Fibers and Polymers 2010, Vol.11, No.7, 996-1002

996

Removal of Benzidine-based Azo Dye from Aqueous Solution Using Amide and

Amine-functionalized Poly(ethylene terephthalate) Fibers

Mustafa Yi ito lu and Zülfikar Temoçin*

K r kkale University, Faculty of Science and Arts, Department of Chemistry, K r kkale 71450, Turkey

(Received September 10, 2009; Revised May 8, 2010; Accepted July 2, 2010)

Abstract: In this study, amide and amine groups bound to poly(ethylene terephthalate) fibers are used to remove the coloredtoxic Congo red dye from aqueous solution. The effects of process variables like pH, contact time, graft yield, and initial dyeconcentration on the adsorption were investigated. The maximum adsorption of Congo red to amide and amine groups wasobserved at pH 3 and 5 respectively. Equilibrium was attained at approximately 60 min for the amine group. The adsorptioncapacity of amine group on the poly(ethylene terephthalate) fiber was 46.5 mg g-1 at 25 oC, which was higher than that of theamide group on the poly(ethylene terephthalate) fiber. Desorption was done using 0.1 M NH3, and recovery was measured at58.2 %. The used adsorbent was regenerated and recycled six times. The results showed that the amine-functionalized fibercould be considered as potential adsorbents for removal of Congo red from aqueous solution.

Keywords: Adsorption, Congo red, Acrylamide, Poly(ethylene terephthalate) fiber

Introduction

Colored compounds comprising pigments and dyes are

used widely in the textile, plastic, food, dye, paper, printing,

pharmaceutical, and cosmetic industries. These dyes color

the water and make penetration of sunlight to the lower

layers impossible, consequently affecting aquatic life. Polluted

water not only damages plants and animals, but also harms

the environment. Discharge of these dyes into water bodies

pollutes the water and makes it unfit for aquatic life, because

of their toxicity [1].

Azo dyes are the most widely used class of industrial dyes,

constituting 60-70 % of all produced dyestuffs. During the

dyeing process, the exhaustion of the dyes is never complete,

resulting in dye-containing effluents. In addition to aesthetic

problems, biotoxicity and possible mutagenic and carcinogenic

effects of azo dyes or their metabolites have been reported [2].

Congo red (1-naphthalenesulfonic acid, 3,3'-(4,4'-biphenylenebis

(azo)) bis (4-amino-) disodium salt) is a benzidine-based

anionic diazo dye. This dye is known to metabolize to

benzidine, a known human carcinogen. Therefore, the removal

of Congo red from waste effluents is environmentally

important. The treatment of dyes in industrial wastewaters

poses several problems since they have complex aromatic

structures that make them physico-chemically, thermally,

and optically stable [3].

Relative to several chemical and physical methods,

adsorption has been found to be superior because of

wastewater treatment in terms of its capability to efficiently

adsorb a broad range of adsorbates and its simplicity of

design. Color removal from industrial wastewaters by

adsorption techniques has been of growing importance due

to the chemical and biological stability of dyestuffs against

conventional water treatment methods and the growing need

for high quality treatment [4].

Several adsorbents, like chitosan hydrobeads [5], activated

carbon [6], cellulosic fibers [7], hydrogel [8,9], fungi [10],

rice husk

[11], silk yarn [12], and pyridine sulphonamide

resin [13] are used for the removal of dyes from aqueous

solution. High-capacity low-cost adsorbents are still under

development to reduce the adsorbent dose and minimize

disposal problems [14].

The poly(ethylene terephthalate) (PET) fiber is one of the

most important synthetic fibers used in the textile industry.

The PET fiber has good resistance to most strong acids,

oxidizing agents, sunlight, and microorganisms [15]. In spite

of these properties, PET has some drawbacks such as lower

moisture regain and difficulty in dyeing due to lack of

reactive functional groups [16]. Certain desirable functional

groups can be imparted to the PET surface by grafting with

different monomers [17].

In this work, modified PET fibers are used as an adsorbent

to remove Congo red from aqueous solution. The effects of

pH, contact time, initial dye concentration, graft yield, and

temperature on the adsorption have been investigated.

Furthermore, desorption of Congo red and reuse of the adsorbent

was done to investigate the feasibility of regeneration.

Experimental

Chemicals

The poly(ethylene terephthalate) fibers (122 dtex, middle

drawing) was provided by SASA Co. (Adana, Turkey).

Acrylamide, sodium hydroxide, benzoyl peroxide, Congo

red, sodium sulfate, sodium nitrate, citric acid, and acetic

acid were purchased from Merck. Ethanol, methanol,

acetonitrile, acetone, sodium chloride, potassium chloride,

sodium dihydrogen phosphate, and disodium hydrogen

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*Corresponding author: zulfikartemocin@hotmail.com

DOI 10.1007/s12221-010-0996-6

Removal of Benzidine-based Azo Dye Fibers and Polymers 2010, Vol.11, No.7 997

phosphate were purchased from Riedel-deHaen. Solutions

were prepared with deionized water (Millipore, Elix 3 water

purification system).

Apparatus

Pharmacia Biotech Ultrospec 2000 model UV-Visible

spectrophotometer was used to determine the optical density

of the solutions in the visible region. The infrared spectrums

were obtained with a Thermo-Nicolet 6700 FT-IR spectrometer

equipped with an attenuated total reflection (ATR) apparatus

using a diamond prism with an incident angle of 45 o. All pH

measurements were performed with a HANNA 221 model

digital pH meter.

Preparation of the Adsorbent

After the fiber samples (0.30±0.01 g) had been swollen in

dichloroethane for 2 h at 90 oC, the solvent on the fiber was

removed by blotting between filter papers [17]. As described

by Co kun and Soykan [18], acrylamide monomer was

grafted onto the PET fiber. After 2 h of polymerization,

homopolymer was removed from the fiber samples by

washing with water at 50 oC for 5 h by changing the washing

water five times. The fiber was dried at 50oC and weighed.

The graft yield (GY) was calculated from the increased

weight of the grafted fiber as follows:

(1)

where Wi and Wg denote the weights of the original and

grafted PET fibers, respectively.

Amine Group Addition to the PET Fibers

The grafted PET fiber was chemically modified as

described in our previous research [19]. The amide groups of

poly(acryl amide) were converted to amine groups via the by

Hofmann degradation reaction [20]. The grafted PET fiber

(0.03 g) was immersed in 15 ml of suitable concentration of

NaOCl and NaOH aqueous solution at 20 oC for 30 min.

After continuous shaking for given period of time, the fiber

was removed from the mixture and washed with 10 ml of

deionized water four times.

Determination of Amine Content

An acid-base titration method, which has been used by

Hou et al. [21], was used to determine the content of the

amine functional groups. Hydrochloric acid (HCl) solution

(30 ml, 0.01 mol l-1) was introduced into the amine fiber

(0.10 g, 41.4 % graft yield), and the mixture was stirred until

the fiber was sufficiently steeped. The excess HCl solution

was titrated and neutralized with a NaOH solution (0.01 mol

l-1

) using phenolphthalein as an indicator. A blank titration

experiment was performed for the PET-g-AAm fiber.

Adsorption Studies

Adsorption experiments were carried out in a batch system

at 25 oC and 100 rpm by contacting 20 ml Congo red

solution at a specific concentration. The pH of the Congo red

solution was adjusted with a suitable buffer solution. The

adsorbent dose was fixed as 0.03 g throughout all experiments.

The pH value of the solutions was adjusted to 6.8 before the

analysis. The Congo red concentration was estimated

spectrophotometrically by monitoring the absorbance at

485 nm. The amount of adsorbed Congo red, qe (mg g-1

),

was calculated by:

(2)

where C0 and Ce (mg l-1) are the liquid-phase concentrations

of the Congo red initially and at equilibrium, respectively, V

is the volume of the solution (l), and W is the mass of

adsorbent used (g).

Desorption Studies

Desorption studies were carried out with a batch system at

25 oC and 100 rpm by contacting 10 ml NH3 and NaOH

solutions. The desorbed dye concentration was determined

as described above. The amount of desorbed Congo red was

calculated by:

(3)

Results and Discussion

The amide and amine groups on PET fibers were used as

adsorbent material for the removal of Congo red from

aqueous solution. It was determined that 13.1 % of the

amide groups on PET fibers were converted to amine groups.

The structure of Congo red and the structure of the functional

groups grafted to the fibers are illustrated in Figure 1.

The infrared spectra of PET (spectrum a), PET grafted

acryl amide (spectrum b) and the grafted PET after the

Hofmann degradation reaction (spectrum c) are shown in

Figure 2. Examination of these spectra (a and b) reveal a

sç

GY %( ) Wg Wi–( )/Wi[ ] 100×=

qe

C0 Ce–( )V

W-------------------------=

Desorption %( )Amount of desorbed Congo red mg( )

Amount of adsorbed Congo red mg( )------------------------------------------------------------------------------------------ 100×=

Figure 1. Chemical structure of Congo red (a) and chemical

structure of functional groups on the PET fiber (b).

998 Fibers and Polymers 2010, Vol.11, No.7 Mustafa Yi ito lu and Zülfikar Temoçingo

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typical amide I band (~1652 cm-1

), due to the C=O stretch of

poly(acryl amide), and an amide II band (~1606 cm-1),

which includes the N-H vibration in the spectrum. These

data show that amide groups were attached onto the fiber

structure. Comparison of spectra b and c show the decreased

intensity of the carbonyl peak at 1652 cm-1

of acryl amide.

This indicates that amide groups were converted to amine

groups on the acryl amide grafted PET fiber by the Hofmann

reaction.

Effect of pH on Adsorption

The pH of the solution is an important controlling parameter

of adsorption. The effect of solution pH on the adsorption of

Congo red was studied by varying the pH of the Congo red

solution from 2 to 9 for an initial dye concentration of 50 mg l-1

and for contact time of 30 min. Adsorption of Congo red by

the amine and the amide groups on the PET fiber was found

to be dependent on the solution pH (Figure 3). The

maximum adsorption of the Congo red on the amine group

was at pH 5 whereas the amide group exhibits maximum

adsorption at pH 3. In addition, high adsorption values of

Congo red on the amine group were observed for a broader

pH range of 5 to 7. The adsorption of Congo red on the

amine group was about 15 mg g-1

and was only 3.49 mg g-1

for the amide group.

These results indicates that a strong interaction exists

between Congo red and the amine group, but there is a weak

interaction between Congo red and the amide group. Amides

are typically weaker bases than corresponding amines.

Consequently, the amine groups are more easily protonated

than the amide groups at neutral and acidic pH values, and

carry a positive charge. At the pH range from 5 to 7,

significantly high electrostatic attraction exists between the

positively charged surface of the adsorbent and negatively

charged anionic dye. The decrease in adsorption at lower pH

(<5) values was attributed to the protonation of the weakly

basic sulfonate group of Congo red, and at higher pH (>7)

values was attributed to the deprotonation of the amine on

the PET surface. A schematic representation of the interaction

between Congo red and the amine group on PET fibers is

shown in Figure 4. A similar interaction was reported for the

removal of dye by chitosan/organomontmorillonite [22],

flyash [23], poly(vinyl pyrrolidone) grafted sulfonamide

Figure 2. FTIR spectra of PET (a), PET grafted acryl amide (b),

and the grafted PET after the Hofmann degradation reaction (c).

Figure 3. Effect of pH on adsorption (Contact time=30 min, initial

dye concentration=50 mg l-1, t=25 oC, V=20 ml and GY(%)=41.4).

Figure 4. Behavior of adsorbent in aqueous medium (a),

interaction between Congo red and adsorbent (b), and protonated

Congo red in acidic medium (c).

Removal of Benzidine-based Azo Dye Fibers and Polymers 2010, Vol.11, No.7 999

based polystyrene resin [24], and activated carbon [6].

Effect of Contact Time on Adsorption

Figure 5 shows the effect of contact time on the adsorption

of Congo red. The amount of Congo red removed is

observed to increase with contact time. The adsorption of

Congo red on amine groups occurred at a higher rate during

the first 40 min and after that Congo red was adsorbed at a

slower rate, reaching adsorption equilibrium at 60 min. For

contact time of 60 min and an initial concentration of 50 mg l-1

at 25 oC, the Congo red adsorption to the amide was 3.52 mg g-1

and for the amine was as high as 23.3 mg g-1 of Congo red.

Bhatnagar et al. [25] reported that the time required for

equilibrium of Congo red in a carbon slurry waste adsorbent

is 1.5 h. Grabowska and Gryglewicz [26] reported that the

adsorption of Congo red on mesoporous activated carbon

reaches equilibrium after 30 h.

Effect of Graft Yield on Adsorption

The effect of graft yield on the adsorption of Congo red

was investigated by performing adsorption experiments in a

grafting range of 3.8-41.4 %. As shown in Figure 6, it is

obvious that Congo red adsorption increases with graft yield.

This increase in adsorption by the PET fiber can be

attributed to the increased functional groups (amide and

amine) on the fiber structure by graft copolymerization.

Therefore, there is increased interaction with the dye.

Effect of Initial Congo Red Concentration on Adsorption

The experiments were performed on Congo red solutions

with concentrations ranging between 20 and 150 mg l-1 at

the optimum pH values. Figure 7 shows that the adsorption

of Congo red by the amine increased with increasing Congo

red concentration up to 120 mg l-1

, where an adsorption plateau

was reached. The maximum amount of adsorbed Congo red

by the amine group on the PET fiber was 46.5 mg g-1 adsorbent

at 25 oC and 120 mg l-1 initial Congo red concentration. The

obtained result was also compared with those reported by

Arslan and Yi ito lu [27], Panda et al. [28], and Vimonses

et al. [29], for Congo red adsorption in aqueous solution.

The 4-vinylpyridine and 2-hydroxyethylmethacrylate grafted

PET fiber obtained by Arslan and Yi ito lu adsorbed 11.87

mg g-1 of Congo red. The Jute stick powder obtained by

Panda et al. adsorbed 35.7 mg g-1

of Congo red. The clay

minerals of bentonite, kaolin, and zeolite obtained by

Vimonses et al. adsorbed 19.9, 5.6, and 4.3 mg g-1 of Congo

red, respectively. The amount of adsorbed Congo red on

amine group represents a satisfying performance when

compared to those mentioned above.

Adsorption isotherms are important to provide a description

of how the adsorbate molecules interact with adsorbent

surface [30]. Two isotherms were selected in this study, the

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Figure 5. Effect of contact time on adsorption (Initial dye

concentration=50 mg l-1, t=25 oC, pH=3 for amide group, pH=5 for

amine group, V=20 ml, GY (%)=41.4).

Figure 6. Effect of graft yield on adsorption (Initial dye

concentration=50 mg l-1, t=25 oC, pH=3 for amide group, pH=5 for

amine group, V=20 ml, contact time=60 min).

Figure 7. Effect of initial Congo red concentration on adsorption

(t=25 oC, pH=3 for amide group, pH=5 for amine group, V=20 ml,

contact time=60 min. GY(%)=41.4).

1000 Fibers and Polymers 2010, Vol.11, No.7 Mustafa Yi ito lu and Zülfikar Temoçingo

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Langmuir and Freundlich isotherms.

The Langmuir isotherm is expressed [31]:

(4)

where Ce is the equilibrium concentration of the adsorbate

(mg l-1), qmax (mg g-1) and b (mg-1) are the Langmuir

constants related to the maximum adsorption capacity and

the adsorption equilibrium constant, respectively.

The Freundlich adsorption isotherm can be expressed as

[32]:

(5)

where kf and n are Freundlich adsorption isotherm constants,

being indicative of the extent of the adsorption and the

degree of nonlinearity between solution concentration and

adsorption, respectively. kf and (1/n) are determined from

the linear plot of ln qe versus lnCe. The Langmuir isotherm is

given in Figure 8. The coefficients of these two isotherm

models are provided in Table 1. The Langmuir isotherm

(R2=0.9906) gave a better fit to the data than the Freundlich

isotherm (Figure not shown).

Effect of Temperature on Adsorption

It is important to investigate the effect of temperature on

adsorption for its practical application. The effect of

increasing temperature on the Congo red adsorption onto

amide and amine groups grafted to PET fibers was studied

by performing adsorption experiments between 30-60 oC.

The experiments were done with an initial dye concentration

of 150 mg l-1 for the amine and 50 mg l-1 for the amide, each

with a 30 min contact time. Figure 9 shows the effect of

temperature on Congo red adsorption onto the amine and

amide groups on PET fiber. The adsorption capacity of the

amine group increased from 29.6 to 80.8 mg g-1 with the

temperature increased from 30-60oC, indicating that high

temperatures facilitated the adsorption of Congo red onto the

amine group. This may be attributed to the fact that

increasing temperature may produce swelling within the

internal structure of PET backbone, which helps the

penetration of dye molecules into the interlayer space of the

PET backbone. Similar observations were reported by Wang

and Wang [22]. However, the adsorption capacity of the

amide was approximately unchanged from 30-60 oC. This

result was attributed to the weak interaction between the dye

molecule and amide group.

Effect of Foreign Ions and Organic Solvents on Adsorption

The adsorption capacity of adsorbent depends on various

factors such as polarity, solubility and presence of other ions

in solution [26,33,34]. Different cations (Na+, K+), anions

(SO4

2−, PO4

3−, NO3

−, Cl−) and organic solvents (acetone,

methanol, ethanol, and acetonitrile) were tested separately

for their effect on the adsorption of Congo red. The

concentrations of the cation solutions (which were prepared

from chloride salts), the anions solutions (which were

prepared from sodium salts), and solvents were adjusted to

0.1 mol l-1 and 10 % (v/v), respectively. The results are given

in Figures 10(a) and (b), and show that the effect of diverse

ions and solvents is negligible on adsorption.

Desorption Study

Desorption studies help reveal the mechanism of adsorption.

They also make the process economically effective by the

1

qe

----1

qmax

---------1

bqmax

Ce

------------------+=

lnqe lnkf

1

n---lnCe+=

Figure 8. Langmuir isotherm of adsorption of Congo red on the

amine-grafted PET fiber.

Figure 9. Effect of temperature on Congo red adsorption (Initial

Congo red concentration=50 mg l-1 and pH=3 for amide group,

Initial Congo red concentration=150 mg l-1 and pH=5 for amine

group, V=20 ml, contact time=30 min. GY(%)=41.4).Table 1. Adsorption isotherm coefficients of Congo red

Langmuir coefficients Freundlich coefficients

qmax

(mg g-1)

b

(l mg-1)R2 kf n R2

66.6 0.0602 0.9906 6.91 1.88 0.9303

Removal of Benzidine-based Azo Dye Fibers and Polymers 2010, Vol.11, No.7 1001

simultaneous recovery of adsorbate and spent adsorbent.

The adsorbed Congo red onto the amine grafted PET fibers

was used for the desorption experiments. The desorption (%)

was measured at different time intervals and is shown in

Figure 11. The desorption (%) obtained was 58.2 % using

NH3 solution for 60 min. Using NaOH for 60 min only

desorbed about 22.1 %. This difference can be attributed to

the similar structure of the adsorbent (-NH2) and desorption

agent (NH3).

Reusability of Adsorbent

Regeneration and reuse of the adsorbent is a very

important issue to be addressed for the industrial application

of the process. To test the long-term capacity of the

adsorbent, the adsorbent was subjected to successive

adsorption and desorption cycles by contacting 20 ml of dye

solution (50 mg l-1) at pH 5 for 60 min, and then desorbing

the dye with 10 ml of NH3 solution. As shown in Figure 12,

the amount of adsorbed Congo red decreased from 24.8 to

15.6 mg g-1

during recycling, due to irreversibly bound dye.

Conclusion

This may be one of few studies on evaluation of functional

groups, amide and amine, for removal of anionic dye from

aqueous solution. Adsorption of Congo red by the amide and

amine groups grafted to PET fibers was shown to be

dependent on the solution pH. The amine group has a higher

adsorption capacity than the amide group. The maximum

amount of Congo red adsorbed by the amine groups on PET

fibers was 46.5 mg g-1 adsorbent at 25

oC for an initial

Congo red concentration of 120 mg l-1

. The equilibrium time

of Congo red adsorption on the amine group was

approximately 60 min. The equilibrium data were best

described by the Langmuir isotherm model. Congo red

adsorption increased with temperature. The effect of ions

and organic solvents on the adsorption of Congo red was

negligible. The adsorbent has the potential for reuse. Thus

the amine-functionalized fiber should be addressed to use in

Figure 10. Effect of ions (a) and organic solvents (b) on the

adsorption of the Congo red (Ion concentration=0.1 mol l-1, solvent

concentration=10 % (v/v), V=20 ml, Contact time=60 min, Initial

Congo red concentration=50 mg l-1, pH=3 for amide group and

pH=5 for amine group).

Figure 11. Desorption kinetics of adsorbed Congo red on the

amine-grafted PET fiber (Eluent concentration=0.1 M, V=10 ml,

t=25 oC).

Figure 12. Effect of multiple reuse cycles of amine-grafted PET

fibers on the adsorption.

1002 Fibers and Polymers 2010, Vol.11, No.7 Mustafa Yi ito lu and Zülfikar Temoçingo

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the treatment of textile effluent and wastewater treatment.

Acknowledgements

We are grateful to the K r kkale University Research Fund

for the financial support of this work.

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