Title

Surfaces, interfaces, and chemical reactivity with manganese oxides

Date of Completion

January 2007

Keywords

Chemistry, Inorganic

Degree

Ph.D.

Abstract

The results described herein are focused on studying the surfaces of manganese oxides and the factors that influence the chemical reactivity, interfacial behaviors, and formation of micrometer-scaled patterns that have well ordered periodicity. The work is separated into two parts. The first part focuses on synthesis, characterization and variables that control the growth and formation of lamellar patterns consisting of manganese oxide nanoparticles in a colloidal state. The second part probes the reactivity of the manganese oxide surfaces with chemicals in the gas phase. ^ A one-pot synthesis of a hexagonal form of a layered manganese oxide material (OL-3) using mild conditions and low temperature is discussed in the first part. The oxidation of an aqueous solution of manganese acetate using tetramethylammonium hydroxide and hydrogen peroxide at 4°C leads to the formation of a colloidal manganese dioxide solution. The manganese oxide nano-flakes are indexed to an R3m rhombohedral structure. The nano-flakes were characterized using X-ray diffraction, electron microscopy, chemical analysis, thermal analysis, N2 sorption, and UV/Visible spectroscopy. The results indicate that the colloidal manganese oxide nano-flakes flocculated into ultra-thin, disorderly-stacked hexagonal lamellar sheets composed of a new layered material designated at OL-3. ^ Pattern formation has been the subject of numerous studies due to the importance in fabricating functional devices and relationships with shape formation in nature. Several micro- and nanometer-scale patterns have been prepared from different types of materials by mainly using soft lithography and self-assembly techniques. Herein the formation of inorganic films is reported, consisting of regular micrometer size parallel lines, spontaneously generated during solvent evaporation starting from a uniform colloidal solution. These lines are made of manganese oxide having a layered structure whose composition and phase can be altered via ion-exchange and thermal treatment. ^ The second part of this work focuses on in-situ methods of photoelectron and infrared spectroscopy to study the reactivity of formic acid on the surface of amorphous manganese oxide (AMO). This study reveals a specific mechanism of adsorption and desorption of the formate species relative to temperature. Spectroscopy results confirm that formic acid undergoes decarboxylation on the surface of AMO. ^