P-Aminophenol sensor based on tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube hybrid

Article abstract of DOI:10.1039/c5ra00755k

A highly efficient catalyst is a key challenge for developing electrochemical sensors for p-aminophenol (4-AP), which widely exists in the environment. In this paper, we describe a feasible synthesis for a tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine

Full text of DOI:10.1039/c5ra00755k

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PAPER
p-Aminophenol sensor based on tetra-b-[3-
dimethylamine)phenoxy] phthalocyanine
cobalt(II)/multiwalled carbon nanotube hybrid†
(
Cite this: RSC Adv., 2015, 5, 23283
a
a
a
a
a
a
Liangxiao Guo, Zhimin Chen,* Jialin Zhang, Hao Wu, Feng Wu, Chunying He,
a
ab
Bin Wang and Yiqun Wu
A highly efficient catalyst is a key challenge for developing electrochemical sensors for p-aminophenol
4-AP), which widely exists in the environment. In this paper, we describe a feasible synthesis for a tetra-
(
b-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(II) (aPcCo) and acid-treated multiwalled carbon
nanotube (CNT) hybrid using a strong p–p stacking interaction. The combination of aPcCo and CNT can
improve the conductivity of aPcCo and the dispersion of CNT simultaneously, which benefits formation
of uniform electrodes, and provides unimpeded pathways for matter diffusion, as well as accelerating
charge-transfer kinetics. As a result, the aPcCo/CNT hybrid we produced can serve as an efficient
electrochemical catalyst for 4-AP oxidation and provide more sensitive detection. The oxidation current
of 4-AP is linear at concentrations from 0.5 mM to 300 mM and 300 mM to 800 mM. The detection limit is
as low as 0.3 mM (S/N ¼ 3). This development offers an attractive catalyst material for electrochemical
sensors.
Received 13th January 2015
Accepted 17th February 2015
DOI: 10.1039/c5ra00755k
www.rsc.org/advances
with low cost, simplicity, and high selectivity and sensitivity, is a
desired method for 4-AP detection. Commonly, bare electrodes
1
. Introduction
p-Aminophenol (4-AP) is important environmentally because it oen suffer from a fouling effect, which causes rather poor
is commonly used as an industrial raw or processed material in selectivity and sensitivity. An effective way to overcome this
cosmetics, photography, and dyes. 4-AP is also widely used in problem is electrode modication, which is capable of reducing
the pharmaceutical industry for the production of paracetamol the overvoltage and improving the slow kinetics processes.
1
,2
and clobrate, but it is highly toxic. The maximum content of
-AP in pharmaceuticals is limited to 50 ppm (0.005%, w/w) by have attracted great research interest in photodynamic
14
Phthalocyanine (Pc) complexes, as tetrapyrrole derivatives,
4
12
13
the standards of European, United States, and Chinese phar- therapy, microbial fuel cells, nonlinear optical materials,
16–19
3
–5
15
macopoeias. So the quick and convenient detection of 4-AP is gas sensors, and especially electrochemical sensors,
oen a necessity.
because of their large conjugated electronic molecular struc-
Many attempts, therefore, have been made to develop an tures and diversiform central metal ions. However, as far as
efficient and selective way of determining 4-AP, such as liquid using electrochemical sensors, it is difficult to attain satisfac-
6
7
chromatography, spectrophotometry, sequential injection tory results when employing pristine Pcs. This is mainly
8
9
analysis, capillary electrophoresis, surface enhanced Raman attributed to their insolubility in water or lower solubility in
scattering, and micellar electrokinetic chromatography.
10
11
organic solvents, and poor conductivity. Poor solubility is not
However, these techniques are expensive, or have complicated conducive to fabricating uniform electrodes. To improve this,
steps, or are time consuming, and, in some cases, even have low Pc complexes are generally modied by introducing solubility-
sensitivity and selectivity, making them unsuitable for routine enhancing substituents at the peripheral of Pc rings and good
detection of 4-AP. In contrast, an electrochemical technique, selection of the right metal ion centre for improving water
20–23
solubility of Pc complexes.
In addition, in terms of the
intrinsic characteristic poor conductivity, the most effective
24
a
solution is to introduce a conductive agent. Thus, it may easily
Key Laboratory of Functional Inorganic Material Chemistry (Ministry of Education of
China), School of Chemistry and Materials Science, Heilongjiang University, Harbin be conceived that, if we could design a novel hybrid to overcome
1
50080, People's Republic of China. E-mail: zmchen@siom.ac.cn; Fax: +86 451
these problems synchronously, this could provide good oppor-
tunities for developing new electrochemical sensors.
As a conductive agent, carbon nanotubes (CNTs) are
receiving much interest, because of their large specic surface
area, high mechanical strength, excellent conductivity, and low
8
660 9145; Tel: +86 451 8660 9145
b
Shanghai Institutes of Optics and Fine Mechanics, Chinese Academy of Sciences,
Shanghai 201800, People's Republic of China
†
Electronic supplementary information (ESI) available: Other detailed
characterization. See DOI: 10.1039/c5ra00755k
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25–27
ꢀ
production cost.
In particular, its one-dimensional (1D) to neutral pH and the sample was dried under vacuum at 50 C
structure helical tube of graphitic-carbon sheets can be overnight. Tetra-b-[3-(dimethylamine)phenoxy] phthalocyanine
employed for directional transmission of electrons and accel- cobalt(II) was synthesized by a template-reaction method in the
28
erate charge-transfer kinetics. However, the intrinsic van der presence of 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) (see
Waals interactions between pristine tubes make CNTs insoluble details in ESI†). 4-Nitrophthalonitrile (99% purity), DBU (98%
29
in routine solvents, thereby reducing available active sites for purity), and Naon (5 wt% in low aliphatic alcohols and water)
electrocatalysis. Recent studies present evidence that Pc were purchased from Sigma-Aldrich Co. LLC. The 3-dimethyl-
complexes with modied CNTs show excellent performance for aminophenol (97% purity) was purchased from Acros Organics
2
2,30
16
31
ꢁ1
determining ascorbic acid,
nitrite, thiocholine, and and 0.1 mol L phosphate buffer solutions (PBS) of different
32
ꢁ1
hydrazine. Evidently, the combination of Pc complexes and pH values were prepared from stock solutions of 0.1 mol L
CNTs may cover each other's shortages.
Based on the above design, we synthesized a tetra-b-[3- throughout the experiments. All other chemicals were of
NaH PO and Na HPO . Milli-Q ultrapure water was used
2
4
2
4
(dimethylamine)phenoxy] phthalocyanine cobalt(II)/multiwalled analytical grade or better quality and used without any further
carbon nanotube hybrid (aPcCo/CNT) by p–p non-covalent inter- purication.
action (as shown in Scheme 1). Besides p–p force, there is a
weak acid–base interaction between aPcCo (base) and acid- 2.2. Preparation of aPcCo/CNT hybrid
33,34
treated CNTs (acid).
The N,N-dimethylaminephenoxyl
The aPcCo/CNT hybrid in dry DMF was synthesized through the
p–p stacking interaction between aPcCo and CNT. Briey,
group of aPcCo could enhance the dispersion of the hybrid, and
benet forming uniform 3D-network electrodes, providing
1
0 mg of CNT were added into 5 mL of DMF containing 30 mg of
aPcCo with successive ultrasonic treatments for 48 hours. The
resultant solution was ltered through 0.22 mm
30
unimpeded pathways for matter diffusion. Meanwhile, the
electrocatalytic current could quickly transfer from aPcCo to
CNTs via p–p interaction, and the latter then promote the
a
PTFE-membrane lter. The lter cake was washed with ethanol
and tetrahydrofuran, aer which the ltrate became colourless,
16,22
orientation transmission of electrons.
Thus, high catalytic
activity of the aPcCo/CNT hybrid for 4-AP results from this
strategy.
ꢀ
and then was dried in a vacuum oven for 3 h at 60 C, affording
the desired aPcCo/CNT hybrid as a black powder.
2
.3. Preparation of aPcCo/CNT modied glassy carbon
2. Experimental
(aPcCo/CNT/GC) electrode
2
.1. Reagents
The glassy carbon electrode (diameter: 3 mm) was carefully
polished with 1 mm, 0.3 mm, and 0.05 mm alumina, followed by
successive sonication with distilled water and ethanol for 3 min
until a mirror like surface was obtained. Then, 5 mL of an aPcCo/
CNT hybrid suspension (1.0 mg mL ), which was prepared by
dispersing aPcCo/CNT in an anhydrous ethanol/Naon mixture
with the aid of ultrasonic treatments, was dropped on the clean
surface of a GC electrode. The solvent was evaporated under an
infrared lamp and denoted as aPcCo/CNT/GC electrode. For
comparison, the aPcCo/GC and CNT/GC electrodes were also
fabricated by similar procedures.
Multi-walled carbon nanotubes (MWCNTs, purity > 95%) were
purchased from Shenzhen Nanotech Port Co. Ltd. To func-
tionalize them with carboxylic acid, they were chemically
ꢁ1
oxidized with strong oxidizing using a H
3 : 1 v/v ratio) for 8 h. Aer that, the resulting dispersion was
diluted in water and ltered. MWCNTs were stirred in the
mixture of H SO (98 wt%) and H (30 wt%) in a 4 : 1 v/v ratio
2 4 3
SO –HNO mixture
(
2
ꢀ
4
2 2
O
for 1 h at 70 C. The acid-treated MWCNT (CNT) was washed up
2.4. Apparatus
UV-vis absorption spectra were recorded with a Lambda 35
UV/VIS spectrometer (PerkinElmer, USA). FT-IR spectra were
recorded on a Nicolet FT-IR NEXUS spectrometer (Thermo
Scientic). Scanning electron microscopy (SEM) images were
recorded with a Hitachi S-4800 eld emission scanning electron
microscope operating at 15 kV. Transmission electron micros-
copy (TEM) images were performed on a JEM-3010 electron
microscope (JEOL, Japan) with an acceleration voltage of
300 kV. X-ray photoelectron spectroscopy (XPS) measures were
performed with AXIS UL TRA DLD. Inductively coupled plasma
atomic emission spectroscopy (ICP-AES) analysis was carried
out by Optima 7000 DV (PerkinElmer, USA). The Raman spectra
were acquired using a Raman spectrophotometer (HR800,
HORIBA Jobin Yvon Company) excited by a laser with 457.9 nm
wavelength. Samples for ICP-AES were prepared by ashing
Scheme 1 Schematic illustration of the synthesis procedure for
aPcCo/CNT hybrid and its electrocatalytic mechanism.
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ꢀ
.0050 g samples in quartz test-tubes at 800 C for 30 min, to CNT by the strong p–p interaction, which could expand the
and then leaching them with concentrated acids (5 mL of macrocyclic conjugated structure of aPcCo.
0
36–38
HCl : HNO in 3 : 1 v/v ratio). Electrochemical measurements
were performed using a computer-controlled CHI 660D CNT, respectively. For CNT, the bands at 1718 cm
electrochemical workstation (CH Instrument, Shanghai, 3431 cm are assigned to (n C]O) and (n O–H),
Fig. 1B shows the FT-IR spectra of aPcCo/CNT, aPcCo and
3
ꢁ1
and
ꢁ
1
39,40
respectively,
China). All the electrochemical measurements were carried implying the existence of large numbers of carboxyl groups, which
ꢀ
ꢁ1
out in 0.1 M PBS at room temperature (25 ꢂ 2 C) using a are further identied by peaks in the range 1000–1300 cm
41
conventional three-electrode system with a modied glassy attributed to the composite of (n C–C). In the FT-IR spectrum of
carbon electrode as a working electrode, a platinum foil as an aPcCo, the peaks at 1266 cm (Ar–O–Ar stretching vibration),
auxiliary electrode, and a saturated calomel electrode (SCE) 1472 cm (n C–N), 1572 (n C]C) cm , 1605 cm (n C]N),
as a reference electrode. All potentials in this study were 1720 cm (n C]O), 2927 cm (nas C–H) and 2953 cm (nas CH3)
ꢁ
1
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
35,42,43
reported with respect to SCE. The electrolyte was purged are the characteristic peaks of pristine aPcCo.
These peaks
with high purity nitrogen for at least 10 min prior to also are present in the spectrum of aPcCo/CNT, except the slight
measurements to remove dissolved oxygen unless otherwise blue shi due to electron delocalization of p–p interactions,
15,22
stated.
which is consistent with the result of UV-vis spectra.
To further gain insight about the interaction between aPcCo
and CNT, Raman spectra of the aPcCo/CNT hybrid and CNT
were recorded as shown in Fig. 2. The Raman spectra of CNT
and the aPcCo/CNT hybrid display two apparent bands:
3
. Results and discussion
3.1. Characterization of aPcCo/CNT hybrid
ꢁ1
ꢁ1
1
347.4 cm (D band) and 1558.8 cm (G band). The D band
3
The as-synthesized aPcCo/CNT hybrid was rst examined by
electronic absorption spectra, and a comparison of UV-vis
spectra of the aPcCo/CNT, aPcCo and CNT in DMF are shown
in Fig. 1A. Two strong absorption peaks, one in the UV region at
about 327 nm (B-band) and the other in the visible region at
(disordered band) is the breathing mode of sp rings that is
related to bond-angle disorder, bond-length disorder, and
4
4,45
hybridization.
The G band is related to the in-plane bond-
2
stretching motion of pairs of sp carbon atoms from the
graphitized structure. It is worth noting that the I /I value of
D G
46
6
66 nm (Q-band), are observed in the UV-vis spectrum of pris-
aPcCo/CNT hybrid is very close to that of CNT (0.52 vs. 0.55).
This result conrms that the main interaction between CNT and
aPcCo is p–p non-covalent, and the modication of CNT with
tine aPcCo, indicating that aPcCo is non-aggregated in DMF
35
solution. Meanwhile, it is evident that the characteristic
Q-band peak of aPcCo also appears in the UV-vis spectrum of
the aPcCo/CNT hybrid, which has a slightly red shi relative to
that of pristine aPcCo (681 vs. 666 nm). The red shi could be
attributed to the electron transfer from the phthalocyanine ring
16
aPcCo does not destroy the surface structure of CNT.
XPS was performed to conrm the surface chemical
compositions, chemical state and electronic state of the
elements existing in the aPcCo/CNT hybrid. As shown in Fig. 3A,
only the C 1s peak (at 284.60 eV) and O 1s peak (532.70 eV) are
present in the XPS spectrum of CNT; whereas two new peaks, N
1s and Co 2p, appear in that of the aPcCo/CNT hybrid, implying
that aPcCo succeeds in anchoring onto the surface of aMWCNT
22
by p–p and acid–base interactions. The Co 2p peaks of
as-obtained aPcCo/CNT could be attributed to four contributors:
two strong peaks correspond to 2p3/2 (780.3 eV) and 2p1/2 (795.5
eV), respectively accompanied by two relatively weaker satellite
2
+
features (Fig. 3B). It is the chemical nature of Co , which is the
18,47,48
primary valence state in electrochemical catalysis.
Fig. 1 (A) UV-vis spectra and (B) FT-IR spectra of CNT, aPcCo, and
aPcCo/CNT hybrid, respectively.
Fig. 2 Raman spectra of aPcCo/CNT hybrid and CNT.
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images of the aPcCo/CNT hybrid. CNT presents as a multiwall
structure, and its diameter is in the range of 10 to 20 nm.
Besides the distinct core and walls of the carbon nanotube, the
surface of CNT is covered by discontinuous amorphous carbon,
further indicating the combination of aPcCo and CNT via p–p
and acid–base interactions. The amount of aPcCo assembled on
the surface of CNT is about 6.48 wt% as determined by ICP-AES.
3.2. Electrocatalytic activity of aPcCo/CNT hybrid to 4-AP
The electrocatalytic activity of the aPcCo/CNT/GC electrode
towards 4-AP was investigated by cyclic voltammetry (CV) in
0.10 M PBS solution as the supporting electrolyte at pH 5.8.
Fig. 5 shows the typical CVs of aPcCo/CNT/GC, CNT/GC, aPcCo/
GC, and bare GC electrodes in PBS solution with 50 mM 4-AP at a
ꢁ
1
scan rate of 50 mV s . It appears that all electrodes present an
electrochemical response towards 4-AP, with an anodic peak
potential (Epa) of ꢃ0.2 V and a cathodic peak potential (Epc) of
ꢃ0.11 V versus SCE, indicating that 4-AP shows quasi-reversible
behaviour. In contrast to bare GC, aPcCo/GC, and CNT/GC
electrodes, for which the redox peaks ascribed to 4-AP at
around 0.2 V are weak, the aPcCo/CNT/GC electrode generates
Fig. 3 (A) XPS spectra of aPcCo/CNT hybrid and CNT; (B) the high- an obvious couple of high redox peaks. These mean that the
resolution Co 2p XPS spectrum of aPcCo/CNT hybrid.
synergic effect between aPcCo and CNT can enhance the elec-
trochemical performance. On one hand, compared with CNT,
aPcCo on the surface of the aPcCo/CNT hybrid offers more
The surface morphology and structure of the synthesized efficient interfacial active sites for electrocatalysis. On the other
aPcCo/CNT hybrid was investigated by SEM and TEM. As shown hand, the reaction charge could be quickly transferred to CNT
in Fig. 4A and B, the three-dimensional network-like structure via p–p interaction, and 1D CNT further promotes the orien-
1
6,30
of aPcCo/CNT hybrid is more uniform and looser as compared tation transmission of electrons.
to CNT, corresponding to its good dispersion, which is mainly reports,
According to previous
51,52
the electrocatalytic oxidation of 4-AP on an aPcCo/
attributed to the modication of CNT by aPcCo. The loose and CNT/GC electrode should undergo the following reaction:
interconnected structure obtained, formed by the aPcCo/CNT
hybrid, simultaneously offers a larger surface area and more
active sites for electrocatalysis, a directional connement for
rapid electronic transmission, and unimpeded pathways for
Apparently, the electrochemical oxidation of 4-AP is relevant
matter diffusion; all of these are important contributors for an
to pH values. To highlight the effect of hydrogen ion concen-
37,49,50
excellent electrocatalyst.
Fig. 4C–E shows typical TEM
tration on the electrocatalytic activity of 4-AP, CVs at different
pH values were carried out (Fig. 6). It is obvious that the redox
current and potential of 4-AP are sensitive to pH values. With
increasing pH from 4.4 to 8.0, the redox current of 4-AP
Fig. 5 CVs of aPcCo/CNT/GC, CNT/GC, aPcCo/GC and GC elec-
Fig. 4 (A and B) SEM images of CNT and aPcCo/CNT hybrid, trodes in 0.1 M PBS (pH ¼ 5.8) solution with 50 mM 4-AP, scan rate:
ꢁ
1
respectively; (C–E) TEM images of aPcCo/CNT hybrid.
50 mV s .
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Fig. 6 (A) CVs of aPcCo/CNT/GC electrode in 0.1 M PBS with 50 mM
ꢁ1
Fig. 7 (A) CVs of aPcCo/CNT/GC electrode in 0.10 M PBS (pH ¼ 5.8)
solution with 50 mM 4-AP measured at different scan rates
4
-AP at different pH values, scan rate: 50 mV s . (B) The relation
between the oxidation peak potentials (black line) and currents (red
ꢁ1
(10–100 mV s ). (B) The calibration plots between the anodic (red line)
line) and the pH values, and the linear regression equation is
2
and cathodic (black line) peak currents and the scan rate.
E
pa (V) ¼ 0.5366 ꢁ 0.0601 ꢄ pH (R ¼ 0.9971), Epa is anodic peak
potential.
With an increase of 4-AP concentration, the oxidation current at
0
.09 V increases (Fig. 8). Increases of the DPV peak currents are
increases to a maximum, and then decreases. Meanwhile, the
redox potential is also negatively shied, and the linear rela-
tionship with the redox process signies that protons and
electrons are involved in redox (Fig. 6B and Fig. S2†). According
proportional to the species concentrations, and the two linear
regression equations for 4-AP are expressed as: I (mA) ¼ 0.0579
ꢁ
1
2
(
0
mA mM ) ꢄ C (mM) + 4.5838 (0.5–300 mM, R ¼ 0.9876), I (mA) ¼
ꢁ
1
2
.0240 (mA mM ) ꢄ C (mM) + 14.325 (300–800 mM, R ¼ 0.9849).
to dE
p
/dpH ¼ 2.303mRT/nF, in which F is the Faraday constant,
The 4-AP sensor has a detection limit as low as 0.3 mM (S/N ¼ 3),
derived from the calibration curve. All of the parameters indi-
cate that the aPcCo/CNT/GC electrode is very effective as a
sensor for determining 4-AP with high activity, which greatly
R is the gas constant, m is the number of protons, and n is the
53
number of electrons, the m/n value of the oxidation process is
.01 and the reduction process is 1.19; this indicates that the
1
number of protons and electrons involved in the electro-
chemical redox processes of 4-AP are equal. Taking into account
the detection sensitivity, a PBS solution at pH 5.8 was selected
as the supporting electrolyte solution.
In order to explore the reaction kinetics of 4-AP oxidation,
the CVs of the aPcCo/CNT/GC electrode at different scan rates
were investigated. As shown in Fig. 7, both of the redox peak
currents increase linearly as the scan rate increases from 10 to
ꢁ
1
1
(
ꢁ
00 mV s , and the linear regression equation is Ipa
2
mA) ¼ 2.5213 + 0.4128 ꢄ V (R ¼ 0.9978) and I (mA) ¼ ꢁ1.9815
pc
2
0.2461 ꢄ V (R ¼ 0.9974), respectively. I , I , and V are
pa pc
anodic, cathodic peak current, and scan rate, respectively. This
suggests that it is an adsorption-controlled electrochemical
5
2,54,55
process,
which is also consistent with the fast charge
propagation in the aPcCo/CNT/GC electrode. CNT seems to
support the charge transport within the hybrid. In other words,
the unimpeded distribution of charge to a 3D matrix is feasible. Fig. 8 DPVs response for the different concentrations of 4-AP at
To evaluate the sensitivity towards 4-AP, a series of differ- aPcCo/CNT/GC electrode in 0.1 M PBS (pH ¼ 5.8) (from bottom to
top: 0.5, 1, 5, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, and
ential pulse voltammograms (DPVs) were recorded on the
aPcCo/CNT/GC electrode with various concentrations of 4-AP.
1
000 mM, respectively). The inset is the calibration linear relationship of
currents versus 4-AP concentration.
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exceeds the linear range of most previously reported 4-AP
detection (Table S1†).
The stability and repeatability of the aPcCo/CNT/GC elec-
trode have also been evaluated by CV measured at different
cycle numbers. As shown in Fig. 9A, the current response at the
hundredth cycle is almost the same as that at the rst cycle.
Moreover, the long-term storage stability of the aPcCo/CNT/GC
electrode was also evaluated by measuring the electrode
responses at intervals of several days. The oxidation peak
current slightly decreased aer being stored for 30 days in PBS
ꢀ
(
pH 5.8) at 4 C, and about 91.55% of initial current response
was retained (Fig. 9B). Such high stability and accuracy of the
aPcCo/CNT/GC electrode is acceptable for most practical Fig. 10 Amperometric response to the addition of different analytes to
5
0 mL of 0.10 M PBS (pH ¼ 5.8), PCT ¼ paracetamol, CC ¼ catechol,
applications.
Glu ¼ glucose, Ani ¼ anilofos, Rs ¼ resorcinol.
In addition, sensitivity and selectivity are also other key
properties for a sensor, especially in practical applications. The
low response potential also indicates that the aPcCo/CNT
hybrid possess excellent selectivity for 4-AP. As expected, in
an I–t curve as shown in Fig. 10, the successive addition of
interferents in the order 250 mM of paracetamol, KCl, NaNO2,
56
of 4-AP aer adding interferents with that in the absence of
interferents, it is clear that the interferents had no impact on
the 4-AP detection performance.
In order to verify the performance and feasibility of the
proposed method for analysis of 4-AP in environmental
samples, the aPcCo/CNT/GC electrode was used for the deter-
mination of 4-AP in tap water. A sample was mixed with PBS
catechol, glucose, anilofos, resorcinol, and MgSO
4
to a PBS (pH
5.8) solution containing 50 mM of 4-AP gives rise to a negligible
current response, while a signicant current response is
observed aer the subsequent addition of 50 mM of 4-AP. The
response time was less than 3.2 s, revealing the rapid response
of the modied electrode toward 4-AP. Such a fast response may
be attributed to the rapid adsorption and activation of 4-AP on
the surface of the aPcCo/CNT hybrid, and the continuous con-
ducting pathways of electrons. Comparing the response current
(
0.1 M, pH 5.8) for 4-AP determination, and the results are
summarized in Table S2.† A good recovery, between 94% and
08%, suggests the practical applicability of the proposed
1
method. Therefore, the proposed method could be effectively
used for determination of 4-AP in real samples.
4. Conclusions
In summary, we demonstrated the synthesis of the aPcCo/
CNT hybrid by a facile p–p stacking interaction. Superior
performance of the aPcCo/CNT hybrid was observed in
determining 4-AP in comparison to pristine aPcCo and CNT.
The enhanced effectiveness was ascribed to the inter-
connected 3D-network structure, and the synergistic effect of
aPcCo and CNT, which favour a large accessible surface
area, more active sites and the orientation transmission of
electrons, as well as unimpeded pathways for matter diffu-
sion. 4-AP sensors such as the ones described herein offer
tremendous potential for applications in environmental
monitoring.
Acknowledgements
This work was nancially supported by the National Natural
Science Foundation of China (51002046, 51202061, 51102082),
the Natural Science Foundation for the Returned Overseas
Scholars of Heilongjiang Province (LC2012C02), the Natural
Science of Heilongjiang Province of China (B201308), the
Research Fund of Heilongjiang Provincial Education Depart-
ment (12511377, 12521399), the Postdoctoral Science-Research
Developmental Foundation of Heilongjiang Province (LBH-
Q11015) and the Innovative Talents Program for the Returned
Overseas Scholars of Harbin of China (2012RFLXG031).
Fig. 9 (A) CVs of the aPcCo/CNT/GC electrode in 0.10 M PBS
(
pH ¼ 5.8) solution with 50 mM 4-AP obtained at the first cycle and
hundredth cycle, respectively. (B) Stability experiment of the aPcCo/
GC electrode to detect 4-AP for 30 days.
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2
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