3D multiporous Co,N co-doped MoO2/MoC nanorods hybrids as improved electrode materials for highly sensitive simultaneous determination of acetaminophen and 4-aminophenol

Article abstract of DOI:10.1016/j.electacta.2019.02.006

3D multiporous Co, N co-doped MoO₂/MoC (3D Co,N-MoO₂/MoC) nanorods hybrids were successfully synthesized via carburizing core-shell ZIF-67-cladded MoO₃ nanorods precursor at high temperature. As-fabricated Co,N-MoO₂/MoC nanorods coated glassy carbon electrodes (GCE) was demonstrated to possess superior electrocatalytic activity for the electro-oxidation of acetaminophen (AC) and 4-aminophenol (4-AP). Such excellent electrochemical performance was largely attributed to the synergistic effect of the unique multiporous structure, the optimal component and abundant active sites of the nanorods. The corresponding electrode reaction mechanisms were studied in detail in this article. Under optimal conditions, the linear detection ranges were 0.05–200.0 μmol/L for AC and 0.05–140.0 μmol/L for 4-AP, respectively, with the low detection limits of 0.013 μmol/L and 0.012 μmol/L. Furthermore, the 3D Co,N-MoO₂/MoC/GCE revealed excellent sensitivity, good reproducibility, stability and anti-interference ability. The developed electrode was evaluated towards the detecting AC and 4-AP in biological fluids, environment water and pharmaceutical formulations with satisfactory recovery, which had a broad application prospect.

Full text of DOI:10.1016/j.electacta.2019.02.006

Accepted Manuscript
3D multiporous Co,N co-doped MoO /MoC nanorods hybrids as improved electrode
2
materials for highly sensitive simultaneous determination of acetaminophen and 4-
aminophenol
Yuanyuan Dong, Min Zhou, Lei Zhang
PII:
S0013-4686(19)30231-2
https://doi.org/10.1016/j.electacta.2019.02.006
EA 33597
DOI:
Reference:
To appear in: Electrochimica Acta
Received Date: 19 October 2018
Revised Date: 2 February 2019
Accepted Date: 2 February 2019
Please cite this article as: Y. Dong, M. Zhou, L. Zhang, 3D multiporous Co,N co-doped MoO /MoC
2
nanorods hybrids as improved electrode materials for highly sensitive simultaneous determination
of acetaminophen and 4-aminophenol, Electrochimica Acta (2019), doi: https://doi.org/10.1016/
j.electacta.2019.02.006.
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Graphical Abstract

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3D multiporous Co,N co-doped MoO2/MoC nanorods hybrids as
improved electrode materials for highly sensitive simultaneous
determination of Acetaminophen and 4-Aminophenol
Yuanyuan Dong, Min Zhou, Lei Zhang
College of Chemistry, Liaoning University, 66 Chongshan Middle Road, Shenyang, Liaoning, 110036,
People’s Republic of China
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* Corresponding author. Tel.: +86 24 62207809; Fax: +86 24 62202380.
E-mail address: zhanglei63@126.com (L. Zhang).
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22 Abstract
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3D multiporous Co, N co-doped MoO2/MoC (3D Co,N-MoO2/MoC) nanorods hybrids
were successfully synthesized via carburizing core-shell ZIF-67-cladded MoO3 nanorods
precursor at high temperature. As-fabricated Co,N-MoO2/MoC nanorods coated glassy carbon
electrodes (GCE) was demonstrated to possess superior electrocatalytic activity for the
electro-oxidation of acetaminophen (AC) and 4-aminophenol (4-AP). Such excellent
electrochemical performance was largely attributed to the synergistic effect of the unique
multiporous structure, the optimal component and abundant active sites of the nanorods. The
corresponding electrode reaction mechanisms were studied in detail in this article. Under
optimal conditions, the linear detection ranges were 0.05-200.0 ꢀmol/L for AC and 0.05-140.0
ꢀmol/L for 4-AP, respectively, with the low detection limits of 0.013 ꢀmol/L and 0.012
ꢀmol/L. Furthermore, the 3D Co,N-MoO2/MoC/GCE revealed excellent sensitivity, good
reproducibility, stability and anti-interference ability. The developed electrode was evaluated
towards the detecting AC and 4-AP in biological fluids, environment water and
pharmaceutical formulations with satisfactory recovery, which had a broad application
prospect.
Keywords: Acetaminophen; 4-Aminophenol; Co,N co-doped; MoO2/MoC nanorods;
Electrochemical simultaneous determination.
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44 1. Introduction
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Acetaminophen (AC) is one of the most widely employed drugs in the world, which is
primarily used to against pain or reduces fever. In therapeutic doses, it is a safe and effective
analgesic agent [1, 2]. However, 4-Aminophenol (4-AP) is the main hydrolytic degradation
product of AC and possesses significant toxic effect, which has been reported to cause
teratogenic effect and nephrotoxicity [3, 4]. That is to say, excessive consumption of AC will
produce the accumulation of toxic metabolites, which may lead to severe diseases. In addition,
due to their increasing use, the excreted AC and 4-AP also increases their presence in the
environment water [5]. So, it is important to simultaneously determine AC and 4-AP in the
mixed solution for the environmental protection and human health. Currently, various types of
chemically
modified
electrodes
using
RGO-TiN
nanohybrid[6],
Au
nanoparticles/functionalized MWCNTs composites[7], Au/Pd/rGO nanocomposites[8],
poly(chromium Schiff base complex)[9] or CdSe microspheres[10] have been employed for
the electrochemical studied of AC and 4-AP in different matrices. Although these methods are
accurate, some requires complex synthesis procedures, rigorous processing conditions and
high cost, posing a big challenge for design and fabricate the simple, ecofriendly and
cost-effective sensing materials.
Rich valence state and good thermostability enable transition metal carbides draw
significant scientific interest in electronics, catalysts, electrochemical sensing and energy
storage over recent decades, which exhibit comparable catalytic properties as the noble metals
in certain aspects [11, 12]. Among all the candidates, MoC has been paid more attention for
high activity and low electrical resistivity, and is widely used as active hydrogen evolution
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reaction electrocatalysts [13, 14] or cathode materials for Li-ion batteries [15]. Research has
demonstrated that the catalytic performance of MoC largely depend on its composition and
structure [16]. Extensive efforts have been devoted to construct different MoC nanostructures
and MoC-based hybrid nanomaterials to improve its overall electrochemical performance,
such as MoC-Mo2C heteronanowires[17], MoC@MoOx nanoparticles[18] and Ni-MoCx/C
composites[19]. In these cases, MoO2 is thought to be a promising electrode material due to
its excellent physical/chemical properties like rich redox activities, good chemical stability
and high electrical conductivity [20, 21]. This means that the hybrid of MoC and MoO2 may
lead to the enhanced electrocatalytic effect than single component owing to the synergetic
effect among the various properties. Thence, it will be interesting to develop a facile and
reliable method to integrate MoC with MoO2 into one entity, which may endow the material
with versatility and offer opportunities for enhancing the sensing performance of the electrode.
Nevertheless, this effective combination remains a great challenge.
As we all know, constructing 3D porous nanostructures is also an efficient and feasible
strategy to enhance electrochemical performances, because the porous structure helps to
increase the effective contact area and shorten the electron transport distance. Recently,
porous materials derived from metal-organic frameworks (MOFs) have attracted much
interest in many fields due to their relatively high surface area, porosity and adjustable
morphology [22, 23]. As a subclass of MOFs, ZIF-67 has been commonly used as precursors
for preparing carbon framework with homogeneous transition metal/metal oxides and
nitrogen doping in view of its higher thermal stability and abundant C, Co and N elements [24,
25]. Further, many experimental results have confirmed that the incorporation of Co, N
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elements can effectively improve electron conductivity and create more electrochemically
active sites [26, 27]. From this point of view, it can be a good choice to introduce ZIF-67 as
the carbon precursor to integrate with Mo-based materials to produce 3D porous MoO2/MoC
hybrids with the N and Co doping.
Based on the above analyses, we developed a facile strategy for the preparation of 3D
porous Co,N-MoO2/MoC hybrids via carburizing core-shell ZIF-67 cladded MoO3 nanorods
precursor at high temperature. The obtained 3D Co, N co-doped nanorods composed of many
irregular MoO2/MoC nanoparticles, with rich porosity and large surface area, which can
provide plenty of electrochemically active sites and effectively accelerate the electron transfer
rate. The as-fabricated 3D Co,N-MoO2/MoC nanorods were successfully employed to the
detection of AC and 4-AP in biological fluids, environmental water and pharmaceutical
formulations.
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2.1. Chemicals and Apparatus
Sodium molybdate (Na2MoO4·2H2O) and cobalt nitrate hexahydrate (Co(NO3)2·6H2O)
were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shenyang, China). AC and
4-AP, 2-methylimidazole (2-MIM) were obtained from Aladdin. Stock solutions of AC and
4-AP (0.1 mol/L) were prepared with absolute ethanol and kept in darkness at 4 ◦C. Phosphate
buffer was prepared as the supporting electrolyte by mixing the stock solution of 0.2 mol/L
NaH2PO4 and 0.2 mol/L Na2HPO4.
The microstructure of the electrode materials were investigated in scanning electron
microscope (HITACHI SU8000, Japan, SEM,) coupled with an energy-dispersive X-ray
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spectroscopy (EDS), and transmission electron microscopy (JEOL JEM-2100, Japan, TEM).
The phase purity and crystal structure of the as-obtained samples were analyzed by the X-ray
diffraction (XRD) measurement using Cu Kα radiation (Siemens D5000 Diffractometer
Germany). Elemental chemical states on the samples surface were obtained by an X-ray
photoelectron spectroscopy (Thermo ESCALAB 250Xi, USA, XPS).
2.2. Materials Synthesis
2.2.1. Synthesis of MoO3 Nanorods
In a typical process, Na2MoO4·2H2O (2.4 g) was first dissolved in 50.0 mL deionized
water, and then HNO3 (4.0 mol/L) was dropwised into the above solution slowly until the pH
around 1. The mixture was transferred into a Teflon autoclave and maintained at 180 °C for
24 h. The white products were harvested by centrifugation, washed repeatedly with deionized
water to remove residue chemicals and then dried at 60 °C overnight.
2.2.2. Synthesis of 3D Multiporous Co,N-MoO2/MoC Nanorods
Briefly, 0.3 g MoO3 nanorods and 1.095 g Co(NO3)2·6H2O were dissolved in 30.0 mL
methanol. A mixture containing 1.23 g 2-MIM and 30.0 mL methanol was rapidly poured into
the above solution with vigorous stirring. After stirring for 6 h, the purple precipitations were
formed. The purple precipitate was obtained by centrifugation and washed repeatedly with
methanol, and dried at 60 °C overnight. The obtained MoO3@ZIF-67 precursor was placed in
a tube furnace under N2 atmosphere and annealed at 800 °C for 3 h with a ramp rate of
5 °C/min. 3D Co,N-MoO2/MoC was collected when the tube furnace was cooled to ambient
temperature naturally.
2.3. Electrode Preparation
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After being coated, the GCE was mechanically polished using alumina slurry (0.05, 0.3,
and 1.0 ꢀm) and cleaned with ethanol and deionized water by ultrasonication. The working
electrode materials were prepared as follows: 15.0 mg Co,N-MoO2/MoC powders were
dispersed in 5.0 mL of sodium dodecyl benzene sulfonate (SDBS) solution with
ultrasonication for 30 min to generate a 3.0 mg/mL homogeneous suspension. After that, 8.0
ꢀL of the stable suspension was dropped onto the cleaned GCE surface and evaporated to
dryness (a coverage study shown in Fig. S4.).
2.4. Electrochemical Tests
All the electrochemical data were measured by CHI660D electrochemical workstation
(Chenhua Instrument Co., Shanghai, China) with a bare or modified glassy carbon electrode
(GCE) as working electrode, an Ag/AgCl (KCl saturated) electrode and a Pt wire electrode as
reference and auxiliary electrodes, respectively. Cyclic voltammetry (CV) measurements were
conducted at a scan rate of 100 mV/s in the range from −0.8 to 0.4 V. The differential pulse
voltammogram (DPV) was recorded from −0.8 to 0.4 V with the parameters as follow: pulse
amplitude, 0.05 V; pulse width, 0.05 s; quiet time, 2 s. Electrochemical impendence
spectroscopy (EIS) was performed in a frequency range from 0.1 to 10 KHz and an amplitude
of 5 mV at the open circuit voltage. Chronocoulometry was measured using a solution of 0.1
mmol/L [Fe(CN)6]3−/4− containing 0.1 mol/L KCl as the supporting electrolyte. Highly
purified N2 was purged for 10 min to remove the dissolved oxygen in phosphate buffer before
analysis. The completely analytical procedure was carried out at room temperature.
2.5. Real sample
Human blood serum, human urine, river water and commercial paracetamol tablets were
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chosen as the real samples in this experiment. Among them, blood serum samples were
collected from the Shenyang First People’s Hospital, and urine samples were obtained from a
volunteer. Then samples were centrifuged for 10 min at 4000 rpm, in which EDTA was added
to the serum samples as an anti-coagulant. The supernatant was filtered with 0.45 ꢀm filter
and further diluted 200-fold with 0.2 mol/L phosphate buffer (pH 6.0). Moreover, the river
water sample that was poured into drug wastes was collected from Xinkai River, Shenyang,
China, which was filtered with a 0.45 ꢀm membrane, and the pH was adjusted with NaH2PO4
and Na2HPO4. All above sample solutions were determined by DPV according to the spiked
recovery method.
The commercial paracetamol (300.0 mg/tablet) was bought from the local pharmacy. Ten
tablets of dispersible tablets were finely ground in an agate mortar. The sample was accurately
weighed and extracted with 50.0 mL ethanol by ultrasonication for 30 min. After centrifuging
for 10 min, the filtrate was collected and diluted 200 times with 0.2 mol/L phosphate buffer.
Then 50.0 ꢀL of the above solution was added into electrochemical cell containing 4950.0 ꢀL
phosphate buffer for the determination using DPV.
Above-mentioned solutions were reserved at 4 °C environment before measurement.
170 3. Results and Discussion
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3.1 Characterization
The preparation procedure of the 3D porous Co,N co-doped-MoO2/MoC nanorods was
illustrated in Scheme 1. The morphological and structural information of the obtained
materials were revealed by SEM and TEM. As the precursor of Mo-based materials, MoO3
nanorods were firstly prepared. Fig. 1A showed that the MoO3 nanorods possessed a quite
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smooth surface with a length of several micrometers. From the TEM image (Fig. S1A), the
morphology of MoO3 nanorods was further observed, and the diameter was around 100 nm.
When ZIF-67 integrated with MoO3 nanorods, numerous ZIF-67 nanocrystals with
well-defined rhombic dodecahedral morphology were densely attached to the surface of
MoO3, bringing about ZIF-67 wrapped MoO3 nanorods precursor, resulting in an increased
width of 500 nm (Fig. 1B). Additionally, a well-defined core-shell structure can be evidently
observed from TEM image (Fig. S1B). Notably, after the calcination treatment, the obtained
Co,N-MoO2/MoC composites could easily turn into a 3D multiporous nanorod structure as
shown in Fig. 1C. TEM image further clarified the microstructure of the nanorod that the
whole nanorod composed of numerous uneven nanoparticles, with rich voids and channels
inside (Fig. S1C and D). Seen from the high-resolution TEM (HRTEM) image in Fig. S1E,
the nanoparticles were coated by a layer of amorphous carbon in thickness around 5 nm.
Furthermore, the (006) and (103) fringes of MoC and the (110) lattice fringes of MoO2 were
identified in Fig. S1F. EDX spectrum of 3D Co,N-MoO2/MoC hybrids (Fig. 1D) confirmed
the co-existence of Mo, O, C, Co and N elements, implying the successful Co and N doping
into samples.
The structural and compositional characteristics of samples were investigated by XRD.
As depicted in Fig. S2, the main diffraction peaks of as-synthesized MoO3 could be indexed
well with orthorhombic MoO3 phase (JCPDS No. 35-0609) [28]. Compared with the pure
MoO3, some new characteristic peaks derived from ZIF-67 were observed in curve b [29],
confirming that ZIF-67 was immobilized on the MoO3 nanorods. After annealing, the
signature peaks located at 26.07°, 37.12°, 49.59°, 53.54°, 60.31° and 66.78° could be assigned
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to the lattice plane of MoO2 (JCPDS No. 73-1249), while peaks observed at 42.82°, 46.64°
and 72.81° could be easily indexed to MoC phase (JCPDS No. 08-0384), demonstrating that
MoO3@ZIF-67 had been converted into the MoO2/MoC hybrids after calcination at 800 °C
[30].
XPS experiment was used to analyze the elemental composition and the valance state,
which further showed the presence of Mo, C, N, O, and Co elements (Fig. S3A). It was
observed from Fig. S3B that the double peaks at 228.9 and 232.3 eV were observed,
corresponding to Mo 3d5/2 and Mo 3d3/2 of Mo4+, which were from MoO2 and MoC. Notably,
another two peaks at 228.2 and 231.2 eV were ascribed to Mo 3d5/2 and Mo 3d3/2 of Mo2+,
while a small peak with binding energy of 235.4 eV to Mo6+, which may be attributed to the
metastable nature of Mo4+ [15, 31]. The C 1s peaks located at about 284.4, 285.0, 285.2,
286.2 and 288.8 eV might correspond to the Mo-C, C-C, C-O, C=O, and O-C=O bonds,
respectively (Fig. S3C) [32]. For the O 1s spectra (Fig. S3D), the peak at 530.3 eV belonged
to the metal–oxygen (Mo–O) bond, and two distinct peaks at 531.8 and 533.3 eV were
assigned to the C-O and C=O, respectively [33]. Fig. S3E showed the N 1s band can be split
into four peaks, which could be ascribed to pyridinic-N, pyrrolic-N, graphitic-N, and
oxidized-N bond, respectively. Co 2p spectrum revealed the presence of Co2+ (781.5 and
797.4 eV) and Co3+ state (780.6 and 796.8 eV) (Fig. S3F) [34]. Integrating the above analysis,
3D Co,N-MoO2/MoC hybrids were successful synthesized.
3.2. Electrochemical characterization
The electrochemical properties of the modified electrode was investigated by CV in an
aqueous solution of 0.1 mmol/L [Fe(CN)6]3-/4- containing 1.0 mol/L KCl. According to the
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redox reaction diagram (Fig. 2A), pure MoO3/GCE could not improve the electron transfer
ability due to its low electrical conductivity. The enhancement in Ipa of MoO3@ZIF-67/GCE
compared with MoO3/GCE might be attributed to the modification of the high surface area
ZIF-67. Whereas, a pair of redox peaks at 0.204 V/0.136 V with highest currents was
observed on the Co,N-MoO2/MoC/GCE, that was because the Co,N-MoO2/MoC hybrids had
excellent electrocatalytic activity, which accelerated the redox reaction process and resulted in
a more sensitive CV response. Moreover, the peak separation potential (ꢀEp) was 0.066 V,
which was slightly increased in reversibility compared with other modified electrodes,
implying the faster electron transfer at the electrolyte/electrode interface.
The chronocoulometry method was applied to evaluate the electrochemical active
surface area of the modified electrode. Fig. 2B exhibited the Q-t curve of the bare GCE,
MoO3/GCE, MoO3@ZIF-67/GCE and Co,N-MoO2/MoC/GCE using a 0.1 mmol/L
[Fe(CN)6]3-/4- solution in 1.0 mol/L KCl, and the effective surface area was calculated by
Anson’s equation [35]:
2nFAcD1/2t1/2
Q(t) =
+ Qdl + Qads
π1/2
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(1)
in which A characterized the electrode effective surface area, D was the diffusion coefficient
of [Fe(CN)6]3-/4- (7.6×10−6 cm2/s [36]), c represented the substrate concentration, F was
Faraday constant, Qdl and Qads presented the double-layer charge and Faradaic charge,
respectively. Accordingly, the electrochemically active surface area of bare GGE, MoO3/GCE,
MoO3@ZIF-67/GCE and Co,N-MoO2/MoC/GCE were calculated to be 0.007, 0.012, 0.017
and 0.045 cm2, respectively (Fig. 2C), showing that the effective area of
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Co,N-MoO2/MoC/GCE was almost 6.5 times greater than that of bare GCE due to
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multichannel porous structure, which greatly increased the electrode effective area, further
increased the catalytic active sites and enhanced the accumulation ability towards targets.
To explore the interfacial charge transfer kinetics, the impedance behavior of the
modified electrode was studied using 1.0 mmol/L [Fe(CN)6]3-/4- as the probe in 0.1 mol/L KCl
(Fig.2D). In the Nyquist diagram, the semicircle diameter in high frequency range represents
the electron transfer resistance (Rct) of the electrode. The minimum semicircle diameter was
obtained at the Co,N-MoO2/MoC/GCE than that of bare GCE, MoO3/GCE and
MoO3@ZIF-67/GCE, implying that 3D Co,N-MoO2/MoC film reduced the electron transfer
resistance and enhanced the electron-transport efficiency of the entire framework.
Furthermore, the electrocatalytic behavior of the Co,N-MoO2/MoC/GCE could be proved by
calculating the heterogeneous electron transfer rate constant (k0) according to the following
equation:
RT
k0 =
n2F2 AR c
ct
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(2)
The k0 value of modified electrode (2.72×10-5 s-1) was much higher than bare GCE (9.53×10-6
s-1), MoO3/GCE (1.36×10-5 s-1) and MoO3@ZIF-67/GCE (1.53×10-5 s-1). The enhanced
electron transfer rate could mainly attribute to the unique 3D porous structure and small-sized
nanoparticles, which provided abundant internal channels, increased the active sites and
reduced the electron transfer distance, resulting in a much faster charge transport, which is
therefore ideal for electrochemical sensor.
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3.3. Electrochemical behaviors of AC and 4-AP at the Co,N-MoO2/MoC/GCE
The electrochemical behavior of AC and 4-AP at the Co,N-MoO2/MoC/GCE was
systematically explored by CV. Firstly, the individual electrochemical properties of two
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targets were investigated. Fig. 3A showed the comparative CVs of 50.0 ꢀmol/L AC on the
modified and unmodified GCE. No cathodic peak was observed on the reverse scan,
indicating the totally irreversible oxidation processes of AC at these electrodes. As illustrated,
bare GCE showed a poor sensitivity toward AC and the corresponding oxidation peak current
was relatively small. By comparison, a broad oxidation peak was observed at MoO3/GCE,
while the peak intensity of AC was slightly increased after a modification with
MoO3@ZIF-67, proving the stronger accumulation ability of ZIF-67 than pure MoO3. On the
other hand, Co,N-MoO2/MoC/GCE exhibited a peak current of 2.38 times higher than that of
the bare GCE, indicating the enhance electron transport towards AC. Similar results were also
observed at Fig. 3B, the Co,N-MoO2/MoC exhibited a powerful ability for amplification
signal of 4-AP. Meanwhile, the ꢀEp between anodic and cathodic peak of 4-AP was decreased,
showing a more quasi-reversible redox process.
Subsequently, the CV responses of a mixture of AC and 4-AP were investigated. As
illustrated in Fig. 3C, three well-separated redox peaks were observed throughout the CVs,
which make it possible to achieve the goal of simultaneously detecting AC and 4-AP.
Moreover, the response signals of AC and 4-AP increased with varying degrees at three
different modified electrodes, and the Co,N-MoO2/MoC/GCE displayed much sharper peaks
and higher currents compared to all other electrodes. Remarkably, it was more obvious in the
simultaneous study that the Epa of analytes on the Co,N-MoO2/MoC/GCE shifted negatively
and the Epc had a positive direction shift compared to the bare GCE, further proving the much
higher sensor activity of the electrode material. These results clearly evidenced the excellent
electrocatalytic performances of Co,N-MoO2/MoC towards targets, which was mainly due to
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the following contributions: (1) 3D porous nanorod structure could produce favorable
channels for molecular transport and provided the efficient electro-transportation paths due to
the abundant nanoporosity, accelerating the electron transfer kinetics; (2) the nanoparticles
provided a high surface-to-volume ratio for accumulating more target molecular, resulting in a
rapid electrochemical reaction process; (3) a small amount of doped Co and N could not only
improve the electronic conductivity, but also afforded abundant catalytic active sites for the
electrode reaction, which could effectively enhance the electrocatalytic performance towards
AC and 4-AP. Indeed, all of these factors indicated that the developed Co,N-MoO2/MoC/GCE
was a suitable electrochemical sensing interface for the electrooxidation of AC and 4-AP.
3.4. Electrochemical reaction mechanism studies
Prior to analysis, an optimized result showed that the phosphate buffer was used in this
experiment for its highest voltammetric responses among the four commonly used buffers
(Fig. S5). In order to investigate the contribution of proton and electron in electrocatalytic
oxidation of AC and 4-AP, the influence of the pH was studied in the range of 4.0-8.0. From
the Fig. 4A, the highest responses were obtained at pH 6.0 for both analytes. Fig. 4B
displayed the Epa were inversely shifted with the increase of pH, suggesting that protons were
directly involved in the electrode reaction processes. The corresponding linear regression
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equations
were
Epa = −0.0581pH + 0.7962
(R2
=
0.993)
and
AC
304
Epa = −0.0599 pH + 0.4758 (R2 = 0.999). The absolute values of the slopes were highly
AP
305
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close to that of Nernstian slope (0.059 V/pH [37]), illustrating that the number of protons was
equal to the number of the transferred electrons in the electrode process, which was in
agreement with previously reported results.
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The kinetics mechanism involved in the electrode reaction were investigated by studying
the influence of the scan rate on the electrochemical signals of AC and 4-AP on the
Co,N-MoO2/MoC/GCE. As was evident in Fig. 5A, the Epa shifted positively and the Epc
shifted negatively with increasing the scan rate from 20 to 550 mV/s, confirming the kinetic
limitation in the electrochemical processes. Furthermore, the linear relationship between peak
currents and the square root of the scan rate (v1/2) represented diffusion-controlled behavior of
the AC and 4-AP on the Co,N-MoO2/MoC/GCE (Fig. 5B and C). Meanwhile, the linear
relationship between LogIp and Logv were presented in the Fig. S6, The slop values of the
plots were very close to the theoretical value of 0.5, indicating a purely diffusion response in
each case (rather than the thin-layer effect) [38].
Furthermore, the electron transfer number (n) involved could be estimated from the slope
of Tafel plot. As presented in Fig. 5 D and E, the redox peak potentials of AC and 4-AP vary
linearly with the logarithm of the scan rate (logv), and the linear regression equations were
320
321
written as: EpaAC = 0.0409log
ν ν
+0.4609 (R2 = 0.990) and EpaAP = 0.0303log +0.1244 (R2 =
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323
0.990), EpcAP = -0.0417log
ν
+0.510 (R2 = 0.99). The Tafel slope (b) could be calculated from
the slope of Ep vs. logv by the following equation [39, 40]:
b
Ep = logv + constant
324
(3)
(4)
2
2.303RT
Slope = b =
(1-α)nF
325
326
327
328
329
where
The value of n could be estimated to be 2 by the Tafel slope assuming that the transfer
coefficient ( ) was about 0.63 and 0.51 for AC and 4-AP, respectively. Thus, it could be
α
deduced that two electrons were involved in the electrode reaction of AC and 4-AP. By
combining the results from pH study, the electrochemical process of AC and 4-AP on the
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Co,N-MoO2/MoC/GCE was a two-proton and two-electron reaction as reported previously [2,
7]. Possible electrochemical mechanism can be described as Scheme 2.
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337
Scheme 2 The electrode reaction mechanisms of AC and 4-AP.
Electrochemical kinetics was further evaluated by Chronoamperometry experiment. Fig.
338
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340
6A showed the I–t plot of for Co,N-MoO2/MoC/GCE in 0.2 mol/L phosphate buffer in the
absence of (a) or presence of 50.0 ꢀmol/L AC (b) or 25.0 ꢀmol/L 4-AP (c). The apparent
catalytic rate constant (kcat) was determined according to the equation [41]:
Icat
341
= (π
kcatc0t)1/ 2
(5)
IL
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where Icat represented the catalytic current of analytes on the Co,N-MoO2/MoC/GCE; IL was
the limiting current in the absence of analytes; c0 and t presented the analyte's concentration
and time elapse, respectively. In the small range of time, the linear regression equation
between Icat/IL with t1/2 was obtained, and the values of kcat were found to be 1.215×103 for
AC and 2.585×103 M-1 S-1 for 4-AP. The results obtained were higher than those of bare GCE
(shown in Fig 6B, 85.52 for AC and 4.669×102 M-1 S-1 for 4-AP), indicating that the
electro-oxidation of AC and 4-AP exhibited a higher electrocatalytic rate at the
Co,N-MoO2/MoC/GCE. Therefore, a predictable conclusion could be described as: the unique
structure as well as abundant porosity of 3D porous nanorods could undoubtedly shorten
diffusion paths, accelerate the molecular diffusion kinetics and mass transport.
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3.5. Voltammetric determination of AC and 4-AP at the Co,N-MoO2/MoC/GCE
Under optimal conditions, the simultaneous determination of AC and 4-AP was
investigated by DPV using Co,N-MoO2/MoC/GCE. During detection process, the
concentration of one analyte changed, while another kept constantly. As can be seen in Fig.
7A, the oxidation peak currents of AC were linearly related to its concentration from 0.05 to
200.0 ꢀmol/L, while the peak currents of 20.0 ꢀmol/L 4-AP were almost constant. The linear
regression equation for AC was IpaAC = 0.1532c + 0.2272(R2 = 0.998), with a detection limit
357
358
359
of 0.015
ꢀ
mol/L (S/N=3). Similarly, in presence of 40.0
ꢀmol/L AC, determination of 4-AP
360
361
exhibited linear range of 0.05-140.0
ꢀ
mol/L with a detection limit of 0.013
ꢀ
mol/L (S/N=3)
，
and the corresponding regression equation was I paAP
= 0.2670c +0.2390 (
R2 = 0.998) (Fig.
362
363
364
365
7B).
Moreover, simultaneous determination of AC and 4-AP was performed by increasing
their concentrations simultaneously. As depicted in Fig.7C, the deviation between oxidation
peak potentials of AC and 4-AP was 368 mV, indicating that the voltammetric signals of AC
and 4-AP at the Co,N-MoO2/MoC/GCE were independent of each other. The linear regression
366
367
equations in Fig. 7D were expressed as I paAC
=
0
.
1530c -0
R2 = 0.998), with the detection limit of 0.013
0.012 ꢀmol/L for 4-AP, respectively. Furthermore, the results in simultaneous detection of AC
.
2511
(
R2 = 0.999) and
368
I paAP
=
0
.
2623c
+
0
.
5269
(
ꢀmol/L for AC and
369
370
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372
373
and 4-AP were very similar to those of individual analysis, indicating that individual or
simultaneous detection of these two analytes using Co,N-MoO2/MoC/GCE could be achieved
with high sensitivity. Such remarkable sensing performance was attributed to the excellent
electrocatalytic activity and rapid electron transfer capability of the Co,N-MoO2/MoC hybrids,
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which might serve as an efficient sensor for detecting AC and 4-AP.
The comparison of the results for the determination of AC and 4-AP with different
modified electrodes in the literature were listed in Table 1. It can be seen that the present
sensor exhibited excellent analytical performance for the determination of AC and 4-AP. The
comparative data showed superiority of the proposed method over some earlier reported
methods, especially for the sensitivity and detection limit. Thus, the fabricated electrode was
suitable for the determination of AC and 4-AP with the advantages of easy fabrication, ease of
use and low cost.
3.6. Repeatability, stability and interferences
Repeatability was investigated by evaluating the electrochemical signals of 10.0 ꢀmol/L
AC and 4-AP using six independent Co,N- MoO2/MoC/GCE, and the results revealed that the
fabricated modified electrode had decent repeatability with the relative standard deviation
(RSD) of 3.5% for AC and 1.93% for 4-AP. Additionally, the stability of storage of
Co,N-MoO2/MoC/GCE was also explored by comparing the current responses of the
modified electrode after storing for two weeks. Initial responses retained more than 93.6%,
clarifying the good stability of the fabricated Co,N-MoO2/MoC/GCE.
Selectivity was an important parameter for evaluating sensor performance. With this
purpose, the anti-interference ability of the developed electrode was studied by addition of
foreign species such as common metal ions, amino acids, phenolic compounds and
macromolecular protein. Under 5.0 % relative error, it was found that 200-fold K+, Na+, Mg2+,
-
Cl-, NO3 , 100-fold L-galactose, glucose, cholesterol, citric acid, human serum albumin,
histamine, tryptamine, genistein, 80-fold ascorbic acid and 50-fold uric acid, dopamine
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catechol and hydroquinone did not interfere the determination of AC and 4-AP.
3.7. Analytical application
To confirm the feasibility of the proposed method, the Co,N-MoO2/MoC/GCE was
applied to the determination of AC and 4-AP in practical samples with different matrixes. The
satisfactory recoveries (Table 2) of two targets ranged between 96.0% and 108.0%.
Additionally, the determination results in the pharmaceutical formulation were found that the
amount of AC in each paracetamol tablet was 295.9 mg with 2.48% error, which was in quite
agreement with the manufacturer’s given content (300.0 mg/tablet). These results
demonstrated that the developed sensor system could effectively determinate AC and 4-AP in
real samples and had a broad application prospect.
406 4. Conclusions
407
408
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417
In summary, we presented a simple and effective strategy to synthesize 3D
Co,N-MoO2/MoC nanorods as the electrode modifier. The resulting hybrids possessed an
unexpected porous nanorod-like morphology which was piled up by many irregular
MoO2/MoC nanoparticles. This 3D multiporous structure can meet the two requirements of
sensing materials, namely abundant electroactive sites and efficient mass transfer. The results
demonstrated that the as-prepared Co,N-MoO2/MoC/GCE exhibited remarkable
electrocatalytic activity for the electrochemical sensing of AC and 4-AP simultaneously.
Moreover, the proposed sensor had the advantages of excellent sensitivity, repeatability and
long-term stability, which was successfully employed to the detection of AC and 4-AP in
actual samples with satisfactory recoveries. In conclusion, the developed modified electrode
provides a simple, economical, and reliable sensing platform for the detection of AC and 4-AP,
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which could be used for a wide range of applications.
419 Conflicts of interest
420
There are no conflicts of interest to declare.
421 Acknowledgements
422
423
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425
426
This project was supported by the National Nature Science Foundation of China
(NSFC51672116), Science and technology foundation of ocean and fisheries of liaoning
province (201408, 201406) and Liaoning Province Science and Technology Planning Project
(20180551203). The authors also thank their colleagues and other students who participated in
this study.
427 Reference
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[1] T. Madrakian, E. Haghshenas, A. Afkhami, Sensors and Actuators B: Chemical, 193 (2014) 451-460.
[2] S. Mehretie, S. Admassie, T. Hunde, M. Tessema, T. Solomon, Talanta, 85 (2011) 1376-1382.
[3] D. Kim, S. Lee, Y. Piao, Journal of Electroanalytical Chemistry, 794 (2017) 221-228.
[4] Y. Yi, G. Zhu, X. Wu, K. Wang, Biosensors & bioelectronics, 77 (2016) 353-358.
[5] A.U. Alam, Y. Qin, M.M.R. Howlader, N.-X. Hu, M.J. Deen, Sensors and Actuators B: Chemical, 254
(2018) 896-909.
[6] F.-Y. Kong, S.-X. Gu, J.-Y. Wang, H.-L. Fang, W. Wang, Sensors and Actuators B: Chemical, 213 (2015)
397-403.
[7] P. Shi, R. Xue, Y. Wei, X. Lei, J. Ai, T. Wang, Z. Shi, X. Wang, Q. Wang, F. Mohammed Soliman, H.
Guo, W. Yang, Arabian Journal of Chemistry, (2017).
[8] H. Wang, S. Zhang, S. Li, J. Qu, Talanta, 178 (2018) 188-194.
[9] S.P. Kumar, K. Giribabu, R. Manigandan, S. Munusamy, S. Muthamizh, A. Padmanaban, T.
Dhanasekaran, R. Suresh, V. Narayanan, Electrochimica Acta, 194 (2016) 116-126.
[10] H. Yin, X. Meng, Z. Xu, L. Chen, S. Ai, Analytical Methods, 4 (2012) 1445.
[11] H.B. Wu, B.Y. Xia, L. Yu, X.Y. Yu, X.W. Lou, Nature communications, 6 (2015) 6512.
[12] R. Liu, M. Pang, X. Chen, C. Li, C. Xu, C. Liang, Catal. Sci. Technol., 7(2017) 1333-1341.
[13] Y. Liu, G. Yu, G.D. Li, Y. Sun, T. Asefa, W. Chen, X. Zou, Angewandte Chemie, 54 (2015)
10752-10757.
[14] C. Wan, Y.N. Regmi, B.M. Leonard, Angewandte Chemie, 53 (2014) 6407-6410.
[15] H. Li, H. Ye, Z. Xu, C. Wang, J. Yin, H. Zhu, Physical chemistry chemical physics : PCCP, 19 (2017)
2908-2914.
[16] Y. Liu, B. Huang, Z. Xie, Applied Surface Science, 427 (2018) 693-701.
[17] H. Lin, Z. Shi, S. He, X. Yu, S. Wang, Q. Gao, Y. Tang, Chemical science, 7 (2016) 3399-3405.
[18] R. Fang, S. Zhao, Z. Sun, D.-W. Wang, R. Amal, S. Wang, H.-M. Cheng, F. Li, Energy Storage
20

ACCEPTED MANUSCRIPT
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
Materials, 10 (2018) 56-61.
[19] Y. Zhang, J. Zang, S. Jia, P. Tian, C. Han, Y. Wang, Applied Surface Science, 412 (2017) 327-334.
[20] L. Li, H. Sui, K. Zhao, W. Zhang, X. Li, S. Liu, K. Yang, M. Wu, Y. Zhang, Electrochimica Acta, 259
(2018) 188-195.
[21] F. Lyu, Y. Bai, Z. Li, W. Xu, Q. Wang, J. Mao, L. Wang, X. Zhang, Y. Yin, Advanced Functional
Materials, 27 (2017) 1702324.
[22] Q. He, J. Liu, Z. Li, Q. Li, L. Xu, B. Zhang, J. Meng, Y. Wu, L. Mai, Small, 13 (2017).
[23] Y.M. Jo, T.H. Kim, C.S. Lee, K. Lim, C.W. Na, F. Abdel-Hady, A.A. Wazzan, J.H. Lee, ACS applied
materials & interfaces, 10 (2018) 8860-8868.
[24] H. Li, X. Qian, C. Xu, S. Huang, C. Zhu, X. Jiang, L. Shao, L. Hou, ACS applied materials &
interfaces, 9 (2017) 28394-28405.
[25] X. Li, J. Li, Y. Shi, M. Zhang, S. Fan, Z. Yin, M. Qin, T. Lian, X. Li, Journal of colloid and interface
science, 528 (2018) 45-52.
[26] L. Shang, H. Yu, X. Huang, T. Bian, R. Shi, Y. Zhao, G.I. Waterhouse, L.Z. Wu, C.H. Tung, T. Zhang,
Adv Mater, 28 (2016) 1668-1674.
[27] H. Guo, M. Wang, L. Zhao, N. Youliwasi, C. Liu, Microporous and Mesoporous Materials, 263 (2018)
21-27.
[28] Q. Xia, H. Zhao, Z. Du, Z. Zeng, C. Gao, Z. Zhang, X. Du, A. Kulka, K. Świerczek, Electrochimica
Acta, 180 (2015) 947-956.
[29] X. Feng, S. Lin, M. Li, X. Bo, L. Guo, Analytica chimica acta, 984 (2017) 96-106.
[30] H.-J. Zhang, K.-X. Wang, X.-Y. Wu, Y.-M. Jiang, Y.-B. Zhai, C. Wang, X. Wei, J.-S. Chen, Advanced
Functional Materials, 24 (2014) 3399-3404.
[31] C. C. Lv, Z. P. Huang, Q. P. Yang, C. Zhang, Inorg. Chem. Front., 5 (2018) 446-453.
[32] Y. Zhu, S. Wang, Y. Zhong, R. Cai, L. Li, Z. Shao, Journal of Power Sources, 307 (2016) 552-560.
[33] R. Ding, Y. Wu, Y. Chen, H. Chen, J. Wang, Y. Shi, M. Yang, Catalysis Science & Technology, 6 (2016)
2065-2076.
[34] H. Lin, N. Liu, Z. Shi, Y. Guo, Y. Tang, Q. Gao, Advanced Functional Materials, 26 (2016) 5590-5598.
[35] F. Anson, Anal. Chem. 36(1964) 932-934.
[36] J.M. Sasian, L. Yu, R.J. Koshel, M.K. Kim, R.C. Juergens, 5875 (2005) 58750L.
[37] H.S. Han, J.-M. You, H. Seol, H. Jeong, S. Jeon, Sensors and Actuators B: Chemical, 194 (2014)
460-469.
[38] D. A. C. Brownson, L. C. S. Figueiredo-Filho, X. B. Ji, M. G. Mingot, J. Iniesta, O. F. Filho, D. K.
Kampourisa, C. E. Banks, J. Mater. Chem. A, 1 (2013) 5962-5972.
[39] H. Beitollahi, S. Tajik, P. Biparva, Measurement, 56 (2014) 170-177.
[40] G. Karim-Nezhad, Z. Khorablou, Analytical Methods, 9 (2017) 6394-6402.
[41] M. Martín, P. Salazar, R. Villalonga, S. Campuzano, J.M. Pingarrón, J.L. González-Mora, J. Mater.
Chem. B, 2 (2014) 739-746.
[42] H. Yin, K. Shang, X. Meng, S. Ai, Microchimica Acta, 175 (2011) 39-46.
[43] H. Filik, S.Aydar, A. A. Avan, Analytical Letters, 48 (2015) 2581-2596.
[44] L. Y. Shiroma, M. Santhiago, A. L. Gobbi, L. T. Kubota, Analytica Chimica Acta 725 (2012) 44-50.
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494 Figure caption
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Scheme 1 The fabrication process for 3D porous Co,N-MoO2/MoC nanorods for
electrochemical sensing applications.
Fig. 1. SEM images of (A) MoO3 nanorods, (B) MoO3@ZIF-67 and (C) 3D porous
Co,N-MoO2/MoC nanorods; (D) EDX image of the 3D porous Co,N-MoO2/MoC
nanorods.
Fig. 2. (A) CVs of bare GCE (a), MoO3/GCE (b), MoO3@ZIF-67/GCE (c) and
Co,N-MoO2/MoC/GCE (d) in 0.1 mmol/L [Fe(CN)6]3-/4- containing 1.0 mol/L KCl; (B)
Plot of Q–t curves of bare GCE (a), MoO3/GCE (b), MoO3@ZIF-67/GCE (c) and
Co,N-MoO2/MoC/GCE (d) in 0.1 mmol/L [Fe(CN)6]3-/4- containing 1.0 mol/L KCl. (C)
Plots of Q–t1/2 curves; (D) EIS curves of bare GCE (a), MoO3/GCE (b),
MoO3@ZIF-67/GCE (c) and Co,N-MoO2/MoC/GCE (d) in 10.0 mmol/L [Fe(CN)6]3-/4-
containing 0.1 mol/L KCl.
Fig. 3. CVs for (A) 50.0 ꢀmol/L AC, (B) 25.0 ꢀmol/L 4-AP, (C) 50.0 ꢀmol/L AC and 25.0
ꢀmol/L 4-AP solutions on the bare GCE, MoO3/GCE, MoO3@ZIF-67/GCE and
Co,N-MoO2/MoC/GCE.
Fig. 4. (A) Influence of pH on the oxidation peak currents of 50.0 ꢀmol/L AC and 25.0
ꢀmol/L 4-AP at the Co,N-MoO2/MoC/GCE in 0.2 mol/L phosphate buffer at different
pH values from 4.0 to 8.0; (B) Influence of pH on the peak potentials for the oxidation of
AC and 4-AP.
Fig. 5. (A) CVs of 50.0 ꢀmol/L AC and 25.0 ꢀmol/L 4-AP at the Co,N-MoO2/MoC/GCE at
various scan rates; (B, C) Plots of the peak current (Ip) versus the square root of scan rate;
(D, E) Plots of the peak potential (Ep) versus logv.
Fig. 6. Chronoamperometry responses on Co,N-MoO2/MoC/GCE (A) and bare GCE (B) in
the absence (a) or presence of 50.0 ꢀmol/L AC (b), 25.0 ꢀmol/L 4-AP (c) in 0.2 mol/L
phosphate buffer; Inset: plots of Icat/IL vs t1/2/s1/2.
Fig. 7. DPVs at /GCE in the presence of (A) 20.0 ꢀmol/L 4-AP and different concentrations
of AC: 0.05, 0.3, 0.7, 1.0, 2.0, 3.5, 10.0, 20.0, 35.0, 60.0, 80.0, 100.0, 120.0, 140.0, 160.0,
180.0, 200.0 ꢀmol/L, and (B) 40.0 ꢀmol/L AC and different concentrations of 4-AP: 0.05,
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0.3, 1.0, 2.0, 2.5, 3.5, 7.0, 10.0, 15.0, 20.0, 40.0, 60.0, 80.0, 100.0, 120.0, 140.0 ꢀmol/L.
The insets show the corresponding calibration curve. (C) DPVs for simultaneous
determination of AC and 4-AP with different concentrations:0.05+0.05, 0.6+0.3, 0.8+0.4,
1.0+0.7, 2.0+1.0, 7.0+3.5, 10.0+5.0, 20.0+10.0, 40.0+20.0, 60.0+30.0, 80.0+50.0,
100+70.0, 120.0+80.0, 140.0+100.0, 180.0+120.0, 200.0+140.0 ꢀmol/L; (D) The related
calibration curve.
529 Table caption
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531
Table 1. Comparison of different electrodes for determination of AC and 4-AP.
Table 2. Results for the determination of AC and 4-AP in real samples.
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Scheme 1 The fabrication process for 3D porous Co,N-MoO2/MoC nanorods for electrochemical sensing
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Fig. 1. SEM images of (A) MoO3 nanorods, (B) MoO3@ZIF-67 and (C) 3D porous Co,N-MoO2/MoC
nanorods; (D) EDX image of the 3D porous Co,N-MoO2/MoC nanorods.
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bare GCE
MoO3/GCE
bare GCE
MoO3/GCE
(B)
(A)
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d
MoO3@ZIF-67/GCE
MoO3@ZIF-67/GCE
Co,N-MoO2/MoC/GCE
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t/s
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(C)
(D)
Co,N-MoO2/MoC/GCE
MoO3@ZIF-67/GCE
MoO3/GCE
Ya=4.239x+1.226
d
Yb=7.467x+2.119
Yc=10.169x+1.966
Yb=27.328x+1.406
bare GCE
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Fig. 2. (A) CVs of bare GCE (a), MoO3/GCE (b), MoO3@ZIF-67/GCE (c) and Co,N-MoO2/MoC/GCE (d)
in 0.1 mmol/L [Fe(CN)6]3-/4- containing 1.0 mol/L KCl; (B) Plot of Q–t curves of bare GCE (a),
MoO3/GCE (b), MoO3@ZIF-67/GCE (c) and Co,N-MoO2/MoC/GCE (d) in 0.1 mmol/L
[Fe(CN)6]3-/4- containing 1.0 mol/L KCl. (C) Plots of Q–t1/2 curves; (D) EIS curves of bare GCE (a),
MoO3/GCE (b), MoO3@ZIF-67/GCE (c) and Co,N-MoO2/MoC/GCE (d) in 10.0 mmol/L
[Fe(CN)6]3-/4- containing 0.1 mol/L KCl.
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10
8
(B)
8
(A)
bare GCE
MoO3/GCE
AC
(C)
4-AP
bare GCE
MoO3/GCE
10
5
bare GCE
MoO3/GCE
6
4
MoO3@ZIF-67/GCE
MoO3@ZIF-67/GCE
Co,N-MoO2/MoC/GCE
Co,N-MoO2/MoC/GCE
6
MoO3@ZIF-67/GCE
Co,N-MoO2/MoC/GCE
4
2
2
0
0
-2
-4
-6
0
-5
-2
-4
-0.2
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
0.0
0.2
0.4
0.6
0.8
-0.4
-0.2
0.0
0.2
0.4
0.6
Potential/V
Potential/V
Potential/V
Fig. 3. CVs for (A) 50.0 ꢀmol/L AC, (B) 25.0 ꢀmol/L 4-AP, (C) 50.0 ꢀmol/L AC and 25.0 ꢀmol/L 4-AP
solutions on the bare GCE, MoO3/GCE, MoO3@ZIF-67/GCE and Co,N-MoO2/MoC/GCE.
0.8
(A)
pH=4
pH=5
pH=6
pH=6.5
pH=7
pH=8
(B)
8
7
6
5
4
3
2
1
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
-0.2
8
7
6
5
4
3
2
1
Epa=-0.0581pH+0.7962
R2=0.993
4
5
6
7
8
pH
Epa=-0.0599pH+0.4758
2
R =0.999
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8
4
5
6
pH
7
8
Potential/V
Fig. 4. (A) Influence of pH on the oxidation peak currents of 50.0 ꢀmol/L AC and 25.0 ꢀmol/L 4-AP at the
Co,N-MoO2/MoC/GCE in 0.2 mol/L phosphate buffer at different pH values from 4.0 to 8.0; (B)
Influence of pH on the peak potentials for the oxidation of AC and 4-AP.
27

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0.58
0.56
0.54
0.52
(B)
(D)
14
Ipa=0.5760v1/2+1.1240
R2=0.998
Epa=0.0409logv+0.4609
20
15
10
5
(A)
R2=0.990
12
10
8
6
4
2
5
10
15
20
25
1.2 1.5 1.8 2.1 2.4 2.7
0
v1/2
/(
mV1/2/s1/2
)
logv/(mV/s)
20
15
10
5
0.21
0.18
0.15
0.12
0.09
0.06
0.03
(C)
(E)
-5
Ipc=0.7470v1/2-0.8618
R2=0.999
Epa=0.0303logv+0.1244
R2=0.990
-10
-15
-20
Epc=-0.0417logv+0.1510
R2=0.991
Ipa=-0.4092v1/2-0.7378
R2=0.996
0
-5
-10
-0.4 -0.2
0.0
0.2
0.4
0.6
0.8
5
10
15
20
25
1.2 1.5 1.8 2.1 2.4 2.7
v1/2/ mV1/2/s1/2
( )
logv/(mV/s)
Potential/V
Fig. 5. (A) CVs of 50.0 ꢀmol/L AC and 25.0 ꢀmol/L 4-AP at the Co,N-MoO2/MoC/GCE at various scan
rates; (B, C) Plots of the peak current (Ip) versus the square root of scan rate; (D, E) Plots of the peak
potential (Ep) versus logv.
(B)
(A)
a
b
c
0
-50
0
-1
-2
-3
-4
-5
-6
a
b
c
2.2
2.0
1.8
1.6
1.4
1.2
1.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
4-AP: y=0.4506x+0.6702
-100
-150
-200
-250
-300
4-AP: y=0.1915x+2.7193
AC: y=0.4368x+0.4574
AC: y=0.1159x+1.9156
1.2 1.6 2.0
2.4 2.8 3.2
1.2 1.6 2.0
2.4 2.8
3.2
Time/s1/2
Time/s1/2
0
10
30
40
50
20 Time/s
0
10
30
40
50
20Time/s
Fig. 6. Chronoamperometry responses on Co,N-MoO2/MoC/GCE (A) and bare GCE (B) in the absence (a)
or presence of 50.0 ꢀmol/L AC (b), 25.0 ꢀmol/L 4-AP (c) in 0.2 mol/L phosphate buffer; Inset: plots
of Icat/IL vs t1/2/s1/2.
28