Bipolar electrospray for the synthesis of defined hetero-aggregates: Process design and in situ diagnostics

两种不同颗粒材料相互接触的聚集体提供了广泛的应用，从能源供应和环境修复到改进的生物传感器。然而，接触形成及其与特定粉末应用的关系的基本理解尚未实现。缺失的环节是接触本身的特征。因此，本项目的目的是建立一种能够合成确定的异质接触的工艺，并开发相应的原位表征技术，将接触性质与合成条件联系起来。合成是使用双极电喷雾（ES）进行的，它允许各种各样的材料组合和颗粒形态，并且由于静电吸引，通常产生杂交颗粒。再加上随后的在线温度处理，这种设置允许接触类型的目标变化，直至扩展界面区域。开发并应用光学原位测量技术来控制过程，包括广角光散射（WALS）来确定液滴和聚集体的尺寸，Exciplex-LIF来获得相反电荷液滴碰撞过程的详细信息，UV-Vis吸收光谱（AS）来确定带隙能量和激光诱导击穿光谱（LIBS）来确定异质聚集体的组成。额外的在线和离线技术，如气溶胶光发射光谱，TEM， XPS和ICP-MS被用来验证光学技术，并更精确地解释异聚集体的性质。由于双极电喷雾的灵活性，可以并且将研究不同的形貌和材料系统，从肖特基触点上的欧姆触点到p-n触点。以Ni/Ag、TiO2/Ag和CeO2/TiO2体系为例，对不同类型的异质触点进行了研究。为了获得接触性质与功能行为之间的关系，以TiO2/Ag在分解有机污染物中的光催化活性为例。上述选择将在项目过程中与优先计划（PP）的其他合作伙伴协调扩大。已同意与PP的不同工作小组合作，其中包括通过支持建模来更好地理解ES过程，以及通过使用专用光学方法来更好地理解其他过程。

Aggregates of two different particle materials in contact with each other offer a wide range of applications, ranging from energy supply and environmental remediation to improved biosensors. However, a basic understanding of contact formation and its relationship to specific powder applications has not yet been achieved. The missing link is the characterization of the contact itself. Therefore, the aim of this project is to establish a process that enables the synthesis of defined hetero-contacts and to develop the corresponding in-situ characterization techniques that relate the contact properties to the synthesis conditions. The synthesis is carried out using a bipolar electrospray (ES), which allows a wide variety of material combinations and particle morphologies and, due to electrostatic attraction, usually yields hybrid particles. Together with a subsequent online temperature treatment, this set-up allows the targeted variation of the contact type up to extended interface areas. Optical in-situ measurement techniques are developed and used to control the process, including wide-angle light scattering (WALS) to determine droplet and aggregate sizes, Exciplex-LIF to obtain detailed information about the collision process of oppositely charged droplets, UV-Vis absorption spectroscopy (AS) to determine the bandgap energy and laser-induced breakdown spectroscopy (LIBS) to determine the composition of hetero-aggregates. Additional online and offline techniques, such as aerosol photoemission spectroscopy, TEM, XPS and ICP-MS are used to verify the optical techniques and to interpret the hetero-aggregate properties more precisely. Due to the flexibility of the bipolar electrospray, different morphologies and material systems can and will be investigated, ranging from Ohm conatcts over Schottky contacts to p-n contacts. Especially the systems Ni/Ag, TiO2/Ag and CeO2/TiO2 were selected as examples, which are of special interest for the different types of hetero-contacts. In order to obtain the relationship between contact properties and functional behavior, the photocatalytic activity of TiO2/Ag in the decomposition of organic pollutants is considered as an example. The above selection is to be extended in the course of the project in coordination with other partners of the Priority Program (PP).Co-operations with different working groups of the PP have been agreed upon, which - among other aspects - serve the better understanding of the ES process by supporting modelling and of other processes by using dedicated optical methods.