Morphological modulation of bimetallic nanostructures for accelerated catalysis

Abstract

Bimetallic nanostructures are of significant technological interest due to their ability to uniformly combine properties of two distinct metals, giving rise to multimodal characteristics. In this work, we have synthesized Au/Ag core/shell bimetallic nanostructures and investigated the role of temperature in controlling the morphological evolution and the corresponding impact on catalytic transformation. By increasing the reaction temperature from 35 °C to 80 °C, the edge morphologies of Au/Ag nanostructures evolved from rounded to sharp corners, which directly impact the catalytic properties. The size of the bimetallic nanostructures also increased when the temperature was raised due to faster Ag⁺ reduction along specific crystallographic planes, giving rise to red shifts in the plasmon resonance. The catalytic activity of Au/Ag nanostructures was compared to commercially purchased Ag nanospheres for the reduction of 4-nitrophenol to 4-aminophenol with NaBH₄. The reaction rate for 4-nitrophenol reduction was significantly higher on Au/Ag-NSs relative to the Ag nanospheres, while the induction time was lowest on the Ag nanospheres. These observations were attributed to the simultaneous effects of (i) surface area available for catalytic reaction, (ii) crystallographic facets supporting the nanostructures, (iii) surface ligands, and (iv) composition of the metal nanostructures.