气体吸附理论及应用概论

多孔物质气体吸附理论及应用概论内容简介公司介绍物理吸附和化学吸附的基本理论和方法各种吸附仪的特点和选择原则©2003,QuantachromeInstruments颗粒特性分析测定仪器英国马尔文公司激光衍射粒度分析仪0.02~3500微米500/1000Hz扫描速率激光动态光散射分析仪1~5000纳米/ZETA电位干粉/喷雾粒度分析仪在线粒度分析仪高浓度超声粒度分析仪绝对分子量分布测定仪100~1e12Daltons美国康塔公司全自动比表面及孔隙度分析仪

(分析站数可选1/2/3/6)>0.0005m2/g3.5~5000埃压汞仪3.6纳米~426微米孔径化学吸附仪(TPR/TPD)流动法快速比表面测定仪全自动真密度计自动堆密度分析仪©2003,QuantachromeInstruments粉体比表面和孔隙度分析_________经典文献来自QUANTACHROME©2003,QuantachromeInstruments粉体比表面和孔隙度分析_________经典文献来自QUANTACHROME2004年出版发行©2003,QuantachromeInstrumentsQUANTACHROME-1968

年由纽约长岛大学化学家Dr.S.Lowell教授建立-著名的当代颗粒技术开创者，革新了比表面和孔隙度测量技术并设计了相应的仪器

-康塔(Quantachrome)的仪器不仅受到科学界的青睐,而且已经向全世界的工业实验室发展。

-被公认是对样品权威分析的优秀供应商,它可为实验室提供全套装备及完美的粉体分析技术,及最佳的性能价格比。

-康塔(Quantachrome)公司——开发粉体及多孔材料特性仪器的世界领导者,向中国用户提供全面服务。©2003,QuantachromeInstrumentsFounded1968byDr.S.Lowell,

ProfessorofPhysicalChemistry,

LongIslandUniversity,NewYorkFirstproduct:QuantasorbSurfaceAreaAnalyzerbasedofdynamicflowmethod.Competitor:In1968Micromeritics(founded1963)wasproducingmanuallyoperatedvacuumvolumetricinstrumentwhichproduceddataveryslowly(manyhours).Quantasorbreducedsurfaceareaanalysistimetoaslittleas30minutesenablingmeasurementtobemoreeffectivelyusedinqualityandprocesscontrollabs.HistoryofInnovativeDevelopmentsforcharacterizationofpowdersandporoussolids1972Monosorb–firstdynamicflow,singlepointsurfaceareaanalyzerwithdirectsurfaceareadisplay1972Stereopycnometer–firstcommerciallyavailablegasexpansionpycnometer1978AutoscanMercuryPorosimeter–firstintroductionofcontinuousscanning/pressurization1982Autosorb-6–firstsix-port,highthroughputgassorptionanalyzersimultaneousandindependentanalysisofsixsamples1990NOVASeries–firsthighspeedsurfaceareaanalyzersthatcouldperformmeasurementswithoutheliumvoidvolumedetermination2001NLDFTforzeoliteandmicroporoussilica–firstfulllibraryofadvancedmicroporemodelsbasedonstatisticalmechanicsforadvancedmicroporesizemeasurements2003Hydrosorb–first,highspeed,vacuumvolumetricwatersorptionanalyzer–reducedanalysistimesfromdaystohours!2004Quadrasorb,firstbenchtop,economicallypricedmulti-stationgassorptionanalyzerwithindependentstations.©2003,QuantachromeInstrumentsQuantachrome’sHeadquarters,

BoyntonBeach,Florida,USAQuantachromeCorporationisdedicatedtoprovidingthehighestqualityparticlecharacterizationinstrumentationwhilemaintainingresponsivecustomerserviceandsupport.Quantachrome’sMissionQuantachromePeopleDr.MartinThomas,Director,AppliedTechnologyhasmorethan20yearsprofessionalexperienceinthefieldofparticlecharacterization,13withQuantachrome.HegainedhisPhDfromtheUniversityofBirmingham’sSchoolofChemistry(UK)ashedidhisMastersdegreeinAnalyticalChemistry.HisindustrialexperiencepriortojoiningQuantachromeInstrumentsin1991wasatCooksonGroup’scentralresearchlabandICI’sCatalysisResearchCenter(nowJohnsonMattheyCatalysts).DrThomashashadpublished7peer-reviewedpapersandoneUSpatent,plusanumberofotherarticlesandposters.Heisajointauthorofanewbook(CharacterizationofPorousSolidsandPowders)tobepublishedAugust2004.DrThomasisactiveonanumberofASTMcommitteesandlecturesoccasionallyfortheCenterforProfessionalAdvancement.KeyContactsforInternationalDistributorSupport:©2003,QuantachromeInstrumentsQuantachromePeopleDr.MatthiasThommes,Director,AppliedScience:DoctoralThesisinPhysicalChemistryatRuhr-UniversityBochum(1989-1991)andTechnicalUniversityBerlin,Germany(1992/93).Morethan30publications(andinvitedreview-articles)inref.journalssuchasJournalofPhysicalChemistryB,Langmuir,JournalofChemicalPhysics,AppliedSurfaceScience,Carbon,StudiesinSurfaceScienceandCatalysiset..

Since2001,morethan33presentations(atleast28oralpresentations)andinvitedseminarsatinternationalconferences,symposiaanduniversitiesallovertheworldProfessionalAffiliations:InternationalAdsorptionSocietyAmericanInstituteofChemicalEngineersAmercianChemicalSocietyAmericanSocietyforTestingandMaterials(ASTM)MemberoftheUS-delegationtoworkintheISO(InternationalStandardOrganization)Committee©2003,QuantachromeInstrumentsQuantachromePeopleMr.JeffDixon,InternationalSalesManagerOver10yearsprofessionalexperienceinparticle/porousmaterialscharacterization.JoinedQuantachromeinOctober2003after8+yearswithPMI(alsoinporousmaterialscharacterization)Involvedinthedesignandengineeringofnewporousmaterialscharacterizationtechnologies/instrumentsincludinggasflowtechniques,diffusionpermeametry,watervaporsorption,waterintrusionporosimetry,membranecharacterization.AtQuantachrome:responsibleforInternationalsalesnetwork,applicationsupport,newproductdesignandengineering.ProfessionalAffiliations:ASTMEDANA,TAPPI,INDA(papers,nonwovens).©2003,QuantachromeInstrumentsQuantachromePeopleDr.JacekJagiello,Manager,ApplicationSupportandTraining.Adsorptionspecialistwithspecialinterestinunderstandingandcharacterizationofactivatedcarbons.DoctoratefromM.Curie-SklodowskaUniversity,Lublin,Poland(1994.PostdoctoralresearchassociateatCNRS,Mulhouse,Francefrom1998to1990.PostdoctoralresearchassociateatSyracuseUniversity,NewYorkfrom1990-1996.From1996-2000intheCarbonResearchGroupofWestvacoCorporation(Charleston,SouthCarolina)Authorandco-authorofmorethan80scientificpublicationswithnumerousinternationalpresentationsandfourUSpatents.©2003,QuantachromeInstrumentsQuantachromePeopleMarkContessa,ServiceManagerMarkbeganhiscareerwitha4yeartermintheUSNavywherehegainedexperienceinelectronics.Markworkedfor10yearsforamajorUSdefensecontractor.JoinedQuantachromeover12yearsago,andhasheldthepositionofServiceManager.Markisresponsibleforallareasofservice,andmanagesateamoffieldserviceengineers.Markhastraveledextensively,including2tripstoChina.©2003,QuantachromeInstrumentsQuantachrome

Firsts

Quantachromehasseveralachievementswhichare:a)DevelopmentoftheMonosorb®,thefirstsingle-point,dynamicflowB.E.T.surfaceareainstrumentb)Developmentofa“continuousscanporosimetry”, utilizedinthePoremaster®poresizeanalyzersc)Developmentofthefirst“commerciallyviable”gaspycnometersd)DevelopmentoftheAutosorb-6®,thefirstmulti-station surfaceareaandporesizeanalyzerwiththeability toconductsimultaneousandindependent measurements©2003,QuantachromeInstrumentsDevelopmentofthefirst“commerciallyviable”gas-expansionpycnometers!AQuantachrome®First!DevelopmentoftheMonosorb®,thefirstsingle-point,dynamic-flowBETinstrumentwithdirectsurfaceareareadout!AQuantachrome®First!Developmentofthepatentedcontinuous-scanningmercuryporosimetersutilizedintheQuantachromePoreMaster®poresizeanalyzers!AQuantachrome®First!DevelopmentoftheAutosorb®-6,thefirstmulti-stationsurfaceareaandporesizeanalyzerwiththeabilitytoconductindependentandsimultaneousmeasurements!AQuantachrome®First!NOVAe系列全自动比表面及孔隙度分析仪时尚流线型外观设计操作空间加大歧管死体积减小1.7ml杜瓦工作时间延至30小时/次4个脱气站和4个分析站，可同时进行8个样品的处理和分析符合美国FDA21CFRPart11标准©2003,QuantachromeInstrumentsQUADRASORBSI全自动4站比表面和孔隙度分析仪©2003,QuantachromeInstrumentsAutosorb-1MP微孔型高端比表面和孔隙度分析仪具有五个压力传感器和一个液位传感器极限真空达10-10mmHgBET比表面微孔,介孔和大孔的孔径分布微孔体积和面积氪吸附测超低比表面CO2andH2吸附研究蒸汽吸附©2003,QuantachromeInstrumentsRifflersRotaryMicroRiffler®InstrumentsforRepresentativeSamplingSpinningrifflersforaccuraterepresentativesamplingofpowdersandgranularmaterial.Operatorselectablefeedrateandcollectorrotationspeed.Maximumcapacity:RotaryMicroRiffler/120ccSievingRiffler/2500ccSievingRiffler®多孔材料的物理吸附理论分析背景知识吸附理论孔隙度测量评注及结论©2003,QuantachromeInstruments多孔材料的应用©2003,QuantachromeInstruments孔隙度©2003,QuantachromeInstruments

什么是表面积?

SurfaceArea–whatisit?“表面是固体与周围环境,特别是液体和气体相互影响的部分;表面的大小即表面积.”“SurfaceAreaisthemeansthroughwhichasolidinteractswithitssurroundings,especiallyliquidsandgases.”表面积可以通过颗粒分割(减小粒度)和生成孔隙而增加.Surfaceareaiscreatedbydivisionofparticles(sizereduction)andthegenerationofporosity.表面积可以通过烧结,熔融和生长而减小.Surfaceareaisdestroyedbysintering(exceedingTg),meltingandOstwaldripening.©2003,QuantachromeInstruments为什么表面积如此重要?

SurfaceArea–Importance?请记住:表面积是固体与周围环境,特别是液体和气体相互作用的手段和途径.Rememberthatsurfaceareaisthemeansthroughwhichasolidinteractswithitssurroundings.

考虑下列三种作用:Considerthefollowingthreeinteractions:固体-固体:自动粘结,流动性(流沙),压塑性Solid-Solid:autohesiveness(cohesiveness)egflow,compactibilityetc.固体-液体:浸润,非浸润,吸附能力等Solid-Liquid:wetting,non-wetting,adsorptioncapacityetc.固体-气体:吸附,催化等Solidgas:adsorption,catalysis,etc.©2003,QuantachromeInstruments孔的类型交联孔(开孔)闭孔盲孔(开孔)通孔(开孔)©2003,QuantachromeInstruments孔形的分类筒形孔筒形孔锥形孔裂隙孔球形孔(墨水瓶孔)©2003,QuantachromeInstruments孔径的分类

(IUPACStandard)

©2003,QuantachromeInstruments表面积测定方法

Suitablemethodsofdetermination气体吸附法是测量所有的表面,包括不规则的表面和开孔内部的面积.

Gasadsorptionallowsprobingofentiresurfaceincludingirregularitiesandporeinteriors.吸附量是温度,压力和亲和力或作用能的函数.

Theamountadsorbedisafunctionoftemperature,pressureandthestrengthofattractionorinteractionpotential.

物理吸附一般是弱的可逆吸附.固体必须被冷却,并且确定一种方法从可能的单分子覆盖中计算表面积.

Physisorptionisgenerallyweakandreversible.Thesolidmustbecooledandamethodusedtoestimatethemonolayercoveragefromwhichsurfaceareacanbecalculated.©2003,QuantachromeInstruments孔隙度测定方法

----气体吸附法仅测量开孔有效范围:0.4-50nm容易操作成熟技术©2003,QuantachromeInstruments孔隙度测定方法

----压汞法类似于气体吸附仅测量开孔有效范围:>3.6nm容易操作成熟技术©2003,QuantachromeInstruments孔隙度测定方法

----透射电镜提供有关孔交联信息如果材料含有有序孔,则可正确反映孔径几乎不用于孔分析©2003,QuantachromeInstruments孔隙度测定方法

----扫描电镜孔径:>5nm几乎不用于孔分析©2003,QuantachromeInstruments孔隙度测定方法

----小角X-射线扫描法任何孔径用于开孔+闭孔的孔分析©2003,QuantachromeInstruments孔隙度测定方法

----小角中子散射法(SAN)任何孔径用于开孔+闭孔的孔分析价格昂贵©2003,QuantachromeInstruments

吸附原理

©2003,QuantachromeInstruments固体材料对气体的吸附现象1、化学吸附--是气体分子与材料表面的化学键合过程只发生单层吸附选择性吸附(特定气体主要H2,CO,O2对体系中各组分的特定吸附)2、物理吸附--是由范得华力引起的气体分子在固体表面及孔隙中的冷凝过程可发生单层吸附,多层吸附非选择性吸附气体分子在固体表面的吸附机理极为复杂，其中包含化学吸附和物理吸附©2003,QuantachromeInstruments物理吸附和化学吸附的比较©CopyrightQuantachromeCorporation2000.Allrightsreserved.气体吸附过程静态描述吸附物吸附物多层饱和吸附随机性非饱和吸附单层饱和吸附可计算比表面积可计算总孔容积©2003,QuantachromeInstruments气体吸附通过固体表面上气体吸附量多少来计算粉体或多孔固体的比表面积比表面积的测量包括能够到达表面的全部气体，无论外部还是内部。©CopyrightQuantachromeCorporation2000.Allrightsreserved.气体吸附一般而言，在范德华力作用下，固体吸附气体是弱键作用。为了使足够气体吸附到固体表面，测量时固体必须冷却，通常冷却到吸附气体的沸点。通常氮气作为被吸附物，因此固体被冷却到液氮温度(77.35K)©CopyrightQuantachromeCorporation2000.Allrightsreserved.气体吸附过程4)©CopyrightQuantachromeCorporation2000.Allrightsreserved.吸附等温线在密封容器中，某种材料在特定温度下对气体的吸附量与吸附平衡后的压力有其特殊的对应关系III0P/P01.0IV0P/P01.0V0P/P01.0II0P/P01.0IIIVVVV0P/P01.0V©2003,QuantachromeInstrumentsVeryLowpressurebehavior(microporefilling)©2003,QuantachromeInstrumentsLowpressurebehavior(monolayer)The“knee”©2003,QuantachromeInstrumentsMediumpressurebehavior(multilayer)©2003,QuantachromeInstrumentsHighpressurebehavior(capillarycondensation)©2003,QuantachromeInstrumentsSchematicillustrationofthesorption,porecondensationandhysteresisbehaviorofafluidinasinglecylindricalmesopore©2003,QuantachromeInstruments具有微孔的氮吸附等温线©2003,QuantachromeInstruments由国际纯粹与应用化学联合会（IUPAC）提出的物理吸附等温线分类©2003,QuantachromeInstrumentsI型等温线的特点在低相对压力区域，气体吸附量有一个快速增长。这归因于微孔填充。随后的水平或近水平平台表明，微孔已经充满，没有或几乎没有进一步的吸附发生。达到饱和压力时，可能出现吸附质凝聚。外表面相对较小的微孔固体，如活性炭、分子筛沸石和某些多孔氧化物，表现出这种等温线。©2003,QuantachromeInstrumentsII型和III等温线的特点II型等温线一般由非孔或大孔固体产生。B点通常被作为单层吸附容量结束的标志。III型等温线以向相对压力轴凸出为特征。这种等温线在非孔或大孔固体上发生弱的气－固相互作用时出现，而且不常见。©2003,QuantachromeInstrumentsIV型等温线的特点IV型等温线由介孔固体产生。典型特征是等温线的吸附曲线与脱附曲线不一致，可以观察到迟滞回线。在p/p0值较高的区域可观察到一个平台，有时以等温线的最终转而向上结束(不闭合)。©2003,QuantachromeInstrumentsV和VI型等温线的特点V型等温线的特征是向相对压力轴凸起。V型等温线来源于微孔和介孔固体上的弱气－固相互作用，而且相对不常见。VI型等温线以其吸附过程的台阶状特性而著称。这些台阶来源于均匀非孔表面的依次多层吸附。这种等温线的完整形式，不能由液氮温度下的氮气吸附来获得。©2003,QuantachromeInstruments迟滞回线类型©2003,QuantachromeInstruments迟滞回线类型

按照IUPAC

13.2节中的约定，划分出了4种特征类型H1型迟滞回线可在孔径分布相对较窄的介孔材料，和尺寸较均匀的球形颗粒聚集体中观察到。©2003,QuantachromeInstruments迟滞回线类型

按照IUPAC

13.2节中的约定，划分出了4种特征类型H2型迟滞回线由有些固体，如某些二氧化硅凝胶给出。其中孔径分布和孔形状可能不好确定，比如，孔径分布比H1型回线更宽。©2003,QuantachromeInstruments迟滞回线类型

按照IUPAC

13.2节中的约定，划分出了4种特征类型H3型迟滞回线由片状颗粒材料，如粘土，或由裂隙孔材料给出，在较高相对压力区域没有表现出任何吸附限制。©2003,QuantachromeInstruments迟滞回线类型

按照IUPAC

13.2节中的约定，划分出了4种特征类型H4型迟滞回线出现在含有狭窄的裂隙孔的固体中，如活性炭中见到，在较高相对压力区域也没有表现出吸附限制。©2003,QuantachromeInstruments迟滞环与孔形的关系©2003,QuantachromeInstruments气体吸附

可见,气体吸附量随着压力的升高而增加，但不是线性的。如何测量? 如果气体充分的覆盖在固体表面(单层)的体积是已知的，就能够精确地计算出比表面积。©CopyrightQuantachromeCorporation2000.Allrightsreserved.气体吸附分析仪分析方法:在等温条件下，通过测定不同压力下材料对气体的吸附量,获得等温吸附线，应用适当的数学模型推算材料的比表面积,多孔材料的孔容积及孔径分布，多组分或载体催化剂的活性组分分散度表面积及孔径分布测量可采用多种不同方法，气体吸附法作为一种应用性最广、测量精度最高的方法被普遍接受©2003,QuantachromeInstruments测量方法流动法把30%氮气(被吸附物)和70%氦气(载体)的混合气体不断在样品上进行流动。当样品冷却到液氮温度时，氮气被吸附，而氦气不被吸附。吸附过程持续，直到氮气吸附量达到30%浓度。这时，吸附量接近于单层表面覆盖的体积。©CopyrightQuantachromeCorporation2000.Allrightsreserved.流动法Flow通过用非吸附的氦气稀释氮气(吸附质)获得P/Po

.

RequiredP/Poisachievedbydilutingnitrogen(adsorbate)withhelium(non-adsorbing).

样品被冷却至液氮温度而引起吸附.

Thesampleiscooledwithliquidnitrogen,tocauseadsorption.吸附(及随后的脱附)过程是由热导检测器监测的.Theadsorption(andsubsequentdesorption)processismonitoredusingathermalconductivitydetector.

©2003,QuantachromeInstruments动态流动法DynamicFlow 信号校正是通过将已知体积的纯氮气注入到气流中进行的.Thesignaliscalibratedagainstaknownvolumeofpurenitrogeninjectedintothegasstream.

该方法极其快速,特别适用于单点BET法对生产过程的监控.Themethodisextremelyrapidandideallysuitedtomanufacturingprocessesusingthesinglepointmethod.

可用氪吸附作超低比表面.Verydiluteconcentrationofkryptonatliquidnitrogentemperatureisusedforextremelylowsurfaceareas.©2003,QuantachromeInstruments(经典的)真空-体积测定法

(Classical)Vacuum-Volumetric需要在降低的温度下,由样品吸附吸附质作为纯吸附作用的函数.

Requiresthatadsorbatebeadsorbedbythesample,atsomereducedtemperature,asafunctionofpressureofpureadsorptiveP/Po值(相对压力)是通过制造局部真空做到的.P/Povaluesareachievedbycreatingconditionsofpartialvacuum.

在吸附过程中由高精度压力传感器监测压力的改变.

Highprecisionandaccuratepressuretransducersmonitorpressurechangesduetotheadsorptionprocess.©2003,QuantachromeInstruments测量方法真空法样品池抽真空测量空体积(样品池空间)A)用氦气测量B) 存储器里存有的校对值.样品冷却到液氮温度，然后氮气注入到已知参考体积(歧管)的样品池。由于氮气注入空体积而膨胀，导致压力下降，而氮气充满空体积时的压力下降是能够计算的。因此通过压力的下降来计算气体吸附量。©CopyrightQuantachromeCorporation2000.Allrightsreserved.真空法-气体体积测量关键样品的前处理(足够的真空脱气去除微孔中的杂质)通过制造局部真空条件测量P/Po值.通过高精准度的压力传感器监测气体吸附过程中的压力变化(微孔测量需多个压力传感器同时监测Po,样品管压力和歧管压力).微孔测量须尽量降低死体积(控制样品管在液氮中的深度.©2003,QuantachromeInstruments样品准备----必须让吸附质”看到”表面

SamplepreparationTheadsorbatehasto“see”therealsurface.

随时发生的微量潮气吸附并不影响单分子层能力,但会影响吸附的强度,所以与在一个清洁表面上比较,单分子层的形成压力会发生改变.

Whilstalittlepre-adsorbedmoisturewouldn'taffectthemonolayercapacity,itwouldaffectthestrengthwithwhichitisadsorbed,sothemonolayerwouldbeformedatadifferentpressurethanonacleansurface.孔道因毛细作用极易被潮气阻塞.

Porescanbeeasilyblockedbymoisture.Waterundergoescapillarycondensationathumiditieswellbelowbulksaturationintheconfinesofthepore(justasnitrogendoesaswewillseelater).微孔能完全被填满,不再是阻塞!

Microporescanbecompletelyfilled,notjustblocked!我们始终提供的是单位干重的表面积.

Wealwaysquotesurfaceareaperunitofdrymass.©2003,QuantachromeInstruments表面脱气OutgassingofSurface在适宜的加热温度下,样品通过真空的应用或干燥惰性气体的流动除去吸附污染物的过程,主要是水汽.Sampleiscleanedofadsorbedcontaminants,mainlymoisture,bytheapplicationofvacuumorflowofdryinertgasandpreferablysomeheat.加热到多高温度?Howmuchheat?©2003,QuantachromeInstruments表面脱气OutgassingofSurface如何选择样品的脱气温度?

Whatisthepropertemperatureforsamplepreparation?在不改变样品表面特性的前提下,应选择足够高的温度以快速除去表面吸附物质.Shouldbehighenoughtopromoterapidremovalofsurfaceadsorbedspecieswithoutchangingthesurfacetexture.不能高于固体的熔点或玻璃的相变点,Tg

.Obviouslynothighenoughtomeltthesolid,norhotenoughtoexceedtheglasstransitionpoint,Tg.EstimateTgasmeltingpt0.7inkelvin(allowsafetymargin).建议不要超过熔点温度的一半.Ornomorethanmeltingpoint0.5(kelvin)–Tammanntemperature.

举例:硬脂酸镁:40°C(for2hours)

Example:MagnesiumStearatemonograph:40°C(for2hours)©2003,QuantachromeInstruments真空脱气还是流动脱气?

Vacuumorflow流动脱气对于除去表面大量弱结合的吸附水是非常好的,但对孔中吸附的水,只有经长时间吹扫使之扩散至表面,才能被带出.

Aflowisgoodatremovinglargequantitiesofweaklybonded“wet”waterbydisplacementofthevaporfromexternalsurfaces.Howeverinthedepthsofapore,watermustdiffuseout…andindoingsomustbattlepastamuchhigherconcentrationofpurgegas.Onlywhenitisoutoftheporewillitbephysicallysweptaway.©2003,QuantachromeInstruments真空脱气还是流动脱气?

Vacuumorflow真空脱气对于除去表面大量弱结合的吸附水是不好的,因为水会在泵中扩散.但对孔中吸附的水,不需要经很长时间就能扩散至表面,继而被带出.

Vacuumisnotsogoodatremovinglargequantitiesofweaklybonded“wet”watersinceonceithasleftthesampleitmustdiffusetowardsthepump.(A“randomwalk”willmaketheactualdistanceneededtotravelMUCHfurtherthanitlookstous!Itwillspendmuchofitstimewanderingbacktowardsthesample!).Howeverinthedepthsofapore,watermustdiffuseout…andindoingsodoesnothavetobattlepastmuch-certainlynotanypurgegas.©2003,QuantachromeInstruments如何防止粉末样品扬析?PowderThimblesCellSealN/ECellkit©2003,QuantachromeInstruments吸附剂被吸附物吸附描述©CopyrightQuantachromeCorporation2000.Allrightsreserved.IrvingLangmuir(1881-1957)GraduatedasametallurgicalengineerfromtheSchoolofMinesatColumbiaUniversityin19031903-1906M.A.andPh.D.in1906fromGöttingen.1906-1909InstructorinChemistryatStevensInstituteofTechnology,Hoboken,NewJersey.1909–1950GeneralElectricCompanyatSchenectadywhereheeventuallybecameAssociateDirector1913-Inventedthegasfilled,coiledtungstenfilamentincandescentlamp.1919to1921,hisinterestturnedtoanexaminationofatomictheory,andhepublishedhis"concentrictheoryofatomicstructure".Initheproposedthatallatomstrytocompleteanouterelectronshellofeightelectrons/alp/plasma/history.html1927Coinedtheuseoftheterm"plasma"foranionizedgas.1935-1937WithKatherineBlodgettstudiedthinfilms.1948-1953WithVincentSchaeferdiscoveredthattheintroductionofdryiceandiodideintoasufficientlymoistcloudoflowtemperaturecouldinduceprecipitation.1932TheNobelPrizeinChemistry"forhisdiscoveriesandinvestigationsinsurfacechemistry"©2003,QuantachromeInstrumentsConfiningadsorptiontoamonolayer,theLangmuirequationcanbewritten

whereVisthevolumeofgasadsorbedatpressureP,Vm

isthemonolayercapacity(i.e.θ=1)expressedasthevolumeofgasatSTPandKisaconstantforanygivengas-solidpair.Rearrangingintheformofastraightline(y=ab+x)gives

Langmuirianbehavior©2003,QuantachromeInstruments吸附剂被吸附物朗格缪尔理论©CopyrightQuantachromeCorporation2000.Allrightsreserved.吸附剂BET理论©CopyrightQuantachromeCorporation2000.Allrightsreserved.比表面积测定原理--BET法对于上述五种等温线有许多种解释，其中最成功的是BRUMAUER-EMMETT-TELLER三人在1938年提出的多分子层吸附理论由该理论得到的方程式称为BET公式

P1C-1PV（P0-P）=VmC+VmC*P0在P/P0为0.05-0.35范围内可得一直线,通过斜率和截距可求得Vm(单层饱和吸附量)比表面积=VmN0/22400WN0为阿佛加得罗常数,为一个吸附分子截面积©2003,QuantachromeInstruments比表面积计算B.E.T.方法1 = 1 C-1 P---------------- ---------------+--------------------V[(Po/P)–1] VmC VmCPowhere:V=吸附气体体积Vm=单层吸附时需要的气体体积C=B.E.T.常数P/Po=被吸附气体的相对压力方程式的等式为

Y=aX+b,plotYvX©CopyrightQuantachromeCorporation2000.Allrightsreserved.比表面积计算B.E.T.图表斜率(s)=C-1VmC截距(i)=1 VmCVm=1 s+iStotal=VmN Axs

22,414P/Po1w[(Po/P)-1]0-10-20-3©CopyrightQuantachromeCorporation2000.Allrightsreserved.Where,N=Avogadro’snumber

Axs=cross-sectionalareaofadsorbatemoleculeBET公式:只能用于类型II,IV常数“C”与吸附能量有关C∝（E吸附-E蒸发）/RT必须为正值低值为弱吸附，低表面的固体“C”值范围C=2-50,有机物,高分子与金属C=50-200,氧化物,氧化硅C=>200活性碳,分子筛©2003,QuantachromeInstruments含有微孔样品的BET计算活性炭样品举例:BET计算范围为0.05-0.1(P/P0)多数符合Langmiur方程务必使C值大于0保持回归系数优于0.9999©2003,QuantachromeInstruments单点与多点的比较相对误差©CopyrightQuantachromeCorporation2000.Allrightsreserved.©2003,QuantachromeInstruments在MONOSORB中对单点BET的校正©2003,QuantachromeInstruments不同孔径的多孔材料吸附等温线比较

NitrogenSorptionat77KintoMesoporousTiO26nm10nm30nm100nmH.Kueppers,B.Hirthe,M.Thommes,G.I.T,3(2001)110©2003,QuantachromeInstruments常用的比表面和孔径分析吸附质

CommonlyusedAdsorptivesforSurface-andPoresizeAnalysis氮气：at77.35K(liquidnitrogentemperature,T/Tc=0.61)比表面分析,微孔,介孔和大孔的孔径分析最常用，易得高纯度，价廉，液氮也易得气固作用较强，公认的分子截面积氩气：at77.35K(T–Tr=-6.5K;Tr:

bulktriplepointtemperature;T/Tc=0.50)at87.27K(liquidargontemperature,T/Tc=0.57)比表面分析,微孔,介孔和大孔的孔径分析最理想，无特别作用，可测微孔及中孔可在较高的相对压力下（10-5-10-3)获得微孔数据（0.3–1nm）扩散快（液氩温度高，87.3K)，平衡快，实验时间短也可用液氮，但不能用于大于12nm的孔，因为77.3K比氩的三相点还低6.5K，所以在较大孔内不能凝聚氪气：at77.35K(T–Tr=-38.5K)

测量超低比表面at87.27K(T–Tr=-28.5K)poresizeanalysisofthinmicro/mesoporousfilms(M.Thommesetal,2004)用于非孔或大孔材料，因为氪气的Po(=2.6t)很小在P/Po=0.05与0.25之间（NOVA不能用）CO2

:

at195K(T/Tc=0.63)at273K(T/Tc=0.89)poresizeanalysisofmicroporesofwidths<1.5nm(particularlyformicroporouscarbons)©2003,QuantachromeInstruments氮气在77.4K的吸附：40小时©2003,QuantachromeInstrumentsCO2在273K的吸附：2.75小时©2003,QuantachromeInstruments孔分布分析©2003,QuantachromeInstruments孔结构的测定气体吸附法测定孔径的经典方法是以毛细管凝聚理论为基础的KELVIN公式(最简化的孔模型):P平面P孔液体在细管中形成弯月面,在细管中凝聚时所需压力较小,P孔<P平面,因此增压时气体先在小孔中凝结,然后才是大孔.©2003,QuantachromeInstrumentsKelvin方程式Pore孔分布-根据样品选择不同的模型理论©CopyrightQuantachromeCorporation2000.Allrightsreserved.孔分布计算方法©2003,QuantachromeInstrumentsBJH(Barrett-Joyner-Halenda)法

只能用于中孔(>5nm),柱状模型在壁上有多重吸附,类似液体,须假定液体密度用吸附与脱附等温线,层层计算法当<10nm时低估孔径,<5nm20%误差MesoporesPn-1rn-1Pnrn©2003,QuantachromeInstrumentsNitrogenadsorption/desorptionat77.35Konadisorderedaluminacatalyst

andporesizedistributioncurves

(TSE现象-张力强度效应)BJH-PSD无序介孔脱附的”突跃”与吸附剂无关,而与吸附质有关©2003,QuantachromeInstrumentsBJH孔径分布:在脱附曲线上的假峰40PoreDiameter(angstrom)dV/dlogDArtifact©2003,QuantachromeInstruments最完全的数据处理方法与模型

比表面：BET,Langmuir(微孔),DR,BJH,DH

中孔分布：BJH,DH

微孔分布：DA(DR理论的扩展),HK,SF

微孔/中孔分布：MP,DFT

微孔体积：t-方法，DR(含平均孔宽,分子筛和活性碳等微孔表征）分形维数：FHH,NK

总孔体积，平均孔径©2003,QuantachromeInstrumentsComparisonsGasSorptionCalculationMethods

P/Porange Mechanism Calculationmodel1x10-7to0.02 microporefilling DFT,GCMC,HK,SF,DA,DR0.01to0.1 sub-monolayerformation DR0.05to0.3 monolayercomplete BET,Langmuir>0.1 multilayerformation t-plot(de-Boer,FHH),>0.35 capillarycondensation BJH,DH 0.1

to0.5capillaryfilling DFT,BJH inM41S-typematerials©2003,QuantachromeInstruments孔径数据孔径与孔体积可从吸附或脱附数据求得孔的总体积(V)从吸附总的气体体积转化成液体体积而得平均孔径从简单的柱状求得A

是BET表面积©2003,QuantachromeInstruments用t-图法估算微孔对每一类材料,用标准的非孔样品得到参考的t-曲线t-曲线由P/Po对t(=Vliq/S)作图得到从等温线与t-曲线中取同P/Po的点作图可得到微孔体积,外表面积(非BET法)如不用参考t-曲线,而用总表面积未知的等温线,则有a-图法©2003,QuantachromeInstruments只有中孔的t-图Slope=V/t=AZerointercept©2003,QuantachromeInstruments有微孔的t-图Intercept=microporevolume©2003,QuantachromeInstruments有”膝”的t-图SlopeA-slopeB=areacontributionbymicroporessizeCACB©2003,QuantachromeInstrumentsAspectsofRecentAdvancesintheCharacterizationofPowdersandPorousSolidsbyGasAdsorption

气体吸附法表征粉末及多孔物质的最新进展QuantachromeINSTRUMENTS

JeffreyYang(杨正红,康塔仪器公司首席代表)andMatthiasThommes(QuantachromeInstruments)©2003,QuantachromeInstruments气体吸附法进行孔径分析

PoreSizeAnalysisbyGasAdsorption宏观的热力学方法(Macroscopic,thermodynamicmethods)Micropores(<2mn):e.g.,Dubinin-RadushkevitchormoreadvancedmethodssuchasHorvath-Kawazoe (HK)andSaito-Foley(SF),t-method,alpha-smethodMeso/Macropores(2-100nm):e.g.,KelvinequationbasedmethodssuchasBJH(Barrett,Joyner,Halenda)现代微观方法-基于在分子水平上描述被吸附分子状态的统计力学:

(Modern,microscopicmethods,basedonstatisticalmechanics家describeconfigurationofadsorbedmoleculesonamolecularlevel)e.g.,DensityFunctionalTheory(DFT),MolecularSimulation

thesemethodsareapplicableforporesizeanalysisofboththemicro-andmesoporesizerange

用统一方法在整个孔分布范围内准确地进行孔径分析Anaccurateporesizeanalysisoverthecompleteporesizerangecanbeperformedbyasinglemethod.©2003,QuantachromeInstruments在87K的氩吸附

ArgonAdsorptionat87.27K由于氩与孔壁的吸引作用较弱(缺少四极矩),它可以比氮在相对高得多的压力下填充0.4-0.8nm的微孔(至少高1.5个数量级).

Due