Iron-based Nanoparticles Research Articles

Optical Study of the Reduction of Hexavalent Chromium by Iron-Based Nanoparticles

In this paper, a simple method was presented to measure the concentration change in the Cr(VI)-contained waste water during treatment by nanoparticles, based on its optical absorption spectral evolution which exhibits a good linear relationship between the absorbance of the peak at 348 nm and Cr6+ ion concentration. The iron and Fe/Pd bimetal nanoparticles were prepared and used for removal of Cr6+ in waste water. It has been found that presented method for concentration determination based on optical spectral evolution is effective and flexible. The nanoparticles have higher efficiency than normal iron powders and Fe/Pd bimetallic nanoparticles show faster removal of the Cr6+ than iron nanoparticles. The study is of importance in environmental remediation or pollution treatment of heavy metal ions in water and even soil.

Synthesis and characterization of carbon-encapsulated iron/iron carbide nanoparticles by a detonation method

Carbon-encapsulated iron-based nanoparticles with a core–shell structure were produced by detonation decomposition of explosive mixture precursors containing iron ion components. The size and magnetic properties of the as-prepared composite particles were revealed by X-ray powder diffraction, transmission electron microscopy and magnetic measurements. Results showed that the different sizes of the iron-based nanocrystal core and the thickness of the carbon shell could be yielded by adjusting the component materials of the explosive precursors during the course of these detonation chemical reactions. The composite particles had a body-centered cubic iron or iron carbide core with a coating of graphitic or amorphous carbon layers. Magnetic measurements indicated these composite nanoparticles were magnetic at the room temperature, with some variation in the values of saturation magnetization, remanences and coercive forces that depend on the size and grain composition.

Synthesis of Photoactive Magnetic Nanoparticles with Atomic Layer Deposition

Iron-based magnetic nanoparticles have been produced by decomposition of iron oxalate powder. The micrometer-size iron oxalate powder was first ground by use of a cryogenic milling process. A titanium dioxide (TiO2) thin film was then deposited on the synthesized iron nanoparticles with an in situ atomic layer deposition (ALD) process at 100 °C with TiCl4 and H2O2 as precursors. However, because of the high surface area, the iron nanoparticles were unstable and spontaneously oxidized when exposed to H2O2 during the TiO2 ALD process, thus reducing the magnetic moment of the core particles. As an improvement in the process, prior to the TiO2 deposition, an aluminum nitride (AlN) film was deposited in situ to coat and passivate the iron core particles. The AlN ALD was performed at 250 °C with trimethylaluminium (TMA) and ammonia (NH3) as precursors. This passivation provided a significant decrease in the iron oxidation as determined by X-ray diffraction and magnetization measurements. Photoactivity of the TiO2 film was demonstrated by decomposition of methylene blue solution under ultraviolet irradiation.

Immobilization of arsenic in soils by stabilized nanoscale zero-valent iron, iron sulfide (FeS), and magnetite (Fe3O4) particles

Arsenic is a widespread contaminant in soils and groundwater. While various iron-based materials have been studied for immobilizing arsenic in contaminated soils, the feasibility of stabilized iron-based nanoparticles has not been reported. This study investigates the effectiveness of using three types of starch-stabilized iron-based nanoparticles, including zero-valent iron (ZVI), iron sulfide (FeS), and magnetite (Fe3O4), for immobilization of arsenic in two representative As-contaminated soils (an orchard soil and a fire range soil). To test the effect of the nanoparticles on the arsenic leachability, As-contaminated soils were amended with the nanoparticles at various Fe/As molar ratios (5:1–100:1) and contact time (3 and 7 d). After three days’ treatments of a field-contaminated sandy soil, the PBET-based bioaccessibility of As decreased from an initial (71.3±3.1)% (mean±SD) to (30.9±3.2)% with ZVI, (37.6±1.2)% with FeS, and (29.8± 3.1)% with Fe3O4 at an Fe/As molar ratio of 100:1. The TCLP-based leachability of arsenic in a spiked fire range soil decreased from an initial (0.51±0.11)% to (0.24±0.03)%, (0.27±0.04)% and (0.17±0.04)% by ZVI, FeS, and Fe3O4 nanoparticles, respectively. The Fe3O4 nanoparticles appeared to be more effective (5% or more) than other nanoparticles for immobilizing arsenic. When the two soils were compared, the treatment is more effective on the orchard soil that has a lower iron content and higher initial leachability than on the range soil that already has a high iron content. These results suggest that these innocuous iron-based nanoparticles may serve as effective media for immobilization of As in iron-deficient soils, sediments or solid wastes.

Metallic iron-based nanoparticles for biomedical applications

This study is focused on the fabrication and characterization of core-shell structured iron/iron-oxide nanoparticles for potential use in biomedical applications. In particular, we have investigated the effect of Pt seeding and the injection temperature of Fe(CO)5 precursor on the particle's morphology and magnetic properties. Injection of the iron precursor at low temperature led to a mixture of core-shell structured particles and separate Fe-oxide particles. Whereas, injection at high temperatures led to only core-shell nanoparticles without any separate iron oxides. The importance of the use of Pt(acac)2 to achieve more uniform and oxide free particles is investigated in detail.

Hit or Miss?: Benefits and Risks of Using Nanoparticles for in Situ Remediation

Nanotechnology holds the promise of vastly expanding our ability to clean up hazardous waste sites and decontaminate polluted ground-water in situ. Polychlorinated biphenyls, organic solvents, petroleum products, arsenic, and many more contaminants are on the list that specifically engineered nanoparticles could rapidly remove from contaminated soil and water, saving billions of dollars that would have been spent on more expensive conventional remediation methods. These possibilitites are discussed in a review of field tests using nano-materials [EHP 117:1823–1831; Karn et al.]. However, the authors caution, our knowledge of the potential environmental and health hazards posed by these nanomaterials is in its infancy. In the United States alone there are hundreds of thousands of sites contaminated with hazardous wastes, with more than 1,200 requiring priority attention. Using traditional remediation technologies, such as pumping out and treating contaminated groundwater and removing contaminated soil, the job of cleaning up U.S. hazardous waste sites could take 35 years and $250 billion. The authors of this review, however, report on results showing that nanoscale zero-valent iron (nZVI) nanoparticles could dramatically reduce the time required to remediate soil and water as well as, according to one report, save 80–90% compared with conventional methods. Although tiny in diameter, the surface area of these iron-based nanoparticles reaches 20–40 m2/g. This relatively large surface area can greatly increase the particles’ reactivity. Flowing with the groundwater they can spread out to react with pollutants, transforming them into safer compounds, including compounds that bacteria can break down. The authors provide many examples of how nZVIs, currently the nanomaterials most widely used for in situ remediation, produced measurable effects within days or, in some cases, hours. However, the authors also emphasize that we do not know much about the potential adverse effects of nano-particles deployed into the environment—agents that could, for example, end up in our drinking water. Some nanomaterials have already been found to enter organisms. Might some be toxic or transport bound pollutants to places they might not otherwise have gone? Can they be biomagnified? How do they affect living organisms? The authors point out that, although the environment is full of naturally occurring nanoparticles, manufactured nanoparticles may behave in unpredictable ways. They recommend that while we improve engineering applications using nanoparticles for in situ remediation, we also develop the analytical tools to enable the study of manufactured nanoparticles in the environment and increase research on the ecosystem effects of these materials.

Gold-Coated Cementite Nanoparticles: An Oxidation-Resistant Alternative to α-Iron

Iron-based nanoparticles are desirable for many applications because of their magnetic properties and inherent biocompatibility. Metallic iron, or α-Fe, is the most sought after because of its high saturation magnetization (up to 220 emu/g). This magnetization in iron nanoparticles is difficult to reach or maintain because of the ease of oxidation, which greatly reduces the magnetization values (90 emu/g or less). Here, we report the synthesis of an iron-based nanoparticle comprising a magnetic cementite core (Fe3C) that is more oxidation-resistant than α-Fe, an oxide layer, and a gold coating for passivation and easy functionalization. The nanoparticle structure was confirmed via X-ray absorption fine structure and Mossbauer experiments, and morphology was confirmed using transmission electron microscopy. Magnetic characterization yielded a saturation magnetization of 110 emu/g, thus demonstrating cementite as more stable alternative to α-Fe with higher magnetic moments than the iron oxides.

Transport of Iron-Based Nanoparticles: Role of Magnetic Properties

The transport of magnetic nanoparticles in aquatic environments was studied using maghemite (gamma-Fe(2)O(3)) and gamma-Fe(2)O(3) based (Fe(x)Ni(1-x))(y)O(z) nanoparticles as a function of pH and particle iron content that induced a different magnetic property. Transport studies were conducted in packed bed columns (1 mM KCl, pH 6 and 9) and stability studies were done by dynamic light scattering and sedimentation measurements. Results showed that the stability and transport of these magnetic nanoparticles were influenced by a combination of electrostatic and magnetic interactions. Transport results showed that the less magnetic nanoparticles (possessing higher nickel content) eluted to a greater extent than the more magnetic particles at both pH 6 and 9. The stability in water at both pH 6 and 9 also increased, as nickel content in particles increased suggesting that magnetic interactions enhance aggregation. The nanoparticles eluted to a greater extent at pH 9, at which they were more negatively charged, than at pH 6. Complementary experiments were conducted with alpha-Fe(2)O(3), a nonmagnetic, highly negatively charged nanoparticle which was transported more than the other magnetic particles. The majority of particles were retained at the column inlet (1-2 cm) for all transport experiments, with the greatest amount of retention being that of the magnetic nanoparticles (gamma-Fe(2)O(3)), indicating that magnetically induced aggregation and subsequent straining resulted in greater retention.

Free Radical Scavenging Magnetic Iron-Based Nanoparticles in Hyperbranched and Linear Polymer Matrices

Magnetic iron nanoparticles are attracting a great deal of research and application interest in diversified fields. In this present investigation, iron nanoparticles were prepared by a in-situ chemical reduction technique in a combination of polyaniline (PANI)-polyacrylamide (PA) and PANI-hyperbranched polyurethane (HBPU) matrices to judge the suitability of hyperbranched system. The formation of the nanoparticles in polymer matrices has been investigated by FTIR, UV, XRD, SEM and TEM studies. Narrower size with better dispersion and more stable nanoparticles were found in a hyperbranched matrix system compared to a linear one. The particle size was found to be in the range of 10–20 nm and 12–35 nm in HBPU-PANI and PA-PANI matrices, respectively. Both the nanocomposites exhibit synergistic free radical scavenging capability towards 2,2-diphenyl-1-picrylhydrazyl (DPPH). The magnetic hysteresis loop of the nanocomposites indicates the super-paramagnetic behavior. The hyperbranched system is more thermostable than the linear system by 70°C.

In Situ Monitoring the Thermal Dependence of the Growth of Carbon Nanotubes by Chemical Vapor Deposition Investigated by Tapered Element Oscillating Microbalance

Recently, it has been shown that the catalytic chemical vapor deposition (CCVD) synthesis at atmospheric pressure of multiwalled carbon nanotubes (MWCNTs) and carbon nanofibers can be very well monitored with a tapered element oscillating microbalance (TEOM) (V. Svrcek et al., J. Chem. Phys. 2006, 124, 184705). In this paper, the temperature dependence of the MWCNTs growth by thermal CCVD is investigated. Iron nanoparticle catalysts are dispersed on porous alumina powders. It is shown by scanning electron microscopy that MWCNTs appear above 903 K. The mass increase obtained from decomposition of an ethane-hydrogen gas mixture, monitored by TEOM, occurs with a large initial transient rate v 1 generally followed by a constant steady-state rate v 2 . Activation energy of around 100 kJ/mol is derived for the constant steady-state mass increase throughout the temperature range. A kinetic three-dimensional model based on finite differences is developed to account for these kinetic results. With only two basic assumptions, the calculations well agree with the experimental results. The first assumption supposes a variable competitive adsorption/desorption kinetics on the catalytic surface, and the other one assumes a transition of the iron catalyst from a solid to a state at 973 K. It is thus inferred that the rate of the steady-state growth is controlled by the competitive adsorption of hydrocarbon with hydrogen on the catalytic surface, the first step of the process. By contrast, the transient step displays abrupt changes that are governed by a partial melting of the iron-based nanoparticles above 973 K. In the solid state below 973K, carbon diffusion is controlled by the surface diffusion. Above 973K, the carbon diffusion is enhanced by several orders of magnitude corresponding to liquidlike diffusion. At high temperature, the suppression of the transient state is accounted for by an enhanced hydrocarbon desorption. A nucleation step involving preliminary carbon saturation of the catalytic nanoparticle as well as carbon surface coverage by the nucleation precursor is observed at low temperatures. From the simulations, it is proposed that a carbyne chain circumventing the catalytic nanoparticle may provide the nucleation precursor. A partial or collective poisoning of the catalyst interferes at high temperatures with this general scheme.

Degradation of Trichloroethylene by Iron-Based Bimetallic Nanoparticles

Degradation of Trichloroethylene by Iron-Based Bimetallic Nanoparticles

Synthesis and Covalent Surface Functionalization of Nonoxidic Iron Core−Shell Nanomagnets

The rapidly growing applications of nanomagnets require acid/base stable, oxidation-resistant shells with chemically controlled surface structure. An ideal core should be metallic and highly magnetic. We demonstrate the production of iron-based nanoparticles, ranging from iron oxide to iron and iron carbide, by systematically modifying the degree of reduction during flame spray synthesis under a controlled atmosphere. At a laboratory scale, continuous production yields iron-based particles of 20−50 nm at a production rate of >10 g h−1. Carbon-encapsulated iron carbide (C/Fe3C) combines exceptionally high saturation magnetization (140 emu g−1), air stability (up to 200 °C), and resistance against acidic dissolution (1 week in 24% HCl). The top graphene-like carbon layer could be covalently functionalized with various linkers, thus allowing us to chemically design the particle surface. Activity was demonstrated by reacting 2-phenyl ethyl amine functionalized nanomagnets with carboxylic acid chlorides as a model reaction. The present nanomagnets consist of biologically well-accepted constituents. They combine the required chemical reliability, improved magnetization if compared to magnetite with the potential for technical scale manufacturing, and therefore open stable nanomagnets to a broad range of fascinating separation problems (extraction/water treatment) and biomedical research.

Degradation of Trichloroethylene and Dichlorobiphenyls by Iron-Based Bimetallic Nanoparticles.

Bimetallic nanoparticles of Ni/Fe and Pd/Fe were used to study the degradation of trichloroethylene (TCE) at room temperature. The activity for different iron-based nanoparticles with nickel as the catalytic dopant was analyzed using iron mass-normalized hydrogen generation rate. Degradation kinetics in terms of surface area-normalized rate constant was observed to have a strong correlation with the hydrogen generated by iron oxidation. A sorption study was conducted, and a mathematical model was derived that incorporates the reaction and Langmuirian-type sorption terms to estimate the intrinsic rate constant and rate-limiting step in the degradation process, assuming negligible mass transfer resistance of TCE to the solid particles phase. A longevity study through repeated cycle experiments was conducted to analyze the effect of activity loss on the reaction mechanistic pathway, and the results showed that the attenuation in the nanoparticles activity did not adversely affect the reaction mechanisms in generating gaseous products such as ethylene and ethane.

EMR Spectra of Iron-Based Nanoparticles Produced by Dissimilatory Bacteria

We have studied electron magnetic resonance spectra of iron-oxide nanoparticles related to iron reduction metabolism of dissimilatory bacterium Thermincola ferriacetica. It is found that the resonance parameters of metabolic products change notably with time. The X-ray diffraction data indicates partial crystallization of iron oxide during long time storage under air open conditions.

Arsenic removal by iron-doped activated carbons prepared by ferric chloride forced hydrolysis

Ferric chloride forced hydrolysis is shown to be a good method for increasing the iron content of activated carbons (ACs). Iron content increased linearly with hydrolysis time, and ACs with iron content as high as 9.4 wt.% at 24 h hydrolysis time could be prepared. The increase in iron content did not produce any modification in the textural parameters determined by nitrogen adsorption at 77 K. Iron-based nanoparticles, homogeneous in size and well-dispersed in the carbon matrix, were obtained. Nanoparticles forming iron (hydr)oxide agglomerates at the outer surface of the carbon grains at hydrolysis times higher than 6 h were also produced. The AC obtained after 6 h of ferric chloride forced hydrolysis removed 94% of the arsenic present in a groundwater from the State of Chihuahua (Mexico), whereas the commercial AC used as precursor allowed the removal of only 14%. The lower performance in arsenic removal observed for AC prepared using long forced hydrolysis time (24 h) is probably due to the existence of iron (hydr)oxides nanoparticles agglomerates, which once hydrated could prevent diffusion of arsenate (HAsO 4 −) towards the inner surface of the AC grain.

Magnetic nano-adsorbent integrated with lab-on-valve system for trace analysis of multiple heavy metals

A novel system for trace analysis of multiple heavy metals was developed wherein we have integrated a magnetic nano-adsorbent with a lab-on-valve system and coupled this to an inductively coupled plasma mass spectrometer. The magnetic nano-adsorbent was prepared by surface modification of iron-based magnetic nanoparticles with polyacrylic acid (MNPs-PAA). The MNPs-PAA possessing the superparamagnetic nature of MNPs could be controllably immobilized in PTFE tubing by an external magnetic force. The high surface density of PAA (3.30 × 1011 molecules cm−2) on MNPs-PAA significantly reduced the amounts of adsorbent needed for adsorption of heavy metals (Mn2+, Co2+, Cu2+, Zn2+, and Pb2+). A detection limit of 0.04–0.06 µg L−1 (except 0.6 µg L−1 for Cu2+ and Zn2+), a precision smaller than 4% (RSD, n = 3), and a linear range of 0.5–50 µg L−1 were obtained by directly injecting an aliquot of 20 µL fortified standard solution analyzed at 5 min per sample. The accuracy was evaluated by analyzing certified reference materials of SRM 2670a (trace elements in urine, low level) and CASS-2 (nearshore seawater reference material for trace metals). Good agreement between the measured and certified values demonstrated that the system is useful for trace analysis of multiple heavy metals in environmental and biological aqueous samples. The potential of integrating functionalized nano-materials to improve the performance of existing analytical systems as an alternative approach to green analytical chemistry is foreseen.

Metallic iron nanoparticles for MRI contrast enhancement and local hyperthermia.

Current magnetic-nanoparticle technology is challenging due to the limited magnetic properties of iron oxide nanoparticles (IONPs). Increasing the saturation magnetization of magnetic nanoparticles may permit more effective development of multifunctional agents for simultaneous targeted cell delivery, magnetic resonance imaging (MRI) contrast enhancement, and targeted cancer therapy in the form of local hyperthermia. We describe the synthesis and characterization of novel iron-based nanoparticles (FeNPs) coated with biocompatible bis-carboxyl-terminated poly(ethylene glycol) (cPEG). In comparison to conventional IONPs similar in size (10 nm), FeNPs particles have a much greater magnetization and coercivity based on hysteresis loops from sample magnetometry. Increased magnetization afforded by the FeNPs permits more effective generation of local hyperthermia than IONPs when subjected to an oscillating magnetic field in a safe frequency range. Furthermore, FeNPs have a much stronger shortening effect on T2 relaxation time than IONPs, suggesting that FeNPs may be more effective MRI contrast agents. Next-generation FeNPs with a biocompatible coating may in the future be functionalized with the attachment of peptides specific to cancer cells for imaging and therapy in the form of local hyperthermia.

Ferritin, a protein containing iron nanoparticles, induces reactive oxygen species formation and inhibits glutamate uptake in rat brain synaptosomes

Nanoparticles are currently used in medicine as agents for targeted drug delivery and imaging. However it has been demonstrated that nanoparticles induce neurodegeneration in vivo and kill neurons in vitro. The cellular and molecular bases of this phenomenon are still unclear. We have used the protein ferritin as a nanoparticle model. Ferritin contains iron particles (Fe3+) with size 7 nm and a protein shell. We investigated how ferritin influences uptake and release of [14C]glutamate and free radical formation as monitored by fluorescent dye DCFDA in rat brain synaptosomes. We found that even a high concentration of ferritin (800 μg/ml) did not induce spontaneous [14C]glutamate release. In contrast the same concentration of this protein inhibited [14C]glutamate uptake two fold. Furthermore ferritin induced intrasynaptosomal ROS (reactive oxygen species) formation in a dose-dependent manner. This process was insensitive to 30 μM DPI, an inhibitor of NADPH oxidase and to 10 μM CCCP, a mitochondrial uncoupler. These results indicate that iron-based nanoparticles can cause ROS and decreased glutamate uptake, potentially leading to neurodegeneration.

Relation between the Redox State of Iron-Based Nanoparticles and Their Cytotoxicity toward Escherichia coli

Iron-based nanoparticles have been proposed for an increasing number of biomedical or environmental applications although in vitro toxicity has been observed. The aim of this study was to understand the relationship between the redox state of iron-based nanoparticles and their cytotoxicity toward a Gram-negative bacterium, Escherichia coli. While chemically stable nanoparticles (gammaFe2O3) have no apparent cytotoxicity, nanoparticles containing ferrous and, particularly, zerovalent iron are cytotoxic. The cytotoxic effects appear to be associated principally with an oxidative stress as demonstrated using a mutant strain of E. coli completely devoid of superoxide dismutase activity. This stress can result from the generation of reactive oxygen species with the interplay of oxygen with reduced iron species (Fe(II) and/or Fe(0)) or from the disturbance of the electronic and/or ionic transport chains due to the strong affinity of the nanoparticles for the cell membrane.

Ex-vivo cellular MRI with b-SSFP: quantitative benefits of 3 T over 1.5 T

The use of MRI with iron-based magnetic nanoparticles for imaging cells is a rapidly growing field of research. We have recently reported that single iron-labeled cells could be detected, as signal voids, in vivo in mouse brains using a balanced steady-state free precession imaging sequence (b-SSFP) and a customized microimaging system at 1.5 T. In the current study we assess the benefits, and challenges, of using a higher magnetic field strength for imaging iron-labeled cells with b-SSFP, using ex vivo mouse brain specimens imaged with near identical systems at 1.5 and 3.0 T. The substantial banding artifact that appears in 3 T b-SSFP images was readily minimized with RF phase cycling, allowing for banding-free b-SSFP images to be compared between the two field strengths. This study revealed that with an optimal 3 T b-SSFP imaging protocol, more than twice as many signal voids were detected as with 1.5 T. There are several factors that contributed to this important result. First, a greater-than-linear SNR gain was achieved in mouse brain images at 3 T. Second, a reduction in the bandwidth, and the associated increase in repetition time and SNR, produced a dramatic increase in the contrast generated by iron-labeled cells.