Experimental and Computational Study of Local Cation Environments in Oxide Photocatalysts

光催化剂利用阳光来增强化学反应的几种应用，包括减少空气和水的污染水平，并提供潜在的可再生氢能源循环。该研究项目的重点是将陶瓷材料中原子排列的细微特征与它们作为光催化剂的有效性联系起来。通过了解陶瓷光催化剂的原子级工作原理，可以设计出新的和改进的材料。直接的实验研究将进行，并支持详细的原子尺度的计算机模拟，以最大限度地获得知识。开发用于从水中制氢的光催化剂可能会产生深远的政治、经济和环境影响。从发电厂运行中去除二氧化碳将使美国的温室气体排放总量减少约35%，而氢动力汽车将额外减少约25%。该计划的教育方面突出了艺术和工程本科生之间的跨学科工作，以吸引新一代的科学家和工程师进入该领域。技术细节：层状Aurivillius陶瓷将被用作宿主系统，以允许在大范围内精确控制Ti-O， Nb-O和Ta-O键长。Aurivillius晶体将允许直接评估层状结构和铁电畴对电荷重组的影响，并将为稀掺杂共价阳离子提供宿主。复杂的Aurivillius相的独特结构特征为改进当前最先进的TiO2光催化剂提供了一个框架。使用简单的陶瓷（如TiO2）预计不会有额外的性能改善，因此需要研究具有不同结构特征的复杂陶瓷。层状陶瓷提供了在理解和光催化剂的性能方面取得突破性进展的机会，而不是寻找渐进改进的方法。实验工作将集中在使用衍射，辅以x射线吸收和光电子能谱来详细表征结构。密度泛函理论计算机模拟将使用能量最小化结构和有意应变结构来跟踪电子能带结构、缺陷能和掺杂团簇趋势。通过将模拟和实验结果联系起来，研究小组将开发现象学模型，以预测催化行为，并为未来关注表面结构和能量学的工作奠定基础。该项目的实验方面将允许参与的学生充分利用新的国家x射线和中子散射设施，并在这些领域发展专业知识。

NON-TECHNICAL DESCRIPTIONPhotocatalysts harness sunlight to enhance chemical reactions for several applications that include reducing pollution levels in air and water and providing a potential renewable hydrogen energy cycle. The research project centers on linking the subtle features of the atomic arrangements in ceramic materials with their effectiveness as photocatalysts. By understanding the atomic-scale workings of ceramic photocatalysts, new and improved materials can be designed. Direct experimental studies will be performed and supported by detailed atomic-scale computer simulations in order maximize the knowledge gained. The development of photocatalysts for generating hydrogen from water could have profound political, economical, and environmental impacts. Removing CO2 from power plant operations will reduce the total greenhouse gas emissions in the US by ~35%, while hydrogen-powered vehicles will lead to an additional ~25% reduction. The educational aspects of the program highlight interdisciplinary work between undergraduates in art and engineering to attract a new generation of scientists and engineers to the field. TECHNICAL DETAILSLayered Aurivillius ceramics will be used as the host system to allow precise control of the Ti-O, Nb-O, and Ta-O bond lengths over a wide range. The Aurivillius crystal will allow a direct evaluation of the effects of the layered structure and ferroelectric domains on charge recombination, and will provide a host for dilute doping of aliovalent cations. The distinct structural characteristics of the complex Aurivillius phases provide a framework in which to improve upon the current state-of-the-art TiO2 photocatalysts. Very little additional performance improvement is anticipated by using simple ceramics such as TiO2, necessitating the study of complex ceramics with different structural features. Instead of searching for methods for incremental improvements, layered ceramics present the opportunity to make breakthrough advances in understanding and performance of photocatalysts. The experimental work will center on the use of diffraction, complemented with X-ray absorption and photoelectron spectroscopy to characterize the structures in detail. Density functional theory computer simulations will be performed using both energy-minimized structures and intentionally strained structures to track the electronic band structure, defect energies, and dopant clustering tendencies in parallel with experiment. By linking the simulation and experimental results, phenomenological models will be developed by the research team that will allow prediction of catalytic behavior and set the foundation for future work focused on surface structures and energetics. The experimental aspects of the project will allow the students involved to take full advantage of new national facilities for X-ray and neutron scattering, and to develop expertise in these areas.