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Prof. Zhong’ Group Made Significant Progress in the Preparation of Hierarchical Pores Metal-Organic Frameworks

Prof. Zhong’ Group Made Significant Progress in the Preparation of Hierarchical Pores Metal-Organic Frameworks

As a new type of porous crystalline solids with tailorable structures and functionalities metal-organic frameworks (MOFs) show great potential in various application fields, including adsorption, separation, catalysis, sensing and so on. However, most of MOFs reported so far are microporous materials with pore sizes of typically smaller than 2 nm. Such microporous MOFs can benefit the adsorption and separation of small molecules, but will restrict the diffusion of these molecules as well as prevent larger molecules from accessing their pores, thus greatly limiting their applications in some specific situations. Consequently, it is practically imperative to design and synthesize MOFs containing mesoporous/large pores, which is a hot topic at the moment but still remains a great challenge.
In literature, there are two main approaches that have been developed to “enlarge” the pore sizes of MOFs. One is to employ large building units (metal clusters and/or organic ligands), while the other is to generate crystal “defects” in materials. With respect to the former, the ligand-extension strategy was widely adopted. However, the pore size in the resulting periodic nanostructures of MOFs is still limited to be smaller than 10 nm. Particularly, with the increase of pore size, the MOF frameworks usually become unstable in most cases. On the other hand, the ligand-extension method normally also results in the interpenetration of structures, which will dramatically decrease the pore sizes of MOFs. In addition, from the viewpoint of cost, synthesis of large linkers is too expensive for practical applications. For the latter approach, the ligands can be cheap, but the fabrication methods are generally pivotal and difficult to follow. Thus, it is still challenging to realize hierarchical-pore MOFs (H-MOFs) with high structural controllability and good stability.

Motivated by the context described above, Prof. Zhong’s group very recently demonstrated a facile and versatile method, an in-situ self-assembly template strategy, for the fabrication of stable H-MOFs with co-existed micropores and mesopores. The main principle of this new method is to use acid/base-sensitive metal-organic assemblies (MOAs) as template and employ the relative stability between them and targeted materials. More specifically, in a self-assembly reaction process, the reversibility of coordination bonds in these coordination complexes could keep the MOAs template forming and disappearing during the stable MOFs forming and growing. Thus, the MOAs could indeed act as a chemical dynamic template to direct the construction of H-MOFs. This general strategy was successfully used to prepare 19 different H-MOFs that exhibit very rich porous properties, and the mesoporous sizes of the resulting materials can be systematically tuned by varying the amount of templates. This study provides a substantial basis for the potential applications of H-MOFs toward various fields such as large molecule adsorption, catalyst and drug delivery.

This work was cooperatively achieved by Prof. Zhong’s group in our university and Prof. Jian-Rong Li in Beijing University of Technology, which have been published on Nature Communications (H. Huang, J-R. Li, K. Wang, T. Han, M. Tong, L. Li, Y. Xie, Q. Yang, D. Liu and C. Zhong, In-situ self-assembly template strategy for the preparation of hierarchical-pore metal-organic frameworks, Nat. Commun., 2015, 6, 8847). Dr. Hongliang Huang (currently he is a postdoc) in our university is the first author.

This work is supported by the National Key Basic Research Program of China (“973”) (No. 2013CB733503), and the Natural Science Foundation of China (No. 21322601, 21136001).  
Written by: | Source: | 2015-12-16