Zugl.: Karlsruhe, Univ., Diss., 2008 / Hergestellt on demand

University, Diss., 2003--Kiel.

Zugl.: Köln, Univ., Diss., 2007

No description available.

Since a large number of polar and often ionizable anthropogenic organic trace compounds, such as pharmaceutical residues, can be detected in various stages of the water cycle, there is a need to elucidate the effects and behavior of such substances in the aquatic environment. Despite the fact that numerous studies on the sorption behavior of ionizable organic trace compounds have already been carried out, reliable sorption models, which allow a sufficiently accurate prediction of the sorption of organic cations, are not yet available. For this reason, the general objective of this thesis was to improve the fundamental process understanding of the interactions between dissolved cationic organic substances and solid surfaces including relevant influence parameters. The investigations were based on a differentiated process consideration in order to ultimately provide the essential prerequisites for a future reliable prediction of the sorption behavior of cationic organic compounds. Due to the complex superposition of several mechanisms, the basic relationships cannot be clearly elucidated with heterogeneous sorbents. Therefore, it was consciously worked with largely homogeneous, synthetic sorbents. The use of well-defined sorbents with different properties as well as the variation of background electrolyte concentration and the targeted use of different sorbates were the 'tools' that were used to identify and to separate the underlying sorption processes. / Da eine Vielzahl polarer und oftmals ionisierbarer anthropogener organischer Spurenstoffe, wie z. B. Pharmakarückstände, in verschiedenen Bereichen des Wasserkreislaufes nachweisbar ist, besteht die Notwendigkeit die Wirkung und das Verhalten solcher Spurenstoffe in der Umwelt näher aufzuklären. Trotz der Tatsache, dass bereits zahlreiche Untersuchungen zum Sorptionsverhalten ionisierbarer organischer Spurenstoffe bestehen, sind zuverlässige prognosefähige Sorptionsmodelle, welche eine ausreichend genaue Vorhersage der Sorption von organischen Kationen ermöglichen, zurzeit noch nicht verfügbar. Das generelle Ziel dieser Arbeit bestand daher darin, das grundlegende Prozessverständnis der Wechselwirkungen zwischen gelösten kationischen organischen Substanzen und festen Oberflächen einschließlich relevanter Einflussgrößen zu verbessern. Die Untersuchungen basierten auf einer differenzierten Prozessbetrachtung, um letztlich die wesentlichen Voraussetzungen für eine zukünftig zuverlässige Prognose des Sorptionsverhaltens kationischer organischer Verbindungen zu liefern. Aufgrund der komplexen Überlagerung mehrerer Mechanismen können die grundlegenden Zusammenhänge mit heterogen zusammengesetzten natürlichen Sorbentien nicht eindeutig aufgeklärt werden. Daher wurde bewusst mit weitgehend homogenen, synthetischen Sorbentien gearbeitet. Die Verwendung wohldefinierter Sorbentien mit unterschiedlichen Eigenschaften sowie die Variation der Elektrolytkonzentration und der gezielte Einsatz verschiedener Sorptive waren die 'Werkzeuge', die verwendet wurden, um die zugrunde liegenden Sorptionsprozesse zu identifizieren und zu separieren.

We developed a three-step colloidal synthesis of near-infrared active Cu-In-Se (CISe)/ZnS core/shell nanocrystals (NCs) via a sequential partial cation exchange. In the first step binary highly copper deficient Cu2‒xSe NCs were synthesized, followed by a partial cation exchange of copper to indium ions yielding CISe NCs. In order to enhance the stability and the photoluminescence (PL) properties of the NCs, a subsequent ZnS shell was grown, resulting in CISe/ZnS core/shell NCs. These core/shell hetero-NCs exhibited a dramatic increase in size and a restructuring to trigonal pyramidal particles. The reaction parameters, e.g. the Cu:Se-ratio, the temperature and the time were carefully tuned enabling a distinct control over the size and the composition of the NCs. By varying only the size of the CISe/ZnS NCs (from 9 to 18 nm) the PL spectra could be tuned covering a wide range with maxima from 990 nm to 1210 nm. Thus, in these experiments we demonstrate a clear dependence of the optical properties of these materials on their size and extend the PL range of CISe-based nanoparticles further to the infrared part of the spectrum. Furthermore, the relatively large size of these NCs allows their detailed structural analysis via electron microscopy techniques, which is particularly challenging in the case of small particles and especially important to relate the size, composition and crystal structure to their optoelectronic properties.