Environmental

Communication

Biosci. Biotech. Res. Comm. 10(2): 311-318 (2017)

Application of single-walled carbon nanotubes for

removal of aniline from industrial waste water

Davoud Balarak

, Ferdos Kord Mostafapour

and Ali Joghataei

Department of Environmental Health, Health Promotion Research Center, School of Public Health, Zahedan

University of Medical Sciences, Zahedan, Iran

Student Research Committee, Qom University of Medical Sciences, Qom, Iran

ABSTRACT

The adsorption behavior of aniline using single-walled carbon nanotubes (SWCNTS) as adsorbents is examined under

ambient conditions. The adsorption equilibrium of aniline on SWCNTS was evaluated by the Langmuir, Freundlich, Dubinin

Radushkevich and Tempkin isotherms. The results showed that the equilibrium data for aniline  tted the Langmuir model

best within the concentration range studied. Experimental results showed that the time taken to attain adsorption equilib-

rium for aniline was 30 min. The adsorption energy obtained was 218.25 J/mg, which indicates that the adsorption process

is endothermic and a strong interaction between SWCNTS and Aniline molecules. The results showed that SWCNTS had

good potential for the removal of aniline from industrial wastewater.

KEY WORDS: ADSORPTION, ANILINE, SINGLE-WALLED CARBON NANOTUBES, ISOTHERMS

311

ARTICLE INFORMATION:

*Corresponding Author: alijoghatayi69@gmail.com

Received 10

March, 2017

Accepted after revision 18

June, 2017

BBRC Print ISSN: 0974-6455

Online ISSN: 2321-4007 CODEN: USA BBRCBA

Thomson Reuters ISI ESC and Crossref Indexed Journal

NAAS Journal Score 2017: 4.31 Cosmos IF : 4.006

reserved.

Online Contents Available at: http//www.bbrc.in/

INTRODUCTION

Rapid increasing of industries and subsequently increas-

ing the disposal of pollutants especially organic com-

pounds, to the water resources and environment caused

serious and adverse environmental impacts (Liu et al.,

2010, Delnavaz et al., 2009, Wu et al., 2012). With the

increasing concern for public health and environmental

quality, the stringent limits on the acceptable environ-

mental levels of organic pollutants have been estab-

lished (Liu et al., 2012, Jonidi Jafari et al., 2012). A com-

mon problem in most industries is the disposal of large

volume of wastewater containing organic compounds

(Jin et al., 2012, Shaobin et al., 2011).

Aniline is an important chemical compound which

is well own for its wide applications in the manufac-

ture of dyestuffs, rubbers, pesticides, plastics and paints

(Tang et al., 2012). However, the aniline-laden waste-

water discharged from these industries has become a

severe environmental problem as well (O’Neill et al.,

312 APPLICATION OF SINGLE-WALLED CARBON NANOTUBES FOR REMOVAL OF ANILINE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Balarak, Mostafapour and Joghataei

2000). It is highly toxic and has harmful inﬂuences on

human health and aquatic life (Leili M et al., 2013). Ani-

line is a blood toxin, causing hemoglobin to convert to

methemoglobin, resulting in cyanosis (Guo et al., 2012).

Lengthy or repeated exposures may result in decreased

appetite, anemia, weight loss, nervous system affects,

and kidney, liver and bone marrow damage. Any expo-

sure may cause an allergic skin reaction (Balarak et al.,

2016).

Due to the negative environmental impact caused by

the high toxicity of aniline, these wastewaters demand

thorough treatment. Traditionally, Aniline-containing

wastewater is usually treated by photocatalysis, cata-

lytic oxidation, biodegradation, advanced oxidation and

adsorption. Among these technologies, adsorption has

been proven to be effective in separating a wide variety

of organic contaminants from aqueous solutions (Shao-

bin et al., 2011). Compared to other treatment processes,

adsorption has the advantages of (1) removing a wide

variety of dissolved organic compounds and (2) not pro-

ducing any harmful byproducts (Ramavandi et al., 2015,

Ma et al., 2012). Various adsorbents have been devel-

oped for the removal of organic pollutants (e.g., dyes,

pesticides, pharmaceuticals/drugs, and phenols) from

water (Zazouli et al., 2014). Activated carbon (AC) is the

most commonly used commercial adsorbent because of

its excellent adsorption capacity for organic contami-

nants (Balarak et al., 2016).

However, it has certain shortcomings that include

limited availability, low adsorption capacity, and dif-

 cult recovery (Zazouli et al., 2014). Recently, a great

deal of attention has been focused on the application of

nano-structured materials as adsorbents to remove toxic

and harmful organic substances from wastewater (Visa

et al., 2012, Jazayeri et al., 2010, Futalan et al., 2011).

Carbon nanotubes (CNTs) are one of the most widely

studied carbon nanomaterials and can serve as excellent

adsorbents. Because of their hollow and layered struc-

ture and large speciﬁc surface area, which is why CNTs

are the most commonly used nanomaterials for adsorb-

ing toxic material. CNT adsorbents can be classiﬁed into

three types: single-walled CNTs (SWCNTs), multi-walled

CNTs (MWCNTs), and functionalized CNTs (f-CNTs). Such

materials have already played an important role in the

effective removal of several organic contaminants from

water (Balarak et al., 2016, Nourmoradi et al., 2013).

In this study, SWCNTs were used to study the removal/

adsorption of aniline from an aqueous solution. The

effects of various operating parameters, such as adsor-

bent dose, temperature, initial aniline concentration and

contact time were studied and optimized. The kinetics

and thermodynamics of the adsorption process of ani-

line were studied. Thermodynamic calculations of the

adsorption process are required to understand the mech-

anism of adsorption, spontaneity, and heat of adsorption

using different thermodynamic parameters.

MATERIALS AND METHODS

The bulk solution of the aniline was prepared by dis-

solving a measured quantity of aniline (molecular for-

mula is C

N and formula weight is 93.13 g/mol) in

1 L of double distilled water.The single-walled carbon

nanotubes with average diameters of 10–20 nm [SMWC-

NTs (10–20)] was obtained from Research Institute of

Petroleum Industry (RIPI), Tehran, Iran and were used

as received. On the basis of the information provided

by the manufacturer, the SWCNTs were synthesized

by catalytic chemical vapor deposition (CVD) method.

All chemicals used in this study were obtained from

Sigma–Aldrich (analytical grade), and all solutions were

prepared using deionized water. Double distilled water

was used in all the experiments.The scanning electron

microscope (SEM) (JEOL JSM 6500F) and transmission

electron microscopy (TEM) (JEOL JEM-1230 operating

at 120 kV) were used to characterize the SWCNTs mor-

phological structure.

Adsorption kinetics was carried out by in batch tech-

nique. Batch experiments were carried out for determin-

ing the adsorption isotherms of aniline onto the various

adsorbent in a glass beaker. The aniline aqueous solutions

were magnetically stirred at a constant rate (180 rpm),

allowing suf cient time for reaching adsorption equilib-

rium. It was assumed that the applied stirring speed allows

all the adsorbent surface area to come in contact with ani-

line molecules over the course of the experiments. In each

experiment a  xed volume (100 mL) of aniline aqueous

solution at constant aniline concentration (25-200 mg/L)

was used. The study was performed at room temperature

to be representative of environmentally relevant condi-

tion. All experiments were carried out in duplicate and

the average value was used for further calculation. The

removal ef ciency and sorption capacity of the SWCNTs

were determined by Eq. (1) and (2), respectively (Rawaj h

et al., 2006, Balarak et al., 2016):

(1)

(2)

Where; R (%) and q

(mg/g) are the removal ef ciency

and adsorption capacity, respectively. Co and Ce are the

concentrations of aniline in solution (mg/L) at time t=0

and t, respectively, M (g) is the mass of the sorbent and

V (L) is the volume of the aniline solution.

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS APPLICATION OF SINGLE-WALLED CARBON NANOTUBES FOR REMOVAL OF ANILINE 313

Balarak, Mostafapour and Joghataei

RESULTS AND DISCUSSION

The scanning electron microscope and transmission

electron microscope imaging was used to study the mor-

phological structure of the pristine SWCNTs; representa-

tive images are presented in Fig. 1. The outer diameters

and inner cavities of SWCNTs (10–20) were 15–25 nm

and 6–10 nm, respectively. In addition, the TEM analysis

veriﬁed the hollow structure of the SWCNTs.

The removal of the Aniline was studied with different

dose of SWCNTS from (0.01 to 0.15 g/L) at the optimum

concentration of 25 mg/L with  xed contact time (30

min), pH (7) and temperature of 30˚C ± 2˚ C. The effect

of the dose rate of SWCNTS on the removal of Aniline

is pictured in Figure 2. It was noted that the percentage

removal of the Aniline ion increases as the concentration

of SWCNTS increases owing to the enhanced total surface

area of the adsorbent. This means that the toxic ions can

be removed effectively from the contaminated water with

the proper amount of the adsorbent, which would pos-

sess more adsorption sites available for the Aniline ion

uptake from the solution (Mojovic

et al., 2011, Jadhav et

al., 2001). The optimum dose rate was found to be 0.8 g/L

for with the effective removal of 98.9%.

ADSORPTION ISOTHERMS

An isotherm describes the equilibrium relationship

between the adsorbate concentration in the liquid phase

and that on the adsorbent’s surface at a given condition

FIGURE 1. Micrographs of SWCNTs (a) SEM and (b) TEM

FIGURE 2. Effect of adsorbent dose on adsorption of aniline (C0= 25 mg/L, contact time=30 min,

pH=7, Temp= 30˚C)

314 APPLICATION OF SINGLE-WALLED CARBON NANOTUBES FOR REMOVAL OF ANILINE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Balarak, Mostafapour and Joghataei

(Suresh et al., 2012). It gives the most appropriate equi-

librium correlation. They are also important for compar-

ing biosorption performance, optimization, design and

prediction purposes. The biosorption of aniline on SWC-

was optimized by analyzing equilibrium curve of

the following three isotherm models.

1. Langmuir Isotherm: The Langmuir Isotherm de-

veloped by Irving Langmuir was originally used to

describe the gas-solid phase and adsorption onto

activated carbon, but is now extended and gener-

ally applied to liquid-solid interaction. The equa-

tion is (Mojovic

et al., 2011, Jadhav et al., 2001):

(3)

Where q

(mg/g) and C

(mg/L) are the solid phase con-

centration and liquid phase concentration of aniline at

equilibrium, respectively. Q

(mg/g) is the maximum

sorption capacity and b (L/mg) is the Langmuir constant

related to the af nity of the adsorbate for the adsorbent.

The linearized form of Equation (3) is given as (Balarak

et al., 2015, Zazouli et al., 2015):

(4)

Values of q

and b are determined from the linear

regression plot of (C

) versus C

, Fig 3 a. Linear plot in

negative direction indicates that Langmuir model fails to

explain the process of adsorption and absence of forma-

tion of monolayer.

FREUNDLICH ISOTHERM

The Freundlich isotherm relates the solute concentration

on the adsorbent surface to the solute concentration in

the liquid phase. The isotherm assumes that adsorption

occurs on a heterogeneous adsorbent surface (i.e. mul-

tilayer adsorption). Freundlich model is represented by

the equation (Balarak et al., 2016, Balarak et al., 2017):

(5)

Equation (5) can be linearized in logarithmic form, Equa-

tion (5) and the Freundlich constants can be determined

(Xin et al., 2011).

(6)

Where Kf and n are the Freundlich constants character-

istic of the system. Kf and n are indicators of adsorp-

tion capacity and adsorption intensity, respectively. A

linear regression plot of log qe versus log Ce, Figure 3b

gives the Kf and n values. The model is applicable to

the adsorption on heterogeneous surfaces by a uniform

energy distribution and reversible adsorption.

2. Tempkin Isotherm: The Tempkin isotherm takes

into account the interaction between adsorbate

and adsorbent and assumes a linear decrease in

the heat of adsorption instead of a logarithmic de-

crease. Tempkin isotherm is expressed as (Senturk

B et al., 2009, Ghaedi et al., 2012):

(7)

Equation can be expressed in a linear form as (Shen B

et al., 2009, Balarak et al., 2017):

(8)

Where , and B is a constant related to adsorption

heat, and Kt is the equilibrium binding constant (L/mol)

corresponding to maximum binding energy. K

and  are

calculated from the slope and intercept of q

versus LnC

Fig 3C The Tempkin equation better holds for the predic-

tion of gas phase equilibrium rather than liquid phase.

The liquid phase is a more complex phenomenon since

the adsorbed molecules do not necessarily organized in

a tightly packed structure with identical orientation.

3. Dubinin Radushkevich Isotherm: This model is in-

volved to estimate the porosity, free energy and

the characteristics of adsorbents. The isotherm as-

sumes the surface heterogeneity and the variation

of adsorption potential during sorption process.

The model has commonly been applied in the fol-

lowing linear Equation (Balarak et al., 2016):

(9)

Polanyi potential, €, can be calculated according the fol-

lowing equation (Agarwal et al., 2016):

(10)

Where B is a constant related to the adsorption energy,

the theoretical saturation capacity. The slope of the

plot of Ln qe versus €

gives B (mol

∙J

−2

) and the intercept

yields the adsorption capacity, Qm (mg∙g

−1

) as shown in

Figure 3d. The mean free energy of adsorption (E) which

is energy require to transfer one mole of the aniline from

in nity in solution to the surface of the solid can be

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS APPLICATION OF SINGLE-WALLED CARBON NANOTUBES FOR REMOVAL OF ANILINE 315

Balarak, Mostafapour and Joghataei

calculated from the B value using the following relation

(Balarak et al., 2016):

(11)

Linear plot with high regression factor indicating the

successful model in explaining the adsorption model.

Table 1 summarizes different isotherms constants. The

graphs in Fig 3-6, the Langmuir Isotherm in Figure 3

gave the highest correlation coef cient (R

=0.8108) rate

to the Freundlich isotherm (R

=0.7999) and Dubinin

Radushkevich (R

=0.7999). The linear coef cient of

determination for the Tempkin Isotherm was not very

high (R

=0.014). The graphs show that both the Freun-

dlich and Langmuir Isotherms models can suf ciently

describe the adsorption data well for aniline. The fact

that the sorption process showed a good  t to the Lang-

muir Isotherm suggests a  nite adsorption capacity and

energetically equivalent sites.

FIGURE 3. Isotherm plots for adsorption of aniline on SWCNTS (a) Langmuir isotherm, (b) Freundlich

isotherm, (c) Tempkin isotherm, (d) Dubinin Radushkevich isotherm.

Balarak, Mostafapour and Joghataei

316 APPLICATION OF SINGLE-WALLED CARBON NANOTUBES FOR REMOVAL OF ANILINE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

FIGURE 3. (Continude)

Table 1. Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich Isotherm constants for the adsorption of

Aniline unto SWCNTS

Langmuir Freundlich Tempkin Dubinin–Radushkevich

B (×10

mol

∙J

−2

)E R

925.2 0.041 0.162 0.996 2.41 5.64 0.958 1.46 25.2 0.724 945.4 6.25 808.95 0.894

Balarak, Mostafapour and Joghataei

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS APPLICATION OF SINGLE-WALLED CARBON NANOTUBES FOR REMOVAL OF ANILINE 317

The adsorption energy obtained from Tempkin plot

218.25 J/mg which indicates that the adsorption process

is endothermic and a strong interaction between SWCNT

and Aniline molecules. Also value of energy obtained

from Dubinin Radushkevich isotherm was 808.95 J/mol,

revealing physisorption of Aniline on SWCNT

CONCLUSION

The results of the present study indicate that SWCNT

have good potential as adsorbents for the removal of

aniline from aqueous solution. The amount of aniline

uptake (mg/g) was found to increase with increase in

aniline concentration and adsorption time. The results

obtained from the plots show that the process of adsorp-

tion follows Langmuir and Freundlich Isotherm model

for adsorbent. Thus, it can be used to estimate the model

parameters. This con rms the fact that Langmuir Iso-

therm best explains the adsorption process of aniline

from aqueous solution. The maximum loading capacity

estimated was 37.59 (mg/g) for Langmuir model.

ACKNOWLEDGEMENT

The authors are grateful from deputy of research and

technology of Qom University of Medical Sciences due

to supporting of this research.

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