Preparazione di carbonio nanosheets 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
Nanostrutture di carbonio bidimensionali attraggono l'attenzione significativa a causa delle proprietà elettriche, termiche, meccaniche e sospeso riportati 1-5. Questi materiali sono tenuti a promuovere il progresso tecnico nei settori dei compositi polimerici 6, dispositivi di accumulo 7, e l'elettronica molecolare 8-10. Nonostante gli sforzi di ricerca intensi negli ultimi anni, tuttavia, l'accesso a grandi quantità di nanomateriali di carbonio ben definiti è ancora limitata, che impedisce loro implementazione su larga scala in applicazioni tecnologiche 11,12.
nanomateriali di carbonio sono accessibili da una top-down o bottom-up. Approcci tipici come le tecniche di esfoliazione 13 o processi ad alta energia su superfici 14-16 offrono la possibilità di ottenere materiali con un alto grado di perfezione strutturale e prestazioni molto buone. Tuttavia, l'isolamento e la purificazione di the prodotti rimane difficile, e la produzione su larga scala di materiali nanostrutturati definiti è difficile 12. D'altra parte, approcci bottom-up possono essere impiegati che si basano sull'uso di precursori molecolari, la loro disposizione in strutture definite, e una successiva carbonizzazione che produce le nanostrutture di carbonio 17-23. In questo caso, i precursori stessi sono più complessi e la loro preparazione richiede spesso più passaggi sintetici. Questi approcci possono offrire un alto grado di controllo sulle proprietà chimiche e fisiche dei materiali risultanti e possono fornire una accesso diretto ai materiali adatti. Tuttavia, la conversione dei precursori in nanomateriali di carbonio è generalmente effettuata a temperature superiori a 800 ° C, che porta ad una perdita di funzionalizzazione chimica incorporato 24-27.
Le limitazioni di cui sopra sono stati affrontati nel nostro gruppo impiegando oligoynes altamente reattive che CAn essere convertito in nanomateriali di carbonio a temperatura ambiente 28,29. In particolare, amphiphiles comprendente un gruppo testa idrofila e un segmento hexayne sono accessibili attraverso una sequenza di bromurazione e reazioni di cross-coupling Negishi palladio-mediata 30,31. La conversione di queste molecole precursori nella struttura di destinazione avviene a temperatura ambiente o inferiore su irraggiamento con luce UV. L'elevata reattività dei amphiphiles oligoyne rende l'uso di modelli morbidi, come l'interfaccia aria-acqua o interfacce liquido-liquido, possibile. Nelle inchieste precedenti, abbiamo preparato con successo vescicole da soluzioni di amphiphiles hexayne glicoside 28. La reticolazione di queste vescicole è stato ottenuto in condizioni blande per irradiazione UV dei campioni. Inoltre, abbiamo recentemente preparato monostrati auto-assemblati da hexaynes con un gruppo metilico testa carbossilato e una coda idrofoba alchil all'interfaccia aria-acqua in una vasca Langmuir. Il pacco densamenteEd precursori molecolari sono stati poi semplicemente convertiti in nanosheets carbonio autoportanti a temperatura ambiente per irraggiamento UV. Negli approcci relativi precursori molecolari definiti sono stati recentemente utilizzati per la preparazione di due-dimensionalmente nanosheets estese all'interfaccia aria-acqua 32-38.
Lo scopo di questo lavoro è quello di dare una concisa, guida pratica dei passaggi di sintesi e di fabbricazione complessivi che permettono la preparazione di nanosheets di carbonio da amphiphiles hexayne. L'attenzione si concentra su un approccio sperimentale e domande preparative.
Protocol
Representative Results
Discussion
Il hexayne amphiphile desiderato (3) è semplicemente preparato mediante bromurazione sequenziale 52,53 e l'allungamento 30,31 del segmento alchino Pd-catalizzata, seguita da una reazione di deprotezione finale del tritylphenyl estere (2) (Figura 1a) 29. La sintesi successo è confermata dal 13 spettro C NMR (figura 1b) e UV-Vis spettro di assorbimento (figura 1c) 31,54. Questo dimostra la natura facile con cui …
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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