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

半导体材料的光催化需要光的吸收激发自由电子和空穴。在半导体表面，它们可以用来产生羟基自由基，羟基自由基在所谓的高级氧化过程（AOP）中参与化学反应，例如用于空气和水的净化。因此，光催化可以消除污染物，而传统方法既不能过滤也不能生物降解。这些光催化剂的效率可以使用纳米级半导体颗粒来提高，其特点是它们的大比表面积。然而，由于粒子内部不存在电子与空穴分离的自然驱动力，因此复合过程会导致光催化效率的显著降低。因此，抑制这些重组过程代表了一种生产效率显著提高的光催化剂的有前途的方法。因此，在水处理过程中可以实现低成本和环保的建筑，而无需添加对环境有害的化学物质。在目前的研究项目中，一个明确的外部驱动力（压力）被施加到纳米级压电光催化系统（如ZnO， CdS）中，在粒子内部产生电场。这个电场不仅在空间上分离电子和空穴，而且还将它们从内部传输到相反的表面区域，在那里它们可以进行光催化过程。空间分离不仅降低了复合概率，提高了催化活性，还显著抑制了反应物的化学反反应。这些效应应通过压力依赖性光致发光（重组）和光催化活性来检测。

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.