Encapsulation of atomically thin gold nanosheets within porous silica for enhanced structural stability and superior catalytic performance

Abstract

Atomically thin gold nanosheets (AuNSs) are fascinating two-dimensional (2D) nanomaterials with distinctive physicochemical properties arising from their ultrathin structure. However, the limited structural stability of these atomically thin AuNSs significantly hinders their practical applications. Here, we report the fabrication of atomically thin AuNSs (two atomic layers thick) encapsulated within a uniform porous silica layer (AuNS@pSiO₂), which show excellent structural stability in dried powder form and superior catalytic activity and stability for the reduction of 4-nitrophenol (4-NPh). For this, the synthesized atomically thin AuNSs are functionalized with thiolated poly(ethylene glycol) (SH-PEG) followed by encapsulation in silica layers of different thicknesses using different amounts of tetraethyl orthosilicate. The UV-ozone treatment removes the PEG molecules within the silica layers to form AuNS@pSiO₂. The AuNS@pSiO₂ shows structural stability in dried powder form while the as-prepared AuNSs aggregate and merge immediately after being dried into a powder. The AuNS@pSiO₂ exhibits superior catalytic activity with a normalized rate constant of 8.8 × 10⁴ min⁻¹ g_Au⁻¹ compared to the previously reported porous silica-encapsulated gold nanostructures for the 4-NPh reduction reaction. In addition, the AuNS@pSiO₂ shows excellent catalytic stability compared to the as-prepared AuNSs during the reusability test at 60 °C. The enhanced structural and catalytic stability of the atomically thin AuNSs could be due to the porous silica layer on their surface.