M.K. was supported by a grant from the National Science Foundation, Division of Chemistry under Award No. CHE-2153240. Additional support for materials and supplies was provided by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under award no. DE-FG02-08ER46519. SEM imaging was performed in part at the San Diego Nano-Technology Infrastructure (SDNI) of U.C. San Diego, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (ECCS-1542148).

1. Surface modification of UiO-66 with cat-DDMAT
<ol>
	<li>Exchange the solvent of UiO-66 from methanol with water.
	<ol>
		<li>Prepare UiO-66 in methanol at a concentration of 20 mg/mL. 
		NOTE: According to Wang et al.20, homogeneous UiO-66 is washed with DMF and methanol after synthesis and then stored in a dispersed state in methanol.</li>
		<li>Transfer the 10 mL of UiO-66 suspension to a 15 mL conical centrifuge tube using a pipette.</li>
		<li>Perform centrifugation at approximately 10,000 &#215; g for 10 min, remove the supernatant, and add 10 mL of deionized (DI) water. 
		NOTE: In cases where the particles do not completely settle under these conditions, an additional 10 min centrifugation step can be performed.</li>
		<li>Redisperse the UiO-66 particles in water. 
		NOTE: For adequate dispersion, the use of sonication and vortexing (maximum speed can be used) at room temperature may be necessary.</li>
		<li>Centrifuge again under the same condition as in step 1.1.3., add 10 mL of fresh DI water, and redisperse.</li>
	</ol>
	</li>
	<li>Dissolve 10 mg of cat-DDMAT in 5 mL of chloroform.
	<ol>
		<li>Weigh 10 mg of cat-DDMAT in a 20 mL vial.</li>
		<li>Add 5 mL of chloroform to the vial using a graduated cylinder.</li>
		<li>Seal the vial and sonicate at room temperature until a clear solution is achieved.</li>
	</ol>
	</li>
	<li>Vortex the cat-DDMAT solution with the UiO-66 solution for 3 min.
	<ol>
		<li>Sequentially transfer the UiO-66 water dispersion from step 1.1 and the cat-DDMAT solution from step 1.2 to a 40 mL conical centrifuge tube.</li>
		<li>Ensure sufficient mixing by vortexing for 3 min.</li>
	</ol>
	</li>
	<li>Add 20 mL of ethanol to the mixture using a cylinder and shake for thorough mixing. 
	NOTE: Some additional vortexing may be required for proper mixing.</li>
	<li>Subject the mixture to centrifugation, wash with 40 mL of ethanol, and disperse in 10 mL of DMSO for storage.
	<ol>
		<li>Centrifuge at approximately 10,000 &#215; g for 10 min, remove the supernatant, and add 40 mL of fresh ethanol. 
		NOTE: In cases where the particles do not completely settle under these conditions, an additional 10 min centrifugation step can be performed.</li>
		<li>Sonicate to ensure proper redispersion.</li>
		<li>Centrifuge again under the same condition as in step 1.5.1, add 40 mL of fresh ethanol, and redisperse. 
		NOTE: Upon centrifugation, it can be observed that the originally white UiO-66 turns into a pale yellow, confirming the functionalization with DDMAT.</li>
		<li>After another round of centrifugation, add 5 mL of DMSO to the tube.</li>
		<li>Sonicate the particles to achieve maximum dispersion and transfer to a 15 mL conical centrifuge tube.</li>
		<li>Add 5 mL of fresh DMSO to a 50 mL tube to disperse the remaining particles.</li>
		<li>Transfer the DMSO dispersion in the 50 mL tube to the 15 mL tube to combine with the original DMSO dispersion.</li>
		<li>Mix through vortexing and sonication, then store the sample. 
		NOTE: The yellow color of cat-DDMAT allows for the observation of surface functionalization through a change in particle color (Figure 3)</li>
	</ol>
	</li>
</ol>
2. Polymerization of methyl acrylate from UiO-66-DDMAT
<ol>
	<li>Transfer 2 mL of the UiO-66-DDMAT dispersion in DMSO to a 10 mL round-bottom flask (RBF) using a pipette. 
	NOTE: If the dispersion has been stored for an extended period, it can be made uniform again through additional vortexing and sonication before transferring to the RBF.</li>
	<li>Add the Ir(ppy)3 catalyst stock solution and the DDMAT stock solution while stirring.
	<ol>
		<li>Place a stirring bar inside the RBF and secure it on a stirring plate.</li>
		<li>Initiate stirring and add 12 &#181;L of the Ir(ppy)3 stock solution (1 mg/mL in DMF) using a micropipette.</li>
		<li>Add 0.45 mL of the DDMAT stock solution (10 mg/mL in DMF) using a micropipette. 
		NOTE: Ir(ppy)3 and DDMAT stock solutions were prepared in advance at their respective concentrations and stored in the refrigerator on a 1-3 mL scale.</li>
	</ol>
	</li>
	<li>Add 1.7 mL of methyl acrylate to a 20 mL vial and dissolve it in 2 mL of fresh DMSO using a micropipette. 
	NOTE: Sonication can be used to achieve the formation of a homogeneous solution.</li>
	<li>Slowly add the solution dropwise to the reaction flask.</li>
	<li>Stop stirring, seal the RBF with a septum, and degas for 15 min.
	<ol>
		<li>Stop stirring and securely seal the RBF with a septum.</li>
		<li>Connect the long needle (in the range of 21 to 22G) to a nitrogen supply manifold.</li>
		<li>Insert the long needle through the septum to reach the internal air layer of the RBF.</li>
		<li>Insert a short needle (in the range of 21 to 22 G) through the septum to create an outlet.</li>
		<li>Open the nitrogen valve and lower the long needle to the bottom of the RBF.</li>
		<li>Raise the long needle after 15 min to the internal air layer of the RBF.</li>
		<li>Remove the short needle first, followed by the long needle, ensuring no external air enters the RBF.</li>
		<li>Close the nitrogen valve.</li>
	</ol>
	</li>
	<li>Initiate the reaction under a blue LED light (&#955; = 455 nm) source.
	<ol>
		<li>Place an in-house built blue light LED photoreactor on a stirring plate. 
		NOTE: The photoreactor was built using a 12 V Waterproof Flexible LED Strip Light (Figure 2).</li>
		<li>Connect the power, verify light emission, and cover the upper part with aluminum foil to prevent excessive exposure to blue light. 
		NOTE: Do not seal it completely to allow the heat generated during polymerization to escape.</li>
		<li>Restart stirring.</li>
	</ol>
	</li>
	<li>Turn off the LED when the viscosity of the reaction solution increases to the point where it can no longer be stirred.</li>
	<li>Add excess acetone to the RBF, dilute the mixture, and transfer to a 50 mL tube.
	<ol>
		<li>Remove the septum from the RBF and add acetone to fill the space.</li>
		<li>Stir for approximately 1 h to achieve a homogeneous mixture.</li>
		<li>Transfer the mixture to a 50 mL conical centrifuge tube.</li>
		<li>Add fresh acetone to the RBF and stir for another hour to collect any remaining products.</li>
		<li>Transfer the mixture in the RBF to the 50 mL tube to combine with the mixture collected at first.</li>
	</ol>
	</li>
	<li>Fill up to 40 mL with acetone and mix to dissolve free polymer.</li>
	<li>Wash the mixture until no more free polymer dissolves in acetone, then change the solvent to toluene.
	<ol>
		<li>After centrifugation and supernatant removal, adjust the volume to 40 mL with fresh acetone.</li>
		<li>Disperse particles through sonication and vortex, followed by another round of centrifugation.</li>
		<li>Repeat until no more free polymer dissolves in the supernatant. 
		NOTE: Overnight soaking in fresh acetone after dispersing may be an effective method to facilitate the release of long-chain polymers.</li>
	</ol>
	</li>
	<li>Disperse the product particles in 10 mL of toluene.
	<ol>
		<li>Add 5 mL of toluene to the product after supernatant removal.</li>
		<li>Disperse particles through sonication and vortex, then transfer to a new 15 mL conical centrifuge tube.</li>
		<li>Add fresh toluene (5 mL) to the 50 mL tube to disperse any remaining particles.</li>
		<li>Transfer the toluene dispersion from the 50 mL tube to the 15 mL tube to combine with the original toluene dispersion.</li>
		<li>Mix through vortex and sonication, then store the sample. 
		NOTE: Homogeneously dispersed UiO-66-pMA is obtained as a translucent suspension. (Figure 3)</li>
	</ol>
	</li>
</ol>
3. Particle self-assembly
<ol>
	<li>After centrifugation, disperse the particles in toluene to a volume less than 20% of the original amount.
	<ol>
		<li>Centrifuge the toluene-dispersed particle suspension under the same condition as in step 1.1.3.</li>
		<li>Remove the supernatant and add toluene to achieve a total suspension volume of 1-2 mL. 
		NOTE: The appropriate concentration may vary depending on the size of the Petri dish used, particle size, and polymer molecular weight.</li>
		<li>Completely disperse the particles through sonication.</li>
	</ol>
	</li>
	<li>Prepare a Petri dish (60 mm diameter) by adding DI water.</li>
	<li>Carefully drop approximately 10 &#181;L of the toluene dispersion (equivalent to a single droplet) onto the DI water&#39;s surface. 
	NOTE: Do not add more than one droplet. When adding the dispersion, the tool used can be adjusted to control the droplet&#39;s size. The suitable droplet size may vary depending on the petri dish size, particle size, and polymer molecular weight.</li>
	<li>Place the dish cover over it to allow the toluene to evaporate slowly.</li>
	<li>After all toluene on the surface has evaporated and a monolayer membrane has formed, remove the cover.</li>
	<li>Use a loop made of copper wire to carefully remove part of the monolayer. 
	NOTE: The copper wire used for scooping the monolayer should be prepared to have a flat, approximately circular shape.</li>
	<li>After evaporating the remaining co-associated water, a free-standing monolayer could be observed.</li>
	<li>To prepare for scanning electron microscopy (SEM) image measurements, carefully scoop up the monolayer formed on the water&#39;s surface using a piece of thin glass.</li>
</ol>

Self-Assembly of Polymer-Grafted Metal Organic Framework Monolayers

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The authors have no conflicts of interest to disclose.

There are several critical steps where specific attention to detail is required to successfully synthesize polymer-grafted MOFs that will produce SAMMs. First, the monomers utilized in RAFT polymerization are supplemented with inhibitors or stabilizers during storage to prevent undesired polymerization (e.g., hydroquinone or monomethyl ether of hydroquinone, MEHQ). To remove these additives, purification through distillation is required before use22. In protocol step 2.4, it is essential to dilute...

Metal-organic frameworks (MOFs) are crystalline, porous materials that offer large surface areas while being readily tunable through modifications of the organic ligands or metal nodes1,2. MOFs are constructed from two components: an organic ligand and metal ions (or metal ion clusters referred to as secondary building units, SBUs). MOFs have been investigated for chemical (e.g., gas) storage, separations, catalysis, sensing, and drug delivery. Generally, MOFs are synthesized in the form of crystalline powders; however, for ease of handling in many applications, formulation into other form factors is desirable if not necessary3,4. For example, mixed matrix membranes (MMMs) of MOFs with polymers have been reported as one particularly useful composite of MOFs and polymers5. However, in some cases, MMMs may have limitations due to the incompatibility/immiscibility between MOF and polymer components5,6. Therefore, strategies have been explored to incorporate polymer grafting directly onto MOF particles to form polymer-grafted MOFs.
Inorganic and metallic nanoparticles exhibit unique behavior in terms of optical, magnetic, catalytic, and mechanical properties7,8. However, they tend to aggregate easily after synthesis, which can hinder their processability. To enhance their processability, polymer chains can be grafted onto the particle surface9. Nanoparticles with high grafting density offer excellent dispersion and stability due to favorable enthalpic interactions between surface polymers and the solvent and entropic repulsion interactions between the particles10. Grafting of polymers onto particle surfaces can be achieved through a variety of strategies11. The most straightforward approach is the &#39;grafting to&#39; particle strategy, where functional groups, such as thiols or carboxylic acids, are introduced at the ends of polymer chains to directly bind to the nanoparticle. When complementary chemical groups, such as hydroxyls or epoxides, are present on the particle surface, polymer chains can be grafted onto these groups via covalent chemical approaches12,13. The &#39;grafting from&#39; particle or surface-initiated polymerization method involves anchoring initiators or chain transfer agents (CTAs) to the surface of nanoparticles and then growing polymer chains on the particle surface through surface-initiated polymerization. This method often achieves higher grafting density than the &#39;grafting to&#39; approach. Furthermore, grafting from enables the synthesis of block copolymers, thereby expanding the diversity of polymer structures that can be immobilized on a particle surface.
Examples of polymer grafting onto MOF particles have begun to emerge, largely focused on installing polymerization sites on the organic ligands of the MOF. In a recent study published by Shojaei and coworkers, vinyl groups were covalently attached to the ligands of Zr(IV)-based MOF UiO-66-NH2 (UiO = Universitetet i Oslo, where the terephthalic acid ligand contains an amino substituent), followed by methyl methacrylate (MMA) polymerization to create polymer-grafted MOFs with a high grafting density (Figure 1A)14. Similarly, Matzger and coworkers functionalized the amine groups on a core-shell MOF-5 (a.k.a., IRMOF-3@MOF-5) particles with 2-bromo-iso-butyl groups. Using polymerization initiated by the 2-bromo-iso-butyl groups, they created poly(methyl methacrylate) (PMMA)-grafted PMMA@IRMOF-3@MOF-515.
In addition to functionalizing the ligand of the MOF for grafting from polymerization, new methods that create sites for polymer grafting via coordination to the metal centers (a.k.a., SBUs) of the MOF have also been explored. For example, a ligand that can bind to the MOF metal centers, such as catechol (Figure 1B), can be used to coordinate to exposed metal sites on the MOF surface. Using a catechol-functionalized chain-transfer agent (cat-CTA, Figure 1B) the MOF surface can be functionalized and made suitable for a grafting from polymerization.
Recently, the aforementioned strategy for synthesizing MOFs-polymer composites has also been used for the creation of free-standing MOF monolayers16,17,18. MOFs such as UiO-66 and MIL-88B-NH2 (MIL = Materials of Institute Lavoisier) were surface-functionalized with pMMA using a ligand-CTA strategy (Figure 1B). The polymer-grafted MOF particles were self-assembled at an air-water interface to form self-supporting, self-assembled metal-organic framework monolayers (SAMMs) with a thickness of ~250 nm. The polymer content in these composites was ~20 wt%, indicating that SAMMs contained ~80 wt% MOF loading. Followup studies showed that different vinyl polymers could be grafted onto UiO-66 to produce SAMMs with different characteristics19. Analytical techniques such as thermogravimetric analysis (TGA), dynamic light scattering (DLS), and gel permeation chromatography (GPC) were used to calculate polymer brush height and grafting density of the surface-grafted MOF-polymer composites.
Herein, the preparation of SAMMs from UiO-66-pMA (pMA = poly(methyl acrylate)) is presented. For the polymerization of methyl acrylate (MA), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT, Figure 1B) is used as the CTA19. The functionalization of the UiO-66 particles with cat-DDMAT is essential for the grafting of pMA. Cat-DDMAT can be synthesized through a two-step acylation procedure from a commercially available CTA&#160;and dopamine hydrochloride19. It is also crucial to use UiO-66 particles of uniform size for the successful formation of SAMMs19; therefore, the UiO-66 used in this study was prepared using the continuous addition method20. The polymerization method employed for forming the polymer-grafted MOF particles is photoinduced reversible addition-fragmentation chain transfer (RAFT) conducted under blue LED light (using an in-house-built photoreactor, Figure 2) with a tris(2-phenylpyridine)iridium (Ir(ppy)3) photocatalyst. RAFT polymerization gives exceptionally narrow polymer dispersity that can be finely controlled. Free CTA is included during the polymerization reaction because the ratio of transfer agent to monomer allows for control over the molecular weight during polymerization. The amount of cat-DDMAT transfer agent on the surface of the MOF particles is small; therefore, excess free CTA is added and the amount of monomer to be used is calculated based off of the amount of free CTA present21. After polymerization, the free polymer produced from the free CTA is removed by washing, leaving only the polymer-grafted UiO-66-pMA. Subsequently, this composite is dispersed in toluene at a high concentration and used to form SAMMs at an air-water interface.

<table><tbody><tr><td>2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT)</td><td>Sigma-Aldrich</td><td>723010</td><td>98%</td></tr><tr><td>10 mL Single Neck RBF</td><td>Chemglass</td><td>CG-1506-82</td><td>14/20 Outer Joint</td></tr><tr><td>Acetone</td><td>Fisher Chemical</td><td>A18-20</td><td>ACS Grade</td></tr><tr><td>Allegra X-30R Centrifuge</td><td>BECKMAN COULTER</td><td>B06320</td><td>1.6 L max capacity, 18,000 RPM, 29,756 x g</td></tr><tr><td>Analog Vortex Mixer</td><td>VWR</td><td>10153-838</td><td>300 - 3,200 rpm</td></tr><tr><td>cat-DDMAT</td><td></td><td></td><td>Prepared according to literature procedure (ref. 17).</td></tr><tr><td>Centrifuge Tube, 50 mL / 15 mL</td><td>CORNING</td><td>430291 / 430766</td><td>Conical Bottom with plug seal cap, polypropylene</td></tr><tr><td>Chloroform</td><td>Fisher Chemical</td><td>AC423550040</td><td>99.8%</td></tr><tr><td>Conventional needles</td><td>Becton Dickinson</td><td>382903051670</td><td>21 G x 1 1/2</td></tr><tr><td>Copper wire</td><td>Malin Co.</td><td></td><td>No. 30 B &amp;amp; S GAUGE</td></tr><tr><td>Dimethyl Sulfoxide (DMSO)</td><td>Fisher Bioreagents</td><td>BP231-1</td><td>&gt;=99.7%</td></tr><tr><td>Disposable Pasteur Pipets</td><td>Fisher Scientific</td><td>13-678-20C</td><td>Borosilicate Glass</td></tr><tr><td>Ethanol</td><td>KOPTEC</td><td>V1001</td><td>200 proof ethanol</td></tr><tr><td>Glass Scintillation Vial, 20 mL</td><td>KIMBIL</td><td>74508-20</td><td></td></tr><tr><td>Graduated Cylinder, 10 mL</td><td>KIMBIL</td><td>20024-10</td><td></td></tr><tr><td>Hypodermic Needles</td><td>Air-Tite</td><td>N224</td><td>22 G x 4&#039;&#039;</td></tr><tr><td>Methanol</td><td>Fisher Chemical</td><td>A412-20</td><td>99.8%</td></tr><tr><td>Methyl Acrylate</td><td>Aldrich Chemistry</td><td>M27301</td><td>99%, contains =&amp;lt; 100 ppm monomethyl ether hydroquinone as inhibitor</td></tr><tr><td>Micropipette P10 (1 - 10 &amp;micro;L)</td><td>GILSON</td><td>F144055M</td><td>PIPETMAN, Metal Ejector</td></tr><tr><td>Micropipette P1000 (100 - 1,000 &amp;micro;L)</td><td>GILSON</td><td>F144059M</td><td>PIPETMAN, Metal Ejector</td></tr><tr><td>Micropipette P20 (2 - 20 &amp;micro;L)</td><td>GILSON</td><td>F144056M</td><td>PIPETMAN, Metal Ejector</td></tr><tr><td>Microscope cover glass</td><td>Fisher Scientific</td><td>12542A</td><td>18 mm x 18 mm</td></tr><tr><td>NN-Dimerhylformamide (DMF)</td><td>Fisher Chemical</td><td>D119-4</td><td>99.8%</td></tr><tr><td>Petri Dish, Stackable Lid</td><td>Fisher Scientific</td><td>FB0875713A</td><td>60 mm x 15 mm</td></tr><tr><td>Septum Stopper</td><td>Chemglass</td><td>CG302401</td><td>14/20 - 14/35</td></tr><tr><td>Stir Bar</td><td>Chemglass</td><td>CG-2005T-01</td><td>Magnetic, PTFE, Turbo, Rare Earth, Elliptical, 10 x 6mm</td></tr><tr><td>SuperNuova+ Stirring Hot Plate</td><td>Thermo Scientific</td><td>SP88857190</td><td>50 - 1,500 rpm, 30 - 450 &amp;deg;C</td></tr><tr><td>Toluene</td><td>Fisher Chemical</td><td>T324-4</td><td>99.5%</td></tr><tr><td>Tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3)</td><td>Sigma-Aldrich</td><td>688096</td><td>97%</td></tr><tr><td>UiO-66 (120 nm edge length)</td><td></td><td></td><td>Prepared according to literature procedure (ref. 18).</td></tr><tr><td>Ultrasonic Cleaner CPX3800H</td><td>EMERSON / BRANSON</td><td>CPX-952-318R</td><td>40 kHz, 5.7 L</td></tr><tr><td>Waterproof Flexible LED Strip Light</td><td>ALITOVE</td><td>ALT-5B300WPBK</td><td>16.4 ft 5050 Blue LED</td></tr></tbody></table>

synthesis and characterization of self-assembled metal-organic framework monolayers using polymer-coated particles

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. Attempts to enhance the utility of MOFs have involved the preparation of various composites, including polymer-grafted MOFs. By directly grafting polymers to the external surface of MOFs, issues of incompatibility between polymers and MOFs can be overcome. Polymer brushes grafted from the surface of MOFs can serve to stabilize the MOF while enabling particle assembly into self-assembled metal-organic framework monolayers (SAMMs) via polymer-polymer interactions.
Control over the chemical composition and molecular weight of the grafted polymer can allow for tuning of the SAMM characteristics. In this work, instructions are provided on how to immobilize a chain transfer agent (CTA) onto the surface of the MOF UiO-66 (UiO = Universitetet i Oslo). The CTA&#160;serves as initiation sites for the growth of polymers. Once polymer chains are grown from the MOF surface, the formation of SAMMs is achieved through self-assembly at an air-water interface. The resulting SAMMs are characterized and shown to be freestanding by scanning electron microscopy imaging. The methods presented in this paper are expected to make the preparation of SAMMs more accessible to the research community and thereby expand their potential use as a&#160;MOF-polymer composite.

When the polymer-grafted MOFs are gently dropped onto water from a concentrated toluene dispersion (as illustrated in Figure 4A), a monolayer is formed in a few seconds with an iridescent appearance. Furthermore, using a mold made from copper wire to lift this monolayer and subsequently drying the obtained water allows for the formation of free-standing SAMMs (Figure 4B). After transferring the monolayer to a glass microscope cover slip and drying it, SEM imagin...

Author Spotlight: Exploring Self-Assembled MOF-Polymer Composites

A protocol for the synthesis and characterization of self-assembled metal-organic framework monolayers is provided using polymer-grafted, metal-organic framework (MOF) crystals. The procedure shows that polymer-grafted MOF particles can be self-assembled at an air-water interface resulting in well-formed, free-standing, monolayer structures as evidenced by scanning electron microscopy imaging.

Synthesis and Characterization of Self-Assembled Metal-Organic Framework Monolayers Using Polymer-Coated Particles

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. ...

synthesis-characterization-self-assembled-metal-organic-framework

Research

JoVE Journal

Chemistry

1.4K Views.  University of California, San Diego. A protocol for the synthesis and characterization of self-assembled metal-organic framework monolayers is provided using polymer-grafted, metal-organic framework (MOF) crystals. The procedure shows that polymer-grafted MOF particles can be self-assembled at an air-water interface resulting in well-formed, free-standing, monolayer structures as evidenced by scanning electron microscopy imaging.

Video: Author Spotlight: Exploring Self-Assembled MOF-Polymer Composites

Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template&#39;s channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

This article describes the preparation of well-ordered nickel nanofoams via electroless metal deposition onto nanoporous templates obtained from self-assembled diblock copolymer based supramolecules.

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, ...

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

A Technique to Functionalize and Self-assemble Macroscopic Nanoparticle-ligand Monolayer Films onto Template-free Substrates

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles1,2. The simple, robust and scalable technique efficiently functionalizes metallic nanoparticles with thiol-ligands in a miscible water/organic solvent mixture allowing for rapid grafting of thiol groups onto the gold nanoparticle surface. The hydrophobic ligands on the nanoparticles then quickly phase separate the nanoparticles from the aqueous based suspension and confine them to the air-fluid interface. This drives the ligand-capped nanoparticles to form monolayer domains at the air-fluid interface.&#160; The use of water-miscible organic solvents is important as it enables the transport of the nanoparticles from the interface onto template-free substrates.&#160; The flow is mediated by a surface tension gradient3,4 and creates macroscopic, high-density, monolayer nanoparticle-ligand films.&#160; This self-assembly technique may be generalized to include the use of particles of different compositions, size, and shape and may lead to an efficient assembly method to produce low-cost, macroscopic, high-density, monolayer nanoparticle films for wide-spread applications.

A simple, robust and scalable technique to functionalize and self-assemble macroscopic nanoparticle-ligand monolayer films onto template-free substrates is described in this protocol.

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles1,2. The simple, robust and ...

Solid-phase Submonomer Synthesis of Peptoid Polymers and their Self-Assembly into Highly-Ordered Nanosheets

Peptoids are a novel class of biomimetic, non-natural, sequence-specific heteropolymers that resist proteolysis, exhibit potent biological activity, and fold into higher order nanostructures. Structurally similar to peptides, peptoids are poly N-substituted glycines, where the side chains are attached to the nitrogen rather than the alpha-carbon. Their ease of synthesis and structural diversity allows testing of basic design principles to drive de novo design and engineering of new biologically-active and nanostructured materials.
Here, a simple manual peptoid synthesis protocol is presented that allows the synthesis of long chain polypeptoids ( up to 50mers) in excellent yields. Only basic equipment, simple techniques (e.g. liquid transfer, filtration), and commercially available reagents are required, making peptoids an accessible addition to many researchers' toolkits. The peptoid backbone is grown one monomer at a time via the submonomer method which consists of a two-step monomer addition cycle: acylation and displacement. First, bromoacetic acid activated in situ with N,N'-diisopropylcarbodiimide acylates a resin-bound secondary amine. Second, nucleophilic displacement of the bromide by a primary amine follows to introduce the side chain. The two-step cycle is iterated until the desired chain length is reached. The coupling efficiency of this two-step cycle routinely exceeds 98% and enables the synthesis of peptoids as long as 50 residues. Highly tunable, precise and chemically diverse sequences are achievable with the submonomer method as hundreds of readily available primary amines can be directly incorporated.
 
Peptoids are emerging as a versatile biomimetic material for nanobioscience research because of their synthetic flexibility, robustness, and ordering at the atomic level. The folding of a single-chain, amphiphilic, information-rich polypeptoid into a highly-ordered nanosheet was recently demonstrated. This peptoid is a 36-mer that consists of only three different commercially available monomers: hydrophobic, cationic and anionic. The hydrophobic phenylethyl side chains are buried in the nanosheet core whereas the ionic amine and carboxyl side chains align on the hydrophilic faces. The peptoid nanosheets serve as a potential platform for membrane mimetics, protein mimetics, device fabrication, and sensors. Methods for peptoid synthesis, sheet formation, and microscopy imaging are described and provide a simple method to enable future peptoid nanosheet designs.

A simple and general manual peptoid synthesis method involving basic equipment and commercially available reagents is outlined, enabling peptoids to be easily synthesized in most laboratories. The synthesis, purification and characterization of an amphiphilic peptoid 36mer is described, as well as its self-assembly into highly-ordered nanosheets.

Peptoids are a novel class of biomimetic, non-natural, sequence-specific heteropolymers that resist proteolysis, exhibit potent biological activity, and ...

Bioengineering

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 ...

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous polymer monoliths. The developed approach is based on the preparation of a macroporous polymer containing carboxylic acid functional groups and the subsequent step-by-step solution-based controlled growth of a layer of a porous coordination polymer on the surface of the pores of the polymer monolith. The prepared metal-organic polymer hybrid has a high specific micropore surface area. The amount of iron(III) sites is enhanced through metal-organic coordination on the surface of the pores of the functional polymer support. The increase of metal sites is related to the number of iterations of the coating process.
The developed preparation scheme is easily adapted to a capillary column format. The functional porous polymer is prepared as a self-contained single-block porous monolith within the capillary, yielding a flow-through separation device with excellent flow permeability and modest back-pressure. The metal-organic polymer hybrid column showed excellent performance for the enrichment of phosphopeptides from digested proteins and their subsequent detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The presented experimental protocol is highly versatile, and can be easily implemented to different organic polymer supports and coatings with a plethora of porous coordination polymers and metal-organic frameworks for multiple purification and/or separation applications.

A procedure for the preparation of porous hybrid separation media composed of a macroporous polymer monolith internally coated by a high surface area microporous coordination polymer is presented.

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

Using Polystyrene-block-poly(acrylic acid)-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are encapsulated in polystyrene-block-poly(acrylic acid) (PSPAA) shells and then used as monomers for their self-assembly. Spherical PSPAA micelles upon acid treatment are known to assemble into cylindrical micelles. Exploiting this tendency, the core-shell nanoparticles are induced to aggregate, coalesce, and then transform into long chains. When more than one type of nanoparticles are used, random and block &#8220;copolymers&#8221; of nanoparticles can be obtained. Detailed procedures are reported for the PSPAA encapsulation of nanoparticles, homo- and co-polymerization of the core-shell nanoparticles, separation and purification of the resulting nanoparticle chains. Transformations of single-line chains into double- and triple-line chains are also presented. The synergy between the polymer shell and the embedded nanoparticles leads to an unusual chain-growth polymerization mode, giving long nanoparticle chains that are distinct from the products of the traditional step-growth aggregation process.

Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We report protocols for &#8220;polymerizing&#8221; various types of polymer-encapsulated metal nanoparticles into long chains of &#8220;homo-&#8220; and &#8220;co-polymers&#8221;.

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are ...

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

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 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 ...

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. ...