Formation Process of Gold-Silver Hollow Nanostructure via Silver Halide Photographic Techniques: An Electrochemical Model Cell Study

Abstract

The photographic development of AgBr microcrystals yields the formation of silver nanofilaments (pAgNF). Subsequent treatment of pAgNF with a gold(I)-thiourea complex solution results in a hollow nanostructure composed of gold and silver (hAuAgNS). The formation mechanism of the hollow structure is believed to be a galvanic reaction. In this study, we investigated the formation process using a macroscopic electrochemical model cell, where the anodic and cathodic half-reactions are spatially separated, enabling independent control of the conditions in each half-cell. The model cell experiments consistently corroborate the two-step mechanism for hollow structure formation: 1) direct galvanic replacement of silver by gold on the pAgNF surface, giving the gold-covered exterior on pAgNF, and 2) galvanic deposition of gold on the pre-deposited gold surface, accompanied by the dissolution of silver from the gold-uncovered sites (galvanic pitting). The transition of pAgNF to hAuAgNS was further traced through chemical analysis and electron micrographic observation, with discussion and interpretation of the results of the model cell experiments.

Keywords

• hollow nanofilament
• silver halide photographic chemistry
• galvanic model cell
• thiourea