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

利用半导体材料的光催化需要由于光的吸收而激发自由电子和空穴。在半导体的表面，它们可用于产生羟基自由基，其参与所谓的高级氧化过程（AOP）中的化学反应，例如用于空气和水的净化。因此，光催化可以消除污染物，这些污染物既不能通过常规方法过滤也不能通过生物降解。这些光催化剂的效率可以使用纳米级半导体颗粒来增强，其特征在于它们的大比表面积。然而，由于在颗粒内部不存在用于电子和空穴分离的自然驱动力，复合过程导致光催化效率的显著降低。因此，这些复合过程的抑制代表了一种有前途的方法，以生产具有显着提高的效率的光催化剂。因此，可以实现低成本和环境友好的结构，而无需在水处理过程中添加对环境有害的化学品。在目前的研究项目中，一个定义明确的外部驱动力（压力）施加到纳米级压电光催化系统（如ZnO，CdS），诱导粒子内部的电场。该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对的表面区域，在那里它们可用于光催化过程。空间分离除了降低复合几率、提高催化活性外，还显着抑制了反应物的化学逆反应。应通过压力相关光致发光（复合）以及光催化活性检测这些效应。

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.