Visible light pre-treatment has been found to be capable of enhancing the catalytic oxygen activation on AuPt/TiO2 by up to seven times. Visible light pre-treatment exploits the localized surface plasmon resonance effect of Au to generate free electrons, which are transferred to the Pt active sites. The electron transfer was evident from a change in Pt speciation observed from X-ray photoelectron spectroscopy, showing the presence of PtO after visible light pre-treatment. Photoluminescence spectroscopy was used to reveal the bimetallic synergistic enhancement, as indicated by an overall decrease in the charge recombination rate. Further examination revealed that a good bimetallic interaction is necessary to achieve the enhancement by visible light pre-treatment. Weak bimetallic interaction, such as the occurrence of element segregation in the bimetallic alloy, inhibits electron transfer from the Au to the Pt and increases electron recombination rates, diminishing the degree to which visible light pre-treatment improves catalytic performance.

1. ChemCatChem
Volume 10, Issue 1, pages 287-295, 20 December 2017, DOI: 10.1002/cctc.201701238
Key Contact
Particles and Catalysis Research Group,
School of Chemical Engineering,
The University of New South Wales,
Sydney, NSW 2052, Australia.
E-mail: r.amal@unsw.edu.au
jason.scott@unsw.edu.au
Surface plasmon promotion: Visible light pre-treatment has been found to be
capable of enhancing the catalytic oxygen (see figure; blue) activation on
AuPt/TiO2 by up to seven times. Visible light pre-treatment exploits the localized
surface plasmon resonance effect of Au (purple) to generate free electrons
(yellow), which are transferred to the Pt (gray) active sites.

2. Introduction
5 % of solar
spectrum
High energy
source
UV
http://www.pveducation.org/
Synergy and UV pre-illumination
enhancement are dependent on Au:Pt ratio.
• ~6 times UV enhancement at high Au:Pt
ratio
• Enhancement decreases as Au:Pt ratio
decreases
Catal. Sci. Technol., 2016, DOI: 10.1039/C6CY01717G

3. 25 nm 25 nm 25 nm
(a) (b)
Au
Pt
2.5 nm2.5 nm2.5 nm
Au
Pt
Au
Pt
(c)
(d) (e) (f)
Figure 1. STEM images of (a) Au0.8Pt0.2/TiO2,
(b) Au0.5Pt0.5/TiO2, and (c) Au0.2Pt0.8/TiO2, and
(d–f) their respective EDS maps.
Au0.5Pt0.5/TiO2
Au0.8Pt0.2/TiO2
Au0.2Pt0.8/TiO2
0.2 at% Pt/TiO2
0.8 at% Au/TiO2
TiO2
Figure 2. UV/Vis-DRS spectra of bimetallic AuPt/TiO2
possessing various Au/ Pt ratios. Absorption spectra
of 0.8 at.% Au/TiO2, 0.2 at.% Pt/TiO2, and TiO2 are
provided as a reference.

4. (b)(a)
Figure 3. (a) Formic acid oxidation rates (R50) for AuPt/TiO2 , possessing different Au/Pt ratios,
following UV light pre-treatment (purple columns), visible light pre-treatment (green columns) and
without light pre-treatment (blue columns) illustrating the beneficial effects of light pre-treatment in
promoting catalytic performance. The pink and grey columns for each bimetallic ratio represent the
R50 values for monometallic Au/TiO2 and monometallic Pt/TiO2 with metal loadings equivalent to
the corresponding bimetallic catalyst. For example, the Au/TiO2 column (pink) in the Au0.8Pt0.2
group refers to 0.8 at.% Au/TiO2 whereas the Pt/TiO2 column (grey) in the same group refers to
0.2 at.% Pt/TiO2 . (b) Synergy and light pre-treatment enhancement factors exhibited by the
various AuPt/TiO2 catalysts as determined from the R50 values. The enhancement factors are
derived from the light pre-treatment activity (i.e., R50) of the bimetallic catalyst divided by the sum
of the corresponding monometallic Au/TiO2 and Pt/TiO2 activities. An enhancement factor of
1.0=no enhancement. Pre-illumination time: 30 min; formic acid loading: 1000 μmol.

5. Figure 4. Photoluminescence spectra of
(a) Au0.8Pt0.2/TiO2, (b) Au0.5Pt0.5/TiO2, and
(c) Au0.2Pt0.8/TiO2 with their respective
monometallic counterparts. Excitation
wavelength: 550 nm; corresponding
emission wavelength: 640 nm.
(a) (b) (c)
Pt0
PtOads
PtO
PtO2
(b)(a)
Pt4fAu4f
Figure 5. XPS (a) Au4f and (b) Pt 4f spectra
of Au0.8Pt0.2/TiO2 showing the binding energy
shifts and change in Pt speciation arising
from UV and visible light pre-treatment.

6. Figure 6. XPS valence band spectra of
Au0.8Pt0.2/TiO2 after UV and visible light pre-
treatment, compared with its monometallic
counterparts. The arrows indicate the
changes in valence band electronic structure
after both UV and visible light pre-treatment.
5 0 n m5 0 n m
10.0 nm
(a)
(d)
(b)
(c) Au
Pt
Figure 7. STEM images of (a) Pt–Au/TiO2 and (b)
Au–Pt/TiO2 , and (c, d) their respective EDS maps.
The arrows in (a) highlight the presence of small Pt
nanoparticles not alloyed with Au. EDS mapping in
(c) shows that the Pt phase is segregated from the
Au within the bimetallic cluster.

7. Pt0
PtOads
PtO
Pt0
PtOads
(b)(a)
Figure 8. XPS Pt4f spectra of (a) Pt–Au/TiO2 and (b) Au–Pt/TiO2 depicting
their resemblance to monometallic Pt/TiO2 and Au0.8Pt0.2/TiO2, respectively.

8. Figure 9. Photoluminescence spectra
of sequentially loaded Pt–Au/TiO2 and
Au–Pt/TiO2 , with their corresponding
monometallic counterparts. Excitation
wavelength: 550 nm; corresponding
emission wavelength: 640 nm. The
spectra of the 0.2 at.% Pt/TiO2 and 0.8
at.% Au/TiO2 samples are offset in the
x-axis by -10 nm for easy comparison.
Figure 10. R50 of sequentially
deposited AuPt/TiO2 compared
with their monometallic
counterparts.
Figure 11. UV/Vis-DRS of
sequentially deposited
AuPt/TiO2 . Pt–Au/TiO2
represents the sample
prepared by depositing Pt first
followed by Au, whereas Au–
Pt/TiO2 represents the sample
prepared by depositing Au
first followed by Pt. The
absorption spectrum of TiO2 is
provided as reference.

9. Conclusion
 The visible light pre-illumination
on bimetallic AuPt/TiO2 is able to
enhance the oxygen activation rate
by ~7 times
 Bimetallic Au-Pt interaction is
important for LSPR synergy
enhancement