Supported Au Nanoparticles on TiO2 for Visible Light Photocatalytic H2O2 Production: Effects of Au Particle Size and Density

Gold nanoparticles supported on titanium dioxide (Au NPs/TiO2) hold great potential as visible-light-driven photocatalysts through plasmon-induced charge separation (PICS). The photo-electrochemical properties of the Au NPs are intrinsically connected to their structure and interfacial interactions with the TiO2 support. Here, we present a highly efficient visible light photocatalytic system for H2O2 production via O2 reduction accomplished by tailoring the particle size and density of Au NPs on TiO2. Oleylamine-stabilized colloidal Au NPs with sub-10 nm particle diameters (d = 3.1, 5.8, and 7.8 nm) were synthesized and uniformly deposited on amine-functionalized TiO2 (P25) with tunable loading amounts (∼0.5–3.4 wt %) through an adsorption approach. These well-controlled Au NPs/TiO2 catalysts allowed us to separately investigate the catalytic effects arising from the Au particle size and particle density. Upon visible light irradiation (λ > 420 nm), increasing particle density of Au NPs proved advantageous for H2O2 formation, wherein injected hot electrons could reduce O2 on another Au NP through interparticle electron transfer. All sizes of the Au NPs/TiO2 catalysts achieved a steady-state H2O2 concentration exceeding 10 mM at elevated particle densities. Moreover, a size-dependent interfacial contact and charge transfer between Au NPs and TiO2 served to modulate the electronic structure of Au NPs, leading to a pronounced enhancement in the PICS efficiency of the smallest Au NP (d = 3.3 nm) with an outstanding apparent quantum yield (10.3%, λ = 528 nm) for visible light photocatalytic H2O2 production.