Size control of Au@Pt core-shell nanoparticles for enhanced catalytic activity using ultrafine bubbles and ultrasound

Abstract Core⎯shell nanoparticles (NPs) composed of an Au core and a Pt shell (Au@Pt NPs) were synthesized. We started with the synthesis of the Au core by sonochemical reduction, followed by the Pt shell deposition by chemical reduction in the presence of a non-ionic surfactant and ultrafine bubbles (UFBs). The Pt shell thickness increased with the UFB concentration. During the shell formation, Pt NPs were thought to adsorb on the surface of UFBs by electrostatic and hydrophobic interactions, which was subsequently followed by UFBs approaching the Au NP surface and providing additional Pt NPs onto the surface. The catalytic activity of Au@Pt NPs for the reduction of 4-nitrophenol was evaluated. At Pt/Au molar ratios of 0.10, 0.20, and 0.33, the catalytic activity was enhanced as the Pt shell thickness decreased. For Pt/Au molar ratios of 0.02 and 0.05, Au@Pt NPs synthesized with UFBs exhibited better catalytic performance than those without UFBs.