Microwave-assisted synthesis of magnetite nanoparticles possessing superior magnetic properties

1. Download high-res image (126KB)
2. Download full-size image

     

Glass crystallization synthesis of ultrafine hexagonal M-type ferrites: Particle morphology and magnetic characteristics

This review concerns the synthesis and functional properties of ultrafine particles of M-type hexagonal ferrites prepared by the most advanced process of oxide glass crystallization. Hexaferrite phase formation during the heat treatment of multicomponent oxide glasses of various chemical compositions containing boron and/or silicon oxides as glass formers is considered. This route is useful to prepare assemblies of single-crystal strontium barium hexaferrite particles in the range of average particle sizes from tens of nanometers to several micrometers. The resulting glass ceramics and magnetic particle assemblies recovered from them are characterized by high coercive forces, approaching the theoretical limit for such compounds, and high magnetizations, close to the magnetization value for coarse-grained materials.     

Facile synthesis of magnetic microcapsules by synchronous formation of magnetite nanoparticles

Magnetite/poly (lactic acid) (PLA) composite microcapsules with controllable composition and magnetic property were synthesized by a facile interfacial coprecipitation joint double emulsion–solvent evaporation process. In this method, the interfacial coprecipitation was performed at the water-in-oil (W₁/O) interface and the generated Fe₃O₄ nanoparticles were incorporated into PLA microcapsules simultaneously. The magnetite content of the resultant composite microcapsules can be controlled as high as 38 wt.%. This novel method not only simplifies the fabrication process but also improves the magnetic property of composite microcapsules.     

Disappearance of long range spin-order in ultrafine magnetite particles

Ferromagnetic properties of ultrafine magnetite (Fe₃O₄) particles were examined by the ESR and the static magnetic susceptibility measurements. Ferromagnetic resonance became to be observed at the particle size larger than 3.4 nm. This finding suggests that the bulk-like ferromagnetic state cannot be formed in the particle less than 3.4 nm diameter for magnetite. Magnetic moments in such a small diameter region were also determined by the analyses of magnetization curves and were found to be smaller than those expected from the particle size. These findings from ESR and magnetization are discussed to clarify the nature of spin-ordering in a finite size sample.     

Iron phosphate mediated magnetite synthesis: a bioinspired approach

The biomineralization of intracellular magnetite in magnetotactic bacteria (MTB) is an area of active investigation. Previous work has provided evidence that magnetite biomineralization begins with the formation of an amorphous phosphate-rich ferric hydroxide precursor phase followed by the eventual formation of magnetite within specialized vesicles (magnetosomes) through redox chemical reactions. Although important progress has been made in elucidating the different steps and possible precursor phases involved in the biomineralization process, many questions still remain. Here, we present a novel in vitro method to form magnetite directly from a mixed valence iron phosphate precursor, without the involvement of other known iron hydroxide precursors such as ferrihydrite. Our results corroborate the idea that phosphate containing phases likely play an iron storage role during magnetite biomineralization. Further, our results help elucidate the influence of phosphate ions on iron chemistry in groundwater and wastewater treatment.

Magnetite was synthesized from a mixed valence iron phosphate precursor through a novel mechanism inspired by biomineralization in magnetotactic bacteria.     

Hydration of monosaccharides: A study by dielectric and nuclear magnetic relaxation

NMR studies indicate that the relaxation rate of¹⁷O-enriched water is enhanced in monosaccharide solutions, and it is greater in hexose solutions than with a pentose, ribose. Three dielectric relaxations have been isolated and assigned to bulk water相似文献   

Optimization of synthesis conditions and the study of magnetic and dielectric properties for MgFe2O4 ferrite

Nano-sized magnesium ferrites were synthesized by the sol-gel auto-combustion method using a variety of chelating/combustion agents: tartaric acid, citric acid, cellulose, glycine, urea and hexamethylenetetramine. The original purpose of this work was the synthesis of nano-sized magnesium ferrite by using, for the first time, cellulose and hexamethylenetetramine as chelating/combustion agents. Synthesized samples were subjected to different heat treatments at 773 K, 973 K and, respectively 1173 K in air. The disappearance of the organic phase and nitrate phase with the spinel structure formation was monitored by infrared absorption spectroscopy. Spinel structure, crystallite size and cation distribution were evaluated by X-ray diffraction data. The morphology of as-prepared powders was studied using scanning electron microscopy. The magnetic and dielectric properties were studied for the obtained samples.      

Size-controlled synthesis of magnetite nanoparticles

Monodisperse magnetite nanoparticles have been synthesized by high-temperature solution-phase reaction of Fe(acac)3 in phenyl ether with alcohol, oleic acid, and oleylamine. Seed-mediated growth is used to control Fe3O4 nanoparticle size, and variously sized nanoparticles from 3 to 20 nm have been produced. The as-synthesized Fe3O4 nanoparticles have inverse spinel structure, and their assemblies can be transformed into gamma-Fe2O3 or alpha-Fe nanoparticle assemblies, depending on the annealing conditions. The reported procedure can be used as a general approach to various ferrite nanoparticles and nanoparticle superlattices.     

Surfactant-assisted one-pot synthesis of superparamagnetic magnetite nanoparticle clusters with tunable cluster size and magnetic field sensitivity

Magnetic nanoparticles (MNPs) have many potential biomedical applications. Improvements in their magnetic properties and solubility are necessary for these applications to realize their full potential. In this study, MNPs in the form of raspberry-like magnetite (Fe(3)O(4)) nanoparticle clusters, consisting of tiny Fe(3)O(4) particles with a diameter of approximately 20 nm, were prepared under hydrothermal conditions at 200 °C in the presence of 3,4-dihydroxyhydroxysinnamic acid (DHCA). The primary particles were connected by DHCA molecules to form the clusters, which were well dispersed in water media because a COOH group from DHCA appeared on their surfaces. The cluster size could be tuned from 50 to 400 nm without changing the primary particle size by controlling the reaction time. Therefore, all prepared clusters displayed superparamagnetic properties at room temperature. In addition, the sensitivity of Fe(3)O(4) to an external magnetic field could also be controlled by the cluster size.     

Bacterial aerobic synthesis of nanocrystalline magnetite

The synthesis of iron oxide nanoparticles of the predominantly magnetite phase by the reaction of aqueous iron complexes with the bacterium, Actinobacter spp., is described. This reaction occurs at room temperature and under aerobic conditions, resulting in the formation of superparamagnetic magnetite.     

Green synthesis of banana flavor using different catalysts: a comparative study of different methods

ABSTRACT

Esterification of isoamyl alcohol with acetic acid was studied using different ion-exchange resins, namely Amberlyst 15 dry, Amberlyst 16 wet, Amberlite 120-IR. Esterification was carried out using different esterification methods that are quite new (ohmic, ultrasonic probe, and ultrasonic bath) and the results were compared with microwave-assisted esterification (MAE). The highest isoamyl acetate yield (99%) was obtained by MAE, using a mixture of acetic acid and isoamyl alcohol (mole ratio of 1:2) after 2?h of reaction time. In this process, 2% Amberlyst 15 dry was used. MAE had the least specific energy consumption (0.42?kWh/g isoamyl acetate) and specific CO₂ emission (34?g/g isoamyl acetate). According to the images obtained by scanning electron microscopy, lower amounts of Amberlyst 15 dry beads were destroyed by MAE method compared to other esterification methods. In conclusion, MAE proved to be an economic and environmentally-friendly method for esterification of different flavoring compounds.     

Solvent extraction of arsenic(V) with dispersed ultrafine magnetite particles.

The solvent extraction of arsenic(V) was investigated using heptane containing ultrafine magnetite particles and hydrophobic ammonium salt. Arsenic(V) was favorably extracted from aqueous solutions of pH ranging over 2-7, where the distribution ratio (10(3)) was independent of the pH. Although the addition of alkyl ammonium salt improved the phase separation, no notable influence was observed on the extraction of arsenic(V). Oleic acid suppressed the distribution ratio of arsenic(V) when the concentration exceeded 10(-2) M. Sulfate did not interfere with the extraction, while the presence of more than 10(-3) M phosphate decreased the distribution ratio. Metal cations including calcium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and lanthanum(III) did not give any serious interference up to the 10(-4) M level. According to equilibrium and kinetic studies, the extraction of arsenic(V) can be interpreted by the adsorption of H2AsO4- onto the surface of dispersed magnetite particles. The relationship between the amount of arsenic(V) extracted in the organic phase and that remaining in an aqueous phase followed a Langmuir-type equilibrium equation. The maximum uptake capacity was determined to be 4.8 x 10(-4) mol/g-magnetite (36 mg As/g). The arsenic(V) extracted in the organic phase was quantitatively recovered by back-extraction with an alkaline solution.     

One-step synthesis and functionalization of hydroxyl-decorated magnetite nanoparticles

Magnetite nanoparticles covered by a layer of omega-hydroxycarboxylic acid were synthesized in one step by high-temperature decomposition of iron(III) omega-hydroxycarboxylates in tri- and tetra-ethylene glycol. The nanoparticles were characterized by TEM, XRD, IR, XPS and NMR techniques in order to show that they comprise a crystalline magnetite core and actually bear on the outer surface terminal hydroxy groups. The latter ones are convenient "handles" for further functionalization as opposed to the chemically-inert aliphatic chains which cover conventionally synthesized nanoparticles. This was shown by several examples in which the hydroxy groups on the nanoparticle surface were easily transformed in other functional groups or reacted with other molecules. For instance, the hydroxyl-decorated nanoparticles were made water soluble by esterification with a PEGylated acetic acid. The reactive behavior of the surfactant monolayer was monitored by degrading the nanoparticles with aqueous acid and isolating the surfactant for NMR characterization. In general, the reactivity of the terminal hydroxyl groups on the nanoparticle surface parallels that observed in the free surfactants. The reported hydroxyl-decorated magnetite nanoparticles can be thus considered as pro-functional nanoparticles, i.e., a convenient starting material to functionalized magnetic nanoparticles.     

Micellar synthesis and characterization of ultrafine silver powders

We have developed methods for the synthesis and coagulation of ultrafine silver powders in the water-Triton N-42-decane inverted-micellar system. Varying AgNO₃ concentration (1–5 mol/L), the type of reducing agent (hydrazine or potassium borohydride), and the coagulation method (spontaneous or induced by acetone or water addition) allowed us to select the parameters that provide powders containing about 98% silver and having particle sizes of 15–80 nm. We propose methodology for characterizing ultrafine silver powders comprising the determination of the total and surface composition and the charge state of impurities using atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), microanalysis, FTIR spectroscopy, and X-ray photoelectron spectroscopy. The impurity composition of the nanomaterial is found to depend on the type of reducing agent, the synthesis parameters, and coagulation conditions.     

Confinement synthesis in porous molecule-based materials: a new opportunity for ultrafine nanostructures

A balance between activity and stability is greatly challenging in designing efficient metal nanoparticles (MNPs) for heterogeneous catalysis. Generally, reducing the size of MNPs to the atomic scale can provide high atom utilization, abundant active sites, and special electronic/band structures, for vastly enhancing their catalytic activity. Nevertheless, due to the dramatically increased surface free energy, such ultrafine nanostructures often suffer from severe aggregation and/or structural degradation during synthesis and catalysis, greatly weakening their reactivities, selectivities and stabilities. Porous molecule-based materials (PMMs), mainly including metal–organic frameworks (MOFs), covalent organic frameworks (COFs) and porous organic polymers (POPs) or cages (POCs), exhibit high specific surface areas, high porosity, and tunable molecular confined space, being promising carriers or precursors to construct ultrafine nanostructures. The confinement effects of their nano/sub-nanopores or specific binding sites can not only effectively limit the agglomeration and growth of MNPs during reduction or pyrolysis processes, but also stabilize the resultant ultrafine nanostructures and modulate their electronic structures and stereochemistry in catalysis. In this review, we highlight the latest advancements in the confinement synthesis in PMMs for constructing atomic-scale nanostructures, such as ultrafine MNPs, nanoclusters, and single atoms. Firstly, we illustrated the typical confinement methods for synthesis. Secondly, we discussed different confinement strategies, including PMM-confinement strategy and PMM-confinement pyrolysis strategy, for synthesizing ultrafine nanostructures. Finally, we put forward the challenges and new opportunities for further applications of confinement synthesis in PMMs.

The space-, coordination-, and/or ion-confinement in porous molecule-based materials (PMMs) endow the PMM-confinement (pyrolysis) synthesis to construct a variety of ultrafine nanostructures.     

等离子体法合成超细碳氮化钛固溶体微粉

本研究以tiCl4、CH4和N3或NH3为原料, 在直流电弧氢等离子体反应器中合成了三元超细碳氮化钛(TiCxN1-x)固溶体微粉。考察了不同氮源及其加入量对产物组成的影响。所得不同固溶度的微粉各自都具有均一的化学组成和相组成, 平均粒径<100um, 比表面>10m^2/g, 主相含量>97±10^-^2┘     

Editorial:Green organic synthesis

正In 1998,Paul Anastas and John Warner defined 12 Principles of Green Chemistry,aiming at cleaner processes,safer products and increasing use of renewable rather than fossil resources.With the growing awareness of environmental issues,the international chemical community is driven to develop novel and environmentally friendly synthetic strategies for the replacement of inefficient and pollutional chemical processes.Delightedly,a lot of ecofriendly synthetic methodologies have been established over the past decades.     

Immobilization of a lactase onto a magnetic support by covalent attachment to polyethyleneimine-glutaraldehyde-activated magnetite

A magnetic immobilized lactase has been prepared using magnetite as the magnetic material. Magnetite was functionalized by treatment with polyethyleneimine and crosslinked with glutaraldehyde. Lactase was then covalently coupled to the activated magnetic matrix via the aldehyde groups. The conditions for optimal immobilization of enzyme are described. Eighty percent of the lactase activity was lost on immobilization and is thought to be owing to the orientation of enzyme binding to the matrix. The amount of protein coupled was 80% of that applied. The maximum lactase activity retained on the matrix following immobilization was 360 U/g matrix. The immobilized lactase showed optimal activity at pH 4.5 and 65 degrees C. The immobilized lactase was more heat stable than the free enzyme, and retained 83% of its original activity after 14 d at 55 degrees C. Galactose competitively inhibited the immobilized lactase preparation (Ki 20 m/M). The presence of high initial concentrations of galactose (10% w/v) did not prevent total hydrolysis of lactose. Glucose and calcium ions were activators of the immobilized enzyme. The immobilized enzyme hydrolyzed high concentrations of lactose (up to 25% w/v) to completion within 4-6 h in a stirred batch reactor at 55 degrees C. There was no evidence of substrate inhibition at high substrate concentrations. The efficiency of hydrolysis of lactose by the immobilized lactase was better than that of the free enzyme. The magnetic immobilized lactase was demonstrated to be suitable for use in the enzymatic hydrolysis of both pure, and cheese whey permeate, lactose.     

Polyhedral magnetite nanocrystals with multiple facets: facile synthesis, structural modelling, magnetic properties and application for high capacity lithium storage

Polyhedral magnetite nanocrystals with multiple facets were synthesised by a low temperature hydrothermal method. Atomistic simulation and calculations on surface attachment energy successfully predicted the polyhedral structure of magnetite nanocrystals with multiple facets. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the crystal structure of magnetite, which is consistent with the theoretical modelling. The magnetic property measurements show the superspin glass state of the polyhedral nanocrystals, which could originate from the nanometer size of individual single crystals. When applied as an anode material in lithium ion cells, magnetite nanocrystals demonstrated an outstanding electrochemical performance with a high lithium storage capacity, a satisfactory cyclability, and an excellent high rate capacity.