title: Synthese und Charakterisierung von Thiol-basierten Polymeren und ihren Organisch-Anorganischen Hybrid Nanopartikeln
Creators: name: Wagner, Maximilian
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024

description: The bottom-up development of novel materials is a challenging task requiring knowledge of physical and chemical properties of the starting materials. It is therefore fundamental to gain deep insights on the molecular level to extrapolate the properties to the future architecture. This should be addressed within this thesis starting from commercially available polymers, to forming polymer-inorganic assemblies and finally to the built-up of a novel disulfide-based polymer which can be used for the integration of yet providing more functionality than the commercial polymer due to the dynamic covalent character of the disulfide bond. The commercial polymer, poly(acrylic acid) (PAA) was used to host CdS nanoparticles in different versions, such as doped with silver ions as well as covered with ZnMnS2 shells. Both systems were further assembled with cationic 5,10,15,20-Tetrakis-(4-aminophenyl)-porphyrin (TAPP) to form an extremely powerful photocatalyst. The origin of the good performance was found in the formation of sitting atop complexes of TAPP with the inorganic nanoparticles. The silver doped CdS and shell covered CdS were investigated in two separate studies. The focus of one study was to achieve high catalytic performance for various reactions via doping of the CdS. For the other study, a ZnMnS2 shell covered CdS was investigated in detail with respect to its adjustable emission and catalytic performance. Both systems were characterized with dynamic light scattering (DLS) and transmission electron microscopy (TEM) to gain access to their structure and UV-vis, steady-state fluorescence spectroscopy to yield insights into the photophysical behavior. To build a novel polymer-inorganic system from scratch a new type of material was explored also having carboxylic acid groups to provide the possibility for electrostatic self-assembly with also respect of templating inorganic particles. The polymer itself is synthesized by a nanoprecipitation technique, where the precursor pentaerythritol-tetrakis (mercaptopropionic acid) (PETMP), dissolved in THF, forms emulsion droplets in aqueous solution. The polymer was formed by oxidative coupling with hydrogen peroxide in presence of soluble thiols. As soluble thiols mercaptopropionic acid (MPA) and mercaptosuccinic acid (MSA) were used in varying PETMP:MPA and PETMP:MSA ratios. IR, NMR and MALDI-TOF were used to characterize the chemical properties. For structure analysis, DLS and static light scattering (SLS) were performed as well as atomic force microscopy (AFM). The multiple weakly covalent disulfide bonds in the structure allow reformation of the polymer nanoparticles when exposed to UV-light, reductive media, and ultrasound. During the rearrangement the hydrophobic PETMP plays a dominant role as the formed fragments rearrange to large particles due to the hydrophobic effect. The anionic character of the system was further exploited for electrostatic self-assembly with cationic porphyrins. The assembly formation was investigated with UV-vis spectroscopy and DLS. These assemblies demonstrate again a response to the previously listed triggers and reorganize to larger aggregates as porphyrin does not interact with the hydrophobic part. The system was further used as a host for the synthesis of gold nanoparticles. Three different synthetic routes were investigated: A single step method, a templated method, and a two-step method. The single step method relates to the synthesis of the pure polymer. However, hydrogen peroxide is replaced with HAuCl4. This allows a simultaneous formation of the disulfide-based polymer and gold nanoparticles. The templated method uses the readily formed polymer via the conventional synthesis route, which is then loaded with HAuCl4 and reduced with hydrazine. In the two-step method, PETMP is loaded with HAuCl4. Hydrazine is added immediately to form the gold nanoparticles. To provide stability in aqueous solution, MPA or MSA are added after the reaction and coupled oxidatively with hydrogen peroxide. Depending on the route and the polymer, a broad variety of gold nanostructures from elongated to raspberry-like are formed. The hybrid particles were investigated with UV-vis, DLS, AFM and transmission electron microscopy (TEM). Due to the disulfide bond within the organic matrix, the particles can respond to ultrasound. Different to the pure organic disulfide polymer this favors disaggregation of gold nanoparticles in a larger assembly. It can be investigated in the UV-vis spectrum, where a shift of the plasmon resonance band occurs. Besides gold nanoparticles the system was used for the synthesis of platinum nanoclusters. In this case, the single step method was used, where Na2PtCl6 replaced hydrogen peroxide in the polymer synthesis. This led to the formation of small Pt nanoclusters on the outer surface of the PETMP emulsion droplets. The hybrid organic-inorganic nanoparticles were characterized with DLS and TEM showing a highly uniform size and shape. The platinum nanoclusters demonstrate an exceptional reactivity for the reducing nitrophenols. The catalysis could be repeated multiple times without noticeable impact on the performance. This shows the versatility of this type of polymer, which is presented in this thesis. It can be used as basic dynamic covalent polymer and can serve as a host for the synthesis of various inorganic structures, which are capable of performing catalysis. The building-block concept for the construction of these complex systems can lead to more cost-effective materials as they avoid time-consuming synthesis.