Synthesis of porous silica-coated Au sponges and its catalytic applications

Abstract

Au sponges have been of great interests in recent years due to their unique morphologies and excellent physical properties that provide a broad spectrum of applications in surface-enhanced Raman, catalysis, energy storage and actuator. However, the structure instability at high temperature or catalytic reaction conditions, which result in the loss of their physical properties, limiting their practical use in many applications. First, we report a facile and green synthesis method for Au sponges using self-assembly of gold nanoparticles induced by thiolated poly (ethylene glycol). The use of very low concentration of SH-PEG (ca. 20-200 nM) in aqueous solution at room temperature makes the method highly eco-friendly as well as results in high-purity as-synthesized gold sponges (98.7 wt %). The gold sponges fabricated with the present method exhibit a high SERS activity, making them highly applicable for sensitive SERS detection of molecules. A new synthetic method, which reported in this dissertation, would be a good candidate to solve the problem in the synthesis of Au sponges. Second, a new method to make Au sponges which prepared by self-assembly of Au NPs stable up to 700 °C by coating the surface of Au sponges with porous silica. Additionally, the porous silica coated Au sponges show very high catalytic activity for the reduction of 4-nitrophenol and excellent reusability as maintaining their activity as high as 93 % after 10 cycles of catalytic reactions. To the best of our knowledge, this is the first report of porous silica coated Au sponges which provide excellent thermal stability, high catalytic activity and reusability simultaneously. The new method, which developed in the dissertation, would be applicable to other Au sponges prepared by dealloying method or deposition of $TiO_2$ on Au sponges instead of $SiO_2$ for synergetic effect.