Structure and photocatalytic activity of a low band gap donor-acceptor-donor (D-A-D) type conjugated polymer: poly(EDOT-pyridazine-EDOT)

Article abstract of DOI:10.1039/c6ra25252d

A donor-acceptor-donor (D-A-D) type monomer (3,6-bis(2-(3,4-ethylenedioxy thiophene))pyridazine, EPE) with pyridazine as an intermediate unit (acceptor) and 3,4-ethylenedioxythiophene (EDOT) as a sealing unit (donor) was prepared. The monomer was then polymerized by adjusting various ratios of FeCl₃/monomer to prepare a donor-acceptor-donor (D-A-D) type conjugated polymer: poly(EPE). The results from a structural analysis indicated that the conjugation length, doping level, thermal stability, crystallinity, as well as the morphologies of the poly(EPE)s can be affected by the oxidant?:?monomer ratio. The resulting products were characterized by ¹H NMR, FT-IR, UV-vis, TGA, XRD, EDX and SEM. Studies were carried out on the photocatalytic performance of the poly(EPE)s for the photocatalytic degradation of different dyes (methylene blue (MB), methyl violet (MU), methyl orange (MO), rhodamine B (RhB) and phenol) (5 mg L^?1) under xenon-lamp irradiation, and the same type of light source and different catalysts (poly(EPE)s and PEDOT) on the degradation efficiency of MU were investigated, which showed that poly(EPE) was an effective photocatalyst, and the presence of Fe ions in the polymer matrix played a significant role in enhancing the photocatalytic activity of poly(EPE). Among the poly(EPE)s, the doped poly(EPE)₂ ([FeCl₃]/[EPE] ratio of 8?:?1) achieved the highest degradation efficiency (95.53%) for MU dye under the simulation of a visible light source for 300 min.

Full text of DOI:10.1039/c6ra25252d

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Structure and photocatalytic activity of a low band
gap donor–acceptor–donor (D–A–D) type
conjugated polymer: poly(EDOT–pyridazine–
EDOT)
Cite this: RSC Adv., 2017, 7, 1877
Lei Yang, Ruxangul Jamal,*ab Fangfang Liu, Yujie Wang and Tursun Abdiryim*ab
ab
ab
ab
A donor–acceptor–donor (D–A–D) type monomer (3,6-bis(2-(3,4-ethylenedioxy thiophene))pyridazine, EPE)
with pyridazine as an intermediate unit (acceptor) and 3,4-ethylenedioxythiophene (EDOT) as a sealing unit
3
(donor) was prepared. The monomer was then polymerized by adjusting various ratios of FeCl /monomer to
prepare a donor–acceptor–donor (D–A–D) type conjugated polymer: poly(EPE). The results from a structural
analysis indicated that the conjugation length, doping level, thermal stability, crystallinity, as well as the
morphologies of the poly(EPE)s can be affected by the oxidant : monomer ratio. The resulting products were
1
characterized by H NMR, FT-IR, UV-vis, TGA, XRD, EDX and SEM. Studies were carried out on the
photocatalytic performance of the poly(EPE)s for the photocatalytic degradation of different dyes (methylene
ꢀ1
blue (MB), methyl violet (MU), methyl orange (MO), rhodamine B (RhB) and phenol) (5 mg L ) under xenon-
lamp irradiation, and the same type of light source and different catalysts (poly(EPE)s and PEDOT) on the
degradation efficiency of MU were investigated, which showed that poly(EPE) was an effective photocatalyst,
and the presence of Fe ions in the polymer matrix played a significant role in enhancing the photocatalytic
Received 14th October 2016
Accepted 30th November 2016
DOI: 10.1039/c6ra25252d
2 3
activity of poly(EPE). Among the poly(EPE)s, the doped poly(EPE) ([FeCl ]/[EPE] ratio of 8 : 1) achieved the
www.rsc.org/advances
highest degradation efficiency (95.53%) for MU dye under the simulation of a visible light source for 300 min.
electron acceptors form massive p-bonds, which can enhance
the intramolecular charge transfer and form a zwitterionic
1
. Introduction
Over the last two decades, organic p-conjugated materials, resonance structure. Furthermore, in p-conjugated polymers,
particularly p-conjugated polymers, have become an important the donor units are connected with the acceptor units and this
research topic in the eld of functional polymers, and have been enhances the property of the double bonds. The enhancement
1,2
employed in several elds such as in sensors, light-emitting of the double bonds broadens the material's valence bands and
3
4
5
diodes, optical displays, electrochromic windows, photode- conduction bands; this can effectively reduce the energy gap,
6
7
8
tectors, transistors, molecular electronics and energy appli- and thus this unique structure displays excellent optoelectronic
9
–11
16,17
cations.
Among the various type of p-conjugated polymers, properties.
p-conjugated systems with a low band gap have attracted
The pyridazine unit is one of the strongest electron-
special attention due to their electrical, optical and photoelec- withdrawing units because it contains two electron-
1
8
tric characteristics, and they have found important applications withdrawing imine nitrogens (–C]N–) in the structure.
in the elds of photovoltaic and optoelectronic devices.
12
Furthermore, the lack of electrical characteristics of the pyr-
Usually, the synthesis of a low band gap structure of p-conju- idazine unit can reduce the minimum energy of the orbital
gated polymers requires the introduction of electron- energy level to effectively decrease the bandwidth of the polymer
1
9
withdrawing and electron-releasing units to the polymer when the unit is combined with an electron-releasing unit.
11
chain, where the electron-releasing units serve as electron Among the electron-releasing units, 3,4-ethylenedioxythiophene
donors, whereas the electron-withdrawing units serve as elec- (EDOT) is a major example of a thiophene derivative and can add
13–15
20,21
tron acceptors.
When the polymer forms a “donor–acceptor– interesting optoelectrical properties to the resulting polymer.
donor” type structure (D–A–D type), the electron donors and Furthermore, EDOT has been universally used as a constitu-
tional unit for several functional p-conjugated systems.
a
Compared to the other thiophene derivatives, the higher
Key Laboratory of Oil and Gas Fine Chemicals, Educational Ministry of China, College
of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, People's electron-donating power of EDOT results in a stronger donor–
22
Republic of China. E-mail: jruxangul@sina.com; tursunabdir@sina.com.cn
b
acceptor interaction and a smaller band gap. Yamamoto et al.
reported a p-conjugated monomer with pyridazine as the
Key Laboratory of Functional Polymers, Xinjiang University, Urumqi 830046, People's
Republic of China
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 1877–1886 | 1877

View Article Online
RSC Advances
Paper
3 4
intermediate unit (electron acceptor) and thiophene as the ferric chloride were purchased from Aldrich. Pd(PPh ) was
29
sealing unit (electron donor), and this triplet compound was synthesized according to a method in the literature. All the
polymerized for achieving a low band gap D–A–D type conju- other chemicals and solvents, including methylene blue, methyl
gated polymer. They found that this type of D–A–D type conju- violet, methyl orange, rhodamine B, phenol, methanol, and
19
gated polymer had the ideal charge transfer rate. Moon et al. chloroform were used as received without further purication.
reported a donor–acceptor–donor type liquid crystal with a pyr-
idazine core (EDOT–pyridazine–EDOT) with two peripheral long
alkyl chains, and the designated D–A–D type core structure could
induce a distinct liquid crystalline smectic phase due to the
strong intermolecular interaction between the donor and
2
.2 Instrumentation
1
The H NMR spectra of the products were obtained on Varian
Inova 400 MHz with DMSO-d as the solvent. GPC analysis was
6
carried on the Waters apparatus GPCV-1525 equipped with an
RI detector using DMF as the eluent at 35 C, and calibration
was accomplished with polystyrene standards (Polysciences,
JP). The FT-IR spectra of the samples were recorded on
a BRUKER EQUINOX-55 Fourier transform infrared spectro-
photometer using KBr pellets (Bruker, Billerica, MA, USA)
23
acceptor units.
ꢁ
In addition, p-conjugated polymers with a favourable semi-
conductor band gap have achieved high photocatalytic activi-
24
ties. Patil et al. studied the degradation of azo dye OG by P3HT,
MEH-PPV, and Degussa P25 under UV light and found that the
highest photocatalytic rate of OG was approximately 80% aer
ꢀ
1
(frequency range from 4000 to 400 cm ). The UV-vis absorption
24
6
0 min. Remita et al. found that the PEDOT nanostructures
spectra of the samples were measured with a UV-visible spec-
trophotometer (UV4802, Unico, USA). The thermal properties of
the polymers were recorded via thermogravimetric analysis. The
possessed better photocatalytic activity than P25-TiO for the
2
degradation of MO under UV light, where the degradation effi-
25
ciency reached 100% aer 15 min. However, in real applica-
tions, these polymers may only achieve low photocatalytic
activities because there is just 5% of UV light in visible light
sources. Hou et al. reported a degradation efficiency of RhB by
a conjugated polyene catalyst under visible light of only 20%
ꢁ
ꢁ
polymers were heated from 25 C to 1000 C at a heating rate of
ꢁ
ꢀ1
10 C min under an argon atmosphere on a Hitachi STA7300
thermal analysis instrument. Phase characterization of the
samples was done by X-ray powder diffraction (XRD, Bruker AXS
D8 diffractometer) with monochromatic CuKa as the irradia-
26
aer 160 min. In principle, shortening the forbidden band
width of the catalyst to visible light absorption spectrum
spreading is key to improving the photocatalytic activity of the
ꢁ
tion source (l ¼ 0.15418 nm), at a scan range (2q) from 10 to
ꢁ
8
0 . SEM and EDX were conducted on a Hitachi SO8010 eld
emission scanning electron microscope.
27
catalyst. Therefore, a p-conjugated polymer with pyridazine as
the intermediate unit (electron acceptor) and EDOT as the
sealing unit (electron donor) with a low band gap and ideal
charge transfer rate should be an ideal catalyst.
2
.3 Synthesis of EPE
EPE was synthesized according to the procedure in ref. 23 and
1
Moreover, the presence of a small amount of Fe ions in the as shown in Scheme 1. H NMR (DMSO-d
6
, ppm): d: 8.079
1
polymer matrix is another important factor for enhancing the (m, 1H), 6.83 (m, 1H), 4.407 (m, 4H), 4.301 (m, 4H). The H NMR
28
photocatalytic activity of the polymer. When the polymer spectrogram is depicted in Fig. 2.
ꢀ
absorbs visible light, it produces an electron (e ) that transfers to
the conduction band of the Fe ions; this will lead to an
2.4 Liquid-phase oxidation polymerization of EPE
enhancement in charge separation and the formation of hydroxyl
The simple solution oxidation polymerization process was
carried out as follows: 10 mL chloroform and 0.179 g (1.1098
mmol) anhydrous ferric chloride were added to the polymeri-
zation bottle; 0.1 g (0.2774 mmol) EPE was dissolved in 10 mL
chloroform solution and then slowly added into the above-
mentioned blend solution. Aer stirring the solution at room
temperature for 12 h, a small amount of cold methanol was
added to the nal product. Finally, the product was removed
from the mixture by repeatedly washing with methanol and
distilled water until the ltrate was colorless. The powder was
ꢀ
and hyperoxide radicals (O
2
c , cOH). Accordingly, a high amount
ꢀ
2
of radicals (O c , cOH) leads to the polymer having a higher
degradation efficiency for dyes under visible light. Furthermore,
there are only a few reports in literature about the application of
D–A–D type polymers in the eld of dye degradation.
Herein, we prepared the donor–acceptor–donor (D–A–D) type
monomer (3,6-bis(2-(3,4-ethylenedioxythiophene))pyridazine,
EPE), which was then polymerized by adjusting various ratios of
3
FeCl /monomer to prepare a donor–acceptor–donor (D–A–D)
type conjugated polymer: poly(EPE). Furthermore, the degra-
dation of different types of dyes by different catalysts was
explored under the simulation of visible light irradiation. In
addition, the possible photocatalytic degradation mechanism
of MU dye by poly(EPE) is presented herein.
ꢁ
dried with a freeze drier at ꢀ55 C for 24 h. The obtained
polymer was noted as poly(EPE) . In the same way, syntheses
1
were carried out by adjusting the molar ratio of the oxidant/
monomer (represented by [FeCl ]/[EPE]) to 8 : 1 and 12 : 1,
3
respectively, and the resulting polymers were named as
2 3
poly(EPE) and poly(EPE) , respectively.
2. Experimental
2.1 Materials
2.5 Measurements of the photocatalytic activities
3,6-Dibromopyridazine
(98%),
3,4-ethylenedioxythiophene The dyes methylene blue (MB), methyl violet (MU), methyl
(99%), n-butyl lithium, N-butyltin chloride (99%) and anhydrous orange (MO), rhodamine B (RhB) and phenol were used as the
1878 | RSC Adv., 2017, 7, 1877–1886
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Scheme 1 Synthetic routes for the synthesis the monomer and
polymer.
model organic pollutants for the photocatalysis experiments. In
addition, the efficacy of the as-prepared catalysts was estimated
by the photodegradation of dyes under simulated visible light
irradiation using a 300 W xenon lamp. Herein, 4 mg of samples
was dispersed in 100 mL quartz beakers containing 40 mL of
dye. Before irradiation, the dye solution was magnetically stir-
red for 60 min in the dark to ensure the establishment of an
adsorption/desorption equilibrium, where the concentration of
0
dye was designated as C . Then, the mixed solutions were
irradiated under a 300 W xenon lamp. At given intervals of
illumination, the mixed solutions were sampled and centri-
fuged using an 800D high speed centrifuge at 4000 rpm for
3
Fig. 1 FT-IR spectra of (a) EPE and (b) poly(EPE)s in different [FeCl ]/
1
min to remove the samples, which were then analyzed using [EPE] ratios: 4 : 1; 8 : 1; 12 : 1.
a Unico 4802 recording spectrophotometer. In order to further
understand the photocatalytic activities of the catalysts, we also
studied the different catalysts for the degradation efficiency of
ꢀ
1
and 1496 cm can be observed, while at about 1442, 1396,
ꢀ1
MU dye. Different samples of (poly(EPE)
1 2
, poly(EPE) ,
1
361, 1238, 1076, 918, 848, 771 and 690 cm are the charac-
teristic bands of 3,4-ethylenedioxy-thiophene (EDOT). The
marked reduction in the relative intensities of the vibration
absorption bands at 3021–3129 cm , corresponding to the C–H
in the pyridazine ring in the poly(EPE)s, suggests that the pol-
poly(EPE) and PEDOT) were tested the same way. In addition,
3
19
in order to study the effect of Fe ions on the photocatalytic
performance of the polymer, different doped states of the
polymer (doped state and dedoped state) were performed in the
same way as described above. Decolorization efficiencies of the
dyes were estimated using the following equation:
ꢀ
1
30
y(EPE)s are partly in the doped state. The bands at approxi-
ꢀ
1
mately 1496, 1442, 1396 and 1361 cm are attributed to the
asymmetric stretching vibration of C]C and the stretching
vibration of C–C in the ring, respectively. The 1238 and 1076
cm bands are assigned to the presence of n(C–O–C) in the
ethylenedioxy group. There are also C–S–C characteristic
stretching vibrations bands at 918, 848 and 690 cm in the
thiophene ring.
approximately 1439 cm (ring stretching vibration) and 848
Degradation (%) ¼ (C
0
ꢀ C
t
/C
0
) ꢂ 100%
(1)
ꢀ
1
where C is the initial concentration of the MU dye and C is the
0
t
concentration at time t.
ꢀ1
31–33
In addition, characteristic bands at
ꢀ
1
3
. Results and discussion
ꢀ
1
0
cm
(C–H out-of-plane vibration) are due to a,a -coupled
thiophene rings. A n(C]N) peak appears at about 1573 cm
1
3.1 FT-IR and H NMR spectra
ꢀ1
,
34
Fig. 1 shows the FT-IR spectra of EPE and poly(EPE)s powders which is a characteristic of the pyridazine unit. According to
obtained with various oxidant/monomer molar ratios. As can be the previous report, the intensity ratios (Isym/Iasym) of the bands
ꢀ
1
ꢀ1
seen in Fig. 1, all the poly(EPE)s show similar spectra. The at 1438–1442 cm compared to the bands at 1489–1494 cm
35
characteristic bands of the pyridazine ring at about 1670, 1573 are indicative of the conjugated length. To compare with
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 1877–1886 | 1879

View Article Online
RSC Advances
Paper
others, the intensity ratio (Isym/Iasym) is the highest in poly(EPE)
2
Table 1 Molecular weight and polydispersity of the polymers
(
[FeCl ]/[EPE] ratio of 8 : 1), suggesting that the longest conju-
3
Polymers
Poly(EPE)
[FeCl
3
]/[EPE]
M
n
M
w
PDI
gated length is in poly(EPE) compared to that of the others.
2
1
Fig. 2 presents the comparison of the H NMR spectra of EPE
1
4 : 1
8 : 1
12 : 1
2063
2576
2495
2902
3955
2902
1.40
1.53
1.16
1
and poly(EPE)
1
([FeCl
3
]/[EPE] ratio of 4 : 1) in DMSO-d
6
. The H Poly(EPE)2
NMR spectrum of EPE shows the typical resonance lines for this Poly(EPE)
3
monomer, and their assignments are shown in Fig. 2(a). As
depicted in Fig. 2(b), poly(EPE) displays the characteristics of
1
two aromatic rings signal at ꢃd 8.1 and 6.8, which are attributed have alkyl chains, while the backbone of the polymers possess
to protons from the pyridazine and thiophene rings, respec- conjugate structures, which together lead to a low solubility and
37
tively. Furthermore, the aliphatic peaks at ꢃd 4.3 and 4.4 are high rigidity. Furthermore, most of the soluble parts come
36
ascribed to the O–CH protons of the O–CH –CH –O band.
from the oligomer of the polymers, and the lower molecular
2
2
2
Except for the characteristic signals for the polymer, the peaks weights of the poly(EPE)s are probably ascribable to the
in the range of d 1.5–0.7 are assigned to the alkyl groups of some increased stability of the radical cations formed from EDOT,
impurities in the polymer matrix. In order to understand the which slows the polymerization rate and leads to low molecular
33
molecular weight of the polymers, GPC was performed on the weight polymers.
samples. The presence of hydrogen atoms at the a-position of
the polymer indicates the low molecular weight of the soluble
fractions of the polymer, which was further evidenced by the gel
permeation chromatography measured results. As shown in
3
.2 Ultraviolet-visible absorption spectra
The UV-vis absorption spectra of the EPE and poly(EPE)s
recorded in N-methyl-2-pyrrolidinone (NMP) solvent are dis-
played in Fig. 3. As depicted in Fig. 3, EPE shows a peak at
w
Table 1, the weight-average molecular weights (M ) of the pol-
y(EPE)s were in the range from 2902 to 3955. However, all the
polymers possessed a rather low molecular weight with low
solubility as the molecular structures of the polymers do not
356 nm, assigned to the p–p* transition of the EDOT and
1
Fig. 2 H NMR spectra of (a) EPE and (b) poly(EPE)
1
3
([FeCl ]/[EPE] ratio
of 4 : 1) in DMSO-d
DMSO-d
6
. Starred peaks come from H
2
3
O, alkyl groups and Fig. 3 UV-vis spectra of (a) EPE and (b) poly(EPE)s in different [FeCl ]/
6
.
[EPE] ratios: 4 : 1; 8 : 1; 12 : 1.
1880 | RSC Adv., 2017, 7, 1877–1886
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
19
pyridazine units, whereas poly(EPE)s have three absorption
bands at ꢃ375, 453 and 484 nm from the conjugated segments
38
having different conjugation lengths, which correspond to p–
39
p* transitions in the polymer backbone. Compared with
poly(EPE) ([FeCl ]/[EPE] ratio of 4 : 1), the relative intensity of
the absorption bands at 453 and 484 nm are higher in the case
of poly(EPE) and poly(EPE) , implying that a higher content of
1
3
2
3
oxidant in the reaction medium leads to a higher conjugation
length in the polymer chains.
Furthermore, the intensity ratio of the absorption band at
484 nm to the band at 375 nm is the highest in the case of
poly(EPE) ([FeCl ]/[EPE] ratio of 12 : 1) among the poly(EPE)s.
3
3
This means that poly(EPE)
3
has the highest conjugation length
among the poly(EPE)s. However, compared with that of
poly(EPE)
poly(EPE)
2
3
, an upward trend is observed in the spectrum of
from 600 to 900 nm, which is a feature typically seen
Fig. 4 TGA of poly(EPE)s in different [FeCl
2 : 1.
3
]/[EPE] ratios: 4 : 1; 8 : 1;
40
in the partially doped state of polymer chains. Therefore, it
1
can be concluded that poly(EPE) has a higher doping level than
2
opt
poly(EPE) . Furthermore, the optical band gaps (Eg ) for
3
poly(EPE) , poly(EPE) and poly(EPE) were determined to be
1
2
3
discussion, the higher initial 5% weight loss temperature of
2.25 eV, 2.06 eV and 2.04 eV, respectively, from their solution
poly(EPE)
poly(EPE)
2
2
suggests that the amount of oligomers for EPE in the
matrix is lower than that of the others. This
absorption edges (lonset) (Table 2).
phenomenon can be a result of the longer conjugated length of
this matrix than that of the others. In addition, the high content
of oxidant (initiator) favours chain propagation, which can
result in longer polymer chains, consequently increasing the
3
.3 Thermal stability
Heat resistance is an important feature to measure the quality
of the polymer to adapt to the environment. Thermogravimetric
analysis (TGA) was utilized to evaluate the thermal properties of
the resulting polymers. Fig. 4 shows the TGA curves analyses of
the poly(EPE)s and reveals that all the polymers lost 5% of their
weight at about 236–253 C under an argon atmosphere. In
addition, poly(EPE)s gave a high residue at 900 C, of 34–39
wt%, indicating that the poly(EPE)s have good thermal stability.
41
conjugation length. Therefore, according to the results of the
ꢁ
FT-IR and UV-vis studies, the lower residue at 900 C for
poly(EPE)
1
than for the others may be due to the lower conju-
ꢁ
gation length in poly(EPE) .
1
ꢁ
3.4 XRD structural analysis
The poly(EPE)s exhibited three important weight loss steps. The Fig. 5 shows the XRD patterns of the poly(EPE)s. As shown in
initial weight loss of less than 5% is attributed to the evapora- Fig. 5, all the polymers display a rather broad diffraction peak
tion of solvents, moisture, and oligomers of EPE. The second with a low intensity at approximately 2q ¼ 24ꢁ due to the
ꢁ
ꢁ
step, from 236–253 C to 420–425 C, may be due to the loss of intermolecular internal p / p* stacking or the (020) reec-
the pendant ethylenedioxyl chain and decomposition of the tion. Compared with that of poly(EPE) , the other two poly(-
1
ꢁ
ꢁ
ꢁ
polymer framework. The last step, occurring from 420–425 C to EPE)s display diffraction peaks between ꢃ2q ¼ 10 and 13 ,
ꢁ
9
00 C is attributed to the loss from thermal destruction of the which can be assigned to the (200) reection. All these
polymer framework. A comparison study indicated that the diffraction peaks are similar to the characteristic diffraction
initial 5% weight loss temperature of poly(EPE)
than that for others, and the residue at 900 C for poly(EPE)
2
was higher peak of PEDOT; this indicates the existence of a crystalline
ꢁ
42
2
1
phase. Therefore, it can be concluded that poly(EPE) is more
was also higher than that for the others. Based on the above amorphous than the others. Moreover, the sharp diffraction
ꢁ
ꢁ
ꢁ
ꢁ
peaks at 2q ¼ 33 , 35 , 49 and 54 with low intensity are
present in all the polymers, which could be attributed to the
Table 2 Summary of the optical data, including maximum absorption existence of the doping agent FeCl . According to the related
4
ꢀ
peak, absorption edge wavelength (lonset) and optical band gap
(E ) of poly(EPE) , poly(EPE) and poly(EPE)
g 1 2 3
literature reports, the synthesized polymers are in a partially
doped state using FeCl
polymerization of thiophene, and the FeCl ion is most likely
3
the counter anion from the FeCl doping into the polymer
opt
3
as an oxidizing agent for the oxidative
4
ꢀ
UV-vis absorption spectra
Solution
max (nm)
42–44
structure.
opt
g
l
lonset (nm)
E
(eV)
3
.5 Energy-dispersive X-ray spectroscopy
Poly(EPE)
Poly(EPE)
Poly(EPE)
1
2
3
375
375
375
550
602
609
2.25
2.06
2.04
Fig. 6 shows the EDX spectra of the polymers. The peaks cor-
responding to C, N, O, S, Cl and Fe are clearly identied.
Furthermore, the peaks for Cl and Fe ions, which result from
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 1877–1886 | 1881

View Article Online
RSC Advances
Paper
Fig. 6 EDX of poly(EPE)s in different [FeCl
2 : 1.
3
]/[EPE] ratios: 4 : 1; 8 : 1;
1
morphologies present in the various oxidant/monomer molar
ratios. As shown in Fig. 7, the morphology of poly(EPE)
1
shows an irregular coral shape, having tentacles extending in
a random fashion, accompanied with the accumulation of
a large number of particles. Moreover, with the increase in
concentration of the oxidant (initiator), poly(EPE) has a more
regular coral-like morphology, with low accumulated parti-
cles. Furthermore, the tentacles have the tendency to adhere
to each other with the increase in the oxidant (initiator),
particularly in the case of poly(EPE) . The possible reasons
3
for such morphologies appearing in the poly(EPE)s may be
correlated with the structural properties of EPE and the
proportion of FeCl /EPE. EDOT units in the triplet unit can
3
immobilize the conjugated chain segment by intramolecular
covalent bond interaction and by the strong electron-
transport effect of EDOT in EPE, and this synergism of
EDOT will cause the polymers structure to have a more
4
5
regular and rigid structure. Moreover, as the concentration
of the oxidant (initiator) increases, the internal diffusion rate
of the monomer decreases, and the induction time of poly-
merization could be shortened. Furthermore, based on the
previous report, when the polymerization time elongates, the
EDOT units containing the monomer, which newly form
nano-briform oligomers, serve as a so template to form the
3
Fig. 5 XRD of poly(EPE)s in different [FeCl ]/[EPE] ratios: 4 : 1; 8 : 1; 12 : 1.
4ꢀ
the doping agent of FeCl , and the content of Fe ions are 0.57,
.79 and 0.68 wt%, respectively. The percentage of Fe ions in the
polymers is in the order of poly(EPE) > poly(EPE) > poly(EPE)
In addition, based on the results of the UV-vis study, compared
with that of poly(EPE) , an upward trend is observed in the
0
2
3
1
.
19
nano-briform structures. Therefore, according to the
abovementioned inference, the poly(EPE) from [FeCl
3
]/[EPE]
2
¼
4 : 1 forms the irregular coral-like shape mostly as
spectrum of the other two from 600 to 900 nm, which is
a feature typically seen in the partially doped state of the poly-
a result of crooked nanobers growing together. As the
content of the oxidant (initiator) increases, the concentration
of the monomer and the newly formed nano-briform olig-
40
mer chains. Therefore, it can be concluded that poly(EPE) has
2
the highest doping level. Comparisons showed that the EDX
results are consistent with the UV-vis results.
2
omers is relatively reduced. As for the poly(EPE) , the
branches of neighboring corals will link together to cause
a shape of hybrid tentacles with particles, whereby the clus-
ters of coral-like morphology of poly(EPE)
to this formation.
3
will be conducive
3
.6 Morphology
The morphologies of the polymers were investigated by
scanning electron microscopy (SEM). Fig. 7 displays different
1882 | RSC Adv., 2017, 7, 1877–1886
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 7 SEM images of (a) poly(EPE) (4 : 1), (b) poly(EPE) (8 : 1) and (c) poly(EPE) (12 : 1).
3
.7 Photocatalytic activity
Organic dyestuffs containing methyl blue (MB), methyl violet
MU), methyl orange (MO), rhodamine B (RhB) and phenol dyes
In addition, comparative experiments were conducted on MU
solution with the presence of different catalysts and poly(EPE)
in different doping states.
2
(
Fig. 8(a) displays the time-dependent absorption spectra of
MU dye degraded by different catalysts and without a catalyst.
The concentration of the dye shows a different degree of
have been widely applied in textile industries, but they raise
concerns as they are toxic to aquatic life and create serious
pollution to the environment. In this study, MB, MU, MO, RhB
and phenol were used as model organic pollutants to demon-
reduction in the presence of PEDOT, poly(EPE)
1 2
, poly(EPE) and
poly(EPE) catalysts for 300 min under a xenon lamp, with the
3
2
strate the effectiveness of poly(EPE) under a 300 W xenon lamp.
photodegradation rate being 11.54%, 53.7%, 95.53% and
Fig. 8 (a) Photocatalytic degradation of MU dye with the change in C
MB, MU, MO, RhB and phenol dyes with the change in C /C of poly(EPE)
different doped states of poly(EPE)
t
/C
0
in the presence of different catalysts. (b) Photocatalytic degradation of
2
. (c) Time-dependent absorption spectra of MU dye degraded by
t
0
2
.
2
Table 3 Comparison of poly(EPE) photocatalyst with other photocatalysts recently used for the degradation of dyes
a
b
ꢀ1
Sample
Dye
D.T
D %
Irradiation source
(mg)sample/(mg(mol) L
)
Dye ꢂ (mL)Dye
Ref.
ꢀ
5
TiO
0
5
2
–Fe
.05 FeT
% Pt–TiO
3
O
4
/RGO
/G
MB
180 min
300 min
360 min
360 min
360 min
300 min
140 min
300 min
600 min
120 min
300 min
300 min
300 min
300 min
100
92
91.06
94
98
99.47
22
98
2.2
40
500 W xenon lamp
150 W Philips CFL bulb
Visible light
Natural sunlight
Natural sunlight
10 mg/5.35 ꢂ 10 (mol Lꢀ1) ꢂ 40 mL
46
47
48
49
ꢀ1
4-NP
AO7
MB
MG
MB
0.5 mg/10 (mg L ) ꢂ 1 mL
ꢀ1
2
10 mg/35 (mg L ) ꢂ 60 mL
ꢀ5 ꢀ1
PANI/ZnO
0.4 mg/1 ꢂ 10 (mol L ) ꢂ 1 mL
ꢀ5 ꢀ1
0.4 mg/1 ꢂ 10 (mol L ) ꢂ 1 mL
ꢀ5 ꢀ1
FNZP/PANI
PNA/ZnO
CdS–TiO
PMPD
PFT
Poly(EPE)
Poly(EPE)
Poly(EPE)
Poly(EPE)
Natural sunlight
0.25 mg/1.5 ꢂ 10 (mol L ) ꢂ 1 mL
50
51
52
53
ꢀ
ꢀ
1
MB
300 W xenon arc lamp
400 W metal halogen lamp
300 W tungsten halogen lamp
Visible light
300 W xenon lamp
300 W xenon lamp
300 W xenon lamp
300 W xenon lamp
200 mg/10 (mg L ) ꢂ 100 mL
1
2
–Au
MO
AR249
MO
MB
MU
RhB
MO
150 mg/10 (mg L ) ꢂ 100 mL
ꢀ1
50 mg/50 (mg L ) ꢂ 50 mL
ꢀ
1
100 mg/20 (mg L ) ꢂ 100 mL
54
ꢀ1
2
2
2
2
97.88
95.53
78.73
30.93
4 mg/5 (mg L ) ꢂ 40 mL
This work
ꢀ1
4 mg/5 (mg L ) ꢂ 40 mL
ꢀ1
4 mg/5 (mg L ) ꢂ 40 mL
ꢀ1
4 mg/5 (mg L ) ꢂ 40 mL
a
b
Degradation time. Degradation percentage.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 1877–1886 | 1883

View Article Online
RSC Advances
1.45%, respectively. It is clear that the catalytic activity of and so on, and the results are shown in Table 3.
Paper
46–54
3
The results
poly(EPE)s is much higher than that of a PEDOT and MU indicate that, in comparison to the others, the D–A–D type
aqueous solution containing 4 mg poly(EPE) as it exhibits the polymer is an efficient photocatalyst. In addition, Fig. 8(c)
2
highest photodegradation efficiency among the four groups of illustrates the photocatalytic degradation of MU dye with
catalysts. Moreover, the results show that the [FeCl
of 8 : 1 is the optimum proportion to use for the photocatalyst. and Fe-dedoped poly(EPE)
Furthermore, the photocatalytic activity of different dyes is position efficiency of the MU dye in the presence of Fe-doped
3
]/[EPE] ratio simulated visible light, in the presence of Fe-doped poly(EPE)
2
2
. As shown in Fig. 8(c), the decom-
shown in Fig. 8(b), and it can be seen that in the presence of poly(EPE)
poly(EPE) , the photodegradation rate for MB, MU, MO, RhB poly(EPE)
2
2
is 95.53% in 300 min, and for Fe-dedoped
, under the same simulated visible light irradiation,
2
and phenol is 97.88%, 95.53%, 30.93%, 78.73% and 3.63% in only about 30.17% of the MU dye is decomposed within the
00 min, respectively, which indicates that the photocatalyst is same time. This result shows that the Fe ions as oxidants play
3
selective to degrading different dyes. Furthermore, the photo- a very major role in improving the degradation efficiency of the
catalytic performance of poly(EPE) was compared to that of the MU dye.
other catalysts for the photodegradation of MO, RhB and MB
3.8 Postulated mechanism
Based on the results from the EDX spectra of the doped poly-
mers (Fig. 6) and dedoped polymers (Fig. 9), the percentage of
Fe ions for the doped poly(EPE) and dedoped poly(EPE) are in
2 2
the order of: doped poly(EPE)2 > dedoped poly(EPE) . This
2
phenomenon further indicates that the degradation efficiency
of MU dye by dedoped polymers is lower than that of the doped
polymers. As it has already been reported, a small number of Fe
ions can narrow the band gap of the polymer and postpone the
electron–hole pair recombination over time, which would be
benecial to an improvement in the photocatalytic activity of
55,56
the polymer.
Therefore, it can be concluded that a higher
percentage of Fe ions in the polymer can lead to a more efficient
photodegradation of MU dye, and that the Fe ions in the poly-
mer matrix play a major role in improving the degradation
efficiency of the MU dye.
A schematic of MU dye decomposition is depicted in
Fig. 10. If the electrons and holes cannot be timely captured,
they will restructure together in a very short period of time,
which will reduce the photocatalytic activity of polymers.
However, for doping Fe ions in the polymers, the presence of
a small amount of Fe ions in the structure means Fe ions can
come not only into an electron capture position but also a hole
capture position, which can cause a decrease in the electron–
hole pair recombination. Then, when the polymers are illu-
minated with simulated visible light, both Fe ions and poly-
mers absorb the photons at their interface, and then charge
3
Fig. 9 EDX of dedoped poly(EPE)s in different [FeCl ]/[EPE] ratios:
4
: 1; 8 : 1; 12 : 1.
Fig. 10 Schematic mechanism of MU dye degradation.
1884 | RSC Adv., 2017, 7, 1877–1886
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
separation occurs at the interface. Since the conduction band D–A–D type of polymer as a new class of photocatalyst in the
of Fe ions and the LUMO level of the polymer are well matched photocatalytic degradation of organic dye waste waters, and it
for the charge transfer, the electrons are promoted from the p enriches the knowledge of the photocatalytic behavior of such
/
p* absorption band of the outside polymers upon visible polymers.
light illumination and are easily injected into the conduction
band of Fe ions. In addition, Fe ions doping in polymers can
2
+
3+
4+
Acknowledgements
result in three types of valence states: Fe , Fe and Fe ,
3
+
28
where Fe is the most stable state among them. Irradiation
The authors are grateful to the National Natural Science Foun-
dation of China (No. 21464014).
leads to the generation of electron–hole pairs [eqn (2)], and
2
+
4+
then Fe ions can trap them to form Fe and Fe ions [eqn (3)
2
+
4+
and (4)]. Finally, the Fe and Fe ions generate hydroxyl
radicals (cOH) and hyperoxide radicals (O c ), and the Fe is
ꢀ
3+
2
Notes and references
formed again [eqn (5) and (6)]. These reactions may delay the
5
7
recombination of electrons and holes, and then Fe ions lead
to a continuation of the degradation reaction by hydroxyl and
1 K. J. Albert, N. S. Lewis, C. L. Schauer, G. A. Sotzing,
S. E. Stitzel, T. P. Vaid and D. R. Walt, Chem. Rev., 2000,
100, 2595.
2
8
hyperoxide radicals.
2
D. T. McQuade, A. E. Pullen and T. M. Swager, Chem. Rev.,
000, 100, 2537.
E. J. List, R. Guentner, P. Scanducci de Freitas and U. Scherf,
Adv. Mater., 2002, 14, 374.
K. Bange and T. Gambke, Adv. Mater., 1990, 2, 10.
C. D. Dimitrakopoulos and P. R. Malenfant, Adv. Mater.,
2002, 14, 99.
Y. Yao, Y. Liang, V. Shrotriya, S. Xiao, L. Yu and Y. Yang, Adv.
Mater., 2007, 19, 3979.
3
+
+
ꢀ
Polymers/Fe + ħn 0 ħ + e
(2)
(3)
(4)
(5)
(6)
2
3
3
+
+
4+
Fe + ħ 0 Fe + hole capture
4
5
3
+
ꢀ
2+
Fe + e 0 Fe + electrons capture
4
+
ꢀ
3+
Fe + OH 0 Fe + cOH
6
7
2
Fe + O
+
3+
ꢀ
2
0 Fe + O c
2
Z. Chen, Y. Zheng, H. Yan and A. Facchetti, J. Am. Chem. Soc.,
2008, 131, 8.
8
9
R. L. McCreery and A. J. Bergren, Adv. Mater., 2009, 21, 4303.
Z. Yin and Q. Zheng, Adv. Energy. Mater., 2012, 2, 179.
4
. Conclusion
In this study, a D–A–D type monomer, namely EPE combining 10 L. Schmidt-Mende, A. Fechtenk ¨o tter, K. M u¨ llen, E. Moons,
ethylenedioxythiophene donor units with a pyridazine acceptor R. H. Friend and J. MacKenzie, Science, 2001, 293, 1119.
unit was prepared. In addition, a D–A–D type conjugated poly- 11 H. Van Mullekom, J. Vekemans, E. Havinga and E. Meijer,
mer, namely poly(EPE), was prepared by adjusting the ratios of Mater. Sci. Eng., R, 2001, 32, 1.
FeCl /monomer. The results of a structural analysis indicated 12 H. Sirringhaus, N. Tessler and R. H. Friend, Science, 1998,
that an increase in the content of the oxidant (initiator) in the 280, 1741.
reaction medium could lead to an increase in the formation of 13 T. Yamamoto, Z.-H. Zhou, T. Kanbara, M. Shimura, K. Kizu,
3
oligomers. However, it also favours the chain propagation,
which could increase the conjugation length. As a result, the
T. Maruyama, Y. Nakamura, T. Fukuda, B.-L. Lee and
N. Ooba, J. Am. Chem. Soc., 1996, 118, 10389.
poly(EPE)s from FeCl /monomer ratios of 8 : 1 and 12 : 1 dis- 14 C. Kitamura, S. Tanaka and Y. Yamashita, Chem. Mater.,
3
played a higher conjugation length, thermal stability, doping
level and crystallinity than the poly(EPE) from the FeCl
1996, 8, 570.
3
/
15 T. Yamamoto and B.-L. Lee, Macromolecules, 2002, 35, 2993.
monomer ratio of 4 : 1. The results also showed that the 16 T. Michinobu, K. Okoshi, H. Osako, H. Kumazawa and
morphology of the polymers could be affected by the ratios of K. Shigehara, Polymer, 2008, 49, 192.
FeCl to the monomer. The poly(EPE) showed a good selectivity 17 M. Nikolou, A. L. Dyer, T. T. Steckler, E. P. Donoghue, Z. Wu,
3
2
for the degradation of different dyes under a xenon lamp. In
N. C. Heston, A. G. Rinzler, D. B. Tanner and J. R. Reynolds,
addition, studies on the photocatalytic degradation of MU dye
Chem. Mater., 2009, 21, 5539.
displayed that poly(EPE)2 was an effective photocatalyst. 18 I. Nenner and G. Schulz, J. Chem. Phys., 1975, 62, 1747.
However, in the presence of PEDOT, the degradation rate was 19 T. Yasuda, Y. Sakai, S. Aramaki and T. Yamamoto, Chem.
only 13.04%. Furthermore, the presence of Fe ions in the
polymer matrix was the main factor for enhancing the photo- 20 L. Groenendaal, G. Zotti, P. H. Aubert, S. M. Waybright and
catalytic activity of poly(EPE). The presence of Fe ions in the J. R. Reynolds, Adv. Mater., 2003, 15, 855.
catalyst structure increased the number of active sites on the 21 L. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik and
grid. Among the poly(EPE)s with the highest doping level and J. R. Reynolds, Adv. Mater., 2000, 12, 481.
crystallinity as well as effective conjugation length, the polymer 22 J. Roncali, P. Blanchard and P. Fr `e re, J. Mater. Chem., 2005,
from the FeCl /monomer ratio of 8 : 1 displayed a higher pho- 15, 1589.
tocatalytic activity in the light source illumination. In summary, 23 Y. S. Park, D. Kim, H. Lee and B. Moon, Org. Lett., 2006, 8,
Mater., 2005, 17, 6060.
3
this study indicated the feasible and potential use of a new
4699.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 1877–1886 | 1885

View Article Online
RSC Advances
Paper
2
4 B. Muktha, G. Madras, T. Guru Row, U. Scherf and S. Patil, J. 41 N. Gospodinova and L. Terlemezyan, Prog. Polym. Sci., 1998,
Phys. Chem. B, 2007, 111, 7994. 23, 1443.
5 S. Ghosh, N. A. Kouame, S. Remita, L. Ramos, F. Goubard, 42 T. Y. Kim, C. M. Park, J. E. Kim and K. S. Suh, Synth. Met.,
2
P.-H. Aubert, A. Dazzi, A. Deniset-Besseau and H. Remita,
Sci. Rep., 2015, 5, 18002.
6 H. Li, W. Hou, X. Tao and N. Du, Appl. Catal., B, 2015, 172–
2005, 149, 169.
43 C. Wang, M. E. Benz, E. LeGoff, J. L. Schindler, J. Allbritton-
Thomas, C. R. Kannewurf and M. G. Kanatzidis, Chem.
Mater., 1994, 6, 401.
2
173, 27.
27 M. Pelaez, N. T. Nolan, S. C. Pillai, M. K. Seery, P. Falaras, 44 J. Xu, H. Chan, S. Ng and T. Chung, Synth. Met., 2002, 132,
A. G. Kontos, P. S. M. Dunlop, J. W. J. Hamilton,
J. A. Byrne and K. O'Shea, Appl. Catal., B, 2012, 125, 331.
8 S. Naghibi, S. Vahed, O. Torabi, A. Jamshidi and
M. H. Golabgir, Appl. Surf. Sci., 2015, 327, 371.
63.
45 T. Abdiryim, R. Jamal, C. Zhao, T. Awut and I. Nurulla, Synth.
Met., 2010, 160, 325.
46 Z.-Q. Li, H.-L. Wang, L.-Y. Zi, J.-J. Zhang and Y.-S. Zhang,
Ceram. Int., 2015, 41, 10634.
2
2
9 H. Meng, D. F. Perepichka, M. Bendikov, F. Wudl, G. Z. Pan,
W. Yu, W. Dong and S. Brown, J. Am. Chem. Soc., 2003, 125, 47 S. Sood, A. Umar, S. K. Mehta and S. K. Kansal, J. Colloid
5151. Interface Sci., 2015, 450, 213.
0 S. Breda, I. Reva, L. Lapinski, M. Nowak and R. Fausto, J. Mol. 48 S. H. Hsieh, W. J. Chen and C. T. Wu, Appl. Surf. Sci., 2015,
Struct., 2006, 786, 193. 340, 9.
1 C. Deetuam, C. Samthong, S. Thongyai, P. Praserthdam and 49 V. Eskizeybek, F. Sarı, H. G u¨ lce, A. G u¨ lce and A. Avcı, Appl.
A. Somwangthanaroj, Compos. Sci. Technol., 2014, 93, 1. Catal., B, 2012, 119–120, 197.
2 Y. Xiao, J. Wu, G. Yue, J. Lin, M. Huang, Z. Lan and L. Fan, 50 S. Kant, S. Kalia and A. Kumar, J. Alloys Compd., 2013, 578,
1
3
3
3
Electrochim. Acta, 2012, 85, 432.
249.
3
3
3 D. Zhang, J. Qin and G. Xue, Synth. Met., 1999, 100, 285.
4 R. Hoogenboom, D. Wouters and U. S. Schubert,
Macromolecules, 2003, 36, 4743.
51 S. Ameen, M. S. Akhtar, Y. S. Kim, O. B. Yang and H.-S. Shin,
Colloid Polym. Sci., 2010, 288, 1633.
52 T. Lv, L. Pan, X. Liu and Z. Sun, Electrochim. Acta, 2012, 83,
216.
3
3
5 A. Buzarovska and L. Arsov, Polym. Bull., 2003, 50, 161.
6 T. Yamamoto, K. Shiraishi, M. Abla and I. Yamaguchi, 53 Y.-G. Peng, J.-L. Ji, Y.-L. Zhang, H.-X. Wan and D.-J. Chen,
Polymer, 2002, 43, 711. Environ. Prog. Sustainable Energy, 2014, 33, 123.
7 G. Zhang, J. Zhang, G. Ding, J. Guo, H. Lu, L. Qiu and W. Ma, 54 R. Qiu, D. Zhang, Y. Mo, L. Song, E. Brewer, X. Huang and
Polymer, 2016, 93, 213. Y. Xiong, J. Hazard. Mater., 2008, 156, 80.
8 A. Ali, R. Jamal, A. Rahman, Y. Osman and T. Abdiryim, Prog. 55 J. Chen, Y. Qian and X. Wei, J. Mater. Sci., 2010, 45, 6018.
3
3
3
4
Nat. Sci., 2013, 23, 524.
9 T. Nie, K. Zhang, J. Xu, L. Lu and L. Bai, J. Electroanal. Chem.,
56 Y. Lu, P. R. Chang, P. Zheng and X. Ma, Chem. Eng. J., 2014,
255, 49.
57 W. Zhao, W. Fu, H. Yang, C. Tian, M. Li, J. Ding, W. Zhang,
X. Zhou, H. Zhao and Y. Li, Nano-Micro Lett., 2011, 3, 20.
2014, 717, 1.
0 T. Yamamoto, T. Shimizu and E. Kurokawa, React. Funct.
Polym., 2000, 43, 79.
1886 | RSC Adv., 2017, 7, 1877–1886
This journal is © The Royal Society of Chemistry 2017