In order to investigate environmental effects on the ligament/pore coarsening of nanoporous gold (NPG), we studied the thermal coarsening of NPG both in air and vacuum by ex situ observation, and found that it has high structural stability against heat treatment in vacuum. To clarify the nature of this phenomenon, we investigated the thermal coarsening of NPG by in situ environmental transmission electron microscopy. At an elevated temperature (400°C), the coarsening of ligaments/pores was triggered by introducing either pure N 2 or O 2 gas into the transmission electron microscopy (TEM) chamber (but not by Ar gas). We thus conclude with a discussion on the mechanism for thermal coarsening of NPG.

Nano-scale noble metallic materials exhibit catalytic activity and can serve as photocatalytic cocatalysts. The effectiveness of nanoporous gold (NPG) as a cocatalyst on TiO 2 depends on NPG pore size and composition. Suitably sized pores ensure that NPG can exhibit surface plasmon resonance, which enhances the photocatalytic activity of TiO 2 for hydroxyl (OH) radical generation. Moreover, Ag on NPG serves as generation sites for reactive oxygen species, because O 2 can be decomposed to atomic oxygen. Owing to these factors, NPG could serve as a high-performance cocatalyst for TiO 2. In this study, we utilized the porous property of NPG to fabricate a nanocomposite material of TiO 2 and NPG (TiO 2 /NPG) without annealing or complicated processing. Moreover, we evaluated the photocatalytic activity of the TiO 2 /NPG composite by measuring the amount of generated OH radicals. Our results suggest that NPG promoted the generation of OH radicals and that the amount of OH radicals increased with particular pore sizes of NPG and amounts of Ag.