of an isothermal heating in a flow of a H2 Ar mixture at temperatures between 260 and 360 °C. The phase evolution at a given temperature, as a function of the thermal treatment time, was monitored by using room temperature Mössbauer spectroscopy and X-ray diffraction analysis (XRD). In the range of temperatures and times studied the only iron oxide that was formed was magnetite. In order to optimize equipment requirements for the quantification of the reaction products a calibration curve was constructed. This allows to estimate the conversion degree (measured as the percentage of magnetite produced) with a short-run XRD pattern. We calculate an apparent activation energy of 98±4 kJ/mol from reaction grade time curves at each temperature.
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A series of experiments has been carried out to investigate the possible formation of magnetite, Fe3O4, under ambient soil-forming conditions. Rapid and easy synthesis of magnetite was achieved through controlled oxidation of Fe2+ solutions at room temperatures and near neutral pH values. The synthetic products were found to range in size between 0.01-0.07 micrometre (mean diameter) and hence span the theoretical superparamagnetic-single-domain grain-size boundary. -Authors
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Magnetite nanorods have been prepared by the sonication of aqueous ironIIacetate in the presence of -cyclodextrin. The properties of the magnetite nanorods were characterized by x-ray diffraction, Mö ssbauer spectroscopy, transmission electron microscopy, thermogravimetric analysis, and magnetization measurements. The as-prepared magnetite nanorods are ferromagnetic and their magnetization at room temperature is 78 emu/g. The particle sizes measured from transmission electron micrographs are about 48/14 nm L/W. A mechanism for the sonochemical formation of magnetite nanorods is discussed. © 2001 American Institute of Physics.
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