FT-IR and FT-FIR studies of vanadium,molybdenum and tungsten oxides supported on different carriers

In the far IR region at low molybdenum loadings, Mo-SiO₂ catalysts present a pseudomolybdate or a polymolybdate species, while bulk-like MoO₃ appears at loadings close to the geometrical monolayer coverage. W-SiO₂ and V-SiO₂ spectra show bands close to those observed on the corresponding bulk oxides.In the case of TiO₂, Al₂O₃, ZrO₂ supported catalysts, a band is observed near 1000 cm^–1 which is assigned to the Mo=O stretching vibration of coordinatively unsaturated Mo ⁿ⁺ ions showing a stronger interaction with the support than one observed on silica.     

Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO₃)₂·6H₂O and Si(OC₂H₅)₄ using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N₂ adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co²⁺ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co²⁺ tetrahedral complexes, while at higher cobalt loading Co₃O₄ was present as the only crystalline phase, besides Co²⁺ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co₂SiO₄ was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.     

Surface oxidation of high-surface-area silicon carbide: FT-IR studies

The surface of ultrafine silicon carbide powders, prepared by a laser-driven gas-phase reaction was studied as a self-supporting disk by FT infrared spectrometry. After evacuation silicon and carbon atoms located at the surface give rise tovSiH andvCH bands. When heating in oxygen, subtraction spectra showed features which could be strictly correlated with a progressive growth of a silica layer: SiH and CH bands were replaced by new bands characteristic of amorphous silica and the typical band of surface silanol groups on silica (3745 cm^–1) simultaneously increased.     

Mesoporous α-Fe(2)O(3) thin films synthesized via the sol-gel process for light-driven water oxidation

This work reports a facile and cost-effective method for synthesizing photoactive α-Fe(2)O(3) films as well as their performances when used as photoanodes for water oxidation. Transparent α-Fe(2)O(3) mesoporous films were fabricated by template-directed sol-gel chemistry coupled with the dip-coating approach, followed by annealing at various temperatures from 350 °C to 750 °C in air. α-Fe(2)O(3) films were characterized by X-ray diffraction, XPS, FE-SEM and electrochemical measurements. The photoelectrochemical performance of α-Fe(2)O(3) photoanodes was characterized and optimized through the deposition of Co-based co-catalysts via different methods (impregnation, electro-deposition and photo-electro-deposition). Interestingly, the resulting hematite films heat-treated at relatively low temperature (500 °C), and therefore devoid of any extrinsic dopant, achieve light-driven water oxidation under near-to-neutral (pH = 8) aqueous conditions after decoration with a Co catalyst. The onset potential is 0.75 V vs. the reversible hydrogen electrode (RHE), thus corresponding to 450 mV light-induced underpotential, although modest photocurrent density values (40 μA cm(-2)) are obtained below 1.23 V vs. RHE. These new materials with a very large interfacial area in contact with the electrolyte and allowing for a high loading of water oxidation catalysts open new avenues for the optimization of photo-electrochemical water splitting.     

Covariant formulation of BPS black holes and the scalar weak gravity conjecture

We find through a systematic analysis that all but 29,223 of the 473.8 million 4D reflexive polytopes found by Kreuzer and Skarke have a 2D reflexive subpolytope. Such a subpolytope is generally associated with the presence of an elliptic or genus one fibration in the corresponding birational equivalence class of Calabi-Yau threefolds. This extends the growing body of evidence that most Calabi-Yau threefolds have an elliptically fibered phase.     

A genetic toolbox for creating reversible Ca2+-sensitive materials

A major goal of polymer science is to develop "smart" materials that sense specific chemical signals in complex environments and respond with predictable changes in their mechanical properties. Here, we describe a genetic toolbox of natural and engineered protein modules that can be rationally combined in manifold ways to create reversible self-assembling materials that vary in their composition, architecture, and mechanical properties. Using this toolbox, we produced several materials that reversibly self-assemble in the presence of Ca2+ and characterized these materials using particle-tracking microrheology. The properties of these materials could be predicted from the dilute solution behavior of their component modules, suggesting that this toolbox may be generally useful for creating new stimuli-sensitive materials.     

First order flows for N=2 extremal black holes and duality invariants

We derive explicitly the superpotential W for the non-BPS branch of $N=2$ extremal black holes in terms of duality invariants of special geometry. Although this is done for a one-modulus case (the $t^3$ model), the example gives $Z\ne 0$ black holes and captures the basic distinction from previous attempts on the quadratic series (vanishing C tensor) and from the other $Z=0$ cases. The superpotential W turns out to be a non-polynomial expression (containing radicals) of the basic duality invariant quantities. These are the same which enter in the quartic invariant $I_4$ for $N=2$ theories based on symmetric spaces. Using the flow equations generated by W, we also provide the analytic general solution for the warp factor and for the scalar field supporting the non-BPS black holes.