Synthetic Magnetite Nanoparticles Research Articles

Magnetite (Fe3O4) nanoparticles as adsorbents for As and Cu removal

The aim of this study consisted to develop novel synthetic magnetite nanoparticles (nFe3O4) with preferential reactivity to trace elements (TE) for possible environmental applications as adsorbents. The synthetic magnetite materials obtained through the co-precipitation of both Fe3+ and Fe2+ ions (Fe2+/Fe3+=0.5) were characterized by a set of complementary techniques: X-ray diffraction, transmission and scanning electron microscopy, Fourier transform infrared and Raman spectroscopy, and BET adsorption method. The resulting nFe3O4 displayed a wide specific surface area (100m2g−1) with particles reaching a size of about 10nm, smaller than those of the well-crystallized commercial ones (cFe3O4) estimated at 80nm while showing a BET surface area of 6.8m2g−1. The adsorption properties of the synthetic nFe304 magnetite nanoparticles were characterized and compared to the commercial analogous with the adsorption of both As and Cu. The equilibrium adsorption isotherms were properly fitted with Langmuir and Freundlich equation models and suggested that the developed iron oxides nanoparticles display a certain potential for removal and/or immobilization of TE from contaminated waters and/or soils, with an increase of 69.5% of the adsorbed amount compared to that of the commercial ones.

Magnetic iron oxide nanoparticles as MRI contrast agents -- a comprehensive physical and theoretical study

Magnetite nanoparticles, especially superparamagnetic iron oxide nanoparticles, are established contrast agents for magnetic resonance imaging. Magnetosomes, which are magnetite nanoparticles of biological origin, have been shown to have better contrast properties than current formulations possibly because of their larger size and high monodispersity. Here, we present an integrated study of magnetosomes and synthetic magnetite nanoparticles of varying size, hence, magnetic properties. We investigate not only the relaxation times as a measure for the contrast properties of these particles, but also their cytotoxicity and demonstrate the higher contrast of the larger particles. A theoretical model is presented that enables us to simulate the R2=R1 ratio of a contrast agent and con�rm that larger particles offer higher contrast. The results from this study illustrate the possibility to obtain colloidal stability of large magnetic nanoparticles for magnetic resonance imaging applications and serve as an impetus for a more quantitative description of the contrast effect as a function of the size.

Ecotoxicity of nanosized magnetite to crustacean Daphnia magna and duckweed Lemna minor

Along with the development of nanotechnology, an increase in production and application of nanosized magnetite (Fe3O4) is expected. Though magnetite is considered relatively safe, information concerning potential hazards of synthetic magnetite nanoparticles with unique physico-chemical characteristics to aquatic organisms is still limited. In this study, we evaluated the toxicity of nanosized (27.2 ± 9.8 nm) and bulk (144.2 ± 67.7 nm) magnetite particles to different life stages of the aquatic crustacean Daphnia magna. In addition, phytotoxicity of the magnetite was evaluated using duckweed Lemna minor. The study did not reveal any statistically significant differences between the biological effects of nanosized and bulk magnetite particles. Both forms of magnetite induced very low toxicity (EC50 > 100 ppm) to D. magna and L. minor in the standard acute assays. However, it was demonstrated that at acutely subtoxic magnetite concentrations (10 and 100 ppm), the number of neonates hatched from D. magna ephippia was decreased. Moreover, short-term (48 h) exposure of neonate daphnids to these concentrations may significantly affect the long-term survival and reproductive potential of daphnids. These results indicate that substantial contamination of aquatic ecosystems by magnetite may disrupt the stability of cladoceran populations.

Transformation mechanism of magnetite nanoparticles

Abstract A simple oxidation synthesis route was developed for producing magnetite nanoparticles with controlled size and morphology. Investigation of oxidation process of the produced magnetite nanoparticles (NP) was performed after synthesis under different temperatures. The phase transformation of synthetic magnetite nanoparticles into maghemite and, henceforth, to hematite nanoparticles at different temperatures under dry oxidation has been studied. The natural magnetite particles were directly transformed to hematite particles at comparatively lower temperature, thus, maghemite phase was bypassed. The phase structures, morphologies and particle sizes of the produced magnetic nanoparticles have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX) and BET surface area analysis.

Distinguishing magnetic particle size of iron oxide nanoparticles with first-order reversal curves

Magnetic nanoparticles encompass a wide range of scientific study and technological applications. The success of using the nanoparticles in various applications demands control over size, dispersibility, and magnetics. Hence, the nanoparticles are often characterized by transmission electron microscopy (TEM), X-ray diffraction, and magnetic hysteresis loops. TEM analysis requires a thin layer of dispersed particles on the grid, which may often lead to particle aggregation thus making size analysis difficult. Magnetic hysteresis loops on the other hand provide information on the bulk property of the material without discriminating size, composition, and interaction effects. First order reversal curves (FORCs), described as an assembly of partial hysteresis loops originating from the major loop are efficient in identifying the domain size, composition, and interaction in a magnetic system. This study presents FORC diagrams on a variety of well-characterized biogenic and synthetic magnetite nanoparticles. It also introduces deconvoluted reversible and irreversible components from FORC as an important method for obtaining a semi-quantitative measure of the effective magnetic particle size. This is particularly important in a system with aggregation and interaction among the particles that often leads to either the differences between physical size and effective magnetic size. We also emphasize the extraction of secondary components by masking dominant coercivity fraction on FORC diagram to explore more detailed characterization of nanoparticle systems.

Size-dependent reactivity of magnetite nanoparticles: a field-laboratory comparison.

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, ∼ 6 nm, ∼ 44 nm, and ∼ 90 nm were emplaced in the subsurface of the USGS research site at the Norman Landfill for up to 30 days using custom-made subsurface nanoparticle holders. 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. Limited dissolution occurred, with the amount of dissolution decreasing as particle size decreased. Conversely, the laboratory analogs without organics revealed greater dissolution of the smaller 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.

Manipulation of Particle Size and Sorption Capability of Nano-Scale Magnetite via Controlling Surface Coating

Non-point source nutrient release from land to water, which leads to the eutrophication and toxic algal blooms in natural water, is not easy to control effectively because in-situ injection of suspended particles is often failed to reach deep soils due to nanoparticles tending to agglomerate into micro particles. In this work, we found that particle sizes of synthetic magnetite nanoparticles (Fe3O4) and sorption capacity of phosphate were controllable by manipulating the surface coverage of stabilizer (starch). The sorption density and starch stabilized particle sizes were positive correlation. In order to enhance the stability and dispersibility of the nanoparticles, the particle sizes were reduced to nano-scale with high dosage of starch, which weakened the phosphate sorption capability. To recover the activity of the nanoparticles, alpha-amylase was employed to degrade the surface coating. The phosphate sorption capacity was almost doubled when alpha-amylase was applied comparing with that without alpha-amylase. Column testes indicated that highly stabilized nanoparticles could be delivered to the targeted depth of soil column, and the sorption activity was recovered by the in-situ biodegradation of starch. The technology provides methods for in situ immobilization of phosphorus in over fertilized soils, which is significant in controlling the eutrophication of aquatic environments.

U(VI) removal kinetics in presence of synthetic magnetite nanoparticles

The interaction of hexavalent U with a freshly synthesized nanoparticulate magnetite (FeIIFeIII2O4) (stochiometric ratio x(Fe(II)/FeTOT)=0.25–0.33), a partly oxidized synthetic nanoparticulate magnetite (x=0.11–0.27) and maghemite nanoparticles (x=0–1) under anoxic conditions and exclusion of CO2 as function of pH, contact time and total U concentration (3×10−5M and 1×10−7M) has been examined. Short term kinetic batch experiments (contact time of 90d) for four different pH values have been conducted. Moreover, classical batch pH sorption edges have been prepared for two different uranium concentrations for a contact time of 550d. Spectroscopic techniques (XPS, XAS) were applied to probe for the presence and amount of reduced U on the magnetite surface. Batch kinetic studies revealed a fast initial U removal from aqueous solution with >90% magnetite associated U after 24h within the pH range 5–11. Long-term contact time batch experiments (550d) showed neither a U removal below pH<3 nor a decrease in the magnetite associated U at pH≥9. Redox speciation by XPS verifies the presence of reduced U (both U(IV) and U(V) were resolved if the satellite structures were used in the fitting procedure) at the near surface of magnetite up to a contact time of 550d and a clear correlation of the amount of available Fe(II) on the magnetite surface and the amount of reduced U is observed. XANES investigation supports presence of U(V)/U(VI) uranate and U(IV). Interpretation of the EXAFS for one sample is consistent with incorporation of U into an Fe oxide phase, after long reaction times. Thermodynamic calculations based on the experimentally determined redox potentials corroborate the spectroscopic findings of U oxidation states. Overall, the results reflect the importance of structurally bound Fe(II) as redox partner for uranyl reduction.

Interfacial properties of natural magnetite particles compared with their synthetic analogue

Understanding of the interactions between iron oxides and flotation reagents is important both for flotation and agglomeration of iron ore. Model systems comprising synthetic iron oxides and pure chemical reagents are commonly applied in experimental work in order to obtain high quality data and to ease the interpretation of the empirical data. Whether the results obtained using model systems are valid for iron ore minerals and commercial reagents is a question seldom addressed in the literature. It is shown in this work that previously reported results obtained from a model system, concerning adsorption of a carboxylate surfactant and sodium metasilicate onto synthetic magnetite nanoparticles, as obtained by in situ ATR-FTIR spectroscopy and contact angle measurements, are applicable to adsorption of flotation reagents on magnetite concentrate. Additionally, the problem of restoring magnetite wetting after flotation is addressed since good wetting of a magnetite concentrate is required to produce iron ore pellets by wet agglomeration. The results from the present work indicate that the wettability of both synthetic magnetite coated with surfactant and magnetite concentrate after flotation can be improved by adsorbing a hydrophilizing agent such as silicate or polyacrylate.

Equilibrium adsorption isotherm of U(VI) at pH 4 and pH 5 onto synthetic magnetite nanoparticles

The adsorption features of synthetic magnetite nanoparticles have been investigated for removal of uranyl ions from nitric solutions. These magnetic nanoparticles can be used to adsorb contaminants in wastewater and can subsequently be removed from the medium by a magnetic process because of their superparamagnetic behaviour. The magnetite nanoparticles were synthesised by simultaneous precipitating of Fe2+ and Fe3+ ions in a NaOH solution. Batch experiments were carried out to investigate the adsorption of UO22+ ions from nitric solution, pH 4 and 5, onto magnetic nanoparticles. Two minutes of application of a magnetic field were sufficient for removing the magnetite nanoparticles from the liquid medium. Equilibrium adsorption isotherm was evaluated using Freundlich and Langmuir models. The adsorption was between 40% and 80% under conditions studied.

Immobilization of non-point phosphorus using stabilized magnetite nanoparticles with enhanced transportability and reactivity in soils

Laboratory batch and column experiments were conducted to investigate the immobilization of phosphorus (P) in soils using synthetic magnetite nanoparticles stabilized with sodium carboxymethyl cellulose (CMC-NP). Although CMC-stabilized magnetite particles were at the nanoscale, phosphorus removal by the nanoparticles was less than that of microparticles (MP) without the stabilizer due to the reduced P reactivity caused by the coating. The P reactivity of CMC-NP was effectively recovered when cellulase was added to degrade the coating. For subsurface non-point P pollution control for a water pond, it is possible to inject CMC-NP to form an enclosed protection wall in the surrounding soils. Non-stabilized “nanomagnetite” could not pass through the soil column under gravity because it quickly agglomerated into microparticles. The immobilized P was 30% in the control soil column, 33% when treated by non-stabilized MP, 45% when treated by CMC-NP, and 73% when treated by both CMC-NP and cellulase.

Stability of concentrated aqueous clay–magnetite suspensions

This work is devoted to study the sedimentation behavior in concentrated suspensions of magnetite-covered clay particles. These core–shell particles were prepared by adhesion of synthetic magnetite nanoparticles on sodium montmorillonite platelets in aqueous solution at pH 3 and 2 × 10 −3 mol/L NaNO 3 ionic strength. A new experimental device, suitable for measuring the time evolution of the local volume fraction in concentrated opaque suspensions of magnetizable particles, is described. The experimental method is based on the variations of the resonant frequency of an oscillating parallel LC circuit in which the coil surrounds a test tube filled with the magnetic suspensions. The sedimentation rate in suspensions with different volume fraction and variable magnetite to clay volume fraction ratio was measured. The results are analyzed considering the effect of both the total energy of interaction between the clay–magnetite (core–shell) particles and the total solid volume fraction of the suspensions.