Incorporation and Characterization of Optical Oxygen Sensors in Silica Aerogel Monoliths

This thesis presents the preparation and spectroscopic characterization of silica aerogel monoliths containing one or more types of entrapped luminescent species. We are characterizing the response of aerogel-platform sensors to environments with varying amounts of oxygen and investigating whether it is possible to detect changes in luminescence signal based on the movement of oxygen through the aerogel monoliths. Our experiments indicate that for platinum(II) octaethylporphyrin (PtOEP) aerogels, the decrease in luminescence in the presence of oxygen is not linear with respect to the increase of concentration of oxygen. Various two-site models can be used to determine the accessibility of the PtOEP probes to oxygen. These techniques follow assumptions that the probes are located in two microenvironments, and either one or both of the microenvironments are accessible to oxygen. Data from both techniques indicate that the probes are accessible in only one microenvironment, with less than 10% inaccessible. PtOEP-doped silica aerogels can be fabricated up to 3 ½ x 3 ½ x ½ ", and luminescence is optically visible when oxygen is removed. The path of the luminescence can be tracked through the sample, indicating that it might be possible to determine the flow rate of gases through aerogels by monitoring the rate of appearance of luminescence.

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