Hierarchical Ag/Ag2S/CuS ternary heterostructure composite as an efficient visible-light photocatalyst

Article abstract of DOI:10.1002/cctc.201500121

A hierarchical Ag/Ag₂S/CuS ternary heterostructure composite has been obtained through cation exchange between as-prepared CuS nanoflowers and AgNO₃ (synthesized under solvothermal conditions) and subsequent in situ UV-light reduction. The prepared CuS nanoflowers not only provide reactive sites for in situ ion exchange with Ag⁺ but also perform as clapboards to prevent the excess aggregation of Ag₂S nanoparticles. After exposure to UV light, a uniform Ag/Ag₂S/CuS ternary heterostructure composite was obtained. In the composite, both Ag and Ag₂S are grown on the surface of CuS nanoflowers. The prepared ternary heterostructure composite exhibited a significant ability for the elimination of some hazardous pollutants under visible-light irradiation, which is much higher than that of either CuS or Ag₂S/CuS. Moreover, the resultant ternary composite possesses excellent stability.

Full text of DOI:10.1002/cctc.201500121

DOI: 10.1002/cctc.201500121
Full Papers
Hierarchical Ag/Ag2S/CuS Ternary Heterostructure
Composite as an Efficient Visible-Light Photocatalyst
Yunhan Shi,[b] Yajie Chen,[a] Guohui Tian,*[a, b] Liyang Wang,[a] Yuting Xiao,[a] and
Honggang Fu*[a]
A hierarchical Ag/Ag2S/CuS ternary heterostructure composite
has been obtained through cation exchange between as-pre-
pared CuS nanoflowers and AgNO3 (synthesized under solvo-
thermal conditions) and subsequent in situ UV-light reduction.
The prepared CuS nanoflowers not only provide reactive sites
for in situ ion exchange with Ag+ but also perform as clap-
boards to prevent the excess aggregation of Ag2S nanoparti-
cles. After exposure to UV light, a uniform Ag/Ag2S/CuS ternary
heterostructure composite was obtained. In the composite,
both Ag and Ag2S are grown on the surface of CuS nanoflow-
ers. The prepared ternary heterostructure composite exhibited
a significant ability for the elimination of some hazardous pol-
lutants under visible-light irradiation, which is much higher
than that of either CuS or Ag2S/CuS. Moreover, the resultant
ternary composite possesses excellent stability.
Introduction
Semiconductor heterogeneous photocatalysis is regarded as
an effective strategy for the removal of hazardous organic con-
taminants from wastewater.[1–3] Studies have shown correla-
tions between photocatalytic activity and physical properties,
such as crystal structure, morphology, and specific surface
structure.[4–6] Compared to single-component semiconductor
photocatalysts, semiconductor composites (especially rational
ternary components) with heterostructures have exhibited sig-
nificantly enhanced photocatalytic performance.[7,8] Especially
in metal-semiconductor composites, surface plasmon reso-
nance (SPR) effects and the formation of a Schottky barrier
through Fermi-level equilibration between metals and semi-
conductor oxides are effective to improve the separation of
photogenerated charge carriers.[9] For example, semiconductor
photocatalysts modified with Ag/AgX (X=Cl, Br, I) have shown
efficient photocatalytic performances and good stability under
visible-light irradiation.[10] The common synthetic method for
multiple semiconductor composites is to precipitate nanoma-
terials on the supports directly. However, this inevitably causes
serious aggregation, poor dispersity, and loose connections be-
tween the different components, which consequently impede
the interfacial charge transfer. To overcome these problems,
the design of a rational synthetic approach to fabricate com-
posites with highly dispersed nanoparticles on the surface of
substrate is necessary to endow a high surface-to-volume ratio
and abundant reactive sites to the photocatalysts.
Semiconductor chalcogenide nanostructures, for example,
copper sulfide (CuS), have been studied widely in photocataly-
sis.[11,12] However, the low charge-separation efficiency of pho-
togenerated electron–hole pairs still constrains their further de-
velopment especially toward commercial production.[13–15] To
enhance the photocatalytic efficiency of CuS, the synthesis of
composite catalysts is needed. However, most previous studies
on CuS-based composite catalysts comprise only two types of
semiconductor, and the photocatalytic activity still needs fur-
ther improvement. So significant challenges remain.[16,17] In-
spired by the study on Ag/AgX-modified semiconductor pho-
tocatalysts, it is expected that the exploration of the synthesis
of Ag/Ag2S-modified chalcogenide photocatalysts will improve
the visible-light photocatalytic activity.
Herein, we report a new hierarchical Ag/Ag2S/CuS ternary
heterostructure composite synthesized by a cation-exchange
reaction under solvothermal conditions and subsequent in situ
UV-light reduction at room temperature. Hierarchical flower-
like CuS was first prepared through a solvothermal route and
used as a starting material to generate the Ag2S/CuS binary
composite by in situ cation exchange with Ag+. Subsequently,
the small content of Ag2S is reduced to Ag nanoparticles upon
UV-light illumination, which can trap the photoexcited elec-
trons. The synergic effects of different components can reduce
the recombination probability of photogenerated electron–
hole pairs and enhance the charge-separation efficiency to
lead to a high photocatalytic performance and remarkable sta-
bility.
[a] Dr. Y. Chen, Prof. G. Tian, L. Wang, Y. Xiao, Prof. H. Fu
Key Laboratory of Functional Inorganic Material Chemistry
Ministry of Education of the People’s Republic of China
Heilongjiang University, Harbin 150080 (P.R. China)
E-mail: tiangh@hlju.edu.cn
fuhg@vip.sina.com
[b] Y. Shi, Prof. G. Tian
Key Laboratory of Chemical Engineering Process & Technology
for High-Efficiency Conversion, College of Heilongjiang Province
School of Chemistry and Materials Science
Heilongjiang University, Harbin 150080 (P.R. China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500121.
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composite. The morphologies of the hierarchical Ag2S/CuS het-
erostructures with different ratios of Ag2S were also character-
ized. The surface distribution densities of the Ag2S particles in-
creased slightly with the increase of the Ag2S content, and
some Ag2S nanoparticle aggregates appeared if the Ag2S con-
tent was relatively high (Figure S2). If the content of Ag2S is
too low, the Ag2S nanoparticles on the surface of the flower-
like CuS superstructures were not clear and the particle size
was smaller (Figure S2A) than that of the Ag-Cu-30 sample
(Figure S2B), which indicates that the formation of more Ag2S
nanoparticles needed a sufficient amount of Ag+. Clearly, a few
Ag2S nanoparticles on the surface will reduce light-harvesting
and thus decrease the quantity of photogenerated electrons
and holes.[18] However, excess Ag2S (Ag-Cu-50) could make too
many nanoparticles with a much larger radius (Figure S2C),
and the surfaces of the CuS nanoflowers were coated entirely
by Ag2S nanoparticles. These Ag2S sites may act as charge-re-
combination centers that do not contribute to the enhance-
ment of the photocatalytic activity.
Results and Discussion
Morphology and structure characterization
SEM images of as-synthesized CuS and Ag2S/CuS are shown in
Figure 1. Flower-like CuS with an average diameter of
TEM observations demonstrate that, compared to flower-like
CuS (Figure 3A), the morphology and structure of the
Figure 1. SEM images of A, C) CuS and B, D) Ag2S/CuS (Ag-Cu-30).
600–700 nm is shown in Figure 1A. The magnified SEM image
in Figure 1C shows that flower-like CuS architectures are con-
structed by several intersectional nanoplates with a smooth
surface and thickness of ꢀ50 nm. For the Ag2S/CuS composite,
the Ag2S nanoparticles formed through the cation-exchange
reaction between CuS and Ag+ were distributed evenly on the
surfaces of the CuS nanoflowers, and the morphology of the
flower-like CuS was not changed (Figure 1B and D).
XRD (Figure 2) and energy-dispersive X-ray analysis (EDX;
Figure S1) also prove the coexistence of CuS and Ag2S in the
Figure 3. SEM images of A) CuS. B) SEM, C) TEM, and D) HRTEM images of
Ag/Ag2S/CuS.
Ag/Ag2S/CuS ternary composite remain intact (Figure 3B, C). To
further confirm the result, the high-resolution transmission
electron microscopy (HRTEM) image presented in Figure 3D
was recorded. In the HRTEM image taken from the edge of the
composites (Figure 3C), the d spacing of 0.32, 0.27, and
0.25 nm can be assigned to the (102) lattice plane of the
cubic CuS, (120) lattice plane of the cubic Ag2S, and the (111)
lattice space of Ag, respectively. These results demonstrate the
existence of interface junctions among the components that
are in close contact in these composites, which play a vital role
in the interfacial charge transfer processes.[19] No characteristic
Figure 2. XRD patterns of a) CuS, b) Ag/Ag2S/CuS, and c) Ag2S/CuS
(Cu-Ag-30).
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diffraction peaks of Ag0 are detected in the XRD pattern (Fig-
ure 2b), which suggests its low content and relatively low dif-
fraction intensity. The corresponding BET surface areas and
pore structures of different samples were investigated by N2
adsorption–desorption experiments (Figure S3). The BET specif-
ic surface area of CuS, Ag2S/CuS, and Ag/Ag2S/CuS is 12.25,
10.12, and 9.88 m2 gÀ1, respectively. The surface area decreases
from CuS to the Ag2S/CuS binary composite and the Ag/Ag2S/
CuS ternary composite. This result implies that Ag and Ag2S
nanoparticles were located within the CuS interlaced nano-
sheets.
Formation mechanism of the hierarchical Ag/Ag2S/CuS ter-
nary composite
The synthesis of the hierarchical Ag/Ag2S/CuS ternary compo-
site is illustrated in Scheme 1. In the formation of the CuS
nanostructure, the mixture of DMF and ethanol not only acts
as the common solvent but also plays a key role as the reduc-
ing agent, which provides the physical reaction environment
and acts as a reactant at the same time.[20] Sulfur powder acts
as an original nuclei to initiate the formation of CuS. Elemental
sulfur could oxidize CuI easily to form the binary sulfide CuS.[21]
The solubility products (Ksp) of CuS (6.3”10À36) and Ag2S
(6.3”10À50) are different. Solvothermal conditions (high tem-
perature and high pressure) provide a strong driving force to
achieve the formation of the hierarchical flower-like Ag2S/CuS
binary composite by cation exchange. Initially, there is a small
amount of S2À ions in the reaction solution around the solid
CuS nanoflowers. Through the cation-exchange reaction be-
tween CuS and Ag+, Ag2S is deposited preferentially on the
surface of the CuS nanoflowers by in situ nucleation, which re-
sults in the formation of Ag2S/CuS heterostructures. UV-light ir-
radiation reduced partial Ag2S
Scheme 1. Illustration of the synthesis of the hierarchical flower-like
Ag/Ag2S/CuS ternary composite.
slight shifts of the Cu2p and S2p peaks for Ag2S/CuS and Ag/
Ag2S/CuS are observed because of the presence of the metal
sulfides[22,23] and electronic exchange at the interfaces from Cu
to Ag caused by the difference of the electronegativity of Cu
(1.9) and Ag (2.0; Figure 4B).[24] The XPS spectra of the S2p
region is characterized by a pair of peaks at binding energies
(BEs) of 162.2 and 163.3 eV, which are attributed to S2+ species
(Figure 4C).[25] Moreover, the slight shift and broadening of the
S2p peak indicates the presence of composite metal sulfides,
as expected.[26] The fitted Ag3d5/2 and Ag3d3/2 peaks of Ag/
Ag2S/CuS (Figure 4D) reveal that there are two valence states,
which are attributed to the high content of Ag2S (BE=
367.7 eV) and low content of Ag0 (BE=368.2 eV), respectively.
Moreover, the binding energy of the Ag3d peak in
to Ag0 species, and the Ag/Ag2S
nanoparticles formed are anch-
ored uniformly on the surface
of the CuS nanoflowers to con-
struct a hierarchical flower-like
Ag/Ag2S/CuS ternary hetero-
structure composite.
X-ray photoelectron spectros-
copy and UV/Vis spectroscopy
The elemental compositions
and chemical status of the dif-
ferent samples were analyzed
by X-ray photoelectron spec-
troscopy (XPS). The XPS survey
spectrum of Ag/Ag2S/CuS indi-
cates the existence of Cu2p,
S2p, and Ag3d (Figure 4A).
High-resolution XPS spectra of
Cu2p, Ag3d, and S2p are
shown in Figure 4B–D, respec-
tively. Compared with pure CuS,
Figure 4. A) Survey XPS spectrum of Ag/Ag2S/CuS and high-resolution scans of B) Cu2p, C) S2p, and D) Ag3d
peaks of the different samples.
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Ag/Ag2S/CuS is 0.2 eV lower than that in Ag2S/CuS, which is
caused by electron transfer at the interfaces between Ag2S and
Ag.
The UV/Vis diffuse reflectance spectra of the different sam-
ples are depicted in Figure 5. In comparison to the absorption
spectrum of CuS, there is an enhanced absorbance in the visi-
ble-light region (before l=550 nm) of the absorption spectra
Figure 5. UV/Vis diffuse reflectance spectra of CuS, Ag2S, Ag2S/CuS
(Cu-Ag-30), and Ag/Ag2S/CuS.
Figure 6. A) Photocatalytic degradation of 2,4-dichlorophenol by different
photocatalysts under visible-light irradiation: a) CuS, b) Cu-Ag-10, c) Cu-Ag-
30, d) Cu-Ag-50, and e) Ag/Ag2S/CuS. B) Trapping experiments for active spe-
cies during the photocatalytic reaction in the presence of different scaveng-
ers under visible-light irradiation.
of Ag2S/CuS and Ag/Ag2S/CuS caused by the addition of Ag2S.
The visible-light absorbance of Ag/Ag2S/CuS is higher than
that of Ag2S/CuS. Therefore, it can be inferred that the intro-
duction of Ag/Ag2S can increase visible-light absorption, and
a more efficient utilization of solar energy can be realized.
radical quantification experiments were designed. The addition
of isopropanol (IPA) and AgNO3 into the 2,4-dichlorophenol so-
Photocatalytic activity
lution has little effect on the photocatalytic activity of Ag/
À
C
The photocatalytic activities of the prepared samples were
evaluated by the degradation of 2,4-dichlorophenol in aqueous
solution under visible-light irradiation. To prove the synergetic
effect of the hybrid structure, control experiments with only
CuS were also performed. C is the concentration of 2,4-di-
chlorophenol after visible-light irradiation for a certain period,
and Co is the concentration of the 2,4-dichlorophenol after
reaching adsorption/desorption equilibrium in the dark (Fig-
ure 6A). All of the composites exhibit higher photocatalytic ac-
tivities than pure CuS (Figure 6A). The Ag/Ag2S/CuS ternary
heterostructure shows the highest photocatalytic performance,
which far exceeds that of pure CuS and Ag2S/CuS. These re-
sults confirm that the addition of Ag/Ag2S plays a positive role
in the photocatalytic process and that the heterojunctions fa-
cilitate charge transfer and separation. The assumption was
further verified by electrochemical impedance spectroscopy
(EIS). The Nyquist plot of Ag/Ag2S/CuS shows the smallest sem-
icircle in the middle-frequency region in comparison to that of
CuS and Ag2S/CuS (Figure S4), which indicates that Ag nano-
particles can function as an electron collector in the hetero-
structure and improve the interfacial charge transfer and sepa-
ration.
Ag2S/CuS, which suggests that both OH and e play a minor
role in the degradation of 2,4-dichlorophenol (Figure 6B). Con-
versely, the photocatalytic degradation of 2,4-dichlorophenol is
clearly inhibited after the addition of ammonium oxalate (AO)
and benzoquinone (BQ). Therefore, we can conclude that h+
CÀ
and O2 are the main active species in the 2,4-dichlorophenol
solution under visible-light irradiation. A similar result was ob-
tained with the Ag2S/CuS binary composite (Figure S5). The
result of the hydroxyl radical quantification experiment shows
that the fluorescent intensities of 2-hydroxyterephthalic acid
(TAOH) have no clear decrease with the extension of visible-
light irradiation time (Figure S6). This indicates that there is
C
C
little OH production and that OH is not the main active
oxygen species in the photocatalytic oxidation process.[27]
Meanwhile, a comparison of the hydroxyl radical quantification
shows that Ag/Ag2S/CuS has a larger output than Ag2S/CuS
(Figure S7), which further illustrates that the photocatalytic ac-
tivity of the Ag/Ag2S/CuS ternary composite is higher than that
of the Ag2S/CuS binary composite.
Based on these experimental results, a possible photocata-
lytic mechanism of the hierarchical Ag/Ag2S/CuS ternary com-
posite photocatalyst is shown in Figure 7. Under visible-light ir-
radiation, both CuS and Ag2S can be excited to form electron–
hole pairs, and the photogenerated electrons in their conduc-
To elucidate the photocatalytic reaction mechanism of this
+
C
CÀ
process, reactive species (h , OH, O2 ) trapping and hydroxyl
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dized to generate small molecular acids and the final products
CO2 and H2O. Hence, the reaction between organic radicals
with the superoxide radical species may be responsible for the
complete mineralization of 2,4-dichlorophenol.
To further investigate the degree of mineralization of 2,4-di-
chlorophenol, the total organic carbon (TOC) removal during
the degradation of 2,4-dichlorophenol by Ag/Ag2S/CuS under
visible-light irradiation was measured. The TOC removal effi-
ciency of the Ag/Ag2S/CuS ternary composite is 82% for 2,4-di-
chlorophenol after 240 min, which is higher than that of Ag2S/
CuS (Cu-Ag-30) and CuS (Figure 8A). These results showed
Figure 7. Possible photocatalytic mechanism of Ag/Ag2S/CuS under visible-
light irradiation.
tion bands (CB) transfer to Ag nanoparticles, which capture
photogenerated electrons in Ag/Ag2S/CuS.[28,29] The holes in
the valence band (VB) of CuS transfer to the VB of Ag2S. Ac-
cordingly, the separation of the photogenerated electron–hole
pairs in Ag/Ag2S/CuS is enhanced greatly. The electrons in the
Ag nanoparticles and the few remaining electrons in the CBs
of Ag2S and CuS display a strong reducing power, and the
holes in the VB of Ag2S and the few remaining holes in the VB
of CuS show a strong oxidizing ability. The highly reducing
CÀ
electrons will react with O2 to form O2 , which can further oxi-
dize 2,4-dichlorophenol. The holes located on the VB of Ag2S
will photocatalytically oxidize 2,4-dichlorophenol directly. The
results of the control experiment in an anoxic suspension (N2-
saturated conditions) showed a low photocatalytic activity,
CÀ
which indicates that O2 acts as an electron trap and that O2 is
the reactive species. For the Ag2S/CuS binary system, the
chance of recombination of the photogenerated electron–hole
pairs increased because of the absence of Ag (electron-capture
centers). This is also confirmed by the experimental photo-
catalysis results.
Figure 8. A) Profiles of TOC removal for the photodegradation of 2,4-di-
chlorophenol (50 mgLÀ1) with different catalysts under visible-light irradia-
tion, a) CuS, b) Ag2S/CuS (Cu-Ag-30), c) Ag/Ag2S/CuS. B) Degradation of 2,4-
dichlorophenol over several cycles with Ag/Ag2S/CuS under visible-light irra-
diation (>420 nm).
In the semiconductor photocatalytic process, many studies
showed that some degradation intermediates may be more
toxic than the initial materials.[30] Hence, the complete minerali-
zation of dye components before their discharge into waste-
water is important. In this study, stable organic intermediate
products generated during the degradation process were de-
tected by HPLC and identified by comparison with commercial
standards. Based on the degradation products identified by
HPLC (Figure S8), possible pathways for the degradation of 2,4-
dichlorophenol are shown in Figure S9. Notably, there are two
intermediates, 4-chlorophenol and phenol, during the initial re-
that, compared to the other systems, a higher degree of pho-
togenerated hole–electron pair excitation occurred for the Ag/
Ag2S/CuS ternary composite, which led to the generation of
more radical species and, in turn, greater pollutant mineraliza-
tion. Moreover, the TOC removal efficiency of the hierarchical
Ag/Ag2S/CuS ternary composite is in agreement with the re-
sults of the photocatalytic test (Figure 6A). This further proves
that the obtained hierarchical Ag/Ag2S/CuS ternary composite
shows a strong structure-induced enhancement of the photo-
catalytic performance in the photodegradation of 2,4-dichloro-
phenol.
C
action. The hot OH radical may undergo reactive collision with
phenol, which is converted rapidly to hydroquinone, and then
three main intermediates, phenol, benzoquinone, and hydro-
quinone, were detected at 60 min. With the extension of the
reaction time, the content of benzoquinone increased gradual-
ly. Benzoquinone might be formed from the oxidation of hy-
In addition to the photocatalytic activity, stability is another
important issue for the practical applications of a metal sulfide
photocatalyst. In our experiments, the stability of the hierarchi-
cal Ag/Ag2S/CuS ternary composite was evaluated by perform-
CÀ
droquinone and phenol by a large number of O2 radicals and
holes. Afterward, these aromatic intermediates are further oxi-
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cipitates were centrifuged and washed using deionized water and
absolute ethanol several times, followed by drying at 608C for 6 h.
ing cycling experiments under the same conditions. The hier-
archical Ag/Ag2S/CuS ternary composite does not exhibit an
evident loss of activity after four cycles, which indicates good
stability (Figure 8B). The high stability of the hierarchical
Ag/Ag2S/CuS ternary composite is attributed to the close inter-
action between CuS, Ag2S, and Ag, which can make the photo-
generated charge transfer and separation easy in the compo-
site system and effectively improves the stability of the
Ag/Ag2S/CuS composite under light irradiation.
Preparation of hierarchical Ag/Ag2S/CuS ternary composite
Ag2S/CuS powder (30 mg) was dispersed in ethanol (20 mL) and
subjected to perpendicular irradiation of 25 min under an 18 W UV
lamp. Afterwards, the product was rinsed with absolute ethanol
and dried at 508C overnight.
Characterization
Conclusions
XRD patterns of powder samples were measured by using a Bruker
D8 X-ray diffractometer using CuKa radiation (l=0.15405 nm,
40 kV, 100 mA). TEM and HRTEM images of samples were recorded
by using a JEOL 2100 microscope with a 200 kV accelerating volt-
age. SEM images were recorded by using a Hitachi S-4800 instru-
ment. UV/Vis diffuse reflectance spectra (DRS) were determined by
using a UV/Vis/NIR Spectrometer (PerkinElmer Lambda950). The
surface elements and their electronic states in the samples were
analyzed by XPS (Kratos-AXIS UL TRA DLD, AlKa X-ray source). The
EIS experiments were conducted by using a computer-controlled
potentiostat (Zahner Elektrik, Germany) and performed by applying
sinusoidal perturbations of 100 mV under a bias of 0 V in the dark
in the frequency range of 10 mHz to 1 MHz.
A new hierarchical Ag/Ag2S/CuS ternary composite has been
synthesized using the prepared flower-like CuS as a starting
material by cation exchange under solvothermal conditions
and subsequent in situ UV-light reduction. In this architecture,
intimate contact between the three components is crucial to
fulfill the heterojunction function for charge separation. There-
fore, the ternary nanostructures exhibit a markedly higher pho-
tocatalytic activity than the Ag2S/CuS binary composite and
single CuS nanoflowers under visible-light irradiation. In addi-
tion, the resultant Ag/Ag2S/CuS ternary composite possesses
excellent stability. The present approach for the construction
of hierarchical heterostructure composites can be extended to
design other complex metal sulfur systems, which might be
useful for applications in photocatalytic degradation and solar-
energy conversion devices.
Evaluation of photocatalytic activities and detection of inter-
mediates and active oxygen species
The photodegradation experiments were performed in a slurry re-
actor that contained 2,4-dichlorophenol (100 mL, 50 mgLÀ1) and
catalyst (0.05 g). A 300 W xenon lamp (Institute of Electric Light
Source, Beijing) was used as the simulated solar light source, and
visible light was achieved with the use of a 420 nm cutoff filter.
Before light irradiation, the suspension was kept in the dark under
stirring for 30 min to ensure the establishment of an adsorption/
desorption equilibrium. Oxygen flow was employed in all experi-
ments as the oxidant. Aliquots (5 mL) of the sample were with-
drawn after periodic intervals, centrifuged at 10000 rpm for 5 min
and filtered through a Milipore filter (pore size 0.22 mm) to
remove the residual catalyst particulates for analysis.
Experimental Section
Preparation of flower-like CuS
Typically, Cu(Ac)2·2H2O (0.5 mmol), ethanol (10 mL), and DMF
(10 mL) were used as the starting materials. Under magnetic stir-
ring, sulfur powder (1.5 mmol) was added to the system to create
a stable solution. The obtained solution was transferred to a 50 mL
Teflon-lined stainless-steel autoclave. The autoclave was sealed and
heated to 1608C, which was maintained for 3 h. After free cooling,
the as-synthesized mazarine product was rinsed with absolute eth-
anol and dried at 608C overnight.
2,4-Dichlorophenol and its degradation intermediates were identi-
fied and quantified by HPLC. The detection of 2,4-dichlorophenol
was performed at 275 nm by using a Varian Prostar 210 chromato-
graph with a UV/Vis detector and a C18 reversed-phase column
(25 cm”4.6 mm”5 mm, Supelco, Inc.). The mobile phase was a mix-
ture of acetonitrile, acetic acid, and water delivered at a ratio of 0.1
v/v at a flow rate of 1 mLminÀ1. The temperature of the column
was kept at 258C throughout the analysis. The injection volume
for all samples was 5 mL. The identification of the intermediates by
HPLC was performed by comparison of the retention time of the
peak in the discharged sample with that in a standard sample. The
concentrations of compounds were calculated using equations de-
rived from the calibration measurements of authentic samples.
Preparation of hierarchical Ag2S/CuS binary composite
The Ag2S/CuS composites were prepared by an in situ cation-ex-
change route. CuS (30 mg) was dispersed in ethanol (20 mL), and
then a specified quality of sliver nitrate solution in ethanol (10 mL)
was added quickly. The two solutions were mixed together and
stirred magnetically for 1 h, and then transferred into a 50 mL
Teflon-lined stainless-steel autoclave. The autoclave was heated
and maintained at 808C for 5 h, and then cooled to RT. The prod-
uct was collected, washed, and dried at 608C and maintained for
6 h. The molar ratios of Cu2+ to Ag+ were 10, 30, and 50, and the
resulting samples were labeled as Cu-Ag-10, Cu-Ag-30, and Cu-Ag-
50, respectively. For comparison, bare Ag2S was obtained by
a method reported previously.[18] In detail, AgNO3 (0.271 mmol) was
added to a stirred solution of l-cysteine (Cys; 0.271 mmol) in etha-
nol (40 mL), which gave a Cys/Ag+ molar ratio of 1:1. After stirring
for 15 min, the mixture was transferred into a 50 mL Teflon-lined
stainless-steel autoclave. The autoclave was sealed and heated to
1808C for 10 h and then cooled to RT naturally. The resulting pre-
To detect the active species during the photocatalytic reaction, IPA,
AO, BQ, and AgNO3 were added to the 2,4-dichlorophenol solution
dispersed with the Ag/Ag2S/CuS photocatalyst to capture hydroxyl
radicals, holes, superoxide radicals, and electrons, respectively, fol-
lowed by the photocatalytic activity test. In addition, an aqueous
solution that contained NaOH (10 mm) and terephthalic acid
C
(3 mm, C8H6O4, TA) was used to test the existence of OH by the
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This research was supported by the National Natural Science
Foundation of China (51272070, 21371053, 21376065), the Natu-
ral Science Foundation of Heilongjiang Province of China
(E201455), and the Postdoctoral science-research developmental
foundation of Heilongjiang province (LBH-Q13136).
Keywords: copper · environmental chemistry · ion exchange ·
photochemistry · silver
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Received: February 9, 2015
Revised: March 20, 2015
Published online on May 8, 2015
ChemCatChem 2015, 7, 1684 – 1690
www.chemcatchem.org
1690
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim