Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Wipf, David O.

Committee Member

Pittman, Charles U., Jr.

Committee Member

Emerson, Joseph

Committee Member

Gwaltney, Steven R.

Committee Member

Henry, William P.

Date of Degree

5-12-2012

Document Type

Dissertation - Open Access

Major

Chemistry

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Arts and Sciences

Department

Department of Chemistry

Abstract

This dissertation focuses on developing new methods using the scanning electrochemical microscope (SECM) to produce chemical concentration maps of different chemical species on various surfaces. Reactive oxygen species (ROS) and transition metal ion maps were generated, indicating the presence or absence of relative types of chemical species on the surface. Imaging of both species was based on a modified scanning UME tip and monitoring the change in the tip impedance. 4-Nitrobenzenediazonium tetrafluoroborate was used as the main modifier, and resultant nitrophenyl groups on the modified electrodes were electrochemically converted to aniline to yield the two types of modified electrodes. In the presence of ROS, a permanent change in the impedance accompanies reaction of the surface layer with the ROS, and this change can be used to map the localized reactive species. The spot scanning method was introduced over continuous scanning to enhance the sensitivity. This enhanced method generated a more effective method to map ROS compared to the diAC/dxmajor image in the continuous scanning method. Images obtained by this sacrificial method show that alternating current SECM (AC-SECM) can be used to map ROS on a surface. The capacitive change gives direct indication of the concentration of these highly reactive species. Transition metal ions showed a partially reversible adsorption with aniline-modified electrodes. Localized concentrations of buffered copper and nickel divalent cations were generated by pumping through a micro-capillary embedded in a substrate. Copper and nickel ions on these substrates were mapped successfully. A solution of calcium ions was used as the negative control. Biased nickel, copper, and lead wire-embedded substrates were line scanned to validate these results. An aniline-modified electrode was placed away from the metal wire and the time taken for metal ions to reach the electrode tip was measured after a voltage pulse. These data were compared with calculated diffusion times. Both systems were optimized using the medium pH, scan rates, and tip potentials. AC-SECM coupled with modified electrodes showed the capability of mapping both ROS and some transition metal ions semi-quantitatively.

URI

https://hdl.handle.net/11668/20559

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