Au nanoparticles with different sizes (10, 20, 30, and 50 nm) were synthesized using a seed-assisted approach and anchored onto Pt/TiO2 employing 3-mercaptopropionic acid as the organic linker. The sizes of the Au nanoparticles were controlled within a narrow range so that the size-dependent surface plasmonic resonance effect on sensitizing Pt/TiO2 can be thoroughly studied. We found that 20 nm Au nanoparticles (Au20) gave the best performance in sensitizing Pt/TiO2 to generate H2 under visiblelight illumination. Photoelectrochemical measurements indicated that Au20-Pt/TiO2 exhibited the most efficient “hot” electrons separation among the studied catalysts, correlating well with the photocatalytic activity. The superior performance of Au-supported Pt/TiO2 (Au20-Pt/TiO2) compared with Au anchored to TiO2 (Au20/TiO2) revealed the important role of Pt as a cocatalyst for proton reduction. To elucidate how the visible-light excited hot electrons in Au nanoparticles involved in the proton-reduction reaction process, Au20/TiO2 was irradiated by visible light (λ > 420 nm) with the presence of Pt precursor (H2PtCl6) in a methanol aqueous solution under deaerated condition. Energy-dispersive X-ray spectroscopy mapping analysis on the recovered sample showed that Pt ions could be reduced on the surfaces of both Au nanoparticles and TiO2 support. This observation indicated that the generated hot electrons on Au nanoparticles were injected into the TiO2 conduction band, which were then subsequently transferred to Pt nanoparticles where proton reduction proceeded. Besides, the excited hot electrons could also participate in the proton reduction on Au nanoparticles surface.

1. ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265
Key Contact
Fenglong Wang (flwangsdu@gmail.com)
Yijiao Jiang (yijiao.jiang@mq.edu.au)
Rose Amal (r.amal@unsw.edu.au)

2. Figure 1. Strategy for synthesis of Au nanoparticles supported on Pt/TiO2 composite catalysts.
ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265

3. Figure 2. TEM images of the synthesized gold
nanoparticles with size of approximately 50 nm (a), 30
nm (b), 20 nm (c), and 10 nm (d); TEM images of
Pt/TiO2 showing 3 nm Pt nanoparticles distributed on
the surface of TiO2 (e) and Au20-Pt/TiO2
nanocomposites displaying Au20 and Pt nanoparticles
supported on the TiO2 surface (f).
ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265

4. Figure 3. (a) XPS Pt 4f spectrum and (b) XPS Au 4f spectrum of the Au20-Pt/TiO2 sample.
Figure 4. Hydrogen-production activity of
different catalysts under visible-light irradiation
(λ > 420 nm) from water/methanol mixture.
ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265

5. Figure 6. Photocurrent responses of Au20Pt/TiO2
under full visible light spectrum (>420 nm), blue
light (400 nm), green light (550 nm), and red light
(675 nm). All measurements were performed with a
420 nm cutoff filter to prevent the excitation of TiO2
support under UV light. Bandpass filters (50 nm
fwhm bandwidth) were used to obtain the 400, 550,
and 675 nm light sources.
Figure 5. Photocurrent response of Au
nanoparticles with different sizes supported on
Pt/TiO2 nanocomposites under visible-light
irradiation (λ > 420 nm). Every 40 s cycle
comprises 20 s of irradiation, followed by 20 s of
dark current measurement.
ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265

6. Figure 7. TEM image of the products obtained
through photodeposition of Pt on Au20/TiO2
nanocomposites (a−d) and the proposed
photocatalytic hydrogen-production process on
the Au-sensitized Pt/TiO2 under visible-light
irradiation (e).
ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265

7. Figure 8. Photocurrent response of Au20Pt/TiO2 in the presence of (a) methanol and (b) ethanol as hole
scavenger. PEC measurement is performed with a 420 nm cutoff filter to prevent the excitation of TiO2. The
photocurrent response is baseline-corrected to show the SPR enhancement under visible light.
ACS Applied Materials & Interfaces
Article ASAP, 22 August 2017, DOI: 10.1021/acsami.7b06265