Three-Dimensionally Ordered Hierarchically Porous Tin Dioxide Inverse Opals and Immobilization of Palladium Nanoparticles for Catalytic Applications

A high surface area 3D ordered SnO2 inverted opal with walls composed of interconnected nanocrystals is reported using a facile approach with tin acetate precursors. The hierarchically porous structure exhibits porosity on multiple lengths scales (cm down to nm). The thickness of the 10 wall structure comprising nanocrystals of the oxide can be tuned by multiple infilling of the precursor. Using highly monodisperse Pd nanoparticles, we show how the SnO2 IO can be functionalized with immobilized Pd NP assemblies. We show that the Pd NP size dispersion is controlled by utilizing weak ligand-metal interactions and strong metal-oxide interactions for the immobilization step. The resulting SnO2-Pd IOs were investigated X-ray photoelectron spectroscopy indicating electronic interactions between the Pd and SnO2 and alterations to NP surface chemistry. Pd NPs assembled with excellent dispersion on the ordered SnO2 IOs show superior catalytic performance for liquid phase chemical synthesis via Suzuki coupling reactions and allow easy removal of the catalyst substrate post reaction. Higher mass electrocatalytic activity is also demonstrated for formic acid oxidation, compared to commercial Pd/C catalysts, which is shown to be due to better access to the catalytically active sites on SnO2-Pd IOs. The high surface area interconnected phase-pure SnO2 IO, with programmable porosity forms a functional material for catalytic applications.