Preparación de nanoláminas de carbono a temperatura ambiente
Summary
We present the synthesis of an amphiphilic hexayne and its use in the preparation of carbon nanosheets at the air-water interface from a self-assembled monolayer of these reactive, carbon-rich molecular precursors.
Abstract
Amphiphilic molecules equipped with a reactive, carbon-rich “oligoyne” segment consisting of conjugated carbon-carbon triple bonds self-assemble into defined aggregates in aqueous media and at the air-water interface. In the aggregated state, the oligoynes can then be carbonized under mild conditions while preserving the morphology and the embedded chemical functionalization. This novel approach provides direct access to functionalized carbon nanomaterials. In this article, we present a synthetic approach that allows us to prepare hexayne carboxylate amphiphiles as carbon-rich siblings of typical fatty acid esters through a series of repeated bromination and Negishi-type cross-coupling reactions. The obtained compounds are designed to self-assemble into monolayers at the air-water interface, and we show how this can be achieved in a Langmuir trough. Thus, compression of the molecules at the air-water interface triggers the film formation and leads to a densely packed layer of the molecules. The complete carbonization of the films at the air-water interface is then accomplished by cross-linking of the hexayne layer at room temperature, using UV irradiation as a mild external stimulus. The changes in the layer during this process can be monitored with the help of infrared reflection-absorption spectroscopy and Brewster angle microscopy. Moreover, a transfer of the carbonized films onto solid substrates by the Langmuir-Blodgett technique has enabled us to prove that they were carbon nanosheets with lateral dimensions on the order of centimeters.
Introduction
Nanoestructuras de carbono bidimensionales atraen la atención significativa debido a las propiedades eléctricas, térmicas, así como mecánicas sobresalientes reportados 1-5. Se espera que estos materiales para promover el progreso técnico en los campos de materiales compuestos poliméricos 6, dispositivos de almacenamiento de energía 7, y la electrónica molecular 8-10. A pesar de intensos esfuerzos de investigación en los últimos años, sin embargo, el acceso a mayores cantidades de nanomateriales de carbono bien definidos todavía es limitada, lo que impide su aplicación a gran escala en aplicaciones tecnológicas 11,12.
nanomateriales de carbono son accesibles por cualquiera de los enfoques de abajo hacia arriba o de arriba hacia abajo. Los enfoques típicos, tales como técnicas de exfoliación 13 o procesos de alta energía en las superficies 14-16 ofrecen la posibilidad de obtener materiales con un alto grado de perfección estructural y muy buen rendimiento. Sin embargo, el aislamiento y purificación de THproductos electrónicos sigue siendo un reto, y la producción a gran escala de materiales nanoestructurados definidos es difícil 12. Por otro lado, los enfoques de abajo hacia arriba se pueden emplear que se basan en el uso de precursores moleculares, su disposición en estructuras definidas, y una posterior carbonización que produce las nanoestructuras de carbono 17-23. En este caso, los propios precursores son más complejos y su preparación a menudo requiere múltiples etapas de síntesis. Estos enfoques pueden ofrecer un alto grado de control sobre las propiedades químicas y físicas de los materiales resultantes y pueden proporcionar un acceso directo a los materiales adaptados. Sin embargo, la conversión de los precursores en los nanomateriales de carbono se lleva a cabo típicamente a temperaturas superiores a 800 ° C, lo que conduce a una pérdida de la funcionalización química incrustado 24-27.
Las limitaciones mencionadas anteriormente se han abordado en nuestro grupo mediante el empleo de oligoynes altamente reactivas que el Can ser convertido en nanomateriales de carbono a temperatura ambiente 28,29. En particular, los anfífilos que comprenden un grupo de cabeza hidrófilo y un segmento hexayne son accesibles a través de una secuencia de bromación y Negishi reacciones de acoplamiento cruzado mediadas por paladio 30,31. La conversión de estas moléculas precursoras en la estructura objetivo se produce a o por debajo de la temperatura ambiente tras la irradiación con luz UV. La alta reactividad de los anfífilos oligoyne hace que el uso de plantillas blandas, como la interfaz aire-agua o las interfaces de líquido fluido, es posible. En investigaciones anteriores, hemos preparado con éxito vesículas a partir de soluciones de amphiphiles hexayne glucósido 28. La reticulación de estas vesículas se alcanzó bajo condiciones suaves por la irradiación UV de las muestras. Por otra parte, recientemente hemos preparado monocapas auto-ensambladas a partir de hexaynes con un grupo de cabeza carboxilato de metilo y una cola hidrofóbica alquilo en la interfase aire-agua en una artesa de Langmuir. El paquete densamenteprecursores moleculares ed se convierten entonces en forma directa nanoláminas carbono autoportantes a temperatura ambiente por irradiación UV. En enfoques relacionados precursores moleculares definidos recientemente se han utilizado para la preparación de dos-dimensionalmente nanoláminas extendidos en la interfase aire-agua 32-38.
El objetivo de este trabajo es dar una visión general concisa, práctica de las etapas de síntesis y fabricación globales que permiten la preparación de nanoláminas de carbono de los anfífilos hexayne. La atención se centra en el enfoque experimental y preguntas de preparación.
Protocol
Representative Results
Discussion
El anfifilo hexayne deseado (3) se prepara forma directa por la bromación secuencial 52,53 y 30,31 alargamiento del segmento de alquino Pd-catalizada, seguido por una reacción de desprotección final del éster tritylphenyl (2) (Figura 1a) 29. La síntesis exitosa se confirma por el espectro de 13 C NMR (Figura 1b), así como la UV-Vis espectro de absorción (Figura 1c) 31,54. Esto demuestra la naturaleza f?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
Funding from the European Research Council (ERC Grant 239831) and a Humboldt Fellowship (BS) is gratefully acknowledged.
Materials
| Methyllithium lithium bromide complex (2.2M solution in diethylether) | Acros | 18129-1000 | air-sensitive, flammable |
| Zinc chloride (0.7M solution in THF) | Acros | 38945-1000 | air-sensitive, flammable |
| 1,1'-Bis(diphenylphosphino)ferrocene] dichloropalladium(II), DCM adduct |
Boron Molecular | BM187 | |
| N-Bromosuccinimide | Acros | 10745 | light-sensitive |
| Silver fluoride | Fluorochem | 002862-10g | light-sensitive |
| n-Butyllithium (2.5M solution in hexanes) | Acros | 21335-1000 | air-sensitive, flammable |
| Sodium methanolate | Acros | 17312-0050 | |
| Tetrahydrofuran (unstabilized, for HPLC) | Fisher Chemicals | T/0706/PB17 | This solvent was dried as well as degassed using a solvent purification system (Innovative Technology, Inc, Amesbury, MA, USA) |
| Toluene (for HPLC) | Fisher Chemicals | T/2306/17 | This solvent was dried as well as degassed using a solvent purification system (Innovative Technology, Inc, Amesbury, MA, USA) |
| Acetonitrile (for HPLC) | Fisher Chemicals | A/0627/17 | This solvent was dried as well as degassed using a solvent purification system (Innovative Technology, Inc, Amesbury, MA, USA) |
| Dichloromethane (Extra Dry over Molecular Sieve) | Acros | 34846-0010 | |
| Chloroforme (p.a.) | VWR International | 1.02445.1000 | |
| Pentane | Reactolab | 99050 | Purchased as reagent grade and distilled once prior to use |
| Heptane | Reactolab | 99733 | Purchased as reagent grade and distilled once prior to use |
| Dichloromethane | Reactolab | 99375 | Purchased as reagent grade and distilled once prior to use |
| Diethylether | Reactolab | 99362 | Purchased as reagent grade and distilled once prior to use |
| Geduran silica gel (Si 60, 40-60µm) | Merck | 1115671000 | |
| Langmuir trough | R&K, Potsdam | ||
| Thermostat | E1 Medingen | ||
| Hamilton syringe | Model 1810 RN SYR | ||
| Vertex 70 FT-IR spectrometer | Bruker | ||
| External air/water reflection unit (XA-511) | Bruker | ||
| UV lamp (250 W, Ga-doped metal halide bulb) | UV-Light Technology | ||
| Brewster angle microscope (BAM1+) | NFT Göttingen | ||
| Sapphire substrates | Stecher Ceramics | ||
| Quantifoil holey carbon TEM grids | Electron Microscopy Sciences | ||
| Nuclear magnetic resonance spectrometer (Bruker Avance III 400) | Bruker | ||
| JASCO V-670 UV/Vis spectrometer | JASCO | ||
| Scanning Electron Microscope (Zeiss Merlin FE-SEM) | Zeiss |
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