The Poly(acrylonitrule-co-acrylic acid)-graft

14 Pages·2017·3.99 MB·English

polymers
Article
β-Cyclodextrin Modified Poly(Acrylonitrile-co-Acrylic
Acid) Hydrogel for Thorium(IV) Adsorption
GuojianDuan1,QiangqiangZhong2,LeiBi2,LiuYang2,TonghuanLiu2,*,XiaoningShi1
andWangsuoWu2
1 CollegeofPharmacy,GansuUniversityofChineseMedicine,Lanzhou730000,China;
[email protected](G.D.);[email protected](X.S.)
2 RadiochemistryLaboratory,SchoolofNuclearScienceandTechnology,LanzhouUniversity,
Lanzhou730000,China;[email protected](Q.Z.);[email protected](L.B.);[email protected](L.Y.);
[email protected](W.W.)
* Correspondence:[email protected];Tel.:[phone]
AcademicEditor:JodieLutkenhaus
Received:18February2017;Accepted:25May2017;Published:31May2017
Abstract: Inthisreport,theβ-CD(AN-co-AA)hydrogelwasusedtoremovethethorium(IV)[Th(IV)]
from the water system, and the new adsorbent was characterized through Fourier transform
infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD).
Theinfluencesofcontacttime,pHvalue,ionicstrength,solid-liquidratio,initialTh(IV)concentration,
andtemperatureonTh(IV)adsorptionontothefunctionalhydrogelwereresearched. Theresults
showedthattheexperimentaldatafollowedtheLangmuirisothermandthemaximumadsorption
capacity(q )forTh(IV)was692mg/gatpH2.95,whichapproachedthecalculated(q )682mg/g.
max e
ThedesorptioncapacityofTh(IV)indifferentHNO concentrationsrangingfrom0.005to0.5Mwas
3
alsostudied,andthepercentageofthemaximumdesorptionwas86.85%intheconditionof0.09M
HNO . Theselectivityofβ-CD(AN-co-AA)hydrogelwasalsobestudied,theresultsindicatedthat
3
thismaterialretainedthegoodadsorptioncapacitytoTh(IV)evenwhentheCa2+, Mg2+, orPb2+
existedinthesystem. Thefindingsindicatethatβ-CD(AN-co-AA)canbeusedasanewcandidate
fortheenrichmentandseparationofTh(IV),oritsanalogueactinides,fromlarge-volumesolutionin
practicalapplication.
Keywords: β-cyclodextrin;functionalhydrogel;adsorbentmaterial;Th(IV)
1. Introduction
Witheconomicdevelopmenttheproblemofenergyshortagesbecomesmoreandmoreserious
and nuclear power has been used significantly in production and living. Thorium, as a potential
nuclearfuel,hasattractedmuchattention[1]. Theusenuclearpowergeneratesspentnuclearfuel,
which contains various fission products, one of them is thorium. Generally, the direct toxicity of
thoriumislowbecauseofitsstablecharacteratroomtemperature[2],butiftheconcentrationofTh(IV)
ionsinthesolutionislargeenough,itwillarouseacutetoxicologicaleffectsforpeople,whichmay
leadtopotentialoccupationalcarcinogensandprogressiveorirreversiblerenalinjury[3]. Atpresent,
therearealsosomeimportanttetravalentactinides,suchasNp(IV),U(IV),andPu(IV),whichappear
intheuseofnuclearfuelprocesses,butthoseareinstableintetravalentform,sothestablethoriumcan
bestudiedasanmodelelementforothers[4–7].
A series of technologies have been introduced to remove thorium from aqueous solutions,
suchaschemicalprecipitation,ionexchange,evaporation,andadsorption[8]. Amongthesemethods,
adsorptionisoneofthemostwidelyappliedinradiation/nuclearchemistry[2,9,10]. Inrecentyears,
manygroupshavesynthesizednewmaterialstoseparateTh(IV)fromthesolution[11–13].
Polymers2017,9,201;doi:10.3390/polym9060201 www.mdpi.com/journal/polymers
Polymers2017,9,201 2of15
Inordertoexpandthescopeoftheadsorptionmaterials,theadsorptionbehaviorofTh(IV)ions
onto β-Cyclodextrin (β-CD) derivatives is studied. β-CD is a cyclic oligosaccharide connected by
α-(1,4)glycosidebondswhichconsistofsevenglucoseunits. Meanwhile,thesecondaryhydroxyl
groupsandprimaryhydroxylgroupsformtheoutersideandthenarrowside,respectively,which
formstheβ-CDasatruncatedcone. Thisconformationgivestheβ-CDhydrophobicinternalcavity
andhydrophilicexternalsurfaceatthesametime,whichcaneasilyforminclusioncomplexeswith
typesofguestmoleculesthroughnon-covalentinteractionsand, therefore, providesidealbinding
sites[14–18]. Thesenewcomplexeshaveexcellentsolubility,bioactivity,andstabilitybecauseofthe
special structure with the guest molecules, which leads to serious applications in food, cosmetics,
and even in pharmaceutical industries. However, very few studies on the adsorption behavior of
metalionsontothefunctionalizationofβ-CD[19]havebeenconducted. Meanwhile,theadsorption
mechanismisstillunclear.
Theaimofthepresentresearchwastostudytheefficiencyofβ-CD(AN-co-AA)forremoving
thorium from wastewater. Fourier transform infrared spectroscopy (FTIR), scanning electron
microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the structure of
β-CD(AN-co-AA).Theeffectofvariousexperimentalparameters,includingthepHofthesolution,
contacttime,initialthoriumconcentration,andtemperature,aswellasadsorptionkinetics,isotherm
models,andthermodynamics,werestudied. Inaddition,thepropertiesofreusabilityandselectivity
ofβ-CD(AN-co-AA)werealsoinvestigated.
2. MaterialsandMethods
2.1. Materials
All chemicals used in our experiment were purchased as analytically pure and no further
purificationwasconducted.
2.2. SynthesisofPoly(acrylonitrule-co-acrylicacid)-graft-β-cyclodextrinHydrogel(β-CD(AN-co-AA))
ThishydrogelwassynthesizedviatheformationofC-CsinglebondsbetweentheANandAA,
esterbondsbetweenthehydroxylgroups(O-H)inβ-CD,andthecarboxylgroups(COOH)inthe
AA.Briefly,β-CD(0.7495g,0.7mmol)wasaddedtoaceticacid(100mL)andstirredfor10minunder
60◦C.NaHSO (0.1040g,1.0mmol)wasaddedtotheabovesolutionandstirredfor15minunder
3
theprotectionofnitrogen. Then,AN(2.6712g,50.4mmol)andAA(3.6318g,50.4mmol)wereadded
totheabovereactiondropwiseatthesametime. Thesolutionwasstirredfor10min,andK S O
2 2 8
(0.3244g,1.2mmol)wasaddedtothereactionsystemonetime. Thereactionwasstirredfor3.0hat
60◦Cundertheprotectionofnitrogen. Then,thereactionsystemwascooledtoroomtemperatureand
letstandfor0.5h. Pouringthesupernatantout,thewhiteprecipitatewaswashedwithdistilledwater
andethanolthreetimes,respectively. Thenthesolidproductwasdriedinavacuumovenat40◦C
for24h. Inordertoavoidthevariationsincharacteristicsdependentonthepreparation,a10glotof
β-CD(AN-co-AA)hydrogelwaspreparedtoconducttheoverallinvestigations.
2.3. Characterizationof β-CD(AN-co-AA)Hydrogel
2.3.1. FourierTransformInfraredSpectroscopy
IRspectraofβ-CD(AN-co-AA)anditsTh(IV)complexwererecordedonaFTIRspectrometer
(NicoletAvatar360,NicoletInstrumentCorportion,Connecticut,USA).Thepowderofthesamplewas
mixedwithpotassiumbromide(KBr)andcompressedintoatransparentKBrtablet. Thespectrawere
shownatwavenumbersfrom4000to400cm−1. TheresultsoftheFTIRanalysis(Figure1)showed
themajoradsorptionbondsatthefollowingfrequencies. Abroadandintensepeakat3469cm−1is
attributedtoO–Hvibrations[20];the–C≡Nstretchingvibrationspeaksareappearedat2244cm−1;
Polymers2017,9,201 3of15
Thepeaksat1732and1453cm−1 areassignedtotheC=OandC–O–Cstretchingbondsoftheester
group[21,22].
PolymeIrns 2t0h17e, 9s,p 2e01c t rum of Th(IV) complex, the intense peak of 1732 cm−1 decreased, but the3p oef a1k4
of 1455 cm−1 showed no obvious change, which means a part of the acrylic acid groups were
In the spectrum of Th(IV) complex, the intense peak of 1732 cm−1 decreased, but the peak of
involved in the combination. At the same time, the bond of O–H vibrations was changed from
Polymers 2017, 9, 201 3 of 14
13445659 ccmm−−1 1ditdo 3n4o3t 6chcman−g1e, owbhviicohusmlye,a wnshtichha tmtheeanTsh a(I pVa)rct hoefl tahteed acwryitlhict ahceidO gHrogurpous pwseirne βin-CvoDlvoefdt hine
the combination, while H–O–H bending vibrations of lattice water molecules in the complexes were
copolymeIrn [t2h3e] .spTehcteruHm– Oof– THh(bIVe)n dcoimngplvexib, rtahtei oinntsenosfe lpatetaikc eowf 1a7t3e2r cmmo−1l edceuclreesasiend,t hbeutc tohme ppleeaxke osf were
eexxpprree1ss4ss5ee5dd c aamtt −111 66d33id55 nccmomt −−c1h.1 a.nge obviously, which means a part of the acrylic acid groups were involved in
the combination, while H–O–H bending vibrations of lattice water molecules in the complexes were
expressed at 1635 cm−1.

Figure1.FTIRspectraofβ-CD(AN-co-AA)(a)andβ-CD(AN-co-AA)-Th4+(b).
Figure 1. FTIR spectra of β-CD(AN-co-AA) (a) and β-CD(AN-co-AA)-Th4+ (b).
Figure 1. FTIR spectra of β-CD(AN-co-AA) (a) and β-CD(AN-co-AA)-Th4+ (b).
2.3.2. ScanningElectronMicroscopyMeasurements
2.3.2. 2S.3ca.2n. nScinangn Einlegc Etrleocntr Moni cMroicsrcooscpoyp yM Meaesausureremmeennttss
TToo lleeTaarornn l ettahhreen mmthooer rmpphohoropllohogogylyoo gofyf t ohthfe tehh hey ydhdyrodrogrogegleelc loc cmoommpoppsooisstieitteep paparatrritcitcileclelsse,,s SS,E ESMMEM mm emeaasesuaursreuemmreeenmntset snwwtesr ewer eceacrrear riceradier drieodn
othne tghooeln d g-tsohpledu g-tstoeplrdue-tdstpesurpettedec riesmdp eesncpsiemwcieminthesn asw JSwitMhit h-6a 7 a0J SJ1SMFMi-n-66s77t00r1u1FFm ieinnnsstttr(ruJuemmoel,neTnt ot( kJe(yJoeolo,, lJT,a opTkaoynok),y. oJBa,ep fJaoanrp)e.a tnBh)ee.f oeBrxeep fetohrreiem tehnet ,
thesaemxppelreimweanst,p trheep saarmedplbe ywdarsi pprpeipnagreads bmya dllriapmpionugn at somfathlle apmaorutinctl eofs uthsep epnarstiiocnle osnustopeancsioovne orngtloa sas and
experiment, the sample was prepared by dripping a small amount of the particle suspension onto a
allowcionvgeri tgtloasasi ar-nddr ayl.lowing it to air-dry.
cover glass and allowing it to air-dry.
FigurFeig2usrheo w2 ssShEoMwsi mSaEgMes oifmtahgeeβs -CoDf (AthNe -cβo--CADA(A)hNy-dcor-oAgAel). Thhyedmroogrepl.h oTlhoeg ymofoβrp-hCoDlo(gAyN -ocfo -AA)
Figure 2 shows SEM images of the β-CD(AN-co-AA) hydrogel. The morphology of
β-CD(AN-co-AA) resembled a cloud sheet, and the size of the gel sheet is 2 μm in length and 1 μm in
hasalooseflocculentstructure. SEMresultsindicatedthatthehydrogels’structureprovidedalarger
β-CD(AN-co-AA) resembled a cloud sheet, and the size of the gel sheet is 2 μm in length and 1 μm in
width, mostly. SEM results indicated that the hydrogels’ structure provided a larger specific surface
specificsurfacearea,whichisbetterforitscombiningwithmetalionsbyprovidingwiderexposed
width, mostly. SEM results indicated that the hydrogels’ structure provided a larger specific surface
area, which is better for its combining with metal ions by providing wider exposed sites for
sitesforadsorption,andtheadsorptionexperimentsalsostronglydemonstratedtheseresults.
area, awdshoircpht ioins , banedtt ethr e faodrs oirtsp ticoonm exbpinerinimge nwtsi tahls om setrtoanl giloyn dse mboyn sptrraotveidd tihnegs ew reisdueltrs . exposed sites for
adsorption, and the adsorption experiments also strongly demonstrated these results.
(a) (b)
Figure 2. SEM of β-CD(AN-co-AA) hydrogel particles in different resolution size 10 μm (a) and 1
Figure2.SEMofβ-CD(AN-co-AA)hydrogelparticlesindifferentresolutionsize10µm(a)and1µm(b).
μm (b). (a) (b)
F igure 2. SEM of β-CD(AN-co-AA ) hydrogel particles in different resolution size 10 μm (a) and 1
μm (b).
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Polymers2017,9,201 4of15
2.3.3. X-ray Diffraction Measurements
2.3.3.PXow-radyerD iXff-rraacyt iodniffMraecatsiounre mise nat smethod that can provide insightful information about the
combination mode between the β-CD, AN, and AA. The XRD pattern of β-CD(AN-co-AA) was
Powder X-ray diffraction is a method that can provide insightful information about the
obtained using a powder X-ray diffractometer (Rigaku, The Woodlands, TX, USA) with copper Kα
combination mode between the β-CD, AN, and AA. The XRD pattern of β-CD(AN-co-AA) was
radiation at 150 mA and 40 kV, and the diffraction intensity data were scanned with a step size of
obtainedusingapowderX-raydiffractometer(Rigaku,Texas,USA)withcopperKαradiationat150
0.02° in the 2θ range from 5° to 50°. Figure 3 shows the XRD patterns of β-CD and β-CD(AN-co-AA).
mAand40kV,andthediffractionintensitydatawerescannedwithastepsizeof0.02◦ inthe2θrange
The XRD pattern of β-CD(AN-co-AA) showed a broad peak, which was consistent with its
from5◦ to50◦. Figure3showstheXRDpatternsofβ-CDandβ-CD(AN-co-AA).TheXRDpatternof
amorphous feature [23] and, at the same time, a number of intense and sharp peaks shown in the
β-CD(AN-co-AA)showedabroadpeak,whichwasconsistentwithitsamorphousfeature[24]and,at
XRD pattern of β-CD [24] proved the crystalline characteristic of β-CD. This further indicates that
thesametime,anumberofintenseandsharppeaksshownintheXRDpatternofβ-CD[25]proved
these three materials, combined by chemical bonds, have formed a hydrogel, and β-CD has lost its
thecrystallinecharacteristicofβ-CD.Thisfurtherindicatesthattheproductofcopolymerisnota
crystalline characteristic.
simplyphysicalmixture.

FFiigguurree 33.. XXRRDD ppaatttteerrnn ooff ββ--CCDD ((aa)) aanndd ββ--CCDD((AANN--ccoo--AAAA)) ((bb))..
22..44.. AAddssoorrppttiioonn EExxppeerriimmeennttss
TThhee TThh((IIVV)) aaqquueeoouuss ssoolluuttiioonn ooff kknnoowwnn ccoonncceennttrraattiioonn wwaass aaddddeedd ttoo 1100 mmLL ppoollyyeetthhyylleennee ttuubbeess,,
wwiitthh aa cceerrttaaininq quuanantittiytyo foafd asdosrobrebnet,nfit,n failnlyaltlhye tmheix medixseodlu stioolnutwioans 5w.0asm 5L.0i nmbLat cinh ebxaptcehri mexepnetsri.mHeNnOts3.
H(0N.1OM3 )(o0.r1N MaO) oHr (N0.a1OMH) w(0a.1s uMse) dwtaosa udsjuedst ttoh eaidnjiutisat ltphHe ionfittihael spoHlu otifo nth.eT hsoelsuytisotenm. Twhaes scyesntetrmif uwgeads
caetnhtrigifhugsepde eadt h(1ig.2h ×sp1e0e4d r(/1m.2 in× )1f0o4 rr/2m0imn)i nfoar ft2e0r mviibnr aatfitnerg vaitbrroatoimng taetm rpoeormat uterme pfoerratthuerer efqour itrhede
rteimquei.reCdo tnimceen. tAra ctieorntaionf vTohlu(ImV)e wofa ssuapnearnlyazteadnt wwiaths dtheteecAterdse tnoa dzoe-teIIrImsipneec tthroe pThh(oItVo)m ceotnriccenmtreatthioond
boyn uasisnpge cat rsoppehctortoopmheotteorm(ePteerrk (iPne-Erklmine-Er,lmWearl,t hWaamlt,hMamA,, MUASA, U).SAA)q auta an twityavoefle1ngmthL oTfh 6(6IV2 )nsmolu, atinodn
tshaem apdlseo,r1ptmioLn 0c.a5pMaciHtyC olfa tnhde β1.-0CmD(LA0N.1-c%o-AAArs)e nhayzdor-oIgIIela qofu eTohu(IsVs)o wluatsio cnalwcuelraeteadd dbeyd thtoe cah2a5ngmeLs
bgelatwsseflena stkh,er iensiptieaclt aivnedly f,inaanld etqhueilfiibnraiulmso lcuotniocnenvtroalutimones.w asfilledupto25mLbyaddingdeionized
water. After15min,theabsorbanceofthemixtureliquidwasmeasuredat662nm,andtheadsorption
2c.a5p. aDceitsyoropftitohne Eβx-pCeDri(mAeNnt- co-AA)hydrogelofTh(IV)wascalculatedbythechangesbetweentheinitial
andfinalequilibriumconcentrations.
In order to examine the adsorption and desorption behaviors of thorium ions from
β-CD(AN-co-AA) hydrogel, to ensure the reusability of adsorbents, at the end of adsorption
2.5. DesorptionExperiment
experiments the suspension was centrifuged and all of the supernatant was poured out and then
In order to examine the adsorption and desorption behaviors of thorium ions from
washed with distilled water. An equal volume of acid solution was added, and the suspension was
β-CD(AN-co-AA) hydrogel, to ensure the reusability of adsorbents, at the end of adsorption
shaken for 4 h. The amount of Th(IV) ions released into the solution was monitored using the same
experiments the suspension was centrifuged and all of the supernatant was poured out and then
spectrophotometric method as in the adsorption experiments. The Th(IV) ions’ recovery percentage
washedwithdistilledwater. Anequalvolumeofacidsolutionwasadded,andthesuspensionwas
upon desorption from the hydrogel was calculated using the initially adsorbed Th(IV) ion amount
shakenfor4h. TheamountofTh(IV)ionsreleasedintothesolutionwasmonitoredusingthesame
and the amount found in the solution at the end of the desorption process, according to Equation. (1):
spectrophotometricmethodasintheadsorptionexperiments. TheTh(IV)ions’recoverypercentage
Polymers2017,9,201 5of15
Polymers 2017, 9, 201 5 of 14
upondesorptionfromthehydrogelwascalculatedusingtheinitiallyadsorbedTh(IV)ionamountand
q −q
theamountfoundinthesolutionatthReeceonvderoefdt h(%ed)=es oreptiond ×p1ro00ce ss,accordingtoEquation(1):
(1)
q
e
q −q
Recovered(%) = e d ×100 (1)
where qe is the number of adsorbed Th(IV) ion (g/g) aqned qd is the amount of desorbed Th(IV) ion
(g/g). The adsorption/desorption cycles were repeated ten times using the same batch of the
whereq isthenumberofadsorbedTh(IV)ion(g/g)andq istheamountofdesorbedTh(IV)ion
hydrogeel (10 mg). d
(g/g). Theadsorption/desorptioncycleswererepeatedtentimesusingthesamebatchofthehydrogel
(31. 0Rmesgu)l.ts and Discussion
3. ResultsandDiscussion
3.1. Adsorption Performance Study
3.1. AdsorptionPerformanceStudy
3.1.1. Adsorption Kinetics
3.1.1.EAqudisloibrprattioionnK tiimneet iicss a key factor which has a direct relationship with the adsorption kinetics of
adsorbent at the set initial adsorbate concentration. Figure 4 shows the impact of the contact time on
Equilibrationtimeisakeyfactorwhichhasadirectrelationshipwiththeadsorptionkineticsof
Th(IV) adsorption onto β-CD(AN-co-AA), from the results of the experiment we can determine that
adsorbentatthesetinitialadsorbateconcentration. Figure4showstheimpactofthecontacttimeon
Tthhe( IsVp)eeadd soofr Tphti(oInV)o andtosoβr-pCtiDo(nA oNn-tcoo β-A-CAD),(AfroNm-coth-AeAre)s iusl vtseoryf tfhaeste ixnp tehreim ineintitawl setacgaen (daebtoeurmt 3i0n emtihna)t.
Tthhee sipneiteidal osfteTehp( IaVd)soardpstoiropnt iboencoomnteos βsl-oCwD,( sAuNbs-ecoq-uAeAnt)lyis, vatetrryibfuatsetdin tot htheei nTihti4a+l isotnasg (ew(aitbho au tra3d0imusi no)f.
Tabhoeuitn 0it.i1a0l2s tnemep),a ndesaorrlpyt aionn ebqeuciolimbreiusmslo swta,tseu bbestewqueeenn ttlhye, astotrluibtuiotned antod tthhee Tahd4s+oirobninsg( wmiathteariraal.d Tiuhsesoef
speed differences of Th(IV) adsorption onto β-CD(AN-co-AA) and desorption from the material are
about0.102nm),nearlyanequilibriumstatebetweenthesolutionandtheadsorbingmaterial. These
ssmpeaeldlerd ifafnedre nscmesalolefrT ha(sI Vth)ea dtsimorep tiionncroeansteosβ. -TChDis( ApNh-ecnoo-AmAen)oann dwdiells ohrpeltpio nusf rotom uthnedmerasttaenrida ltahree
adsorption modality (chemical adsorption or physical adsorption) [25,26]. In order to ensure the
smallerandsmallerasthetimeincreases. Thisphenomenonwillhelpustounderstandtheadsorption
adsorption equilibria were reached, the stir time was set for 4.0 h for all remaining batch
modality (chemical adsorption or physical adsorption) [26,27]. In order to ensure the adsorption
experiments.
equilibriawerereached,thestirtimewassetfor4.0hforallremainingbatchexperiments.

Figure 4F.igureE 4ff. eEcftfecot fof eeqquuiilliibbrriiuumm timtime eon Tonh(IVT)h a(dIVso)rpatdiosno ropnttioo nβ-CoDn(tAoN-βc-oC-ADA(A). N-co-AA).
([Th(VI)] =6.5334×10−4M,pH=2.95±0.05,T=298.15±1.00K,I=0.50MNaNO ).
0 3
In order to describe the kinetic mechanism clearly, which was controlled by the process of
Th(IVIn) oarddseorrptotiodnes cornibtoe tβh-eCkDin(AetNic-cmo-eAchAa)n, isthme cplesaerulyd,ow-sheiccohnwd-aosrcdoenr trmololeddelbs ywthaes pursoecde stsoo tfeTsht (tIhVe)
eaxdpsoerrpimtioenntoanl dtoatβa-.C TDh(iAs mN-ocdo-eAl iAs )g,itvheenp asse:u do-second-ordermodelswasusedtotesttheexperimental
data. Thismodelisgivenas:
t 1 t
qttq=t =k1qk2eqe2++qtqee, , (2()2 )
wwhheerree qqtt ((gg//gg)) iiss tthhee aammoouunntt ooff TThh((IIVV)) aaddssoorrbbeedd oonn ββ--CCDD((AANN--ccoo--AAAA)) aatt ttiimmee tt,, aanndd qqee ((gg//gg)) iiss tthhee
eeqquuiilliibbrriiuumm aaddssoorrpptitoionnc acpaapcaictyit,yk, (gk /((gg/·(mg∙imn)i)nr)e) prreepserenstesnthtse stheceo nsedc-oonrdde-orrrdateer croantset acnotnosftathnet koifn ethtiec
kminoedteilc. mFiogduerel. 5Fisghuorwe s5t hsheorwessu tlhtseo rfeususilntsg otfh eusEinqug atthioen E(q2u)atotiofint t(h2e) teox pfiet rtihmee enxtpaledriamtae.nTtahle deaqtua.a tTiohne
equation of pseudo-second-order is y = 1.4788x + 29.844; as is known from the calculation, according
to the slope and intercept, k is 0.0660 g/(g∙min); the qe equal to 0.6820 g/g and the linear correlation
Polymers2017,9,201 6of15
ofpseudo-second-orderisy=1.4788x+29.844;asisknownfromthecalculation,accordingtotheslope
Polymers 2017, 9, 201 6 of 14
andintercept,kis0.0660g/(g·min);theq equalto0.6820g/gandthelinearcorrelationcoefficient
e
cRo2e=ffi0c.i9e8n8t 3R.2T =h e0s.9e8r8e3s.u Tlthsessheo rwestuhlatst tshheowps ethuadto t-hsee cposnedu-doord-seercorantde-oeqrdueart iroantei seaqusuatiitoanb lies ma estuhiotadbtloe
mdeestchroibde ttoh deeksicnreibtiec tahdes okrinpetitoicn a.dsorption.

Figure5.Testofpseudo-second-orderadsorptionkineticsplotforTh(IV).([Th(VI)] =6.5334×10−4M,
0
Figure 5. Test of pseudo-second-order adsorption kinetics plot for Th(IV).
pH=2.95±0.05,T=298.15±1.00K,I=0.50MNaNO ).
3
3.1.2. Effect of pH on Th(IV) Adsorption onto β-CD(AN-co-AA)
3.1.2. EffectofpHonTh(IV)Adsorptionontoβ-CD(AN-co-AA)
The pH value of the adsorption system is an important parameter which is a direct impact on
ThepHvalueoftheadsorptionsystemisanimportantparameterwhichisadirectimpactonthe
the uptake of metal ions from aqueous solution. At the same time, it affects the adsorbent surface
uptakeofmetalionsfromaqueoussolution. Atthesametime,itaffectstheadsorbentsurfacecharge,
charge, the ionization degree and the adsorbate speciation [27,28]. From Figure 6, the pH value of the
theionizationdegreeandtheadsorbatespeciation[28,29]. FromFigure6,thepHvalueoftheaqueous
aqueous solution directly affects the adsorption results of Th(IV) onto β-CD(AN-co-AA). The
solution directly affects the adsorption results of Th(IV) onto β-CD(AN-co-AA). The adsorption
adsorption progress of Th(IV) onto β-CD(AN-co-AA) can be divided into two stages. The first is the
progressofTh(IV)ontoβ-CD(AN-co-AA)canbedividedintotwostages. Thefirstistheadsorption
adsorption percentage (from ~25% to ~95%) of Th(IV) onto β-CD(AN-co-AA), increasing with the
percentage(from~25%to~95%)ofTh(IV)ontoβ-CD(AN-co-AA),increasingwiththechangingof
changing of pH value (from 1.8 to 4.0) of adsorption system. The second is the adsorption percentage
pHvalue(from1.8to4.0)ofadsorptionsystem. Thesecondistheadsorptionpercentageinastable
in a stable range (from ~90 to ~95%) with the changing of pH value (from 4.0 to 5.6) of adsorption
range (from ~90 to ~95%) with the changing of pH value (from 4.0 to 5.6) of adsorption system.
system. The changed trend of stage one may be attributed to the surface properties of
Thechangedtrendofstageonemaybeattributedtothesurfacepropertiesofβ-CD(AN-co-AA),such
β-CD(AN-co-AA), such as the surface charge and the ionization of surface functional groups of
asthesurfacechargeandtheionizationofsurfacefunctionalgroupsofβ-CD(AN-co-AA).Thebest
β-CD(AN-co-AA). The best result of adsorption in the pH range of 3–4 may be due to the formation
result of adsorption in the pH range of 3–4 may be due to the formation of the Th(IV) complexes
of the Th(IV) complexes with carboxyl groups of the acrylic acid unit and hydroxyl groups of the
withcarboxylgroupsoftheacrylicacidunitandhydroxylgroupsoftheβ-CDunitonthesurface
β-CD unit on the surface of β-CD(AN-co-AA). It is well known that, increasing with the pH, the
ofβ-CD(AN-co-AA).Itiswellknownthat,increasingwiththepH,themorecarboxylicgroupstend
more carboxylic groups tend to deprotonate, and the more carboxylate ions form stable complexes
todeprotonate,andthemorecarboxylateionsformstablecomplexeswithTh(IV)ions. Atthesame
with Th(IV) ions. At the same time, this operation of decreasing the positive charge density of the
time,thisoperationofdecreasingthepositivechargedensityoftheadsorptionedgesincreasesthe
adsorption edges increases the adsorption capacity of this kind of hydrogel through electrostatic
adsorptioncapacityofthiskindofhydrogelthroughelectrostaticattraction[30]. Therearecertainform
attraction [29]. There are certain form features of the Th(IV) complex in a specific solution pH which
featuresoftheTh(IV)complexinaspecificsolutionpHwhichmaybeimportantfactorsthataffectthe
may be important factors that affect the uptake efficiency of β-CD(AN-co-AA) for Th(IV) adsorption
uptakeefficiencyofβ-CD(AN-co-AA)forTh(IV)adsorption[31].Accordingtothehydrolysisconstants
[30]. According to the hydrolysis constants of Th(IV) in aqueous solution, in the range of 2.0 to 4.0 of
ofTh(IV)inaqueoussolution,intherangeof2.0to4.0ofthepHvalue,Th4+and[Th(OH)]3+arethe
the pH value, Th4+ and [Th(OH)]3+ are the main species [7,31]. If the value of the solution pH is over
mainspecies[7,32]. IfthevalueofthesolutionpHisover4.0,Th(OH) isgraduallybecomingthemain
4
4sp.0e, cTiehs(.OTHh)e4r eisfo grera,dthuealglyo obdecreosmuilntgo ftTheh (mIVa)ino nstpoeβci-eCsD. T(AhNer-ecfoo-rAe,A t)hme agyoobde artetsruibltu toefd Ttho(tIhVe) soonltido
β-CD(AN-co-AA) may be attributed to the solid Th(OH)4 on the surface of the hydrogel. We take into
Th(OH) onthesurfaceofthehydrogel. Wetakeintoaccountbothofthefactorsofadsorptionpercent
4
account both of the factors of adsorption percent and Th(IV) species present at different pH values
andTh(IV)speciespresentatdifferentpHvaluesand,inthefollowingexperiments,pH=2.95±0.05
and, in the following experiments, pH = 2.95 ± 0.05 was selected as the value of the experiment
wasselectedasthevalueoftheexperimentsystems.
systems.
3.1.3. Effect of Ionic Strength
Figure 7 shows the relationship between ionic strength and the adsorption ability of Th(IV) onto
β-CD(AN-co-AA) hydrogel. From the results we can find that the adsorption results of Th(IV) onto
β-CD(AN-co-AA) do not change significantly when the ionic strength increases from 0.00 to 0.60
mol/L NaNO3 at a pH value in the range of 2.95 ± 0.05, which indicates that, under this experimental
Polymers2017,9,201 7of15
3.1.3. EffectofIonicStrength
Figure 7 shows the relationship between ionic strength and the adsorption ability of Th(IV)
ontoβ-CD(AN-co-AA)hydrogel. FromtheresultswecanfindthattheadsorptionresultsofTh(IV)
onto β-CD(AN-co-AA) do not change significantly when the ionic strength increases from 0.00 to
Polymers 2017, 9, 201 7 of 14
0.60 mol/L NaNO at a pH value in the range of 2.95 ± 0.05, which indicates that, under this
3
Polymers 2017, 9, 201 7 of 14
ecxopnedriitmioenn, ttahlec oinndnietrio-snp,htehree insnuerfra-scpe hceormespulerfxaecse bcoetmwpeleenx eTshb(eIVtw) eaenndT hβ(-ICVD)(aAnNd-βco-C-ADA(A) Nha-cso -bAeAen)
hfcooarsnmdbeietdeion n[f3,o 2rt,mh3e3e ]d.i n[Tn3he3er,3-rs4ep]in.h,Te hrieoe nrse uienrx,faciohcena necgxoecm hhpaanlesgx eensho a bscenotwnotecreoibnnu trtTiiobhnu(I tVitoo)n attnhodet hβaed-aCsdoDsr(opArtpiNotni-oc ono-Aof fATT)hh (h(IIVaVs)) obonenettono
βfβo--CrCmDDe((dAA NN[3--c2coo,-3-AA3]AA. )).T. ChCoeormmebinbin,i neiedodnw wietihxthcth htaehnepg rpee rvehivoaiusos uncsoo cn otcenontnetstnr,titsbh,u etthaioedn sa odrtsopo tritophntei odnaedp dseeonprdpesntiodonns t ohonef pthTHeh v(pIaVHlu) evoaanlnutdoe
iaβsn-iCdnD dise( ApineNdn-edcpeoe-nAntdAoef)n.t htC eoofim othnbeiic niosetdnri ecwn sgitttrhhe .nthgeth p. r evious contents, the adsorption depends on the pH value
and is independent of the ionic strength.

FiFgiugruere6 .6.E Efffefectcto offt htheep pHHv vaalluuee ooff tthhee ssoolluuttiioonn oonn tthhee aaddssoorrppttiioonn ooff TThh((IIVV)) oonnttoo ββ-C-CDD(A(ANN-c-oc-oA-AAA).) .
([TFihg(uVrIe)] 6.= E6ff.e5c3t3 o4f× th1e0 p−H4 Mva,lmue/ Vof =th0e. 1s8olgu/tiLo,nT o=n 2t9h8e. 1a5ds±or1p.0ti0oKn ,oIf =Th0.(5IV0)M onNtoaN β-OCD).(AN-co-AA).
0 3

Figure 7. Effect of the ionic strength of the solution on the adsorption of Th(IV) onto
FFβii-ggCuuDrre(eA 7N.7E.- cffoEe-fcAfteAocft) .t hoef iotnhiec sitorennicg thstorefnthgeths olouft iotnheo nstohleutaidonso ropnti onthoef Tahd(sIoVr)potniotno βo-Cf DT(Ah(NIV-c)o -AonAto).
(β[T-ChD(V(AI)]N]0-c=o-6A.5A33).4 ×10−4M,m/V=0.18g/L,pH=2.95±0.05,T=298.15±1.00K).
3.1.4. Effect of Solid-Liquid Ratio
33..11..44..T EEhffeffee crctet looafft iSSooonllsiiddh-i-LpLi iqqbuueitiddw ReReaanttii ooa dsorbent content and adsorption percentage of Th(IV) from the
aqueTTohuhese rseroelalluatittoiioonnnsh sohipniptbo e bβtwe-tCeweDen(eAandN sao-dcrosb-oeArnbAtec)n oitns ctseohnnottwaennndt iaandn Fsdio graupdrtseioo 8nr.p pFteirorocnme np tteahrgece eronefstauTglhtes( I Viotf ) ifsTr okhmn(IoVtwh) enfa rtoqhmuaet ottuhhsee
saaodqlusuoetiroopuntsioo snno tloruatβtiio-oCn o Dof( nATtohN (βI-Vc-oC)- ADonA(At)oNi sβ-sc-Coh-oDAw(AAn)N iins- cFsohi-gAouwAren) 8iis.n F kFreoipgmut rateht e8a. r reFesrluoalmttisv teihtlyeis rsketnasbuolwlets nv iatth liuas etk tnwhoeiwtahdn ts htohera pstto itolhinde
caodnsoternptt iionnc rreaatsioin ogf inT hth(IeV r) aonngteo oβf- C0.D00(A8~N0.-2c og-/ALA. T) hise nk etphte aatd as orreplatitoivne rlya tsiota dbelec rveaalsuees wwiitthh tthhee ssoolliidd
ccoonntteenntt iinnccrreeaassiinngg iwn hthene rtahneg seo olifd 0 c.0o0n8t~e0n.t2 egx/cLe. eTdhse 0n. 2t hge/ La.d Hsoorwpteiovne rr, atthioe dcoecnrceeanstersa twiointh o tfh eT hso(IlVid)
acodnsoternbte din ocnretaos βin-Cg Dw(hAeNn- ctoh-eA sAo)l igdi vceosn tthene tr eesxuceltesd tsh a0t. 2f igrs/tLly. Hinocwreeavseer, ,a tnhde tchoennc ebnectroamtioe ns toabf lTe hw(IiVth)
tahdes oinrbcreeda soinntgo hβy-CdrDo(gAelN c-ocno-tAenAt )( tghiev etsu rtnhien rge spuolitns tt ihsa at tf i0r.s2t lgy/ Lin, carse awseel,l )a.n Tdh tehseen r ebseuclotsm cea nst abbe lde uwei ttho
tthweo i rnecarseoansisn [g3 4h]y. dFirrosgt,e tlh ceo Tnhte(nIVt )( tchaen t buer neiansgil yp ocionmt bisi naet d0 .w2 igth/L t,h aes switeesll )o.f T thhee shey rdersougltesl caannd ,b teh duus,e w toe
towbtoa irne aas ohnigsh [ 3a4b]s. oFriprstti,o tnh era Tteh.( TIVh)i sc aisn b beec aeuassiel yth ceo amdbsionrepdti wonit ohf t thhee s piteers uonf itth me hasysd orof gβe-Cl aDn(dA, Nth-ucos-,A wAe )
iosb ktaeipnt aa ht iag hh iagbhs olrepvteilo nw rhaetne . tThhei ss oisli bde ccoaunsteen tth eis a rdesloatripvteiolyn loofw th, er apnegri nugn ift rmomas s0 .o0f0 β8-–C0.D2 (gA/NL -icno -tAhAis )
eisx pkeerpitm aetn ata hl icgohn dleivtieoln w, ahnedn athlle o sfo tlhide caodnstoernptt iiosn r esliatetisv aerlye sloawtu,r aratendg iwngh efnro tmhe 0 s.0o0li8d–-0li.2q ugi/dL riant itoh iiss
e xperimental condition, and all of the adsorption sites are saturated when the solid-liquid ratio is
Polymers2017,9,201 8of15
ratio of Th(IV) onto β-CD(AN-co-AA) is kept at a relatively stable value with the solid content
increasingintherangeof0.008~0.2g/L.Thentheadsorptionratiodecreaseswiththesolidcontent
increasingwhenthesolidcontentexceeds0.2g/L.However,theconcentrationofTh(IV)adsorbed
ontoβ-CD(AN-co-AA)givestheresultsthatfirstlyincrease,andthenbecomestablewiththeincreasing
hydrogelcontent(theturningpointisat0.2g/L,aswell). Theseresultscanbeduetotworeasons[35].
First,theTh(IV)canbeeasilycombinedwiththesitesofthehydrogeland,thus,weobtainahigh
absorptionrate. Thisisbecausetheadsorptionoftheperunitmassofβ-CD(AN-co-AA)iskeptat
aPohlyimghersl e20v1e7l, w9, 2h0e1n thesolidcontentisrelativelylow,rangingfrom0.008–0.2g/Linthisexperime8 noft a1l4
condition,andalloftheadsorptionsitesaresaturatedwhenthesolid-liquidratioisbelow0.2g/L,
sboeltohweq 0.i2s gsi/mL,i lsaor wthieth qee aicsh soimthielarra nwditthh eeaacdhs oortphteior nanpder cthenet aagdesohrapstsioignn pifiecracnentltyaignec rheaass esdig.nSiefcicoanndtllyy,
e
increased. Secondly, the adsorption percentage can approach the maximum with enough adsorbent.
the adsorption percentage can approach the maximum with enough adsorbent. However, in this
However, in this aspect the content of Th(IV) is fixed, and when the β-CD(AN-co-AA) is over 0.2 g/L,
aspectthecontentofTh(IV)isfixed,andwhentheβ-CD(AN-co-AA)isover0.2g/L,therewillnot
btheeerne owuigllh nmote btae leinoonusgtho mcoemtabl iinonesw toit hcotmhebiandes woribthe ntht,e saodwsoerbceannt,fi snod wteh ceaqn fiisndd ethcree qaes iesd dwecirtehatsheed
e
with the increasing amount of β-CD(AN-co-AA), while the percent of absorption is at its maximum.
increasingamountofβ-CD(AN-co-AA),whilethepercentofabsorptionisatitsmaximum.

Figure8. EffectofsolidcontentontheadsorptionofTh(IV)ontoβ-CD(AN-co-AA),squarepoint
Figure 8. Effect of solid content on the adsorption of Th(IV) onto β-CD(AN-co-AA), square point
showthevalueofqe(g/g)anddotshowthevalueof“adsorption%”([Th(VI)]0=6.5334×10−4M,
psHho=w2 t.h9e5 v±al0u.0e5 o,fT q=e (2g9/g8.)1 a5n±d d1.o0t0 sKho,Iw= th0.e5 0vaMluNe oaNf “Oad)s.orption %”.
3
3.1.5. Effect of Initial Th(IV) Concentration
3.1.5. EffectofInitialTh(IV)Concentration
The initial concentration of Th(IV) directly affects the adsorption process and efficiency. To
TheinitialconcentrationofTh(IV)directlyaffectstheadsorptionprocessandefficiency. Tostudy
study the relationship between the adsorption and the metal ions concentration in the aqueous
therelationshipbetweentheadsorptionandthemetalionsconcentrationintheaqueousphasewillhelp
phase will help us to understand the adsorption behavior. Therefore, the initial concentration of
ustounderstandtheadsorptionbehavior. Therefore,theinitialconcentrationofTh(IV)variedwithin
Th(IV) varied within the range of 3.92 × 10−4~1.26 × 10−3 mol/L, with the other parameters being kept
therangeof3.92×10−4~1.26×10−3mol/L,withtheotherparametersbeingkeptconstant. Figure9
constant. Figure 9 shows the trend of adsorption capacity (g/g) with the increase of the initial metal
shows the trend of adsorption capacity (g/g) with the increase of the initial metal concentration.
concentration. The changing curve indicates that, in the range of 3.92 × 10−4 to 7.19 × 10−4 mol/L of the
Thechangingcurveindicatesthat, intherangeof3.92 × 10−4 to7.19 × 10−4 mol/LoftheTh(IV)
Th(IV) concentration, the adsorption amount increases with the metal concentration. Combined with
concentration, theadsorptionamountincreaseswiththemetalconcentration. Combinedwiththe
the above results of Section 3.1.4, the larger part of the active sites was used in the adsorption process
aboveresultsofSection3.1.4,thelargerpartoftheactivesiteswasusedintheadsorptionprocesswhen
when more Th(IV) ions were contained in the reaction system. However, if the Th(IV) concentration
moreTh(IV)ionswerecontainedinthereactionsystem.However,iftheTh(IV)concentrationexceeded
exceeded 7.19 × 10−4 mol/L, adsorption capacity will saturate the available binding sites on the
7.19 × 10−4 mol/L, adsorption capacity will saturate the available binding sites on the adsorbent.
adsorbent. Under the present experimental conditions, the maximum adsorption reached was 0.692
Underthepresentexperimentalconditions,themaximumadsorptionreachedwas0.692g/g.
g/g.

Figure 9. Effect of the initial concentration of Th4+ on the adsorption behavior onto β-CD(AN-co-AA).
Polymers 2017, 9, 201 8 of 14
below 0.2 g/L, so the qe is similar with each other and the adsorption percentage has significantly
increased. Secondly, the adsorption percentage can approach the maximum with enough adsorbent.
However, in this aspect the content of Th(IV) is fixed, and when the β-CD(AN-co-AA) is over 0.2 g/L,
there will not be enough metal ions to combine with the adsorbent, so we can find the qe is decreased
with the increasing amount of β-CD(AN-co-AA), while the percent of absorption is at its maximum.

Figure 8. Effect of solid content on the adsorption of Th(IV) onto β-CD(AN-co-AA), square point
show the value of qe (g/g) and dot show the value of “adsorption %”.
3.1.5. Effect of Initial Th(IV) Concentration
The initial concentration of Th(IV) directly affects the adsorption process and efficiency. To
study the relationship between the adsorption and the metal ions concentration in the aqueous
phase will help us to understand the adsorption behavior. Therefore, the initial concentration of
Th(IV) varied within the range of 3.92 × 10−4~1.26 × 10−3 mol/L, with the other parameters being kept
constant. Figure 9 shows the trend of adsorption capacity (g/g) with the increase of the initial metal
concentration. The changing curve indicates that, in the range of 3.92 × 10−4 to 7.19 × 10−4 mol/L of the
Th(IV) concentration, the adsorption amount increases with the metal concentration. Combined with
the above results of Section 3.1.4, the larger part of the active sites was used in the adsorption process
when more Th(IV) ions were contained in the reaction system. However, if the Th(IV) concentration
exceeded 7.19 × 10−4 mol/L, adsorption capacity will saturate the available binding sites on the
adsorbent. Under the present experimental conditions, the maximum adsorption reached was 0.692
Polymers2017,9,201 9of15
g/g.

FFiigguurree 99.. EEffffeecctt ooff tthhee iinniittiiaall ccoonncceennttrraattiioonn ooff TThh44++ oonn ththee aaddssoorrpptitoionn bbeehhaavvioiorr oonnttoo ββ-C-CDD(A(ANN-c-coo-A-AAA)). .
([pH=2.95±0.05,m/V=0.18g/L,T=298.15±1.00K,I=0.50MNaNO3).
3.1.6. AdsorptionIsotherm
The adsorption isotherms are mathematical models when the adsorption process reaches
an equilibrium state which is used to describe the distribution of the adsorbate species between
theliquidandadsorbent. Inthisreport,theLangmuirandFreundlichmodelsarethemostcommonly
usedtodescribetheadsorptionequilibriumisotherms. Iftherearesomeimportantfacts,suchasthe
adsorptionislocalizedinamonolayerandtheadsorbatemoleculesdonotinteractwitheachother,
theadsorptionisothermusestheLangmuirmodel,whereastheFreundlichisothermmodelisalways
usedasanempiricalrelationshipwhichassumesthattherearemanyadsorptionenergiesindifferent
adsorptionsitestodescribetheadsorptionofsolutesfromaliquidtoasolidsurface.
TheLangmuirisothermequationwasusedinthelinearizedform[28]:
C /q =1/(q ·b)+C /q , (3)
e e max e max
wherebandq areLangmuirconstantsrelatedtoadsorptionenergyandadsorptionmaximum,
max
separately. AlinearizedplotofC /q againstC givesbandq .
e e e max
TheFreundlichequation,basedontheadsorptiononaheterogeneoussurface,isrepresentedas
follows[36]:
lgq =lgK +(1/n)lgC , (4)
e F e
whereK andnareFreundlichtheadsorptionisothermconstants. K andncanbegainedfromthe
F F
linearplotoflgq againstlgC .
e e
ThelinearizedLangmuirandFreundlichplotsareshowninFigure10a,b,respectively. Fromthese
results, the Langmuir model is presented with higher correlation coefficients than the Freundlich
model, so we can say that the Langmuir model is much better suited to describe the adsorption
mannerthantheFreundlichmodelintherangeofrelevantconcentration,combinedwiththeresults
above,whichmeansthattheadsorptionprocessmatcheswiththechemisorptioncharacteristicsin
amonolayer.
Polymers 2017, 9, 201 9 of 14
3.1.6. Adsorption Isotherm
The adsorption isotherms are mathematical models when the adsorption process reaches an
equilibrium state which is used to describe the distribution of the adsorbate species between the
liquid and adsorbent. In this report, the Langmuir and Freundlich models are the most commonly
used to describe the adsorption equilibrium isotherms. If there are some important facts, such as the
adsorption is localized in a monolayer and the adsorbate molecules do not interact with each other,
the adsorption isotherm uses the Langmuir model, whereas the Freundlich isotherm model is
always used as an empirical relationship which assumes that there are many adsorption energies in
different adsorption sites to describe the adsorption of solutes from a liquid to a solid surface.
The Langmuir isotherm equation was used in the linearized form [27]:
C /q =1/(q ⋅b)+C /q , (3)
e e max e max
where b and q are Langmuir constants related to adsorption energy and adsorption maximum,
max
separately. A linearized plot of C /q against C gives b and q .
e e e max
The Freundlich equation, based on the adsorption on a heterogeneous surface, is represented
as follows [35]:
lgq =lgK +（1/n)lgC , (4)
e F e
where K and n are Freundlich the adsorption isotherm constants. K and n can be gained from the
F F
linear plot of lgq against lgC
e e
The linearized Langmuir and Freundlich plots are shown in Figure 10a,b, respectively. From
these results, the Langmuir model is presented with higher correlation coefficients than the
Freundlich model, so we can say that the Langmuir model is much better suited to describe the
adsorption manner than the Freundlich model in the range of relevant concentration, combined with
the results above, which means that the adsorption process matches with the chemisorption
Polymers2017,9,201 10of15
characteristics in a monolayer.
(a) (b)
Figure 10. Adsorption isotherms of Langmuir model (a) and Freundlich model (b).
Figure10.AdsorptionisothermsofLangmuirmodel(a)andFreundlichmodel(b).
The essential feature of the Langmuir isotherm is that it can be described as a dimensionless
The essential feature of the Langmuir isotherm is that it can be described as a dimensionless
constant separation coefficient, R , which is used to express whether the adsorption system is
constant separation coefficient, RL , which is used to express whether the adsorption system is
L
“favorable” or “unfavorable”. The separate coefficient, R is given as [36]:
“favorable”or“unfavorable”. Theseparatecoefficient,R Lisgivenas[37]:
L
R =1/(1+bC ), (5)
R =L1/(1+bC )0, (5)
L 0
where C and b are the initial Th(IV) concentration (mg/L) and Langmuir adsorption constant (L/mg),
0
whereC andbaretheinitialTh(IV)concentration(mg/L)andLangmuiradsorptionconstant(L/mg),
0
respectively. Table 1 shows the results of the computation. Based on the impact of the separation
respectively. Table1showstheresultsofthecomputation. Basedontheimpactoftheseparationfactor
factor on the form of the isotherm, the R values are significantly smaller than one, which indicates
ontheformoftheisotherm,theR valueLsaresignificantlysmallerthanone,whichindicatesthatthe
L
thaβt -tChDe (βA-CND-c(oA-ANA-)coh-yAdAro)g helysdarroegaeflasv aorrea bal feaavdosroarbbleen atdtosoTrhb(eIVn)t [t3o8 T].h(IV) [37].
Table1.RLvaluesbasedontheLangmuirisotherm.
InitialTh4+
No. Concentration(mmol/L) RLValue
1 0.000327 0.0455
2 0.000392 0.0382
3 0.000457 0.0329
4 0.000523 0.0289
5 0.000588 0.0258
6 0.000653 0.0233
7 0.000719 0.0212
8 0.000784 0.0195
9 0.000849 0.018
10 0.000915 0.0167
11 0.00098 0.0156
12 0.00105 0.0147
3.1.7. EffectofTemperature
InordertofurtherstudytheadsorptionpatternofTh(IV)ionsonβ-CD(AN-co-AA),aseriesof
experimentswerepresentatdifferenttemperatures,suchas298.15,318.15,and338.15K,whichwas
usedtoindicatetheeffectoftemperature,withtheconcentrationofTh(IV)rangingfrom4.45×10−4
to1.05×10−3mol/L,andallotherparametersconstantattheiroptimumvalues. FromFigure11we
canknowthatthetemperaturerisehasimprovedtheadsorptionabilities,whichrepresentsthatthe
adsorptionisanendothermicprocess. Inordertoensurethethermodynamicfeatures, threebasic