Efficient Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels Using Sunlight

0927262格莱姆斯这个奖项是根据2009年美国复苏和再投资法案(公共法律第111-5条)资助的。在最初的工作中，PI利用氮掺杂的二氧化钛纳米管阵列实现了二氧化碳和水蒸气到甲烷和其他碳氢化合物的高效太阳能转换，其壁厚足够低，以促进有效的载体转移到吸附物种，并用铂和/或铜的纳米维助催化剂岛敏化。所有实验都是在宾夕法尼亚州大学公园的室外阳光下进行的。还检测到中间反应产物氢和一氧化碳，它们的相对浓度取决于纳米管阵列表面上的助催化剂的性质而决定了碳氢化合物的产生速率。使用功率密度在75至102 mW/cm2之间的室外阳光，归一化为100 mW/cm2的全球AM 1.5阳光，当纳米管阵列样品同时用铜和铂纳米粒子敏化时，获得111ppm cm-2小时-1(约160微升/克小时)的碳氢化合物产生速率。1这一在室外阳光下获得的二氧化碳与碳氢化合物的产生速率至少是先前发表的报道的20倍，这些报道是在实验室条件下使用紫外光进行的。PIs试图了解其高光催化二氧化碳转化率所固有的反应，以进一步显著改善这些反应。初步目标包括：{1}均匀敏化。在初步工作中，纳米管阵列样品的顶表面被铜和铂共催化剂颗粒敏化。PI相信，对纳米管阵列样品在其整个表面积上进行均匀敏化将显著提高光催化转化率。他们寻求使用原子层沉积或溶液化学技术均匀地敏化纳米管阵列样品，直接变量包括纳米颗粒类型(铜、CuO、Cu2O、铂)、负载、间距、尺寸和相对于纳米管壁厚的尺寸分布。他们将阐明助催化剂所起的作用(S)，以及相关的潜在物理机制，包括半反应，从而使光催化材料的设计能够提高性能。{2}增强了可见光吸收。将二氧化碳转化为碳氢化合物燃料的有用的大规模太阳能转换将需要对可见光做出反应的光催化剂。私营机构督导提出两条途径以达致这个目标。首先，通过扩大他们在二氧化钛氮掺杂方面的初步努力，这可以通过修改结晶退火的条件来最容易地实现，以保持晶格中的氮并最大限度地减少与掺杂相关的载流子陷阱态密度。另一种方法是通过对成分梯度金属膜进行阳极氧化来获得相应金属氧化物的纳米管阵列，从而合成用于广谱太阳能吸收的成分梯度TiCuO纳米管阵列。{3}光催化膜。通过提高敏化纳米管阵列的光催化性能，并通过减小孔径来增加表面积，PI寻求获得机械坚固的高表面积光催化膜，其中CO2和水蒸气流入其中，碳氢化合物退出，减少了回流反应的机会，从而提高了转化率，因为产物不会在纳米管表面附近积累。纳米管的孔径将被优化，以限制二氧化碳和水蒸汽物种的流入，以实现完全(或几乎完全)转化为碳氢化合物和中间体，从而获得完全的反应-产品分离。广泛影响：一种利用太阳能和二氧化碳生产碳氢燃料的可行方法，从而提供一种以化学燃料的形式存储太阳能的方法。在这个极其重要的领域对博士生进行跨学科培训，并积极参与REU。知识价值：提高对光催化材料和反应的了解，使先进的光催化剂的设计成为可能，增强对氧化物材料及其带隙工程的了解，增强对三元氧化物半导体的合成、材料特性和性能的了解。

0927262 Grimes This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In initial work the PIs have achieved efficient solar conversion of carbon dioxide and water vapor to methane and other hydrocarbons using nitrogen doped titania nanotube arrays, with a wall thickness low enough to facilitate effective carrier transfer to the adsorbing species, sensitized with nano dimensional islands of co-catalysts platinum and/or copper. All experiments have been conducted in outdoor sunlight at University Park, PA. Intermediate reaction products, hydrogen and carbon monoxide, are also detected, with their relative concentrations underlying hydrocarbon production rates as dependent upon the nature of the co-catalysts on the nanotube array surface. Using outdoor sunlight with a power density between 75 to 102 mW/cm2, normalized to global AM 1.5 sunlight at 100 mW/cm2, a hydrocarbon production rate of 111 ppm cm-2 hr-1 (about 160 microliters/g hr) is obtained when the nanotube array samples are sensitized with both Cu and Pt nanoparticles.1 This rate of CO2 to hydrocarbon production obtained under outdoor sunlight is at least 20 times higher than previous published reports, which were conducted under laboratory conditions using UV illumination. The PIs seek to understand the reactions inherent in their high rates of photocatalytic CO2 conversion, with a further aim of significantly improving them. Initial objectives include: {1} Uniform sensitization. In preliminary efforts the top surface of the nanotube array samples were sensitized with Cu and Pt co-catalyst particles. The PIs believe uniform sensitization of the nanotube array samples over their entire surface area would significantly enhance photocatalytic conversion rates. They seek to uniformly sensitize the nanotube array samples using atomic layer deposition, or solution chemistry techniques, with immediate variables including nanoparticle type (Cu, CuO, Cu2O, Pt), loading, spacing, size, and size distribution in relationship to the nanotube wall thickness. They will elucidate the role(s) the co-catalysts play, and the associated underlying physical mechanisms including half-reactions, thereby enabling design of photocatalytic materials for enhanced performance. {2} Enhanced Visible Light Absorption. Useful, scale solar conversion of CO2 to hydrocarbon fuels will require photocatalysts responsive to visible light. The PIs propose two routes to achieve this. First, by extending their preliminary efforts on nitrogen doping of titania, which can most readily be accomplished by modifying the conditions of the crystallization anneal to maintain nitrogen within the lattice and minimize the density of carrier trap states associated with doping. Another approach is the synthesis of compositionally graded Ti-Cu-O nanotube arrays designed for broad spectrum solar energy absorption, by anodization of compositionally-graded metal films to achieve nanotube arrays of the corresponding metal oxides. {3} Photocatalytic Membranes. By enhancing the photocatalytic properties of the sensitized nanotube arrays, and increasing the surface area through decreased pore size the PIs seek to achieve a mechanically robust high-surface area photocatalytic membrane into which CO2 and water vapor flow, and hydrocarbons exit reducing the chances of back reactions, thereby enhancing the conversion rate, as the products will not accumulate near the nanotube surface. The nanotube pore size will be optimized to limit the inflow of CO2 and H2O vapor species to achieve a complete (or nearly complete) conversion to hydrocarbons and intermediates, thus obtaining a complete reactant-product separation.Broader Impacts: A viable means to generate hydrocarbon fuels using solar energy and CO2, thereby providing a means to store solar energy in the form of chemical fuel. Interdisciplinary training of a Ph.D. student in this vitally important field, and significant REU participation. Intellectual Merit:Improved understanding of photocatalytic materials and reactions enabling design of advanced photocatalysts, enhanced understanding of oxide materials and their bandgap engineering, enhanced understanding of the synthesis, material properties and performance of ternary oxide semiconductors.