Evaluation of the Effective Photoexcitation Distances in the Photocatalytic Production of H₂ from Water using Au@Void@TiO₂ Yolk–Shell Nanostructures

Fundamental properties associated with the photocatalytic production of hydrogen from water by metal/semiconductor catalysts were studied by using Au@Void@TiO 2 yolk–shell nanostructures. Independent control of the geometrical parameters of those nanostructures could be exercised during synthesis and used to systematically probe their effect on photocatalytic activity. Both shell thickness and shell diameter affect the rate of H 2 production, with thicker and bigger shells displaying higher activity. The trends could be described by simple exponential decays in activity as a function of distance from the gold nanoparticle. However, each parameter yielded a different characteristic length: a 28 nm value was measured for the thickness, associated with the penetration of light into the titania, whereas a 186 nm estimate was obtained for the shell diameter, possibly related to the diffusion of hydrogen atoms on the titania surface toward the gold nanoparticles. The size of the gold nanoparticles does not significantly affect the photocatalytic activity.