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Interfacial Water Organization and Ion Distributions Investigated with Vibrational Sum Frequency Spectroscopy: Answering Fundamental Questions for Environmental Chemistry

Hua, Wei
http://rave.ohiolink.edu/etdc/view?acc_num=osu1385593745

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Environmental Science.
Knowledge of interfacial water organization and ion distributions is necessary to elucidate questions regarding atmospheric aerosol chemistry, thundercloud electrification, geochemistry, and ocean surface processes, among others. Water organization at air/aqueous interfaces is strongly influenced by inorganic ions, specifically, ion distributions that exist in the interfacial region, where the molecular environment changes from three-dimensions to two-dimensions. Over the past century, the study of water has been a major focus of experimental and theoretical work. Although much progress has been made, interfacial water behavior and ion distributions are still incompletely understood. Here, interface-specific nonlinear optical spectroscopies, conventional vibrational sum frequency generation (VSFG) and heterodyne-detected vibrational sum frequency generation (HD-VSFG), are employed to probe interfacial water molecules at the molecular level. HD-VSFG spectroscopy allows for direct interrogation of the average orientation of the transition dipole moment of interfacial water molecules that is intrinsically contained in the sign of the second-order nonlinear susceptibility, X(2). The water organization and ion distributions at air/aqueous interfaces of inorganic salt solutions are inferred from Im X(2) spectra obtained by HD-VSFG spectroscopy. It is shown here that salt purity grade and/or pretreatment have a tremendous impact on the interfacial water spectrum of aqueous salt solutions. It is determined that the presence of trace organic contamination is primarily responsible for spectral distortion for the bare air/ aqueous interfaces of salt solutions while the presence of trace polyvalent cations proves to be critical in exploring the alkali cation-carboxylate binding and comparing relative binding affinity of different cations at the air/aqueous surfactant interfaces. A standard pretreatment procedure for inorganic salts and their solutions is established for VSFG spectroscopy via a series of systematic studies. Results indicate that the ion-induced interfacial electric field is in the opposite direction for solutions containing sulfate and carbonate salts relative to solutions of chloride, nitrate and perchlorate salts. It is found that bicarbonate and its counterion do not significantly perturb the interfacial water organization. These findings are attributed to charge separation, or lack thereof, arising from ion distributions within the air/aqueous interfaces tested. It is also suggested that the cation identity (lithium, sodium, ammonium, magnesium) as well as the concentration changes result in the partial reversal of the net direction of the interfacial electric field in the nitrate salt solutions. These findings have great significance for understanding the differences observed in aerosol reactivity as a function of aerosol salt composition. In addition, we now have a better understanding of cloud droplet electrification and ocean surface properties. Moreover, a fundamental appreciation of ions at aqueous surfaces has been gained such that we now know that monovalent anions exist in the interfacial region and on average above their counterions. However, high valency anions exist below their counter cations, causing a reversal in electric field direction. Although various specific ion properties such as polarizability, size, charge (surface charge density), geometry (shape) have been suggested to account for interfacial ion distribution, it is indicated here that charge effect exerts a greater impact than the other factors in the case of oxyanions.
Heather Allen (Advisor)
Barbara Wyslouzil (Committee Member)
Anne Carey (Committee Member)
Lingying Zhao (Committee Member)
244 p.
Analytical Chemistry; Atmospheric Chemistry; Chemistry; Environmental Science; Physical Chemistry

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Citations

  • Hua, W. (2013). Interfacial Water Organization and Ion Distributions Investigated with Vibrational Sum Frequency Spectroscopy: Answering Fundamental Questions for Environmental Chemistry [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1385593745

    APA Style (7th edition)

  • Hua, Wei. Interfacial Water Organization and Ion Distributions Investigated with Vibrational Sum Frequency Spectroscopy: Answering Fundamental Questions for Environmental Chemistry. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1385593745.

    MLA Style (8th edition)

  • Hua, Wei. "Interfacial Water Organization and Ion Distributions Investigated with Vibrational Sum Frequency Spectroscopy: Answering Fundamental Questions for Environmental Chemistry." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1385593745

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.