Temperature-Controlled Evolution of Nanoporous MOF Crystallites into Hierarchically Porous Superstructures
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2019 Elsevier Inc. Sophisticated multichannel tubular structures have long been utilized in biological systems. However, the well-controlled assembly of biomimetic materials utilizing these features still remains a challenge. Herein, we report an unexpected one-pot fabrication of biomimetic hierarchically porous metal-organic framework (MOF) tubular superstructures. This temperature-controlled structural evolution was investigated under solvothermal conditions: crystalline hollow MOF tubes can be obtained via self-templating and self-healing at higher temperatures, whereas hierarchical helical or multichannel tubular superstructures are fabricated through a helical or oriented evolution process at lower temperatures. Our work here presents the first example of tubular MOF superstructures and highlights the unexpected power of self-assembly and healing during structural evolution process. It has been widely observed in various scales that complex systems have a hierarchical or multilevel organization. For instance, hierarchical tubular structures are commonly adopted in natural systems, including bears and bamboo, as a result of long-term evolution, which can help enhance fluid transportation in plants, reduce the overall weight of animals, and prevent heat transfer. Our discovery here mimics the natural evolution and generates a series of hierarchically porous metal-organic framework (MOF) superstructures through self-templating, self-healing, and oriented evolution. This facile strategy provides fresh insights into MOF growth and oriented evolution mechanisms, enabling the state-of-the-art design of multichannel materials with promising applications in water harvesting and transport, multicomponent drug delivery, efficient catalysis, and fabrication of multichannel carbon rods for energy storage. Hierarchically porous superstructures have been successfully assembled from nanoporous MOF crystallites. Benefiting from the dynamic coordination bond formation, hierarchical helical or multichannel tubular superstructures can be accessed through oriented assembly of MOF crystallites. This temperature-controlled structural evolution also enables the formation of crystalline hollow MOF tubes via self-templating and self-healing processes. Further incorporation of multiple components into these frameworks provides a fresh route for preparing stable, multivariate, and hierarchical frameworks with accessible catalytically active sites for heterogeneous catalysis.
