DSpace at VNU: Synthesis of organoclays and their application for the adsorption of phenolic compouds from aqueous solution

Journal of Industrial and Engineering Chemistry 19 (2013) 640–644

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Journal of Industrial and Engineering Chemistry
journal homepage: www.elsevier.com/locate/jiec

Synthesis of organoclays and their application for the adsorption of phenolic
compounds from aqueous solution
Van Noi Nguyen a, Thi Dieu Cam Nguyen b,*, Thanh Phuong Dao a, Hung Thuan Tran c,
Dinh Bang Nguyen a, Dae Hee Ahn d
a

Faculty of Chemistry, Hanoi University of Science, Vietnam National University, Hanoi, Viet Nam
Faculty of Chemistry, Quy Nhon University, Viet Nam
Advanced Materials Technology Center, National Center for Technological Progress, Hanoi, Viet Nam
d
Department of Environmental Engineering and Biotechnology, Myongji University, Republic of Korea
b
c

A R T I C L E I N F O

Article history:
Received 12 May 2012
Accepted 22 September 2012
Available online 28 September 2012
Keywords:
Organoclays
Quaternary ammonium salts
Organic

Sorption

A B S T R A C T

Organoclays were synthesized by exchanging inorganic cations between layers in Thanh Hoa bentonite
using organic cations including benzylhexadecyldimethylammonium (BHDDM+), dimethyldioctadecylammonium (DMDOD+) and benzylstearyldimethylammonium (BSDM+). Inserting organic cations
increases material interlayer distance significantly (from 15 A˚ to 40 A˚) and simultaneously enhances
affinity of materials toward organic pollutants. The results show that adsorption capacity of organics on
organoclays strongly depends on affinity between organic substances and ammonium cations rather
than on interlayer distance of organoclays. This means that the sorption of organoclays for organic
contaminants was significantly influenced by the nature of the surfactants added to the clay.
ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights
reserved.

1. Introduction
During recent decades, zeolite with microporous system has
been applied in many industrial processes, such as adsorptive
materials, oxidation catalysts. However, applications of zeolite are
limited, because small pore size (d < 1.5 nm) makes it hard for
transformation of complex and large molecules. Therefore, finding
new materials with larger pore system has been an interest of
many scientists [1,2]. The use of bentonite in wastewater
treatment has received increasing attention and currently offers
a very attractive method for pollution remediation. Besides it is
plentiful, inexpensive and available in many countries, bentonite is
known having layered structure and to be quite porous material. It
is widely used in a large number of many fields. In environmental
treatment, bentonite is often used as a natural adsorptive material
[3]. Bentonite is naturally capable of adsorbing organic substances;
however, the adsorption capacity is not high enough to be applied

in practice. Hence, it needs to be modified to enhance adsorption
capacity, and amine salts have been generally employed as costeffective reagents. Once hydrocarbon chain inserted into layers can
increase interlayer distance and hydrophobic property, leading to
higher affinity toward organic substances [4,5]. Organoclays,

* Corresponding author. Tel.: +84 98 322 2831.
E-mail address: (T.D.C. Nguyen).

prepared by intercalating clays with surfactant cations, have been
considered as potential sorbents for removing organic pollutants
from water [6–12]. Quaternary ammonium organoclays may be
divided into two groups depending on the structure of the organic
cation and the mechanism of sorption [13]. The first group, called
adsorptive organoclays, includes clays that contain short-chain
quaternary ammonium ions, such as tetramethylammonium or
trimethylbenzylammonium. Sorption on this type of organoclays
is characterized by Langmuir-type isotherms, which are commonly
associated with specific sorption sites. The second group of
organoclays, called organophilic organoclays, is composed of clays
that contain long-chain quaternary ammonium ions, such as
hexadecyltrimethylammonium or didodecyldimethylammonium.
Sorption by this group is also characterized by Langmuir or
Freundlich-type isotherms, but linear interval is over wider range
of solute concentrations.
In this work, bentonite from Thanh Hoa, Vietnam was modified
for the first time by different organic quaternary ammonium
cations, such as benzylhexadecyldimethylammonium, dimethyldioctadecylammonium and benzylstearyldimethylammonium to
adsorb phenolic compounds, including phenol, phenol red and
direct blue DB 53 (Table 1). These aromatic compounds are
common pollutants that can be found in different types of polluted

water as dye wastewater, wood manufacturing wastewater
[14,15]. It was shown that organoclays containing surfactants
with aromatic rings were better suited for removing toxic aromatic

1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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V.N. Nguyen et al. / Journal of Industrial and Engineering Chemistry 19 (2013) 640–644
Table 1
Surfactants and phenolic compounds used in this study.

641

Table 3
Effect of pH of bentonite suspension on d0 0 1 value of organoclays.

Compound

Formula

MW

BHDDM chloride
BSDM chloride
DMDOD chloride
Phenol
Phenol red (phenolsulfonphthalein)
DB 53 (direct blue 53)

CH3(CH2)15N(CH3)2CH2C6H5Cl

CH3(CH2)17N(CH3)2CH2C6H5Cl
[CH3(CH2)17]2N(CH3)2Cl
C6H5OH
C19H14O5S
C34H24N6Na4O14S4

381.5
409.5
585.50
94.11
354.38
960.80

organic compounds, such as phenolic compounds, from aqueous
solution [16,17].
2. Materials and methods

pH

d0 0 1 value of organoclay (A˚)
Bent-BHDDM

Bent-DMDOD

Bent-BSDM

6
7
8
9

10

34.87
35.69
34.87
35.07
34.87

38.89
39.53
38.82
40.57
38.55

37.00
37.23
36.50
37.81
37.93

To characterize adsorption of different phenolic compounds
using organoclays, the Langmuir adsorption isotherm was
employed. The linear form of Langmuir adsorption isotherm
equation is presented as follows:
Ce
Ce
1
¼
þ
q

qmax k Á qmax

2.1. Synthesis of organoclays
Bentonite from Thanh Hoa, Vietnam has undergone a
purification protocol composed of several stages: disintegration
to disperse the layers of clay and recovery of the fraction of clay
lower than 2 mm, and then saturated by sodium chloride
solution (0.1 mol/L). Thus the recovered bentonite known as
sodium bentonite was washed several times with distilled water
until free of chloride ions as indicated by AgNO3, and then dried
at ambient temperature. The surfactants used to modify the
bentonite are cationic surfactants, including benzylhexadecyldimethylammonium chloride (BHDDM chloride), benzylstearyldimethylammonium
chloride
(BSDM
chloride),
and
dimethyldioctadecylammonium bromide (DMDOD bromide)
provided by Sigma–Aldrich (Table 1). Organoclays were prepared
by insertion of the aforementioned quaternary ammonium salt
between the layers of the bentonite by a simple cationic
exchange. The effects of various parameters such as surfactant
dose, temperature, pH and reaction time on d0 0 1 value of
organoclays were investigated. All the samples were maintained
under constant agitation during 24 h, and washed several time
with distilled water until no chloride ions were detected by
AgNO3. Organoclays were recovered by centrifugation and dried
at 70 8C.
2.2. Adsorption experiments
All experiments were performed in batch with 0.1 g
ogranoclays and 100 ml of synthetic wastewater containing

from 50 to 1500 mg/L aqueous phenol compounds solution.
Phenol concentration was measured by spectrophotometric
method employing 4-aminoantipyrin as coloring agent, complex
formed has maximum absorption at 510 nm. Phenol red and DB
53 concentrations were determined through their absorption at
lmax of 432 nm and 622 nm, respectively [18].

where q is the adsorption capacity at certain time, qmax is the
maximum adsorption capacity, Ce is the concentration of adsorbate
at equilibrium, k is the Langmuir constant.
3. Results and discussion
3.1. Effects of synthesis parameters on engineered organoclays
properties
3.1.1. Effect of the nature and dose of quaternary ammonium salts
Interlayer distances of organoclay at different amount of
quaternary ammonium salts obtained from XRD patterns are
shown in Table 2. It is clear that interlayer distance of organoclay
depends on nature and amount of organic ammonium salts. BentDMDOD has larger distance than Bent-BSDM, and Bent-BHDDM
has the smallest value. In details, interlayer distances of BentBHDDM, Bent-BSDM, and Bent-DMDOD with 100% cation exchange capacity (CEC) organic ammonium salt are 27.01 A˚, 32.16 A˚
and 40.57 A˚, respectively. According to Lagaly and Hackett [19,20],
for organoclay with interlayer distance larger than 22.7 A˚, organic
cations lie between bentonite layers as pseudo-three layers. The
obtained results are higher than those in some other publications
[21–24].
From data in Table 2, it can be concluded that the optimal
ammonium salts dose to synthesize Bent-BHDDM, Bent-DMDOD
and Bent-BSDM are 125, 100 and 150% CEC, respectively.
3.1.2. Effect of pH
It is clear that when pH is in the range of 6–10, under optimal
doses of ammonium salts, interlayer distances of organoclays do

not vary significantly (Table 3). This observation agrees with
explanations of some authors that charge of quaternary ammonium cations in clay does not change with pH, and they are kept
between layers by electrostatic force [25].

Table 2
Effect of quaternary ammonium salt dose on d0 0 1 of organoclays.
Quaternary ammonium
salt dose (%CEC)
0
25
50
75
100
125
150
175
a

d0 0 1 value of organoclay (A˚)
Bent-BHDDM

Bent-DMDOD

Bent-BSDM

15.60a
18.48
21.88
23.80
27.01

35.59
–
–

15.60a
25.12
27.36
37.51
40.57
40.86
41.52
–

15.60a
19.05
21.32
23.82
32.16
35.59
37.05
37.01

The distance of natural bentonite.

Table 4
Effect of temperature on d0 0 1 of organoclays.
Temperature (8C)

d0 0 1 value (A˚)
Bent-BHDDM

Bent-DMDOD

Bent-BSDM

35
45
55
65
75
85

32.47
33.28
35.09
35.58
33.89
32.97

39.39
39.12
40.57
39.76
38.97
38.26

35.17
34.97
37.80
37.20

37.00
36.89


V.N. Nguyen et al. / Journal of Industrial and Engineering Chemistry 19 (2013) 640–644

642
Table 5
Effect of reaction time on d0 0 1 value.
Time (h)

d0 0 1 (A˚)
Bent-BHDDM

Bent-DMDOD

Bent-BSDM

2
3
4
5
6

33.89
33.34
35.59
34.30
32.76

38.65
39.22
39.52
39.39
39.36

36.60
37.23
37.93
37.40
34.51

From results in Table 2, the pH of 9 was chosen for the synthesis
of Bent-BHDDM and Bent-DMDOD, while the pH of 10 was chosen
for the synthesis of Bent-BSDM.
3.1.3. Effect of temperature
It can be seen from Table 4 that interlayer distance of three
studied organoclays, under optimal doses of ammonium salts, does
not depend significantly on temperature.
From the data in Table 4 the temperature of 65 8C was chosen
for synthesizing Bent-BHDDM, and the temperature of 55 8C was
chosen for synthesizing Bent-DMDOD and Bent-BSDM.

3.1.4. Effect of reaction time
Although exchange reaction is quite fast (about 40–120 min), in
order for cations to be stable between clay layers, reaction solution
should be kept in longer time, the optimal reaction time to
synthesize Bent-BHDDM, Bent-DMDOD and Bent-BSDM are 4 h
(Table 5).
To prove that quaternary ammonium cations were successfully

immobilized on bentonite layers in organoclays, samples synthesized at optimal conditions were characterized by IR spectroscopy
(Figs. 1–3).
It can be seen that in IR spectra of Bent-BHDDM, BentDMDOD and Bent-BSDM, there are peaks characterized for (i) –
CH3 and –CH2– stretching modes at 2850 cmÀ1 and 2920 cmÀ1,
and (ii) C–N stretching of organic ammonium cations at
1467 cmÀ1. Results obtained from IR spectra agree with reports
of other authors [26,27]. There are also peaks characterized for
bentonite, such as peaks of Si–O vibration in SiO4 tetrahedron at
420–470 cmÀ1; peaks of Al–O vibration in octahedron at
815 cmÀ1. The presence of OH groups in the water absorbed
is proved by the appearance of peaks at 3400–3600 cmÀ1.
However, the peak intensity in the IR spectra of organoclays is
lower than that in bentonite’s IR spectrum, and these results

Fig. 1. IR spectra of bentonite and Bent-BHDDM.

Fig. 2. IR spectrum of Bent-BSDM.


V.N. Nguyen et al. / Journal of Industrial and Engineering Chemistry 19 (2013) 640–644

643

Fig. 3. IR spectrum of Bent-DMDOD.

In organoclays, N atoms are held on bentonite surface through
attractive electrostatic force with negative-charged bentonite
surface, and alkyl tails (RR1R2R3)N+ orient toward inside pores.
These alkyl tails can act as liquefied organic solvent, and they have
affinity toward organic substances [28,29]. Phenols adsorption

takes place on organophilic centers of organoclays.
Experiment data were obtained at temperature 30 Æ 1 8C, and
the pH values of phenol, phenol red, and DB 53 solutions were 6, 5 and
2, respectively. Straight lines were obtained by plotting Ce/q against Ce
for the adsorption of phenolic compounds onto organocalys as shown
in Figs. 4–6. The values of qmax and k calculated from the slopes and
intercepts of the Langmuir plots and r-square are reported in Table 6.
Results in Table 6 show that adsorption of phenolic compounds
on Bent-BHDDM, Bent-BSDM and Bent-DMDOD fits well with
Langmuir isotherm model. Maximum adsorption capacity values
obtained from this model indicate that the organoclays are capable
of adsorbing phenols in aqueous solution. Ability to adsorb phenol

red and DB 53 (substances with aromatic rings) of Bent-DMDOD is
much lower than those of Bent-BHDDM and Bent-BSDM. This
shows that adsorption capacity strongly depends on affinity
between organic substances and ammonium cations rather than
on interlayer distance. Although Bent-DMDOD possesses largest
interlayer distance (39.22 A˚) but its adsorption capacity is lower
than Bent-BHDDM (33.34 A˚) and Bent-BSDM (37.41 A˚). It can be
explained through the fact that for Bent-BHDDM and Bent-BSDM
the ammonium cations containing aromatic rings were employed,
these two materials attract phenols more than Bent-DMDOD,
which does not contain aromatic rings. On the other hand, for
phenolic compounds with less aromatic rings (phenol), adsorption
capacity does not depend much on nature of organic ammonium
cation.
Phenol, phenol red and DB 53 molecules have smaller size than
interlayer distances of organoclays. It means that these molecules
can diffuse into pore system of organoclays. Organoclays adsorb

molecules with small size stronger than those with bulk structure.
This can be explained by the fact that DB 53 and phenol red
molecules have large size, they could hinder a part of adsorption
centers of organoclays, prevent other molecules to get to
adsorption centers, resulting in a lower adsorption capacity.

Fig. 4. Langmuir adsorption isotherm of phenolic compounds on Bent-BHDDM.

Fig. 5. Langmuir adsorption isotherm of phenolic compounds on Bent-BSDM.

show that organophilic property of organoclays is higher than
that of bentonite.
3.2. Adsorption of phenolic compounds on organoclays


V.N. Nguyen et al. / Journal of Industrial and Engineering Chemistry 19 (2013) 640–644

644

Modified bentonites possess higher organophilic property. Phenol,
phenol red, and DB 53 were found to be adsorbed strongly on
organoclays comprising alternating organic and inorganic layers.
Adsorption behavior of the three adsorbate–adsorbent systems
was described well by Langmuir isotherm model. Langmuir
maximum adsorption capacities of Bent-BHDDM, Bent-BSDM
and Bent-DMDOD on phenol, phenol red and DB 53 are quite
high. From this study, it can be concluded that the natural
bentonite source in Vietnam would be used as precursor materials
to synthesize potential adsorbents for treating phenolic compounds in wastewater.
Acknowledgement

Fig. 6. Langmuir adsorption isotherm of phenolic compounds on Bent-DMDOD.

Table 6
Langmuir isotherm constants for adsorption of phenolic compounds.

This project is supported by Vietnam National Foundation for
Science and Technology Development, project number 104.99.
153.09.
References

Compound

qmax (mmol/g)

k (L mmolÀ1)

r-squared

Bent-BHDDM
Phenol
Phenol red
DB 53

0.92
0.54
0.50

0.20 Â 10À2
3.06 Â 10À2
2.93 Â 10À2

0.99
0.99
0.99

Bent-BSDM
Phenol
Phenol red
DB 53

0.70
0.67
0.49

0.89 Â 10À2
1.85 Â 10À2
3.28 Â 10À2

0.98
0.98
0.98

Bent-DMDOD
Phenol
Phenol red
DB 53

0.64
0.303
0.335

0.69 Â 10À2
1.43 Â 10À2
0.28 Â 10À2

0.98
0.98
0.98

3.3. Discussion on adsorption mechanism
From literature and experimental data, it can be suggested that
when modifying bentonite using quaternary ammonium cations,
these cations are kept between bentonite layers, replacing Na+
cations in original bentonite. Then, these organic cations exist in
‘‘liquid form’’ [30] and they have affinity toward organic
substances. It can be observed that increasing pH leads to a
decrease in adsorption capacity of phenolic compounds. At high pH
phenols exist in ion forms, hence they are more polar. Attractive
force between quaternary ammonium cations and polar molecules
is weaker than that between these cations and non-polar
molecules. This again verifies the idea of ‘‘liquid form’’ above.
4. Conclusions
Thanh Hoa bentonite was successfully modified by three
different ammonium salts: benzyl hexadecyl dimethyl ammonium
chloride, benzyl stearyl dimethyl ammonium chloride and
dimethyl dioctadecyl ammonium bromide by wet method.

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