On the True Photoreactivity Order of {001}, {010}, and {101} Facets of Anatase TiO2 Crystals

摘要

Design and morphological control of crystal facets is a commonly employed strategy to optimize the performance of various crystalline catalysts from noble metals to semiconductors.The basis of this strategy is that surface atomic configuration and coordination, which inherently determine their heterogeneous reactivity, can be finely tuned by morphological control. The conventional understanding of the surface atomic structure of a crystal is that facets with a higher percentage of undercoordinated atoms are usually more reactive in heterogeneous reactions. For instance, {001} facets of anatase TiO2, which is one of the most important photocatalysts, are considered to be more reactive than {101}. We have now discovered, by investigating a set of anatase crystals with predominant {001}, {101}, or {010} facets, that, contrary to conventional understanding, clean {001} exhibits lower reactivity than {101} in photooxidation reactions for OH radical generation and photoreduction reactions for hydrogen evolution. Furthermore, the {010} facets showed the highest photoreactivity. However, these three facets had similar photoreactivity when partially terminated with fluorine. We concluded that a cooperative mechanism of surface atomic structure (the density of undercoordinated Ti atoms) and surface electronic structure (the power of photoexcited charge carriers) is the determining factor for photoreactivity. The findings of this work open up new opportunities for maximizing photoreactivity through morphological control of photocatalysts.