A novel electroless method for the deposition of single-crystalline platinum nanoparticle films on an organic solid matrix in the presence of gold single crystals

Abstract

Single-crystalline platinum nanoparticles (Pt-NPs) were directly deposited on and inside an organic solid matrix by a novel electroless galvanic method. The reducing agent was a solid phase confined with both a reducing agent and a stabilizer combined with initially deposited minute gold single crystals (Au-SCs) on the surface (Au-SM). The oxidizing agent (K₂PtCl₄) was in the aqueous solution phase. The reaction was carried out at the solid–liquid interface system at 80 °C and pH 1. The deposited Pt-NPs formed a uniform silver-grey conductive coating on the top of the Au-SM when the concentration of K₂PtCl₄ in the solution was 50 mM. The film consisted of single-crystalline Pt-NPs nearly identical in shape and size (∼250 nm). The initially deposited minute Au-SCs by the electroless deposition process were found to catalyze the formation of Pt-NPs having fcc crystal structures with dominating {111} crystal facets. The formation of Pt-NPs was not observed in the absence of initially deposited Au-SCs on the solid matrix. This method was also applicable for the deposition of deep ruby-red, optically transparent and mechanically stable Pt-NPs on and inside the Au-SM for lower concentrations of K₂PtCl₄ (1 to 5 mM) in the solution phase. This characteristic color was due to the strong surface plasmon absorption of Pt-NPs in the visible range. The Pt atoms initially deposited on the surface and diffused through the entire Au-SM to the opposite side that was not in contact with the oxidizing agent during the period of the reaction. The Pt-NPs on the solution-side of the Au-SM were partially naked and stabilized only from the bottom side, i.e., the upper sides of these nanocrystals were free from the stabilizer coating. The Au-SCs immobilized thiol-based epoxy resin was used as the Au-SM. The proposed Au-SM method was also applicable for the formation of ruby-red iron, palladium and beautiful, rainbow-like colorful silver nanoparticles on the Au-SM surface.