A novel electroless method for the deposition of single-crystalline gold nanocrystals on and inside an organic solid-matrix

Abstract

Single-crystalline gold nanocrystals were directly deposited by a novel electroless galvanic method on and inside an organic solid matrix (SM) confined with both a reducing agent and a stabilizer. The reducing agent and stabilizer were in the solid phase, and the oxidizing agent (HAuCl₄) was in the aqueous solution phase. The reaction was carried out at the solid–liquid interface at 60 °C and pH 1. This method differs from the classical electroless galvanic displacement deposition process in several ways. (1) The deposited gold atoms penetrate and form nanoparticles, Au-NPs, through aggregation inside the SM. (2) The galvanic process occurs at the organic polymer matrix/metal ion solution interface instead of at the inorganic material/metal ion solution interface. (3) The entire SM participates in the deposition of gold nanocrystals on and inside the organic SM. (4) Proton transfer is accompanied by gold deposition from the solid to the solution phase to maintain the overall electrical neutrality of the system. (5) Single-crystalline gold nanocrystals are deposited on and inside the SM. The proposed method is applicable to the deposition of large gold nanosheets, Au-NSs (up to 50 μm in diameter), together with Au-NPs on the top of the SM. The Au-NPs inside the SM are three-dimensionally stabilized. The nanocrystals on the solution-side of the SM are partially naked and stabilized only from the bottom side, i.e., the upper sides of these nanocrystals are free from stabilizer coating. Both thiol- and amine-based epoxy resins were used as solid matrices. This method is applicable to direct deposition of optically transparent and mechanically stable Au-NPs on and inside a SM with a lower concentration of HAuCl₄ (0.1 to 0.3 mM) in the solution phase. The formation of platinum and palladium nanoparticles was only possible with this SM method when the reaction was carried out in the presence of a few gold nanocrystals on the surface of the SM.