Thermal degradation of magnetite nanoparticles with hydrophilic shell

The aim of this study was the investigation of thermal degradation process at the interface of a core–shell type structure. Such hybrid compound was comprised of an inorganic core of magnetite nanoparticles and an organic shell consisting of 3-aminopropyltriethoxysilane. The thermal degradation has been studied by thermogravimetry in nitrogen atmosphere, up to 500 °C. The evolved gases analysis was performed using a coupling to a quadrupole mass spectrometer and a Fourier transform infrared spectrophotometer equipped with external modulus for gas analyses. Isoconversional kinetic study was conducted and a three stage thermal degradation mechanism was proposed.     

Solid state synthesis of water-dispersible silicon nanoparticles from silica nanoparticles

A solid state synthesis for obtaining nanocrystalline silicon was performed by high temperature reduction of commercial amorphous nanosilica with magnesium powder. The obtained silicon powder contains crystalline silicon phase with lattice spacings characteristic of diamond cubic structure (according to high resolution TEM), and an amorphous phase. In ²⁹Si CP MAS NMR a broad multicomponent peak corresponding to silicon is located at −61.28 to −69.45 ppm, i.e. between the peaks characteristic of amorphous and crystalline Si. The powder has displayed red luminescence while excited under UV illumination, due to quantum confinement within the nanocrystals. The silicon nanopowder was successfully dispersed in water containing poly(vinyl alcohol) as a stabilizing agent. The obtained dispersion was also characterized by red photoluminescence with a band maximum at 710 nm, thus enabling future functional coating applications.     

水分散性硫化镉纳米粒子的制备研究进展

表面修饰的硫化镉纳米粒子荧光性能优异而稳定,激发光谱宽,发射光谱窄而对称且发射波长可通过改变材料的粒径大小和组成来调控,因而在生物样本尤其是活组织的多色成像中极为有用,能有效避免因样本自身发光和光散射导致的信号干扰。硫化镉纳米粒子的研究已被许多科研工作者所青睐,是目前热点研究领域之一。近年来,水分散性硫化镉纳米粒子作生物荧光标记物的研究取得了长足的进展。本文综述了水分散性硫化镉纳米粒子的制备方法研究进展,分析了各种制备方法的优点与不足之处。     

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.     

Sorption of uranium on magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticle was synthesized using a solid state mechanochemical method and used for studying the sorption of uranium(VI) from aqueous solution onto the nanomaterial. The synthesized product is characterized using SEM, XRD and XPS. The particles were found to be largely agglomerated. XPS analysis showed that Fe(II)/Fe(III) ratio of the product is 0.58. Sorption of uranium on the synthesized nanomaterials was studied as a function of various operational parameters such as pH, initial metal ion concentration, ionic strength and contact time. pH studies showed that uranium sorption on magnetite is maximum in neutral solution. Uranium sorption onto magnetite showed two step kinetics, an initial fast sorption completing in 4–6 h followed by a slow uptake extending to several days. XPS analysis of the nanoparticle after sorption of uranium showed presence of the reduced species U(IV) on the nanoparticle surface. Fe(II)/Fe(III) ratio of the nanoparticle after uranium sorption was found to be 0.48, lower than the initial value indicating that some of the ferrous ion might be oxidized in the presence of uranium(VI). Uranium sorption studies were also conducted with effluent from ammonium diuranate precipitation process having a uranium concentration of about 4 ppm. 42% removal was observed during 6 h of equilibration.     

Growing ZnO crystals on magnetite nanoparticles

We report herein on the oriented growth of ZnO crystals on magnetite nanoparticles. The ZnO crystals were grown by hydrolyzing a supersaturated aqueous solution of zinc nitrate. The seeds for the growth were magnetite nanoparticles with a diameter of 5.7 nm and a narrow size distribution. Hollowed ZnO hexagons of 0.15 microm width and 0.5 microm length filled with Fe(3)O(4) particles were obtained. HR-TEM (high-resolution transmission electron microscopy) and selected-area EDS (energy-dispersive spectroscopy) show that the nanoparticles are homogenously spread in the ZnO tubes. Zeta potential measurements were employed to understand the relationship between the nanoparticles and the oriented growth of the ZnO crystals. The results show that the surfactants induced the directional growth of the ZnO crystals.     

Synthesis and characterization of polystyrene-grafted magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticles were synthesized by chemical precipitation. To reduce the aggregation of Fe₃O₄ nanoparticles, an effective surface modification method was proposed by grafting polystyrene onto the Fe₃O₄ particles. The results of Fourier transform infrared spectra and elemental analysis showed that the polymer chains have been successfully grafted from the surface of the Fe₃O₄ nanoparticles and that the percentage of grafting can reach 73%. Transmission electron microscope showed that grafted polymer chains on nanoparticles could prevent the aggregation of Fe₃O₄ nanoparticles markedly in toluene and improve their compatibility with organic phase. Another finding was the grafting reaction did not alter the crystalline structure of the Fe₃O₄ nanoparticles according to the X-ray diffraction patterns, and the saturation magnetization of PS-Fe₃O₄ nanoparticles was found to be lower than bulk magnetite.     

Dendrimer modified magnetite nanoparticles for protein immobilization

A cascading polyamidoamine (PAMAM) dendrimer was synthesized on the surface of magnetite nanoparticles to allow enhanced immobilization of bovine serum albumin (BSA). Characterization of the synthesis revealed exponential doubling of the surface amine from generations one through four starting with an amino silane initiator. Furthermore, transmission electron microscopy (TEM) revealed clear dispersion of the dendrimer-modified magnetite nanoparticles in methanol solution. The dendrimer-modified magnetite nanoparticles were used to carry out magnetic immobilization of BSA. BSA immobilizing efficiency increased with increasing generation from one to five and BSA binding amount of magnetite nanoparticles modified with G5 dendrimer was 7.7 times as much as that of magnetite nanoparticles modified with only aminosilane. There are two major factors that improve the BSA binding capacity of dendrimer-modified magnetite nanoparticles: one is that the increased surface amine can be conjugated to BSA by a chemical bond through glutaraldehyde; the other is that the available area has increased due to the repulsion of surface positive charge.     

Effect of polar solvents on the optical properties of water-dispersible thiol-capped cobalt nanoparticles

We were able to stabilize cobalt nanoparticles dispersible in water by optimizing the synthetic procedure using small polar thiol containing compounds as the capping agents. The nanoparticles were found to be spherical. The optical properties of the cobalt nanoparticles were investigated by monitoring the changes in the surface plasmon resonance (SPR) spectrum in various polar solvents. The extent of solvent dependence of the SPR spectrum was found to be dependent on the nature of the capping agent, the size of the cobalt nanoparticles, as well as the nature of the solvent. The Drude model was applicable for the particles capped with mercaptopropionic acid, while the effect of variations in the free electron density in the particles at different solvents became predominant in the nanoparticles capped with mercaptoethanol. The absorption spectra of the Co nanoparticles were simulated with the help of the classical Mie theory, and the results supported the effect of free electron density due to different capping agents on the spectra of the particles.     

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.     

Thermal analysis of two types of dextran-coated magnetite

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160–450 °C and the other at 530–800 °C.     

Interaction between blood plasma proteins and magnetite nanoparticles

Spin label EPR spectroscopy and dynamic and Rayleigh light scattering are employed to study the interaction between magnetite nanoparticles with a diameter of 17 nm and plasma proteins (fibrinogen and albumin). Protein molecules are shown to be adsorbed on nanoparticle surface with the formation of multilayer shells. When a buffer solution (pH 8.5) contains 0.01 vol % nanoparticles, 90–100 fibrinogen molecules are adsorbed per one particle and the thickness of an adsorbed layer is 30–40 nm. For albumin, the layer thickness is 10–15 nm. In a constant magnetic field, large linear microsized aggregates oriented parallel to field lines are formed in dispersions of nanoparticles covered with adsorbed protein molecules. The study of fibrin gel formation resulting from the action of thrombin enzyme on fibrinogen suggests that, in the presence of nanoparticles, the rate of gelation decreases by a factor of approximately two, while the ratio between the average mass and average length of fibrin polymer fibers rises.     

Facile method to synthesize oleic acid-capped magnetite nanoparticles

<正>We described a simple one-step process for the synthesis of oleic acid-capped magnetite nanoparticles using the dimethyl sulfoxide(DMSO) to oxidize the precursor Fe~(2+) at 140℃.By adjusting the alkalinity of the reaction system,magnetite nanoparticles with two sizes of 4 and 7 nm could be easily achieved.And the magnetite nanoparticles coated by oleate were well-monodispersed in organic solvent.     

Superparamagnetism of magnetite nanoparticles: dependence on surface modification

Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (Au), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravimetric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of M?ssbauer spectroscopy as a function of an external magnetic field Hext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under Hext, and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to M?ssbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.     

Liquid–liquid phase transfer of magnetite nanoparticles

The study presents first experimental results of the transfer of magnetite nanoparticles from an aqueous to a second non-miscible non-aqueous liquid phase. The transfer is based on the adsorption of macromolecular surfactants onto the particle surface at the liquid–liquid interface. For a successful direct phase transfer, it is essential to have cations, like ammonium ions, present in the aqueous phase as well as a threshold concentration of surfactant in the organic liquid phase. While penetrating the liquid–liquid interface, the particles are covered with the surfactant and therefore a partial de-agglomeration is initiated. Based on literature and experimental data a mechanism of surfactant adsorption is proposed. The competing adsorption of the surfactant molecules at the liquid–liquid interface leads to the formation of emulsions and therefore to a hindrance for particles passing the interface. Nevertheless a high efficiency of 100% yield can be reached using optimized process parameters for the phase transfer process.     

Microwave-assisted synthesis of magnetite nanoparticles possessing superior magnetic properties

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

     

One-step continuous flow synthesis of aminopropyl silica-coated magnetite nanoparticles

One-step continuous flow synthesis was developed and applied for the preparation of amino propyl silica-coated nanoparticles (APSMNPs). This was accomplished in one step through continuous flow synthesis and amino propyl silica coating. Magnetite nanoparticles (MNPs) are generated in situ using a continuous flow synthesis system before being coated with amino propyl silica using tetraethyl orthosilicate (TEOS) condensation process and 3-aminopropyl triethoxysilane (APTES) condensation process in different ratios. The effect of the molar ratio of TEOS to APTES on the structure and physicochemical properties of the corresponding APSMNPs was examined by N₂ adsorption–desorption isotherm, transmission electron microscope (TEM), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope energy dispersive X-ray (SEM-EDX). This continuous flow process has advantages such as easy scalability, convenient production, easy control, an economical method with less time and reagents than traditional synthetic methods. It is a good choice for industrial production of APSMNPs.     

Morphology control in the plant-mediated synthesis of magnetite nanoparticles

Green synthesized magnetite nanoparticles and main applications.

1. Download : Download high-res image (176KB)
2. Download : Download full-size image

     

Facile synthesis of superparamagnetic magnetite nanoparticles in liquid polyols

Magnetite nanoparticles have been successfully synthesized in liquid polyols at elevated temperature. Polyol solvent plays a crucial role in determining the morphology and colloidal stability of the resulting particles. The structure and morphology of the nanoparticles were studied using XRD, TEM, SAED, TGA and FTIR. The magnetic properties of the samples were measured using physical properties measurement system (PPMS) of Quantum Design. The results show that as-prepared magnetite nanoparticles are monodisperse, highly crystalline and superparamagnetic at room temperature. The nanoparticles can be easily dispersed in aqueous media and other polar solvents due to coated by a layer of hydrophilic polyol ligands in situ. This approach provides a facile route to prepare magnetite nanoparticles.