NOVEL AND ENHANCED FUNCTIONAL MATERIALS PROPERTIES VIA BLOCK COPOLYMER STRUCTURE DIRECTED POROSITY
Functional materials are at the heart of materials science, providing utility beyond their structure alone as semiconductors, magnetic materials, and more. While their core properties are dictated by their composition and crystal structure, much of their utility is derived from larger length scales. Research typically is constrained to studying functional materials as thin films, powders, or single crystals. Yet these forms can themselves limit the performance of functional materials or conceal exotic behavior at surfaces and interfaces. This work seeks to explore the properties and performance of materials in extremely high aspect ratios as mesoporous structures dominated by surfaces. Described below are three chapters discussing the synthesis and characterization of mesoporous functional metal oxides. First, mesoporous TiO2 and Ta2O5 are fabricated in different mesoporous morphologies and evaluated as photocatalyst supports for low-temperature dry reforming of methane. Results show over two orders of magnitude enhancement in activity versus traditional powder materials, unable to be accounted for by surface area alone. Next, the synthesis of mesoporous strontium titanate (STO) in the alternating gyroid morphology is discussed utilizing a non-traditional form of low-water-content sol-gel synthesis in acetic acid acting as both acid catalyst and solvent. The details of the entire synthesis process are discussed in depth, with emphasis on the key controlling factors driving the stoichiometry, phase, and structure-retention of the final produced materials. The last chapter addresses the key finding from this mesoporous STO material, that it exhibits an exotic form of nearly-temperature-independent surface ferromagnetism from cryogenic to room temperatures.This ferromagnetic behavior is consistent with the giant orbital paramagnetism mechanism, enabled through the combination of STO’s high dielectric constant, inherent surface oxygen vacancies, and the mesoporous material’s extremely high surface-to-bulk ratio. This magnetic behavior is the first report of surface ferromagnetism in undoped STO, with substantially higher mass-normalized magnetic moment than had been observed in doped single crystals. This finding paves the way toward multifunctional materials with inherent functional properties that can be combined with a mesostructure-derived temperature-independent ferromagnetism. The following chapters emphasize how the addition of mesoscale dimensions to functional materials can both substantially enhance their performance in practical applications and bring into focus normally dilute physical phenomena of surfaces.