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- Synthesis and Characterization of immobilized Gold Nanoparticles and Binary Gold Nanoalloys on Cationic Spherical Polyelectrolyte Brushes and their Application as a Catalyst (2008)
- First of all the up scaled synthesis for cationic and anionic spherical polyelectrolyte brushes (SPB) was introduced and a reproducible method for the synthesis was established (Chapter 3.1). For a better understanding of anionic SPB the complexation of the anionic polyelectrolyte chains with the cationic surfactant cetyl trimethyl ammonium bromide was studied in detail. The models were proved by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS), if it’s in good agreement with the resulting systems (Chapter 3.2). It was possible to show, that cationic SPB could be used for the generation of gold nanoparticles (Chapter 3.3). The synthesized carrier systems were characterized in detail by transmission electron microscopy (TEM), cryo-TEM and disc centrifuge (DCP). The more detail examination of the Au/SPB system by DLS, TEM/cryo-TEM, showed that a reversible immobilization system for gold nanoparticles was synthesized. The immobilized gold nanoparticles@SPB could be complexed by cyanid ions and oxygen. After the complexation of the gold nanoparticles we get the previous carrier system back. Detailed studies by wide angle X-ray scattering (WAXS) and high resolution transmission electron microscopy (HR-TEM) show an amorphous morphology of the gold nanoparticles in the range of 1 nm. This kind of generation allow us to generate gold nanoparticles in the range of 1.0 and 2.5 nm on the surface of the carrier particle. In the following part of the thesis the concepts described above were used for the synthesis of binary gold nanoalloys (Chapter 3.4 and 3.6). The binary systems Au-Pt, Au-Ru, Au-Rh and Au-Ir were sucessfully generated. In the next step the nanoparticular structure of these binary systems were completely clarified by different HR-TEM methods and WAXS. It was shown, that there is a different behaviour between macroscopic and nanoscopic world. Bulk Au-Pt alloys show miscibility gaps, whereas Au-Pt nanoalloys have no such miscibility gap. This alloy obeys the Vegard’s law. For the generation of facetted Pt nanocrystals (Chapter 3.5), the complexation of gold atoms by cyanid ions and oxygen is used. By this way it’s possible to synthesize well-ordered PtNP structures starting from the Au-Pt nanoalloy. In the second part of the thesis the immobilized gold nanoparticles and the binary gold nanoalloys applied as catalysts for industrial interesting oxidation reactions of alcohols and epoxidation reactions (Chapter 3.4 and 3.6) were studied. All reactions could be conducted at room temperature and in water as reaction media. The catalytic activities have a strong dependency on the composition in the nanoalloy. Cryo-TEM characterization showed us no change of the morphology of the catalyst before and after a catalyst cyclus. Concluding this thesis showed successfully a new route for the synthesis of monodispers and well defined gold nanoparticles, gold nanoalloys and facetted platinum nanocrystals. The particle sizes ranges between 1.0 and 7.0 nm. All systems can be used as green catalysts. This is an important point in the discussion of sustainability. All dispersions are not light and air sensitive, so they can be handled without any problems.