(474a) Adsorption of Gold Nanospheres in Cylindrical Pores of SBA-15: From Packing to Catalytic Response

Controlled adsorption and assembly of functional nanomaterials in narrow pores provides an effective method to stabilize their non-equilibrium states. 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 confinement on NP assemblies remains poorly understood. This lack of knowledge is due to the non-trivial nature of the interactions between pore wall-NP and NP-NP. These interactions are greatly influenced by the degree of pore confinement, thus influencing the self-assembly process. In this study, we use adsorption isotherms and small angle neutron scattering to develop a better understanding of the effect of spatial confinement on the assembly and adsorption of gold nanospheres (diameter ~ 3 nm) in the cylindrical nanopores of amine-functionalized SBA-15 (diameter ~ 8 nm) silica materials. We show that the amount of gold NPs adsorbed in the pores is strongly dependent on the pH, where large amount of NPs adsorb in the pH range where opposite charges exist on the pore wall and NPs. We use SANS to quantify the change in interparticle spacing in the pores upon increasing the adsorbed amount. Furthermore, we investigate the effect of this change in interparticle spacing on plasmonic coupling between gold NPs and their catalytic behavior. Our experiments show four times increase in the rate of catalytic reduction of 4-nitrophenol into 4-aminophenol upon adsorbing the gold NPs in the pores in comparison to nanoparticles dispersed in medium. The fundamental knowledge gained here may provide a platform for designing new nanoporous supports for enhanced plasmonic and catalytic properties.