Synergistic effect of Au-Ag nano-alloying: intense SEIRA and enhanced catalysis.

Abstract

The well-known AuAg nanohybrid system was effectively synthesized, utilizing polyvinyl pyrrolidone (PVP) as a multiple metal precursor reducing agent (based solely on their reduction potentials), thereby drastically decreasing their activation energy of diffusion and readily facilitating the homogenous alloy nanoparticle formation, duly confirmed by Vegard's law. Furthermore, the crucial parameters in determining the local electric field enhancement in the vicinity of the alloy nanoparticles such as the quality factor Q, dephasing time, T2 and the homogenous line width Γ were also evaluated in a systematic manner, in correlation with their unique visible optical absorption spectra. Optical band gap calculations of this robust AuAg/PVP nanocomposite system demonstrate the formation of trap levels between the HOMO and LUMO energy states with increasing Urbach's energy for decreasing Au content. The surface enhanced infrared (SEIRA) measurements with the analyte bromophenol, not only highlight the differential metal-PVP-analyte binding, but also corroborate the optical constants of the nanohybrids. Moreover, the catalytic conversion of 4-nitro-aniline (4-NA) to p-phenylenediamine (p-PDA) in the presence of AuAg nanohybrids visibly distinguishes their excellent stability and reproducibility along with their moderate rate constant in direct contrast to the poor recycling ability of their individual metal counterparts.