Understanding the formation and evolution of ceria nanoparticles under hydrothermal conditions

Supercritical growth: The formation and evolution of ceria nanoparticles during hydrothermal synthesis was investigated by in?situ total scattering and powder diffraction. The nucleation of pristine crystalline ceria nanoparticles originated from previously unknown cerium dimer complexes. The nanoparticle growth was highly accelerated under supercritical conditions.     

Mechanism of the platinum nanoparticles formation under conditions of nonstationary electrolysis

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Thermal analysis of formation of ZrO2 nanoparticles under hydrothermal conditions

The formation of ZrO₂ nanoparticles during the hydrothermal treatment of zirconium oxyhydroxide has been investigated depending on the chemical and thermal history of the initial material. It has been shown that the crystallization of c(t)-ZrO₂ and m-ZrO₂ under hydrothermal conditions proceeds virtually simultaneously, and the amount of one or another polymorph depends mainly on the ratio of rates of these processes.     

Thermodynamic approach to calculating the surface tension of single-component liquids by computer simulations

A thermodynamic method for computing the surface tension at a flat liquid-vapor interface by the Monte Carlo or molecular dynamics methods over a wide temperature range was proposed. The approach is based on the Gibbs separating surface method; it does not require information on the mechanical state of the surface layer.     

Carbon-gold core-shell structures: formation of shells consisting of gold nanoparticles

Carbon spheres were obtained via the St?ber method using phenolic resin followed by carbonization. Spherical carbon-gold core-shell particles were fabricated by deposition of gold nanoparticles on the modified surface of carbon spheres.     

Probing amyloid fibril formation of the NFGAIL peptide by computer simulations

Amyloid fibril formation, as observed in Alzheimer's disease and type II diabetes, is currently described by a nucleation-condensation mechanism, but the details of the process preceding the formation of the nucleus are still lacking. In this study, using an activation-relaxation technique coupled to a generic energy model, we explore the aggregation pathways of 12 chains of the hexapeptide NFGAIL. The simulations show, starting from a preformed parallel dimer and ten disordered chains, that the peptides form essentially amorphous oligomers or more rarely ordered beta-sheet structures where the peptides adopt a parallel orientation within the sheets. Comparison between the simulations indicates that a dimer is not a sufficient seed for avoiding amorphous aggregates and that there is a critical threshold in the number of connections between the chains above which exploration of amorphous aggregates is preferred.     

Thermodynamic properties of benzene under shock conditions

We present in this paper a thermodynamic analysis of benzene properties under shock conditions as given by molecular dynamics (MD) simulations. Reactive MD simulations of benzene predict a decomposition threshold corresponding to the flection point on the experimental Hugoniot curve. A polymerlike carbonated structure is observed for pressures above this threshold, but the calculated Hugoniot curve is in disagreement with the experimental one at high pressure. On the contrary, a system consisting of a diamond cluster in hydrogen gas leads to a correct prediction of the pressure on the Hugoniot curves. The central question is then linked to the kinetics of the transition between the polymerlike structure and the diamond cluster.     

Direct formation of mesoporous upconverting core-shell nanoparticles for bioimaging of living cells

We have developed a one-step method for the synthesis of mesoporous upconverting nanoparticles (MUCNs) of the type NaYF₄:Yb,Er@mSiO₂ in ammoniacal ethanol/water solution. The mesoporous silica is directly encapsulating the hydrophobic upconversion nanoparticles (UCNs) due to the presence of the template CTAB. Intense green emission (between 520 and 560 nm) and weaker red emission (between 630 and 670 nm) is observed upon 980-nm laser excitation. The MUCNs display low cytotoxicity (as revealed by an MTT test) and were successfully applied to label and image human nasopharyngeal epidermal carcinoma (KB) cells.

Raman probing carbon&aqueous electrolytes interfaces and molecular dynamics simulations towards understanding electrochemical properties under polarization conditions in supercapacitors

Raman probing of carbon electrode and electrolyte under dynamic conditions is performed here using different aqueous electrolytes to elucidate the fundamental e...     

The effect of periodic boundary conditions on homogeneous nucleation observed in computer simulations

The sudden rapid crystallization observed after a variable induction time in molecular dynamics simulations of the supercooled Lennard-Jones liquid is an artifact of periodic boundary conditions and is not related to formation of a critical nucleus.     

The formation of Pt-Ru alloy nanoparticles in a carbon matrix under IR pyrolysis conditions

Nanosized Pt-Ru alloy and Pt₁₃Ru₂₇ intermetallic compound particles dispersed in a carbon matrix were obtained for the first time directly during the preparation of the composite. The alloying of the Pt and Ru particles occurred at IR pyrolysis intensities corresponding to temperatures above 700°C over the whole homogeneity range of solid solutions based on platinum. Metallic nanoparticles were round-shaped (the mean size 6–8 nm) and had a narrow particle-size distribution.     

An electrochemical cell for simultaneous electrochemical and spectroelectrochemical measurements under semi-infinite diffusion conditions and thin-layer conditions

A combination cell to accomplish simultaneous electrochemical and spectroelectrochemical measurements under both thin-layer and semi-infinite diffusion conditions is described and characterized. Fibre optics and a reflective electrode are used to couple the cell to the spectrophotometer. This allows different electrode materials to be used. Moreover, the cell is thermostatically controlled and equipped with a magnetic stirrer, and can be used for temperatures down to −40°C.The application of electrochemical pulse and sweep techniques are demonstrated. Dynamic spectroelectrochemical techniques such as linear sweep and cyclic voltabsorptometry (LSVA and CVA) as well as the corresponding derivative voltabsorptometric techniques derivative linear voltabsorptometry (DLSVA) and derivative cyclic voltabsorptometry (DCVA) are also applicable under thin-layer conditions. DLSVA and DCVA are the optical analogues of linear sweep and cyclic voltammetry. No epoxy cement or other sealing compounds are required and the solution comes in contact with only quartz, Teflon and the electrodes. Under aprotic conditions the cell response is in accordance with theory down to a solution thickness of 15 μm, where rapid exhaustive electrolysis intrinsic to thin-layer electrochemistry can be achieved in less than 1 s.The electrochemical and spectroelectrochemical characterization of the cell demonstrated that this design is very well suited to different electrochemical pulse and sweep techniques with simultaneous spectroscopic characterization of reaction products under finite and semi-infinite diffusion conditions in organic solvents. This offers the opportunity for cross-correlations of the electrochemical and spectroscopic information, which should lead to more reliable results. The adjustment of different thin-layer thicknesses is highly reproducible and the exchange of the solution inside the thin-layer cavity with the bulk solution after each thin-layer experiment can be easily performed. The electrochemical behaviour of the cell is in accordance with theory for cyclovoltammetric measurements under both bulk and thin-layer conditions. Derivative voltabsorptometric techniques are applicable and the response of the cell is in accordance with theory, particularly under finite diffusion conditions. The use of a bifurcated optical fibre bundle allows a more flexible experimental arrangement, and the application of a triple split bundle for the investigation of light-sensitive electron-transfer compounds [34,35] is in progress. The third end of the optical fibre bundle will be used to apply additional selective irradiation to convert electron-transfer-active photochromic compounds inside the thin-layer cavity depending on the redox state.An additional aspect of the current investigations is the application of the present cell for electrogenerated chemiluminescence (ECL) [36,37]. The highly reflecting electrode and the integrated stirrer are advantageous for this type of measurement. Finally, further work is in progress to utilize the integrated temperature control of the cell for spectroelectrochemistry at low temperatures, particularly with more unusual solvents like liquid sulphur dioxide [38] and liquid dimethylamine [39].     

Protein aggregation and gel formation studied with scattering methods and computer simulations

We review recent scattering experiments on the reversible and irreversible aggregation and gelation of globular proteins. Globular proteins are compact with a well-defined structure in the native state, but are not perfect spheres and the details of the interaction between proteins may be intricate involving for instance specific binding sites. Nevertheless, it turns out that often the structure of globular protein aggregates and gels can be understood by treating them as spherical colloids with relatively simple interaction potentials. Computer simulations of interacting hard spheres give detailed structural information that can be used to understand some aspects of protein aggregation and gel formation.     

Ultrasensitive photometric and visual determination of organophosphorus pesticides based on the inhibition of enzyme-triggered formation of core-shell gold-silver nanoparticles

The authors describe a colorimetric assay for the determination of organophosphorous pesticides (OPPs) based on enzyme-triggered deposition of silver nanoparticles on the surface of gold nanoparticles (AuNP). In this method, alkaline phosphatase (ALP) catalyzes the dephosphorylation of the substrate p-aminophenyl phosphate (p-APP) to form p-aminophenol (p-AP) which is capable of reducing Ag(I) ion to Ag metal which is spontaneously deposited on the surface of AuNP to form Au@Ag NPs. As a result, the color of the colloidal solution first changes from red to yellow, and then to gray with further increases in the thickness of the Ag shell. This can be detected visually or by spectrophotometry. OPPs act as inhibitors of ALP so that the dephosphorylation of p-APP is blocked and silver deposition on the AuNP is retarded or completely suppressed. As a result, the color change from red to yellow is less distinct. This finding forms the basis for the determination of OPPs. Under optimum conditions, the absorbance at 370 nm depends linearly on the logarithm of inhibitor concentration over the ranges from 0.05 to 500 μg?L^?1 and from 0.1 to  500 μg?L^?1, with detection limits of 0.025 μg?L^?1 for methamidophos and 0.036 μg?L^?1 for malathion (at an S/N ratio of 3). Both values are much lower than the maximum residue limits specified in the U.S. Department of Agriculture and European Union pesticide regulations. The validation and practicability of this method for the measurement of OPPs was demonstrated by analyzing (spiked) tap water and lake water.

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Graphical abstract The alkaline phosphatase (ALP) activity is inhibited by organophosphorus pesticides (OPPs). As a result, the ALP-trigged formation of core-shell gold-silver nanoparticles depends on the amount of OPPs, which showed different absorbances and colors.

     

Structure and deformations of Pd-Ni core-shell nanoparticles

Homogeneous collections of Pd-Ni core-shell nanoparticles have been prepared by decomposition of metal-organic compounds and studied by several electron microscopy techniques: transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), energy-filtered microscopy (EFTEM), and by X-ray photoelectron spectroscopy (XPS). The physical and chemical properties of the Pd shell are supposed to depend on its electronic properties, which are influenced by the presence of the Ni core and by the deformation in the Pd lattice. Here, the interfacial structure of Pd/Ni and the lattice deformations in the core and the shell are studied in detail. The catalytic properties of the pure metal and the bimetallic particles, toward CO oxidation, have been investigated.     

Au-Pd alloy and core-shell nanostructures: one-pot coreduction preparation, formation mechanism, and electrochemical properties

It is a known fact that Pd-based bimetallic nanostructures possess unique properties and excellent catalytic performance. In this work, the Au-Pd alloy and core-shell nanostructures have been prepared by a simple one-pot hydrothermal coreduction route, and their formation process and mechanism are discussed in detail. A reducing capacity-induced controlled reducing mechanism is proposed for the formation process of Au-Pd bimetallic nanostructures. CTAB plays a key role in the formation of alloy Au-Pd nanostructures. When CTAB is absent, the products are typical core-shell nanostructures. Moreover, the as-prepared nanostructures exhibit excellent electrocatalytic ORR performance in alkaline media, especially for Au-Pd alloy nanostructures. The overpotential of oxygen reduction gets reduced significantly, and the peak potential is positive-shifted by 44 and 34 mV in comparison with the core-shell ones and Pd/C catalyst, respectively. Thus, the controllable preparation and excellent electrocatalytic properties will make them become a potentially cheaper Pd-based cathodic electrocatalyst for DAFCs in alkaline media.     

Thermodynamic considerations of screening halide molten-salt electrolytes for electrochemical reduction of solid oxides/sulfides

Journal of Solid State Electrochemistry - Molten salt is an indispensable electrolyte for electrochemically extracting reactive metals that cannot be obtained by a carbothermic reduction or a...     

Self-organization and pattern formation of janus particles in two dimensions by computer simulations

The phase behavior and associated pattern formation of two-dimensional systems of hard disks decorated with amphiphilic coronae (Janus disks) are studied by means of Monte Carlo computer simulations. A primitive interaction potential that captures the essential interparticle interactions is introduced. Despite its simplicity, the system exhibits a very rich phase polymorphism. Apart from the isotropic phase and depending upon the coronal thickness, the simulated systems self-organize in a number of two-dimensional mesophases of various symmetries exhibiting a variety of novel patterns. The results of these simulations suggest that 2D Janus particles are promising candidates for bottom-up design of precise two-dimensional templates.