In situ synthesis of hierarchical In2S3-graphene nanocomposite photocatalyst for selective oxidation

Article abstract of DOI:10.1039/c4ra13764g

We report a simple, in situ hydrothermal way to fabricate In₂S₃-graphene (GR) nanocomposites in which hierarchical In₂S₃ "petals" spread over the surface of GR sheets in virtue of the "structure directing" role of graphene oxide (GO) as the precursor of GR in a solution phase. With the addition of an appropriate amount of GO, the hierarchical petal-like In₂S₃ structures have been successfully grown on the two-dimensional (2D) GR "mat". The as-synthesized In₂S₃-GR nanocomposites featuring good interfacial contact exhibit much higher photocatalytic activity toward selective oxidation of alcohols under visible light irradiation than blank In₂S₃. A series of characterization results disclose that the significantly enhanced photocatalytic performance of In₂S₃-GR nanocomposites can be ascribed to the integrative effect of the increased separation and transfer efficiency of photogenerated electron-hole pairs and the larger surface area. This work highlights the wide scope of fabricating GR-based semiconductor nanocomposites with specific architectural morphology by rationally utilizing the "structure directing" property of GO and extending their applications toward photocatalytic selective transformations. This journal is

Full text of DOI:10.1039/c4ra13764g

RSC Advances
View Article Online
View Journal | View Issue
PAPER
In situ synthesis of hierarchical In S –graphene
2
3
nanocomposite photocatalyst for selective
Cite this: RSC Adv., 2014, 4, 64484
oxidation†
Xiuzhen Li, Bo Weng, Nan Zhang and Yi-Jun Xu*ab
ab
ab
ab
We report a simple, in situ hydrothermal way to fabricate In
hierarchical In “petals” spread over the surface of GR sheets in virtue of the “structure directing” role
of graphene oxide (GO) as the precursor of GR in a solution phase. With the addition of an appropriate
amount of GO, the hierarchical petal-like In structures have been successfully grown on the two-
dimensional (2D) GR “mat”. The as-synthesized In –GR nanocomposites featuring good interfacial
contact exhibit much higher photocatalytic activity toward selective oxidation of alcohols under visible
light irradiation than blank In . A series of characterization results disclose that the significantly
enhanced photocatalytic performance of In –GR nanocomposites can be ascribed to the integrative
2 3
S –graphene (GR) nanocomposites in which
2 3
S
2 3
S
2 3
S
2 3
S
2 3
S
Received 30th September 2014
Accepted 14th November 2014
effect of the increased separation and transfer efficiency of photogenerated electron–hole pairs and the
larger surface area. This work highlights the wide scope of fabricating GR-based semiconductor
nanocomposites with specific architectural morphology by rationally utilizing the “structure directing”
property of GO and extending their applications toward photocatalytic selective transformations.
DOI: 10.1039/c4ra13764g
www.rsc.org/advances
Generally, the synthetic method for fabrication of GR–
Introduction
semiconductor nanocomposites can be summarized as two
9,12,34
In recent years, with the advance of two-dimensional (2D) gra- categories.
One is the hard integration of GR with solid
1
phene (GR) as an electrically conductive platform, there has semiconductor components and the other is the so integration
been increasing interest in designing GR–semiconductor of graphene oxide (GO), as the precursor of GR, with soluble
10,21
composites as efficient photocatalysts for converting solar semiconductor precursors.
For the hard integration method,
2–10
energy into chemical energy.
the brilliant physical and chemical properties of GR,
GR–semiconductor nanocomposites have been extensively contact is oen poor.
Through taking advantage of the GR–semiconductor composites are obtained by the simple
1
1–16
diverse integration of GR with solid semiconductor, and the interfacial
21,35,36
In contrast, for the so integration
reported to show enhanced photocatalytic performance toward method, the “structure directing” role of GO in an aqueous
a myriad of applications, including photodegradation of phase can be readily utilized, which could promote the in situ
pollutants (dyes, volatile organic pollutant, and bacteria), anchoring of semiconductor particles onto the surface of
hydrogen production from water splitting, and photocatalytic reduced graphene oxide (RGO, also oen called GR) mat in a
4
,10,17–35
selective organic transformations.
solution phase. In this way, the as-obtained GR–semiconductor
nanocomposites oen have good interfacial contact, which is
advantageous to the efficient separation of photogenerated
charge carriers across the interfacial domain, thereby contrib-
uting to the enhanced photocatalytic performance of the GR–
a
State Key Laboratory of Photocatalysis on Energy and Environment, College of
Chemistry, Fuzhou University, Fuzhou, 350002, P. R. China
10,32,33
b
College of Chemistry, Fuzhou University, New Campus, Fuzhou, 350108, P. R. China. semiconductor nanocomposites.
E-mail: yjxu@fzu.edu.cn; Tel: +86 591 83779326
Electronic supplementary information (ESI) available: Experimental section for
preparation of graphene oxide; the chemical structure of L-cysteine; the Fourier
transformed infrared spectra (FTIR) of In –1%GR and the original GO; the
plot of transformed Kubelka–Munk function versus the energy of light for blank
In and In –GR nanocomposites with different weight addition ratios of GR;
Indium sulde (In S ), as one of the common studied
2 3
†
semiconductors, is well crystallized into three polymorphic
forms, including a-In , b-In and g-In . Among these
three forms, b-In with a narrow band gap, has been widely
used as a kind of potential photocatalyst under visible light
2
S
3
2
S
3
2 3
S
2 3
S
2 3
S
2
S
3
2 3
S
remaining fraction of various alcohols aer the adsorption–desorption irradiation due to its excellent photosensitivity, photoconduc-
equilibrium is achieved over blank In
2
S
3
and In
2
S
3
–1%GR; ESR spectra of
tivity, stable chemical and physical properties, and low
ꢀ
radical adduct trapped by DMPO (DMPO–O
2
c ) over In
2
S
3
–1%GR suspension in
37–42
toxicity.
erties for b-In2S3 in photocatalysis, much effort has been
devoted to constructing In based materials with different
Thus far, in order to make better use of the prop-
the BTF solution without or with the visible light irradiation; summary of BET
surface area and pore volume of blank In and In –1%GR. See DOI:
0.1039/c4ra13764g
2
S
3
2 3
S
2 3
S
1
64484 | RSC Adv., 2014, 4, 64484–64493
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
3
7,38,43,44
morphologies,
such as one-dimensional (1D) In
2
S
3
adjusted to 8 by adding 1 M NaOH dropwise. Aer stirring for 1
37,45
nanotubes and nanorods,
2D In S nanoplates and nano- h, the mixture was transferred into a 50 mL Teon-lined
2 3
41,46
sheets,
three-dimensional (3D) owerlike In S and hierar- stainless steel autoclave, which was sealed and treated at 180
2 3
chical architectures.
38,40,47
ꢁ
Among them, hierarchical
C for 16 h. Subsequently, the as-synthesized products were
architectures, with modied structural, optical, and surface separated by centrifugation and washed with distilled water and
properties, are potentially useful for the application of absolute ethanol for three times and one time, respectively.
48,49
ꢁ
photocatalysis.
Herein, we report a facile, in situ wet chemistry way to obtained.
fabricate hierarchical In –GR nanocomposites to boost the (c) Preparation of blank owerlike In
photoactivity of 3D In S . To the best of our knowledge, this is owerlike In S structures were fabricated through the same
Aer drying at 60 C overnight, the target products were
2
S
3
2 3
S structures. Blank
2
3
2 3
the rst report on the application of In S –GR nanocomposites procedure as above except for the addition of GO.
2
3
as visible light-driven photocatalyst for selective oxidation
process. The higher photoactivity achieved on In –GR than
blank In toward selective oxidation of alcohols under visible
2 3
S
Characterization
2 3
S
light is mainly ascribed to the enhanced photogenerated elec- The crystal-phase information of the samples was measured on
tron–hole pairs separation and transfer as well as the larger a Bruker D8 Advance X-ray diffractometer with Cu Ka radiation
ꢁ
ꢁ
surface area, resulting from the hierarchical architectures at 40 kV and 40 mA in the 2q ranging from 10 to 80 with a scan
ꢁ
ꢀ1
which are oriented by the “structure directing” role of GO. It is rate of 0.02
s . The UV-vis diffuse reectance spectroscopy
hoped that this work could provide useful information for (DRS) was used to characterize the optical properties of the
careful design of GR–semiconductor nanocomposites with samples using UV-vis spectrophotometer (Cary 500, Varian) in
controllable architectures by making better use of the “structure which BaSO4 was employed as a reference. Field-emission
directing” property of GO and extending their applications scanning electron microscopy (FESEM) was employed to
toward various photocatalytic selective transformations.
detect the morphology of the samples on a FEI Nova NANOSEM
30 spectrophotometer. Transmission electron microscopy
TEM) images and high-resolution transmission electron
2
(
Experimental section
Materials
microscopy (HRTEM) images were obtained using a JEOL model
JEM 2010 EX instrument at an accelerating voltage of 200 kV.
The Fourier transformed infrared spectroscopy (FTIR) was
measured on a Nicolet Nexus 670 FTIR spectrophotometer at a
Indium(III) nitrate hydrate (In(NO
3
)
3
$4.5H
S), graphite powder, sulfuric acid (H SO
), hydrochloric acid (HCl), sodium hydroxide (NaOH),
), phosphorus pentoxide (P ),
potassium permanganate (KMnO ), hydrogen peroxide 30%
2
O), L-cysteine
(C
3
H
7
NO
2
2
4
), nitric acid
ꢀ
1
resolution of 4 cm . The photoluminescence (PL) spectra were
obtained using an Edinburgh FL/FS900 spectrophotometer with
an excitation wavelength of 420 nm. The nitrogen adsorption–
desorption isotherms and Brunauer–Emmett–Teller (BET)
specic surface areas were obtained on Micromeritics
ASAP2010 equipment. The electron spin resonance (ESR) signal
of the radicals spin-trapped by 5,5-dimethyl-1-pyrroline-N-oxide
(HNO
3
potassium persulfate (K
2
S
2
O
8
2 5
O
4
(
H O ), ethanol (C H O), benzyl alcohol (C H O), ammonium
2 2 2 6 7 8
oxalate (N H C O , AO), benzoquinone (C H O , BQ), and tert-
2
8
2
4
6
4 2
butyl alcohol (C
chemical reagent Co., Ltd. (Shanghai, China). Benzotriuoride
, BTF), 4-methylbenzyl alcohol (C 10O), 4-methoxy-
benzyl alcohol (C ), 4-nitrobenzyl alcohol (C NO ),
-chlorobenzyl alcohol (C OCl), 4-uorobenzyl alcohol
C H OF), cinnamyl alcohol (C H O), and 3-methyl-2-buten-1-
4
H10O, TBA) were supplied by Sinopharm
(DMPO) was measured on a Bruker EPR A300 spectrometer. The
(C
7
H
5
F
3
8
H
sample (5 mg) was dispersed in 0.5 mL puried benzotriuoride
into which 25 mL of DMPO–benzyl alcohol solution (1 : 10, v/v)
was added. The mixture was oscillated to obtain well-blending
suspension. The irradiation source (l > 420 nm) was a 300 W
Xe arc lamp system, the very light source for our photocatalytic
selective oxidation of alcohols. The settings for the ESR spec-
trometer were as follows: center eld ¼ 3512 G, microwave
frequency ¼ 9.86 GHz, and power ¼ 6.35 mW. The photo-
electrochemical analysis was conducted in a homemade three
electrode cell. A Pt plate was employed as the counter electrode
8
H
10
O
2
7
H
7
3
4
7 7
H
(
7
7
9
10
ol (C H O) were purchased from Alfa Aesar Co., Ltd. (Tianjin,
5
10
China). All the reagents were analytical grade and used without
further purication. The deionized water was from local
sources.
Synthesis
(
a) Synthesis of graphene oxide (GO). GO was synthesized by and an Ag/AgCl electrode was used as the reference electrode.
50–55
a modied Hummers method,
which was also expatiated in The electrolyte was 0.2 M Na
The detail of the preparation additive (pH 6.8). The working electrode was prepared on
2 4
SO aqueous solution without
21,33,56,57
our previous works.
procedure is presented in the ESI.†
b) Fabrication of In
uorine doped tin oxide (FTO) glass that was sonicated in
ꢁ
(
2
S
3
–GR nanocomposites with different ethanol and dried at 80 C before use. The boundary of FTO
weight addition ratios of GR. In a typical procedure, the given glass was protected using Scotch tape. The 2 mg sample was
amount of as-prepared GO was ultrasonically dispersed in 40 adequately dispersed in 0.5 mL of N,N-dimethylformamide with
mL distilled water and mixed with 0.5 mmol In(NO ) $4.5H O. sonication. The as-obtained slurry was spread onto the pre-
3
3
2
Aer stirring for 0.5 h, 2 mmol L-cysteine was added into the treated FTO glass. Aer air drying, the working electrode was
ꢁ
above mixture under vigorous stirring. Aer that, the pH was further dried at 120 C for 2 h to improve adhesion. Then, the
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64484–64493 | 64485

View Article Online
RSC Advances
Paper
Scotch tape was unstuck, and the uncoated part of the electrode portrayed in Scheme 1. For blank In
2
S
3
, the functional groups in
was isolated with epoxy resin. The visible light irradiation L-cysteine molecule, such as –NH , –COOH, and –SH (Fig. S1†),
2
source was a 300 W Xe arc lamp system equipped with a UV-CUT are crucial for the formation of owerlike In2S3 structure.
3
+

lter (l > 420 nm). The electrochemical impedance spectroscopy Firstly, a complex is formed via the coordination between In
40,49
(
EIS) experiments and cyclic voltammograms were conducted ions and L-cysteine due to their strong interactions.
on a CHI660D workstation (CH instrument, USA) in the elec- the hydrothermal process, the complex is decomposed to form
trolyte of 0.5 M KCl aqueous solution containing 0.01 M In nuclei, followed by crystal growth at the expense of the
[Fe(CN) ]–K [Fe(CN) ] (1 : 1) under open circuit potential small crystals. With the evolution of the hydrothermal reaction,
conditions. the owerlike In structures are gradually assembled using
L-cysteine as a sulde source and graing molecular. As for the
fabrication of In S –GR nanocomposites, In(NO ) aqueous
During
2 3
S
K
3
6
4
6
2 3
S
49
Catalytic activity
Photocatalytic selective oxidation of a range of alcohols was
2
3
3 3
solution is rstly mixed with a certain amount of GO, during
which In ions primarily anchor on the surface of GO mat
through electrostatic attractive interaction between them. In the
process of the subsequent hydrothermal treatment, L-cysteine is
decomposed to provide S and simultaneously hierarchical
3+
10,32,33,58–60
conducted according to the previous works.
Typically,
0.1 mmol of alcohol and 8 mg of the as-synthesized catalyst
were suspended in 1.5 mL of benzotriuoride (BTF), which was
saturated with molecular oxygen. Subsequently, the above
mixture was transferred into a 10 mL Pyrex glass bottle, which
was lled with molecular oxygen at a pressure of 0.1 MPa and
stirred for 20 min to establish the adsorption–desorption
equilibrium. The mixture was irradiated by a 300 W Xe arc lamp
2ꢀ
2 3
petal-like In S architectures grow on conductive GR sheets
formed by the reduction of nonconductive GO. The efficient
reduction of GO to GR aer the hydrothermal process can be
evidenced by the Fourier transformed infrared spectroscopy
as displayed in Fig. S2 (ESI†). According to the FT-IR
spectra of the pristine GO, the stretching vibrations including
O–H (3426 cm ), C]O (1720 cm ), C]C (1622 cm ), C–O–H
1408 cm ), C–OH (1224 cm ), and C–O–C (1057 cm ) are
observed, indicating the existence of various oxygen-containing
35,61
(FT-IR),
(PLS-SXE 300, Beijing Perfect light Co., Ltd.) with a UV-CUT

lter to cut off light of wavelength less than 420 nm. Aer
ꢀ1
ꢀ1
ꢀ1
that, the mixture was centrifuged at 12 000 rpm for 10 min to
remove the catalyst particles. The remaining solution was
analyzed using an Agilent gas chromatograph (GC-7820).
Conversion of alcohol, yield and selectivity for aldehyde were
dened as follows:
ꢀ1
ꢀ1
ꢀ1
(
35,57,61
functional groups on the GO surface.
For In S –1%GR, the
2 3
intensity of various oxygen-containing functional groups is
signicantly decreased, which manifests the efficient reduction
of GO to GR aer the hydrothermal treatment.
Conversion (%) ¼ [(C
Yield (%) ¼ C
Selectivity (%) ¼ [C /(C
where C is the initial concentration of alcohol and C and C
p
0
ꢀ C
/C
ꢂ 100
ꢀ C )] ꢂ 100
r
)/C
0
] ꢂ 100
Typical SEM analysis is used to observe the morphology of
blank In
2 3 2 3
S and In S –GR nanocomposites. As shown in Fig. 1A,
p
0
without addition of GO, owerlike structures for blank In
2 3
S
with the average diameter of 1 mm are obtained. Once GO is
introduced, the morphology of owerlike In2S3 structure
changes dramatically. As displayed in Fig. 1B, when the weight
p
0
r
0
r
are the concentrations of the substrate alcohol and the corre- addition ratio of GR is 0.1%, the owerlike morphology of blank
sponding product aldehyde, respectively, at a certain time aer
the photocatalytic reaction.
Results and discussion
The synthesis of blank In2S3 and In S –GR nanocomposites
2
3
with different weight addition ratios of GR is graphically
Scheme 1 The schematic illustration for the preparation of blank
flowerlike In structure and In –GR nanocomposites via a facile, in Fig. 1 Typical FESEM images of (A) blank In
situ hydrothermal method. In –1%GR, and (D) In –2%GR.
2
S
3
2
S
3
2 3 2 3
S , (B) In S –0.1%GR, (C)
S
2 3
2 3
S
64486 | RSC Adv., 2014, 4, 64484–64493
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
2 3 2 3
In S has been damaged apparently and petal-like In S archi-
tectures start to grow along the 2D GR platform. With the
further increase of GR to 1%, the compact hierarchical petal-
like architectures of In2S3 grown onto the GR mat become
more obvious (Fig. 1C). When the weight addition ratio of GR is
increased to 2% (Fig. 1D), the petal-like architectures of In
disappear, and the evident agglomeration of In particles
occurs. The SEM results reveal that the addition of GO has a
great inuence on the morphology of the as-obtained In –GR
nanocomposites, and the synthesis of In S –GR with an
2 3
S
2 3
S
2 3
S
2
3
appropriate amount of GO is a key factor for achieving different
morphology of In S spreading onto the 2D GR scaffold.
2
3
To further obtain the microscopic structure information of
blank In and In –GR, transmission electron microscopy
TEM) analysis has been conducted as displayed in Fig. 2. It can
be seen from Fig. 2A that without the addition of GO, owerlike
structure of blank In
has been obtained. In comparison, with Fig.
2
S
3
2 3
S
(
S
3
3
The XRD spectra of the as-synthesized blank In
2 3
S and
2
In S –GR nanocomposites with different weight addition ratios of GR.
2 3
the addition of an appropriate amount of GO such as 1%, as
shown in Fig. 2B and C, it is obvious to see that the hierarchical
petal-like architectures of In S are growing onto the GR mat
2
3
blank In
2 3 2 3
S . It can be seen that the In S –GR nanocomposites
compactly which ensures the good interfacial contact between
In and GR. The results are in good accordance with the SEM
with different weight ratios of GR display similar XRD patterns
to that of blank In
2 3
S
ꢁ
ꢁ
2
S
3
. The peaks located at ca. 14.2 , 20.9 ,
analysis. The image of high resolution TEM (HRTEM) in Fig. 2D
shows the distinct lattice fringe and the spacing is measured to
be 0.324 nm, which is corresponding to the (311) planes of cubic
b-In2S3 phase. The selected area electron diffraction (SAED)
pattern indicates that the In S –1%GR nanocomposite
ꢁ
ꢁ
ꢁ
ꢁ
27.4 , 28.7 , 33.2 , and 47.7 can be indexed to the (111), (211),
(
311), (222), (400), and (440) crystal planes for the cubic b-In2S
3
phase (JCPDS no. 32-0456), respectively. No diffraction peaks of
other crystal phases are observed, manifesting that the pure
2
3
cubic b-In
Notably, as compared to blank In
peaks for the separate GR in the In
detected, which can be probably ascribed to the relatively low
2
S
3
is formed during the current synthesis conditions.
, there are no apparent
–GR nanocomposites to be
possesses polycrystalline structure, which is consistent with the
following XRD results.
The XRD patterns in Fig. 3 exhibit the crystallographic
2 3
structure and phase purity of the In S –GR nanocomposites and
2 3
S
S
2 3
addition amount of GR in the In
2
S
3
–GR nanocomposites and
ꢁ
the overlapping of the main characteristic peak of GR at 26.0
with the (311) peak at 27.4 for cubic b-In S .
ꢁ
10,32,33,58,62
2
3
Fig. 4 displays the UV-vis diffuse reectance spectra (DRS) for
characterization of the optical properties of In –GR nano-
composites and blank In . It can be found that the addition of
different amounts of GR has a great inuence on the visible
2 3
S
2 3
S
Fig. 2 TEM images of (A) blank In
high-resolution TEM (HR-TEM) image of (D) In
D) is the image of SAED pattern of In –1%GR.
2
S
3
, (B) and (C) In
–1%GR; the inset of Fig. 4 The UV-vis DRS spectra of blank In
2 3
S composites with different weight addition ratios of GR.
2 3
S –1%GR, and
2
S
3
2 3 2 3
S and In S –GR nano-
(
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64484–64493 | 64487

View Article Online
RSC Advances
Paper
2 3
light absorption property of In S –GR nanocomposites. With
the increase of the weight addition ratios of GR, there is grad-
ually enhanced absorption intensity in the visible light region of
560–800 nm, which should be ascribed to the intrinsic
absorption of black colored GR. From the plot for the samples
via the transformation based on the Kubelka–Munk function
versus the energy of light, as shown in Fig. S3 (ESI†), the band
gap values of the samples can be estimated to be ca. 2.54, 2.53,
2.49, and 2.46 eV, corresponding to blank In
2 3 2 3
S , In S –0.1%GR,
In S –1%GR, and In S –2%GR, respectively, indicating a band
2
3
2 3
gap narrowing of the semiconductor In2S3 due to the intro-
duction of GR into the matrix of In S –GR nanocomposites.
2
3
Such an extended optical absorption has also been observed in
previous works regarding GR–semiconductor photocatalysts for
21,27,28,63,64
solar-driven catalytic applications.
The photocatalytic performance of the In
2 3
S –GR nano-
composites is initially estimated by selective oxidation of benzyl
alcohol to benzaldehyde under visible light irradiation (l > 420
nm). It can be seen from Fig. 5 that the In S –GR nano-
2
3
composites with different weight addition ratios of GR exhibit
higher photoactivity than blank In toward selective oxidation
of benzyl alcohol. Meanwhile, In –1%GR exhibits the highest
2 3
S
S
2 3
photocatalytic activity, over which the conversion of benzyl
alcohol is about 55% with high selectivity (ca. 99%) aer the
visible light irradiation for 2 h. When the weight addition ratio
Fig.
6
Time-online photocatalytic selective oxidation of benzyl
of GR reaches 2%, the photoactivity and selectivity are both alcohol to benzaldehyde over the as-prepared blank In
2 3
S and
2 3
In S –1%GR under visible light irradiation (l > 420 nm).
reduced, which could be ascribed to the lowered contact surface
of semiconductor In S with the light irradiation in In S –2%
2
3
2 3
2
1,33
GR.
the target product aldehyde may not be easily desorbed from the selective oxidation of benzyl alcohol over blank In
surface of photocatalyst due to the higher adsorption ability of optimal In –1%GR indicate that the conversion of benzyl
carbon material GR with relatively higher addition in In
–2% alcohol and yield of benzaldehyde increase gradually with the
GR nanocomposite. Under this circumstance, further deep irradiation time and the superior photoactivity of In
oxidation of aldehyde may occur, therefore resulting in the drop over blank In is obvious.
To further conrm the higher photoactivity of In
than blank In
Another reason for the decline in the selectivity is that
S and the
2 3
S
2 3
2 3
S
2
S
S
3
3
–1%GR
–1%GR
2 3
S
33
in selectivity. As shown in Fig. 6, time-online proles of
2
2
S
3
, we have also conducted the activity testing on
oxidation of other benzylic alcohols and allylic alcohols under
visible light irradiation. As demonstrated in Table 1, the
In S –1%GR nanocomposite exhibits higher photocatalytic
2
3
activity than blank In
it is clear that with the addition of appropriate amount of GR,
the as-prepared In –1%GR shows remarkably enhanced
photoactivity toward selective oxidation of a range of alcohols
under visible light irradiation as compared to blank In
2 3
S in all selected reaction systems. Hence,
2 3
S
2 3
S .
To understand and explore the origins of the higher photo-
activity of In S –1%GR for selective oxidation of alcohols than
2
3
blank In S , a series of characterizations have been carried out.
2
3
The transient photocurrent density of In
In electrodes under visible light irradiation has shown in
Fig. 7. It is clear to see that the photocurrent density of
In –1%GR under visible light illumination is much higher
than that of blank In . It is well known that the photocurrent
2 3
S –1%GR and blank
2 3
S
2 3
S
2 3
S
is generated mainly by the diffusion of photo-induced electrons
to the back contact, and at the same time, the photogenerated
Fig. 5 Photocatalytic selective oxidation of benzyl alcohol to benz-
aldehyde over blank In and In –GR nanocomposites with
different weight addition ratios of GR under visible light irradiation
l > 420 nm) for 2 h.
33,65
holes are taken up by the hole acceptor in the electrolyte.
Therefore, the enhanced photocurrent over In –1%GR
2
S
3
2 3
S
2 3
S
(
implies more efficient separation of photo-induced charge
64488 | RSC Adv., 2014, 4, 64484–64493
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Table 1 The photocatalytic performance of blank In
diation (l > 420 nm) for 2 h
2
S
3
and In
2
S
3
–1%GR for selective oxidation of a range of alcohols under visible light irra-
Blank In
2
S
3
2 3
In S –1%GR
Entry
1
Substrate
Product
Time (h)
2
Conv. (%)
14
Yield (%)
14
Conv. (%)
55
Yield (%)
54
2
3
4
2
2
2
18
43
10
15
39
9
32
56
20
30
56
20
5
6
2
2
24
14
23
14
50
31
49
29
7
8
2
2
10
14
7
18
25
15
25
12
contact between In S and GR. This can be further conrmed by
2
3
the photoluminescence (PL) spectra measurements. The PL
spectra give the information about photoexcited energy/
33,36,66–68
electron transfer and recombination processes.
As
Fig. 7 Transient photocurrent density of as-prepared blank In
In –1%GR electrodes in the electrolyte of 0.2 M Na SO aqueous
solution without bias versus Ag/AgCl under visible light irradiation
l > 420 nm).
2 3
S and
S
2 3
2
4
(
carriers and longer lifetime of the photogenerated electron–
hole pairs as compared with blank In , which can be ascribed
to the introduction of conductive GR and the good interfacial
2 3
S
2 3 2 3
Fig. 8 Photoluminescence (PL) spectra of blank In S and In S –1%GR
with an excitation wavelength of 420 nm.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64484–64493 | 64489

View Article Online
RSC Advances
Paper
2 3
displayed in Fig. 8, the PL intensity observed for In S –1%GR is
weaker than that of blank In S with the excitation wavelength
2
3
of 420 nm, thus indicating the more effective inhibition of the
recombination of photogenerated charge carriers over In S –1%
2
3
2 3
GR than blank In S .
Additionally, electrochemical impedance spectroscopy (EIS)
has been performed to study the migration of charge carriers in
69
the electrode materials. From the EIS Nyquist plots of blank
In and In –1%GR electrode materials cycled in 0.5 M KCl
aqueous solution containing 0.01 M K [Fe(CN) ]–K [Fe(CN) ]
2
S
3
2 3
S
3
6
4
6
(1 : 1) electrolyte solution (Fig. 9), we can see that both of the
samples show semicycles at high frequencies. Under the similar
preparation of the electrodes and electrolyte, the high-
frequency arc corresponds to the charge transfer limiting
process and can be attributed to the charge transfer resistance
at the contact interface between the electrode and electrolyte
Fig. 10 Nitrogen adsorption–desorption isotherms of blank In
In –1%GR.
2 3
S and
33,35,58,61
solution.
2 3
The smaller arc of In S –1%GR than that of
2 3
S
blank In S indicates that the In S –1%GR photocatalyst has
2
3
2 3
faster interfacial electron transfer than blank In S .
2
3
Furthermore, to understand the role of GR on affecting the
surface area and pore structure of the samples, the Brunauer–
To investigate the possible mechanism for the photo-
catalytic performances over the samples, controlled experi-
ments with addition of various radical scavengers for the
photocatalytic selective oxidation of benzyl alcohol over
blank In S and In S –1%GR in the BTF solvent have been
Emmett–Teller (BET) surface area and porosity for In
and blank In have also been investigated. It can be found
2 3
from Fig. 10 that both of the In –1%GR and blank In S
2 3
S –1%GR
2 3
S
2
S
3
2
3
2 3
exhibit type IV isotherm with a typical H3 hysteresis loop
characteristic of mesoporous solids according to the IUPAC
32,71,72
carried out.
The results displayed in Fig. 11 suggest that
the primary active radical species are photogenerated holes,
62,70
classication.
As illustrated in Table S1 (ESI†), the specic
ꢀ
electrons and activated oxygen (e.g., O
2
c ), which can be also
surface area and pore volume for In S –1%GR are measured to
2
3
evidenced by the ESR spectra displayed in Fig. S5 (ESI†), as
reected by the decreased photoactivity obtained with the
addition of AO, BQ, and K S O as scavenger of photo-
2 2 8
generated holes, superoxide radicals, and photogenerated
electrons, respectively. Notably, although the photo-
generated electrons can not directly participate in the
2
ꢀ1
3
ꢀ1
be ca. 37 m g and 0.23 cm g , respectively, which are larger
than those for blank In S (ca. 18 m g and 0.11 cm g ).
2 3
2
ꢀ1
3
ꢀ1
Besides, adsorption experiments in the dark for various alco-
hols have been conducted (Fig. S4, ESI†). The results indicate
that the In
2 3
S –1%GR with larger surface area shows enhanced
adsorptivity toward various alcohols than blank In S , which is
2
3
10–12
favorable to promote the photoactivity.
Fig. 11 Controlled experiments using different radical scavengers for
the photocatalytic selective oxidation of benzyl alcohol over blank
In
l > 420 nm) for 2 h; ammonium oxalate (AO) is scavenger for pho-
–1%GR togenerated holes, K for photogenerated electrons, benzoqui-
2 3 2 3
S and In S –1%GR in the BTF solvent under visible light irradiation
(
Fig. 9 Nyquist impedance plots of blank In
2
S
3
and In
2
S
3
2 2 8
S O
electrodes in 0.5
M
KCl aqueous solution containing 0.01
] (1 : 1).
M
none (BQ) for superoxide radicals and tert-butyl alcohol (TBA) for
hydroxyl radicals.
K
3
[Fe(CN) ]–K [Fe(CN)
6
4
6
64490 | RSC Adv., 2014, 4, 64484–64493
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
oxidation reaction, they can activate molecular oxygen. Thus,
we can observe the decrease of conversion when the scav-
enger K S O for photogenerated electrons is added into the
2
2
8
reaction system. The addition of TBA as scavenger for
hydroxyl radicals has almost no inuence on the photo-
activity of blank In
2 3 2 3
S and In S –1%GR. This is reasonable
because there are no strong and nonselective hydroxyl radi-
1
0,32,33,73
cals present in the BTF solvent system.
The photostability of In –1%GR has also been investi-
gated, as shown in Fig. 12. In S –1%GR has the excellent recy-
2 3
S
2
3
cled performance in four successive recycling tests toward
photocatalytic selective oxidation of benzyl alcohol in the
organic solvent of BTF under visible light. Aer four recycles,
Scheme 2 Schematic diagram of the charge carriers transfer and
proposed mechanism for selective oxidation of alcohols to corre-
sponding aldehydes over the In S –GR nanocomposites under visible
2 3
light irradiation (l > 420 nm).
the In
suggesting that In
2
S
3
–1%GR nanocomposite shows almost no deactivation,
–1%GR can serve as a stable visible light
2 3
S
responsive photocatalyst toward selective oxidation of alcohols
in our reaction conditions.
Based on the above discussions, the remarkable enhance-
ment of photoactivity for In S –GR nanocomposites over blank
2
3
Conclusions
In S can be attributed to the efficient separation and transfer
2
3
efficiency of photogenerated electron–hole pairs and the larger
surface area.
Scheme 2 shows the possible mechanism in which the
electrons are rstly excited from the valence band (VB) to
In summary, we have successfully fabricated In
2
S
3
–graphene
over-
(GR) nanocomposites with hierarchical petal-like In S
2 3
spreading the GR sheets. In virtue of the “structure directing”
role of graphene oxide (GO) as the precursor of GR, the as-
synthesized In S –GR featuring the good interfacial contact
the conduction band (CB) (ꢀ0.8 V vs. NHE) of In
2 3
S in the
2
3
In S –GR nanocomposites, leaving holes in the VB. Then,
2
3
between In
2
S
3
and GR exhibit much higher photocatalytic
photogenerated electrons can transfer to GR sheets (its work
activity toward selective oxidation of alcohols to aldehydes
under visible light irradiation than blank owerlike In . It is
revealed that the signicantly enhanced photocatalytic perfor-
mance of In –GR is ascribed to the integrative effect of the
function is ꢀ0.08 V vs. NHE). Due to the good interfacial
2 3
S
2 3
contact between In S and GR, the photoexcited electrons can
readily transfer to GR, which efficiently hampers the recom-
bination of electrons and holes. The adsorbed alcohol can be
oxidized by the hole to form alcohol radical cation, reacting
with molecular oxygen or superoxide radicals to produce
2 3
S
boosted separation and transfer efficiency of photogenerated
electron–hole pairs and the larger surface area. Our work
highlights the promising scope of fabricating GR-based semi-
conductor nanocomposites with controllable architectural
nanostructures by rationally utilizing the “structure directing”
property of GO and extending their applications toward pho-
tocatalytic selective transformations.
7
4
target aldehyde.
Acknowledgements
The support by the National Natural Science Foundation of
China (NSFC) (20903023, 21173045), the Award Program for
Minjiang Scholar Professorship, the Natural Science Founda-
tion (NSF) of Fujian Province for Distinguished Young Investi-
gator Grant (2012J06003), and Program for Returned High-Level
Overseas Chinese Scholars of Fujian province is gratefully
acknowledged.
Notes and references
1
K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang,
S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Science, 2004,
306, 666–669.
2
N. Zhang, Y. Zhang and Y.-J. Xu, Nanoscale, 2012, 4, 5792–
2 3
Fig. 12 Recycled testing of In S –1%GR toward selective oxidation of
benzyl alcohol under visible light irradiation (l > 420 nm) for 2 h.
5813.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64484–64493 | 64491

View Article Online
RSC Advances
Paper
3
4
G. Xie, K. Zhang, B. Guo, Q. Liu, L. Fang and J. R. Gong, Adv. 32 N. Zhang, M.-Q. Yang, Z.-R. Tang and Y.-J. Xu, ACS Nano,
Mater., 2013, 25, 3820–3839. 2014, 8, 623–633.
C. Han, M.-Q. Yang, N. Zhang and Y.-J. Xu, J. Mater. Chem. A, 33 N. Zhang, Y. Zhang, X. Pan, X. Fu, S. Liu and Y.-J. Xu, J. Phys.
014, 2, 19156–19166. Chem. C, 2011, 115, 23501–23511.
M. Zhu, P. Chen and M. Liu, ACS Nano, 2011, 5, 4529–4536. 34 M.-Q. Yang and Y.-J. Xu, Phys. Chem. Chem. Phys., 2013, 15,
2
5
6
Q. Zhang, C. Tian, A. Wu, T. Tan, L. Sun, L. Wang and H. Fu,
J. Mater. Chem., 2012, 22, 11778–11784.
J. Zhang, J. Yu, M. Jaroniec and J. R. Gong, Nano Lett., 2012,
19102–19118.
35 S. Liu, Z. Chen, N. Zhang, Z.-R. Tang and Y.-J. Xu, J. Phys.
Chem. C, 2013, 117, 8251–8261.
7
8
9
1
2, 4584–4589.
36 M.-Q. Yang, B. Weng and Y.-J. Xu, Langmuir, 2013, 29, 10549–
10558.
W. Tu, Y. Zhou, Q. Liu, Z. Tian, J. Gao, X. Chen, H. Zhang,
J. Liu and Z. Zou, Adv. Funct. Mater., 2012, 22, 1215–1221.
A. Iwase, Y. H. Ng, Y. Ishiguro, A. Kudo and R. Amal, J. Am.
Chem. Soc., 2011, 133, 11054–11057.
37 Y. Hee ´a Kim, J. Hak ´a Lee, S. Min ´a Park, J. Soo ´a Moon and
J. Gyu ´a Nam, Chem. Commun., 2010, 46, 2292–2294.
38 S. Rengaraj, S. Venkataraj, C.-w. Tai, Y. Kim, E. Repo and
M. Sillanp ¨a ¨a , Langmuir, 2011, 27, 5534–5541.
39 W. Qiu, M. Xu, X. Yang, F. Chen, Y. Nan, J. Zhang, H. Iwai
and H. Chen, J. Mater. Chem., 2011, 21, 13327–13333.
40 L.-Y. Chen, Z.-D. Zhang and W.-Z. Wang, J. Phys. Chem. C,
2008, 112, 4117–4123.
1
1
1
1
1
0 Y. Zhang, Z.-R. Tang, X. Fu and Y.-J. Xu, ACS Nano, 2011, 5,
7
426–7435.
1 C. Han, M.-Q. Yang, B. Weng and Y.-J. Xu, Phys. Chem. Chem.
Phys., 2014, 16, 16891–16903.
2 M.-Q. Yang, N. Zhang, M. Pagliaro and Y.-J. Xu, Chem. Soc.
Rev., 2014, 43, 8240–8254.
41 K. H. Park, K. Jang and S. U. Son, Angew. Chem., Int. Ed.,
2006, 45, 4608–4612.
3 Q. Xiang, J. Yu and M. Jaroniec, Chem. Soc. Rev., 2012, 41,
7
82–796.
4 I. V. Lightcap and P. V. Kamat, Acc. Chem. Res., 2012, 46,
235–2243.
42 B. Pejova and I. Bineva, J. Phys. Chem. C, 2013, 117, 7303–
7314.
2
43 Y. Gu and Y. Wang, RSC Adv., 2014, 4, 8582–8589.
1
1
5 L. Han, P. Wang and S. Dong, Nanoscale, 2012, 4, 5814–5825. 44 F. Ye, G. Du, Z. Jiang, Y. Zhong, X. Wang, Q. Cao and
6 W. Fan, Q. Zhang and Y. Wang, Phys. Chem. Chem. Phys.,
013, 15, 2632–2649.
7 O. Akhavan and E. Ghaderi, J. Phys. Chem. C, 2009, 113,
0214–20220.
8 P. Gao, J. Liu, S. Lee, T. Zhang and D. D. Sun, J. Mater. Chem.,
012, 22, 2292–2298.
9 W. Fan, Q. Lai, Q. Zhang and Y. Wang, J. Phys. Chem. C, 2011,
15, 10694–10701.
J. Z. Jiang, Nanoscale, 2012, 4, 7354–7357.
45 W. Du, J. Zhu, S. Li and X. Qian, Cryst. Growth Des., 2008, 8,
2130–2136.
46 F. Ye, C. Wang, G. Du, X. Chen, Y. Zhong and J. Jiang, J.
Mater. Chem., 2011, 21, 17063–17065.
47 L. Liu, H. Liu, H.-Z. Kou, Y. Wang, Z. Zhou, M. Ren, M. Ge
and X. He, Cryst. Growth Des., 2008, 9, 113–117.
48 Y. He, D. Li, G. Xiao, W. Chen, Y. Chen, M. Sun, H. Huang
and X. Fu, J. Phys. Chem. C, 2009, 113, 5254–5262.
49 X. An, J. C. Yu, F. Wang, C. Li and Y. Li, Appl. Catal., B, 2013,
129, 80–88.
2
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
2
2
1
0 J. Zhou, G. Tian, Y. Chen, X. Meng, Y. Shi, X. Cao, K. Pan and
H. Fu, Chem. Commun., 2013, 49, 2237–2239.
1 Y. Zhang, Z.-R. Tang, X. Fu and Y.-J. Xu, ACS Nano, 2010, 4,
303–7314.
2 J. Zhang, Z. Xiong and X. Zhao, J. Mater. Chem., 2011, 21,
634–3640.
3 Y. H. Ng, A. Iwase, A. Kudo and R. Amal, J. Phys. Chem. Lett.,
010, 1, 2607–2612.
4 I. Y. Kim, J. M. Lee, T. W. Kim, H. N. Kim, H. i. Kim, W. Choi 52 L. J. Cote, F. Kim and J. Huang, J. Am. Chem. Soc., 2008, 131,
and S. J. Hwang, Small, 2012, 8, 1038–1048. 1043–1049.
5 A. Mukherji, B. Seger, G. Q. Lu and L. Wang, ACS Nano, 2011, 53 D. Pan, S. Wang, B. Zhao, M. Wu, H. Zhang, Y. Wang and
, 3483–3492. Z. Jiao, Chem. Mater., 2009, 21, 3136–3142.
6 J. Du, X. Lai, N. Yang, J. Zhai, D. Kisailus, F. Su, D. Wang and 54 D. Li, M. B. M u¨ ller, S. Gilje, R. B. Kaner and G. G. Wallace,
L. Jiang, ACS Nano, 2010, 5, 590–596. Nat. Nanotechnol., 2008, 3, 101–105.
7 H. Zhang, X. Lv, Y. Li, Y. Wang and J. Li, ACS Nano, 2009, 4, 55 L. J. Cote, F. Kim and J. Huang, J. Am. Chem. Soc., 2008, 131,
80–386. 1043–1049.
8 C. Chen, W. Cai, M. Long, B. Zhou, Y. Wu, D. Wu and 56 Y. Zhang, N. Zhang, Z.-R. Tang and Y.-J. Xu, J. Phys. Chem. C,
Y. Feng, ACS Nano, 2010, 4, 6425–6432. 2014, 118, 5299–5308.
9 E. Gao, W. Wang, M. Shang and J. Xu, Phys. Chem. Chem. 57 Y. Zhang, N. Zhang, Z.-R. Tang and Y.-J. Xu, ACS Nano, 2012,
Phys., 2011, 13, 2887–2893. 6, 9777–9789.
0 Y. Fu, P. Xiong, H. Chen, X. Sun and X. Wang, Ind. Eng. 58 N. Zhang, Y. Zhang, X. Pan, M.-Q. Yang and Y.-J. Xu, J. Phys.
Chem. Res., 2012, 51, 725–731. Chem. C, 2012, 116, 18023–18031.
1 X. An, X. Yu, C. Y. Jimmy and G. Zhang, J. Mater. Chem. A, 59 M. Zhang, C. Chen, W. Ma and J. Zhao, Angew. Chem., Int.
013, 1, 5158–5164. Ed., 2008, 47, 9730–9733.
7
50 W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc., 1958,
80, 1339.
3
51 N. I. Kovtyukhova, P. J. Ollivier, B. R. Martin, T. E. Mallouk,
S. A. Chizhik, E. V. Buzaneva and A. D. Gorchinskiy, Chem.
Mater., 1999, 11, 771–778.
2
5
3
2
64492 | RSC Adv., 2014, 4, 64484–64493
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
6
6
6
6
6
6
6
6
0 M. Zhang, Q. Wang, C. Chen, L. Zang, W. Ma and J. Zhao, 68 M.-Q. Yang, B. Weng and Y.-J. Xu, J. Mater. Chem. A, 2014, 2,
Angew. Chem., Int. Ed., 2009, 48, 6081–6084. 1710–1720.
1 Z. Chen, S. Liu, M.-Q. Yang and Y.-J. Xu, ACS Appl. Mater. 69 T. Lu, Y. Zhang, H. Li, L. Pan, Y. Li and Z. Sun, Electrochim.
Interfaces, 2013, 5, 4309–4319. Acta, 2010, 55, 4170–4173.
2 N. Zhang, Y. Zhang, M.-Q. Yang, Z.-R. Tang and Y.-J. Xu, J. 70 R. Pierotti and J. Rouquerol, Pure Appl. Chem., 1985, 57, 603–
Catal., 2013, 299, 210–221. 619.
3 Y.-J. Xu, Y. Zhuang and X. Fu, J. Phys. Chem. C, 2010, 114, 71 Y. Zhang, N. Zhang, Z.-R. Tang and Y.-J. Xu, Chem. Sci., 2013,
669–2676. 4, 1820–1824.
4 X.-Y. Zhang, H.-P. Li, X.-L. Cui and Y. Lin, J. Mater. Chem., 72 Y. Zhang, N. Zhang, Z.-R. Tang and Y.-J. Xu, Chem. Sci., 2012,
010, 20, 2801–2806. 3, 2812–2822.
5 S. Soedergren, A. Hagfeldt, J. Olsson and S.-E. Lindquist, J. 73 Q. Wang, M. Zhang, C. Chen, W. Ma and J. Zhao, Angew.
Phys. Chem., 1994, 98, 5552–5556. Chem., Int. Ed., 2010, 49, 7976–7979.
6 J. Yang, H. Yan, X. Wang, F. Wen, Z. Wang, D. Fan, J. Shi and 74 N. Zhang, X. Fu and Y.-J. Xu, J. Mater. Chem., 2011, 21, 8152–
2
2
C. Li, J. Catal., 2012, 290, 151–157.
8158.
7 A. Cao, Z. Liu, S. Chu, M. Wu, Z. Ye, Z. Cai, Y. Chang,
S. Wang, Q. Gong and Y. Liu, Adv. Mater., 2010, 22, 103–106.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64484–64493 | 64493