Determination of vanadium in titanate-based ferroelectrics by INAA with discriminating gamma-ray spectrometry

Instrumental neutron activation analysis was used for determination of vanadium mass fraction in crystals of incipient ferroelectric strontium titanate and ferroelectric barium titanate. In order to improve vanadium limit of detection, discriminating gamma-ray spectrometry was used by inserting an absorption filter between the samples and an HPGe detector. The use of the absorption lead filter 6-mm thick yielded improvement of the vanadium limit of detection by a factor of two. The vanadium mass fraction determined in a quality control sample, which was NIST standard reference material SRM 1648 Urban Particulate Matter, was in close agreement with the certified value.

     

Rapid qualitative and quantitative ultra high performance liquid chromatography method for simultaneous analysis of twenty nine common phenolic compounds of various structures

Twenty nine phenolic compounds comprising nine phenolic acids, sixteen flavonoids (including eight tea catechins, glycosides and aglycones), four coumarins plus caffeine were analysed within 20 min using ultra high performance liquid chromatography (UHPLC) with PDA detection. UHPLC system was equipped with C18 analytical column (100 mm × 2.1 mm, 1.7 μm), utilising 0.1% formic acid and methanol mobile phase in the gradient elution mode. The developed method was tested for the system suitability: resolution, asymmetry factor, peak capacity, retention time repeatability and peak area repeatability. The method was fully validated in the terms of linearity (r² > 0.9990 for all 30 compounds), range (typically 1-100 mg L⁻¹), LOD, LOQ, inter/intra-day precision (<3% and <9% respectively) and inter/intra-day accuracy (typically 100 ± 10%). Subsequently the method was applied to the identification (spectral information and peak purity calculations were profited) and quantification of phenolic compounds and caffeine present in tea infusions and extracts.     

Nickel(II) N‐Benzyl‐N‐methyldithiocarbamato Complexes as Precursors for the Preparation of Graphite Oxidation Accelerators

The nickel(II) N‐benzyl‐N‐methyldithiocarbamato (BzMedtc) complexes [Ni(BzMedtc)(PPh₃)Cl] ( 1 ), [Ni(BzMedtc)(PPh₃)Br] ( 2 ), [Ni(BzMedtc)(PPh₃)I] ( 3 ), and [Ni(BzMedtc)(PPh₃)(NCS)] ( 4 ) were synthesized using the reaction of [Ni(BzMedtc)₂] and [NiX₂(PPh₃)₂] (X = Cl, Br, I and NCS). Subsequently, complex 1 was used for the preparation of [Ni(BzMedtc)(PPh₃)₂]ClO₄ ( 5 ), [Ni(BzMedtc)(PPh₃)₂]BPh₄ ( 6 ), and [Ni(BzMedtc)(PPh₃)₂]PF₆ ( 7 ). The obtained complexes 1 – 7 were characterized by elemental analysis, thermal analysis and spectroscopic methods (IR, UV/Vis, ³¹P{¹H} NMR). The results of the magnetochemical and molar conductivity measurements proved the complexes as diamagnetic non‐electrolytes ( 1 – 4 ) or 1:1 electrolytes ( 5 – 7 ). The molecular structures of 4 and 5· H₂O were determined by a single‐crystal X‐ray analysis. In all cases, the Ni^II atom is tetracoordinated in a distorted square‐planar arrangement with the S₂PX, and S₂P₂ donor set, respectively. The catalytic influence of selected complexes 1 , 3 , 5 , and 6 on graphite oxidation was studied. The results clearly indicated that the presence of the products of thermal degradation processes of the mentioned complexes has impact on the course of graphite oxidation. A decrease in the oxidation start temperatures by about 60–100 °C was observed in the cases of all the tested complexes in comparison with pure graphite.     

AC susceptibility of thin Pb films in intermediate and mixed state

Thin films of type I superconductors of a thickness comparable or less than a flux penetration length behave like type II superconductors in a mixed state. With decreasing film thickness normal domains carrying a magnetic flux get smaller with smaller number of flux quanta per domain and finally transform into single quantum flux lines, i.e. quantum vortices similar to those found in type II superconductors. We give an evidence of this behavior from the measurements of the nonlinear response of a total magnetic moment to an applied AC magnetic field, directly from the temperature dependence of an AC susceptibility.     

On R-linear convergence of semi-monotonic inexact augmented Lagrangians for saddle point problems

A variant of the inexact augmented Lagrangian algorithm called SMALE (Dostál in Comput. Optim. Appl. 38:47–59, 2007) for the solution of saddle point problems with a positive definite left upper block is studied. The algorithm SMALE-M presented here uses a fixed regularization parameter and controls the precision of the solution of auxiliary unconstrained problems by a multiple of the norm of the residual of the second block equation and a constant which is updated in order to enforce increase of the Lagrangian function. A nice feature of SMALE-M inherited from SMALE is its capability to find an approximate solution in a number of iterations that is bounded in terms of the extreme eigenvalues of the left upper block and does not depend on the off-diagonal blocks. Here we prove the R-linear rate of convergence of the outer loop of SMALE-M for any regularization parameter. The theory is illustrated by numerical experiments.     

Misfit‐Layered Bi1.85Sr2Co1.85O7.7−δ for the Hydrogen Evolution Reaction: Beyond van der Waals Heterostructures

Recent research on stable 2D nanomaterials has led to the discovery of new materials for energy‐conversion and energy‐storage applications. A class of layered heterostructures known as misfit‐layered chalcogenides consists of well‐defined atomic layers and has previously been applied as thermoelectric materials for use as high‐temperature thermoelectric batteries. The performance of such misfit‐layered chalcogenides in electrochemical applications, specifically the hydrogen evolution reaction, is currently unexplored. Herein, a misfit‐layered chalcogenide consisting of CoO₂ layers interleaved with an SrO–BiO–BiO–SrO rock‐salt block and having the formula Bi_1.85Sr₂Co_1.85O_7.7?δ is synthesized and examined for its structural and electrochemical properties. The hydrogen‐evolution performance of misfit‐layered Bi_1.85Sr₂Co_1.85O_7.7?δ, which has an overpotential of 589 mV and a Tafel slope of 51 mV per decade, demonstrates the promising potential of misfit‐layered chalcogenides as electrocatalysts instead of classical carbon.     

Iridium‐ and Osmium‐decorated Reduced Graphenes as Promising Catalysts for Hydrogen Evolution

Renewable energy sources are highly sought after as a result of numerous worldwide problems concerning the environment and the shortage of energy. Currently, the focus in the field is on the development of catalysts that are able to provide water splitting catalysis and energy storage for the hydrogen evolution reaction (HER). While platinum is an excellent material for HER catalysis, it is costly and rare. In this work, we investigated the electrocatalytic abilities of various graphene–metal hybrids to replace platinum for the HER. The graphene materials were doped with 4f metals, namely, iridium, osmium, platinum and rhenium, as well as 3d metals, namely, cobalt, iron and manganese. We discovered that a few hybrids, in particular iridium‐ and osmium‐doped graphenes, have the potential to become competent electrocatalysts owing to their low costs and—more importantly—to their promising electrochemical performances towards the HER. One of the more noteworthy observations of this work is the superiority of these two hybrids over MoS₂, a well‐known electrocatalyst for the HER.