Local Interfacial Structure Influences Charge Localization in Titania Composites: Beyond the Band Alignment Paradigm

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.