Iron Nanoclusters Research Articles

Green synthesized nanoclusters of ultra-small zero valent iron nanoparticles as a novel dye removing material

Iron based nanoparticles have gained much attention in recent years due to their unique physicochemical properties especially in the environmental remediation practices. There has been an increasing demand for new sustainable techniques for production of these nanoparticles. In the present work, a novel iron nanostructure was successfully fabricated by a facile and green approach using the aqueous extract of Mediterranean cypress (Cupressus sempervirens). In fact, nanoclusters of highly reactive ultra-small (~1.5nm in diameter) iron nanoparticles were constructed. Diameters of iron nanoclusters were measured to be from 9 to 31nm with mean diameter of 19nm. Appearance of the characteristic X-ray diffraction peak of zero valent iron at 2θ=43.5° indicates the great potential of Mediterranean cypress leaf extract for complete reduction of ferric ions. The presence of phytochemicals as organic capping agent was confirmed by IR radiation absorption at 1020cm−1 and 1623cm−1 corresponding to the presence of CO and carbonyl groups, respectively. The fabricated nanoclusters also showed a great potential for dye removal from aqueous solution in a time dependent manner. Decolourization efficiency was calculated to be 95% in a 6h process for methyl orange removal. The results of this study suggest the possibility of using iron nanoclusters for future pollutants removal applications from aqueous environments.

Axel Jacobi von Wangelin

Axel Jacobi von Wangelin

Thermal stabilities of iron nanoparticles under hydrostatic pressure

The present study aimed to apply molecular dynamics simulation to study the thermal stability and melting behavior of bcc iron nanoclusters under the pressure of up to 40 GP. Several factors were calculated, including the bulk modulus, melting temperature, melting enthalpy changes, melting volume changes and radial distribution function. In addition, size effects were investigated in the melting process. The bulk modulus was observed to raise a thigh external pressure and decrease in enlarged sizes. Pressure and size were significant determinants of the melting temperature. In the melting process, rate of enthalpy changes increased with greater pressure and size, while the volume changes reduced at higher pressure and size. On the other hand, small nanocluster size augmented the ΔVm slope. Finally, g(r) values of the first shell declined with greater nanocluster sizes, and iron atoms appeared closer in the nanocluster structure at high pressure.

Investigation of solvation of iron nanoclusters in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate using molecular dynamics simulations: Effect of cluster size at different temperatures

The systems composed of metal nanoclusters in ionic liquids are relevant for applications in lubrication, electrochemical devices, catalysis, and chemical processes. The mechanism of solvation and interactions of these systems are not understood at present. In this work, we have simulated iron nanoclusters with different sizes in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate [N1114][C1SO3] at two temperatures (300 and 500K) and at atmospheric pressure. We have investigated the effects of cluster size and the temperature on some of the thermodynamics, structural and dynamical properties of the systems. Our results also show that the absolute value of solvation energy increases as the nanocluster size increases. Also the absolute solvation energy increases as the temperature increases. It is also shown that the effect of the cluster size is much more than the effect of the temperature. Our structural investigations indicate at least two shells (a double layer) around the nanocluster and the anions are closer to the cluster surface than the cations. The self-diffusion coefficients of cations, anions, and iron clusters have been also presented and discussed in this work.

Iron Nanoclusters as Template/Activator for the Synthesis of Nitrogen Doped Porous Carbon and Its CO2 Adsorption Application.

We propose a facile synthesis approach for nitrogen doped porous carbon and demonstrate a novel pore-forming method that iron nanoclusters act as a template or activator at different carbonization temperatures based on Fe3+-poly(4-vinyipyridine) (P4VP) coordination. P4VP will completely decompose even in an inert atmosphere, but under the coordination and catalysis of Fe3+, it can be converted to carbon at a very low temperature (400 °C). The aggregation of iron nanoclusters in the carbonization process showed different pore-forming methods at different temperatures. The as-prepared materials possess high specific surface area (up to 1211 m2 g-1), large pore volume (up to 0.96 cm3 g-1), narrow microporosity, and high N content (up to 9.9 wt %). Due to these unique features, the materials show high CO2 uptake capacity and excellent selectivity for CO2/N2 separation. The CO2 uptake capacity of NDPC-2-600 is up to 6.8 and 4.3 mmol g-1 at 0 and 25 °C; the CO2/N2 (0.15/0.85) selectivity at 0 and 25 °C also reaches 18.4 and 15.2, respectively.

Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts

AbstractThe replacement of noble metal technologies and the realization of new reactivities with earth‐abundant metals is at the heart of sustainable synthesis. Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron‐catalyzed hydrogenation protocol for tri‐ and tetra‐substituted alkenes of unprecedented activity and scope under mild conditions (1–4 bar H2, 20 °C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.

Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts.

The replacement of noble metal technologies and the realization of new reactivities with earth‐abundant metals is at the heart of sustainable synthesis. Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron‐catalyzed hydrogenation protocol for tri‐ and tetra‐substituted alkenes of unprecedented activity and scope under mild conditions (1–4 bar H2, 20 °C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.

Handheld energy-efficient magneto-optical real-time quantitative PCR device for target DNA enrichment and quantification

A PCR provides not only valuable genetic information that enables precise differential disease diagnosis but also quantitative data to assess various clinical states. We report the successful integration of novel dual-mode magnetic Fe3O4 nanoclusters that deliver photothermal conversion. The clusters can be excited with pulsed laser light for precision thermal cycle modulation to develop an ultrafast quantitative PCR system. Traditional PCR heats and cools the sample from outside the PCR tube; the heat needs to pass through the heat block, tube wall and transfer to the DNA through water molecules. In contrast, our system uses nanoparticles inside the liquid phase as numerous ‘nanoheaters’; thus the thermal transfer between particles and adjacent water or DNA molecules becomes extremely efficient because of proximity at the molecular level. Moreover, the defective mitochondrial DNA from cybrid cell lines of a patient with chronic progressive external ophthalmoplegia syndrome, a mitochondrial disease, was efficaciously detected. The system has a simple design, is extremely energy efficient and is faster than traditional qPCR. Our finding provides new insight into rapid and accurate quantitative diagnostics for future point-of-care applications. Iron nanoparticles play double duty as ‘nanoheaters’ for DNA amplification and as molecular manipulators in a new point-of-care prototype. Polymerase chain reaction (PCR) devices create multiple copies of small DNA strands for genetic testing, but usually require bulky heating and cooling mechanisms. Dar-Bin Shieh and colleagues from National Cheng Kung University in Taiwan have found that tiny clusters of iron oxide nanocubes can improve heat transfer in PCR devices by entering the liquid phase next to the target DNA. When irradiated by laser light, the iron nanoclusters release heat to precisely modulate DNA temperatures. Furthermore, functionalizing the nanoparticles with nucleotide probes enables them to attach to and extract specific disease-indicating mitochondria using magnetic fields. The portable, battery-powered prototype can wirelessly interface with tablet computers and is twice as efficient at isolating mitochondria as commercial kits. A novel dual-mode magnetic Fe3O4 nanoclusters was developed that exhibit efficient photothermal conversion and superparamagnetism. The particles served as numerous ‘nanoheaters’ in a PCR reaction mixture while enabling effective magnetic-based macromolecular manipulation. The thermal transfer between particles and adjacent water and DNA molecules thus become extremely efficient because of molecular-level proximity and allowed rapid amplification cycle progression. The defective mitochondrial DNA from cybrid cell lines of a patient with chronic progressive external ophthalmoplegia syndrome was efficaciously quantified by fluorescence intensity detection. Our finding provides new insight into rapid and accurate quantitative DNA diagnostics for future point-of-care applications.

Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures.The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples.The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves.The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.

Identifying the active sites for CO dissociation on Fe–BCC nanoclusters

CO dissociation rate is fundamental for determining selectivity and yield for growing carbon chains on iron catalysts in, e.g., Fischer–Tropsch and carbon nanotube syntheses. CO dissociation is a highly structure sensitive reaction; on crystal surfaces and large particles CO dissociation is facile only at step sites. However, small (<3nm) nanoparticles cannot contain steps and even in macroscopic clusters step concentration is small. Here, density functional theory is used systematically to map several CO dissociation pathways to find and explain the nature of active sites in small BCC iron nanoclusters. It is shown that BCC(100-110) edges of the particle are responsible for the reactivity of small Fe–BCC clusters and that low CO dissociation barrier is achievable even without stepped surfaces. Careful analysis proves the essential role of local geometry at the active site leading to strong interaction between the metal and 2π* orbitals and accessible, empty states. Furthermore, CO dissociation on Fe–BCC particles is more facile than on smooth crystal surfaces and icosahedral and amorphous iron particles exemplifying the importance of nanoparticle geometry on reactivity. Providing suitable particle geometry is used, CO dissociation on Fe–BCC nanoparticles occurs even under mild conditions, enabling controlled synthesis of carbon structures from CO.

Amalgamation of complex iron(III) ions and iron nanoclusters with MWCNTs as a route to potential T2 MRI contrast agents.

Iron-filled multiwall carbon nanotubes (Fe@MWCNTs) were functionalized toward a variety of potential magnetic resonance imaging contrast agents. Oxidized Fe@MWNCTs were covered with PEG5000 via direct esterification or using acyl chloride derivatives. Alternatively, the latter were functionalized with an aminophenol ligand (Fe@O-MWCNT-L). Moreover, pristine Fe@MWCNTs were functionalized with N-phenylaziridine groups (Fe@f-MWCNT) via [2+1] cycloaddition of nitrene. All of these chemically modified nanotubes served as a vehicle for anchoring Fe3+ ions. The new hybrids – Fe(III)/Fe@(f-/O-)MWCNTs – containing 6%–14% of the “tethered” Fe3+ions were studied in terms of the acceleration of relaxation of water protons in nuclear magnetic resonance. The highest transverse relaxivity r2=63.9±0.9 mL mg−1 s−1 was recorded for Fe(III)/Fe@O-MWCNT-L, while for Fe(III)/Fe@f-MWCNT, with r2=57.9±2.9 mL mg−1 s−1, the highest impact of the anchored Fe(III) ions was observed. The T1/T2 ratio of 30–100 found for all of the nanotube hybrids presented in this work is a very important factor for their potential application as T2 contrast agents. Increased stability of the hybrids was confirmed by ultraviolet–visible spectrophotometry.

Investigation on Sized-Regulated Iron Nanoparticles Prepared by Liquid Phase Plasma Reduction Process

The liquid-phase plasma reduction method has been applied to prepare iron nanoparticles from iron chloride solution using a bipolar pulsed electrical discharge system. The excited states of atomic iron, hydrogen, and oxygen as well as the molecular bands of hydroxyl radicals were detected in the emission spectra. The iron nanoclusters formed at the initial stage convert to dispersion of small iron nanoparticles, which then grows slowly to form anisotropic, tetragonal shape. The cationic surfactant of CTAB was shown to exhibit a large influence on the particle generation procedure.

Magnetic properties of Fe and Co nanoclusters embedded in the first Cu(100) surface layer

The magnetic anisotropy energies, as well as spin and orbital magnetic moments of the atoms involved in the simplest nanostructures formed due to the self-organization within the first Cu(100) surface layer, are calculated in the framework of the density functional theory. The critical role of the surface relaxation, which leads to the rotation of the easy magnetization axis in iron nanoclusters, is demonstrated in the calculations of magnetic anisotropy.

Technology for production of magnetic carbon nanopowders doped with iron and cobalt nanoclusters

Abstract Complex scanning electron microscope and Auger electron spectroscope structure and composition measurements, along with the vibrating sample magnetometer and NMR studies, were carried out on carbon nanoparticles doped with magnetic clusters, which were synthesized by a technology which combines the ethanol vapor pyrolysis method and the chemical vapor deposition process in a horizontal continuous reactor with certain temperature gradients and controlled partial oxygen pressure. The structure and composition data of the synthesized magnetic carbon nanopowders showed that the nanopowders consisted of randomly distributed carbon nanoparticle aggregations that are 200 nm in diameter doped with magnetic clusters. The magnetometry and NMR data are in agreement with the results of the structure analysis, pointing to the existence of a significant superparamagnetic contribution to the synthesized carbon nanoparticles doped with cobalt nanoclusters.

Magnetocrystalline anisotropy energy ofFe(001)andFe(110)slabs and nanoclusters: A detailed local analysis within a tight-binding model

We report tight-binding (TB) calculations of magnetocrystalline anisotropy energy (MAE) of Iron slabs and nanoclusters with a particuler focus on local analysis. After clarifying various concepts and formulations for the determination of MAE, we apply our realistic TB model to the analysis of the magnetic anisotropy of Fe$(001)$, Fe$(110)$ slabs and of two large Fe clusters with $(001)$ and $(110)$ facets only: a truncated pyramid and a truncated bipyramid containg 620 and 1096 atoms, respectively. It is shown that the MAE of slabs originates mainly from outer layers, a small contribution from the bulk gives rise, however, to an oscillatory behavior for large thicknesses. Interestingly, the MAE of the nanoclusters considered is almost solely due to $(001)$ facets and the base perimeter of the pyramid. We believe that this fact could be used to efficiently control the anisotropy of Iron nanoparticles and could also have consequences on their spin dynamics.

Magnetic distributions of iron–(nickel zinc ferrite) nanocomposites from first order reversal curve analysis

First order reversal curve measurements offer a powerful approach to quantify the magnetic property distributions in materials. Here, we have used this approach to quantify magnetic property distributions and understand the nano-scale mechanisms contributing to the magnetic anisotropy of Fe-(Ni0.5Zn0.5)Fe2O4 nanocomposites. The Fe-(Ni0.5Zn0.5)Fe2O4 nanocomposite powders were synthesized using a chemical method involving ferrite precipitation and controlled reduction which resulted in the formation of iron nanoclusters within the ferrite. Two samples with a ∼65% and ∼6% iron composition, respectively, were studied. Transmission electron microscopy measurements yielded an average particle size of ∼15 nm (∼65% Fe) and ∼60 nm (∼6% Fe). The magnetizations at 7 T for the synthesized nanocomposites (M7T = 58 Am2 kg−1 for the ∼65% Fe sample and 55 Am2 kg−1 for the ∼6% Fe sample) are close to that of the bulk saturation magnetization (∼60 Am2 kg−1) of (Ni0.5Zn0.5)Fe2O4. This is not typical in these ferrite systems, due to poor crystallinity. In our samples, the observed large M7T may result from the presence of the iron nanoclusters, as well as improved crystallinity. However, there is a slope to the magnetization at high fields which has typically been attributed to surface spin canting. This may instead be an indication of reduced crystallinity at the surface of the nanoparticles, especially in the ∼65% Fe sample. Furthermore, a difference in interactions between the ferrite and the iron nanoclusters in the two samples results in different anisotropy distributions, as evidenced by a broad transition to saturation for the first sample, and a much sharper transition for the second sample, and confirmed through first order reversal curve measurements.

X-Ray Absorption and Mössbauer Spectroscopies Characterization of Iron Nanoclusters Prepared by the Gas Aggregation Technique

Partially oxidized iron nanoclusters have been prepared by the gas-phase aggregation technique with typical sizes of 2-3 nm. This preparation technique has been reported to obtain clusters with interesting magnetic properties such as very large exchange bias. In this paper, a sample composition study carried out by Mössbauer and X-ray absorption spectroscopies is reported. The information reached by these techniques, which is based on the iron short range order, results to be an ideal way to have a characterization of the whole sample since the obtained data are an average over a very large amount of the clusters. In addition, our results indicate the presence of ferrihydrite, which is a compound typically ignored when studying this type of systems.

Influence of the Brönsted and Lewis acid sites on the catalytic activity and selectivity of Fe/MCM-41 system

The system Fe2O3/MCM-41, with high iron dispersion, was synthesized in order to introduce Lewis acid sites into the MCM-41 structure. Two calcination atmospheres (inert and oxidant) were used to produce iron nanoclusters with different structural properties. Besides, a silylation treatment was realized on both solids with the aim of neutralizing the Brönsted acidity associated with the MCM-41 silanol groups. The samples were characterized by atomic absorption spectroscopy, X-ray diffraction at low angles, N2 adsorption, temperature-programmed reduction, Fourier transform infrared spectroscopy, nuclear magnetic resonance of 29Si, and Mössbauer spectroscopy. The influence of the structural changes of the nanoclusters and the effect of the simultaneous presence of Lewis and Brönsted acid sites were evaluated studying the product distribution from the α-pinene oxide isomerization reaction. It was determined that the Brönsted acidity of the Fe/MCM-41 system has not the sufficient acid strength to modify the product distribution which is mainly governed by the Lewis sites.

Carbo-Iron®—Synthesis and stabilization of Fe(0)-doped colloidal activated carbon for in situ groundwater treatment

Carbo-Iron – a novel composite material is presented, which consists of nanoscale zero-valent iron (nZVI) clusters on activated carbon colloids (ACC). The material is especially designed for the in situ generation of reactive zones and contaminant source removal when applied in groundwater remediation processes. This paper deals with the tailored synthesis of the composite material to create a reducing agent with properties optimized for subsurface transport of the particles and improved source affinity when compared to pure nZVI. Various iron precursors and impregnation methods are discussed with regard to their influence on the material properties. The impregnated ACCs were reduced by either H2 or C/CO in order to achieve the desired Carbo-Iron colloids. By means of thermogravimetric analysis the optimal reduction temperatures were determined for H2 (500°C) and for the carbon carrier material (700°C) as reducing agent. For stabilization of the initially generated pyrophoric highly dispersed iron nanoclusters various approaches were studied in order to generate an air-stable material without significant loss of metallic iron. Stabilization with traces of gaseous HCl gave the best results. Finally, the influence of the nZVI and residual iron oxide deposits on the sorption properties of the ACC carrier is discussed.

Exchange bias and magnetic behaviour of iron nanoclusters prepared by the gas aggregation technique

Iron nanoclusters have been deposited by the gas-phase aggregation technique to form multilayered structures with outstanding exchange-bias (HE) values up to HE=3300Oe at low temperatures. In order to explain the observed magnetic properties, composition and crystallographic phase have been determined by X-ray absorption spectroscopy. A metal-oxide core–shell arrangement has to be discarded to explain the large obtained values of HE since structural results show nanoclusters formed by the antiferromagnetic α-Fe2O3 oxide. Moreover, nanoparticles of few nanometers formed by substoichiometric α-Fe2O3 explain the observed weak ferromagnetism and let to understand the origin of large exchange bias by the interaction between different spin sublattice configurations provided by the low iron coordination at surface.