Environmental Materials Beyond and Below Nanoscale: Palladium Single Atom

在过去的几十年里，纳米技术一直是催化材料和工艺科学进步的主要驱动力。当材料被设计成纳米级时，独特的物理化学和电子特性就会出现。这个项目探索的是，如果同样的材料在亚纳米尺度上被设计得更小，甚至小到“单原子”，会发生什么。单原子催化剂是材料小型化的理论极限，是当今材料研究的前沿。单原子催化剂是通过将单个贵金属或过渡金属原子紧密地固定在支撑材料上而合成的。这种结构允许每个原子都可以用于催化反应，不像纳米粒子中原子不可避免地隐藏在原子簇中。单原子催化剂对于昂贵的贵金属催化剂尤其具有吸引力，例如钯，它们通常用于环境修复的还原性污染物降解过程。该研究项目旨在研究如何在原子尺度上控制钯，以便在与水处理相关的应用中最好地利用材料的催化性能。该项目的成功完成将带来更具成本效益和更可持续的环境修复解决方案。该项目将利用研究者建立的外展计划，让当地高中生参与STEM研究。调查员还将为高中教师提供课程。该项目的首要目标是评估钯催化剂在从纳米颗粒缩小到单原子极限时的表现差异。钯单原子催化剂材料的性能将通过各种先进的表征技术，如高能x射线吸收和扫描透射电子显微镜，与合成参数相关联。其他性质，包括原子分散、局部配位环境和活性金属位点的氧化状态，将进一步与还原去除有毒卤化有机化合物和硝酸盐（以及潜在的其他氧化离子，如亚硝酸盐、溴酸盐、铬酸盐和高氯酸盐）的催化性能相关，这些氧化离子对环境和人类健康造成重大影响。此外，PI将研究钯单原子催化剂在长期使用和复杂水基质下的表现与纳米颗粒催化剂的不同，以评估它们的环境命运。参与该项目的研究生和本科生将获得跨学科的知识，特别是在材料科学，先进光谱学和环境工程的界面。该项目将利用PI建立的外展计划，让当地高中生参与STEM研究。PI还将为高中教师提供课程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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. 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.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.