(30h) Controlling Metal Organic Framework Morphology, Polymorphism and Flexibility

Metal organic frameworks (MOFs) are periodic, highly porous materials that are made by combining metal ion clusters with organic linkers. The diversity available in metal ions as well as organic linkers can be used to create numerous MOFs, with thousands of structures already synthesized over the past two decades. Due to their chemical tunability as well as the control over pore size, shape and volume, MOFs have been studied for a wide variety of applications, including gas storage, separations, catalysis, energy storage, sensing and drug delivery. However, most of the research on MOFs have focused on controlling the chemical structure, and there is comparatively less work available on controlling the crystalline morphology of MOFs. For example, for many of the applications mentioned above, such as sensing, separations and charge/ion transport, it is beneficial for the MOF to be grown as a thin film with large aspect ratios, instead of as compact single crystals.

This presentation will focus on the control of non-equilibrium MOF crystal morphologies and crystal packing structures. Using nanoconfined crystallization techniques, we show that the crystal nucleation and growth profiles of MOFs can be shifted to be able to create controllable and large aspect ratio crystals and thin films, with aspect ratios exceeding 1:2500. This presentation will discuss both chemical as well as processing parameters that can control MOF crystallization and how these processes can be used to create different MOF shapes for selective sensing and separations. Downstream integration of these crystals to microfluidic devices for flow-based sensing will also be discussed.

In addition, the use of chemical and chemical engineering principles will be used to control the crystal structure of prototypical MOFs ZIF-8 and NU-1000. The delicate interplay of synthetic conditions and crystallization conditions will be studied to understand the phase behavior of these MOFs. Finally, methods to obtain phase-pure structures when different MOF crystal structures are available will be discussed.