Efficient oxidation of cinnamon oil to natural benzaldehyde over Β-cyclodextrin-functionalized MWCNTs

Article abstract of DOI:10.1016/S1872-2067(16)62543-3

We have designed and prepared β-cyclodextrin (β-CD)-functionalized multi-walled nanotubes (MWCNTs-g-CD) for the oxidation of cinnamon oil to natural benzaldehyde under aqueous conditions. The synergistic effect of combining MWCNTs with β-CD led to a remarkable increase in the performance of the MWCNTs-g-CD for the catalytic oxidation of cinnamaldehyde, which exhibited 95% cinnamaldehyde conversion and 85% selectivity to natural benzaldehyde with a short reaction time of 10 min. The MWCNTs-g-CD also exhibited outstanding recyclability with good stability, showing no discernible decrease in their catalytic activity over five reaction cycles.

Full text of DOI:10.1016/S1872-2067(16)62543-3

ChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097
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ꢀ ꢀ ꢀ
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a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
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j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
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Article
Efficientꢀoxidationꢀofꢀcinnamonꢀoilꢀtoꢀnaturalꢀbenzaldehydeꢀoverꢀ
β‐cyclodextrin‐functionalizedꢀMWCNTsꢀ
ꢀa,c
ꢀd
ꢀd
ꢀa,c,
ꢀb,c,#
ZujinꢀYang ,ꢀXiaꢀZhang ,ꢀYanxiongꢀFang ,ꢀZebaoꢀRui *,ꢀHongbingꢀJi
ꢀ
aꢀSchoolꢀofꢀChemicalꢀEngineeringꢀandꢀTechnology,ꢀSunꢀYat‐senꢀUniversity,ꢀGuangzhouꢀ510275,ꢀGuangdong,ꢀChinaꢀ
bꢀSchoolꢀofꢀChemistry,ꢀSunꢀYat‐senꢀUniversity,ꢀGuangzhouꢀ510275,ꢀGuangdong,ꢀChinaꢀ
cꢀHuizhouꢀResearchꢀInstituteꢀofꢀSunꢀYat‐senꢀUniversity,ꢀHuizhouꢀ516216,ꢀGuangdong,ꢀChinaꢀ
dꢀFacultyꢀofꢀChemicalꢀEngineeringꢀandꢀLightꢀIndustry,ꢀGuangdongꢀUniversityꢀofꢀTechnology,ꢀGuangzhouꢀ510006,ꢀGuangdong,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Weꢀ haveꢀ designedꢀ andꢀ preparedꢀ β‐cyclodextrinꢀ (β‐CD)‐functionalizedꢀ multi‐walledꢀ nanotubesꢀ
(MWCNTs‐g‐CD)ꢀforꢀtheꢀoxidationꢀofꢀcinnamonꢀoilꢀtoꢀnaturalꢀbenzaldehydeꢀunderꢀaqueousꢀcondi‐
tions.ꢀTheꢀsynergisticꢀeffectꢀofꢀcombiningꢀMWCNTsꢀwithꢀβ‐CDꢀledꢀtoꢀaꢀremarkableꢀincreaseꢀinꢀtheꢀ
performanceꢀofꢀtheꢀMWCNTs‐g‐CDꢀforꢀtheꢀcatalyticꢀoxidationꢀofꢀcinnamaldehyde,ꢀwhichꢀexhibitedꢀ
Receivedꢀ20ꢀJulyꢀ2016ꢀ
Acceptedꢀ1ꢀSeptemberꢀ2016ꢀ
Publishedꢀ5ꢀDecemberꢀ2016ꢀ
95%ꢀcinnamaldehydeꢀconversionꢀandꢀ85%ꢀselectivityꢀtoꢀnaturalꢀbenzaldehydeꢀwithꢀaꢀshortꢀreactionꢀ
timeꢀ ofꢀ 10ꢀ min.ꢀ Theꢀ MWCNTs‐g‐CDꢀ alsoꢀ exhibitedꢀ outstandingꢀ recyclabilityꢀ withꢀ goodꢀ stability,ꢀ
showingꢀnoꢀdiscernibleꢀdecreaseꢀinꢀtheirꢀcatalyticꢀactivityꢀoverꢀfiveꢀreactionꢀcycles.ꢀ
Keywords:ꢀ
β‐cyclodextrinꢀ
Cinnamonꢀoilꢀ
Selectiveꢀoxidationꢀ
Benzaldehydeꢀ
©ꢀ2016,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
Multi‐walledꢀcarbonꢀnanotubeꢀ
Synergisticꢀeffect
1
.ꢀ ꢀ Introductionꢀ
lowꢀselectivityꢀofꢀthisꢀtransformationꢀtowardsꢀnaturalꢀbenzal‐
dehydeꢀ[8–10].ꢀTheꢀoxidationꢀofꢀcinnamaldehydeꢀinꢀtheꢀliquidꢀ
phaseꢀthereforeꢀrepresentsꢀaꢀpromisingꢀrouteꢀforꢀtheꢀmanufac‐
tureꢀ ofꢀ naturalꢀ benzaldehydeꢀ underꢀ mildꢀ conditionsꢀ [11].ꢀ
However,ꢀtheꢀbiggestꢀchallengeꢀtoꢀrealizingꢀthisꢀapproachꢀisꢀtheꢀ
availabilityꢀofꢀanꢀeffectiveꢀcatalyst,ꢀespeciallyꢀeconomicallyꢀvia‐
bleꢀnobleꢀmetal‐freeꢀcatalysts.ꢀ
Cyclodextrinsꢀ(CDs)ꢀ areꢀ anꢀimportantꢀ classꢀofꢀcyclicꢀoligo‐
saccharidesꢀthatꢀcontainꢀ6–8ꢀD‐glucoseꢀunitsꢀlinkedꢀtogetherꢀbyꢀ
α‐1,4‐glucoseꢀbonds,ꢀwhichꢀareꢀcalledꢀα‐,ꢀβ‐ꢀandꢀγ‐CDs,ꢀrespec‐
tively.ꢀTheꢀcentralꢀcavityꢀofꢀaꢀCDꢀsystemꢀprovidesꢀaꢀhydropho‐
bicꢀspaceꢀinꢀwhichꢀaꢀsuitableꢀguestꢀmoleculeꢀcanꢀbeꢀsequesteredꢀ
Benzaldehydeꢀ (BzH)ꢀ isꢀ theꢀ secondꢀ mostꢀ commonlyꢀ usedꢀ
flavorꢀcompoundꢀinꢀtheꢀworld,ꢀwithꢀaꢀwideꢀrangeꢀofꢀimportantꢀ
applicationsꢀinꢀtheꢀfoodꢀandꢀdrink,ꢀcosmeticsꢀandꢀpharmaceu‐
ticalꢀ industriesꢀ [1–5].ꢀ Increasingꢀ concernsꢀ surroundingꢀ foodꢀ
qualityꢀhasꢀledꢀtoꢀaꢀgrowingꢀdemandꢀforꢀnaturalꢀbenzaldehyde.ꢀ
Theꢀ naturalꢀ benzaldehydeꢀ usedꢀ inꢀ commercialꢀ applicationsꢀ isꢀ
mainlyꢀ obtainedꢀ byꢀ theꢀ aqueousꢀ hydrolysisꢀ ofꢀ naturalꢀ cinna‐
monꢀoil,ꢀwhichꢀcontainsꢀmoreꢀthanꢀ80%ꢀcinnamaldehydeꢀ[6,7].ꢀ
However,ꢀtheꢀwidespreadꢀapplicationꢀofꢀthisꢀprocessꢀhasꢀbeenꢀ
limitedꢀbyꢀtheꢀpoorꢀaqueousꢀsolubilityꢀofꢀcinnamonꢀoilꢀandꢀtheꢀ
*
ꢀ
ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐20‐84113663;ꢀE‐mail:ꢀruizebao@mail.sysu.edu.cnꢀ ꢀ
Correspondingꢀauthor.ꢀTel:ꢀ+86‐20‐84113658;ꢀE‐mail:ꢀjihb@mail.sysu.edu.cnꢀ ꢀ
#
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21376279,ꢀ21276102,ꢀ21425627),ꢀGuangdongꢀTechnologyꢀResearchꢀ
CenterꢀforꢀSynthesisꢀandꢀSeparationꢀofꢀThermosensitiveꢀChemicalsꢀ(2015B090903061),ꢀtheꢀFundamentalꢀResearchꢀFundsꢀforꢀtheꢀCentralꢀUniversitiesꢀ
(14lgpy28),ꢀandꢀGuangzhouꢀScienceꢀandꢀTechnologyꢀPlanꢀProjectsꢀ(2014J4100125).ꢀ
DOI:ꢀ10.1016/S1872‐2067(16)62543‐3ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ37,ꢀNo.ꢀ12,ꢀDecemberꢀ2016ꢀ ꢀ

ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
2087ꢀ
underꢀ aqueousꢀ conditions.ꢀ CDsꢀ areꢀ knownꢀ toꢀ formꢀ inclusionꢀ
complexesꢀ withꢀ aꢀ wideꢀ rangeꢀ ofꢀ compounds,ꢀ especiallyꢀ aro‐
maticꢀcompoundsꢀ[12–14].ꢀConsiderableꢀresearchꢀeffortsꢀhaveꢀ
beenꢀ directedꢀ towardsꢀ theꢀ developmentꢀ ofꢀ CDsꢀ capableꢀ ofꢀ
mimickingꢀ naturalꢀ enzymesꢀ withꢀ highꢀ catalyticꢀ activityꢀ andꢀ
substrateꢀselectivityꢀduringꢀtheꢀlastꢀdecade.ꢀAmongꢀthem,ꢀβ‐CDꢀ
hasꢀ beenꢀ widelyꢀ usedꢀ toꢀ mediateꢀ aꢀ broadꢀ rangeꢀ ofꢀ organicꢀ
transformationꢀunderꢀaqueousꢀconditions,ꢀincludingꢀoxidation,ꢀ
reduction,ꢀ ringꢀ openingꢀ andꢀ hydrolysisꢀ reactionsꢀ [15–20].ꢀ
However,ꢀβ‐CDꢀisꢀsolubleꢀinꢀwaterꢀandꢀmustꢀbeꢀimmobilizedꢀonꢀ
anꢀappropriateꢀsolidꢀsupportꢀsoꢀthatꢀitꢀcanꢀbeꢀreadilyꢀrecycled.ꢀ
β‐CDꢀwasꢀrecentlyꢀimmobilizedꢀonꢀcelluloseꢀandꢀchitosan,ꢀandꢀ
theꢀresultingꢀsupportedꢀsystemsꢀwereꢀappliedꢀtoꢀtheꢀcatalyticꢀ
oxidationꢀ ofꢀ cinnamaldehydeꢀ underꢀ aqueousꢀ conditionsꢀ
Theꢀ mainꢀ goalꢀ ofꢀ thisꢀ workꢀ wasꢀ toꢀ designꢀ β‐CDꢀ graftedꢀ
MWCNTsꢀ(MWCNTs‐g‐CD)ꢀforꢀtheꢀoxidationꢀofꢀcinnamonꢀoilꢀtoꢀ
naturalꢀbenzaldehydeꢀunderꢀaqueousꢀconditionsꢀ(Schemeꢀ1).ꢀItꢀ
wasꢀ investigatedꢀ thatꢀ theꢀ MWCNTs‐g‐CDꢀ wouldꢀ allowꢀ forꢀ theꢀ
supramolecularꢀ recognitionꢀ ofꢀ β‐CD,ꢀ asꢀ wellꢀ asꢀ showingꢀ goodꢀ
adsorptionꢀ andꢀ chemicalꢀ stabilityꢀ properties.ꢀ Theꢀ resultingꢀ
catalystꢀwasꢀinitiallyꢀevaluatedꢀforꢀtheꢀoxidationꢀofꢀcinnamal‐
dehydeꢀusingꢀhydrogenꢀperoxideꢀasꢀtheꢀterminalꢀoxidantꢀunderꢀ
theꢀmildꢀreactionꢀconditions.ꢀAꢀplausibleꢀmechanismꢀwasꢀpro‐
posedꢀforꢀtheꢀoxidationꢀofꢀcinnamaldehyde.ꢀTheꢀMWCNTs‐g‐CDꢀ
exhibitedꢀ enhancedꢀ catalyticꢀ activityꢀ comparisonꢀ withꢀ theꢀ
MWCNTsꢀ andꢀ β‐CDꢀ inꢀ isolation,ꢀ whichꢀ wasꢀ attributedꢀ toꢀ theꢀ
occurrenceꢀ ofꢀ aꢀ synergisticꢀ effectꢀ betweenꢀ β‐CDꢀ andꢀ theꢀ
MWCNTs.ꢀ ꢀ
[21–24].ꢀ Theꢀ resultsꢀ revealedꢀ thatꢀ β‐CDꢀ andꢀ theꢀ functionalꢀ
groupsꢀofꢀtheꢀsupportꢀactedꢀsynergisticallyꢀtoꢀallowꢀforꢀtheꢀoxi‐
dationꢀ ofꢀ cinnamaldehyde.ꢀ However,ꢀ fromꢀ anꢀ industrialꢀ pro‐
ductionꢀperspective,ꢀtheꢀapplicationꢀofꢀtheseꢀcatalystsꢀcouldꢀbeꢀ
limitedꢀ byꢀ theirꢀ lowꢀ mechanicalꢀ strengthꢀ andꢀ poorꢀ durabilityꢀ
towardsꢀsuccessiveꢀreactionꢀcycles.ꢀ
2.ꢀ ꢀ Experimentalꢀ
2.1.ꢀ ꢀ Materialsꢀ
MWCNTsꢀ wereꢀ purchasedꢀ fromꢀ Shenzhenꢀ Nanotechꢀ Portꢀ
Co.,ꢀLtdꢀ(Shenzhen,ꢀChina).ꢀ‐CDꢀ(>99%)ꢀwasꢀpurchasedꢀfromꢀ
Shanghaiꢀ Boaoꢀ Biotechnologyꢀ (Shanghai,ꢀ China).ꢀ Cinnamalde‐
hydeꢀ(>99%)ꢀwasꢀobtainedꢀfromꢀSinopharmacyꢀChemicalꢀRea‐
gentꢀ(Shanghai,ꢀChina).ꢀAllꢀofꢀtheꢀotherꢀchemicalsꢀusedꢀinꢀthisꢀ
studyꢀwereꢀpurchasedꢀasꢀtheꢀanalyticalꢀgradeꢀandꢀusedꢀwithoutꢀ
furtherꢀpurification.ꢀAllꢀofꢀtheꢀaqueousꢀsolutionsꢀwereꢀpreparedꢀ
usingꢀMilli‐Qꢀwaterꢀunderꢀambientꢀconditions.ꢀ
Carbonꢀ nanotubesꢀ (CNTs)ꢀ haveꢀ alsoꢀ beenꢀ studiedꢀ exten‐
sivelyꢀ asꢀ catalystsꢀ (orꢀ supports)ꢀ andꢀ adsorbentꢀ materialsꢀ forꢀ
liquidꢀ phaseꢀ reaction‐adsorptionꢀ systemsꢀ becauseꢀ ofꢀ theirꢀ
uniqueꢀ properties,ꢀ includingꢀ theirꢀ excellentꢀ electricalꢀ andꢀ
thermalꢀconductivity,ꢀgoodꢀchemicalꢀstabilityꢀandꢀrecyclability,ꢀ
environmentalꢀ acceptabilityꢀ andꢀ lowꢀ costꢀ [25–28].ꢀ Severalꢀ
studiesꢀ haveꢀ shownꢀ thatꢀ CNTsꢀ areꢀ effectiveꢀ adsorbentsꢀ thanꢀ
activatedꢀ carbonꢀ forꢀ theꢀ removalꢀ ofꢀ organicꢀ pollutantsꢀ fromꢀ
aqueousꢀsolutionsꢀbecauseꢀofꢀtheirꢀexcellentꢀadsorptionꢀcapac‐
ityꢀ[29,30].ꢀCNTsꢀhaveꢀalsoꢀbeenꢀusedꢀasꢀmetal‐freeꢀcatalystsꢀinꢀ
numerousꢀ reactions,ꢀ includingꢀ theꢀ oxidativeꢀ dehydrogenationꢀ
ofꢀaromaticꢀhydrocarbonsꢀandꢀalkanes,ꢀtheꢀreductionꢀofꢀoxygen,ꢀ
theꢀoxidationꢀofꢀhydrocarbonsꢀandꢀphenols,ꢀandꢀtheꢀdecompo‐
sitionꢀofꢀammoniaꢀ[31–34].ꢀFurthermore,ꢀCNTsꢀhaveꢀbeenꢀusedꢀ
toꢀ catalyzeꢀ theꢀ oxidationꢀ ofꢀ benzylꢀ alcoholꢀ toꢀ benzaldehydeꢀ
usingꢀmolecularꢀoxygenꢀasꢀanꢀoxidantꢀ[35,36].ꢀThereꢀhaveꢀbeenꢀ
numerousꢀreportsꢀinꢀtheꢀliteratureꢀaimedꢀatꢀmodifyingꢀtheꢀsur‐
facesꢀofꢀCNTsꢀbyꢀtheꢀintroductionꢀofꢀspecificꢀfunctionalꢀgroupsꢀ
toꢀ improveꢀ theirꢀ performanceꢀ asꢀ catalystsꢀ andꢀ adsorbentsꢀ
2.2.ꢀ ꢀ PreparationꢀofꢀMWNTs‐g‐CDꢀ
MWNTsꢀ wereꢀ purifiedꢀ andꢀ oxidizedꢀ accordingꢀ toꢀ aꢀ previ‐
ouslyꢀ reportedꢀ procedureꢀ [40].ꢀ Briefly,ꢀ MWCNTsꢀ (200ꢀ mg)ꢀ
wereꢀ addedꢀtoꢀ aꢀ solutionꢀofꢀHNO
ꢀ(3ꢀmol/L,ꢀ20ꢀmL),ꢀandꢀtheꢀ
3
resultingꢀmixtureꢀwasꢀagitatedꢀunderꢀultrasonicꢀirradiationꢀatꢀ
25ꢀ°Cꢀforꢀ30ꢀmin.ꢀTheꢀmixtureꢀwasꢀthenꢀheatedꢀatꢀ120ꢀ°Cꢀwithꢀ
anꢀagitationꢀspeedꢀofꢀ120ꢀr/minꢀforꢀ24ꢀh.ꢀUponꢀcompletionꢀofꢀ
theꢀreaction,ꢀtheꢀmixtureꢀwasꢀcooledꢀtoꢀroomꢀtemperatureꢀandꢀ
theꢀsolidsꢀwereꢀseparatedꢀbyꢀcentrifugationꢀ(1ꢀmin),ꢀwashedꢀtoꢀ
neutralꢀpHꢀwithꢀdistilledꢀwaterꢀandꢀdriedꢀunderꢀvacuumꢀtoꢀgiveꢀ
MWNTs‐COOH.ꢀ Aꢀ smallꢀ portionꢀ ofꢀ thisꢀ materialꢀ (60ꢀ mg)ꢀ wasꢀ
[37–39].ꢀAsꢀpartꢀofꢀourꢀongoingꢀinterestꢀinꢀsuchꢀmaterials,ꢀweꢀ
reportꢀhereinꢀtheꢀdevelopmentꢀofꢀsurface‐modifiedꢀCNTꢀsystemꢀ
bearingꢀβ‐CDsꢀasꢀaꢀhighꢀperformanceꢀcatalystꢀforꢀtheꢀoxidationꢀ
ofꢀ cinnamaldehyde.ꢀ Toꢀ theꢀ bestꢀ ofꢀ ourꢀ knowledge,ꢀ thisꢀ studyꢀ
representsꢀtheꢀfirstꢀreportedꢀexampleꢀofꢀtheꢀsystematicꢀevalua‐
tionꢀofꢀβ‐CD‐functionalizedꢀmulti‐walledꢀCNTsꢀ(MWCNTs)ꢀasꢀaꢀ
recyclableꢀ heterogeneousꢀ catalystꢀ forꢀ theꢀ oxidationꢀ ofꢀ cinna‐
monꢀoilꢀforꢀindustrialꢀapplication.ꢀ
dispersedꢀinꢀSOCl ꢀ(25ꢀmL)ꢀunderꢀsonicationꢀconditionsꢀforꢀ30ꢀ
minꢀ inꢀ theꢀ presenceꢀ ofꢀ DMFꢀ (1ꢀ mL).ꢀ Theꢀ mixtureꢀ wasꢀ thenꢀ
heatedꢀatꢀ80ꢀ°Cꢀunderꢀnitrogenꢀovernight.ꢀUponꢀcompletionꢀofꢀ
2
theꢀreaction,ꢀtheꢀsolventꢀandꢀexcessꢀSOCl ꢀwereꢀremovedꢀunderꢀ
2
reducedꢀ pressureꢀ toꢀ giveꢀ theꢀ acylꢀ chloride‐functionalizedꢀ
MWNTsꢀ (MWNTs‐COCl).ꢀ Thisꢀ materialꢀ wasꢀ immediatelyꢀ dis‐
persedꢀinꢀDMFꢀ(10ꢀmL)ꢀunderꢀsonicationꢀconditionsꢀforꢀ5ꢀminꢀ
Schemeꢀ1.ꢀSchematicꢀdiagramꢀofꢀtheꢀMWCNTs‐g‐CDꢀpreparationꢀprocess.ꢀ

2088ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
beforeꢀ beingꢀ treatedꢀ withꢀ ‐CDꢀ (1ꢀ mmol)ꢀ andꢀ triethylamineꢀ
0.5ꢀmL).ꢀTheꢀresultingꢀmixtureꢀwasꢀheatedꢀinꢀanꢀoilꢀbathꢀatꢀ80ꢀ
Cꢀforꢀ96ꢀh.ꢀTheꢀproductꢀofꢀthisꢀreactionꢀwasꢀwashedꢀrepeatedlyꢀ
withꢀ deionizedꢀ waterꢀ toꢀ removeꢀ allꢀ ofꢀ theꢀ freeꢀ ‐CD.ꢀ Theꢀ
washedꢀproductꢀwasꢀthenꢀdriedꢀinꢀanꢀovenꢀatꢀ80ꢀ°Cꢀforꢀ24ꢀhꢀtoꢀ
giveꢀtheꢀMWCNTs‐g‐CD.ꢀ
plexationꢀ energiesꢀ ofꢀ theꢀ host,ꢀ guestꢀ andꢀ host‐guestꢀ inclusionꢀ
complexꢀ wereꢀ optimizedꢀ usingꢀ aꢀ localꢀ densityꢀ approximationꢀ
(LDA)ꢀinꢀtheꢀPerden‐Wangꢀ(PWC)ꢀformꢀatꢀtheꢀDoubleꢀNumeri‐
calꢀplusꢀd‐functionsꢀ(DND)ꢀbasisꢀsetꢀlevelꢀ[23,41].ꢀEachꢀcomplexꢀ
wasꢀ minimizedꢀ inꢀ energyꢀ inꢀ anꢀ aqueousꢀ environment.ꢀ Theꢀ
bindingꢀenergyꢀ(BE)ꢀvaluesꢀwereꢀexpressedꢀasꢀfollows:ꢀ
(
°
BEꢀ =ꢀ ECꢀ ꢀ E
ꢀisꢀtheꢀtotalꢀenergyꢀofꢀtheꢀinclusionꢀcomplex,ꢀE
sumꢀtotalꢀenergyꢀofꢀtheꢀguest,ꢀandꢀE ꢀisꢀtheꢀtotalꢀenergyꢀofꢀtheꢀ
G
ꢀ ꢀ E
H
ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ (1)ꢀ ꢀ
2.3.ꢀ ꢀ Catalystꢀcharacterizationꢀ
whereꢀE
C
G
ꢀisꢀtheꢀ
H
Fourierꢀtransformꢀinfraredꢀ(FTIR)ꢀspectraꢀwereꢀrecordedꢀonꢀ
host.ꢀTheꢀMWCNTsꢀandꢀcinnamaldehydeꢀwereꢀselectedꢀasꢀtheꢀ
hostꢀandꢀmodelꢀguestꢀmolecules,ꢀrespectively.ꢀ
aꢀTENSORꢀ37ꢀFTIRꢀspectrometerꢀ(Bruker,ꢀEttlingen,ꢀGermany)ꢀ
–1
asꢀ KBrꢀdisksꢀ forꢀwavelengthsꢀinꢀtheꢀrangeꢀofꢀ 4000–400ꢀ cm .ꢀ
Thermogravimetricꢀ analysisꢀ (TGA)ꢀ wasꢀ performedꢀ onꢀ aꢀ
STA‐449Cꢀ thermalꢀ analysisꢀ systemꢀ (Netzsch,ꢀ Selb,ꢀ Germany).ꢀ
Theꢀ TGAꢀ measurementsꢀ (weightꢀ loss)ꢀ wereꢀ performedꢀ usingꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3.1.ꢀ ꢀ Catalystꢀcharacterizationꢀ
driedꢀ samplesꢀ underꢀ N ꢀ withꢀ aꢀ flowꢀ rateꢀ ofꢀ 50ꢀ mL/min.ꢀ Theꢀ
2
temperatureꢀ ofꢀ eachꢀ measurementꢀ wasꢀ increasedꢀ fromꢀ roomꢀ
temperatureꢀtoꢀ800ꢀ°Cꢀatꢀaꢀrateꢀofꢀ10ꢀ°C/min.ꢀTheꢀX‐rayꢀcrystalꢀ
structureꢀ ofꢀ theꢀ catalystꢀ wasꢀ measuredꢀ byꢀ X‐rayꢀ diffractionꢀ
3.1.1.ꢀ ꢀ Ramanꢀanalysisꢀ ꢀ
TheꢀRamanꢀspectraꢀofꢀtheꢀMWCNTsꢀandꢀMWCNTs‐g‐CDꢀareꢀ
shownꢀ inꢀ Fig.ꢀ 1.ꢀ Theꢀ mainꢀ peaksꢀ inꢀ theꢀ spectraꢀ atꢀ 1350ꢀ andꢀ
–1
(
(
(
XRD)ꢀ analysisꢀ usingꢀ aꢀ D/max‐2200/PCꢀ X‐rayꢀ diffractometerꢀ
Rigaku,ꢀTokyo,ꢀJapan)ꢀequippedꢀwithꢀaꢀCuꢀK ꢀradiationꢀsourceꢀ
λꢀ =ꢀ 1.54056ꢀ Å).ꢀ Ramanꢀ spectraꢀ wereꢀ recordedꢀ usingꢀ aꢀ
1590ꢀcm ꢀwereꢀattributedꢀtoꢀtheꢀdisorderedꢀ(Dꢀmode)ꢀandꢀtheꢀ
graphiteꢀ(Gꢀmode)ꢀstructuresꢀofꢀtheꢀMWCNTs,ꢀrespectively.ꢀTheꢀ
Gꢀ andꢀ Dꢀ bandsꢀ usuallyꢀ representꢀ theꢀ E2gꢀ phononsꢀ ofꢀ theꢀ sp2ꢀ
α
Lab‐RAMꢀ Aramaicꢀ microꢀ Ramanꢀ spectrometerꢀ (Renishawꢀ Di‐
agnostics,ꢀGloucestershire,ꢀ UK)ꢀ withꢀanꢀexcitationꢀwavelengthꢀ
ofꢀ 514.5ꢀ nmꢀ toꢀ investigateꢀ theꢀ surfaceꢀ structuresꢀ ofꢀ theꢀ
MWCNTsꢀ andꢀ MWCNTs‐g‐CD.ꢀ Transmissionꢀ electronꢀ micros‐
copyꢀ(TEM,ꢀS‐520,ꢀJEOL,ꢀTokyo,ꢀJapan)ꢀwasꢀusedꢀtoꢀdetermineꢀ
theꢀsurfaceꢀmorphologyꢀandꢀtheꢀparticleꢀsizeꢀcharacteristicsꢀofꢀ
theꢀ catalysts.ꢀ Theꢀ BETꢀ specificꢀ surfaceꢀ areasꢀ wereꢀ measuredꢀ
usingꢀanꢀASAPꢀ2020ꢀacceleratedꢀsurfaceꢀareaꢀandꢀporosimetryꢀ
analyzerꢀ(Micromeritics,ꢀNorcross,ꢀGA,ꢀUSA).ꢀ
atomsꢀandꢀtheꢀbreathingꢀmodeꢀofꢀtheꢀk‐pointꢀphononsꢀwithꢀA1g
ꢀ
symmetry,ꢀrespectively.ꢀTheꢀintensityꢀratioꢀ(I /I )ꢀofꢀtheꢀDꢀandꢀ
D
G
Gꢀbandsꢀinꢀgraphiticꢀmaterialsꢀcanꢀbeꢀusedꢀtoꢀevaluateꢀtheꢀsizeꢀ
2
ofꢀ sp ꢀ domainsꢀ [43].ꢀ Theꢀ I
D
/I ꢀ ratiosꢀ ofꢀ theꢀ MWCNTsꢀ andꢀ
G
MWCNTs‐g‐CDꢀwereꢀdeterminedꢀtoꢀbeꢀ0.96ꢀandꢀ1.21,ꢀrespec‐
2
tively,ꢀindicatingꢀthatꢀtheꢀsp ꢀdomainsꢀwereꢀlargerꢀinꢀtheꢀlatterꢀ
ofꢀtheseꢀtwoꢀsystems.ꢀTheseꢀresultsꢀthereforeꢀindicatedꢀthatꢀtheꢀ
degreeꢀofꢀdisorderꢀonꢀtheꢀsurfacesꢀofꢀtheꢀMWCNTsꢀincreasedꢀ
afterꢀtheꢀgratingꢀofꢀtheꢀ‐CDꢀmolecules.ꢀ ꢀ
2.4.ꢀ ꢀ Selectiveꢀoxidationꢀofꢀcinnamaldehydeꢀ
3.1.2.ꢀ ꢀ TEMꢀanalysisꢀ ꢀ
TEMꢀ imagesꢀ ofꢀ theꢀ MWCNTsꢀ andꢀ MWCNTs‐g‐CDꢀ areꢀ pre‐
sentedꢀinꢀFig.ꢀ2.ꢀItꢀshowedꢀthatꢀtheꢀMWCNTsꢀwereꢀtubularꢀinꢀ
shapeꢀwithꢀaꢀsmoothꢀsurface,ꢀverticalꢀsidewallsꢀandꢀaꢀdiameterꢀ
inꢀtheꢀrangeꢀofꢀ10–30ꢀnm.ꢀTheꢀMWCNTs‐g‐CDꢀexhibitedꢀaꢀmoreꢀ
compactꢀ stackingꢀ morphology.ꢀ Theꢀ diametersꢀ ofꢀ theꢀ
MWCNTs‐g‐CDꢀwereꢀinꢀtheꢀrangeꢀofꢀ20–40ꢀnm,ꢀwhichꢀisꢀlargerꢀ
thanꢀthatꢀofꢀtheꢀMWCNTs.ꢀThisꢀdifferenceꢀinꢀtheꢀdiametersꢀwasꢀ
attributedꢀtoꢀtheꢀgraftingꢀofꢀtheꢀ‐CDꢀmoleculesꢀtoꢀtheꢀsurfacesꢀ
ofꢀ theꢀ MWCNTs,ꢀ whichꢀ isꢀ consistentꢀ withꢀ previousꢀ studiesꢀ
Theꢀ catalyticꢀ oxidationꢀ ofꢀ cinnamaldehydeꢀ wasꢀ performedꢀ
accordingꢀtoꢀaꢀpreviouslyꢀreportedꢀprocedureꢀ[41].ꢀTypically,ꢀaꢀ
mixtureꢀofꢀtheꢀcatalystꢀ(60ꢀmg)ꢀandꢀcinnamaldehydeꢀ(1ꢀmmol)ꢀ
inꢀdeionizedꢀwaterꢀwasꢀaddedꢀtoꢀaꢀ100ꢀmLꢀthreeꢀneckedꢀflaskꢀ
fittedꢀwithꢀaꢀrefluxꢀcondenserꢀandꢀmagneticꢀstirrer.ꢀTheꢀmix‐
tureꢀwasꢀthenꢀheatedꢀatꢀ60ꢀ°Cꢀforꢀ0.5ꢀh,ꢀbeforeꢀbeingꢀtreatedꢀ
withꢀaꢀsolutionꢀofꢀH
2
O
2
ꢀ(2.5ꢀmL,ꢀ30ꢀwt%)ꢀcontainingꢀNaHCO ꢀ(2ꢀ
3
mmol),ꢀwhichꢀwasꢀaddedꢀtoꢀtheꢀreactionꢀmixtureꢀinꢀaꢀdropwiseꢀ
mannerꢀ underꢀ stirring.ꢀ Samplesꢀ wereꢀ takenꢀ atꢀ appropriateꢀ
intervalsꢀandꢀextractedꢀwithꢀethylꢀacetateꢀ(5ꢀmL)ꢀbeforeꢀbeingꢀ
centrifuged.ꢀTheꢀsupernatantsꢀwereꢀanalyzedꢀandꢀidentifiedꢀbyꢀ
gasꢀ chromatography‐massꢀ spectrometryꢀ (GC‐MS)ꢀ usingꢀ anꢀ
Agilentꢀ 7890Bꢀ gasꢀ chromatographꢀ (Agilent,ꢀ Santaꢀ Clara,ꢀ CA,ꢀ
USA)ꢀequippedꢀwithꢀaꢀHP‐5ꢀcolumnꢀ(30ꢀmꢀ×ꢀ0.25ꢀmmꢀid,ꢀ0.25ꢀ
μm),ꢀ whichꢀ wasꢀ coupledꢀ toꢀ anꢀ Agilentꢀ HP5977Aꢀ massꢀ spec‐
trometer.ꢀTheꢀreproducibilitiesꢀforꢀtheseꢀdataꢀwereꢀdeterminedꢀ
toꢀbeꢀwithinꢀ5%.ꢀ
MWCNTs
MWCNTs-g-CD
2.5.ꢀ ꢀ Computationalꢀchemistryꢀcalculationsꢀ
1000
1200
1400
Raman shift (cm )
Fig.ꢀ1.ꢀRamanꢀspectraꢀofꢀMWCNTsꢀandꢀMWCNTs‐g‐CD.ꢀ
1600
1800
2000
Allꢀ ofꢀ theꢀ calculationsꢀ wereꢀ performedꢀ usingꢀ theꢀ DMol3ꢀ
methodꢀinꢀversionꢀ8.0ꢀofꢀtheꢀMaterialsꢀStudioꢀsoftwareꢀ(Accel‐
rysꢀ Inc.,ꢀ Sanꢀ Diego,ꢀ CA,ꢀ USA)ꢀ [42].ꢀ Theꢀ geometriesꢀ andꢀ com‐
1

ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
2089ꢀ
MWCNTs
MWCNTs-g-CD
Fig.ꢀ2.ꢀTEMꢀimagesꢀofꢀMWCNTsꢀ(a)ꢀandꢀMWCNTs‐g‐CDꢀ(b).ꢀ
10
20
30
40
o
/( )
50
60
70
2
[44,45].ꢀ Furthermore,ꢀ severalꢀ porousꢀ interspacesꢀ wereꢀ ob‐
servedꢀonꢀtheꢀsurfacesꢀofꢀtheꢀMWCNTs‐g‐CD,ꢀwhichꢀcouldꢀen‐
hanceꢀtheꢀcatalyticꢀactivityꢀofꢀthisꢀsystem.ꢀ ꢀ
Fig.ꢀ4. XRDꢀpatternsꢀofꢀMWCNTsꢀandꢀMWCNTs‐g‐CD.ꢀ
theꢀgraftingꢀprocessꢀ[48].ꢀTherefore,ꢀtheꢀresultsꢀclearlyꢀsuggestꢀ
thatꢀ β‐CDꢀ isꢀ successfullyꢀ immobilizedꢀ onꢀ theꢀ surfaceꢀ ofꢀ
MWCNTs.ꢀ
3
.1.3.ꢀ ꢀ FTIRꢀanalysisꢀ
TheꢀFTIRꢀspectraꢀofꢀtheꢀMWCNTs,ꢀβ‐CDꢀandꢀMWCNTs‐g‐CDꢀ
areꢀ shownꢀ inꢀ Fig.ꢀ 3.ꢀ Theꢀ MWCNTsꢀ containedꢀ twoꢀ prominentꢀ
–
1
absorptionꢀbandsꢀatꢀ3400ꢀandꢀ1630ꢀcm ,ꢀwhichꢀwereꢀattribut‐
edꢀtoꢀtheꢀstretchingꢀvibrationsꢀofꢀtheꢀwaterꢀmoleculesꢀadsorbedꢀ
onꢀtheꢀsurfacesꢀofꢀtheꢀMWCNTsꢀandꢀtheꢀC=Oꢀstretchingꢀvibra‐
tionsꢀofꢀtheꢀquinoneꢀgroupsꢀonꢀtheꢀsurface,ꢀrespectivelyꢀ[46].ꢀ
TheꢀFTIRꢀspectrumꢀofꢀβ‐CDꢀcontainedꢀmajorꢀabsorptionꢀbandsꢀ
3.1.4.ꢀ ꢀ XRDꢀandꢀBETꢀanalysisꢀ
Theꢀ XRDꢀ patternsꢀ ofꢀ theꢀ MWCNTsꢀ andꢀ MWCNTs‐g‐CDꢀ areꢀ
shownꢀinꢀFig.ꢀ4.ꢀBothꢀofꢀtheseꢀmaterialsꢀgaveꢀpeaksꢀatꢀ26°,ꢀ44°ꢀ
andꢀ 54°,ꢀ whichꢀ areꢀ characteristicꢀ ofꢀ MWCNTsꢀ [49].ꢀ Theseꢀ re‐
sultsꢀindicatedꢀthatꢀtheꢀβ‐CDꢀmoleculesꢀhadꢀbeenꢀgraftedꢀontoꢀ
theꢀsurfacesꢀofꢀtheꢀMWCNTsꢀinꢀaꢀwayꢀthatꢀdidꢀnotꢀinterfereꢀwithꢀ
theirꢀstructuralꢀframework.ꢀSimilarꢀresultsꢀtoꢀtheseꢀhaveꢀbeenꢀ
reportedꢀelsewhereꢀinꢀtheꢀliteratureꢀ[50].ꢀTheꢀgraftingꢀofꢀβ‐CDꢀ
ontoꢀtheꢀsurfaceꢀofꢀtheꢀMWCNTsꢀledꢀtoꢀaꢀdecreaseꢀinꢀtheꢀBETꢀ
–1
–1
atꢀ 3400ꢀ cm ꢀ (–OHꢀ stretchingꢀ vibrations),ꢀ 2910ꢀ cm ꢀ (–CH ꢀ
stretchingꢀvibrations),ꢀ1630ꢀcm ꢀ(H–O–Hꢀbending),ꢀ1164ꢀcm ꢀ
C–Oꢀ stretchingꢀvibrations)ꢀ andꢀ1030ꢀcm ꢀ (C–O–Cꢀ stretchingꢀ
vibrations).ꢀ Theꢀ FTIRꢀ spectrumꢀ ofꢀ theꢀ MWCNTs‐g‐CDꢀ clearlyꢀ
showedꢀseveralꢀfunctionalꢀgroupsꢀbelongingꢀtoꢀβ‐CD,ꢀincludingꢀ
CH ꢀ (2910ꢀ cm ),ꢀ C–Oꢀ (1164ꢀ cm )ꢀ andꢀ C–O–Cꢀ (1030ꢀ cm )ꢀ
groups,ꢀ whichꢀ indicatedꢀ thatꢀ theꢀ graftingꢀ ofꢀ β‐CDꢀ toꢀ theꢀ
MWCNTsꢀ wasꢀ successful.ꢀ Notably,ꢀ theꢀ intensityꢀ ofꢀ theꢀ peakꢀ
observedꢀatꢀ3400ꢀcm ꢀforꢀtheꢀMWCNTs‐g‐CDꢀwasꢀgreaterꢀthanꢀ
thatꢀofꢀtheꢀMWCNTs,ꢀwhichꢀcouldꢀbeꢀattributedꢀtoꢀthereꢀbeingꢀ
moreꢀhydroxylꢀgroupsꢀinꢀtheꢀformerꢀofꢀtheseꢀtwoꢀspeciesꢀbe‐
causeꢀofꢀtheꢀβ‐CDꢀmolecules.ꢀMoreover,ꢀtheꢀpeakꢀobservedꢀatꢀ
2
–1
–1
–1
(
2
2
surfaceꢀ areaꢀ fromꢀ 101ꢀ m /gꢀ (MWCNTs)ꢀ toꢀ 22ꢀ m /gꢀ
(MWCNTs‐g‐CD),ꢀasꢀwellꢀasꢀaꢀdecreaseꢀinꢀtheꢀporeꢀvolumeꢀfromꢀ
–1
–1
–1
–
2
3
0.4806ꢀtoꢀ0.1284ꢀcm /g.ꢀSimilarꢀresultsꢀwereꢀalsoꢀobservedꢀinꢀ
ourꢀ previousꢀ studyꢀ [51].ꢀ Theꢀ averageꢀ poreꢀ diametersꢀ ofꢀ theꢀ
MWCNTsꢀandꢀMWCNTs‐g‐CDꢀwereꢀdeterminedꢀtoꢀbeꢀ23.2ꢀandꢀ
19.2ꢀnm,ꢀrespectively.ꢀ
–1
3.1.5.ꢀ ꢀ TGꢀanalysisꢀ
−1
9
50ꢀ cm ꢀinꢀtheꢀ MWCNTs‐g‐CDꢀisꢀcharacteristicꢀofꢀanꢀ α‐(1,4)ꢀ
TGꢀ curvesꢀ forꢀ theꢀ MWCNTs,ꢀ β‐CDꢀ andꢀ MWCNTs‐g‐CDꢀ areꢀ
shownꢀ inꢀ Fig.ꢀ 5.ꢀ Theꢀ TGꢀ curveꢀ forꢀ theꢀ MWCNTsꢀ showedꢀ twoꢀ
separateꢀ weightꢀ lossꢀ steps.ꢀ Theꢀ firstꢀ weightꢀ lossꢀ occurredꢀ atꢀ
100ꢀ°C,ꢀwhichꢀwasꢀcausedꢀbyꢀdehydration,ꢀwhereasꢀtheꢀsecondꢀ
−1
glucopyranoseꢀ [47].ꢀ Theꢀ newꢀ peakꢀ atꢀ 1735ꢀ cm ꢀ wasꢀ dueꢀ toꢀ
esterꢀ groups,ꢀ indicatingꢀ thatꢀ theꢀ carboxylicꢀ acidꢀ groupsꢀ inꢀ
MWCNTs‐COOHꢀreactedꢀwithꢀhydroxylꢀgroupsꢀofꢀβ‐CDꢀduringꢀ
1630
100
(1)
(1)
1030
(
2)
2910
80
60
40
20
0
1
164
(
3)
2)
(
3)
(
1
735
950
800
3400
0
200
400
Temperature ( C)
600
800
4
000
3200
2400
1600
1
o
Wavenumber (cm )
Fig.ꢀ3.ꢀFTIRꢀspectraꢀofꢀMWCNTsꢀ(1),ꢀβ‐CDꢀ(2),ꢀandꢀMWCNTs‐g‐CDꢀ(3).
Fig.ꢀ5.ꢀTGAꢀcurvesꢀofꢀMWNTsꢀ(1),ꢀβ‐CDꢀ(2)ꢀandꢀMWCNTs‐g‐CDꢀ(3).ꢀ

2090ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
weightꢀ lossꢀ occurredꢀ atꢀ 450–700ꢀ °C,ꢀ whichꢀ wasꢀ attributedꢀ toꢀ
theꢀ decompositionꢀ ofꢀ theꢀ MWCNTs.ꢀ Theꢀ TGꢀ curveꢀ ofꢀ β‐CDꢀ
showedꢀ threeꢀ degradationꢀ stages,ꢀ includingꢀ twoꢀ weightꢀ lossꢀ
stepsꢀatꢀ50–110ꢀandꢀ320–450ꢀ°C,ꢀwhichꢀwereꢀattributedꢀtoꢀtheꢀ
evaporationꢀ ofꢀ waterꢀ adsorbedꢀ byꢀ β‐CDꢀ andꢀ theꢀ thermalꢀ de‐
compositionꢀ ofꢀ β‐CD,ꢀ respectively.ꢀ Theꢀ thirdꢀ weightꢀ lossꢀ stepꢀ
occurredꢀatꢀtemperaturesꢀaboveꢀ450ꢀ°Cꢀandꢀwasꢀattributedꢀtoꢀaꢀ
carbonizationꢀ process.ꢀ Theꢀ MWCNTs‐g‐CDꢀ showedꢀ aꢀ weightꢀ
lossꢀatꢀ100ꢀ°C,ꢀwhichꢀwasꢀattributedꢀtoꢀtheꢀlossꢀofꢀmoistureꢀandꢀ
solventsꢀ incorporatedꢀ inꢀ theꢀ polymer.ꢀ Theꢀ TGꢀ curveꢀ ofꢀ
MWCNTs‐g‐CDꢀ alsoꢀ showedꢀ weightꢀ lossesꢀ atꢀ 280–450ꢀ andꢀ
theꢀoutcomeꢀofꢀtheꢀoxidationꢀofꢀcinnamaldehyde,ꢀincludingꢀtheꢀ
reactionꢀtime,ꢀreactionꢀtemperature,ꢀamountꢀofꢀMWCNTs‐g‐CD,ꢀ
amountꢀofꢀH
2
O
2
ꢀandꢀamountꢀofꢀNaHCO .ꢀItꢀisꢀnoteworthyꢀthatꢀ
3
theꢀ agitationꢀ speedꢀ alsoꢀ hadꢀ anꢀ impactꢀ onꢀ thisꢀ reactionꢀ (Fig.ꢀ
7(a)).ꢀ Cinnamaldehydeꢀ conversionsꢀ ofꢀ 19.7%,ꢀ 58.5%ꢀ andꢀ
74.2%ꢀwereꢀachievedꢀinꢀtheꢀsolutionꢀphaseꢀforꢀagitationꢀspeedsꢀ
ofꢀ0,ꢀ100,ꢀandꢀ200ꢀr/min,ꢀrespectively,ꢀafterꢀaꢀreactionꢀtimeꢀofꢀ
12ꢀmin.ꢀAtꢀaꢀlowꢀagitationꢀspeed,ꢀtheꢀconversionꢀofꢀcinnamal‐
dehydeꢀ wouldꢀ beꢀ dependentꢀ onꢀ theꢀ lowꢀ transferꢀ rateꢀ ofꢀ theꢀ
oxidantꢀ fromꢀ theꢀ aqueousꢀ phaseꢀ intoꢀ theꢀ solid‐liquidꢀ phase.ꢀ
Higherꢀagitationꢀspeedsꢀwouldꢀenhanceꢀtheꢀextentꢀofꢀtheꢀcon‐
tactꢀbetweenꢀtheꢀtwoꢀphasesꢀandꢀtheꢀperformanceꢀofꢀtheꢀcata‐
lyst.ꢀ Agitationꢀ speedsꢀ ofꢀ 300ꢀ andꢀ 400ꢀ r/minꢀ resultedꢀ inꢀ cin‐
namaldehydeꢀ conversionsꢀ ofꢀ 93.0%ꢀ andꢀ 98.2%,ꢀ respectively,ꢀ
afterꢀ12ꢀmin.ꢀHowever,ꢀfurtherꢀincreasesꢀinꢀtheꢀagitationꢀspeedꢀ
didꢀnotꢀresultꢀinꢀfurtherꢀincreasesꢀinꢀtheꢀcinnamaldehydeꢀcon‐
version,ꢀindicatingꢀthatꢀtheꢀmassꢀtransferꢀwasꢀnoꢀlongerꢀdrivingꢀ
thisꢀ process.ꢀ Anꢀ agitationꢀ speedꢀ ofꢀ 400ꢀ r/minꢀ wasꢀ thereforeꢀ
selectedꢀasꢀtheꢀoptimumꢀagitationꢀspeedꢀtoꢀeliminateꢀtheꢀeffectsꢀ
ofꢀtheꢀliquid‐solidꢀmassꢀtransfer.ꢀThisꢀvalueꢀwasꢀusedꢀtoꢀevalu‐
ateꢀ theꢀ otherꢀ parameters.ꢀ Theꢀ conversionꢀ ofꢀ cinnamaldehydeꢀ
overꢀ theꢀ MWCNTs‐g‐CDꢀ increasedꢀ withꢀ increasingꢀ reactionꢀ
timeꢀandꢀreachedꢀ95%ꢀafterꢀaꢀreactionꢀtimeꢀofꢀ10ꢀmin.ꢀTheꢀse‐
lectivityꢀtoꢀbenzaldehydeꢀforꢀthisꢀreactionꢀremainedꢀinꢀtheꢀre‐
gionꢀofꢀ85%ꢀfromꢀ1ꢀtoꢀ10ꢀmin.ꢀAꢀslightꢀdecreaseꢀwasꢀobservedꢀ
inꢀtheꢀselectivityꢀwhenꢀtheꢀreactionꢀtimeꢀwasꢀincreasedꢀtoꢀ12ꢀ
minꢀmostꢀlikelyꢀbecauseꢀofꢀtheꢀdeepꢀoxidationꢀofꢀbenzaldehyde.ꢀ
Theseꢀresultsꢀdemonstratedꢀthatꢀtheꢀoptimalꢀreactionꢀtimeꢀforꢀ
thisꢀ transformationꢀ wasꢀ 10ꢀ min,ꢀ whichꢀ isꢀ muchꢀ shorterꢀ thanꢀ
thoseꢀ reportedꢀ forꢀ otherꢀ cinnamaldehydeꢀ oxidationꢀ systemsꢀ
[21–23,41],ꢀtherebyꢀhighlightingꢀtheꢀ excellentꢀ performanceꢀofꢀ
MWCNTs‐g‐CD.ꢀTheꢀcinnamaldehydeꢀconversionꢀandꢀselectivityꢀ
toꢀbenzaldehydeꢀincreasedꢀfromꢀ38%ꢀandꢀ53%ꢀinꢀtheꢀabsenceꢀ
ofꢀMWCNTs‐g‐CDꢀtoꢀ95%ꢀandꢀ85%,ꢀrespectively,ꢀfollowingꢀtheꢀ
additionꢀ ofꢀ 100ꢀ mgꢀ ofꢀ MWCNTs‐g‐CDꢀ atꢀ 60ꢀ °Cꢀ overꢀ 3ꢀ hꢀ (Fig.ꢀ
7(c)).ꢀ Thisꢀ resultꢀ indicatedꢀ thatꢀ theꢀ MWCNTs‐g‐CDꢀ playedꢀ anꢀ
importantꢀ roleꢀ inꢀ theꢀ oxidationꢀ ofꢀ cinnamaldehyde.ꢀ However,ꢀ
theꢀadditionꢀofꢀanꢀexcessꢀofꢀtheꢀMWCNTs‐g‐CDꢀ(e.g.,ꢀ120ꢀmg)ꢀ
ledꢀtoꢀaꢀdecreaseꢀinꢀtheꢀbenzaldehydeꢀselectivity,ꢀwhichꢀisꢀat‐
tributedꢀ toꢀ theꢀ oxidationꢀ ofꢀ benzaldehydeꢀ toꢀ benzoicꢀ acidꢀ
[21,23].ꢀ
450–700ꢀ °Cꢀ correspondingꢀtoꢀtheꢀ decompositionꢀofꢀ β‐CDꢀandꢀ
theꢀ oxidationꢀ ofꢀ theꢀ MWCNTsꢀ andꢀ theꢀ β‐CDꢀ residues,ꢀ respec‐
tively.ꢀ Basedꢀ onꢀ theseꢀ TGAꢀ results,ꢀ theꢀ weightꢀ percentageꢀ ofꢀ
surfaceꢀgraftedꢀβ‐CDꢀwasꢀestimatedꢀtoꢀbeꢀaroundꢀ40%ꢀinꢀtheꢀ
MWCNTs‐g‐CD.ꢀ Thisꢀ resultꢀ isꢀ consistentꢀ withꢀ previouslyꢀ find‐
ingsꢀ[52].ꢀ
3.2.ꢀ ꢀ CatalyticꢀperformanceꢀofꢀMWCNTs‐g‐CDꢀ
AꢀcomparisonꢀofꢀtheꢀcatalyticꢀperformancesꢀofꢀtheꢀMWCNTs,ꢀ
‐CDꢀandꢀMWCNTs‐g‐CDꢀforꢀtheꢀoxidationꢀofꢀcinnamaldehydeꢀisꢀ
shownꢀinꢀFig.ꢀ6.ꢀAꢀblankꢀreactionꢀwasꢀalsoꢀconductedꢀwithoutꢀ
anyꢀcatalyst,ꢀwhichꢀgaveꢀaꢀlowꢀbenzaldehydeꢀyieldꢀofꢀonlyꢀ16%ꢀ
afterꢀ3ꢀh.ꢀMWCNTsꢀaloneꢀcannotꢀeffectivelyꢀpromoteꢀtheꢀoxida‐
tionꢀofꢀcinnamaldehyde.ꢀTheꢀadditionꢀofꢀ‐CDꢀwasꢀbeneficialꢀforꢀ
theꢀ reaction,ꢀ affordingꢀ aꢀ cinnamaldehydeꢀ conversionꢀ ofꢀ 72%ꢀ
afterꢀ3ꢀhꢀwithꢀaꢀbenzaldehydeꢀselectivityꢀofꢀ62%,ꢀwhichꢀisꢀcon‐
sistentꢀ withꢀ previousꢀ resultsꢀ fromꢀ theꢀ literatureꢀ [21,23,41].ꢀ
Amongꢀ theseꢀ catalysts,ꢀ MWCNTs‐g‐CDꢀ wasꢀ foundꢀ toꢀ beꢀ theꢀ
mostꢀeffective,ꢀachievingꢀaꢀcinnamaldehydeꢀconversionꢀofꢀ95%ꢀ
withꢀaꢀbenzaldehydeꢀselectivityꢀofꢀ85%ꢀafterꢀaꢀreactionꢀtimeꢀofꢀ
10ꢀ min.ꢀ Theseꢀ resultsꢀ clearlyꢀ showꢀ thatꢀ ‐CDꢀ andꢀ MWCNTsꢀ
wereꢀactingꢀsynergisticallyꢀtoꢀallowꢀforꢀtheꢀefficientꢀoxidationꢀofꢀ
cinnamaldehyde.ꢀ
Fig.ꢀ7ꢀshowsꢀtheꢀeffectsꢀofꢀseveralꢀdifferentꢀparametersꢀonꢀ
100
Conversion of cinnamaldehyde
Selectivity for benzaldehyde
80
60
40
20
0
TheꢀeffectꢀofꢀtheꢀamountꢀofꢀH
2
O ꢀonꢀtheꢀperformanceꢀofꢀtheꢀ
2
MWCNTs‐g‐CDꢀ forꢀ theꢀ oxidationꢀ ofꢀ cinnamaldehydeꢀ wasꢀ alsoꢀ
evaluatedꢀ(Fig.ꢀ7(d)).ꢀTheꢀcinnamaldehydeꢀconversionꢀandꢀse‐
lectivityꢀtoꢀbenzaldehydeꢀincreasedꢀfromꢀ14%ꢀandꢀ45.7%ꢀinꢀtheꢀ
absenceꢀofꢀH
additionꢀ ofꢀ 2.5ꢀ mLꢀ H
increasingꢀtheꢀamountꢀofꢀH
benzaldehydeꢀ selectivityꢀtoꢀ80%.ꢀBasedꢀonꢀtheꢀstoichiometry,ꢀ
2 2
O
ꢀtoꢀ95%ꢀandꢀ85%,ꢀrespectively,ꢀfollowingꢀtheꢀ
ꢀ atꢀ 60ꢀ °Cꢀ overꢀ 3ꢀ h.ꢀ However,ꢀ furtherꢀ
ꢀtoꢀ3ꢀmLꢀledꢀtoꢀaꢀdecreaseꢀinꢀtheꢀ
O
2 2
O
2 2
2 2
theꢀmolarꢀratioꢀofꢀH O ꢀtoꢀcinnamaldehydeꢀwasꢀ1:1.ꢀInꢀpractice,ꢀ
(a)
(b)
(c)
(d)
2 2
aꢀsmallꢀexcessꢀofꢀH O ꢀwasꢀusedꢀinꢀthisꢀreactionꢀtoꢀovercomeꢀ
theꢀlossesꢀencounteredꢀasꢀaꢀconsequenceꢀofꢀtheꢀdecompositionꢀ
ofꢀ H ꢀ atꢀ highꢀ temperatures.ꢀ Notably,ꢀ theꢀ oxygenꢀ releasedꢀ
duringꢀtheꢀdecompositionꢀofꢀH ꢀwouldꢀhaveꢀnoꢀimpactꢀonꢀtheꢀ
oxidationꢀ ofꢀ cinnamaldehydeꢀ [22,23].ꢀ Basedꢀ onꢀ theseꢀ results,ꢀ
2.5ꢀmLꢀofꢀH ꢀwasꢀselectedꢀasꢀtheꢀoptimumꢀamountꢀforꢀthisꢀ
reaction.ꢀ Althoughꢀ H ꢀ isꢀ anꢀ oxygen‐rich,ꢀ environmentallyꢀ
Fig.ꢀ6.ꢀPerformanceꢀcomparisonꢀoverꢀvariousꢀcatalysts.ꢀ(a)ꢀBlankꢀtest,ꢀ
0ꢀwt%ꢀH ꢀ(2.5ꢀmL),ꢀNaHCO ꢀ(2ꢀmmol),ꢀ3ꢀh;ꢀ(b)ꢀMWNTsꢀ(100ꢀmg),ꢀ30
wt%ꢀH ꢀ(2.5ꢀmL),ꢀNaHCO ꢀ(2ꢀmmol),ꢀ3ꢀh;ꢀ(c)ꢀβ‐CDꢀ(1ꢀmmol),ꢀ30ꢀwt%ꢀ
ꢀ(4ꢀmL),ꢀNaHCO ꢀ(2.5ꢀmmol),ꢀ3ꢀh;ꢀ(d)ꢀMWCNTs‐g‐CDꢀ(100ꢀmg),ꢀ30
wt%ꢀ H ꢀ (2.5ꢀ mL),ꢀ NaHCO ꢀ (2ꢀ mmol),ꢀ 10ꢀ min.ꢀ Reactionꢀ conditions:ꢀ
cinnamaldehydeꢀ(1ꢀmmol),ꢀH Oꢀ(25ꢀmL),ꢀ60ꢀC.ꢀ
O
2 2
3
2
O
2
3
O
2 2
2
O
2
3
H
O
2 2
3
2
O
2
3
O
2 2
2
O
2 2

ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
2091ꢀ
100
(a)
(b)
Benzaldehye
Epoxide
Benzoic acid
100
0
r/min
100
80
60
40
20
0
100 r/min
2
3
00 r/min
00 r/min
8
0
80
400 r/min
00 r/min
5
60
60
40
20
0
4
0
0
0
2
0
3
6
9
12
0
2
4
6
8
10
12
14
16
t (min)
Reation time (min)
(c)
Benzaldehye
Epoxide
Benzoic acid
1
00
Benzaldehye
Epoxide
Benzoic acid
(d)
1
00
100
80
100
80
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
60
6
0
0
40
4
20
20
0
0
0.0
0.5
1.0
1.5
2.0
(mL)
2.5
3.0
3.5
0
20
40
60
80
100 120 140
Amout of catalyst (mg)
Amount of H
2
O
2
Benzaldehye
Epoxide
Benzoic acid
(
e)
Benzaldehye
Epoxide
Benzoic acid
(f)
100
80
60
40
20
0
100
80
60
40
20
0
1
00
100
8
0
0
80
60
40
20
0
6
40
20
0
0
.0
0.5
1.0
1.5
2.0
2.5
30
40
50
60
70
o
Amount of NaHCO
3
(mmol)
Temperature ( C)
Fig.ꢀ7.ꢀ(a)ꢀEffectꢀofꢀagitationꢀspeedꢀunderꢀtheꢀconditions:ꢀcinnamaldehydeꢀ(1ꢀmmol),ꢀMWCNTs‐g‐CDꢀ(100ꢀmg),ꢀNaHCO
wt%),ꢀ60ꢀ°C,ꢀ12ꢀmin;ꢀ(b)ꢀEffectꢀofꢀreactionꢀtimeꢀunderꢀtheꢀconditions:ꢀcinnamaldehydeꢀ(1ꢀmmol),ꢀMWCNTs‐g‐CDꢀ(100ꢀmg),ꢀNaHCO
2.5ꢀmL,ꢀ30ꢀwt%),ꢀ60ꢀ°C;ꢀ(c)ꢀEffectꢀofꢀtheꢀamountꢀofꢀMWCNTs‐g‐CDꢀemployedꢀunderꢀtheꢀconditions:ꢀcinnamaldehydeꢀ(1ꢀmmol),ꢀNaHCO
ꢀ(2.5ꢀmL,ꢀ30ꢀwt%),ꢀ60ꢀ°C,ꢀ10ꢀmin;ꢀ(d)ꢀEffectꢀofꢀtheꢀamountꢀofꢀH ꢀemployedꢀunderꢀtheꢀconditions:ꢀcinnamaldehydeꢀ(1ꢀmmol),ꢀMWCNTs‐g‐CDꢀ
100ꢀ mg),ꢀ NaHCO ꢀ (2ꢀ mmol),ꢀ 60ꢀ °C,ꢀ 10ꢀ min;ꢀ (e)ꢀ Effectꢀ ofꢀ theꢀ amountꢀ ofꢀ NaHCO ꢀ employedꢀ underꢀ theꢀ conditions:ꢀ cinnamaldehydeꢀ (1ꢀ mmol),ꢀ
MWCNTs‐g‐CDꢀ(100ꢀmg),ꢀH ꢀ(2.5ꢀmL,ꢀ30ꢀwt%),ꢀ60ꢀ°C,ꢀ10ꢀmin;ꢀ(f)ꢀEffectꢀofꢀreactionꢀtemperatureꢀunderꢀtheꢀconditions:ꢀcinnamaldehydeꢀ(1ꢀmmol),ꢀ
MWCNTs‐g‐CDꢀ(100ꢀmg),ꢀH ꢀ(2.5ꢀmL,ꢀ30ꢀwt%),ꢀNaHCO ꢀ(2ꢀmmol),ꢀ10ꢀmin.ꢀ
3
ꢀ(2ꢀmmol),ꢀH
ꢀ(2ꢀmmol),ꢀH
ꢀ(2ꢀmmol),ꢀ
2
O
2
ꢀ(2.5ꢀmL,ꢀ30
3
O
2 2
(
3
H O
2 2
O
2 2
(
3
3
O
2 2
O
2 2
3
friendlyꢀoxidant,ꢀwhichꢀgeneratesꢀwaterꢀasꢀitsꢀonlyꢀbyproduct,ꢀitꢀ
isꢀaꢀslow‐actingꢀoxidantꢀinꢀtheꢀabsenceꢀofꢀactivation.ꢀRichardsonꢀ
hydeꢀ conversionꢀ andꢀ benzaldehydeꢀ selectivityꢀ wereꢀ 7%ꢀ andꢀ
57%,ꢀ respectively,ꢀ whenꢀ theꢀ reactionꢀ wasꢀ conductedꢀ inꢀ theꢀ
etꢀal.ꢀ[53–55]ꢀreportedꢀaꢀnewꢀmethodꢀforꢀactivatingꢀH
bicarbonateꢀions.ꢀTheꢀtreatmentꢀofꢀH ꢀwithꢀbicarbonateꢀionsꢀ
resultedꢀ inꢀ theꢀ formationꢀ ofꢀ peroxymonocarbonateꢀ ionsꢀ
HCO
−),ꢀwhichꢀeffectivelyꢀoxidizedꢀcinnamaldehydeꢀtoꢀproduceꢀ
benzaldehydeꢀ[22,23].ꢀ AsꢀshownꢀinꢀFig.ꢀ7(e),ꢀtheꢀ cinnamalde‐
2
O
2
ꢀwithꢀ
absenceꢀofꢀNaHCO
ledꢀ toꢀ aꢀ considerableꢀ improvementꢀ inꢀ theꢀ cinnamaldehydeꢀ
conversionꢀtoꢀ95%,ꢀasꢀwellꢀasꢀanꢀincreaseꢀinꢀtheꢀbenzaldehydeꢀ
selectivityꢀtoꢀ85%,ꢀindicatingꢀthatꢀNaHCO
inꢀ theꢀ oxidationꢀ ofꢀ cinnamaldehyde.ꢀ Furthermore,ꢀ increasingꢀ
3
.ꢀNotably,ꢀtheꢀadditionꢀofꢀNaHCO ꢀ(2ꢀmmol)ꢀ
3
O
2 2
(
4
3
ꢀplayedꢀaꢀcrucialꢀroleꢀ

2092ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
Tableꢀ1ꢀ
Performanceꢀcomparisonꢀamongꢀvariousꢀβ‐CDꢀbasedꢀcatalystsꢀforꢀtheꢀoxidationꢀofꢀcinnamaldehydeꢀtoꢀbenzaldehyde.ꢀ
Conversionꢀ Selectivityꢀ
Reactionꢀ
ꢀ timeꢀ(min)ꢀ
Catalystꢀ
Conditionsꢀ
Cinnamaldehydeꢀ(1ꢀmmol),ꢀMWCNTs‐g‐CDꢀ(100ꢀmg),ꢀH
Ref.ꢀ
ꢀ
(%)ꢀ
(%)ꢀ
MWCNTs‐g‐CDꢀ
95ꢀ
84.5ꢀ
ꢀ 10ꢀ
150ꢀ
150ꢀ
2
O
2
ꢀ(2.5ꢀmL,ꢀ30ꢀwt%),ꢀ Thisꢀwork
NaHCO ꢀ(2ꢀmmol),ꢀH Oꢀ(25ꢀmL),ꢀ60ꢀCꢀ
Cinnamaldehydeꢀ(1ꢀmmol),ꢀβ‐CD‐CTSꢀ(100ꢀmg),ꢀH ꢀ(4ꢀmL,ꢀ30ꢀwt%),ꢀ ꢀ
NaHCO ꢀ(2.5ꢀmmol),ꢀβ‐CDꢀ(1ꢀmmol),ꢀH Oꢀ(25ꢀmL),ꢀ60ꢀCꢀ
Cinnamaldehydeꢀ(1ꢀmmol),ꢀβ‐CDPꢀ(2ꢀg),ꢀH ꢀ(4ꢀmL,ꢀ30ꢀwt%),ꢀ ꢀ
NaHCO ꢀ(1.5ꢀmmol),ꢀH Oꢀ(25ꢀmL),ꢀ60ꢀC,ꢀ600ꢀr/minꢀ
β‐CDPꢀ(1ꢀg),ꢀHClOꢀ(4ꢀmL,ꢀ7.5ꢀwt%),ꢀH Oꢀ(25ꢀmL),ꢀ70ꢀCꢀ
Cinnamaldehydeꢀ(1ꢀmmol),ꢀβ‐CDCPꢀ(1ꢀg),ꢀH ꢀ(4ꢀmL,ꢀ30ꢀwt%),ꢀ ꢀ
NaHCO ꢀ(2ꢀmmol),ꢀH Oꢀ(25ꢀmL),ꢀ70ꢀCꢀ
Cinnamaldehydeꢀ(1ꢀmmol),ꢀ2‐HP‐β‐CDCPꢀ(0.4ꢀg),ꢀH ꢀ(2ꢀmL,ꢀ30ꢀwt%),ꢀ ꢀ
Na CO ꢀ(1.5ꢀmmol),ꢀH Oꢀ(25ꢀmL),ꢀ60ꢀCꢀ
3
2
β‐CD‐CTSꢀ
β‐CDPꢀ
96ꢀ
99ꢀ
78.0ꢀ
63.0ꢀ
2
O
2
[21]ꢀ
[22]ꢀ
3
2
O
2 2
3
2
β‐CDPꢀ
β‐CDCPꢀ
92ꢀ
95ꢀ
62.0ꢀ
71.0ꢀ
120ꢀ
180ꢀ
2
[23]ꢀ
[24]ꢀ
O
2 2
3
2
2‐HP‐β‐CDCPꢀ
97ꢀ
83.5ꢀ
ꢀ 60ꢀ
2
O
2
[41]ꢀ
2
3
2
ꢀ
theꢀamountꢀofꢀNaHCO
3
ꢀtoꢀ2.5ꢀmmolꢀledꢀtoꢀfurtherꢀaꢀincreaseꢀinꢀ
canꢀbeꢀseparatedꢀbyꢀextractionꢀfromꢀtheꢀaqueousꢀreactionꢀmix‐
ture,ꢀitꢀwasꢀinvestigatedꢀthatꢀtheꢀcatalystꢀcouldꢀbeꢀrecoveredꢀbyꢀ
filtrationꢀandꢀreusedꢀforꢀtheꢀoxidationꢀofꢀaꢀfreshꢀbatchꢀofꢀcin‐
namaldehyde.ꢀTableꢀ2ꢀprovidesꢀaꢀsummaryꢀofꢀtheꢀrecyclabilityꢀ
propertiesꢀofꢀtheꢀMWCNTs‐g‐CD.ꢀAfterꢀeachꢀreaction,ꢀtheꢀben‐
zaldehydeꢀwasꢀisolatedꢀbyꢀextraction,ꢀandꢀtheꢀresultingꢀprecip‐
itateꢀwasꢀwashedꢀsequentiallyꢀwithꢀethanolꢀandꢀwaterꢀatꢀ80ꢀCꢀ
forꢀ2ꢀh.ꢀAfterꢀdrying,ꢀtheꢀcatalystꢀwasꢀreusedꢀforꢀtheꢀnextꢀrunꢀ
underꢀ theꢀ sameꢀ conditions.ꢀ Asꢀ shownꢀ inꢀ Tableꢀ 2,ꢀ theꢀ
MWCNTs‐g‐CDꢀshowsꢀoutstandingꢀrecyclabilityꢀoverꢀfiveꢀcata‐
lyticꢀcycles,ꢀasꢀwellꢀasꢀgoodꢀstability.ꢀ ꢀ
Scanningꢀ electronꢀmicroscopeꢀ(SEM)ꢀwasꢀusedꢀtoꢀevaluateꢀ
changesꢀ inꢀ theꢀ morphologicalꢀ characteristicsꢀ andꢀ sizesꢀ ofꢀ theꢀ
usedꢀ catalysts.ꢀ SEMꢀ imagesꢀ ofꢀ theꢀ MWCNTsꢀ andꢀ theꢀ usedꢀ
MWCNTs‐g‐CDꢀareꢀshownꢀinꢀFig.ꢀ8.ꢀTheꢀMWCNTsꢀwereꢀfoundꢀ
toꢀbeꢀtubularꢀinꢀshapeꢀwithꢀaꢀdiameterꢀinꢀtheꢀrangeꢀofꢀ10–30ꢀ
nmꢀ (Fig.ꢀ 8(a)).ꢀ Inꢀ contrast,ꢀ theꢀ diametersꢀ ofꢀ theꢀ usedꢀ
MWCNTs‐g‐CDꢀ (20–40ꢀ nm)ꢀ wereꢀ largerꢀ thanꢀ thoseꢀ ofꢀ theꢀ
MWCNTs,ꢀwhichꢀindicatedꢀthatꢀ‐CDꢀwasꢀuniformlyꢀdispersedꢀ
onꢀtheꢀsurfacesꢀofꢀtheꢀMWCNTsꢀ(Fig.ꢀ8(b)).ꢀThisꢀdifferenceꢀinꢀ
theꢀdiametersꢀwasꢀattributedꢀtoꢀchemicalꢀbondingꢀbetweenꢀtheꢀ
MWCNTsꢀ andꢀ ‐CD,ꢀ andꢀ hydrogen‐bondingꢀ interactionsꢀ be‐
tweenꢀtheꢀadjacentꢀ‐CDꢀmolecules.ꢀAꢀcomparisonꢀofꢀtheꢀSEMꢀ
imagesꢀ forꢀ theꢀ MWCNTsꢀ andꢀ theꢀ usedꢀ MWCNTs‐g‐CDꢀ con‐
firmedꢀ thatꢀ theꢀ morphologicalꢀ characteristicsꢀ ofꢀ theꢀ usedꢀ
MWCNTs‐g‐CDꢀ wereꢀ notꢀ affectedꢀ byꢀ theꢀ oxidationꢀ ofꢀ cin‐
namaldehyde.ꢀ
theꢀ cinnamaldehydeꢀ conversionꢀ toꢀ 100%.ꢀ However,ꢀ thisꢀ in‐
creaseꢀ wasꢀ accompaniedꢀ byꢀ aꢀ decreaseꢀ inꢀ theꢀ benzaldehydeꢀ
selectivityꢀtoꢀ80%,ꢀwhichꢀwasꢀcausedꢀbyꢀtheꢀoxidationꢀofꢀben‐
zaldehydeꢀtoꢀbenzoicꢀacid.ꢀTakenꢀtogether,ꢀtheseꢀresultsꢀshowꢀ
thatꢀtheꢀadditionꢀofꢀanꢀappropriateꢀamountꢀofꢀNaHCO
essaryꢀforꢀtheꢀreaction.ꢀ
3
ꢀisꢀnec‐
Theꢀreactionꢀtemperatureꢀalsoꢀhadꢀaꢀpronouncedꢀeffectꢀonꢀ
theꢀ oxidationꢀ ofꢀ cinnamaldehydeꢀ (Fig.ꢀ 7(f)).ꢀ Forꢀ example,ꢀ in‐
creasingꢀ theꢀ reactionꢀ temperatureꢀ increasedꢀ theꢀ cinnamalde‐
hydeꢀ conversionꢀandꢀ benzoicꢀ acidꢀ selectivityꢀ butꢀledꢀtoꢀ aꢀ de‐
creaseꢀ inꢀ theꢀ benzaldehydeꢀ selectivity.ꢀ Theꢀ optimalꢀ reactionꢀ
temperatureꢀ forꢀ theꢀ oxidationꢀ ofꢀ cinnamaldehydeꢀ wasꢀ there‐
foreꢀsetꢀasꢀ60ꢀ°C,ꢀwhichꢀrepresentsꢀaꢀcompromiseꢀbetweenꢀtheꢀ
benzaldehydeꢀselectivityꢀandꢀcinnamaldehydeꢀconversion.ꢀ
TheꢀperformanceꢀcharacteristicsꢀofꢀtheꢀMWCNTs‐β‐CDꢀwereꢀ
evaluatedꢀunderꢀtheꢀoptimizedꢀconditionsꢀandꢀtheꢀresultsꢀwereꢀ
comparedꢀ withꢀ thoseꢀ ofꢀ severalꢀ otherꢀ β‐CD‐basedꢀ catalystsꢀ
fromꢀ theꢀ literatureꢀ (Tableꢀ 1).ꢀ Theꢀ resultsꢀ revealedꢀ thatꢀ theꢀ
MWCNTs‐β‐CDꢀ developedꢀ inꢀ theꢀ currentꢀ studyꢀ performedꢀ
comparablyꢀ orꢀ betterꢀ thanꢀ theꢀ otherꢀ systemsꢀ inꢀ termsꢀ ofꢀ theꢀ
cinnamaldehydeꢀconversionꢀandꢀbenzaldehydeꢀselectivity.ꢀTheꢀ
MWCNTs‐β‐CDꢀalsoꢀrequiredꢀmuchꢀshorterꢀreactionꢀtimesꢀthenꢀ
theꢀotherꢀβ‐CD‐basedꢀcatalysts,ꢀtherebyꢀhighlightingꢀtheꢀexcel‐
lentꢀcatalyticꢀperformanceꢀofꢀtheꢀMWCNTs‐β‐CDꢀforꢀtheꢀoxida‐
tionꢀ ofꢀ cinnamaldehyde.ꢀ However,ꢀ theꢀ MWCNTs‐β‐CDꢀ couldꢀ
decomposeꢀ overꢀ timeꢀ leadingꢀ toꢀ aꢀ decreaseꢀ inꢀ theirꢀ catalyticꢀ
activity,ꢀandꢀsmallꢀchangesꢀinꢀtheꢀcrystallinityꢀofꢀthisꢀmaterialꢀ
couldꢀ goꢀ undetectedꢀ byꢀ XRD.ꢀ Toꢀ evaluateꢀ thisꢀ possibility,ꢀ weꢀ
conductedꢀaꢀseriesꢀofꢀexperimentsꢀtoꢀassessꢀtheꢀreusabilityꢀofꢀ
theꢀcatalyst,ꢀwhichꢀisꢀanꢀimportantꢀindexꢀforꢀassessingꢀtheꢀprac‐
ticalꢀapplicationꢀofꢀaꢀcatalyticꢀsystem.ꢀGivenꢀthatꢀtheꢀbenzalde‐
hydeꢀproductꢀofꢀthisꢀreactionꢀisꢀsolubleꢀinꢀethylꢀacetate,ꢀwhichꢀ
3.3.ꢀ ꢀ Theꢀoxidationꢀofꢀsubstitutedꢀcinnamaldehydesꢀ
Inꢀlightꢀofꢀtheꢀresultsꢀachievedꢀforꢀtheꢀefficientꢀoxidationꢀofꢀ
Tableꢀ2ꢀ
CyclicꢀstabilityꢀtestꢀofꢀMWCNTs‐g‐CDꢀforꢀtheꢀoxidationꢀofꢀcinnamalde‐
hydeꢀtoꢀbenzaldehyde.ꢀ
Cycleꢀ ꢀ
Conversionꢀ(%)ꢀ 95.0ꢀ
Selectivityꢀ(%)ꢀ 84.5ꢀ
1ꢀ
2ꢀ
94.8ꢀ
84.0ꢀ
3ꢀ
94.2ꢀ
84.0ꢀ
4ꢀ
93.8ꢀ
83.8ꢀ
5ꢀ
93.1ꢀ
82.9ꢀ
6ꢀ
90.2ꢀ
78.6ꢀ
Reactionꢀ conditions:ꢀ cinnamaldehydeꢀ derivativeꢀ (1ꢀ mmol),ꢀ
MWCNTs‐g‐CDꢀ (100ꢀ mg),ꢀ H ꢀ (2.5ꢀmL,ꢀ 30ꢀwt%),ꢀNaHCO ꢀ (2ꢀ mmol),ꢀ
Oꢀ(25ꢀmL),ꢀ60ꢀC,ꢀ10ꢀmin.ꢀ
O
2 2
3
H
2
Fig.ꢀ8.ꢀSEMꢀimagesꢀofꢀMWCNTsꢀ(a)ꢀandꢀtheꢀusedꢀMWCNTs‐g‐CDꢀ(b).ꢀ

ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
2093ꢀ
cinnamaldehyde,ꢀweꢀalsoꢀevaluatedꢀtheꢀoxidationꢀofꢀaꢀseriesꢀofꢀ
substitutedꢀcinnamaldehydesꢀusingꢀtheꢀMWCNTs‐g‐CDꢀcatalyst,ꢀ
andꢀtheꢀresultsꢀareꢀlistedꢀinꢀTableꢀ3.ꢀPleasingly,ꢀallꢀofꢀtheꢀsub‐
stitutedꢀ cinnamaldehydesꢀ wereꢀ smoothlyꢀ convertedꢀ toꢀ theꢀ
correspondingꢀ benzaldehydesꢀ withꢀ goodꢀ conversionsꢀ andꢀ se‐
lectivity.ꢀ However,ꢀ theꢀ electronicꢀ natureꢀ ofꢀ theꢀ substituentꢀ
groupꢀhadꢀaꢀpronouncedꢀimpactꢀonꢀtheꢀoutcomeꢀofꢀtheꢀoxida‐
tionꢀ reaction.ꢀ Forꢀ example,ꢀ cinnamaldehydesꢀ bearingꢀ anꢀ oxy‐
gen‐containingꢀ substituentꢀ (Tableꢀ 3,ꢀ entriesꢀ 1–3ꢀ andꢀ 10–12)ꢀ
producedꢀ theꢀ correspondingꢀ benzaldehydesꢀ inꢀ 81%–85%ꢀ se‐
lectivity,ꢀwhichꢀwereꢀhigherꢀthanꢀthatꢀofꢀcinnamaldehyde.ꢀThisꢀ
increaseꢀinꢀtheꢀselectivityꢀcouldꢀbeꢀattributedꢀtoꢀtheꢀformationꢀ
ofꢀ aꢀ weakꢀ ternaryꢀ complexꢀ betweenꢀ theꢀ oxygen‐containingꢀ
dehydesꢀincreasedꢀgoingꢀfromꢀtheꢀo‐substitutedꢀsystemsꢀ(Tableꢀ
3,ꢀentriesꢀ1,ꢀ4,ꢀ7ꢀandꢀ10)ꢀtoꢀtheꢀm‐substitutedꢀsystemsꢀ(entriesꢀ
2,ꢀ5,ꢀ8ꢀandꢀ11),ꢀandꢀincreasedꢀagainꢀgoingꢀtoꢀtheꢀp‐substitutedꢀ
cinnamaldehydesꢀ(Tableꢀ3,ꢀentriesꢀ3,ꢀ6,ꢀ9ꢀandꢀ12).ꢀTheseꢀresultsꢀ
alsoꢀ indicatedꢀ thatꢀ theꢀ oxidationꢀ ofꢀ theꢀ substitutedꢀ cinnamal‐
dehydesꢀwasꢀalsoꢀaffectedꢀbyꢀtheꢀβ‐CDꢀcavity.ꢀCinnamaldehydesꢀ
bearingꢀanꢀelectron‐richꢀmethoxyꢀgroupꢀ(Tableꢀ3,ꢀentriesꢀ1–3)ꢀ
orꢀanꢀelectron‐neutralꢀmethylꢀgroupꢀ(Tableꢀ3,ꢀentriesꢀ4–6)ꢀgaveꢀ
theꢀ correspondingꢀ benzaldehydesꢀ inꢀ 63%–100%ꢀ conversionsꢀ
withꢀ selectivitiesꢀ ofꢀ 72%–85%.ꢀ Inꢀ contrast,ꢀ cinnamaldehydesꢀ
bearingꢀanꢀelectron‐withdrawingꢀchloride‐ꢀorꢀnitro‐substituentꢀ
gaveꢀconversionsꢀandꢀselectivitiesꢀofꢀ63%–78%ꢀandꢀ72%–85%,ꢀ
respectively,ꢀ(Tableꢀ3,ꢀentriesꢀ6–12)ꢀevenꢀafterꢀaꢀlongerꢀreac‐
tionꢀtimeꢀ(180ꢀmin).ꢀTheꢀresultsꢀinꢀTableꢀ3ꢀalsoꢀshowedꢀthatꢀtheꢀ
formationꢀ ofꢀ weakꢀ interactionsꢀ betweenꢀ β‐CDꢀ andꢀ theꢀ sub‐
stratesꢀenhancedꢀtheirꢀreactivityꢀdependingꢀonꢀtheꢀsize,ꢀshapeꢀ
andꢀhydrophobicityꢀofꢀtheꢀguestꢀmoleculeꢀ[3,56].ꢀ
substituentꢀ(e.g.,ꢀ–OCH
3
ꢀorꢀ–NO )ꢀandꢀtheꢀsecondaryꢀhydroxylꢀ
2
groupsꢀonꢀtheꢀrimꢀofꢀtheꢀβ‐CDꢀthroughꢀhydrogenꢀbondingꢀin‐
teractions.ꢀ Theꢀ positionꢀofꢀtheꢀ substituentꢀonꢀ theꢀ phenylꢀringꢀ
hadꢀaꢀconsiderableꢀimpactꢀonꢀtheꢀcatalyticꢀactivityꢀthroughꢀste‐
ricꢀ hindrance.ꢀ Forꢀ example,ꢀ theꢀ conversionsꢀ ofꢀ theꢀ cinnamal‐
3.4.ꢀ ꢀ Reactionꢀmechanismꢀ
Tableꢀ3ꢀ
Oxidationꢀ ofꢀ substitutedꢀ cinnamaldehydesꢀ toꢀ theꢀ correspondingꢀ alde‐
hydesꢀoverꢀMWCNTs‐g‐CD.ꢀ
Ourꢀ previousꢀ resultsꢀ [21–23,41]ꢀ indicatedꢀ thatꢀ theꢀ β‐CDꢀ
sitesꢀcouldꢀbeꢀregardedꢀasꢀtheꢀactiveꢀsitesꢀinꢀtheꢀcatalyticꢀoxida‐
tionꢀ ofꢀ cinnamaldehydeꢀ withꢀ H
ꢀ activatedꢀ byꢀ bicarbonateꢀ
Reactionꢀ Con‐ Selec‐
En‐
O
2 2
Reactantꢀ
Productꢀ
timeꢀ version tivity
tryꢀ
ionsꢀinꢀwater.ꢀBasedꢀonꢀtheꢀexperimentalꢀdataꢀpresentedꢀabove,ꢀ
weꢀproposedꢀaꢀplausibleꢀmechanismꢀforꢀthisꢀreaction,ꢀwhichꢀisꢀ
presentedꢀinꢀFig.ꢀ9.ꢀFirstly,ꢀcinnamaldehydeꢀwouldꢀbeꢀquicklyꢀ
adsorbedꢀontoꢀtheꢀsurfaceꢀofꢀtheꢀMWCNTsꢀthroughꢀelectrostat‐
icꢀattractionꢀunderꢀmechanicalꢀstirringꢀ(Fig.ꢀ10).ꢀCinnamalde‐
hydeꢀ wouldꢀ alsoꢀ beꢀ encapsulatedꢀ inꢀ theꢀ cavitiesꢀ ofꢀ β‐CDꢀ
throughꢀ host‐guestꢀ interactions.ꢀ However,ꢀ theꢀ changesꢀ ob‐
servedꢀinꢀtheꢀenergyꢀduringꢀtheꢀcourseꢀofꢀtheꢀinclusionꢀprocessꢀ
wouldꢀbeꢀdependentꢀofꢀtheꢀstabilityꢀofꢀtheꢀhost‐guestꢀcomplex‐
esꢀbetweenꢀtheꢀMWCNTꢀorꢀβ‐CDꢀandꢀtheꢀdifferentꢀguests.ꢀPre‐
viousꢀreportsꢀinꢀthisꢀareaꢀhaveꢀindicatedꢀthatꢀincreasinglyꢀnega‐
tiveꢀ bindingꢀ energiesꢀ leadꢀ toꢀ increasinglyꢀ stableꢀ host‐guestꢀ
(min)ꢀ
(%)ꢀ (%)
1
ꢀ
10ꢀ
100ꢀ
96ꢀ
84ꢀ
ꢀ
ꢀ
ꢀ
O
2ꢀ
10ꢀ
84.5
OCH3
ꢀ
3
ꢀ
10ꢀ
15ꢀ
93ꢀ
97ꢀ
85ꢀ
72ꢀ
ꢀ
ꢀ
4ꢀ
ꢀ
ꢀ
ꢀ
5ꢀ
15ꢀ
94ꢀ
76ꢀ
complexesꢀ [41].ꢀ Theꢀ bindingꢀ energyꢀ forꢀ theꢀ MWCNT‐
cin‐
ꢀ
ꢀ
namaldehydeꢀcomplexꢀisꢀlistedꢀinꢀTableꢀ4.ꢀTheꢀresultsꢀshowedꢀ
thatꢀtheꢀMWCNTsꢀcouldꢀinteractꢀwithꢀcinnamaldehydeꢀtoꢀformꢀ
stableꢀ inclusionꢀ complexꢀ throughꢀ aromatic‐aromaticꢀ (π‐πꢀ
stacking)ꢀinteractionsꢀ[57].ꢀHowever,ꢀtheꢀbindingꢀenergyꢀforꢀtheꢀ
cinnamaldehyde‐β‐CDꢀ complexꢀ wasꢀ lowerꢀ thanꢀ thatꢀ ofꢀ theꢀ
MWCNT‐cinnamaldehydeꢀ complexꢀ [8],ꢀ indicatingꢀ thatꢀ cin‐
namaldehydeꢀ wasꢀ beingꢀ preferentiallyꢀ absorbedꢀ inꢀ theꢀ β‐CDꢀ
cavities.ꢀTheꢀβ‐CDꢀsitesꢀthereforeꢀinteractedꢀwithꢀcinnamalde‐
hydeꢀtoꢀformꢀmoreꢀstableꢀinclusionꢀcomplexꢀthanꢀtheꢀMWCNTsꢀ
throughꢀ intermolecularꢀ hydrogenꢀ bondꢀ interactions,ꢀ whichꢀ
O
6
ꢀ
15ꢀ
92ꢀ
78ꢀ
78ꢀ
72ꢀ
H3C
ꢀ
ꢀ
7ꢀ
180ꢀ
ꢀ
ꢀ
8ꢀ
180ꢀ
71ꢀ
74ꢀ
ꢀ
ꢀ
9
ꢀ
180ꢀ
180ꢀ
65ꢀ
75ꢀ
76ꢀ
81ꢀ
1
ꢀ
ꢀ
wereꢀconfirmedꢀbyꢀ HꢀNMRꢀandꢀ2DꢀROESYꢀexperimentsꢀ[11].ꢀ
Secondly,ꢀtheꢀnucleophilicꢀhydroxylꢀgroupsꢀofꢀβ‐CDꢀwouldꢀat‐
tackꢀtheꢀβ‐carbonꢀatomꢀofꢀtheꢀα,β‐unsaturatedꢀcarbocationꢀtoꢀ
formꢀ aꢀ hydratedꢀ moleculeꢀ viaꢀ theꢀ hydrolysisꢀ ofꢀ sodiumꢀ car‐
bonate.ꢀThisꢀwouldꢀleadꢀtoꢀaꢀ6%ꢀyieldꢀofꢀbenzaldehydeꢀbyꢀtheꢀ
deprotonationꢀofꢀtheꢀhydratedꢀmolecule,ꢀwhichꢀwouldꢀleadꢀtoꢀ
1
0ꢀ
1ꢀ
ꢀ
ꢀ
1
180ꢀ
180ꢀ
68ꢀ
63ꢀ
82ꢀ
84ꢀ
ꢀ
ꢀ
O
theꢀ cleavageꢀ ofꢀ theꢀ C=Cꢀ bond.ꢀ Inꢀ contrast,ꢀ theꢀ activeꢀ peroxy‐
12ꢀ
–
monocarbonateꢀionsꢀ(HCO
4
)ꢀformedꢀviaꢀtheꢀactivationꢀofꢀH
O ꢀ
2 2
ꢀ O2N
ꢀ
withꢀbicarbonateꢀwouldꢀbeꢀadsorbedꢀontoꢀtheꢀsurfacesꢀofꢀtheꢀ
Reactionꢀ conditions:ꢀ cinnamaldehydeꢀ derivativeꢀ (1ꢀ mmol),ꢀ
MWCNTs‐g‐CDꢀ(100ꢀmg),ꢀH
Oꢀ(25ꢀmL),ꢀ60ꢀC.ꢀ
2 2 3
O ꢀ(2.5ꢀmL,ꢀ30ꢀwt%),ꢀNaHCO ꢀ(2.5ꢀmmol),ꢀ
MWCNTs.ꢀTheꢀMWCNTsꢀcouldꢀalsoꢀaccelerateꢀtheꢀformationꢀofꢀ

H
2
theꢀactiveꢀspeciesꢀaccordingꢀtoꢀreactionꢀ(2).ꢀTheꢀHCO
ꢀspeciesꢀ
4

2094ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
O
O
O
O
O
:
O
O
OH-
:
(
1)
(1)
OH
OH
OH
O
O
O
:
O
O
O
O
O
O
O
O
O
OH
OH
OH
O
O
O
-
HCO4
2)
-
HCO4
(2)
(
2)
(
O
O
O
O
O
O
Fig.ꢀ9.ꢀProposedꢀmechanismꢀforꢀtheꢀoxidationꢀofꢀcinnamaldehydeꢀoverꢀMWCNTs‐g‐CD.ꢀ
generatedꢀinꢀthisꢀwayꢀcouldꢀreactꢀwithꢀcinnamaldehydeꢀtoꢀyieldꢀ
kꢀ =ꢀ k
0
exp(–E /RT)ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ (4)ꢀ
a

–1
theꢀcorrespondingꢀepoxide.ꢀInꢀsitu‐generatedꢀHCO
4
ꢀcouldꢀthenꢀ
whereꢀkꢀisꢀtheꢀrateꢀconstantꢀofꢀtheꢀreactionꢀ(min ),ꢀk
constant‐frequencyꢀfactorꢀ(min ),ꢀE
theꢀ reactionꢀ (kJ/mol),ꢀ Rꢀ isꢀ theꢀ gasꢀ constantꢀ (8.314ꢀ ×ꢀ 10 ꢀ
0
ꢀisꢀtheꢀ
–1
reactꢀ withꢀ newlyꢀ formedꢀ epoxideꢀ toꢀ formꢀ theꢀ benzaldehyde.ꢀ
Theꢀcatalystꢀwouldꢀthenꢀbeꢀrestoredꢀtoꢀitsꢀinitialꢀstate.ꢀ
a
ꢀisꢀtheꢀactivationꢀenergyꢀofꢀ
–3
–
–
–
1ꢀ –1
HCO
3
ꢀ +ꢀ H
2
Oꢀ =ꢀ H
2
CO
4
3
ꢀ +ꢀ OH ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ (2)ꢀ
kJꢀmol K ),ꢀandꢀTꢀisꢀtheꢀabsoluteꢀtemperatureꢀ(K).ꢀ
TheꢀrateꢀconstantsꢀshownꢀinꢀTableꢀ5ꢀwereꢀusedꢀtoꢀgenerateꢀ
a
–
–
HCO
3
ꢀ +ꢀ H
2
O
2
ꢀ =ꢀ HCO
ꢀ +ꢀ H Oꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ (3)ꢀ
2
Lastly,ꢀweꢀevaluatedꢀoxidationꢀofꢀcinnamaldehydeꢀoverꢀβ‐CDꢀ
andꢀ MWCNTs‐g‐CDꢀ basedꢀ onꢀ theꢀ apparentꢀ activationꢀ energyꢀ
theꢀArrheniusꢀplotsꢀofꢀlnkꢀandꢀ1/TꢀshownꢀinꢀFig.ꢀ11.ꢀTheꢀE ꢀval‐
uesꢀwereꢀcalculatedꢀinꢀtheꢀpresenceꢀofꢀtheꢀMWCNTs‐g‐CDꢀandꢀ
β‐CDꢀ andꢀ foundꢀ toꢀ beꢀ 16.33ꢀ andꢀ 45.66ꢀ kJ/mol,ꢀ respectively.ꢀ
TheseꢀresultsꢀclearlyꢀshowꢀthatꢀtheꢀMWCNTs‐g‐CDꢀledꢀtoꢀaꢀre‐
ductionꢀ inꢀ theꢀ activationꢀ energyꢀ andꢀ improvedꢀ theꢀ oxidationꢀ
(E ).ꢀTheꢀresultsꢀrevealedꢀthatꢀtheꢀrateꢀconstantsꢀincreasedꢀwithꢀ
a
theꢀ increasingꢀ temperature,ꢀ andꢀ thatꢀ theꢀ rateꢀ constantsꢀ wereꢀ
higherꢀinꢀtheꢀpresenceꢀofꢀMWCNTs‐g‐CDꢀthanꢀtheyꢀwereꢀinꢀtheꢀ
absenceꢀofꢀβ‐CD,ꢀwhichꢀimpliedꢀthatꢀMWCNTs‐g‐CDꢀcouldꢀsig‐
nificantlyꢀimproveꢀtheꢀoxidationꢀreactionꢀ(Tableꢀ 5).ꢀTheꢀrela‐
tionshipꢀ betweenꢀ theꢀ rateꢀ constantꢀ andꢀ theꢀ temperatureꢀ wasꢀ
fittedꢀaccordingꢀtoꢀtheꢀfollowingꢀequation:ꢀ
Tableꢀ5ꢀ
Theꢀrateꢀordersꢀandꢀrateꢀconstantsꢀatꢀvariousꢀreactionꢀtemperaturesꢀinꢀ
theꢀpresenceꢀofꢀβ‐CDꢀandꢀMWCNTs‐g‐CD.ꢀ
β‐CDꢀ
Correlationꢀ ꢀ
coefficientꢀ(R )ꢀ
ꢀ
ꢀ
MWCNTs‐g‐CDꢀ
kꢀ ꢀ
Tꢀ(K)ꢀ
kꢀ ꢀ
Correlationꢀ ꢀ
–
1
2
–1
2
(min )
(min )ꢀ
0.1847ꢀ
0.2225ꢀ
coefficientꢀ(R )
303ꢀ
313ꢀ
323ꢀ
333ꢀ
0.00614
0.01236
0.02280
0.03050
0.9921ꢀ
0.9945ꢀ
0.9978ꢀ
0.9961ꢀ
ꢀ
ꢀ
0.9867ꢀ
0.9789ꢀ
0.9912ꢀ
0.9812ꢀ
ꢀ
ꢀ
0.2637ꢀ
0.3345ꢀ
-
-
-
1.2
1.8
2.4
MWCNTs-g-CD
= 16.33 kJ/mol
E
a
Fig.ꢀ10.ꢀ Minimumꢀenergyꢀ structuresꢀofꢀ MWCNT‐cinnmaldehydeꢀcom‐
plexꢀcalculatedꢀbyꢀDMol3.ꢀ
-3.0
3.6
-4.2
4.8
-5.4
-
Tableꢀ4ꢀ
Energiesꢀ inꢀ theꢀ inclusionꢀ complexationꢀ ofꢀ host‐guestsꢀ calculatedꢀ byꢀ
DMol3.ꢀ
-CD
E = 45.66 kJ/mol
a
-
Energyꢀ
Bindingꢀenergyꢀ
(ꢁE,ꢀkJ/mol)ꢀ
Entryꢀ
(kJ/mol)ꢀ
3
.00
3.06
3.12
3.18
3.24
3.30
MWCNTꢀ
Cinnmaldehydeꢀ
MWCNTꢀ‐Cinnmaldehydeꢀ
–23074523.92ꢀ
ꢀ –1100811.63ꢀ
–24175344.63ꢀ
—ꢀ
—ꢀ
–9.08ꢀ
1
1000/T (K )
Fig.ꢀ11.ꢀArrheniusꢀplotsꢀforꢀcinnamaldehydeꢀoxidation.ꢀ

ꢀ
ZujinꢀYangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ2086–2097ꢀ
2095ꢀ
rateꢀofꢀcinnamaldehydeꢀcomparedꢀwithꢀβ‐CD.ꢀInꢀaddition,ꢀtheꢀ
inclusionꢀofꢀβ‐CDꢀledꢀtoꢀanꢀincreaseꢀinꢀtheꢀsubstrateꢀspecificityꢀ
andꢀmassꢀtransfer,ꢀasꢀreportedꢀpreviouslyꢀ[22].ꢀTakenꢀtogetherꢀ
withꢀtheꢀsynergisticꢀeffectsꢀofꢀMWCNTsꢀandꢀβ‐CD,ꢀtheseꢀresultsꢀ
highlightꢀ theꢀ potentialꢀ ofꢀ MWCNTs‐g‐CDꢀ forꢀ theꢀ oxidationꢀ ofꢀ
cinnamaldehyde.ꢀ
[10] H.ꢀR.ꢀChen,ꢀH.ꢀB.ꢀJi,ꢀL.ꢀF.ꢀWang,ꢀFineꢀChem.,ꢀ2010,ꢀ27,ꢀ579–583.ꢀ
[11] H.ꢀR.ꢀChen,ꢀH.ꢀB.ꢀJi,ꢀX.ꢀT.ꢀZhou,ꢀJ.ꢀXu,ꢀL.ꢀF.ꢀWang,ꢀCatal.ꢀCommun.,ꢀ
2009,ꢀ10,ꢀ828–832.ꢀ
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Efficientꢀoxidationꢀofꢀcinnamonꢀoilꢀtoꢀnaturalꢀbenzaldehydeꢀ
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O
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Natural benzaldehyde
β‐cyclodextrinꢀ (β‐CD)ꢀ functionalizedꢀ MWNTsꢀ (MWCNTs‐g‐CD)ꢀ
wereꢀ designedꢀ forꢀ theꢀ oxidationꢀ ofꢀ cinnamonꢀ oilꢀ toꢀ naturalꢀ ben‐
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manceꢀ ofꢀ MWCNTs‐g‐CDꢀ forꢀ theꢀ catalyticꢀ oxidationꢀ ofꢀ cinnamal‐
dehyde.ꢀ
Conversion: 95%
Selectivity: 85%

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