Solution Properties of Graphite and Graphene
Sandip Niyogi,Elena Bekyarova,Mikhail E.Itkis,Jared L.McWilliams,Mark A.Hamon,and
Robert C.Haddon*
Department of Chemistry,Department of Chemical and En V ironmental Engineering,and Center for Nanoscale Science and Engineering,Uni V ersity of California,Ri V erside,California92521-0403
Received January29,2006;E-mail:robert.haddon@ucr.edu
Recent transport measurements indicate that graphene has great
promi as an electronic material.1-3Graphene is the hypothetical
infinite aromatic sheet of sp2-bonded carbon that is the2-D
counterpart of naturally occurring3-D graphite.4It is found in the
π-stacked hexagonal structure of graphite with an interlayer spacing
of3.34Å,which is the van der Waals distance for sp2-bonded
carbon.The interlayer cohesive energy or exfoliation energy for
pyrolytic graphite has been experimentally determined as61meV/C
atom.5The area occupied by a carbon atom in graphite is(33/2/4)-
l2,6where l is the carbon-carbon bond length(0.1421nm);7thus,产生英文
a1-nm square of graphene contains about38carbon atoms,and
the paration energy of two1-nm squares of graphene is over2
eV.Graphene itlf does not occur naturally and prior work on the
fabrication of electronic devices has primarily relied on the physical
paration of the sheets or on preparation under specialized
conditions.1-3,8-10In the prent communication we show that
chemistry offers opportunities for overcoming the very large
cohesive energies and provides attractive routes for the manipulation
of functionalized graphene.
Commercially available microcrystalline graphite exists as extremely hydrophobic1-20µm particles that aggregate into thin films on contact with solvent.11When treated under strongly oxidizing acidic conditions,graphite oxide is formed.12,13Structur-ally,graphite oxide is an epoxidized form of the sp2-bonded carbon network together with acidic functional groups at the edges with the oxidants intercalated in the interlaminar space;this leads to a route for the exfoliation of graphite by rapid de-intercalation.13,14 Variations of this oxidative route have been studied in the quest to find applications for graphite oxide.11,15-18The materials formed unstable dispersions and the thickness of the graphitic films had a minimum value of1.4nm.15-18
As a part of our interest in the dissolution of carbon materials, we have explored the derivatization of
graphite,following the procedure we previously demonstrated for the chemical processing of single-walled carbon nanotubes.19,20We find that exfoliation with strong acid,followed by functionalization with a long-chain alkylamine gives ri to stable solutions of this material in organic solvents.
欺诈游戏下载Microcrystalline graphite(Aldrich,5g)was sonicated in120 mL of a3:1mixture of H2SO4(18M)and HNO3(17M)for2h, in a Cole-Parmer cup-horn sonicator at a power level of200W, while maintaining the temperature at40°C.The dispersion was allowed to stand at room temperature for4days during which time the color of the dispersion turned purple-brown.After repeated washing with water(total4L),by centrifugation and decantation, the oxidized graphite was filtered through a0.2µm PTFE membrane,with a final ethanol wash.The product was allowed to dry under vacuum overnight;the material had a grayish appearance and was not as shiny as the starting material.
Oxidized graphite from the acid reaction(100mg),was refluxed in20mL of SOCl2in the prence of0.5mL of N,N-dimethyl-formamide(DMF),at70°C for24h,using a CaCl2guard tube.At the end of the reaction,the excess SOCl2was removed by distillation,and67mg of the product was allowed to react with 545mg of octadecylamine(ODA)at120°C for4days.The product was disperd in hot ethanol,filtered through a0.2µm PTFE membrane,and washed with200mL of hot ethanol.The dried product was dissolved in50mL of THF and filtered through a Fisher P8coar filter paper.The yield of
the reaction was20wt %,with respect to the oxidized graphite.The product octadecyl-amido graphite,G-CONH(CH2)17CH3has a solubility of0.5mg/ mL in THF and is also soluble in CCl4and1,2-dichloroethane. The absorption spectrum of the G-CONH(CH2)17CH3in carbon tetrachloride is shown in Figure1A.The electronic absorption process associated with theπ-valence and conduction bands in graphite,show a maximum around4.2eV,similar to previous solid-state obrvations21and to the calculated optical absorption spectrum.22We obrve the asymmetric C-H stretch of the alkyl groups at2854and2925cm-1;the corresponding bands in free ODA occur at2848and2918cm-1.The mid-IR spectra of films of G-CONH(CH2)17CH3,the acid-oxidized graphite,and free ODA are shown in Figure1B.The peak at1653cm-1in the G-CONH-(CH2)17CH3corresponds to carbonyl stretch of the amide,although the signals corresponding to the acidic form in the oxidized graphite are weak.
The graphite solutions obey Beer’s law(Figure2),and for the G-CONH(CH2)17CH3the extinction coefficient( )was determined to be40L mol-1cm-1at10000cm-1.Dispersions of the oxidized graphite were not very stable,but a value of )46L mol-1cm-1 (10000cm-1)was found.Earlier spectroscopic studies of thin ctions of graphitic coal gave similar low values for the extinction coefficient;23,24for single-walled carbon nanotubes,values of ≈400L mol-1cm-1were determined.25It is important to note the different spectral character of the dispersions;clearly,the
length Figure1.(A)Absorption spectrum of a CCl4solution of G-CONH(CH2)17-CH3at a concentration of0.156mg/mL,measured in a quartz cell of1cm path length.The spectrum from2500to6000cm-1was collected on a Nicolet Nexus FT-IR spectrometer and from5000to38000cm-1on a Varian Cary500spectrophotometer,using the same sample.(Int)Absor-bance associated with the asymmetric C-H stretch of the alkyl groups.
(B)Mid-IR spectra collected from thin films on ZnSe of product and the starting
materials.
Published on Web05/19/2006
77209J.AM.CHEM.SOC.2006,128,7720-772110.1021/ja060680r CCC:$33.50©2006American Chemical Society
scale of the oxidized graphite particles is sufficient to scatter the incident light,thereby producing the featureless spectrum en in Figure 2B.美藤
To characterize the soluble species,THF solutions were evapo-rated on mica and examined by AFM (Figure 3);the solutions consisted of irregular graphite crystallites (G n )with a measured thickness of 1.5-2.5nm (Figure 3A)and circular graphene layers
(G 1)with a measured height of ∼5.3Å(Figure 3B).The acid oxidation reaction is known to etch graphitic crystallites into the larger structures obrved in the prent study.11,15,16We note that previous AFM obrvations of G 1found a thickness of 3.4Å26and 4Åwith a dead space of 5Å,between graphene and the substrate that is occupied by trapped solvent.1The extensive edge functionalization employed in our approach may be expected to increa the dead space and thus,we expect that the material imaged in Figure 3B is compod of single-layer graphene sheets.
The thermogravimetric analysis shows that the starting graphite oxidizes at ∼800°C (Figure 4A);after acid oxidation reaction,the bulk material oxidizes at ∼600°C,with substantial weight loss around 200°C due to the loss of the acidic functional groups and residues (Figure 4B).18The G-CONH(CH 2)17CH 3product shows a 7wt %loss around 300°C (Figure 4C),due to the oxidative decomposition of the organic functional groups.
Acknowledgment.This work was supported by DOD/DARPA/DMEA under award number DMEA90-02-2-0216.
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JA060680R
Figure 2.Absorption spectra as a function of concentration.(A)G -CONH(CH 2)17CH 3in THF;(B)dispersions of oxidized graphite in
DMF.
Figure 3.Tapping mode AFM height images of soluble graphite on mica.Two components were obrved,(A)1.5-2.5nm thick G n films and (B)G 1sheets of (uncorrected)height 5.3
考研英语一
Å.
Figure 4.Thermogravimetric analysis data,under dry air with a temperature ramp rate of 10°C/min.(A)Graphite starting material has an oxidation ont at 700°C.(B)Acid-oxidized graphite suffers significant weight loss at 600°C.Residual water is removed at 120°C,and acidic residues and functional groups are oxidized between 180and 220°C.(C)High-temperature bulk oxidation of G-CONH(CH 2)17CH 3is similar to (B),with an additional feature due to the loss of the organic functionalities between 220and 350°C.
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