Self-Assembled Bimetallic Core-Satellite Nanostructures

This study explores the self-assembly of bimetallic core-satellite nanostructures, which have potential applications in photocatalysis and sensing. More specifically, the Langmuir-Blodgett technique is used to prepare composite thin films composed of palladium nanoparticles (PdNPs), gold nanoparticles (AuNPs), and a block copolymer, poly(styrene-b-2-vinylpyridine). First, PdNPs of different sizes and shapes, capped with alkanethiols of various lengths, are prepared. When assembled alone with PS-b-P2VP, the arrangement of PdNPs within the composite films depends on the NP size and the length of the capping agent. By cospreading 5.4 nm PdNPs coated with octadecanethiol and 6 nm AuNPs capped with octanethiol with poly(styrene-b-2-vinylpyridine) at the air-water interface, bimetallic core-satellite nanostructures (NSs) are obtained. These NSs are composed of satellite AuNPs assembled into a ring, which surrounds PdNP islands that constitute the core. The substrate-supported core-satellite NSs were immersed in a growth solution containing a gold precursor and a reducing agent. This treatment resulted in a doubling of the size of the AuNPs, whereas the size of the PdNPs remained unchanged. Further investigation demonstrates that the preferential growth of the AuNPs is kinetically controlled. Optical extinction spectra of the core-satellite NSs suggest that the surface plasmons of the AuNPs and PdNPs behave independently. The absence of coupled plasmonic modes can be attributed to the small size of the PdNPs. Nevertheless, this work presents an effective way to prepare substrate-supported hybrid core-satellite NSs over macroscopic surface areas for potential applications in photocatalysis and sensing.