Proceedings of International Forum for Green Asia 2019
5th International Exchange and Innovation Conference on Engineering & Sciences (IEICES 2019)

GA06 / P18
Investigation of imidazole bearing surfactant modified montmorillonite
for the adsorption of perchlorate
Li Zhang, Srinivasarao Kancharla, Keiko Sasaki
Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan
Email: keikos@mine.kyushu-u.ac.jp
Abstract: Insoluble gemini surfactants 1,3-(3-alkyl imidzolium) xylene dichloride ((CxIm)2Xy·2Cl) with different alkyl
chain length as the hydrophobic “tail” of surfactants was used to modify montmorillonite (Mt) and the obtained
nanocomposite was applied for removal of perchlorate in aqueous solutions. The (CxIm)2Xy-Mt nanocomposites withdifferent length of the alkyl chain were characterized by XRD, FTIR, CHN analysis, SEM and TEM observation. These
were supplied for batch adsorption experiments to obtain kinetic model and adsorption isotherm. Based on the XRD
patterns, the molecular configuration of the surfactants in interlayer of Mt was illustrated. Kinetic data was fit to pseudosecond-order model and adsorption isotherm was well fit to Langmuir model, indicating that the adsorption mechanism
is dominated by ion-exchange. No organic release of the modified nanocomposites during adsorption of perchlorate wasobserved, indicating that the highly chemical stability of (CxIm)2Xy-Mt nanocomposites is caused by the double positive
charged sites on one (CxIm)2Xy·2Cl gemini surfactant to interact with Mt surfaces.
Keywords: Imidazole, Gemini surfactant, Modifier release
1. INTRODUCTION
The toxicity of perchlorate (ClO4-) has been recognizedin the public water system. The main health concern
regarding perchlorate is that it interferes with iodide
uptake in the thyroid gland. However, it is difficult toimmobilize perchlorate compare with other anionicspecies, due to its large ionic size and small charge.
Destruction technologies for the treatment of large
hazardous anions need the assistance of catalysts,electricity, etc. The microbial reduction is limited by theenvironmental conditions pathology concern. Adsorption
was extensively studied and applied to anion remediation.
Compare to activated carbon, resin or membrane,
modified montmorillonite is a more cost-effective
material in water treatment.
Montmorillonite (Mt) is one of the most abundant clay
minerals in nature. The isomorphic substitutions (e.g.,Al3+ replaced by Mg2+ or Fe2+ in the octahedral sheet andSi4+ replaced by Al3+ in the tetrahedral sheet) creates
permanent negative charge which is balanced byintroducing exchangeable cations such as Na+, K+, andCa2+ in the interlayer. These interlayer cations could besubstituted by quaternary ammonium compounds (QACs)
to expand the interlayer space and create a hydrophobicenvironment. Both QACs anchored on Mt by static
electricity and hydrophobic interaction could be released
during the adsorption of perchlorate leading to the second
contamination to treated water [1].
In this study, Insoluble gemini surfactants 1,3-(3-alkyl
imidzolium) xylene dichloride ((CxIm)2Xy·2Cl) withdifferent alkyl chain length as the hydrophobic “tail” ofsurfactants was used to modify montmorillonite bymixing montmorillonite and (CxIm)2Xy·2Cl gemini
surfactant in methanol at 60℃. Differently fromconventional cationic surfactants, the double positive
charged sites on one (CxIm)2Xy·2Cl gemini surfactant
anchored on montmorillonite can be expected to stabilize
functional groups for perchlorate. X-ray diffraction(XRD), and Fourier transform infrared spectroscopy(FTIR) were used to interpret structural changes ofPVBMeIm-Mt nanocomposites depending on theamounts of PVBMeImCl added. The corresponding
maximum adsorption capacities of perchlorate wereevaluated using adsorption isotherms and the adsorption
kinetics was evaluated.
2. EXPERIMENTAL(CxIm)2Xy-Mt were synthesized by mixing 1 CEC of(CxIm)2Xy·2Cl with Mt in methanol at 60℃, and thesolid residue was lyophilized, ground and sieved. Theloading amount of (CxIm)2Xy·2Cl was calculated fromCHN analysis and TG-DTA. The configuration of(CxIm)2Xy·2Cl in the interlayer of Mt was characterized
by XRD and FTIR. Adsorption isotherms wereconducted in 0.001 mM to 0.3 mM ClO4- solution.
Kinetics, and influence of pH and co-ion tests wereoperated with 0.2 mM ClO4-. The concentration of coions was fifty times higher. ClO4- and released Cl- weredetermined by IC. The amount of adsorbed ClO4- (Qe)and released Cl- on materials was calculated by massbalance.
3. RESULTS AND DISCUSSION
3.1 Characterization of modified montmorillonites
TG-DTA and CHN analysis were utilized to calculate theloading amount of the gemini surfactants on thenanocomposites (Table. 1). It can be indicated that theloading of (CxIm)2Xy·2Cl gemini surfactant will increaseas the chain length of the alkyl chain increase. Based on
previous researches [2], this is because the improvedhydrophobicity of the modifier promoted the loading
processes. FTIR result indicated the successfulintercalation of the modifier onto the Mt. the adsorption
peak of perchlorate after adsorption experiment is locatedaround 1200 cm-1. The XRD pattern for (CxIm)2Xy-Mt
nanocomposites showed two predominant peaks in thosewith modifier having alkyl chain length more than 16
carbons, the others showed single peak. Since the initial
stoichiometric adding amount of the modifier were equalwith any chain length, we can clearly predict how thechain length of the (CxIm)2Xy·2Cl gemini surfactant
influence the loading behavior of itself. Both the peaks at- 15 -Where 𝐾ST (mol2/J2) is a DR constant and ε (J/mol) isa Polanyi potential, which is related to Ce by thefollowing equation:
ε = 𝑅𝑇 ln (1 + 1⁄𝐶D )(8)
The adsorption data was best fit to Langmuir model. TheLangmuir model assumes that the adsorption sites aredistributed homogeneously and adsorption takes place atthe specific surface. As expected, the ion-exchange ofperchlorate with chloride is the dominant mechanism ofadsorption. The highest adsorption capacity achieved on(C20Im)2Xy-Mt with the highest loading which wascalculated by CHN analysis. The empirical Freundlich
equation is applicable to the heterogeneous adsorption
with multilayer of adsorbates is generated during
adsorption, this model didn’t fit the isotherms well. The
D-R modeling is also related to the heterogeneousadsorption and is generally applied to distinguishphysical adsorption from chemical adsorption by themean free energy 𝐸 (kJ/mol) expressed in (Eq. 9)
𝐸 = (2𝐾ST )KE/0(9)The 𝐸 values of the materials are in the range of 8-16
kJ/mol that is correspondent to ion exchange. The valueof the correlation coefficient for the D-R model werehigher than 0.96, therefore, the mean free energy 𝐸 could
be taken as a reliable coefficient.

the lower angle in (C18Im)2Xy-Mt and (C20Im)2Xy-Mt
are assigned as pseudo-trilayer pillaring configuration.
As is illustrated in Fig. 1, two gemini surfactants
overlapped together to expand the interlayer space of theMt. because there are three layers of alkyl chains in thisconfiguration, therefore, the definition of thisconfiguration is made to continue with previous
researches. Besides this configuration, the sufficient
expanded space provided enough space for the formationof other configurations, for instance, a paraffin-like
configuration but with twisted alkyl chain. In general, thepseudo-trilayer configuration is the dominantconfiguration in such case and is directly responsible forthe pillaring of the Mt layer. The peaks at higher angle in(C18Im)2Xy-Mt and (C20Im)2Xy-Mt are ascribed aslateral monolayer configuration. As is shown in Fig. 1,
one layer of (CxIm)2Xy-Mt lie in parallel with Mt layers.
The only configuration in (C16Im)2Xy-Mt wasdetermined as pseudo-trilayer configuration as describedin (C18Im)2Xy-Mt and (C20Im)2Xy-Mt nanocomposites.
however, the only configuration in the (CxIm)2Xy-Mt
nanocomposites with shorter chain length are ascribed aslateral bilayer pillaring configuration (Fig. 1). Same as
pseudo-trilayer pillaring configuration, the sufficientinterlayer spaces due to the pillaring of this lateral bilayer
configuration supported adequate possibility for theformation of other configurations but this lateral bilayer
configuration is the predominant configuration.
3.2 Adsorption kinetics and isotherms
The adsorption kinetics of perchlorate onto (CxIm)2XyMt nanocomposites could approximately reach to theequilibrium within 2 hours. Adsorption data was tried to
fit to pseudo-second-order model and pseudo-first-ordermodels. The equations are described as follows:(2)
Pseudo-second-order: 𝑑𝑄t⁄𝑑𝑡 = 𝑘1(𝑄e − 𝑄t)(3)
Pseudo-first-order: 𝑑𝑄t⁄𝑑𝑡 = 𝑘2(𝑄e − 𝑄t)0
Where 𝑄e (mmol/g) is the adsorbed perchlorate at
equilibrium and 𝑄t (mmol/g) is the adsorbed perchlorate
at time 𝑡 (min). The parameters 𝑘1 (min−1) and 𝑘2(g·mmol−1·min−1) are the rate constant of pseudo-firstorder model and pseudo-second-order model. The initialsorption rate ℎ (mmol.g-1.min-1) of pseudo-second-ordermodel could be calculated by the equation: ℎ = 𝑘2𝑄e0.
The correlation coefficient for the pseudo-second-ordermodels are larger than 0.99, in comparison, thecorrelation coefficient for the pseudo-first-order models
are relatively lower. Pseudo-second-order model cancorrectly predict the kinetics. This model can be applied
to reaction with limited reaction sites which is in good
agreement with the assumed ion-exchange mechanism.
Adsorption data of perchlorate on the (CxIm)2Xy-Mt
nanocomposites were fit to Langmuir, Freundlich andDubinin-Radushkevich (D-R) models were used:(5)
Langmuir: 𝑄e = 𝑄m𝑏𝐶e ⁄ (1 + 𝑏𝐶e)
Freundlich: 𝑄e = 𝐾C 𝐶D E/G(6)
Where 𝑄e (mmol/g) is the adsorbed perchlorate atequilibrium and 𝐶e (mmol/L) is the equilibrium
concentration of perchlorate (mM). 𝑄m (mmol/g) is themaximum adsorption capacity, b (L/mmol) is theLangmuir constant relating to adsorption intensity. 𝐾C((mmol/g) (L/mmol)), is the Freundlich constant and 1/n
is a dimensionless exponent.
PD-R: 𝑄e = 𝑄I 𝑒 KLMNO(7)Fig. 1. Illustration of the intercalation modes of(CxIm)2Xy-Mt.
Table 1. Calculation of surfactant loading
Adding
Surfactant loading2
ChainH2O1
meq/g
length(wt. %) (mmol/g) mmol/g
101214
161820
12

2.104
2.068
3.120
2.156
2.828
2.990

0.726
0.695
0.663
0.644
0.618
0.596

0.441
0.449
0.398
0.502
0.557
0.624

0.882
0.898
0.795
1.004
1.114
1.248

Estimated from TG curves. Weight loss at 150℃.
Estimated by mass balance based on CHN analysis.

4. REFERENCES[1] W. Luo, T. Hirajima, and K. Sasaki, Optimization ofhexadecylpyridinium-modified montmorillonite forremoval of perchlorate based on adsorption
mechanisms, Appl. Clay Sci., 123, (Apr. 2016) 29–36.
[2] W. Luo, K. Sasaki, and T. Hirajima, Effect of
surfactant molecular structure on perchlorate removal
by various organo-montmorillonites, Appl. Clay Sci.,
114, (2015) 212–220- 16 -