Title page for ETD etd-06242010-222951


Type of Document Dissertation
Author Rebodos, Robert Louie Fermo
Author's Email Address rrebodos@vt.edu
URN etd-06242010-222951
Title Implications of Oxidation on the Colloidal Stability of Magnetite Nanoparticles and Cluster
Degree PhD
Department Civil Engineering
Advisory Committee
Advisor Name Title
Vikesland, Peter J. Committee Chair
Edwards, Marc A. Committee Member
Little, John C. Committee Member
Novak, John T. Committee Member
Walz, John Y. Committee Member
Keywords
  • Maghemite
  • Sedimentation
  • Cluster-cluster aggregation
  • Magnetite
  • Oxidation
Date of Defense 2010-06-10
Availability unrestricted
Abstract
Synthetic nanomagnetite has been suggested as a potential reactant for the in-situ treatment of contaminated groundwater. Although the application of nanomagnetite for environmental remediation is promising, a full understanding of its reactivity has been deterred by the propensity of the nanoparticles to aggregate and form clusters. To characterize the factors responsible for this aggregation behavior, we determined the magnetic properties of magnetite using a superconducting quantum interference device (SQuID). Importantly, because magnetite readily reacts with O2 to produce maghemite, we analyzed the effect of oxidation on its magnetic properties. We observed that oxidation caused a decrease in the saturation magnetization and the anisotrophic barrier of magnetite resulting in less significant magnetic interactions between particles. Consequently, a decrease in the aggregation of magnetite clusters and a potential increase in stability are expected after oxidation. To support these findings, an extended series of experiments to measure the aggregation and the sedimentation of clusters of unoxidized and oxidized magnetite nanoparticles were conducted. Although the individual particle diameter remained constant after oxidation, the cluster size and the aggregation and sedimentation kinetics of magnetite were determined to be different. Oxidized samples of magnetite tended to have lower aggregation rates and were more resistant to sedimentation. These findings can be used to have a better understanding of the overall fate, transport, and reactivity of nanomagnetite, and to gain new insights on its role as a remediation agent in the subsurface environment.

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