Nanotechnology has been the main driver of scientific advances in catalytic materials and processes over the past few decades. Unique physicochemical and electronic properties emerge as materials are engineered at the nanoscale. This project explores what would happen if the same material were engineered to be even smaller at the sub-nanoscale, even down to the ?single atom'. Single-atom catalysts are the theoretical limit of material downsizing and represent a frontier of materials research today. Single-atom catalysts are synthesized by tightly anchoring individual noble metal or transition metal atoms onto a support material. This configuration allows every atom to be available for catalytic reaction, unlike nanoparticles in which atoms are inevitably buried inside a cluster of atoms. Single-atom catalysts are is particularly attractive for costly noble metal catalysts, such as palladium, that are often sought in reductive pollutant degradation processes for environmental remediation. This research project seeks to examine how palladium can be controlled at the atomic scale to best exploit the material?s catalytic properties in an application relevant to water treatment. Successful completion of this project will enable more cost-effective and more sustainable environmental remediation solutions. The project will leverage an outreach program that the investigator has established to engage local high school students in STEM research. The investigator will also offer classes to high school teachers. <br/><br/>The overarching goal of the project is to evaluate how palladium catalysts behave differently when downsized from nanoparticles to the single atom limit. Palladium single-atom catalyst material properties will be correlated with synthetic parameters by employing various advanced characterization techniques such as high energy X-ray absorption and scanning transmission electron microscopy. Other properties, including atomic dispersion, local coordination environment, and oxidation state of the active metal site, will be further correlated to catalytic performance for the reductive removal of toxic halogenated organic compounds and nitrate (and potentially other oxyanions, such as nitrite, bromate, chromate, and perchlorate) that pose significant environmental and human health concerns. In addition, the PI will investigate how palladium single-atom catalysts behave differently from their nanoparticle counterparts over long-term use and under a complex water matrix to evaluate their environmental fate. Graduate and undergraduate students participating in this project will gain interdisciplinary knowledge, particularly at the interface of materials science, advanced spectroscopy, and environmental engineering. The project will leverage an outreach program that the PI has established to engage local high school students in STEM research. The PI will also offer classes to high school teachers.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.