Date of Completion

12-16-2016

Degree Type

Honors Thesis - Campus Access

Discipline

Chemistry (CHEM)

First Advisor

Emily A. Jarvis

Abstract

Titanium dioxide (TiO2) is one of the best characterized metal oxides due to its use in many fields, notably photocatalysis and solar energy conversion. Surface reactivity and thus the efficacy of TiO2 as a heterogeneous catalyst is greatly affected by stoichiometric deviations at the surface due to localized oxygen depletion. This effect has been characterized previously in two of the three crystallographic forms of TiO2, anatase and rutile. Due to difficulty preparing macroscale samples, the third phase, brookite, has not been well characterized, though recent studies suggest brookite has increased photocatalytic ability compared to the other two forms. In this study TiO2 nanopowders consisting of mostly brookite were synthesized by laser evaporation and the extent of oxygen depletion was analyzed by nuclear reaction analysis. Density functional calculations are coupled with these experimental studies to examine the geometry and electronic structure of three oxygen-depleted brookite surfaces, (210), (010), and (001) representing the lowest energy terminations likely present in a brookite sample. Geometry optimizations and density of states analyses revealed that Ti atoms present on oxygen-depleted surfaces tend to relax toward the interior oxide and regain metallic geometry and electronic structure. Both experimental and ab initio results therefore indicate the surface of the synthesized TiO2 nanopowders is markedly metallic in character due to localized oxygen depletion. These preliminary results hold significant implications for the success of brookite in surface chemistry applications of catalysis and solar materials.

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