Préparation de nanofeuillets carbone à température ambiante
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
Nanostructures de carbone en deux dimensions attirent beaucoup d' attention en raison des propriétés électriques, thermiques, ainsi que mécaniques exceptionnelles signalées 1-5. Ces matériaux sont censés favoriser le progrès technique dans les domaines des composites polymères 6, des dispositifs de stockage d'énergie 7, et l' électronique moléculaire 8-10. En dépit des efforts intensifs de recherche au cours des dernières années, toutefois, l' accès à de grandes quantités de nanomatériaux de carbone bien définies est encore limitée, ce qui nuit à leur mise en œuvre à grande échelle dans des applications technologiques 11,12.
nanomatériaux de carbone sont accessibles par haut vers le bas ou les approches bottom-up. Les approches habituelles telles que les techniques d'exfoliation 13 ou des procédés de haute énergie sur les surfaces 14-16 offrent la possibilité d'obtenir des matériaux avec un haut degré de perfection structurelle et de très bonnes performances. Cependant, l'isolement et la purification de the produits reste difficile, et la production à grande échelle de matériaux nanostructurés définis est difficile 12. D'autre part, les approches bottom-up peuvent être employés qui reposent sur l'utilisation de précurseurs moléculaires, leur disposition dans les structures définies, et un carbonisation subséquente qui donne les nanostructures de carbone 17-23. Dans ce cas, les précurseurs eux-mêmes sont plus complexes et leur préparation nécessite souvent des étapes de synthèse multiples. Ces approches peuvent offrir un degré élevé de contrôle sur les propriétés physiques et chimiques des matériaux résultants et peuvent fournir un accès direct à des matériaux adaptés. Toutefois, la conversion des précurseurs en les nanomatériaux de carbone est typiquement réalisée à des températures supérieures à 800 ° C, ce qui conduit à une perte de la fonctionnalisation chimique incorporé 24-27.
Les limitations mentionnées ci-dessus ont été abordées dans notre groupe en employant oligoynes hautement réactifs que can convertis en des nanomatériaux de carbone à température ambiante , 28,29. En particulier, amphiphiles comprenant un groupe de tête hydrophile et un segment de hexayne sont accessibles par une séquence de bromation et Negishi réactions croisées de couplage au palladium médiée 30,31. La conversion de ces molécules précurseurs dans la structure cible se produit au niveau ou en dessous de la température ambiante lors d'une irradiation avec une lumière UV. La forte réactivité des amphiphiles oligoyne rend l'utilisation de modèles souples, tels que l'interface air-eau ou d'interfaces liquide-liquide, est possible. Dans les enquêtes précédentes, nous avons préparé avec succès des vésicules à partir de solutions de amphiphiles hexayne glycosidiques 28. La reticulation de ces vésicules a été réalisée dans des conditions douces par irradiation UV des échantillons. De plus, nous avons récemment préparé monocouches auto-assemblées à partir de hexaynes avec un groupe de tête de carboxylate de méthyle et une queue d'alkyle hydrophobe à l'interface air-eau dans une cuvette de Langmuir. Le pack denseed précurseurs moléculaires ont ensuite été converties en nanofeuilles carrément de carbone autoportants à la température ambiante par irradiation UV. Dans les approches connexes précurseurs moléculaires définis ont récemment été utilisés pour la préparation de deux dimensions nanofeuillets étendues à l'interface air-eau 32-38.
Le but de ce travail est de donner un aperçu pratique concise de la synthèse et la fabrication des mesures globales qui permettent la préparation de nanofeuillets de carbone de amphiphiles hexayne. L'accent est mis sur l'approche expérimentale et des questions de préparation.
Protocol
Representative Results
Discussion
L'agent amphiphile hexayne désiré (3) est carrément préparé par la bromation séquentielle 52,53 et 30,31 allongement du segment alcyne catalysées par Pd, suivie d'une réaction de déprotection finale de l'ester tritylphenyl (2) (figure 1a) 29. La synthèse réussie est confirmée par le spectre RMN 13 C (figure 1b), ainsi que le spectre UV-Vis d'absorption (figure 1c) 31,54. Cela démontre le…
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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