Metal Nanoshell Synthesis via H ₂ –Assisted Plasmon-Driven Photoreduction

Synthesizing metal nanoshells with well-defined surfaces is a persistent challenge, as conventional methods often require harsh reductants or structure-directing surfactants that contaminate the final product. Here, we report a general, long-chain surfactant-free strategy that utilizes plasmon-induced hot carriers to synthesize a diverse array of metal nanoshells (Au, Ag, Pt, Pd, and Cu) on mesoporous silica supports. The process is initiated by a photocatalyst of high-density, sub-5 nm Au nanoparticles that efficiently generate hot carriers under mild green light illumination. The key innovation is the introduction of molecular hydrogen (H2), which creates a powerful reduction pathway. Our results strongly suggest this occurs through the activation of H2 by plasmon-generated hot electrons. This H2-assisted method dramatically accelerates deposition kinetics and overcomes thermodynamic barriers, enabling the formation of uniform nanoshells of Pt and Pd, and even Cu, which is otherwise inaccessible. Mechanistic studies confirm the enhancement is a true hot-carrier-mediated effect, distinct from bulk photothermal heating.