Formaldehyde catalytic oxidation over hydroxyapatite modified with various organic molecules

Article abstract of DOI:10.1016/S1872-2067(14)60129-7

Hydroxyapatite (HAP) was modified by adding various organic molecules, such as cetyltrimethylammonium bromide, sodium dodecyl sulfate, and sodium citrate, during the precipitation of HAP. Sodium citrate-modified HAP displayed the best activity for formaldehyde oxidation, achieving complete conversion at 240 °C. The influence of the organic modifiers on the structure of HAP was assessed by X-ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption-desorption, scanning electron microscopy, and thermogravimetry/derivative thermogravimetry. The higher specific surface area and pore volume, and smaller pores, owing to modification with sodium citrate, favored adsorption, mass transfer, and interaction process during formaldehyde oxidation. Furthermore, the higher hydroxyl group content observed in sodium citrate-modified HAP enhanced interactions between formaldehyde and HAP, thus resulting in higher catalytic activity.

Full text of DOI:10.1016/S1872-2067(14)60129-7

ChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
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
ꢀ
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
ꢀ
ꢀ
Article
Formaldehydeꢀcatalyticꢀoxidationꢀoverꢀhydroxyapatiteꢀmodifiedꢀ
withꢀvariousꢀorganicꢀmoleculesꢀ
ꢀa
ꢀa,
ꢀa
ꢀa
ꢀb
ꢀbꢀ
YahuiꢀSun ,ꢀZhenpingꢀQu *,ꢀDanꢀChen ,ꢀHuiꢀWang ,ꢀFanꢀZhang ,ꢀQiangꢀFu
aꢀKeyꢀLaboratoryꢀofꢀIndustrialꢀEcologyꢀandꢀEnvironmentalꢀEngineeringꢀ(MOE),ꢀSchoolꢀofꢀEnvironmentalꢀScienceꢀandꢀTechnology,ꢀDalianꢀUniversityꢀofꢀ
Technology,ꢀDalian116024,ꢀLiaoning,ꢀChinaꢀ
bꢀStateꢀKeyꢀLaboratoryꢀofꢀCatalysis,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences,ꢀDalianꢀ116023,ꢀLiaoning,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Hydroxyapatiteꢀ (HAP)ꢀ wasꢀ modifiedꢀ byꢀ addingꢀ variousꢀ organicꢀ molecules,ꢀ suchꢀ asꢀ cetyltrime‐
thylammoniumꢀ bromide,ꢀ sodiumꢀ dodecylꢀ sulfate,ꢀ andꢀ sodiumꢀ citrate,ꢀ duringꢀ theꢀ precipitationꢀ ofꢀ
HAP.ꢀSodiumꢀcitrate‐modifiedꢀHAPꢀdisplayedꢀtheꢀbestꢀactivityꢀforꢀformaldehydeꢀoxidation,ꢀachieving
completeꢀconversionꢀatꢀ240ꢀ°C.ꢀTheꢀinfluenceꢀofꢀtheꢀorganicꢀmodifiersꢀonꢀtheꢀstructureꢀofꢀHAPꢀwasꢀ
Receivedꢀ13ꢀAprilꢀ2014ꢀ
Acceptedꢀ28ꢀAprilꢀ2014ꢀ
Publishedꢀ20ꢀDecemberꢀ2014ꢀ
assessedꢀbyꢀX‐rayꢀdiffraction,ꢀFourierꢀtransformꢀinfraredꢀspectroscopy,ꢀN
2
ꢀadsorption‐desorption,ꢀ
ꢀ
scanningꢀ electronꢀ microscopy,ꢀ andꢀ thermogravimetry/derivativeꢀ thermogravimetry.ꢀ Theꢀ higherꢀ
specificꢀsurfaceꢀareaꢀandꢀporeꢀvolume,ꢀandꢀsmallerꢀpores,ꢀowingꢀtoꢀmodificationꢀwithꢀsodiumꢀcitrate,
favoredꢀ adsorption,ꢀ massꢀ transfer,ꢀ andꢀ interactionꢀ processꢀ duringꢀ formaldehydeꢀ oxidation.ꢀ Fur‐
Keywords:ꢀ
Modifiedꢀhydroxyapatiteꢀ
Sodiumꢀcitrateꢀ
Specificꢀsurfaceꢀareaꢀ
Hydroxylꢀgroupꢀ
Formaldehydeꢀcatalyticꢀoxidation
thermore,ꢀtheꢀhigherꢀhydroxylꢀgroupꢀcontentꢀobservedꢀinꢀsodiumꢀcitrate‐
ꢀ
modifiedꢀHAPꢀenhancedꢀ
interactionsꢀbetweenꢀformaldehydeꢀandꢀHAP,ꢀthusꢀresultingꢀinꢀhigherꢀcatalyticꢀactivity.ꢀ
©ꢀ2014,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
oxidesꢀ areꢀ usuallyꢀ employedꢀ asꢀ substrateꢀ forꢀ loadingꢀ nobleꢀ
metalꢀ catalystsꢀ [10–13].ꢀ Nobleꢀ metal‐loadedꢀ catalystsꢀ showꢀ
relativelyꢀbetterꢀactivitiesꢀtowardsꢀHCHOꢀoxidationꢀ(completeꢀ
conversionꢀisꢀ generallyꢀachievedꢀatꢀ aroundꢀ100ꢀ°Cꢀorꢀbelow)ꢀ
[5,14].ꢀHowever,ꢀtheꢀhighꢀcostꢀofꢀnobleꢀmetalꢀlimitsꢀtheꢀwideꢀ
practicalꢀ applicationꢀ ofꢀ nobleꢀ metalꢀ catalysts.ꢀ Forꢀ transitionꢀ
metalꢀ oxides,ꢀ completeꢀ HCHOꢀ conversionꢀ temperaturesꢀ areꢀ
generallyꢀ aboveꢀ 100ꢀ °C,ꢀ andꢀ evenꢀ aboveꢀ 200ꢀ °Cꢀ underꢀ someꢀ
circumstancesꢀ[7,9,13].ꢀBesidesꢀpoorꢀperformance,ꢀtheꢀtoxicityꢀ
Asꢀ oneꢀ ofꢀ theꢀ mostꢀ commonꢀ volatileꢀ organicꢀ compounds,ꢀ
formaldehydeꢀ (HCHO)ꢀ isꢀ generatingꢀ increasingꢀ attentionꢀ asꢀ itꢀ
posesꢀpotentialꢀhealthꢀrisksꢀtoꢀhumansꢀevenꢀatꢀlowꢀconcentra‐
tions.ꢀ Thus,ꢀ theꢀ removalꢀ ofꢀ HCHOꢀ hasꢀ becomeꢀ anꢀ importantꢀ
issueꢀ [1,2].ꢀ Numerousꢀ studiesꢀ haveꢀ beenꢀ carriedꢀ outꢀ forꢀ theꢀ
abatementꢀ ofꢀ HCHO;ꢀ theꢀ mainꢀ techniquesꢀ beingꢀ investigatedꢀ
areꢀ adsorption,ꢀ plasmaꢀ decomposition,ꢀ biological/botanicalꢀ
filtration,ꢀ andꢀ catalyticꢀ oxidationꢀ [1].ꢀ Amongꢀ allꢀ theseꢀ tech‐
niques,ꢀ catalyticꢀ oxidationꢀ isꢀ aꢀ promisingꢀ methodꢀ forꢀ HCHOꢀ
removalꢀbecauseꢀofꢀitsꢀefficiency,ꢀconvenience,ꢀandꢀnoꢀsecond‐
aryꢀpollution.ꢀCommonlyꢀstudiedꢀcatalystsꢀincludeꢀnobleꢀmetalsꢀ
ofꢀsomeꢀcommonlyꢀusedꢀtransitionꢀmetalꢀoxidesꢀ(MnO
)ꢀlimitsꢀ
x
theꢀapplicationꢀofꢀsuchꢀcatalystꢀsystemsꢀ[15,16].ꢀInꢀrecentꢀyears,ꢀ
manyꢀstudiesꢀonꢀHCHOꢀcatalyticꢀoxidationꢀhaveꢀbeenꢀconductedꢀ
toꢀ improveꢀ theꢀ catalyticꢀ performance.ꢀ However,ꢀ theꢀ studiedꢀ
catalyticꢀsystemsꢀareꢀstillꢀfocusedꢀonꢀnobleꢀmetalꢀcatalystsꢀandꢀ
(e.g.,ꢀPt,ꢀAu,ꢀPd,ꢀandꢀAg)ꢀ[3–6]ꢀandꢀtransitionꢀmetalꢀoxideꢀcata‐
lystsꢀ (e.g.,ꢀ MnO
x
ꢀ andꢀ CeO )ꢀ [7–9].ꢀ Moreover,ꢀ transitionꢀ metalꢀ
2
transitionꢀ metalꢀ oxidesꢀ suchꢀ asꢀ MnO
x
,ꢀ Ag/CeO
2
,ꢀ Co
3
O ,ꢀ andꢀ
4
*ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐15542663636ꢀFax:ꢀ+86‐411‐84708083;ꢀE‐mail:ꢀquzhenping@dlut.edu.cnꢀ ꢀ
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(21377016),ꢀtheꢀFundamentalꢀResearchꢀFundsꢀforꢀtheꢀCentralꢀUniver‐
sitiesꢀ(DUT13LK27),ꢀandꢀtheꢀProgramꢀforꢀChangjiangꢀScholarsꢀandꢀInnovativeꢀResearchꢀTeamꢀinꢀUniversityꢀ(IRT_13R05).ꢀ
DOI:ꢀ10.1016/S1872‐2067(14)60129‐7ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ35,ꢀNo.ꢀ12,ꢀDecemberꢀ2014ꢀ ꢀ

1928ꢀ
YahuiꢀSunꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936ꢀ
Pt/CeO2ꢀ[17–22].ꢀTheꢀdrawbacksꢀofꢀsuchꢀcatalyticꢀsystemsꢀareꢀ
yetꢀtoꢀbeꢀaddressed.ꢀThus,ꢀeconomical,ꢀsafe,ꢀandꢀnon‐toxicꢀnovelꢀ
materialsꢀareꢀrequiredꢀforꢀHCHOꢀcatalyticꢀoxidation.ꢀ
thesizedꢀusingꢀtheꢀsameꢀprocedureꢀforꢀcomparisonꢀstudiesꢀandꢀ
denotedꢀasꢀHAPBLANK.ꢀ ꢀ
Asꢀtheꢀmainꢀinorganicꢀcomponentꢀofꢀnaturalꢀboneꢀandꢀteeth,ꢀ
withꢀaꢀwideꢀapplicationꢀinꢀtheꢀfieldꢀofꢀbiomedicalꢀmaterialsꢀasꢀ
biologicalꢀ activeꢀ materials,ꢀ hydroxyapatiteꢀ (HAP)ꢀ isꢀ safeꢀ andꢀ
non‐toxicꢀ[23].ꢀMoreover,ꢀunlikeꢀnobleꢀmetals,ꢀHAPꢀisꢀaꢀcheaperꢀ
alternative.ꢀInꢀ2010,ꢀXuꢀetꢀal.ꢀ[24]ꢀreportedꢀHAPꢀasꢀaꢀpromisingꢀ
novel,ꢀ non‐preciousꢀ metalꢀ catalystꢀ forꢀ HCHOꢀ combustion,ꢀ
2.2.ꢀ ꢀ Characterizationꢀofꢀcatalystsꢀ
Theꢀcrystallinityꢀofꢀtheꢀcatalystsꢀwasꢀestablishedꢀandꢀidenti‐
fiedꢀbyꢀX‐rayꢀdiffractionꢀ(XRD,ꢀRigakuꢀD/max‐γbꢀX‐rayꢀdiffrac‐
tometer,ꢀ Japan)ꢀ usingꢀ Cuꢀ K ꢀ radiationꢀ inꢀ theꢀ 2θꢀ rangeꢀ ofꢀ
α
10°–80°ꢀ atꢀ roomꢀ temperature.ꢀ Fourierꢀ transformꢀ infraredꢀ
spectroscopyꢀ (FTIR)ꢀwasꢀ carriedꢀoutꢀonꢀspecimensꢀthatꢀwereꢀ
preparedꢀ intoꢀ pelletsꢀ containingꢀ theꢀ HAPꢀ samplesꢀ andꢀ KBr.ꢀ
FTIRꢀ spectraꢀ wereꢀ recordedꢀ onꢀ aꢀ Shimadzuꢀ IRPrestige‐21ꢀ
spectrophotometerꢀ (Japan)ꢀ inꢀ theꢀ rangeꢀ ofꢀ 4000–400ꢀ cm .ꢀAꢀ
backgroundꢀspectrumꢀofꢀKBrꢀwasꢀsubtractedꢀfromꢀeachꢀsampleꢀ
spectrum.ꢀ Scanningꢀ electronꢀ microscopyꢀ (SEM)ꢀ analysisꢀ wasꢀ
performedꢀonꢀaꢀJEOLꢀJSM‐6360ꢀscanningꢀelectronꢀmicroscopeꢀ
2+
wherebyꢀtheꢀhydroxylꢀgroupsꢀbondedꢀtoꢀtheꢀCa ꢀchannelsꢀmayꢀ
actꢀasꢀactiveꢀsites.ꢀ ꢀ
Toꢀdate,ꢀtheꢀexaminationꢀofꢀHAPꢀasꢀaꢀcatalyticꢀmaterialꢀforꢀ
HCHOꢀ oxidationꢀ remainsꢀ rare.ꢀ However,ꢀ asꢀ aꢀ novel,ꢀ non‐pre‐
ciousꢀmetalꢀcatalystꢀwithꢀdemonstratedꢀactivityꢀtowardsꢀHCHOꢀ
oxidation,ꢀHAPꢀisꢀworthꢀexploringꢀfurther.ꢀItꢀisꢀwellꢀknownꢀthatꢀ
theꢀ catalystꢀ performanceꢀ isꢀ closelyꢀ relatedꢀ toꢀ itsꢀ structure.ꢀ
Basedꢀonꢀtheꢀreportedꢀstudyꢀ[1],ꢀHCHOꢀadsorptionꢀandꢀitsꢀin‐
teractionꢀwithꢀtheꢀsupportꢀareꢀrelatedꢀtoꢀtheꢀHCHOꢀoxidationꢀ
process.ꢀ Inꢀ thatꢀ case,ꢀ largerꢀ adsorptionꢀ areasꢀ andꢀ abundantꢀ
interactionꢀ betweenꢀ theꢀ reactionꢀ gasꢀ andꢀ catalystꢀ willꢀ beꢀ im‐
portantꢀforꢀactivityꢀenhancement.ꢀOrganicꢀmodifiersꢀhaveꢀbeenꢀ
widelyꢀ usedꢀ inꢀ morphology‐ꢀ andꢀ size‐controlledꢀ synthesisꢀ ofꢀ
nano‐sizedꢀ metalsꢀ andꢀ inorganicꢀ materials,ꢀ asꢀ wellꢀ asꢀ forꢀ theꢀ
generationꢀofꢀporesꢀandꢀvacanciesꢀinꢀtheꢀstructureꢀ[25–30].ꢀToꢀ
thisꢀ effect,ꢀ inꢀ thisꢀ study,ꢀ organicꢀ modifiersꢀ (i.e.,ꢀ cetyltri‐
methylammoniumꢀ bromideꢀ (CTAB),ꢀ sodiumꢀ dodecylꢀ sulfateꢀ
−
1
(USA)ꢀoperatingꢀatꢀanꢀaccelerationꢀvoltageꢀofꢀ20–30ꢀkV.ꢀN ꢀad‐
2
sorption‐desorptionꢀ measurementsꢀ wereꢀ carriedꢀ outꢀ onꢀ aꢀ
Quantachromeꢀ Quadrasorbꢀ S1ꢀ (USA).ꢀ Priorꢀ toꢀ analysis,ꢀ eachꢀ
sampleꢀ wasꢀ heatedꢀ atꢀ 200ꢀ °Cꢀ forꢀ 4ꢀ hꢀ underꢀ vacuum.ꢀ Surfaceꢀ
areasꢀwereꢀcalculatedꢀusingꢀtheꢀBETꢀmethod.ꢀTheꢀporeꢀsizeꢀwasꢀ
calculatedꢀusingꢀtheꢀBJHꢀmodel.ꢀThermogravimetry/derivativeꢀ
thermogravimetryꢀ analysisꢀ (TG/DTG)ꢀ wasꢀ performedꢀ onꢀ aꢀ
WCT‐1C thermobalanceꢀ (Beijing)ꢀ inꢀ thetemperatureꢀ rangeꢀ ofꢀ
20–900ꢀ°C.ꢀ
(SDS),ꢀ andꢀ sodiumꢀ citrateꢀ (SC))ꢀ wereꢀ employedꢀ duringꢀ theꢀ
2.3.ꢀ ꢀ Catalyticꢀactivityꢀtestsꢀ
synthesisꢀ ofꢀ HAPꢀ toꢀ modifyꢀ itsꢀ structure.ꢀ Variousꢀ characteri‐
zationꢀ techniquesꢀ andꢀ subsequentꢀ activityꢀ testsꢀ wereꢀ condu‐
ctedꢀtoꢀelucidateꢀtheꢀstructure‐performanceꢀrelationship.ꢀ
HCHOꢀ oxidationꢀ activityꢀ testsꢀ wereꢀ carriedꢀ outꢀ inꢀ aꢀ
fixed‐bedꢀflowꢀreactorꢀunderꢀatmosphericꢀpressure.ꢀTypically,ꢀ
0.2ꢀgꢀcatalystꢀwasꢀloadedꢀinꢀaꢀquartzꢀtubeꢀreactorꢀforꢀactivityꢀ
2.ꢀ ꢀ Experimentalꢀ ꢀ
test.ꢀTheꢀcatalystꢀwasꢀcalcinedꢀatꢀ400ꢀ°Cꢀforꢀ1ꢀhꢀinꢀanꢀO
2
/Arꢀflowꢀ
beforeꢀ theꢀ reaction.ꢀ Duringꢀ theꢀ reaction,ꢀ gaseousꢀ HCHOꢀ wasꢀ
generatedꢀbyꢀflowingꢀHeꢀoverꢀtrioxymethyleneꢀ(99.5%,ꢀAcrosꢀ
Organics)ꢀinꢀanꢀincubatorꢀplacedꢀinꢀanꢀice‐waterꢀmixture.ꢀTheꢀ
2.1.ꢀ ꢀ Preparationꢀofꢀcatalystsꢀ
HAPꢀpowderꢀ wasꢀ preparedꢀthroughꢀanꢀ aqueousꢀ precipita‐
feedingꢀstreamꢀconsistedꢀofꢀ500ꢀppmꢀHCHO,ꢀ20ꢀvol%ꢀO ,ꢀandꢀ
2
tion‐hydrothermalꢀ methodꢀ usingꢀ (NH
Chemicalꢀ Reagentꢀ Co.,ꢀ Ltd,ꢀ Tianjin)ꢀ andꢀ Ca(NO
DamaoꢀChemicalꢀReagentꢀFactory,ꢀTianjin)ꢀasꢀprecursors.ꢀAm‐
moniaꢀ (NH )ꢀ solutionꢀ (AR,ꢀ Sinopharmꢀ Chemicalꢀ Reagentꢀ Co.,ꢀ
Ltd,ꢀShanghai)ꢀwasꢀusedꢀforꢀpHꢀadjustmentsꢀduringꢀtheꢀprecip‐
itationꢀprocess.ꢀAꢀsolutionꢀofꢀ0.2ꢀmol/LꢀCa(NO ·4H Oꢀ(4.72ꢀgꢀ
4
)
2
HPO
4
ꢀ (AR,ꢀ Kemiouꢀ
balancedꢀ He;ꢀ theꢀ totalꢀ flowꢀ rateꢀ throughoutꢀ theꢀ reactorꢀ wasꢀ
maintainedꢀatꢀ30ꢀmL/minꢀbyꢀaꢀmassꢀflowꢀmeter.ꢀTheꢀeffluentsꢀ
fromꢀ theꢀ reactorꢀ wereꢀ analyzedꢀ byꢀ anꢀ onlineꢀ gasꢀ chromato‐
graphꢀ (GCꢀ 7890II,ꢀ Techcomp,ꢀ China)ꢀ equippedꢀ withꢀ aꢀ flameꢀ
ionizationꢀdetectorꢀ(FID).ꢀToꢀdetermineꢀtheꢀexactꢀconcentrationꢀ
3 2
)
·4H Oꢀ (AR,ꢀ
2
3
3
)
2
2
2
ofꢀproducedꢀCO ,ꢀaꢀnickelꢀcatalystꢀconverterꢀwasꢀpositionedꢀinꢀ
inꢀ100ꢀmLꢀdeionizedꢀwater)ꢀcontainingꢀanꢀorganicꢀmodifierꢀ(5ꢀ
wt%,ꢀCTABꢀ(AR,ꢀSinopharmꢀChemicalꢀReagentꢀCo.,ꢀLtd,ꢀShang‐
hai),ꢀSDSꢀ(AR,ꢀKemiouꢀChemicalꢀReagentꢀCo.,ꢀLtd,ꢀTianjin),ꢀorꢀSCꢀ
frontꢀofꢀtheꢀFIDꢀtoꢀconvertꢀCO
theꢀ presenceꢀ ofꢀ hydrogen.ꢀ Generally,ꢀ theꢀ reactionꢀ dataꢀ wereꢀ
collectedꢀ untilꢀ reactionꢀ balanceꢀ wasꢀ reached.ꢀ Noꢀ otherꢀ car‐
2
ꢀquantitativelyꢀintoꢀmethaneꢀinꢀ
(
AR,ꢀReagentꢀNo.ꢀ1ꢀFactoryꢀofꢀShanghaiꢀChemicalꢀReagentꢀCo.,ꢀ
Ltd.,ꢀ Shanghai))ꢀ wasꢀ stirredꢀ underꢀ aꢀ constantꢀ temperatureꢀ ofꢀ
0ꢀ °C.ꢀ Aꢀ solutionꢀ ofꢀ 0.3ꢀ mol/Lꢀ (NH HPO ꢀ (1.58ꢀ gꢀ inꢀ 40ꢀ mLꢀ
deionizedꢀ water)ꢀ wasꢀ addedꢀ dropwiseꢀ toꢀ theꢀ Ca(NO ·4H Oꢀ
bon‐containingꢀcompoundsꢀexceptꢀforꢀCO
detectedꢀforꢀallꢀtheꢀtestedꢀcatalysts.ꢀThus,ꢀtheꢀHCHOꢀconversionꢀ
wasꢀ calculatedꢀ as:ꢀ HCHOꢀ conversionꢀ =ꢀ [CO ]/[CO ]*ꢀ ×ꢀ 100%,ꢀ
whereꢀ[CO ]*ꢀandꢀ[CO ]ꢀrepresentꢀrespectiveꢀconcentrationsꢀofꢀ
CO ꢀdetectedꢀinꢀtheꢀeffluentꢀwhenꢀHCHOꢀisꢀcompletelyꢀoxidizedꢀ
2
ꢀinꢀtheꢀproductsꢀwereꢀ
4
)
4 2
4
2
2
)
3 2
2
2
2
solution.ꢀ Then,ꢀ theꢀ pHꢀ ofꢀ theꢀ suspensionꢀ wasꢀ adjustedꢀ toꢀ 10ꢀ
withꢀammoniaꢀsolutionꢀ(35%),ꢀfollowedꢀbyꢀ8ꢀhꢀofꢀreactionꢀun‐
derꢀ stirring.ꢀ Subsequently,ꢀ theꢀ reactionꢀ solutionꢀ wasꢀ trans‐
ferredꢀtoꢀaꢀTeflon‐linedꢀautoclaveꢀandꢀheatedꢀatꢀ100ꢀ°Cꢀforꢀ12ꢀh.ꢀ
Finally,ꢀ theꢀ resultingꢀ powdersꢀ wereꢀ centrifugedꢀ andꢀ washedꢀ
multipleꢀtimesꢀandꢀdriedꢀatꢀ100ꢀ°Cꢀovernightꢀandꢀthenꢀcalcinedꢀ
atꢀ700ꢀ°Cꢀforꢀ2ꢀh.ꢀTheꢀobtainedꢀHAPꢀsamplesꢀwereꢀdenotedꢀasꢀ
HAPCTAB,ꢀHAPSDS,ꢀandꢀHAPSC.ꢀNon‐modifiedꢀHAPꢀwasꢀalsoꢀsyn‐
2
andꢀatꢀaꢀgivenꢀreactionꢀtemperature,ꢀrespectively.ꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
3.1.ꢀ ꢀ CatalyticꢀactivityꢀforꢀHCHOꢀoxidationꢀ
TheꢀcatalyticꢀactivitiesꢀofꢀHAPBLANKꢀandꢀmodifiedꢀHAPꢀsam‐

ꢀ
YahuiꢀSunꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936ꢀ
1929ꢀ
3

1
00
HAPBLANK
HAPCTAB
HAPSDS
HAPSC
HAPSC-used
PO4
OH
HAPBLANK

8
6
4
2
0
0
0
0
0
HAPCTAB
HAPSDS
HAPSC
HAPSC-used
1
60 180 200 220 240 260 280 300
4000
3600
3200 1200
Wavenumber (cm )
800
400
o
1
Temperature ( C)
Fig.ꢀ1.ꢀHCHOꢀconversionꢀoverꢀHAPBLANKꢀandꢀmodifiedꢀHAPꢀsamples.ꢀ
Fig.ꢀ3.ꢀFTIRꢀspectraꢀofꢀHAPBLANKꢀandꢀmodifiedꢀHAPꢀsamples.ꢀ
plesꢀ towardsꢀ theꢀ oxidationꢀ ofꢀ HCHOꢀ areꢀ shownꢀ inꢀ Fig.ꢀ 1.ꢀ Asꢀ
noted,ꢀtheꢀHAPSCꢀsampleꢀdisplayedꢀtheꢀbestꢀactivityꢀwithꢀ100%ꢀ
HCHOꢀ conversionꢀ atꢀ 240ꢀ °C.ꢀ Inꢀ contrast,ꢀ theꢀ remainingꢀ threeꢀ
samplesꢀexhibitedꢀHCHOꢀconversionꢀlevelsꢀofꢀlessꢀthanꢀ50%ꢀatꢀ
theꢀsameꢀtemperature.ꢀMoreover,ꢀtheꢀadditionꢀofꢀeitherꢀCTABꢀ
orꢀ SDSꢀ duringꢀ sampleꢀ preparationꢀ resultedꢀ inꢀ catalystsꢀ withꢀ
lowerꢀactivitiesꢀwhenꢀcomparedꢀwithꢀthatꢀofꢀtheꢀblankꢀsample.ꢀ
Completeꢀconversionꢀwasꢀnotꢀobservedꢀevenꢀatꢀ300ꢀ°Cꢀforꢀtheꢀ
HAPCTABꢀandꢀHAPSDSꢀ samples.ꢀ Furtherꢀactivityꢀtestsꢀwereꢀ per‐
formedꢀonꢀtheꢀusedꢀHAPSCꢀcatalystꢀtoꢀdetermineꢀtheꢀstabilityꢀofꢀ
theꢀsample.ꢀTheꢀresultsꢀareꢀalsoꢀshownꢀinꢀFig.ꢀ1.ꢀAsꢀobserved,ꢀ
theꢀ activityꢀ ofꢀ HAPSC‐usedꢀ onlyꢀ decreasedꢀ veryꢀ slightlyꢀ whenꢀ
comparedꢀwithꢀthatꢀofꢀHAPSC‐fresh,ꢀindicatingꢀtheꢀgoodꢀstabilityꢀ
ofꢀtheꢀcatalyst.ꢀ
thatꢀtheꢀadditionꢀofꢀdifferentꢀorganicꢀmoleculesꢀdoesꢀnotꢀinsti‐
gateꢀanyꢀdifferencesꢀinꢀtheꢀcrystallinityꢀforꢀsamplesꢀcalcinedꢀatꢀ
theꢀ sameꢀ temperature.ꢀ Moreover,ꢀ theꢀ goodꢀ agreementꢀ ofꢀ theꢀ
XRDꢀpatternsꢀofꢀtheꢀsamplesꢀ(calcinedꢀatꢀ700ꢀ°C)ꢀwithꢀcharac‐
teristicꢀ HAPꢀ peaksꢀ reflectsꢀ theꢀ goodꢀ thermalꢀ stabilityꢀ ofꢀ theꢀ
catalysts.ꢀ
3.2.2.ꢀ ꢀ FTIRꢀspectroscopyꢀ ꢀ
Figureꢀ3ꢀpresentsꢀtheꢀFTIRꢀspectraꢀofꢀtheꢀHAPꢀsamples.ꢀNoꢀ
organicꢀmodifierꢀremainedꢀonꢀtheꢀsurfaceꢀofꢀHAPꢀafterꢀcalcina‐
tionꢀatꢀ700ꢀ°C.ꢀTheꢀpresenceꢀofꢀPO ꢀandꢀOHꢀfunctionalꢀgroupsꢀ
4
wasꢀ confirmedꢀ byꢀ variousꢀ characteristicꢀ bandsꢀ inꢀ theꢀ FTIRꢀ
spectra.ꢀ Theꢀ peaksꢀ atꢀ aroundꢀ 1035ꢀ andꢀ 1091ꢀ cm−1ꢀ wereꢀ as‐
signedꢀ toꢀ asymmetricalꢀ stretchingꢀ modesꢀ ofꢀ PO ꢀ groups,ꢀ theꢀ
4
asymmetricalꢀbendingꢀmodesꢀofꢀwhichꢀwereꢀdetectedꢀatꢀaroundꢀ
565ꢀandꢀ602ꢀcm−1ꢀ[32].ꢀTheꢀsymmetricalꢀstretchingꢀvibrationsꢀ
3.2.ꢀ ꢀ Catalystꢀcharacterizationꢀ ꢀ
ofꢀPO ꢀgroupsꢀwereꢀreflectedꢀbyꢀbandsꢀatꢀaroundꢀ470ꢀandꢀ962ꢀ
4
3.2.1.ꢀ ꢀ XRDꢀanalysisꢀ
cm−1ꢀ[32].ꢀTheꢀpeaksꢀobservedꢀatꢀ631ꢀandꢀ3580ꢀcm−1ꢀwereꢀat‐
XRDꢀ patternsꢀ ofꢀ theꢀ preparedꢀ HAPꢀ samplesꢀ areꢀ shownꢀ inꢀ
tributedꢀtoꢀtheꢀbendingꢀandꢀstretchingꢀmodesꢀofꢀOHꢀgroupsꢀinꢀ
theꢀ hydroxyapatiteꢀ structure,ꢀ respectivelyꢀ [33].ꢀ Althoughꢀ noꢀ
residualꢀmodifiersꢀwereꢀdetectedꢀinꢀtheꢀobtainedꢀsamples,ꢀtheꢀ
peakꢀatꢀ3580ꢀcm−1ꢀthatꢀcorrespondsꢀtoꢀOHꢀshowsꢀdistinctꢀdif‐
Fig.ꢀ 2.ꢀ Characteristicꢀ peaksꢀ ofꢀ HAPꢀ (PDFꢀ No.ꢀ 09‐0432)ꢀ [31]ꢀ
wereꢀ clearlyꢀ observedꢀ inꢀ allꢀ patterns,ꢀ indicatingꢀ successfulꢀ
formationꢀ ofꢀ theꢀ HAPꢀ structure.ꢀ Besidesꢀ theꢀ goodꢀ agreementꢀ
withꢀ theꢀ standardꢀ HAPꢀ pattern,ꢀ noꢀ impuritiesꢀ orꢀ distinctꢀ dif‐
ferencesꢀwereꢀobservedꢀinꢀtheꢀXRDꢀpatterns,ꢀtherebyꢀimplyingꢀ
ferentꢀintensitiesꢀamongꢀtheꢀsamples.ꢀBecauseꢀtheꢀintensityꢀofꢀ
ꢀ
theꢀpeaksꢀisꢀinfluencedꢀbyꢀtheꢀamountꢀofꢀsamplesꢀtested,ꢀtheꢀOH
contentꢀ ofꢀ theꢀ samplesꢀ cannotꢀ beꢀ directlyꢀ determinedꢀ byꢀ theꢀ
intensityꢀofꢀtheꢀOHꢀcharacteristicꢀpeaks.ꢀTherefore,ꢀtheꢀrelativeꢀ
4
peakꢀintensityꢀofꢀtheꢀOHꢀgroupsꢀtoꢀtheꢀPO ꢀgroupsꢀwasꢀusedꢀtoꢀ
HAPBLANK
HAPCTAB
HAPSDS
HAPSC
estimateꢀtheꢀOHꢀcontentꢀinꢀeachꢀsample.ꢀTheꢀcalculatedꢀareasꢀofꢀ
−1
theꢀpeakꢀatꢀ3580ꢀcm ꢀthatꢀwasꢀassignedꢀtoꢀtheꢀstretchingꢀmodeꢀ
−1
ofꢀOHꢀgroupsꢀandꢀtheꢀpeakꢀatꢀ962ꢀcm ꢀthatꢀwasꢀascribedꢀtoꢀtheꢀ
stretchingꢀmodeꢀofꢀPO
ratiosꢀwereꢀalsoꢀcalculatedꢀbasedꢀonꢀtheꢀcalculatedꢀareas.ꢀHAPSC
featuredꢀhigherꢀOH/PO
ofꢀOHꢀgroupsꢀwereꢀformedꢀonꢀtheꢀsurfaceꢀofꢀHAP
4
ꢀgroupsꢀareꢀshownꢀinꢀTableꢀ1;ꢀOH/PO
4
ꢀ
ꢀ
4
ꢀratios,ꢀindicatingꢀthatꢀhigherꢀamountsꢀ
ꢀ
afterꢀmodifi‐
cationꢀwithꢀSC.ꢀItꢀhasꢀbeenꢀproposedꢀthatꢀOHꢀgroupsꢀplayꢀanꢀ
importantꢀ roleꢀ inꢀ theꢀ adsorption/activationꢀ ofꢀ HCHOꢀ [24].ꢀ
Therefore,ꢀtheꢀhighꢀcontentꢀofꢀOHꢀgroupsꢀinꢀHAPSCꢀwasꢀrespon‐
sibleꢀforꢀitsꢀsignificantlyꢀimprovedꢀactivity.ꢀ
TheꢀFTIRꢀspectrumꢀofꢀHAPSC‐usedꢀisꢀalsoꢀshownꢀinꢀFig.ꢀ3.ꢀAsꢀ
observed,ꢀ theꢀ shapeꢀ ofꢀ theꢀ spectrumꢀ ofꢀ HAPSC‐usedꢀ wasꢀ notꢀ
20
25 30 35 40 45 50 55 60 65 70
o
2
/( )
Fig.ꢀ2.ꢀXRDꢀpatternsꢀofꢀHAPBLANKꢀandꢀmodifiedꢀHAPꢀsamples.ꢀ

1930ꢀ
YahuiꢀSunꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936ꢀ
Tableꢀ1ꢀ
700
OHꢀandꢀPO
ciatedꢀrelativeꢀOH/PO
4
ꢀpeakꢀareasꢀofꢀdifferentꢀsamplesꢀdetectedꢀbyꢀFTIRꢀandꢀasso‐
ꢀratios.ꢀ
(a)
600
4
HAPBLANK
HAPCTAB
HAPSDS
OHꢀpeakꢀareaꢀ PO ꢀpeakꢀareaꢀ
4
500
Sampleꢀ
OH/PO ꢀ
4
−1
(962ꢀcm−1)ꢀ
198ꢀ
(3580ꢀcm )ꢀ
4
00
00
HAPBLANK
ꢀ
466ꢀ
2.35ꢀ
2.26ꢀ
2.69ꢀ
3.76ꢀ
3.64ꢀ
HAPCTAB
HAPSDS
HAPSC
HAPSC‐usedꢀ
ꢀ
617ꢀ
273ꢀ
3
ꢀ
580ꢀ
215ꢀ
ꢀ
828ꢀ
220ꢀ
200
637ꢀ
175ꢀ
100
HAPSC
0.2
0
0
distinctivelyꢀdifferentꢀfromꢀthatꢀofꢀfreshꢀHAPSC,ꢀfurtherꢀindicat‐
ingꢀtheꢀgoodꢀstabilityꢀofꢀtheꢀsample.ꢀMoreover,ꢀtheꢀintensityꢀofꢀ
theꢀ OHꢀ groupsꢀ didꢀ notꢀ changeꢀ considerably.ꢀ Forꢀ betterꢀ com‐
parison,ꢀtheꢀsameꢀcalculationꢀwasꢀadoptedꢀtoꢀevaluateꢀtheꢀOHꢀ
contentꢀinꢀtheꢀtwoꢀsamplesꢀ(Tableꢀ1).ꢀBasedꢀonꢀtheꢀcalculatedꢀ
.0
0.4
0.6
0.8
1.0
p/p
0
0
0
0
.010
.008
.006
HAPSC
(b)
4
results,ꢀtheꢀOH/PO ꢀratioꢀonlyꢀdecreasedꢀslightlyꢀfromꢀ3.76ꢀtoꢀ
3
.64.ꢀ Therefore,ꢀtheꢀcontentꢀofꢀ theꢀOHꢀ groupsꢀ canꢀ beꢀ consid‐
HAPCTAB
eredꢀ toꢀ beꢀ stableꢀ beforeꢀ andꢀ afterꢀ theꢀ reaction,ꢀ therebyꢀ ex‐
plainingꢀtheꢀsimilarityꢀinꢀtheꢀactivitiesꢀofꢀfreshꢀHAPSCꢀandꢀusedꢀ
HAPSC.ꢀ
HAPBLANK
HAPSDS
0.004
0
.002
.000
3.2.3.ꢀ ꢀ SEMꢀandꢀBETꢀanalysesꢀ ꢀ
0
TheꢀSEMꢀimagesꢀofꢀtheꢀfourꢀsamplesꢀ(Fig.ꢀ4)ꢀdisplayꢀtheꢀfea‐
turesꢀandꢀstructuresꢀofꢀtheꢀHAPꢀsamples.ꢀHAPBLANKꢀandꢀHAPSC
ꢀ
0
20
40
60
D/nm
80
100
120
possessedꢀaꢀuniformꢀsheetꢀstackingꢀstructureꢀwithꢀaꢀfluffyꢀsur‐
face.ꢀTheꢀadditionꢀofꢀsodiumꢀcitrateꢀduringꢀtheꢀsynthesisꢀpro‐
cessꢀdidꢀnotꢀchangeꢀtheꢀintegrityꢀorꢀuniformityꢀofꢀ HAPꢀstruc‐
ture.ꢀ Inꢀ contrast,ꢀ theꢀ additionꢀ ofꢀ CTABꢀ (HAPCTAB)ꢀ andꢀ SDSꢀ
Fig.ꢀ5.ꢀN ꢀadsorption‐desorptionꢀisothermsꢀ(a)ꢀandꢀporeꢀsizeꢀdistribu‐
tionꢀ(b)ꢀofꢀHAPBLANKꢀandꢀmodifiedꢀHAPꢀsamples.ꢀ
2
(
HAPSDS)ꢀdestroyedꢀtheꢀuniformityꢀofꢀtheꢀsamplesꢀandꢀfeaturedꢀ
sheetꢀstackingꢀstructureꢀinꢀtheꢀsamples,ꢀwhichꢀisꢀinꢀaccordanceꢀ
withꢀtheꢀSEMꢀanalysis.ꢀInꢀcomparisonꢀwithꢀtheꢀisothermsꢀofꢀtheꢀ
threeꢀ otherꢀ samples,ꢀ HAPSCꢀ featuredꢀ aꢀ differentꢀ desorptionꢀ
aꢀrelativelyꢀcompactꢀsurface.ꢀ
Differencesꢀ inꢀ theꢀ structureꢀ canꢀ beꢀ evaluatedꢀ fromꢀ theꢀ N ꢀ
2
adsorption‐desorptionꢀ studies.ꢀ Asꢀ shownꢀ inꢀ Fig.ꢀ 5(a),ꢀ allꢀ HAPꢀ
samplesꢀ featuredꢀ aꢀ typeꢀ IVꢀ adsorption‐desorptionꢀ isothermꢀ
withꢀ anꢀH3ꢀhysteresisꢀloopꢀ accordingꢀtoꢀtheꢀIUPACꢀclassifica‐
tionꢀ[29,32].ꢀTheꢀH3ꢀhysteresisꢀloopꢀindicatesꢀtheꢀpresenceꢀofꢀaꢀ
branchꢀatꢀtheꢀhigherꢀp/p ꢀvaluesꢀthatꢀisꢀindicativeꢀofꢀtheꢀpres‐
0
enceꢀofꢀrelativelyꢀuniformꢀandꢀsmallꢀpores,ꢀowingꢀtoꢀtheꢀexist‐
ingꢀresistanceꢀduringꢀtheꢀdesorptionꢀprocess.ꢀThisꢀtrendꢀcanꢀbeꢀ
observedꢀinꢀFig.ꢀ5(b)ꢀthatꢀshowsꢀtheꢀporeꢀsizeꢀdistributionꢀofꢀallꢀ
fourꢀ HAPꢀ samples;ꢀ accordingly,ꢀ theꢀ poreꢀ sizeꢀ distributionꢀ ofꢀ
HAPSCꢀshiftsꢀtoꢀtheꢀlowerꢀporeꢀsizeꢀregion.ꢀ ꢀ
HAPBLANK
HAPSC
Theꢀtexturalꢀproperties,ꢀincludingꢀtheꢀspecificꢀsurfaceꢀarea,ꢀ
poreꢀvolume,ꢀandꢀaverageꢀporeꢀdiameter,ꢀofꢀtheꢀstudiedꢀsam‐
plesꢀareꢀlistedꢀinꢀTableꢀ2.ꢀTheꢀspecificꢀsurfaceꢀareasꢀofꢀtheꢀfourꢀ
2
samplesꢀ wereꢀ inꢀ theꢀ rangeꢀ ofꢀ 26–40ꢀ m /g.ꢀ Theꢀ averageꢀ poreꢀ
sizeꢀwasꢀaroundꢀ40ꢀnm.ꢀAsꢀobserved,ꢀtheꢀsampleꢀmodifiedꢀwithꢀ
SC,ꢀ whichꢀ presentedꢀ theꢀ bestꢀ catalyticꢀ activity,ꢀ possessedꢀ theꢀ
2
highestꢀ specificꢀ surfaceꢀ areaꢀ (40.36ꢀ m /g)ꢀ andꢀ poreꢀ volumeꢀ
3
(
0.3692ꢀm /g),ꢀandꢀtheꢀsmallestꢀaverageꢀporeꢀdiameterꢀ(36.58ꢀ
nm).ꢀInꢀcontrast,ꢀtheꢀSDS‐modifiedꢀHAPꢀsampleꢀshowedꢀoppo‐
HAPCTAB
HAPSDS
Tableꢀ2ꢀ
2
TexturalꢀpropertiesꢀofꢀsamplesꢀanalyzedꢀbyꢀN ꢀadsorption‐desorptionꢀ
method.ꢀ
BETꢀsurfaceꢀareaꢀ Poreꢀvolumeꢀ
Averageꢀdiameterꢀ
(nm)ꢀ
Sampleꢀ
2
3
(m /g)ꢀ
(m /g)ꢀ
HAPBLANK
ꢀ
26.42ꢀ
27.52ꢀ
23.13ꢀ
40.36ꢀ
0.3004ꢀ
0.3049ꢀ
0.2801ꢀ
0.3692ꢀ
45.48ꢀ
44.32ꢀ
48.44ꢀ
36.58ꢀ
HAPCTAB
HAPSDS
HAPSC
ꢀ
ꢀ
ꢀ
Fig.ꢀ4.ꢀSEMꢀimagesꢀofꢀHAPBLANKꢀandꢀmodifiedꢀHAPꢀsamples.ꢀ

ꢀ
YahuiꢀSunꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936ꢀ
1931ꢀ
siteꢀtrends.ꢀTheꢀhigherꢀspecificꢀsurfaceꢀareaꢀandꢀporeꢀchannelꢀofꢀ
HAPSCꢀ provideꢀ additionalꢀ sitesꢀforꢀHCHOꢀadsorption,ꢀ whereasꢀ
theꢀsmallerꢀporesꢀcontributeꢀtoꢀlongerꢀretentionꢀtimesꢀandꢀfa‐
vorꢀreactionsꢀbetweenꢀHCHOꢀandꢀoxygenꢀonꢀHAP.ꢀ
0
.5
.0
1
00
9
9
9
9
8
7
0
-0.5
-1.0
-1.5
-2.0
3.3.ꢀ ꢀ Effectꢀofꢀorganicꢀmodifiersꢀandꢀstructure‐performanceꢀ
relationshipꢀ
96
9
5
4
Basedꢀonꢀtheꢀcharacterizationꢀresultsꢀdiscussedꢀabove,ꢀitꢀcanꢀ
9
beꢀ seenꢀ thatꢀ theꢀ additionꢀ ofꢀ organicꢀ modifiersꢀ didꢀ notꢀ causeꢀ
considerableꢀ differencesꢀ inꢀ theꢀ crystallinityꢀ ofꢀ theꢀ resultingꢀ
samples,ꢀ andꢀ noꢀ organicꢀ modifiersꢀ wereꢀ retainedꢀ inꢀ theꢀ ob‐
tainedꢀHAPꢀsamples.ꢀThus,ꢀinꢀtheꢀpresentꢀwork,ꢀitꢀcanꢀbeꢀde‐
ducedꢀthatꢀneitherꢀtheꢀcrystallinityꢀnorꢀtheꢀpresenceꢀofꢀtheꢀnewꢀ
groupsꢀintroducedꢀintoꢀHAPꢀcontributesꢀtoꢀtheꢀimprovedꢀper‐
formanceꢀ ofꢀ HAPSC.ꢀ Inꢀ contrast,ꢀ theꢀ specificꢀ surfaceꢀ areaꢀ andꢀ
poreꢀ structure,ꢀ whichꢀ usuallyꢀ influenceꢀ adsorptionꢀ andꢀ massꢀ
transferꢀduringꢀtheꢀreaction,ꢀareꢀsignificantlyꢀinfluencedꢀbyꢀtheꢀ
additionꢀofꢀvariousꢀorganicꢀmodifiers.ꢀ
TheꢀFTIRꢀspectrumꢀofꢀnon‐calcinedꢀHAPSCꢀisꢀshownꢀinꢀFig.ꢀ6;ꢀ
characteristicꢀ peaksꢀ assignedꢀ toꢀ theꢀ stretchingꢀ vibrationsꢀ ofꢀ
carboxylꢀ andꢀ C–Oꢀ groupsꢀ wereꢀ detectedꢀ [30],ꢀ indicatingꢀ theꢀ
presenceꢀ ofꢀ citrateꢀ onꢀ theꢀ SC‐modifiedꢀ HAPꢀ sample.ꢀ Thoseꢀ
peaksꢀwereꢀnotꢀobservedꢀinꢀtheꢀcalcinedꢀHAPSCꢀsample,ꢀtherebyꢀ
suggestingꢀ thatꢀ theꢀ citrateꢀ couldꢀ beꢀ completelyꢀ decomposedꢀ
duringꢀcalcination.ꢀTheꢀdecompositionꢀofꢀcitrateꢀcouldꢀalsoꢀbeꢀ
confirmedꢀ fromꢀ theꢀ thermogravimetry/derivativeꢀ thermogra‐
vimetryꢀ(TG/DTG)ꢀcurveꢀofꢀHAPSCꢀ(non‐calcined)ꢀshownꢀinꢀFig.ꢀ
93
1
00 200 300 400 500 600 700 800 900
o
Temperature ( C)
Fig.ꢀ7.ꢀTG/DTGꢀcurvesꢀofꢀtheꢀHAPSCꢀsampleꢀbeforeꢀcalcination.ꢀ
contributeꢀtoꢀtheꢀhigherꢀspecificꢀsurfaceꢀareaꢀandꢀporeꢀvolumeꢀ
observedꢀ[29].ꢀInꢀaddition,ꢀtheꢀminorꢀweightꢀlossꢀ(600–900ꢀ°C)ꢀ
partlyꢀreflectsꢀtheꢀgoodꢀthermalꢀstabilityꢀofꢀtheꢀmaterial.ꢀ
Basedꢀ onꢀ theꢀ characterizationꢀ results,ꢀ HAPSCꢀ possessedꢀ
largerꢀspecificꢀsurfaceꢀareaꢀandꢀporeꢀvolumeꢀowingꢀtoꢀtheꢀde‐
compositionꢀ ofꢀ SCꢀ duringꢀ calcination.ꢀ Theseꢀ featuresꢀ contrib‐
utedꢀtoꢀtheꢀimprovedꢀactivityꢀofꢀtheꢀresultingꢀcatalystꢀbyꢀfacili‐
tatingꢀ theꢀ adsorptionꢀ processꢀ duringꢀ theꢀ reaction.ꢀ Moreover,ꢀ
theꢀsmallerꢀporesꢀofꢀHAPSCꢀledꢀtoꢀlongerꢀretentionꢀtimesꢀofꢀtheꢀ
HCHOꢀmoleculesꢀinꢀtheꢀpores.ꢀAlso,ꢀmodificationꢀofꢀHAPꢀwithꢀSCꢀ
resultedꢀ inꢀ increasedꢀ amountsꢀ ofꢀ hydroxylꢀ groupsꢀ inꢀ theꢀ re‐
sultingꢀHAPSC;ꢀitꢀhasꢀbeenꢀproposedꢀthatꢀhydroxylꢀgroupsꢀareꢀ
responsibleꢀ forꢀ theꢀ HCHOꢀ catalyticꢀ oxidationꢀ onꢀ HAPꢀ [24].ꢀ
Therefore,ꢀbetterꢀadsorptionꢀproperties,ꢀlongerꢀretentionꢀtimes,ꢀ
andꢀlargerꢀcontentsꢀofꢀOHꢀgroupsꢀallꢀleadꢀtoꢀbetterꢀinteractionsꢀ
betweenꢀtheꢀreactionꢀgasꢀandꢀactiveꢀsitesꢀofꢀtheꢀcatalysts,ꢀcon‐
sequentlyꢀ resultingꢀ inꢀ significantlyꢀ enhancedꢀ performanceꢀ ofꢀ
HAPSCꢀtowardsꢀHCHOꢀoxidation.ꢀ
7.ꢀTheꢀTGꢀcurveꢀofꢀtheꢀHAPꢀsampleꢀmodifiedꢀwithꢀSCꢀ(beforeꢀ
calcination)ꢀshowedꢀaꢀsingleꢀandꢀcontinuousꢀweightꢀloss.ꢀHow‐
ever,ꢀ accordingꢀ toꢀ theꢀ DTGꢀ curve,ꢀ whichꢀ reflectsꢀ theꢀ ratesꢀ ofꢀ
weightꢀloss,ꢀthreeꢀmainꢀweightꢀlossꢀstagesꢀunderꢀ600ꢀ°Cꢀwereꢀ
observed.ꢀTheꢀfirstꢀstageꢀ(<ꢀ150ꢀ°C)ꢀcorrespondsꢀtoꢀevaporationꢀ
ofꢀwaterꢀ[34],ꢀwhichꢀaccountsꢀforꢀaꢀweightꢀlossꢀofꢀaboutꢀ2%.ꢀ
Theꢀsecondꢀandꢀthirdꢀweightꢀlossꢀstages,ꢀobservedꢀatꢀtheꢀhigherꢀ
temperaturesꢀ (200–600ꢀ °C)ꢀ correspondꢀ toꢀ theꢀ decompositionꢀ
ofꢀtheꢀanhydrousꢀcitrateꢀandꢀtheꢀproducedꢀintermediateꢀcom‐
plexꢀ[35].ꢀTheꢀtotalꢀweightꢀlossꢀ(<ꢀ600ꢀ°C)ꢀisꢀaboutꢀ5.7%,ꢀwhichꢀ
isꢀslightlyꢀhigherꢀthanꢀtheꢀamountꢀofꢀSCꢀaddedꢀtoꢀtheꢀsolutionꢀ
duringꢀtheꢀsynthesisꢀprocedureꢀ(i.e.,ꢀ5%),ꢀandꢀcanꢀbeꢀrelatedꢀtoꢀ
theꢀwaterꢀloss.ꢀFurtherꢀweightꢀlossꢀaboveꢀ600ꢀ°Cꢀmayꢀbeꢀdueꢀtoꢀ
carbonꢀlossꢀfromꢀtheꢀsystemꢀ[34].ꢀTheꢀdecompositionꢀofꢀsodiumꢀ
citrateꢀattachedꢀtoꢀHAPꢀcanꢀgenerateꢀstructuralꢀvacanciesꢀandꢀ
CTABꢀandꢀSDSꢀareꢀtypicallyꢀusedꢀtoꢀregulateꢀtheꢀmorphologyꢀ
ofꢀHAP;ꢀporesꢀareꢀgeneratedꢀuponꢀeliminationꢀofꢀtheꢀmodifiersꢀ
25,27,28,36].ꢀ Uponꢀ additionꢀ ofꢀ templateꢀ CTAB,ꢀ theꢀ positiveꢀ
[
headꢀofꢀCTABꢀisꢀassembledꢀontoꢀHAP;ꢀaꢀlargeꢀamountꢀofꢀNH
4
+ꢀ
ionsꢀareꢀpresentꢀinꢀtheꢀprecipitatedꢀHAP.ꢀDuringꢀcalcination,ꢀtheꢀ
organicꢀ CTABꢀ templatingꢀ structuresꢀ andꢀ ammoniumꢀ saltꢀ areꢀ
decomposed,ꢀleadingꢀtoꢀtheꢀgenerationꢀofꢀporesꢀinꢀtheꢀHAꢀskel‐
etonꢀ [28].ꢀ However,ꢀ theꢀ sizeꢀ ofꢀ theꢀ poresꢀ inducedꢀ byꢀ theꢀ de‐
compositionꢀ ofꢀ theꢀ organicꢀ CTABꢀ templatingꢀ structureꢀ isꢀ dif‐
ferentꢀfromꢀthatꢀofꢀporesꢀgeneratedꢀbyꢀremovalꢀofꢀtheꢀammo‐
niumꢀsalt,ꢀtherebyꢀexplainingꢀtheꢀnon‐uniformityꢀofꢀtheꢀresult‐
ingꢀsampleꢀstructureꢀ[28].ꢀAꢀsimilarꢀdecompositionꢀprocessꢀofꢀ
theꢀsulfateꢀgroupsꢀwasꢀalsoꢀobservedꢀforꢀSDSꢀ[27].ꢀItꢀisꢀknownꢀ
fromꢀtheꢀchemicalꢀstructureꢀofꢀCTAB,ꢀSDS,ꢀandꢀSCꢀthatꢀatꢀleastꢀ
twoꢀtypesꢀofꢀgasesꢀwereꢀreleasedꢀduringꢀcalcinationꢀofꢀHAPCTAB
ꢀ
(
CO ,ꢀ NH )ꢀ andꢀ HAPSDSꢀ (CO ,ꢀ SO ).ꢀ Thisꢀ causedꢀ theꢀ poorꢀ uni‐
2
3
2
2
formityꢀofꢀtheꢀ poresꢀinꢀtheꢀsamples,ꢀ asꢀreflectedꢀ byꢀtheꢀwideꢀ
poreꢀsizeꢀdistributionsꢀandꢀtheꢀnon‐uniformꢀstructuresꢀshownꢀ
inꢀtheꢀSEMꢀimages.ꢀMoreover,ꢀtheꢀpresenceꢀofꢀtheꢀlongerꢀalkylꢀ
chainꢀlengthsꢀofꢀCTABꢀandꢀSDSꢀalsoꢀinstigatedꢀtheꢀformationꢀofꢀ
largerꢀporesꢀ[37,38].ꢀTherefore,ꢀtheꢀlargerꢀporesꢀandꢀpoorꢀuni‐
formityꢀofꢀtheꢀstructuresꢀofꢀHAPCTABꢀandꢀHAPSDSꢀwereꢀdueꢀtoꢀtheꢀ
structureꢀandꢀcompositionꢀofꢀCTABꢀandꢀSDS,ꢀasꢀwellꢀasꢀtheꢀde‐
Carboxyl
CO
4000
3500
2000
Wavenumber (cm )
Fig.ꢀ6.ꢀFTIRꢀspectrumꢀofꢀnon‐calcinedꢀHAPSC.ꢀ
1500
1000
500

1

1932ꢀ
YahuiꢀSunꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936ꢀ
compositionꢀpropertiesꢀofꢀtheꢀsurfactant.ꢀInꢀcontrast,ꢀCO
2
ꢀwasꢀ
[9] WangꢀRꢀH,ꢀLiꢀJꢀH.ꢀCatalꢀLett,ꢀ2009,ꢀ131:ꢀ500ꢀ
[
[
[
[
10] TangꢀXꢀF,ꢀChenꢀJꢀL,ꢀHuangꢀXꢀM,ꢀXuꢀYꢀD,ꢀShenꢀWꢀJ.ꢀ ApplꢀCatalꢀB,ꢀ
mostlyꢀ generatedꢀ duringꢀ theꢀ calcinationꢀ ofꢀ HAPSC,ꢀ andꢀ theꢀ
smallerꢀSCꢀmoleculesꢀledꢀtoꢀtheꢀformationꢀofꢀsmallerꢀpores.ꢀ ꢀ
2008,ꢀ81:ꢀ115ꢀ
11] LiꢀCꢀY,ꢀShenꢀYꢀN,ꢀJiaꢀMꢀL,ꢀShengꢀSꢀS,ꢀAdebajoꢀMꢀO,ꢀZhuꢀHꢀY.ꢀCatalꢀ
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4.ꢀ ꢀ Conclusionsꢀ
ModificationꢀofꢀHAPꢀwithꢀdifferentꢀorganicꢀmodifiersꢀ(CTAB,ꢀ
SDS,ꢀandꢀSC)ꢀresultedꢀinꢀdifferencesꢀinꢀtheꢀspecificꢀsurfaceꢀareaꢀ
andꢀporeꢀstructureꢀofꢀtheꢀfinalꢀmodifiedꢀHAPꢀsamples.ꢀModifi‐
cationꢀ withꢀ SCꢀ significantlyꢀ improvedꢀ theꢀ activityꢀ ofꢀ HAPꢀ to‐
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2
40ꢀ °C.ꢀ HAPSCꢀ featuredꢀ largerꢀ specificꢀ surfaceꢀ areaꢀ andꢀ poreꢀ
1
volumeꢀ thatꢀ enhancedꢀ theꢀ adsorptionꢀ capacityꢀ forꢀ HCHO,ꢀ
whereasꢀtheꢀsmallerꢀporesꢀaffordedꢀsufficientꢀtimeꢀforꢀinterac‐
tionꢀbetweenꢀtheꢀcatalystꢀandꢀreactionꢀgas.ꢀBesidesꢀtheꢀstruc‐
turalꢀdifferencesꢀthatꢀinfluencedꢀadsorptionꢀandꢀmassꢀtransfer,ꢀ
theꢀ contentꢀ ofꢀ hydroxylꢀ groupsꢀ thatꢀ isꢀ responsibleꢀ forꢀ HCHOꢀ
oxidationꢀ wasꢀ higherꢀ inꢀ theꢀ SC‐modifiedꢀ HAPꢀ sample.ꢀ Betterꢀ
adsorptionꢀproperties,ꢀlongerꢀretentionꢀtimes,ꢀandꢀlargerꢀcon‐
tentsꢀofꢀOHꢀgroupsꢀofꢀHAPSCꢀallꢀleadꢀtoꢀbetterꢀinteractionꢀbe‐
tweenꢀ theꢀ reactionꢀ gasꢀ andꢀ activeꢀ sitesꢀ ofꢀ theꢀ catalysts,ꢀ andꢀ
subsequentꢀ significantlyꢀ enhancedꢀ performanceꢀ ofꢀ HAPSCꢀ to‐
wardsꢀHCHOꢀoxidation.ꢀ
3
1
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GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2014,ꢀ35:ꢀ1927–1936ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(14)60129‐7
Formaldehydeꢀcatalyticꢀoxidationꢀoverꢀhydroxyapatiteꢀmodifiedꢀwithꢀvariousꢀorganicꢀmodifiersꢀ
ꢀ
YahuiꢀSun,ꢀZhenpingꢀQu*,ꢀDanꢀChen,ꢀHuiꢀWang,ꢀFanꢀZhang,ꢀQiangꢀFuꢀ
DalianꢀUniversityꢀofꢀTechnology;ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciencesꢀ
3
2
2
00
50
00
1
00
100
80
60
40
20
0
0
.010
HAPBLANK
HAPSC
Specific surface area
Catalytic activity
0.008
8
6
4
2
0
0
0
0
0
0
0
.006
.004
150
00
0.002
.000
0
1
0
20
40
60
D/nm
80 100 120
HAPSC
5
0
0
HAPBLANK
0
.0
0.2
0.4
0.6
0.8
1.0
HAPBLANK
HAPSC
p/p
0
ꢀ
Betterꢀadsorptionꢀproperties,ꢀlongerꢀretentionꢀtimes,ꢀandꢀlargerꢀcontentsꢀofꢀOHꢀgroupsꢀofꢀhydroxyapatiteꢀmodifiedꢀwithꢀsodiumꢀcitrateꢀ
SC)ꢀ(HAPSC)ꢀleadꢀtoꢀbetterꢀinteractionꢀbetweenꢀtheꢀreactionꢀgasꢀandꢀactiveꢀsitesꢀandꢀhigherꢀactivityꢀtowardsꢀHCHOꢀoxidation.ꢀ
(

ꢀ
YahuiꢀSunꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1927–1936ꢀ
1933ꢀ
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