article · Angewandte Chemie International Edition
Hierarchically porous metal-organic frameworks combine micropores and mesopores, yet controlling their synthesis at the molecular scale remains challenging. A new method demonstrates reversible and controllable mesopore generation and renovation in the microporous framework HKUST-1. Using an ammonia-gas etching process, mesopores are introduced into carboxylate-based frameworks by cleaving carboxylate-metal bonds along specific planes. This gas-phase etching generates uniform internal mesopores while preserving crystal size and outer morphology. Crucially, the size of the mesopores is determined by the etching temperature, whereas the pore volume is adjusted via etchant gas pressure. Furthermore, treating the etched structures with precursor solutions allows the mesopores to be repaired or closed, facilitating the encapsulation of adsorbed molecules. This approach provides a precise molecular-scale protocol for tailoring framework properties.
Metal-organic frameworks are porous materials used to capture and store molecules, but rigid pore architectures often restrict their performance. By establishing a reversible method to create and repair larger internal pores without damaging crystal morphology, this technique allows researchers to customise pore dimensions and securely trap guest molecules, broadening the functional scope of porous materials.
This work represents early-stage laboratory research. The protocol could enable chemical and materials developers to produce customised hierarchically porous materials, particularly for applications involving molecular encapsulation and adsorption. However, the abstract demonstrates the technique on HKUST-1 under controlled conditions and does not report scale-up, cost analyses, or testing in real-world operating environments, indicating the process is still far from market deployment.
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Abstract Hierarchically porous MOFs (HP‐MOFs) present advantageous synergism of micro‐ and mesopore but challenging in synthetic control at molecular scale. Herein, we present the first example of reversible and controllable mesopore generation and renovation in a microporous MOF of HKUST‐1 via synthetic manipulation at molecular scale. An ammonia‐gas etching strategy is proposed to create mesopores in carboxylate‐based microporous MOFs and thus produce HP‐MOFs. Gas‐phase etching ensures uniform mesopore formation inside the MOF crystals via plane‐oriented cutting the carboxylate‐metal bonds off without affecting the crystal size and morphology. The mesopore size is controlled by the etching temperature, while the mesopore volume could be tuned by adjusting etchant pressure. The generated mesopores could be renovated using MOF precursors solutions so that to achieve controllable mesopore generation/closure, and encapsulation of the adsorbed molecules. This work demonstrates a powerful protocol for precisely tailoring and tuning the properties of MOF materials at molecular scale.
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DOI: 10.1002/anie.202103104
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