Copper Oxide Microtufts on Natural Fractals for E ffi cient Water Harvesting - Sharma et al. - 2021 - Unknown

《Copper Oxide Microtufts on Natural Fractals for E ffi cient Water Harvesting - Sharma et al. - 2021 - Unknown》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

pubs.acs.org/LangmuirArticleCopperOxideMicrotuftsonNaturalFractalsforEfficientWaterHarvestingVipulSharma,*HarriAli-Löytty,AnastasiaKoivikko,KyriacosYiannacou,KimmoLahtonen,andVeikkoSariola*CiteThis:Langmuir2021,37,3370−3381ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Hierarchicalsurfacesthataidinthedropletnucleation,growth,andremovalishighlydesirableforfogandmoistureharvestingapplications.Takinginspirationfromtheuniquearchitectureofleafskeletons,wepresentamultiscalesurfacecapableofrapidlynucleating,growing,anddirectionaltransportofthewaterdroplets.CopperoxidemicrotuftswerefabricatedontotheFicusreligiosaleafskeletonsviaelectroplatingandchemicaloxidationtechniques.Thefabricatedsurfaceswithmicrotuftshadhighwettabilityandverygoodfogharvestingability.CuOsurfacestendtobecomehydrophobicovertimebecauseoftheadsorptionoftheairbornespecies.Thesurfaceswereefficientinfogharvestingevenwhenthehydrophobiccoatingispresent.Theoverallwatercollectionefficienciesweredetermined,andtheroleofthemicrotufts,fractalstructures,andtheorientationofleafveinswasinvestigated.Comparedtotheplanarcontrolsurfaces,thenoncoatedandhydrophobiclayer-coatedcopperoxidemicrotuftsontheleafskeletonsdisplayedasignificantincreaseinthefogharvestingefficiency.Forsuperhydrophilicskeletonsurfaces,thewatercollectionratewasalsoobservedtoslightlyvarywiththeveinorientation.TheCuOmicrotuftsalongwithhighsurfaceareafractalsallowedaneffectiveandsustainablewaytocaptureandtransportwater.Thestudyisexpectedtoprovidevaluableinsightsintothedesignandfabricationofsustainableandefficientfogharvestingsystems.16■INTRODUCTIONphobicstructuresonitsback.CactusspeciessuchasOpuntia1718microdasysandothercactibelongingtoaridregionsrapidlyBillionsofpeoplearoundtheworldaresufferingfromthelackcollectwatertofulfilltheirneedsbecauseoftheconicalspinesofdrinkingwaterbecauseofpopulationexplosion,rapid1integratedwiththetrichomesandotherhierarchicalstructures.Downloadedvia49.36.95.139onMay14,2021at07:31:37(UTC).industrialdevelopment,andheavypollution.ThisshortageorSomefernssuchasDryopterismarginataareknowntolackoffreshwaterresourcesis,directlyandindirectly,affecting13efficientlycollectthewaterbyefficientchanneling.Inallofthelivesofbillionsofpeopleacrosstheglobeandisamatterofthesementionedsystems,therearewell-studiedmechanismsseriousconcern.Inrecenttimes,theproblemhasescalated23relatedtotheefficientwaternucleation,growth/storage,andbeyondaridregions,andAsia,SouthAfrica,andtheCzechSeehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.4transport.Republicareafewexamples.DesalinationisoneoftheBasedonthebioinspiredprinciples,waterharvestingimportantmethodscurrentlytoresolvethewatercrisisand19−245materialsanddevicesarebeingrapidlydeveloped.Mostmainlyinvolvesdistillation-basedmechanisms.However,ofthebioinspiredwaterharvestingsurfacesderiveinspirationdesalinationprocessesrequireatremendousamountofenergyfromthreebiologicalsystems:silkfibersfromthespiders,andhighoperatingcosts,meaninghugeinvestments,high6hydrophobic/-philicpatternedsurfacesinspiredbyNamibmaintenancecosts,andsignificantcarbonemission.Apartdesertbeetle,andconicalspinesinspiredbycacti.Therearefromthedesalinationofseawater,watercollectionfromthealsomanyrecentreportswhichhavetakenwaterharvestingatmosphere(moistureandfog)isapromisingmethodto25267−9inspirationfromspeciessuchasNepenthesalata,Sarracenia,addressthewatercrisis.Thismethodisrelativelysimple,2728desertmossSyntrichiacaninervis,greenbristlegrass,cost-effective,andisasustainablewayforwatercollection.Numerousfloraandfaunaspeciescancollectwaterfromfog,andtheirstudymayofferendlessinspirationsforscientificReceived:December8,2020research.10−14SomegrasssuchasCynodondactylon12andRevised:February26,2021Stipagrostissabulicolahas15haveuniqueconicalmicrostructuresPublished:March11,2021thathelpinthecollectionoffogfromtheair.Stenocaragracilipes,atypeofNamibdesertbeetle,canefficientlycapturewaterfromhumidairusingtheuniquehydrophilic−hydro-©2021TheAuthors.PublishedbyAmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.langmuir.0c034973370Langmuir2021,37,3370−3381

1Langmuirpubs.acs.org/LangmuirArticle29303120shorebirds,wheatawns,Burkheyapurpureas,etc.Arraysgrowth,andtransport.Leafskeletonspossessafractal-likeofhydrophilicbumpswithsuperhydrophobictroughsonthestructureatthemicroscalealongwiththemultiscalarelytraofStenocarahavebeenreportedtoacceleratethefoginterconnectedveins.Toincreasetheeffectivesurfacearea16harvestingability.Takinginspirationfromthisstudy,andtoincreasedropletcapturesitesonthesurface,coppersuperwettablepatternsinvolvingcirclearray,squarearray,oxidemicrotuftsweregrownontotheleafskeletonsviaa32andstar-shapedarraywerethenfabricatedforwatercombinationofsputteringandelectrodepositionmethods.Thecollection.Thesesurfaceshadsuperiorperformancescom-morphologicalandcompositionalpropertiesofcopperoxideparedtoconventionalsuperhydrophilicandsuperhydrophobicmicrotuftsontheleafskeletonsurfacearestudiedusingfieldsurfaces.Fiber-likenetworkstructuresinspiredbythespideremissionscanningelectronmicroscopy(FESEM)andX-raywebandmeshwerealsousedforwatercollection.Meshlikephotoelectronspectroscopy(XPS).3DorientationandthearchitectureismorecapablethanplanarsurfacesbecauseitshapeofthecopperoxidemicrotuftsprovideuniqueincreasestheStokes’snumberoffogdropletsflowingaroundwettabilitytothesurfacesandallowthemtocapturetinyfogthemesh,andthusleadstoincreasedimpactsofdropswiththedropletsfromthemiststream.Theinterconnectedveins33presentontheleafskeletonhelpindirectionaltransport.Themesh.Duetothisfact,meshesarewidelyusedinfog34veinsdrawthewaterfromacrossthefractalnetworkandaidinharvestingatmanydifferentlocations.Tofurtherimprovethefogcollectionefficiency,micro-/nanostructureswerethedirectionalandefficientcollection.Thesurfacewasintegratedontothemeshlikemacroscalesurfaces.Theefficientevenwhenitwasmadehydrophobicviasilanemicro-/nanostructuresenablethemeshlikesurfacestocapturetreatment.Thevastnetworkofthefractalsalongtheskeletonfogdropletseffectivelybychangingthemicroscopicwettingsurfacetendstofacilitatethedropletgrowthviarapidandnucleationpropertiesofthesurfaces.Someuniqueshapescoalescenceofthedropletsandeventuallyleadtothedropletsuchasconicalmicrostructuredarraysmayalsohelpindeparture.WettingpropertiesofthemicrotuftsontheleafincreasingfogcaptureandtransportratebythevirtueoftheskeletonwerestudiedandtheircorrelationwiththefogdifferenceintheLaplacepressureandgradientofthesurfacecollectioncapabilitywasestablished.Mechanismsrelatedtofreeenergy.Numerousmethodshavebeenreportedtothewatercaptureandthedynamictransportonbothfabricatethemeshlikespecialwettingsurfacespossessinghydrophilicandhydrophobicleafskeletonsurfaceshavebeenmicro/nanostructures.35,36Forexample,electrospunpoly-highlighted.(vinylidenefluoride)(PVDF)microfiberswerefoundtoimprovethewatercollectingefficiencyofcommercialRaschel■EXPERIMENTALSECTION37Materials.Forthefabricationoftheleafskeletonelectrode,leafmeshby∼305%.ThereareeffortstoimprovethedesignofmesheshavingmultiscalehierarchicalfunctionalitiesastheskeletonsofFicusreligiosawerepurchasedfrom“SkeletonLeaf-JustcondensatesthatnucleateandgrowonthesurfacestendtotheLeaves,”UnitedKingdom.Forelectrodeposition,H2SO4andinhibitfurtherwatercondensation.CuSO4werepurchasedfromMerck,HClfromRomil,andpoly(ethyleneglycol)(PEG)waspurchasedfromSigma-Aldrich,TimelyremovalofthecapturedwaterisveryimportantinFinland.Fortheoxidationofcopper,NaOH,(NH4)2S2O8,anywaterharvestingsystem.Thedirectionalwatertrans-1H,1H,2H,2H-perfluorodecyltriethoxysilane,andCTABwerepur-portabilitydependsonmanyexternalfactorsandstructuralchasedfromSigma-Aldrich,Finland.Allofthechemicalswereusedasorganization.Thesefactorscandelaythefogcollectioncyclereceived.fromrestartingandmayleadtodropletre-evaporation.ThisMethods.DepositionofCopperLayerontotheLeafSkeleton.happensbydelayingthetimelyremovalofthenucleatedandTomaketheleafskeletonsurfacesuitablefortheelectrodeposition,agrowndroplet/filmandevenbyprematureremovaloftheseedlayerofAu(∼30nm)wassputter-coatedontobothsidesofthenucleateddroplets.7,38Thecaptureddropletsusuallyrollorskeleton.CufilmswereelectrodepositedonAu-coatedleafskeletonsfromanacidicplatingsolutionincludingCl−promoterandPEGslidedownthesurfacesrandomlyandfoulthenucleationsites.42suppressor.AdditiveswerechosentopromoteuniformCuTherefore,itisimportanttolookforthedesignsthataidinelectrodepositiononleafskeleton.Theplatingsolutionconsistedofdirectionaltransport,especiallyinthehydrophilicsurfaces.To1MH2SO4,0.5MCuSO4,1μMHCl,and100ppmPEGat1500g/14facilitatecondensatemovement,straightline,wedge-mol(PEG1500)andwasmadeusingCuSO4(copper(II)sulfate3940shaped,andbranch-patternedtrackswereinvestigatedforanhydrous,1.02791.0250MerckEmsure),95−97%H2SO4directionalwatercollection.Sometracksweregravity-assisted(1.00731.1011MerckEmsure),34−37%HCl(H396Romil-SpAandafewintegratedYoung−LaplacepressuredifferenceandSuperpurityacid),PEG1500(86101-250G-FSigmaBioUltra),andsurfaceenergygradientstodrivethecondensatessponta-ultrapuredeionizedH2O(18.2MΩcm,MerckMilli-Q).neouslyandefficiently.Thus,thewatercollectioncanbeElectrodepositionwasperformedina1Lthermostatedelectro-chemicalcellusingathree-electrodesystemcontrolledbyanAutolabincreasedusingdirectionalandspontaneouscollectionbyPGSTAT204potentiostat(MetrohmAG,Switzerland).Agraphitedecreasingtheresidualwaterandrenewalofactivesurfaceforrod(8mmdiameter,15cmlength,GamryInstruments,USA)andawatercollection.ToimprovethedesignsforbettertransportofleaklessAg/AgClelectrode(ET069,eDAQPtyLtd,Australia)werethecapturedwater,complexpatternscombiningspecialusedasthecounterandreferenceelectrodes,respectively.Thegeometryhavebeenreported,whichincludesthedesignconnectiontotheleafskeletonwasmadeusingacrocodileclip3941attachedtotheleafstem.AlloftheelectrodesweresupportedintheinspirationfromMulberryandBananaleaves.Inourpreviouswork,wehavealsoproposedtheuseofleaf-inspiredcellbyastativ.Theelectrodepositionwasdonegalvanostaticallyat−10mA/cm2superhydrophilictracksforefficientwatertransportand7at30°Cunderforcedconvectionconditionsinducedbyamagneticcollection.Inmeshlikedesignsalso,theimportanceofstirrer.Thedurationofelectrodepositionwasfixedat2721sthatefficienttransportofwaterhasbeendemonstratedand2correspondsto10μm/cmCufilmthicknessassuming100%currentbioinspireddesignshavebeenusedtofacilitatewaterefficiencyandhomogeneousfilmthickness.Forthesakeofsimplicity,collection.theelectrochemicallyactivesurfaceareawasapproximatedastheInthiswork,wedemonstrateleafskeleton-basedthree-planarprojectedsurfaceareaofanintactleaf.Beforethecathodicdimensional(3D)surfaceforefficientwaternucleation,electrodeposition,thesamplewassubjectedto10potentialcycles3371https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

2Langmuirpubs.acs.org/LangmuirArticleFigure1.Schematicsandphotographs(insets)ofthepreparationprocedure.between−0.35and+0.55Vat50mV/sforsurfacepreconditioning.in-lensapertureyieldingarectangularanalysisareaof1.54(dispersive)×4.09(nondispersive)mm2.ThesurfacecompositionAftertheelectrodeposition,thesamplewasrinsedindeionizedH2OandblowndrywithN2.FigureS1showsarepresentativepotential−wasidentifiedbyanalyzingthemaincore-leveltransitionsandCutimecurvefortheCuelectrodepositiononanAu-coatedleafskeleton.LMM.Thebackground-subtractedphotoelectronpeakswereleast-Planarcontrolsampleswerepreparedbyelectrodepositionof10μmsquaresfittedwithacombinationofGaussian−LorentziancomponentCufilmonAu-coatedglasssheets.lineshapes.TherelativeatomicconcentrationswerecalculatedusingChemicalOxidationofCutoCuO.Inthefirststep,theCu-coatedScofieldphotoionizationcrosssectionsandanexperimentallyleafskeletonsandcontrolswerecleanedwithethanolanddeionizedmeasuredtransmissionfunctionoftheArgusanalyzer.TheXPSwater(ELGAPURELABOption-R7)viaultrasonicationfor15mininformationdepths(i.e.,3×inelasticmeanfreepath)througheach.ThesurfaceswerethendriedinagentlestreamofN2gas.IntheC16H19F17O3SisilaneoverlayerusingCu2p3/2andCuL3M45M45nextstep,theCu-coatedleafskeletonsandcontrolsweregentlysignalswere3.6and7.7nm,respectively,ascalculatedusingthe43transferredtoaglasscontainerwithanaqueoussolutionof1wt%TPP2Mequation.NaOHand(NH4)2S2O8ina1:1ratio.ThesolutionwasstirredgentlyFogCollectionExperiments.Fogcollectionexperimentswereatroomtemperaturefor15mintomakesurethatthecopperlayerdonebyexposingsurfacestothefinemistofultrapurewaterdoesnotetchoutcompletely.After15min,thesamplewasrinsedgeneratedbytwocommercialcoolmistultrasonichumidifiersseveraltimeswithethylalcoholandDIwater,followedbydryingwith(BionaireBU1300W-I).SampleswerekeptinaverticalorientationcompressedN.Thesamplesweretransferredtoanovenandwereandfacingthehumidifierat50mmasdisplayedinFigure5a.The2driedat150°Cfor2h.Thisleadstothephasetransitionofthehumidifiergeneratedacoolmistthathitthesurfaceattherateof50−150mms−1(measuredusingaJessiekervinYY3hand-splitdigitalcopperhydroxide(bluishbrown)tothecopperoxide(darkbrown)anemometer).ThisiscomparabletothetypicalwindspeedofthefogHydrophobicCoatingProcedure.Tomakethepreparedoxideinadesertwhichisaround10−50mms−1.16Thetotalairflowfromsurfaceshydrophobic,fluorosilanetreatmentwasusedtodecreasethethehumidifierswasestimatedasca.260±60mL/h(accordingtothesurfaceenergy.Thesamples(leafskeletonswithCuOmicrotuftsandspecificationsheetofthemanufacturer).Theexperimentalsetuphadcontrols)wereplacedinasealeddesiccatorwithafewdropsofarelativehumidityabove99%,andallofthemeasurementswere1H,1H,2H,2H-perfluorodecyltriethoxysilane(C16H19F17O3Si)init.conductedatroomtemperature.ThevolumeofwaterwascollectedThedesiccatorwiththesampleswasthenkeptfor2hwithaandmeasuredwithaweightbalanceatintervalsof10minthroughoutvacuumatroomtemperaturebeforethesamplesweretakenout.The1h.Threesetsoftrialswereperformedonthreeindependentsilane-treatedplateswerethenplacedinanoven(∼120°C)for30samples,andtheaveragevaluesalongwiththestandarddeviationmintogetridofanyunattachedsilaneontothesurface.werecalculated.SpecialcarewastakentoensurethesametrailCharacterizationTools.Themorphologyofthemicrostructuresconditionsforallmeasurementrounds.wasdeterminedusinganFESEM(fieldemissionscanningelectronmicroscope)(ZeissUltraPlus)operatingat5kV.ElementalanalysiswasdoneusinganEDS(energy-dispersiveX-rayspectroscopy)■RESULTSANDDISCUSSIONattachmentlinkedtotheFESEM(OxfordInstrumentsX-MaxN80Figure1showsthefabricationoftheCuOmicrotuftsontheEDS).Thefognucleation,growth,dropletdynamics,andwatersurfaceoftheF.religiosaleafskeleton.Inthisstudy,atransportwerestudiedusinganopticalcamera(BasleracA2040-combinationofsimpleelectrodepositionandoxidationmethod120uc,Germany).wasintroduced,whichcancoatthesurfaceoftheleafskeletonLens-definedselected-areaX-rayphotoelectronspectroscopy(SAXPS)wasperformedemployingaDAR400X-raysource(Mgconformallyin3D.ThismethodisfacileandcanbesubjectedKα,1253.6eV)andanArgushemisphericalelectronspectrometertoalargescaleaswell.(OmicronNanotechnologyGmbH).Thecore-levelspectrawereThemicrotuftswereconceivablycomposedofhydratedcollectedatanormalemissionanglewithapassenergyof20eVandcopperoxidethattypicallyformsduringtheoxidationprocess3372https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

3Langmuirpubs.acs.org/LangmuirArticleFigure2.FESEMimagesoftheleafskeletonhavingAucoating(a−c),electrodepositedCucoating(d−f),andCuOmicrotufts(g−i)atdifferentresolutions.ofcopperusingNaOHand(NH4)2S2O8.TheoxidationblockingtheCulayerbybisulfateionsduringtheoxidation7processproceedsinthreesteps:Inthefirststep,Cuoxidizesprocess.rapidlytoformCu(OH)2duetothepresenceofstrongToconfirmthesurfacemicrostructures,FESEMwasoxidizingagentsNaOHand(NH4)2S2O8.Duringthisprocess,employed.TheFESEMimagesatdifferentlengthscalesarereleasedCu2+cationsreactwiththehydroxideanionsoftheshowninFigure2.Figure2a−cshowsthebareleafskeleton,NaOHtoformCu(OH)2.wherethevascularbundlesalongwiththeperipheralinterconnectedfibersarevisible.ThesefibersarearrangedinCu(s)++4NaOH(aq)(NH)SO(aq)4228thefractal-likeassemblyandareresponsibleformechanical→++Cu(OH)(s)222NaSO(aq)42NH(g)32+2HOstabilityandflexibility.Figure2d−fshowstheleafskeletonafterCudeposition.ItisclearfromtheimagesthattheCuhas(1)depositedconformallyontothesurfaceastheunderneathGasbubbleshavingacharacteristicammoniaodorwerevascularbundlesandfibersarenotvisible.DuetotheirregularnotedthatindicatedthepresenceofNH3.Inthesecondstep,surfaceoftheskeleton,thesurfaceoftheCudisplayingnano-Cu(OH)2transformsveryrapidlyintotetrahydroxocupratebumpornano-mountain-likemorphologyisevidentatthe(II)anionsCu(OH)42−duetothealkalinityofthesolution.44nanoscale(Figure2f,inset).Theoxidationprocessledtothe−−2formationoftheCuOmicrotufts,whichcanbeseeninFigureCu(OH)(s)24+→2OH(aq)Cu(OH)(aq)(2)2g−i.TheseCuOmicrotuftsrangefrom∼5to15μminInthefinalstep,acondensationreactionleadstothediameterandhavehigh-aspect-ratiofragments.ItisalsoformationofCuOparticlesfromCu(OH)2−evidentfromthemicrographsthatthefractal-likegeometry4wasperfectlypreservedevenafterthefabricationprocedure2−−Cu(OH)4(aq)↔+CuO(s)2OH(aq)+H2O(3)andCuOmicrotuftsareevenlydistributedthroughoutthesurface.ToconfirmthepresenceofCuontheleaffractalThetinyCuOparticlespreparedonthesurfaceofCu-surface,energy-dispersivespectrometry(EDS)measurementscoatedskeletonhavehighsurfaceenergyandarehighlyweredone.TheEDSdatacorrespondingtotheFESEMimagesreactive.ThesesmallCuOparticlesaggregatearoundtheareshowninFiguresS3−S5(SupportingInformation),whichnanomountainscreatedduringtheCudepositionduetotheconfirmsthepresenceofCuandCuOonthesurfaceoftheleafunevensurfaceoftheleafskeleton(Figure2f,inset).Thisskeleton.X-rayphotoelectronspectroscopyanalysisshowedformsthelongmicrofiber-likestructure,andmanyofthese(FigureS6,SupportingInformation)thatbeforechemicalfibersalongwiththeuneven3Dgeometryoftheskeletoncollectivelymakethesestructureslooklikemicrotufts.Intheoxidationtreatment,thesurfaceconsistedofCu°andsomeCu2+speciestypicalforanair-oxidizedCusurface.Aftertheabsenceofthesenanomountain-likestructures,nanostructureschemicaloxidationtreatment,onlyCu2+specieswerepresentinarandomshapeandorientationwereexpected.Toconfirmthis,Cuwasdepositedonaplanarglasssubstrateandwasonthesurface,confirmingthechemicalstateofmicrotuftsassubjectedtooxidationinthesamewayasabove.Asexpected,CuO.Aftertheapplicationofthesilanecoating,theXPStherandommicro-grass-likemorphologywasevidencedandspectrumwasdominatedbythestrongF1ssignaloriginatingcanbeseeninFigureS2(SupportingInformation).ItisalsofromtheC16H19F17O3SisilanecompoundandonlyaweakCunoteworthytomentionthattheshapeandsizeofthesecopperLMMsignalfromtheleafskeletonsubstratewasdetected.TheoxidestructurescanbecontrolledbyblockingoftheCulayers.intensityofCu2psignal,whichismoresurfacesensitivethanForexample,inourpreviousstudy,wehaveshownthathigh-CuLMMsignal,wasbelowthedetectionlimit.Therefore,thedensityCuOnanoneedle-likemorphologycanbeobtainedbyaveragethicknessofsilanecoatingwasapproximatedtobe3373https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

4Langmuirpubs.acs.org/LangmuirArticleFigure3.Snapshotsofinitialnucleation,dropletformationonfractalsurfacebearing(a).CuOmicrotufts,(b)CuOmicrotuftswithhydrophobiccoating,(c)bareCuonly,and(d)Cuonlywithhydrophobiccoating.Thescalebarinallcasesis200μm.closetotheinformationdepthoftheXPSanalysis(i.e.,5−10dropletspreadsonthesurfaceveryslowlyandmaintainedanm).contactlineoveraperiod.ThisconfirmsthattheCuOWettability.Hydrophilicsurfacesaremoreattractivetomicrotuftsareresponsibleforthesuperhydrophilicityofthewater,andtheirobservedwettabilitiesarefurtherincreasedbysurface.45roughness,accordingtotheWenzelequationFogHarvestingStudies.TheCuOmicrotufts,fractalsoftheleafskeleton,andtheinterconnectionofveinspresenttwocosθθm=rcosY(4)phasesintheefficientcollectionofwater.Themicrotuftstructureshelpintheinitialdropletcaptureandnucleation.whereθmisthemeasuredcontactangle,θYistheintrinsicThefractal-likestructuresaidinthedropletgrowthandswiftYoung’scontactangle,andristheroughnessratio(ratiomovementofthewater.Finally,theleafvein-likestructuresaidbetweentheactualandprojectedsolidsurfaceareas).Fromtheintheefficienttransportandcollectionofwater.model,itcanbededucedthatthesurfaceroughnessisdirectlyThefogharvestingabilityoftheCuOmicrotuftsembeddedproportionaltothewettabilityoftheoriginalsurfacei.e.,leafskeletonalongwiththecontrolsampleswasestimatedinhydrophilicsurfacebecomesmorehydrophilicandthethreeindependentcycles.ThedetailsoftheexperimentarehydrophobicsurfacebecomesmorehydrophobiconincreasinggivenintheMaterialsandMethodssections.Theleafskeletonthesurfaceroughness.Inourcase,thegrowthoftheCuOwithjustCucoatingwasusedasacontrol.Figure3showsthemicrotuftsonthefractalsurfacesleadstothesuperhydrophiliccharacteristicssnapshotsofthefractalstructuresduringthesurfaces,whicharedirectlyinlinewiththeWenzelmodel.initialnucleationcycle.InthecaseofthesurfacesbearingtheHowever,itisverydifficulttocalculateexactcontactanglesonCuOmicrotufts,thesurfaceiswettedinstantaneouslyassoontheleafskeletonsurfacesbecauseofthe3Darchitectureofasthefirstfogdropletshitthesurface(Figure3a).Asthefogmicroscalefractalsandtheunevensurfaceoftheleafskeletonstreamcontinuestoreachthesurface,thenewfogdropletsatmacroscale.Therefore,toshowthewettabilityofthesurfaces,thewaterspreadingonthefractalsurfaceswascoalescewiththewateralreadydepositedoverthesurfaceandinvestigatedusingthedropletspreadingexperiments.Theformacontinuousfilmatleastonthelargerveinsofthedropletspreadingof3μLwaterdropletsonthefractalsurfacessurfacethatarevisibleinthemicrograph.ThisfilmremainshavingCuOmicrotuftscanbeseeninVideoV1,SupportingconstantevenifmorefogdropletsarecapturedbythesurfaceInformation.Assoonasthewaterdroplettouchesthesurface,asthereisaconstantwatermovementonthesurface,whichthedropletinstantaneouslyspreadsanddisplaysanextremelycanbeseeninVideoV4(SupportingInformation).Inthecaselowcontactangle.ItcanbeseenthatthewaterkeepsonofthesilanizedCuOmicrotuftsontheleafskeleton,tinyspreadingacrossthefractalstructuresandeventuallydropletsareimmediatelyvisibleassoonasthefogstreamdisappearsafterapproximately4min.Onthehydrophobictouchesthesurface.Inatypicalmicro/nanostructuredsurfacesbearingCuOmicrotufts,thedropletstaysinthehydrophobicsurface,jumpingoffofthedropletsisusually46sphericalcap,whichcanbeseeninVideoV2,Supportingobservedonthesilanizedsurfaces.However,inthiscase,theInformation.ThisexperimentwasalsoconductedonthenucleateddropletscontinuetogrowduetothecoalescencefractalsurfaceshavingjustCucoating,whichcanbeseeninwiththenearbydroplets.ItisevidentfromFigure3bandVideoV3,SupportingInformation.Inthiscase,thewaterVideoV5(SupportingInformation)thatthefractal-like3374https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

5Langmuirpubs.acs.org/LangmuirArticleFigure4.Snapshotsshowingwatertransportontheleafveinsbearing(a)CuOmicrotufts,(b)CuOmicrotuftswithhydrophobiccoating,(c)bareCuonly,and(d).Cuonlywithhydrophobiccoating.Thescalebarinallcasesis10mm.Figure5.(a)Schematicofthewatercollectionsetup.(b)Fogharvestingdynamicsasvolumeofwatercollected(g)intime,t(min),overskeletonsurfacesofdimensions40mm×40mm.(c)Overallwatercollectedovertheperiodof1hwhensamplesweretiltedinthevertical(0°),tilted(45°),horizontal(90°),andflipped(180°)positions.Errorbarsshowthestandarddeviationscalculatedfromthreeindependentmeasurements.geometryaidsinthecoalescenceofthegrowingdropletsandwatercanbeevidencedasseeninFigure3candVideoV6avoidssheddingorjumpingoffofsmallerdropletsprematurely.(SupportingInformation).UnlikethehydrophilicsurfacewithAfterafewseconds,dropletswithsizesrangingfromtensofCuOmicrotufts,waterremainsonthesurfaceandcontinuestomicrometerstoafewmillimetersareobservedinthiscase.Ingrowfurtherstartingfromthefractalcurves.Withtime,thethecaseofcontrolhydrophilicCu-coatedskeleton,afilmofwatertakestheshapeofalargedropletthatremainspinnedto3375https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

6Langmuirpubs.acs.org/LangmuirArticleFigure6.(a)Mechanismofinitialnucleationandmicrotufts.(b)SchematicofwatergrowthandmovementinCuOmicrotuftsbearingfractalsurfaces.thesurface.Inthecaseofsilane-coated,Cu-coatedfractalroleinthetransportofthewater.Asimilartrendwasseeninsurface(Figure3dandVideoV7,SupportingInformation),thecontrolsilanizedCu-coatedskeletonswherethegrownseveralsmalldropletscouldbeobserved,whicheventuallydropletsslidedownthroughthesurface(Figure4d).Thetimegrowbiggerandtakeasphericalshape.takeninthiscaseislongerincomparisontothehydrophobicFigure4showsthecharacteristicssnapshotsoftheCuO-skeletonsbearingCuOmicrotufts.andCu-coatedleafskeletonsurfacesduringthetransportofThewatercaptureandremovalefficiencyofthedifferentthecapturedwater.InthecaseofthehydrophilicsurfacessurfacesisdirectlyrelatedtothedifferentforcesactingonthebearingCuOmicrotufts,thewatertravelsacrosstheleafveins.dropletandthearchitectureofthesurface.ToquantifytheThenetworkofthefractalsdirectsthecontinuouswaterfilmtowatercollectionperformanceontheleafskeletonsbearingthecentralveinwherethewateraccumulatesandcanbeCuOmicrotuftsandcontrolsurfaces,thesurfaceswerecollectedasseeninFigure4a.AsimilarwatermovementcansubjectedtofogflowinahomemadesetupasshowninbeseeninthecontrolCu-coatedhydrophilicsurfaces(FigureFigure5a.Allofthesampleswerecutina40mm×40mm4b),wherethewatertravelsacrosssubveinstothemaincentraldimension.Theamountofwaterdrippingfromtheleafveinsandgetsaccumulatedatthecenterbeforebeingskeletonswasquantifiedevery10min,andthedataarecollected.However,theoverallcollectiontimewasslowandpresentedinFigure5b.Throughoutthe1hofthefogbiggerdropletscanbeseenacrossthesurfaceofthecontrolcollectionexperiments,theleafskeletonsbearingtheCuOhydrophilicsample.microtuftswithoutandwithhydrophobiccoatingcollected7.3Figure4cshowsthewatertransportontheskeletonsurfaces±0.6and6.5±0.9gofwater,respectively.NormalizingthishavingsilanizedCuOmicrotufts.Inatypicalhydrophobictothesamplesize,theoverallefficiencyintermsofwatersurface,perfectlysphericaldropletsareexpectedwhicheithercollectedperunitareawascalculatedas0.45and0.39gcm−2jumpoffthesurfaceorrolloffthesurfacequickly.However,inh−1fortheCuOmicrotuftleafskeletonswithoutandwiththiscase,thedropletsinitiallyappearspherical,butwithtime,hydrophobiccoating,respectively.Thehydrophilicskeletontheytakerandomshapesasthesecontinuetogrow.ThiscouldsurfacesbearingtheCuOmicrotuftscollectedmorewaterbeduetothefractal-likestructurethatdoesnotallowdropletscomparedtothehydrophobicsurfaces.Thecollectionofwatertojumpandrolloffquickly.Thesedropletscoalescewitheachwasalsocontinuousthroughoutthewatercollectioncycleinotherasexpectedinameshlikesurface.ThedropletsgrowthecaseofhydrophilicskeletonswithCuOmicrotuftshavingbiggerandremainpinnedtothesurfaceforaprolongedlinearregression,r2≈0.99asseeninFigure5b.Controlperiod,whichcanbeduetotheinstabilitiesintheirCassiesurfacesontheotherhandcollectedasignificantlylesserstates.Eventually,thedropletsbecomebiggerandslideamountofwatercomparedtotheCuOmicrotuftsbearingleafthroughthesurfacewiththeaidofgravity.Unlikeintheskeletons.Thisisincontrasttotheslownucleationofwaterhydrophilicsurfaces,theleafveinsdonottendtoplayamajordropletsatthesurfacesthatcanbeseeninFigures3and4.3376https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

7Langmuirpubs.acs.org/LangmuirArticleTheoverallquantitiesofwatercollectedwere4.8±0.5and3.1whichisleadstothewatercloggingbetweenthefractal±0.4gforskeletonswithCucoatingandCu-coatedskeletonsurfacesandresponsibleforthecomparativelylowwaterwithhydrophobiccoating,respectively.Thewaterharvestingharvestingonthesesurfaces.Ontheleafskeletonsbearingefficiencywas0.30gcm−2h−1fortheleafskeletonswithonlyCuOmicrotuftstructures,athinfilmofwaterwasimmediatelytheCucoating,and0.19gcm−2h−1fortheleafskeletonswithobservedonthesurfaceassoonasthesurfacewasexposedtotheCucoatingandthehydrophobicsilanecoating.Inthefogflow.Microtuft-likeshapeiscomposedoflongconicaladdition,hydrophilicandhydrophobicplanarcontrols(CuOthread-likefragmentsoriginatingfromacommonbase.Hence,onglasssubstrate)havingdimensions40mm×40mmwerethewatercollectionontheindividualfragmentcanbedefinedalsotestedforwatercollection.Theoverallwatercollectioninviapressuregradientsontheconicalstructures.Forallanhourwas3.3±0.4and2.3±0.4gforthehydrophilicandmicroconicalfragmentswheretheradiusoftheconesincreaseshydrophobicsamples,respectively.Theplanarsurfacesfromtiptobase,thepressuregradientduetothesurface47,48displayednormalizedwaterharvestingefficienciesof0.20tensiononthefilmofwaterisand0.14gcm−2h−1forhydrophilicandhydrophobicsurfaces,dpdκrespectively.=γToquantitivelychecktheroleofthemicrotufts,hydro-dssd(5)phobicity,andveinorientationinthewatertransport,samplesHere,pistheliquidpressure(water),sisthepositionofthewereexposedtomistinvertical(0°),tilted(45°),horizontalfibers,κisthecurvature,andγisthesurfacetension.Dueto(90°),andflipped(180°)positions,asshownintheinsetofthispressuregradient,watermigratesfromtheconvextipstoFigure5c.Thewaterwascollectedandquantifiedaccordingtotheconcavepartsbetweenthefibersofthemicrotufts.thesetupshowninFigure5a.Overall,thewatercollectionwasAccordingtoeq5,liquidpressuredecreasesalongthemaximumwithsuperhydrophilicsurfaceswithCuOmicrotuftsdirectionoftheincreasingradiusonmicrofibers.TheliquidandminimumwithhydrophobicCu-coatedskeletons.TopressurealsodecreasesalongthedirectionofadecliningradiusconfirmiftheeffectsoftheCuOmicrotufts,hydrophobicity,orbetweenthemicrofibers.Therefore,thewatercondensedondirectionofthesampleonthewatercollectionefficiencywerethetipofthemicrofiberwillbepulledtowardtheperipherystatisticallysignificant,weconductedathree-wayANOVAtest(lowerradiusofthemicrofiber).Inthesameway,thewaterforthedata(SupportinginformationTableS1).Thedepositedaroundtheperipheryofthemicrofiberwillbedrawnmicrotufts(P<0.001)andhydrophobicity(P<0.001)havetowardthebottomsurface.Theradiusofthemicrofibertiprtisastatisticallysignificanteffectonthewatercollectionsmallercomparedtotheradiusofmicrofiberperipheryrp(rp>efficiency.Theorientationofthesamplehadalesssignificantrt).Also,theradiusofthebaserbismuchlargercomparedtoeffectbutstillhadaP-valueof0.01.Inthecaseofthetheperiphery(rb>rp,seeFigure6a).Thismeansthatthesuperhydrophilicsurfaces,wenotedthatthewatercollectionwatergetsdepositedasacontinuousfilm.Thisfilmwillbewasmaximumwhenthesampleswereintheverticalpositionpulledtowardtheregionneartheperipheryofthemicrofiber(mostoftheveinspointingdownward).Thehorizontalbytheinfluenceofthepressuregradient.Minimaloverfloodingpositionhadthelowestyield,whichcouldbecorrelatedtothewasobserved,whichcouldbeduetotheassemblyofthelongorientationoftheveins.Thewatercollectionwasonaveragemicrofibersinthemicrotuft-likeorientationandtheproximity∼20%lesswhenthesurfacewastiltedhorizontallythanintheofnumerousmicrotufts.Thedecreaseintheoverfloodingonverticalposition.Inthecaseofskeletonsurfaceshavingthehydrophilicsurfacesleadstoanincreaseincondensationhydrophobiccoatings,theorientationhadanegligiblecoefficientandabetterwatercollectionefficiency.48,49influenceonthewatercollection.ThiswasalsoconfirmedThehydrophilicskeletonsurfacesbearingCuOmicrotuftswithtwo-wayinteractionbetweenthedirectionoftheleafanddisplayedaunidirectionalwatermovementthroughoutthehydrophobicity,whichwasfoundsignificant(P=0.004).veins.ThemovementwasswiftandcontinuousasseeninHence,inhydrophobicleafskeletons,onlythepresenceoftheFigure4a.ThevenationpatternoftheleafskeletonissuchthatCuOmicrotuftstendstoplayaroleinthewatercollectionthesmallerveinskeeponincreasingtheorderandeventuallyefficiencyratherthantheveinorientation.However,itismergewiththecentralvein.Thereisaprogressiveincreaseinnoteworthytomentionthatwhenthesurfacesaredesignedinthediameteroftheveinsfromtheprimarytothesecondarycontrastingwettability,theveinorientationmayplayamajorlevel.So,whenthewaterfilmisformedonthesuper-roleinwatertransport.hydrophilicsurfaceduringtheinitialphase,itleadstotheInthisstudy,theuniquemicrostructures,fractals,and17Young−Laplacepressuredifferencebetweentheveins.Thisskeletonveinsplayamajorroleintheoverallwaterharvestingwillleadtoacontinuouswatermovementfromsmallerveinsefficiency.Thewaterharvestingmechanisms,inthiscase,cantothebiggerveins.Theshapeoftheveinsprovidesthebedividedintonucleation,growth,andtransport.Theinitialcontinuouscurvaturegradient,whichfurthermoreaidsinthenucleationandgrowthofwaterinCuOmicrotuftscanbe39smoothmovementofthewaterattheturns.ThisexplainedbytheschematicsinFigure6.Themorphologyandarrangementensuresthatthereisnobackflowofthemergedthewettabilityofthesurfaceshaveadirectimpactonthewaterwaterandtheunidirectionaltransportofthewaterisharvestingability.Undernormalcircumstancesonthesurfacesmaintainedalongtheveins.However,therewereplaceswithindevoidofanymicro/nanostructures,itstartswiththetinythefractalstructureswithunevenbumpsoruneventhickness.dropletscondensationonthesurface,whichgraduallybecomesAtthoseplaces,thewatergetsaccumulated,leadingtosmalllargerwithfurthercondensationasreportedinref7.Thisisdroplets/waterpocket-likeappearance.However,thesewaterfollowedbythefurthercoalesceofthedepositeddropletsofaccumulationsdidnotaffecttheoverallwatercollectionandrandomsizeandshapewiththeneighboringdrops,whichtheoverallmovementwasswiftasevidencedinFigure4a.eventuallyleadstotheformationoftheliquidfilmovertheOnthehydrophobicleafskeletonsbearingCuOmicrotufts,surface(Figure3candVideoV6).Theflowofthesewateradifferenttypeofwatercollectionwasobserved.TheCuOfilmswiththeaidofgravitywasobservedtobeveryslow,microtuftspossessahighersurfaceareaandhavemore3377https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

8Langmuirpubs.acs.org/LangmuirArticleFigure7.(a)SchematicofinitialdropletnucleationandgrowthonhydrophobicCuOmicrotuftsbearingfractalsurfaces.(b)DropletgrowthinthecaseofhydrophobicCuOmicrotuftsbearingfractals.nucleationsitesfortheinitialfogdropletcondensation(seecontactanglehysteresis,whichisevidentinFigure4b.IntheFigure7a).Thenucleatedandcoalesceddropletseitherjumpcaseofhydrophobicskeletonsurfaceswithoutanymicrotufts,offorrolldownthelow-energymicrofibersurface.Duetothecomparativelyfewerdropletsgotnucleatedinitiallyduetothehighsurfaceareaandarrangementofthemicrofibersinthesurfacebeingabarriertothefogflow.Theinitialdepositionmicrotuft-likestructure,theprobabilityofthedropletsmergingprocesswascomparativelyslow,asseeninVideoV7,withotherdropletsincreases.ThistypeofassemblyalsoSupportingInformation.ThecaptureddropletsgrewintheensuresthatthereisminimallossofwaterdropletsfromthesamewayasthehydrophobicskeletonsbearingCuOsurfaceduetothefogflowandmaximumdropletsaretrapped.microtufts,aidedbythefractalstructures.WhenthedropletThesilanecoatingmayalsoleadtothejumpingoffoftheattainsacriticalsize,itslidesoffthesurface.Thedropletdroplets,andthedropletsthatjumpoffthemicrofibersurfacesslidingandthesheddingprocessweremuchslowerinthiscase.gettrappedbyneighboringmicrofibers.ThesecoalescedThisprovesthatthepresenceoftheCuOmicrostructuresdropletscontinuetogrowquickly,asevidencedinFigure3b.facilitatestheinitialfogdropletcaptureanddepositionontoThefractalstructuresdisplaythehighsurfaceareaandthesurfaces.50maximumsurfacecoverageacrosstheleafskeleton.ThisTocheckhowmechanicaldamageaffectsthefogcollectionensuresthatthesedropletsgrowingatmultiplesitesfurtherperformance,weconductedthesandpaperweartest.First,thecoalesce/collidewitheachothertoformthebiggerdropletssamplewasplacedonsandpaper(grade:P120)tomakea(Figures3band7b).Ideally,inthesuperhydrophobicsurfaces,contactandaweightof400gwasplacedonthesurface.Theithasbeenseenthatthedropletsthatfalloffthesurfacearesamplewaspushed∼5cminonedirectionandthenrotated7tinyandthesheddingisquick.However,inthiscase,these180°andmoved∼5cmintheoppositedirection.Each10cmtinydropletsgraduallybecamebiggertoeventuallymergewithwasnotedasacycle,foratotalof25cycles.Thecameraandtheotherdroplets.Whenthedropletattainedacriticalsize,SEMimagesofthewornsampleareshowninFigureS7.Theinsteadofrollingoff,itslidesoffthesurface.Thecriticalsizeofabrasionisevidentfromthecameraimages.However,onclosethedropletpinnedtoasurfaceundertheinfluenceofgravityinspectionoftheSEMimages,itcanbeconcludedthatthe51canbeestimatedusingthefollowingequationabrasionoccursonlyatthetopofthesurfaces.TherearesignificantareaswheretheCuOmicrotuftscanbeseen.ThisisρgA=−γθ(cosracos)θ(6)duetothethree-dimensionalsurfacearchitectureofthefractalsHere,ρisthedensityofthedroplet,γisthesurfacetension,Athatprovideshieldingagainsttheabrasionundernormalisthecross-sectionalareaofthedrop,θrandθarepresentthecircumstances.Therewasnosignificantdifferenceintherecedingandadvancingcontactangles,respectively,andgoverallfogcollectionefficiencyoftheabratedsurfacesdenotesthegravitationalforce.Thesurfacedisplayedlargecomparedtotheoriginalsurfaces,whichcanbeseeninFiguredropletsduringfogharvestingexperimentsbecauseofitshighS8.3378https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

9Langmuirpubs.acs.org/LangmuirArticleSimilarly,tocheckthelong-termstabilityofthefabricated■CONCLUSIONSsurfaces,fogcollectionexperimentson∼100-day-oldsamplesInthisstudy,wehaveexploitedanewconceptofproducingwereconducted.TheSEMimagesofthe∼100-day-oldmicrotuftsontothefractal-likeleafskeletonstodemonstratesamples,whichwereusedinthefogcollectionstudies,arerapidnucleation,dropletgrowth,andunidirectionaltransport.showninFigureS9.ItcanbeseenthatthemicrotuftsgotFirst,copperoxidemicrotuftswerefabricatedontotheF.convertedtotherandommicrostructuresafter100daysandreligiosaleafskeletonsviaelectroplatingandchemicaloxidationthreecyclesofthefogharvestingtests.Thismightbeduetotechniques.Thefabricatedsurfaceswithmicrotuftsdisplayedthefurtheroxidationofthesurfacesovertimeinthepresencehighwettabilityandexcellentwatercapture.Asilanecoatingofairborneimpurities.Thefogcollectiononthesampleswasappliedtothesurfacetomakethesurfacehydrophobic.(∼100daysold)ispresentedinFigureS10.TherewasaFogharvestingexperimentswereconductedonhydrophilicnotablechangeinoverallwatercollectionefficiencyinthecaseandhydrophobicsurfaces.Theoverallwatercollectionofhydrophilicsurfaces.Ingeneral,superhydrophilicCuOefficienciesweredetermined,andtheroleofthemicrotufts,micro/nanostructurestendtobecomehydrophobicovertimefractalstructures,andtheorientationleafveinswasduetotheadsorptionoftheairbornecarbonspecies.52investigated.About52and85%increasesinfogharvestingHowever,thefractalstructuresandthealreadyhydrophobicefficiencywereachievedwithsuperhydrophilicandhydro-surfacesbearingCuOmicrotuftsmaintainedacomparablephobicleafskeletonsurfacesbearingCuOmicrotufts,performanceovertime.Takingalloftheseresultstogetherrespectively,comparedtotheplanarcontrolsurfaces.ThecombinationofmicrostructureswithcontrollingroughnesswiththeresultsshowninFigure5b,theresultssuggestthatwiththeuniquefractal-likearchitectureoftheleafskeletonwhilethehydrophobiccoatingreducestheinitialfogcollectionenablesthemosteffectivemechanisminwatercollectioninefficiency,itmaymaketheCuOmicrotuftsmorestableoverboththesuperhydrophilicand-hydrophobicsurfaces.Onlongperiods.surfaceswithoutsilanecoating,theCuOmicrotuftsdisplayTheaboveobservations,analysisofwatercollectiononleafexcellentwettabilityandunidirectionalwatertransferaidedbyskeletonswithCuOmicrotufts,andcomparisonwiththefractalsandveins.Insurfacesbearingthesilanecoating,theliteraturereportssuggestthatmultilevelwater-collectingCuOmicrotuftsaidinrapidnucleationandgrowthofthenetworksdisplayhierarchicalstructuresthatplayvariouswaterdroplet,whichaidsinefficientwaterharvesting.Futurerolesinwatercollection.Micro/nanostructures,suchasthestudieswillincludethestudyonthedifferentleafskeleton-CuOmicrotuftsinthiswork,aidintheinitialcaptureofthebaseddesignsandtheirbiomimeticreplicationtoachieveeven7,48fogdropletsfromthefogstream.Inthecaseofbetterwaterharvestingefficiencies.superhydrophilicsurfaces,thesemicrostructuresexpandtheareaofthesurfacethatencountersthefog/miststream,which■ASSOCIATEDCONTENTenhancesthecaptureofthefogdroplets.Thewettability*sıSupportingInformationgradientarisingfromthemicrotuftsdrivesthewaterfilmalongTheSupportingInformationisavailablefreeofchargeattheskeletonsurface.Inaddition,thefractalstructuresaidinhttps://pubs.acs.org/doi/10.1021/acs.langmuir.0c03497.efficientwatermovement.Finally,theveinsplayamajorroleinSEMimagesofCuOnanograssonglasssubstrates;EDStheefficientcollectionofthecapturedwaterbyenhancing/mappingofleafskeletonshavingdifferentcoatings;SEMfacilitatingunidirectionaltransport.Inhydrophobicsurfacesimagesofabratedsurfacesand100-day-oldsurfaces;fogalso,theCuOmicrotuftsandfractalstructuresaidinthequickcollectionresultsontheabratedsurfacesand100-day-nucleationanddropletgrowth.Themeshlikeshapeeventuallyoldsamples;analysisofvariance;andcomparisonoffogleadstofurtherdropletgrowthuntilthedropletslidesoffthecollectionperformance(PDF)surface.Wettabilityvideo;dropletsonthefractalsurfaceshavingThequantitativewatercollectionresultsindicatethatifCuOmicrotufts(MP4)subjectedtoalargescale,thesurfacescanharvestadecentdropletstaysinthesphericalcap(MP4)amountofwaterforhumanconsumption.ComparingwiththefractalsurfaceshavingjustCucoating(MP4)reportedcopperandcopperoxide-basedfogharvestingmorefogdropletsarecapturedbythesurfaceasthereissurfaces,CuOmicrotuft-basedsurfacesshowedacomparableaconstantwatermovementonthesurface(MP4)fogharvestingefficiency(seeTableS2,SupportingInforma-nucleateddropletscontinuetogrowduetothetion).Inaddition,theleafsurfacesareinabundanceandthecoalescencewiththenearbydroplets(MP4)integrationofCuOmicrotuftsontothemisfacile,whichmakescontrolhydrophilicCu-coatedskeleton,afilmofwatertheirmassproductionpossible.Itisalsonoteworthyto(MP4)mentionthattheleafskeletonsofF.religiosausedinthisstudysilane-coated,Cu-coatedfractalsurface,severalsmallarenottheonlynaturalsurfacesthatcanbeusedforthisdropletscouldbeobserved,whicheventuallygrowapplication.Manyleafskeletonsdisplaydifferentfractalbiggerandtakeasphericalshape(MP4)architecturesatthemicroandmacroscales,andourdeposition53,54techniqueshouldapplytoanykindofleafskeletons.Some■AUTHORINFORMATIONuniquefractalarchitecturesmayaidinevenbetterwaterCorrespondingAuthorscollectionsandsomefractalarchitecturemayhindertheVipulSharma−FacultyofMedicineandHealthTechnology,dropletformationandefficientwatercollection.However,theTampereUniversity,33720Tampere,Finland;orcid.org/techniqueislimitedtoleavesthatcanbeskeletonized:leaves0000-0002-4460-4610;Email:vipul.sharma@tuni.fifrommanyplantspeciesarefragileandtendtobreakwhenVeikkoSariola−FacultyofMedicineandHealthTechnology,theyareskeletonized,soitisdifficulttoproducetheTampereUniversity,33720Tampere,Finland;orcid.org/freestandingfractalstructuresfromthem.0000-0001-8307-6120;Email:veikko.sariola@tuni.fi3379https://dx.doi.org/10.1021/acs.langmuir.0c03497Langmuir2021,37,3370−3381

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