TiO2 nanosheet-anchoring Au nanoplates: High-energy facet and wide spectra surface plasmon-promoting photocatalytic efficiency and selectivity for CO2 reduction

Article abstract of DOI:10.1039/c6ra14821b

An Au-TiO₂ nanocomposite consisting of (001) exposed TiO₂ nanosheet-anchored Au nanoplates was successfully fabricated using bifunctional linker molecules and applied for the photocatalytic reduction of CO₂ into hydrocarbon fuels. This unique nanocomposite benefits from the combination of the higher photocatalytic activity of TiO₂ (001) and the visible to near-infrared region plasma resonances of anisotropic Au nanostructures. Several carbon fuels were selectively produced over the Au-TiO₂ nanocomposite, including CO, CH₄, CH₃OH and CH₃CH₂OH, under different forms of light irradiation and in different reaction systems. Both photoresponse testing and electrochemical impedance spectroscopy measurements confirm the importance of the Au surface plasmon for the photocatalytic activity.

Full text of DOI:10.1039/c6ra14821b

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Y. Zhou, Z. zou, P.
Li, M. Wang , L. Tang, W. Tu and Q. Han, RSC Adv., 2016, DOI: 10.1039/C6RA14821B.
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

Please do not adjust margins
RSC Advances
Page 1 of 7
View Article Online
DOI: 10.1039/C6RA14821B
Journal Name
ARTICLE
TiO2 Nanosheet-Anchoring Au nanoplates: High-energy
Facet and Wide Spectra Surface Plasmon-Promoting
Photocatalytic Efficiency and Selectivity of CO2 Reduction
Received 00th January 20xx,
Accepted 00th January 20xx
Meng Wang,a,b,c,d,†Qiutong Han, a,b,c,d,†Yong Zhou,*,a,b,c,d Ping Li,a,b,c,d Wenguang Tu,a,b,c,d
Lanqin Tang,a,b,c,d,e Zhigang Zou,*,a,c,d
DOI: 10.1039/x0xx00000x
www.rsc.org/
The Au-TiO2 nanocomposite consisting of (001) exposed TiO2 nanosheet-anchored Au nanoplate was successfully
fabricated by using bifunctional linker molecules. Being applied for photocatalytic reduction of CO2 into hydrocarbon fuels,
this unique nanocomposite benefits for the combination of higher photocatalytic activity of TiO2 (001) and the visible to
near-infrared region plasma resonances of the anisotropic Au nanostructure. Several carbon fuels were selectively
produced over the Au-TiO2 nanocomposite, including CO, CH4, CH3OH, and CH3CH2OH and so on under different light
irradiation and reaction systems. Both photoresponse test and electrochemical impedance spectroscopy measurement
confirm the importance of the Au surface plasmon on the photocatalytic activity.
Ag, which are then transferred to the conduction band of the
adjacent TiO2 to take part in the redox reaction.4, 5 The surface
plasmon frequency is determined with not only the dispersion
Introduction
The rapid development of human society based on fossil fuels
results in serious environmental and energy problems. Excessive
consumption of fossil fuels leads to an energy crisis. Subsequently,
the unregulated emissions of greenhouse gases, particularly carbon
dioxide (CO2), could deteriorate the global climate. As solar energy
is a clean and abundant energy source, photocatalytic reduction of
CO2 to yield fuels/chemicals is a promising route to solve the above
problems. During the reaction process, photocatalysts play a
critically important role. In order to find appropriate photocatalysts,
various materials such as TiO2, Zn1.7GeN1.8O, ZnAl2O4, Bi2WO6,
InTaO4, ZnGaNO and so on have been researched.1
relation of the metal but also a number of other parameters, such
as particle size and shape, surface modification of the particle, and
changes in dielectric constant of the surrounding medium.6 While
spherical nanoparticles were widely studied for surface plasmon-
enhanced photocatalytic efficiency of semiconductors, both
experiment data and theoretical calculation show that the plasma
resonances of anisotropic nanostructures, in particular for one-
dimensional nanorods, are strong and tunable throughout the
visible to near-infrared (NIR) region in the spectrum. Not only
transversal plasma is similar to sphere particles, but also the
resonance of the longitudinal mode is red-shifted and strongly
depends on aspect ratio of the anisotropic nanostructures. A wide-
range visible and NIR light harvesting of TiO2 nanoparticles was
frequently reported through introducing Au nanorods as antennas.7
The order of the average surface energies of anatase TiO2 is 0.90
J/m2 for (001) > 0.53 J/m2 for (100) > 0.44 J/m2 for (101).8, 9 The
(001)-exposed TiO2 was demonstrated to possess more effective
photocatalytic performance.10, 11 While Au nanoparticles-promoted
SPR enhancement of photoactivity of the TiO2 nanosheet was
exploited through anchoring the metal nanoparticle onto it,12, 13
however, benefit combination of higher photocatalytic activity of
TiO2 (001) and the visible to near-infrared region plasma resonances
of anisotropic Au nanostructures has not yet reported because of
technique difficulty of tight attachment of TiO2 nanosheets onto
anisotropic metal nanostructures, typically like Au nanorods due to
its curve surface.
Irradiation of noble metals (e.g. Au or Ag) with light near their
surface plasmon resonance (SPR) frequency will generate intense
local electric fields near the surface of the metals.2,3 The electric
field intensity of local plasmonic “hot spots” can reach much higher
than that of the incident electric field. Thus an increased amount of
photo-induced electron-hole pair is generated locally in the
photocatalyst due to the local field enhancement of the plasmonic
metal nanoparticles. Tatsuma’s group first proposed a charge
transfer mechanism in 2004 that the SPR excites electrons in Au or
a.Jiangsu Key Laboratory for Nano Technology, Nanjing University, Nanjing 210093,
P. R. China
b.Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, School of
Physics, Nanjing University, Nanjing 210093, P. R. China
c. Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University,
Nanjing, Jiangsu 210093, P. R. China
d.National Laboratory of Solid State Microstructures, Collaborative Innovation
Center of Advanced Microstructures, Nanjing University, Nanjing 210093, P. R.
China
Two-dimensional, regular Au nanoplates with flat surface attract
much attention for wide-range spectrum-based SPR-promoting
photocatalytic efficiency of TiO2 nanosheets. The nanoplates not
only exhibit strong surface plasmon absorption in visible region and
e.
College of Chemistry and Chemical Engineering, Yangcheng Institute of
Technology, Yancheng 22401, P. R. China
f.
†
M.W. and H. Q. contributed equally to the work.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 7
View Article Online
DOI: 10.1039/C6RA14821B
ARTICLE
Journal Name
the NIR region14, but also are feasible to combine with TiO2
The morphology of the samples was observed by the field
nanoplates from the viewpoint of morphology configuration. In this emission scanning electron microscopy (FE-SEM) (FEI NOVA
paper, we report the synthesis of the Au-TiO2 nanocomposite NanoSEM230, USA) and Transmission electron microscopy (TEM)
through anchoring nm-sized (001) exposed TiO2 nanosheets onto (JEOL 3010, Japan). The atom force microscopy (AFM) image was
µm-sized Au nanoplates. The unique Au-TiO2 nanocomposite collected by a MFP3D microscope (Asylum Research, MFP-3D-SA,
exhibits great performance for the efficient photoreduction CO2 USA). The crystallographic phase of these as-prepared products was
into renewable hydrocarbon fuel under visible light, of even NIR determined by powder X-ray diffraction (XRD) (Rigaku Ultima III,
region. The enhancement of large photoactivity was induced by Japan) using Cu-Ka radiation (λ
= 0.154178 nm). The X-ray
both transversal and longitudinal plasma of Au nanoplates. Various photoelectron spectroscopy (XPS) spectrum (K-Alpha, THERMO
carbon fuel from the photoreduction of CO2 including CO, CH4, FISHERSCIENTIFIC) was calibrated with respect to the binding
CH3OH, and CH3CH2OH can be produced over the present Au-TiO2 energy of the adventitious C 1s peak at 284.8 eV. The UV-visible
nanocomposite, depending on the both applied light wavelength (UV-vis) diffuse reflectance spectra were recorded with a UV-vis
and reaction media.
spectrophotometer (UV-2550, Shimadzu) and the UV-vis-NIR at
room temperature diffuse reflectance spectra were recorded with a
UV-vis-NIR
spectrophotometer
(UV-3600,
Shimadzu)and
Experimental Section
transformed to the absorption spectra according to the Kubelka–
Munk relationship.
Preparation of Au-TiO2 composites.
Measurement of Photocatalytic Activity
Typically, 20 ml ethylene glycol (EG) in the round-bottom flask was
heated to 150 ◦C in air atmosphere in an oil bath stirring
magnetically. 4 ml HAuCl4 solution (0.05 M, in EG) and 8 ml
hexadecyl trimethyl ammonium bromide (CTAB) solution (0.05 M,
in EG) were mixed together and then kept at 80 ◦C in an oven for 10
minutes.14After preheating, the mixture was injected quickly into
In the photocatalytic reduction of CO2 in gas-solid reaction system,
0.1 g of the as-prepared Au-TiO2 samples was uniformly dispersed
on the circular glass reactor with an area of 4.2 cm2. A 300 W Xe
lamp was used as the light source for the photoreduction. The
volume of the reaction system was about 230 ml. The reaction
setup was vacuum-treated several times, and then the high purity
of CO2 gas was maintained in the reaction setup for reaching
ambient pressure. 0.4 ml of deionized water was injected into the
reaction system as a reducer. The samples were allowed to
equilibrate in the CO2–H2O atmosphere for several hours to ensure
that the adsorption of gas molecules was completed. During the
irradiation, 1 ml of gas was continually taken from the reaction cell
at given time intervals for subsequent CH4 or CO concentration
analysis by using a gas chromatograph (GC-2014, Shimadzu Corp.,
Japan).
the heated EG solution within 15 seconds. Then
6 ml
polyvinylpyrrolidone (PVP) solution (111 mg/ml, in EG) was injected
dropwise during a period of 2 min. The reactant mixture was
◦
continuously stirred at 150 C for 30 min. For the subsequent use,
the samples were centrifuged with acetone at ∼3000 rpm for 20
min. To remove the possible contamination, the product was
centrifuged with ultrapure deionized water twice. The final samples
were kept in the ultrapure deionized water.
The TiO2 nanosheet with (001) exposed active facets were
prepared through
a
modified method.15 Typically, 1.5 ml of
tetrabutyl titanate and 0.7 ml of hydrofluoric acid (30% m/m) was
injected into a mixture of 20 ml of propanol and 20 ml isopropanol,
and the white suspension was obtained. The reactant was
magnetically stirred for 3 h, and then transferred to a Teflon–lined
stainless–steel autoclave. The autoclave was heated at 200 °C for 18
h and cool down naturally. At last, white precipitates were collected,
washed, and dried by lyophilization.
In the photocatalytic reduction of CO2 in aqueous solution, 0.1 g
of photocatalyst was dispersed in 100 ml of l.0 M NaHCO3 aqueous
solution. The suspension was placed into a quartz photoreactor,
which had an effective volume of 300 ml. Pure CO2 gas was
subsequently bubbled through the photocatalyst suspension for at
least 30 min to purge air and to saturate the solution. Then the
reactor was sealed with rubber stopper and the reaction solution
To obtain Au-TiO2 composites with TiO2 nanosheets loading on
Au nanoplates, 157 mg (calculated according to 0.8 mmol of
participant HAuCl4) as-prepared Au nanoplates were first incubated
in mercaptopropionic acid (MPA) solution to create a monolayer on
the nanoplates surface with the thiol group attached to Au and the
carboxylic acid group exposed outward. 300 mg TiO2 nanosheets
were dispersed in deionized water, and then injected into the
above Au nanoplates solution while the solution was magnetically
stirred. The mixed solution was stirred wildly at room temperature
for 24 h. After 10 hours’ standing, there were precipitates on the
bottom of the beaker. Removing the supernatant white precipitates,
the lower purplish grey precipitates were collected and dried by
lyophilization. Finally, the samples were heated at 300°C for 4 h to
remove the contamination.
was stirred continuously with
a magnetic stirrer to prevent
sedimentation of photocatalyst. The reactor was irradiated by a 300
W Xe lamp and was cooled by using recirculating cooling water
system. During the irradiation, 2 ml of solution was continually
taken from the photoreactor at given time intervals for subsequent
constituent and concentration analysis by using
a headspace
autosampler and a gas chromatograph (Agilent 7697A HS and
Agilent 7890B GC).
In situ DRIFTS analysis.
In situ diffuse reflectance infrared Fourier transform spectroscopy
(DRIFTS) is one of the most powerful tools to identify and
characterize adsorption species and reaction intermediates on the
catalyst surface. The IR spectra were recorded with a Nicolet 6700
spectrometer. The spectra were displayed in absorbance units and
acquired with a resolution of 4 cm-1, using 32 scans. The dome of
Characterization of Au-TiO2 composites.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 7
View Article Online
DOI: 10.1039/C6RA14821B
Journal Name
ARTICLE
the DRIFTS cell has two KBr windows allowing IR transmission and a COOH). The preparation procedure was schematically illustrated in
third (quartz) window allowing transmission of irradiation.
Fig 3 FE-SEM images of TiO2 nanosheet-attached Au nanoplate.
Fig 1. For anchoring of the TiO2 onto the Au nanoplate, the Au
nanoplate surface was firstly modified with MPA solution as the
thiol group tends to attach to the Au nanoplate. Thus, the
carboxylic acid group on the other side of the MPA molecular
Fig 1. Schematic illustration of the preparation procedure of the Au-TiO2
exposed outward. With injection of the suspension of TiO2
composites.
nanosheets into the above MPA-modified Au nanoplate suspension,
Prior to the adsorption/desorption, the sample was purged by N2
the TiO2 nanosheets then adhere onto the Au nanoplate through
for 1 h at 300 °C to clean the catalyst surface. A CO2–H2O mixture
bonding the carboxylic acid group.16 Finally, calcination to remove
was continuously introduced to the DRIFTS cell for 20 min, followed
MPA allows for production of clean Au-TiO2 composites.
by a 20 min stream of N2 to purge physical absorption over the
The FE-SEM image shows that the TiO2 nanosheet exhibits
catalyst surface. Finally, the UV-visible irradiation was introduced to
regular square shape (Fig 2a). TEM images clearly reveal that the
the cell for 20 min to investigate the effect of photo irradiation on
nanosheet possess regular lamellar shape with the edge size of ~20-
the conversion of reaction intermediates and desorption of
30 nm and the thickness of 7-8 nm. (Fig 2b). The high resolution
products.
TEM (HRTEM) image shows the clear lattice fringes, perfectly
aligning across the entire surface (Fig 2c), indicating a single-
crystalline structure of the TiO2 nanosheet. The distances of the 2D
crystal lattices are both 3.52 Å, which can be indexed to (101)
planes of anatase TiO2. The HRTEM image of a vertically standing
Photoresponse test and Electrochemical Impedance Spectroscopy
(EIS) measurement.
Au-TiO2 composites were deposited on FTO electrodes via
electrophoresis. The photoelectrochemical properties of Au-TiO2
were tested in a three-electrode cell using an electrochemical
analyzer (CHI-630D, Shanghai Chenhua). The electrolyte was 1 M
NaOH aqueous solution (pH 13.6). The hematite photoanode was
used as a working electrode. A Pt wire and a saturated calomel
electrode (SCE) were used as a counter and a reference electrode,
respectively. The film area exposed to the light was 0.28 cm2. The
light source was a 500 W xenon lamp. The light intensity was 128
mW cm-2. The electrochemical impedance spectra (EIS) of the
samples were measured using an electrochemical analyzer
(Solartron 1260 + 1287) with a 10 mV amplitude perturbation and
frequencies between 0.1 Hz and 1 MHz. 0.1 M Na2SO4 aqueous
solution was used as an electrolyte for EIS measurements.
nanosheet shows the basal (001) plane with the lattice fringe of
d
= 2.37 Å (Fig 2d).17 These data demonstrate that the TiO2
(001)
nanosheet grows preferentially along the {101} surrounding planes,
and was enclosed by {001} top and bottom surfaces. The typical FE-
SEM image of Au nanoplates shows that the products were
dominated by hexagonal and triangular nanoplates (Fig 4a). The
edge size of the nanoplates distributes from about 1 μm to 5 μm.
The section analysis on the AFM image shows that the nanoplate is
of a quite smooth surface over the width and about 26 nm in
average thickness (Fig S1, see Supporting Information). Fig 3 give
the FE-SEM images of the TiO2 nanosheet-attached Au nanoplate.
Relative to the bare Au nanoplates, numerous TiO2 nanosheets
were sticked on the Au nanoplate tightly, typically replicating the
triangle morphology of the Au nanoplate. The TEM image further
reveals that the considerable small TiO2 nanosheets were attached
on the Au nanoplates (Fig 4b). The electron diffraction pattern
identifies the presence of Au and TiO2 (Fig 4c).
Results and discussion
We decorated Au nanoplates with TiO2 nanosheets by using a
bifunctional linker molecular, mercaptopropionic acid (MPA, HS-R-
Fig 2 (a) FE-SEM image of TiO2 nanosheets, (b) TEM image and (c), (d) HRTEM images of TiO2 nanosheets.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 7
View Article Online
DOI: 10.1039/C6RA14821B
ARTICLE
Journal Name
Fig 4 (a) FE-SEM image of Au nanoplates; (b) TEM image of TiO2
nanosheet-attached Au nanoplate and (c) the electron diffraction
pattern.
Fig 6 CH4 evolution rate of (a) TiO2 and (b) Au-TiO2 under UV-vis
light irradiation; (c) CH4 and (d) CO evolution rate of Au-TiO2
under visible-light irradiation.
The XRD pattern of the Au-TiO2 nanocomposite confirms the
presence of the anatase TiO2 and cubic-phase Au, respectively (Fig
S2). The XPS spectrum of the Au-TiO2 composites also shows the
presence of Au 4f, Ti 2p, and O 1s peaks (Fig S3). The bonding
energies of the Au 4f7/2 peak and Au 4f5/2 peak are located at 82.75
eV and 86.51 eV, respectively, indicating that the Au element is
persisted in metallic format. The Ti 2p peaks appear at 458.3 eV and
463.9 eV, and the O 1s peak at 529.4 eV.
NIR spectrum, assigned to the weak SPR absorption peak at 1350
nm. It should be mentioned that CO was not detected with NIR
irradiation, possibly due to too lower yield beyond the minimum
limitation of detection. The visible and NIR light activity of the
photocatalysis obviously originate from the SPR effect of both
transversal and longitudinal models of the Au nanoplate.
UV-visible diffuse reflectance spectroscopy shows that the
pristine TiO2 nanosheets with an absorption edge at about 380 nm
display
a bandgap of 3.2 eV (Fig 5a), which indicates TiO2
nanosheets only respond to ultraviolet light. The Au-TiO2
nanocomposite exhibits very strong light absorbance in UV-visible
and near infrared range (Fig 5b).18 While the absorption wavelength
shorter than 400 nm is assigned to TiO2, the peak near 500 nm
originated from the transverse mode of plasmon resonance of the
Au nanoplate, and the peaks near 730 nm and near-infra 1350 nm
are referred to the longitudinal mode of plasmon resonance.19-21
Fig 7 Schematic illustration of the charge separation and transfer
in the Au-TiO2 system and photoreduction of CO2 into different
products.
Considering different products generated under UV-vis
irradiation and visible light irradiation (Fig 7), on the one hand, the
formation of CH4 (Eredox/SCE = − 0.48 V) is thermodynamically more
feasible than the formation of CO (Eredox/SCE = −0.77 V) if the supply
of protons and electrons is high enough.22 On the other hand, the
sorts of products also kinetically depend on the number of
Fig 5 (a) UV-vis diffuse reflectance spectroscopy of TiO2 and (b) UV-
vis-NIR
diffuse
reflectance
spectroscopy
of
Au-TiO2
To evaluate the photocatalytic activity of the Au-TiO2 composites,
we performed the photocatalytic CO2 reduction in the presence of
water vapor. Under UV-visible light irradiation, the CH4 evolution
rate of the Au-TiO2 nanocomposite was detected ~0.65 μmol h-1g-1,
twice higher than that for pure TiO2 nanosheets (0.32 μmol h-1g-1)
(Fig 6, curve b and a, respectively). Blank experiment with identical
condition and Ar to replace CO2 shows no appearance of CH4,
proving that the carbon source is completely derived from CO2.
With visible light (λ > 420 nm) irradiation, the pure TiO2 nanosheet
with wide bandgap of 3.2 eV exhibited no apparent photocatalysis
activity, and no any hydrocarbon species were reasonably detected.
In contrast, visible-light irradiation of the Au-TiO2 nanocomposite
enables to produce not only CH4 but also CO with the evolution
rates of 0.039 μmol h-1g-1 and 0.049 μmol h-1g-1, respectively (Fig 6,
curve c and d). Interestingly, the Au-TiO2 composite irradiated
under NIR light (λ > 800 nm) also produced CH4 of 0.0125
µ
mol h-1 g-
8 h irradiation. It demonstrates that the Au-TiO2
Fig 8 In situ DRIFTS spectra of (a) CO2 and H2O adsorption on Au-
TiO2 in the dark, (b) under UV-vis irradiation for 20 min, and (c)
under visible irradiation for 20 min.
1
after
nanocomposite truly exhibit photocatalytic response toward the
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 7
View Article Online
DOI: 10.1039/C6RA14821B
Journal Name
ARTICLE
electrons and protons. CO is formed by reacting with two protons of irradiation, as displayed in Table 1. UV-visible light irradiation of
and two electrons, while CH4 formation needs eight electrons and both pure TiO2 and the Au-TiO2 nanocomposite generates CH3OH,
eight protons. The simultaneous formation of CH4 and CO under the and the yield with the Au-TiO2 nanocomposite was reasonably
visible light irradiation is possibly owing to the compromise higher than that of the pure TiO2. In addition, C2 species including
between charge transfer and thermodynamics. CO was produced CH3CH2OH and CH3CHO were also detected under visible light
under visible light possibly due to the paucity of electrons. UV- irradiation. Obviously, the selectivity of products with C1 or C2 is
visible light promotes the generation of electron-hole pairs on the also closely related to the irradiation spectral region in the aqueous
TiO2 of the Au-TiO2 composites. Because the Fermi level of Au is reaction medium. While the reaction mechanism of the CO2
lower than the TiO2 conduction band, the Schottky barriers can photoreduction is much complex, the present C2 species may come
remove the photoexcited electrons from the surface of TiO2 to Au from coupling reaction between intermediate radicals, such as ·CH3.
and accumulates therein, subsequently reducing the electron–hole The detail mechanism is currently under investigation.
recombination.2 At the same time, the SPR excitation in the Au
To further demonstrate the SPR effect on the enhancement of
nanoplate also generates hot electrons that occupy energy levels photocatalytic performance of the Au nanoplate, the
above the Fermi level of the Au. Thus, enough number of electrons photoresponses of the Au-TiO2 electrodes were studied (Fig 9). The
and protons were available for CO2 molecules to get eight electrons photoresponses curves were measured with light on/off cycles at 0
to converse into CH4. Under visible-light irradiation, in contrast, V versus SEC (saturated calomel electrode). Compare to TiO2, A fast
only energetic hot electrons in Au injecting into the conduction and uniform photocurrent response is observed for each light on
band of TiO2 participate in the photoreduction of CO2. Therefore, and light-off in the Au-TiO2 electrode under both UV-visible and
local electron density would be relative low, which makes part of visible light irradiation. The photocurrent density of the Au-TiO2
CO2 molecules to obtain only two electrons to form CO.
electrode is detected 5.5 µA/cm2 under UV-visible irradiation (Fig
To further understand originality of the different products of 9a), which originate from both TiO2 excitation and Au SPR effect. To
photoreduction of CO2 under different light irradiation, in situ only consider SPR effect and elimination of TiO2 excitation, the Au-
DRIFTS spectra of CO2 and H2O co-interaction with the Au-TiO2 TiO2 electrode was visible-light irradiated and still shows obvious
catalyst was traced under light irradiation. CO2 and H2O were firstly photocurrent response, reaching about ~ 3.5 µA/cm2 (Fig 9b). Fig
adsorbed on Au-TiO2, and a stream of N2 was then introduced
continuously to the DRIFTS cell for 20 min to purge physi-
desorption. Several peaks were observed including bidentate
carbonate (b-CO32-, 1230, 1411 and 1479 cm-1), monodentate
carbonate (m-CO32-, 1294 cm-1), surface H2O (1624 cm-1) and
-
-
bicarbonate (HCO3 , 1660 cm-1) (Fig 8a). Bicarbonate (HCO3 ) was
possibly formed from CO2 interaction with OH groups and Ti3+
sites,23, 24 while b-CO3 is produced by CO2 coordination with an
2-
unsaturated O2 and OH groups are produced by surface H2O. Upon
UV-vis irradiation, the peak for the surface H2O disappeared due to
the photosplitting (Fig 8b). Under visible light irradiation, a new
peak which represents adsorption of formic acid (HCOOH, 1725 cm-
1) appeared via CO2 + 2H+ + 2e– → HCOOH25 (Fig 8c), compared to
that under UV-vis light irradiation. HCOOH was generally considered
to be the intermediates of CO through HCOOH → CO + H2O.26 The
apparent peaks for the surface H2O may also possibly originate from
HCOOH disassociation.
The product selectivity is dependent on not only different light
Table 1 Photocatalytic products yields in aqueous solution after
6 hours of irradiation.
Photocatalytic product yield (μmol g-1)
Spectral region
CH3OH
14.71
20.98
0
CH3CH2OH
CH3CHO
(TiO2) UV-visible light
(Au-TiO2) UV-visible light
(Au-TiO2) Visible light
0
0
0
0
Fig 9 Photoresponses of Au-TiO2 (a) under UV-visible irradiation, (b)
under visible irradiation and pure TiO2 (c) under UV-visible
irradiation, (d) under visible irradiation
3.77
0.86
irradiation, but also on the reaction media. While CO and CH4 were
generated as the major C1 chemicals in the solid-gas system, other
hydrocarbon fuels (e.g., CH3OH, CH3CH2OH etc) can be mainly
produced in a solid-liquid system. We test the CO2 photoreduction
in CO2-saturaed NaHCO3 aqueous solution (pH was adjusted to
~8.0). The diverse sort of C1 and C2 products were obtained after 6 h
10 shows the EIS Nyquist plots of the Au-TiO2 nanocomposite in
dark, under visible irradiation, and UV-visible irradiation. The radius
of the arc on the EIS spectra reflects the reaction rate occurring at
the surface of the electrode.27-30 The smaller arc radius on the EIS
Nyquist plot measured under visible or UV-visible irradiation
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 7
View Article Online
DOI: 10.1039/C6RA14821B
ARTICLE
Journal Name
1490-1501. (c) K. H. Kim, A. Husakou and J. Herrmann, Optics
Express, 2010, 18, 7488-7496. (d) T. Atay, J. H. Song and A. V.
Nurmikko, Nano Lett., 2004, 4, 1627-1631.
7 (a) L. Q. Liu, S. X. Ouyang and J. H. Ye, Angewandte Chemie-
International Edition, 2013, 52, 6689-6693. (b) B. H. Wu, D. Y. Liu, S.
Mubeen, T. T. Chuong, M. Moskovits and G. D. Stucky, J. Am. Chem.
Soc., 2016, 138, 1114-1117.
8 M. Lazzeri, A. Vittadini and A. Selloni, Physical Review B, 2002, 65.
9 U. Diebold, Surf. Sci. Rep., 2003, 48, 53-229.
10 X. G. Han, Q. Kuang, M. S. Jin, Z. X. Xie and L. S. Zheng, J. Am.
Chem. Soc., 2009, 131, 3152-+.
11 J. S. Chen, Y. L. Tan, C. M. Li, Y. L. Cheah, D. Y. Luan, S. Madhavi, F.
Y. C. Boey, L. A. Archer and X. W. Lou, J. Am. Chem. Soc., 2010, 132,
6124-6130.
Fig 10 EIS Nyquist plots of Au-TiO2 composites in dark, under visible
12 M. Diak, E. Grabowska and A. Zaleska, Appl. Surf. Sci., 2015, 347,
275-285.
irradiation and under UV-visible irradiation.
indicates that a more effective separation of photogenerated
electron–hole pairs and a faster interfacial charge transfer occurred.
The depressed arc radius measured under UV-visible irradiation
than visible irradiation also agrees with the efficiency of
photocatalytic reduction of CO2 under different irradiation.
13 C. Hu, X. Zhang, X. S. Li, Y. Yan, G. C. Xi, H. F. Yang and H. Bai,
Chemistry-a European Journal, 2014, 20, 13557-13560.
14 C. Wang, C. Kan, J. Zhu, X. Zeng, X. Wang, H. Li and D. Shi, Journal
of Nanomaterials, 2010, 2010, 1-9.
15 S. W. Liu, J. G. Yu and M. Jaroniec, J. Am. Chem. Soc., 2010, 132
,
11914-11916.
16 H. Choi, P. K. Santra and P. V. Kamat, ACS Nano, 2012, 6, 5718-
5726.
Conclusions
17 M. Liu, L. Y. Piao, L. Zhao, S. T. Ju, Z. J. Yan, T. He, C. L. Zhou and
W. J. Wang, Chem. Commun. , 2010, 46, 1664-1666.
18 W. B. Hou, W. H. Hung, P. Pavaskar, A. Goeppert, M. Aykol and S.
B. Cronin, Acs Catalysis, 2011, 1, 929-936.
The Au-TiO2 nanocomposite consisting of (001) exposed TiO2
nanosheet-anchored Au nanoplate was successfully fabricated by
using bifunctional linker molecules. The nanocomposites exhibit
promising activity for photoreduction of CO2 to renewable fuels in
the presence of water under visible light and even near-infrared
light. The enhancement of large photocatalytic activity was induced
by both transversal and longitudinal plasma of Au nanoplates. The
diverse sorts of photoredution product including CH4, CO, CH3OH,
and CH3CH2OH were detected, which is closely related to not only
different light irradiation, but also the reaction media.
19 T. A. El-Brolossy, T. Abdallah, M. B. Mohamed, S. Abdallah, K.
Easawi, S. Negm and H. Talaat, European Physical Journal-Special
Topics, 2008, 153, 361-364.
20 E. T. Castellana, R. C. Gamez, M. E. Gomez and D. H. Russell,
Langmuir, 2010, 26, 6066-6070.
21 W. Ni, X. Kou, Z. Yang and J. F. Wang, ACS Nano, 2008, 2, 677-
686.
22 A. J. Morris, G. J. Meyer and E. Fujita, Acc. Chem. Res., 2009, 42,
1983-1994.
Acknowledgements
This work was supported by 973 Programs (No. 2014CB239302 and
2013CB632404), National Natural Science Foundation of China (No.
21473091, 51272101, and 51202005).
23 L. J. Liu, C. Y. Zhao, D. Pitts, H. L. Zhao and Y. Li, Catalysis Science
& Technology, 2014, 4, 1539-1546.
24 L. J. Liu, C. Y. Zhao and Y. Li, J. Phys. Chem. C, 2012, 116, 7904-
7912.
25 C. C. Chuang, W. C. Wu, M. C. Huang, I. C. Huang and J. L. Lin, J.
Catal., 1999, 185, 423-434.
Notes and references
1 (a).A. Dhakshinamoorthy, S. Navalon, A. Corma and H. Garcia,
Energy & Environmental Science, 2012, 5, 9217-9233. (b) W. G. Tu,
Y.Zhou and Z. G. Zou, Adv. Mater., 2014, 26, 4607-4626. (c) G. A.
Ozin, Adv. Mater., 2015, 27, 1957-1963.
26 L. J. Liu, H. L. Zhao, J. M. Andino and Y. Li, Acs Catalysis, 2012, 2,
1817-1828.
27 H. Liu, S. A. Cheng, M. Wu, H. J. Wu, J. Q. Zhang, W. H. Li and C. N.
Cao, J. Phys. Chem. A, 2000, 104, 7016-7020.
2 S. Linic, P. Christopher and D. B. Ingram, Nat. Mater., 2011, 10,
28 W. H. Leng, Z. Zhang, J. Q. Zhang and C. N. Cao, J. Phys. Chem. B
2005, 109, 15008-15023.
,
911-921.
3 W. B. Hou and S. B. Cronin, Adv. Funct. Mater., 2013, 23, 1612-
29 Y. J. Wang, R. Shi, J. Lin and Y. F. Zhu, Applied Catalysis B-
Environmental, 2010, 100, 179-183.
1619.
4
Y. Tian and T. Tatsuma, Chem. Commun., 2004, DOI:
30 Y. J. Wang, X. J. Bai, C. S. Pan, J. He and Y. F. Zhu, J. Mater. Chem.
,
10.1039/b405061d, 1810-1811.
2012, 22, 11568-11573.
5 Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 2005, 127, 7632-7637.
6 (a) J. J. Mock, M. Barbic, D. R. Smith, D. A. Schultz and S. Schultz, J.
Chem. Phys., 2002, 116, 6755-6759. (b) K. Kolwas, A. Derkachova
and M. Shopa, J. Quant. Spectrosc. Radiat. Transfer, 2009, 110,
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 7
View Article Online
DOI: 10.1039/C6RA14821B
Journal Name
ARTICLE
Table of Contents
TiO2 Nanosheet-Anchoring Au nanoplates: High-energy Facet
and Wide Spectra Surface Plasmon-Promoting Photocatalytic
Efficiency and Selectivity of CO2 Reduction
Meng Wang, Qiutong Han, Yong Zhou,* Ping Li, Wenguang Tu,
Lanqin Tang, Zhigang Zou,*
The Au-TiO2 nanocomposite consisting of (001) exposed TiO2
nanosheet-anchored Au nanoplate was successfully fabricated by
using bifunctional linker molecules. Being applied for photocatalytic
reduction of CO2 into hydrocarbon fuels, this unique
nanocomposite benefits for the combination of higher
photocatalytic activity of TiO2 (001) and the visible to near-infrared
region plasma resonances of the anisotropic Au nanostructure.
Several carbon fuels were selectively produced over the Au-TiO2
nanocomposite, including CO, CH4, CH3OH, and CH3CH2OH and so
on under different light irradiation and reaction systems.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins