Au-Ag and Pt-Ag bimetallic nanoparticles@halloysite nanotubes: morphological modulation, improvement of thermal stability and catalytic performance.

In this study, Au-Ag and Pt-Ag bimetallic nanocages were loaded on natural halloysite nanotubes (HNTs) via galvanic exchange based on Ag@HNT. By changing the ratio of Au to Ag or Pt to Ag in exchange processes, Au-Ag@HNT and Pt-Ag@HNT with different nanostructures were generated. Both Au-Ag@HNT and Pt-Ag@HNT systems showed significantly improved efficiency as peroxidase-like catalysts in the oxidation of o -phenylenediamine compared with monometallic Au@HNT and Pt@HNT, although inert Ag is dominant in the composition of both Au-Ag and Pt-Ag nanocages. On the other hand, loading on HNTs enhanced the thermal stability for every system, whether monometallic Ag nanoparticles, bimetallic Au-Ag or Pt-Ag nanocages. Ag@HNT sustained thermal treatment at 400 °C in nitrogen with improved catalytic performance, while Au-Ag@HNT and Pt-Ag@HNT maintained or even had slightly enhanced catalytic efficiency after thermal treatment at 200 °C in nitrogen. This study demonstrated that natural halloysite nanotubes are a good support for various metallic nanoparticles, improving their catalytic efficiency and thermal stability.