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1925
ISSN 1229-9197 (print version)
ISSN 1875-0052 (electronic version)
Fibers and Polymers 2015, Vol.16, No.9, 1925-1934
Preparation and Adsorption Behavior of Diethylenetriamine/Polyacrylonitrile
Composite Nanofibers for a Direct Dye Removal
Arash Almasian, Mohammad Ebrahim Olya*, and Niyaz Mohammad Mahmoodi
Department of Environmental Research, Institute for Color Science and Technology, Tehran 1668814811, Iran
(Received September 3, 2014; Revised July 27, 2015; Accepted August 2, 2015)
Abstract: The diethylenetriamine (DETA)/polyacrylonitrile (PAN) composite nanofibers were prepared by usingelectrospinning technique. The surface morphology and chemical characterization of PAN/DETA composite nanofibers wereinvestigated using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Releasingpossibility of DETA from nanofibers was tested by total organic carbon (TOC) analysis. Results indicated that theincorporation of DETA into PAN affects the morphology of nanofibers. In order to hinder DETA releasing, this compoundwas fixed to the polymer using alkali treatment. The obtained PAN/DETA composite nanofibers were evaluated foradsorption of C.I direct red 80 (DR80). The amount of the dye adsorbed onto the PAN/DETA nanofiber mats was influencedby the initial pH, DETA amount, contact time, and the initial concentration of the dye solutions. The maximal adsorptioncapacity of the dye on the PAN/DETA nanofiber mats was calculated from the Langmuir model.
Keywords: Polyacrylonitrile, Electrospinning, Direct Red 80, Adsorption isotherm, Dye kinetic
Introduction
Nowadays, stress of water shortages is increased due to
deteriorating water quality, urbanization, and climate change
and wastewater reclamation. Water reuse is becoming a
widely endorsed strategy for augmenting freshwater resources.
In this regard, many methods such as adsorption, chemical
flocculation, chemical oxidation, froth flotation, ultra filtration,
and biological treatment technologies have been employed.
Among all, adsorption has been shown to be a highly
efficient process due to its sludge-free clean flexible operation,
simplicity of design, and complete removal of dyes from
dilute solutions. The adsorption properties of adsorbents
depend on the type and amount of functional groups of on
their surfaces. It was previously found that an adsorbent
containing nitrogen-based ligands are effective in forming
complexes with metal ions and dyes [1,2]. There are many
forms of nano adsorbents in different shapes including
cubes, spheres [3], plates [4], and fibers [5]. Nanofiber can
give an enormous surface area per unit volume, high
porosity, high gas permeability, and small interfibrous pore
size due to having diameter between tens and hundreds of
nanometer. Among the various methods reported in literatures
[6] for producing the nanosized fibers, electrospinning has
shown a great deal of attention due to simplicity, convenient,
low cost, and ability to produce ultrafine continuous fibers
from many polymeric [7] and ceramic [8] materials. One
advantage of production of nanofiber mats for application in
wastewater treatment is that they can be easily removed
from the solutions, which reduces the operation cost.
Polyacrylonitrile (PAN), a common and inexpensive
commercial polymer, has desirable chemical and thermal
properties [9] as well as good solubility in organic solvents
[10]. This polymer has extensively been studied for the
production of nanofibers by electrospinning process [9].
Since the properties of adsorbents used to remove dyes
changes with the solution conditions, the mechanism of
adsorption on the adsorbents is also changed significantly,
depending on different types of interaction between adsorbents
and dyes. Commonly, for this purpose the electrostatic
interaction has been identified as the major adsorption
mechanism for adsorption of dyes.
The combination of polymers and compounds with different
functional groups such as carboxyl and amine, enable their
utilization as effective adsorbents in dyes removed from
wastewater [11]. Previous research works stated PAN as a
desirable polymer for electrospinning and subsequent wastewater
treatment [12,13]. It is therefore of our interest to investigate
the feasibility of using a composite nanofiber mat bearing
amine groups for anionic dye removal from wastewater.
Some attempts were performed on surface modification of
PAN fibers. The amidoximated PAN nanofibers and aminated
PAN fibers were studied for ion adsorption by Saeed et al.
[11] and Shin et al. [14] respectively. However, no research
was reported to investigate the dye removal efficiency of the
polyacrylonitrile/diethylenetriamine (PAN/DETA) composite
nanofibers.
In the present work, PAN/DETA composite nanofiber mat
was synthesized and characterized by Fourier transform
infrared spectroscopy (FT-IR) and scanning electron microscopy
(SEM). The effect of the amount of DETA, the pH, the
contact time, and initial dye concentration on the adsorption
capacity of a direct dye was examined using a UV-vis
spectrophotometer.
*Corresponding author: [email protected]
DOI 10.1007/s12221-015-4624-3
1926 Fibers and Polymers 2015, Vol.16, No.9 Arash Almasian et al.
Experimental
Materials
Polyacrylonitrile copolymer (93.7 % acrylonitrile and
6.3 % vinylacetate with Mw=100.000 g /mol) was purchased
from Isfahan Polyacryl Inc. (Iran). N,N-dimethylformamide
(DMF), potassium carbonate, and diethylenetriamine (DETA;
~99 % purity) were used as received from Merck. DR80 was
supplied by Alvan Sabet Co. Iran. The chemical structure of
the dye is shown in Figure 1.
Preparation of PAN/DETA Composite Nanofibers
Electrospinning solution was prepared by 10 w/w% PAN
dissolved in DMF. Mechanical stirring was applied for 12 h
at room temperature in order to obtain homogeneous PAN
solution. The mixture of PAN/DETA solutions were then
prepared by adding a 10, 20, and 40 w/w% of DETA into
10 w/w% PAN solution, respectively. The mixtures were
stirred on a magnetic stirrer, and the reactions were allowed
to proceed at 95 oC for 240 min. The as-prepared solutions
were then electrospun under a fixed electric field of 15, 17,
and 19 kV, using a Gamma High Voltage Research RR60
power supply, onto aluminum (Al) sheet which was used as
the collector. The distance from the tip to the collector was
15 cm and the feeding rate of the polymer solution was
1.2 ml/h. The electrospun composite nanofiber mats were
placed at a vacuum oven (65 oC, 5 h) to ensure evaporation
of the solvent.
Composite Nanofibers Fixation Process
In order to provide bonding between DETA and PAN with
nanofiber, the mats were immersed in a distilled water batch
containing 100 % (w/w) potassium carbonate at 80 oC for
2 h. Finally, composite nanofibers were dried at an oven
(60 oC, 3 h).
Characterization
The FTIR spectra of pure PAN and PAN/DETA composite
nanofibers were examined by the FTIR spectroscopy
(ThermoNicolet NEXUS 870 FTIR from Nicolet Instrument
Corp., USA). The surface morphology of pure PAN and
PAN/DETA nanofibers were investigated using a scanning
electron microscope (SEM, LEO1455VP, and ENGLAND).
The releasing amount of DETA from composites was tested
by a TOC analyzer (TOC-L, Shimadzu).
Adsorption Studies
DR80 was selected as a dye to evaluate the adsorption
capacity of the membranes. For this purpose, 0.004 g of the
adsorbents were added to 90 ml of the dye solutions with
concentration of 40 mg/l. The pH of each solution was
adjusted to the desired value using HCl or NaOH solution. A
single-beam UV spectrophotometer (CECIL CE2021) is used
for adsorption measurements. The amounts of decolorization
from solutions were determined as a function of time
according to the following equation:
(1)
where A0 and A are dye concentration at t=0 and t,
respectively.
Results and Discussion
FTIR of PAN/DETA Composite Nanofibers
FTIR spectra were recorded for pure PAN and various
composites before and after the fixation process and results
are shown in the spectral range of 4000-450 cm-1 in Figure 2.
The PAN spectrum (curve a) exhibited the absorption peaks
of stretching vibrations at 3446 cm-1 (OH), 2242 cm-1 (C≡N)
[15], 1737 cm-1 (C=O) [9,16], 2966 cm-1 (CH stretching in
CH, CH2, and CH3 groups) [16,17] and 1200-300 cm-1 (C-
O) [18-20], which suggests that PAN is a copolymer
containing both of acrylonitrile and vinylacetate polymers.
In the spectra of the composite nanofibers mats (curves b-d),
the band at 3436 cm-1, corresponding to the overlapping of
the stretching vibration bands of OH and NH groups is
intensified and shifted to the lower wavenumbers compared
to that at pure PAN. This clearly states that the OH groups
are generated by the hydrolysis of the ester groups in the
PAN nanofiber. Such a result is further supported by the
disappearance of the band at 2966 cm-1 (CH stretching), and
decreasing in the intensity of the band at 1734 cm-1 (C=O
stretching), confirming hydrolysis of the acetate ester
groups. The spectra of composite fibers also showed shifting
of the band at 1631 to 1663 cm-1 and appearance of a new
band at 1562 cm-1 (c,d). These changes can be assigned to
the stretching vibrations of the amidine group (N-C=N) and
the bending vibrations of the secondary amine of DETA,
respectively [21-23]. Decreasing the intensity of the carbonyl
ester peak with an increase in the amount of DETA further
confirm the reaction of PAN with DETA [23]. The peak
associated with the nitrile group of the PAN composite
nanofiber mats at 2242 cm-1 also decreased in its intensity as
the amount of DETA increased. Results obtained from FTIR
suggested, the number of converted nitrile groups to amidine
Dec%A0 A–
A0
-------------- 100×=
Figure 1. The chemical structure of Direct Red 80.
DETA/PAN Composite Nanofiber and Dye Removal Ability Fibers and Polymers 2015, Vol.16, No.9 1927
increase with increment in the amount of DETA in composite
nanofibers.
Figure 2(a-g) showed the FTIR spectra of various
composites after the fixation process with alkali solution. It
can be seen that there is not a significant change between the
spectra of composites before and after the fixation process,
except for the band intensity at 1667 cm-1 which is related to
amidine group. The peak shifting, occurred from 1631 to
1667 cm-1 related to N-C=N group in amidine groups [24].
Here we conclude that the number of converted nitrile group
to amidine group is increased after the fixation process
relating to the amount of DETA.
Morphology of PAN/DETA Composite Nanofibers
Figures 3-5 show SEM images of pure PAN and different
PAN-DETA composite nanofibers electrospun before the
fixation process at three different applied voltages: 15, 17,
and 19 kV. The SEM images in Figure 3 show that the
nanofibers obtained at 15 kV are not taut and some irregularities
and beads are present on the surfaces of the nanofibers,
especially for those with higher amount of DETA. It can also
be observed that the diameters of nanofibers with higher
amount of DETA is more varied compared with those
having lower amount due to strong interactions between
PAN and DETA causing strong viscosity of electrospinning
solution. DETA is therefore used as a strong crosslinkers for
PAN matrix through chemical reactions between the nitrile
groups of PAN and amine groups of DETA [24,25].
According to Figure 4, PAN-DETA fibers electrospun at
17 kV showed less defects and beads compared to those
electrospun at 15 kV. Such beads and non-uniformity are
also observed for PAN-DETA nanofibers electrospun at
19 kV, confirming that an optimum voltage for electrospining
of PAN-DETA composites is 17 kV.
In the electrospinning process, a balance between the
electrostatic repulsion, surface tension, and viscoelastic
force is very important [24]. When the applied voltage is
15 kV, the electric field is not strong enough to provide the
necessary electrostatic repulsion in order to balance the
surface tension and viscoelastic force, and hence the liquid
jet is not stable. On the other hand, a voltage of 19 kV is too
high for electrospinning and the balance cannot be maintained.
The voltage of 17 kV can therefore provide a balance between
the electrostatic repulsion, surface tension and viscoelastic
forces, resulting to stabilization of the liquid jet and formation
of smooth surface morphology of fibers. The SEM results
are in good agreement with FTIR spectra.
Figure 6 showed the SEM image of composite nanofibers
(20 % w/w) at magnification of 21,000×. Here we found that
the surface of the composite became much rougher after
fixation process than that of untreated. Also the diameter of
the nanofibers slightly increased. This roughness and increasing
in nanofibers diameter occurred by alkali treatment and
further diffusion within the composite matrix. This result is
also observed by other researchers [15,26].
TOC Analysis
Table 1 showed the TOC analysis result of fixed and
unfixed composite fibers after immersing in distilled water.
As can be seen for unfixed samples, with increasing the
amount of DETA in composites, the TOC values increase.
For fixed samples, much less releasing of DETA is observed
confirming successful fixation and bonding of DETA to
PAN.
Adsorption Studies
DR80 Adsorption Time Studies for PAN/DETA Composite
Fibers
Figure 7 showed the effect of duration on DR80 removal
Figure 2. FTIR spectra of (a) pure PAN, (b) PAN-DETA
composite nanofibers mat (10 % w/w), (c) PAN-DETA composite
nanofibers mat (20 % w/w), (d) PAN-DETA composite nanofibers
mat (40 % w/w) before the fixation process, (e) PAN-DETA
composite nanofibers mat (10 % w/w), (f) PAN-DETA composite
nanofibers mat (20 % w/w), and (g) PAN-DETA composite
nanofibers mat (40 % w/w) after the fixation process.
1928 Fibers and Polymers 2015, Vol.16, No.9 Arash Almasian et al.
Figure 3. SEM images of (a) pure PAN, (b) PAN-DETA composite nanofibers (10 % w/w), (c) PAN-DETA composite nanofibers (20 %
w/w), and (d) PAN-DETA composite nanofibers (40 % w/w) (electrospinning voltage: 15 kV).
Figure 4. SEM images of (a) pure PAN, (b) PAN-DETA composite nanofibers (10 % w/w), (c) PAN-DETA composite nanofibers (20 %
w/w), and (d) PAN-DETA composite nanofibers (40 % w/w) (electrospinning voltage: 17 kV).
DETA/PAN Composite Nanofiber and Dye Removal Ability Fibers and Polymers 2015, Vol.16, No.9 1929
by PAN/DETA composite nanofibers. As it is shown in
Figure 7, the adsorption was initially quite rapid during the
first 10 min. Nearly 90 % of the ultimate adsorption occurred
within 10 min, and the adsorption then slowed down,
reached the equilibrium. The uptake of dye molecules by the
adsorbent and the time required for establishment of
Figure 5. SEM images of (a) pure PAN, (b) PAN-DETA composite nanofibers (10 % w/w), (c) PAN-DETA composite nanofibers (20 %
w/w), and (d) PAN-DETA composite nanofibers (40 % w/w) (electrospinning voltage: 19 kV).
Figure 6. High magnification SEM images showing the surface morphologies of (a) the composite nanofibers mat before the fixation
process and (b) the composite nanofibers mat after the fixation process.
Table 1. TOC values
Before fixation After fixation
SampleDistilled
water
PAN-10%w/w
DETA
PAN-20%w/w
DETA
PAN-40%w/w
DETA
PAN-10%w/w
DETA
PAN-20%w/w
DETA
PAN-40%w/w
DETA
TOC value
(mg/l)0.107 2.002 3.258 5.012 0.100 0.110 0.101
1930 Fibers and Polymers 2015, Vol.16, No.9 Arash Almasian et al.
equilibrium suggest the effectiveness of our synthesized
nanocomposite fibers for wastewater treatment. A decrease
in the amount of dye adsorbed for more than 10 min duration
of treatment is due to aggregation of dye molecules on the
surface of adsorbents. This problem may hinder the migration
of the dye, as the adsorption sites become saturated, and
resistance to diffusion of dye molecules in the adsorbents
increased. As can be seen from the Figure 8, PAN-40 % w/w
DETA had a high adsorption capacity as compared to other
two composites. The percentages of dye removal for PAN-
20 % w/w DETA and PAN-40 % w/w DETA are higher than
PAN-10 % w/w DETA and there is negligible difference
between PAN-40 % w/w DETA and PAN-20 % w/w DETA.
In this regard, PAN-20 % w/w DETA was chosen as an
optimum sample in this study, and it was used for further
studies.
Effect of Adsorbent Dosage on Dye Removal
The effect of variation of the adsorbent dosage on the
DR80 dye removal was studied by changing the adsorbent
dosage from 0.001 to 0.006 g and results are illustrated in
Figure 8. The adsorption experiments with variation of
adsorbent doses were carried out at fixed dye concentration
of 40 mg/l. It is clear from Figure 8 that the adsorbent
dosage had a great effect on the amount of adsorbed dye by
composite fibers. The enhancement in dye adsorption with
increasing the adsorbent dosage is most probably due to the
stronger driving forces and larger surface area available for
adsorption. However, if the adsorption capacity of composite
fibers is expressed in mg of adsorbed dye per gram of
material, the adsorption capacity decreased with increasing
the amount of PAN/DETA nanofiber mat. This result is
probably attributed to overlapping or aggregation of adsorption
sites resulting in a decrease in total adsorbent surface area
available to the dye. This results to further increase in
diffusion path length [27].
Effect of Initial Dye Concentration
Effect of initial dye concentration as a function of time
was considered and results are shown in Figure 9. For this
purpose, different concentrations of dye were used to study
adsorption of 0.004 g adsorbent including 20, 40, 60, and
100 mg/l. The amount of the dye adsorbed onto PAN/DETA
nanofiber mat increases with an increase in the initial dye
concentration of solution. If the amount of adsorbent is kept
unchanged, this is due to the increase in the driving force of
the concentration gradient with the higher initial dye
concentration. The adsorption of dye by PAN/DETA nanofiber
mat is very rapid and reaches equilibrium very quickly at
low initial concentration. At a fixed PAN/DETA composite
nanofiber mat dosage, the amount of dye adsorbed is
increased with increasing concentration of solution, but the
percentage of adsorption is decreased. In other words, the
Figure 7. Dye removal ability of the prepared composites fibers
(pH=2.1, 0.004 g, 40 mg/l).
Figure 8. The effect of adsorbent dose on dye removal at different
time intervals for PAN-20 % w/w DETA (pH=2.1, 40 mg/l).
Figure 9. The effect of initial dye concentration on dye removal at
different time intervals for PAN-20 % w/w DETA (pH=2.1, 0.004 g).
DETA/PAN Composite Nanofiber and Dye Removal Ability Fibers and Polymers 2015, Vol.16, No.9 1931
residual dye concentration will be higher for more initial dye
concentrations than 40 mg/l. In the case of lower concen-
trations, the ratio of initial number of dye molecules to the
available adsorption sites is low and subsequently the
fractional adsorption becomes independent from initial
concentration [28-31].
Effect of pH
Solution pH plays an important role in the adsorption
behavior of adsorbents. This parameter affects the surface
charge of adsorbent, degree of ionization of the dye in
solution, and separation of functional groups on the active
sites of adsorbent and solution chemistry. Adsorption
behavior of the PAN-DETA composite nanofiber mats at
different pHs was studied and the results are shown in Figure
10. Maximum adsorption of anionic dye occurred at pH=2.1.
Significant electrostatic interaction exists between the positively
charged surface of the PAN-DETA composite nanofiber mat
on one hand and dye on the other hand, due to the ionization
of functional groups of mat in water and negatively charged
anionic dye.
As the pH of the system increases, the number of positively
charged sites decreases. It does not favor the adsorption of
anionic dye due to the decreasing of electrostatic attraction
[32]. Lower adsorption of dyes at alkaline pH can be due to
the presence of excess OH− ions destabilizing anionic dyes
and competing with the dye anions for the adsorption sites.
The effective pH was 2.1 and it was used for further studies.
Adsorption Isotherms
Adsorption is the accumulation of mass transfer process
that can generally be defined at the interface between solid
and liquid phases. Equilibrium relationships between sorbent
and sorbet are described by sorption isotherms, which is the
ratio between the quantity of sorbet and that remained in
solution at a fixed temperature of equilibrium. In order to
have a suitable model of isotherm data should accurately fit
into different isotherms [33].
Langmuir, Freundlich, and Tempkin isotherm equations
were used in this work. The Langmuir equation is shown as
the following equation:
(2)
where qe is the amount of dye adsorbed on the composites at
equilibrium (mg/g), Ce is the equilibrium concentration of
dye solution (mg/l), KL is the equilibrium constant (l/g), and
Q0 is the maximum adsorption capacity (mg/g). This equation
has been successfully applied to many adsorption processes
[34,35]. The Langmuir isotherm is applied for those adsorption
processes with mono-layer coverage of the dye on the
surface of the composites.
The linear form of Langmuir equation is:
(3)
The, Isotherm data was also studied by the Freundlich
isotherm, which can be expressed by the following equation
[36,37]
(4)
where KF is the adsorption capacity at unit concentration and
1/n is the adsorption intensity.
1/n values indicate the type of isotherm to be irreversible
(1/n=0), favorable 0 < 1/n < 1), and unfavorable (1/n > 1).
Equation (4) can be rearranged to a linear form:
(5)
The Tempkin isotherm is given as:
(6)
which can be linearized as:
(7)
where
(8)
Tempkin isotherm contains a factor that explicitly takes
into the account for adsorbing of species of adsorbent. This
isotherm assumes that the heat of adsorption of all the
molecules in the layer decreases linearly with coverage due
to adsorbent—adsorbate interactions, and the adsorption is
characterized by a uniform distribution of binding energies,
up to some maximum binding energy. A plot of qe versus ln
Ce enables the determination of the isotherm constants B1
and KT from the slope and the intercept, respectively. KT is
qe
Q0KLCe
1 KLCe+--------------------=
Ce
qe
-----1
KLQ0
------------Ce
Q0
------+=
qe KFCe
1/n=
logqe logKF
1
n---+ logCe×=
qe
RT
b-------ln KTCe( )=
qe B1lnKT B1lnCe+=
B1
RT
b-------=
Figure 10. The effect of pH on dye removal at different time
intervals for PAN-20 % w/w DETA (0.004 g, 40 mg/l).
1932 Fibers and Polymers 2015, Vol.16, No.9 Arash Almasian et al.
the equilibrium binding constant (l/mol) corresponding to
the maximum binding energy and constant B1 is related to
the heat of adsorption.
Figure 11 showed the adsorption Isotherms of DR80 using
PAN-DETA composite nanofiber mat. The Q0, KL, R2
(correlation coefficient for Langmuir isotherm), KF, n and R2
(correlation coefficient for Freundlich isotherm), and the B1,
KT, R2 (correlation coefficient for Tempkin isotherm) are
given in Table 2. Results indicated that the correlation
coefficient of the one for Langmuir equation is better than
the fitted model for Freundlich and Tempkin equations. This
means that the adsorption of dye takes place at specific
homogeneous sites and one layer adsorbed onto the PAN-
DETA composite nanofibers mat surface.
Adsorption Kinetics
Kinetic data were analyzed with the Lagergren and Ho
equations [38]. A linear form of pseudo-first- order model
was described by Lagergren of following equation:
(9)
where qe is the amount of dye adsorbed at equilibrium (mg/
g), qt is the amount of dye adsorbed at t time (mg/g), and K1
is the equilibrium rate constant of pseudo-first-order adsorption
(min-1) [39].
According to a linear form of pseudo-second-order model
(equation (10)) [40], the values obtained with Ho equation is
illustrated in Figure 12,
(10)
In equation (10), qe is the amount of dye adsorbed at
equilibrium (mg/g) and K2 is the pseudo-second-order
equilibrium rate constant (g/mg·min).
The possibility of intra particle diffusion resistance
affecting adsorption was explored by using the intra particle
diffusion model as [41]:
(11)
where kp and I are the intra particle diffusion rate constant
and intercept, respectively.
The values of K1, R2 (correlation coefficient for pseudo-
first-order sorption kinetics), K2, R2 (correlation coefficient
for pseudo-second-order sorption kinetics), and kp, I, R2
(correlation coefficient for intra particle diffusion) were
calculated and are shown in Table 3. Results indicated that
the adsorption kinetic of dye on the PAN-DETA composite
log qe qt–( ) log qe( )K1
2.303-------------t–=
t
qt
----1
Kqe
2---------
1
qe
----t+=
qt kpt1/2
I+=
Figure 11. Adsorption isotherm of DR80; (a) Langmuir, (b)
Freundlich, and (c) Tempkin.
Table 2. Linearized isotherm coefficients for dye adsorption onto the composite nanofibers mat at different dye concentration
Langmuir Freundlich Tempkin
Q0 KL R2 KF 1/n R2 KT B1 R2
1250 0.25 0.999 724.43 0.177 0.613 92.077 775.46 0.981
DETA/PAN Composite Nanofiber and Dye Removal Ability Fibers and Polymers 2015, Vol.16, No.9 1933
nanofiber mat follows the pseudo-second-order rate expression.
Conclusion
In this paper, PAN-DETA composite nanofibes mat with
various amounts of DETA in composites were prepared and
their dye removal abilities were investigated. Direct red 80
(DR80) was used as model compound. The results indicated
that the addition of diethylenetriamine in the PAN polymer
affects the chemical and morphological structure of the
nanofibers through changing the viscosity of the spinning
solution. In order to fix and hinder DETA releasing from
fibers, an alkali treatment using potassium carbonate was
performed. It was observed that the nanofiber diameter
increased and the surface of nanofiber mats became much
rougher after the fixation process. This roughness can
increase the dye adsorption capacity. It was also found that
with increasing the amount of DETA in composites, the
number of nitrile groups converted to amidine groups
increased. The dye adsorption obeyed Langmuir isotherm
and the adsorption kinetic of dye was found to conform to
pseudo-second order model. The dye removal rate of
composite nanofibers mats in acidic solution was rapid due
to the adsorption of anionic dye onto the positively charged
composite nanofibers. It can be concluded that the PAN-
DETA composite nanofiber mat being a novel fibrous
adsorbent with high dye adsorption capacity is a suitable
alternative substrate to remove anionic dyes from the
colored aqueous solutions.
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Figure 12. (a) Pseudo-first-order sorption kinetic of DR80, (b)
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Table 3. Kinetic constants for dye adsorption on various composite nanofibers at different dye concentration
Pseudo-first order Pseudo-second order Intraparticle diffusion
AdsorbentConcentration
(mg/l)(qe)exp (qe)cal k1 R2 (qe)cal k2 R2 kp I R2
PAN/DETA
composite
nanofibers
(20 % w/w)
20
40
60
100
443.29
871.20
1280.34
1181.92
177.8
354.81
707.94
596.34
0.10
0.11
0.13
0.08
0.800
0.596
0.875
0.803
454.54
909.09
1250
1111.1
0.0005
0.0007
0.0010
0.0020
0.999
0.997
0.997
0.961
50.62
106.11
158.70
138.12
161.36
267.27
383.83
371.05
0.608
0.668
0.681
0.683
1934 Fibers and Polymers 2015, Vol.16, No.9 Arash Almasian et al.
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