In Situ Generation of Two-Dimensional Au–Pt Core–Shell Nanoparticle Assemblies

Two-dimensional assemblies of Au–Pt bimetallic nanoparticles are generated in situ on polyethyleneimmine (PEI) silane functionalized silicon and indium tin oxide (ITO) coated glass surfaces. Atomic force microscopy (AFM), UV–Visible spectroscopy, and electrochemical measurements reveal the formation of core–shell structure with Au as core and Pt as shell. The core–shell structure is further supported by comparing with the corresponding data of Au nanoparticle assemblies. Static contact angle measurements with water show an increase in hydrophilic character due to bimetallic nanoparticle generation on different surfaces. It is further observed that these Au–Pt core–shell bimetallic nanoparticle assemblies are catalytically active towards methanol electro-oxidation, which is the key reaction for direct methanol fuel cells (DMFCs).     

CO Oxidation of Au–Pt Nanostructures: Enhancement of Catalytic Activity of Pt Nanoparticles by Au

The CO oxidation activity of Pt deposited on Ta₂O₅/Ta was studied with various amounts of Au post-deposited on Pt/Ta₂O₅/Ta. For Pt nanoparticles with a mean size of 2–4 nm, an enhancement in the CO oxidation activity with increasing amount of post-deposited Au was found. The mixed Au–Pt nanoparticles with sizes in the range of 2–4 nm exhibited higher stability than the bare Au nanoparticles with a similar size range. In contrast to the results obtained with the Pt nanoparticles, the catalytic activity of a thicker Pt film gradually decreased with increasing amount of Au deposited. Based on the CO desorption experiments, it is suggested that the surface of the catalytically active Au–Pt bimetallic structures consists of both Au and Pt sites.     

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO₄ · 7H₂O and CrCl₃ · 6H₂O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.     

Preparation and characterization of the bimetallic Pt–Au/ZnO/Al2O3 catalysts: Influence of Pt–Au molar ratio on the catalytic activity for toluene oxidation

The bimetallic Pt–Au catalysts supported on ZnO/Al₂O₃ with different Pt/Au molar ratios were prepared by impregnation (IMP) method using a mixed solution of Pt and Au precursor. These were characterized by X-ray diffraction (XRD), CO chemisorption, temperature programmed reduction (TPR), and transmission electron microscopy (TEM) equipped energy dispersive spectroscopy (EDS). Catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. In the results, the aggregation of Au particles depended on the molar ratio in the bimetallic Pt–Au catalyst, and Pt particles was well dispersed homogeneously even by the IMP method. The Pt₇₅Au₂₅ and Pt₆₇Au₃₃ catalysts concurrently coated with Pt and Au precursors by IMP method showed higher activity than monometallic Pt and Au catalyst for toluene oxidation. Also, in order of the catalytic activity for toluene was very good agreement compare with the TPR results. The Au particles might promote the toluene oxidation over the bimetallic catalyst concurrently coated with Pt and Au particles. Therefore, the size of Pt and Au particles and catalytic activity were confirmed to be correlated to molar ratio of Pt and Au loaded.     

Preparation and Characterization of Layered Double Hydroxides – PMMA Nanocomposites by Solution Polymerization

Layered double hydroxides (LDH) – poly(methyl methacrylate) (PMMA) intercalated-exfoliated nanocomposites were synthesized by solution polymerization of methyl methacrylate (MMA) in the presence of aminobenzoate organically-modified LDH. Preparations of 4-aminobenzoate organically modified LDHs were carried out by applying a chemical co-precipitation reaction. Structural and compositional details of LDH-AB were obtained with Fourier transformed infrared (FT-IR) spectroscopy, ²⁷Al magic-angle spinning nuclear magnetic resonance (²⁷Al MAS NMR), elemental analysis (EA), inductively coupled plasma (ICP) atomic absorption spectrometry and X-ray diffraction (XRD). The morphology of the LDH-AB in the PMMA matrix was identified by employing transmission electron microscopy (TEM), XRD, and UV/visible transmission spectroscopy. The thermal properties of the nanocomposites were enhanced and their Tg values as well as the decomposition temperatures shifted to a high temperature region as identified by the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). For example, the Tg value and the decomposition temperature of the nanocomposites with 6.4% LDH-AB increased by 19 °C and 24 °C, respectively.     

Preparation of Pt–Co alloy catalysts by electrodeposition for oxygen reduction in PEMFC

Direct current (DC) and pulse current (PC) electrodeposition of Pt–Co alloy onto pretreated electrodes has been conducted to fabricate catalyst electrodes for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). The effect of plating mode and pulse plating parameters on the Pt–Co alloy catalyst structure, composition and electroactivity for the ORR in PEMFC has been investigated. The electrodeposited Pt–Co alloy catalyst indicates higher electrocatalytic activity towards the ORR than the electrodeposited Pt catalyst. The activity of the electrodeposited Pt–Co catalysts is further improved by applying the current in a pulse waveform pattern. The electrodeposition mode and the pulse plating parameters do not have the significant effect on the Pt:Co composition of deposited catalysts, but show the substantial effect on the deposit structures produced. The Pt–Co catalysts prepared by PC electrodeposition have finer structures and contain smaller Pt–Co catalyst particles compared to that produced by DC electrodeposition. By varying the Pt concentration in deposition solution, the Pt:Co composition of the electrodeposited catalyst that exhibits the highest activity is found. The Pt–Co alloy catalyst with the Pt:Co composition of 82:18 obtained at the charge density of 2 C cm⁻², the pulse current density of 200 mA cm⁻², 5% duty cycle and 1 Hz was found to yield the best electrocatalytic activity towards the ORR in PEMFC.     

Investigation of Alumina Wetting by Fe–Ti,Fe–P and Fe–Ti–P Alloys

Abstract

The wetting of alumina substrates by Fe–Ti, Fe–P and Fe–Ti–P alloys has been investigated using sessile drop experiments conducted under an inert gas atmosphere in the temperature range of 1550 to 1620°C. The surface and interfacial structures have been explored by scanning electron microscopy and energy dispersive X-ray spectroscopy. Substantial additions of titanium are known to induce steel melts to wet alumina due to the formation of a Ti-rich reaction product at the alloy/ceramic interface, but the present work has shown that even low Ti concentrations can induce a reactive wetting process leading to an improvement of the wettability of alumina by Fe alloys. The contact angle of molten steel containing phosphorus on alumina decreased with increasing P content. The improvement of the wetting behaviour in this system was attributed solely to the adsorption of P onto the surface of the Fe melt. The addition of P as a ternary alloying element to the system Fe–Ti proved to be beneficial to the wetting behaviour. The measured contact angles were much lower than those in the binary systems Fe–Ti and Fe–P. This effect was related to the fact that P enhances the activity of Ti in the Fe melt. According to experimental observations, it turns out that the wettability of liquid Fe-based alloys, when an Al2O3 surface is present, is not only a property of the metal/oxide couple but is also dependent on the oxygen partial pressure, whereas temperature variations bring about a comparatively small effect. This work is of interest in understanding the phenomena pertaining to inclusion engineering and steel– refractory interactions, such as the clogging of submerged entry nozzles by agglomerated alumina particles during the continuous casting process.     

Selective Modification of Pt Active Sites on Pt–Au/C Catalysts Prepared by Surface Redox Reactions

This study focused on the selective deposition of Au⁰ onto (111), (100) faces and (111)/(100) edges of cuboctahedral Pt particles present on the Pt/C(graphite) model system. The Pt–Au/C catalysts were prepared by novel surface redox methods involving the direct reduction (DR) of AuCl ₄ ^– species onto the Pt particles or reducing these species on the Pt–H interface, i.e., the refilling (RE) method. The presence of Au on the Pt particles was verified by means of high-resolution energy dispersive spectroscopy (EDS), and, after treatment at 300°C in H₂, the formation of crystalline Au⁰ aggregates was verified by X-ray wide-angle diffraction; further treatments at 500°C in H₂ led to a true Pt–Au solid solution. The Monte Carlo simulation methods indicated the selective deposition of Au⁰ onto the (111)/(100) edges of the Pt cuboctahedral particles when the relative Au concentration varied from 10 to 50 wt% Au. The catalytic conversion of n-heptane on the Pt–Au/C (DR and RE solids) catalysts presented an oscillatory behavior with respect to Pt/C, indicating modification of the active Pt ensembles, driven by the energy released during the exothermic n-C₇ dehydrogenation and cracking reactions, which should enhance the Au⁰ mobility at the Pt particle surface level.     

Preparation and structural properties of Fe3O4–polyimide hybrid nanocomposites

Polyimide films in which magnetic Fe₃O₄ nanoparticles are uniformly distributed are prepared. Before the preparation of the Fe₃O₄–polyimide composites, pure magnetite nanoparticles (Fe₃O₄) have been synthesized in water by co-precipitation (from ferric chlorides). Its surface was firstly modified with the 3-aminopropyl triethoxysilane. The prepared polyimide–Fe₃O₄ nanocomposite films were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy, scanning electron micrograph, X-ray diffraction, and thermal analysis (DTA/TGA/DSC) techniques.     

Synthesis and characterization of carbon-supported Pt–Ru–WOx catalysts by spectroscopic and diffraction methods

Carbon-supported Pt–Ru–WO_x/C catalysts for application in PEMFC anodes were synthesized by a modified Bönnemann method. Their electrocatalytic activity for the oxidation of H₂/CO mixtures and CH₃OH was measured by E/i-curves in PEM single cell arrangements under working conditions. Information about composition, microstructure and nanomorphology was obtained by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence analysis (XFA) and transmission electron microscopy (TEM). X-ray diffraction data at room temperature show only one single Pt f.c.c. phase; no evidence of Ru, W and their oxides, respectively, is found. Hence, the presence of W and Ru as amorphous oxide species seems likely. Surface-sensitive XPS measurements detect Pt⁰, platinum oxide and hydroxide species, metallic Ru, ruthenium oxide, hydrous ruthenium oxide and WO₃. For the crystalline platinum phase particle sizes of less than 2 nm were determined by TEM images and XRD patterns via solving the Scherrer equation. Temperature-dependent XRD measurements were performed to show the influence of ageing on the catalyst structure.     

Study of geometrical and electronic effects induced by hydrogen chemisorption on supported Pt particles. Analysis of Pt–H EXAFS and Pt–H anti-bonding state shape resonances

Geometrical and electronic effects induced by hydrogen chemisorption on supported Pt particles are studied by analysing the Pt–H anti-bonding shape resonance. The fundamental principles of a new analysis method of the L₂ and L₃ X-ray absorption edges are summarised. The method is used for studying the Pt–H bonding properties of weakly and strongly bonded hydrogen on surfaces of supported metal catalysts. Also the interaction of hydrogen with a Pt/CeO₂ catalyst as a function of the reduction temperature is investigated. The new analysis method makes it possible to follow the changes in the electronic structure of a Pt/Al₂O₃ catalyst as a function of the metal particle size. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis of Hetroaromatic Polyamide and Imide–Acid-Functional Fe3O4 Nanoparticle and Their Effect on Thermal Degradation of PLA

A new hetroaromatic polyamide-reinforced polylactic acid (PLA)/functional Fe₃O₄ nanocomposite system was prepared through solution casting method. The hetroaromatic polyamide (PA) was synthesized from 2,5-pyridinedicarboxylic acid and 3,3′-diaminodiphenyl sulfone by direct polycondensation reaction. An imide–acid-functional Fe₃O₄ nanoparticle was prepared using pyromellitic dianhydride and coupling agent. As a potential reinforcement, PA and imide–acid-functionalized Fe₃O₄ were used in a PLA system. Combination of the functional Fe₃O₄ with PA showed a good effect on improving the thermal properties of PLA. The temperature at 5 mass% loss (T₅) was increased from 309°C to 337°C in PLA–PA containing 5 mass% of PA (PLA–PA 5) as compared to the neat PLA. The char yield of PLA–PA–FN 10 was increased from 0.5% to 8.9% as compared to the neat PLA and it was much high as compared to the system containing only 5 mass% of PA or the functional Fe₃O₄.     

Preparation and dielectric properties of dense and amorphous alumina film by sol–gel technology

Dense and crack-free aluminum oxide films were fabricated by sol–gel spin-coating technology. Aluminum nitrate (Al(NO₃)₃.9H₂O) was used as the precursor material. X-ray diffraction shows that the fabricated films are amorphous. X-ray photoelectron spectroscopy confirms that the thin films are alumina (Al₂O₃). Field-emission scanning electron microscopy images of the films reveal that the films are compact with a dense cross section. Dielectric measurements were carried out on samples with a metal–insulator–metal structure. The electrical characteristics of the films were affected by the thermal sintering temperature of the films. The leakage current density of the films decreases with the increase in the sintering temperature and increases with the increase in the measuring temperature. The leakage current shows a linear dependence on the voltage in the low-electric field-regime. The current density ascends to higher values due to the effect of space charges in the high-electric-field regime. The ionization energy of the top-electrode metals (Au, Pt or Ti–Au) has a strong effect on the leakage current.     

Preparation and Characterization of Nano-Sized Iron–Titanium Mixed Oxide for Removal of Some Lanthanides from Aqueous Solution

Nano-structured iron(III)–titanium(IV) mixed oxide, Fe–O–Ti, was prepared by co-precipitation technique and characterized using Transmission Electron Microscopy, Fourier Transform Infra Red, Energy Dispersive X-ray spectroscopy, and Thermal Analysis. The particle size of the prepared material was found to be 10–15 nm. The sorptive potential of nano-composite, Fe–O–Ti, for the removal of some lanthanide elements (including, Ce, Nd, and Gd) was assessed in this work. The percent uptake was found to be 95.6%, 89.5, and 81.9 for Ce³⁺, Nd³⁺, and Gd³⁺ ions, respectively. Three kinetic models, pseudo-first-order, pseudo-second-order, and intra particle diffusion models, were tested. The results indicated that the pseudo-second-order model is more applicable for the sorption process. The experimental equilibrium data were tested for the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models; it was well predicted by the Freundlich model. The thermodynamic parameters were calculated. The results indicated that the nano-sized iron-titanium mixed oxide can be considered as a promising material for the removal of some lanthanides from aqueous solution.     

Preparation of nano-AlN powder by sol–gel foaming and its sintering properties

Uniformly dispersed nano-sized aluminum nitride powders were prepared by the sol–gel foaming method using aluminum nitrate as the aluminum source, sucrose as the carbon source, and ammonium chloride as the foaming agent. The effects of ammonium chloride content on the particle size and the sintering properties of aluminum nitride were investigated. The results showed that when the molar ratio of ammonium chloride to aluminum nitrate was .5, the colloidal foams were uniform, large, and fluffy, and amorphous alumina precursors with uniform particles could be prepared. Aluminum nitride powder with a particle size of 22–27 nm can be obtained by calcining these precursors in nitrogen atmosphere at 1400°C for 2 h. At the same time, aluminum nitride bulk material with a relative density of 95% can be obtained by sintering the compact samples in nitrogen atmosphere at 1700°C for 2 h.