A bromine-catalysis-synthesized poly(3,4-ethylenedioxythiophene)/graphitic carbon nitride electrochemical sensor for heavy metal ion determination

Article abstract of DOI:10.1039/c9ra02161b

In this paper, poly(3,4-ethylenedioxythiophene)/graphitic carbon nitride (PEDOT/g-C₃N₄) composites were prepared by the bromine catalysed polymerization (BCP) method with varying weight ratios of monomer to g-C₃N₄. For comparison, solid-state polymerization (SSP) and metal oxidative polymerization (MOP) methods were also used for the synthesis of PEDOT/g-C₃N₄ composites. Electrochemical determination of heavy metal ions (Cd²⁺ and Pb²⁺) was carried out by differential pulse voltammetry (DPV) on composite-modified glass carbon electrodes (GCEs), which were prepared by different methods. The obtained composites were analysed by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible absorption spectroscopy (UV-vis), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the bromine catalysed polymerization (BCP) method is an effective way to prepare the PEDOT/g-C₃N₄ composite, and the combination of PEDOT with g-C₃N₄ can improve the electrochemical activity of electrode materials. And, the composite from the BCP method modified electrode (PEDOT/10 wt% g-C₃N₄/GCE) exhibited the widest linear responses for Cd²⁺ and Pb²⁺, ranging from 0.06-12 μM and 0.04-11.6 μM with detection limits (S/N = 3) of 0.0014 μM and 0.00421 μM, respectively.

Full text of DOI:10.1039/c9ra02161b

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PAPER
A bromine-catalysis-synthesized poly(3,4-
ethylenedioxythiophene)/graphitic carbon nitride
electrochemical sensor for heavy metal ion
determination†
Cite this: RSC Adv., 2019, 9, 34691
ab
ab
ab
ab
ab
Wei Wu, Ahmat Ali, Ruxangul Jamal,* Mihray Abdulla, Tursunnisahan Bakri
ab
and Tursun Abdiryim
*
In this paper, poly(3,4-ethylenedioxythiophene)/graphitic carbon nitride (PEDOT/g-C
N
3 4
) composites were
prepared by the bromine catalysed polymerization (BCP) method with varying weight ratios of monomer to
g-C . For comparison, solid-state polymerization (SSP) and metal oxidative polymerization (MOP)
methods were also used for the synthesis of PEDOT/g-C composites. Electrochemical determination
and Pb ) was carried out by differential pulse voltammetry (DPV) on
3 4
N
3 4
N
2+
2+
of heavy metal ions (Cd
composite-modified glass carbon electrodes (GCEs), which were prepared by different methods. The
obtained composites were analysed by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible
absorption spectroscopy (UV-vis), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS),
scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed
that the bromine catalysed polymerization (BCP) method is an effective way to prepare the PEDOT/g-
Received 20th March 2019
Accepted 21st October 2019
C
N
3 4
composite, and the combination of PEDOT with g-C
3 4
N can improve the electrochemical activity
of electrode materials. And, the composite from the BCP method modified electrode (PEDOT/10 wt% g-
DOI: 10.1039/c9ra02161b
2+
2+
3 4
C N /GCE) exhibited the widest linear responses for Cd and Pb , ranging from 0.06–12 mM and
rsc.li/rsc-advances
0.04–11.6 mM with detection limits (S/N ¼ 3) of 0.0014 mM and 0.00421 mM, respectively.
Carbon-based materials typically include carbon nanotubes,
single-wall carbon nanohorns, bucky papers, graphene, and
Conducting polymers (CPs), such as polyaniline (PANI), poly- fullerenes. New features of carbon materials increase the wide
pyrene (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT), variability of multifunctional carbon-based sensing electrodes
have been prevalent in the eld of photoelectric materials for that exhibit high sensitivity and low sensing limits for a variety
several decades since they were rst discovered by Shirakawa of chemical and biological analytes due to the extraordinary
1
. Introduction
15
1
–3
et al. PEDOT is one of the most widely used conductive specic surface area, electrical conductivity, chemical dura-
polymers due to its good electrochemical stability and high bility, biocompatibility and mechanical strength of carbon-
4
16–19
electrical conductivity. Since Leverkusen Bayer rst synthe- based materials.
Graphene-like two-dimensional nano-
sized this compound in 1988, much research has been done on materials have been extensively studied for electrochemical
PEDOT. Due to its unique p-conjugation system, high conduc- sensing applications due to their structural properties similar to
20
tivity, easy processing and lm formation, PEDOT has been those of graphene and tuneable bandgap capability, such as
5
,6
21,22
used in many applications, such as energy storage, electro- transition metal dichalcogenides,
hexagonal boron nitride
and graphitic carbon nitride (g-C ) nano-
Among these, g-C has attracted massive attention
7
8
9
23,24
chromic devices, ion sensing and biosensors. In general, nanosheets,
PEDOT is not used alone but is compounded with other mate- sheets.
3 4
N
25–27
3 4
N
10
11,12
rials such as metals,
materials.
metal oxides,
and carbon due to its simple synthesis, satisfactory catalytic activity, excel-
lent chemical stability and environmental friendliness.
According to reports, the strong electron donor properties of
nitrogen can affect the electronic structure and result in
13,14
a
Key Laboratory of Oil and Gas Fine Chemicals, Ministry of Education, Xinjiang Uygur
Autonomous Region, Xinjiang University, Urumqi, 830046, P. R. China. E-mail:
20
different activity-enhancing mechanisms. In addition, g-C
ultrathin sheets demonstrate a strong affinity towards heavy
groups of g-C
and this affinity is very benecial for metal ions detection.
However, the mediocre electroconductivity of g-C seriously
3 4
N
tursunabdir@sina.com.cn; jruxangul@sina.com
b
Key Laboratory of Functional Polymers, Xinjiang University, Urumqi 830046, People's metal ions due to the intrinsic –NH and –NH
2
3 4
N ,
2
8
Republic of China
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra02161b
3 4
N
1
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27,29–31
affects its application in reality.
Therefore, modifying it by Br
2
were purchased from Aladdin. Anhydrous ethanol, iso-
compounding with other materials, such as graphene or CPs, is propanol, tetrahydrofuran (THF), anhydrous ferric chloride,
necessary to enable efficient electron transfer. CHCl , and CH COONa were purchased from Tianjin ZhiYuan
3
3
Recently, a number of PEDOT/g-C N composites have been Chemical Reagent Ltd. for use without further purication. The
3
4
ꢀ
1
synthesized for studies on supercapacitors, biosensors, photo- 0.1 mol L
catalysis and catalytic hydrogen production. For example, a g- 0.1 mol L
acetate buffer solution (ABS) was prepared by
ꢀ
1
sodium acetate and acetic acid, and standard
2
+
2+
3 4
C N nanobre-doped PEDOT-modied electrode was used for solutions of 0.001 M Cd and Pb were obtained by dissolving
the simultaneous determination of ascorbic acid and acetamin- Pb(AcO)
2
and Cd(AcO)
2
in ultrapure water, respectively.
32
ophen; a new type of carbon nitride-based polymer composite
33,34
was used for enhanced photocatalytic hydrogen production.
2.2 Synthesis of g-C N
3
4
However, there is no research in the eld of heavy metal ion
49
3 4
The g-C N sample was synthesized according to the literature.
detection. Hence, the preparation of PEDOT/g-C N nano-
3
4
First, 10 g of carbamide was added to a 40 mL crucible and placed
in a muffle furnace. Aer that, the precipitate was heated to
00 C for 2 h at a rate of 10 C per minute, followed by heating to
50 C for an additional 2 h. Finally, the crucible was cooled to
composites is a feasible method for determining heavy metal ions.
In general, the methods employed to prepare polymer-based
ꢁ
ꢁ
ꢁ
5
5
35
composites include electrochemical polymerization, chemical
3
6
37
oxidation polymerization, metal-catalysed coupling, solid-
ambient temperature, and a yellowish solid powder was obtained
38
39
state polymerization (SSP), acid-assisted polymerization,
aer washing with absolute ethanol and distilled water.
40
and photoinduced polymerization. However, polymer-based
composites synthesised by SSP oen have performance uctu-
ations due to uneven mixing of the inorganic phase and organic
phase. Furthermore, the metals used in the abovementioned
chemical polymerization methods are difficult to remove and
2.3. Synthesis of monomer DBEDOT
DBEDOT was prepared according to a method used in previous
50,51
research.
a mixture of THF and HAc (200 mL, 1 : 1 by volume). NBS (8.6 g,
8.3 mmol) was added to the mixture. Aer stirring at room
EDOT (3.0 g, 21.1 mmol) was dissolved in
41
3
act as dopants. For example, FeCl -catalysed polymerization
4
can result in residual iron, and aer several cycles of de-doping,
temperature and in the dark for 2 h, a certain amount of ice was
added to the solution, and some silvery white crystals appeared.
The crystals were then ltered, washed with iced ethanol and
dried over a vacuum at room temperature to obtain the pure
product (3.9 g, 61.7% yield).
an obvious electron paramagnetic resonance signal and sharp
ꢀ
42–46
XRD peaks (FeCl4 -doping) are still observed.
Hence,
obtaining a metal-free polymer is essential for improving the
performance of devices, such as OLEDs, solar cells and heavy
metal ion sensors, because the metal present in the polymer
occupies the active sites, which act as quenching sites for
47
2
.4 Preparation of PEDOT/g-C
To obtain composites with different contents of g-C
DOT (0.3 g, 1 mmol) was added to 20 mL CHCl
different ratios of g-C and was ultrasonically dispersed for
0 min. Then, Br (0.64 g, 4 mmol) solution was added to CHCl
3 4
N composites by BCP
excitons. In summary, the selection of a suitable polymeriza-
tion method is important for the preparation of polymer
composites. Patra et al. reported a metal free bromine catalyzed
polymerization for the synthesis of PEDOT and found this
method providing metal free and virtually defect free PEDOT
3
N
4
, DBE-
3
that had
3 4
N
2
2
3
48
under mild reaction conditions. However, there is no report
for preparation of composites with PEDOT by this method.
(
2 mL) at room temperature. Next, the reaction mixture was heat
ꢁ
to 50 C and stirred for 48 h. Aer completion of the reaction,
a purple-black solid precipitate was obtained. A black solid
powder was obtained aer washing with acetone and CHCl3.
Pure PEDOT was obtained using the same method without
In this paper, PEDOT/g-C
the bromine catalyzed polymerization (BCP) method with
varying weight ratios of monomer to g-C . For comparison,
3 4
N composites were prepared by
3 4
N
the SSP and metal oxidative polymerization (MOP) methods
were also used for the synthesis of PEDOT/g-C N composites.
3 4
adding g-C N .
3
4
And, the composites are used as electrochemical sensors for
determination of heavy metal ions (Cd and Pb ). The results
showed that among the composites from the bromine catalyzed
2
.5 Preparation of PEDOT/g-C
A mixture of DBEDOT (0.3 g, 1 mmol) and a certain amount of g-
in 10 mL CHCl was ultrasonicated for 20 min. Aer
3 4
N composites by SSP
2
+
2+
C
3
N
4
3
polymerization method, PEDOT/10 wt% g-C
3 4
N exhibited the
ultrasonication, the mixture was placed in an agate mortar to
completely evaporate the chloroform. Then, the mixture was
gently ground for 60 min until the DBEDOT was evenly mixed
widest linear responses and excellent sensitivity for heavy metal
2
+
2+
ions (Cd and Pb ). Furthermore, compared with the SSP and
MOP method composites, the reliability and linear detection
ꢁ
with g-C N ; the mixture was kept in a vacuum oven at 60 C for
3
4
range of the composite from the Br -catalysed polymerization
2
24 h. Finally, the residue was washed with CHCl and absolute
3
method were signicantly improved.
ꢁ
ethanol and then dried at 60 C for 24 h.
2. Experimental
2.6 Preparation of PEDOT/g-C
3 4
N composites by MOP
2.1 Reagents
First, EDOT (0.3 g, 1 mmol) and a certain amount of g-C N were
3
4
3,4-Ethylenedioxythiophene (EDOT) and carbamide were ob- added to chloroform (30 mL) and ultrasonically dispersed for
tained from J&K Scientic Ltd. N-Bromosuccinimide (NBS) and 30 min. Aer ultrasonication, anhydrous ferric chloride (0.65 g, 4
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mmol) was added to the mixture by ultrasonication for an addi-
tional 30 min. Then, the reaction was magnetically stirred at room
temperature for 24 h. Finally, the reaction product was ltered to
give a black solid, which was washed sequentially with chloro-
form, distilled water and anhydrous ethanol until the ltrate was
ꢁ
colourless and then dried under vacuum at 60 C for 24 h.
2.7 Preparation of modied electrodes
In general, the GCEs were sequentially polished with 1.0, 0.3,
and 0.05 mm aluminium oxide abrasives and then modied by
a simple method. A 5 mL aliquot of the PEDOT/g-C N suspen-
3 4
sion (1 mg/4 mL) was dropped onto the surface of the GCE and
Fig. 1 FTIR spectra of (a) PEDOT (BCP) and PEDOT/g-C
composites with different weight percentages of g-C (b) PEDOT/
0 wt% g-C prepared by different polymerization methods.
3 4
N nano-
3 4
N
1
3 4
N
ꢁ
dried at 40 C for 30 min. g-C
3
N
4
/GCE, PEDOT (BCP)/GCE and
/GCE (obtained by different methods)
were prepared by the same procedure.
3 4
PEDOT/10 wt% g-C N
in the heterocyclic ring cause the characteristic peaks in the
ꢀ
1
53
range of 1230–1650 cm
in the 3000–3500 cm
.
The wide vibration band appearing
region is caused by the stretching
vibration of the aromatic N–H bond and the uncondensed
ꢀ
1
2.8 Characterization and instruments
54
The FTIR spectra of the g-C , PEDOT and PEDOT/g-C
3
N
4
N
3 4
amino group (–NH2). For pure PEDOT (BCP), the characteristic
ꢀ
1
composites were obtained using a BRUKER EQUINOX-55 Fourier peaks at 1515 and 1320 cm are the typical C–C asymmetric
transform infrared spectrometer (Bruker, Billerica, MA, USA) stretching vibration and inter-ring stretching vibration,
ꢀ
1
(
frequency range 4000 to 500 cm ). The UV-vis spectra of the respectively. The peaks at approximately 1209, 1139 and
ꢀ
1
samples were recorded on a UV-vis spectrophotometer (UV4802, 1088 cm
Unico, Dayton, NJ, USA). The XRD patterns of the samples were enedioxy group. The bands at approximately 974, 918, 833,
conducted on a Bruker AXS D8 diffractometer with Cu-Ka radi- and 693 cm are the characteristic absorption bands of the
are the C–O–C bending vibrations in the ethyl-
55
ꢀ1
ꢁ
ꢁ
56
ation (l ¼ 0.154 nm); the scan range (2q) was 10 to 80 . The C–S–C bond in the thiophene ring.
morphology analysis of the g-C , PEDOT and PEDOT/g-C
For the composites, as shown in Fig. 1(a) and (b), the main
composites was obtained on a scanning electron microscope vibration bands are similar to those of PEDOT indicating that the
JSM7610F Plus, JEOL, Japan, operating voltage, 5 kV) and successful incorporation of PEDOT component in composites.
3
N
4
3 4
N
(
transmission electron microscope (JEOL model 2100, JEOL Ltd., Fig. 1(a) and (b) show that the positions of the characteristic
Tokyo, Japan). The elemental compositions of the samples were peaks for the PEDOT/10 wt% g-C N composites prepared by the
3
4
measured using energy-dispersive X-ray spectroscopy (EDS), SSP, MOP and BCP methods are basically identical. Furthermore,
43
which was conducted on a Leo 1430VP microscope (Carl Zeiss according to report, the intensity ratio of the vibration bands at
ꢀ
1
Inc., Oberkochen, Germany). The real samples were veried by approximately 1470/1515 cm is indicative of the conjugation
atomic absorption spectrometry (AAS) (Shimadzu AA6300C, lead degree of the composites, with a smaller ratio indicating a higher
wavelength 283.3 nm, lamp current 5.0 mA; cadmium wave- degree of conjugation. Therefore, it is clear from Fig. 1(a) and (b)
length 228.8 nm, lamp current 5.0 mA; slit 0.4 nm).
3 4
that PEDOT/10 wt% g-C N has a longer conjugated bond
57
The electrochemical performances were investigated via length. However, there are no characteristic peaks correspond-
a three-electrode system on an electrochemical workstation. ing to g-C N in the spectra of the PEDOT/g-C N composites,
3
4
3 4
(ChenHua, CHI660C, Instruments Co.). The modied GCEs which may caused by overlapping of characteristic peak of
were used as the working electrode, a platinum electrode was PEDOT and g-C N . In addition, the g-C N can also be enwrap-
3
4
3 4
the counter electrode and a calomel electrode was the reference ped by PEDOT in some extent, consequently bring a decrease in
electrode. Cyclic voltammetry (CV) was performed in a mixture peak intensity of g-C N .
3
4
3
ꢀ/4ꢀ
ꢀ1
of 5.0 mM [Fe(CN)
6
]
and 0.1 M KCl at 50 mV s . Differ-
ential pulse voltammetry (DPV) was performed in 0.1 M ABS (pH
3
.2 UV-vis spectra
¼
ꢀ
4.5) with an incremental potential of 2 mV from ꢀ1.2 to
0.2 V, with a pulse width of 50 ms and pulse period of 100 ms. The UV-vis spectra of g-C N , PEDOT (BCP), and the PEDOT/g-
3
4
C
3
N
4
composites are presented in Fig. 2. It is clear from Fig. 2(a)
that the UV-vis spectral peaks of g-C appears from 270 to
30 nm, which are absorption peaks characteristics of carbon
3 4
N
3. Results and discussion
4
3.1 FT-IR spectra
nitride. The absorption bands of PEDOT (BCP) at approximately
Fig. 1 shows the FTIR spectra of g-C
3
N
4
, PEDOT (BCP) and the 399, 426 and 460 nm can be ascribed to different conjugation
PEDOT/g-C N nanocomposites. In the spectrum of g-C N , the lengths, and they are assigned to the p–p transition of the
3
4
3 4
ꢀ1
58
band at 813 cm was identied as the bending vibration of the thiophene ring. Furthermore, the absorption peaks of PEDOT/
planar triazine ring mode. The weak peak appearing at g-C N (BCP) at 550, 600 and 667 nm are assigned to the polaron
3
4
ꢀ
1
59,60
8
90 cm can be attributed to the deformation mode of cross- and/or bipolaron band,
linked heptazine. The stretching vibrations of C–N and C]N between PEDOT and g-C
which indicates a strong interaction
3 4
. In Fig. 2(b), PEDOT/10 wt% g-C N
52
3
N
4
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ꢁ
shows broader diffraction peaks at 26.2 and sharp diffraction
ꢁ
ꢁ
ꢁ
ꢁ
ꢀ
peaks at 2q z 33 , 35 , 49 and 54 due to FeCl doping in the
4
composite.
3
.4 EDS analysis
Fig. 4 shows the EDS analysis of PEDOT (BCP) and the PEDOT/g-
composites on a silicon wafer. As shown in Fig. 4(a), the
EDS spectrum of the pure PEDOT sample indicates the presence
of C, S, O, and Br. Aer the addition of g-C , some N was
detected in the PEDOT/g-C composites prepared by the three
3 4
C N
3 4
N
Fig. 2 UV-vis spectra of (a) PEDOT (BCP) and PEDOT/g-C
3
N
4
nano-
(b) PEDOT/
3 4
N prepared by different polymerization methods.
3 4
N
composites with different weight percentages of g-C
0 wt% g-C
3 4
N
different methods. In Fig. 4(d), anhydrous ferric chloride was
added as a catalyst in the reaction, which introduced Fe in the
composites. Compared with PEDOT, the weight percentage of N
1
in the composites increased with the addition of g-C
3
N
4
.
(
SSP) shows characteristic peaks at 437, 465 and 498 nm, which
can also be assigned to the p–p transition of the thiophene ring.
Moreover, very weak absorption bands are also observed at 3.5 Morphology studies
06 nm, which indicates that the p–p interaction between
PEDOT and g-C is weak.
In the spectrum of PEDOT/10 wt% g-C N (MOP), the
6
Fig. 5 and S1† show the SEM and TEM images of g-C
3
N
4
, PEDOT
3 4
N
(BCP), PEDOT/10 wt% g-C
3
N
4
(BCP), PEDOT/10 wt% g-C
3 4
N
3
4
(SSP) and PEDOT/10 wt% g-C
3 4
N (MOP), respectively. The pure
absorption peak is located in the range of 400–600 nm, which is
PEDOT prepared by SSP presents a rule and plate-like structure,
as shown in Fig. 5(b) and 6(b). Aer sonication for a period of
time, due to p–p stacking and aromatic electrostatic attraction,
the DBEDOT monomer will be adsorbed onto the surface of
45
in good agreement with that previously reported. By compar-
ison, among composites, PEDOT/10 wt% g-C (BCP) shows
the highest p–p interaction between PEDOT and g-C , while
it is the lowest in the case of PEDOT/10 wt% g-C (SSP).
3 4
N
3 4
N
3 4
N

ake g-C
3 4
N , which will allow the polymer to be uniform on the
surface of g-C
3 4
N .
3
.3 XRD analysis
Fig. 3 shows the XRD patterns of g-C
PEDOT/g-C N nanocomposites. In Fig. 3(a), the diffraction
3 4
N , PEDOT (BCP) and the
3
4
ꢁ
ꢁ
peaks of g-C N can be seen at 27.3 and 13.1 , which can be
3
4
attributed to the (002) and (100) diffraction planes, respectively,
of the graphite material. Among them, the stronger diffraction
peak is assigned to the typical planes of graphitic structures,
ꢁ
and the weaker peak at 13.1 is attributed to the hole-to-hole
arrays of the tri-s-triazine units. The XRD pattern of PEDOT
(
2
BCP) also shows two characteristic peaks at approximately 2q ¼
ꢁ ꢁ
6.2 and 12.8 , which are due to intermolecular p–p stacking.
In the patterns of the PEDOT/g-C N composites (BCP), as the g-
3
4
C N content increases, the intensity of the diffraction peak at
3
4
ꢁ
1
2.8 decreases, which is consistent with the increasing g-C
3
N
4
.
In Fig. 3(b), PEDOT/g-C
peaks as PEDOT/g-C
3
N
4
(SSP) shows the same characteristic
3 4
Fig. 4 EDS of (a) PEDOT (BCP), (b) PEDOT/10 wt% g-C N (BCP), (c)
3
N
4
(BCP). However, PEDOT/g-C
3
N
4
(MOP) PEDOT/10 wt% g-C N4 (SSP), (d) PEDOT/10 wt% g-C N4 (MOP).
3
3
Fig. 3 The XRD patterns of FTIR spectra of (a) PEDOT (BCP) and
PEDOT/g-C nanocomposites with different weight percentages of Fig. 5 SEM images of (a) g-C
g-C (b) PEDOT/10 wt% g-C prepared by different polymeri- g-C
zation methods.
N
3 4
3
N
4
(b) PEDOT (BCP), (c) PEDOT/10 wt%
N
3 4
N
3 4
3
N
4
(BCP), (d) PEDOT/10 wt% g-C
3 4
N (SSP), (e) PEDOT/10 wt% g-
3 4
C N (MOP).
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the lowest peak current resulting from the low p–p interaction
between PEDOT and g-C N in composite from SSP method.
3
4
2
+
2+
Fig. S2† shows the DPV curves for 2.0 mM Cd and Pb in
a 0.1 M ABS (pH ¼ 4.5) solution with the different modied
GCEs. As shown in Fig. S2,† the distance between the charac-
2
+
2+
teristic peaks of Cd and Pb is sufficiently wide, and the peak
2
+
2+
positions of Cd and Pb are at approximately ꢀ0.81 V and
ꢀ
0.58 V, respectively. As shown in Fig. S2,† the g-C presents
3 4
N
a similar electrocatalytic performance with that of PEDOT and
PEDOT/10 wt% g-C N from SSP method. This can understood
3 4 3 4
Fig. 6 CV measured with g-C N , PEDOT (BCP), PEDOT/g-C N
3
4
composite-modified glassy carbon electrode (GCE) in a solution of
by the large number of nitrogen-containing groups in g-C N ,
3
4
3ꢀ/4ꢀ
5
mM Fe(CN)
composites with different weight percentages of g-C
0 wt% g-C prepared by different polymerization methods.
6
containing 0.1 M KCl. (a) PEDOT/g-C
3 4
N nano-
which can coordinate with metal ions to enhance the electro-
3 4
N
(b) PEDOT/
28,63
catalytic activity.
The comparison also indicates that the
1
3 4
N
composite from BCP method displayed a higher peak current
than others. The reason for this can be that the plate-like
morphology of PEDOT from the BCP method, which is bene-
Therefore, the PEDOT/10 wt% g-C N composite prepared by
BCP has a layered morphology, as shown in Fig. 5(c) and S1(c).†
Furthermore, as shown in Fig. 5(d), (e) and S1(d), (e),† the
3
4
cial for a uniform combination of PEDOT and g-C
3 4
N akes,
and the strong p–p interaction between PEDOT and g-C N ,
3
4
coordination effect of g-C N with metal ions as well as the fast
3
4
PEDOT/10 wt% g-C
3 4
N composite prepared by SSP and MOP
charge transfer ability and large surface of g-C N can increase
3
4
showed fragmented and irregular groups, respectively.
the synergetic effect of the components, which can also enhance
the electrochemical properties of the composite. In the case of
3
C
.6 Electrochemical characterization of PEDOT (BCP), g-
and PEDOT/g-C composites
Cyclic voltammetry was performed with different modied low p–p interaction between PEDOT and g-C
PEDOT/10 wt% g-C
inventible mixing of the inorganic and organic phase as well as
in SSP method
and 0.1 M is the negative effect for the electrocatalytic oxidation of metal
3 4
N from SSP and MOP methods, the
3
N
4
3 4
N
3 4
N
3
ꢀ/4ꢀ
GCEs in a mixture solution of 5 mM [Fe(CN) ]
6
KCl (50 mL, 1 : 1 by volume). As shown in Fig. 6, the anodic peak ions, while iron ion doping MOP method can play negative for
potentials are 0.38 V and 0.25 V for pure PEDOT (BCP) and g- the electrocatalytic oxidation of metal ions. In summary,
C
3
N
4
modied GCEs, respectively. And, the anodic peak current PEDOT/g-C
3 4
N prepared by BCP not only effectively increases
intensity is lower in g-C N -modied GCE than that of PEDOT the electron transfer kinetics of the electrode surface but also
3
4
(
BCP) modied GCE. The main reason for this is that the lower avoids doping with iron ions. In addition, the interaction
electrical conductivity of g-C than that of PEDOT (BCP) can between the conjugated structure of PEDOT and akes, such as
lead a low peak potential and current occurred in g-C g-C , through p–p stacking allows strong adsorption of heavy
modied GCE than that of PEDOT (BCP) modied GCE. Aer metal ions.
combination of g-C with PEDOT, the peak potential of
3 4
N
3
N
4
-
3 4
N
27
63
3 4
N
samples shied to low potential at about 0.22 V with high
current intensity than that of PEDOT (BCP). All these results
showed that the of PEDOT (BCP) and g-C N cannot be used
alone as a high sensitive materials for ions with their lower
electrochemical activity than that of composites. However, the
2+
2+
3
.7 Individual determination of Cd and Pb
To systematically study the performance difference among the
composites prepared by three different methods, under opti-
mized conditions, various modied GCEs were used for elec-
trochemical determination of Cd and Pb in 0.1 M ABS (pH ¼
.5) by DPV. Fig. 7 and S3, S4† show the DPV responses of
PEDOT/10 wt% g-C N (BCP), PEDOT/10 wt% g-C N (SSP), and
3
4
2
+
2+
heterojunction of PEDOT (BCP) and g-C
enhancement in electrochemical activity of electrode materials.
According to previous report, although g-C is poor in elec-
trical conductivity, it has fast charge transfer ability and large
3 4
N can bring an
4
3
4
3 4
3 4
N
PEDOT/10 wt% g-C N (MOP) composite-modied GCEs
3
4
61,62
surface area with p–p conjugation structure.
The enhance-
ment in electrochemical activity composites should be assigned
to the strong p–p interaction between PEDOT and g-C N by p–
3
4
3 4
p stacking effect. And, the fast charge transfer ability of g-C N
as well as the high electrical conductivity of PEDOT can cause
a rapid electron transfer occurring at the interface of composite
electrodes, which can promote the electrochemical perfor-
mance of composite electrodes. As shown in Fig. 6(b), the
PEDOT/10 wt% g-C N (BCP) composite-modied GCE exhibits
3 4
the highest peak current than that of other composite/GCEs,
which can be explained by the strong p–p interaction between
3 4
Fig. 7 DPV response of the PEDOT/10 wt% g-C N (BCP) composite-
modified GCE for the individual analysis of (a) Cd (b) Pb . The inset
2+
2+
PEDOT and g-C
3
N
4
in the composite prepared by BCP, while
PEDOT/10 wt% g-C
N
3 4
(SSP) composite modied GCE exhibits shows their linear equations as well as correlation coefficient.
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2+
2+
3 4
Table 1 Performance of the PEDOT/10 wt% g-C N /GCE for individual determination of Cd and Pb
2
Methods
BCP
Analytes
Linear range (mM)
Linear regression equation
R
Detection limit (mM)
2
+
Cd
0.06–12.0
0.04–11.6
0.1–6.8
0.1–6.0
0.1–3.6
y ¼ 3.0645x + 1.27673
y ¼ 8.8135x + 6.90977
y ¼ 0.63559x ꢀ 0.3114
y ¼ 10.6259x ꢀ 1.4879
y ¼ 1.6021x + 0.2147
y ¼ 27.3213x + 5.1612
0.9987
0.9956
0.9821
0.9934
0.9923
0.9844
0.0014
0.00421
0.0521
0.0263
0.0065
0.0637
2+
Pb
Cd
2
+
SSP
2+
Pb
Cd
2
+
MOP
2
+
Pb
0.1–2.8
there may be two factors affecting the performance results: the
active sites on the modied electrode and the competitive effect
between different ions. The PEDOT/10 wt% g-C
3 4
N (BCP)
exhibited the widest linear ranges of those tested with a linear
2
+
2+
range of 0.04–11.4 mM for Cd and Pb and detection limits of
0
2
+
2+
.00547 mM and 0.00694 mM for Cd and Pb , respectively.
(Other detailed results are shown in Table 2). This result indi-
cates that the composite prepared by the BCP method has
a larger number of active sites than the other two composites
and no iron bonding.
Fig.
3 4
8 (a) DPV response of the PEDOT/10 wt% g-C N (BCP)
2+
composite-modified GCE for the simultaneous analysis of Cd and
2
+
2+
2+
Pb (b) the respective calibration curves of Cd and Pb
.
3.9 Real sample analysis
2
+
2+
To quantify Cd and Pb in real samples and estimate the
applicability of PEDOT/10 wt% g-C N (BCP), a standard addi-
tion method was carried out with a tap water sample. First,
2
+
2+
towards Cd and Pb , and the inset shows their linear equa-
3
4
tions and correlation coefficients (Fig. 7 and S3, S4† inset). As
from the above results, PEDOT/10 wt% g-C
3 4
N (BCP) exhibited
0
.1 M ABS (pH ¼ 4.5), which included certain amounts of tap
2+
detection limits of 0.0014 mM and 0.0042 mM with linear ranges
water, was prepared. Subsequently, different amounts of Cd
and Pb standard solutions were added to the testing system.
The test sample was found by DPV and the recoveries of Cd
and Pb were 96–103.5% and 96–101.7%, respectively. The ion
concentration of the test sample was veried by AAS and the
2
+
2+
2
+
of 0.06–12.0 mM and 0.04–11.6 mM for Cd and Pb , respec-
2
+
tively. (Other detailed results are shown in Table 1). It is clear
2
+
that the PEDOT/10 wt% g-C N (BCP)/GCE shows a wide linear
3
4
range and low detection limit, and the detection limit was lower
than that of the WHO standard, illustrating that the PEDOT/
2
+
2+
recoveries of Cd and Pb were 89–98.5% and 92–106.6%,
3 4
10 wt% g-C N prepared by BCP provides a large number of
respectively (Table 3). Based on the above results, the PEDOT/
active sites, thereby increasing the adsorption of heavy metal
ions.
1
3 4
0 wt% g-C N (BCP)/GCE has practical application for the
2
+
2+
determination of Cd and Pb in tap water samples with
excellent sensitivity and recovery.
To compare with the SSP and MOP method composites, the
results from electrochemical tests showed that the reliability
2
+
2+
3
.8 Simultaneous determination of Cd and Pb
The analytical performance of the PEDOT/10 wt% g-C N /GCE and linear detection range of the composite from the bromine
3
4
(
BCP), PEDOT/10 wt% g-C N /GCE (SSP), and PEDOT/10 wt% g- catalysed polymerization method were signicantly improved,
3 4
C
3 4
N /GCE (MOP) was investigated through simultaneous which can be related to the absence of iron bonding enhancing
2
+
2+
2+
2+
determination of Cd and Pb in 0.1 M ABS (pH ¼ 4.5). Fig. 8 the absorption of Cd and Pb . Moreover, the plate-like
and S5, S6† show the linear equations and correlation coeffi- morphology of PEDOT from the Br -catalysed polymerization
cients for each modied electrode. For simultaneous detection, method is benecial for a uniform composition of PEDOT and
2
2+
2+
3 4
Table 2 Performance of the PEDOT/10 wt% g-C N /GCE for simultaneous determination of Cd and Pb
2
Methods
BCP
Analytes
Linear range (mM)
0.04–11.4
Linear regression equation
R
Detection limit (mM)
2
+
Cd
y ¼ 7.7152x ꢀ 0.9641
y ¼ 10.2302x ꢀ 2.1586
y ¼ 1.5714x + 1.3715
y ¼ 17.0702x + 2.4552
y ¼ 2.3403x + 1.4897
y ¼ 21.9224x + 3.0524
0.9937
0.9928
0.9927
0.9887
0.9994
0.9911
0.0068
0.0079
0.0054
0.064
0.0011
0.0059
2+
Pb
Cd
2
+
SSP
0.1–4.0
2+
Pb
Cd
2
+
MOP
0.1–2.8
2
+
Pb
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2+
2+
Table 3 Determination of Cd and Pb in tap water by PEDOT/ surface of g-C
N
, which could enhance the electrochemical
3
4
1
0 wt% g-C
3
N
4
(BCP)
properties of the composite from BCP by strong synergetic effect
of the components. In the case of PEDOT/10 wt% g-C N from
SSP and MOP methods, the inventible mixing of the inorganic
3
4
DPV
AAS
Added
Found
(mM)
Recovery
(%)
Found
(mM)
Recovery
(%)
and organic phase as well as low p–p interaction between
PEDOT and g-C N in SSP method is the negative effect for the
3 4
(
mM)
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
electrocatalytic oxidation of metal ions, while iron ion doping
MOP method can play negative for the electrocatalytic oxidation
No. Cd
Pb
Cd
Pb
Cd
Pb
96
Cd
Pb
Cd
Pb
1
1
2
3
1
2
3
1
2
3
1
2
3
0.97 0.96 97
2.07 1.93 103.5 96.5 1.90 2.11 95
2.95 3.02 98.3 100.7 2.87 2.94 95.6 98
0.96 1.08 96
2.02 1.98 101
0.89 0.94 89
94
of metal ions. Furthermore, the PEDOT/10 wt% g-C
3 4
N (BCP)
105.5
composite possesses a high sensitivity and low detection limit
2+
2+
for Cd and Pb , this will have potential applications in areas
such as wastewater treatment and environmental protection.
2
108
99
0.94 0.92 94
1.97 2.16 98.5 108
92
2.99 3.05 99.7 101.7 2.78 3.20 92.6 106.6
Conflicts of interest
There are no conicts to declare.
Acknowledgements
The authors acknowledge the research grant provided by
National Natural Science Foundation of China (No. 21564014,
No. 21865034).
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