Name: electrophoretic crystallization of ultrathin high-performance metal-organic framework membranes
Uploaded: 2018-08-16T15:00:00
Description: Watch this Scientific Journal Video about Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes at JoVE.com

We acknowledge our home institution, the &#201;cole Polytechnique F&#233;d&#233;rale de Lausanne (EPFL), for its generous support. This project has received funding from the European Union&#39;s Horizon 2020 Research and innovation program under the Marie Sk&#322;odowska-Curie grant agreement No. 665667. The authors thank Pascal Alexander Schouwink for his help with XRD.

CAUTION: Read carefully the material safety data sheets (MSDS) of the chemicals involved. Some of the chemicals used in the experiment are toxic. The present method involves the synthesis of nanoparticles. Therefore, take appropriate precautions. The entire synthesis procedure must be performed in a well-ventilated fume hood.
NOTE: The details of the instruments, the chemicals, and the materials involved in the synthesis of the MOF films are listed in Table 1.
<p class="jo...

<ol>
	<li>Knebel, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Defibrillation+of+soft+porous+metal-organic+frameworks+with+electric+fields.">Defibrillation of soft porous metal-organic frameworks with electric fields.</a> Science. 358, 347-351 (2017).</li><li>Brown, A. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interfacial+microfluidic+processing+of+metal-organic+framework+hollow+fiber+membranes.">Interfacial microfluidic processing of metal-organic framework hollow fiber membranes.</a> Science. 345, 72-75 (2014).</li><li>Dzubak, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ab+initio+carbon+capture+in+open-site+metal-organic+frameworks.">Ab initio carbon capture in open-site metal-organic frameworks.</a> Nature Chemistry. 4, 810-816 (2012).</li><li>Gascon, J., Kapteijn, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal-organic+framework+membranes-high+potential,+bright+future.">Metal-organic framework membranes-high potential, bright future.</a> Angewandte Chemie International Edition. 49, 1530-1532 (2010).</li><li>Liu, X., Wang, C., Wang, B., Li, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+Organic-Dehydration+Membranes+Prepared+from+Zirconium+Metal-Organic+Frameworks.">Novel Organic-Dehydration Membranes Prepared from Zirconium Metal-Organic Frameworks.</a> Advanced Functional Materials. 27, 1-6 (2017).</li><li>Zhang, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+selective+NH2-MIL-53(Al)+MOF+membranes+with+high+permeability.">Hydrogen selective NH2-MIL-53(Al) MOF membranes with high permeability.</a> Advanced Functional Materials. 22, 3583-3590 (2012).</li><li>Kwon, H. T., Jeong, H. -. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+synthesis+of+thin+zeolitic-imidazolate+framework+ZIF-8+membranes+exhibiting+exceptionally+high+propylene/propane+separation.">In situ synthesis of thin zeolitic-imidazolate framework ZIF-8 membranes exhibiting exceptionally high propylene/propane separation.</a> Journal of the American Chemical Society. 135, 10763-10768 (2013).</li><li>Hou, J., Sutrisna, P. D., Zhang, Y., Chen, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+ultrathin,+continuous+metal-organic+framework+membranes+on+flexible+polymer+substrates.">Formation of ultrathin, continuous metal-organic framework membranes on flexible polymer substrates.</a> Angewandte Chemie International Edition. 55, 3947-3951 (2016).</li><li>Barankova, E., Tan, X., Villalobos, L. F., Litwiller, E., Peinemann, K. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+metal+chelating+porous+polymeric+support:+the+missing+link+for+a+defect-free+metal-organic+framework+composite+membrane.">A metal chelating porous polymeric support: the missing link for a defect-free metal-organic framework composite membrane.</a> Angewandte Chemie International Edition. 56, 2965-2968 (2017).</li><li>He, G., Dakhchoune, M., Zhao, J., Huang, S., Agrawal, K. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophoretic+Nuclei+Assembly+for+Crystallization+of+High-Performance+Membranes+on+Unmodified+Supports.">Electrophoretic Nuclei Assembly for Crystallization of High-Performance Membranes on Unmodified Supports.</a> Advanced Functional Materials. , (2018).</li><li>Li, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-area+synthesis+of+high-quality+and+uniform+graphene+films+on+copper+foils.">Large-area synthesis of high-quality and uniform graphene films on copper foils.</a> Science. 324, 1312-1314 (2009).</li><li>Rodriguez, A. T., Li, X., Wang, J., Steen, W. A., Fan, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+synthesis+of+nanostructured+carbon+through+self-assembly+between+block+copolymers+and+carbohydrates.">Facile synthesis of nanostructured carbon through self-assembly between block copolymers and carbohydrates.</a> Advanced Functional Materials. 17, 2710-2716 (2007).</li><li>Huang, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-area+single-layer+graphene+membranes+by+crack-free+transfer+for+gas+mixture+separation.">Large-area single-layer graphene membranes by crack-free transfer for gas mixture separation.</a> Nature Communications. , (2018).</li><li>Agrawal, K. V., Dakachoune, M., Huang, S., He, G., Dudani, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ultrahigh flux gas-selective nanoporous carbon membrane and manufacturing method thereof. , (2017).</li><li>Liu, J., W&#246;ll, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-supported+metal-organic+framework+thin+films:+fabrication+methods,+applications,+and+challenges.">Surface-supported metal-organic framework thin films: fabrication methods, applications, and challenges.</a> Chemical Society Reviews. 46, 5730-5770 (2017).</li></ol>

The standout feature of the ENACT method with respect to the existing methods15 is that the ENACT method enables the synthesis of highly intergrown, ultrathin MOF films on a wide range of porous and nonporous substrates. Any substrate pretreatment is avoided, making this method quite straightforward for the synthesis of MOF films. Although EPD equipment has to be used for the deposition of a nuclei film, the equipment is composed of a power source, a metal electrode, and a beaker, which is quite s...

Thin molecular sieving membranes offer a high-energy efficiency in the separation of molecules and can reduce the overall cost of fuels, CO2 capture, water purification, solvent recovery, etc.1,2. MOFs are a promising class of material for the synthesis of molecular sieving membranes because of the involved isoreticular synthetic chemistry and relatively straightforward crystallization3. To date, MOF membranes comprising of diverse crystalline structures, including that of ZIF-4, -7, -8, -9, -11, -67, -90, and -93, and UiO-66, HKUST-1, and MIL-53 have been reported4,5. These membranes are synthesized by crystallizing high-quality polycrystalline MOF films on a porous support. Generally, to obtain a high separation selectivity, it is necessary to reduce the defects in the polycrystalline MOF film (such as pinholes and grain-boundary defects). A convenient approach to reduce the defects is to crystallize a thick film. Not surprisingly, several of the earlier reported on MOF membranes are extremely thick (over 5 &#181;m). Unfortunately, thick films lead to a long diffusion path, which limits the membrane permeance. Therefore, while selectivity is improved, permeance is sacrificed. To circumvent this trade-off, it is imperative to develop methods to crystallize ultrathin (&#60; 0.5 &#181;m-thick), defect-free MOF films.
ZIF-8 is the most intensively studied MOF for membrane synthesis, due to its exceptional chemical and thermal stability and a simple crystallization chemistry6,7. So far, the reported ultrathin ZIF-8 membranes have been realized by changing the surface chemistry or topology of the underlying porous substrate, favoring the heterogeneous nucleation of ZIF-8, which is essential for an intergrown polycrystalline film. For instance, Chen et al. reported the synthesis of 1 &#181;m-thick ZIF-8 film on (3-aminopropyl)triethoxysilane-modified TiO2-coated poly(vinylidene fluoride) (PVDF) hollow fibres8. They observed a high heterogeneous nucleation density and attributed it to the simultaneous modification of the surface chemistry and nanostructure. The Peinemann group reported an ultrathin ZIF-8 membrane on a metal-chelating, polythiosemicarbazide (PTSC) support9. This unique metal-chelating capability of PTSC led to the binding of zinc ions, promoting the heterogeneous nucleation of ZIF-8 which, subsequently, led to high-performance ZIF-8 membranes. In general, tuning the substrate chemistry and nanostructure facilitates the synthesis of high-performance MOF membranes; however, these methods are quite complex, and usually cannot be reapplied to synthesize MOF membranes from other attractive MOF structures.
Herein, we report the synthesis of ultrathin, highly intergrown ZIF-8 films using a simple and versatile crystallization approach that can be reapplied to form a thin intergrown film of several crystalline materials10. We show examples of ZIF-8 and ZIF-7 films prepared without any substrate pretreatment, which greatly simplifies the preparation process. The ZIF-8 films are prepared on a wide range of substrates (ceramic, polymer, metal, carbon, and graphene). The 500 nm-thick ZIF-8 film on an anodic aluminum oxide (AAO) support displays an attractive separation performance. A high H2 permeance of 8.3 x 10-6 mol m-2 s-1 Pa-1 and attractive ideal selectivities of 7.3 (H2/CO2), 15.5 (H2/N2), 16.2 (H2/CH4), and 2655 (H2/C3H8) are achieved.
The crystallization approach that enables the above-mentioned feat is ENACT. ENACT deposits ZIF-8 nuclei onto a substrate directly from the crystal&#39;s precursor sol. The approach utilizes EPD for a very short period of time (1 - 4 min) right after the induction time (the time when the nuclei appear in the precursor sol). The application of an electric field to the charged MOF nuclei drives them toward an electrode with a flux that is proportional to the strength of the applied electric field (E), the electrophoretic mobility of the colloid (&#956;), and the concentration of nuclei (Cn) as shown in the Equations 1 and 2.
<img alt="Equation 1" src="/files/ftp_upload/58301/58301eq1.jpg" /> 
(Equation 1)
<img alt="Equation 2" src="/files/ftp_upload/58301/58301eq2.jpg" /> 
(Equation 2)
Here, 
v = the drift velocity, 
&#950; = the zeta potential of the nuclei, 
&#949;o = the permittivity of vacuum, 
&#949;r = the dielectric constant, and 
&#951; = the viscosity of the precursor sol.
Therefore, by controlling E and the solution pH (which determines &#950;&#160;), the packing density of nuclei can be controlled. The subsequent growth of the densely-packed nuclei in the precursor sol allows researchers to obtain a highly intergrown polycrystalline film.

<table>
	<tbody>
		<tr>
			<td>Zinc nitrate hexahydrate</td>
			<td>Sigma-Aldrich</td>
			<td>96482-500G</td>
			<td>98% purity</td>
		</tr>
		<tr>
			<td>2-Methylimidazole</td>
			<td>Sigma-Aldrich</td>
			<td>M50850-500G</td>
			<td>99% purity</td>
		</tr>
		<tr>
			<td>Benzimidazole</td>
			<td>TCI</td>
			<td>B0054-500G</td>
			<td>98% purity</td>
		</tr>
		<tr>
			<td>Tape</td>
			<td>DuPont</td>
			<td>KPT-1/8</td>
			<td></td>
		</tr>
		<tr>
			<td>Epoxy</td>
			<td>GC Electronics</td>
			<td>19-823</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper foil</td>
			<td>Alfa Aesar</td>
			<td>13380.CV</td>
			<td>99.9% purity</td>
		</tr>
		<tr>
			<td>Power source for EPD</td>
			<td>Gamry Instruments</td>
			<td>Interface 1000E Potentiostat</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonic cleaner</td>
			<td>MTI corporation</td>
			<td>VGT-1860QTD</td>
			<td></td>
		</tr>
		<tr>
			<td>AAO</td>
			<td>GE Healthcare Life Sciences&#8206;</td>
			<td>6809-7013</td>
			<td></td>
		</tr>
		<tr>
			<td>PAN</td>
			<td>Shandong MegaVision</td>
			<td></td>
			<td>The molecular weight cut-off is 100 kDa</td>
		</tr>
	</tbody>
</table>

electrophoretic crystallization of ultrathin high-performance metal-organic framework membranes

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and non-porous supports (polymer, ceramic, metal, carbon, and graphene). We developed a novel crystallization technique, which is termed the ENACT approach: the electrophoretic nuclei assembly for the crystallization of highly intergrown thin films (ENACT). This approach allows for a high density of heterogeneous nucleation of MOFs on a chosen substrate via the electrophoretic deposition (EPD) directly from the precursor sol. The growth of well-packed MOF nuclei leads to a highly intergrown polycrystalline MOF film. We show that this simple approach can be used for the synthesis of thin, intergrown zeolite imidazole framework (ZIF)-7 and ZIF-8 films. The resulting 500 nm-thick ZIF-8 membranes show a considerably high H2 permeance (8.3 x 10-6 mol m-2 s-1 Pa-1) and ideal gas selectivities (7.3 for H2/CO2, 15.5 for H2/N2, 16.2 for H2/CH4, and 2655 for H2/C3H8). An attractive performance for C3H6/C3H8 separation is also achieved (a C3H6 permeance of 9.9 x 10-8 mol m-2 s-1 Pa-1 and a C3H6/C3H8 ideal selectivity of 31.6 at 25 &#176;C). Overall, the ENACT process, owing to its simplicity, can be extended to synthesize intergrown thin films of a wide range of nanoporous crystalline materials.

A homemade EPD set-up was used to synthesize the MOF films (Figure 1). Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns were collected for the ZIF-8 nuclei film (Figure 2). SEM was used to image the surface and cross-sectional morphologies of the AAO support, ZIF-8/AAO membrane, PAN support, ZIF-8/PAN membrane, ZIF-8/graphene film, and ZIF-7/AAO membrane (Figure 3). The ...

Watch this Scientific Journal Video about Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes at JoVE.com

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

A simple, reproducible, and versatile approach for the synthesis of intergrown, polycrystalline metal-organic framework membranes on a wide range of unmodified porous and non-porous supports is presented.

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and ...

This method can help answer the key question in the synthesis of polycrystalline MOF films such as how to reproducibly synthesize MOF membranes. The main advantage of this technique is that we can control the heterogeneous nucleation over a wide range of substrates leading to ultrathin, pinhole-free MOF films. With the help of crystal engineering involving controlled nucleation and growth we aim to simplify the synthesis protocol of MOF films.First cut a high purity copper foil into four by four centimeter pieces. For ease of clamping the cut foil with a set of copper crocodile clips draw a line 0.5 centimeters from one of the edges of each square foil. Then flatten each foil using a cylindrical roller on a clean surface.Clean the copper foils thoroughly by bath sonication in acetone for 15 minutes followed by bath sonication in isopropanol for 15 minutes. Then dry the copper foils in a glass dish. Carefully position the desired substrate on the center of the copper electrode using tape.Rinse the substrate electrode assembly for one minute with water followed by isopropanol and again with water. Following this attach a bare copper electrode to an anode. Then attach the substrate electrode assembly to a cathode.Place the two electrodes in a 100 milliliter glass beaker and adjust the separation between them to one centimeter. Add 31.6 grams of zinc hexahydrate solution and 35 grams of benzimidazole solution to a 100 milliliter beaker and stir for 30 seconds at room temperature to form the precursor sol. Transfer the precursor sol to the beaker containing the electrodes.Then immerse both the electrodes up to the 3.5 centimeter mark by adjusting the height of the beaker. Carry out electrophoretic deposition with the deposition voltage of one volt for four minutes by turning on the power of the power source. At the end of the deposition lower the beaker slowly to avoid disturbing weak adhesion between the freshly deposited nuclei and the substrate.After drying the substrate transfer it to a microscopic glass slide using tape to hold the substrate in place. For crystal growth mix 31.6 grams of zinc hexahydrate solution and 35 grams of 2-Methylimidazole solution in a 100 milliliter beaker. Place the microscopic glass slide with the substrate vertically in the precursor solution and leave it undisturbed for 10 hours at 30 degrees Celsius.After 10 hours of crystal growth rinse the substrate with water for 30 minutes. Then dry the substrate in a clean atmosphere. To prepare the sealant thoroughly mix an equal proportion of epoxy and hardener and leave the mixture for one hour.Place the ZIF-8 membrane on a 24 millimeter wide steel disc with a five millimeter diameter hole at the center. Apply the epoxy along the edges of the substrate and subsequently cover the substrate except for the five millimeter diameter hole at the center. After allowing the epoxy to dry overnight use a stereomicroscope to scan the membrane along with the known reference scale.Use graphical software to calculate the exposed area of the membrane from the scanned image. Next place the steel disc with the membrane in the stainless steel permeation cell and place the cell in an oven. Ensure a leak tight fit by placing Viton O-rings above and below the steel disk and fastening the screws.Set the gas flow rates on the feed and the sweep sides to 30 milliliters per minute. To remove the absorbed water during synthesis heat the membrane cell using hydrogen as the feed gas and argon as this sweep gas at 130 degrees Celsius for two hours. Maintain a pressure of 0.1 megapascal at the feed and the sweep side by adjusting the needle valves on the on the retentate and the permeate side, respectively.Change the gas flow in the feed side to target gas and set the gas flow rate to 30 milliliters per minute. Set the temperature of the oven to the desired temperature. Then calculate the permeance in Excel once a steady state is established according to the data from the mass spectrum.The SEM images and XRD patterns show that the ZIF-8 nuclei film is compact and demonstrates that the ENACT method is quite efficient in controlling the heterogenous nucleation density over a substrate. Post growth the film morphology observed by SEM is compact and pinhole free and appears to be highly intergrown. The surface and cross sectional morphologies of the AAO support, ZIF-8/AAO membrane, PAN support, and ZIF-8/PAN membrane are shown here.The gas permanence data of ZIF-8/AAO and ZIF-8/PAN membranes show that their hydrogen propane selectivity are 2700 and 190, respectively, proving that the MOF film is nearly defect free. The ZIF-8/AAO membrane shows ultra high hydrogen permeance because of the ultra thin thickness. While attempting this procedure it is important to wait for the crystal induction to occur before applying electrophoretic deposition.For example crystal induction can be ratified by studying the precursor sol in a transmission electron microscope. This protocol allows one to precisely control the heterogeneous nucleation density and the thickness of the nuclei film by simply controlling the electric field and the electrophoretic deposition time and can be extended to synthesize polycrystalline films of various structures. After the development of this technique it paved the way for us to conduct systematic studies on engineering MOF films of thickness less than 100 nanometers.Don't forget working with methylimidazole and zinc nitrate can be hazardous and precautions such as wearing gloves and operating in a fume hood should always be taken while performing this procedure.

electrophoretic-crystallization-ultrathin-high-performance-metal

Research

JoVE Journal

Chemistry

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

Synthesis of a Water-soluble Metal&amp;#8211;Organic Complex Array

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids with adsorbates. Vibrational spectra provide information on the chemical nature of adsorbed species and their structure. Thus, they are very useful for obtaining molecular level understanding of surface species. The IR spectrum of the sample itself gives some direct information about the material. General conclusions can be drawn concerning hydroxyl groups, some stable surface species and impurities. However, the spectrum of the sample is &#34;blind&#34; with respect to the presence of coordinatively unsaturated ions and gives rather poor information about the acidity of surface hydroxyls, species decisive for the adsorption and catalytic properties of the materials. Furthermore, no discrimination between bulk and surface species can be made. These problems are solved by the use of probe molecules, substances that interact specifically with the surface; the alteration of some spectral features of these molecules as a result of adsorption provides valuable information about the nature, properties, location, concentration, etc., of the surface sites.
The experimental protocol for in-situ IR studies of gas/sample interaction includes preparation of a sample pellet, activation of the material, initial spectral characterization through the analysis of the background spectra, characterization by probe molecules, and study of the interaction with a particular set of gas mixtures. In this paper we investigate a zirconium terephthalate metal organic framework, Zr6O4(OH)4(BDC)6 (BDC = benzene-1,4-dicarboxylate), namely UiO-66 (UiO refers to University of Oslo). The acid sites of the UiO-66 sample are determined by using CO and CD3CN as molecular probes. Furthermore, we have demonstrated that CO2 is adsorbed on basic sites exposed on dehydroxylated UiO-66. Introduction of water to the system produces hydroxyl groups acting as additional CO2 adsorption sites. As a result, CO2 adsorption capacity of the sample is strongly enhanced.

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

The use of FTIR spectroscopy for investigation of the surface properties of polycrystalline solids is described. Preparation of sample pellets, activation procedures, characterization with probe molecules and model studies of CO2 adsorption are discussed.

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids ...

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.

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. ...

Synthesis and Discovery of Phosphonate-Based MOFs: A Solvothermal Approach

Discovery and Synthesis Optimization of Isoreticular Al(III) Phosphonate-Based Metal-Organic Framework Compounds Using High-Throughput Methods

High-throughput (HT) methods are an important tool for the fast and efficient screening of synthesis parameters and the discovery of new materials. This manuscript describes the synthesis of metal-organic frameworks (MOFs) from solution using an HT reactor system, resulting in the discovery of various phosphonate-based MOFs of the composition [Al2H12-x(PMP)3]Clx&#8729;6H2O (H4PMP = N,N &#39;-piperazine bis(methylenephosphonic acid)) for x = 4, 6, denoted as Al-CAU-60-xHCl, containing trivalent aluminum ions. This was accomplished under solvothermal reaction conditions by systematically screening the impact of the molar ratio of the linker to the metal and the pH of the reaction mixture on the product formation. The protocol for the HT investigation includes six steps: a) synthesis planning (DOE = design of&#160;experiment) within the HT methodology, b) dosing and working with in-house developed HT reactors, c) solvothermal synthesis, d) synthesis workup using in-house developed filtration blocks, e) characterization by HT powder X-ray diffraction, and f) evaluation of the data. The HT methodology was first used to study the influence of acidity on the product formation, leading to the discovery of Al-CAU-60&#8729;xHCl (x = 4 or 6).

Author Spotlight: Accelerating Discovery in Microporous Material Chemistry 

The targeted synthesis of new metal-organic frameworks (MOFs) is difficult, and their discovery depends on the knowledge and creativity of the chemist. High-throughput methods allow complex synthetic parameter fields to be explored quickly and efficiently, accelerating the process of finding crystalline compounds and identifying synthetic and structural trends.

High-throughput (HT) methods are an important tool for the fast and efficient screening of synthesis parameters and the discovery of new materials. This ...