Surface chemistry of zinc oxide powder for catalysis and sensing applications

Gao, Jia
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University of Delaware
ZnO has been regarded as one of most promising materials that has been studied extensively in the past few decades. Its wide bandgap promoted new interest for using it as a semiconducting material in electronics, photovoltaics, etc. The history of widely using polycrystalline ZnO is almost one hundred years old. It includes facial products to prevent UV damage, pigments, and rubber additives. However, a number of questions arising from ZnO surface chemistry still remain unanswered. Previous single crystalline studies and investigations of polycrystalline ZnO were focused on different aspects of the surface reactions and many hypotheses need to be reconsidered and reconciled. In this dissertation, we focus on the surface chemistry studies of several catalytic, sensing, or environmentally important reactions of powder ZnO. The molecules described here include ethanol, acetaldehyde, acetone, acetic acid, and 2-chlorophenol. Some discrepancies among previous studies are researched to resolve ambiguity of these surface reactions. Mechanisms are provided to explain the chemical interactions of these molecules with ZnO powder. The surface analysis techniques employed include Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD). DFT cluster computations are used to simulate the surface adstructures, reaction transition states and also to predict the spectroscopic characteristics of surface adstructures such as IR vibrations and electron binding energies.