Synthesis and characterization of L10 FePt nanoparticles from Pt–Fe3O4 core-shell nanoparticles

Pt/Fe₃O₄ core-shell nanoparticles have been prepared by a modified polyol method. Pt nanoparticles were first prepared via the reduction of Pt(acac)₂ by polyethylene glycol-200 (PEG-200), and layers of iron oxide were subsequently deposited on the surface of Pt nanoparticles by the thermal decomposition of Fe(acac)₃. The nanoparticles were characterized by XRD and HR-TEM. The as-prepared Pt/Fe₃O₄ nanoparticles have a chemically disordered FCC structure and transformed into chemically ordered fct structure after annealing in reducing atmosphere (4% H₂, 96% Ar) at 700 °C. The ordered fct FePt phase has high magnetic anisotropy with coercivity reaching 7.5 kOe at room temperature and 9.3 kOe at 10 K.     

Magnetic and structural characterizations on nanoparticles of FePt,FeRh and their composites

The various compositions of FePt and FeRh nanoparticles, and their composite particles have been fabricated by the solution-phase chemical method and their magnetic properties characterized. High-resolution transmission electron microscopic observations indicate that mono-dispersed FeRh and FePt/FeRh nanoparticles are fabricated with the average size of 3–5 nm. However, larger size particles are distributed in the annealed state. From X-ray diffraction results, the as-deposited FeRh nanoparticles reveal a chemically disordered fcc structure which can be transformed into CsCl-type structure through thermal annealing. Similarly, the annealed FePt nanoparticles show the L1₀-phase fct structure although the fcc structure is apparent in the as-deposited state. It is also found that the first time in the exchange bias effect in the composite of ferromagnetic (FePt) and anti-ferromagnetic (FeRh) nanoparticles; result in a shift of the hysteresis loop after field cooling process.     

Prussian blue modified FePt nanoparticles for the electrochemical reduction of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

FePt nanoparticles were synthesized by polyol process with chloride salts, and the equiatomic composition was surface modified with prussian blue (PB). From the magnetic studies, the fraction of PB present in the surface-modified fcc-FePt was found to be 18 %. The FePt nanoparticles with an average particle size of 5 nm forms cluster like morphology, which were embedded in the PB matrix. The electrocatalytic reduction of hydrogen peroxide (H₂O₂) by the PB-modified FePt nanoparticles was studied. The reduction peak current showed linear response for H₂O₂ in the concentration range up to 3.5 mM. The FePt nanoparticles did not exhibit significant H₂O₂ reduction whereas the PB-modified FePt showed reduction of H₂O₂ with the addition of 0.35 mM of H₂O₂.     

Synthesis and characterization of multi–wall carbon nanotubes supported-hydrated iron phosphate cathode material for lithium–ion cells by a novel homogeneous precipitation method

Iron phosphate (FePO₄) is a promising candidate for the cathode material in lithium-ion cells due to its easy synthesis and low cost. However, the intrinsic drawbacks of FePO₄ material (i.e., the low electronic conductivity and the low lithium-ion diffusion coefficient) result in poor capacity. To overcome the shortcomings, multi-wall carbon nanotubes (MWNTs) supported hydrated iron phosphate nanocomposites (FePO₄·2H₂O/MWNTs) are prepared using a novel homogeneous precipitation method. Meanwhile, the formation mechanism of highly dispersed and ultrafine FePO₄·2H₂O nanoparticles is discussed in detail. Electrochemical measurements show that FePO₄·2H₂O/MWNTs nanocomposites have a superior discharge capacity and stability. For example, FePO₄·2H₂O/MWNTs nanocomposites exhibit a high initial discharge capacity (129.9?mAhg^?1) and a stable capacity retention (114.3?mAhg^?1 after 20 cycles). The excellent electrochemical performance is attributed to the small particle size of FePO₄·2H₂O nanoparticles, the good electronic conductivity of MWNTs, and the three-dimensional conductive network structure of FePO₄·2H₂O/MWNTs nanocomposites.     

Quasi-Hexagonal Ordered Arrays of FePt Nanoparticles Prepared by a Micellar Method

Hexagonally ordered arrays of magnetic FePt nanoparticles on Si substrates are prepared by a self assembly of diblock copolymer PS-b-P2VP in toluene, a dip coating process and finally plasma treatment. The as-treated FePt nanoparticles are covered by an oxide layer that can be removed by a 40 s Ar＋ sputtering. The effects of the sequence of adding salts on the composition distribution are revealed by x-ray photoelectron spectroscopy measurements. No particle agglomeration is observed after 600℃annealing for the present ordered array of FePt nanoparticles, which exhibits advantages in patterning FePt nanoparticles by a micellar method. Moreover, magnetic properties of the annealed FePt nanoparticles at room temperature are investigated by a vibrating sample magnetometer.     

Effects of target-substrate geometry and ambient gas pressure on FePt nanoparticles synthesized by pulsed laser deposition

FePt nanoparticles, in the forms of nanoparticle agglomerates and floccules-like nanoparticle networks, can be synthesized by pulsed laser deposition (PLD) at different ambient gas pressures. Backward plume deposition (BPD), as special target-substrate geometry, can achieve higher uniformity in terms of agglomerate size and size distribution, compared to conventional PLD. Both as-deposited FePt nanoparticles exhibit low K_u fcc phase and post-annealing at 600 °C is required for the phase transition to high K_u fct phase. FePt nanoparticle agglomerates deposited by BPD were found to have better fct phase crystallinity after annealing, which may be caused by the higher kinetic energy of backward moving ablated species due to shorter travel distance.     

Monolayer deposition of L10 FePt nanoparticles via electrospray route

The deposition monolayers of L1₀ FePt nanoparticles via an electrospraying method and the magnetic properties of the deposited film were studied. FePt nanoparticles in a size of around 2.5 nm in diameter, prepared by a liquid process, were used as a precursor. The size of the deposited particles can be controlled up to 35 nm by controlling the sprayed droplet size that is formed by adjusting the precursor concentration and the precursor flow rate. The droplets were heated in a tubular furnace at a temperature of up to 900 °C to remove all organic compounds and to transform the FePt particles from disordered face centered cubic to an ordered FCT phase. Finally, the particles were deposited in the form of a monolayer film on a silicon substrate by electrostatic force and characterized by scanning electron microscopy. The monolayer of particles was obtained by the high charge on particles obtained during the electrospraying process. The magnetic properties of the monolayer were investigated by magneto-optic Kerr effect measurements. Coercivity up to 650 Oe for a film consisting of 35 nm L1₀ FePt nanoparticles was observed after heat treatment at a temperature of 800 °C.     

Magnetic Properties and Nanostructures of FePtCu：C Thin Films with FePt Underlayers

Magnetic properties and nanostructures of FePtCu：C thin films with FePt underlayers （ULs） are studied. The effect of FePt ULs on the orlentation and magnetic properties of the thin films are investigated by adjusting FePt UL thicknesses from 2nm to 14nm. X-ray diffraction （XRD） scans reveal that the orientation of the films is dependent on FePt UL thickness. For a 5-nm FePtCu：C nanocomposite thin film with a 2-nm FePt UL, the coercivity is 6.S KOe, the correlation length is 59 nm, the desired face-centred-tetragonal （fct） ordered structure [Llo phase] is formed and the c axis normal to the film plane [（001） texture] is obtained. These results indicate that the beffer orientation and magnetic properties of the films can be tuned by decreasing the thockness of the FePt UL.     

KxCoO2·yH2O(x<0.2,y≤0.8)的晶体结构、输运及磁学性质

利用熔融KOH和Co₃O₄在较低温度(480℃)下反应制备出K_0.36CoO₂，然后用高锰酸钾溶液和饱和的过硫酸钾溶液进行氧化处理.氧化的同时伴随有水分子嵌入.K_0.36CoO₂用高锰酸钾和过硫酸钾溶液处理后分别得到K_0.12CoO₂·0.8H₂O和K_0.16CoO₂·0.6H₂O.这两种化合物都属于六角晶系，表现出金属行为，脱水后主相变为正交结构并且呈现出半导体特性.K_0.16CoO₂·0.6H₂O在56K附近可能存在自旋玻璃转变行为或其他涨落.随着钾含量的减少和水含量的增多，样品的自旋玻璃行为受到抑制或发生磁性相分离.样品K_0.12CoO₂·0.8H₂O在零场冷却和有场冷却曲线上的分叉现象基本上消失.还讨论了产生K_xCoO₂与Na_xCoO₂体系结构和物性差别的原因. 关键词： xCoO₂')" href="#">K_xCoO₂ 晶体结构 自旋玻璃态 磁性     

Electrochemical characterization on layered lithium ruthenate for electrochemical supercapacitors

Electrochemical characteristics of lithium ruthenate (Li_xRuO_2+0.5x·nH₂O) for electrochemical capacitors' electrode material were first examined in this paper by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Results show that Li_xRuO_2+0.5x·nH₂O has electrochemical capacitive characteristic within the potential range of − 0.2–0.9 V (vs. SCE) in 1 M Li₂SO₄ solution. The capacitance mainly arises from pseudo-capacitance caused by lithium ions' insertion/extraction into/out of the Li_xRuO_2+0.5x·nH₂O electrode. The specific capacitance of 391 F g^− 1 can be delivered at 1 mA charge–discharge current for Li_xRuO_2+0.5x·nH₂O electrode with an energy density of 65.7 W h kg^− 1. This material also exhibits an excellent cycling performance and there is no attenuation of capacitance over 600 cycles.     

Synthesis and characterization of magnetite nanopowders

We have synthesized the iron oxide nanoparticles using the newly developed mechanical ultrasonication method with the FeSO₄ · 7H₂O. We have also investigated the crystallographic structural properties, morphology, and magnetic properties of the nanopowders. According to the high resolution X-ray diffraction result, the as-synthesized iron oxide nanoparticles were magnetite (Fe₃O₄). The particle size of the magnetite nanoparticles was about 6 nm confirmed by transmission electron microscopy image. The particle shape was almost a sphere confirmed by scanning electron microscopy image. The coercivity and saturation magnetization of the as-synthesized iron oxide nanopowders were 114 Oe, and 3.7 emu/g, respectively.     

Facile synthesis and characterization of high-performance NiMoO<Subscript>4</Subscript> · <Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O nanorods electrode material for supercapacitors

One-dimensional NiMoO₄ · xH₂O nanorods were synthesized by a facile template-free hydrothermal method as a potential electrode material for supercapacitors. The influences of reaction temperature, reaction time, and nickel source on the properties of resultant samples were investigated. Electrochemical data reveal that the as-synthesized one-dimensional NiMoO₄ · xH₂O nanorod superstructures can deliver a remarkable specific capacitance (SC) of 1131 F g^?1 at a current density of 1 A g^?1 and remain as high as 914 F g^?1 at 10 A g^?1 in a 6 M KOH aqueous solution. Moreover, there is only 6.2 % loss of the maximum SC after 1000 continuous charge–discharge cycles at the high current density of 10 A g^?1. Such outstanding electrochemical performance may be owing to the unique one-dimensional hierarchical structures, which can facilitate the electrolyte ions and electrons to easily contact the NiMoO₄ nanorod building blocks and then allow for sufficient faradaic reactions to take place, even at high current densities.     

Structure and lithium storage performances of nickel hydroxides synthesized with different nickel salts

Nickel hydroxides with hierarchical micro-nano structures are prepared by a facile homogeneous precipitation method with different nickel salts (Ni(NO₃)₂·6H₂O, NiCl₂·6H₂O, and NiSO₄·6H₂O) as raw materials. The effect of nickel sources on the microstructure and lithium storage performance of the nickel hydroxides is studied. It is found that all the three prepared samples are α-nickel hydroxide. The nickel hydroxides synthesized with Ni(NO₃)₂·6H₂ or NiCl₂·6H₂O show a similar particle size of 20–30 μm and are composed of very thin nano-sheets, while the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O shows a larger particle size (30–50 μm) and consists of very thin nano-walls. When applied as anode materials for lithium-ion batteries (LIBs), the nickel hydroxide synthesized with NiSO₄·6H₂O exhibits the highest discharge capacity, but its cyclic stability is very poor. The nickel hydroxides synthesized with NiCl₂·6H₂O exhibit higher discharge capacity than the nickel hydroxides synthesized with Ni(NO₃)₂·6H₂O, and both of them show much improved cyclic stability and rate capability as compared to the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O. Moreover, pseudocapacitive behavior makes a great contribution to the electrochemical energy storage of the three samples. The discrepancies of lithium storage performance of the three samples are analyzed by ex-situ XRD, FT-IR, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests.     

Facile synthesis and characterization of Co nanoplatelets with tunable dimensions via solution reduction process

Plate-like Co nanoparticles with different sizes were synthesized by solution reduction process. The size of Co nanoplatelets can be tuned by varying the concentration of CoCl₂·6H₂O and the dosage of N₂H₄·2H₂O. The Co nanoplatelets with the different size all exist in both fcc and hcp crystal structures. The normal direction of the nanoplatelets is perpendicular to the (002) planes of hcp phase or to the (111) planes of fcc phase. The saturation magnetizations of the samples are lower than the corresponding bulk value. The coercivities of the samples vary with the phase content and the particle size. The shape control mechanism was discussed.     

Fabrication and surface transformation of FePt nanoparticle monolayer

The monolayer of FePt nanoparticles with the mean size of ∼4 nm was fabricated on a glass substrate by the Langmuir––Blodgett (LB) technology. The monolayer of FePt nanoparticles has a smooth surface and a high density structure as shown by the AFM image. The array structure of FePt nanoparticles on the surface of the film is clearly with a cubic symmetry in appropriate condition. Small-angle X-ray diffraction (SXRD) measurement of multilayer structure for the FePt nanoparticles has indicated that the superlattices consist of well-defined smooth layers. The transfer of nanoparticle layers onto a solid substrate surface was quite efficient for the first few layers, exhibiting a proportional increase of optical absorption in the UV–vis range. This results potentially opens up a new approach to the long-range ordered array of FePt nanoparticles capped by organic molecules on substrate and provide a promising thin film, which may exhibit the excellent ultra-high density magnetic recording properties.     

Preparation of PtSnRh/C-Sb2O5·SnO2 electrocatalysts by an alcohol reduction process for direct ethanol fuel cell

PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts with different Pt/Sn/Rh atomic ratios (90:05:05, 70:25:05, and 50:45:05) were prepared by an alcohol reduction process using H₂PtCl₆·6H₂O, SnCl₂·2H₂O, RhCl₃·xH₂O as metal sources, ethylene glycol as solvent and reducing agent, and a physical mixture of Vulcan XC72 (85?wt%) and Sb₂O₅·SnO₂ (15?wt%) as support. The electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry and chronoamperometry at 25 and 50?°C and in single direct ethanol fuel cell (DEFC) at 100?°C. The diffractograms of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the peaks characteristic of Pt face-centered cubic structure and several others peaks associated with ·SnO₂ and Sb₂O₅·SnO₂. Transmission electron micrographs of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the metal nanoparticles distributed on the supports with particle sizes of about 2?C3?nm. The electrochemical measurements and the experiments in a single DEFC showed that PtSnRh/C-Sb₂O₅·SnO₂ (90:05:05) and PtSnRh/C-Sb₂O₅·SnO₂ (70:25:05) electrocatalysts exhibited higher performance for ethanol oxidation in comparison with PtSnRh/C electrocatalyst.     

A chemical strategy to control the shape of oxide nanoparticles

A new strategy, epoxide-assisted precipitation route presented in this work, allows the shape control synthesis of Co₃O₄ nanoparticles. The shape of the nanoparticles is determined by the nature of the precursor cobalt salts (Co(NO₃)₂ · 6H₂O, CoCl₂ · 6H₂O) used for the preparation of the particles. The different reaction dynamics of the two salts in ethanolic and aqueous solutions with propylene oxide result in precursor particles with different structures, which lead to the formation of oxide nanoparticles with different shapes during the heat treatment. Spherical particles of about 20 nm are obtained from the ethanolic solution of Co(NO₃)₂ · 6H₂O; cubic-shaped particles of about 30 nm can be prepared from the ethanolic solution of CoCl₂ · 6H₂O; whereas platelet-like particles of more than 100 nm are synthesized from the aqueous solution of the mixture of Co(NO₃)₂ · 6H₂O and CoCl₂ · 6H₂O.     

Sonochemical preparation of pure t-LaVO4 nanoparticles with the aid of tris(acetylacetonato)lanthanum hydrate as a novel precursor

Herein a simple and fast method is introduced for the synthesis of lanthanum orthovanadate (LaVO₄) nanoparticles under ultrasound irradiation. The effect of tris(acetylacetonato)lanthanum hydrate ([La(acac)₃·3H₂O]) and La(OAc)₃ as two different precursors on the morphology and phase purity of LaVO₄ was investigated. To optimum the particle size of the products, sonication time and the kind of surfactants have been changed. The as-synthesized products were characterized by XRD, FT-IR, SEM, TEM, and EDS. Based on the obtained results, it was found that the size and shape of the sonochemically formed LaVO₄ nanoparticles were dramatically dependent on the sonication time, type of surfactant and lanthanum precursor. According to the XRD results, it was observed that pure tetragonal phase lanthanum orthovanadate (t-LaVO₄) could be obtained only by using [La(acac)₃·3H₂O] as precursor under ultrasound irradiation for 30 min. On the other hand, monoclinic phase lanthanum orthovanadate (m-LaVO₄) with poor crystallinity has been produced by vigorous stirring at room temperature without sonication.     

Hydrothermal synthesis and photocatalytic properties of WO3 nanorods by using capping agent SnCl4·5H2O

Hexagonal tungsten trioxide (h-WO₃) nano-rods of different sizes are prepared via hydrothermal synthesis using a capping agent of SnCl₄·5H₂O. The size of the synthesized WO₃ nanoparticles can be controlled by changing concentration of the capping agent SnCl₄·5H₂O alone. We also investigate microstructures and optical properties of the WO₃ nanorods and propose a synthesis mechanism for the nanorods. The photocatalytic activities of the h-WO₃ nanorods are evaluated by degradation of Rhodamine-B (RhB), revealing that these nanorods exhibit excellent photocatalytic properties. The capping agent SnCl₄·5H₂O is found to be critical to governing sizes and properties of the h-WO₃ nanorods. Our results demonstrate that functional nano-crystallites with tunable size and morphology can be synthesized via a facile hydrothermal synthesis process by adjusting the concentration of capping agent alone. Such a facile hydrothermal synthesis process should be applicable to other types of nanomaterials and relevant to a wide range of applications.     

Decoration of carbon nanotube with size-controlled L10-FePt nanoparticles for storage media

In this work, first multi-wall carbon nanotubes (MWCNTs) with outer diameter about 20–30 nm are synthesized by a CVD method; they have been purified and functionalized with a two-step process. The approach consists of thermal oxidation and subsequent chemical oxidation. Then, monosize FePt nanoparticles along carbon nanotubes surface are synthesized by a Polyol process. The synthesized FePt nanoparticles are about 2.5 nm in size and they have superparamagnetic behavior with fcc structure. The CNTs surfaces as a substrate prevent the coalescence of particles during thermal annealing. Annealing at the temperature higher than 600 ^°C for 2 h under a reducing atmosphere (90 % Ar + 10 % H₂) leads to phase transition from fcc to fct-L1₀ structure. So, the magnetic behavior changes from the superparamagnetic to the ferromagnetic. Furthermore, after the phase transition, the FePt nanoparticles have finite size with an average of about 3.5 nm and the coercivity of particles reaches 5.1 kOe.