Honeycomb Carbon A Review of Graphene 石墨烯综述(4)

纳米材料在生物医学中的应用

134ChemicalReviews,2010,Vol.110,No.1nitride4andmolybdenumdisul de.High,in-planeelectrical(～10 -1cm-1)andthermalconductivity(～3000W/mK)enablegraphitetobeusedinelectrodesandasheatingelementsforindustrialblastfurnaces.53,54Highmechanicalstiffnessofthehexagonalnetwork(1060GPa)isalsoutilizedincarbon berreinforcedcomposites.Theseusesandothersgenerateanannualdemandofmorethan1milliontonsofgraphiteworldwide.55

Theanisotropyofgraphite’smaterialpropertiescontinuestofascinatebothscientistsandtechnologists.Thes,patomicorbitalsoneachcarbonhybridizetoformstrongx,andpcovalentysp2bonds,givingriseto120°C-C-Cbondanglesandthefamiliarchicken-wire-likelayers.Theremainingporbitaloneachcarbonoverlapswithitsthreeneighboringzcarbonstoformabandof lledπorbitals,knownasthevalenceband,andabandofemptyπ*orbitals,calledtheconductionband.Whilethreeofthefourvalenceelectronsoneachcarbonformtheσ(single)bonds,thefourthelectronformsone-thirdofaπbondwitheachofitsneighborsproducingacarbon-carbonbondorderingraphiteofoneandone-third.Withnochemicalbondinginthec-direction,out-of-planeinteractionsareextremelyweak.Thisincludesthepropagationofchargeandthermalcarriers,whichleadstoout-of-planeelectricalandthermalconductivitiesthatarebothmorethan103timeslowerthanthoseoftheirin-planeanalogues.56

2.1.ChemistryofGraphite

Graphitehasarichchemistryinwhichitcanparticipateinreactionsaseitherareducingagent(electrondonor)oranoxidizer(electronacceptor).Thisisadirectconsequenceofitselectronicstructure,whichresultsinboth53

anelectronaf nityandanionizationpotentialof4.6eV.Alargenumberofexperimentsforgraphitefocusontheinsertionofadditionalchemicalspeciesbetweenthebasalplanes,orintercalation.Shaffaultiscreditedwiththe rstintercalationcompoundusingpotassium,datingbackto1841.57Graphiteintercalationcompounds(GICs)appeartobetheonlylayeredcompoundssuf cientlyorderedtoexhibit“staging”inwhichthenumberofgraphiticlayersinbetweenadjacentintercalantscanbevariedinacontrolledfashion.Thestageofacompoundreferstothenumberofgraphiticlayersinbetweenadjacentplanesofintercalant.Theinter-layerspacingcanincreasefrom0.34nm(3.4Å)innativegraphitetomorethan1nminsomeGICs,whichfurtherexaggeratestheanisotropyofmanyproperties.56,58

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