GOALI: The Structure Sensitivity of Photochemical Reactions on Titanium Dioxide Surfaces

9712606基于太阳能活化二氧化钛光催化剂的Rohrer系统具有有效和经济地去除或降解空气和水中有毒杂质的潜力。该提案的首席研究员最近进行的研究表明，二氧化钛的某些表面（TiO2）比其他表面更擅长催化相关反应。如果能更全面地了解这种催化性质的各向异性，就有可能通过结构或微观结构的修饰来提高二氧化钛光催化剂的反应性。因此，本项目的目标是定义这种取向-反应性关系，并确定导致这种现象的机制。已知取向表面的光催化活性将通过直接显微分析来确定。电子背散射衍射图将用于确定二氧化钛多晶中许多晶粒的表面取向，俄歇电子能谱将用于评估相同晶粒的表面化学成分。使用原子力显微镜（AFM）确定每个表面的形态结构后，它们将用于光催化从水溶液中还原Ag+。沉积在每个颗粒上的银量将根据原子力显微镜图像估计，并作为每个表面相对反应性的衡量标准。平行实验将对生长在蓝宝石上的低指数、均匀、高纯度钛外延层进行。基于这些测量，我们将确定相对光催化活性的取向依赖性。这个GOALI项目的结果将是二氧化钛光催化活性的表面取向-表面性质关系。确定这种关系不仅将提高我们对二氧化钛光化学的了解，还将展示可用于系统地确定其他表面现象（如腐蚀和磨损）完全依赖取向的方法。＊＊＊

9712606 Rohrer Systems based on solar activated titania photocatalysts have the potential to effectively and economically remove or degrade toxic impurities in air and water. Recent research conducted by the principal investigator of this proposal has recently demonstrated that some surfaces of titania, TiO2, are better at catalyzing the relevant reactions than others. If the anisotropy of this catalytic property were understood more completely, it might be possible to improve the reactivity of titania photocatalysts through structural or microstructural modifications. Therefore, the objective of this project is to define this orientation-reactivity relationship and to identify the mechanism responsible for this phenomenon. The photocatalytic activity of surfaces with known orientations will be determined using direct microscopic analysis. Electron back scattered diffraction patterns will be used to determine the surface orientations of many grains in a titania polycrystal and Auger electron spectroscopy will be used to assess the surface chemical compositions of the same grains. After using atomic force microscopy (AFM) to determine the morphological structure of each surface, they will be used to photocatalyze the reduction of Ag+ from aqueous solution. The amount of silver deposited on each grain will be estimated on the basis of AFM images and taken as a measure of the relative reactivity of each surface. Parallel experiments will be conducted on low index, homogeneous, high purity titania epi-layers grown on sapphire. Based on such measurements, we will determine the orientation dependence of the relative photocatalytic activity. %%% The outcome from this GOALI project will be a surface orientation-surface property relationship for the photocatalytic activity of titania. Defining this relationship will not only advance our inowledge of titania photochemistry, it will also demonstrate methods that can be used to systematically determine the full orientation dependence of other surface phenomena such as corrosion and wear. ***