From single Cu atoms to sub-nanometric copper clusters deposited on TiO2: a DFT study

The growing interest in a material composed of Cu single atoms and/or their sub-nanometric clusters deposited on titania prompted us to perform systematic theoretical studies on the system comprising the anatase phase of titania, modelled by a (TiO2)34 cluster with copper particles of 1–7 atoms on top of it. The ground-state geometric structures were proposed and compared with the available literature data derived from EXAFS experiments done for Cu-TiO2 materials. Copper atoms prefer to aggregate and form larger clusters on TiO2, as seen from the computed nucleation energies. The models were characterised by the following electronic properties: electronic band structure, natural population charges, and frontier orbitals (HOMO, LUMO, and SOMO). The copper phase becomes oxidised once it is deposited on titania. The charge distribution in the resulting structures indicates that the atoms that are the closest to the Cu-TiO2 interface would become the active sites for catalytic processes; copper atoms would act as electrophilic, while oxygen atoms would act as nucleophilic. The calculated binding energies between the two phases show that the formation of the composite system is favourable from the thermodynamic point of view, and the interaction between the small copper clusters and the titania surface is mostly of electrostatic nature.