Synthesis of Au@Pd core-shell nanoparticles by ultrafine bubbles and ultrasound without capping and reducing agents

This paper, for the first time, reports on the synthesis of Au@Pd core-shell nanoparticles in the absence of any capping and reducing agents by ultrafine bubbles and ultrasound. The mean diameter of the bimetallic core-shell nanoparticles was controlled by the ultrafine bubble concentration during the synthesis. Pd's shell thickness also varied with the concentration of Pd(II) ions. These Au@Pd core-shell nanoparticles showed excellent catalytic performance due to the pure surface without any capping and reducing agents. Graphical Abstract The size of Au@Pd core-shell nanoparticles synthesized by ultrafine bubbles and ultrasound decreased as the ultrafine bubble concentration increased. This is because the size of the core Au nanoparticles was reduced by ultrafine bubbles. Ultrafine bubbles have the effects of increasing the amount of ultrasonic cavitation and inhibiting the aggregation of Au nanoparticles. These Au@Pd core-shell nanoparticles without capping and reducing agents indicated superior catalytic performance for reduction of 4-nitrophenol.