Bacterial Superoleophobic Fibrous Matrices A Naturally Occurring Liquid-Infused System for Oil − Water Separation - Ashra et al. - 2021

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pubs.acs.org/LangmuirArticleBacterialSuperoleophobicFibrousMatrices:ANaturallyOccurringLiquid-InfusedSystemforOil−WaterSeparationZahraAshrafi,ZimuHu,LucianLucia,*andWendyKrauseCiteThis:Langmuir2021,37,2552−2562ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Nanocellulosefibersbioengineeredbybacteriaareahigh-performancethree-dimensionalcross-linkednetworkwhichcanconfineadispersedliquidmediumsuchaswater.Thestrongchemicalandphysicalinteractionsofdispersedwatermoleculeswiththeentangledcellulosicnetworkallowthesematerialstobeidealsubstratesforeffectiveliquidseparation.Thistypeofphenomenoncanbecharacterizedasgreenwithnoequivalentprecedent;itsperformanceandsustainabilityrelativetoothercellulose-basedorsyntheticmembranesareshownhereintobesuperior.Inthiswork,wedemonstratedthattherenewablebacterialnanocellulosicmembranecanbeusedasastableliquid-infusedsystemforthedevelopmentofsoftsurfaceswithsuperwettabilityandspecialadhesionpropertiesandthusaddressintractableissuesnormallyencounteredbysolidsurfaces.■INTRODUCTIONsuperhydrophilicitybypursuitofa“Cassiestate”model.InSuperwettabilityofbioinspirednano-/microstructuredsurfacesfact,fromthesurfacetensionperspective,iftheenergyofahasbeeninvestigatedintensivelyforvariousapplicationswithinsurfaceissufficientlylowtorepelorganicliquids,itwillrepel1−5waterdroplets,too.12Thishappensbecausethesurfacetensionnumerousdisciplinesofscienceandengineering.Amongtheseapplications,oil−waterseparationisofparamountofwaterisrelativelyhighduetotheattractionofwaterimportanceforaddressingenvironmentalremediationarisingmoleculestoeachotherthroughawebofhydrogenbonds.Tofromindustrialoilwastewatergenerationandspills.Therefore,overcomethisintrinsicdilemma,apromisingalternativesuperhydrophobic−superoleophilicsurfacesshowingextremestrategyistointroducearepulsiveliquidlayersuchaswaterrepulsionofwaterandextremeattractionforoilwithhighintothesurfacemicro-/nanoroughnessstructures.1,12−14separationefficiencyhavebeenthesubjectofintenseFigure1providesasimplepictorialrepresentationshowingexplorationoverthelastfewdecades.These“oil-removing”whypreparingmaterialsthatsimultaneouslydisplayhydro-membranes,anumberofwhicharebasedonharmfulfluoride-philicityandoleophobicityisverychallengingandhowacontainingcompounds,tendtoclogfromthepassageand6,7water-infusedstrategycanovercomethisdeficiency.Furthercontaminationofoildroplets;theresidualadheredoilisdifficulttoberemovedandrecycledandcanleadtoainformationonliquid-infusedsystemsandtheirmeritstotheDownloadedviaUNIVOFCALIFORNIASANTABARBARAonMay16,2021at07:54:12(UTC).Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.Cassiestatemodelisdiscussedindetailsinourspecializedsignificantdecreaseinseparationfluxandthematerial’s8,9reviewarticle.12lifetime.Furthermore,superhydrophobic−superoleophilicmaterialsarenotsuitableforgravity-drivenseparationbecauseWater-infusedsystemsasdescribedabovearethuswatersettlesdownduetoitshigherdensitythanoil,formsapromisingcandidatestoaddressthesurfacetensionchallengebarrierlayerwhichpreventsoilfromcontactingthemembrane,foroil−waterseparationapplications.Moreprecisely,theandmakesthistypeofmembranealessenergy-efficientoption.modeofoperationisasfollows:aprototypicalseparatingSuperoleophobic−superhydrophilicmaterialsknownasmembraneisinfusedwithwaterfollowedbyexposingittoan“water-removing”haveproventobehighlypotentinpracticaloil−waterfeedstream;theentrappedwaterlayerservesinaapplications.Theyaremuchlesspronetofoulinganddisplaysimpleandfluoride-freewaytorepeltheoilphase,whilehigheroil−waterseparationefficiencythantheoil-removingfiltrationsystemsdescribedabove.Also,becauseofthelowerviscosityandhigherdensityofwatercomparedtomostorganicReceived:September15,2020liquids,water-removingmaterialsareexpectedtoshowhigherRevised:January20,2021fluidfluxandcanbeusedingravity-drivenseparation;Published:February19,202110,11therefore,theyareamuchmoreenergy-efficientoption.Despitetheseadvantages,itisverychallengingtofabricateasurfacethatsimultaneouslydisplayssuperoleophobicityand©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.langmuir.0c027172552Langmuir2021,37,2552−2562

1Langmuirpubs.acs.org/LangmuirArticle(1)Theuniquethree-dimensionalporousnetworkmadeupofcellulosenanofiberstogiveanextraordinarilyhighsurfaceareafortrappingwatermolecules.Moreover,theentangledcellulosicnetworknotonlyprovidesaconfinedstructuretoentrapalargeamountofsolvent,e.g.,water,butalsodisplaysasurfacerichinfreeandpendanthydroxylgroupsthatplayacrucialroleinoilrepellency.(2)Thenativehydrophilicityofthecellulosebackbone.Thelargenumberofhydroxylgroupsoncellulosepolymerchainscreateanenormousnumberofhydrogenbondingopportunitieswithwatermoleculestoformastableliquidlayer.Topreparealiquid-infusedsystemforoil−waterseparation,avarietyofporoussubstrateshavebeenrecentlyfabri-16−19cated.TheidealporoussubstrateshouldprovidestrongFigure1.(toprow)Asuperoleophobicsurfacemadefromverylow-chemicalorphysicalinteractionswiththedispersedliquidsurface-energymaterialsinaCassiestateiscapableofrepellingoilmolecules.Forthatreason,gelsincludinghydrogels,9organo-droplets.However,thissurfacewillrepelwaterdroplets,too,becausegels,20andaerogels21,22havegainedextensiveattention.thesurfacetensionofwaterishigherthanthoseofmostoils,thusManyattemptshavebeenmadetoengineersustainablesignificantlylimitingtheapplicabilityofthesemembranestomaterialsthatutilizenaturalpolymerssuchascellulose,butaddressingoil−waterseparations.(bottomrow)Liquid-infusedstrategyinwhichthesurfaceismadeofmaterialsthatcantraptheyoftenrequiretime-consumingmultistepprocessing,andwatermolecules;entrappedwateractsbyitselfasabarrierlayertomoreimportantly,theytendtorequireharshchemicalreagents23−27preventoilmoleculesfrompenetrationwhileallowingwaterandhightemperatures.Forinstance,Changetal.moleculestopenetrateintothemembrane.fabricatedananoporouscellulosemembranefromrenewablemarineresourcesforoil−waterseparationasasustainablereplacementforcarbonnanotubes.However,toisolatesimultaneouslyactingasareconfigurablegatetoallowthecellulosefromnaturalresources,strongacidhydrolysisat7028waterphasetopassthrough.°Candbleachingarenecessary.Inanotherexample,aInthecurrentstudy,water-infusednanocellulosicmem-cellulosespongewithrobustsuperwettabilityforseparationbranesproducedbybacteriabyastaticcultivationmethodapplicationswasreported.Althoughthemembraneiseffectivewereinvestigatedasgreenpromisingmaterialsthatcomplyandgreenerthanitspolymericcounterparts,thefabricationwiththefeaturesofliquid-infusedsystemsforoil−waterrequiresdissolutionofcellulosepowderinZnCl2at80°Cwith29separation.Bacterialnanocellulosemembraneshavealreadyadditionalpore-formingagents.Acomparisonofvariousbeenthesubjectofmanystudies;however,thepurposeofthecellulose-basedfiltrationmembranesforoil−waterseparationcurrentworkwastoexaminetheextremelyuniqueliquidisshowninTable1.interactionsofthesedistinctivematerialsfromafundamentalFromasustainabilityperspective,theproductiontimeofperspective.Thisaspectofthebacterialcellulosemembranebacteria-derivedcelluloserequiresseveraldaysdependingonhasnotbeenstudiedbeforetoanygreatdepth.Therefore,thisspeciesandgrowthmedia,whilethecommensuratetimeforArticleintroducesaproofofconceptforemployingBNCplant-derivedsimilarlyorderedandhigh-molecular-weightmembranesasaliquid-infusedsystem.Furtherin-depthstudiescellulosecanbeupwardofyears.Bacteria-derivedcelluloseisarerequiredtofullyutilizetheintrinsicpotentialofthesepure;however,tolikewiseobtainplant-derivedcellulose,asuperiorbiomaterialsforpracticalapplicationsandtechnicallengthypurificationprocessisrequiredforremovingall15developments.Weshowedthatthesemembranesnever-undesiredcomponentssuchaslignin,pectin,andhemi-thelessdisplaysuperhydrophilicityandsuperoleophobicitycelluloses.Moreover,thebiosynthesisofbacterialcelluloseiswithultralowoil-adhesionproperties.Thesepropertiesarehighlyenergyleanandatomeconomicalinthatitcanbegenerallyderivedfromthefollowing:performedatroomtemperaturewithvirtuallynowaste.Table1.ComparisonofVariousCelluloseBasedFiltrationMembranesforOil−WaterSeparationwettabilityfiltrationmaterialsWCAOCAefficiencyenvironmentalimpactreffibroustunicate0°<175.9°≥93.3−99.9%alkalineandbleachingtreatmenttoremoveproteins,fats,andpigmentsfromtunics;28cellulosenanocrystalsprolongedtreatmentwithstrongacid(sulfuricacid65%)toobtaintunicatecellulose(TCNCs)nanocrystals(TCNCs)cellulosesponge0°<160°>99.9%concentratedZnCl2solutionathightemperatureemployedtodissolvecellulosepowder;pore-29formingagentandcoolingat−10°Cusedtoformthestructuredspongenanofibrouscellulosicnot<165°>99.7%mixtureofacetoneandDMAcusedtodissolvecelluloseacetate23membranereportedcellulosemicrofiltration40°<160°>99%NaOH−ureaaqueoussolutioncontainingdifferenttypesofPEGusedtopreparecasting30membranecellulose(cottonlinterpulp)solutionbacterialnanocellulose0°<177°>99.9%sustainableandgreenmembrane;inherentlynontoxictolivingthingsandtheenvironmentthiswork2553https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

2Langmuirpubs.acs.org/LangmuirArticleBacterialcellulosehasalreadybeenproducedattheindustrialandthenplacedinadesiccatortocool.Immediatelyuponcooling,thescaleasafoodproductandforbiomedicaldevices/woundspecimenswereweighed.Thematerialwasthensubmergedinwaterhealingapplications.Moreimprovedprocessestofacilitateatroomtemperaturefor24h.Specimenswereremoved,patteddry31withalintfreecloth,andweighed.Waterabsorptionwasmeasuredashigh-yieldBNCproductioninscale-upareyetlacking.■follows:EXPERIMENTALSECTIONwaterholdingcapacity%Materials.GluconacetobacterhanseniiwaspurchasedfromAmericanTypeCultureCollectionATCC23769.Mannitol,yeast=[(wetweight−dryweight)/wetweight]×100extract,Bactopeptone(Becton,DickinsonandCompany),disodiumphosphate,andcitricacidwereusedforpreparingtheappropriateContactAngleandSurfaceTensionMeasurements.Theoilculturemedia.Aceticacidandpotassiumhydroxidesolution1N(N/contactanglesinair,underwater−oilcontactanglesandadhesion10)(Certified)wereusedtopurifymembranes.n-Dodecanewasusedbehavior,andunderoil−watercontactanglesweremonitoredbythetoprepareoil-in-watermixtures.AllthereagentswerepurchasedfromData-PhysicscontactanglesystemOCA15ECatambienttemper-Sigma-Aldrichandusedasreceivedunlessotherwisenoted.ature.Theoil(n-dodecane)drops(3μL)weredroppedcarefullyPreparationofBacterialCelluloseMembranes.Thisworkontothematerials,whichwereinvarioussurroundingmedia.TheutilizedATCC23769Gluconacetobacterhanseniiforallcelluloseaveragevalueofthreemeasurementsperformedatdifferentpositionsproduction.DriedbacterialsamplesfromAmericanTypeCultureonthesamesamplewasadoptedasthecontactangle.ThependantCollection(ATCC)wererevivedaccordingtothestandardATCCdropmethodwasusedtomeasuresurfacetensionsofn-dodecane.Itprotocol.Inoculationmediawaspreparedusingthestandardmannitolisbasedonanalyzingtheshapeofadrophangingfromacapillarybroththatconsistsof(w/v)2.5%mannitol,5%yeastextract,and3%tubereadytodetach.peptoneindeionized(DI)water.ThemannitolbrothmediawasCoefficientofFrictionMeasurements.Tribologicalpropertiesautoclavedat121°Cforatleast15minbeforeproceeding.ThisoftheBNCmembraneinthewetanddrystatewerecarriedoutusinginoculationmediumwasusedastheseedculturemedium.auniversalmechanicaltester(UMT)inreciprocatingslidingThestandardHestrin&Schrammmedia(HSmedia)consistsofconditions.Thereciprocatingslidingfrequencywasfixedat1Hzthefollowingingredients(w/v):glycerol2%,peptone0.3%,yeastwithslidingpairsoperatingat200mNnormalload.Thefrictionextract0.5%,andcitricacid0.114%.Theculturevesselwasfilledwithcoefficientwascontinuouslymeasuredforthreewetanddrysamples.50mLoffresh,sterileHSmedia.Tothatwasadded5%(v/v)seedSurfaceRoughnessMeasurements.Atomicforcemicroscopyculturemedium.Theinoculatedvesselwasthenplacedinastatic(AFM),averyhigh-resolutiontypeofscanningprobemicroscopy,incubatorunderatmosphericconditionsat30°Cfor5daystowasusedtoaccuratelycharacterizethevariationofsurfacedevelopBNCpellicles.microstructureswithresolutionontheorderoffractionsofananometerforscannedareasof1and100μm2.InordertokeepthePurificationSteps.Afterward,theBNCmembranesweresoakedina1MKOHbathatroomtemperaturefor48htoremovenon-porestructuresthatareavailableinthewetstatewithindrysamples,cellulosicmaterialssuchasproteinsandnucleicacidsfrombacterialthesamplesweredriedinaFreeZonefreeze-dryerfromLABCONCOcellsandtheculturebroth.Oncethebulkofthemediawasremoved,at<50Paand−50°Cforatleast48hwithoutanyprevioustheBNCmembranesweretransferredtoa0.5Maceticacidbathtoprefreezing.neutralizethebase.After1hofneutralization,thecellulosewasForthepreparationofathinpressedBNCfilm,alaboratoryrepeatedlyrinsedinDIwateruntilpHneutral.Finally,themembranesuctionBuchnerfunnelwasused.AslurryofBNCnanocellulosewaswasstoredinfreshDIwaterat4°Cforfurtherexperiments.Itshouldpreparedbyhomogenizingapre-weighedBNCsampleinDIwaterbenotedthatboththeKOHandaceticacidaredilute,innocuous,usinganIKAT25dispersinginstrument.Filterpaperwasplacedinandbiocompatible.theBuchnerfunneltotrapthenanocellulosesduringthefiltrationMorphologyandPorosityCharacterization.Thesurfaceandprocessandensureformationofasmoothfilm.WhentheslurrywasbulkmorphologyoftheBNCmembranewereobservedbyfieldpouredinthesuctionfunnel,mostofthewaterwasremovedbyemissionscanningelectronmicroscopy(FEIVerios460L,FESEM).suction,afterwhichawetgel-likefilmwasformed,whichwasmovedSamplesweregold−palladium(50:50)coated(∼15mthickness)withtoanovenfordrying.theTechnicsHummerVsputtercoatertoreducechargeinterruptionsFiltrationandWaterFluxExperiments.ThewetpurifiedBNCbeforetakingSEMimages.membranewastestedforoil−waterfiltration.ThemixturewasToobtainporosity,apparentvolume(V1)wascalculatedusingthepreparedbymixingn-dodecaneandwaterinavolumeratioof50:50averagethicknessofthesample.TheactualvolumeoftheBCsampleunderstirringfor1h.Thefiltrationperformancetestswerecarried(V)wasdeterminedbasedoncellulosedensity(1.5g/cm3),andtheoutwithadead-endfiltrationassembly(Kontes47mm).Theoil2porosityofthesamplewasdeterminedaccordingtothefollowingcontentsinthefiltratesobtainedfromfiltrationexperimentswereequation.measuredbyatotalorganiccarbonanalyzer(ShimadzuScientificInstruments,TOC-VCPN).ThefiltrationefficiencyisdefinedasÄÅÅÉÑÑÅÅV2ÑÑfollows:porosity=−×ÅÅ1ÑÑ100ÅÅÑÑÅÅÇV1ÑÑÖfiltrationefficiency(%)=−(1CC/)×100f0Capillaryflowporometry(PorousMaterialsInc.,CFP-1100_AEL)wasusedtomeasuretheflowporediameterdistribution.ThesampleswhereCf(mg)istheoilconcentrationofthefiltrate,andC0(mg)isweredriedinafreeze-dryerat<50Paand−50°Cforatminimum48theoilconcentrationoftheoriginaloil−watermixture.Inaddition,hwithoutanyprefreezingtomaintaintheporestructures.theoil−watermixtureflowratethroughBNCsampleswasmeasuredSubsequently,afullywettedsampleinGalwicksolutionwithausingacustomizedfiltrationassembly.Thesetupwasconnectedtoasurfacetensionof15.9Dynescm−1wasplacedinasamplechamber,controllableexternalpressurepumpthatenabledtheapplicationofandthechamberwassealed.Nitrogengaswasthenallowedtoflowpressuretothesystemupto20psiandsoftwarecapableofmeasuringintothechamberbehindthesample.theweightofthewaterthatpassesthemembraneversustime(FigureTheoverallporesizedistributionofBNCsampleswasmeasuredby2).gasadsorption−desorptiontechniquesobtainedfromMicrometricsUsingthissystem,200mLofdeionizedwaterpassedacrossthe3FLEXSurfaceCharacterization,Version4.04.Priortoanalysis,BCBNCmembraneshavingdifferentthicknessesundervariouspressurestomeasurethepurewaterflux(J,Lm−2h−1),calculatedasfollows:samplesweresubjectedtodegassingat80°Cfor24h.WaterHoldingCapacity.Tomeasurewaterabsorption,thespecimensweredriedinanovenforaspecifiedtimeandtemperatureJVAt=×/()2554https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

3Langmuirpubs.acs.org/LangmuirArticleFigure2.Schematicofthefiltrationsetupwithexternalpressureapparatus.(1)Filtrationcell.(2)Aircylinderpump.(3)Pressuregauge.(4)Digitalweightingbalance.(5)Graduatedvesselforpermeatecollection.(6)Computerequippedwithappropriatesoftware.whereVisthevolumeofthewaterfiltered(L),Aistheeffectivefiltrationmembranearea(m2),andtisthefiltrationtime(h).Theaveragevaluewasreportedfromtriplicatemeasurements.■RESULTSANDDISCUSSIONThebacterialnanocellulosemembraneusedinthecurrentsetofexperimentswasproducedbyGluconacetobacterhansenii.Fortheinoculationofthisbacteriastrain,thestandardsterilizedHestrin&Schramm(HS)mediawasusedwhichcontainsgreencomponentssuchassugarandproteinasnutrientsourcesforthebacteria(Figure3a).AsshowninFigure3b−d,bacteriagrowninthisculturemediagraduallysynthesizeacellulose-basedextracellularmatrix(ECM)whichformsattheair−liquidinterfaceandbecomesthickerovertime.Thebacterialnanocellulosemembraneishighinpurity;yet,toexposemanymorehydroxylgroupsandagreaterporeFigure3.Schematicillustrationofthenanocellulosemembranevolume,treatmentwithverymildalkalisolutionisneededtocultivationmethod.(a)SterilizedstandardHestrin&Schrammmediaatroomtemperature(seethePreparationofBacterialCelluloseremovebacteriaandotherresiduefromthebulkoftheMembranessectionfortheingredients).(b)RevivedGluconaceto-membrane(Figure3e).Treatmentwithamildandsafealkalibacterhanseniibacteria(seedculture)areaddedtotheinoculationsolutionremovestheimpuritiesfromthegrowthcultureandmedia.Thebacteriagrow,multiply,andbegintosecretecelluloseresultsinmorevoidspacestotrapwatermolecules(Figurenanofibers.(c)Afterseveraldays,athinlight-coloredmembrane3f,g).Figure3g,hshowthefieldemissionscanningelectronformsattheinterfaceofinoculationmediaandair.(d)Theunpurifiedmicroscopy(FESEM)imagesofthenanocellulosicmembrane.membranedisplaysayellowish/brownishcolor;theSEMimageThecellulosenanofibershavediametersof35±19nmwithinshowsthepresenceofnoncellulosicmaterialssuchasbacterialcellswhichexistmicroporesthatcanbefilledwithliquids,forandthecultureimpuritiesinthestructureofthebiofilm.(e)example,water(Figure3i).Chemicalcompositionofthefibersalongwithinter-andintra-Westudiedthesuperwettabilityandadhesionpropertiesofahydrogenbondsbetweencellulosicchains.(f)Afterpurifyingthemembrane(seethePurificationStepssection),thecolorchangestowater-infusedbacterialnanocellulosemembrane.Figure4Awhite/transparent.(g,h)Noncellulosicmaterialsarecompletelydemonstratesadropletoflightoil(n-dodecane3μL,surfaceremovedfromthebulkstructureofthemembrane;FESEMtension24.91at20°CinmN/m)onaBNCmembranemicrographsofthemembranewithascalebarof5and1μm,immersedinwater.Theoilcontactangleof174.5±2.5°respectively.(i)Cellulosenanofibers’diameterdistribution.exceedsbyalargemargintheestablishedsuperoleophobicitythreshold(>150°).BNCmembranesurfaceswithastable,intercalatedlubricantwaterlayershownocontactlinepinning,wellastheemptyporesavailableinthestructureoftheBNCandhence,theoildropletbaseiscircularinshapeandnotmembrane.elongated;thislatterresultprovesthatitisextremelydifficultToevaluatetheroleofthechemicalcompositionoftheforasmallunderwater−oildroplettoadhereandfoultheBNCmembraneonrepellingproperties,apieceofBNCsurfaceofthewater-infusedBNCmembrane.Figure4Bmembranewasfreeze-driedtomaintainitsporestructures.demonstratessuperspreadingpropertiesofthemembraneforThen,thedrymembranewassoakedinann-dodecaneliquidwater.Thiscanbejustifiedbythechemicalcompositionasuntilitwasfullywetted.Oncethewaterdroplettouchesthe2555https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

4Langmuirpubs.acs.org/LangmuirArticleFigure4.(A)IllustrationoftheunderwatersuperoleophobicitypropertiesoftheBNCmembranebycapturingthestaticcontactangleofanoildroplet(n-dodecane)onthewater-infusedBNCmembrane.(B)SuperhydrophilicitypropertiesoftheBNCmembrane;nomatterifthemembraneisinthedryorwetstate,thewaterdropletspreadsonthesurfaceimmediately.(C)Underoilstaticcontactangleofawaterdropletonanoil-infusedBNCmembrane.Thewaterdropletwithinafewsecondsspreadsoutonthesurfaceofanoil-infusedmembrane.(D)Ultralowoil-adhesionpropertiesofaBNCmembraneinwatershownbydynamicallyforcingtheoildroplettowardthemembranesurface.surfaceoftheoil-infusedBNCmembraneimmersedinoilpresenceofthewaterlayer,exhibitedaverylowcontactmedia(Figure4C),itinfiltratesthemembraneinlessthan2s.anglehysteresisof1.2±0.3towardtheoildroplets.OneveryplausibleexplanationforsuchabehavioristhattheTobetterassesstheslipperypropertyofthewater-infusedsurfaceenergyofthelubricatingliquidandimpregnatedBNCmembrane,thecoefficientoffrictionwasobtainedforsubstrateshouldbewellmatchedtohaveastableliquid-BNCsamplesinthedryandhydratedstate.Asshownininfusedsystem.TheavailablehydroxylgroupsshowbetterFigure5a,thewaterlayerinterlockedintheBNCmembraneinchemicalcompatibilitywiththewatermoleculesratherthanoilthewetstatefacilitatesslidingactionandresultsinacoefficientandcreateamuchmoredurablesystem.offrictionof5timeslowerthanthedrystate.ThedrysampleUnderwater−oiladhesionwasdynamicallymeasuredusinginitiallyshowsalowerresistanceatthebeginningwhichanoildroplet(n-dodecane,3μL)suspendedonamicrosyringegraduallygrowsastheslidingactioncontinueswithtimewhileneedletip(Figure4D).First,theoildropletwasincontactwater-infusedBNCshowsasteady-statefrictionregimeunderwiththemembranesurface,thenpushedagainstthesurface,loadduringthetestwhichisabout1hlong.Thislatterandfinallyretracted.Theoildropletwasyetrepelledfromtheobservationsuggeststhedurableencapsulationofwaterinthesurfaceandshowednoadhesionforcetowardthesurface.Infact,theoildropletdidnotleavetheneedleduringtheentirefibrousmatrix.Figure5brepresentstheroleofstableprocessevenafterpushingitforcefullytowardthesurface.encapsulationintheoil−water/solidsystem;thegapbetweenWhenthemicrosyringewaslifted,theoildropletdidnothefibersonthesurfaceisfilledwithwater.Thus,oildropletsdeformandleaveanyresidueonthesurfaceofthemembrane.arerejectedeffectivelyassubstrantiatedbytheobservationofAsshown,thewater-impregnatedlayeroftheBNCmembrane,highcontactangles,lowcontactanglehysteresis,andnowhosesurfaceishomogeneousandsmoothduetothecontactlinepinningeffect.2556https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

5Langmuirpubs.acs.org/LangmuirArticleFigure5.(a)Coefficientoffrictionasafunctionoftimeinthewetanddrystate.(b)Schematicoftheoil−waterseparationprocessbyaBNCmembrane(inset)illustratingpossiblewettingconfigurationsofaslipperywater-infusedBNCmembrane;theschematicindicatesthattheoildropletisseparatedfromthesurfacebyathinwaterlayerinterlockedbetweencellulosicnanofibers.Figure6.SurfaceroughnessofBNCmembrane:(a)OriginalBNC.(b)PressedBNCmembrane.Themeasurementresultsareexpressedin3Dbasedonheightinformation.ThesurfaceoftheBNCmembranehasalargeroughnessnanofibersandmicrostructuredporeswhichcanimprovethefactorbecauseoftheinherentre-entrantcurvatureofthestabilityofasolid−liquidcompositeinterface.Atomicforce2557https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

6Langmuirpubs.acs.org/LangmuirArticleFigure7.(a)Poresizedistributionofthefreeze-driedBNCmembraneobtainedbythegasadsorption−desorptiontechnique.(b)ThroughporesizedistributionpresentintheBNCmembraneobtainedbycapillaryflowporometry.microscopy(AFM)equippedwithacantileverwithaTheresultofthenitrogenadsorptiontestconfirmedthatnanometer-scaletipwasusedtoscansurfacefeaturesandBNChasalargeporesizedistributionofmacroporesandroughness.Tobetterinvestigatetheeffectofthethree-mesoporespresentinitsstructure.MostporesarelessthandimensionalporousstructuresoftheBNCmembraneon200nmindiameterasshowninFigure7a.surfaceroughness,athinfilmofpressedBNCnanocelluloseWater-infusedBNCmembranescanrepelimmiscibleliquidswaspreparedandscanned(detailsintheExperimentalofvirtuallyanysurfacetension.Forinstance,theoil−waterSection).TheresultsareshowninFigure6.Three-dimensionalseparationpowerofthemembranewashereininvestigatedporousstructurescanbeclearlyseenontheBNCsurface.(Figure8).Afeedofoil−watermixture(20mL:25mL)wasHowever,theporousstructuresdisappearfromthesurfaceofpassedthroughawetBNCmembrane(effectivediameter,47thepressedsample.Therootmeansquare(RMS)roughnessmm;thickness,∼1mm)withoutanyexternalpressureofsurfaceswas56.83and30.28nmfortheoriginalBNC(gravity-driven)toyieldaclearpermeate(water)withnooilmembraneandpressedsample,respectively.droplets,qualitativelyhighlightingthefactthatanoilphasecanAporousroughmicrostructureisconsideredakeyfactortobeseparatedfromthemixturewithhighseparationefficiency.influencesurfacewettabilityandtrappingcapacitytotherebyOurfiltrationsetupwasabletocreateexternalpressureuptoprovidedifferentwettingperformances.32,33TheBNC20psi.Theunder-pressurefiltrationefficiencyresultsdemonstratedthattheoilphasecouldnotpassthismembrane,membranedemonstratedanextremelyexcellentwaterholdingandthemembranecanwithstandpressuresupto20psicapacityof98.3%.Inourpreviouswork,wedemonstratedthatwithoutaconcomitantreductioninfiltrationefficiency(FiguretheporestructureoftheBNCmembranecanbetailored349c).Thecollectedwaterunderdifferentpressureswastestedunderanappropriateenergysource.Herein,weobtainedbyatotalorganiccarbonanalyzertomeasurethefiltrationBNCmembranesbysupplyingglycerolasthecarbonsourceinefficiencyoftheBNCmembrane(Figure9c).thegrowthmedia.TheporestructureofthemembraneisveryTheunderlyingmechanismbehindthisseparationphenom-complicatedtoassess;thus,severaltechniqueswereemployedenonisreferredtoasgating.toevaluatetheporosityarchitectureoftheBNCmembrane.Basedonthismechanism,thecapillary-stabilizedwaterinTheoverallporosityofsampleswas84.3±2.3%.Capillarythemembraneporestructuresformsareconfigurabledoorwayflowporometrywasusedtodeterminethesizeofthroughwhichselectivelyallowswatertopassthroughthemembraneporesinthemembrane.Throughporesareresponsibleforwhileprohibitingoilmoleculesfrompenetration.Therefore,itpermeationbehaviorbecausetheytravelallthewaythroughenableswater-infusedBNCmembranestoeffectivelysuppressthemembrane.Duetocomplextortuosity,therearealsodead-foulingandoilclogging.Thisgatingmechanismcanbeendporeswhichareopenatoneendbutdonotparticipateinengineeredtoberesponsivetoenvironmentalstimulisuchaspermeability;however,theyarestillsubjecttoadsorptionandpressureandtemperatureforselectivefluidtransportation.35desorptionofgas,particles,etc.CapillaryflowporometryMeanwhile,thereusabilityofthemembranewastestedresults,Figure7b,showedthattherearethroughporesinthenumeroustimesbyaddingnewoil−watermixturetotheupperrange0.06−0.130μm.Themainmechanicaldurabilitythatistubetorevealnoreductioninseparationefficiencyandnoimportantforseparationapplicationsreferstotheintegrityofchangeinfiltrationflux.Theseresultsprovethatthisthemembraneunderpressure.Thecapillaryflowporometrymembranehashighresistancetooilfouling;therefore,testconfirmedthattheBNCmembranecanwithstand100psiseparationcanberepeatedaslongastheBNCmembraneappliedpressurewithoutshowinganysignsofrupture(Figureremainshydrated.AnotheradvantageoftheBNCmembraneis7b).Infact,thegas/liquidflowrategrowssteadilybythatitcanbewashedforreusewithamildalkalisolutionafterincreasingtheexternalpressurewithoutanysuddenchangeseachusetoremoveanycontaminationfromhandlingandwhichindicatestheintegrityofthemembraneunderexternalutilization.Themembranestillmaintainedaseparationpressure.efficiency>99.9%andstablerecyclabilityafter5cyclesof2558https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

7Langmuirpubs.acs.org/LangmuirArticleFigure8.Oil−waterseparationusingawater-infusedBNCmembrane.(a)Experimentalsetup.(b)Amixtureofwater25mL(yellow)andn-dodecane20mL(purple)waspouredintotheupperglassjar.(c−e)Filtrationtakesplace.(f)Thefiltrate(left)andtheoilphasesremainedontopofthemembrane(right).(g)Membraneafterthefiltrationexperiments.Theyellowhuerevealsthatitcanevenconcentrateaqueousdyesfromthefeedsolution.separationevenwithoutrinsingbetweeneachcycle(Figurelackofproperentrappingandthusnegativelyimpactthe37,389a).operationofthewholesystem.Theunder-pressureThepermeabilityofawater−oilmixturethroughBNCfiltrationefficiencyresultsshowedthatathinBNCmembranemembranesofdifferentthicknesseswasmeasured.Asshowninisabletowithstandpressuresupto20psiwithoutaFigure9b,thewaterfluxwasinverselyproportionaltotheconcomitantreductioninfiltrationefficiency(Figure9C).thicknessofthemembranes.Incontrast,waterpermeanceEvenpressuresashighas100psipressuredidnotcauseanythroughthemembranesincreasedlinearlywithfeedpressuredamagetothemembraneintegrity.overtherange0−20psi(Figure9c).Amembranewiththicknessof1.1±0.054mmexhibitedanappreciablegravity-■CONCLUSIONSdrivenpurewaterfluxof140.35±15Lm−2h−1whichisintheThisreportprovidesthefirstaccountwithsufficientevidence36rangeofcommercialfilters.ofabacterialcellulosemembranedisplayingunderwaterItisverycriticalandchallengingtodesignaliquid-infusedsuperoleophobicitywithultralowoil-adhesionpropertiesduesubstratethatconfinestheliquidlayerrobustly;otherwise,thetoitsintrinsicallypowerfulwaterabsorbingandretentionlackofinteractionbetweentheimpregnatedliquidandcapacities.Meanwhile,thepresenceofamicro-re-entrantsubstratecancompromisetherepellencyperformanceandsurfacetextureduetotheinherentcurvatureofnanofibersledstabilityofthewholesystem.Infact,theinfusedliquidfilmtotheestablishmentofastableinterfacewherewaterformsamaydrainunderexternalshearflowandpressureduetothecontinuousdefect-freeoverlyingfilm.Bacterialnanocellulose2559https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

8Langmuirpubs.acs.org/LangmuirArticleFigure9.(a)Reusabilityandanti-oil-foulingpropertiesofthemembrane.(b)Thickness-dependentchangesinpermeabilityofthefiltratethroughthemembrane.(c)Influenceofthepressureonthewaterfluxandfiltrationefficiency.membranecanthusbeapromisingalternativetoovercomethe■ASSOCIATEDCONTENTweakintermediaryliquidtrappingabilityofartificialporous*sıSupportingInformationmatricesmadeofcellulosicfibers.VideoS1:.PDFS1:.TheSupportingInformationisavailableThewatertrappedinaBNCmembraneisinherentlyfreeofchargeathttps://pubs.acs.org/doi/10.1021/acs.lang-muir.0c02717.uniformlydistributedanddefect-freeatthemolecularscaleforDemonstrationofoil−waterseparation(MP4)thepossibilityofallowingrapidself-healingafterphysicalSEMandCRYO-SEM,confocalmicroscopy,anddamage.Infact,withrespecttoself-healingability,thethermogravimetricanalysis(PDF)lubricantwaterlayerintheporousstructureoftheBNCmembranecanflowtowardanydamagedareasduetosurface-■AUTHORINFORMATIONenergy-drivencapillaryactionandprovideimmediateself-CorrespondingAuthorrepairing.12,21,22LucianLucia−FiberandPolymerScienceandDepartmentofForestBiomaterial,NCStateUniversity,Raleigh,NorthTheabilitydemonstratedinthisarticletoproduceanCarolina27695,UnitedStates;StateKeyLaboratoryofBio-antifoulingmembranewithdifferentsizes,shapes,durabilities,BasedMaterials&GreenPapermaking,QiluUniversityofandeaseofcyclingmatcheswellwiththerequirementsforTechnology/ShandongAcademyofSciences,Jinan250353,P.treatingrealworldproblems.Inadditiontooil−waterR.China;orcid.org/0000-0003-0157-2505;separation,thisstudycanleadtoanunderstandingandEmail:lalucia@ncsu.edudevelopmentofwater-impregnatedbacterialnanocelluloseAuthorsmembranesforantifoulingcoatings,oil-basedmicroreactors,ZahraAshrafi−FiberandPolymerScience,NCStatedropletmanipulationsystems,andlab-on-a-chipdevices.ItcanUniversity,Raleigh,NorthCarolina27695,UnitedStatesZimuHu−FiberandPolymerScience,NCStateUniversity,alsobeextendedtowettabilitybyliquiddropletsotherthanoilRaleigh,NorthCarolina27695,UnitedStatesthataresubmergedinanimmiscibleliquidotherthanWendyKrause−FiberandPolymerScience,NCState39−42water.University,Raleigh,NorthCarolina27695,UnitedStates2560https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562

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10Langmuirpubs.acs.org/LangmuirArticle(36)Shi,Z.;etal.Ultrafastseparationofemulsifiedoil/watermixturesbyultrathinfree-standingsingle-walledcarbonnanotubenetworkfilms.Adv.Mater.2013,25,2422−2427.(37)Jacobi,I.;Wexler,J.S.;Stone,H.A.Overflowcascadesinliquid-infusedsubstrates.Phys.Fluids2015,27,082101−082113.(38)Zhang,P.;etal.Groovedorganogelsurfacestowardsanisotropicslidingofwaterdroplets.Adv.Mater.2014,26,3131−3135.(39)Yao,X.;etal.Self-ReplenishableAnti-WaxingOrganogelMaterials.Angew.Chem.,Int.Ed.2015,54,8975−8979.(40)Beebe,D.J.;etal.Functionalhydrogelstructuresforautonomousflowcontrolinsidemicrofluidicchannels.Nature2000,404,588−590.(41)Meng,X.;Wang,Z.;Wang,L.;Heng,L.;Jiang,L.Stablesolidslipperysurfacewiththermallyassistedself-healingability.J.Mater.Chem.A2018,6,16355−16360.(42)Xiang,T.;etal.Slipperyliquid-infusedporoussurfaceforcorrosionprotectionwithself-healingproperty.Chem.Eng.J.2018,345,147−155.2562https://dx.doi.org/10.1021/acs.langmuir.0c02717Langmuir2021,37,2552−2562