Tailoring AgI nanoparticles for the assembly of AgI/BiOI hierarchical hybrids with size-dependent photocatalytic activities

Article abstract of DOI:10.1039/c3ta10849j

A facile ion exchange route between BiOI hierarchical microspheres and AgNO₃ solution is explored to synthesize AgI/BiOI hierarchical hybrids that consist of AgI nanoparticles (NPs) uniformly anchored on the surface of BiOI nanosheets. With the addition of poly(vinylpyrrolidone) (PVP) surfactant molecules, the size of the AgI NPs can be tailored in the range of 55-16 nm. Evaluated by the photodecomposition of 2,4-dichlorophenol (2,4-DCP) solution under visible light irradiation, the AgI NPs/BiOI hybrids displayed highly efficient photocatalytic activities. What is more, as the size of the AgI NPs decreases, the AgI/BiOI hybrids exhibit enhanced photocatalytic performance, which is believed to be related to the larger number of surface active sites and faster spatial charge transfer. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ta10849j

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Materials Chemistry A
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Tailoring AgI nanoparticles for the assembly of AgI/BiOI
hierarchical hybrids with size-dependent photocatalytic
activities†
Cite this: DOI: 10.1039/c3ta10849j
a
a
a
a
a
Hefeng Cheng, Wenjun Wang, Baibiao Huang,* Zeyan Wang, Jie Zhan,
a
a
b
Xiaoyan Qin, Xiaoyang Zhang and Ying Dai
A facile ion exchange route between BiOI hierarchical microspheres and AgNO
3
solution is explored to
synthesize AgI/BiOI hierarchical hybrids that consist of AgI nanoparticles (NPs) uniformly anchored on
the surface of BiOI nanosheets. With the addition of poly(vinylpyrrolidone) (PVP) surfactant molecules,
the size of the AgI NPs can be tailored in the range of 55–16 nm. Evaluated by the photodecomposition
of 2,4-dichlorophenol (2,4-DCP) solution under visible light irradiation, the AgI NPs/BiOI hybrids
displayed highly efficient photocatalytic activities. What is more, as the size of the AgI NPs decreases,
the AgI/BiOI hybrids exhibit enhanced photocatalytic performance, which is believed to be related to
the larger number of surface active sites and faster spatial charge transfer.
Received 28th February 2013
Accepted 4th April 2013
DOI: 10.1039/c3ta10849j
www.rsc.org/MaterialsA
photocatalysts could exhibit strong visible light absorption,
which extends their eld of application. It is appealing that
Introduction
Since the rst report on the discovery of water splitting on the
when coupled with scaffold materials such as TiO
2 2 3
and Al O ,
1
TiO photoelectrode, semiconductor photocatalysis has been
2
the supported AgX hybrids show enhanced photocatalytic
21–23
paid immense attention in terms of solar energy conversion and performance as well as stability.
For instance, Hu and co-
2–5
22
the removal of harmful pollutants. However, single hetero- workers have prepared Ag/AgI supported on mesoporous
geneous photocatalysts, such as TiO and CdS, are restricted by alumina (Ag–AgI/Al O ), which showed high and stable activity
2
2
3
6
–8
their intrinsic wide band gaps or photocorrosion features. In for the photocatalytic mineralization of phenol derivatives. Very
order to take full advantage of the sunlight that concentrates in recently, we have demonstrated the highly efficient Ag/AgBr/
the visible and infrared regions, it is of great importance to BiOBr photocatalyst by ion exchange and subsequent photore-
24
exploit novel photocatalysts which work under visible light.
duction. The plasmonic oscillation processes of Ag NPs enable
Fortunately hybrid photocatalysts, which are generally
the Ag/AgBr/BiOBr hybrid to harvest light and transfer the
comprised of two or more active components, including metal/ photogenerated electrons effectively, guaranteeing its high
9–11
12–15
semiconductor hybrids
and composite semiconductors,
activity and stability. Nevertheless, in most cases the newly
have been proposed and well developed. For example, Zong deposited AgX phases are micron-sized agglomerates and lack
16
et al. loaded MoS
2
on CdS catalyst, and found that the H
2
close connection with the original supports, thereby leading to
evolution rate was greatly enhanced with respect to their indi- the increased recombination of the photogenerated carriers. In
vidual counterparts. These hybrid photocatalysts integrate the contrast, nanomaterials, which are dened as materials with
synergistic effects of the species at several levels, which provides
the feasibility and versatility to optimize their optical and
catalytic performances.
sizes ranging from 1 to 100 nm in at least one dimension,
usually display exceptional physicochemical properties that are
25–27
derived from their quantized sizes.
Moreover, nano-
Recently, AgX-based (X ¼ Cl, Br and I) photocatalysts have materials will bring photocatalysts with more active sites and
attracted interest for their considerable activities in the photo- higher surface/volume ratio. Therefore, in view of the highly
17–20
oxidation of organic contaminants.
Due to the localized efficient semiconductor photocatalysis, it is signicant and
surface plasmon resonance (LSPR) of Ag NPs that are derived indispensable to design rational approaches to synthesize silver
from the partial reduction of the silver halides, the Ag/AgX halide nanomaterials with controlled sizes and shapes, which
endow the hybrids with enhanced activity and chemical
State Key Lab of Crystal Materials, Shandong University, Jinan 250100, China. stability, however this remains a challenge.
a
E-mail: bbhuang@sdu.edu.cn
Herein, we demonstrate a facile ion exchange route between
b
School of Physics, Shandong University, China
BiOI hierarchical microspheres and AgNO solution to synthe-
3
†
Electronic supplementary information (ESI) available: Fig. S1–S8. See DOI:
size AgI NPs/BiOI hybrids. AgI NPs are uniformly anchored
1
0.1039/c3ta10849j
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in situ onto the surface of BiOI nanosheets, and can be tailored were collected on a Shimadzu UV 2550 recording spectropho-
in the range of 55–16 nm in the presence of PVP surfactant tometer equipped with an integrating sphere.
molecules. The AgI/BiOI hybrids could decompose 2,4-DCP
solution efficiently under visible light irradiation, and also
displayed activity dependent on the size of the AgI NPs. The
Photocatalytic evaluation
The photocatalytic activities of the samples were evaluated by
the decomposition of 2,4-DCP under visible light irradiation at
room temperature. A 300 W Xe arc lamp (PLS-SXE300, Beijing
Trusttech Co., Ltd.) equipped with an ultraviolet cutoff lter to
provide visible light (l $ 420 nm) was used as the light source.
controlled ion exchange route to the AgI/BiOI hybrids provides
operational simplicity, and may allow generalized access to
other heterostructured inorganic materials.
Experimental
Preparation of BiOI microspheres
The sample powder (100 mg) was suspended in 2,4-DCP (20 mg
ꢁ1
L
, 100 mL) solution with constant stirring. Prior to irradia-
The BiOI hierarchical microspheres were synthesized by an tion, the suspension was stirred in the dark for 1 h to ensure
ionic liquid-assisted solvothermal approach. In brief, adsorption–desorption equilibrium. At intervals, 5 mL of the
Bi(NO ) $5H O (0.97 g) was dissolved in 40 mL of ethylene suspension was abstracted for the following analysis with
3
3
2
glycol (EG) solution with magnetic stirring, and another EG centrifugation. The 2,4-DCP decomposition was analyzed by
40 mL) solution containing 1-hexyl-3-methylimidazolium UV-Vis spectrophotometry.
iodide ([C Mim]I, 0.88 g) was introduced. The resulting mixture
(
6
was stirred for a further 10 min and transferred into a 100 mL
Results and discussion
Teon-lined stainless steel autoclave. The autoclave was heated
ꢀ
and maintained at 160 C for 6 h, and then cooled down to As a category of ternary semiconductors, BiOX (X ¼ Cl, Br and I)
room temperature naturally. The product was washed and dried materials that crystallize in layered structures have displayed
ꢀ
at 80 C.
important applications in pharmaceuticals, pigments as well as
29–33
photocatalysis.
Among them, BiOI is the most attractive as it
Preparation of the AgI/BiOI hybrids
has the smallest band gap (ꢂ1.7 eV), which makes it a prom-
ising candidate for visible light-driven photocatalysis. To date, a
variety of BiOI architectures across multiple dimensions,
The AgI/BiOI hierarchical hybrids were prepared by an ion
exchange route. AgNO (0.085 g) was rst dissolved in 100 mL
3
34
35
including nanoparticles, nanosheets or nanoplates, and
EG containing different concentrations of PVP (K-30) with
magnetic stirring. Then the as-obtained BiOI sample (0.352 g)
was added to the solution with ultrasonic dispersion for 2 min
and vigorously stirred for a further 2 h. The product was
36,37
microspheres
have been reported. Despite much progress,
single BiOI nanomaterials can hardly meet practical demands,
and great efforts are required to boost their photocatalytic
activity by semiconductor hybridization.
In our strategic design, the prerequisite is to prepare the
BiOI hierarchical architectured scaffolds. By adopting an ionic
liquid-assisted solvothermal approach, we have synthesized
ꢀ
collected, washed and dried at 80 C. For comparison, bulk AgI
was prepared through the direct precipitation of AgNO and KI
3
aqueous solutions. The AgI/BiOI composite was also prepared
by a one-step co-precipitation method according to our previous
19
study. As an extension, AgCl/BiOCl hybrids were also
prepared. Firstly, BiOCl hierarchical microspheres were
14
obtained as described elsewhere. Aerwards, the AgCl/BiOCl
hybrids were obtained by the ion exchange method mentioned
above. In addition, N-doped TiO
2
(N-P25), which was used as the
reference photocatalyst, was prepared according to the method
28
previously reported.
Materials characterization
Powder X-ray diffraction (XRD) patterns were recorded on a
Bruker AXS D8 advance powder diffractometer with Cu Ka
radiation. Scanning electron microscopy (SEM) images were
obtained on a Hitachi S-4800 microscope. Nitrogen adsorption–
desorption measurements were performed on a BEL-SORP max
(BEL Japan, Inc.) apparatus, and the surface area was deter-
mined by the Brunauer–Emmett–Teller (BET) method at a
relatively low P/P range (0.05–0.35). X-ray photoelectron spec-
0
troscopy (XPS) measurements were carried out on a Thermo
Fisher Scientic Escalab 250 spectrometer with mono-
chromated Al Ka excitation, and C 1s (284.6 eV) was used to
Fig. 1 (a) XRD pattern and (b–d) typical SEM images of the BiOI hierarchical
calibrate the peak position. UV-vis diffuse reectance spectra microspheres with different magnifications.
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3 3 6
BiOI hierarchical microspheres using Bi(NO ) and [C Mim]I
ionic liquid as the starting materials. The XRD pattern (Fig. 1a)
shows that the microspheres can be assigned to tetragonal BiOI.
With diameters of 3–5 mm, the as-obtained three dimensional
(3D) BiOI hierarchical microspheres are constructed by
numerous two dimensional (2D) interlaced nanosheets, and
enlarged microscopy shows that the surface of the BiOI nano-
sheets is clean (Fig. 1b–d). In addition, the N
erties of the BiOI hierarchical microspheres were determined
Fig. S1, ESI†). We can see that the N adsorption–desorption
2
sorption prop-
(
2
isotherm is a representative type-IV isotherm, suggesting the
presence of mesopores. The BET surface area of the BiOI hier-
2
ꢁ1
archical microspheres was measured to be 44.7 m g . Such a
D hierarchical architecture with high surface area provides
3
more surface sites for coupling with other semiconductor
nanomaterials.
Aerwards, the ion exchange reaction between the BiOI
microspheres and AgNO in EG solution at room temperature
3
was carried out and gave rise to AgI NPs, thereby leading to the
AgI NPs/BiOI hierarchical hybrids. PVP, a kind of organic
surfactant, was introduced to tailor the sizes of the AgI NPs.
Fig. 2 presents the SEM images of the as-synthesized AgI NPs/
BiOI hybrids by ion exchange reactions with different concen-
trations of PVP in EG. From the low magnication images of the
single microspheres (Fig. 2a–d) and macroscale products
(Fig. S2, ESI†), it can be observed that the AgI/BiOI hybrids
maintain similar sizes and hierarchical architectures to the
BiOI microspheres during the ion exchange reaction. However,
the detailed surface information differs in the higher magni-
cation SEM images (Fig. 2e–h) of these AgI/BiOI hybrids. In the
absence of PVP, the prepared AgI NPs with sizes of 55 ꢃ 15 nm
are intricately dispersed on the surface of the BiOI nanosheets,
and some have dropped off (Fig. 2e, corresponding to sample 1
in Table 1). Intriguingly, with the addition of PVP (Fig. 2f–h,
corresponding to samples 2–4 in Table 1), smaller AgI NPs are
anchored onto the BiOI nanosheets with a high degree of
uniformity, and a narrower size distribution of AgI NPs is also Fig. 2 SEM images of the AgI/BiOI hybrids prepared by ion exchange reactions
found. It is worth noting that in the case of the AgI/BiOI hybrid with different concentrations of PVP in EG: (a and e) 0, (b and f) 0.5, (c and g) 1.0
ꢁ
1
ꢁ
1
and (d and h) 2.0 g L . The mean sizes of the AgI nanoparticles were measured to
prepared with a PVP concentration of 2.0 g L (Fig. 2h), AgI NPs
with the smallest sizes of 16 ꢃ 3 nm are formed on the surface
of the BiOI nanosheets. Nevertheless, a higher PVP concentra-
be 55 ꢃ 15, 36 ꢃ 7, 24 ꢃ 5 and 16 ꢃ 3 nm, respectively, from the evaluation of
60 particles.
ꢁ
1
tion (3.0 g L ) does not favor the production of AgI NPs with
smaller sizes (Fig. S3, ESI†), but increases the complexity of the
procedure instead. The BET surface areas of the AgI NPs/BiOI
hybrids synthesized with PVP concentrations of 0, 0.5, 1.0 and
38–42
new way to synthesize diverse nanostructures.
experiments, the BiOI hierarchical architectures are employed
as the iodine source to react with Ag in solution by ion
In our
+
ꢁ1
2
ꢁ1
2
.0 g L were measured to be 28.5, 26.9, 26.4 and 25.5 m g ,
respectively. The surface area of the AgI/BiOI hybrids is smaller
than that of the BiOI microspheres, and this indicates that ion
exchange indeed degrades the BiOI nanosheets, which could be
seen from the partial replacement of BiOI nanosheets’ surface
by AgI NPs in the higher magnication SEM images (Fig. 2e–h).
The textural properties of the AgI/BiOI hybrids synthesized by
ion exchange routes are summarized in Table 1.
Due to its low solubility (KSP ¼ 8.52 ꢄ 10 ), AgI is inclined
to grow into bigger particles under non-equilibrium solution
conditions. Ion exchange, which allows mutual diffusion of ions
between the precursor and incoming species, has opened up a
Table 1 The AgI NPs sizes, surface area and photocatalytic activities towards 2,4-
DCP decomposition under visible light irradiation for 1 h of the AgI/BiOI hybrids
synthesized with different PVP concentrations
C
PVP
Decomposed 2,4-DCP
(%)
ꢁ1
2
ꢁ1
Samples (g L
)
DAgI (nm)
S
BET (m g )
ꢁ
17
1
2
3
4
0
55 ꢃ 15
36 ꢃ 7
24 ꢃ 5
16 ꢃ 3
28.5
26.9
26.4
25.5
40.7
51.1
65.8
77.8
0.5
1.0
2.0
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ꢁ
1
exchange to synthesize the AgI/BiOI hybrid photocatalyst, as 2.0 g L , respectively. The results match well with SEM
shown in eqn (1) below.
BiOI + Ag / AgI + BiO
It is noted that the ion exchange reaction between BiOI and
observations, verifying the rational control of AgI NPs in the
presence of PVP surfactant.
+
+
(1)
XPS measurements were also carried out to examine the
surface chemical states of the Ag element before and aer the
photocatalytic cycling experiments (Fig. 3B). As can be seen, both
of the Ag 3d core spectra exhibit narrow Gauss-shaped
symmetry. The Ag 3d5/2 binding energy values of the fresh and
used AgI/BiOI hybrids are located at 367.4 and 367.6 eV,
respectively, which suggests that the Ag element exists only in
+
Ag proceeds in EG solvent, preventing the unwanted precipi-
+
tation of BiO ions. Different from the conventional ion
exchange that takes place in ionic compounds such as metal
chalcogenides, the presence of covalent bonding in the multi-
element BiOI semiconductor increases the solvation energy and
0
19
the form of AgI, and no metallic Ag is present. On the basis of
the XRD and XPS results, their structural stability towards pho-
tocorrosion makes the AgI/BiOI hybrids potential candidates for
highly efficient photocatalysis. The UV-vis diffuse reectance
spectra of the as-prepared AgI/BiOI hybrids were measured to
investigate their optical properties (Fig. S5, ESI†). It can be seen
that both bulk AgI and BiOI hierarchical microspheres show a
strong visible light response, while their absorption edges are
located at around 460 and 700 nm, respectively. Aer the surface
decoration with AgI NPs, the absorption of the the resulting AgI/
BiOI hybrids also cover the visible light range. In addition, with
the increase of the PVP concentration in the ion exchange
synthesis, the photoabsorption intensity of the corresponding
AgI/BiOI hybrids becomes weaker, which may arise from the
shielding effect of the smaller AgI NPs that are anchored on the
40
impedes the extent of transformation into AgI. In addition, the
interlaced BiOI nanosheets prevent the aggregation of AgI NPs
in the subsequent growth by self-connement. For comparison,
bulk AgI and AgI/BiOI composites were also prepared by direct
19
precipitation and co-precipitation methods, respectively.
However, only irregular AgI agglomerates (Fig. S4a and b, ESI†)
and AgI particles with sizes of about 400 ꢃ 100 nm scattered on
the BiOI nanoplates (Fig. S4c and d, ESI†) are observed. It is
generally accepted that under the action of charged ions (e.g.,
ꢁ
ꢁ
ꢁ
43,44
F , Cl and Br )
or polymeric species (e.g., PVP and oleyl-
18,45
amine),
inorganic nanocrystals can be tuned by separation
of the nucleation and growth stages. Therefore, in our experi-
ments, AgI NPs are nucleated in situ on the BiOI nanosheets and
then tuned by the addition of PVP surfactant with moderate
concentrations in the following growth stage. Aer ion
exchange for 2 h, the sizes of the AgI NPs were tailored in the
range of 55 to 16 nm.
Powder XRD was used to determine the phase structure of
the products. As shown in Fig. 3A, AgI (JCPDS no. 09-0374) and
BiOI (JCPDS no. 73-2062) co-exist in all the AgI/BiOI hybrid
samples formed by ion exchange reaction, regardless of the
PVP concentration. In addition, it is found that with the
increase of PVP addition, the (110) diffraction peak of AgI
becomes wider, indicating the smaller size of AgI. According to
the Scherrer equation, the grain sizes of the AgI NPs are esti-
mated to be 55.6, 33.6, 24.8 and 18.2 nm for the AgI/BiOI
hybrids synthesized with PVP concentrations of 0, 0.5, 1.0 and
13
BiOI nanosheets surface.
In the present study, the addition of PVP allows us to
successfully tune the sizes of the AgI NPs. As an extension, we
have also applied this synthetic protocol to obtain the AgCl/
BiOCl hybrids using BiOCl hierarchical architectures by ion
exchange (Fig. 4). Without PVP, the cube-like AgCl particles
(
mean size: 340 ꢃ 100 nm) are unevenly dispersed on the BiOCl
hierarchical microspheres, and some aggregates are also
observed (Fig. 4a). When PVP (2.0 g L ) was introduced, the ion
ꢁ1
Fig. 3 (A) XRD patterns of the AgI/BiOI hybrids prepared by ion exchange
reactions with different concentrations of PVP in EG: (a) 0, (b) 0.5, (c) 1.0 and (d)
Fig. 4 SEM images of the AgCl/BiOCl hybrids synthesized by ion exchange
reactions (a) without PVP and (b) with the addition of PVP; (c) XRD patterns of the
AgCl/BiOCl hybrids; (d) UV-vis diffuse reflectance spectra of BiOCl and the AgCl/
BiOCl hybrid.
ꢁ1
2
.0 g L . The asterisks denote the diffraction peaks of AgI. (B) XPS spectra of (a)
the freshly prepared and (b) used AgI/BiOI hybrid samples after the photo-
catalytic recycling experiments.
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exchange reaction between the BiOCl architectures and AgNO
3
AgI/BiOI hybrid synthesized by ion exchange in the presence of
ꢁ1
gave rise to AgCl nanocubes with an edge length of 130 ꢃ 30 nm, PVP (2.0 g L ) showed the best photocatalytic performance,
which were dispersed quasi-uniformly on the surface of the which could reach as high as 77.7% in only 60 min (Fig. S6,
BiOCl hierarchical microspheres (Fig. 4b). Under the synergistic ESI†) and nally reached 80.3% aer visible light irradiation for
effect of ion exchange and the polymeric surfactant molecules, 90 min. The photocatalytic decomposition of 2,4-DCP solution
AgCl nucleates and grows slowly into nanocubes with smaller over the AgI/BiOI hybrid synthesized by ion exchange was about
18,44
sizes.
JCPDS no. 31-1238) and tetragonal BiOCl (JCPDS no. 73-2060) by co-precipitation mentioned above. The particle sizes of AgI
in the AgCl/BiOCl hybrids. From the UV-vis diffuse spectra against the photocatalytic performance of the AgI/BiOI hybrids
Fig. 4d), the BiOCl sample has strong response in the ultravi- are plotted in Fig. 5b. A monotonic decreasing correlation is
XRD patterns (Fig. 4c) show the presence of cubic AgCl 3 times faster than that of the AgI/BiOI composites synthesized
(
(
olet region with an absorption edge at 380 nm. In contrast, the observed between AgI size and the photocatalytic performance
AgCl/BiOCl hybrid displays evident absorption across the visible of the AgI/BiOI hybrids. When the AgI particle size decreased
light region. The dramatic visible light absorption enhance- from 400 to 55, and ultimately to 16 nm, the corresponding
ment with a convex peak around 550 nm is attributed to the photocatalytic efficiency of the AgI/BiOI hybrid increased from
0
LSPR of metallic Ag nanoparticles, which stems from the 22.6% to 40.6%, and to 77.7%. As summarized in Table 1,
17
partial reduction of AgCl upon light exposure.
obviously, smaller AgI NPs are more active than larger ones,
To elucidate the relationship between microstructure and thus leading to the size-dependent photocatalytic properties of
properties, the photocatalytic activities of the AgI/BiOI hybrids the AgI/BiOI hybrids.
were evaluated by the decomposition of 2,4-DCP solution under
In consideration of the practical applications, an efficient
visible light irradiation (l $ 420 nm), eliminating inuences photocatalyst is supposed to be stable to photocorrosion. Aer
such as dye sensitization. As shown in Fig. 5a, the BiOI hierar- ve cycles of photocatalytic experiments, the AgI/BiOI hybrids
chical microspheres could decompose about 56.5% of the 2,4- did not show a clear decrease in photocatalytic activity (Fig. S7,
DCP molecules aer irradiation for 90 min, while bulk AgI ESI†). In addition, the structural stability of the AgI/BiOI
showed negligible photocatalytic performance. As a reference hybrids was also veried by XRD (Fig. S8, ESI†) and XPS (Fig. 3B)
material, the N-doped TiO (N-P25) sample displayed a rather results. The good stability of the structure as well as perfor-
2
low photocatalytic efficiency of ca. 4% aer irradiation for 90 mance makes the AgI/BiOI hybrids efficient photocatalysts
min. In the case of the AgI/BiOI composites, it could decompose working under visible light.
31.8% of 2,4-DCP molecules in 90 min. It is noted that the
The highly efficient photocatalytic performances of the AgI
NPs/BiOI hybrids are associated with their interfacial structures,
as is depicted in Fig. 5c. According to our previous band potential
calculations, the conduction band (CB) edge of AgI (ꢁ0.55 eV) is
more negative than that of BiOI (0.58 eV), while the valence band
(
(
VB) edge of BiOI (2.31 eV) is more positive than that of AgI
2.25 eV). Upon exposure to visible light, both AgI and BiOI are
19
excited to generate the electron–hole pairs. The staggered band
potentials of the AgI and BiOI semiconductors are benecial to
reduce the recombination of photoexcited carriers in the AgI/
BiOI hybrids. Meanwhile, the stability of AgI is also ensured by
ꢁ
the interfacial transfer of the photogenerated electrons (e ) from
+
AgI to BiOI, preventing its coupling with the interstitial Ag to
0
form metallic Ag . Once they have migrated to the surface of
BiOI, the photoexcited electrons would then be trapped by the
ꢁ
dissolved oxygen to form the superoxide radical (O _ ) or other
2
22
oxidative species. At the same time, the photoexcited holes le
in the VB of AgI and BiOI could also oxidize and further miner-
24
alize the organics. Therefore, in comparison with their single
counterparts (BiOI microspheres or bulk AgI), the effective
interfacial charge transfer enables the AgI/BiOI hybrids to
exhibit superior photocatalytic performances.
On the other hand, by means of ion exchange reactions, AgI
NPs are generated and anchored in situ onto the surface of the
BiOI nanosheets. This synthetic process means the AgI NPs are
dispersed uniformly on the BiOI architectures with close
contact, facilitating the interfacial charge transfer more effi-
ciently. In contrast, poor dispersity and loose connection
appears in the AgI/BiOI composites prepared by co-precipita-
tion, which increases the recombination rate of the
Fig. 5 (a) Photocatalytic activities towards 2,4-DCP decomposition over different
samples under visible light irradiation (l $ 420 nm); (b) the photocatalytic effi-
ciencies of the AgI/BiOI hybrids versus the particle size of AgI under visible illu-
mination for 1 h; (c) scheme of the charge transfer process of the AgI/BiOI hybrids
exposed to visible light.
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Acknowledgements
This work was nancially supported by the National Basic 30 X. Zhang, Z. H. Ai, F. L. Jia and L. Z. Zhang, J. Phys. Chem. C,
Research Program of China (2013CB632401), the National 2008, 112, 747.
Natural Science Foundation of China (20973102, 51021062 and 31 H. F. Cheng, B. B. Huang, Z. Y. Wang, X. Y. Qin, X. Y. Zhang
51072098) and the Natural Science Foundation of Shandong
and Y. Dai, Chem.–Eur. J., 2011, 17, 8039.
Province (ZR2010EM028).
32 J. Jiang, K. Zhao, X. Y. Xiao and L. Z. Zhang, J. Am. Chem. Soc.,
2012, 134, 4473.
3
3 Y. Y. Liu, W.-J. Son, J. B. Lu, B. B. Huang, Y. Dai and
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J. Mater. Chem. A
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