Adventitious Hydrocarbon Adsorption and Its Effect on the Solid-Liquid Interface

Hurst, Justin (2020) Adventitious Hydrocarbon Adsorption and Its Effect on the Solid-Liquid Interface. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Abstract

Atmospheric hydrocarbon adsorption has recently been revealed to mask the intrinsic properties of some surfaces. The prevalence of hydrocarbon adsorption was previously only understood in vacuum science, but as new sensitive techniques developed it became possible to study the adsorption behavior in ambient air. In this work, we have studied the effect of atmospheric adsorption on graphite and soil minerals.

We studied the change in capacitance on aqueous graphite electrodes when exposed to air and while in solution. We found that exposing a freshly exfoliated highly oriented pyrolytic graphite (HOPG) surface to ambient air and 1-octadecene vapor (ca. 1 ppm) caused a ca. 30% and 70% decrease in its double layer capacitance, respectively. Similarly, a 38% decrease of capacitance was observed within 1500 min after a freshly cleaved HOPG was immersed in 1 M NaCl solution; liquid phase ellipsometry data showed that a contamination layer of ca. 0.6 - 2 nm was formed on the HOPG surface within the same time frame. The capacitance of a contaminated sample can be partially and temporarily restored by applying a high or low potential (-1.222 V or 0.778 V vs. Ag/AgCl). For graphite in 1-butyl-3-methylimidazolium hexafluorophosphate, we found a slight difference between the capacitance in a clean hood and in a glove box. Solution phase capacitance reduction is between 25-30% in both pure solution and with added contaminant. This work also emphasized the U-shaped capacitance vs. potential curve of the graphite-ionic liquid system, contrary to recent literature.

The second system of study is the soil-water interface. In this work we showed how airborne adventitious hydrocarbons can adsorb to mineral surfaces to contribute to soil-water repellency. The water contact angle (WCA) was shown to increase from 0° to 25° for silica, and to 65° for alumina after 4 days of exposure in ambient air. The change in the amount of hydrocarbons was monitored by spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS). Water drop penetration time (WDPT) was measured on kaolinite after treatments with either heat or ozone to show that adsorption of airborne hydrocarbons can increase the WDPT of mineral powders.

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Details

Item Type:	University of Pittsburgh ETD
Status:	Unpublished
Creators/Authors:	Creators Email Pitt Username ORCID Hurst, Justin jmh226@pitt.edu jmh226 0000-0003-3636-0473
ETD Committee:	Title Member Email Address Pitt Username ORCID Committee Chair Liu, Haitao hliu@pitt.edu Committee Member Li, Lei lel55@pitt.edu Committee Member Amemiya, Shigeru amemiya@pitt.edu Committee Member Star, Alexander astar@pitt.edu
Date:	16 September 2020
Date Type:	Publication
Defense Date:	12 June 2020
Approval Date:	16 September 2020
Submission Date:	22 July 2020
Access Restriction:	No restriction; Release the ETD for access worldwide immediately.
Number of Pages:	177
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:	Electrode, Soil water repellency, Adventitious Carbon
Date Deposited:	16 Sep 2020 14:08
Last Modified:	16 Sep 2020 14:08
URI:	http://d-scholarship.pitt.edu/id/eprint/39542

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