Functionalization of Metal Oxide Surfaces through Chemical Reactions and Physical Adsorption
The synthesis of high surface area metal oxides is an area of extensive research with potential applications in catalysis, adsorption, and materials chemistry. The functionalization of a material’s surface can dramatically change its physical and chemical properties. The research described herein is built on the foundation of traditional techniques used for synthesis, characterization, and functionalization of metal oxides and develops new mechanisms and materials for the functionalization of surfaces. We began with Methyl-terminated poly(dimethylsiloxanes) (PDMSs), which are typically considered to be inert and not suitable for surface functionalization reactions because of the absence of readily hydrolysable groups. Nevertheless, these siloxanes do react with silica and other oxides, producing chemically grafted organic surfaces. Whether ignored or simply forgotten, this reaction provides a versatile, yet simple method for the covalent functionalization of inorganic surfaces. In this research, we explored the reactions of linear methyl-terminated and cyclic PDMS as well as bis-fluoroalkyl disiloxanes for the surface functionalization of mesoporous silica. FTIR and chemical analysis, as well as contact angle measurements and water adsorption confirmed the formation of high quality hydrophobic surfaces. An additional study of the reactions of silica with different degrees of hydration demonstrated the critical role of water in initiating the grafting of the siloxanes. We proposed a mechanism for the reaction that involved the hydrolysis of the adsorbed siloxanes by the Lewis acidic centers, followed by the coupling of silanols to the surface to produce grafted siloxanes. We then explored Phthalocyanines (Pcs), an interesting class of catalytically active molecules with unique spectroscopic, photoelectric, and sometimes magnetic properties. This research involved a systematic study of the solution adsorption of two series perfluorinated Pcs on various surfaces to generate heterogeneous Pc materials for several applications. Initial adsorption studies focused on metal oxides and functionalized silicas in acetone. Characterization of the adsorption was performed by solution UV/Vis, solid-state reflectance UV/Vis/NIR, and elemental analysis. Additional mechanistic studies focused on the role of Lewis acid/base interactions between the electron donating surfaces and electron deficient Pcs. Comparison studies were completed in a moderately polar, non-coordinating solvent, methylene chloride. Our results demonstrated solution adsorption as a viable technique for the production of phthalocyanine thin films on metal oxide surfaces.
adsorption, surface chemistry, functionalization, metal oxides, porous materials, polydimethylsiloxane, phthalocyanine, silica, alumina, Chemistry, Physical Chemistry
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