Tolman, Nathan L
(2021)
Adventitious Hydrocarbon Adsorption on Carbon and Gold Surfaces and Its Effect on Surface Properties.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
For approximately 50 years researchers have considered graphitic carbon materials to be hydrophobic but recent research has shown that the true surface energy of graphite/graphene is higher than previously believed. The masking of this surface property is caused by an adsorption layer of adventitious hydrocarbon contamination from the ambient air environment. Chapter 2 reports the effect of physisorption of organic compounds on the double layer capacitance of activated carbon electrodes. For example, exposure of activated carbon electrodes to chloroform vapor for only one minute resulted in a capacitance loss of 84.4%. It was also found that there was an adsorbate size dependence: above a certain threshold, a larger adsorbate could have more than twice the impact on capacitance as a slightly smaller one. The results were consistent with the hypothesis that volatile organic contaminants (VOCs) block access of the electrolyte to the carbon electrode surface. Chapter 3 describes a new model for conductive atomic force microscopy (CAFM) where the adsorption of adventitious hydrocarbons from the air to a graphite surface can significantly affect CAFM measurements; in particular, the liquid bridge at the probe/sample interface should not be assumed to consist of only water; airborne hydrocarbons alone can form a liquid bridge. The presence of hydrocarbons at the tip-sample interface makes the liquid bridge just as much a variable resistor as the sample surface itself is. We show that the composition and geometry of the meniscus between the probe and sample greatly affects CAFM data both in imaging mode and in local spectroscopy. Finally, Chapter 4 makes use of a single-molecule-detection capable Surface Enhanced Raman Spectroscopy (SERS) substrate to characterize adsorbates in the air that adsorb to a gold/silver surface. The data shows that aromatics, carboxylic acids, and amorphous carbon are the primary adsorbates while thiol and nitrogen species with stronger affinities for gold are absent. Amorphous carbon has been a troublesome contaminant in previously published SERS studies and the data here shows that the contaminant can come from the ambient air which is a source that has not been identified before.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
18 December 2021 |
| Date Type: |
Publication |
| Defense Date: |
29 November 2021 |
| Approval Date: |
24 October 2024 |
| Submission Date: |
10 January 2022 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
176 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Hydrocarbon, Contamination, Supercapacitor, SERS, Raman, AFM |
| Date Deposited: |
24 Oct 2024 15:37 |
| Last Modified: |
24 Oct 2024 15:49 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/42176 |
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