Titania and Its Outstanding Properties: Insights from First Principles Calculations

Titanium dioxide (TiO2) is one of the most widely used photocatalytic materials due its abundance, non-toxicity, and high stability in different environments and conditions. TiO2 is also considered a prototypical metal oxide and a model system for experimental and theoretical studies of materials properties and surface reactions. TiO2 has several polymorphs, rutile and anatase being the most common ones. Rutile is the thermodynamically most stable bulk phase; anatase is stable in nanoparticles and shows higher activity in many photocatalytic reactions, making it the most interesting phase for use in high surface area photocatalytic and photovoltaic devices. While insulating when stoichiometric, TiO2 is most frequently reduced and electrically conducting due to the presence of intrinsic defects and their induced excess electrons, which transform it into an n-type semiconductor with many technologically relevant properties. As surfaces have a prominent role in most of TiO2’s applications, intense efforts have been devoted to the characterization of TiO2 surfaces and their interactions with various molecular species and environments. In this chapter, we present an overview of recent theoretical/computational studies on TiO2, focusing mainly on reduced anatase surfaces and their interactions with molecular oxygen and water, which have a central role in various fields, from photocatalysis and nanomaterial synthesis to geochemistry and environmental chemistry. These studies highlight the effectiveness of combined experimental and theoretical approaches as well as the important role of simulations in bridging the gap between experiments under vacuum conditions and in realistic environments.