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Aberration-corrected Scanning Transmission Electron Microscopy and Spectroscopy of Nonprecious Metal Nanoparticles in Titania Aerogels

By exhibiting high surface area and efficient photochemistry, titania aerogels are being considered as potential photocatalysts for solar energy conversion and environmental remediation. However, titania’s large bandgap does not efficiently match the main solar spectrum; hence, development of titania-based systems active in the visible has been a significant thrust in recent materials research. One approach is to add metal nanoparticles with local surface plasmon resonances to titania aerogel so that incident photons are absorbed at lower energies. The effects of the as-incorporated metal nanoparticle size, shape, and distribution on the photocatalytic activity have been well documented for a variety of semiconductors. The behavior of the supported metal nanoparticles following synthesis is critical, because even small, initially well-dispersed metal nanoparticles can oxidize, aggregate, or disperse over time or upon extended illumination and exposure to ambient. With such concerns, transmission electron microscopy is ideally suited to characterize these emerging photocatalytic metal-nanoparticle/titania-aerogel composites: the metal nanoparticles are typically in the few-nanometer range and often have a metal/oxide junction that requires additional investigation to properly understand the photochemistry of these complex systems.