Block copolymer derived three-dimensional ordered hybrid materials for energy storage and conversion

In this thesis, block copolymers are used to rationally structure inorganic and hybrid materials into ordered, percolating nanostructures. The tunability of the microstructure, chemical composition, and porosity is explored and correlated with the materials’ performance in energy storage and conversion applications. Dense and thick mesoporous TiO2/C hybrid monoliths were prepared by co-assembly with a triblock copolymer and characterized as potential lithium ion battery anodes. The structure-directing polymer was carbonized to retain a thin conductive carbon layer at the electrolyte|electrode interface that increases the intrinsic conductivity of the active material. Polymer electrolytes were prepared by tailoring the individual blocks of the block copolymer. A minor conductive block decoupled ionic mobility from slow polymer relaxation, while sufficient mechanical stability was provided by covalently linked, mechanically stronger, insulating blocks. This combination overcomes a common trade-off between high conductivity and strength. Photocatalysis requires direct access of reactants and incident photons to a catalysts’ surface. The final part of the thesis shows that complete thermal removal of the template can create a mesoporous inorganic percolating network. Structuring the catalyst in this way improved the efficiency of photocatalysis as it combines high pore diffusibility with improved charge carrier transport properties.Diese Doktorarbeit untersucht die Herstellung hochgeordneter, perkolierender Nanostrukturen mittels Blockcopolymeren und diskutiert deren Einfluss auf die Leistungsfähigkeit darauf basierender Materialien in Anwendungen der modernen Energiespeicherung und –umwandlung. In einer ersten Studie wurden mesoporöse, monolithische TiO2/C-Hybride mittels eines Triblockcopolymers hergestellt und als Lithium-Ionen-Batterieanode getestet. Die Karbonisierung des strukturgebenden Polymers ergab eine leitfähige Kohlenstoffschicht an der Grenzfläche zum Elektrolyten und erhöhte so die intrinsische Leitfähigkeit. Einzelne Polymerblöcke wurden optimiert, um makroskopische Eigenschaften von Polymerelektrolyten unabhängig voneinander einzustellen. Eine besonders kleine, leitfähige Komponente erlaubte die Entkopplung der ionischen Leitfähigkeit von der Kettenmobilität, während kovalent gebundene, isolierenden Blöcke gleichzeitig hohe mechanische Stabilität gewährleisteten. Der verbreitete Widerspruch zwischen hoher Leitfähigkeit und Stabilität dieser Materialklasse konnte so vermieden werden. Photokatalyse erfordert direkten Zugang der Reaktanden und der Ladungsträger zur katalytisch aktiven Oberfläche. Im letzten Teil der Arbeit wird gezeigt, dass die Entfernung des strukturgebenden Polymers zu mesoporösen, perkolierenden, anorganischen Netzwerken führte. Diese erhöhten die Effizienz der Photokatalyse, da verbesserte Porendiffusivität und hohe Ladungsträgermobilitäten kombiniert wurden

Ordered Mesoporous TiO2 Gyroids: Effects of Pore Architecture and Nb-Doping on Photocatalytic Hydrogen Evolution under UV and Visible Irradiation

Pure and Nb-doped TiO2 photocatalysts with highly ordered alternating gyroid architecture and well-controllable mesopore size of 15 nm via co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer are synthesized. A combined effort by electron microscopy, X-ray scattering, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory simulations reveals that the addition of small amounts of Nb results in the substitution of Ti4+ with isolated Nb5+ species that introduces inter-bandgap states, while at high concentrations, Nb prefers to cluster forming shallow trap states within the conduction band minimum of TiO2. The gyroidal photocatalysts are remarkably active toward hydrogen evolution under UV and visible light due to the open 3D network, where large mesopores ensure efficient pore diffusion and high photon harvesting. The gyroids yield unprecedented high evolution rates beyond 1000 µmol h−1 (per 10 mg catalyst), outperforming even the benchmark P25-TiO2 more than fivefold. Under UV light, the Nb-doping reduces the activity due to the introduction of charge recombination centers, while the activity in the visible triple upon incorporation is owed to a more efficient absorption due to inter-bandgap states. This unique pore architecture may further offer hitherto undiscovered optical benefits to photocatalysis, related to chiral and metamaterial-like behavior, which will stimulate further studies focusing on novel light–matter interactions

Endopeptidase-Mediated Beta Lactam Tolerance

In many bacteria, inhibition of cell wall synthesis leads to cell death and lysis. The pathways and enzymes that mediate cell lysis after exposure to cell wall-acting antibiotics (e.g. beta lactams) are incompletely understood, but the activities of enzymes that degrade the cell wall (‘autolysins’) are thought to be critical. Here, we report that Vibrio cholerae, the cholera pathogen, is tolerant to antibiotics targeting cell wall synthesis. In response to a wide variety of cell wall- acting antibiotics, this pathogen loses its rod shape, indicative of cell wall degradation, and becomes spherical. Genetic analyses revealed that paradoxically, V. cholerae survival via sphere formation required the activity of D,D endopeptidases, enzymes that cleave the cell wall. Other autolysins proved dispensable for this process. Our findings suggest the enzymes that mediate cell wall degradation are critical for determining bacterial cell fate - sphere formation vs. lysis – after treatment with antibiotics that target cell wall synthesis