Single Molecule Spectroscopy Studies of the Nanoscale Properties of Microporous/Mesoporous Silicate Films Prepared by the Sol-Gel Process

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Professors Daniel Higgins and Maryanne Collinson of Kansas State University are supported by the Analytical and Surface Chemistry Program to study microporous silicate thin films prepared using the sol-gel process using single molecule spectroscopy. These include inorganic silicates, organically modified silicates (ORMOSILS) and silicate films containing surfactant-templated mesopores. These materials are being used to develop new catalytic supports, chemical sensors, and chemical separations media. Important film properties to be explored include local diffusion rates of entrapped molecules, the local pH and site-specific variations in the pKa's of acidic surface groups, such as silanols, and intrinsic local polarity of the silicate matrix. Time- and frequency-resolved optical work utilizing pH-sensitive flurophores is a key approach. These studies will also allow the exploration of phase separation of inorganic and organic-rich domains. Single molecule methods are required in these studies because the materials are highly heterogeneous, and averaging over sites as in bulk spectroscopy does not allow one to quantify types of similar sites.This impact of this work lies in materials chemistry, chemical separation, catalysis, and sensor development. Characterization of the chemical sites within the material can lead to more rugged and better performing materials. Applications include environmental engineering and energy storage.