FePd Nanoparticles Research Articles

Multiwalled Cabon Nanotubes Functionalized Magnetic Fepd Alloy with Enhanced Activity for Ethanol Oxidation Reaction

Ultrafine Palladium iron alloy (FePd) nanoparticles (NPs) deposited on gamma phased iron oxide (r-Fe2O3), FePd-Fe2O3, which were further anchored on Multi-walled carbon nanotubes (MWNTs), FePd-Fe2O3/MWNTs, was successfully synthesized by a facile one-pot solution based method as thermal decomposing palladium acetylacetonate (Pd(acac)2) and iron pentacarbonyl (Fe(CO)5) in a refluxing dimethylformamide (DMF) solution in the presence of carboxylic groups functionalized MWNTs (MWNTs-COOH). The formation of FePd alloy was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) through investigating the crystalline structures and verifying specific bonding energy. Transmission electron microscope (TEM) revealed that the ultrafine FePd NPs were uniformly deposited on the surface of superparamagnetic r-Fe2O3 NPs which were further evenly distributed on the MWNTs surface. A 3.65 increase of peak current density after normalizing to Pd mass was observed in cyclic voltammetry (CV) for ethanol oxidation reaction compared with that of Pd/MWNTs. Greatly enhanced tolerance stability towards poisoning species and largely reduced charge resistances were also obtained in chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) due to the formation of FePd alloy and the unique double deposited Pd structure. Experimental 100.0 mg MWNTs-COOH was first dispersed in 60 mL DMF solution undergoing 1h sonication, the solution was then transferred to a 250-mL 3-neck flask and heated to reflux (~160 °C) in ~ 20 min. For the synthesis of FePd-based nanocatalysts, 202.0 mg well dispersed Pd(acac)2 in 20 mL DMF was added to the refluxing MWNTs-COOH/DMF solution. Fe(CO)5 (130.2, 437.0, and 875.0 mg) was following added to the solution after boiling again in ~ 5 min, the products were donated as FePd-Fe3C/MWNTs, FePd-Fe2O3(3:5)/MWNTs and FePd-Fe2O3(3:10)/MWNTs, respectively(the composition was determined by Mössbauer spectrometer). For the control synthesis of Pd/MWNTs and Fe3O4/MWNTs, only 202.0 mg Pd(acac)2 or 875.0 mg Fe(CO)5 was added to the refluxing MWNTs-COOH/DMF solution. All the solutions were maintained refluxing for an additional 3 hours to complete the whole reaction. Finally, after cooling down to room temperature, the solid iron containing products were removed from the suspension using a permanent magnet and Pd/MWNTs were filtered under vacuum. All the final products were rinsed with acetone 3 times and collected after vacuum drying at 60 °C for 24 hours. Results and Discussion The Mössbauer spectrometer and XPS has successfully determined the compositions of catalysts with varying the amount of Fe(CO)5. Typical peaks of Fe2O3, Fe3O4 and FePd are clearly observed in XRD indicating the successful synthesis of FePd-Fe2O3/MWNTs. The interaction between NPs and MWNTs and the loading of catalysts was determined by Raman spectra and TGA. An greatly enhanced the peak current in CV and improved tolerance stability toward poisoning species are also demonstrated by CV, CV and EIS, which indicates the positive role of the FePd alloy and the Fe2O3 substrates. Conclusion Highly catalytic active and magnetic FePd-Fe2O3/MWNTs nanocatalysts have been prepared by simple thermal decomposing Pd(acac)2 and Fe(CO)5 in a refluxing dimethylformamide (DMF) solution in the presence of MWNTs-COOH. The formation of FePd alloy has been confirmed by the crystalline structures and composition investigation by XRD and XPS spectra. A unique structure as FePd NPs first deposited on Fe2O3 NPs which further uniformly dispersed on MWNTs was disclosed by TEM. Electro-characterizations as CV, CA and EIS demonstrated an enhanced catalytic performance compared with Pd/MWNTs towards EOR after the introduction of Fe. Modified electronic properties of Pd by Fe, easily proceeded poisoning species on γ-Fe2O3 and the optimal combination of promoter Fe2O3 and MWNTs substrate are mainly account for the greatly enhanced activity. This simple method is of great significance for the facile preparation of recyclable Pd catalysts with high catalytic activity. Acknowledgments The financial supports from University of Tennessee Knoxville are kindly acknowledged. Figure 1. CV of (a) Fe3O4/MWNTs, (b) Pd/MWNTs, (c) FePd-Fe2O3(3:10)/MWNTs, (d) FePd-Fe3C/MWNTs and (e) FePd-Fe2O3(3:5)/MWNTs in 1.0 M KOH solution containing 1.0 M ethanol with current density normalized to Pd mass at a scan rate of 50 mV/s. Background is the HRTEM of FePd-Fe2O3(3:5)/MWNTs. References 1 Y. Wang, Q. He, J. Guo, H. Wei, K. Ding et al, ChemElectroChem, 2(4) (2015) 559-570. 2. Z. Zhang, J. Ge, L. Ma, J. Liao, T. Lu, W. Xing, Fuel Cells, 9 (2) (2009) 114-120 Figure 1

Synthesis and Paraconductivity Studies of Fe–Pd Nanoparticles Added Cu0.5Tl0.5Ba2Ca3Cu4 O 12−δ Superconductors

Cu0.5Tl0.5Ba2Ca3Cu4O12−δ/(Fe–Pd 0, 0.5, 1.0, 1.5 %) superconductors are prepared at normal pressure by using three-step method. Alloy of Cu0.5Tl0.5Ba2Ca3 Cu4O12−δ/(Fe–Pd 1 %) have shown maximum increase in the magnitude of superconductivity. Cu 0.5Tl 0.5 Ba2Ca 3Cu 4O12−δ/(Fe–Pd 0, 0.5, 1.0, 1.5 %) samples have shown Tc(R= 0) around 106, 105.3, 102, and 100 K and the onset of diamagnetism around 113, 110, 102, and 105 K, respectively. A comparison of X-ray diffraction (XRD) scans of Fe–Pd nanoparticles with Cu0.5Tl0.5Ba2Ca3Cu4O12−δ/(Fe–Pd 0.5, 1.0, 1.5 %) superconducting samples have shown that the nanoparticles of Fe–Pd are quite stable in the matrix of Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples even after repeated firing at 890 ∘C. With increase addition of Fe–Pd nanoparticles, the axes length increases, showing some inclusion of nanoparticle into the unit cell of Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples from the termination ends of crystal.The inclusion of Fe–Pd in the superconducting Cu0.5Tl0.5Ba2Ca3Cu4O12−δ grains is also evidenced in Fourier transform infrared spectroscopy (FTIR) absorption measurements. The Fe–Pd nanoparticles added in Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples have been found to decrease the population of inter-grain voids that is found to increase the coherence length along the c-axis and the inter-layer coupling J. The FIC analysis of conductivity data haveshown the Fe–Pd nanoparticles diffusing into the inter-grain sites promoted an increase of penetration depth λp.d and Ginzburg–Landau parameter, κ. Due to the this possible diffusion of the Fe–Pd nanoparticles in the superconducting grains, the Tc(R= 0), Bc0(T), Bc1(T), and Jc(0) values are suppressed in Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples.

Bimetallic nanoparticles for arsenic detection.

Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As(III) detection. We show that trace amounts of As(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb(-1). The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic.

Novel Fe-Pd/SiO2 catalytic materials for degradation of chlorinated organic compounds in water

AbstractNovel reactive materials for catalytic degradation of chlorinated organic compounds in water at ambient conditions have been prepared on the basis of silica-supported Pd-Fe nanoparticles. Nanoscale Fe-Pd particles were synthesized inside porous silica supports using (NH4)3[Fe(C2O4)3] and [Pd(NH3)4]Cl2 or Pd acetate as reaction precursors. According to temperature programmed reduction (TPR) studies, Pd introduction decreased the reduction temperature of the supported Fen+ species and nearly complete reduction with H2 was observed at 400 °C. The successful surface loading with Pd was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Characterization of the samples by X-ray diffraction (XRD) and X-ray absorption near-edge structure + extended X-ray absorption fine structure (XANES + EXAFS) verified the presence of highly dispersed Pd0, Pdx Fe1–x and Fe0 phases. Reduction of the supported precursors in hydrogen resulted in materials that were highly active in perchloroethene (PCE) degradation and 2-chlorobiphenyl (2-ClBP) dechlorination. It was found that highly dispersed amorphous Fe-Pd bimetallic nanoparticles on silica support showed superior catalytic activity against PCE dechlorination in comparison to the free-standing Fe-Pd nanoparticles. For the samples with the same Fe content, the conversion of chlorinated organics as well as the stability increased with the Pd loading, e.g., the most effective degradation of PCEs and 2-ClBP was achieved at a Pd loading of 2.3–3.2 wt. %.

L1-FePd nanocluster wires by template-directed thermal decomposition and subsequent hydrogen reduction

This paper reports the nanostructure, formation mechanism, and magnetic properties of tetragonal L10-type Fe55Pd45 (at. %) nanocluster wires (NCWs) fabricated by thermal decomposition of metal nitrates and subsequent hydrogen reduction in nanoporous anodized aluminum oxide templates. The as-synthesized NCWs have diameters in the range of 80–300 nm, and lengths in the range of 0.5–10 μm. The NCWs are composed of roughly round-shaped nanoclusters in the range of 3–30 nm in size and a weighted average size of 10 nm with a mixture of single-crystal and poly-crystalline structures. The obtained intrinsic coercivity iHc of 3.32 kOe at room temperature for the tetragonal Fe55Pd45 NCWs is higher than those of electrodeposited Fe-Pd solid nanowires while among the highest values reported so far for L10-type FePd nanoparticles.

One-Pot Synthesis of Urchin-like FePd–Fe3O4 and Their Conversion into Exchange-Coupled L10–FePd–Fe Nanocomposite Magnets

We report a one-pot synthesis of urchin-like FePd-Fe3O4 nanocomposites, spherical clusters of FePd nanoparticles (NPs) with spikes of Fe3O4 nanorods (NRs), via controlled thermal decomposition of Fe(CO)5 and reduction of Pd(acac)2. The FePd NPs with sizes between 6 and 9 nm self-aggregate into 60 nm superparticles (SPs), and Fe3O4 NRs grow on the surface of these SPs. Reductive annealing at 500 °C converts the FePd-Fe3O4 into exchange-coupled nanocomposites L1(0)-FePd-Fe with their Hc tunable from 0.8 to 2.6 kOe and Ms controlled from 90 to 190 emu/g. The work provides a general approach to L1(0)-FePd-Fe nanocomposite magnets for understanding exchange coupling at the nanoscale. The concept may be extended to other magnetic nanocomposite systems and may help to build superstrong magnets for magnetic applications.

The synthesis and characterisation of magnetic nanoparticles and their interaction with a zinc phthalocyanine

A variety of nanoparticles (NPs), including FePt nanoparticles with Fe as the shell ( 2 ) or Pt as the shell ( 3 ), Pt NPs ( 4 ), and FePd ( 5 ) were synthesised, characterised and their effect on a zinc phthalocyanine ( 1 ) tetra-substituted with a pyridyl-oxy substituent studied using UV/Vis and fluorescence spectroscopy (including time correlated single photon counting, TCSPC). The nanoparticles were characterised using a number of techniques including UV/Vis and inductively coupled plasma-optical emission (ICP-OES) spectroscopies, transmission electron microscopy (TEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and electron paramagnetic resonance (EPR) spectroscopy. Nanocomposites (NCs, 6 , 7 ) where the ZnPc ( 1 ) was used as the stabiliser, instead of oleic acid and or oleylamine, were also synthesised and characterised. FePt nanoparticles (NPs) with Fe ( 2 ) or Pt as the shell ( 3 ), Pt NPs ( 4 ), and FePd NPs ( 5 ) were synthesised. Their effect on the UV/Vis absorption and fluorescence spectra of a zinc phthalocyanine (ZnPc) was studied. Nanocomposites (NCs, 6 , 7 ), with ZnPc as the stabiliser, were also synthesized and studied. ► A range of magnetic nanoparticles were synthesized and characterized. ► Zinc phthalocyanine (ZnPc) ligand exchange was accomplished. ► ZnPc was successfully employed as a stabilizer for NP synthesis. ► Significant Q band red shifting observed in the UV/Vis and fluorescence spectra.

Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: Effects of sorption, surfactants, and natural organic matter

Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe–Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1×cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5×cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe–Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.

Effect of structural transition on the temperature-dependent magnetic properties of epitaxial FePd alloy nanoparticles

We have studied atomic ordering and magnetic properties of epitaxial FePd nanoparticles 3−14 nm in diameter. Thermal fluctuation of magnetic moment of L10-FePd nanoparticles becomes prominent when particle size is smaller than about 8 nm. Atomic images of high-resolution transmission electron microscopy revealed the formation of the ordered phase in FePd nanoparticles as small as 4 nm in diameter, while the superlattice reflections were quite weak compared to those of the larger sized particles (>8nm). The experimental results indicate that the degradation of magnetic anisotropy is induced by the size-dependent decay of long-range atomic order.

Stabilization of Fe–Pd bimetallic nanoparticles with sodium carboxymethyl cellulose for catalytic reduction of para-nitrochlorobenzene in water

The reactivity of Fe–Pd bimetallic nanoparticles with sodium carboxymethyl cellulose (CMC) as a stabilizer toward para-nitrochlorobenzene (p-NCB) was investigated in this study. The CMC-stabilized Fe–Pd nanoparticles exhibited markedly greater reactivity than non-stabilized iron counterparts when used for the degradation of p-NCB in aqueous solution. Batch kinetic tests demonstrated that the pseudo-first order rate constant with the stabilized bimetallic particles was four times greater than that for the non-stabilized iron. At a dose of 0.2gL−1, the Fe–Pd bimetallic nanoparticles were able to remove 100% of p-NCB (C0=50mgL−1) within 40min, small amounts of p-chloroaniline (p-CAN) as an intermediate were detected in the final stage of degradation, with no other products except aniline (AN) and inorganic chloride (Cl−). Insignificant reactions were observed with the unpalladized iron, suggesting that the presence of Pd could significantly enhance the reductive dechlorination. The degradation efficiency of p-NCB increased with the increasing addition of Pd bulk loading, Fe–Pd mass concentration and temperature, with the decrease of pH values and humic acid (HA) dosage.

Enhanced stability and dechlorination activity of pre-synthesis stabilized nanoscale FePd particles

Nanoscale zero-valent iron (NZVI) particles are promising materials for the in-situ remediation of a wide variety of source zone contaminants. This study presents the results of a systematic investigation of the stability of bimetallic FePd nanoparticle suspensions in water and their capability to degrade trichloroethylene (TCE) synthesized in the presence of various stabilizers (i.e., carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), and guar gum). Results indicate a dramatic improvement in FePd suspension stability when the stabilizer is present in the matrix during the nanoparticle synthesis step. Stability enhancement is controlled by iron nanoparticle/stabilizer electrostatic and steric interactions, which are a function of the molecular structure of the stabilizer. Stabilization mechanisms differed for each stabilizer with CMC and guar gum exhibiting the best nanoparticle suspension stability improvement. Results suggest that the complexation of iron precursors with the stabilizer, during synthesis, plays a key role in nZVI stability improvement. In case of guar gum, gelation during synthesis significantly increased suspension viscosity, enhancing suspension stability. The capability of these materials to degrade TCE was also investigated. Results demonstrated that when stabilizers were present in the matrix dechlorination rates increased significantly. FePd nanoparticles in CMC had the highest observed rate constant; however the highest surface area-normalized rate constant was obtained from FePd stabilized in PVP360K. Results from this study can be used to aid in the selection of appropriate iron nanoparticle stabilizers. Stabilizer selection should be assessed on a case by case basis as no stabilizer will meet the needs of all in-situ remediation applications.

Consolidation of FePd nanoparticles by spark plasma sintering

Nanoparticles of FePd alloys in the size range of 5–8nm have been processed in gram quantities using the polyol process and were further consolidated into bulk magnets by spark plasma sintering (SPS). The as-prepared FePd nanoparticles showed disordered fcc structure; while their SPSed counterparts displayed typical L10-ordered fct structure with interesting magnetic properties.

In situ testing of metallic iron nanoparticle mobility and reactivity in a shallow granular aquifer

This paper describes the results of a series of single well push–pull tests conducted to evaluate the in situ transport of carboxymethyl cellulose (CMC) stabilized nanoscale zero-valent iron (ZVI) particles in saturated sediments and their reactivity toward chlorinated ethenes. CMC-stabilized nanoscale ZVI particles were synthesized on site by reducing ferrous ions with borohydride in water in the presence of CMC. Nanoscale ZVI and bimetallic ZVI-Pd nanoparticle suspensions were prepared and injected into depth-discrete aquifer zones during three push–pull tests. The injected nanoparticle suspensions contained a conservative tracer (Br −) and were allowed to reside in the aquifer pore space for various time periods prior to recovery by groundwater extraction. The comparison between Br − and Fe concentrations in extracted groundwater samples indicated that the CMC-stabilized nanoscale ZVI particles were mobile in the aquifer but appeared to lose mobility with time, likely due to the interactions between particles and aquifer sediments. After 13 h in the aquifer, the nanoscale ZVI particles became essentially immobilized. During the push–pull test with injection of Fe–Pd nanoparticles, ethane concentrations increased from non-detectable to 65 μg/L in extracted groundwater within less than 2 h of reaction time, indicating the rapid abiotic degradation of chlorinated ethenes. The amount of total chlorinated ethene mass destroyed was low presumably because the injected solutions “pushed” the dissolved chlorinated ethenes away from the injection well, without substantial mixing, and because stationary (sorbed) chlorinated ethene mass on the aquifer sediments was low. In situ remediation programs using highly reactive metallic nanoparticles should incorporate delivery methods that maintain high groundwater pore velocities during injection to increase advective transport distances (e.g. groundwater circulation wells). Also, source zones with abundant stationary contaminant mass that is accessible by advective transport should be targeted for remediation with the nanoparticles, as opposed to portions of dissolved plumes, in order to maximize the in situ destruction of contaminants.

Three-dimensional shapes and distribution of FePd nanoparticles observed by electron tomography using high-angle annular dark-field scanning transmission electron microscopy

We have studied three-dimensional shapes and distribution of FePd nanoparticles, prepared by electron beam deposition and postdeposition annealing, by means of single-axis tilt tomography using atomic number contrasts obtained by high-angle annular dark-field scanning transmission electron microscopy. Particle size, shape, and locations were reconstructed by weighted backprojection (WBP), as well as by simultaneous iterative reconstruction technique (SIRT). We have also estimated the particle size by simple extrapolation of tilt-series original data sets, which proved to be quite powerful. The results of the two algorithms for reconstruction have been compared quantitatively with those obtained by the extrapolation method and those independently reported by electron holography. It was found that the reconstructed intensity map by WBP contains a small amount of dotlike artifacts, which do not exist in the results by SIRT, and that the particle surface obtained by WBP is rougher than that by SIRT. We demonstrate, on the other hand, that WBP yields a better estimation of the particle size in the z direction than SIRT does, most likely due to the presence of a “missing wedge” in the original data set.

Reductive dechlorination of γ-hexachlorocyclohexane using Fe–Pd bimetallic nanoparticles

Nanoscale Fe–Pd bimetallic particles were synthesized and used for degradation of lindane (γ-hexachlorocyclohexane) in aqueous solution. Batch studies showed that 5 mg/L of lindane was completely dechlorinated within 5 min at a catalyst loading of 0.5 g/L and the degradation process followed first-order kinetics. GC–MS analysis in corroboration with GC-ECD results showed the presence of cyclohexane as the final degradation product. The proposed mechanism for the reductive dechlorination of lindane involves Fe corrosion-induced hydrogen atom transfer from the Pd surface. The enhanced degradation efficiency of Fe–Pd nanoparticles is attributed to: (1) high specific surface area of the nanoscale metal particles (60 m 2/g), manyfold greater that of commercial grade micro- or milli-scale iron particles (∼1.6 m 2/g); and, (2) increased catalytic reactivity due to the presence of Pd on the surface. Recycling and column studies showed that these nanoparticles exhibit efficient and sustained catalytic activity.

Increase in the Curie temperature and magnetic anisotropy in FePd/Pt–iron oxide core-shell nanoparticles

Partially oxidized fcc FePd and FePt nanoparticles with mean diameters of 5 and 3 nm, respectively, were synthesized by a reverse micelle polyol process. In situ measurements of magnetic and structural properties during annealing showed a large increase in the magnetocrystalline anisotropy and in the Curie temperature of the nanoparticles due to (i) a phase transition from A1 to L10 and (ii) a simultaneous phase separation between a metallic core and an iron oxide shell. These occurred at 675 K in the FePd nanoparticles and at above 850 K for the FePt. The Curie temperature of the nanoparticles was found to be about 850 K, an increase of more than 100 K from the bulk L10 phase. The ferromagnetic resonance results are discussed and compared with a phenomenological model that makes it possible to estimate the magnetocrystalline anisotropy as 1.6×105 and 1.5×106 J m−3 in FePd and FePt, respectively. Exchange coupling between the core and the shell explains both the high magnetocrystalline anisotropy of the core and the high Curie temperature of the shell.

Intermetallic ordering and structure in Fe–Pd alloy nanoparticles

We report an in situ study of epitaxial island formation and alloying of FePd nanoparticles using reflection high-energy electron diffraction (RHEED) followed by ex situ atomic structure characterization. We used aberration corrected (AC) scanning transmission electron microscopy (STEM) with a high-angle annular dark field (HAADF) detector for the study of chemical ordering. The FePd nanoparticles were formed by sequential deposition of Pd and Fe onto NaCl substrates, which was then followed by heating to high temperatures to promote chemical ordering during a short period of annealing. We show that the epitaxial island growth and subsequent alloying of Fe into Pd can be clearly detected by RHEED. The high resolution and the atomic number (Z) contrast of AC HAADF-STEM allow a clear observation of nanometer-sized local chemical order in very small nanoparticles. The results revealed complex chemical structures at an intermediate stage of the ordering process with ordered regions of both L10 and L12 phases.

Atomic structure imaging of L1-type FePd nanoparticles by spherical aberration corrected high-resolution transmission electron microscopy

The atomic structure of FePd nanoparticles has been studied by spherical aberration (Cs) corrected high-resolution transmission electron microscopy. The periodic arrangement of atoms arising from chemical order is clearly seen as bright contrast due to the small negative value of corrected Cs. The amount of optimal defocus (Scherzer defocus) is markedly reduced by the small Cs value. The interface between crystalline particles and the amorphous matrix can also be observed, free of imaging artifacts, at a small defocus value. The reconstructed phase image directly shows the projected potential distribution within the specimen and reveals the elemental differences due to chemical order. The clear-cut long-range order is lost when particle size is smaller than about 5 nm, at which locally ordered mixed-phase particles begin to dominate.

Size-Controlled Synthesis and Magnetic Studies of Monodisperse FePd Nanoparticles

Monodisperse FePd nanoparticles were prepared through thermal decomposition of iron carbonyl and reduction of palladium acetylacetonate in the presence of mixing capping agents. The size of FePd nanoparticles can be easily tuned from 8 nm, up to 27 nm by controlling the molar ratio of surfactants and reaction temperature. The magnetic studies indicate that the blocking temperature and coercivity of the FePd nanoparticles exhibit a size-dependent behavior.

Synthesis and characterization of FePd magnetic nanoparticles modified with chiral BINAP ligand as a recoverable catalyst vehicle for the asymmetric coupling reaction

The initial thermal decomposition of iron carbonyl (Fe(CO)(5)), followed by reduction of palladium acetylacetonate (Pd(acac)(2)) produced FePd nanoparticles (NPs) with an Fe(x)O(y)-rich core and a Pd-rich shell. The as-synthesized NPs were subsequently treated with (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthene ((S)-BINAP) as a chiral modifier, which provides them with the optical activity to show a negative Cotton effect in the circular dichroism (CD) spectrum. Characterization by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), superconducting quantum interface device (SQUID) and X-ray absorption fine structure (XAFS) measurements was performed. The FePd NPs modified with (S)-BINAP had a mean diameter of ca. 5.6 nm, and exhibited superparamagnetic behavior at 300 K with zero remanence and coercivity. The FePd-(S)-BINAP was shown to catalyze the asymmetric Suzuki-Miyaura coupling reaction with easy recovery from the reaction mixture by applying an external magnet. The designed architecture enabled the powerful combination of two functionalities, magnetism that responds to a magnetic field for easy recycling, as well as an optically active catalytic center that promotes the asymmetric coupling reaction.