Investigation of a Nanoporous Gold / TiO2 Catalyst by Electron Microscopy and Tomography

Nanoporous gold is a material with many possible applications e.g. in catalysts, sensors and electrode materials. We studied the functionalization of the nanoporous gold with TiO2 particles. Aiming at the low temperature oxidation of CO, the nanoporous gold can be coated with TiO2 in order to enhance catalytic activity. Structure and distribution of the TiO2 on the gold surface are important structural features, which were investigated by transmission electron microscopy. The preparation of the porous gold was tested with focused ion beam - preparation, conventional Ar+ ion beam preparation of nanoporous gold embedded in epoxy and ultramicrotome preparation of nanoporous gold embedded in epoxy. Considering the beam damage on the structure and the contamination of the surface, ultramicrotome preparation turned out to be the best solution. It was shown, that the gold ligaments are abundantly covered by approximately 5 nm TiO2 particles. The determination of the largest lattice fringe distance in high resolution mode revealed that the crystalline nanoparticles consist of the anatase phase. The spatial Ti distribution was measured with energy filtered transmission electron microscopy. Scanning transmission electron microscopy tomography was applied to reconstruct the three-dimensional structure of the gold coated with TiO2 particles.