One-Step Room-Temperature Synthesis of Bimetallic Nanoscale Zero-Valent FeCo by Hydrazine Reduction: Effect of Metal Salts and Application in Contaminated Water Treatment

The effect of initial salt composition on the formation of zero-valent bimetallic FeCo was investigated in this work. Pure crystalline zero-valent FeCo nanoparticles (NPs) were obtained using either chloride or nitrate salts of both metals. Smaller NPs can be obtained using nitrate salts. Comparing the features of the FeCo prepared at room temperature and the solvothermal method revealed that both materials are almost identical. However, the room-temperature method is simpler, quicker, and saves energy. Energy-dispersive X-ray (EDX) analysis of the FeCo NPs prepared using nitrate salts at room temperature demonstrated the absence of oxygen and the presence and uniform distribution of Fe and Co within the structure with the atomic ratio very close to the initially planned one. The particles were sphere-like with a mean particle size of 7 nm, saturation magnetization of 173.32 emu/g, and surface area of 30 m²/g. The removal of Cu²⁺ and reactive blue 5 (RB5) by FeCo in a single-component system was conformed to the pseudo-first-order and pseudo-second-order models, respectively. The isotherm study confirmed the ability of FeCo for the simultaneous removal of Cu²⁺ and RB5 with more selectivity toward Cu²⁺. The RB5 has a synergistic effect on Cu²⁺ removal, while Cu²⁺ has an antagonistic effect on RB5 removal.

Ultrastable Magnetic Nanoparticles Encapsulated in Carbon for Magnetically Induced Catalysis

Magnetically induced catalysis using magnetic nanoparticles (MagNPs) as heating agents is a new efficient method to perform reactions at high temperatures. However, the main limitation is the lack of stability of the catalysts operating in such harsh conditions. Normally, above 500 °C, significant sintering of MagNPs takes place. Here we present encapsulated magnetic FeCo and Co NPs in carbon (Co@C and FeCo@C) as an ultrastable heating material suitable for high-temperature magnetic catalysis. Indeed, FeCo@C or a mixture of FeCo@C:Co@C (2:1) decorated with Ni or Pt-Sn showed good stability in terms of temperature and catalytic performances. In addition, consistent conversions and selectivities regarding conventional heating were observed for CO₂ methanation (Sabatier reaction), propane dehydrogenation (PDH), and propane dry reforming (PDR). Thus, the encapsulation of MagNPs in carbon constitutes a major advance in the development of stable catalysts for high-temperature magnetically induced catalysis.

Chemical Ordering in Bimetallic FeCo Nanoparticles: From a Direct Chemical Synthesis to Application As Efficient High-Frequency Magnetic Material

Single-crystalline FeCo nanoparticles with tunable size and shape were prepared by co-decomposing two metal-amide precursors under mild conditions. The nature of the ligands introduced in this organometallic synthesis drastically affects the reactivity of the precursors and, thus, the chemical distribution within the nanoparticles. The presence of the B2 short-range order was evidenced in FeCo nanoparticles prepared in the presence of HDAHCl ligands, combining ⁵⁷Fe Mössbauer, zero-field ⁵⁹Co ferromagnetic nuclear resonance (FNR), and X-ray diffraction studies. This is the first time that the B2 structure is directly formed during synthesis without the need of any annealing step. The as-prepared nanoparticles exhibit magnetic properties comparable with the ones for the bulk ( M_s = 226 Am²·kg^-1). Composite magnetic materials prepared from these FeCo nanoparticles led to a successful proof-of-concept of the integration on inductor-based filters (27% enhancement of the inductance value at 100 MHz).

Non-volatile iron carbonyls as versatile precursors for the synthesis of iron-containing nanoparticles

The most commonly used method for the formation of well-defined iron and iron-containing heterometallic nanoparticles is the thermal decomposition of iron pentacarbonyl (Fe(CO)₅). However, iron pentacarbonyl is highly toxic and volatile, which introduces safety concerns and drastically diminishes control over the reaction stoichiometry. Here we alleviate these issues by beginning with an easy-to-handle solid, triiron dodecacarbonyl (Fe₃(CO)₁₂). The issue of poor solubility of this cluster is addressed by its reaction with amine, which renders the cluster fully soluble in common high boiling point solvents. This reaction generates non-volatile anionic iron carbonyl species in solution which are subsequently used as the nanoparticle precursor. We demonstrate that the thermolysis of this novel precursor solution yields well-defined Fe, Fe_1-xCo_x, and Fe_1-xPt_x nanoparticles. In addition, the same approach overcomes the solubility issue of another poorly soluble iron carbonyl compound, diiron nonacarbonyl (Fe₂(CO)₉). By using these precursors in an array of nanoparticle-forming reactions, we demonstrate a convenient replacement for the commonly used Fe(CO)₅, producing particles of similar quality, but without the drawbacks of the precursor volatility and high toxicity.

Size- and composition-dependent radio frequency magnetic permeability of iron oxide nanocrystals

We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals. All nanocrystalline samples are confirmed to be in the superparamagnetic state at room temperature by SQUID magnetometry. Through the one-turn inductor method, the ac magnetic properties of the nanocrystalline oxides are characterized. In magnetite-rich iron oxide nanocrystals, size-dependent magnetic permeability is not observed, while maghemite iron oxide nanocrystals show clear size dependence. The inductance, resistance, and quality factor of hand-wound inductors with a superparamagnetic composite core are measured. The superparamagnetic nanocrystals are successfully embedded into hand-wound inductors to function as inductor cores.

Tuning deposition of magnetic metallic nanoparticles from periodic pattern to thin film entrainment by dip coating method

In this work, we report on the self-assembly of bimetallic CoFe carbide magnetic nanoparticles (MNPs) stabilized by a mixture of long chain surfactants. A dedicated setup, coupling dip coating and sputtering chamber, enables control of the self-assembly of MNPs from regular stripe to continuous thin films under inert atmosphere. The effects of experimental parameters, MNP concentration, withdrawal speed, amount, and nature of surfactants, as well as the surface state of the substrates are discussed. Magnetic measurements revealed that the assembled particles were not oxidized, confirming the high potentiality of our approach for the controlled deposition of highly sensitive MNPs.

Precision synthesis of colloidal inorganic nanocrystals using metal and metalloid amides

Rational selection of molecular precursors is the key consideration in the synthesis of inorganic nanocrystals and nanoparticles. This review highlights the state-of-the-art and future potential of metal amides as precursors in the solution-phase synthesis of monodisperse colloidal nanocrystals of metals and metal alloys, as well as metal oxides and chalcogenides. We exclusively focus on homoleptic metal and metalloid alkylamides M(NR2)n and silylamides M[N(SiMe3)2]n as predominant choice of element-nitrogen bonded precursors, which are often advantageous to commonly used metal-oxygen and metal-carbon bonded counterparts. In particular, these amides are highly reactive in oxidation, reduction and metathesis reactions; they are oxygen-free, easy-to-make and/or commercially available. A comprehensive literature review is complemented by our theoretical studies on the thermal stability of metal silylamides using molecular dynamics simulations.

High-magnetic-moment nanoparticles for biomedicine

Magnetic nanoparticles play an important role in biomedical applications, such as MR imaging, drug delivery and hyperthermia. Nanoparticles made of high-moment materials like Fe-Co and Fe have become active in the field due to superior performance. Protected by a biocompatible shell (Au/Ag/Si/C), high-moment nanoparticles can retain their magnetic property over a long time and disperse well. By using a physical gas condensation technique, such high-moment nanoparticles and core-shell structured nanoparticles can be made and used for biomedicine.