2015-Chitosan Sporopollenin Microcapsules Preparation, Characterisation and Application in Heavy Metal Removal

International Journal of Biological Macromolecules 75 (2015) 230238

Contents lists available at ScienceDirect

International Journal of Biological Macromolecules

j ourna l ho me pa g e: www.elsev ier .com/ locate / i jb iomac

Chitosa atiand ap

Idris Sarga Selcuk Univerb Selcuk Univer

a r t i c l

Article history:Received 22 NReceived in reAccepted 27 JaAvailable onlin

Keywords:ChitosanSporopolleninHeavy metal

ts fobent mer san/sning etion p(II) an

timetosan

Cd(II): 0.77, Cr(III): 0.99, Ni(II): 0.58 and Zn(II): 0.71 mmol g1. Plain chitosan beads showed higherafnity for the ions; Cu(II): 1.46, Cr(III): 1.16 and Ni(II): 0.81 mmol g1 but lower for Cd(II): 0.15 andZn(II): 0.25 mmol g1. Sporopollenin enhanced Cd(II) and Zn(II) ions sorption capacity of the chitosanmicrocapsules. Chitosan/sporopollenin microcapsules can be used in Cd(II) and Zn(II) metal removal.

2015 Elsevier B.V. All rights reserved.

1. Introdu

Water bdischarge omining, texThe waste eeven treateHeavy metato the livingmobility, stmental effeheavy meta

There haventional tefciently. adsorption use, effectiv

Selectionheavy meta

CorresponE-mail add

http://dx.doi.o0141-8130/ ction

odies are contaminated with heavy metal ions throughf waste from many industries such as metal plating,tile and electric/electronic devices manufacturing [1,2].fuents from these industrial operations, untreated ord, can have signicant amounts of heavy metal ions.l ions in aquatic systems and ground water pose risks

organisms by accumulating in food chain due to theirability and non-biodegradability [3]. When their detri-cts and toxicity are considered, it is critical to removel ions to save diminishing water resources.ve been increasing interest and efforts to improve con-echniques to treat the metal contaminated efuentsAmong the conventional physicochemical methods,has been extensively employed because of its ease ofeness and feasibility [1,4].

of sorbent is a key parameter when sorbents forl removal are designed. In addition to physicochemical

ding author: Tel.: +90 332 223 3852; fax: +90 332 241 2499.ress: [email protected] (I. Sargn).

characteristics of a sorbent such as its selectivity towards certainspecies and sorption capacity, its cost and production proceduresshould be assessed. Many materials with natural or articial ori-gin such as activated carbon, resins, y ash, oxides, silicates, clays,zeolites, pine bark and cotton waste have been used as adsorbentsand reported in the literature [5,6]. These studies on sorbents havedemonstrated the need for more efcient, inexpensive and renew-able adsorbents. Bio-based sorbents can full these needs; bioma-terials are abundant in nature, and also many functional groupsfor metal interaction are present on them or they can be easilyfunctionalised.

Chitin, a carbohydrate with nitrogen content, is the second mostabundant biopolymer in the biosphere. Chitosan, a derivative ofchitin produced via deacetylation of chitin in high alkaline condi-tions, is a biocompatible and biodegradable [7,8] polymer with highafnity for metal ions [8,9]. The alkaline hydrolysis of chitin exposesfree amino groups (NH2) and gives the polymer unique cationicnature [10]. The pendant amino groups of chitosan are primarycause of its higher metal ion sorption capacity and its solubility inaqueous solutions when compared to chitin. Amino and hydroxylgroups (especially at the C-3 position) on chitosan can serve aselectrostatic interaction and complexation sites for metal cations[11,12]. This makes chitosan an appropriate sorbent in heavy metal

rg/10.1016/j.ijbiomac.2015.01.0392015 Elsevier B.V. All rights reserved.n/sporopollenin microcapsules: Preparplication in heavy metal removal

na,, Gulsin Arslanb

sity, Faculty of Science, Department of Chemistry, 42075 Konya, Turkeysity, Faculty of Science, Department of Biochemistry, 42075 Konya, Turkey

e i n f o

ovember 2014vised form 10 January 2015nuary 2015e 3 February 2015

a b s t r a c t

Use of natural polymers as biosorbenstudy aiming to design a novel biosorof chitin, and sporopollenin, a biopolychemical and biological attack. Chitoand characterised by employing scanand thermogravimetric analysis. Sorpwere tested for Cu(II), Cd(II), Cr(III), Niof sorbent, temperature and sorptionand the sorption capacity of the chion, characterisation

r heavy metal removal is advantageous. This paper reports afrom two biomacromolecules; chitosan, a versatile derivativewith excellent mechanical properties and great resistance toporopollenin microcapsules were prepared via cross-linkinglectron microscopy, Fourier transform infrared spectroscopyerformance of the microcapsules and the plain chitosan beadsd Zn(II) ions at different metal ion concentration, pH, amount. The adsorption pattern followed Langmuir isotherm model/sporopollenin microcapsules was found to be Cu(II): 1.34,

I. Sargn, G. Arslan / International Journal of Biological Macromolecules 75 (2015) 230238 231

uptake [13]. Many workers have opted for chitosan composites assorbent and prepared chitosan composites from natural products[14,15]. However, preparation of a chitosan-based biosorbent withsporopollenin has not been reported in the literature.

Sporopollenin is a natural biomacromolecule present in theouter wall meric mateattack and millions of performed available onifying. Nevemainly an aor conjugamolecule c[19].

Sporopo(common care reasonareported thto heat an250300 Cnature of raw or func[2225].

Once disinto insolustructural sporation of forms threemetal uptakdifferent soforms Schifused in synbents [27].

In this based adsochitosan ancharacteriseFourier tranmetric anahow heavyinteract witlinked chitcompare thmicrocapsuSporopollensignicantlymicrocapsuused in treacations.

2. Experim

2.1. Materi

MediumSigmaAldrticle size (Cu(NO3)23were purchSigmaAldrfrom Merc(Dubuque, Iexperiment

2.2. Preparation of chitosan/sporopollenin microcapsules

Preparation of chitosan/sporopollenin microcapsules was car-ried out as follows: Chitosan solution was prepared by dissolving3.00 g chitosan in 150 mL of acetic acid solution (2% v/v). The mix-

as continuously stirred for 20 h. Subsequently, 1.500 g ofollenin particles was added into the chitosan solution ande mporoe wa

of wcroca

ach to tsed

tral pollentheird traldehn waes ween wles. ere . ThePlaind bun.

icroc

surfere

EISS)obta. Thapsuetsyns wtome

etal s

tal sot (ch

was at 2

The 04centtiontudietermand

i CW

qe isn bephase vot inte(also called exine) of spores and pollens. This poly-rial is highly resistant to chemical and biologicalcan retain its morphology in geological strata overyears [16,17]. Many analytical techniques have beento reveal its chemical nature; however, information

its chemical structure is still limited and needs clar-rtheless, some studies indicated that sporopollenin isliphatic polymer with phenolic and aromatic groups

ted side chains [18]; it is considered as a macro-omposed mainly of carotenoid and carotenoid esters

llenin particles extracted from Lycopodium clavatumlub moss) has excellent mechanical strength andbly monodisperse [20]. Recently, Fraser et al. (2014)at sporopollenin from L. clavatum is also resistantd its chemistry does not alter until a threshold of

[21]. Many researchers have appreciated the uniquethe sporopollenin and have conducted works withtionalised form of it including metal removal studies

solved in acidic solutions, chitosan can be transformedble gel form via cross-linking; giving the polymertability in acidic media. Cross-linking also enables incor-ne particles into the polymeric matrice. Cross-linking

dimensional sites within the networks; enhancing thee [26]. Preparation of chitosan composite sorbents fromurces has been reported earlier. Glutaraldehyde, whichf bases with amines, is one of the cross-linking agentsthesis and modication of these chitosan-based adsor-

paper, we describe the preparation of a novel bio-rbent combining physicochemical properties of bothd sporopollenin. The synthesised microcapsules wered by employing scanning electron microscopy (SEM),sform infrared spectroscopy (FT-IR) and thermogravi-lysis (TGA). We attempted to provide insights into

metal ions; Cu(II), Cd(II), Cr(III), Ni(II) and Zn(II),h chitosan/sporopollenin microcapsules and the cross-osan beads without sporopollenin. Also, we tried toe metal ion uptake capacities of the sorbents. Theles exhibited higher efciency over the chitosan beads.in grains entrapped in the chitosan polymeric matrice

improved the metal ion capture capacity of theles. The chitosan/sporopollenin microcapsules can betment of the waters contaminated with heavy metal

ental

als

molecular weight chitosan was obtained fromich. Sporopollenin from L. clavatum with 20 m par-was purchased from Fluka Chemicals. Metal saltsH2O, Cr(NO3)39H2O, Ni(NO3)26H2O, Zn(NO3)24H2O)ased from Merck, Cd(NO3)24H2O was obtained fromich. Glutaraldehyde (25% in water, v:v) was obtainedk. Double distilled water puried with BarnsteadA) ROpure LP reverse osmosis system was used in thes.

ture wsporopthen thtosan/smixtur200 mLing mi24 h tocolourand rinof neusporopretain tion anglutarasolutiocapsuland thmolecusteps wvapourature. methosolutio

2.3. M

Thesules wLS 10 Zwere ter 2.5microclyzer/Ssolutiotropho

2.4. M

Mesorbenbeads)for 4 hpaper.time (6ion conon sorpwere swas deinitial

qe = (C

wherechitosaliquid-V is thsorbenixture was stirred for 3 h until homogeneity. The chi-pollenin mixture was transferred into a burette. Thiss dropped into the coagulation solution (a mixture ofater, 300 mL of methanol and 60.0 g NaOH [28]). Result-psules were incubated in the coagulation solution forieve a complete gelation, giving a yellow-brownish

he medium. Then, the microcapsules were recoveredthoroughly with distilled water until the ltrate wasH and free of coloured decomposition products of thein grains. Wet microcapsules (otherwise they could not

spherical shape when dried) were recovered by ltra-nsferred into cross-linking reaction solution (0.9 mL ofyde solution in 90 mL of methanol). The cross-linkings reuxed at 70 C for 6 h. Finally, cross-linked micro-re recovered and washed thoroughly rst with ethanolith water to remove any unreacted glutaraldehyde

The cross-linking treatment and the following washingperformed in a fume hood to arrest any glutaraldehyde

microcapsules were allowed to dry at room temper- chitosan beads were synthesised following the samet without adding sporopollenin grains to the chitosan

apsule characterisation and analytical methods

ace morphology of chitosan/sporopollenin microcap-investigated with Scanning electron microscope (EVO. FT-IR spectra of chitosan/sporopollenin microcapsulesined with a Perkin Elmer 100 FT-IR Spectrome-ermogravimetric analysis of chitosan/sporopolleninles were done with a Setaram Thermogravimetric Ana-s (EXSTAR S11 7300). Metal ion concentration in theas determined using a ame atomic absorption spec-ter (Contr AA 300, Analytik jena).

orption experiments

rption studies were done as follows: 0.1500 g of theitosan/sporopollenin microcapsules or plain chitosan

placed into 25 mL of metal ion solution and agitated00 rpm. Then, the sorbent was ltered through a ltereffects of amount of sorbent (0.05000.2500 g), contact80 min.), metal ion solution pH (3.05.8), initial metalrations (212 mg/L) and temperature (25, 35 and 45 C)

behaviour of the microcapsules and the chitosan beadsd. The amount of metal ions adsorbed by the sorbentined from the difference of metal concentrations in thenal solutions employing following equation below:

e)V (1)

the metal sorption capacity of the microcapsules orads (mmol g1), Ci and Ce are the initial and equilibriume concentrations of metal ions (mmol L1), respectively;lume of metal solution (L), and W is the mass of theracted with metal ion solution in grams.

232 I. Sargn, G. Arslan / International Journal of Biological Macromolecules 75 (2015) 230238

3. Results and discussion

3.1. Characterisation of chitosan/sporopollenin microcapsules

3.1.1. SEM SEM ima

the microcacles in chitothe effects sporopollenthe chitosanpersity andtreatmentsextent; butand as a res

As mensporopollenalkaline meies on acid[29]. They stepwise; aspectroscopof the sporobserved microcapsusporopollenobserved insules can begrains; indilenin grainsgelation trea detailed athe sporoposhould be d

3.1.2. FT-IRThe ana

methanol-Nchitosan/sploaded microf the metaafter the bastretching vband that ca1706 cm1

attributableThe CN st1194 cm1.stretching der. The baappeared aspectrum ois correspothe cross-li1640 cm1

absorption in the specshifted aftealterations could be atmetal interaat 3293 cmvibration oflinking. Buthydrogen bwas shifted

and asymmetric modes of CH2 group vibration) appeared in spec-trum of cross-linked chitosan/sporopollenin microcapsules. Thesetwo peaks were also observed in the presence of metal ions butwith some alterations. These observations demonstrated that the

tionino, tionworktal iher malysi

in tropotal io

Therm therted becomuld he opolymicrocres (one et alrainnd 3ondoropapsu

fect o

effend th m

amotent

did all thd at

fect o

tact ion fcrocaid up

Zn(II

fect o

ngestion ih proer s

) mad ca

ive hdrox

andyl ant low

ensporoimagesges clearly demonstrated the almost spherical shape ofpsules and the entrapment of the sporopollenin parti-san polymeric matrice (Fig. 1). The images also showedchemical treatment on the surface morphology of thein grains. As depicted in Fig. 1, prior to introduction into

network, the sporopollenin grains had high monodis- consistency of size. After coagulation and cross-linking, the grains could retain their structural integrity to some

their surface characteristics were partially disrupted;ult, the cavities were compressed or disappeared.tioned in the section 2.2, partial decomposition ofin grains in the gelation solution, which was highthanol solution, took place. Bubert et al. conducted stud-ic methanolysis of sporopollenin of Typha angustifoliaexposed the sporopollenin grains to HCl in methanolnd they analysed the decomposition products usingic techniques. They observed substantial weight losses

opollenin grains at the end of each step. Similarly, we16.8% mass loss on average upon drying the cross-linkedles with comparison to the chitosan beads withoutin. We can conclude that the higher mass losses

preparation of the chitosan/sporopollenin microcap- attributable to the decomposition of the sporopollenincating the act of methanolic alkali solution on sporopol-

incorporated in the chitosan microcapsules during theatment. However, this phenomenon needs clarifying;nalysis of the decomposition products released fromllenin grains during the incubation in the basic mediaone.

spectra analysislysis of the FT-IR spectra of sporopollenin (Fig. 2a),aOH treated sporopollenin (Fig. 2b), chitosan (Fig. 2c),oropollenin microcapsules (Fig. 2d) and metal ionocapsules (Fig. 3) could provide insights into the naturel ion-microcapsule interactions. As seen from Fig. 2,sic methanolysis of the sporopollenin grains, the OH-ibrations at 3378 cm1 did not shift, but the 1709 cm1

n be assigned to carboxylic/ketone stretching shifted towith lesser intensity, and the sharp peak at 1561 cm1

to the presence of aromatic C C group appeared.retching vibration band (1187 cm1) was observed at

The band at1606 cm1, assigned to aromatic C C ringshowed weak absorbance at 1603 cm1 as a shoul-nd at 1260 cm1 representing aromatic ether groupst 1258 cm1 with strong absorbance [30]. In the FT-IRf chitosan, the absorption band at 1589 cm1, whichnded to the NH2 groups stretching, disappeared afternking with glutaraldehyde, and the band appearing atcan be corresponded to the imine stretching [31]. Thebands, observed at 1656, 1640, 1575 and 1549 cm1

trum of chitosan/sporopollenin microcapsules werer forming complexes with metal ions. Additionally, thein the intensity of CH2 scissoring bands at 1418 cm1

tributed to the contribution of CH2OH side chains inction (Fig. 3) [32]. Here, the characteristic broader band

1 (assigned to stretching vibration of NH and axial OH groups present in chitosan) did not shift after cross-, the band at 2873 cm1 (assigned to intermolecularonds of chitosan and the axial CH stretching [33])

and two peaks, at 2919 and 2849 cm1 (symmetric

interacvia aminteracThese the meand etthe an(Fig. 2)on spothe me

3.1.3. The

evaluathree dstep co[36]; ttosan The mperatubeads Fraser lenin gat aroucorrespthat spmicroc

3.2. Ef

Thesules afor eacdid thetain exdosageent forreache

3.3. Ef

Conmetal the miing rapCr(III),

3.4. Ef

Chaspeciathroug

Low(Fig. 7ions anexcessand hyity of Ncarbonened a

Thetosan/ of metal ions with the microcapsules occurred mainlyhydroxyl and phenolic groups. Earlier workers studieds of metal ions with raw and modied sporopollenin.ers reported that sporopollenin itself had an afnity forons due to the functional hydroxyl, carbonyl/carboxyloieties on it. Based on ndings reported [34,35] and

s of FT-IR spectra of pristine and treated sporopolleninhis study, it can be commented that functional groupsllenin particles could also contribute to the sorption ofns.

ogravimetric analysismal stability of the microcapsules and the beads wasy TGA (Fig. 4). In the thermogram of the microcapsules,position steps were observed. The rst decomposition

be resulted from the evaporation of water moleculesthers can be ascribed to the degradation of the chi-er and the sporopollenin grains within the matrice.

apsules exhibited two maximum decomposition tem-DTGmax) (272.4 and 278.8 C); whereas the chitosanat lower temperature 269.3 C. In a recent paper by. (2014) [21], it has been reported that the sporopol-s are heat-resistant and the grains start to decompose00 C. Therefore, the higher DTGmax (278.8 C) could beed to the degradation of sporopollenin grains. It appearsollenin grains contributed to the thermal stability of theles.

f the adsorbent dosage on metal uptake

ct of the amount of chitosan/sporopollenin microcap-he chitosan beads on metal sorption was investigatedetal ion (Fig. 5). As the sorbent dose was increased, sount of metal ions sorbed by the microcapsules to a cer-. Sorption saturation point, where increase in sorbentnot contribute much to the metal sorption, was differ-e metal ions studied. As seen, such saturation point was

about 0.1500 g of microcapsules or the beads.

f contact time

time determining studies were conducted for eachor 6 h (Fig. 6). Initial adsorption rate of Cu(II) ions ontopsules was relatively higher than the rest; demonstrat-take process in rst 120 min. Sorption equilibrium for), Cd(II) and Ni ions was attained nearly at 240 min.

f solution pH on metal sorption

in pH of the metal solution can affect both metal ionn the solution and the nature of the sorbent especiallytonation/deprotonation of the functional moieties.

orption percentage observed in more acidic conditionsy be explained by the competition between hydrogentionic species for the same binding sites. Presence ofydrogen ions could lead to protonation of the aminoyl groups of chitosan, lowering electron-donating abil-

O atoms. Additionally, metal binding ability of hydroxyl,d carboxyl groups on sporopollenin [35] could be weak-er pH values.hancement observed in sorption capacity of chi-pollenin microcapsules at higher pHs may be attributed


Fig. 1. SEM im 5000(magnication

to the characompetition

3.5. Effect o

The amoincreased i12 mg L1) 5.40; Cr(IIICd(II): 0.070.160.65 mremoval oCd(II): 0.040.040.25 mconcentratithe mass tr

3.6. Thermo

The linethermodynmetal ions sChanges inentropy (versus 1/T,

G = RT

G = H

logKC =(

2

where KC iratio of thebent to th8.314 J mol

standard encalculated fof vant HoGibbs free eThermodynCr(III), Ni(IIare present

s (f meinddyn

ing t(II) i

surfrptiodothollenorptonto es the in s othn onres. Ting tto thserveadsriuminkediffeages of the sporopollenin grains (ad) (magnication: a: 1000, b: 3000, c: : e: 80, f: 250, g: 1000 and h: 5000).

cteristic of chelation mechanism [37] and the weakened of hydrogen ions for the sorption sites.

f initial metal ion concentration

unt of metal ions adsorbed onto the microcapsulesn more concentrated metal ion solutions (from 2 toat initial pH the metal solutions (Cd(II): 5.69; Cu(II):): 4.02, Ni(II): 5.80; Zn(II): 5.62.); Cu(II):0.141.16,0.66, Cr(III): 0.380.90, Ni(II): 0.260.50, Zn(II):mol g1. Similar behaviour was observed in the

f the ions with chitosan beads; Cu(II):0.040.89,0.13, Cr(III): 0.330.94, Ni(II): 0.080.30, Zn(II):mol g1. This could be explained with the increasingon gradient of metal ions, acting as a driving force foransfer of the metal ions to the solid phase [37].

dynamic analysis

ar form of the vant Hoff equation was used to deriveamics parameters governing sorption behaviour of thetudied onto the microcapsules and the chitosan beads.

standard free energy (G), enthalpy (H), and

changetion oof G

thermoregardand Cdon the[39]. Sowas ensporopCd(II) sZn(II) capsulincreasthe ionsorptioperatuindications onwas obtosan bequilibcross-lof the S), obtained from the linear vant Hoff plot of log KCwere analysed and discussed.

lnKC (2)

T S (3)S

.303R

)(

H

2.303RT

)(4)

s the thermodynamic equilibrium constant i.e., the equilibrium concentration of metal ions on the adsor-at in the solution and R is universal gas constant,1 K1 and T is the temperature (K). The value oftropy change, S and the standard enthalpy, H arerom the slope (H/2.303R) and intercept (S/2.303R)ff plot, log KC versus 1/T. Operating the equation (3),nergy values were obtained for each temperature [38].amic parameters for the adsorption of Cu(II), Cd(II),) and Zn(II) on chitosan/sporopollenin microcapsulesed in Table 1. While the positive value of enthalpy

a recent paanalysis to the thermodees simpexperiment

3.7. Adsorp

To makemetal ions, binding of mFreundlich (DR) [43] the sorption

i. The Freu

log qe = and d: 10000) and chitosan/sporopollenin microcapsules (eh):

H) conrming the endothermic nature of the sorp-tal ions onto the microcapsules, the negative valuesicated that the sorption process was spontaneous andamically feasible at studied temperatures. Additionally,he high enthalpy changes, particularly in case of Cu(II)ons, it appeared that metal sorption primarily occurredace of the microcapsules rather than within the poresn of the metal ions onto the cross-linked chitosan beadsermic. On the other hand, after the incorporation ofin grains into the chitosan microcapsules, Cu(II) andion occurred exothermically. The sorption of Cd(II) andthe beads were nonspontaneous, but onto the micro-e sorption was opposite in nature. Also, considering thenegative values of G with increasing temperature forer than Ni(II) ions, it can be suggested that metal ion

the microcapsules was more efcient at higher tem-he standard entropy changes were found to be positive,he increase in the entropy during the adsorption of thee chitosan/sporopollenin microcapsules. Similar trended for the Cu(II), Cd(II) and Cr(III) ions onto the chi-

with exception Ni(II) and Zn(II) ions. The entropy of the system decreased upon sorption of these ions onto the

d chitosan beads. This complex thermodynamic naturerent ions onto the same sorbent has been dealt with in

per by Liu and Lee [40]. The authors performed meta-critically assess these phenomena and concluded thatdynamic assessment of any metal or dye-sorbent systemle explanations and needs clarifying by more elaborateal study.

tion isotherms

quantitative evaluation of the sorption behaviour of theadsorption isotherm model analysis was done. Althoughetal ions to biosorbents often ts the Langmuir [41] and

models [42], two other models, DubininRadushkevichand Scatchard plot analysis [44], were used to describe

equilibrium as well.

ndlich model:

logKF +(

1n

)log Ce (5)


Fig. 2. FT-IR spectra of sporopollenin (a), methanol-NaOH treated sporopollenin (b), chitosan (c) and chitosan/sporopollenin microcapsules (c).

Table 1Thermodynamic parameters for the adsorption of Cu(II), Cd(II), Cr(III), Ni(II) and Zn(II) on sporopollenin/chitosan microcapsules and chitosan beads.

Metals Sorbents H (J mol1) S (J K1 mol1) G (J mol1)

T = 298.15 (K) T = 308.15 (K) T = 318.15 (K)

Cu(II) Microcapsules 3626.650 14.112 7834.190 7975.310 8116.430Beads 2364.790 15.835 2356.560 2514.910 2673.270

Cd(II) Microcapsules 1748.600 3.676 2844.730 2881.500 2918.260Beads 6933.527 7.927 4569.999 4490.725 4411.452

Cr(III) Microcapsules 2115.865 10.397 984.125 1088.100 1192.070Beads 275.924 1.762 249.304 266.921 284.573

Ni(II) Microcapsules 5323.172 16.027 544.734 368.464 224.195Beads 385.834 8.578 2943.469 3029.252 3115.036

Zn(II) Microcapsules 5736.771 19.512 80.706 275.826 470.945Beads 2814.771 2.068 3431.343 3452.023 3472.703


Fig

with qe,librium (mmol gcapacity

ii. The Lang

Ceqe

= CeQ0

with qe,librium mmol g

adsorptiiii. The DR

ln qe = l. 3. FT-IR spectra of chitosan/sporopollenin microcapsules loaded with copper(II) (a), zin

amount of solute adsorbed in mmol g1, Ce, the equi-concentration of the adsorbate in mM L1 and KF1) and n Freundlich constants denoting adsorption

and intensity of adsorption, respectively.muir model:

+ 1Q0b

(6)

amount of solute adsorbed in mmol g1, Ce, the equi-concentration of the adsorbate in mmol L1, Q0 (in1) and b (in L mmol1) Langmuir constants related toon capacity and energy of adsorption.

model:

nXm K2 (7)

where of soluteXm is theto the awere cal2 plots.free ene

E = (2K

iv. The Scat

qeCe

= Ks(

where Cmmol Lc(II) (b), cadmium(II) (c), chromium(III) (d), nickel(II) (e).

(Polanyi Potential) is [RT ln(1 + (1/Ce))], qe is the amount adsorbed per unit weight of adsorbent (mmol g1) and

adsorption capacity (mmol g1), K is a constant relateddsorption energy in mol2 kJ2. The values of Xm and Kculated from the intercept and slope of the ln qe versus

By using the K values in the equation below, the meanrgy of adsorption (E) was obtained:

)0.5 (8)

chard plot analysis:

Qs qe) (9)

e, the equilibrium concentration of the adsorbate in1, qe, equilibrium adsorbate capacity in mmol L1, Ks


Fig. 4. TG-DTG curves of chitosan/sporopollenin microcapsules (a) and chitosan beads (b).

Fig. 5. Effect of the adsorbent dosage on metal uptake; chitosan/sporopollenin microcapsules and chitosan beads (at initial pH; metal concentration 10 mg L1; volume ofsolution 25 mL; temperature 25 C; contact time 4 h).

Fig. 6. Effect of contact time on metal uptake; chitosan/sporopollenin microcapsules and chitosan beads (at initial pH; metal concentration 10 mg L1; volume of solution25 mL; temperature 25 C; adsorbent dosage 0.15 g).

Fig. 7. Effect of pH on metal uptake; chitosan/sporopollenin microcapsules and chitosan beads (metal concentration 10 mg L1; volume of solution 25 mL; temperature 25 C;contact time 4 h; adsorbent dosage 0.15 g).


Table

2Th

e

par

amet

ers

of

Freu

ndlich

, Lan

gmuir, S

catc

har

d

and

DR

isot

her

ms

for

sorp

tion

of

Cu(II), C

d(II), C

r(III), N

i(II)

and

Zn(II)

on

chitos

an

bead

s

and

spor

opol

lenin

/chitos

an

mic

roca

psu

les.

Isot

her

ms

Freu

ndlich

Langm

uir

Scat

char

d

DR

Met

al

ions

Sorb

ents

KF(m

mol

/g)

n

R2

Q0(m

mol

/g)

b

(L/m

mol

)

R2

Ks(L

/mm

ol)

Qs(m

mol

/g)

R2

Xm

(mm

ol/g

)

K

(mol

2/k

J2)

E

(kJ/m

ol)

R2

Cu(II)

Mic

roca

psu

les

14.3

88

2.10

5

0.83

3

1.34

4

1344

.086

0.95

5

1156

.000

1.15

7

0.79

9

1.93

5

0.00

4

11.1

80

0.97

3Bea

ds

5.88

8

1.70

6

0.99

0

1.45

6

60.6

50

0.91

6

23.3

40

1.62

1

0.71

7

1.19

1

0.00

8 7.

906

0.97

2

Cd(II)

Mic

roca

psu

les

12.0

50

1.40

6

0.87

8

0.77

3

85.9

30

0.94

4

40.7

10

1.36

7

0.37

9

1.90

2

0.01

2 6.

455

0.93

1Bea

ds

0.32

1

2.11

9

0.91

7

0.15

2

0.82

7

0.95

9

25.8

80

0.17

0

0.84

8

0.18

7

0.01

2

6.45

5

0.95

4

Cr(

III)

mic

roca

psu

les

1.66

7

3.30

0

0.93

7

0.99

3

47.2

88

0.99

1

51.1

90

0.98

3

0.90

4

1.08

4

0.00

8

7.90

6

0.96

5Bea

ds

2.72

3

2.19

8

0.94

1

1.16

4

38.8

05

0.98

8

25.0

90

1.22

2

0.94

8

1.35

9

0.01

2

6.45

5

0.97

9

Ni(II)

Mic

roca

psu

les

1.02

8

4.27

4

0.73

9

0.58

3

72.8

86

0.99

1

108.

500

0.64

9

0.81

6

0.72

8 0.

005

10.0

00

0.83

1Bea

ds

1.15

3

1.36

2

0.91

0

0.81

3

2.39

8

0.94

9

3.44

9

0.87

4

0.23

4

0.44

4 0.

020

5.00

0

0.86

1

Zn(II)

Mic

roca

psu

les

2.11

3

2.42

1

0.82

3

0.70

7

50.4

80

0.94

0

60.0

00

0.85

3

0.57

1

0.95

4

0.00

8

7.90

6

0.86

6Bea

ds

0.55

2

3.20

5

0.89

0

0.24

6

10.6

90

0.95

4

460.

900

0.29

6

0.81

1 0.

340

0.00

5

10.0

00

0.94

2 (in L mmol1) and Qs (in mmol g1) are the Scatchard isotherm

constants.

The paraplots of Frand DR (vs. qe) areanalysis shions onto cexplained btosan/sporoNi(II) and lowing ordand Ni(II): plain chito1.16 and NCd(II): 0.15tosan/sporothan the othese ions sules exhiblowest radithe microcaslightly lessthe chitosanity of the chthe value otion about the adsorbaical adsorpion-exchanfree energyisotherm mthe microcthan physisearity in thethan one tymicrocapsuof the sporoof the chitocidate the cbeen still so[18].

4. Conclus

This pretosan/sporoChitosan/spnatural antreatment. molecules; biopolymertant macromentrapped to the sorsules. Sporomicrocapsumicrocapsution of micanalysis stution equilibmodel, indface of the mthat Cd(II) meters and correlation coefcients obtained from theeundlich (log qe vs. log Ce), Langmuir (Ce/qe vs. Ce)ln qe vs. 2) and the Scatchard plot analysis (qe/Ce

listed in Table 2. The adsorption isotherm dataowed that the adsorption behaviour of the metalhitosan/sporopollenin microcapsules could be bettery the Langmuir model. The adsorption degrees of chi-pollenin microcapsules for the Cd(II), Cr(III), Cu(II),Zn(II) ions at room temperature were in the fol-er; Cu(II): 1.34, Cr(III): 0.99, Cd(II): 0.77, Zn(II): 0.710.58 mmol g1. The model analysis also showed thatsan beads had higher afnity for Cu(II): 1.46, Cr(III):i(II): 0.81 mmol g1 but lower for Zn(II): 0.25 and

mmol g1. The Langmuir adsorption capacity of chi-pollenin microcapsules for Cd(II) and Zn(II) was higherther metal ions studied. The ionic radius order ofis Ni(II) < Cu(II) < Zn(II) < Cd(II) < Cr(III). The microcap-ited lower afnity for the Ni(II) ions, which has theus but the highest charge density. On the other hand,psules had much higher afnity for Cd(II) and Zn(II) but

for Cu(II) and Cr(III) ions. Sporopollenin entrapped in matrix enhanced Cd(II) and Zn(II) ions sorption capac-itosan microcapsules. In DR isotherm model analysis,f mean free energy of adsorption, E, can give informa-the nature of the interaction between the surface andte. Values higher than 16 kJ mol1 may indicate chem-tion while values in a range of 816 kJ mol1 show ange mechanism [28]. Considering the values of mean

of adsorption (E) calculated in the analysis of DRodel, it appears that the adsorption of metal ions ontoapsules could proceed through chemisorption ratherorption. As seen from Table 2, the deviation from lin-

Scatchard plot analysis indicated the presence of morepe of the sorption sites on the chitosan/sporopolleninles [45]. This may be explained by the chemical naturepollenin grains already entrapped within the network

san polymer. As mentioned, in spite of the efforts to elu-hemical composition of sporopollenin grains, there haveme uncertainties regarding its exact chemical structure

ions

sent study reports an easy way of preparing chi-pollenin microcapsules for heavy metal removal.oropollenin microcapsules take the advantages of beingd its preparation does not require much chemicalThe microcapsules composed of two natural biomacro-chitosan, the derivative of the second most abundant

and sporopollenin, a chemically and physically resis-olecule of direct biological origin. Sporopollenin grains

within the polymeric matrice signicantly contributedption of Cd(II) and Zn(II) ions onto the microcap-pollenin grains enhanced the thermal stability of theles. Physical features and surface morphology of theles were investigated by SEM studies. The interac-rocapsules with the metal ions was evaluated in FT-IRdies. Adsorption isotherm analysis showed that sorp-rium could be well dened by Langmuir adsorption

icating homogeneity of the sorption sites on the sur-icrocapsules. Thermodynamic analysis demonstratedand Zn(II) ions sorption by chitosan/sporopollenin


microcapsules thermodynamically feasible and spontaneous. Thestudy also revealed the partial decomposition of sporopolleninin methanol-NaOH solution; which requires further investigating.In further studies on chitosan/sporopollenin composite microcap-sules, molecular weight of chitosan, chitosan/sporopollenin ratioand incubation time in gelation solution can be manipulated andthis novel bio-based sorbent can be tested in removal of other heavymetal ions and dyes in aqueous solutions.

Conict of interest

The authors declare no conict of interest.

Acknowledgements

The authors are greatly indebted to the Selcuk UniversityResearch Foundation for providing a nancial support (projectnumber: BAP-14201082).

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Chitosan/sporopollenin microcapsules: Preparation, characterisation and application in heavy metal removal1 Introduction2 Experimental2.1 Materials2.2 Preparation of chitosan/sporopollenin microcapsules2.3 Microcapsule characterisation and analytical methods2.4 Metal sorption experiments

3 Results and discussion3.1 Characterisation of chitosan/sporopollenin microcapsules3.1.1 SEM images3.1.2 FT-IR spectra analysis3.1.3 Thermogravimetric analysis

3.2 Effect of the adsorbent dosage on metal uptake3.3 Effect of contact time3.4 Effect of solution pH on metal sorption3.5 Effect of initial metal ion concentration3.6 Thermodynamic analysis3.7 Adsorption isotherms

4 ConclusionsConflict of interestAcknowledgementsReferences

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2015-Chitosan Sporopollenin Microcapsules Preparation, Characterisation and Application in Heavy Metal Removal