Seed surface doping-mediated seeded growth of Au–Ag Janus nanoparticles with tunable sizes and multiple plasmonic absorption modes

Noble metal Janus nanocrystals involving components with the same crystal structure and close lattice constants are technically difficult to produce as anisotropic growth is not favored under general deposition conditions. Herein, taking Au and Ag, we describe a feasible synthetic strategy to create Au–Ag Janus nanoparticles (JNPs) with tunable sizes, which exhibit multiple plasmonic absorptions in the UV-vis range. The success of the current synthesis lies in the surface doping of trisoctahedral (TOH) Au seeds with limited amount of Pt/Ag atoms to introduce a relatively large lattice strain during the seeded growth, which is found crucial to facilitate the anisotropic deposition of Ag. In contrast, the use of undoped Au seeds leads to the formation of Au@Ag core–shell nanoparticles. The size of resulting products could be tuned by varying the amount of the added Ag precursor or the size/quantity of Au seeds. Compared to core–shell counterparts, the current Au–Ag Janus nanoparticles exhibit more plasmonic absorption peaks. Owing to such advantages, the current Au–Ag Janus nanoparticles show enhanced catalytic properties in the reduction of 4-nitrophenol under UV-vis light irradiation. The current study provides a feasible strategy that allows the fabrication of Janus bimetallic nanocrystals with elements having a close lattice constant and validates the promising use as plasmonic catalysts, which could be potentially extended to other metals or alloys.