| The fabrication of optical sensors often involves immobilizing a chemical reagent to a surface. The introduction of the interface often changes the chemical properties of the reagent compared to its corresponding free solution form. To study these surface effects, an immobilized chemical reagent system was designed to model the interfacial behavior of chemical reagents covalently bound to silica. The reagent system involved synthesizing 8-hydroxyquinoline covalently bound to silica through an alkyl chain. This procedure preserved the fluorescent properties of the chelate and enabled in-situ fluorescence measurements of aluminum ion complexation. Studies of the reaction of the surface bound ligand with aluminum ion were performed as a function of pH, ionic strength, and aluminum ion concentration. It was found that electrical effects, induced by specific ion adsorption of the aluminum ion on silica, altered the equilibria of the metal chelate.;In addition to surface charge effects, the theoretical nature of the diffuse layer in porous media was investigated. It was proposed that the amorphous geometry could be modeled by using well-defined Euclidean geometrical surfaces as extreme limits to bracket the intermediate asymmetry. Approximate analytical solutions of the Poisson-Boltzmann equation were derived for cylindrical geometry and compared to a numerical solution of the Poisson-Boltzmann equation. Planar solutions were also derived, and found to have wide ranges of agreement with the numerical solution to the Poisson-Boltzmann equation for cylindrical symmetry.;The dissociation kinetics of the silica immobilized aluminoquinolate complex was studied as a function of pH, ionic strength, and aluminum ion concentration. The reactions were performed under pseudo-first order conditions; however the kinetics were found to be nonexponential. A model that takes into account a variable surface potential was formulated that fits the data well.;The nature of the ion adsorption on silica was further investigated using Europium ion, which is luminescent. Changes in the emission spectra of the Europium ion gave information about surface complexation and surface coverage. Comparison to titration data gave information about the role of cation hydrolysis in the formation of surface layers of complexed europium ion. |
