Thomas S. Müller

Synthesis of colloidal nanoscaled copper–indium–gallium–selenide (CIGS) particles for photovoltaic applications

In this work, Cu(In,Ga)Se(2) (CIGS) nanoparticles were synthesized using a wet chemical method. The method is based on a non-vacuum thermal process that does not use selenization. The effects of temperature, source materials, and growth conditions on the phase and particle size were investigated. X-ray diffraction results confirm the formation of a tetragonal CIGS structure as the main phase with the purity more than 99% obtained by energy-dispersive X-ray spectroscopy (EDX). The morphology and size of the samples were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using these methods, 20-80nm particles were obtained. Through measurements of the absorption spectra of CIGS nanoparticles, the band gap of the synthesized material was determined to be about 1.44eV, which corresponds to an acceptable wavelength region for absorber layers in solar cells.

The formation of gradients in wet deposited coatings with photocatalytically active nanoparticles

A total of 81 doped and undoped anatase nano-particles were synthesised by a precipitation/co-precipitation process followed by a hydrothermal treatment to obtain increased visible light photocatalytic activity. The screening process was performed utilising a high throughput analysis system based on the photometric monitoring of the photocatalytic degradation of organic dyes (Rhodamine B, Malachite Green, Acid Blue 29). Photocatalytically active coatings were prepared with selected catalysts with high and low rankings from the screening. Degradation experiments with stearic acid could confirm the varying grades of visible light activity as seen in the screening process.

Doped nanoparticles for photocatalytically active surfaces

For the fabrication of transparent coatings, various routes have been investigated. Doped and undoped TiO2 nanoparticles have been prepared by hydrothermal and reflux synthesises. Fully crystallied systems down to 4-5 nm, fully redispersible in organic solvents as well as in water have been obtained. The doped systems show significantly higher activities in the decomposition of organic dyes, and the band edge could be shifted to the visible range. These particles have been additionally surface modified to be able to disperse them in the matrix of the coating material. Single and double layer doatings with self-cleaning adn hydrophilic properties.

Photocatalytic gradient coatings on plastics by spray techniques

Transport coating systems applicable on plastics surfaces by a spray technique are presented. The coatings are based on highly photocatalytically active nanoscaled titania powders, surface modified with silanes containing organic or fluoro-organic side chains. The modification allows for the introduction of the particles in organic inorganic hybrid NANOMER coating systems. In the wet film - due to the evaporation of the solvents - a decompatibilisation of the coated particles to the matrix results in a self organising gradient layer formation with an up-concentration of the active particles at the interface layer between coating and air. After activation by irradiation with artificial or natural UV-light, highly active transparent photocatalysis coatings for a great variety of materials are obtained.

Zur Entwicklung von superparamagnetischen Kompositpartikeln zur Entfernung von Schwermetallionen aus Industrieabwässern

Es wurden neue Kompositpartikel zur Abtrennung von Schwermetallionen aus wassrigen Abwasserstromen entwickelt. Die Kompositpartikel bestehen aus superparamagnetischen Eisenoxid-Nanopartikeln in einer Borosilikatglasmatrix. Die Oberflache der Kompositpartikel ist mit Organosilanen modifiziert. Eine Siloxanfunktion erlaubt die chemische Anbindung an die Partikel, eine Komplexbildnerfunktionalitat erlaubt die reversible Bindung von Metallionen. Die Kombination der grosen freien Oberflache der superparamagnetischen Kompositpartikel (SPMK) mit einer schnellen Bindungskinetik ermoglicht Abtrennungen insbesondere bei geringen Schwermetallkonzentrationen, die mit herkommlichen Trennverfahren nur unzureichend durchfuhrbar sind. Ein moglicher Einsatz der neuen Technik lohnt sich daher vor allem dann, wenn das abzutrennende Schwermetall hochgiftig ist (z.B. Cd) und deshalb besonders niedrige Grenzwerte zu erfullen sind.