Effect of nickel doping on structural, surface, and photocatalytic properties of TiO ₂ thin films prepared via sol-gel method

Abstract In this study, nickel-doped titanium dioxide (Ni/TiO 2 ) thin films with varying nickel concentrations (0, 2, and 7 at%) were synthesized using the sol–gel dip-coating technique and deposited onto Si(001) substrates. The films were annealed at 900 °C for 2 h and comprehensively characterized by XRD, Raman spectroscopy, SEM, EDX, AFM, and electrostatic force microscopy (EFM). Structural analysis confirmed the coexistence of anatase, rutile, and NiTiO 3 phases regardless of the nickel content. Increasing Ni incorporation reduced the crystallite size of anatase while enhancing the growth of rutile and NiTiO 3 phases. Morphological studies revealed that NiTiO 3 was preferentially formed at the grain boundaries between anatase and rutile, significantly affecting the surface structure. EFM analysis demonstrated a decrease in surface potential from 1.3 V to 0.6 V with increasing Ni content, suggesting enhanced electron–hole recombination. Photocatalytic performance, evaluated through RhB dye degradation under UV irradiation, showed that pure TiO 2 films exhibited the highest activity (k = 1.98 × 10 −3 min −1 , degradation efficiency = 51% after 6 h), while Ni incorporation led to reduced photocatalytic efficiency. These findings offer valuable insights into how Ni incorporation affects the structural and surface properties of TiO 2 thin films, there by contributing to the development of more efficient photocatalysts for environmental pollutant degradation.