Name: preparation of hydrophobic metal-organic frameworks via plasma enhanced chemical vapor deposition of perfluoroalkanes for the removal of ammonia
Uploaded: 2013-10-10T22:00:00
Description: Watch this Scientific Journal Video about Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia at JoVE.com

The authors thank the Defense Threat Reduction Agency for funding under project number BA07PRO104, Martin Smith, Corrine Stone, and Colin Willis of the Defence Science and Technology Laboratory (DSTL) for their expertise in low pressure plasma technology, and Matthew Browe and Wesley Gordon of the Edgewood Chemical Biological Center (ECBC) for microbreakthrough testing and contact angle measurements, respectively.

1. Cu-BTC Synthesis and Preparation
<ol>
	<li>Stir 12.5 ml of deionized water and 12.5 ml of dimethylformamide in a 100 ml screw cap jar for approximately 5 min.</li>
	<li>Add 0.87 g (3.6 mmol) copper(II) nitrate trihydrate followed by 0.50 g (2.4 mmol) of trimesic acid to the solution in the jar and stir for approximately 5 min. The solution will turn blue in color. Place the capped jar in a preheated oven at 120 &#176;C for approximately 24 hr.</li>
	<li>Remove the jar from the oven. Once the jar has cooled to room t...

<ol>
	<li>Montoro, C., 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=Capture+of+Nerve+Agents+and+Mustard+Gas+Analogues+by+Hydrophobic+Robust+MOF-5+Type+Metal-Organic+Frameworks.">Capture of Nerve Agents and Mustard Gas Analogues by Hydrophobic Robust MOF-5 Type Metal-Organic Frameworks.</a> J. Am. Chem. Soc. 133, 11888-11891 (2011).</li><li>Glover, T. G., Peterson, G. W., Schindler, B. J., Britt, D., Yaghi, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MOF-74+building+unit+has+a+direct+impact+on+toxic+gas+adsorption.">MOF-74 building unit has a direct impact on toxic gas adsorption.</a> Chem. Eng. Sci. 66, 163-170 (2011).</li><li>Britt, D., Tranchemontagne, D., Yaghi, O. M. <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+frameworks+with+high+capacity+and+selectivity+for+harmful+gases.">Metal-organic frameworks with high capacity and selectivity for harmful gases.</a> Proc. Natl. Acad. Sci. U.S.A. 105, 11623-11627 (2008).</li><li>Peterson, G. W., 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=Ammonia+Vapor+Removal+by+Cu(3)(BTC)(2)+and+Its+Characterization+by+MAS.">Ammonia Vapor Removal by Cu(3)(BTC)(2) and Its Characterization by MAS.</a> NMR. J. Phys. Chem. Nanomater. Interfaces. 113 (3), 13906-13917 (2009).</li><li>Gul-E-Noor, 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=Effects+of+varying+water+adsorption+on+a+Cu(3)(BTC)(2)+metal-organic+framework+(MOF)+as+studied+by+(1)H+and+(13)C+solid-state+NMR+spectroscopy.">Effects of varying water adsorption on a Cu(3)(BTC)(2) metal-organic framework (MOF) as studied by (1)H and (13)C solid-state NMR spectroscopy.</a> Phys. Chem. Chem. Phys. 13 (3), 7783-7788 (2011).</li><li>DeCoste, J. B., 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=The+effect+of+water+adsorption+on+the+structure+of+the+carboxylate+containing+metal-organic+frameworks+Cu-BTC,+Mg-MOF-74,+and+UiO-66.">The effect of water adsorption on the structure of the carboxylate containing metal-organic frameworks Cu-BTC, Mg-MOF-74, and UiO-66.</a> J. Mater. Chem. , (2013).</li><li>K&#252;sgens, P., 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=Characterization+of+metal-organic+frameworks+by+water+adsorption.">Characterization of metal-organic frameworks by water adsorption.</a> Microporous and Mesoporous Mater. 120, 325-330 (2009).</li><li>Cavka, J. H., 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=A+New+Zirconium+Inorganic+Building+Brick+Forming+Metal+Organic+Frameworks+with+Exceptional+Stability.">A New Zirconium Inorganic Building Brick Forming Metal Organic Frameworks with Exceptional Stability.</a> J. Am. Chem. Soc. 130, 13850-13851 (2008).</li><li>DeCoste, J. B., 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=Stability+and+degradation+mechanisms+of+metal-organic+frameworks+containing+the+Zr6O4(OH)4+secary+building+unit.">Stability and degradation mechanisms of metal-organic frameworks containing the Zr6O4(OH)4 secary building unit.</a> J. Mater. Chem. A. 1, 5642-5650 (2013).</li><li>Yang, S. J., Park, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+Highly+Moisture-Resistant+Black-Colored+Metal+Organic+Frameworks.">Preparation of Highly Moisture-Resistant Black-Colored Metal Organic Frameworks.</a> Adv. Mater. 24, 4010-4013 (2012).</li><li>Li, H., 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=Enhanced+Hydrostability+in+Ni-Doped+MOF-5.">Enhanced Hydrostability in Ni-Doped MOF-5.</a> Inorg. Chem. 51, 9200-9207 (2012).</li><li>Jasuja, H., Huang, Y. -. g., Walton, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adjusting+the+Stability+of+Metal+-+Organic+Frameworks+under+Humid+Conditions+by+Ligand+Functionalization.">Adjusting the Stability of Metal - Organic Frameworks under Humid Conditions by Ligand Functionalization.</a> Langmuir. 28, 16874-16880 (2012).</li><li>Jasuja, H., Burtch, N. C., Huang, Y. -. g., Cai, Y., Walton, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetic+Water+Stability+of+an+Isostructural+Family+of+Zinc-Based+Pillared+Metal+-+Organic+Frameworks.">Kinetic Water Stability of an Isostructural Family of Zinc-Based Pillared Metal - Organic Frameworks.</a> Langmuir. 29, 633-642 (2012).</li><li>Decoste, J. B., Peterson, G. W., Smith, M. W., Stone, C. A., Willis, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+Stability+of+Cu-BTC+MOF+via+Perfluorohexane+Plasma-Enhanced+Chemical+Vapor+Deposition.">Enhanced Stability of Cu-BTC MOF via Perfluorohexane Plasma-Enhanced Chemical Vapor Deposition.</a> J. Am. Chem. Soc. 134, 1486-1489 (2012).</li><li>Bradley, R. H., Smith, M. W., Andreu, A., Falco, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+studies+of+novel+hydrophobic+active+carbons.">Surface studies of novel hydrophobic active carbons.</a> Appl. Surf. Sci. 257, 2912-2919 (2011).</li><li>Poire, E., 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=Modification+of+active+carbon+by+hydrophobic+plasma+plymers.">Modification of active carbon by hydrophobic plasma plymers.</a> Plasma Deposition of Polymeric Thin Films. 54, 185-196 (1994).</li><li>Hozumi, A., Takai, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+ultra+water-repellent+films+by+microwave+plasma-enhanced+CVD.">Preparation of ultra water-repellent films by microwave plasma-enhanced CVD.</a> Thin Solid Films. 303 (97), 222-225 (1997).</li><li>Dolbier, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Guide to Fluorine NMR for Organic Chemists. , (2009).</li><li>Maricq, M. M., Waugh, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NMR+IN+ROTATING+SOLIDS.">NMR IN ROTATING SOLIDS.</a> J. Chem. Phys. 70, 3300-3316 (1979).</li><li>Kim, M., Cahill, J. F., Su, Y., Prather, K. A., Cohen, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Postsynthetic+ligand+exchange+as+a+route+to+functionalization+of+'inert'+metal-organic+frameworks.">Postsynthetic ligand exchange as a route to functionalization of 'inert' metal-organic frameworks.</a> Chem. Sci. 3, 126-130 (2012).</li><li>d'Agostino, R., 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=.">.</a> Advanced Plasma Technology. , (2008).</li><li>DeCoste, J. B., 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=+The+effect+of+water+adsorption+on+the+structure+of+the+carboxylate+containing+metal-organic+frameworks+Cu-BTC,+Mg-MOF-74,+and+UiO-66."> The effect of water adsorption on the structure of the carboxylate containing metal-organic frameworks Cu-BTC, Mg-MOF-74, and UiO-66.</a> J. Mater. Chem. A. , (2013).</li></ol>

The synthesis of Cu-BTC, as in most MOFs, can be heavily dependent on the ratio of reactants used and the temperature the synthesis is carried out at. Varying the temperature or solvent used in synthesis has been shown to produce different morphologies of a MOF structure20. Therefore it is of strong importance to follow the procedure set forth in the literature for any MOF being synthesized. Furthermore, one should consider the reactants, solvents, and synthesis conditions when choosing a vessel in which to co...

Metal-organic frameworks (MOFs) have become a leading class of porous materials for toxic gas removal1-3. MOFs have an unprecedented ability to tailor functionality for targeted chemical interaction. Cu-BTC (also known as HKUST-1 or Cu3(BTC)2) has been previously found to have an exceptionally high ammonia loading; however, this is at a cost of the material&#39;s structural stability4 . Further studies on Cu-BTC have indicated that moisture itself is capable of degrading the MOF structure, rendering it ineffective for many potential applications5,6,21. The structural instability of certain carboxylate containing MOFs in the presence of liquid water or high humidity has been a major deterrent to use in commercial or industrial applications7 .
It would be most ideal for MOFs used for chemical removal to have inherent stability in the presence of humidity. However, many MOFs with superior stability, such as UiO-66, have poor chemical removal capabilities, while many MOFs with open metal sites like MOF-74 and Cu-BTC have superior chemical removal capabilities2,4,8,9. The open metal sites in MOF-74 and Cu-BTC enhance the uptake of toxic gases such as ammonia, but these sites are also susceptible to binding water, poisoning the active sites and in many cases leading to structural breakdown. In order to preserve the chemical properties of a water unstable MOF, various attempts to enhance the water stability of MOFs have been made. MOF-5 has been shown to have an enhancement in moisture resistance upon thermal treatment, by creating a carbonaceous layer around the MOF; however, the increased hydrophobicity is at the expense of surface area and ultimately functionality10. MOF-5 has also been shown to have its hydrostability increased through doping with Ni2+ ions11. Furthermore, 1,4-diazabicyclo[2.2.2]octane containing MOFs (also known as DMOFs) have been used to show the tuning of water stability through incorporation of various pendant groups on the 1,4-benzene dicarboxylate linker12,13.
The lack of hydrostability of certain of MOFs, specifically ones with high toxic gas uptake, led to the use of plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes to create fluorinated groups on the surfaces of the MOF to increase its hydrophobicity14. This technique offers the unique benefit that it can be used to alter any MOF containing aromatic hydrogens, as well as other potential functional groups on the inner surfaces of MOFs. However, the technique can be difficult to control due to the formation of highly reactive radicals in the plasma. The radicals not only react with the aromatic hydrogen atoms, but also with CFx groups already reacted onto the MOF surfaces. Careful control of the procedure is necessary to ensure pore blockage does not occur, rendering the MOF ineffective. This technique has been used by others to alter the wetting properties of carbon materials; however, to our knowledge it had never previously been used to enhance hydrostability of microporous material.15,16.

<table border="1">
	<tbody>
		<tr>
			<td>Name of Material/ Equipment</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments/Description</td>
		</tr>
		<tr>
			<td>Copper (II) Nitrate Trihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>61194</td>
			<td></td>
		</tr>
		<tr>
			<td>Trimesic acid</td>
			<td>Sigma-Aldrich</td>
			<td>482749</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>130147</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl Formamide</td>
			<td>Sigma-Aldrich</td>
			<td>319937</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Sigma-Aldrich</td>
			<td>187332</td>
			<td></td>
		</tr>
		<tr>
			<td>Hexafluoroethane</td>
			<td>Synquest Labs</td>
			<td>1100-2-05</td>
			<td></td>
		</tr>
		<tr>
			<td>Femto-Plasma System</td>
			<td>Diener Electronic</td>
			<td>Basic unit type B</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasma Generator</td>
			<td>Diener Electronic</td>
			<td>Type D</td>
			<td>0-100 W at 13.56 MHz</td>
		</tr>
		<tr>
			<td>Rotary Vane Pump for Plasma System</td>
			<td>Leybold</td>
			<td>D16BCS PFPE</td>
			<td>Appropriate for corrosive gases</td>
		</tr>
		<tr>
			<td>Powder Treatment Device</td>
			<td>Diener Electronic</td>
			<td>Option 5.9</td>
			<td>Glass bottle and rotating devise within plasma system</td>
		</tr>
		<tr>
			<td>Environmental Chamber</td>
			<td>Associated Environmental Systems</td>
			<td>HD-205</td>
			<td></td>
		</tr>
		<tr>
			<td>Gas Chromatograph</td>
			<td>Hewlet Packard</td>
			<td>HP5890 Series II</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoionization Detector</td>
			<td>O-I Analytical</td>
			<td>4430/5890</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoionization Detector Lamp</td>
			<td>Excilitis</td>
			<td>FK-794U</td>
			<td></td>
		</tr>
		<tr>
			<td>Water bath</td>
			<td>NESLAB</td>
			<td>RTE-111</td>
			<td></td>
		</tr>
		<tr>
			<td>Fritted glass tubes</td>
			<td>CDA Analytical</td>
			<td>MX062101</td>
			<td>Dynatherm sampling tubes</td>
		</tr>
	</tbody>
</table>

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.

Within the representative results the authors chose to display the characteristics of a 0.50 g sample of Cu-BTC treated with hexafluoroethane (C2F6) for 4 hr at a pressure of 0.30 mbar and a plasma power of 50 W. MOFs treated with a perfluoroalkane plasma under adequate conditions should display enhanced hydrophobicity. This can be demonstrated by placing the powder on top of liquid water and determining if the sample floats or measuring the contact angle water on a pressed pellet as seen in <strong...

Watch this Scientific Journal Video about Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia at JoVE.com

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

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 ...

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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 ...

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at &#60;60 &#176;C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 &#176;C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 &#176;C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.

Columnar zinc oxide structures in the form of rods are synthesized via aerosol-assisted chemical vapor deposition without the use of pre-deposited catalyst-seed particles. This method is scalable and compatible with various substrates based on either silicon, quartz or polymers.

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, ...

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. ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...

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. ...

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural tunability. However, the progression of MOF-based photochemistry has been hindered by the difficulty in spectrally characterizing these materials. Given that MOFs are typically larger than 100 nm in size, they are prone to excessive light scatter, thereby rendering data from valuable analytical tools like transient absorption and emission spectroscopy nearly uninterpretable. To gain meaningful insights of MOF-based photo-chemical and physical processes, special consideration must be taken toward properly preparing MOFs for spectroscopic measurements, as well as the experimental setups that garner higher quality data. With these considerations in mind, the present guide provides a general approach and set of guidelines for the spectroscopic investigation of MOFs. The guide addresses the following key topics: (1) sample preparation methods, (2) spectroscopic techniques/measurements with MOFs, (3) experimental setups, (3) control experiments, and (4) post-run stability characterization. With appropriate sample preparation and experimental approaches, pioneering advancements toward the fundamental understanding of light-MOF interactions are significantly more attainable.

Here, we use a polymer stabilizer to prepare metal-organic framework (MOF) suspensions that exhibit markedly decreased scatter in their ground-state and transient absorption spectra. With these MOF suspensions, the protocol provides various guidelines to characterize the MOFs spectroscopically to yield interpretable data.

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

Synthesis of Low-Valent MOFs from Multitopic Phosphine Linkers

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, energy, and catalysis. Recently, low-valent MOFs (LVMOFs) have been explored for their potential use as heterogeneous catalysts, and multitopic phosphine linkers have been shown to be a useful building block for the formation of LVMOFs. However, the synthesis of LVMOFs using phosphine linkers requires conditions that are distinct from those in the majority of the MOF synthetic literature, including the exclusion of air and water and the use of unconventional modulators and solvents, making it somewhat more challenging to access these materials. This work serves as a general tutorial for the synthesis of LVMOFs with phosphine linkers, including information on the following: 1) the judicious choice of the metal precursor, modulator, and solvent; 2) the experimental procedures, air-free techniques, and required equipment; 3) the proper storage and handling of the resultant LVMOFs; and 4) useful characterization methods for these materials. The intention of this report is to lower the barrier to this new subfield of MOF research and facilitate advancements toward novel catalytic materials.

Author Spotlight: Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers  

Here, we describe a protocol for the synthesis of low-valent metal-organic frameworks (LVMOFs) from low-valent metals and multitopic phosphine linkers under air-free conditions. The resulting materials have potential applications as heterogeneous catalyst mimics of low-valent metal-based homogeneous catalysts.

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...

Magnetometric Characterization of Redox-Active MOFs Solid-State Electrochemistry

Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs show outstanding performance in terms of gravimetric or areal capacitance and cyclic stability, unfortunately their electrochemical mechanisms are not well understood in most cases. Traditional spectroscopic techniques, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), have only provided vague and qualitative information about valence changes of certain elements, and the mechanisms proposed based on such information are often highly disputable. In this article, we report a series of standardized methods, including the fabrication of solid-state electrochemical cells, electrochemistry measurements, the disassembly of cells, the collection of MOF electrochemical intermediates, and physical measurements of the intermediates under the protection of inert gases. By using these methods for quantitatively clarifying the electronic and spin state evolution within a single electrochemical step of redox-active MOFs, one can provide clear insight into the nature of electrochemical energy storage mechanisms not only for MOFs, but also for all other materials with strongly correlated electronic structures.

Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks  

Ex situ magnetic surveys can directly provide bulk and local information on a magnetic electrode to reveal its charge storage mechanism step by step. Herein, electron spin resonance (ESR) and magnetic susceptibility are demonstrated to monitor the evaluation of paramagnetic species and their concentration in a redox-active metal-organic framework (MOF).

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs ...