The authors thank their collaborators at RTI International, US Army Natick Soldier RD&#38;E Center, and Edgewood Chemical and Biological Center. They also thank their funding source, the Defense Threat Reduction Agency.

1. Atomic Layer Deposition (ALD) of Al2O3 on Fiber Mats
<ol>
	<li>Place a 2.54 x 2.54 cm2 polypropylene fabric sample in the reactor boat (a thin, rigid, metal mesh holder). A schematic of the reactor is presented in Figure 2.</li>
	<li>Open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the LabView system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>After removing the reactor cap, load the fabric sample into the ALD reactor. Replace the reactor cap and open the gate valve. Close the vent and open the carrier nitrogen. Turn off manual control.</li>
	<li>Load the recipe for Al2O3 on fabrics. The recipe will alternately dose trimethylaluminum (TMA) for 1.2 s, followed by a 30 s dry nitrogen purge or dose water for 1 s followed by a 60 s dry nitrogen purge. Set the recipe to run 1000 cycles.</li>
	<li>Set the mass flow controller to 20 cfm and the furnace temperature to 90 &#176;C (84 &#176;C on the furnace interface).</li>
	<li>Open the manual valve to the TMA and water. Close the pressure gauge. Replace the clasp on the reactor cap. Press Start on the interface.</li>
	<li>Upon completion of the recipe, open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>Remove the reactor cap and sample boat. Re-seal the reactor. 
	NOTE: The procedure may be paused at this point.</li>
</ol>
2. Atomic Layer Deposition (ALD) of TiO2 on Polyamide-6 (PA-6) Fiber Mats
<ol>
	<li>Place a 2.54 x 2.54 cm2 PA-6 fabric sample in the reactor boat (a thin, rigid, metal mesh holder).</li>
	<li>Open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the LabView system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>After removing the reactor cap, load the fabric sample into the ALD reactor. Replace the reactor cap and open the gate valve. Close the vent and open the carrier nitrogen. Turn off manual control.</li>
	<li>Load the recipe for TiO2 on fabrics. The recipe will alternately dose TiCl4 for 1 s, followed by a 40 s dry nitrogen purge or dose water for 1 s followed by a 60 s dry nitrogen purge. Set the recipe to run 300 cycles.</li>
	<li>Set the mass flow controller to 20 cfm and the furnace temperature to 90 &#176;C (84 &#176;C on the furnace interface).</li>
	<li>Open the manual valve to the TiCl4 and water. Close the pressure gauge. Replace the clasp on the reactor cap. Press Start&#160;on the interface.</li>
	<li>Upon completion of the recipe, open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>Remove the reactor cap and sample boat. Re-seal the reactor. 
	NOTE: The procedure may be paused at this point.</li>
</ol>
3. Solvothermal Synthesis of MIL-96
<ol>
	<li>Add 0.0878 g of H3BTC to an 80 mL glass beaker.</li>
	<li>Add 12 mL of H2O and 12 mL of ethanol to the beaker.</li>
	<li>Stir magnetically for 10 min or until the H3BTC is fully dissolved.</li>
	<li>Place the solution in a Teflon lined pressure vessel.</li>
	<li>Add the Al2O3 coated polypropylene to the solution and prop the fabric on a mesh support so it does not lie flat against the bottom of the vessel.</li>
	<li>Seal the pressure vessel and place it in the furnace at 110 &#176;C for 24 h.</li>
	<li>After allowing the sample to cool, place the fabric sample in a mesh basket in a beaker. Wash twice with ethanol, each for 12 h.</li>
	<li>Sample activation requires heating at 85 &#176;C for 6 h under vacuum, followed by heating at 110 &#176;C for 12 h under vacuum. 
	NOTE: The procedure can be stopped here. All samples should be stored in a desiccator to maintain sample activation.</li>
</ol>
4. Solvothermal Synthesis of UiO-66-NH2
<ol>
	<li>Add 0.08 g of ZrCl4 to a 20 mL glass scintillation vial.</li>
	<li>Add 20 mL of N,N-dimethylformamide (DMF) to the ZrCl4 in 5 mL increments. Cap the vial between increments and allow fumes to dissipate.</li>
	<li>Sonicate the solution for 1 min.</li>
	<li>Add 0.062 g of 2-aminoterephthalic acid to the vial, and magnetically stir the solution for 5 min.</li>
	<li>Add 25 &#181;L of deionized water to the vial.</li>
	<li>Add 1.33 mL of concentrated HCl to the vial.</li>
	<li>Submerge the TiO2 ALD coated fabric swatch in the solution and cap the vial.</li>
	<li>Place the sample in the furnace at 85 &#176;C for 24 h.</li>
	<li>After allowing the sample to cool, place the fabric sample in a mesh basket in a beaker. Wash twice with 80 mL of DMF, each for 12 h. Wash 3 times with 80 mL of ethanol, each for 12 h.</li>
	<li>After removing the fabric swatch, filter the residual MOF powder. Wash twice with 80 mL of DMF, each for 12 h. Wash 3 times with 80 mL of ethanol, each for 12 h.</li>
	<li>Sample activation requires heating at 85 &#176;C for 6 h under vacuum, followed by heating at 110 &#176;C for 12 h under vacuum. 
	NOTE: The procedure can be stopped here. All samples should be stored in a desiccator to maintain sample activation.</li>
</ol>

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The authors have nothing to disclose.

The ALD coating strongly influences the adhesion and loading of the MOF. First, depending on the type of substrate and ALD precursor, the ALD layer can either form a distinct outer shell around the fiber, or diffuse into the fiber to create a gradual transition to the metal oxide coating20. The hard shell has been observed on cotton and nylon substrates, while diffusive layers can be observed in polypropylene under proper conditions. Second, the diffusion into the fiber can also be controlled by v...

Metal-organic frameworks are crystalline structures consisting of reactive metal cluster centers bridged by organic molecule linkers to provide large porosities and surface areas. Their structure, porosity, and functionality can be designed by choosing appropriate clusters and linkers, leading to surface areas as high as&#160;7,000 m2/gMOF1,2. Their high porosity and surface area have made MOFs diversely applicable in adsorption, separation, and heterogeneous catalysis in fields ranging from energy production to environmental concerns to biological processes1,3,4,5,6.
Numerous MOFs have proven successful in selectively adsorbing volatile organic compounds and greenhouse gases or to catalytically degrade chemicals that may prove harmful to human health or the environment. In particular, MIL-96 (Al) has shown to selectively adsorb nitrogenous volatile organic compounds (VOCs) due to the availability of lone pair electrons in the nitrogen groups to coordinate with the weak Lewis acid Al present in the metal clusters7. MIL-96 has also been shown to adsorb gases such as CO2, p-xylene, and m-xylene8,9. MOF adsorption selectivity is dependent on both the Lewis acid of the metal cluster, as well as pore size. The pore size of MIL-96 increases with temperature, resulting in increased adsorption capacity of trimethylbenzene with increased temperature, and presents the opportunity of tuning selectivity with adsorption temperature9.
The second MOF of focus here, UiO-66-NH2 has been shown to catalytically degrade chemical warfare agents (CWAs) and simulants. The amine group on the linker provides a synergistic effect in degrading nerve agents, while preventing agent degradation products from binding irreversibly to the zirconium clusters and poisoning the MOF10. UiO-66-NH2 has catalytically hydrolyzed dimethyl p-nitrophenylphosphate (DMNP) with a half-life as short as 0.7 minutes in buffered conditions, nearly 20 times faster than its base MOF UiO-6611,12.
While these adsorption and catalytic properties are promising, the physical form of the MOFs, primarily bulk powder, can be difficult to incorporate into platforms for gas capture and filtration without adding significant bulk, clogging pores, or reducing MOF flexibility. An alternative is to create MOF functionalized fabrics. MOFs have been incorporated into fabrics in myriad ways, including electrospinning MOF powder/polymer slurries, adhesive mixes, spray coating, solvothermal growth, microwave syntheses, and a layer-by-layer growth method13,14,15,16,17,18. Of these, electrospinning and polymer adhesives can result in blocked functional sites on the MOF as they are encapsulated in the polymer, significantly decreasing adsorption capacity and reactivity. Additionally, many of these techniques fail to create conformal coatings on the fibers due to line of sight difficulties or poor adhesion/nucleation and the reliance on purely electrostatic interactions. An alternative method is to first coat the fabric with a metal oxide to allow for stronger surface interactions with the MOF18,19.
One method of metal oxide deposition is atomic layer deposition (ALD). ALD is a technique for depositing conformal thin films, controllable to the atomic scale. The process utilizes two half reactions that occur only at the surface of the substrate to be coated. The first step is to dose a metal containing precursor, which reacts with hydroxyls on the surface, leaving a metallated surface while excess reactant is purged from the system. The second reactant is an oxygen-containing reactant, typically water, which reacts with the metal sites to form a metal oxide. Again, excess water and any reaction products are purged from the system. These alternating doses and purges can be repeated until the desired film thickness is achieved (Figure 1). Atomic layer deposition is particularly useful because the small-scale vapor phase precursors allow for conformal films on every surface of substrates with complex topology, such as fiber mats. Additionally, for polymers such as polypropylene, the ALD conditions can allow the coating to diffuse into the fiber surface, providing a strong anchor for future MOF growth20.
The metal oxide coating allows for increased nucleation sites on the fibers during traditional solvothermal synthesis by increasing functional groups and roughness18,20. Our group has previously shown the ALD metal oxide base layer is effective for UiO-6X, HKUST-1, and other syntheses through various routes of solvothermal, layer-by-layer, and hydroxy-double salt conversion methods13,17,18,21,22,23. Here we demonstrate two synthesis types. The MIL materials are formed by converting the Al2O3 ALD coating directly to MOF by diffusion of the organic linker. By submerging an Al2O3 ALD coated fiber mat in trimesic acid solution and heating, the organic linker diffuses into the metal oxide coating to form MIL-96. This results in a strongly adhered, conformal MOF coating on every fiber surface. The second synthesis approach calls for typical UiO-66-NH2 hydrothermal synthesis using metal and organic precursors, but adds a metal oxide coated fiber mat on which the MOF nucleates. For both synthesis approaches, the resulting products consist of conformal thin films of MOF crystals strongly adhered to the supporting fabric. In the case of MIL-96, these can be incorporated into filters for adsorption of VOCs or greenhouse gases. For UiO-66-NH2 these fabrics can be easily incorporated into lightweight protective clothing for military personnel, first responders, and civilians for continuous defense against CWA attacks.

<table><tbody><tr><td>trimethylaluminum</td><td>Strem Chemicals</td><td>93-1360</td><td></td></tr><tr><td>home-built ALD reactor</td><td>N/A</td><td></td><td></td></tr><tr><td>nitrogen cylinder</td><td>Arc3</td><td>UN1066</td><td></td></tr><tr><td>trimesic acid</td><td>Sigma-Aldrich</td><td>482749-500G</td><td></td></tr><tr><td>ethanol</td><td>Koptec</td><td>V1001</td><td></td></tr><tr><td>teflon lined autoclave</td><td>PARR Instrument Company</td><td>4760-1211</td><td></td></tr><tr><td>isotemp furnace</td><td>Fisher Scientific</td><td>F47925</td><td></td></tr><tr><td>Zirconium (IV) chloride</td><td>Alfa Aesar</td><td>12104</td><td></td></tr><tr><td>2-aminoterephthalic acid</td><td>Acros Organics</td><td>278031000</td><td></td></tr><tr><td>N,N-dimethylformamide</td><td>Fisher Scientific</td><td>D119-4</td><td></td></tr><tr><td>Hydrochloric Acid</td><td>Fisher Scientific</td><td>A481-212</td><td></td></tr><tr><td>Polypropylene fiber mats</td><td>N/A</td><td></td><td></td></tr><tr><td>Polyamide fiber mats</td><td>N/A</td><td></td><td></td></tr></tbody></table>

solvothermal synthesis of mil-96 and uio-66-nh2 on atomic layer deposited metal oxide coatings on fiber mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD). This process creates conformal films of controllable thickness on each fiber, while providing a more reactive surface for MOF nucleation. By submerging the ALD coated fabric in solution during solvothermal MOF synthesis, the MOFs create a conformal, well-adhered coating on the fibers, resulting in a MOF-functionalized fabric, without additional adhesion materials that may block MOF pores and functional sites. Here we demonstrate two solvothermal synthesis methods. First, we form a MIL-96(Al) layer on polypropylene fibers using synthetic conditions that convert the metal oxide to MOF. Using initial inorganic films of varying thicknesses, diffusion of the organic linker into the inorganic allows us to control the extent of MOF loading on the fabric. Second, we perform a solvothermal synthesis of UiO-66-NH2 in which the MOF nucleates on the conformal metal oxide coating on polyamide-6 (PA-6) fibers, thereby producing a uniform and conformal thin film of MOF on the fabric. The resulting materials can be directly incorporated into filter devices or protective clothing and eliminate the maladroit qualities of loose powder.

To describe the MOF/fabric materials, we delineate two terms related to measured surface area. First, projected surface area, cm2projected, refers to the macroscopic size of the fabric swatch as measured with a ruler, i.e., the area of the sample&#39;s projected shadow. The second surface area of interest is the BET surface area, calculated from a nitrogen isotherm obtained at 77 K. These values are given in units of m2/gFabric, m2...

Watch this Scientific Journal Video about Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats at JoVE.com

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven ...

solvothermal-synthesis-mil-96-uio-66-nh2-on-atomic-layer-deposited

Universidad de Cartagena UDEC

Research

JoVE Journal

Chemistry

11.4K Views.  North Carolina State University. Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Video: Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

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 ...

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

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 ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Molten-Salt Synthesis of Complex Metal Oxide Nanoparticles

The development of feasible synthesis methods is critical for the successful exploration of novel properties and potential applications of nanomaterials. Here, we introduce the molten-salt synthesis (MSS) method for making metal oxide nanomaterials. Advantages over other methods include its simplicity, greenness, reliability, scalability, and generalizability. Using pyrochlore lanthanum hafnium oxide (La2Hf2O7) as a representative, we describe the MSS protocol for the successful synthesis of complex metal oxide nanoparticles (NPs). Furthermore, this method has the unique ability to produce NPs with different material features by changing various synthesis parameters such as pH, temperature, duration, and post-annealing. By fine-tuning these parameters, we are able to synthesize highly uniform, non-agglomerated, and highly crystalline NPs. As a specific example, we vary the particle size of the La2Hf2O7&#160;NPs by changing the concentration of the ammonium hydroxide solution used in the MSS process, which allows us to further explore the effect of particle size on various properties. It is expected that the MSS method will become a more popular synthesis method for nanomaterials and more widely employed in the nanoscience and nanotechnology community in the upcoming years.

Here, we demonstrate a unique, relatively low-temperature, molten-salt synthesis method for preparing uniform complex metal oxide lanthanum hafnate nanoparticles.

The development of feasible synthesis methods is critical for the successful exploration of novel properties and potential applications of nanomaterials. ...

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, &#60;10-5 mbar). The preparation of SiO2-700 (silica dehydroxylated at 700 &#176;C) and subsequent applications (the grafting of complexes and catalytic runs) requires the use of HVLs and double-Schlenk techniques. Several well-known characterization methods are used, such as Fourier-transform infrared spectroscopy (FTIR), elemental microanalysis, solid-state nuclear magnetic resonance spectroscopy (SSNMR), and state-of-the-art dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS). FTIR and elemental microanalysis permit scientists to establish the grafting and its stoichiometry. 1H and 13C SSNMR allows the structural determination of the hydrocarbon ligands coordination sphere. DNP SENS is an emerging powerful technique in solid characterization for the detection of poorly sensitive nuclei (15N, in our case). SiO2-700 is treated with about one equivalent of the metal precursor compared to the amount of surface silanol (0.30 mmol&#183;g-1) in pentane at room temperature. Then, volatiles are removed, and the powder samples are dried under dynamic high vacuum to afford the desired materials [(&#8801;Si-O-)Hf(&#951;2&#960;-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)]. After a thermal treatment under high vacuum, the grafted complex is converted into metal imido silica complex [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)]. [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] effectively promotes the metathesis of imines, using the combination of two imine substrates, N-(4-phenylbenzylidene)benzylamine, or N-(4-fluorobenzylidene)-4-fluoroaniline, with N-benzylidenetert-butylamine as substrates. A significantly lower conversion is observed with the blank runs; thus, the presence of the imido group in [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is correlated to the catalytic performance.

A new group IV metal catalyst for imine metathesis is prepared by grafting amine metal complex onto dehydroxylated silica. Surface metal fragments are characterized using FT-IR, elemental microanalysis, and solid-state NMR spectroscopy. Further dynamic nuclear polarization surface enhanced NMR spectroscopy experiments complement the determination of the coordination sphere.

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared ...

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. ...

Triazole and Tetrazole Functionalized Zr-MOFs Synthesis and Characterization

Synthesis of Triazole and Tetrazole-Functionalized Zr-Based Metal-Organic Frameworks Through Post-Synthetic Ligand Exchange

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. Given their coordinative nature, the organic ligands and strut framework can be readily removed from the MOF and/or exchanged with other coordinative molecules. By introducing target ligands to MOF-containing solutions, functionalized MOFs can be obtained with new chemical tags via a process called post-synthetic ligand exchange (PSE). PSE is a straightforward and practical approach that enables the preparation of a wide range of MOFs with new chemical tags via a solid-solution equilibrium process. Furthermore, PSE can be performed at room temperature, allowing the incorporation of thermally unstable ligands into MOFs. In this work, we demonstrate the practicality of PSE by using heterocyclic triazole- and tetrazole-containing ligands to functionalize a Zr-based MOF (UiO-66; UiO = University of Oslo). After digestion, the functionalized MOFs are characterized via various techniques, including powder X-ray diffraction and nuclear magnetic resonance spectroscopy.

Author Spotlight: Functionalizing Metal-Organic Frameworks: Advancements, Challenges, and the Power of Post-Synthetic Ligand Exchange 

Post-synthetic ligand exchange (PSE) is a versatile and powerful tool for installing functional groups into metal-organic frameworks (MOFs). Exposing MOFs to solutions containing triazole- and tetrazole-functionalized ligands can incorporate these heterocyclic moieties into Zr-MOFs through PSE processes.

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. ...

Solvothermal Synthesis of MIL-96 and UiO-66-NH₂ on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

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