(73a) Assembled State and Catalytic Performance of Gold Nanoparticles Under Confinement

The assembled state of nanoparticles (NPs) within porous matrices plays a governing role in directing their biological, electronic, and catalytic properties. However, the effect of external stimuli such as temperature, salinity, and pH on NP assemblies within the pores is poorly understood. In this study, we use adsorption isotherms, spectrophotometry, and small angle neutron scattering to develop an understanding of the effect of spatial confinement on the assembled state and catalytic performance of gold (Au) NPs in the nanopores of amine-functionalized SBA-15 silica materials (mSiO₂). We investigate the effect of pH and ionic strength on the packing and spatial distribution of Au NPs within mSiO₂. We find that a combination of confinement and electrostatic attraction between Au NPs and pore wall increases the available surface area of Au NPs by restricting their aggregation in high ionic strength solution. We show that the ability of the adsorbed NPs to withstand the aggregation allows retaining their catalytic activity for a model reaction, here reduction of p-nitrophenol, which otherwise is significantly diminished due to bulk aggregation of the NPs. This fundamental study demonstrates the critical role of confinement on the adsorption and catalytic performance of nanoparticles, thus establishes a link between the structure-property relationship of such nanomaterials.