Visible light photo-oxidation of model pollutants using CaCu3Ti4O12: an experimental and theoretical study of optical properties, electronic structure, and selectivity

Charge transfer between metal ions occupying distinct crystallographic sublattices in an ordered material is a strategy to confer visible light absorption on complex oxides to generate potentially catalytically active electron and hole charge carriers. CaCu3Ti4O12 has distinct octahedral Ti4+ and square planar Cu2+ sites and is thus a candidate material for this approach. The sol?gel synthesis of high surface area CaCu3Ti4O12 and investigation of its optical absorption and photocatalytic reactivity with model pollutants are reported. Two gaps of 2.21 and 1.39 eV are observed in the visible region. These absorptions are explained by LSDA+U electronic structure calculations, including electron correlation on the Cu sites, as arising from transitions from a Cu-hybridized O 2p-derived valence band to localized empty states on Cu (attributed to the isolation of CuO4 units within the structure of CaCu3Ti4O12) and to a Ti-based conduction band. The resulting charge carriers produce selective visible light photodegradation of 4-chlorophenol (monitored by mass spectrometry) by Pt-loaded CaCu3Ti4O12 which is attributed to the chemical nature of the photogenerated charge carriers and has a quantum yield comparable with commercial visible light photocatalysts.     

Chemical Bonding and Atomic Structure in Y(2) O(3) :ZrO(2) -SrTiO(3) Layered Heterostructures

Repeating boundaries: The buried interfaces in artificial heterostructures produced by sequential deposition of nanosized units are critical to their properties. With density functional theory it was shown that in Y(2) O(3) :ZrO(2) (YSZ) and SrTiO(3) (STO) heterostructures reconstruction of the interfaces between the component units is required to access the most favorable structure.     

Artificial construction of the layered Ruddlesden-Popper manganite La2Sr2Mn3O10 by reflection high energy electron diffraction monitored pulsed laser deposition

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden-Popper structure La(2)Sr(2)Mn(3)O(10) in epitaxial thin film form by sequentially layering La(1-x)Sr(x)MnO(3) and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr(2+) predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature T(g) ≈ 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.     

Novel chromium(III)/(VI) adducts of XPS-determined mixed valence,from electroreduced chromium(VI)

Summary Conditions of chromium(VI) and acidity have been found at which a novel brown deposit from electroreduction. Its 11 chromium(III):chromium(VI) composition, and the 21 ratio of the alkali-leached product, were established by XPS. The composition bounds for electrodeposition of the 11 solid and the competing insulative chromium(III) film were established electrochemically. Earlier reported chromium(III) and chromium(VI) solid or gels, some deposited from alkali, differ in colour and composition properties.     

Hydrogenation of

The course of the hydrogenation of [5]- and [6]metacyclophane (1b and 1c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13b and 12c. The accompanying hydrogenation enthalpies are -220 and -141 kJmol(-1), respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJmol(-1) were derived for 1b and 1c.