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Colloids and Surfaces A: Physicochem. Eng. Aspects 425 (2013) 122–128 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects j our nal homepage: www. el sevi er . com/ l ocat e/ col sur f a Enhanced soil washing of phenanthrene by a plant-derived natural biosurfactant, Sapindus saponin Wenjun Zhou a,b,∗ , Xuehao Wang a , Cuiping Chen a , Lizhong Zhu a,b a Department of Environmental Science, Zhejiang University,
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  ColloidsandSurfacesA:Physicochem.Eng.Aspects 425 (2013) 122–128 ContentslistsavailableatSciVerseScienceDirect Colloids   and   Surfaces   A:   Physicochemical   andEngineering   Aspects  journalhomepage:www.elsevier.com/locate/colsurfa Enhanced   soil   washing   of    phenanthrene   by   a   plant-derived   naturalbiosurfactant,   Sapindus   saponin Wenjun   Zhou a , b , ∗ ,   Xuehao   Wang a ,   Cuiping   Chen a ,   Lizhong   Zhu a , b a DepartmentofEnvironmentalScience,ZhejiangUniversity,Hangzhou,Zhejiang310058,China b  ZhejiangProvincialKeyLaboratoryofOrganicPollutionProcessandControl,Hangzhou,Zhejiang310058,China h   i   g   h   l   i   g   h   t   s ã  Enhancing   soilwashing   of    anatu-ralbiosurfactant   of    Sapindus   saponinwasstudied. ã  Sapindus   saponin   showed   greatwashing   capability   for   phenanthrenecontaminated   soil. ã  Sorption   of    Sapindus   saponin   onsoilwasmuch   less   thansynthetic   surfac-tants. ã  Sapindus   saponin   solution   can   berecovered   after   soil   washing. g   r   a   p   h   i   c   a   l   a   b   s   t   r   a   c   t The   washing   efficiencies   of    Sapindus   saponin   for   phenanthrene   contaminated   soilwere   only   slightly   lessthanthose   of    Tween   80,   and   Sapindus   saponin   solutions   can   be   recovered   for   their   reusage   after   soilwashing   byusing   organo-bentonite   to   remove   phenanthrene   from   the   washed   surfactant   solutions   withanappropriate   dosage. a   r   t   i   c   l   e   i   n   f   o  Articlehistory: Received8November2012Receivedinrevisedform17February2013Accepted28February2013 Available online 6 March 2013 Keywords: Biosurfactant Sapindus saponinSoilwashingPhenanthrenepHRecovery a   b   s   t   r   a   c   t Biosurfactants   have   great   advantages   for   using   in   environmental   remediation   as   their   environmentalfriendly   nature.   Inthis   study,   a   plant-derived   natural   biosurfactant   of    Sapindus   saponin   was   extractedfromthe   fruit   pericarps   of    Sapindus   mukorossi   (Chinese   soapberry),   and   the   properties   of    this   biosurfactantinenhancing   washing   for   phenanthrene   contaminated   soilwere   investigated   and   compared   with   those   of Tween80,   arepresentative   synthetic   nonionic   surfactant.   Sapindus   saponin   showed   alinear   solubilizationenhancement   for   phenanthrene   and   the   weight   solubilization   ratio   was   0.0312   and   about   one   third   of that   of    Tween   80.   However,   Sapindus   saponin   can   effectively   remove   phenanthrene   from   contaminatedsoil   with   amaximum   removal   percentage   of    about   87.4%,   which   was   only   slightly   less   than   that   of    Tween80(about   91.5%)   because   the   sorption   of    Sapindus   saponin   onto   soil   was   much   less   thanthat   of    Tween80.   The   solubilization   enhancement   of    Sapindus   saponin   for   phenanthrne   and   the   sorption   of    Sapindus saponin   onto   soil   both   decreased   with   increasing   solution   pH,   the   net   results   of    which   resulted   in   that   themaximumwashing   efficiency   of    Sapindus   saponin   for   phenanthrene   contaminated   soil   was   obtained   atpHaround   6.0.   Sapindus   saponin   solutions   can   be   recovered   for   their   reusage   after   soil   washing   byusingorgano-bentonite   to   remove   phenanthrene   from   the   washed   surfactant   solutions   with   an   appropriatedosage.   Sapindus   saponin   showed   afavorable   performance   in   enhancing   soil   washing   and   should   havethe   potential   application   in   soilwashing   technology   for   the   remediation   of    organic   contaminated   soilsand   groundwater. © 2013 Elsevier B.V. All rights reserved. ∗ Correspondingauthorat:DepartmentofEnvironmentalScience,ZhejiangUniversity,Hangzhou,Zhejiang310058,China.Tel.:+8657188982591;fax:   +8657188982591. E-mailaddress: wenjunzhou@zju.edu.cn (W.   Zhou).0927-7757/$–seefrontmatter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfa.2013.02.055  W.    Zhouetal./ColloidsandSurfacesA:Physicochem.Eng.Aspects 425 (2013) 122–128 123 1.Introduction Thecontaminationofsoilsandgroundwaterbytoxicand/orhaz-ardousorganicpollutantsisawidespreadenvironmentalproblem.Theremovalofhydrophobicorganiccompounds(HOCs)fromcon-taminatedsoilsorgroundwaterisbecomingamajorconcernastheirwater-insolublecharacteristicsmay   retainthosecompoundsinsolidphaseandthenposealong-termthreattoecologicalsafetyandhumanhealth[1].   SurfactantenhancedsoilwashinghasbeensuggestedasoneofthepromisingtechnologiesfortheremediationofHOCs-contaminatedsoilsandgroundwaterinrecentyears[2,3].Afewstudiesforthepracticalapplicationofsurfactantsin insitu or exsitu soilwashingindicatedthepotentialofusingsurfactantstocleanuptheresidualandsorbedHOCsfromthefield-contaminatedsoilsandsubsurfaceenvironments[1].Enhancedsoilwashinggenerallyhasbeenperformedwithsyn-theticsurfactants,includinganionic,nonionic,cationicandmixedsurfactants,andsomeofthemhaveshowngreatwashingcapa-bilitiesforHOCsfromcontaminatedsoilsandgroundwater[1].However,theresidualsyntheticsurfactantsinsoilsandground-waterhavethepotentialtoxicityriskorhazardtoenvironmentandhumanhealth.So,animprovedstrategyforsoilwashingtech-nologyistousethesurfactantswithlowenvironmentalimpact.Recently,biosurfactantscausedincreasinginterestinsoilwashingtechnologybecausetheygenerallyexhibitedgreaterenvironmen-talcompatibility,lowertoxicity,andhigherbiodegradabilityincomparingwithsyntheticsurfactants[4–7].Biosurfactantsarenaturalcompoundsandfoundinanimals,plantsandmicrobes.Somestudieshaveshownthatbiosurfactantscanalsoeffectivelyenhancetheremovaland/orbiodegradationof HOCsincontaminatedsoils[5,6].Therefore,biosurfactantsseemto bebettercandidatesforusinginsoilwashingtechnology.However,literaturedataindicatedthatmostofpreviousstudieshavefocusedonmicrobialbiosurfactantsproducedbyyeastorbacteria,includ-ingrhamnolipids,surfactin,sophorolipidsandsoon[4–6].More otherbiosurfactantsshouldbeinvestigatedfortheirpropertiesinenhancingsoilwashingbecausetheymay   havemorepromisingproperties, e.g. ,   theplant-derivedbiosurfactants.Saponinsareaclassofnaturalbiosurfactantsandwidelydis-tributedinplantkingdom[8].   Somenaturalsaponinshavebeentraditionallyusedasdetergentforfabricwashing,hairandbodycleaningandinfolkmedicine.Afewstudieshaveshownthatsaponinscaneffectivelyremoveheavymetalorcrudoilfromcontaminatedsoils[6,9–11]andalsoshowedgreatsolubilization capabilityforPAHs[7].   So,saponinshavethepotentialcapabilityinenhancingHOCsremovalfromcontaminatedsoilsandground-water.Saponinsexistingindiverseplantspeciesgenerallyshowgreatdifferenceintheirstructureandproperties[8].However,almost allofpreviousstudiesforsaponinsinenvironmentapplicationfocusedon Quillaja saponinobtainedfromthebarkextractsoftheSouthAmericantree QuillajaSaponaria [5–7,9–11]becausethereexistsonlyafewplantsprovidingalargersourceofsaponins,henceareworthextractingforcommercialuse. Sapindusmukorossi Gaerth(Chinesesoapberry)isasaponin-richplantwithitsfruitsandwidelydistributedinChinaandothertropicalandsubtropicalregionsofAsia[12–14].Thefruitpericarpof  S.mukorossi containsofupto10%byweightof  Sapindus saponinthatmakesittobeoneofthestrongestcommercialsourcesforsaponin. Sapindus saponinhaswideapplicationcurrentlyasadditivesinmedicines,cleansers,beverages,confectioneryandcosmetics[8,15].   However,fewsci-entificresearcheshavereportedtheenvironmentapplicationof  Sapindus saponin.Inthisstudy,theplant-derivednaturalbiosurfactantof  Sapin-dus saponinwasextractedfromthefruitpericarpof  S.mukorossi ,andthepropertiesofthisbiosurfactantinenhancingsolubilizationandsoilwashingforphenanthrenewereinvestigated,meanwhilethecorrespondingeffectofpHwas   evaluatedandtherecoveryof  Sapindus saponinsolutionsaftersoilwashingwas   tested.Thespecificobjectivesofthisstudyaretoinvestigateandevaluatetheperformanceof  Sapindus saponininenhancingwashingforphenanthrene-contaminatedsoilsandthenprovidevaluableinfor-mationfortheapplicationof  Sapindus saponininsoilwashingtechnologyfortheremediationofHOCs-contaminatedsoilsandgroundwater. 2.Materialsandmethods  2.1.Materials Dryfruitsof  S.mukorossi weregatheredfromHangzhoucity,China.Theouterfruitpericarpsweredriedinanovenat50 ◦ Cforabout2daysandthengroundandsievedthroughastandardsieveof60meshes,whichwasusedasrawmaterialsfortheextractionof  Sapindus saponin.Phenanthrenewas   selectedasarepresentativepolycyclicaromatichydrocarbon(PAH)tomodelHOCsandobtainedfromAcrosOrganics(USA)withapurityof99%.Tween80wasobtainedfromAcrosOrganics(USA)asarepresenta-tivesyntheticnonionicsurfactant.HederageninwasobtainedfromTautoBiotechCo.(China)withapurity>98%andusedtodeter-minesapogenincontentintheextracted Sapindus saponin.SelectedphysicochemicalpropertiesforthesechemicalswerepresentedinTable1.Allotherchemicalsusedwereofreagentgradequalityandhigher.Anaturalbentonite(Na + -montmorillonite)wascollectedfromInnerMongoliaofChinaforthesorptionexperimentsofsurfactants,ofwhichtheorganiccarboncontent,specificsurfacearea(BET-N 2 )andcationexchangecapacity(CEC)are0.04%,60.9m 2 /gand105mequiv/100g,respectively.Organo-bentonitewaspreparedbymodifyingthenaturalbentonitewithacationicsurfactant(hexade-cyltrimethylammoniumbromide,HDTMAB)at1.0timesCECwiththemethodsasdescribedbyZhuetal.[18],whichwas   usedtotesttherecoveryof  Sapindus saponinsolutionaftersoilwashing.Acleannaturalsoilwas   collectedfromHangzhoucity,China,whichwas   air-driedandsievedtoobtainparticleslessthan1mmforthepreparationofphenanthrenecontaminatedsoil.Thesoilcontains5.9%sand,67.5%siltand26.6%clay,whichwasanalyzedwithLaserParticleSizeAnalyzer(MalvernMAM-5005,UK).Thesoilorganiccarboncontentwasdeterminedtobe1.54%,andthepHof soilsolutionwasmeasuredtobe6.5.PhenanthrenecontaminatedsoilwaspreparedwiththemethodsdescribedbyZhouandZhu[19],andthepreparedcontaminatedsoilwasagedforabouttwoweeksbeforetheexperiments,whichhadafinalconcentrationof 178mg/kgforphenanthreneandwasuseddirectlyinthebatchexperiments.  2.2.ExtractionofSapindussaponinSapindus saponinwasextractedandpurifiedwiththemethodsasdescribedbyMa   etal.[14].Briefly,thefruitpericarppowerof  S.mukorossi was   extractedtwotimeswith75%ethanolbyultrasoni-cationfor30minatasolid/liquidratioof1:6(w/v).Afterfiltrationandevaporation,theextractwas   redissolvedindistilledwaterandthenflowedthroughacolumnfilledwithmacroporousresin(D101).Afterthat,thecolumnwaselutedsequentiallywithdis-tilledwater,30%ethanoland70%ethanolinthevolumeofthreetimesthebreakthroughvolume(BV).Theeluentfrom70%ethanolwascollectedandevaporatedtodryness,andtheresultingprod-uctwas   theextracted Sapindus saponin.Thesolidofextractwasdirectlydissolvedindistilledwatertoprepare Sapindus saponin  124  W.Zhouetal./ColloidsandSurfacesA:Physicochem.Eng.Aspects 425 (2013) 122–128  Table1 Selectedphysicochemicalpropertiesofcompoundsinthisstudy a CompoundsMolecularformulaMWlog K  ow  S  w  (mg/L)CMC   (mg/L)PhenanthreneC 14 H 10  178.234.571.18-Tween80 C 8 H 17 C 6 H 4 O(OCH 2 CH 2 ) 9.5 H 1310 – –40Hederagenin C 30 H 48 O 4  472.7––– a PhenanthrenedatafromYaws[16]andTween80datafromZhuandZhou[17]. solutions,andtheconcentrationsofthemwereexpressedwiththemassofsolidextractinunitvolumeofsolution.Sapogenincontentintheextracted Sapindus saponinwas   mea-suredwiththemethodsdescribedbyLiandLi[20]andusedto expressthepurityoftheextracted Sapindus saponin.pHof  Sapin-dus saponinsolutionwasdeterminedinthevaryingconcentrationfrom0.1g/Lto1.0g/L.Surfacetensionof  Sapindus saponinsolutionsoverawideconcentrationrangeweredeterminedwithaModel20surfacetensionmeter(FisherScientific,USA).Criticalmicellecon-centration(CMC)of  Sapindus saponinsolutionwasobtainedwiththemethodsasdescribedbyZhouetal.[7].  2.3.Surfactantsorptionexperiments Bentonitewasusedtoevaluatethesorptionof  Sapindus saponinontosoilincomparingwiththatofTween80.Batchsorptionexper-imentswereconductedintriplicatewiththemethodsasdescribedbyZhuandZhou[17].Briefly,0.5gofbentonitewas   mixedwith20mL    ofsurfactantsolutionsin22mL    CorexcentrifugetubewithTeflon-linedscrewcaps.Aftershaking(24h,20 ± 1 ◦ C)andsubse-quentlycentrifugation(30min,3000rpm),anappropriatealiquotofthesupernatantwaswithdrawnandanalyzedforsurfactants.Thesorptionamountofsurfactantsontobentonitewascomputedsimplyfromthedifferenceoftheinitialandfinalconcentrationsof surfactantsinsolution.  2.4.Solubiliationenhancementexperiments Batchexperimentswereconductedinduplicatetomeasurethesolubilityenhancementofphenanthreneby Sapindus saponinandTween80.20mL    ofsurfactantsolutionswithaseriesofcon-centrationswereplacedin22mL    Corexcentrifugetubes,andsolidphenanthrenewassubsequentlyaddedtoeachtubeinamountslightlymorethanrequiredtosaturatethesolution.Aftershaking(24h,20 ± 1 ◦ C)andsubsequentlycentrifugation(30min,3000rpm),anappropriatealiquotofthesupernatantwas   thencarefullywithdrawnwithavolumetricpipetteandtheaqueousconcentrationsofphenanthrenewereanalyzedbyHPLC,themeanvaluesofwhichwereusedtoplotsolubilizationcurves.  2.5.Soilwashingexperiments Enhancedwashingofsurfactantsolutionsforphenanthrenefromcontaminatedsoilwasconductedtriplyinbatchexperiment.2.0gofcontaminatedsoilwasweighedinto22mL    Corexcentrifugetube,towhich20mL    ofsurfactantsolutionswithdifferentconcen-trationswereadded.Allaqueoussolutionsforsoiltestscontained0.01MNaCltokeepaconstantionicstrengthand0.01%(w/w)NaN 3  toinhibitmicrobialgrowth.Aftershaking(24h,20 ± 1 ◦ C)andsubsequentlycentrifugation(30min,3000rpm),anappro-priatealiquotofthesupernatantwasremovedandanalyzedforphenanthrenebyHPLC.Thelossesofphenanthrenebyphotochem-icaldecomposition,volatilizationandbiodegradationwerefoundtobenegligibleduringtheexperimentprocess.Theremovaleffi-cienciesofphenanthrenebysurfactantsolutionswerecalculatedinaccordingtotheequilibriumconcentrationsofphenanthreneinaqueoussolutionanditsinitialconcentrationoncontaminatedsoil.  2.6.RecoveryofSapindussaponinsolutionaftersoilwashing  Therecoveryof  Sapindus saponinsolutionwastestedinbatchexperimentswithaninitialsurfactantconcentrationof10g/L.Afterthefirstsoilwashingexperiments,organo-bentonitewasaddedintothewashed Sapindus saponinsolutionsatthedosagesof1g/L,2g/Land5g/L,respectively,whichwas   shakenfor6hat20 ± 1 ◦ Candthencentrifugatedat5000rpmfor30min.Afterdetermin-ingphenanthreneconcentrationinaqueoussolution,therecovered Sapindus saponinsolutionswerereusedforsoilwashingwithaboveexperimentprocess.  2.7.Analyticalmethods Insurfactantsorptionexperiments,theaqueousconcentrationsof  Sapindus saponinandTween80werequantifiedbyUV   spec-trophotometer(ShimadzuUV-2401PC,Japan)atthewavelengthsof210and234nm,   respectively.Allphenanthreneconcentra-tionsinaqueoussolutionswerequantifiedbyaAgilent1100HPLC(USA)fittedwithUVdetectorandEclipseXDB-C18column(4.6mm × 150mm,   5  m)   usingmethanol-water(v/v,90/10)asthemobilephaseataflowrateof1mL/min.TheUVwavelengthforphenanthrenewas   setat250nm. 3.Resultsanddiscussion  3.1.StructureandpropertiesofSapindussaponin Saponinsareastructurallydiverseclassofcompoundsinmanynaturalplants,whicharecharacterizedbyaskeletonderivedof the30-carbonprecursoroxidosqualenetowhichglycosylresiduesareattached.Traditionally,theyaresubdividedintosteroidalandtriterpeneglycosides,whichconsistofnonpolaraglyconescoupledwithoneormoremonosaccharidemoieties[8].Thecombination ofpolarandnon-polarstructuralelementsinsaponinmoleculesexplainstheirsurface-activitiesinaqueoussolutions. Sapindus saponinextractedfromthefruitpericarpof  S.muko-rossi containssomecomplexcomponentswithdifferentstructure,andthenitisfairlydifficulttoaccuratelydefinethestructureandcompositionofthisnaturalbiosurfactant.Recently,severalcom-ponentsfor Sapindus saponinwereisolatedandcharacterizedinsomestudies[15,21].Amongthem,themostcommonstructure reportedistheoleanane-typetriterpenoidsaponinthatconsistsof ahederageninastheaglycones,whichissubstitutedwithadi-ortrisaccharideatC-3(Fig.1).Thesecharacterizedcomponentsfor Sapindus saponinhavethevariedmolecularweightfrom604to966withthecorrespondingmolecularformulaofC 35 H 56 O 8  andC 50 H 78 O 18  [21].Inthisstudy,ayieldofabout23.3%(m/m)wasobtainedfortheextracted Sapindus saponin,whichstillwasacomplexmixturecontaining Sapindus saponin,glycosides,andothersugars.Gen-erally,sapogenincontentcanbeusedtoexpresssaponinspurity[20].WithFig.1,hederageninisthesapogeninof  Sapindus saponin,anditscontentintheextracted Sapindus saponinwas   determinedtobeabout14.4%.Withthecharacterizedstructurefor Sapindus saponininFig.1,hederagenincontentshouldbeabout48.9–78.3% inthepurecomponentof  Sapindus saponin.So,itcanbeinferred  W.    Zhouetal./ColloidsandSurfacesA:Physicochem.Eng.Aspects 425 (2013) 122–128 125 Fig.1. Mainstructuresof  Sapindus saponinsextractedfromthefruitpericarpsof  Sapindusmukorossi Garetn[15,21]. that Sapindus saponincontentintheextractofthisstudyisabout18.4–29.4%.Theextracted Sapindus saponininthisstudywascharacterizedbydeterminingpH,surfacetension,CMC   andelementalcomposi-tion.ThepHof  Sapindus saponinsolutionvariedfrom5.8to5.0astheconcentrationincreasedfrom0.1g/Lto10.0g/Landthendidnotvarybeyond1%.Theacidicnatureof  Sapindus saponinsolu-tioncanbeduetotheacidicandionizablefunctionalgroupsinthehydrophilicfractionof  Sapindus saponinmolecules.TheCMC   valueof  Sapindus saponinsolutionwasdeterminedtobeabout120mg/L,whichissimilartothatofsomecommercialnonionicsurfactant.WithsurfactantconcentrationaboveCMC,astablevalueofabout32mN/mwasobtainedforsurfacetension,whichissimilartotherangeof30–40mN/mreportedforseveralcommercialsurfactants.Accordingtheelementalanalysis,theelementpercentagecompo-sitionsoftheextracted Sapindus saponinwere55.4%forcarbon,37.1%foroxygenand7.5%forhydrogen.  3.2.Sorptioncomparisonofsurfactantsontosoil SorptionofsurfactantsontosoilwoulddecreasetheeffectiveconcentrationsofsurfactantinaqueoussolutiontosolubilizeHOCs,andthesoil-sorbedsurfactantscanalsoenhancesoilretardationcapabilityforHOCs,bothofwhichwouldreducesoilwashingeffi-ciencyandresultinanincreaseinremediationtimesandcosts.Thus,aquantitativeevaluationforanypotentialsurfactantwash-ingapproachmustconsiderthesorptionofsurfactantontosoilstomaximizeefficiencyandminimizeremediationcosts.Asthedisturbanceofsoilorganicmatter,itisfairlydifficulttoaccuratelyquantifythetotalconcentrationsof  Sapindus saponininaqueoussolutionbyUVspectrophotometeraftersoilsorptionexperiments.So,anaturalclayofbentonitewithloworganiccarboncontentwasusedtoinvestigatethesorptionof  Sapindus saponininthisstudy,whichwascomparedwiththatofTween80.Thesorp-tionof  Sapindus saponinandTween80ontobentonitewas   showninFig.2asafunctionofsurfactantequilibriumconcentration.BothsorptionisothermsarenonlinearwithtypicalS-shapecurves,buttheyshowdifferentvariationtendencywithincreasingsur-factantconcentrations.ThesorptionisothermofTween80showsasharpincreaseandthenreachesaplateauatequilibriumcon-centrationaroundtheCMC,butagradualincreaseisobservedforthesorptionamountsof  Sapindus saponinwithincreasingequilib-riumconcentrationandthesorptionplateaucouldnotbeobservedinthestudiedconcentrationseventhoughequilibriumconcentra-tionsaboveCMC.Theexperimentaldataforthesorptionof  Sapindus saponinwerefittedtotheLangmuirisothermequation q e  = q m K  L  C  e 1 + K  L  C  e (1) Fig.2. Comparisonofthesorptionof  Sapindus saponinsandTween80ontoben-tonite. where q m  isthemaximumsorptionamount(g/kg); K  L   isthemodelconstant; C  e  istheequilibriumconcentrationofsorbateinaque-oussolution(g/L).ThemodelresultswereshowninFig.2,which indicatedthatLangmuirisothermmodelcandescribethesorptionof  Sapindus saponinwell,supportedbythehighcorrelationcoef-ficient( R 2 >0.995)andthegoodagreementofexperimentaldatawithsimulatedcurve.WithFig.2,thesorptionamountsofTween80ontobentonite areobviouslyhigherthanthoseof  Sapindus saponin.Withagiveninitialconcentrationof10g/L,about44%Tween80was   adsorbedontobentonite,butthesorptionlossof  Sapindus saponinwas   onlyabout8%.So,thesorptionof  Sapindus saponinontosoilismuchlessthanthatofTween80.Thesorptionofsurfactantsontosoilsisgenerallyattributedtothehydrogenbondingandelectrostaticattractionbetweenthenegativelychargedsoilsurfaceandthesur-factantmolecules.WithFig.1, S apindus saponinmoleculescontainionizablecarboxylgroupsandthensomespecieswithnegativechargeexistinsurfactantsolutions,whichcanenhancetheelec-trostaticrepulsionbetween Sapindus saponinmoleculesandthenegativelychargedsoilsurfaceandthenrestrainthesorptionof  Sapindus saponinmoleculesontosoils.  3.3.SolubilizationenhancementofphenanthrenebySapindussaponin EnhancedsolubilizationforHOCsisalwaysusedasanindexinevaluatingthecapabilitiesofsurfactantsinsoilwashing.Sol-ubilizationenhancementofphenanthreneby Sapindus saponinsolutionswas   measured,andtheapparentsolubilities( S  ∗ w )of phenanthreneinaqueoussolutionwereshowninFig.3asafunc- tionof  Sapindus saponinconcentrations.Obviously,the S  ∗ w  valuesforphenanthrenehavealinearincreasewithincreasing Sapin-dus saponinconcentrationsabovetheCMC(thelinearequationswerelistedinFig.3),whichisconsistentwithamicellarsolubili- zationmechanism[22–24].   TheenhancementextentofsurfactantsforHOCssolubilizationgenerallycanbeevaluatedbytheratioof  S  ∗ w / S  w ,where S  w  isthewatersolubilityofHOCs.Thecorrespond-ing S  ∗ w / S  w  valuesforphenanthrenein Sapindus saponinsolutionswerealsoshowninFig.3,withwhich Sapindus saponinshowsgreatcapabilityinenhancingphenanthrenesolubilization.Forexample,the S  ∗ w  valuesofphenanthrenein3000mg/Lof  Sapindus saponinsolutionsisabout26.5timesofits S  w  values.Theenhancedsolu-bilizationofTween80forphenanthrenewas   alsoshowninFig.3,whichisobviouslygreatthanthatof  Sapindus saponin.Withagiven

Contraception (1)

Jul 30, 2017

Serina Nall

Jul 30, 2017
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