ABSTRACT
Thin-film nanocrystalline hematite electrodes were fabricated by electrochemical deposition and loaded with electrodeposited zinc oxide in various amounts. Under visible light illumination, these electrodes demonstrate high activity in the photoelectrochemical degradation of methanol, ethylene glycol and, in particular, glycerol. Results of intensity-modulated photocurrent spectroscopy show that the photoelectrocatalysis efficiency is explained by the suppression of the electron-hole pair recombination and an increase in the rate of photo-induced charge transfer. Thus, zinc oxide can be considered an effective modifying additive for hematite photoanodes.
Subject(s)
Zinc Oxide , Motion Pictures , Electrodes , ElectronsABSTRACT
In recent years, cryoconite has received growing attention from a radioecological point of view, since several studies have shown that this material is extremely efficient in accumulating natural and anthropogenic radionuclides. The Novaya Zemlya Archipelago (Russian Arctic) hosts the second largest glacial system in the Arctic. From 1957 to 1962, numerous atmospheric nuclear explosions were conducted at Novaya Zemlya, but to date, very little is known about the radioecology of its ice cap. Analysis of radionuclides and other chemical elements in cryoconite holes on Nalli Glacier reveals the presence of two main zones at different altitudes that present different radiological features. The first zone is 130-210 m above sea level (a.s.l.), has low radioactivity, high concentrations of lithophile elements and a chalcophile content close to that of upper continental crust clarkes. The second zone (220-370 m a.s.l.) is characterized by high activity levels of radionuclides and "inversion" of geochemical behaviour with lower concentrations of lithophiles and higher chalcophiles. In the upper part of this zone (350-370 m a.s.l.), 137Cs activity reaches the record levels for Arctic cryoconite (5700-8100 Bq/kg). High levels of Sn, Sb, Bi and Ag, significantly exceeding those of upper continental crust clarkes, also appear here. We suggest that a buried layer of contaminated ice that formed during atmospheric nuclear tests serves as a local secondary source of radionuclide contamination. Its melting is responsible for the formation of this zone.
ABSTRACT
The occurrence of moissanite (SiC), as xenocrysts in mantle-derived basaltic and kimberlitic rocks sheds light on the interplay between carbon, hydrogen and oxygen in the lithospheric and sublithospheric mantle. SiC is stable only at ƒO2 < ΔIW-6, while the lithospheric mantle and related melts commonly are considered to be much more oxidized. SiC grains from both basaltic volcanoclastic rocks and kimberlites contain metallic inclusions whose shapes suggest they were entrapped as melts. The inclusions consist of Si0 + Fe3Si7 ± FeSi2Ti ± CaSi2Al2 ± FeSi2Al3 ± CaSi2, and some of the phases show euhedral shapes toward Si0. Crystallographically-oriented cavities are common in SiC, suggesting the former presence of volatile phase(s), and the volatiles extracted from crushed SiC grains contain H2 + CH4 ± CO2 ± CO. Our observations suggest that SiC crystalized from metallic melts (Si-Fe-Ti-C ± Al ± Ca), with dissolved H2 + CH4 ± CO2 ± CO derived from the sublithospheric mantle and concentrated around interfaces such as the lithosphere-asthenosphere and crust-mantle boundaries. When mafic/ultramafic magmas are continuously fluxed with H2 + CH4 they can be progressively reduced, to a point where silicide melts become immiscible, and crystallize phases such as SiC. The occurrence of SiC in explosive volcanic rocks from different tectonic settings indicates that the delivery of H2 + CH4 from depth may commonly accompany explosive volcanism and modify the redox condition of some lithospheric mantle volumes. The heterogeneity of redox states further influences geochemical reactions such as melting and geophysical properties such as seismic velocity and the viscosity of mantle rocks.
ABSTRACT
A combined synchrotron X-ray diffraction, Raman scattering, and infrared spectroscopy study of the pressure-induced changes in H(3)BO(3) to 10 GPa revealed a new high-pressure phase transition between 1 and 2 GPa followed by chemical decomposition into cubic HBO(2), ice-VI, and ice- VII at approximately 2GPa. The layered triclinic structure of H(3)BO(3) exhibits a highly anisotropic compression with maximum compression along the c direction, accompanied by a strong reduction of the interlayer spacing. The large volume variation and structural changes accompanying the decomposition suggest high activation energy. This yields a slow reaction kinetics at room temperature and a phase composition that is highly dependent on the specific pressure-time path followed by the sample. The combined results have been used to propose a mechanism for pressure-induced dehydration of H(3)BO(3) that implies a proton disorder in the system.
