Three-dimensional nanoporous Ag fabricated by a reduction-induced approach for sensitive surface-enhanced Raman scattering

Nanoporous metals with high specific surface area, excellent conductivity, and unique surface structure have attracted attention in a variety of applications such as catalysis, energy storage, and sensing. However, there is a significant challenge for the fabrication of uniform nanoporous architectures in metals through a simple and cost-effective process. In this study, we report a facile approach to create monolithic nanoporous Ag (MNPA) from the direct reduction of insoluble Ag₂O precursor in an aqueous solution, fundamentally avoiding the introduction of secondary components and complex preparation of precursors. The formation of porous structures is attributed not only to the volume shrinkage but also to the spontaneous reconstruction of reserved Ag atoms during the reduction process. Furthermore, for a typical application, the optimized MNPA with a small grain size (∼113 nm) is used as a surface-enhanced Raman scattering (SERS) substrate, which exhibits ultrahigh SERS sensitivity with an enhancement factor of ∼10⁹.