重金屬水處理

Heavymetalremovalfromaqueoussolutionbyadvancedcarbonnanotubes(CNTs)

Introduction1Mechanism2Factors3Carbonnanotubetoxicity4Challengesandfurtherresearch5MainContents

IntroductionThemainsourcesofheavymetalsarethewastewatersfrommodernchemicalindustriessuchasmetalplatingfacilities,batterymanufacturing,fertilizer,mining,paperandpesticides,metallurgical,fossilfuel,tanneryandproductionofdifferentplasticssuchaspolyvinylchloride.IntroductionThepossiblesymptomsofthetoxicmetalsincludeshighbloodpressure,speechdisorders,fatigue,sleepdisabilities,aggressivebehavior,poorconcentration,irritability,moodswings,depression,increasedallergicreactions,autoimmunediseases,vascularocclusion,andmemorylossIntroductionAvailabletechniquesfortheremovalofheavymetalsfromwater:oxidationreduction,bioremediation,reverseosmosis,electrochemicaltreatment,coagulation,limesoftening,precipitation,membranefiltration,ionexchangeandadsorptionIntroductionAllthesemethodshavetheirowncapabilitiesandlimitations.Adsorptionisproventobeeconomicalandeffectivemethodfortheremovalofanumberofcontaminatesfromwater.Inrecentyears,CNTshavebeenemployedextensivelyasanewadsorbentfortheremovalofanumberofheavymetalsfromwaterIntroductionAdvantage:largesurfacearea,lightmassdensity,highporousandhallowstructure,andstronginteractionbetweenthepollutantmoleculesandCNTsAdsorptionpropertiesofCNTsdependontheirpurity，porosity,surfacefunctionalgroups,surfacearea,sitedensityandtypeofCNTs(openendedorclosedended).MechanismSchematicdiagramofthemajormechanismforsorptionofdivalentmetalionsontoCNTsurfaceFactorsaffectingtheadsorptionofheavymetalionsonCNTsThemainfactorsaffectingadsorptionofheavymetalionsonCNTssurfaceincludetheinitialmetalionconcentration,pH,contacttime,CNTdosage,agitationspeed,temperature,surfacecharge,ionicstrength,isoelectricpointandforeignions.FactorsaffectingtheadsorptionofheavymetalionsonCNTs1、PHpHplaysavitalroleintheadsorptionofheavymetalionsontotheCNTssurface.AtpHvaluehigherthanpointofzerocharge(pHPZC),theadsorptionofcationsishigherduetoelectrostaticinteractionsbetweenthecationionsandnegativesurfacecharge.Ontheotherhand,theadsorptionofcationionsisloweratlowpHduetoneutralizationofsurfacechargeFactorsaffectingtheadsorptionofheavymetalionsonCNTs1、PHFactorsaffectingtheadsorptionofheavymetalionsonCNTs2、IonicstrengthGenerally,increasingtheionicstrengthhasanadverseeffectonthesorptionofheavymetals.Ⅰ：TheionicstrengthaffectstheactivitycoefficientsofmetalionsandhencethetransferofionstoCNTssurfaceislimited.Ⅱ:TheformationofelectricaldoublelayercomplexesbetweenthecationsandtheCNTslimittheadsorptionathighconcentrationofionsFactorsaffectingtheadsorptionofheavymetalionsonCNTs3、DosageofCNTsIncreasinginCNTsdosagecaneitherincreaseordecreasethesorptionofheavymetals.EffectofadsorbentdoseonCd(II)ionremovalcapacityFactorsaffectingtheadsorptionofheavymetalionsonCNTs4、ContacttimeGenerally,withincreaseincontacttime,theremovalpercentageofheavymetalsincreasesuntilequilibriumisestablished.TheeffectofcontacttimeontheadsorptionofPb2+ionsbydifferenttypesofMWCNTsFactorsaffectingtheadsorptionofheavymetalionsonCNTs5、TemperatureThemostcommonobservationistheincreaseinsorptioncapacitywithriseintemperature.Forexample,sorptionofPb2+andZn2+andisendothermicprocessandincreaseswithriseintemperature.Thismightbeduetofasterdiffusionofmetalionsthroughthesolutionduetodecreaseinsolutionviscosityathightemperature.FactorsaffectingtheadsorptionofheavymetalionsonCNTs5、Temperature.EffectoftemperatureonthesorptionrateofZn2+byCNTsCarbonnanotubetoxicityReleaseofCNTsintotheenvironmentcanleadtoseriousenvironmentalproblems：Ⅰ：Thenanosizedcarbonparticlesposeanoccupationalinhalationexposurehazardifenteredintheworkingenvironmentassuspendedparticulatematter(PM)Ⅱ：Inwatertreatmentplant,thereisariskthattheCNTsmightleachaftercertaincyclesandcanharmthetreatmentplantCarbonnanotubetoxicityⅢ：CNTs,notonly,candisruptthemetabolicfunctionsofmicrobesinthetreatmentplantbutcanalsoaffecttheaquaticlifeifenterstotheenvironmentⅣ：

CNTshavebeenobservedtoinducelungcellularproliferationandpulmonaryinflammationinratsChallengesandNeedforfurtherresearchⅠ：

TheresearchersshouldfocusonthelargescaleeconomicalproductionofCNTsⅡ：

ExploringnoveltechniquestomodifythesurfaceofCNTstofurtherimprovetheirpropertiesⅢ：

SeparationofCNTsfromtheaqueoussolutionischallen