Name: A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction (Video) | JoVE Journal
Uploaded: 2018-06-18T15:00:00.000+00:00
Duration: 10 min 37 s
Description: Learn a rapid solution-based reduction method to synthesize Au, Pd, and Pt aerogels directly from aqueous solutions. This technique reduces synthesis time and enables applications in catalysis and sensing.

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5 minutes

The authors are grateful to Stephen Steiner at Aerogel Technologies for his inspiration and technical insights, and to Dr. Deryn Chu at the Army Research Laboratory-Sensors and Electron Devices Directorate, Dr. Christopher Haines at the Armament Research, Development and Engineering Center, U.S. Army RDECOM-ARDEC, and Dr. Stephen Bartolucci at the U.S. Army Benet Laboratories for their assistance. This work was supported by a Faculty Development Research Fund grant from the United States Military Academy, West Point.

CAUTION: Consult all relevant safety data sheets (SDS) before use. Use appropriate safety practices when performing chemical reactions, to include the use of a fume hood and personal protective equipment. Rapid hydrogen gas evolution can cause high pressure in reaction tubes causing caps to pop and solutions to spray out. Ensure that reaction tube caps remain open as specified in the protocol.
1. Metal Gel Preparation
<ol>
	<li>Preparation of metal ion solutions. 
	<ol>
		<li>Prepare 2 mL of 0.1 M solutions of the following salts: HAuCl4&#8226;3H2O and Na2PdCl4 in deionized water. Prepare 2 mL of 0.1 M K2PtCl6 in a 1:1 (v/v) water and ethanol solvent. Vigorously shake and vortex solutions to aid in the dissolution of the salts.</li>
	</ol>
	</li>
	<li>Preparation of reducing agent solutions. 
	<ol>
		<li>Prepare 10 mL of 0.1 M solutions of the following reducing agents: dimethylamine borane (DMAB) and NaBH4 (sodium borohydride).</li>
	</ol>
	</li>
	<li>Preparation of Au gels. 
	<ol>
		<li>Pipette 0.5 mL of 0.1 M HAuCl4&#8226;3H2O solution into a 1.7 mL or 2.0 mL microcentrifuge tube. Forcefully pipette 0.5 mL of DMAB into the microcentrifuge tube with gold solution to ensure a rapid mix of salt and reducing agent solutions. Once the solutions are mixed, place the microcentrifuge tube vertically in a tube rack with the tube cap open. 
		Note: If the tube cap is left closed, hydrogen gas evolution will cause the pressure inside to force the cap to pop open and potentially spray the reduction mixture.</li>
	</ol>
	</li>
	<li>Preparation of Pd gels. 
	<ol>
		<li>Pipette 0.5 mL of 0.1 M Na2PdCl4 solution into a 1.7 mL or 2.0 mL microcentrifuge tube. Forcefully pipette 0.5 mL of NaBH4 into the microcentrifuge tube with palladium solution. Place the microcentrifuge tube vertically in a tube rack with the tube cap open.</li>
	</ol>
	</li>
	<li>Preparation of Pt gels. 
	<ol>
		<li>Pipette 0.5 mL of 0.1 M K2PtCl6 solution into a 1.7 mL or 2.0 mL microcentrifuge tube. Forcefully pipette 0.5 mL of DMAB into the microcentrifuge tube with platinum solution. Place the microcentrifuge tube vertically in a tube rack with the tube cap open.</li>
	</ol>
	</li>
	<li>Tube inversion. 
	<ol>
		<li>At approximately 5 min, cap the microcentrifuge tubes and gently invert 3-5 times to aid in the coalescence of metal particles not part of the metal gel. Ensure that the tube caps are immediately uncapped after inverting tubes, and replace tubes in a rack to maintain the vertical orientation of the tube.</li>
	</ol>
	</li>
	<li>Equilibration.
	<ol>
		<li>While Au, Pd, and Pt gels initially form within minutes, leave nascent gels in reducing agent solution for 3 &#8211; 6 h to allow for complete reduction of metal ions and for surface free energy minimization to occur. 
		Note: Metal gels occupy a smaller volume than the initial volume of mixed metal ion and reducing agent solution. Some additional slight volume contraction may be observed during equilibration time, and is more pronounced for gold gels and believed to be due to Ostwald ripening25.</li>
	</ol>
	</li>
	<li>Gel rinsing.
	<ol>
		<li>For Au, Pd, and Pt gels after the equilibration period, remove excess reducing agent solution, but leave enough solution volume so that the metal gel remains submerged. Ensure that the solution meniscus does not come in contact with the metal gel. 
		Note: Although the metal gels are stable enough to transfer between solutions with a spatula, capillary forces due to contact with the solution meniscus will deform and compress the gels resulting in an increase in the final aerogel density. This requires that some reducing agent solution remains in the tube with the gel submerged when transferring to deionized water.</li>
		<li>Slowly pipette deionized water to the top of the reaction microcentrifuge tubes. Submerge the microcentrifuge tube in a 50 mL conical tube full of deionized water and allow the gel to slide out of the microcentrifuge tube.</li>
		<li>Leave the gel in the deionized water for 24 h, and replace the water at 12 h. Do not to allow a liquid meniscus to come in contact with the gel.</li>
	</ol>
	</li>
</ol>
2. Electrochemical Surface Area (ECSA) Characterization of Wet Metal Gels
Note: Electrochemical characterization is performed on wet metal gels prior to conducting freeze drying. The resulting ECSA is then an estimate of the surface of the final aerogel structure. Nitrogen adsorption measurements are used to estimate the surface area of the dried aerogels.
<ol>
	<li>Solvent exchange.
	<ol>
		<li>Remove as much of the deionized water from the Au, Pd, and Pt rinse solutions as possible and ensure that the liquid meniscus does not come in contact with the gel.</li>
		<li>Add 50 mL, 0.5 M KCl to the conical tubes in order to exchange the deionized water with supporting electrolyte within the gel pores. Leave the gels in KCl solution for 24 h.</li>
	</ol>
	</li>
	<li>Working electrode preparation.
	<ol>
		<li>Coat a 1 mm platinum wire electrode with non-reactive lacquer using a fine bristle brush or other application device leaving a 4-5 mm length of the wire tip exposed.</li>
		<li>Allow 20 minutes for the lacquer to dry.</li>
		<li>Apply at least two coats of lacquer.</li>
	</ol>
	</li>
	<li>3-electrode cell set-up.
	<ol>
		<li>Use a 3-electrode cell set-up with an Ag/AgCl (3 M saturated) reference electrode, a 0.5 mm diameter Pt wire auxiliary/counter electrode, and the lacquer coated working electrode.</li>
		<li>Cut a plastic 50 mL conical tube in half and use as an electrochemical vial.</li>
		<li>Contact the gel with the working electrode with one of two methods: 1) impaled gel, or 2) contact mode.
		<ol>
			<li>Working electrode - impaled gel.
			<ol>
				<li>With the gel at the bottom of the modified 50 mL conical tube, gently insert the lacquer coated electrode into the gel. 
				Note: The impaled gel method proves more effective with Au gels, whereas Pd and Pt gels fracture more frequently upon electrode insertion.</li>
			</ol>
			</li>
			<li>Working electrode - contact mode.
			<ol>
				<li>Insert the lacquer coated working electrode into the conical tube along the inner surface and rest the metal gel on the top of the exposed Pt wire of the working electrode.</li>
			</ol>
			</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Electrochemical impedance spectroscopy (EIS).
	<ol>
		<li>Perform potentiostatic EIS scans with frequencies between 100 MHz and 1 mHz using a 10 mV amplitude sine wave. In the event of current overflows, use galvanostatic EIS with the same frequency range and a 100 &#8211; 200 mA amplitude sine wave.</li>
	</ol>
	</li>
	<li>Determination of electrochemical surface area (ECSA) from EIS data.
	<ol>
		<li>For Z&#34;, the imaginary component of impedance, at the lowest EIS frequency f of 1 mHz, and dividing by the sample mass, m, use the following equation to determine specific capacitance, Csp: 
		Csp = 1/(2&#960;fZ&#34;m)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(1) 
		Note: Given that the ECSA is determined from a wet gel prior to freeze drying in Step 3 below, determine mass by assuming all of the metal ions in solution are reduced to form the gel. Based on this assumption, any actual yield less than 100% will result in underestimating Csp.</li>
	</ol>
	</li>
	<li>Cyclic voltammetry (CV).
	<ol>
		<li>Use scan rates of 100, 75, 50, 25, 10, 5, and 1 mV/s for CV measurements. Use voltage ranges of -0.2 to 0.2 V (vs Ag/AgCl) for Au gels, and select 0.1 to 0.4 V for Pd and Pt gels to avoid hydrogen adsorption and desorption, and oxidation-reduction of the metals.</li>
	</ol>
	</li>
	<li>Determination of electrochemical surface area (ECSA) from CV data.
	<ol>
		<li>Use the slowest CV scan rate of 1 mV/s, and calculate specific capacitance with the equation: 
		Csp = (&#8747;ivdv) / (2&#956;m&#916;V)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(2) 
		Note: Here i and v are the current and potential in the CV scan (A and V), scan rate is &#956; (V/s), mass of the gel is m (g), and &#916;V is the potential window of discharge (vs Ag/AgCl).</li>
	</ol>
	</li>
</ol>
3. Aerogel Preparation and Characterization.
<ol>
	<li>Remove the deionized rinse water for Au, Pd, and Pt gels in Step 1.8 and ensure that the water meniscus does not come in contact with the metal gels.</li>
	<li>Place the gels in a -80 &#176;C freezer for no less than 30 min. Transfer the frozen metal gels to a freeze dryer with a set point pressure of 4 Pa or lower.</li>
</ol>

<ol><li>Rolison, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Catalytic+Nanoarchitectures-the+Importance+of+Nothing+and+the+Unimportance+of+Periodicity%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">Catalytic Nanoarchitectures-the Importance of Nothing and the Unimportance of Periodicity.</a> Science. 299, 1698-1701 (2003).</li>
<li>Wei, T., Chen, C., Chang, K., Lu, S., Hu, C. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/cm9007365">Cobalt Oxide Aerogels of Ideal Supercapacitive Properties Prepared with an Epoxide Synthetic Route.</a> Chemistry of Materials. 21, 3228-3233 (2009).</li>
<li>Anderson, M., Morris, C., Stroud, R., Merzbacher, C., Rolison, D. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/la980784i">Colloidal Gold Aerogels: Preparation, Properties, and Characterization.</a> Langmuir. 15, 674-681 (1999).</li>
<li>Gaponik, N., Herrmann, A., Eychmuller, A. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/jz201357r">Colloidal Nanocrystal-Based Gels and Aerogels: Material Aspects and Application Perspectives.</a> Journal of Physical Chemistry Letters. 3, 8-17 (2012).</li>
<li>Olsson, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Making+flexible+magnetic+aerogels+and+stiff+magnetic+nanopaper+using+cellulose+nanofibrils+as+templates%5BTitle%5D)+AND+%22Nature+Nanotechnology%22%5BJournal%5D)">Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates.</a> Nature Nanotechnology. 5, 584-588 (2010).</li>
<li>Anderson, M., Morris, C., Stroud, R., Merzbacher, C., Rolison, D. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/la980784i">Colloidal Gold Aerogels: Preparation, Properties, and Characterization.</a> Langmuir. 15, 674-681 (1999).</li>
<li>Gaponik, N., Herrmann, A., Eychmuller, A. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/jz201357r">Colloidal Nanocrystal-Based Gels and Aerogels: Material Aspects and Application Perspectives.</a> Journal of Physical Chemistry Letters. 3, 8-17 (2012).</li>
<li>Hodge, A., Hayes, J., Cao, J., Biener, J., Hamza, A. <a target="_blank" href="https://onlinelibrary.wiley.com/doi/abs/10.1002/adem.200600079">Characterization and Mechanical Behavior of Nanoporous Gold.</a> Advanced Engineering Materials. 8, 853-857 (2006).</li>
<li>Hodge, A., et al. <a target="_blank" href="https://www.sciencedirect.com/science/article/pii/S1359645406007221">Scaling equation for yield strength of nanoporous open-cell foams.</a> Acta Materialia. 55, 1343-1349 (2007).</li>
<li>Ambrosi, A., Chua, C., Bonanni, A., Pumera, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Electrochemistry+of+Graphene+and+Related+Materials%5BTitle%5D)+AND+%22Chemical+Reviews%22%5BJournal%5D)">Electrochemistry of Graphene and Related Materials.</a> Chemical Reviews. 114, 7150-7188 (2014).</li>
<li>Maillard, F., et al. <a target="_blank" href="http://pubs.rsc.org/is/content/articlelanding/2005/cp/b411377b">Influence of particle agglomeration on the catalytic activity of carbon-supported Pt nanoparticles in CO monolayer oxidation.</a> Physical Chemistry Chemical Physics. 7, 385-393 (2005).</li>
<li>Zhao, P., Li, N., Astruc, D. <a target="_blank" href="https://www.sciencedirect.com/science/article/pii/S0010854512002305">State of the art in gold nanoparticle synthesis.</a> Coordination Chemistry Reviews. 257, 638-665 (2013).</li>
<li>Wen, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Controlling+the+Growth+of+Palladium+Aerogels+with+High-Performance+toward+Bioelectrocatalytic+Oxidation+of+Glucose%5BTitle%5D)+AND+%22Journal+of+American+Chemical+Society%22%5BJournal%5D)">Controlling the Growth of Palladium Aerogels with High-Performance toward Bioelectrocatalytic Oxidation of Glucose.</a> Journal of American Chemical Society. 136, 2727-2730 (2014).</li>
<li>Jana, N., Gearheart, L., Murphy, C. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/1521-4095%28200109%2913:18%3C1389::AID-ADMA1389%3E3.0.CO;2-F/abstract">Seed-Mediated Growth Approach for Shape-Controlled Synthesis of Spheroidal and Rod-like Gold Nanoparticles Using a Surfactant Template.</a> Advanced Materials. 13, 1389-1392 (2001).</li>
<li>Ding, Y., Chen, M., Erlebacher, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metallic+Mesoporous+Nanocomposites+for+Electrocatalysis%5BTitle%5D)+AND+%22Journal+of+American+Chemical+Society%22%5BJournal%5D)">Metallic Mesoporous Nanocomposites for Electrocatalysis.</a> Journal of American Chemical Society. 126, 6876-6877 (2004).</li>
<li>Liu, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High-Performance+Electrocatalysis+on+Palladium+Aerogels%5BTitle%5D)+AND+%22Angewandte+Chemie.+International+Edition%22%5BJournal%5D)">High-Performance Electrocatalysis on Palladium Aerogels.</a> Angewandte Chemie. International Edition. 51, 5743-5747 (2012).</li>
<li>Herrmann, A., et al. <a target="_blank" href="https://pubs.acs.org/doi/abs/10.1021/cm4033258">Multimetallic Aerogels by Template-Free Self-Assembly of Au, Ag, Pt, and Pd Nanoparticles.</a> Chemistry of Materials. 26, 1074-1083 (2014).</li>
<li>Ameen, K., Rajasekharan, T., Rajasekharan, M. <a target="_blank" href="https://www.sciencedirect.com/science/article/pii/S0022309306001852">Grain size dependence of physico-optical properties of nanometallic silver in silica aerogel matrix.</a> Journal of Non-Crystalline Solids. 352, 737-746 (2006).</li>
<li>Qin, G., et al. <a target="_blank" href="https://pubs.acs.org/doi/abs/10.1021/jp800923h">A Facile and Template-Free Method to Prepare Mesoporous Gold Sponge and Its Pore Size Control.</a> Journal of Physical Chemistry C. 112, 10352-10358 (2008).</li>
<li>Krishna, K., Sandeep, C., Philip, R., Eswaramoorthy, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mixing+Does+the+Magic%3A+A+Rapid+Synthesis+of+High+Surface+Area+Noble+Metal+Nanosponges+Showing+Broadband+Nonlinear+Optical+Response%5BTitle%5D)+AND+%22ACS+Nanotechnology%22%5BJournal%5D)">Mixing Does the Magic: A Rapid Synthesis of High Surface Area Noble Metal Nanosponges Showing Broadband Nonlinear Optical Response.</a> ACS Nanotechnology. 5, 2681-2688 (2010).</li>
<li>Kistler, S. <a target="_blank" href="https://www.nature.com/articles/127741a0">Coherent Expanded Aerogels and Jellies.</a> Nature. 127, 741-741 (1931).</li>
<li>Du, A., Zhou, B., Zhang, Z., Shen, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Special+Material+or+a+New+State+of+Matter%3A+A+Review+and+Reconsideration+of+the+Aerogel%5BTitle%5D)+AND+%22Materials%22%5BJournal%5D)">A Special Material or a New State of Matter: A Review and Reconsideration of the Aerogel.</a> Materials. 6, 941-968 (2013).</li>
<li>Tappan, B., Steiner, S., Luther, E. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/anie.200902994/pdf">Nanoporous Metal Foams.</a> Angewandte Chemie. International Edition. 49, 4544-4565 (2010).</li>
<li>Burpo, F., et al. <a target="_blank" href="https://www.cambridge.org/core/journals/journal-of-materials-research/article/direct-solutionbased-reduction-synthesis-of-au-pd-and-pt-aerogels/F91C878FD9BDC2523DA004ED342FBB39">Direct solution-based reduction synthesis of Au, Pd, and Pt aerogels.</a> Journal of Materials Research. 32, 4153-4165 (2017).</li>
<li>Ostwald, W. Blocking of Ostwald ripening allowing long-term stabilization. PhysicalChemistry. 37, 385(1901).</li>
<li>Wang, S., Tseng, W. <a target="_blank" href="https://link.springer.com/article/10.1007/s11051-008-9482-0">Aggregate structure and crystallite size of platinum nanoparticles synthesized by ethanol reduction.</a> Journal of Nanoparticle Research. 11, 947-953 (2009).</li>
<li>Schneider, C., Rasband, W., Eliceiri, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((NIH+Image+to+ImageJ%3A+25+years+of+image+analysis%5BTitle%5D)+AND+%22Nature+Methods%22%5BJournal%5D)">NIH Image to ImageJ: 25 years of image analysis.</a> Nature Methods. 9, 671-675 (2012).</li>
<li>Thommes, M., et al. <a target="_blank" href="https://www.degruyter.com/view/j/pac.2015.87.issue-9-10/pac-2014-1117/pac-2014-1117.xml?format=INT&intcmp=trendmd">Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report).</a> Pure and Applied Chemistry. 87, 1051-1069 (2015).</li>
<li>Barrett, E., Joyner, L., Halenda, P. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/ja01145a126">The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms.</a> Journal of the American Chemical Society. 73, 373-380 (1951).</li>
<li>Brunauer, B., Emmett, P., Teller, P. <a target="_blank" href="https://pubs.acs.org/doi/abs/10.1021/ja01269a023">Adsorption of Gases in Multimolecular Layers.</a> Journal of the American Chemical Society. 60, 309-319 (1938).</li>
<li>Herrmann, A., et al. <a target="_blank" href="https://pubs.acs.org/doi/abs/10.1021/cm4033258">Multimetallic Aerogels by Template-Free Self-Assembly of Au, Ag, Pt, and Pd Nanoparticles.</a> Chemistry of Materials. 26, 1074-1083 (2014).</li>
<li>Kornyshev, A., Irbakh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Double-layer+capacitance+on+a+rough+metal+surface%5BTitle%5D)+AND+%22Physical+Review+E%22%5BJournal%5D)">Double-layer capacitance on a rough metal surface.</a> Physical Review E. 53, 6192-6199 (1996).</li>
<li>Bisquert, J. <a target="_blank" href="http://pubs.rsc.org/en/content/articlelanding/2000/cp/b001708f">Influence of the boundaries in the impedance of porous film electrodes.</a> Physical Chemistry Chemical Physics. 2, 4185-4192 (2000).</li>
<li>Bisquert, J. <a target="_blank" href="https://pubs.acs.org/doi/abs/10.1021/jp011941g">Theory of the Impedance of Electron Diffusion and Recombination in a Thin Layer.</a> Journal of Physical Chemistry B. 106, 325-333 (2002).</li>
<li>Lu, K., Yuan, L., Xin, X., Xu, Y. <a target="_blank" href="https://www.sciencedirect.com/science/article/pii/S0926337317311815">Hybridization of graphene oxide with commercial graphene for constructing 3D metal-free aerogel with enhanced photocatalysis.</a> Applied Catalysis B. 226, 16-22 (2018).</li>
<li>Nystron, G., Roder, L., Fernandez-Ronco, M., Mezzenga, R. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/adfm.201703609/full">Amyloid Templated Organic Inorganic Hybrid Aerogels.</a> Advanced Functional Materials. , 1703609-1703620 (2017).</li>
</ol>

The authors have nothing to disclose.

The noble metal aerogel synthesis method presented here results in the rapid formation of porous, high surface area monoliths that are comparable to slower synthesis techniques. The 1:1 (v/v) metal ion solution to reducing agent solution ratio is critical in facilitating the proposed gel formation model. The rapid hydrogen gas evolution as a by-product of the electrochemical reduction of metal ions serves as a secondary reducing agent and facilitates the densification, and fusion of growing nanoparticles during gel forma...

A wide range of energy storage and conversion, catalysis, and sensor applications benefit from three-dimensional metallic nanostructures which provide control over chemical reactivity, and mass transport properties1,2,3,4,5. Such 3-dimensional metallic nanostructures further enhance conductivity, ductility, malleability, and strength8,9. Integration into devices necessitates that materials be free-standing or combined with support materials. Incorporation of nanomaterials onto support structures provides a means of minimizing active material, but may suffer from weak adsorption and eventual agglomeration during device operation10,11.
While there are a variety of synthesis methods to control individual nanoparticle size and shape, few approaches enable control over contiguous 3-dimensional nanomaterials12,13,14. Noble metal 3-dimensional nanostructures have been formed through dithiol linkage of monodisperse nanoparticles, sol-gel formation, nanoparticle coalescence, composite materials, nanosphere chains, and biotemplating15,16,17,18. Many of these approaches require synthesis times on the order of days to weeks to yield desired materials. Noble metal nanofoams synthesized from the direct reduction of precursor salt solutions have been prepared with a faster synthesis timescale and with short-range order of hundreds of micrometers in length, but require mechanical pressing for device integration19,20.
First reported by Kistler, aerogels provide a synthesis route to achieve porous structures with high specific surface areas that are orders of magnitude less dense than their bulk material counterparts21,22,23. Extending 3-dimensional structures to the macroscopic length scale of bulk materials offers an advantage over nanoparticle aggregates or nanofoams that require support materials or mechanical processing. While aerogels provide a synthesis route to control porosity and particle feature size, however, extended synthesis times, and in some cases the use of capping agents or linker molecules, increases overall processing steps and time.
Here a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented24. Combining various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. The use of a microcentrifuge tube or small volume conical tube takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step facilitating a proposed nucleation, growth, densification, fusion, equilibration model for gel formation. A close correlation in aerogel nanostructure feature sizes is determined with scanning electron microscopy image analysis, X-ray diffractometry, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

<table><tbody><tr><td>HAuCl&lt;sub&gt;4&lt;/sub&gt;&amp;Yuml;&amp;bull;3H&lt;sub&gt;2&lt;/sub&gt;O&amp;nbsp;</td><td>Sigma-Aldrich</td><td>16961-25-4</td><td></td></tr><tr><td>Na&lt;sub&gt;2&lt;/sub&gt;PdCl&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>13820-40-1</td><td></td></tr><tr><td>K&lt;sub&gt;2&lt;/sub&gt;PtCl&lt;sub&gt;6&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>16921-30-5</td><td></td></tr><tr><td>Pd(NH&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>13933-31-8</td><td></td></tr><tr><td>K&lt;sub&gt;2&lt;/sub&gt;PtCl&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>10025-99-7</td><td></td></tr><tr><td>Pt(NH&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt;&amp;Yuml;&amp;bull;H&lt;sub&gt;2&lt;/sub&gt;O</td><td>Sigma-Aldrich</td><td>13933-31-8</td><td></td></tr><tr><td>dimethylamine borane (DMAB)</td><td>Sigma-Aldrich</td><td>74-94-2</td><td></td></tr><tr><td>NaBH&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>16940-66-2</td><td></td></tr><tr><td>NaH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;2&lt;/sub&gt;&amp;Yuml;&amp;bull;H&lt;sub&gt;2&lt;/sub&gt;O</td><td>Sigma-Aldrich</td><td>10039-56-2</td><td></td></tr><tr><td>Ethanol</td><td>Sigma-Aldrich</td><td>792780</td><td></td></tr><tr><td>Snap Cap Microcentrifuge Tubes, 2.0 mL</td><td>Cole Parmer</td><td>UX-06333-70</td><td></td></tr><tr><td>Snap Cap Microcentrifuge Tubes, 1.7 mL</td><td>Cole Parmer</td><td>UX-06333-60</td><td></td></tr><tr><td>Conical Centrifuge Tubes 15mL</td><td>Stellar Scientific</td><td>T15-101&amp;nbsp;</td><td></td></tr><tr><td>Ag/AgCl Reference Electrode</td><td>BASi</td><td>MF-2052</td><td></td></tr><tr><td>Pt wire electrode</td><td>BASi</td><td>MF-4130</td><td></td></tr><tr><td>Miccrostop Lacquer</td><td>Tober Chemical Division</td><td>NA</td><td></td></tr><tr><td>Potentiostat</td><td>Biologic-USA</td><td>VMP-3</td><td>Electrochemical analysis-EIS, CV</td></tr><tr><td>Freeze Dryer</td><td>Labconco</td><td>Freezone 2.5 Liter</td><td>Aerogel freeze drying</td></tr><tr><td>XRD</td><td>PanAlytical</td><td>Empyrean</td><td>X-ray diffractometry</td></tr><tr><td>Surface and Pore Analyzer</td><td>Quantachrome</td><td>NOVA 4000e</td><td>Nitrogen gas adsorption</td></tr><tr><td>ImageJ, Image analysis software</td><td>National Institute of Health</td><td>NA</td><td>SEM image analysis</td></tr></tbody></table>

a rapid synthesis method for au, pd, and pt aerogels via direct solution-based reduction

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

The addition of metal ion and reducing agent solutions together results in solutions immediately turning a dark black color with vigorous gas evolution. Observation of the reaction progress suggests the proposed gel formation mechanism shown in Figure 1. Gel formation proceeds through five steps of 1) nanoparticle nucleation, 2) growth, 3) densification, 4) fusion, and 5) equilibration. The first four steps are observed to occur during the first few minutes o...

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

a-rapid-synthesis-method-for-au-pd-pt-aerogels-via-direct-solution

Research

JoVE Journal

Chemistry

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Learn a rapid solution-based reduction method to synthesize Au, Pd, and Pt aerogels directly from aqueous solutions. This technique reduces synthesis time and enables applications in catalysis and sensing.

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

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