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.