meriem bendjelloul, el hadj elandaloussi, louis-charles de...
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1 © 2017 The Authors Journal of Water Reuse and Desalination | in press | 2017
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Quaternized triethanolamine-sebacoyl moieties in highly
branched polymer architecture as a host for the
entrapment of acid dyes in aqueous solutions
Meriem Bendjelloul, El Hadj Elandaloussi, Louis-Charles de Ménorval
and Abdelhadi Bentouami
ABSTRACT
This paper reports the synthesis of a hyperbranched polymer by a cost-effective one-step
copolymerization of A3 and B2 monomers, namely, triethanolamine and sebacoyl chloride,
respectively, followed by methylation of tertiary amine groups. The structure of the hyperbranched
polymer QTEAS as an efficient material for the removal of acid dyes was demonstrated by Fourier
transform infrared spectroscopy (FTIR), cross polarization magic angle spinning (CPMAS) 13C NMR,
thermogravimetric analysis, powder X-ray diffraction (DRX) and scanning electron microscopy (SEM).
The removal of indigo carmine (IC) and Evans blue (EB) was expected to be driven by the electrostatic
attraction between positively charged quaternary ammonium groups within the hyperbranched
polymer and the negatively charged dyes. The removal process was found to be closely connected to
the total number of sulfonate groups on the surface of the dyes. Nonetheless, the ionic strength does
not affect the dyes’ removal efficiency by the hyperbranched polymer. The sorption capacities at
saturation of the monolayer qmax were determined to be 213.22 mg g�1 and 214.13 mg g�1, for IC and
EB, respectively, thus showing the greater affinity of QTEAS sorbent for both dyes. Despite its extended
molecular structure, EB is removed with the same effectiveness as IC. Finally, the great efficiency of
the highly branched polymer for dye removal from colored wastewater was clearly demonstrated.
This is an Open Access article distributed under the terms of the Creative
Commons Attribution Licence (CC BY 4.0), which permits copying,
adaptation and redistribution, provided the original work is properly cited
(http://creativecommons.org/licenses/by/4.0/).
doi: 10.2166/wrd.2016.191
Meriem BendjelloulEl Hadj Elandaloussi (corresponding author)Abdelhadi BentouamiEquipe Matériaux Polymériques, Laboratoire de
Valorisation des Matériaux,Université Abdelhamid Ibn Badis,B.P. 227,27000 Mostaganem,AlgeriaE-mail: [email protected]
Louis-Charles de MénorvalICG–AIME–UMR 5253, Université Montpellier 2,
Place Eugène Bataillon CC 1502,34095 Montpellier Cedex 05,France
Key words | Evans blue, hyperbranched polymer, indigo carmine, ion exchange, regeneration,
removal of dyes
INTRODUCTION
Wastewaters originating from the textile industry are pol-
luted, as they contain residual color and other chemical
substances (O’Neill et al. ). The non-biodegradable
nature of the residual dye in the wastewaters may also
obstruct light penetration, thus inhibiting aquatic life in
the ecosystem (Walsh et al. ; Kuo ; Forgacs
et al. ; Rai et al. ). In addition, many dyes are
toxic and even carcinogenic and pose a serious threat to
various microbiological or animal species (Willcock
et al. ).
Apart from adsorption using low-cost adsorbents deriving
from renewable resources or less expensive natural materials
(Bouzaida & Rammah ; Aygun et al. ; Nakamura
et al. ; Prado et al. ; Ozacar & Sengil ; Ferrero
; Amin ), numerous methods such as biological (Aba-
dulla et al. ), electrochemical (Fernandez-Sanchez &
Costa-Garcia ), photochemical (Hachem et al. ;
Barka et al. ; Tahiri Alaoui et al. ; Benalioua et al.
), and membrane filtration (Ma et al. ) technologies
have been successfully employed for the removal of dyes
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from wastewaters. Recently, several studies have shown the
effectiveness of dendritic nanomaterials for water treatment
due to their outstanding removal capacity, higher surface
area and large number of active sites for interactionwith pollu-
tants (Qu et al. ; Saeed et al. ; Zhou et al. ).
Dendrimers are a class of highly branched three-dimen-
sional polymers characterized by a compact shape that have
numerous reactive functional end groups and room between
branches for taking up guest molecules (Tomalia & Fréchet
). Dendrimers have been shown to be effective for dyeing
fibers. For instance, Burkinshaw et al. () used a dendrimer
containing primary amino groups for the pretreatment of
cotton in order to enhance the color strength of the fiber
with reactive dyes. Polyamidoamine dendrimers have also
been reported as promising candidates for different appli-
cations including water purification (Diallo et al. ; Xu &
Zhao ). Extraction and encapsulation of dyes by dendri-
mers have been reported by several authors. At sufficiently
low pH, dendrimers containing tertiary amine groups are
able to give an acid–base interaction with acid dyes. The pro-
cess is totally reversible since at alkaline pH, the number of
positively charged sites on the surface of the dendrimer
decreases, thus favoring the dyes’ release. In this regard,
Baars et al. () investigated poly(propylene imine) dendri-
mers for the extraction of an acid dye from water by amine
groups in an apolar solvent. The same principle of dye encapsu-
lation has been applied byCooper et al. () for the extraction
of an acid dye by a modified dendrimer in liquid CO2.
One of the major factors that influences the perform-
ance of polymeric sorbents is the nature of the functional
groups available on their surface for interactions with con-
taminants. These functional groups determine the removal
capacity, stability, and reusability of the sorbent material.
According to the literature (Wawrzkiewicz & Hubicki
a, b, c), the use of commercially available
anion-exchanger resins to remove acid dyes from water
has been thoroughly investigated. These resins showed
high potential for adsorption of anionic dyes and excellent
adsorption capacity due to their high content of positively
charged functional groups. Moreover, complete regener-
ation without loss of their sorption capacity can be
achieved in alkaline media (Karcher et al. , ).
The current study was set to prepare a hyperbranched
polymer as an efficient material for solid–liquid extraction of
acid dyes. The hyperbranched polymer QTEAS was
synthesized by a cost-effective one-step copolymerization of
multifunctional A3 and B2 monomers, namely, triethanol-
amine and sebacoyl chloride, followed by methylation of
amine groups. Quaternization of tertiary amine groups was
necessary to lead to a material with plenty of positively
charged sites on its surface, and this was also intended for
rightly avoiding pH adjustment in our sorption studies. Seba-
coyl monomer was chosen for its chain length (8 sp3
carbons) in order to get ample room between the branches
in the QTEAS hyperbranched material, thus facilitating the
encapsulation of guest molecules. Although its structure is
not as perfect as that of dendrimers, QTEAS will still have
many similar characteristics and properties of dendrimers,
such as the three-dimensional globular architecture and abun-
dant quaternary amine groups required for the removal of
targeted dyes by electrostatic interactions. Two negatively
charged dyes were chosen for the study: indigo carmine (IC),
a divalent anion that is a real concern in textile wastewaters
and a diazo dye with extended molecular structure; Evans
blue (EB), a tetravalent anion (see Table 1). Furthermore, the
structure of the prepared macromolecule is demonstrated by
FTIR, cross polarization magic angle spinning (CPMAS) 13C
NMR, thermogravimetric analysis (TGA), powder x-ray dif-
fraction (DRX), and scanning electron microscopy (SEM).
Sorption kinetics, isotherms, effect of pH, ionic strength, and
effect of temperature have been investigated to identify a sorp-
tionmechanism of the dyes.Moreover, the datawere analyzed
using different well-known adsorption isotherms and kinetics
models. The high performance of the QTEAS material after
regeneration cycles has been carefully examined to ascertain
its stability and reusability. Finally, the great efficiency of the
hyperbranched polymer for dye removal from colored waste-
water was clearly demonstrated.
EXPERIMENTAL
Preparation of QTEAS material
All chemicals were analytical reagent grade and were used
without further purification. The procedure for the
preparation of hyperbranched QTEAS from A3 and B2
monomers (2:3 molar ratio) is depicted in Figure 1. Trietha-
nolamine (5.60 g, 37.50 mmol) in a 500 mL solution of
toluene/pyridine (V/V) was placed into a 1 L three-neck
Figure 1 | Synthesis of ideal QTEAS hyperbranched polymer from A3 and B2 monomers.
Table 1 | Molecular structures of targeted dyes
Dyes Molecular structureMW (gmol–1)
λmax
(nm)Charges onsurface
Indigocarmine(IC)
466.35 610 2
Evans blue(EB)
960.81 610 4
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flask equipped with a condenser and a mechanical stirrer.
This solution was kept at 0 WC, and neat sebacoyl chloride
(12 mL, 56.25 mmol) was slowly added. During the whole
addition (30 min), the reaction temperature was kept at
0 WC and was then allowed to gradually rise to 10 WC. After
stirring at 10 WC for 2 h, a dark brown chunk was formed
and stuck to the stirring rod, allowing no further efficient
stirring. Then, excess iodomethane (20 mL) was added and
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the reaction mixture was heated to 40 WC for 2 h. The solid
was collected by suction filtration and abundantly washed
with hot water then with acetone. The product was further
Soxhlet extracted with acetone for 2 days and finally dried
in an electric drying oven at 100 WC for 24 h. The material
was sieved to a particle size of 250 μm to produce 12.76 g
of QTEAS as a dark brown solid.
Characterization
An infrared spectrumwas obtained on a (2.5wt%) sample in a
KBr disk from 400 to 4,000 cm�1 using a Nicolet Avatar 330
Fourier transform IR spectrometer. The CPMAS 13C NMR
spectrum of QTEAS was recorded on a Bruker 300 (Digital
NMR Avance) spectrometer. X-ray diffraction (XRD)
patterns were recorded from 2θ¼ 3.5 to 70 W on a Phillips
X’Pert MPD diffractometer using monochromatic CuKα radi-
ation (λ¼ 1.5418 Å) at 40 kVand 30 mA. The thermal stability
of the samplewas performed using TGA on aNETZSCHSTA
409 PC/PG simultaneous thermal analyzer at a heating rate of
10 WC/min under nitrogen atmosphere. Themorphology of the
QTEAS hyperbranched polymer was examined at highmagni-
fication using a HITACHI S-4800, SEM.
Sorption experiments
Stock solutions (500 mg L–1) of the dyes were prepared by dis-
solving IC and EB in distilled water, and test solutions of
desired concentrations were obtained by further dilution
with distilled water. Dye solutions of desired pH values
were adjusted using HCl (0.1 N) and NaOH (0.1 N). The con-
centrations of the dyes were measured with a HACH
DR4000 U UV-visible spectrophotometer at 610 nm for both
dyes. The sorbed amounts of the dyes were determined from
the difference between the initial and final concentrations
by the following mass balance equation, qe¼ (Ci�Ce)V/w,
where qe is the amount (mg g�1) of dye sorbed, Ci and Ce
are the initial and equilibrium dye concentrations (mg L�1)
in solution, respectively, V is the adsorbate volume (L) and
w is the sorbent weight (g). All experiments described below
were undertaken in either duplicate or triplicate.
The removal of IC and EB by QTEAS was investigated in
batch experiments by stirring 50 mg ofmaterial with 50 mLof
dye solution in 200 mL stoppered glass bottles at 25 WC for 3
and 6 h for IC and EB, respectively. Each isotherm consisted
of ten dye concentrations varying from 50 to 500 mg L–1. The
equilibrium concentrations of different combinations were
measured by the spectrophotometer and referenced with
the calibration curves. The kinetic measurements were car-
ried out using similar equipment and conditions. The
sample mass was 50 mg, and the volume of the dye solution
was 50 mL (50 mg L�1) in this series of tests. The mixtures
were stirred at predetermined intervals of time, and were
drawn for dye concentration analysis. Experiments with
each dye were performed to determine the effect of pH on
dye removal. The pH range studied was from 2 to 10. The
sample mass was 50 mg, and the dye concentration was
50 mg L�1 (50 mL) in this series of tests. The influence of
temperature on the removal process was studied at three
different temperatures (25, 35, and 45 WC) with QTEAS sus-
pensions in IC and EB solutions (50 mg L�1). The
suspensions were stirred during 3 h and 6 h for IC and EB,
respectively, and then the dye concentration was analyzed.
Desorption and reusability
To assess the feasibility for consecutive reuse ofQTEAS, sorp-
tion–desorption studies of IC and EB on the hyperbranched
polymer were carried out at room temperature using 50 mg
of material and 50 mL of dye solution at a concentration of
50 mg L�1. Initially, the sorbent material was loaded with
the dye following the general sorption procedure described
above. The recovered material was washed with distilled
water, air dried, and then suspended in 50 mL of aqueous
NaOH solution (0.1 M) for desorption of the dye. The
obtained suspensions were stirred for 15 min, then centri-
fuged and the regenerated material was thoroughly washed
with distilled water and subsequently suspended in dye sol-
utions under the same conditions as above. The sorption–
desorption cycles were repeated three times.
RESULTS AND DISCUSSION
Characterization of QTEAS
The prepared hyperbranched polymer is absolutely insolu-
ble in a wide range of solvents including high boiling polar
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aprotic solvents such as DMF and DMAc. Owing to exper-
imental difficulty, we were not able to characterize the
material by using established methods such as MALDI-TOF
mass spectrometry for the determination of the degree of
branching, purity, and structural integrity of the polymer.
Nevertheless, the morphology of QTEAS was determined
by SEM, and Figure 2(a) shows an overview image indicat-
ing a globular topology of the prepared material typical of
hyperbranched macromolecules with three-dimensional
architecture. The average thickness diameter of QTEAS
was estimated to be in the range of 300–350 μm. Figure 2
(b) and 2(c) show the detailed view of the hyperbranched
polymer and reveal that mesoporous spongelike scaffolds
could be produced upon efficient polymerization. The
detailed image (Figure 2(c)) shows a highly smooth surface
with irregularly distributed pores of different sizes and
shapes bound together in a three-dimensional network.
The random orientation of the pores within the polymer net-
work suggests that growth defects occur due to steric
crowding within the branches. The XRD pattern of
QTEAS is shown in Figure 3(a). A wide and blunt peak
between 15 W and 32 W and centered at 20.7 W in the XRD
pattern is an indication of the amorphous nature of QTEAS.
The high degree of polymerization is evidenced by
common features present in the FTIR spectrum. As shown
in Figure 3(b), the spectrum of the QTEAS hyperbranched
polymer features a strong carbonyl–carboxylic absorption
band at 1,745 cm–1, stemming from the large number of car-
bonyl bonds of both esters and carboxylic acid termini
groups. The two absorption bands appearing at 2,932 and
2,847 cm�1 are mainly due to the stretching vibration of
sp3 carbons of alkyl groups. In addition, the band centered
at 3,444 cm–1 is characteristic of the OH stretching band
Figure 2 | SEM images of QTEAS hyperbranched polymer.
of both the carboxylic acid and alcohol termini groups.
The appearance of the absorption bands at 1,160 cm–1 and
1,094 cm–1, assigned for C–O antisymmetric stretching and
C–O–C bond stretching, respectively, is an indication of an
efficient esterification. Moreover, Figure 3(b) shows two dis-
tinguished absorption bands, one appearing at 1,462 cm–1
assigned to the sp3 C–H of methylene substituent of quatern-
ary amine groups and a shoulder around 1,523 cm–1,
belonging to the C–Nþ groups (Colthup et al. ). Finally,
the band centered at 1,642 cm–1 in the spectrum could be
assigned to a symmetric deformation of quaternary
ammonium, which proves the successful quaternization of
tertiary amine groups of the hyperbranched polymer
(Jin et al. ).
To obtain more structural information, the QTEAS
hyperbranched polymer was subjected to solid state CP-
MAS 13C NMR. The spectrum (Figure 4(a)) is well resolved
and shows a sharp intense signal at 173.7 ppm which is con-
sistent with carbon atoms of carbonyl C55O (ester and
carboxylic acid) groups. The efficiency of the polymerization
reaction is also confirmed by the appearance of two broad
signals of low intensities assigned around 59.9 ppm and
50.4 ppm, characteristic of ethylene groups of triethanola-
mine and methyl groups of quaternary ammonium salt
moieties, respectively. Lastly, the strong overlapped signal
centered at 30.7 ppm is attributable to the 8 sp3 carbons of
sebacoyl branches. Nevertheless, residual molecules of the
solvents entrapped inside the hyperbranched polymer,
most likely placed between the inner branches which
makes drying unattainable, give rise to a broad signal
around 127 ppm in the spectrum.
The thermal stability of the synthesized QTEAS was
studied by TGA (Figure 4(b)). The first derivative of the
Figure 3 | XRD pattern of QTEAS (a) and FTIR spectrum of QTEAS (b).
Figure 4 | Solid state CPMAS 13C NMR spectrum of QTEAS (a) and TGA response and its
derivative of QTEAS at a rate of 10W
C/min, in nitrogen (b).
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TG curve is proportional to the rate of decomposition, and
represents the temperature corresponding to the maximum
rate of weight loss (Tmax). As shown in Figure 4(b), the
mass loss occurs in multiple steps within the temperature
range of 78–426 WC. The initial decomposition temperature
(TDi) is approximately 158 WC. Upon initial heating, the gra-
dual loss of mass (1.71%) proceeded with a TD of 78 WC,
which is probably due to the loss of physically adsorbed
water and/or residual solvent entrapped in the polymer net-
work from the reaction workup. This was followed by two
major mass losses at 178.3 WC and 310.5 WC corresponding
to the degradation of the alcohol/carboxylic acids termini,
which are subject to rapid thermal degradation and ester
bond breaking in the branches of QTEAS, respectively.
Further heating above 300 WC resulted in extensive chain
scission and QTEAS decomposition, with a mass loss of
about 73% at 455 WC. The TGA data indicate that 13% of
the total weight of the sample remains after heating to the
highest temperature (800 WC).
Effect of contact time
Figure 5(a) shows the effect of contact time on the removal
of dyes by QTEAS. For an initial dye concentration of
50 mg L�1, the results revealed that the removal process is
rather faster for IC than for EB. Thus, a quite fast sorption
of IC occurs during the first hour of the process so that
the maximum dye, up to 83%, is sequestered from the sol-
ution vs. 59% for EB, for which the process is marked by
a slower stage as the sorbed amount of dye reaches equili-
brium. Then, the sorption rate continues to increase at a
relatively slow speed with contact time until total removal
of the dyes was reached. This was accomplished approxi-
mately after 3 h and 6 h for IC and EB, respectively.
Similar behavior has been observed for the sorption of C.I.
Table 2 | Kinetics constants for IC and EB dyes’ sorption onto QTEAS
Pseudo-first order modelPseudo-second ordermodel
Dyeqe, exp
(mg g�1)k1
(min�1)qe,cal(mg g�1) R2
k2 (gmg�1
min�1)qe,cal(mg g�1) R2
IC 49.92 0.025 30.48 0.884 4.0310�3
50.15 1
EB 49.67 0.011 32.77 0.941 8.9310�4
50.65 1
Figure 5 | Effect of contact time on the sorption rate of IC and EB dyes by QTEAS (a) and
pseudo-first order plot; pseudo-second order plot (inset) for IC and EB dyes’
removal by QTEAS (b).
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Direct Blue 86 and C.I. Direct Red 23 onto multiwalled
carbon nanotubes modified by a poly(propylene imine) den-
drimer (Eskandarian et al. ). The authors have found
that the removal of direct dyes by the dendritic material is
rapid during the initial period of time, followed by a slow-
down, then becomes stagnant as contact time increases.
The dye molecules are encapsulated by the dendritic
material via surface exchange reactions (encapsulation
mechanism) until the surface functional sites are fully occu-
pied (Froehling ; Yiyun & Jiepin ; Mahmoodi et al.
). Accordingly, the presence of abundant readily accessi-
ble sorption sites at each branching point of the
hyperbranched material suggests that the removal process
is very likely driven by strong ionic interactions between
the positively charged quaternary amine groups on the sur-
face of the QTEAS material and anionic dyes in solution.
In order to examine the controlling mechanism of the
sorption process, pseudo-first order model and pseudo-
second order kinetic models were used to analyze the exper-
imental data.
The pseudo-first order model can be expressed in its
linear form by Equation (1):
log (qe � qt) ¼ log qe � k1t (1)
The pseudo-second order model can be expressed in its
linear form by Equation (2):
tqt
¼ 1k2q2e
þ 1qe
t (2)
where k1 (min�1), k2 (g mg�1 min�1) are the rate constants
of the pseudo-first order and the pseudo-second order for
the sorption process, respectively, qe and qt (mg g–1) are
the amounts of dye sorbed at equilibrium and at time t
(min), respectively.
Figure 5(b) and Figure 5(b) inset, show the linear fit
plots of the pseudo-first order and pseudo-second order
models, respectively. The equilibrium sorption capacity
(qe), the rate constants (k1, k2), and the coefficient (R2)
values were calculated from the linear plots. The parameters
obtained for the two models are presented in Table 2. Per-
fect correlation is however observed between experimental
data and the pseudo-second order kinetic model with excel-
lent correlation coefficients. Additionally, the calculated qevalues from the model were totally in agreement with exper-
imental sorption capacities, emphasizing therefore the
efficiency of the model. In the literature, many studies
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have shown that adsorption kinetics of numerous dyes onto
various polymer-based adsorbents are well fitted by the
pseudo-second order model. For example, Renault et al.
() have found that the pseudo-second order was the
best model for describing the adsorption kinetics of AB 25
dye on cross-linked starch ion-exchanger.
Effect of pH
The pH of the solution is a key factor when evaluating the
removal efficiency of dyes on pH variation. The influence
of pH was examined at target pH values set between 2
and 10 for preventing alteration of the ionic character and
aggregation state of the anionic dyes and alkaline hydrolysis
of the QTEAS polyester. Figure 6(a) shows the effect of
Figure 6 | Effect of pH on the sorption of IC and EB dyes by QTEAS (a) and UV-vis. spectra
of aqueous solutions of RhB/IC (3/2) (anionic dye IC (100 mg L�1); cationic dye
RhB, (100 mg L�1)) mixture before and after the adsorption process (b).
solution pH on IC and EB removal by the QTEAS hyper-
branched material at room temperature. First of all, it is
noteworthy to point out that the pH of the solution has prac-
tically no effect on the amount of dyes sorbed onto QTEAS.
Indeed, within the wide pH range (from pH 2 to 10) of dye
solutions, sorption efficiencies of IC and EB onto QTEAS
are actually steady and removal percentages are higher
than 98% within the whole pH range. Similar results have
been already reported by Greluk & Hubicki () for the
sorption of Acid Orange 7 by strongly basic quaternary
ammonium resins. QTEAS adsorbent with a high number
of charge sites at any pH showed high performance in IC
and EB uptake in the whole pH range suggesting the ion-
exchange mechanism. However, analysis of the literature
data show that the predominant adsorption mechanism
during adsorption of the organic anions by strongly basic
quaternary ammonium resins is not only ion-exchange, but
other cooperative adsorption mechanisms occur besides
the predominant ion-exchange which take place through
hydrogen bonding and hydrophobic interactions (Wawrz-
kiewicz & Hubicki a, b, c).
Although the surface of the QTEAS adsorbent is tidy, with
positively charged quaternary ammonium groupswhichmake
it a powerful reactant toward anionic dyes, the presence of
alcohol/carboxylic acid termini groups within the polymer
could however participate in the removal process via covalent,
coulombic, hydrogen bonding or weak van der Waals forces
with the dyes’ functional groups (�OH, �NH2, �SO3Na,
�N¼N�). To shed light on the adsorption mechanism of
the anionic dyes on the QTEAS material, a selective adsorp-
tion experiment was carried out using a mixture of cationic
and anionic dyes in aqueous solutions. Figure 6(b) (photo in
the left corner) shows that preliminary tests revealed that
QTEAS was not able to remove the cationic dye Rhodamine
B (RhB) at a concentration of 50 mg L�1 from aqueous sol-
utions after 16 h of contact time. Figure 6(b) shows also the
UV–vis. spectra of aqueous solutions ofRhB/IC (3/2) (cationic
dye RhB (100 mg L�1); anionic dye IC (100 mg L�1)) mixture
before and after the adsorption process. As shown in Figure 6
(b), after 16 h of contact time, IC was almost completely
removed from the mixture solution by the QTEAS adsorbent,
whereas RhB remained intact in the solution. These results
suggest that the removal process of anionic dyes by
QTEAS could be an ion-exchange mechanism and also
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confirm that the QTEAS adsorbent has a selective adsorption
property for anionic dyes and could have potential for appli-
cation in purification of cationic dyes from anionic dyes.
Sorption isotherms
The sorption isotherms of anionic dyes IC and EB onto
QTEAS are reported in Figure 7(a). The isotherms are super-
imposed and characterized by a regular shape with a steep
initial slope, and are concave to the concentration axis. The
great affinity of QTEAS material for the dyes is suggested by
the quantitative removal at low dye concentrations. The
adsorption of IC and EB onto QTEAS increases with increas-
ing initial dye concentration to reach equilibrium.
The experimental data were analyzed by using Lang-
muir and Freundlich isotherm models.
Figure 7 | Sorption isotherm for IC and EB dyes onto QTEAS (a) and Freundlich and
Langmuir (inset) plots for IC and EB dyes’ removal by QTEAS (b).
The linear form of Langmuir’s isotherm model is given
by the following equation:
Ce
qe¼ Ce
qmaxþ 1qmaxb
(3)
The Freundlich isotherm equation can be written in the
linear form as given below:
log qe ¼ 1nlogCe þ logKF (4)
where qe (mg g�1) is the amount of dye adsorbed per gram of
sorbent, qmax (mg g�1) is the maximum sorption capacity per
gram of adsorbent, Ce (mg L�1) is the equilibrium concen-
tration of dye in solution, and b (L mg�1) is the Langmuir
constant related to the energy of adsorption, KF (L g�1) is
the relative adsorption capacity constant of the adsorbent
and 1/n is the intensity of the adsorption constant.
As shown in Figure 7(b), the analysis of the equilibrium
experimental data of IC and EB sorption onto QTEAS by
utilizing the Freundlich and Langmuir isotherm equations
gave linear plots. The linearized forms of both Freundlich
and Langmuir isotherms were found to be linear over a
broad concentration range with good to excellent corre-
lation coefficient values (see Table 3). These results clearly
indicate that both models adequately fitted the experimental
data of the dyes’ removal by QTEAS material.
As shown in Table 3, both dyes are removed with the same
order ofmagnitude by the hyperbranched polymer. The greater
affinity ofQTEAS sorbent for both dyes ICandEB is confirmed
by the sorption capacities at saturation of the monolayer.
Despite its extended molecular structure, EB is sorbed onto
QTEAS with quite similar effectiveness (0.891 meq g–1 for EB
vs. 0.914 meq g–1 for IC). These results suggest that EB has
greater access to the surface of QTEAS without inducing a
Table 3 | Langmuir and Freundlich isotherm constants for the sorption of IC and EB dyes
onto QTEAS dendritic polymer
Langmuir constants Freundlich constants
Dye qmax (mg g�1) b (L mg�1) R2 KF (L g�1) 1/n R2
IC 213.22 0.42 0.999 146.05 0.07 0.911
EB 214.13 0.32 0.999 121.88 0.11 0.947
Table 5 | Thermodynamic parameters for IC and EB removal by QTEAS
ΔG (KJ mol–1)
Dye ΔH (KJ mol–1) ΔS (J K–1mol–1) 298 K 308 K 318 K
IC �50.495 �62.893 �31.752 �31.123 �30.495
EB �87.714 �193.715 �29.986 �28.049 �26.112
10 M. Bendjelloul et al. | Removal of acid dyes from aqueous solutions by a dendritic polymer Journal of Water Reuse and Desalination | in press | 2017
Uncorrected Proof
quick saturation of sorption sites because of steric hindrance
and clearly show that the dyes’ removal is closely linked to
the total charge on the surface of the dyes’molecules. Nonethe-
less, the highest b value found for IC dye (0.42 vs. 0.32 for EB)
indicates thatQTEAS shows a little preference on binding diva-
lent anion IC than the tetravalent anion EB. Finally, these
results also confirm the presence of readily accessible sorption
sites and strongly suggest the homogeneous distribution of
active quaternary ammonium groups on the surface of the
hyperbranched polymer. The QTEAS hyperbranched polymer
showedbetter sorption capacities for ICandEBdyes compared
to those of other adsorbents reported in the literature for the
removal of these dyes (see Table 4).
Thermodynamic parameters
The removal of IC and EB by the QTEAS sorbent was
studied at three temperatures to determine the thermodyn-
amic parameters, and the results are summarized in
Table 5. The dyes’ uptake decreased with an increase in
temperature, indicating an exothermic process.
The thermodynamic parameters ΔG, ΔH, and ΔS were
calculated by using the following equation (Zhu et al. ):
logKL ¼ �ΔGRT
¼ ΔSR
� ΔHRT
(5)
where T is the temperature (K), R is the ideal gas constant
(8.314 J mol–1 K–1), and KL is the Langmuir equilibrium con-
stant (L mg–1).
Table 4 | Sorption capacities for IC and EB dyes on various adsorbents
Adsorbent Dyeqmax
(mg g–1) Reference
Anion-exchanger (LewatitMonoPlus M-600)
IC 43.6 Wawrzkiewicz &Hubicki (d)
Carbonaceous material IC 92.83 Gutiérrez-Seguraet al. ()
Pyrolyzed sewage sludge IC 30.82 Otero et al. ()
QTEAS IC 213.22 This study
QTEAS EB 214.13 This study
Commercial activatedcarbon (PAC)
EB 135.2 Prola et al. ()
Natural bentonite EB 160.45 Chandra et al. ()
Mg-Al-CO3 LDH EB 107.5 Bouraada et al. ()
The vant’Hoff plot of log KL versus 1/T gave straight
lines. The calculated slope and intercept from the plot
were used to determine ΔH and ΔS, respectively (Table 5).
The negative value of ΔG (�31.75 to �26.11 kJ·mol�1) at
each temperature implies a favorable and spontaneous
adsorption process and confirms the affinity of the QTEAS
material for IC and EB dyes. In general, the change in free
energy for physisorption is between �20 and 0 kJ·mol�1,
whereas chemisorption is in the range of �80 to 400
kJ·mol�1 (Renault et al. ; Abdel Salam et al. ; Eskan-
darian et al. ). These values are in the intervals between
physisorption and chemisorption, thus suggesting that the
process is a physical adsorption enhanced by a chemical
effect (Renault et al. ). The negative value of ΔH
indicates that the adsorption is exothermic and also suggests
that the sorption process is a physical adsorption enhanced
by chemical interactions between the anionic dyes and the
quaternary amine groups through ion-exchange.
Influence of ionic strength on IC and EB adsorption
process on QTEAS
Textile wastewaters usually contain inorganic salts to
improve the dying process and to promote the transfer of
dye to fabrics (Arslan et al. ). The use of salts can
alter the properties of the adsorbent surface charge and
adsorbate such as its solubility, ionic nature, which ulti-
mately affects the adsorption process by either increasing
or decreasing the adsorption capacity (Arafat et al. ;
Bautista-Toledo et al. ). Figure 8 shows the influence
of NaCl concentration varying from 0.1 to 1 mol L–1 on
the removal efficiency of IC and EB dye solutions of
50 mg L–1 using the hyperbranched QTEAS polymer. As
shown in Figure 8, both dyes are quantitatively removed
from solutions (R> 95%) even when the NaCl concen-
tration is up to 1 mol L–1. The results showed that IC and
Figure 9 | Percentages of IC and EB dyes removal by QTEAS sorbent over three repeated
adsorption–desorption cycles.
Figure 8 | Effect of NaCl concentration on the removal efficiency of IC and EB dyes by
QTEAS.
11 M. Bendjelloul et al. | Removal of acid dyes from aqueous solutions by a dendritic polymer Journal of Water Reuse and Desalination | in press | 2017
Uncorrected Proof
EB adsorption on the hyperbranched QTEAS polymer were
not affected by the presence of NaCl in the whole range of
the salt concentration. Similar results have been reported
by Karcher et al. (, ) on the effect of the presence
of inorganic salts on the adsorption of the reactive dyes on
anion-exchanger resins.
Desorption and reusability
The desorption studies contribute to elucidating the nature
of the adsorption process and allow the recovery of the
dyes as well as the regeneration of the adsorbent to make
the treatment process economical. The QTEAS hyper-
branched material can be readily regenerated with a 0.1M
NaOH aqueous solution. Therefore, quantitative desorption
rates were achieved for both dyes over three repeated sorp-
tion–desorption cycles. IC and EB dyes were instantly
released as soon as the dye-loaded sorbent made contact
with the alkaline solution. This was illustrated by instan-
taneous coloration of the solution. Nonetheless, the
sorbent material was left in contact with the alkaline sol-
ution for 15 min of contact time, a period considered as
sufficient for the dyes’ desorption to be achieved, and on
the other hand to prevent alkaline hydrolysis of the hyper-
branched polymer. As shown in Figure 9, the third
repeated use of QTEAS material for the removal of IC and
EB dyes showed neither signs of deterioration nor any
decrease in its capacity for the dyes’ sorption. Finally, the
high performance of the QTEAS ion-exchanger indicates
that its reusability is quite feasible.
CONCLUSIONS
In the present study, the sorption of two acid dyes onto
QTEAS hyperbranched polymer was investigated. The
results demonstrated that the hyperbranched polymer
performs efficiently in a wide pH range of dye solutions.
From the kinetic studies, it was found that the sorption pro-
cess followed the pseudo-second order model. The sorption
isotherms were adequately fitted by the Langmuir isotherm
model and the removal process was found to take place by
the electrostatic attraction between the positively charged
hyperbranched polymer and the negatively charged dyes.
Nevertheless, the ionic strength does not affect the dyes’
removal efficiency by the hyperbranched polymer. More-
over, the removal capacity is closely connected to the total
sulfonate groups on the surface of the dyes. The calculated
thermodynamic parameters indicated the exothermic and
spontaneous nature of the removal process. Finally, the
third repeated use of QTEAS material for the dyes’ removal
showed no decrease of its capacity for the dyes’ sorption.
12 M. Bendjelloul et al. | Removal of acid dyes from aqueous solutions by a dendritic polymer Journal of Water Reuse and Desalination | in press | 2017
Uncorrected Proof
The overall results illustrated that QTEAS can be effectively
used as an ion-exchanger for the removal of acid dyes from
colored wastewaters.
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First received 31 October 2015; accepted in revised form 23 January 2016. Available online 3 March 2016