Name: preparation of carbon nanosheets at room temperature
Uploaded: 2016-03-08T13:00:00
Description: Watch this Scientific Journal Video about Preparation of Carbon Nanosheets at Room Temperature at JoVE.com

Funding from the European Research Council (ERC Grant 239831) and a Humboldt Fellowship (BS) is gratefully acknowledged.

Caution:&#160;Please&#160;make sure to consult the relevant materials safety data sheets (MSDS) before the use of any chemical compounds. Some of the chemicals used in these syntheses are acutely toxic and carcinogenic. Prepared nanomaterials may have additional hazards compared to their bulk counterpart. It is imperative to use all appropriate safety practices when performing reactions (fume hood) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes). If not otherwise ...

The desired hexayne amphiphile (3) is straightforwardly prepared by the sequential bromination52,53 and Pd-catalyzed elongation30,31 of the alkyne segment, followed by a final deprotection reaction of the tritylphenyl ester (2) (Figure&#160;1a)29. The successful synthesis is confirmed by the 13C NMR spectrum (Figure&#160;1b) as well as the UV-Vis absorption spectrum (Figure&#160;1c)31,54. This demonstrates the facile...

Two-dimensional carbon nanostructures attract significant attention due to the reported outstanding electrical, thermal, as well as mechanical properties1-5. These materials are expected to further the technical progress in the fields of polymer composites6, energy storage devices7, and molecular electronics8-10. Despite intensive research efforts in recent years, however, access to larger amounts of well-defined carbon nanomaterials is still limited, which impedes their large-scale implementation in technological applications11,12.
Carbon nanomaterials are accessible by either top-down or bottom-up approaches. Typical approaches such as exfoliation techniques13 or high-energy processes on surfaces14-16 offer the possibility to obtain materials with a high degree of structural perfection and very good performance. However, the isolation and purification of the products remains challenging, and the large-scale production of defined nanostructured materials is difficult12. On the other hand, bottom-up approaches can be employed that rely on the use of molecular precursors, their arrangement into defined structures, and a subsequent carbonization that yields the carbon nanostructures17-23. In this case, the precursors themselves are more complex and their preparation often requires multiple synthetic steps. These approaches may offer a high degree of control over the chemical and physical properties of the resulting materials and may furnish a direct access to tailored materials. However, the conversion of the precursors into carbon nanomaterials is typically performed at temperatures above 800 &#176;C, which leads to a loss of the embedded chemical functionalization24-27.
The above mentioned limitations have been addressed in our group by employing highly reactive oligoynes that can be converted into carbon nanomaterials at room temperature28,29. In particular, amphiphiles comprising a hydrophilic head group and a hexayne segment are accessible through a sequence of bromination and palladium-mediated Negishi cross-coupling reactions30,31. The conversion of these precursor molecules into the target structure occurs at or below room temperature upon irradiation with UV light. The high reactivity of the oligoyne amphiphiles makes the use of soft templates, such as the air-water interface or fluid-fluid interfaces, possible. In previous investigations, we successfully prepared vesicles from solutions of hexayne glycoside amphiphiles28. Cross-linking of these vesicles was achieved under mild conditions by UV irradiation of the samples. Moreover, we recently prepared self-assembled monolayers from hexaynes with a methyl carboxylate head group and a hydrophobic alkyl tail at the air-water interface in a Langmuir trough. The densely packed molecular precursors were then straightforwardly converted into self-supporting carbon nanosheets at room temperature by UV irradiation. In related approaches defined molecular precursors have recently been used for the preparation of two-dimensionally extended nanosheets at the air-water interface32-38.
The aim of this work is to give a concise, practical overview of the overall synthesis and fabrication steps that allow for the preparation of carbon nanosheets from hexayne amphiphiles. The focus is on the experimental approach and preparative questions.

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			<td height="21" style="height:21px;width:513px;">Methyllithium lithium bromide complex (2.2M solution in diethylether)</td>
			<td style="width:195px;">Acros</td>
			<td style="width:119px;">18129-1000</td>
			<td style="width:731px;">air-sensitive, flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Zinc chloride (0.7M solution in THF)</td>
			<td style="width:195px;">Acros</td>
			<td style="width:119px;">38945-1000</td>
			<td>air-sensitive, flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">1,1&#39;-Bis(diphenylphosphino)ferrocene] 
			dichloropalladium(II), DCM adduct&#160;</td>
			<td style="width:195px;">Boron Molecular</td>
			<td style="width:119px;">BM187</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">N-Bromosuccinimide</td>
			<td style="width:195px;">Acros</td>
			<td style="width:119px;">10745</td>
			<td>light-sensitive</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Silver fluoride</td>
			<td style="width:195px;">Fluorochem</td>
			<td style="width:119px;">002862-10g</td>
			<td>light-sensitive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">n-Butyllithium (2.5M solution in hexanes)</td>
			<td style="width:195px;">Acros</td>
			<td style="width:119px;">21335-1000</td>
			<td>air-sensitive, flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Sodium methanolate</td>
			<td style="width:195px;">Acros</td>
			<td style="width:119px;">17312-0050</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Tetrahydrofuran (unstabilized, for HPLC)</td>
			<td style="width:195px;">Fisher Chemicals</td>
			<td style="width:119px;">T/0706/PB17</td>
			<td>This solvent was dried as well as degassed using a solvent purification system (Innovative Technology, Inc, Amesbury, MA, USA)</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Toluene (for HPLC)</td>
			<td style="width:195px;">Fisher Chemicals</td>
			<td style="width:119px;">T/2306/17</td>
			<td>This solvent was dried as well as degassed using a solvent purification system (Innovative Technology, Inc, Amesbury, MA, USA)</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Acetonitrile (for HPLC)</td>
			<td style="width:195px;">Fisher Chemicals</td>
			<td style="width:119px;">A/0627/17</td>
			<td>This solvent was dried as well as degassed using a solvent purification system (Innovative Technology, Inc, Amesbury, MA, USA)</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Dichloromethane (Extra Dry over Molecular Sieve)</td>
			<td style="width:195px;">Acros</td>
			<td style="width:119px;">34846-0010</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Chloroforme (p.a.)</td>
			<td style="width:195px;">VWR International</td>
			<td style="width:119px;">1.02445.1000</td>
			<td></td>
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			<td height="21" style="height:21px;width:513px;">Pentane</td>
			<td style="width:195px;">Reactolab</td>
			<td style="width:119px;">99050</td>
			<td>Purchased as reagent grade and distilled once prior to use</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Heptane</td>
			<td style="width:195px;">Reactolab</td>
			<td style="width:119px;">99733</td>
			<td>Purchased as reagent grade and distilled once prior to use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Dichloromethane</td>
			<td style="width:195px;">Reactolab</td>
			<td style="width:119px;">99375</td>
			<td>Purchased as reagent grade and distilled once prior to use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Diethylether</td>
			<td style="width:195px;">Reactolab</td>
			<td style="width:119px;">99362</td>
			<td>Purchased as reagent grade and distilled once prior to use</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Geduran silica gel (Si 60, 40-60&#181;m)</td>
			<td style="width:195px;">Merck</td>
			<td style="width:119px;">1115671000</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Langmuir trough</td>
			<td style="width:195px;">R&#38;K, Potsdam</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thermostat&#160;</td>
			<td style="width:195px;">E1 Medingen</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hamilton syringe&#160;</td>
			<td>Model 1810 RN SYR</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Vertex 70 FT-IR spectrometer&#160;</td>
			<td style="width:195px;">Bruker</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">External air/water reflection unit (XA-511)&#160;</td>
			<td style="width:195px;">Bruker</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">UV lamp (250 W, Ga-doped metal halide bulb)</td>
			<td style="width:195px;">UV-Light Technology</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Brewster angle microscope (BAM1+)&#160;</td>
			<td style="width:195px;">NFT G&#246;ttingen</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Sapphire substrates</td>
			<td style="width:195px;">Stecher Ceramics</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:513px;">Quantifoil holey carbon TEM grids</td>
			<td style="width:195px;">Electron Microscopy Sciences</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Nuclear magnetic resonance spectrometer (Bruker Avance III 400)</td>
			<td style="width:195px;">Bruker</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">JASCO V-670 UV/Vis spectrometer</td>
			<td style="width:195px;">JASCO</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:513px;">Scanning Electron Microscope (Zeiss Merlin FE-SEM)</td>
			<td style="width:195px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
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preparation of carbon nanosheets at room temperature

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.

The 13C nuclear magnetic resonance (NMR) spectrum of the prepared precursor molecule 3 displays the 12&#160;sp-hybridized carbon atoms of the hexayne segment with the corresponding chemical shifts of &#948; = 82-60 ppm (Figure 1b). Moreover, the signals at &#948; = 173 ppm and at &#948; = 52&#160;ppm are assigned to the carbonyl and methyl carbon of the ester, respectively. The signals between &#948; = 33-14 ppm are ascribed to the ali...

Watch this Scientific Journal Video about Preparation of Carbon Nanosheets at Room Temperature at JoVE.com

Preparation of Carbon Nanosheets at Room Temperature

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.

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into ...

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