Rutile Surface Reactivity Provides Insight into the Structure-Directing Role of Peroxide in TiO2 Polymorph Control

摘要

The peroxo ligand is one of the most promising structure-directing agents in TiO2 nanocatalyst synthesis; however, its role in nanocatalyst growth and polymorph control is not well understood. Using a combination of scanning tunneling microscopy, X-ray photoemission spectroscopy, and kinetic Monte Carlo simulation, we show that the base-catalyzed reaction of H2O2 targets very particular sites on the rutile (110) surface, sites that are present in concentrations of less than 1% of a monolayer, producing highly homogeneous surfaces characterized by flat terraces and straight atomic-height steps. This reaction produces surface steps with a different orientation, different structure, and different reactivity from those prepared in ultrahigh vacuum studies. The observed reactivity is explained by a simple, site-specific model that is based on metal oxo coordination chemistry. This study shows that one of the principle roles of peroxide in etching and growth reactions is destabilizing neighboring bonds and increasing their lability. As a result, the peroxo ligand adds a degree of reversibility to growth reactions, thereby promoting the formation of well ordered crystals.