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05 Feb 11:15

Systematic variation of Fock exchange in hybrid functionals: Effect on the structural, electronic and energetic properties of VO2

Publication date: March 2018
Source:Chemical Physics Letters, Volume 695
Author(s): Thomas Bredow, Berenike Stahl
The metal-semiconductor phase transition of vanadium dioxide VO2 is difficult to describe with conventional density-functional theory methods. In the present study we systematically varied the Fock exchange contribution in hybrid functionals in order to obtain a functional that can accurately describe the structural, electronic and energetic properties of both VO2-phases. For this purpose the hybrid functionals PBE0, HSE06 and LC- ω PBE, that are all derived from the GGA functional PBE, have been tested. Best results for the fundamental band gap and the relative phase stability of the re-parameterized functionals were obtained for 10 % Fock exchange in PBE0, 20 % Fock exchange in LC- ω PBE and 12.5 % Fock exchange in HSE06. The re-parameterized functionals were furthermore tested in terms of their accuracy for calculated structural parameters. It was observed that PBE0-10 and HSE06-12.5 give the overall most accurate results.

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01 Feb 12:12

Fate of Photoexcited Molecular Antennae - Intermolecular Energy Transfer versus Photodegradation Assessed by Quantum Dynamics

by Stephan Kupfer, Daniel Kinzel, Michael Siegmann, Jule Philipp, Benjamin Dietzek and Stefanie Gräfe

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The Journal of Physical Chemistry C
DOI: 10.1021/acs.jpcc.7b12190
31 Jan 11:01

The serendipity test

The serendipity test

The serendipity test, Published online: 31 January 2018; doi:10.1038/d41586-018-01405-7

Scientists often herald the role of chance in research. A project in Britain aims to test the popular idea with evidence.
23 Jan 09:05

Water-Assisted Hole Trapping at the Highly Curved Surface of Nano-TiO2 Photocatalyst

by Kenji Shirai, Gianluca Fazio, Toshiki Sugimoto, Daniele Selli, Lorenzo Ferraro, Kazuya Watanabe, Mitsutaka Haruta, Bunsho Ohtani, Hiroki Kurata, Cristiana Di Valentin and Yoshiyasu Matsumoto

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Journal of the American Chemical Society
DOI: 10.1021/jacs.7b11061
22 Jan 12:28

Photocatalytic hydrogen production using TiO2 coated iron-oxide core shell particles

Publication date: 22 February 2018
Source:International Journal of Hydrogen Energy, Volume 43, Issue 8
Author(s): A. Madhumitha, V. Preethi, S. Kanmani
Photocatalytic water splitting plays a challenging role as it is one of the most important reactions for solving energy, environmental problems and sustainability. Photocatalytic water splitting was improved by using a novel kind of magnetically separable core shell nano photocatalyst TiO2/Fe2O3, prepared by co-precipitation method. It was characterised for particle size (XRD), band gap (UV-DRS), morphology (SEM), particle size (HRTEM), elemental composition (EDS) and electrochemical studies. Photocatalytic splitting of water was examined in tubular reactor of 500 mL capacity with various sacrificial agents viz., methanol, ethanol, acetic acid, lactic acid, EDTA and triethanolamine. To enhance the hydrogen production, various operating parameters viz., effect of sacrificial agents, catalytic dosage, light irradiation and recycle flow rate were optimized. With the optimized operating parameters (0.2 g catalyst dosage, 60 mL/min recycle flow rate, 96 W/m2 light irradiation and EDTA as sacrificial agent) the maximum hydrogen achieved was 2700 μmol/h for the quantum yield of 3.86% at 550 nm. The reusability studies were conducted and the TiO2 coated Fe2O3 core shell particles were found to be stable than the plain TiO2 nano particles. Effective charge transfer from TiO2 to Fe2O3 and the suppression of e/h+ pair recombination attributed significant enhancement in photoactivity, thereby increasing the hydrogen production.

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18 Jan 11:20

Bleichsysteme für Haushaltswaschmittel

by Michael Dreja, André Hätzelt, Nadine Bluhm

Zusammenfassung

Die Weiterentwicklung von chemischen Bleichsystemen, insbesondere von aktivierter und katalysierter Persauerstoffbleiche in festen Waschmitteln, hat zu signifikanten Verbesserungen bei der Leistungsfähigkeit solcher Produkte in Bezug auf Fleckentfernung, Weißgrad und Hygiene geführt. Heute existieren metallhaltige und metallfreie organische Katalysatoren, die in Kombination mit dem weit verbreiteten System Percarbonat/TAED die Lücke zwischen 20 °C und 40 °C schließen. Umwelt und Verbraucher profitieren neben der Reduktion der Dosierung um 75 % in den letzten 40 Jahren von direkten Kosteneinsparungen durch geringeren Energieverbrauch bei Reduktion der Waschtemperatur. Die Kompaktierung hat neue Produktformen wie vordosierte Waschmittelportionen ermöglicht. Offen sind weiterhin die Anwendung katalytischer Bleichsysteme in Flüssigwaschmitteln und die Nutzung von Sauerstoff aus der Luft. Die weiter voranschreitende Integration von Waschmitteln in Waschmaschinen, etwa durch automatische Dosierung und verbesserte Fleckensensorik, wird dazu führen, dass Bleichsysteme in Zukunft weiter optimiert und noch gezielter eingesetzt werden können, um das Waschen noch nachhaltiger und verbraucherfreundlicher zu gestalten.

Summary

The development of chemical bleach systems, especially of activated and catalysed peroxygen bleach in solid detergents, has led to significant advances in the performance profile with regards to stain removal, whiteness and hygiene. Today a variety of metal-containing and metal-free organic catalysts exists, which are able to close the gap between 20 °C and 40 °C compared to the broadly used sodium percarbonate/TAED system. This has led to considerable savings and benefits for consumers and the environment, by enabling a dosage reduction of about 75% during the last 40 years and providing direct cost savings to consumers via less use of energy by reduced washing temperatures. New compact detergent formats like pre-dosed pouches have thus become viable. The use of catalytic bleach systems in liquid detergents and the activation of aerial O2 are still challenges. Future integration of detergents and washing machines, e.g. via controlled dosing and stain detection, will lead to further optimization. Future bleach systems will contribute to make the washing process even more sustainable and convenient.

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Auf saubere Wäsche möchte niemand verzichten. Wir verdanken sie den Haushaltswaschmitteln, die weltweit zu Hygiene und Gesundheit beitragen. Feste Universalwaschmittel enthalten dafür oft chemische Bleichsysteme, während flüssige Waschmittel bislang ohne Bleiche formuliert werden. In den letzten Jahren haben sich zahlreiche neue Entwicklungen, insbesondere bei der katalytischen Bleichaktivierung sowie durch neue Anwendungsformen wie einzelportionierte Waschmittelpäckchen (Pouches, Pods, Caps) ergeben. Wir beleuchten in diesem Artikel die neueren Entwicklungen auf dem Gebiet der Bleiche und Bleichkatalyse und diskutieren den Einfluss auf Waschleistung, Hygiene und Nachhaltigkeit.

18 Jan 11:19

Consequences of realistic embedding for the L2,3 edge XAS of [small alpha]-Fe2O3

Phys. Chem. Chem. Phys., 2018, 20,4396-4403
DOI: 10.1039/C7CP06926J, Paper
Paul S. Bagus, Connie J. Nelin, Michel Sassi, Eugene S. Ilton, Kevin M. Rosso
Cluster models of condensed systems are often used to simulate the core-level spectra obtained with X-ray Photoelectron Spectroscopy, XPS, or with X-ray Absorption Spectroscopy, XAS, especially for near edge features.
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18 Jan 11:19

Properties of Single Oxygen Vacancies on a Realistic (TiO2)84 Nanoparticle: A Challenge for Density Functionals

by Ángel Morales-García, Oriol Lamiel-García, Rosendo Valero and Francesc Illas

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The Journal of Physical Chemistry C
DOI: 10.1021/acs.jpcc.7b11269
07 Dec 14:57

A topological screening heuristic for low-energy, high-index surfaces

Publication date: March 2018
Source:Surface Science, Volume 669
Author(s): Wenhao Sun, Gerbrand Ceder
Robust ab initio investigations of nanoparticle surface properties require a method to identify candidate low-energy surface facets a priori. By assuming that low-energy surfaces are planes with high atomic density, we devise an efficient algorithm to screen for low-energy surface orientations, even if they have high (hkl) miller indices. We successfully predict the observed low-energy, high-index { 10 12 ¯ } and { 10 1 ¯ 4 } surfaces of hematite α-Fe2O3, the {311} surfaces of cuprite Cu2O, and the {112} surfaces of anatase TiO2. We further tabulate candidate low-energy surface orientations for nine of the most common binary oxide structures. Screened surfaces are found to be generally applicable across isostructural compounds with varying chemistries, although relative surface energies between facets may vary based on the preferred coordination of the surface atoms.

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