Name: reverse microemulsion-mediated synthesis of monometallic and bimetallic early transition metal carbide and nitride nanoparticles
Uploaded: 2015-11-27T14:00:00
Description: Watch this Scientific Journal Video about Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles at JoVE.com

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 m...

<ol>
	<li>Oyama, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Chemistry of Transition Metal Carbides and Nitrides. , (1996).</li><li>Michalsky, R., Zhang, Y. -. J., Medford, A. J., Peterson, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Departures+from+the+Adsorption+Energy+Scaling+Relations+for+Metal+Carbide+Catalysts.">Departures from the Adsorption Energy Scaling Relations for Metal Carbide Catalysts.</a> J. Phys. Chem. C. 118 (24), 13026-13034 (2014).</li><li>Kimmel, Y. C., Xu, X., Yu, W., Yang, X., Chen, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trends+in+Electrochemical+Stability+of+Transition+Metal+Carbides+and+Their+Potential+Use+As+Supports+for+Low-Cost+Electrocatalysts.">Trends in Electrochemical Stability of Transition Metal Carbides and Their Potential Use As Supports for Low-Cost Electrocatalysts.</a> ACS Catal. 4 (5), 1558-1562 (2014).</li><li>Levy, R. B., Boudart, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum-like+behavior+of+tungsten+carbide+in+surface+catalysis.">Platinum-like behavior of tungsten carbide in surface catalysis.</a> Science. 181, 547-549 (1973).</li><li>Chen, Z., Higgins, D., Yu, A., Zhang, L., Zhang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+non-precious+metal+electrocatalysts+for+PEM+fuel+cells.">A review on non-precious metal electrocatalysts for PEM fuel cells.</a> Energy Environ. Sci. 4 (9), 3167-3192 (2011).</li><li>Esposito, D. V., Chen, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monolayer+platinum+supported+on+tungsten+carbides+as+low-cost+electrocatalysts:+opportunities+and+limitations.">Monolayer platinum supported on tungsten carbides as low-cost electrocatalysts: opportunities and limitations.</a> Energy Environ. Sci. 4, 3900 (2011).</li><li>Stottlemyer, A. L., Kelly, T. G., Meng, Q., Chen, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reactions+of+oxygen-containing+molecules+on+transition+metal+carbides:+Surface+science+insight+into+potential+applications+in+catalysis+and+electrocatalysis.">Reactions of oxygen-containing molecules on transition metal carbides: Surface science insight into potential applications in catalysis and electrocatalysis.</a> Surf. Sci. Rep. 67, 201-232 (2012).</li><li>Bell, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+impact+of+nanoscience+on+heterogeneous+catalysis.">The impact of nanoscience on heterogeneous catalysis.</a> Science. 299, 1688-1691 (2003).</li><li>Kimmel, Y. C., Esposito, D. V., Birkmire, R. W., Chen, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+surface+carbon+on+the+hydrogen+evolution+reactivity+of+tungsten+carbide+(WC)+and+Pt-modified+WC+electrocatalysts.">Effect of surface carbon on the hydrogen evolution reactivity of tungsten carbide (WC) and Pt-modified WC electrocatalysts.</a> Int. J. Hydrogen Energy. 37, 3019-3024 (2012).</li><li>Yang, X., Kimmel, Y. C., Fu, J., Koel, B. E., Chen, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+Tungsten+Carbide+Catalysts+by+Use+of+an+Oxygen+Plasma+Pretreatment.">Activation of Tungsten Carbide Catalysts by Use of an Oxygen Plasma Pretreatment.</a> ACS Catal. 2, 765-769 (2012).</li><li>Garcia-Esparza, A. T., 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=Tungsten+carbide+nanoparticles+as+efficient+cocatalysts+for+photocatalytic+overall+water+splitting.">Tungsten carbide nanoparticles as efficient cocatalysts for photocatalytic overall water splitting.</a> ChemSusChem. 6, 168-181 (2013).</li><li>Yan, Z., Cai, M., Shen, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanosized+tungsten+carbide+synthesized+by+a+novel+route+at+low+temperature+for+high+performance+electrocatalysis.">Nanosized tungsten carbide synthesized by a novel route at low temperature for high performance electrocatalysis.</a> Sci. Rep. 3, 1646 (2013).</li><li>Giordano, C., Erpen, C., Yao, W., Antonietti, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+Mo+and+W+carbide+and+nitride+nanoparticles+via+a+simple+'urea+glass'+route.">Synthesis of Mo and W carbide and nitride nanoparticles via a simple 'urea glass' route.</a> Nano Lett. 8, 4659-4663 (2008).</li><li>Abdullaeva, Z., 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=High+temperature+stable+WC1&#8722;x@C+and+TiC@C+core&#8211;shell+nanoparticles+by+pulsed+plasma+in+liquid.">High temperature stable WC1&#8722;x@C and TiC@C core&#8211;shell nanoparticles by pulsed plasma in liquid.</a> R. Soc. Chem. Adv. 3, 513 (2013).</li><li>Vallance, S. 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=Probing+the+microwave+interaction+mechanisms+and+reaction+pathways+in+the+energy-efficient,+ultra-rapid+synthesis+of+tungsten+carbide.">Probing the microwave interaction mechanisms and reaction pathways in the energy-efficient, ultra-rapid synthesis of tungsten carbide.</a> Green Chem. 14, 2184 (2012).</li><li>Shen, P. K., Yin, S., Li, Z., Chen, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+performance+of+nanosized+tungsten+carbides+for+electrocatalysis.">Preparation and performance of nanosized tungsten carbides for electrocatalysis.</a> Electrochim. Acta. 55, 7969-7974 (2010).</li><li>Nikiforov, A. V., 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=WC+as+a+non-platinum+hydrogen+evolution+electrocatalyst+for+high+temperature+PEM+water+electrolysers.">WC as a non-platinum hydrogen evolution electrocatalyst for high temperature PEM water electrolysers.</a> Int. J. Hydrogen Energy. 37, 18591-18597 (2012).</li><li>Fang, Z. Z., Wang, X., Ryu, T., Hwang, K. S., Sohn, H. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis,+sintering,+and+mechanical+properties+of+nanocrystalline+cemented+tungsten+carbide+&#8211;+A+review.">Synthesis, sintering, and mechanical properties of nanocrystalline cemented tungsten carbide &#8211; A review.</a> Int. J. Refract. Met. Hard Mater. 27, 288-299 (2009).</li><li>Liu, Y., Kelly, T. G., Chen, J. G., Mustain, W. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal+Carbides+as+Alternative+Electrocatalyst+Supports.">Metal Carbides as Alternative Electrocatalyst Supports.</a> ACS Catal. 3, 1184-1194 (2013).</li><li>Nie, M., Shen, P. K., Wei, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanocrystaline+tungsten+carbide+supported+Au&#8211;Pd+electrocatalyst+for+oxygen+reduction.">Nanocrystaline tungsten carbide supported Au&#8211;Pd electrocatalyst for oxygen reduction.</a> J. Power Sources. 167 (1), 69-73 (2007).</li><li>Ham, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palladium-nickel+alloys+loaded+on+tungsten+carbide+as+platinum-free+anode+electrocatalysts+for+polymer+electrolyte+membrane+fuel+cells.">Palladium-nickel alloys loaded on tungsten carbide as platinum-free anode electrocatalysts for polymer electrolyte membrane fuel cells.</a> Chem Commun (Camb). 47 (20), 5792-5794 (2011).</li><li>Yan, Y., 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=Template-free+pseudomorphic+synthesis+of+tungsten+carbide+nanorods.">Template-free pseudomorphic synthesis of tungsten carbide nanorods.</a> Small. 8, 3350-3356 (2012).</li><li>Esposito, D. V., 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=Low-cost+hydrogen-evolution+catalysts+based+on+monolayer+platinum+on+tungsten+monocarbide+substrates.">Low-cost hydrogen-evolution catalysts based on monolayer platinum on tungsten monocarbide substrates.</a> Angew. Chem. Int. Ed. 49, 9859-9862 (2010).</li><li>Esposito, D. V., Hunt, S. T., Kimmel, Y. C., Chen, J. G. <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+class+of+electrocatalysts+for+hydrogen+production+from+water+electrolysis:+metal+monolayers+supported+on+low-cost+transition+metal+carbides.">A new class of electrocatalysts for hydrogen production from water electrolysis: metal monolayers supported on low-cost transition metal carbides.</a> J. Am. Chem. Soc. 134, 3025-3033 (2012).</li><li>Kelly, T. G., Hunt, S. T., Esposito, D. V., Chen, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monolayer+palladium+supported+on+molybdenum+and+tungsten+carbide+substrates+as+low-cost+hydrogen+evolution+reaction+(HER)+electrocatalysts.">Monolayer palladium supported on molybdenum and tungsten carbide substrates as low-cost hydrogen evolution reaction (HER) electrocatalysts.</a> Int. J. Hydrogen Energy. 38, 5638-5644 (2013).</li><li>Hunt, S. T., Nimmanwudipong, T., Roman-Leshkov, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+non-sintered,+metal-terminated+tungsten+carbide+nanoparticles+for+catalysis.">Engineering non-sintered, metal-terminated tungsten carbide nanoparticles for catalysis.</a> Angew. Chem. Int. Ed. Engl. 53 (20), 5131-5136 (2014).</li><li>Mehrota, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alkoxides+and+Alkylalkoxides+of+Metals+and+Metalloids.">Alkoxides and Alkylalkoxides of Metals and Metalloids.</a> Inorg. Chim. Acta. 1, 99-112 (1967).</li><li>Munoz-Aguado, M., Gregorkiewitz, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sol-Gel+Synthesis+of+Microporous+Amorphous+Silica+from+Purely+Inorganic+Precursors.">Sol-Gel Synthesis of Microporous Amorphous Silica from Purely Inorganic Precursors.</a> J. Colloid Interface Sci. 185, 459-465 (1997).</li></ol>

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 ...

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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.
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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 ...