MnCo2O4+: X nanowire arrays grown on carbon sponge: Improved electrochemical and catalytic performances

Article abstract of DOI:10.1039/c8ce01793j

MnCo₂O_4+x nanowire arrays have been successfully grown on carbon sponge (CS) via a simple hydrothermal route with sequential thermal treatment, employing CoSO₄·7H₂O, MnSO₄·H₂O and urea as t

Full text of DOI:10.1039/c8ce01793j

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MnCo2O4+x nanowire arrays grown on carbon
sponge: improved electrochemical and catalytic
performances
Cite this: CrystEngComm, 2019, 21,
403
Received 19th October 2018,
Accepted 12th December 2018
*
Shifeng Li, Jie Wang, Meifang Wang and Yonghong Ni
DOI: 10.1039/c8ce01793j
rsc.li/crystengcomm
MnCo2O4+x nanowire arrays have been successfully grown on
carbon sponge (CS) via simple hydrothermal route with
morphologies; and simultaneously, the electrochemical prop-
erties of the as-obtained products were investigated.8–10 Re-
cently, another typical spinel material, MnCo2O4, has been
paid increasing attention because of its ultrahigh theoretical
specific capacity and excellent rate capability for super-
capacitors as the electrode. In practical application, however,
MnCo2O4-based electrode materials only displayed relatively
low specific capacitance and cycle stability.11,12 Hence, to
boost the electrochemical performance of the MnCo2O4
electrode materials, a variety of MnCo2O4-based composites
were designed.13–16
Although binary transition metal oxides have many advan-
tages as electrode materials, some of their shortcomings, such
as low conductivity and easy structure collapse during charge–
discharge processes, need to be further improved. It is well
known that carbon is an often-used electrode material for elec-
tric double layer capacitors (EDLCs) due to its good conductiv-
ity. Simultaneously, it can also serve as the support skeleton of
metal oxide electrode materials to prevent structure collapse
during charge–discharge processes. To date, various carbon
materials, including carbon nanotubes (CNTs),17,18 carbon
nanosheets,19 activated carbon,20 carbon nanofibers,20–22 and
graphene,23,24 have been widely used in battery-like electro-
chemical capacitors for improving the electrochemical perfor-
mances of metal oxide electrode materials.
a
sequential thermal treatment, employing CoSO4·7H2O, MnSO4·H2O
and urea as the initial reactants. The as-prepared product, labeled
MnCo2O4+x/CS, was characterized by X-ray powder diffraction
(XRD), field emission scanning electron microscopy (FESEM), (high
resolution) transmission electron microscopy (TEM/HRTEM), nitro-
gen adsorption–desorption isotherms, Raman spectrometry and
X-ray photoelectron spectroscopy (XPS). The experiments showed
that the presence of CS could affect the phase and morphology of
the final manganese cobaltite. Without the presence of CS, a
MnCo2O4.5 phase with spherical microstructures was produced;
and with the presence of CS, a mixed phase of MnCo2O4.5 and
MnCo2O4 with wire-like nanostructures was obtained. It was found
that the final MnCo2O4+x/CS markedly improved the electro-
chemical and catalytic properties against MnCo2O4.5. At a current
density of 1.0 A g−1, the as-prepared product exhibited a specific
capacitance of 405 F g−1, which was far higher than 158.8 F g−1 of
pure MnCo2O4.5. Under the same experimental conditions, simul-
taneously, the MnCo2O4+x/CS catalyst only took ∼6 min for cata-
lyzing 92% of 4-nitrophenol (4-NP) to 4-nitroaniline (4-AP), which
was shorter than ∼10 min of the pure MnCo2O4.5 catalyst.
1. Introduction
Binary transition metal oxides, especially with spinel struc-
tures, have attracted extensive research interest owing to their
outstanding electrochemical properties and potential applica-
tions as electrode materials in Li-ion batteries and super-
capacitors, and as catalysts for HER and OER in the recent
decade.1–7 For example, NiCo2O4 has been a representative in
various spinel materials. Many methods were developed for
the synthesis of NiCo2O4 micro/nanostructures with various
Generally, the chemical environments of reaction systems
can affect the nucleation and growth of inorganic nanostruc-
tures. For example, our research uncovered that the introduc-
tion of water molecules could induce the phase conversion of
nickel phosphides under the same experimental conditions.25
Then, what phenomenon can occur when a carbon material
is introduced into a system to prepare metal oxide?
In this work, we designed a simple one-step hydrothermal
route with sequential thermal treatment to prepare manga-
nese cobaltite in the absence/presence of carbon sponge (CS),
employing CoSO4·7H2O, MnSO4·H2O and urea as the initial
reactants. Experiments showed that MnCo2O4.5 microspheres
were prepared from the system without carbon sponge and
College of Chemistry and Materials Science, Key Laboratory of Functional
Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Ma-
terials, Anhui Key Laboratory of Functional Molecular Solids, Anhui Normal Uni-
versity, 189 Jiuhua Southern Road, Wuhu, 241002, PR China.
E-mail: niyh@mail.ahnu.edu.cn; Fax: +86 553 3869303
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that a mixture of MnCo2O4 and MnCo2O4.5 was obtained from
the system with carbon sponge, which was labeled
MnCo2O4+x. The final product presented a wire-like nano-
structure and homogeneously grew on carbon sponge (la-
beled MnCo2O4+x/CS). The above facts indicated that the pres-
ence of carbon sponge not only induced the phase
conversion of MnCo2O4.5, but also varied the morphology of
the product. Further investigations uncovered that the as-
obtained MnCo2O4+x/CS exhibited better electrochemical per-
Performance tests
Electrochemical experiments were performed using a CHI
660E electrochemical analyzer (CHI 660E, CH Instruments,
Shanghai) in 3.0 M KOH with a three-electrode system. The
working electrode was prepared by pressing the active mate-
rial, acetylene black and a polyvinylidene fluoride (PVDF)
binder with a weight ratio of 80 : 10 : 10 on Ni foam (1 cm × 1
cm) with the assistance of N-methyl-2-pyrrolidone (NMP) and
absolute ethanol, and dried at 60 °C for 10 h under vacuum
conditions. A platinum wire and an Hg/HgO electrode were
used as the counter and reference electrodes, respectively.
The mass of the active matter on the nickel foam was calcu-
lated by weighing the nickel foam before and after pressing.
Cyclic voltammetry (CV) tests were performed in a potential
range between 0 and 0.6 V at various scan rates. Charge–dis-
charge processes were performed in a potential window from
0 to 0.5 V at different current densities. Electrochemical im-
pedance spectroscopy (EIS) measurement was conducted over
a frequency range of 0.01 Hz to 100 kHz at an open circuit
potential with an AC potential amplitude of 5 mV.
formances and catalytic activity than MnCo2O4.5
.
2. Experimental section
All the chemicals and reagents were analytically pure, pur-
chased from Sinopharm Chemical Reagent Company and
used without further purification. Deionized water was used
throughout.
Preparation of MnCo2O4+x
In a typical synthesis, 2 mmol of CoSO4·7H2O, 1 mmol of
MnSO4·H2O and 12 mmol of urea were dissolved in 20 mL de-
ionized water with vigorous magnetic stirring. Then, the as-
formed pink solution was poured into a 50 mL Teflon-lined
stainless steel autoclave without/with the presence of carbon
sponge (CS, which was obtained from combusting a commer-
cial sponge in air). The autoclave was sealed and heated at 95
°C for 8 h. The produced precipitate was washed with deion-
ized water and absolute ethanol in turn several times, and
dried at 60 °C for 10 h under vacuum conditions. Subse-
quently, the precipitate was calcined at 450 °C in air for 2 h
in a tube furnace.
The specific capacitance (C) of the electrode was calcu-
lated according to the equation below:26–28
It
mV
(1)
C 
where I (A), Δt (s), ΔV (V) and m (mg) are the discharge cur-
rent, the discharge time, the voltage window, and the mass
of the active material, respectively.
Catalytic activity for the reduction of 4-nitrophenol
To compare the catalytic activity of the products prepared
from the systems without/with the CS for the reduction of
4-nitrophenol (4-NP) in NaBH4 solution, the catalyst suspen-
sion was prepared via dispersing the catalyst powder in ap-
propriate amounts of deionized water with ultrasonic assis-
tance. In a typical experiment, an appropriate amount of
4-NP and the catalyst was firstly mixed; subsequently, a cer-
tain volume of NaBH4 solution was added into the system to
obtain 3 mL of the solution. Here, the concentrations of
4-NP, NaBH4 and the catalyst were 3.0 × 10−4 mol L−1, 3.0 ×
10−2 mol L−1 and 30 mg L−1, respectively. The reducing pro-
cesses of 4-NP were monitored with a Metash 6100 UV-vis
spectrophotometer.
Characterization
The X-ray powder diffraction patterns of the products were
obtained on a Bruker D8 Advance X-ray diffractometer
equipped with Cu Kα radiation (k = 0.154060 nm), employing
a scanning rate of 0.2° s−1 and a 2θ range from 10° to 80°.
The transmission electron microscopy (TEM) images were
obtained using a Hitachi HT7700 transmission electron
microscope, employing an accelerating voltage of 100 kV. The
high resolution transmission electron microscopy (HRTEM)
images were obtained using an FEI Tecnai G2 transmission
electron microscope, employing an accelerating voltage of
200 kV. The field emission scanning electron microscopy
(FESEM) and EDS mapping images were obtained using a
Hitachi S-4800/Regular-8100 field emission scanning electron
microscope, employing an accelerating voltage of 5 kV or 15
kV. The nitrogen adsorption–desorption isotherms were mea-
sured at the liquid nitrogen temperature (77 K), using a
Micromeritics ASAP 2460 analyzer. The surface areas were
calculated by the Brunauer–Emmett–Teller (BET) method.
The Raman spectra were recorded using a Raman spectrome-
ter (RENISHAW inVia system, UK) using a 514.4 nm He/Ne
laser.
3. Results and discussion
Structure and morphology characterization
Fig. 1a shows the X-ray diffraction patterns of the carbon
sponge and the products prepared from the systems without/
with the carbon sponge. At a 2θ degree range from 20–30°,
the CS presents a wide peak, implying its amorphous struc-
ture. The diffraction pattern of the product prepared from
the system without the CS matches well with the standard
pattern of the cubic MnCo2O4.5 phase in comparison with the
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Fig. 1 (a) XRD patterns and (b) Raman spectra of the carbon sponge and the products prepared from the systems without/with the carbon
sponge.
PDF card files no. 32-0297. The product prepared from the
system with the CS exhibits a similar diffraction pattern with
the cubic MnCo2O4.5 phase. However, the peak sites shift to-
wards a low 2θ degree range. According to the PDF card files,
the cubic MnCo2O4 and MnCo2O4.5 phases display similar dif-
fraction patterns (see the bottom part in Fig. 1a, PDF no. 23-
1237 and 32-0297), and the corresponding peak sites of
MnCo2O4 are located at the lower 2θ degree range. From
Fig. 1a, one can readily see that the diffraction peaks of the
product prepared from the system with the CS are located at
the middle of the cubic MnCo2O4 and MnCo2O4.5 phases (see
the dashed line), implying the formation of a mixed phase of
MnCo2O4 and MnCo2O4.5. The above phase conversion from
MnCo2O4.5 to MnCo2O4 can be explained as follows: at raised
temperature, the cubic MnCo2O4.5 phase was formed, but si-
multaneously, the carbon atoms at the surface of the CS were
activated, which could react with oxygen in MnCo2O4.5. Thus,
partial MnCo2O4.5 was converted into MnCo2O4, which caused
the formation of the mixed phase.
The morphologies of the products prepared from the sys-
tems without/with the carbon sponge are shown in Fig. 2. As
shown in Fig. 2a, the carbon sponge presents a skeleton-like
structure with several branches and its surfaces are smooth
(see the inset in Fig. 2a). MnCo2O4.5 is mainly composed of
microspheres with polydisperse sizes (see Fig. 2b). Fig. 2c ex-
hibits a typical FESEM image of MnCo2O4+x/CS. Uniform
nanowire arrays grow on the surfaces of the CS. In the light
of an enlarged FESEM image shown in the inset of Fig. 2c,
the mean length of the nanowires is ∼400 nm. The
MnCo2O4+x nanowire array grown on the surface of the CS
was also proven by TEM observations. Fig. 3a depicts the rep-
resentative TEM image of the MnCo2O4+x nanowire array.
One can readily find that the nanowires are porous and
constructed from plenty of nanoparticles, which should be at-
tributed to the pyrolysis of the precursor at raised tempera-
ture. The SAED pattern shown in the inset of Fig. 3a proves
the polycrystalline nature of the nanowires. The HRTEM im-
age of the nanowires is shown in Fig. 3b. The distances of
several neighboring planes are measured separately to be
0.285 nm, 0.244 nm, 0.249 nm and 0.250 nm. In comparison
with PDF card files no. 32-0297 and 23-1237, four d-spacings
in turn correspond to the (220) and (311) planes of cubic
MnCo2O4.5, and the (311) plane of cubic MnCo2O4. The above
results confirm the co-presence of the cubic MnCo2O4.5 and
cubic MnCo2O4 phases in the nanowires, which is in good
Fig. 1b displays the Raman spectra of the carbon sponge and
the products prepared from the systems without/with the carbon
sponge. Obviously, the product prepared from the system with
the CS simultaneously presents the peaks of the CS and manga-
nese cobaltite. Nonetheless, some differences can be distinguished
in the region of 100–800 cm−1, which should be attributed to the
phase change of manganese cobaltite caused by the CS.
Fig. 2 FESEM images of the carbon sponge (a), MnCo2O4.5 (b) and MnCo2O4+x/CS (c).
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Fig. 3 (a) TEM and (b) HRTEM images of MnCo2O4+x/CS. The inset in (a) is the SAED pattern of the nanowires.
agreement with the XRD analyses shown in Fig. 1a. Obvi-
ously, it is probable that the different phases and morphol-
ogies will affect the performances of the products. Further-
more, the distributions of various elements in the CS were
also investigated by the EDS mapping technology. As shown
in Fig. 4, the distributions of Co, Mn and O elements are
homogeneous.
electrodes in 3.0 M KOH solution with the three-electrode
system at a scan rate of 100 mV s−1. Obviously, the CV curve
of the MnCo2O4+x/CS/NF electrode encloses the larger area
than that of the MnCo2O4.5/NF one, implying that the
MnCo2O4+x/CS electrode exhibits the higher capacity. A simi-
lar conclusion was also obtained from the galvanostatic
charge–discharge (GCD) curves of the two electrodes. As
shown in Fig. 5b, at a current density of 1 A g−1, the
MnCo2O4+x/CS electrode has a longer discharge time, indicat-
ing its higher specific capacitance. According to eqn (1), the
specific capacitances of the MnCo2O4.5 and MnCo2O4+x/CS
electrodes are calculated to be 158.8 and 405 F g−1, respec-
tively. The latter is more than 3 times larger than the former.
Fig. 5c exhibits the specific capacitance changes of
MnCo2O4.5 and MnCo2O4+x/CS with the increase of the cur-
rent density from 1 to 10 A g−1. It can be seen that the spe-
cific capacitances of MnCo2O4.5 are 158.8, 140.8, 112, 88.8, 72
Electrochemical performance
As a binary transition metal oxide with spinel structures,
manganese cobaltites have been investigated as the
electrodes for supercapacitors. In this work, therefore, we
compare the electrochemical performances of the products
prepared from the systems without/with the CS as the
electrodes for supercapacitors. Fig. 5a depicts the CV curves
of the as-obtained MnCo2O4.5/NF and MnCo2O4+x/CS/NF
Fig. 4 EDS mapping images of MnCo2O4+x/CS.
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Fig. 5 (a) CV curves of MnCo2O4.5 and MnCo2O4+x/CS at a scan rate of 100 mV s−1; (b) galvanostatic charge–discharge (GCD) curves of
MnCo2O4.5 and MnCo2O4+x/CS at a current density of 1 A g−1; (c) specific capacitances of MnCo2O4.5 and MnCo2O4+x/CS at various current
densities; (d) long-term stability curves of MnCo2O4.5 and MnCo2O4+x/CS at a current density of 4 A g−1. The inset in (d) is the electrochemical im-
pedance spectroscopy (EIS) analyses of the MnCo2O4.5 and MnCo2O4+x/CS electrodes at an open circuit potential from 0.01 Hz to 100 kHz.
and 58 F g−1, respectively. However, those of MnCo2O4+x/CS
are 405, 352, 288, 253.2, 228.8 and 208 F g−1, respectively.
Distinctly, MnCo2O4+x/CS has the larger specific capacitance
under the same current density. Furthermore, the specific ca-
pacitances of the two products gradually reduce with the in-
crease of current density. Nonetheless, ∼36.5% (for
MnCo2O4.5) and 51.4% (for MnCo2O4+x/CS) of the original ca-
pacitances are still obtained at a current density of 10 A g−1,
indicating that MnCo2O4+x/CS has better charge–discharge
properties even at high current density. Furthermore, the
long-term cycle stability of the two products as electrode ma-
terials is also compared at a current density of 4 A g−1 for
3000 cycles. As shown in Fig. 5d, after 3000 cycles, the loss in
the specific capacitance is only 28.9% (for MnCo2O4.5) and
9% (for MnCo2O4+x/CS). Obviously, the electrode made from
the MnCo2O4+x/CS nanowire array displays better cycling sta-
bility. Generally, the specific capacitance of the super-
capacitors is related to the transmission and diffusion rates
of electrons and ions. In the present work, the MnCo2O4+x/CS
nanowire arrays present porous microstructures (see Fig. 3),
which contribute to the transmission and diffusion of
electrons and ions. This conclusion is proven by the electro-
chemical impedance spectroscopy (EIS) analyses of the two
products. As shown in the inset of Fig. 5d, each Nyquist plot
comprises a semicircle in the high frequency region and a
straight line in the low frequency one. The semicircle repre-
sents the charge-transfer resistance and the straight line
stands for the diffuse resistance. The smaller the diameter of
the semicircle is and/or the bigger the slope of the straight
line is, the smaller the EIS value is.29–31 In the EIS plots,
MnCo2O4+x/CS exhibits a smaller diameter of the semicircle
and bigger slope of the straight line than MnCo2O4.5, indicat-
ing that MnCo2O4+x/CS has better conductivity than
MnCo2O4.5. Moreover, Fig. 6 shows the N2 adsorption–desorp-
tion curves of MnCo2O4.5 and MnCo2O4+x/CS. Their specific
surface areas and pore volume are 47.6 m2 g−1 and 0.17
cm3 g−1 for the MnCo2O4.5 microspheres, respectively, and
89.1 m2 g−1 and 0.23 cm3 g−1 for the MnCo2O4+x/CS nanowire
arrays. Markedly, the MnCo2O4+x/CS nanowire arrays possess
the bigger pore size and volume than the MnCo2O4.5 micro-
spheres, which should also be
a possible reason that
MnCo2O4+x/CS exhibits better electrochemical performances.
Catalytic activity
Further investigations showed that the as-prepared MnCo2O4.5
and MnCo2O4+x/CS also exhibited obviously different catalytic
activities for the reduction of 4-nitrophenol (4-NP) in a NaBH4
solution. Generally, the 4-NP aqueous solution presents a
strong absorption peak at 317 nm. After NaBH4 is added into
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Fig. 6 N2 adsorption–desorption curves of MnCo2O4.5 (a) and MnCo2O4+x/CS (b). The insets are the pore diameter distribution plots.
the solution, the absorption peak at 317 nm disappears and a
new absorption peak at ∼400 nm appears, implying the forma-
tion of an intermediate.32,33 When no catalyst is introduced
into the above system, the intermediate can stably exist for sev-
eral days. After adding the catalyst, the peak at 400 nm will
gradually decrease, which indicates that the reduction of 4-NP
to 4-amiophenol (4-AP) takes place.34,35 At present, the catalytic
reduction of 4-NP to 4-AP is used as a model to determine the
catalytic activity of the catalyst. Fig. 7a and b display the UV-
vis absorption spectra of the 4-NP-NaBH4 system in the pres-
ence of 30 mg L−1 MnCo2O4+x/CS and MnCo2O4.5 catalysts for
various durations, respectively. With the prolonging of the re-
action time, the peak at 400 nm gradually decreases. However,
different change trends can be seen. When MnCo2O4+x/CS was
used as the catalyst, the peak intensity markedly reduced with
the reaction time after 6 min, and the reduction of 4-NP
Fig. 7 UV-vis absorption spectra of the 4-NP-NaBH4 system in the presence of 30 mg L−1 different catalysts for various durations: (a) MnCo2O4+x
/
CS and (b) MnCo2O4.5. (c) The correlations between the relative concentration (Ct/C0) of 4-NP and the catalytic duration in the presence of 30 mg
L−1 different catalysts and (d) the corresponding linear relationships between lnIJCt/C0) and the reaction time.
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Fig. 8 SEM images of MnCo2O4+x/CS after 3000 cycles for the electrochemical (a) and catalytic tests (b).
almost finished; while MnCo2O4.5 as the catalyst, the peak
intensity slowly decrease at the initial stage. Subsequently, the
peak intensity rapidly reduced. Nonetheless, the peak at 400
nm still displayed the higher intensity after 6 min. Till 12 min,
the reduction of 4-NP almost finished. The above experimental
phenomena showed that an obvious inducing effect existed
when the MnCo2O4.5 microspheres were employed as the cata-
lyst, and no inducing effect occurred in the system containing
the MnCo2O4+x/CS catalyst. Obviously, the morphology of the
catalyst should be the main factor to cause the inducing effect.
The nanowire array possessed a bigger contact area for the re-
actants than the microspheres, which has been confirmed by
the BET results shown in Fig. 6. Of course, the good conductiv-
ity of the MnCo2O4+x/CS catalyst was also favorable for the re-
duction of 4-NP. Fig. 7c clearly depicts the concentration
changes of 4-NP with the reaction time under the presence of
different catalysts. Under the same experimental conditions,
the MnCo2O4+x/CS catalyst only took ∼6 min for catalyzing
92% of 4-NP to 4-AP, which was shorter than ∼10 min of the
pure MnCo2O4.5 catalyst. Obviously, the MnCo2O4+x/CS catalyst
has superior catalytic activity than MnCo2O4.5. In addition,
Akhtar and coworkers also studied the catalytic activity of pure
MnCo2O4 in 2016, and found that it took 8 min for catalyti-
cally reducing 1.0 × 10−4 mol L−1 of 4-NP in the presence of 1.0
mg mL−1 (1000 mg L−1) MnCo2O4.36 Obviously, the present
MnCo2O4+x/CS catalyst also exhibits the stronger catalytic activ-
ity than pure MnCo2O4.
MnCo2O4.5 does not match well with the pseudo-first-order
equation due to the inducing effect. The corresponding k
value is 0.297 min−1.
Moreover, we also investigated the SEM images of
MnCo2O4+x/CS after the electrochemical and catalytic tests. As
shown in Fig. 8a, after 3000 cycles, MnCo2O4+x/CS could still
maintain the microstructures well except from the slight ret-
rogradation of the nanowires; and after the catalytic test, the
morphology of MnCo2O4+x/CS hardly varies, implying that it
can still be used for the catalytic reduction of 4-NP.
4. Conclusions
In summary, a mixture of MnCo2O4.5 and MnCo2O4 with wire-
like microstructures was successfully grown on carbon
sponge through a facile hydrothermal method followed by
subsequent pyrolysis in air. The introduction of carbon
sponge not only promoted the partial conversion of the cubic
MnCo2O4.5 phase to cubic MnCo2O4 phase, but also markedly
varied the morphology of the final manganese cobaltite, and
further improved the electrochemical and catalytic perfor-
mances. As the electrode materials for supercapacitors,
MnCo2O4+x/CS exhibited the higher specific capacitance, the
better cycle stability and the better conductivity than
MnCo2O4.5. At a current density of 1 A g −1, the specific capac-
itance reached 405 F g−1, which was more than 3 times larger
than that of MnCo2O4.5. Also, MnCo2O4+x/CS exhibited supe-
rior catalytic activity for the reduction of 4-NP to 4-AP in a
NaBH4 solution without the inducing effect. The present
work is of importance in theory for understanding the influ-
ence of the substrate on the nucleation and growth of inor-
ganic nanostructures.
Generally, the reduction of 4-NP to 4-AP in NaBH4 solution
can be described as a pseudo-first-order kinetic process. The
corresponding kinetics equation can be written as
follows:37,38
ln(Ct/C0) = kt
(2)
Conflicts of interest
where C0 and Ct separately represent the initial and instanta-
neous concentrations of 4-NP, k and t are the rate constant
and the reaction time, respectively. Fig. 7d shows the relation
of lnIJCt/C0) and the reaction time in the presence of the dif-
ferent catalysts. Owing to the absence of the inducing effect,
the reduction reaction catalyzed by MnCo2O4+x/CS is well con-
sistent with the pseudo-first-order equation. The rate con-
stant is 0.424 min−1. The reduction reaction catalyzed by
There are no conflicts to declare.
Acknowledgements
The authors thank the National Natural Science Foundation
of China (21571005), High School Leading talent incubation
programme of Anhui province (gxbjZD2016010), and The
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Recruitment Program for Leading Talent Team of Anhui Prov-
ince for the fund support.
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