Monodisperse Gold Nanoparticles Supported By Rice Husk Silica for Heterogeneous Catalysis Applications

Gold nanoparticles (Au NPs) based catalysts have received more and more attentions in the past two decades because of their unique catalytic properties in many important industrial processes. Both the experimental findings and theoretical predictions have demonstrated that the size of Au NPs plays a critical role in governing the catalytic activity. Smaller Au NPs typically exhibit higher catalytic activity. Herein, we report a facile method to synthesize Au NPs based heterogeneous catalyst using silica from rice husks (RHs) as a support. Although silica supported Au NPs have been extensively studied, the silica supports are typically synthesized from tetraethyl orthosilicate (TEOS) via a sol-gel process. Notably, in this study, silica from RHs was first used as the catalyst support. The silica nanoparticles obtained by calcining HCl treated RHs, which possess a rough surface, was first modified by (3-aminopropyl)triethoxysilane (APTES), which was designed to play a dual role: one was to absorb Au precursor (AuCl₄^-) to silica surface and the other was to stabilize the resultant Au NPs obtained by reducing AuCl₄^- using sodium borohydride (NaBH₄). Characterizations of the nanostructures revealed that the Au NPs were formed with narrow size distribution around 2-5 nm, which was very critical for essential catalytic activities. The RH silica supported Au NPs exhibited excellent catalytic activity for the reduction of 4-nitrophenol by NaBH₄.