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Active electrocatalysts are the key to water splitting for hydrogen production through the electrolysis. In this paper, 50 nm silver nanoplates were used as templates for synthesis of Au–Ag island-shaped nanoplates by controlling the surface chemistry. The guiding mechanism of polyvinylpyrrolidone (PVP, Mw = 40 000) to Au–Ag island-shaped nanoplates crystal was also further investigated. It is found that the surface energy of Ag nanoplates between (100) and (111) crystal planes can be regulated by varying the amount of PVP in the system. Then a uniform Au-Ag triangular island nanostructure was obtained. Compared with the Ag nanoplates catalysts, the Au–Ag island nanoplates catalysts show the superior catalytic performances in hydrogen evolution electrocatalysis (HER). These results demonstrate a new surface chemistry modification by PVP and a galvanic displacement reaction for designing the active electrocatalysts. More importantly, the Au–Ag island-shaped nanoplates show an unconventional growth mode of preserving the original Ag nano-triangular crystal structure. The enhanced performance in electrocatalysis can be mainly attributed to Au–Ag alloy structure, which allows the appearance of synergistic effects. The present work demonstrates the crucial roles of surface chemistry in catalysts synthesis, which may guide the design of active bimetallic catalysts.

Although the regulation of silver nanostructures has been reported a lot, there are few reports on the simple green preparation method of ultra-long silver nanobelts and the formation mechanism of silver nanostructures is not uniform. In this paper, ultra-long silver nanobelts and dendrite silver were synthesized through a galvanic displacement and the growth mechanism of the silver nanosturture were investigated in detail. In the primary battery reaction, the introduction of copper ions could change the electric double layer and then affected the growth of silver nanosturcture. Different concentration of copper ion lead to different silver nanostructures. The greater the concentration of copper ions, the more the silver nanostructures grow in three dimensions.

In this study, naked Au(core)/Fe3O4(shell) hybrid nanostructures are rapidly synthesized by a plasmon-driven anti-replacement reaction. The Au nanoparticles are prepared by pulsed laser ablation in water. The mixture of Au nanoparticles and FeCl3 solution is irradiated under a laser with a specific wavelength. The Fe3+ ions are reduced to low valence species by the 'hot electrons' in Au, and form the Fe3O4 spindles on the surface of Au nanoparticles. The Au nanoparticles are synchronously oxidized to Au+ and Au3+ ions by the 'hot holes'. The saturation magnetization and coercivity of Fe3O4 spindles are 48.7 emu g-1 and 218.9 Oe, respectively. Our work provides a facile route to obtain the naked Au/Fe3O4 plasmonic/magnetic nanostructures.

The application of Au nanoparticles (Au NPs) often requires surface modification with chemical surfactants, which dramatically reduce the surface activity and increase the chemical contamination and cost of Au NPs. In this research, we have developed a novel Au NPs/reduced graphene oxide/Ni foam hybrid (Au NPs/RGO/NiF) by in situ reduction through ascorbic acid and replacement reaction. This method is green, facile and efficient. The Au NPs are free of chemical surfactants and are homogeneously distributed on the surface of the RGO/NiF. The as-prepared Au NPs/RGO/NiF hybrid is uniform, stable and exhibits not only a high reduction efficiency for the reduction of 4-nitrophenol with a catalytic kinetic constant of up to 0.46 min−1 (0.15 cm3 catalysis) but also a sensitive and selective detection of H2O2 with a detection limit of ~1.60 μM.

We investigate the nanostructure, surface plasmon resonance (SPR) absorption and nonlinear enhancement of Au/Ag alloyed hollow nanoshells prepared by the replacement reaction of Ag nanoparticles in a HAuCl4 aqueous solution. As the volume of HAuCl4 increases from 0mL to 0.5 mL, the SPR band of the Au/Ag alloyed nanoshells is tuned from 430 nm to 780 nm, and the third-order nonlinear optical susceptibility is enhanced nearly by an order of magnitude, which indicates a large enhancement of local field in the Au/Ag alloyed hollow nanoshells with hole defects.

Ceria powders were synthesized by two different methods, solid-state displacement reaction and wet chemical precipitation, and the influence of the physical characteristics of cerium oxide on the removal rate of plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) nitride films in chemical mechanical planarization (CMP) was investigated. The fundamental physicochemical property and electrokinetic behavior of ceria particles in aqueous suspending media were investigated to identify the correlation between the colloidal property of ceria and the CMP performance. The surface potentials of two different ceria particles are found to have different isoelectric point (pHiep) values and differences in physical properties of ceria particles such as porosity and density were found to be the key parameters in CMP of PETEOS films. Ceria powders synthesized by the solid-state displacement reaction method yielded a higher removal rate of PETEOS and higher selectivity than powders synthesized by the wet chemical precipitation method.

Alkali zeolite is often used as an ion source material owing to its easy extraction of alkali ions. In our laboratory, we fabricated zeolite containing a particular alkali species through a replacement reaction with sodium zeolite. In this paper, we present a simple mathematical model for describing this replacement reaction for making zeolite containing a particular alkali species. In this model, the fraction of alkali ions trapped in the zeolite lattice is expressed as a function of the numbers of substitution reactions in a concise recursion formula. This formula gives a simple estimation of efficiency for fabricating alkali zeolite in terms of the consumptions of time and chemicals.

The effect of surfactant in a ceria slurry on the impact of nanotopography on post-CMP oxide thickness deviation (OTD) was investigated in a blanket wafer study. The ceria slurry was prepared using the solid-state displacement reaction method and an anionic organic surfactant was added with the concentration from 0 to 0.8 wt%. Under the condition of a fixed removal depth, the magnitude of post-CMP OTD due to nanotopography increased with the surfactant concentration in the slurry, demonstrating that the impact of nanotopography can be controlled using the slurry characteristics.

The surface plasmon resonance (SPR) of Au nanostructures can be precisely tuned in the visible to near-infrared (vis–NIR) region with the size and morphology. The photothermal effect induced by the SPR can raise the temperature of Au nanostructures and the surrounding matrix under external illumination. In this work, hollow Au nanostructures such as nanoboxes and nanorings with a tunable SPR in the region of 650–1100 nm were obtained by a replacement reaction between HAuCl4 and the as-prepared Ag nanostructures as the sacrificed templates. Compared with the solid Au nanorods, studies on the photothermal conversion and stability of hollow Au nanostructures were systematically carried out with the assistance of the near-infrared (NIR) lasers available. Under NIR laser irradiation, the temperatures of the colloidal Au nanostructures increased rapidly from ~30 °C to ~65 °C. Combining the experimental results with a finite-different time-domain (FDTD) numerical simulation, the heat generation of different Au nanostructures was investigated. With the consideration of the concentration of the Au nanostructures, it is indicated that hollow Au nanostructures are superior to solid Au nanorods in photothermal conversion. On increasing the NIR laser power (3 W), Au nanorods undergo a shape deformation from nanorods to spherical nanoparticles, while the SPR and morphology of hollow Au nanoboxes and nanorings maintain high stability, promising to be candidates for nanoheaters. This work provides a standard to design optimized plasmonic nanoheaters.

An original numerical model, based on the standard Berg model, is used to simulate the growth mechanism of N-doped VOx deposited with changing oxygen flow in the reactive gas mixture. In order to compare with the numerical model, N-doped VOx films are prepared by reactive magnetron sputtering from a metallic vanadium target immersed in a reactive gas mixture of Ar+O2+N2. Both experimental and numerical results show that the addition of N2 to the process alleviates the hysteresis effect with respect to the oxygen supply. Film compositions obtained from the XPS analysis are compared to the numerical results and the agreement is satisfactory. The results also show that the compound of VN is only found at very low O concentration because of the replacement reaction of VN by O2 atoms with higher oxygen flow rate.

A novel approach is developed to synthesize PtIr or Pt nanowires (NWs) supported on the reduced graphene oxide (RGO) using Te NWs as template based on the replacement reaction. The resulting RGO-supported PtIr and Pt electrocatalysts are characterized by transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy and electrochemical techniques. TEM images show that these Pt based catalysts are uniformly distributed in the matrix of graphene with a characteristic of one-dimensional (1D) nanoporous structure. As one of promising anode materials used in the direct methanol fuel cells, these 1D nanoporous PtIr/RGO (or Pt/RGO) hybrids exhibit an enlarged electroactive surface and enhanced catalytic activity toward the methanol reaction relative to those PtIr or Pt NWs without graphene support.

This paper describes how the preparation and heat treatment of TiC/Si powders influences the phase reactions during firing. The powders are prepared by milling and some effects of powder preparation are discussed. A solid state displacement reaction according to: 3TiC + 2Si → Ti3SiC2 + SiC is a priori expected to take place during heat treatment. The firing procedure is investigated with respect to the effect of heat treatment time and temperature on the phases produced, especially Ti3SiC2. Samples were heat treated in a graphite lined furnace. Heat treated samples are analysed by x-ray diffraction, scanning electron microscope and energy dispersive spectroscopy. Ti3SiC2, TiC and SiC are dominant in the final products. The highest amount of Ti3SiC2 is achieved for short holding times (2-4 hours) at high temperatures (1350-1400°C). Ti3SiC2 appears to decompose at elevated temperatures or extended times, through a Ti3SiC2 → TiC + Si(g) type reaction. The activation energy of Ti3SiC2 phase formation is determined to be 289 kJ/mol, using the Mehl-Avrami-Johnson model. Validerad; 2009; 20090916 (idaker)

This paper reports for the first time the exact mechanism of the selective metal nanoscale etch method (SMNEM), which is a simply controllable and cost-effective approach for metal nanoscale etching and size reduction. This method is based on the galvanic displacement, Kirkendall effect, and selective etching. The size reduction is linearly controlled by the galvanic displacement in the early stage (1 min). In the later stage, a Kirkendall void is formed between the Ni and Au layer, which is well understood from Fick's law of diffusion. As matching with the experimental results, Ni nanowires with 30 +/- 4 nm width and 50 +/- 7 nm height were easily fabricated from nanostructures with 150 +/- 3 nm width and 110 +/- 2 nm height. The morphology and position of the Ni nanostructures are all predetermined by their initial conditions. Also achieved was the fabrication of complicated three-dimensional nanostructures such as Au nanowires and nanochannels from reduced Ni nanowires by a full replacement reaction.

Hollow Ag/Pd triangular nanoplates have been successfully prepared by a galvanic displacement reaction, in which added Pd(2+) ions react with Ag triangular nanoplates as templates. By altering the sizes of the Ag nanotemplates, Ag/Pd triangular nanoplates of different sizes can be prepared. Additionally, the large alloy nanoplates show maximum electrochemical activity when Ag/Pd triangular nanoplates of different sizes are applied as new activators for electroless nickel deposition.

Ag?Au alloy nanoparticles with tunable size and composition were prepared by a replacement reaction between Ag nanoparticles and HAuCl4 at elevated temperatures. The formation of homogeneous alloy nanoparticles was confirmed by selected-area energy-dispersive x-ray spectroscopy (SAEDX), UV?visible absorption spectroscopy, high resolution transmission electron microscopy (HRTEM) and electron diffraction. This method leverages upon the rapid interdiffusion of Ag and Au atoms in the reduced dimension of a nanoparticle, elevated temperatures and the large number of vacancy defects created in the replacement reaction. This method of preparation has several notable advantages: (1)?independent tuning of the size and composition of alloy nanoparticles; (2)?production of alloy nanoparticles in high concentrations; (3)?general utility in the synthesis of alloy nanoparticles that cannot be obtained by the co-reduction method.

In this paper, we report a simple method of fabricating silver and gold nanostructures at the air - water interface, which can be spontaneously assembled through the reduction of AgNO3 and HAuCl4 with ultraviolet (UV) irradiation in the presence of polyacrylic acid (PAA), respectively. It was found that the building blocks in the silver nanostructure are mainly interwoven silver nanofilaments, while those of the gold nanostructure are mainly different sizes of gold nanoparticles and some truncated gold nanoplates, and even coalescence into networks. At the air - water interface, these silver and gold nanostructures can be easily transferred onto the surface of indium tin oxide (ITO) slides and used for electrochemical measurements. After a replacement reaction with H2PdCl4, the silver nanostructure is transformed into a Ag - Pd bimetallic nanostructure, with good electrocatalytic activity for O-2 reduction. The gold nanostructure can also show high electrocatalytic activity to the oxidation of nitric oxide (NO) with a detection limit of about 10 mu M NaNO2 at S/N = 3.

TSEE from Cu-primary solid solutions which were abrabed was measured using a GM counter. The glow curve of a Cu solution involving Zn or Al could hardly be observed after one heating. This result indicates that the alloy surfaces were covered with a ZnO or Al2O3 film. The formation of a ZnO or Al2O3 film was due to a displacement reaction during the oxidations of the alloy surface. This lead to an enhancement of the solute atom concentration on the oxide surface. The oxygen concentration change with the solute content in Cu–Zn and Cu–Al could be interpreted in terms of the starting temperatures and activation energies determined from the glow curves. The TSEE of Cu–Ni and Cu–Ge had similar profiles and developed within the temperature range of the pure Cu glow curve.