A combined XAS/XES investigation of photochemically-driven water capture and release in azopyridine-appended metal-organic frameworks

Water scarcity is one of the key contemporary environmental issues. Metal Organic Frameworks (MOFs) have emerged as unique materials for atmospheric water harvesting even at very low relative humidity levels, with facile uptake and release kinetics. In order to rationally design improved water harvesting MOFs it is however critical to reach a detailed mechanistic, structural, and electronic understanding of the dynamic adsorption-desorption process. Here, we propose a combined in situ hard XAS/XES study to investigate the local structural and electronic modifications that occur during water adsorption and desorption in MOF systems appended with azopyridine molecules that undergo photochemically induced cis/trans transitions, which regulate the water uptake and release. We expect our results to unveil the stages of water capture by selected MOFs with unprecedented detail, thereby paving the way for the rational design of improved MOF water harvesting systems.

水资源短缺是当代核心环境议题之一。金属有机框架（Metal Organic Frameworks, MOFs）已成为极具潜力的大气取水材料，即便在极低相对湿度条件下，也具备出色的吸附与解吸动力学性能。然而，若要合理设计性能更优异的取水用MOFs，就必须深入掌握其动态吸附-解吸过程在机理、结构与电子层面的详细信息。本研究提出采用原位硬X射线吸收谱（X-ray Absorption Spectroscopy, XAS）/X射线发射谱（X-ray Emission Spectroscopy, XES）联合表征手段，探究接枝偶氮吡啶分子的MOF体系在水吸附与解吸过程中的局部结构与电子变化——该偶氮吡啶分子可发生光诱导顺反异构转变，进而调控水的吸附与解吸过程。我们预期本研究结果将以前所未有的精细程度揭示目标MOFs的取水过程各阶段，从而为性能更优化的MOF基大气取水系统的合理设计铺平道路。