Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Application of factor analysis to XPS valence band of superparamagnetic iron oxide nanoparticles

X-Ray photoelectron spectra of nano-sized superparamagnetic iron oxide nanoparticles were examined with the aim to discriminate the different degree of iron oxidation. Careful analysis of the valence band regions reveals the presence of both Fe₃O₄ and Fe₂O₃. The application of factor analysis enabled us to extract the relative molar concentrations of these oxides in the nanoparticles. This is of particular interest in improving the magnetic properties of iron oxide nanoparticles whose superparamagnetic character can be optimized to obtain better contrast in images from nuclear magnetic resonance. As a result, the factor analysis allows tuning the nanoparticle synthesis conditions in order to obtain the optimal magnetic properties for imaging. Results obtained by the XPS valence band analysis were compared to the transmission electron microscopy, X-ray diffraction and Raman measurements.     

Water-soluble magnetic nanoparticles with biologically active stabilizers

We present the results of the interaction of iron oxide nanoparticles with some biologically active surfactants, namely, oleic acid and cytotoxic alkanolamine derivatives. Physico-chemical properties, as magnetization, magnetite concentration and particle diameter, of the prepared magnetic samples were studied. The nanoparticle size of 11 nm for toluene magnetic fluid determined by TEM is in good agreement with the data obtained by the method of magnetogranulometry. In vitro cytotoxic effect of water-soluble nanoparticles with different iron oxide:oleic acid molar ratio were revealed against human fibrosarcoma and mouse hepatoma cells. In vivo results using a sarcoma mouse model showed observable antitumor action.     

Nanoparticles: Implication of Ligand Choice on Surface Properties,Crystal Structure,and Magnetic Properties of Iron Nanoparticles (Part. Part. Syst. Charact. 3/2013)

The behavior of iron nanoparticles is heavily influenced by their highly reactive surfaces. A better understanding of organic ligand/particle interactions must be achieved in order to synthesize iron nanoparticles with magnetic saturations (σ _sat) equivalent to bulk iron. Even when synthesized using careful, air‐free chemistry techniques and ligands more weakly interacting than those often reported in the literature, the magnetic saturation of iron nanoparticles generally only approaches, but not equals, the magnetic saturation of bulk iron. Here, iron nanoparticles are synthesized using Schlenk line chemistry methods and two different weakly interacting ligands: 2,4‐pentanedione and hexaethylene glycol monododecylether. These particles have saturation magnetizations slightly lower than bulk iron, which is believed to be caused by interactions between the passivating ligands and the surface of the nanoparticles. Using X‐ray absorption fine structure studies, it is shown that oxidized species of iron exist at the nanoparticles’ surface and can be attributed to iron/ligand interaction. The percentage of oxidized species scales with the surface to volume ratio of the nanoparticles, and therefore appears limited to the nanoparticle surface. X‐ray absorption fine structure analysis also shows that the nanoparticles have an expanded crystalline lattice, which can further impact their magnetic properties.     

Colloidal Flower‐Shaped Iron Oxide Nanoparticles: Synthesis Strategies and Coatings

The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self‐assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi‐core nanoparticles are determined. In addition, a self‐consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower‐shaped iron oxide assemblies in the size range 25–100 nm are examined. The routes are based on the partial oxidation of Fe(OH)₂, polyol‐mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long‐term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi‐core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower‐shaped nanoparticles.     

Enhanced transport of zerovalent iron nanoparticles in saturated porous media by guar gum

In order to ensure adequate mobility of zerovalent iron nanoparticles in natural aquifers, the use of a stabilizing agent is necessary. Polymers adsorbed on the nanoparticle surface will give rise to electrosteric stabilization and will decrease attachment to the surface soil grains. Water saturated sand-packed columns were used in this study to investigate the transport of iron nanoparticle suspensions, bare or modified with the green polymer guar gum. The suspensions were prepared at 154 mg/L particle concentration and 0.5 g/L polymer concentration. Transport experiments were conducted by varying the ionic strength, ionic composition, and approach velocity of the fluid. Nanoparticle deposition rates, attachment efficiencies, and travel distances were subsequently calculated based on the classical particle filtration theory. It was found that bare iron nanoparticles are basically immobile in sandy porous media. In contrast, guar gum is able to ensure significant nanoparticle transport at the tested conditions, regardless of the chemistry of the solution. Attachment efficiency values for guar gum-coated nanoparticles under the various conditions tested were smaller than 0.066. Although the calculated travel distances may not prove satisfactory for field application, the investigation attested the promising role of guar gum to ensure mobility of iron nanoparticles in the subsurface environment.     

Comparative analysis of the 1H NMR relaxation enhancement produced by iron oxide and core-shell iron-iron oxide nanoparticles

Physicochemical and magnetorelaxometric characterization of the colloidal suspensions consisting of Fe-based nanoparticles coated with dextran have been carried out. Iron oxide and iron core/iron oxide shell nanoparticles were obtained by laser-induced pyrolysis of Fe(CO)₅ vapours. Under different magnetic field strengths, the colloidal suspension formed by iron oxide nanoparticles showed longitudinal (R₁) and transverse (R₂) nuclear magnetic relaxation suspension (NMRD) profiles, similar to those previously reported for other commercial magnetic resonance imaging (MRI) contrast agents. However, colloidal suspension formed by ferromagnetic iron-core nanoparticles showed a strong increase of the R₁ values at low applied magnetic fields and a strong increase of the R₂ measured at high applied magnetic field. This behaviour was explained considering the larger magnetic aggregate size and saturation magnetization values measured for this sample, 92 nm and 31 emu/g Fe, respectively, with respect to those measured for the colloidal suspensions of iron oxide nanoparticles (61 nm and 23 emu/g Fe). This suspension can be used both as T₁ and T₂ contrast agent.     

Influence of synthesis parameters on iron nanoparticle size and zeta potential

Zero valent iron nanoparticles are of increasing interest in clean water treatment applications due to their reactivity toward organic contaminants and their potential to degrade a variety of compounds. This study focuses on the effect of organophosphate stabilizers on nanoparticle characteristics, including particle size distribution and zeta potential, when the stabilizer is present during nanoparticle synthesis. Particle size distributions from DLS were obtained as a function of stabilizer type and iron precursor (FeSO₄·7H₂O or FeCl₃), and nanoparticles from 2 to 200 nm were produced. Three different organophosphate stabilizer compounds were compared in their ability to control nanoparticle size, and the size distributions obtained for particle volume demonstrated differences caused by the three stabilizers. A range of stabilizer-to-iron (0.05–0.9) and borohydride-to-iron (0.5–8) molar ratios were tested to determine the effect of concentration on nanoparticle size distribution and zeta potential. The combination of ferrous sulfate and ATMP or DTPMP phosphonate stabilizer produced stabilized nanoparticle suspensions, and the stabilizers tested resulted in varying particle size distributions. In general, higher stabilizer concentrations resulted in smaller nanoparticles, and excess borohydride did not decrease nanoparticle size. Zeta potential measurements were largely consistent with particle size distribution data and indicated the stability of the suspensions. Probe sonication, as a nanoparticle resuspension method, was minimally successful in several different organic solvents.     

In Situ Dimensional Characterization of Magnetic Nanoparticle Clusters during Induction Heating

The study and fundamental understanding of magnetic nanoparticle induction heating remains critical for the advancement of magnetic hyperthermia technologies. Complete characterization of not only the nanoparticles themselves but their interparticle behavior in a sample matrix is necessary to accurately predict their heating response. Herein, an in situ method for measuring the extent of nanoparticle clustering during induction heating using small-angle and ultrasmall-angle neutron scattering facilities at the National Institute of Standards and Technology Center for Neutron Research is described and implemented by comparing two sets of iron oxide nanoparticles with differing structures and magnetic properties. By fitting the scattering profiles to a piecewise model covering a wide Q-range, the magnitude of nanoparticle clustering during induction heating is quantified. Observations of the low-Q intensity before and after heating also allow for relative measurement of the cluster volume fraction during heating. The use of this method can prove to be advantageous in both developing more encompassing models to describe magnetic nanoparticle dynamics during heating as well as optimizing nanoparticle synthesis techniques to reduce aggregation during heating.     

Characterization of magnetic core-shell nanoparticles by fluxgate magnetorelaxometry, ac susceptibility, transmission electron microscopy and photon correlation spectroscopy—A comparative study

We have compared the structure parameters of magnetic core-shell nanoparticles determined from fluxgate magnetorelaxometry measurements applying the moment superposition model with the results from other methods. For the characterization of the magnetic cores, the nanoparticles are immobilized by freeze-drying. The core size distribution estimated for superparamagnetic Fe₃O₄ magnetic nanoparticles (MNPs) with polyacrylic acid shell agrees well with that from transmission electron microscopy measurements. The distribution of hydrodynamic diameters of nanoparticle suspensions estimated from magnetorelaxometry measurements is in good agreement with that obtained from ac susceptibility and photon correlation spectroscopy measurements. Advantages of magnetorelaxometry compared to the other two integral techniques are that it is fast and the signal is less dominated by larger particles.     

Dispersion of nanoparticles: From organic solvents to polymer solutions

This work is devoted to a systematic study of nanoparticle dispersion by ultrasonication in different solutions: from organic solvents to polymer solutions. The cluster size of nanoparticles at different concentrations in both organic solvents and polymer solutions were directly characterized by Dynamic Light Scattering to study the effect of solid concentration, surfactant and polymer on the dispersion. It reveals that in stabilized suspensions, the smallest attainable size or aggregate size of nanoparticles is independent of solvent type and solid content over the tested range. Furthermore, nanoparticles in simple solvent and in polymer solutions had the similar evolution of cluster size and almost the same final size, which could be very helpful to optimize the dispersion of nanofillers in polymer solutions and nanocomposites. It is also shown that, with appropriate sonication amplitudes, the dispersion procedure developed for very dilute suspensions could be transferred to higher concentration suspensions or even to polymer suspensions.     

α-Fe粉体浓悬浮体系的制备及磁流变效应

报道使用价格低廉的还原铁粉制备磁性粒子浓悬浮体系 ,对体系磁流变效应进行研究 ,并研究了磁性颗粒尺寸和氧化物对悬浮体系力学性质及沉降稳定性的影响 .     

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.     

Synthesis and nonlinear light scattering of microemulsions and nanoparticle suspensions

Microemulsions composed of normal or inverse micellar solutions and aqueous suspensions of pristine (uncoated) or silica-coated iron oxide nanoparticles, mainly γ-Fe₂O₃, were synthesised and their optical limiting properties investigated. The microemulsions are colorless solutions with high transparency for visible wavelengths while the aqueous suspensions of iron oxide are of pale yellow colour. Optical limiting experiments performed in 2 mm cells using a f/5 optical system with a frequency doubled Nd:YAG laser delivering 5 ns pulses with 10 Hz repetition rate, showed clamping levels of ∼3 μJ for the suspensions of both pristine and silica-coated iron oxide nanoparticles. A strong photoinduced nonlinear light scattering was observed for the water-in-oil microemulsion and the aqueous suspensions of nanoparticles while oil-in-water microemulsions did not show a significant nonlinear effect. Measurements carried out using an integrating sphere further verified that the photoinduced nonlinear light scattering is the dominating nonlinear mechanism while the nonlinear absorption of iron oxide nanoparticles is negligible at 532 nm.     

Investigation into the antibacterial behaviour of suspensions of ZnO nanoparticles (ZnO nanofluids)

The antibacterial behaviour of suspensions of zinc oxide nanoparticles (ZnO nanofluids) against E. Coli has been investigated. ZnO nanoparticles from two sources are used to formulate nanofluids. The effects of particle size, concentration and the use of dispersants on the antibacterial behaviour are examined. The results show that the ZnO nanofluids have bacteriostatic activity against E. coli. The antibacterial activity increases with increasing nanoparticle concentration and increases with decreasing particle size. Particle concentration is observed to be more important than particle size under the conditions of this work. The results also show that the use of two types of dispersants (Polyethylene Glycol (PEG) and Polyvinylpyrolidone (PVP)) does not affect much the antibacterial activity of ZnO nanofluids but enhances the stability of the suspensions. SEM analyses of the bacteria before and after treatment with ZnO nanofluids show that the presence of ZnO nanoparticles damages the membrane wall of the bacteria. Electrochemical measurements using a model DOPC monolayer suggest some direct interaction between ZnO nanoparticles and the bacteria membrane at high ZnO concentrations. On visiting from the Tianjin University of Science & Technology, Tianjin, P.R. China.     

The detection of HBV DNA with gold-coated iron oxide nanoparticle gene probes

Gold-coated iron oxide nanoparticle Hepatitis B virus (HBV) DNA probes were prepared, and their application for HBV DNA measurement was studied. Gold-coated iron oxide nanoparticles were prepared by the citrate reduction of tetra-chloroauric acid in the presence of iron oxide nanoparticles which were added as seeds. With a fluorescence-based method, the maximal surface coverage of hexaethiol 30-mer oligonucleotides and the maximal percentage of hybridization strands on gold-coated iron oxide nanoparticles were (120 ± 8) oligonucleotides per nanoparticle, and (14 ± 2%), respectively, which were comparable with those of (132 ± 10) and (22 ± 3%) in Au nanoparticle groups. Large network aggregates were formed when gold-coated iron oxide nanoparticle HBV DNA gene probe was applied to detect HBV DNA molecules as evidenced by transmission electron microscopy and the high specificity was verified by blot hybridization. Our results further suggested that detecting DNA with iron oxide nanoparticles and magnetic separator was feasible and might be an alternative effective method.     

Controlled flame synthesis of αFe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: effect of flame configuration,flame temperature,and additive loading

Superparamagnetic iron oxide nanoparticles are used in diverse applications, including optical magnetic recording, catalysts, gas sensors, targeted drug delivery, magnetic resonance imaging, and hyperthermic malignant cell therapy. Combustion synthesis of nanoparticles has significant advantages, including improved nanoparticle property control and commercial production rate capability with minimal post-processing. In the current study, superparamagnetic iron oxide nanoparticles were produced by flame synthesis using a coflow flame. The effect of flame configuration (diffusion and inverse diffusion), flame temperature, and additive loading on the final iron oxide nanoparticle morphology, elemental composition, and particle size were analyzed by transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. The synthesized nanoparticles were primarily composed of two well known forms of iron oxide, namely hematite αFe₂O₃ and magnetite Fe₃O₄. We found that the synthesized nanoparticles were smaller (6–12 nm) for an inverse diffusion flame as compared to a diffusion flame configuration (50–60 nm) when CH₄, O₂, Ar, and N₂ gas flow rates were kept constant. In order to investigate the effect of flame temperature, CH₄, O₂, Ar gas flow rates were kept constant, and N₂ gas was added as a coolant to the system. TEM analysis of iron oxide nanoparticles synthesized using an inverse diffusion flame configuration with N₂ cooling demonstrated that particles no larger than 50–60 nm in diameter can be grown, indicating that nanoparticles did not coalesce in the cooler flame. Raman spectroscopy showed that these nanoparticles were primarily magnetite, as opposed to the primarily hematite nanoparticles produced in the hot flame configuration. In order to understand the effect of additive loading on iron oxide nanoparticle morphology, an Ar stream carrying titanium-tetra-isopropoxide (TTIP) was flowed through the outer annulus along with the CH₄ in the inverse diffusion flame configuration. When particles were synthesized in the presence of the TTIP additive, larger monodispersed individual particles (50–90 nm) were synthesized as observed by TEM. In this article, we show that iron oxide nanoparticles of varied morphology, composition, and size can be synthesized and controlled by varying flame configuration, flame temperature, and additive loading.     

Characterizing the dynamic behavior of nano-TiO<Subscript>2</Subscript> agglomerates in suspensions by photocorrelation spectroscopy

Metal oxide nanoparticles are small but easily form agglomerates in suspension, depending on the strength of particle–particle and particle–media interactions. To understand the agglomeration behavior of nanoparticles in media and relate to it to product performance testing, measurement methods are desired to characterize highly scattering metal oxide nanoparticle suspensions without dilution. In this article, we describe the advantages of using photocorrelation spectroscopy (PCS) in a backscattering detection configuration to carry out a realistic agglomerate size measurement in multiple scattering media found in most metal oxide nanoparticle suspensions. The dynamic behavior of nano-titanium dioxide (TiO₂) particles in buffer solutions of different chemical composition and pH values was investigated as a sample system using PCS. The resulting autocorrelation functions (AFs) at different time intervals, particle concentrations, and pH values were measured at several detection angles. The AF exhibits a multi-mode relaxation time feature and the calculated hydrodynamic diameters strongly depended on media composition and detection angle. This result indicates that the size and dispersion of nano-TiO₂ agglomerates are significantly affected by solution media. A measurement protocol for determining size and dispersion of metal oxide particles in media is proposed and related to a performance test found in industry.     

Size effect of Mössbauer parameters in iron oxide nanoparticles

The size dependence of Mössbauer parameters for iron oxide nanoparticles in the 10–25 nm range was investigated. It was shown that the isomer shift and hyperfine field parameters decrease with the nanoparticle size. Only at 25 nm the presence of magnetite was detected.     

Electrochemical synthesis of magnetic iron oxide nanoparticles with controlled size

We present a novel and facile method enabling synthesis of iron oxide nanoparticles, which are composed mainly of maghemite according to X-ray diffraction (XRD) and Mössbauer spectroscopy studies. The proposed process is realized by anodic iron polarization in deaerated LiCl solutions containing both water and ethanol. Water seems to play an important role in the synthesis. Morphology of the product was studied by means of transmission electron microscopy and XRD. In the solution containing almost 100% of water a black suspension of round shaped maghemite nanoparticles of 20–40 nm size is obtained. Regulating water concentration allows to control nanoparticle size, which is reduced to 4–6 nm for 5% of water with a possibility to reach intermediate sizes. For 3% or lower water concentration nanoparticles are of a needle-like shape and form a reddish suspension. In this case phase determination is problematic due to a small particle size with the thickness of roughly 3 nm. However, XRD studies indicate the presence of ferrihydrite. Coercivities of the materials are similar to those reported for nanoparticle magnetite powders, whereas the saturation magnetization values are considerably smaller.