Eco-friendly synthesis and morphology-dependent superior electrocatalytic properties of CuS nanostructures

Article abstract of DOI:10.1016/j.electacta.2017.06.077

Copper sulfide with desired structure is of special interest for electrocatalytical application due to their unique physicochemical properties, simple synthesis and less toxic in nature. In this study, simple and eco-friendly (without using any template or surfactant) route for the fabrication of copper sulfide nanostructure morphologies were tuned from cauliflower, microflower to nanoparticles inter-connected network-like structures by changing the polarity of solvent medium during solvothermal synthesis. However, to the best of our knowledge, no such kinds of special three types of CuS nanostructure with excellent electro-catalytic properties using only H₂O and C₂H₅OH as the solvents have been reported in the literature. The as-prepared different CuS nanostructure was characterized using FE-SEM, HR-TEM, XRD, XPS and cyclic voltammetry. This morphological alteration able to produce several precise nanostructures with improved electrocatalytic properties that led to an excellent performance towards enzymeless glucose oxidation. The CuS inter-connected nanoparticles modified electrode displayed a synergistic effect towards the oxidation of glucose (i_pa: 103?±?5?μA) when compared to that of cauliflower (i_pa: 68?±?3.7?μA) and microflower (i_pa: 60?±?2.4?μA) modified electrode surfaces. Further, the CuS inter-connected nanoparticles modified electrode showed a wide linear range (2.0?×?10^?5?2.5?×?10^?3?M), high sensitivity (1085?μA?mM^?1?cm^?2), low detection limit (2?μM), rapid response time (

Full text of DOI:10.1016/j.electacta.2017.06.077

Accepted Manuscript
Title: Eco-friendly synthesis and morphology-dependent
superior electrocatalytic properties of CuS nanostructures
Authors: A. Venkadesh, S. Radhakrishnan, J. Mathiyarasu
PII:
S0013-4686(17)31315-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.electacta.2017.06.077
EA 29715
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Electrochimica Acta
Received date:
Accepted date:
13-4-2017
14-6-2017
Please cite this article as: A.Venkadesh, S.Radhakrishnan, J.Mathiyarasu, Eco-friendly
synthesis and morphology-dependent superior electrocatalytic properties of CuS
nanostructures, Electrochimica Actahttp://dx.doi.org/10.1016/j.electacta.2017.06.077
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Eco-friendly synthesis and morphology-dependent superior electrocatalytic
properties of CuS nanostructures
A. Venkadesh, S. Radhakrishnan*, J. Mathiyarasu
Electrodics and Electrocatalysis Division, CSIR-Central Electrochemical Research
Institute, Karaikudi-630003, Tamilnadu, India.
Corresponding Author: S Radhakrishnan
E-mail: s.rkn168@gmail.com
Fax: +91-04565-227779; Tel: +91-04565-241340
Abstract
Copper sulfide with desired structure is of special interest for electrocatalytical
application due to their unique physicochemical properties, simple synthesis and less toxic in
nature. In this study, simple and eco-friendly (without using any template or surfactant) route
for the fabrication of copper sulfide nanostructure morphologies were tuned from cauliflower,
microflower to nanoparticles inter-connected network-like structures by changing the polarity
of solvent medium during solvothermal synthesis. However, to the best of our knowledge, no
such kinds of special three types of CuS nanostructure with excellent electro-catalytic
properties using only H
2
O and C
2
5
H OH as the solvents have been reported in the literature.
The as-prepared different CuS nanostructure was characterized using FE-SEM, HR-TEM,
XRD, XPS and cyclic voltammetry. This morphological alteration able to produce several
precise nanostructures with improved electrocatalytic properties that led to an excellent
1

performance towards enzymeless glucose oxidation. The CuS inter-connected nanoparticles
modified electrode displayed a synergistic effect towards the oxidation of glucose (ipa : 103 ±
5
µA) when compared to that of cauliflower (ipa : 68 ± 3.7 µA) and microflower (ipa : 60 ± 2.4
µA) modified electrode surfaces. Further, the CuS inter-connected nanoparticles modified
-5
-3
electrode showed a wide linear range (2.0 × 10 – 2.5 × 10 M), high sensitivity (1085 µA
-1
-2
mM cm ), low detection limit (2 µM), rapid response time (˂ 3 s), good stability, selectivity
and reproducibility. The obtained sensing parameters based on CuS inter-connected
nanoparticles modified electrode were superior with many reports and also comparable with
few reports in the available literatures.
Keywords:
copper sulphide, nanostructures, electrocatalyst, biosensor, glucose detection
1
.
Introduction
The development of simple and efficient glucose biosensor is considerable importance
in clinical diagnostics, food industry, biotechnology and environmental protection [1].
Different methodologies were applied for the investigation of various glucose sensors.
Electrochemical detection of glucose is more popular and huge interest because of its
simplicity, inexpensive, reliable and real-time analysis [2-4]. Previous investigations on this
area involve the use of glucose oxidase (GOx) enzyme, which effectively catalyses
conversion of glucose into gluconolactone and enzyme based electrodes showed excellent
sensitivity and stability [5]. However, the main shortcoming arises with the enzyme method
is the loss of enzyme activity due to the adsorption of proteins from blood sample, high cost,
complicated process for enzyme immobilization and susceptibility to temperature, pH,
humidity etc. [6,7]. Therefore, enzymeless detection is more promising due to their
2

simplicity, low cost, reproducible, higher stability in different environment and durability
8,9]. In recent years, many efforts have been made to develop enzymeless detection of
[
glucose on noble metals, transition metal oxides/sulfides, carbon nanostructures and
composites of these materials [10-16]. Among the various nanomaterials, copper based
nanomaterials such as metallic copper (Cu), cupric oxide (CuO), cuprous oxide (Cu O) and
2
copper sulfide (CuS) etc. has been deeply investigated for the non-enzymatic glucose
detection due to their simple synthesis, low cost and excellent electrochemical and electro-
catalytic properties [12,17-22]. In the recent past, CuS has been extensively used and studied
for different potential applications including electrochemical biosensor, gas sensors, batteries,
optical filter, solar cell and energy storage applications [23-25]. However, its performance in
electrochemical application is mainly depends on its unique and special morphologies with
huge electrolyte accessible area [26]. In this context, several researchers have been made
considerable efforts for the fabrication of CuS nanomaterials with diverse morphologies
including nanoflakes, microflower, hollow sphere, nanorods, nanotubes, etc. [23-39].
However, these morphologies were usually obtained with the support of surfactants/templates
and expensive/hazardous chemicals. Hence, it is highly necessary to develop an efficient and
eco-friendly protocol for the preparation of CuS nanostructures for practical applications.
Interestingly, the morphology of CuS can be simply controlled by changing the nature
of the solvent [30]. The physiochemical property of the solvent strongly influences the
reaction system by controlling the structure and morphology of the resulting product.
However, there is very few studies are reported in the literature regarding the preparation of
CuS by solvent-assisted synthesis [31,32]. Hence, it is highly desirable to fabricate CuS
nanostructure for sensor applications by a simple and eco-friendly route with improved
electrochemical performance.
3

In this work, we have reported an eco-friendly (without surfactant/templates and with
water and/or ethanol as solvent) and simple (solvothermal method) synthesis of CuS with
different nanostructures (cauliflower, microflower and nanoparticle inter-connected network-
like structures) by simply altering the solvent during solvothermal synthesis. The obtained
nanostructures of CuS exhibited interesting electrocatalytic properties for enzymeless
detection of glucose.
2
.
Experimental
2
.1
Materials and reagents
Copper (II) acetate monohydrate and Nafion (5 wt%) were purchased from Sigma
Aldrich. Glucose, thiourea and ethanol were obtained from SRL, India. All the reagents were
of analytical grade and used without further purification. All aqueous solutions were prepared
with deionized (DI) water (18.2 MΩ.cm, Elix water system).
2
.2
Apparatus and measurements
The phase purity and crystalline nature of CuS products was investigated using
powder X-ray diffraction technique (Bruker D8 Advance) using CuKα radiation (λ=1.5418).
The surface morphologies of the CuS products were characterized using a field emission-
scanning electron microscope (FE-SEM; Carl Zeiss AG, Supra 55VP) with an accelerating
voltage of 30 kV and high resolution transmission electron microscopy (HR-TEM) using a
Tecnai G2F20S-TWIN at 200 kV (operating voltage). The electronic states of the as-prepared
materials were studied by X-ray photo electron spectroscopy (XPS: ESCA 2000
spectrometer). The electrochemical experiments, including cyclic voltammetry (CV), linear
sweep voltammetry (LSV), and chronoamperometry (CA) were performed with a PalmSens
electrochemical workstation at room temperature using a conventional three-electrode system
4

composed of CuS modified glassy carbon electrode (GC, 3 mm in diameter) as a working
electrode, a Ag/AgCl (3M KCl) as the reference electrode and a platinum wire as an auxiliary
electrode. All electrochemical measurements were carried out in 0.1 M NaOH solution.
2
.3
Preparation of CuS nanostructure
Solvothermal method was employed to synthesis copper sulfide material. In a typical
synthesis, copper acetate (0.7 mmol) and thiourea (2.1 mmol) were dissolved in 70 mL of
solvent (water and/or ethanol). The homogenous reaction mixture was then transferred into a
1
1
00 mL Teflon-lined stainless-steel autoclave. The autoclave was tightly closed and kept at
60°C for 16 h, and then cooled to room temperature. The residues obtained were
centrifuged and washed several times sequentially with DI water / isopropanol and dried
under vacuum. The as-prepared CuS from water, ethanol and water/ethanol mixture (1:1)
were designated as CuS-W, CuS-E and CuS-W/E, respectively (Fig. 1).
2
.4
Electrode preparation and modification for ethanol electro-oxidation
The glassy carbon (GC) electrode surface modified with CuS products was prepared
by simple drop-cast method. Initially, the GC electrode surface for each experiment was
mechanically cleaned with alumina powders (0.3 and 0.5 µM, respectively), and rinsed with
deionized (DI) water followed by sonication with ethanol-water mixture. Finally, 10 µL
aliquot of as-prepared CuS products (a homogeneous sonicated solution of 1 mg of CuS
suspended in a mixture of 0.1 mL of Nafion and 0.9 mL of DI water) was drop-cast on the
surface of GC electrode and dried at room temperature.
3
Results and Discussion
3.1
Materials characterization
5

The preparation of CuS of different morphologies is schematically represented in Fig.
. In this illustration, when solvent proportion is changed, the morphologies of CuS product
1
significantly altered from cauliflower like structure to microflower and nanoparticles inter-
connected network-like structure. For example, Fig. 2A (FE-SEM) and Fig. 3A & B (TEM)
shows the images of CuS-W sample that clearly indicates the fine dispersion cauliflower like
morphology of 300 ± 20 nm diameters. This cauliflower structure composed of several
primary nanoparticles of size 43 ± 5 nm (Fig. 2A). In the case of ethanol, the resulting
nanostructure exhibited a nice flower-like structure (Fig. 2B (FE-SEM) and Fig. 3D & E
(TEM)) with diameter in the range of 2.5 ± 0.3 µm.
<
Fig 1 & Fig. 2 >
From the high-resolution FE-SEM image (Fig. S1), the flower-like structure are composed of
several petals of interleaving 2D nanosheets with uniform thickness of about 20 ± 3 nm.
Interestingly, we have observed small nanoparticles (30 ± 3 nm) assembled as porous
interconnected network-like structure for CuS prepared from water-ethanol (1:1) solvent
mixture (Fig. 2C (FE-SEM) and Fig. 3 G & H (TEM)). It is well known that the porous
structure provides easy electrolyte diffusion and improve the charge transfer reaction between
modified electrode surface and electrolyte, which is essential for better electrochemical
applications [33]. From the high-resolution TEM (HR-TEM) images of cauliflower (Fig.
3
C), microflower (Fig. 3F) and nanoparticles network-like structure (Fig. 3I), it is clear that
each CuS nanostructures are well-resolved 2D lattice fringe. The space between two adjacent
crystal planes is found to be 0.306 nm, which is promise with the d spacing for the (102)
crystallographic plane of hexagonal CuS product.
6

<
Fig. 3 >
Fig. 4 shows the diffraction pattern of the as-prepared CuS-W (curve a), CuS-E (curve
b) and CuS-W/E (curve c) products. X-ray diffraction peaks in the pattern can be assigned to
pure hexagonal phase CuS (JCPDS No. 06-0464; P63/mmc space group) without any
observable impurities (including Cu
7
S
4
, Cu1.8S, Cu S or CuO etc.) and deviation. Further,
2
closer examination of the XRD pattern revealed that solvent has a significant effect on the
peak intensity of the product. For instance, the XRD pattern of CuS prepared in water
exhibited high intensity when compared to that of CuS prepared in ethanol and water-ethanol
medium. From these investigations, it can be concluded that the resulted CuS morphologies
and structure depend on the solvents utilized during the solvothermal synthesis. The physical
and chemical properties and coordinating ability of solvents play a significant role for
obtaining different morphologies. Hence, the nature of the solvent and its polarity eventually
influences the morphological features of the resulted CuS.
<
Fig. 4 >
In addition, clear information on the surface elemental chemical states and
composition of CuS-W/E was studied by XPS spectrum (Fig. 5) in the survey region between
5
to 1040 eV. Fig. 5 illustrates the presence of Cu 2p and S 2p in the CuS nanoparticle inter-
connected (Fig. 5A) structure. Fig. 5B shows the high-resolution spectrum of Cu 2p; it is
clearly showed that the presence of two strong peaks at 931.7 and 951.6 eV can be assigned
to Cu 2p3/2 and Cu 2p1/2, respectively. The binding energy between Cu 2p3/2 and Cu 2p1/2 was
2
+
around 20 eV, representing the existence of copper as Cu ions in the inter-connected
nanoparticle CuS structure. The XPS spectrum of Sulfur region shows a couple of peaks at
7

1
61.9 and 163 eV (Fig. 5C), which correspond to the S 2p3/2 and S 2p1/2, respectively and
2
+
also these binding energies are good agreement with the S species.
<
Fig. 5 >
3
.2
Electrochemical characterization of CuS
To investigate the electrochemical performance of the as-prepared CuS products,
cyclic voltammogram (CVs) were recorded in 0.1 M NaOH (Fig. 6). The CV curve for CuS-
W/E modified electrode shows a broad redox peak at 250 to 600 mV due to the well-known
2
+
3+
redox reaction of Cu (Cu /Cu ) in alkaline condition [34].
<
Fig. 6 >
The effect of scan rate on the CuS-W, CuS-E and CuS-W/E modified GC electrodes
were also investigated in 0.1 M NaOH (Fig. 6B-D). When the scan rate was increased from
5
0 to 500 mV/s, both anodic and cathode oxidation peak currents were linearly increased and
it is observed as scan rate dependent (Inset of Fig. 6B-D) which confirmed that the electrode
reaction is surface confined and reversible diffusion-less redox transition on the CuS
modified electrode.
The CV technique was further used to investigate the electrochemical behavior of the
CuS modified electrode for enzymeless electrochemical oxidation of glucose. Fig. 7A-C
compares the glucose oxidation responses at CuS modified GCs in 0.1 M NaOH. The CVs
were collected for the CuS modified electrodes in the absence (curve a) and presence of
(curve b) of 1 mM of glucose at a scan rate of 50 mV/s. The anodic peak current greatly
increased in the presence of glucose for the CuS modified electrodes (Fig. 7A-C). The
8

obtained peak current (measured at Epa 0.5 V) for the CuS-W, CuS-E and CuS-W/E modified
electrodes are given as bar diagram in Fig. 7D. Compared to CuS-W (68 ± 3.7 µA) and CuS-
E (60 ± 2.4 µA) modified electrodes, a remarkable large oxidation peak current was obtained
at CuS-W/E modified electrode (103 ± 5 µA). This anodic peak current obtained for the CuS-
W/E modified electrode is nearly 1.5 and 1.7 fold higher compared to CuS-W and CuS-E
modified electrodes respectively. It is also noted here that the onset potential of glucose
oxidation start at 300 mV for CuS-W/E modified electrode, which is lower compared to
numerous reports for copper based materials employed for enzymeless oxidation of glucose
[
14,35-39]. These results clearly suggested that the CuS-W/E modified electrode has
improved electrocatalytic performance towards enzymeless oxidation of glucose when
compared to CuS-W and CuS-E modified electrodes. The higher peak current and lower
oxidation potential (less anodic one) of the CuS-W/E may be due to the smaller particle size
with porous network-like structure and high surface area of the as-prepared CuS that can
effectively access large number of glucose molecule at the interface and also improve the
electron transfer passage between the CuS modified electrode surface and glucose. Hence, the
CuS-W/E modified electrode is utilized for further detailed study.
<
Fig. 7 >
The electrochemical oxidation mechanism of glucose on CuS-W/E modified electrode
in an alkaline medium is identical with that of copper materials [40]. Hence, the non-
enzymatic electro-oxidation of glucose on CuS modified electrode in alkaline medium can be
3
+
simply expressed by the equation (1). In which, the Cu has high oxidizing state (Cu ) during
the conversion of CuS into CuSOH. Followed by, the glucose analyte has deprotanated in
9

NaOH medium to form enediol structure, which is further oxidized into gluconolactone when
3
+
interact with Cu and then further hydrolyzes into gluconic acid (scheme 1).
–
–
CuS + OH  CuSOH + e
(1)
Further, the scan rate effect on the electro-oxidation of glucose (1 mM) at the CuS-
W/E modified GC electrode was studied by CV (Fig. 7E). The CV curves show a gradual
increase in oxidation peak current (ipa) with scan rate (50-500 mV/s) in 0.1 M NaOH solution
(Fig. 7E). The oxidation peak current was found proportional with the square root of scan rate
(
inset of Fig. 7E) and the regression equation for glucose is ipa (µA) = 11.65 (υ) + 9.80 (R2=
0
.998). It clearly indicates that the electro oxidation reaction of glucose at CuS-W/E modified
electrode surface follows diffusion controlled process [8].
<
Scheme 1 >
Fig. 7F shows the linear sweep voltammograms (LSVs) obtained for glucose in the
concentration range of 0 - 500 µM at CuS-W/E modified GC electrode. The electro-oxidation
current found to increase with each 50 µM glucose addition. The anodic oxidation current of
glucose is found to proportional with glucose concentration and a correlation coefficient
value of 0.9998 (inset of Fig. 7F) is obtained.
3
.3
Detection of glucose by chronoamperometry (CA)
The optimization of applied potential in CA measurement is much important
parameters to obtain perfect amperometric signal. Hence, we have carried out CA
1
0

measurement for CuS-W/E modified electrode at different potentials (0.3 to 0.55 V) with
successive addition of glucose (10 µM) in 0.1 M NaOH and the obtained data are given in
Fig. 8A. The obtained current response with respect to applied potential was given as a bar
diagram in the inset of Fig. 8A. It can be clearly observed that the CA signal greatly
increased with the applied potential (Fig. 8A).
<
Fig. 8 >
However, an applied potential of 0.5 - 0.55 V led to a remarkable enhancement in the
current response upon successive addition of glucose when compared to that of other applied
potential range 0.3 to 0.45 V. Further, the detection of glucose at lower potential is greater
advantages due to the fact that reduction in the background current and noise, restrict the
interference species to react with the modified electrode surface and consequently these
factors may affect the sensitivity and stability of the modified electrode to determine accurate
concentration of glucose molecule in real time applications. Hence, 0.5 V is fixed as the
optimum working potential in the following experiments.
CA measurement was further applied to study the sensitivity of CuS-W/E modified
electrode towards the detection of glucose under optimized conditions. The CA response of
the CuS-W/E modified electrode was investigated with the injection of different
concentration of glucose in 0.1 M NaOH solution as shown in Fig. 8B. The modified
electrode produces a swift response with the addition of glucose and also the CA signal
reached 95 % of the steady state current within 3 s. The catalytic oxidation peak current
-5
-3
increased linearly with the glucose concentration in the range from 2.0 × 10 – 2.5 × 10 M.
The sensitivity of the CuS-W/E modified electrode, calculated from the calibration curve
1
1

-1
-2
(
inset of Fig. 8B) is observed as 1085 µA mM cm with a detection limit of 2 µM. Further,
we have compared the performance of the fabricated CuS-W/E electrode with existing
nonenzymatic glucose detection reported in the literature (Table S1). The comparison
suggests superiority of the present sensor system over some reported nonenzymatic glucose
sensor and the possible reason being that the porous structure of CuS-W/E with high surface
area favours access of large number of analyte molecules with minimal diffusion resistance.
The accurate and reliable detection of glucose concentration is much important in real
applications. However, oxygen deficiency and chloride ions play major roles for the
inaccuracy and unreliable results during the glucose detection [41]. Hence, we have carried
out CA measurement in different environment using CuS-W/E modified electrode for the
demonstration of the poisoning resistance of the present modified electrode. Fig. 8C-E shows
the CA measurements recorded in ambient conditions (Fig. 8C), in the presence of NaCl (Fig.
8
D) and N gas saturated (Fig. 8E) conditions. It should be noted here that we does not
2
observe any significant change in the CA signal and all CA signals are found to be similar to
each other, which clearly suggested that the our fabricated CuS-W/E has more poisoning
resistance against oxygen deficiency and chloride ions. In addition, we have verified the
selective determination of glucose (50 µM) in the presence of important physiological
interfering molecules (20 µM) such as dopamine, uric acid, ascorbic acid, fructose, nitrite
ions and calcium ions. As shown in bar diagram of Fig. 8F, the interference currents obtained
from physiological interferents are negligible, unlike the strong response observed by
glucose. These results clearly demonstrate the excellent selective behavior of CuS-W/E
modified electrode and ascertain its possible applicability in the practical physiological
conditions.
1
2

The durability of the CuS-W/E electrode was investigated by CA measurement for
continuous measurements up to 20 days. The fabricated CuS-W/E based electrode was kept
in closed air atmosphere at room temperature and glucose samples were determined every 10
days, the CA current response is retained 96 % of the original value (Fig. S2), suggesting that
the electrode has better stability even after 20 days. To confirm the reproducibility of the
results, four different GC electrodes were modified with the CuS-W/E and their CA current
response was measured under identical conditions (Fig. S3). The current response obtained
in the measurement of four separate electrodes showed a relative standard deviation of 4.39
%, confirming that the results are reproducible. The above results showed that the CuS-W/E
based electrode was very much stable and reproducible for glucose detection.
The main advantages of the current work is that the different morphologies of copper
sulfide preparation by simple chemical and eco-friendly route (using copper acetate and
thiourea as Cu and S sources in water/ethanol as solvent) without using any template and
hazardous materials. Further, the as-prepared CuS products has been successfully applied for
the non-enzymatic detection of glucose and also the performance of the fabricated glucose
sensor is very much attractive one compared to the reports available in the literature.
4
Conclusions
In summary, we have reported a simple and eco-friendly method for the fabrication of
different nanostructure of CuS without employing any surfactant or template systems. These
CuS nanostructures modified GC surface have been utilized for enzymeless electrochemical
detection of glucose and have exhibited significant response. The nanoparticle network-like
structure showed a higher electrocatalytic performance, which can serve as highly sensitive
and selective nonenzymatic detection of glucose. The present work opens a new avenue for
the design of different morphologies of CuS for energy storage to biomedical applications.
1
3

Acknowledgements
Dr. S. Radhakrishnan acknowledges the DST, New Delhi, India for the DST-
Inspire Faculty Award (DST/INSPIRE/04/2015/002259). The authors thank the Mr.
V. Prabu for FE-SEM measurement and Central Instrumentation Facility, CSIR-
CECRI, Karaikudi.
1
4

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Figure Captions
Fig. 1 Schematic illustration of the surface morphological alteration caused by changing the
polarity of solvent.
Fig. 2 FE-SEM images of (A) CuS-W, (B) CuS-E, (C) CuS-W/E and (D).
Fig. 3 HR-TEM images of (A-C) CuS-W, (D-F) CuS-E, (G-I) CuS-W/E.
Fig. 4 XRD pattern of (a) CuS-W, (b) CuS-E and (c) CuS-W/E.
Fig. 5 (A) XPS survey spectrum of CuS-W/E product; (B) High-resolution XPS spectra of
copper 2p and (C) sulfur 2p regions.
Fig. 6 Cyclic voltammograms of (A) CuS-W/E modified electrode in 0.1 M NaOH at a scan
rate of 50 mV/s. (B) CuS-W, (C) CuS-E and (D) CuS-W/E modified GC electrodes
recorded in 0.1 M NaOH solution at different scan rates (50-500 mV/s). Inset shows
the resulting calibration plot.
Fig. 7 Cyclic voltammograms (CVs) of the (A) CuS-W (B) CuS-E and (C) CuS-W/E
modified electrode in the absence (curve a) and presence of (curve b) 1 mM glucose
0
.1 M NaOH solution; Scan rate: 50 mV/s. (D) Comparative bar diagram of peak
current against modified electrodes. (E) CVs response of CuS modified GC electrode
at different scan rate 50–500 mV/s in 0.1 M NaOH solution containing 1 mM
glucose. Inset shows the corresponding calibration plot. (F) Linear sweep
voltammetry (LSV) obtained for glucose in the concentration ranging from 0 to 500
µM. Glucose was added in aliquots of 50 µM each at CuS-W/E modified GC
electrode in 0.1 M NaOH; Inset shows the resulting calibration plot.
Fig. 8 (A) Amperometric response for the CuS modified GC electrode at different applied
potential with successive addition of 10 µM glucose in 0.1 M NaOH.(B)
Amperometric response of the CuS modified GC electrode with addition of different
concentrations of glucose in 0.1 M NaOH solution; inset shows the corresponding
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calibration curve of glucose concentration versus peak current response at an applied
potential of 0.5 V. Amperometric response of the CuS modified GC electrode with
successive addition of 10 µM glucose in 0.1 M NaOH solution (C) ambient condition
(D) 0.1 M NaOH solution containing NaCl (0.1 M) and (E) N2 saturated 0.1 M NaOH
solution. (F) Bar diagram representing normalized current response obtained in
amperometric measurement for the addition of glucose (50 µM) and interference
compounds (20 µM) at CuS modified GC electrode in 0.1 M NaOH; applied potential
of 0.5 V.
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Fig. 1
2
0

Fig. 2
2
1

Fig. 3
2
2

Fig. 4
2
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Fig. 5
2
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Fig. 6
2
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Fig. 7
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Fig. 8
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Scheme 1
Glucose detection scheme using CuS modified electrode.
Scheme 1
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