INTERFACIAL OXIDATION REACTIONS AND FILM NUCLEATION ON IRON SURFACES IN COMPLEX ENVIRONMENTS USING SPECTROSCOPY AT THE LIQUID/SOLID AND GAS/SOLID INTERFACE

Abstract

Iron (Fe) and its oxides are known heterogeneous catalysts in both industrial and laboratory experiments. Fe is shown to undergo oxidation forming mineral scales based on its chemical environment. A surface science approach was used to investigate chemical processes occurring at liquid/solid and gas/solid interfaces under various chemical environments to understand how Fe oxidation impacts the quality of drinking water, the catalytic ability of iron derivatives, and geological mineral formation processes. Polarized Modulated Infrared Reflection Absorption Spectroscopy (PM-IRRAS) is a surface-sensitive vibrational spectroscopic technique that is used to identify the adsorbed molecules on a reflective surface. A new PM-IRRAS method was developed to observe in situ adsorption of molecules at the air/liquid/solid interface, using 1-octadecanethiol adsorption on gold as a model system. A three-phase model was used to estimate the liquid layer thickness at the air/ethanol/Au interface. This new method was applied for investigating interfacial oxidation, corrosion, and mineral formation for understanding environmental science and heterogeneous catalytic reactions at the air/electrolyte/Fe interfaces. These studies revealed the impact of the electrolyte pH, anion concentration, effect of cations (Na+, K+, Mg2+, Ca2+, and Fe2+), and adsorption of atmospheric gases (O2, CO2) on the rate of corrosion, mineral formation, and composition of the corrosion products. The results obtained by PM-IRRAS were corroborated by the in situ liquid atomic force microscope (AFM), ex situ AFM, attenuated total reflectance Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy. The initial stages of Fe surface corrosion were studied under the influence of alkali salt (NaCl) with controlled H2O and O2 pressure. Adventitious hydrocarbon on the Fe surface was found to transform into surface adsorbed carbonates in the initial stages of Fe surface oxidation. The added anions (Cl-) on the surface migrated into the bulk during oxidation in the presence of O2 and H2O pressure. Iron catalyzes the decomposition of disinfectant by-products (DBP). Halohydrocarbons can lead to severe health hazards from consumption above the threshold limits. CDCl3 was used as a model halohydrocarbon to investigate the ability to use Fe as a heterogeneous catalyst for the dehalogenation of CDCl3. The adsorption of CDCl3(g)on Fe(111) at both cryogenic and room temperatures was measured by infrared reflection absorption spectroscopy (IRRAS) and Auger Electron Spectroscopy (AES). The dissociative chemisorption of CDCl3 on the Fe(111) surface occurs and OH groups from water block adsorption sites on Fe(111) for adsorption of CDCl3. CDCl3 adsorption at the liquid/Fe interface was not observed under the