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: andalou777@yahoo.com

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

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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

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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