Synthesis of organoclays and their application for the adsorption of phenolica Faculty of Chemistry, Hanoi University of Science, Vietnam National University, Hanoi, Viet Nam b Faculty o
Trang 1Synthesis of organoclays and their application for the adsorption of phenolic
a
Faculty of Chemistry, Hanoi University of Science, Vietnam National University, Hanoi, Viet Nam
b
Faculty of Chemistry, Quy Nhon University, Viet Nam
c
Advanced Materials Technology Center, National Center for Technological Progress, Hanoi, Viet Nam
d Department of Environmental Engineering and Biotechnology, Myongji University, Republic of Korea
1 Introduction
During recent decades,zeolite withmicroporoussystemhas
been appliedin many industrial processes, such as adsorptive
materials,oxidationcatalysts.However,applicationsofzeoliteare
limited,becausesmall poresize(d<1.5nm)makesit hard for
transformationofcomplexandlargemolecules.Therefore,finding
newmaterialswithlargerporesystem hasbeenaninterest of
many scientists [1,2] The use of bentonite in wastewater
treatmenthasreceivedincreasingattentionandcurrentlyoffers
averyattractivemethodforpollutionremediation.Besidesitis
plentiful,inexpensiveandavailableinmanycountries,bentoniteis
knownhavinglayeredstructureandtobequiteporousmaterial.It
iswidelyusedinalargenumberofmanyfields.Inenvironmental
treatment,bentoniteisoftenusedasanaturaladsorptivematerial
[3].Bentoniteisnaturallycapableofadsorbingorganicsubstances;
however,theadsorptioncapacityisnothighenoughtobeapplied
inpractice.Hence,itneedstobemodifiedtoenhanceadsorption
capacity,andaminesaltshavebeengenerallyemployedas
cost-effectivereagents.Oncehydrocarbonchaininsertedintolayerscan
increaseinterlayerdistanceandhydrophobicproperty,leadingto
higher affinity toward organic substances [4,5] Organoclays,
preparedbyintercalatingclayswithsurfactantcations,havebeen consideredaspotentialsorbentsforremovingorganicpollutants fromwater[6–12].Quaternary ammoniumorganoclays maybe dividedintotwogroupsdependingonthestructureoftheorganic cationandthemechanismofsorption[13].Thefirstgroup,called adsorptive organoclays, includes claysthat contain short-chain quaternary ammonium ions,suchas tetramethylammonium or trimethylbenzylammonium.Sorptiononthistypeoforganoclays
ischaracterizedbyLangmuir-typeisotherms,whicharecommonly associated with specific sorption sites The second group of organoclays,calledorganophilicorganoclays,iscomposedofclays that contain long-chain quaternary ammonium ions, such as hexadecyltrimethylammoniumordidodecyldimethylammonium Sorption by this group is also characterized by Langmuir or Freundlich-typeisotherms,butlinearintervalisoverwiderrange
ofsoluteconcentrations
Inthiswork,bentonitefromThanhHoa,Vietnamwasmodified for the first time by different organic quaternary ammonium cations,suchasbenzylhexadecyldimethylammonium, dimethyl-dioctadecylammonium andbenzylstearyldimethylammonium to adsorb phenolic compounds, including phenol, phenolred and direct blue DB 53 (Table 1 These aromatic compounds are commonpollutantsthatcanbefoundindifferenttypesofpolluted water as dye wastewater, wood manufacturing wastewater
[14,15] It was shown that organoclays containing surfactants witharomaticringswerebettersuitedforremovingtoxicaromatic
A R T I C L E I N F O
Article history:
Received 12 May 2012
Accepted 22 September 2012
Available online 28 September 2012
Keywords:
Organoclays
Quaternary ammonium salts
Organic
Sorption
A B S T R A C T
OrganoclaysweresynthesizedbyexchanginginorganiccationsbetweenlayersinThanhHoabentonite usingorganiccationsincludingbenzylhexadecyldimethylammonium(BHDDM+), dimethyldioctadecy-lammonium (DMDOD+) and benzylstearyldimethylammonium (BSDM+) Inserting organic cations increasesmaterialinterlayerdistancesignificantly(from15A˚ to40A˚)andsimultaneouslyenhances affinityofmaterialstowardorganicpollutants.Theresultsshowthatadsorptioncapacityoforganicson organoclaysstronglydependsonaffinitybetweenorganicsubstancesandammoniumcationsrather thanoninterlayerdistanceoforganoclays.This meansthatthesorptionoforganoclaysfororganic contaminantswassignificantlyinfluencedbythenatureofthesurfactantsaddedtotheclay
ß2012TheKoreanSocietyofIndustrialandEngineeringChemistry.PublishedbyElsevierB.V.Allrights
reserved
* Corresponding author Tel.: +84 98 322 2831.
E-mail address: nguyendieucam@hus.edu.vn (T.D.C Nguyen).
ContentslistsavailableatSciVerseScienceDirect
j o urna l hom e pa ge : ww w e l s e v i e r c om/ l o ca t e / j i e c
1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry Published by Elsevier B.V All rights reserved.
Trang 2solution[16,17]
2 Materialsandmethods
2.1 Synthesisoforganoclays
Bentonite from Thanh Hoa, Vietnam has undergone a
purificationprotocolcomposedofseveralstages:disintegration
todispersethelayersofclayandrecoveryofthefractionofclay
lower than 2mm, and then saturated by sodium chloride
solution (0.1mol/L) Thus the recovered bentonite known as
sodiumbentonitewaswashedseveraltimeswithdistilledwater
untilfreeofchlorideionsasindicatedbyAgNO3,andthendried
at ambient temperature The surfactants used to modify the
bentonite are cationic surfactants, including
benzylhexadecyl-dimethylammonium chloride (BHDDM chloride),
benzylstear-yldimethylammonium chloride (BSDM chloride), and
dimethyldioctadecylammonium bromide (DMDOD bromide)
providedbySigma–Aldrich(Table1).Organoclayswereprepared
byinsertionoftheaforementionedquaternaryammoniumsalt
between the layers of the bentonite by a simple cationic
exchange.Theeffectsof variousparameterssuchassurfactant
dose, temperature, pH and reaction time on d001 value of
organoclayswereinvestigated.Allthesamplesweremaintained
underconstantagitationduring24h,andwashedseveral time
with distilled water until no chloride ions were detected by
AgNO3.Organoclayswererecoveredbycentrifugationanddried
at708C
2.2 Adsorptionexperiments
All experiments were performed in batch with 0.1g
ogranoclays and 100ml of synthetic wastewater containing
from 50 to 1500mg/L aqueous phenol compounds solution
Phenol concentration was measured by spectrophotometric
methodemploying4-aminoantipyrinascoloringagent,complex
formedhasmaximumabsorptionat510nm.PhenolredandDB
53concentrationsweredeterminedthroughtheirabsorptionat
lmaxof432nmand622nm,respectively[18]
To characterize adsorption of different phenolic compounds using organoclays, the Langmuir adsorption isotherm was employed The linear form of Langmuir adsorption isotherm equationispresentedasfollows:
Ce
q ¼
Ce
qmaxþ
1
kqmax where q is theadsorptioncapacity at certaintime, qmaxis the maximumadsorptioncapacity,Ceistheconcentrationofadsorbate
atequilibrium,kistheLangmuirconstant
3 Resultsanddiscussion 3.1 Effectsofsynthesisparametersonengineeredorganoclays properties
3.1.1 Effectofthenatureanddoseofquaternaryammoniumsalts Interlayer distances of organoclay at different amount of quaternary ammonium salts obtained from XRD patterns are showninTable2.Itisclearthatinterlayerdistanceoforganoclay dependsonnatureandamountoforganicammoniumsalts Bent-DMDOD haslargerdistancethanBent-BSDM,andBent-BHDDM has thesmallest value In details, interlayer distances of Bent-BHDDM, Bent-BSDM, and Bent-DMDOD with 100% cation ex-changecapacity(CEC)organicammoniumsaltare27.01A˚,32.16A˚ and40.57A˚,respectively.AccordingtoLagalyandHackett[19,20], fororganoclaywithinterlayerdistancelargerthan22.7A˚,organic cationsliebetweenbentonitelayersaspseudo-threelayers.The obtainedresultsarehigherthanthoseinsomeotherpublications
[21–24] From data in Table 2, it can beconcluded that theoptimal ammoniumsaltsdosetosynthesizeBent-BHDDM,Bent-DMDOD andBent-BSDMare125,100and150%CEC,respectively 3.1.2 EffectofpH
ItisclearthatwhenpHisintherangeof6–10,underoptimal dosesofammoniumsalts,interlayerdistancesoforganoclaysdo not vary significantly (Table 3 This observation agrees with explanationsofsomeauthorsthatchargeofquaternary
ammoni-umcationsinclaydoes notchangewithpH,andtheyarekept betweenlayersbyelectrostaticforce[25]
Table 1
Surfactants and phenolic compounds used in this study.
BHDDM chloride CH 3 (CH 2 ) 15 N(CH 3 ) 2 CH 2 C 6 H 5 Cl 381.5
BSDM chloride CH 3 (CH 2 ) 17 N(CH 3 ) 2 CH 2 C 6 H 5 Cl 409.5
DMDOD chloride [CH 3 (CH 2 ) 17 ] 2 N(CH 3 ) 2 Cl 585.50
Phenol red (phenolsulfonphthalein) C 19 H 14 O 5 S 354.38
DB 53 (direct blue 53) C 34 H 24 N 6 Na 4 O 14 S 4 960.80
Table 4 Effect of temperature on d 0 0 1 of organoclays.
Temperature (8C) d 0 0 1 value (A˚)
Table 2
Effect of quaternary ammonium salt dose on d 0 0 1 of organoclays.
Quaternary ammonium
salt dose (%CEC)
d 0 0 1 value of organoclay (A˚)
15.60 a
15.60 a
a
Table 3 Effect of pH of bentonite suspension on d 0 0 1 value of organoclays.
pH d 0 0 1 value of organoclay (A˚)
Trang 3ofBent-BHDDMandBent-DMDOD,whilethepHof10waschosen
forthesynthesisofBent-BSDM
3.1.3 Effectoftemperature
ItcanbeseenfromTable4that interlayerdistanceofthree
studiedorganoclays,underoptimaldosesofammoniumsalts,does
notdependsignificantlyontemperature
FromthedatainTable4thetemperatureof658Cwaschosen
forsynthesizingBent-BHDDM,andthetemperatureof558Cwas
chosenforsynthesizingBent-DMDODandBent-BSDM
3.1.4 Effectofreactiontime Althoughexchangereactionisquitefast(about40–120min),in orderforcationstobestablebetweenclaylayers,reactionsolution should be kept in longer time, the optimal reaction time to synthesizeBent-BHDDM, Bent-DMDOD and Bent-BSDMare 4h (Table5
Toprovethatquaternaryammoniumcationsweresuccessfully immobilizedonbentonitelayersinorganoclays,samples synthe-sizedatoptimalconditionswerecharacterizedbyIRspectroscopy (Figs.1–3)
It can be seen that in IR spectra of Bent-BHDDM, Bent-DMDODandBent-BSDM,therearepeakscharacterizedfor(i)–
CH3and–CH2–stretchingmodesat2850cm1and2920cm1, and (ii) C–N stretching of organic ammonium cations at
1467cm1.ResultsobtainedfromIRspectraagreewithreports
ofotherauthors[26,27].Therearealsopeakscharacterizedfor bentonite,suchaspeaksofSi–OvibrationinSiO4tetrahedronat 420–470cm1; peaks of Al–O vibration in octahedron at
815cm1 The presence of OH groups in the water absorbed
is proved by the appearance of peaks at 3400–3600cm1 However,thepeakintensityintheIRspectra oforganoclaysis lower than that in bentonite’s IR spectrum, and these results
Fig 1 IR spectra of bentonite and Bent-BHDDM.
Table 5
Effect of reaction time on d 0 0 1 value.
Time (h) d 0 0 1 (A˚)
Trang 4showthatorganophilic propertyof organoclaysis higherthan
thatofbentonite
3.2 Adsorptionofphenoliccompoundsonorganoclays
Inorganoclays,Natomsareheldonbentonitesurfacethrough
attractive electrostatic force with negative-charged bentonite
surface,and alkyl tails(RR1R2R3)N+orient toward inside pores
Thesealkyltailscanactasliquefiedorganicsolvent,andtheyhave
affinity toward organic substances [28,29] Phenols adsorption
takesplaceonorganophiliccentersoforganoclays
Experimentdatawereobtainedattemperature3018C,and
thepHvaluesofphenol,phenolred,andDB53solutionswere6,5and
2,respectively.StraightlineswereobtainedbyplottingCe/qagainstCe
fortheadsorptionofphenoliccompoundsontoorganocalysasshown
inFigs.4–6.Thevaluesofqmaxandkcalculatedfromtheslopesand
interceptsoftheLangmuirplotsandr-squarearereportedinTable6
ResultsinTable6showthatadsorptionofphenoliccompounds
on Bent-BHDDM, Bent-BSDM and Bent-DMDOD fits well with
Langmuirisothermmodel.Maximumadsorptioncapacityvalues
obtainedfromthismodelindicatethattheorganoclaysarecapable
ofadsorbingphenolsinaqueoussolution.Abilitytoadsorbphenol
redandDB53(substanceswitharomaticrings)ofBent-DMDODis much lower than those of Bent-BHDDM and Bent-BSDM This shows that adsorption capacity strongly depends on affinity betweenorganicsubstancesandammoniumcationsratherthan
on interlayerdistance.AlthoughBent-DMDODpossesseslargest interlayerdistance(39.22A˚)butitsadsorptioncapacityislower thanBent-BHDDM(33.34A˚)andBent-BSDM(37.41A˚).Itcanbe explainedthroughthefactthatforBent-BHDDMandBent-BSDM theammoniumcationscontainingaromaticringswereemployed, these two materials attract phenols more than Bent-DMDOD, which does not contain aromaticrings On theotherhand, for phenoliccompoundswithlessaromaticrings(phenol),adsorption capacitydoesnotdependmuchonnatureoforganicammonium cation
Phenol,phenolredandDB53moleculeshavesmallersizethan interlayerdistancesoforganoclays.Itmeansthatthesemolecules candiffuseintoporesystemoforganoclays.Organoclaysadsorb moleculeswithsmallsizestrongerthanthosewithbulkstructure This can beexplained by the fact that DB 53 and phenol red moleculeshavelargesize,theycouldhinderapartofadsorption centers of organoclays, prevent other molecules to get to adsorptioncenters,resultinginaloweradsorptioncapacity
Fig 3 IR spectrum of Bent-DMDOD.
Trang 53.3 Discussiononadsorptionmechanism
Fromliteratureandexperimentaldata,itcanbesuggestedthat
whenmodifyingbentoniteusingquaternaryammoniumcations,
thesecations arekept between bentonite layers, replacingNa+
cationsinoriginalbentonite.Then,theseorganiccationsexistin
‘‘liquid form’’ [30] and they have affinity toward organic
substances It can be observed that increasing pH leads to a
decreaseinadsorptioncapacityofphenoliccompounds.AthighpH
phenolsexistinionforms,hencetheyaremorepolar.Attractive
forcebetweenquaternaryammoniumcationsandpolarmolecules
is weaker than that between these cations and non-polar
molecules.Thisagainverifiestheideaof‘‘liquidform’’above
4 Conclusions
Thanh Hoa bentonite was successfully modified by three
differentammoniumsalts:benzylhexadecyldimethylammonium
chloride, benzyl stearyl dimethyl ammonium chloride and
dimethyl dioctadecyl ammonium bromide by wet method
Modifiedbentonitespossesshigherorganophilicproperty.Phenol, phenolred, andDB 53 werefoundtobeadsorbedstrongly on organoclayscomprisingalternatingorganicandinorganiclayers Adsorption behavior of thethree adsorbate–adsorbentsystems was described well by Langmuir isotherm model Langmuir maximum adsorption capacities of Bent-BHDDM, Bent-BSDM and Bent-DMDOD on phenol, phenol red and DB 53 are quite high From this study, it can be concluded that the natural bentonitesourceinVietnamwouldbeusedasprecursormaterials
to synthesize potential adsorbents for treating phenolic com-poundsinwastewater
Acknowledgement ThisprojectissupportedbyVietnamNationalFoundationfor Science and Technology Development, project number 104.99 153.09
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Fig 6 Langmuir adsorption isotherm of phenolic compounds on Bent-DMDOD.
Table 6
Langmuir isotherm constants for adsorption of phenolic compounds.
Bent-BHDDM
0.99
0.99
Bent-BSDM
Bent-DMDOD
0.98
0.98