Journal
SMALL
Volume 13, Issue 41, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/smll.201702049
Keywords
core-shell; hybrid; kinetics; metal-organic frameworks; turbidity
Categories
Funding
- National Natural Science Foundation of China [51772008]
- National Key Research and Development Program of China [2017YFA0206701]
- National Program for Support of Topnotch Young Professionals
- Changjiang Scholar Program
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Heterometallic metal-organic frameworks (MOFs) are constructed from two or more kinds of metal ions, while still remaining their original topologies. Due to distinct reaction kinetics during MOF formation, partial distribution of different metals within a single MOF crystal can lead to sophisticated heterogeneous nanostructures. Here, this study reports an investigation of reaction kinetics for different metal ions in a bimetallic MOF system, the ZIF-8/67 (M(2-mIM)(2), M = Zn for ZIF-8, and Co for ZIF-67, 2-mIM = 2-methylimidazole), by in situ optical method. Distinct kinetics of the two metals forming single-component MOFs are revealed, and when both Co and Zn ions are present in the starting solution, homogeneous distributions of the two metals are only achieved at high Co/Zn ratio, while at low Co/Zn ratio concentration gradient from Co-rich cores to Zn-rich shells is observed. Further, by adding the two metals in sequence, more sophisticated structures are achieved. Specifically, when Co2+ is added first, ZIF-67@ZIF-8/67 core-shell nanocrystals are achieved with tunable core/shell thickness ratio depending on the time intervals; while when Zn2+ is added first, only agglomerates of irregular shape form due to the weak nucleation ability of Zn2+.
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