Novel and Facile Strategy for Controllable Synthesis of Multilayered Core-Shell Zeolitic lmidazolate Frameworks

Core-shell metal organic framework (MOF) crystals have attracted increasing attention due to their specific structure and remarkable properties. Herein, we demonstrate a facile approach for the synthesis of uniform multilayered core shell MOF crystals including ZIF-67@ZIF-8@ZIF-67 and ZIF-8@ZIF-67@ZIF-8 for the first time, by adopting the condition for the preparation of relatively larger sized crystals to fabricate the shells on the surface of relatively smaller sized seeds without any auxiliary condition. Compared with the control experiments opposite our strategy, there are two dominant factors determining the successful synthesis: (i) the homological feature between ZIF-8 and ZIF-67 favors the heterogeneous nucleation and continuous crystal growth on the surface of seeds; (ii) by controlling a relatively lower nucleation rate and a longer crystal growth stage, it enables the shell formation on the surface of the seed but avoids other monocomponent crystals generated in solution. In addition, the size of the core and the thickness of the shell could also be easily controlled by using the seeds in different size and varying the molar feeding ratio of Zn2+/Co2+, respectively, during the preparation process. Furthermore, such a strategy is also expected to extend to the synthesis of other multilayered core-shell MOFs.