TiO2-based nanocomposites for solar fuel production: Engineering the solid-solid interface for specialized photocatalytic function

CBET-0829146灰色在我们目前对太阳能的使用与其巨大的未开发潜力之间有很大的差距。这是由于各种技术挑战，但其中最主要的是需要开发高效的光活性材料来捕捉阳光，在这种情况下，需要将其转化为化学燃料。这项研究的目的是利用直流反应磁控溅射法合成可见光驱动二氧化碳还原的二氧化钛基纳米复合材料，从而选择性和高效地生产能源丰富的燃料。我们认为，实现这一目标的关键是了解纳米结构复合材料的固-固界面所起的作用。我们实验室的最新发现揭示了一些令人惊讶的见解，即为什么二氧化钛复合材料往往表现出比纯相材料更高的光活性，并指出固体-固体界面作为催化“热点”位置的关键作用。探索固体固体界面在光催化中的作用的努力受到阻碍，因为无法在充分受控的条件下和足够的数量合成“界面”，这样就可以进行结构表征和功能询问。我们假设可以通过磁控溅射来合成二氧化钛基纳米复合材料的固-固界面，从而获得光学、电学和化学性质的最佳组合，从而通过二氧化碳还原来提高太阳能燃料的产生。拟议的工作的重点是询问并操纵溅射的固-固界面的关键特征，这些特征是高效、可见光将二氧化碳还原为CH4或CH3OH等高能量燃料的基础。溅射二氧化钛复合材料固-固界面上发生的相变会引起Ti4+配位状态的变化。在各种光催化材料中，四面体配位的钛被认为是催化二氧化碳还原的催化活性中心。我们认为，界面四面体配位的钛位置解释了混合相二氧化钛粉末的高活性，并表明这一点在Degussa P25和溶胶-凝胶材料中都是如此。在这项拟议的工作中，我们回答了以下问题：(1)在氧缺乏(TiO2x)锐钛矿/金红石纳米复合材料的相界面上是否形成了四面体配位的钛：(2)在我们的溅射复合材料中，这种局域位置是否与CO2光还原有关，以及如何在可见光激活下优化其功能；(3)溅射的V、Nb或Ta的阳离子取代是否会对我们的材料产生大量的电子和光学修饰，从而在吸收边产生红移，而不改变我们的复合材料的表面或界面催化性能以减少二氧化碳？智能优点：本研究将解释反应磁控溅射制备的TiO2基纳米复合材料光催化活性的结构和功能基础。这项拟议的研究改变了对二氧化钛的研究，二氧化钛被广泛认为是研究得很好的材料，但也是最适合能源和环境用途的材料之一。我们致力于设计、研究和开发混合相、非化学计量比纳米复合材料的关键特性。我们的目标是可重复地创建和识别驱动还原化学的界面缺陷位置。我们提议的工作结果将产生一系列知识，将合成、结构和功能之间的关系联系起来，所有这些知识都集中在光催化二氧化碳还原以产生能源丰富的燃料上。有了这样的理解，我们将能够更好地调整催化性能，以实现高效的太阳能收集和存储。广泛影响：拟议工作的更广泛意义在于，这种更深层次的理解将允许我们设计适合能源应用的新一代材料系统，特别是与太阳能收集、转换和存储相关的材料系统。拟议的工作是基础性的，但也对广泛的应用工程领域产生影响，特别是与可持续、碳中性技术和可再生资源开发有关的领域。这项拟议的工作有望推动光活性材料的设计远远超出目前的技术水平。这项研究具有很强的跨学科性质，涉及材料、化学和环境工程领域，以促进教职员工、本科生、研究生和研究生干部以及更广泛的社区的高级教学和学习。随着这个项目与我们学生群体对能源和环境相关主题的狂热兴趣相联系，本科生的研究机会比比皆是。该项目还为非理科学生、初中和高中理科教师和普通公众提供了许多工具。私人投资机构已经建立了专门知识和正在进行的合作，特别适合本提案中描述的雄心勃勃的研究计划。

CBET-0829146 Gray There is a large gap between our present use of solar energy and its enormous untapped potential. This is due to a variety of technical challenges, but primary among them is the need to develop highly efficient, photo-active materials for sunlight capture and in this case, conversion to chemical fuels. The aim of the proposed research is to synthesize using dc-reactive magnetron sputtering TiO2-based nanocomposite materials that harvest visible light to drive CO2 reduction, thereby producing energy rich fuels selectively and efficiently. We believe that the key to this goal is to understand the role played by the solid-solid interface of the nano-structured composites. Recent findings in our laboratory reveal a number of surprising insights as to why TiO2 composites tend to display higher photo-activity than pure phase materials and point to the critical role of the solid-solid interface as the location of catalytic "hot spots." Efforts to probe the role of the solid solid interface in photocatalysis are stymied by an inability to synthesize under sufficiently controlled conditions and in sufficient quantities the "interface," which would then allow structural characterization and functional interrogation. We hypothesize that the solid-solid interface of TiO2-based, nanostructured composite materials can be synthesized by magnetron sputtering to yield an optimum combination of optical, electronic and chemical properties to improve solar fuel generation by CO2 reduction.The focus of the proposed work is to interrogate and then, manipulate the critical features of the sputtered solid-solid interface that are fundamental to the high efficiency, visible light photoreduction of CO2 to energy rich fuels such as CH4 or CH3OH. The phase transition occurring at the solid-solid interface of sputtered TiO2 composites may induce changes in the coordination state of Ti4+. The tetrahedral coordinated Ti has been proposed as the catalytic active site in a variety of photoactive materials that catalyze the reduction of CO2. We believe that interfacial tetrahedrally coordinated Ti sites explain the high activity of mixed phase titania powders and have shown this to be the case in both Degussa P25 and sol-gel materials. In this proposed work, we answer the following questions: (1) Is tetrahedrally coordinated Ti formed at the phase interface of oxygen deficient (TiO2-x) anatase/rutile nanocomposites; (2) Is this localized site associated with CO2 photoreduction in our sputtered composite materials and how can we optimize its function under visible light activation; (3) Will sputtered cation substitution of V, Nb or Ta produce bulk electronic and optical modification of our material to yield a red shift in the absorption edge without altering the surface or interfacial catalytic properties of our composites to reduce CO2?Intellectual Merit: This research will explain the structural and functional basis of the photocatalytic activity in TiO2-based nanostructured composites synthesized by reactive magnetron sputtering. The proposed research redirects the investigation of TiO2, widely regarded as well studied materials, but among the best suited for energy and environmental use. We seek to engineer, interrogate and exploit critical features of mixed phase, non-stoichiometric nanocomposites. Our goal is to reproducibly create and identify interfacial defects sites that drive reductive chemistry. The results of our proposed work will produce a continuum of knowledge that links the relationships between synthesis, structure and function, all focused on photocatalytic CO2 reduction to generate energy rich fuels. With this understanding we will be better able to tune catalytic performance for efficient solar energy harvest and storage.Broader Impact: The broader significance of the proposed work is that this deeper understanding will allow us to design a new generation of material systems tailored to energy applications, especially those associated with solar energy harvest, conversion and storage. The proposed work is fundamental, but also has implications to a wide range of applied engineering areas, particularly those related to the development of sustainable, carbon neutral technologies and renewable resources. The proposed work promises to push the design of photoactive materials far beyond where the technology exists today. The research has a strong interdisciplinary nature reaching across the materials, chemical and environmental engineering fields to facilitate advanced teaching and learning among a cadre of faculty, undergraduate, graduate and postgraduate students and the larger community. Undergraduate research opportunities abound as this project connects to the avid interest among our student population in topics related to energy and the environment. This project also provides numerous vehicles for reaching non-science students, middle and high school science teachers and the general public. The PIs have established expertise and ongoing collaboration particularly well suited to the ambitious research program described within this proposal.