Signatures of non-monotonic d-wave gap in electron-doped cuprates

We address the issue whether the data on optical conductivity and Raman scattering in electron-doped cuprates below $T_c$ support the idea that the $d-$wave gap in these materials is non-monotonic along the Fermi surface. We calculate the conductivity and Raman intensity for elastic scattering, and find that a non-monotonic gap gives rise to several specific features in optical and Raman response functions. We argue that all these features are present in the experimental data on Nd$_{2-x}$Ce$_{x}$CuO$_4$ and Pr$_{2-x}$Ce$_{x}$CuO$_4$ compounds.Comment: 7 pages, 6 figure

Mössbauer study of nanodimensional nickel ferrite-mechanochemical synthesis and catalytic properties

Iron-nickel spinel oxide NiFe2O4 nanoparticles have been prepared by the combination of chemical precipitation and subsequent mechanical milling. For comparison, their analogue obtained by thermal synthesis is also studied. Phase composition and structural properties of iron-nickel oxides are investigated by X-ray diffraction and Mössbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. An influence of the preparation method on the reduction and catalytic properties of iron-nickel samples is established

Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni1-xZnxFe2O4 (x ¼ 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium

Condensation energy in Eliashberg theory -- from weak to strong coupling

We consider two issues related to the condensation energy in superconductors described by the Eliashberg theory for various forms of the pairing interaction, associated either with phonon or electronic mechanisms of superconductivity. First, we derive a leading correction to the BCS formula for the condensation energy to first order in the coupling $\lambda$. Second, we show that at a given $\lambda$, the value of the condensation energy strongly depends on the functional form of the effective pairing interaction $\Gamma (\omega)$.Comment: 6 pages, 5 figures, published in PRB; missing reference has been adde

Heterogeneous Catalysis through Microcontact Printing

Here, we investigate four different chemical pathways (Scheme 1a–d) relevant to the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction.[13] Three of those pathways lead to surfaces functionalized with organic molecules.[5, 11, 14] At the outset, our practical goal was to identify surface-functionalization protocols that are capable of attaining 1) spatial selectivity, 2) high surface coverage, and 3) rapid reaction kinetics. Our ultimate goal is to achieve a fundamental understanding of how different reaction pathways influence the chemical outcome as it applies to the organic functionalization of surfaces

Catalytic VOCs elimination over copper and cerium oxide modified mesoporous SBA-15 silica

[EN] Copper and cerium oxide bi-component materials with different Cu/Ce ratio were prepared using ordered SBA-15 silica as a support and compared with their bulk analogs. The samples were characterized by nitrogen physisorption, XRD, UV-Vis, FTIR, XPS, Raman spectroscopy and TPR with hydrogen. Cyclohexanol conversion was used as a catalytic test to obtain more information for the surface properties of the supported materials. The catalytic properties of the samples were studied in VOCs oxidation using toluene and ethyl acetate as probe molecules. A strong effect of mesoporous silica support and samples composition on the formation of catalytic sites was established. (C) 2012 Elsevier B.V. All rights reserved.Financial support of Bulgarian Academy of Science and National Scientific Fond of Ministry of Education Projects DTK 02/64 and ДНTC/Киtай 01/8, financial support from DGICYT in Spain (Project CTQ-2009-14495) and bilateral project Bulgarian-Spain Inter-academic Exchange Agreement (Project 2009BG0002) are acknowledged.Tsoncheva, T.; Issa, G.; Blasco Lanzuela, T.; Dimitrov, M.; Popova, M.; Hernández Morejudo, S.; Kovacheva, D.... (2013). Catalytic VOCs elimination over copper and cerium oxide modified mesoporous SBA-15 silica. Applied Catalysis A General. 453:1-12. https://doi.org/10.1016/j.apcata.2012.12.007S11245

Nanosized iron and iron–cobalt spinel oxides as catalysts for methanol decomposition

Nanosized iron and mixed iron–cobalt oxides supported on activated carbon materials and their bulk analogues prepared by thermal synthesis are studied by X-rays diffraction, Mo¨ssbauer spectroscopy, magnetic measurements and temperature programmed reduction. Their catalytic behavior in methanol decomposition to H2, CO and methane is tested. Phase transformations in the metal oxides affected by the reaction medium are also investigated. Changes in the reaction mechanism of the methanol decomposition after the metal oxides deposition on the support as compared to the bulk phases are discussed

Activated Carbon Modified with Copper for Adsorption of Propanethiol

Activated carbons were characterized texturally and chemically before and after treatment, using surface area determination in the BET model, Boehm titration, TPR, DRX and immersion calorimetry. The adsorption capacity and the kinetics of sulphur compound removal were determined by gas chromatography. It was established that the propanethiol retention capacity is dependent on the number of oxygenated groups generated on the activated carbon surface and that activated carbon modified with CuO at 0.25 M shows the highest retention of propanethiol. Additionally is proposed a mechanism of decomposition of propenothiol with carbon-copper system

H5PW10V2O40@VOx/SBA-15-NH2 catalyst for the solventless synthesis of 3-substituted indoles

Functionalization of mesoporous SBA-15 frameworks by transition metal oxides offers a flexible route to fabricate new heterogeneous catalysts. Here, an inorganic-organic hybrid nanoporous catalyst H5PW10V2O40@VOx/SBA-15-NH2, was prepared and utilized as an efficient, eco-friendly, and recyclable catalyst for the one-pot, multi-component synthesis of 3-substituted indoles by indole substitution with aldehydes and malononitrile under solvent-free conditions. Catalysts were prepared by the non-covalent attachment of H5PW10V2O40 to a 3 wt%VOx/SBA-15 nanoporous support through a 3-(triethoxysilyl)propylamine linker. VOx/SBA-15 was prepared by a one-pot hydrothermal synthesis from TEOS and vanadium(V) oxytri-tert-butoxide [VO(O-tBu)3]. The resulting H5PW10V2O40@VOx/SBA-15-NH2 material was characterized by bulk and surface analysis including N2 porosimetry, FE-SEM, XRD, XPS, FT-IR, TGA-DTA, UV–Vis and ICP-OES, evidencing retention of the heteropolyacid Keggin structure. H5PW10V2O40@VOx/SBA-15-NH2 exhibits high activity and excellent yields (70–95%) of 3-substituted indoles under mild conditions, with negligible deactivation