Theoretical investigation of Cu₅/silicates deposited on rutile TiO₂ as a photocatalyst

Titanium dioxide (TiO₂) is an exceptional compound with unique optical properties, which have been intensively used for applications in photocatalysis. Recent studies show that Cu₅ atomic quantum clusters (AQCs) could facilitate visible light absorption and enhance the photocatalytic properties of rutile TiO₂ by creating mid-gap states. In this work, to move the theory of these catalysts closer to the experiment, we investigate the electronic structures of Cu₅ adsorbed on a perfect and reduced rutile TiO₂ surface in the absence and presence of silicate SiO₃^2- ions, which are introduced for the purification of Cu₅ AQCs. Encouragingly, our DFT simulations predict that the presence of SiO₃^2- does not reduce the gap states of the Cu₅@TiO₂ composite and could even enhance them by shifting more states into the band gap. Our results also demonstrate that the polarons created by oxygen vacancies (O_v) and Cu₅ coexist within the band gap of TiO₂. Indeed an O_v behaves like a negative gate on the electronic states located on the AQCs, thereby shifting states out of the valence band into the band gap, which could lead to enhanced photocatalytic performance.