Cu/CuxS-Embedded N,S-Doped Porous Carbon Derived in Situ from a MOF Designed for Efficient Catalysis

Article abstract of DOI:10.1002/chem.202101560

The reasonable design of the precursor of a carbon-based nanocatalyst is an important pathway to improve catalytic performance. In this study, a simple solvothermal method was used to synthesize [Cu(TPT)(2,5-tdc)] ? 2H₂O (Cu-MOF), which contains N and S atoms, in one step. Further in-situ carbonization of the Cu-MOF as the precursor was used to synthesize Cu/Cu_xS-embedded N,S-doped porous carbon (Cu/Cu_xS/NSC) composites. The catalytic activities of the prepared Cu/Cu_xS/NSC were investigated through catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The results show that the designed Cu/Cu_xS/NSC has exceptional catalytic activity and recycling stability, with a reaction rate constant of 0.0256 s^?1, and the conversion rate still exceeds 90 % after 15 cycles. Meanwhile, the efficient catalytic reduction of dyes (CR, MO, MB and RhB) confirmed its versatility. Finally, the active sites of the Cu/Cu_xS/NSC catalysts were analyzed, and a possible multicomponent synergistic catalytic mechanism was proposed.

Full text of DOI:10.1002/chem.202101560

Accepted Article
Accepted Article
Title: Cu/CuxS Embedded N,S-doped Porous Carbon In Situ Derived
from a Novelly Designed MOF for Efficient Catalysis
Authors: Dongsheng Wang, Minyue Fan, Tingyu He, Fanming Zeng,
Xiaoli Hu, Chun Li, and Zhong-Min Su
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1/2020

Chemistry - A European Journal
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Cu/Cu
x
S Embedded N,S-doped Porous Carbon In Situ Derived
from a Novelly Designed MOF for Efficient Catalysis
Dongsheng Wang,[a,b] Mingyue Fan,[a,b] Tingyu He, Fanming Zeng,*
[a]
[a.b]
Xiaoli Hu,*[a,b] Chun Li and
[a]
Zhongmin Su*[a,b,c]
[
a]
D. Wang, M. Fan, T. He, Prof. F. Zeng, Dr. X. Hu, Dr. C. Li, Prof. Z. Su
School of Materials Science and Engineering
Changchun University of Science and Technology
Changchun, 130022, People’s Republic of China
E-mail: zengfm@cust.edu.cn; huxiaoli1113@cust.edu.cn; zmsu@nenu.edu.cn
D. Wang, M. Fan, Prof. F. Zeng, Dr. X. Hu, Prof. Z. Su
Jilin Provincial Science and Technology Innovation Center of Optical Materials and Chemistry
Changchun University of Science and Technology
Changchun, 130022, People’s Republic of China
[
[
b]
c]
Prof. Z. Su
Joint Sino-Russian Laboratory of Optical Materials and Chemistry
Changchun University of Science and Technology
Changchun, 130022, People’s Republic of China
Supporting information for this article is given via a link at the end of the document
Abstract: The reasonable design of the precursor of the carbon-
based nanocatalyst is an important pathway to improve its catalytic
performance. In this study, a simple solvothermal method was used
two different heteroatoms into the carbon-based material (such as
N,B-doped, N,P-doped and N,S-doped) can produce a synergistic
effect between the heteroatoms and further optimize the catalytic
performance of the material.[6] Therefore, it is of great significance
to design and synthesize precursors containing different
heteroatoms to prepare porous carbon-based non-noble metal
catalysts doped with different heteroatoms.[7]
to synthesize [Cu(TPT)(2,5-tdc)]·2H
atoms in one step. Further in-situ carbonization of the Cu-MOF as the
precursor was used to synthesize Cu/Cu S embedded N,S-doped
porous carbon (Cu/Cu S/NSC) composites. The catalytic activities of
the prepared Cu/Cu S/NSC were investigated through catalytic
reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The
results show that the designed Cu/Cu S/NSC has exceptional
catalytic activity and recycle stability, showing the reaction rate
2
O (Cu-MOF) containing N and S
x
x
x
Recently, porous carbon-based materials derived from various
metal-organic frameworks (MOFs) have attracted widespread
attention due to their high specific surface area, uniformly
dispersed active units, easy design and control of composition
and morphology.[8] MOFs have been shown to be a perfect
sacrificial template for the manufacture of various nanomaterials,
including metals, metal carbides, metal oxides, metal sulfides and
metal phosphides.[9] Among them, copper and its compounds
doped carbon-based nanomaterials synthesized by pyrolyzing
various copper-containing MOFs precursors are considered as
potential catalysts.[ Niu et al. used HKUST-1 and phenolic resin
as copper and carbon precursors to synthesize a hybrid catalyst
x
-
1
constant is 0.0256 s , and the conversion rate still exceeds 90 % after
5 cycles. Meanwhile, the efficient catalytic reduction of dyes (CR,
MO, MB and RhB) confirmed its versatility. Finally, the active sites of
the Cu/Cu S/NSC catalysts were analyzed and a possible multi-
1
x
component synergistic catalytic mechanism was proposed.
10]
Introduction
with Cu/Cu
2
O nanoparticles supported on porous carbon which
has excellent catalytic activity for reducing 4-NP.[ Sun et al.
11]
Porous carbon-based materials have broad application prospects
in the fields of gas storage, photoelectric catalysis, and
biomedicine due to their excellent physical and chemical
properties, structural controllability, and diversity of synthesis
methods.[ Noble metal catalysts have been researched for high
catalytic activity, but limited to the high cost.[2] Carbon-based
catalysts were considered to be the most possibilities alternative
to precious metal catalysts owing to potential catalytic activity and
x
successfully synthesized a N-doped Cu/Cu O/C foam catalyst
using N-coordinated HKUST-1/cellulose as raw material and
applied it to the efficient reduction of 4-NP.[12] However, few
reports have been reported on the application of Cu
x
S hybrid
1]
materials in NaBH -assisted reduction of 4-NP. Carbon-based
4
materials prepared by in-situ pyrolysis of MOFs in an inert
atmosphere, heteroatoms in the parent MOFs will be doped into
the carbon matrix during the pyrolysis process. Therefore, we
expected to synthesize a Cu-MOF with nitrogen-containing and
sulfur-containing ligands, which can be used as a precursor for
preparing efficient carbon-based nanocatalysts.
[
3]
low synthesis cost. How to develop carbon-based non-precious
metal nanomaterials into highly active catalysts is an aroused
general interest issue. In recent years, heteroatom (such as N, O,
S, P and B) doping of carbon-based materials is considered to be
an effective way to further improve the catalytic performance of
carbon-based materials.[4] Heteroatoms have different
electronegativity and atomic sizes, which can change the spin
density and charge distribution of carbon atoms. In addition,
2
In the present work, [Cu(TPT)(2,5-tdc)]·2H O (TPT = 2,4,6-
tris(4-pyridyl)-1,3,5-triazine, 2,5-tdc = 2,5-thiophenedicarboxylic
acid) was successfully synthesized through a simple one-step
solvothermal reaction. The prepared Cu-MOF was pyrolyzed
under N
2
atmosphere to obtain the Cu/Cu
x
S embedded N,S-
[
5]
defects caused by doping can also generate active sites. Doping
doped porous catalyst, denoted Cu/Cu
x
S/NSC. We employ the
1
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catalytic reduction of 4-NP to 4-AP, which is an important reaction
MOF. When the temperature rises from 366 to 401 °C, there is
approximately 47% weight loss rate due to the collapse of the
structure and the thermal decomposition of the crystal (Figure S2).
in pollution treatment and industrial synthesis, to evaluate the
catalytic activity of Cu/Cu
assistance of NaBH , the designed Cu/Cu
x
S/NSC (Scheme 1).[
13]
With the
4
x
S/NSC catalyst has
exceptional catalytivity and recyclability for reduction of 4-NP to
-AP in water, which is exceeded the great majority Cu-based
4
catalysts and even precious metal catalysts. This catalytic
reduction system can also be applied for degradation of dyes with
high efficiency. Finally, the synergy of the components in
Cu/Cu S/NSC carbon-based nanocatalyst was analyzed, and a
x
reasonable mechanism for the catalytic reduction of 4-NP was
proposed.
Figure 1. (a) The asymmetric unit of Cu-MOF; (b) Stacked graph of Cu-MOF;
(c) Binuclear units of Cu(II); (d) Experimental and simulated XRD patterns.
Characteristics of catalyst: The microstructure of Cu/Cu
was characterized by SEM and TEM. After calcination in N
atmosphere, copper ions form Cu and Cu S particles, and the
x
S/NSC
2
x
coordinating organic ligands are transformed to N and S doped
Scheme 1. Synthetic route of high-efficiency catalyst Cu/Cu
precursor Cu-MOF.
x
S/NSC and its
carbon framework due to the presence of heteroatoms in the Cu-
MOF precursor. SEM images show that Cu/Cu S/NSC has a
x
certain regular morphology, which is a strip octahedron with a
regular quadrilateral cross-section (Figure 2a). Micron-level
cracks (Figure 2c) and nano-level holes (Figure 2d) can be clearly
seen on the surface of the material, these cracks and holes can
adsorb reactants and provide a favorable place for the catalytic
reduction reaction. TEM shows the internal state of the material
Results and Discussion
Characteristics of precursor: The crystallographic structure of
Cu-MOF was analyzed by X-ray single crystal diffraction, and the
parameters are shown in Table S1. The precursor crystallizes in
the monoclinic C2/c space group and its molecular formula is
more intuitively. The Cu and Cu S nanoparticles are evenly
x
embedded in the carbon skeleton, with the diameter
expressed as [Cu(TPT)(2,5-tdc)]·2H
2
O. The asymmetric unit of
approximately 20-50 nm, and no obvious agglomeration (Figure
Cu-MOF is shown in Figure 1a, which includes a Cu(II) ion, a TPT
ligand and a 2,5-tdc ligand. Cu (II) as a 5-connect node
coordinates with the N atoms (N1, N2) from two TPT ligands and
the O atoms (O1, O2, O4) from three 2,5-tdc ligands (Cu-O1
2b). Moreover, high-resolution TEM (HRTEM) was applied to
observe the lattice of Cu/Cu S/NSC. We can distinctly observe
x
2
the lattice fringes of Cu particles (Figure 2f), Cu S particles
(Figure 2g), Cu1.96S particles (Figure 2h), and graphite carbon in
1
2
.935 Å, Cu-O2 2.354 Å, Cu-O4 1,941 Å, Cu-N1 2.042 Å, Cu-N2
.028 Å). Figure 1b is the stacking diagram of Cu-MOF, which we
Cu/Cu S/NSC. The measured lattice plane spacing were 0.21,
0.24, 0.27 and 0.34 nm, and separately equivalent to the Cu
x
can see Cu(II) ions and TPT ligands are sequentially linked to
form a plane. TPT ligands between two adjacent planes have a
π-π stacking with the spacing of 3.7540 Å (Figure S1). Two
adjacent Cu(II) ions with a distance of 4.3369 Å form a binuclear
unit (Figure 1c), and then similar binuclear units are linked by 2,5-
tdc ligands to form a three-dimensional structure. The simulated
XRD pattern is consistent with the tested XRD pattern, indicating
that structure analysis of Cu-MOF is correct and with certain purity
lattice plane (111), Cu
2
S lattice plane (012), Cu1.96S lattice plane
(103) and graphite carbon lattice plane (002).[ Three types of
15]
nanoparticles can be observed in Cu/Cu S/NSC: Figures 2f to 2h
x
show that the three nanoparticles are partially covered by the
carbon layer. There are two other cases where the nanoparticles
are not covered by the carbon layer or covered completely
(Cu1.96S particles as an example) (Figure S3). The EDX mapping
of SEM show that Cu, S, C, N and O elements are evenly
(
Figure 1d). The FTIR spectrum of Cu-MOF is shown in the figure
S2, the absorption peaks observed at 1754.80, 1594.65 and
425.66 cm-1 are attributed to the vibration of C=O, C=N and C-
x
distributed in Cu/Cu S/NSC (Figure 2e). The S element has the
maximum density because it has two sources, respectively from
1
Cu S and NSC. The O element is attributed to the carboxylic acid
x
-1
N, respectively. The characteristic peak at 1333.30 cm belong to
the vibration of C=S in the thiophene dicarboxylic acid structure.
The absorption peak of C-OH appears at 1045.41 cm . TGA
analysis under a nitrogen atmosphere shows that there is about
group in the 2,5-tdc ligand and the O-containing substance in the
air adsorbed by the porous material. In addition, inductively
coupled plasma measurements were done to analyze the content
-1
of each element in Cu/Cu S/NSC. The mass percentages of C, H,
x
6
% weight loss before 194 °C, which shows that the heat
O, N, S and Cu and are respectively 63.59, 0.67, 5.44, 6.32, 8.32
and 15.66 % after normalization.
treatment removes the solvent in the surface and pores of Cu-
2
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x
Figure 3. XRD pattern (a) and Raman spectra (b) of Cu/Cu S/NSC.
For the purpose of studying the chemical state of the elements
in the surface Cu/Cu S/NSC composite material, the detailed
x
element valence states of Cu, S, N, C and O were observed by X-
ray photoelectron spectroscopy (XPS). Figure 4a presented the
elements detected in Cu/Cu
x
S/NSC. In the high-resolution
spectrum of Cu 2p (Figure 4b), the peaks at 932.1 and 952.3 eV
+
0
Figure 2. SEM (a, c, d) images of Cu/Cu
x
S/NSC; (b) TEM image and particle
1/2
belong to 2p3/2 and 2p core levels of Cu /Cu , the similar binding
size distribution of Cu/Cu
x
S/NSC; (e) Elemental mapping of Cu/Cu
x
S/NSC;
+
0
[14]
energies of Cu and Cu make it difficult to distinguish them.
Simultaneously, the peaks located at 933.8 and 954.1 eV can be
contributed to 2p3/2 and 2p1/2 core levels of Cu .
HRTEM (f, g, h) of the Cu/Cu
x
S/NSC.
2+
The crystal phase of the sample was studied by XRD analysis
Figure 3a). The XRD pattern of Cu/Cu S/NSC shows that the
diffraction peaks of Cu (JCPDS No. 04-0839), Cu1.96S (JCPDS No.
9-0578) and Cu S (JCPDS No. 26-1116) which were caused by
(
x
2
2
simultaneous partial sulfidation during the carbonization. The
distinguishing characteristic peaks of the XRD pattern appear at
2
(
θ = 43.30, 50.43 and 74.13° which can be attributed to the (111),
200) and (220) diffraction planes of metallic Cu. Peaks appearing
at 27.25° (102), 31.62° (110), 32.66° (103), 39.10° (104), 45.45°
114), 46.11° (201), 48.29° (202), 53.75° (212) and 66.71° (215)
are representative of the Cu1.96S. The characteristic peaks of
Cu S appear at 37.43° (102), 45.78° (110), 48.49° (103) and
3.67° (112). Moreover, different pyrolysis temperatures will
(
2
5
affect the composition of the hybrid material. While the pyrolysis
temperature is reduced to 600 °C, the hybrid material exhibits the
characteristic peak of Cu1.96S, Cu S and weak Cu. After the
2
pyrolysis temperature increases to 800 °C, the characteristic peak
of Cu disappeared completely, showing a strong characteristic
2
peak of Cu1.96S and Cu S. Therefore, the Cu particles have the
best crystallization at 700 °C pyrolysis (Figure S4). The Raman
spectrum was used to further analyze the degree of graphitization
of carbon in the Cu/Cu
The intensity ratio (I /I ) of the characteristic G-band (1582 cm )
and D-band (1338 cm ) was generally used to judge the disorder
and crystallinity of carbon in composite material. The I /I ratio of
Cu/Cu S/NSC composite material is 1.01, which proves that the
carbon is well graphitized. In addition, the wide 2D band at about
800 cm-1 is also a feature of the graphitic carbon lattice. The N
adsorption-desorption isotherm illustrates the porosity of
Cu/Cu S/NSC (Figure S5), which exhibits a typical type IV
x
S/NSC composite material (Figure 3b).
-1
G
D
1
-
G
D
x
x
Figure 4. XPS analysis of Cu/Cu S/NSC: full spectra (a); high-resolution
spectrum of Cu 2p (b), S 2p (c), N1s (d), C1s (e) and O 1s (f).
2
2
x
adsorption isotherm with an H3-type hysteresis loop. The BJH
mesoporous size distribution shows that the pore size of
The high-resolution spectrum of S 2p was shown in Figure 4c,
the peaks located at 161.7 and 162.9 eV assigned to 2p3/2 and
2p1/2 core levels of Cu-S. The peaks at 163.7 and 164.8 eV
appertain to the C-S-C covalent bond which indicating sulfur
atoms were doped into carbon lattice successfully.[16] Meanwhile,
the peak at 168.1 eV with high intensity is attributed to the partly
Cu/Cu
HK micropore size distribution proves the pore size distribution of
Cu/Cu S/NSC is between 0.55 and 2.28 nm. Compared with Cu-
MOF, Cu/Cu S/NSC produces more mesoporous structures
x
S/NSC is concentrated around 3.85 nm. Meanwhile, the
x
x
during pyrolysis and has a larger specific surface area (Table S2).
This porosity is of great significance for catalytic applications.
oxidized sulfur species (C-SO
x
-C) on the surface of the carbon
matrix.[17] The peaks located at 398.4, 399.4 and 400.9 eV
3
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correspond to pyridinic-N (N-6), pyrrolic-N (N-5), and graphitic-N
and lattice defects caused by doping.
(
N-Q) (Figure 4d), which show that nitrogen atoms were also
doped into the carbon lattice. In the C 1s high-resolution spectrum,
the peaks at 284.5, 285.3, 286.4, and 288.8 eV were ascribed to
the bonds C-C, C-S, C-N, and C-O, respectively (Figure 4e).[18]
As for the O 1s high-resolution spectrum in Figure 4f, the peaks
at 533.4 and 531.8 eV were related to the C=O and C-OH on the
surface of the carbon matrix. In contrast, the high-resolution O 1s
spectral peaks of Cu-MOF appear at 532.9 nm and 531.6 nm,
2 4
which were related to the presence of the Cu (OOC) group
Figure S6).[ Therefore, the designed Cu-MOF was heat treated
11]
(
in situ to successfully synthesize Cu/Cu
with N and S co-doping.
x
S/NSC hybrid material
Catalytic reduction performance: The catalytic activity of the
Cu/Cu S/NSC catalyst was investigated by studying the catalytic
x
conversion of 4-NP to 4-AP, and the progress of the 4-NP
reduction reaction was observed by ultraviolet-visible
spectroscopy. The 4-NP in the aqueous solution has a strong
absorption peak at 317 nm. While NaBH
nitrophenol ion will be generated, the characteristic peak shifts to
00 nm (Figure 5a), and the solution changes from light yellow to
4
was added, 4-
4
bright yellow. The absorption peak at 400 nm remains almost
unchanged with no catalyst added, which indicates that the
reduction reaction of 4-NP will not start without the catalyst.
x 4
Adding the prepared Cu/Cu S/NSC to the 4-NP/NaBH aqueous
solution, the absorption peak at 400 nm dropped rapidly, and a
new absorption peak was generated at 300 nm which was due to
the formation of the reduction product 4-AP (Figure 5b). The entire
catalytic reduction reaction was completed in 145 s, the
absorption peak at 400 nm disappeared completely (Figure 5c).
Figure 5. (a) Characteristic absorption peak of 4-NP (black) and after adding
NaBH (red). (b) Characteristic absorption peak after adding catalyst. UV-vis
spectrum after adding (c) Cu/Cu S/NSC and (d) NSC. (e) Relationship between
time and C/C and of different systems. (f) Relationship between ln(C/C ) versus
4
x
0
0
time of different systems.
x
This benefit from the porous structure of the Cu/Cu S/NSC
catalyst, which can quickly adsorb 4-nitrophenol ions and provide
favorable conditions for the catalytic reduction reaction. However,
the reaction proceeds extremely slowly while pure Cu S was used
2
as a catalyst, with only about 9.85% reduction conversion in 30
minutes. In order to explore the distribution information of different
4
Since the initial concentration of NaBH was higher than 4-NP,
the catalytic reduction process can be evaluated with pseudo-first
order kinetics (ln(C /C )=-kt), where the ratio of C /C can be
t
0
t
0
obtained from the absorbance ratio at 400nm . Therefore, the
apparent rate constant k was obtained through the relationship
components and the catalytic active sites in the Cu/Cu
Treat the catalyst with concentrated hydrochloric acid to
selectively dissolve Cu particles to obtain Cu S/NSC
Cu+HCl→Cu(Cl) +H (Figure S7). The distribution of Cu S on
NSC was shown in Figure S8. The catalytic activity of Cu S was
evaluated by the reduction reaction of 4-NP, and it was found that
00% reduction efficiency can be reached in 330 s under the
same conditions (Figure S9). The catalytic efficiency of Cu S/NSC
has decreased compared with Cu/Cu S/NSC, indicating that Cu
is one of the catalytically active sites. To further explore the active
components in the catalyst, the Cu/Cu S was removed by treating
Cu/Cu S/NSC with dilute nitric acid to obtain porous NSC (Cu+
HNO →Cu(NO +NO+H O; Cu S+HNO →Cu(NO +CuSO
NO+H O) (Figure S10). It was found that the mass percentages
x
S/NSC.
between ln(C
the reaction constant k of Cu/Cu
t 0
/C ) and time. As shown in Figure 5f, the value of
-1
x
S/NSC is 0.0256 s , which is
x
much higher than the previously reported copper-based catalysts
or even noble metal catalysts.[19] The detailed comparison of the
corresponding rate constants, catalyst mass and 4-NP
concentration are listed in Table S3.
Recyclability is an important feature of the catalyst. Therefore,
a cyclic experiment of reducing 4-NP was carried out to study the
(
2
2
)
x
x
1
x
x
stability and reusability of Cu/Cu
x
S/NSC. As shown in the Figure
6
a, after fifteen rounds of experiments, the catalytic efficiency of
Cu/Cu S/NSC slowly decreases, but 4-NP can be reduced more
x
x
x
than 90%. The XRD pattern after the cycling experiment still has
the same diffraction peaks of Cu, Cu1.96S and Cu S (Figure 6b).
3
3
)
2
2
x
3
3
)
2
4
+
2
2
The distribution and the density of internal nanoparticles have not
changed after the cycles (Figure 6c). The solution system after
the 15th reaction completed was filtered and then detect the
concentration of Cu ions by inductively coupled plasma
measurement. The average value of Cu ion concentration is
of N and S elements were 8.10 % and 2.64 % in NSC through
inductively coupled plasma measurements. The same method
was used to monitor the catalytic activity of NSC, found that NSC
can reduce about 78.2% of 4-NP in 30 min (Figure 5d). Therefore,
x
the partial catalytic activity of Cu/Cu S/NSC hybrid material may
0
.0025 ppm, which indicates that very little dissolution and
exudation happened during the reaction which can be ignored.
These prove that Cu/Cu S/NSC has a certain degree of cycle
come from NSC. Nano carbon black (CB) was replaced NSC as
a control experiment, it was found that the catalytic reduction
reaction could not start (Figure 5e). This explains the active
ingredients in NSC are caused by the doping of N, S heteroatoms
x
4
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stability and will not undergo physical or chemical changes after
the catalytic reduction reaction.
NaBH
4
, Cu/Cu
x
S/NSC shows excellent catalytic reduction activity
for various dyes. The absorbance at the maximum wavelength of
CR (λmax=499 nm) (Figure 7a), MO (λmax=465 nm) (Figure 7b), MB
(
λ
max=663 nm) (Figure 7c) and RhB (λmax=553 nm) (Figure 7d)
disappears only in 140, 175, 25 and 130 s, which indicates almost
00% of the catalytic reduction has been completed. The
mechanism of Cu/Cu S/NSC catalytic reduction of various dyes is
1
x
similar to the reduction of 4-NP, which is the catalytic
hydrogenation of chromogenic groups (C=N or N=N) in the dye
with the assistance of NaBH
naphthionic acid and benzidine, respectively, and
4
. The reduction products of CR are
new
a
absorption peak is generated at 250 nm in the UV-vis spectrum
due to benzidine (Figure S11).[22] The final product of MO is 4-
amino-benzenesulfonate based on the cleavage of the azo
bond.[ The colorless form MB (LMB) was observed to be the
reduction product of MB, it can be slowly oxidized in the air
atmosphere, and then will be reduced again due to excessive
23]
NaBH
4
.[24] As for RhB, the final reduction products will be CO
2
,
2 0
H )
O and some other products.[ Relationship between ln(C/C
25]
versus time of different dyes was shown in Figure 7e. The
favorable linear relationship between them further confirms the
pseudo-first order kinetics, the apparent rate constant k were
-
1
Figure 6. (a) Catalytic efficiency of Cu/Cu
XRD and (c) TEM after fifteen cycle experiments.
x
S/NSC for the reduction of 4-NP. (b)
0.0269, 0.0156, 0.1149 and 0.0266 s , respectively (Figure 7f).
The reduction rate of each dye is different, and the reduction rate
of MB is the fastest. The structural formulas of these dyes were
given in Figure S12, one possible reason is that dyes with simple
molecules and few color groups are relatively easy to reduce.
Furthermore, simple small molecules have less steric hindrance
and are easier to generate electrostatic attraction or adsorption
with the catalyst, then increase the contact with the active site and
When the catalytic reaction progresses, there are two possible
reduction processes: The first is surface catalysis, component A
(
Cu/NSC) adsorbs BH4- ions in the solution, and electrons and
4
-
2
active hydrogen atoms migrate to the surface of A (A+BH +H O
-
2-
[26]
→
A(e , H)+BO ), then these electrons and active hydrogen atoms
speed up the reduction rate.
-
attack 4-NP to generate 4-AP (A(e , H)+4-NP→A+4-AP+H
2
O).
This reduction process only applys to Cu and NSC active
components not applicable to Cu S. The reason is that Cu S has
narrow band gap value, which means the electrons
x
x
a
4
-
accumulated by adsorbing BH ions can quickly reduce Cu
Cu instead of attacking 4-NP.[20] The second reduction process is
intrapore catalysis, B component (Cu S/Cu) combine with NSC to
x
S to
x
transfer electrons to a suitable catalytic reaction site. NSC can
quickly adsorb 4-NP (NSC+4-NP→NSC(4-NP)), when B adsorbs
BH4- to generate electrons (B+BH +H
4-
O→B(e , H)+BO ), NSC
-
2-
2
can be a good charge carrier which quickly transfers electrons
from B to 4-NP adsorbed by NSC, completing the reduction
reaction (B(e-, H)+NSC(4-NP)→B+NSC(4-AP)+H
O), 4-AP
2
returns to the solution after the reaction is completed (NSC(4-
AP)→NSC+4-AP). This catalytic reduction process greatly
improves the catalytic efficiency of Cu S active component and
x
also suite for Cu active component. The most commonly used
model for the adsorption of this reactant on the catalyst surface is
the Langmuir-Hinshelwood mechanism.[21] The efficient catalytic
reduction performance of the Cu/Cu
inseparable from the synergistic catalysis of each component.
Including the electron transfer of Cu S and Cu to NSC for
intrapore catalysis. Furthermore, Cu S can dilute the surface Cu
x
S/NSC catalyst is
x
x
particles to improve the dispersion of Cu active sites and increase
the catalytic efficiency.
In order to prove the universality of Cu/Cu S/NSC catalysis, we
x
further extended the system to catalytically reduce the aqueous
solution of dyes, including Congo Red (CR), Methyl Orange (MO),
Methylene Blue (MB) and Rhodamine B (RhB) UV-vis absorption
used to monitor the reaction progress, with the participation of
Figure 7. Dynamic UV-vis spectra of (a) CR, (b) MO, (c) MB and (d) RhB. (e)
Relationship between ln(C/C
different dye systems.
0
) versus time. (f) The apparent rate constant k of
5
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Chemistry - A European Journal
10.1002/chem.202101560
FULL PAPER
Conclusion
2
confocal Raman microscope. Record the N adsorption-desorption
isotherm on the ASAP2020M automatic adsorption analyzer. The specific
surface area of the material was calculated by Brunauer-Emmett-Teller
In conclusion, we use a nitrogen-containing ligand TPT and a
sulfur-containing ligand 2,5-tdc to design and synthesize a novel
(
BET) method, and the pore size distribution was evaluated using the
Barrett-Joyner-Halenda (BJH) model. X-ray photoelectron spectroscopy
XPS) from Kratos Analytical was used to analyze elemental composition.
[
Cu(TPT)(2,5-tdc)]·2H
Cu/Cu S/NSC was successfully prepared using Cu-MOF as the
precursor. Cu/Cu S/NSC has a fixed octahedral morphology, Cu
and Cu S particles are uniformly embedded in N, S-doped porous
carbon. The doping of N and S provides more active sites,
Cu/Cu S/NSC has excellent catalytic reduction performance. In
2
O. The carbon-based nanocatalyst
(
x
The UV-Vis spectrum characterization was performed on JASCO V-770
UV-Vis spectrometer.
x
x
Catalytic activity: The catalytic activity of Cu/Cu
monitored by UV-visible spectrophotometer. Drip 0.2 mL 4-NP solution
2.5 mM) into the cuvette, then add 2.5 mL distilled water and 0.2 mL newly
prepared NaBH aqueous solution (0.2 M) separately, finally 0.1 mL of
x
S/NSC catalyst was
x
(
the 4-NP catalytic reduction experiment, only 0.1 mg of catalyst
can complete the reduction reaction in 145 s, and the reduction
efficacy remains above 90 % after 15 cycles. The apparent rate
constant of the 4-NP reduction reaction is 0.0256 s , which
exceed most reported catalysts. Simultaneously, Cu/Cu S/NSC
catalyst has high catalytic activity for the reduction of dyes. The
efficient catalytic reduction performance of Cu/Cu S/NSC is
attributed to the synergy of the active components of the hybrid
material. As a scalable carbon-based material, Cu/Cu S/NSC has
4
catalyst and water mixed solution (1 mg/mL) was added to start the
reaction. In the cycle test, the catalyst was centrifuged and washed with
ethanol to use in the next cycle. The catalytic reduction of the dye is similar
to that of 4-NP. A mixture of 2.7 mL (10 ppm) dye solution and 0.1 mL
catalyst (1 mg/mL) were placed in a cuvette, then 0.2 mL of NaBH solution
4
(0.2 M) was added to start the reaction. Record the characteristic
absorbance with time changes.
-1
x
x
x
great application prospects in the fields of photo-electro catalysis,
supercapacitors and electrode batteries.
Acknowledgements
This work was financially supported by National Natural Science
Foundation of China (21801021), Jilin Provincial Department of
Education (JJKH20200758KJ, JJKH20200761KJ, JJKH2021
Experimental Section
Chemicals: Cu(NO
thiophenedicarboxylic acid (2,5-tdc), 4-nitrophenol (4-NP), sodium
borohydride (NaBH ) and various dyes were obtained from Energy
Chemical. Cu S was purchased from Macklin Biochemical Technology.
N,N-Dimethylacetamide (DMA), Methanol (MeOH), nitric acid (HNO
3 2 2
) ·6H O, 2,4,6-Tri(4-pyridyl)-1,3,5-triazine (TPT), 2,5-
0
803KJ), the Government Funded Projects (61409220309) and
the Science and Technology Development Plan of Jilin Province
20180520150JH, 20180520170JH).
4
(
2
3
)
were purchased from Tokyo Chemical Industry. The chemical reagents
used above are of analytical grade, all from commercial sources, and used
without further purification.
Keywords: Metal-organic frameworks • carbon-based
nanomaterials • non-precious metal catalyst • catalytic reduction
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Entry for the Table of Contents
Cu/Cu
synthesized. Porous Cu/Cu
which is better than many copper-based catalysts and even precious metal catalysts. The efficient catalytic reduction performance of
x
S embedded N,S-doped porous carbon (Cu/Cu
x
S/NSC) in situ derived from a novelly designed Cu-MOF was successfully
-1
x
S/NSC has a high catalytic reduction efficiency for 4-NP (k = 0.0256 s ) and dyes (CR, MO, MB and RhB)
the Cu/Cu
x
S/NSC catalyst is inseparable from the synergistic catalysis of each component.
8
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