mekanisme bilayer

8/19/2019 mekanisme bilayer

1/7

Studies of anions sorption on natural zeolites q

K. Barczyk ⇑ , W. Mozgawa, M. KrólFaculty of Material Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland

h i g h l i g h t s

We modied different naturalzeolites with the

hexadecyltrimethylammoniumcations. Surfactant-modied zeolites wereused to immobilization of inorganicanions. We showed that anions’ sorptioncauses changes in IR spectra of theHDTMA–zeolites.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 1 December 2013Received in revised form 2 May 2014Accepted 9 June 2014Available online 19 June 2014

Keywords:Natural zeoliteSurfactant modicationAnions sorptionFT-IR spectra

a b s t r a c t

This work presents results of FT-IR spectroscopic studies of anions–chromate, phosphate and

arsenate – sorbed from aqueous solutions (different concentrations of anions) on zeolites. The sorptionhas been conducted on natural zeolites from different structural groups, i.e. chabazite, mordenite,ferrierite and clinoptilolite. The Na-forms of sorbents were exchanged with hexadecyltrimethylammoni-um cations (HDTMA+) and organo-zeolites were obtained. External cation exchange capacities (ECEC) of organo-zeolites were measured. Their values are 17 mmol/100 g for chabazite, 4 mmol/100 g for morde-nite and ferrierite and 10 mmol/100 g for clinoptilolite. The used initial inputs of HDTMA correspond to100% and 200% ECEC of the minerals. Organo-modicated sorbents were subsequently used for immobi-lization of mentioned anions.

It was proven that aforementioned anions’ sorption causes changes in IR spectra of the HDTMA-zeolites. These alterations are dependent on the kind of anions that were sorbed. In all cases, variationsare due to bands corresponding to the characteristic Si–O(Si,Al) vibrations (occurring in alumino- andsilicooxygen tetrahedra building spatial framework of zeolites). Alkylammonium surfactant vibrationshave also been observed. Systematic changes in the spectra connected with the anion concentration inthe initial solution have been revealed.

The amounts of sorbed CrO42–, AsO43– and PO43– ions were calculated from the difference between theirconcentrations in solutions before (initial concentration) and after (equilibrium concentration) sorptionexperiments. Concentrations of anions were determined by spectrophotometric method.

2014 Elsevier B.V. All rights reserved.

Introduction

Natural zeolites are a group of crystalline, hydrated tectoalumi-nosilicates characterized by varied and extremely valuable physi-cochemical properties. One of the most signicant is the abilityof sorption and separation of ions and molecules. Due to the high

http://dx.doi.org/10.1016/j.saa.2014.06.065

1386-1425/ 2014 Elsevier B.V. All rights reserved.

q Selected paper presented at XIIth International Conference on Molecularspectroscopy, Kraków – Białka Tatrzan´ska, Poland, September 8–12, 2013.⇑ Corresponding author. Tel.: +48 126175220; fax: +48 126337161.

E-mail address: [email protected] (K. Barczyk).

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 876–882

Contents lists available at ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

j ou rna l homepa ge : w ww.e l s e v i e r. com/ lo ca t e / s aa

http://dx.doi.org/10.1016/j.saa.2014.06.065mailto:[email protected]://dx.doi.org/10.1016/j.saa.2014.06.065http://www.sciencedirect.com/science/journal/13861425http://www.elsevier.com/locate/saahttp://www.elsevier.com/locate/saahttp://www.sciencedirect.com/science/journal/13861425http://dx.doi.org/10.1016/j.saa.2014.06.065mailto:[email protected]://dx.doi.org/10.1016/j.saa.2014.06.065http://crossmark.crossref.org/dialog/?doi=10.1016/j.saa.2014.06.065&domain=pdf


2/7

cation exchange capacity (CEC), these minerals are widely used inthe process removing of heavy metal cations from aqueous solu-tion [1,2]. One the other hand, the presence of uncompensatednegative charge of zeolites crystal lattice, causes their very lowafnity for inorganic anions or nonpolar particles. The increasingof the anion exchange capacity can be achieved by changing thechemical surface properties. The treatment of these minerals withlarge cationic surfactants, such like hexadecyltrimethylammoniumamine (HDTMA), leads to changes in the external surface charge of the zeolite from negative to positive [3]. Molecules of HDTMA typeare long-chain forms, which dissolve in water and hydrolyze to theorganic cation and inorganic ion (Br– or Cl–). Surfactant cationsexchange with inorganic cations (i.e. Na+, K+, Ca2+), which occupyion exchange position on the outer surface of the zeolite and formfull or partial surfactant bilayer. In this way net charge of zeolite ischanged from negative to positive [4–6], which provides sites forexchange of inorganic anions. Such modication does not limit cat-ion exchange capacity of sorbents, so they can be used in doublerole. Thus, the result of surfactant modication is ability of org-ano-zeolites to sorb both anions and cations and non-polar organicmolecules from aqueous solutions [7]. Some of the related papersdescribe changes on IR spectra caused HDTMA-modication[8–10].

Organo-zeolites can be successfully used in the processes of sorption such anions like: chromate [11,12], arsenate [13,14],phosphate [15], nitrate [16,17], sulphate [18], etc. from aqueoussolutions.

The aim of this work was to compare the sorption properties of natural zeolites modied with the hexadecyltrimethylammoniumcations (HDTMA+), to the selected inorganic anions (CrO42 , AsO43and PO43 ), with results of IR spectroscopic studies of sorbents.The results of sorption and structural studies of modied clinoptil-olite, presented in the paper [19] shows that comparison of thespectra before and after the organic modication and before andafter the sorption of various inorganic anions, allows to determinetheir inuence on the structure of sorbents.

In the presented work, studies were extended to concern zeo-lites from different structural groups, i.e. chabazite, mordenite, fer-rierite and clinoptilolite. The typical chemical composition of chabazite is given by Ca2[Al4Si8O24] 12H2O formula and its alumi-nosilicate structure (framework type code – CHA) consist SBU (Sec-ondary Building Units) built of double 6-ring (D6R). Mordenite(Na8[Al8Si40O96] 24H2O) and ferrierite (Mg2Na2[Al6Si30O72] 18H2-O), which framework type code is MOR and FER respectively, areexample of the group of zeolite in which SBU is the 5–1 complex(T8O16 units). Clinoptilolite ((K2,Na2,Ca)3[Al6Si30O72] 20H2O)belongs to heulandite group (framework HEU) of zeolites and itsSBU is the 4–4 = 1 complex (T10O20 units) [20].

Experimental

Studies presented in this work were divided into several stages:(1) transformation zeolites into sodium form; (2) modication of them with HDTMA-Br; (3) sorption of selected anions usingobtained sorbents; and (4) MIR spectroscopic studies of organo-zeolites after anions sorption.

In order to improve the ion exchange properties, all zeoliteswere transformed into sodium forms. The Na-forms of sorbentswere exchanged with hexadecyltrimethylammonium cations(HDTMA+) [8,10] in amount equivalent to 100% (1.0) and 200%(2.0) ECEC of each of the zeolites. The value of ECEC in relation toHDTMA+, determined by sorption of alkylammonium ions, are

17 mmol/100 g, 4 mmol/100 g, 4 mmol/100 g and 10 mmol/100 grespectively for chabazite, mordenite, ferrierite and clinoptilolite.

Organic modication was carried out in the following way:aqueous suspensions of the zeolites and the organic salts were stir-red for 24 h at 80 C, left for 24 h at 30 C, after which the superna-tants were removed by decanting and the samples were washedtwice with a small amount of redistilled water to a negative reac-tion for bromide ions. The residues were then dried and homoge-nized. The effectiveness of modication has been conrmed bymeasurement of electrokinetic (zeta) potential and infrared spec-troscopy (FT-IR) studies.

Obtained organo-zeolites were subsequently used for immobili-zation of CrO42 , AsO43 , PO43 ions. Anions were introduced into thesorbents’ structure from aqueous solutions with the initial concen-trations from 0.01 to 5 mmol/dm3 at a weight sorbent/solutionratio of 1:50. For this purpose 0.1 g (±0.00001 g) of the organo-sil-icate was placed in a tube and 5 cm3 of appropriate anions solutionwas added. The pH 4 was adjusted with 1 M hydrochloric acid. Themixture was shaken for 24 h at 25 C and centrifuged. All the sorp-tion experiments were done in triplicates for each anionconcentration.

The amounts of sorbed anions were calculated from the differ-ence between their concentrations in solutions before (initial con-centration) and after (equilibrium concentration) sorptionexperiments. Concentrations of all ions were determined spectro-photometrically (UV–VIS HITACHI U-1800) using the biphenylcar-bazide method for chromates and molybdenum blue method forphosphates and arsenates.

The change in the surface charge of sorbents from negative topositive was conrmed by measurement of electrokinetic poten-tial, which was made using Zetasizer Nano ZS Instrument. Themedium of measurement was anaqueous solutionof NaCl at a con-centration of 10 2 mol/dm3. The zeta potential value was esti-mated as an average of 5 measurements.

Spectroscopic studies of organo-zeolite before and after anionssorption were measured on a Bruker Vertex 70v spectrometer.Infrared spectra were collected in the mid infrared (MIR) region(4000–400 cm 1) after 512 scans at 1 cm 1 resolution. Sampleswere prepared using the standard KBr (Merck) pellets method.

Fig. 1. FT-IR spectra of mordenite modied with increasing amount of HDMTA-Br.

K. Barczyk et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 876–882 877

http://-/?-


3/7

Fig. 2. Sorption isotherm of: (a) chromate, (b) phosphate and (c) arsenate ions on chabazite, mordenite, ferrierite and clinoptilolite after HDTMA-modication.

878 K. Barczyk et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 876–882


4/7

Result and discussion

The results of the zeta potential measurements indicated thatthe negative surface charge of natural zeolites ( 39 mV for chabaz-ite, 59 mV for ferrierite, 53 mV for mordenite and 45 mV forclinoptilolite) was changed to positive after organic modication.When the HDTMA+ loading equals to 100% (1.0) ECEC of each of the zeolites, the initial negative charge was neutralized by surfac-tant cations. Introduction of additional amount of surfactant cat-ions resulted in a gradual increase of the zeta potential. Atmaximum load with HDTMA+, the zeta potential reached: +38,+22, +22 and +47 mV for chabazite, ferrierite, mordenite andclinoptilolite respectively. The charge reversal conrmed that sur-factant cations form an organic bilayer or patchy bilayer coating onthe external surface of zeolite.

Chabazite, mordenite, ferrierite and clinoptilolite modied withdifferent amount of HDTMA-Br were mainly investigated with the

use of infrared spectroscopy (FT-IR). Due to the fact that HDTMA+

sorption process occurs only on the surface of sorbents, the bandsconnected with the internal Si–O(Si) and Si–O(Al) vibrations intetrahedra or alumino- and silico-oxygen (in the range of 1200–400 cm 1) remain unchanged.

However, organic modication causes that in the MIR spectra of zeolites bands associated with the presence of HDTMA appear.

In the range of 3060–2820 cm–1 (Fig. 1), the two intense bands,at about 2920 cm 1 and 2851 cm 1, are associated respectivelywith asymmetric and symmetric stretching vibrations of CH2groups [21]. With the increase in the initial concentration of sur-factant, these bands are shifted towards lower wavenumbers toabout 2920 and 2851 cm 1, respectively. Simultaneously, theirintegral intensity increases with increase of HDTMA+ packing den-

sity. The observed shift is a consequence of the conformationalchanges of the chain on the zeolite surface (transition from gauche

to trans conformation) [10]. At small amount of surfactant cationson the zeolite surface, these bands appear at higher wavenumbers.This is due to disordered arrangement of chains of HDTMA+, which

adopt gauche conformations. With the increase of the content of surfactant on the surface, chains gradually adopt highly orderedtrans conformations characteristic of crystalline HDTMABr, forwhich these bands are respectively at 2918 and 2850 cm 1 [22].

Fig. 2 presents spectrophotometric study (UV–VIS) results of chromates, arsenates and phosphates sorption on chabazite, mord-enite, ferrierite and clinoptilolite unmodied and modied withHDTMA-Br in amount equivalent to 1.0 and 2.0 of ECEC of eachof the zeolites, as a function of the equilibrium anions concentra-tion in the solution. Sorption of mentioned anions depends onthe kind of anion and its initial concentration in the solution, aswell as on the type of zeolite and its surfactant loading level.

As shown in Fig. 2, all anions are slightly exchanged on theunmodied zeolites. The low afnity of natural zeolites for anio-

nic species results from negative charge of their crystal lattice,which provides sites for exchanging cations but not for anions.In contrast, surfactant-modied zeolites (SMZ) show signicantsorption of all three oxyanions from aqueous solution. The abilityof SMZ to sorb anions is due to anion exchange with charge-balancing anions (initially Br ) on the headgroups of thesurfactant bilayer.

The removal capacity of anions gradually increased withincreasing of the initial concentration of the solution. It relates toboth the zeolites treated with HDTMA at amount equal to 1.0and 2.0 the ECEC of each of the sorbents. This trend can be easyexplained by the increase in the amount of ions in solution, whichcan be adsorbed. Additionally, higher difference in the initial solu-tion concentration is the driving force mass diffusion from the

solution to the solid phase, which in turn increases the probabilityof contact the anion with exchange site on SMZ surface [12].

Fig. 2 (continued )


http://-/?-


5/7

The most effectively sorbed anions are chromates, which sorp-tion capacities on zeolites modied with 2.0 of ECEC are 198, 112,77 and 56 mmol/kg, respectively for chabazite, clinoptilolite, fer-rierite and mordenite. In contrast, sorbents modied with HDTMAin amount equivalent to 1.0 the ECEC removed little more than ahalf of maximum amount sorbed anions on zeolites modied withdouble layer of HDTMA. Trivalent anions, like phosphates and ars-enates, are removed to a much lesser extent, and their anionexchange capacities do not exceed 50 mmol/kg for AsO43 and35 mmol/kg for PO43 .

These results clearly show that differences in sorption capacityare caused by many factors, like the type of anion, its charge andspeciation in aqueous solution. The removal of oxyanions fromaqueous solution depends strongly on the pH of the solution,

which affects the surface charge of the sorbent and determinesthe kind of anion species [11]. The pH of each of anions solutionwas adjusted to pH 4. According to the Cr(VI) speciation diagram[23], at this value of pH, predominant Cr(VI) species are HCrO4anions. These univalent forms require one exchange site fromSMZ for sorption one molecule of HCrO4 on zeolite surface at thatpH. At the higher pH predominant forms of Cr(VI) are divalent ions(CrO42 and Cr2O72 ), which need two surface sites from SMZ. Thiscauses, that more chromate ions can be removed by organo-zeo-lites at pH 4 than at higher pH.

In contrast, at the pH study, arsenates(V) and phosphates(V)exist mostly also as univalent ions, H2AsO4 and H2PO4 respec-tively. However, neutral forms: H3AsO4 and H3PO4 are also com-mon in the aqueous solution [24,25]. Probably, the presence of these neutral forms results in lower removal capacity of As(V)and P(V) than Cr(VI) at pH = 4. This follows from mechanism of

Fig. 3. MIR spectra of: (a) chabazite and (b) clinoptilolite modied with 2.0 ECEC of HDTMA before and after sorption of different ions form the aqueous solution with5 mmol/dm3 initial concentration.

Fig. 4. MIR spectra of: (a) clinoptilolite and (b) mordenite modied with 2.0 ECEC of HDTMA before and after sorption of different ions form the aqueous solution with5 mmol/dm3 initial concentration in the range of 3040–2800 cm 1.



6/7

retaining these anions, which is mainly limited to ion exchangewith charge-balancing anions (Br ) in surfactant bilayer on zeolitessurface, therefore physical sorption of neutral form does not occur.However, other potential sorption mechanisms cannot beexcluded. The surface precipitation of oxyanions with HDTMAand/or chemical reduction of anions to less soluble forms mayinuence the removal of inorganic anions form aqueous solution[6].

The anion sorption properties also strongly depend on the typeof zeolites. Amongthe analyzed minerals, chabazite has the highestanion exchange capacity, while mordenite and ferrierite have thelowest. These differences result from i.a. the value of the negativesurface charge of aluminosilicate network. The higher the charge,the lower the ratio of Si/Al, which causes the zeolite to have moreexchange sites and thus enables it to sorb more HDTMA+ to coverthe surface, and to exhibit higher value ions sorption capacity.Chabazite has the lowest Si/Al ratio from examined zeolites(Si/Al = 6.9) and shows the highest anion exchange capacities,whilst for mordenite and ferrierite (zeolites belonging to high silicaminerals) this ratio is the highest (in case of mordenite Si/Al = 12.1and ferrierite Si/Al = 19.3), so their anion sorption properties arelower.

The results of anion sorption properties of zeolites indicatedspectrophotometrically (UV/VIS) have been compared with thoseobtained by FT-IR spectroscopy studies. The MIR spectra of differ-ent zeolites modied with 2.0 ECEC of HDTMA before and afteranion sorption from the solution with the maximum initial con-centration equal to 5 mmol/dm3, are presented in Fig. 3.

All bands occurring in the spectra can be divided into severalgroups [19] associated with different types of vibrations realizedin samples structure:

3800–1600 cm 1 vibrations related to the presence of OHgroups and zeolite water in the structure;

3040–2800 cm 1 vibrations associated with the presence of HDTMA+ on the external surface of zeolites;

1300–800 cm 1 internal, anti-symmetric Si–O(Si) and Si–O(Al) vibrations in tetrahedra or alumino- and silicooxygenbridges;

820–680 cm 1 pseudolattice vibrations of aluminosilicatestructure and vibrations characteristic for HDTMA+;

1500–1400 cm 1 internal vibrations connected with methy-lene chains of surfactant molecules.

Due to small amount of ions retained on zeolite surface, thebands originating from the anions were not observed.

Comparison of the spectra presented in Fig. 3 and detailed anal-ysis in particular ranges of wavenumbers show that noticeable dif-ferences between them are observed in the second and fourthgroup of mentioned bands.

In the region of 3040–2800 cm1

(Fig. 4) bands connecteddirectly with the organic modication of the sorbents occur. Thetwo most intense of them at ca. 2922 and 2852 cm 1 correspondto the anti-symmetric and symmetric CH2 stretching modes of amine respectively. As was mentioned, their intensity stronglydepends on the packing density of amine chains, thus visiblechanges in the spectra are observed mainly for organo-zeolitesmodied with 2.0 ECEC of HDTMA+. Comparison of the spectra of organo-zeolites before and after sorption of different anions showsthat their presence in zeolite structure causes change in the posi-tion of these bands. Replacement of the small Br ions by largeinorganic anions (HCrO4 , H2AsO4 and H2PO4 ) results in a shift of the bands responsible for C–H stretching vibrations toward higherwavenumbers. The magnitude of this shift depends on amount of

anions retained on external zeolite surface. The maximum anionsorption capacities are obtained in the case of chromates, hence

the biggest shift is visible for these anions (about 4 cm1), whilstthe smallest shift refers to AsO43 and PO43 ions, which are sorbedto a much lesser extent.

In the fourth analyzed region (860–680 cm 1) bands which con-cern two types of vibrations realized in zeolites structure occur(g. 5). The rst type related to bands at ca. 776 cm1 and635 cm 1 originates from pseudolattice vibrations of aluminosili-cate structure of zeolites. The anion sorption process is limitedonly to external surface of organo-zeolites, hence the bands con-nected with the internal Si–O(Si) and Si–O(Al) vibrations in tetra-

hedra or alumino- and silico-oxygen bridges remain unchanged.The second group of bands is connected with HDTMA+ modica-tion. The bands at ca. 730 and 720 cm1 correspond to theCH2-rocking mode [22]. The bands responsible for these vibrationsare splitted, which is a consequence of intermolecular interactionbetween the two adjacent hydrocarbon chains in perpendicularorthorhombic cell [21,22]. As can be noticed, the rocking vibrationsin methylene group are preserved at essentially unchanged fre-quencies during anions sorption process. At the same time, theintegral intensity of these bands decreases with the increase of concentration in the initial solution. As in the case of the bandsin the second analyzed region, the most visible changes areobserved for chromates, because CrO42 ions are sorbed the mosteffectively form all anions.

Conclusions

Based on obtained results the following conclusions can bedrawn:

Organic modication with the use of HDTMA+ leads to changeof the surface properties of all analyzed zeolites, giving themthe ability to anions sorption.

The anion sorption capacity of SMZ depends on the kind of anion and its initial concentration in the solution, as well ason the type of zeolite and its surfactant loading level.

Sorbents modied with 2.0 of ECEC of each of zeolites showgreater anion sorption than materials modied with 1.0 of

ECEC, and have a bigger afnity for chromates than forarsenates and phosphates.

Fig. 5. MIR spectra of chabazite modied with 2.0 ECEC of HDTMA before and aftesorption of different ions form the aqueous solution with 5 mmol/dm3 initialconcentration in the range of 840–680 cm 1.



7/7

In the MIR spectra of all zeolites after surfactant modicationadditional bands associated with HDTMA+ appear. With theincrease of the surfactant content, these bands are shiftedtoward lower wavenumbers with simultaneous increase of their integral intensity.

Anion sorption process causes changes in the MIR spectra of zeolites. These changes relate to the two ranges of wavenum-bers (3040–2800 cm 1 and 820–680 cm 1) and depend onamount of anions retained on external zeolite surface. In theregion of 3040–2800 cm 1 (related to the presence of HDTMA+in the structure) bands at ca. 2922 and 2852 cm 1, correspondto the anti-symmetric and symmetric CH2 stretching modesrespectively are shifted to higher wave numbers with theincrease of the sorbed anions.

In the 820–680 cm 1 region, the anion sorption process causes adecrease in the intensity of the bands connected with zeolitesmodication by HDTMA+ at 730 and 720 cm 1. The bands atca. 776 and 635 cm 1 connected with the internal Si–O(Si)and Si–O(Al) vibrations in tetrahedra or alumino- and silico-oxygen remain unchanged. This conrms that anions sorptionprocess occurs only on the surface of sorbents.

Acknowledgments

Financial support this work was provided by AGH University of Science and Technology in Krakow under Grant No. 15.11.160.114.

The authors would like to thank Dr. T. Bajda from Faculty of Geology, Geophysics and Environmental Protection AGH Univer-sity of Science and Technology for his help during measurementsof anion sorption capacity of SMZ.

References

[1] E. Erdem, N. Karapinar, R. Donat, J. Colloid Interface Sci. 280 (2004) 309–314.[2] C. Cabrera, C. Gabaldon, P. Marzal, J. Chem. Technol. Biotechnol.80 (2005) 477–

481.[3] H. He, R.L. Frost, T. Bostrom, P. Yuan, L. Duong, D. Yang, Y. Xi, J.T. Kloprogg

Appl. Clay Sci. 31 (2006) 262–271.[4] E.J. Sullivan, J.W. Carey, R.S. Bowman, J. Colloid Interface Sci. 206 (1998) 369–

380.

[5] R.S. Bowman, Microporous Mesoporous Mater. 61 (2003) 43–56.[6] G.M. Haggerty, R. Bowman, Environ. Sci. Technol. 28 (1994) 452–458.[7] H. Chao, S. Chen, Chem. Eng. J. 193–194 (2012) 283–289.[8] M. Rozˇ ić, S. Miljanic´, J. Hazard. Mater. 185 (2011) 423–429.[9] H. Guan, E. Bestland, Ch. Zhu, H. Zhu, D. Albertsdottir, J. Hutson, C.T. Simmons,

M. Ginic-Markovic, X. Tao, A.V. Ellis, J. Hazard. Mater. 183 (2010) 616–621.[10] M. Rozˇ ić, D.I. Šipušic´, L. Sekovanic´, S. Miljanic´, L. Ćurković, J. Hrenovic´, J. Colloid

Interface Sci. 331 (2009) 295–301.[11] R. Leyva-Ramos, A. Jacobo-Azuara, P.E. Diaz-Flores, R.M. Guerrero-Coronado, J.

Mendoza-Barron, M.S. Berber-Mendoza, Colloids Surf. A: Physicochem. Eng.Aspects 330 (2008) 35–41.

[12] Y. Zeng, H. Woo, G. Lee, J. Park, Desalination 257 (2010) 102–109.[13] P. Chutia, S. Kato, T. Kojima, S. Satokawa, J. Hazard. Mater. 162 (2009) 204–

211.[14] A.M. Yusof, N.A. Nizam, N. Malek, J. Hazard. Mater. 162 (2009) 1019–1024.[15] J. Hrenovic, M. Rozic, L. Sekovanic, A. Anic-Vucini, J. Hazard. Mater. 156 (2008)

576–582.[16] J. Schick, P. Caullet, J. Paillaud, J. Patarin, C. Mangold-Callarec, Microporous

Mesoporous Mater. 132 (2011) 395–400.[17] D. Bhardwaj, M. Sharma, P. Sharma, R. Tomar, J. Hazard. Mater. 227–228(2012) 292–300.[18] A.D. Vujakovic, M.R. Tomasevic-Canovic, A.S. Dakovic, V.T. Dondur, Appl. Clay

Sci. 17 (2000) 265–277.[19] W. Mozgawa, M. Król, T. Bajda, J. Mol. Struct. 993 (2011) 109–114.[20] D.W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1974.[21] H. Hongping, F.L. Ray, Z. Jianxi, Spectrochim. Acta A 60 (2004) 2853–2859.[22] Z. Li, W. Jiang, H. Hong, Spectrochim. Acta A 71 (2008) 1525–1534.[23] B. Saha, R.J. Gill, D.G. Bailey, N. Kabay, M. Arda, React. Funct. Polym. 60 (2004)

223–244.[24] P.L. Smedley, D.G. Kinniburgh, Appl. Geochem. 17 (2002) 517–568.[25] Y. Liu, X. Sheng, Y. Dong, Y. Ma, Desalination 289 (2012) 66–71.

http://refhub.elsevier.com/S1386-1425(14)00953-6/h0005http://refhub.elsevier.com/S1386-1425(14)00953-6/h0010http://refhub.elsevier.com/S1386-1425(14)00953-6/h0010http://refhub.elsevier.com/S1386-1425(14)00953-6/h0010http://refhub.elsevier.com/S1386-1425(14)00953-6/h0015http://refhub.elsevier.com/S1386-1425(14)00953-6/h0015http://refhub.elsevier.com/S1386-1425(14)00953-6/h0020http://refhub.elsevier.com/S1386-1425(14)00953-6/h0020http://refhub.elsevier.com/S1386-1425(14)00953-6/h0020http://refhub.elsevier.com/S1386-1425(14)00953-6/h0025http://refhub.elsevier.com/S1386-1425(14)00953-6/h0030http://refhub.elsevier.com/S1386-1425(14)00953-6/h0035http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0045http://refhub.elsevier.com/S1386-1425(14)00953-6/h0045http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0060http://refhub.elsevier.com/S1386-1425(14)00953-6/h0065http://refhub.elsevier.com/S1386-1425(14)00953-6/h0065http://refhub.elsevier.com/S1386-1425(14)00953-6/h0070http://refhub.elsevier.com/S1386-1425(14)00953-6/h0075http://refhub.elsevier.com/S1386-1425(14)00953-6/h0075http://refhub.elsevier.com/S1386-1425(14)00953-6/h0075http://refhub.elsevier.com/S1386-1425(14)00953-6/h0080http://refhub.elsevier.com/S1386-1425(14)00953-6/h0080http://refhub.elsevier.com/S1386-1425(14)00953-6/h0085http://refhub.elsevier.com/S1386-1425(14)00953-6/h0085http://refhub.elsevier.com/S1386-1425(14)00953-6/h0085http://refhub.elsevier.com/S1386-1425(14)00953-6/h0090http://refhub.elsevier.com/S1386-1425(14)00953-6/h0090http://refhub.elsevier.com/S1386-1425(14)00953-6/h0090http://refhub.elsevier.com/S1386-1425(14)00953-6/h0095http://refhub.elsevier.com/S1386-1425(14)00953-6/h0100http://refhub.elsevier.com/S1386-1425(14)00953-6/h0100http://refhub.elsevier.com/S1386-1425(14)00953-6/h0105http://refhub.elsevier.com/S1386-1425(14)00953-6/h0110http://refhub.elsevier.com/S1386-1425(14)00953-6/h0115http://refhub.elsevier.com/S1386-1425(14)00953-6/h0115http://refhub.elsevier.com/S1386-1425(14)00953-6/h0115http://refhub.elsevier.com/S1386-1425(14)00953-6/h0120http://refhub.elsevier.com/S1386-1425(14)00953-6/h0125http://refhub.elsevier.com/S1386-1425(14)00953-6/h0125http://refhub.elsevier.com/S1386-1425(14)00953-6/h0120http://refhub.elsevier.com/S1386-1425(14)00953-6/h0115http://refhub.elsevier.com/S1386-1425(14)00953-6/h0115http://refhub.elsevier.com/S1386-1425(14)00953-6/h0110http://refhub.elsevier.com/S1386-1425(14)00953-6/h0105http://refhub.elsevier.com/S1386-1425(14)00953-6/h0100http://refhub.elsevier.com/S1386-1425(14)00953-6/h0100http://refhub.elsevier.com/S1386-1425(14)00953-6/h0095http://refhub.elsevier.com/S1386-1425(14)00953-6/h0090http://refhub.elsevier.com/S1386-1425(14)00953-6/h0090http://refhub.elsevier.com/S1386-1425(14)00953-6/h0085http://refhub.elsevier.com/S1386-1425(14)00953-6/h0085http://refhub.elsevier.com/S1386-1425(14)00953-6/h0080http://refhub.elsevier.com/S1386-1425(14)00953-6/h0080http://refhub.elsevier.com/S1386-1425(14)00953-6/h0075http://refhub.elsevier.com/S1386-1425(14)00953-6/h0075http://refhub.elsevier.com/S1386-1425(14)00953-6/h0070http://refhub.elsevier.com/S1386-1425(14)00953-6/h0065http://refhub.elsevier.com/S1386-1425(14)00953-6/h0065http://refhub.elsevier.com/S1386-1425(14)00953-6/h0060http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0055http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0050http://refhub.elsevier.com/S1386-1425(14)00953-6/h0045http://refhub.elsevier.com/S1386-1425(14)00953-6/h0045http://refhub.elsevier.com/S1386-1425(14)00953-6/h0040http://refhub.elsevier.com/S1386-1425(14)00953-6/h0035http://refhub.elsevier.com/S1386-1425(14)00953-6/h0030http://refhub.elsevier.com/S1386-1425(14)00953-6/h0025http://refhub.elsevier.com/S1386-1425(14)00953-6/h0020http://refhub.elsevier.com/S1386-1425(14)00953-6/h0020http://refhub.elsevier.com/S1386-1425(14)00953-6/h0015http://refhub.elsevier.com/S1386-1425(14)00953-6/h0015http://refhub.elsevier.com/S1386-1425(14)00953-6/h0010http://refhub.elsevier.com/S1386-1425(14)00953-6/h0010http://refhub.elsevier.com/S1386-1425(14)00953-6/h0005

mekanisme bilayer

Documents