Oxidation Behavior and Microstructural Evolution of ZrB2–35MoSi2–10Al Composite Coating

The problem of creating and implementing high-temperature coatings for the protection of carbon–carbon (C/C) composites remains relevant due to the extremely low or insufficient heat resistance of C/C composites in an oxygen-containing environment. In the present work, detonation spraying was used for preparing new ZrB2–35MoSi2–10Al coatings on the surface of C/C composites without a sublayer. As a stabilizer of high-temperature modification of zirconia, and to increase the wettability of the surface of C/C composites, 5 wt.% Y2O3 and 10 wt.% Al were added to the initial powder mixture, respectively. The structure of the as-sprayed coating presents many lamellae piled up one upon another, and is composed of hexagonal ZrB2 (h- ZrB2), tetragonal MoSi2 (t-MoSi2), monoclinic ZrO2 (m-ZrO2), tetragonal ZrO2 (t-ZrO2), monoclinic SiO2 (m-SiO2), and cubic Al phases. The oxidation behavior and microstructural evolution of the ZrB2–35MoSi2–10Al composite coating were characterized from RT to 1400 °C in open air. During oxidation at 1400 °C, a continuous layer of silicate glass was formed on the coating surface. This layer contained cubic ZrO2 (c-ZrO2), m-ZrO2, and small amounts of mullite and zircon. The results indicated that a new ZrB2–35MoSi2–10Al composite coating could be used on the surface of C/C composites as a protective layer from oxidation at elevated temperatures.

Molecular Dye-Sensitized Photocatalysis with Metal-Organic Framework and Metal Oxide Colloids for Fuel Production

Colloidal dye-sensitized photocatalysis is a promising route toward efficient solar fuel production by merging properties of catalysis, support, light absorption, and electron mediation in one. Metal-organic frameworks (MOFs) are host materials with modular building principles allowing scaffold property tailoring. Herein, we combine these two fields and compare porous Zr-based MOFs UiO-66-NH2(Zr) and UiO-66(Zr) to monoclinic ZrO2 as model colloid hosts with co-immobilized molecular carbon dioxide reduction photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and photosensitizer Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine). These host-guest systems demonstrate selective CO2-to-CO reduction in acetonitrile in presence of an electron donor under visible light irradiation, with turnover numbers (TONs) increasing from ZrO2, to UiO-66, and to UiO-66-NH2 in turn. This is attributed to MOF hosts facilitating electron hopping and enhanced CO2 uptake due to their innate porosity. Both of these phenomena are pronounced for UiO-66-NH2(Zr), yielding TONs of 450 which are 2.5 times higher than under MOF-free homogeneous conditions, highlighting synergistic effects between supramolecular photosystem components in dye-sensitized MOFs.

Translational dependence of the geometry of metallic mono- and bilayers optimized at semi-ionic supports. The cases of Pd at γ-Al2O3(110), monoclinic ZrO2(001), and rutile TiO2(001).

A simplified computational scheme for “deposition” of metallic (Pd) monolayer at semi-ionic supports is considered. An arbitrary selection of the initial position of the deposited layer relative to the surface...