TiO2
Photocatalysis
Interfaces
Rutile
Anatase
DFT+U
Charge localisation,
Coordination
Mixed-phase TiO2
Visible-light absorption
Photocatalytic activity
Anatase TiO2
Rutile TiO2
Molecular dynamics
Carrier separation
Bilayer films
Surface
Nanocomposites
The phase junction of nanocomposite materials is key to enhanced performance but is largely ignored in recent theoretical examinations of photocatalytic interactions in titania-based composites. Computational advances now allow more precise modeling of the electronic and optical properties of composites, and focusing on mixed-phase TiO2 as a model, we use density functional theory (DFT) to interrogate the essential structural feature, namely, the rutile anatase interface, and its relationship to photogenerated charge localization, bulk band alignments, and defect formation. The interfacial region is disordered and distinct from rutile and anatase and contains low coordinated Ti sites and oxygen vacancies, both drivers of charge localization. The relaxations of the interface upon formation of excited electrons and holes determine the final location of charges which cannot always be predicted from bulk band alignments. A detailed understanding of the interfacial phase junction lays the foundation for directed synthesis of highly active and efficient composite photocatalysts.