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

• Applicants: Professor Dr. Franz Faupel; Professor Dr. Lorenz Kienle
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448935424

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.

• DFG Programme: Research Grants