Highly Dispersed ZnSe Nanoparticles Embedded in N‐Doped Porous Carbon Matrix as an Anode for Potassium Ion Batteries

Advanced nanostructured functional materials obtained from the precursors of metal–organic frameworks show several unique advantages, including plentiful porous structures and large specific surface areas. Based on this, designed and constructed are highly dispersed ZnSe nanoparticles anchored in a N‐doped porous carbon rhombic dodecahedron (ZnSe@NDPC) by a sequential high‐temperature pyrolysis and selenization method. The specific synthesis process involves a two‐step heat treatment of the template‐engaged reaction between zinc‐based zeolitic imidazolate framework (ZIF‐8) and selenium power. By optimizing the calcination temperature, the as‐synthesized ZnSe@NDPC‐700 as an advanced anode of potassium ion batteries demonstrates the best electrochemical performance, including a high capacity (262.8 mA h g^?1 over 200 cycles at 100 mA g^?1) and a good rate capability (109.4 mA h g^?1 at 2000 mA g^?1 and 52.8 mA h g^?1 at 5000 mA g^?1). Moreover, the capacitance and diffusion mechanisms are also investigated by the qualitative and quantitate analysis, finally accounting for the superior K storage.     

Colloidal Crystals of NaYF4 Upconversion Nanocrystals Studied by Small‐Angle X‐Ray Scattering (SAXS)

Spherical NaYF₄ upconversion nanocrystals with mean radii of about 5 and 11 nm are observed to form colloidal crystals, i.e., 3D assemblies of the particles with long‐range order. The colloidal crystals of the larger particles form directly in solution when dispersions of the particles in toluene are stored at room temperature for several weeks. Crystallization of the smaller particles takes place when their dispersions in hexane are slowly dried at elevated temperatures. The formation and the structure of the colloidal crystals are studied by small‐angle X‐ray scattering (SAXS). SAXS measurements show that the smaller as well as the larger particles assemble into a face‐centered cubic lattice with unit cell dimensions of a = 18.7 nm and a = 35.5 nm, respectively. The SAXS data also show that the particles in the colloidal crystals still bear a layer of oleic acid on their surfaces. The thickness of this layer is 1.5–1.8 nm, as determined by comparing the unit cell dimensions of the colloidal crystals with the mean particle sizes. The latter could be very precisely determined from the distinct oscillations observed in the SAXS data of dilute colloidal dispersions of the nanocrystals.     

Two‐photon absorption induced anti‐Stokes emission in single InGaN/GAN quantum‐dot‐like objects

We observed crossed transitions and anti‐Stokes emissions in single quantum‐dot‐like objects embedded in the active layer of InGaN/GaN quantum disks by two‐photon absorption techniques. We proposed a phenomenological model based on the interplay between Auger effect and crossed transitions to explain the origin of anti‐Stokes emissions and the preferential excitation of 0D objects at the expense of their surroundings. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assessing Carrier Recombination Processes in Type‐II SiGe/Si(001) Quantum Dots

In this work, it is shown how different carrier recombination paths significantly broaden the photoluminescence (PL) emission bandwidth observed in type‐II self‐assembled SiGe/Si(001) quantum dots (QDs). QDs grown by molecular beam epitaxy with very homogeneous size distribution, onion‐shaped composition profile, and Si capping layer thicknesses varying from 0 to 1100 nm are utilized to assess the optical carrier‐recombination paths. By using high‐energy photons for PL excitation, electron‐hole pairs can be selectively generated either above or below the QD layer and, thus, clearly access two radiative carrier recombination channels. Fitting the charge carrier capture‐, loss‐ and recombination‐dynamics to PL time‐decay curves measured for different experimental configurations allows to obtain quantitative information of carrier capture‐, excitonic‐emission‐, and Auger‐recombination rates in this type‐II nano‐system.     

A Nano‐Micro Hybrid Structure Composed of Fe7S8 Nanoparticles Embedded in Nitrogen‐Doped Porous Carbon Framework for High‐Performance Lithium/Sodium‐Ion Batteries

Iron sulfides are attractive anode materials for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) due to their high theoretical capacities, low cost, and eco‐friendliness. However, their real application is greatly hindered by the rapid capacity fading caused by the large volume changes and sluggish kinetics of iron sulfides during the charge and discharge processes. Combining with carbonaceous materials and tuning the structure at nanoscale are essential to address this issue. Here, a facile hydrothermal method coupled with a carbonization process is developed to synthesize a nano‐micro hybrid porous structure, which is composed of Fe₇S₈ nanoparticles embedded in nitrogen‐doped carbon framework (Fe₇S₈@NC‐PS). This hierarchical sphere is constructed by interconnected 2D nanowalls. The as‐prepared Fe₇S₈@NC‐PS electrodes reveal excellent rate capability and cycling stability in LIBs and SIBs. The remarkable electrochemical properties are attributed to the porous nano‐micro hybrid architecture and the high conductivity and structural stability of the nitrogen‐doped carbon framework.     

A miniature X‐ray emission spectrometer (miniXES) for high‐pressure studies in a diamond anvil cell

Core–shell X‐ray emission spectroscopy (XES) is a valuable complement to X‐ray absorption spectroscopy (XAS) techniques. However, XES in the hard X‐ray regime is much less frequently employed than XAS, often as a consequence of the relative scarcity of XES instrumentation having energy resolutions comparable with the relevant core‐hole lifetimes. To address this, a family of inexpensive and easily operated short‐working‐distance X‐ray emission spectrometers has been developed. The use of computer‐aided design and rapid prototype machining of plastics allows customization for various emission lines having energies from ～3 keV to ～10 keV. The specific instrument described here, based on a coarsely diced approximant of the Johansson optic, is intended to study volume collapse in Pr metal and compounds by observing the pressure dependence of the Pr Lα emission spectrum. The collection solid angle is ～50 msr, roughly equivalent to that of six traditional spherically bent crystal analyzers. The miniature X‐ray emission spectrometer (miniXES) methodology will help encourage the adoption and broad application of high‐resolution XES capabilities at hard X‐ray synchrotron facilities.     

A novel approach to determine leucomalachite green and malachite green in fish fillets with surface‐enhanced Raman spectroscopy (SERS) and multivariate analyses

The use of illegal fish drugs, such as malachite green (MG) in aquaculture has raised growing concerns over the safety of aquatic food products, and sensitive and rapid methods for detection of these drugs in fish muscle are much needed. Simplified extraction methods coupled with surface‐enhanced Raman spectroscopy were used for analysis of MG and its metabolite leucomalachite green (LMG) in tilapia fillets containing 0–50 ng g⁻¹ LMG or MG. Principal component analysis and partial least squares (PLS) regression were used for spectral data analyses. High sensitivity (MG or LMG could be detected at 1–2 ng g⁻¹ levels) and PLS models with good predictability [root mean square error of validation (RMSEV) = 1.97–2.21 ng g⁻¹, R² = 0.984–0.988] were possible with suitable sample extraction methods. The simplest extraction method developed provided an RMSEV of 9.32 ng g⁻¹ and R² of 0.788, and although this was not ideal, detection of MG and LMG at 5 ng g⁻¹ level with this method could reduce sample throughput time and provide for faster detection of LMG and MG. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of N and O‐atoms and N2 (A) Metastable Molecule Densities in the Afterglows of N2‐H2, Ar‐N2‐H2 and Ar‐N2‐O2 Microwave Discharges

Early afterglows of N₂‐H₂, Ar‐N₂‐H₂ and Ar‐N₂‐O₂ flowing microwave discharges are characterized by optical emission spectroscopy. The N and O atoms and the N₂ (A) metastable molecule densities are determined by optical emission spectroscopy after calibration by NO titration for N and O‐atoms and measurements of NO and N₂ band intensities. If an uncertainty of 30% is estimated on N‐atomic density, an inaccuracy of one order of magnitude is obtained on the O and N₂ (A) densities. In N₂‐(0.05‐2.5%)H₂ and Ar‐(1‐50%)N₂‐(0.05‐2.5%) H₂ gas mixtures, the O‐atoms are coming from O₂ impurities in the discharge. Concentrations of N and O‐atoms and of N₂ (A) densities are compared to the ones obtained in Ar‐(5‐50%)N₂‐(0.2‐2.5%) O₂ gas mixtures in which a controlled amount of O₂ is added. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A reaction cell for time‐resolved in situ XAS studies during wet chemical synthesis: the Cu2(OH)3Cl case

The use of in situ time‐resolved dispersive X‐ray absorption spectroscopy (DXAS) to monitor the formation of Cu₂(OH)₃Cl particles in an aqueous solution is reported. The measurements were performed using a dedicated reaction cell, which enabled the evolution of the Cu K‐edge X‐ray absorption near‐edge spectroscopy to be followed during mild chemical synthesis. The formed Cu₂(OH)₃Cl particles were also characterized by synchrotron‐radiation‐excited X‐ray photoelectron spectroscopy, X‐ray diffraction and scanning electron microscopy. The influence of polyvinylpyrrolidone (PVP) on the electronic and structural properties of the formed particles was investigated. The results indicate clearly the formation of Cu₂(OH)₃Cl, with or without the use of PVP, which presents very similar crystalline structures in the long‐range order. However, depending on the reaction, dramatic differences were observed by in situ DXAS in the vicinities of the Cu atoms.     

Determination of N and O – Atom and N2(A) Metastable Molecule Densities in the Afterglows of N2 and N2‐O2 Microwave Discharges

Early afterglows of N₂ and N₂‐O₂ flowing microwave discharges are characterized by optical emission spectroscopy. The N and O atom and N₂(A) metastable molecule densities are determined by optical emission spectroscopy after calibration by NO titration for N‐atoms and measurements of NO and N₂ band intensities for O‐atoms and N₂(A) metastable molecules. By using N₂ tanks with 50 and 10 ppm impurity, it is determined in the afterglow an O‐ atom impurity of 150‐200 ppm. Variations of the N and O‐atom and N₂(A) metastable molecule densities are obtained in the early afterglow of N₂–(9·10^–5–3·10^–3)O₂ gas mixtures. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non‐linear Hammett

Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)₃]³⁺ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)₃]³⁺ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron‐withdrawing and electron‐releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron‐releasing to electron‐withdrawing groups. Electron‐releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron‐withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H₂O which leading to low magnitude of ρ⁺ compared to high ρ^? values of electron‐releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright © 2016 John Wiley & Sons, Ltd.