Mesostructural Engineering of Faceted Gold Nanoparticles in 3D KIT-6 Silica for Enhanced Catalytic Efficiency

Gold nanoparticles (Au NPs) supported on ordered mesoporous silica have attracted significant attention as robust nanocatalysts. In this study, high-gold-content three-dimensional (3D) mesoporous silica (KIT-6-Au NPs) was synthesized, which exhibited a 3D cubic Ia3d mesostructure with uniformly dispersed Au NPs (∼8 nm) predominantly exposing the (111) facets. Structural analyses were conducted by Brunauer-Emmett-Teller surface area measurement, Raman spectroscopy, solid-state Si²⁹ NMR spectroscopy, Transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy, confirming high gold loading 15.5 wt% and strong metal-support interaction. Catalytic performance was evaluated through the reduction of 4-nitrophenol (4-NP) with NaBH₄ as a model reaction, exhibiting a maximum apparent rate constant of 0.0086 ± 0.0002 s^{- 1} at 25°C. It surpasses comparable Au-mesoporous silica systems and is competitive with other silica-supported metallic nanocatalysts. The findings further confirm that the reduction of 4-NP by NaBH₄ in the presence of the KIT-6-Au NP catalyst proceeds via a heterogeneous catalytic pathway and that the catalyst is structurally robust under the reaction conditions. This work highlights the potential of facet-engineered, high-loading Au NPs integrated within a 3D mesoporous silica framework as an efficient catalyst capable of promoting diverse reactions under mild conditions.