Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 55: Metal Oxide Surfaces III: Adsorption and Reactivity

O 55.8: Vortrag

Mittwoch, 3. April 2019, 16:45–17:00, H5

STM Reveals the Mechanism of Anatase (001) Nanocatalyst Activation — •William DeBenedetti and Melissa Hines — Cornell University, Ithaca NY, USA

Metal oxide nanocrystals such as TiO₂ have garnered a great deal of attention for environmental remediation applications and photocatalysis. Despite years of study, an atomic-scale picture of the surface chemistry and structure of these materials under operating conditions remains elusive, due to the complex nature of ambient reaction environments. Do these nanocatalysts adopt a bulk-terminated structure in solution environments, or do they reconstruct to minimize their reactivity? Using a newly developed solution-based approach, we will show that shape-controlled crystal growth methods produce films of oriented anatase (001) nanocrystals that are amenable to scanning probe techniques such as STM. Despite being grown in solution and handled in air, the surface of these nanocrystals are surprisingly clean and passivated by a monolayer of fluorine, protecting the surface against adventitious contamination. Using a combination of STM, XPS, and ab initio simulations, we will then show that carboxylic acid solutions, the most common TiO₂ functionalization chemistry, cause a spontaneous reorganization of the surface sites, giving rise to a five-fold increase in the number of reactive sites on the surface, which reveals a mechanism of nanocatalyst site activation. This structural transformation is not observed in analogous reactions in vacuum and demonstrates the importance of studying these materials under operating conditions.