Nanocrystalline Ag-C Composites Containing a Hexagonal Diamond Structure to Inhibit Tarnishing of Sterling Silver

Abstract

Three-dimensional nanocrystalline Ag-C composites containing a hexagonal diamond structure were produced by electrochemical reduction of acetic acid and electrodeposition of Ag(NO3) (0.01 M) at −1.1 V vs Ag/AgCl at ambient conditions. After applying the negative potential, an ultrathin layer of Ag (<0.1 μm) was first deposited, and subsequently, competitive electrodeposition of Ag and electroreduction of acetic acid resulted in the formation of nanocrystalline Ag-C products on the electrodes. A combination of microscopic, structural, and spectroscopic characterization results reveals that the nanocrystalline Ag-C contains a hexagonal diamond structure with an average crystallite size of 26 nm. The nanodiamond phase remained unchanged throughout 15-140 min reaction time. However, increasing the reaction time, the thickness of nanocrystalline Ag-C films increased to ∼2 μm with some large polyhedra carbon structures. The nanocrystalline Ag-C composites were utilized in the casting process of sterling silver to enhance its antitarnish properties. The antitarnishing of sterling silver upon exposure to a H2S environment was significantly improved by 50% with 0.005 wt % loading of the Ag-C composite. © 2023 American Chemical Society.