Formation Of Fe Nanoparticles Research Articles

Operando electron spin probes for the study of battery processes

Operando electron spin probes, namely magnetometry and electron paramagnetic resonance (EPR), provide real-time insights into the electrochemical processes occurring in battery materials and devices. In this work, we describe the design criteria and outline the development of operando magnetometry and EPR electrochemical cells. Notably, we show that a clamping mechanism, or springs, are needed to achieve sufficient compression of the battery stack and an electrochemical performance on par with that of a standard Swagelok-type cell. The tandem use of operando EPR and magnetometry allows us to identify five distinct and reversible redox processes taking place on charge and discharge of the intercalation-type LiNi0.5Mn0.5O2 Li-ion cathode. While redox processes in conversion-type electrodes are notoriously difficult to investigate using standard characterization methods (e.g. X-ray based) and/or post mortem analysis, due to the formation of poorly crystalline and metastable reaction intermediates and products during cycling, we show that operando magnetometry provides unique insight into the kinetics and reversibility of Fe nanoparticle formation in the Na3FeF6 electrode for Na-based batteries. Step increases in the cell magnetization upon extended cycling indicate the build-up of Fe nanoparticles in the system, hinting at only partially reversible charge–discharge processes. The broad applicability of the tools developed herein to a range of electrode chemistries and structures, from intercalation to conversion electrodes, and from crystalline to amorphous systems, makes them particularly promising for the development of electrochemical energy storage technologies and beyond.

Enhancement of oxygen flux through Nb-doped La0.4Sr0.6FeO3-δ ceramic hollow fiber membranes by Fe exsolution

In recent years, numerous studies have focused on the use of mixed ionic-electronic conducting oxides for coupled oxygen separation and catalytic reactions in membrane reactors. A promising strategy for the efficient fabrication of oxygen separation membranes involves modification of the membrane surface via exsolved metal nanoparticles decoration. Here, we present a detailed characterization of the structural and transport properties of a novel membrane material La0.4Sr0.6Fe0.95Nb0.05O3−δ (LSFNb5). The exsolution of Fe nanoparticles was observed after heating of LSFNb5 in a reducing atmosphere (5 % Н2/Ar) and was confirmed by X-ray diffraction analysis, Mössbauer spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The formation of Fe nanoparticles on the surface of LSFNb5 hollow fiber membrane in the reduction process leads to the enhancement of oxygen fluxes and reduces the apparent activation energy. Kinetic parameters for oxygen transport through LSFNb5 hollow fiber membrane estimated using two different models, are in good agreement with the experimental results. Furthermore, LSFNb5 hollow fiber membrane demonstrates stable performance both before and after surface treatment.

Exsolution versus particle segregation on (Ni,Co)-doped and undoped SrTi0.3Fe0.7O3-δ perovskites: Differences and influence of the reduction path on the final system nanostructure

Exsolution is one of the most successful functionalization techniques to improve the catalytic activity of electrodes in solid oxide fuel and electrolyzer cells (SOFC/SOEC). The objective of this technique is to produce the highest possible number of metallic nanoparticles on the surface of a host-oxide, without significantly altering its structure. In this work, we compare three similar SOFC electrodes: STF (SrTi0.3Fe0.7O3), STFN (Sr0.93Ti0.3Fe0.63Ni0.07O3), and STFNC (Sr0.93Ti0.3Fe0.56Ni0.07Co0.07O3), revealing that there is a significant difference between Ni–Fe/Ni–Co–Fe nanoparticle formation in STFN/STFNC and pure Fe0 particle formation in STF, which is evidenced by the size and amount of produced nanoparticles, but also by their anchoring to the host-oxide. The terms exsolution and particle segregation will be used, respectively, to distinguish these phenomena. Next, we explore two different reduction methods and observe that the characteristics of exsolution do not only depend on temperature, atmosphere and reduction times, but also on the reduction path taken to reach such conditions.

Highly active La0.35Sr0.35Ba0.3Fe1-xCoxO3 oxygen carriers with the anchored nanoparticles for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) has the potential as a viable technology to achieve carbon neutrality in terms of converting CH4 and CO2 to various value-added products with the minimal separation requirements. However, the design and development of an appropriate oxygen carrier (OC) with the remarkable reactivity and stability make the CL-DRM process challenging. Herein, the Co-substituted La0.35Sr0.35Ba0.3Fe1-xCoxO3 (LSBFC) perovskite oxides with the anchored nanoparticles as the novel OCs were synthesized and investigated for the redox performance in the CL-DRM process. It is found that the best substitution proportion of Co in the anchored perovskite oxides can be set in range of 0.2–0.6. The optimized OCs can greatly improve the reactivity of the chemical looping process based on various characterizations. Among all samples, La0.35Sr0.35Ba0.3Fe0.6Co0.4O3 OC increases the oxygen mobility and shows a higher oxygen diffusion rate to achieve the CH4 conversion of 84.3% and syngas yield of 15.23 mmol⋅g−1 in the CH4 reduction step, respectively. A detailed analysis of the anchored perovskite oxides reveals the substitution of Co can greatly weaken the perovskite lattice to result in the migration of Fe and the formation of Fe nanoparticles, which tremendously promote the activation of CH4 for the further conversion. Furthermore, the excellent OCs also exhibit the high stability in the enhanced reaction performance, the preservation of material structure and the stable regenerability by CO2 during the successive redox cycles. These features demonstrate that the new perovskite materials with anchored nanoparticles can be the promising oxygen carriers for the CL-DRM process.

Preparation and formation mechanism of biomass-based graphite carbon catalyzed by iron nitrate under a low-temperature condition.

Graphite is a widely used industrial material, which experienced a marked shortage caused by the growing demand for electrode anode material and the increased costs for raw material. Graphitic carbon from biomass is a promising approach that will result in low-cost and efficient preparation. Herein, Fe(NO3)3 was selected as the catalyst for pine sawdust, and the effects of temperature and iron content on the graphitization of biochar were investigated. Additionally, the formation mechanism of the graphitic crystallite structure was explored. Results showed that the formation of pyrolysis gas increased with the increase in the amount of catalyst added or pyrolysis temperature. The change in pyrolysis gas, such as H2 and CO, was a critical auxiliary factor reflecting the conversion process. As temperature was increased from 600°C to 800°C, the solid products showed high graphitization and low solid yield. Graphite structure mainly formed at 700°C because of the formation of Fe nanoparticles. The increase in the amount of catalyst could provide more reaction sites and promote the contact between Fe and C, showing that amorphous carbon is dissolved on Fe nanoparticles and precipitated into ordered graphitic carbon. On this basis, a mechanism of "carbon dissolution-precipitation" was proposed to explain the formation of graphite structure, and the whole pyrolysis process included the transformation of the iron element were analyzed.

Effect of HF wet-etching and H2-plasma polishing on the low-temperature growth of carbon nanotubes on stainless-steel substrates

Direct growth of carbon nanotubes (CNTs) on 316 stainless-steel (SS) substrates could facilitate versatile commercial applications. For the successful synthesis of CNTs on SS substrate, hydrofluoric acid (HF) etching renders suitable surface roughness to promote CNT growth. For catalyst preparation and also subsequent CNT growth, H2-plasma treatment plays essential roles. Reversing the aging effect of Fe/Ni from its unwanted oxides of reduced catalytic activity and formation of Fe nanoparticles from the sheet are accomplished using H2-plasma. High-density plasma, along with specific gas precursors with its energetic ions, required for uniform CNT growth is attained by microwave plasma-enhanced chemical vapor deposition. By using CO2, providing suitable oxidizer precursors, in (CH4 + H2) diffuse plasma, necessary ambience for low-temperature nucleation (300 °C) and high-yield CNT growth is obtained. Reduction in the deposition rate by highly-energetic ion collisions in high-power plasma is resolved by introducing remote plasma configuration using a specially designed mask assembly. Considering the optimum magnitudes of the intensity ratios of D- and 2D-peaks to the G-peak in the Raman spectra of CNTs, a time span of 2 h of HF-etching appears optimum for proper functioning of the Fe/Ni nanoparticle catalyst. Furthermore, H2-plasma polishing is effectively utilized as the last step of pretreatment, leading to the growth of lower-diameter CNTs. Finally, using a shadow mask assembly and weak oxidizing gas, low-temperature growth of CNTs is successfully accomplished on SS substrates, pretreated by optimum HF-etching and H2-plasma polishing on the Fe-nanoparticle catalyst layer, avoiding the conventional steps of high-temperature annealing for catalyst nanoparticle formation as well as high-temperature nucleation for CNT growth. Even without the use of a separate Fe-catalyst layer, CNT growth is accomplished directly on HF-etched and H2-plasma polished SS substrates, utilizing mostly Fe/Ni nano-grains that originate from the intrinsic composition of SS as the nucleation sites. Use of limited action-steps and of a low-temperature (~300 °C) distinguish this as a realistic avenue for commercial production of CNTs.

Urtica Diocia Leaves Extract: A Natural Resource to Reduce Iron Salt to Synthesize Fe Nanoparticles

This paper demonstrates synthesis of iron nanoparticles by using leaves extract of Urtica Dioica plant, a natural resource to reduce the iron salt. Moreover, leaves extract also acts as a stabilizing agent in protecting dispersed Fe nanoparticles. The absorption peak is observed in the range of 367-427 nm, indicating formation of Fe nanoparticles, however with partial oxidation. The Fe nanoparticles were obtained in powder form after centrifugation, thorough washing and drying processes. Fe nanoparticles were further analyzed by different analytical techniques like; XRD, SEM, TEM and XPS. The size range of the synthesized Fe nanoparticles was found to be dependent on leaves extract concentration which further influences structure and hence stability. Signature of oxidation also was revealed by XPS studies after long exposure to air ambient.

Facile one-pot green synthesis of Ag–Fe bimetallic nanoparticles and their catalytic capability for 4-nitrophenol reduction

The synergy between two different metals provides a dramatic enhancement in the bimetallic nanoparticles' catalytic properties since bimetallization improves the properties associated with the presence of two individual metals. Therefore, herein, we reported the facile, seedless, one-pot green synthesis of Ag–Fe bimetallic nanoparticles via reduction process using phytochemicals present in the Salvia officinalis aqueous extract. During the Phyto-assisted nanofabrication of Ag–Fe nanoparticles, the reduction of Ag+ and Fe3+ metal ions to Ag–Fe NPs takes place according to their reduction potential. The UV–visible spectroscopic technique was initially used for the Ag–Fe nanoparticle formation in which the absorption band at 450 nm, 350 nm, and 352 nm were observed for AgNPs, FeNPs, and Ag–Fe nanoparticles, respectively. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis were used to investigate the size and shape of biosynthesized Ag–Fe nanoparticles, and it was revealed that the as-synthesized Ag–Fe nanoparticles are nearly spherical with an average size of 30 nm. X-ray diffraction (XRD) study was carried out to analyze the purity of the Ag–Fe nanoparticles. Fourier transform infrared spectroscopy (FTIR) analysis was performed to confirm the role of reducing and capping/stabilizing agents in the synthesis of Ag–Fe bimetallic nanoparticles. The successful biosynthesis of Ag–Fe nanoparticles was also confirmed by X-ray energy-dispersive spectrometry (EDX) analysis. Thermogravimetric analysis (TGA) was used to investigate the decomposition pattern of the Ag–Fe bimetallic nanoparticles. The catalytic behavior of as-synthesized Ag–Fe nanoparticles was investigated for the catalytic degradation of 4-nitrophenol to 4-aminophenol. The observed results revealed that Ag–Fe nanoparticles showed an efficient reduction of 4-Nitrophenol (4-NP) to 4-Aminophemol (4-AP) after 45 min of treatment.

In situ TEM oxidation study of Fe thin-film transformation to single-crystal magnetite nanoparticles

In this work, we present an in situ transmission electron microscopy (TEM) study of Fe thin films to Fe nanoparticle formation and their oxidation to single-crystal magnetite nanoparticles. Amorphous Fe thin films were prepared by sputtering on TEM carbon grids. The thin Fe films were continuously heated in situ from room temperature to 700 °C under vacuum (4 × 10–4 Pa). With the increase in temperature, the continuity of the thin film starts breaking, and Fe nanoparticle nucleation centers are formed. At 600 °C, the thin film transforms into metallic Fe nanoparticles (NPs) with a small presence of different Fe oxide NPs. Further increase in the temperature to 700 °C resulted in the full oxidation of the NPs (i.e., no core–shell were found). Zero-loss energy filtered diffraction and HRTEM analysis of the lattice spacing reveals that all NPs have fully transformed into single-phase magnetite NPs. The structural study of the magnetite NPs shows that magnetite NPs are free of antiphase domain boundary defects. This work demonstrates that under low partial pressure of oxygen at elevated temperatures a complete oxidation of Fe NPs into magnetite single-crystal nanoparticles can be achieved.

Modifying the Surface Structure of Perovskite-Based Catalysts by Nanoparticle Exsolution

In heterogeneous catalysis, surfaces decorated with uniformly dispersed, catalytically-active (nano)particles are a key requirement for excellent performance. Beside standard catalyst preparation routines—with limitations in controlling catalyst surface structure (i.e., particle size distribution or dispersion)—we present here a novel time efficient route to precisely tailor catalyst surface morphology and composition of perovskites. Perovskite-type oxides of nominal composition ABO3 with transition metal cations on the B-site can exsolve the B-site transition metal upon controlled reduction. In this exsolution process, the transition metal emerges from the oxide lattice and migrates to the surface where it forms catalytically active nanoparticles. Doping the B-site with reducible and catalytically highly active elements, offers the opportunity of tailoring properties of exsolution catalysts. Here, we present the synthesis of two novel perovskite catalysts Nd0.6Ca0.4FeO3-δ and Nd0.6Ca0.4Fe0.9Co0.1O3-δ with characterisation by (in situ) XRD, SEM/TEM and XPS, supported by theory (DFT+U). Fe nanoparticle formation was observed for Nd0.6Ca0.4FeO3-δ. In comparison, B site cobalt doping leads, already at lower reduction temperatures, to formation of finely dispersed Co nanoparticles on the surface. These novel perovskite-type catalysts are highly promising for applications in chemical energy conversion. First measurements revealed that exsolved Co nanoparticles significantly improve the catalytic activity for CO2 activation via reverse water gas shift reaction.

Formation of Fe Nanoparticles by Ion Implantation Technique for Catalytic Graphitization of a Phenolic Resin

Ion implantation technique was employed to introduce iron nanoparticles (Fe NPs) into a carbon precursor polymer with the aim of forming of a graphitic nanostructure through catalytic graphitization by the introduced Fe NPs. A phenolic resin was implanted by 100 keV Fe+ ions with ion fluence of 1 × 1014–1 × 1016 ions/cm2 at ambient temperature under vacuum, and subsequently heat-treated at 800 °C in a nitrogen gas atmosphere. It was found that the particle size of Fe NPs could be controlled in the range of 5–30 nm by the Fe+ ion fluence. Additionally, it was found that a nanosized turbostratic graphite structure with mean interlayer distance of 0.3531 nm, which is consisted of shell-like carbon layers and intricately distorted carbon layers, was formed around the Fe NPs. The ion implantation technique is one of the advantageous ways to introduce size-controlled fine metal NPs which are effective for the formation of graphitic nanostructure from a carbon precursor polymer.

Surface Roughening with Iron Nanoparticles for Promoted Adhesion of Spin Coated Microsupercapacitor Electrodes

AbstractMicrosupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things’ sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.

Formation of Fe nanoparticles on water-washed coal fly ash for enhanced reduction of p-nitrophenol

The catalytic reduction of p-nitrophenol (p-NP) by coal fly ash (FA) washed with water was investigated in this study. A significant increase in pH (from 7.0 to 10.1) was observed in the suspension of raw fly ash (RFA), while water-washed fly ash (WFA) showed a relatively lower increase in pH (7.2), which was caused by the dissolution of Ca species during the water-washing process. Almost 33.4% of p-NP reduction was observed in the RFA suspension with NaBH4 in 1 h, while the enhanced reduction of p-NP (87.2%) was observed in the WFA suspension. The catalytic reduction of p-NP was inhibited by addition of CaO and Ca(OH)2, indicating that higher amount of CaO dissolved from RFA resulted in the inhibition effect. Similar experiments using different oxides (i.e., Al2O3, SiO2, CaO and MgO) revealed no significant reduction of p-NP, which was comparable with Fe2O3 (75.8%). Results from various surface analyses revealed that iron oxides on the surface of WFA can be reduced to elemental Fe nanoparticles, which can effectively reduce p-NP with NaBH4. No significant leaching of heavy metals such as Cr, Pb, and As was observed during the catalytic reduction of p-NP and in the suspension of WFA after reaction at pH 3, 5, 7, and 9 for 24 h, which can solve the toxic effect when the FA is used for environmental applications. We also observed a good reusability of WFA during the recycling test, indicating the potential use of WFA for the treatment of wastewater containing reductively degradable pollutants.

In-Situ Formation of Fe Nanoparticles from FeOOH Nanosheets on γ-Al2O3 as Efficient Catalysts for Ammonia Synthesis

The preparation process of industrial Fe-based catalysts for ammonia synthesis involves energy-intense and sophisticated treatments. It is thus highly desirable to develop new catalysts with sufficient catalytic performance within smart and more economic approaches. Herein, γ-Al2O3-supported FeOOH nanosheets are employed for the first time as ammonia synthesis catalysts. To monitor the potential of these new materials, unsupported FeOOH and K-promoted catalysts are additionally investigated for comparison. While no activity is observed from the unsupported catalyst, the activity of γ-Al2O3-supported catalysts shows an inverse relationship with respect to the amount of Fe. Upon correlation of the catalytic performance with the final state of catalysts, the activity is closely related to the particle size of metallic Fe. Higher activity and lower apparent activation energy can be reached for smaller nanoparticles that are likely to contain more step–kink structures serving as active sites. The best catalyti...

In situ experimental formation and growth of Fe nanoparticles and vesicles in lunar soil

AbstractWe report the results of the first dynamic, in situ heating of lunar soils to simulate micrometeorite impacts on the lunar surface. We performed slow‐ and rapid‐heating experiments inside the transmission electron microscope to understand the chemical and microstructural changes in surface soils resulting from space‐weathering processes. Our slow‐heating experiments show that the formation of Fe nanoparticles begins at ~575 °C. These nanoparticles also form as a result of rapid‐heating experiments, and electron energy‐loss spectroscopy measurements indicate the Fe nanoparticles are composed entirely of Fe0, suggesting this simulation accurately mimics micrometeorite space‐weathering processes occurring on airless body surfaces. In addition to Fe nanoparticles, rapid‐heating experiments also formed vesiculated textures in the samples. Several grains were subjected to repeated thermal shocks, and the measured size distribution and number of Fe nanoparticles evolved with each subsequent heating event. These results provide insight into the formation and growth mechanisms for Fe nanoparticles in space‐weathered soils and could provide a new methodology for relative age dating of individual soil grains from within a sample population.

Preparation of FePd‐RGO Bimetallic Composites with High Catalytic Activity for Formic Acid Electro‐Oxidation

AbstractFePd‐RGO composites through the growth of uniformly dispersed iron‐palladium bimetallic nanoparticles (NPs) on reduced graphene oxide (RGO) nanosheets were prepared by a two‐step method. The firstly formed Fe is used as the seed for the subsequent Pd growth. The formation of Fe NPs on RGO in the first step is performed by an in‐situ reduction reaction with the reducer ethylene glycol under oil bath at 180°C. NPs in the as‐prepared FePd‐RGO have an average particle size of 6.5 nm, and Pd is added to one side of Fe which leads to the formation of Fe‐Pd bimetallic interfaces. As compared with the commercial Pd black at the same loading, the composites have higher electro‐catalytic activity, better electrochemical stability and higher resistance to CO poisoning for formic acid electro‐oxidation.

Probing the Rate Limiting Steps in Conversion Reactions of Nanostructured Iron Oxide in Li- and Na-Ion Batteries

Na-ion batteries have gained a remarkable interest during the last decade due to their attractive features of reduced costs and possible use of more environmentally friendly materials. These characteristics could promote the development of this type of electrochemical storage technology as a possible alternative to Li-ion cells for a cost-effective large-scale stationary storage of electricity. Yet, the advancement of suitable Na-ion batteries for such a purpose has to face more severe challenges than those occurred during the initial development of Li-ion battery technology. In fact, the noticeable differences in mass and size between Li+ and Na+ ions have considerable effects on the associated electrochemical performances for the corresponding battery systems. These factors heavily affect also the choice of convenient materials for Na-ion cells, especially for negative electrodes. In fact, graphite cannot be employed as insertion host [1], although possible Na+ incorporation via solvent co-intercalation phenomena [2] has been reported. The most suitable materials for negative electrodes in Na-ion batteries so far are disordered carbons [3], since they can offer a convenient trade-off in terms of specific capacities, rate capabilities and cycle performances. Nevertheless, such specifications could be advanced and definitely there is room for further improvements. In this regard, more abundant and cheaper materials, which can be synthesized in simpler ways at lower temperatures, have also been proposed. Among these, iron oxide is certainly one of the most attractive because of its earth-abundance and environmental friendliness. For these reasons, this compound has been investigated in a number of preliminary studies [4-6] in Na-half cells. The reaction pathway of iron oxide upon its initial phases of Na+ uptake resembles to a good extent that occurring upon similar Li+ incorporation. However, noticeable differences characterize the respective electrochemical mechanisms, being the subsequent conversion reaction of iron oxide into Fe and Na2O clearly hampered [4-6] compared to its analogue mechanism upon lithiation, in which the extensive formation of Fe nanoparticles surrounded by a Li2O matrix is involved [7]. The objectives of this study are to identify the limiting factors occurring during the conversion reaction of iron oxide upon sodiation and to assess its feasibility for possible enhancement of Na storage. These aims are pursued by comparing its features to those displayed by its analogous mechanism driven by Li+. A systematic analysis via cyclic voltammetry (CV) has been conducted on different types of iron oxide nanostructures (e.g. nanopowders, nanowires and thin films) cycled in parallel in Li- and Na-half cells containing analogous electrolytes (i.e. LiClO4 and NaClO4 respectively). In this approach, the characteristic behaviours of these particular electrochemical systems have been compared. The roles played by their intrinsic structures, textures, as well as by the different electrical wiring throughout the associated electrodes embedding these active materials, will be presented and highlighted. The limiting factors influencing the conversion reactions of these iron oxide nanostructures upon their respective lithiation and sodiation will be discussed and the issues arising from such limitations will be identified and addressed. It will be shown that the porosity of the active materials and their mutual electrical contact, as well as that with the current collector, play a crucial role in the electrochemical processes. Finally, Na storage in iron oxide via conversion reactions is demonstrated to be intrinsically limited, irrespectively of the type of nanostructure employed for this specific purpose, thus posing restrictions on the ultimate usage of this type of material in combination with Na+ ions.

Synthesis and Characterization of Iron Nanoparticles for Biological Applications

Iron (Fe) nanoparticles have been synthesized by simple co-precipitation method. The x-ray diffraction studies indicated the formation of Fe nanoparticles with cubic phase. Surface morphology of Fe and has been studied using scanning electron microscopy (SEM). Transmission electron microscopy (TEM) images reveal that Fe nanoparticle have size ranging from 25-41 nm. Also we have reported about the changes in the growth of piglets such as its body weight (kg), its haemoglobin (g %) level, its hematocrit (%) level and its erythrocyte count, when it was supplemented with different compositions of iron nanoparticles since iron is an integral component of hemoglobin which plays major role in supply of oxygen for normal functioning of body cells. Besides that iron is necessary for activity of several enzymes and catalytic pathways at cellular level.

Growth of carbon nanotube forests on metallic thin films

Growing carbon nanotube (CNT) forests on metals for integrated circuits interconnections or active layers applications is currently a challenge. CNT forests easily develop on insulators but their growth on metallic substrates is subject to interdiffusion and wettability effects that hamper the formation of the catalyst nanoparticles. This paper reports the successful growth of dense CNT forests on some metallic layers (Mo, Ta, W, and Ir) in comparison to other metallic films (Au, Cu, and Ti) over which CNTs are hardly achieved. The CNT forests are grown by thermal decomposition of C2H2 diluted in NH3 and characterized by Raman spectroscopy and scanning electron microscopy. Stabilizing Al thin films placed between the metallic substrates and the Fe catalyst promote the formation of Fe nanoparticles. Metallic substrates, thickness of the Al stabilizer, and temperature and raise time during nanoparticles formation are all instrumental parameters in the growth and final structure of the CNT forests.

Synthesis of pure iron nanoparticles at liquid–liquid interface using pulsed plasma

Pure α-Fe nanoparticles with ≤10 nm size were synthesized using a simple method—pulsed plasma in liquid. This is the first time that pure metallic nanoparticles were prepared by arc discharge method using water–toluene interface as a medium. Several experiments made evident that toluene–water ratio in emulsion influences the purity and size of Fe nanoparticles. The purity of the nanoparticles gradually increased from 48 to 98 %, while particle size decreased from 21 to 9.5 nm with smaller toluene volume fraction (from 40 to 5 %) in the microemulsions. Finally, toluene:water with 95:5 (%) ratio was found to be the most appropriate medium for pure Fe nanoparticle formation. Lattice parameters of the obtained Fe samples calculated from XRD found to be larger (a = 0.2927 nm) than those previously reported Fe (a(BCC-Fe) = 0.2866 nm). HRTEM showed spherical-shaped Fe nanoparticles with partial aggregation. Vibrating sample magnetometer indicated superparamagnetic properties of particles with high-saturation magnetization (Ms = 125 emu g−1) at room temperature.