Title page for ETD etd-11042011-100135


Type of Document Dissertation
Author Davis, Erin Durke
Author's Email Address edurke@vt.edu
URN etd-11042011-100135
Title Ultrahigh Vacuum Studies of the Kinetics and Reaction Mechanisms of Ozone with Surface-Bound Fullerenes
Degree PhD
Department Chemistry
Advisory Committee
Advisor Name Title
Morris, John R. Committee Chair
Brewer, Karen J. Committee Member
Long, Gary L. Committee Member
Troya, Diego Committee Member
Wi, Sungsool Committee Member
Keywords
  • fullerenes
  • ozone
  • C60
  • ozonolysis
  • ultrahigh vaccum
  • endohedrals
Date of Defense 2011-10-10
Availability restricted
Abstract
Acquiring in depth knowledge of the ozone oxidation of surface-bound fullerenes

advances the understanding of fullerene fate in the environment, as well as the reactivity of

ozone with carbonaceous nanomaterials. Recent ultrahigh vacuum studies of the reaction of gasphase

ozone with surface-bound fullerenes have made it possible to observe the formation and

subsequent thermal decomposition of the primary ozonide (PO). As the use of nanomaterials,

such as C60, continues to increase, the exposure of these molecules to humans and the

environment is of growing concern, especially if they can be chemically altered by common

pollutants. These experiments are made possible by combining ultrahigh vacuum surface

analysis techniques with precision dosing using a pure O3 gas source. The experimental setup

also provides the capability of monitoring surface-bound reactants and products in situ with

reflection-absorption IR spectroscopy, while gas-phase products are detected with a mass

spectrometer. Our results indicate that ozone adds across a 6/6 bond on the C60 cage, forming an

unstable intermediate, the primary ozonide. The observed initial reaction probability for the PO

is γ = 4.1 x 10-3. Energies of activation for the formation and decomposition of the PO were

obtained via temperature-dependent studies. After formation, the primary ozonide thermally

decomposes into the Criegee Intermediate which can rearrange or, upon further exposure to

ozone, react with another ozone molecule to form a variety of products such as carbonyls,

anhydrides, esters, ethers, and ketenes. Larger fullerenes (C70, C76, C78, and C84) were also

exposed to gas-phase ozone, in order to observe the reaction rate for ozonolysis and to propose

an initial mechanism for ozone exposure. The results indicate that the structure of the fullerenes

has little to no impact on the rate of oxidation via ozone. Lastly, Terbium endohedral were

exposed to ozone, in an effort to determine whether ozone was capable of oxidizing both the

outer fullerene cage, as well as the Tb atom sequestered inside. The preliminary XPS data

suggests ozone oxidizes both within an hour of continuous exposure. Understanding this

atmospherically-relevant reaction from both a mechanistic and kinetic standpoint will help

predict the environmental fate of fullerenes and their oxides.

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