Comparison of NiS2 and α-NiS hollow spheres for supercapacitors, non-enzymatic glucose sensors and water treatment

Article abstract of DOI:10.1039/c5dt02724a

NiS₂ hollow spheres are successfully prepared by a one-step template free method. Meanwhile, α-NiS hollow spheres can also be synthesized via the calcination of the pre-obtained NiS₂ hollow spheres at 400°C for 1 h in air. The electrochemical performances of the as-prepared NiS₂ and α-NiS hollow sphere products are evaluated. When used for supercapacitors, compared with NiS₂ hollow spheres, the α-NiS hollow sphere electrode shows a large specific capacitance of 717.3 F g^-1 at 0.6 A g^-1 and a good cycle life. Furthermore, NiS₂ and α-NiS hollow spheres are successfully applied to fabricate non-enzymatic glucose sensors. In particular, the α-NiS hollow spheres exhibit good catalytic activity for the oxidation of glucose, a fast amperometric response time of less than 5 s, and the detection limit is estimated to be 0.08 μM. More importantly, compared with other normally co-existing interfering species, such as ascorbic acid, uric acid and dopamine, the electrode modified with α-NiS hollow spheres shows good selectivity. Moreover, the α-NiS hollow spheres also present good capacity to remove Congo red organic pollutants from wastewater by their surface adsorption ability.

Full text of DOI:10.1039/c5dt02724a

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ARTICLE
Comparison of NiS and -NiS hollow spheres for
2
supercapacitors, non-enzymatic glucose sensors and water
treatment
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
a
a
a
a
a
a
www.rsc.org/
Chengzhen Wei,* Cheng Cheng, Yanyan Cheng, Yan Wang, Yazhou Xu, Weimin Du
a,b
and Huan Pang*
NiS hollow spheres are successfully prepared by one-step template free method. Meanwhile,
-NiS
2
hollow spheres can also be synthesized via the calcination of pre-obtained NiS hollow spheres under
2
4
00
°C for 1 h in air. The electrochemical performances of the as-prepared NiS and -NiS hollow
2
spheres products are evaluated. When used for supercapacitors, compared with NiS hollow spheres,
2
-1
-1
the

-NiS hollow spheres electrode shows a large specific capacitance of 717.3 F g at 0.6 A g and a
-NiS hollow spheres are successfully applied to fabricate non-
enzymatic glucose sensors. Especially, the -NiS hollow spheres exhibits good catalytic activity for
good cycle life. Furthermore, NiS and

2

the oxidation of glucose, a fast amperometric response time of less than 5 s, and the detection limit
is estimated to be 0.08 μM. More importantly, compared with other normally co-existing interfering
species, such as ascorbic acid, uric acid and dopamine, the electrode modified with
spheres shows good selectivity. Moreover, the -NiS hollow spheres also present good capacity to
remove Congo red organic pollutants from waste water by their surface adsorption ability.
-NiS hollow

1
3-16
materials.
To overcome these problems, a number of template-
1
7-19
free routes have been devised for preparing hollow materials.
Despite the intense efforts have been dedicated, it is still of huge
challenge to develop a facile, reliable, and scalable route for the
rational synthesis of hollow structured materials.
1
. Introduction
In recent years, the synthesis of micro/nano structured materials
Electrochemical energy storage provides a promising technology
with controlled size, shape, composition and internal structure have for portable energy supplies in fields such as electric vehicles and
received tremendous interest for achieving novel morphology- mobile electronic products. Supercapacitors that store energy have
1
-6
dependent chemical-physical properties.
nanostructures materials with interior voids, low density, and power density, excellent charge-discharge characteristics, long
In particular, hollow recently received considerable attention because of their high
2
0, 21
surface permeability has potential applications in many fields, such cycling life and good safety.
as energy storage, catalysis, sensors, drug delivery, and water including carbonaceous
In general, hollow materials are prepared via oxides/hydroxides and hybrid composite, have been widely studied
Up to date, various materials,
materials, transition metal
7-12
treatment.
template directed approaches. However, this kind of synthetic as electrodes for supercapacitors.
22-25
Compared to carbonaceous
route is quite costly, tedious, and low yield. Moreover, template materials, transition-metal oxides show larger electrochemical
contamination mostly decreased the activity of synthesized capacitances and energy densities as they can provide variable
oxidation states for efficient redox charge transfer. In particular,
supercapacitors based on RuO2 have exhibited a high specific
capacitance and excellent reversibility. However, the high cost of
a.
College of Chemistry and Chemical Engineering, Anyang Normal University,
Anyang, 455000 Henan, P. R. China.
Ru-based materials makes this material unsuitable for practical
26
applications. Hence, searching for alternative electrode materials
with good capacitive properties becomes important.
E-mail:chengzhenweichem@126.com, huanpangchem@hotmail.com.
College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou,
25002, Jiangsu, P. R. China.
b
2
Semiconducting transition metal sulfides, such as MoS , ZnS, CuS,
2
Ni S , Co S , CoS and NiS , etc. are reported to be viable
7
6
3
4
2
2
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2
7-33
candidates.
Among them, Ni-based sulfides materials are of The working electrode was prepared by mixing the electroactive
View Article Online
DOI: 10.1039/C5DT02724A
particular interest owing to their high theoretical specific material
capacitance and low cost.
The development of highly sensitive, low-cost, reliable, fast mixture was then pressed onto a nickel grid (1 cm ). The
(NiS2
or
-NiS),
acetylene
black,
and
34
polytetrafluoroethylene (PTFE) with a weight ratio of 85:10:5. The
-2
glucose sensors is becoming gradually important because of their electrochemical performance of the NiS and -NiS sample were
2
applications in clinical diagnostics, biotechnology and food evaluated by using a three-electrode cell with Pt foil as the counter
3
5
industry. The conventional glucose sensors involve the use of electrode and a saturated calomel electrode (SCE) as the reference
glucose oxidase (GOD). However, these GOD-based biosensor electrode in 3.0 M KOH aqueous solution.
approaches suffer greatly from the influences of various 2.3 Fabrication of the glucose sensor
environmental factors such as temperature, humidity, pH value, The glassy carbon (GC) electrodes were carefully polished with
organic reagents, and toxic chemicals, which limit their wide alumina slurry, rinsed thoroughly with distilled water and ethanol,
36
applications. To solve this problem, the non-enzymatic glucose and then dried at room temperature. To fabricate NiS or -NiS
2
biosensors have been pursued increasingly. The recent researches containing GC electrodes, an aqueous dispersion of NiS or -NiS
2
-1
exhibit that many nano/microstructured materials have been (1.0 mg mL ) was prepared and 8 L of the suspension was cast on
successfully used for the construction of non-enzymatic glucose the surface of the GC electrodes. Subsequently, the solvent was
37-41
sensors, such as Ni, Cu, NiO, NiS and CuS materials, etc.
allowed to evaporate at room temperature, leaving the as-prepared
Furthermore, these nano/microstructured materials also exhibit NiS or -NiS material immobilized onto the GC electrode surface.
2
good performance for the detection of glucose in the absence of 2.4 Removal of Congo red
enzyme. However, there are few reports on the fabrication of non- 60 mg of the as-prepared NiS and -NiS hollow spheres powder
2
enzymatic glucose detectors based on Ni-based sulfides were mixed with 150 mL of aqueous solution of Congo red with a
-1
micro/nanomaterials.
concentration of 100 mg L in a beaker, respectively. The
Herein, NiS hollow spheres were successfully prepared via a suspension was stirred at room temperature. At given time
2
simple and general hydrothermal synthetic route. Interestingly, - intervals, a series of aqueous solution were taken out and
-1
NiS hollow spheres could also be synthesized by the calcination of separated through centrifugation (10000 rpm min ). The
NiS hollow spheres under 400 °C for 1 h in air, which inspired us to supernatant solutions were analyzed with UV-vis spectroscopy
2
study the performance of NiS and -NiS hollow spheres under the (Hitachi U-3900) to determine the concentrations of Congo red in
2
same conditions. The electrochemical performances of the NiS and solution.
2

-NiS hollow spheres were evaluated. Especially, -NiS hollow 2.5 Characterization
-1
spheres showed a large specific capacitance of 717.3 F g at 0.60 A
X-ray diffraction (XRD) patterns were recorded on a Rigaku-Ultima
-1
g
and a good cycle life. More importantly, the NiS and -NiS
2
III with Cu-K radiation (=1.5418 Å). The morphologies of the as-

hollow spheres were also tested as electrochemical catalysts. It is
found that -NiS hollow spheres exhibited a high selectivity, high
sensitivity and low detection limit toward the oxidation of glucose.
Moreover, the as-prepared -NiS hollow spheres also displayed a
good ability to remove the organic pollutant Congo red from water
compared with that of NiS2 hollow spheres. These results
demonstrate that -NiS hollow spheres hold great potential
applications in supercapacitors, enzyme-free determination of
glucose and waste water treatment.
prepared samples were observed using a field-emission scanning
electron microscope (FESEM, JEOL JSM-6701F) operated at an
acceleration voltage of 3.0 kV. Transmission electron microscopy
(
(
TEM) and high-resolution transmission electron microscopy
HRTEM) were taken on the JEOL JEM-2100 microscope at an
acceleration voltage of 200 kV. The nitrogen adsorption and
desorption isotherms were measured on
ASAP2020 physisorption analyzer. The
a
Micromimetrics
electrochemical
supercapacitor measurements were measured by using an
electrochemical analyzer system CHI660D (Chenhua, Shanghai,
China).
2. Experimental
3. Results and discussion
2
.1 Synthesis of NiS and -NiS hollow spheres
2
The typical procedure for NiS and -NiS hollow spheres is as
follows : 0.5 mmol Ni(NO ) ·6H O was dissolved in 20 mL distilled
2
6
3
2
2
water at room temperature. Then, L-cysteine (2.0 mmol) and urea
0.5 mmol) were added to the above mentioned solution under an
(
ultrasonic treatment. The homogeneous solution was transferred
into a 35 mL Teflon-lined autoclave. Then the autoclave was sealed
and maintained at 140 °C for 24 h, and allowed to cool to room
temperature naturally. The resulting NiS2 hollow spheres
precipitate was repeatedly washed with ethanol several times, then
dried at 50 °C for 12 h. -NiS hollow spheres were obtained after
calcination of the as-prepared NiS hollow spheres in air at 400 °C
2
for 1 h.
Fig. 1 XRD patterns of as-synthesized samples: (a) NiS ; (b) -NiS.
2
2
.2 Fabrication of the three-electrode supercapacitors
2
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Typical XRD patterns of the as-synthesized samples are shown in hollow spheres are uniform distribution of Ni and S elements (Fig.
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DOI: 10.1039/C5DT02724A
Fig. 1. The obtained diffraction peaks are labeled in Fig. 1a and b S2).
agreed well with the standard patterns of the NiS (JCPDS card No.
In our paper, NiS and -NiS hollow spheres were prepared via
2
2
6
5-3325) and -NiS (JCPDS card No. 65-5762). No peaks of any the previous reported methods, in which the NiS hollow spheres
2
6
impurity phase could be observed from these patterns, indicating were formed via the Ostwald ripening process. In the preparation
the high purity of the as-synthesized NiS and -NiS products.
system, urea plays an important role for the formation of hollow
2
structured NiS . Without adding urea, irregular nanoparticles were
2
obtained (Fig. S3). We believed that L-cysteine is not only provided
S source but also can be capped by Ni ions due to the coordination
of functional groups in the L-cysteine molecules. Meanwhile, urea
can be used to provide an alkaline environment, after reaction for
2
4 h under 140 °C, the NiS hollow spheres were obtained under
2
the hydrothermal conditions. In addition, we also found out that
the NiS hollow spheres can be obtained under the 160 °C and 200
2
°C (Fig. S4), which demonstrates that the reaction temperature has
no effect on the preparation of NiS hollow spheres.
2
The surface area and pore size distribution of the NiS and -NiS
2
with hollow interiors were further determined by nitrogen
adsorption-desorption measurements. As revealed by the nitrogen
adsorption-desorption measurement (Fig. 3), the BET specific
surface areas of the NiS and -NiS hollow spheres are 15.3 and
2
2
-1
3
2.2 m g , respectively. The pore sizes of NiS hollow spheres are
2
Fig. 2 (a, b) SEM and TEM images of the NiS ; (c, d) SEM and TEM
2
about 2.8 nm, while the -NiS hollow spheres contain two types of
mesopores (ca. 2.4 and 3.0 nm).
images of the -NiS. The inset in b and d show SAED patterns and
HRTEM images of the NiS and -NiS, respectively.
2
The morphologies and structures of the NiS and -NiS products
2
were characterized by field emission scanning electron microscopy
(
FESEM) and transmission electron microscopy (TEM). Panoramic
FESEM image of NiS exhibited in Fig. S1a clearly presents that the
2
product is entirely composed of large amounts of spherical
structures. Several broken nanostructures in Fig. S1a obviously
reveal the hollow nature of the as-prepared NiS spheres. Close-up
2
FESEM micrograph of an individual hollow NiS spheres (Fig. 2a)
2
shows that the NiS hollow spheres possess quite rough surfaces,
2
which are built up from numerous densely packed nanoparticles.
The hollow interior of NiS spheres could also be clearly identified
2
by the sharp contrast between the dark edge and the pale center in
the TEM image of an individual NiS sphere (Fig. 2b). Selected-area
2
electron diffraction (SAED) pattern (inset in the Fig. 2b) shows that
NiS hollow spheres are composed of high crystalline nanocrystals.
2
The lattice fringes in high-resolution TEM (HRTEM) image (inset in
the Fig. 2b) shows a spacing of 0.28 nm, corresponding to the (200)
planes of the NiS . After being annealed at 400 °C in air for 1 h, the
2
as-prepared NiS hollow spheres are fully converted to -NiS (Fig.
2
1
b). It is interesting and exciting that -NiS remains the hollow
sphere structure (Fig. S1b and Fig. 2c). The corresponding TEM
image (Fig. 2d) confirms the formation of hollow structure. A
representative high-resolution transmission electron microscopy
image of the α-NiS shows a typical lattice fringe spacing of 0.26 nm,
corresponding to the (101) plane of the -NiS. The SAED pattern
shows that the -NiS hollow sphere is polycrystalline (inset of Fig.
Fig. 3 Nitrogen adsorption-desorption isotherm (with the BJH pore
size distribution plot in the inset) of the as-synthesized samples: (a)
NiS ; (b) -NiS.
2
2
d). To illustrate the spatial distribution of Ni and S elements in the
In particular, hollow sphere structures have several advantages in
NiS2 and α-NiS hollow spheres, the EDS elemental mapping is electrochemical, catalysis and adsorption property. The hollow
performed on hollow spheres under SEM observation. The EDS interior space effectively reduces the mass weight and enhances
elemental mapping results demonstrate that the NiS and α-NiS the spatial dispersion, which results in not only high surface area
2
42-45
but also better mass transportation.
In order to explore the
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advantages of the NiS and -NiS hollow spheres, the as prepared discharging of NiS and -NiS electrodes were performed in 3.0 M
2
2
View Article Online
DOI: 10.1039/C5DT02724A
products were firstly evaluated as electrochemical materials to KOH solution. The specific capacitance of the electrode can be
48, 49
study their electrochemical properties. Cyclic voltammetry (CV) estimated by the following formula:
measurements were conducted on the NiS and -NiS electrodes in C=(I△t)/(m△V)
.0 M KOH solution. Fig. 4a and b show the CV curves of the NiS2 Where C (F g ) is the specific capacitance, I (A) is the discharge
(4)
2
-
1
3
and -NiS electrode at different scan rates. The shapes of the CV current, △t is the time for discharge duration, m (g) is the mass of
reveal that the capacitance characteristic is very different from that the active material within the electrode, △V is the voltage interval
of traditional electric double-layer capacitance, indicating that the of the discharge.
4
6, 47
capacity mainly results from pseudocapacitive capacitance.
The
The specific capacitances were calculated from the galvanostatic
-
mechanisms of the NiS and -NiS supercapacitors occur like below: discharge (Fig. 4c and d) curves at current densities of 0.6-6.0 A g
2
1
-1
NiS + H O + 1/2 O
Ni(OH) + 2S
(1)
(2)
(3)
are shown in Fig. 4e. The specific capacitances are 547.2 F g (NiS )
2
2
2
2
2
-
1
-1
and 717.3 F g (-NiS) at 0.6 A g in 3.0 M KOH solution. At a high
current density of 6.0 A g , the specific capacitance of -NiS was
25.4 F g , while that of NiS was reduced to 93.8 F g . Moreover,
2
-1
NiS + H O + 1/2 O
Ni(OH) + 2S
2
2
2
-1
-1
1
-
-1
Ni(OH) + OH
NiOOH + H O + e
2
2
compared with other electrode materials, the specific capacitance
of α-NiS hollow sphere electrode is significantly better than some
A pair of redox peaks can be observed (Fig. 4a and b), which is
-1
-1 50
electrode materials, such as MoS (1 A g , 168 F g ), β-NiS (0.6 A
2
corresponding to the reversible conversion between Ni(OH) and
-1
-1 40
-1
-1 51
2
34
g , 501.5 F g ), Co-Ni-Mn oxide (0.5 A g , 578 F g ). However,
NiOOH. Fig. S5 shows CV curves of NiS and -NiS hollow sphere
electrodes at 50 mV s in 3.0 M KOH electrolyte. Interestingly, the
2
-1
the specific capacitance of the α-NiS hollow sphere electrode is not
29, 52
greater than that of some metal sulfides materials.
CV curve of -NiS electrode has a bigger surrounded area compared
Electrochemical stability is another important parameter to
evaluate the active materials for supercapacitor applications. Fig. 4f
to that of the NiS electrode, suggesting that the capacitance of -
2
NiS electrode might be larger than that of the NiS electrode.
2
presents the cycling performance of the NiS and -NiS electrode
2
-1
within 1000 cycles at the current density of 1.2 A g . After
subsequent 1000 cycles, there is only a small (1.5 %) loss of
capacitance for -NiS electrode. It is notable that the retention
ratio of the NiS2 electrode is approximately 96.5 %. This high
specific capacitance of -NiS can mainly be attributed to the high
2
-1
2
-1
surface area (-NiS: 32.2 m g , NiS : 15.3 m g ) and hollow
2
nanostructure, which provide effective diffusion channels for the
electrolyte ions. More importantly, compared with the NiS crystal
2
structure at the atomic scale, there are more Ni atoms exposed on
the surface of -NiS than the NiS (Fig. S6 and S7), which is also
2
beneficial for Faradic reactions during the charge-discharge process.
40, 53, 54, 55
Fig. 4 (a, b) CV curves of NiS and -NiS hollow sphere electrodes at
2
-1
a scan rate of 5 to 100 mV s ; (c, d) The galvanostatic charge-
discharge curves of NiS and -NiS hollow sphere electrodes at Fig. 5 Cyclic voltammograms of the bare GC electrode (a); NiS -GC
2
2
different current densities in 3.0 M KOH electrolyte; (e) The specific electrode (b); and -NiS-GC electrode (c) in 0.1M NaOH with 5 mM
-1
capacitances calculated from the discharging curves at different glucose at a scan rate of 50 mV s .
current densities; and (f) Plots of the specific capacitance as a
-
1
function of cycle number at a current density of 1.2 A g .
The development of nonenzymatic glucose sensors with high
sensitivity, fast response, and good stability has become one of the
most attractive subjects of investigation in electrochemistry due to
the practical applications. Transition metal sulfides materials by
To further evaluate the electrochemical properties of the as-
prepared NiS and -NiS hollow sphere, galvanostatic charging and
2
4
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virtue of low cost, good electrocatalytic properties are of particular 0.1 M NaOH solution for (e) NiS /GC electrode and (f) -NiS /GC
2
View Article Online
DOI: 10.1039/C5DT02724A
interest, which make them suitable for the electrochemical electrode.
40, 41, 56
sensors.
The possible mechanism for oxidation of glucose by
the NiS and -NiS hollow spheres materials could be represented
Fig. 6a and b show typical amperometric response curves of
by the following reactions: First, Ni could be electro-oxidized to different concentrations of glucose at the NiS /GC electrode and -
2
2+
2
3+
Ni in alkaline solution, where the release of electron resulted in NiS/GC electrode, respectively. The proposed sensors rapidly
the formation of oxidation peak current. Then, glucose could be responded to the changes of glucose concentration and achieved
oxidized to gluconic acid by Ni , which was deoxidized to Ni at the steady-state current within 5s, demonstrating the good
3+
2+
3
5
same time. To demonstrate the sensing application of the NiS2 electrocatalytic ability of the NiS /GC electrode and -NiS/GC
2
and -NiS hollow spheres, nonenzymatic glucose sensor was electrode for glucose oxidation. To our surprise, it is noted that the
constructed by deposition of the aqueous dispersion of NiS or - current signals increase more rapidly with a higher sensitivity for
2
NiS hollow spheres on a GC electrode surface. Fig. 5 presents the the -NiS/GC electrode compared with the NiS /GC electrode. The
2
CVs of bare GC electrode and NiS or -NiS hollow spheres modified calibration curves for the NiS /GC electrode and -NiS/GC electrode
2
2
GC electrode in 0.1 M NaOH solution in the presence of 5.0 mM sensors are shown in Fig. 6c and d. The NiS /GC electrode sensor
2
-1
glucose at a scan rate of 50 mV s . It is found that the bare GC displays a linear range from 4.0 µM to 0.15 mM glucose (R=
-1
electrode shows no obvious oxidation peak in the presence of 0.9936), a sensitivity of 5 µA mM and a detection limit of 0.45 µM
glucose, demonstrating that the response of bare GC electrode (S/N = 3), whereas the -NiS/GC electrode sensor displays the
toward the oxidation of glucose is pretty weak (Fig. 5a). In contrast, glucose detection concentration range of 0.125 µM-0.2 mM
-1
upon the addition of 5.0 M glucose, a more dramatic increase can (R=0.9969), and the calculated sensitivity is 80 µA mM . The limit of
be found after the GC electrode was modified with NiS or -NiS detection is calculated to be as low as 0.08 µM (S/N = 3).
2
(
Fig. 5b and c), indicating good electrocatalytic activity in response Furthermore, the -NiS/GC electrode sensor was also used for
to glucose. Furthermore, the -NiS /GC electrode shows a much detection of glucose with a relatively wide concentrations ranging
stronger signal than that of NiS /GC electrode.
from 0.24 mM to 1.0 mM. The performance of the as-prepared -
NiS/GC electrode sensor was also compared to some existing non-
enzymatic sensors. The detection limits of some previously
reported materials are lower than that of our system, such as NiO/C
2
57
nanoblets (9.12 nM), MnCo O nanofibers (0.01 µM ) and CuO-
2
4
58, 59
NiO microfibers (1 nM).
However, the detection limit of glucose
for the -NiS/GC electrode sensor is better than those of many non-
4
0
41
enzymatic sensors, such as β-NiS (20 µM), CuS (0.25 µM), NiO
(
57
60
61
0.23 µM), Ni(OH) hollow spheres (0.1 µM), Cu-NiO (0.5 µM),
2
NaCoPO -Co O hollow microspheres (0.125 µM) and Nitrogen-
4
3 4
6
2, 63
doped carbon-copper nanohybrids (5 µM).
The results confirm
that -NiS hollow sphere can be a promising functional material for
the electroanalytical detection of glucose. The excellent sensing
properties of the as-fabricated -NiS/GC glucose sensor can be
attributed to the improved electrochemical and electrocatalytic
performances of -NiS/GC electrode. Firstly, the electro-oxidation
of glucose at the modified electrode can be catalyzed by -NiS
hollow sphere that was directly immobilized onto the GC electrode
surface. Secondly, the conductive -NiS hollow sphere is able to
keep electrical connection between the hollow spheres and
electrode, and thus facilitates the charge transfer in those
interfaces. That is to say, direct electron transfer can be achieved
between -NiS hollow sphere and electrode, which is an important
reason of fast and sensitive catalytic performances. Thirdly, more Ni
atoms are exposed on the surface of -NiS hollow spheres (Fig. S7),
the oxidation of glucose by -NiS hollow spheres could occur easily.
Finally, the hollow structure of -NiS ensures that the glucose can
enter into the interior of the -NiS and thus shorten the diffusion
distance for glucose to access the electrode surface, resulting in an
Fig. 6 Current-time response at a potential of 0.60 V upon
successive injection of different amounts of glucose into 0.1M
NaOH with stirring for (a) NiS /GC electrode and (b) -NiS /GC
2
57, 64, 65
improved signal-to-noise ratio and faster response time.
electrode; (c, d) Plots of the electrocatalytic current of glucose
One of the most important performance parameters for a non-
enzymatic sensor is the ability to discriminate interfering species
from the target analyte. It is well known that some easily oxidative
species such as ascorbic acid (AA), uric acid (UA), dopamine (DA)
usually co-exist with glucose and can cause interfering signals.
versus glucose concentration for (c) NiS /GC electrode and (d) -NiS
2
/
GC electrode; (e, f) Amperometric response of modified electrodes
with successive addition of glucose, AA, UA, DA, KCl, and glucose in
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Therefore, the electrochemical response of the interfering species
Journal Name
The as-synthesized NiS and -NiS hollow spheres samples were
2
View Article Online
DOI: 10.1039/C5DT02724A
was also examined at the NiS /GC electrode and -NiS/GC also used to study their possible applications in water purification
2
electrode. The results showed that addition of 200 μM AA, DA, and treatment. Congo red usually used dye in the textile industry, which
UA induces the increasing the current of NiS /GC electrode, the was chosen as a typical organic water pollutant. Fig. 7a and b show
2
-1
intensity increased is much stronger than that of glucose (Fig. 6e). It the absorption spectra of an aqueous solution of 100 mg L Congo
indicates that NiS /GC electrode shows not good selectivity toward red in the presence of 60 mg of the as synthesized NiS and -NiS
2
2
AA, DA, and UA. As shown in Fig. 6f, although the addition of 200 hollow spheres samples. It can be found that -NiS hollow spheres
μM AA, DA, and UA also induces the increasing the current of - present good adsorption ability for Congo red dye. Fig. 7c gives
NiS/GC electrode, these interfering species produced negligible curves of the adsorption extent of Congo red as a function of
current responses compared to glucose, revealing that the non- contact time for NiS and -NiS hollow spheres. It also reveals that
2
enzymatic -NiS/GC electrode sensor showed high selectivity for -NiS hollow spheres show better adsorption ability than NiS2
glucose detection. -NiS/GC electrode sensor shows a much better hollow spheres. IR characterizations of Congo red and the hollow
selectivity than that of NiS /GC electrode sensor, which might be spheres before and after adsorption were carried out to confirm
2
explained that the use of -NiS hollow spheres on the surface of the adsorption of Congo red on the hollow spheres. From the IR
electrodes can modify the mass transport regime, and this spectra shown in Fig. S8, it can be seen that the IR spectrum of NiS2
alteration can in favorable circumstances facilitate the and -NiS hollow spheres show the characteristic peaks of Congo
amperometric discrimination between species. In addition, there red after the measurement, demonstrating the adsorption of the
are more Ni atoms exposed on the surface of -NiS hollow spheres Congo red on the surface of NiS and -NiS hollow spheres. The
2
compared with NiS2 hollow spheres (Fig. S6 and S7), which NiS and -NiS hollow spheres have specific surface areas of 15.3
2
2
-1
2
-1
facilitates contacts with glucose in the case of -NiS hollow spheres. m g and 32.2 m g , respectively. Therefore, the difference in the
Thus, non-enzymatic -NiS/GC electrode sensor presented high removal ability of NiS and -NiS hollow spheres might result from
2
68
selectivity for glucose detection compared with NiS /GC electrode their different specific surface areas. Although the removal ability
2
4
0, 56, 66, 67
sensor.
of NiS2 and -NiS hollow spheres is not better than NiO and
68, 69
FeOOH,
these results show that the -NiS hollow spheres can
significantly remove Congo red, which might have application
potential in wastewater treatment.
4
. Conclusions
In summary, NiS hollow spheres were synthesized by a facile one-
2
step hydrothermal route. Meanwhile, -NiS hollow spheres could
be simply prepared by the calcination of NiS hollow spheres under
2
4
00 °C in air. NiS and -NiS hollow spheres were subsequently
2
evaluated for their comparative electrochemical performances. It is
found that the -NiS hollow spheres electrode shows a better
supercapacitor behavior than the NiS2 hollow sphere electrode.
Moreover, non-enzymatic glucose sensors based on the NiS and -
2
NiS hollow spheres have been successfully developed for the
detection of glucose. The amperometric response indicates that the
as-prepared -NiS/GCE electrode sensor has a high sensitivity, low
detection limit, and excellent selectivity compared with the
NiS /GCE electrode sensor. The results show that -NiS hollow
2
spheres are a promising material for applications in supercapacitors
and electroanalysis. In addition, the as-prepared -NiS hollow
spheres display a good adsorption ability to remove the organic
pollutant Congo red from water, which makes them have
application potentials in water treatment. This work sheds new light
on the material design philosophy for transition metal sulfides,
especially for potential applications in supercapacitor,
electrocatalysts and waste water treatment.
-1
Fig. 7 (a) Absorption spectra of an aqueous solution of 100 mg L
Congo red in the presence of 60 mg of hollow NiS spheres; (b)
2
-1
absorption spectra of an aqueous solution of 100 mg L Congo red Acknowledgements
in the presence of 60 mg of hollow -NiS spheres; (c) curves of the
adsorption extent of Congo red as a function of contact time for Talents of the University in China (grant no. NCET-13-0645) and
This work is supported by the Program for New Century Excellent
NiS and -NiS hollow spheres.
National Natural Science Foundation of China (NSFC-21201010,
U1404203), Program for Innovative Research Team (in Science and
2
6
| J. Name., 2012, 00, 1-3
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ARTICLE
Technology) in University of Henan Province (14IRTSTHN004), the 29 Y. Wang, F. Y. Liu, Y. Ji, M. Yang, W. Liu, W. Wang, Q. S. SVuienw, ZA.rtQic.leZOhnalninge,
Science Technology Foundation of Henan Province
122102210253, 13A150019,142102210587,14B150001), the China
&
DOI: 10.1039/C5DT02724A
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Table of Contents
NiS and
-NiS hollow spheres are successfully prepared
2
via a template-free method. When evaluated NiS and -
2
NiS hollow spheres for supercapacitors, glucose sensors
and waste water treatment. It is found that the hollow α-
NiS spheres exhibit better performance than that of the
NiS hollow sphere.
2
8
| J. Name., 2012, 00, 1-3
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