Microbial synthesis of magnetite and Mn-substituted magnetite nanoparticles: influence of bacteria and incubation temperature

Microbial synthesis of magnetite and metal (Co, Cr, Ni)-substituted magnetites has only recently been reported. The objective of this study was to examine the influence of Mn ion on the microbial synthesis of magnetite nanoparticles. The reductive biotransformation of an akaganeite (beta-FeOOH) or a Mn-substituted (2-20 mol%) akaganeite (Fe(1-x)Mn(x)OOH) by Shewanella loiha (PV-4, 25 degrees C) and Thermoanaerobacter ethanolicus (TOR-39, 60 degrees C) was investigated under anaerobic conditions at circumneutral pH (pH = 7-8). Both bacteria formed magnetite nanoparticles using akaganeite as a magnetite precursor. By comparison of iron minerals formed by PV-4 and TOR-39 using Mn-mixed akaganeite as the precursor, it was shown that PV-4 formed siderite (FeCO3), green rust [Fe2+Fe3+(OH)16CO3 x 4H2O], and magnetite at 25 degrees C, whereas TOR-39 formed mainly nm-sized magnetite at 60 degrees C. The presence of Mn in the magnetite formed by TOR-39 was revealed by energy dispersive X-ray analysis (EDX) is indicative of Mn substitution into magnetite crystals. EDX analysis of iron minerals formed by PV-4 showed that Mn was preferentially concentrated in the siderite and green rust. These results demonstrate that coprecipitated/sorbed Mn induced microbial formation of siderite and green rust by PV-4 at 25 degrees C, but the synthesis of Mn-substituted magnetite nanoparticles proceeded by TOR-39 at 60 degrees C. These results indicate that the bacteria have the ability to synthesize magnetite and Mn-substituted magnetite nano-crystals. Microbially facilitated synthesis of magnetite and metal-substituted magnetites at near ambient temperatures may expand the possible use of specialized ferromagnetic nano-particles.     

Synthesis and kinetic shape and size evolution of magnetite nanoparticles

Eleven nanometers of magnetite nanoparticles were synthesized by using 6 nm magnetite nanoparticles as seeds and Fe(acac)₃ as precursor at high temperature. Growth kinetics of magnetite nanoparticles was studied during the progress of reaction. Magnetite nanoparticles with different shapes including near-sphere, tetrahedral, truncated tetrahedral and cubic were observed at different reaction time. Transmission electron microscopic results show that the shape and size distributions are time- and temperature-dependent. Hydrodynamic diameter results give the kinetic size distribution changes of magnetite nanoparticles during the reaction, which suggest that this synthesis underwent a “growth-controlled nucleation”.     

Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.     

Optimization and evaluation of microwave-assisted synthesis of magnetite as a carrier for targeted drug delivery system

ABSTRACT

The present research work is a novel cost-effective method for synthesis of magnetite. Magnetite is a carrier which is used in the targeted drug delivery system. The conventional methods of preparation of magnetite take around 6–7 h for the completion of reaction; moreover, the particle size of magnetite which we get by the conventional methods is above 5 µm, so the present work aims at preparing magnetite with microwave assistance which has found to reduce reaction time with particle size obtained below 5 µm. The aim of this study was to optimize magnetite synthesis using 2³ factorial design by Design-Expert software. Magnetites were synthesized using oxidation of ferrous sulfate. In the next step, the effects of different variables on particle size are studied, including the stirring speed, microwave power (W), and stirring time. Based on the type and the variables studied, eight formulations were designed using factorial design method, and were then prepared, and their particle size was determined. Finally, selected magnetite syntheses were evaluated from the viewpoints of scanning electron microscopy (SEM) and x-ray diffraction (XRD). Results revealed that magnetite obtained from the solutions generated Design-Expert software could be selected as the best and optimized formulations due to their lowest particle size.     

Magnetic properties of biosynthesized magnetite nanoparticles

Magnetic nanoparticles, which are unique because of both structural and functional elements, have various novel applications. The popularity and practicality of nanoparticle materials create a need for a synthesis method that produces quality particles in sizable quantities. This paper describes such a method, one that uses bacterial synthesis to create nanoparticles of magnetite. The thermophilic bacterial strain Thermoanaerobacter ethanolicus TOR-39 was incubated under anaerobic conditions at 65/spl deg/C for two weeks in aqueous solution containing Fe ions from a magnetite precursor (akaganeite). Magnetite particles formed outside of bacterial cells. We verified particle size and morphology by using dynamic light scattering, X-ray diffraction, and transmission electron microscopy. Average crystallite size was 45 nm. We characterized the magnetic properties by using a superconducting quantum interference device magnetometer; a saturation magnetization of 77 emu/g was observed at 5 K. These results are comparable to those for chemically synthesized magnetite nanoparticles.     

Synthesis of monodisperse iron oxide and iron/iron oxide core/shell nanoparticles via iron-oleylamine complex

Monodisperse magnetic nanoparticles are of great scientific and technical interests. This paper reports a single-step synthesis of monodisperse magnetite nanoparticles with particle size of 8 nm. Iron/maghaemite core/shell nanoparticles with particle size of 11 nm were obtained by reducing the concentration of oleylamine. TEM and in-situ FTIR results suggested that iron-oleylamine intermediate was generated in-situ and decomposed at higher temperature. Oleylamine was also found on the surface of nanoparticles, indicating its role as capping agent which provided steric protection of as-synthesized nanoparticles from agglomeration. Both magnetite and iron/maghaemite core/shell nanoparticles were superparamagnetic at room temperature with a blocking temperature at 80 K and 67 K, respectively.     

An experimental investigation of aqueous-phase synthesis of magnetite nanoparticles via mechanochemical reduction of goethite

A newly developed mechanochemical process for the simple aqueous phase synthesis of crystalline magnetite nanoparticles has been experimentally investigated. In this process, a suspension of ferric hydroxide precursor is milled at room temperature using a horizontal tumbling ball mill consisting of a stainless steel pot and balls. Ferric hydroxide is transformed to magnetite without the use of a reducing agent. As a model starting material for the investigation, a pH-adjusted suspension of crystalline goethite was used. As the milling time increased, goethite disappeared along with the simultaneous formation of magnetite. A single phase of magnetite was obtained after 16 h of milling. A reaction mechanism for the formation of magnetite has been proposed based on oxidation–reduction reactions, in which the corrosion of iron in the pot and balls plays an important role. Free electrons are generated by the release of ferrous ions from the stainless steel in an anodic reaction, which then reduce goethite to ferrous hydroxide in a cathodic reaction. The solid phase reaction between ferrous hydroxide and goethite produces magnetite. Not only could the mechanochemical effect induced by the collision of balls accelerate the corrosion even under alkaline conditions, it can also promote the formation and crystallization of magnetite.     

Hierarchical magnetite/silica nanoassemblies as magnetically recoverable catalyst-supports

We report the synthesis of magnetically responsive hierarchical assemblies of silica colloids that can be used as recoverable supports for nanocatalysts. Each assembly is composed of a central magnetite/silica composite core and many small satellite silica spheres. The two regions are held together as a stable unit by a polymer network of poly(N-isopropylacrylamide). The central magnetite particles are superparamagnetic at room temperature with strong magnetic response to external fields, thus providing a convenient means for separating the entire assembly from the solution. The satellite silica particles provide large surface areas for loading nanocatalysts through the well-developed silane chemistry. As an example, we demonstrate the use of such magnetically responsive hierarchical assemblies as recoverable supports for Au nanocatalysts for the reduction of 4-nitrophenol with NaBH4.     

Sustained release of doxorubicin from zeolite-magnetite nanocomposites prepared by mechanical activation

Nanocomposites consisting of magnetite and FAU zeolite with a high surface area and adsorption capacity have been prepared by mechanical activation using high-energy milling at room temperature. FTIR results, as well as HRTEM, EFTEM, and XPS measurements, show that the resulting magnetic nanoparticles are covered by a thin aluminosilicate coating. A saturation magnetization as high as 16?emu?g(-1) and 94.2?Oe of coercivity were observed for the obtained composites. The main advantages of this synthesis procedure are (i) simplicity of the preparation procedure, (ii) prevention of agglomeration of the magnetite nanoparticles to a large extent, and (iii)?absence of free magnetite outside the zeolitic matrix. In addition, in vitro experiments revealed that the nanoparticles prepared were able to store and release substantial amounts of doxorubicin. In view of these advantages, these magnetic nanoparticles can be considered as potential candidates for drug-delivery applications.     

Structure and Magnetic Properties of Polymer Microspheres Filled with Magnetite Nanoparticles

The structure and magnetic properties of collagen microspheres filled with magnetite nanoparticles are studied. The average interparticle separation in the polymer matrix and the size of magnetite nanoparticles before and after the introduction of the nanoparticles into the matrix are determined using electron microscopy. The magnetization curve of the microspheres has a superparamagnetic character. The magnetite nanoparticles undergo no aggregation during the synthesis of microspheres and are evenly distributed over the matrix. The magnetic susceptibility data for magnetic polymer microspheres of different diameters suggest that, at small diameters (<300 m), all of the nanoparticles, aligned in chains, contribute to magnetization; at large diameters, some of the chains give way to clusters, the chains are shorter, and, accordingly, the susceptibility is lower.     

Synthesis of magnetite/amphiphilic polymer composite nanoparticles as potential theragnostic agents

This study describes the synthesis of magnetite/amphiphilic polymer composite nanoparticles that can be potentially used simultaneously for cancer diagnosis and therapy. The synthesis method was a one-shot process wherein magnetite nanoparticles were mixed with core-crosslinked amphiphilic polymer (CCAP) nanoparticles, prepared using a copolymer of a urethane acrylate nonionomer (UAN) and a urethane acrylate anionomer (UAA). The CCAP nanoparticles had a hydrophobic core and a hydrophilic exterior with both PEG segments and carboxylic acid groups, wherein the magnetite nanoparticles were coordinated and stabilized. According to DLS data, the ratio of UAN to UAA and the ratio of magnetite to polymer are keys to controlling the size and thus, the stability of the composite nanoparticles. The magnetic measurement indicated that the composite nanoparticles had superparamagnetic properties and high saturation magnetization. The preliminary magnetic resonance imaging showed that the particles produced an enhanced image even when their concentration was as low as 80 microg/ml.     

X-ray photoelectron spectra of magnetite nanopowders after chromium(VI) sorption from aqueous solutions

Fe₃O₄ nanopowders prepared by three different procedures (vapor-phase synthesis, chemical precipitation from aqueous solutions, and laser evaporation) have been characterized by X-ray photoelectron spectroscopy before and after chromium(VI) sorption from aqueous solutions. The results demonstrate that, during sorption, the chromium is concentrated in the magnetite at a level of several atomic percent, and its oxidation state is 3+. The mechanism of chromium sorption on magnetite particles is discussed.     

Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens

The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50?nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form.     

Influence of polyols on the formation of iron oxide nanoparticles in solvothermal system

We reported a simple solvothermal route in phase-controllable synthesis of iron oxide nanoparticles by using polyols as solvent. Magnetite and hematite are selectively synthesized while Fe(NO3)3.9H2O is used as single iron source and without any additives. While ethylene glycol, 1,2propanediol, 1,3-butanediol, or glycerol is used as solvents, magnetite nanoparticles are obtained, and the average particle sizes vary from 10 to 40 nm. While 1,4-butanediol or 1,5-pentanediol is used as solvents, hematite nanoparticles are obtained. Our results suggest that the polyols with neighboring hydroxyl groups is favorable for the formation of magnetite nanoparticles.     

One-step wet chemistry for preparation of magnetite nanorods

A magnetite with high aspect ratio has been synthesized by a wet chemical process. A surfactant, polyethylene glycol, was used as the template, and a ferrous ammonia sulphate was used as iron source. In the one-step synthesis, a suitable ratio between the rates of deposition and oxidation of ferrous ions was achieved by adjusting the diffusion of ammonia and resulted in the iron oxide deposited with nanorod morphology. According to X-ray powder diffraction analysis, these nanorods crystallize in structure of magnetite phase. Transition electron microscopy and selected area electron diffraction investigations have revealed that nanorods are single crystal and up to 2000 nm long and their diameters generally range from 20 to 100 nm. The measurement by vibration sample magnetization shows the magnetization of the as-synthesized nanorods is higher than 50 emu/g. The presented one-step synthesis approach provides an advantageous access to large quantity of this important anisotropic nanomaterial.     

Magnetic properties of magnetite nanoparticles synthesized by forced hydrolysis

We report the synthesis of superparamagnetic nanoparticles of iron oxide in magnetite phase with diameters of approximately 15 nm. Nanoparticles of magnetite were synthesized by forced hydrolysis method, controlling the oxidation with a nitrogen atmosphere during the synthesis. Nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometry. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profiles. In order to obtain nanometers sizes of magnetite phase solely, the parameters of formation such a pH and molar concentration were analyzed and determined by an equilibrium thermodynamics model with the chemical computer code MINTEQA [Allison Geoscience Consultants, Inc., HydroGeoLogic, Inc., MINTEQA2 for Windows, Equilibrium Speciation Model. Ver 1.5(2003)].     

Synthesis of nanocrystalline magnetite by mechanical alloying of iron and hematite

The synthesis of magnetite has been studied by mechanical alloying in an inert atmosphere of a stoichiometric mixture of micrometric particle size iron and hematite powders. The final products have been characterised by chemical analysis, SEM, TEM, XRD, Mössbauer spectroscopy as well as specific surface and magnetic measurements. The magnetite obtained in this way exhibits a high magnetic hardness. The formation of a wüstite layer on the magnetite core, because of the reaction between magnetite and iron contamination coming from the bowls and grinding balls, tends to decrease the coercive force of magnetite. The formation of this phase would be avoided by controlling the grinding time.     

Influence of the precipitation pH of magnetite in the oxidation process to maghemite

The aim of this work is to study about the synthesis of maghemite starting from cubic magnetite, using a mathematical model, which not only includes factors associated to the oxidation process of magnetite, but also factors related with precursor characteristics, such as the precipitation pH for the Fe(OH)₂. Two samples of magnetite, obtained by oxidation of Fe(OH)₂ to pH 8–9 and pH > 11, respectively, were air-heated under different conditions, planned according to the fractional factorial design 2⁶⁻³. The experiment was done in two zones, one (zone 1) that considered the values reported in the literature and tentative experiments and another (zone 2), whose values are far removed from the first set. Based on the results of the statistical analysis, it was concluded that the model was adequate to zone 1 (M and N samples) where the relevant parameters are those corresponding to: the independent term, the air flow, the time, the mass, the pH (of the magnetite precipitation) and the interaction of the time and pH variables. In zone 2 (O and P samples) it was impossible to write a corresponding equation due to parameter interactions; also, the model proved inadequate. The oxidation process of Fe₃O₄ to γ-Fe₂O₃ also depends on the precursor characteristics. The magnetite obtained at pH between 8 and 9 is oxidized to maghemite more completely than magnetite synthesized at pH > 11.     

Solvothermal synthesis and magnetic properties of magnetite nanoplatelets

Nanostructured magnetite plates were synthesized by a simple solvothermal route where ethylenediamine was used as the solvent and reducing agent. The morphology and structure of the as-prepared platelets were characterized using X-ray diffraction, infrared spectroscopy and transmission electron microscopy. The results showed that the products are magnetite crystals with plate like morphology whose thickness is estimated to be 20 nm. Magnetic measurements at 300 K gave the saturation magnetization and the coercive field of nanostructured magnetite 87.4 emu/g and 178 Oe, respectively, which are higher than those of cubic nanoparticles, due to the higher shape anisotropy of magnetite nanoplatelets.     

超顺磁性纳米Fe3O4的热分解法制备及表征

以单甲氧基聚乙二醇、对甲苯磺酰氯、邻苯二甲酰亚胺钾等为原料,根据盖布瑞尔合成法原理,合成了一端为氨基的单甲醚聚乙二醇(mPEG-NH2)。并以其为还原剂,聚乙二醇(PEG)为溶剂,利用热分解法制备了水分散性的超顺磁性纳米Fe3O4。采用红外光谱(FT-IR)、X射线衍射(XRD)、透射电镜(TEM)、热重分析(TG)、超导量子干涉仪(SQUID)和纳米粒度与Zeta电位分析仪等测试技术对其性能进行表征,实验结果表明,所制得的纳米Fe3O4粒子结晶度高,粒度均匀,分散良好,平均粒径为(12.2±1.6)nm,具有超顺磁性,饱和磁化强度为54 emu/g,在中性水溶液中其表面带正电,Zeta电位为+33 mV。TG测试结果表明,Fe3O4纳米粒子表面有机物的含量约为28%,Fe3O4的产率为57%左右。