Date of Completion

6-10-2013

Embargo Period

12-7-2013

Keywords

Silicatein, Silica, Titania, N-Nitrosodimethylamine, Photodegradation

Major Advisor

Prof. Douglas H. Adamson

Associate Advisor

Prof. Bryan D. Huey

Associate Advisor

Prof. Richard S. Parnas

Associate Advisor

Prof. Steven L. Suib

Field of Study

Polymer Science

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Silicatein α, an enzyme found at the center of silica spicules in the marine sponge Tethya Aurantia, is known to play a role in silica condensation from seawater. It has also been shown to catalyze the formation of silica from various silica precursors such as tetraethyl orthosilicate (TEOS). Inspired by the finding that the serine26 and histidine165 amino acids in Silicatein α are required for silica formation from TEOS, we synthesized poly(hydroxylated isoprene-b-2-vinylpyridine) block copolymers to mimic these amino acid residues.

The block copolymer architecture was chosen for the mimic polymer so that the structures formed by the polymer could be used as a template for condensed silica. To demonstrate the templating function, we investigated: the formation of hierarchical structures, the presence of dual mechanisms of condensation at low pH, the mechanism of templation as hydrolyzed species diffuse from the site of hydrolysis, and the formation of silica at the polymer surface. We found our bio-inspired polymer combines the features of neutral pH, low temperature, and structure control in silica formation.

Since the basic condensation mechanism is the same for silica and titania, the same mimic polymer was used as a catalyst in titania condensation as well. Our silicatein α mimic was shown to condense titania at neutral pH and room temperature and was compared to material produced by standard sol-gel methods. DSC and XRD analysis suggest a higher degree of titania condensation with the Silicatein α mimic. Results from TGA, surface area analysis and TEM indicate the condensation of titania around nano-sized polymer domains.

Titania made from the silicatein α mimic also showed a higher catalytic activity than commercial Degussa P25 TiO2 for the photodegradation of N-nitrosodimethylamine (NDMA). Furthermore, in an effort to develop a continuous photodegradation process, mimic polymer was electrospun to form a fiber mat. This fiber mat was treated with ceramic precursor to form ceramic-coated mimic polymer fibers. Synthesis of ceramic thin films was also explored.

As imidazole better mimics the histidine functionality of silicatein α than pyridine, using the controlled radical polymerization of 4-vinyl imidazole developed by Long et al., poly(vinyl alcohol-b-4-vinyl imidazole) was synthesized. An increase in the efficiency of the mimic polymer was observed. In addition, efforts were made to characterize the forces between mimic polymer and ceramic using AFM.

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