Atomically Dispersed Single Co Sites in Zeolitic Imidazole Frameworks Promoting High-Efficiency Visible-Light-Driven Hydrogen Production

Article abstract of DOI:10.1002/chem.201901250

As photocatalysis technology could transform renewable and clean solar energy into green hydrogen (H₂) energy through solar water splitting, it is regarded as the “Holy Grail” in chemistry field in the 21st century. Unfortunately, the bottleneck of this technique still lies in the exploration of highly active, cost-effective, and robust photocatalysts. This work reports the design and synthesis of a novel zeolitic imidazole framework (ZIF) coupled Zn_0.8Cd_0.2S hetero-structured photocatalyst for high-performance visible-light-induced H₂ production. State-of-the-art characterizations and theoretical computations disclose that the interfacial electronic interaction between ZIF and Zn_0.8Cd_0.2S, the high distribution of Zn_0.8Cd_0.2S on ZIF, and the atomically dispersed coordinately unsaturated Co sites in ZIF synergistically arouse the significantly improved visible-light photocatalytic H₂ production performance.

Full text of DOI:10.1002/chem.201901250

A Journal of
Accepted Article
Title: Atomically Dispersed Single Co Site in Zeolitic Imidazole
Framework Propelling High-efficiency Visible-light-driven
Hydrogen Production
Authors: Jingrun Ran, jiangtao Qu, Hongping zhang, bingquan xia,
shuangming chen, li song, xuliang zhang, liqiang jing,
rongkun zheng, and Shizhang Qiao
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201901250
Link to VoR: http://dx.doi.org/10.1002/chem.201901250
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Atomically Dispersed Single Co Site in Zeolitic Imidazole
Framework Propelling High-efficiency Visible-light-driven
Hydrogen Production
[a]
[b]
[c]
[a]
[d]
[e]
Jingrun Ran, Hongping Zhang, Jiangtao Qu, Bingquan Xia, Xuliang Zhang, Shuangming Chen,
Li Song,[e] Liqiang Jing, Rongkun Zheng, and Shi-Zhang Qiao*
[d]
[c]
[a]
Abstract: Since the photocatalysis technology could transform the
renewable and clean solar energy into green hydrogen (H ) energy
have been developed, their activities and stabilities are still far
from satisfactory.[3,6,8-10] Besides, noble-metal Pt co-catalyst is
2
[
8-
via solar water splitting, it is regarded as the ‘Holy Grail’ in chemistry
field in the 21st century. Unfortunately, the bottleneck of this technique
still lies in the exploration of highly-active, cost-effective and robust
photocatalysts. Herein, we report the design and synthesis of a novel
usually employed to boost their photocatalytic performance.
1
0,22,24,26-30]
However, the high price and low abundance of Pt
seriously obstruct the practical application of photocatalysts.
Hence, the development of noble-metal-free photocatalysts with
high activity and long-term stability is of great importance.
As a sub-family of metal organic frameworks (MOFs), zeolitic
imidazole frameworks (ZIFs) comprised of imidazole linkers and
metal ions have attracted explosive research in recent years,
owing to their intriguing features of exceptional thermal and
chemical stabilities, high crystallinities, ultrahigh surface area,
numerous functionalities and atomically-dispersed single metal
site.[31-52] Hence, ZIFs hold great promise for applications in
zeolitc imidazole framework (ZIF) coupled Zn0.8Cd0.2
structured photocatalyst for high performance visible-light-induced H
production. State-of-art characterizations and theoretical
S hetero-
2
computations disclose that the interfacial electronic interaction
between ZIF and Zn0.8Cd0.2S, the high distribution of Zn0.8Cd0.2S on
ZIF and the atomically-dispersed coordinately-unsaturated Co sites in
ZIF synergistically arouse the significantly-raised visible-light
2
photocatalytic H -production performance.
photocatalytic
2
H production because of their i) excellent
stabilities in water, ii) large surface area facilitating the high
dispersion of supported nano-structured photocatalysts, iii)
abundant functionalities favouring the strong combination with
Introduction
supported photocatalysts and iv)
coordinately-unsaturated (ADCU) metal sites serving as highly-
active catalytic centres to promote surface redox reactions.
Nevertheless, the employment of ZIFs in photocatalytic H
production is still in infancy.
atomically-dispersed
Photocatalysis, which can harvest solar energy and convert it into
clean and carbon-free hydrogen (H ) energy via solar water
2
splitting, is deemed as an ideal technique to achieve the
sustainable and environmentally-benign production of solar
fuels.[1-30] To date, although numerous types of photocatalysts
2
Here, we combined Co-based ZIF-9 (ZF9) with Zn0.8Cd0.2
ZCS) nanoparticles (NPs) by a self-assembly method through
physical mixing at ambient conditions. The assembled noble-
metal-free ZF9/ZCS hetero-structure shows significantly-
-production activity of 6420
S
(
[
a]
Dr. J. Ran, B. Xia, Prof. S.-Z. Qiao
School of Chemical Engineering
The University of Adelaide
a
boosted visible-light photocatalytic H

2
Adelaide, SA 5005, Australia
mol h-1 g-1, 35.47 times higher than that of bare ZCS. This activity
E-mail: s.qiao@adelaide.edu.au
Dr. H. Zhang
even exceeds that of Pt loaded ZCS by 1.41 times under the
identical conditions. This ZF9/ZCS composite ranks among one
of the most active noble-metal-free ZCS based photocatalysts.
The advanced characterization techniques, e.g., Synchrotron-
based X-ray absorption near edge structure (XANES) and time-
resolved photoluminescence (PL) spectroscopy, as well as
density function theory (DFT) based calculations were employed
to probe into the origin of the greatly-enhanced photocatalytic
performance. The results confirm that the strong electronic
coupling between ZF9 and ZCS, the well-dispersed ZCS NPs on
ZF9 and the highly-active ADCU Co sites in ZF9 together conduce
to this remarkable photocatalytic activity. Furthermore, ZF9 can
also tremendously raise the photocatalytic activity of CdS,
[
b]
State Key Laboratory of Environmental Friendly Energy Materials
Engineering Research Center of Biomass Materials (Ministry of
Education)
School of Materials Science and Engineering
Southwest University of Science and Technology
Sichuan 621010, China
[
[
c]
d]
Dr. J. Qu, Prof. R. Zheng
School of Physics
The University of Sydney
NSW 2006, Australia
X. Zhang, Prof. L. Jing
Key Laboratory of Functional Inorganic Material Chemistry (Ministry
of Education)
School of Chemistry and Materials Science
International Joint Research Center for Catalytic Technology
Heilongjiang University
demonstrating its
generality as
a
high-performance
Harbin 150080, P. R. China
support/promoter for nano-structured photocatalysts. This study
highlights the great importance of employing MOFs with ADCU
metal sites to improve the photocatalytic performance without
using noble-metal co-catalyst.
[
e]
National Synchrotron Radiation Laboratory
CAS Center for Excellence in Nanoscience
University of Science and Technology of China
Hefei, Anhui 230029, China
Supporting information for this article is given via a link at the end of
the document.
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Results and Discussion
First, we have synthesized ZF9 by a solvothermal autoclaving
approach.[40] The as-synthesized ZF9 was characterized by X-ray
diffraction (XRD) (Figure S1), transmission electron microscopy
characterized by TEM, HRTEM and EDS. Figure 1d presents that
ZCS NPs with sizes of ca. 13-50 nm are dispersed on the surface
of sub-micrometer sized ZF9 crystals. The better dispersion of
ZCS NPs on ZF9 in Z2.0 compared to ZCS NPs alone (Figure
S5a) implies the more exposed surface reactive sites and the
better light absorption of ZCS NPs in Z2.0, in favor of achieving
the higher photocatalytic activity. The HRTEM image of Z2.0 in
Figure 1e shows a lattice spacing value of 0.31 nm, corresponding
to the (111) facet of ZCS in Z2.0. Moreover, the EDS spectrum of
Z2.0 (Figure 1f) indicates the presence of Zn, Cd, S, Co, C and N
elements, again confirming the coupling of ZF9 and ZCS in Z2.0.
Moreover, the TEM image of Z2.0 (Figure S6a) and the
corresponding EDS elemental mapping images (Figure S6b-d)
confirm that the NPs and the sub-micrometer sized crystals in
Figure S6a are ZCS and ZF9, respectively, thus in agreement with
the above results.
(
TEM, Figure 1a), energy-dispersive X-ray spectroscopy (EDS,
Figure 1b), high-resolution X-ray photoelectron spectroscopy
(
(
XPS, Figure S2) and UV-Vis diffuse reflectance spectroscopy
Figure S3), respectively. The presence of abundant ADCU Co
sites in the atomic structure of ZF9 (Figure S4a and b) imply the
huge potential of using these ADCU Co sites as highly-efficient
reactive centers in photocatalysis.[53] Then the ZCS NPs were
fabricated by a precipitation-hydrothermal approach. The TEM
and high-resolution (HR)TEM images of the as-prepared ZCS
NPs are displayed in Figure S5a and b, respectively. Finally, 0.0,
0.5, 2.0, 4.0 and 7.5 mg ZF9 was hybridized with 100 mg ZCS
NPs, respectively. The resulting samples were labelled as Z0.0,
Z0.5, Z2.0, Z4.0 and Z7.5, respectively. As displayed in Figure 1c,
the XRD patterns of Z0.0, Z0.5, Z2.0, Z4.0 and Z7.5 all present a
slight shift to the left compared with the standard cubic sphalerite-
structured ZnS (JCPDS #05-0566), due to the formation of
To explore the electronic coupling between ZF9 and ZCS in
ZF9/ZCS hetero-junction, both the advanced characterizations
and DFT based computations were carried out. First, the surface-
sensitive XPS technique was utilized to study the chemical status
x
Zn Cd1-xS solid solution. No apparent alteration on the positions
and intensities of the XRD peaks for the ZF9/ZCS composites (i.e., of elements in Z0.0 and Z2.0. The high-resolution XPS peaks of
Z0.5, Z2.0, Z4.0 and Z7.5) are observed in contrast with those of
Z0.0, suggesting that no obvious change occurs in the crystal
structures of ZF9/ZCS composites compared to that of Z0.0. No
diffraction peaks of ZF9 are found in Figure 1c, due to its low
content and uniform dispersion in the ZF9/ZCS composites. Then
the microstructure and elemental compositions of Z2.0 were
Zn 2p for Z2.0 show a shift of 0.1 eV towards the high binding
energy direction compared to that of Z0.0 (Figure 2a), implying
the electron migration from ZCS to ZF9 in Z2.0. However, the
high-resolution XPS peaks of Cd 3d for Z2.0 exhibit negligible shift
compared with those of Z0.0 (Figure 2b), probably due to the high
Figure 1. (a) A high-magnification TEM image of ZF9. The inset in Figure 1a shows the low-magnification TEM image of ZF9. (b) The EDS spectrum of ZF9. (c)
XRD patterns of Z0.0, Z0.5, Z2.0, Z4.0 and Z7.5. (d) A TEM image of Z2.0. (e) A HRTEM image of ZCS NPs in Z2.0. (f) The EDS spectrum of Z2.0.
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Figure 2. High-resolution XPS spectra of (a) Zn 2p, (b) Cd 3d and (c) S 2p for Z0.0 and Z2.0. (d) High-resolution XPS spectra of Co 2p for ZF9 and Z2.0. Synchrotron-
based XANES of (e) Zn K edge, (f) Cd K edge and (g) S L edge for Z0.0 and Z2.0. (h) Synchrotron-based XANES of Co L edge for ZF9 and Z2.0.
electron density of the Cd atom. In addition, the high-resolution
XPS peaks of S 2p for Z2.0 show a shift of 0.2 eV towards the low
binding energy direction (Figure 2c), in contrast to those of Z0.0.
Notably, due to the very low Co content (0.57 wt%) in Z2.0 as
determined by the inductively coupled plasma atomic emission
spectroscopy (ICP-AES), the XPS Co 2p signal of Z2.0 is too
weak to be distinguishable from the background noise (Figure 2d).
Moreover, Synchrotron-based XANES were also performed. As
displayed in Figure 2e, f and g, no obvious shift of the XANES of
Zn K edge, Cd K edge and S L edge of Z2.0 is found, compared
with those of Z0.0, respectively. This is probably due to the
combined effects of the following factors: (i) The content of ZCS
is much larger than that of ZF9 in Z2.0; (ii) The XANES technique
can detect the chemical state of Zn, Cd and S atoms both at the
surface and in the bulk. However, the electron transfer occurs at
the surface of ZCS and ZF9 in Z2.0. Moreover, it should be noted
that the XANES of Co L edge of Z2.0 (Figure 2h) also displays no
apparent shift compared to that of ZF9. The reason is that only
the Co atoms at the surface of ZF9 accept the electron from ZCS.
But the XANES of Co L edge of Z2.0 is the averaged signal from
the Co atoms both at the surface and in the bulk of ZF9.
and b) show that their flat band potentials (Efb) are determined to
be -0.71 and -0.06 V vs. SHE, respectively. Thus, the Fermi level
(E ) position of ZCS is higher than that of ZF9, again confirming
F
the electron migration from ZCS to ZF9 after their combination in
Z2.0, in agreement with the DFT calculation results. Hence, both
the experimental and theoretical calculation results corroborate
the electronic interaction between ZCS and ZF9 in Z2.0.
The intimate electronic interaction in ZF9/ZCS hetero-junction
implies its efficient interfacial photo-excited charge carrier
separation and migration, which plays a major role in determining
2
the overall photocatalytic activity. Hence, the photocatalytic H -
production activities of all the above samples were tested. As
shown in Figure 3c, pure ZCS only exhibits a photocatalytic
activity of 181 mol h-1 g-1. After modification with only 0.5 wt%
ZF9, Z0.5 demonstrates an obviously increased photocatalytic
activity of 2944 mol h-1 g-1. Surprisingly, with the loading of 2.0
2
wt% ZF9, Z2.0 exhibits the highest photocatalytic H -production
activity of 6420 mol h-1 g-1, exceeding that on pristine ZCS by
3547%. Such an activity is even higher than that of 2.0 wt% Pt
loaded ZCS (Pt-ZCS, 4562 mol h-1 g-1) by 141%. This
outstanding activity also renders Z2.0 as one of the most efficient
noble-metal-free ZCS based photocatalysts (Table S1). Further
increasing the amount of ZF9 (4.0 wt%) leads to a decrease in
activity to 4915 mol h-1 g-1. As the content of ZF9 reaches 7.5
wt%, Z7.5 exhibits an even lower activity of 2441 mol h-1 g-1. The
reduction in the activities of Z4.0 and Z7.5 is ascribed to the
excessive ZF9 blocking the light and covering the surface reactive
To further study the electronic coupling between ZF9 and ZCS,
the DFT based computations were conducted. As displayed in
Figure 3a and b, the work functions () of ZCS and ZF9 are
calculated to be 4.05 and 5.91 eV, respectively. Thus, their Fermi
F
level (E ) positions are determined to be at -0.39 and 1.47 V vs.
standard hydrogen electrode (SHE), respectively, suggesting the
electron transport from ZCS to ZF9 after their contact. Besides,
the Mott-Schottky plots of both ZCS (Z0.0) and ZF9 (Figure S7a
centers. Moreover, we have also tested the photocatalytic H
2
-
production activities of Z2.0 in the presence of 20 v% methanol,
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Figure 3. Average potential profile along Z-axis direction for (a) ZCS and (b) ZF9. (c) A comparison of photocatalytic H
2
-production activities of Z0.0,
Z0.5, Z2.0, Z4.0, Z7.5 and Pt-ZCS in the presence of 20 v% triethanolamine aqueous solution under visible-light irradiation ( > 420 nm). (d) UV-Vis
diffuse reflectance spectra of Z0.0, Z0.5, Z2.0, Z4.0 Z7.5 and ZF9. The inset in Figure 3d shows the colours of Z0.0, Z0.5, Z2.0, Z4.0, Z7.5 and ZF9.
Steady-state (e) SPV spectra and (f) PL spectra of Z0.0 and Z2.0. (g) Time-resolved PL spectra of Z0.0 and Z2.0. (h) Transient photocurrent density
2 4
measurement of Z0.0 and Z2.0 electrodes in 0.5 M Na SO .
2
0
v% ethanol and 20 v% 1-propanol aqueous solution,
respectively, under the identical conditions. The results in Figure
S8 show that the photocatalytic H -production activities of Z2.0 in
band gap of ZCS was not changed in Z2.0. Moreover, Z2.0 shows
an increased absorption in the range of ~510-800 nm, due to the
presence of violet-coloured ZF9 (Figure S3 inset). Considering
that this increased absorption arises from the absorption peak of
ZF9 centred at 585 nm (Figure S3), we used a single-wavelength
light emitting diode (LED) at 595 nm to excite the ZF9 instead of
the ZCS in Z2.0. Under 595-nm LED irradiation, Z2.0 exhibits
negligible H production, suggesting that the increased light
2
absorption by ZF9 in Z2.0 actually doesn’t contribute to its highly-
enhanced photocatalytic activity.
2
the above three kinds of aqueous solutions are much lower than
that of Z2.0 in 20 v% triethanolamine aqueous solution. This
indicates that triethanolamine serves as the most effective
sacrificial reagent to donate the electrons for consuming the
photo-induced holes in Z2.0 among these four types of sacrificial
reagents.
The robustness of Z2.0 was examined by a 6-h photocatalytic
reaction. As shown in Figure S9, the H
Z2.0 in the second round still retains about 74.1% of that in the
2
-production amount of
The efficiency of the charge-carrier dissociation and migration
in Z2.0 was explored by a variety of characterization methods,
first round, indicating the reasonable stability of Z2.0. Furthermore, e.g., steady-state surface photovoltage (SPV) spectroscopy,
the TEM image (Figure S10a) and EDS spectrum (Figure S10b)
of Z2.0 after the 6-h photocatalytic reaction exhibit no obvious
alteration compared to those of Z2.0 (Figure 1d and f), again
confirming its stability.
steady-state PL spectroscopy, time-resolved PL spectroscopy
and transient photocurrent (TPC) density measurement. The
steady-state SPV spectra in Figure 3e presents that Z2.0
possesses a stronger SPV signal compared to Z0.0, suggesting
that more efficient separation and transfer of photo-excited
electrons and holes to the surface of Z2.0 is realized. Moreover,
similar to Z0.0, no SPV signal at wavelength longer than 567 nm
is observed for Z2.0, again confirming that the enhanced light
absorption from ZF9 in Z2.0 (Figure 3d) doesn’t contribute to its
improved photocatalytic activity. Moreover, as displayed in Figure
3f, the steady-state PL peak intensity of Z2.0 is diminished
compared with that of Z0.0, indicating that the charge carrier
recombination in Z2.0 is suppressed. Besides, the time-resolved
PL spectra in Figure 3g also present that the charge-carrier
To explain the greatly-improved photocatalytic activity of Z2.0,
various characterization approaches were adopted to study its
physicochemical properties, which are directly correlated with the
three crucial steps in photocatalysis: i) the light absorption to
generate photo-excited electron-hole pairs; ii) the dissociation
and transportation of photo-excited electrons and holes to the
surface; iii) the surface catalytic redox reactions driven by these
photo-excited electrons and holes. As a result, the light absorption
property of Z2.0 was studied by the UV-Vis diffuse reflectance
spectroscopy. As presented in Figure 3d, the absorption edge of
Z2.0 was not altered compared to that of Z0.0, suggesting the
lifetimes of Z2.0 (
1
2
= 0.20 ns;  = 5.50 ns) are elongated in
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confirmed by the I-V curve results in Figure S11. Hence, the
integration of ZF9 with ZCS NPs in Z2.0 accelerates its surface
catalytic reactions.
The above experimental results and theoretical computations
inspire us to put forward a possible photocatalytic mechanism in
ZF9/ZCS system. Based on the Mott-Schottky Plot (Figure 4b) of
pure ZCS (Z0.0), its flat band potential (Efb) is determined to be -
0
.71 V vs. SHE. Thus, the conduction band (CB) edge potential
of n-type semiconductor ZCS is estimated to be -0.81 V vs. SHE
Figure 4c). And the valence band (VB) edge potential of ZCS is
(
estimated to be 1.59 V vs. SHE (Figure 4c) based on its UV-Vis
diffuse reflectance spectrum in Figure 4b inset. As shown in
Figure 4c, the visible-light illumination ( > 420 nm) on ZF9/ZCS
generates the photo-excited electrons and holes on the CB and
VB of ZCS, respectively. Then, the photo-excited electrons on the
CB of ZCS migrate to the ZF9. Subsequently, these photo-excited
electrons further transfer to the abundant ADCU single Co sites
in ZF9, where the protons from the aqueous solution are reduced
by these electrons to form H
2
gas. Meanwhile, the triethanolamine
(
TEOA) molecules are oxidized by the photo-excited holes left on
the VB of ZCS to form the oxidation products.
To investigate whether ZF9 could also greatly boost the
photocatalytic H -production activity of the other semiconductor
2
Figure 4. (a) N
Schottky plot of Z0.0 in 0.5 M Na
Figure 4b shows the onset absorption edge position of Z0.0. (c) Proposed
mechanism of ZF9/ZCS system for photocatalytic H production under
visible-light ( > 420 nm) illumination. Hydrogen atoms are omitted in the
2
sorption isotherms of Z0.0 and Z2.0. (b) The Mott-
photocatalysts, we have coupled 5.0 mg of ZF9 with the 100 mg
CdS NPs by the self-assembly approach through mechanical
mixing. The as-synthesized ZF9/CdS composite was denoted as
CZ5.0. And the pure CdS NP was denoted as CZ0.0. The XRD
patterns and UV-Vis diffuse reflectance spectra of CZ0.0 and
CZ5.0 are displayed in Figure S12a and b, respectively. A
2
SO aqueous solution. The inset in
4
2

packing diagram of ZF9.
significantly-boosted photocatalytic H
2
production activity of
13249 mol h-1 g is observed on CZ5.0 (Figure S12c), exceeding
-1
comparison to those of Z0.0 (
1
= 0.17 ns; 
2
= 4.00 ns).
-
1
-1
Furthermore, a larger TPC density value is observed on Z2.0 than
of Z0.0 (Figure 3h), again supporting that the higher efficiency of
excitons dissociation and migration is achieved in Z2.0. All the
above results corroborate that more photo-excited electrons and
holes are rapidly separated and transported to the surface after
combining ZF9 with ZCS, due to the strong electronic coupling at
the interface of ZF9 and ZCS.
that of CZ0.0 (405 mol
h
g ) by more than 3271%,
demonstrating the huge potential of using ZF9 with ADCU single
Co sites as a highly-effective, general and earth-abundant
support/promoter to advance the activity of different
semiconductor photocatalysts.
The efficiency of surface redox reactions on photocatalysts is Conclusions
usually dictated by the number and intrinsic activities of their
surface reduction and oxidation reactive sites. Thus, we study the
Brunauer-Emmett-Teller (BET) surface area and pore volume of
In summary, we for the first time fabricated Zn0.8Cd0.2
nanoparticles dispersed zeolitic imidazole framework (ZIF)
S
Z0.0 and Z2.0 using N
the N sorption isotherm of Z2.0 exhibits an apparent decrease in
adsorption at the relative pressure range of ~0.9-1.0, in
2
sorption analysis. As shown in Figure 4a,
hetero-junction by
synthesized ZIF/Zn0.8Cd0.2
a
facile self-assembly route. The as-
hetero-structure exhibits
2
S
a
N
2
tremendously-increased photocatalytic H -production rate of
2
6420 mol h-1 g , surpassing that of bare Zn0.8Cd0.2S by 3547%.
-1
comparison to that of Z0.0, corresponding to the reduction in large
mesopores and macropores formed by the aggregation of
secondary particles of ZCS NPs in Z2.0. The reason is that the
presence of ZF9 in Z2.0 promotes the better dispersion of ZCS
NPs on the surface of ZF9. The higher dispersion of ZCS NPs in
Z2.0 arouses their increased exposed surface area, in agreement
This photocatalytic activity even exceeds that of Pt loaded
Zn0.8Cd0.2S by 141% under the identical conditions. The origin of
such a high performance was investigated by the advanced
characterization methods (e.g., Synchrotron-based X-ray
absorption spectroscopy and time-resolved photoluminescence
spectroscopy) combined with the theoretical calculations. The
electronic interaction at the interface of ZIF/Zn0.8Cd0.2S hetero-
junction, the high dispersion of Zn0.8Cd0.2S on ZIF as well as the
abundant atomically-dispersed coordinately-unsaturated single
Co sites in ZIF together arouses the greatly-boosted
2
-1
with the larger BET surface area of Z2.0 (SBET = 46.5 m g ) in
2
-1
contrast with that of Z0.0 (SBET = 45.0 m g ) as displayed in Table
S2. However, such a small increase in the BET surface area (1.5
2
-1
m g ) of Z2.0 compared to that of Z0.0 can’t truly reflect the
significant activity enhancement of Z2.0 compared with that of
Z0.0 (see Figure 3c). In fact, the presence of ZF9 in Z2.0
introduces a large quantity of highly-active ADCU single Co sites
accessible through the mesopore networks of ZF9. These ADCU
photocatalytic H -production activity. Our contribution not only
2
highlights the great importance of utilizing those atomically-
dispersed coordinately-unsaturated single metal sites in the metal
organic framework (MOF) as highly-active sites to promote the
2
Co sites in Z2.0 obviously boost the H evolution process as
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photocatalytic reactions in the absence of noble-metal co-catalyst, Physicochemical characterization
but also sheds lights on the rational design and preparation of
MOF-based composites for catalysis in energy conversion and
storage.
A powder X-ray diffractometer (Miniflex, Rigaku) was employed to obtain
XRD patterns using Cu K radiation. The TEM, HRTEM images and the
EDS spectra were acquired on a JEM-2100F electron microscope (JEOL,
Japan). The XPS measurement was conducted on a VG ESCALAB 210
XPS spectrometer system using Mg K source. The C 1s peak at 284.8
eV for the surface adventitious carbon was utilized as the reference for all
the binding energies. The UV-Visible diffuse reflectance spectra were
obtained on a UV-Vis spectrometer (UV-2600, Shimadzu, Japan). The
Synchrotron-based XANES measurements were performed at the
Australian Synchrotron and Shanghai Synchrotron Radiation Facility
Computation Method
We employed the Perdew-Burke-Ernzerhof (PBE) generalized gradient
approximation (GGA)[55] for the exchange correlation energy and DFT
semi-core pseudopotentials for the core-valence interactions. The double
numerical basis set with polarisation function (DNP), which is comparable
to the 6-31G** basis set, was used in the calculations. Special point
sampling integration over the Brillouin zone was employed utilizing
Monkhorst-Pack schemes with a 5 × 5 × 1 k-point mesh A Fermi smearing
of 0.005 Ha and a global orbital cutoff of 7 Å were employed. The
convergence criteria for the geometric optimization and energy calculation
were set as follows: (1) self-consistent field tolerance of 1.0 × 10-6 Ha/atom,
(SSRF). The steady-state surface photovoltage (SPV) spectra were
acquired on a home-made apparatus, consisting of a monochromatic light
source, a lock-in amplifier (SR830-DSP) with a light chopper (SR540), a
sample cell and a computer.[55] The steady-state photoluminescence (PL)
spectra were acquired on
Shimadzu, Japan). The BET specific surface area and pore volumes of
the samples were obtained on a Micrometrics ASAP 2020 N adsorption
a RF-5301PC spectrofluorophotometer
(
2
instrument (USA). The actual Co content of the as-synthesized samples
was acquired on a Prodigy 7 spectrometer (Leeman Labs, USA) by ICP-
AES measurement. The transient-state PL spectra were obtained on a
FLS1000 fluorescence lifetime spectrometer (Edinburgh Instruments, UK).
(
2) energy tolerance of 1.0 × 10-5 Ha/atom and (3) maximum force
tolerance of 0.002 Ha/Å.
Experimental Section
Photocatalytic H production test
2
2
The photocatalytic H -production experiments were conducted in a 100 ml
Materials synthesis
Pyrex flask sealed with silicone rubber septa at room temperature and
under atmospheric pressure. A 300 W Xenon arc lamp with a UV-cutoff
filter ( > 420 nm) was used to trigger the photocatalytic reaction. 20 mg
photocatalyst was dispersed under steady stirring in 80 ml 20 vol%
triethanolamine aqueous solution. Argon gas was then purged into the
dispersion of photocatalyst for 0.5 hour to remove the air prior to irradiation
and ensure that the reactor is in anaerobic condition. 0.200 ml gas was
ZF9 was synthesized following the process reported by Park et al.[40] with
some modifications. In detail, 210 mg Co(NO ) ·6H O and 60 mg
3 2 2
benzimidazole were dissolved in 18 ml dimethylformamide (DMF). After
stirring for 0.5 h, the resulting solution was capped in a 20 ml glass vial.
The vial was stored at 130 °C for 48 h in an oven, with an increasing rate
of 5 °C·min-1 and a decreasing rate of 0.4 °C·min-1. The acquired purple
cubic crystals were separated, washed three times with DMF and
dichloromethane, and dried in a vacuum oven. Finally, the dried crystals
were crushed in a mortar for usage. ZCS NP was synthesized by a
2
sampled through the septum, and the produced H was quantified by gas
chromatograph (Clarus 480, Perkin Elmer, USA) with 5 Å molecular sieve
column and Argon as the carrier gas.
precipitation-hydrothermal approach. In detail, 0.21 g Cd(NO
.69 g Zn(NO ·6H O were added into 21 ml deionized water and stirred
for 1 hour. Then 4.8 ml 0.9 M Na S aqueous solution was added dropwise
into the above solution and stirred for 1 hour. Finally, the suspension was
transferred to a 48 ml Teflon-lined autoclave and maintained at 180 °C for
3 2 2
) ·4H O and
0
3
)
2
2
Electrochemical and photoelectrochemical tests
2
An electrochemical analyser (CHI650D instrument) was utilized to acquire
the Mott-Schottky plots in 0.5 M Na SO aqueous solution in a standard
2 4
three-electrode system, using the as-synthesized samples as the working
electrode, a Pt wire as the counter electrode and Ag/AgCl (saturated KCl)
as the reference electrode. 1200 Hz is selected as the applied alternating
current (AC) frequency. The polarization curves were also acquired in the
above-mentioned three-electrode system with a step size of 5 mV. 0.5 M
Na SO was utilized as the electrolyte. In addition, the TPC density
2 4
measurement was carried out on the same three-electrode system. The
light source is a 300 W Xenon light with a UV-cutoff filter ( > 420 nm). The
electrolyte is 0.5 M Na SO aqueous solution. The afore-mentioned
2 4
1
2 hours. The resulting products were washed by deionized water and
ethanol two times, respectively, and dried at 60 °C for 5 hours. ZF9
supported ZCS NP was prepared via mechanically mixing the as-
synthesized ZF9 with the as-prepared ZCS NP in a mortar. In detail, 100
mg ZCS NP was added into the mortar, followed by adding 0.0, 0.5, 2.0,
4.0 and 7.5 mg ZF9, respectively. Then 5.0 ml ethanol was added into the
mortar, and the suspension was mechanically ground for 5 min. After the
natural evaporation of ethanol, the solid left was ground into fine powders.
And the resultants were denoted as Z0.0, Z0.5, Z2.0, Z4.0 and Z7.5,
respectively. CdS NP was fabricated by a precipitation-hydrothermal
method. First, 0.82 g Cd(NO
water followed by stirring for one hour. Then, 4.8 ml 0.9 M Na
solution was added dropwise into the above solution, followed by stirring
for one hour. Finally, the suspension was transferred to a 48 ml Teflon-
lined autoclave and kept at 180 °C for 12 hours. The final products were
washed by deionized water and ethanol twice, respectively, and dried at
working electrodes were fabricated as follows: 10 mg sample, 15 mg
polyethylene glycol (PEG; molecular weight: 20000) and 1.0 ml ethanol
were ground together to make a slurry. Then the slurry was coated onto a
3
)
2 2
·4H O was added into 21 ml deionized
2
S aqueous
2
cm × 1.5 cm FTO glass electrode by a doctor blade method. At last, the
coated electrode was dried and heated at 350 °C for 0.5 hour under flowing
nitrogen gas.
60 °C for 5 hours. ZF9 supported CdS NP was fabricated by mechanically
mixing the as-synthesized ZF9 with the as-prepared CdS NP in a mortar.
Firstly, 100 mg of the as-prepared CdS NP was added into the mortar,
followed by adding 5.0 mg ZF9 and 5.0 ml ethanol. Then the suspension
was physically ground for 5 min. After the natural evaporation of ethanol,
the solid remained was again ground into fine powders. The resulting
sample is labelled as CZ5.0. The pure ZCS is labelled as CZ0.0.
Acknowledgements
The authors gratefully acknowledge financial support from the
Australian Research Council (ARC) through the Discovery Project
programs (FL170100154, DP160104866, DP170104464) and the
Linkage Project program (LP160100927), and support from the
Natural Science Foundation of China (No. 21576202). XANES
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Chemistry - A European Journal
10.1002/chem.201901250
FULL PAPER
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Chemistry - A European Journal
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FULL PAPER
Entry for the Table of Contents
FULL PAPER
The novel Zn0.8Cd0.2S coupled zeolitic
imidazole framework composite
exhibits a greatly-enhanced visible-
Jingrun Ran, Hongping Zhang, Jiangtao
Qu, Bingquan Xia, Xuliang Zhang,
Shuangming Chen, Li Song, Liqiang
Jing, Rongkun Zheng, Shizhang Qiao*
2
light photocatalytic H production
activity due to the synergistic effects
of strong electronic coupling, high
dispersion of Zn0.8Cd0.2S and the
atomically-dispersed single Co sites in
zeolitic imidazole framework.
Page No. – Page No.
Atomically Dispersed Single Co Site
in Zeolitic Imidazole Framework
Propelling High-efficiency Visible-
light-driven Hydrogen Production
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