Name: synthesis of single-crystalline core-shell metal-organic frameworks
Uploaded: 2023-02-10T13:35:00
Description: Watch this Scientific Journal Video about Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks at JoVE.com

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).

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...

<ol>
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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&#183;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...

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 characteristics of both MOFs by designing a more elaborated system5,6,7,8,9,10. Although many examples of core-shell MOFs have been reported, single-crystalline core-shell MOFs are uncommon and have been successfully synthesized mostly from isostructural pairs11,12,13. Moreover, single crystalline core-shell MOFs constructed using non-isostructural MOF pairs have seldom been reported, owing to the difficulty in selecting a pair that exhibit a well-matched crystal lattice3. To achieve seamless interfaces of the single-crystalline core-shell MOFs, a well-matched crystal lattice and chemical connection points between the two MOFs are critical. Here, the chemical connection point is defined as the spatial location where the linker/metal node of one MOF meets the metal node/linker of the second MOF through a coordination bond. In our previous reports14, the computational algorithm was used to screen for optimal targets for synthesis, and six suggested MOF pairs were successfully synthesized.
This paper demonstrates a protocol for synthesizing a single-crystalline core-shell MOF of an HKUST-1 and MOF-5 pair, which are iconic MOFs composed of totally different constituents and topologies. HKUST-1 was chosen as the core because it is more stable than MOF-5 under solvothermal reaction conditions15,16. Furthermore, because the chemical connection points between MOF-5 and HKUST-1 are well-matched in both the (001) and (111) planes, cubic and octahedral HKUST-1 crystals in which each plane is exposed were used as the core MOF. This protocol suggests the possibility of synthesizing more diverse core-shell MOFs with lattice-matching.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acetic acid</td>
			<td>DAEJUNG</td>
			<td>1002-4400</td>
			<td>Synthesis of HKUST-1 (protocol steps 1.4, and 2.4)</td>
		</tr>
		<tr>
			<td>Copper(II) nitrate hemipentahydrate</td>
			<td>Sigma Aldrich</td>
			<td>223395-100G</td>
			<td>Synthesis of HKUST-1 (protocol steps 1.1, and 2.1)</td>
		</tr>
		<tr>
			<td>D2 PHASER</td>
			<td>Bruker AXS</td>
			<td>DOC-B88-EXS017-V3</td>
			<td>Powder X-ray diffraction&#160;</td>
		</tr>
		<tr>
			<td>Digital stirring hot plate</td>
			<td>Thermo Scientific</td>
			<td>SP131320-33Q</td>
			<td>Hotplate for heating and stirring (protocol steps 1.2, and 2.2)</td>
		</tr>
		<tr>
			<td>Direct-Q3UV water purification system</td>
			<td>MILLIPORE</td>
			<td>ZRQSVP030</td>
			<td>Deionized water (protocol steps 1.1, and 2.1)</td>
		</tr>
		<tr>
			<td>Ethyl alcohol anhydrous, 99.9%</td>
			<td>DAEJUNG</td>
			<td>4023-4100</td>
			<td>Synthesis of HKUST-1 (protocol steps 1.2, and 2.2)</td>
		</tr>
		<tr>
			<td>Forced convection oven (OF-02P/PW)</td>
			<td>JEIO TECH</td>
			<td>EDA8136</td>
			<td>Oven for heating reaction (protocol steps 1.5, 2.5, and 3.4)</td>
		</tr>
		<tr>
			<td>N,N-diethylformamide</td>
			<td>TCI</td>
			<td>D0506</td>
			<td>Synthesis of HKUST-1@MOF-5 (protocol step 3.1)</td>
		</tr>
		<tr>
			<td>N,N&#39;-Dimethylformamide</td>
			<td>DAEJUNG</td>
			<td>6057-4400</td>
			<td>Synthesis of HKUST-1 (protocol steps 1.1, and 2.1)</td>
		</tr>
		<tr>
			<td>Stereo microscopes</td>
			<td>Nikon</td>
			<td>SMZ745T</td>
			<td>Optical Microscope&#160;</td>
		</tr>
		<tr>
			<td>Terephthalic acid</td>
			<td>Sigma Aldrich</td>
			<td>185361-500G</td>
			<td>Synthesis of HKUST-1@MOF-5 (protocol step 3.1)</td>
		</tr>
		<tr>
			<td>Trimesic acid</td>
			<td>Sigma Aldrich</td>
			<td>482749-100G</td>
			<td>Synthesis of HKUST-1 (protocol steps 1.2, and 2.2)</td>
		</tr>
		<tr>
			<td>Ultrasonic cleaner</td>
			<td>BRANSONIC</td>
			<td>CPX-952-338R</td>
			<td>Sonicator with bath for dissolving solution (protocol step 3.1)</td>
		</tr>
		<tr>
			<td>Zinc nitrate hexahydrate</td>
			<td>Sigma Aldrich</td>
			<td>228737-100G</td>
			<td>Synthesis of HKUST-1@MOF-5 (protocol step 3.1)</td>
		</tr>
	</tbody>
</table>

synthesis of single-crystalline core-shell metal-organic frameworks

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.

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...

Watch this Scientific Journal Video about Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks at JoVE.com

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

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.

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...

Our protocol suggests the possibility of synthesizing diverse lattice-matched, core-shell MOFs, and can be extended to multiple pairs. Non-isostructural MOF pair can be integrated into single-crystalline core-shell MOFs with a seamless interface by the solvothermal reaction. By using MOFs with different pro-environment, core-shell materials for efficient gas separation or catalytic application can be designed and synthesized.To begin, add 4.72 grams of copper nitrate hemi-pentahydrate to a 100-milliliter Erlenmeyer flask and dissolve in 60 milliliters of deionized water and DMF mixture. Swirl the flask manually. Place six milliliters of this solution into a 20-milliliter vial.Next, add 1.76 grams of 1, 3, 5-benzenetricarboxylic acid and 22 milliliters of ethanol to a 50-milliliter Erlenmeyer flask, and stir the solution at 90 degrees Celsius on a heated hot plate until dissolution. Add 2.2 milliliters of this solution to the vial containing the solution prepared earlier and immediately add 12 milliliters of acetic acid. Close the lid of the vial and place it in a convection oven heated to 55 degrees Celsius for 60 hours.Decant the mother liquor. Wash the crystals by first adding fresh ethanol to the vial using a dropper, and then removing it. Wash the crystals two more times.For core-shell synthesis, store the cubic crystals of HKUST-1 in a 20-milliliter vial full of N, N-Diethylformamide, or DEF, solvent. Add 0.760 grams of zinc nitrate hexahydrate and 10 milliliters of DEF in a 20-milliliter vial and dissolve it using a sonicator. Similarly, dissolve 0.132 grams of terephthalic acid in 10 milliliters of DEF in a 20-milliliter vial.Mix the total volume of both solutions in a 35-milliliter glass jar. Quickly weigh the filtered HKUST-1 crystals and place them in the glass jar containing the mixed solution. Seal the jar tightly with a silicon cap.After spreading the HKUST-1 crystals well on the bottom of the glass jar, place the jar in a convection oven and heat at 85 degrees Celsius for 36 hours. Decant the mother liquor and wash the resultant crystals by first adding fresh DEF to the jar, and then removing the DEF. Wash the crystals two more times.For the solvent exchange, discard the storing solvent and DEF from the vial containing HKUST-1@MOF-5, and add dichloromethane into the vial. Shake it manually for effective exchange and change the dichloromethane solvent three to four times every four hours. The computational structure models for the HKUST-1@MOF-5 system at the 001 and 111 plane are shown here.The optical microscope images of cubic-shaped HKUST-1, octahedral-shaped HKUST-1, and cubic and octahedral-shaped HKUST-1@MOF-5 core-shell are presented in this figure. The HKUST-1 crystal is located in the center of the colorless MOF-5 crystal, with a seamless interface to provide a core-shell structure. Photographs of HKUST-1@MOF-5 in diethylformamide and dichloromethane and the corresponding optical images of the cores-shell MOF using cubic and octahedral-shaped HKUST-1 are shown here.The images represent the PXRD patterns of HKUST-1, HKUST-1@MOF-5 with cubic and octahedral-shaped HKUST-1, and the simulated patterns of HKUST-1 and MOF-5. These PXRD measurements proved the phase purity of the core-shell crystal. placing the glass jar in the convection oven where the expression of the core MOF is important for synthesizing a singly-grown core-shell MOF.PCN-68@MOF-5, UiO-66@MIL-88B, and others can be synthesized by following this procedure, which means that it is expandable to other core-shell pairs. This technology can provide a systematic pathway to design and synthesize core-shell MOFs to improve performance in a specific application.

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