UC Irvine

X – ray photoelectron spectroscopy (XPS) has traditionally been used to characterize the chemistry at solid surfaces. Recently, work has been done to expand the utility of XPS to other interfaces such as liquids. Work carried out in this thesis focused on a wide range of experimentation using photoelectron spectroscopy. XPS under ultra-high vacuum conditions is used to characterize the photodeposition of Pt nanoparticles on the surface TiO2 nanoparticles supported on highly oriented pyrolytic graphite (HOPG). Following the Pt 4f peak, photodeposition and photoreduction of the Pt nanoparticles on the surface of TiO2 can be observed. A shift from a oxidized Pt(IV) state (75.2 eV) to a Pt(II) state (72.5 eV) is observed over longer illumination times. Pt(0) is only observed after heating is applied. Temperature programmed desorption showed a decrease of the desorption temperature of water with Pt in its reduced form on the surface of TiO2.

Liquid interfaces using a liquid jet were also characterized in later Chapters of this thesis. Fe(II) salts were dissolved in acidic aqueous solution and the interaction between iron and halides were characterized. A small shift in the Cl 2p binding energy (0.4 eV) was observed for Cl- but not observed for Br-. The association of Cl- to Fe(II) also leads to changes in the relative contributions of Fe and Cl species near the interface. In a subsequent chapter, changes to the intramolecular interactions of acetic acid lead to relative binding energy shifts in the C 1s region of the spectrum. These shifts are related to the hydrogen bonding present in the solvation sphere of the acetic acid in aqueous and methanol solutions. Finally, a mixing jet was generated and characterized using sodium iodide. The signal intensity is related to the relative flow rate input in the microfluidic chips which form the foundation for kinetic reaction experiments of complex solutions using XPS.