Colloidal Metal Deposition onto Functionalized Polystyrene Microspheres

Abstract

Three different methods are described for uniformly anchoring metal colloids (Pt, Pd, and Au) onto the surface of polystyrene microspheres (PSMS). The first method we have employed is electrostatic deposition of preformed anionic colloidal particles onto a polycationic surface. In this method the functional groups on the surfaces of the microspheres (amine or carboxylic acid) are used to give the surface a net charge. These ionic spheres were then treated with polyelectrolytes of the opposite charge, which uniformly cover the surface. When the spheres have a net positive charge at the surface they show excellent adhesion of Au colloids. These metal-derivatized spheres can be prepared with electroactive viologen groups as well. In the second method investigated here, metal colloids are adsorbed to the surface of neutral functionalized PSMS. We report the synthesis and characterization of catalytically important noble monometallic colloids using various chemical and sonochemical methods. These metal colloids are then adsorbed onto suitably functionalized PSMS. The metal-immobilized microspheres are reacted with a linker such as 4-mercaptobutyl phosphonic acid and subsequently used for growing multilayers of ZrPV(Cl) (zirconium and N,N‘-dialkyl-4,4‘-bipyridinium dichloride) by alternating Zr 4+ and PV(Cl). The third method described here for supporting metal particles on PSMS involves depositing a precursor metal oxide or hydroxide onto the PSMS, followed by reduction to give fine metal particles on the surface of the PSMS. Metal particle sizes formed by this method are 2−4 nm. The colloids, microspheres, and resulting catalysts prepared by all three methods have been characterized by electron microscopy (TEM and SEM) and by energy-dispersive X-ray (EDX) microanalysis, and those prepared by method 2 have been characterized by diffuse reflectance UV−vis spectroscopy as well.