The Effect of La 3+ on the Methylene Blue Dye Removal Capacity of the La/ZnTiO 3 Photocatalyst, a DFT Study.

Theoretically, lanthanum can bond with surface oxygens of ZnTiO 3 to form La-O-Ti bonds, resulting in the change of both the band structure and the electron state of the surface. To verify this statement, DFT calculations were performed using a model with a dispersed lanthanum atom on the surface (101) of ZnTiO 3 . The negative heat segmentation values obtained suggest that the incorporation of La on the surface of ZnTiO 3 is thermodynamically stable. The bandgap energy value of La/ZnTiO 3 (2.92 eV) was lower than that of ZnTiO 3 (3.16 eV). TDOS showed that the conduction band (CB) and the valence band (VB) energy levels of La/ZnTiO 3 are denser than those of ZnTiO 3 due to the participation of hybrid levels composed mainly of O2 p and La5 d orbitals. From the PDOSs, Bader's charge analysis, and ELF function, it was established that the La-O bond is polar covalent. MB adsorption on La/ZnTiO 3 (-200 kJ/mol) was more favorable than on ZnTiO 3 (-85 kJ/mol). From the evidence of this study, it is proposed that the MB molecule first is adsorbed on the surface of La/ZnTiO 3 , and then the electrons in the VB of La/ZnTiO 3 are photoexcited to hybrid levels, and finally, the MB molecule oxidizes into smaller molecules.