(601e) Development of Novel Bottom-up Thin Film Fabrication Techniques for Metal-Organic Frameworks (MOFs)

Porous crystalline frameworks can be defined as a class of nano-polymers with high surface areas and wide ranges of pore volumes, mainly for applications involving adsorption, storage, and separations. Due to the exceptional reputation of high porosities and stabilities of MOFs/COFs, most of the research focus has been on synthesis for specific application. The obtained nanocrystalline material is obtained in powdered form, therefore, they must be further processed, and engineered to cater to the needs of the field of application. These post-processing approaches are mainly termed as top-down methods. Developments were further made to skip the two-step process and fabricate them in-situ, also termed as bottom-up approach. The majority of the applications of MOFs, COFs and other nanopolymers are in the form of films or membranes. Therefore, to cater to these needs, a novel semi-continuous percolation-assisted coating (PAC) technique and electrodeposition of MOFs respectively. In both the efforts, the fabricating technique is coupled with the fundamental kinetic studies that provide insight into the nucleation and growth of the MOFs under study. The PAC technique has been benchmarked on a Copper (Cu) paddlewheel based HKUST-1 MOF. The established in-situ kinetic protocol on FTIR coupled with COMSOL reactor modeling was utilized for successful development of the PAC technique. The PAC technique enables fabrication of thin films on a variety of porous substrates like nylon, Teflon (PTFE) and polyvinyl (PVDF). These composites are essential towards separation of gas- and liquid- mixtures (demonstrated to separate CH₄-H₂ mixtures).

Electrodeposition of MOFs is a relatively new approach, which has been introduced recently and has been demonstrated on a handful of MOFs. This is mainly because a precise control of the experimental parameters is required to increase the selectivity of the MOF formation and avoid any unnecessary hydroxides and oxides of the metallic species. In the MOF field, Zirconium (Zr) based MOFs have gained significant importance and have a wide range of applicability. Zr MOFs undergo an extremely complex reaction pathway which has been controlled solvothermally in previous studies. Electrochemically, only one Zr MOF i.e UIO-66 has been reported. In this work, four Zr MOFs (previously reported through solvothermal routes) have been synthesized electrochemically. A polymorphic system of porphyrin-Zr MOFs namely MOF-525 / PCN-222 has been studied and by precise control of the synthesis conditions, phase pure MOFs have been obtained. While undergoing cathodic deposition, the fundamental pathways and transformation of the Zr polynuclear structure has been proposed in conjunction with DFT calculations.