Los autores agradecemos a Stephen Steiner en tecnologías Aerogel para su inspiración y conocimientos técnicos y a Dr. Deryn Chu en el ejército laboratorio de investigación-sensores y electrónica dispositivos de dirección, el Dr. Christopher Haines en la investigación de armamento, Desarrollo y centro de ingeniería, los E.E.U.U. ejército RDECOM-ARDEC y Dr. Stephen Bartolucci en los laboratorios de Benet de ejército de Estados Unidos para su asistencia. Este trabajo fue financiado por una subvención del fondo de investigación de desarrollo de Facultad de la Academia de militar de Estados Unidos, West Point.

PRECAUCIÓN: Consulte todas hojas de datos de seguridad (SDS) antes de su uso. Utiliza prácticas de seguridad apropiadas cuando se realizan las reacciones químicas, para incluir el uso de una campana y equipo de protección personal. Evolución de gas hidrógeno rápida puede causar alta presión en tubos de reacción causando tapones pop y soluciones para rociar hacia fuera. Asegurar que tapas del tubo de reacción abiertos tal como se especifica en el protocolo.
1. preparación del Gel metal
<ol><li>
Preparación de soluciones de iones metálicos.
	<ol>
<li>Preparar 2 mL de soluciones de 0,1 M de las siguientes sales: HAuCl4•3H2O y Na2PdCl4 en agua desionizada. Preparar 2 mL de 0.1 M K2PtCl6 en un 1:1 (v/v) agua y solvente de etanol. Vigorosamente agitar y agitar soluciones para ayudar en la disolución de las sales.</li>
	</ol>
</li>
	<li>
Preparación de soluciones de agente reductor.
	<ol>
<li>Preparar 10 mL de soluciones de 0,1 M de los siguientes agentes reductores: dimetilamina borano (DMAB) y NaBH4 (borohidruro de sodio).</li>
	</ol>
</li>
	<li>
Preparación de Au geles.
	<ol>
<li>Pipetear 0.5 mL de solución de2O de4•3H de HAuCl de 0.1 M en un tubo de microcentrífuga de 1,7 mL o 2,0 mL. Fuerza pipetear 0.5 mL de DMAB en el tubo de microcentrífuga con solución de oro para asegurar una mezcla rápida de soluciones de sal y agente reductor. Una vez que las soluciones se mezclan, coloque el tubo de microcentrífuga verticalmente en un bastidor de tubo con la tapa del tubo abierto. Nota: Si se deja la tapa del tubo cerrado, hidrógeno evolución de gas hará que la presión interior para forzar la tapa para abrir pop y potencialmente rociar la mezcla de reducción.</li>
	</ol>
</li>
	<li>
Geles de preparación de la EP.
	<ol>
<li>Pipetear 0.5 mL de solución de 0.1 M Na2PdCl4 en un tubo de microcentrífuga de 1,7 mL o 2,0 mL. Con fuerza pipetear 0.5 mL de NaBH4 en el tubo de microcentrífuga con solución de paladio. Lugar el tubo de microcentrífuga verticalmente en un bastidor de tubo con la tapa del tubo abierto.</li>
	</ol>
</li>
	<li>
Geles de preparación del Pt.
	<ol>
<li>Pipetear 0.5 mL de 0.1 M K2PtCl6 solución en un tubo de microcentrífuga de 1,7 mL o 2,0 mL. Fuerza pipetear 0.5 mL de DMAB en el tubo de microcentrífuga con solución de platino. Lugar el tubo de microcentrífuga verticalmente en un bastidor de tubo con la tapa del tubo abierto.</li>
	</ol>
</li>
	<li>
Inversión del tubo.
	<ol>
<li>En aproximadamente 5 minutos, tapa los tubos de microcentrífuga e invierta suavemente 3 - 5 veces a ayudar en la coalescencia de las partículas del metal no forma parte del gel del metal. Asegurar que los tapones de tubo son inmediatamente destapado después de invertir los tubos, y reemplazar los tubos en un bastidor para mantener la orientación vertical del tubo.</li>
	</ol>
</li>
	<li>
Conseguir el equilibrio.<ol>
<li>Mientras que los geles de Au, Pd y Pt inicialmente forman dentro de minutos, dejan geles nacientes en la solución de agente reductor para 3 – 6 h permitir la reducción completa de los iones del metal y de minimización de energía libre superficial ocurrir. Nota: Geles Metal ocupan un volumen menor que el volumen inicial de solución mixta de metal ion y agente reductor. Algunos contracción de volumen adicional leve puede observarse durante el tiempo de equilibrado, es más pronunciada para geles de oro y cree que es debido a la maduración25de Ostwald.</li>
	</ol>
</li>
	<li>
Gel de lavado.<ol>
<li>Para geles de Au, Pd y Pt después del periodo de equilibrio, eliminar exceso de agente reductor de la solución, pero deje suficiente volumen de solución para que el gel metal permanece sumergido. Asegúrese de que el menisco de la solución no entre en contacto con el gel de metal. Nota: Aunque el metal geles son lo suficientemente estables como para transferir entre las soluciones con una espátula, capilar las fuerzas debido al contacto con el menisco de la solución deformará y comprimir los geles resultando en un incremento en la densidad final de aerogel. Esto requiere que una solución de agente reductor permanece en el tubo con el gel sumergido cuando transfieren a agua desionizada.</li>
		<li>Lentamente pipeta agua desionizada para la parte superior de los tubos de microcentrífuga de reacción. Sumerja el tubo de microcentrífuga en un tubo cónico de 50 mL de agua desionizada y permita que el gel se deslice fuera del tubo de microcentrífuga.</li>
		<li>Dejar el gel en agua desionizada durante 24 h y cambiar el agua a las 12 h. No permita que un menisco de líquido entren en contacto con el gel.</li>
	</ol>
</li>
</ol>2. superficie electroquímica (ECSA) caracterización de geles de Metal mojados
Nota: Caracterización electroquímica se realiza en geles de metal mojados antes de realizar la liofilización. La ECSA resultante es entonces una estimación de la superficie de la estructura final del aerogel. Las medidas de adsorción de nitrógeno se utilizan para estimar la superficie de los aerogels secos.
<ol><li>
Cambio de solvente.<ol>
<li>Eliminar tanto el agua desionizado de la Au, Pd y Pt enjuague soluciones como sea posible y aseguran de que el menisco de líquido no entre en contacto con el gel.</li>
		<li>Añadir 50 mL, 0,5 M de KCl a los tubos cónicos para intercambiar el agua desionizado con el apoyo de electrolitos dentro de los poros de gel. Deja los geles en una solución de KCl durante 24 h.</li>
	</ol>
</li>
	<li>
Preparación del electrodo de trabajo.
	<ol>
<li>Capa de un electrodo de alambre de 1 mm de platino con la laca no reactiva utilizando un cepillo de cerdas finas u otro dispositivo de aplicación, dejando una longitud de 4-5 mm de la punta del cable expuesta.</li>
		<li>Espere 20 minutos para la laca se seque.</li>
		<li>Aplicar al menos dos capas de laca.</li>
	</ol>
</li>
	<li>
configuración de 3 electrodos de la célula.
	<ol>
<li>Utilice una configuración de 3 electrodos de la célula con un Ag/AgCl (3 M saturado) de referencia electrodos, un electrodo 0,5 mm diámetro Pt alambre contador/auxiliar y el electrodo de trabajo recubierto de laca.</li>
		<li>Cortar un tubo cónico de plástico de 50 mL a la mitad y utilizar como un frasco electroquímico.</li>
		<li>En contacto con el gel con el electrodo de trabajo con uno de dos métodos: gel 1) empalado o modo 2) contacto.<ol>
<li>
Funcionamiento de electrodo - gel empalado.<ol>
<li>Con el gel en la parte inferior del tubo cónico de 50 mL modificado, inserte suavemente el electrodo revestido de laca en el gel. Nota: El método de gel empalado resulta más eficaz con geles de Au, mientras que Pd y Pt geles de fractura con más frecuencia a la inserción del electrodo.</li>
			</ol>
</li>
			<li>
Electrodo de trabajo - modo de contacto.<ol>
<li>Insertar el electrodo de trabajo recubierto de laca en el tubo cónico a lo largo de la superficie interna y descansar el gel metal en la parte superior el alambre de Pt expuesto del electrodo de trabajo.</li>
			</ol>
</li>
		</ol>
</li>
	</ol>
</li>
	<li>
Espectroscopia de impedancia electroquímica (EIS).<ol>
<li>Realizar potentiostatic que EIS analiza con frecuencias entre 100 MHz y 1 mHz, usando una onda de seno de amplitud mV 10. En caso de desbordamientos actuales, utilice galvanostáticos EIS con el mismo rango de frecuencia y una onda de seno de 100 – 200 mA amplitud.</li>
	</ol>
</li>
	<li>
Determinación del área superficial electroquímico (ECSA) de los datos EIS.<ol>
<li>Para Z «, el componente imaginario de la impedancia en la EIS de más baja frecuencia f de 1 mHz y dividiendo por la masa de la muestra, m, utilizar la siguiente ecuación para determinar la capacitancia específica, Csp: C SP = 1 / (2πfZ "m) (1) Nota: dado que la ECSA se determina de un gel húmedo previo a la liofilización en el paso 3 a continuación, determinar masa asumiendo que todos los iones del metal en solución se reducen para formar el gel. Partiendo de esta premisa, cualquier rendimiento real inferior al 100% dará lugar a subestimar Csp.</li>
	</ol>
</li>
	<li>
Voltametría cíclica (CV).<ol>
<li>Usar tarifas de exploración de 100, 75, 50, 25, 10, 5 y 1 mV/s para la medición de la CV. Utilizar rangos de voltaje de -0.2 a 0,2 V (vs Ag/AgCl) para geles de Au y seleccione 0.1 a 0.4 V para Pd y Pt los geles evitar la adsorción de hidrógeno y la desorción y la óxido-reducción de los metales.</li>
	</ol>
</li>
	<li>
Determinación del área superficial electroquímico (ECSA) de datos de CV.<ol>
<li>Utilice la tasa más lenta de la exploración del CV de 1 mV/s y calcular la capacitancia específica con la ecuación: C SP = (∫ivdv) / (2μmΔV) (2) Nota: Aquí la i y v son la corriente y el potencial en el análisis de CV (A y V), velocidad de lectura es μ (V/s), masa del gel es m (g) y ΔV es la potencial ventana de descarga (vs Ag/AgCl).</li>
	</ol>
</li>
</ol>3. Aerogel preparación y caracterización.
<ol><li>Quitar el agua de aclarado desionizada para geles de Au, Pd y Pt en paso 1.8 y asegúrese de que el menisco del agua no entran en contacto con el metal geles.</li>
	<li>Colocar el gel en un congelador de-80 ° C por no menos de 30 min transferencia el metal congelado geles a una congelación de secador con una presión de punto de ajuste de 4 Pa o inferior.</li>
</ol>

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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="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+of+Gases+in+Multimolecular+Layers.">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="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multimetallic+Aerogels+by+Template-Free+Self-Assembly+of+Au,+Ag,+Pt,+and+Pd+Nanoparticles.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Double-layer+capacitance+on+a+rough+metal+surface.">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://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+the+boundaries+in+the+impedance+of+porous+film+electrodes.">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="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theory+of+the+Impedance+of+Electron+Diffusion+and+Recombination+in+a+Thin+Layer.">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="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hybridization+of+graphene+oxide+with+commercial+graphene+for+constructing+3D+metal-free+aerogel+with+enhanced+photocatalysis.">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://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amyloid+Templated+Organic+Inorganic+Hybrid+Aerogels.">Amyloid Templated Organic Inorganic Hybrid Aerogels.</a> Advanced Functional Materials. , 1703609-1703620 (2017).</li></ol>

Los autores no tienen nada que revelar.

El método de síntesis de aerogel de metal noble presentamos resultados en la formación rápida de monolitos de superficie porosa, de alta que son comparables a las técnicas de síntesis más lentas. La solución de iones metálicos de 1:1 (v/v) a proporción de la solución de agente reductor es fundamental facilitar el modelo de formación propuesto gel. La evolución de gas hidrógeno rápida como un subproducto de la reducción electroquímica de los iones del metal sirve como un agente de reducción secundario y ...

Beneficiarse de una amplia gama de almacenamiento de energía, conversión, catálisis y usos del sensor de nanoestructuras metálicas tridimensionales que proporcionan control sobre reactividad química y transporte masivo propiedades1,2, 3,4,5. Tales nanoestructuras metálicas 3-dimensional más mejoran la conductividad, ductilidad, maleabilidad y resistencia8,9. Integración en dispositivos requiere que los materiales ser libre o combinado con materiales de apoyo. Incorporación de nanomateriales en estructuras de apoyo proporciona un medio de minimizar el material activo, pero puede sufrir de adsorción débil y eventual aglomeración durante la operación de dispositivo10,11.
Si bien hay una variedad de métodos de síntesis para el control de forma y tamaño de nanopartículas individuales, algunos enfoques permiten control sobre nanomateriales 3 dimensiones contiguas12,13,14. Nanoestructuras de 3 dimensiones de metal noble que se han formado a través acoplamiento ciclarla de nanopartículas monodispersa, formación de sol-gel, fusión de nanopartículas, materiales compuestos, nanosphere cadenas y biotemplating15,16 , 17 , 18. muchos de estos enfoques requieren tiempos de síntesis del orden de días a semanas para producir los materiales deseados. Metal noble nanofoams sintetizados a partir de la reducción directa de soluciones de sal del precursor han sido preparados con un calendario de síntesis más rápido y con orden de corto alcance de cientos de micrómetros de longitud, pero requiere mecánicos para la integración del dispositivo 19 , 20.
Primero divulgado por Kistler, aerogeles proporcionan una ruta de síntesis para lograr estructuras porosas con altas superficies específicas que son órdenes de magnitud menos densas que su bulto materiales homólogos21,22,23 . Ampliar las estructuras 3-dimensionales en la escala de longitud macroscópicas de materiales a granel ofrece una ventaja sobre agregados de nanopartículas o nanofoams que requieren materiales de apoyo o tratamiento mecánico. Mientras que los aerogeles proporcionan una ruta de síntesis para controlar la porosidad y tamaño de función partícula, sin embargo, extendido veces de síntesis y en algunos casos el uso de agentes o vinculador moléculas, aumenta total de pasos y tiempo de procesamiento para envases.
Aquí se presenta un método para sintetizar oro, paladio y platino aerogeles mediante una reducción rápida y directa solución24. Combinando diversos iones de metal noble precursor con agentes de reducción en una 1:1 (v/v) relación resultados en la formación de geles de metal dentro de segundos a minutos comparados con mucho tiempo de síntesis para otras técnicas tales como sol-gel. El uso de un tubo cónico de pequeño volumen o tubo de microcentrífuga aprovecha la evolución de gas hidrógeno vigoroso como un subproducto de la etapa de reducción facilitar una propuesta nucleación, crecimiento, densificación, fusión, modelo equilibrado para la formación del gel. Una correlación estrecha en tamaños de característica de nanoestructura de aerogel se determina con el análisis de análisis de imágenes de microscopía electrónica, difractometría de rayos x, adsorción de gas nitrógeno, espectroscopía de impedancia electroquímica y voltametría cíclica. El área superficial específica accesible solvente se determina con la espectroscopía de impedancia electroquímica y voltametría cíclica. Este método de síntesis para aerogeles de metal noble demuestra eso alta superficie específica monolitos pueden lograrse con un enfoque de reducción rápida y directa.

<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

Aquí, se presenta un método para sintetizar oro, paladio y platino aerogeles mediante una reducción basada en la solución rápida y directa. La combinación de varios iones de metal noble precursor con reductores en los resultados de un cociente de 1:1 (v/v) en la formación de geles de metal dentro de segundos a minutos en comparación con mucho tiempo de síntesis para otras técnicas tales como sol-gel. Llevar a cabo el paso de reducción en una microcentrífuga tubo o tubo cónico pequeño volumen facilita una propuesta nucleación, crecimiento, densificación, fusión, modelo equilibrado para la formación del gel, con geometría de gel final menor que el volumen inicial de reacción. Este método aprovecha la evolución de gas hidrógeno vigoroso como un subproducto de la etapa de reducción y como consecuencia de las concentraciones de reactivo. El área superficial específica accesible solvente se determina con la espectroscopía de impedancia electroquímica y voltametría cíclica. Después de enjuagar y liofilización, la estructura resultante del aerogel se examina con análisis de microscopia electrónica, difractometría de rayos x y adsorción de nitrógeno gas. Las técnicas de método y caracterización de síntesis resultan en una estrecha correspondencia de tamaños de ligamento de aerogel. Este método de síntesis para aerogeles de metal noble demuestra eso alta superficie específica monolitos pueden lograrse con un enfoque de reducción rápida y directa.

La adición de metal ion reductor soluciones juntos resultados y soluciones inmediatamente vuelta color negro con la evolución de gas vigoroso. Observación del progreso de la reacción sugiere el mecanismo de formación de gel propuesto que se muestra en la figura 1. Formación de gel se procede a través de cinco pasos de nucleación 1) nanopartículas 2), 3) densificación, 4) fusión y el crecimiento equilibrado de 5). Los primeros cuatro pasos se observ...

Watch this Scientific Journal Video about A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction at JoVE.com

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

Un método de síntesis rápida de Au, Pd y Pt Aerogels vía reducción directa basada en la solución

Se presenta un método de síntesis de reducción rápida y directa solución a obtener aerogels Au, Pd y Pt.

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

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8.6K vistas.  United States Military Academy, West Point. Se presenta un método de síntesis de reducción rápida y directa solución a obtener aerogels Au, Pd y Pt.

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

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.

This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

Preparación de sílice aerogel monolitos a través de un método de extracción supercrítica rápida

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

Investigación

Química

Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties of the materials were investigated. We used a one pot sol-gel approach to intercalate gold nano particles in the walls of mesoporous silica. To start with the synthesis, P123 was used as template to form micelles. Then TESPTS was used as a surface modification agent to intercalate gold nano particles. Following this process, TEOS was added in as a silica source which underwent a polymerization process in acid environment. After hydrothermal processing and calcination, the final product was acquired. Several techniques were utilized to characterize the porosity, morphology and structure of the gold intercalated mesoporous silica. The results showed a stable structure of mesoporous silica after gold intercalation. Through the oxidation of benzyl alcohol as a benchmark reaction, the GMS materials showed high selectivity and recyclability.

Here, we present a protocol with a sol-gel process to synthesize gold intercalated in the walls of mesoporous materials (GMS), which is confirmed to possess a mesoporous matrix with gold intercalated in the walls imparting great stability and recyclability.

Síntesis y rendimiento catalítico de Oro intercalados en las Murallas de sílice mesoporoso

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties ...

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl4 to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na+[Au(OH4-x)Clx]-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated &#62;300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.

We describe a simple method for producing highly stable oligomeric clusters of gold nanoparticles via the reduction of chloroauric acid (HAuCl4) with sodium thiocyanate (NaSCN). The oligoclusters have a narrow size distribution and can be produced with a wide range of sizes and surface coats.

Un método simple para la síntesis controlada de tamaño estables Clusters oligómeros de nanopartículas de oro bajo condiciones ambientales

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like ...

Generation of Zerovalent Metal Core Nanoparticles Using n-(2-aminoethyl)-3-aminosilanetriol

In this work, a facile one-pot reaction for the formation of metal nanoparticles in a water solution through the use of n-(2-aminoethyl)-3-aminosilanetriol is presented. This compound can be used to effectively reduce and complex metal salts into metal core nanoparticles coated with the compound. By controlling the concentrations of salt and silane one is able to control reaction rates, particle size, and nanoparticle coating. The effects of these changes were characterized through transmission electron microscopy (TEM), UV-Vis spectrometry (UV-Vis), Nuclear Magnetic Resonance spectroscopy (NMR) and Fourier Transform Infrared spectroscopy (FTIR). A unique aspect to this reaction is that usually silanes hydrolyze and cross-link in water; however, in this system the silane is water-soluble and stable. It is known that silicon and amino moieties can form complexes with metal salts. The silicon is known to extend its coordination sphere to form penta- or hexa-coordinated species. Furthermore, the silanol group can undergo hydrolysis to form a Si-O-Si silica network, thereby transforming the metal nanoparticles into a functionalized nanocomposites.

Generation of Zerovalent Metal Core Nanoparticles Using n-2-aminoethyl-3-aminosilanetriol

A novel method for metal core nanoparticle synthesis using a water stable silanol is described.

Generación de valencia cero metal Core nanopartículas usando N- (2-aminoetil) -3-aminosilanetriol

In this work, a facile one-pot reaction for the formation of metal nanoparticles in a water solution through the use of ...

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Fabricación y pruebas de Aerogels catalíticos preparados vía rápida extracción supercrítica

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

A synthesis method for cellulose nanofiber biotemplated palladium composite aerogels is presented.The resulting composite aerogel materials offer potential for catalysis, sensing, and hydrogen gas storage applications.

Método de síntesis para la celulosa nanofibra Biotemplated Palladium Composite Aerogels

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often ...

A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.

A synthesis method to obtain porous platinum-based macrotubes and macrobeams with a square cross section through chemical reduction of insoluble salt-needle templates is presented.

Un método de síntesis con plantillas de sal para macrobeames y macrotubos basados en platino poroso

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed ...

Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

Presented here is a protocol for the synthesis of silver-palladium (Ag-Pd) alloy nanoparticles (NPs) supported on ZrO2 (Ag-Pd/ZrO2). This system allows for harvesting energy from visible light irradiation to accelerate and control molecular transformations. This is illustrated by nitrobenzene reduction under light irradiation catalyzed by Ag-Pd/ZrO2 NPs.

Preparación de nanopartículas de aleación silver-palladium para catálisis plásmiónica bajo iluminación de luz visible

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular ...

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid supercritical extraction method, large silica aerogel monolith (10 cm x 11 cm x 1.5 cm) can be fabricated in about 10 h. Dyes incorporated into the precursor mixture result in yellow-, pink- and orange-tinged aerogels. Text, patterns, and images can be etched onto the surface (or surfaces) of the aerogel monolith without damaging the bulk structure. The laser engraver can be used to cut shapes from the aerogel and form colorful mosaics.

This protocol describes a method for etching text, patterns, and images onto the surface of silica aerogel monoliths in native and dyed form and assembling the aerogels into mosaic designs.

Aerogel de sílice estéticamente mejorado mediante la incorporación de grabado láser y tintes

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid ...

Ingeniería

Gold Nanoparticle Synthesis

Gold nanoparticles (Au nanoparticles) that are ~12 nm in diameter were synthesized by rapidly injecting a solution of 150 mg (0.15 mmol) of tetrachloroauric acid in 3.0 g (3.7 mmol, 3.6 mL) of oleylamine (technical grade) and 3.0 mL of toluene into a boiling solution of 5.1 g (6.4 mmol, 8.7 mL) of oleylamine in 147 mL of toluene. While boiling and mixing the reaction solution for 2 hours, the color of the reaction mixture changed from clear, to light yellow, to light pink, and then slowly to dark red. The heat was then turned off, and the solution was allowed to gradually cool down to room temperature for 1 hour. The gold nanoparticles were then collected and separated from the solution using a centrifuge and washed three times; by vortexing and dispersing the gold nanoparticles in 10 mL portions of toluene, and then precipitating the gold nanoparticles by adding 40 mL portions of methanol and spinning them in a centrifuge. The solution was then decanted to remove any remaining byproducts and unreacted starting materials. Drying the gold nanoparticles in a vacuum environment produced a solid black pellet; which could be stored for long periods of time (up to one year) for later use, and then redissolved in organic solvents such as toluene.

A protocol for synthesizing ~12 nm diameter gold nanoparticles (Au nanoparticles) in an organic solvent is presented. The gold nanoparticles are capped with oleylamine ligands to prevent agglomeration. The gold nanoparticles are soluble in organic solvents such as toluene.