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- All Subjects: Biochemistry
- All Subjects: Non-van der Waals solids
Description
Liquid-phase exfoliation (LPE) is a straightforward and scalable method of producing two-dimensional nanomaterials. The LPE process has typical been applied to layered van der Waals (vdW) solids, such as graphite and transition metal dichalcogenides, which have layers held together by weak van der Waals interactions. However, recent research has shown that solids with stronger bonds and non-layered structures can be converted to solution-stabilized nanosheets via LPE, some of which have shown to have interesting optical, magnetic, and photocatalytic properties. In this work, two classes of non-vdW solids – hexagonal metal diborides and boron carbide – are investigated for their morphological features, their chemical and crystallographic compositions, and their solvent preference for exfoliation. Spectroscopic and microscopic techniques are used to verify the composition and crystal structure of metal diboride nanosheets. Their application as mechanical fillers is demonstrated by incorporation into polymer nanocomposite films of polyvinyl alcohol and by successful integration into liquid photocurable 3D printing resins. Application of Hansen solubility theory to two metal diboride compositions enables extrapolation of their affinities for certain solvents and is also used to find solvent blends suitable for the nanosheets. Boron carbide nanosheets are examined for their size and thickness and their exfoliation planes are computationally analyzed and experimentally investigated using high-resolution transmission electron microscopy. The resulting analyses indicate that the exfoliation of boron carbide leads to multiple observed exfoliation planes upon LPE processing. Overall, these studies provide insight into the production and applications of LPE-produced nanosheets derived from non-vdW solids and suggest their potential application as mechanical fillers in polymer nanocomposites.
ContributorsGilliam, Matthew Scott (Author) / Green, Alexander A (Thesis advisor) / Wang, Qing Hua (Committee member) / Moore, Gary F (Committee member) / Arizona State University (Publisher)
Created2020
Description
Hydrogenase enzymes capable of catalyzing proton reduction to produce H2 have generated a considerable interest due to increasing motivation in finding sustainable carbon free energy sources. A considerable amount of research has been focused on producing synthetic structures mimicking the hydrogenase catalytic site, but the activity seen in hydrogenase enzymes in aqueous near neutral pH has yet to be replicated. It is now clear that the protein structure surrounding the H-cluster enables the high activity by fine tuning characteristics of the catalyst, but the structure and complexity of hydrogenase enzymes makes it difficult to predict exactly how the secondary coordination sphere affects catalysis. This work looks at incorporating both synthetic molecular catalysts and hydrogenase mimics into peptide scaffolds to improve the activity for photo-driven H2 production in aqueous solutions. The first chapter of this dissertation shows a de novo heme binding peptide improving the activity of cobalt protoporphyrin IX (CoPPIX) upon coordination inside a four-helix bundle. The peptide bound CoPPIX exhibited a 5.5-fold increase in anaerobic and an 8.3-fold increase in aerobic activity compared to free CoPPIX, while also showing dramatic increases to stability and solubility. In the second chapter, this work is expanded by using a randomly mutated cytochrome b562 library to identify beneficial attributes for downstream implementation of an ideal coordination site. A high-throughput assay was developed to measure H2 production using WO3/Pd deposited on a glass plate for a colorimetric first-pass screen. This assay successfully measured H2 production from CoPPIX bound cytochrome b562 in the periplasm of cells and identified a possible mutant showing 70% more H2 production compared to the wildtype. The third chapter incorporated a hydrogenase mimic into a four-helix bundle using a semi-synthetic strategy yielding a 3-fold increase in activity due to catalyst encapsulation. The method created will allow for easy modifications to the synthetic catalyst or peptide sequence in future work. The systems developed in this work were designed to facilitate the identification and implementation of beneficial characteristics for future development of an optimal secondary coordination sphere for a peptide bound molecular catalyst.
ContributorsHalloran, Nicholas Ryan (Author) / Ghirlanda, Giovanna (Thesis advisor) / Mills, Jeremy H (Committee member) / Moore, Gary F (Committee member) / Arizona State University (Publisher)
Created2021