In-situ transmission electron microscopy observation of particle size effect of nanoscale platinum catalysts on the formation of fullerenelike carbon shells

Drastically different catalytic behaviors of nanometer-sized platinum particles which have diverse sizes are observed using in-situ transmission electron microscopy. For small platinum catalyst particles (with diameters less than 5 nm), carbon shells form on the surfaces of the platinum catalyst particles. The formation of the carbon shells starts from the nucleation of amorphous carbon on the preferred (1 1 1) planes of platinum nanoparticles. For these small platinum catalyst particles encapsulated in graphitic shells, they are passivated by the carbon shells and their coalescence is hindered by the surrounding shells. After the platinum catalyst particles ultimately coalesce, they interact to form a compact platinum particle after breaking the encapsulating shells. For larger platinum nanoparticles (with diameters larger than 5 nm), no encapsulation of platinum nanoparticles is observed and there occurs only the coalescence of platinum nanoparticles.     

Structure and magnetic properties of carbon encapsulated Fe nanoparticles obtained by arc plasma and combustion synthesis

Carbon encapsulated Fe nanoparticles were obtained using two methods: arc plasma and combustion synthesis. These powders were characterized by the following methods: SQUID magnetization measurements, transmission electron microscopy (TEM) and Mössbauer spectroscopy. The last two methods showed that Fe nanoparticles, obtained by both techniques belong to metallic and/or carbide phases, and are partially encapsulated by graphitic carbon. The particles had 10-100 nm in diameter, and were covered by carbon 5-15 nm thick layers. The transmission Mössbauer spectra revealed two magnetic and two paramagnetic components. In the plasma samples the largest part of iron was contained in the carbide phase while in the combustion samples the bcc α-Fe encompassed most of iron. The combustion sample has much higher content of carbon, indicating that the Fe particles were not covered by graphite layer totally, and were dissolved in the etching process. The dominant portion of combustion samples was not vaporized, thus the iron phase solidified from the liquid. The plasma-arc samples were synthesized via dual mechanism: growth of nanocrystals from the vapor phase (carbide) and solidification of the liquid micro-droplets in the cold zone (α-Fe and γ-Fe).     

Gadolinium and europium catalyzed growth of single-walled carbon nanotubes

The inner transition metals, gadolinium (Gd) and europium (Eu) have been shown to catalyze the growth of single-walled carbon nanotubes (SWCNTs) using chemical vapor deposition. The Gd and Eu nanocatalysts, prepared using a diblock copolymer templating method and characterized by atomic force microscopy, were uniformly spaced over a large deposition area with an average diameter of 1.9 nm and narrow size distribution. Characterization by transmission electron microscopy and Raman spectroscopy confirms the presence of SWCNTs catalyzed by Gd and Eu with an average diameter of 2.05 nm.     

Growth of magnetic carbon with a nanoporous and graphitic structure

A porous magnetic composite is synthesized in which each magnetic nanoparticle is closely encapsulated by several graphitic layers and the resulting units are embedded in a carbon matrix with a nanoporous and graphitic structure. The experiments involve preparation of an iron-containing carbon precursor by thermal pyrolysis and subsequent heat treatment of the precursor. Both magnetic particles and porous carbon with a graphitic structure are formed at the same time. After the heat treatment, no additional treatment is needed. The prepared sample has a high surface area of 275-395 m² g⁻¹, a high saturation magnetism of 43-65 emu g⁻¹ and a high coercivity of 370-650 Oe.     

镧、钇掺杂铕-樟脑酸-1,10-菲咯啉三元配合物的合成及荧光性能

实验合成了单核铕-樟脑酸-1,10-菲咯啉三元配合物和La、Y掺杂异核铕-樟脑酸-1,10-菲咯啉三元配合物。通过配位滴定、元素分析和红外光谱等测试,确定其组成为RE2(CA)3(phen)2(RE为Eu、La和Y;CA为樟脑酸;phen为1,10-菲咯啉);通过三维荧光光谱图确定其最佳激发波长为330.0 nm,即在330.0 nm激发光下的发射光谱图中均显示出Eu3+离子5D0→7F0(579nm),5D0→7F1(594 nm)和5D0→7F2(612 nm)等三条特征谱线,其中5D0→7F2(612 nm)为最强跃迁峰。荧光强度变化研究表明,适量镧和钇离子的掺杂并没有降低铕离子的荧光强度,说明镧和钇对铕离子荧光发射有敏化作用。     

Transmission electron microscopy characterization of nanostructured carbon derived from Cr3C2 and Cr(C5H7O2)3

The preparation, characterization and comparison of nanostructured carbons derived by direct chlorination of Cr₃C₂ and Cr(C₅H₇O₂)₃ are reported in this work. Cr₃C₂ precursor was treated at 400 and 900 °C with a reaction time of 1 h. The nanostructure of the products has been characterized in some detail by means of transmission electron microscopy and associated techniques, such as electron energy-loss and X-ray energy dispersive spectroscopies and high-angle annular dark field imaging. Remains of Cr₃C₂ encapsulated in an amorphous carbon shell were observed at 400 °C, whereas carbon with higher ordering degree was produced at 900 °C. In the latter case, the sample can be described as a continuous variation from poorly-stacked graphene-like carbon to graphitic agglomerates. Remains of the reaction by-product, CrCl₃, are detected in the carbon particles, forming monolayers intercalated inside the graphitic agglomerates and amorphous nanoparticles. As a comparison, carbon samples derived from Cr(C₅H₇O₂)₃ were prepared at 300 and 900 °C. They mainly consist of highly disordered carbon, with local graphite-like stacking in the sample prepared at 900 °C.     

Ethanol steam reforming reactions over Al2O3 · SiO2-supported Ni-La catalysts

Nickel-based catalysts supported on Al₂O₃ · SiO₂ were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al₂O₃ · SiO₂ (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al₂O₃ · SiO₂ indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature.     

Direct synthesis of carbon nanotubes decorated with size-controllable Fe nanoparticles encapsulated by graphitic layers

A simple method has been developed for direct synthesis of magnetic multi-walled carbon nanotubes (MWCNTs) homogeneously decorated with size-controllable Fe nanoparticles (Fe-NPs) encapsulated by graphitic layers on the MWCNT surface by pyrolysis of ferrocene. These composites have similar C/Fe atomic ratio of ∼10 and exhibit sufficiently high saturation magnetization for magnetic separation in a liquid phase. Moreover, with 0, ∼1, ∼2 wt% sulfur as growth promoter, the size of Fe-NPs can be controlled with an average diameter of ∼5, ∼22 and ∼42 nm, respectively. When compared to time-consuming wet-chemical methods, the simplicity of this method should allow easy large-scale production of these magnetically functionalized MWCNTs, which can be used as catalyst supports with high stability for effective magnetic separation in liquid-phase reactions, especially under acid/basic conditions.     

Synthesis of hermetically-sealed graphite-encapsulated metallic cobalt (alloy) core/shell nanostructures

Hermetically-sealed graphite encapsulated cobalt core/shell nanostructures have been prepared by the CO Boudouard reaction using in situ generated cobalt as the catalyst. Only core/shell nanostructures were obtained, rather than a mixture of cobalt nanoparticles with carbon nanotubes or nanofibers. The magnetic cobalt nanoparticles are highly crystallized with a hexagonal-close packed crystal phase (average diameter of ca. 25 nm) and coated with an 8–9 nm thick graphitic shell. The nanostructures have a high saturation magnetization of 85 emu/g and can be easily separated by an external magnet. The creation of the hermetically-sealed graphitic shell not only keeps the magnetic cobalt nanoparticles from reacting with strong mineral acids, but also has biocompatibility and makes further functionalization easy. A pseudo-planar aromatic molecule, xylenol orange, was used as the model molecule because it can be absorbed on the graphitic shell mainly by π–π stacking interaction. This was confirmed by Raman and ultraviolet–visible spectroscopy. Graphite encapsulated Fe₂Co and Fe_0.64Ni_0.36 alloy core/shell nanostructures were also fabricated by this method.     

Electrochemical transient techniques for determination of uranium and rare-earth metal separation coefficients in molten salts

The main step in the pyrometallurgical recycling process of spent nuclear fuel is a molten salt electrorefining. The knowledge of separation coefficients of actinides (U, Np, Pu and Am) and rare-earth metals (Y, La, Ce, Nd and Gd) is very important for this step. Usually the separation coefficients are evaluated from the formal standard potentials of metals in melts containing their own ions, i.e. values obtained by potentiometric method. Electrochemical experiments were carried out at 723-823 K in order to estimate separation coefficients in LiCl-KCl eutectic melt containing uranium and lanthanum trichlorides. The electrochemical behaviour of UCl₃ in LiCl-KCl melt was studied by different electrochemical methods. The diffusion coefficients of U(III) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry. The standard rate constants of charge transfer for electroreduction of uranium, U(III) + 3e⁻ → U, were calculated by the impedance spectroscopy method. The values of constants testify that electroreduction of U(III) to U is mainly controlled by the rate of charge transfer. La(III) discharge on uranium electrode was also investigated. It was shown that for the calculation of uranium and lanthanum separation coefficients it is necessary to determine the voltammetric peak potentials of U(III) and La(III), their concentration in the melt and the kinetic parameters relating to U(III) discharge such as transfer and diffusion coefficients, and standard rate constants of charge transfer.     

EXTRACTIVE PROPERTIES TOWARDS RARE-EARTH METAL IONS OF CALIX[ 4] ARENES SUBSTITUTED AT THE NARROW RIM BY PHOSPHORYL AND AMIDE GROUPS

ABSTRACT

The extractive properties of the cone and partial-cone isomers of 5,11,17,23-tetra-?ert-butyl-25,27-bis( diethylcarbamoylmethoxy)-26,28-bisi( diphenylphospninoylmethoxy) calyx[ 4] arene ( cone-1 and partial-cone -1) in 1,2-dichloroethane towards rare-earth metal ions in nitrate media at 25 ° C were investigated. The analysis of the extraction equilibrium obtained from a mixture of four rare-earths ( La, Eu, Er and Y) revealed that the extracted species have a 1 1 metal/ ligand ratio for both ligands. The intra-group separation efficiercies of the ligandls have been evaluated in a competitive extraction process of 11 rare-earth metal ions ( La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb and Y). Significantly higher extractive properties were found for cone-1 with respect to partial-cone-1, suggesting the crucial role of the phosphoryl groups in the complexation of the rare-earth ions. These findings were     

Nanodiamond crystallites embedded in carbon films prepared by thermionic vacuum arc method

Nanostructured carbon films with thicknesses of 100 and 200 nm have been deposited from pure vapour carbon plasma using an original thermionic vacuum arc method. Silicon single crystalline wafers, glass and stainless steel held at 400 °C were used for substrates. The films consist of diamond nanoparticles of 5 nm diameter on the average embedded in a disordered graphite matrix as revealed by HRTEM, XPS and visible Raman measurements. The graphitic cluster diameters La range from 1.5 to 2.3 nm. Thicker films (200 nm) on stainless steel exhibit the largest clusters.     

Dispersion of graphite encapsulated nickel nanoparticles in a NP-9 colloidal system

Graphite encapsulated metal nickel (Ni-GEM) nanoparticles are a relatively new material. With an inner ferromagnetic metal core and several layers of outer graphitic shells, Ni-GEM (5-100 nm in diameter) can survive in severe environments and still preserve its nanocrystalline properties. The as-made Ni-GEM particles agglomerate due to both the van der Waals and strong magnetic forces between the nanoparticles. To reduce the negative influence of severe agglomeration, several dispersants were added and tested for effective dispersion; among these, one non-ionic surfactant, nonyl phenol ethoxylate (NP-9), showed the best results. In addition, two different sized Ni-GEM (23 nm and 14 nm in diameter) were synthesized by using a modified tungsten arc-discharge method in this research; the strength of the saturated magnetization was decreased from 30-40 emg/g to 11.6 emg/g for the smaller 14 nm Ni-GEM particles. Based on three separate test results of steady-stage, transient, and dynamic tests on a rheometer, the 14 nm Ni-GEM in a 40% NP-9 colloid showed the best dispersive property. Preliminary results showed that the key to the success of dispersion is the reduction of the average particle sizes of GEM, whereby the magnetic forces could be decreased and the effective surface areas for the surfactant NP-9 increased. Based on this research, it was found that the rheological measurements, which are closely related to the surfactant concentrations, particle sizes and internal structure development, can be efficiently and conveniently used to detect the various behaviors of a GEM-dispersed colloidal system.     

Effects of surrounding confinements of Si nanoparticles on Si-based anode performance for lithium ion batteries

We report herein the effects of various surrounding confinements of Si nanoparticles on the electrochemical performance of Si nanoparticles based anode for lithium ion batteries (LIBs). Three different types of surrounding confinements are incorporated onto or around the surface of Si nanoparticles: Si nanoparticles-embedded carbon nanofibers (Si@CNF) via electrospinning, carbon nitride encapsulated Si nanoparticles with core/shell structure (Si@CND), and binder enriched Si nanoparticles-based anode (Si@RBD). Morphology and microstructure of the samples are characterized using X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and the results were discussed in relation to the electrochemical performances. It is found that Si@CNF which has conducting hard surrounding confinements and Si@RBD exhibited high reversible specific capacity of 620 mA hg⁻¹ and 1200 mA hg⁻¹, up to 30th cycle, respectively. Meanwhile, Si@CND that has mechanically hard but poor electrical conductivity exhibits low specific capacity compared with the other two samples.     

Catalytic etching of {100}-oriented diamond coating with Fe, Co, Ni, and Pt nanoparticles under hydrogen

Etching of a highly {100}-oriented diamond coating, {100}HODC, with hydrogen gas using Fe, Co, Ni, and Pt nanoparticles as a catalyst was examined at high temperatures over 700 °C by high-resolution scanning electron microscopy and Raman spectroscopy. The metal atoms vacuum-evaporated onto the {100}HODC formed nanoparticles themselves when heated at high temperatures; e.g. 700 °C, in a flowing gas mixture of H₂ (10%) + N₂ (90%). At 800 °C, short nano-channels and etch pits holding metal nanoparticles were formed by Fe, Co, and Ni. The shapes of the Co and Ni nanoparticles in the etch pits were affected by the shape of the etch pits; reversed pyramidal shape. On the other hand, the top view of the Fe nanoparticles embedded in the etch pits showed a distorted round shape, probably due to the formation of something such as iron carbide, while the carbon content was unknown. Apparently, etching of the {100}HODC by Pt nanoparticles was observed after the treatment at 1000 °C. The difference in the catalytic etching behavior among these metal particles, the potential etching mechanism of diamonds with hydrogen by metal nanoparticles, probably as melted metal nanoparticles, and the formation mechanism of vacant etch pits were discussed.     

Preparation of ZnO/Eu mixed films by electrochemical precipitation

The electrochemical preparation of europium doped zinc oxide and europium oxide/hydroxide as thin films is investigated. First, a thermodynamic study of the Eu-Cl-H₂O system has been carried out at 25 and 70 °C in order to predict the electrochemical behaviour of Eu(III) dissolved in aqueous solution containing chloride ions. A comparison of the Eu-Cl-H₂O and Zn-Cl-H₂O systems indicates the possible coprecipitation of ZnO and Eu(OH)₃ from deposition solutions containing well-adjusted Eu(III)/Zn(II) concentrations ratio. The thermodynamic predictions have been confirmed experimentally by the electrochemical co-deposition of ZnO/Eu thin films on conducting electrode substrates at −1.4 V versus MSE. The presence of europium in the film is detected for Eu(III)/Zn(II) concentration ratio at (0.6 mM/5 mM) which is lower than the predicted value. Increasing Eu(III) concentration leads to the rapid appearance of two phases: dispersed zinc oxide nanorods and, at the bottom of the rods, a covering layer containing Eu(OH)₃ and zinc. The density of ZnO rods decreases and the rod size increases with increasing Eu(III) concentration in the bath. Above 1 mM EuCl₃, a dramatic fall in the current density is observed with the formation of a less conducting ZnO/Eu mixed deposit.     

Highly dispersed platinum nanoparticles on carbon nanocoils and their electrocatalytic performance for fuel cell reactions

Highly graphitic carbon nanocoils (GCNC) were synthesized through the catalytic graphitization of carbon microspheres obtained by the hydrothermal carbonization of different saccharides (sucrose, glucose and starch) and were used as a support for Pt nanoparticles. The Pt nanoparticles were deposited by means of a polymer mediated-polyol method. The Pt catalysts were characterized both physically (XRD, TEM, HRTEM and XPS) and electrochemically (electrooxidation of methanol in an acid medium). The electrocatalysts thus prepared show a high dispersion of Pt nanoparticles, with diameters in the 3.0-3.3 nm range and a very narrow particle size distribution. These catalytic systems possess high electroactive Pt surface areas (up to 85 m² g⁻¹ Pt) and they exhibit large catalytic activities towards methanol electrooxidation (up to 201 A g⁻¹ Pt). Moreover, they have a high resistance against oxidation, which is considerably greater than that of the Pt/Vulcan system.     

Synthesis of carbon nanotubes over gold nanoparticle supported catalysts

The synthesis of carbon nanotubes (CNTs) through the catalytic decomposition of acetylene was carried out over gold nanoparticles supported on SiO₂-Al₂O₃. Monodispersed gold nanoparticles with 1.3-1.8 nm in diameter were prepared by the liquid-phase reduction method with dodecanethiol as protective agent. The carbon products formed after acetylene decomposition consist of multi-walled carbon nanotubes with layered graphene sheets, carbon nanofilaments (CNFs), and carbon nanoparticles encapsulating gold particles. The observed CNTs have outer diameters of 13-25 nm under 850 °C. The influence of several reaction parameters, such as kind of carriers, reaction temperature, gas flow rate, was investigated to search for optimum reaction conditions. The CNTs were observed at a relatively low temperature (550 °C). The silica-alumina carrier showed higher activity for the formation of CNTs than others used in the screening test. With increasing temperature, the CNTs showed cured structures having thick diameters and inside compartments. When Au content on the support was over 5 wt.%, the gold nanoparticles coagulated to form large ones >20 nm in diameter and became encapsulated with graphene layers after decomposition of acetylene.     

Synthesis of carbon nanocapsules and carbon nanotubes by an acetylene flame method

The fabrication of carbon nanocapsules and carbon nanotubes (CNTs) using an acetylene flame method was investigated. Carbon nanocapsules, a graphitic structure of nanoparticles with a hollow core, were synthesized using catalyst-free acetylene flames while CNTs were formed with the presence of cobalt-based catalysts in addition to acetylene flames. When the synthesis of these materials was carried out, the results showed that a massive amount of high-purity carbon nanocapsules with a particle size in the range of 15-30 nm can be produced with the acetylene flame method. The CNTs produced were multi-walled carbon nanotubes measuring a few micrometers in length and 20-30 nm in diameter. The acetylene flame method holds great potential for the cost-effective production of CNTs as well as carbon nanocapsules.     

Synthesis and luminescent properties of a novel Eu-containing nanoparticle

We synthesized Eu-containing nanoparticles using the ultra-dilute solution method and characterized by FT-IR, NMR, GPC, DSC, and UV-visible absorption/photoluminescence spectra. The size of Eu-containing nanoparticles was 30-150 nm and the nanoparticles were soluble in common organic solvents. A study of the dependence of emission intensities of the Eu-containing nanoparticles on the Eu content showed that the emission intensities increased nearly linearly with increasing Eu content. In addition, no significant emission concentration quenching phenomenon was observed at the Eu content of 0-9.5 mol%.