Simple Oxides as Model Systems to Study Reactive Surface Area by Solid-state NMR

Open Access
Author:
Estok, Suzanne Kathryn
Graduate Program:
Chemistry
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 07, 2015
Committee Members:
  • Karl Todd Mueller, Thesis Advisor
Keywords:
  • NMR
  • surfaces
  • reactivity
  • oxides
Abstract:
Studying the reactions at the surfaces of natural solids is important for understanding and regulating a number of environmental processes, including concentration and distribution of contaminants and nutrients in Earth’s aqueous systems. Mineral surfaces, specifically, control permeability and exchange of contaminants and nutrients in soils, in part through the reactions that take place on these surfaces. In this work, organic acid probe molecules (such as trifluoroacetic acid, TFA) were used to determine the type of binding sites and the species binding to the surfaces of environmentally relevant model solids, such as kaolinite (KGa-2, KGa-1b), gibbsite and fumed silica. These determinations of surface chemistries and “reactive surface area” (RSA) provide a more comprehensive description of how a material will behave in the environment. In this context, reactive surface area is a measurement of the surface sites or functional groups that directly participate in surface reactions. Therefore, RSA represents the quantity of material available for reaction in a particular system and under specific conditions. Solid-state nuclear magnetic resonance (NMR) was used in this work for structural information about specific nuclei and their surrounding environments, thus enabling a determination of RSA binding sites and the species being bound to the surfaces. Bloch-decay magic angle spinning (MAS) NMR experiments were used to study the bulk structures of the materials and to determine the coordination environments of NMR-active nuclei, such as fluorine (19F), within probe molecules. Attenuated Total Reflectance Infrared Fourier-transform (ATR-FTIR) spectroscopy was also used (by our collaborators at PSU) to help elucidate the RSA of the environmentally relevant solids used in this work.