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Chemistry

Preparação de Nanofolhas de Carbono à Temperatura Ambiente

Published: March 08, 2016
doi:
10.3791/53505
, , , , ,
1Institute of Materials,Ecole Polytechnique Fédérale de Lausanne (EPFL), 2Colloid Chemistry Department,Max Planck Institute of Colloids and Interfaces

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

Bidimensionais nanoestruturas de carbono atrair uma atenção significativa devido às propriedades eléctricas, térmicas, mecânicas, bem como em circulação relatados 1-5. Estes materiais são esperados para promover o progresso técnico nas áreas de compósitos poliméricos 6, dispositivos de armazenamento de energia 7 e eletrônica molecular 8-10. Apesar dos esforços de investigação intensiva nos últimos anos, no entanto, o acesso a grandes quantidades de nanomateriais de carbono bem definidas é ainda limitada, o que impede a sua aplicação em grande escala em aplicações tecnológicas 11,12.

nanomateriais de carbono são acessíveis por qualquer uma das top-down ou abordagens bottom-up. Abordagens típicas, como técnicas de esfoliação 13 ou processos de alta energia em superfícies 14-16 oferecem a possibilidade de obter materiais com um alto grau de perfeição estrutural e desempenho muito bom. No entanto, o isolamento e purificação do the produtos continua sendo um desafio, ea produção em larga escala de materiais nanoestruturados definidos é difícil 12. Por outro lado, as abordagens de baixo para cima pode ser empregue que se baseiam na utilização de precursores moleculares, a sua disposição em estruturas definidas, e uma carbonização subsequente que produz as nanoestruturas de carbono 17-23. Neste caso, os próprios precursores são mais complexos e a sua preparação, muitas vezes requer múltiplos passos de síntese. Estas abordagens podem oferecer um alto grau de controle sobre as propriedades químicas e físicas dos materiais resultantes e pode fornecer um acesso directo aos materiais adaptados. No entanto, a conversão dos precursores para nanomateriais de carbono é tipicamente realizada a temperaturas acima de 800 ° C, o que leva a uma perda da funcionalização química incorporado 24-27.

As limitações acima referidas foram abordados em nosso grupo, empregando oligoynes altamente reativas que a CAn ser convertidos em nanomateriais de carbono à temperatura ambiente 28,29. Em particular, compostos anfifílicos que compreendem um grupo de cabeça hidrófilo e um segmento hexayne são acessíveis através de uma sequência de bromação e reacções de acoplamento cruzado de Negishi mediada por paládio 30,31. A conversão destas moléculas precursoras na estrutura alvo ocorre na ou abaixo da temperatura ambiente, após irradiação com luz UV. A elevada reactividade dos compostos anfifílicos oligoyne faz com que a utilização de modelos macios, tais como a interface ar-água ou de interfaces de líquido fluido, possível. Em investigações anteriores, nós preparamos com sucesso vesículas a partir de soluções de amphiphiles hexayne glicosídeo 28. A ligação cruzada destas vesículas foi conseguida em condições suaves, por irradiação de UV das amostras. Além disso, recentemente preparado monocamadas auto-montadas de hexaynes com um grupo de cabeça carboxilato de metilo e uma cauda hidrofóbica alquilo na interface ar-água, em uma calha de Langmuir. O pacote densamenteed precursores moleculares foram então convertidos em diretamente nanofolhas carbono auto-suportados, à temperatura ambiente por meio de irradiação UV. Em abordagens relacionadas precursores moleculares definidos recentemente têm sido utilizados para a preparação de dois-dimensionalmente nanofolhas estendidos na interface ar-água 32-38.

O objetivo deste trabalho é dar uma visão geral concisa, prática das etapas gerais de síntese e fabricação que permitem a preparação de nanofolhas de carbono de amphiphiles hexayne. O foco é na abordagem experimental e questões de preparação.

Protocol

Atenção: Por favor certifique-se de consultar as folhas de dados de materiais de segurança pertinentes (MSDS) antes da utilização de quaisquer compostos químicos. Alguns dos produtos químicos utilizados nestas sínteses são altamente tóxicos e cancerígenos. nanomateriais preparados podem ter riscos adicionais em comparação com o seu homólogo granel. É imperativa a utilização de todas as práticas de segurança adequadas ao realizar reações (exaustor) e equipamentos de proteção individual (óculos de …

Representative Results

A 13 C ressonância magnética nuclear (RMN) do espectro da molécula precursora preparado 3 exibe os 12 com hibridação sp átomos de carbono do segmento hexayne com os desvios químicos correspondentes de δ = 82-60 ppm (Figura 1b). Além disso, os sinais a δ = 173 ppm e em δ = 52 ppm são atribuídos ao grupo carbonilo e de metilo de carbono do éster, respectivamente. Os sinais entre δ = 33-14 ppm são atribuídas aos carbonos…

Discussion

O hexayne anfifilo desejado (3) é francamente preparado por bromação sequencial 52,53 e 30,31 alongamento do segmento alcino catalisada por Pd, seguido por uma reacção de desprotecção final do tritylphenyl éster (2) (Figura 1a) 29. A síntese bem sucedida é confirmada pelo espectro de 13 C RMN (Figura 1b), bem como o de UV-Vis do espectro de absorção (Figura 1c) 31,54. Isto demonstra a natureza fácil, at…

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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Tags

Carbon NanosheetsRoom TemperatureWet Chemical PreparationSelf-assemblyAmphiphilic MoleculesCarbonizationUV IrradiationHexayneLangmuir TroughInfrared Reflection Absorption Spectroscopy

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Schrettl, S., Schulte, B., Stefaniu, C., Oliveira, J., Brezesinski, G., Frauenrath, H. Preparation of Carbon Nanosheets at Room Temperature. J. Vis. Exp. (109), e53505, doi:10.3791/53505 (2016).
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