New Frontiers in Metal-Organic Frameworks: Chemical, Optical, and Electrochemical Control of Pore Size/Aperture

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The research program focuses on using porous materials to address challenges in sustainable chemistry. For example, sponges are porous materials. A sponge can be characterized by how much water it can absorb. In my lab, we will work on porous materials known as Metal-Organic Frameworks (MOFs). MOFs are made from inorganic metals (nodes) which are connected to one another by organic molecules (linkers). In MOFs, 80% of the crystal is empty. This 80 % is available for me as a researcher to investigate. Unlike the sponge example, the advantage of MOFs is that their pores are very regular and well defined. A well-defined pore has an internal volume and a pore aperture (i.e., the size of the opening into the pore). My research team will focus on tuning the volume of the pore and the opening of the pore in order to change how molecules are stored or interact with the MOF. The research program will focus on 2 objectives. The research team and I will utilize a MOF known as UiO-66. UiO-66 is a very sturdy MOF, making it ideal for a variety of industrial applications. When the MOF is heated, two water molecules are removed from each node. Although this reaction is reversible, we will explore how alcohols, instead of water molecules, are attached to the node. In this objective, the node will present a carbon chain into the pore instead of a hydrogen atom from the water molecule. By changing the length of the carbon chain, then the pore size can be tuned for applications in gas storage (e.g., CO2 sequestration), and water purification (e.g., mercury adsorption). The previous portion of the objective focused on adjusting every pore inside the MOF. However, if the alcohol that is being used is long enough, then only the outside of the MOF particle will be modified. Depending on the type of alcohol used, we will make MOFs that are soluble in water so that they can be easily processable into films, or easily incorporated into plastics. The research team and I will investigate MOFs which have switches built into them. Switching molecules change their shape when they are exposed to light. This switching is reversible. The switch will be placed in one of two places of the MOF. If the switch is placed by the aperture of the MOF, then the switch can be used to open and close, or, at the very least, constrict the size of the aperture. In this system, molecules can be trapped inside the MOF by simply shining light on it. Molecules used for gas-storage (e.g., methane for methane-powered cars), catalysts, and potentially even drugs can be stored in these MOFs. In the second type of switchable MOFs, the switch will point into the middle of the pore. In this system, the research team will tackle conducting MOFs in which the conductivity of the MOF can be turned on and off. The switching will occur inside the pore, and thus the pore size itself will change. The impact of this research program is that two new tools will be explored and utilized for applications in sustainability chemistry.