Adsorption of Small Molecules on MgO and Graphite

Abstract

The physical adsorption of molecules on metal oxide surfaces has direct implications in a number of industrial applications such as; catalysis, electronics, and fuel cells to name a few. Despite the large number of adsorption studies to date, only a small number of systems can be explained with the most advanced ab initio calculations currently available. One of the simplest metal oxide systems to study is magnesium oxide due to its simple cubic rock-salt structure. Using a patented method, nearly defect-free MgO cubes can be synthesized with a narrow size distribution exposing exclusively the (100) equilibrium crystal face. The use of this material minimizes the heterogeneity of adsorption sites due to surface defects and edge effects and allows for comparison with theoretical calculations. This study is a continued work on various homologous groups of normal alkanes and cyclic molecules. The study of n-hexane, cyclohexane, benzene, and pyridine were conducted in this work. These molecules in were chosen because of their molecular symmetry and are physically well-characterized. These systems are experimentally studied using high-resolution adsorption isotherms and neutron diffraction techniques. The results of these experiments are then matched with theoretical calculations. Analogous adsorption experiments and calculations were also conducted on graphite. Graphite is a physically well-defined surface and provides comparison with MgO. In understanding more ideal systems one can attempt to better understand more complex metal oxide surfaces. Another facet of this study is the role molecular and surface symmetry have on the adsorption characteristics of the system. Adsorbing molecules of different molecular symmetry onto surfaces of different symmetry one can better determine the importance symmetry considerations play in the adsorption characteristics of the system. Results indicate both symmetry properties drastically affect the wetting properties of these systems