Abstract
Metal-organic frameworks (MOF) are an emerging class of microporous materials with promising applications. MOF nanocrystals, and their assembled super-structures, can display unique properties and reactivities when compared with their bulk analogues. MOF nanostructures of 0-D, 2-D, and 3-D dimensions can be routinely obtained by controlling reaction conditions and ligand additives, while formation of 1-D MOF nanocrystals (nanowires and nanorods) and super-structures has been relatively rare. We report here a facile templated interfacial synthesis methodology for the preparation of a series of 1-D MOF nano- and micro-structures with precisely controlled shapes and sizes. Specifically, by applying track-etched polycarbonate (PCTE) membranes as the templates and at the oil/water interface, we rapidly and reproducibly synthesize zeolitic imidazolate framework-8 (ZIF-8) and ZIF-67 nano- and micro structures of sizes ranging from 10 nm to 20 μm. We also identify a size confinement effect on MOF crystal growth, which leads to single crystals under the most restricted conditions and inter-grown polycrystals at larger template pore sizes, as well as surface directing effects that influence the crystallographic preferred orientation. Our findings provide a potentially generalizable method for controlling the size, morphology, and crystal orientations of MOF nanomaterials, as well as offering fundamental understanding into MOF crystal growth mechanisms.
Highlights
Metal-organic frameworks (MOF) are an emerging class of microporous materials with promising applications
X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements are performed directly on the templates after synthesis to confirm the formation of Zeolitic imidazolate frameworks (ZIFs) within the template pores
The previous synthesis of MOF nano- and super-structures using nanoporous templates, such as anodic aluminum oxide and polymer membranes, via interfacial or counter-diffusion manners exclusively led to the formation of 2-D MOF membranes on one side of the templates[69,70,71,72,73]
Summary
Metal-organic frameworks (MOF) are an emerging class of microporous materials with promising applications. We report here a facile templated interfacial synthesis methodology for the preparation of a series of 1-D MOF nano- and micro-structures with precisely controlled shapes and sizes. Complex super-structures can be produced through a controlled assembly of MOF nanoparticles, which often leads to emerging properties from cooperative interactions among discrete building blocks[28,29]. Such controlled assembly requires the synthesis of monodisperse MOF nanoparticles with uniform sizes and shapes. Zeolitic imidazolate frameworks (ZIFs), which are composed of imidazolate linkers and metal ions, are an extensively investigated subset of MOFs and possess attractive properties including crystallinity, micro-porosity, high surface area, and high thermal and chemical stability[39,40]. In comparison with 0-D and 2-D nanostructures, the preparation of
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