Impedance spectroscopy of vanadium modified BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

In recent years a wide range of Aurivillius layered materials have been introduced. These novel materials are produced in many various forms such as fibers, thin films as well as bulk by using a number of processing routes. As advanced materials they are they have many interesting properties which include a number of useful electrical properties related to separated grain and grain boundary conductivity, impedance, activation energies, etc. In this paper these properties are described and discussed in detail. The electrical properties of the vanadium doped BaBi₂Nb₂O₉ ceramic was measured over a wide range of temperatures by impedance spectroscopy (IS). The separated grain activation energy, calculated from Arrhenius characteristics at temperatures between room temperature and 600 °C, was 1 eV for 0 at.% of vanadium dopant and 1.2 eV for 10 at.%, whereas the activation energies in the grain boundary region were 0.97 and 1.15 eV, respectively. The obtained results suggest the significant role of vanadium dopant, causing ordering the crystalline structure.     

Light‐Induced Water Splitting Causes High‐Amplitude Oscillation of pH‐Sensitive Layer‐by‐Layer Assemblies on TiO2

We introduce a simple concept of a light induced pH change, followed by high amplitude manipulation of the mechanical properties of an adjacent polymer film. Irradiation of a titania surface is known to cause water splitting, and this can be used to reduce the environmental pH to pH 4. The mechanical modulus of an adjacent pH sensitive polymer film can thus be changed by more than an order of magnitude. The changes can be localized, maintained for hours and repeated without material destruction.     

Synthesis,Isolation and Structure of Trifluoromethylated Fullerene D3‐C78, C78(1)(CF3)10−18

High‐temperature trifluoromethylation of fullerene C₇₈ followed by HPLC separation of C₇₈(CF₃)_n derivatives resulted in the isolation and X‐ray structural characterization of 15 compounds, that is, two C₇₈(1)(CF₃)₁₀, three C₇₈(1)(CF₃)₁₂, four C₇₈(1)(CF₃)₁₄, and five C₇₈(1)(CF₃)₁₆ isomers as well as one isomer of C₇₈(1)(CF₃)₁₈. The addition patterns of the C₇₈(1)(CF₃)_n molecules are discussed in terms of trifluoromethylation pathways and relative formation energies.     

New Anderson-Based Polyoxometalate Covalent Organic Frameworks as Electrodes for Energy Storage Boosted Through Keto-Enol Tautomerization

The unique electrochemical properties of polyoxometalates (POMs) render them ideal components for the fabrication of next-generation high-performance energy storage systems. However, their practical applications have been hindered by their high solubility in common electrolytes. This problem can be overcome by the effective hybridization of POMs with other materials. Here we present the design and synthesis of two novel polyoxometalate-covalent organic frameworks (POCOF) via one-pot solvothermal strategy between an amino-functionalized Anderson-type POM and a trialdehyde-based building unit. We show that structural and functional complexity can be enriched by adding hydroxyl groups in the 2,4,6 position to the benzene-1,3,5-tricarbaldehyde allowing to exploit for the first time in POCOFs the keto-enol tautomerization as additional feature to impart greater chemical stability to the COFs and enhanced properties leading to large specific surface area (347 m²/g) and superior electrochemical performance of the POCOF-1 electrodes, when compared with POCOF-2 electrodes that possess only imine-type linkage and with pristine POM electrodes. Specifically, POCOF-1 electrodes display remarkable specific, areal, and volumetric capacitance (125 F/g, 248 mF/cm² and 41.9 mF/cm³, respectively) at a current density of 0.5 A/g, a maximum energy density (56.2 Wh/kg), a maximum power density (3.7 kW/kg) and an outstanding cyclability (90 % capacitance retention after 5000 cycles).     

A Porous Crystalline Nitrone-Linked Covalent Organic Framework**

Herein, we report the synthesis of a nitrone-linked covalent organic framework, COF-115, by combining N, N′, N′, N′′′-(ethene-1, 1, 2, 2-tetrayltetrakis(benzene-4, 1-diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid-state ¹³C multi cross-polarization magic angle spinning NMR spectroscopy of the ¹³C-isotope-labeled COF-115 and Fourier-transform infrared spectroscopy. The permanent porosity of COF-115 was evaluated through low-pressure N₂, CO₂, and H₂ sorption experiments. Water vapor and carbon dioxide sorption analysis of COF-115 and the isoreticular imine-linked COF indicated a superior potential of N-oxide-based porous materials for atmospheric water harvesting and CO₂ capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF-115 to the associated amide-linked material was successfully demonstrated.     

Simple dimer containing dissociatively stable mono-imidazole ligated ferrohemes

In weakly coordinating solvents FeII meso-(N-methylimidazol-2-yl)porphine Fe exists as a stable dimer (Kd=50+/-30 nM) that binds ligands without undergoing dissociation and is presently the simplest complex in which the mono-imidazole ligation of a ferroheme is enforced without excess imidazole in solution.     

Near-infrared spectroscopy of natural alunites

Near-infrared spectroscopy (NIR) has been used to analyse alunites of formula K(Al3+)6(SO4)4(OH)12. Whilst the spectra of the alunites shows a common pattern differences in the spectra are observed which enable the minerals to be distinguished. These differences are attributed to subtle variations in alunite composition. The NIR bands in the 6300-7000 cm(-1) region are attributed to the first fundamental overtone of both the infrared and Raman hydroxyl stretching vibrations. A set of bands are observed in the 4700-5500 cm(-1) region which are assigned to combination bands of the hydroxyl stretching and deformation vibrations. NIR spectroscopy has the ability to distinguish between the alunite minerals even when the formula of the minerals is closely related. The NIR spectroscopic technique has great potential as a mineral exploratory tool on planets and in particular Mars.     

A thermogravimetric and infrared emission spectroscopic study of alunite

Thermogravimetric and differential thermogravimetric analysis has been used to characterize alunite of formula [K₂(Al³⁺)₆(SO₄)₄(OH)₁₂]. Thermal decomposition occurs in a series of steps (a) dehydration up to 225°C, (b) well defined dehydroxylation at 520°C and desulphation which takes place as a series of steps at 649, 685 and 744°C.The alunite minerals were further characterized by infrared emission spectroscopy (IES). Well defined hydroxyl stretching bands at around 3463 and 3449 cm^?1 are observed. At 550°C all intensity in these bands is lost in harmony with the thermal analysis results. OH stretching bands give calculated hydrogen bond distances of 2.90 and 2.84–7 Å. These hydrogen bond distances increase with increasing temperature. Characteristic (SO₄)^2? stretching modes are observed at 1029.5, 1086 and 1170 cm^?1. These bands shift to lower wavenumbers on thermal treatment. The intensity in these bands is lost by 550°C.     

CF3-Carbenoid functionalization of N-(pyrimidin-2-yl)indole catalyzed by cobalt complexes: Ligand control of selectivity

The carbonyl cobalt complex Cp*Co(CO)I₂ catalyzes carbenoid Co alkylation of N-(pyrimidin-2-yl)indole with methyl 3,3,3-trifluoro-2-diazopropionate regioselectively giving 2-substituted indole, while the N,N’-ligated cations [CpCo(L)I]⁺ (L = bipy, phen) provide 3-substitution exclusively. The structure of [CpCo(phen)I]PF₆ was investigated by X-ray diffraction.

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Diffusion in complementary pore spaces

The rate of mass transfer is among the key numbers determining the efficiency of nanoporous materials in their use for matter upgrading by heterogeneous catalysis or mass separation. Transport enhancement by pore space optimization is, correspondingly, among the main strategies of efficiency promotion. Any such activity involves probing and testing of the appropriate routes of material synthesis and post-synthesis modification just as the exploration of the transport characteristics of the generated material. Modelling and molecular simulation is known to serve as a most helpful tool for correlating these two types of activities and their results. The present paper reports about a concerted research activity comprising these three types of activities. Recent progress in producing pore space replicas enabled focusing, in these studies, on “complementary” pore spaces, i.e. on pairs of material, where the pore space of one sample did just coincide with the solid space of the other. We report about the correlations in mass transfer as observable, in this type of material, by pulsed field gradient NMR diffusion studies, with reference to the prediction as resulting from a quite general, theoretical treatment of mass transfer in complementary pore spaces.