Temperature Programmed Desorption and Infrared Spectroscopic Studies of Interfacial Hydrogen Bonds for Small Molecules Adsorbed on Silica and Within Metal Organic Frameworks

Abelard, Joshua Erold Robert

Temperature Programmed Desorption and Infrared Spectroscopic Studies of Interfacial Hydrogen Bonds for Small Molecules Adsorbed on Silica and Within Metal Organic Frameworks

dc.contributor.author	Abelard, Joshua Erold Robert	en
dc.contributor.committeechair	Morris, John R.	en
dc.contributor.committeemember	Tissue, Brian M.	en
dc.contributor.committeemember	Troya, Diego	en
dc.contributor.committeemember	Morris, Amanda J.	en
dc.contributor.department	Chemistry	en
dc.date.accessioned	2017-05-16T08:00:34Z	en
dc.date.available	2017-05-16T08:00:34Z	en
dc.date.issued	2017-05-15	en
dc.description.abstract	Hydrogen bonds are arguably the most important reversible intermolecular forces. However, surprisingly few studies of their fundamental nature at the gas-surface interface have been performed. Our research investigated sulfur mustard (HD) adsorption by characterizing interfacial hydrogen bonding and dispersion forces for the simulant molecules 2-chloroethyl ethyl sulfide (2-CEES) and methyl salicylate on well-characterized hydroxyl-functionalized surfaces (silica and UiO-66). Our approach utilized infrared spectroscopy to study specific surface-molecule interactions and temperature-programmed desorption to measure activation energies of desorption. 2-CEES has two polar functional groups, the chloro and thioether moieties, available to accept hydrogen bonds from free surface silanol groups. Diethyl sulfide and chlorobutane were investigated to independently assess the roles of the chloro and thioester moieties in the overall adsorption mechanism and to explore the interplay between the charge transfer and electrostatic contributions to total hydrogen bond strength. The results indicate that both SiOH---Cl and SiOH---S hydrogen bonds form when 2-CEES adsorbs to silica or hydroxylated UiO-66. However, a more stable configuration in which both polar groups interact simultaneously with adjacent silanol groups likely does not form. A systemaic study of chloroalkanes revealed that dispersion forces involving the methylene units in 2-CEES contribute to nearly half of the total activation energy for desorption from silica. Methyl salicylate possesses aromatic, hydroxyl, and ester functional groups, each of which is a potential hydrogen bond acceptor. We found that uptake on silica is mainly driven by the formation of carbonyl-silanol and hydroxyl-silanol hydrogen bonds with additional contributions from weaker interactions. In an effort to learn more about the SiOH---π bond, the adsorption of simple substituted benzene derivatives on silica was investigated to probe the effects of electron withdrawing and donating substituents. Results indicate that the substituted benzene derivatives adsorb to silica via a cooperative effect involving SiOH---π hydrogen bonds and additional substituent-surface interactions. The strength of the SiOH---π bond is enhanced by electron donating groups and weakened by electron withdrawing groups.	en
dc.description.abstractgeneral	Hydrogen bonding and dispersion forces are arguably the most important reversible intermolecular forces. The fundamental nature of both forces has been studied extensively in the gas and solution phases. However, only a few analogous studies have been performed at the gas-surface interface. The primary objective for the research described here was to investigate the fundamental nature of sulfur mustard (HD) adsorption by characterizing interfacial hydrogen bonding and dispersion forces for the surrogate (simulant) molecules 2-chloroethyl ethyl sulfide (2-CEES) and methyl salicylate. From these studies, we have gained a richer understanding of several types of important hydrogen bonds including SiOH˗˗˗Cl, SiOH˗˗˗S, SiOH˗˗˗π, SiOH˗˗˗HO, and SiOH˗˗˗O=C. Additionally, we have measured the strength of surface-adsorbate dispersion forces for methylene units in straight-chain hydrocarbons and halide moieties in substituted benzene derivatives. Together with previous work in the Morris group, this thesis provides the most comprehensive experimental study of interfacial hydrogen bonding and dispersion forces to date. Part of the ultimate impact of this research will be to guide new filtration, decontamination, and soldier protection strategies.	en
dc.description.degree	Ph. D.	en
dc.format.medium	ETD	en
dc.identifier.other	vt_gsexam:10987	en
dc.identifier.uri	http://hdl.handle.net/10919/77660	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	silica	en
dc.subject	desorption	en
dc.subject	MOF	en
dc.subject	hydrogen bond	en
dc.subject	surface	en
dc.subject	spectroscopic	en
dc.subject	TPD	en
dc.title	Temperature Programmed Desorption and Infrared Spectroscopic Studies of Interfacial Hydrogen Bonds for Small Molecules Adsorbed on Silica and Within Metal Organic Frameworks	en
dc.type	Dissertation	en
thesis.degree.discipline	Chemistry	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en