The principal objective of this research is to establish a novel method for in-situ mapping and identification of multi-adsorbates on metal oxide surfaces using electrochemical scanning tunneling microscopy (EC-STM) and scanning tunneling spectroscopy (STS). A multi-adsorbate system containing arsenate, phosphate, calcium, and hematite will be used as a model competitive adsorption system because phosphate and calcium significantly influence the adsorption of arsenic by iron oxides in the environment and in water treatment systems.
The proposed research is based on the hypotheses that adsorbed anions and cations can have various distributions and interactions on metal oxide surfaces, such as patch and mixed distributions, preferential adsorption to different surface hydroxyl groups, formation of surface and three dimensional clusters, electrostatic repulsion among adsorbed anions, cation-bridging of anionic surface species, and surface-induced hydrogen bonds. Currently, there are no technologies to determine these fundamental surface features, which limit our ability to develop multi-component adsorption models for prediction of the fate and transport of pollutants in the environment and the adsorption capacity of adsorbents in water treatment systems. The surface analysis methods established in this study will enable scientists and engineers to investigate competitive adsorption of pollutants and co-existing compounds on mineral and adsorbent surfaces, chemical reactions on catalyst (such as titanium dioxides) and nano-material surfaces, and poisoning of catalysts by irreversible adsorption of co-existing compounds in solutions, at molecular levels. Understanding the distribution and interaction of adsorbed multi-component species will lead to the development of new adsorption models and invention of more effective adsorbents and catalysts.
This project integrates cutting-edge research and broader education of graduate, undergraduate, and pre-college students, and underrepresented groups. A graduate student will be trained by performing the proposed research under the PI?s supervision. An undergraduate student will participate in some of the research through a Stevens Summer Scholarship program. The PI and graduate research assistant will demonstrate the EC-STM imaging process to undergraduate students in the EN375LA Environmental Engineering Laboratory class and to middle and high school students and school teachers through existing outreach programs. The PI will integrate the research findings into the course materials of EN 551 Environmental Chemistry of Soils and Natural Surfaces. The key findings will be published in scientific journals and reported at scientific and non-scientific meetings.
