Plasmonic Applications of Gold-Copper Bimetallic Alloy Nanoparticles

Plasmonic metal nanoparticles due to their characteristic localized surface plasmon resonance (LSPR) in the optical region of the electromagnetic wave are of much interest right from the medieval ages. Herein, we present a robust single-step synthetic protocol for the synthesis of Au and Cu alloy nanoparticles, which are typically used in various catalytic and sensing applications. For alloy formation, co-reduction of Au and Cu salts was used in four different Au/Cu mass ratios (1:1, 1:2, 1:3, and 1:4) yielding "marigold" like nanostructures. The formation of the desired alloy composition was confirmed from their optical spectra giving an LSPR peak among the specific peak nature of Au and Cu and also, from the XRD pattern, displaying diffraction peaks corresponding to Au and Cu only, but not the copper oxides. Additionally, the effect of plasmonic damping due to inter-band transition and polydispersity in the formed alloys was also discussed. Moreover, their optical spectra confirm a broadband bathochromic shifted LSPR peak alongside a lowering intensity with the surge in Cu concentration. For the respective compositions of the alloy nanoparticles, optical spectra (compared with experimental data) and the electric field enhancement data were also simulated using the MATLAB-based boundary element method to investigate their application in antennas for SERS, SEIRA, etc. Furthermore, these AuCu nanoalloys were utilized in crystal violet dye degradation, which provides an enhanced catalytic character in comparison with that of pure Au nanoparticles. Subsequently, the turnover frequency of the degradation process provides the superlative AuCu composition. A similar enhanced nature was likewise obtained for simulated refractive index sensitivity for n = 1-1.5, establishing not only the inherent cost-effectiveness and single-step procedure of our versatile synthetic protocol, but also the formation of robust alloy with different combinations of nanoparticles.