Date of Award

Spring 5-6-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Carl P. Tripp

Second Committee Member

Aria Amirbahman

Third Committee Member

William Gramlich

Additional Committee Members

Alice Bruce

Matthew Brichacek

Abstract

Surface modifications of metal oxides and polymer substrates are widely adopted approaches to alter the properties of these materials for use with specific applications. In the first part of my thesis, I describe how we have modified the surface of magnetic particles (Fe3O4) with layers of SiO2 and TiO2 to generate photocatalysts that remove toxic chemicals from drinking water. Semiconductor photocatalysts, such as TiO2 have gained much interest over the last 20 years as promising materials for water treatment. However, a main drawback centers on the difficulty to remove the catalyst from the water which has made it very difficult to implement this material in real-world applications. To solve this issue, we have developed novel photocatalysts that have the commercially available, and what are widely accepted as the “gold standard”, TiO2 particles sintered to the magnetic core. These coated magnetic particles are then rendered robust by applying an overcoat of a SiO2 or TiO2 sol-gel layer. This multilayered material showed excellent performance in terms of reusability, photocatalytic activity, and particle recovery when tested in aqueous environments. In the second part of my thesis, I have developed a novel approach for surface modifying a naturally abundant biopolymer nanomaterial, cellulose nanofiber (CNF), for application in additive manufacturing or 3D printing. The biggest challenges to making CNF suitable for this technology involve the dewatering/drying of CNF suspensions and tuning the surface chemistry of CNF to render the material compatible with 3D printable thermoplastics. The novelty of our approach involves the use of supercritical CO2 (scCO2) for both drying the CNF and as a solvent for performing surface reactions. Using in situ IR spectroscopy, we show that the main reason that scCO2 is effective at drying CNF is because the solvent has no surface tension and thus, fully wets the CNF, which in turn, enables the water to transfer into the fluid phase. Furthermore, there is no aggregation of the fibers upon removal of the scCO2 which results in fewer water molecules trapped between the fibers of the CNF. IR spectroscopic studies, using D2O as a probe molecule, show that scCO2 is an effective solvent for bringing reagents into the interior of the fiber structure This translates to high levels of esterification which occurs when CNF was reacted with acetic anhydride in the presence of pyridine as a catalyst. To show the practical use of these materials, a 3D printable composite was fabricated by blending surface-modified CNF with thermoplastics. We also demonstrated that scCO2 provides an avenue to post- surface treat CNF based films. Films of CNF/CaCO3 were rendered hydrophobic and shown to maintain mechanical properties after immersion in water. This has implications for the use of bio-based plastics, as a substitute for traditional petroleum-based plastics, for use as disposable plates, utensils, and straws, to name a few.

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