Influence of a pressure induced piezoelectric field on the recombination processes in photocatalytically active nanoparticles

• Applicants: Professor Dr.-Ing. Frank. A. Müller; Professor Dr. Carsten Ronning
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 249762625

Photocatalysis with semiconductor materials requires the excitation of free electrons and holes due to the absorption of light. At the surface of the semiconductor they can be utilized to generate hydroxyl radicals, which take part at chemical reactions in so called advanced oxidation processes (AOP) e.g. for air and water purification. Photocatalysis can thus eliminate pollutants, which can neither be filtered nor degraded biologically by conventional methods. The efficiency of these photocatalysts can be enhanced using nanoscale semiconductor particles, which are characterized by their large specific surface area. However, since no natural driving force for the separation of electrons and holes exists inside the particles, recombination processes cause a significant reduction of the photocatalytic efficiency. The suppression of these recombination processes thus represents a promising approach to produce photocatalysts with significantly improved efficiency. As a result low cost and environmentally friendly constructions can be realized without adding environmentally harmful chemicals during water treatment. In the present research project a well-defined external driving force (pressure) is impressed to nanoscale piezoelectric photocatalytic systems (e.g. ZnO, CdS) inducing an electrical field inside the particles. This electrical field not only separates the electrons and holes spatially, but also transports them from inside to opposite surface areas where they are available for photocatalytic processes. Besides decreasing the recombination probability and increasing the catalytic activity, chemical back reactions of the reactants is also significantly inhibited by the spatial separation. These effects shall be detected by pressure dependent photoluminescence (recombination) as well as photocatalytic activity.

• DFG Programme: Research Grants