An estimate of shape distribution of small CdS particles with luminescence spectra

The optical properties of CdS particles with different shapes are compared. The particles, characterized by spherical and rectangular shapes, were obtained with chemical and pounding methods, respectively. Then the particles were calibrated against their shapes. Obtained particles were investigated with the help of transmission electron microscopy, photoluminescence technique, and theoretical modeling. Absorption spectra were calculated via dissipative function in terms of local field approach. It was established that the comparison of experimental and theoretical results can give the additional information on particles, in particular, its shape and the shape distribution.     

Thermally Stable and Regenerable Platinum–Tin Clusters for Propane Dehydrogenation Prepared by Atom Trapping on Ceria

Ceria (CeO₂) supports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single-atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The single-atom Pt/CeO₂ catalysts are stable during propane dehydrogenation, but are not selective for propylene. DFT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions. In contrast, when tin (Sn) is added to CeO₂, the single-atom Pt catalyst undergoes an activation phase where it transforms into Pt–Sn clusters under reaction conditions. Formation of small Pt–Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO₂-supported Pt–Sn clusters are very stable, even during extended reaction at 680 °C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore, upon oxidation the Pt–Sn clusters readily revert to the atomically dispersed species on CeO₂, making Pt–Sn/CeO₂ a fully regenerable catalyst.     

New aspects of the low-concentrated aniline polymerization in the solution and in SiC nanocrystals dispersion

Results of the simultaneous in-situ UV-vis and open-circuit potential (OCP) monitoring of the low-concentrated aniline (An) polymerization in the presence of camphorsulfonic acid (CSA) suggested that during the induction period (IP) step a transition state formed, which probably included anilinium cation and the oxidant anion, antecedent to a propagation step. No aniline oligomers were registered at this stage but they appeared at the beginning of the propagation step under the investigation conditions. The moments of formation of insoluble pernigraniline phase and appearance of emeraldine units in the growing pernigraniline chains were ascertained by the comparison of kinetic and OCP profiles of the polymerization process both in the solution and in SiC dispersion water mediums. It is deduced that pernigraniline reduction by aniline molecules begins earlier than it is generally accepted (i.e., earlier than OCP maximum is reached) and probably in parallel to a continuing appearance of pernigraniline units even in the same chains that undergo the reduction. It was found that an addition of the SiC dispersion phase into the polymerization mixture accelerates differently all stages of the aniline polymerization. Finally, this polymerization process leads to the formation of polyaniline (PANI)-CSA shell with thickness in the range from 0.5 nm to a few nm at the SiC nanocrystals surface.     

Modified Isoindolediones as Bright Fluorescent Probes for Cell and Tissue Imaging

New L -shaped fluorophores possessing five conjugated rings have been synthesized through a four-step procedure involving diketopyrrolopyrrole synthesis and its double N-alkylation, followed by trimethylsilyl bromide-mediated rearrangement to thieno[2,3-f]isoindole-5,8-dione and an intramolecular Friedel–Crafts reaction. In comparison with the parent isoindolediones and π-expanded diketopyrrolopyrroles, these new dyes show red-shifted absorption and emission (up to ≈630 nm). Their structural rigidity is responsible for both the observed small Stokes shifts and large fluorescence quantum yields. Tissue imaging studies revealed that these new dyes show advantageous features including minimal autofluorescence interference and pronounced solvent-sensitive emission. Interestingly, there is a fundamental difference between a dye possessing an amino group and its analog bearing an N-alkyl substituent. The former dye under two-photon excitation at 900 nm gives bright images whereas its N-alkylated counterpart does not. A new type of membrane localization has been discovered by an N-alkylated isoindoledione possessing a benzofuryl substituent. In spite of the fact that the fluorescence quantum yield of this dye in a range of solvents is rather low, it does stain cell membranes exclusively. This new mode of cellular staining opens the door towards further development of membrane staining dyes.     

Influence of Nanoparticle Processing on the Thermoelectric Properties of (BixSb1−X)2Te3 Ternary Alloys

The synthesis of phase-pure ternary solutions of tetradymite-type materials (Bi_xSb_1−x)₂Te₃ (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties - Seebeck coefficient as well as electrical and thermal conductivity - is demonstrated.     

Model Identification for Flow Simulations in Geothermal Reservoirs: Towards Optimally Drilling Boreholes

In geothermal reservoir engineering, one is interested in determining the location of boreholes such that measurements taken therein, say temperature, will allow the estimation of unknown parameters such as porosity and permeability. We formulate such a particular borehole location problem and find its solution by techniques from optimal experimental design. More precisely, we minimize the D-optimality criterion to find an optimal location of a single borehole to estimate hydraulic permeability from temperature measurements in two boreholes. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

K2M(III)2(M(VI)O4)(PO4)2 (M(III) = Fe, Sc; M(VI) = Mo, W), novel members of the lagbeinite-related family: synthesis, structure, and magnetic properties

The possibility of PO(4)(3-) for MoO(4)(2-) partial substitution in the langbeinite framework has been studied by exploration of the K-Fe(Sc)-Mo(W)-P-O systems using the high-temperature solution method. It was shown that 1/3PO(4)(3-) for MoO(4)(2-) substitution leads to formation of three novel compounds K(2)Fe(MoO(4))(PO(4))(2), K(2)Sc(MoO(4))(PO(4))(2), and K(2)Sc(WO(4))(PO(4))(2) with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations.     

Structure and magnetic properties of AgFeP2O7

AgFeP₂O₇ has been synthesized by flux crystallization and characterized by single crystal and powder X-ray diffraction (sp. gr. P2₁/c, a=7.3298(2), b=7.9702(2), c=9.5653(2) Å, β=111.842(1)°, V=518.68(2) Å³) and FTIR-spectroscopy. The structure is composed of isolated iron octahedra and phosphate tetrahedra interconnected into 3D network with hexagonal channels, where silver counter-ions are located. The magnetic behavior of the compound approaches the Curie-Weiss equation with a Weiss constant θ=−165.9 K indicating strong antiferromagnetic interaction between iron(III) ions.     

Platinum group metal-free oxygen reduction electrocatalysts used in neutral electrolytes for bioelectrochemical reactor applications

The oxygen reduction reaction is one of the limiting steps in microbial fuel cell performance. M–N–C catalysts (M as transition metal) represent the best compromise of optimal cost, electrocatalytic activity and durability. The Fe-based catalysts were shown to be the best compared with Co-, Mn-, Ni-based catalysts. The addition of the second transition metal such as Mn was shown to increase the selectivity of the reaction and reduce peroxide production. The use of different N–C precursors resulted in diverse surface chemistry that directly affects the performance. Generally, surface chemistry plays a critical role in the electrocatalytic activity. Integration of the catalyst in the air-breathing cathode is also discussed with a performance that is enhanced by: (i) increased catalyst loading; (ii) the addition of graphene to structure.