Halide Perovskite-Derived Compounds Rb2TeX6 (X = Cl, Br, and I): Electronic Structure of the Ground and First Excited States.

Herein, we report a study of the electronic structure of the ground and first excited states of Rb2TeCl6, Rb2TeBr6, and Rb2TeI6 halide-perovskite-derived crystals. Using X-ray photoelectron spectroscopy (XPS) measurements and density functional theory and multiconfiguration self-consistent field (MCSCF) calculations, the experimental and theoretical XPS spectra of the valence region were obtained. In addition, the effects of the cations and halogen atoms on the electronic structure were determined, and the classification of the excited states in double point group representation was carried out. Furthermore, a possible reason for the luminescence quenching in an isostructural series of crystals containing the [TeI6]2- anions was determined.

The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice.

Sustained release of methane (CH(4)) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH(4) from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH(4) emissions from this shelf are likely to be determined by the state of subsea permafrost degradation. We observed CH(4) emissions from two previously understudied areas of the ESAS: the outer shelf, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH(4) emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in ice extent could result in a significant increase in CH(4) emissions from the ESAS.

Enhancing Lithium and Sodium Storage Properties of TiO2(B) Nanobelts by Doping with Nickel and Zinc.

Nickel- and zinc-doped TiO2(B) nanobelts were synthesized using a hydrothermal technique. It was found that the incorporation of 5 at.% Ni into bronze TiO2 expanded the unit cell by 4%. Furthermore, Ni dopant induced the 3d energy levels within TiO2(B) band structure and oxygen defects, narrowing the band gap from 3.28 eV (undoped) to 2.70 eV. Oppositely, Zn entered restrictedly into TiO2(B), but nonetheless, improves its electronic properties (Eg is narrowed to 3.21 eV). The conductivity of nickel- (2.24 × 10-8 S·cm-1) and zinc-containing (3.29 × 10-9 S·cm-1) TiO2(B) exceeds that of unmodified TiO2(B) (1.05 × 10-10 S·cm-1). When tested for electrochemical storage, nickel-doped mesoporous TiO2(B) nanobelts exhibited improved electrochemical performance. For lithium batteries, a reversible capacity of 173 mAh·g-1 was reached after 100 cycles at the current load of 50 mA·g-1, whereas, for unmodified and Zn-doped samples, around 140 and 151 mAh·g-1 was obtained. Moreover, Ni doping enhanced the rate capability of TiO2(B) nanobelts (104 mAh·g-1 at a current density of 1.8 A·g-1). In terms of sodium storage, nickel-doped TiO2(B) nanobelts exhibited improved cycling with a stabilized reversible capacity of 97 mAh·g-1 over 50 cycles at the current load of 35 mA·g-1.

Effect of Hf-doping on electrochemical performance of anatase TiO2 as an anode material for lithium storage.

Hafnium-doped titania (Hf/Ti = 0.01; 0.03; 0.05) had been facilely synthesized via a template sol-gel method on carbon fibre. Physico-chemical properties of the as-synthesized materials were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry analysis and Brunauer-Emmett-Teller measurements. It was confirmed that Hf4+ substitute in the Ti4+ sites, forming Ti1-x Hf x O2 (x = 0.01; 0.03; 0.05) solid solutions with an anatase crystal structure. The Ti1-x Hf x O2 materials are hollow microtubes (length of 10-100 µm, outer diameter of 1-5 µm) composed of nanoparticles (average size of 15-20 nm) with a surface area of 80-90 m2 g-1 and pore volume of 0.294-0.372 cm3 g-1. The effect of Hf ion incorporation on the electrochemical behaviour of anatase TiO2 in the Li-ion battery anode was investigated by galvanostatic charge/discharge and electrochemical impedance spectroscopy. It was established that Ti0.95Hf0.05O2 shows significantly higher reversibility (154.2 mAh g-1) after 35-fold cycling at a C/10 rate in comparison with undoped titania (55.9 mAh g-1). The better performance offered by Hf4+ substitution of the Ti4+ into anatase TiO2 mainly results from a more open crystal structure, which has been achieved via the difference in ionic radius values of Ti4+ (0.604 Å) and Hf4+ (0.71 Å). The obtained results are in good accord with those for anatase TiO2 doped with Zr4+ (0.72 Å), published earlier. Furthermore, improved electrical conductivity of Hf-doped anatase TiO2 materials owing to charge redistribution in the lattice and enhanced interfacial lithium storage owing to increased surface area directly depending on the Hf/Ti atomic ratio have a beneficial effect on electrochemical properties.

Current rates and mechanisms of subsea permafrost degradation in the East Siberian Arctic Shelf.

The rates of subsea permafrost degradation and occurrence of gas-migration pathways are key factors controlling the East Siberian Arctic Shelf (ESAS) methane (CH4) emissions, yet these factors still require assessment. It is thought that after inundation, permafrost-degradation rates would decrease over time and submerged thaw-lake taliks would freeze; therefore, no CH4 release would occur for millennia. Here we present results of the first comprehensive scientific re-drilling to show that subsea permafrost in the near-shore zone of the ESAS has a downward movement of the ice-bonded permafrost table of ∼14 cm year-1 over the past 31-32 years. Our data reveal polygonal thermokarst patterns on the seafloor and gas-migration associated with submerged taliks, ice scouring and pockmarks. Knowing the rate and mechanisms of subsea permafrost degradation is a prerequisite to meaningful predictions of near-future CH4 release in the Arctic.

Colloid stable sorbents for cesium removal: preparation and application of latex particles functionalized with transition metals ferrocyanides.

In this paper we suggest a principally new approach to preparation of colloid stable selective sorbents for cesium uptake using immobilization of transition metals (cobalt, nickel, and copper) ferrocyanides in nanosized carboxylic latex emulsions. The effects of ferrocyanide composition, pH, and media salinity on the sorption properties of the colloid stable sorbents toward cesium ions were studied in solutions containing up to 200 g/L of sodium nitrate or potassium chloride. The sorption capacities of the colloid sorbents based on mixed potassium/transition metals ferrocyanides were in the range 1.3-1.5 mol Cs/mol ferrocyanide with the highest value found for the copper ferrocyanide. It was shown that the obtained colloid-stable sorbents were capable to penetrate through bulk materials without filtration that made them applicable for decontamination of solids, e.g. soils, zeolites, spent ion-exchange resins contaminated with cesium radionuclides. After decontamination of liquid or solid radioactive wastes the colloid-stable sorbents can be easily separated from solutions by precipitation with cationic flocculants providing localization of radionuclides in a small volume of the precipitates formed.