Thesis (M. Sc.) - Asian Institute of Technology, 2023

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Bio-Nano Material Science and Engineering, School of Engineering and Technology

This study was principally aimed at using photocatalysis as a tool to induce the degradation of flexible polyurethane foam (PUf) and subsequently deduce its degradation patterns, assess the various products born out of the process, and characterize the photocatalytic effects of the synthesized plasmonic photocatalysts on flexible polyurethane foam. SEM and TEM micrographs of the photocatalysts revealed an effective deposition of metal on the ZnO surface with near-spherical configuration and average sizes of 10, 8, and 9 nm for Au, Pt, and Co metals, respectively. Moreover, EDX elemental analyses revealed 7.57% Au, 2.57% Pt, and 1.42% Co weight content on the respective plasmonic photocatalyst. Slightly elevated Au content was noted due to the gold coating used in the sample preparation. The General Factorial Design of the factors namely; type of photocatalyst, reaction time, and catalyst loading revealed that there was an improved photocatalytic efficiency with Pt/ZnO causing the highest mass loss at 49.29%, Au/ZnO at 39.39%, and Co/ZnO at 36.89%. All of the three factors considered returned statistically significant main effects and interaction tendencies. FTIR spectra of the foam residues revealed a photocatalyst type-dependent increase in carbonyl indices (CI) with pronounced changes in the -NH and -OH peaks. Pt/ZnO reported the highest CI value consistent with its high mass loss outcome. DSC thermograms revealed a shift and broadening of the foam melting point ranges indicating dominant rearrangements of the macromolecular structure. Moreover, foam SEM images before and after irradiation show cellular collapse with remarkable voids and cracks on the surface showing significant embrittlement and disintegration. GC MS results show the presence of low-molecular-weight compounds with traces of substituted amines, alcohols, carboxylic acids, and some isocyanate components revealing degradation at the molecular state. The increase of carbonyl content in some of the products led to the conclusion that the process follows the Norrish Type I photodegradation pathway. A basic degradation pathway was deduced based on this set of observations.