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Physics Procedia 00 (2008) 000–000

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Proceedings of the JMSM 2008 Conference

Physicochemical characterization of organophilic clay

A. EL Messabeb-Ouali a*, M. Benna-Zayania, N. Kbir-Ariguiba, M. Trabelsi-Ayadia

aLaboratoire d’Applications de la Chimie aux Ressources et Substances Naturelles et à l’Environnement,Faculté des sciences de Bizerte, 7021 Zarzouna, Bizerte, Tunisia.

Elsevier use only: Received date here; revised date here; accepted date here

Abstract

Organophilic smectite were obtained by intercalation of hexadecyltrimethyl ammonium bromide (HDTMA) in the interlayerspace of a purified Tunisian sodic-smectite. The HDTMA amounts were varied from 0.5 to 3 times the cation exchange capacity(CEC) of the purified clay. Adsorption isotherm shows a total adsorption of HDTMA by purified smectite when the quantity ofsalt is less or equal to 2 CEC. Beyond this value, adsorption becomes limited and tends to saturation. All organoclays werecharacterized by X-ray diffraction which shows an increase of the basal distance. Infrared spectroscopy and differential thermicand thermogravimetric analysis results confirm the intercalation HDTMA.© 2009 Elsevier B.V. All rights reserved

PACS: Type pacs here, separated by semicolons ;

Keywords: Smectite, cation exchange capacity, HDTMA, intercalation, organophilic clay.

1-Introduction

Smectite is a kind of 2:1 type layered clay mineral. He Hongping et al. [1] indicate that smectite had been widelyused in various branches of industry due to their high cation exchange capacity, swelling ability and high surfacearea. Lagaly and Weiss [2] show that the adsorption of organic molecules on clay minerals has been studiedextensively. Then [3] discovered that alkylammonium-clay derivatives are mostly prepared by stoechiometricallyexchange of interlayer cations in 2:1clays. Lee and Kim [4] showed that in intercalated phyllosilicates with straight-chains alkylammonium, the organic cations are arranged with monolayer, bilayer, pseudolayer, or paraffine typeconfigurations. The results of Lee et al. [5] show that the configuration observed depends on the carbon chainslength of alkyl ammonium cation (nc) and on the layer charge of the clay mineral.Characteristic basal spacing,respectively of 13.6; 17.6; and 22 � distinguish the monolayer, bilayer and pseudolayer configurations, whereasbasal spacing for samples with paraffin type configurations increase linearly with nc. Jaynes and Boyd [6] and Leeand Kim [7] indicate that smectite surfaces have a high selectivity for organic cations such as HDTMA cations;adsorption can proceed beyond the cation exchange capacity (CEC) of the clay mineral .Thus Andini et al [8] provethat smectite can be effectively employed as adsorbents of many waste water pollutants. Khan et al. [9] and Tiller[10] point out that in adsorption processes, raw smectite acts as an inorganic stationary phase and able to effectively

* Corresponding author. Tel.: (+216) 97 532 272; Fax: (+216) 72 590 566E-mail address: mesoua@yahoo.fr; amel.el.messabeb@umontreal.ca

Received 1 January 2009; received in revised form 31 July 2009; accepted 31 August 2009

Physics Procedia 2 (2009) 1031–1037

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doi:10.1016/j.phpro.2009.11.059

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adsorb heavy metal ions. However results of Jordan[11] ,[12] discovered that nature of smectite can be easily turnedto organophilic as the group IA and IIA loosely bound metal ions (Li+,Na+, K+,Mg2+ ,Ca2+ and Ba2+) presentbetween alumina and silica layers can be readily exchanged with quaternary ammonium, ion such as [R4N]+. Themetal ions expulsion with coordinated water molecules strongly reduces the hydrophilicity of the clay. Andini et al.[13] showed that if at least one of the nitrogen constituents is a long aliphatic chain, the interlayer space increasesand the adsorption ion capacity increase ever more. In addition, favourable interactions can arise with the R groupsof the quaternary ammonium ions. Organic molecules can be more easily attracted into the expanded interlayerspace of the clay. In this case a number of Van Der Waals interactions and chemical bounds can occur.

Moreover Lee et al. [14] discovered that in some other cases mixed organics\heavy metals pollution occurs,especially in sediments. When this happens some of them concerns arise on the effectiveness of quaternaryammonium salt-smectite in waste pollution.

2. Materials and methods

The smectite used in this work is from the southern west of Tunisia and particularly from Oued El Bagra near thetown of Gafsa. It is noted OBb.

El Messabeb et al. [15] indicate that raw smectite contains some quartz, gypsum and calcite as impurities. It waspurified with a sodium chloride solution to obtain a Na-exchanged smectite (OBp) because the organic cationsstrongly preferred in the exchange sites relative to Na+ ions. Hence the clay was saturated with Na+ cations bywashing repeatedly the clay with NaCl solution .This step was performed by shaking 4g of clay with 120 cm3 of a1M NaCl solution, then centrifuging the suspensions. This process was repeated seven times .The Na saturatedsmectite was then washed many times with distilled water .This cleaning is stopped when the AgNO3 test forchloride ions was negative. After that the purified clay was dried at 60°C. After drying the clay was crushed andsheaved at 80�m. The chemical composition of OBp is given in table1 and its cation exchange capacity (CEC) wasdetermined by the methylene blue method and is equal to 73.84 meq/100g of calcined OBp.

HDTMA bromide of 99% purity was purchased from Panreac Synthesis and used as received without anytreatment.

Organoclays were prepared by dispersing 5 g of OBp in 300 mL of HDTMA in aqueous solution at a desiredconcentration. Different HDTMA concentrations were used, expressed in term of CEC and are given in table 2. Thedispersion shacked during 12 hours then centrifuged at 9000 tr.mn-1 during 30 mn.

The organoclays were washed with distilled water at 60°C and centrifuged at 9000tr.mn-1 during 30 mn in orderto eliminate the non adsorbed HDTMA cations .The supernatants of each organoclay were mixed and analyzed byU.V spectrophotometry at the wave length of 385 nm. The apparatus is a Perkin Elmer 306. Organoclays have beencharacterized by XRD, IR spectroscopy and ATD-ATG. For X-ray diffraction the diffractometer is a Siemens D8000 with a turning anode and analysis were performed by Kα1 copper radiation 1,5405 Å and alimented by agenerator of 40 kV with an intensity of 20 mA. The IR spectrometer is a spectrometer Fourier type Perkin Elmer1000. For thermal analysis apparatuses is setaram 92 witch carrier argon gas and heating speed is 10°C min-1.

3. Results and discussion

Table1. Chemical composition of the purified smectite (OBp),�w/w

LOIa SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O TiO2 TO

22.08 60.84 18.01 8.67 5.90 2.65 0.52 0.93 0.71 98.20a Loss on ignition at 1000°C

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Table 2. Number of moles HDTMA adsorbed by Na- smectite OBp

mmol initial 1.477 2.954 4 .431 5.908 7.385 8.862

initial (CEC) 0.5 1 1.5 2 2.5 3

mmol adsorbed 1.446 2.913 4.398 5.873 6.897 7.266

Adsorbed(CEC) 0.49 0.98 1.48 1.98 2.33 2.46

It is well known that organic cations replace inorganic ions in smectites. The same results were obtained for theOBp smectite with the quaternary alkylammonium cations. The adsorption isotherm of HDTMA-bromide on OBpclay is showed in figure 1.

Fig.1. Adsorption isotherm of HDTMA by Na-smectite OBp

Results show that the HDTMA is adsorbed on Na-smectite OBp until the maximum investigated value of 2.46time of CEC. Moreover, the HDTMA adsorption is total for amount of HDTMA less or equal to 2 CEC. After thisvalue, adsorption becomes partial and the phenomenon tends to the saturation.

The XRD patterns of organoclays prepared at surfactant / OBp ratios ranging from 0 to3.0 CEC and presented infigure 2 and 3, show the presence of (001) reflections with basal spacing of smectite, respectively, about 13.93 and19.45 � for sodic smectite OBp and organoclay relative to 3CEC of HDTMA.

Fig.2. X ray patterns of Na- smectite OBp (0.5CEC) and HDTMA-smectite OBp

0CEC:Na-smectiteOBP

0.5 CEC

1CEC1.5CEC

2CEC2.5CEC3CEC

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4000

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0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

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Since 2 CEC of HDTMA, two new reflexions appeared in patterns at 9.7 and 12.6 �. The first reflexion can beattributed to the d(001) of smectite, and the second to the d(003) distance basal of the organophilic smectite. Indeed,Othmani et al. [16] showed that a basal distance d(001) of about 35-40A’ can be reached beyond 2CEC of thealkylammonium.

Fig.3. Variation of (001) reflexion

The FTIR spectra of Na-smectite OBp, HDTMA-smectite OBp given in figure 4 show that typical infraredbands of smectite due to OH stretching at 3435cm-1 and Si-O-Si bending at 1043 cm-1 OBp smectite shows also awide and intense band at 1042 and two weaker bands at 918 and 875 cm-1 .These bands are due to OH bending,respectively, Ca2+, Mg2+, Fe3+ hydratation water. The spectrum of HDTMA-smectite OBp results an exception ofthe bands at 1042, 917 and 872.6 cm-1 that become less intense. However it is the almost perfect superium positionof the seven previous traces ,meaning that the ion exchange of Na-smectite OBp with HDTMA takes place asexpected . Also, the FTIR results show that no new bonds are formed between HDTMA and OBp after intercalation.Vibrationnel spectroscopy has been extensively used for probing the conformation in amine chain assemblies.Farmer [17] and He Hong ping et al.[18] indicate that infrared spectroscopic studies lead to detailed correlation ofthe spectra with structural features such as chain conformation, chain packing, and even specific conformationalsequences. The position, line shape, and splitting of the methylene stretching and bending modes have been used todetermine the conformation of methylene units in various phases of n-alkanes. As shown for OBp, the intensities ofthe two intense adsorption bands at 2916 and 2849 cm-1, corresponding, respectively, to the antisymetric andsymmetric CH2 stretching modes of amine increase gradually with the packing density of amine chains as in thesmectite galleries.

5

7

9

11

13

15

17

19

0 0,5 1 1,5 2 2,5 3 3,5

Quantity of salt with Na-smectite OBp(CEC).

d (Å)

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Fig.4. FTIR spectra of Na- smectite OBp and HDTMA-smectite OBp (0.5-1-1.5-2-2.5-3CEC)

The frequencies of the CH2 stretching adsorption bands of amine chains are extremely sensitive of theconformational changes of the chains and only when the chains are highly ordered for all-trans conformation; thenarrow adsorption bands appear around 2916 cm-1 ,�as (CH2) and 2849 cm-1 ,�s (CH2), in the infrared spectrum. Thefrequency and band of antisymmetric and symmetric CH2 stretching modes of the confined amine strongly dependson the concentration of amine. In the high concentration range, the frequency of antisymmetric CH2 stretchingadsorption bands keeps relatively constant frequency of the pure amine .By means of this relatively highconcentration range, the confined amine chains adopt an essentially all-trans conformation. However, in therelatively low amine concentration range, the frequency shifts significantly to high wavenumber, indicating that alarge number of the gauche conformer is introduced in to the amine chain.

At the same time, we observed that 0.5 CEC, a shoulder occurs on the main adsorption band at 711 cm-1

corresponding to CH2 rocking mode .While the adsorption band at 1467 cm-1 corresponding to the CH2 scissoringmode, begins to split into two bands with similar intensity. With the further increase of surfactant concentration,especially for samples adopting parrafin-type bilayer, two well resolved adsorption bands, respectively, at 711 cm-1

and 1467 cm-1, are adsorbed, corresponding to the CH2 rocking and scissoring modes. These modes are split due tointerchain interaction between contiguous CH2 groups of adjoining chains.

TGA results of Na-smectite OBp and HDTMA- smectite OBp shown in figure5 present an interaction betweenthem. In these ATG patterns of HDTMA- smectite OBp superim posed present thermical accident temperaturewhich repaired by ATD.The thermical analyses permitted to confirmed organic cation intercalation clay. Indeedthermogrammes comparison of organoclays with smectite OBp show many thermical accidents. At the first, a waterhydratation departure produced, respectively, at 151 and 73°C with a weight loss of 10.51 and 4.33 % for Na-smectite OBp and HDTMA- smectite OBp; from 2 CEC .As far as this value, hydratation water loos can be constantpractically corresponding at interfoliair water which was imprisoned by ammonium salt in interfoliair spaces of Na-smectite OBp.

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Fig. 5. TGA thermograms of OBp (0CEC) and HDTMA- OBp for different amounts of HDTMA

At the second, a new thermical accident becomes visible between 268 and 300°C with a weight loss of 6.2 % forHDTMA-smectite OBp at 1times of CEC, but this loss becomes very important for clay more organophilic .ATGpatterns endothermic deshydratation of clay at 523.9°C for Na-smectite OBP ,transfer at 500°C for HDTMA-smectite OBp, proposed that departure of alkyls groupement with a long chains produced between 200 and500°C.This can be confirmed the thermical accident and loss of weight which observed, respectively, at 268-300°Cand at 433°C correspond at departure of organic matter. Bergaya [19] indicate that phenomenon is probably relativeat cations alkyls groupement which binds on easily accessible extern surface and boards .In deed at 0.5 CEC, all saltquantity was interferior into a CEC of Na-smectite OBp, so cation which adsorbed observed, situated in interfoliairspace. Hence any think can be observed between 268 and 300°C. Vaia [20] add that another endothermicphenomenon appear at 727-765°C correspond at loss of weight for 3 % of Na-smectite OBp and for 3.29-4.43 % forHDTMA-smectite OBp. This phenomenon reveal in one hand the calcite departure for Na-smectite OBp, in otherhand the organic carbon departure which stayed in organoclay.

4. Conclusion

The analyses concord to OBb, its principal impurity is calcite, gypsum and quartz. The intercalation ofammonium alkyl in OBp was happen .Adsorption isotherm reveal a practically total adsorption of HDTMA by Na-smectite OBp as far as equal at 2 times of CEC value ; further than 2 times of CEC, adsorption isotherm cease to belimited and the phenomenon stretch at saturation .

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�

OBP

0, 5 CEC1.5 CEC

2 CEC2.5 CEC3 CEC

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

0 100 200 300 400 500 600 700 800 900 1000 1100

Temperature (°C)

% lossof

weight

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