Este trabajo fue apoyado por las pilas de combustible de Europa y Hydruogen empresa común bajo BOR4STORE colaborativa de proyectos (Acuerdo de Subvención No. 303428) y el programa de infraestructura H2FC (Convenio de Donación No. FP7-284522).

1. Aparato <ol><li> Use un aparato básico de secado supercrítico (SCD) compuesto de cuatro componentes primarios conectados por tubos de gas de alta presión: el suministro de gas, un sistema de vacío, sensores (temperatura y presión), y el medio ambiente de la muestra (que puede ser sumergido en un baño). Asegúrese de que la construcción es de válvulas de alta calidad de acero inoxidable, accesorios y tubería, una clasificación de la presión de al menos 10 MPa dentro del rango de temperatura entre 80 a 300 K. Nota: Un diagrama esquemático que se muestra en la Figura 1. </li><li> Por nitrógeno ScD (nscd) tratamientos, asegúrese de que el suministro de gas es la pureza de investigación (&gt; 99.999%) de gas nitrógeno equipado con un regulador de presión para el control de la presión de salida entre 0 a 10 MPa. Adjuntar una botella de 50 L (20 MPa) al aparato, y purgar el sistema con nitrógeno puro varias veces antes de su uso. </li><li> Asegúrese de que el sistema de vacío es capaz de alcanzar presiones de vacío a &lt;0,1 Pa y está conectado al aparato con unaválvula de aguja de control de bien. Preferiblemente, utilice una bomba de desbaste sin aceite y una bomba turbo molecular arrastre, colocado en serie. </li><li> Utilice al menos dos sensores de presión para la medición precisa de la presión durante los tratamientos de SCD: un sensor de presión baja para la medición de vacío y un sensor de alta presión para lograr un rango de presión medible total entre 0,1-10 7 Pa. </li><li> Utilice al menos dos sensores de temperatura de la exactitud mínima necesaria para llevar a cabo tratamientos típicos SCD: un sensor en contacto térmico con la muestra y un sensor dentro del colector de dosificación de gas primario para mediciones precisas entre 77 a 300 K (por ejemplo, termopares de tipo K) . </li><li> Compruebe que el soporte de la muestra tiene un volumen interno apropiado para contener la cantidad de muestra necesaria para el tratamiento, y está construido de acero inoxidable. Atención: alargadas ayudas de diseño cilíndricos en contacto térmico con el baño. </li><li> Asegúrese de que el accesorio que cierra el recipiente de la muestra es correspondIATE para altas presiones y el uso repetido (por ejemplo, Swagelok VCR). Conectar el volumen de recipiente de la muestra a una válvula para el aislamiento del ambiente exterior a través de una longitud apropiada de tubo (el tubo de inmersión) para la inmersión completa de el soporte de muestras en el baño. </li></ol><img alt="Figura 1" src="/files/ftp_upload/52817/52817fig1.jpg" /> . Figura 1. El nitrógeno supercrítico de secado (NSCD) Aparato Una representación esquemática del aparato NSCD simplificado para uso en el laboratorio típico: (A) a temperatura ambiente y (B) después de la inmersión de la muestra en el baño. El suministro de gas para el proceso descrito en este trabajo es nitrógeno, pero este aparato general es generalizable a otros fluidos SCD con un punto crítico acostado dentro de un rango práctico de la temperatura y de presión, tal como CO 2. Los componentes están etiquetados para mantener la coherencia con la famie protocolo descrito en el presente documento. <a href="https://www.jove.com/files/ftp_upload/52817/52817fig1highres.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a> 2. Preparación <ol><li> Cargar 0,2-0,5 g de muestra (γ-Mg (BH 4) 2, en forma de polvo, después de la síntesis química en húmedo y métodos de secado estándar) en el soporte de la muestra bajo condiciones apropiadas, típicamente en una atmósfera inerte tal como una caja de guantes de argón, a temperatura ambiente o por debajo. Cierre el soporte de la muestra (F2 montaje) con una junta del filtro y cierre la válvula (válvula V4). Transferir el soporte de la muestra al aparato y adjuntar (F1 apropiado). </li><li> Abra el colector de dosificación para aspirar a través de V2 y evacuar. Abrir V3 y evacuar. Purgar el aparato con nitrógeno a través de V1 y evacuar a través de V2. Abrir V4 y evacuar la muestra a temperatura ambiente durante un máximo de 24 horas, para llegar a la presión mínima del sistema (&lt;0.1 Pa). </li><li> Instale el baño de la muestra (ver <strong&gt; Figura 2) alrededor del soporte de la muestra. Realice esta elevando el baño en su posición en un elevador de tijera, o mecanismo similar. </li><li> Ajuste el calentador para el futuro deseado de temperatura del líquido (T l, consulte el paso 3.1) de 110 K, y continuar a evacuar el aparato hasta que la temperatura se equilibra. </li></ol><img alt="Figura 2" src="/files/ftp_upload/52817/52817fig2.jpg" /> Figura 2. criogénico horno de baño de la muestra. Una representación esquemática (izquierda) y fotografía (a la derecha) de un entorno baño termal cryostatic apropiado para contener el soporte de muestra durante el procesamiento NSCD, permitiendo la medición y el control de la temperatura de la muestra entre 77 a 298 K. <a href="https://www.jove.com/files/ftp_upload/52817/52817fig2highres.jpg" target="_blank">Por favor haga clic aquí para ver una versión más grande de esta figura.</a> 3. supercrítica Nitrógeno exposición <ol&gt; <li> Para el procesamiento NSCD de γ-Mg (BH 4) 2, (el tema de la manifestación en este protocolo) seleccionar una temperatura del líquido (T l) de 110 K. Esto corresponde a una densidad de disolvente líquido moderada (~ 0,6 g ml -1) ; Ajuste según sea necesario para la aplicación de este protocolo para otros procesos de tratamiento NSCD (véase la nota más abajo). </li><li> Cerrar el sistema de vacío mediante el cierre de V2. Acelerador abierto V1 lentamente, permitiendo que la presión aumente en la región de líquido del diagrama de fases. Equilibrar el sistema a 2 MPa y T l. </li><li> Remoje la muestra en N 2 líquido durante 4 horas. </li><li> Ajuste el calentador a 150 K con un min -1 rampa ≤2 K. Permitir que la presión para aumentar no superior a la presión nominal máxima del aparato (esto P max debe ser ≥10 MPa); si es necesario, ventilar con cuidado el exceso de presión al vacío a través de V2. Equilibrar el sistema en P max y 150 K. </li><li> Remoje la muestra en supercritical N 2 durante 1 hora. </li></ol><img alt="Figura 3" src="/files/ftp_upload/52817/52817fig3.jpg" /> Figura 3. Diagrama de Fase de nitrógeno. Un diagrama de fases detallada de nitrógeno, donde la densidad del fluido (mostrado en la escala de grises lineal) se calcula utilizando REFPROP (una ecuación Webb-Benedict-Rubin modificada de estado). 41 Varias líneas de densidad constante se muestran en púrpura. Los límites de fase sólida y líneas de transición de ebullición se muestran en rojo. Las líneas azules indican el límite de la región del diagrama de fase que es relevante para el secado o la extracción de procesamiento usando N 2. <a href="https://www.jove.com/files/ftp_upload/52817/52817fig3highres.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a> Nota: Para la aplicación de este protocolo a otros materiales, establecer un tratamiento schem NSCD apropiadae eligiendo las condiciones necesarias para la solvatación efectiva de la especie objetivo. Consulte el diagrama de fase de N 2, que se muestra en la Figura 3. Para lograr una densidad de fluido de alta en la fase líquida (por ejemplo, 0,8-1 g ml -1), seleccione un T l de 80 a 90 K. Para la densidad del líquido moderada (por ejemplo, 0,6 a 0,8 g ml -1), seleccione un T l de 90 a 115 K. Un ensayo y error puede ser necesario. 4. supercrítica nitrógeno de lanzamiento <ol><li> Romper con cuidado el sistema de vacío estrangulando V2, permitiendo que la presión para disminuir lo más lentamente posible. En repetidas ocasiones romper el sistema a mayores tasas, según sea necesario para lograr una disminución gradual de alto vacío (&lt;0,1 Pa) en el lapso de tiempo aproximado de 12 a 24 horas de vacío. </li><li> Retire la muestra y baño totalmente V2 abierta para evacuar completamente la muestra. Equilibrar a temperatura ambiente y alto vacío (&lt;0,1 Pa). </li><li> Desgasificar la muestra a temperatura ambiente y &lt;0.1 Pa durante 1-24 horas, como desired. </li></ol> 5. Tratamiento del anuncio <ol><li> Cierre las válvulas V3 y V4, y retire el soporte de muestras del aparato (montaje F1). </li><li> Transferir el soporte de la muestra a un ambiente inerte para la manipulación, tal como una caja de guantes de argón-llenado. Retire la muestra desde el soporte de muestra (ajuste F2) y guardar en un recipiente hermético a temperatura ambiente o por debajo. </li></ol>

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G., Baricco, M., Bordiga, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+carbon+dioxide+recycling+by+reaction+with+&#947;-Mg(BH4)2.">Fast carbon dioxide recycling by reaction with &#947;-Mg(BH4)2.</a> Phys. Chem. Chem. Phys. 16, 22482-22486 (2014).</li><li>Paskevicius, M., 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=In-Situ+X-ray+Diffraction+Study+of+&#947;-Mg(BH4)2+Decomposition.">In-Situ X-ray Diffraction Study of &#947;-Mg(BH4)2 Decomposition.</a> J. Phys. Chem. C. 116, 15321-15240 (2012).</li><li>Lemmon, E. W., Huber, M. L., McLinden, M. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NIST+standard+reference+database+23:+reference+fluid+thermodynamic+and+transport+properties.">NIST standard reference database 23: reference fluid thermodynamic and transport properties.</a> Standard Reference Data Program. , (2008).</li><li>Moquin, P. H. L., Temelli, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetic+modeling+of+hydrolysis+of+canola+oil+in+supercritical+media.">Kinetic modeling of hydrolysis of canola oil in supercritical media.</a> J. Supercrit. Fluid. 45, 94-101 (2008).</li><li>Myers, M. N., Giddings, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-High-Pressure+Gas+Chromatography+in+Micro+Columns+to+2000+Atmospheres.">Ultra-High-Pressure Gas Chromatography in Micro Columns to 2000 Atmospheres.</a> Sep. Sci. 1 (6), 761-776 (1966).</li><li>McLeary, E. E., Jansen, J. C., Kapteijn, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zeolite+based+films,+membranes+and+membrane+reactors:+Progress+and+prospects.">Zeolite based films, membranes and membrane reactors: Progress and prospects.</a> Microporous Mesoporous Mater. 90, 198-220 (2006).</li><li>Richter, B., Ravnsb&#230;k, D. B., Tumanov, N., Filinchuk, Y., Jensen, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Manganese+borohydride;+synthesis+and+characterization.">Manganese borohydride; synthesis and characterization.</a> Dalton Trans. , (2015).</li><li>Liang, S., Tilotta, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extraction+of+petroleum+hydrocarbons+from+soil+using+supercritical+argon.">Extraction of petroleum hydrocarbons from soil using supercritical argon.</a> Anal. Chem. 70 (3), 616-622 (1998).</li></ol>

Los autores no tienen nada que revelar.

Tal vez debido a su relativamente baja temperatura crítica (126 K), N 2 ha históricamente sido pasado por alto como un disolvente eficaz ScD. En informes anteriores, 3,17,42,43 que sólo se ha aludido en el contexto de procesamiento de las temperaturas en o por encima de la ambiente, donde se exhibe sólo el poder de solvatación modesta debido a su densidad de fluido de baja en esta región de su diagrama de fases (excepto a muy altas presiones 43). El paso clave en la realización de...

Extracción con fluidos supercríticos (SFE) y el secado de los métodos (SCD) están bien establecidos en una amplia gama de aplicaciones prácticas, especialmente en las industrias de alimentos y del petróleo, sino también en la síntesis química, análisis y procesamiento de materiales. 1-6 El uso de secado o medios de extracción en condiciones por encima de sus puntos críticos es a menudo más rápido, más limpio y más eficiente que (líquido) técnicas tradicionales, y tiene la ventaja añadida de ser altamente ajustable con respecto a la potencia de solvatación del fluido por ligero ajuste de las condiciones de funcionamiento . 3,7 Un método ScD simple comprende tres pasos básicos. El primer paso está exponiendo el material sólido (o quizás líquido) de partida que contiene el compuesto de impureza objetivo a un fluido ScD elegido apropiadamente en su líquido (o casi líquido supercrítico) de fase, donde su alta densidad corresponde a una alta (y quizás selectiva 7) poder disolvente con respecto a las especies objetivo. Tél segundo paso se está calentando y comprimiendo el sistema por encima del punto crítico del fluido ScD elegido en un recipiente cerrado de manera que el fluido y sus especies objetivo disueltos no pasan un límite de fase que podría resultar en la separación. El paso final está reduciendo lentamente la presión del fluido ScD a vacío a una temperatura por encima de la temperatura crítica, lo que permite la solución de fluido que contiene las especies objetivo para escapar, de nuevo sin encontrar un límite de fase ni de cualesquiera efectos perjudiciales de tensión superficial a lo largo del camino. El material de partida se deja agotado de las especies objetivo y puede ser sometido a tratamientos iterados si es necesario. En los casos de extracción de fluido supercrítico, las especies de soluto objetivo es el producto deseado, y se recoge a partir de solución para su uso posterior. 8,9 En otros casos, el material de partida secado o purificado es el producto deseado, y las impurezas extraídas se descartan. Este último escenario, denominado en este documentocomo el enfoque ScD, fue descubierto a ser una estrategia eficaz para el tratamiento previo de alta superficie, materiales microporosos tales como armazones organometálicos (MOF), donde los métodos tradicionales de tratamiento térmico al vacío son en muchos casos no es suficiente en la limpieza de los poros de todos los invitados no deseados, o resultar en el colapso de los poros. dióxido de carbono 10 ScD procesamiento (cscd) es ahora un proceso de post-sintética de rutina para MOF, 11 que conduce al aumento de las superficies de nitrógeno accesible sobre los materiales no tratados de hasta 1000% 12 y otras mejoras, como por ejemplo en la actividad catalítica. 13 Otras aplicaciones de fluidos supercríticos son notables como un medio ampliamente sintonizable para las reacciones químicas, 14-16 de cromatografía de fluidos supercríticos (SCFC) 6,17,18 y síntesis de aerogeles y materiales compuestos avanzados. 19- 22 Para el secado de las aplicaciones, un fluido ScD se eligen en base a dos criterios: a) la proximidad de supunto crítico a las condiciones ambientales (por comodidad y para reducir los costos de energía o la complejidad del proceso) y b) su poder de solvatación con respecto a las especies objetivo. El dióxido de carbono (CO 2) ha demostrado ser conveniente un fluido ScD en muchas aplicaciones, ya que no es tóxico, no inflamable, y barato, y puede ser sintonizado a exhibir un alto poder de solvatación hacia un número de especies comunes de destino orgánicos en su casi líquida estado (a presiones de &lt;10 MPa y temperaturas de 273 a 323 K). 1-3,7-9 Otros disolventes supercríticos comunes (o co-disolventes) incluyen agua (que abarca una notable variedad de propiedades disolventes entre su ambiente y estado supercrítico 23), acetona, etileno, metanol, etanol, y etano, que abarca el espectro de polar (prótico y aprótico) a no polar, y que tiene puntos críticos relativamente cerca de las condiciones ambientales. El dióxido de carbono es de lejos el fluido ScD más común utilizado. En los métodos cscd establecidos, la reactividaddel material de partida no es un factor inhibidor ya que el CO 2 es sólo muy débilmente reactiva a temperaturas cerca de su punto crítico. Sin embargo, ciertas clases de materiales, tales como los llamados hidruros complejos (por ejemplo, alanatos y borohidruros) presentan desafíos únicos en el manejo debido a su fuerte reactividad en presencia de agua o CO 2, además de su (tal vez adaptado intencionalmente) la inestabilidad bajo calentamiento 24-26. Por otra parte, existe un gran interés internacional en materias tales como compuestos de almacenamiento de hidrógeno de alta densidad, 27-30 y por lo tanto también en nanoestructurado y / o variedades porosas 31-33. Para la purificación eficaz de tales, y materiales nanoestructurados inestables reactivos, métodos de SCD son una estrategia prometedora. 34 A ScD fluido debe ser utilizado que tiene un pequeño diámetro molecular apropiado para la penetración en las cavidades estrechas y que también tiene un alto poder de solvatación hacia el impurezas objetivo, whiLe restante no reactivo hacia el material de partida en sí. En este documento, se presenta la utilización de nitrógeno supercrítico (N 2) como un fluido eficaz para tal extracción y aplicaciones especialmente de secado. Una metodología específica de secado de nitrógeno supercrítico (NSCD) se describe a continuación para la purificación de borohidruro de magnesio γ-fase en la que la especie objetivo incluyen tanto diborano y un compuesto de n-butilo (similar a pero no específicamente identificable como n butano). El siguiente protocolo se puede modificar fácilmente para la extensión global a otros procesos de secado de nitrógeno o extracción supercrítica.

<table><tbody><tr><td>Compressed Nitrogen Gas</td><td>Messer Schweiz AG</td><td></td><td>50 L bottle, purity &gt; 99.999%, &amp;lt;3 ppmv H&lt;sub&gt;2&lt;/sub&gt;O</td></tr><tr><td>Liquid Nitrogen</td><td>Pan Gas AG</td><td></td><td>Bulk storage, on site</td></tr><tr><td>Custom Supercritical Drying Apparatus</td><td>Empa</td><td></td><td>Swagelok (compression fitting and VCR) components</td></tr><tr><td>Custom Cryogenic Furnace Bath</td><td>Empa</td><td></td><td></td></tr><tr><td>Custom Labview Interface</td><td>Empa</td><td></td><td></td></tr></tbody></table>

supercritical nitrogen processing for the purification of reactive porous materials

Supercritical fluid extraction and drying methods are well established in numerous applications for the synthesis and processing of porous materials. Herein, nitrogen is presented as a novel supercritical drying fluid for specialized applications such as in the processing of reactive porous materials, where carbon dioxide and other fluids are not appropriate due to their higher chemical reactivity. Nitrogen exhibits similar physical properties in the near-critical region of its phase diagram as compared to carbon dioxide: a widely tunable density up to ~1 g ml-1, modest critical pressure (3.4 MPa), and small molecular diameter of ~3.6 &#197;. The key to achieving a high solvation power of nitrogen is to apply a processing temperature in the range of 80-150 K, where the density of nitrogen is an order of magnitude higher than at similar pressures near ambient temperature. The detailed solvation properties of nitrogen, and especially its selectivity, across a wide range of common target species of extraction still require further investigation. Herein we describe a protocol for the supercritical nitrogen processing of porous magnesium borohydride.

Borohidruros de metales alcalinos y alcalinotérreos son materiales de almacenamiento de hidrógeno potenciales, que ofrecen un gran contenido de hidrógeno gaseoso tras la descomposición. 27,29 Otros productos de descomposición tal como diborano haber a veces también se ha detectado en el gas desorbido, pero su origen no es a priori clara ; es posible que son productos de la descomposición de fase pura, pero también pueden ser impurezas o productos de reacciones de impurezas sobrante de síntesis quími...

Watch this Scientific Journal Video about Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials at JoVE.com

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

El nitrógeno es un fluido supercrítico eficaz para procesos de extracción o de secado debido a su pequeño tamaño molecular, de alta densidad en el régimen supercrítico-cerca de líquido, e inercia química. Se presenta un protocolo de secado de nitrógeno supercrítico para el tratamiento de purificación de materiales reactivos, porosos.

Procesamiento de nitrógeno supercrítico para la purificación de reactivos Materiales porosos

Supercritical fluid extraction and drying methods are well established in numerous applications for the synthesis and processing of porous materials. ...

supercritical-nitrogen-processing-for-purification-reactive-porous

Research

JoVE Journal

Chemistry

14.7K vistas.  Empa, Swiss Federal Laboratories for Materials Science and Technology.  El nitrógeno es un fluido supercrítico eficaz para procesos de extracción o de secado debido a su pequeño tamaño molecular, de alta densidad en el régimen supercrítico-cerca de líquido, e inercia química. Se presenta un protocolo de secado de nitrógeno supercrítico para el tratamiento de purificación de materiales reactivos, porosos. 

Video: Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Síntesis y funcionalización de nitrógeno dopados Copas de nanotubos de carbono con nanopartículas de oro como tapones de corcho

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Investigación

Ingeniería

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 ...

Química

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous polymer monoliths. The developed approach is based on the preparation of a macroporous polymer containing carboxylic acid functional groups and the subsequent step-by-step solution-based controlled growth of a layer of a porous coordination polymer on the surface of the pores of the polymer monolith. The prepared metal-organic polymer hybrid has a high specific micropore surface area. The amount of iron(III) sites is enhanced through metal-organic coordination on the surface of the pores of the functional polymer support. The increase of metal sites is related to the number of iterations of the coating process.
The developed preparation scheme is easily adapted to a capillary column format. The functional porous polymer is prepared as a self-contained single-block porous monolith within the capillary, yielding a flow-through separation device with excellent flow permeability and modest back-pressure. The metal-organic polymer hybrid column showed excellent performance for the enrichment of phosphopeptides from digested proteins and their subsequent detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The presented experimental protocol is highly versatile, and can be easily implemented to different organic polymer supports and coatings with a plethora of porous coordination polymers and metal-organic frameworks for multiple purification and/or separation applications.

A procedure for the preparation of porous hybrid separation media composed of a macroporous polymer monolith internally coated by a high surface area microporous coordination polymer is presented.

Preparación de altamente poroso Coordinación Polymer Coatings en macroporosas Polymer Monolitos de Enriquecimiento mejorada de Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

Procedures of Laboratory Fumigation for Pest Control with Nitric Oxide Gas

Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control. This paper provides detailed protocols for conducting NO fumigation on fresh products and procedures for residue analysis and product quality evaluation. An airtight fumigation chamber containing fresh fruit and vegetables is first flushed with nitrogen (N2) to establish an ultralow oxygen (ULO) environment followed by injection of NO. The fumigation chamber is then kept at a low temperature of 2 - 5 &#176;C for a specified time period necessary to kill a target pest to complete a fumigation treatment. At the end of a fumigation treatment, the fumigation chamber is flushed with N2 to dilute NO prior to opening the chamber to ambient air to prevent the reaction between NO and O2, which produces NO2 and may damage delicate fresh products. At different times after NO fumigation, NO2 in headspace and nitrate and nitrite in liquid samples were measured as residues. Product quality was evaluated after 2 weeks of post-treatment cold storage to determine effects of NO fumigation on product quality. Keeping&#160;O2 from reacting with NO is critical to NO fumigation and is an important part of the protocols. Measuring NO levels is challenging and a practical solution is provided. Possible protocol modifications are also suggested for measuring NO levels in the fumigation chambers as well as residues. NO fumigation has the potential to be a practical alternative to methyl bromide fumigation for postharvest pest control on fresh and stored products. This publication is intended to assist other researchers in conducting NO fumigation research for postharvest pest control and accelerating the development of NO fumigation for practical applications.

This paper describes nitric oxide (NO) fumigation protocols for postharvest pest control. Fumigation chambers are flushed with nitrogen (N2) to establish ultralow oxygen conditions before NO is injected. At the end, chambers are flushed with N2 to dilute NO before exposing products to ambient air to prevent exposure to NO2.

Procedimientos de laboratorio fumigación Control de plagas con Gas de óxido nítrico

Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control. This paper provides detailed protocols for conducting NO fumigation on ...

Medio ambiente

On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The composition of heavy crude oils and shale oils varies substantially depending on the origin of the mixture. In particular they contain an increased amount of nitrogen containing compounds compared to the conventionally used sweet crude oils. As nitrogen compounds have an influence on the operation of thermal processes occurring in coker units and steam crackers, and as some species are considered as environmentally hazardous, a detailed analysis of the reactions involving nitrogen containing compounds under pyrolysis conditions provides valuable information. Therefore a novel method has been developed and validated with a feedstock containing a high nitrogen content, i.e., a shale oil. First, the feed was characterized offline by comprehensive two-dimensional gas chromatography (GC &#215; GC) coupled with a nitrogen chemiluminescence detector (NCD). In a second step the on-line analysis method was developed and tested on a steam cracking pilot plant by feeding pyridine dissolved in heptane. The former being a representative compound for one of the most abundant classes of compounds present in shale oil. The composition of the reactor effluent was determined via an in-house developed automated sampling system followed by immediate injection of the sample on a GC &#215; GC coupled with a time-of-flight mass spectrometer (TOF-MS), flame ionization detector (FID) and NCD. A novel method for quantitative analysis of nitrogen containing compounds using NCD and 2-chloropyridine as an internal standard has been developed and demonstrated.

A method combining comprehensive two-dimensional gas chromatography with nitrogen chemiluminescence detection has been developed and applied to on-line analysis of nitrogen containing compounds in a complex hydrocarbon matrix.

Análisis on-line de compuestos que contienen nitrógeno en matrices complejas de hidrocarburos

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The ...

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for Cu(II) Through Microwave Pre-Pyrolysis

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is proposed. Bagasse impregnated with phosphoric acid is utilized as the precursor. To pyrolyze the precursor, two separate heating modes are used: microwave pyrolysis and conventional electric-heating pyrolysis. The resulting bagasse-derived carbon samples are modified with nitrification and reduction modification. Nitrogen (N)/oxygen (O) functional groups are simultaneously introduced to the surface of activated carbon, enhancing its adsorption of Cu(II) by complexing and ion-exchange. Characterization and copper adsorption experiments are performed to investigate the physicochemical properties of four prepared carbon samples and determine which heating method favors the subsequent modification for doping of N/O functional groups. In this technique, based on analyzing data of nitrogen adsorption, Fourier transform infrared spectroscopy, and batch adsorption experiments, it is proven that microwave-pyrolyzed carbon has more defect sites and, therefore, time-saving effective microwave pyrolysis contributes more N/O species to the carbon, although it leads to a lower specific surface area. This technique offers a promising route to synthesis adsorbents with higher nitrogen and oxygen content and a higher adsorption capacity of heavy-metal ions in wastewater remediation applications.

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for CuII Through Microwave Pre-Pyrolysis

Here, we present a protocol to synthesize nitrogen/oxygen dual-doped mesoporous carbon from biomass by chemical activation in different pyrolysis modes followed by modification. We demonstrate that the microwave pyrolysis benefits the subsequent modification process to simultaneously introduce more nitrogen and oxygen functional groups on the carbon.

Preparación de biomasa carbono mesoporoso con mayor nitrógeno-/ adsorción quelantes de oxígeno para Cu(II) a través de microondas pre-pirolisis

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is ...

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

The importance of understanding the fate of nitrate (NO3&#8722;), which is the dominant N species transferred from terrestrial to aquatic ecosystems, has been increasing because global nitrogen loads have dramatically increased following industrialization. Dissimilatory nitrate reduction to ammonium (DNRA) and denitrification are both microbial processes that use NO3&#8722; for respiration. Compared to denitrification, quantitative determinations of the DNRA activity have been carried out only to a limited extent. This has led to an insufficient understanding of the importance of DNRA in NO3&#8722; transformations and the regulating factors of this process. The objective of this paper is to provide a detailed procedure for the measurement of the potential DNRA rate in environmental samples. In brief, the potential DNRA rate can be calculated from the 15N-labeled ammonium (15NH4+) accumulation rate in 15NO3&#8722; added incubation. The determination of the 14NH4+ and 15NH4+ concentrations described in this paper is comprised of the following steps. First, the NH4+ in the sample is extracted and trapped on an acidified glass filter as ammonium salt. Second, the trapped ammonium is eluted and oxidized to NO3&#8722; via persulfate oxidation. Third, the NO3&#8722; is converted to N2O via an N2O reductase deficient denitrifier. Finally, the converted N2O is analyzed using a previously developed quadrupole gas chromatography&#8211;mass spectrometry system. We applied this method to salt marsh sediments and calculated their potential DNRA rates, demonstrating that the proposed procedures allow a simple and more rapid determination compared to previously described methods.

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

A series of methods to determine the potential DNRA rate based on 14NH4+/15NH4+ analyses is provided in detail. NH4+ is converted into N2O via several steps and analyzed using quadrupole gas chromatography&#8211;mass spectrometry.

Medición de las tasas potenciales de reducción de nitrato disimilado a amonio basada en 14NH4+/15NH4+ Análisis a través de la conversión secuencial a N2O

The importance of understanding the fate of nitrate (NO3&#8722;), which is the dominant N species transferred from terrestrial to aquatic ecosystems, has ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

Propiedades de superficie de carbono nanoporosos sintetizada y Matrices de sílice

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Ammonia Synthesis at Low Pressure

Ammonia can be synthesized at low pressure by the use of an ammonia selective absorbent. The process can be driven with wind energy, available locally in areas requiring ammonia for synthetic fertilizer. Such wind energy is often called &#34;stranded,&#34; because it is only available far from population centers where it can be directly used.
In the proposed low pressure process, nitrogen is made from air using pressure swing absorption, and hydrogen is produced by electrolysis of water. While these gases can react at approximately 400 &#176;C in the presence of a promoted conventional catalyst, the conversion is often limited by the reverse reaction, which makes this reaction only feasible at high pressures. This limitation can be removed by absorption on an ammine-like calcium or magnesium chloride. Such alkaline metal halides can effectively remove ammonia, thus suppressing the equilibrium constraints of the reaction. In the proposed absorption-enhanced ammonia synthesis process, the rate of reaction may then be controlled not by the chemical kinetics nor the absorption rates, but by the rate of the recycle of unreacted gases. The results compare favorably with ammonia made from a conventional small scale Haber-Bosch process.

Ammonia can be synthesized at low pressure by using a conventional catalyst and an ammonia selective absorbent.

Síntesis del amoníaco a baja presión

Ammonia can be synthesized at low pressure by the use of an ammonia selective absorbent. The process can be driven with wind energy, available locally in ...

Bioingeniería

<meta charset="utf8"></head><body>Versátil sistema casero asistido por microondas para la síntesis de péptidos

An Inexpensive Adaptation of a Commercial Microwave Reactor for Solid Phase Peptide Synthesis

A home-built apparatus to perform solid phase peptide synthesis (SPPS), assisted by microwave irradiation and heating, is presented. In contrast to conventional SPPS reaction vessels, which drain solvent and byproducts via a frit located at the bottom of the vessel, the presented apparatus employs a gas dispersion tube under vacuum to remove solvent, byproducts, and excess reagents. The same gas dispersion tube supplies nitrogen gas agitation of the SPPS beads during the reaction steps of coupling and deprotection. Microwave heating is beneficial for SPPS couplings of sterically hindered residues, such as alpha-aminoisobutyric acid (Aib), an alpha,alpha-dialkylated amino acid residue. This home-built apparatus has been used to prepare, via manual Fmoc SPPS methods, heptameric and octameric peptides dominated by the Aib residue, which is notoriously difficult to couple under standard room temperature conditions and reagents. Further, typical commercial microwave SPPS reactors are dedicated exclusively to SPPS synthesis rendering them inaccessible to non-SPPS users. In contrast, the presented apparatus preserves the versatility of the microwave reactor for conventional microwave acceleration of chemical reactions, as the apparatus is trivially removed from the commercial microwave reactor.

<meta charset="utf8"></head><body>Una adaptación económica de un reactor de microondas comercial para la síntesis de péptidos en fase sólida

A simple, inexpensive, and novel apparatus for performing solid phase peptide syntheses in a commercial microwave reactor is presented.

Una adaptación económica de un reactor de microondas comercial para la síntesis de péptidos en fase sólida

A home-built apparatus to perform solid phase peptide synthesis (SPPS), assisted by microwave irradiation and heating, is presented. In contrast to ...

Procesamiento de nitrógeno supercrítico para la purificación de reactivos Materiales porosos

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