Origin of High Photocatalytic Properties in the Mixed-Phase TiO2: A First-Principles Theoretical Study

We present a step-by-step theoretical protocol based on the first-principles methods to reveal the insight into the origin of the high photocatalytic activity achieved by the mixed phase TiO2, consisting of anatase and rutile. The interfacial geometries, density of states, charge densities, optical absorption spectrum, electrostatic potential, and band offsets have been calculated. The most stable mixed-phase structures have been identified, the interfacial tensile strain-dependent electronic structures have been observed, and the energy level diagram of band alignment has been given. We find that the geometrical reconstruction around the interfacial area has a negligible influence on the light absorption of the heterojunction and the interfacial sites seem not to dominantly contribute to the band-edge states. For the most stable heterojunction, the calculated valence-band maximum and conduction-band minimum of rutile, respectively, lie 0.52 and 0.22 eV above those of anatase, which agrees well with the experimental measurements and other theoretical predications. The good match of band energies to reaction requirements, large driving force for the charge immigration across the interface, and the difference of electrostatic potentials around the interface successfully explain the high photocatalytic activity achieved by the mixed-phase TiO2.