Divergent bandgap responses in Cu- and Zn-doped NiTiO3 nanoparticles

Nickel titanate (NiTiO 3 ) nanoparticles doped with Cu and Zn were successfully synthesized via a modified Pechini sol-gel method to investigate the influence of dopant electronic configuration on the structural, optical, and photocatalytic properties of NiTiO 3 . The synthesized materials were systematically characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and UV–Vis diffuse reflectance spectroscopy. Structural analyses confirmed the formation of phase-pure rhombohedral NiTiO 3 with nanocrystalline morphology, while the result revealed slight lattice expansion resulting from the substitution of larger Cu 2+ and Zn 2+ ions at the Ni site without altering the host crystal structure. Optical investigations demonstrated distinctly different electronic responses for the two dopants. Cu doping produced a pronounced redshift in the absorption edge and reduced the optical band gap from approximately 2.1 to 1.75 eV, whereas Zn doping caused negligible changes in the band gap. This contrasting behavior is attributed to the partially filled Cu 2+ (3d 9 ) electronic configuration, which introduces Cu 3d-derived impurity states and enhances O 2p-Cu 3d hybridization near the valence band, while the fully filled Zn 2+ (3d 10 ) configuration does not significantly modify the electronic structure. The improved electronic structure of Cu-doped NiTiO 3 resulted in superior visible-light photocatalytic performance toward cationic thiazine dye degradation. These findings demonstrate that dopant electronic configuration plays a decisive role in tailoring the band structure and photocatalytic activity of NiTiO 3 , providing an effective strategy for designing high-performance visible-light-responsive oxide photocatalysts.