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Novel Nanostructured Materials for Optoelectronic, Photocatalytic, and Thermocatalytic Applications

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Schünemann,  Stefan
Research Group Tüysüz, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Schünemann, S. (2018). Novel Nanostructured Materials for Optoelectronic, Photocatalytic, and Thermocatalytic Applications. PhD Thesis, Ruhr-Universität Bochum, Bochum.


Cite as: http://hdl.handle.net/21.11116/0000-0002-B63A-0
Abstract
In this thesis, the design of novel nanostructured materials for optoelectronic, photocatalytic, and thermocatalytic applications is investigated. The thesis is divided into two parts. Firstly, nanostructured halide perovskites, which are semiconductors with intriguing optoelectronic properties and considered as promising photovoltaic materials, are applied as distributed feedback lasers and as efficient photocatalysts for different catalytic reactions. Secondly, ordered-mesoporous Cu-Al2O3 catalysts, as a promising alternative to noble metal catalysts, are investigated for the selective oxidation of glycerol. Templating of halide perovskites is challenging, because of their incompatibility with common templating approaches and the rapid crystallization of these materials. In the first part of the thesis, colloidal crystal templating was employed as a templating protocol to prepare halide perovskite thin films with precise morphology control on the nanoscale. The protocol allows the fabrication of thin films with inverse opal morphology of various halide perovskite compositions with controllable thickness and periodicity. The periodic refractive index contrast in these inverse opal films results in a photonic band structure in which stop gaps open up resulting in anisotropic propagation of light within the inverse opal film. This unique property is applied to generate laser radiation via a so-called distributed feedback mechanism. The presented approach is the first all-solution based protocol for the preparation of halide perovskite distributed feedback structures and is a starting point for the preparation of low-cost halide perovskite laser devices. Furthermore, the photocatalytic properties of powdered inverse opal halide perovskites (CsPbBr3) are studied. Templating increases the surface area and reduces charge carrier diffusion paths and recombination rates, which results in enhanced photocatalytic activities, as compared to non-templated samples. In addition, heterojunction photocatalysts consisting of halide perovskite nanoparticles deposited on TiO2 are prepared via different protocols and successfully employed in the photocatalytic selective oxidation of benzyl alcohol to benzaldehyde under visible light irradiation. Moreover, a series of earth abundant ordered mesoporous Cu-Al2O3 catalysts is presented for the selective oxidation of glycerol, a promising renewable platform molecule obtained from biomass processing, to glyceric acid and glycolic acid. Also here, nanostructuring is employed to increase the catalytic activity of the material. Special focus is placed on the effect of different co-solvents that increase the initial reaction rate up to a factor of three. The presented catalyst can be an alternative to the cost-intensive noble metal catalysts based on Au, Pt, and Pd that are, up to now, the most studied catalysts for the selective oxidation of glycerol in the aqueous phase.