Spontaneous self-assembly of silver nanoparticles into lamellar structured silver nanoleaves

Uniform lamellar silver nanoleaves (AgNLs) were spontaneously assembled from 4 nm silver nanoparticles (AgNPs) with p-aminothiophenol (PATP) as mediator under mild shaking at room temperature. The compositions of the AgNLs were verified to be ∼1 nm Ag25 nanoclusters and PATP molecules in quinonoid model. The underlying assembly mechanism was systematically investigated and a two-step reaction process was proposed. First, the 4 nm AgNPs were quickly etched to ∼1 nm Ag25 nanoclusters by PATP in the form of [Ag25(PATP)n]n+ (n<12), which were then further electrostatically or covalently interconnected by PATP to form the repeated unit cells of [Ag25(PATP)n-1](n-1)+-PATP-[Ag25(PATP)n-1](n-1)+ (abbreviated as Ag25-PATP-Ag25). Second, these Ag25-PATP-Ag25 complexes were employed as building blocks to construct lamellar AgNLs under the directions of the strong dipole-dipole interaction and the π-π stacking force between the neighboring benzene rings of PATP. Different reaction parameters including the types and concentrations of ligands, solvents, reaction temperature, ionic strength, and pH, etc., were carefully studied to confirm this mechanism. Finally, the preliminary investigations of the applications for AgNLs as "molecular junctions" and SERS properties were demonstrated. We expect that this convenient and simple method can be in principle extended to other systems, or even mixture system with different types of NPs, and will provide an important avenue for designing metamaterials and exploring their physicochemical properties.