Comparative study of Ag-Au NPs and Ag-Au@SiO2 nanostructures synthesized by conventional chemical and plant-mediated chemical reduction routes: activity-stability relationships

Bimetallic Ag-Au nanostructures exhibit tunable surface and electronic properties, making them versatile platforms for functional nanomaterial design. In this study, Ag-Au nanoparticles synthesized by conventional chemical reduction and a plant-mediated chemical reduction route were systematically compared with their silica-coated counterparts (Ag-Au@SiO 2 ) to examine how synthesis strategy and surface modification influence electrochemical response, surface accessibility, and functional stability. Silica encapsulation was employed as a model surface modification approach to regulate interfacial properties while maintaining the overall nanostructure. Comprehensive characterization using UV-Vis spectroscopy, FT-IR, TEM, DLS, and zeta potential analysis was combined with electrochemical techniques (CV, DPV, and CA) to probe surface-mediated redox behavior and comparative electrochemical response. Catalytic reduction of 4-nitrophenol and methylene blue was applied as a well-established model reaction to assess surface accessibility and functional stability rather than application-specific catalytic performance. Uncoated Ag-Au nanoparticles showed faster apparent reaction kinetics, whereas silica-coated nanostructures exhibited a characteristic trade-off between apparent reaction kinetics and durability, which may be related to differences in surface accessibility and transport-related effects. Notably, chemically synthesized Ag-Au@SiO 2 nanostructures retained apparent catalytic performance after four weeks of ambient storage, despite a measurable decrease in apparent rate constants, while uncoated nanoparticles showed a more pronounced decline in apparent catalytic performance. Electrochemical analyses revealed synthesis-dependent differences in the comparative electrochemical response following silica encapsulation, particularly in systems obtained by plant-mediated chemical reduction. This work identifies qualitative relationships between synthesis route, surface modification, and electrochemical response under identical experimental conditions. By employing model reactions as probes of surface functionality, the study provides a reproducible framework for evaluating durability and performance in surface-engineered nanomaterials.