Gold nanoparticle-modified TiO2/SBA-15 nanocomposites as active plasmonic photocatalysts for the selective oxidation of aromatic alcohols

Article abstract of DOI:10.1039/c6ra11390g

The catalytic performance of noble-metal on mesoporous silica hosts has been widely investigated because the effects of surface plasmon resonance can open new avenues for the improvement of catalytic performance under light irradiation. In this study, a s

Full text of DOI:10.1039/c6ra11390g

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Y. Chen, W. Li, J.
Wang, Q. Yang, Q. Hou and M. Ju, RSC Adv., 2016, DOI: 10.1039/C6RA11390G.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Gold nanoparticles-modified TiO2/SBA-15 nanocomposites as active plasmonic
photocatalysts for the selective oxidation of aromatic alcohols
Yu Chen, Weizun Li, Jingyu Wang, Qian Yang, Qidong Hou, Meiting Ju*
College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China
Abstract
The catalytic performance of noble-metal nanocatalysts on mesoporous silica hosts has been
widely investigated because the effects of localized surface plasmon resonance (LSPR) can open
new avenues for the improvement of catalytic performance under light irradiation. In this study, a
series of photoactive Au/TiO2/SBA-15 catalysts were developed for the selective oxidation of
alcohols to corresponding aldehydes and ketones. The catalysts thus developed were characterized
by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, transmission electron
microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy
(HAADF-STEM), scanning transmission electron microscopy energy–dispersive spectrometry,
X-ray photoelectron spectroscopy (XPS), transient photocurrent response and electrochemical
impedance spectroscopy (EIS). Au and small TiO2 nanoparticles (NPs) were uniformly anchored
into the SBA-15 channels by the microwave-assisted alcohol reduction, resulting in the increase of
the interfacial area between gold and titania; this increase in turn results in better catalytic
performance for the Au2/TiO2/SBA-15 catalysts toward the selective oxidation of aromatic
alcohols to aromatic aldehydes (ketones) as a result of the efficient pore confinement and
visible-light absorption by the LSPR effect. A scheme with respect to the enhancement of
photooxidation induced by the LSPR effect on the Au NP-decorated TiO2/SBA-15 composite was
proposed.
Keywords: Photocatalysis; Gold nanoparticles; Porous materials; Aromatic alcohols; Selective
oxidation
* Corresponding author. Tel.: +86 022-23500589
Email：jumeit@nankai.edu.cn (M. Ju)

RSC Advances
Page 2 of 29
View Article Online
DOI: 10.1039/C6RA11390G
Introduction
In organic synthesis, the selective oxidation of alcohols to corresponding carbonyl
compounds (such as aldehydes or ketones) is a crucial reaction because carbonyl compounds are
valuable as both intermediates as well as high-value components in the perfume, confectionery,
and pharmaceutical industries1-6. Typically, aldehydes and ketones are oxidized using
stoichiometric amounts of oxidizing agents, such as chromate or permanganate; however, these
reagents are toxic and not cost-effective 7. From an environmental viewpoint, it is of significance
to develop methods involving the use of molecular oxygen as the primary oxidant in the presence
of a catalyst.
The photocatalytic selective oxidation of alcohols by semiconductor materials such as
titanium dioxide (TiO2) with molecule oxygen (O2) as an oxidant at room temperature has been
proposed as an attractive, environmentally benign method for organic synthesis 8-14. Several types
of substrates, such as alcohols, amines, hydrocarbons, and sulfides, are successfully oxidized at
atmospheric pressure and room temperature 15-17. However, one of the typical drawbacks for the
practical application of photocatalytic processes includes poor visible-light harvesting and low
quantum efficiencies under visible-light irradiation, which is the main component of solar
irradiation. Recently, plasmonic metal nanoparticles (NPs) have demonstrated promise for
harvesting photon energy for chemical reactions, attributed to their extraordinary and tailorable
localized surface plasmon resonance (LSPR) properties 18-21. Upon light irradiation, plasmonic
metal nanoparticles supported on semiconductors produce hot electrons (e−) via the intraband
transition of 6sp band electrons, which are injected into the semiconductor, resulting in direct
charge separation on the plasmonic NPs. In this manner, plasmonic NPs can transfer solar energy
to neighboring semiconductors or molecular complexes for driving chemical reactions.
This scenario has motivated the advantage of the plasmonic effect for aerobic oxidation.
Tsukamoto et al. 22 have reported the aerobic oxidation of benzylic alcohols with TiO2-loaded Au
particles at room temperature under visible-light irradiation (λ > 420 nm) and found that the
location of Au NPs is crucial for the promotion of electron transfer from LSPR-excited Au NPs to
TiO2. The Au NPs, with a diameter of less than 5 nm, located at the interface between anatase and

Page 3 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
rutile TiO2 particles behave as the active sites for the photoreaction, affording high yields of
23
aldehyde or ketone products in toluene under visible-light irradiation. Schünemann et al. have
reported a remarkably small bimetallic AuCu nanoparticles with diameter of 2 nm supported on
ordered mesoporous silica (SBA-15, KIT-6, and MCM-41) and highly selective (90%) for the
oxidation of glycerol to dihydroxyacetone. They also found that the small gold–copper bimetal
NPs are sufficiently large to permit the absorption of visible light by LSPR while simultaneously
providing a large catalytically active surface area, contributing to high activity. Typically, the
24
catalytic properties of Au strongly depend on its particle size and active surface area
.
Considering the previous pioneering studies, ordered mesoporous materials such as MCM-41 and
SBA-15 with multiple channel structures and high surface areas have emerged as one of the most
promising candidates, in which Au NPs can be anchored in channels; hence, the diameter of Au
NPs can be sufficiently large to permit visible-light absorption by LSPR and to provide a large
catalytically active surface area.
These previous studies have enlightened us to design and synthesize
gold-nanoparticle-modified TiO2/SBA-15 nanocomposites as active plasmonic photocatalysts,
where Au NPs are sufficiently large to permit visible-light absorption by LSPR while
simultaneously providing a catalytically large active surface area. Herein, we report the
preparation of a series of Au/TiO2/SBA-15 composite photocatalysts with varying contents of gold
in the range from 0.5 wt% to 5 wt%. The photocatalytic selective aerobic oxidation of alcohols at
ambient temperature was performed under visible-light irradiation for evaluating the
characteristics of Au/TiO2/SBA-15 based on its nanoscale architectures. The effects of precursor
concentration and synthetic process on the gold particle size and light absorption were
characterized by sophisticated techniques, such as XRD, HRTEM, HAADF-STEM, FESEM, XPS,
nitrogen adsorption, Fourier transform-IR, UV–vis absorption spectroscopy, transient photocurrent
response and electrochemical impedance spectroscopy. Interdependent interactions between the
loading and size of gold particles and support material were investigated in detail. The dependence
of the photocatalytic oxidation of benzyl alcohol on wavelength was also discussed. Based on the
results, the photocatalytic selective aerobic oxidation of alcohols over Au/TiO2/SBA-15 under
visible-light irradiation in the photocatalytic process was proposed.

RSC Advances
Page 4 of 29
View Article Online
DOI: 10.1039/C6RA11390G
Experimental section
The Au/TiO2/SBA-15 composites were synthesized by two-step microwave assisted
hydrothermal reaction approach, which can be seen in our previous works 25. A typical procedure
was as follows: SBA-15 (1.0 g) and was sonicated in 20 mL ethanol for 2 h, and then, tetrabutyl
orthotitanate (2.0 g) was added dropwise with stirring for 1 h. Next, the homogeneous solution
was transferred into a 100 mL Teflon-lined autoclave, which was then placed in a
microwave-hydrothermal synthesis system (MDS-6, Sineo, Shanghai, China) and maintained at
180oC for 30 min. After the hydrothermal reaction, the resulting composite was collected and
washed with distilled water, followed by rinsing in ethanol, and then dried in an oven at 80oC, for
24 h, in air. The TiO2/SBA-15 was dried under reduced pressure at 120oC to remove absorbed
water. The dried powder (0.5g) and a desired amount of H2AuCl4 solution (10 mg/ml) was quickly
injected into system. The mixed solution was placed under reduced pressure to incorporate the Au
precursor into the mesopores of TiO2/SBA-15 by capillary forces. The suspension were irradiated
by microwave under an Ar atmosphere for 5min. After filtration and washing with ethanol and
o
distilled water, the resulting powder was dried at 80 C overnight under air. A series of Au
supported TiO2/SBA-15 labeled as Aux/TiO2/SBA-15 (Au wt.% = 0.5, 1.0, 2.0, 5.0 respectively)
with different amount of Au were obtained by the adding desired amount of H2AuCl4 solution in
the reaction system. For reference, the Au supported by P25 TiO2 nanoparticles and SBA-15 were
also prepared using the same method and Au/TiO2/SBA-15 sample with similar Au loading
(~2.0%) was prepared through photodeposition method, which was denoted as
Au/TiO2/SBA-15-PD.
To identify the TiO2 and gold phases, X-Ray diffraction (XRD) measurements were performed
using a PANalytical X'pert MRD with a step size of 0.02° in the region of 2θ=10-80°. Diffuse
reflectance UV-Vis spectra of the samples (ca.20 mg diluted in ca. 80 mg of BaSO4) were
recorded in the air against BaSO4 in the region of 200 to 800 nm on a Shimadzu 3600 UV-Vis
spectrophotometer. The morphologies of the TiO2 composites were measured by scanning electron
microscopy (SEM) on a Hitachi S-4800 microscope. Transmission electron microscopy (TEM)
and high angle annular dark field detector (HAADF) images were recorded using an FEI Tecnai
G2-F20 microscope at an accelerating voltage of 200 kV. Energy-dispersive X-ray (EDX) and

Page 5 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
EDX elemental mapping were performed on Oxford-Instruments X-MaxN to visualize the
elemental compositions of the products. X-ray photoelectron spectra (XPS) of the samples were
recorded on a Thermo Fisher Scientific ESCALAB 250XI using a monochromated Al-Ka X-ray
source. The specific surface areas were determined through N2 adsorption/desorption isotherms
collected at -196oC on a TriStar II 3020 adsorption analyzer. The samples were degassed under
vacuum at 200oC for 4 hours prior to analysis. The FTIR spectra were recorded on Nicolet IS50
spectrophotometer equipped with a diamond attenuated total reflectance (ATR) smart accessory.
The samples for IR were prepared by mixing the catalysts (100 mg) and benzyl alcohol (1 mL)
together for 4 h in the dark at room temperature, followed by drying the specimens at 80oC for 24
h. The samples were held in glass surface dishes and no washing was performed after adsorbing
benzyl alcohol. The spectrum of pure benzyl alcohol was also collected for comparison. The
photocurrent measurement and electrochemical impedance spectroscopy (EIS) measurement, were
carried out in a standard three electrode cell containing 0.5 mol L-1 Na2SO4 aqueous solution with
a platinum foil and a saturated calomel electrode as the counter electrode and the reference
electrode, respectively, on a CHI 760D workstation (Shanghai, China). A 300 W Xe lamp with a
420 nm cutoff filter was chosen as a visible light source. All of the electrochemical measurements
were performed at room temperature.
Photocatalytic selective oxidation of alcohols was performed in a 15-mL a home-made reactor
sealed with rubber stoppers. Typically, 50 mg of Au/TiO2/SBA-15 was spread into the reactor,
then 5 mL of toluene (solvent) and 50 ꢀmol of alcohol (reactant) were injected into the reactor.
The bottle was filled with molecular oxygen for 5 min and sealed with a rubber septum cap. Then,
the bottle was ultrasonicated at room temperature for 5 min to distribute the catalyst evenly in the
solution. The reactor was photoirradiated under magnetic stirring using a 300 W xenon lamp
(PLS-SXE 300, Beijing Perfectlight, Co. Ltd.) filtered through a glass filter to provide light with
wavelengths λ > 420 nm. The reaction temperature was controlled at room temperature by a
water-cooling system. Control photoactivity experiments using different radical scavengers
(ammonium oxalate (AO) as a scavenger for photogenerated holes, tert-butyl alcohol as a
scavenger for hydroxyl radicals, AgNO3 as a scavenger for electrons, and benzoquinone as a
scavenger for superoxide radical species) were performed similar to the above photocatalytic
oxidation of alcohols except that radical scavengers (50 ꢀmol) were added to the reaction system.

RSC Advances
Page 6 of 29
View Article Online
DOI: 10.1039/C6RA11390G
After the reactions, the organic products were analyzed by a GC (Thermo Fisher TRACE 1310GC)
equipped with a flame ionization detector. GC-MS analysis using a Thermo Fisher TRACE ISQ
GCMS, equipped with a TR-50MS capillary column (Thermo Fisher, 30 m×0.320 mm×0.25ꢀm),
was used for product identification. The colimn oven temperature was programmed from 40oC
(held for 1min) to 280 oC at a rate of 20 oC min-1. The catalyst was recovered by carefully washed
with anhydrous ethanol and deionized water and dried in an oven at 80°C overnight for the
following cycling photoactivity test. The conversion of alcohol and yield of aldehyde were defined
as follows:
ꢈ
ꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇꢁꢂ % = [ꢈꢀꢊ − ꢀꢋꢌꢍꢎꢏꢎꢌꢉ/ꢀꢊ] × 100
ꢈ
ꢉ
ꢐꢇꢄꢑꢒ % = ꢀꢋꢌꢓꢔꢏꢕꢓꢔ/ꢀꢊ × 100
ꢈ
ꢉ
ꢖꢑꢄꢗꢘꢇꢃꢇꢘꢙ % = [ꢀꢋꢌꢓꢔꢏꢕꢓꢔ/ꢈꢀꢊ − ꢀꢋꢌꢍꢎꢏꢎꢌꢉ] × 100
where C0 is the total amount of alcohols in the solution prior to illumination; Calcohol is the amount
of alcohols in the solution after illumination for 4h; Caldehyde is the amount of aldehyde in the
solution after illumination for 4h.
Results and discussion
Fig S1 shows the SEM image of the Au/TiO2/SBA-15 composites thus prepared; short
rod-like morphologies were observed, which retain the original shape of pristine SBA-15. Fig S2
(c–d) and Fig 1a show the TEM images of the as-prepared TiO2/SBA-15 and Au2/TiO2/SBA-15
catalyst, respectively; highly ordered parallel nanotubular pores were observed along the [100]
direction. The introduction of Au and titania in Au2/TiO2/SBA-15 did not substantially alter the
regular ordered structure of the mesopores as compared with that in host SBA-15 (Fig S2 (a-b)).
As can be observed from the TEM image, the Au NPs of the Au2/TiO2/SBA-15 catalyst were
uniformly distributed in the channels of the SBA-15 support, with an average particle size of
approximately 5.1 nm. For better observing the size distribution of the Au particles in these
samples, the catalysts were further characterized by HAADF-STEM. The results (Fig 1b, d) show
that the mean diameter of the Au NPs in the Au2/TiO2/SBA-15 sample is approximately 4.8 nm.
Furthermore, Fig. 1(e) shows a high-resolution TEM (HRTEM) image of the Au NPs; lattice
fringes with a d spacing of 0.235 nm were observed, corresponding to the Au(111) lattice planes.

Page 7 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
This result indicates that the HAuCl4 precursor is successfully converted to metallic Au
nanoparticles, having a face-centered cubic structure, during reduction. In addition, another type
of a lattice fringe was observed around the Au NPs, with a d spacing of approximately 0.352 nm,
which can be indexed to the (101) plane of anatase TiO2. Moreover, the EDS elemental mapping
of the STEM image shows that the Au, Ti, O, and Si elements are homogeneously distributed
throughout the sample. Au was clearly observed in the mapping data, and the Au signals indicate
that Au and TiO2 NPs are in close contact with each other; this close contact and good
incorporation between Au and TiO2, achieved by the microwave-assisted hydrothermal method,
are believed to favor the transfer of photogenerated electrons through the interface between the Au
NPs and TiO2, which in turn enhances charge separation and photocatalytic efficiency 26. The
above deduction was further authenticated by the compositional line scanning profiles across the
Au2/TiO2/SBA-15 catalyst (as shown in Fig 1(f)), obtained by HAADF-STEM-EDX, where Au
and TiO2 nanoparticles were uniformly distributed in the channels of the SBA-15 support. The
further experiments were conducted with a series of specific amounts of Au (Au loading of 0, 0.5,
1, and 5): at a low Au loading of 0.5 and 1 wt% (Fig S2 (e-f)), small Au NPs with mean diameters
of 3.7 and 4.4 nm were observed, indicating that the Au NPs are confined in the inner pores of
mesoporous silica material rather than on the external surface. However, with further increase in
the Au loading to 5 wt% (Fig S2 (g)), a small number of isolated Au NPs were observed, attributed
to extensive particle agglomeration, with significant increase in the Au particle size to 8.3 nm.
Moreover, the Au2/TiO2/SBA-15-PD synthesized by photodeposition exhibited several gold
aggregates on the surface of the support material (Fig S2 (h)). Hence, it can be concluded that the
porous supports suppress the aggregation of Au nanoparticles, especially at low gold loading.

RSC Advances
Page 8 of 29
View Article Online
DOI: 10.1039/C6RA11390G

Page 9 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Fig 1 TEM image (a), HAADF-STEM image (b, d) and the STEM-EDS elemental mapping (c) of
the Au2/TiO2/SBA-15 catalyst. HRTEM image (e) of interface between Au and TiO2 and line-scanning
profile (f) of Au2/TiO2/SBA-15 catalyst, which is indicated in the inset of (d).
Fig. 2 (a) shows the wide-angle XRD patterns of Aux/TiO2/SBA-15, Au2/SBA-15,
Au2/TiO2/SBA-15-PD and Au2/P25 composites. All samples exhibited characteristic broad peaks
between 20° and 30°, attributed to amorphous silica in the SBA-15 framework 27. Titania-containing
samples exhibited strong diffraction peaks at 2θ= 25.5, 37.7, 48.1, 53.9, 55 and 62.9 o, attributed to
(101), (004), (200), (105), (211) and (204) reflections respectively, these peaks indicate the presence of
anatase TiO2 and are in good agreement with JCPDS 21-1272. Diffraction peaks at 2θ= 38.2, 44.6, 64.7,
o
and 77.5 , indexed to Au (111), (200), (220), and (311) reflections, respectively. The average
crystalline sizes of Aux/TiO2/SBA-15 composites were in the range of 5.9 - 6.8 nm calculated
according to the Scherrer formula (Table 1). This result is probably attributed to the generation of the
titania seed crystals in the pore of SBA-15 and the limitation of the growth of titania crystals by the
pore wall. On the other hand, by the introducing of Au into the TiO2/SBA-15 sample, the
Aux/TiO2/SBA-15 composites clearly exhibited diffraction peaks corresponding to Au: a broad, weak
Au (111) diffraction peak indicated that the Au particles are well dispersed on the composites.
However, the Au5/TiO2/SBA-15 sample clearly exhibited a diffraction peak of Au, suggesting that

RSC Advances
Page 10 of 29
View Article Online
DOI: 10.1039/C6RA11390G
the introduction of excessive Au in the sample results in the deposition of Au on the surface of the
support material. Moreover, as compared to the Au2/TiO2/SBA-15 catalyst prepared by
microwave-assisted alcohol reduction, the Au2/TiO2/SBA-15-PD sample only exhibited clear Au
diffraction peaks without titania, attributed to the aggregated of the Au NPs on the SBA-15 surface
during the photo-deposition and blocking of most of the support channels, which is in accordance
with the TEM results. Fig.2 (b) shows an integrated small-angel XRD pattern of pristine SBA-15,
TiO2/SBA-15, and the Au1/TiO2/SBA-15 composite. Three well-resolved peaks were observed, indexed
to the 100, 110, and 200 planes of the 2D hexagonal mesostructure with p6mm symmetry, respectively
28. As compared with that of pristine SBA-15, the primary diffraction peaks of TiO2/SBA-15 and
Au/TiO2/SBA-15 shifted to higher angles, indicative of the marginal deposition of TiO2 and Au in the
mesopores.

Page 11 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Fig 2 wide-(a) and small-angel (b) XRD patterns of TiO2/SBA-15 and Aux/TiO2/SBA-15 samples
The structure parameters obtained from N2 adsorption–desorption isotherms listed in Table 1. As
can be observed, the Brunauer–Emmet–Teller (BET) surface area, pore volume, and average pore
diameter decreased with the loading of titania, implying that most of the TiO2 nanocrystals are loaded
within the ordered channels of the support. Moreover, the pore distribution curves and isotherms of
TiO2/SBA-15 and Au/TiO2/SBA-15 were almost the same, with barely any change in their pore
diameters, indicating that the loading of small amount of Au NPs does not affect the mesoporous
structure. Upon the introducing of a large amount of Au into TiO2/SBA-15, the surface area and pore
size of the catalyst significantly decreased, except for the Au2/TiO2/SBA-15-PD, which exhibited an
average pore diameter greater than those of the other Aux/TiO2/SBA-15 samples. This result is
attributed to the fact that the Au NPs aggregated on the surface can block most of the support channels,
with a few channels remaining unfilled.
Table 1. Physicochemical properties of pristine SBA-15, TiO2/SBA-15, Aux/TiO2/SBA-15 and
Au2/P25.
Titania
c
d
e
Samples
Au loading a
SBET
Vt
DBJH
Size b
nm
(wt %)
0.00
m2/g-1
671.16
464.91
cm-3g-1
0.961
0.685
nm
SBA-15
n.a.
6.1
7.362
5.905
TiO2/SBA-15
0.00

RSC Advances
Page 12 of 29
View Article Online
DOI: 10.1039/C6RA11390G
Au2/SBA-15
Au0.5/TiO2/SBA-15
Au1/TiO2/SBA-15
Au2/TiO2/SBA-15
Au5/TiO2/SBA-15
Au2/TiO2/SBA-15-PD
Au2/P25
1.98
n.a.
5.9
527.98
466.83
463.07
459.81
385.21
408.62
43.09
0.79
6.614
5.882
5.901
5.764
5.166
5.982
17.47
0.29
0.96
1.87
4.63
2.28
2.08
0.687
0.683
0.685
0.604
0.574
0.193
6.6
6.5
6.8
n.a.
24.9
a Weight percentage of Au measured by EDS; b Crystal size of TiO2 calculated according to the Scherrer
c
formula; SBET, BET surface areas calculated by the adsorption branch of the N2 isotherm; Vt, total pore
d
volume; e DBJH , pore diameter determined by BJH model.
Fig.
3 shows the UV–vis absorption spectra of the as-prepared TiO2/SBA-15 and
Aux/TiO2/SBA-15 samples. Pure SBA-15 did not exhibit optical absorption 29. Hence, the absorption
band edges observed between 300 and 400 nm in the titania-functionalized materials are associated
with anatase. Furthermore, blue shifts were observed in the absorption spectra as compared to the
spectrum position of bulk P25 TiO2 powder. As had been previously reported for supported TiO2, these
blue shifts are attributed to quantum effects, which are observed for TiO2 semiconductor having
dimensions of less than 10 nm 30. Therefore, the shifts of the absorption spectra suggest that TiO2 NPs
were successfully loaded on porous silica in a dispersed state. Apparently, as compared to
TiO2/SBA-15, Aux/TiO2/SBA-15 exhibited a stronger absorption in the visible-light region, which was
assigned to the characteristic LSPR peak of Au NPs. The surface plasmon absorption in the metal NPs
arises from the collective oscillations of the free conduction band electrons that are enhanced by the
incident electromagnetic radiation 31. Moreover, the intensity of the LSPR band initially increased with
increasing of Au loading amount up to 5.0%. It has been reported that the band position and intensity of
the plasmon absorption strongly depend on the Au content, particle size of Au NPs, and the
surrounding environment. Therefore, the increasing of SPR absorption peaks was probably ascribed to
the increase in the particle sizes of Au for Au5/TiO2/SBA-15 and Au2/TiO2/SBA-15-PD, as partially
evidenced by the TEM images shown in Fig. S2.

Page 13 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Fig 3. UV–vis diffuse reflectance spectra of as-prepared TiO2/SBA-15, Aux/TiO2/SBA-15 and
Au2/P25.
XPS measurements were performed for Au2/TiO2/SBA-15 and Au2/SBA-15 catalysts for obtaining
further information about the chemical states of the Au species on the surface. As can be seen from Fig
4, Au2/SBA-15 photocatalyst exhibited a doublet at 83.2 eV and 87.0 eV corresponding to Au 4f7/2
and Au 4f5/2 peaks, respectively, implying the presence of metallic Au0 in the Au2/SBA-15 sample
32, 33. However, in the Au2/TiO2/SBA-15, Au 4f XPS peaks were significantly different, depending on
the chemical states of Au34. As shown in the deconvolution results, for Au2/TiO2/SBA-15, the Au
species clearly existed in mixed oxidation states of Au0 and Au+, which may be related to the electronic
interaction between Au and TiO2. The catalytic activity of supported Au catalysts has been widely
accepted to depend on the particle size of gold and the type and structure of oxide support 35-38. For
reducible supports such as TiO2, the presence of oxygen vacancies on the surface enables the
adsorption and activation of O2, and the Au-oxide interface plays a crucial role in the oxidation of CO
and alcohols3, 39-41. The oxygen activated by the oxide active sites generated partially by the interaction
with Au is thought to react with a substrate (CO or alcohol) adsorbed on gold in close vicinity of the
Au-oxide interface. On the other hand, for a non-reducible support such as SBA-15, oxygen adsorption

RSC Advances
Page 14 of 29
View Article Online
DOI: 10.1039/C6RA11390G
was suggested to occur on the defect sites of Au; thus, the photoactivity of this type of photocatalysts
strongly depends on the Au particle size 42-46
.
Fig 4. High-resolution XP spectra of Au 4f for the Au2/TiO2/SBA-15 and Au2/SBA-15 samples.
For investigating the photocatalytic performance of Aux/TiO2/SBA-15 composites toward the
oxidation of aromatic alcohols, the selective oxidation of benzyl alcohol was used as a model
reaction 47-49. First, the oxidation of benzyl alcohol was investigated without catalysts under
visible-light irradiation. In this case, benzaldehyde was barely formed. Next, the reaction was
performed by adding 50 mg of the catalyst under 1 atm O2. The solution temperature was
rigorously maintained at 303 K by a water-cooling system. Fig 5 summarizes the amounts of
benzaldehyde formed after 4 h of reaction conducted in the dark or under visible-light irradiation
(Xe lamp, 300 W, λ > 420 nm). Notably, benzaldehyde was selectively obtained in the presence of
the catalyst, where the mass balance of benzyl alcohol and benzaldehyde was greater than 99%,
and byproducts were not detected. In the dark, bare TiO2 (TiO2/SBA-15) cannot proceed the
benzyl alcohol oxidation reaction, only 0.5% benzyl alcohol converted, while 27% benzyl alcohol
was oxidized under visible light irradiation; this visible-light-driven activity is attributed to the
ligand-to-metal charge transfer (LMCT) of the surface complex formed by the adsorption of

Page 15 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
benzyl alcohol on the TiO2 surface. 50, 51. Subsequently, compared with P25, TiO2/SBA-15
exhibited enhancement in activity, attributed to the decrease of the TiO2 nanoparticle size with
loading on the porous support, and small particles afforded high surface areas; hence, active site
densities for heterogeneously catalyzed reactions.
Upon introducing Au into the TiO2/SBA-15 sample, remarkable catalytic activity was
observed for the oxidation of benzyl alcohol both in the dark and under visible-light irradiation.
Among the supported gold catalysts, Au2/TiO2/SBA-15 exhibited the best performance. Under
dark conditions, the Au2/TiO2/SBA-15 catalyst afforded 7.57 ꢀmol of benzaldehyde, and light
irradiation further enhanced the reaction: 45.54 ꢀmol of benzaldehyde was produced, which is
approximately 3.3 times greater than that obtained by the use of the TiO2/SBA-15 catalyst; this
result is consistent with previous studies in that Au-loaded TiO2 markedly affected the catalytic
activity with or without light irradiation. However, at a Au loading of 5 wt%, the photoassisted
reaction resulted in a benzyl alcohol conversion less than that obtained with a lower gold loading.
The statistic from the TEM survey (Fig S2) suggested that the mean Au particle diameter
significantly increases in case of the excessive loading of the support material (TiO2/SBA-15),
resulting in
a low active surface area, and hence low benzaldehyde yield. When
Au2/TiO2/SBA-15-PD was used as the catalyst, a yield of only 14.9 ꢀmol of benzaldehyde was
obtained. The decrease of yield under the same experiment conditions is attributed to the blocking
of pores by several Au aggregates formed during photodeposition, resulting in the diffusion
limitations of the reactants. Such a remarkable photoactivity enhancement of Au2/TiO2/SBA-15
could be attributed to the several factors. First of all, owing to the limit of host material SBA-15,
the growth of TiO2 particles were restricted by the walls of the channels, thus small and well
dispersed TiO2 nanoparticles were obtained. Small titania particles were in favor of the migration
of charge carriers so that the recombination rate of them could be largely decreased. Secondly, the
SBA-15 decorated by TiO2 preserved a high surface area and possess a strong surface adsorption
ability to alcohol molecules. Thus, the adsorbed alcohol molecules on catalytic sites can be
supplied by the enriched adsorption sites near the TiO2 particles, which can effectively decrease
the diffusion limits of substrate and directly accelerate the reaction rate. And then, the intense
LSPR-enhanced electromagnetic fields were generated on the surface of the Au nanoparticles, which
significantly increased the yield of “hot electrons” at the interface. Thus, the localized electronic states

RSC Advances
Page 16 of 29
View Article Online
DOI: 10.1039/C6RA11390G
in the band gap of TiO2 can be excited, and electrons can be transferred to the conduction band of TiO2.
At last, the Schottky barrier at the Au–TiO2 interface functions as a barrier for the transferred electrons,
preventing them from traveling back to the Au nanoparticles and thus leading to an accumulation of
these transferred electrons in the TiO2 conduction band.
Fig 5. Amount of benzaldehyde formed during the oxidation of benzyl alcohol in the dark and
under visible light irradiation (λ >420 nm) over TiO2/SBA-15, Aux/TiO2/SBA-15, Au2/P25 and
P25.
According to the previous research works, the porous silicate materials such as clays, zeolites and
mesoporous silica are superior supports for accommodating photocatalysts nanoparticles, owing to
their tunable pore sizes (2–50 nm), large surface areas, and fine connectivity of the pores facilitating
the transfer of organic substrates43, 52. In the present study, SBA-15, Au2/TiO2/SBA-15 and Au2/P25
catalysts were selected as a model catalyst for FTIR measurement to determine the adsorption of
benzyl alcohol on the mesoporous silica support. As the FTIR spectra (Fig 6) show that all samples
exhibit a very broad band between 2750-3750 cm-1, indicating the presence of hydrogen-bonded
perturbed hydroxyl groups. As for the absorption spectrum of benzyl alcohol, the band at 1455 cm-1 is
readily assigned to skeletal vibration of the aromatic ring. This absorption band can also be observed

Page 17 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
on the SBA-15 and Au2/TiO2/SBA-15, which were treated by benzyl alcohol, indicating that molecular
benzyl alcohol exists on these solid samples. On the contrary, the molecular benzyl alcohol was barely
adsorbed on the catalyst of Au2/P25. The result reflected that the adsorption of porous support
(SBA-15) can effectively enrich the alcohol molecules in the tunnels, which played an identical role in
photocatalytic processes.
Figure 6. FTIR spectra of SBA-15, Au2/TiO2/SBA-15 and Au2/P25 catalysts with adsorbed benzyl
alcohol.
To better understand the enhancement mechanism of photocatalytic performance over
Au2/TiO2/SBA-15 catalyst, the effects of wavelength range on the photoactivity were investigated.
we used specific optical filter glasses (filter 1: 460 nm–800 nm, filter 2: 490 nm–800 nm, filter 3:
560 nm–800 nm, and filter 4: 620 nm–800 nm) for blocking light below cut-off wavelengths, and
Fig 7 shows the results. Without any filter, light irradiation with wavelength in the complete 420
nm to 800 nm range resulted in a reaction yield of 91.08%. Using a filter transmitting
wavelengths between 460 and 800 nm, the reaction yield decreased to 81.67%. On the other hand,
by increasing the cut-off wavelength to 490 nm, the yield decreased to 75.84%, while increasing

RSC Advances
Page 18 of 29
View Article Online
DOI: 10.1039/C6RA11390G
the cut-off wavelength to 560 nm and then 620 nm resulted in yields decreasing to 37.06% and
20.23%, respectively. Under dark conditions, the thermal reaction yield of benzaldehyde was
approximately 15.15%. As the reaction temperature was maintained constant (303K), the thermal
effect contribution remained constant. Hence, we can estimate the contribution of the light in
different wavelength ranges from the results acquired by irradiation with cut-off filters. Light
irradiation in the wavelength range of 460 nm–620 nm resulted in the greatest enhancement in
yield, accounting for 61.44% of the total light irradiation enhancement. The obtained reaction
yields were also confirmed by irradiation using monochromatic light LEDs (Fig 8). When the
reactor was illuminated with light of different wavelengths, such as blue (465–470 nm), yellow
(485–490 nm), green (525–530 nm), and red (625–630 nm) with other experimental conditions
constant, the trend of quantum yield was similar to that observed in the absorption spectrum.
Given that the LSPR absorption of Au NPs occurs in the wavelength range between 460 nm and
600 nm, the Au2/TiO2/SBA-15 photocatalyst harvests visible light, resulting in a significant
difference with respect to the enhancement of the reaction yield in photocatalysis.
Fig 7. Dependence of yield and irradiation wavelength over the Au2/TiO2/SBA-15 catalyst for the
selective oxidation of benzyl alcohol.

Page 19 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Fig 8. Diffuse-reflectance UV–vis spectra of the Au2/TiO2/SBA-15 catalyst and the quantum yield
for the formation of benzaldehyde under LED lamp irradiation of different wavelengths, such as
blue, green, yellow, and red light. The apparent quantum yield was calculated using the equation
ꢈ
ꢉ
/ N × 100%, where ꢐ and ꢐ
Φꢚꢛꢜ = ꢐꢝꢞꢟ − ꢐ
denote the yield of benzaldehyde
ꢓꢋꢠꢡ
ꢝꢞꢟ
ꢓꢋꢠꢡ
under light and dark conditions, respectively. N denotes the number of incident photons in the
reaction vessel.

RSC Advances
Page 20 of 29
View Article Online
DOI: 10.1039/C6RA11390G
Fig 9. Photocurrent transient response (a) and electrochemical impedance spectroscopy Nyquist
plots (b) of the sample electrodes of Au2/TiO2/SBA-15 and TiO2/SBA-15 under visible light irradiation.
In order to determine the formation and transfer of photogenerated electrons from semiconductor

Page 21 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
under light illumination, the photoelectrochemical characterizations were further authenticated. As
shown in Fig 9(a), under visible light irradiation, the photocurrent intensity for Au2/TiO2/SBA-15 is
much higher than that of TiO2/SBA-15. The obvious increase in the transient photocurrent was
mainly due to two aspects: (i) the Au NPs present can absorb visible light and generate more
photoelectrons due to the LSPR effect. (ii) the formation of a Schottky junction at the Au-TiO2
interface can separate the photoelectrons and holes, and thus increase the photocurrent. We
subsequently utilized the electrochemical impedance spectra (EIS) experiments to investigate the
electron generation and the charge transport characteristics of Au2/TiO2/SBA-15 and TiO2/SBA-15.
As can be seen from Fig 9(b), the Au2/TiO2/SBA-15 sample shows the smaller semicircle in the
middle-frequency region, in comparison to the TiO2/SBA-15, which indicates the more efficient
interfacial electron transfer. Owing to the fact that the surface plasmon resonance effect of the Au
NPs broadens the visible light response of the TiO2, and the excellent electron transport properties
hinders the fast recombination of photoelectron and hole pairs, such composite photocatalyst are
largely beneficial for improving visible light photoactivity toward aerobic oxidation of alcohols.
Fig 10. Controlled experiments using different radical scavengers (a) AgNO3 for photogenerated
electrons, (b) p-benzoquinone (BQ) for superoxide radicals; (c) ammonium oxalate (AO) for
photogenerated holes; (d) tert-butyl alcohol (TBA) for hydroxyl radicals; (e) absence of radical

RSC Advances
Page 22 of 29
View Article Online
DOI: 10.1039/C6RA11390G
scavengers for the photocatalytic selective oxidation of benzyl alcohol over Au2/TiO2/SBA-15.
React in the nitrogen atmosphere (f) and air atmosphere (g).
Herein, the underlying reaction mechanism involved for the photocatalytic oxidation of
benzyl alcohol in water over Au2/TiO2/SBA-15 was investigated in detail. Previous studies have
proven that molecular oxygen is the oxidizing agent for many photo-oxidation processes that are
catalyzed by TiO2. Moreover, this process is dominated by the adsorption of molecular oxygen on
the surface of TiO2 during the photocatalytic reaction. To better understand this process, we used
different radical scavengers in controlled experiments to probe the reaction mechanism for the
selective oxidation of benzyl alcohol over Au2/TiO2/SBA-15 under visible-light irradiation. As
shown in Fig. 10, no significant change in the reaction process was observed when TBA was
.
added to the reaction system to capture OH radicals. However, an abrupt decrease in the
conversion was observed upon the addition of either ammonium oxalate to capture photogenerated
holes (h+), AgNO3 to capture photoelectrons (e-), or benzoquinone to capture •O2- radicals.
Moreover, to investigate the role of molecular oxygen, the experiment was also conducted under
nitrogen and air atmospheres. The trace conversion of benzyl alcohol in the nitrogen atmosphere
was 17.3 %, but in the air atmosphere, a higher conversion was obtained (63.7%), but this
conversion was still less than that in pure oxygen (91.1%). These results demonstrated that for
aerobic oxidation of alcohols over Au2/TiO2/SBA-15 under visible light irradiation the positive
holes, oxygen, or superoxide radicals play important roles instead of hydroxyl radicals.

Page 23 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Fig 11. Expected reaction mechanism for the production of benzaldehyde from benzyl alcohol over
Au2/TiO2/SBA-15 under visible-light irradiation. Fermi level (EF), conduction (Ec) and valence (Ev)
bands energy for Au, wide-bandgap semiconductor (TiO2) of fabricated plasmonic nanostructure.
Considering the above results, the possible mechanism for the photocatalytic oxidation of
aromatic alcohols over Au2/TiO2/SBA-15 was proposed, and Fig 11 shows the mechanism. Once
Au and TiO2 come into contact, a Schottky junction was formed at the interface between Au and
TiO2, with the conduction and valence bands bending upward toward the TiO2 interface 53. Under
visible-light irradiation (λ > 420 nm), the incoming photons excited the LSPR of the Au NPs.
Electrons oscillating collectively by LSPR excitation may result in intraband excitation,
generating some hot electrons, the energies of which are greater than 1.0 eV with respect to the Au
Fermi level. Then, the hot electrons with energies sufficiently high to overcome the Schottky
barrier (φSB) are injected into the conduction band (Ec) of the neighboring TiO2. The hot electrons
on the TiO2 surface can be scavenged by molecular oxygen molecules, yielding an anion O–O−
species 54, 55. These superoxide species can abstract the α-H atoms of benzyl alcohol, affording a
transient alkoxide intermediate, which is considered to be the rate-determining step. Subsequently,
the transient alkoxide intermediate undergoes the rapid transfer of hydride from C–H to positively
charged Au, resulting in the elimination of β-H and affording the product. The proposed
mechanism provides reasonable explanation for the enhancement of photooxidation induced by

RSC Advances
Page 24 of 29
View Article Online
DOI: 10.1039/C6RA11390G
the LSPR effect under the visible-light irradiation of the Au2/TiO2/SBA-15 nanocomposite.
Initiated by the photoactivity of Au2/TiO2/SBA-15 for the selective oxidation of benzyl
alcohol, we further investigated the photocatalytic oxidation of various aromatic alcohols over
Au2/TiO2/SBA-15, TiO2/SBA-15, and Au2/P25, and Table 2 shows the results. As expected,
Au2/TiO2/SBA-15 exhibited high activity for the oxidation of aromatic alcohols as well as good
selectivity to carbonyl compounds, and the photocatalytic activity was several times greater than
those obtained for reference TiO2/SBA-15 and P25. Furthermore, the yields of different aromatic
aldehydes or ketones were clearly different. The formation rate of para-substituted benzaldehyde
over Au2/TiO2/SBA-15 decreased in the following order: –OCH3 > –CH3 > –H > –Cl, which is
governed by the Hammett rule. This order indicates that the substitution of para-substituted
benzylic alcohols with electron-releasing group such as –OCH3 and –CH3 increases the activity,
while substitution with –Cl decreases the activity 51. The above results suggested that the
Au2/TiO2/SBA-15 composite is an excellent photocatalyst for the selective oxidation of aromatic
alcohols to corresponding aldehydes.
It is important to note that the Au2/TiO2/SBA-15 nanocomposite exhibit good recyclability for
the photocatalytic oxidation of benzyl alcohol. Fig S3 shows the reaction results. Using the fresh
catalyst, the yield of benzaldehyde was 91.08%. After the first reaction cycles, the solid catalyst
was recovered by centrifugation and dried for the next reaction cycle. For recycling, fresh benzyl
alcohol and toluene were added, and the reaction conditions were the same as those employed in
the first reaction cycle. From the second to the fourth reaction cycle, yields of 90.52%, 85.34%,
and 84.3% were afforded. For the fifth reaction cycle, a conversion of greater than 79.15% was
still achieved. By-products were not detected throughout these consecutive reaction cycles.
Table 2. Aerobic oxidation of aromatic alcohols over Au2/TiO2/SBA-15, TiO2/SBA-15 and
Au2/P25 catalysts a.
Yield b
(%)
Selectivity c
(%)
Reaction rate
(ꢀmol gcat−1h−1)
227.4
Entry
1
Substrate
Product
Catalyst
Au2/TiO2/SBA-15
TiO2/SBA-15
91.1
>99
27.1
>99
67.68

Page 25 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
Au2/P25
Au2/TiO2/SBA-15
TiO2/SBA-15
Au2/P25
43.1
56.8
12.7
19.8
93.9
39.9
64.5
75.1
18.7
30.0
99.9
54.4
89.1
87.3
41.2
70.6
77.6
23.5
44.6
>99
97.1
84.6
89.8
>99
83.1
91.7
80.4
54.1
71.2
>99
82.5
96.1
87.6
55.5
73.8
91.5
60.1
74.2
107.63
137.8
26.8
2
3
4
5
6
7
44.45
234.5
82.89
147.87
150.9
25.29
53.4
Au2/TiO2/SBA-15
TiO2/SBA-15
Au2/P25
Au2/TiO2/SBA-15
TiO2/SBA-15
Au2/P25
Au2/TiO2/SBA-15
TiO2/SBA-15
Au2/P25
250.0
112.2
214.06
191.2
57.16
130.26
177.5
35.31
82.73
Au2/TiO2/SBA-15
TiO2/SBA-15
Au2/P25
Au2/TiO2/SBA-15
TiO2/SBA-15
Au2/P25
a Reaction conditions: toluene (5 mL), alcohol (50
b Aromatic aldehyde yield at time-on-stream of 4 h.
c selective of aldehyde or ketone at time-on-stream of 4 h.
ꢀmol), catalyst (50 mg), O2 (1 atm).
Conclusion
In summary, a series of gold-promoted TiO2/SBA-15 catalysts were prepared by a facile,
rapid microwave-assisted alcohol reduction method, exhibiting visible-light response for the
photocatalytic selective oxidation of alcohols. Comprehensive experimental measurements were
conducted using these catalysts for correlating the catalytic activity with the corresponding
loading amount and size of Au NPs. As compared with that of benchmark P25, the surface area of

RSC Advances
Page 26 of 29
View Article Online
DOI: 10.1039/C6RA11390G
anatase TiO2 nanoparticles and absorption ability dramatically increased through interaction with
these porous supports as the key parameter affecting photocatalytic activity. In addition, small
domains of monodisperse mesoporous silica resulted in the homogeneous deposition of Au NPs
inside the pores of the support, resulting in small Au NPs with a mean diameter of 4.8 nm for a Au
loading at 2 wt%. And the gold nanoparticles deposited onto TiO2 can greatly improve the
photocatalytic performance of alcohol oxidation. This enhancement effect may be attributed to the
increase in the formation rate of electron–hole pairs induced by LSPR of Au NPs and higher
efficiency of electron transfer due to the Schottky barrier at the Au–TiO2 interface. The simple
strategy and materials developed here dramatically improved photocatalytic activity and can also
be applied to other traditional catalytic reactions.
Acknowledgements
This work was supported by International Joint Research Projects in the Science & Technology
Pillar Program of Tianjin, China (13RCGFSF14300), Research Projects in the Science &
Technology Pillar Program of Tianjin, China (14TXGCCX00012), Research Projects in the
Science & Technology Pillar Program of Tianjin, China (15JCTPJC63300), Research Projects in
the Science & Technology Program of Jinnan District Tianjin, China (2015JNKW0005) and the
Ph.D. Candidate Research Innovation Fund of Nankai University.
References
1.
2.
T. Mallat and A. Baiker, Chem. Rev., 2004, 104, 3037-3058.
D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu, A. F. Carley, A. A. Herzing, M.
Watanabe, C. J. Kiely, D. W. Knight and G. J. Hutchings, Science, 2006, 311, 362-365.
A. Abad, P. Concepción, A. Corma and H. García, Angew. Chem. Int. Ed., 2005, 44,
4066-4069.
3.
4.
C. Y. Ma, B. J. Dou, J. J. Li, J. Cheng, Q. Hu, Z. P. Hao and S. Z. Qiao, Appl. Catal. B
Environ., 2009, 92, 202-208.
5.
6.
7.
8.
A. Tanaka, K. Hashimoto and H. Kominami, J. Am. Chem. Soc., 2012, 134, 14526-14533.
G. J. Ten Brink, I. W. C. E. Arends and R. A. Sheldon, Science, 2000, 287, 1636-1639.
F. M. Menger and C. Lee, Tetrahedron Letters, 1981, 22, 1655-1656.
V. Augugliaro, G. Camera-Roda, V. Loddo, G. Palmisano, L. Palmisano, J. Soria and S.
Yurdakal, J. Phys. Chem. Lett., 2015, 6, 1968-1981.
9.
J. C. Colmenares and R. Luque, Chem. Soc. Rev., 2014, 43, 765-778.

Page 27 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
10.
11.
N. Zhang, Y. Zhang, X. Pan, X. Fu, S. Liu and Y. J. Xu, J. Phys. Chem. C, 2011, 115,
23501-23511.
S. Yurdakal, G. Palmisano, V. Loddo, V. Augugliaro and L. Palmisano, J. Am. Chem. Soc.,
2008, 130, 1568-1569.
12.
13.
M. Zhang, C. Chen, W. Ma and J. Zhao, Angew. Chem. Int. Ed., 2008, 47, 9730-9733.
M. Zhang, Q. Wang, C. Chen, L. Zang, W. Ma and J. Zhao, Angew. Chem. Int. Ed., 2009, 48,
6081-6084.
14.
15.
S. Sarina, H. Zhu, E. Jaatinen, Q. Xiao, H. Liu, J. Jia, C. Chen and J. Zhao, Journal of the
American Chemical Society, 2013, 135, 5793-5801.
Y. Chen, W. Li, J. Wang, Y. Gan, L. Liu and M. Ju, Applied Catalysis B: Environmental, 2016,
191, 94-105.
16.
17.
X. Pan and Y. J. Xu, ACS Appl. Mater. Interfaces, 2014, 6, 1879-1886.
X. Dai, M. Xie, S. Meng, X. Fu and S. Chen, Appl. Catal. B Environ., 2014, 158-159,
382-390.
18.
19.
20.
C. Wang and D. Astruc, Chem. Soc. Rev., 2014, 43, 7188-7216.
S. Linic, P. Christopher and D. B. Ingram, Nature Materials, 2011, 10, 911-921.
K. Awazu, M. Fujimaki, C. Rockstuhl, J. Tominaga, H. Murakami, Y. Ohki, N. Yoshida and T.
Watanabe, Journal of the American Chemical Society, 2008, 130, 1676-1680.
P. Zhang, T. D. Wang and J. Gong, Adv Mater, 2015, 27, 5328-5342.
D. Tsukamoto, Y. Shiraishi, Y. Sugano, S. Ichikawa, S. Tanaka and T. Hirai, J. Am. Chem. Soc.,
2012, 134, 6309-6315.
21.
22.
23.
24.
S. Schünemann, G. Dodekatos and H. Tüysüz, Chem. Mater., 2015, 27, 7743-7750.
K. Qian, B. C. Sweeny, A. C. Johnston-Peck, W. Niu, J. O. Graham, J. S. Duchene, J. Qiu, Y.
C. Wang, M. H. Engelhard, D. Su, E. A. Stach and W. D. Wei, Journal of the American
Chemical Society, 2014, 136, 9842-9845.
25.
26.
27.
28.
Y. Chen, J. Wang, W. Li and M. Ju, Mater Lett, 2015, 159, 131-134.
D. Ding, K. Liu, S. He, C. Gao and Y. Yin, Nano Lett., 2014, 14, 6731-6736.
X. Li, W. Zheng, H. Pan, Y. Yu, L. Chen and P. Wu, J. Catal., 2013, 300, 9-19.
X. F. Qian, T. Kamegawa, K. Mori, H. X. Li and H. Yamashita, J. Phys. Chem. C, 2013, 117,
19544-19551.
29.
30.
31.
A. Corma and H. Garcia, Chem. Commun., 2004, DOI: 10.1039/B400147H, 1443-1459.
M. Anpo and J. M. Thomas, Chem. Commun., 2006, DOI: 10.1039/b606738g, 3273-3278.
M. Murdoch, G. I. N. Waterhouse, M. A. Nadeem, J. B. Metson, M. A. Keane, R. F. Howe, J.
Llorca and H. Idriss, Nat. Chem., 2011, 3, 489-492.
32.
S. Zhu, S. Liang, Q. Gu, L. Xie, J. Wang, Z. Ding and P. Liu, Applied Catalysis B:
Environmental, 2012, 119-120, 146-155.
33.
34.
35.
36.
N. Kruse and S. Chenakin, Appl. Catal. A Gen., 2011, 391, 367-376.
Y. Wang, J. Yu, W. Xiao and Q. Li, J. Mater. Chem. A, 2014, 2, 3847-3855.
T. Wang, X. Yuan, S. Li, L. Zeng and J. Gong, Nanoscale, 2015, 7, 7593-7602.
M. P. Casaletto, A. Longo, A. M. Venezia, A. Martorana and A. Prestianni, Appl. Catal. A Gen.,
2006, 302, 309-316.
37.
38.
M. Han, X. Wang, Y. Shen, C. Tang, G. Li and R. L. Smith Jr, J. Phys. Chem. C, 2010, 114,
793-798.
F. Ying, S. Wang, C. T. Au and S. Y. Lai, Gold Bulletin, 2010, 43, 241-251.

RSC Advances
Page 28 of 29
View Article Online
DOI: 10.1039/C6RA11390G
39.
M. Farnesicamellone, J. Zhao, L. Jin, Y. Wang, M. Muhler and D. Marx, Angew. Chem. Int.
Ed., 2013, 52, 5780-5784.
40.
41.
J. Wang, B. Li, T. Gu, T. Ming, J. Wang, P. Wang and J. C. Yu, ACS Nano, 2014, 8, 8152-8162.
B. Mei, C. Wiktor, S. Turner, A. Pougin, G. Van Tendeloo, R. A. Fischer, M. Muhler and J.
Strunk, ACS Catal., 2013, 3, 3041-3049.
42.
C. J. Liu, Y. Zhao, Y. Li, D. S. Zhang, Z. Chang and X. H. Bu, ACS Sustainable Chem. Eng.,
2014, 2, 3-13.
43.
44.
X. Zhang, X. Ke and H. Zhu, Chemistry - A European Journal, 2012, 18, 8048-8056.
X. Yang, C. Huang, Z. Fu, H. Song, S. Liao, Y. Su, L. Du and X. Li, Appl. Catal. B Environ.,
2013, 140-141, 419-425.
45.
46.
47.
48.
49.
50.
51.
52.
L. Guczi, G. Petö, A. Beck, K. Frey, O. Geszti, G. Molnár and C. Daróczi, J. Am. Chem. Soc.,
2003, 125, 4332-4337.
H. Tsunoyama, H. Sakurai, Y. Negishi and T. Tsukuda, J. Am. Chem. Soc., 2005, 127,
9374-9375.
S. Verma, R. B. N. Baig, M. N. Nadagouda and R. S. Varma, ACS Sustainable Chemistry &
Engineering, 2015, DOI: 10.1021/acssuschemeng.5b01163.
Y. Sugano, Y. Shiraishi, D. Tsukamoto, S. Ichikawa, S. Tanaka and T. Hirai, Angewandte
Chemie - International Edition, 2013, 52, 5295-5299.
T. Jiang, C. Jia, L. Zhang, S. He, Y. Sang, H. Li, Y. Li, X. Xu and H. Liu, Nanoscale, 2015, 7,
209-217.
S. Higashimoto, N. Kitao, N. Yoshida, T. Sakura, M. Azuma, H. Ohue and Y. Sakata, J. Catal.,
2009, 266, 279-285.
S. Higashimoto, N. Suetsugu, M. Azuma, H. Ohue and Y. Sakata, Journal of Catalysis, 2010,
274, 76-83.
K. Mori, P. Verma, R. Hayashi, K. Fuku and H. Yamashita, Chemistry - A European Journal,
2015, 21, 11885-11893.
53.
54.
55.
C. Clavero, Nature Photonics, 2014, 8, 95-103.
P. Christopher, H. Xin, A. Marimuthu and S. Linic, Nat. Mater., 2012, 11, 1044-1050.
P. Christopher, H. Xin and S. Linic, Nat. Chem., 2011, 3, 467-472.

Page 29 of 29
RSC Advances
View Article Online
DOI: 10.1039/C6RA11390G
229x146mm (96 x 96 DPI)