Earth-abundant solar energy materials

In this project, we have developed a novel photochemical/photoelectrochemical concept for converting water and carbon dioxide into small organic molecules, which are raw materials for solar energy storage, pharmaceutical and chemical engineering industries. The research target focuses on formation and mechanism of methane and methanol from CO2 and H2O by using a sandwich type flow-through TiO2 membrane as photocatalysts. The key challenges are exploring suitable photochemical reduction and oxidation for synthesizing the solar fuels. During this project period, we have worked on studying earth-abundant materials (i.e. MoS2, CdS) co-catalysts to enhance visible light application for TiO2 nanotube photocatalyst. Both of amorphous thin film MoS2 and crystalline thin film CdS have been prepared by magnetron sputtering at HSN labs and loaded on the nanotube substrates. The amorphous thin films MoS2 expose large amount of edges of triangle atomic structure that build up a high number of reduction centers. By dual loadings of the co-cotalysts, this project created a Z-scheme photoelectrocataltyst for high efficiency conversion of solar fuels. In addition, quantum dots PbS and Au nanoparticles modified TiO2 nanotubes have been examined and their photoelectrical effect have been studied for oxidation reaction. A unique photoreactor was built up (see report attachment) and efficiency of optimized Z-scheme photocatalyts have been examined in this reactor. The project can lead to significant improvement of photocatalytic conversion efficiency due to special construction of light-harvesting antenna. The science presentations from this project have been performed to promote this project at local, national and international levels and attracting great interests from international research society.

This project deals with developing sandwich-type free-standing and flow-through TiO2 nanotube (TNT) membrane (CdS/TNT membrane/MoS2) photocatalysts for converting carbon dioxide into small hydrocarbon molecules. The TNT membranes with highly mechanical st rength are fabricated by electrochemical anodization of sandwich type Al/Ti/Al metal foils and subsequent wet etching. Then co-catalysts are loaded on the front and back surface of the freestand, flow-through TNT membranes. Structure and photocatalytic me chanism of the photocatalysts are studied by advanced analytical methods, such as XRD, SEM/TEM, XPS, IR and gas chromatography. The optimized photocatalyst TiO2 membranes are integrated into a photocatalytic reactor. The processes of single and multiphase reaction are simulated under various flow patterns. An optimized reactor will be demonstrated for the solar fuel/CO2 conversion at a continuous model. The core idea is that the electron donor and acceptor materials are precisely loaded on the front and b ack surface of the TNT membranes, which will enhance the efficiency of the charge separation due to the controllable isolation along the axial direction of the TNT arrays. Furthermore, a stronger titania-hydrocarbon interaction by using the flow-through TNT nanochannels would be expected when hydrocarbon concentration increases to high values. The new elements in this proposal: - Fundamental: Extending the process of randomly loading multiple co-catalysts to precisely engineering, which is realized through loading the co-catalysts on front and back surfaces of 2-D free-stand, flow-through TNT membrane. - Engineering: The solar-driven reactor provides "linkers" that optical system and nanotube membranes are integrated together for a high yield sola r fuel conversion.