Magnetic composites based on metallic nickel and molybdenum carbide : a potential material for pollutants removal.

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ContentslistsavailableatSciVerseScienceDirect

Journal

of

Hazardous

Materials

j o ur na l ho me p a g e : w w w . e l s e v i e r . c o m / l o ca t e / j h a z m a t

Magnetic

composites

based

on

metallic

nickel

and

molybdenum

carbide:

A

potential

material

for

pollutants

removal

Raquel

V. Mambrini

a

_,

_Thales

_L.

_Fonseca

a

_,

_Anderson

_Dias

b

_,

_Luiz

_C.A.

_Oliveira

a

_,

_Maria

_Helena

_Araujo

a

_,

Flávia

C.C.

Moura

a,∗

a_Departamento_de_Química,_Universidade_Federal_de_Minas_Gerais,_Belo_Horizonte,_MG_31270-901,_Brazil b_Departamento_de_Química,_Universidade_Federal_de_Ouro_Preto,_Ouro_Preto,_MG_35400-000,_Brazil

h

i

g

h

l

i

g

h

t

s

NewmagneticmolybdenumcarbidecompositescanbepreparedbyCVDfromethanol.

Magneticmolybdenumcarbideshowspromisingresultsforpollutantsremoval.

Thecarbidecompositescanbeeasilyrecoveredmagneticallyandreused.

a

r

t

i

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l

e

i

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Articlehistory: Received14May2012

Receivedinrevisedform15August2012 Accepted2September2012

Available online 7 September 2012 Keywords:

Carbides Magneticmaterials Vapordeposition Sulfurandnitrogenremoval

a

b

s

t

r

a

c

t

Newmagneticcompositesbasedonmetallicnickelandmolybdenumcarbide,Ni/Mo2C,havebeen

pro-ducedviacatalyticchemicalvapordepositionfromethanol.Scanningelectron microscopy,thermal

analysis,RamanspectroscopyandX-raydiffractionstudiessuggestthattheCVDprocessoccursina

singlestep.ThisprocessinvolvesthereductionofNiMooxidesatdifferenttemperatures(700,800and

900◦C)withcatalyticdepositionofcarbonfromethanolproducingmolybdenumcarbideonNisurface.

IntheabsenceofmolybdenumtheformationofNi/Cwasobserved.Themagneticmolybdenumcarbide

wassuccessfullyusedaspollutantsremovalbyadsorptionofsulfurandnitrogencompoundsfrom

liq-uidfuelsandmodeldyessuchasmethyleneblueandindigocarmine.Thedibenzothiofeneadsorption

processoverNi/Mo2Creachedapproximately20mgg−1,notablyhigherthanothermaterialsdescribed

intheliteratureandalsoremovedalmostallmethylenebluedye.Thegreatadvantageofthesecarbide

compositesisthattheymaybeeasilyrecoveredmagneticallyandreused.

1. Introduction

Transition metal carbides have been widely investigated in recentyearsbecauseoftheirgoodcatalyticactivityandselectivity for hydrogenation, hydrodesulfurization and hydrodenitrogena-tionreactionsinpetroleumreﬁning[1].Amongthemmolybdenum carbidehasbeenextensivelystudiedduetoitsuniquephysicaland chemicalpropertiesincludingmechanicalhardness,thermal sta-bility,superconductivityandsurfacereactivity.Also,ithasbeen reportedthatitpossessescatalyticbehaviorcomparabletonoble metals[2–4].ThesynthesisofMo2Cistypicallycarriedoutusing

Temperature Programmed Reaction(TPRe) where molybdenum oxideisheatedunderanatmosphereofhydrogen/hydrocarbon(e.g. CH4,C2H6,C2H2,etc.)[5–7].Hereinwereportthepreparationofthe

∗ Correspondingauthor.Tel.:+553134097556;fax:+553134095700. E-mailaddress:ﬂaviamoura@ufmg.br(F.C.C.Moura).

magneticcompositeNi/Mo2Cviachemicalvapordeposition(CVD)

usingethanolasthecarbonsource.

Magneticparticleshavemanypotentialtechnological applica-tions,e.g.supportforcatalysts[8,9],magneticresonanceimaging

[10,11],drugdelivery[12],adsorptionprocesses[13,14]and envi-ronmentalremediation[8,15–17].Magneticparticlescanbecoated withaprotectivelayerofdifferentmaterialstoimprovetheir sta-bilityandtointroducenewsurfacepropertiesandfunctionalities. Someofthesecoatingmaterialsaresilica[18],alumina[19],gold

[20],andpolymers,suchaspolystyrene[21],polyaniline[22], poly-methylmethacrylate [23] and polyacrylamide[24]. Carbonis a versatilecoatingmaterialduetoitschemicalstability, biocompat-ibility,possibilityofsurfacemodificationandporecreation[25], andhavebeenusedasefficientadsorbentindifferentapplications. Theuseofcommercialfuelsandtheemissionsfromrefineries areofgreatenvironmentalimpactandareamongthemaintargets ofthenewenvironmentalstandardsthatsuggeststhereductionof sulfurandnitrogeninfuelslikegasolineandoildiesel.Theremoval ofthesecompoundsisamajoroperationinpetroleumrefiningand 0304-3894/$–seefrontmatter © 2012 Elsevier B.V. All rights reserved.

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reﬁning[1].

Molybdenumcarbidehasbeenextensivelystudieddue toits unique physical and chemical properties including mechanical hardness,thermalstability,superconductivity,andsurface reactiv-ity.Also,itisreportedthatmolybdenumcarbidepossessescatalytic behaviorcomparabletothenoblemetals[2–4].

Thesynthesisofmolybdenumcarbideistypicallycarriedout usingTemperatureProgrammed Reaction(TPRe)where a given amountofthemolybdenumoxideisheatedwhileitis exposed toamixtureofhydrogenwithahydrocarbonlikeCH4,C2H6,C2H2,

etc.[5–7].Hereinwereporttheproductionofmolybdenum car-bidecoveringthesurfaceofNi0_metallic._The_magnetic_composite

Ni/Mo2Cwasobtainedbychemicalvapordeposition(CVD)using

ethanolascarbonsource.Magneticparticleshavemanypotential technologicalapplicationsindifferentareas,suchasincatalysis assupport[8,9],inbiomedicineasmagneticresonance imaging

[10,11]indrugdelivery,inadsorptionprocess[13,14]andin envi-ronmentalremediation[8,15–17].Magneticparticlescanbecoated withaprotectivelayerofdifferentmaterialstoimprovetheir sta-bilityandtointroducenewsurfacepropertiesandfunctionalities. Someofthesecoatingmaterialsaresilica[18],alumina[19],gold

[20],andpolymers,suchaspolystyrene[21],polyaniline[22], poly-methylmethacrylate[23] and polyacrylamide[24].Carbon is a versatilecoatingmaterialduetoitschemicalstability, biocompat-ibility,possibilityofsurfacemodificationandporecreation[25], andhavebeenusedasefficientadsorbentindifferentapplications. Theuseofcommercialfuelsandtheemissionsfromrefineries areofgreatenvironmentalimpactandareamongthemaintargets ofthenewenvironmentalstandardsthatsuggestthereductionof sulfurandnitrogeninfuelslikegasolineandoildiesel.Theremoval ofthesecompoundsis amajor operationin petroleumrefining andisachievedbycatalyticprocessesoperatedathighpressures andtemperatures[26,27].Thereforeresearchhasbeendeveloped fornewmaterialcapableofloweringtheconditionsreactionsto removalofsulfurcompoundsandnitrogencompounds[28].

Thestudyofmagneticparticlescoatedwithcarbonforsulfur andnitrogenremovalisofgreatinterest.Inthisworktheproduced magneticmolybdenumcarbidewasusedasanadsorbentofsulfur andnitrogencompoundsusingmodelmoleculesdibenzotiophene andquinolineandalsohasbeenusedasorganicdyesadsorbent.

2. Experimental

Commerciallyavailablesolvents and reagents of highpurity wereusedasreceived.Nickeloxide,NiO,wasobtainedbyheating 2gofnickelchloride,NiCl2,(Synth)inair10◦Cmin−1upto450◦C

during4h.NiOwasimpregnatedwith(NH4)6Mo7O24·4H2O

(Rio-Lab)atdifferentNi:MomolarratiostoproduceNiMooxides.Forthe preparationofNi/CorNi/Mo2Cachemicalvapordeposition(CVD)

reactionusingethanol(Synth)ascarbonsourcewasinvestigated. About500mgofNiOorNi/Mooxidesinaquartztubeof30mm

75 (2)atascanrateof4min .Magnetizationmeasurements werecarried outin a magnetometerLakeShore7404VSM Sys-tem.Thesurfaceareawasdeterminedbynitrogenadsorptionusing theBET method with22 nitrogen adsorption/desorption cycles in an Autosorb 1 Quantachrome instrument. Scanning electron microscopy(SEM)analyseswerecarriedoutinaJeolJSM840Aand aQuanta200ESEM-FEGfromFEI.Adsorptionexperimentswere carriedoutwith30mgofthemagneticcompositesand5mLof quinoline,dibenzonthiopheneor dye(methyleneblueorindigo carmine)solutions(50mgL−1).Allsystemswerekeptfor24hat roomtemperature.Theconcentrationsofthedyesweremeasured byUV/VisspectrophotometryusinganUVmini-1240Shimadzu. Theconsumptionofquinolineanddibenzothiophenewere moni-toredbygaschromatography(Shimadzu,GC17Amodelequipped withaFIDdetector)usinganEquity-5columnandargonas car-riergas.ZetapotentialatdifferentpH’sweremeasurementusinga DispersionTechonoly,Inc.,model:DT1200SN:447.

3. Resultsanddiscussion

3.1. Preparationandcharacterizationofmagneticcomposites The magnetic composites wereprepared by chemical vapor depositionreactionwithethanolasthecarbonsourceat700,800 and900◦C,usingNiOandNiMooxides,whicharenotmagnetic,as startingmaterials.Allthematerialsbecamestronglymagneticafter theethanol/CVDprocessandpresentedverylowspeciﬁcareaca. 15m2_/g,_which_is_expected_considering_the_preparation_method.

Diffractogrampatternsofthematerials(Fig.1a)showedthatthe ethanolreducedNi2+_(NiO)_to_form_Ni/C_composites._Metallic_nickel

wasformedat700◦Candasmallamountofcarbonwasproduced onitssurface(Fig.1aindetail).Whenmolybdenumisintroduced (NiMooxides)theformationofcarbonispreferentiallyobserved at700◦C.However,athighertemperatures(800–900◦C)the car-bonamountdecreasestoformhigherquantitiesofmolybdenum carbide,Mo2C.Thepresenceofmetallicnickelinallsamplescan

explainthemagneticbehaviorofthematerialsduetoitshigh sat-urationmagnetizationpresentedbyNi0_._This_magnetic_property_is

veryusefultotheadsorptionapplicationsthatallowthematerials tobeeasilyremovedfromdereactionssystembyapplicationofa magneticﬁeld.

Regardingtheremovalof themagneticparticlesfroma cat-alyticreactionbymeansoftheapplicationofamagneticforce,this magneticforcewillbeproportionaltothefieldgradientapplied andtothemagneticmomentoftheparticles.Hence,themagnetic forceactingintheparticlewillbeproportionaltoits magnetiza-tion.Inconsequenceifthefieldappliedissufficienttosaturatethe particlethenthemagneticforcewillbeproportionaltothe satura-tionmagnetizationoftheparticle.Themagneticpropertiesofthese materialsarestrategicandveryimportantfortheintended appli-cation.Beingmagnetic,thematerialscanberemovedeasilyfroma

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Fig.1.XRDfortheNi/C(a)andNi/Mo2C(b),afterethanol/CVDprocessatdifferenttemperatures.

reactionsystemafterapplicationofamagneticﬁeldgradientand bepulledintothestrongestmagneticﬁeldregionfacilitatingtheir removal[29].

Theroom-temperaturemagnetizationcurve(Fig.2)showsa sat-urationmagnetizationvalueof49.9and13.2emug−1,forNi/C800 andNi/Mo2C800,respectively.Thesesaturationmagnetization

val-uesarecoherentoncethesampleNi/Cpresentshigheramountof NicomparedtoNi/Mo2C.

Scanning electron micrographs of Ni and NiMooxides after ethanol/CVDprocessareshowninFigs.3and4,respectively.Ni particleswerepartiallycoatedwithﬁlamentouscarbonascanbe seenintheSEMimagesofallNiOsamplesafterCVD(Fig.3).Insome casesitispossibletoobservecarbonﬁlaments,approximately1␮m longanddiametersofafewnanometersandalsosomeNiparticles completelycoatedbycarbon.Incontrast,whenMoisintroduced inthesample themorphologycompletelychanges (Fig.4).The ethanol/CVDprocessofNiMooxidesproduceshigheramountsof coatedmaterialsprobablybytheformationofmolybdenumcarbide assuggestedbyXRD.

Further information regarding the carbon structures was obtainedbyRamanspectroscopy(Fig.5).IntheRamanspectraof theNiOafterCVDitispossibletoseetwointensebandsattributed toDandG-bandsofcarbonmaterials,suggestingtheformation oftheNi/Ccomposites.TheG-band,relatedtothevibrationofsp2

hybridizedcarboninthetwo-dimensionalgraphiteforordered car-bonspecies,canbeobservedat1578cm−1.TheD-bandishighly

Fig.2.MagnetichysteresiscurvesfortheNi/C800andNiMo/C800materialsandin detailmagneticseparationofthematerialsafterutilization.

sensitivetoamorphouscarbonordefectsinthecarbonmaterials andappearsat1331cm−1andcanbeascribedtothedefectsinthe ﬁbrouscarbonstructure.TheintensityoftheD-bandincomparison withthegraphiticcarbonG-bandsuggeststhatdefectivecarbon ismoreabundantinthesampleafterethanol/CVDat700◦C.The moreintenseandnarrowG-bandwithIG/IDratioof4.3,observedas

theethanol/CVDprocesstemperatureincreases,reﬂectsthemore organizedandcrystallinecarbonstructures.Thisorganizedcarbon wasalsoobservedintheXRDpatternswithreﬂectionpeakswith 2atapproximately26◦.

The Raman spectra of the Ni/Mo2C material after the

ethanol/CVDprocessshowscharacteristicbandsofmolybdenum carbide,Mo2C[30],asthemainproduct,inagreementofXRD

pat-terns.AlsosomepeakscanbeobservedrelatedtoGandDbandfor carbon.

Theamountsofcarbondepositedonthematerialswere esti-matedbythermalanalysisTG/DTG(Fig.6).ForallNi/Ccomposites, it is possibletoobservea weightlossbetween500and 620◦C relatedtocarbonoxidationaccordingtoEq.(1),andaweightgain relatedtoNioxidation(Eq.(2))athighertemperatures(Fig.6aand b).

C(s)+O2(g)→ CO2(g) (1)

Ni(s)+½O2(g)→ NiO(s) (2)

Therefore, theresults clearly show that the temperature of the ethanol/CVD process directly affects theamount of carbon depositedonthesurfaceofthematerialswith14,16and19%,for thesamplestreatedat700,800and900◦C,respectively.Also,itis interestingtoobservefromDTGcurves(Fig.6b)thatthevelocity ofcarbondecompositionisdifferentforthematerialspreparedat 700,800and900◦C.ForthesampleNi/C700thecarbon decom-posesinamaximumofvelocityat512◦CandforthematerialsNi/C 800thistemperaturesismuchhigherof616◦C.Theseresults sug-gestthatthecarbondepositedduringtheCVDprocessat800◦C ismorestableandcrystallinethanthecarbondepositedat700◦C. TheseresultsareinagreementwiththeonesobtainedbyXRDwith aslightincreaseintheintensityofthepeakattributedtothe car-bonaswellasbyRamanspectroscopythatpresentsapronounced increaseintheintensityoftheGband,relatedtobetter graphi-tizedcarbon,andspeciallyinIG/IDratiowiththeincreaseinthe

temperatureofCVDprocess.

Thethermalbehaviorofthematerialcompletelychangeswith the addition of molybdenum. It is possible to observe an ini-tialweightgainafter350◦CrelatedtotheNioxidation(Eq.(2)). At higher temperatures (ca. 800◦C) it is possible to observe a weightlossthatcanberelatedtodecompositionoftheverystable

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Fig.3.SEMimagesofNi/Cobtainedbyethanol/CVDprocessat700◦_C_(Ni/C700),₈₀₀◦_C_(Ni/C800),_and₉₀₀◦_C_(Ni/C900).

molybdenumcarbide,formingmolybdenumoxide(Eq.(3)), con-ﬁrmedbytheXRDresultsobtainedfortheTGresidue.

Mo2C(s)+4O2(g)→2MoO3(s)+CO2(g) (3)

Also,astrongincreaseintheamount(50%)ofcarbondeposited ascarbideonthematerialsisobservedfortheNi/Mo2Cmaterials

(Fig.6candd)at900◦C.

TGresultsstronglyindicatethatthecarbonaceousmaterialsin Ni/Mo2CmaterialsarecompletelydifferentfromthosewithoutMo.

Theﬁrstonedecomposesat700◦Candforthelatterthe decompo-sitionstartsat480◦C.Webelievethattheseresultsarerelatedto thedecompositionofverystableandhighlycrystalline molybde-numcarbideformedduringtheCVDprocess,asobservedbyXRD. Ontheotherhand,theoxidationofcarbonat480◦Cisrelatedto theformationofalesscrystallinecarbon,suchasgraphiteor car-bonﬁlaments.Itiseasytoobservethatthetemperatureofnickel oxidation increase with the temperature of CVD.Probably the

highestthetemperatureofCVDthehigherthecoatingofNi parti-clesbyMo2C,makingtheNimoredifﬁculttooxidize.

Fromtheresultspresentedaboveweproposedthattheethanol decompositionmechanismtoformthecarbonaceousphasesinthe solidphase seemstobedifferentin themolybdenumpresence. Metallicnickelshowedactivityforethanoldecomposition, espe-ciallyathightemperatures,toformgraphiticoramorphouscarbon. However,inthepresenceofmolybdenum,initiallythereaction withethanoltakesplacewiththeactivationofethanol toform atomiccarbononthesurfaceoftheparticleswithchemical reduc-tionofNiandMo.Inasecondstep,thereducedmolybdenumis abletoreactwiththecarbontoformhighlycrystallineandstable molybdenumcarbide.Inthisstep,thesurfaceofnickelremainsin themetallicform(Ni/Mo2C).Itisinterestingtonotethatthe

pres-enceofmolybdenuminhibitstheformationofgraphiticcarbonon thenickelsurface(Fig.7),whichavoidsthepoisoningofsurface nickelwithcarbondeposits.

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Fig.4. SEMimagesofNi/Mo2Cobtainedbyethanol/CVDprocessat700◦C,800,and900◦C.

TheformationoftheNi/Mo2Ccompositewasstudiedwith

dif-ferentamountsofmolybdenum.TheCVDprocesswascarriedout withNioxideimpregnatedwithdifferentNi:Momolarratio(NiMo, NiMo0.5andNiMo0.25).

TheXRD(Fig.8)andRaman(Fig.9)analysesofthematerials showthat themolybdenumcarbideamountincreases withthe molybdenumimpregnation.Thisincreasehappensconcomitantly withadecreaseofcarbonformation.Theseresultsareinagreement withtheproposalin Fig.7thatmolybdenumfavorsthe activa-tionofethanolcomparedtothecarbonformationonthenickel surface.

3.2. Adsorptionstudies

The magnetic Ni/Cand Ni/Mo2C materialsobtained by CVD

atdifferenttemperatureswereusedas adsorbentsfordifferent contaminants,i.e.dibenzothiophene,quinoline,andorganicdyes methyleneblue(MB)andindigocarmine(IC).Theobtainedresults areshowninFigs.10and11.

Theadsorption of IC dyein the Ni/Ccomposites is low, 32, 22 and 22% for the materials treated at 700, 800 and 900◦C,

respectively.TheadsorptionofMBwaslower(lessthan10%)for allNi/Cmaterials(Fig.10a).

AfteradditionofMo,Ni/Mo2C,itispossibletoobservethatthe

adsorptioncapacitystronglyincreases(Fig.10b).Thisislikelydue tointeractionsofthemolybdenumcarbidecoatingwiththedye molecules.Moreover,itisworthnotingthatthetreatment tem-peratureledtoacompletelydifferentbehavioroftheadsorption propertiesofthematerials.

AdsorptionofICdyeoncompositestreatedat700and800◦Care relativelylow,i.e.,43and31%,respectively.However,the adsorp-tionofmethyleneblueisvery high,reachingalmost100% after 20min.Adifferentbehaviorwasobservedforthecompositetreated at 900◦C withadsorption capacities of34% for methyleneblue and99%forindigocarmine.Theseresultssuggestthat,beyondthe hydrophobicinteraction,theelectroniccharacteristicsofthedyes arealsoanimportantfactorintheadsorptionpropertiesonthe materialssurface.

Inordertounderstandtheseelectrostaticinteractionsbetween thedyesandtheadsorbentmaterials,zetapotentialmeasurements atdifferentpHwerecarriedout(Fig.12).Thezetapotentialat differ-entpHcurvesallowsthedeterminationofthepointofzerocharge

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Fig.5. RamanspectraofthecompositeNi/C(a)andNi/Mo2C(b),obtainedafterethanol/CVDprocessatdifferenttemperatures.

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Fig.7. RepresentationofthereactionofNiandNiMooxideswithethanolduringtheCVDprocesstoformthemagneticcomposites.

Fig.8.XRDanalysesoftheNi/Mo2Cwithdifferentamountsofmolybdenum,

obtainedbyCVDofethanolat800◦_C.

(PZC)ofthematerialsandanevaluationofthesurfacechargeofthe particlesunderstudy.

Fig.12showsapointofzerocharge(PZC)atpH2.6and3.0for theNi/Mo2C700andNi/Mo2C800materials,respectively.Since

theinitialpHofthedyesolutionswas4.0,thoseresultsindicated thatthesurfaceofthematerialsisnegativelychargedand there-forepreferentially adsorbpositively chargedmolecules suchas methylenebluedye.Ontheotherhand,theNi/Mo2C900material,

Fig.9. RamanspectraoftheNi/Mo2Cwithdifferentamountsofmolybdenum,

obtainedbyCVDofethanolat800◦_C.

withPZCatpH5.1,wouldhaveapositivelychargedsurfaceatpH 4.0andthereforewouldabsorbmoreanionicdyessuchasindigo carmine.

ThetypeofcarbonproducedbytheCVDprocess,inthepresence ofMo,mayexplainthehigheradsorptionpropertiesoftheNi/Mo2C

composites,oncethespeciﬁcareaareverysimilarforallthe mate-rials.Moreover,chemicalgroupssuchasphenolic,carboxilicacid

S N O N O S O O O --_O O O

a

b

c

d

H H _CH 3 CH3 H3C H3C N S N N

S

N

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Ni/C700

N

i/C800

N

i/C900

0

NiMo/C700 NiMo/C800 NiMo/C900

0

Ni/Mo

2

C 700

Ni/Mo

2

C 800

Ni/Mo

2

C 900

Fig.11.IndigoCarmineandmethyleneblueadsorptionfortheNi/C(a),andNi/Mo2C(b)materials,obtainedaftertheethanol/CVDprocessatdifferenttemperatures(pH=4,

naturalpHofthedyesolution).

2 4 6 8 10 12 -40 -30 -20 -10 0 10 20 30 40 50 60 Zeta Potential / mV

pH

Ni/Mo

2

C 700

Ni/Mo

₂

C 800

Ni/Mo

2

C 900

PZC

Fig. 12. Zeta potential measurements for Ni/Mo2C materials obtained after

ethanol/CVDprocessat700,800and900◦_C.

canbeformedonthecarbon,whichcaninﬂuencetheadsorption process.

Anothergroupofpollutants(nitrogenandsulfurcompounds) was tested in the adsorption process. The preliminary results

are displayed in Fig. 13. In general, the molybdenum carbide presents a slightly betteradsorption capacity compared tothe materialwithoutMo.Thebestadsorbent wastheNi/Mo2C 700

withanadsorptioncapacity of approximately20mgg−1, which is higher in comparison withother materialsdescribed in the literature.

Themagneticpropertiescanbeusefulfortheseparationofthe adsorbentfromthereactionmixture,whichmayberecoveredafter beenusedintheadsorptionprocess.Thematerialwithadsorbed pollutantswasseparatedbyamagneticﬁeld,fromthemixture. Then,thematerialwaswashedwithethanol toreleasethe pol-lutants,driedat60◦C,andtheregeneratedmaterialswereusedas adsorbentinanewsolution.After4cyclesofadsorption/desorption the sample still showed almost the same adsorption capacity (Supplementarymaterial).

Analyses of the liquid mixtures after the adsorption experiementsbyatomic absorptionspectrometry didnotshow anysigniﬁcantconcentrationofNiorMoionsinsolution. More-over, kinetic experiments showed that the adsorption stopped whenthematerialwasmagneticallyremovedfromthemedium. Theseresultsstronglysuggesttheoccurrenceoftheadsorptionin heterogeneousphase.

Theseresultsandpromisingcatalyticactivityaccreditedthem tobeusedincatalyticprocessesthatusecatalyststoreplacenoble metalsasanactivephase.

NiO

Ni/C700 Ni/C800 Ni/C900

0 4 8 12 16 20

a

b

Q

ads

/ mg

g

-1 material S N 0 4 8 12 16 20

Q

ads

/ mg

g

-1 material S N

NiMo Ni/Mo₂C 700 Ni/Mo₂C 800 Ni/Mo₂C 900

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4. Conclusion

TheCVDreactionofNiandNiMooxideswithethanolat tem-peraturesrangingfrom700–900◦Cproducesmagneticcomposites basedonNimagneticparticlewithcarbonaceousmaterialdeposits Ni/CandNi/Mo2C.

Preliminarystudiesintheuseofthemagneticcompositesas adsorbentofmodeldyesandespeciallyfordibenzothiopheneand quinoline,importantcontaminantsintheliquidfuelspresentgreat potentialtobeusedintechnologicalapplications.Thegreat advan-tageof thesecompositesis thattheycouldbeeasilyrecovered magneticallyandreused.

Acknowledgements

The ﬁnancial support for this research work provide by FAPEMIG,CNPqandCAPESis gratefullyacknowledged.Wealso thanktheUFMGmicroscopycenterfortheuseoftheSEMfacilities. AppendixA. Supplementarydata

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.jhazmat.2012.09.002.

References

[1]T.Chen,B.Yang,S.Li,K.Wang,X.Jiang,Y.Zhang,G.He,Ni2Pcatalystssupported

ontitania-modiﬁedaluminaforthehydrodesulfurizationofdibenzothiophene, Ind.Eng.Chem.Res.50(2011)11043–11048.

[2] N.M.Schweitzer,J.A.Schaidle,O.K.Ezekoye,X.Pan,S.Linic,L.T.Thompson,High activitycarbidesupportedcatalystsforwatergasshift,J.Am.Chem.Soc.133 (2011)2378–2381.

[3]Z.-Q. Wang, Z.-B. Zhang, M.-H. Zhang, The efﬁcient synthesis of a molybdenum carbide catalyst via H2-thermal treatment of a

Mo(vi)-hexamethylenetetraminecomplex,DaltonTrans.40(2010)1098–1104. [4]S.Cetinkaya,S.Eroglu,ThermodynamicanalysisandsynthesisofporousMo2C

spongebyvapor-phasecondensationandinsitucarburizationofMoO3,J.Alloys

Compd.489(2010)36–41.

[5] Z.Yao,Z.Lai,X.Zhang,F.Peng,H.Yu,H.Wang,Structuralstabilityandmutual transformationsofmolybdenumcarbide,nitrideandphosphide,Mater.Res. Bull.46(2011)1938–1941.

[6] T.C.Xiao,H.T.Wang,J.W.Da,K.S.Coleman,M.L.H.Green,Studyofthe prepa-rationandcatalyticperformanceofmolybdenumcarbidecatalystsprepared withC2H2/H-2carburizingmixture,J.Catal.211(2002)183–191.

[7]A.F. Lamic,C.H.Shin,G.Djega-Mariadassou,C.Potvin,Characterizationof Mo2C-WO2compositecatalystsforbifunctionalisomerization:anewpulse

methodtoquantifyacidsites,Appl.Catal.A302(2006)5–13.

[8]C.S.Castro,M.C.Guerreiro,M.Gonc¸alves,L.C.A.Oliveira,A.S.Anastácio, Acti-vatedcarbon/ironoxidecompositesfortheremovalofatrazinefromaqueous medium,J.Hazard.Mater.164(2009)609–614.

[9]C.M. Piqueras, I.O.Costilla, P.G. Belelli, N.J. Castellani, D.E. Damiani, Pd-␥Al2O3 appliedtotriglycerideshydrogenation withsupercriticalpropane:

experimentalandtheoreticalcatalystscharacterization,Appl.Catal.A347 (2008)1–10.

[10]D.L.J.Thorek,A.Chen,J.Czupryna,A.Tsourkas,Superparamagneticironoxide nanoparticleprobesformolecular imaging, Ann.Biomed. Eng.34(2006) 23–38.

[11]D.E.Sosnovik,M.Nahrendorf,R.Weissleder,MagneticnanoparticlesforMR imaging:agents,techniquesandcardiovascularapplications,BasicRes.Cardiol. 103(2008)122–130.

[12]F.Yang,C.Jin,S.Subedi,C.L.Lee,Q.Wang,Y.J.Jiang,J.Li,Y.Di,D.L.Fu,Emerging inorganicnanomaterialsforpancreaticcancerdiagnosisandtreatment,Cancer Treat.Rev.38(2012)566–579.

[13] Z.H.Sun,L.F.Wang,P.P.Liu,S.C.Wang,B.Sun,D.Z.Jiang,F.S.Xiao,Magnetically motiveporousspherecompositeanditsexcellentpropertiesfortheremovalof pollutantsinwaterbyadsorptionanddesorptioncycles,Adv.Mater.18(2006) 1968–1973.

[14] S.B.C.Pergher,L.C.A.Oliveira,A.Smaniotto,D.I.Petkowicz,Magneticzeolites forremovalofmetalsinwater,Quim.Nova28(2005)751–755.

[15] L.C.R.Machado,F.W.J.Lima,R.Paniago,J.D.Ardisson,K.Sapag,R.M.Lago, Poly-mercoatedvermiculite-ironcomposites:novelﬂoatablemagneticadsorbents forwaterspilledcontaminants,Appl.ClaySci.31(2006)207–215.

[16]I.R.Guimarães,L.C.A.Oliveira,P.F.Queiroz,T.C.Ramalho,M.Pereira,J.D.Fabris, J.D.Ardisson,Modiﬁedgoethitesascatalystforoxidationofquinoline:evidence ofheterogeneousFentonprocess,Appl.Catal.A347(2008)89–93.

[17]L.C.A.Oliveira,R.V.R.A.Rios,J.D.Fabris,V.Garg,K.Sapag,R.M.Lago,Activated carbon/ironoxidemagneticcompositesfortheadsorptionofcontaminantsin water,Carbon40(2002)2177–2183.

[18]S.Veintemillas-Verdaguer,Y.Leconte,R.Costo,O.Bomati-Miguel,B. Bouchet-Fabre,M.P.Morales,P.Bonville,S.Pérez-Rial,I.Rodriguez,N.Herlin-Boime, Continuousproductionofinorganicmagneticnanocompositesfor biomed-ical applications by laser pyrolysis, J. Magn. Magn. Mater. 311 (2007) 120–124.

[19]G.M.Shi,Z.D.Zhang,H.C.Yang,Al2O3/Fe2O3composite-coatedpolyhedralFe

nanoparticlespreparedbyarcdischarge,J.AlloyComps.384(2004)296–299. [20] Z.Wang, P.Xiao,N.He,Synthesisandcharacteristicsofcarbon encapsu-latedmagneticnanoparticlesproducedbyahydrothermalreaction,Carbon 44(2006)3277–3284.

[21]P.Y.Keng,I.Shim,B.D.Korth,J.F.Douglas,J.Pyun,Synthesis,Self-assemblyof polymer-coatedferromagneticnanoparticles,ACSNano1(2007)279–292. [22]E.N.Konyushenko,N.E.Kazantseva,J.Stejskal,M.Trchova,J.Kovarova,I.

Sapu-rina,M.M.Tomishko,O.V.Demicheva,J.Prokes,Ferromagneticbehaviourof polyaniline-coatedmulti-wallcarbonnanotubescontainingnickel nanoparti-cles,J.Magn.Magn.Mater.320(2008)231–240.

[23]S.Gyergyek,M.Huskic,D.Makovec,M.Drofenik,Superparamagnetic nanocom-positesofironoxideinapolymethylmethacrylatematrixsynthesizedbyinsitu polymerization,ColloidsSurf.A317(2008)49–55.

[24] M.K.Hong,B.J.Park,H.J.Choi,Preparationandphysicalcharacterizationof polyacrylamidecoatedmagnetiteparticles,Phys.StatusSolidi204(2007) 4182–4185.

[25]L.C.A.Oliveira,E.Pereira,I.R.Guimaraes,A.Vallone,M.r.Pereira,J.P.Mesquita, K.Sapag,PreparationofactivatedcarbonsfromcoffeehusksutilizingFeCl3and

ZnCl2asactivatingagents,J.Hazard.Mater.165(2009)87–94.

[26]P. Tétényi,T. Ollár, T. Szarvas, Sulfurexchange capacity and thiophene hydrodesulfurizationactivityofsulﬁdedmolybdena–aluminacatalysts pro-motedbynickel,Catal.Today181(2011)148–155.

[27] I.Bezverkhyy,S.Schneefeld,J.Skrzypski,J.P.Bellat,Reactionofthiophenewith mono-andbimetallicNi–Coparticlessupportedongamma-Al2O3andHDS

activitiesofobtainedsulﬁdes,Appl.Catal.A:Gen.371(2009)199–204. [28]E.Rossetto,R. Beraldin,F.G.Penha, S.B.C.Pergher,Bentonites,Diatomites

clayscharacterizationandapplicationinadsorption,Quim.Nova32(2009) 2064–2067.

[29]R.Gerber,Magneticseparation,in:AppliedMagnetism,vol.253,Erice,Italy, 1994,pp.165–220.

[30]T.-C.Xiao,A.P.E.York,H.Al-Megren,C.V.Williams,H.-T.Wang,M.L.H.Green, Preparationandcharacterisationofbimetalliccobaltandmolybdenum car-bides,J.Catal.202(2001)100–109.