UC San Diego

Interfacial chemistry is important in many key molecular processes that are critical to water quality and treatment and can also drive the fate and transport of chemical contaminants in the environment. There are three key constituents of these environmentally-relevant water systems that are well-known to interact with geochemical interfaces: organic matter, oxyanions, and biological components. Mineral surfaces in particular are extremely diverse in composition and structure; they can include iron oxides, clay minerals, and carbonates. Therefore, these different geochemical interfaces present a complex array of surface compositions and structures whereby surface catalyzed reactions can occur and potential byproducts can lead to chemical contaminants in the environment. Traditional IR spectroscopy has offered valuable information in understanding how environmental adsorbates interact with mineral surfaces. The reason for this is due to the inherent molecular-level information that can be obtained due to changes in the vibrational mode frequencies for adsorbed versus solution phase species. To date, there still remains a bit of uncertainty with how individual components interact both as isolated components and when co-adsorbed with other species and the degree to which there is heterogeneity within these systems. In this dissertation, micro-spectroscopic probes such as Atomic Force Microscopy-Infrared (AFM-IR) spectroscopy and Optical Photothermal Infrared (O-PTIR) spectroscopy are compared to more traditional infrared methods in order to provide insights and a different perspective on these interactions as they probe both morphology and spectral signals with submicron spatial resolution. Overall, these novel studies have shown that micro-spectroscopic probes offer new insights into the chemistry occurring on solid mineral surfaces in the environment and provide examples of how these techniques can be used in future work.