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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Here, we demonstrate a protocol for the two-step synthesis of single-crystalline core-shells using a non-isostructural metal-organic framework (MOF) pair, HKUST-1 and MOF-5, which have well-matched crystal lattices.

Abstract

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Introduction

MOF-on-MOF is a type of hybrid material comprising two or more different metal-organic frameworks (MOFs)1,2,3. Owing to the various possible combinations of constituents and structures, MOF-on-MOFs provide varied novel composites with remarkable properties, which have not been achieved in single MOFs, offering great potential in many applications4,5,6. Among the various types of MOF-on-MOFs, a core-shell structure in which one MOF surrounds another has the advantage of optimizing the....

Protocol

CAUTION: Before conducting the experiment, thoroughly read and comprehend the material safety data sheets (MSDSs) of the chemicals used in this protocol. Wear appropriate protective gear. Utilize a fume hood for all synthesis procedures.

1. Synthesis of cubic HKUST-1

NOTE: The experimental procedure was based on a previously reported method14. For core-shell synthesis, 10 pots were synthesized at a time. Therefore, 10 pots of t.......

Representative Results

According to the two calculated structures of the HKUST-1@MOF-5 core-shell system14, in both the (001) and (111) planes, the Cu sites from the metal nodes of HKUST-1 and the oxygen sites from the carboxylates of MOF-5 are well-matched as the chemical connection points at the interface between the two MOFs (Figure 1). Therefore, cubic and octahedral crystals of HKUST-1, in which the (001) and (111) planes are exposed, respectively, were synthesized as the core MOFs for.......

Discussion

In this protocol, cubic- and octahedral-shaped HKUST-1 crystals were synthesized, referring to a previously reported method14. For the synthesis of HKUST-1, H3BTC solution was added while heating and stirring the solution of Cu(NO3)2·2.5H2O to prevent the precipitation of H3BTC as the temperature decreased. Subsequently, acetic acid was added immediately to prevent fast nucleation and ensure the growth of a large single crystal. As soon a.......

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Ministry of Science and the ICP (No. NRF-2020R1A2C3008908 and 2016R1A5A1009405).

....

Materials

NameCompanyCatalog NumberComments
Acetic acidDAEJUNG1002-4400Synthesis of HKUST-1 (protocol steps 1.4, and 2.4)
Copper(II) nitrate hemipentahydrateSigma Aldrich223395-100GSynthesis of HKUST-1 (protocol steps 1.1, and 2.1)
D2 PHASERBruker AXSDOC-B88-EXS017-V3Powder X-ray diffraction 
Digital stirring hot plateThermo ScientificSP131320-33QHotplate for heating and stirring (protocol steps 1.2, and 2.2)
Direct-Q3UV water purification systemMILLIPOREZRQSVP030Deionized water (protocol steps 1.1, and 2.1)
Ethyl alcohol anhydrous, 99.9%DAEJUNG4023-4100Synthesis of HKUST-1 (protocol steps 1.2, and 2.2)
Forced convection oven (OF-02P/PW)JEIO TECHEDA8136Oven for heating reaction (protocol steps 1.5, 2.5, and 3.4)
N,N-diethylformamideTCID0506Synthesis of HKUST-1@MOF-5 (protocol step 3.1)
N,N'-DimethylformamideDAEJUNG6057-4400Synthesis of HKUST-1 (protocol steps 1.1, and 2.1)
Stereo microscopesNikonSMZ745TOptical Microscope 
Terephthalic acidSigma Aldrich185361-500GSynthesis of HKUST-1@MOF-5 (protocol step 3.1)
Trimesic acidSigma Aldrich482749-100GSynthesis of HKUST-1 (protocol steps 1.2, and 2.2)
Ultrasonic cleanerBRANSONICCPX-952-338RSonicator with bath for dissolving solution (protocol step 3.1)
Zinc nitrate hexahydrateSigma Aldrich228737-100GSynthesis of HKUST-1@MOF-5 (protocol step 3.1)

References

  1. Liu, C., Wang, J., Wan, J., Yu, C. MOF-on-MOF hybrids: Synthesis and applications. Coordination Chemistry Reviews. 432, 213743 (2021).
  2. Hong, D. H., Shim, H. S., Ha, J., Moon, H. R. MOF-on-MOF architectures: Applications in separa....

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