Determination of Crystallographic Orientation and Exposed Facets of Titanium Oxide Nanocrystals

Titanium dioxide (TiO2) nanocrystals have attracted great attention in heterogeneous photocatalysis and photoelectricity fields for decades. However, contradicting conclusions on the crystallographic orientation and exposed facets of TiO2 nanocrystals frequently appear in the literature. Herein, using anatase TiO2 nanocrystals with highly exposed {001} facets as a model, the misleading conclusions that exist on anatase nanocrystals are clarified. Although TiO2‐001 nanocrystals are recognized to be dominated by {001} facets, in fact, anatase nanocrystals with both dominant {001} and {111} facets always co‐exist due to the similarities in the lattice fringes and intersection angles between the two types of facets (0.38 nm and 90° in the [001] direction, 0.35 nm and 82° in the [111] direction). A paradigm for determining the crystallographic orientation and exposed facets based on transmission electron microscopy (TEM) analysis, which provides a universal methodology to nanomaterials for determining the orientation and exposed facets, is also given. TiO2 nanosheets with dominant {001} and {111} facets are identified by transmission electron microscopy, which are very close because of similar morphology and lattice parameters. The importance of the determination of exposed facets, which is the prerequisite of surface performance study, is emphasized and a paradigm applied to all nanocrystalline materials is given.