Exploring the Water-Induced Local Degradation of Metal–Organic Framework Films Using Nanoscale Infrared Spectroscopy

A plethora of applications for metal–organic frameworks (MOFs) rely on the loading of molecules into their nanoporous structures. Some MOFs, especially those containing carboxylate linkers, degrade in humid environments, detracting from their use in many applications. In the case of HKUST-1, humidity-induced hydrolysis of its Cu–O bonds can severely impair the uptake of guest molecules into its pores. However, most studies have analyzed HKUST-1 degradation in batches of crystals, while single-crystal degradation remains largely unexplored. We employ nanoinfrared spectroscopy to monitor single nanoscale HKUST-1 thin film crystals exposed to humidified gas over several days. Our results show degradation follows first-order kinetics and is accompanied by morphological changes including crack formation and the growth of large crystals of a hydrated phase. This study provides nanoscale insight into the humidity-induced degradation of MOF thin films, which can offer understanding to support long-term performance in applications such as gas separation, sensing or catalysis.