Facile Synthesis of CTAB Coated Au-Ag Core-Shell Nanoparticles and their Catalytic and Antibacterial Activity

This work reports the synthesis of cationic surfactant-coated Au-Ag core-shell (Au@Ag) nanoparticles (NPs) via a straightforward seed-mediated approach. The UV-Vis analysis showed that the plasmon peak position of synthesized Au@Ag NPs correlated with the thickness of the Ag shell encapsulating the Au core. The Au@Ag NPs have shown impressive catalytic performance for the reduction reactions of 4-nitrophenol (4-NP) and methyl orange (MO) where the apparent rate constant experienced a remarkable increase by 67-fold and 90-fold, respectively, when Au@Ag NPs with the Ag-shell thickness of 6.3 nm were employed as a catalyst, compared to Au NPs. This multifold improvement in the activity cannot be simply accounted for by the increase in surface area of NPs and is attributed to the electronic synergistic effects between Au and Ag in the core-shell NPs. Furthermore, while Au@Ag NPs exhibited heightened antibacterial activity against both Gram-positive S. aureus and Gram-negative E. coli bacteria, this enhancement is modest. Notably, the anticipated significant enhancement attributed to Ag's renowned antibacterial properties was not observed. The presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) enables both Au and Au@Ag NPs to effectively bind with the negatively charged bacterial cell membranes through electrostatic interactions. Apparently, CTAB enables both types of NPs to effectively target and eliminate bacteria with comparable efficiency.