Ionic nanoparticle networks : Hybrid materials with versatile properties

Abstract

In the course of this work the synthesis and versatile properties of novel inorganic-organic hybrid materials, so-called Ionic Nanoparticle Networks (INN), were investigated. The metal oxide nanoparticles, prepared by sol-gel processing, were modified with various differently substituted trimethoxysilanes. The final synthesis of the hybrid materials was the crosslinking of cyclic nitrogen base modified nanoparticles and chloroalkyl modified nanoparticles or chloromethylene (-CH2Cl) disubstituted aromatic linker molecules by a nucleophilic substitution. The obtained hybrid materials showed a very versatile processing and were characterized by various analysis techniques. The kinetics of the INN materials formation was also investigated by Quartz Crystal Microbalance (QCM). Short Angle X-ray Scattering (SAXS) measurements were executed on the INN materials revealing a short range order in the material, which most likely is caused by --- stacking interactions between the aromatic rings in the material. For a deeper understanding of the interactions in the material as well as of the composition of the INN materials solid state NMR measurements, ab-initio calculations and DFT calculations were conducted. These measurements confirmed the presence of --- stacking interactions between the aromatic rings in the INN materials. The core of the work was the investigation of the photoluminescence properties of the materials. Especially the tailoring of the excitation and emission wavelengths, by varying the substituents on the C2 position of the imidazolium moiety as well as by variation of the aromatic linker, was investigated for more than twenty different INN materials. The influence of the different linker molecules on the short range order and the resulting changes in photoluminescence activity was also evaluated. Furthermore, metal chlorides, which are known to form chloro metalate complexes, were used for the complexation with the chloride ion of the INN materials and the resulting properties, such as thermochromism and photoluminescence features, of the INN materials were explored. In addition, it could be shown that the INN materials are efficient heterogeneous catalysts for the conversion of CO2 and different epoxides into organic cyclic carbonates. Reactions with epichlorohydrin showed that a quantitative conversion could be reached for all the tested materials under relatively mild conditions. The INN materials could be easily recycled for at least four runs without a loss in conversion, but a decrease in selectivity was observed. Finally, first attempts on silica nanoparticle based self-healing materials were made by the transfer of principles from self-healing polymers to silica nanoparticle networks.