Imparting Chemical Stability
in Nanoparticulate Silver
via a Conjugated Polymer Casing Approach
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Abstract
Only limited information is available on the design and
synthesis
of functional materials for preventing corrosion of metal nanostructures.
In the nanometer regime, even noble metals are subject to chemical
attack. Here, the corrosion behavior of noble metal nanoparticles
coated with a conjugated polymer nanolayer was explored for the first
time. Specifically, electrochemical corrosion and sulfur tarnishing
behaviors were examined for Ag-polypyrrole (PPy) core–shell
nanoparticles using potentiodynamic polarization and spectrophotometric
analysis, respectively. First, the Ag-PPy nanoparticles exhibited
enhanced resistance to electrochemically induced corrosion compared
to their exposed silver counterparts. Briefly, a neutral PPy shell
provided the highest protection efficiency (75.5%), followed by sulfate
ion- (61.3%) and dodecylbenzenesulfonate ion- (53.6%) doped PPy shells.
However, the doping of the PPy shell with chloride ion induced an
adverse effect (protection efficiency, −120%). Second, upon
exposure to sulfide ions, the Ag-PPy nanoparticles preserved their
morphology and colloidal stability while the bare silver analog underwent
significant structural deformation. To further understand the function
of the PPy shell as a protection layer for the silver core, the catalytic
activity of the nanostructures was also evaluated. Using the reduction
of 4-nitrophenol as a representative example of a catalytic reaction,
the rate constant for that reduction using the PPy encased Ag nanoparticles
was found to be 1.1 × 10<sup>–3</sup> s<sup>–1</sup>, which is approximately 33% less than that determined for the parent
silver. These results demonstrate that PPy can serve as both an electrical
and chemical barrier for mitigating undesirable chemical degradation
in corrosive environments, as well as provide a simple physical barrier
to corrosive substances under appropriate conditions