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

相互接触的两种不同颗粒材料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，尚未实现对接触形成及其与特定粉末应用的关系的基本理解。缺少的环节是联系人本身的特征。因此，本项目的目的是建立一个过程，使定义的异质接触的合成，并开发相应的原位表征技术，将接触性能的合成条件。使用双极电喷雾（ES）进行合成，其允许各种各样的材料组合和颗粒形态，并且由于静电吸引，通常产生混合颗粒。与后续的在线温度处理一起，这种设置允许有针对性地改变接触类型，直至扩展界面区域。光学原位测量技术被开发并用于控制该过程，包括广角光散射（WALS）以确定液滴和聚集体尺寸，Exciplex-LIF以获得关于带相反电荷的液滴的碰撞过程的详细信息，UV-Vis吸收光谱（AS）以确定带隙能量和激光诱导击穿光谱（LIBS）以确定异质聚集体的组成。附加的在线和离线技术，如气溶胶光电子能谱，TEM，XPS和ICP-MS用于验证光学技术，并更精确地解释异质聚集体的属性。由于双极电喷雾的灵活性，不同的形态和材料系统可以并将被研究，范围从欧姆接触肖特基接触p-n接触。特别地，选择Ni/Ag、TiO 2/Ag和CeO 2/TiO 2系统作为示例，这些系统对于不同类型的异质接触特别感兴趣。以TiO2/Ag光催化降解有机污染物为例，研究了接触性能与功能行为之间的关系。在项目实施过程中，将与优先计划（PP）的其他合作伙伴协调，扩大上述选择范围。已就与优先计划不同工作组的合作达成一致意见，这些合作除其他方面外，有助于通过支持建模更好地理解ES过程，并通过使用专用光学方法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.