In Situ Formation of Au/Pt Bimetallic Colloids on Polystyrene Microspheres:  Control of Particle Growth and Morphology

This paper reports in situ formation of Au/Pt bimetallic nanoparticles on the surface of polystyrene microspheres. This was accomplished by dispersion copolymerization of styrene and a poly(N-isopropylacrylamide) (PNIPAAm) macromonomer in ethanol−water media in the presence of HAuCl 4 and H 2 PtCl 6 . The particle size and morphology of the polystyrene microspheres can be changed by varying the molar ratio of Au/Pt. The propagation of oligomer radicals and nucleation of polystyrene microspheres were controlled by the Au/Pt molar ratio. A monodisperse polystyrene microsphere, with polystyrene as the core and PNIPAAm as the corona, was obtained at the Au/Pt molar ratio of 2/8. Well-dispersed Au/Pt bimetallic nanoparticles were generated on the microsphere surface via in situ reduction of gold and platinum ions by radicals generated from the initiator, 2,2‘-azobisisobutyronitrile (AIBN). The mean diameter of Au/Pt bimetallic colloids decreased with increasing Pt molar fraction. The nucleation and growth of the formed nuclei became controllable at higher Pt molar ratios owing to the lower reduction rate of gold ions and strong coordination affinity of PNIPAAm to the Pt atoms. The materials resulting from this study were characterized by transmission electron microscopy (TEM); atomic force microscopy (AFM); and FTIR, UV−visible, and X-ray photoelectron spectroscopy.