Galvanic synthesis of bi-modal porous metal nanostructures using aluminum nanoparticle templates

Galvanic replacement reaction has been used to synthesize various metal nanostructures, in which a more cathodic (less active) metal was generated by the replacement reaction between the metal precursor solution and a more anodic (active) metal (template material). To date, Ag, Cu, Ni, and Co have been used as template materials to fabricate new nanomaterials and nanostructures. In the previous research, we showed that aluminum (Al) nanoparticles can be used to synthesize porous Ni and Co nanoparticles. In this paper, we show the galvanic synthesis of bi-modal nanostructures using Al nanoparticle templates. The template particle, Al nanoparticle (∼120 nm diameter), owing to its very low redox potential (-1.66 V vs. standard hydrogen electrode, SHE), can be replaced by metals such as Ni, Co, In, Fe, Au, Ag, Cu, Pt, Pd, and Pb. Replacement with Ni, Co, In, and Fe results in dispersed porous nanoparticles with single or multiple pores. Continuous, porous nanostructures of larger micron sized aggregates are formed by replacement with Ag, Au, Pd, and Pb, and spherical porous particles by replacement with Cu and Pt. We speculate that growth kinetics play an important role in the formation of the porous nanostructures. Growth mechanisms are proposed to explain the formation of bi-modal porous nanostructures.