Gas-Phase Synthesis of Hetero-Oxide Structures and Understanding Their Photocatalytic Properties

杂氧化物结构因其协同的结构和化学性质而备受关注，从而使其具有优异的催化性能。该项目的主要目标是通过了解杂氧化物的结构、化学和物理以及界面性质，开发出具有更高光催化效率的杂氧化物结构。对于光催化剂的合成，湿化学法(液体环境中的胶体化学)因其相对简单和低成本而被广泛使用。另一方面，湿化学法在控制光催化剂的化学计量比、尺寸和形状方面存在一定的局限性。因此，该项目的目标是通过气相合成路线来制备杂氧化物结构。首先，我们将使用多靶单磁控气体聚集源(GAS)方法来制备异质氧化物结构。多元素(分段)溅射靶将通过调整每个组分的比例和几何位移来制备，以实现不同的化学计量比和化学有序性的氧化物组合。系统地研究了压力、功率和气体流量等工艺参数对杂氧化物结构尺寸、成分和形貌的影响。作为另一种途径，我们将把GAS(用于多元素靶方法)与定制的直流磁控溅射系统相结合，以实现核-卫星或核-壳异质氧化物结构。而高角度环形暗场(HAADF)-STEM(扫描透射式电子显微镜)由于其高Z对比度，将被用来分析异质氧化物结构的尺寸和形貌，此外，我们还将进行STEM层析以获得3D信息。将特别注意使用选区电子衍射(SAED)和高分辨率扫描电子显微镜相结合进行物相分析和成分分析。此外，还将使用电子能量损失谱和X射线光电子能谱(XPS)来获得所制备的杂氧化物结构的详细化学状态。这些详细的分析将与杂氧化物结构的光催化性能相关联。通过监测有机染料分子在UV-Vis光照射下的光漂白能力来分析光催化性能。此外，我们将使用一种新的基于衰减全反射红外(ATR-IR)的方法来测量STIRA(浅陷阱红外吸收)，它清楚地指示了浅陷阱电子从浅陷阱到光催化剂导带(CB)中的状态连续统的激发。

The hetero-oxide structures have received great attention owing to their synergistic structural and chemical properties which lead to superior catalytic properties. The primary objective of this project is to develop such hetero-oxide-structures with improved photocatalytic efficiency, by understanding their structural, chemical and physical as well as interfacial properties. For the synthesis of photocatalysts wet chemical methods (colloidal chemistry in liquid environments) have been extensively used due to their relative simplicity and low cost. On the other hand, wet chemical methods have some limitations in controlling stoichiometry, size and shape of such photocatalysts. Therefore, the project aims fabrication of hetero-oxide structures through a gas-phase synthesis route. First, we will use a multi-target single magnetron Gas Aggregation Source (GAS) approach to prepare hetero-oxide structures. Multi-element (sectioned) sputtering targets will be prepared by adjusting the portion and geometrical displacement of each component to achieve different oxide combinations in terms of stoichiometry and as well as chemical ordering. The effect of process parameters including pressure, power and gas flow rate on the size, the composition, and the morphology of hetero-oxide structures will be studied systematically. As an alternative route we will combine GAS (used for multi-element target approach) with a custom-built DC magnetron sputtering system to achieve core-satellite or core-shell hetero-oxide structures. While High Angle Annular Dark Field (HAADF)-STEM (Scanning Transmission Electron Microscopy) will be used to analyze the size and morphology of hetero-oxide structures due to its high Z-contrast, additionally we will perform STEM tomography to obtain 3D information. A special attention will be given to phase and compositional analysis by using the combination of SAED (Selected Area Electron Diffraction) and High-Resolution STEM. In addition, Electron Energy Loss Spectroscopy and X-Ray Photoelectron spectroscopy (XPS) will be used to get details of chemical states of prepared hetero-oxide structures. These detailed analyses will be correlated with photocatalytic properties of hetero-oxide structures. Photocatalytic properties will be analyzed by monitoring the ability of photo-bleaching organic dye molecules under UV-Vis light irradation. Additionally, we will use a novel Attenuated Total Reflection Infra-Red (ATR-IR) based method to measure STIRA (shallow trap IR absorption) which is a clear indication of the excitation of the shallow trapped electrons from a shallow trap to a continuum of states in the conduction band (CB) of a photocatalyst.