This work was sponsored by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, grant no. DE-FG02-12ER16352. S.T.H. thanks the National Science Foundation for financial support through the National Science Foundation Graduate Research Fellowship under Grant No. 1122374.

1. Synthesis of Silica-encapsulated Monometallic or Bimetallic Metal Oxide Nanoparticles
<ol>
	<li>Prepare the reverse microemulsion
	<ol>
		<li>Add 240 ml of anhydrous n-heptane to a clean, oven-dried 1 L round bottom flask (RBF) containing an oven-dried magnetic stir bar using a clean, oven-dried graduated cylinder.</li>
		<li>Add 54 ml of polyoxyethylene (4) lauryl ether to the n-heptane under constant stirring. 
		Note: Because of the high viscosity and low surface tension of this surfactant, a clean, dry 60 ml syringe should be used to obtain accurate volumes instead of a graduated cylinder.</li>
		<li>Add 7.8 ml of ultrapure, deionized (DI) water under constant stirring using a pipette. Seal the RBF with a rubber stopper and Parafilm wax. Let the RME mix for at least 10 min.</li>
		<li>Add 0.1 to 0.5 ml of reagent-grade NH4OH to the emulsion if it is desired to reduce the hydrolysis time. 
		Note: Some metal alkoxide precursors hydrolyze slowly at neutral pH. Let the RME mix for at least another 10 min after adding NH4OH. As a representative example, adding 0.5 ml of NH4OH is recommended for syntheses involving titanium (IV) isopropoxide.</li>
	</ol>
	</li>
	<li>Prepare a metal alkoxide precursor, alcohol, and n-heptane solution
	<ol>
		<li>Connect a clean, oven-dried 250 ml RBF to a Schlenk line and flush with nitrogen. Alternatively, place the clean, oven-dried 250 ml RBF into a dry nitrogen glovebox.</li>
		<li>Add 12 ml of 5% w/v tungsten isopropoxide (WIPO) in isopropanol using a clean, dry syringe. At this stage, other metal alkoxides can also be added, such as tantalum (V) isopropoxide (TaIPO), molybdenum (V) isopropoxide (MoIPO), niobium (V) isopropoxide (NbIPO), titanium (IV) isopropoxide (TiIPO), nickel (II) methoxyethoxide (NiMEO), cobalt (II) isopropoxide (CoIPO), etc. 
		Note: Metal alkoxides can be purchased commercially or synthesized by the addition of an anhydrous alcohol to the corresponding metal chloride salt using a Schlenk line as described elsewhere (Caution: metal alkoxide synthesis from the metal chloride releases gaseous HCl and must be performed in a well-ventilated fume hood).27</li>
		<li>Using a clean, oven-dried cannula, transfer 120 ml of anhydrous n-heptane to the 250 ml RBF containing the metal alkoxide solution</li>
	</ol>
	</li>
	<li>Using a clean, oven-dried cannula, transfer the metal alkoxide-alcohol-n-heptane solution into the RME under constant stirring over the span of 10 min. 
	Note: For metal alkoxides that react vigorously with water, such as tellurium (IV) isopropoxide, a much slower drop-wise rate of addition is required. The final solution should be optically clear regardless of the metal alkoxide precursor used, but can be various colors depending on the metal alkoxides used and their oxidation states. We note that whether the emulsion is transparent or translucent is dependent on particle size while the color is dependent on metal oxidation state.</li>
	<li>After 4 hr, use a clean, dry syringe to inject 1.4 ml of reagent-grade NH4OH into the solution dropwise. Then, using another clean, dry syringe, inject 1.2 ml of reagent-grade tetraethyl orthosilicate (TEOS) dropwise. 
	Note: Sodium hydroxide (NaOH) should not be used as it can lead to densification of the silica shells during carburization/nitridation and result in sodium impurities in the lattice of the final nanoparticles. Residual NH4OH on the other hand conveniently decomposes during the heat treatments.</li>
	<li>After 16.5 hr, remove the rubber stopper and use a clean, dry graduated cylinder to add 300 ml of methanol to the solution under constant stirring.</li>
	<li>After 10 min of stirring, remove the stir bar and allow the solution to settle. 
	Note: There will be two liquid phases present: a heptane-rich upper phase and a methanol-rich lower phase. The silica-encapsulated metal oxide nanoparticles, designated as SiO2/MOx will sediment to the bottom of the flask from the lower phase.</li>
	<li>After 1 hr, decant the liquid phases into an organic waste container and collect the solid phase SiO2/MOx in clean 50 ml centrifuge tubes. 
	Note: if polypropylene or polystyrene centrifuge tubes are being used, the precipitant cannot be stored long-term in this state as the residual heptane will slowly dissolve the centrifuge tube, causing it to elongate. Furthermore, residual NH4OH and TEOS can cause the SiO2 to continue to grow beyond what was desired.</li>
	<li>Centrifuge the SiO2/MOx phase at 2,056 x g for 5 min, then decant the supernatant into an organic waste container.</li>
	<li>Add 10-30 ml of acetone to each 50 ml centrifuge tube and disperse the powder into the acetone by shaking or sonicating. This helps remove excess surfactant before calcination.</li>
	<li>Centrifuge the SiO2/MOx and acetone mixture at 4,626 x g for 10 min and then decant the supernatant into an organic waste container. Allow the SiO2/MOx gel to dry overnight.</li>
</ol>
2. Heat Treatment of the Synthesized Powder
Caution Statement: Hydrogen, methane, and ammonia gas are extremely flammable. Ammonia gas is toxic. A thorough leak-check should be performed before all heat treatments, and the treatments should be performed in quartz-tubular furnace kept in a well-ventilated fume hood with an oil bubbler at the gas outlet. All gas cylinders should be equipped with flame arrestors and stored away from the furnace. If required by law or institutional regulations, excess ammonia gas should be bubbled through a large volume of water and either discarded as base waste or neutralized to pH 7 ammonium chloride solution using HCl.
<ol>
	<li>Calcination of the SiO2/MOx powder in air
	<ol>
		<li>Crush the dried SiO2/MOx gel into a fine powder using a glass stir bar or mortar and pestle. Put the powder in alumina crucible boats and load into a quartz-tube furnace.</li>
		<li>Using a 2 &#176;C/min heating rate, calcine the SiO2/MOx powder under 100 sccm of air at 450 &#176;C for 1 hr. This removes any residual surfactant and also increases the microporosity of the silica shells. After the furnace has cooled, remove the calcined SiO2/MOx powders and store in ambient conditions.</li>
	</ol>
	</li>
	<li>Carburization of the SiO2/MOx powder in a methane/hydrogen atmosphere
	<ol>
		<li>Load the calcined SiO2/MOx powder into an unglazed alumina crucible boat and place into a quartz-tube furnace. Flush the quartz-tube furnace with nitrogen for at least 30 min to remove oxygen. Perform a leak check by spraying all joints with soapy water.</li>
		<li>Using a 2 &#176;C/min heating rate, carburize the SiO2/MOx powder under 120 sccm of hydrogen and 33 sccm of methane at 850 &#176;C for 4 hr to form SiO2/MCx.</li>
		<li>After 4 hr, stop the flow of methane and hold the powder at 850 &#176;C for 1 hr in just 120 sccm of hydrogen to scavenge any excess surface carbon.</li>
		<li>Allow the furnace to slowly cool to room temperature under 120 sccm of hydrogen. Then, flush the furnace with nitrogen for at least 30 min to remove hydrogen.</li>
		<li>Flow 95 sccm of nitrogen and 5 sccm of air over the powder for 3 hr to slowly passivate the carbides before exposure to air.</li>
		<li>Remove the SiO2/MCx powder from the furnace and store in a vacuum dessicator or in a dry nitrogen glovebox to prevent long-term bulk oxidation of the metal carbide nanoparticles in air.</li>
	</ol>
	</li>
	<li>Nitridation of the SiO2/MOx powder in an ammonia atmosphere
	<ol>
		<li>Load the calcined SiO2/MOx powder into an alumina crucible boat and place into a quartz-tube furnace.</li>
		<li>Flush the quartz-tube furnace with nitrogen for at least 30 min to remove oxygen.</li>
		<li>Using a 2 &#176;C/min heating rate, nitridize the SiO2/MOx powder under 100 sccm of ammonia at 800 &#176;C for 4 hr to form SiO2/MNx.</li>
		<li>Allow the furnace to slowly cool to room temperature. Then, flush the furnace with nitrogen for at least 30 min to remove ammonia.</li>
		<li>Flow 95 sccm of nitrogen and 5 sccm of air over the powder for 3 hr to slowly passivate the nitrides before exposure to air.</li>
		<li>Remove the SiO2/MNx powder from the furnace and store in a vacuum dessicator or in a dry nitrogen glovebox to prevent long-term bulk oxidation of the metal nitride nanoparticles in air.</li>
	</ol>
	</li>
</ol>
3. Removing the Silica Shells and Supporting the Nanoparticles
Caution Statement: ammonium bifluoride (ABF) is highly toxic. It should only be handled in a well-ventilated fume hood using proper personal protective equipment, including butyl-rubber gloves, a face shield, and an HF-resistant labcoat with HF-resistant sleeves. Glass and metal lab equipment should never be used when handling ABF.
<ol>
	<li>Silica Dissolution in Ammonium Bifluoride for Acid-Stable Metal Carbides and Nitrides (such as WC and W2N)
	<ol>
		<li>Weigh out 200 mg of SiO2/MCx or SiO2/MNx and put in a 30 ml sealable polypropylene container with a Teflon-coated magnetic stir bar.</li>
		<li>If it is desired to support the nanoparticles on a high surface area catalyst support, such as carbon black or carbon nanotubes, weigh out the material and add it to the sealable polypropylene container. 
		Note: The mass weighed out will depend on the desired loading of nanoparticles on the support. For catalyst supports that are not stable in ABF, such as alumina, the support can be added after the silica has been removed and the ABF is neutralized. If no support is added, a nanodispersion will be obtained.</li>
		<li>Add 20 ml of ultrapure DI water and begin mixing to form a suspension. Alternatively, add 20 ml of pre-made 20 wt% ABF solution.</li>
		<li>Weigh out 5 g of ABF and then add to the stirring mixture. Once added, seal the polypropylene container. 
		Note: Dissolution of ABF in water is endothermic, so the temperature of the solution will drop.</li>
		<li>To ensure complete dissolution of the silica and good dispersion of the nanoparticles on the catalyst support, stop the reaction after 16 hr by adding reagent-grade NH4OH dropwise to neutralize the ABF solution to a pH of 6-7. Caution: this reaction is exothermic.</li>
		<li>Empty the neutralized mixture into a centrifuge tube and centrifuge at 2,056 x g for 10 min.</li>
		<li>Empty the supernatant into an alkaline waste container (to ensure total neutralization) and redisperse the catalyst powder in 20 ml of ultrapure DI water.</li>
		<li>Centrifuge at 4,626 x g for 10 min, discard the supernatant, and do one final 20 ml DI water rinse. Up to 12,850 x g may be required for unsupported nanoparticles.</li>
		<li>Dry the powder under vacuum and then store in a vacuum dessicator or a dry nitrogen glovebox to prevent long-term bulk oxidation of the metal carbide or nitride nanoparticles.</li>
	</ol>
	</li>
	<li>Silica Dissolution in Sodium Hydroxide for Alkaline-Stable Carbides and Nitrides (such as TaC and Ta3N5)
	<ol>
		<li>Weigh out 200 mg of SiO2/MCx or SiO2/MNx and put in a 50 ml glass RBF with a magnetic stir bar. Weigh out and add a catalyst support if desired.</li>
		<li>Add 30 ml of at least 0.1 M aqueous NaOH solution. Attach a condenser to the RBF or seal with a rubber stopper and Parafilm wax.</li>
		<li>Heat at 60 &#176;C under constant stirring for 16 hr. After cooling, centrifuge the solution at 2,056 x g for 10 min.</li>
		<li>Empty the supernatant into an alkaline waste container and redisperse the catalyst powder in 20 ml of ultrapure DI water.</li>
		<li>Centrifuge at 4,626 x g for 10 min, discard the supernatant, and do one final 20 ml DI water rinse. Up to 12,850 x g may be required for unsupported nanoparticles.</li>
		<li>Dry the powder under vacuum and then store in a vacuum dessicator or a dry nitrogen glovebox to prevent long-term bulk oxidation of the metal carbide or nitride nanoparticles.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

A procedure for synthesizing non-sintered, metal terminated transition metal carbide and nitride nanoparticles with tunable sizes and structure is presented here.26 Critical steps in the method include: using a moisture-free RBF to contain the diluted metal alkoxide precursor, avoiding alkali metal impurities during all steps, precipitating the RME with excess methanol as opposed to acetone or isopropanol, performing a proper leak check before carburizing or nitridizing the components, and using proper PPE whe...

Early transition metal carbides (TMCs) are low-cost, earth-abundant materials that exhibit high thermal and electrochemical stability as well as unique catalytic activities.1-3 In particular, tungsten carbide (WC) and molybdenum carbide (Mo2C) have been studied extensively for their catalytic similarities to the platinum group metals (PGMs).4,5 Due to these favorable properties, TMCs have been identified as candidates for replacing expensive PGM catalysts in emerging renewable energy technologies, such as biomass conversion, fuel cells, and electrolyzers.6,7
To maximize catalytic activity, commercial catalysts are almost always formulated as ultrasmall nanoparticles (diameters &#60;10 nm) dispersed on a high surface area support, such as carbon black.8 However, the synthesis of TMCs requires temperatures higher than ~700 &#176;C. This leads to extensive sintering of the nanoparticles (NPs), excess surface carbon deposition (coke), and thermal support degradation. Both particle sintering and support degradation lead to decreased material surface areas. Excess surface impurity deposition blocks active metal sites, which has been shown to greatly reduce or in some instances completely eliminate the catalytic activity of TMCs.9,10 As such, the fundamental study of TMC reactivity is predominantly performed on bulk microparticles or thin films with finely controlled surfaces rather than on high surface area TMC nanomaterials.
Many methods have been developed to synthesize TMC NPs, but these methods are not suitable for synthesizing catalytically active TMC NPs. Traditional wet impregnation techniques use metal salt solutions impregnated on a high surface area support. On heating, wet impregnation methods can expose the catalyst support to destructive carburizing conditions leading to support degradation. Furthermore, sintering can only be mitigated at low wt% loadings of the metal on the support, and it is also not possible to synthesize unsupported TMC nanopowders using wet impregnation. Several newer methods involve mixing a metal precursor with a carbon precursor and applying conventional and unconventional heating techniques.11-18 Excess carbon is used to prevent sintering, but this excess carbon results in extensive surface carbon, making these materials not suitable for catalytic applications.
Due to these synthetic challenges, TMCs have traditionally been studied as co-catalysts11 for PGMs, catalyst supports for PGMs,19-22 or supports for active PGM monolayers.23-25 The method presented here offers the ability to synthesize both non-sintered and metal-terminated TMC NPs as well as transition metal nitride (TMN) NPs with tunable sizes, crystalline phases, and metallic composition.26 The method presented also offers the ability to obtain TMC or TMN nanodispersions or deposit the TMC and TMN NPs on a high surface area catalyst support at room-temperature, thereby mitigating thermal support degradation. This method is therefore suitable for standalone catalytic applications of TMC and TMN NPs, the development of advanced multimetallic TMC and TMN NPs, or other applications requiring finely controlled particle sizes and surfaces.26
The method presented here uses a three step protocol to synthesize TMC and TMN NPs. In the first step, a reverse microemulsion (RME) is used to coat early transition metal oxide (TMO) NPs in silica nanospheres. The emulsion is prepared by dispersing water droplets in a nonpolar medium using a commercial nonionic surfactant. The silica-encapsulated TMO NPs are then subjected to either carburizing or nitridizing heat treatments. Here, the silica prevents particle sintering at high temperatures while allowing the reactive gases to diffuse to the TMO NPs and convert them to TMC or TMN NPs. In the final step, the silica shells are removed using either acidic or alkaline treatment to obtain TMC or TMN nanodispersions that can be dispersed on a high surface area support, such as carbon black.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>n-heptane</td>
			<td>Sigma-Aldrich</td>
			<td>246654</td>
			<td></td>
		</tr>
		<tr>
			<td>polyoxyethylene (4) lauryl ether</td>
			<td>Sigma-Aldrich</td>
			<td>235989</td>
			<td>Brij&#174; L4</td>
		</tr>
		<tr>
			<td>tungsten (VI) isopropoxide</td>
			<td>Alfa Aesar</td>
			<td>40247</td>
			<td>W(VI)IPO</td>
		</tr>
		<tr>
			<td>tungsten (VI) chloride</td>
			<td>Sigma-Aldrich</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/aldrich/241911?lang=en&amp;region=US">241911</a></td>
			<td>To prepare W(VI)IPO, homemade</td>
		</tr>
		<tr>
			<td>tungsten (IV) chloride</td>
			<td>Strem Chemicals</td>
			<td>74-2348</td>
			<td>To prepare W(IV)IPO, homemade</td>
		</tr>
		<tr>
			<td>tantalum (V) isopropoxide</td>
			<td>Alfa Aesar</td>
			<td><a href="http://www.alfa.com/en/catalog/40038">40038</a></td>
			<td>Ta(V)IPO</td>
		</tr>
		<tr>
			<td>niobium (V) isopropoxide</td>
			<td>Alfa Aesar</td>
			<td><a href="http://www.alfa.com/en/catalog/36572">36572</a></td>
			<td>Nb(V)IPO</td>
		</tr>
		<tr>
			<td>nickel (II) methoxyethoxide</td>
			<td>Alfa Aesar</td>
			<td>42377</td>
			<td>Ni(II)MEO</td>
		</tr>
		<tr>
			<td>titanium (IV) isopropoxide</td>
			<td>Sigma-Aldrich</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/aldrich/87560?lang=en&amp;region=US">87560</a></td>
			<td>Ti(IV)IPO</td>
		</tr>
		<tr>
			<td>molybdenum (V) isopropoxide</td>
			<td>Alfa Aesar</td>
			<td><a href="http://www.alfa.com/en/catalog/39159">39159</a></td>
			<td>Mo(V)IPO</td>
		</tr>
		<tr>
			<td>molybdenum (V) chloride</td>
			<td>Sigma-Aldrich</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/aldrich/208353?lang=en&amp;region=US">208353</a></td>
			<td>To prepare Mo(V)IPO, homemade</td>
		</tr>
		<tr>
			<td>tetraethyl orthosilicate</td>
			<td>Sigma-Aldrich</td>
			<td>333859</td>
			<td>TEOS</td>
		</tr>
		<tr>
			<td>ammonium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>320145</td>
			<td></td>
		</tr>
		<tr>
			<td>methanol</td>
			<td>Sigma-Aldrich</td>
			<td>34860</td>
			<td></td>
		</tr>
		<tr>
			<td>anhydrous isopropanol</td>
			<td>Sigma-Aldrich</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/sial/278475?lang=en&amp;region=US">278475</a></td>
			<td>To prepare homemade alkoxides</td>
		</tr>
		<tr>
			<td>ammonium bifluoride</td>
			<td>Sigma-Aldrich</td>
			<td>224820</td>
			<td></td>
		</tr>
		<tr>
			<td>carbon black</td>
			<td>Cabot Corp.</td>
			<td>Vulcan&#174; XC72R</td>
			<td></td>
		</tr>
		<tr>
			<td>Methane</td>
			<td>AirGas</td>
			<td>ME R300</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrogen</td>
			<td>AirGas</td>
			<td>HY UHP300</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonia</td>
			<td>AirGas</td>
			<td>AM AH80N705</td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz Tube Furnace</td>
			<td>MTI Corp.</td>
			<td>OTF-1200X-S-UL</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

In the first step of the protocol, the goal is to encapsulate the monometallic or bimetallic transition metal oxide (TMO) NPs within microporous silica spheres. Figure 1 shows images taken of representative syntheses before and after precipitation with methanol. Two reproducible morphological outcomes have been observed during this step that appear to be dependent on the metals used in the synthesis: the TMO NPs can be singly coated with a silica sphere (Figure 2b) or multiple TMO NPs ca...

Watch this Scientific Journal Video about Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles at JoVE.com

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

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 ...

reverse-microemulsion-mediated-synthesis-monometallic-bimetallic

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Chemistry

10.8K 조회수.  Massachusetts Institute of Technology. A “removable ceramic coating method” 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.

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

Anticancer Metal Complexes: Synthesis and Cytotoxicity Evaluation by the MTT Assay

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; therefore their preparation should be conducted under an inert atmosphere. Evaluation of the anticancer activity of these complexes can be achieved by the MTT assay.
The MTT assay is a colorimetric viability assay based on enzymatic reduction of the MTT molecule to formazan when it is exposed to viable cells. The outcome of the reduction is a color change of the MTT molecule. Absorbance measurements relative to a control determine the percentage of remaining viable cancer cells following their treatment with varying concentrations of a tested compound, which is translated to the compound anticancer activity and its IC50 values. The MTT assay is widely common in cytotoxicity studies due to its accuracy, rapidity, and relative simplicity.
Herein we present a detailed protocol for the synthesis of air sensitive metal based drugs and cell viability measurements, including preparation of the cell plates, incubation of the compounds with the cells, viability measurements using the MTT assay, and determination of IC50 values.

A method for synthesis of air-sensitive titanium and vanadium anticancer agents is described, along with the evaluation of their cytotoxic activity towards human cancer cell line by the MTT Assay.

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; ...

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 ...

Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

Ynones are a valuable functional group and building block in organic synthesis. Ynones serve as a precursor to many important organic functional groups and scaffolds. Traditional methods for the preparation of ynones are associated with drawbacks including harsh conditions, multiple purification steps, and the presence of unwanted byproducts. An alternative method for the straightforward preparation of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts is described herein. The adoption of organotrifluoroborate salts as an alternative to organometallic reagents for the formation of new carbon-carbon bonds has a number of advantages. Potassium organotrifluoroborate salts are shelf stable, have good functional group tolerance, low toxicity, and a wide variety are straightforward to prepare. The title reaction proceeds rapidly at ambient temperature in the presence of a Lewis acid without the exclusion of air and moisture. Fair to excellent yields may be obtained via reaction of various aryl and alkyl acid chlorides with alkynyltrifluoroborate salts in the presence of boron trichloride.

The goal of this manuscript is to demonstrate a straightforward method for the preparation of ynones from acyl chloride and potassium alkynyltrifluoroborate salt starting materials. The one-pot reaction proceeds rapidly in the presence of boron trichloride without exclusion of air and moisture.

Ynones are a valuable functional group and building block in organic synthesis. Ynones serve as a precursor to many important organic functional groups ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution of capping ligands during the synthesis reaction, their role in regulating the nucleation and growth rates of colloidal nanoparticles is not well understood. In this work, we demonstrate a mechanistic investigation of the role of trioctylphosphine (TOP) in Pd nanoparticles in different solvents (toluene and pyridine) using in situ SAXS and ligand-based kinetic modeling. Our results under different synthetic conditions reveal the overlap of nucleation and growth of Pd nanoparticles during the reaction, which contradicts the LaMer-type nucleation and growth model. The model accounts for the kinetics of Pd-TOP binding for both, the precursor and the particle surface, which is essential to capture the size evolution as well as the concentration of particles in situ. In addition, we illustrate the predictive power of our ligand-based model through designing the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can be applied to other synthesis systems and therefore serves as an effective strategy for predictive synthesis of colloidal nanoparticles.

The main goal of this work is to elucidate the role of capping agents in regulating the size of palladium nanoparticles by combining in situ small angle x-ray scattering (SAXS) and ligand-based kinetic modeling.

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution ...

Synthesis of Bimetallic Pt/Sn-based Nanoparticles in Ionic Liquids

We demonstrate a method for the synthesis of bimetallic nanoparticles consisting of Pt and Sn. A synthesis strategy is used in which the particular physico-chemical properties of ionic liquids (ILs) are exploited to control both nucleation and growth processes. The nanoparticles form colloidal sols of very high colloidal stability in the IL, which is particularly interesting in view of their use as quasi-homogeneous catalysts. Procedures for both nanoparticle extraction in conventional solvents and for nanoparticle precipitation are presented. The size, structure and composition of the synthesized nanocrystals are confirmed using inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX). By this, we show that the nanocrystals are random-type alloy and of small (2-3 nm) size. The catalytic activity and selectivity in the hydrogenation of &#945;,&#946;-unsaturated aldehydes is tested in a semi-continuous batch-type reactor. In this context, the bimetallic Pt/Sn-based nanoparticles reveal a high selectivity towards the unsaturated alcohol.

A protocol for the synthesis of bimetallic nanoparticles in ionic liquids and the procedure of their catalytic testing in the selective hydrogenation of unsaturated aldehydes are described.

We demonstrate a method for the synthesis of bimetallic nanoparticles consisting of Pt and Sn. A synthesis strategy is used in which the particular ...

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. ...

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

Amphiphilic gold nanoparticles can be used in many biological applications. A protocol to synthesize gold nanoparticles coated by a binary mixture of ligands and a detailed characterization of these particles is presented.

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...