Tailoring Disorder and Dimensionality: Strategies for Improved Solid Oxide Fuel Cell Electrolytes

Towards cooler solid oxide fuel cells: Disorder and dimensionality (see picture) play an important role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity.

     

Non‐Covalent Interactions in Supramolecular Assemblies Investigated with Electron Spectroscopies

A new view: A picture of the different non‐covalent interactions relevant for the self‐assembly of organic layers and their spectroscopic fingerprints is provided (see figure). In particular, state‐of‐the‐art spectroscopic measurements are performed for supramolecular assemblies, comparing the electronic structure of single‐component layers with that of binary organic layers.

     

A note on semiextensions of stable circuits

A semiextension of a circuit C in a graph G provides a possible means of finding a cycle double cover of G with C as a prescribed circuit. Recently we conjectured [E.E. García Moreno, T.R. Jensen, On semiextensions and circuit double covers, J. Combin. Theory Ser. B 97 (2007) 474-482] that if G is cubic and 2-edge-connected, then a semiextension of C in G exists. If true, this would imply several long-standing conjectures.If there is a circuit C^′ in G with C^′≠C and V(C)⊆V(C^′), then C^′ is called an extension of C, a special case of a semiextension. If there is no such circuit, then C is said to be stable in G. Hence the existence question for semiextensions is easy except for stable circuits. Not many examples of graphs with stable circuits have been published. In this note we show that the members of a particular class of stable circuits described by M. Kochol have semiextensions.     

Isolation and Screening of Microorganisms for R-(+)-Limonene and (−)-β-Pinene Biotransformation

This work is focused on the biotransformation of R-(+)-limonene and (?)-β-pinene to bioflavor production. To carry out the present study, 405 microorganisms were tested for their ability to bioconvert the substrates. From the isolated microorganisms, 193 were selected in the prescreening using mineral medium for limonene degradation. At the screening step, eight strains were able to convert R-(+)-limonene and 15 to transform (?)-β-pinene, both in α-terpineol. The highest concentration in α-terpineol from R-(+)-limonene was about 3,450 mg/L for Penicillium sp. isolated from eucalyptus steam. From (?)-β-pinene, the highest product concentration of 675.5 mg/L was achieved using an Aspergillus sp. strain isolated from orange tree stem.     

Porous phosphate heterostructures containing CdS quantum dots: assembly, characterization and photoluminescence

The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption–desorption analysis by N₂ at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups.     

Vanadium oxide-porous phosphate heterostructure catalysts for the selective oxidation of H2S to sulphur

Vanadium oxide–containing mesoporous materials, based on a surfactant expanded zirconium phosphate with silica galleries into the interlayer space, named porous phosphate heterostructure (PPH), were prepared by using TEOS and vanadium oxytripropoxide in n-propanol as sources of Si and V, respectively; with different Si/V molar ratios of 1, 2, 5 and 25; and calcining at 550 °C for 6 h. Using this method, vanadium can be partially incorporated to the structure of the gallery, but the surface area strongly decreases and the appearance of V₂O₅ crystallites increases when increasing the vanadium content. The catalysts were characterized by XRD, XPS, TEM, and Raman, and tested in the selective catalytic oxidation of H₂S using a fixed bed reactor, at atmospheric pressure, at 180–260 °C. The catalysts with high contents of vanadium are very active at 200 °C, showing H₂S conversions of 85–99%, with a high selectivity to elemental sulphur and with a low formation of SO₂. Accordingly V₂O₅ crystallites can be proposed as active and selective although the catalytic behavior is related to the number of accessible V-sites in the surface of the catalyst.     

The thioantimonate anion [Sb4S8]4− acting as a tetradentate ligand: Solvothermal synthesis,crystal structure and properties of {[In(C6H14N2)2]2Sb4S8}Cl2 exhibiting unusual uniaxial negative and biaxial positive thermal expansion

The new compound {[In(C₆H₁₄N₂)₂]₂Sb₄S₈}Cl₂ was prepared under solvothermal conditions reacting InCl₃, Sb and S using 1,2-trans-diaminocyclohexane as solvent and structure directing molecule. The compound crystallizes in the monoclinic space group C2/c with a = 29.0259(12), b = 6.7896(2), c = 24.2023(12) Å, β = 99.524(4)°, V = 4703.9(3) ų. The central structural motif is the thioantimonate(III) anion [Sb₄S₈]^4? acting as a tetradentate ligand thus joining two symmetry related In³⁺ centered complexes. This binding mode was never observed before for the [Sb₄S₈]^4? anion. The optical band gap was determined as 2.03 eV in agreement with the red color of the compound. The thermal decomposition was monitored with in-situ X-ray diffraction experiments. After the emission of the amine molecules an amorphous intermediate is formed followed by the crystallization of InSbS₃ which is stable up to about 590 °C. On further heating, InSbS₃ is destroyed and reflections of γ-In₂S₃ appear being contaminated with some elemental Sb. Temperature dependent in-situ X-ray powder diffractometry performed between 30 and 220 °C reveals an unusual reversible negative and positive thermal expansion. The decrease of the a-axis in the temperature range is about 0.74 Å and the increase of the c-axis ca. 0.54 Å. Interestingly, the b-axis exhibits also a thermal expansion, i.e., a biaxial positive and an uniaxial negative thermal expansion coexist which is very unusual. The relative negative expansion coefficients for the a-axis of ?194 × 10^?6K^?1 (30–120 °C) and ?82 × 10^?6K^?1 (120–220 °C) are in the region of so-called colossal thermal expansion.     

Uranium(VI) bis(imido) disulfonamide and dihalide complexes: Synthesis density functional theory analysis

Novel cis- and trans-bis(imido) uranium disulfonamide derivatives have been prepared from iodide metathesis reactions between two equivalents of K[N(Me)(SO₂Ar’)] (Ar’ = 4-Me-C₆H₄) and U(N^tBu)₂(I)₂(L)_x (L = OPPh₃, x = 2; Me₂bpy, x = 1; Me₂bpy = 4,4’-dimethyl-2,2’-bipyridyl). These bis(amide) derivatives serve as useful precursors for the synthesis of the trans-diphenolate complex U(N^tBu)₂(O-2-^tBuC₆H₄)₂(OPPh₃)₂ (5), cis- and trans-dithiolate complexes U(N^tBu)₂(SPh)₂(L)_x (L = OPPh₃ (6); Me₂bpy (7)), and cis- and trans-dihalide complexes with the general formulas U(N^tBu)₂(X)₂(L)_x (X = Cl, L = OPPh₃ (8), L = Me₂bpy (10); X = Br, L = OPPh₃ (9), L = Me₂bpy (11)). DFT calculations performed on the trans-dihalide series U(N^tBu)₂(X)₂(L)₂ and the UO₂²⁺ analogues UO₂X₂(OPPh₃)₂ suggest that the uranium centers in the [U(N^tBu)₂]²⁺ ions possess more covalent character than analogous UO₂²⁺ derivatives but that the U-X bonds in the U(N^tBu)₂X₂L₂ complexes possess a more ionic nature.